Curable liquid silicone composition, cured product, and electronic component

Abstract

Disclosed is a curable liquid silicone composition which contains (A) a diorganopolysiloxane that has an average of at least 0.3 alkenyl group in each molecule, (B) an organohydrogen polysiloxane that has at least two hydrogen atoms, which are each bonded to a silicon atom, in each molecule, (C) a platinum catalyst, and (D) melamine resin particles at a specific ratio. The curable liquid silicone composition gives a silicone cured product (a silicone rubber cured product or a silicone gel cured product) which has excellent heat resistance at high temperatures.

Description

Curable liquid silicone composition, cured product, and electronic component

[0001] The present invention relates to a curable liquid silicone composition (a curable liquid silicone rubber composition or a curable liquid silicone gel composition) that can give a silicone cured product (a silicone elastomer elastic material (a silicone rubber cured product) or a silicone gel cured product) that has excellent heat resistance at high temperatures, a cured product of the curable liquid silicone composition, and an electronic component encapsulated with the cured product of the curable liquid silicone composition.

[0002] In recent years, power modules, primarily consisting of insulated gate bipolar transistors (IGBTs), have become widely used in power conversion equipment. The inside of the power module case is filled with a low-elasticity silicone gel to insulate and protect the surface of the ceramic insulating substrate and the power semiconductor chips on the substrate.

[0003] In recent years, SiC (silicon carbide) power semiconductors have been actively studied because they can handle larger power levels due to their lower energy loss and heat generation when current is applied, as well as their high heat resistance, compared to conventional silicon power semiconductors. While the heat resistance limit of silicon power semiconductor devices is approximately 150°C, SiC power semiconductor devices are being considered for use at temperatures of 200-300°C, and even higher heat resistance is being required for the resins used in SiC power semiconductors and the additives used in these resins. In fact, to ensure continuous high-temperature operation of IGBT power modules, they must pass tests specified by, for example, UL1557.

[0004] This test requires that the dielectric breakdown voltage specified in the product standard can be maintained for a specified period of time at high temperatures, for example, exceeding 150° C. However, when exposed to such high temperatures for a long period of time, the silicone gel hardens and deteriorates, causing the silicone gel to crack or peel off from the components at locations where stress is concentrated inside the IGBT power module, and if this occurs near the insulating substrate, it becomes difficult to maintain the dielectric breakdown voltage.

[0005] As a method for suppressing such hardening degradation, it is possible to improve the heat resistance of ordinary silicone oils and rubbers by adding fillers such as iron oxide or titanium oxide to them. However, this method leads to a decrease in insulating properties, sedimentation of the filler, and a decrease in workability due to an increase in viscosity, making it unsuitable as a silicone gel material for IGBT power modules, which require low viscosity and insulating properties.

[0006] Furthermore, as described in JP 2008-291148 A (Patent Document 1), there is a method of imparting heat resistance using a metal salt of cerium. However, even when cerium is used, significant hardening deterioration is observed at temperatures exceeding 230°C. Therefore, a new method of imparting heat resistance has been desired.

[0007] There is also a method of imparting heat resistance using an iron carboxylate, as described in Japanese Patent No. 5,962,599 (Patent Document 2), but in both Japanese Patent Laid-Open No. 2008-291148 and Japanese Patent No. 5,962,599, the iron carboxylate must be mixed with the organopolysiloxane in advance, heat-treated to obtain a reaction product, and then added. In addition, as in the above-mentioned Japanese Patent Laid-Open No. 2008-291148, significant curing degradation is observed at temperatures exceeding 230°C.

[0008] In Japanese Patent Laid-Open No. 9-286919 (Patent Document 3) and the like, it is said that heat resistance can be obtained by adding an organic iron complex / compound, but similarly, at temperatures exceeding 230°C, significant hardening degradation is observed.

[0009] In addition, there is also a heat resistance imparting means using carboxylates of nickel and niobium, as described in JP 2017-025232 A (Patent Document 4), but similar to JP 2008-291148 A and Japanese Patent No. 5962599, this also shows significant hardening degradation at temperatures exceeding 230° C. In addition to the above-mentioned documents, the following documents can be cited as prior art related to the present invention.

[0010] Japanese Patent Application Publication No. 2008-291148 Japanese Patent No. 5962599 Japanese Patent Application Publication No. 9-286919 Japanese Patent Application Publication No. 2017-025232 International Publication No. 2023 / 243436

[0011] The present invention has been made in light of the above circumstances, and has as its object the provision of a curable liquid silicone composition which contains a platinum catalyst as a hydrosilylation addition reaction catalyst and which is capable of curing to give a cured silicone rubber or cured silicone gel product that has excellent heat resistance, as well as a cured product of the curable liquid silicone composition, and an electronic component encapsulated with the cured product of the curable liquid silicone composition.

[0012] In order to achieve the above object, the present inventors have proposed in International Publication No. 2023 / 243436 (Patent Document 5) that the use of urethane resin particles or urea resin particles can improve heat resistance and suppress a decrease in needle penetration at 230°C. However, a technology for further improving heat resistance has been an issue.

[0013] After further investigation, the present inventors discovered that in conventional addition reaction curable silicone compositions, the platinum compound added as a curing catalyst deteriorates the silicone crosslinking component at high temperatures, which is the cause of deterioration of the silicone cured product (cured silicone rubber or cured silicone gel) at high temperatures after curing. Therefore, they investigated ways to prevent the platinum compound, which functions as a curing catalyst, from becoming a cause of deterioration at high temperatures after the composition has reacted and cured. They discovered that adding melamine resin particles having an amine structure (—NH—) in the molecule can produce an addition reaction curable silicone composition that can give a silicone cured product (cured silicone rubber or cured silicone gel) with excellent heat resistance. The present invention is particularly useful for silicone gel compositions that exhibit low hardness after curing, and they discovered that they can produce silicone gel cured products with excellent heat resistance, with a small rate of change in low stress, as evaluated by indicators such as penetration, even under heat resistance conditions exceeding 250°C, thereby leading to the present invention.

[0014] Accordingly, the present invention provides the following curable liquid silicone composition, cured product, and electronic device. [1] A curable liquid silicone composition comprising: (A) a diorganopolysiloxane having an average of at least 0.3 alkenyl groups per molecule; (B) an organohydrogenpolysiloxane having at least two silicon-bonded hydrogen atoms per molecule, in an amount such that there are 0.5 to 4 moles of silicon-bonded hydrogen atoms in component (B) per mole of alkenyl groups in component (A); (C) a platinum catalyst in an amount such that the platinum atoms in component (C) are 0.1 to 1,000 ppm by mass relative to the total mass of components (A) and (B); and (D) melamine resin particles, in an amount of 0.001 to 5% by mass relative to the total mass of components (A) and (B). [2] The curable liquid silicone composition according to [1], wherein the melamine resin particles of component (D) are a polycondensate of melamine and formaldehyde. [3] The curable liquid silicone composition according to [1] or [2], further comprising (E) at least one additive / filler containing a metal atom as a heat resistance imparting agent: 0.001 to 5 parts by mass per 100 parts by mass of component (A). [4] The curable liquid silicone composition according to any one of [1] to [3], which cures to give a silicone gel cured product. [5] A cured product of the curable liquid silicone composition according to any one of [1] to [4]. [6] An electronic component sealed with the cured product according to [5]. [7] The electronic component according to [6], which is an IGBT power module.

[0015] The curable liquid silicone composition of the present invention exhibits less change in hardness at high temperatures than conventional compositions, and as a result is able to maintain excellent adhesion and stress relaxation properties over long periods of time to substrates used in IGBT power modules, etc. In particular, if the cured silicone gel obtained by curing the curable liquid silicone composition of the present invention is used to protect the electronic components in silicon power semiconductor devices, particularly SiC power semiconductor devices, it is expected to be of great help in ensuring continuous high-temperature operation in atmospheres above 250°C.

[0016] The curable liquid silicone composition of the present invention contains the following components (A) to (D) as essential components. In the present invention, a curable liquid silicone gel composition is one that cures to give a cured silicone gel product, and a cured silicone gel product (or silicone gel) refers to a cured product with a low crosslink density that is primarily composed of an organopolysiloxane and has a consistency (hereinafter referred to as "penetration") according to JIS K2220 (1 / 4 cone) of 10 to 100. This corresponds to a rubber hardness measurement according to JIS K6301 that gives a measured value (rubber hardness value) of 0, and is so low in hardness (i.e., soft) and elasticity that it does not exhibit a valid rubber hardness value. In this respect, it is distinct from so-called cured silicone rubber products (rubber-like elastomers).

[0017] The present invention will be described in detail below.

[0018] [Curable Liquid Silicone Composition] The curable liquid silicone composition of the present invention (curable liquid silicone rubber composition or curable liquid silicone gel composition) is a composition containing the components (A) to (D) described below, and, if necessary, other components.

[0019] [(A) Alkenyl Group-Containing Diorganopolysiloxane] The alkenyl group-containing diorganopolysiloxane of component (A) is a linear or branched diorganopolysiloxane containing an average of at least 0.3 alkenyl groups per molecule, and functions as the main component (base polymer) of the curable liquid silicone composition of the present invention (hereinafter also referred to as the composition of the present invention). Typically, it is a linear diorganopolysiloxane whose main chain is basically composed of repeating diorganosiloxane units and whose molecular chain is terminated at both ends with triorganosiloxy groups; however, it may also be a branched diorganopolysiloxane containing a branched structure as part of the siloxane structure that makes up the molecular chain.

[0020] The alkenyl-containing diorganopolysiloxane of component (A) contains an average of at least 0.3 alkenyl groups per molecule, preferably 0.3 to 50 alkenyl groups, more preferably 0.5 to 20 alkenyl groups, and particularly preferably 0.5 to 10 alkenyl groups. The alkenyl groups preferably have 2 to 8 carbon atoms, more preferably 2 to 4 carbon atoms, and examples thereof include vinyl, allyl, propenyl, isopropenyl, butenyl, hexenyl, and cyclohexenyl groups. Preferred are lower alkenyl groups such as vinyl and allyl. The alkenyl groups may be bonded to silicon atoms at the molecular chain terminals or non-terminal (intermediate) silicon atoms in the molecular chain. Preferably, the alkenyl groups contain alkenyl groups bonded to silicon atoms at at least one or both molecular chain terminals. In this case, the alkenyl groups may be present only at the molecular chain terminals, or may be present at both the molecular chain terminals and non-terminal (intermediate) silicon atoms in the molecular chain.

[0021] Examples of such alkenyl-containing diorganopolysiloxanes include linear diorganopolysiloxanes represented by the following average unit formula (1). (In the formula, R 1 are independently unsubstituted or substituted monovalent hydrocarbon groups that do not contain aliphatic unsaturated bonds. X is an alkenyl group, and at least 0.3 are contained per molecule on average. g, h, j, and k are each a number from 0 to 2, g + h + j + k is 2, n is a number of 0 or more, m is a number of 0 or more, and h + 2j + 3k + m is a positive number of 0.3 or more.

[0022] In the above formula (1), R 1Examples of the unsubstituted or substituted monovalent hydrocarbon group not containing an aliphatic unsaturated bond include those having 1 to 12 carbon atoms, preferably 1 to 10 carbon atoms, and more preferably 1 to 6 carbon atoms. Specific examples include alkyl groups such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, pentyl, neopentyl, hexyl, heptyl, octyl, nonyl, decyl, and dodecyl; cycloalkyl groups such as cyclopentyl, cyclohexyl, and cycloheptyl; aryl groups such as phenyl, tolyl, xylyl, naphthyl, and biphenylyl; and aralkyl groups such as benzyl, phenylethyl, phenylpropyl, and methylbenzyl. and groups in which some or all of the hydrogen atoms bonded to the carbon atoms of these groups have been substituted with halogen atoms such as fluorine, chlorine or bromine, or with a cyano group, for example, a chloromethyl group, a 2-bromoethyl group, a 3-chloropropyl group, a 3,3,3-trifluoropropyl group, a chlorophenyl group, a fluorophenyl group, a cyanoethyl group, a 3,3,4,4,5,5,6,6,6-nonafluorohexyl group, and the like, preferably unsubstituted or substituted alkyl groups having 1 to 3 carbon atoms such as a methyl group, an ethyl group, a propyl group, a chloromethyl group, a bromoethyl group, a 3,3,3-trifluoropropyl group, a cyanoethyl group, and the like, and unsubstituted or substituted phenyl groups such as a phenyl group, a chlorophenyl group, a fluorophenyl group, and the like. R 1 As the alkyl group, a methyl group and a phenyl group are preferred.

[0023] In the above formula (1), examples of the alkenyl group for X include those having 2 to 8 carbon atoms, preferably 2 to 4 carbon atoms, such as vinyl, allyl, propenyl, isopropenyl, butenyl, hexenyl, and cyclohexenyl groups, and among these, lower alkenyl groups such as vinyl and allyl are preferred.

[0024] In the above formula (1), g is a number from 0 to 2, preferably a number from 0 to 1.5, h is a number from 0 to 2, preferably a positive number from 0.5 to 2, j is a number from 0 to 2, preferably 0, k is a number from 0 to 2, preferably 0, and g + h + j + k is 2. In the above formula (1), n ​​is a number of 0 or more, preferably a positive number from 10 to 2,000, more preferably a positive number from 50 to 1,200, and m is a number of 0 or more, preferably a number from 0 to 40, more preferably a number from 0 to 20. Furthermore, n and m are preferably positive numbers that satisfy 10≦n+m≦2,000, more preferably 50≦n+m≦1,200, and are numbers that satisfy 0≦m / (n+m)≦0.2. In this case, the bonding order of each siloxane unit in parentheses enclosed by n and m is not limited to the above, and each siloxane unit may form a block unit or may be bonded randomly. The number of X's present in the molecule is at least 0.3 on average, and h+2j+3k+m is a positive number of 0.3 or more, preferably a positive number of 0.3 to 50, and more preferably a positive number of 0.5 to 20.

[0025] The amount of alkenyl groups contained in the alkenyl group-containing diorganopolysiloxane of component (A) is preferably 0.001 to 0.05 mol / 100 g, and more preferably 0.002 to 0.02 mol / 100 g. If the amount of alkenyl groups is too low, the composition may not cure, while if it is too high, bleeding may occur. In the present invention, the amount of alkenyl groups can be measured using a method based on the iodine value measurement method described in JIS K0070.

[0026] Furthermore, it is preferable that such alkenyl-containing diorganopolysiloxanes have a viscosity at 23°C of 10 to 1,000,000 mPa·s, and particularly 100 to 500,000 mPa·s.

[0027] In the present invention, the number of repeating diorganosiloxane units in a molecule (or degree of polymerization) can be determined as the polystyrene-equivalent number average molecular weight (or number average degree of polymerization) by gel permeation chromatography (GPC) analysis using toluene or the like as a developing solvent. Viscosity can be measured using a rotational viscometer (e.g., BL type, BH type, BS type, cone-plate type, rheometer, etc.) at 23°C.

[0028] The alkenyl group-containing diorganopolysiloxane of component (A) may be used alone or in combination of two or more. In order to avoid impairing the function of the platinum catalyst of component (C), which will be described later, it is advisable to reduce the oxygen and water contents in the alkenyl group-containing diorganopolysiloxane of component (A) before blending it into the composition. This can be achieved, for example, by replacing the atmosphere with an inert gas such as nitrogen gas, by heating or reducing the pressure, or by a combination of these methods.

[0029] [(B) Organohydrogenpolysiloxane] The organohydrogenpolysiloxane of component (B) is an organohydrogenpolysiloxane with a linear, cyclic, branched, or three-dimensional network structure that contains at least two hydrogen atoms bonded to silicon atoms (SiH groups) per molecule, and functions as a curing agent (crosslinking agent) for the curable liquid silicone composition of the present invention.

[0030] The organohydrogenpolysiloxane of component (B) acts as a curing agent (crosslinking agent) for the composition of the present invention and contains at least two, preferably 2 to 200, and more preferably 3 to 100 silicon-bonded hydrogen atoms (SiH groups) per molecule, and may have a linear, branched, cyclic, or three-dimensional network structure (resin structure).

[0031] Examples of such organohydrogenpolysiloxanes include organohydrogenpolysiloxanes represented by the following average composition formula (2): b R 2 c SiO (4-b-c) / 2 (2) (wherein, R 2are independently an unsubstituted or substituted monovalent hydrocarbon group containing no aliphatic unsaturated bonds, and b and c are positive numbers satisfying 0.001≦b≦1.2, 0.8≦c≦2, and 0.8<b+c≦3, and preferably 0.05≦b≦1, 1.5≦c≦2, and 1.8≦b+c≦2.7.

[0032] In the above formula (2), R 2 The unsubstituted or substituted monovalent hydrocarbon group not containing an aliphatic unsaturated bond includes R 1 Examples include those having 1 to 12 carbon atoms, preferably 1 to 10 carbon atoms, and more preferably 1 to 7 carbon atoms, and particularly preferred are lower alkyl groups having 1 to 3 carbon atoms such as a methyl group, a phenyl group, and a 3,3,3-trifluoropropyl group.

[0033] The number of silicon atoms in one molecule of component (B) is preferably 2 to 300, particularly preferably 2 to 150, and especially preferably 2 to 100. Component (B) that is liquid at room temperature (23°C ± 15°C, the same applies hereinafter) is preferably used. The hydrogen atoms bonded to silicon atoms (SiH groups) may be located at either the terminals of the molecular chain, midway along the molecular chain (non-terminal), or both.

[0034] As such an organohydrogenpolysiloxane, a linear organohydrogenpolysiloxane represented by the following average unit formula (3) is preferred. (In the formula, R 2 is the same as above. d is a number from 0 to 2, e is a number equal to or greater than 0, f is a number equal to or greater than 0, and d+f is a positive number equal to or greater than 2.

[0035] In the formula, e is a number equal to or greater than 0, preferably a number between 0 and 298, more preferably a number between 0 and 148, and f is a number equal to or greater than 0, preferably a number between 0 and 200, more preferably a number between 0 and 100. Furthermore, e and f preferably satisfy the relationship 0≦e+f≦298, more preferably 0≦e+f≦148, and even more preferably 0≦e+f≦98. In this case, the bonding order of the siloxane units in the parentheses enclosed by e and f is not limited to the above, and the siloxane units may form block units or be bonded randomly. In the formula, d is a number between 0 and 2 for each silicon atom bonded, preferably 0 or 1 to 2. The number of hydrogen atoms bonded to silicon atoms (SiH groups), i.e., d+f, is a positive number of 2 or greater, preferably a positive number between 2 and 200, and more preferably a positive number between 3 and 100.

[0036] The amount of SiH groups contained in the organohydrogenpolysiloxane of component (B) is preferably 0.00001 to 0.1 mol / g, and more preferably 0.00002 to 0.05 mol / g. If the amount of SiH groups is too small, the composition may not cure, while if it is too large, bleeding may occur. In the present invention, the amount of SiH groups can be measured by adding an alkali to a weighed amount of organohydrogenpolysiloxane and measuring the volume of hydrogen gas generated.

[0037] Examples of organohydrogenpolysiloxanes of component (B) include methylhydrogencyclosiloxane oligomers such as 1,1,3,3-tetramethyldisiloxane, 1,1,3,3,5,5-hexamethyltrisiloxane, 1,3,5,7-tetramethyltetracyclosiloxane, and 1,3,5,7,9-pentamethylpentacyclosiloxane; tris(dimethylhydrogensiloxy)methylsilane; tris(dimethylha (hydrogensiloxy)phenylsilane, methylhydrogenpolysiloxane terminated at both molecular chain ends with trimethylsiloxy groups, dimethylsiloxane-methylhydrogensiloxane copolymer terminated at both molecular chain ends with trimethylsiloxy groups, diphenylsiloxane-methylhydrogensiloxane copolymer terminated at both molecular chain ends with trimethylsiloxy groups, methylphenylsiloxane-methylhydrogensiloxane terminated at both molecular chain ends with trimethylsiloxy groups copolymer, dimethylsiloxane-diphenylsiloxane-methylhydrogensiloxane copolymer terminated at both molecular chain ends with trimethylsiloxy groups, dimethylpolysiloxane terminated at both molecular chain ends with dimethylhydrogensiloxy groups, methylhydrogenpolysiloxane terminated at both molecular chain ends with dimethylhydrogensiloxy groups, dimethylsiloxane-methylhydrogensiloxane copolymer terminated at both molecular chain ends with dimethylhydrogensiloxy groups, diphenylsiloxane-methylhydrogensiloxane copolymer terminated at both molecular chain ends with dimethylhydrogensiloxy groups, methylphenylsiloxane-methylhydrogensiloxane copolymer terminated at both molecular chain ends with dimethylhydrogensiloxy groups, dimethylsiloxane-diphenylsiloxane-methylhydrogensiloxane copolymer terminated at both molecular chain ends with dimethylhydrogensiloxy groups, 4 / 2 Examples of such silicone resins include silicone resins having a three-dimensional network structure consisting of units and which may optionally contain trimethylsiloxy units, dimethylsiloxane units, methylhydrogensiloxane units, hydrogensilsesquioxane units, and / or methylsilsesquioxane units, and compounds in which some or all of the methyl groups in the above-mentioned exemplary compounds have been substituted with other alkyl groups or the like.

[0038] The organohydrogenpolysiloxane used in the composition of the present invention can be obtained by known methods, for example, a compound represented by the general formula: R 2 SiHCl2 and R 2 2SiHCl (wherein R 2 is the same as above.) or by subjecting the chlorosilane to co-hydrolysis condensation with a compound having the general formula: R 2 3SiCl and R 2 2SiCl2 (wherein, R 2 are the same as above.) and at least one chlorosilane selected from the group consisting of chlorosilanes ...

[0039] From the viewpoint of providing a silicone rubber or silicone gel that does not bleed and has good curing properties, the amount of organohydrogenpolysiloxane of component (B) blended is an amount such that the number of silicon-bonded hydrogen atoms (SiH groups) in the organohydrogenpolysiloxane of component (B) is 0.5 to 4 moles, preferably 0.6 to 2.5 moles, and more preferably 0.8 to 2 moles per mole of alkenyl groups in the alkenyl group-containing diorganopolysiloxane of component (A).

[0040] The organohydrogenpolysiloxane of component (B) may be used alone or in combination of two or more. In order not to impair the function of the platinum catalyst of component (C), which will be described later, it is advisable to reduce the oxygen and water contents in the organohydrogenpolysiloxane of component (B) before blending it into the composition. This can be done, for example, by replacing the atmosphere with an inert gas such as nitrogen gas, by heating or reducing the pressure, or by a combination of these methods.

[0041] [(C) Platinum Catalyst] The platinum catalyst of component (C) is a catalyst comprising platinum or a platinum compound that has been conventionally used to promote a hydrosilylation addition reaction, such as platinum (including platinum black) alone; HPtCl.xH0, HPtCl.xH0, NaHPtCl.xH0, KHPtCl.xH0, NaPtCl.xH0, KPtCl.xH0, PtCl.xH0, PtCl, NaHPtCl.xH0 (wherein x is an integer of 0 to 6, preferably 0 or 6); Examples of suitable platinum complexes include platinum chloride, chloroplatinic acid, and chloroplatinic salts; alcohol-modified chloroplatinic acid (see U.S. Pat. No. 3,220,972); complexes of chloroplatinic acid with olefins (see U.S. Pat. Nos. 3,159,601, 3,159,662, and 3,775,452); complexes of platinum chloride, chloroplatinic acid, or chloroplatinic salts with vinyl group-containing siloxanes, particularly vinyl group-containing cyclic siloxanes; and complexes of platinum with alcohols or vinyl group-containing siloxanes.

[0042] The amount of component (C) to be blended is 0.1 to 1,000 ppm, preferably 1 to 300 ppm, calculated as platinum atom mass relative to the total mass of components (A) and (B). If this blending amount exceeds the upper limit, the heat resistance of the resulting cured product will decrease. If this blending amount is below the lower limit, the product will not cure or the curing time will increase.

[0043] [(D) Melamine Resin Particles] Component (D) is a melamine resin particle that acts to prevent the platinum catalyst of component (C) from causing deterioration of the silicone matrix structure (silicone cross-linked component) formed by the cross-linked structure of components (A) and (B) when the cured product is exposed to temperatures exceeding 180°C after the platinum catalyst of component (C) above has demonstrated its function as a curing catalyst (hydrosilylation addition reaction catalyst) during curing of the composition at temperatures from room temperature to 180°C.

[0044] As mentioned above, the present inventors have discovered that in hydrosilylation addition reaction curing silicone compositions, the cause of deterioration of the cured silicone product at high temperatures after curing is the tendency of the platinum compound added as a curing catalyst to deteriorate the silicone crosslinking component (the silicone matrix structure formed by the crosslinked structure of component (A) and component (B)) at high temperatures. They have also discovered that the addition of melamine resin particles is an effective means of inhibiting the deterioration of the silicone crosslinking component caused by the platinum compound.

[0045] That is, the present inventors have discovered that adding a nitrogen compound that forms a stable complex with platinum even at high temperatures is effective in neutralizing the oxidation catalyst function of the platinum atoms remaining in the cured silicone product after curing (deactivating the catalyst). However, simply adding a nitrogen compound or sulfur compound to a composition will neutralize (deactivate) the activity of the platinum atoms as a hydrosilylation addition reaction catalyst from the early stages of mixing, inhibiting the curability of the composition itself.

[0046] On the other hand, when the melamine resin particles of the present invention are added to a composition, the activity of the platinum atoms as a curing catalyst (hydrosilylation addition reaction catalyst) is not hindered under the temperature conditions of room temperature to 180°C when curing the curable liquid silicone composition, and further, at temperatures above 180°C, where heat resistance is required, the melamine resin particles in the cured product decompose due to heat, reducing the bulkiness around the nitrogen atoms, thereby invalidating (deactivating) the function of the platinum atoms as an oxidation catalyst after curing, thereby achieving good heat resistance. In this way, it is possible to maintain the activity of the platinum catalyst in the temperature range from room temperature to curing temperature, while also inactivating the platinum catalyst in the heat-resistant temperature range.

[0047] The melamine resin particles of component (D) are preferably a polycondensate of melamine and formaldehyde.

[0048] The melamine resin particles of component (D) preferably have an average particle size of 0.01 to 500 μm, more preferably 0.02 to 300 μm, and even more preferably 0.05 to 100 μm. If the average particle size is too small, the viscosity of the curable liquid silicone composition of the present invention may become significantly high, while if it is too large, the melamine resin particles may settle and separate in the curable liquid silicone composition. In the present invention, the average particle size can be measured as the cumulative volume average diameter D50 (or median diameter) in particle size distribution measurement using a centrifugal sedimentation light transmission particle size distribution analyzer (e.g., LUMiSizer manufactured by LUM (Germany)).

[0049] Furthermore, when the melamine resin particles are added to the composition, they may be blended into the composition in the form of solid particles, or they may be blended into the composition in the form of a dispersion in an appropriate dispersion medium (for example, a so-called silicone oil, such as a non-functional diorganopolysiloxane, which does not have in its molecule any functional groups involved in a hydrosilylation addition reaction, such as an alkenyl group or an SiH group).Furthermore, the melamine resin particles may be blended into the composition in the form of a dispersion containing the melamine resin particles dispersed in the dispersion medium, which is obtained by mixing melamine and formaldehyde in the dispersion medium to cause addition polymerization and then heating to cause polycondensation.

[0050] The amount of melamine resin particles in component (D) is 0.001 to 5% by mass, preferably 0.005 to 4% by mass, and more preferably 0.01 to 3% by mass, based on the total mass of components (A) and (B). If the amount is less than 0.001% by mass, the desired effect will not be achieved. If the amount is more than 5% by mass, thermal degradation of the melamine resin particles may adversely affect the properties of the cured product, particularly the electrical properties. The amount of melamine resin particles in component (D) is preferably at least 5 times, more preferably 7 to 50,000 times, and even more preferably 10 to 10,000 times, the amount of platinum atoms in component (C). If the amount is less than 5 times, the desired effect may not be achieved. The melamine resin particles in component (D) may be used alone or in combination of two or more types.

[0051] [Other Components] In addition to the components (A) through (D) described above, the curable liquid silicone composition of the present invention can contain various optional components, as described below, as needed, provided that the object of the present invention is not impaired.

[0052] [(E) Heat Resistance Imparting Agent] A heat resistance imparting agent (E) can be added to the curable liquid silicone composition of the present invention in order to further improve heat resistance. The heat resistance imparting agent can be at least one additive / filler containing a metal atom, with additives / fillers containing iron or cerium atoms being preferred. Additives / fillers containing iron or cerium atoms are highly effective in improving heat resistance and are also effective in reducing cure degradation of the resulting silicone cured product due to air oxidation at high temperatures. The combined effect of the (D) melamine resin particles suppressing platinum atoms, which promote oxidation reactions, and the (E) heat resistance imparting agent's suppression of natural oxidation can further improve the heat resistance of the silicone cured product.

[0053] Specific examples of additives / fillers containing iron or cerium atoms include heat-treated mixtures obtained by heating a mixture of an iron or cerium carboxylate and an organopolysiloxane, typically at a temperature ranging from 150 to 310°C. Specific examples of iron / cerium (iron or cerium) carboxylates include iron or iron-based metal compound salts such as 2-ethylhexanoic acid (octylic acid), naphthenic acid, oleic acid, lauric acid, and stearic acid. Specific examples of organopolysiloxanes include dimethylpolysiloxane (dimethylsilicone oil), dimethylsiloxane-diphenylsiloxane copolymer (dimethyl-diphenylsilicone oil), and dimethylsiloxane-methylphenylsiloxane copolymer (dimethyl-methylphenylsilicone oil). The molecular chain terminals of these linear diorganopolysiloxanes may be blocked with hydroxyl groups (silanol groups) or trialkylsilyl groups such as trimethylsilyl groups, and the molecular backbone may also contain a small amount of branching. The heating conditions for the heat-treated mixture are preferably 150 to 250°C, more preferably 170 to 220°C, and the heat treatment is preferably carried out under reduced pressure in order to remove organic acids as by-products of the heat treatment. The iron or cerium content in the heat-treated mixture is preferably 10 to 50,000 ppm, more preferably 50 to 10,000 ppm, and even more preferably 100 to 5,000 ppm.

[0054] In addition to the above-mentioned silicone-modified iron or cerium carboxylates, ferrocene or a derivative thereof can also impart excellent heat resistance to the cured product. Preferred examples of ferrocene or a derivative thereof include ferrocene, acetylferrocene, vinylferrocene, ethynylferrocene, ferrocenylmethanol, bis(η-cyclopentadienyl)iron(III) tetrachloroferrate(III), tetracarbonylbis(η-cyclopentadienyl)diiron(I), 1,1'-bis(trimethylsilyl)ferrocene, 1,1'-(dimethylphenoxysilyl)ferrocene, and 1,1'-bis(dimethylethoxysilyl)ferrocene, with ferrocene and acetylferrocene being particularly preferred.

[0055] Furthermore, as the filler containing iron atoms or cerium atoms, iron oxide, ferrous oxide, ferric oxide, and cerium oxide, an oxide of cerium, can also be selected.

[0056] When ferrocene or a derivative thereof, or oxides of iron or cerium, etc. are used, they may be added to the composition in the form of solid particles, or may be dissolved in a suitable dispersion medium (for example, a so-called silicone oil, such as a non-functional diorganopolysiloxane that does not have in its molecule any functional group that participates in a hydrosilylation addition reaction, such as an alkenyl group or a SiH group).

[0057] When the heat resistance imparting agent of component (E) is blended, the blending amount is preferably 0.001 to 5 parts by mass, and more preferably 0.002 to 3 parts by mass, per 100 parts by mass of component (A). If the blending amount of component (E) is too small, the heat resistance improving effect may not be fully exerted, whereas if the blending amount is too large, the heat resistance imparting agent may separate and settle.

[0058] [(F) Addition Reaction Inhibitor] If necessary, it is useful to further incorporate an addition reaction inhibitor, component (F), as an optional component in the curable liquid silicone composition of the present invention. Examples of the addition reaction inhibitor for component (F) include compounds selected from the group consisting of acetylene alcohols such as 1-ethynylcyclohexanol and 3-methyltridec-1-yn-3-ol (EMDC), silanes of acetylene alcohols such as dimethylbis(1,1-dimethyl-2-propynyloxy)silane (PLR-22) and 3-(trimethylsilyloxy)-3-methyl-1-butyne (PLR-31), siloxane-modified products, phosphorous compounds (particularly phosphite esters) such as tri(isopropyl)phosphite, tris(di-tert-butylphenyl)phosphite, triphenyl phosphite, and tris(2-ethylhexyl)phosphite, ethylenediamines such as tetramethylethylenediamine, benzotriazoles such as 5-methyl-1H-benzotriazole, and mixtures thereof.

[0059] When an addition reaction retarder of component (F) is added, the amount added is preferably 0.001 to 5 parts by mass, and particularly 0.01 to 1 part by mass, per 100 parts by mass of component (A). If the amount of component (F) added is too small, the reaction retarding effect may be insufficient (unstable), while if the amount is too large, the curing properties may be unsatisfactory, such as a failure to achieve uniform curability.

[0060] [(G) Inorganic Filler] The curable liquid silicone composition of the present invention can further contain an inorganic filler (G) as an optional component, as needed, to adjust the viscosity when uncured, improve the strength of the cured silicone rubber or cured silicone gel, and adjust the appearance color. Examples of inorganic fillers that can be added as component (G) include reinforcing inorganic fillers such as fumed silica and fumed titanium dioxide; and non-reinforcing inorganic fillers such as calcium silicate, titanium dioxide, and carbon black. The specific surface area of ​​the inorganic filler, as measured by the BET method, is preferably 10 to 2,000 m. 2 / g, and 20 to 1,000m 2 It is more preferable that the SiO2 content is 1 / g.

[0061] When an inorganic filler of component (G) is added, the amount added is usually 200 parts by mass or less, preferably 0.1 to 200 parts by mass, and more preferably 0.5 to 50 parts by mass, per 100 parts by mass of component (A). If the amount of inorganic filler used is less than 0.1 part by mass, the effect of adding it may not be obtained, while if it exceeds 200 parts by mass, it may be difficult to mix it uniformly into a mixture.

[0062] [(H) Adhesion Promoting Agent] When a high level of self-adhesion is required for an application, the curable liquid silicone composition of the present invention may further contain, as an optional component, an adhesion promoter (component (H)) such as an alkoxysilane containing a monovalent hydrocarbon group having a functional group containing a heteroatom selected from oxygen and sulfur atoms (e.g., an epoxy group, a (meth)acryloxy group, a mercapto group), and / or a partial hydrolysis condensate thereof, in order to improve the adhesion of the cured product to various substrates.

[0063] When the adhesion promoter of component (H) is added, the amount added is preferably 0.1 to 20 parts by mass, and more preferably about 0.2 to 10 parts by mass, per 100 parts by mass of component (A). If the amount of adhesion promoter is less than 0.1 part by mass, the desired adhesiveness may not be fully achieved, while if it is more than 20 parts by mass, the viscosity of the composition may be significantly reduced.

[0064] [(I) Plasticizer] The curable liquid silicone composition of the present invention may further contain, as an optional component, component (I) plasticizer, in order to adjust the viscosity of the composition and the hardness of the cured product, as needed. This may include so-called non-functional silicone oils, such as dimethylpolysiloxanes (dimethylsilicone oils) terminally capped with trimethylsilyl groups, dimethylsiloxane-diphenylsiloxane copolymers terminally capped with trimethylsilyl groups, and dimethylsiloxane-methylphenylsiloxane copolymers terminally capped with trimethylsilyl groups (methylphenylsilicone oils), which do not contain functional groups involved in hydrosilylation addition reactions in the molecule, such as alkenyl groups or hydrosilyl groups (SiH groups).

[0065] When a plasticizer of component (I) is added, the amount added is preferably 0.1 to 50 parts by mass, and more preferably about 0.5 to 20 parts by mass, per 100 parts by mass of component (A). If the amount of plasticizer added is less than 0.1 part by mass, the intended plasticization may not be achieved, whereas if it is more than 50 parts by mass, the plasticizer may separate and bleed out of the cured material.

[0066] In addition to the optional components (E) heat resistance imparting agent, (F) addition reaction inhibitor, (G) inorganic filler, (H) adhesion imparting agent, and (I) plasticizer described above, the curable liquid silicone composition of the present invention may further contain, as necessary, other optional components such as pigment pastes that use as binders components similar to the non-functional silicone oils used as plasticizers described above, or reinforcing silicone resins, provided that the object of the present invention is not impaired.

[0067] The curable liquid silicone composition of the present invention can be obtained by uniformly mixing the above components (A) to (D) and other optional components in predetermined amounts in accordance with conventional methods. The curable liquid silicone composition of the present invention can provide a cured silicone rubber or cured silicone gel product after curing, which exhibits reduced deterioration upon curing at higher temperatures. In the present invention, compositions that can provide a cured silicone gel product are particularly preferred.

[0068] (Method for curing the curable liquid silicone composition) The method for curing the curable liquid silicone composition of the present invention comprises the step of curing the above-mentioned curable liquid silicone composition of the present invention at room temperature or under heating. When heated, the curing conditions are preferably 30 to 180°C, particularly 60 to 160°C, for 0.1 to 3 hours, particularly 0.5 to 1 hour.

[0069] The silicone rubbers and silicone gels that are the cured products of the curable liquid silicone composition of the present invention obtained in this manner have excellent heat resistance and electrical insulation properties, and are applicable to automotive parts, aircraft, home appliances, and the like, and are particularly suitable for use in electronic parts such as IGBT power modules.

[0070] 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. The viscosity is a measurement value at 23°C using a rotational viscometer (digital viscometer TVB-10M model, BM3-30, manufactured by Toki Sangyo Co., Ltd.), the degree of polymerization is the number average degree of polymerization converted into polystyrene in GPC analysis using toluene as a developing solvent, and the average particle size is the measurement value (cumulative volume average diameter D50) in particle size distribution measurement using a centrifugal sedimentation light transmission particle size distribution analyzer (LUMiSizer, manufactured by LUM (Germany)). The ratio of constituent units in the average unit formula of organopolysiloxane is as follows: 1 The vinyl group content and SiH group content were determined by a method based on the iodine value measurement method described in JIS K0070, and by adding an alkali to a weighed amount of organohydrogenpolysiloxane and measuring the volume of hydrogen gas generated. Me represents a methyl group, Ph represents a phenyl group, and Vi represents a vinyl group. "Room temperature" refers to 23°C.

[0071] Examples 1 to 3, Comparative Examples 1 to 5 Curable liquid silicone compositions were prepared as follows. (Preparation of Curable Liquid Silicone Composition) At room temperature (23°C), the components were uniformly mixed in a plastic cup in the amounts shown in Table 1 below, and each composition was stored by sealing in a glass bottle. The ingredients were added while mixing in the following order: (A) alkenyl group-containing diorganopolysiloxane, (C) platinum catalyst, (F) addition reaction inhibitor, (G) inorganic filler, (D) melamine resin particles, (E) heat resistance imparting agent, and (B) organohydrogenpolysiloxane.

[0072] The details of each component are as follows: (A) Alkenyl group-containing diorganopolysiloxane: (A-1) A vinyl group-containing linear dimethyl-diphenylpolysiloxane (vinyl group amount: 0.005 mol / 100 g) having a viscosity of 700 mPa·s at 23°C and represented by the following average unit formula: (A-2) A vinyl group-containing linear dimethyldiphenylpolysiloxane (vinyl group content: 0.007 mol / 100 g) having a viscosity of 4,500 mPa·s at 23°C and represented by the following average unit formula:

[0073] (B) Organohydrogenpolysiloxane: (B-1) Linear methylhydrogenpolysiloxane (SiH group amount: 0.0054 mol / g) represented by the following average unit formula: (B-2) Linear methylhydrogenpolysiloxane (SiH group amount: 0.0013 mol / g) represented by the following average unit formula: (B-3) Linear methylhydrogenpolysiloxane (SiH group amount: 0.0029 mol / g) represented by the following average unit formula:

[0074] (C) Platinum catalyst: platinum-divinyltetramethyldisiloxane complex / toluene solution (platinum atom content: 0.5% by mass)

[0075] (D) Melamine resin particles: Resin particles of a polycondensate of melamine and formaldehyde having an average particle size of 0.1 μm

[0076] (E) Heat resistance imparting agent: A mixture of iron octylate and dimethyl diphenyl silicone oil with a viscosity of 800 mPa·s at 23°C, heated at 170°C. Iron concentration: approximately 1,500 ppm

[0077] (F) Addition reaction inhibitor: 3-methyltridec-1-yn-3-ol

[0078] (G) Inorganic filler: fumed silica (specific surface area by BET method: 200 m 2 / g)

[0079] The prepared curable liquid silicone compositions were used to measure the penetration and evaluate the heat resistance using the methods described below. The results are shown in Tables 1 and 2.

[0080] [Penetration] The hardness (penetration) of the heat-cured product of the prepared curable liquid silicone composition was evaluated as follows: The cured product hardness was determined by casting the curable liquid silicone rubber composition immediately after preparation as obtained above into a glass petri dish and heating at 100°C for 1 hour to obtain a cured product having a thickness of approximately 12 mm. The gel-like cured product was subjected to measurement of the penetration specified in JIS K 6249 (¼ cone consistency according to JIS K 2220).

[0081] [Penetration after heat resistance test] The curable liquid silicone composition obtained immediately after preparation in the same manner as above was poured into a glass Petri dish and heated at 100°C for 1 hour. The resulting gel-like cured product, approximately 12 mm thick, was stored at 230°C for 1,500 hours, 250°C for 300 hours, or 250°C for 1,000 hours. The cured product was then cooled to room temperature (23°C), and its hardness (penetration) was measured in the same manner as above.

[0082] [Evaluation of Heat Resistance] Heat resistance was evaluated by measuring the penetration after storage according to the following index: ○: 1 / 2 or more of the initial penetration △: Less than 1 / 2 of the initial penetration and a penetration of 10 or more after storage ×: Less than 1 / 2 of the initial penetration and a penetration of 9 or less after storage

[0083]

[0084]

[0085] From the above results, it is apparent that the curable liquid silicone composition of the present invention can provide a cured product (silicone gel) that has suitable heat curing properties and excellent heat resistance at high temperatures.

Claims

1. A curable liquid silicone composition comprising: (A) a diorganopolysiloxane having an average of at least 0.3 alkenyl groups per molecule; (B) an organohydrogenpolysiloxane having at least two silicon-bonded hydrogen atoms per molecule, in an amount such that there are 0.5 to 4 moles of silicon-bonded hydrogen atoms in component (B) per mole of alkenyl groups in component (A); (C) a platinum catalyst, in an amount such that the platinum atoms in component (C) are 0.1 to 1,000 ppm by mass relative to the combined mass of components (A) and (B); and (D) melamine resin particles, in an amount of 0.001 to 5% by mass relative to the combined mass of components (A) and (B).

2. The curable liquid silicone composition according to claim 1, wherein the melamine resin particles of component (D) are a polycondensation product of melamine and formaldehyde.

3. The curable liquid silicone composition according to claim 1, further comprising (E) at least one additive / filler containing a metal atom as a heat resistance imparting agent: 0.001 to 5 parts by mass per 100 parts by mass of component (A).

4. The curable liquid silicone composition according to claim 1, which cures to give a silicone gel cured product.

5. A cured product of the curable liquid silicone composition according to any one of claims 1 to 4.

6. An electronic component sealed with the cured product according to claim 5.

7. The electronic component according to claim 6, which is an IGBT power module.

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