JP2003221507A - Thermosetting silicone rubber composition - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thermosetting silicone rubber composition exhibiting less mold soiling. <P>SOLUTION: This thermosetting silicone rubber composition is characterized by containing (A) 100 pts.wt. organopolysiloxane unvulcanized rubber containing an alkenyl group and having terminal units of which ≤20 mol % of terminals are blocked by a silanol group, (B) 1-20 pts.wt. silicone oil containing a phenyl group, (C) 5-100 pts.wt. silica filler having ≥50 m<SP>2</SP>/g specific surface area and (D) a curing agent of necessary amount, and exhibiting ≤8 whiteness (L-value) of a stainless steel plate after setting the stainless steel plate as mirror-finished to have ≤2 whiteness (L-value) in a mold and performing injection molding by 100 shots continuously at 170°C, and by 150 sec. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat-curable silicone rubber composition which is less likely to stain the mold during molding.

[0002]

2. Description of the Related Art Generally, a rubber composition is formed into a molded product by using a mold under high temperature and high pressure. The most important thing in the manufacturing process of this molded product is to use a rubber composition with little mold stain. If there is a lot of mold stains, the surface of the molded product loses its luster,
The defective rate increases. Further, when such a phenomenon occurs, the mold must be washed, but this work has a problem that it takes a very long time.

This mold stain has been a problem for a long time, but the mold stain evaluation method is a qualitative evaluation by visual observation of the mold surface and the surface of a molded product during continuous molding. Due to inadequate systematic analysis, a sufficient mechanism has not yet been clarified.

Therefore, an object of the present invention is to establish a method for quantitatively evaluating mold stains during continuous molding, and to provide a heat-curable silicone rubber composition with little mold stains.

[0005]

Means for Solving the Problems and Modes for Carrying Out the Invention The present inventor has made extensive studies as a result of achieving the above object,
Mirror-finished stainless steel plate in the mold (SUS
Plate) was set, the SUS plate was taken out of the mold at regular intervals, and the change in the surface was traced with a spectrocolorimeter. However, when it exceeds 8, it is clearly soiled. Therefore, we found that it is possible to quantitatively evaluate the soiling of the mold during continuous molding by the whiteness, and as a result of diligent study on the soiling factor, we found that the base polymer It was found that the mold fouling is remarkably improved by making the ratio of the terminal terminated by the silanol group in the alkenyl group-containing organopolysiloxane raw rubber which is 10 mol% or less of the terminal unit, and the present invention is completed. Came to.

[0006] Conventionally, as the alkenyl group-containing organopolysiloxane raw rubber which is the base polymer of this type of heat-curable silicone rubber composition, it is known to use the one whose end is blocked with a triorganosiloxy group. It is described in. However, in spite of the above description, the alkenyl group-containing organopolysiloxane raw rubber that has been actually used in the past has a terminal unit of 20 units.
The silanol groups were present in excess of mol%.
This is because the alkenyl group-containing organopolysiloxane raw rubber of this kind was mainly obtained by equilibration in the presence of a basic catalyst, and in the equilibration reaction, a trace amount of water contained in the raw material was used. Since it acts as a terminal stopper, the terminal was blocked with a silanol group in a considerable proportion, but the present inventor, as described above, was blocked with a silanol group in such a significant proportion. When an alkenyl group-containing organopolysiloxane raw rubber is used, mold fouling is liable to occur, whereas the terminal terminated by a silanol group is 20 mol% or less of the terminal unit, in other words, the terminal blocking rate by a triorganosiloxy group. When using an alkenyl group-containing organopolysiloxane raw rubber with a content of 80 mol% or more, mold stains do not easily occur It has been found the door. In this case, the silanol groups generally do not adversely affect mold fouling, but the terminal silanol groups of the alkenyl group-containing organopolysiloxane raw rubber having a high degree of polymerization, which is the base polymer, adversely affect mold fouling. The thing is
As will be described later, the fact that the terminal silanol group-containing organosilicon compound of the formula (2) is recommended to be added as the component (E) is also recognized.

Therefore, according to the present invention, (A) 100 parts by weight of alkenyl group-containing organopolysiloxane raw rubber having 20 mol% or less of terminal units terminated with silanol groups (B) Phenyl group-containing silicone oil 1-20 Parts by weight (C) Silica filler having a specific surface area of 50 m ² / g or more 5 to 100 parts by weight (D) A stainless steel plate containing a necessary amount of a curing agent and having a mirror finish of whiteness (L value) of 2 or less. Set in the mold at 170 ℃, 1
Provided is a heat-curable silicone rubber composition, wherein the whiteness (L value) of the stainless steel plate after continuous injection molding for 100 times in 50 seconds is 8 or less.

The present invention will be described in more detail below.
The heat-curable silicone rubber composition of the present invention is particularly suitable for injection molding and contains an organopolysiloxane raw rubber, a phenyl group-containing silicone oil, a silica filler, and a curing agent.

Here, as the alkenyl group-containing organopolysiloxane raw rubber having a silanol group-terminated terminal of the component (A), which is 20 mol% or less of the terminal unit, one represented by the following average composition formula (3) is used. can do. R ² _a SiO _{(4-a) / 2} (3) In the formula, R ² is an alkyl group such as a methyl group, an ethyl group, a propyl group, a butyl group, a cycloalkyl group such as a cyclohexyl group, a vinyl group, an allyl group, Butenyl group, alkenyl group such as hexenyl group, phenyl group, aryl group such as tolyl group or part or all of the hydrogen atoms bonded to carbon atoms of these groups are halogen atoms, chloromethyl group substituted with a cyano group, The same or different, preferably selected from a trifluoropropyl group, a cyanoethyl group, etc., preferably having 1 to 1 carbon atoms.
10, more preferably an unsubstituted or substituted monovalent hydrocarbon group having 1 to 8 carbon atoms. Also, a is 1.98 to 2.02.
Is a positive number, and the end of the molecular chain is blocked with a triorganosiloxy group (R ² ₃ SiO group) such as a trimethylsiloxy group, a dimethylphenylsiloxy group, a dimethylvinylsiloxy group, a methyldivinylsiloxy group, a trivinylsiloxy group. However, 50 mol% or more, particularly 80 mol% or more of R ² in the above formula (3) is a methyl group, and about 0.01 to 15 mol%, particularly 0.1.
It is preferable to have 02 to 5 mol% of an alkenyl group, particularly a vinyl group. Although this organopolysiloxane is linear, it may be branched within a range that does not impair rubber elasticity, and its molecular weight is an average degree of polymerization of 2,000 to 100,
000, particularly preferably 3,000 to 20,000.

The end of the organopolysiloxane is capped with a triorganosiloxy group such as dimethylvinylsiloxy group or trimethylsiloxy group as described above.
It is desirable that the content is 0 mol%, but even if a terminal stopper is used, there are cases where the terminal group is terminated by a silanol group due to a small amount of water mixed in during the polymerization, but in the component (A) of the present invention, In some organopolysiloxanes, the terminals terminated by silanol groups are 20 mol% or less of the terminal units, and particularly preferably 10 mol% or less. If it exceeds 20 mol%, the mold becomes heavily soiled.

In this case, the term “terminal terminated with a silanol group” means 1 of R of triorganosiloxy group (R ₃ SiO group).
Individual replacement of OH groups, ie R ₂ (OH) Si
An O group and 20 mol% or less of the terminal unit means that it is 20 mol% or less of all the end groups (that is, the total of the end groups terminated with the triorganosilyl group and the silanol group). Therefore, the proportion of triorganosiloxy groups is
It is preferably 80 mol% or more of the terminal unit, and particularly preferably 90 mol% or more.

An alkenyl group-containing organopolysiloxane having a high end-blocking ratio with a triorganosiloxy group is disclosed in Japanese Patent Publication No. 61-12931 and JP-A 2000-1438.
It can be synthesized by a known method described in Japanese Patent Publication No. 09. Japanese Examined Patent Publication No. 61-12931 discloses a method of neutralizing an alkaline catalyst with triorganohalosilane and hexaorganodisilazane to simultaneously silylate a terminal silanol group. Moreover, even if the organopolysiloxane polymer which already contains a part of silanol groups at the end is treated with a silylating agent such as hexaorganodisilazane or hexaorganosilylamine to reduce the amount of terminal silanol groups. I don't care.

In the present invention, polymerization is carried out under reduced pressure in the presence of an alkaline catalyst to remove water present in the system to produce a high molecular weight organopolysiloxane raw rubber having a small amount of terminal silanol groups. Is particularly preferable. Specifically, JP-A No. 2000-143809, which is produced by polymerizing a cyclic organopolysiloxane with a low molecular weight organopolysiloxane having a terminal blocked with a triorganosilyl group in the presence of an alkaline catalyst under reduced pressure. Is preferred.

The phenyl group-containing silicone oil as the component (B) is a component for imparting lubricity to the cured silicone rubber molded product and for imparting mold releasability during heat molding.

The component (B) is preferably a phenyl group-containing silicone oil represented by the following formula (1).

[0016]

[Chemical 3] (In the formula, R is a substituted or unsubstituted monovalent hydrocarbon group containing no aliphatic unsaturated group, which may be the same or different, but at least one is a phenyl group, and n is 1 to 1;
It is an integer of 1,000. )

Here, R in the formula is an identical or different substituted or unsubstituted monovalent hydrocarbon group containing no aliphatic unsaturated group, and preferably has 1 to 10 carbon atoms, particularly 1 to 8 carbon atoms. , May be the same or different. Specifically, an alkyl group such as a methyl group, an ethyl group, a propyl group, a butyl group, and a hexyl group, a cycloalkyl group, an aryl group such as a phenyl group and a tolyl group, an aralkyl group such as a benzyl group, and one of these hydrogen atoms. Part or all substituted with halogen atoms,
Examples thereof include 3,3,3-trifluoropropyl group and the like, and a methyl group is preferable. At least one of R is a phenyl group, and the content of the phenyl group is preferably 5 to 50 mol%, particularly 10 to 40 mol% of the total R. Examples of such a phenyl group-containing organopolysiloxane include dimethylsiloxy group-capped dimethylsiloxane / phenylmethylsiloxane copolymers having both terminals trimethylsiloxy group-capped dimethylsiloxane / diphenylsiloxane copolymers having both terminals trimethylsiloxy group-capped dimethyl. Examples thereof include siloxane / phenylmethylsiloxane / methyl (3,3,3-trifluoropropyl) siloxane copolymer. Further, n is an integer of 1 to 1,000, preferably 10 to 800, particularly preferably 50 to 500.

The content of the phenyl group-containing silicone oil as the component (B) is 1 to 100 parts by weight of the component (A).
20 parts by weight. If the compounding amount exceeds 20 parts by weight, the adhesive force of the silicone rubber composition increases and the roll processability deteriorates. If it is less than 1 part by weight, the lubricity becomes insufficient.

The silica filler having a specific surface area of component (C) of 50 m ² / g or more is used as a reinforcing material. From the viewpoint of reinforcement and transparency, it is necessary that the specific surface area is 50 m ² / g or more. Examples of such silica include fumed silica and precipitated silica, and these may be used alone or in combination of two or more. The surface of the silica-based filler may be treated with, for example, a chain organopolysiloxane, a cyclic organopolysiloxane, an organochlorosilane, an organoalkoxysilane, hexamethyldisilazane, or the like.

The compounding amount of the component (C) is 5 to 1 with respect to 100 parts by weight of the organopolysiloxane raw rubber of the component (A).
The amount is 00 parts by weight, preferably 10 to 70 parts by weight. If the blending amount is too large or too small, the processability of the obtained silicone rubber composition decreases, and
The obtained cured product does not have sufficient mechanical strength such as tensile strength and tear strength.

The component (D) curing agent cures the silicone rubber composition. Examples of the method for curing the silicone rubber composition include a method utilizing a hydrosilylation reaction and a method involving vulcanization using an organic peroxide as a catalyst.

In the case of curing using a hydrosilylation reaction, an organohydrogenpolysiloxane as a curing agent and a platinum group metal-based catalyst are blended in the silicone rubber composition. In this case, as the organopolysiloxane raw rubber of the component (A), one having two or more alkenyl groups in one molecule, preferably 0.01 to 5 mol% in R ² of the above average composition formula (3). Those that are alkenyl groups are used.

The organohydrogenpolysiloxane may be any organopolysiloxane having two or more, preferably three or more SiH groups in one molecule, and may be linear, cyclic or branched. However, those having a degree of polymerization of 300 or less are preferable. Further, such SiH group may be at the end of the polysiloxane chain or may be in the middle thereof. Such an organohydrogenpolysiloxane is usually a SiH based on 1 mol of the alkenyl group of the organopolysiloxane raw rubber of the component (A).
A ratio in which the group is 0.5 to 3 mol, particularly 1.0 to 2 mol is preferable.

The platinum group metal-based catalyst used at the same time acts as a catalyst for the hydrosilylation reaction between the alkenyl group in the organopolysiloxane raw rubber (A) and the SiH group in the organohydrogenpolysiloxane. And is usually 0.1 to 1000 ppm, preferably 1 to 1 with respect to the total amount of the component (A) organopolysiloxane raw rubber and the organohydrogenpolysiloxane.
Used in the range of 00 ppm (as platinum group metal).
Examples of platinum group metal-based catalysts include, for example, US Pat. No. 2,970.
150, finely divided metal platinum catalysts described in US Pat. No. 2,823,218, chloroplatinic acid catalysts described in US Pat. Nos. 3,159,601 and 3,159,662, platinum-hydrocarbon complex compounds, US Pat. Chloroplatinic acid-olefin complex compounds described in US Pat. No. 3,516,946, US Pat. No. 3,775,452, 3814.
The platinum-vinyl siloxane complex etc. which are described in No. 780 can be used.

In the case of curing by hydrosilylation reaction, in order to have good storage stability at room temperature and to maintain an appropriate pot life, it is necessary to add a reaction control agent such as methylvinylcyclotetrasiloxane and acetylene alcohols. You can also

On the other hand, when an organic peroxide is used as the curing agent, the organopolysiloxane raw rubber as the component (A) preferably has 0.01 to 5 mol% of alkenyl groups in one molecule. Examples of the organic peroxide include benzoyl peroxide, t-butyl perbenzoate, o-
Methyl benzoyl peroxide, p-methyl benzoyl peroxide, di-t-butyl peroxide, dicumyl peroxide, 1,1-bis (t-butylperoxy) -3,3,5-trimethylcyclohexane,
2,5-Dimethyl-2,5-di (t-butylperoxy) hexane, 2,5-dimethyl-2,5-di (t-butylperoxy) hexyne, 1,6-bis (p-toluoylperoxide) Examples thereof include oxycarbonyloxy) hexane and di (4-methylbenzoylperoxy) hexamethylene biscarbonate. These may be used alone or in combination of two or more. It is preferable to add 0.01 to 5 parts by weight, particularly 0.05 to 3 parts by weight, based on 100 parts by weight of the organopolysiloxane, which enables extrusion and heat curing.

In the heat-curable silicone rubber composition of the present invention, it is preferable to add, as the component (E), a terminal silanol group-containing organosilicon compound represented by the following formula (2).

[0028]

[Chemical 4] (In the formula, R ¹ is a methyl group or a vinyl group, and m is 1 to 100.
Is an integer. )

The component (E) acts as a dispersant when producing a silicone rubber compound.
In the component (E), R ¹ in the above formula (2) is a methyl group or a vinyl group. Further, m is an integer of 1 to 100, preferably 1 to 60, particularly preferably 1 to 30.
The compounding amount of the component (E) is preferably 0.1 to 20 parts by weight with respect to 100 parts by weight of the component (A). If the compounding amount is less than 0.1 part by weight, the dispersity of the silica filler may be deteriorated, and if it exceeds 20 parts by weight, the rubber bound becomes sticky, the workability is deteriorated, and the mechanical properties of the cured product are deteriorated. There is a possibility that the characteristics may deteriorate.

The heat-curable silicone rubber composition of the present invention may be blended with an extender such as crushed quartz and a filler such as calcium carbonate, if necessary, and may be colored if necessary. It is optional to add various additives such as agents, heat resistance improvers, and filler dispersants. Particularly when a component (E) or a dispersant is added, it is preferable to add a catalyst such as hydrochloric acid. The addition amount of the catalyst is preferably 0.01 to 5 parts by weight with respect to 100 parts by weight of the component (A).

The heat-curable silicone rubber composition of the present invention has a whiteness (L value) of 2 or less, and in particular, a mirror-finished stainless steel plate set in a mold for injection molding at 170 ° C. , The whiteness (L value) of the stainless steel plate after continuous injection molding 100 times in 150 seconds is 8 or less,
Particularly, it is 5 or less.

When the heat-curable silicone rubber composition is molded using a mold, particularly, injection molding is performed, the mirror-finished stainless steel plate is set in the mold, and the stainless steel plate is set. Whiteness (L
While the value) is 8 or less, particularly 5 or less, the molding is repeated. In this case, known molding conditions can be adopted. For example, in the case of injection molding, 100 to 250 ° C., particularly 150 to 190 ° C.
The conditions can be 0 second to 30 minutes, and particularly 1 to 10 minutes.

[0033]

EXAMPLES The present invention will be specifically described below with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples.

Example 1 Dimethylsiloxane unit 9
9.85 mol%, methyl vinyl siloxane unit 0.12
5 mol%, dimethyl vinyl siloxane unit 0.024 mol%, dimethyl hydroxy siloxane unit 0.001 mol%, average degree of polymerization is about 8,000, and dimethyl vinyl siloxane unit has a terminal blocking rate of 96 mol%. To 100 parts by weight of organopolysiloxane raw rubber, 41 parts by weight of precipitated silica having a specific surface area of 200 m ² / g and an average particle diameter of 1.9 μm, 3.9 parts by weight of dimethoxydimethylsilane, and dimethylpolysiloxane having a hydroxyl group at the molecular end ( Polymerization degree 20) 1 part by weight, 1.28 parts by weight of a hydrochloric acid aqueous solution having a pH of 3.5 are uniformly kneaded in a kneader, and then 1
Heat treatment was performed at 80 ° C. for 1 hour to obtain a silicone rubber compound.

With respect to 100 parts by weight of this silicone rubber compound, 8 parts by weight of a terminal trimethylsilyl group-blocked organopolysiloxane having a diphenylsiloxane unit content of 28 mol% and a viscosity of 400 mPa · s, and 1 part by weight of dicumyl peroxide were treated with a two-roll mill. A silicone rubber composition (A) was produced by mixing and dispersing.

Example 2 Dimethylsiloxane unit 9
9.85 mol%, methyl vinyl siloxane unit 0.12
5 mol%, 0.022 mol% of dimethylvinylsiloxane units, and 0.003 mol% of dimethylhydroxysiloxane units, the average degree of polymerization is about 8,000, and the end-blocking rate by dimethylvinylsiloxane units is 88 mol%. A silicone rubber composition (B) was produced in the same manner as in Example 1 except that the organopolysiloxane raw rubber was used.

Example 3 Dimethylsiloxane Unit 9
9.85 mol%, methyl vinyl siloxane unit 0.12
5 mol%, 0.021 mol% of dimethylvinylsiloxane units, and 0.004 mol% of dimethylhydroxysiloxane units, the average degree of polymerization is about 8,000, and the end-blocking rate by dimethylvinylsiloxane units is 84 mol%. A silicone rubber composition (C) was produced in the same manner as in Example 1 except that the organopolysiloxane raw rubber was used.

[Example 4] Dimethylsiloxane unit 9
9.85 mol%, methyl vinyl siloxane unit 0.12
5 mol%, dimethylvinylsiloxane unit 0.021 mol%, trimethylsiloxane unit 0.004 mol%, the average degree of polymerization is about 8,000, the terminal blocking rate by dimethylvinylsiloxane unit is 84 mol%, Example 1 except that an organopolysiloxane raw rubber in which the remaining end was a trimethylsiloxane unit (terminal blocking rate by the triorganosiloxane unit was 100 mol%) was used.
A silicone rubber composition (D) was produced in the same manner as.

[Example 5] Dimethylsiloxane unit 9
9.85 mol%, methyl vinyl siloxane unit 0.12
5 mol%, 0.022 mol% of dimethylvinylsiloxane units, and 0.003 mol% of dimethylhydroxysiloxane units, the average degree of polymerization is about 8,000, and the end-blocking rate by dimethylvinylsiloxane units is 88 mol%. To 100 parts by weight of organopolysiloxane raw rubber, 41 parts by weight of precipitated silica having a specific surface area of 200 m ² / g and an average particle diameter of 1.9 μm, 3.9 parts by weight of dimethoxydimethylsilane, and dimethylpolysiloxane having a hydroxyl group at the molecular end ( Polymerization degree 20) 1 part by weight, 1.28 parts by weight of a hydrochloric acid aqueous solution having a pH of 3.5 are uniformly kneaded in a kneader, and then 1
Heat treatment was performed at 80 ° C. for 1 hour to obtain a silicone rubber compound.

With respect to 100 parts by weight of this silicone rubber compound, 8 parts by weight of a terminal trimethylsilyl group-blocked organopolysiloxane having a diphenylsiloxy unit content of 26 mol% and a viscosity of 400 mPa · s, and a chloroplatinic acid-vinylsiloxane complex (platinum content: 1% by weight) 0.05 part by weight, ethynyl-methyl-decylcarbinol 0.06
By weight, 1.2 parts by weight of a methyl hydrogen polysiloxane with a trimethylsiloxy group blocked at both ends of the molecular chain (content of silicon-bonded hydrogen atoms = 0.5% by weight) is mixed and dispersed with a two-roll mill to give a silicone rubber composition. The product (E) was produced.

Example 6 Dimethylsiloxane Unit 9
9.85 mol%, methyl vinyl siloxane unit 0.12
5 mol%, 0.022 mol% of dimethylvinylsiloxane units, and 0.003 mol% of dimethylhydroxysiloxane units, the average degree of polymerization is about 8,000, and the end-blocking rate by dimethylvinylsiloxane units is 88 mol%. 100 parts by weight of organopolysiloxane raw rubber, 25 parts by weight of fumed silica having a specific surface area of 200 m ² / g,
2 parts by weight of dimethylpolysiloxane having a hydroxyl group at the molecular end (polymerization degree: 5) was uniformly kneaded in a kneader and then heat-treated at 180 ° C. for 1 hour to obtain a silicone rubber compound.

With respect to 100 parts by weight of this silicone rubber compound, 8 parts by weight of a terminal trimethylsilyl group-blocked organopolysiloxane having a diphenylsiloxane unit content of 24 mol% and a viscosity of 200 mPa · s, and a chloroplatinic acid-vinylsiloxane complex (platinum content: 1% by weight) 0.05 part by weight, ethynyl-methyl-decylcarbinol 0.06
By weight, 1.2 parts by weight of a methyl hydrogen polysiloxane with a trimethylsiloxy group blocked at both ends of the molecular chain (content of silicon-bonded hydrogen atoms = 0.5% by weight) is mixed and dispersed with a two-roll mill to give a silicone rubber composition. The product (F) was produced.

[Comparative Example 1] Dimethylsiloxane unit 9
9.85 mol%, methyl vinyl siloxane unit 0.12
5 mol%, 0.019 mol% of dimethylvinylsiloxane units, and 0.006 mol% of dimethylhydroxysiloxane units, the average degree of polymerization is about 8,000, and the terminal blocking rate by dimethylvinylsiloxane units is 76 mol%. A silicone rubber composition (G) was produced in the same manner as in Example 1 except that the organopolysiloxane raw rubber was used.

Comparative Example 2 Dimethylsiloxane Unit 9
9.85 mol%, methyl vinyl siloxane unit 0.12
5 mol%, 0.017 mol% of dimethylvinylsiloxane units, and 0.008 mol% of dimethylhydroxysiloxane units, having an average degree of polymerization of about 8,000 and a terminal blocking rate of 68 mol% by dimethylvinylsiloxane units. A silicone rubber composition (H) was produced in the same manner as in Example 1 except that the organopolysiloxane raw rubber was used.

[Comparative Example 3] Dimethylsiloxane unit 9
9.85 mol%, methyl vinyl siloxane unit 0.12
5 mol%, 0.017 mol% of dimethylvinylsiloxane units, and 0.008 mol% of dimethylhydroxysiloxane units, having an average degree of polymerization of about 8,000 and a terminal blocking rate of 68 mol% by dimethylvinylsiloxane units. A silicone rubber composition (I) was produced in the same manner as in Example 5 except that the organopolysiloxane raw rubber was used.

The silicone rubber compositions (A) to (I) were subjected to a mold stain test (visual observation / whiteness measurement) under the following conditions. The results are shown in Table 1.

Mold stain test Injection molding machine (Matsuda Seisakusho: VI-50P (E) -40 /
50 SPS II-P) was used to perform a soiling test on the mold under the following molding conditions. Molding conditions Injection time: 10 seconds Vulcanization time: 150 seconds Waiting for weighing: 30 seconds Mold temperature: 170 ° C (setting) Specular plate temperature: 158-160 ° C (actual measurement) Hot oil: 30 ° C (about 40 ° C during molding) )

Measurement of whiteness (L value) A SUS plate (thickness 1 with a surface (L value) of 1.8) mirror-finished in a mold (180 mm × 180 mm × 2 mm)
mm), and silicone rubber compositions (A) to (I)
Is cured at 170 ° C. for 150 seconds, and after 100 times of continuous injection molding, the whiteness (L
(Value) was measured with a color spectrocolor 368, a reflection type spectrocolorimeter manufactured by JIKI Corporation. The results are shown in Table 1.

[0049]

[Table 1] Mirror finish SUS plate; initial L value = 1.8

[0050]

EFFECTS OF THE INVENTION According to the present invention, it is possible to provide a heat-curable silicone rubber composition having less mold stains.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) C08L 83:04) (72) Inventor Naoki Yamakawa 1 Hitotsumi Hitomi, Matsuida-cho, Usui-gun, Gunma 10 Shin-Etsu Chemical Co., Ltd. F term in Silicon Electronics Materials Research Laboratory Co., Ltd. (reference) 4J002 CP032 CP063 CP141 DA117 DE187 DE197 DJ016 FD016 FD147 FD157

Claims (4)

[Claims] 1. An alkenyl group-containing organopolysiloxane raw rubber having (A) a silanol group-terminated terminal of 20 mol% or less of the terminal unit (B) 100 parts by weight (B) a phenyl group-containing silicone oil 1 to 20 parts by weight (C) ) A silica filler having a specific surface area of 50 m ² / g or more 5 to 100 parts by weight (D) A necessary amount of a curing agent is contained, and a stainless steel plate mirror-finished with a whiteness (L value) of 2 or less is in a mold. Set to 170 ℃, 1
A heat-curable silicone rubber composition, wherein the whiteness (L value) of the stainless steel plate after continuous injection molding 100 times in 50 seconds is 8 or less. 2. The component (B) is represented by the following formula (1): (In the formula, R is a substituted or unsubstituted monovalent hydrocarbon group containing no aliphatic unsaturated group, which may be the same or different, but at least one is a phenyl group, and n is 1 to 1;
It is an integer of 1,000. The composition according to claim 1, which is a phenyl group-containing silicone oil represented by the formula (1). 3. Further, as the component (E), the following formula (2): (In the formula, R ¹ is a methyl group or a vinyl group, and m is 1 to 100.
Is an integer. ) The terminal silanol group-containing organosilicon compound represented by the formula (A) is 0.1 to 100 parts by weight of the component (A).
The heat-curable silicone rubber composition according to claim 1, which contains 20 parts by weight. 4. The alkenyl group-containing organopolysiloxane raw rubber of component (A) is obtained by polymerizing under reduced pressure in the presence of an alkaline catalyst.
The heat-curable silicone rubber composition according to any one of items 1 to 3.