WO1997039044A1 - Epoxy adhesive compositions and methods of making same - Google Patents

Abstract

An epoxy composition having good sag resistance, green strength, and the capability to develop good ultimate bond strength is disclosed. The epoxy composition includes an epoxy component and a curative component. The epoxy component includes at least one epoxide and at least one isocyanate additive, the epoxide having been capped with at least one capping isocyanate to impart controlled viscosity and storage stability to the epoxy component. Methods of making and using the epoxy composition are also disclosed.

Description

EPOXY ADHESIVE COMPOSITIONS AND METHODS OF MAKING SAME

Field of the Invention

The present invention relates to epoxy adhesive compositions and to methods of preparing and using the same. More particularly, the present invention relates to two-component epoxy adhesive compositions.

Background of the Invention

Epoxy adhesives are widely used in numerous applications for bonding various materials. Epoxy resins are characterized by a tight, crosslinked polymer network, and thus they typically exhibit toughness and good adhesion. However, while crosslinking associated with epoxy adhesives can provide many benefits, crosslinking can also result in increased adhesive viscosity due to the reaction of the various adhesive reactants. This, in turn, can result in storage and handling difficulties.

For this reason, epoxy adhesives typically include two components which are prepared and stored in separate containers prior to use. Conventional two-component epoxy adhesives include an "epoxy" component, including epoxides optionally combined with isocyanates, acrylates, methacrylates, or combinations thereof. Epoxy adhesives also include a "curative" component, typically comprising an amine curing or hardening agent.

One common use for two part epoxy adhesives is to bond sheet molding compounds (SMCs). An adhesive for a sheet molding compound generally should possess ceitain properties including good green strength and bond strength. In addition, the components that form the adhesive should have sufficiently low viscosity to be easily applied by pumping means or gravity. Further, because adhesives are often applied to vertical surfaces, sag resistance can be an important property in the epoxy adhesive.

U.S. Pat. No. 5,385,990 to Abbey et al., U.S. Pat. No. 4,775,728 to Goel, and U.S. Pat. No. 4,695,605, also to Goel, disclose various epoxy adhesives possessing these properties. For example, U.S. Patent No. 4,775,728 is directed to a two part adhesive composition having a first component comprising a polyepoxide, carboxylic acid terminated rubber, and optionally phenol or oxime blocked isocyanate prepolymers, and a second component comprising a finely dispersed solid salt of an amine and a polyphenol in a liquid adduct.

Although conventional two-part epoxy adhesives can possess desirable properties, the epoxy component can also exhibit instability upon storage. Specifically, isocyanates and hydroxyl functionalities of the epoxides of the epoxy component react and thus increase the viscosity of the epoxy when stored for relatively short periods of time, e.g., within a few weeks. As a result, the epoxy component is no longer easily pumpable or gravity feedable when stored and must be pressure pumped, if it can be used at all. Further, drums or other containers which contain highly viscous materials can be difficult to clean to meet environmental disposal standards. In addition, as isocyanate functionality is consumed, the epoxy can lose its anti-sag characteristics.

Still further, reactions between epoxides and moisture can result in a build¬ up of C0₂ gas, thus creating an undesirable pressure build-up in the storage container. Excess CO₂ can also result in bubbles of gas which can be trapped once the adhesive is applied to a substrate and interfere with the strength of the adhesive bond. U.S. Pat. No. 4,695,605 to Goel relates to a two-component epoxy adhesive composition which includes a first component comprising an epoxide and a polyisocyanate and a second component comprising a polyamine. The Goel '605 patent discloses prereacting the polyisocyanate with a polyamine compound prior to mixing the polyisocyanate with the epoxide to increase storage stability and maintain the thixotropic properties of the first component.

U.S. Pat. No. 5,134,126 to Jansen et al. relates to a two-component polyurethane adhesive which includes a first component comprising isocyanates with some epoxides and a second component comprising amino and hydroxyl containing substituents. The Jansen '126 patent discloses the use of an alkylating agent in the first component to prevent side reactions between the epoxide hydroxyl groups and the isocyanate and thus increase the storage stability of the first component. Although polyisocyanates may be present during the alkylation step, the polyisocyanates are not involved in the prereaction of the hydroxyl groups in the epoxide compounds. It is also to be noted that when the alkylating agents described by Jansen et al. are added to compositions with high epoxide concentrations, an epoxide self-reaction can result, which can cause the epoxy component to solidify. Thus, the alkylating agents described by Jansen et al. arc not feasible for use in epoxy adhesive, particularly easily pumpable or gravity feedable epoxy adhesives.

Summary of the Invention The present invention provides two-part epoxy adhesive compositions which exhibit several desirable properties, such as sag resistance, green strength and bond strength. The viscosity of the individual components of the epoxy adhesive composition can be controlled so that the components are substantially storage stable for periods up to and exceeding six months. Further, because viscosity can be controlled, the components can be easily applied to a substrate surface by pumping means or gravity. Still further, excess build-up of CO-, gas can be avoided. The epoxy adhesive composition of the invention includes an epoxy component and a curative component, which are stored separately and combined prior to use The epoxy component includes at least one epoxide and at least one isocyanate additive The epoxide is stabilized with regard to its reactivity to isocyanate groups prior to formulating the epoxy component, 1 e , prior to mixing the epoxide with the isocyanate additive The epoxide is stabilized by "prereacting" or "capping" hydioxyl groups of the epoxide (and moisture, when present) with at least one capping isocyanate to form a capped epoxide The capped epoxide is then mixed with the isocyanate additive to form the epoxy component Additionally, the epoxy component can contain a filler containing hydroxyl groups and/or endogenous water, which can also be prereacted or capped to minimize or eliminate its reactivity with regard to the isocyanate additive

The curative component includes at least one amine, and can also include other agents, such as a hydroxy-substituted aromatic compound, a filler, a rubber component, and various additives When combined, the epoxy and curative components form a viscoelastomeπc composition with sag resistance and a predetermined rheology which allows the epoxy adhesive composition to be easily applied as a bead to the surface of a substrate The composition can be subsequently cured to provide a desired level of adherence, i.e , bond strength The compositions of the invention are particularly advantageous for assembling parts made from sheet molding compounds

The present invention also provides methods of making the capped epoxides and methods of applying the epoxy adhesive composition of the invention to a surface of a substrate.

Detailed Description of the Invention

The epoxy adhesive compositions of the present invention are two- component compositions comprising an epoxy component and a curative component The epoxy component generally compπses at least one epoxide and at least one isocyanate additive In the invention, the epoxide is stabilized with regard to its reactivity to isocyanate groups prior to formulating the epoxy component, I e , pπor to mixing the epoxide with the isocyanate additive In this regard, hydroxyl groups present on the epoxide are "prereacted" or "capped" with at least one capping isocyanate to form a urethane linkage (-NHC(O)O-) between hydroxyl groups of the epoxide and the capping isocyanate This is believed to decrease the reactivity oi the epoxide with the isocyanate additive when the epoxy component is formulated and thus increase the storage stability of the epoxy component in the presence of isocyanate additive The viscosity of the epoxy component can also be controlled to provide a viscosity within a desired range, suitable for gravity or pump feeding. Further, when present, moisture in the epoxides can also be prereacted or capped by the capping isocyanate to form urea linkages or oligomers.

The epoxides of the present invention can be any of the types of compounds that contain at least one epoxy group having the general formula: o

/ \

— c— c —

The epoxides can be monomeric or polymeric, saturated or unsaturated, and include aliphatic, cycloaliphatic, aromatic and heterocyclic epoxides, and mixtures thereof. 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 polyepoxide; and polymers having pendant epoxy groups, e.g., a glycidyl methacrylate polymer or copolymer.

Advantageously, epoxides used in accordance with the present invention are liquids having a viscosity of about 200 centipoise or higher at 25°C. The epoxides also preferably have, on the average, at least 1.5 polymerizable epoxy groups per molecule, and more preferably about 2.0 or more epoxy groups per molecule. In addition, the epoxides generally have, on the average, up to about one hydroxyl group per molecule, and more typically from 0.05 to 0.15 hydroxyl groups per molecule. The "average" number of epoxy groups or hydroxyl groups per molecule is determined by dividing the total number of epoxy groups or hydroxyl groups in the epoxide by the total number of epoxide molecules present.

The epoxides can vary greatly in the nature of their backbone and substituent groups. For example, the backbone can be of any type and substituent groups thereon can be of any group free of an active hydrogen which is reactive with an oxirane ring at room temperature. Exemplary substituent groups include halogens, esters, ethers, sulfonates, siloxanes, nitro groups, phosphates, and the like. The molecular weight of the epoxides may vary from about 50 to about 100,000 or more. Mixtures of various epoxides can also be used in the compositions of the invention. As noted above, the epoxides of the present invention can be cycloaliphatic epoxides. Exemplary cycloaliphatic epoxides include diepoxides of cycloaliphatic esters of dicarboxylic acids such as bis(3,4-epoxycyclohexylmethyl)oxalate, bis(3.4- epoxycyclohexylmethyl)adipate, bis(3,4-epoxy-6-methylcyclohexylmethyl)adipate, bis(3,4-epoxycyclohexylmethyl)pimelate, and the like. Other suitable diepoxides of cycloaliphatic esters of dicarboxylic acids are described in, e.g., U.S. Pat. No. 2,750,395, which is incoφorated herein by reference.

Other cycloaliphatic epoxides include 3,4-epoxycyclohexylmethyl-3,4- epoxycyclohexane carboxylates such as 3,4-epoxycyclohexylmethyl-3,4- epoxycyclohexane carboxylate, 3,4-epoxy- l -methylcyclohexylmethyl-3,4-epoxy-l- methylcyclohexane carboxylate, 6-methyl-3,4-epoxycyclohexylmethyl-6-methyl-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-epoxycyclohexylmethyl- 3,4-epoxycyclohexane carboxylates are described in, e.g., U.S. Pat. No. 2,890,194, which is incoφorated herein by reference.

Further epoxides which are particularly useful in the practice of the invention include glycidyl ether monomers of the formula:

where R' is alkyl or aryl and n is an integer from 1 to 6. Examples are diglycidyl ethers of polyhydric phenols obtained by reacting a polyhydric phenol with an excess of chlorohydrin such as epichlorohydrin, e.g., the diglycidyl ether of 2,2-bis(4- hydroxyphenyl)propane. Further examples of epoxides of this type which can be used in the practice of the invention are described in U.S. Pat. No. 3,018,262, and in "Handbook of Epoxy Resins", by Lee and Norville, McGraw-Hill Book Co., New York, 1967, both of which are incoφorated herein by reference.

There are a host of commercially available epoxides, commonly known as epoxy resins, which can be used in the epoxy component in this invention. In particular, epoxides which are readily available include octadecylene oxide; glycidylmethacrylate; diglycidyl ethers of bisphenol A, e.g., those available under the trade designations EPON 828, EPON 1004 and EPON 1010 from Shell Chemical Co. and DER-331 , DER-332, and DER-334, from Dow Chemical Co.; vinylcyclohexane dioxide, e.g., ERL-4206 from Union Carbide Corp.; 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylate, e.g. ERL-4221 from Union Carbide Corp.; 3,4-epoxy-6-methylcyclohexylmethyl-3,4- epoxy-6-methylcyclohexane carboxylate, e.g., ERL-4201 from Union Carbide Coφ.; bis(3,4-epoxy-6-methylcyclohexylmethyl) adipate, e.g., ERL-4289 from Union Carbide Coφ.; bis(2,3-epoxycyclopentyl) ether, e.g., ERL-0400 from Union Carbide Coφ.; aliphatic epoxy modified with propylene glycol, e.g. ERL-4050 and ERL-4052 from Union Carbide Coφ.; dipentenc oxide, e.g., ERL-4269 from Union Carbide Corp.; epoxidized polybutadiene, e.g., OXIRON 2001 from FMC Coip.; silicone resin containing epoxy functionality; flame retardant epoxy resins, e.g., DER-580, a brominated bisphenol type epoxy resin available from Dow Chemical Co.; 1 ,4-butancdiol diglycidyl ether of phenolformaldehyde novolak, e.g., DEN-431 and DEN-438 from Dow Chemical Co.; resorcinol diglycidyl ether, e.g. KOPOX1TE from Koppers Company, Inc; and the like. A preferred epoxide is a diglycidyl ether of bisphenol A such as EPON 828 from Shell Chemical Co.

Still other epoxides 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-glycidylmethacrylate, 1:1 methyl-methacrylateglycidylacrylate and a 62.5:24: 13.5 methylmethacrylate-ethyl acrylateglycidylmethacrylate.

Exemplary epoxides which can be used in the invention are described in U.S. Pat. No. 5,385,990 to Abbey et al., which is incoφorated herein by reference.

The epoxy component of the epoxy adhesive compositions of the present invention also includes at least one isocyanate additive. The isocyanate additives can be any of the organic isocyanate compounds known in the art having at least one free isocyanate group, including aliphatic, cycloaliphatic, and aromatic mono- and polyisocyanates. Preferably, the isocyanate additive is a polyisocyanate. As will be appreciated by the skilled artisan, the isocyanate additive reacts with amines present in the curative component of the epoxy adhesive compositions to form urea oligomers which precipitate and act essentially as fillers. In addition, the urea oligomers associate to form a network structure through hydrogen bonding, which helps increase the sag resistance of the epoxy adhesive composition.

Exemplary polyisocyanates include ethylene diisocyanate, trimethylene diisocyanate, dodecamethylene diisocyanate, tetraethylene diisocyanate, pentamethylene diisocyanate, propylene- 1 ,2-diisocyanate, 2-3 dimethyl tetramethylene diisocyanate, butylene- 1,2-diisocyanate, 1 ,4-diisocyanato cyclohexane, cyclopentene- 1,3-diisocyanate, l-methylphenylene-2,4-diisocyanate, diphenyl-4,4-diisocyanate, benzene- 1 ,2,4- triisocyanate, 4,4'-diphenylene propane diisocyanate, 1 ,2,3,4-tetraisocyanato butane, butane- 1 ,2,3-triisocyanate, polymethylene polyphenyl isocyanate, toluene-2,4- diisocyanate, 2,2,4-trimethylhexamethy lene- 1 ,6-diisocy anate, hexamethylene- 1 ,6- diisocyanate and the trimer thereof, diphenylmethane-4,4'-diisocyanalc, m-phenylene diisocyanate, p-phenylenc diisocyanate, 2,6-toluene diisocyanate, 1,5-naphthalene diisocyanate, naphthalene- 1,4-diisocyanate, diphenylene-4,4'-diisocyanate, 3.3'-bitoluene- 4,4'-dnsocyanate, 1 ,4-cyclohexylene dimethylene diisocyanate, xylene- 1.4-dιιsocyanate, xylene- 1 ,3-dπsocyanate, cyclohexyl- 1 ,4-dιιsocyanate, 4,4'-methylene-bιs(cyclohexyl isocyanate), 3,3'-dιmethyldιphenylmethane-4,4'-dnsocyanate, isophorone diisocyanate, bιs(4-ιsocyanatocyclohexyl) methane (e g DESMODUR W from Bayer Corp ), meta- a,a,a\a -tetramethyl xylene diisocyanate (e.g. TMXDI from Cyanamide, Inc ), mixtures thereof, and the like These polyisocyanates have an isocyanate functionality of at least two as more fully disclosed in U S Pat Nos 3,350,362 and 3,382,215. which are incoφorated herein by reference. Preferred polyisocyanates include TMXDI and bιs(4- lsocyanatocyclohexyl) methane. In the present invention, hydroxyl groups present in the epoxides of the epoxy component (and moisture, when present) are prereacted or capped by at least one capping isocyanate to form a capped epoxide pπor to formulating the epoxy component This reduces the hydroxyl functionality of the epoxide and prevents side reactions between hydroxyl groups of the epoxide and isocyanate additives duπng storage Although not wishing to be bound by any particular theory of the invention, it is believed that prereacting epoxides under controlled conditions can limit the degree of crosslinking, and therefore limit subsequent increases in molecular weight and viscosity of the epoxy component. As a result, the isocyanate functionality of the epoxy component can remain relatively high in epoxy components including capped epoxides, as compared to epoxy components which include non-capped epoxides. The importance of isocyanate functionality with respect to viscosity and sag resistance is described below

Suitable isocyanates for capping or prereacting the epoxide include any of the isocyanates noted above, I e., having at least one free isocyanate group, and including aliphatic, cycloaliphatic, and aromatic mono- and polyisocyanates Polymeric polyisocyanates such as isocyanate prepolymers can also be used to cap the epoxide Preferably, the capping isocyanate is a monoisocyanate, diisocyanate or combination thereof or any other isocyanate having an average isocyanate functionality of not greater than two

Exemplary monoisocyanates include, but are not limited to, monofunctional aliphatic isocyanates (e.g TMI from Cyanamide, Inc ), phenyl isocyanate, halo-substituted phenyl isocyanates, halo-substituted alkyl isocyanates, undecyl isocyanate, tert-octyl isocyanate, tert-dodecyl isocyanate, n-octyl isocyanate, 2-ethylhexyl isocyanate, and the like A preferred monoisocyanate is phenyl isocyanate

The capping isocyanate may be the same as the isocyanate additive of the epoxy component, however, the capping isocyanate generally has an isocyanate functionality which is less than or equal to the functionality of the isocyanate additive of the epoxy component.

The epoxy component can also include other components, such as any of the types of fillers known in the art. Filler can be added to the adhesive using techniques known in the art, for example, by dispersing filler in the epoxide prior to adding other components thereto.

The use of fillers in epoxy type adhesives can be advantageous in increasing the sag resistance of the resulting epoxy adhesive composition. However, many fillers can include active hydroxyl groups and/or endogenous water, either of which can also react during storage with isocyanate components. Thus the use of fillers can also adversely affect adhesive viscosity, i.e., can increase viscosity of the epoxy components over time, and thus decrease storage stability. Accordingly, in one aspect of the present invention, fillers are also prereacted with at least one capping isocyanate to provide improved storage stability and controlled viscosity to the adhesive composition. For fillers which contain active hydroxyl groups and/or water, the filler is preferably added to the epoxide prior to capping the epoxide and formulating the epoxy component. Alternatively, a portion of the filler can be added to the epoxide prior to capping the epoxide, and the remaining portion of the filler can be added to the epoxy component after epoxide capping, depending on the type of fillers used (i.e., whether the filler is reactive with isocyanate, whether a combination of isocyanate reactive and non¬ reactive fillers is used, desired viscosity, etc.). In a particularly preferred embodiment of the invention, filler is added to the epoxide, and both the filler and the epoxide are capped with capping isocyanate prior to the formulation of the epoxy component. As noted above, this is believed to prevent crosslinking and viscosity increases in the epoxy component during storage.

The addition of filler to the epoxide prior to prereaction with the capping isocyanate can be advantageous in other respects. For example, prereaction of filler with the capping isocyanate can prevent the build-up of carbon dioxide in the epoxy component when it is stored. When present in the filler, water can react with the isocyanate additive in the epoxy component to form carbon dioxide during storage. Because the epoxy component tends to increase in viscosity during storage, the viscosity can increase to a point where it is difficult to remove the CO₂ present in the epoxy component. The CO₂ gas consequently weakens the final epoxy adhesive composition. Thus, prereaction of filler with the capping isocyanate can also minimize CO₂ buildup. Carbon dioxide build-up can also occur during prereaction of filler with the capping isocyanate. Accordingly, advantageously, the prereacted epoxide/filler is degassed prior to being combined with the isocyanate additive of the epoxy component.

Moreover, the addition of filler prior to epoxide capping can help maintain a desired degree of isocyanate functionality in the epoxy component of the adhesive. This can be advantageous when the epoxy adhesive composition is applied to a substrate surface, i.e., for bead formation.

Exemplary fillers include, but are not limited to, metal oxides such as titanium dioxide or alumina, calcium carbonate, silicates, talcs, clays, mica, kaolin, powdered quartz, metal powders, glass fibers, carbon fibers, polyamide fibers, glass spheres, ceramic spheres, coal tar, bitumen, and the like. Preferably, talc fillers are used in the epoxy component of the invention. Commercially available talc fillers include MISTRON VAPOR R Talc from Cyprus Ind. and BEAVER WHITE 325 Talc, the former being preferred. A catalyst can also be added to the epoxide, the capping isocyanate, and the filler (when involved in the prereaction) to increase the rate of the reaction between the capping isocyanate and the hydroxyl groups of the epoxide and the hydroxyl groups and/or water in the filler. Exemplary catalysts include organic tin catalysts, e.g., tin acetate; tin octoate; tin oleate; tin 2-ethylhexoate; tin laurate; the dialkyl tin salts or carboxylic acids such as dibutyl tin diacetate, dibutyl tin dilaurate, dibutyl tin maleate, dibutyl tin di-2-ethyl- hexoate, dilauryl tin diacetate, dioctyl tin diacetate and the like; trialkyl tin hydroxides such as trimethyl tin hydroxide, tributyl tin hydroxide, trioctyl tin hydroxide and the like; dialkyl tin oxides such as dibutyl tin oxide, dioctyl tin oxide, dilauryl tin oxide and the like; and dialkyl tin chlorides such as dibutyl tin dichloride, dioctyl tin dichloride, and the like. Preferably, the catalyst used in the prereaction is a dialkyl tin salt of a carboxylic acid and more preferably is dibutyl tin diacetate. When present, the amount of catalyst can range from about 0 to about 1 percent, preferably from about 0 to about 0.5 percent, and more preferably from about 0 to about 0.1 percent, by weight of the epoxy component.

As noted above, preferred isocyanates for capping epoxides (and filler when present) in accordance with the invention include monoisocyanates and diisocyanates. Monoisocyanates can greatly reduce crosslinking between the capping isocyanate and the epoxide during capping, and therefore can provide an epoxy component with a relatively lower viscosity prior to storage than if the epoxide is capped with a diisocyanate. However, certain monoisocyanates are considered to be hazardous materials. Accordingly, diisocyanates can also be used to impart the desired storage stability to the epoxy component. When diisocyanates are used, the diisocyanates tend to "bridge" two adjacent epoxide molecules, i.e , react with hydroxyl groups of adjacent epoxide molecules, to form a urethane linkage between the epoxide molecules and to form a higher molecular weight capped epoxide. In a particularly preferred embodiment of the invention, the epoxide is prereacted with a combination of monoisocyanate and diisocyanate to provide advantages of both, i e , to keep the viscosity relatively low and to provide some bridged epoxides. which can impart toughness to the epoxy adhesive composition

Several factors can influence the amount of capped epoxide present in the epoxy component of the adhesives of the invention, such as the degree of viscosity desired for the epoxy component, storage times and temperatures, the type and amount ol additional epoxy components such as filler, and the like Generally, capped epoxides are present in the epoxy component in an amount from about 55 to about 99, preferably about 70 to about 98, and more preferably about 82 to about 98 percent, by weight based on the total weight of the epoxy component

Similarly, the amount of capping isocyanate used to cap epoxide (and filler, when present) can vary depending upon factors such as those listed above Generally, the amount of capping isocyanate is based on the hydroxyl functionality of the epoxide as determined by the isocyanate demand of the components to be prereacted, and can be determined using known techniques. For example, isocyanate demand, and thus the amount of capping isocyanate required for prereaction of a given amount of epoxide and filler, can be determined by adding an excess of capping isocyanate to the epoxide and filler and monitoring the loss of isocyanate functionality under conditions essentially equivalent to prereaction conditions, described in further detail below When the isocyanate functionality no longer decreases, l e , when the isocyanate functionality levels off, the difference in the initial and the final isocyanate content can be calculated, and the isocyanate demand of the epoxide and the filler determined therefrom In evaluating the filler and very viscous epoxides or additives, a dry solvent such as azeotropically dried toluene, xylene, or n-heptane, is advantageously used as an inert carrier

Generally, the amount of capping isocyanate used to cap the epoxide, and optionally the filler, ranges from about 10 to about 150 percent, preferably about 70 to about 1 10 percent, and more preferably about 80 to about 95 percent, ot the amount necessary to cap the hydroxyl groups of the epoxide, and optionally the filler, based upon isocyanate demand of the epoxide and filler, determined as descπbed above Lower levels of capping isocyanate are preferred when using monoisocyanates to prereact epoxide and tiller. Total isocyanate additive content in the epoxy component of the adhesives ot the invention ranges from greater than 0 to about 25 percent, preferably about 2 to about 20 percent, and more preferably about 2 to about 10 percent by weight of the total weight of the epoxy component. Further, preferably the epoxy component has an average total isocyanate functionality of greater than about 1.5, with the preferred range being between 1.8 and 2.5. The epoxy component preferably includes filler in an amount from about 0 to about 60, preferably about 10 to about 30, percent by weight based on the total weight of the epoxy component. In this regard, generally filler is dispersed in epoxide to form an epoxide/filler composition prior to prereacting or capping the epoxide (and filler, as needed). Advantageously, the amount of total filler added to the epoxy component is less than about 30 percent, due to high epoxy component viscosity associated with high filler content. However, higher or lower filler amounts can be used, particularly as epoxide content varies.

For example, in one aspect of the invention, multiple batches of capped epoxides are prepared and thereafter combined to give a single epoxy component. In this aspect of the invention, filler content of the various capped epoxide batches can vary. Advantageously, essentially all of a filler to be added to the epoxy component is mixed with an epoxide and the filler/epoxide mixture capped or prereacted to form a single capped epoxide/filler masterbatch, aliquots of which can thereafter be mixed with other epoxide (both capped and/or non-capped) batches to provide the desired epoxy component. The capped epoxide/filler masterbatch can include from about 20 to about 80 percent by weight of all capped epoxides in the resultant epoxy component.

When a masterbatch is prepared as described above, the filler content thereof is relatively high, e.g., greater than about 30 weight percent. In this aspect of the invention, preferably epoxides in the masterbatch are capped using diisocyanates, and epoxides in other epoxide batches that are intended for mixing with the masterbatch, or for non-masterbatch addition, are preferably capped using monoisocyanates. Although not wishing to be bound by any theory of the invention, it is believed that the use of diisocyanates to cap epoxides having a high filler content (e.g., greater than about 30 percent by weight) reduces the hydroxyl functionality of the epoxide and filler in the capped epoxide, and can also beneficially affect the properties of the filler in the final epoxy adhesive composition.

In one particularly preferred embodiment of the invention, the epoxy component is prepared by combining a first batch that includes at least one capped epoxide and capped filler; a second batch that includes at least one capped epoxide without filler; and a polyisocyanate additive. The first batch is present in an amount from about 25 to about 80, preferably about 30 to about 75, and more preferably about 40 to about 70, percent by weight of the epoxy component The second batch is present in an amount from about 10 to about 70, preferably about 15 to about 55, and more preferably about 20 to about 50, percent by weight of the epoxy component. The isocyanate additive is present in an amount trom about 1 to about 25, preferably about 2 to about 20, and more preferably about 2 to about 10, percent by weight of the epoxy component In this embodiment of the invention, an exemplary epoxy component includes 69 percent of the first batch, 23 percent of the second batch and 7 percent of the isocyanate additive by weight of the epoxy component.

It should be noted that the amount of filler and the amount of isocyanate additive present in the epoxy component can also depend on the desired end use viscosity of the epoxy, and, in turn, the desired means for transferring the epoxy component from the storage container to a substrate surface. As apparent to one skilled in the art, increased filler content can provide greater sag resistance, but can also generally increase the viscosity of the epoxy component. In addition, increased isocyanate functionality in the epoxy component can also increase the sag resistance of the composition.

For example, for gravity feedable applications, filler content can be relatively low, e.g., about 0 to about 15 percent by weight of the epoxy component, and conversely the total isocyanate additive content can be relatively high, e.g., about 10 to about 20 percent by weight of the epoxy component to provide a sag resistant adhesive. Typically, the preferred viscosity range for gravity feeding is from about 20 to about 40,000 cs (centistokes) using the Gardner Bubble Tube Standards at about 25°C.

For pump feedable applications, filler content can be relatively high, e.g., about 15 to about 30 percent by weight of the epoxy component, and the isocyanate additive content can be relatively low, e.g., about 1 to about 10 percent by weight of the epoxy component to provide a sag resistant adhesive A preferred viscosity range for pumping epoxy components is from about 200 to about 2,000,000 cs.

The epoxy component of the invention can also include a rubber component to provide toughness and flexibility to the epoxy adhesive composition. The rubber component can be present as a dispersion of precrosshnked rubber in the epoxy component as will readily be apparent to one skilled in the art. Examples of precrosshnked rubber compounds available as dispersion in epoxides include polyacrylates, polybutadienes, polyisoprenes, and the like. The rubber component can also be a liquid rubber precursor such as acrylate-terminated butadienes and acrylate- and epoxy-terminated butadiene- acrylonitrile copolymer rubbers. The rubber component can be present in amounts from about 0 to about 50 percent by weight, based on the total weight of the epoxy component In addition, the epoxy component may also include other additives in conventional amounts, such as diluents (e.g. triacrylate and difunctional glycidyl ether), colorants (e.g. titanium dioxide and aluminum powder), thixotropic agents, wetting agents, plasticizers, and the like, provided the components are non-reactive with the isocyanate groups and the epoxy groups of the epoxy component. The capped epoxides are thereafter combined with isocyanate additive to form the epoxy component of the two-part epoxy adhesive system of the invention. The total isocyanate additive content and functionality of the epoxy component preferably is sufficient so that when the epoxy component is combined with the curative component (described below), a non-sagging bead can be formed to apply the epoxy adhesive to a substrate surface. Generally, bead formation can be affected by many factors, such as the reaction of isocyanate additive and amine to form urea oligomers when the epoxy component and the curative component are mixed, filler content, and others. Advantageously, total isocyanate additive and filler content of the epoxy component is sufficiently high to allow the epoxy adhesive composition to be extruded to form a bead. The isocyanate additive level, however, should also be sufficiently low to prevent rapid viscosity increases in the epoxy adhesive composition to the level at which the epoxy adhesive composition cannot be applied by normal pumping means.

The curative part of the adhesive compositions of the invention preferably comprise at least one amine. Any of the types of amines known in the art as epoxy curing or hardening agents can be used. The amines can be aliphatic polyamines, aromatic polyamines, polyamidoamines, alicyclic polyamines, tertiary amines, and mixtures thereof. Suitable amines are disclosed in U.S. Pat. No. 5,385,990 to Abbey et al., which is incoφorated herein by reference.

Polyamidoamines useful in the present invention are typically the reaction products of aliphatic amines with dimerized fatty acids of 12 to 28 carbon atoms. Polyamidoamines are well known as amine hardeners and are commercially available. A typical example is VERSAMLD 140 from Henkel, USA, which is a polyamidoamine of dimerized linoleic acid. Mixtures of amine hardeners may also be used in the invention.

It is particularly preferred to use an unhindered aliphatic amine. Unhindered aliphatic amines as described herein refer to amine compounds containing a primary amine group attached to a primary carbon atom. Unhindered amines can be effective in developing green strength. Examples of unhindered aliphatic amines include diethylenetriamine, triethylenetetramine, tetraethylenepentamine, 2-methyl- l ,5- pentanediamine, pentaethylenehexamine, ethylenediamine, tetramethylenediaminc, hexamethylenediamine, bis-hexamethylenetriamine, 3,9-bis(3-aminopropyl)-2,4,8, 10- tetraoxaspiro[5,5]-undecane, 1 ,3-bis-aminomethylcyclohexane, and the like. Preferably. the unhindered aliphatic amines of the invention are selected from the group consisting of diethylenetriamine, tπethylenetetramine, tetraethylenepentamine, 2-methy!- l ,5- pentanediaminc, and 1 ,3-bιs-amιnomethylcyclohexane polyamidoamines

The curative component preferably contains a hydroxy-substituted aromatic compound as descnbed in U S Pat No 5,385,990 to Abbey et al , referenced above A hydroxy-substituted aromatic compound as discussed herein is essentially any aromatic compound having at least one hydroxy substituent and, optionally, at least one electron- withdrawing substituent attached to the aromatic compound The aromatic compound has a pKa in the range from about 5 to 9 7, preferably from about 6 to 9 6, and more preferably from about 7 to 9 5 All pKa values referred to and cited herein are as determined in water at 25°C The hydroxy-substituted aromatic compound generally also has a boiling point greater than about 210°C, preferably greater than about 215°C

The hydroxy-substituted aromatic compound typically corresponds to the following formula

wherein ® is a 5- or 6- membered, heterocyclic, nonheterocychc, monocyclic, oi multicyclic aromatic πng, X is an electron-withdrawing group, m is 1 , 2 or 3, n is 0, 1 , 2 or 3 with the proviso that (1 ) n cannot be zero when the aromatic πng is benzene and (2) the locations of OH and X on the aromatic πng are such that the overall compound has a pKa within the range from about 5 to 9 7 Examples of ® are described in U S Pat No 5,385,990 to Abbey et al Specific examples of electron-withdrawing groups that can be used as the X substituent in the present invention include -Cl, -NO₂, -CF,, -CO₂R, - CH₂OR, -CN, and -SO₂R, where R is an alkyl radical having from 1 to 5 carbon atoms or aryl and R is preferably methyl, ethyl, propyl or phenyl

Preferred classes of hydroxy-substituted aromatic compounds include halogenated phenolic compounds, hydroxy benzoic acid esters, hydroxy-substituted naphthalene, hydroxy-substituted pyridines, hydroxy-substituted pyπmidines, and hydroxy-substituted quinohnes The halogenated phenolic compounds are presently the most preferred hydroxy-substituted aromatic compounds The curative component of the invention preferably also comprises a rubber component in conventional amounts to provide toughness and flexibility to the epoxy adhesive composition. The rubber component is preferably an amine-terminated butadiene- acrylonitrile copolymer rubber. Useful amine-terminated butadiene-acrylonitrile copolymer rubbers are described in U.S. Pat. No. 5,385,990 to Abbey et al. Methods for preparing amine-terminated butadiene-acrylonitrile copolymers are described in more detail in, for instance, U.S. Pat. No. 4, 129,670, which is incoφorated in its entirety. Commercially available amine-terminated butadiene-acrylonitrile copolymer rubbers can be obtained under various trade names including HYCAR ATBN (B.F. Goodrich Co.), H-3932 (ACR Co. ), and X-3995 (ACR Co.).

The curative component also preferably contains a filler to increase the sag resistance of the epoxy adhesive composition. Exemplary fillers include metal oxides such as titanium dioxide or alumina, calcium carbonate, silicates, talcs, clays, mica, kaolin, powdered quartz, metal powders, glass fibers, carbon fibers, polyamide fibers, glass spheres, ceramic spheres, coal tar, bitumen, and the like. Preferably, a talc is used in the curative component of the invention. Commercially available talc fillers include MISTRON VAPOR R Talc from Cyprus Ind. and BEAVER WHITE 325 Talc, the former being preferred.

In a preferred embodiment of the invention, the curative component contains from about 0 to about 35 percent filler, from about 15 to about 60 percent amine, from about 0 to about 60 percent rubber component and from about 1 to about 15 percent hydroxy-substituted aromatic compound by weight of the curative component. More preferably, the curative component contains from about 10 to about 30 percent filler, from about 25 to about 50 percent amine, from about 0 to about 45 percent rubber component and from about 3 to about 10 percent hydroxy-substituted aromatic compound by weight of the curative component.

The curative component may also include additives such as diluents, colorants (e.g. titanium dioxide and aluminum powder), thixotropic agents, wetting agents, plasticizers, and the like. In another aspect of the invention, methods of making and using the epoxy adhesive composition of the invention are provided. To make the epoxy adhesive composition of the invention, at least one epoxide having at least one hydroxyl group is prereacted with at least one capping isocyanate to form a capped epoxide. As noted above, filler can also be combined with the epoxide before the epoxide capping step. The isocyanate/epoxide combination (and filler, when present) is preferably agitated at a temperature of from about 50 to about 1 10°C, and more preferably from about 70 to about 100°C. The reaction conditions are maintained until the isocyanate functionality of the mixture levels off, thus indicating completion of the prereaction of the capping isocyanate with the hydroxyl groups of the epoxide (and of filler, when present).

As previously described, if a catalyst such as an organic tin catalyst is added during the prereaction, the rate of the prereaction increases substantially. For instance, without the catalyst, the prereaction of an epoxide (EPON 828) and a capping isocyanate (TMXDI) continued for approximately four days at a temperature of 100°C before the isocyanate functionality leveled off. With the addition of a catalyst (dibutyl tin diacetate). the isocyanate functionality leveled off within four hours at a prereaction temperature of 80°C. Thus, the rate of the prereaction can be increased up to 20 to 25 times, and greater, using a catalyst. Further, the use of a catalyst is advantageous because the epoxides can be capped at lower temperatures.

As described above, the prereaction of the epoxide and the filler with the capping isocyanate typically results in the formation of CO₂ gas. The CO₂ gas can be removed from the capped epoxide by conventional degassing procedures well known to the skilled artisan prior to mixing the capped epoxide with the isocyanate additive to form the epoxy component. Additionally, other components as desired can be added to the capped epoxides prior to mixing with the isocyanate additive. Once capping has been completed, the isocyanate additive can be combined with the capped epoxide using conventional methods.

Once the epoxy component has been formed, it can be stored at various temperatures, typically between about 0°C and about 50°C, and preferably at around room temperature, i.e., about 20°C to about 25°C, until it is combined with the curative component. The epoxy component can be stored for long periods of time with essentially no or minimal changes in viscosity, although as the skilled artisan will appreciate, storage time will depend upon factors such as storage temperature. For example, typically the epoxy component can be stored at room temperature for at least about 120 days, and preferably at least about 180 days, and longer, without exhibiting substantial increases in viscosity (i.e., no greater than about 200% increase). At higher temperatures (i.e., approaching 50°C), the epoxy component can be stored for up to about 30 days, preferably about 60 days, and longer, without a substantial increase in viscosity, i.e., again no greater than about 200% increase.

The curative component can be prepared using conventional methods sufficient to combine the components, i.e., by agitation or stirring at temperatures from about 20°C to about 100°C. Typically, the curative component is stored at similar conditions to the epoxy component storage conditions. Generally, the curative component is stored at between about 0°C and about 50°C, and preferably at room temperature, i.e. , about 20°C to about 25°C, until it is combined with the epoxy component.

To prepare the epoxy adhesive, the epoxy component and the curative component are combined prior to application of the epoxy adhesive to the surface of a substrate. The epoxy adhesive composition generally includes from about 20 to about 80 percent, preferably from about 30 to about 70 percent, and more preferably from about 40 to about 60 percent, by weight of the epoxy component based on the total weight of the epoxy adhesive composition. The epoxy adhesive composition generally includes from about 20 to about 80 percent, preferably from about 30 to about 70 percent, and more preferably from about 40 to about 60 percent, by weight of the curative component based on the total weight of the epoxy adhesive composition.

The adhesive can be applied using conventional techniques, such as conventional pumping and/or gravity feed devices as known in the art. The surface of the substrate is then contacted or mated with the surface of a second substrate. The resultant composite product is thereafter treated to completely cure or set the adhesive bond. The epoxy adhesive can be cured using conventional techniques and conditions. For example, the composition can be cured at ambient conditions, i.e., room temperature. Alternatively, the composition can be cured using conventional curing stations at elevated temperatures, for example, between about 70^DC and about 190°C. Cure times vary, ranging from about 0.5 to about 24 hours at ambient temperatures to about 1 minute to about 1 hour, preferably for about 5 minutes to about 40 minutes, at elevated temperatures.

Although capable of bonding any substrate or surface capable of receiving an adhesive, the adhesives are particularly suited for bonding fiber reinforced unsaturated resin SMC parts to other SMC parts or metals. In this regard, the epoxy adhesive composition can be applied to an automotive metal body part, which is then mated with a second substrate surface, typically a second automotive body part, and the resultant composite is thereafter subjected to a bonding cycle ranging from about 1 to about 10 minutes at temperatures ranging from about 90°C to about 150°C in which the adhesive composition is allowed to develop green strength. Green strength refers to the ability of the adhesive composition to develop an initial tackiness or adhesion upon application of the adhesive to a substrate surface so that surfaces adhered to one another with the adhesive will remain securely bonded together before the adhesive is fully cured. This is particularly important in the automobile industry where parts are initially placed together in a bonding press but are shortly thereafter hung in a curing oven or the like; in this example, it is essential that the parts remain securely attached to one another during the final curing process. If an adhesive composition docs not possess sufficient green strength, the mated parts may shift.

The curing process is then completed by subjecting the mated parts to temperatures ranging from about 135°C to about 160°C for a period of about 20 to about 40 minutes. After the curing process is completed, the bonded parts are frequently subjected to a paint bake cycle at temperatures up to about 205°C for as long as about 1 hour.

A preferred viscosity range for the adhesive compositions which are useful in bead applications is between about greater than about 1 ,000,000 cp. However, the adhesive can be formulated to have higher or lower viscosities. Further, the adhesives can exhibit open times of at least 10 minutes at ambient temperature.

The epoxy adhesive compositions of the invention also have the unusual ability to quickly develop significant green strength and are capable of withstanding the elevated temperature conditions associated with the paint bake cycle. In addition, the resultant epoxy adhesive composition possesses a strength similar to substrates, such as SMC and other plastics, thus providing a strong bond between the substrates. These properties make the adhesives particularly useful in SMC applications, as described above.

The present invention will be further illustrated by the following non- limiting examples.

EXAMPLE 1

Determination of Isocyanate Demand A. Epoxide

Into a pre-dried three-neck 250 ml round bottom flask was placed 100 g of a 20% TMXDI (meta-α,α,α',α'-tetramethyl xylene diisocyanate from Cyanamide, Inc.)/EPON 828® solution. To the flask was added 0.50 g dibutyl tin diacetate (tin catalyst). A magnetic stir bar was placed into the flask and the flask was attached to a Frederick condenser under a dry N₂ purge. The flask was lowered into a hot oil bath. The reaction flask contents were stirred and heated to 80°C, then kept there, regulated by a Therm-O-Watch. A sample (3-5 ml) was withdrawn periodically (every one to two hours) for determination of percent NCO loss, until two to three of the periodic determinations leveled off. The isocyanate determinations were all done via indirect titration with n- dibutylamine and hydrochloric acid, and calculated according to Part C of this example. The theoretical initial % NCO was determined according to Part D of this example. The isocyanate demand is determined according to Part E of this example. B Filler

Into a three-neck 250 ml round bottom flask was placed 21 4 g of talc (dried or "as is"), 45 0 g of azeotropically dried m-xylene, and 5 0 g of m-tetramethylxylene isocyanate TMI-(meta) To the flask was added 0 50 g of the tin catalyst (dibutyl tin diacetate) A magnetic stir bar was placed into the flask and the flask was attached to a Frederick condenser with a dry N₂ purge The pot was lowered into a hot oil bath and the temperature was set for 80°C A sample (3-5 ml) was drawn periodically (every one to two hours) for determination of percent NCO loss The sample was allowed to cool to room temperature (RT) then filtered through a fine pore Buchner filter funnel with vacuum adapter to remove the talc

The filtrate was then titrated to determine the percent NCO loss This was done until two to three of the periodic determinations leveled off The isocyanate determinations were all done via indirect titration with n-dibutylamme and hydrochloric acid, and calculated according to Part C of this example The theoretical initial % NCO was determined according to Part D of this example (the weight percent of the isocyanate in the solution was determined without adding in the weight of the talc because it has been filtered out for accuracy The isocyanate demand was determined according to Part E of this example

C. Determination of Isocyanate Level by Titration

This method defines a procedure for measuring the weight percent of -NCO groups in an epoxy/talc system. Any "free -NCO" group rapidly and stoichiometrically reacts with amines. In this method the -NCO group reacts with an excess of di-N- substituted amme The unreacted amine is then titrated with standard acid The titration is carried out using the following reagents ( 1 ) di-n-butylamine

- 0 1 N in toluene (reagent grade); (2) hydrochloric acid - 0.1 N; (3) bromophenol-blue indicator solution - 0.1 %; (4) isopropyl alcohol - reagent grade (IPA), and (5) tetrahydrofuran - reagent grade (THF)

Exactly 12.0 g of 0 1 N di-n-butylamine solution was dispensed into a clean dry Erlenmeyer flask Next, 0 4 - 0.8 g of the capped epoxy/talc - isocyanate sample was added to the flask and the weight is recorded to the nearest 0 1 mg Approximately 25 ml THF was added to the flask to help solubilize the same The contents of the flask were then stirred for five minutes to ensure all -NCO groups are reacted Next, three to five drops of bromophenol-blue indicator were added to 25 ml of IPA and this solution was added to the flask. The flask contents were then titrated with 0 1 N HCl until the yellow endpoint was reached A blank volume was determined by titrating, following the above procedure, without the sample. The % NCO and % isocyanate are then calculated according to the following equation where 42.02 is the molecular weight for NCO:

1. % NCO = 42.02(blank vol. - sample vol. in L) (Normality) x KK) sample wt (g)

2. 7c Isocyanate = °k NCO x (Equiv. wt. of isocyanate)

42.02

D. Determination of Theoretical Initial NCO Percentage The theoretical initial % NCO is determined by calculating weight percent of the isocyanate in the solution, dividing by the equivalent weight of the isocyanate ( 122.1 g/eq) to get the isocyanate equivalence in (eq/g) and multiplying by the isocyanate functionality (42.027) to get the theoretical initial % NCO.

E. Determination of Isocyanate Demand

The isocyanate demand or meq/g of hydroxyls and/or water present in the epoxy, filler, or epoxy/filler composition is determined by the following equation:

Meq/g of hydroxyl = (meq/g init. - meq/g final of isocyanate) wt. fraction of epoxy and/or filler where the meq/g initial of isocyanate (isocyanate equivalence) is determined as in Part D of this example and converted to meq/g and the meq/g final of the isocyanate is determined by the following equation:

Meq/g final = (IV of titrant (blank) - FV of titranO x N(acid) wt. of sample where IV = the initial volume of the titrant (blank), FV = the final volume of the titrant, and N(acid) is the Normality of the acid.

EXAMPLE 2

Capping Process with a Slight Deficiency of Isocyanate This process is particularly advantageous when volatile, strongly sensitizing isocyanates, typically monoisocyanates, are to be used so that very low residual levels of these hazardous isocyanates are caπied into the final formulation. The following weight percentages are based on a 2 kg batch using EPON

828® (a diglycidyl ether of bisphenol A from Shell Chemical Co.)/Beaver White Talc as the epoxide/filler composition. The isocyanate demand of the EPON 828® and the Beaver White Talc was determined according to the procedure in Example 1. The catalyst used was dibutyl tin diacetate. a) Epoxide: 66 wt% - 1319.6g x 0.5136 meq/g = 6777 meq b) Talc: 34 wt% - 680.4g x 0.2993 meq/g = 203.6 meq Total equivalence: 0.8813 eq

At 100% isocyanate demand: 0.8813 eq x 122.1 g/eq (equiv. wt. of TMXDI) = 107.5g TMXDI

For 90% capping: (0.9 x 107.5g = 96.76g TMXDI)

Catalyst concentration: 2000g x 0.25% = 5.0g catalyst

Into a 2 L kettle was placed 1319.6 g of epoxy, and 680.4g of talc. The kettle was attached to mechanical stirrer with two propellers for good agitation, and a nitrogen purge. After dispersing the talc into the epoxy, 97g of TMXDI was mixed in as a capping isocyanate at a temperature of between 50 - 80°C (addition time was 5 minutes). After the TMXDI was added, the mixture was heated and stirred at 80°C for one hour. The heat was then turned off, and the kettle allowed to cool to at least 70°C before adding the catalyst in portions. The first portion (0.31 g of catalyst) was added and mixed for 30 mins. The second portion (0.52 g) was then added, mixed in and heated for 30 mins.

The remaining catalyst was added, in portions to minimize foaming, over a 30 minute period (total time one and a half hours). The heat was then turned on, set at 80°C, and the mixture was heated and stirred until the %NCO leveled off. The disappearance of NCO functionality was monitored via indirect titration using n- dibutylamine and hydrochloric acid.

EXAMPLE 3 Capping Process with Excess Diisocyanate

This process is similar to the process in Example 2 except that all of the TMXDI (that which is required for capping plus that used as an additive for bead rheology control) was added before the dibutyl tin diacetate was added. The detailed steps for a 2 L batch is given below. Into a 2 L kettle was placed 622.00 g of Beaver White talc (previously dried). To the kettle was added 1206.40 g of EPON 828®. The two components were mixed together, dispersing the talc, before 260.35g of TMXDI was added. The kettle was clamped into an oil bath, the kettle head was then attached, and to it a condenser, mechanical stirrer, and a thermocouple was assembled. Dry nitrogen was allowed to purge the kettle. The oil bath was set for 80°C, controlled via a Therm-O-Watch, and the kettle's content was allowed to heat and stir. To the flask was added in two portions, 9.87 g of dibutyl tin diacetate (4.00 g, then 5.87 g with 30 minutes between additions). Due to foaming, approximately 30 minutes after the last addition, the heat was turned off and the kettle's content was allowed to stir until the foaming ceased Heating continued for an additional four hours (total heating time was six houis) A sample was drawn and titrated for percent isocyanate (%NCO) remaining, every hour beginning at the two hour point The titrations revealed that the %NCO had leveled off (at 2.6) after four hours of heating There was no significant loss in the %NCO foi an additional two hours, therefore the cooking was terminated

EXAMPLE 4

Capping Process at High Talc Loading In a process similar to the process described in the preceding examples, equal amounts of talc and epoxy (talc's weight percent being greater than desired for final formulation) are capped to better control/vary the level of talc in formulation. This process could have a commercial advantage by being an intermediate common to several products A procedure for a 1.5 L (50:50 epoxy:talc without the tin catalyst) batch is described below.

Into a 2 L kettle was placed 7340 g of both EPON 828® and Beaver White talc (previously dπed). The kettle was transferred to an oil bath and the kettle head, mechanical stirrer, condenser, and thermometer were assembled. To ease the stirring, the mixture was heated up to 70°C before stirring. To the flask was added 90 0 g of TMXDI through an addition funnel (no catalyst). A sample was drawn and the temperature was increased to 105°C. Periodic sampling to titrate the samples for percent isocyanate was done daily After seventy-two hours of heating, the %NCO leveled off at 0 36%

EXAMPLE 5 Capping Process for Capped Epoxide without Talc

This process is similar to the process of previous examples except the capping agent is a monofunctional isocyanate The mateπal is used to blend with the talc concentrate above, to achieve the desired talc loading Described below is a condensed procedure with emphasis on the amount of catalyst. Into a 2 L kettle was placed 1500 00 g of EPON 828®. The kettle was assembled as usual. To the flask was added 167 92 g of TMI (meta) unsaturated aliphatic isocyanate, then heating and stirring was done at 80°C for one hour. To the flask was added 1 64 g (0.10%) of the tin catalyst via a 3cc syringe (foaming did not occur because there is essentially no water to form CO,) Heating was continued for an additional nine hours A sample was drawn and titrated periodically until the %NCO leveled off The titrations revealed that the %NCO had leveled off after eight hours of heating. EXAMPLE 6

One Pot Process Method for Capped Epoxides and Talc The following procedure is for a 800 g batch of a capped epoxide and talc with 17.5 wt % talc. Into a dry bowl for the Ross mixer was placed 615.50 g of Epon 828®. To the bowl is added 16.44 g of phenyl isocyanate and 0.10 g of dibutyl tin diacetate (tin catalyst). The components are mixed at 80°C for approximately two hours. After the phenyl isocyanate is consumed 140.0 g of Mistron Vapor R talc was mixed in with care to avoid clumping. Desmodur W (bis-(4-isocyanatocyclohexyl) methane from Bayer Coφ.), 27.46 g, was added and heating was continued at 80°C.

After heating for one hour, 0.45 g of tin catalyst was added, in one portion, and the disappearance of isocyanate functionality was monitored by titration until zero NCO was obtained. The batch was then mixed and degassed at 80°C. The new epoxy equivalent weight was 244.53 g/eq. Pure difunctional isocyanate additive (Desmodur W) was then added for sag resistance control. Normally, 8 wt. % is added (a new epoxy equivalent weight is determined) but the concentration of both talc and Desmodur W could be changed for specific applications.

EXAMPLE 7 Comparison of Capped and Non-Capped Epoxides

The stability of epoxy adhesive compositions including epoxides capped as described above were compared to the stability of conventional epoxy adhesive without capped epoxides. The results are set forth in Table 1 below:

TABLE 1

LPON 828 with 20% TMXDI m-TMI Capped F.l'ON 828 with 20% additive at 50°C TMXDI additive at 50°C

Initial Viscosity (cs) 1 ,200+100 2,000±100

One Month 9.800±1.000 3.400±200

Six Months 39,00012.000 9.800+1,000

Table 1 demonstrates the substantially reduced viscosity of epoxy components containing capped epoxides compared to epoxy components containing non- capped epoxides for stored epoxy components. The epoxides are capped according to the procedures described in the preceding examples. The capping technology was used to prepare storage samples using a modified EPON 828® wherein about 86% of the active hydroxyl groups were pre-reacted with TMI (meta), a liquid unsaturated aliphatic monoisocyanate manufactured by Cyanamide, Inc.

EXAMPLES 8-12 Storage Stability of Capped Epoxides

Samples 8-12 were prepared as described below and evaluated with regard to storage stability. Examples 8 and 9 were each prepared using a masterbatch of a mixture of talc and EPON 828® capped with TMXDI; a second masterbatch of EPON 828® capped with m-TMI without filler; and 16.6% by weight of the epoxy component of a TMXDI isocyanate additive. Example 8 was stored at room temperature and Example 9 was stored at 50°C.

Example 10 was prepared by mixing EPON 828®, 20% by weight TMXDI (isocyanate additive), and dibutyl tin diacetate catalyst. The mixture was heated at 80°C until the %NCO leveled off to 5.05. The sample was stored at 50°C. Examples 1 1 and 12 were prepared as one batch and separated for storage.

The composition consisted of 29.4% by weight talc, EPON 828®, 13.2% TMXDI (excess over the isocyanate demand of the epoxide and talc (4.6%)), and dibutyl tin diacetate catalyst. Only enough TMXDI was added during the capping process to satisfy 90% of the isocyanate demand of the epoxide and the talc. The capping operation was continued until the isocyanate titration showed only 0.07% NCO. The remaining TMXDI was added rapidly to the 80°C batch dropping the temperature to 73°C. The mixture was allowed to stir for 30 minutes before the heat was turned off and the sample allowed to cool to room temperature. Example 1 1 was stored at room temperature and Example 12 was stored as 50°C. Table 2 below sets forth the results of the storage samples in Examples 8-

12.

TABLE 2

Storage Stability of Capped Epoxide Samples

^a Settled the most. ^b Settled hard. ^l Some settling.

^J Prepared 3 months prior to the other formulations ^c Tested after only 20 days of storage

The numbers in parenthesis are initial isocyanate.

Note.

The %NCO values are all within ±0.1 %. The dispenser's accuracy is within ±0.02g (21.16g dispensed) and the digital burel is within ±0.03ml. The weighing balance is within 0.005g. Oxirane retention is measured using ASTM method D- 1652-88. Because the masterbatches used in the examples contained some titratable isocyanate, the initial percent isocyanate represents a sum of all contributing components

EXAMPLE 13

Preparation of Gravity-Feedable Curative Component

The following is a procedure for forming a 400g batch of the curative component. Into a Ross mixer bowl was placed 102.96 g of Unirez 2140 (an amine curing agent from Union Camp Co.). To the bowl was added 25.35 g of 4-chlorophenol, 22.80 g of diethylenetriamine (DETA), and 25.35 g of Euredur 3251 (an amine curing agent from

Schering Berlin Polymers). The bowl was attached and the mixture was stirred and heated at 80°C for 20 minutes to obtain a homogenous mixture. To the bowl was added 42.00 g of Mistron Vapor R talc and stirring continued at five Hz. After the talc was adequately mixed, the stirring rate was increased to 30 Hz for 15 minutes. To the bowl was then added 181.52 g of ATBN 1300 x 21 rubber and mixing continued at five Hz for five minutes.

A vacuum was applied while stirring and heating in order to degas the mixture. After 15 minutes, the mixture appeared homogenous and no foaming was evident. Stirring and heating under vacuum continued for an additional 15 minutes before the vacuum pump was turned off and the stirrer was turned off and the material was bottled.

EXAMPLES 14-20 Performance of Adhesives

Examples 14-15 were prepared with variations in the epoxy component and tested with a common curative component. Examples 16-20 were prepared with variations in the curative component and tested with a common epoxy component. All percentages are by weight. The epoxy components were prepared from the following materials:

I . Desmodur W capped EPON 828/Mistron Vapor R talc masterbatch:

32.49% talc, 60.33% epoxide, 0.10% dibutyl tin diacetate, and 7.08% Desmodur W (72% of the Desmodur W used for capping at 90% of NCO demand, remainder used to dilute the masterbatch for more handleable viscosity). II. Desmodur W capped EPON 828/Beaver White talc masterbatch:

32.46% talc, 60.29% epoxide, 0.10% dibutyl tin diacetate, and 7.08% Desmodur W (72% of the Desmodur W used for capping at 90% of NCO demand, remainder used to dilute the masterbatch for more handleable viscosity).

III. Phenyl isocyanate capped EPON 828 masterbatch: 94.78% epoxide, 5.18% phenyl isocyanate, and 0.04% dibutyl tin diacetate. IV. Desmodur W

The curative components were prepared from the following materials: V. Uni-Rez 2140 (a polyamidoamine from Union Camp, Inc.)

VI. DETA (diethylene triamine)

VII. 4-chlorophenol (cure accelerator)

VIII. Euredur 3251 (a tertiary amine compound from Shering-Berlin)

IX. Hycar ATBN 1300X21 (an amine terminated rubber from B.F. Goodrich)

X . Mistron Vapor R talc (from Cyprus Minerals, Inc.)

XI. Beaver White talc (from Luzenac Corp.)

XII. Sphericel^rM Hollow Glass Spheres (from Potter Industries)

Examples 14 and 15 used the same curative component composition to evaluate various epoxy component compositions. The curative component used to evaluate the epoxy component variations in Examples 14 and 15 contained the following composition:

V = 16.08%, VI = 3.56%, VII = 4.00%. VIII = 4.00%, IX = 28.37%, X = 6.56%

Examples 16-20 used the same epoxy component compositions to evaluate various curative component compositions. The epoxy component used to evaluate the curative component variations in Examples 16-20 contained the following composition: I = 69.44%, III = 23.39%, and IV = 7.17% The compositions of Example 14 consisted of varying amounts of II, III and TV to yield three samples with 1 1.0%, 15.0%, and 19.0% Beaver White talc, respectively, all with a total of 8.0% Desmodur W from residual unreacted in II and added from IV. A portion of each of these materials was stored at ambient room temperature and a second portion of each material was stored in an oven at 40°C for about 19 weeks. The compositions of Example 15 consisted of varying amounts of I, III and

IV to yield three samples with 10.5%, 14.1% and 17.8% Mistron Vapor R talc, respectively, all with a total of 8.0% Desmodur W from residual unreacted in I and added from IV. (The talc weights are such that they yield the same volume percentage of talc as in Example 14). A portion of each of these materials was stored at ambient room temperature and a second portion of each material was stored in an oven at 40°C for about 19 weeks.

Example 16 is a mixture of V (58.3%), VI (12.9%), VII ( 14.4%), and VUI (14.4%). This mixture was combined in parts with various amounts of X so as to provide three final compositions that contained talc at 28, 31 , and 33% by weight. A portion of each material was stored at 40°C. Example 17 is a mixture of V (58.3%), VI ( 12.9%), VII ( 14.4%), and VUI

(14.4%). This mixture was combined in parts with various amounts of XI so as to provide three final compositions that contained talc at 30, 41 , and 43% by weight. A portion of each material was stored at 40°C.

Example 18 is a mixture of V (58.3%), VI ( 12.9%), VII ( 14.4%), and VUI ( 14.4%). This mixture was combined in parts with various amounts of XII so as to provide three final compositions that contained talc at 38, 41 , and 44% by weight. A portion of each material was stored at 40°C.

Example 19 is a mixture of V (58.3%), VI (12.9%), VII ( 14.4%), and Vlll ( 14.4%). This mixture was combined with IX so that the new mixture contained 50.7% of IX. This new mixture was combined in parts with various amounts of X so as to provide three final compositions that contained talc at 8, 9, and 1 1 % by weight. A portion of each material was stored at ambient room temperature and a second portion was stored at 40°C.

Example 20 is a mixture of V (58.3%). VI ( 12.9%), VII ( 14.4%), and VUI

(14.4%). This mixture was combined with IX so that the new mixture contained 50.7% of IX. This new mixture was combined in parts with various amounts of XII so as to provide three final compositions that contained hollow glass spheres at 8, 9, and 1 1 % by weight.

A portion of each material was stored at 40°C.

The adhesive strength of Examples 14-20 were evaluated using the following wedge plaque test. Wedge Plaque Test

Wedge plaques were prepared by bonding two 2 x 4 inch SMC coupons into a sandwich configuration in which adhesive is applied to only half (2 x 2 inch) of the assembly. To help maintain 2 x 4 inch bond area, half of each coupon was covered with masking tape prior to assembly. All wedge plaques were cured in a forced air oven at 300°F for 30 minutes, cooled to room temperature, then half the amount cured were also postbaked for one hour at 400°F. The samples were tested by lying them on a flat surface and prying them open with a large screwdriver either at room temperature (RT) or immediately after exposure to 180°F for 30 minutes. Sets of five lap joints were tested at RT and 180°F for both cure cycles (30 mins. at 300°F and postbake at 400°F for 1 hr.) for a total of four sets.

The results of tests of adhesive performance of Examples 14-20 are set forth in Table 3:

TABLE 3

Wedge Plaque Results for Epoxy and Curative Components

The rating of the test results is based on the percentage of the surface area of the bonded part of the plaque. The descriptors are as follows. Fiber tear failure (FT) is failure in the SMC stock such that the glass fibers of the stock are visible Cohesive failure (COH) is failure in the adhesive such that only bulk adhesive is visible Thm-layer- cohesive failure (TLC) is failure near the interface between the adhesive and the SMC stock Often TLC failure is within the "gel coating" on the surface of the SMC For SMC and other plastic bonding applications, the most prefened failure mode is FT and the least preferred failure mode is TLC

EXAMPLE 21

Isocyanate Functionality Dependence on Bead Formation Four samples with different isocyanate additives were tested two samples with monoisocyanates, one sample with a diisocyanate and one control without isocyanate The samples were shot (1 : 1 25 epoxy xurative) from a static mixing gun onto a SMC panel stnp fixed at 20° from vertical. The isocyanates were placed into capped EPON 828® without talc, hand mixed and degassed The curative component descπbed in Example 13 was used for all samples. Results are set forth in Table 4:

TABLE 4

Isocyanate Functionality Dependence on Bead Formation

Table 4 demonstrates that the isocyanate functionality of the additive is important in forming the desired bead when applying the epoxy adhesive composition to a substrate Both of the monoisocyanate samples provided results which were similar to the control containing no isocyanate In particular, the phenyl isocyanate samples contained the greatest NCO equivalence but failed to show any indication of a bead when shot. EXAMPLE 22

Gravity Feed Epoxy Adhesive An epoxide-talc composition was capped with isocyanate as follows EPON 828 (608 g), phenyl isocyanate ( 16 44 g) and dibutyl tin diacetate (0 10 g) were placed in a 1 L Ross mixei and heated with agitation at 80°C for 1 5 hours at which time no residual isocyanate was detectable Mistron Vapor R talc, 140.00 g, was added to the mixer bowl along with Desmodur W, 27.56 g. After initial mixing to yield an apparently homogeneous composition, an additional 0.45g of dibutyl tin diacetate was added in small portions over the next 30 minutes while monitoring closely for excessive foaming. The combined mixture was agitated at 80°C for a further 4.5 hours during which the residual isocyanate content leveled off at 0.21 %.

A second identical batch was prepared, but Us final isocyanate content was determined to be 0.34% The two batches were combined, heated to 60°C, mixed and degassed before use.

The tπal composition was prepared by combining 920 04 g of the above capped epoxy-talc composition and 80.05 g of Desmodur W The composition was determined to have an isocyanate content of 8.03% by titration.

For the curative component, Uni-Rez 2140 (205.8 g), diethylene tπamine (45.6 g), 4-chlorophenol (50.7 g) and Euredur 3251 (50.7 g) were combined in the bowl of a 1 L Ross mixer. The ingredients were mixed for 20 minutes before adding Hycar

ATBN 1300X21 (368.0g) and Mistron Vapor R talc (84.0 g) Mixing was continued for

1.25 hours and then degassed

A second batch was made identical to the above These two batches were combined, heated to 200°F for 15 minutes, and then agitated by rolling on ajar mill roller to assure complete mixing.

The two components were combined at a volume ratio of 1 ^■ 1.25 using a static mixer dispenser The samples were evaluated using the wedge plaque test described above, as well as the lap shear joint test described below Lap Shear Joint Test

Lap shear joints were individually made by adhering two 1 x 4 inch SMC coupons to form a one-inch overlap The coupons were then cured in a forced air oven at

300°F for 30 minutes and postbaked for 1 hour at 400°F In all cases, a 30 mil bondlme thickness was maintained by sprinkling a small amount (est 20-50) of 30 mil glass beads onto the bondlme before assembly. Lap shear strengths were tested on an Instron (model # 4204) fitted with an environmental chamber using a crosshead speed of 0.5" per minute and a gauge length of five inches. Five lap joints were tested each at room temperature and 180°F for both cure cycles (30 mins. at 300°F and postbake at 400°F for 1 hr.) for a total of four sets.

Lap shear joints and wedge plaques were prepared as previously specified as sets of five samples for each test condition. The average values and the corresponding standard deviations are reported in the following Tables 5A and 5B.

TABLE 5A

Lap Shear Strength Performance of

Gravity Feed Epoxy Adhesive

Note: Reported values are the average psi and standard deviation for a set of five plaques.

TABLE 5B

Wedge Plaque Performance of the Gravity Feed Epoxy Adhesive

The data in Tables 5A and 5B show that the ultimate bond performance of the adhesive is not negatively impacted by aging either at ambient laboratory temperatures nor negatively impacted by aging at 40°C which simulates even longer aging times at room temperature.

The foregoing examples are illustrative of the present invention, and are not to be construed as limiting thereof.

Claims

THAT WHICH IS CLAIMED:

1 . An epoxy composition comprising: an epoxy component comprising at least one epoxide and at least one isocyanate additive, said at least one epoxide having been capped with at least one capping isocyanate; and a curative component comprising at least one amine.

2. The epoxy composition of Claim 1 , wherein said at least one epoxide includes at least one hydroxyl group, and wherein said at least one hydroxyl group is capped with said at least one capping isocyanate to form a urethane linkage between said at least one epoxide and said at least one capping isocyanate.

3. The epoxy composition of Claim 1, wherein said at least one epoxide has an initial isocyanate demand prior to being capped with said at least one capping isocyanate, and wherein said at least one epoxide is capped with said at least one capping isocyanate in an amount of about 10 to about 150 percent of said initial isocyanate demand.

4. The epoxy composition of Claim 1 , wherein said at least one isocyanate additive is a polyisocyanate and said at least one capping isocyanate is a monoisocyanate.

5. A two-part epoxy adhesive composition system comprising: about 20 to about 80 percent by weight of an epoxy component comprising at least one epoxide selected from the group consisting of aliphatic, cycloaliphatic, aromatic and heterocyclic epoxides, said epoxide having been capped with at least one capping isocyanate; and at least one isocyanate additive selected from the group consisting of aliphatic, cycloaliphatic, and aromatic mono- and polyisocyanates, wherein said epoxide has an initial isocyanate demand prior to being capped with said capping isocyanate, and wherein said epoxide is capped with said capping isocyanate in an amount of about 70 to about 1 10 percent of said initial isocyanate demand; and about 80 to about 20 percent by weight of a curative component comprising at least one amine. 6 The two-part epoxy adhesive composition system of Claim 5 , wherein said at least one isocyanate additive is a polyisocyanate and said at least one capping isocyanate is a monoisocyanate

7 An epoxy component for use in an epoxy composition compπsing at least one epoxide and at least one isocyanate additive, said at least one epoxide having been capped with at least one capping isocyanate.

8 A method of making a capped epoxide comprising mixing at least one precursor epoxide having at least one hydroxyl group with at least one capping isocyanate; and subjecting said mixture to reactive conditions so that said at least one capping isocyanate reacts with said at least one hydroxyl group to form a urethane linkage between said at least one epoxide and said at least one capping isocyanate.

9 The method of Claim 8, wherein said subjecting step comprises heating the epoxide and the isocyanate mixture at a temperature between about 50°C and about 1 10°C.