JP2005325158A - Addition-curing silicone rubber composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an addition-curable silicone rubber composition capable of preventing yellowing with time and heat while maintaining the transparency of silicone rubber and obtaining a silicone rubber excellent in safety.
(A) Organopolysiloxane containing an alkenyl group bonded to at least two silicon atoms in one molecule: 100 parts by mass
(B) Organohydrogenpolysiloxane containing hydrogen atoms (Si-H groups) bonded to at least two silicon atoms in one molecule: 0.2 to 30 parts by mass
(C) Fumed silica having a specific surface area of 100 m ² / g or more by BET method: 10 to 40 parts by mass,
(D) Blue pigment containing ultramarine blue: 0.0001 to 0.01 parts by mass,
(E) Addition reaction catalyst: Addition-curing silicone rubber composition whose main component is a catalyst amount [Selection] None

Description

  The present invention relates to a silicone rubber composition comprising an organopolysiloxane as a main component and cured by an addition reaction to give a silicone rubber, and more specifically, a silicone rubber having excellent transparency is obtained by curing. In addition, the present invention relates to an addition-curable silicone rubber composition that does not cause a decrease in transparency or yellowing over time or at a high temperature.

  Silicone rubber is widely used in various fields, taking advantage of heat resistance, cold resistance, electrical properties, and the like. In particular, the addition reaction curing type silicone rubber composition does not produce by-products due to decomposition of the peroxide unlike the organic peroxide curing type, so it is particularly excellent in safety and appearance (transparency). As a material for molding diving equipment such as underwater glasses, goggles, snorkel, etc. due to its good touch and durability, plus play equipment, tableware, toothbrushes for infants, especially nipples for baby bottles and baby pacifiers Widely used. In addition, it has been used as a molding material for cultural assets and arts and crafts because of its excellent releasability.

  A composition that cures by addition reaction to give silicone rubber is obtained by mixing an alkenyl group-containing organopolysiloxane that is a base polymer with an organohydrogenpolysiloxane that is a crosslinking agent and a catalyst that causes the addition reaction of both, even at room temperature. The reaction proceeds and eventually a gel or cured product is formed. However, these reactions at room temperature take time and are inefficient to produce a large amount of molded products.

  Therefore, in order to actually produce these molded products in large quantities, compression molding and injection molding of addition curable millable silicone rubber composition, injection molding of addition curable liquid silicone rubber composition, high temperature of 150 to 220 ° C. In general, the molding is performed in a short time of several seconds to several minutes. However, such addition-curing silicone rubber molded products are excellent in transparency, but become turbid and yellowed over time, especially when exposed to high temperatures during curing and use, the transparency decreases and yellows. Is remarkable. Accordingly, there is a demand for a transparent silicone rubber molded product that does not impair transparency even when exposed to high temperatures and does not cause yellowing.

  In JP-A-9-221597 (Patent Document 1), in order to prevent yellowing of transparent silicone rubber, a composition containing polyorganosiloxane, a fine powdery silica filler and a catalytic amount of a curing agent is used. Alternatively, a small amount of black pigment is disclosed. However, the compositions described in the examples of the publication use an organic peroxide as a curing agent, and attack and crosslink with radicals generated by thermal decomposition of the peroxide. Therefore, although transparency is described, safety is not mentioned at all. Further, only the keyboard switch is described for the use, and there is no description for baby items such as pacifiers and diving items such as snorkels that place importance on safety.

  Japanese Patent Application Laid-Open No. 2003-192898 (Patent Document 2) describes a method of adding a blue to purple or black cobalt compound to a liquid addition-curable polyorganosiloxane composition. There are compounds that are suspected of having sex and are problematic in terms of safety. Actually, cobalt compounds are exemplified, but there is no description in terms of safety, and no specific application examples are described.

Japanese Patent Laid-Open No. 9-221597 JP 2003-192898 A

  The present invention has been made in view of the above circumstances, and is an addition-curable silicone rubber that can prevent yellowing with time and heat while maintaining the transparency of silicone rubber, and that can provide a silicone rubber with further safety. An object is to provide a composition.

  As a result of intensive studies to achieve the above object, the present inventors have found that a cured product obtained by adding a specific amount of blue pigment containing ultramarine to an addition curable silicone rubber composition has silicone rubber. It has been found that the yellowing during time and heat can be prevented while maintaining transparency, and that it can be further improved in safety, and has led to the present invention.

That is, the present invention
(A) 100 parts by mass of an organopolysiloxane containing an alkenyl group bonded to at least two silicon atoms in one molecule;
(B) 0.2-30 parts by mass of an organohydrogenpolysiloxane containing a hydrogen atom (Si-H group) bonded to at least two silicon atoms in one molecule;
(C) Fumed silica having a specific surface area of 100 m ² / g or more by the BET method
10 to 40 parts by mass,
(D) Blue pigment containing ultramarine blue
0.0001 to 0.01 parts by mass,
(E) Addition reaction catalyst An addition-curable silicone rubber composition having a catalyst amount as a main component is provided.

  In the addition-curable silicone rubber composition of the present invention, the cured product is safe and has good transparency, and can prevent a decrease in transparency and yellowing with time and heat.

The addition-curable silicone rubber composition of the present invention is
(A) an organopolysiloxane containing an alkenyl group bonded to at least two silicon atoms in one molecule;
(B) an organohydrogenpolysiloxane containing a hydrogen atom (Si-H group) bonded to at least two silicon atoms in one molecule;
(C) a fumed silica having a specific surface area of 100 m ² / g or more by the BET method,
(D) a blue pigment containing ultramarine blue,
(E) The main component is an addition reaction catalyst.

As the component (A) of the present invention, an organopolysiloxane having an average of at least two alkenyl groups in one molecule represented by the following average composition formula (I) can be used.
R ¹ _a SiO _{(4-a) / 2} (I)

In the above formula (I), R ¹ is a substituted or unsubstituted monovalent hydrocarbon group having the same or different carbon number of 1 to 10, preferably 1 to 8, and a is 1.5 to 2.8, Preferably, it is a positive number of 1.8 to 2.5.

Here, examples of the substituted or unsubstituted monovalent hydrocarbon group bonded to the silicon atom represented by R ¹ include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a tert-butyl group, Pentyl group, neopentyl group, hexyl group, cyclohexyl group, octyl group, nonyl group, alkyl group such as decyl group, aryl group such as phenyl group, tolyl group, xylyl group, naphthyl group, benzyl group, phenylethyl group, phenylpropyl Aralkyl groups such as groups, vinyl groups, allyl groups, propenyl groups, isopropenyl groups, butenyl groups, hexenyl groups, cyclohexenyl groups, octenyl groups and other alkenyl groups, and some or all of the hydrogen atoms of these groups are fluorine. Substituted with halogen atoms such as bromine, chlorine, cyano groups, etc., such as chloromethyl group, chloropro Group, bromoethyl group, trifluoropropyl group, but cyanoethyl group and the like, it is preferable more than 80 mol% of all R ¹ is a methyl group.

Further, among R ¹ , at least 2, preferably 2 to 20, more preferably 2 to 10 are alkenyl groups (preferably those having 2 to 8 carbon atoms, more preferably 2 to 6 carbon atoms, and particularly preferably Is a vinyl group).
The alkenyl group content in the organopolysiloxane is 1.0 × 10 ⁻⁶ mol / g to 1.0 × 10 ⁻³ mol / g, particularly 1.0 × 10 ⁻⁵ mol / g to 5.0. It is preferable to set it as x10 < ^-4 > mol / g. If the amount of the alkenyl group is less than 1.0 × 10 ⁻⁶ mol / g, the rubber hardness may be too low to be gelled, and if it exceeds 1.0 × 10 ⁻³ mol / g, the crosslinking density May become too high and become brittle rubber.

  This alkenyl group may be bonded to a silicon atom at the end of the molecular chain, may be bonded to a silicon atom in the middle of the molecular chain, or may be bonded to both. The structure of the organopolysiloxane basically has a linear structure, but may be partially a branched structure, a cyclic structure, or the like. The molecular weight is preferably liquid or raw rubber at room temperature (25 ° C.), and the average degree of polymerization is preferably 100 to 20,000, more preferably 150 to 10,000. If the average degree of polymerization is less than 100, a sufficient rubber feeling may not be obtained, and if it is higher than 20,000, molding may be difficult.

  The component (B) of the present invention is an organohydrogenpolysiloxane having at least two hydrogen atoms (Si—H groups) bonded to silicon atoms in one molecule, and the Si—H group in the molecule is the above (A ) It crosslinks with an alkenyl group bonded to a silicon atom in the component by a hydrosilyl addition reaction, and acts as a curing agent for curing the composition.

This (B) component organohydrogenpolysiloxane has the following average composition formula (II)
R ² _b H _c SiO _{(4-bc) / 2} (II)
(Wherein R ² is a substituted or unsubstituted monovalent hydrocarbon group having 1 to 10 carbon atoms, b is 0.7 to 2.1, c is 0.001 to 1.0, and b + c is a positive number satisfying 0.8 to 3.0.)
And those having at least 2, preferably 3 to 100, more preferably 3 to 50 silicon atoms in one molecule are suitably used.

Here, examples of the monovalent hydrocarbon group for R ² include the same groups as those exemplified for R ¹ , but those having no aliphatic unsaturated group are preferred. Further, b is preferably 0.8 to 2.0, c is preferably 0.01 to 1.0, b + c is preferably 1.0 to 2.5, and the molecular structure of the organohydrogenpolysiloxane is: The structure may be any of linear, cyclic, branched, and three-dimensional network. In this case, the number of silicon atoms in one molecule (or the degree of polymerization) is preferably 2 to 300, particularly about 4 to 200 at room temperature (25 ° C.). In addition, the hydrogen atom couple | bonded with a silicon atom may be located in any of the molecular chain terminal and the middle of a molecular chain, and may be located in both.

Specific examples of the organohydrogenpolysiloxane of the component (B) include trimethylsiloxy group-blocked methylhydrogenpolysiloxane at both ends, trimethylsiloxy group-blocked dimethylsiloxane / methylhydrogensiloxane copolymer at both ends, and dimethylhydro at both ends. Gensiloxy group-blocked dimethylpolysiloxane, both ends dimethylhydrogensiloxy group-blocked dimethylsiloxane / methylhydrogensiloxane copolymer, both ends trimethylsiloxy group-blocked methylhydrogensiloxane / diphenylsiloxane copolymer, both ends trimethylsiloxy group-blocked A methylhydrogensiloxane / diphenylsiloxane / dimethylsiloxane copolymer, a copolymer comprising (CH ₃ ) ₂ HSiO _1/2 units and SiO _4/2 units, (CH ₃ And a copolymer composed of ₂ HSiO _1/2 units, SiO _4/2 units, and (C ₆ H ₅ ) SiO _3/2 units.

  The compounding amount of the organohydrogenpolysiloxane is 0.2 to 30 parts by mass, preferably 0.3 to 20 parts by mass with respect to 100 parts by mass of the component (A). When the amount of the organohydrogenpolysiloxane is less than 0.2 parts by mass, the curing is insufficient and a gel-like cured product is obtained. It becomes a cured product. Further, the molar ratio of the hydrogen atom (Si-H group) bonded to the silicon atom of the organopolysiloxane to the total amount of alkenyl groups bonded to the silicon atom in the component (A) is Si-H group / alkenyl group = 0. .8 to 2.5, particularly 1.0 to 2.3 is preferable. If this ratio is less than 0.8, crosslinking may be insufficient, resulting in a sticky rubber, and if it is more than 2.5, yellowing during aging and heat may be increased.

The fumed silica which is the component (C) of the present invention is essential for giving sufficient strength to the silicone rubber. BET specific surface area of the fumed silica, 100 m ² / g or more, preferably 150 to 400 m ² / g, more preferably 150~350m ² / g. If the specific surface area is less than 100 m ² / g, sufficient strength cannot be obtained, and the transparency of the molded product also decreases. If it exceeds 400 m ² / g, blending may become difficult or discoloration may occur. is there.

  These fumed silicas may be used as they are, but those previously treated with a surface hydrophobizing agent may be used, or those treated by adding a surface treating agent during kneading with silicone oil may be used. preferable. These surface treatment agents may be any known ones such as alkylalkoxysilanes, alkylchlorosilanes, alkylsilazanes, silane coupling agents, titanate treatment agents, fatty acid esters, etc. You may use simultaneously or at a different timing.

  Moreover, the compounding quantity of these fumed silicas is 10-40 mass parts with respect to 100 mass parts of (A) component, Preferably it is 15-35 mass parts. If the blending amount is less than 10 parts by mass, sufficient rubber strength cannot be obtained, and if it is 40 parts by mass or more, blending becomes difficult.

The blue pigment containing ultramarine which is the component (D) of the present invention is essential for preventing the yellowing of the present invention over time or heat. Here, ultramarine is a chemical name “ultraviolet”, an English name “Ultramarine blue”, and a structural formula is represented by Na ₆ Al ₆ Si ₆ O ₂₄ S ₄ . It is classified into Chemical Substances Control Law 1-22, FDA 21 CFR · 178 · 3970, and LD50 (Rats and Mice) is 10,000 mg / kg <and there is no problem with respect to safety.

As for ultramarine, those having an average particle diameter of 0.1 to 20 μm are preferable, and those having an average particle diameter of 0.5 to 10 μm are particularly preferable. If the average particle size is smaller than 0.1 μm, blending may be difficult. If the average particle size is 20 μm or more, the dispersion is insufficient and the yellowing prevention effect may not be obtained.
In the present invention, the average particle diameter can be determined, for example, as a cumulative weight average value (or median diameter) in particle size distribution measurement by a laser light diffraction method.

  In addition to the ultramarine blue, the blue pigment includes inorganic pigments such as cobalt blue and iron blue, and organic pigments such as phthalocyanine blue. However, some cobalt compounds are suspected to be carcinogenic, and are not preferable for inclusion in the mouth, such as snorkels and nipples for baby bottles. Further, bitumen and organic pigments have a problem that their heat resistance is insufficient and they discolor when heated. Therefore, when a pigment other than the above-mentioned ultramarine blue is blended as a blue pigment, the blending ratio of the non-ultraviolet pigment in the blue pigment is 0 to 50% by mass, particularly 0 to 30% by mass, especially 0 to 10% by mass. It is preferable that

  Moreover, you may use what carried out the surface hydrophobization treatment of the said ultramarine blue. Surface treatment agents include fatty acid esters such as ethyl stearate, silanes such as trialkoxyvinylsilane and silane coupling agents, silazanes such as hexamethyldisilazane, organofunctional group-containing siloxanes such as hydroxysiloxane at both ends, and octane. Any known surface treating agent such as silica, such as low molecular silicone such as methylcyclotetrasiloxane, titanate, etc. can be used without any problem. In addition, about the usage-amount of a surface treating agent and the surface treatment method, it is the same as that of surface treatments, such as a silica, and it does not restrict | limit in particular.

  As a compounding quantity of these blue pigments, it is 0.0001-0.01 mass part with respect to 100 mass parts of (A) component, Preferably it is 0.0002-0.005 mass part. If it is less than 0.0001 part by mass, the yellowing prevention effect is insufficient, and if it exceeds 0.01 part by mass, the blue color becomes strong and the transparency is lost.

  Here, the blending method of the component (D) may be blended in the composition as it is, but there is a possibility that dispersion is insufficient with a small amount blending. Therefore, first, silicone oil (specifically, the component (A) and / or the component (B)) and a blue pigment are mixed so that the blue pigment is about 0.5 to 2% by mass. A method of strengthening the dispersion with a roll or the like and then blending it into the composition is preferred.

  (E) Component addition reaction catalyst includes platinum black, platinous chloride, chloroplatinic acid, reaction product of chloroplatinic acid and monohydric alcohol, complex of chloroplatinic acid and olefins, platinum bisacetoacetate, etc. Platinum-based catalysts, palladium-based catalysts, rhodium-based catalysts, and the like. In addition, the compounding quantity of this addition reaction catalyst can be made into a catalyst quantity, and is about 0.5-1,000 ppm with respect to (A) component as a platinum group metal normally, Especially about 1-500 ppm.

  In the addition-curable silicone rubber composition of the present invention, as other components, if necessary, a filler such as precipitated silica, quartz powder, diatomaceous earth, calcium carbonate, carbon black, conductive zinc white, metal powder, etc. Conductive agent, nitrogen-containing compound, acetylene compound, phosphorus compound, nitrile compound, carboxylate, tin compound, mercury compound, sulfur compound and other hydrosilylation reaction control agent, iron oxide, heat-resistant agent such as cerium oxide, dimethyl silicone oil, etc. The internal release agent, adhesiveness-imparting agent, thixotropic property-imparting agent, and the like can be arbitrarily selected as long as the transparency of the cured rubber is not impaired.

  The addition-curable silicone rubber composition of the present invention can be prepared by uniformly mixing the above components using a normal mixing stirrer, kneader or the like such as a kneader or a planetary mixer.

  The curing conditions for the addition curable silicone rubber composition of the present invention may be the same as those for known addition reaction curable silicone rubber compositions. For example, the curing may be sufficiently carried out at room temperature, but may be heated as necessary. In this case, it can be cured by heating at 80 to 250 ° C., particularly 120 to 220 ° C. for 3 seconds to 10 minutes, particularly 5 seconds to 3 minutes.

  The cured product (silicone rubber) of the addition curable silicone rubber composition of the present invention thus obtained has a total light transmittance of 70% or more measured by a haze meter (manufactured by Suga Test Instruments Co., Ltd.), in particular. It is preferably 75% or more, particularly 80% or more. If the total light transmittance is less than 70%, it may not be suitable for diving equipment, swimming equipment, baby equipment, and the like. The upper limit is 100%, but when it is too transparent, yellowish color can be seen, it can be 90% or less, particularly 85% or less.

  The cured product of the addition curable silicone rubber composition of the present invention is safe and excellent in transparency, and does not cause a decrease in transparency or yellowing over time or at a high temperature, and particularly its excellent appearance and safety. Therefore, it can be suitably used as infant equipment such as play equipment for children, tableware, toothbrushes, nipples for baby bottles, pacifiers for babies, diving and swimming equipment such as underwater glasses, goggles straps and snorkel parts.

EXAMPLES Hereinafter, although an Example and a comparative example are shown and this invention is demonstrated concretely, this invention is not restrict | limited to the following Example. In the following examples, “part” means “part by mass”, “specific surface area” shows a value measured by the BET adsorption method, and “average particle size” is measured by a cumulative weight average value (D ₅₀ ) by a particle size distribution measuring apparatus by laser light diffraction method Value.

[Example 1]
60 parts of dimethylpolysiloxane (1) having an average degree of polymerization of 750 blocked at both ends by dimethylvinylsiloxy groups and a specific surface area of 300 m ² / g (manufactured by Nippon Aerosil Co., Ltd., Aerosil 300) 30 parts, 6 parts of hexamethyldisilazane and 1.5 parts of water were mixed at room temperature (25 ° C.) for 30 minutes, heated to 150 ° C., stirred for 3 hours, cooled, and further dimethylpolysiloxane (1) 20 parts was added and stirring was continued for 30 minutes to obtain a silicone rubber base.
Into 110 parts of this silicone rubber base, 20 parts of dimethylpolysiloxane (2) having an average degree of polymerization of 250 blocked at both ends with dimethylvinylsiloxy groups and having a mean polymerization degree of 250 were added, and stirring was continued for 30 minutes. And methyl hydrogen polysiloxane having a Si—H group in the side chain (3) [degree of polymerization 17, amount of Si—H group 0.0050 mol / g] 1.6 parts [Si—H group / alkenyl group = 1.6 ], 0.10 parts of ethinylcyclohexanol and 0.4 parts of ultramarine paste (A) shown below were added as reaction control agents, and stirring was continued for 15 minutes to obtain a silicone rubber composition.
100 parts of this silicone rubber composition was mixed with 0.1 part of a platinum catalyst (Pt concentration: 1%), and a rubber cured product having a thickness of 10 mm was obtained from a press cure at 150 ° C./10 minutes. Table 1 shows the results of measuring the total light transmittance of the 10 mm thick rubber sheet using a haze meter (manufactured by Suga Test Instruments Co., Ltd.). Furthermore, Table 1 shows the results of visual observation of the degree of yellowing for the initial three months and the one left in an oven at 150 ° C. for one week.

* Ultramarine paste (A): 99.5 parts of dimethylpolysiloxane (1) + ultramarine No. A mixture of 0.5 parts of 2000 (Daiichi Kasei Kogyo Co., Ltd., average particle size: about 1 μm) mixed and passed twice through three rolls

[Example 2]
60 parts of dimethylpolysiloxane (4) having an average degree of polymerization of 500 blocked at both ends with dimethylvinylsiloxy groups and a specific surface area of 200 m ² / g (manufactured by Nippon Aerosil Co., Ltd., Aerosil 200) 40 parts, 5 parts of hexamethyldisilazane and 1.0 part of water were mixed at room temperature (25 ° C.) for 30 minutes, heated to 150 ° C., stirred for 3 hours and cooled, and then dimethylpolysiloxane (4) 20 Part was added and stirring was continued for 30 minutes to obtain a silicone rubber base.
Dimethylpolysiloxane (5) [vinyl group content 0.00038 mol / g] 20 having an average polymerization degree of 300 having both ends blocked with trimethylsiloxy groups and vinyl groups in the side chains on 120 parts of this silicone rubber base Part, methyl hydrogen polysiloxane (6) as a crosslinking agent [polymerization degree 50, Si—H group amount 0.0068 mol / g] 1.75 parts [Si—H group / alkenyl group = 1.0], reaction control agent Were added 0.05 parts of ethynylcyclohexanol and 0.2 parts of ultramarine paste (A) of Example 1 and stirring was continued for 30 minutes to obtain a silicone rubber composition.
100 parts of this silicone rubber composition was mixed with 0.1 part of a platinum catalyst (Pt concentration: 1%), and a rubber cured product having a thickness of 10 mm was obtained from a press cure at 150 ° C./10 minutes. As in Example 1, Table 1 shows the results of visual observation of the degree of yellowing of the total light transmittance, the initial stage, left for three months outdoors, and left for one week in an oven at 150 ° C.

[Example 3]
In 100 parts of a raw rubber-like organopolysiloxane (7) [vinyl group content 0.000088 mol / g] having both degrees of molecular chain blocked with trimethylsiloxy groups and having a vinyl group in the side chain and a degree of polymerization of about 8,000, 40 parts of fumed silica (Aerosil 200, manufactured by Nippon Aerosil Co., Ltd.) having a specific surface area of 200 m ² / g, and 8 parts of dimethyldimethoxysilane, 1 part of hexamethyldisilazane, and 2 parts of water as a dispersant are uniformly added. And heat-treated at 150 ° C. for 4 hours, and then dissolved by two rolls and plasticized to obtain a silicone rubber compound.
To 140 parts of this silicone rubber compound, 3.5 parts of methyl hydrogen polysiloxane (3) of Example 1 as a crosslinking agent [Si—H group / alkenyl group = 2.0] and ethynylcyclohexanol 0 as a reaction control agent .05 parts and 0.2 parts of ultramarine paste (B) shown below were added and blended with two rolls to obtain a silicone rubber composition.
100 parts of this silicone rubber composition was further mixed with 0.1 part of a platinum catalyst (Pt concentration 1%), and a cured rubber product having a thickness of 10 mm was obtained from a press cure at 150 ° C./10 minutes. As in Example 1, Table 1 shows the results of visual observation of the degree of yellowing of the total light transmittance, the initial stage, left for three months outdoors, and left for one week in an oven at 150 ° C.

* Ultramarine paste (B): 99.5 parts of dimethylpolysiloxane (1) + 0.5 part of ultramarine AP-205 (Daiichi Kasei Kogyo Co., Ltd., average particle size: about 1 μm) surface-treated with silicone Mixed and passed twice through three rolls

[Comparative Example 1]
60 parts of dimethylpolysiloxane (1) of Example 1, 30 parts of fumed silica (Aerosil 300, manufactured by Nippon Aerosil Co., Ltd.) having a specific surface area of 300 m ² / g, 6 parts of hexamethyldisilazane, and 1.5 parts of water After mixing for 30 minutes at room temperature (25 ° C.), the temperature was raised to 150 ° C. and stirring was continued for 3 hours. After cooling, 20 parts of dimethylpolysiloxane (1) was further added and stirring was continued for 30 minutes. Got the base.
To 110 parts of this silicone rubber base, 20 parts of dimethylpolysiloxane (2) of Example 1 was added, and stirring was continued for 30 minutes. Then, methylhydrogenpolysiloxane (3) of Example 1 as a crosslinking agent was added to 1.6 parts. [Si—H group / alkenyl group = 1.6] and ethynylcyclohexanol 0.10 parts as a reaction control agent were added and stirring was continued for 15 minutes to obtain a silicone rubber composition.
100 parts of this silicone rubber composition was mixed with 0.1 part of a platinum catalyst (Pt concentration: 1%), and a rubber cured product having a thickness of 10 mm was obtained from a press cure at 150 ° C./10 minutes. As in Example 1, Table 1 shows the results of visual observation of the degree of yellowing of the total light transmittance, the initial stage, left for three months outdoors, and left for one week in an oven at 150 ° C.

[Example 4]
60 parts of dimethylpolysiloxane (4) of Example 2, 40 parts of fumed silica (Aerosil 200 manufactured by Nippon Aerosil Co., Ltd.) having a specific surface area of 200 m ² / g, 5 parts of hexamethyldisilazane, 1.0 of water After mixing 30 parts at room temperature (25 ° C.), the temperature was raised to 150 ° C. and stirring was continued for 3 hours. After cooling, 20 parts of dimethylpolysiloxane (4) was added, and stirring was continued for 30 minutes. Got.
To 120 parts of this silicone rubber base, 20 parts of dimethylpolysiloxane (5) [vinyl group content 0.00038 mol / g] of Example 2 and 4.20 parts of methyl hydrogen polysiloxane (6) as a crosslinking agent [Si- H group / alkenyl group = 2.4], 0.05 part of ethynylcyclohexanol as reaction control agent and 0.2 part of ultramarine paste (A) of Example 1 were added, and stirring was continued for 30 minutes to obtain a silicone rubber composition. Got.
100 parts of this silicone rubber composition was mixed with 0.1 part of a platinum catalyst (Pt concentration: 1%), and a rubber cured product having a thickness of 10 mm was obtained from a press cure at 150 ° C./10 minutes. As in Example 1, Table 1 shows the results of visual observation of the degree of yellowing of the total light transmittance, the initial stage, left for three months outdoors, and left for one week in an oven at 150 ° C.

[Comparative Example 2]
100 parts of the raw rubber-like organopolysiloxane (7) of Example 3 and 40 parts of fumed silica (Aerosil 200, manufactured by Nippon Aerosil Co., Ltd.) having a specific surface area of 200 m ² / g, and dimethyldimethoxysilane 8 as a dispersant Part, 1 part of hexamethyldisilazane and 2 parts of water were kneaded uniformly, heat-treated at 150 ° C. for 4 hours, and then interpreted with two rolls and plasticized to obtain a silicone rubber compound.
To 140 parts of this silicone rubber compound, 3.5 parts of methyl hydrogen polysiloxane (3) of Example 1 as a crosslinking agent [Si—H group / alkenyl group = 2.0] and ethynylcyclohexanol 0 as a reaction control agent .05 parts, 0.1 part of bitumen paste (C) shown below was added and blended with two rolls to obtain a silicone rubber composition.
To 100 parts of this silicone rubber composition, 0.1 part of platinum catalyst (Pt concentration 1%) was further blended to obtain a cured rubber product having a thickness of 10 mm from a press cure at 150 ° C./10 minutes. As in Example 1, the results of visual observation of the degree of yellowing of the total light transmittance, the initial stage, three months standing outdoors, and one week standing in an oven at 150 ° C. are shown in Table 1.

* Bituminous paste (C): A mixture of 99.5 parts of dimethylpolysiloxane (1) + 0.5 part of bitumen (Iron Blue) having an average particle size of 0.2 μm and passed twice through a three roll.

[Comparative Example 3]
A silicone rubber composition was prepared in the same manner as in Example 4 except that 0.2 part of ultramarine paste (A) was not blended. Table 1 shows the results of visual observation of the degree of yellowing in the oven left at 150 ° C. for 1 week.

黄ばみの判定 ◎：黄ばみなし
○：わずかに黄ばみあり
△：黄ばみあり
×：強い黄ばみあり

Judgment of yellowing ◎: No yellowing
○: Slightly yellowish
Δ: Yellowish
×: Strong yellowing

Claims (7)

(A) 100 parts by mass of an organopolysiloxane containing an alkenyl group bonded to at least two silicon atoms in one molecule;
(B) 0.2-30 parts by mass of an organohydrogenpolysiloxane containing a hydrogen atom (Si-H group) bonded to at least two silicon atoms in one molecule;
(C) Fumed silica having a specific surface area of 100 m ² / g or more by the BET method
10 to 40 parts by mass,
(D) Blue pigment containing ultramarine blue
0.0001 to 0.01 parts by mass,
(E) Addition reaction catalyst An addition-curable silicone rubber composition having a catalyst amount as a main component.   The addition-curable silicone rubber composition according to claim 1, wherein the cured silicone rubber has a light transmittance of 70% or more.   The addition curable silicone according to claim 1 or 2, wherein the ultramarine of component (D) is surface-treated with a surface treating agent selected from fatty acid esters, siloxane compounds, silane compounds and titanate esters. Rubber composition.   The addition curable silicone rubber composition according to any one of claims 1 to 3, wherein the ultramarine of component (D) has an average particle size of 0.1 to 20 µm.   The molar ratio of the alkenyl group bonded to the silicon atom in the component (A) to the Si—H group in the component (B) is Si—H group / alkenyl group = 0.8 to 2.5. The addition-curable silicone rubber composition according to any one of claims 1 to 4.   The addition-curable silicone rubber composition according to any one of claims 1 to 5, which is used for diving or swimming equipment. The addition-curable silicone rubber composition according to any one of claims 1 to 5, wherein the composition is used for baby products.