Stabilized Cyanoacrylate Adhesives containing Bis-Trialkylsilyl Esters of Sulfuric Acid

United States Patent [19] Waniczek et al. [54] STABILIZED CY ANOACRYLATE ADHESIVES CONTAINING BIS-TRIALKYLSILYL ESTERS OF SULFURIC ACID [75] Inventors: I-Ielmut Waniczek, Cologne; Wilfried Kniege, Bergisch-Gladbach, both of Fed. Rep. of Germany Bayer Aktiengesellschaft, Leverkusen, Fed. Rep. of Germany [21] Appl. No.: 720,635 [22] Filed: Apr. 8, 1985 [30] Foreign Application Priority Data Apr. 19, 1984 [DE] Fed. Rep. of Germany ..... .. 3414805 [51] Int. c1.4 ......................... .. cosx 5/s4;.cosJ 3/oo; cos1= 2/40 [52] U.S. c1. .................................. .. 524/730; 524/156; 524/262; 524/731; 524/850 [73] Assignee: [11] Patent Number: 4,650,826 [45] Date of Patent: Mar. 17, 1987 [58] Field of Search ............. 524/156, 262, 730, 731,» 524/850 [56] References Cited U.S. PATENT DOCUMENTS 4,565,883 1/ 1986 Sieger et al. ...................... .. 549/475 FOREIGN PATENT DOCUMENTS 2128985 1/1973 Fed. Rep. of Germany . 2535335 4/1984 France . 2129003 5/ 1984 United Kingdom . 2148312 5/1985 United Kingdom . 2148313 5/1985 United Kingdom . Primary Examiner-——I-Ierbert J. Lilling Attomey, Agent, or Firm—Conno1ly and Hutz [57] ABSTRACI‘ This invention relates to stabilized adhesives, to which silyl esters are added for stabilization. 1 Claim, No Drawings 4,650,826 1 STABILIZED CY ANOACRYLATE ADHESIVES CONTAINING BIS-TRIALKYLSILYL ESTERS OF SULFURIC ACID This invention relates to stabilized adhesives, to which silyl esters are added for stabilization. It is known that monomeric cyanacrylic acid esters can be stabilized with respect to polymerization by addition of small quantities of acidic gases, such as S02 and radical scavengers, such as hydroquinone (e. g. U.S. Pat. Nos. 2,794,783 and 2,765,332). However, the use of S02 suffers from a series of dis- advantages: A concentration of from 0.001 to 0.01% by weight has to be observed as the setting speed of the cyanacry- lates decreases with higher S02 concentrations, and the cyanacrylates are not sufficiently stabilized with lower concentrations. The quantity can only be adjusted with difficulty owing to the gaseous state of the stabilizer and the low concentration. The monomeric cyanacrylates are conventionally obtained by depolymerisation of polycyanacrylates. In this production method more of the acidic stabilizing gas is suitably added during the gas phase than is re- quired for stabilization. After cooling, excess S02 has to be removed by means of time—consuming operations in order to provide a product which has sufficient stability and cuning speed. Continual determination of the S02 content is required. The monomer which has been stabi- lized in this manner yields S02 under certain conditions. The known non-gaseous stabilizers, such as sulphonic acids, have either only a moderately-stabilizing effect or they seriously reduce the setting speed. Thus, for exam- ple, a cyanacrylate adhesive which can firmly bond two nitrile rubber sections together in two seconds, can be so modified by the addition of only 0.5% by weight of methane sulphonic acid that adhesion no longer takes place even within 10 seconds. It is also known to add sulphonic acid anhydrides to reduce the delay in setting of cyanacrylates (e.g. Ger- man 2 128 985). However, the rapid setting speed and good stability in storage desired in modern methods of adhesive production are not always achieved by using sulphonic acid anhydrides. Owing to their hydrolysis sensitivity, they almost always contain sulphonic acids. As traces of water can only be excluded with difficulty from the storage or use of an adhesive, the proportion of sulphonic acids in the adhesive can be even higher. Silicon compound-containing cyanacrylates are known and described, for example, in Japanese Pat. No. 73 103 633. However, these Si compounds serve to make the cyanacrylates hydrophobic and do not con- tribute to the improvement of stability in storage. It has now been found that cyanacrylate adhesives can be stabilized, while avoiding the above disadvan- tages, by the addition of silyl esters of strong mono- or poly-valent inorganic or organic mono- or polyacids. The setting speed and stability in storage is markedly greater than with hitherto known stabilized cyanacry- late adhesives. Thus, this invention relates to stabilized adhesives consisting of anionically polymerisable monomeric ole- fins corresponding to the formula (I) ' IO 20 25 30 35 45 50 55 60 65 2 X (I) Cl-I2=C:Y, wherein X represents CN and COOR, and Y represents CN, halogen, such as chlorine and bro- mine, SO3R and ~—-COOR, and R represents a C1-C2‘) alkyl or alkenyl group, a C5—C1o cycloalkyl group or an aryl group having 6 carbon atoms, such as phenyl, and a silyl ester of a strong acid and optionally other conventional additives. Cyanacrylic acid esters corresponding to the formula (11) CN I , CH2=C--COOR, (11) wherein R is as defined in formula (I), methylene malodinitrile or compounds corresponding to for- mula (III) SO3R __ / CH2—C\ , CN (III) wherein R is also as defined in formula (I), can, for example, be used as anionically polymeiisable monomer olefms. Cyanacrylic acid esters corresponding to formula (II) are preferably used. 2 Silyl esters of strong mono- or poly-valent inorganic or organic mono- or poly-acids, such as mono-, di- or tri-alkyl silyl esters of strong acids such as hydrohalic acids, mono-, di- or tri-sulphuric acid, mono-, di- or poly-phosphoric acid, substituted or unsubstituted al- kyl-, cycloalkyl-, aryl- or aralkyl-sulphonic acids, chlo- rosulphonic acid, sulphinic acid esters, nitric acid or substituted or unsubstituted carboxylic acids are used according to the invention. Examples of silyl esters of strong mono- or polybasic inorganic or organic mono- or poly-acids are tetra- chlorosilane, methyl-, ethyl- and butyltrichlorosilane, dimethyl-, diethyl- or dibutyldichlorosilane, trimethyl-, triethyl- or tributylchlorosilane, bis-trimethylsilyl sul- phuric acid, bis-triethylsilyl-disulphuric acid, bis- tributyltrisulphuric acid, dimeric dimethylsilylsulphate, tris-trimethyl-, tris-triethyl- or tris-tributylphosphate, 6-butyl-4,6—dimethyl-l,2,6-oxathiosilinane-2,2-dioxide, trimethylsilylchlorosulphonate, trimethylsilylmethane, sulphinate, trimethylsilylnitrate or trimethylsily1tri- fluoroacetate. Bis-trialkylsilyl esters of mono-, di- and tri-sulphuric acid corresponding to formula (IV) lfl R4 I R2--Si-O-(-SO20-);,Si-R5, I I R3 R6 wherein R1 to R5 are the same or different and represent a C1—C1o alkyl-, aryl- or aralkyl group, and n represents an integer of from 1 to 3, are preferably used. 4,650,826 3 Bis-trialkylsilyl esters of monosulphuric acid, such as bis-trimethylsilyl sulphate are most preferably used. The stabilizers for adhesives used according to the invention are produced by known methods. Their pro- duction is summarized in, for example, Houben-Weyl, Methoden der organischen Chemie, Vol 13/5, pages 163 to 175, 4th edition, Georg Thieme Verlag Stuttgart New York, 1980. The superiority of the stabilizers used according to the invention for anionically readily polymerisable monomers resides in the fact that they are straightfor- ward to produce and simple to handle and that the adhesives set more rapidly and have greater stability in storage than in the state of the art. A further advantage of the stabilizers according to the invention resides in the fact that they can be used as anionic inhibitors in the synthesis of anionically readily polymerising monomers, such as a-cyanacrylates. This makes redundant the addition of known stabilizers in the production thereof so that they do not have to be trivially removed by costly methods. The stabilizers used according to the invention, such as the silyl esters of inorganic acids, such as phosphoric acid or sulphuric acid, also have the advantage that their decomposition products do not yield distillable acidic compounds under the effects of moisture, for example. If, for example, cyanacrylates are stabilized with sulphonic acid anhydrides, this cyanacrylate can scarcely be freed by distillation from sulphonic acid which may be present. However, if a cyanacrylate con- tains bis-trimethylsilylsulphuric acid according to the invention, for example, sulphuric acid and hexamethyl- disiloxane are produced under the effects of moisture. If a cyanacrylate which has been stabilized in this manner 10 15 20 25 30 4 methyl methacrylate, fillers, such as highly-dispersed silica, or plasticisers, such as tricresylphosphate. The stabilized anionically readily polymerisable mon- omers according to the invention, such as a-cyanacry- lates, are very suitable as rapid-setting single-compo- nent adhesives which are stable in storage. They set rapidly particularly when in the form of thin layers. The most varied substrates, such as plastic materials, metal, earthenware, wood or glass, can be bonded with the cyanacrylates which have been stabilized according to the present invention. EXAMPLE 1 100 g of the a-cyanacrylic acid methyl ester pro- duced by depolymerisation of polycyanacrylic acid methyl esters are mixed with the quantities of bis-trime- thylsilyl sulphate (BTSS) given in the following Table. In order to test the stability in storage, the samples are poured into flasks of polyethylene and are stored in a heating chamber at 77° C. The stability in storage is measured by cooling the samples at regular time inter- vals to room temperature and assessing their state of aggregation. In order to test the setting speed, single-row over- lapped adhesives are produced with the cyanacrylate adhesives which have been stabilized as given above, as described in VDI 229 (5.l.l.), iron (ST 1303) and SMC (cross-linked unsaturated glass fibre-reinforced polyes- ter resin) being used as joining materials. The samples are produced and the adhesive strength is determined by the shear tension test according to DIN 53 283. The combined tension and shear resistances are determined at various time intervals after the adhesive has been produced. State of aggregation after x hours of storage at 77° C. BTSS x hours (mg) 12 24 36 48 60 72 (a) 25.6 low viscosity low viscosity low viscosity slightly more viscous viscous wax-like (b) 12.8 " " " low viscosity slightly viscous viscous (c) 6.4 " ” ” " low viscosity slightly more viscous (d) 3.2 " " slightly more viscous viscous wax-like (e) 1.6 " ” viscous wax-like hard is distilled, then only the stabilizer and the cyanacrylate distill off under suitable conditions. The hexamethyl- disiloxane which in certain cases also distills off does not have a detrimental effect. The quantity of stabilizer added to the monomeric olefm is from 0.0005 to 3% by weight. The stabilizer content according to the present invention is preferably from 0.001 to 1% by weight, most preferably from 0.001 to 0.1% by weight, based on the quantity by weight of olefm used. In exceptional cases, further additives, such as stabi- lizers of anionic and radical polymerisation, such as S02, sulphonic acids, sulphonic acid anhydrides, hydro- quinone,‘ p-methoxyphenol or quinone can be added to the anionically readily polymerisable monomers in ad- dition to the stabilizers used according to the invention. Furthermore, the stabilized adhesives according to the invention can contain further conventional addi- tives, which, for example, influence the viscosity or reduce the brittleness of the cured adhesive. These mea- sures have already been described in the relevant litera- ture. Thus, it is possible to add polymers, such as poly- 50 55 65 Combined tension and shear resistance (MP3! iron/iron setting SMC/SMC BTSS time (minutes! setting time {minutes} (mg) 15 30 1440 7.5 15 30 1440 (a) 25.6 1.7 3.3 5.1 9.9’ (b) 12.8 3.1 8.4 8.7‘ 10.0‘ (c) 6.4 9.2 10.0 10.1 7.6 9.0‘ 9.6‘ 11.3‘ (d) 3.2 11.5 9.2 9.6 8.3‘ 10.3’ 8.7‘ 10.0’ (e) 1.6 11.4 11.2 11.0 9.7‘ 9.9‘ 10.7‘ 10.3‘ ‘predominantly a strip from the joining part. The combined tension and shear resistance values are average values of 10 individ- ual measurements respectively. COMPARATIVE EXAMPLE As in Example 1, 100 g of cyanacrylic acid methyl ester are mixed with the quantities given in the follow- ing Table of methane sulphonic acid anhydride (MSA) and the stability in storage and setting speed are mea- sured: 4,650,826 5 MSA State of aggregation after x hours storage at 77' C. (mg) 12 24 36 48 60 72 (a) 25.6 viscous highly-viscous hard (b) 12.8 viscous highly-viscous hard (c) 6.4 viscous highly-viscous hard (d) 3.2 highly-viscous hard (e) 1.6 hard hard Combined tension and shear resistance gMPa! iron/iron setting SMC/SMC MSA time gminutes] setting time {minutes} (mg) 15 30 1440 7.5 15 30 1440 (a) 25.6 0.1 0.1 0.6 8.5‘ (b) 12.8 0.1 1.5 1.1 8.5‘ (c) 6.4 6.8 5.7 10.1 0.1 2.6 2.8 8.6‘ (d) 3.2 5.4 5.5 12.4 4.8 5.6 4.7 8.3 (e) 1.6 7.5 7.1 10.1 6.0 4.2 5.2 8.5‘ ‘predominantly strips from the joining part The above combined tension and shear resistance values are average values from 10 individual measurements respectively. The measured results given show that the adhesives which have been stabilized according to the invention have a very rapid setting speed and good stability in storage. ~ ‘ 10 15 20 25 30 35 45 50 55 65 6 We claim: _ 1. Stabilized adhesives comprising anionically poly- merizable monomeric olefins corresponding to the for- mula x CH2=C:Y wherein X represents CN and COOR, Y represents halogen, SO3R and —COOR, and R represents a C1—C2o alkyl or alkenyl group, a C5—C1o cycloalkyl group or an aryl group, and a bis-trialkylsilyl ester of mono- , di- or tri-sulphuric acid corresponding to the formula V ]fl ]'{4 R2-Sli-O-(-S02-0-)-S'i-R5 R3 R6 wherein R1 to R5 are the same or different and represent a C1-C10 alkyl, -aryl or -aralkyl group, and n rerpesents an integer of from 1 to 3, as a stabilizer. * i * # t