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WO2015088037A1 - Adhesive for food packaging films - Google Patents

Adhesive for food packaging films Download PDF

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Publication number
WO2015088037A1
WO2015088037A1 PCT/JP2014/083316 JP2014083316W WO2015088037A1 WO 2015088037 A1 WO2015088037 A1 WO 2015088037A1 JP 2014083316 W JP2014083316 W JP 2014083316W WO 2015088037 A1 WO2015088037 A1 WO 2015088037A1
Authority
WO
WIPO (PCT)
Prior art keywords
food packaging
adhesive
packaging films
acid
film
Prior art date
Application number
PCT/JP2014/083316
Other languages
French (fr)
Inventor
Noriyoshi KAMAI
Yasushi Yamada
Hitoshi Ikeda
Original Assignee
Henkel Ag & Co. Kgaa
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Henkel Ag & Co. Kgaa filed Critical Henkel Ag & Co. Kgaa
Publication of WO2015088037A1 publication Critical patent/WO2015088037A1/en

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Classifications

    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09J—ADHESIVES; NON-MECHANICAL ASPECTS OF ADHESIVE PROCESSES IN GENERAL; ADHESIVE PROCESSES NOT PROVIDED FOR ELSEWHERE; USE OF MATERIALS AS ADHESIVES
    • C09J175/00—Adhesives based on polyureas or polyurethanes; Adhesives based on derivatives of such polymers
    • C09J175/04—Polyurethanes
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B15/00—Layered products comprising a layer of metal
    • B32B15/04—Layered products comprising a layer of metal comprising metal as the main or only constituent of a layer, which is next to another layer of the same or of a different material
    • B32B15/08—Layered products comprising a layer of metal comprising metal as the main or only constituent of a layer, which is next to another layer of the same or of a different material of synthetic resin
    • B32B15/085—Layered products comprising a layer of metal comprising metal as the main or only constituent of a layer, which is next to another layer of the same or of a different material of synthetic resin comprising polyolefins
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B15/00—Layered products comprising a layer of metal
    • B32B15/04—Layered products comprising a layer of metal comprising metal as the main or only constituent of a layer, which is next to another layer of the same or of a different material
    • B32B15/08—Layered products comprising a layer of metal comprising metal as the main or only constituent of a layer, which is next to another layer of the same or of a different material of synthetic resin
    • B32B15/09—Layered products comprising a layer of metal comprising metal as the main or only constituent of a layer, which is next to another layer of the same or of a different material of synthetic resin comprising polyesters
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B15/00—Layered products comprising a layer of metal
    • B32B15/20—Layered products comprising a layer of metal comprising aluminium or copper
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B27/00—Layered products comprising a layer of synthetic resin
    • B32B27/18—Layered products comprising a layer of synthetic resin characterised by the use of special additives
    • B32B27/20—Layered products comprising a layer of synthetic resin characterised by the use of special additives using fillers, pigments, thixotroping agents
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B7/00—Layered products characterised by the relation between layers; Layered products characterised by the relative orientation of features between layers, or by the relative values of a measurable parameter between layers, i.e. products comprising layers having different physical, chemical or physicochemical properties; Layered products characterised by the interconnection of layers
    • B32B7/04—Interconnection of layers
    • B32B7/12—Interconnection of layers using interposed adhesives or interposed materials with bonding properties
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
    • C08G18/00—Polymeric products of isocyanates or isothiocyanates
    • C08G18/06—Polymeric products of isocyanates or isothiocyanates with compounds having active hydrogen
    • C08G18/28—Polymeric products of isocyanates or isothiocyanates with compounds having active hydrogen characterised by the compounds used containing active hydrogen
    • C08G18/40—High-molecular-weight compounds
    • C08G18/42—Polycondensates having carboxylic or carbonic ester groups in the main chain
    • C08G18/4205—Polycondensates having carboxylic or carbonic ester groups in the main chain containing cyclic groups
    • C08G18/4208—Polycondensates having carboxylic or carbonic ester groups in the main chain containing cyclic groups containing aromatic groups
    • C08G18/4211—Polycondensates having carboxylic or carbonic ester groups in the main chain containing cyclic groups containing aromatic groups derived from aromatic dicarboxylic acids and dialcohols
    • C08G18/4216—Polycondensates having carboxylic or carbonic ester groups in the main chain containing cyclic groups containing aromatic groups derived from aromatic dicarboxylic acids and dialcohols from mixtures or combinations of aromatic dicarboxylic acids and aliphatic dicarboxylic acids and dialcohols
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
    • C08G18/00—Polymeric products of isocyanates or isothiocyanates
    • C08G18/06—Polymeric products of isocyanates or isothiocyanates with compounds having active hydrogen
    • C08G18/28—Polymeric products of isocyanates or isothiocyanates with compounds having active hydrogen characterised by the compounds used containing active hydrogen
    • C08G18/40—High-molecular-weight compounds
    • C08G18/42—Polycondensates having carboxylic or carbonic ester groups in the main chain
    • C08G18/46—Polycondensates having carboxylic or carbonic ester groups in the main chain having heteroatoms other than oxygen
    • C08G18/4615—Polycondensates having carboxylic or carbonic ester groups in the main chain having heteroatoms other than oxygen containing nitrogen
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
    • C08G18/00—Polymeric products of isocyanates or isothiocyanates
    • C08G18/06—Polymeric products of isocyanates or isothiocyanates with compounds having active hydrogen
    • C08G18/28—Polymeric products of isocyanates or isothiocyanates with compounds having active hydrogen characterised by the compounds used containing active hydrogen
    • C08G18/40—High-molecular-weight compounds
    • C08G18/48—Polyethers
    • C08G18/50—Polyethers having heteroatoms other than oxygen
    • C08G18/5021—Polyethers having heteroatoms other than oxygen having nitrogen
    • C08G18/5036—Polyethers having heteroatoms other than oxygen having nitrogen containing -N-C=O groups
    • C08G18/5045—Polyethers having heteroatoms other than oxygen having nitrogen containing -N-C=O groups containing urethane groups
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
    • C08G18/00—Polymeric products of isocyanates or isothiocyanates
    • C08G18/06—Polymeric products of isocyanates or isothiocyanates with compounds having active hydrogen
    • C08G18/70—Polymeric products of isocyanates or isothiocyanates with compounds having active hydrogen characterised by the isocyanates or isothiocyanates used
    • C08G18/72—Polyisocyanates or polyisothiocyanates
    • C08G18/74—Polyisocyanates or polyisothiocyanates cyclic
    • C08G18/75—Polyisocyanates or polyisothiocyanates cyclic cycloaliphatic
    • C08G18/751—Polyisocyanates or polyisothiocyanates cyclic cycloaliphatic containing only one cycloaliphatic ring
    • C08G18/752—Polyisocyanates or polyisothiocyanates cyclic cycloaliphatic containing only one cycloaliphatic ring containing at least one isocyanate or isothiocyanate group linked to the cycloaliphatic ring by means of an aliphatic group
    • C08G18/753—Polyisocyanates or polyisothiocyanates cyclic cycloaliphatic containing only one cycloaliphatic ring containing at least one isocyanate or isothiocyanate group linked to the cycloaliphatic ring by means of an aliphatic group containing one isocyanate or isothiocyanate group linked to the cycloaliphatic ring by means of an aliphatic group having a primary carbon atom next to the isocyanate or isothiocyanate group
    • C08G18/755—Polyisocyanates or polyisothiocyanates cyclic cycloaliphatic containing only one cycloaliphatic ring containing at least one isocyanate or isothiocyanate group linked to the cycloaliphatic ring by means of an aliphatic group containing one isocyanate or isothiocyanate group linked to the cycloaliphatic ring by means of an aliphatic group having a primary carbon atom next to the isocyanate or isothiocyanate group and at least one isocyanate or isothiocyanate group linked to a secondary carbon atom of the cycloaliphatic ring, e.g. isophorone diisocyanate
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B2439/00—Containers; Receptacles
    • B32B2439/70—Food packaging

Definitions

  • the present invention relates to an adhesive for food packaging films.
  • Food packaging films are composite laminate films, and are composed of various plastic films and/or metallic foils having a thickness of approximately 5 to 100 ⁇ .
  • plastic films contain films produced by polyolefins such as polyethylenes and polypropylenes (PP) , copolymers of olefins, polyvinyl chlorides, polyvinylidene chlorides, polyesters and polyamides, and examples of the metallic foils contain foils produced by such as aluminum and stainless-steel etc.
  • plastic films and metallic foils are characterized by properties such as strength, water resistance, moisture permeability resistance, oxygen permeability resistance and heat resistance. Therefore, high performance food packaging films which cannot be obtained by using only a single film can be provided by laminating two or more kinds of films, if necessary.
  • adhesives used for producing food packaging films contain predominantly urethane adhesives.
  • Patent Documents 1-3 disclose that a food packaging film is produced by laminating a plastic film using a urethane adhesive .
  • Patent Document 1 discloses an adhesive for food packaging films in which a phosphoric oxyacid, a carboxylic acid, an acid anhydride thereof, and an epoxy resin are mixed into a urethane resin (see [claim 1] and [Examples] of Patent Document 1) .
  • Patent Document 2 discloses a urethane adhesive comprising a phosphoric oxyacid and a silane coupling agent (see [claim 1] and [Table 1] of Patent Document 2) .
  • Patent Document 3 discloses a urethane adhesive obtainable by reacting a partly acid modified polyol with a polyisocyanate (see [claim 1] and [Table 1] of Patent Document 3) .
  • Patent Documents 1-3 disclose urethane adhesives in which peel strength, heat resistance and acid resistance are improved. Each of these urethane adhesives is suitable for producing food packaging films by laminating a plastic film and so on.
  • an adhesive for food packaging films that appearance of a food packaging film is not affected, even though an inclusion (or enclosed material) (for example a food) is enclosed in a food packaging bag made from the food packaging film by using the adhesive, sterilized, and then stored for a certain period of time. That is, it is needed for an adhesive for food packaging films to be excellent in inclusion- resistance (resistance to an inclusion or enclosed material) .
  • the urethane adhesives of References 1-3 comprise an epoxy resin, a silane coupling agent and various acid components, each of the urethane adhesives has improved peel strength (please note that there is no inclusion), but has insufficient inclusion-resistance.
  • Patent Document 1 JP 2683937 B
  • Patent Document 2 JP 2002-003813 A
  • Patent Document 3 JP 2005-132902 A Summary of Invention
  • the present invention has been made so as to solve such a problem and an object thereof is to provide an adhesive for food packaging films, which adhesive does not cause delamination of a plastic film when a food packaging film (or a laminate film) is produced by laminating the plastic film, and moreover, which adhesive can maintain the appearance of the food packaging film for a long time (be excellent in inclusion-resistance or resistance to an enclosed material) after an inclusion (or enclosed material) is enclosed in a food packaging bag (or pouch) produced from the food packaging film and sterilized.
  • the present inventors have intensively studied and found, surprisingly, that it is possible to obtain an adhesive for food packaging films, which adhesive has high peel strength and is excellent in inclusion-resistance, when a urethane adhesive is produced by using an aromatic compound having a specific structure.
  • the present invention provides, in an aspect, an adhesive for food packaging films, comprising a urethane resin obtainable by mixing:
  • a food packaging film can be suitably produced by using the adhesive.
  • an adhesive for food packaging films wherein the aromatic compound (C) comprises at least one selected from gallic acid, gallic acid alkyl esters and tannic acid, is provided.
  • an adhesive for food packaging films wherein the polyol component (A) comprises a polyester polyol and/or a polyesterpolyurethane polyol, is provided.
  • an adhesive for food packaging films wherein the isocyanate component (B) comprises a polyfunctional isocyanate compound derived from an alicyclic diisocyanate compound and/or an aliphatic diisocyanate compound, is provided.
  • an adhesive for food packaging films wherein the aromatic compound (C) is mixed in an amount of 0. Ol- IO.0 parts by weight per 100 parts by weight of the total weight of the polyol component (A) , the isocyanate component (B) and the aromatic compound (C) , is provided.
  • the adhesive according to the present invention comprises a urethane resin obtainable by mixing: (A) a polyol component; (B) an isocyanate component; and (C) an aromatic compound having both a phenolic hydroxyl group, and a carboxyl group or an ester group. Therefore, the adhesive is excellent in peel strength and inclusion- resistance. Thus, the adhesive is much suitable so as to produce food packaging films.
  • a food packaging film produced by using the present adhesive for food packaging films does not cause delamination (or peeling) of a film and can maintain its appearance, even though the food packaging film is sterilized and stored at 60 °C for 2 weeks.
  • the adhesive for food packaging films has further improved inclusion-resistance, when the aromatic compound (C) comprises at least one selected from gallic acid, gallic acid alkyl esters and tannic acid.
  • the adhesive for food packaging films has further improved inclusion-resistance, when the polyol component (A) comprises a polyester polyol and/or a polyesterpolyurethane polyol.
  • the adhesive for food packaging films has further improved heat resistance, when the isocyanate component (B) comprises a polyfunctional isocyanate compound derived from an alicyclic diisocyanate compound and/or an aliphatic diisocyanate compound.
  • the adhesive for food packaging films has further improved inclusion-resistance, when the aromatic compound (C) is mixed in an amount of 0.01-10.0 parts by weight per 100 parts by weight of the total weight of the polyol component (A) , the isocyanate component (B) and the aromatic compound (C) .
  • Fig. 1 is a sectional view showing an embodiment of a food packaging film according to the present invention.
  • An adhesive for food packaging films comprises a urethane resin obtainable by mixing: (A) a polyol component; (B) an isocyanate component; and (C) an aromatic compound having both a phenolic hydroxyl group, and a carboxyl group or an ester group (hereinafter referred to as an "aromatic compound (C)").
  • the urethane resin according to the present invention is not particularly limited by mixing orders and mixing methods etc. of the components (a) - (c) as long as the objective adhesive can be obtained.
  • the urethane resin may be obtained by mixing the three kinds of components of the polyol component (A) , the isocyanate component (B) and the aromatic compound (C) at a time.
  • the urethane resin may be obtained by previously reacting the component (A) or the component (C) with the component (B) , and then mixing the remaining one component.
  • the urethane resin is more preferably obtained by previously mixing the component (A) and the component (C) to give a mixture and then by mixing the mixture with the component (B) .
  • the reaction of the component (A) , the component (C) and the component (B) can be carried out according to known methods.
  • the urethane resin may be obtained by the reaction of the components (A) - (C) in a solvent, and the urethane resin may be obtained by the reaction of the components (A) - (C) with no solvent.
  • the urethane resin may be obtained by using a polyol and an excess amount of isocyanate to prepare a urethane prepolymer having an NCO end (or terminal) and then by reacting the urethane prepolymer with a short chain polyol.
  • the "polyol component (A) " in the present invention is not particularly limited as long as the objective present adhesive for food packaging films can be obtained and the polyol component (A) does not exert an adverse influence on the production (or synthesis) of the urethane resin.
  • the component (A) may be a polyol commonly used so as to obtain urethane resins.
  • Examples of the component (A) contain polyester polyols, acrylic polyols, polyether polyols, polyetherester polyols, polyesterpolyurethane polyols, polyetherpolyurethane polyols, and modifications of these polyols.
  • polyester polyol means a compound which belongs to “main chain type” polyesters and has ester bonds and hydroxyl groups in the "main chain”.
  • the hydroxyl group is generally positioned on the end of the main chain, and acts as a functional group reacting with an isocyanate group.
  • the polyester polyol may be obtained by the condensation polymerization reaction of a low molecular weight polyol with a dicarboxylic acid and/or an acid anhydride thereof .
  • dicarboxylic acid examples contain oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, dodecanedioic acid, 2 -methylsuccinic acid, 2 -methyladipic acid, 3 -methyladipic acid, 3 -methylpentanedioic acid, 2- methyloctanedioic acid, 3 , 8 -dimethyldecanedioic acid, 3,7- dimethyldecanedioic acid, phthalic acid, terephthalic acid, isophthalic acid, naphthalenedicarboxylic acid, trimelitic acid, trimesic acid and cyclohexanedicarboxylic acid etc. These are used alone or in combination.
  • acid anhydride examples include acetic anhydride, propionic anhydride, succinic anhydride, maleic anhydride, phthalic anhydride, trimelitic anhydride and pyromellitic anhydride etc. These can be used alone or in combination.
  • the low molecular weight polyol preferably has from 1 to 3 functional groups, and is particularly preferably a bifunctional polyol, that is, a so called diol .
  • the low molecular weight polyol can be used alone or in combination Examples of the diol contain low molecular weight diols such as ethylene glycol, 1-methylethylene glycol, 1- ethylethylene glycol, diethylene glycol, propylene glycol, butanediol, pentanediol, hexanediol, heptanediol, octanediol, nonanediol, decanediol, neopentyl glycol, 2- methyl-1, 3 -propanediol, cyclohexanedimethanol , 2,4- dimethyl-1 , 5 -pentanediol and 2 , 4 -dibutyl - 1 , 5 -d
  • the "acrylic polyol” means a compound which can be obtained by the addition polymerization reaction of a (meth) acrylate having a hydroxyl group and which have an ester bond in the "side chain".
  • the "acrylic polyol” may be a homopolymer of the
  • Examples of the " (meth) acrylate having a hydroxyl group” contain 2 -hydroxyethyl (meth) acrylate , 2 -hydroxy- propyl (meth) acrylate , 3 -hydroxypropyl (meth) acrylate , glycerin mono (meth) acrylate and 4 -hydroxybutyl acrylate.
  • the "other polymerizable monomer” means a "radical polymerizable monomer having an ethylenic double bond" except for the " (meth) acrylate having a hydroxy group”.
  • Concrete examples contain (meth) acrylic acid, methyl
  • polyether polyol examples contain polyoxytetramethylene glycols (PT G) , polyoxypropylene glycols (PPG) and polyoxyethylene glycols (PEG) etc.
  • PT G polyoxytetramethylene glycols
  • PPG polyoxypropylene glycols
  • PEG polyoxyethylene glycols
  • polyetherpolyurethane polyol may be a compound in which urethane bonds are formed by the chain extension reaction of the above polyether polyol with an isocyanate compound .
  • polyesterpolyurethane polyol may be a compound in which urethane bonds are formed by the chain extension reaction of the above polyester polyol with an isocyanate compound .
  • polyetherester polyol means a polyol having both an ester group and an ether group in the main chain.
  • the “isocyanate component (B) " according to the present invention is not limited as long as examples of the isocyanate component contain aliphatic isocyanates, aromatic isocyanates and alicyclic isocyanates, and the objective present adhesive for food pakcaging films can be obtained. Furthermore, considering that the present invention relates to an adhesive for food packaging films, it is not so preferable to use an aromatic isocyanate which may generate an aromatic amine having carcinogenicity. Therefore, the isocyanate component (B) comprising only aromatic isocyanate is excluded.
  • the isocyanate component (B) does not mean that the isocyanate component comprises only an aliphatic isocyanate and/or an alicyclic isocyanate.
  • the isocyanate component (B) may comprise an aromatic isocyanate, as long as the present objective adhesive for food packaging films can be obtained, that is, an adverse influence on the peel strength and inclusion- resistance of the present adhesive for food packaging films is not exerted, and elution of the aromatic amine is not found .
  • the "aliphatic isocyanate” means a compound which has a chain-like hydrocarbon chain to which an isocyanate group is directly bonded, and also has no cyclic hydrocarbon chain.
  • the “aliphatic isocyanate” may have an aromatic ring, but the isocyanate group is not bonded directly to the aromatic ring.
  • the cyclic hydrocarbon chain does not contain aromatic rings.
  • the "alicyclic isocyanate” means a compound which has a cyclic hydrocarbon chain, and may have a chain- like hydrocarbon chain.
  • the isocyanate group may be directly bonded to the cyclic hydrocarbon chain, or may be directly bonded to a chain- like hydrocarbon chain which may be present.
  • the “alicyclic isocyanate” may have an aromatic ring, the isocyanate group is not directly bonded to the aromatic ring.
  • aromatic isocyanate means a compound which has an aromatic ring and in which the isocyanate group is directly bonded with the aromatic ring. Therefore, even though an isocyanate compound has an aromatic ring in the molecule, when the isocyanate group is not directly bonded to the aromatic ring, the isocyanate compound is classified into the aliphatic isocyanate or alicyclic isocyanate.
  • 4 , 4 ' -diphenylmethane diisocyanate (OCN-C 6 H4-CH 2 -C 6 H4-NCO) is corresponding to the aromatic isocyanate, since the isocyanate group is directly bonded to the aromatic ring.
  • xylylene diisocyanate (OCN-.CH 2 -C 6 H4-CH 2 -NCO) is corresponding to the aliphatic isocyanate, although it has an aromatic ring, since the isocyanate group is not directly bonded to the aromatic ring and is bonded to the methylene group.
  • the aromatic ring may have a ring-fused structure in which two or more benzene rings are condensed.
  • Examples of the aliphatic isocyanate contain 1,4- diisocyanatobutane , 1 , 5-diisocyanatopentane , 1,6- diisocyanatohexane (hereinafter referred to as HDI) , 1,6- diisocyanato-2 , 2 , 4 -trimethylhexane , methyl 2,6- diisocyanatohexanate (lysine diisocyanate) and 1,3- bis ( isocyanatomethyl ) benzene (xylylene diisocyanate)
  • Examples of the alicyclic isocyanate contain 5- isocyanato-l-isocyanatomethyl-1 , 3 , 3 -trimethylcyclohexane (isophorone diisocyanate) (hereinafter referred to as IPDI) , 1, 3 -bis (isocyanatomethyl) cyclohexane (hydrogenated xylylene diisocyanate), bis (4- isocyanatocyclohexyl) methane (hydrogenated diphenylmethane diisocyanate) and 1,4- diisocyanatocyclohexane etc.
  • IPDI isophorone diisocyanate
  • aromatic isocyanate examples include 4,4'- diphentylmethane diisocyanate (hereinafter referred to as MDI) , toluene diisocyanate (hereinafter referred to as TDI) , p-phenylene diisocyanate and m-phenylene diisocyanate etc.
  • isocyanate compounds can be used alone or in combination .
  • the isocyanate component (B) preferably comprises at least one selected from HDI, IPDI, XDI and modifications thereof, and more preferably comprises at least one selected from isocyanurate of 1 , 6 -diisocyanatohexane (HDI), trimethylolpropane adduct of isophorone diisocyanate (IPDI) , and trimethylolpropane adduct of xylylene diisocyanate (XDI) .
  • HDI isocyanurate of 1 , 6 -diisocyanatohexane
  • IPDI trimethylolpropane adduct of isophorone diisocyanate
  • XDI trimethylolpropane adduct of xylylene diisocyanate
  • the isocyanate component (B) is ecologically preferable when the isocyanate component (B) comprises the above isocyanate, since it becomes difficult for the isocyanate component (B) to be volatilized and an aromatic amine having carcinogenicity is never eluted. Further, the inclusion-resistance of the adhesive for food packaging films is also improved.
  • the aromatic compound (C) in the the present invention has a carboxyl group or an ester group, and a phenolic hydroxy1 group .
  • phenolic hydroxyl group means a hydroxyl group which directly bonds to an aromatic ring.
  • the carboxyl group means a hydrophilic functional group in which a carbon atom is bonded to a hydroxyl group by a single bond, and is bonded to an oxygen atom by a double bond.
  • the carboxyl group can contain a carboxylic acid base group (- COO " ) in which a hydrogen of the hydroxyl group is dissociated.
  • the counter cation is not particularly limited as long as the adhesive according to the present invention can be obtained. Examples of the counter cation contain sodium ion, potassium ion and magnesium ion etc.
  • ester group is represented by (-C00R), and means a functional group in which the hydrogen atom of the carboxyl group is replaced with an R.
  • the R represents an alkyl group and an aryl group .
  • aromatic compound (C) examples are concretely presented as follows, but the present invention is not limited by the following concrete examples.
  • Preferable embodiments of the aromatic compound (C) contain:
  • gallic acid alkyl esters such as methyl gallate, ethyl gallate and propyl gallate etc.
  • acids and esters thereof such as tannic acid, aminosalicylic acid, hydroxyphenylacetic acid, methyl hydroxyphenylacetate , salicylic acid, methyl salicylate, hydroxybenzoic acid, methyl hydroxybenzoate , diphenolic acid and mycophenolate mofetil etc.
  • the aromatic compound (C) preferably comprises at least one selected from gallic acid, gallic acid alkyl esters and tannic acid, and particularly preferably comprises gallic acid.
  • the aromatic compound (C) is preferably used in an amount of 0.01-10.0 parts by weight (solid content), more preferably used in an amount of 0.01-5.0 parts by weight (solid content), and particularly preferably used in an amount of 0.1-2.0 parts by weight (solid content), per 100 parts by- weight of the total weight of the components (A) - (C) .
  • the adhesive for food packaging films according to the present invention may comprise the other component in addition to the components (A) - (C) .
  • the other component contain solvents, tackifier resins, pigments (or colorants), plasticizers , catalysts and adhesion promoters etc.
  • tackifier resin examples contain styrene based resins, terpene based resins, aliphatic petroleum resins, aromatic petroleum resins, rosin esters, acrylic resins, polyester resins (excluding polyester polyols) and the like.
  • the tackifier resin generally may have a molecular weight less than 1500 g/mol, particularly a low molecular weight less than 1000 g/mol.
  • the tackifier resin can be used preferably in an amount of from 0 to 50 parts by weight, more preferably in an amount of not more than 30 parts by weight, per 100 parts by weight of the total weight of the adhesive for food packaging films.
  • Examples of the pigment contain such as nanopigments based on Ti0 2 , Si0 2 , Fe 2 0 3 , similar oxides and oxyhydrates etc. These ⁇ pigments preferably have a particle size of not more than 500 nm, and more preferably have a particle size of not more than 100 nm.
  • plasticizer examples contain white oils, naphthenic mineral oils, paraffinic hydrocarbon oils, polypropylene oligomers, polybutene oligomers, polyisoprene oligomers, hydrogenated polyisoprene oligomers, hydrogenated polybutadine oligomers, phthalates, adipates, benzoate esters, vegetable oils, animal oils, and derivatives thereof etc.
  • the present adhesive is used for producing food packaging films, the vegetable oils, animal oils and derivatives thereof are preferable, since they can be generally used for foods and they seem to be safer.
  • Examples of the "catalyst” contain metal based catalysts such as tin based catalysts (trimethyltin laurate, trimethyltin hydroxide, dibutyltin dilaurate and dibutyltin dimaleate etc.), lead based catalysts (lead oleate, lead naphthenate and lead octenate etc . ) and other metal based catalysts (metal naphthenate such as cobalt naphthenate) , and amine based catalysts such as triethylenediamine , tetramethylethylenediamine , tetramethylhexylenediamine , diazabicycloalkenes and diakylaminoalkylamines etc.
  • metal based catalysts such as tin based catalysts (trimethyltin laurate, trimethyltin hydroxide, dibutyltin dilaurate and dibutyltin dimaleate etc.), lead based catalysts (le
  • Silane compounds are exemplified as the "adhesion promoter" .
  • Known organic functional silanes such as (meth) acryloyloxy functional, epoxy functional, amine functional and non-reactive functional substituted silanes can be used as the adhesion promoter.
  • Examples thereof contain vinyltrialkoxysilanes , alkyltrialkoxysilanes , tetraalkoxysilanes , 3 -acryloyloxypropyltrialkoxysilanes , 3- methacryloyloxypropyltrialkoxysilanes , 3 -aminopropyl- trimethoxysilane , 3 -aminopropyltriethoxysilane , 3-amino- propylmethyldimethoysilane , N- (2 -aminoethyl ) -3 -aminopropyl- trimethoxysilane , 3 -gycidyloxymethyltrimethoxysilane , 3- glycidyloxymethyltriethoxysilane and 2 -glycidyloxy- ethyltrimethoxysilane etc.
  • the adhesive for food packaging films preferably comprises the adhesion promoter in an amount of 0.1-5 parts by weight per 100 parts by weight of the total weight of the adhesive.
  • the adhesive for food packaging films according to the present invention can be produced by mixing the component (A), (B) and (C) components as mentioned above.
  • the other component (s) may be mixed.
  • the mixing method is not particularly limited as long as the objective present adhesive for food packaging films can be obtained.
  • the mixing order of the components etc. is also not particularly limited.
  • the adhesive for food packaging films according to the present invention can be produced without special mixing methods and special mixing orders etc.
  • the obtained adhesive for food packaging films can be excellent in both peel strength and inclusion-resistance.
  • the adhesive for food packaging films according to the present invention is applied to a film at a temperature of 15-100 °C, the adhesive should have a low viscosity in this temperature range.
  • the adhesive for food packaging films preferably has a viscosity not more than 500 mPa-s, considering the coatability, when the viscosity is measured by means of Brookfield viscometer.
  • the food packaging film according to the present invention means a laminate film produced by using the above mentioned adhesive for food packaging films.
  • Examples of the film contain a film in which a metallic layer is formed on a plastic substrate and is not formed on a plastic substrate.
  • the adhesive for food packaging films according to the present invention is applied to a film.
  • the application can be performed by various methods such as gravure coating, wire bar coating, air knife coating, die coating, lip coating and comma coating methods.
  • Plural films coated with the present adhesive for food packaging films can be laminated and bonded each other to produce a food packaging film.
  • the adhesive for food packaging films is applied to a film
  • the adhesive is applied preferably in an amount of 1-100 g/m 2 and more preferably in an amount of 2-35 g/m 2 [0051]
  • FIG. 1 An embodiment of the food packaging film according to the present invention is exemplified in Fig. 1, but the present invention is not limited to these embodiments.
  • Fig. 1 displays a sectional view of a food packaging film 10.
  • This food packaging film 10 is a laminate comprising one metallic foil 14 and two plastic films 12 and 13, and the two plastic films 12 and 13 are adhered on both sides of the metallic foil 14 by using adhesive layers 11, respectively.
  • the plastic film 12 is preferably a polyethylene terephthalate (PET) film
  • the film 13 is preferably a polyolefin film, particularly more preferably a PP film and most preferably a CPP film.
  • the metallic foil 14 is inserted between them.
  • the metallic foil 14 may be, for example, an aluminum foil.
  • the film 12 is bonded to the metallic foil 14, and the film 13 is bonded to the metallic foil 14 by the adhesive layers for food packaging films 11, respectively.
  • the film to be laminated contain plastic films produced from such as polyethylene terephthalates , nylons, polyethylenes , polypropylenes and polyvinyl chlorides; metallic foils such as aluminum foil; deposited films such as metal deposited films and silica deposited films; metallic films produced from such as stainless, steel, copper and lead.
  • the plastic film preferably has a thickness of 5-200 ym.
  • a food packaging bag can be produced, for example, by heat-sealing the food packaging film according to the present invention.
  • the food packaging bag can include (or enclose) a food.
  • Examples of the food to be included contain pressurized, heated and sterilized foods (that is, retort foods) , and examples of the retort foods contain curries, stews, meat sauces and soups etc.
  • the food packaging film according to the present invention can be preferably used so as to produce a food packaging bag for including and sealing the retort foods, a so called retort pouch. Since the food packaging film according to the present invention is produced by using the above mentioned adhesive for food packaging films, it is difficult for the food packaging film to cause delamination and the appearance of the film does not change, even though the food packaging film enclosing an inclusion (or a food) is sterilized and stored for 2 weeks. Therefore, the food packaging film is excellent in inclusion-resistance compared to prior food packaging films.
  • polyester polyol (A2) having a number average molecular weight of 10,000 and a hydroxyl number of 11.2 mgKOH/g.
  • Addition of ethyl acetate to the polyester polyol (A2) gave a solution (non-volatile content: 50 wt%) of the polyester polyol (A2) .
  • polyesterpolyurethane polyol (A3) having a number average molecular weight of 10,000 and a hydroxyl number of 10.0 mgKOH/g. Addition of ethyl acetate to the polyesterpolyurethane polyol (A3) gave a solution (nonvolatile content: 50 wt%) of the polyesterpolyurethane polyol (A3) .
  • Adhesives for food packaging films used in examples and comparative examples were produced by mixing (A1)-(A4) and (A6) prepared in the synthetic examples 1-6, (A5) general -purpose diethylene glycol, isocyanate components (B) and aromatic compounds (C) .
  • the components (B) and (C) as raw materials of the adhesives for food packaging films are described below.
  • Components (A) - (C) were mixed at ratios (or in amounts) (solid content) as shown in Tables 1-3, and further ethyl acetate was mixed in a suitable amount and stirred to give solutions at a concentration of 30 wt% (solid content) .
  • an aromatic compound (C) was mixed with a polyol component (A) and stirred. After confirming that they dissolved completely, an isocyanate component (B) and ethyl acetate were added, further stirred and mixed.
  • the adhesive of each of the examples and comparative examples was applied to a PET film at a normal temperature by an applicator such that the weight of the solid component becomes 4.0 g/m 2 , the solvent was vaporized, and then the adhesive coated surface of the PET film was laid on and bonded to a surface of an aluminum foil.
  • the adhesive of each of the examples and comparative examples was applied to a corona treated surface of a CPP (Cast Polypropylene) film, and the solvent was vaporized by using a similar manner to the above mentioned method. Then, the adhesive coated surface of the CPP film was laid on and bonded to the other surface of the aluminum foil of the previously produced double layered material to produce a composite film.
  • CPP Chemical Polypropylene
  • the composite film was aged at 50 °C for 4 days, and the adhesive composition was cured to give an objective triple layered composite film.
  • the above mentioned triple layered composite film was cut out into test pieces of 300 mm X 15 mm.
  • T type peel tests were carried out at a temperature of 23 °C at a relative humidity of 50 % at a peeling speed of 300 mm/min, and then the peel strength (N/15 mm) of the aluminum foil/CPP film was measured.
  • the peel strength was measured five times, and the average value is shown in the Tables 1-3.
  • a packaging bag of 14 cm X 28 cm was produced from the above triple layered film by using a heat sealer.
  • grain vinegar produced by Tamanoi Vinegar Co., Ltd.
  • silica ketchup produced by RIKEN Nosan- ako Co., Ltd.
  • tomato ketchup Karloman Corporation
  • the completely sealed packaging bag was subjected to a pressurization hot-water sterilization treatment at a temperature of 121 °C for 30 minutes under a pressure of 0.20 MPa in a sterilization testing machine. Then, the packaging bag was cut and opened, and was cut out into test pieces of 300 mm X 15 mm. Using a similar manner to the above mentioned peel strength test, the peel strength (N/15 mm) between the aluminum foil and the CPP film of each of the test pieces was measured, and appearance of each of the films just after the sterilization was visually evaluated.
  • Results of the evaluation of the appearance just after the sterilization of the aluminum foil/CPP film are shown in Tables 1-3 (2-1)
  • Results of the peel strength just after the sterilization of the aluminum foil/CPP film are shown in Tables 1-3 (2-2) .
  • the evaluation criteria for the appearance (2-1) just after the sterilization are shown as follows:
  • the above mentioned packaging bag after the sterilization treatment was stored at 60 °C for 2 weeks in a constant temperature oven, and then the appearance of the aluminum foil/CPP film was visually observed (2-3).
  • the evaluation criteria for the appearance (2-3) of the film after the storage at 60 °C for 2 weeks are the same as those for the appearance (2-1) of the film just after the sterilization.
  • the amount of each component means weight per 100 part by weight of the total solid content of the (A) [0073]
  • the amount of each component means weight per 100 parts by weight of the total solid content of the (A) - (C) .
  • the amount of each component means weight per 100 part by weight of the total solid content of the (A) - (C) .
  • the adhesives for food packaging films of the examples 1-17 were obtained by using the three kinds of the components (A) - (C) , they were excellent in peel strength and inclusion-resistance as shown in Tables 1 and 2. Even though the triple layered composite films of the examples 1-17 were sterilized and stored at 60 °C for 2 weeks, the films show no deamination.
  • the adhesives for food packaging films of the comparative examples comprise no component (C) , their inclusion-resistances are inferior to those of the adhesives of the present examples as shown in Table 3.
  • the triple layered composite films of the comparative examples clearly showed delamination after they were sterilized and stored at 60 °C for 2 weeks.
  • the present invention provides an adhesive for food packaging films.
  • the adhesive for food packaging films according to the present invention is suitably used for producing a food packaging film having excellent inclusion- resistance, particularly a retort pouch. Description of Reference Numerals [0077]

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Abstract

Provided is an adhesive for food packaging films, which adhesive does not cause delamination of a plastic film when a food packaging film is produced by laminating the plastic film, and which adhesive can maintain appearance of the food packaging film for a long time after sterilization of a food packaging bag (or pouch) produced from the food packaging film. Disclosed is an adhesive for food packaging films, comprising a urethane resin obtainable by mixing: (A) a polyol component; (B) an isocyanate component; and (C) an aromatic compound having both a phenolic hydroxyl group, and a carboxyl group or an ester group. The adhesive for food packaging films is excellent in peel strength and inclusion-resistance (or resistance to inclusions). Therefore, the adhesive is very suitable so as to adhere (or produce) food packaging films.

Description

DESCRIPTION
ADHESIVE FOR FOOD PACKAGING FILMS
Cross-Reference to Related Application
[0001]
This application claims priority under Article 4 of the Paris Convention based on Japanese Patent Application No. 2013-256754 filed on December 12, 2013 in Japan, which is incorporated herein by reference in its entirety.
Technical Field
[0002]
The present invention relates to an adhesive for food packaging films.
Background Art
[0003]
Food packaging films are composite laminate films, and are composed of various plastic films and/or metallic foils having a thickness of approximately 5 to 100 μπι. Examples of the plastic films contain films produced by polyolefins such as polyethylenes and polypropylenes (PP) , copolymers of olefins, polyvinyl chlorides, polyvinylidene chlorides, polyesters and polyamides, and examples of the metallic foils contain foils produced by such as aluminum and stainless-steel etc.
[0004]
These plastic films and metallic foils are characterized by properties such as strength, water resistance, moisture permeability resistance, oxygen permeability resistance and heat resistance. Therefore, high performance food packaging films which cannot be obtained by using only a single film can be provided by laminating two or more kinds of films, if necessary. Examples of adhesives used for producing food packaging films contain predominantly urethane adhesives. Patent Documents 1-3 disclose that a food packaging film is produced by laminating a plastic film using a urethane adhesive .
[0005]
Patent Document 1 discloses an adhesive for food packaging films in which a phosphoric oxyacid, a carboxylic acid, an acid anhydride thereof, and an epoxy resin are mixed into a urethane resin (see [claim 1] and [Examples] of Patent Document 1) . Patent Document 2 discloses a urethane adhesive comprising a phosphoric oxyacid and a silane coupling agent (see [claim 1] and [Table 1] of Patent Document 2) . Patent Document 3 discloses a urethane adhesive obtainable by reacting a partly acid modified polyol with a polyisocyanate (see [claim 1] and [Table 1] of Patent Document 3) .
[0006]
Patent Documents 1-3 disclose urethane adhesives in which peel strength, heat resistance and acid resistance are improved. Each of these urethane adhesives is suitable for producing food packaging films by laminating a plastic film and so on.
However, recently it is needed for an adhesive for food packaging films that appearance of a food packaging film is not affected, even though an inclusion (or enclosed material) (for example a food) is enclosed in a food packaging bag made from the food packaging film by using the adhesive, sterilized, and then stored for a certain period of time. That is, it is needed for an adhesive for food packaging films to be excellent in inclusion- resistance (resistance to an inclusion or enclosed material) . Since the urethane adhesives of References 1-3 comprise an epoxy resin, a silane coupling agent and various acid components, each of the urethane adhesives has improved peel strength (please note that there is no inclusion), but has insufficient inclusion-resistance.
[0007]
Patent Document 1: JP 2683937 B
Patent Document 2: JP 2002-003813 A
Patent Document 3: JP 2005-132902 A Summary of Invention
Problems to be Solved by the Invention
[0008]
The present invention has been made so as to solve such a problem and an object thereof is to provide an adhesive for food packaging films, which adhesive does not cause delamination of a plastic film when a food packaging film (or a laminate film) is produced by laminating the plastic film, and moreover, which adhesive can maintain the appearance of the food packaging film for a long time (be excellent in inclusion-resistance or resistance to an enclosed material) after an inclusion (or enclosed material) is enclosed in a food packaging bag (or pouch) produced from the food packaging film and sterilized.
Means for Solving the Problems
[0009]
The present inventors have intensively studied and found, surprisingly, that it is possible to obtain an adhesive for food packaging films, which adhesive has high peel strength and is excellent in inclusion-resistance, when a urethane adhesive is produced by using an aromatic compound having a specific structure.
[0010] Namely, the present invention provides, in an aspect, an adhesive for food packaging films, comprising a urethane resin obtainable by mixing:
(A) a polyol component ;
(B) an isocyanate component; and
(C) an aromatic compound having both a phenolic hydroxyl group, and a carboxyl group or an ester group.
A food packaging film can be suitably produced by using the adhesive.
[0011]
In an embodiment of the present invention, an adhesive for food packaging films, wherein the aromatic compound (C) comprises at least one selected from gallic acid, gallic acid alkyl esters and tannic acid, is provided.
In another embodiment of the present invention, an adhesive for food packaging films, wherein the polyol component (A) comprises a polyester polyol and/or a polyesterpolyurethane polyol, is provided.
[0012]
In a preferable embodiment of the present invention, an adhesive for food packaging films, wherein the isocyanate component (B) comprises a polyfunctional isocyanate compound derived from an alicyclic diisocyanate compound and/or an aliphatic diisocyanate compound, is provided. In a further preferable embodiment of the present invention, an adhesive for food packaging films, wherein the aromatic compound (C) is mixed in an amount of 0. Ol- IO.0 parts by weight per 100 parts by weight of the total weight of the polyol component (A) , the isocyanate component (B) and the aromatic compound (C) , is provided.
Effects of the Invention
[0013]
The adhesive according to the present invention comprises a urethane resin obtainable by mixing: (A) a polyol component; (B) an isocyanate component; and (C) an aromatic compound having both a phenolic hydroxyl group, and a carboxyl group or an ester group. Therefore, the adhesive is excellent in peel strength and inclusion- resistance. Thus, the adhesive is much suitable so as to produce food packaging films.
A food packaging film produced by using the present adhesive for food packaging films does not cause delamination (or peeling) of a film and can maintain its appearance, even though the food packaging film is sterilized and stored at 60 °C for 2 weeks.
[0014]
The adhesive for food packaging films has further improved inclusion-resistance, when the aromatic compound (C) comprises at least one selected from gallic acid, gallic acid alkyl esters and tannic acid.
The adhesive for food packaging films has further improved inclusion-resistance, when the polyol component (A) comprises a polyester polyol and/or a polyesterpolyurethane polyol.
[0015]
The adhesive for food packaging films has further improved heat resistance, when the isocyanate component (B) comprises a polyfunctional isocyanate compound derived from an alicyclic diisocyanate compound and/or an aliphatic diisocyanate compound.
The adhesive for food packaging films has further improved inclusion-resistance, when the aromatic compound (C) is mixed in an amount of 0.01-10.0 parts by weight per 100 parts by weight of the total weight of the polyol component (A) , the isocyanate component (B) and the aromatic compound (C) .
Brief Description of Drawings
[0016]
Fig. 1 is a sectional view showing an embodiment of a food packaging film according to the present invention.
Description of Embodiments [0017]
An adhesive for food packaging films according to the present invention comprises a urethane resin obtainable by mixing: (A) a polyol component; (B) an isocyanate component; and (C) an aromatic compound having both a phenolic hydroxyl group, and a carboxyl group or an ester group (hereinafter referred to as an "aromatic compound (C)").
[0018]
The urethane resin according to the present invention is not particularly limited by mixing orders and mixing methods etc. of the components (a) - (c) as long as the objective adhesive can be obtained. For example, the urethane resin may be obtained by mixing the three kinds of components of the polyol component (A) , the isocyanate component (B) and the aromatic compound (C) at a time. Moreover, the urethane resin may be obtained by previously reacting the component (A) or the component (C) with the component (B) , and then mixing the remaining one component. The urethane resin is more preferably obtained by previously mixing the component (A) and the component (C) to give a mixture and then by mixing the mixture with the component (B) .
[0019]
The reaction of the component (A) , the component (C) and the component (B) can be carried out according to known methods. The urethane resin may be obtained by the reaction of the components (A) - (C) in a solvent, and the urethane resin may be obtained by the reaction of the components (A) - (C) with no solvent.
Moreover, the urethane resin may be obtained by using a polyol and an excess amount of isocyanate to prepare a urethane prepolymer having an NCO end (or terminal) and then by reacting the urethane prepolymer with a short chain polyol.
[0020]
The "polyol component (A) " in the present invention is not particularly limited as long as the objective present adhesive for food packaging films can be obtained and the polyol component (A) does not exert an adverse influence on the production (or synthesis) of the urethane resin.
The component (A) may be a polyol commonly used so as to obtain urethane resins. Examples of the component (A) contain polyester polyols, acrylic polyols, polyether polyols, polyetherester polyols, polyesterpolyurethane polyols, polyetherpolyurethane polyols, and modifications of these polyols.
[0021]
The "polyester polyol" means a compound which belongs to "main chain type" polyesters and has ester bonds and hydroxyl groups in the "main chain". The hydroxyl group is generally positioned on the end of the main chain, and acts as a functional group reacting with an isocyanate group.
The polyester polyol may be obtained by the condensation polymerization reaction of a low molecular weight polyol with a dicarboxylic acid and/or an acid anhydride thereof .
[0022]
Examples of the dicarboxylic acid contain oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, dodecanedioic acid, 2 -methylsuccinic acid, 2 -methyladipic acid, 3 -methyladipic acid, 3 -methylpentanedioic acid, 2- methyloctanedioic acid, 3 , 8 -dimethyldecanedioic acid, 3,7- dimethyldecanedioic acid, phthalic acid, terephthalic acid, isophthalic acid, naphthalenedicarboxylic acid, trimelitic acid, trimesic acid and cyclohexanedicarboxylic acid etc. These are used alone or in combination.
[0023]
Examples of the acid anhydride contain acetic anhydride, propionic anhydride, succinic anhydride, maleic anhydride, phthalic anhydride, trimelitic anhydride and pyromellitic anhydride etc. These can be used alone or in combination.
[0024] The low molecular weight polyol preferably has from 1 to 3 functional groups, and is particularly preferably a bifunctional polyol, that is, a so called diol . The low molecular weight polyol can be used alone or in combination Examples of the diol contain low molecular weight diols such as ethylene glycol, 1-methylethylene glycol, 1- ethylethylene glycol, diethylene glycol, propylene glycol, butanediol, pentanediol, hexanediol, heptanediol, octanediol, nonanediol, decanediol, neopentyl glycol, 2- methyl-1, 3 -propanediol, cyclohexanedimethanol , 2,4- dimethyl-1 , 5 -pentanediol and 2 , 4 -dibutyl - 1 , 5 -pentanediol etc. Particularly, at least one selected from ethylene glycol, diethylene glycol, butanediol, hexanediol and neopentyl glycol may be used.
[0025]
The "acrylic polyol" means a compound which can be obtained by the addition polymerization reaction of a (meth) acrylate having a hydroxyl group and which have an ester bond in the "side chain".
The "acrylic polyol" may be a homopolymer of the
(meth) acrylate having a hydroxyl group or a copolymer of the (meth) acrylate having a hydroxyl group with the "other polymerizable monomer" in the present invention. The hydroxyl group of the acrylic polyol is allowed to react with an isocyanate group. [0026]
Examples of the " (meth) acrylate having a hydroxyl group" contain 2 -hydroxyethyl (meth) acrylate , 2 -hydroxy- propyl (meth) acrylate , 3 -hydroxypropyl (meth) acrylate , glycerin mono (meth) acrylate and 4 -hydroxybutyl acrylate.
[0027]
The "other polymerizable monomer" means a "radical polymerizable monomer having an ethylenic double bond" except for the " (meth) acrylate having a hydroxy group".
Concrete examples contain (meth) acrylic acid, methyl
(meth) acrylate , ethyl (meth) acrylate , butyl (meth) acrylate , cyclohexyl (meth) acrylate , 2-ethylhexyl (meth) acrylate , dicyclopentanyl (meth) acrylate , isobornyl (meth) acrylate , styrene and vinyltoluene etc.
Examples of the "polyether polyol" in the present invention contain polyoxytetramethylene glycols (PT G) , polyoxypropylene glycols (PPG) and polyoxyethylene glycols (PEG) etc.
[0028]
The "polyetherpolyurethane polyol" may be a compound in which urethane bonds are formed by the chain extension reaction of the above polyether polyol with an isocyanate compound .
The "polyesterpolyurethane polyol" may be a compound in which urethane bonds are formed by the chain extension reaction of the above polyester polyol with an isocyanate compound .
The "polyetherester polyol" means a polyol having both an ester group and an ether group in the main chain.
[0029]
The "isocyanate component (B) " according to the present invention is not limited as long as examples of the isocyanate component contain aliphatic isocyanates, aromatic isocyanates and alicyclic isocyanates, and the objective present adhesive for food pakcaging films can be obtained. Furthermore, considering that the present invention relates to an adhesive for food packaging films, it is not so preferable to use an aromatic isocyanate which may generate an aromatic amine having carcinogenicity. Therefore, the isocyanate component (B) comprising only aromatic isocyanate is excluded.
[0030]
The isocyanate component (B) according to the present invention does not mean that the isocyanate component comprises only an aliphatic isocyanate and/or an alicyclic isocyanate. The isocyanate component (B) may comprise an aromatic isocyanate, as long as the present objective adhesive for food packaging films can be obtained, that is, an adverse influence on the peel strength and inclusion- resistance of the present adhesive for food packaging films is not exerted, and elution of the aromatic amine is not found .
[0031]
In the present specification, the "aliphatic isocyanate" means a compound which has a chain-like hydrocarbon chain to which an isocyanate group is directly bonded, and also has no cyclic hydrocarbon chain. The "aliphatic isocyanate" may have an aromatic ring, but the isocyanate group is not bonded directly to the aromatic ring.
Furthermore, in the present specification, the cyclic hydrocarbon chain does not contain aromatic rings.
[0032]
The "alicyclic isocyanate" means a compound which has a cyclic hydrocarbon chain, and may have a chain- like hydrocarbon chain. The isocyanate group may be directly bonded to the cyclic hydrocarbon chain, or may be directly bonded to a chain- like hydrocarbon chain which may be present. Although the "alicyclic isocyanate" may have an aromatic ring, the isocyanate group is not directly bonded to the aromatic ring.
The "aromatic isocyanate" means a compound which has an aromatic ring and in which the isocyanate group is directly bonded with the aromatic ring. Therefore, even though an isocyanate compound has an aromatic ring in the molecule, when the isocyanate group is not directly bonded to the aromatic ring, the isocyanate compound is classified into the aliphatic isocyanate or alicyclic isocyanate.
[0033]
Therefore, for example, 4 , 4 ' -diphenylmethane diisocyanate (OCN-C6H4-CH2-C6H4-NCO) is corresponding to the aromatic isocyanate, since the isocyanate group is directly bonded to the aromatic ring. On the other hand, for example, xylylene diisocyanate (OCN-.CH2-C6H4-CH2-NCO) is corresponding to the aliphatic isocyanate, although it has an aromatic ring, since the isocyanate group is not directly bonded to the aromatic ring and is bonded to the methylene group. Further, the aromatic ring may have a ring-fused structure in which two or more benzene rings are condensed.
[0034]
Examples of the aliphatic isocyanate contain 1,4- diisocyanatobutane , 1 , 5-diisocyanatopentane , 1,6- diisocyanatohexane (hereinafter referred to as HDI) , 1,6- diisocyanato-2 , 2 , 4 -trimethylhexane , methyl 2,6- diisocyanatohexanate (lysine diisocyanate) and 1,3- bis ( isocyanatomethyl ) benzene (xylylene diisocyanate)
(hereinafter referred to as XDI) etc.
[0035]
Examples of the alicyclic isocyanate contain 5- isocyanato-l-isocyanatomethyl-1 , 3 , 3 -trimethylcyclohexane (isophorone diisocyanate) (hereinafter referred to as IPDI) , 1, 3 -bis (isocyanatomethyl) cyclohexane (hydrogenated xylylene diisocyanate), bis (4- isocyanatocyclohexyl) methane (hydrogenated diphenylmethane diisocyanate) and 1,4- diisocyanatocyclohexane etc.
[0036]
Examples of the aromatic isocyanate contain 4,4'- diphentylmethane diisocyanate (hereinafter referred to as MDI) , toluene diisocyanate (hereinafter referred to as TDI) , p-phenylene diisocyanate and m-phenylene diisocyanate etc.
These isocyanate compounds can be used alone or in combination .
[0037]
The isocyanate component (B) preferably comprises at least one selected from HDI, IPDI, XDI and modifications thereof, and more preferably comprises at least one selected from isocyanurate of 1 , 6 -diisocyanatohexane (HDI), trimethylolpropane adduct of isophorone diisocyanate (IPDI) , and trimethylolpropane adduct of xylylene diisocyanate (XDI) . The isocyanate component (B) is ecologically preferable when the isocyanate component (B) comprises the above isocyanate, since it becomes difficult for the isocyanate component (B) to be volatilized and an aromatic amine having carcinogenicity is never eluted. Further, the inclusion-resistance of the adhesive for food packaging films is also improved.
[0038]
The aromatic compound (C) in the the present invention has a carboxyl group or an ester group, and a phenolic hydroxy1 group .
In the present specification, the "phenolic hydroxyl group" means a hydroxyl group which directly bonds to an aromatic ring.
[0039]
In the present specification, the carboxyl group (- COOH) means a hydrophilic functional group in which a carbon atom is bonded to a hydroxyl group by a single bond, and is bonded to an oxygen atom by a double bond. The carboxyl group can contain a carboxylic acid base group (- COO") in which a hydrogen of the hydroxyl group is dissociated. The counter cation is not particularly limited as long as the adhesive according to the present invention can be obtained. Examples of the counter cation contain sodium ion, potassium ion and magnesium ion etc.
In the present specification, the ester group is represented by (-C00R), and means a functional group in which the hydrogen atom of the carboxyl group is replaced with an R. The R represents an alkyl group and an aryl group . [0040]
Examples of the aromatic compound (C) are concretely presented as follows, but the present invention is not limited by the following concrete examples. Preferable embodiments of the aromatic compound (C) contain:
gallic acid;
gallic acid alkyl esters such as methyl gallate, ethyl gallate and propyl gallate etc.; and
the other acids and esters thereof such as tannic acid, aminosalicylic acid, hydroxyphenylacetic acid, methyl hydroxyphenylacetate , salicylic acid, methyl salicylate, hydroxybenzoic acid, methyl hydroxybenzoate , diphenolic acid and mycophenolate mofetil etc.
[0041]
In an embodiment of the present invention, the aromatic compound (C) preferably comprises at least one selected from gallic acid, gallic acid alkyl esters and tannic acid, and particularly preferably comprises gallic acid.
[0042]
In an embodiment of the present invention, the aromatic compound (C) is preferably used in an amount of 0.01-10.0 parts by weight (solid content), more preferably used in an amount of 0.01-5.0 parts by weight (solid content), and particularly preferably used in an amount of 0.1-2.0 parts by weight (solid content), per 100 parts by- weight of the total weight of the components (A) - (C) .
When the aromatic compound (C) is used within the above mentioned range, the peel strength and the inclusion- resistance of the present adhesive for food packaging films are still further improved.
[0043]
The adhesive for food packaging films according to the present invention may comprise the other component in addition to the components (A) - (C) . Examples of the other component contain solvents, tackifier resins, pigments (or colorants), plasticizers , catalysts and adhesion promoters etc.
[0044]
Examples of the "tackifier resin" contain styrene based resins, terpene based resins, aliphatic petroleum resins, aromatic petroleum resins, rosin esters, acrylic resins, polyester resins (excluding polyester polyols) and the like. The tackifier resin generally may have a molecular weight less than 1500 g/mol, particularly a low molecular weight less than 1000 g/mol. The tackifier resin can be used preferably in an amount of from 0 to 50 parts by weight, more preferably in an amount of not more than 30 parts by weight, per 100 parts by weight of the total weight of the adhesive for food packaging films. [0045]
Examples of the pigment contain such as nanopigments based on Ti02, Si02, Fe203, similar oxides and oxyhydrates etc. These■ pigments preferably have a particle size of not more than 500 nm, and more preferably have a particle size of not more than 100 nm.
Examples of the plasticizer contain white oils, naphthenic mineral oils, paraffinic hydrocarbon oils, polypropylene oligomers, polybutene oligomers, polyisoprene oligomers, hydrogenated polyisoprene oligomers, hydrogenated polybutadine oligomers, phthalates, adipates, benzoate esters, vegetable oils, animal oils, and derivatives thereof etc. Considering that the present adhesive is used for producing food packaging films, the vegetable oils, animal oils and derivatives thereof are preferable, since they can be generally used for foods and they seem to be safer.
[0046]
Examples of the "catalyst" contain metal based catalysts such as tin based catalysts (trimethyltin laurate, trimethyltin hydroxide, dibutyltin dilaurate and dibutyltin dimaleate etc.), lead based catalysts (lead oleate, lead naphthenate and lead octenate etc . ) and other metal based catalysts (metal naphthenate such as cobalt naphthenate) , and amine based catalysts such as triethylenediamine , tetramethylethylenediamine , tetramethylhexylenediamine , diazabicycloalkenes and diakylaminoalkylamines etc.
[0047]
Silane compounds are exemplified as the "adhesion promoter" . Known organic functional silanes such as (meth) acryloyloxy functional, epoxy functional, amine functional and non-reactive functional substituted silanes can be used as the adhesion promoter. Examples thereof contain vinyltrialkoxysilanes , alkyltrialkoxysilanes , tetraalkoxysilanes , 3 -acryloyloxypropyltrialkoxysilanes , 3- methacryloyloxypropyltrialkoxysilanes , 3 -aminopropyl- trimethoxysilane , 3 -aminopropyltriethoxysilane , 3-amino- propylmethyldimethoysilane , N- (2 -aminoethyl ) -3 -aminopropyl- trimethoxysilane , 3 -gycidyloxymethyltrimethoxysilane , 3- glycidyloxymethyltriethoxysilane and 2 -glycidyloxy- ethyltrimethoxysilane etc.
In an embodiment of the present invention, the adhesive for food packaging films preferably comprises the adhesion promoter in an amount of 0.1-5 parts by weight per 100 parts by weight of the total weight of the adhesive.
[0048]
The adhesive for food packaging films according to the present invention can be produced by mixing the component (A), (B) and (C) components as mentioned above. Optionally, the other component (s) may be mixed. The mixing method is not particularly limited as long as the objective present adhesive for food packaging films can be obtained. The mixing order of the components etc. is also not particularly limited. The adhesive for food packaging films according to the present invention can be produced without special mixing methods and special mixing orders etc. The obtained adhesive for food packaging films can be excellent in both peel strength and inclusion-resistance.
[0049]
Since the adhesive for food packaging films according to the present invention is applied to a film at a temperature of 15-100 °C, the adhesive should have a low viscosity in this temperature range. The adhesive for food packaging films preferably has a viscosity not more than 500 mPa-s, considering the coatability, when the viscosity is measured by means of Brookfield viscometer.
The food packaging film according to the present invention means a laminate film produced by using the above mentioned adhesive for food packaging films. Examples of the film contain a film in which a metallic layer is formed on a plastic substrate and is not formed on a plastic substrate.
[0050]
In the case of producing a food packaging film, the adhesive for food packaging films according to the present invention is applied to a film. The application can be performed by various methods such as gravure coating, wire bar coating, air knife coating, die coating, lip coating and comma coating methods. Plural films coated with the present adhesive for food packaging films can be laminated and bonded each other to produce a food packaging film.
When the adhesive for food packaging films is applied to a film, the adhesive is applied preferably in an amount of 1-100 g/m2 and more preferably in an amount of 2-35 g/m2 [0051]
An embodiment of the food packaging film according to the present invention is exemplified in Fig. 1, but the present invention is not limited to these embodiments.
Fig. 1 displays a sectional view of a food packaging film 10. This food packaging film 10 is a laminate comprising one metallic foil 14 and two plastic films 12 and 13, and the two plastic films 12 and 13 are adhered on both sides of the metallic foil 14 by using adhesive layers 11, respectively. More concretely, for example, the plastic film 12 is preferably a polyethylene terephthalate (PET) film, the film 13 is preferably a polyolefin film, particularly more preferably a PP film and most preferably a CPP film. The metallic foil 14 is inserted between them. The metallic foil 14 may be, for example, an aluminum foil. The film 12 is bonded to the metallic foil 14, and the film 13 is bonded to the metallic foil 14 by the adhesive layers for food packaging films 11, respectively.
[0052]
Examples of the film to be laminated contain plastic films produced from such as polyethylene terephthalates , nylons, polyethylenes , polypropylenes and polyvinyl chlorides; metallic foils such as aluminum foil; deposited films such as metal deposited films and silica deposited films; metallic films produced from such as stainless, steel, copper and lead. Moreover, with regard to the thickness thereof, for example, the plastic film preferably has a thickness of 5-200 ym.
[0053]
A food packaging bag can be produced, for example, by heat-sealing the food packaging film according to the present invention. The food packaging bag can include (or enclose) a food.
Examples of the food to be included contain pressurized, heated and sterilized foods (that is, retort foods) , and examples of the retort foods contain curries, stews, meat sauces and soups etc.
The food packaging film according to the present invention can be preferably used so as to produce a food packaging bag for including and sealing the retort foods, a so called retort pouch. Since the food packaging film according to the present invention is produced by using the above mentioned adhesive for food packaging films, it is difficult for the food packaging film to cause delamination and the appearance of the film does not change, even though the food packaging film enclosing an inclusion (or a food) is sterilized and stored for 2 weeks. Therefore, the food packaging film is excellent in inclusion-resistance compared to prior food packaging films.
Examples
[0054]
The present invention will be described below by way of Examples and Comparative Examples; these Examples are merely for illustrative purposes and are not meant to be limiting on the present invention.
[0055]
<Synthetic Examples of (A) Polyol Components and (B) Isocyanate Component>
Synthetic Example 1: Synthesis of (Al) Polyester Polyol
265.8 g of isophthalic acid, 23.6 g of 1 , 6 -hexanediol and 244.1 g of diethylene glycol were charged and the esterification reaction was carried out at 180-220 °C for 6 hours. After distillation of a predetermined amount of water, 131.5 g of adipic acid was added and the esterification reaction was further carried out at 180-220 °C for 6 hours. After distillation of a predetermined amount of water, 0.15 g of tetra (isopropyl) titanate was added. While reducing pressure gradually, the ester- exchange reaction was carried out at 200-250 °C for 3 hours to give a polyester polyol (Al) having a number average molecular weight of 8,000 and a hydroxyl number of 14.0 mgKOH/g. Addition of ethyl acetate to the polyester polyol (Al) gave a solution (non-volatile content: 50 wt%) of the polyester polyol (Al) .
[0056]
Synthetic Example 2: Synthesis of (A2) Polyester Polyol
265.8 g of isophthalic acid, 40.3 g of ethylene glycol, 67.7 g of neopentyl glycol and 118.2 g of 1 , 6-hexanediol were charged and the esterification was carried out at 180- 220 °C for 6 hours. After distillation of a predetermined amount of water, 73.1 g of adipic acid was added and the esterification was further carried out at 180-220 °C for 6 hours. After distillation of a predetermined amount of water, 0.15 g of tetra ( isopropyl ) titanate was added. While reducing pressure gradually, the ester-exchange reaction was carried out at 200-250 °C for 3 hours to give a polyester polyol (A2) having a number average molecular weight of 10,000 and a hydroxyl number of 11.2 mgKOH/g. Addition of ethyl acetate to the polyester polyol (A2) gave a solution (non-volatile content: 50 wt%) of the polyester polyol (A2) .
[0057]
Synthetic Example 3: Synthesis of (A3) Polyester- polyurethane Polyol
265.8 g of isophthalic acid, 74.5 g of ethylene glycol and 239.7 g of neopentyl glycol were charged and the esterification reaction was carried out at 180-220 °C for 2 hours. After distillation of a predetermined amount of water, 262.9 g of sebacic acid was added and the esterification was further carried out at 180-220 °C for 2 hours. After distillation of a predetermined amount of water, 0.15 g of tetra ( isopropyl ) titanate was added. While reducing pressure gradually, the excess ethylene glycol was removed at 200-250 °C over 2 hours to give a polyester polyol. 300 g of the polyester polyol was heated, depressurized and dehydrated at 120 °C, and then reacted with 21.0 g of isophorone diisocyanate (NCO/OH=0.7 ) at 130 °C until the NCO groups disappeared to give a polyesterpolyurethane polyol (A3) having a number average molecular weight of 10,000 and a hydroxyl number of 10.0 mgKOH/g. Addition of ethyl acetate to the polyesterpolyurethane polyol (A3) gave a solution (nonvolatile content: 50 wt%) of the polyesterpolyurethane polyol (A3) . [0058]
Synthetic Example 4: Synthesis of (A4) Polyether- polyurethane Polyol
A mixed solution of 500 g of polyoxypropylene glycol (having a number average molecular weight of 1,000), 93.9 g of dipropylene glycol, 188.0 g of toluenediisocyanate , 335 g of ethyl acetate and 0.15 g of tin octylate as a urethanization catalyst was allowed to react at 65 °C for 8 hours. Then, 13.4 g of trimetylolpropane was added and the mixed solution was further allowed to react for 2 hours to give a polyetherpolyurethane polyol (A4) having a number average molecular weight of 6,000 and a hydroxyl number of 21.0 mgKOH/g. Addition of ethyl acetate to the polyetherpolyurethane polyol (A4) gave a solution (non- volatile content: 70 wt%) of the polyetherpolyurethane polyol (A4) .
[0059]
Synthetic Example 5: Synthesis of (B4) Urethane Prepolymer Having NCO at the End.
265.8 g of isophthalic acid and 265.3 g of diethylene glycol were charged and the esterification reaction was carried out at 180-220 °C for 3 hours. After distillation of a predetermined amount of water, 119.9 g of adipic acid was added and the esterification reaction was further carried out for 3 hours. After distillation of a predetermined amount of water, 0.15 g of tetra ( isopropyl ) titanate was added. While reducing pressure gradually, the reaction was carried out at 200-250 °C for 3 hours to give a polyester polyol. 300 g of the polyester polyol was heated, depressurized and dehydrated at 120 °C. 65.0 g of isophorone diisocyanate (NC0/0H=2.0 ) and 0.80 g of tin octylate as a urethanization catalyst were added to the polyester polyol, and then allowed to react at 130 °C for 3 hours to give a urethane prepolymer (B4) having NCO at the end having a number average molecular weight of 5,000 and NCO% of 4.0% (NCO% = 4.0%). Addition of ethyl acetate to the urethane prepolymer (B4) having NCO at the end gave a solution (non-volatile content: 50 wt%) of the urethane prepolymer (B4) having NCO at the end.
[0060]
Synthetic Example 6: Synthesis of (A6) Partly Acid-modified Polyol
265.8 g of isophthalic acid, 40.3 g of ethylene glycol, 67.7 g of neopentyl glycol and 118.2 g of 1 , 6 -hexanediol were charged and the esterification reaction was carried out at 200-230 °C for 6 hours. After distillation of a predetermined amount of water, 73.1 g of adipic acid was added and the esterification reaction was further carried out for 6 hours. After distillation of a predetermined amount of water, while reducing pressure gradually, the esterification reaction was carried out at 230-250 °C for 5 hours to give a polyester polyol. 300 g of the polyester polyol was heated, depressurized and dehydrated at 120 °C, and then was reacted with 10.3 g of isophorone diisocyanate (NCO/OH=0.75) at 130 °C until the NCO groups disappeared to give a polyesterpolyurethane polyol having a number average molecular weight of 14,000 and a hydroxyl number of 8.0 mgKOH/g. 2.9 g of trimellitic anhydride and 6.2 g of ethylene glycol bisanhydrotrimellitate were added to 300 g of the polyesterpolyurethane polyol and allowed to react at 180 °C for 2 hours to give a partly acid-modified polyol (A6) . Addition of ethyl acetate to the partly acid- modified polyol (A6) gave a solution (non-volatile content: 50 weight %) of the partly acid-modified polyol (A6) .
[0061]
Adhesives for food packaging films used in examples and comparative examples were produced by mixing (A1)-(A4) and (A6) prepared in the synthetic examples 1-6, (A5) general -purpose diethylene glycol, isocyanate components (B) and aromatic compounds (C) . The components (B) and (C) as raw materials of the adhesives for food packaging films are described below.
[0062]
(B) Isocyanate components
(Bl) Isocyanurate of 1 , 6 -diisocyanatohexane (HDI) (Sumidur N3300 (trade name) produced by Sumika Bayer Urethane Co., Ltd., NCO¾=21.8%)
(B2) TMP (trimethylolpropane) adduct of xylylene diisocyanate (XDI) , ethyl acetate solution having the adduct at a concentration of 75 wt% (Takenate D-110N (trade name) produced by Mitsui Chemicals, Inc., NCO%=11.5)
(B3) TMP adduct of isophorone diisocyanate (IPDI) , ethyl acetate solution having the adduct at a concentration of 75 wt% (Takenate D-140N (trade name) produced by Mitsui Chemicals, Inc., NCO%=10.5)
(B4) the solution of the urethane prepolymer produced in the Synthetic example 5
[0063]
(C) Aromatic compounds
(CI) Gallic acid (Gallic acid Anhydrous (trade name) ) (C2) Tannic acid
(C3) Ethyl gallate
(C4) Propyl gallate
(C5) Aminosalicylic acid (4 -Aminosalicylic acid (trade name) )
(C6) 3 , 4 -Hydroxyphenylacetic acid
(C'7) Benzoic acid
(C8) Resorcinol
(C'9) Orthophosphoric acid 85 wt% (Phosphoric acid-d3, 85%w/w Solution (trade name) ) (CIO) Phthalic Anhydride (Phthalic Anhydride (trade name) )
(C'll) Epoxy resin (jER1002 (trade name) produced by Mitsubishi Chemical Corporation)
(C'12) 3 -Glycidoxypropyl trimethoxysilane (KBM-403
(trade name) produced by Shin-Etsu Chemical Co., Ltd.)
Moreover, all of the (CI) -(CIO) were produced by Wako Pure Chemical Industries, Ltd. Furthermore, when a trade name of the above aromatic compound is not recited, the trade name of the compound is the same as the name of the compound .
[0064]
The following adhesives for food packaging films of examples 1-17 and comparative examples 1-10 were produced by using the above mentioned components, and performances thereof were evaluated. The production methods and evaluation methods are described below.
[0065]
<Synthesis of Adhesives for Food Packaging Films>
Components (A) - (C) were mixed at ratios (or in amounts) (solid content) as shown in Tables 1-3, and further ethyl acetate was mixed in a suitable amount and stirred to give solutions at a concentration of 30 wt% (solid content) .
Concretely, for example, first an aromatic compound (C) was mixed with a polyol component (A) and stirred. After confirming that they dissolved completely, an isocyanate component (B) and ethyl acetate were added, further stirred and mixed.
[0066]
<Production of Composite Films>
The adhesive of each of the examples and comparative examples was applied to a PET film at a normal temperature by an applicator such that the weight of the solid component becomes 4.0 g/m2, the solvent was vaporized, and then the adhesive coated surface of the PET film was laid on and bonded to a surface of an aluminum foil.
Next, the adhesive of each of the examples and comparative examples was applied to a corona treated surface of a CPP (Cast Polypropylene) film, and the solvent was vaporized by using a similar manner to the above mentioned method. Then, the adhesive coated surface of the CPP film was laid on and bonded to the other surface of the aluminum foil of the previously produced double layered material to produce a composite film.
Then, the composite film was aged at 50 °C for 4 days, and the adhesive composition was cured to give an objective triple layered composite film.
[0067]
<Evaluation> Evaluations of the adhesive for food packaging films were performed as follows.
[0068]
1. Peel Strength Test
The above mentioned triple layered composite film was cut out into test pieces of 300 mm X 15 mm. Using a tensile strength testing machine (TENSILON RTM-250 (trade name) manufactured by ORIENTEC Co., Ltd.), T type peel tests were carried out at a temperature of 23 °C at a relative humidity of 50 % at a peeling speed of 300 mm/min, and then the peel strength (N/15 mm) of the aluminum foil/CPP film was measured. With regard to the adhesive of each of the examples and comparative examples, the peel strength was measured five times, and the average value is shown in the Tables 1-3.
[0069]
2. Inclusion-Resistance Test
A packaging bag of 14 cm X 28 cm was produced from the above triple layered film by using a heat sealer. On the other hand, previously, grain vinegar (produced by Tamanoi Vinegar Co., Ltd.) /salad oil (produced by RIKEN Nosan- ako Co., Ltd.) /tomato ketchup (Kikkoman Corporation) were mixed and stirred at a weight ratio of 1/1/1 to give a mixture. The mixture was used as an inclusion (or enclosed material) for the packaging bag. The packaging bag was filled with 100 g of the inclusion, the lid of the packaging bag was heat-sealed and the packaging bag was completely closed and sealed. The completely sealed packaging bag was subjected to a pressurization hot-water sterilization treatment at a temperature of 121 °C for 30 minutes under a pressure of 0.20 MPa in a sterilization testing machine. Then, the packaging bag was cut and opened, and was cut out into test pieces of 300 mm X 15 mm. Using a similar manner to the above mentioned peel strength test, the peel strength (N/15 mm) between the aluminum foil and the CPP film of each of the test pieces was measured, and appearance of each of the films just after the sterilization was visually evaluated.
[0070]
Results of the evaluation of the appearance just after the sterilization of the aluminum foil/CPP film are shown in Tables 1-3 (2-1) , and Results of the peel strength just after the sterilization of the aluminum foil/CPP film are shown in Tables 1-3 (2-2) . The evaluation criteria for the appearance (2-1) just after the sterilization are shown as follows:
A: All right
B: Although the surface of the aluminum foil was partly corroded, no delamination was observed.
C: Although the surface of the aluminum foil was wholly corroded, no delamination was observed. D: The surface of the aluminum foil was wholly corroded, and delamination was partly observed.
E: The surface of the aluminum foil was wholly corroded, and broad delamination was observed.
[0071]
Furthermore, the above mentioned packaging bag after the sterilization treatment was stored at 60 °C for 2 weeks in a constant temperature oven, and then the appearance of the aluminum foil/CPP film was visually observed (2-3). The evaluation criteria for the appearance (2-3) of the film after the storage at 60 °C for 2 weeks are the same as those for the appearance (2-1) of the film just after the sterilization.
[0072]
[Table 1]
Figure imgf000039_0001
The amount of each component means weight per 100 part by weight of the total solid content of the (A) [0073]
[Table 2]
Figure imgf000040_0001
*1: The amount of each component means weight per 100 parts by weight of the total solid content of the (A) - (C) . [0074]
[Table 3]
Figure imgf000041_0001
The amount of each component means weight per 100 part by weight of the total solid content of the (A) - (C) . [0075]
Since the adhesives for food packaging films of the examples 1-17 were obtained by using the three kinds of the components (A) - (C) , they were excellent in peel strength and inclusion-resistance as shown in Tables 1 and 2. Even though the triple layered composite films of the examples 1-17 were sterilized and stored at 60 °C for 2 weeks, the films show no deamination.
On the other hand, since the adhesives for food packaging films of the comparative examples comprise no component (C) , their inclusion-resistances are inferior to those of the adhesives of the present examples as shown in Table 3. Particularly, the triple layered composite films of the comparative examples clearly showed delamination after they were sterilized and stored at 60 °C for 2 weeks.
Industrial Applicability
[0076]
The present invention provides an adhesive for food packaging films. The adhesive for food packaging films according to the present invention is suitably used for producing a food packaging film having excellent inclusion- resistance, particularly a retort pouch. Description of Reference Numerals [0077]
: Food packaging film, 11: Adhesive layer, 12: Plastic (PET) film, 13: Plastic (PP) film, 14: Metallic (aluminum)

Claims

1. An adhesive for food packaging films, comprising a urethane resin obtainable by mixing:
(A) a polyol component;
(B) an isocyanate component and
(C) an aromatic compound having both a phenolic hydroxyl group, and a carboxyl group or an ester group.
2. The adhesive for food packaging films according to claim 1, wherein the aromatic compound (C) comprises at least one selected from gallic acid, gallic acid alkyl esters and tannic acid.
3. The adhesive for food packaging films according to claim 1 or 2, wherein the isocyanate component (B) comprises a polyfunctional isocyanate compound derived from an alicyclic diisocyanate compound and/or an aliphatic diisocyanate compound.
4. The adhesive for food packaging films according to any one of claims 1-3, wherein the aromatic compound (C) is mixed in an amount of 0.01-10.0 parts by weight per 100 parts by weight of the total weight of the polyol component (A) , the isocyanate component (B) and the aromatic compound (C) .
5. A food packaging film obtainable by using the adhesive for food packaging films according to any one of claims 1-4.
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