Cyanoacrylate Adhesive Paste Compostion

United States Patent [11] Gleave [54] CYANOACRYLATE ADHESIVE PASTE COMPOSITIONS [75] Inventor: Edward Roger Gleave, Dublin, Ireland [73] Assignee: Loctite (Ireland) Limited, Dublin, Ireland [30] Filed: Jul. 11, 1977 Foreign Application Priority Data Jul. 14, 1976 [IE] [51] Int. Cl.2 [52] U.S. Cl Ireland 2,794,788 3,607,542 3,663,501 3,692,752 3,836,377 4,042,442 Aug. 8, 1978 References Cited U.S. PATENT DOCUMENTS 6/1957 9/1971 5/1972 9/1972 9/1974 8/1977 Coover et aI. 260/17 Leonard 156/285 Adams et aI. 260/41 R Setsuda et aI. 260/78.5 N Delahunty........................... 106/287 Dombroski et aI. 156/310 Primary Examiner-Richard B. Turer Attorney, Agent, or Firm-Jean B. Mauro [21] Appl. No.: 814,581 [22] [56] 4,105,715 [45] [19] 1553/76 C08L 33/00 260/881; 156/331; 156/334; 260/873; 260/878 R; 260/884; 526/298 526/298; 260/881, 884 [58] Field of Search ABSTRACT [57] A cyanoacrylate adhesive composition in thixotropic paste form is made by mixing a liquid cyanoacrylate ester with powdered organic fillers selected from (i) polycarbonates, (ii) polyvinylidene fluorides, (iii) polyethylenes, and (iv) acrylic block copolymer resins containing saturated elastomer segments. Concentration of the filler is about 5 to 100 parts by weight. Particle size of the filler is about 2 to 200 microns. 5 Claims, No Drawings 1 CYANOACRYLATE ADHESIVE PASTE COMPOSITIONS BACKGROUND OF THE INVENTION 4,105,715 2 SUMMARY OF THE INVENTION According to the invention, there is provided a thixotropic, curable adhesive composition comprising: (a) a monomeric ester of 2-cyanoacrylic acid, (b) to each 100 parts by weight of monomeric ester, about 5 to about 100 parts by weight of a finely divided organic powder selected from the group consisting of: (i) polycarbonates (ii) polyvinylidene fluorides (iii) polyethylenes (iv) acrylic block copolymer resins containing saturated elastomer segments. The composition also preferably contains one or more known acidic and free radical inhibitors, and optionally other functional additives for such purposes as improving thermal resistance, providing color, accelerating the cure reaction, providing crosslinking, etc. By adjusting the quantity and kind of filler, the compositions of this invention may be prepared in various forms, from a loose jelly to a thick paste. In all forms, however, they have thixotropic properties. It is a surprising and important advantage of these compositions that they retain most of the bond strength of the unfilled cyanoacrylate adhesive even when heavily filled. 5 1. Field of the Invention This invention relates to cyanoacrylate adhesive compositions which are improved by being rendered thixotropic and nondripping by incorporation of finely divided organic powders. 10 2. Description of the Prior Art Liquid cyanoacrylate compositions have long been known in the art as excellent adhesives. Having achieved wide acceptance in industrial applications, 15 cyanoacrylates have recently made enormous advances in sales in the consumer adhesive market. Various of the inherent characteristics of cyanoacrylates, which caused no particular difficulties in industrial automatic application equipment, have been detrimental to their 20 unqualified acceptance in consumer use. Chief among these characteristics are (I) the adhesives' relatively low viscosity, causing it to run or drip off the point of application to some undesired point, and (2) its extremely rapid cure speed when catalyzed by 25 small amounts of moisture, as found in human skin. These characteristics have often made cyanoacrylates troublesome and inconvenient to use by unskilled consumers. Accordingly, a cyanoacrylate adhesive compoDETAILED DESCRIPTION OF THE sition with controlled flow characteristics and easier 30 INVENTION applicability, while yet retaining desirably rapid cure The benefits of this invention are achievable with speed and bond strength, would be a great boon to the essentially all adhesive compositions based upon cyanoconsumer market, as well as to industrial applications acrylate esters. Most commonly, the esters have the where such properties would be advantageous. A variety of fillers has been incorporated into cyano- 35 formula acrylate adhesive compositions to bring about certain CN changes in properties. U.S. Pat. No. 2,794,788 teaches I thickening of cyanoacrylate adhesives by dissolving CH 2=C-COOR therein quantities of polymeric alkyl cyanoacrylates, as well as other compounds including polyacrylates and 40 wherein R represents a C I_16 alkyl, cycloalkyl, alkenyl, methacrylates, and cellulose esters such as acetate, procycloalkenyl, phenyl or heterocyclic (such as furfuryl) pionate and butyrate. radical. Naturally, the above R group can contain any U.S. Pat. No. 3,836,377 notes among the additional linkages or substituents which do not adversely affect known thickeners polyvinyl ethers such as polyvinylthe monomer in the performance of its intended funcmethyl ether. U.S. Pat. No. 3,692,752 discloses thick- 45 tion in the cyanoacrylate adhasive compositions, such ened cyanoacrylate solutions containing certain polyas strongly basic substituents which may adversely afether acrylates/methacrylates, acrylic/methacrylic esfect the stability of the adhesive composition. For purters of bis(hydroxyalkyl) phosphonic acid derivatives, poses of this invention, the preferred monomers are and acrylic/methacrylic esters of tris(hydroxyalkyl) 50 those wherein R is a cyclohexyl or a C 1 to C 6 alkyl, or cyanuric acid derivatives. alkenyl radical. Most preferred are methyl and ethyl The preceding references relate to thickened homocyanoacrylates. The esters may be used singly or in geneous solutions containing organic compounds as admixture. thickeners. Various inorganic materials have also been The above monomeric esters of 2-cyanoacrylic acid proposed as fillers, which also have the effect of thick- 55 can be prepared by methods known in the art, such as ening the composition. Thus, U.S. Pat. No. 3,663,501 those described in U.S. Pat. Nos. 2,467,927 to Ardis, teaches preparation of a dental cement containing inert, issued Apr. 9, 1949 and 3,254,111 to Hawkins et aI., finely-divided solids such as fused silica, quartz and issued May 31, 1966. alumina. Similarly, U.S. Pat. No. 3,607,542 teaches the Cyanoacrylate esters adhesive compositions generpreparation of a water-resistant cyanoacrylate paste 60 ally contain an anionic inhibitor, e.g., an acidic subcontaining insoluble, inert fillers such as salts of calstance, soluble in the ester of 2-cyanoacrylic acid, cium, titanium, zinc, tin, aluminum, iron and cooper, which inhibits anionic polymerization. The specific among others. inhibitor chosen is not critical to this invention, and a None of the known references relates to use of certain number of suitable inhibitors of anionic polymerization finely-divided organic powders which are not dissolved 65 are well known in the art. or not fully dissolved in the cyanoacrylate monomer The best known are the soluble acidic gases such as sulfur dioxide, sulfur trioxide, nitric oxide, and hydroand which convert the liquid cyanoacrylate to a nongen fluoride. More recently, organic sultone inhibitors drip, thixotropic gel or paste. 4,105,715 3 have been developed, the sultone being generally represented by the formula o II 0--5=0 ,-XJ 5 4 (d) about 10 to 20 parts by weight, preferably about 12 to 15 parts. The filler may be added gradually to the monomer with good agitation so as to form a smooth, homogeneous fluid. Preferably, high-shear mixing will be used. Preparation of a homogeneous mixture can also be achieved by dissolving or suspending the organic filler in a volatile solvent compatible with the cyanoacrylate, stirring the solvent thoroughly into the cyanoacrylate and thereafter evaporating the solvent. The composition thus formed also will preferably be formulated to contain one or more inhibitors and stabilizers well known to the art, as previously described. Particle size of the organic powders used as fillers in this invention will be found to vary according to commercial source, type of polymerization used in manufacture, etc. For purposes of this invention, useful particle size ordinarily occurs in the range of about 2 microns to about 200 microns, preferably from about 5 to about 50 microns. Selection of appropriate particle size (or commercial grade, as the case may be) will be a matter of routine experimentation. The invention is illustrated, but not limited, by the following examples. wherein X isan organic radical joining the -S(Oz)Ogroup in a 4, 5, or 6 member heterocyclic ring, prefera- 10 bly a 5 member heterocyclic ring. Preferably, X is a hydrocarbon group, although it can contain any substituents or linkages which do not adversely affect the suitone for its intended use as a stabilizer of the adhesive composition. Another excellent class of stabilizers are 15 the organic sulfonic acids, preferably having a molecular weight less than about 400. To be optimally useful as a stabilizer in the adhesive compositions, the sulfonic acid should have a pKA value (dissociation constant in water) of less than about 2.8, and preferably less than 20 about 1.5. While not essential, the cyanoacrylate adhesive compositions of this invention generally also contain an inhibitor of free radical polymerization. The most desirable of these inhibitors are of the phenolic type, such as 25 quinone, hydroquinone, t-butyl catechol, p-rnethoxyEXAMPLES phenol, etc. EXAMPLE 1 The above inhibitors may be used within wide ranges; but the following general guidelines are representative A cyanoacrylate paste composition was prepared by of common practice, all figures being weight percent of 30 mixing the following materials: the adhesive composition: acidic gases-from about ethyl cyanoacrylate - 100 parts by weight, contain0.001 to about 0.06% by weight; sultones-from about ing 40 parts per million hydroxypropane sulfonic 0.1% to about 10% by weight; sulfonic acids -from acid as inhibitor about 0.0005% to about 0.1% by weight; free radical polyvinylidene fluoride powder - 65 parts by weight, approximately 5 microns particle size, inhibitors-from about 0.001% to about 1%. 35 Other common additives for cyanoacrylate adhesive trade named Kynar 301 and supplied by Penn walt compositions are plasticizers. Plasticizers serve to make (U.K.) Limited. The resulting product was a smooth, white paste which the cured bonds less brittle and, therefore, more durawas thixotropic and non-drip and could be easily ble. The most common of these plasticizers are C 1 to CIQ alkyl esters of dibasic acids such as sebasic acid and 40 spread. Adhesive bonds formed with this product cured malonic acid. Other plasticizers, such as diaryl ethers rapidly and were only slightly less strong than similar and polyurethanes, also may be used, and a variety of bonds made with the corresponding unfilled (control) other plasticizers are also known. cyanoacrylate. In addition to the monomer, the second required EXAMPLE 2 ingredient is a filler selected from: 45 Example I was repeated except that methyl cyanoac(a) Polycarbonates, i.e., polyesters of carbonic acid rylate was used. Equivalent results were obtained. (b) Polyvinylidene fluoride (various grades) (c) Polyethylene, and EXAMPLE 3 (d) Acrylic block copolymer resins containing satuExample I was repeated except that the polyvinylirated acrylic elastomer segments. 50 dene fluoride was replaced by an equivalent amount of Preferred fillers of the type (d) include acrylic block copolymers made by polymerizing a mixture of methaceither polycarbonate or polyethylene. Except for the rylate monomers in the presence of a latex of acrylate color, equivalent results were obtained in both cases. As already mentioned, the compositions of this invenester polymer (the ratios of the various components being chosen so as to maximize the impact strength of 55 tion have non-Newtonian viscosity characteristics, as mixtures of the copolymers with polyvinyl chloride, shown by the following observations: and simultaneously to minimize the incidence of swell(1) The compositions do not flow under their own weight, but can be made to flow easily by the appliing of extrudate during extrusion of these mixtures. These procedures are well known in the art). Mixtures cation of a slightly larger force. This indicates either Bingham plastic or pseudoplastic behavior, of these fillers can also be used. Corresponding useful 60 concentrations of these materials are, respectively per viz., a form of fluid behavior in which a certain threshold stress must be applied to a fluid before 100 parts by weight of monomer, (a) about 5 to 15 parts by weight, preferably about 8 flow occurs. (2) When stirred for a short time, the composition to 12 parts; (b) about 35 to 100 parts by weight, preferably about 65 changes its consistency so that it does not flow under its own weight. On standing, the composi60 to 80 parts; tion reverts to its original consistency and no (c) about 60 to 100 parts by weight, preferably about longer flows under its own weight. This indicates 70 to 80 parts; and 5 4,105,715 thixotropic behavior in its true sense, i.e., a change of apparent viscosity with time when a fluid is stirred. While the invention should not be construed as limited by the terms of any theoretical explanation, it would seem that the interaction between the cyanoacrylate monomer and the filler substance is responsible for producing the thixotropic consistency which is the prime feature of this invention. The filler substances incorporated, all of which are organic polymers, have low solubility in cyanoacrylate monomers. However, a certain amount of cyanoacrylate monomer is absorbed into the particles of the polymers and causes them to swell and soften. The polymers are prevented from completely dissolving either (i) by virtue of being crystalline polymers which are below their crystalline melting temperature, and therefore "frozen" out of solution (as are polycarbonate and polyvinylidene fluoride); (ii) by being of a sufficiently insoluble nature to preclude any possibility of solution (polythene); or (iii) by being composed of molecules containing segments which are soluble, attached to segments which are not (acrylic block copolymers). 5 IO 15 20 25 30 35 40 45 50 55 60 65 6 These characteristics of the filler substance give rise to a liquid structure comprising swollen polymer particles of a somewhat jellyish consistency, in tight contact with each other, and surrounded by a thin liquid which fills the interstices between the particles. This obviously leads to flow behavior substantially different from that of a continuous liquid. What is claimed is: 1. A thixotropic, curable adhesive composition comprising: (a) a monomeric ester of 2-cyanoacrylic acid, (b) for each 100 parts by weight of monomeric ester, about 5 to about 100 parts by weight of a polyvinylidene fluoride powder. 2. A composition of claim 1 containing in addition a stabilizing amount of an acidic stabilizer and a free radical inhibitor. 3. A composition of claim 1 wherein the monomeric ester is methyl cyanoacrylate or ethyl cyanoacrylate. 4. A composition of claim 1 wherein the concentration of the organic powder is about 60 to about 80 parts by weight. S. A composition of claim 1 wherein the particle size of the organic powder is about 5 to about 50 microns. * * * * *