TWO-COMPONENT COATING FORMULATION

Abstract: A catalyst system for effecting polymerization in a two-part formulation, which contains an oxygen-containing ethylenically unsaturated monomer, consists of a selected acid, a selected aromatic amine compound, and a transition metal compound; active-oxygen, free-radical catalysts are excluded. Because of the nature of the catalyst system, efficient reaction does not require intimate mixing of the two components of the formulation, which may therefore be applied effectively as fine-droplet sprays from a common, ultrasonically vibrated head (10) fitted with a driver portion (14), head portion (12) with opposed parallel planar faces (16), a pair of liquid delivery nozzles (18, 22) and a traverse (normally horizontal) bottom plane (20). The spray converge and intersperse in the region "X" and deposit on the workpiece "W" as a complete formulation.

Description: TWO-COMPONENT COATING FORMULATION BACKGROUND OF THE INVENTION Two-part aerylate formulations are well known in the art for use as adhesives, potting compounds, conformal coatings, and the like. In addition to including polymerizable acrylat mono- mers, such formulations typically include elastomeric fillers (e.g., urethane oligomers, preferably capped to provide sites of unsaturation for enhanced reactivity) , adhesion promoters in the form of organic acids (e.g., acrylic and methacrylic) , inert fillers, supplemental adhesion promoters (e.g., silanes) , level- ing agents, and other ingredients. Reaction in formulations of this kind is normally initiated by use of a free-radical, active-oxygen catalyst (i.e., a peroxide, a hydroperoxide, or a perester) , activated thermally, chemically (e.g., with an amine/aldehyde adduct and transition metal accelerator) , aero- bically, anaerobically, etc; they may additionally or alterna¬ tively include a photoinitiator that is responsive to actinic radiation. Illustrative of the prior art that is germane to the acry- late formulations hereinabove referred to are the following Bachmann and Bachmann et al United States patents, all of which are of common assignment herewith: No. 4,348,503, issued September 7, 1982, No. 4,429,088, issued January 31, 1984, No. 4,432,829, issued February 21, 1984, No. 4,963,220, issued October 16, 1990, No. 4,974,938, issued October 23, 1990, and No. 5,039,715, issued August 13, 1991. Other prior art of interest to the subject matter to which the instant application pertains are the following, each of which is also a patent of the United States: Lappala, No. 2,859,200, issued November 4, 1958, DiMartino No. 2,921,045, issued January 12, I960, Lees No. 3,658,624, issued April 25, 1972, Skoultchi No. 4,052,244, issued October 4, 1977, olinski et al No. 4,126,504, issued November 21, 1978, Nativi No. 4,424,252, issued January 3, 1984, Kubota et al No. 4,820,744, issued April 11, 1989, Gutek No. 4,956,221, issued September 11, 1990, and Chao Registration No. H509, published August 2 , 1988. The Lappala and DiMartino patents disclose the combined use of a number of ingredients for the catalysis of aerylate systems; for example, DiMartino describes a methylmethacrylate cement that includes methacrylic acid and is catalyzed by co¬ balt nap-tithenate, MEK peroxide, and diethylaniline, used in combination. The Lees patent lists complimentary accelerators, including a monocyclic carbocyclic aromatic acid (e.g., ben- zoic) , trichloroacetic acid, and phenoxyacetic acid. The two- part adhesive disclosed by Skoultchi includes p-toluene sulfinic acid, and Wolinski et al disclose a system that includes an acid (e.g., acrylic) and a free-radical, active-oxygen catalyst (e.g., benzoyl peroxide), in which reaction is initiated by a tertiary amine (e.g., dimethyl-p-toluidine) . Both Nativi and Gutek provide compositions that afford shadow curing capability, and Gutek discloses UV-curing as being suitable for printed circuit board applications. Despite the activity in the art indicated by the foregoing, a demand exists for a highly effective two-part formulation comprised of polymerizable, oxygen-containing ethylenically unsaturated (e.g., acrylate) monomers, which is suitable for use as an adhesive, for potting, for conformal coating, and for other like applications, which formulation does not depend upon a ree-radical, active-oxygen catalyst for initiation of reac¬ tion. Accordingly, it is a broad object of the present inven¬ tion to provide a novel formulation having such features and advantages. A related object of the invention is to provide such a formulation from which highly satisfactory cured deposits can be produced despite the lack of intimate admixture of the two components of which it is comprised. A corresponding object of the invention is to provide a novel catalyst system for use in such formulations. Another corresponding object is to provide a novel method for the production of an adherent, solid deposit in a highly facile and yet efficient manner, utilizing a two-part formula¬ tion of the character described. SUMMARY OF THE INVENTION It has now been found that certain of the foregoing and related objects of the invention are attained by the provision of a two-part, solvent-free liquid formulation, comprising a first component that includes an acid ingredient that is sub¬ stantially soluble in the polymerizable composition, and a second component that includes an aromatic amine compound having the general formula: wherein each of "R^" and "R 2 " is selected from the class con¬ sisting of hydrogen and an alkyl group, and wherein "Ar" is selected from the class consisting of a monocyclic and poly- cyclic aromatic groups. At least one of the components of the 10 formulation additionally includes a transition metal compound, and the acid ingredient employed must be capable of forming a coordination compound with the metal thereof. Either or both of the components of the formulation are comprised predomi¬ nantly of a polymerizable composition that includes one or more 15 oxygen-containing ethylenically unsaturated polymerizable in¬ gredients; the formulation is free from any free-radical, active-oxygen polymerization catalyst (i.e., a compound con¬ taining the peroxy group) . In preferred embodiments, the aromatic amine compound 20 employed will be selected from the group consisting of N,N- (alkyl)-toluidines in which the alkyl group contains one to three carbon atoms, N-methylaniline, N,N-dimethylaniline, aniline, N,N-bis(2-hydroxyethyl)-p-toluidine, dimethyl a ino- styrene, 4-dimethylaminobenzoic acid, ethyl-4-dimethylamino 25 benzoate, N,N-dimethyl-p-amino benzyl alcohol, and mixtures thereof. The metal compound utilized in the formulation will desirably be an ingredient of the first component, and will normally be of a metal selected from the class consisting of cobalt, iron, cerium, copper, lead, manganese and vanadium. 30 The acid or acids employed will preferably be selected from the class consisting of acrylic, methacrylic, acetic, ascorbic, oxalic, phthalic, itaconic, crotonic, 4-methoxyphenyl acetic, 3,5-dihydroxybenzoic, 3,3-dimethylaminobenzoic, and p-toluene- sulfonic. The polymerizable ingredient will preferably be an 35 acrylate monomer, and will, for many applications, desirably be •t admixed with a prepolymer selected from the group consisting of urethane (meth)acrylates, epoxy (meth)acrylates, and urethane epoxy-(meth)acrylates. In especially preferred embodiments, at least one of the components of the formulation will addition- ally include an effective amount of a photoinitiator that is capable, when activated, of catalyzing polymerization of the polymerizable ingredient. The formulation may more specifically comprise (in percent- ages based upon the total weight thereof) 0.05 to 10, and pref¬ erably 1 to 4, of the acid ingredient, 0.05 to 10.0 of the aro¬ matic amine compound, 0.002 to 1.5 of the metal compound, and 20 to 96 of the polymerizable composition. The polymerizable monomer may itself comprise 20 to 96 weight percent of the form- ulation; and when included, the prepolymer may constitute as much as 60 weight percent of the formulation, and more typically 20 to 40 percent thereof. Other objects of the invention are attained by the provi¬ sion of a catalyst system comprising the above-identified acid, amine compound, and transition metal compound. Still other objects of the invention are attained by the provision of a method for the production of an adherent solid deposit upon a substrate, utilizing the two-part formulation described herein to form a liquid deposit upon a substrate, which is cured to produce the solid. The method will desirably be carried out using a formulation that includes an effective amount of a photoinitiator, in which instance the curing step will normally be initiated by exposure of the liquid deposit to actinic radiation. In preferred embodiments of the method, admixture of the components of the formulation will be effected immediately prior to their contact with the substrate, as will desirably be achieved by interspersal of fine-droplet sprays thereof; ultrasonic apparatus, comprised of a spray head and delivery means, will most desirably be used for that purpose. The spray head of such apparatus may, more particularly, have opposite side surface portions, or faces, that are preferably planar, are oriented substantially parallel to one another, and term¬ inate at a common transverse plane at one end of the head. The delivery means serves to deliver the formulation components separately but concurrently, and generally continuously, to the opposite faces of the head at points spaced from the common plane at which they terminate, so as to form a thin film of each of the formulation components moving therealong. Operation of the apparatus will cause the spray head to vibrate ultrason- ically, on an axis parallel to its side faces, thereby producing adjacent sprays of the components issuing from the end of the head. The substrate is disposed outwardly of the common plane, and is spaced from the spray head a distance sufficient to permit substantial interspersion of the formulation components prior to contact therewith. For optimal use in such ultrasonic applications, each of the formulation components will desirably have a viscosity in the range 80 to 200 centipoise, as measured at 25° Centigrade, albeit that heating may be necessary to lower the viscosity (e.g., to 50 centipoise or less) for actual appli¬ cation; the technique will normally be carried out on a continu¬ ous basis, as by conveying the substrates to be coated under the spray head and thereafter past a UV irradiation source. BRIEF DESCRIPTION OF THE DRAWING Figure 1 of the drawing is a diagrammatic elevational view of an ultrasonic delivery system suitable for use in carrying out the method of the instant invention. DETAILED DESCRIPTION OF THE PREFERRED AND ILLUSTRATED EMBODIMENTS The system diagrammatically illustrated in Figure l is comprised of an ultrasonic head assembly, generally designed by the numeral 10, and a pair of liquid delivery nozzles 18, 22. The head assembly consists of a head portion 12 and a drive portion 14, the latter serving to vibrate ultrasonically the head portion 12 along its longitudinal (normally vertical) axis; i.e., in the direction indicated by the double-headed arrow. The head portion 12 has parallel, planar faces 16 on its op¬ posite sides, terminating at an end surface 20 disposed in a transverse (normally horizontal) , bottom plane. The two components of the coating formulation are deliv¬ ered separately to the opposite faces 16 of the head portion 12, through one or the other of the nozzles 18, 22, moving along -the faces under the influence of the ultrasonic vibration and being atomized to issue from the free end as two adjacent sprays. The sprays converge and intersperse at a point (such as "X") outwardly of the end surface 20, to mix and. thereafter deposit upon the workpiece "W" as a complete formulation. Exemplary of the efficacy of the present invention are the following Examples, in which all parts and percentages stated are by weight, unless indicated otherwise; viscosities are ex¬ pressed as measured at 25° Centigrade. Except where other pro- ducts are identified, the prepolymer used in these Examples is a polyetherurethane acrylate oligomer produced from an aromatic isocyanate and a polypropyleneoxide diol, and capped with 2- hydroxyethylacrylate, commercially available from Bomar, Inc. , of Winsted, Connecticut; it contains only trace amounts of term- inal isocyanate. EXAMPLE ONE To 40 parts of the above-identified oligomer is added 5 parts of 2-hydroxyethylmethacrylate, 39.5 parts of isobornyl- acrylate (IBOA) , 2 parts of dimethoxy-2-phenylacetophenone (Ciba-Geigy IRGACURE 651) , 2 parts of 1-hydroxycyclohexylphenyl ketone (Ciba-Geigy IRGACURE 184), and 1.5 parts of a methacryl- oxypropyltrimethoxy silane adhesion promotor commercially available from Union Carbide Corporation under the trade desig¬ nation SILANE 174. The mixture is stirred until all of the ingredients are dissolved, resulting in a solution containing approximately 44.4 percent of the polyetherurethane acrylate oligomer. To 45 parts of the oligomer solution is added 5 parts of N,N-dimethyl-p-toluidine, to provide component A of a formula- tion embodying the invention. Component B is provided by adding to 45 parts of the same oligomer solution 4.7 parts of acrylic acid, and 0.3 part of a solution of cobalt naphthenate in IBOA monomer, made by dissolving one part of a commercially available, 8 percent cobalt naphthenate solution in 10 parts of IBOA. Equal amounts (by volume) of components A and B are admixed and thereafter sprayed (from a commercially available spray can system containing a non-flammable propellant) onto the surface of a printed circuit board (PCB) substrate, to which a number of components are surface mounted. The damp boards are exposed to ultraviolet radiation for a period of about two seconds and at an energy level of 1.70 milliwatts/cm 2 , while being conveyed past the UV lamp at a speed of 10 feet/minute; the coating is there¬ upon found to have developed a tack-free surface. After stand- ing for about 10 minutes at room temperature, several of the surface mounts are removed from the PCB substrate to reveal unirradiated "shadow" areas, which are found to be dry and tack- free. EXAMPLE TWO A solution is prepared by admixing 40 parts of the capped polyether urethane oligomer with 40 parts of IBOA, 6.5 parts of 2-hydroxyethyl methacrylate, 2 parts of IRGACURE 651, 2 parts of IRGACURE 184, and small amounts of other additives and stabil- izers known in the industry for use in acrylate adhesive form¬ ulations. To 45 parts of the resultant oligomer solution is added 5 parts of acrylic acid, to form component A of the formulation used herein; component B is prepared from 48.5 parts of the same solution, to which are added 1 part of N,N-dimethyl-p-toluidine and 0.5 part of the cobalt naphthenate/IBOA solution described in Example One. Both components (A and B) have a viscosity of about 100 centipoise, and are sprayed simultaneously, and at substantially the same volumetric rate, onto a PCB substrate bearing a number of surface-mounted electronic components; the sprays intersperse with one another prior to contact with the PCB surface. The damp boards are exposed to ultraviolet irradiation for a period of 20 seconds, using a lamp rated at 170 milliwatts/cm 2 , whereupon the coating is found to be tack-free. Following a 24-hour rest period at room temperature, unirradi¬ ated areas under the surface mounts are examined, and found to be fully cured. EXAMPLE THREE This Example employs ultrasonic coating apparatus like that of Figure 1, which includes a titanium head or "horn" driven by a piezoelectric crystal and having parallel, planar opposite side faces that are vertically oriented in the apparatus and that terminate at a flat, horizontal end face. Quantities of components A and B of the formulation of Example Two are deliv- ered continuously, and at substantially the same rate, to the side faces of the ultrasonic head. The head is vibrated at 20 kilohertz to produce mist-like sprays of both components issuing adjacently from the end face, the droplets of which sprays are believed to be approximately 30 to 50 microns in average dia¬ meter. A PCB substrate is placed several inches below the oper¬ ating head, so that the sprays of the two components of the formulation intersperse and coalesce prior to contact with the surface, ultimately producing a uniform deposit on the sub¬ strate. After curing under UV irradiation, in the manner here- above described in Example Two, a clear and tough, dry, solid conformal coating is produced on the substrate. EXAMPLE FOUR Part A A masterbatch for a potting and encapsulating formulation is prepared by mixing 50 parts of urethane oligomer, 25 parts of 2-hydroxyethylmethacrylate, 212 parts of IBOA, 25 parts of a cellulosic-acrylate thickener (commercially available from Bomar, Inc. under the trade designation J-LINK) , 25 parts IRGACURE 184, 25 parts of acrylic acid, and 12.5 parts of SILANE 174. A first component is prepared by adding 1 part of N,N- dimethyl-p-toluidine to 24 parts of the above-described master- batch; a second component is prepared by adding 1 part of the previously described cobalt naphthenate/IBOA solution to 22.5 parts of the masterbatch. The two components are mixed with one another and allowed to cure for approximately one hour, produc¬ ing a clear, tough gel with a slightly tacky surface; exposure to UN-light for 15 seconds renders the surface dry and tack- free. Part B A fresh mixture of the same two components is introduced into the cavity of a nylon shell, and cured in the manner de- scribed above. A tough plug is produced, which displays good adhesion to the nylon surface. Part C Repeating Part A hereof, but using 2.5 parts (rather than 1 part) of the cobalt naphthenate solution, results in a deposit of the same character but which cures to the gelled state in approximately 10 minutes 1 time. EXAMPLE FIVE Component A of a potting formulation is prepared by admix¬ ture of 63 parts of 2-hydroxyethylmethacrylate, 60 parts of IBOA, 24 parts of tetrahydrofurfurylacrylate, 15 parts IRGACURE 184, 111 parts of the urethane-acrylate oligomer, 6 parts of Silane 174, and 6 parts of N,N-dimethyl-p-toluidine. Component B employs the same ingredients in the same amounts, but excludes the amine ingredient and substitutes 30 parts of acrylic acid and 1.5 parts of the above-described cobalt naphthenate/IBOA solution. An equal-parts admixture of components A and B is intro¬ duced into the power chamber of a metal golf club; cure occurs in less than one hour. After allowing the part to stand over¬ night at room temperature, pull tests demonstrate that the deposit attains an excellent level of adhesion to the walls of the chamber. EXAMPLE SIX The acrylate monomers listed in Table One below are used to form potting compounds in which no prepolymer is included, utilizing a masterbatch having the composition: 21.9 parts of the selected acrylate monomer; 2 parts of acrylic acid; 0.1 part of the previously described cobalt naphthenate/IBOA solution, and 1 part of N,N-dimethyl-p-toluidine. Gel times realized following simple admixture, expressed in minutes, are set forth in the Table. TABLE ONE MONOMER GEL TIME hydroxyethyl methacrylate 4 isobornyl acrylate 3 octyl/decyl acrylates (mixture) 8 tripropyleneglycol diacrylate Instantaneous trimethylolpropane triacrylate Instantaneous di-trimethylolpropane tetraacrylate Instantaneous di-pentacrythritol pentacrylate Instantaneous EXAMPLE SEVEN A masterbatch is prepared by admixture of 88 parts of 2-hydroxyethylmethacrylate, 8 parts of acrylic acid, and 0.4 part of the cobalt naphthenate/IBOA solution described. To 24 parts of this masterbatch is added 1 part of each of the amines set forth in Table Two, which follows; gel times (in minutes) are indicated. TABLE TWO AMINE GEL TIME N,N-dimethyl-p-toluidine 4 N,N-dimethyl-o-toluidine 8 N,N-dimethyl-m-toluidine 3.5 N,N-dimethylaniline 5 N-methylaniline 75 aniline 120 ethyl-4-dimethylamino benzoate 20 Comparable results are achieved using the N,N-diethyl-, N,N- dipropyl-, and N,N-diisopropyl- toluidines (with the ring sub¬ stitution in all positions) , as well as with N,N-dimethyl-p- amino benzyl alcohol. EXAMPLE EIGHT A masterbatch is prepared by admixture of the following ingredients: 22 parts of hydroxyethylmethacrylate, 1 part of N,N-dimethyl-p-toluidine, and 0.1 part of the cobalt naphthenate/IBOA solution described; the mixture is heated to promote solubility. To 23.1 parts of the foregoing masterbatch (cooled to room temperature) is added 2 parts of each of the following acids; polymerization occurs in all instances, but at varying rates: oxalic, methacrylic, acetic, ascorbic, phthalic, 4-methoxyphenyl acetic, itaconic, crotonic, 3,3-dimethylamino- benzoic, and 3,5-dihydroxybenzoic. EXAMPLE NINE Admixture of 10 parts of polyethyleneglycol dimethacrylate (600 molecular weight) with 1 part of a 37 percent solution of hydrochloric acid, 1 part of N,N-dimethyl-p-toluidine, and 0.2 part of the cobalt naphthenate/IBOA solution previously de¬ scribed, produces a blue/green colored plug after 40 minutes reaction time. EXAMPLE TEN Component A of an encapsulating formulation is prepared by admixing 5 parts of 2-hydroxyethylmethacrylate, 52 parts of IBOA, 10 parts of tetrahydrofurfuryl acrylate, 25 parts of the urethane-acrylate oligomer, and 8 parts of N,N-dimethyl-p- toluidine. Component B consists of the same ingredients, but includes in addition 20 parts of acrylic acid and 1 part of the cobalt naphthenate/IBOA solution hereinabove described, and omits the amine. To 25 parts of each of the components is added 25 parts of calcium carbonate, 2 parts of titanium dioxide, and 0.5 part of 2-hydroxy-2-methyl-l-phenylpropane-l-one (a photoinitiator com- mercially available from EM Industries under the trade designa¬ tion DAROCUR 1173) . A reactive mass is prepared by mixing equal quantities of the two components, and is poured into the cavity of a nylon shell; curing to the gel state is achieved in five minutes, and subsequent curing to produce a tack-free surface is effected by ultraviolet irradiation. EXAMPLE ELEVEN Part A A formulation is prepared utilizing a masterbatch contain¬ ing 30 parts of the urethane acrylate oligomer, 20 parts of 2-hydroxyethylmethacrylate, 34 parts of an octyl/decyl acrylate mixture, 5 parts of DAROCUR 1173 and 100 parts of cornstarch (ARGO brand, commercially available from Best Foods Corporation of Engelwood Cliffs, New Jersey) . Component A of the formula¬ tion additionally contains l part of the above-described cobalt naphthenate/IBOA solution and 10 parts of acrylic acid; compo¬ nent B utilizes a second masterbatch of the same composition, to which is added 2.5 parts of N,N-dimethyl-o-toluidine and 1.2 parts of N,N-dimethyl-p-toluidine. The two components are admixed in equal amounts, and the resultant formulation is poured into the cavity of an ABS plastic part. The mixture is found to have gelled within 15 minutes; the surface is rendered tack-free by exposure to UV- radiation (20 milliwatts/cm 2 ) for 15 seconds, and the deposit is found to display excellent adhesion to the plastic part. Part B Substituting varying amounts of other commercially avail¬ able fillers (i.e., kaolin, mica, titanium dioxide, and wood flower, each suspended in hydroxyethylmethacrylate monomer) for the cornstarch used in Part A hereof is found to produce similar results. EXAMPLE TWELVE To 100 parts of bisphenol A diglycidyl ether (commercially available from Ciba-Geigy Corporation under the trade designa¬ tion ARALDITE GY 6010) are added 10 parts of 2-hydroxyethylmeth¬ acrylate, 5 parts of acetic acid, 5 parts of N,N-dimethyl-p- toluidine, and 2 parts of the previously described cobalt naph¬ thenate/IBOA solution. Gel is observed to have occurred within 15 minutes, and a hard, intractable mass is obtained after 24 hours. EXAMPLE THIRTEEN To 500 parts of the diglycidyl ether utilized in the prev¬ ious Example are added 50 parts of divinyl ether, 10 parts of acetic acid, 5 parts of N,N-dimethyl-p-toluidine and 2 parts of the cobalt naphthenate/IBOA solution. Gel is observed after a short period of time, and full curing to a hard, stiff mass is obtained in 18 hours at room temperature. EXAMPLE FOURTEEN A series of reactive products are prepared by admixing, with 20.8 parts of each of the monomers hereinafter designated, 0.2 part of the cobalt naphthenate/IBOA solution, 3 parts of acrylic acid and 1 part of N,N-dimethyl-p-toluidine: (1) SIPOMER Q5-80 (a quaternization product of dimethylaminoethyl methacrylate and dimethyl sulfate, available from Alcolac Inc. , of Baltimore, Maryland) , (2) ethyleneglycol divinyl ether, (3) triethyleneglycol divinyl ether, (4) diethyleneglycol divinyl ether, and (5) 4-acetoxystyrene. Curing is observed in all of the products, at varying rates. Notwithstanding the foregoing Example, showing the desir¬ ability of using vinyl ethers in carrying out the invention, the polymerizable composition of the instant formulations will nor¬ mally comprise a polymerizable acrylate monomer and a reactive oligomer or other prepolymer; albeit preferred in most in- stances, the prepolymer is not essential. Suitable such mono¬ mers and prepolymers are well known in the art, and are at least in part disclosed at line 53, ' column 6, through line 35, column 7 of the above-mentioned Bachmann et al patent No. 4,429,088, and at line 14, column 4 through line 52, column 5 of the above- mentioned Nativi et al patent No. 4,451,523, which disclosures are hereby incorporated by reference hereinto. Nevertheless, it will be appreciated from the Examples herein that preferred acrylate monomers include the following acrylates and corre- sponding methacrylates, used alone or in combination with one another: hydroxyethylacrylate, isobornyl acrylate, tetrahydro- furfuryl acrylate, octylacrylate and decylacrylate (normally in admixture) , tripropyleneglycol diacrylate, trimethylolpropane triacrylate, di-trimethylolpropane tetraacrylate, and di-penta- erythritol pentaacrylate. As will also be appreciated from the foregoing, the preferred prepolymer will be a urethane-acrylate, an epoxy-acrylate, a urethane-acrylate-epoxy oligomer, or the corresponding methacrylate oligomers. The acid constituent functions as one component of the catalyst system for the formulation; it is believed that the acid forms a coordination compound with the metal of the tran¬ sition metal compound, and that such a mechanism is essential to the functionability of the formulations hereof. Organic acids used can be aromatic, aliphatic or aryl-aliphatic, and typical examples have been provided hereinabove. Furthermore, it need not be a carboxylic acid, and may for example be a sul- fonic acid or, indeed, an inorganic acid such as hydrochloric or sulfuric. Although no specific pK values appear applicable, it has been observed that acids of excessive strength can effec- tively preclude a polymerization reaction that would otherwise take place if a weaker acid were used. A second essential ingredient of the catalyst system is of course the aromatic amine. As will be appreciated from the general structural formula provided hereinabove, primary, secondary, and tertiary amines may be used; also, the aromatic ring may be monocyclic or polycyclic (e.g., a coumarin, fulvene or naphthalene derivative) , and the chemical species and posi¬ tion of ring substitution may vary. It might be observed that the hardness of the cured deposit, as well as the cure rate of the formulation, tend to decrease in the order of tertiary, to secondary, to primary. The speed of cure, as well as colora¬ tion, also appear to relate somewhat to the position of sub- stituents; the fastest rates are usually observed when para- and meta-substituted compounds are used, and the intensity of any coloration that is exhibited will tend to decrease with substitution in the eta, para, and ortho positions, in that order-- The third essential ingredient of the catalyst system is the transition metal compound, effective species of which have been listed hereinabove. Suitable compounds for use herein to provide the metal ion will be evident to those skilled in the art; the following are however exemplary: cobaltous naphthen¬ ate, ferric sulfate, cerium naphthenate, cupric naphthenate, manganese naphthenate, cobaltic acetylacetonate hydrate, vanad¬ ium acetylacetonate, and lead linoleate. The concentration in which this ingredient is used may vary widely, and will depend to an extent upon the other ingredients of the system and the results desired; however, the metal compound concentration will generally be such as to provide in the formulation an amount of the metal ion ranging from a trace to perhaps one part per thousand. It has been shown that increasing the amount of metallic ion present can produce a correspondingly pronounced affect upon the rate of cure, albeit that relatively high con- centrations may produce excessive coloration. As has been pointed out above, the instant formulations do not require the presence of any active-oxygen (i.e., peroxy group-containing) , free-radical catalyst. Indeed, the incor¬ poration of such compounds will often be deleterious from the standpoints of reducing the pot-life of any component in which they are incorporated (sometimes causing the same to set-up immediately) , producing degradation due to a continuing exotherm following initiation of polymerization, causing em- brittlement of the deposit, etc. Although the theory by which the instant formulations cure is not fully understood, it is believed to involve the formation of radical cations (see Barton and Borsig "Complexes In Free- Radical Polymerization," Polymer Science Library 6, Elsevier 1988, pp 42-50) , by proton transfer from the amine compound (e.g., the loss of hydrogen by an alkyl group adjacent the nitrogen atom) . In any event, the reaction does not rely upon the presence of moisture, upon the presence or absence of oxy¬ gen, or upon heat to achieve the desired cure; needless to say. however, the rate of cure may be increased by temperature eleva¬ tion. It will often be highly desirable, as a practical matter, to include a photoinitiator in the formulation of the invention, 5 and it will be self-evident that a photoinitiator will be pre¬ requisite to certain applications. In those instances in which such an initiator is employed, the aromatic amine ingredient will serve a dual function; i.e., it will function as an inte¬ gral component of the chemical catalyst system, and also to 10 improve the efficiency of photoinitiation. Suitable photo- initiators are well known in the art, and specific illustrative compounds have been identified hereinabove; a further listing may be obtained by reference to the above-mentioned Kubota patent No. 4,820,744, particularly at line 43, column 4 through 15 line 7, column 7. When used, the photoinitiator will normally be incorporated in a concentration of 1 to 8, and preferably no more than 4, percent, based upon the weight of the formulation. Particularly in instances in which the formulation is to be used as a potting compound, it may be especially desirable to 20 incorporate a chain transfer agent of the kind that is typically used in compositions cured by electron beam initia¬ tion; e.g., halogen compounds, sulfur compounds, and secondary and tertiary aromatic hydrocarbons such as cumeme, carbon tetrachloride, 1,4-disopropyl benzene, t-butyl benzene, bis- 25 phenol A and glycidyl ether derivatives thereof, etc. The use of chain transfer agents may serve to increase the Shore D hard¬ ness of the resultant polymer, the degree of which will depend to an extent upon the concentration of the agent in the formula¬ tion, which typically will be 0.5 to 5.0, and usually 0.1 to 30 1.0, weight percent. Compounds such as silane derivatives are well known as adhesion promoters in polymerizable acrylate compositions, and ^ can be employed herein for that purpose. The low-molecular weight reactive acids (such as acrylic and methacrylic) , which ^35 may be employed as the acid ingredient of the catalyst system, also function as highly effective adhesion promoters, and con¬ sequently the effect of silanes and the like is regarded to be supplementary. Plasticizers, inert fillers, and other ingredi- ents conventionally employed in similar formulations may of course also be included, if so desired. The two components of the formulation will be so formulated so as to produce, in combination, the desired final properties of the cured deposit, consistent with the provision of satisfac¬ tory shelf-life and pot-life of the individual and mixed com¬ ponents, good rheological and flow characteristics, and other necessary or desirable properties. Although the formulation is "solvent-free," it will be appreciated that small amounts of water and/or other solvents may be present, such as for the practical introduction of an ingredient (e.g., the metal com¬ pound, an acid, etc.). It will often be convenient to use the two components of the formulation in a 1:1 volumetric ratio, especially in those instances in which automatic application (such as by the ultrasonic spraying technique described above) is to be employed, and the components will be formulated accord¬ ingly; other ratios may of course be preferred in given instances. Indeed, it is believed that a primary reason why the form- ulations embodying the invention can so readily and effectively be utilized without intimate mixing (e.g., by mere interspersal of sprays) stems from the fact that stoichiometric relationships are not required among the reactive ingredients. This is con¬ sistent with the hypothesis that reaction in these formulations occurs through a radical cationic mechanism; i.e., the growing polymer chains do not self-terminate or quench themselves, as does tend to occur in conventional free-radical propagated re¬ actions. Thus, it can be seen that the present invention provides a novel and highly effective two-part formulation comprised of polymerizable, oxygen-containing ethylenically unsaturated (e.g., acrylate) monomers, which is suitable for use as an ad¬ hesive, for potting, for conformal coating, and for other like applications. The formulation does not depend upon the use of a free-radical, active-oxygen catalyst for initiation of reaction, and highly satisfactory cured deposits can be produced from it despite the lack of intimate admixture of the two constituent components. The invention also provides a novel catalyst system for use in such formulations, as well as a novel method for the production of an adherent, solid deposit in a highly facile and yet efficient manner.

Claims: THE CLAIMS Having thus described the invention, what is CLAIMED is: 1. A two-part, solvent-free liquid formulation that is innately curable to an adhesive solid, comprising a first com- ponent that includes an acid ingredient, and a second component that includes an aromatic amine compound having the general ormula: wherein each of "R^" and "R 2 " is selected from the class con¬ sisting of hydrogen and an alkyl group, and wherein "Ar" is selected from the class consisting of a monocyclic and poly- cyclic aromatic groups, at least one of said components addi- tionally including a transition metal compound, and at least one of said components being comprised predominantly of a poly¬ merizable composition including at least one oxygen-containing ethylenically unsaturated polymerizable ingredient, said acid ingredient being substantially soluble in said polymerizable composition and being capable of forming a coordination compound with the metal of said metal compound, said formulation being devoid of any free-radical, active-oxygen polymerization catalyst. 2. The formulation of Claim 1 wherein said amine compound is selected from the group consisting of N,N-(alkyl)-toluidines in which the alkyl group contains one to three carbon atoms, N- methylaniline, N,N-dimethylaniline, aniline, N,N-bis(2-hydroxy- ethyl)-p-toluidine, dimethyl aminostyrene, 4-dimethylamino- benzoic acid, ethyl-4-dimethylamino benzoate, N,N-dimethyl-p- amino benzyl alcohol, and mixtures thereof. 3. The formulation of Claim 1 wherein said metal compound is admixed in said first component, and wherein both of said components are comprised predominantly of said polymerizable composition. 4. The formulation of Claim 1 wherein said metal compound is a compound of a metal selected from the class consisting of cobalt, iron, cerium, copper, lead, manganese and vanadium. 5. The formulation of Claim 4 wherein said acid is a low molecular weight carboxylic acid selected from the class con- sisting or acrylic, methacrylic, acetic, ascorbic, oxalic, phthalic, itaconic, crotonic, 4-methoxyphenyl acetic, 3,5-di- hydroxybenzoic, and 3,3-dimethylaminobenzoic acids. 6. The formulation of Claim 1 wherein said polymerizable ingredient is an acrylate monomer. 7. The formulation of Claim 1 wherein said polymerizable ingredient is a prepolymer selected from the group consisting of urethane (meth)acrylates, epoxy (meth)acrylates, and urethane epoxy-(meth)acrylates. 8. The formulation of Claim 1 wherein at least one of said components additionally includes an effective amount of a photo¬ initiator capable, when activated, of catalyzing polymerization of said polymerizable ingredient. 9. The formulation of Claim 1 wherein said components are formulated for use in equal amounts. 10. The formulation of Claim 1 comprising, in percentages based upon the total weight thereof, 0.05 to 10 of said acid ingredient, 0.05 to 10 of said aromatic amine compound, and 0.002 to 1.5 of said metal compound. 11. The formulation of Claim 7 wherein said polymerizable composition comprises at least 20 weight percent of at least one acrylate monomer, and at least 20 weight percent of at least one prepolymer selected from said prepolymer group, based upon the weight of said formulation. 12. As a polymerization catalyst system for a formulation that includes at least one oxygen-containing ethylenically un- saturated polymerizable ingredient, the combination consisting essentially of an acid ingredient, an aromatic amine compound, and a transition metal compound, said acid ingredient being capable of forming a coordination compound with the metal of said compound, and said aromatic amine compound having the general formula: wherein each of "R^" and "R2" is selected from the class con¬ sisting of hydrogen and an alkyl group, and wherein "Ar" is selected from the class consisting of a monocyclic and poly- cyclic aromatic groups, said system optionally including a photoinitiator, and being devoid of any free-radical, active- oxygen polymerization catalyst. 13. The system of Claim 12 wherein said aromatic amine compound is selected from the group consisting of N,N-(alkyl)- toluidines in which the alkyl group contains one to three car¬ bon atoms, N-methylaniline, N,N-dimethylaniline, aniline, N,N- bis(2-hydroxyethyl)-p-toluidine, dimethyl aminostyrene, 4- dimethylaminobenzoic acid, ethyl-4-dimethylamino benzoate, N,N-dimethyl-p-amino benzyl alcohol, and combinations thereof. 14. The system of Claim 13 wherein said acid ingredient is selected from the class consisting of acrylic, methacrylic, acetic, ascorbic, oxalic, phthalic, itaconic, crotonic, 4-meth- oxyphenyl acetic, 3,5-dihydroxybenzoic, 3,3-dimethylamino- benzoic, and p-toluenesulfonic acids, and mixtures thereof. 15. The system of Claim 13 wherein said metal compound is a compound of a metal selected from the class consisting of cobalt, iron, cerium, copper, lead, manganese and vanadium. 16. The system of Claim 13 additionally including an effective amount of a photoinitiator capable, when activated, of catalyzing polymerization of the polymerizable ingredient. 17. In a method for the production of an adherent solid deposit upon a substrate, the steps comprising: (a) providing a two-part, solvent-free liquid formulation that is innately curable to an adhesive solid, comprising a first component that includes an acid ingredient, and a second component that includes an aromatic amine compound having the general formula: wherein each of "R^" and "R2 11 is selected from the class con¬ sisting of hydrogen and an alkyl group, and wherein "Ar" is selected from the class consisting of a monocyclic and poly- cyclic aromatic groups, at least one of said components addi¬ tionally including a transition metal compound, and at least one of said components being comprised predominantly of a poly¬ merizable composition including at least one oxygen-containing ethylenically unsaturated polymerizable ingredient, said acid ingredient being substantially soluble in said polymerizable composition and being capable of forming a coordination compound with the metal of said metal compound, said formulation being devoid of any free-radical, active-oxygen polymerization cat- * 5 alyst. (b) forming a liquid deposit of said formulation upon a substrate; and (c) effecting curing of said liquid deposit to produce an adherent solid deposit on said substrate. 10 18. The method of Claim 17 wherein said aromatic amine compound is selected from the group consisting of N,N-(alkyl)- toluidines in which the alkyl group contains one to three carbon atoms, N-methylaniline, N,N-dimethylaniline, aniline, N,N-bis(2-hydroxyethyl)-p-toluidine, dimethyl aminostyrene, 15 4-dimethylaminobenzoic acid, ethyl-4-dimethylamino benzoate, N,N-dimethyl-p-amino benzyl alcohol and combinations thereof. 19. The method of Claim 17 wherein said step (b) includes producing, from each of said formulation components, a spray of fine droplets, and interspersing said sprays just prior to con- 20 tact of said substrate therewith. 20. The method of Claim 19 wherein each of said sprays is produced by subjecting thin films of said formulation compo¬ nents, each moving along a given axis, to ultrasonic vibratory motion on said axes. 25 21. The method of Claim 20 including, as additional steps: providing ultrasonic apparatus comprised of a spray head having opposite side surface portions that are substantially parallel to one another and that terminate at one end at a common transverse plane, and delivery means for the delivery of 30 said components of said formulation separately to said side surface portions; operating said apparatus to cause said spray head to vibrate ultrasonically along an axis parallel to said surface portions while concurrently delivering said formulation components, at relative rates suitable for reaction there- 35 between, separately to said side surfaces at points spaced from said common plane, so as to produce adjacent sprays of said components issuing from said one end of said head; and dispos¬ ing said substrate outwardly of said common plane, spaced from said spray head a distance sufficient to permit substantial interspersion of said sprays of formulation components prior to contact of said substrate thereby. 22. The method of Claim 19 wherein each of said formula¬ tion components has a viscosity, measured at 25° Centigrade, in the range 80 to 200 centipoise. 23. The method of Claim 17 wherein said formulation addi¬ tionally includes an effective amount of a photoinitiator cap¬ able, when activated, of catalyzing polymerization of said poly¬ merizable ingredient, and wherein said curing step (c) is in- itiated by exposure of said liquid deposit to actinic radiation for said photoinitiator. 24. The method of Claim 18 wherein, in said formulation, said acid ingredient is selected from the class consisting of acrylic, methacrylic, acetic, ascorbic, oxalic, phthalic, ita- conic, crotonic, 4-methoxyphenyl acetic, 3,5-dihydroxybenzoic, 3,3-dimethylaminobenzoic, and p-toluenesulfonic acids, and mix¬ tures thereof, and wherein said metal compound is a compound of a metal selected from the class consisting of cobalt, iron, cer¬ ium, copper, lead, manganese and vanadium.

Inventors: BACHMANN ANDREW G, GROSCLAUDE GARY V, BACHMANN, ANDREW, G., GROSCLAUDE, GARY, V.
Applicants: DYMAX CORP, DYMAX CORPORATION
Application year: 1993
Main classification: C08F2
IPC codes: C08F4, C09J4