Inorganic adhesive composition

Abstract: Disclosed is an inorganic adhesive composition comprising (a) an aqueous silica sol and (b) an inorganic refractory powder along with one or more selected from (c) a fine powdery silica, (d) an aqueous alkali silicate solution and (e) a silane coupling agent. After hardened, the hardened product of the composition displays noticeably improved adhesion strength and electric insulating property.

Description: FIELD OF THE INVENTION The present invention relates to an improvement of an inorganic composition comprising a silica sol and an inorganic refractory powder. The inorganic composition of the present invention displays, after hardened, a particularly excellent electric insulating property and an extremely high adhesion strength and therefore it may be used for adhesion of materials of the same kind or different kinds, such as ceramics, glass, slates, aluminium, stainless steel, iron and other metal materials which are required to have not only a high adhesion strength but also a high insulating property. BACKGROUND OF THE INVENTION JP-B-39-8547 (the term "JP-B" as used herein means an "examined Japanese patent publication") discloses an improvement of an adhesive for electric appliances, which contains an aqueous silica sol and a refractory powder (such as silica powder) having a particle size of from 5 to 150 microns and which additionally contains boron oxide, lead oxide, antimony trioxide or the like. JP-A-48-93636 (the term "JP-A" as used herein means an "unexamined published Japanese patent application") discloses a composition which is prepared by blending an acidic silica sol having a particle size of from 7 to 150 millimicrons, an alkali metal ion-free crystalloid silicate liquid and an inorganic refractory powder. JP-B-56-38544 discloses an inorganic composition which is prepared by blending an aqueous silica sol and an inorganic fiber or refractory powder having a particle size of from 0.1 micron to 20 microns along with pigment, aggregate and other aids. As an adhesive comprising a silica sol and a refractory powder or a ceramic fiber is composed of substantially only inorganic components and is free from any vitrifying component, it displays a high heat-resistance capable of being resistant to a high temperature. However, the adhesive does not display a sufficient adhesion strength when it is in a stage as hardened by drying. An adhesive comprising from 20 to 70 parts of an aqueous silica sol having a concentration of from 2 to 40 %, from 30 to 95 parts of talc, silica, mica, sillimanite, asbestos, clay, glass for electric insulation, synthetic mica, magnesium silicate, aluminium silicate, magnesium oxide, aluminium oxide or the like powder having a particle size of from 5 to 150 microns, and from 10 to 100 parts of boron oxide, lead oxide, antimony trioxide or the like, which is described in JP-B-39-8547, must be subjected to stepwise heat-treatment to be effected in the vicinity of 100°C, then 300°C and then 600°C in order, after having been left to stand at room temperature for a while, when it is actually used for adhesion. Such stepwise heat-treatment process is not simple but is extremely complicated. Additionally, the hardened product of the adhesive vitrifies at a high temperature and therefore the heat-resistance thereof is not sufficient. The composition illustrated in the above-mentioned JP-A-48-93636, which is composed of an acidic silica sol and a crystalloid silicate liquid does not have a sufficient storage stability, and it could not form an adhesive having a high adhesion strength. On the other hand, the composition illustrated in the above-mentioned JP-B-56-38544, which is composed of an aqueous silica sol, an inorganic fiber and a refractory powder, could not form an adhesive having a sufficient electric insulating property. US-A-3 920 578 describes an adhesive composition comprising an inorganic filler and a binder consisting of silica sol, an alkali silicate and an acid for adjusting the pH of the binder from 5 to 9.5. The composition gels in 5 to 300 seconds. The document does not teach to incorporate coupling agents into the composition nor suggests to use a filler composed of a powdery silica in an amorphous form and in a size of 5 to 200 nm in combination with a refractory powder in a grain size of 0.5 to 1000 µm. GB-A-2 058 818 discloses an adhesive composition comprising a solution of alkali metal silicate finely divided inorganic powder in an aount of 1 to 10 % by weight, finely divided silicate in an amount up to 5 % by weight and an alkali metal salt of methylsilicic acid in an amount of 0.1 to 10 % by weight. JP-A-55-94 976 describes an adhesive composition comprising a silica sol, a fine powder of refractory metal oxide and superfine silica, preferably having a particle size of 25 to 100 nm in an amount of 0.1 to 50 parts by weight to 100 parts by weight of the sol. Additionally, it has been found that the hardened products of the conventional adhesives adsorb water from the aerial atmosphere to thereby gradually lower the adhesion strength. Where an adhesive containing a silica sol and a refractory powder is applied to adhesion of various materials, only solution of the above-mentioned problems on the adhesion strength, long-time storage stability and heat-resistance is still insufficient and the adhesive is desired to have further additional higher properties. For instance, when an adhesive is to be fully filled even to fine slits between substances to be bonded with the adhesive by the use of an automatic adhesive-injector, the adhesive to be used for the purpose is desired to have a high fluidity and a good workability. Specifically, the dispersion stability of the adhesive is indispensable so that the components of the adhesive do neither precipitate nor coagulate during handling it. In addition, where an adhesive is hardened by drying, the hardened product is desired to be free from uneven shrinkage, cracking and foaming. That is, the adhesive is desired to have a good hardening property. On the other hand, where the parts as bonded via an adhesive, are exposed to temperature variation between a low temperature condition and a high temperature condition in practical use thereof, the adhesive used is desired to have an extremely high adhesion strength and additionally the hardened adhesive layer between the parts as bonded therewith is further desired to have a properly controlled thermal expansion coefficient. In particular, in an electric-light bulb or an electric heater, the joint part between the bulb glass or jacket glass to cover the heating element and the lamp base is exposed to such a temperature variation in an extremely short period of time, or that is, it is exposed to a so-called heat shock. Accordingly, the adhesive to be applied to such a joint part is indispensable to have a sufficient heat-shock resistance enough to be resistant to repeated heat-shock of the kind without breakage of the bonded joint part. Additionally, where at least one part of the parts to be bonded with an adhesive is a metal material, the adhesive is desired to be free from corrosion of the metal material because of the hardened adhesive layer during practical use. SUMMARY OF THE INVENTION The object of the present invention is to overcome the above-mentioned problems in the conventional adhesive compositions and to provide a novel inorganic composition to be able to give an adhesive which has a high electric insulating property and a high adhesion strength and which may satisfactorily bond materials of the same kind or different kinds such as ceramics, glass, slates, hardened cement products, aluminium, stainless steel, iron, and other various metal materials. The adhesive derived from the composition of the invention is free from lowering of the adhesion strength even after absorption of water. Specifically, the present invention provides an inorganic adhesive composition which comprises the following components (a), (b), (c), (d) and (e): (a) an aqueous silica sol having a mean particle size of from 5 to 200 millimicrons and a molar ratio of SiO₂/M₂O (where M represents an alkali metal atom, an amine molecule, or a quaternary ammonium group) of being from 30 to 2000, in an amount of 100 parts by weight as SiO₂; (b) an inorganic refractory powder having a particle size of from 0.5 to 1000 microns, in an amount of from 100 to 100000 parts by weight; (c) a fine powdery silica in amorphous form having a particle size of from 5 to 200 millimicrons, in an amount of from 0.5 to 500 parts by weight; (d) an aqueous solution of an alkali silicate having a molar ratio of SiO₂/M'₂O (where M' represents Na, K, Li, an amine molecule, or a quaternary ammonium group) of being from 1 to 10 and having an alkali silicate concentration of being from 5 to 50 % by weight, in an amount of from 0.1 to 500 parts by weight as the alkali silicate component; and (e) one or more coupling agents selected from the group consisting of a silane compound of a general formula (I): R¹Si(OR)₃ (I) where OR represents an alkoxy or acyloxy group having from 1 to 3 carbon atoms, and R¹ represents a monovalent organic group having from 2 to 9 carbon atoms, or a hydrolysate thereof, and a silane compound of a general formula (II): R¹SiCH₃(OR)₂ (II) where OR and R¹ have the same meanings as defined above, or a hydrolysate thereof, in an amount of from 0.05 to 100 parts by weight; the solid content of the components (a), (b), (c), (d) and (e) being from 40 to 95 % by weight; and which has a viscosity of from 1 to 10000 poise at 20°C. DETAILED DESCRIPTION OF THE INVENTION The aqueous silica sol (a) to be employed in the present invention is obtained with ease by known methods, for example, by way of treating a diluted aqueous solution of water glass with a cation-exchange substance for removal of alkali therefrom or by way of neutralizing the water glass with an acid followed by deflocculating of the silica, and it is generally in the form of a stable dispersion liquid where a colloidal silica is stably dispersed in a medium of water. The colloidal silica may have a mean particle size of from 5 to 200 millimicrons, preferably from 10 to 150 millimicrons. The shape of the colloidal silica particles may be either spherical or non-spherical. The aqueous silica sol may be either alkaline or acidic. The sol is preferred to have a molar ratio of SiO₂/M₂O of being from approximately 30 to 2000, where M has the same meaning as defined above. Examples of amines to be in the sol include methylamine, ethylamine, triethanolamine, other ethanolamine and the like; and those of quaternary ammonium groups therein include tetramethylammonium, monomethyltriethanolammonium, isopropyltriethanolammonium, tetraethanolammonium and the like. It is preferable that the aqueous silica sol has an SiO₂ concentration of from approximately 1 to 50 % by weight. It is also preferable to use a mixture comprising two or more aqueous silica sols each having a different mean particle size for obtaining a favorable composition. The fine powdery silica (c) to be employed in the present invention has a particle size of from 5 to 200 millimicrons. The shape of the particles in the powder may be either spherical or non-spherical. The particles are in amorphous form (non-crystalline). As methods of preparing the fine powdery silica (c), there are known, for example, a gas phase method of using silicon tetrachloride as a starting material and a neutralization method of using sodium silicate as a starting material. Either of them can be employed for preparing the fine powdery silica (c) for use in the present invention. When the fine powdery silica is added to the aqueous silica sol, the former may be added to the latter directly or in the form of an aqueous suspension of the powdery silica. The aqueous alkali silicate solution (d) which is employed in the present invention is an aqueous solution of a silicate of an alkali metal ion such as lithium, sodium or potassium ion or of an amine or a quaternary ammonium group. Examples of the amine include methylamine, ethylamine, triethanolamine, other ethanolamine and the like; and examples of the quaternary ammonium groups include tetramethylammonium, monomethyltriethanolammonium, tetraethanolammonium and the like. The alkali silicate has a molar ratio of SiO₂/M'₂O of being from 1 to 10, where M' has the same meaning as defined above. The aqueous solution has a concentration of from 5 to 50 % by weight. It may contain one or more alkali silicates singly or in admixture. As examples of the inorganic refractory powder (b) for use in the present invention, there are mentioned powders of quartz, silica, feldspar, aluminium silicate, zirconium silicate, mullite, zirconia, alumina, silicon nitride, silicon carbide, talc, mica and the like. The particles in the powder may have a particle size of from approximately 0.5 to 1000 microns, preferably from approximately 0.5 to 400 microns. Additionally, powders of glass fiber, potassium titanate fiber and the like may also be employed, where the fibrous particles have a length of from approximately 0.5 to 1000 microns and a diameter of from approximately 0.1 to 20 microns. These inorganic refractory powders may be employed singly or as an admixture comprising two or more appropriately selected therefrom. The coupling agents (e) which are employed in the present invention are silane compounds which are represented by the above-mentioned formula (I) or (II) and capable of forming two or three silanol groups in the molecule after hydrolysis, as well as hydrolysates of the compounds. Preferred examples of the agents include vinyltris(β-methoxyethoxy)silane CH₂=CHSi(OC₂H₄-OCH₃)₃, vinyltriethoxysilane CH₂=CHSi(OC₂H₅)₃, vinyltrimethoxysilane CH₂=CHSi(OCH₃)₃, vinyltriacetoxysilane γ-methacryloxypropyltrimethoxysilane β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane γ-glycidoxypropyltrimethoxysilane γ-glycidoxypropylmethyldiethoxysilane N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane H₂NC₂H₄NHC₃H₆Si(OCH₃)₃, N-β (aminoethyl)-γ-aminopropylmethyldimethoxysilane γ-aminopropyltriethoxysilane H₂NC₃H₆Si(OC₂H₅)₃ or γ-anilinopropyltrimethoxysilane C₆H₅NHC₃H₆Si(OCH₃)₃ and the like. Additionally, an aqueous solution of a hydrolysate to be obtained by blending the silane compound and water may also be employed in the present invention. The composition of the present invention can contain any other optional components in addition to the above-mentioned components, so far as it may attain the objects of the present invention. Examples of additional components which may optionally be incorporated into the composition of the present invention are a powder of a bentonite clay mineral as an anti-settling agent, as well as cellulose acetate, ethyl cellulose, hydroxyethyl cellulose, and synthetic organic polymers such as polyvinyl pyrrolidone, polyvinyl alcohol and the like. A colorant may also be added to the composition, which includes, for example, inorganic or organic pigments for coloration, such as titanium oxide, iron oxide, chromium oxide or poster color. For the purpose of enhancing the fluidity and the adhesion property of the composition, various kinds of surface active agents or surface-treating agents as well as a small amount of hydrophilic organic solvents such as methanol, ethanol or the like may also be added to the composition. For blending the respective components to prepare the composition of the invention, any known stirrers or mixers may be used and the components may well be blended with ease. In blending the components, they may be added to a container all at a time or one by one in any desired order. Blending of the components is desired to be effected under the condition of pertinent temperature and pressure so that the components are not dried during blending. For instance, the components are blended at a temperature of approximately 5°C to 40°C for a period of time of approximately 0.5 to 5 hours in an atmospheric condition to obtain a preferred composition. The composition of the invention has a solid content of from approximately 40 to 95 % by weight and has a viscosity of from 1 to 10000 poise at 20°C. Where it is stored in a closed vessel at room temperature, it has a storage stability without deteriorating for several months or more. The composition of the present invention is hardened by drying at a temperature higher than the freezing temperature. Preferably, it is hardened by drying at a temperature of from 80 to 300°C to obtain an especially advantageous hardened product. The interaction between the components in the composition of the present invention is complicated and could not completely be clarified up to the present. The interaction between the plural components could be considered to be as follows: Precisely, silica particles in the aqeuous silica sol have alkali ions as adsorbed to the surfaces thereof for stabilizing the dispersion of the particles in the sol. Where the composition does not contain the fine powdery silica, the electric insulating resistance of the hardened product of the composition gradually lowers with absorption of water in air immediately after drying, since the above-mentioned alkali ions may freely move in the hardened product under a high voltage condition. However, by adding the fine powdery silica, which has an extremely large specific surface area, to the aqueous silica sol, the alkali ions in the aqueous silica sol are to be adsorbed to the surfaces of the fine silica particles in the fine powdery silica. As a result, the molar ratio of SiO₂/M₂O (where M has the same meaning as mentioned above) is elevated as a whole so that the electric insulating resistance of the hardened product would not lower. Additonally, the alkali silicate as added may cover the surface of the silica particles in the aqueous silica sol, the particles in the fine powdery silica and the particles in the inorganic refractory powder so that the specific surface area of the dried and hardened product of the composition is thereby noticeably reduced. As a result, the number of the -OH groups as existing in the unit surface area of the particles would decrease so that the adsorption of water to the dried and hardened product would be lowered. Because of the reasons, the electric insulating property of the hardened product is considered to be improved. The silane compounds as represented by the above-mentioned formula (I) or (II) are, when added to the aqueous silica sol, brought into contact with water contained in the sol so that the alkoxy group of the compound is converted into a silanol group. The resulting silanol group is chemically or physically bonded to the surfaces of the colloidal silica particles, those of the powdery inorganic refractory particles and those of the fine powdery silica particles, during blending the compound with the aqueous silica sol, the inorganic refractory powder and the fine silica powder. Where an aqueous solution of the hydrolysate of the said silane compound is employed, the same bonds are also formed. As a result, in the blend system of the adhesive composition, the dispersibility of the inorganic refractory powder is noticeably elevated; and the bonds between the colloidal silica particles with the surfaces of the powdery inorganic refractory particles and those of the fine powdery silica particles extremely increase in the dried and hardened product from the adhesive composition. As a result, after the composition has been hardened to form a hardened product, the mechanical strength of the hardened product is extremely improved. The function of the silanol group to be derived by hydrolysis of the silane compound shows itself also in the bonds between the surfaces of the substances to be bonded with the adhesive and the colloidal silica particles because of the same reason as above. As a result, after the adhesive composition as applied to the substances to be bonded therewith has been hardened, the bonding between the hardened product layer and the surfaces of the substances to be bonded is considered to be improved and elevated noticeably. Precisely, the coupling agents of the present invention have a function of forming a hardened product layer which is dense and has an extremely improved mechanical strength and of extremely elevating the bonding strength between the hardened product layer and the surfaces of the substances to be bonded with the layer. Additionally, improvement of the dispersibility of the inorganic refractory powder because of the function of the silanol group to be derived by hydrolysis of the silane compounds results in improvement of fluidity and workability of the composition of the invention. Moreover, the proportion of the inorganic refractory powder to the colloidal silica in the composition may be increased because of the improvement of the dispersibility of the inorganic refractory powder and, as a result, uneven shrinkage, cracking or foaming which often occurs during hardening of the adhesive composition could remarkably be inhibited and the thermal expansion coefficient of the hardened product layer may easily be controlled. Furthermore, the organic group as bonded to the silicon atom via the carbon atom in the silane compound has a function of remarkably lowering the water-absorption of the hardened product layer and of thereby elevating the electric insulating property of the layer. Where a conventional adhesive composition comprising only an aqueous silica sol and an inorganic refractory powder is used, the strength of the dried and hardened product layer would often lower because of adsorption of water to the layer so that the hardened adhesive layer would often separation from the substrate substance. As opposed to this, water hardly adsorbs to the hardened product layer to be formed from the adhesive composition of the present invention, such an unfavorable lowering of the strength of the hardened product layer does not occur. However, the particle size of the silica particles in the aqueous silica sol used is smaller than 5 millimicrons, the stability of the composition would be poor. On the other hand, if it is more than 200 millimicrons, the silica particles in the aqueous sol would frequently precipitate in the composition whereby the aqueous silica sol is ineffective for expressing a high bonding powder. If the molar ratio of SiO₂/M₂O (where M has the same meaning as defined above) is less than 30, a part of the surfaces of the colloidal silica particles would be dissolved with ease and the stability of the sol tends to be poor. Therefore, the molar ratio is preferably higher. However, a sol having a higher molar ratio than 2000 is hardly obtained. If the SiO₂ concentration in the aqeuous silica sol to be employed in the present invention is too high, the stability of the sol is poor so that the composition would become too thick and would therefore gel frequently. However, if the SiO₂ concentration is too low, the bonding power of the hardened product from the composition would be poor. Therefore, the preferred concentration range is from approximately 1 % by weight to 50 % by weight. The aqueous silica sol is preferably alkaline rather than acidic, since the former may impart a higher adhesive strength to the hardened product of the composition. It is desirable to employ a mixture comprising plural aqueous silica sols each having a different mean particle size. This is because the filled density of the coagulated silica particles is elevated and a hardened product having a high adhesion strength may be obtained advantageously. Where the fine powdery silica (c) to be employed in the present invention has a particle size of more than 200 millimicrons, it would have a small specific surface area. However, if it is less than 5 millimicrons, the particles could not exist stably. Accordingly, the fine powdery silica is to have a particle size of from approximately 5 to 200 millimicrons, as being generally available and being expected to have the intended effect. However, in preparing the composition, when the proportion of the fine powdery silica is more than 500 parts by weight relative to 100 parts by weight as SiO₂ of the aqueous silica sol, the molar ratio of SiO₂/M₂O (where M has the same meaning as defined above) would rise too much so that the stability of the composition would be lost. If, on the other hand, it is less than 0.2 part by weight, a hardened product having a high electric insulating property could not be obtained. The particle size of the particles of the refractory powder to be in the composition of the invention does not have any significant influence on the properties of the adhesive composition itself, but the refractory powder is advantageously a non-fibrous powder having a particle size of from approximately 0.5 to 350 millimicrons or a fibrous powder having a diameter of from approximately 0.1 to 20 microns and a length of 1000 microns or less. In particular, the refractory powder is preferably in the form of a mixture comprising particles of plural types each having a different mean particle size so that the filled density of the hardened product form the composition may be elevated. By adjusting the particle size of the particles of the refractory powder to be employed in the present invention, a composition having a good workability can be obtained. However, if the proportion of the refractory powder is less than 50 parts by weight to 100 parts by weight of SiO₂ of the aqueous silica sol, the shrinkage would be too large when the composition is hardened. That is, the hardened product would be ununiformly shrunk, or cracked, or foamed. On the contrary, if the proportion of the refractory powder is more than 100000 parts by weight relative to 100 parts by weight of SiO₂ of the aqueous silica sol, the fluidity and the workability of the adhesive composition would worsen. Additionally, since the amount of the colloidal silica would be relatively lowered, a composition capable of forming a hardened adhesive product layer having a high adhesion strength could not be obtained. By adding the aqueous alkali silicate solution, an improved adhesive composition can be obtained. If the molar ratio of SiO₂/M'₂O (where M' has the same meaning as defined above) of the aqueous alkali silicate solution to be employed is more than 10, the alkali silicate would have an insufficient capacity of covering the surfaces of the above-mentioned refractory powder particles and fine silica particles. On the contrary, if the molar ratio of SiO₂/M'₂O is less than 1, the hardened product of the composition tends to absorb much more of water and results lowering of the strength of the hardened products. If the concentration of the aqueous alkali silicate solution to be added is more than 50 % by weight, the resulting composition would have a poor stability so that it would often be thickened or gelled. On the other hand, if it is less than 5 % by weight, the covering capacity over the surfaces of the said particles would be poor. Where the aqueous alkali silicate solution is added to the composition, if the solution is more than 500 parts by weight as the solid content thereof to 100 parts by weight of SiO₂ of the aqueous silica sol, the comosition would have a poor stability. However, if it is less than 0.1 part by weight thereto, the effect by addition of the solution could not be attained. If the amount of the coupling agents to be added to the composition is less than 0.05 part by weight to 100 parts by weight of SiO₂ of the aqueous silica sol, a hardened product having the above-mentioned improved properties could not be formed from the adhesive composition. On the contrary, if it is more than 100 parts by weight to 100 parts by weight of SiO₂ of the aqueous silica sol, the stability of the resulting adhesive composition would noticeably lower. Thus, the coupling agents are added in an amount of from 0.5 to 100 parts by weight to 100 parts by weight of SiO₂ of the aqueous silica sol, so as to obtain a favorable adhesive composition. In preparing the composition of the present invention by adding both the aqueous silica sol and the coupling agents thereto in the proportion defined above, if the components are blended at a too high temperature, the resulting composition would be gelled. Therefore, the temperature for blending the composition is preferably approximately 40°C or lower, more preferably room temperature. If the solid concentration in the adhesive composition obtained by blending the constitutive components mentioned above is too high, the composition may be diluted with water to obtain a desired composition having an intended solid concentration. The present invention will be explained in more detail by way of the following examples, which, however, are not intended to restrict the scope of the present invention. The following substance to be used in the following examples were prepared. Precisely, (A₁) is a commercial product of an aqueous silica sol; (B₁) and (B₂) are commercial products of an inorganic refractory powder; (C₁) is a commercial product of a fine powdery silica; (D₁) and (D₂) are commercial products of an aqueous alkali silicate solution; and (E₁) is a commercial product of a coupling agent. (A₁) : An acidic aqueous sol having a particle size of colloidal silica of being from 10 to 20 millimicrons, a molar ratio of SiO₂/Na₂O of being 500, and an SiO₂ concentration of being 20 % by weight. (B₁) : A quartz powder having a particle size distribution of from 0.5 to 400 microns. (B₂) : An alumina powder having a particle size distribution of from 0.5 to 400 microns. (C₁) : A commercial fine powdery silica prepared by gas phase process and having a particle size of 12 millimicrons. (D₁) : An aqueous lithium silicate solution having a concentration of 20 % by weight and a molar ratio of SiO₂/Li₂O of being 4.5. (D₂) : An aqueous potassium silicate solution having a concentration of 30 % by weight and a molar ratio of SiO₂/K₂O of being 4.0. (E₁) : γ-glycidoxypropyltrimethoxysilane. Properties of the composition as prepared in the following examples and the hardened products derived there from were tested by the following methods. Stability Test: A composition to be tested is stored in a closed glass container at 20°C for 24 hours, and the fluidity of the thus stored composition was visually checked with the naked eye. Workability Test: A composition to be tested is put in a glass container in an amount to have a depth of 15 cm and then stored therein as it is at 20°C for 24 hours. Then a stainless steel bar having a diameter of 5 mm is inserted vertically into the composition, whereupon it is observed as to whether or not the top edge of the bar could reach the bottom of the container. Accordingly, the presence or absence of the precipitated solid in the composition is checked. Hardenability Test: A composition to be tested is coated over the complete surface of a glass sheet having a square of 20 mm x 20 mm, the thickness of the coated composition being 2 mm. Then, the thus coated glass sheet is put in a drier and dried at 110 °C for 30 minutes and thereafter taken out therefrom. Presence or absence of cracks on the surface of the thus hardened product is visually checked with the naked eye. Additionally, the pencile hardness of the surface of the hardened product is measured, whereupon the surface having a pencil hardness of 2H or higher is determined to be hard, whilst others having a lower hardness than the former are determined to be insufficient (not hard). Electric Insulating Property Test: A composition to be tested is put into a glass tube having an outer diameter of 8 mm, an inner diameter of 6 mm and a length of 20 mm, and lead wires each having a diameter of 0.7 mm were inserted from the center part of the both ends of the tube in a depth of 5 mm. The composition is then dried at 110 °C for 30 minutes and further heated at 150 °C for 30 minutes, and then allowed to stand in a room having a temperature of 20 °C and a relative humidity of 90 % for 24 hours. Afterwards, an voltage of 500 V is imparted from a direct current battery whereupon the electric resistance through the hardened product is measured. Adhesion Strength Test: Two glass sheets each having a square of 20 mm x 20 mm are bonded over the complete surfaces thereof via a compostion to be tested. Then the composition is hardened by heating and drying at 110 to 150 °C for 30 minutes and subsequently at 200 °C for 30 minutes, whereby the two sheets are bonded to each other. Next, fixing tools are attached to both sides of the thus bonded glass sheets with a commercial high-strength adhesive, and a tension is applied to the direction perpendicular to the bonded glass sheets by the use of a tensile tester at a speed of 1 mm/min, whereupon the tension with which the bonded part of the glass sheets is broken is measured. Additionally, the broken surface of the bonded part is visually observed with the naked eye. "L" indicates that the bonded part was broken because of breakage of the adhesive layer; while "S" indicates that the bonded part was broken because of separation of the glass sheet from the adhesive layer. EXAMPLE 1 An aqueous silica sol, an aqueous alkali silicate solution, a fine powdery silica, an inorganic refractory powder and a silane coupling agent, which are indicated in Table 1 below, were mixed at room temperature for 3 hours, to prepare compositions (Q₁) and (Q₂). Next, the properties of these compositions (Q₁) and (Q₂) and the hardened products thereof were tested in accordance with the above-mentioned test methods. The results obtained are shown in Table 2 below. The adhesive composition of the present invention can be prepared with ease and it may simply be hardened by drying at room temperature or by heating up to a temperature of approximately 300°C to give a hardened product having a noticeably improved electric insulating property. Accordingly, it may advantageously be used for adhesion of materials of the same kind or different kinds which are required to have a high insulating property, such as ceramics, glass, slates, hardened cement products, aluminium stainless steel, iron and other metal materials, whereupon the bonded part displays an extremely improved electric insulating property and mechanical strength. Additionally, the adhesive composition of the present invention may also be used for adhesion of a metal plate and a ceramic fiber mat and for adhesion of mortar plates. As other advantageous merits, the composition of the present invention has a sufficient storage stability for an extremely long period of time and has excellent fluidity and workability in operation of adhesion or coating with the composition. Additionally, after hardened, the composition gives a hardened adhesive product with neither cracks nor shrinkage. Even repeated heat-shocks are applied to the hardened adhesive product, the bonded part or the coated part is not broken. That is, the hardened product from the composition of the invention has an extremely excellent heat shock-resistance. Therefore, the composition of the invention may conveniently be used for adhesion or coating of various electric parts or electronic parts, such as sensor, as well as other various parts of electric or electronic appliances. While the invention has been described in detail and with reference to specific embodiments thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope thereof.

Claims: An inorganic adhesive composition, which contains: (a) an aqueous silica sol having a mean particle size of from 5 to 200 millimicrons and a molar ratio of SiO₂/M₂O (where M represents an alkali metal atom, an amine molecule, or a quaternary ammonium group) of being from 30 to 2000, in an amount of 100 parts by weight as SiO₂; (b) an inorganic refractory powder having a particle size of from 0.5 to 1000 microns, in an amount of from 100 to 100000 parts by weight; (c) a fine powdery silica in amorphous form having a particle size of from 5 to 200 millimicrons, in an amount of from 0.5 to 500 parts by weight; (d) an aqueous solution of an alkali silicate having a molar ratio of SiO₂/M'₂O (where M' represents Na, K, Li, an amine molecule, or a quaternary ammonium group) of being from 1 to 10 and having an alkali silicate concentration of being from 5 to 50 % by weight, in an amount of from 0.1 to 500 parts by weight as the alkali silicate component; and (e) one or more coupling agents selected from the group consisting of a silane compound of a general formula (I): R¹Si(OR)₃ (I) where OR represents an alkoxy or acyloxy group having from 1 to 3 carbon atoms, and R¹ represents a monovalent organic group having from 2 to 9 carbon atoms, or a hydrolysate thereof, and a silane compound of a general formula (II): R¹SiCH₃(OR)₂ (II) where OR and R¹ have the same meanings as defined above, or a hydrolysate thereof, in an amount of from 0.05 to 100 parts by weight; the solid content of the components (a), (b), (c), (d) and (e) being from 40 to 95 % by weight; and which has a viscosity of from 1 to 10000 poise at 20°C. The inorganic adhesive composition as claimed in claim 1, in which the aqueous silica sol (a) has a mean particle size of from 10 to 150 millimicrons and has an SiO₂ concentration of from 1 to 50 % by weight and in which M represents Na, K, Li, methylamine, ethylamine, ethanolamine, tetramethylammonium, monomethyltriethanolammonium, isopropyltriethanolammonium or tetraethanolammonium group. The inorganic adhesive composition as claimed in claim 1, in which the inorganic refractory powder (b) is a powder of a non-fibrous quartz, silica, feldspar, aluminium silicate, zirconium silicate, mullite, zirconia, alumina, silicon nitride, silicon carbide, talc or mica, or a mixture thereof, or a fibrous powder of a glass fiber or a potassium titanate fiber, or a mixture thereof, or a mixture of the said non-fibrous powder(s) and the said fibrous powder(s). The inorganic adhesive composition as claimed in claim 1, in which the aqueous alkali silicate solution (d) has a molar ratio of SiO₂/M'₂O of being from 1 to 10 and has an alkali silicate concentration of from 5 to 50 % by weight and in which M' represents Na, K, Li, methylamine, ethylamine, ethanolamine, tetramethylammonium, monomethyltriethanolammonium, isopropyltriethanolammonium or tetraethanolammonium group. The inorganic adhesive composition as claimed in claim 1, in which the coupling agent (e) is vinyltris(β-methoxyethoxy) silane, vinyltriethoxysilane, vinyltrimethoxysilane, vinyltriacetoxysilane, γ-methacryloxypropyltrimethoxysilane, β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane, N-β-(aminoethyl)-γ-aminopropylmethyldimethoxysilane, γ-aminopropyltriethoxysilane or γ-anilinopropyltrimethoxysilane, or a mixture thereof, or a hydrolysate of the silane, or a mixture of the non-hydrolyzed silanes and/or hydrolysates of the silanes. A method of bonding materials of the same kind or different kinds of ceramics, glass, slates, hardened cement products and metal materials, wherein two surfaces of the said materials are bonded via an adhesive composition as set forth in anyone of claims 1 to 5 and the composition is dried and hardened between the surfaces. The method as claimed in claimed in claim 6, in which the drying is effected at a temperature higher than the freezing temperature of the composition up to 300°C or lower.

Inventors: EMA KIYOMI C O NISSAN CHEMICAL, KITAJIMA AKIRA C O NISSAN CHEM, OKUBI KEN-ICHI C O NISSAN CHEM, SATO HISAYUKI C O NISSAN CHEMI, EMA, KIYOMI, KITAJIMA, AKIRA, OKUBI, KEN-ICHI, SATO, HISAYUKI, EMA, KIYOMI, C/O NISSAN CHEMICAL IND., LTD., KITAJIMA, AKIRA, C/O NISSAN CHEMICAL IND., LTD., OKUBI, KEN-ICHI, C/O NISSAN CHEMICAL IND., LTD., SATO, HISAYUKI, C/O NISSAN CHEMICAL IND., LTD.
Applicants: NISSAN CHEMICAL IND LTD, NISSAN CHEMICAL INDUSTRIES LTD.
Application year: 1990
Main classification: C09J1
IPC codes: C09J1