JP7409090B2 - Silicone rubber composition for mold making and silicone rubber mold - Google Patents

Description

The present invention relates to a silicone rubber composition for mold making and a silicone rubber mold, and more specifically, to an addition-curing thermally conductive silicone rubber composition and a silicone mold matrix (so-called female mold) obtained by curing the composition. .

Manufacturing multiple products by using a silicone rubber mold as an inverted matrix, filling it with resin and curing it is widely practiced, from hobby miniature models to industrial prototype models.
The silicone rubber used in these products is liquid before being cured, and when mixed with a curing agent, it is easily cured at room temperature or by heating, and has the advantage that an inverted mold can be made. On the other hand, however, since it is made of rubber, there is a problem in that the injection-molded resin and the rubber mold come into close contact with each other, making it difficult to release the mold.
As a solution to this problem, mold release agents have generally been used, but this has caused problems in reducing process time.

As a means to solve this problem, Patent Document 1 proposes adding a non-crosslinking silicone polymer having a chain length longer than the crosslinking base polymer, and this has achieved great results in improving mold releasability.
Further, in Patent Document 2, the addition of an oily substance having a refractive index difference of 0.01 or more with the base polymer and a melting point of 100° C. or less has achieved great results in improving mold releasability.
However, this method requires casting into a large mother mold and heating and curing to create an inverted mold, or when creating a resin model that crosslinks at high temperatures, the inverted mold will reach a workable temperature. The problem was that it took a very long time.

Japanese Unexamined Patent Publication No. 7-118534 Japanese Patent Application Publication No. 2000-289034

The present invention was made in view of the above circumstances, and an object of the present invention is to provide a silicone rubber composition for mold making that provides a silicone rubber mold that has excellent thermal conductivity and heat dissipation properties and can be quickly released from the mold. .

As a result of intensive studies to solve the above problems, the present inventors found that a specific addition-curing silicone rubber composition provides a silicone rubber mold that has excellent thermal conductivity and heat dissipation properties and can be quickly released from the mold. They discovered this and completed the present invention.

That is, the present invention
1. (A) 100 parts by mass of organopolysiloxane having at least two alkenyl groups bonded to silicon atoms in one molecule and having a viscosity of 30 to 50,000 mPa·s at 25°C;
(B) Crystalline silica with an average particle diameter of 0.1 to 50 μm: 100 to 400 parts by mass,
(C) Amorphous silica with a specific surface area of 50 m ² /g or more by BET method: 3 to 40 parts by mass,
(D) Organopolysiloxane having at least two hydrogen atoms bonded to a silicon atom in one molecule: for one alkenyl group bonded to a silicon atom in component (A), one silicon atom in component (D) A mold-making silicone rubber composition containing an amount such that the number of bonded hydrogen atoms is 0.3 to 5, and (E) a platinum-based catalyst;
2. 1. A mold-making silicone rubber composition, wherein the crystalline silica has a spherical or irregular shape;
3. 1 or 2 silicone rubber composition for mold making, wherein the crystalline silica is surface-treated with a surface treatment agent;
4. 3. The silicone rubber composition for mold making, wherein the surface treatment agent is a siloxane compound having an alkoxysilyl group at the end;
5. A mold-making agent consisting of the silicone rubber composition for mold-making according to any one of 1 to 4;
6. a silicone rubber mold obtained by curing the silicone rubber composition for mold making according to any one of 1 to 4;
7. 6 a silicone rubber mold having a thermal conductivity of 0.4 W/(m·K) or more;
8. Provided is a silicone rubber mold 6 or 7 having a tear strength of 5 (kN/m) or more.

The silicone rubber mold obtained by curing the mold-making silicone rubber composition of the present invention has excellent thermal conductivity and heat dissipation, so the time required to cool it to a temperature that allows mold release can be shortened. It is particularly useful as a mold for resins with high curing temperatures such as nylon, and as an inverted mold for large parts for aircraft and automobiles.

The present invention will be specifically explained below.
In the present invention, the silicone rubber composition for mold-making is fluid in an uncured state and is applied to the entire surface or a part of the surface of the mold by a method such as casting or coating. It refers to an uncured (liquid) composition that is cured in an uncured state to form a mold (matrix for mold making) for replication using resin or the like.

The silicone rubber composition for mold making according to the present invention contains the following components (A) to (E).
(A) Organopolysiloxane having at least two alkenyl groups bonded to silicon atoms in one molecule and having a viscosity of 30 to 50,000 mPa・s at 25°C (B) Average particle size of 0.1 to 50 μm Crystalline silica (C) Amorphous silica with a specific surface area of 50 m ² /g or more by BET method (D) Organopolysiloxane (E) platinum-based organopolysiloxane having at least two hydrogen atoms bonded to silicon atoms in one molecule catalyst

[1] Component (A) Component (A), an organopolysiloxane having at least two alkenyl groups bonded to a silicon atom in one molecule, can be crosslinked with the silicone rubber composition for mold making of the present invention to form a rubber. It is the main ingredient for becoming
The viscosity of component (A) is 30 to 50,000 mPa·s, preferably 50 to 10,000 mPa·s, and more preferably 100 to 1,000 mPa·s. If the viscosity exceeds 50,000 mPa·s, the filling properties of the crystalline silica described below will deteriorate, and if the viscosity is less than 30 mPa·s, the cured product will become brittle. Note that the viscosity in the present invention is a value measured at 25° C. using a rotational viscometer.

Such an organopolysiloxane is not particularly limited as long as it satisfies the above viscosity and alkenyl group content, and any known organopolysiloxane can be used, and its structure may be linear or branched, or may have a different structure. It may also be a mixture of two or more organopolysiloxanes having different viscosities.

The alkenyl group bonded to the silicon atom is not particularly limited, but an alkenyl group having 2 to 10 carbon atoms is preferable, and an alkenyl group having 2 to 8 carbon atoms is more preferable.
Specific examples thereof include vinyl, allyl, 1-butenyl, and 1-hexenyl groups. Among these, a vinyl group is preferred from the viewpoint of ease of synthesis and cost.
Further, the number of alkenyl groups is not particularly limited as long as it is 2 or more, but 2 to 10 is preferred.
Note that alkenyl groups may be present at the ends (both ends or one end) of the molecular chain of organopolysiloxane, or in the middle, but in terms of flexibility of the resulting silicone rubber mold, only both ends are required. Preferably, it exists in

The organic group other than the alkenyl group bonded to the silicon atom is not particularly limited, but is preferably a monovalent hydrocarbon group with 1 to 20 carbon atoms, more preferably a monovalent hydrocarbon group with 1 to 10 carbon atoms. .
Specific examples thereof include alkyl groups such as methyl, ethyl, n-propyl, n-butyl, n-hexyl, and n-dodecyl groups; aryl groups such as phenyl groups; 2-phenylethyl, 2-phenylpropyl groups, etc. Examples include aralkyl groups.
Further, some or all of the hydrogen atoms of these hydrocarbon groups may be substituted with halogen atoms such as chlorine, fluorine, and bromine. Specific examples thereof include fluoromethyl, bromoethyl, chloromethyl, 3, Examples include halogen-substituted monovalent hydrocarbon groups such as 3,3-trifluoropropyl group.
Among these, alkyl groups having 1 to 5 carbon atoms are preferred, and from the viewpoint of ease of synthesis and cost, it is more preferred that 90 mol% or more be methyl groups.

Specific examples of component (A) include dimethylsiloxane/methylvinylsiloxane copolymer with trimethylsiloxy groups endblocked at both molecular chain ends, methylvinylpolysiloxane endblocked with trimethylsiloxy groups at both molecular chain ends, and methyl endblocked with trimethylsiloxy groups at both molecular chain ends. Vinylsiloxane/methylphenylsiloxane copolymer, dimethylsiloxane/methylvinylsiloxane/methylphenylsiloxane copolymer blocked with trimethylsiloxy groups at both molecular chain ends, dimethylpolysiloxane blocked with dimethylvinylsiloxy groups at both molecular chain ends, dimethyl at both molecular chain ends Dimethylsiloxane/methylvinylsiloxane copolymer blocked with vinylsiloxy groups, methylvinylpolysiloxane blocked with dimethylvinylsiloxy groups at both molecular chain ends, methylvinylsiloxane/methylphenylsiloxane copolymer blocked with dimethylvinylsiloxy groups at both molecular chain ends, molecular chain Dimethylsiloxane/methylvinylsiloxane/methylphenylsiloxane copolymer with dimethylvinylsiloxy groups blocked at both ends, dimethylsiloxane/methyl(3,3,3-trifluoropropyl)siloxane copolymer with dimethylvinylsiloxy groups blocked at both molecular chain ends, Examples include dimethylsiloxane, methylvinylsiloxane, methyl(3,3,3-trifluoropropyl)siloxane copolymers with dimethylvinylsiloxy groups blocked at both molecular chain ends, and among them, dimethylpolymer with dimethylvinylsiloxy groups blocked at both molecular chain ends. Particularly preferred are siloxanes.
In addition, (A) component may be used individually by 1 type, or may use 2 or more types together.

[2] Component (B) Component (B) crystalline silica is a component for improving the thermal conductivity of a silicone rubber mold obtained by curing the silicone rubber composition for mold making of the present invention.
The shape of component (B) is not limited and may be spherical, plate-like, or irregular.
Furthermore, the average particle diameter of component (B) is within the range of 0.1 to 50 μm, but is preferably within the range of 0.1 to 20 μm in order to prevent sedimentation in the composition.
Furthermore, component (B) is added using the ignition loss method specified in JIS H 1901 (heating temperature 1,100°C, heating time 1 hour) in order to improve the thermal stability of the hardness of the obtained cured product. It is preferable that the loss on ignition is 0.25% by mass or less as measured according to .

Component (B) is preferably surface-treated with a surface treatment agent, thereby facilitating mixing with component (A) and preventing separation and sedimentation of component (B) from the composition. , the viscosity of the composition can be lowered.
As surface treatment agents, organoalkoxysilanes such as methyltrimethoxysilane, methyltriethoxysilane, vinyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane, n-octyltrimethoxysilane; tetramethoxysilane, tetrapropoxysilane, Tetraalkoxysilanes such as ethyl polysilicate or their partially hydrolyzed condensates; organohalosilanes such as dimethyldichlorosilane and methyltrichlorosilane; organosilazanes such as hexamethyldisilazane; dimethylhydroxysiloxy group-blocked diorganosiloxane oligomers, cyclopolysilanes, etc. Examples include organosilicon compounds such as organosiloxane and organopolysiloxane represented by the following formula (1); amine compounds such as tri-n-butylamine and tri-n-octylamine.
Among these, organoalkoxysilanes, tetraalkoxysilanes or partially hydrolyzed condensates thereof, and organopolysiloxanes represented by the following general formula (1) are preferred from the viewpoint of ease of surface treatment operation.

（式中、Ｒ¹は、それぞれ独立して、非置換または置換の一価炭化水素基を表し、Ｒ²は、それぞれ独立して、アルキル基、アルコキシアルキル基、アルケニル基またはアシル基を表し、ｎは、２～１００の整数を表し、ａは、１～３の整数を表す。）

(wherein R ¹ each independently represents an unsubstituted or substituted monovalent hydrocarbon group, R ² each independently represents an alkyl group, an alkoxyalkyl group, an alkenyl group, or an acyl group, n represents an integer from 2 to 100, and a represents an integer from 1 to 3.)

The monovalent hydrocarbon group of R ¹ is not particularly limited, but is preferably a monovalent hydrocarbon group having 1 to 10 carbon atoms, more preferably a monovalent hydrocarbon group having 1 to 6 carbon atoms, and is preferably a monovalent hydrocarbon group having 1 to 6 carbon atoms. One to three monovalent hydrocarbon groups are more preferred.
Specific examples of monovalent hydrocarbon groups include alkyl groups, alkenyl groups, aryl groups, aralkyl groups, and some or all of the hydrogen atoms of these monovalent hydrocarbon groups are substituted with halogen atoms such as chlorine, fluorine, and bromine. Examples include halogenated monovalent hydrocarbon groups such as halogenated alkyl groups.

The alkyl group may be linear, branched, or cyclic, and specific examples thereof include linear alkyl groups such as methyl, ethyl, n-propyl, n-hexyl, and n-octyl; isopropyl, Examples include branched alkyl groups such as isobutyl, tert-butyl, and 2-ethylhexyl groups; and cyclic alkyl groups such as cyclopentyl and cyclohexyl groups.
Specific examples of alkenyl groups include vinyl, allyl, 1-butenyl, 1-hexenyl, and the like.
Specific examples of the aryl group include phenyl and tolyl groups.
Specific examples of the aralkyl group include 2-phenylethyl, 2-methyl-2-phenylethyl, and the like.
Specific examples of the halogenated alkyl group include 3,3,3-trifluoropropyl, 2-(nonafluorobutyl)ethyl, and 2-(heptadecafluorooctyl)ethyl groups.
Among these, R ¹ is preferably an alkyl group, more preferably an alkyl group having 1 to 6 carbon atoms, and even more preferably a methyl group.

Examples of the alkyl group and alkenyl group for R ² include the same groups as those exemplified for R ¹ above, examples of the alkoxyalkyl group include methoxyethyl and methoxypropyl groups, and examples of the acyl group include: Examples include acetyl and octanoyl groups.
Among these, R ² is preferably an alkyl group, more preferably a methyl group or an ethyl group.
n is an integer of 2 to 100, preferably an integer of 5 to 80.
a is an integer from 1 to 3, preferably 3.

Surface treatment may be performed in advance by adding a surface treatment agent to component (B) and heating and stirring in a mixer, or when combining component (B) with component (A), the surface treatment agent may be added at the same time. Alternatively, the mixture may be heated and stirred using a mixer.
The amount of the surface treatment agent to be blended is not particularly limited, but is preferably 0.05 to 30% by mass based on component (B).

The amount of component (B) to be blended is within the range of 100 to 400 parts by weight, preferably 140 to 300 parts by weight, per 100 parts by weight of component (A). If it is less than the lower limit of the above range, sufficient thermal conductivity cannot be imparted to the silicone rubber, and if it exceeds the upper limit of the above range, the viscosity and density of the composition will increase excessively, resulting in a decrease in workability.

[3] Component (C) Component (C) is amorphous silica having a specific surface area of 50 m ² /g or more, preferably 50 to 500 m ² /g, more preferably 150 to 350 m ² /g, as measured by the BET method. is a component for imparting mechanical properties such as tensile strength, tear strength, and elongation at break to the cured product obtained from the silicone rubber composition of the present invention.
Examples of the amorphous silica include fumed silica, precipitated silica, and silica whose surface has been hydrophobized, and these may be used alone or in combination of two or more.

Examples of such silica include hydrophilic silica such as Aerosil 130, 200, 300 (manufactured by Nippon Aerosil Co., Ltd.), Cabosil MS-5, MS-7 (manufactured by Cabot), Rheorosil QS-102, 103 (( Fumed silica such as Tokuyama Co., Ltd.); precipitated silica such as Tokusil US-F (Tokuyama Co., Ltd.) and Nipsil LP (Nippon Silica Kogyo Co., Ltd.); examples of hydrophobic silica include Fumed silica such as Aerosil R-812, R-812S, R-972, R-974 (manufactured by Nippon Aerosil Co., Ltd.), Rheosil MT-10 (manufactured by Tokuyama Co., Ltd.); Nipsil SS series (manufactured by Nippon Silica Kogyo Co., Ltd.); Examples include precipitated silica such as those manufactured by Co., Ltd.).

These amorphous silicas may be used as they are, but they may be treated with a surface treatment agent to make the surface hydrophobic, or a surface treatment agent may be added to the amorphous silica when kneading component (A). It is preferable to use the surface after hydrophobic treatment. Examples of the surface treatment agent include alkylalkoxysilane, alkylhydroxysilane, alkylchlorosilane, alkylsilazane, silane coupling agent, low molecular weight polysiloxane, titanate treatment agent, fatty acid ester, etc., and preferably alkyldisilazane, more preferably is hexamethyldisilazane. These surface treating agents may be used alone or in combination of two or more at different timings.
The amount of surface treatment agent used is preferably 0.5 to 50 parts by weight, more preferably 1 to 40 parts by weight, and even more preferably 2 to 30 parts by weight, based on 100 parts by weight of amorphous silica. When the amount of the surface treatment agent used is within the above range, no surface treatment agent or its decomposition product remains in the composition, fluidity is obtained, and increase in viscosity over time can be suppressed.

The blending amount of component (C) is 3 to 40 parts by weight per 100 parts by weight of component (A), from the viewpoint of ease of handling the composition and mechanical strength of the cured product, but 5 to 30 parts by weight is preferred. preferable. If the amount of component (C) is less than 3 parts by mass, the mechanical properties of the resulting cured product will be insufficient, and if it exceeds 50 parts by mass, the viscosity of the composition will become high, making it difficult to cast into a matrix. becomes.

[4] Component (D) Component (D) is an organopolysiloxane having at least two hydrogen atoms (SiH groups) bonded to silicon atoms in one molecule, and has a hydrosilyl group with an alkenyl group in component (A). This is a component for crosslinking and curing the silicone rubber composition of the present invention.
The molecular structure of component (D) is not particularly limited as long as it satisfies the content of hydrogen atoms bonded to silicon atoms, and may be linear, partially branched, branched, or cyclic. Among these, straight chain shape and partially branched straight chain shape are particularly preferred.

The weight average molecular weight of component (D) is not particularly limited, but in consideration of improving the workability of the composition and the mechanical properties of the cured product, it is preferably 1,000 to 30,000, and 1,500 to 30,000. ˜10,000 is more preferable. Note that the weight average molecular weight is a standard polystyrene equivalent value determined by gel permeation chromatography (GPC).

Specific examples of the organohydrogenpolysiloxane of component (D) include dimethylpolysiloxane with dimethylhydrogensiloxy groups at both ends of the molecular chain, methylhydrogenpolysiloxane with dimethylhydrogensiloxy groups at both ends of the molecular chain, and methylhydrogenpolysiloxane with dimethylhydrogensiloxy groups at both ends of the molecular chain. dimethylsiloxane/methylhydrogensiloxane copolymer blocked with dimethylhydrogensiloxy groups, methylhydrogenpolysiloxane blocked with trimethylsiloxy groups at both molecular chain ends, dimethylsiloxane/methylhydrogensiloxane copolymer blocked with trimethylsiloxy groups at both molecular chain ends, Methylhydrogenpolysiloxane with silanol groups at both ends of the molecular chain, dimethylsiloxane/methylhydrogensiloxane copolymer with silanol groups at both ends of the molecular chain, siloxane unit represented by the formula: (CH ₃ ) ₃ SiO _1/2 and the formula: Organopolysiloxane consisting of a siloxane unit represented by (CH ₃ ) ₂ HSiO _1/2 and the formula: SiO _4/2 , a siloxane unit represented by the formula (CH ₃ ) ₂ HSiO _1/2 and the formula : Organopolysiloxane consisting of siloxane units represented by the formula: (CH ₃ )HSiO _2/2 and siloxane units represented by the formula: CH ₃ SiO _{3/2 or} formula: HSiO ₃ Examples include organopolysiloxanes consisting of siloxane units represented by _/2 , and organopolysiloxanes in which some of the methyl groups of these organopolysiloxanes are substituted with phenyl groups, 3,3,3-trifluoropropyl groups, etc.

The amount of component (D) to be blended is such that the number of silicon-bonded hydrogen atoms in this component is within the range of 0.3 to 5 per alkenyl group in component (A), and is preferably , the number of silicon-bonded hydrogen atoms in this component is within the range of 0.5 to 3 per alkenyl group in component (A). If it is less than the lower limit of the above range, the crosslinking density of the cured product will be insufficient, resulting in inferior heat resistance and mechanical properties, and if it exceeds the upper limit of the above range, foaming will likely occur due to the generation of hydrogen gas during curing. The rubber strength decreases due to the generation of voids inside the cured product.
In addition, (D) component may be used individually by 1 type, or may use 2 or more types together.

[5] Component (E) The platinum-based catalyst of component (E) is a hydrosilylation reaction catalyst for promoting the hydrosilylation reaction between the alkenyl group in component (A) and the SiH group in component (B). .
Specific examples include fine particle platinum, chloroplatinic acid, alcohol-modified products of chloroplatinic acid, platinum chelate compounds, complexes of platinum and diketones, coordination compounds of chloroplatinic acid and olefins, and combinations of chloroplatinic acid and alkenylsiloxanes. Examples include complexes and those supported on carriers such as alumina, silica, and carbon black.
Among these, complexes of chloroplatinic acid and alkenylsiloxane are preferred because they have high activity as catalysts for hydrosilylation reactions, and platinum alkenylsiloxane complexes as disclosed in Japanese Patent Publication No. 42-22924 are particularly preferred.
Further, it is also possible to use a spherical fine particle catalyst made of a thermoplastic resin containing a platinum-based catalyst in an amount of 0.01% by mass or more as platinum metal atoms.
In addition, (E) component may be used individually by 1 type, or may be used in combination of 2 or more types.

The amount of component (E) to be blended is not limited as long as it promotes curing (hydrosilylation reaction) of the composition, and the amount of metal atoms in this component is 0 in terms of mass relative to the mass of component (A). The range is preferably from .01 to 500 ppm, and more preferably from 1 to 50 ppm. Within this range, the reaction rate of the addition reaction will be appropriate.

[6] (F) Component In the silicone rubber composition for mold making of the present invention, hydrosilyl is added to the silicone rubber composition for mold making to prevent thickening or gelling during preparation of the composition or before heat curing during mold making. For the purpose of controlling the reactivity of the reaction catalyst, (F) a reaction control agent may be added as necessary.
Specific examples of reaction controlling agents include 3-methyl-1-butyn-3-ol, 3-methyl-1-pentyn-3-ol, 3,5-dimethyl-1-hexyn-3-ol, 1-ethynyl -1-cyclohexanol, ethynylmethyldecylcarbinol, 3-methyl-3-trimethylsiloxy-1-butyne, 3-methyl-3-trimethylsiloxy-1-pentyne, 3,5-dimethyl-3-trimethylsiloxy-1 -Hexyne, 1-ethynyl-1-trimethylsiloxycyclohexane, bis(2,2-dimethyl-3-butynoxy)dimethylsilane, 1,3,5,7-tetramethyl-1,3,5,7-tetravinylcyclo Examples include tetrasiloxane, 1,1,3,3-tetramethyl-1,3-divinyldisiloxane, and these may be used alone or in combination of two or more.
Among these, 1-ethynylcyclohexanol, ethynylmethyldecylcarbinol, and 3-methyl-1-butyn-3-ol are preferred.

When using component (F), the amount added is preferably 0.01 to 3.0 parts by weight, more preferably 0.01 to 1.5 parts by weight, per 100 parts by weight of component (A). Within this range, the effect of reaction control is fully exhibited.

[7] Other components In addition to the above-mentioned components (A) to (F), the silicone rubber composition for mold making of the present invention may contain other components as exemplified below, as long as they do not impair the purpose of the present invention. You may.
Other ingredients include conductive agents such as iron oxide, carbon black, conductive zinc white, and metal powder; heat-resistant agents such as titanium oxide and cerium oxide; internal mold release agents such as dimethyl silicone oil; adhesion imparting agents; A coloring agent, etc. may be mentioned.

Specific examples of colorants include inorganic pigments such as ultramarine, iron oxide, titanium oxide, titanium yellow, carbon black, zinc white, and chrome green; anthraquinone violet, anthraquinone blue, industhrene blue, alizanine green, perison red, etc. organic pigments; metal powder pigments such as aluminum powder, copper powder, bronze powder, and tin powder; phosphorescent pigments; fluorescent pigments; and dyes that do not inhibit curing. You can choose.

Also, an organopolysiloxane consisting of a siloxane unit represented by the formula: (CH ₃ ) ₃ SiO _1/2 and a siloxane unit represented by the formula: SiO _4/2 , the formula: CH ₂ =CH(CH ₃ ) ₂ SiO _1/ Organopolysiloxane consisting of siloxane units represented by ₂ and the formula: (CH ₃ ) ₃ SiO _1/2 and siloxane units represented by the formula: SiO _4/2 , formula: CH ₂ =CH (CH ₃ ) ₂ SiO _1/2 siloxane unit and formula: (CH ₃ ) ₃ SiO _1/2 silicon atom bond such as organopolysiloxane consisting of siloxane unit and formula: SiO _3/2 siloxane unit and formula: (CH 3 ) 3 Organopolysiloxane resins that do not have hydrogen atoms and are solid at 25° C. may also be used.
When an organopolysiloxane resin is used, the amount thereof is preferably 0.1 to 80 parts by weight, more preferably 1 to 50 parts by weight, per 100 parts by weight of component (A).

The mold-making silicone rubber composition of the present invention can be prepared by mixing the above-mentioned components (A) to (E) and other components by a known method using a kneader, planetary mixer, or the like.
The silicone rubber composition for mold making of the present invention comprises a first agent consisting of component (A), component (B), component (C), component (E), and other components as necessary; Component (B) component, (C) component, (D) component, and if necessary, a second component consisting of components and other components are prepared separately, and the first component and second component are mixed before use. It may also be a mold composition. Note that there may be components that are commonly used in the first part and the second part. By making the composition into such a two-dose form, further storage stability can be ensured.

A silicone rubber mold can be obtained by casting the mold-making silicone rubber composition of the present invention in a predetermined mold and curing it. In particular, it is preferable to perform casting using vacuum casting, and the curing conditions include, for example, curing proceeds at room temperature (5 to 35°C), but curing can also be accelerated by heating, and when it is desired to improve mass productivity. This method is effective for
When heat curing is carried out, it can usually be carried out at a temperature of 40 to 60°C for about 2 to 20 hours.

The silicone rubber mold obtained from the mold-making silicone rubber composition of the present invention can be effectively used for molding resin moldings such as nylon resin, epoxy resin, urethane resin, and the like. It is particularly suitable for molding nylon resin, which requires a heat distortion temperature of 50 to 200°C, preferably 70 to 180°C, for melting.

The thermal conductivity of the cured product of the mold-making silicone rubber composition of the present invention is preferably 0.4 W/(m·K) or more, more preferably 0.6 W/(m·K) or more. The upper limit of thermal conductivity is not particularly limited, but is usually 3.0 W/(m·K) or less.
Furthermore, the tear strength of the cured product of the silicone rubber composition for mold making of the present invention is preferably 5 kN/m or more, more preferably 10 kN/m or more. The upper limit of tear strength is not particularly limited, but is usually 30 kN/m or less.

EXAMPLES Hereinafter, the present invention will be explained in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples.

[Examples 1 to 4, Comparative Examples 1 to 3]
The following components were mixed at the blending ratio (parts by mass) shown in Table 1 to prepare a silicone rubber composition. Specifically, component (A), component (B), component (C), 4 parts by mass of hexamethyldisilazane, and 1.2 parts by mass of water were mixed at 25°C for 1 hour using a kneader, and then mixed at 150 °C. ℃ for 2 hours, 1.2 parts by mass of organopolysiloxane represented by the following average formula (2) was added, and after further mixing at 150℃ for 2 hours, the mixture was cooled to 25℃, and component (D) and ( After adding and mixing component F), component (E) was added in an amount of 10 ppm based on the entire composition in terms of mass of platinum, and after mixing, degassing was performed under reduced pressure to obtain a silicone rubber composition. Ta.

(A) Component:
(A-1) Dimethylpolysiloxane with a viscosity of 600 mPa·s at 25°C with both ends blocked with dimethylvinylsilyl groups (vinyl value: 0.0124 mol/100 g)
(A-2) Dimethylpolysiloxane with a viscosity of 30,000 mPa・s at 25°C with both ends blocked with dimethylvinylsilyl groups (vinyl value: 0.00277 mol/100 g)
(A-3) Dimethylpolysiloxane with a viscosity of 10,000 mPa·s at 25°C with both ends blocked with dimethylvinylsilyl groups (vinyl value: 0.00430 mol/100 g)

(B) Component:
(B-1) Crystalline silica (manufactured by CBC Co., Ltd., KAIDA SP5, average particle size 5 μm, amorphous)

(C) Component:
(C-1) Fumed silica (manufactured by Nippon Aerosil Co., Ltd., Aerosil 200, BET specific surface area 200 m ² /g)

（式中、シロキサン単位の配列はランダムまたはブロックである。） (D) Component:
(D-1) Methyl hydrogen polysiloxane represented by the following average formula (3) (weight average molecular weight: 3,000)

(In the formula, the arrangement of siloxane units is random or block.)

(D-2) Methyl hydrogen polysiloxane represented by the following average formula (4) (weight average molecular weight: 2,500)

（式中、シロキサン単位の配列はランダムまたはブロックである。） (D-3) Methyl hydrogen polysiloxane represented by the following average formula (5) (weight average molecular weight: 1,500)

(In the formula, the arrangement of siloxane units is random or block.)

(E) Component:
(E-1) Chloroplatinic acid octyl alcohol complex

(F) Ingredient:
(F-1) 1-ethynyl-1-cyclohexanol

¹⁾（Ａ）成分に対して白金が１０質量ｐｐｍとなる量
²⁾（Ａ）成分中の珪素原子に結合するアルケニル基１個に対する（Ｄ）成分中の珪素原子に結合する水素原子の数の比

¹⁾ Amount that makes platinum 10 mass ppm relative to component (A)
²⁾ Ratio of the number of hydrogen atoms bonded to silicon atoms in component (D) to one alkenyl group bonded to silicon atoms in component (A)

The following properties were evaluated using the silicone rubber compositions prepared in Examples 1 to 4 and Comparative Examples 1 to 3 above. The results are shown in Table 2.
[Thermal conductivity]
The silicone rubber composition was poured into a mold with a size of 5 cm x 15 cm x 1 cm, and the cured product was cured at 60 °C for 2 hours. The thermal conductivity at an environmental temperature of 25 °C was measured using a hot disk method thermophysical property measuring device ( Measurement was performed using TPA-501 (manufactured by Kyoto Electronics Industry Co., Ltd.).
[Time to reach 30℃]
The cured product used for the thermal conductivity measurement was further exposed to an environment of 150°C for 30 minutes, then taken out to an environment of 23°C, and the surface temperature of the cured product was measured using a thermocouple (manufactured by Keyence Corporation, TR-W550). The time required for the temperature to reach 30°C was measured.
[hardness]
The silicone rubber composition was poured into a mold to a thickness of 2 mm and cured at 60° C. for 2 hours. The hardness (durometer A) of the cured product was measured in accordance with JIS K 6253-3:2012. Further, the hardness of a cured product prepared in the same manner was measured in the same manner as above after being exposed to a 180° C. environment for 150 hours.
[Tensile strength, elongation at break]
The tensile strength (MPa) and The elongation at break (%) was measured for each.
Further, a dumbbell-shaped test piece prepared in the same manner was exposed to an environment of 180° C. for 150 hours, and then the above-mentioned physical properties were measured.
[Tear strength]
A silicone rubber composition was poured into a mold to a thickness of 2 mm, and the tear strength (kN/m) of the crescent-shaped test piece was cured at 60°C for 2 hours in accordance with JIS K 6252-1:2015. It was measured.
Further, the tear strength of a crescent-shaped test piece prepared in the same manner was measured in the same manner as above after being exposed to a 180° C. environment for 150 hours.

As shown in Table 2, the cured products obtained from the mold-making silicone rubber compositions of the present invention prepared in Examples 1 to 4 have excellent heat conduction properties and heat dissipation properties, sufficient strength, It can be seen that it has excellent hardness stability even when held at high temperatures for a long period of time.
On the other hand, in Comparative Example 1, which does not contain component (B) of the present invention, and Comparative Example 3, in which the amount of component (B) added is insufficient, the thermal conductivity is low and it takes time for heat dissipation after heating. Furthermore, it can be seen that Comparative Example 2, which does not contain component (C) of the present invention, is inferior in tensile strength, elongation at break, and tear strength, and is not suitable for molding.

Claims (8)

(A) 100 parts by mass of organopolysiloxane having at least two alkenyl groups bonded to silicon atoms in one molecule and having a viscosity of 30 to 50,000 mPa·s at 25°C;
(B) Crystalline silica with an average particle diameter of 0.1 to 50 μm: 100 to 400 parts by mass,
(C) Amorphous silica with a specific surface area of 50 m ² /g or more by BET method: 3 to 40 parts by mass,
(D) Organopolysiloxane having at least two hydrogen atoms bonded to a silicon atom in one molecule: for one alkenyl group bonded to a silicon atom in component (A), one silicon atom in component (D) Contains an amount such that the number of bonded hydrogen atoms is 0.3 to 5, and (E) a platinum-based catalyst,
A silicone rubber composition for mold making, wherein the crystalline silica is surface-treated with a surface treatment agent, and the surface treatment agent is an organopolysiloxane represented by the following general formula (1) having an alkoxysilyl group at a terminal. thing.

(wherein R ¹ each independently represents an unsubstituted or substituted monovalent hydrocarbon group, R ² each independently represents an alkyl group, an alkoxyalkyl group, an alkenyl group, or an acyl group, n represents an integer from 2 to 100, and a represents an integer from 1 to 3.) The silicone rubber composition for mold making according to claim 1, wherein the crystalline silica has a spherical or irregular shape. The silicone rubber composition for mold making according to claim 1 or 2, wherein the R ¹ is an alkyl group having 1 to 6 carbon atoms, and the R ² is a methyl group or an ethyl group . The silicone rubber composition for mold making according to any one of claims 1 to 3, wherein the a is 3 and the n is an integer of 5 to 80 . A mold-making agent comprising the silicone rubber composition for mold-making according to any one of claims 1 to 4. A silicone rubber mold obtained by curing the silicone rubber composition for mold making according to any one of claims 1 to 4. The silicone rubber mold according to claim 6, which has a thermal conductivity of 0.4 W/(m·K) or more. The silicone rubber mold according to claim 6 or 7, which has a tear strength of 5 (kN/m) or more.