Thixotropic silicone gel composition for spot potting, its cured product, and photocoupler

Abstract

Provided is a silicone gel composition which contains, as a base polymer, a silicon-bonded alkenyl group-containing straight-chain or branched-chain organopolysiloxane containing a specific amount of a diphenylsiloxane unit in the molecule, and contains a specific blending amount of a cross-linking agent having a specific molecular structure, a platinum-based curing catalyst, a hydrophobized fine silica powder, and an isocyanuric acid derivative having a specific molecular structure having at least two trialkoxysilyl-substituted alkyl groups in the molecule, wherein the curing of the silicone gel composition gives a silicone gel cured product having a penetration of 10-100 as specified in JIS K6249. Since the silicone gel composition exhibits little spread when applied to substrates of various electronic boards such as control circuit boards, little change in shape before and after thermal curing, and little change in the penetration of the cured product under high temperature conditions, a specific semiconductor element such as a photocoupler mounted on a control board can be exclusively coated (so-called spot potting) and the element and the like can be sealed in a desired shape. Thus, the silicone gel composition is useful as a silicone gel composition for sealing a photocoupler and the like.

Description

[Technical Field]

[0001] The present invention relates to a thixotropic silicone gel composition for spot potting (particularly for spot potting used to seal photocouplers) that spreads little when applied to a substrate and that undergoes little change in shape before and after heat curing, and little change in the penetration of the cured product under high temperature conditions; a cured product (silicone gel) made from the composition; and a photocoupler sealed with the cured product. [Background technology]

[0002] Silicone gel has excellent properties such as electrical insulation, stable electrical characteristics, and flexibility, and is used as a coating material for potting and sealing electrical and electronic components, covering control circuit elements such as ICs and capacitors, and protecting them from thermal and mechanical damage.

[0003] Silicone gel compositions used for such purposes are intended to be injected (potted) into a case, and therefore often have high fluidity, making them unsuitable for spot potting, which covers only specific semiconductor elements mounted on a control circuit board.

[0004] Meanwhile, silicone gel compositions having thixotropy that allow for spot potting have been investigated. Patent Document 1 (Japanese Patent No. 3073888) proposes an addition-curing silicone gel composition containing an organopolysiloxane having 3,3,3-trifluoropropyl groups in the molecular side chains and hydrophobic silica, while Patent Document 2 (Japanese Patent Laid-Open No. 9-132718) proposes an addition-curing silicone gel composition containing an organopolysiloxane having alkenyl groups and a silica gel having a specific surface area of ​​50 to 500 m. 2 A two-component curable silicone composition containing an inorganic filler having a viscosity of 1 / g has been proposed.

[0005] However, even with these thixotropic silicone compositions, although the composition retains its shape immediately after application, it spreads during the heat-curing process, resulting in the problem that the cured product is applied to areas other than the intended specific sealing area (near the specific semiconductor element) on the control circuit board.

[0006] Patent Document 3 (Japanese Patent No. 3746394) proposes an addition-curing silicone gel composition containing a branched organopolysiloxane having alkenyl groups, silica powder, and an epoxy compound and / or a polyhydric alcohol. This composition exemplifies a low-viscosity silicone gel composition with a viscosity of 10 Pa·s or less, which exhibits insufficient shape retention during the heat-curing process, and when a polyhydric alcohol is used, there is a risk of changes in properties over time (poor curing). [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent No. 3073888 [Patent Document 2] Japanese Patent Application Publication No. 9-132718 [Patent Document 3] Patent No. 3746394 Summary of the Invention [Problem to be solved by the invention]

[0008] The present invention has been made in view of the above circumstances, and has as its object the provision of a thixotropic silicone gel composition for spot potting, which spreads little when applied to a substrate such as a control circuit board, changes little in shape before and after heat curing, and changes little in the penetration of the cured product under high temperature conditions, and which can be used to cover only specific semiconductor elements such as photocouplers mounted on a control circuit board by potting, as well as a cured product thereof, and a photocoupler sealed with the cured product. [Means for solving the problem]

[0009] As a result of extensive research into achieving the above object, the present inventors have discovered that the diphenylsiloxane unit ((C6H5)2SiO 2 / 2 The present inventors have discovered that the above-mentioned problems can be solved by a silicone gel composition which uses a silicon-bonded alkenyl-containing linear or branched organopolysiloxane as a base polymer, the organopolysiloxane containing a specific amount of (III)-( ...

[0010] That is, the present invention provides the following thixotropic silicone gel composition for spot potting, a cured product thereof (silicone gel), and a photocoupler. [1] (A) (C6H5)2SiO as a diorganosiloxane unit in the main chain 2 / 2 100 parts by mass of a linear or branched organopolysiloxane having 0.1 to 10 mol% of diorganosiloxane units in the main chain and 0.001 to 10 mol / 100 g of alkenyl groups bonded to silicon atoms, (B) The following average composition formula (1) [ka] (In the formula, R 1 are the same or different monovalent hydrocarbon groups having 1 to 10 carbon atoms and containing no aliphatic unsaturated bonds, a is 0 or 1, b is a positive number from 0.002 to 0.3, and c is a positive number from 0.1 to 0.6. and containing at least three silicon-bonded hydrogen atoms per molecule: an organohydrogenpolysiloxane in which the amount of silicon-bonded hydrogen atoms in component (B) is 0.01 to 3 moles per mole of alkenyl groups in component (A), (C) a platinum-based curing catalyst: a catalytically effective amount; (D) Both The surface is hydrophobized with organosilazane, organochlorosilane, organoalkoxysilane, or organopolysiloxane, which has only methyl groups as monovalent hydrocarbon groups bonded to silicon atoms, and the specific surface area (BET adsorption method) is 50 to 500 m 2 / g: 2 to 30 parts by mass of finely powdered silica, and (E) an isocyanuric acid derivative having, among the three nitrogen atoms forming an isocyanuric acid skeleton, one trialkoxysilyl-substituted alkyl group on each of two nitrogen atoms (two in total in the molecule) and one alkyl group substituted with an alkenyl group or a silicon-bonded hydrogen atom (SiH group)-containing silyl group or siloxanyl group on the remaining nitrogen atom, and / or an isocyanuric acid derivative having one trialkoxysilyl-substituted alkyl group on each of the three nitrogen atoms forming an isocyanuric acid skeleton (three in total in the molecule): 0.01 to 3 parts by mass It contains (However, the organohydrogenpolysiloxane of the crosslinking agent consists solely of the above average composition formula (1).) , hardened TeJ A thixotropic silicone gel composition for spot potting that gives a cured silicone gel having a penetration of 10 to 100 as specified in IS K6249. [2] The silicone gel composition for spot potting according to [1], wherein component (E) is at least one selected from isocyanuric acid derivatives represented by any one of the following formulas (2) to (7): [ka] [ka] [ka] [ka] [ka] [ka] (In the above formulas, Me represents a methyl group, and Et represents an ethyl group.) [3] The thixotropic silicone gel composition for spot potting according to [1] or [2] has an apparent viscosity (25°C) measured at a rotation speed ratio of 1:10 using a method in accordance with JIS K7117, and an SVI value calculated using the following formula of 3.0 to 10.0: SVI value = (apparent viscosity at lower RPM) / (apparent viscosity at higher RPM) [4] The thixotropic silicone gel composition for spot potting according to any one of [1] to [3], wherein Dd is 3 mm or less, where d mm is the diameter of the droplet formed by the composition after 1 g of the uncured composition is dropped onto a glass plate and left to stand for 30 minutes in an atmosphere of 25°C, and D mm is the diameter of a cured product of the composition formed on the glass plate after 1 g of the uncured composition is dropped onto the glass plate and left to stand for 30 minutes in an atmosphere of 130°C. [5] The thixotropic silicone gel composition for spot potting according to any one of [1] to [4], wherein the penetration of a cured silicone gel obtained by curing an uncured composition, after being left in an atmosphere at 200°C for 72 hours, decreases by 20% or less compared to the penetration immediately after curing. [6] The thixotropic silicone gel composition for spot potting according to [1], which upon curing gives a cured silicone gel product having a penetration of 20 to 100 as specified in JIS K6249. [7] The thixotropic silicone gel composition for spot potting according to [1], wherein the crosslinking agent of component (B) consists solely of an organohydrogenpolysiloxane represented by the following average molecular formula (1'): [ka] (In the formula, R 1 a is the same as in the above average composition formula (1), c' is an integer of 1 to 300, d' is an integer of 4 to 700, and c'+d' is an integer of 5 to 998, provided that there are three or more SiH groups in one molecule. [8] [1]~[ 7 10. A cured silicone gel product obtained by curing the thixotropic silicone gel composition for spot potting according to any one of claims 1 to 9. [9] [ 810. A photocoupler sealed with the silicone gel cured product according to claim 9. [Effects of the Invention]

[0011] The thixotropic silicone gel composition for spot potting of the present invention spreads little when applied to substrates such as various electronic substrates, including control circuit boards, and there is little change in shape before and after heat curing, and little change in the penetration of the cured product under high temperature conditions (change in flexibility or change in stress relaxation properties).As a result, it is possible to cover by potting (so-called spot potting) only specific semiconductor elements, such as photocouplers, mounted on control circuit boards, and furthermore, to seal the elements in the desired shape, making it useful as a silicone gel composition for sealing photocouplers and the like. DETAILED DESCRIPTION OF THE INVENTION

[0012] The thixotropic silicone gel composition for spot potting of the present invention comprises the following components (A) to (E) as essential ingredients. In the present invention, a silicone gel cured product (sometimes simply referred to as "silicone gel") refers to a cured product with a low crosslink density that is primarily composed of organopolysiloxane and has a penetration (also referred to as cone penetration) of 10 to 100 as specified in JIS K6249 using the JIS K2220 consistency test method (1 / 4 cone). This corresponds to a product with such low hardness (i.e., softness) and low elasticity that it does not exhibit a valid rubber hardness value, resulting in a measured value (rubber hardness value) of 0 when measured according to JIS K6301. In this respect, it is distinct from so-called silicone rubber cured products (rubber-like elastomers). The present invention will be described in detail below.

[0013] [Component (A)] The organopolysiloxane of component (A) is the main component (base polymer) of the thixotropic silicone gel composition for spot potting of the present invention, and contains bifunctional diorganosiloxane units (RSiO 2 / 2where R is an unsubstituted or substituted monovalent hydrocarbon group), 2 / 2 The main chain of the diorganosiloxane copolymer contains 0.1 to 10 mol % of trifunctional organosilsesquioxane units (RSiO) as branch points in the repeating structure of the linear or branched difunctional diorganosiloxane units that constitute the main chain, and has a silicon-bonded alkenyl group (hereinafter sometimes referred to as a "silicon-bonded alkenyl group") in one molecule. 3 / 2 and R is an unsubstituted or substituted monovalent hydrocarbon group) (i.e., a linear or branched alkenyl group-containing organopolysiloxane that essentially has a specific amount of diphenylsiloxane units in the molecule). In the present invention, the linear organopolysiloxane refers to a polysiloxane having a difunctional diorganosiloxane unit (D unit) constituting the main chain and a monofunctional triorganosiloxy unit (RSiO 1 / 2 and R is an unsubstituted or substituted monovalent hydrocarbon group), and the branched organopolysiloxane refers to an organopolysiloxane that is composed of trifunctional organosilsesquioxane units (T units) that constitute the branch points, difunctional diorganosiloxane units (D units) that constitute the main chain, and monofunctional triorganosiloxy units (M units) that constitute the molecular chain terminals, and has branches within the molecule, and may also have a cyclic structure within the molecule. Examples of R herein include a phenyl group, an alkenyl group as described below, and a "silicon atom-bonded organic group" as described below.

[0014] The alkenyl group preferably has 2 to 10 carbon atoms, and specific examples include vinyl, allyl, propenyl, isopropenyl, butenyl, isobutenyl, pentenyl, hexenyl, cyclohexenyl, and heptenyl groups, with vinyl being particularly preferred. The bonding position of this silicon-bonded alkenyl group in the organopolysiloxane molecule may be at the molecular chain terminal, a non-terminal position (i.e., a molecular chain side chain), or both. The amount of silicon-bonded alkenyl groups in component (A) is preferably 0.001 to 10 mol / 100g, more preferably 0.002 to 1 mol / 100g, particularly preferably 0.003 to 0.1 mol / 100g, and even more preferably 0.004 to 0.05 mol / 100g.

[0015] In the organopolysiloxane of component (A), the silicon-bonded organic groups other than the silicon-bonded alkenyl groups and the phenyl groups constituting the diphenylsiloxane units (hereinafter also referred to as "silicon-bonded organic groups") are not particularly limited as long as they do not contain aliphatic unsaturated bonds, and examples thereof include unsubstituted or substituted monovalent hydrocarbon groups excluding aliphatic unsaturated bonds, typically having 1 to 12 carbon atoms, preferably 1 to 10. Examples of such unsubstituted or substituted monovalent hydrocarbon groups include alkyl groups such as methyl, ethyl, propyl, butyl, pentyl, hexyl, and heptyl; cycloalkyl groups such as cyclohexyl; aryl groups (excluding phenyl) such as tolyl, xylyl, and naphthyl; aralkyl groups such as benzyl and phenethyl; and halogenated alkyl groups in which some or all of the hydrogen atoms of these groups have been substituted with halogen atoms such as chlorine, fluorine, or bromine, such as chloromethyl, 3-chloropropyl, and 3,3,3-trifluoropropyl. In view of ease of synthesis, alkyl groups, aryl groups and halogenated alkyl groups are preferred, methyl groups and trifluoropropyl groups are more preferred, and methyl groups are particularly preferred.

[0016] The organopolysiloxane of component (A) is a polymer having a molecular chain main chain consisting of repeating difunctional diorganosiloxane units, and the total diorganopolysiloxane units are (C6H5)2SiO 2 / 2 The (C6H5)2SiO unit is contained in an amount of usually 0.1 to 10 mol %, preferably 0.5 to 8 mol %, and particularly preferably 1 to 6 mol %. 2 / 2 If the content of the unit exceeds the upper limit of the above range, the viscosity of the resulting composition will be significantly increased, resulting in a decrease in coating workability.

[0017] The viscosity of component (A) at 25°C is preferably 100 to 100,000 mPa·s, and particularly preferably 300 to 10,000 mPa·s, as this improves the workability of the composition and the mechanical properties of the cured product (silicone gel cured product). In the present invention, viscosity can be measured using a rotational viscometer (e.g., BL type, BH type, BS type, cone-plate type, rheometer, etc.) (the same applies hereinafter). For the same reasons, the number of silicon atoms (or degree of polymerization) in component (A) is generally 30 to 1,200, preferably 50 to 1,000, and more preferably 80 to 800. In the present invention, the degree of polymerization (or molecular weight) can be determined, for example, as the polystyrene-equivalent number-average degree of polymerization (or number-average molecular weight) by gel permeation chromatography (GPC) analysis using toluene or the like as a developing solvent (the same applies hereinafter).

[0018] Specific examples of such component (A) include the following: Dimethylsiloxane-diphenylsiloxane copolymer both ends capped with dimethylvinylsiloxy groups, Dimethylsiloxane-methylvinylsiloxane-diphenylsiloxane copolymer both ends capped with dimethylvinylsiloxy groups, Dimethylsiloxane-vinylmethylsiloxane-diphenylsiloxane copolymer both ends capped with trimethylsiloxy groups, Dimethylsiloxane-diphenylsiloxane copolymer with one end capped with trimethylsiloxy groups and one end capped with dimethylvinylsiloxy groups, Dimethylsiloxane-diphenylsiloxane copolymer with one end capped with trimethylsiloxy groups and one end capped with dimethylvinylsiloxy groups, Dimethylsiloxane-diphenylsiloxane-methylvinylsiloxane copolymer with both ends capped with methyldivinylsiloxy groups, Dimethylsiloxane-diphenylsiloxane copolymer with both ends capped with methyl Examples of suitable organosilsesquioxanes include diorganopolysiloxanes end-blocked at both molecular chain ends with triorganosiloxy groups, such as a methyldivinylsiloxy-blocked dimethylsiloxane-methylvinylsiloxane-diphenylsiloxane copolymer, a dimethylsiloxane-diphenylsiloxane copolymer end-blocked at both ends with trivinylsiloxy groups, and a dimethylsiloxane-methylvinylsiloxane-diphenylsiloxane copolymer end-blocked at both ends with trivinylsiloxy groups, as well as branched (straight-chain with some branching) organopolysiloxanes in which 1 to 5, preferably 1 to 3, and more preferably 1 or 2 of the bifunctional diorganosiloxane units that make up the main chain of these linear diorganopolysiloxanes have been substituted with a branched structure (trifunctional organosilsesquioxane unit).

[0019] The organopolysiloxane of component (A) may be used alone or in combination with two or more different compounds, so long as the component (A) as a whole satisfies the requirement that it has an average of at least 0.5 silicon-bonded alkenyl groups per molecule.

[0020] [(B) Component] The organohydrogenpolysiloxane of component (B) used in the present invention is a component that acts as a crosslinking agent (curing agent) in the hydrosilylation addition curing reaction with component (A). Component (B) is represented by the following average composition formula (1), and is a linear organohydrogenpolysiloxane (more specifically, an organohydrogensiloxane-diorganosiloxane copolymer capped at both molecular chain terminals with triorganosiloxy groups or an organohydrogensiloxane-diorganosiloxane copolymer capped at both molecular chain terminals with diorganohydrogensiloxy groups) containing at least 3, preferably 4 to 300, and more preferably 5 to 100, silicon-bonded hydrogen atoms (hereinafter also referred to as "silicon-bonded hydrogen atoms" (i.e., SiH groups)) per molecule. While the component (B) must have silicon-bonded hydrogen atoms (SiH groups) at non-terminal locations (in the middle of the molecular chain) within the molecule, it may also have silicon-bonded hydrogen atoms (SiH groups) at the molecular chain terminals. [ka] (In the formula, R 1 are the same or different monovalent hydrocarbon groups having 1 to 10 carbon atoms and containing no aliphatic unsaturated bonds, a is 0 or 1, b is a positive number from 0.002 to 0.3, and c is a positive number from 0.1 to 0.6.

[0021] In the above average composition formula (1), R 1are the same or different monovalent hydrocarbon groups containing no aliphatic unsaturated bonds, and are preferably unsubstituted or substituted monovalent hydrocarbon groups containing no aliphatic unsaturated bonds, having usually 1 to 10 carbon atoms, and preferably 1 to 6 carbon atoms. Examples include alkyl groups such as methyl, ethyl, propyl, butyl, pentyl, hexyl, and heptyl; cycloalkyl groups such as cyclohexyl; aryl groups such as phenyl, tolyl, xylyl, and naphthyl; aralkyl groups such as benzyl and phenethyl; and halogenated alkyl groups in which some or all of the hydrogen atoms in these groups have been substituted with halogen atoms such as chlorine, fluorine, and bromine atoms, such as chloromethyl, 3-chloropropyl, and 3,3,3-trifluoropropyl. Preferred are alkyl groups and aryl groups, and more preferably methyl and phenyl groups.

[0022] In the above formula (1), a is 0 or 1. Furthermore, b is 0.002 to 0.3, preferably 0.006 to 0.2, and more preferably 0.013 to 0.1, and c is a positive number of 0.1 to 0.6, and preferably 0.1 to 0.4. If b is less than 0.002, a cured silicone gel product with the desired penetration cannot be obtained. On the other hand, if b exceeds 0.3, not only is it difficult to obtain a cured silicone gel product with a low elastic modulus and low stress, but density variations will occur on the surface of the cured product, reducing the displacement durability of the cured product.

[0023] From the average composition formula (1) above, the molecular structure of component (B) is either an organohydrogensiloxane-diorganosiloxane copolymer endblocked at both molecular chain terminals with triorganosiloxy groups or an organohydrogensiloxane-diorganosiloxane copolymer endblocked at both molecular chain terminals with diorganohydrogensiloxy groups, and can be represented by the following average molecular formula (1'): [ka] (In the formula, R 1a is the same as in the above average composition formula (1), c' is an integer of 1 to 300, preferably an integer of 2 to 50, and more preferably an integer of 3 to 30, d' is an integer of 4 to 700, preferably an integer of 6 to 280, and more preferably an integer of 15 to 120, and c'+d' is an integer of 5 to 998, preferably an integer of 8 to 328, and more preferably an integer of 18 to 148, provided that there are three or more SiH groups in one molecule. The component (B) is synthesized by a conventionally known method.

[0024] The viscosity of the organohydrogenpolysiloxane of component (B) at 25°C is preferably 0.1 to 5,000 mPa·s, more preferably 0.5 to 1,000 mPa·s, and particularly preferably 2 to 500 mPa·s, so that the composition is liquid at room temperature (25°C), as this improves the workability of the composition and the optical or mechanical properties of the cured product. When this viscosity is satisfied, the number of silicon atoms (or degree of polymerization) per molecule of the organohydrogenpolysiloxane is typically 7 to 1,000, preferably 10 to 330, and more preferably about 20 to 150. Furthermore, the content of hydrogen atoms bonded to silicon atoms (SiH groups) in component (B) is preferably 0.0005 to 0.008 mol / g, and particularly preferably 0.001 to 0.006 mol / g.

[0025] Specific examples of the linear organohydrogenpolysiloxane of component (B) include those represented by the average composition formula below. [ka] (In each formula, Me represents a methyl group, and b and c are the same as above, with the proviso that each molecule contains three or more SiH groups.)

[0026] Specific examples of the linear organohydrogenpolysiloxane of component (B) include those represented by the average molecular formula shown below. [ka] (In the formula, Me represents a methyl group, c' and d' are the same as above, c" represents an integer of 3 to 300, preferably an integer of 3 to 50, and more preferably an integer of 3 to 30, and c"+d' represents an integer of 7 to 998, preferably an integer of 9 to 328, and more preferably an integer of 18 to 148.)

[0027] The organohydrogenpolysiloxane of component (B) may use either a single compound, or a combination of two or more different compounds.

[0028] The amount of component (B) added is such that the number of silicon-bonded hydrogen atoms (SiH groups) in component (B) is 0.01 to 3 moles, preferably 0.05 to 2 moles, more preferably 0.1 to 1.8 moles, even more preferably 0.2 to 1.5 moles, and especially preferably 0.3 to 1.2 moles per mole of silicon-bonded alkenyl groups in component (A). If the number of silicon-bonded hydrogen atoms in component (B) is less than 0.01 mole per mole of silicon-bonded alkenyl groups in component (A), a silicone gel cured product with the desired penetration will not be obtained. If the number of silicon-bonded hydrogen atoms in component (B) is more than 3 moles, the cured product will no longer exhibit a gel state or will have reduced heat resistance.

[0029] [(C) component] Component (C) used in the present invention is used as a catalyst to promote the hydrosilylation addition reaction between silicon-bonded alkenyl groups in component (A) and silicon-bonded hydrogen atoms (SiH groups) in component (B). Component (C) is a platinum-based curing catalyst (platinum or a platinum-based compound), and known catalysts can be used. Specific examples include platinum-based catalysts such as platinum black, chloroplatinic acid, alcohol-modified chloroplatinic acid, and complexes of chloroplatinic acid with olefins, aldehydes, vinylsiloxanes, or acetylene alcohols.

[0030] The amount of component (C) blended should be an effective amount as a catalyst, and can be increased or decreased as needed depending on the desired curing rate. However, it is usually in the range of 0.1 to 1,000 ppm, preferably 1 to 300 ppm, in terms of platinum atom mass, relative to the total amount of components (A) and (B). If this blending amount is too high, the heat resistance of the resulting cured product may decrease. If the blending amount is too low, the hydrosilylation addition reaction may not proceed sufficiently under the specified curing conditions, and a gel-like cured product may not be obtained.

[0031] [(D) component] The component (D) used in the present invention is an organosilazane, organochlorosilane, organoalkoxysilane, or organopolysiloxane having only methyl groups as monovalent hydrocarbon groups bonded to silicon atoms, and having a specific surface area (BET adsorption method) of 50 to 500 m. 2 / g, which, when used in combination with component (E) described later, imparts thixotropy to the composition before curing and reduces spreading during application. This finely powdered silica interacts with component (E) described later to impart sufficient thixotropy to the composition of the present invention, and for this purpose, a concentration of 50 to 500 m 2 / g, preferably 50 to 400m 2 / g (BET method), and its surface must be hydrophobized with an organosilazane, organochlorosilane, organoalkoxysilane, or organopolysiloxane having only methyl groups as organic substituents (monovalent hydrocarbon groups) bonded to silicon atoms.

[0032] Specific examples of the surface treatment agent include hexamethyldisilazane; trimethylchlorosilane, dimethyldichlorosilane, methyltrichlorosilane; trimethylalkoxysilane, dimethyldialkoxysilane, methyltrialkoxysilane (here, examples of the alkoxy group include methoxy, ethoxy, propoxy, and butoxy groups); and cyclic or linear polydimethylsiloxane, which may be used alone or in combination of two or more. The dimethylpolysiloxane may be cyclic or linear.

[0033] Examples of finely powdered silica include fumed silica (dry silica), crushed silica, fused silica, crystalline silica (fine quartz powder), precipitated silica (wet silica), and colloidal silica, and fumed silica is preferred in terms of the desired specific surface area (or average particle size).

[0034] The specific surface area (BET adsorption method) of the hydrophobized fine silica powder is 50 to 500 m 2 / g, preferably 50 to 400m 2 / g. The specific surface area is 50m 2 If the viscosity is less than 500m / g, it is difficult to impart sufficient thixotropy to the composition. 2 If it exceeds 1 / g, the viscosity of the composition becomes too high, resulting in a significant decrease in coating workability.

[0035] As such finely powdered silica having a hydrophobic surface, commercially available products can be used, such as DM-30S (manufactured by Tokuyama Corporation), NSX-200 (manufactured by Nippon Aerosil Co., Ltd.), and CAB-O-SIL TS-610 (manufactured by Cabot Corporation, USA).

[0036] The amount of component (D) blended is in the range of 2 to 30 parts by mass, preferably 3 to 20 parts by mass, and more preferably 5 to 15 parts by mass per 100 parts by mass of component (A). If the amount of component (D) blended is too small, sufficient thixotropy cannot be imparted to the composition, making it difficult to control spreadability during application, while if the amount blended is too large, the viscosity of the composition will increase significantly, reducing application workability.

[0037] [(E) component] The component (E) used in the present invention is an isocyanuric acid derivative with a specific molecular structure having at least two trialkoxysilyl-substituted alkyl groups in the molecule, selected from isocyanuric acid derivatives having, on two of the three nitrogen atoms that form the isocyanuric acid skeleton, one trialkoxysilyl-substituted alkyl group on each of the nitrogen atoms (a total of two in the molecule) and one alkyl group substituted with an alkenyl group, or a silicon-bonded hydrogen atom (SiH group)-containing silyl group or siloxanyl group on the remaining nitrogen atom, and / or isocyanuric acid derivatives having one trialkoxysilyl-substituted alkyl group on each of the three nitrogen atoms that form the isocyanuric acid skeleton (a total of three in the molecule). This component, together with the component (D), imparts thixotropy to the composition of the present invention and reduces spreadability upon application without impairing the fluidity of the composition.

[0038] More specifically, the component (E) is (i) an isocyanuric acid derivative having one trialkoxysilyl-substituted alkyl group, such as a trimethoxysilylpropyl group or a triethoxysilylpropyl group, on each of three nitrogen atoms forming an isocyanuric acid skeleton (a total of three in the molecule), as represented by the following formulas (2) and (5); (ii) isocyanuric acid derivatives represented by the following formulas (3) and (6), in which, of the three nitrogen atoms forming an isocyanuric acid skeleton, two nitrogen atoms each have one trialkoxysilyl-substituted alkyl group such as a trimethoxysilylpropyl group or a triethoxysilylpropyl group (total of two in the molecule), and the remaining nitrogen atom has one alkenyl group such as an allyl group; Examples include (iii) isocyanuric acid derivatives represented by the following formulas (4) and (7), in which, of the three nitrogen atoms forming the isocyanuric acid skeleton, two nitrogen atoms each have one trialkoxysilyl-substituted alkyl group such as a trimethoxysilylpropyl group or a triethoxysilylpropyl group (total of two in the molecule), and the remaining nitrogen atom has one alkyl group substituted with a silicon-bonded hydrogen atom (SiH group)-containing silyl group or siloxanyl group, such as a [dimethyl(hydrogen)siloxy]dimethylsilylpropyl group.

[0039] Here, examples of the alkyl group of the trialkoxysilyl group-substituted alkyl group or the alkyl group substituted with a silyl group or siloxanyl group containing a hydrogen atom bonded to a silicon atom (SiH group) include C2-C10 groups such as ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, pentyl, neopentyl, hexyl, and octyl, and among these, propyl is preferred. Examples of the alkoxy group in the trialkoxysilyl-substituted alkyl group include methoxy, ethoxy, propoxy, and butoxy groups having 1 to 10 carbon atoms, with methoxy and ethoxy being preferred.

[0040] As the component (E), it is preferable to use an isocyanuric acid derivative represented by the following formulas (2) to (7): The isocyanuric acid derivative of the component (E) may be used alone or in combination of two or more.

[0041] [ka] [ka] [ka] [ka] [ka] [ka] (In the above formulas, Me represents a methyl group, and Et represents an ethyl group.)

[0042] The blend amount of component (E) is preferably 0.01 to 3 parts by mass, and particularly preferably 0.05 to 1 part by mass, per 100 parts by mass of component (A). Less than 0.01 part by mass will not impart sufficient thixotropy to the composition, while more than 3 parts by mass will increase the viscosity and significantly reduce application workability.

[0043] In addition to the components (A) through (E) above, the thixotropic silicone gel composition for spot potting of the present invention can contain optional components within the scope of the present invention. These optional components include, for example, reaction inhibitors, inorganic fillers other than component (D) above, non-functional organopolysiloxanes that do not contain silicon-bonded hydrogen atoms (SiH groups) or silicon-bonded alkenyl groups involved in hydrosilylation addition reactions (so-called non-functional silicone oils such as dimethylpolysiloxane and dimethylsiloxane-diphenylsiloxane copolymers), adhesion promoters such as alkoxyorganosilanes that contribute to improving adhesion or tackiness, heat-resistant additives, flame retardants, pigments, dyes, etc.

[0044] The reaction inhibitor is a component for inhibiting the reaction of the composition, and specific examples thereof include acetylene-based, amine-based, carboxylic acid ester-based, and phosphite-based reaction inhibitors.

[0045] Examples of inorganic fillers include inorganic fillers such as crystalline silica other than component (D), precipitated silica, and other finely powdered silica, inorganic hollow fillers (silica hollow filler, titanium oxide hollow filler, etc.), silsesquioxane, fumed titanium dioxide, magnesium oxide, zinc oxide, iron oxide, aluminum hydroxide, magnesium carbonate, calcium carbonate, zinc carbonate, layered mica, diatomaceous earth, and glass fiber; and inorganic fillers obtained by subjecting these inorganic fillers to surface hydrophobic treatment with organosilicon compounds such as organoalkoxysilane compounds, organochlorosilane compounds, organosilazane compounds, and low-molecular-weight siloxane compounds. Silicone rubber powder, silicone resin powder, etc. may also be blended.

[0046] The thixotropic silicone gel composition for spot potting of the present invention can be obtained by uniformly mixing the predetermined amounts of the above components (A) to (E) and other optional components. If necessary, the components to be mixed can be divided into two or more parts and mixed. For example, it is possible to divide and mix a part consisting of a portion of component (A) and components (C), (D), and (E) and a part consisting of the remainder of component (A) and component (B). Examples of mixing means that can be used include a homomixer, paddle mixer, homodisper, colloid mill, vacuum mixing and stirring mixer, and planetary mixer, but there are no particular limitations as long as they can uniformly mix at least the above components (A) to (E).

[0047] The apparent viscosity (25°C) of the thixotropic silicone gel composition for spot potting of the present invention is measured at a rotation speed ratio of 1:10 using a method in accordance with JIS K7117, and the SVI value calculated from the following formula is preferably 3.0 to 10.0, and especially 4.0 to 8.0. If the apparent viscosity ratio (SVI value) is less than 3.0, sufficient thixotropy may not be achieved, and the composition may spread excessively during application, while if it exceeds 10.0, it may not be possible to apply the composition in the desired shape. SVI value = (apparent viscosity at lower RPM) / (apparent viscosity at higher RPM)

[0048] Here, the specific method for calculating the SVI value, which is the ratio of apparent viscosities, is a method in accordance with JIS K7117, in which the viscosity of the thixotropic silicone gel composition for spot potting is measured using a rheometer (ARES G2 manufactured by TA Instruments) at a rotation speed of 1 s at 25°C. -1 , 10s -1 The apparent viscosity of each of the solutions is measured, and the viscosity can be calculated by the following formula using the apparent viscosities. SVI value = (rotation speed 1s -1 Apparent viscosity at 10 s -1 apparent viscosity at

[0049] In the present invention, the SVI value (apparent viscosity ratio) of the thixotropic silicone gel composition for spot potting can be adjusted to fall within the above range by appropriately adjusting the amount of finely powdered silica (component (D)) and / or the isocyanuric acid derivative (component (E)) blended.

[0050] The curing conditions for the thixotropic silicone gel composition for spot potting of the present invention can be 23 to 150°C, particularly 50 to 130°C, for 10 minutes to 8 hours, particularly 30 minutes to 5 hours.

[0051] The thixotropic silicone gel composition for spot potting of the present invention preferably has a Dd of 3 mm or less, and more preferably 2 mm or less, where Dd is defined as the diameter of the droplet formed by the composition after dropping 1 g of the uncured composition onto a glass plate and leaving it in a 25°C atmosphere for 30 minutes, and Dmm is the diameter of the cured product of the composition formed on the glass plate after dropping 1 g of the uncured composition onto the glass plate and leaving it in a 130°C atmosphere for 30 minutes. Here, this diameter is preferably the average value of the length and width, which are two perpendicular directions. If Dd exceeds 3 mm, it may not be possible to pot only in the desired location. In the thixotropic silicone gel composition for spot potting of the present invention, the above Dd can be adjusted to 3 mm or less by appropriately adjusting the amount of finely powdered silica (component (D)) and / or the isocyanuric acid derivative (component (E)) blended.

[0052] The cured silicone gel obtained by curing the thixotropic silicone gel composition for spot potting of the present invention has a penetration as specified in JIS K6249 of 10 to 100, preferably 20 to 70. If the penetration is less than 10, the adhesion to the sealed substrate may be insufficient, while if it exceeds 100, the strength of the sealing gel itself may be low and cracks may form when heated. In the present invention, the penetration of the cured silicone gel product can be adjusted to the above range by appropriately adjusting the blending ratio of components (A) and (B) (i.e., the molar ratio of silicon-bonded hydrogen atoms (SiH groups) in component (B) to silicon-bonded alkenyl groups in component (A)).

[0053] Furthermore, the cured silicone gel obtained by curing the thixotropic silicone gel composition for spot potting of the present invention preferably exhibits a reduction in penetration as specified in JIS K6249 of no more than 20%, and particularly no more than 15%, after the cured silicone gel is left in an atmosphere at 200°C for 72 hours, relative to the penetration as specified in JIS K6249 immediately after curing. If this reduction exceeds 20%, cracks may occur in the cured product, and adhesion to the substrate may be significantly reduced. In the present invention, the above reduction rate can be kept to 20% or less by appropriately adjusting the blending ratio of components (A) and (B) (i.e., the molar ratio of silicon-bonded hydrogen atoms (SiH groups) in component (B) to silicon-bonded alkenyl groups in component (A)), and / or by blending a heat resistance improver.

[0054] The thixotropic silicone gel composition for spot potting of the present invention spreads little when applied to substrates such as various electronic substrates, including control circuit boards, and there is little change in shape before and after heat curing, and little change in the penetration of the cured product under high temperature conditions (change in flexibility or change in stress relaxation properties). Therefore, it is possible to cover by potting (so-called spot potting) only specific semiconductor elements, such as photocouplers, mounted on a control circuit board, and further, to seal the elements in the desired shape, making it possible to seal only the elements that are to be sealed. Therefore, the composition is useful as a sealant for electrical and electronic components that require spot potting, such as photocouplers, and in particular photocouplers.

[0055] [Photocoupler] The photocoupler of the present invention is sealed with a cured silicone gel obtained by curing the above-mentioned thixotropic silicone gel composition for spot potting of the present invention, and is useful in that it can be potted as designed and therefore can prevent the occurrence of defective products. [Example]

[0056] The present invention will be explained in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples. In the following examples, parts refer to parts by mass, and the viscosity of each exemplified component is measured using a rotational viscometer at 25°C. Me represents a methyl group. The degree of polymerization indicates the number-average degree of polymerization in terms of polystyrene measured by gel permeation chromatography (GPC) analysis using toluene as the developing solvent. The SVI value and spreadability of the silicone gel composition, and the heat resistance of the cured silicone gel were evaluated as follows.

[0057] [SVI value of silicone gel composition] The viscosity of the silicone gel composition was measured by a method conforming to JIS K7117. Specifically, the silicone gel composition was measured at 25°C using a rheometer (ARES G2 manufactured by TA Instruments) at a rotational speed (1 s -1 and 10s -1The apparent viscosity at each temperature was measured, and the SVI value was calculated using the following formula. SVI value = (rotation speed 1s -1 Apparent viscosity at 10 s -1 apparent viscosity at

[0058] [Spreadability of Silicone Gel Composition] Approximately 5 g of silicone gel composition was placed in a 5 ml microsyringe, and 1 g was slowly dispensed onto the center of a 50 mm x 50 mm glass plate. After leaving the plate in a 25°C atmosphere for 30 minutes, the diameter of the silicone gel composition that had spread into a circle was measured in two perpendicular directions, the vertical and horizontal, and the average value was calculated. This value was used as an index of spreadability before curing. The glass plate coated with the silicone gel composition was cured by heating it in an oven at 130°C for 30 minutes. The diameter of the resulting cured silicone gel was measured in two perpendicular directions, the vertical and horizontal directions, and the average value was calculated. This value was used as an index of spreadability upon curing. The difference between the spreadability upon curing measured above and the spreadability before curing was calculated.

[0059] [Heat resistance of cured silicone gel] The silicone gel composition was heated at 130°C for 30 minutes to obtain a cylindrical silicone gel cured product measuring approximately 40 mm in diameter and 20 mm in thickness. The penetration was measured at this time and recorded as the initial value at the time of curing. The penetration was measured using the JIS K2220 consistency test method (1 / 4 cone) specified in JIS K6249. The silicone gel cured product obtained above was exposed to a 200°C atmosphere for 72 hours, and the penetration of the resulting sample was measured. This was recorded as the penetration after heat resistance at 200°C.

[0060] Component (A) (A-1) A branched, terminally terminated polysiloxane ((C6H5)2SiO) with dimethylvinylsiloxy and trimethylsiloxy groups, having a viscosity of approximately 1 Pa·s at 25°C, represented by the following average molecular formula (8): 2 / 2Unit: 2 mol% of all diorganopolysiloxane units, alkenyl group content: 0.011 mol / 100g) [ka]

[0061] (A-2) A linear polysiloxane ((C6H5)2SiO) terminated at its molecular chain terminals with dimethylvinylsiloxy and trimethylsiloxy groups, having a viscosity of approximately 0.7 Pa·s at 25°C, represented by the following average molecular formula (9): 2 / 2 Unit: 5 mol% of all diorganopolysiloxane units, alkenyl group content: 0.005 mol / 100g) [ka] [Notes] The linear polysiloxane terminally capped with dimethylvinylsiloxy and trimethylsiloxy groups, represented by the average molecular formula (9), is a homogeneous mixture of linear polysiloxane [9a], represented by the average molecular formula (9a) below, in which one molecular chain end is capped with a dimethylvinylsiloxy group and the other molecular chain end is capped with a trimethylsiloxy group, and linear polysiloxane [9b], represented by the average molecular formula (9b) below, in which both molecular chain ends are capped with trimethylsiloxy groups, in a ratio of [9a]:[9b] = 6:4 (molar ratio ≒ mass ratio). [ka] [ka]

[0062] (A-3) A branched, terminally terminated polysiloxane ((C6H5)2SiO) with dimethylvinylsiloxy and trimethylsiloxy groups, having a viscosity of approximately 0.8 Pa·s at 25°C, represented by the following average molecular formula (10): 2 / 2 Unit: 0 mol% of all diorganopolysiloxane units, alkenyl group content: 0.012 mol / 100g) [ka] [Notes] The branched-chain polysiloxane terminally blocked with dimethylvinylsiloxy and trimethylsiloxy groups, represented by the average molecular formula (10), is a homogeneous mixture of a branched-chain polysiloxane [10a], represented by the average molecular formula (10a) below, in which two molecular chain terminals are blocked with dimethylvinylsiloxy groups, and a branched-chain polysiloxane [10b], represented by the average molecular formula (10b) below, in which two molecular chain terminals are blocked with trimethylsiloxy groups, in a ratio of [10a]:[10b]=4:6 (molar ratio ≒ mass ratio). [ka] [ka]

[0063] (A-4) A branched, terminally terminated polysiloxane ((C6H5)2SiO) with dimethylvinylsiloxy and trimethylsiloxy groups, having a viscosity of approximately 1 Pa·s at 25°C, represented by the following average molecular formula (11): 2 / 2 Unit: 0 mol% of all diorganopolysiloxane units, alkenyl group content: 0.011 mol / 100g) [ka]

[0064] (A-5) A linear polysiloxane ((C6H5)2SiO) terminated at its molecular chain terminals with dimethylvinylsiloxy and trimethylsiloxy groups, having a viscosity of approximately 0.8 Pa·s at 25°C and represented by the following average molecular formula (12): 2 / 2 Unit: 0 mol% of all diorganopolysiloxane units, alkenyl group content: 0.004 mol / 100g) [ka] [Notes] The linear polysiloxane terminally capped with dimethylvinylsiloxy and trimethylsiloxy groups, represented by the average molecular formula (12), is a homogeneous mixture of linear polysiloxane [12a], represented by the average molecular formula (12a) below, in which one molecular chain end is capped with a dimethylvinylsiloxy group and the other molecular chain end is capped with a trimethylsiloxy group, and linear polysiloxane [12b], represented by the average molecular formula (12b) below, in which both molecular chain ends are capped with trimethylsiloxy groups, in a ratio of [12a]:[12b] = 6:4 (molar ratio ≒ mass ratio). [ka] [ka]

[0065] (A-6) A linear polysiloxane ((C6H5)2SiO) terminated at its molecular chain terminals with dimethylvinylsiloxy and trimethylsiloxy groups, which has a viscosity of approximately 0.8 Pa·s at 25°C and is represented by the following average molecular formula (13): 2 / 2 Unit: 0 mol% of all diorganopolysiloxane units, alkenyl group content: 0.005 mol / 100g) [ka] [Notes] The linear polysiloxane terminally capped with dimethylvinylsiloxy and trimethylsiloxy groups, represented by the average molecular formula (13), is a homogeneous mixture of linear polysiloxane [13a], represented by the average molecular formula (13a) below, in which one molecular chain end is capped with a dimethylvinylsiloxy group and the other molecular chain end is capped with a trimethylsiloxy group, and linear polysiloxane [13b], represented by the average molecular formula (13b) below, in which both molecular chain ends are capped with trimethylsiloxy groups, in a ratio of [13a]:[13b] = 6:4 (molar ratio ≒ mass ratio). [ka] [ka]

[0066] (B) Component (B-1) Methylhydrogenpolysiloxane (SiH group content: 0.004 mol / g) having a viscosity of 30 mPa s at 25°C and represented by the following average molecular formula (14): [ka]

[0067] (B-2) Methylhydrogenpolysiloxane (SiH group content: 0.006 mol / g) having a viscosity of 110 mPa s at 25°C and represented by the following average molecular formula (15): [ka]

[0068] (B-3) Methylhydrogenpolysiloxane (SiH group content: 0.001 mol / g) having a viscosity of 20 mPa s at 25°C and represented by the following average molecular formula (16): [ka]

[0069] (C) Component (C-1) A solution of a chloroplatinic acid-vinylsiloxane complex (platinum atom content: 1% by mass) in a solvent of a dimethylpolysiloxane capped at both molecular chain terminals with vinyldimethylsiloxy groups, represented by the following formula (17): [ka]

[0070] (D) Component (D-1) BET specific surface area is 300m 2 / g, fumed silica surface-treated with dimethyldichlorosilane (trade name: DM-30S, manufactured by Tokuyama Corporation) (D-2) BET specific surface area is 140m 2 / g, fumed silica surface-treated with trimethylchlorosilane (product name: NSX-200, manufactured by Nippon Aerosil Co., Ltd.)

[0071] (E) Component (E-1) Isocyanuric acid derivative represented by the following formula (18): [ka]

[0072] (E-2) Isocyanuric acid derivative represented by the following formula (19) [ka]

[0073] (E-3) 3-Glycidoxypropyltrimethoxysilane (trade name: KBM-403, manufactured by Shin-Etsu Chemical Co., Ltd.) (E-4) 8-Glycidyloxyoctyltrimethoxysilane (trade name: KBM-4803, manufactured by Shin-Etsu Chemical Co., Ltd.) (E-5) Methoxy group-containing siloxane oligomer having a methoxy group content of 28% by mass and a viscosity of 25 mPa·s at 25°C (trade name: KR-500, manufactured by Shin-Etsu Chemical Co., Ltd.)

[0074] [Examples 1 to 4, Comparative Examples 1 to 7] Silicone gel compositions S1 to S11 were prepared by mixing the components (A) to (E) as shown in Tables 1 and 2. The viscosities of these silicone gel compositions were measured using the rheometer described above, and the SVI values ​​were calculated. The changes in spreadability of these silicone gel compositions before and after curing were also confirmed using the method described above. Furthermore, the heat resistance of the cured products of these silicone gel compositions was evaluated using the method described above. The results are shown in Tables 1 and 2.

[0075] As shown in Tables 1 and 2, the silicone gel compositions of Examples 1 to 4 satisfy the requirements of the present invention. They are thixotropic silicone gel compositions that exhibit almost no spreading during heat curing, making them useful for spot potting on encapsulating elements. Furthermore, they exhibit small changes in penetration in a 200°C atmosphere and have good heat resistance, which prevents cracks from forming in the cured silicone gel even during high-temperature operation, thereby minimizing the load on the encapsulating element.

[0076] [Table 1] *: The molar number of silicon-bonded hydrogen atoms (SiH groups) in component (B) per mole of silicon-bonded alkenyl groups in component (A).

[0077] [Table 2] *: The molar number of silicon-bonded hydrogen atoms (SiH groups) in component (B) per mole of silicon-bonded alkenyl groups in component (A).

Claims

1. (A) As a diorganosiloxane unit in the main chain, (C 6 H 5 ) 2 SiO 2 / 2 100 parts by mass of a linear or branched organopolysiloxane having 0.1 to 10 mol% of a diorganosiloxane unit based on all diorganosiloxane units in the main chain and having 0.001 to 10 mol / 100 g of alkenyl groups bonded to silicon atoms, (B) The following average composition formula (1): 【Chemical 1】 (In the formula, R 1 are the same or different monovalent hydrocarbon groups having 1 to 10 carbon atoms and containing no aliphatic unsaturated bonds, a is 0 or 1, b is a positive number from 0.002 to 0.3, and c is a positive number from 0.1 to 0.

6. and containing at least three silicon-bonded hydrogen atoms per molecule: an organohydrogenpolysiloxane in which the amount of silicon-bonded hydrogen atoms in component (B) is 0.01 to 3 moles per mole of alkenyl groups in component (A); (C) a platinum-based curing catalyst: a catalytically effective amount; (D) The surface is hydrophobized with an organosilazane, organochlorosilane, organoalkoxysilane, or organopolysiloxane, all of which have only methyl groups as monovalent hydrocarbon groups bonded to silicon atoms, and the specific surface area (BET adsorption method) is 50 to 500 m 2 / g: 2 to 30 parts by mass of finely powdered silica, and (E) 0.01 to 3 parts by mass of an isocyanuric acid derivative having, among the three nitrogen atoms forming the isocyanuric acid skeleton, one trialkoxysilyl-substituted alkyl group on each of two nitrogen atoms (two in total in the molecule) and one alkyl group substituted with an alkenyl group, or a silyl group containing a hydrogen atom bonded to a silicon atom (SiH group) or a siloxanyl group on the remaining nitrogen atom, and / or an isocyanuric acid derivative having one trialkoxysilyl-substituted alkyl group on each of the three nitrogen atoms forming the isocyanuric acid skeleton (three in total in the molecule). (wherein the organohydrogenpolysiloxane crosslinking agent consists solely of that represented by the average composition formula (1) above), and upon curing gives a silicone gel cured product having a penetration of 10 to 100 as specified in JIS K6249.

2. 2. The silicone gel composition for spot potting according to claim 1, wherein component (E) is at least one selected from the group consisting of isocyanuric acid derivatives represented by any one of the following formulas (2) to (7): 【Chemistry 2】 【Chemistry 3】 【Chemistry 4】 【Chemistry 5】 【Chemistry 6】 【Chemistry 7】 (In the above formulas, Me represents a methyl group, and Et represents an ethyl group.)

3. The thixotropic silicone gel composition for spot potting according to claim 1, wherein the apparent viscosity (25°C) is measured at a rotation speed ratio of 1:10 using a method in accordance with JIS K7117, and the SVI value calculated using the following formula is 3.0 to 10.0: SVI value = (apparent viscosity at lower rotation speed) / (apparent viscosity at higher rotation speed)

4. The thixotropic silicone gel composition for spot potting according to claim 1, wherein d mm is defined as the diameter of a droplet formed by the composition after dropping 1 g of the uncured composition onto a glass plate and leaving it in an atmosphere at 25°C for 30 minutes, and D mm is defined as the diameter of a cured product of the composition formed on the glass plate after dropping 1 g of the uncured composition onto the glass plate and leaving it in an atmosphere at 130°C for 30 minutes, and wherein D mm is defined as the diameter of a cured product of the composition formed on the glass plate.

5. 2. A thixotropic silicone gel composition for spot potting according to claim 1, wherein the penetration of the cured silicone gel obtained by curing the uncured composition after leaving the cured silicone gel in an atmosphere at 200°C for 72 hours decreases by 20% or less compared to the penetration immediately after curing.

6. A thixotropic silicone gel composition for spot potting according to claim 1, which upon curing gives a silicone gel cured product having a needle penetration of 20 to 100 as specified in JIS K6249.

7. A thixotropic silicone gel composition for spot potting as described in claim 1, wherein the crosslinking agent of component (B) consists solely of an organohydrogenpolysiloxane represented by the following average molecular formula (1'): 【Chemistry 8】 (In the formula, R 1 and a are the same as those in the above average composition formula (1), c' is an integer of 1 to 300, d' is an integer of 4 to 700, and c'+d' is an integer of 5 to 998, with the proviso that each molecule contains three or more SiH groups.)

8. A cured silicone gel obtained by curing the thixotropic silicone gel composition for spot potting according to any one of claims 1 to 7.

9. A photocoupler sealed with the silicone gel cured product according to claim 8.

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