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
  • C09J133/00—Adhesives based on homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by only one carboxyl radical, or of salts, anhydrides, esters, amides, imides, or nitriles thereof; Adhesives based on derivatives of such polymers
  • C09J133/04—Homopolymers or copolymers of esters
  • C09J133/06—Homopolymers or copolymers of esters of esters containing only carbon, hydrogen and oxygen, the oxygen atom being present only as part of the carboxyl radical
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B82—NANOTECHNOLOGY
  • B82B—NANOSTRUCTURES FORMED BY MANIPULATION OF INDIVIDUAL ATOMS, MOLECULES, OR LIMITED COLLECTIONS OF ATOMS OR MOLECULES AS DISCRETE UNITS; MANUFACTURE OR TREATMENT THEREOF
  • B82B3/00—Manufacture or treatment of nanostructures by manipulation of individual atoms or molecules, or limited collections of atoms or molecules as discrete units
• • 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
  • C09J2301/00—Additional features of adhesives in the form of films or foils
  • C09J2301/30—Additional features of adhesives in the form of films or foils characterized by the chemical, physicochemical or physical properties of the adhesive or the carrier
  • C09J2301/302—Additional features of adhesives in the form of films or foils characterized by the chemical, physicochemical or physical properties of the adhesive or the carrier the adhesive being pressure-sensitive, i.e. tacky at temperatures inferior to 30°C

Definitions

• PSAs Pressure sensitive adhesives
• Materials that have been found to function well as PSAs include polymers designed and formulated to exhibit the requisite viscoelastic properties resulting in a desired balance of tack, peel adhesion, and shear holding power.
• PSAs are characterized by being normally tacky at room temperature (e.g., 20 0 C). PSAs do not embrace compositions merely because they are sticky or adhere to a surface.
• U.S. Pat. No. Re. 24,906 discloses a pressure sensitive adhesive tape, the adhesive layer of which comprises a copolymer of acrylic acid ester and a copolymerizable monomer such as acrylic acid, described therein as an "acrylic pressure sensitive adhesive tape".
• acrylic pressure sensitive adhesive tape may provide high shear strength and good adhesion, there has been a need for even higher shear strength, especially at elevated temperatures, without any reduction in adhesion, particularly in peel strength.
• the present invention is directed to an adhesive composition
• an adhesive composition comprising a (meth)acrylate copolymer, a polyfunctional aziridine crosslinking agent and silica nanoparticles.
• the addition of the nanoparticles results in a significant increase in the overlap shear properties of the adhesive while maintaining the peel adhesion.
• only a small amount of nanoparticles (1-8 weight percent, relative to the weight of the adhesive (meth)acrylate copolymer) are needed to observe the increase in shear properties with the acrylic pressure sensitive adhesives described herein.
• the combination of the polyfunctional aziridines with the nanoparticles exhibits a synergistic effect with respect to peel and shear measurements, relative to the same adhesive polymer composition having only the nanoparticle component or only the aziridine component.
• the present invention provides an aqueous emulsion comprising a (meth)acrylate copolymer and a silica nanoparticle, which may be coated and dried to yield a pressure sensitive adhesive.
• a particle size dependence on the shear properties the smaller the size of the nanoparticles ( ⁇ 20 nanometers) in the adhesive, the greater the increase in the shear performance, while maintaining a constant level of peel performance. Larger particle sizes, above 20 nanometers, have little reinforcing effect on shear properties.
• VOCs volatile organic solvents
• aqueous systems are desirable for cost, environmental, safety, and regulatory reasons.
• the aqueous system may be readily coated, and provides a pressure sensitive adhesive when dried.
• emulsion refers to a stable mixture of two or more immiscible liquids held in suspension by one or more surfactants, more specifically it refers to a stable mixture of the instant polymerizable monomer mixture, or resultant polymer, and water;
• latex refers to an aqueous suspension or emulsion of a polymer, more specifically it refers to an aqueous emulsion of the instant polymer;
• oil-in- water emulsion refers to a mixture in which the water forms a continuous phase and the monomers (oil) is in discontinuous droplets;
• oil phase in an oil-in-water emulsion refers to all components in the formulation that individually exceed their solubility limit in the water phase; these are materials that generally have solubilities of less than 1% in distilled water, however, water phase components such as salts may decrease the solubility of certain oils resulting in their partitioning into the oil phase;
• water phase in an oil-in-water emulsion refers to the water present and any components that are water soluble, i.e., have not exceeded their solubility limit in water;
• (meth)acrylate monomers are acrylic acid esters or methacrylic acid esters of alcohols;
• silica sol refers to a dispersion of discrete, amorphous silica particles in a liquid, typically water. "hydrophobic” is used herein to mean that the monomer lacks substantial affinity for water, that is, it neither substantially adsorbs nor absorbs water at room temperature.
• hydrophilic in the context of silica nanoparticles refers to those nanoparticles that are readily dispersed in water. In the context of monomers, it refers to monomers that have a substantial affinity for water.
• the present invention provides a pressure sensitive adhesive composition comprising:
• (c) 1 to 8 parts by weight, preferably 2 to 5 parts by weight, of silica nanoparticles having an average particle diameter of 20 nanometers or less, based on 100 parts of polymer.
• the present invention further provides an aqueous emulsion having a pH of greater than 7 comprising 70 to 30 weight percent of (a), (b) and (c), and 30 to 70 weight percent of an aqueous phase.
• the emulsion comprises: (a) a polymer comprising the reaction product of: (i) 90 to 99 parts by weight, preferably 90 to 95 parts be weight, of an (meth)acrylic acid ester of non-tertiary alcohol, said alcohol having from 1 to 14 carbon atoms, with the average number of carbon atoms being from about 4 to about 12; (ii) 1 to 10 parts by weight, preferably 2 to 7 parts by weight,-of an acid functional monomer;
• the emulsion comprises about 50 to about 65 percent by weight (a) + (b)
• the emulsion may be coated and dried to produce a pressure sensitive adhesive.
• the polymer component of the adhesive composition may comprise one or more polymers.
• Examples of monomers suitable for use as the acrylate ester monomer include the esters of either acrylic acid or methacrylic acid with non-tertiary alcohols such as ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, 1-pentanol, 2-pentanol, 3-pentanol, 2- methyl-1-butanol, 1-hexanol, 2-hexanol, 2 -methyl- 1-pentanol, 3 -methyl- 1-pentanol, 2- ethyl- 1-butanol, 3,5,5-trimethyl-l-hexanol, 3-heptanol, 1-octanol, 2-octanol, isooctylalcohol, 2-ethyl- 1-hexanol, 1-decanol, 1-dodecanol, 1-tridecanol, 1-tetradecanol and the like.
• non-tertiary alcohols
• the preferred acrylate ester monomer is the ester of acrylic acid with butyl alcohol or isooctyl alcohol, or a combination thereof, although combinations of two or more different acrylate ester monomer are suitable.
• the acrylate ester monomer is preferably present in an amount of 90 to 99 parts by weight based on 100 parts total monomer content used to prepare the polymer (i.e. the total of i through v in the composition supra). More preferably acrylate ester monomer is present in an amount of 90 to 95 parts by weight based.
• the polymer further comprises an acid functional monomer, where the acid functional group may be an acid per se, such as a carboxylic acid, or a salt thereof such as an alkali metal carboxylate.
• acid functional monomers include, but are not limited to, those selected from ethylenically unsaturated carboxylic acids, ethylenically unsaturated sulfonic acids, ethylenically unsaturated phosphonic acids, and mixtures thereof.
• Such compounds include those selected from acrylic acid, methacrylic acid, itaconic acid, fumaric acid, crotonic acid, citraconic acid, maleic acid, oleic acid, ⁇ -carboxy ethyl acrylate, 2-sulfoethyl methacrylate, styrene sulfonic acid, 2- acrylamido-2-methylpropanesulfonic acid, vinylphosphonic acid, and mixtures thereof. Due to their availability, acid functional monomers of the present invention are generally selected from ethylenically unsaturated carboxylic acids, i.e. (meth)acrylic acids.
• acidic monomers include the ethylenically unsaturated sulfonic acids and ethylenically unsaturated phosphonic acids.
• the acid functional monomer is generally used in amounts of 1 to 10 parts by weight, preferably 2 to 7 parts by weight, based on 100 parts by weight total monomer.
• the polar monomers useful in preparing the adhesive polymer are both somewhat oil soluble and water soluble, resulting in a distribution of the polar monomer between the aqueous and oil phases in an emulsion polymerization.
• Useful second polar monomers are non-acid functional.
• the polar monomers comprise 1 to 10 parts by weight, preferably 1 to 5 parts by weight, on 100 parts by weight total monomer.
• Suitable polar monomers include but are not limited to 2-hydroxylethyl (meth)acrylate; N-vinylpyrrolidone; N-vinylcaprolactam; acrylamide; mono- or di-N-alkyl substituted acrylamide; t-butyl acrylamide; dimethylaminoethyl acrylamide; N-octyl acrylamide; poly(alkoxyalkyl) acrylates including 2-(2- ethoxyethoxy)ethyl acrylate, 2-ethoxyethyl acrylate, 2-methoxyethoxyethyl acrylate, 2- methoxyethyl methacrylate, polyethylene glycol mono(meth)acrylates; alkyl vinyl ethers, including vinyl methyl ether; and mixtures thereof.
• Preferred polar monomers include those selected from the group consisting of 2-hydroxyethyl (meth)acrylate and N- vinylpyrrolidinone.
• Multifunctional acrylates are particularly useful for emulsion polymerization.
• useful multifunctional acrylates include, but are not limited to, diacrylates, triacrylates, and tetraacrylates, such as 1,6-hexanediol diacrylate, poly(ethylene glycol) diacrylates, polybutadiene diacrylate, polyurethane diacrylates, and propoxylated glycerin triacrylate, and mixtures thereof.
• the amount and identity of a multifunctional acrylate is tailored depending upon application of the adhesive composition. Typically, the multifunctional acrylate is present in amounts less than 5 parts based on total dry weight of adhesive composition. More specifically, the multifunctional acrylate may be present in amounts from 0.01 parts to 1 part based on 100 parts total monomers of the adhesive composition.
• the pressure sensitive adhesive further comprises a polyfunctional aziridine crosslinking agent to increase cohesive strength of the adhesive.
• the polyfunctional aziridine has an average functionality of greater than two (aziridine groups), and preferably an average of at least 3.
• the polyfunctional aziridines crosslink the polymer by forming linkages between the pendent carboxylic acid groups of the polymer and the aziridine groups. It has been found that the combination of the polyfunctional aziridines with the nanoparticles exhibits a synergistic effect with respect to peel and shear measurements, relative to the same adhesive polymer composition having only the nanoparticle component or only the aziridine component.
• Such chemical crosslinkers can be added into emulsion PSAs after polymerization and activated by heat during oven drying of the coated adhesive.
• the polyfunctional aziridine crosslinking agent are used in amounts of 0.001 to 1 parts, preferably 0.01 to 0.1 parts, based on 100 parts of the acrylate polymer. It is preferred that the polyfunctional aziridine be soluble or dispersible in the emulsion in the amounts used.
• Suitable polyfunctional aziridines include, for example, those disclosed in U.S. Pat. No. 3,225,013 (Fram); U.S. 4,769,617 (Canty); U.S. 4,490,505 (Pendergrass) and U.S. Pat. No. 5,534,391 (Wang).
• suitable polyfunctional aziridines include those disclosed in U.S. Pat. No. 3,225,013.
• the polyfunctional aziridine is a trifunctional aziridine.
• the composition further comprises silica generally used and compounded in the form of a colloidal dispersion that does not readily precipitate or agglomerate.
• Colloidal silica is a dispersion of substantially spherical, submicron-sized silica (SiO 2 ) particles in an aqueous or other solvent medium.
• the nanoparticles used in the invention may be acid stabilized or base stabilized.
• the colloidal silicas used in this composition are dispersions of submicron size silica particles in an aqueous or in a water/organic solvent mixture and having and average particle diameter of 20 nanometers or less, preferably 10 nanometers or less, and more preferably 5 nanometers or less. The average particle size may be determined using transmission electron microscopy.
• the nanoparticles generally have a surface area greater than about 150 m 2 /gram, preferably greater than 200 m 2 /gram, and more preferably greater than 400 m 2 /gram.
• the particles preferably have narrow particle size distributions, that is, a polydispersity of 2.0 or less, preferably 1.5 or less. If desired, minor amounts of larger silica particles may be added, but such additions do not contribute to the increase in shear values.
• Non-aqueous silica sols may also be used and are silica sol dispersions wherein the liquid phase is an organic solvent, or an aqueous organic solvent.
• the silica sol is chosen so that its liquid phase is compatible with the emulsion, and is typically aqueous or an aqueous organic solvent.
• the nanoparticles may be surface-modified.
• a surface- modified nanoparticle is a particle that includes surface groups attached to the surface of the particle. The surface groups modify the hydrophobic or hydrophilic nature of the particle. In some embodiments, the surface groups may render the nanoparticles more hydrophobic.
• the surface groups may render the nanoparticles more hydrophilic.
• the surface groups may be selected to provide a statistically averaged, randomly surface-modified particle.
• the surface groups are present in an amount sufficient to form a monolayer, preferably a continuous monolayer, on the surface of the particle.
• less than 25%, preferably less that 10%, of the available surface functional groups i.e. Si-OH groups
• Si-OH groups are modified with a hydrophilic surface modifying agent to retain hydrophilicity and dispersibility, and are modified with a hydrophilic surface modifying agent.
• the silica nanoparticles are not surface modified, although they may be acid- or base-stabilized, or the counter ion may be exchanged.
• a variety of methods are available for modifying the surface of nanoparticles including, e.g., adding a surface modifying agent to nanoparticles (e.g., in the form of a powder or a colloidal dispersion) and allowing the surface modifying agent to react with the nanoparticles.
• a surface modifying agent e.g., in the form of a powder or a colloidal dispersion
• Other useful surface modification processes are described in, e.g., U.S. 2,801,185 (Her) and U.S. 4,522,958 (Das et al).
• additives can be added in order to enhance the performance of the adhesive compositions.
• leveling agents ultraviolet light absorbers, hindered amine light stabilizers (HALS), oxygen inhibitors, rheology modifiers, wetting agents, defoamers, biocides, dyes and the like. All of these additives and the use thereof are well known in the art. It is understood that any of these compounds can be used so long as they do not deleteriously affect the adhesive properties.
• UV absorbers and hindered amine light stabilizers are also useful as additives to the present compositions.
• UV absorbers and hindered amine light stabilizers act to diminish the harmful effects of UV radiation on the final cured product and thereby enhance the weatherability, or resistance to cracking, yellowing and delamination of the coating.
• a preferred hindered amine light stabilizer is bis( 1,2,2,6, 6-pentamethyl-4- piperidinyl) [3,5-bis(l,l-dimethylethyl-4-hydroxyphenyl)methyl]butylpropanedioate, available as TinuvinTM144, from CIBA-GEIGY Corporation, Hawthorne, NY.
• UV absorbers and combinations thereof in concentrations of less than parts by weight based on the total monomer composition may produce desirable results : bis( 1 ,2,2,6,6-pentamethyl-4-piperidinyl)(3 ,5-bis( 1 , 1 -dimethylethyl 1 -A- hydroxyphenyl)methyl) butylpropanedioate, 2-ethylhexyl-2-cyano-3,3'-diphenylacrylate, 2-hydroxyl-4-n-octoxybenzophenone, 2-(2'-hydroxy-5'-methylphenyl)benzotriazole, poly(oxy-l,2-ethanediyl), alpha-(3-(3-(2H-benzotriazol-2-yl)-5-(l,l-dimethylethyl)-4- hydroxylphenyl) -l-oxopropyl)-omega-hydroxy, and UvinulTM D-50 and MS-40, sold by BASF
• the polymers herein can be prepared by any conventional free radical polymerization method, including solution, radiation, bulk, dispersion, emulsion, and suspension processes.
• the acrylate polymers may be prepared via suspension polymerizations as disclosed in U.S. Pat. Nos. 3,691,140 (Silver); 4,166,152 (Baker et al); 4,636,432 (Shibano et al); 4,656,218 (Kinoshita); and 5,045,569 (Delgado).
• the acrylate polymer is prepared by an emulsion polymerization process in the presence of a free-radical initiator.
• Suitable water-soluble initiators include but are not limited to those selected from the group consisting of potassium persulfate, ammonium persulfate, sodium persulfate, and mixtures thereof; oxidation-reduction initiators such as the reaction product of the above - mentioned persulfates and reducing agents such as those selected from the group consisting of sodium metabisulf ⁇ te and sodium bisulfite; and 4,4'-azobis(4-cyanopentanoic acid) and its soluble salts (e.g., sodium, potassium).
• the preferred water-soluble initiator is potassium persulfate.
• Suitable oil-soluble initiators include but are not limited to those selected from the group consisting of azo compounds such as VAZO 64 (2,2'- azobis(isobutyronitrile)) and VAZO 52 (2,2'-azobis(2,4-dimethylpentanenitrile)), both available from E.I. du Pont de Nemours Co., peroxides such as benzoyl peroxide and lauroyl peroxide, and mixtures thereof.
• the preferred oil-soluble thermal initiator is (2,2'- azobis(isobutyronitrile)).
• initiators may comprise from about 0.05 to about 1 part by weight, preferably about 0.1 to about 0.5 part by weight based on 100 parts by weight of monomer components in the pressure sensitive adhesive.
• the copolymerizable emulsion mixture may optionally further comprise chain transfer agents to control the molecular weight of the resultant polymer.
• chain transfer agents include but are not limited to those selected from the group consisting of carbon tetrabromide, alcohols, mercaptans, and mixtures thereof. When present, the preferred chain transfer agents are isooctylthioglycolate and carbon tetrabromide.
• the emulsion mixture may further comprise up to about 0.5 parts by weight of a chain transfer agent, typically about 0.01 to about 0.5 parts by weight, if used, preferably about 0.05 parts by weight to about 0.2 parts by weight, based upon 100 parts by weight of the total monomer mixture.
• Polymerization via emulsion techniques may require the presence of an emulsifier (which may also be called an emulsifying agent or a surfactant).
• an emulsifier which may also be called an emulsifying agent or a surfactant.
• Useful emulsif ⁇ ers for the present invention include those selected from the group consisting of anionic surfactants, cationic surfactants, nonionic surfactants, and mixtures thereof.
• Useful anionic surfactants include but are not limited to those whose molecular structure includes at least one hydrophobic moiety selected from the group consisting of from about C 6 - to C12 -alkyl, alkylaryl, and/or alkenyl groups as well as at least one anionic group selected from the group consisting of sulfate, sulfonate, phosphate, polyoxyethylene sulfate, polyoxyethylene sulfonate, polyoxyethylene phosphate, and the like, and the salts of such anionic groups, wherein said salts are selected from the group consisting of alkali metal salts, ammonium salts, tertiary amino salts, and the like.
• useful anionic surfactants include sodium lauryl sulfate, available from Stepan Chemical Co. as POLYSTEP B-3; sodium lauryl ether sulfate, available from Stepan Chemical Co. as POLYSTEP B-12; and sodium dodecyl benzene sulfonate, available from Rhone -Poulenc as SIPONATE DS-IO.
• Useful nonionic surfactants include but are not limited to those whose molecular structure comprises a condensation product of an organic aliphatic or alkyl aromatic hydrophobic moiety with a hydrophilic alkylene oxide such as ethylene oxide.
• the HLB hydrophilic alkylene oxide
• HLB Hydrophilic-Lipophilic Balance
• nonionic surfactants useful in the present invention include but are not limited to nonylphenoxy or octylphenoxy poly(ethyleneoxy)ethanols available from Rhone-Poulenc as the IGEPAL CA or CO series, respectively; C ⁇ ⁇ -C ⁇ 5 secondary-alcohol ethoxylates available from Union Carbide as the TERGITOL 15-S series; and polyoxyethylene sorbitan fatty acid esters available from ICI Chemicals as the TWEEN series of surfactants.
• Useful cationic surfactants include alkylammonium salts having the formula C n H 2n+ iN + (CH 3 ) 3 X " , where X is OH, Cl, Br, HSO 4 or a combination thereof, and where n is an integer from 8 to 22, and the formula C n H 2n+ iN + (C 2 Hs) S X " , where n is an integer from 12 to 18; gemini surfactants, for example those having the formula: [Ci 6 H.
• the surfactant may be an ionic surfactant copolymerizable with the monomer mixtures, and is incorporated into the polymer chain during polymerization.
• useful copolymerizable ionic surfactants include but are not limited to those described in WO 89/12618 (Tang et al).
• the surfactants described therein have a hydrophobic portion containing alpha-beta ethylenic unsaturation, a hydrophilic portion containing a poly(alkyleneoxy) segment, and an ionic segment.
• the reactive surfactants arise from successive condensation polymerizations of an ethylenically-unsaturated alcohol with a prescribed amount of a first cyclic ether, e.g., propylene oxide, butylene oxide or a mixture thereof, followed by condensation with a prescribed amount of ethylene oxide.
• a first cyclic ether e.g., propylene oxide, butylene oxide or a mixture thereof
• Cationic or anionic end-group functionality is added via the terminal hydroxyl group, as desired.
• the ionic copolymerizable surfactant has at least one group, preferably one group, capable of reacting with the copolymerizable monomer mixture.
• reactive groups include but are not limited to those groups selected from the group consisting of ethylenically unsaturated groups such as vinyl groups, acrylate groups, etc.
• the preferred copolymerizable surfactant which has the trade name MAZON SAM-211, is available from PPG Industries, Inc. and is described as an alkylene polyalkoxy ammonium sulfate, wherein the number of alkoxy groups is between about 5 and about 25, with a typical example having about 15 to about 20 ethoxy groups.
• additional useful copolymerizable surfactants include alkyl allyl sulfosuccinates such as TREM-LF40, available from Diamond Shamrock Company. Additional useful copolymerizable surfactants are disclosed in U.S. Pat. Nos. 3,925,442 and 3,983,166, assigned to The Kendall Company.
• the emulsion of the present invention can be made using a mixture of a copolymerizable surfactant as delineated above and a typical ionic or nonionic noncopolymerizable surfactant commonly known in the art of emulsion polymerization, in place of the ionic copolymerizable surfactant above.
• a typical ionic or nonionic noncopolymerizable surfactant commonly known in the art of emulsion polymerization in place of the ionic copolymerizable surfactant above.
• Example of such noncopolymerizable surfactants can be found in "Emulsion Polymerization: theory and practice", by D. C. Blackley, New York, J. Wiley (1975).
• the surfactant mixture comprises about 40 to about 99.5 percent by weight of an ionic copolymerizable surfactant and about 0.5 to about 60 percent by weight of a noncopolymerizable surfactant, based upon the total weight of the surfactant mixture.
• the emulsion polymerization of this invention is carried out in the presence of anionic surfactant(s).
• a useful range of emulsif ⁇ er concentration is from about 0.5 to about 8 weight percent, preferably from about 1 to about 5 weight percent, based on the total weight of all monomers of the emulsion pressure sensitive adhesive.
• the emulsion pressure sensitive adhesives of the invention may also contain one or more conventional additives.
• Preferred additives include tackif ⁇ ers, plasticizers, dyes, antioxidants, and UV stabilizers. Such additives can be used if they do not affect the superior properties of the emulsion pressure sensitive adhesives. If tackifiers are used, then up to about 40% by weight, preferably less than 30% by weight, and more preferably less than 5% by weight based on the dry weight of the total adhesive polymer and silica, would be suitable. In some embodiments, 25 to about 60 phr based on dry weight of the total adhesive component would also be suitable.
• Suitable tackifiers for use with (meth)acrylate polymer dispersions include rosin acids, rosin esters, terpene phenolic resins, hydrocarbon resins, and cumarone indene resins.
• the type and amount of tackifier can affect properties such as contactability, bonding range, bond strength, heat resistance and specific adhesion.
• the tackifier will generally be used in the form of an aqueous dispersion.
• tackifiers that are suitable include TACOLYN 1070, 5001 and 5002 (aqueous, 55% solids synthetic resin dispersions based on low molecular weight thermoplastic resins, available from Hercules Inc.), SE 1055 (an aqueous dispersion of a rosin ester, available from Hercules Inc.), ESCOREZ 9271 (an aliphatic hydrocarbon resin emulsion, available from Exxon), DERMULSENE 82, DERMULSENE 92, DERMULSENE DT or DERMULSENE DT50 (aqueous dispersions of modified terpene phenolic resins, available from DRT) and AQUATAK 4188 (a modified rosin ester, available from Arizona Chemical Company).
• TACOLYN 1070, 5001 and 5002 aqueous, 55% solids synthetic resin dispersions based on low molecular weight thermoplastic resins, available from Hercules Inc.
• SE 1055 an aqueous dis
• the (meth)acrylate copolymer may be prepared by an emulsion polymerization process.
• emulsion polymerization a reaction occurs in micelles or emulsion microdrops suspended in aqueous medium. Any heat generated in the microdrops or micelles is quickly moderated by the effect of the heat capacity of the surrounding water phase.
• Emulsion polymerization proceeds with better control of exothermic reactions, and the resulting adhesive composition is non-flammable as the aqueous medium is the dominant component.
• the pressure sensitive adhesives of the present invention are prepared by a batch, continuous or semi-continuous emulsion polymerization process.
• the polymerization generally comprises the steps of:
• a surfactant selected from the group consisting of anionic surfactants, nonionic surfactants, cationic surfactants, amphoteric surfactants, polymeric surfactants, and mixtures thereof,
• a flask is charged with a seed monomer mixture comprising deionized (DI) water, surfactant, acid functional monomers, acrylate ester monomers, optional co-polymerizable monomers, including optional polar monomers, vinyl monomer, and multifunctional acrylate plus any optional chain transfer agents, pH modifiers or other additives.
• DI deionized
• surfactant acid functional monomers
• acrylate ester monomers optional co-polymerizable monomers
• optional chain transfer agents including optional polar monomers, vinyl monomer, and multifunctional acrylate plus any optional chain transfer agents, pH modifiers or other additives.
• the batch temperature is then raised to the feed reaction temperature, about 70 to about 85°C
• the monomer pre-emulsion comprising DI water, surfactant acid functional monomers, acrylate ester monomers, optional co-polymerizable monomers, including optional polar monomers, chain transfer agents or other additives is added to the stirred flask over a period of time, typically 2 to 4 hours, while the temperature is maintained.
• the second initiator charge if used, is added to the reaction to further reduce residual monomers in the emulsion. After additional hour of heating, the mixture is cooled to room temperature (about 23°C) and the emulsion is collected for evaluation.
• the pH of the emulsion is at least 7, typically about 8-12.
• the acidity of the emulsion may be modified following latex formation using a pH modifier such as a basic solution (e.g., solutions of sodium hydroxide, ammonium hydroxide, lithium hydroxide and the like) or buffer solutions (e.g., sodium bicarbonate and the like), to the desired pH levels.
• a basic solution e.g., solutions of sodium hydroxide, ammonium hydroxide, lithium hydroxide and the like
• buffer solutions e.g., sodium bicarbonate and the like
• the composition containing the polyfunctional aziridine rapidly gels at lower pH ( ⁇ 7), so the emulsion is desirably basic to allow the emulsion to be coated and cured to produce a pressure sensitive adhesive article.
• the adhesive composition It is preferable to coat the adhesive composition soon after preparation. It has been found that the viscosity of the composition increases with time, and this viscosity increase is believed to be due to agglomeration of the silica nanoparticles.
• the emulsion (containing the adhesive polymer, polyfunctional aziridine, and silica nanoparticles) are easily coated upon suitable flexible backing materials by conventional coating techniques to produce adhesive coated sheet materials.
• the flexible backing material may be any material conventionally utilized as a tape backing, optical film or any other flexible material.
• Typical examples of flexible backing materials employed as conventional tape backing that may be useful for the adhesive compositions include those made of paper, plastic films such as polypropylene, polyethylene, polyurethane, polyvinyl chloride, polyester (e.g., polyethylene terephthalate), cellulose acetate, and ethyl cellulose.
• Backings may also be prepared of fabric such as woven fabric formed of threads of synthetic or natural materials such as cotton, nylon, rayon, glass, ceramic materials, and the like or nonwoven fabric such as air laid webs of natural or synthetic fibers or blends of these.
• the backing may also be formed of metal, metallized polymer films, or ceramic sheet materials may take the form of any article conventionally known to be utilized with pressure sensitive adhesive compositions such as labels, tapes, signs, covers, marking indicia, and the like.
• compositions are coated on a substrate using conventional coating techniques modified as appropriate to the particular substrate.
• these compositions can be applied to a variety of solid substrates by methods such as roller coating, flow coating, dip coating, spin coating, spray coating knife coating, and die coating. These various methods of coating allow the compositions to be placed on the substrate at variable thicknesses thus allowing a wider range of use of the compositions.
• Coating thicknesses may vary, but coating thicknesses of 2-50 microns (dry thickness), preferably about 25 microns, are contemplated.
• the emulsions may be of any desirable concentration for subsequent coating, but is typically between 30 to 70 wt.% water, and more typically between 50 and 65 wt.% water.
• the desired concentration may be achieved by further dilution of the emulsion, or by partial drying.
• the adhesives of the present invention may be suited for use in wet lamination applications, the adhesives may also perform well in dry lamination applications, wherein the resultant lamination is subjected to high heat and humidity conditions.
• pressure sensitive adhesive is coated onto backings with the desired coating thickness and then dried before lamination. Then, water is sprayed onto glass or other substrate, sometimes along with a small amount of surfactant to lower the water's surface tension, to obtain a thin water layer on the substrate surface. The film is then positioned properly on the substrate, and most of the excess of water is squeezed out to yield a substrate/PSA/film laminate. The remaining water in the laminate will be evaporated in a few days, depending on the materials used in the laminate.
• a PSA is coated onto films (backings) with the desired coating thickness, and then dried before lamination. Such PSA coated film is then adhered onto substrate surface with pressure and/or high temperature to bond the film onto the substrate surface.
• the pressure sensitive adhesives can be used in a variety of traditional pressure sensitive adhesive articles, such as tapes, labels, decals, transfer tapes and other articles.
• Suitable materials useful as the flexible support or backing for the adhesive articles of the invention include, but are not limited to, paper, latex saturated paper, polymeric film, cellulose acetate film, ethyl cellulose film, cloth (i.e., woven or nonwoven sheeting formed of synthetic or natural materials), metallic foil, and ceramic sheeting.
• Examples of materials that can be included in the flexible support include polyolef ⁇ ns such as polyethylene, polypropylene (including isotactic polypropylene), polystyrene, polyester, polyvinyl alcohol, poly(ethylene terephthalate), poly(butylene terephthalate), poly(caprolactam), poly(vinylidene fluoride), polylactides and the like.
• polyolef ⁇ ns such as polyethylene, polypropylene (including isotactic polypropylene), polystyrene, polyester, polyvinyl alcohol, poly(ethylene terephthalate), poly(butylene terephthalate), poly(caprolactam), poly(vinylidene fluoride), polylactides and the like.
• backing materials useful in the invention include kraft paper (available from Monadnock Paper, Inc.); cellophane (available from Flexel Corp.); spun- bond poly(ethylene) and poly(propylene), such as TyvekTM and TyparTM (available from DuPont, Inc.); and porous films obtained from poly(ethylene) and poly(propylene), such as TeslinTM (available from PPG Industries, Inc.), and CellguardTM (available from Hoechst-Celanese).
• the flexible support may also comprise a release-coated substrate.
• substrates are typically employed when an adhesive transfer tape is provided.
• release- coated substrates are well known in the art. They include, by way of example, silicone - coated kraft paper and the like.
• Tapes of the invention may also incorporate a low adhesion backsize (LAB). Typically this LAB is applied to the tape backing surface that is opposite that bearing the pressure sensitive adhesive. LABs are known in the art.
• Peel Adhesion Test The test method used was similar to test method ASTM D 3330-78 except that a glass substrate was used in place of stainless steel. Tape samples were prepared by coating adhesives onto polyester film of 50.8 micrometers (2 mil) thickness and drying to give an adhesive dry coating thickness of about 38 micrometers (1.5 mils). Two 1.3 centimeter (0.5 inch) strips of these tapes were adhered to a glass plate by rolling a 2 kilogram (4.5 pounds) roller onto the tape. The two tape samples were averaged. Platen speed was 229 centimeters per minute (90 inches per minute). Peel force was measured in ounces per 0.5 inches and converted to Newtons per decimeter. Shear Strength Test
• test method ASTM D-3654-78, PSTC-7 Tape samples were prepared by coating adhesives onto polyester film of 50.8 micrometers (2 mil) thickness and drying to give an adhesive dry coating thickness of about 38 micrometers (1.5 mils). Strips of these tapes 1.3 centimeter (0.5 inch) wide were adhered to stainless steel plates and cut down to leave 1.3 centimeter by 1.3 centimeter (0.5 inch by 0.5 inch) square on the steel plates. A weight of 2 kilograms (4.5 pounds) was rolled over the adhered portion. A weight of 1,000 grams was attached to each sample which was suspended until the sample failed. The time of failure as well as the mode of failure was noted. Samples were run in triplicate and averaged. The tests were run at 23 C and 50% relative humidity.
• Synthesis Example 1 Preparation of PSA-3 To a 1 -liter stainless steel Waring blender container was added 360 grams of deionized water, 8 grams of RHODACAL DS-10, 1.0 gram of lithium hydroxide, 1.2 grams of triethanolamine, 344 grams of 2-Octyl acrylate (2-OA), 15 grams of acrylic acid (AA), and 15 grams of methyl methacrylate (MMA). The content was homogenized with the blender at low speed setting for 2 minutes then poured into a 2- liter resin flask equipped with a thermometer, mechanical agitation with Teflon impeller, condenser and nitrogen inlet tube. 0.8 grams of potassium persulfate was then added.
• PFAZ 322 was added to PSA-I adhesive emulsion at a weight ratio of 0.05%. Upon mixing the crosslinker into the solution, the adhesive gelled up and could not be coated or tested.
• PSA-I was blended with various concentrations of NALCO 2326.
• Adhesive solutions were also prepared with and without PFAZ 322 as shown in Table 1. Samples without PFAZ 322 are Comparative Examples C3A-C3C. A comparative sample was also prepared with no NALCO 2326 particles, Comparative Example C4. Peel Adhesion and Shear Strength were measured for tapes prepared from these adhesive emulsion solutions as described in the test methods above. Weight percents listed are calculated with respect to the dried polymer.
• PSA-3 was blended with various concentrations of NALCO 2326.
• Adhesive solutions were also prepared with and without PFAZ 322 as shown in Table 3. Samples without PFAZ 322 are Comparative Examples C9A-C9B. A comparative sample was also prepared with no NALCO 2326, Comparative Example C8. Peel Adhesion and Shear Strength were measured for tapes prepared from these adhesive emulsion solutions as described in the test methods above. Weight percents listed are calculated with respect to the dried polymer.

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• Chemical & Material Sciences (AREA)
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• Crystallography & Structural Chemistry (AREA)
• Nanotechnology (AREA)
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• Adhesives Or Adhesive Processes (AREA)
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