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WO1998010724A1 - Silicone-containing polyolefin film - Google Patents

Silicone-containing polyolefin film Download PDF

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Publication number
WO1998010724A1
WO1998010724A1 PCT/CA1997/000665 CA9700665W WO9810724A1 WO 1998010724 A1 WO1998010724 A1 WO 1998010724A1 CA 9700665 W CA9700665 W CA 9700665W WO 9810724 A1 WO9810724 A1 WO 9810724A1
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WO
WIPO (PCT)
Prior art keywords
polyolefin
layer
film
resin
vinyl
Prior art date
Application number
PCT/CA1997/000665
Other languages
French (fr)
Inventor
Peter Yates Kelly
Original Assignee
Dupont Canada Inc.
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 Dupont Canada Inc. filed Critical Dupont Canada Inc.
Priority to AU41965/97A priority Critical patent/AU4196597A/en
Priority to CA002265868A priority patent/CA2265868A1/en
Publication of WO1998010724A1 publication Critical patent/WO1998010724A1/en

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Classifications

    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
    • C08L23/00—Compositions of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Compositions of derivatives of such polymers
    • C08L23/02—Compositions of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Compositions of derivatives of such polymers not modified by chemical after-treatment
    • C08L23/04—Homopolymers or copolymers of ethene
    • C08L23/08—Copolymers of ethene
    • C08L23/0807—Copolymers of ethene with unsaturated hydrocarbons only containing four or more carbon atoms
    • C08L23/0815—Copolymers of ethene with unsaturated hydrocarbons only containing four or more carbon atoms with aliphatic 1-olefins containing one carbon-to-carbon double bond
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
    • C08F255/00—Macromolecular compounds obtained by polymerising monomers on to polymers of hydrocarbons as defined in group C08F10/00
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
    • C08F255/00—Macromolecular compounds obtained by polymerising monomers on to polymers of hydrocarbons as defined in group C08F10/00
    • C08F255/02—Macromolecular compounds obtained by polymerising monomers on to polymers of hydrocarbons as defined in group C08F10/00 on to polymers of olefins having two or three carbon atoms
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
    • C08L23/00—Compositions of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Compositions of derivatives of such polymers
    • C08L23/02—Compositions of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Compositions of derivatives of such polymers not modified by chemical after-treatment
    • C08L23/04—Homopolymers or copolymers of ethene
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
    • C08L23/00—Compositions of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Compositions of derivatives of such polymers
    • C08L23/02—Compositions of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Compositions of derivatives of such polymers not modified by chemical after-treatment
    • C08L23/04—Homopolymers or copolymers of ethene
    • C08L23/06—Polyethene
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
    • C08L23/00—Compositions of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Compositions of derivatives of such polymers
    • C08L23/02—Compositions of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Compositions of derivatives of such polymers not modified by chemical after-treatment
    • C08L23/10—Homopolymers or copolymers of propene
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
    • C08L83/00—Compositions of macromolecular compounds obtained by reactions forming in the main chain of the macromolecule a linkage containing silicon with or without sulfur, nitrogen, oxygen or carbon only; Compositions of derivatives of such polymers
    • C08L83/04—Polysiloxanes

Definitions

  • the present invention relates to resins for films or coatings having release or peelability characteristics and modified surface tension properties, which makes them suitable for use in release films such as those used to protect adhesive films. It especially relates to so-called release films formed from polyolefin, a polysiloxane, a vinyl silane, and an ultra-high molecular weight silicone polymer.
  • the invention relates particularly to a multi-layer film comprising the release films formed from polyolefin, a polysiloxane, a vinyl silane, and an ultra- high molecular weight silicone polymer as a layer and a polyolefin forming another layer.
  • the release film of this invention can also be adhered to or coated onto a subweb of paper, aluminum, plastics such as nylon and polyester, or other subwebs suitable for coating.
  • the multi-layer film can be used in liquid-absorbing products, such as feminine hygiene pads, baby diapers and incontinence products.
  • Films containing a polyolefin, a polysiloxane, an organo-peroxide agent and a vinyl silane are known from U.S. Pat. Nos. 4,978,436 and 5, 169,900, both incorporated herein by reference. Such films are useful for their slip, release, peelability or related characteristics, making them suitable for use as peelable coatings on adhesive materials, as removable protective layers for substrates, and as slip layers used in high-speed coating and packaging apparatuses.
  • the patents suggest a nominal film thickness of 25 microns and a gauge uniformity for such films of 25 to 30 microns. While these films perform their functions well, they have the disadvantage of being expensive, particularly in comparison with films made entirely of polyolefin. It has now been found that a thin film, one with thickness of about 1 to about 10 microns, can be made to perform the function of the much thicker films.
  • topsheets In the field of feminine hygiene pads, baby diapers, incontinence products and the like, perforated polyolefin films have long been used as a topsheet. These topsheets typically have tapered capillaries of critical diameters and tapers with a base in the plane of the topsheet and an apex remote from the plane and in contact with an absorbent element.
  • the most commonly used polyolefin employed in such topsheets is low density polyethylene, which is ideal from a liquid wicking standpoint.
  • polyolefin film having a thin surface layer or coating of polysiloxane with a surface tension of about 23 dynes/centimeter, can provide superior performance in these applications. While the lower surface tension would be expected to cause reduced liquid flow (that is, fluid drainage normally decreases with decreases in surface tension), it has been found that the polysiloxane-coated polyolefin has improved soiling resistance and generally allows for more rapid transfer of liquid through the topsheet to the absorbent material.
  • the present invention provides a silicone-containi ⁇ g polyolefin resin that in film-form has superior uniformity and efficacy at surprisingly low thickness.
  • This film comprises (i) a polyolefin, ( ⁇ ) a dimethyl polysiloxane having functional end-groups, (iii) at least one vinyl silane compound, and (iv) ultra-high molecular weight silicone polymer. Additionally, the film is preferably formed using an organic peroxide and an organo-metallic moisture curing agent, the organic peroxide preferably being at a level that not all the vinyl silane grafts to the polyolefin.
  • the invention provides a multi-layer structure comprising (a) a subweb layer, preferably a polyolefin, and (b) a surface layer of the silicone-containing polyolefin film of this invention placed, preferably by coextrusion, on the subweb, the surface layer being a film having a thickness of about 1 to about 10 microns.
  • the silicone-containing polyolefin film preferably is surface treated, for example by corona discharge, to improve its release properties.
  • the present invention further encompasses the use of the films hereindescribed as release layers, and, when the subweb is a polyolefin, in the aforementioned absorbent products.
  • Polyolefin whether used in layer (a) or layer (b) of the film of the present invention, means homopolymers and copolymers of unsaturated hydrocarbons having 2 - 20 carbon atoms. They can be made by processes well known in the art, including metallocene processes. In particular, the polymers are homopolymers of ethylene or propylene or copolymers of ethylene with one or more alpha-olefin hydrocarbons having 3 - 10 carbon atoms, especially propylene, butene- 1 , hexene- 1 and octene- 1 and styrene.
  • Suitable alpha-olefins also include dienes, that is, monomers with more than 1 site of unsaturation, especially 1,3 butadiene, 1,5 hexadiene and norbornadiene.
  • the Polyolefins are copolymers of ethylene with a hydrocarbon alpha-olefin having from 4 - 8 carbon atoms and having a density in the range of about 0.850 to about 0.970 grams per cubic centimeter (g/cm ⁇ ) and especially in the range of 0.920 to 0.930 g/cm
  • the polymers have a melt index (MI) in the range of 0.05 to 120 dg/min, especially 0.1 to 75 dg/min and in particular 1 to 10 dg/min. (as measured per ASTM D-1238, condition E).
  • the Polymers are of the type that may be extruded in the form of film.
  • the Polyolefin may contain additives, for example antioxidants and other stabilizers, anti-block and slip agents and the like.
  • the Polyolefin may also contain fillers, e.g., talc, mica, calcium carbonate, and the like and/or pigments such as titanium dioxide.
  • the Polyolefin may contain modifying polymers, e.g., rubber-like modifying polymers such as ethylene propylene/diene, styrene butadiene styrene, and other elastomers. It is to be understood that any additive must not cause undue adverse effects on the release and/or surface tension properties of the film.
  • direct copolymers or blends of copolymers of ethylene and a polar monomer e.g., ⁇ , ⁇ -ethylenically-unsaturated C 3 - Cs carboxylic acid
  • ethylene-acid copolymers e.g., ⁇ , ⁇ -ethylenically-unsaturated C 3 - Cs carboxylic acid
  • directly copolymer it is meant that the copolymer is made by polymerization of monomers together at the same time, as distinct from a "graft copolymer” where a monomer is attached or polymerized onto an existing polymer chain. Preparation of the direct ethylene-acid copolymers is described in U.S. Pat. No. 4,351,931.
  • the ethylene-acid copolymers can be E/X/ ⁇ copolymers where E is ethylene; X is a modifying comonomer and Y is the ⁇ , ⁇ -ethylenically-unsaturated C3- Ce carboxylic acid, particularly acrylic or methacrylic acid, or ester thereof.
  • the ethylene-acid copolymer is a dipolymer (no modifying comonomer).
  • the preferred acid moieties are methacrylic acid and acrylic acid. .
  • Suitable modifying comonomers (X) are selected from alkyl acrylate and alkyl methacrylate, the alkyl groups having from 1 - 12 carbon atoms, which, when present, may be up to 30 (preferably up to 25, most preferably ⁇ p to 15) wt.% of the ethylene-acid copolymer.
  • X may also be vinyl acetate or carbon monoxide.
  • a wide range of percent acid moiety in the ethylene-acid copolymer may be used.
  • the acid moiety may be present in a range of about 1 to 30 weight percent of the acid copolymer, preferably in a range of about 5 to 25, alternatively about 10 to about 20.
  • the ethylene-acid copolymers with high levels of acid are difficult to prepare in continuous polymerizers because of monomer-polymer phase separation. This difficulty can be avoided however by use of "cosolvent technology" as described in U.S. Pat. No. 5,028,674 or by employing somewhat higher pressures than those at which copolymers with lower acid can be prepared.
  • copolymers examples include ethylene/acrylic acid copolymers, ethylene/methacrylic acid copolymers, ethylene/itaconic acid copolymers, ethylene/alkyl acrylate copolymers and ethylene/alkyl methacrylate copolymers especially where the alkyl group is methyl, ethyl, propyl or butyl, and ethylene vinyl acetate copolymers.
  • copolymers include ethylene/alkyl acrylate/acrylic acid, ethylene/alkyl acrylate/methacrylic acid, ethylene/alkyl acrylate/maleic anhydride, and ethylene alkyl methacrylate/maleic anhydride, wherein the alkyl group can have 1-10 carbon atoms, preferably n-butyl, iso butyl, or methyl, ethylene/vinyl acetate/methacrylic acid, ethylene/vinyl acetate/maleic anhydride, ethylene vinyl acetate/carbon monoxide, ethylene/alkyl acrylate/carbon monoxide, ethylene/alkyl methacrylate/carbon monoxide, ethylene/carbon monoxide/acrylic acid, ethylene/vinyl tri-alkoxy silane, ethylene/vinyl acetate tri-alkoxy silane, ethylene/alkyl acrylate/vinyl tri-alkoxy silane, ethylene/vinyl acetate/g
  • ionomeric copolymers may be employed as the Polyolefins or may be blended therewith.
  • These ionomers are derived from direct copolymers of ethylene and ethylene-acid copolymers by neutralization with metal ions. Methods of preparing such ionomers are well known and are described in U.S. Pat. No. 3,264,272.
  • the ethylene-acid copolymers are partially neutralized (15 to 75 percent) with metal cations, particularly monovalent and/or bivalent metal cations. Preferably about 25 to about 60 of the acid is neutralized.
  • Preferred metal cations include lithium, sodium, and zinc, or a combination of such cations. Zinc is most preferred.
  • graft copolymers or blends of graft copolymers of polyolefins may be used as the Polyolefin, either by themselves or blended with the Polyolefins, ethylene/polar-monomer direct copolymers, or inomeric copolymers. These graft copolymers are made by means well known in the art with one or more graft monomers.
  • the graft monomers can be selected from the group consisting of ethylenically unsaturated acidic monomers and their derivatives including acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid, crotonic acid, 5- norbornene-2,3-dicarboxylic acid, maleic anhydride, monosodium maleate, disodium maleate, itaconic anhydride, citraconic anhydride, monomethyl fumarate and monomethyl maleate.
  • ethylenically unsaturated acidic monomers and their derivatives including acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid, crotonic acid, 5- norbornene-2,3-dicarboxylic acid, maleic anhydride, monosodium maleate, disodium maleate, itaconic anhydride, citraconic anhydride, monomethyl fumarate and monomethyl maleate.
  • the graft monomers can be selected from ethylenically unsaturated monomers containing amino or hydroxy functional groups including vinyl pyridines, vinyl silanes, 4-vinyI pyridine, vinyltriethoxysilane, and hydroxy ethyl methacrylate.
  • the graft monomers can also include styrene and glycidyl methacrylate.
  • the grafting monomers, and mixtures thereof, can be present in the graft polymer in an amount of about 0.05 to about 5 weight percent.
  • Preferred polyolefins for grafting include polyethylene, polypropylene, ethylene propylene diene terpolymer and copolymers of ethylene with vinyl acetate, carbon monoxide, or ethylenically unsaturated carboxylic acids or esters thereof.
  • Polysiloxane means a dimethyl polysiloxane having functional end groups. The preferred functional end group is a hydroxyl group. Such dimethyl polysiloxanes are commercially available, for example as silanol-terminated dimethyl polysiloxane from Huls America Inc., U.S.A. under the trade name OHEB.
  • dimethyl polysiloxanes having other terminal groups that are reactable with vinyl silanes, especially when grafted onto polyolefins may be used, e.g., polysiloxanes with amine, epoxy, methoxy groups or the like.
  • the Polysiloxane may be a moisture-crosslinkable polysiloxane, in which event the amount of vinyl silane used in the manufacture of the release film may be lowered.
  • the dimethyl polysiloxane is of the formula: Me
  • Organic Peroxides which serve as grafting agents in the present invention, are known in the art and include di-tertiary alkyl peroxides, especially dicumyl peroxide, which is available under the trade name LUPEROX® 500, and 2,5-dimethyl-2,5-di(t-butylperoxy) hexane, or Lupersol® 101.
  • Other organic peroxides include acetylenic diperoxy compounds especially 2,5-dimethyl-2,5-di(t- butylperoxy) hexyne-3, which is available under the trade names LUPERSOL® 130, .
  • organic peroxides include peroxyesters, preferably t-amyl peroxypivalate and t-butyl peroxypivalate, peroxydicarbonates, preferably di(sec- butyl)peroxydicarbonate, and acylperoxides, preferably dibenzoyl peroxide .
  • the grafting agent serves to graft a portion of the vinyl silane onto the polyolefin. Absence of grafted vinyl silane may adversely affect properties of the films, especially the processability of the compositions that form the films.
  • Vinyl Silane Compounds are known in the art and include vinyl trimethoxy silane, vinyl triethoxy silane, vinyl triacetoxy silane, trisbutanoxime vinyl silane, divinyl tetramethoxy disiloxane, hexamethyl bisdimethyiaminoxy cyclotetrasiloxane and the like. Mixtures of such silanes may be used.
  • Organic-metallic Moisture Curing Agents are known in the art, and for use in the present invention, will typically be organo-tin or organo-titanium compounds.
  • the preferred cross-linking agent is dibutyl tin dilaurate.
  • Compositions containing vinyl silane, organic peroxide and cross-linking agent are available under the trade name SILCAT®R, which is believed to contain vinyl trimethoxy silane, dicumyl peroxide and dibutyl tin dilaurate.
  • UHMW Silicone Polymer means an ultrahigh molecular weight silicone polymer with a molecular weight range from about 250,000 to about 1 million.
  • the UHMW Silicone Polymer will have a viscosity in the range of about 10 million to about 50 million centistokes. It may preferably be used in the form of a masterbatch in a polyolefin carrier resin, typically about 25 to about 50 weight % UHMW Silicone Polymer in a suitable polyolefin carrier resin such as LDPE or PP.
  • the UHMW Silicone Polymer may be made "in situ" by crosslinking vinyl silane with Polysiloxane.
  • Tie Layer means an extrudable adhesive layer well known in the art selected for its capability to bond a core layer to outer layers.
  • adhesive, tie layer polymer are based on either polyethylene or ethylene vinyl acetate copolymers.
  • Ethylene-based and propylene-based homopolymers and copolymers, modified to enhance adhesion, are marketed by E. I. du Pont de Nemours and Company under the tradename, BYNEL®. They are typically modified with carboxyl groups such as anhydride.
  • the silicone-containing resin or film mad therefrom of the present invention comprises
  • polyolefin homopolymer or copolymer of unsaturated hydrocarbons having 2 - 20 carbon atoms particularly homopoiymers of ethylene or propylene or copolymers of ethylene with alpha-olefin hydrocarbons having 3 - 10 carbon atoms, especially butene-1 and octene-1,
  • dimethyl polysiloxane having functional end groups, preferably a hydroxyl end group, the polysiloxane preferably being of the formula,
  • vinyl silane compound preferably one selected from the group consisting of vinyl trimethoxy silane, vinyl triethoxy silane, vinyl triacetoxy silane, trisbutanoxime vinyl silane, divinyl tetramethoxy disiloxane, and hexamethyl bisdimethyiaminoxy cyclotetrasiloxane and mixtures thereof, and
  • ultra-high molecular weight silicone polymer having a molecular weight range from about 250,000 to about 1 million, preferably having a viscosity in the range of about 10 million to about 50 million centistokes, plus optionally
  • organic peroxide grafting agent preferably one selected from the group consisting of di-tertiary alkyl peroxides, especially dicumyl peroxide and 2,5- dimethyl-2,5-di(t-butylperoxy) hexane; acetylenic diperoxy compounds, especially 2,5-dimethyl-2,5-di(t-butylperoxy) hexyne-3; peroxyesters, especially t-amyl peroxypivalate and t-butyl peroxyprivalate; peroxydicarbonates, especially di(sec-butyl) peroxydicarbonate; and acylperoxides, especially dibenzoyl peroxide to graft a portion of the vinyl silane onto the polyolefin, and
  • organo-metallic moisture curing agent preferably an organo-tin compound, more preferably dibutyl tin dilaurate, or an organo-titanium compound.
  • the silicone-containing resin or film made therefrom comprises, based on total weight of polymer components,
  • polystyrene resin 1. about 85 to about 98.89% (preferably about 91.0 to about 95.9%) polyolefin homo or copolymer, 2. about 1 to about 10% (preferably about 3 to about 7%) dimethyl polysiloxane having functional end groups,
  • the amount of organic peroxide is sufficiently low that not all of the vinyl silane compound grafts to the polyolefin under grafting conditions.
  • conditions i.e. process parameters and feed rates
  • Polyolefins used preferably are copolymers of ethylene with a hydrocarbon alpha-olefin having from 4 - 8 carbon atoms and having a density in the range of about 0.850 to about 0.970 grams per cubic centimeter (g/cm.3) and especially in the range of 0.920 to 0.930 g/cm
  • the polymers have a melt index (MI) in the range of 0.05 to 120 dg/min, especially 0.1 to 75 dg/min and in particular in the range of 1 to 10 dg/min. (as measured per ASTM D-1238, condition E).
  • the present invention is a multi-layer structure which comprises a subweb as layer (a) and the silicone-containing polyolefin film or this invention as layer (b) placed on the subweb.
  • Layer (a) will typically have a thickness of about 10 to about 100 microns (micrometers), preferably from about 15 to about 25 microns.
  • Layer (b) will typically have a thickness of about 1 to about 10 microns, preferably from about 2 to about 6 microns. Particularly, if it is desired to prevent migration of silicone through layer (a), layer (b) preferably should have lower thickness, say about 1 to about 3 microns.
  • Layer (a), the subweb may be any subweb known in the art suitable for coating or being laminated to the silicone-containing polymer of layer (b).
  • the subweb may be paper particularly kraft paper, non-wovens, metal foil such as steel or aluminum, plastics such as nylon and polyesters particularly polyethylene terephthalate, or other subwebs suitable for coating.
  • the subweb is a Polyolefin, particularly the same Polyolefin used in the film of layer (b).
  • the multi-layer film wherein the subweb is Polyolefin can be used in liquid- absorbing products, such as feminine hygiene pads, baby diapers and incontinence products.
  • the silicone-containing polyolefin film of this invention preferably is surface treated, preferably by a corona discharge.
  • the corona discharge is applied after formation of the film, preferably shortly after formation of the film, e.g., prior to the film being wound up, and prior to the film being subjected to significant amounts of moisture.
  • the corona discharge is formed between two elongated electrodes, using techniques that are known to those skilled in the art, at a sufficient level to improve the release properties of the film.
  • the film is passed between the electrodes while the corona discharge is formed between the electrodes. Subjecting the silicone-containing polyolefin film to a corona discharge results in a release film having superior release characteristics compared with film that has not been so treated.
  • the film may conveniently be treated at the speeds at which film is extruded from an extruder in the manufacture thereof.
  • Other techniques for chemically activating the surface of the film such as flame treatment and plasma discharge, may be used in place of corona discharge. Such techniques and the associated equipment are known to those skilled in the art.
  • the corona-discharge treated films of the present invention may be used in a variety of end-uses.
  • the film may be in the form of a film that is peelable from another substrate.
  • Such films usually require that the layer of adhesive material be readily removed from the release film and then the layer be adhered to another substrate.
  • multi-layer films wherein layer (a) is a Polyolefin may be perforated using known techniques and employed in the aforementioned feminine hygiene pads, baby diapers and incontinence products.
  • Multi-layer films preferably are made by coextrusion of layer (a) and layer (b).
  • this first polyolefin is fed to one extruder to form layer (a)
  • a second polyolefin dimethyl polysiloxane, vinyl silane compound, ultra-high molecular weight silicone polymer, organic peroxide grafting agent and organo- metallic moisture curing agent is fed in a suitable manner to a second extruder to form layer (b).
  • the second extruder should be capable of forming a uniform mixture of such components and of extruding a uniform mixture in the form of a molten web so as to form a uniform film, which may be in the form of a sheet or a coating on layer (a).
  • the process should be operated in the absence of excessive moisture prior to the extrusion of the composition from the extruder, to reduce premature cross-linking reactions of the vinyl silane.
  • layer (b) may be coextruded with a tie layer between layer (a) and layer (b).
  • the components that form the layer (b) may be fed to the extruder in a number of ways. For instance, all components may be fed to the hopper of the extruder, using suitable carrier materials where appropriate, as is described in greater detail below. In alternative procedures, some of the components may be fed through the hopper of the extruder and the remainder fed directly into the extruder. For example, the polyolefin may be fed to the hopper and heated in the extruder until in a molten condition.
  • the remaining ingredients may be introduced into the extruder by means of suitable feed ports on the extruder.
  • the remaining ingredients may be fed into a cavity transfer mixer located in the extruder after the barrel of the extruder containing the extruder screw and prior to the extrusion die or other orifice through which the polymer is extruded.
  • Cavity transfer mixers are known and are used for admixing of two or more materials in an extruder immediately prior to extrusion.
  • the remaining ingredients may be introduced into the extruder through a gear pump, which is also known for the introduction of ingredients into an extruder.
  • a composition of polyolefin, dimethyl polysiloxane, and vinyl silane compound, plus organic peroxide grafting agent and organo-metallic moisture curing agent if used may be melt-blended as one component in a twin- screw extruder, and allowed to age (cure) for a sufficient time prior to pellet (dry blending) or melt blending with a melt-blended composition of polyolefin and dimethyl polysiloxane, as well as with the ultra-high molecular weight silicone polymer , all of which in combination form the composition of layer (b) to be extruded.
  • This final composition for layer (b) can be extruded using a single-screw extruder.
  • the aforementioned composition for forming layer (b) may be blended with any polyolefin compatible with polyolefin used to make layer (b), for example low density polyethylene (LDPE), without adversely effecting the properties of the resulting film.
  • LDPE low density polyethylene
  • Such blending can range from 0.1 parts to 1.5 parts LDPE to 1 part layer (b) composition.
  • Other additives as defined above may also be added.
  • a suitable procedure for extruding a film according to the present invention is as follows: a first polyolefin is fed to a first extruder; and simultaneously, a second modified polyolefin is fed to a second extruder through the hopper of the extruder.
  • the modified polyolefin in the second extruder is preferably a blend of two or more compositions, which in combination form the composition to be extruded, and is heated in the extruder to form molten polymer.
  • a composition of polyolefin, dimethyl polysiloxane, and vinyl silane compound, plus organic peroxide grafting agent and organo-metallic moisture curing agent if used may be melt-blended as one component in a twin-screw extruder and allowed to cure for a sufficient amount of time prior to dry blending or melt blending with a composition of polyolefin and dimethyl polysiloxane, as well as with the ultra-high molecular weight silicone polymer.
  • This final blend can be extruded into film using a single- screw extruder. It is important that the introduction of the components of the composition and the mixing capabilities of the apparatus being used be such that a uniform mixture be formed in the extruder and extruded therefrom.
  • dimethyl polysiloxane may be used at levels up to about 15%, which may be advantageous to the properties of the product that is obtained.
  • Component A is polydimethyl siloxane, silanol terminated, 1000 centistokes (cSt)
  • Component B is SILFIN® 6, a proprietary mixture of vinyl trimethoxy silane, organic peroxide and organic tin curing accelerator. SILFIN® 6 is made by H ⁇ ls. • Component C is vinyl triethoxy silane.
  • Component D is UHMW Silicone Polymer with a viscosity in the range of 10 to 50 million centistokes as a 25 % masterbatch in LDPE.
  • a two-layer film was made by a blown-film process using a 200 mm diameter die and a blow-up ratio of 2.1 : 1 and a film line speed of about 14 meters/minute.
  • layer (a) a 23 micron thick film of a 5 MI LDPE, was extruded at 180 - 190°C at an extruder RPM of 40
  • layer (b) a 5 micron film formed from a dry pellet blend of 50% 5 MI LDPE + 50% (10 MI LLDPE + 6 % component A + 160 ppm component B and 240 ppm component C) by melt-blending in the extruder, was extruded at 160 - 170°C at an extruder RPM of 8.
  • the film was corona treated on the layer (b) side.
  • the resulting film had film thickness variations of +/- 15%. Surface tension on the 5 micron side of the film was 25 dynes/cm, but silicone was found to have also migrated through layer (a) of the film to the opposite side.
  • the film was tested using a modified TAPPI UM502 test wherein the film (surface of layer (b)) was placed on the adhesive tape of a commercial sanitary napkin and heat-aged for 20 hours at 70°C.
  • the film release force from the adhesive was about 50 grams/inch.
  • the adhesive release force from a stainless steel plate (after the film was peeled off the adhesive tape) was 50 - 60 grams inch. Silicon was found to have migrated from the film surface into the adhesive.
  • Layer (a) was a 23 micron film of a 5 MI LDPE.
  • Layer (b) was a 2 micron film formed from of a blend of: 70 % (10 MI LLDPE + 6 % component A + 160 ppm component B + 240 ppm component C), 25 % 5 MI LDPE, and 5 % component D.
  • the film was corona treated on layer (b) side at the same level of discharge as in Example 1. This film extruded stabily. The resulting film thickness variations were +/- 5%. Surface tension on the 2 micron side was found to be 25 dynes cm. No silicone was found to have migrated through layer (a) of the film.
  • Example 2 Using the same adhesive test as in Example 1, the film release force from the adhesive was about the same as in Example 1 (50 grams/inch). The release force of the adhesive from the stainless steel plate (after the film was peeled off the adhesive tape), however, was about 150 - 200 grams/inch, indicating significant reduction of silicone migration into the adhesive.

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Abstract

A silicone-containing resin, film and film on a subweb are described. The resin and film are formed from (i) polyolefin, (ii) dimethyl polysiloxane having functional end-groups, (iii) vinyl silane compound, and (iv) ultra-high molecular weight silicone polymer optionally using (v) an organo-peroxide agent and (vi) an organo-metallic moisture curing agent. The film is suitable for use in release films and in liquid-absorbing products.

Description

TITLE SILICONE-CONTAINTNG POLYOLEFIN FILM
Field of the Invention
The present invention relates to resins for films or coatings having release or peelability characteristics and modified surface tension properties, which makes them suitable for use in release films such as those used to protect adhesive films. It especially relates to so-called release films formed from polyolefin, a polysiloxane, a vinyl silane, and an ultra-high molecular weight silicone polymer.
The invention relates particularly to a multi-layer film comprising the release films formed from polyolefin, a polysiloxane, a vinyl silane, and an ultra- high molecular weight silicone polymer as a layer and a polyolefin forming another layer. The release film of this invention can also be adhered to or coated onto a subweb of paper, aluminum, plastics such as nylon and polyester, or other subwebs suitable for coating. The multi-layer film can be used in liquid-absorbing products, such as feminine hygiene pads, baby diapers and incontinence products.
Background of the Invention
Films containing a polyolefin, a polysiloxane, an organo-peroxide agent and a vinyl silane are known from U.S. Pat. Nos. 4,978,436 and 5, 169,900, both incorporated herein by reference. Such films are useful for their slip, release, peelability or related characteristics, making them suitable for use as peelable coatings on adhesive materials, as removable protective layers for substrates, and as slip layers used in high-speed coating and packaging apparatuses. The patents suggest a nominal film thickness of 25 microns and a gauge uniformity for such films of 25 to 30 microns. While these films perform their functions well, they have the disadvantage of being expensive, particularly in comparison with films made entirely of polyolefin. It has now been found that a thin film, one with thickness of about 1 to about 10 microns, can be made to perform the function of the much thicker films.
In the field of feminine hygiene pads, baby diapers, incontinence products and the like, perforated polyolefin films have long been used as a topsheet. These topsheets typically have tapered capillaries of critical diameters and tapers with a base in the plane of the topsheet and an apex remote from the plane and in contact with an absorbent element. U.S. Pat. No. 3,929,135, incorporated herein by reference, describes such topsheets. The patent discusses the product's ability to allow passage of fluid through the topsheet (away from the user) to the absorbent material, while preventing backflow from the absorbent material to the user. The most commonly used polyolefin employed in such topsheets is low density polyethylene, which is ideal from a liquid wicking standpoint. With its relatively high surface tension (about 32 dynes/centimeter), liquid drainage through the topsheet is good. On the other hand, as a result of the high surface tension, certain discharge products such as menstrual fluids and feces adhere somewhat to the surface of the film, soiling the surface in contact with the user and occluding perforations with a resultant reduction in fluid transfer.
It has now been found that polyolefin film having a thin surface layer or coating of polysiloxane, with a surface tension of about 23 dynes/centimeter, can provide superior performance in these applications. While the lower surface tension would be expected to cause reduced liquid flow (that is, fluid drainage normally decreases with decreases in surface tension), it has been found that the polysiloxane-coated polyolefin has improved soiling resistance and generally allows for more rapid transfer of liquid through the topsheet to the absorbent material. Summary of the Invention
The present invention provides a silicone-containiπg polyolefin resin that in film-form has superior uniformity and efficacy at surprisingly low thickness. This film comprises (i) a polyolefin, (ϋ) a dimethyl polysiloxane having functional end-groups, (iii) at least one vinyl silane compound, and (iv) ultra-high molecular weight silicone polymer. Additionally, the film is preferably formed using an organic peroxide and an organo-metallic moisture curing agent, the organic peroxide preferably being at a level that not all the vinyl silane grafts to the polyolefin. The invention provides a multi-layer structure comprising (a) a subweb layer, preferably a polyolefin, and (b) a surface layer of the silicone-containing polyolefin film of this invention placed, preferably by coextrusion, on the subweb, the surface layer being a film having a thickness of about 1 to about 10 microns. The silicone-containing polyolefin film preferably is surface treated, for example by corona discharge, to improve its release properties.
The present invention further encompasses the use of the films hereindescribed as release layers, and, when the subweb is a polyolefin, in the aforementioned absorbent products.
Detailed Description of the Invention
As used herein, the following terms have the meanings given below.
"Polyolefin", whether used in layer (a) or layer (b) of the film of the present invention, means homopolymers and copolymers of unsaturated hydrocarbons having 2 - 20 carbon atoms. They can be made by processes well known in the art, including metallocene processes. In particular, the polymers are homopolymers of ethylene or propylene or copolymers of ethylene with one or more alpha-olefin hydrocarbons having 3 - 10 carbon atoms, especially propylene, butene- 1 , hexene- 1 and octene- 1 and styrene. Suitable alpha-olefins also include dienes, that is, monomers with more than 1 site of unsaturation, especially 1,3 butadiene, 1,5 hexadiene and norbornadiene. In particularly preferred embodiments, the Polyolefins are copolymers of ethylene with a hydrocarbon alpha-olefin having from 4 - 8 carbon atoms and having a density in the range of about 0.850 to about 0.970 grams per cubic centimeter (g/cm^) and especially in the range of 0.920 to 0.930 g/cm Preferably, the polymers have a melt index (MI) in the range of 0.05 to 120 dg/min, especially 0.1 to 75 dg/min and in particular 1 to 10 dg/min. (as measured per ASTM D-1238, condition E).
Mixtures and blends of the Polyolefins may be used. In general, the polymers are of the type that may be extruded in the form of film. The Polyolefin may contain additives, for example antioxidants and other stabilizers, anti-block and slip agents and the like. The Polyolefin may also contain fillers, e.g., talc, mica, calcium carbonate, and the like and/or pigments such as titanium dioxide. In addition, the Polyolefin may contain modifying polymers, e.g., rubber-like modifying polymers such as ethylene propylene/diene, styrene butadiene styrene, and other elastomers. It is to be understood that any additive must not cause undue adverse effects on the release and/or surface tension properties of the film.
In alternative embodiments, direct copolymers or blends of copolymers of ethylene and a polar monomer, e.g., α,β-ethylenically-unsaturated C3- Cs carboxylic acid ("ethylene-acid copolymers"), or ester thereof, or an ethylenically unsaturated ester of a carboxylic acid may be employed as the Polyolefins or may be blended with the Polyolefins. By "direct copolymer", it is meant that the copolymer is made by polymerization of monomers together at the same time, as distinct from a "graft copolymer" where a monomer is attached or polymerized onto an existing polymer chain. Preparation of the direct ethylene-acid copolymers is described in U.S. Pat. No. 4,351,931.
The ethylene-acid copolymers can be E/X/Υ copolymers where E is ethylene; X is a modifying comonomer and Y is the α,β-ethylenically-unsaturated C3- Ce carboxylic acid, particularly acrylic or methacrylic acid, or ester thereof. Preferably, however, the ethylene-acid copolymer is a dipolymer (no modifying comonomer). The preferred acid moieties are methacrylic acid and acrylic acid. . Suitable modifying comonomers (X) are selected from alkyl acrylate and alkyl methacrylate, the alkyl groups having from 1 - 12 carbon atoms, which, when present, may be up to 30 (preferably up to 25, most preferably μp to 15) wt.% of the ethylene-acid copolymer. X may also be vinyl acetate or carbon monoxide.
A wide range of percent acid moiety in the ethylene-acid copolymer may be used. The acid moiety may be present in a range of about 1 to 30 weight percent of the acid copolymer, preferably in a range of about 5 to 25, alternatively about 10 to about 20. The ethylene-acid copolymers with high levels of acid are difficult to prepare in continuous polymerizers because of monomer-polymer phase separation. This difficulty can be avoided however by use of "cosolvent technology" as described in U.S. Pat. No. 5,028,674 or by employing somewhat higher pressures than those at which copolymers with lower acid can be prepared.
Examples of such copolymers include ethylene/acrylic acid copolymers, ethylene/methacrylic acid copolymers, ethylene/itaconic acid copolymers, ethylene/alkyl acrylate copolymers and ethylene/alkyl methacrylate copolymers especially where the alkyl group is methyl, ethyl, propyl or butyl, and ethylene vinyl acetate copolymers.
Specific other copolymers include ethylene/alkyl acrylate/acrylic acid, ethylene/alkyl acrylate/methacrylic acid, ethylene/alkyl acrylate/maleic anhydride, and ethylene alkyl methacrylate/maleic anhydride, wherein the alkyl group can have 1-10 carbon atoms, preferably n-butyl, iso butyl, or methyl, ethylene/vinyl acetate/methacrylic acid, ethylene/vinyl acetate/maleic anhydride, ethylene vinyl acetate/carbon monoxide, ethylene/alkyl acrylate/carbon monoxide, ethylene/alkyl methacrylate/carbon monoxide, ethylene/carbon monoxide/acrylic acid, ethylene/vinyl tri-alkoxy silane, ethylene/vinyl acetate tri-alkoxy silane, ethylene/alkyl acrylate/vinyl tri-alkoxy silane, ethylene/vinyl acetate/glycidyl methacrylate, ethylene/glycidyl methacrylate, ethylene/alkyl acrylate/glycidyl methacrylate and ethylene/alkyl methacrylate/glycidyl methacrylate where the alkyl or alkoxy group can have 1-10 carbon atoms.
In the alternate embodiments, ionomeric copolymers may be employed as the Polyolefins or may be blended therewith. These ionomers are derived from direct copolymers of ethylene and ethylene-acid copolymers by neutralization with metal ions. Methods of preparing such ionomers are well known and are described in U.S. Pat. No. 3,264,272. The ethylene-acid copolymers are partially neutralized (15 to 75 percent) with metal cations, particularly monovalent and/or bivalent metal cations. Preferably about 25 to about 60 of the acid is neutralized. Preferred metal cations include lithium, sodium, and zinc, or a combination of such cations. Zinc is most preferred. Further, graft copolymers or blends of graft copolymers of polyolefins may be used as the Polyolefin, either by themselves or blended with the Polyolefins, ethylene/polar-monomer direct copolymers, or inomeric copolymers. These graft copolymers are made by means well known in the art with one or more graft monomers. The graft monomers can be selected from the group consisting of ethylenically unsaturated acidic monomers and their derivatives including acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid, crotonic acid, 5- norbornene-2,3-dicarboxylic acid, maleic anhydride, monosodium maleate, disodium maleate, itaconic anhydride, citraconic anhydride, monomethyl fumarate and monomethyl maleate. Also, the graft monomers can be selected from ethylenically unsaturated monomers containing amino or hydroxy functional groups including vinyl pyridines, vinyl silanes, 4-vinyI pyridine, vinyltriethoxysilane, and hydroxy ethyl methacrylate. The graft monomers can also include styrene and glycidyl methacrylate. The grafting monomers, and mixtures thereof, can be present in the graft polymer in an amount of about 0.05 to about 5 weight percent. Preferred polyolefins for grafting include polyethylene, polypropylene, ethylene propylene diene terpolymer and copolymers of ethylene with vinyl acetate, carbon monoxide, or ethylenically unsaturated carboxylic acids or esters thereof. "Polysiloxane" means a dimethyl polysiloxane having functional end groups. The preferred functional end group is a hydroxyl group. Such dimethyl polysiloxanes are commercially available, for example as silanol-terminated dimethyl polysiloxane from Huls America Inc., U.S.A. under the trade name OHEB. However, dimethyl polysiloxanes having other terminal groups that are reactable with vinyl silanes, especially when grafted onto polyolefins, may be used, e.g., polysiloxanes with amine, epoxy, methoxy groups or the like. In addition, the Polysiloxane may be a moisture-crosslinkable polysiloxane, in which event the amount of vinyl silane used in the manufacture of the release film may be lowered. In preferred embodiments, the dimethyl polysiloxane is of the formula: Me
HO - (SiO)π - H
I
Me where Me = methyl and n is the range of 100 to 100,000. "Organic Peroxides", which serve as grafting agents in the present invention, are known in the art and include di-tertiary alkyl peroxides, especially dicumyl peroxide, which is available under the trade name LUPEROX® 500, and 2,5-dimethyl-2,5-di(t-butylperoxy) hexane, or Lupersol® 101. Other organic peroxides include acetylenic diperoxy compounds especially 2,5-dimethyl-2,5-di(t- butylperoxy) hexyne-3, which is available under the trade names LUPERSOL® 130, . Other organic peroxides include peroxyesters, preferably t-amyl peroxypivalate and t-butyl peroxypivalate, peroxydicarbonates, preferably di(sec- butyl)peroxydicarbonate, and acylperoxides, preferably dibenzoyl peroxide . The grafting agent serves to graft a portion of the vinyl silane onto the polyolefin. Absence of grafted vinyl silane may adversely affect properties of the films, especially the processability of the compositions that form the films.
"Vinyl Silane Compounds" are known in the art and include vinyl trimethoxy silane, vinyl triethoxy silane, vinyl triacetoxy silane, trisbutanoxime vinyl silane, divinyl tetramethoxy disiloxane, hexamethyl bisdimethyiaminoxy cyclotetrasiloxane and the like. Mixtures of such silanes may be used.
"Organo-metallic Moisture Curing Agents" are known in the art, and for use in the present invention, will typically be organo-tin or organo-titanium compounds. The preferred cross-linking agent is dibutyl tin dilaurate. Compositions containing vinyl silane, organic peroxide and cross-linking agent are available under the trade name SILCAT®R, which is believed to contain vinyl trimethoxy silane, dicumyl peroxide and dibutyl tin dilaurate.
"UHMW Silicone Polymer" means an ultrahigh molecular weight silicone polymer with a molecular weight range from about 250,000 to about 1 million. The UHMW Silicone Polymer will have a viscosity in the range of about 10 million to about 50 million centistokes. It may preferably be used in the form of a masterbatch in a polyolefin carrier resin, typically about 25 to about 50 weight % UHMW Silicone Polymer in a suitable polyolefin carrier resin such as LDPE or PP. Alternatively, the UHMW Silicone Polymer may be made "in situ" by crosslinking vinyl silane with Polysiloxane.
"Tie Layer" means an extrudable adhesive layer well known in the art selected for its capability to bond a core layer to outer layers. Examples of such adhesive, tie layer polymer are based on either polyethylene or ethylene vinyl acetate copolymers. Ethylene-based and propylene-based homopolymers and copolymers, modified to enhance adhesion, are marketed by E. I. du Pont de Nemours and Company under the tradename, BYNEL®. They are typically modified with carboxyl groups such as anhydride. The silicone-containing resin or film mad therefrom of the present invention comprises
1. polyolefin homopolymer or copolymer of unsaturated hydrocarbons having 2 - 20 carbon atoms, particularly homopoiymers of ethylene or propylene or copolymers of ethylene with alpha-olefin hydrocarbons having 3 - 10 carbon atoms, especially butene-1 and octene-1,
2. dimethyl polysiloxane having functional end groups, preferably a hydroxyl end group, the polysiloxane preferably being of the formula,
Me
HO - (SiO)n - H
Me where Me = methyl and n is the range of 100 to 100,000, 3. vinyl silane compound, preferably one selected from the group consisting of vinyl trimethoxy silane, vinyl triethoxy silane, vinyl triacetoxy silane, trisbutanoxime vinyl silane, divinyl tetramethoxy disiloxane, and hexamethyl bisdimethyiaminoxy cyclotetrasiloxane and mixtures thereof, and
4. ultra-high molecular weight silicone polymer having a molecular weight range from about 250,000 to about 1 million, preferably having a viscosity in the range of about 10 million to about 50 million centistokes, plus optionally
5. organic peroxide grafting agent, preferably one selected from the group consisting of di-tertiary alkyl peroxides, especially dicumyl peroxide and 2,5- dimethyl-2,5-di(t-butylperoxy) hexane; acetylenic diperoxy compounds, especially 2,5-dimethyl-2,5-di(t-butylperoxy) hexyne-3; peroxyesters, especially t-amyl peroxypivalate and t-butyl peroxyprivalate; peroxydicarbonates, especially di(sec-butyl) peroxydicarbonate; and acylperoxides, especially dibenzoyl peroxide to graft a portion of the vinyl silane onto the polyolefin, and
6. organo-metallic moisture curing agent, preferably an organo-tin compound, more preferably dibutyl tin dilaurate, or an organo-titanium compound.
Preferably, the silicone-containing resin or film made therefrom comprises, based on total weight of polymer components,
1. about 85 to about 98.89% (preferably about 91.0 to about 95.9%) polyolefin homo or copolymer, 2. about 1 to about 10% (preferably about 3 to about 7%) dimethyl polysiloxane having functional end groups,
3. about 0.01 to about 1.0% (preferably about 0.01 to about 0.5%) vinyl silane compound, and 4. about 0.1 to about 5% (preferably about 0.25 to about 3%) ultra-high molecular weight silicone polymer, plus
5. about 1 to about 100 parts per million (preferably about 5 to about 75 parts per million), based on weight of total polymer, of organic peroxide grafting agent, and 6. about 1 to about 100 parts per million (preferably about 3 to about 50 parts per million), based on weight of total polymer, of organo-metallic moisture curing agent.
Preferably, the amount of organic peroxide is sufficiently low that not all of the vinyl silane compound grafts to the polyolefin under grafting conditions. Expressed in an alternative way, conditions (i.e. process parameters and feed rates) are chosen such that only a portion of the vinyl silane is grafted to the polyolefin leaving some free vinyl silane after grafting.
Polyolefins used preferably are copolymers of ethylene with a hydrocarbon alpha-olefin having from 4 - 8 carbon atoms and having a density in the range of about 0.850 to about 0.970 grams per cubic centimeter (g/cm.3) and especially in the range of 0.920 to 0.930 g/cm Preferably, the polymers have a melt index (MI) in the range of 0.05 to 120 dg/min, especially 0.1 to 75 dg/min and in particular in the range of 1 to 10 dg/min. (as measured per ASTM D-1238, condition E). The present invention is a multi-layer structure which comprises a subweb as layer (a) and the silicone-containing polyolefin film or this invention as layer (b) placed on the subweb. Layer (a) will typically have a thickness of about 10 to about 100 microns (micrometers), preferably from about 15 to about 25 microns. Layer (b) will typically have a thickness of about 1 to about 10 microns, preferably from about 2 to about 6 microns. Particularly, if it is desired to prevent migration of silicone through layer (a), layer (b) preferably should have lower thickness, say about 1 to about 3 microns.
Layer (a), the subweb, may be any subweb known in the art suitable for coating or being laminated to the silicone-containing polymer of layer (b). In particular, the subweb may be paper particularly kraft paper, non-wovens, metal foil such as steel or aluminum, plastics such as nylon and polyesters particularly polyethylene terephthalate, or other subwebs suitable for coating. Preferably, the subweb is a Polyolefin, particularly the same Polyolefin used in the film of layer (b). The multi-layer film wherein the subweb is Polyolefin can be used in liquid- absorbing products, such as feminine hygiene pads, baby diapers and incontinence products.
The silicone-containing polyolefin film of this invention preferably is surface treated, preferably by a corona discharge. The corona discharge is applied after formation of the film, preferably shortly after formation of the film, e.g., prior to the film being wound up, and prior to the film being subjected to significant amounts of moisture. In preferred embodiments, the corona discharge is formed between two elongated electrodes, using techniques that are known to those skilled in the art, at a sufficient level to improve the release properties of the film. The film is passed between the electrodes while the corona discharge is formed between the electrodes. Subjecting the silicone-containing polyolefin film to a corona discharge results in a release film having superior release characteristics compared with film that has not been so treated. The film may conveniently be treated at the speeds at which film is extruded from an extruder in the manufacture thereof. Other techniques for chemically activating the surface of the film, such as flame treatment and plasma discharge, may be used in place of corona discharge. Such techniques and the associated equipment are known to those skilled in the art.
The corona-discharge treated films of the present invention may be used in a variety of end-uses. For example, the film may be in the form of a film that is peelable from another substrate. Such films usually require that the layer of adhesive material be readily removed from the release film and then the layer be adhered to another substrate. In addition, multi-layer films wherein layer (a) is a Polyolefin may be perforated using known techniques and employed in the aforementioned feminine hygiene pads, baby diapers and incontinence products.
Processes for the manufacture of films of the type described above are known, including blowing, casting and extruding. Optionally, films can be monaxially or biaxially oriented using methods known in the art to improve properties and reduce thickness. Multi-layer films preferably are made by coextrusion of layer (a) and layer (b). In such coextrusions, using polyolefin as an example of layer (a), this first polyolefin is fed to one extruder to form layer (a), and a second polyolefin, dimethyl polysiloxane, vinyl silane compound, ultra-high molecular weight silicone polymer, organic peroxide grafting agent and organo- metallic moisture curing agent is fed in a suitable manner to a second extruder to form layer (b). The second extruder should be capable of forming a uniform mixture of such components and of extruding a uniform mixture in the form of a molten web so as to form a uniform film, which may be in the form of a sheet or a coating on layer (a). The process should be operated in the absence of excessive moisture prior to the extrusion of the composition from the extruder, to reduce premature cross-linking reactions of the vinyl silane.
In circumstances where the silicone-containing polyolefin will not effectively adhere to the substrate desired for layer (a), layer (b) may be coextruded with a tie layer between layer (a) and layer (b). The components that form the layer (b) may be fed to the extruder in a number of ways. For instance, all components may be fed to the hopper of the extruder, using suitable carrier materials where appropriate, as is described in greater detail below. In alternative procedures, some of the components may be fed through the hopper of the extruder and the remainder fed directly into the extruder. For example, the polyolefin may be fed to the hopper and heated in the extruder until in a molten condition. Subsequently, the remaining ingredients may be introduced into the extruder by means of suitable feed ports on the extruder. For instance, the remaining ingredients may be fed into a cavity transfer mixer located in the extruder after the barrel of the extruder containing the extruder screw and prior to the extrusion die or other orifice through which the polymer is extruded. Cavity transfer mixers are known and are used for admixing of two or more materials in an extruder immediately prior to extrusion. Alternatively, the remaining ingredients may be introduced into the extruder through a gear pump, which is also known for the introduction of ingredients into an extruder. As a further example, a composition of polyolefin, dimethyl polysiloxane, and vinyl silane compound, plus organic peroxide grafting agent and organo-metallic moisture curing agent if used, may be melt-blended as one component in a twin- screw extruder, and allowed to age (cure) for a sufficient time prior to pellet (dry blending) or melt blending with a melt-blended composition of polyolefin and dimethyl polysiloxane, as well as with the ultra-high molecular weight silicone polymer , all of which in combination form the composition of layer (b) to be extruded. This final composition for layer (b) can be extruded using a single-screw extruder.
In addition, the aforementioned composition for forming layer (b) may be blended with any polyolefin compatible with polyolefin used to make layer (b), for example low density polyethylene (LDPE), without adversely effecting the properties of the resulting film. Such blending can range from 0.1 parts to 1.5 parts LDPE to 1 part layer (b) composition. Other additives as defined above may also be added.
A suitable procedure for extruding a film according to the present invention is as follows: a first polyolefin is fed to a first extruder; and simultaneously, a second modified polyolefin is fed to a second extruder through the hopper of the extruder. The modified polyolefin in the second extruder is preferably a blend of two or more compositions, which in combination form the composition to be extruded, and is heated in the extruder to form molten polymer. Thus, for the modified polyolefin in the second extruder, a composition of polyolefin, dimethyl polysiloxane, and vinyl silane compound, plus organic peroxide grafting agent and organo-metallic moisture curing agent if used, may be melt-blended as one component in a twin-screw extruder and allowed to cure for a sufficient amount of time prior to dry blending or melt blending with a composition of polyolefin and dimethyl polysiloxane, as well as with the ultra-high molecular weight silicone polymer. This final blend can be extruded into film using a single- screw extruder. It is important that the introduction of the components of the composition and the mixing capabilities of the apparatus being used be such that a uniform mixture be formed in the extruder and extruded therefrom.
If the components are fed in part directly into the extruder, e.g., using a cavity transfer mixer, then higher levels of, for example, dimethyl polysiloxane may be used at levels up to about 15%, which may be advantageous to the properties of the product that is obtained.
Examples
The invention is illustrated through the following examples, wherein: • Component A is polydimethyl siloxane, silanol terminated, 1000 centistokes (cSt)
• Component B is SILFIN® 6, a proprietary mixture of vinyl trimethoxy silane, organic peroxide and organic tin curing accelerator. SILFIN® 6 is made by Hϋls. • Component C is vinyl triethoxy silane.
• Component D is UHMW Silicone Polymer with a viscosity in the range of 10 to 50 million centistokes as a 25 % masterbatch in LDPE.
Example 1
A two-layer film was made by a blown-film process using a 200 mm diameter die and a blow-up ratio of 2.1 : 1 and a film line speed of about 14 meters/minute. Employing two 50 mm extruders, layer (a), a 23 micron thick film of a 5 MI LDPE, was extruded at 180 - 190°C at an extruder RPM of 40, and layer (b), a 5 micron film formed from a dry pellet blend of 50% 5 MI LDPE + 50% (10 MI LLDPE + 6 % component A + 160 ppm component B and 240 ppm component C) by melt-blending in the extruder, was extruded at 160 - 170°C at an extruder RPM of 8. The film was corona treated on the layer (b) side.
The resulting film had film thickness variations of +/- 15%. Surface tension on the 5 micron side of the film was 25 dynes/cm, but silicone was found to have also migrated through layer (a) of the film to the opposite side. The film was tested using a modified TAPPI UM502 test wherein the film (surface of layer (b)) was placed on the adhesive tape of a commercial sanitary napkin and heat-aged for 20 hours at 70°C. The film release force from the adhesive was about 50 grams/inch. The adhesive release force from a stainless steel plate (after the film was peeled off the adhesive tape) was 50 - 60 grams inch. Silicon was found to have migrated from the film surface into the adhesive.
Example 2
A two-layer blown film construction was made on the same equipment and under the same conditions as Example 1. Layer (a) was a 23 micron film of a 5 MI LDPE. Layer (b) was a 2 micron film formed from of a blend of: 70 % (10 MI LLDPE + 6 % component A + 160 ppm component B + 240 ppm component C), 25 % 5 MI LDPE, and 5 % component D. The film was corona treated on layer (b) side at the same level of discharge as in Example 1. This film extruded stabily. The resulting film thickness variations were +/- 5%. Surface tension on the 2 micron side was found to be 25 dynes cm. No silicone was found to have migrated through layer (a) of the film. Using the same adhesive test as in Example 1, the film release force from the adhesive was about the same as in Example 1 (50 grams/inch). The release force of the adhesive from the stainless steel plate (after the film was peeled off the adhesive tape), however, was about 150 - 200 grams/inch, indicating significant reduction of silicone migration into the adhesive.

Claims

CLAIMS:
1. A silicone-containing resin comprising: a) polyolefin homopolymer or copolymer of unsaturated hydrocarbons having 2 - 20 carbon atoms or mixtures thereof, b) dimethyl polysiloxane having functional end groups, c) vinyl silane compound, and d) ultra-high molecular weight silicone polymer having a molecular weight range from about 250,000 to about 1 million.
2. The resin of claim 1 further comprising: a) organic peroxide grafting agent to graft a portion of the vinyl silane onto the polyolefin, and b) organo-metallic moisture curing agent.
3. The resin of claim 1 or 2 wherein the polyolefin is a homopolymer of ethylene or propylene or copolymer of ethylene with alpha-olefin hydrocarbons having 3 - 10 carbon atoms or mixture thereof.
4. The resin of claim 3 wherein the polyolefin is a copolymer of ethylene with a hydrocarbon alpha-olefin having from 4 - 8 carbon atoms and a density of about 0.850 to about 0.970 grams per cubic centimeter (g/cm3).
5. The resin of claim 4 wherein the polyolefin has a density of 0.920 to 0.930 g/cm3.
6. The resin of claim 2 wherein the polyolefin has a melt index (MI) of 0.05 to 120 dg/min. (as measured per ASTM D-1238, condition E).
7. The resin of claim 6 wherein the polyolefin has an MI of 1 to 10 dg min.
8. The resin of claim 2 wherein: a) the polysiloxane has the formula,
Me
I
HO - (SiO)n - H
I Me where Me = methyl and n is the range of 100 to 100,000, b) the vinyl silane is one selected from the group consisting of vinyl trimethoxy silane, vinyl triethoxy silane, vinyl triacetoxy silane, trisbutanoxime vinyl silane, divinyl tetramethoxy disiloxane, and hexamethyl bisdimethyiaminoxy cyclotetrasiloxane and mixtures thereof, c) the ultra-high molecular weight silicone polymer has a viscosity in the range of about 10 million to about 50 million centistokes, d) the organic peroxide is selected from the group consisting of di- tertiary alkyl peroxides, peroxyesters, peroxydicarbonates, acylperoxides, and acetylenic diperoxy compounds, and e) the moisture curing agent is an organo-tin or organo-titanium compound.
9. The resin of claim 2 comprising, based on total weight of polymer components: a) about 85 to about 98.89% polyolefin homo or copolymer, b) about 1 to about 10% dimethyl polysiloxane having functional end groups, c) about 0.01 to about 1.0% vinyl silane compound, and d) about 0.1 to about 5% ultra-high molecular weight silicone polymer, plus e) about 1 to about 100 parts per million of organic peroxide grafting agent, and about 1 to about 100 parts per million of organo-metallic moisture curing agent.
10. The resin of claim 9 comprising, based on total weight of polymer components: a) about 91.0 to about 95.9 % polyolefin homo or copolymer, b) about 3 to about 7 % dimethyl polysiloxane having functional end groups, c) about 0.01 to about 0.5 % vinyl silane compound, and d) about 0.25 to about 3 % ultra-high molecular weight silicone polymer, plus e) about 5 to about 75 parts per million of organic peroxide grafting agent, and f) about 3 to about 50 parts per million of organo-metallic moisture curing agent.
11. The resin of claim 8 wherein the vinyl silane is present in an amount sufficient that only a portion of the vinyl silane is grafted to the polyolefin leaving some free vinyl silane after grafting.
12. A silicone-containing film comprising the resin of claim 1 or 2.
13. The film of claim 12 wherein the film is surface treated.
14. The film of claim 13 wherein the film is surface treated by corona discharge.
15. A multi-layer structure comprising layer (a) a subweb and layer (b) the silicone-containing polyolefin film of claim 12 thereon.
16. The multi-layer structure of claim 15 wherein layer (a) has a thickness of about 10 to about 100 microns (micrometers), and layer (b) has a thickness of about 1 to about 10 microns.
17. The multi-layer structure of claim 16 wherein layer (a) has a thickness of about 15 to about 25 microns, and layer (b) has a thickness of about 2 to about 6 microns.
18. The multi-layer structure of claim 17 wherein layer (a) has a thickness of about 15 to about 25 microns, and layer (b) has a thickness of about 2 to about 4 microns.
19. The multi-layer structure of claim 18 wherein the subweb is paper.
20. The multi-layer structure of claim 13 wherein the subweb is polyolefin homopolymer or copolymer of unsaturated hydrocarbons having 2 - 20 carbon atoms or mixtures thereof.
21. The multi-layer structure of claim 20 that has been perforated.
22. A composite structure comprising the multi-layer structure of claim 21 and, adjacent to layer (a), an absorbent material.
PCT/CA1997/000665 1996-09-13 1997-09-12 Silicone-containing polyolefin film WO1998010724A1 (en)

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US60/025,251 1996-09-13

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EP0974617A1 (en) * 1998-07-21 2000-01-26 Mitsui Chemicals, Inc. Resin compositions for skin members and laminates thereof
EP1018533A3 (en) * 1999-01-08 2001-07-04 Dupont Canada Inc. Silicone-containing low surface tension film
US6291050B1 (en) 1998-10-30 2001-09-18 The Procter & Gamble Company Topsheet systems for absorbent articles exhibiting improved hydrophilicity gradients
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WO2003011955A1 (en) * 2001-07-31 2003-02-13 Compco Pty Ltd Methods of recycling and/or upgrading olefin (co)polymers
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US6833414B2 (en) 2002-02-12 2004-12-21 Arkema Inc. Cross-linkable aqueous fluoropolymer based dispersions containing silanes
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EP1679343A1 (en) * 2005-01-06 2006-07-12 A. Schulman Plastics Polymer compound
US7326751B2 (en) 2003-12-01 2008-02-05 Kimberly-Clark Worlwide, Inc. Method of thermally processing elastomeric compositions and elastomeric compositions with improved processability
US20080299347A1 (en) * 2007-06-04 2008-12-04 Nitto Denko Corporation Release liner and pressure-sensitive adhesive sheet comprising same
WO2011034836A1 (en) * 2009-09-16 2011-03-24 Union Carbide Chemical & Plastics Technology Llc Process for producing crosslinked, melt-shaped articles
WO2014105292A1 (en) * 2012-12-31 2014-07-03 Dow Global Technologies Llc A composition, articles made therefrom, and method of making the articles
WO2017208081A1 (en) 2016-06-03 2017-12-07 Multibase Sa Plastic films
US10513609B2 (en) 2013-06-25 2019-12-24 Dow Global Technologies Llc Polyolefin elastomer and polysiloxane blends

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WO1999020707A1 (en) * 1997-10-16 1999-04-29 4P Folie Forchheim Gmbh Plastic separating layer
EP0974617A1 (en) * 1998-07-21 2000-01-26 Mitsui Chemicals, Inc. Resin compositions for skin members and laminates thereof
US6497960B1 (en) 1998-07-21 2002-12-24 Kyoko Kobayashi Resin compositions for skin members and laminates thereof
US6440566B1 (en) 1998-10-01 2002-08-27 Airtech International, Inc. Method of molding or curing a resin material at high temperatures using a multilayer release film
US6818311B2 (en) 1998-10-09 2004-11-16 4P Folie Forchheim Gmbh Plastic film
US6291050B1 (en) 1998-10-30 2001-09-18 The Procter & Gamble Company Topsheet systems for absorbent articles exhibiting improved hydrophilicity gradients
EP1018533A3 (en) * 1999-01-08 2001-07-04 Dupont Canada Inc. Silicone-containing low surface tension film
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WO2003011955A1 (en) * 2001-07-31 2003-02-13 Compco Pty Ltd Methods of recycling and/or upgrading olefin (co)polymers
US6833414B2 (en) 2002-02-12 2004-12-21 Arkema Inc. Cross-linkable aqueous fluoropolymer based dispersions containing silanes
EP1533339A1 (en) * 2003-11-21 2005-05-25 Tosoh Corporation Resin composition for use in release film and release film produced therefrom
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EP1679343A1 (en) * 2005-01-06 2006-07-12 A. Schulman Plastics Polymer compound
US20080299347A1 (en) * 2007-06-04 2008-12-04 Nitto Denko Corporation Release liner and pressure-sensitive adhesive sheet comprising same
WO2011034836A1 (en) * 2009-09-16 2011-03-24 Union Carbide Chemical & Plastics Technology Llc Process for producing crosslinked, melt-shaped articles
WO2011034838A1 (en) * 2009-09-16 2011-03-24 Union Carbide Chemilcals & Plastics Technology Llc Crosslinked, melt-shaped articles and compositions for producing same
US8835548B2 (en) 2009-09-16 2014-09-16 Union Carbide Chemicals & Plastics Technology Llc Process for producing crosslinked, melt-shaped articles
US9272469B2 (en) 2009-09-16 2016-03-01 Union Carbide Chemicals & Plastics Technology Llc Crosslinked, melt-shaped articles and compositions for producing same
US9387625B2 (en) 2009-09-16 2016-07-12 Union Carbide Chemicals & Plastics Technology Llc Process for producing crosslinked, melt-shaped articles
WO2014105292A1 (en) * 2012-12-31 2014-07-03 Dow Global Technologies Llc A composition, articles made therefrom, and method of making the articles
US10513609B2 (en) 2013-06-25 2019-12-24 Dow Global Technologies Llc Polyolefin elastomer and polysiloxane blends
WO2017208081A1 (en) 2016-06-03 2017-12-07 Multibase Sa Plastic films

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