COLOR CHANGING TWO-PART SYSTEM AND METHOD OF DETERMINING THE CURING OF AN ADHESIVE

Abstract: A two-part system wherein the first part includes (i) at least one curable component; (ii) at least one reducing agent; and (iii) at least one initially colorless color change additive and the second part includes a peroxide oxidizing agent. When the first and second parts are mixed, the resulting curing material turns a color that is different than the initial color of the first and second parts individually. This color change can be used to indicate working time for the material.

Description: COLOR CHANGING TWO-PART SYSTEM AND METHOD OF DETERMINING THE CURING OF AN ADHESIVE Background of the Invention The present invention relates to a two-part curable system that undergoes a color change during curing. Two-part curable systems, such as two-part adhesives, in which curing of the system does not occur until two distinct compositions or parts are mixed together are well known. An example of such a two-part system is a system that includes (1) a curable component such as an ethylenically unsaturated compound and (2) a redox catalyst system that includes a peroxide. A common problem with such systems is that it can be difficult to determine when curing is complete. A further problem is determining whether the two parts have been thoroughly mixed together. It would be very advantageous to a user of such two-part systems if there was a simple way to determine complete mixing and curing. US-A-3,773,706 relates to the use of phenosafranin with crosslinkable synthetic organic polymer resins as a visible degree-of-cure indicator. US-A-4, 155,950 relates to a two-part adhesive composition whose one part consists of a non-acid methacrylic or acrylic monomer, a methacrylic or acrylic monomer, and a peroxy catalyst and whose other part consists of an activator to activate the peroxy catalyst wherein the activator has the structure wherein R=H or phenyl, a=0 or 1, a+b=3 and when R is phenyl, a is 1. US-A-4, 164,492 relates to a method for determining the degree of cure of two part polyester and epoxy resins that includes adding a methyl derivative of azobenzene 4-azo-2 naphthol pigment to one part, mixing the two parts together and curing the mixture until the color disappears. US-A-4,775,727 relates to an acrylic adhesive composition that includes a curing accelerator that is a reactive dye that has a structure that includes at least two tertiary nitrogen atoms linked by one or more conjugated double bonds. The only examples of dyes given are methylene blue and crystal violet. There is no mention of any color change occurring when the acrylic adhesive cures. US-A-4 ,780,393 relates to a photopolymerizable composition that includes a polymeric binder, an ethylenically unsaturated polymerizable compound, a photoinitiator, a leuco base of a triarylmethane dye and a particular type of a photochromatic spiro- indolinobenzopyran compound. The composition is useful for photoresists, printing plates and other recording mediums. Benzophenone, thioxanthone, benzoin and their derivatives are listed as possible photoinitiators. Upon exposure to light the composition exhibits color corresponding to the leuco dye that is present. US-A-5,302,627 relates to a UV-curable acrylic adhesive system that includes a dye with a visible color that changes color or disappears when exposed to UV light. Summary of the Invention According to the present invention there is provided a two-part system wherein the first parts comprises: (i) at least one curable component; (ii) at least one reducing agent; and (iii) at least one color change additive having a structure represented by wherein R 1 is individually H or OH; R 2 is individually H, phenyl, C,-C 8 alkyl or R 3 is individually H, C,-C 8 alkyl or hydroxy C,-C 8 alkyl; and a and b are each 0 or 1, provided a+b=l or 2; and the second part comprises a peroxide oxidizing agent. According to a further embodiment of the invention the color change additive has a structure represented by wherein R 4 is individually H, phenyl, C,-C 8 alkyl or hydroxy C,-C 8 alkyl; R 5 is individually H, C,-C 8 alkyl or hydroxy C,-C 8 alkyl; and a and b are each 0 or 1 , provided a+b=l or 2. There also is provided according to the invention a method for determining working time of a two-part curable system, the method comprising contacting a first part that includes a color change additive and at least one curable component and a second part that includes a peroxide oxidizing agent so that the resulting composition begins to assume a color that is different than the initial color of the first and second parts individually; monitoring the resulting composition for cessation of the color change; and applying the resulting composition to a substrate prior to the cessation of the color change. Detailed Description of the Preferred Embodiments The color changing two-part system of the invention can be useful in an adhesive formulation, particularly a structural adhesive used in the bonding of lightweight metal and plastic materials in the fabrication, repair and reconstruction of transportation vehicle bodies and component parts. In typical applications, the two parts of the system are mixed together, the mixed material is applied to a first substrate for bonding, then the second substrate is contacted to the adhesive-applied first substrate. Such mixing, applying and contacting is referred to herein as "working" the adhesive. Of course, the mixed material must be applied and the second substrate contacted prior to final cure of the adhesive. The color changing two-part system also can be useful in body putty or filler formulations. These fillers are used, for example, to repair voids, scratches, chips, dents and the like in body panels of transportation vehicles. In this instance, working of the material involves applying it to the repair area and then shaping the material prior to final cure. Regardless of the specific use of the material, the time from mixing the two parts to final cure is referred to herein as "working time". As used herein, "color" means a color that can be seen under ordinary visible light other than white or off-white. As used herein, "color change" means formation of a color (other than white or off-white) different than the color of the first part or second part of the system individually and different than the color of a mixed or cured system that does not include a color change additive. For example, the formed color could be red, green, blue, violet, yellow, orange or various shades thereof. The color change additive by itself is colorless under ordinary visible light and is included in the first part of the system that includes the curable component. The color of the first part by itself is not changed permanently with the addition of the color change additive. However, after the color change additive-containing first part is contacted, preferably by mixing, with the peroxide-containing second part of the two-part system the color change additive begins to impart a visible color to the resulting material. If the color change does not begin to occur uniformly throughout the material, the two parts have not been mixed together thoroughly and thus mixing should continue or be reinitiated. The complete color change or final color is achieved when the material is completely cured or at a short time before the system is completely cured. Achievement of the final color can be determined by monitoring the material until it is no longer undergoing any more color change or by comparing the color of the material to a separate color chart or indicator. Preferably, the monitoring can simply be performed by visually observing the mixed material. By monitoring the changing color of the mixed material the person using the material can determine how much working time remains for the material. In other words, once the final color has been achieved the material can no longer be worked. A unique advantage is that the system can be adjusted to achieve final color a short time before cure is complete. This adjustment can be accomplished by varying the amount of the color change additive. In this instance, the user of the material is given a warning that curing is reaching completion and thus there is limited time available for continued working of the material. All of the color change additives useful in the present invention are also referred to as latent dyes. Latent dyes are colorless substances that can undergo a chemical reaction under certain conditions resulting in a strongly colored substance. Consequently, it should be recognized that the color change additive of the invention does not include visible light- colored dyes such as methylene blue, crystal violet or malachite green. According to one embodiment, illustrative color change additives have a structure represented by wherein R is individually H or OH; R is individually H, phenyl, C,-C 8 alkyl or R 3 is individually H, C,-C 8 alkyl or hydroxy C C 8 alkyl; and a and b are each 0 or 1, provided a+b=l or 2. Preferably, R 1 is individually H or OH, R 2 is individually H, phenyl or R 3 is individually H or hydroxy C,-C 8 alkyl; and a and b are each 1. Preferred color change additives of the first embodiment include leuco crystal violet, leuco malachite green, N,N,N',N'-tetramethyl(methylene dianiline), N,N,N',N'-tetraisopropanol(methylene dianiline), and 4,4'-bis(dimethylamino)benzhydrol. According to a second embodiment, illustrative color change additives have a structure represented by « R4 > N O N(R5) -ΛO>— ( N (R4 2 wherein R 4 is individually H, phenyl, C,-C 8 alkyl or hydroxy C,-C 8 alkyl; R 5 is individually H, C,-C 8 alkyl or hydroxy C,-C 8 alkyl; and a and b are each 0 or 1, provided a+b=l or 2. Preferably, R 4 is individually H, phenyl or hydroxy C r C 8 alkyl; and R 5 is individually H or hydroxy C,-C 8 alkyl. Preferred color change additives of the second embodiment include triisopropanol-p-aminodiphenyl amine and diphenyl phenylene diamine. More than one color change additive of either embodiment can be present in the first part in order to achieve a blended final color. The amount of the color change additive is only required to be sufficient to show a visible color change upon curing of the system. The first part should include 0.01 to 1.0, preferably 0.03 to 0.1 , weight percent of the color change additive(s), based on the total weight of all components of the first part individually (i.e., including other components in addition to the curable component and the reducing agent). Of course, dyes and pigments can be added to the system despite the presence of the color change additive if desired provided that these are selected so as to not interfere with the color change additive. For example, it may be desirable to provide either part of the two part system with a certain color prior to mixing or it may be desirable to modify the final color of the adhesive. The color change additive can be used in any curable system that also includes a polymerizable or curable component such as an ethylenically unsaturated compound. It is particularly useful in free radical polymerizable or curable systems, such as described in U.S. Patents Nos. 2,981,650; 3,321,351; 3,890,407; 4,223,115; 4,293,665; 4,467,071; 4,452,944; 4,536,546; 5,206,288 and 4,769,419, all incorporated herein by reference. Such free radical polymerizable systems include a curable component that includes at least one free radical polymerizable ethylenically unsaturated monomer characterized by the presence of a -C=C- group, polymer derived from such monomer or mixtures of monomer and polymer. (Meth)acrylic-based monomers and/or polymers derived from (meth)acrylic-based monomers are particularly useful as at least part of the polymerizable component. As used herein, "(meth)acrylic-based compound" means a monomer of acrylic acid, methacrylic acid or an amide, ester, salt or nitrile thereof or a polymer derived from such monomer. Representative (meth)acrylic-based monomers include, but are not limited to, methyl methacrylate, ethyl methacrylate, butyl methacrylate, methyl acrylate, butyl acrylate, cyclohexyl acrylate, hexyl acrylate, 2-ethylhexyl acrylate, lauryl acrylate, ethyl acrylate, diethylene glycol dimethacrylate, dicyclopentadienyloxyethyl methacrylate, 2-ethylhexyl methacrylate, hexyl methacrylate, cyclohexyl methacrylate, lauryl methacrylate, tetrahydrofuryl methacrylate, methacrylic acid, acrylic acid, acrylonitrile, methacrylonitrile, glycidyl methacrylate, cyanoacrylate, acrylamide and methacrylamide. Other ethylenically unsaturated monomer classes include maleate esters; fumerate esters; vinyl esters such as vinyl acetate; conjugated dienes such as 2,3-dichloro-l,3- butadiene and 2-chloro-l,3-butadiene; itaconic acid and esters thereof; styrene; substituted styrenes such as chlorostyrene, methylstyrene, butylstyrene and vinyl styrene; and vinylidene halides. Preferred free radical polymerizable monomers are methyl methacrylate and tetrahydrofuryl methacrylate. The polymerizable component typically is present in the composition in an amount from 10 to 90, preferably 20 to 70, weight percent based on the total weight of all components of the first part of the system. Particularly in the instance of an adhesive composition, the polymerizable composition of the invention can also include at least one polymeric material, preferably an elastomer, which can act as a toughening agent to provide improved impact and shatter resistance to the cured adhesive and to decrease the brittleness of the cured adhesive. The polymeric material may or may not include an ethylenically unsaturated structure that is capable of being polymerized per se or copolymerized with at least one of the ethylenically unsaturated monomers described above. The polymeric material can be, for example, polychloroprene as described in U.S. Patent No. 2,981,650; a polymer-in-monomer syrup as described in U.S. Patents Nos. 3,725,504 and 4,223,115; various solid and liquid elastomeric polymeric materials (e.g., butadiene-based elastomers and urethane-modified butadiene-based elastomers as described in U.S. Patents Nos. 4,223,115; 4,452,944 and 4,769,419); chlorosulfonated polyethylene rubbers and or a mixture of sulfonyl chloride with chlorinated polyethylene as described in U.S. Patents Nos. 3,890,407, 5,206,288 and 4,536,546; and olefinic urethane reaction products of an isocyanate-functional prepolymer and a hydroxy-functional monomer, as described in U.S. Patents Nos. 4,223,115; 4,452,944; 4,467,071; and 4,769,419. Such elastomers can be present in the compositions of the invention in amounts from 10 to 80, preferably 20 to 50, weight percent based on the total weight of the first part of the system. Polymer-in-monomer syrups are well known in the art. The monomer can be any of the ethylenically unsaturated monomers described above. The monomer of the polymer- in-monomer syrup can itself serve as the polymerizable component of the composition or a pre-formed polymer-in-monomer syrup can be mixed with an ethylenically unsaturated monomer. Exemplary polymer-in-monomer syrups are described in U.S. Patents Nos. 3,725,504 and 4,223,115. Representative liquid olefinic-terminated elastomers include homopolymers of butadiene; copolymers of butadiene and at least one monomer copolymerizable therewith, for example, styrene, acrylonitrile, methacrylonitrile; as well as modified elastomeric polymeric materials, such as butadiene homopolymers and copolymers as noted above modified by copolymerization therewith of trace amounts or up to about 5 percent by weight of the elastomeric material of at least one functional monomer (such as acrylic acid, methacrylic acid, maleic anhydride, fumaric acid, styrene and methyl methacrylate). The secondary hydroxyl group of liquid butadiene-based elastomers can be reacted with an isocyanate to form a liquid urethane-modified butadiene elastomer as described in U.S. Patent No. 4,769,419. Other useful elastomers include a homopolymer or copolymer of epichlorohydrin and ethylene oxide and copolymers of ethylene and acrylate esters, such as methyl acrylate and ethyl acrylate, wherein the copolymer contains at least 30 weight percent acrylate ester that are available from E.I. duPont under the tradename VAMAC. The chlorosulfonated polyethylene and sulfonyl chloride/chlorinated polyethylene mixture embodiments can have a chlorine content of 25 to 67 weight percent and 3 to 160 mmols sulfonyl chloride moiety per 100 grams of polymer. Further, the polyethylene from which the chlorosulfonated polyethylene is made preferably has a melt index of 4 to 500. A particularly preferred adhesive system is an ambient temperature-curable structural adhesive that includes (a) 10-90, preferably 20-70, weight percent of an ethylenically unsaturated monomer selected from the group consisting of (meth)acrylic acid; esters, amides or nitriles of (meth)acrylic acid; maleate esters; fumerate esters; vinyl esters; conjugated dienes; itaconic acid and esters thereof; styrene; substituted styrenes and vinylidene halides; (b) 10-80, preferably 20-50, weight percent of a diene-based elastomer; (c) 0-40, preferably 1-25, weight percent of an olefinic urethane reaction product of an isocyanate-functional prepolymer and a hydroxy-functional monomer having at least one unit of polymerizable unsaturation, such reaction product being characterized by the presence of at least two units of unsaturation and the substantial absence of free isocyanate products; (d) 0-20, preferably 2-10, weight percent of a phosphorus-containing compound having one or more olefinic groups and no less than one P-OH group; (e) an ambient temperature-active catalyst system that includes at least one reducing agent and at least one oxidizing agent that are co-reactive at ambient temperature to generate free radicals that are capable of initiating and propagating the cure of said adhesive composition; and (f) a color change additive, wherein the weight percents are based on the total weight of components (a)-(d). As described above, the free radical-polymerizable adhesive compositions of the invention are normally provided as two-part or package systems, with the parts being mixed or contacted at the time of use to provide a free radical curing adhesive. In more detail, these two-part systems can include (I) a first part comprising (a) 10-90, preferably 20-70, weight percent of an ethylenically unsaturated monomer selected from the group consisting of (meth)acrylic acid; esters, amides or nitriles of (meth)acrylic acid; maleate esters; fumerate esters; vinyl esters; conjugated dienes; itaconic acid and esters thereof; styrene; substituted styrenes; and vinylidene halides; (b) 10-80, preferably 20-50, weight percent of a diene-based elastomer; (c) 0-40, preferably 1-25, weight percent of an olefinic urethane reaction product of an isocyanate-functional prepolymer and a hydroxy-functional monomer having at least one unit of polymerizable unsaturation, such reaction product being characterized by the presence of at least two units of unsaturation and the substantial absence of free isocyanate products; (d) 0-20, preferably 2-10, weight percent of a phosphorus-containing compound having one or more olefinic groups and no less than one P-OH group (e) 0.05-10, preferably 0.1-6, weight percent of at least one reducing agent which is interactive with a peroxide oxidizing agent to produce free radicals which are capable of initiating and propagating free radical polymerization reactions; (f) less than 1.0, preferably less than 0.1 , weight percent of the color change additive, wherein the weight percents are based on the total amount of the first part; and (II) a second part comprising a bonding activator containing a peroxide oxidizing agent of a room temperature-active redox couple catalyst system, the peroxide oxidizing agent being reactive at room temperature with agent (e) when the first and second parts are mixed to produce free radicals which are capable of initiating and propagating free radical polymerization, the amount of the peroxide oxidizing agent being sufficient to interact with agent (e). The isocyanate-functional prepolymers which are suitable for producing the olefinic urethane reaction product are well-known. Typically, such prepolymers are adducts or condensation products of polyisocyanate compounds having at least two free isocyanate groups and monomeric or polymeric polyols having at least two hydroxy groups, including mixtures of such polyols. The reaction between the polyisocyanate and the polyols is effected employing an excess amount of polyisocyanate to ensure that the isocyanate- functional prepolymer will contain at least two free, unreacted isocyanate groups. Polyols useful in preparing the isocyanate-functional prepolymer preferably have an number average molecular weight of from about 50 to about 3,000. Suitable polyols include polyalkylene glycols such as polyethylene glycols; polyetherpolyols such as those prepared by additional polymerization of ethylene oxide and a polyol such as trimethylol propane; organic hydroxylated elastomers exhibiting glass transition temperatures below about 5°C such as poly(butadiene-styrene) polyols and poly(butadiene) polyols; polyester polyols such as are prepared by polymerizing polyols such as diethylene glycol, trimethylol propane or 1 ,4-butanediol with polycarboxylic acids such as phthalic, terephthalic, adipic, maleic or succinic acids, in a ratio to provide unreacted hydroxyl groups in the product; glyceride esters of hydroxylated fatty acids such as castor oil, glycerol monoricinoleate, blown linseed oil and blown soya oil; and polyester polyols such as are prepared by the polymerization of a lactone such as epsilon caprolactone. Polyisocyanates which can be reacted with polyols to form isocyanate-functional prepolymers can be any isocyanate compound having at least two free isocyanate groups, including aliphatic, cycloaliphatic and aromatic compounds. Representative isocyanates include, without limitation, 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, 4,4'- diphenylmethane diisocyanate, m- and p-phenylene diisocyanate, polymethylene poly(phenyl isocyanate), hexamethylene diisocyanate, 4,4'-methylenebis(cyclohexyl isocyanate), isophorone diisocyanate, and other aliphatic, heterocyclic and aromatic polyisocyanates, and including mixtures of such polyisocyanates. Currently, cycloaliphatic and aromatic polyisocyanates are preferred. Hydroxyl-functional monomers that can be reacted with the isocyanate-functional prepolymer to provide unsaturation in the olefinic urethane reaction product include, without limitation, hydroxyethyl acrylate, hydroxyethyl methacrylate, and allyl alcohol. Phosphorus-containing compounds that enhance metal adhesion as well as slow cure rate can be any derivative of phosphinic acid, phosphonic acid or phosphoric acid having at least one P — OH group and at least one organic moiety characterized by the presence of an olefinic group, which is preferably terminally located. A listing of such phosphorus compounds is found in U.S. Patent No. 4,223,115. However, an advantage of the present invention is that a less expensive vinyl aromatic compound can be substituted for a portion or all of the more-expensive phosphorus-containing compound. If a phosphorus-containing compound is still desirable for enhanced metal adhesion, a preferred phosphorus-containing compound has a structure that may be represented by the formula O II II (CH 2 =C-C-O-A) m P(OR21) 2 . m R20 I OH wherein R 20 is selected from the group consisting of hydrogen, an alkyl group having from one to 8, preferably one to 4, carbon atoms, and CH 2 =CH — ; R 21 is selected from the group consisting of hydrogen, an alkyl group having from one to 8, preferably one to 4 carbon atoms; A is selected from the group consisting of — R 22 O — and (R 23 O) n , wherein R 22 is an aliphatic or cycloaliphatic alkylene group containing from one to 9, preferably 2 to 6, carbon atoms; R 23 is an alkylene group having from one to 7, preferably 2 to 4, carbon atoms; n is an integer from 2 to 10, and m is one or 2, preferably one. Phosphorous-containing compounds having vinyl unsaturation are preferred over such compounds having allylic unsaturation, with monoesters of phosphinic, phosphonic and phosphoric acids having one unit of vinyl or allylic, especially vinyl, unsaturation presently being preferred. Representative phosphorus-containing compounds include, without limitation, 2-hydroxyethyl methacrylate phosphate; bis-(2-methacryloyloxyethyl) phosphate; 2-acryloyloxyethyl phosphate; bis-(2-acryloyloxyethyl) phosphate; methyl-(2- methacryloyloxyethyl) phosphate; ethyl methacryloyloxyethyl phosphate; methyl acryloyloxyethyl phosphate; ethyl acryloyloxyethyl phosphate; compounds of the above formula wherein R 8 is hydrogen or methyl and R 9 is propyl, isobutyl, ethylhexyl, halopropyl, haloisobutyl or haloethylhexyl; vinyl phosphonic acid; cyclohexene-3- phosphonic acid; alpha-hydroxybutene-2 phosphonic acid; 1 -hydroxy- 1-phenylmethane- 1,1-diphosphonic acid; 1 -hydroxy- 1 -methyl- 1-diphosphonic acid: 1-amino-l phenyl- 1,1- diphosphonic acid; 3-amino-l-hydroxypropane-l,l-diphosphonic acid; amino- tris(methylenephosphonic acid); gamma-amino-propylphosphonic acid; gamma- glycidoxypropylphosphonic acid; phosphoric acid-mono-2-aminoethyl ester; allyl phosphonic acid; allyl phosphinic acid; β-methacryloyloxyethyl phosphinic acid; diallylphosphinic acid; β-methacryloyloxyethyl) phosphinic acid and allyl methacryloyloxyethyl phosphinic acid. The compositions of the invention can also contain from 0 to about 10 percent by weight based on the total weight of the composition of at least one unsaturated polyester resin. Such resin esters are derived from polycarboxylic acids and polyhydric alcohols, preferably dicarboxylic acids and dihydric alcohols, with at least one of the acid and alcohol components being unsaturated. Preferably, the unsaturated polyester resin component will contain a relatively large number of double bonds and be derived from short chain aliphatic polyhydric polyols, such as ethylene glycol and 1,3-propylene glycol, and short chain unsaturated polybasic acids, such as fumaric acid and maleic acid. Such resins can contain quantities of longer chain polyols such as 1 ,6-hexanediol, as well as higher polybasic acids, such as adipic acid and phthalic acid. Still further, the compositions of the invention can optionally contain from 0 to about 50 percent by weight based on the total weight of the composition of at least one polyvinyl alkyl ether. Polyvinyl alkyl ethers are well-known in the art. Such ethers will preferably contain 1-8, more preferably 1-4, carbon atoms in the alkyl moiety of the ether. The compositions of the invention can also include up to about 60, preferably not more than about 30, percent by weight based on the total weight of the composition of a pre-formed polymeric component (in addition to the polymeric materials listed above) having an intrinsic viscosity of 0.1 to 1.3 that are obtained by the polymerization of at least one (meth)acrylic, styrene, substituted (meth)acrylic and non-acrylic olefinic monomers. Exemplary additional pre-formed polymeric materials include poly(methyl methacrylate/n- butylacry late/ethyl acrylate) (90/5/5); poly (n-butyl methacrylate/isobutyl methacrylate) (50/50); poly (n-butyl methacrylate) and poly (ethyl methacrylate). The preferred composition can optionally include 0 to 40, preferably 0 to 20 weight percent, based on the total weight of the composition, of an epoxy component that can be any monomeric or polymeric compound or mixture of compounds having an average of greater than one 1,2-epoxy groups per molecule. The polymeric epoxide materials can have a number-average molecular weight of 300 to 10,000. Useful epoxy compounds are well-known and include the polyglycidyl ethers of polyhydric alcohols such as ethylene glycol, triethylene glycol, 1 ,2-propylene glycol, 1,5-pentanediol, 1,2,6-hexanetriol, glycerol and 2,2-bis(4-hydroxy-cyclohexyl) propane; the polyglycidyl esters of aliphatic or aromatic polycarboxylic acids such as oxalic acid, succinic acid, glutaric acid, terephthalic acid, 2,6-naphthalene dicarboxylic acid and dimerized linolenic acid; the polyglycidyl ethers of polyphenols such as bisphenol A, l,l-bis(4-hydroxyphenyl)ethane, 1,1- bis(hydroxyphenyl)isobutane, 2,2-bis(4-hydroxy-t-butylphenyl)propane, 1 ,5- dihydroxynaphthalene and novolak resins; and cycloaliphatic polyglycidyl compounds. Another optional component is up to 1 percent by weight of a waxy substance selected from the group consisting of paraffin wax, beeswax, ceresin wax and spermaceti wax. The environmental resistance of an adhesive system made from the composition of the invention can be improved by the optional addition of 0.005 to 15, preferably 0.1 to 10, percent by weight, based on the total weight of components (a)-(f), of a mixture of a metal molybdate such as zinc molybdate, calcium molybdate, barium molybdate and/or strontium molybdate and an inert filler such as zinc phosphate, calcium phosphate, magnesium phosphate and/or calcium carbonate. Such mixtures are more fully described in U.S. Patent No. 4,017,315. The compositions can also optionally include polybasic lead salts of phosphorus acid and saturated and unsaturated organic dicarboxylic acids and acid anhydrides, particularly dibasic lead phthalate, monohydrous tribasic lead maleate, tetrabasic lead fumarate, dibasic lead phosphite and mixtures thereof; and zinc oxide, in an amount of about 0.1 to about 15, preferably about 1 to about 10, percent by weight, based on the total weight of the composition. These compounds can be effective in improving environmental resistance. The ambient temperature-reactive catalyst systems that may be employed are well- known redox couple systems. Basically, such systems comprise at least one oxidizing agent and at least one reducing agent which are co-reactive at room temperature to generate free radicals effective to initiate addition polymerization reactions and cure the adhesive. The oxidizing agent (also known as free radical generator) should be a peroxide. The peroxide should not be in the same part of the system as the color change additive. Representative peroxides include, without limitation, organic peroxides, such as benzoyl peroxide, dicumyl peroxide and other diacyl peroxides, hydroperoxides such as cumene hydroperoxide and tertiary butyl hydroperoxide, peresters such as β-butylperoxybenzoate and tertiary butyl peroxide acetate, and ketone hydroperoxides such as methyl ethyl ketone hydroperoxide. Representative reducing agents (also known as initiators or accelerators) include, without limitation, sulfinic acids; alpha-aminosulfones such as bis(tolysulfonmethyl)- benzyl amine; tertiary amines such as diisopropyl-p-toluidine, dimethyl aniline and dimethyl-p-toluidine; and aminealdehyde condensation products, for example, the condensation products of aliphatic aldehydes such as butyraldehyde with primary amines such as aniline or butylamine. It should be recognized that the tertiary amines useful as reducing agents in the invention are chemically different than, and do not include, the color change additives. The use of known promoters (such as an organic salt of a transition metal, such as cobalt, nickel, manganese or iron naphthenate, copper octoate, copper acetylacetonate, iron hexoate or iron propionate) with the redox couple catalyst systems can be advantageous. Preferably, the amount of reducing agent is in the range from about 0.05 to about 10, preferably about 0.1 to about 6, percent by weight of the first part that includes the curable component. The amount of the reducing agent should be greater than the amount of the color change additive. The second part can include a bonding activator that includes the peroxide oxidizing agent for the redox catalyst system. The bonding activator can include: (1) from about 0.5 to about 50 percent by weight, based on total weight of bonding activator, of at least one peroxide oxidizing agent which can function as an oxidant of a redox couple catalyst system; and (2) from about 30 to about 99.5 percent by weight, based on total weight of bonding activator, of a carrier vehicle. In addition, the bonding activator also can contain either the epoxy component or the phosphorus-containing compound. The carrier vehicles which are suitable for use in the bonding activators can be a simple inert solvent or diluent such as methylene chloride, or butyl benzyl phthalate, including mixtures of such solvents or diluents. The carrier vehicle should contain no more than 5% by weight of any moiety which is reactive with the oxidizing agent at room temperature. The carrier vehicle can be a more complex mixture including at least one film- forming binder in addition to inert solvent or diluent. In this case, the film-forming binder is preferably substantially inert with respect to the oxidant which is present in the accelerator composition. A particularly preferred carrier vehicle comprising at least one film-forming binder is an admixture comprising from about 0.05 to about 50 percent by weight of, (1), at least one saturated organic polymeric film-forming binder having a glass transition temperature in the range from about 0° C to about 150° C. or, (2), at least one polymer-in-monomer syrup as described herein; and from about 40 to about 99 percent by weight of at least one organic solvent capable of maintaining the film-forming binder, phosphorus-containing compound when incorporated into the bonding activator composition, and oxidizing agent as a stable solution or dispersion. Among the polymeric film-forming binder materials that can be employed in the carrier vehicle are, without limitation, polyalkylacrylates and methacrylates and copolymers thereof, polystyrene and copolymers thereof, vinyl polymers and copolymers, polyesters, polyketones, polysulfones, phenolic resins, polyvinyl butyrals and polycarbonates. The carrier vehicle can contain, in addition to solvent or solvent and film-forming binder, additives such as external plasticizers, flexibilizers, suspenders and stabilizers, providing that any such additives do not unacceptably adversely affect the stability of the activator composition. Another optional component is 0.01 to 10, preferably 0.5 to 5, percent by weight, based on the total weight of components (a)-(f), of tertiary amines represented by the structure wherein Z is methylene; Y is selected from the group consisting of hydrogen, hydroxy, amino, halogen, alkyl having 1 to 8, preferably 1 to 4, carbon atoms, and alkoxy having 1 to 8, preferably 1 to 4, carbon atoms; a is 0 or 1 ; and b is 1 or 2. This tertiary amine is advantageous in accelerating the cure of such compositions containing the unsaturated organophosphorus compounds. Especially preferred tertiary amines are N,N-dimethyl aniline and N,N-dimethylaminomethylphenol. The components of the composition are mixed together by means well known in the art. The catalyst, of course, is not activated until curing of the composition is desired. Examples of the invention are described below in more detail. EXAMPLE 1 Versilok® 406 is a commercially available adhesive from Lord Corporation that includes methacrylate monomer and diisopropyl-p-toluidine as a reducing agent. To lOO g of Versilok® 406 adhesive is added 0.10 g of N,N,N',N'-tetramethyl(methylene dianiline) (commercially available from Sigma Aldrich Chem.) to form the first part of the adhesive system. The first part is mixed in a 4: 1 volume ratio with Accelerator 19, a benzoyl peroxide oxidizing agent commercially available from Lord Corporation. Both the first and second parts are an off-white color prior to mixing. After mixing the curing adhesive system gradually turns a pleasing blue color. EXAMPLE 2 To 100 g of Versilok® 406 adhesive is added 0.10 g of N,N,N',N'- tetraisopropanol(methylene dianiline) to form the first part of the adhesive system. The first part is mixed in a 4: 1 volume ratio with Accelerator 19, a benzoyl peroxide oxidizing agent commercially available from Lord Corporation. Both the first and second parts are an off- white color prior to mixing. After mixing the curing adhesive system gradually turns a pleasing blue color. The N,N,N',N'-tetraisopropanol(methylene dianiline) is prepared by fitting a 300 ml, 4 necked, round bottomed flask with a nitrogen inlet, Teflon inlet tube for propylene oxide, thermometer, magnetic stirrer, and a Ahlin condenser vented to a bubble tube. The nitrogen was passed through a calcium sulfate drying tower before entering the reactor. The cooling water was controlled to =10°C using a circulating bath. The reactor was heated using a silicone oil bath. A Fluid Metering Incorporated G-6 pump was used to give the required slow delivery of propylene oxide. A 100 gram charge of methylene dianiline was melted at 110°C. Then 129 grams of propylene oxide is added over a six hour period. The extent of conversion was estimated by proton NMR. No purification was done on the reaction product. EXAMPLE 3 To 100 g of Versilok® 406 adhesive is added 0.10 g of leuco malachite green to form the first part of the adhesive system. The first part is mixed in a 4: 1 volume ratio with Accelerator 19, a benzoyl peroxide oxidizing agent commercially available from Lord Corporation. Both the first and second parts are an off-white color prior to mixing. After mixing the curing adhesive system gradually turns a pleasing green color. EXAMPLE 4 To 100 g of Versilok® 406 adhesive is added 0.10 g of leuco crystal violet to form the first part of the adhesive system. The first part is mixed in a 4: 1 volume ratio with Accelerator 19, a benzoyl peroxide oxidizing agent commercially available from Lord Corporation. Both the first and second parts are an off-white color prior to mixing. After mixing the curing adhesive system gradually turns a pleasing violet color. EXAMPLE 5 The first part of an adhesive system is prepared by mixing 64.2 g 50 wt % polystyrene in styrene monomer; 8.5 g of 20 wt % neoprene in styrene monomer; 4.0 g of divinyl benzene; 2.6 g acrylic acid; 3.3 g dimethyl fumarate; 0.8 g diethanol-p-toluidine; and 0.3 g leuco malachite green. The resulting composition is translucent and colorless. This first part is mixed in a 24: 1 volume ratio with benzoyl peroxide dispersion (available from Akzo Nobel under the tradename CADOX 40e). When the parts are first mixed, a green color is observed. Upon further mixing, the entire adhesive mass gradually turns blue. EXAMPLE 6 An adhesive masterbatch is prepared by mixing 35.5 g methacrylated polybutadiene rubber (described in US-A-4,769,419); 17.5 g Wollastonite pigment; 4.6 g fumed silica; 3.0 g 2-hydroxyethyl methacrylate phosphate; 2.5 g methacrylic acid; 29.0 g methyl methacrylate and 1.2 g wax. To a 46.7 g portion of the masterbatch is added 0.025 g leuco crystal violet and 0.50 g diisopropanol-p-toluidine dissolved in 2.825 g methyl methacrylate to obtain a first part having 0.05 weight percent color additive. The first part is mixed in a 24: 1 volume ratio with Accelerator 19. Both parts of the system are on off- white color prior to mixing. After mixing the curing adhesive gradually turns a blue-gray color. EXAMPLE 7 To 100 g of Versilok® 410 adhesive (similar to Versilok® 406 adhesive, but it has less diisopropyl-p-toluidine) is added 0.10 g of 4,4'-bis(dimethylamino)benzhydrol to form a first part that immediately turns blue, but the blue fades upon overnight storage. The first part is mixed in a 4: 1 volume ratio with Accelerator 19. Both parts are an off- white color prior to mixing. After mixing the curing adhesive gradually turns a pleasing blue color. EXAMPLE 8 To 100 g of Versilok® 410 adhesive is added 0.10 g of triisopropanol-p- aminodiphenyl amine to form a first part. The first part is mixed in a 4: 1 volume ratio with Accelerator 19. Both parts are an off-white color prior to mixing. Immediately after mixing a series of rapid color changes takes place - from blue to violet to plum. After about 35 minutes the curing adhesive system turns a pleasing chocolate color. EXAMPLE 9 To 100 g of Versilok® 410 adhesive is added 0.10 g of diphenyl phenylene diamine. The first part is mixed in a 4: 1 volume ratio with Accelerator 19. Both parts are an off-white color prior to mixing. Immediately after mixing a series of rapid color changes takes place - from green to olive to brown. After about 25 minutes the curing adhesive system turns a pleasing butterscotch color.

Claims: Claims What is claimed is: 1. A two-part system comprising: (A) a first part comprising (i) at least one curable component; (ii) at least one reducing agent; and (iii) at least one color change additive having a structure represented by wherein R is individually H or OH; R is individually H, phenyl, C,-C 8 alkyl or R 3 is individually H, C,-C 8 alkyl or hydroxy C,-C 8 alkyl; and a and b are each 0 or 1, provided a+b=l or 2, or having a structure represented by wherein R 4 is individually H, phenyl, C,-C 8 alkyl or hydroxy C,-C 8 alkyl; R 5 is individually H, C,-C 8 alkyl or hydroxy C,-C 8 alkyl; and a and b are each 0 or 1, provided a+b=l or 2; (B) and a second part comprising a peroxide oxidizing agent. 2. A two-part system according to claim 1 wherein R 1 is individually H or OH, R 2 is individually H, phenyl or R 3 is individually H or hydroxy C,-C 8 alkyl; and a and b are each 1. 3. A two-part system according to claim 1 wherein the color change additive is selected from the group consisting of leuco crystal violet, leuco malachite green, N,N,N',N'- tetramethyl(methylene dianiline), N,N,N',N'-tetraisopropanol (methylene dianiline), 4,4'- bis(dimethylamino)benzhydrol, triisopropanol-p-aminodiphenyl amine and diphenyl phenylene diamine. 4. A two-part system according to claim 1 wherein the curable component comprises a (meth)acrylic-based compound. 5. A two-part system according to claim 1 wherein the first part further comprises (iv) 10-80 weight percent of an elastomer; (v) 0-40 weight percent of an olefinic urethane reaction product of an isocyanate- functional prepolymer and a hydroxy-functional monomer having at least one unit of polymerizable unsaturation, such reaction product being characterized by the presence of at least two units of unsaturation and the substantial absence of free isocyanate products; and (vi) 0-20 weight percent of a phosphorus-containing compound having one or more olefinic groups and no less than one P-OH group, wherein the weight percents are based on the total weight of the first part. 6. A method for determining working time of a two-part curable system, the method comprising contacting a first part that includes a color change additive and at least one curable component and a second part that includes a peroxide oxidizing agent so that the resulting composition begins to assume a color that is different than the initial color of the first and second parts individually; monitoring the resulting composition for cessation of the color change; and working the resulting composition prior to the cessation of the color change. 7. A method according to claim 6 wherein the first part further comprises a reducing agent and the contacting step initiates curing of the system. 8. A method according to claim 6 wherein the color change additive has a structure represented by wherein R 1 is individually H or OH; R 2 is individually H, phenyl, C r C 8 alkyl or R 3 is individually H, C,-C 8 alkyl or hydroxy C,-C 8 alkyl; and a and b are each 0 or 1, provided a+b=l or 2; or a structure represented by wherein R 4 is individually H, phenyl, C,-C 8 alkyl or hydroxy C,-C 8 alkyl; R 5 is individually H, C,-C 8 alkyl or hydroxy C,-C 8 alkyl; and a and b are each 0 or 1, provided a+b=l or 2. 9. A method according to claim 6 wherein the curable component comprises a (meth)acrylic-based compound. 10. A method according to claim 6 wherein the color change additive is colorless prior to contacting the first and second parts.

Inventors: ABBEY KIRK J, DAWDY TERRENCE H, HATCHER JEFFREY A, RIGHETTINI ROBIN F, ABBEY, KIRK, J., DAWDY, TERRENCE, H., HATCHER, JEFFREY, A., RIGHETTINI, ROBIN, F.
Applicants: LORD CORP, LORD CORPORATION
Application year: 1997
Main classification: C08K5
IPC codes: C08G18, C08K5, C08L21, C08L75, C08L101, C09J4, C09J5