Curable resin compositions, their preparation and use

Abstract: A curable resin composition contains (A) a curable resin and (B) a ketimine structure-bearing organosilicon compound obtained by reacting an amino-functional alkoxysilane with a monocarbonyl compound, the organosilicon compound having a monomer purity of 50-95% and an amino group blockage of at least 90%. The composition has good shelf stability and tight adhesion and is useful as an adhesive.

Description: This invention relates to a curable resin composition comprising a curable resin such as an epoxy or urethane resin and a ketimine structure-bearing organosilicon compound. It also relates to an adhesive comprising the same. BACKGROUND Organoalkoxysilanes having a ketimine structure are known in the art (see US-A-2,942,019). The ketimine structure is inactive as such with its amino group remaining non-reactive. Upon contact with moisture or water, the ketimine structure readily degrades to regenerate a primary amino group so that the reactivity of amino group is resumed. By virtue of this characteristic, the ketimine structure can serve as an adhesion modifier when added to mixtures of an epoxy resin and a polyamide resin. It is also known from JP-B 57-11582 to use the ketimine structure as a curing agent. JP-B 2-19866 discloses that a ketimine structure-bearing organosilicon compound obtained by reacting an aminosilane with a dicarbonyl compound is used as an additive to polyurethane resins. JP-A 3-263421 discloses that the ketimine structure-bearing organosilicon compound serves as an adhesion modifier and curing agent in mixtures of an epoxy resin and a modified silicone resin. Other documents describe ketimine-containing silanes for incorporation in resin compositions include JP-A-08/027447, in a one-pack chloroprene-based adhesive and JP-A-9/111220 in an epoxy/rubber composition for bathroom floor repair. These disclosures do not specify monomeric purity or amino blockage rate; commercial reagents are used. EP0890597 and EP0072473 describe the manufacture of ketimine-containing silanes for incorporation in resin compositions. Carbonyl compounds and amines are heated together, the aim being to achieve significant hydrolysis of the resulting ketimine molecule. Finally JP-A-7/247294 and DE-A-34 14 877 describe making the ketimine-containing silane by addition of amino alkoxysilane to monocarbonyl compound. Water is separated subsequently; in the JP document it is distilled off as an azeotrope with the carbonyl compound; the monomer contents resulting in the examples ranging from 20.1 to 31.5%. Analyzing the ketimine structure-bearing organosilicon compounds used in known resin composition and adhesives, the inventors found that these compounds have not completed reaction and some of the amino group-containing organosilicon compound used as the reactant is left in the system. Since water resulting from the synthesis has not been fully removed from the system, the end compound contains a substantial proportion of oligomers and is not fully shelf stable. The aim herein is to provide new and useful curable resin compositions, e.g. adhesive compositions, including organosilicon compound having a ketimine moiety, as well as methods of preparation and use of such compositions. Preferred aims include good shelf stability and good adhesion. One aspect herein provides a curable resin composition comprising (A) a curable resin and (B) a ketimine structure-bearing organosilicon compound obtainable, and preferably obtained, by reacting an amino group-containing organosilicon compound of the following general formula (1) with a monocarbonyl compound of the following general formula (2). R 1 is ethyl group, R 2 is a divalent hydrocarbon group of 1 to 10 carbon atoms, and n is equal to 1, 2 or 3. R 3 and R 4 each are hydrogen or a monovalent hydrocarbon group of 1 to 10 carbon atoms, with the proviso that both R 3 and R 4 are not hydrogen at the same time, and R 3 and R 4 may form a cyclic structure with the carbon atom of the carbonyl group. The ketimine structure-bearing organosilicon compound should have a monomer purity of 70 to 95% and an amino group blockage of at least 90%. We find that such compositions can combine shelf stability with good adhesion. Other aspects herein are an adhesive comprising a curable resin composition as defined above; a method comprising the preparation of such a composition or adhesive by blending the ingredients thereof - optionally including synthesis of the ketimine-bearing organosilicon compound, preferably without distillation to separate said organosilicon compound from e.g. alkoxysilane oligomers - and the use of such compositions/ adhesives for adhesive bonding to substrates. Please refer to the claims. FURTHER EXPLANATIONS; OPTIONAL AND PREFERRED FEATURES The curable resin composition of the invention contains (A) a curable resin and (B) a ketimine structure-bearing organosilicon compound as essential components. The curable resin (A) may be selected from among epoxy resins, phenolic resins, urethane resins, melamine resins, polyimide resins, and furan resins, and mixtures of two or more of these resins. Of these, epoxy and urethane resins are desirable. Any of prior art well-known epoxy resins may be used. Examples include bisphenol A and bisphenol F type epoxy resins obtained by reacting bisphenol A or bisphenol F with epichlorohydrin, hydrogenated ones of these epoxy resins, glycidyl ester type epoxy resins, novolac type epoxy resins, urethane-modified epoxy resins, nitrogenous epoxy resins, and rubber-modified epoxy resins. Any of prior art well-known urethane resins may be used. Exemplary urethane resins are those based on urethane prepolymers obtained by reacting polyols such as polyoxyalkylene polyols, polyester polyols, hydroxyl group-containing polybutadiene polyols, acrylic polyols, castor oil derivatives, and tall oil derivatives, with an excess of polyisocyanate compounds. Component (B) is a ketimine structure-bearing organosilicon compound obtainable, usually obtained, by reacting amino group-containing organosilicon compound of the following general formula (1) with a monocarbonyl compound of the following general formula (2). In formula (1), R 1 is an ethyl group, R 2 is a divalent hydrocarbon group of 1 to 10 carbon atoms, and n is equal to 1, 2 or 3. Illustrative groups represented by R 2 are alkylene groups such as methylene, ethylene, propylene and butylene, arylene groups such as phenylene, and alkylene arylene groups, with the alkylene groups being preferred. The letter n is preferably equal to 2 or 3. Illustrative examples of the amino group-containing organosilicon compound of formula (1) are given below. (CH 3 CH 2 O) 3 SiCH 2 NH 2 (CH 3 CH 2 O) 3 Si (CH 2 ) 3 NH 2 Of these, the second and third compounds are preferred for practical use. In formula (2), R 3 and R 4 each are hydrogen or a monovalent hydrocarbon group of 1 to 10 carbon atoms, with the proviso that R 3 and R 4 are not both hydrogen at the same time, and R 3 and R 4 may form a cyclic structure with the carbon atom of the carbonyl group. Exemplary groups represented by R 3 and R 4 include hydrogen, alkyl groups such as methyl, ethyl, propyl, butyl, cyclohexyl and octyl, aryl groups such as phenyl and tolyl, aralkyl groups such as benzyl and phenylethyl, and substituted ones of these groups in which some or all of the hydrogen atoms are replaced by halogen atoms. Both R 3 and R 4 are not hydrogen at the same time. R 3 and R 4 may bond together to form a divalent saturated hydrocarbon group (such as an alkylene group of 5 to 10 carbon atoms) which forms a cyclic structure with the carbon atom of the carbonyl group. Illustrative examples of the monocarbonyl compound of formula (2) are given below. In the following formulae, Ph is phenyl. O=CH-CH 2 -Ph O=CH-CH 2 CH 2 CH 2 CH 3 Of these, the following compounds are preferable because they are more hydrophobic. O=CH-CH 2 -Ph The ketimine structure-bearing organosilicon compound used herein may be prepared by any desired method, although the following method is preferred, in order to prepare the end compound having a monomer purity of 70 to 95% and an amino group blockage (or percentage of blocked amino groups) of at least 90%. An amino group-containing organosilicon compound or amino-functional alkoxysilane is reacted with a monocarbonyl compound by introducing the amino-functional alkoxysilane to the monocarbonyl compound under heating. During this introduction, reaction takes place to form water which is azeotroped off with the monocarbonyl compound. The molar ratio of the monocarbonyl compound to the amino-functional alkoxysilane is preferably 2/1 to 10/1, and more preferably from 3/1 to 5/1. If the monocarbonyl compound is less than 2 mol per mol of the amino-functional alkoxysilane, active amino groups would be left after reaction, whereas one wants an amino group blockage of at least 90%. Thus the molar ratio should preferably be at least 2. If the molar ratio exceeds 10, the pot yield is rather low leading to an increased cost. The temperature at which the amino-functional alkoxysilane is introduced, that is, the reaction temperature, is preferably from approximately the azeotropic temperature of a mixture of the monocarbonyl compound and water to approximately the reflux temperature of the monocarbonyl compound. In one typical example, the monocarbonyl compound is methyl isobutyl ketone which is reacted with an amino-functional alkoxysilane. A mixture of methyl isobutyl ketone and water has an azeotropic temperature of about 80°C and methyl isobutyl ketone has a reflux temperature of 130°C. Then the introduction temperature of the amino-functional alkoxysilane may be from 80 to 130°C. The manner of introducing the amino-functional alkoxysilane for reaction is not critical. Preferably the amino-functional alkoxysilane is introduced into a solution of the monocarbonyl compound in order that the alkoxysilane react quickly with the monocarbonyl compound. The introduction time is not critical although it is preferably from about 1/2 to about 20 hours. Since the reaction product will hydrolyse in the presence of moisture, the reaction is preferably carried out in an inert gas such as nitrogen or argon. It is preferable to minimize the water content of the monocarbonyl compound. As described above, the ketimine structure-bearing organosilicon compound is preferably prepared by introducing the amino-functional alkoxysilane to the monocarbonyl compound under heating for reaction, and azeotroping off water (resulting from reaction) with the monocarbonyl compound during the introduction. After the completion of introduction of the amino-functional alkoxysilane, azeotropic distillation of water with the monocarbonyl compound is preferably continued in order to remove water from the system. To this end, an appropriate distilling temperature is selected. In one preferred mode, the temperature is raised to the reflux temperature of the monocarbonyl compound and distillation is continued for about 1/2 to about 2 hours after the reflux temperature is reached. Alternatively, immediately after the completion of introduction of the amino-functional alkoxysilane, the unreacted monocarbonyl compound is distilled off from the system by vacuum concentration. It is noted that although continuous distillation for about 1/2 to about 2 hours after reaching the reflux temperature causes the system to be depleted of water and renders the system stable so that hydrolytic condensation may no longer proceed, it is desirable to distill off the unreacted monocarbonyl compound from the system as fast as possible. The end ketimine structure-bearing organosilicon compound is thus obtained in admixture with alkoxysilane oligomers resulting from hydrolytic condensation of alkoxy groups. As compared with the prior art process, the content of oligomers is very low and the content of residual amino groups is also low. To recover the product in high purity, the ketimine structure-bearing organosilicon compound can be isolated by distillation. However, the product isolated by distillation becomes not only expensive, but also less adhesive. This is undesirable for use in the curable resin composition and the adhesive according to the invention. The ketimine structure-bearing organosilicon compound used herein is the one prepared, e.g. by the above-described method, to a monomer purity or content of 70 to 95%, more preferably 80 to 95%, and an amino group blockage of at least 90%, preferably at least 95%. If the monomer purity is too low the composition becomes less stable during shelf storage. A monomer purity of more than 95% renders the composition less adhesive. An amino group blockage of less than 90% detracts from the shelf stability of the composition. In addition to the curable resin and the ketimine structure-bearing organosilicon compound as essential components, the curable resin composition of the invention may contain other components, for example, curing agents, fillers, pigments, dyes, antioxidants, antistatic agents, UV absorbers, leveling agents, plasticizers, and dehydrating agents. There may also be added solvents, for example, ketones such as methyl ethyl ketone and methyl isobutyl ketone, esters such as ethyl acetate and methyl acetate, aromatic hydrocarbons such as toluene and xylene, aliphatic hydrocarbons such as pentane, hexane and decane, and ethers such as tetrahydrofuran and propylene glycol monomethyl ether. The adhesive of the invention is comprised of the curable resin composition defined above. The adhesive is suitable for forming a bond between inorganic members such as glass plates, mica plates, and metal plates such as aluminum, iron, copper and stainless steel, plastic members such as polyethylene, polypropylene, polyesters, acrylic resins, polycarbonate resins, and polyvinyl chloride resins, and members of wood and paper, and between any two of these members. EXAMPLE Examples of the invention are given below by way of illustration and not by way of limitation. All parts are by weight. Synthesis Example 1 A 1-liter separable flask equipped with a nitrogen inlet tube, thermometer, ester adapter, Dimroth condenser, and dropping funnel was charged with 500 g (5.0 mol) of methyl isobutyl ketone. Under a nitrogen gas stream, 221 g (1.0 mol) of 3-aminopropyltriethoxysilane was slowly added dropwise at 110°C. This dropwise addition was continued for one hour. After 15 minutes from the start of addition, azeotropic distillation by reflux of methyl isobutyl ketone and water formed was commenced. The distillate amount collected until the end of dropwise addition of 3-aminopropyltriethoxysilane was 130 g. Distillation was further continued by heating to an internal temperature of 130°C. The distillate amount eventually summed to 380 g. Immediately thereafter, the residual or unreacted methyl isobutyl ketone was distilled off under vacuum at 80°C, leaving a yellow clear liquid. The product showed physical properties including a viscosity of 3.4 centistokes, a specific gravity of 0.920 and a refractive index of 1.4436, as measured at 25°C. The product was analyzed by IR absorption spectroscopy, finding no absorption of NH. CH 3 MgI was added to an aliquot whereupon CH 4 gas evolved which was collected by a gas burette. By quantitative analysis, the amount of active hydrogen was found to be 2.05 cc/g. Since the amount of active hydrogen at a conversion of 0% is 101 cc/g, it was confirmed that this compound had an amino group blockage of 98.0%. On gas chromatographic analysis using decane as the internal standard, the product was found to have a monomer content of 85%. Synthesis Example 2 In Example 1, the flask was charged with 3-aminopropyltriethoxysilane along with methyl isobutyl ketone. By heating and processing as in Example 1, azeotroping off water formed along with methyl isobutyl ketone, and subsequently processing as in Example 1, there was obtained a yellow clear liquid having a viscosity of 9.91 centistokes, a specific gravity of 0.943 and a refractive index of 1.4432 at 25°C. The product had an amino group blockage of 96.1% and a monomer content of 43%. Synthesis Example 3 In Example 1, the flask was charged with 200 g (2.0 mol) of methyl isobutyl ketone. By processing as in Example 1, azeotroping off water formed along with methyl isobutyl ketone, and subsequently processing as in Example 1, there was obtained a yellow clear liquid having a viscosity of 4.5 centistokes, a specific gravity of 0.930 and a refractive index of 1.4427 at 25°C. The product had an amino group blockage of 83.5% and a monomer content of 89%. Synthesis Example 4 A 1-liter separable flask equipped with a nitrogen inlet tube, thermometer, ester adapter, Dimroth condenser, and dropping funnel was charged with 500 g of toluene, 221 g (1.0 mol) of 3-aminopropyltriethoxysilane and 200 g of a molecular sieve as a dehydrating agent. With stirring at room temperature, 200 g (2 mol) of methyl isobutyl ketone was added dropwise. After the completion of addition, agitation was continued for a further 4 hours at room temperature to drive reaction. At the end of reaction, the molecular sieve was filtered off and the toluene and unreacted methyl isobutyl ketone were distilled off in vacuum. The product had an amino group blockage of 88.5% and a monomer content of 23.4%. Synthesis Example 5 A 1-liter separable flask equipped with a nitrogen inlet tube, thermometer, ester adapter, Dimroth condenser, and dropping funnel was charged with 500 g of toluene and 221 g (1.0 mol) of 3-aminopropyltriethoxysilane. With stirring at room temperature, 200 g (2 mol) of methyl isobutyl ketone was added dropwise. After the completion of addition, the reaction solution was heated to distill off the toluene and water at 110 to 120°C and drive reaction. At the end of reaction, the toluene and unreacted methyl isobutyl ketone were distilled off in vacuum. The product had an amino group blockage of 82.2% and a monomer content of 14.8%. Synthesis Example 6 A 1-liter separable flask equipped with a nitrogen inlet tube, thermometer, ester adapter, Dimroth condenser, and dropping funnel was charged with 300 g (3 mol) of methyl isobutyl ketone and 57 g of magnesium sulfate. With stirring at room temperature, 221 g (1.0 mol) of 3-aminopropyltriethoxysilane was added dropwise. After the completion of addition, the reaction solution was stirred for a further 5 hours at room temperature. Immediately after the completion of reaction, the hydrated magnesium sulfate was filtered off and the low-boiling fraction was distilled off in vacuum. The product had an amino group blockage of 94.6% and a monomer content of 33.3%. Synthesis Example 7 The ketimine-bearing organosilicon compound synthesized in Example 1 was isolated by distillation, collecting a fraction having an amino group blockage of 98.6% and a monomer content of 97.8%. Example 1 A resin composition was prepared by blending 5 g of the ketimine-bearing organosilicon compound synthesized in Synthesis Example 1, 50 g of an epoxy resin (Epikote 827 by Yuka Shell Epoxy K.K.) and 50 g of toluene. To evaluate shelf stability, the composition was kept at 50°C for 14 days while its viscosity (centistoke) was measured at intervals. The results are shown in Table 1. Comparative Examples 1-6 Resin compositions were prepared as in Example 1 except that the ketimine-bearing organosilicon compounds synthesized in Synthesis Examples 2 to 7 were used. They were similar evaluated for shelf stability. The results are shown in Table 1. Viscosity (centistoke) Initial 1 day 3 days 5 days 7 days 14 days E1 4.19 4.28 4.38 4.46 4.55 4.80 CE1 4.22 4.34 4.46 4.60 4.73 5.10 CE2 4.13 5.10 5.55 5.98 6.10 6.23 CE3 4.20 4.95 5.43 5.90 6.06 6.20 CE4 4.24 5.02 5.60 5.99 6.15 6.24 CE5 4.20 4.45 4.50 4.64 4.69 5.08 CE6 4.13 4.20 4.30 4.41 4.50 4.75 As is evident from Table 1, the curable resin composition within the scope of the invention keeps good stability with the lapse of time as compared with the curable resin compositions containing prior art known ketimine-bearing organosilicon compounds (Comparative Examples 1-5). The inventive composition shows equivalent shelf stability to the curable resin composition containing a distillation-purified product (Comparative Example 6). Example 2 & Comparative Examples 7-12 Epoxy resin compositions were prepared in accordance with the formulation shown in Table 2. Aluminum and iron plates were bonded with the compositions and their bond was examined. The bonded assembly was boiled for 3 hours and the bond was examined again. The bond was rated "Excellent" when members were firmly bonded and could not be separated, "Good" when members were firmly bonded, but could be separated by force, and "Fair" when members were bonded, but could be readily separated. The results are shown in Table 3. Formulation Epikote 827 Compound of Synthesis Example Triethylenetetramine E2 50 parts SE1 1 part 5 parts CE7 50 parts SE2 1 part 5 parts CE8 50 parts SE3 1 part 5 parts CE9 50 parts SE4 1 part 5 parts CE10 50 parts SE5 1 part 5 parts CE11 50 parts SE6 1 part 5 parts CE12 50 parts SE7 1 part 5 parts Bond test Aluminum plates Iron plates Initial After 3hr boiling Initial After 3hr boiling E2 Excellent Good Excellent Good CE7 Excellent Fair Excellent Fair CE8 Excellent Fair Excellent Fair CE9 Excellent Good Excellent Good CE10 Excellent Fair Excellent Fair CE11 Excellent Fair Excellent Good CE12 Good Fair Good Fair As is evident from Table 3, the curable resin composition within the scope of the invention keeps a firm bond unchanged as compared with the curable resin compositions containing prior art known ketimine-bearing organosilicon compounds (Comparative Examples 7-11). The inventive composition shows a superior bond to the curable resin composition containing a distillation-purified product (Comparative Example 12). Curable resins embodying these teachings showed good shelf stability against aging and are useful as an adhesive because they ensure tight adhesion. Japanese Patent Application No. 10-229327 is incorporated herein by reference. Although some preferred embodiments have been described, many modifications and variations may be made thereto in light of the above teachings. It is therefore to be understood that the invention may be practiced otherwise than as specifically described in the examples.

Claims: A curable resin composition comprising (A) curable resin and (B) ketimine structure-bearing organosilicon compound, obtainable by reacting amino group-containing organosilicon compound of the following general formula (1): wherein R 1 is ethyl group, R 2 is a divalent hydrocarbon group of 1 to 10 carbon atoms, and n is equal to 1, 2 or 3, with monocarbonyl compound of the following general formula (2): wherein R 3 and R 4 each are hydrogen or a monovalent hydrocarbon group of 1 to 10 carbon atoms, with the proviso that R 3 and R 4 are not both hydrogen at the same time, and R 3 and R 4 may form a cyclic structure with the carbon atom of the carbonyl group, said ketimine structure-bearing organosilicon compound having a monomer purity of 70 to 95% and an amino group blockage of at least 90%. A curable resin composition of claim 1 wherein the curable resin (A) comprises an epoxy resin or urethane resin. A curable resin composition according to claim 1 or claim 2 in which the monomer purity of the ketimine structure-bearing organosilicon compound is from 80 to 95%. A curable resin composition according to any one of the preceding claims in which the amino blockage of the ketimine structure-bearing organosilicon compound is at least 95%. A curable resin composition according to any one of the preceding claims in which said amino group-containing organosilicon compound corresponding to said ketimine structure-bearing organosilicon compound is selected from (CH 3 CH 2 O) 3 SiCH 2 NH 2 (CH 3 CH 2 O) 3 Si(CH 2 ) 3 NH 2 A curable resin composition according to any one of the preceding claims in which said monocarbonyl compound corresponding to said ketimine structure-bearing organosilicon compound is selected from O=CH-CH 2 -Ph O=CH-CH 2 CH 2 CH 2 CH 3 An adhesive compromising a curable resin composition of any one of claims 1 to 6. Use, as an adhesive for bonding to a substrate, of a curable resin composition according to any one of claims 1 to 6. A method of preparing a curable resin composition comprising (i) reacting amino group-containing organosilicon compound and monocarbonyl compound as specified in any one of claims 1, 5 and 6 so as to produce a ketimine-bearing organosilicon product composition having monomer purity and amino group blockage as specified in any one of claims 1, 3 and 4, and (ii) blending said product composition with curable resin. A method according to claim 9 in which the molar ratio of the monocarbonyl compound to the amino group-containing organosilicon compound in step (i) is from 2/1 to 10/1. A method according to claim 10 in which said molar ratio is from 3/1 to 5/1. A method according to any one of claims 9 to 11 in which the amino group-containing organosilicon compound is introduced gradually into a solution of the monocarbonyl compound with heating for reaction, the water formed being progressively removed as an azeotrope with the monocarbonyl compound. A method according to claim 12 in which the introduction of the amino group-containing organosilicon compound is over a period of from ½ to 20 hours, and the reaction is carried out under inert gas. A method according to claim 12 or 13 in which azeotropic distillation of water with the monocarbonyl compound is continued after all the amino group-containing organosilicon compound has been introduced, for from ½ to 2 hours after the reflux temperature for the monocarbonyl compound is reached. A method according to claim 12 or 13 in which, immediately after the completion of introduction of the amino group-containing organosilicon compound, unreacted monocarbonyl compound is distilled off by vacuum concentration. A method according to any one of claims 12 to 15 in which the ketimine-bearing organosilicon product composition is blended with the curable resin without first using distillation to isolate the ketimine-bearing organosilicon compound monomer from oligomers thereof in the product composition.

Inventors: YAMAYA MASAAKI, YANAGISAWA HIDEYOSHI, YAMAYA, MASAAKI, YANAGISAWA, HIDEYOSHI, Yamaya, Masaaki, c/o Silicone-Electr.Mat. Res.Ctr., Yanagisawa, Hideyoshi, c/o Silicone El.Mat res.ctr
Applicants: SHINETSU CHEMICAL CO, SHIN-ETSU CHEMICAL CO., LTD.
Application year: 1999
Main classification: C08G59
IPC codes: C09J163, C08L101, C08G18, C08L63, C09J175, C08L75, C08K5, C08G59, C09J201