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WO1993005099A1 - One hundred percent solids acrylic adhesives - Google Patents

One hundred percent solids acrylic adhesives Download PDF

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Publication number
WO1993005099A1
WO1993005099A1 PCT/US1992/007109 US9207109W WO9305099A1 WO 1993005099 A1 WO1993005099 A1 WO 1993005099A1 US 9207109 W US9207109 W US 9207109W WO 9305099 A1 WO9305099 A1 WO 9305099A1
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WO
WIPO (PCT)
Prior art keywords
adhesive composition
recited
oligomer
lower alkyl
polyisocyanate
Prior art date
Application number
PCT/US1992/007109
Other languages
French (fr)
Inventor
Gary Lee Linden
Original Assignee
Dap, 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 Dap, Inc. filed Critical Dap, Inc.
Publication of WO1993005099A1 publication Critical patent/WO1993005099A1/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
    • 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
    • C08F8/00—Chemical modification by after-treatment
    • C08F8/30—Introducing nitrogen atoms or nitrogen-containing 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
    • C08G18/08—Processes
    • C08G18/10—Prepolymer processes involving reaction of isocyanates or isothiocyanates with compounds having active hydrogen in a first reaction step
    • 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
    • C08G18/62—Polymers of compounds having carbon-to-carbon double bonds
    • C08G18/6216—Polymers of alpha-beta ethylenically unsaturated carboxylic acids or of derivatives thereof
    • C08G18/622—Polymers of esters of alpha-beta ethylenically unsaturated carboxylic acids
    • C08G18/6225—Polymers of esters of acrylic or methacrylic acid
    • 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
    • C08G18/62—Polymers of compounds having carbon-to-carbon double bonds
    • C08G18/6216—Polymers of alpha-beta ethylenically unsaturated carboxylic acids or of derivatives thereof
    • C08G18/625—Polymers of alpha-beta ethylenically unsaturated carboxylic acids; hydrolyzed polymers of esters of these acids
    • C08G18/6254—Polymers of alpha-beta ethylenically unsaturated carboxylic acids and of esters of these acids containing hydroxy groups
    • 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
    • C08F2800/00—Copolymer characterised by the proportions of the comonomers expressed
    • C08F2800/20—Copolymer characterised by the proportions of the comonomers expressed as weight or mass percentages
    • 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
    • C08G2170/00—Compositions for adhesives
    • C08G2170/40—Compositions for pressure-sensitive adhesives

Definitions

  • the invention relates to adhesive compositions, more particularly to pressure sensitive adhesives compositions.
  • PSAs Pressure sensitive adhesives
  • Typical PSAs can be made to adhere to a variety of substrates upon mere application of finger or hand pressure .
  • PSAs included blends of natural rubber and wood rosins. Subsequently, other elastomers were used and the original wood rosin tackifiers were chemically modified to include a large variety of tackifier resins.
  • Sundry styrene-butadiene , polyisobutylene , butyl rubber, ethylene-vi nyl acetate, and acrylic PSA systems have been used throughout the years.
  • tall oil rosin, petroleum fraction oligomers, ⁇ -methyl styrene , vinyl toluene copolymers and coumarone-indene resins have been used as tackifiers in PSA formulations.
  • an acrylic oligomer is admixed with a polyisocyanate compound to provide a PSA system having 100% solids and being devoid of any solvent, either water-based or organically-based.
  • the acrylic oligomer is an oily liquid having a viscosity of between about 2,500 to 50,000 cps and a molecular weight of between about 500-3000 (M ).
  • the oligomer is composed of repeat units derived from lower alkyl acrylate, and substituted lower alkyl acrylate monomers wherein the substituent contains an active hydrogen atom to react with the isocyanate component.
  • this active hydrogen-containing substituent is represented by the formula ( H ) with Z chosen from 0, S, or N.
  • Acrylic acid is an optional monomeric component of the oligomer.
  • the polyurethane compound is preferably a urethane prepolymer that is formed via reaction of a polyisocyanate having a functionality of 2 or greater and a compound having two or more active hydrogens so that the reaction forms an isocyanate-terminated product.
  • the polyisocyanate/active hydrogen compound reactant ratio for prepolymer preparation is controlled so as to provide a prepolymer compound having unreacted NCO functional groups for preferable, subsequent curing under ambient conditions.
  • the acrylic oligomer/polyisocyanate compound components are mixed in a ratio of 90-10:10-90 (by weight) and are ready for use as a solvent-less, 100% solids acrylic PSA.
  • Polyurethane-type adhesives containing non- aqueous solutions of acrylate polymers are disclosed in U.S. Patent 4,731,416 ( Saunders ) .
  • an acrylic resin is synthesized in a polyol to produce a resin having a Mn of greater than 3500.
  • the acrylic resin in polyol (1) is reacted with an organic polyisocyanate (2) and (3) a polyahl chain extender.
  • the adhesives are reputedly effective in bonding steel, plastic, and aluminum substrate .
  • U.S. Patent 4,914,173 (Ansell) skin friendly pressure sensitive adhesives comprising an acrylic- functional polyurethane are disclosed.
  • the polyurethane is radiation cured to a solid product (tape) and provided as such for wound dressings.
  • a solventless, storage-stable, low temperature, heat curable urethane composition is provided in U.S. Patent 4,722,969 (Huynh-Tran et al ) in which the composition comprises:
  • a branched, blocked isocyanate prepolymer comprising the reaction product of a polyol having a functionality of at least 2, an aromatic polyisocyanate having a functionality of at least 2, the combined functionality of the polyol and the polyisocyanate being greater than 4 and a ketoxime blocker; (2) a polyol crosslinking agent containing at least two OH groups;
  • composition requires heat curing on the order of 100 * -120""C for a period of 10-30 minutes.
  • the composition can be combined with polymeric powder to yield cured reactive plastisols.
  • the compositions are ponderedly useful as sealants, coatings or adhesives.
  • Polyisocyanate-acrylate polymer adhesives are disclosed in U.S. Patent 3,532,652 (Zang et al ) in which acrylic interpolymers are blended with polyisocyanates, including the polyisocyanate prepolymers formed from - o -
  • polyisocyanate-polyol reaction As indicated at column 6, lines 22-32, of the disclosure, the ingredients are blended in a solvent selected from esters, aromatic hydrocarbons, and aliphatic hydrocarbons and ketones. Curing is preferably conducted under elevated temperature of 150°F-300°F for from 1 to 15 minutes.
  • Sag-resistant compositions comprising an isocyanate prepolymer dispersed in a cross-linked polymer matrix are taught in U.S. Patent 4,243,768 (Simpson).
  • the compositions have high viscosities (i.e. , on the order of at least 10 cps ) and may comprise, for example, isocyanate prepolymer in acrylate matrix.
  • the mix may be heated in the presence of a polymerization initiator to, in situ, to form a cross-linked matrix.
  • a 100% solids acrylic based adhesive is provided that requires no solvent, either water or organically based, for its application.
  • the preferred adhesive is a liquid mixture of acrylic oligomer and polyisocyanate, preferably urethane prepolymer, that may simply be applied to the desired substrate and allowed to cure under ambient conditions.
  • a variety of substrates can be bonded with the solvent-less adhesives of the invention, including steel, wood, polyurethane, plastics, aluminum, etc.
  • the adhesives, in accord with the invention can be used in a broad variety of applications in which pressure sensitive adhesives have traditionally been employed, including packaging masking tapes.
  • the adhesive is a solventless, oily, low- viscosity liquid blend of acrylic oligomer and polyisocyanate compound present in a weight ratio of oligomer: polyisocyanate compound of from 10-90:90-10.
  • the oligomer is present in an amount of 50 wt.% with "the polyisocyanate present in equal weight.
  • the acrylic oligomer is prepared under free radical generating conditions, such as the use of a free radical initiator, such as cumene hydroperoxide, benzoyl peroxide, etc. , in the presence of an inert organic solvent, such as toluene, xylene, cyclohexane, etc.
  • the acrylic oligomer is formed under high pressure and temperature conditions, with the solvent being stripped after formation of the resulting oligomer, possibly for recycling.
  • the resulting acrylic oligomer is characterized by having a low molecular weight MW of about 500-3,000 and a viscosity of about 2,500 to 50,000 cps.
  • the preferred viscosity is from about 2,500-7,500 cps.
  • the acrylic oligomer is formed from predominately lower alkyl (C,-Cg) acrylate monomer, optional acrylic acid, and cross-linkable lower alkyl acrylate monomer components.
  • the cross-linkable lower alkyl acrylate monomer comprises an active hydrogen- containing functional group adapted to react with the isocyanate component of the PSA.
  • such substituent is represented by the formula (ZH ) with Z being chosen from 0, S, or N atoms.
  • the active hydrogen-containing functional group is an hyd-roxy group.
  • the acrylic oligomer comprises the following monomer proportions by weight.
  • lower alkyl acrylate monomer 50-99% acrylic acid 0-10% active hydrogen substituted lower alkyl acrylate 1-50%
  • the lower alkyl acrylate component of the oligomer may comprise a single monomer type or combination of lower alkyl (C,-_ o ) acrylate monomers.
  • Exemplary lower alkyl monomers include methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, amyl acrylate, hexyl acrylate, heptyl acrylate, and 2-ethylhexyl acrylate.
  • the active hydrogen-containing lower alkyl acrylate compound may, for instance, comprise OH, NH, or SH functionality. Preferred for use are the hydroxylated lower alkyl acrylates.
  • hydroxylated lower alkyl (C j —C jj ) acrylate components these may comprise one or more monomers, such as hydroxyethylacrylate, 2-hydroxypropyl acrylate, 2-hydroxybutyl acrylate, etc.
  • This constituent Is adapted to provide a source of active hydrogen ion for subsequent cross-linking with the available NCO groups of the isocyanate prepolymer.
  • the oligomerization of the acrylic monomer constituents is conducted in a pressurized reaction system maintained at elevated pressure ( « 50-100 psi) and elevated temperature (* 175-200'C) to effect oligomerization of substantially all of the monomers.
  • the acrylic monomer constituents may be slowly added to the reaction mixture of solvent and initiator over a period of hours. Reaction time will vary upon size of the charge but generally will be completed in about 2-8 hours.
  • Exemplary polyisocyanates include: 1 ,4-tetramethylene diisocyanate
  • isocyanate component Preferred for use as the isocyanate component are the urethane prepolymers. These are defined as organic polyisocyanates, such as those specified above, modified with a compound having two or more active hydrogens to provide an isocyanate terminated product.
  • a multiplicity of compounds having two or more active hydrogens, for reaction with the polyisocyanate, are readily available and are well known.
  • the following functional groups contain active hydrogen and will react with the isocyanato groups: OH, SH, NH, NH, etc.
  • Polyester polyols are made by esterification of polyols with dicarboxylic acids using reactant amounts, such that .the product contains free hydroxyl groups.
  • One example of polyester polyol formation is that of excess propylene glycol with adipic acid.
  • Polyether polyols are hydroxyl-containing compounds containing ' ether linkages. These are commonly prepared via reaction of an alkylene oxide with a polyhydric compound.
  • Suitable polyols include polyethylene glycol, polybutylene glycol, polypropylene oxide triol, polymethylene ether glycol, polyethylene ether glycol, polypropylene ether glycol, polybutylene ether glycol, etc.
  • the molecular weight of the polyol can vary widely within the range of about 45-4,000.
  • Preferred are the polymeg ® series of polyols available from C Chemicals. These comprise poly( oxyalkylene diol ) compounds of the formula HO ( CHJCHJCHJCHJ0 ) H.
  • Commercially available "Polymeg ® " products have molecular weights of 650, 1000, and 2000.
  • the prepolymers are generally prepared by heating the components together in the requisite proportions and at elevated temperatures, for example, 90 ° C for 2 hours in the presence of a conventional polyurethane catalyst, such as dibutyl tin dilaurate.
  • a conventional polyurethane catalyst such as dibutyl tin dilaurate.
  • the NCO/OH ratio of the prepolymer reactants is normally maintained at from about 2.0-4.0:1 with the so-formed prepolymer containing from 5 to 50 wt.% free NCO groups.
  • the acrylic oligomer and urethane prepolymer are prepared, they are mixed together in the desired proportion and provide a solventless, 100% solids, pressure sensitive composition that is preferably capable of curing under ambient conditions. Conversely, curing can be effected via conventional techniques, such as heat or radiation.
  • epoxy curing agents may be used.
  • F.xample 1 - An acrylic oligomer is prepared as follows: a premix is prepared composed of 60% butyl acrylate, 18% methyl acrylate, 15% ethyl acrylate, 1.8% 2- hydroxyethyl acrylate and 5.2% acrylic acid (glacial). Sufficient cumene hydroperoxide (CHP) is added as an initiator to produce a 1% concentration of the CHP in the premix. A weight of toluene equal to the premix weight is added to a pressure reactor equipped with a stirrer, thermoregulato , heating and cooling compatibility, addition and discharge valves and sight glasses.
  • CHP cumene hydroperoxide
  • the reactor is closed and heated to 190"C with attendant stirring; the pressure of the reactor at 190°C is 80 psi.
  • the premix is then pumped into the reactor over a 2-4 hour period.
  • the temperature in the reactor is maintained at 190°C with pressure remaining between 80-100 psi during addition of the premix and falling to 60 psi after premix addition has been computed.
  • additional increments of CHP 80% in toluene
  • the product oligomer is an oily viscous liquid having a viscosity of about 5000 cps.
  • the acrylic oligomer is then mixed with isocyanate prepolymer for use as an adhesive.
  • the isocyanate prepolymer was prepared by reaction of 57% of a commercially available aromatic isocyanate mixture (Mondur-MRS-4-Mobay- 4 ,4 ' -diphenylmethane diisocyanate MDI ; plus higher oligomers of MDI ) and 43% of a commercially available polyether diol ( Polymeg 2,000 - O Chemicals, Inc. ; mws-2,000 - polytetramethylene ether glycol ) .
  • a commercially available aromatic isocyanate mixture (Mondur-MRS-4-Mobay- 4 ,4 ' -diphenylmethane diisocyanate MDI ; plus higher oligomers of MDI )
  • a commercially available polyether diol Polymeg 2,000 - O Chemicals, Inc. ; mws-2,000 - polytetramethylene
  • the isocyanate prepolymer has a viscosity of 4500-5500 cps (RTV #60, 20 rpm, 77F); % NCO of 16.23% (theoretical) and a density of 9.25-9.35 lbs./gal.
  • Example 2 50 weight % of the acrylic oligomer (Example 1) and 50 weight % of the isocyanate prepolymer (Example 1) were mixed. The mixture was applied as a bonding layer to a steel-steel interface and allowed to stand under ambient conditions overnight. The next day, a peel strength test (Instron) indicated a value of 163.636 psi. This demonstrated that an excellent bond had formed.
  • a peel strength test Instron

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  • Chemical & Material Sciences (AREA)
  • Organic Chemistry (AREA)
  • Health & Medical Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Medicinal Chemistry (AREA)
  • Polymers & Plastics (AREA)
  • General Chemical & Material Sciences (AREA)
  • Polyurethanes Or Polyureas (AREA)

Abstract

Pressure-sensitive adhesive composition is disclosed wherein the adhesive is a 100 % solids, no solvent, tacky oil that can cure at ambient conditions. The adhesive comprises an acrylic oligomer component and a polyurethane prepolymer in combination. The oligomer comprises repeat units, corresponding to acrylic acid, lower alkyl acrylate and hydroxylated lower alkyl acrylate monomers. The prepolymer is formed via polyisocyanate reaction with a multifunctional active hydrogen containing compound, such as a polyol.

Description

ONE HUNDRED PERCENT SOLIDS ACRYLIC ADHESIVES Field of the Invention The invention relates to adhesive compositions, more particularly to pressure sensitive adhesives compositions.
Background of the Invention Pressure sensitive adhesives (PSAs) are widely used in a variety of applications, such as in masking tapes, office tapes, Band-Aids, labels and decals. Typical PSAs can be made to adhere to a variety of substrates upon mere application of finger or hand pressure .
Early PSAs included blends of natural rubber and wood rosins. Subsequently, other elastomers were used and the original wood rosin tackifiers were chemically modified to include a large variety of tackifier resins.
Sundry styrene-butadiene , polyisobutylene , butyl rubber, ethylene-vi nyl acetate, and acrylic PSA systems have been used throughout the years. Moreover, tall oil rosin, petroleum fraction oligomers, α-methyl styrene , vinyl toluene copolymers and coumarone-indene resins have been used as tackifiers in PSA formulations.
Recently, due to the concern for volatile organic carbon emissions in the atmosphere, emphasis has centered on attempts to eliminate such volatile organic solvent components, such as hexane and toluene, from PSA systems. The trend has turned toward aqueous-based PSA syste s, but these too are not without problems. For example, water is harmful to certain substrates. It can raise the grain on wood finishes and it contributes to corrosivity problems when applied to ferrous substrates. Additionally, water requires time and energy to remove before the adhesive may be used.
Accordingly, there is a need to provide a PSA system capable of providing quick, effective adhesion to a variety of substrate types that does not require the presence of organic or aqueous solvents.
Summary of the Invention In accordance with the invention, an acrylic oligomer is admixed with a polyisocyanate compound to provide a PSA system having 100% solids and being devoid of any solvent, either water-based or organically-based.
Briefly, the acrylic oligomer is an oily liquid having a viscosity of between about 2,500 to 50,000 cps and a molecular weight of between about 500-3000 (M ). The oligomer is composed of repeat units derived from lower alkyl acrylate, and substituted lower alkyl acrylate monomers wherein the substituent contains an active hydrogen atom to react with the isocyanate component. Preferably, this active hydrogen-containing substituent is represented by the formula ( H ) with Z chosen from 0, S, or N. Acrylic acid is an optional monomeric component of the oligomer. The polyurethane compound is preferably a urethane prepolymer that is formed via reaction of a polyisocyanate having a functionality of 2 or greater and a compound having two or more active hydrogens so that the reaction forms an isocyanate-terminated product. The polyisocyanate/active hydrogen compound reactant ratio for prepolymer preparation is controlled so as to provide a prepolymer compound having unreacted NCO functional groups for preferable, subsequent curing under ambient conditions.
The acrylic oligomer/polyisocyanate compound components are mixed in a ratio of 90-10:10-90 (by weight) and are ready for use as a solvent-less, 100% solids acrylic PSA.
Prior Art
Polyurethane-type adhesives containing non- aqueous solutions of acrylate polymers are disclosed in U.S. Patent 4,731,416 ( Saunders ) . Here, an acrylic resin is synthesized in a polyol to produce a resin having a Mn of greater than 3500. The acrylic resin in polyol (1) is reacted with an organic polyisocyanate (2) and (3) a polyahl chain extender. The adhesives are reputedly effective in bonding steel, plastic, and aluminum substrate . In U.S. Patent 4,914,173 (Ansell), skin friendly pressure sensitive adhesives comprising an acrylic- functional polyurethane are disclosed. The polyurethane is radiation cured to a solid product (tape) and provided as such for wound dressings.
A solventless, storage-stable, low temperature, heat curable urethane composition is provided in U.S. Patent 4,722,969 (Huynh-Tran et al ) in which the composition comprises:
(1) a branched, blocked isocyanate prepolymer comprising the reaction product of a polyol having a functionality of at least 2, an aromatic polyisocyanate having a functionality of at least 2, the combined functionality of the polyol and the polyisocyanate being greater than 4 and a ketoxime blocker; (2) a polyol crosslinking agent containing at least two OH groups;
(3) a deblocking and curing catalyst for (1); and
(4) a dessicant. The composition requires heat curing on the order of 100*-120""C for a period of 10-30 minutes. The composition can be combined with polymeric powder to yield cured reactive plastisols. The compositions are reputedly useful as sealants, coatings or adhesives. Polyisocyanate-acrylate polymer adhesives are disclosed in U.S. Patent 3,532,652 (Zang et al ) in which acrylic interpolymers are blended with polyisocyanates, including the polyisocyanate prepolymers formed from - o -
polyisocyanate-polyol reaction. As indicated at column 6, lines 22-32, of the disclosure, the ingredients are blended in a solvent selected from esters, aromatic hydrocarbons, and aliphatic hydrocarbons and ketones. Curing is preferably conducted under elevated temperature of 150°F-300°F for from 1 to 15 minutes.
Sag-resistant compositions comprising an isocyanate prepolymer dispersed in a cross-linked polymer matrix are taught in U.S. Patent 4,243,768 (Simpson). The compositions have high viscosities (i.e. , on the order of at least 10 cps ) and may comprise, for example, isocyanate prepolymer in acrylate matrix. The mix may be heated in the presence of a polymerization initiator to, in situ, to form a cross-linked matrix. Other patents located which may be of some interest include 4,954,199 (Rains et al ) ; 4,920,157 (Schulz et al); 4,717,739 ( Chevreux et al ) ; 4,762,866 (Shih et al); 4,491,646 (Gruber); 4,380,613 (Nativi); 4,891,269 (Markevka et al ) ; and 4,806,616 ( Baumanno et al).
Despite the foregoing prior art efforts, there remains a need for a versatile PSA as described above that requires no solvent in its application.
Detailed Description In accordance with the invention, a 100% solids acrylic based adhesive is provided that requires no solvent, either water or organically based, for its application. The preferred adhesive is a liquid mixture of acrylic oligomer and polyisocyanate, preferably urethane prepolymer, that may simply be applied to the desired substrate and allowed to cure under ambient conditions. A variety of substrates can be bonded with the solvent-less adhesives of the invention, including steel, wood, polyurethane, plastics, aluminum, etc. The adhesives, in accord with the invention, can be used in a broad variety of applications in which pressure sensitive adhesives have traditionally been employed, including packaging masking tapes.
The adhesive is a solventless, oily, low- viscosity liquid blend of acrylic oligomer and polyisocyanate compound present in a weight ratio of oligomer: polyisocyanate compound of from 10-90:90-10. Preferably, the oligomer is present in an amount of 50 wt.% with "the polyisocyanate present in equal weight. Generally, the acrylic oligomer is prepared under free radical generating conditions, such as the use of a free radical initiator, such as cumene hydroperoxide, benzoyl peroxide, etc. , in the presence of an inert organic solvent, such as toluene, xylene, cyclohexane, etc. The acrylic oligomer is formed under high pressure and temperature conditions, with the solvent being stripped after formation of the resulting oligomer, possibly for recycling. The resulting acrylic oligomer is characterized by having a low molecular weight MW of about 500-3,000 and a viscosity of about 2,500 to 50,000 cps. The preferred viscosity is from about 2,500-7,500 cps.
The acrylic oligomer is formed from predominately lower alkyl (C,-Cg) acrylate monomer, optional acrylic acid, and cross-linkable lower alkyl acrylate monomer components. The cross-linkable lower alkyl acrylate monomer comprises an active hydrogen- containing functional group adapted to react with the isocyanate component of the PSA. Preferably, such substituent is represented by the formula (ZH ) with Z being chosen from 0, S, or N atoms. Most preferably, the active hydrogen-containing functional group is an hyd-roxy group. The acrylic oligomer comprises the following monomer proportions by weight.
lower alkyl acrylate monomer 50-99% acrylic acid 0-10% active hydrogen substituted lower alkyl acrylate 1-50%
The foregoing percentages add up to 100%. The lower alkyl acrylate component of the oligomer may comprise a single monomer type or combination of lower alkyl (C,-_o ) acrylate monomers. Exemplary lower alkyl monomers include methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, amyl acrylate, hexyl acrylate, heptyl acrylate, and 2-ethylhexyl acrylate. The active hydrogen-containing lower alkyl acrylate compound may, for instance, comprise OH, NH, or SH functionality. Preferred for use are the hydroxylated lower alkyl acrylates. As to the hydroxylated lower alkyl (Cj—Cjj ) acrylate components, these may comprise one or more monomers, such as hydroxyethylacrylate, 2-hydroxypropyl acrylate, 2-hydroxybutyl acrylate, etc. This constituent Is adapted to provide a source of active hydrogen ion for subsequent cross-linking with the available NCO groups of the isocyanate prepolymer.
The oligomerization of the acrylic monomer constituents is conducted in a pressurized reaction system maintained at elevated pressure ( « 50-100 psi) and elevated temperature (* 175-200'C) to effect oligomerization of substantially all of the monomers. The acrylic monomer constituents may be slowly added to the reaction mixture of solvent and initiator over a period of hours. Reaction time will vary upon size of the charge but generally will be completed in about 2-8 hours.
Additional charges of initiator may be added after acrylic constituent addition to the reaction mixture in order to ensure monomer reaction. After the solvent is separated from the reaction medium via vacuum stripping or other conventional technique, the tacky, oily, low viscosity* acrylic oligomer is ready to be mixed with polyisocyanate compound. The polyisocyanates which are to be mixed with the acrylic oligomer are generally represented by the formula R(N=C=0) wherein R is an aliphatic radical having from about 2 to about 20 carbon atoms, a cycloaliphatic radical having from about 4 to about 20 carbon atoms, an aromatic or alkyl aromatic radical having from about 6 to about 20 carbon atoms, and wherein n is an integer of greater than or equal to 2 (preferably 2 or 3). Exemplary polyisocyanates include: 1 ,4-tetramethylene diisocyanate
1 , 6-hexamethylene diisocyanate
2,2,4-trimeth l-- , 6-diisocyanate
1 , 10-decamethylene diisocyanate
1 , 4-cyclohexylene diisocyanate 1 - i socyanato-3 isocyanato methyl-3 , 5 , 5- trimethy.1eyelohexane m- and p-phenylene diisocyanate
2,6 and 2,4-toluene diisocyanate (TDI) xylene diisocyanate \ chloro- 1 , 3-phenylene diisocyanate
4 , ' -methylene diphenylisocyanate ( MDI )
1 , 5-naphthylene diisocyanate
1 , 5-tetrahydro-naphthylene diisocyanate triphenylmethane p, ' , p"-triisocyanate (Desmodur R) polymethylene polyphenylisocyanate (PAPI) TDI-trimethylol propane adduct (Mondur CB-75 )
Preferred for use as the isocyanate component are the urethane prepolymers. These are defined as organic polyisocyanates, such as those specified above, modified with a compound having two or more active hydrogens to provide an isocyanate terminated product.
A multiplicity of compounds having two or more active hydrogens, for reaction with the polyisocyanate, are readily available and are well known. For example, the following functional groups contain active hydrogen and will react with the isocyanato groups: OH, SH, NH, NH,, etc. Preferred are the polyol compounds, including the polyalkylene glycols, polyester polyols, and polyether polyols. Polyester polyols are made by esterification of polyols with dicarboxylic acids using reactant amounts, such that .the product contains free hydroxyl groups. One example of polyester polyol formation is that of excess propylene glycol with adipic acid. Polyether polyols are hydroxyl-containing compounds containing' ether linkages. These are commonly prepared via reaction of an alkylene oxide with a polyhydric compound.
Suitable polyols include polyethylene glycol, polybutylene glycol, polypropylene oxide triol, polymethylene ether glycol, polyethylene ether glycol, polypropylene ether glycol, polybutylene ether glycol, etc. The molecular weight of the polyol can vary widely within the range of about 45-4,000. Preferred are the polymeg® series of polyols available from C Chemicals. These comprise poly( oxyalkylene diol ) compounds of the formula HO ( CHJCHJCHJCHJ0 ) H. Commercially available "Polymeg®" products have molecular weights of 650, 1000, and 2000.
The prepolymers are generally prepared by heating the components together in the requisite proportions and at elevated temperatures, for example, 90°C for 2 hours in the presence of a conventional polyurethane catalyst, such as dibutyl tin dilaurate. The NCO/OH ratio of the prepolymer reactants is normally maintained at from about 2.0-4.0:1 with the so-formed prepolymer containing from 5 to 50 wt.% free NCO groups. After the acrylic oligomer and urethane prepolymer are prepared, they are mixed together in the desired proportion and provide a solventless, 100% solids, pressure sensitive composition that is preferably capable of curing under ambient conditions. Conversely, curing can be effected via conventional techniques, such as heat or radiation. Additionally, well-known tertiary amines and tin compounds can be used as curing catalysts. In those instances in which the active hydrogen-containing lower alkyl acrylate component of the acrylic oligomer does not comprise hydroxy functionality, epoxy curing agents may be used.
Examples
F.xample 1 - An acrylic oligomer is prepared as follows: a premix is prepared composed of 60% butyl acrylate, 18% methyl acrylate, 15% ethyl acrylate, 1.8% 2- hydroxyethyl acrylate and 5.2% acrylic acid (glacial). Sufficient cumene hydroperoxide (CHP) is added as an initiator to produce a 1% concentration of the CHP in the premix. A weight of toluene equal to the premix weight is added to a pressure reactor equipped with a stirrer, thermoregulato , heating and cooling compatibility, addition and discharge valves and sight glasses.
The reactor is closed and heated to 190"C with attendant stirring; the pressure of the reactor at 190°C is 80 psi. The premix is then pumped into the reactor over a 2-4 hour period. The temperature in the reactor is maintained at 190°C with pressure remaining between 80-100 psi during addition of the premix and falling to 60 psi after premix addition has been computed. To insure completion of monomer reaction, additional increments of CHP (80% in toluene) are added at 1.5 hour and 2.5 hours after the premix has been completely added.
Toluene is then removed from the reaction medium via vacuum distillation and is recycled for further use. The product oligomer is an oily viscous liquid having a viscosity of about 5000 cps.
The acrylic oligomer is then mixed with isocyanate prepolymer for use as an adhesive. The isocyanate prepolymer was prepared by reaction of 57% of a commercially available aromatic isocyanate mixture (Mondur-MRS-4-Mobay- 4 ,4 ' -diphenylmethane diisocyanate MDI ; plus higher oligomers of MDI ) and 43% of a commercially available polyether diol ( Polymeg 2,000 - O Chemicals, Inc. ; mws-2,000 - polytetramethylene ether glycol ) . The isocyanate prepolymer has a viscosity of 4500-5500 cps (RTV #60, 20 rpm, 77F); % NCO of 16.23% (theoretical) and a density of 9.25-9.35 lbs./gal.
Example 2 - 50 weight % of the acrylic oligomer (Example 1) and 50 weight % of the isocyanate prepolymer (Example 1) were mixed. The mixture was applied as a bonding layer to a steel-steel interface and allowed to stand under ambient conditions overnight. The next day, a peel strength test (Instron) indicated a value of 163.636 psi. This demonstrated that an excellent bond had formed.
While T have shown and described herein certain embodiments of the invention, it is intended that these be covered as well as any change or modification therein which may be made without departing from the spirit and scope of the invention as defined in the appended claims.
What is claimed is:

Claims

1. Adhesive composition comprising, in combination, acrylic oligomer and organic polyisocyanate, said oligomer consisting essentially of repeat units of lower alkyl acrylate and substituted lower alkyl acrylate moieties wherein the substituent includes an active hydrogen atom to react with said polyisocyanate, said composition being devoid of organic or water-based solvent.
2. Adhesive composition as recited in claim 1 wherein said organic polyisocyanate comprises a compound having the formula R(N=C=0) wherein R is an aliphatic radical, a cycloaliphatic radical, or an aromatic or alkylaromatic radical and wherein n is 2 or greater.
3. Adhesive composition as recited in claim 1 wherein said organic polyisocyanate comprises a polyurethane prepolymer formed from reaction of a polyisocyanate having the formula R(N=C=0) wherein R is an aliphatic radical, a cycloaliphatic radical, or an aromatic or alkylaromatic radical and wherein n is 2 or greater, with a polyfunctional active hydrogen-containing compound.
4. Adhesive composition as recited in claim 3 wherein said polyfunctional active hydrogen-containing compound comprises a polyol.
5. Adhesive composition as recited in claim 1 wherein said oligomer is a tacky, viscous liquid having a viscosity of between about 2,500-50,000 cps and a MW of about 500-3,000.
6. Adhesive composition as recited in claim 1 wherein said oligomer has a viscosity of between about 2,500-7,500 cps.
7. Adhesive composition comprising, in combination, acrylic oligomer and urethane prepolymer, said oligomer consisting essentially of repeat units of lower alkyl acrylate, and hydroxylated lower alkyl acrylate moieties, said composition being devoid of organic or water-based solvent.
8. Adhesive composition as recited in claim 7 wherein said urethane prepolymer is formed from reaction of a polyisocyanate compound with a polyfunctional active hydrogen containing compound.
9. Adhesive composition as recited in claim 8 wherein said polyisocyanate compound has the formula R(N=C=0) wherein R is an aliphatic radical, a cycloaliphatic radical, or an aromatic or alkylaromatic radical and wherein n is 2 or greater.
10. Adhesive composition as recited in claim 9 wherein said polyfunctional active hydrogen containing compound comprises a polyol.
11. Adhesive composition as recited in claim 10 wherein said polyol is a polyalkylene glycol, polyester polyol or polyether polyol.
12. Adhesive composition as recited in claim 11 wherein said polyether polyol is a poly(oxyalkylene ) diol compound having a molecular weight of about 45-4,000.
13. Adhesive composition as recited in claim 12 wherein said polyoxyalkylene diol compound has the formula
Figure imgf000018_0001
) H and has a molecular weight of between about 450-2000.
14. Adhesive composition as recited in claim 11 wherein said polyisocyanate compound comprises 4,4'- methylene diphenyl isocyanate (MDI).
15. Adhesive composition as recited in claim 10 comprising, by weight, about 10-90 wt.% acrylic oligomer and about 90-10 wt.% said prepolymer.
16. Adhesive composition as recited in claim 15 comprising about 50 wt.% acrylic oligomer, and about 50 wt.% said prepolymer.
17. Adhesive composition as recited in claim 7 wherein, based on the total weight of said oligomer, said lower alkyl acrylate moieties are present in an amount of about 50-99% and said hydroxylated lower alkyl acrylate moieties are present in an amount of about 1-50 wt.%.
18. Adhesive composition as recited in claim 17 wherein said lower alkyl acrylate moieties comprise a mixture of methyl acrylate, ethyl acrylate, and butyl acrylate moieties and wherein said hydroxylated lower alkyl acrylate moieties comprise 2-hydroxyethyl acrylate.
19. Adhesive composition as recited in claim 7 wherein said acrylic oligomer has a MW of between about 500-3, .00 and a viscosity of about 2,500 to 50,000 cps.
20. Adhesive composition as recited in claim 19 wherein said acrylic oligomer has a viscosity of about 2,500-7,500 cps.
21. Adhesive composition as recited in claim 19 wherein said acrylic oligomer has a viscosity of about 5,000 cps.
22. Adhesive composition as recited in claim 7 wherein said urethane prepolymer has a free NCO content of from about 5-50 wt.%.
AMENDED CLAIMS
[received by the International Bureau on 2 February 1993 (02.02.93); original claims 1 and 7 amended; remaining claims unchanged (2 pages)]
1. Adhesive composition comprising, in combination, acrylic oligomer and organic polyisocyanate, said oligomer consisting of repeat units of: D a first acrylate member selected from the group consisting of acrylic acid and lower alkyl acrylate moieties and mixtures thereof; 2) a second acrylate member consisting of a substituted lower alkyl acrylate moiety wherein the substituent includes an active hydrogen atom to react with said polyisocyanate, said composition being devoid of organic or water-based solvent.
2. Adhesive composition as recited in claim 1 wherein said organic polyisocyanate comprises a compound having the formula R(N=C=0)n wherein R is an aliphatic radical, a cycloaliphatic radical, or an aromatic or alkylaromatic radical and wherein n is 2 or greater.
3. Adhesive composition as recited in claim 1 wherein said organic polyisocyanate comprises a polyurethane prepolymer formed from reaction of a polyisocyanate having the formula R(N=C=0)„ wherein R is an aliphatic radical, a cycloaliphatic radical, or an aromatic or alkylaromatic radical and wherein n is 2 or greater, with a polyfunctional active hydrogen-containing compound.
4. Adhesive composition as recited in claim 3 wherein said polyfunctional active hydrogen-containing compound comprises a polyol. 5. Adhesive composition as recited in claim 1 wherein said oligomer is a tacky, viscous liquid having a viscosity of between about 2,500-50,000 cps and a MW of about 500-3,000.
6. Adhesive composition as recited in claim 1 wherein said oligomer has a viscosity of between about 2,500-7,500 cps.
7. Adhesive composition comprising, in combination, acrylic oligomer and urethane prepolymer, said oligomer consisting of repeat units of: 1) a first acrylate member selected from the group consisting of acrylic acid and lower alkyl acrylate moieties, and mixtures thereof; 2) a second acrylate member consisting of hydroxylated lower alkyl acrylate moieties, said composition being devoid of organic or water-based solvent.
8. Adhesive composition as recited in claim 7 wherein said urethane prepolymer is formed from reaction of a polyisocyanate compound with a polyfunctional active hydrogen containing compound.
9. Adhesive composition as recited in claim 8 wherein said polyisocyanate compound has the formula R(N=C-0)n wherein R is an aliphatic radical, a cycloaliphatic radical, or an aromatic or alkylaromatic radical and wherein n is 2 or greater.
PCT/US1992/007109 1991-09-04 1992-08-24 One hundred percent solids acrylic adhesives WO1993005099A1 (en)

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FR2717178A1 (en) * 1994-03-14 1995-09-15 Hoechst France Acrylate-styrene resins cross-linked by a blocked polyisocyanate, preparation and applications as paint and / or varnish.
WO2014138218A1 (en) * 2013-03-06 2014-09-12 H.B. Fuller Company Gas transmitting polyurethane adhesive
CN108003774A (en) * 2017-12-21 2018-05-08 新纳奇材料科技江苏有限公司 A kind of nano-material modified no-solvent polyurethane woodcare paint and preparation method thereof
WO2018132648A1 (en) * 2017-01-12 2018-07-19 Basf Se Physical property improvement of polyurethanes
CN115851206A (en) * 2022-11-29 2023-03-28 珠海科技学院 Solvent-free polyurethane modified acrylate adhesive and preparation method thereof

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Cited By (15)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2717178A1 (en) * 1994-03-14 1995-09-15 Hoechst France Acrylate-styrene resins cross-linked by a blocked polyisocyanate, preparation and applications as paint and / or varnish.
EP0672690A1 (en) * 1994-03-14 1995-09-20 Societe Francaise Hoechst Acrylate-Styrene resins crosslinked by blocked polyisocyanates, manufacture and use thereof as paints and/or lacqueurs
US5567762A (en) * 1994-03-14 1996-10-22 Societe Francaise Hoechst Acrylate-styrene resins cross-linked by a blocked polyisocyanate preparation and uses as paint and/or lacquer
WO2014138218A1 (en) * 2013-03-06 2014-09-12 H.B. Fuller Company Gas transmitting polyurethane adhesive
US9181460B2 (en) 2013-03-06 2015-11-10 H.B. Fuller Company Gas transmitting polyurethane adhesive
AU2014225799B2 (en) * 2013-03-06 2016-12-15 H.B. Fuller Company Gas transmitting polyurethane adhesive
KR20190102276A (en) * 2017-01-12 2019-09-03 바스프 에스이 Improved physical properties of polyurethane
WO2018132648A1 (en) * 2017-01-12 2018-07-19 Basf Se Physical property improvement of polyurethanes
CN110167985A (en) * 2017-01-12 2019-08-23 巴斯夫欧洲公司 The physical property of polyurethane is improved
JP2020504218A (en) * 2017-01-12 2020-02-06 ビーエーエスエフ ソシエタス・ヨーロピアＢａｓｆ Ｓｅ Improvement of physical properties of polyurethane
US11267929B2 (en) 2017-01-12 2022-03-08 Basf Se Physical property improvement of polyurethanes
KR102564146B1 (en) 2017-01-12 2023-08-08 바스프 에스이 Improving physical properties of polyurethane
CN108003774A (en) * 2017-12-21 2018-05-08 新纳奇材料科技江苏有限公司 A kind of nano-material modified no-solvent polyurethane woodcare paint and preparation method thereof
CN115851206A (en) * 2022-11-29 2023-03-28 珠海科技学院 Solvent-free polyurethane modified acrylate adhesive and preparation method thereof
CN115851206B (en) * 2022-11-29 2025-05-02 珠海科技学院 A solvent-free polyurethane modified acrylate adhesive and preparation method thereof

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