WO2017096343A1

WO2017096343A1 - Primer for pressure sensitive adhesive

Info

Publication number: WO2017096343A1
Application number: PCT/US2016/064892
Authority: WO
Inventors: Pat WARREN
Original assignee: Lord Corporation
Priority date: 2015-12-04
Filing date: 2016-12-05
Publication date: 2017-06-08

Abstract

A primer composition for use with pressure sensitive adhesives which improves the environmental resistance of the bond formed between the pressure sensitive adhesive and the coated substrate. The primer can be used on many different substrates to improve performance. The primer is free of halogenated materials. The primer comprises: A) a polyester polyurethane polymer, B) an epoxy silane, C) an optional polymeric isocyanate crosslinker, and D) solvents capable of dissolving/carrying the polyester polyurethane polymer and optional polymeric isocyanate crosslinker. Preferably, the primer is free of halogen-containing materials.

Description

PRIMER FOR PRESSURE SENSITIVE ADHESIVE

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] The present application claims priority under 35 U. S.C. § 119(e) from U.S. Provisional Patent Application Serial No. 62/263,077 filed December 4, 2015, entitled "Primer for Pressure Sensitive Adhesive", the disclosure of which is incorporated herein by reference.

FIELD OF THE INVENTION

[0002] The invention relates to a primer composition particularly suitable for use with a pressure sensitive adhesive (PSA) to enhance the adhesion of the PSA to a substrate, such as glass, stainless steel, aluminum, and zirconium.

BACKGROUND OF THE INVENTION

[0003] A pressure sensitive adhesive is an adhesive that forms a bond when pressure is applied to marry the adhesive with a substrate. Typically, no solvent, water, or heat is needed to activate the adhesive. Typical adhesives are acrylic, natural rubber, or synthetic rubber. Special adhesives with a smaller application base are silicone, butyl, or EVA (ethylene - vinyl - acetate). A pressure sensitive adhesive maintains a fine balance between adhesion (holding power of the adhesive on extemal substrates) and cohesion (holding power of the combined internal components of the adhesive).

[0004] While many PSAs form adequate bonds without the need for primers or surface treatments, some applications present a need for a primer that can be applied to different substrates (glass, stainless steel, aluminum, zirconium, etc .. ) to improve the adhesion and environmental resistance of the bond formed between a pressure sensitive adhesive and the substrate. The bond must survive exposure to a variety of environmental conditions, as well as chemical and radiation exposure. SUMMARY OF THE INVENTION

[0005] In a first embodiment of the present invention, a primer composition is provided comprising: A) a polyester polyurethane, B) an epoxy silane, and C) an optional isocyanate crosslinking compound. In one embodiment of the present invention, the polyester polyurethane is prepared by reacting an isocyanate-functional urethane polyester prepolymer with a low molecular weight chain extending diol. In another embodiment of the present invention, the urethane polyester prepolymer is prepared by reacting at least one linear polyester having 2 active hydrogen atoms with a diisocyanate; wherein the linear polyester is selected from the group consisting of 1,6-hexane diol phthalate polyester diol, 1 ,6-hexane diol adipate diol, and 1,6-hexane diol ethylene glycol adipate diol; and wherein the diisocyanate is selected from the group consisting of toluene diisocyanate and diphenylmethane-4,4'-diisocyanate. In a further embodiment of the present invention, the chain extending diol is selected from the group consisting of 1,4-butane diol, ethylene glycol, diethylene glycol, 1,3-propane diol and 1,6-hexane diol.

[0006] In an additional embodiment of the present invention, the epoxy silane comprises an epoxy group-containing organoalkoxy silane, and in a preferred embodiment the epoxy silane comprises glycidoxypropyl trimethoxy silane. In another preferred embodiment of the present invention, the primer composition is free of halogen-containing polymers, and alternately the primer composition is free of any halogen-containing materials.

[0007] In one embodiment of the present invention, the isocyanate crosslinking compound comprises a polymeric isocyanate, and in a preferred embodiment the isocyanate crosslinking compound comprises polymeric diphenylmethane-4,4'-diisocyanate.

[0008] In another embodiment of the present invention, the primer composition further comprises a solvent, preferably at least one of methyl ethyl ketone and xylene. In one embodiment of the present invention, the primer composition is applied to a substrate, preferably at least one of glass, stainless steel, aluminum, and zirconium. In a further embodiment of the present invention, the primer composition has a pressure sensitive adhesive applied thereon, and most preferably an acrylic-based pressure sensitive adhesive.

[0009] In an additional embodiment of the present invention, the polyester polyurethane is present in an amount ranging from about 10 to 95, preferably from about 30 to 75, and most preferably about 35 percent by weight based on the total weight of components A-C. And in another embodiment of the present invention, the epoxy silane is present in an amount ranging from about 0.1 to 5 percent, preferably from about 0.5 to 5 percent, and most preferably about 2 percent by weight based on the total weight of components A-C. In a further embodiment of the present invention the isocyanate cross-linking compound is present in an amount from about 1 to 90, preferably from about 25 to 70, and most preferably about 60 weight percent based on the total weigh of components A-C. In another embodiment of the present invention, the primer composition consists essentially of A) a polyester polyurethane, B) an epoxy silane C) an isocyanate crosslinking compound, and D) a solvent.

[0010] In one embodiment of the present invention, a method for enhancing adhesion between a substrate and a pressure sensitive adhesive is provided comprising the steps of: a) providing a substrate, b) coating the substrate with a primer composition comprising A) a polyester polyurethane, B) an epoxy/silane adduct, C) an optional isocyanate cross-linking compound, and D) a solvent, c) allowing the primer composition to dry, and d) applying a pressure sensitive adhesive to the primer-coated substrate.

[0011] Thus, there has been outlined, rather broadly, the more important features of the invention in order that the detailed description that follows may be better understood and in order that the present contribution to the art may be better appreciated. There are, obviously, additional features of the invention that will be described hereinafter and which will form the subject matter of the claims appended hereto. In this respect, before explaining several embodiments of the invention in detail, it is to be understood that the invention is not limited in its application to the details and construction and to the arrangement of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced and carried out in various ways.

[0012] It is also to be understood that the phraseology and terminology herein are for the purposes of description and should not be regarded as limiting in any respect. Those skilled in the art will appreciate the concepts upon which this disclosure is based and that it may readily be utilized as the basis for designating other structures, methods and systems for carrying out the several purposes of this development. It is important that the claims be regarded as including such equivalent constructions insofar as they do not depart from the spirit and scope of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0013] The present invention relates to a primer which improves the environmental resistance of the bond formed between the pressure sensitive adhesive and the coated substrate. The primer can be used on many different substrates to improve performance in conjunction with pressure sensitive adhesives. The primer of the present invention is also free of halogenated materials, particularly halogenated polymers, which are commonly used in primer compositions.

[0014] In a first embodiment of the present invention, the primer comprises: A) a polyester polyurethane polymer, B) an epoxy silane, C) an optional polymeric isocyanate crosslinker, and D) solvents capable of dissolving/carrying the polyester polyurethane polymer and optional polymeric isocyanate crosslinker.

[0015] In another embodiment of the present invention, a primer for PSAs is provided comprising A) a polyester polyurethane polymer, B) an epoxy silane, C) an optional polymeric isocyanate crosslinker, and D) optionally solvents capable of dissolving/carrying the polyester polyurethane polymer and optional polymeric isocyanate crosslinker.

A) Polyester Polyurethane:

[0016] In a first embodiment of the present invention, the primer comprises a polyester polyurethane polymer, preferably a linear polyester polyurethane prepolymer. The linear polyester polyurethanes of the invention are typically prepared by reacting isocyanate- functional urethane polyester prepolymers with low molecular weight chain extending diols employing conventional techniques well known in the art. An extensive description of some of the useful techniques for preparing polyester urethane prepolymers can be found in Saunders and Frisch: "Polyurethanes, Chemistry and Technology," Part II, Interscience, (New York 1964), especially at pages 8 to 49, and in the references cited therein. Other preparative techniques which are known in the art can also be employed.

[0017] More specifically, the linear polyester polyurethanes which can be employed in the adhesive compositions of the present invention typically are prepared by reacting at least one linear polyester having two active hydrogen atoms with a diisocyanate in order to form an isocyanate-functional urethane polyester prepolymer. The urethane polyester prepolymer is then reacted with a low molecular weight chain extending diol in order to prepare the linear polyester polyurethane useful in the present invention. [0018] The hydrogen atom-containing linear polyesters used to produce the polyurethanes of the invention are generally hydroxy-terminated polyesters having an average molecular weight in the range from about 500 to 4000.

[0019] The linear polyesters are typically formed from bifunctional monomers having either aliphatic or aromatic segments therein. For example, the linear polyesters may be formed by reacting dihydric alcohols with polycarboxylic acids in hydroxylxarboxyl ratios ranging from 2: 1 to 15: 14. Exemplary linear polyesters useful for forming the polyurethanes of the invention include condensation products of succinic acid, adipic acid, suberic acid, azelaic acid, sebacic acid, phthalic acid, isophthalic acid or terephthalic acid acid with difunctional hydroxy compounds such as ethylene glycol, di ethylene glycol, 1,4-butane diol, 1,3-propane diol, 1,6-hexane diol, poly(ethylene oxide) diol, poly(ethylene oxide/propylene oxide) diol and poly(tetramethylene oxide) diol in various combinations well known in the art. Presently preferred active hydrogen-containing linear polyesters include 1,6-hexane diol phthalate polyester polyols, prepared according to methods known in the art by reacting a lactone such as caprolactone with a difunctional hydroxy compound as defined immediately above, may also be utilized in the present invention.

[0020] Any of the diisocyanates having two reactive isocyanate groups can be reacted with the linear polyester prepolymers suitable for use in the practice of the invention. Such diisocyanates include, without limitation, diisocyanates such as 1,6-hexamethylene diisocyanate; 1,8-octomethylene diisocyanate; 1,12-dodecamethylene diisocyanate; 2,2,4- trimethylhexamethylene diisocyanate and similar isocyanates; 3,3'diisocyanatodipropyl ether; 3-isocyanatomethyl-3,5,5'4rimethy1cyclohexyl isocyanate; cyclopentalene-1 ,3-diisocyanate; cycl.ohexyl.ene- 1 ,4-diisocyanate; methyl 2,6-dii socyanatocaprolate; bis-(2-isocyanatoethyl)- fumarate; 4-methyl-l,3-diisocyanatoeyclohexane: trans-vmylene diisocyanate and similar unsaturated polyisocyanates; 4,4'-methy1ene-bis-(cyclohexylisocya.nate) and related polyisocyanates; methane diisocyanates; bis-(2-isocyanatoethyl) carbonate and similar carbonate polyisocyanates: N,N'N"-tris-(6-isocyanatohexamethyiene) biuret and related polyisocyanates as well as other known polyisocyanates derived from aliphatic polyamines; toluene diisocyanates; xylene diisocyanates; dianisidine diisocyanate; 4,4'-diphenylmethane diisocyanate; 1 -ethoxy-2,4-diisocyanatobenzene; 1 -chloro-2,4-diisocyanatobenzene; tris(4- isocyanatophenyl) methane; naphthalene diisocyanates; 4,4'-biphenyl diisocyanate; phenylene diisocyanates; 3,3'-dimethyl-4,4'-biphenyl diisocyanate; p-isocyanatobenzoyl isocyanate and tetrachloro-l,3-phenylene diisocyanate and mixtures thereof. Preferred diisocyanates include toluene diisocyanate and diphenylmethane-4,4'-diisocyanate.

[0021] The urethane polyester polyurethane employed in the practice of this invention has a molecular weight of at least 50,000, but preferably has a molecular weight greater than 100,000. At the present time, the preferred linear polyester with toluene diisocyanate and chain extending the prepolymer thus formed with 1 ,4-butane dioi. The urethane preferably has a hydroxyl content of between about 0.08 and 0.12 percent and a solution viscosi ty (15% by weight in methyl ethyl ketone) of between about 400 and 800 centipois. The linear polyester polyurethane is typically utilized in an amount ranging from about 10 to 95, preferably from about 30 to 75, and most preferably about 35 percent by weight based on the total weight of components A-C.

B) Epoxy Silane

[0022] In a preferred embodiment of the present invention, the epoxy silane comprises an epoxy group-containing organoalkoxy silane. Particularly preferred examples of such epoxy group-containing organoalkoxy silanes include 2-glycidoxyethyl trimethoxy silane, 2- glycidoxyethyl triethoxy silane, 3-glycidoxypropyl trimethoxy silane, 3-glycidoxypropyl triethoxy silane, 3-glycidoxypropyl methyl dimethoxy silane, 3-glycidoxypropyl methyl diethoxy silane, 2-(3,4-epoxycyclohexyl)ethyl trimethoxy silane and 2-(3,4- epoxycyclohexyl)ethyl triethoxy silane.

[0023] In another embodiment of the present inveninto, the epoxy silane comprises an epoxy/silane adduct. The epoxy silane adduct comprises the reaction product of an epoxy compound and an alkoxy silane compound. The epoxy compound useful for preparing the epoxy/silane adducts of the present invention can be any compound that contains an epoxy group and has a viscosity of about 200 centipoise or higher at 25°C. Such materials, broadly called epoxides, include monomeric epoxy compounds and epoxides of the polymeric type and can be aliphatic, cycloaliphatic, aromatic or heterocyclic These materials generally have, on the average, at least 1.5 polymerizable epoxy groups per molecule (preferably two or more epoxy groups per molecule). The polymeric epoxides include linear polymers having terminal epoxy groups (e.g. , a diglycidyl ether of a polyoxyalkylene glycol), polymers having skeletal oxirane units (e.g. , polybutadiene poly epoxide), and polymers having pendent epoxy groups (e.g., a glycidyl methacrylate polymer or copolymer). The epoxides may be pure compounds but are generally mixtures containing one, two, or more epoxy groups per molecule. The "average" number of epoxy groups per molecule is determined by dividing the total number of epoxy groups in the epoxy -containing material by the total number of epoxy molecules present,

[0024] The epoxy-contaimng materials may vary from low molecular weight monomelic materials to high molecular weight polymers and may vary greatly in the nature of their backbone and substituent groups. For example, the backbone may be of any type and substituent groups thereon can be any group free of an active hydrogen atom which is reactive with an oxirane ring at room temperature. Illustrative of permissible substituent groups include halogens, ester groups, ethers, sulfonate groups, siloxane groups, nitro groups, phosphate groups, etc. The molecular weight of the epoxy -containing materials may vary from about 50 to 100,000 or more. Mixtures of various epoxy -containing materials can also be used in the compositions of this invention.

[0025] The epoxy compounds of the present invention may be cycloaliphatic epoxides. Examples of cycloaliphatic epoxides include diepoxides of cycloaliphatic esters of dicarboxylic acids such as bis(3,4-epoxycyciohexyimethyl)oxalate, bis(3,4- epoxycyclohexylmethyl)adipate, bis{3,4-epoxy-6~methylcyclohexylmethyl)adipate, bis(3,4- epoxyeyclohexylmethyl)pimelate, and the like. Other suitable diepoxides of cycloaliphatic esters of dicarboxylic acids are described in, for example, U. S. Pat. No. 2,750,395, which is incorporated herein by reference.

[0026] Other cycloaliphatic epoxides include 3,4-epoxy eyclohexylmethyl-3,4- epoxycyclohexane carboxylates such as 3,4-epoxy cyclohexylmethyl-3,4-epoxycyclohexane carboxyl ate; 3,4-epoxy- 1 -methyl cy cl oh exy 1 methyl-3 ,4-epoxy- 1 -methyl cyclohexane carboxylate; 6-methyl~3,4-epoxycyclohexylmethyl-6-methyi-3,4~epoxycyclohexane carboxylate; 3,4~epoxy-2~methylcyclohexylmethyl- 3,4~epoxy-2~methylcyclohexane carboxylate, 3,4-epoxy-3-methylcyclohexylmethyl-3,4-epoxy-3-methylcyclohexane carboxylate; 3,4-epoxy-5-methylcyclohexylmethyl-3,4-epoxy-5-methylcyclohexane carboxylate and the like. Other suitable 3,4-epoxy cyclohexylmethyl-3,4-epoxycyclohexane carboxylates are described in, for example, U.S. Pat. No. 2,890,194, which is incorporated herein by reference.

Further epoxy-comaining materials which are particularly useful in the practice of this invention include giycidyl ether monomers. Examples are glycidyl ethers of polyhydric phenols obtained by reacting a polyhydric phenol [e.g., 2,2-bis(4-hydroxyphenyl)-propane, commonly known as Bisphenol A] with an excess of chlorohydnn such as epiclilorohydrm. Further examples of epoxides of this type which can be used in the practice of this invention are described in U. S. Pat. No. 3,01 8,262, and in "Handbook of Epoxy Resins" by Lee and Neville, McGraw-Hill Book Co., New York, 1967, both the disclosures of which are incorporated herein by reference.

[0028] There are a host of commercially available epoxy -containing materials, commonly known as epoxy resins, which can be used as the epoxy compound in this invention. In particular, epoxy compounds which are readily available include octadecylene oxide, glycidylmethacrylate, diglycidyl ether of Bisphenol A (e.g., those available under the trade designations EPON 828, EPON 1004 and EPON 1010 from Shell Chemical Co., DER-331 , DER-332, and DER-334, from Dow Chemical Co.), vinylcyclohexene dioxide (e.g., ERL- 4206 from Union Carbide Corp.), 3,4~epoxycyclohexylmethyi-3,4-epoxycyciohexane carboxylate (e.g., ERL-4221 from Union Carbide Corp.), 3,4-epoxy-6- methylcyclohexylmethyl- 3,4-epoxy-6-methylcyclohexene carboxylate (e.g. , ERL-4201 from Union Carbide Corp.), bis(3,4-epoxy-6-methylcyclohexylmethyl) adipate (e.g. ERL-4289 from Union Carbide Corp.), bis(2,3-epoxycyciopentyl) ether (e.g., ERL-0400 from Union Carbide Corp.), aliphatic epoxy modified with polypropylene glycol (e.g., ERL-4050 and ERL-4052 from Union Carbide Corp.), dipentene dioxide (e.g. , ERL-4269 from Union Carbide Corp.), epoxidized poiybutadiene (e.g., OXIRON 2001 from FMC Corp.), silicone resin containing epoxy functionality, flame retardant epoxy resins (e.g., DER-580, a brorninated bisphenol-type epoxy resin available from Dow Chemical Co.), 1 ,4-butanediol diglycidyl ether of phenolformaldehyde novolak (e.g., DEN-431 and DEN-438 from Dow Chemical Co.), and resorcinol diglycidyl ether (e.g., ΚΟΡΟΧITΈ from Koppers Company, Inc.).

[0029]

[0030] Still other epoxy-contaraing materials are copolymers of acrylic acid esters of glycidol such as glycidylacrylate and glycidylmethacrylate with one or more copolymerizable vinyl compounds. Examples of such copolymers are 1 : 1 styrene-glycidyimethacrylate, 1 : 1 methylmethacrylateglycidylacrylate and a 62.5:24: 13.5 methylmethacry late-ethyl acrylateglycidylmethacrylate .

[0031] The alkoxy silane compounds useful for preparing the epoxy/silane adducts of the present invention correspond to the general formula:

wherein R₁, R₂, and R₃ are the same or different monovalent aliphatic hydrocarbon residues of sufficient molecular weight that the silane is stable during preparation of the primer composition and yet do not prejudice hydrolysis of the silane under conditions of use of the primer composition, and R₄ is a straight chain, branched, cyclic or aromatic hydrocarbon radical being substituted with a group capable of a chemical reaction by condensation (for example, with isocyanate groups), such as an epoxy, mercapto, amino, or hydroxyl group, and having from about 1 to 10 carbon atoms. Preferably R₁, R₂, and R₃ each have 1 to 5 carbon atoms and more preferably each is a methyl or ethyl group. Preferably, R₄ is a straight chain hydrocarbon radical substituted with a group capable of a chemical reaction by condensation (for example, with isocyanate groups), such as an epoxy, mercapto, amino, or hydroxyl group. The alkoxy silane compound may also be a combination of two or more alkoxy silane compounds as long as at least one of the alkoxy silane compounds is as defined above. The other alkoxy silane compounds in such a combination can correspond to the structure defined above with the proviso that R4 can also be an unsubsti luted straight chain, branched, cyclic or aromatic hydrocarbon radical and is preferably an unsubstituted aromatic hydrocarbon radical such as phenyl. Examples of suitable alkoxy silane compounds include gamma-glycidoxypropyltrimethoxy silane, gamma-arainopropyltriethoxy silane, N-beta (aminoethyl) gamma-aminopropyi-trimethoxy silane, phenyitriethoxy silane, and

combinations thereof, with a combination of gamma-aminopropyltriethoxy silane and phenyitriethoxy silane being presently preferred.

[0032] The epoxy/silane adducts of the invention are typically prepared by combining the epoxy compound and the silane compound in an epoxy:silane ratio ranging from about 1 : 1 to 1 : 10, preferably from about 1 :3 to 1 :7, in an appropriate solvent and heating the resulting mixture to a temperature ranging from about 85° C. to 99° C, preferably from about 90° C. to 95° C, for a period of time ranging from about 2 to 12 hours, preferably from about 4 to 7 hours. The solvent can essentially be any solvent capable of dissolving the epoxy compound, the alkoxy silane compound and the resulting epoxy/silane adduct. Examples of typical solvents include toluene and xylene, with toluene being preferred. [0033] A particularly preferred epoxy/silane adduct is prepared by reacting a Bisphenol A-type epoxy resin, gamma-aminopropyUriethoxy silane and phenyl triethoxy siiane in an approximate 1 : 1:4 weight ratio in the presence of toluene at approximately 90° C. to 95° C. for approximately 4 to 7 hours.

[0034] The epoxy/silane adduct of the present in vention is typically utilized in an amount ranging from about 0.1 to 5 percent, preferably from about 0.5 to 5 percent, and most preferably about 2 percent by weight based on the total weight of components A-C.

C) Isocyanate crosslinker

[0035] In one embodiment of the present invention, the isocyanate crosslinker comprises a diisocyanate compound such as 2,4-toluene diisocyanate, diphenylrnethane-4,4'- diisocyanate, p-phenylene diisocyanate, m-phenylene diisocyanate, 1 ,4-cyciohexyl diisocyanate, tetramethylxylyl diisocyanate and dimethyidiphenyl diisocyanate, with diphenylmethane-4,4' -diisocyanate being the preferred diisocyanate compound. In a preferred embodiment of the present the isocyanate crosslinker comprises a polymeric isocyanate, such as polymeric isocyanate. The polymeric isocyanates employed in the present invention comprise those that are typically employed in adhesive compositions, including typical aromatic, aliphatic and cycioaliphatic isocyanate polymers. Representative aromatic isocyanate polymers include 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 4,4'^'- methylene bisiphenyi isocyanate), 1,3-phenylene diisocyanate, triphenylmethane triisocyanate, 2,4,4'-triisocyanatodiphenyl ether, 2,4-bis(4-isocyanatobenzyl) phenyl isocyanate and related polyaryl polyiscocyanates, 1,5-naphthalene diisocyanate and mixtures thereof. Representative aliphatic isocyanate polymers include hexamethylene diisocyanate, xylylene diisocyanate, 1,12-dodecane diisocyanate and lysine ethyl ester diisocyanate. Representative cycioaliphatic isocyanate polymers include 4,4'-methylenebis (cyclohexyl isocyanate), 1,4-cyclonexylene diisocyanate, 1 -methy 1-2,4-cyclohexy lene diisocyanate and 2,4-bis(4-isocyanatocyclohexylmethyl) cyclohexyl isocyanate. The cross- linker is typically utilized in an amount from about 1 to 90, preferably from about 25 to 70, and most preferably about 60 weight percent based on the total weigh of components A-C.

D) Solvent

[0036] In an embodiment of the present invention, the primer is provided in a hydrocarbon-solvent based system. Non-limiting examples of suitable solvents are solvents which are inert towards isocyanate groups, such as hexane, toluene, xylene, chlorobenzene, ethyl acetate, butyl acetate, di ethylene glycol dimethyl ether, dipropylene glycol dimethyl ether, ethylene glycol monomethyl or monoethyl ether acetate, diethylene glycol-ethyl and butyl ether acetate, propylene glycol monomethyl ether acetate, l-methoxyprop-2-yl acetate, 3-methoxy-n-butyl acetate, propylene glycol diacetate, acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, lactones such as β-propiolactone, γ-butyrolactone, ε- caprolactone and ε-methyl caprolactone, for example, but also solvents such as N- methylpyrrolidone and N-methylcaprolactam, 1 ,2-propylene carbonate, methylene chloride, dimethyl sulphoxide, tri ethyl phosphate or any mixtures of such solvents. In a preferred embodiment of the present invention, the primer formulation comprises a mixture of xylene and methyl ethyl ketone in amounts sufficient to cany the reactive constituents A-C.

Optional Additives

[0037] The primer compositions of the present invention can optionally contain other well-known additives including plasticizers, fillers, pigments, surfactants, dispersing agents, wetting agents, rheology modifiers, reinforcing agents and the like.

[0038] Although the present invention has been described with reference to particular embodiments, it should be recognized that these embodiments are merely illustrative of the principles of the present invention. Those of ordinary skill in the art will appreciate that the compositions, apparatus and methods of the present invention may be constructed and implemented in other ways and embodiments. Accordingly, the description herein should not be read as limiting the present invention, as other embodiments also fall within the scope of the present invention as defined by the appended claims.

EXAMPLES

[0039] To demonstrate the effectiveness of the primer, the formulation above was prepared and brushed on substrates, then dried at room temperature for 1/2 hour, then baked for 10 minutes at 66 C. A Mylar-backed pressure sensitive adhesive was applied to the primed surfaces and then rolled 5 times with the ASTM D3330 roller. The taped parts where allowed to sit overnight, then primary adhesion was tested.

[0040] For Primary Adhesion testing, parts were pulled on the Instron using a 180 degree peel angle and a test speed of 12 in/min. Peak and average peel values (in N/mm) were recorded, along with failure mode. Five trials of with each substrate were tested and the average values are presented below:

Claims

CLAIMS What is claimed is:

1. A primer composition comprising: A) a polyester polyurethane, B) an epoxy silane, and C) an optional isocyanate crosslinking compound.

2. The primer according to claim 1, wherein the polyester polyurethane is prepared by reacting an isocyanate-functional urethane polyester prepolymer with a low molecular weight chain extending diol.

3. The primer composition according to claim 2, wherein the urethane polyester prepolymer is prepared by reacting at least one linear polyester having 2 active hydrogen atoms with a diisocyanate; wherein the linear polyester is selected from the group consisting of 1,6-hexane diol phthalate polyester diol, 1,6-hexane diol adipate diol, and 1,6-hexane diol ethylene glycol adipate diol; and wherein the diisocyanate is selected from the group consisting of toluene diisocyanate and diphenylmethane-4,4'-diisocyanate.

4. The primer composition according to claim 2, wherein the chain extending diol is selected from the group consisting of 1,4-butane diol, ethylene glycol, di ethylene glycol, 1,3- propane diol and 1,6-hexane diol.

5. The primer composition according to claim 1, wherein the epoxy silane comprises an epoxy group-containing organoalkoxy silane.

6. The primer composition according to claim 5, wherein the epoxy group- containing organoalkoxy silane comprises glycidoxypropyl trimethoxy silane.

7. The primer composition according to claim 1, wherein the primer composition is free of halogen-containing polymers.

8. The primer composition according to claim 1, wherein the primer composition is free of halogen-containing materials.

9. The primer composition according to claim 1 wherein the isocyanate crosslinking compound comprises a polymeric isocyanate.

10. The primer composition according to claim 9, wherein the crosslinking compound comprises polymeric diphenylmethane-4,4'-diisocyanate.

1 1. The primer composition according to claim 1, further comprising a solvent.

12. The primer composition according to claim 1 1, wherein the solvent comprises at least one of methyl ethyl ketone and xylene.

13. The primer composition according to claim 1, applied to a substrate.

14. The primer composition according to claim 13, wherein the substrate comprises at least one of glass, stainless steel, aluminum, and zirconium.

15. An assembly comprising the primer composition of claim 13, having a pressure sensitive adhesive applied thereon.

16. The assembly of claim 15, wherein the pressure sensitive adhesive is an acrylic- based pressure sensitive adhesive.

17. The primer composition of claim 1, wherein the polyester polyurethane is present in an amount ranging from about 10 to 95, preferably from about 30 to 75, and most preferably about 35 percent by weight based on the total weight of components A-C.

18. The primer composition of claim 1, wherein the epoxy silane is present in an amount ranging from about 0.1 to 5 percent, preferably from about 0.5 to 5 percent, and most preferably about 2 percent by weight based on the total weight of components A-C.

19. The primer composition of claim 1, wherein the isocyanate cross-linking compound is present in an amount from about 1 to 90, preferably from about 25 to 70, and most preferably about 60 weight percent based on the total weigh of components A-C.

20. The primer of claim 1, consisting essentially of A) a polyester polyurethane, B) an epoxy silane C) an isocyanate crosslinking compound, and D) a solvent.

21. A method for enhancing adhesion between a substrate and a pressure sensitive adhesive comprising: a) providing a substrate;

b) coating the substrate with a primer composition comprising A) a

polyester polyurethane, B) an epoxy/silane adduct, C) an optional isocyanate cross- linking compound, and D) a solvent;

c) allowing the primer composition to dry; and,

d) applying a pressure sensitive adhesive to the primer-coated substrate.