WO1992020753A1

WO1992020753A1 - One-part primerless structural adhesive

Info

Publication number: WO1992020753A1
Application number: PCT/US1992/004280
Authority: WO
Inventors: Heimo Josef Langer; Harvey Richards; Gary Michael Carlson
Original assignee: Ashland Oil, Inc.
Priority date: 1991-05-23
Filing date: 1992-05-21
Publication date: 1992-11-26
Also published as: AU2316392A

Abstract

In its broadest aspects, the present invention is directed to a one-part adhesive that joins fibrous-reinforced composite to similar or dissimilar material wherein no priming of the composite is required. The adhesive is heat-curable and comprises the following listed ingredients: an ethylenically-unsaturated oligomeric resin; an ethylenically-unsaturated diluent free-radically reactive with said resin; a stabilizing amount of a polymerization inhibitor; an effective amount of a free-radical polymerization initiator; and filler. At least one of said resin or said diluent contains acrylic unsaturation. The method for joining the parts as well as the resulting bonded parts comprise further aspects of the present invention.

Description

ONE-PART PRIMERLESS STRUCTURAL ADHESIVE

Background of the Invention

The present invention relates to one-part structural engineering, primerless adhesives for bonding fibrous-reinforced composite (e.g. sheet molding compounds

(SMC), fiberglass reinforced polyesters (FRP), resin transfer moldings (RTM), and the like) parts to a variety of similar and dissimilar substrates which find use in the manufacture of cars, trucks, boats, and a host of other products.

Sheet molding compound (SMC), for example, is defined (ASTM) as a molding compound in integral sheet form comprising a thermosetting resin, fibrous reinforcement, and additives required for processing or product performance, e.g., resin, catalyst, thickener, mold release agent, paniculate filler, pigment, shrink control agent, etc. Fibrous reinforced polyester (FRP) comprises polyester thermosetting resins retaining fibrous reinforcement and conventional additives. These materials and others generally are known as fibrous-reinforced composites, reinforced composites, or simply composites. Typically, structural adhesives useful in adhering composite parts to the same and to different substrates are two-part polyurethane adhesives. These adhesives are made by combining a prepolymer and a curative just before use. The ratio in which these materials are combined will vary depending upon the functionality of the prepolymer and the curative. Accurate combination of the materials requires a certain skill level of the worker and, unfortunately, there is substantial waste of adhesive during the mixing process even using automatic pumping equipment.

Although primers are usually used to treat the composite substrates before applying certain adhesives it is better to eliminate the primer step if possible because primers often contain chlorinated hydrocarbons and because eliminating any single step in a multiple step process is an improvement.

Structural adhesives are used by application to the surface of a part made of, e.g. SMC, and positioning a surface of second part (of the same or different material) over the adhesively-covered SMC covered surface. Since the parts often have uneven surfaces, it is desirable that the adhesive possess the ability to fill the resulting voids of varying depth. It is important that the adhesive remain uncured and fluid for sufficient time to permit placing of the second substrate into contact with the adhesive. An adhesive which hardens too quickly does not permit flexibility in the assembly line process. Thus, the length of time the adhesive is fluid is measured and is referred to as "open time". The adhesive is cured by placing the adhered parts in an oven

SUBSTITUTE SHEET maintained at, e.g., 150° C (300° F) for, e.g., 30 minutes to cure or harden the adhesive.

A commercially useful adhesive also must exhibit a number of physical properties. The best adhesives of this type are primerless, having a long open time, cure at temperatures lower than about 150° C (300° F) and are sufficiently strong after curing that, when bonds are broken, the substrate delaminates or fails before the adhesive itself fails. If such an adhesive requiring 150° C (300° F) cure could be replaced by an equivalently performing adhesive which required curing at only 116° C (240° F), such a lower temperature curing adhesive would save energy during the heat cure cycle and also permit lower temperature bake cycles in subsequent steps of the automobile assembly line procedure, e.g., when the adhesively-joined parts are painted.

Adhesives formulated of acrylic components and cured by free-radical polymerization have been used for many years, but such adhesives have been provided in two packages or parts (a so-called two-part adhesive) due to the reactivity of the initiator and acrylic molecules which results in insufficient open time for it to be provided in a single package [see Skeist, Handbook of Adhesives, Third Edition, p. 448, Van Nostrand Reinhold, New York, New York (1990)]. Acrylic adhesives in general offer excellent physical characteristics, so that it would be desirable to perfect a one-part acrylic structural adhesive.

The most preferred adhesives for SMC parts should be curable at about 116° C (240° F) and should exhibit a failure of the substrate at 82.2° C (180° F) when force is applied to separate the adhered parts. When the adhesive itself fractures, the result is called "cohesive failure" (CF). When the adhesive releases from the SMC surface, the result is called "adhesive failure" (AF). When the substrate itself breaks, the result is called "delamination" (DL). When an adhesive is said to have exhibited 100% substrate delamination, the entire broken interface between adhesive and substrates shows only the torn fibers and disrupted structure of the substrate itself.

Broad Statement of the Invention

In its broadest aspects, the present invention is directed to a one-part adhesive that joins fibrous-reinforced composite to similar or dissimilar material wherein no priming of the composite is required. The adhesive is heat-curable and comprises the following listed ingredients: an ethylenically-unsaturated oligomeric resin; an ethylenically-unsaturated diluent free-radically reactive with said resin; a stabilizing amount of a polymerization inhibitor; an effective amount of a free-radical polymerization initiator, and filler. At least one of said resin or said diluent contains

SUBSTITUTE SHEET acrylic unsaturation. The method for joining the parts as well as the resulting bonded parts comprise further aspects of the present invention.

In one embodiment of the present invention, the primerless, one-part structural engineering adhesive composition formulated to be stable at room temperature for up to about three months and is curable aerobically at about 116° C (240° F). After curing, the adhesive delaminates the SMC substrate when subjected to a lap shear test at 82.2° C (180° F) in accordance with ASTM method D1002. Such adhesive preferably is applied at thicknesses of greater than about 20 mils wet, and often at least about 30 mils wet on up to at least about 400 mils wet.. Such formulated adhesive comprises a vinyl urethane oligomer resin, an unsaturated allylic diluent, a quinone type free-radical inhibitor, a peroxide free-radical initiator, and one or more fillers. The vinyl urethane oligomer resin component of such adhesive can be made by reacting a prepolymer prepared by reacting a polyol of about 250-6000 molecular weight with a polyisocyanate, followed by further reaction of said prepolymer with a hydroxyl alkyl acrylate or a hydroxyl alkyl methacrylate.

Advantages of the present invention include a structural adhesive that is formulated in a single package or part. Another advantage is a structural adhesive whose performance does not mandate that the composite surface be primed, i.e. a primerless structural adhesive. A further advantage is a structural adhesive that possesses sufficient integrity such that the substrate to which it is applied delaminates rather than the adhesive itself failing. Yet another advantage is a structural adhesive that readily cures in the presence of air. These and other advantages will be readily apparent to those skilled in this art based upon the disclosure contained herein.

Detailed Description of the Invention

The first ingredient of the inventive adhesive is an ethylenically-unsaturated polymer or oligomer which can be cured in the presence of free radicals which are generated from the free-radical initiator in the adhesive. This unsaturated polymer can include, for example, acrylated urethanes, acrylated epoxies, vinyl terminated butadiene nitrile (VTBN) resins, unsaturated polyester resins, vinyl modified acrylic resins, or any other polymeric or oligomeric material having ethylenic unsaturation which is capable of copolymerizing free radically with the diluent and optional other components in the adhesive.

The term vinyl is used to denote any terminally unsaturated material having the structure:

CH₂ = C(R^*)— R

SUBSTITUTE SHEET where the R' can be either H or methyl. If the R group is chosen to be -C(0)-0-R" and the R' group is an H atom, then the unsaturated group is known as an acrylic group. If the R' group is methyl and the R group is -C(O)-O-R", then the unsaturated group is a methacrylic group. Typical R groups include, for example, alkyl, cycloalkyl, aromatic, or benzylic groups, optionally substituted with heteroatoms. If R^* is -H and R is -CH₂-R", then the unsaturation is allylic, and methallylic if R' is methyl. By convention, the parentheticals used herein designate optional content, i.e. (meth)acrylate means "acrylate" or "methacrylate", and the same is true for the parenthetical plurals used herein. Acrylated urethane resins can be prepared by capping a polyol with an equivalent excess of polyisocyanate and then reacting the remaining isocyanate with an unsaturated species having a hydroxyl group. The molar ratio of isocyanate to polyol can be selected to give chain extension of the polyol. The ratio also can be chosen such that excess unreacted isocyanate is present after the capping reaction. The polyols used can be difunctional or can include polyfunctional polyols such as triols, tetraols or mixtures of polyols of varying functionality. Polyols used can include polyether polyols, including, for example, poly(propylene oxide), poly(tetramethylene oxide), poly(ethylene oxide), ethylene oxide capped polyφropylene oxide), and the like and mixtures thereof. The polyol additionally can be a polyester polyol such as, for example, polycaprolactone, poly(ethylene adipate), poly(propylene adipate), poly(butylene adipate), or any other polyester having the proper structure to provide the desired performance. Further, the polyol can be based on a polycarbonate polyol.

The molecular weight of the polyol can range from about 62 to 8000, and is chosen to provide the proper balance of properties in the final adhesive. A lower molecular weight polyol provides higher modulus and lower elongation, while a higher molecular weight polyol provides a lower modulus and higher elongation.

The polyisocyanate used to prepare the acrylated urethane resin can be chosen from a wide variety of aromatic, aliphatic, or cycloaliphatic isocyanates having, on average, two or more isocyanate groups per molecule. These polyisocyanates include, for example, methylene diphenyl isocyanate (MDI), toluene diisocyanate (TDI), xylylene diisocyanate (XDI), polyphenylene diisocyanates available commercially as, for example, Mondur MR or Mondur MRS, isophorone diisocyanate (IPDI), hydrogenated methylene diphenyl isocyanate (HMDI), tetramethyl xylene diisocyanate (TMXDI), hexamethylene diisocyanate (HDI), or oligomer materials of these materials such as a trimer of IPDI, HDI or a biuret of HDI, and the like and mixtures thereof.

SUBSTITUTE SHEET The unsaturated hydroxyl-containing species also can be selected from a wide range of materials which have at least one hydroxyl group and at least one free- radically polymerizable unsaturated group per molecule on average. These species include, for example, hydroxyethyl acrylate (HEA), hydroxyethyl methacrylate (HEMA), butanediol monoacrylate (BDMA), acrylated poly(caprolactone) available commercially from Union Carbide as Tone M-100; mono-, di-, and triallyl ethers of trimethylolpropane; and the like and mixtures thereof. Where excess unreacted isocyanate is present, the hydroxyl species will react with the excess isocyanate to form a low molecular weight adduct which, in some instances, can improve the performance of the final adhesive.

The unsaturated oligomer or polymer includes, for example, vinyl ester resins which are the reaction products of epoxy resins with acrylic or methacrylic acids. The epoxy resin used can be based on the diglycidyl ether of Bisphenol A (e.g. Epon 826 of Shell Chemical Company ) or higher oligomers of these resins (e.g. Epon 1001). The process for making these materials is well known to those skilled in the art.

Similarly, the unsaturated oligomer or polymer can include a vinyl terminated butadiene nitrile resin (VTBN) resin available commercially from B.F. Goodrich. These materials also are well known in the formulation of adhesives and provide good impact resistance and toughness to the product. It also is possible to prepare vinyl modified acrylic resins by reacting acid- containing acrylic polymers with epoxy-containing unsaturated materials such as, for example, glycidyl acrylate or glycidyl methacrylate. Likewise, hydroxyl-containing acrylic polymers can be reacted with an isocyanate-containing unsaturated material such as, for example, isocyanato ethyl methacrylate (IEM). These materials will have the vinyl functionality attached randomly along the backbone of the acrylic polymer.

Unsaturated polyesters additionally can be used in the present invention.

These materials are synthesized, for example, by reacting maleic anhydride or a mixture of maleic anhydride and other diacids with a diol or a mixture of diols. The mixture is heated in the presence of a catalyst to temperatures sufficient to remove the water formed in the condensation reaction. These materials have molecular weights of , for example, about 1,000-100,000, and have the free-radically polymerizable unsaturated groups present in the polymer backbone.

The next ingredient of the inventive adhesive is a reactive diluent having at least one ethylenically-unsaturated group per molecule on average which is reactive with the ethylenical unsaturation of the resin. The diluent also serves to reduce the viscosity of the ethylenically-unsaturated resin, and, thus, serves as a solvent in the adhesive. Low molecular weight unsaturated materials that are compatible with the unsaturated resin and which adequately disperse the resin are suitable. By properly

Si

E SHEST choosing the nature of the diluent or diluents, it also is possible to fine tune the physical properties of the final cured adhesive to meet commercial requirements. Commonly, blends of mono-, di-, and tri-functional diluents are chosen to provide the proper balance of properties. The diluent can be chosen from a wide range of unsaturated, for example,

(meth)allylic materials having at least one (meth)allylic group per molecule, but in many cases containing two or more (meth)allylic groups per molecule. Commonly used (meth)allylic diluents include, for example, allylic diluents such as diallyl phthalate, diallyl adipate, allyl alcohol, allyl glycidyl ether, triallyl ether of trimethylol propane, diallyl ether of trimethylolpropane, monoallyl ether of trimethylolpropane, triallyl isocyanurate, and the like and mixtures thereof.

The unsaturated diluent also can be chosen from a wide range of (meth)acrylic materials having at least one (meth)acrylic group per molecule on average, but in many cases containing two or more (meth)acrylic groups per molecule including, for example, methyl, ethyl, propyl, butyl, hexyl, cyclohexyl, octyl, decyl, dodecyl, lauryl, phenoxyethyl, isobornyl, trimethylcyclohexyl, or any other unsaturated (meth)acrylic species. (Meth)acrylic diluents also include polyfunctional (meth)acrylics such as, for example, ethylene glycol di(methacrylate), butanediol di(meth)acrylate, hexanediol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, ethoxylated trimethylolpropane tri(meth)acrylate, and the like and mixtures thereof.

The diluent additionally can be chosen from a variety of vinyl containing species. Vinyl diluents include, for example, styrene, vinyl toluene, vinyl laurate, vinyl benzyl chloride, and the like and mixtures thereof.

For enhancing adhesive performance in the rigorous SMC automobile use of the inventive adhesive composition, it is believed important to balance the amount of allylic-type functionality. The allylic material appears to help provide the stability at ambient temperature needed for a one-part adhesive and also appears to help balance the properties of the final product. Presently, it is believed important that at least about 10 percent of the equivalents of unsaturation present in the inventive adhesive composition be allylic or methallylic groups. The remaining 90 percent of the equivalents of unsaturation can be either allylic, methallylic, acrylic, methacrylic, or vinyl unsaturation. If the unsaturated resin does not provide allylic unsaturation the diluent must provide enough allylic functionality to meet the 10% minimum requirement. If the vinyl unsaturated resin contains enough allylic functionality to provide the 10% equivalents in the final formulation, it may be possible to use only acrylic or methacrylic diluents.

A key feature of the invention is the ability to provide a one-part or package adhesive stable at ambient temperatures for a period of time sufficient for the material s

ui SHE to be prepared, packaged, shipped, stored, and applied for the bonding of parts. When heated, the adhesive then must cure rapidly and provide a structural bond between a variety of substrates, at least one of which is a fibrous-reinforced composite substrate. A balance between shelf stability and cure speed is achieved by controlling the levels and types of free-radical initiators and inhibitors included in the adhesive formulation. The presence of an inhibitor is particularly important since these adhesives must be stable when packaged in the absence of oxygen, a very effective inhibitor of free-radical polymerization.

The free-radical initiator can be chosen from a wide variety of well-known initiators including, for example, peroxides, peroxyketals, percarbonates, and azo compounds, which decompose at a sufficient rate at the cure temperature to provide a satisfactory cure during the heating cycle. The initiator can be one or a combination of materials such as, for example, t-amyl perbenzoate, t-butyl perbenzoate, methyl ethyl ketone peroxide, benzoyl peroxide, and the like and mixtures thereof. The choice of peroxide is dependent on the bake schedule and the level of peroxide is dependent on the level and type of inhibitor used. Typical initiator levels are as low as about 0.5 wt-% up to about 5 wt-% of the final adhesive formulation.

The free-radical inhibitor likewise can be chosen from a wide range of well- known inhibitors which are active in the absence of oxygen. These can include quinones such as, for example, hydroquinone, benzoquinone, and napthoquinone, and other inhibitors such as, for example, phenothiazine, and the like and mixtures thereof. The concentration of the inhibitor is chosen such that the stability of the adhesive is sufficient at ambient temperature, while the cure speed is still adequate to provide a structural bond following the bake schedule. The amount of inhibitor required is dependent on the type and level of initiator with typical concentrations ranging from about 200 to 5,000 ppm by weight of the total final adhesive.

Fillers are needed in the adhesive to help maintain viscosity, improve sag resistance, and provide reinforcement to the final cured material, as well as reduce the final cost of the product. Useful fillers include, for example, talc, mica, clay, calcium carbonate, any of the alkaline earth inorganic salts, metals such as powdered aluminum or iron, metal oxides such as ferric oxide or aluminum oxide, silica, ceramic beads such as those available under the trademark Zeeospheres from Zeelan Industries, Inc., or any other filler (and mixtures thereof) well-known to those skilled in the art of formulating adhesives. The adhesive of the present invention is particularly well adapted for use on a variety of fibrous-reinforced composites, including, for example, fiberglass- reinforced polyester substrates (FRP) and sheet molding compound (SMC) substrates. FRP substrates typically are made from the reaction product of

SUBSTITUTE SH ir - dipropylene glycol, maleic anhydride, high molecular weight polyvinyl acetate, styrene, peroxide polymerization initiator, and fillers. Among the fiberglass reinforced polyester substrates useful in the practice of this invention are those provided by GenCorp, Marion, Indiana (GC-7113, GC-8002 and GC-7101 substrates), Rockwell International Corporation, Centralia, Illinois (RW 9468 Substrate), Budd Company, Madison Heights, Michigan (DSM 950 Substrate) and Eagle Hcher Plastics, Grabill, Indiana (EP SLI-233-1 Substrate). Car and truck body parts made of sheet molding compound (SMC) also are adhered using structural urethane adhesives and can now be adhered using the one-part acrylic adhesive of this invention.

The inventive adhesive is adaptable for use on a variety of other plastics such as reaction injection molding (RIM) polyurethanes, acrylonitrile-butadiene-styrene (ABS) terpolymers, styrene acrylonitrile copolymers (SAN), thermoplastic polyolefins (TPO), and thermoplastic alloys such as, for example, polycarbonate- polyester blends and polycarbonate-ABS blends. Among the useful fibers used in reinforcing the substrates are fiberglass, graphite, and polymeric fibers, e.g. polyamide fiber.

The adhesive composition is formulated by simple blending, often under high shear conditions, of the ingredients. For SMC uses, the adhesive composition preferably is applied by extrusion techniques by robot-application through a follower plate, though it may be applied by conventional roller coating, both direct and indirect, spray application, dip application, or any application technique that is necessary, desirable, or convenient. No priming of the composite is required when using the inventive adhesive. The parts then are joined under pressure and subjected to baking at a temperature as low as about 116° C for times ranging from about 10 to 120 minutes.

The following Examples show how the present invention has been practiced, but they should not be construed as limiting. In this application, all proportions and percentages are by weight and all units are in the metric system, unless otherwise expressly indicated. Also, all citations are expressly incorporated herein by reference.

IN THE EXAMPLES

I. General synthesis procedure for a vinyl urethane polymer, specifically an acrylated urethane polymer.

A prepolymer is prepared by reacting a calculated amount of a polyisocyanate at 50°± 3" C with a calculated amount of polyol or mixtures of polyols in the presence of a standard urethane catalyst. When this reaction is complete, as

SUEST.TUTE _SHEET predetermined by NCO titration, a calculated amount of hydroxy-alkyl acrylate is added to cap the remaining isocyanate. The temperature then is raised to 60° ± 2° C to complete the reaction. Throughout the reaction a sparge of dry air is used to prevent acrylic polymerization. An unsaturated diluent, e.g. diallyl phthalate (DAP) may be used to decrease the viscosity. An appropriate inhibitor is added to the reaction when about 98% of the isocyanate has been converted. The product is collected at about 99% isocyanate conversion.

II. Hydroxyethyl acrylate-capped prepolymer of isophorone diisocyanate (IPDI) and a 4,000 molecular weight polypropylene glycol. (Reference C4853-128.)

To a clean, dry 2-liter reactor equipped with an agitator, temperature control for heating and cooling, sparge tube for dry air, and addition funnel, was charged IPDI (669.6 g.) and dibutyl tin dilaurate urethane catalyst (3.19 g.). The dry air sparge rate was set at 75 mlJmin. and the reactor contents heated to 50° C. Over a 45 minute period, a polypropylene glycol having a hydroxyl number of 27.0 (3,117.0 g.) was added to the reactor. After completion of the polyol addition, an unsaturated diluent, diallyl phthalate (220.4 g.), was added to reduce the viscosity. The temperature was controlled at 50° ± 3° C during this addition and reaction. After completion of the pre-polymer formation, the dry air sparge rate was increased to 150 mlJmin. Hydroxyethyl acrylate (617.8 g.) was added over a 12 minute interval and the reaction temperature was increased to 60° ± 2° C. The reaction was maintained under these conditions for about 3 hours whereupon the NCO value was determined to be 0.26% NCO. The inhibitor, hydroquinone monomethyl ether (0.88 g.), then was added to the reactor and the reaction continued for an additional 1.5 hours. The acrylated urethane product was canned out at a final NCO value of 0.14% NCO.

III. Composition for similarly prepared acrylated urethanes

Reference IPDI DBTDL DAP Polvol* HEA Inhib. * Polvol Type

C4753-176 290.2 1.34 0 1350.8 267.7 0.38 MEHQ 4000 MW Poly¬ propylene glycol)

C4753-186 385.0 1.30 185.4 1124.1 157.9 0.33 BQ lOOO MW Poly-

(tetramethylene glycol)

SN1031R 32.7 0.154 10.50 146.9 30.20 0.042 MEHQ 4000 MW Poly- (propylene glycol) Deflnitions: IPDI - isophorone diisocyanate DBTDL - dibutyl tin dilaurate DAP • diallyl phthalate HEA - hydroxyethyl acrylate MEHQ • hydroquinone monomethyl ether BQ ■ para-benzoquinone

IV. Procedure for preparation of Adhesive Formulations.

Initially, the resin is charged into an uncovered 1-liter resin kettle. , Next, the diluents and inhibitor are added to the kettle. Then, slowly begin agitating the mixture with a high shear blade using an air powered stirrer. The components are mixed to form a homogeneous solution. During the entire process, the temperature of the mixture must be kept below 50° C with a water bath. The thixotrope is added in portions. When the thixotrope addition is completed, it is dispersed with the mixing blade set at 3000 rpm for 15 minutes. The filler then is added in portions. When the filler addition is complete, the mixture is mixed under shear conditions at 3000 rpm for 10 minutes. The mixture then is cooled to between 25° and 30° C with the water bath. The initiator next is added and the mixture stirred at 500 rpm for 5 minutes. The kettle is covered, the lid clamped, and the stirrer restarted at a low speed, i.e.500 rpm. A vacuum then is applied to the adhesive to remove any air. A vacuum equivalent to 36 ± 13 mm of Hg is applied for 30 minutes. At the end of the deaeration procedure, the disperser blade is removed under vacuum and the stirring stopped. Air is bled into the system, the cover removed, and the sample withdrawn.

EXAMPLE 1 This example shows the use of a vinyl urethane resin based on polypropylene glycol. An adhesive was prepared using the following ingredients.

SUBSTITUTE SHEET

*t-APB tert-amyl perbenzoate. TS-720 is hydrophobic fumed silica, Cabot Corp. DAP is diallyl phthalate. BQ is para-benzoquinone.

Lap shear bonds having 30 mils of adhesive between SMC substrates were then heated for 1 hour at 121.1° C (250° F) and the bonds tested to produce the following results.

Test Temperature Strength (psi Failure Mode

Room Temperature 594 Delamination 82.2° C (180"F) 488 Delamination

This adhesive also has good impact resistance as shown by the following side impact data. Test Temperature Strength (in-lb) Failure Mode

Room Temperature 60 Delamination -29.9° C (-22T) 60 Delamination

Lap shear bonds having 9 mm of adhesive between SMC substrates were tested after curing at 121.1° C (250° F) for one hour and produced the following results.

Test Temperature Strength (psi) Failure Mode

Room Temperature 197

82.2° C (180°F) 148 Delamination

The impact resistance of this adhesive when used at a thickness of 9 mm also was excellent as the following data reveals.

^*U^' Έ Test Temperature Strength (in-lb Failure Mode

Room Temperature 60 in-lb Delamination -29.9° C (-22T. 51 in-lb Delam/Cohesive

EXAMPLE 2 An adhesive was prepared using the following ingredients, where the ability to use a vinyl urethane resin based on polytetramethylene oxide diol as the backbone polymer is demonstrated.

In redient* Amount wt- arts

*t-APB tert-amyl perbenzoate. TS-720 is hydrophobic fumed silica, Cabot Corp. Photomer 4149 is trimethylolpropane ethoxylate triacrylate, Henkel

Corp.

DAP is diallyl phthalate. BQ is para-benzoquinone.

for one hour at 121.1° C (250°F) and the bonds tested to produce the following results.

Test Temperature Strength (psi) Failure Mode

Room Temperature 565 Delamination 82.2° C Q80°F) 401 Delamination

This adhesive also had good impact resistance as shown by the following side impact data.

Test Temperature Strength (in-lb) Failure Mode

Room Temperature 60 Delamination: -29.9° C (-22T. 60 Delamination EXAMPLE m

Lap shear bonds having 30 mils of adhesive between SMC substrates were heated for 1 hour at 121.1° C (250°F) and the bonds tested to produce the following results.

Test Temperature Strength (psi) Failure Mode

Room Temperature 560 Delamination 82.2° C Q80°F 503 Delamination

This example shows the ability to use a vinyl urethane resin based on polypropylene glycol prepared with no diallyl phthalate diluent. This adhesive, then, has no allylic functionality.and shows the ability of an all acrylic system to provide good bond strength and failure mode. An adhesive was prepared using the following ingredients.

SUBSTITUTE SHEET

*MFM-413 is triethylene glycol dimethylacrylate available from Rohm-Tech. t-APB tert-amyl perbenzoate. TS-720 is hydrophobic fumed silica, Cabot Corp. BQ is para-benzoquinone.

Test Temperature Strength (psi) Failure Mode

Room Temperature 561 Delamination 82.2° C (180° F) 425 Delam/Adhesive Failure

Test Temperature Strength (in-lb) Failure Mode

Room Temperature 60 Delamination -29.9° C (-22°F) 60 Delamination

EXAMPLE V An adhesive was prepared using the following ingredients showing the ability to use a commercially available resin (Ebecryl 8804 is an aUphatic urethane diacrylate oligomer, Hi-Tek Polymers).

*t-BPB tert-butyl perbenzoate. TS-720 is hydrophobic fumed silica, Cabot Corp. DAP is diallyl phthalate. BQ is para-benzoquinone.

Lap shear bonds having 30 mils of adhesive between SMC substrates were fixture cured for 3 minutes and postbaked for 30 minutes at 149° C (300°F), and the bonds tested to give the following results.

Test Temperature Strength (psi) Failure Mode

Room Temperature 488 Delamination 82.2° C ISO'F) 489 Delam/Adhesive Failure

EXAMPLE VI An adhesive prepared using the following ingredients showing the ability to use a commercially available resin (Ebecryl 6700 is an aromatic urethane diacrylate oligomer, Hi-Tek Polymers).

In redient* Amount (wt- arts)

*Mhoromer BM-504 is a mono-functional acrylic monomer available commercially from Rohm-Tech. t-BPB tert-butyl perbenzoate. TS-720 is hydrophobic fumed silica, Cabot Corp. DAP is diallyl phthalate.

BQ is para-benzoquinone.

SUBSTITUTE SHEET Lap shear bonds having 30 mils of adhesive between SMC substrates were fixture cured for 3 minutes and postbaked for 30 minutes at 149° C (300°F), and the bonds tested to produce the following results.

Test Temperature Strength (psi) Failure Mode

Room Temperature 518 Delamination 82.2° C (180°F) 404 Delam Adhesive Failure

Claims

We claim:

1. A method for adhesively joining two parts, one of which comprises a fibrous-reinforced composite part, with a layer of a heat-curable adhesive, which comprises:

(a) applying to a surface of one said parts a layer of a heat-curable adhesive which comprises:

(1) a free-radically reactive, ethylenically-unsaturated polymeric resin; (2) an ethylenically-unsaturated diluent free-radically reactive with said resin;

(3) a stabilizing amount of a free-radical polymerization inhibitor;

(4) an effective amount of a free-radical polymerization initiator; and (5) filler, at least one of said resin or said diluent containing (meth)acrylic unsaturation;

(b) joining the other part to said adhesively applied part, said composite part being unprimed;

(c) heat-curing said joined parts.

2. The method of claim 1 wherein said adhesive is applied at a thickness of greater than about 0.5 mm.

3. The method of claim 2 wherein said adhesive is applied at a thickness of greater than about 3 mm.

4. The method of claim 1 wherein said polymeric resin contains acrylic or methacrylic unsaturation.

5. The method of claim 1 wherein said diluent contains acrylic unsaturation.

6. The method of claim 1 wherein said diluent contains allylic or methallyli unsaturation.

7. The method of claim 1 wherein said polymeric resin is selected from the group consisting of a vinyl urethane resin, an acrylated urethane resin, an

SUBST^ITUTE SHBE" acrylated epoxy resin, a vinyl-terminated butadiene nitrile resin, an unsaturated polyester resin, a vinyl modified acrylic resin, and mixtures thereof.

8. The method of claim 7 wherein said resin comprises a vinyl urethane resin made by preparing a prepolymer by reacting a polyol of about 62 to 8,000 molecular weight with an excess of a polyisocyanate, and then by further reacting said prepolymer with a hydroxyl-containing free-radically polymerizable ethylenically- unsaturated compound.

9. The method of claim 1 wherein said diluent is selected from the group consisting of: an alkyl (meth)acrylate, an alkyl-aryl (meth)acrylate, ethylene glycol di(meth)acrylate, butanediol di(meth)acrylate, hexanediol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, ethoxylated trimethylolpropane tri(meth)acτylate, styrene, vinyl toluene, vinyl laurate, vinyl benzyl chloride, diallyl phthalate, diallyl adipate, allyl alcohol, allyl glycidyl ether, triallyl ether of trimethylol propane, diallyl ether of trimethylolpropane, monoallyl ether of trimethylolpropane, triallyl isocyanurate, and mixtures thereof.

10. The method of claim 1 wherein at least about 10% equivalents of unsaturation in said adhesive comprises allylic or methallylic unsaturation.

11. The method of claim 1 wherein said free-radical inhibitor is selected from the group of a quinone or phenothiazine.

12. The method of claim 1 wherein the proportion of said free-radical inhibitor ranges from about 200 to 5,000 ppm by weight.

13. The method of claim 11 wherein said inhibitor is selected from hydroquinone, benzoquinone, napthoquinone, and mixtures thereof.

14. The method of claim 1 wherein said free-radical initiator is present in a proportion of between about 0.5 wt-% and 5 wt-%.

15. The method of claim 1 wherein said initiator is selected from a peroxide, a peroxyketal, a percarbonate, an azo compound, and mixtures thereof.

SUBSTITUTE SHEET

16. The method of claim 15 wherein said initiator is selected from t-amyl perbenzoate, t-butyl perbenzoate, methyl ethyl ketone peroxide, benzoyl peroxide, and mixtures thereof.

17. The method of claim 1 wherein the proportion of filler ranges from about 1 to 50 wt-%.

18. The method of claim 1 wherein said filler is selected from talc, mica, a clay, calcium carbonate, an alkaline earth metal salt, a powdered metal or metal oxide, a ceramic bead, and mixtures thereof.

19. The method of claim 1 wherein said composite is selected from a reaction injection molding part, a sheet molding part, a polyurethane part, an acrylonitrile-butadiene- styrene terpolymer (ABS) part, a styrene acrylonitrile polymeric part, a thermoplastic olefin part, a polycarbonate-polyester blend, a polycarbonate-ABS part, and a polyester part.

20. The method of claim 1 wherein said reinforcement of said composite is selected from glass fiber, graphite fiber, polymeric fiber, and mixtures thereof.

21. The method of claim 1 wherein said heat-curing is at a temperature not substantially above about 121° C.

22. The method of claim 1 wherein said adhesive applied comprises: (a) a (meth)acrylic polymeric resin;

(b) an allylic or methallylic diluent;

(c) a quinone free-radical inhibitor;

(d) a peroxide free-radical initiator,

(e) a filler.

23 The method of claim 1 wherein said adhesive is stable at room temperature for at least about 3 months.

24. A heat-curable, one-part adhesive which comprises a mixture of the following ingredients:

(a) a free-radically reactive, ethylenically-unsaturated polymeric resin;

(b) a (meth)allylic diluent free-radically reactive with said resin;

(c) a stabilizing amount of a free-radical polymerization inhibitor,

SUBSTITUTE SHEFT (d) an effective amount of a free-radical polymerization initiator, and

(e) filler, the heat-curable ingredients consisting essentially of ingredients (a) and (b).

25. The adhesive of claim 24 wherein said polymeric resin contains acrylic or methacrylic unsaturation.

26. The adhesive of claim 24 wherein said polymeric resin is selected from the group consisting of a vinyl urethane resin, an acrylated urethane resin, an acrylated epoxy resin, a vinyl-terminated butadiene nitrile resin, an unsaturated polyester resin, a vinyl modified acrylic resin, and mixtures thereof.

27. The adhesive of claim 26 wherein said resin comprises a vinyl urethane resin made by preparing a prepolymer by reacting a polyol of about 62 to 8,000 molecular weight with an excess of a polyisocyanate, and then by further reacting said prepolymer with a hydroxyl-containing free-radically polymerizable ethylenically-unsaturated compound.

28. The adhesive of claim 24 wherein said diluent is selected from the group consisting of: an diallyl phthalate, diallyl adipate, allyl alcohol, allyl glycidyl ether, triallyl ether of trimethylol propane, diallyl ether of trimethylolpropane, monoallyl ether of trimethylolpropane, triallyl isocyanurate, and mixtures thereof.

29. The adhesive of claim 24 wherein said free-radical inhibitor is selected from the group of a quinone or phenothiazine.

30. The adhesive of claim 24 wherein the proportion of said free-radical inhibitor ranges from about 200 to 5,000 ppm by weight.

31. The adhesive of claim 29 wherein said inhibitor is selected from hydroquinone, benzoquinone, napthoquinone, and mixtures thereof.

32. The adhesive of claim 24 wherein said free-radical initiator is present in a proportion of between about 0.5 wt-% and 5 wt-%.

33. The adhesive of claim 24 wherein said initiator is selected from a peroxide, a peroxyketal, a percarbonate, an azo compound, and mixtures thereof.

SUBSTITUTE SHEET

34. The adhesive of claim 33 wherein said initiator is selected from t-amyl perbenzoate, t-butyl perbenzoate, methyl ethyl ketone peroxide, benzoyl peroxide, and mixtures thereof .

35. The adhesive of claim 24 wherein the proportion of filler ranges from about 1 to 60 wt-%.

36. The adhesive of claim 24 wherein said filler is selected from talc, mica, a clay, calcium carbonate, an alkaline earth metal salt, a powdered metal or metal oxide, a ceramic bead, and mixtures thereof.

AMENDED CLAIMS

[received by the International Bureau on 27 October 1992 (27.10.92) ; original claims 1-36 replaced by amended claims 1-34 (4 pages) ]

1. In a method for adhesively joining two parts, one of which comprises a fibrous-reinforced composite part, with a layer of a heat-curable adhesive, wherein a layer of heat-curable adhesive is applied to a surface of one of said parts, the other

5 part is joined to said adhesive layer on said surface, and the joined parts heated cured, the improvement characterized by:

(a) the heat-curable adhesive applied to said surface comprising:

(1) a free-radically reactive, ethylenically-unsaturated polymeric resin;

(2) a (meth)allylic diluent free-radically reactive with said resin; (3) a stabilizing amount of a free-radical polymerization inhibitor,

(4) an effective amount of a free-radical polymerization initiator; and

(5) filler, and

(b) said composite part being unprimed.

5. The method of claim 1 wherein said polymeric resin is selected from the group consisting of a vinyl urethane resin, an (meth)acrylated urethane resin, an

(meth)acrylated epoxy resin, a vinyl-terrninated butadiene nitrile resin, an unsaturated polyester resin, a vinyl modified (meth)acrylic resin, and mixtures thereof.

6. The method of claim 5 wherein said resin comprises a vinyl urethane resin made by preparing a prepolymer by reacting a polyol of about 62 to 8,000 molecular weight with an excess of a polyisocyanate, and then by further reacting said prepolymer with a hydroxyl-containing free-radically polymerizable ethylenically- unsaturated compound.

7. The method of claim 1 wherein said diluent is selected from the group consisting of: allyl alcohol, allyl glycidyl ether, triallyl ether of trimethylol propane, diallyl ether of trimethylolpropane, monoallyl ether of trimethylolpropane, triallyl isocyanurate, and mixtures thereof. 8. The method of claim 1 wherein at least about 10% equivalents of unsaturation in said adhesive comprises allylic or methallylic unsaturation.

9. The method of claim 1 wherein said free-radical inhibitor is selected from the group of a quinone or phenothiazine.

10. The method of claim 1 wherein the proportion of said free-radical inhibitor ranges from about 200 to 5,000 ppm by weight.

11. The method of claim 9 wherein said inhibitor is selected from hydroquinone, benzoquinone, napthoquinone, and mixtures thereof.

12. The method of claim 1 wherein said free-radical initiator is present in a proportion of between about 0.5 wt-% and 5 wt-%.

13. The method of claim 1 wherein said initiator is selected from a peroxide, a peroxyketal, a percarbonate, an azo compound, and mixtures thereof.

14. The method of claim 13 wherein said initiator is selected from t-amyl perbenzoate, t-butyl perbenzoate, methyl ethyl ketone peroxide, benzoyl peroxide, and mixtures thereof.

15. The method of claim 1 wherein the proportion of filler ranges from about 1 to 60 wt-%.

16. The method of claim 1 wherein said filler is selected from talc, mica, a clay, calcium carbonate, an alkaline earth metal salt, a powdered metal or metal oxide, a ceramic bead, and mixtures thereof.

17. The method of claim 1 wherein said composite is selected from a reaction injection molding part, a sheet molding part, a polyurethane part, an aery lonitrile-butadiene- styrene terpolymer (ABS) part, a styrene acrylonitrile polymeric part, a thermoplastic olefin part, a polycarbonate-polyester blend, a polycarbonate-ABS part, and a polyester part.

18. The method of claim 1 wherein said reinforcement of said composite is selected from glass fiber, graphite fiber, polymeric fiber, and mixtures thereof. 19. The method of claim 1 wherein said heat-curing is at a temperature not substantially above about 116° C.

20. The method of claim 1 wherein said adhesive applied comprises:

(a) a (meth)acrylated polymeric resin;

(b) an allylic or methallylic diluent;

(c) a quinone free-radical inhibitor,

(d) a peroxide free-radical initiator,

(e) a filler.

21 The method of claim 1 wherein said adhesive is stable at room temperature for at least about 3 months.

22. In a heat-curable, one-part adhesive of a mixture of the following ingredients:

(a) a free-radically reactive, ethylenically-unsaturated polymeric resin;

(b) a diluent free-radically reactive with said resin;

(c) a stabilizing amount of a free-radical polymerization inhibitor,

(d) an effective amount of a free-radical polymerization initiator, and (e) filler, the improvement characterized by the heat-curable ingredients consisting essentially of ingredients (a) and (b),wherein said diluent (b) is a (meth)allylic diluent free-radically reactive with said resin.

23. The adhesive of claim 22 wherein said polymeric resin contains acrylic or methacrylic unsaturation.

24. The adhesive of claim 22 wherein said polymeric resin is selected from the group consisting of a vinyl urethane resin, a (meth)acrylated urethane resin, an (meth)acrylated epoxy resin, a vinyl-terminated butadiene nitrile resin, an unsaturated polyester resin, a vinyl modified (meth)acrylic resin, and mixtures thereof.

25. The adhesive of claim 22 wherein said resin comprises a vinyl urethane resin made by preparing a prepolymer by reacting a polyol of about 62 to 8,000 molecular weight with an excess of a polyisocyanate, and then by further reacting said prepolymer with a hydroxyl-containing free-radically polymerizable ethylenically-unsaturated compound. 26. The adhesive of claim 24 wherein said diluent is selected from the group consisting of: an diallyl phthalate, diallyl adipate, allyl alcohol, allyl glycidyl ether, triallyl ether of trimethylol propane, diallyl ether of trimethylolpropane, monoallyl ether of trimethylolpropane, triallyl isocyanurate, and mixtures thereof.

27. The adhesive of claim 26 wherein said free-radical inhibitor is selected from the group of a quinone or phenothiazine.

28. The adhesive of claim 26 wherein the proportion of said free-radical inhibitor ranges from about 200 to 5,000 ppm by weight.

29. The adhesive of claim 27 wherein said inhibitor is selected from hydroquinone, benzoquinone, napthoquinone, and mixtures thereof.

30. The adhesive of claim 22 wherein said free-radical initiator is present in a proportion of between about 0.5 wt-% and 5 wt-%.

31. The adhesive of claim 22 wherein said initiator is selected from a peroxide, a peroxyketal, a percarbonate, an azo compound, and mixtures thereof.

32. The adhesive of claim 31 wherein said initiator is selected from t-amyl perbenzoate, t-butyl perbenzoate, methyl ethyl ketone peroxide, benzoyl peroxide, and mixtures thereof.

33. The adhesive of claim 22 wherein the proportion of filler ranges from about 1 to 60 wt-%.

34. The adhesive of claim 22 wherein said filler is selected from talc, mica, a clay, calcium carbonate, an alkaline earth metal salt, a powdered metal or metal oxide, a ceramic bead, and mixtures thereof.

STATEMENT UNDER ARΗC E 19

Submitted herewith are substitute pages 17-21, inclusive, wherein claims 1-36 have been revised and reduced in number to claims 1-34. Additionally, the reduction in the number of claims has necessitated the renumbering of the Abstract page.

Specifically, independent claims 1 and 23 have been recast in Jepson style in order to facilitate their review internationally. Additionally, the diluent component has been restricted to be a "(meth)allylic diluent", as such preferred diluent is discussed in the first full paragraph on page 3 of the international application. These amendments necessitated the cancellation of claims 5 and 6, which resulted in page 21 being blank. Accordingly, a new Abstract, renumbered to page 21 also is submitted herewith.

It is noted that Brenner, U.S. Pat. No. 4,049,750, cited in the international search report relates to an anaerobic adhesive which requires an accelerator, which component is not required nor disclosed in the PCT application under consideration. It is noted further that Brenner proposes acrylated epoxies, whereas the preferred resin in the PCT application are vinyl urethanes. Finally, and most importantly, Brenner does not disclose adhesively joining two parts, one of which is a composite part which is unprimed.