RADIATION-CUREI* ADHESIVE S _Y S _TEM CONTAINING AMIDES

BACKGROUND OF THE INVENTION

Reactive acrylic adhesiveε are well known in the art, and are widely utilized due to the numerous advantageous characteristics that they exhibit. Curing of such adheεives ma be activated by various chemical initiators, and the use of actinic radiation (particularly in the ultraviolet region of th spectrum) has taken on considerable importance in recent years. Although compositions are commercially available which respond t UV and other actinic radiation to cure at high rates of speed, increased reactivity will generally be regarded to be advantageous, and will in fact be a fundamental criterion (together of course with appropriate adhesive, chemical and physical properties) for certain applications.

Accordingly, it is the broad object of the present inventio to provide a novel reactive acrylic adhesive composition that i activated by radiation and that cures at high rates of speed to produce a tough and strong solid adhesive material.

It is also an object of the invention to provide a novel method for bonding surfaces utilizing such an adhesive composition.

SUMMARY OF THE INVENTION It has now been found that certain of the foregoing and related objects of the invention are readily attained by the

provision of a liquid composition comprising a major proportion of polymerizable acrylate monomer and a filler providing elastomeric domains, an effective amount of an actinic radiation-responsive photoinitiator, and at least about 0.1 percent, by weight of the composition, of a beta-unsaturated organic amide compound. Preferably, the amide compound will be selected from the group consisting of dimethyla inopropyl methacrylamide, N,N-dimethylacrylamide, tert-butylacrylaraide, tert-butylmethacrylamide, methylmethacrylaraide, butoxymeth- acryla ide, iso-butoxymethacrylamide, cyclohexylmethacrylamide, benzylmethacrylamide, methacrylamide, isooctyl acrylamide, acrylamide, diacetone acrylamide, p-hydroxyacrylamidoaniline, N,N-methylene-bis-methac ylamide, 1,1,5,5-tetraac ylamido- pentane, and N-methylene-bis-acrylamide.

Generally, the filler employed will be a reactive acrylate polyurethane oligomer having a molecular weight of about 400 to 6000; preferably, it will be a diisocyanate-capped polyether acrylated by reaction with hydroxyethyl acrylate or methacrylate The acrylate monomer will preferably be isobornyl acrylate, hydroxyethyl methacrylate, polyethyleneglycol dimethacrylate, trirαethylcyclohexyl acrylate, and mixtures of the foregoing. Phenyl ketones, such as 1-hydroxycyclohexylphenyl ketone and 2,2-dimethoxy-2-phenyl acetophenone, will often be preferred fo use as the photoinitiator.

The usual amounts of the ingredients of the composition wil be about one to ten percent of the amide compound, about 30 to 6 percent of the monomer, about 5 to 60 percent of the filler, an about one to five percent of the photoinitiator, all based upon the weight of the composition. In preferred embodiments, the composition will additionally include about two to six weight percent of acrylic acid.

Other objects of the invention are attained by the provisio of a bonding method, in accordance with which the adhesive composition hereinabove described is applied to at least one of the surfaces to be bonded. After effecting contact between the surfaces, the composition is exposed to actinic radiation for a period of time sufficient to effect curing to an adhesive solid The curing period will normally be less than about one minute, and curing times of less than ten seconds are possible and will be highly desirable for many applications. The method of the invention may be employed to effect bonding of preassembled part between which the clearance- 'is very small, in which case a viscosity-reducing capolymerizable monomer, such as methylmethacrylate, may be incoporated into the composition. Alternatively, the composition may be used for gap-filling and coating applications, in which case the inclusion of a thixotrop or thickening agent may be beneficial.

DETAI ED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Exemplary of the efficacy of the present invention are the following examples:

Example One A series of adhesive compositions are prepared and tested; the ingredients and amounts, in parts by weight, are set forth i Table One, which follows. Cure rates are determined by applying a drop of the adhesive composition to a glass microscope slide, covering it with a second slide (in offset relationship), and applying finger pressure to distribute the adhesive (the amount of adhesive is εufficient->to cover an area of about one square inch, when spread). The assembly is held at about the focal point o.f a focused medium-pressure mercury UV lamp having a measured intensity (at the focal point) of about 100 milliwatts per square centimeter (about 30 milliwatts per square centimeter of 365 nanometer radiation), and gentle to and fro shear force i manually applied to the slides along the shear plane. The perio that elapses from initial exposure until relative movement is n longer possible is taken to be the curing time for the composition.

TABLE ONE

Formulation Deεignation

Ingredient A B C D E F G H

Oligomer 1 12 7 10 6

Oligomer 2 5 4

Oligomer 3 12 10

Oligomer 4 12 10

IBOA 13 13 13 13 13 13 13 13

HEMA 8 8 8 8 8 8 8 8

Acrylic Acid 1 1 1 1 1 1 1 1

Silane 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4

IRGACURE 651 1.6 2.6 1.6 1.6 1.6 1.6 1.6 1.6

Amide - - - — 2 2 2 2

Cure Time (Sec): 4 4 4 10 2 2 2 3

In the foregoing Table, the oligomers are all acrylated polyurethanes; oligomers "1", "3" and "4" are toluene diisocyanate-capped polypropylene glycol polyethers, acrylated b reaction with hydroxyethyl acrylate, the molecular weight of the oligomer "1" polyether backbone being about 400, and the polyethers of oligomers "2" and "4" being the successive next higher homologues; oligomer "2" is a product that is commerciall available from Mila Company. The ingredient designated "IBOA" is iεobornyl acrylate, "HEMA" is hydroxyethyl methacrylate, the silane is a typical glass adhesion promotor, IRGACURE 651 is the trade designation used by Ciba-Geigy Company for its 2,2-dimethoxy-2-phenyl acetophenone photoinitiator, and the amide employed is dimethylaminopropyl methacrylamide. As can be seen, substitution of the amide for an equal weight of the oligomer effects a reduction in the cure time values of at least fifty

percent. In all instances the physical and chemical properties of the cured adheεiveε are found to be excellent.

Example Two Substitution of an equal weight of IRGACURE 184 (Ciba-Geigy trade designation for 1—hydroxycyclohexyphenyl ketone) for the IRGACURE 651 as the catalyst iε found to provide comparable (but leεε dramatic) decreaεes in cure times, as compared to the amide-free formulationε . The times for a series of compositions into which IRGACURE 184 iε substituted, but otherwise identical to formulations E-H, are 3,3,4 and 5 seconds, respectively.

Example Three A series of compositions embodying the invention are prepared utilizing various beta-unsaturated organic amides. The formulation consistε of 15.7 parts of oligomer "1" (Table One), 39.3 parts isobornyl acrylate, 20.0 parts hydroxyethyl methacrylate, 4.0 parts IRGACURE 651, 2.5 parts of the -silane, 20.0 parts triethyleneglycol diacrylate, and 5.7 parts of the selected amide (all parts on a weight baεiε). The amides employed are: (1) dimethylaminopropyl methacrylamide (as used in Examples One and Two), (2) iεo-butoxymethacrylamide, (3) iεooctyl acrylamide, (4) acrylamide, (5) diacetone acrylamide, (6) N,N- raethylene-bis-methacrylamide, (7) 1, 1, 5, 5-tetraacrylamido- pentane, and (8) N,N-methylene-bis-acrylamide . Cure is effected

by exposure to a black light source, having a measured intensit at the bond line of about 0.1 milliwatt per square centimeter.

The formulations containing amides (1) and (3) both cure i about six seconds; the remaining formulations cure in about fiv seconds, and all of the cured adhesives exhibit excellent properties. Thus, beta-unεaturated amideε in general are seen t be effective cure accelerators in these compositions, and it wil be appreciated by those skilled in the art that any of numerous other amides may be employed to good advantage, such aε N,N- dimethyl acrylamide, tert-butylacrylamide, tert-butylmeth- acrylamide, methylmethacrylamide, butoxymethacrylamide, cyclo- hexyl methacrylamide, benzylmethacrylamide and methacrylamide.

Example Four

The adhesive composition of Example One is modified by substituting an equivalent amount of camphroquinone for the IRGACURE 651 photoinitiator employed therein, to render the composition responεive to radiation in the visible range. Results comparable to those reported above are achieved upon exposure to such light (filtered to block UV radiation) under th conditions described, with the amide-modified compositions exhibiting substantially faster cure speeds that those from whic the ingredient iε omitted.

Example Five

An adhesive composition is prepared by admixing 480 parts o an oligomer prepared by acrylatinq with HEMA a 4000 molecular

-β -

weight, toluene diisocyanate-capped polypropylene glycol polyether, 210 parts of IBOA, 70 parts HEMA, 20 parts IRGACURE 651, 12 parts maleic acid, 12 parts silane, and 1.5 parts phenolic antioxidant, all on a weight baεiε. A εecond composition is prepared from the same amountε of the same ingredients, but additionally including about 45 parts of dimethylaminopropyl methacrylamide. A quantity of each composition iε spread upon one surface of a painted, flexible steel measuring rule balde, and a strip of 5 mil Mylar film is applied over the adhesive, following which the assembly iε exposed at the focuε point of the UV radiation source described in connection with Example One. The blade is then bent back upon itself and flattened until it εnaps; the adheεive iε deemed εatiεfactory if the Mylar film simultaneously fractures, and unsatisfactory if instead delamination occurs.

Exposure of the samples for 10 seconds produces a positive (film-fracturing bond) only with the amide-containing composition; the unmodified adhesive fails after either 10 or 15 seconds exposure, and requires 20 seconds in the actinic radiation beam to produce such a result.

The acrylate monomer employed in the instant compoεitions will generally be a reaction product of acrylic acid and/or methacrylic acid with one or more mono- or polybasi , .substituted or unsubstituted, alkyl (C. to C, _β ), aryl or aralkyl alcohols. Preferred acrylateε will often be those in which the alcohol

moiety contains a polar substituent (e.g., an hydroxyl, amine, halogen, cyano, heterocyclic or cyclohexyl group), since crosslinking or other intermolecular bonding is promoted thereby General disclosure of suitable acrylic eεter onomerε are provided in the prior art, εuch aε in United States Letters Patent Nos. 3,218,305 (line 65, column 1 through line 47, colum 2); 3,425,988 (line 49, column 2 through line 21, column 3); 3,651,036 (line 69, column 1 through line 12, column 2); 3,658,624 (line 74, column 1 through line 58, column 2); 3,826,756 (line 49, column 2 through line 5, column 3); and 3,855,040 (line 20, column 3 through line 55, column 4), which portions of the foregoing specifications are hereby incorporate by reference into this specification. It is believed that the choice of appropriate ester monomers will be evident to those skilled in the art, and that further generalized description thereof will therefore be unnecessary.

Nevertheleεε, it might be pointed out that εpecific acrylateε which can advantageously be employed, alone or in combination, include (in addition to the HEMA and IBOA used in the foregoing Examples) the tetraethyleneglycol, iεodecyl and hydroxyethyl esters of acylic acid; the butyl, iεodecyl, methyl, tetrahydrofurfuryl, isobornyl, and dicyclopentadienyl esters of methacrylic acid; diacrylates, triacrylates and tetracrylates (i.e., the polyacrylic and polymethacrylic esters) of butyleneglycol, triethyleneglycol, tetraethyleneglycol,

polyethylene glycol, biεphenol A, pentaerythritol (particularly the triacrylate eεter), trimethylcyclohexyl acrylate, and the like .

Turning now more εpecifically to the filler, virtually any material that iε εoluble (to at leaεt a εignificant degree) in the monomer fraction, and that εerves to toughen, flexibilize and/or strengthen the cured adhesive, may be used. The filler need not be introduced as a rubbery solid; liquids and waxy substances are also entirely suitable. It is most desirable tha the filler be reactive with the monomeric components to produce intermolecular bonding, since that will enhance compatibility an tend to maximize the ultimate properties of the adhesive. In an event, it is believed that the effective fillers toughen or otherwiεe desirably modify the adhesive by dispersing in the momomer formulation to provide elasto eric domains; generally, they will be rubbery or elastomeric materials, thermoplastic polymers, or macromerε.

Although the εelection of εpecific appropriate elaεtomeric domain-providing fillerε will be evident to thoεe εkilled in th art, it might be mentioned that typical εuitable aterialε include vinyl poly erε, acrylic polymers, polyester elastomers, glycol polymers, acrylated epoxies, natural and synthetic rubbers, and the like. More particularly, fillers such as VINA B-7 (polyvinyl acetate sold by Airco Chemical Company) , polyethyleneglycol 6000, HYCAR CTBN and HYCAR 1022 (liquid

rubbers sold by the B. F. Goodrich Chemical Company), X-80 (polyester oligomer sold by Union Carbide Corporation), and KM-229, KM-288 and KM-323B (arylic elastomers sold by the Rohm Haas Company) are advantageously used in the formulations of th invention.

In many instances, however, the urethane polymers and prepolymers will be preferred, with the latter being especially desirable due to the potential that they afford for further reaction of their pendant iεocyanate groups with a reactive functionality (e.g., an hydroxyl group) provided by a suitable acrylate monomer. Typical specific urethane elastomers that ar advantageously used include the rubber sold by B.F. Goodrich Chemical Company under the trade designation ESTANE 5730, and th prepolymers sold respectively by Witco Chemical Company and by N L. Industries under the designations CASTOMER 0002 and VORITE. Particularly preferred are such urethaneε capped with an acryli monomer, e.g., the oligomers used in the foregoing Examples, an the polyacrylate esters of organic polyisocyanates deεcribed a "monomers" in the above-mentioned United States Letters Patent No. 3,425,988 (the portion of the discloεure thereof in column 2 line 35 through column 4, line 58 iε hereby incorporated hereint by reference). In view of all of the foregoing, however, it wil be appreciated that the selection of a particular elastomeric domain-providing filler is not critical, and that the specific material used may vary widely, depending upon the application for, and the properties desired in, the adhesive.

The amount of filler utilized will depend upon several factors, including again the properties desired in the ultimate product, the nature of the components employed, and the like. Generally, at least about five weight percent will be employed, and in the preferred compositions the filler will usually constitute about 20 to 50 weight percent.

As will be appreciated, a primary feature of the instant compositions resides in the use of the beta-unεaturated organic amide constituent, the incorporation of which has been found to produce a surprising increase in curing speed; typically, the modified adhesiveε cure 25 to 50 percent faster than the same compositions without the amide, as discussed above with reference to the Examples. It is believed that virtually any such amide that is subεtantially soluble in the formulation can be employed to good effect, be it mono- or polyfunctional, and a list of exemplary compounds has been set forth hereinabove. However, the onofunctional amldε will often provide the faεteεt cure rateε and prove to be effective in the lowest concentrations; they will therefore generally be preferred over the polyfunctional compounds. Di ethylaminopropyl methacrylamide has been found to be particularly effective, and to produce substantial decreaεeε in cure times in concentrations as low as 0.1 percent by weight of the composition.

It has also been found that virtually any compatible photoinitiator may be employed in the instant compositions, and

appropriate compounds will be evident to thoεe εkilled in the art. Nevertheleεε , it might be noted that 1-hydroxycyclo- hexylphenyl ketone, 2, 2-dimethoxy-2-phenyl acetophenone, dietho acetophenone, and 2-methyl-l-(methylethiophenyl )-2-( 4-morpho- linyl )-l-propanone can be used to good effect for responεe to actinic radiation in the UV range, and camphroquinone and suitably sensitized compositions using the above-listed photoinitiators can, for example, be employed in visible-light reactive systems; other appropriate initiators include benzo- phenone, benzil, tetramethyldiaminobenzophenone (Michler's ketone), benzoin eithers, alpha,alpha-diethoxyacetophenone and ketocoumarins . Typically, about one to five weight percent, an preferably about four percent, of the photoinitiator will be employed.

In addition to the principal components hereinabove described, it will be evident that other materials may also be incorporated into the instant compositions. For example, acryli acid, used in the amountε indicated, is ^specially desirable fro the standpoint of maximizing adhesion and curing rate; "inert" fillers, such as wood flour, glasε fiberε, cotton linterε, mica alumina, εilica, and the like, are conventionally uεed to modif viscosity, improve impact resistance, and for other purposes, a they may be employed in the instant compositions if so desired. It is also conventional to include small percentages of silane monomers to increase moisture resistance as well as to enhance

the bond strength of the adhesive to glaεε and εimilar εurfaceε. Other εubεtances, such as dyes, fire retarderε, εtabilizerε (e.g., the quinones and hydroquinones) , thixotropeε, thickenerε, viscosity reducers, plasticizerε, antioxidants, and the like, may additionally be incorporated, although it will be appreciated that such additives will often be furnished in the principal ingredients, making their separate introduction unnecessary.

Despite the fact that all of the compositions of the invention exhibit adhesive properties, it will of course be understood that they can be used for other purpoεeε aε well. For example, they may serve as coatings, for applicationε in which gap-filling iε of primary importance, etc.

Thus, it can be seen that the present invention provides a novel reactive acrylic adhesive composition that is activated by actinic radiation and that cures at high rates of speed to produce a tough and strong solid adhesive material. The invention also provides a novel method for bonding surfaceε utilizing εuch an adhesive composition.