Polyurethane adhesives with improved adhesion to metals

Abstract

Polyurethane adhesive compositions contain phosphate groups and an epoxysilane compound, each in defined amounts. The phosphate groups are present in a polyol component of the adhesive composition or in an isocyanate-terminated prepolymer made from a polyol that contains phosphate groups. The adhesive compositions can be formulated as one-part adhesives that are moisture-cured, or as two-part adhesives comprising a curative and a polyisocyanate component that are combined and cured to produce the adhesive. The adhesive bonds tenaciously to metal substrates, reducing or even eliminating the need to pretreatment the substrates.

Description

Atty Ref: 157928.221086 (86222)POLYURETHANE ADHESIVES WITH IMPROVED ADHESION TO METALSCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to and all advantages of U.S. Provisional Patent Application No. 63 / 699,209 filed on 26 September 2024, the content of which is incorporated herein by reference.FIELD OF THE DISCLOSURE

[0002] This disclosure generally relates to polyurethane adhesives and, more specifically, one or two part polyurethane adhesives with excellent adhesion to metals and other substrates.BACKGROUND

[0003] Polyurethane adhesives are widely used in manufacturing settings, often to glue metal parts together or to adhere a metal to another material. Polyurethanes are typically strong adhesives, but nonetheless their adhesion to metals is sometimes inadequate. It is often necessary to precondition the metal to obtain satisfactory adhesion. Pretreatment steps may include, for example, the application of primers, etching, abrading or otherwise altering the surface of the metal. These steps are time-consuming and add costs. As such it would be desired to eliminate them.

[0004] It has been attempted to improved adhesion to certain substrates through the use of polyols that contain phosphate groups. See, for example, US Published Patent Application No. 2017 / 0226391 A. Somewhat mixed results are reported when the adhesive is applied to various plastic films intended for use in food packaging.BRIEF SUMMARY

[0005] One aspect of this disclosure is a one-part urethane adhesive composition comprising a mixture of: i) one or more polyisocyanates comprising an isocyanate-terminated prepolymer, the prepolymer containing residues, after reaction with an isocyanate group, of one or more polyols having hydroxyl equivalent weights of at least 800 g / equivalent, wherein said residues comprise residues of at least one polyol having phosphate ester groups (“phosphate-modified prepolymer”), and ii) an epoxysilane compound having a formula molecular weight of up to 500 g / mol, the at least one epoxysilane compound constituting 0.25 to 2.5 weight percent of the combined weights of i) and ii), wherein phosphorus contained in said phosphate ester groups constitutes 0.05 to 0.2 weight percent of the combined weight of i) and ii).Atty Ref: 157928.221086 (86222)

[0006] Such a one-part adhesive system is optionally combined with one or more additives of various types such as are described below and is typically moisture-cured by exposure to atmospheric moisture, liquid water or both atmospheric moisture and liquid water.

[0007] The disclosure in another aspect is a two-part urethane adhesive composition comprisingA) a curative containing one or more curing agents having hydroxyl and / or primary or secondary amino groups andB) a separately packaged polyisocyanate component comprising an organic polyisocyanate, wherein a) the one or more curing agents comprise a polyol having a hydroxyl equivalent weight of at least 800 g / equivalent and contains phosphate ester groups (“phosphate-modified polyol”), and / or b) the organic polyisocyanate comprises an isocyanate-terminated prepolymer, the prepolymer containing residues, after reaction with an isocyanate group, of one or more polyols having hydroxyl equivalent weights of at least 800 g / equivalent, wherein said residues comprise residues of at least one polyol having phosphate ester groups (“phosphate-modified prepolymer”); wherein the curative, the polyisocyanate component or both further comprise(s) an epoxysilane compound having a formula molecular weight of up to 500 g / mol, the epoxysilane compound constituting from 0.25 to 2.5 weight percent of the combined weights of the one or more curing agents, the organic polyisocyanate and the epoxysilane compound, and wherein phosphorus contained in said phosphate ester groups constitutes 0.05 to 0.2 weight percent of the combined weight of the one or more curing agents, the organic polyisocyanate and the epoxysilane compound.DETAILED DESCRIPTION

[0008] Disclosed is a one-part urethane adhesive composition comprising a mixture of: i) one or more polyisocyanates comprising an isocyanate-terminated prepolymer, the prepolymer containing residues, after reaction with an isocyanate group, of one or more polyols having hydroxyl equivalent weights of at least 800 g / equivalent, wherein said residues comprise residues of at least one polyol having phosphate ester groups (“phosphate-modified prepolymer”), and ii) an epoxysilane compound having a formula molecular weight of up to 500 g / mol, the at least one epoxysilane compound constituting from 0.25 to 2.5 weight percent of the combined weights of i) and ii), wherein phosphorus contained in said phosphate ester groups constitutes from 0.05 to 0.2 weight percent of the combined weight of i) and ii).

[0009] Such a one-part adhesive system is optionally combined with one or more additives of various types such as are described below and is typically moisture-cured by exposure to atmospheric moisture, liquid water or both atmospheric moisture and liquid water.Atty Ref: 157928.221086 (86222)

[0010] The disclosure in another aspect is a two-part urethane adhesive composition comprisingA) a curative containing one or more curing agents having hydroxyl and / or primary or secondary amino groups andB) a separately packaged polyisocyanate component comprising an organic polyisocyanate, wherein a) the one or more curing agents comprise a polyol having a hydroxyl equivalent weight of at least 800 g / equivalent and contains phosphate ester groups (“phosphate-modified polyol”), and / or b) the organic polyisocyanate comprises an isocyanate-terminated prepolymer, the prepolymer containing residues, after reaction with an isocyanate group, of one or more polyols having hydroxyl equivalent weights of at least 800 g / equivalent, wherein said residues comprise residues of at least one polyol having phosphate ester groups (“phosphate-modified prepolymer”); wherein the curative, the polyisocyanate component or both further comprise(s) an epoxysilane compound having a formula molecular weight of up to 500 g / mol, the epoxysilane compound constituting from 0.25 to 2.5 weight percent of the combined weights of the one or more curing agents, the organic polyisocyanate and the epoxysilane compound, and wherein phosphorus contained in said phosphate ester groups constitutes from 0.05 to 0.2 weight percent of the combined weight of the one or more curing agents, the organic polyisocyanate and the epoxysilane compound.

[0011] Two-part adhesive systems of the disclosure can be broadly categorized into three types. In a first type, the organic polyisocyanate of the polyisocyanate component comprises a phosphate-modified prepolymer in an amount such that phosphorus contained in said phosphate ester groups of the phosphate-modified prepolymer constitutes from 0.05 to 0.2 weight percent of the combined weight of the curing agents in the curative, the organic polyisocyanates of the polyisocyanate component and the epoxysilane compound, and the curative excludes any phosphate-modified polyol.

[0012] In a second type of two-part adhesive system of the disclosure, the organic polyisocyanate of the polyisocyanate component includes a phosphate-modified prepolymer, the curing agents of the curative also comprise a phosphate-modified polyol, and phosphorus contained in said phosphate ester groups of the phosphate-modified polyol and the phosphate- modified prepolymer together constitute from 0.05 to 0.2 weight percent of the combined weight of the organic polyisocyanate(s) and the curing agent(s).

[0013] In a third type of two-part adhesive system of the disclosure, the curing agents in the curative include a phosphate-modified polyol in an amount such that phosphorus contained in said phosphate ester groups of the phosphate-modified polyol constitutes from 0.05 to 0.2 weight percent of the combined weight of the curing agents in the curative, the organic polyisocyanates in the polyisocyanate component and the epoxysilane compound, and the organicAtty Ref: 157928.221086 (86222) polyisocyanates of the polyisocyanate component exclude any phosphate-modified polyisocyanate.

[0014] In any of these types of two-part adhesive systems, the epoxysilane compound may be present in that curative, the polyisocyanate component, or divided between them in any arbitrary manner. Either the curative or the polyisocyanate component, or both, may contain one or more optional additives such as those described below.

[0015] A phosphate-modified polyol is used as an ingredient of the curative and / or as a starting material for a phosphate-modified prepolymer. The phosphate ester groups of the phosphate- modified polyol may be terminal or internal. In some embodiments, both terminal and internal phosphate groups are present. Terminal phosphate groups have the structure Polyol-O- P(O)(OH)2 where “Polyol” represents the residue of a starting polyol after removal of a hydroxyl group; internal phosphate groups have the structure (Polyol)-O-P(O)(OR1)-O-Polyol, where R^ is hydrogen or the residue of a starting polyol after removal of a hydroxyl group.

[0016] The phosphate-modified polyol can be produced by reacting a starting polyol that does not contain phosphate groups and has a hydroxyl equivalent weight of at least 800 g / equivalent with phosphoric acid and / or polyphosphoric acid. The starting polyol in specific embodiments has a hydroxyl equivalent weight of at least 800 g / equivalent and up to 4000 g / equivalent, up to 3500 g / equivalent or up to 3000 g / equivalent, as determined by measuring hydroxyl number according to ASTM D6342-22 and converting to equivalent weight using the relationship equivalent weight = 56, 100 / hydroxyl number. It may have a nominal functionality of from 2 to 6, alternatively from 2 to 4, alternatively from 2 to 3 hydroxyl groups per molecule. The starting polyol may comprise or be, for example, a polyether polyol, a polyester polyol, a polyacrylate polyol or a hydroxylterminated poly(butadiene). Polyether polyols are most typical. Among polyether polyols, of particular interest are homopolymers of propylene oxide and random and / or block copolymers of propylene oxide and ethylene oxide. Mixtures of two or more starting polyols having an equivalent weight of at least 800 g / equivalent may be used. In a particular embodiment, the starting polyol is a mixture of a first polyether polyol, typically a homopolymer of propylene oxide or a random and / or block copolymer of propylene oxide, which has a nominal functionality of 2 and a hydroxyl equivalent weight of 800 to 3000 g / equivalent and a second polyether polyol, also typically a homopolymer of propylene oxide or a random and / or block copolymer of propylene oxide, which has a nominal functionality of 3 and a hydroxyl equivalent weight of from 800 to 3000 g / equivalent.

[0017] The reaction of the starting polyol and (poly)phosphoric acid is conveniently performed by combining the starting polyol and phosphoric acid and / or polyphosphoric acid and heating the resulting combination to an elevated temperature such as 50 to 100°C for a period of 10 minutes to 5 hours. The phosphoric acid or polyphosphoric acid in specific embodiments is a 100% to 115% phosphoric acid.Atty Ref: 157928.221086 (86222)

[0018] Because the phosphate-modified polyol typically will be combined with other ingredients, either to produce an isocyanate-terminated prepolymer or formulate it into a two-part adhesive system (or both), it is generally produced at a higher phosphate content than that of the final adhesive. A useful amount of (poly)phosphoric acid is from 0.3 to 1.2 parts by weight per 100 parts by weight of the starting polyol. This produces a phosphate-modified polyol that contains phosphate groups, the phosphorus in those phosphate groups constituting from 0.1 to 0.4 percent of the weight of the phosphate-modified polyol. A typical amount of (poly)phosphoric acid is from 0.3 to 1 part, alternatively from 0.3 to 0.8 part, alternatively from 0.3 to 0.6 part, on the same basis. These amounts produce phosphate-modified polyols containing from 0.1 to 0.35, alternatively from 0.1 to 0.28, alternatively from 0.1 to 0.2 weight percent phosphorus, respectively. It is also within the scope of the disclosure to use a somewhat greater amount of phosphoric acid and / or polyphosphoric acid, such as from 1.21 to 3 parts by weight per 100 parts by weight of the starting polyol. In this case, the phosphate-modified polyol contains a greater amount of phosphorus and typically is combined with other polyols having equivalent weights of at least 800 g / equivalent, such that the combination contains from 0.1 to 0.4 weight percent phosphorus.

[0019] The reaction of the starting polyol and (poly)phosphoric acid typically increases the viscosity of resulting phosphate-modified polyol relative to that of the starting polyol.

[0020] The phosphate-modified polyol may be modified contain urethane groups. This is conveniently done by reacting an excess of a starting phosphate-modified polyol as described above with an organic polyisocyanate having an isocyanate equivalent weight of up to 300 g / equivalent. This produces a urethane-group containing phosphate-modified polyol.

[0021] In certain embodiments of the disclosure, the phosphate-modified polyol is used as a starting material to make phosphate-modified prepolymer. The prepolymer is conveniently made by reacting an excess of an organic poly isocyanate having an isocyanate equivalent weight of up to 300 g / equivalent with a phosphate-modified polyol as described above. If desired, one or more other polyols may be present in the reaction including, for example, non-phosphate-modified polyols having hydroxyl equivalent weights of at least 800 g / equivalent. One or more chain extenders and / or crosslinkers as described below also may be present in the reaction. The reaction is conveniently performed by combining the polyol(s) and organic polyisocyanate, and other isocyanate reactive materials (if any) and heating them under an inert atmosphere to a temperature of from 50 to 100°C until a constant isocyanate content is obtained.

[0022] In certain embodiments, an organic polyisocyanate used to produce a phosphate- modified prepolymer of the disclosure has an isocyanate equivalent weight of up to 300 g / equivalent, alternatively up to 250 g / equivalent, alternatively up to 175 g / equivalent, such as from 580 to 175 g / equivalent, as measured according to ISO 14896 / 3. Examples of such polyisocyanates include m-phenylene diisocyanate, toluene-2,4-diisocyanate, toluene-2,6-Atty Ref: 157928.221086 (86222) diisocyanate, hexamethylene-1 ,6-diisocyanate, tetramethylene- 1 ,4-diisocyanate, cyclohexane- 1,4-diisocyanate, hexahydrotoluene diisocyanate, naphthylene-1,5-diisocyanate, 1,3- and / or 1,4- bis(isocyanatomethyl)cyclohexane (including cis- and / or trans isomers) methoxyphenyl-2,4- diisocyanate, diphenylmethane-4,4'-diisocyanate, diphenylmethane-2,4’-diisocyanate, hydrogenated diphenylmethane-4,4’-diisocyanate, hydrogenated diphenylmethane-2,4’- diisocyanate, 4,4'-biphenylene diisocyanate, 3,3'-dimethoxy-4,4'-biphenyl diisocyanate, 3,3'- dimethyl-4-4'-biphenyl diisocyanate, 3,3 -dimethyldiphenyl methane-4,4'-diisocyanate, 4, 4', 4"- triphenyl methane triisocyanate, a polymethylene polyphenylisocyanate (PMDI), toluene-2,4,6- triisocyanate and 4,4'-dimethyldiphenylmethane-2,2',5,5,-tetraisocyanate. In specific embodiments, the poly isocyanate comprises or is diphenylmethane-4,4'-diisocyanate, diphenylmethane-2,4'-diisocyanate, PMDI, toluene-2,4-diisocyanate, toluene-2,6-diisocyanate, biuret-, allophonate-, carbodiimide, urea- or urethane-containing derivatives of any of these, or mixtures any two or more thereof. Diphenylmethane-4,4’-diisocyanate, diphenylmethane-2,4’- diisocyanate and mixtures thereof are generically referred to as MDI, and all can be used. Toluene-2,4-diisocyanate, toluene-2,6-diisocyanate and mixtures thereof are generically referred to as TDI, and all can be used.

[0023] The phosphate-modified prepolymer may have an isocyanate content of, for example 3 to 20% by weight. A phosphate-modified prepolymer used in a one-component adhesive composition may have an isocyanate content of from 3 to 18%, alternatively from 3 to 16%, alternatively from 8 to 15%, alternatively from 8 to 12.5% by weight. When used in a two- component adhesive composition, the phosphate-modified prepolymer may have an isocyanate content of from 10 to 24%, by weight, alternatively from 10 to 18% by weight. The phosphate- modified prepolymer contains residues of the phosphate-modified polyol, said residues being the portion of the phosphate-modified polyol that remain after removal of terminal hydroxyl groups. The phosphate-modified prepolymer will also contain the residues of any other isocyanatereactive materials that may have been used to make the prepolymer.

[0024] The phosphorus of the phosphate ester groups in some embodiments may constitute from 0.05 to 0.4 weight percent of the weight of the phosphorus-modified prepolymer. When used in a one-part adhesive system, the phosphate-modified prepolymer typically contains at least 0.05, alternatively or at least 0.075 weight percent phosphorus (contained in phosphate groups) and to 0.2, alternatively up to 0.175, alternatively up to 0.15, alternatively up to 0.125 weight percent of such phosphorus.

[0025] The epoxysilane compound contains at least one oxirane group and at least one -Si(OR)zgroup, where each R is hydrocarbyl, such as methyl or phenyl, and subscript z is 1-3, alternatively 2-3, alternatively 3. The epoxysilane compound may correspond to the structureAtty Ref: 157928.221086 (86222)where R is as before and A is a linking group such that the epoxysilane compound has a molecular weight of no greater than 500 g / mol, alternatively no greater than 300 g / mol. The linking group A may be a hydrocarbon, such as alkylene, e.g. alkylene having from 1 to 3 carbon atoms. A specific example is (3-glycidoxypropyl)trimethoxysilane. Examples of suitable epoxysilane compounds are commercially available as Dynasylan™ Glymo, from Evonik and Silquest™ A- 187 from Momentive.

[0026] A one-part adhesive of the disclosure includes one or more organic polyisocyanates, including the phosphate-modified prepolymer described herein, in admixture with the epoxysilane compound and optionally additional ingredients such as are described below. The phosphate- modified prepolymer is present in an amount to provide from 0.05 to 0.2 weight percent phosphorus contained in said phosphate ester groups, based on the combined weight of the organic polyisocyanates and epoxysilane compound. The phosphate-modified prepolymer may constitute the entire weight of organic poly isocyanates. Alternatively, other organic polyisocyanates also may be present, including, for example, one or more organic polyisocyanates having isocyanate equivalent weights of 300 g / mol or less, including those described above in connection with the preparation of the phosphate-modified prepolymer.

[0027] The epoxysilane compound constitutes from 0.25 to 2.5 weight percent of the combined weights of the polyisocyanates and epoxysilane compound in a one-part adhesive system of the disclosure. It has been found that greater amounts of the epoxysilane compound not only fail to increase adhesion to metal substrates but actually tend to cause it to decrease, whereas smaller amounts provide little benefit. In specific embodiments, the content of the epoxysilane compound is from 0.5 to 1.75 weight percent, especially from 1 to 1.75 weight percent, on the same basis.

[0028] Two-part adhesive systems of the disclosure contain a polyisocyanate component that comprises an organic polyisocyanate and a curative that contains one or more curing agents that contain hydroxyl, primary amino and / or secondary amino groups. The polyisocyanate component and curative are separately packaged and kept separate until they are used.

[0029] In the first type of such a two-part adhesive system, the organic polyisocyanate of the isocyanate component comprises a phosphate-modified prepolymer as described herein in an amount such that phosphorus contained in said phosphate ester groups of the phosphate- modified prepolymer constitutes from 0.05 to 0.2 weight percent of the combined weight of the polyols, the organic polyisocyanate(s) and the epoxysilane compound. Other organic polyisocyanates, including organic polyisocyanates having isocyanate equivalent weights of up to 300 g / equivalent as described above, are optionally present in the polyisocyanate component as well, but may be excluded. In this type of two-part adhesive system, the curative excludes anyAtty Ref: 157928.221086 (86222) phosphate-modified polyol as described herein and instead contains one or more optional curing agents as described further below. The epoxysilane compound is present in the prepolymer component, the curative, or both. The total amount of epoxysilane compound in the polyisocyanate component and the curative combined is from 0.25 to 2.5 weight percent of the combined weights of the organic polyisocyanates contained in the poly isocyanate component, the curing agents in the curative and epoxysilane compound. A specific example of a suitable amount of epoxysilane compound is from 0.5 to 1.75 weight percent, alternatively from 1 to 1.75, weight percent, on the same basis. Either or both of the polyisocyanate component and the curative may contain one or more additional optional ingredients as described below.

[0030] In a second type of two-part adhesive system of the disclosure, the organic polyisocyanates of the poly isocyanate component include a phosphate-modified prepolymer as described herein, and the curing agents of the curative include a phosphate-modified polyol as described herein. In particular embodiments, the phosphate-modified polyol may be or include a urethane-group containing phosphate-modified polyol as described before. Alternatively, the phosphate-modified polyol may not contain urethane groups. Other organic polyisocyanates, including organic polyisocyanates having isocyanate equivalent weights of up to 300 g / equivalent as described above, are optionally present in the polyisocyanate component as well, but may be excluded. The curative may contain one or more additional curing agents, in addition to the phosphate-modified polyol. Phosphorus contained in the phosphate ester groups of the phosphate-modified polyol and the phosphate-modified prepolymer together constitute 0.05 to 0.2 weight percent of the combined weight of all organic polyisocyanates in the polyisocyanate component and all curing agents in the curative. An epoxysilane compound is present in either or both of the curative and the polyisocyanate component, in amounts as indicated before with respect to the first type of two-part adhesive system. Either or both of the polyisocyanate component and the curative may contain one or more additional optional ingredients as described below.

[0031] In a third type of two-part adhesive system of the disclosure, the polyisocyanate component excludes any phosphate-modified polyisocyanate. In this third type, the organic polyisocyanate may be or include an organic poly isocyanate having an equivalent weight of up to 300 g / equivalent as described before, and / or a prepolymer made by reacting such an organic polyisocyanate with one or more polyols that are not phosphate-modified. The curing agents in the curative include a phosphate-modified polyol as described herein. The phosphate-modified polyol may be or include a urethane group-containing phosphate-modified polyol as described before. Alternatively, the phosphate-modified polyol may not contain urethane groups. Other curing agents such as are described below are optionally present in the curative. Phosphorus contained in said phosphate ester groups of the phosphate-modified polyol constitutes from 0.05 to 0.2 weight percent of the combined weight of the curing agents, the organic poly isocyanatesAtty Ref: 157928.221086 (86222) and the epoxysilane compound. The epoxysilane compound is present in either or both of the curative and the polyisocyanate component, in amounts as indicated before with respect to the first type of two-part adhesive system. Either or both of the polyisocyanate component and the curative may contain one or more additional optional ingredients as described below.

[0032] An adhesive of the disclosure may include various optional ingredients.

[0033] One optional ingredient is an organic polyisocyanate that is not phosphate-modified. Such an optional organic poly isocyanate may be mixed with the phosphate-modified polyisocyanate and epoxysilane compound in a one-part adhesive of the disclosure. It may be present by itself or in combination with a phosphate-modified prepolymer in the polyisocyanate component of a two-part adhesive of the disclosure. Examples of such organic polyisocyanates include any of the polyisocyanates having isocyanate equivalent weights of up to 300 g / equivalent described above, as well as prepolymers made by reacting any of such organic polyisocyanates with one or more polyols that are not phosphate-modified.

[0034] The curative component of a two-part adhesive of the disclosure optionally may contain one or more curing agents that are not phosphate-modified. Such curing agents include one or more hydroxyl, primary amino or secondary amino groups, alternatively at least two such groups. Examples of such optional curing agents include:-One or more additional polyols having hydroxyl equivalent weights of at least 800 g / equivalent, such as are described above as starting materials for making the phosphate- modified polyol, with polyether polyols being most typical and homopolymers of propylene oxide and random and / or block copolymers of propylene oxide and ethylene oxide being particularly suitable.-One or more chain extenders and / or crosslinkers having an equivalent weight per isocyanate-reactive group of less than 150, alternatively less than 125, alternatively less than 75 g / equivalent. These in specific embodiments do not contain phosphorus. The isocyanate-reactive groups may be hydroxyl and / or primary and / or secondary amino groups. Examples include 1,2- ethane diol, 1,2- or 1,3-propane diol, 1,4-butane diol, diethylene glycol, triethylene glycol, dipropylene glycol, tripropylene glycol, neopentyl glycol, ethylene diamine, piperazine, diethylene triamine, triethylene tetraamine, tetraethylenepentaaminepiperazine, N-(2- aminoethyl)piperazine, N,N’-bis(2-aminoethyl)piperazine, cyclohexane diamine (including any one or more of the 1 ,2-, 1,3- and 1,4- isomers), bis(aminomethyl)cyclohexane (including any one or more of the 1,2-, 1,3- and 1,4- isomers) and bis(2-aminoethyl)cyclohexane, toluene diamine, diethyltoluenediamine, methylenediphenyldiamine phenylene diamine and bis(aminomethyl)benzene, glycerin, trimethylolpropane, sucrose, mannitol, sorbitol, trimethylolethane, erythritol, pentaerythritol, triethanolamine, diethanolamine and alkoxylates of any of the foregoing having a hydroxyl equivalent weight of less than 150.Atty Ref: 157928.221086 (86222)--Other polyols and polyamines having equivalent weights of from 150 to 799 per isocyanate-reactive group, which typically do not contain phosphorus.

[0035] Another optional ingredient is a urethane catalyst. The urethane catalyst is a material which catalyzes the reaction of an isocyanate group with a hydroxyl group or water. Suitable catalysts include, for example, including tertiary amines, cyclic amidines, tertiary phosphines, various metal chelates, acid metal salts, strong bases, various metal alcoholates and phenolates and metal salts of organic acids. The most typical urethane catalysts are tertiary amine catalysts, cyclic amidines, and tin catalysts. Examples of tertiary amine catalysts include trimethylamine, triethylamine, N-methylmorpholine, N-ethylmorpholine, N,N-dimethylbenzylamine, N,N- dimethylethanolamine, N,N,N',N'-tetramethyl-1,4-butanediamine, N,N-dimethylpiperazine, 1,4- diazobicyclo-2,2,2-octane, bis(dimethylaminoethyl)ether, dimorpholinodiethyl ether) triethylenediamine and dimethylalkylamines where the alkyl group contains 4 to 18 carbon atoms. Mixtures of these tertiary amine catalysts are often used. Examples of tin catalysts are stannic chloride, stannous chloride, stannous octoate, stannous oleate, dimethyltin dilaurate, dibutyltin dilaurate, other tin compounds of the formula SnRn(OR)4.n, wherein each R is independently alkyl or aryl and subscript n is from 0-2, and the like. The urethane catalyst, when present, is mixed with the phosphate-modified prepolymer and epoxysilane compound in a one-part adhesive. In a two-part adhesive, the urethane catalyst may be present in either the curative or the polyisocyanate component or divided between the curative and polyisocyanate component.

[0036] Another optional ingredient is a preservative and / or stabilizer such as an antioxidant, benzoyl chloride and diethyl malonate. A preservative or stabilizer is mixed with the phosphate- modified prepolymer and epoxysilane compound in a one-part adhesive of the disclosure. In a two-part adhesive, the preservative and / or stabilizer may be present in either the curative or the polyisocyanate component, or divided between the curative and poly isocyanate component.

[0037] Another optional ingredient is a defoaming agent such as, for example, that sold commercially as SAG 47 defoamer from Momentive. A defoaming agent may be present in a one-part adhesive of the disclosure because the moisture-curing reaction produces a gas that can produce bubbles in the cured adhesives and weaken the adhesive layer. A defoaming agent helps to reduce or even eliminate bubble formation.

[0038] Another optional ingredient is a chemical or physical blowing agent, in the event that foaming is wanted. Examples of chemical blowing agents include water, formic acid, carbonate compounds, various peroxy blowing agents and azo blowing agents. Chemical blowing agents, if used at all, typically are incorporated into the curative of a two-part adhesive of the disclosure. Physical blowing agents include, for example, low-boiling chlorofluorocarbons, fluorocarbons, hydrocarbons, so-called HFOs and the like. Physical blowing agents may be incorporated into either part of a two-part adhesive or combined with the phosphate-modified prepolymer and epoxysilane compound in a one-part adhesive. It is often typical to omit any chemical or physicalAtty Ref: 157928.221086 (86222) blowing agent from the adhesive compositions of the disclosure, other than small amounts of water that may be present in the starting materials. In some particular embodiments, a one-part adhesive contains no more than 500 ppm water by weight. Similarly, in specific embodiments the curative and polyisocyanate component of a two-part adhesive of the disclosure each contain no more than 500 ppm water by weight.

[0039] If a blowing agent is present, it is typical, but not required, that a foam-stabilizing surfactant is also present. Examples of such surfactants include silicone surfactants and propylene oxide-ethylene oxide block copolymers.

[0040] Other optional ingredients include pigments and / or colorants such as titanium dioxide, iron oxide, chromium oxide, azo / diazo dyes, phthalocyanines, dioxazines and carbon black; water scavengers; plasticizers; a solvent or diluent; rheology modifiers such as silica, fillers such as melamine and calcium carbonate; reinforcing agents such as fiber glass, carbon fibers, flaked glass, mica, talc and the like; biocides; preservatives; flame retardants; and the like.

[0041] Adhesives of the disclosure are useful for bonding two substrates. A layer of adhesive composition is applied to a bondline between the substrates and cured there to form an adhesive bond between the substrates. In general, no special conditions are needed to apply the adhesive or cure it. Thus, adhesives of the disclosure can be applied and curing using well-established methods for polyurethane adhesives.

[0042] In the case of a one-part adhesive, the adhesive layer is exposed to atmospheric moisture and / or liquid water to effect the cure. In case of curing by exposure to atmospheric moisture, curing typically is performed under ambient conditions of temperature (such as from 10 to 35°C) and humidity, although an elevated temperature such as from 40 to 100°C and / or moisture- enhanced atmosphere may be applied when a faster cure is desired. Curing with liquid water can be done at similar temperatures. Liquid water may be combined with the one-part adhesive composition of the disclosure and the resulting mixture applied to the bondline. Alternatively, liquid water may be applied to one or both of the substrates before or after the one-part adhesive composition is applied to the bondline. A convenient amount of liquid water is from 5 to 20 parts by weight per 100 parts by weight of the one-part adhesive composition.

[0043] In the case of a two-part adhesive, the polyisocyanate component and curative are combined and applied to the bondline and then cured. Curing can be performed at ambient temperature (such as from 10 to 35°C) or at an elevated temperature of, for example, from 40 to 100°C.

[0044] In some embodiments, the cured adhesive has a density of at least 750 g / L, alternatively at least 900 g / L, i.e., is substantially non-foamed.

[0045] The substrates are not particularly limited. Examples include wood, metals, organic polymers, ceramic materials such as glass, paper, leather and, especially, metals. The disclosure is of particular interest for metal-to-metal bonding as it adheres strongly to metal surfaces. AAtty Ref: 157928.221086 (86222) metal substrate may be surface treated prior to applying the adhesive, but an advantage of this disclosure is that the adhesive bonds tenaciously even to untreated metal surfaces, so the surface treatment step may be eliminated. Surface treatments include, for example, the application of primers, surface roughening (which can be done mechanically and / or chemically (as by acid etching)), and exposure to flame, plasma or corona discharge.

[0046] Specific examples of metal substrates include aluminum and aluminum alloys such as aluminum series Ixxx to 9xxx, steel (including stainless steel), nickel, titanium, iron, magnesium, copper, bronze, brass and the like.

[0047] The disclosure is particularly useful to bond substrates, and metal substrates in particular, having a thickness of at least 0.1 mm, alternatively at least 0.25 mm, alternatively at least 0.5 mm and up to, for example, 25 mm. alternatively up to 12.5 mm. Substrates having thicknesses such as these are often used as structural components of manufactured goods. The performance requirements for the substrates and the adhesives in these structural applications are much different than for films such as plastic films or metallized plastic films (in which the metal layer typically has a thickness of less than 0.001 mm and thus provides essentially no mechanical strength), which stretch and deform easily under load. Adhesives bonding structural members are often required to bear significant weights and withstand much greater forces than adhesive bonds between layers of plastic films and metallized plastic films. In the latter case, the adhesive bears very little weight and experiences only small loads because the substrate dissipates energy easily due to becoming stretched or otherwise deforming. In structural applications involving thicker substrates, stretching or deformation seldom occurs under conditions of normal use, so strains are transferred to the adhesive layer and the bondline, which much carry the load without failure.

[0048] The following examples are provided to illustrate the disclosure but are not intended to limit the scope thereof. All parts and percentages are by weight unless otherwise indicated.

[0049] Phosphate-modified (PPA) Polyol 1 is prepared by combining 50 parts of a 2000 number average molecular weight polypropylene oxide) diol, 50 parts of 6000 number average molecular weight polypropylene oxide) triol and 0.36 parts of 115% polyphosphoric acid), and heating the resulting mixture under nitrogen for 2 hours at 70°C to produce a polyol mixture that contains phosphate groups. PPA Polyol 1 contains about 0.12 weight-% phosphorus in the form of phosphates provided by the polyphosphoric acid.

[0050] Phosphate-modfied (PPA) Polyol 2 is prepared in the same manner, increasing the amount of 115% polyphosphoric acid to 0.5 parts. PPA Polyol 2 contains about 0.17 weight-% phosphorus in the form of phosphates provided by the polyphosphoric acid.

[0051] Phosphate-modified (PPA) Polyol 3 is prepared in the same manner, increasing the amount of 115% polyphosphoric acid to 0.8 parts. PPA Polyol 3 contains about 0.27 weight-% phosphorus in the form of phosphates provided by the polyphosphoric acid.Atty Ref: 157928.221086 (86222)

[0052] Polyisocyanate 1 is a 50 / 50 by weight mixture of the 4,4’- and 2,4’-isomers of diphenylmethane diisocyanate.

[0053] Polyisocyanate 2 is a polymeric MDI having an isocyanate content of about 31.5% by weight and an average functionality of about 2.7.

[0054] The Defoamer is a silicone antifoam compound commercially available as SAG™ 47 from Momentive.

[0055] The Epoxysilane compound is a glycidyl trimethoxysilane commercially available as Silquest™ A- 187 from Momentive.

[0056] DBTDL is dibutyltin dilaurate.

[0057] DMDEE is dimorpholinodiethyl ether.

[0058] Prepolymer 1 is made by combining 49 parts of PPA Polyol 1, 14.68 parts of Polyisocyanate 1 and 34.32 parts of Polyisocyanate 2, and heating the resulting mixture under nitrogen for 3 hours at 70 to 80°C. About 50 ppm benzoyl chloride is added. Prepolymer 1 has an isocyanate content of about 14.2% by weight.

[0059] Prepolymer 2 is made in the same manner as Prepolymer 1, substituting an equal weight of PPA Polyol 2 for PPA Polyol 1. Prepolymer 2 has an isocyanate content of about 14.2% by weight.

[0060] Prepolymer 3 is made in the same manner as Prepolymer 1, substituting an equal weight of PPA Polyol 3 for PPA Polyol 1. Prepolymer 3 has an isocyanate content of about 14.2% by weight.

[0061] Prepolymer A is made by combining 24 parts of a 2000 number average molecular weight polypropylene oxide) diol, 24 parts of 6000 number average molecular weight polypropylene oxide) triol, 14.68 parts of Polyisocyanate 1 and 34.32 parts of Polyisocyanate 2, and heating the resulting mixture under nitrogen for 3 hours at 70 to 80°C. About 50 ppm benzoyl chloride is added. Prepolymer 1 has an isocyanate content of about 14.1% by weight.

[0062] Adhesive Examples 1-3 and Comparative Samples A-E are prepared by combining ingredients as indicated in Table 1 under nitrogen with continuous mixing for about 15 minutes.Atty Ref: 157928.221086 (86222)Table 1•Comparative.1The amount of PPA used to produce the prepolymer, calculated as a percentage of the total weight of all starting materials used to make the designated amount of prepolymer (including those used to make the starting PPA Polyol in each case).2Phosphorus contained in phosphate groups, based on the weight of the prepolymer.

[0063] The viscosity of each of the adhesives is measured at 25°C using an AR2000 rheometer according to ASTM D445, with 50 mm parallel plates geometry with 50 diameter plates was used.

[0064] Gel times for each of the adhesives is measured using ASTM D5895, using a BYK Dry Timer.

[0065] Tensile lap shear testing is conducted according to ASTM D1002. Test specimens are prepared by removing surface oil from and spraying water mist onto each of two 6061-T6 aluminum test panels and forming a sandwich structure having a 10 mil (0.254 mm) layer of the adhesive between the test panels. The adhesive is cured for 7 days at 72°F (22°C) and 50% + 10% relative humidity before testing. Results in each case are the average of 4 test samples.

[0066] Results of the testing are as indicated in Table 2.Atty Ref: 157928.221086 (86222)Table 21Phosphorus contained in phosphate groups, based on the weight of the prepolymer.2Based on combined weight of prepolymer and epoxysilane compound.

[0067] Comparative Adhesive A represents a baseline case, having neither a polyol with phosphate groups nor an epoxysilane compound. Adding 2 parts of an epoxysilane compound, without a phosphate-modified polyol or prepolymer (Comp. Adhesive 2) actually reduces the tensile lap shear adhesion by about 13%.

[0068] Comparative Adhesive C-E show the effect of using a polyol having phosphate groups to make the prepolymer. A small positive effect is seen when the phosphorus content of the prepolymer is about 0.06%. A larger positive benefit is seen when the phosphorus content is 0.09% or 0.14%, although the lower adhesion of Comparative Adhesive E compared to Comparative Adhesive D suggests that increasing the phosphorus content beyond about 0.125% or 0.1% add no further benefit and may be deleterious.

[0069] Examples 1-2 and Comparative Adhesive F all have phosphorus contents of about 0.09% based on prepolymer weight. Adding 0.5 parts of the epoxy silane results in a 15% increase in tensile lap shear adhesion over Comparative Adhesive F, which has the same phosphorus content but lacks the epoxysilane compound. Increasing the epoxy silane to 1 part as in Example 2 leads to an improvement of 23% in tensile lap shear adhesion, compared to Comparative Adhesive D.

[0070] Example 3 shows the effect of further increasing the epoxy silane level to 2%. Although a small increase in tensile lap shear adhesion is seen relative to Comparative Adhesive D, this adhesive exhibits diminished adhesion performance relative to Examples 1-2, suggesting thatAtty Ref: 157928.221086 (86222) too much epoxysilane compound is disadvantageous and the best performance is seen when the amount of epoxysilane compound is somewhat less than 2% by weight.

Claims

Atty Ref: 157928.221086 (86222)CLAIMS1. A one-part urethane adhesive composition comprising a mixture of: i) one or more polyisocyanates comprising an isocyanate-terminated prepolymer, the prepolymer containing residues, after reaction with an isocyanate group, of one or more polyols having hydroxyl equivalent weights of at least 800 g / equivalent, wherein said residues comprise residues of at least one polyol having phosphate ester groups, and ii) an epoxysilane compound having a formula molecular weight of up to 500 g / mol, the at least one epoxysilane compound constituting 0.25 to 2.5 weight percent of the combined weights of i) and ii); wherein phosphorus contained in said phosphate ester groups constitutes 0.05 to 0.2 weight percent of the combined weight of i) and ii).

2. The one-part urethane adhesive composition of claim 1, wherein the isocyanate- terminated prepolymer is a reaction product of the at least one polyol having phosphate ester groups and an organic polyisocyanate having an isocyanate equivalent weight of up to 300 g / equivalent.

3. The one-part urethane adhesive composition of claim 2, wherein the organic polyisocyanate having an isocyanate equivalent weight of up to 300 g / equivalent comprises diphenylmethane-4,4'-diisocyanate, diphenylmethane-2,4'-diisocyanate, PMDI, toluene-2,4- diisocyanate, toluene-2,6-diisocyanate and biuret-, allophonate-, carbodiimide, urea- or urethane-containing derivatives of any of thereof.

4. The one-part urethane adhesive composition of any one preceding claim, wherein said residues comprise residues of a polyether polyol having phosphate ester groups.

5. The one-part urethane adhesive composition of any one preceding claim, wherein the isocyanate-terminated prepolymer has an isocyanate content of 3 to 18% by weight.

6. The one-part urethane adhesive composition of any one preceding claim, where the at least one epoxysilane compound constitutes 0.5 to 1.75 weight percent of the combined weights of i) and ii).

7. A two-part urethane adhesive composition comprisingA) a curative containing one or more curing agents andAtty Ref: 157928.221086 (86222)B) a separately packaged polyisocyanate component comprising an organic polyisocyanate, wherein a) the one or more curing agents comprise a polyol having a hydroxyl equivalent weight of at least 800 g / equivalent and has phosphate ester groups, and / or b) the organic polyisocyanate comprises an isocyanate-terminated prepolymer, the prepolymer containing residues, after reaction with an isocyanate group, of one or more polyols having hydroxyl equivalent weights of at least 800 g / equivalent, wherein said residues comprise residues of at least one polyol having phosphate ester groups; wherein the curative, the polyisocyanate component or both further comprise an epoxysilane compound having a formula molecular weight of up to 500 g / mol, the epoxysilane compound constituting 0.25 to 2.5 weight percent of the combined weights of the one or more curing agents, the organic polyisocyanates and the epoxysilane compound, and further wherein phosphorus contained in said phosphate ester groups constitutes 0.05 to 0.2 weight percent of the combined weight of the one or more curing agents, the organic polyisocyanates and the epoxysilane compound.

8. The two-part urethane adhesive composition of claim 7, wherein the polyisocyanate component comprises an isocyanate-terminated prepolymer containing residues, after reaction with an isocyanate group, of one or more polyols having hydroxyl equivalent weights of at least 800 g / equivalent, wherein said residues comprise residues of at least one polyol having phosphate ester groups.

9. The two-part urethane adhesive composition of claim 8, wherein the isocyanate- terminated prepolymer is a reaction product of the at least one polyol having phosphate ester groups and an organic polyisocyanate having an isocyanate equivalent weight of up to 300 g / equivalent.

10. The two-part urethane adhesive composition of claim 9, wherein the organic polyisocyanate having an isocyanate equivalent weight of up to 300 g / equivalent is one or more of diphenylmethane-4,4'-diisocyanate, diphenylmethane-2,4'-diisocyanate, PMDI, toluene-2,4- diisocyanate, toluene-2,6-diisocyanate and biuret-, allophonate-, carbodiimide, urea- or urethane-containing derivatives of any of thereof.11 . The two-part urethane adhesive composition of any one of claims 7-10 wherein said residues comprise residues of a polyether polyol having phosphate ester groups.Atty Ref: 157928.221086 (86222)12. The two-part urethane adhesive composition of any one of claims 7-11, wherein the isocyanate-term inated prepolymer has an isocyanate content of 10 to 18% by weight.

13. The two-part urethane adhesive composition of any one of claims 7-12, wherein the one or more curing agents comprise a polyol having a hydroxyl equivalent weight of at least 800 g / equivalent and has phosphate ester groups.

14. The two-part urethane adhesive composition of claim 7, wherein the one or more curing agents comprise a polyol having a hydroxyl equivalent weight of at least 800 g / equivalent and has phosphate ester groups.

15. The two-part polyurethane adhesive composition of claim 14, wherein the polyol having a hydroxyl equivalent weight of at least 800 g / equivalent and has phosphate ester groups is a polyether.

16. The two-part polyurethane adhesive composition of claim 14 or 15, wherein the polyol having a hydroxyl equivalent weight of at least 800 g / equivalent and has phosphate ester groups contains 0.1 to 0.4 weight percent phosphorus.

17. The two-part polyurethane adhesive composition of any one of claims 14-16, wherein the polyisocyanate component comprises one or more of diphenylmethane-4,4'- diisocyanate, diphenylmethane-2,4'-diisocyanate, PMDI, toluene-2,4-diisocyanate, toluene-2,6- diisocyanate and biuret-, allophonate-, carbodiimide, urea- or urethane-containing derivatives of any of thereof and excludes an isocyanate-terminated prepolymer containing residues, after reaction with an isocyanate group, of one or more polyols having hydroxyl equivalent weights of at least 800 g / equivalent, wherein said residues comprise residues of at least one polyol having phosphate ester groups.

18. The two-part polyurethane adhesive of any one of claims 7-17, wherein the epoxysilane compound constitutes 0.5 to 1.75 weight percent of the combined weights of the one or more curing agents, the organic polyisocyanates and the epoxysilane compound.

19. A method of bonding substrates, comprising applying a layer of the one-part adhesive composition of any of claim 1-6, to a bondline between two substrates and curing the layer of the one-part adhesive composition by exposing it to atmospheric moisture, liquid water or both atmospheric moisture and liquid water.Atty Ref: 157928.221086 (86222)20. A method of bonding substrates, comprising combining the curative and the polyisocyanate component of the two-part adhesive composition of any one of claims 7-18 to form an uncured adhesive, applying the uncured adhesive to form an adhesive layer at a bondline between two substrates and curing the adhesive layer.

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