Patent Publication Number: US-8119744-B2

Title: Curable silicone composition

Description:
RELATED APPLICATIONS 
     This application claims priority to and all the advantages of International Patent Application No. PCT/JP2007/074606, filed on Dec. 14, 2007, which claims priority to Japanese Patent Application No. JP2006-346866, filed on Dec. 25, 2006. 
     TECHNICAL FIELD 
     The present invention relates to a curable silicone composition, in particular, to a curable silicone composition that is characterized by excellent handleability and reduced oil-bleeding during curing, and that, when cured, forms a cured body of excellent flexibility and adhesion. 
     BACKGROUND ART 
     Cured bodies obtained by curing conventional curable resin compositions, such as curable epoxy resin compositions, etc., used for sealing and bonding parts of electrical and electronic devices are characterized by a high modulus of elasticity and therefore by high rigidity. Therefore, the use of such bodies in conjunction with electrical or electronic devices is associated with problems such as development of high stress, which develops under conditions of thermal expansion. Another problem associated with the use of cured bodies of the aforementioned compositions is buckling of the electrical or electronic devices or substrates and formation of cracks in the body of the cured resin or gaps in the interface between the cured resin and the electrical or electronic device, which in some cases may lead to destruction of the respective devices. 
     In order to reduce stress that may develop in the aforementioned cured bodies, it was suggested to prepare a curable silicone composition from an epoxy-containing organopolysiloxane and a curing agent for organopolysiloxane resin (see Japanese Unexamined Patent Application Publications (hereinafter referred to as “Kokai”) H05-105758, 2005-154766, 2006-306953 and 2006-306954). However, when such curable silicone compositions are used for bonding parts of electrical or electronic devices, the problem of oil bleeding of some components of the composition to the outer surface of the cured bodies occurs during curing, and this contaminates the devices. 
     It is an object of the present invention to provide a curable silicone composition that is characterized by excellent handleability and reduced oil-bleeding during curing, and that, when cured, forms a cured body of excellent flexibility and adhesion. 
     DISCLOSURE OF INVENTION 
     A curable silicone composition comprising at least the following components: 
     100 parts by mass of (A) an epoxy-containing organopolysiloxane; 
     0.1 to 500 parts by mass of (B) a phenolic-type curing agent; and 
     0.01 to 100 parts by mass of (C) an acidic-anhydride type curing agent. 
     EFFECTS OF INVENTION 
     The curable silicone composition of the present invention is efficient in that it is characterized by excellent handleability and allows significant shortening of curing time or decrease of curing temperature. A cured body of the composition is less subject to contamination because oil bleeding is reduced. Furthermore, since the cured body of the composition possesses excellent flexibility and adhesion, it develops reduced internal stress under the effect of thermal expansion and can be bonded to various substrates. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Let us first consider in more detail the curable silicone composition of the present invention. 
     Component (A) is a main component of the composition. There are no special restrictions with regard to component (A), provided that this component is an epoxy-containing organopolysiloxane, but it may be recommended that component (A) has a branched molecular structure. Component (A) is (A 1 ) an organopolysiloxane represented by the following average unit formula:
 
(R 1   3 SiO 1/2 ) a (R 2   2 SiO 2/2 ) b (R 3 SiO 3/2 ) c  
 
and/or (A 2 ) a diorganosiloxane represented by the following general formula:
 
A-R 5 —(R 4   2 SiO) m R 4   2 Si—R 5 -A.
 
     In component (A 1 ), R 1 , R 2 , and R 3  may be the same or different and constitute substituted or unsubstituted monovalent hydrocarbon groups or epoxy-containing monovalent organic groups. The aforementioned monovalent hydrocarbon groups can be represented by methyl, ethyl, propyl, isopropyl, n-butyl, sec-butyl, t-butyl, pentyl, hexyl, or similar alkyl groups; cyclopentyl, cyclohexyl, cycloheptyl, or similar cycloalkyl groups; vinyl, allyl, butenyl, pentenyl, hexenyl, or similar alkenyl groups; phenyl, tolyl, xylyl, or similar aryl groups; benzyl, phenethyl, phenylpropyl, or similar aralkyl groups; chloromethyl, 3-chloropropyl, 3,3,3-trifluoropropyl, or similar halogenated alkyl groups. Most preferable are alkyl and aryl groups, especially methyl and phenyl groups. Epoxy-containing monovalent organic groups can be represented by 2-glycidoxyethyl, 3-glycidoxypropyl, 4-glycidoxybutyl, or similar glycidoxyalkyl groups; or 2-(3,4-epoxycyclohexyl)ethyl, 3-(3,4-epoxycyclohexyl)propyl, 2-(3,4-epoxy-3-methylcyclohexyl)-2-methylethyl, or similar epoxycycloalkylalkyl groups; and 4-oxiranylbutyl, 8-oxiranyloctyl, or similar oxiranylalkyl groups. Most preferable of these groups are glycidoxyalkyl and epoxycycloalkylalkyl, especially 3-glycidoxypropyl and 2-(3,4-epoxycyclohexyl)ethyl groups. In the above formula, at least two groups designated by R 1 , R 2 , and R 3  are the aforementioned epoxy-containing monovalent organic groups. 
     In the above formula, at least 20 mole %, preferably at least 50 mole %, and most preferably at least 80 mole % of all groups designated by R 3  are aryl groups. If the content of the aryl groups among all groups designed by R 3  in one molecule is below the recommended lower limit, this will either impair adhesive properties or will reduce the mechanical strength of the cured body of the composition. It is recommended that such aryl groups comprise phenyl groups. 
     In the above formula, “a”, “b”, and “c” are numbers that satisfy the following conditions:
 
0≦ a≦ 0.8;0≦ b≦ 0.8;0.2 ≦c≦ 0.9; a+b+c= 1
 
Here, “a” is a number that shows the percentage of siloxane units represented by formula: R 1   3 SiO 1/2 . When this component is composed of only siloxane units represented by formula: R 3 SiO 3/2 , the present, component will become too viscous, and because this will impair handleability of the obtained composition, it is recommended that “a” be a number that satisfies the following condition: 0&lt;a≦0.8, and preferably the following condition: 0.3≦a≦0.8. Furthermore, “b” is a number that shows the percentage of siloxane units represented by formula: R 2   2 SiO 2/2 . In order to provide this component with optimal molecular weight, to prevent this composition from bleeding out from the obtained cured body and to provide the cured body with excellent mechanical strength, “b” should be a number that satisfies the following condition: 0≦b≦0.6. In the above formula, “c” shows the percentage of siloxane units represented by formula: R 3 SiO 3/2 . In order to provide good handleability of the composition and to provide a cured body with good adhesion, good mechanical properties, and flexibility, “c” should be a number that satisfies the following condition: 0.4≦c≦0.9.
 
     There are no special restrictions with regard to the content of epoxy-containing monovalent organic groups in component (A 1 ); however, it may be recommended to use these groups in an epoxy-equivalent quantity of this component (i.e., number obtained by dividing mass average molecular weight of this component by the number of epoxy groups in one molecule) in the range of 100 to 2,000, preferably 100 to 1,000, and most preferably 100 to 700. If the epoxy-equivalent quantity is less than the recommended lower limit of the above range, this will impair flexibility of a cured body obtained from the composition. On the other hand, if the epoxy-equivalent is greater than the recommended upper limit, this will impair curability of the composition and will reduce adhesion and mechanical strength of the cured body obtained by curing the composition. Furthermore, component (A 1 ) may comprise an organopolysiloxane of one type or a mixture of organopolysiloxanes of two or more types. There are no special restrictions with regard to the form of component (A 1 ) at 25° C., and it can be liquid or solid. When component (A 1 ) is in a solid form, in order to uniformly mix it with other components, component (A 1 ) may be dissolved in an organic solvent or heated. Use of this component in a liquid form at 25° C. is preferable from the viewpoint of better compoundability and handleability. Also, there are no special restrictions with regard to the mass-average molecular weight of component (A 1 ), but it may be recommended that this characteristic range from 500 to 10,000, preferably from 750 to 3,000. 
     The aforementioned component (A 1 ) can be exemplified by organopolysiloxanes that are represented by the formulas given below, where “a”, “b”, and “c” are the same as defined above but where “a” and “b” cannot be equal to zero; “c′” and “c″” are numbers that satisfy the following conditions: 0.1&lt;c′&lt;0.8; 0&lt;c″&lt;0.2; 0.2≦(c′+c″)≦0.9; and 0.2≦c′/(c′+c″); “G” designates a 3-glycidoxypropyl group; and “E” designates a 2-(3,4-epoxycyclohexyl)ethyl group.
         [G(CH 3 ) 2 SiO 1/2 ] a [C 6 H 5 SiO 3/2 ] c      [E(CH 3 ) 2 SiO 1/2 ] a [C 6 H 5 SiO 3/2 ] c      [G(CH 3 ) 2 SiO 1/2 ] a [(CH 3 ) 2 SiO 2/2 ] b [C 6 H 5 SiO 3/2 ] c      [E(CH 3 ) 2 SiO 1/2 ] a [(CH 3 ) 2 SiO 2/2 ] b [C 6 H 5 SiO 3/2 ] c      [GCH 3 SiO 2/2 ] b [C 6 H 5 SiO 3/2 ] c      [ECH 3 SiO 2/2 ] b [C 6 H 5 SiO 3/2 ] c      [G(CH 3 ) 2 SiO 1/2 ] a [C 6 H 5 SiO 3/2 ] c′ [CH 3 SiO 3/2 ] c″     [E(CH 3 ) 2 SiO 1/2 ] a [C 6 H 5 SiO 3/2 ] c′ [CH 3 SiO 3/2 ] c″     [C 6 H 5 SiO 3/2 ] c′ [GSiO 3/2 ] c″     [C 6 H 5 SiO 3/2 ] c′ [ESiO 3/2 ] c″         

     There are no special restrictions with regard to the method of preparation of component (A 1 ). For example, the following methods are possible: (1) a method, in which a phenyltrialkoxysilane and an alkoxysilane with epoxy-containing monovalent organic groups, e.g., 3-glycidoxypropyltrimethoxysilane or 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane are subjected to co-hydrolyzation and condensation; (2) a method, in which an alkoxysilane having the aforementioned epoxy-containing monovalent organic groups and a silanol-containing organopolysiloxane obtained by subjecting a phenyltrichlorosilane or a phenyltrialkoxysilane to hydrolyzation and condensation are subjected to a dealcoholization reaction; (3) a method, in which a reaction is carried out between an olefin that has epoxy-containing monovalent organic groups and an organopolysiloxane having silicon-bonded hydrogen atoms prepared by subjecting a phenyltrichlorosilane or a phenyltrialkoxysilane to co-hydrolysis and condensation in the presence of a dimethylchlorosilane or a similar silane having a silicon-bonded hydrogen atom; (4) a method, in which a copolymer of a dimethylsiloxane and a methyl {2-(3,4-epoxycyclohexyl)ethyl}siloxane capped at both molecular terminals with trimethylsiloxy groups or a copolymer of a dimethylsiloxane and a methyl(3-glycidoxypropyl)siloxane capped at both molecular terminals with trimethylsiloxy groups and an organopolysiloxane prepared by subjecting a phenyltrichlorosilane or a phenyltrialkoxysilane to hydrolysis and condensation) is subjected to an equilibrium reaction in the presence of a basic catalyst; (5) a method, in which a cyclic methyl {2-(3,4-epoxycyclohexyl)ethyl}siloxane or a cyclic methyl(3-glycidoxypropyl)siloxane and an organopolysiloxane composed of siloxane units of the following formula: C 6 H 5 SiO 3/2  are subjected to an equilibrium reaction in the presence of a basic catalyst; and (6) a method, in which a cyclic dimethylsiloxane and a cyclic methyl {2-(3,4-epoxycyclohexyl)ethyl}siloxane or a cyclic methyl(3-glycidoxypropyl)siloxane and an organopolysiloxane composed of siloxane units of the following formula: C 6 H 5 SiO 3/2  are subjected to an equilibrium reaction in the presence of an acidic or a basic catalyst. 
     In component (A 2 ), the groups designated by R 4  may be substituted or unsubstituted monovalent hydrocarbon groups, which are free of unsaturated aliphatic groups. Specific examples of groups designated by R 4  are the following: methyl, ethyl, propyl, isopropyl, n-butyl, sec-butyl, t-butyl, pentyl, hexyl, or similar alkyl groups; cyclopentyl, cyclohexyl, cycloheptyl, or similar cycloalkyl groups; phenyl, tolyl, xylyl, or similar aryl groups; benzyl, phenethyl, phenylpropyl, or similar aralkyl groups; 3-chloropropyl, 3,3,3-trifluoropropyl, or similar halogenated alkyl groups. Most preferable are alkyl groups, especially methyl groups. In the above formula, R 5  is a bivalent organic group, such as ethylene, methylethylene, propylene, butylene, pentylene, hexylene, or a similar alkylene group; ethyleneoxyethylene, ethyleneoxypropylene, ethylenoxybutylene, propylenoxypropylene, or a similar alkyleneoxyalkylene group. Preferable are alkylene groups, in particular, ethylene groups. In the formula, “m” is an integer, which is equal to or greater than 1 and which represents a degree of polymerization of the diorganopolysiloxane contained in the main molecular chain. From the viewpoint of improved flexibility of a cured body of the composition, “m” should be equal to or greater than 10. There are no special restrictions with regard to the upper limit of the value of “m”, but it is recommended that the value of “m” does not exceed 500. 
     Furthermore, in the above formula, “A” designates a siloxane-residual radical represented by the following average unit formula:
 
(XR 4   2 SiO 1/2 ) d (SiO 4/2 ) e  
 
where R 4  stands for a substituted or unsubstituted monovalent hydrocarbon group that is free of unsaturated aliphatic bonds. This group may be the same as exemplified above, of which alkyl groups, and especially methyl groups, are preferable. In the above formula, “X” is a single bond, a hydrogen atom, a group designated by R 4 , an epoxy-containing monovalent organic group, or an alkoxysilylalkyl group. Groups designated by R 4  may be exemplified by the same groups as given above. The aforementioned epoxy-containing monovalent organic groups may be the same as those designated by R 1 , R 2 , or R 3 . The alkoxysilylalkyl group can be exemplified by a trimethoxysilylethyl, trimethoxysilylpropyl, dimethoxymethylsilylpropyl, methoxydimethylsilylpropyl, triethoxysilylethyl, or a tripropoxysilylpropyl group. However, at least one group designated by “X” in one molecule is a single bond, which is used for bonding to the group designated by R 5  in the aforementioned diorganosiloxane. Furthermore, at least one group in one molecule designated by “X” should comprise an epoxy-containing monovalent organic group, preferably such as a glycidoxyalkyl group, and most preferably a 3-glycidoxypropyl group. In the above formula “d” is a positive number, “e” is a positive number, and “d/e” is a number ranging from 0.2 to 4.
 
     There are no special restrictions with regard to molecular weight of component (A 2 ); however, it is recommended that mass-average molecular weight be in the range of 500 to 1,000,000. Also, there are no special restrictions with regard to the form of component (A 2 ) at 25° C., but the liquid form is preferable. It is recommended that component (A 2 ) have a viscosity at 25° C. in the range of 50 to 1,000,000 mPa·s. The method of preparation of component (A 2 ) is described, e.g., in Kokai H06-56999. 
     In the composition of the present invention, component (A) may comprise either aforementioned component (A 1 ) or component (A 2 ), or a mixture of both. However, at least one component (A 2 ) can be used. In other words, component (A) may comprise only component (A 2 ), or a mixture of components (A 1 ) and (A 2 ). There are no special restrictions with regard to the amount in which component (A 2 ) can be used when component (A) is represented by a mixture of components (A 1 ) and (A 2 ), but it may be recommended that component (A 2 ) be contained in the amount of 0.1 to 800 parts by mass, preferably 1 to 500 parts by mass, and, most preferably, 10 to 200 parts by mass per 100 parts by mass of component (A 1 ). If component (A 2 ) is added in an amount less than the recommended lower limit, this will impair flexibility of a cured body produced by curing the composition, and if, on the other hand, the content of component (A 2 ) exceeds the recommended upper limit, the obtained composition will have increased viscosity. 
     Component (B), which is a phenolic-type curing agent, reacts with epoxy groups of component (A) and is used for curing the composition. This agent is a compound that contains in one molecule at least two phenolic hydroxyl groups. Component (B) can be specifically exemplified by phenol novolak resin, cresol novolak resin, bisphenol A-type compound; or an organosiloxane having phenolic hydroxyl groups. It is preferable to use an organosiloxane that contains in one molecule at least two phenolic hydroxyl groups. It is recommended that the equivalent amount of phenolic hydroxyl groups (which is a value obtained by dividing the mass average molecular weight of the present component by the number of phenolic hydroxyl groups contained in one molecule) does not exceed 1,000 and, for better reactivity, does not exceed 500. 
     Since provision of organosiloxane with phenolic hydroxyl groups in component (B) improves flexibility of a cured body obtained by curing the composition, it is recommended that the organosiloxane be represented by the following general formula:
 
R 6   3 SiO(R 6   2 SiO) n SiR 6   3  
 
In the above formula, the groups that are designated by R 6  may be the same or different and represent substituted or unsubstituted monovalent hydrocarbon groups or monovalent organic groups that contain phenolic hydroxyl groups. The aforementioned monovalent hydrocarbon groups may be the same as those exemplified above, of which alkyl groups and aryl groups, especially methyl groups and phenyl groups, are preferable. Organic groups that contain phenolic groups may be exemplified by the groups shown by the formulae given below. In these formulae, R 7  designates bivalent organic groups such as ethylene, methylethylene, propylene, butylene, pentylene, hexylene, or similar alkylene groups; ethyleneoxyethylene, ethyleneoxypropylene, ethylenoxybutylene, propylenoxypropylene, or similar alkyleneoxyalkylene groups. Preferable are alkylene groups and, in particular, propylene groups.
 
     
       
         
         
             
             
         
       
     
     In the above formulas, “n” is an integer ranging from 0 to 1,000, preferably 0 to 100, and most preferably 0 to 20. If “n” exceeds the recommended upper limit, this will impair compounding with component (A) and industrial handleability. 
     Aforementioned component (B) is exemplified by organosiloxanes represented by the formulas given below, where “x” is an integer from 1 to 20, and “y” is an integer from 2 to 10. 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     There are no special restrictions with regard to the method that can be used for manufacturing component (B). For example, this component can be obtained by subjecting an alkenyl-containing phenol compound and an organopolysiloxane that has silicon-bonded hydrogen atoms to a hydrosilylation reaction. 
     There are no special restrictions with regard to the form of component (B) at 25° C., and it can be in a liquid or in a solid form. The liquid form is preferred from the viewpoint of easier handling. It is recommended that the viscosity of a liquid component (B) at 25° C. be in the range of 1 to 1,000,000 mPa·s, preferably 10 to 5,000 mPa·s. If the viscosity at 25° C. is below the recommended lower limit, the obtained cured body will have reduced mechanical strength. If, on the other hand, the viscosity exceeds the recommended upper limit, this will impair industrial handleability of the composition. 
     It is recommended to use component (B) in an amount of 0.1 to 500 parts by mass, preferably in the range of 0.1 to 200 parts by mass per 100 parts by mass of component (A). It is recommended that the mole ratio of the phenolic hydroxyl groups contained in component (B) to all epoxy groups contained in the composition be in the range of 0.2 to 5, preferably 0.3 to 2.5, and most preferably 0.8 to 1.5. If the mole ratio of the phenolic hydroxyl groups contained in component (B) to all epoxy groups contained in the composition is below the recommended lower limit, it will be difficult to ensure complete curing of the obtained composition. If, on the other hand, the aforementioned ratio exceeds the recommended upper limit, this will impair mechanical properties of the cured body obtained from the composition. 
     Component (C), which is an acidic-anhydride type curing agent reacts with epoxy groups of component (A) and is used for curing the composition. In combination with component (B), component (C) restricts bleeding of oil during curing of the composition, and when the composition is cured, this component imparts to the cured body improved flexibility and adhesive properties. There are no special restrictions with regard to the molecular structure and molecular weight of component (C), and various known acidic anhydrides known as curing agents for epoxy resins can be used as component (C). Specific examples are the following: succinic anhydride, maleic anhydride, itaconic anhydride, octenylsuccinic anhydride, dodecenylsuccinic anhydride, phthalic anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, methyltetrahydrophthalic anhydride, methylhexahydrophthalic anhydride, tetrabromophthalic anhydride, himic anhydride (known as 5-norbornene-2,3-dicarboxylic anhydride), methylnadic anhydride (methyl-5-norbornene-2,3-dicarboxylic anhydride), dodecyl succinic acid anhydride, chlorendic anhydride, trialkyltetrahydrophthalic anhydride, diphenic anhydride, or a similar monofunctional acid anhydride; pyromellitic anhydride, benzophenone tetracarboxylic dianhydride, ethyleneglycol bis(anhydrotrimate), methylcyclohexane tetracarboxylic anhydride (known as 5-(2,5-dioxotetrahydro-3-furanyl)-3-methyl-3-cyclohexe-1,2-dicarboxylic anhydride), biphenyl tetracarboxylic dianhydride, diphenylether tetracarboxylic dianhydride, butane tetracarboxylic dianhydride, cyclopentatetracarboxylic dianhydride, bicyclo[2,2,2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride, or similar bifunctional anhydrides; β,γ-aconitic anhydride, glycolic anhydride, trimellitic anhydride, polyazelaic anhydride, or similar free-acid anhydrides. These anhydrides can be used individually or in combinations of two or more. In order to facilitate compounding with other components, it is recommended that component (C) be in a liquid form. Most preferable are methyltetrahydrophthalic anhydride, methylhexahydrophthalic anhydride, methylnadic anhydride, trialkyltetrahydrophthalic anhydride, or tetradecenylsuccinic anhydride. 
     In the composition of the invention, component (C) is used in the amount of 0.01 to 100 parts by mass, preferably, 0.01 to 50 parts by mass, and most preferably, 0.01 to 20 parts by mass. If component (C) is used in the amount less than the recommended lower limit, it will be difficult to restrict oil bleeding in the curing stage, and, if, on the other hand, the added amount of component (C) exceeds the recommended upper limit, this will increase modulus of elasticity of the cured body. 
     The composition of the invention may contain (D) a curing accelerator as an arbitrary component. Such component (D) may be represented by a tertiary amine compound, aluminia, zirconia, or a similar organometallic compound; phosphine or a similar organophosphorous compound; as well as a heterocyclic amine compound, boron complex compound, organic ammonium salt, organic sulfonium salt, organic peroxide, and reaction products of the above compounds. Specific examples of such compounds are the following: triphenylphosphine, tributylphosphine, tri(p-methylphenyl)phosphine, tri(nonylphenyl)phosphine, triphenylphosphine-triphenylborate, tetraphenylphosphine-tetraphenylborate, or similar phosphorous compounds; triethylamine, benzyldimethylamine, α-methylbenzyldimethylamine, 1,8-diazobicyclo[5.4.0]undecene-7, or a similar tertiary amine; 2-methylimidazole, 2-phenylimidazone, 2-phenyl-4-methylimidazole, or a similar imidazole compound. In order to extend the pot life of the composition of the invention, the curing accelerator can be in an encapsulated form. Such an encapsulated curing-accelerating agent may comprise an encapsulated amine-type curing accelerator made from a bisphenol-A epoxy resin that contains an amine-type curing-accelerating substance (can be purchased from Asahi Kasei Co., Ltd.; trademark HX-3088). 
     There are no special restrictions with regard to the amount in which component (D) can be added to the composition, but in general it can be recommended that this component be contained in the amount not exceeding 50 parts by mass, in particular, in the amount of 0.01 to 50 parts by mass, and most preferably, 0.1 to 5 parts by mass, per 100 parts by mass of component (A). 
     In order to improve mechanical strength of a cured body, the composition may contain (E) a filler. Such component (E) can be represented by the following: glass fiber, alumina fiber, ceramic fiber composed of alumina and silica, boron fiber, zirconia fiber, silicon carbide fiber, metallic fiber, or a similar fibrous filler; fused silica, crystalline silica, precipitated silica, fumed silica, baked silica, zinc oxide, baked clay, carbon black, glass beads, alumina, talc, calcium carbonate, clay, aluminum hydroxide, magnesium hydroxide, barium sulfate, aluminum nitride, boron nitride, silicon carbide, magnesia, titania, beryllium oxide, kaolin, mica, zirconia, barium sulfate, or a similar inorganic filler; powders of gold, silver, copper, aluminum, nickel, palladium, alloys and brasses of the aforementioned metals, solders, memory alloys, or other fine metal powders; gold, silver, nickel, copper, or other metal powders vapor-deposited or deposited via metallization onto the surfaces of finally powdered ceramic, glass, quartz, organic resin, etc. The above fillers can be used separately or in combinations of two or more. From the viewpoint of better thermal conductivity of the obtained cured body, the following fillers are preferable: thermally conductive powders such as alumina, crystalline silica, aluminum nitride, boron nitride; as well as reinforcing powders made from fused silica, precipitated silica, fumed silica, colloidal silica, etc. In order to impart good thermal conductivity and electrical conductivity to cured bodies, the use of silver powder is preferable. In order impart thermally conductive properties to a cured body of the composition, it is preferable to use alumina powder. The powder particles may have the shape of ground particles, or may be spherical, fibrous, rod-like, flake-like, scale-like, plate-like, coil-like, etc. There are no special restrictions with regard to the size of the particles, but in general their maximum dimension should not exceed 200 μm, and on average should be within the range of 0.001 to 50 μm. 
     Also, there are no special restrictions with regard to the content of component (E), but it is recommended to add this component in an amount of not more than 5,000 parts by mass, preferably within the range of 10 to 4,000 parts by mass, and even more preferably, within the range of 50 to 4,000 parts by mass per 100 parts by mass of component (A). When component (E) contains fillers other than the aforementioned fine metal powders or thermally conductive powdered materials, component (E) should be used in an amount of not more than 2,000 parts by mass, preferably within the range of 10 to 2,000 parts by mass, and even more preferably, within the range of 50 to 1,000 parts by mass per 100 parts by mass of component (A). When the powder particles have a plate-like or scale-like shape, it becomes possible to reduce shrinkage during curing by using specific orientation of the particles in the obtained cured body. 
     In order to improve curability and workability of the composition and to improve adhesive properties of the cured body of the composition, or to adjust the modulus of elasticity, the composition can further be combined with (F) an organic epoxy compound. 
     There are no special restrictions with regard to the form of component (F) at 25° C., and it may be liquid or solid, but the liquid form is preferable. This component can be exemplified by a bisphenol-A type of epoxy resin, a bisphenol-F type of epoxy resin, an alicyclic epoxy resin, or an organic epoxy resin of the following general formula (I): 
     
       
         
         
             
             
         
       
     
     In the above formula, R 8  designates a substituted or unsubstituted monovalent hydrocarbon group having one to 10 carbon atoms. The aforementioned monovalent hydrocarbon group can be exemplified by methyl, ethyl, propyl, isopropyl, n-butyl, sec-butyl, t-butyl, pentyl, hexyl, octyl, decyl, or similar alkyl groups; cyclopentyl, cyclohexyl, cycloheptyl, or similar cycloalkyl groups; methoxyethyl, ethoxyethyl, or similar alkoxy-substituted alkyl groups; vinyl, allyl, butenyl, or similar alkenyl groups; cyclopentenyl, cyclohexenyl, or similar cycloalkenyl groups; phenyl, tolyl, xylyl, ethylphenyl, butylphenyl, t-butylphenyl, dimethylnaphthyl, or similar aryl groups; benzyl, phenethyl, phenylpropyl, or similar aralkyl groups; 3-chloropropyl, 3,3,3-trifluoropropyl, or similar halogenated alkyl groups; methoxyphenyl, ethoxyphenyl, butoxyphenyl, t-butoxyphenyl, methoxynaphthyl, or similar alkoxy-substituted aryl groups. Furthermore, in the above formula, “f” is an integer from 0 to 4. The aforementioned component (F) can be obtained as a commercial product known under the trademark Epicoat 630 produced by Japan Epoxy Resin Company. 
     There are no special restrictions with regard to the amount in which component (F) can be used in the composition, but it may be recommended to add this component in the amount not exceeding 500 part by mass per 100 parts by mass of component (A), preferably in the amount of 0.1 to 500 part by mass per 100 parts by mass of component (A). When the epoxy resin represented by aforementioned general formula (I) is used as component (F), it is recommended to add component (F) in the amount of 0.01 to 50 mass %, preferably, 0.01 to 20 mass %, and most preferably, 0.01 to 10 mass %. If component (F) is added in the amount less than the recommended lower limit, it will be difficult to restrict bleed of oil prior to curing, and, if, on the other hand, the added amount exceeds the recommended upper limit, this will increase the modulus of elasticity in a cured body obtained from the composition. 
     In order to improve dispersity of component (E) in component (A) or to improve adhesion of the obtained cured body to semiconductor chips, substrates, or the like, the composition can be combined with a coupling agent. This coupling agent may comprise a titanate coupling agent, a silane coupling agent, or a similar coupling agent. A titanate coupling agent may comprise i-propoxytitanium tri(i-isostearate). A silane coupling agent may comprise 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyl methyldiethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, or a similar epoxy-containing alkoxysilane; N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, 3-aminopropyl triethoxysilane, N-phenyl-3-aminopropyltrimethoxysilane, or a similar amine-containing alkoxysilane; 3-mercaptopropyltrimethoxysilane or a similar mercapto-containing alkoxysilane; octadecyltrimethoxysilane or a similar long chain alkyl-containing silane. There are no special restrictions with regard to the amount in which the aforementioned silane coupling agent can be used, but in general it is recommended to add this agent in an amount not exceeding 10 parts by mass, preferably 0.01 to 10 parts by mass per 100 parts by mass of component (A). 
     Other arbitrary components of the composition may be exemplified by tetramethoxysilane, tetraethoxysilane, dimethyldimethoxysilane, methylphenyldimethoxysilane, methylphenyldiethoxysilane, phenyltrimethoxysilane, methyltrimethoxysilane, methyltriethoxysilane, vinyltrimethoxysilane, allyltrimethoxysilane, allyltriethoxysilane, or a similar alkoxysilane. 
     The composition of the invention is prepared by mixing components (A), (B), and (C), with an addition of other components if necessary. There are no special restrictions with regard to the method used for mixing the components. For example, components (A), (B), and (C) and, if necessary, arbitrary components, can be mixed simultaneously, or the aforementioned arbitrary components can be added after premixing components (A), (B), and (C). Also, there are no limitations with regard to equipment that can be used for mixing. For example, this can be a single-shaft-type or a two-shaft-type continuous mixer, a two-roll mill, a three-roll mill, a Ross® mixer, a Hobart mixer, a dental mixer, a planetary mixer, a kneader mixer, or a grinding mixer. 
     Apart from use as a protective agent for semiconductor chips or electrical wiring, the cured bodies of the composition may be used to form insulating layers or shock-absorbing layers on semiconductor chips or printed circuit boards. There are no special restrictions with regard to the form of the cured bodies obtained from the composition, and the cured bodies may be made in the form of rubber, hard rubber, or resin, but, most preferably, with a complex modulus of elasticity not exceeding 2 GPa. 
     The composition of the invention can also be used for transfer molding, injection molding, potting, casting, powder coating, immersion coating, drop-wise application, etc. The method of use can be selected from potting, dispensing, screen printing, or coating; however, from the viewpoint of ease of use and decreased consumption of material, a liquid or paste form of the composition is preferable. Since the composition of the invention is suitable for forming cured bodies that are characterized by excellent flexibility and adhesion, the composition is most suitable for use as a sealing agent, casting agent, coating agent, adhesive agent, or the like, for use in conjunction with electrical devices or electronic elements. 
     EXAMPLES 
     The curable silicone composition of the invention will be further described in more detail with reference to practical and comparative examples. All values of viscosities used in the examples correspond to 25° C. Mass-average molecular weights are values obtained by using toluene as a solvent and were measured by gel-permeation chromatography and calculated with reference to polystyrene. 
     [Viscosity] 
     This characteristic was measured by means of an E-type viscometer (Digital Viscometer DV-U-E II-type, the product of Tokimec Company, Ltd.) at 25° C. with rotation speed of 2.5 rpm. 
     [Adhesive Properties] 
     A 50-μm-thick layer of a curable silicone composition on an alumina panel was pasted to a silicone tube having a square cross-section of 10 mm by 10 mm, and then a test piece was produced by curing the aforementioned curable silicone composition as a result of heating for 1 hour at 150° C. The obtained test piece was tested on a bond tester (Model SS-100KP, the product of Seishin Trading Company, Ltd.) by measuring resistance to peeling (kgf/cm 2 ) at 25° C. and a peeling speed of 50 mm/min. 
     [Complex Modulus of Elasticity] 
     After deaeration, a curable silicone composition was loaded into a mold cavity having a width of 10 mm, length of 50 mm, and depth of 2 mm and was subjected to pressure-curing for 60 minutes at 150° C. under pressure of 2.5 MPa and then to secondary heating in an oven for 2 hours at 180° C., whereby a test specimen of a cured body of the composition was obtained. Complex modulus of elasticity of this test specimen was measured by means of an ARES viscoelasticity analyzer of Rheometric Scientific, Inc. Measurements were carried out at 25° C. using a strain of 0.05% and a vibration frequency of 1 Hz. 
     [Oil Bleeding Property (1)] 
     A curable silicone composition in the amount of 0.2 g was dropped onto the surface of a ground-glass plate, and after retention for 48 hours at 25° C., the bleed characteristic was evaluated by means of the following formula: 100×(L 1 −L 0 )/L 0 , where L 0  is the diameter of the curable silicone rubber, and L 1  is the diameter formed by the bleeding oil. 
     [Oil Bleeding Property (2)] 
     A curable silicone composition in the amount of 0.2 g was dropped onto the surface of a ground-glass plate, and a cured body was obtained by curing the composition for 1 hour at 150° C. The bleed characteristic at curing was evaluated by means of the following formula: 100×(L 1 −L 0′ )/L 0′ , where L 0′  is the diameter of the cured body, and L 1  is the diameter formed by the bleeding oil. 
     Practical Examples 1 to 3, and Comparative Example 1 
     Curable silicone compositions were prepared for the purpose of evaluation by mixing 9.5 parts by mass of a dimethylpolysiloxane of the following average formula:
 
X—CH 2 CH 2 (CH 3 ) 2 SiO[(CH 3 ) 2 SiO] 162 Si(CH 3 ) 2 CH 2 CH 2 —X
 
{where “X” is an organopolysiloxane residual radical of the following average unit formula:
 
[Y(CH 3 ) 2 SiO 1/2 ] 1.6 (SiO 4/2 ) 1.0  
 
(where “Y” consists of a single bond, a trimethoxysilylpropyl group, and a 3-glycidoxypropyl group; at least one “Y” is one molecule is a single bond, and the remaining part of “Y” consists of trimethoxysilylpropyl and 3-glycidoxypropyl groups used in a (1:4) mole ratio)} (mass-average molecular weight=51,000; viscosity=12,000 mPa·s); 8.50 parts by mass of a diorganopolysiloxane represented by the following formula:
 
                         
0.4 parts by mass of an octadecyl trimethoxysilane; 61.84 parts by mass of spherical alumina particles having an average particle size of 8.6 μm; 16.86 parts by mass of irregular-shaped alumina particles having an average particle size of 3 μm; 2.00 parts by mass of an epoxy resin represented by the following formula:
 
                         
and 0.9 parts by mass of a mixture of a bisphenol-A-type epoxy resin and a bisphenol-F-type epoxy resin comprising a 33 mass % encapsulated amine-type catalyst (HX-3922HP, the product of Asahi Kasei Company, Ltd.).
 
     Curable silicone compositions of three types were prepared by mixing 5 parts by mass of the obtained curable silicone compositions respectively with 0.05 part by mass (Practical Example 1), 0.1 part by mass (Practical Example 2), and 0.3 part by mass (Practical Example 3) of a methylhexahydrophthalic anhydride (the product of Asahi Kasei Co., Ltd. known as HN-5500). Characteristics of the aforementioned curable silicone compositions, as well as characteristics of the curable silicone composition (Comparative Example 1) that did not contain methylhexahydrophthalic anhydride and was used for evaluation purposes are given in Table 1. 
     
       
         
           
               
               
             
               
                   
                 TABLE 1 
               
             
            
               
                   
                   
               
               
                   
                 Example 
               
            
           
           
               
               
               
            
               
                   
                 Practical 
                   
               
               
                   
                 Examples 
                 Comp. Ex. 
               
            
           
           
               
               
               
               
               
            
               
                 Characteristics 
                 1 
                 2 
                 3 
                 1 
               
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 Viscosity (Pa · s) 
                 160 
                 150 
                 120 
                 200 
               
               
                 Adhesive property (kgf/cm 2 ) 
                 11 
                 16.9 
                 34.2 
                 8.7 
               
               
                 Complex modulus of elasticity (MPa) 
                 145 
                 130 
                 95 
                 165 
               
               
                   
               
            
           
         
       
     
     Practical Example 4 
     A curable silicone composition was prepared by mixing 2.01 parts by mass of an organopolysiloxane of the following average unit formula: 
                         
(mass average molecular weight=1,000; viscosity=1,290 mPa·s; epoxy equivalent=276); 6.69 parts by mass of a dimethylpolysiloxane of the following average formula:
 
X—CH 2 CH 2 (CH 3 ) 2 SiO[(CH 3 ) 2 SiO] 162 Si(CH 3 ) 2 CH 2 CH 2 —X
 
{where “X” is an organopolysiloxane residual radical of the following average unit formula:
 
[Y(CH 3 ) 2 SiO 1/2 ] 1.6 (SiO 4/2 ) 1.0  
 
(where “Y” consists of a single bond, a trimethoxysilylpropyl group, and a 3-glycidoxypropyl group; at least one “Y” is one molecule is a single bond, and the remaining part of “Y” consists of trimethoxysilylpropyl and 3-glycidoxypropyl groups used in a (1:4) mole ratio)} (viscosity=12,000 mPa·s); 7.8 parts by mass of an organotrisiloxane of the following formula:
 
                         
(viscosity=2,600 mPa·s; phenolic hydroxyl group equivalent=330); 62.86 parts by mass of spherical alumina particles having an average particle size of 8.6 μm; 17.14 parts by mass of irregular-shaped alumina particles having an average particle size of 3 μm; 1.00 part by mass of an epoxy resin represented by the following formula:
 
                         
1.50 parts by mass of a mixture of a bisphenol-A-type epoxy resin and a bisphenol-F-type epoxy resin comprising a 35 mass % encapsulated amine-type catalyst (HX-3941HP, the product of Asahi Kasei Company, Ltd.); and 1.00 part by mass of a methylhexahydrophthalic anhydride (the product of Asahi Kasei Co., Ltd. known as HN-5500). Characteristics of the compositions are shown in Table 2.
 
     Comparative Example 2 
     A curable silicone composition was prepared by mixing 1.85 parts by mass of an organopolysiloxane of the following average unit formula: 
                         
(mass average molecular weight=1,000; viscosity=1,290 mPa·s; epoxy equivalent=276); 6.15 parts by mass of a dimethylpolysiloxane of the following average formula:
 
X—CH 2 CH 2 (CH 3 ) 2 SiO[(CH 3 ) 2 SiO] 162 Si(CH 3 ) 2 CH 2 CH 2 —X
 
{where “X” is an organopolysiloxane residual radical of the following average unit formula:
 
[Y(CH 3 ) 2 SiO 1/2 ] 1.6 (SiO 4/2 ) 1.0  
 
(where “Y” consists of a single bond, a trimethoxysilylpropyl group, and a 3-glycidoxypropyl group; at least one “Y” is one molecule is a single bond, and the remaining part of “Y” consists of trimethoxysilylpropyl and 3-glycidoxypropyl groups used in a (1:4) mole ratio)} (viscosity=12,000 mPa·s); 9.5 parts by mass of an organotrisiloxane of the following formula:
 
                         
(viscosity=2,600 mPa·s; phenolic hydroxyl group equivalent=330); 62.86 parts by mass of spherical alumina particles having an average particle size of 8.6 μm; 17.14 parts by mass of irregular-shaped alumina particles having an average particle size of 3 μm; and 1.00 part by mass of an epoxy resin represented by the following formula:
 
                         
1.50 parts by mass of a mixture of a bisphenol-A-type epoxy resin and a bisphenol-F-type epoxy resin comprising a 35 mass % encapsulated amine-type catalyst (HX-3941 HP, the product of Asahi Kasei Company, Ltd.). Characteristics of the compositions are shown in Table 2.
 
     
       
         
           
               
               
             
               
                   
                 TABLE 2 
               
             
            
               
                   
                   
               
               
                   
                 Example 
               
            
           
           
               
               
               
            
               
                   
                   
                 Comparative 
               
               
                 Characteristics 
                 Practical Example 4 
                 Example 2 
               
               
                   
               
            
           
           
               
               
               
            
               
                 Viscosity (Pa · s) 
                 120 
                 150 
               
               
                 Adhesive property (kgf/cm 2 ) 
                 3.6 
                 77 
               
               
                 Oil bleeding (1) 
                 1.5 
                 20 
               
               
                 Oil bleeding (2) 
                 1.7 
                 8.1 
               
               
                 Complex modulus of elasticity (MPa) 
                 72 
                 810 
               
               
                   
               
            
           
         
       
     
     INDUSTRIAL APPLICABILITY 
     Since the curable silicone composition of the invention is characterized by excellent handleability, it is suitable for transfer molding, injection molding, potting, casting, powder application, application by immersion, drop-wise application, etc. Furthermore, since after curing, the composition forms a cured body that is characterized by excellent flexibility and adhesion, the composition is suitable for use as a sealing agent, casting agent, coating agent, adhesive agent, etc., in conjunction with parts of electrical and electronic devices. In particular, when the composition contains a thermally conductive filler, the composition can be used as heat-radiating materials and heat-radiating interface elements (TIM).