MXPA95000040A - Acrylic adhesives structure - Google Patents

Abstract

A two-part structural acrylic adhesive, characterized by long open time, relatively fast cure time, good strength properties and ability to fill large spaces, comprising a polymerizable acrylic monomer and peroxy polymerization initiator in one part and a mixture of a transition metal compound and o-benzosulfimide in acrylic monomer in the second part. The present invention is directed to a two-part structural adhesive system, mixable, applied as a single part and characterized by a long open time, good strength properties and relatively fast curing, both anaerobic and aerobic, as well as filling spaces. More particularly, this invention involves a two part acrylic adhesive comprising in one part a polymerizable acrylic monomer and a peroxy polymerization initiator and in the second part a mixture of a transition metal compound and saccharin (o-benzosulfimide) as well as a monomer acrylic

Description

/ STRUCTURAL ACRYLIC ADHESIVES BACKGROUND OF THE INVENTION Many acrylic adhesive systems have various characteristic properties known in the art, as described in the Polymer Science and Technology Encyclopedia volume 1, p. 571-572, 1985. The first acrylic engineering adhesives include well-known Dupont technology directed to two-part adhesives involving methyl methacrylate, as the main monomer, chlorosulfonated polyethylene as the elastomer and eumeno hydroperoxide (HP) as the initiator (Patent of US No. 3,890,407 issued June 17, 1975 to P. Briggs, et al.) These adhesives are characterized by rapid cure and have two other distinctive properties, first, the cured polymer contains elastomeric domains, derived from grafting to dispersed rubber and Second, the monomers are able to dissolve the oil that is often found on metal surfaces. These additives are therefore much stronger and impact resistant than ordinary acrylic adhesives and can additionally be used on unprepared metal surfaces. TECHNICAL FIELD The US patent. No. 3,591,438 issued July 6, 1971 to A. Tobac et al., Discloses increasing the rate of curing of acrylate adhesives initiated by peroxy by treating one or more of the surfaces to be bonded with a binding accelerator which contains a condensation product. aldehyde-amine and as a reducing activator either a free radical accelerator containing sulfur or a compound containing an oxidizable transition metal. The patent of the U.S.A. No. 4,223,115 granted on September 16, 1980 to D. Zaluche, et al. Discloses structural adhesive systems for metal bonding which comprises a solution of polymerizable material which has incorporated certain compounds containing phosphorus and characterized by a capacity to provide strong adhesion to metal. untreated metal surfaces. The patents of the U.S.A. No. 4,348,503 and 4,432,829 issued September 7, 1982 and February 21, 1984, respectively to A. Bachman, describe adhesive compositions capable of functioning either aerobically or anaerobically and include an acrylate monomer, a suitable elastomeric filler, an ester catalyst -aromatic and a dibasic acid capable of cyclic tautomerism and optionally a quantity of a transition metal cure accelerator. The patent of the U.S.A. No. 3,046,262 issued July 24, 1962 to V. Krieble, discloses accelerated anaerobic cure compositions wherein a peroxy catalyst and a sulfimide accelerator are employed. The patents of the U.S.A. Nos. 4,052,244 and 4,081,308 issued October 4, 1977 and March 28, 1978, respectively to M. Skoultchi, disclose two-part fast curing structural acrylic adhesives, wherein the first part comprises an acrylic monomer and saccharin or copper saccharinate and the second part contains p-toluenesulfonic acid salt as a separate activator in the '244 patent and a solution of alpha-hydroxysulfone or alpha-aminosulfone in the' 308 patent. A recent patent, patent of the U.S.

No. 5,106,928 issued April 21, 1992 to M. Skoultchi et al. Describes structural acrylic adhesives that can be mixed in two parts, using complex organoboroamine initiators. These adhesives have good strength and stability properties with a relatively short open time of a few seconds to a few minutes. Increasing the open time to 30 minutes or more, as is the case in large structural applications, results in reduced strength and extremely slow surface cure of the product outside the bond line. While the acrylic adhesives described in the prior art as noted above provide a variety of properties and different characteristics, they do not have all the required characteristics to adhere to the very large parts found in many structural applications. These adhesives are often applied as a separate activator and adhesive to different substrates making mixing and the desired degree of hard-to-reach intimate contact, when large parts are attached. Adhesives of this type also cure through a space or bond line of limited size (usually a maximum of approximately 1016 mm (40 mils), since curing occurs by diffusion of the activator from the surface to the adhesive. If the joint is not homogenous with large spaces, the adhesive will remain incompletely cured In contrast to this, a blendable two-part adhesive applied through a static mixer can fill very large spaces as large as approximately 6.35 mm (250 mils) of The adhesives of the prior art frequently do not cure aerobically and this results in adhesive outside the bond line which does not cure to a tack-free state within 24 hours.Two available two part formulations have a short open time ( Open time refers to the time after the adhesive has been applied until the part has been assembled.) An adhesive with a short time open (for example less than 15 minutes) must necessarily be used in parts of limited size since if the part is large, the adhesive will advance significantly before the entire part can be covered and assembled completely. Accordingly, for very large parts, an adhesive with a long open time (about 30 or 40 minutes or more) is desired. It is also convenient that once the assembly is complete, the cure to the driving resistance should occur as quickly as possible, usually in about 1 hour. Finally, after the cure is completed, the adhesive must have adequate levels of overlap shear, peel and impact resistance. In this way, the two-part mixable adhesive optimal for large parts regulates a precise curing behavior, initially very slow to provide sufficient open time, then increase the speed to achieve handling resistance and finally adequate aerobic cure to set the material outside. of the line of union. DESCRIPTION OF THE INVENTION This invention relates to a two-part structural acrylic adhesive applied as a single part or combined entity, wherein one part comprises a polymerizable acrylic monomer and a peroxy polymerization initiator and the second part comprises a mixture of a composed of transition metal and saccharin (o-benzosulfimide) in acrylic monomer. This adhesive provides long open time, quick cure to handling time, fillet cure (aerobic cure) and can be used to fill large spaces up to approximately 6. 35 mm (250 mils). The two-part structural adhesive of this invention comprises polymerizable acrylic monomer, a peroxy initiator and a mixture of transition metal and saccharin (o-benzolsulfimide). The polymerizable acrylic monomer can be monofunctional, polyfunctional or a combination thereof. Particularly useful monomers are monofunctional acrylate and methacrylate esters and their substituted derivatives such as hydroxy, cyano, chlorine and silane derivatives. Monomers of this type are represented by the general formula: 0 CH2 = C - C OR R 'wherein R is an alkyl, cycloalguyl or heterocyclic group (for example containing 0, N or S) of 1 to 12 carbon atoms, an aryl, aralguyl or ayl group of 6 to 14 carbon atoms and R' is hydrogen or methyl. These monomers include for example methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, isobornyl methacrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, butyl acrylate, n-octyl acrylate, 2- ethylhexyl acrylate, 2-etilexilmetilacrilato, decyl methacrylate, dodecylmethacrylate, cyclohexyl methacrylate, terbutilmetacrilato, fenoxietilmetacrilato , gamma-methacryloxypropyltrimethyloxylane, 2-,. cyanoethyl acrylate, 3-cyanopropyl acrylate, tetrahrofururylmethacrylate, tetrahydroforphuryl chloroacrylate, glycidyl acrylate, glycidyl methacrylate and the like. A second class of polymerizable monomers useful in the present compositions corresponds to the general formula: wherein R is selected from the group consisting of hydrogen, methyl and ethyl. 0 II -CH2OH and -CH2-0-C-C = CH2; I R 'R' is selected from the group consisting of hydrogen, chlorine, methyl and ethyl, -R "is selected from the group consisting of hydrogen, hydroxy and O II -0-C-C = CH2; I R 'm is an integer equal to at least one, for example from 1 to 8, or higher and preferably from 1 to 4 inclusive, -n is an integer equal to at least 1, for example from 1 to 20 or more; and p is one of the following: 0 or l. Monomers useful in this invention and falling within the above general formula include for example ethylene glycol dimethacrylate, ethylene glycol diacrylate, polyethylene glycol diacrylate, tetraethylene glycol dimethacrylate, diglycerol diacrylate, diethylene glycol dimethacrylate, pentaerythritol triacrylate, trimethylolpropanetrimethacrylate and other polyether The former class of monomers is described in U.S. Patent No. 3,043,820 issued Jul. 10, 1962 (to RH Krieble.) Another class of polymerizable monomers useful in the present compositions correspond to the general formula: RR H2C = C C = CH- C-0-- (-R '-0--) - C-R' '-C-- (-O-R' -) O-C II n || || n || 0 0 0 or wherein n represents hydrogen, chlorine, methyl or ethyl; R 'represents alguylene with 2 to 6 carbon atoms; and R "'represents ( n represents an integer of 4. Typical monomers of this class include, for example, bis (ethylene glycol) adipate dimethyl acrylate, bis (ethylene glycol) dimethylacrylate maleate, bis (diethylene glycol) phthalate dimethacrylate, bis (tetraethylene glycol) dimethacrylate. phthalate, dimethacrylate bis (tetraethylene glycol) sebacate, 'Bis (tetraethylene glycol) maleate iimethacrylate and the diacrylates and chloroacrylates corresponding to dimethacrylates and the like. The above class of monomers is described in U.S. Pat. No. 3,457,212 granted on July 22, 1969 (Sumitomo Chemical Company, Ltd.). Also useful are monomers which are isocyanate-hydroxyacrylate or isocyanato-aminoacrylate reaction products which can be characterized as polyurethanes terminated in acrylate or polyurides and polyureas. These monomers correspond to the general formula: wherein X is selected from the group consisting of -O- and RI-N-, and R is a member selected from the group consisting of hydrogen and lower alkoyl of the 7 carbon atoms, - A represents the organic residue of an ester acrylic containing active hydrogen, where the active hydrogen is removed, the ester is substituted with hydroxy or amino, or its portion alguilo and its homologs methyl, ethyl and chlorine; n is an integer from 1 to 6 inclusive, and B is a mono- or poly-valent organic group selected from the group consisting of alkyl, alkenylene, alkenyl, isoalguyl, cycloalguylene, aryl, aralguyl, alkaryl, poly (oxyalogylene) groups , poly (carboalkoxyalguylene) and heterocyclics both substituted and unsubstituted. Typical monomers of this class include the reaction product of mono- or poly-isocyanate, for example toluene disocyanate, with an acrylic ester containing a hydroxy group or amino in its non-acrylate moiety, for example hydroxyethyl methacrylate; The above class of monomers is described in U.S. Pat. No. 3,425,988 issued on February 4, 1969 (Loctite Corporation). Another class of monomers useful in the present application are the mono- and polyacrylate and methacrylate esters of bisphenol-type compounds. These monomers can be described by the formula: wherein R1 is methyl, ethyl, carboxyalkyl or hydrogen, - R2 is hydrogen, methyl or ethyl; R3 is hydrogen, methyl or hydroxyl; R 4 is hydrogen, chlorine, methyl or ethyl; and n is a value having an integer from 0 to 8. Representative monomers of the class described above include: dimethacrylate and diacrylate esters of 4,4'-bis-hydroxyethoxy-bisphenol A; dimethacrylate and diacrylate esters of bisphenol A; These monomers are described in Japanese Patent Publication No. 70-15640 (to Toho Chemical Manuf. Ltd.) In addition to the acrylic monomers described above, the adhesive may include acrylic and methacrylic acid as part of the monomer portion of the adhesive. This acid is generally used in an amount of about 2 to 30%, preferably 5 to 10%, based on the total weight of the composition. The useful monomers are viewed as polymerizable monomers having one or more acrylic or substituted acrylic groups as a common unifying feature, and for convenience may be referred to generically as acrylic monomers. Preferred adhesive compositions are adhesives containing elastomeric or rubber polymers in compatible polymerizable acrylic monomers. The rubberized or elastomeric polymers may be any of the typically available synthetic rubbers or other materials which are soluble in the monomer such as those based on polyisoprenes, polybutanes, polyolefins, polyurethanes, polyethers, etc. Examples of elastomeric materials include homopolymers such as polybutadiene, polyisoprene and polyisobutylene, diene-type blog copolymers such as styrene / butadiene / styrene and styrene / isoprene / styrene; and graft or random copolymers such as butadiene / styrene copolymer, butadiene / acrylonityl copolymer, butadiene / methylmethacrylate copolymer and butadiene / alkylacrylate copolymer, - ethylene / vinyl acetate copolymers, - ethylene / alkylacrylate copolymers (1 to 8 carbon atoms) carbon in the alguilo group), polyalguil-acrylates or co-polymers thereof, - polyurethane; chlorinated polyethylenes; and EPDM (ethylene / propylene / diene terpolymers). The elastomers of these structures may contain a functional group at one or both ends or within a particular segment or repeating unit of the copolymer. Suitable functional groups include vinyl, epoxy, carboxyalogyl and mercapto groups. Other functional groups may be employed as deemed useful as determined by routine experimentation. A preferred group of elastomers are the blog copolymers. Several of these blogue copolymers are manufactured by Shell Chemical Company under the tradename Kraton and by Firestone under the tradename Stereon. In particular, Stereon 840 A, a blog copolymer of poly (styrene-b-butadiene-b-styrene) has been found especially useful in the present adhesive composition. Other preferred blog copolymers of this type are available under the tradename Solprene 416, manufactured by Phillips Petroleum Co. The monomer solution containing the rubbery polymer or elastomer is commonly prepared by dissolving the elastomer in the monomer, which may be in the Form of a syrup. In some cases, the monomer solution can be prepared by removing a rubberized polymer from a latex of the water-kneaded mixture, as used for suspension polymerization, and then dissolving in the monomer. The peroxy polymerization initiator employed in this invention can be any peroxy compound which is useful for initiating the polymerization and more particularly is an organic hydroperoxide having the formula R-OOH, an organic peroxide having the formula of ROOR ', and a perester which has the formula 0 II RCOOR 'wherein R and R' in each of the above formulas represents a hydrocarbon group containing up to about 18 carbon atoms. More particularly the groups R and R 'in the above formulas are an alkyl group of 1 to 18 carbon atoms, preferably 3 to 12 carbon atoms or an aryl or alkaryl group of 6 to 18, preferably 6 to 14 carbon atoms. R and R 'may contain any substituent or bond, hydrocarbon or otherwise, which does not adversely affect peroxy for the purposes described above. Typical examples of these peroxy initiators are hydroperoxide eumeno, t-butyl hydroperoxide, hydroperoxide, methyl ethyl ketone hydroperoxide and hydroperoxides formed by oxygenation of various hydrocarbons, such as methylbutene cetane and cyclohexene and various ketones and ethers, dicumyl peroxide, di-t-butyl peroxide , 2, 5-dimethyl-2, 5-di-t-butylperoxyhexane, t-butyl perbenzoate, di-t-butyl diperfalate, and 2,5-dimethyl-2,5-bis (benzoylperoxy) hexane. The amounts of these hydroperoxy compounds which are typically employed are in the range of 0.1 to 10% and preferably about 3 to 6% by weight, based on the weight of the part or component in which they are contained. The second part of the two-part acrylic adhesive of this invention contains a mixture of a transition metal compound and saccharin (o-benzolsulfimide). The transition metal may be introduced as any salt or appropriately soluble organic compound. The transition metals are those which comprise the classes Illb, IVb, Vb, VIb, Vllb, VHIb and Ib of the Periodic Table of the elements. The preferred group of transition metals is copper, iron, cobalt, nitrile, manganese and vanadium, with copper being particularly preferred. Useful soluble compounds are those of the formula ROM, wherein M is the transition metal and R is the residue of an organic acid or alcohol having up to 20 hydrocarbons. Examples of compounds of this type are copper naphthenate, cobalt naphthenate, manganese naphthenate, copper octate, iron propinate, copper hexoate and iron hexoate. The transition metal compound will normally be employed in amounts of 100 or more parts per million (ppm) of metal based on the weight of the adhesive and more particularly about 100 to 1500 ppm and preferably about 300 to 750 ppm. Saccharin or o-benzosulfimide is the second component found in the second part of the adhesive system.

While the preferred component is o-benzosulfimide, other organic imides may also be employed. Useful organic moieties include imides such as succinimide and particularly organic sulfimides of the formula: o H or R l __ I __ J R1 II or As well as organic disulfonylimides of the formula: wherein R and R1 in each of the above formulas is a hydrocarbon group containing up to about 20 carbon atoms and more particularly is an alkyl aryl cycloalkyl group and substituted hydrocarbon aryl having up to about 10 carbon atoms. The groups R and R1 may contain any bond or substituent that does not adversely affect the compound for its intended use in the : and can also be joined to bind the imide group in a heterocyclic ring of a polynuclear heterocyclic ring system. Saccharin or other organic imide is employed in an amount of about 0.01 to 5% by weight based on the weight of the adhesive composition and preferably about 0.25 to 2%.

The amount of acrylic monomer to be used in this invention may vary somewhat depending on the specific properties desired but in general about 10 to 90% by weight of the acrylic monomer based on the weight of the composition and preferably about 15 to 80% by weight. weights are used. The elastomer is generally present in amounts of about 5 to 80% by weight and preferably about 20 to 60% by weight based on the weight of the composition. These amounts refer to the total amounts of the acrylic monomer and elastomer included in both parts of the composition and can be varied or the same in both parts. Also, the acrylic monomer and elastomer may be the same or different in each of the parts of the composition. The two parts that are mixed together can be in any ratio or ratio as long as all the ingredients are dissolved in the monomer and the peroxy initiator in one part and the transition metal and organic imide compound are in the other part. More particularly the two parts may be in a miscible ratio of about 20: 1 to 1:20 and preferably 2: 1 to 1: 2 parts by volume. More preferably it is the system having approximately a 1: 1 miscible ratio of the two parts by volume. Adjustments within these ranges are easily made within the skill of the specialty.

Other additives such as adhesion promoters, inhibitors, thickeners, plasticizers and diluents can be employed in the adhesive composition of this invention. Adhesive compositions of this invention provide 1: 1, miscible, easily handled (low odor, non-flammable, space filling) adhesive systems that advantageously give long open times of approximately 15-45 minutes, preferably approximately 30-40 minutes, reasonably short handling times of less than about 5 to 6 hours, preferably less than about 2 hours, and aerobic cure in 24 hours or less, making them particularly useful in large structural applications. In the following example, which is merely illustrative of the embodiments of this invention, all parts and percentages are given by weight and all temperatures in degrees Celsius unless otherwise noted. EXAMPLE I The following two part structural acrylic adhesive system was prepared by dissolving Stereon 840 A rubber (styrene-butadiene block copolymer) in methacrylate and indicated methacrylic acid and mixing for 12-16 hours at room temperature. In part A, eumeno hydroperoxide is stirred slowly at room temperature for approximately 15 minutes. This was followed by mixing in fumed silica about 30 minutes. In part B, saccharin was slowly mixed at room temperature for about one hour, followed by addition of copper naphtannate with mixing for 15 minutes and then addition of fumed silica. Mixing is continued for 30 minutes. PART A Steron 840 A (styrene-butadiene block copolymer) 23.77 Isobornyl methacrylate 57.04 2-ethylexyl methacrylate 14.26 Eumeno hydroperoxide 2.91 Cabosil M-5 (smoked silica) 2.00 PART B Stereon 840 A 23.45 2-ethylexyl methacrylate 14.07 Tetrahydrofurfuryl methacrylate 46.90 Methacrylic acid 9.38 Saccharin 0.95 Copper Naftanate 1.25 Cabosil M-5 (smoked silica) 4.00 The two separate parts were added in equal volumes to a dual cartridge connected to a static mixer containing eight elements. A caulking gun with two plugs is used to supply the adhesive again from the static mixer. The adhesive was applied to a suitable steel substrate for shear testing. No substrate cleaning was performed. After 30 minutes, a second sub-layer is used to form a shear strength test specimen. The two walls of the specimen could not be moved after 60 minutes and the following mechanical properties were obtained in the adhesive system: Shear strength, k / cm2 (psi) 147.63 (2,100) (25 ° C, 25h, steel) Resistance to detachment, g-cm (pli) 7,501.2 (42) (25 ° C, 24h, 180 °, steel, space of .127 mm (5 mils)) Peel strength, g-cm (pli) 5,715.2 (32) (25 ° C, 24h, 90 °, Al , space of .127 mm (5 mils)) The adhesive that was squeezed out of the joint line when preparing the test specimen exhibited no stickiness after 20 hours. EXAMPLE II A two part structural acrylic adhesive system was prepared as in Example I and had the following formulation: Part A Parts Stereon 840A (styrene-butaidene block copolymer) Isobornyl methacrylate 40 2-ethylhexyl methacrylate 35 Eumeno hydroperoxide 3 Cabosil M5 (fumed silica) 1.5 Part B Stereon 84OA (styrene-butadide block copolymer) 25 Tetrahydrofurfuryl methacrylate 45 Isobornyl acrylate 20 Acid methacrylate 10 Saccharin 1 .Cabosil M-5 (fumed silica) 2.25 Copper Naphthenate 1.32 The adhesive system was mixed and applied as Example I and had an open time of 30 minutes, time to handle 60 minutes, fillet cure achieved in 16 hours and reheating of shear to bringer after 72 hours of 196.84 kg / cm2 (2800 psi). EXAMPLE III A two-part structural acrylic adhesive system is prepared as in Example II, with the same formulation except for t-butyl perbenzoate was replaced by eumeno hydroperoxide in part A. The open time was 30 minutes and the time for handling resistance was three hours.

Claims (10)

1. CLAIMS 1.- Curable two-part curable adhesive composition, which has a long open time, short handling time, and provides aerobic cure, comprising a polymerizable acrylic monomer and an effective amount of a peroxy polymerization initiator in one part and the second part contains a mixture of a transition metal compound and an organic sulfimide or organic disulfonylimide in acrylic monomer.
2. 2. The composition as described in claim 1, wherein the organic sulfimide is o-benzo-sulfonyl.
3. 3. The composition as described in claim 2, wherein the transition metal is copper.
4. 4. The composition as described in claim 3, wherein from about 100 to 1500 ppm of transition metal and 0.01 to 5% by weight of o-benzosulfimide are employed based on the weight of the composition.
5. 5. The composition as described in claim 4, wherein the peroxy polymerization initiator is an organic hydroperoxide having the formula R-OOH, an organic peroxide having the formula ROOR 'or a peryester of the formula 0 II RCOOR 'wherein R and R' in each of the above formulas represents a hydrocarbon group of 1 to 18 carbon atoms.
6. 6. - Composition of any one of the present claims, wherein either or both parts of the composition contain a rubberized or elastomeric copolymer.
7. 7. - Composition according to claim 6, wherein from about 10 to 90% by weight of the acrylic monomer and from about 5 to 80% by weight of the polymer or rubberized elastomer based on the total weight of the composition, are used .
8. 8. Composition according to claim 7, wherein from about 0.01 to 10% by weight of the peroxy initiator are used.
9. 9. - Composition in accordance with the claim 8, wherein the transition metal compound is copper naphthenate, the acrylic monomer contains acrylic or methacrylic acid and a mixing ratio of 1: 1 by volume of the two parts,
10. 10.- A method for joining facing surfaces, which comprises interposing between the surface the curable adhesive composition of one of the preceding claims, placing the surfaces in confining relationship and allowing the adhesive to cure.