JP2024162627A - Millable type silicone rubber compound and millable type silicone rubber composition - Google Patents

Abstract

To provide a millable silicone rubber compound that yields a cured product with low hardness, even though the millable silicone rubber compound exhibits high plasticity and low plastic rebound, as well as a millable silicone rubber composition.SOLUTION: A millable silicone rubber compound is provided that contains (A) organopolysiloxane raw rubber having two or more alkenyl groups bound to silicon atoms in one molecule, with an average degree of polymerization of 3000-100000, (B) reinforcing silica with a predetermined specific surface area, and 3-glycidyloxypropyl silanol oligomer represented by the formula (1) (where R1 is a monovalent hydrocarbon group, R2 is a monovalent hydrocarbon group optionally substituted with a glycidyloxy group, R3 is a monovalent aliphatic hydrocarbon group, a, b, c and d are numbers fulfilling a≥0.5, b≥0, c≥0, d≥0, and a+b+c+d=1, and x and y are numbers fulfilling x≥1.0 and y≤0.5). A millable silicone rubber composition is also provided that contains the silicone rubber compound combined with (D) a curing agent.SELECTED DRAWING: None

Description

The present invention relates to a millable type silicone rubber compound and a millable type silicone rubber composition.

When manufacturing millable silicone rubber compounds or silicone rubber compositions, it is necessary to knead the organopolysiloxane raw rubber with a reinforcing filler. At that time, a surface treatment agent for the reinforcing filler, called a dispersant (wetter), is used. Usually, an organosilane or siloxane having a silanol group is used as the surface treatment agent.
However, when a large amount of surface treatment agent is used, the plasticity of the silicone rubber composition is reduced, and depending on the molding method, the molded product may deform under its own weight, resulting in a defective product. In addition, there is a drawback that the surface of the silicone rubber composition may feel sticky, resulting in poor processability. Conversely, when the amount of surface treatment agent added is insufficient, the plasticity increases, but there is a problem that crepe hardening (plastic reversion) becomes large.

In order to solve the above problems, methods have been used to increase the plasticity by adding resins or polycyclic aromatic compounds, but this has not solved the problem of plastic reversion. There is also a method of suppressing plastic reversion by heating the silicone rubber compound at a high temperature of 200°C or more for a long period of time, but this is not economical in terms of energy costs, etc. Patent Document 1 reports that the plasticity can be increased by condensing silanols by adding a catalyst for the condensation reaction of a specific organometallic compound to the silicone rubber compound and performing a heat treatment. This method is certainly effective in increasing the plasticity of the silicone rubber compound, but it is insufficient in terms of stability over time, and when it is made into a composition, the compression set of the cured product can be significantly deteriorated.

JP 2014-109014 A

The present invention has been made in consideration of the above circumstances, and aims to provide a millable type silicone rubber compound and a millable type silicone rubber composition that have high plasticity and little reversion to plasticity, even in a millable type silicone rubber compound that gives a cured product with low hardness.

As a result of intensive research into achieving the above object, the inventors discovered that by blending a specific 3-glycidyloxypropylsilanol oligomer with a millable type silicone rubber compound containing organopolysiloxane raw rubber (base polymer) and reinforcing silica, the plasticity of the silicone rubber compound increases and plastic reversion is reduced, which led to the creation of the present invention.

（式中、Ｒ¹は、炭素数１～１０の１価炭化水素基であり、Ｒ²は、それぞれ独立して、グリシジルオキシ基で置換されていてもよい炭素数１～１０の１価炭化水素基であり、Ｒ³は、炭素数１～１０の１価の脂肪族炭化水素基であり、ａ、ｂ、ｃ及びｄは、ａ≧０．５、ｂ≧０、ｃ≧０、ｄ≧０、かつａ＋ｂ＋ｃ＋ｄ＝１を満たす数であり、ｘ及びｙは、ｘ≧１．０、ｙ≦０．５を満たす数である。）
を含むミラブル型シリコーンゴムコンパウンド。
２． 上記（Ｃ）成分の重量平均分子量が、５００～１０，０００である１記載のミラブル型シリコーンゴムコンパウンド。
３． 上記式（１）において、ｂ、ｃ、ｄが、ｂ＝０、０≦ｃ≦０．５、０≦ｄ≦０．２を満たす数である１記載のミラブル型シリコーンゴムコンパウンド。
４． １～３のいずれかに記載のミラブル型シリコーンゴムコンパウンド１００質量部、
（Ｄ）硬化剤：硬化有効量
含むミラブル型シリコーンゴム組成物。
５． 前記（Ｄ）成分が、（Ｄ１）付加反応型硬化剤であって、前記（Ｄ１）成分は、
（ａ）１分子中に２個以上のヒドロシリル基を有するオルガノハイドロジェンポリシロキサン：上記（Ａ）成分中のケイ素原子に結合したアルケニル基に対する（ａ）オルガノハイドロジェンポリシロキサン中のヒドロシリル基のモル比（ヒドロシリル基／アルケニル基）が、０．５～１０となる量、及び
（ｂ）ヒドロシリル化触媒：（Ａ）成分の質量に対して白金族金属の質量に換算して１ｐｐｍ～１質量％
を含むものである４記載のミラブル型シリコーンゴム組成物。
６． 前記（Ｄ）成分が、（Ｄ２）有機過酸化物硬化剤であって、前記ミラブル型シリコーンコンパウンド１００質量部に対して前記（Ｄ２）成分を０．１～８質量部含有する４記載のミラブル型シリコーンゴム組成物。 That is, the present invention provides the following millable type silicone rubber compound and silicone rubber composition. Note that in the present invention, a mixture containing the following components (A) to (C) before blending with a curing agent is referred to as the silicone rubber compound, and this compound blended with a curing agent is referred to as the silicone rubber composition.
1. (A) organopolysiloxane gum having two or more alkenyl groups bonded to silicon atoms in each molecule and an average degree of polymerization of 3,000 to 100,000: 100 parts by mass,
(B) reinforcing silica having a specific surface area of 50 to 450 m ² /g as measured by the BET adsorption method: 5 to 50 parts by mass,
(C) 3-glycidyloxypropylsilanol oligomer represented by the following formula (1): 0.1 to 15 parts by mass

(In the formula, R ¹ is a monovalent hydrocarbon group having 1 to 10 carbon atoms, R ² are each independently a monovalent hydrocarbon group having 1 to 10 carbon atoms which may be substituted with a glycidyloxy group, R ³ is a monovalent aliphatic hydrocarbon group having 1 to 10 carbon atoms, a, b, c, and d are numbers which satisfy a ≧ 0.5, b ≧ 0, c ≧ 0, d ≧ 0 and a + b + c + d = 1, and x and y are numbers which satisfy x ≧ 1.0 and y ≦ 0.5.)
A millable type silicone rubber compound comprising:
2. The millable type silicone rubber compound according to 1, wherein the weight average molecular weight of component (C) is 500 to 10,000.
3. The millable type silicone rubber compound according to 1, wherein in the above formula (1), b, c, and d are numbers satisfying b=0, 0≦c≦0.5, and 0≦d≦0.2.
4. 100 parts by mass of the millable type silicone rubber compound according to any one of 1 to 3,
(D) Curing agent: A millable type silicone rubber composition containing an effective curing amount.
5. The component (D) is an addition reaction type curing agent (D1), and the component (D1) is
(a) an organohydrogenpolysiloxane having two or more hydrosilyl groups per molecule: an amount such that the molar ratio of hydrosilyl groups in the organohydrogenpolysiloxane (a) to alkenyl groups bonded to silicon atoms in the component (A) (hydrosilyl groups/alkenyl groups) is 0.5 to 10; and (b) a hydrosilylation catalyst: 1 ppm to 1% by mass, calculated as the mass of platinum group metal relative to the mass of component (A).
5. The millable type silicone rubber composition according to claim 4, which comprises
6. The millable type silicone rubber composition according to 4, wherein the component (D) is an organic peroxide curing agent (D2), and the millable type silicone rubber composition contains 0.1 to 8 parts by mass of the component (D2) per 100 parts by mass of the millable type silicone compound.

According to the present invention, it is possible to provide millable type silicone rubber compounds and millable type silicone rubber compositions that have high plasticity and little reversion to plasticity, even in the case of millable type silicone rubber compounds that give cured products with low hardness.

1 is a ¹ H-NMR spectrum chart of the 3-glycidyloxypropylsilanol oligomer (C) used in the present invention, synthesized in Synthesis Example 1.

The present invention will now be described in more detail.
(1) Silicone Rubber Compound The millable type silicone rubber compound of the present invention contains the following components (A) to (C):
(A) an organopolysiloxane gum having an average degree of polymerization of 3,000 to 100,000 and containing two or more alkenyl groups bonded to silicon atoms in each molecule; (B) a reinforcing silica having a specific surface area of 50 to 450 m ² /g as measured by the BET adsorption method; and (C) a 3-glycidyloxypropylsilanol oligomer represented by the following formula (1):

-Component (A)-
In the present invention, component (A) is an organopolysiloxane raw rubber having two or more silicon-bonded alkenyl groups per molecule. Here, raw rubber refers to a state in which there is no self-flowing property at 25°C.

The alkenyl group preferably has 2 to 8 carbon atoms, and more preferably has 2 to 6 carbon atoms. Specific examples include vinyl, allyl, butenyl, pentenyl, hexenyl, and cyclohexenyl groups. Of these, the vinyl group is preferred.

Component (A) is also characterized by having two or more of the above alkenyl groups in one molecule, preferably 2 to 50, and more preferably 2 to 20 alkenyl groups. In this case, it is preferable that 0.01 to 20 mol %, and particularly 0.02 to 10 mol %, of all siloxane units in the organopolysiloxane are siloxane units having an alkenyl group. The alkenyl group may be bonded to a silicon atom at the molecular chain terminal, or to a silicon atom in the middle of the molecular chain (non-terminal of the molecular chain), or both, but it is preferable that the alkenyl group is bonded to a silicon atom at at least the molecular chain terminal.
In addition, it is preferable that 80 mol % or more, preferably 90 mol % or more, more preferably 95 mol % or more, of all siloxane units in the organopolysiloxane, and even more preferably all siloxane units except for siloxane units having alkenyl groups, are dialkylsiloxy groups, and more preferably dimethylsiloxy groups.

Substituents other than alkenyl groups bonded to silicon atoms are not particularly limited, and examples thereof include monovalent hydrocarbon groups having 1 to 12 carbon atoms, preferably 1 to 8 carbon atoms. The monovalent hydrocarbon group may be linear, branched, or cyclic, and specific examples thereof include alkyl groups such as methyl, ethyl, propyl, butyl, hexyl, and octyl groups; cycloalkyl groups such as cyclopentyl and cyclohexyl groups; aryl groups such as phenyl and tolyl groups; and aralkyl groups such as benzyl and 2-phenylethyl groups.
Furthermore, halogen-substituted monovalent hydrocarbon groups such as fluoroalkyl groups in which some of the hydrogen atoms of these monovalent hydrocarbon groups have been substituted with halogen atoms may also be used.
Of these, a methyl group and a phenyl group are preferred, and a methyl group is more preferred.

The molecular structure of the organopolysiloxane, component (A), is preferably linear or partially branched. Specifically, the repeating structure of the diorganosiloxane units constituting the main chain of the organopolysiloxane is preferably one consisting of repeating dimethylsiloxane units alone, or one in which diorganosiloxane units such as diphenylsiloxane units, methylphenylsiloxane units, or methylvinylsiloxane units have been introduced as part of this.

In addition, both molecular chain terminals are preferably capped with a group selected from the group consisting of trimethylsiloxy groups, dimethylphenylsiloxy groups, vinyldimethylsiloxy groups, divinylmethylsiloxy groups, trivinylsiloxy groups, methylphenylvinylsiloxy groups, etc., and are particularly preferably capped with vinyldimethylsiloxy groups.
Specific examples of the organopolysiloxane of component (A) include dimethylpolysiloxanes capped at both molecular chain terminals with dimethylvinylsiloxy groups, dimethylpolysiloxanes capped at both molecular chain terminals with methylphenylvinylsiloxy groups, dimethylsiloxane-methylphenylsiloxane copolymers capped at both molecular chain terminals with dimethylvinylsiloxy groups, dimethylsiloxane-methylvinylsiloxane copolymers capped at both molecular chain terminals with dimethylvinylsiloxy groups, dimethylsiloxane-methylvinylsiloxane copolymers capped at both molecular chain terminals with trimethylsiloxy groups, etc. Among these, preferred is dimethylsiloxane-methylvinylsiloxane copolymers capped at both molecular chain terminals with dimethylvinylsiloxy groups.

Such organopolysiloxanes can be obtained, for example, by (co)hydrolytic condensation of one or more organohalogenosilanes, or by ring-opening polymerization of cyclic polysiloxanes (siloxane trimers, tetramers, etc.) using an alkaline or acidic catalyst.

The average degree of polymerization of the organopolysiloxane is from 3,000 to 100,000, preferably from 3,500 to 50,000, more preferably from 4,000 to 30,000, even more preferably from 4,500 to 20,000, and particularly preferably from 4,500 to 10,000. If the average degree of polymerization is too low, the dispersion of the silica of component (B) may result in the formation of agglomerates, or the agglomerates may make dispersion difficult.
The average degree of polymerization is calculated from the weight average molecular weight determined by gel permeation chromatography (GPC) analysis measured under the conditions shown below, using polystyrene of known molecular weight as a standard substance.
[Measurement conditions]
Apparatus: Tosoh Corporation HLC-8320GPC
Developing solvent: tetrahydrofuran (THF)
Flow rate: 0.6mL/min
Detector: Refractive index detector (RI)
Column: TSK Guard column Super H-H
TSKgel SuperHM-N (6.0mm I.D. x 15cm x 1)
TSKgel SuperH2500 (6.0mm I.D. x 15cm x 1)
(All manufactured by Tosoh Corporation)
Column temperature: 40°C
Sample injection volume: 50 μL (THF solution with a concentration of 2.0% by mass)

Component (A) may be used alone or as a mixture of two or more types with different molecular weights (degrees of polymerization) or molecular structures.

-Component (B)-
Component (B) is reinforcing silica. Component (B) reinforcing silica is a filler added to obtain a silicone rubber composition with excellent mechanical strength. For this purpose, the specific surface area of the reinforcing silica, as measured by the BET adsorption method, must be 50 to 450 m ² /g, preferably 100 to 450 m ² /g, and more preferably 100 to 300 m ² /g. If the specific surface area is less than 50 m ² /g, the mechanical strength of the cured product will be reduced.

Examples of such reinforcing silica include fumed silica and precipitated silica, and those whose surfaces have been hydrophobized with chlorosilane, hexamethyldisilazane, etc. are also preferably used. Among these, fumed silica, which has excellent dynamic fatigue properties, is preferred. Regarding the hydrophobization treatment, the reinforcing silica may be mixed while being treated with the hydrophobizing agent when mixed, or commercially available reinforcing silica fine powder that has been hydrophobized may be used.
The component (B) may be used alone or in combination of two or more types.

The amount of reinforcing silica in component (B) is 5 to 50 parts by mass, preferably 10 to 45 parts by mass, per 100 parts by mass of the organopolysiloxane in component (A). If the amount of component (B) is too small, the reinforcing effect is not obtained, and if the amount is too large, processability is poor, mechanical strength is reduced, and dynamic fatigue durability is also deteriorated.

--Component (C)--
In the present invention, 3-glycidyloxypropylsilanol oligomer represented by the following formula (1) is used as component (C). This component (C) is an essential component for interacting or reacting with hydroxyl groups present on the surface of silica, which is the aforementioned component (B), and for quickly dispersing component (B) in component (A).

In the above formula, R ¹ is a monovalent hydrocarbon group having 1 to 10 carbon atoms, preferably a monovalent hydrocarbon group having 1 to 6 carbon atoms. The monovalent hydrocarbon group of R ¹ may be linear, branched, or cyclic, and specific examples thereof include alkyl groups such as methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, and decyl groups; cycloalkyl groups such as cyclopentyl and cyclohexyl groups; alkenyl groups such as vinyl and allyl groups; and aryl groups such as phenyl and naphthyl groups. Among these, methyl, ethyl, propyl, and phenyl groups are preferred, methyl and ethyl groups are more preferred, and methyl is even more preferred.

Each R ² is independently a monovalent hydrocarbon group having 1 to 10 carbon atoms, which may be substituted with a glycidyloxy group, and preferably a monovalent hydrocarbon group having 1 to 6 carbon atoms. The monovalent hydrocarbon group of R ² may be linear, branched, or cyclic, and specific examples thereof include the same as those exemplified for R ¹ above, and glycidyloxy-substituted alkyl groups such as glycidyloxypropyl and glycidyloxyoctyl groups. In addition, when R ² is a monovalent hydrocarbon group substituted with a glycidyloxy group, the number of carbon atoms does not include the number of carbon atoms of the glycidyloxy group. Among these, methyl, ethyl, propyl, glycidyloxypropyl, and phenyl groups are preferred, methyl and ethyl groups are more preferred, and methyl groups are even more preferred.

^R3 is an aliphatic hydrocarbon group having 1 to 10 carbon atoms, preferably 1 to 4 carbon atoms, more preferably 1 or 2 carbon atoms, and even more preferably an alkyl group having 1 or 2 carbon atoms. The aliphatic hydrocarbon group of ^R3 may be linear, branched, or cyclic, and specific examples thereof include alkyl groups such as methyl, ethyl, propyl, and butyl groups; and alkenyl groups such as vinyl and allyl groups, with methyl, ethyl, propyl, and butyl groups being preferred, with methyl and ethyl groups being more preferred, and methyl being even more preferred.

a, b, c, and d each represent a molar ratio of the respective siloxane units present, and are numbers that satisfy a≧0.5, b≧0, c≧0, d≧0, and a+b+c+d=1.
It is preferable that a is a number that satisfies 0.5≦a≦1. If a is less than 0.5, the amount of available epoxy groups will be so small that the intended effect cannot be expected, and the resulting silanol oligomer will have a high viscosity or become gummy or solid, making it difficult to handle.
The number b is preferably a number that satisfies 0≦b<0.5, and 0 is more preferable.
It is preferable that c is a number that satisfies 0≦c≦0.5.
The number d is preferably a number that satisfies 0≦d≦0.2, and 0 is more preferable.

x and y are the numbers of hydroxyl groups or alkoxy groups bonded to 1 mole of silicon atoms in the siloxane units a to d, and are numbers that satisfy x≧1.0 and y≦0.5.
It is preferable that x is a number that satisfies 1≦x≦2.
The value of y is preferably a number that satisfies y≦0.4, and more preferably a number that satisfies y≦0.3.

The component (C) is preferably one represented by the following formula (1a), and more preferably one represented by the following formula (1a').

In the above formula, ^R2 and ^R3 are the same as above, a1, c1, and d1 are numbers that satisfy a1 ≧ 0.5, 0 ≦ c1 ≦ 0.5, 0 ≦ d1 ≦ 0.2, and a1 + c1 + d1 = 1, and x1 and y1 are numbers that satisfy x1 ≧ 1, y1 ≦ 0.5.
As the component (C), those in which, in the above formula (1a'), R ² is a methyl group or a 3-glycidyloxypropyl group, and R ³ is a methyl group are more preferable.
The component (C) may be used alone or in combination of two or more types.

The weight average molecular weight of the oligomer of the (C) component is preferably 500 to 10,000, more preferably 500 to 1,000, from the viewpoint of the handling viscosity of the composition of the present invention. When an oligomer having a weight average molecular weight of less than 500 is used as the (C) component, the (C) component is easily volatile, and may volatilize during kneading, resulting in an unstable plasticity of the compound composition. In addition, the amount of volatile components is large, which may be industrially dangerous. On the other hand, when the weight average molecular weight of the (C) component exceeds 10,000, the viscosity of the (C) component becomes very high, making it difficult to mix, or the ability to wet the (B) component decreases, resulting in an extension of the mixing time or an unstable plasticity of the compound composition obtained, or in the worst case, the silica of the (B) component and the polymer of the (A) component may remain separated, making it impossible to obtain a compound composition.
The weight average molecular weight is a value determined by GPC under the same conditions as those described for component (A).

The method for producing component (C) used in the present invention is not particularly limited, but it can be produced, for example, by using a 3-glycidyloxypropyl group-containing silane compound such as 3-glycidyloxypropyltrimethoxysilane or 3-glycidyloxypropyltriethoxysilane represented by the following formula (i) or a mixture thereof as the essential silane monomer raw material, and, if necessary, (co)hydrolyzing under acidic conditions a silane monomer containing one or more of a silane compound represented by the following formula (ii), a silane compound represented by the following formula (iii), and a silane compound represented by the following formula (iv).

（式中、Ｒ¹～Ｒ³は、上記と同じである。）

(wherein R ¹ to R ³ are the same as above).

Specific examples of the 3-glycidyloxypropyl group-containing silane compound represented by the above formula (i) include 3-glycidyloxypropyltrimethoxysilane, 3-glycidyloxypropyltriethoxysilane, 3-glycidyloxypropyltripropoxysilane, 3-glycidyloxypropyltributoxysilane, and the like.
Specific examples of the silane compound represented by the above formula (ii) include methyltrimethoxysilane, methyltriethoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, propyltrimethoxysilane, propyltriethoxysilane, butyltrimethoxysilane, butyltriethoxysilane, hexyltrimethoxysilane, hexyltriethoxysilane, cyclohexyltrimethoxysilane, cyclohexyltriethoxysilane, phenyltrimethoxysilane, phenyltriethoxysilane, octyltrimethoxysilane, octyltriethoxysilane, decyltrimethoxysilane, and decyltriethoxysilane.
Specific examples of the silane compound represented by the above formula (iii) include dimethyldimethoxysilane, dimethyldiethoxysilane, diethyldimethoxysilane, diethyldiethoxysilane, methylethyldimethoxysilane, methylethyldiethoxysilane, methylpropyldimethoxysilane, methylpropyldiethoxysilane, 3-glycidyloxypropylmethyldimethoxysilane, 3-glycidyloxypropylmethyldiethoxysilane, cyclopentylmethyldimethoxysilane, cyclohexylmethyldimethoxysilane, methylphenyldimethoxysilane, methylphenyldiethoxysilane, diphenyldimethoxysilane, diphenyldiethoxysilane, methyloctyldimethoxysilane, and the like.
Specific examples of the silane compound represented by the above formula (iv) include tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, and tetrabutoxysilane.
In addition, hydrolysis condensation products of these may also be used. These may be used alone or in combination of two or more.

The amount of water used in the hydrolysis and condensation reaction is preferably 0.8 to 1.1 times by mole per mole of Si(OR ³ ) group (R ³ is the same as above) such as an alkoxysilyl group of the silane monomer used as a raw material.

The acid component used to adjust the acidic conditions during the hydrolysis reaction is not particularly limited as long as it is a commercially available Brønsted acid, but from the viewpoint of ease of availability, formic acid, acetic acid, citric acid, hydrochloric acid, and nitric acid are preferred. The amount of acid used is preferably 0.0001 to 0.01 mole per mole of silane monomer from the viewpoint of suppressing an increase in the molecular weight of the organopolysiloxane obtained by an excessive dehydration condensation reaction between silanols and a decrease in water solubility due to a decrease in the amount of silanol groups.

In the hydrolysis reaction, an organic solvent may be used as necessary within a range that does not inhibit the reaction. The organic solvent used is preferably one that is compatible with water, which is the raw material for the reaction, and is preferably an alcohol, an ester, a ketone, an ether, or the like. In addition, taking into consideration the distillation conditions for removing the generated alcohol, the organic solvent preferably has a low boiling point, and is preferably a solvent having a boiling point of 150° C. or less under atmospheric pressure.
Specific examples of alcohols include methanol, ethanol, propanol, isopropanol, butanol, isobutanol, pentyl alcohol, neopentyl alcohol, hexyl alcohol, and cyclohexyl alcohol.
Specific examples of esters include ethyl acetate and butyl acetate.
Specific examples of ketones include acetone, methyl ethyl ketone, and cyclohexanone.
Specific examples of ethers include tetrahydrofuran, tetrahydropyran, and dioxane.

As reaction conditions, it is preferable to mix the above silane monomer with water and stir at 55 to 70°C for 1 to 5 hours to allow the hydrolysis and condensation reaction of the silane monomer to proceed, and then distill off the water/alcohol mixture under reduced pressure at a temperature range of 30 to 80°C.

The 3-glycidyloxypropylsilanol oligomer used in the present invention preferably contains 1% by mass or less of water and free alcohol. Such a composition allows the composition to be free of volatile organic compounds (VOCs), which is advantageous in reducing the VOCs of the entire silicone composition to which it is added. In the present invention, "free of VOCs" means that the content of free alcohol in the oligomer or the composition of the present invention is preferably 1% by mass or less. Here, alcohol refers in particular to methanol or ethanol. Water does not fall under the category of VOCs, but if present in excess, it may react with epoxy groups, so it is desirable to avoid water as much as possible. If the content is 1% by mass or less, there is little risk of a decrease in the active ingredient due to volatilization during storage, or of alcohols being generated by hydrolysis due to moisture in the silicone composition or moisture in the air, and there is no concern about foaming or pinholes occurring when the silicone composition is heated and cured, and a drying process before use is not required.

The amount of 3-glycidyloxypropylsilanol oligomer (C) added is 0.1 to 15 parts by mass, preferably 0.5 to 10 parts by mass, and more preferably 1 to 8 parts by mass, per 100 parts by mass of the (A) component. If the amount of (C) added is less than 0.1 parts by mass, plastic reversion occurs, causing problems in subsequent processability, and in the worst case, the compound composition cannot be obtained. If the amount of (C) added exceeds 15 parts by mass, the resulting compound composition becomes sticky, causing subsequent processability to deteriorate, and the mechanical properties of the silicone rubber obtained by curing this compound composition are reduced.

(2) Method for Producing Silicone Rubber Compound There are no particular limitations on the method for producing the silicone rubber compound of the present invention. For example, the silicone rubber compound of the present invention can be obtained by uniformly mixing the above-described components using a rubber kneader such as a two-roll mixer, a Banbury mixer, or a dough mixer (kneader), and then subjecting the mixture to a heat treatment as necessary.

The base compound of components (A) to (C) may be mixed under heating. The preferred temperature is 0 to 200°C, more preferably 10 to 180°C, and even more preferably 20 to 170°C. There are no particular restrictions on the time for mixing components (A) to (C), but in consideration of production efficiency, it is preferably 1 to 300 minutes, and more preferably 10 to 120 minutes.

When mixing under heat, it is preferable to mix the (A) to (C) components in predetermined amounts uniformly to form a compound, and then perform low-temperature mixing (cold blending) at a temperature range of 20 to 80°C for 10 to 60 minutes. By providing a low-temperature mixing time, there is no need to worry about the silanol oligomer (C) component being thermally decomposed or volatilizing during blending, and the surface treatment reaction of (B) component can be promoted.

(3) Silicone Rubber Composition By further compounding the millable type silicone rubber compound obtained as described above with (D) a curing agent (vulcanizing agent), a millable type silicone rubber composition can be obtained.

-Component (D)-
The curing agent for component (D) is not particularly limited as long as it can cure component (A), but generally, any known rubber curing agent can be used, such as the following components (D1) and (D2), etc. Of these, the organic peroxide for component (D2) is preferred.
(D1) An addition reaction (hydrosilylation reaction) type curing agent, that is, a hydrosilylation reaction curing agent consisting of a combination of an organohydrogenpolysiloxane (crosslinking agent) and a hydrosilylation catalyst. (D2) An organic peroxide.

(D1) Addition reaction type curing agent (a) Organohydrogenpolysiloxane The organohydrogenpolysiloxane used as the crosslinking agent for the above-mentioned (D1) addition reaction type curing agent is preferably one having two or more hydrosilyl groups in one molecule, and particularly preferably an organohydrogenpolysiloxane represented by the following formula (2):

Here, R ⁴ is independently a hydrogen atom, or a group selected from an alkyl group having 1 to 8 carbon atoms, preferably 1 to 6 carbon atoms; a cycloalkyl group having 6 to 10 carbon atoms, preferably 6 to 8 carbon atoms; an aryl group having 6 to 10 carbon atoms, preferably 6 to 8 carbon atoms, and an aralkyl group having 7 to 10 carbon atoms, preferably 7 to 9 carbon atoms. However, in one molecule, 2 or more, preferably 2 to 200, more preferably 2 to 130 R ^4s are hydrogen atoms. Note that two or more hydrogen atoms cannot be present on the same silicon atom.

The alkyl group of R ⁴ may be either linear or branched, and specific examples thereof include methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, pentyl, and hexyl groups.
Specific examples of the cycloalkyl group include cyclopentyl and cyclohexyl groups.
Specific examples of the aryl group include phenyl and tolyl groups.
Specific examples of the aralkyl group include benzyl and 2-phenylpropyl groups.
In addition, fluoroalkyl groups in which some or all of the hydrogen atoms of these groups have been substituted with halogen atoms such as fluorine atoms may also be used.

e is an integer satisfying 2≦e≦30, preferably 2≦e≦20.
f is an integer satisfying 0≦f≦300, preferably 3≦f≦200.
g is an integer satisfying 0≦g≦10, preferably 0≦g≦5.
h is an integer satisfying 0≦h≦30, preferably 0≦h≦20.
The siloxane units may be bonded in a block or random manner.

The molecular structure of the organohydrogenpolysiloxane may be any of linear, cyclic, branched, and three-dimensional network structures. In this case, the number of silicon atoms (or degree of polymerization) in one molecule is preferably 2 to 300, more preferably about 4 to 200, and those that are liquid at 25°C are preferably used. The hydrosilyl group may be at the molecular chain terminal, in the side chain (in the middle of the molecular chain), or both. The method for measuring the degree of polymerization is as explained for component (A).
The organohydrogenpolysiloxanes may be used alone or in combination of two or more.

Specific examples of such organohydrogenpolysiloxanes include 1,1,3,3-tetramethyldisiloxane, 1,3,5,7-tetramethylcyclotetrasiloxane, tris(dimethylhydrogensiloxy)methylsilane, tris(dimethylhydrogensiloxy)phenylsilane, methylhydrogenpolysiloxanes blocked at both ends with trimethylsiloxy groups, dimethylsiloxane-methylhydrogensiloxane copolymers blocked at both ends with trimethylsiloxy groups, dimethylpolysiloxanes blocked at both ends with dimethylhydrogensiloxy groups, Dimethylhydrogensiloxane-methylhydrogensiloxane copolymer terminated at both ends with dimethylhydrogensiloxy groups, methylhydrogensiloxane-diphenylsiloxane copolymer terminated at both ends with trimethylsiloxy groups, methylhydrogensiloxane-diphenylsiloxane-dimethylsiloxane copolymer terminated at both ends with trimethylsiloxy groups, cyclic methylhydrogenpolysiloxane, cyclic methylhydrogensiloxane-dimethylsiloxane copolymer, cyclic methylhydrogensiloxane-diphenylsiloxane-dimethylsiloxane copolymer, (CH _and copolymers consisting of ( _CH3 ) _{2HSiO1 / 2} units, SiO4 _{/2 units} and ( _{C6H5 )} SiO3 _/2 units, as well as copolymers in which part or all of the methyl groups in the above exemplary compounds have been substituted with other alkyl groups, such as ethyl groups, propyl groups, or aryl groups, such as _phenyl groups.
Specific examples of such organohydrogenpolysiloxanes include compounds of the following structural formulas:

（式中、ｋは、２～１０の整数、ｓ及びｔは、それぞれ０～１０の整数、ｐ及びｑは、それぞれ１～３０の整数である。）

(In the formula, k is an integer from 2 to 10, s and t are each an integer from 0 to 10, and p and q are each an integer from 1 to 30.)

The organohydrogenpolysiloxane of component (a) preferably has a viscosity at 25°C of 0.5 to 10,000 mPa·s, and more preferably 1 to 300 mPa·s. The above viscosity is measured using a rotational viscometer according to the method described in JIS K7117-1:1999.

The organohydrogenpolysiloxane of component (a) is preferably blended in an amount such that the molar ratio of hydrosilyl groups in the organohydrogenpolysiloxane to the alkenyl groups bonded to silicon atoms in component (A) (hydrosilyl groups/alkenyl groups) is 0.5 to 10, more preferably 0.8 to 6, and even more preferably 1 to 5. If it is less than 0.5, crosslinking will be insufficient and sufficient mechanical strength may not be obtained after curing, while if it exceeds 10, the physical properties after curing will decrease, and in particular the heat resistance and compression set resistance may be significantly deteriorated.

(b) Hydrosilylation Catalyst The hydrosilylation catalyst used in the (D1) addition reaction type curing agent is a catalyst that promotes the addition reaction of the alkenyl groups in the (A) component with the hydrosilyl groups in the organohydrogenpolysiloxane used as a crosslinking agent.
Examples of hydrosilylation catalysts include platinum group metal catalysts such as ruthenium and platinum. Platinum group metal catalysts include platinum group metals and their compounds. For these, catalysts that have been known as catalysts for addition reaction curing silicone rubber compositions can be used.
Specific examples thereof include platinum-based catalysts such as particulate platinum metal adsorbed on a carrier such as platinum black, silica, alumina or silica gel, platinic chloride, chloroplatinic acid, a reaction product of chloroplatinic acid with a monohydric alcohol, a complex of chloroplatinic acid with an olefin, a complex of chloroplatinic acid with a vinyl group-containing (poly)siloxane, a complex of chloroplatinic acid with a phosphorous ester, and a complex of these with a vinyl group-containing (poly)siloxane; a palladium catalyst; a rhodium catalyst; a ruthenium catalyst, etc. Among these, platinum or a platinum compound is particularly preferred.

The amount of hydrosilylation catalyst added may be a catalytic amount capable of promoting the addition reaction, and is usually preferably 1 ppm to 1 mass %, and more preferably 10 to 500 ppm, calculated as the mass of platinum group metal relative to the mass of component (A). If the amount added is less than 1 ppm, the addition reaction may not be promoted sufficiently, resulting in insufficient curing. On the other hand, if the amount exceeds 1 mass %, adding more than this amount has little effect on reactivity and may be uneconomical.

In addition to the above catalysts, an addition crosslinking inhibitor may be used to adjust the curing rate. Specific examples include ethynylcyclohexanol and tetramethyltetravinylcyclotetrasiloxane.

(D2) Organic Peroxide On the other hand, examples of the (D2) organic peroxide include benzoyl peroxide, 2,4-dichlorobenzoyl peroxide, p-methylbenzoyl peroxide, o-methylbenzoyl peroxide, 2,4-dicumyl peroxide, 2,5-dimethyl-2,5-bis(t-butylperoxy)hexane, di-t-butyl peroxide, t-butyl perbenzoate, 1,6-hexanediol-bis-t-butylperoxycarbonate, etc. Among these, 2,5-dimethyl-2,5-bis(t-butylperoxy)hexane is preferred.

The amount of organic peroxide added is an effective curing amount, and is preferably 0.1 to 8 parts by mass, and more preferably 0.2 to 3 parts by mass, per 100 parts by mass of component (A). If the amount added is sufficient, the crosslinking reaction will proceed sufficiently and there will be no deterioration in physical properties such as a decrease in hardness, insufficient rubber strength, or an increase in compression set. Furthermore, if the amount added does not exceed the above amount, it is economically preferable, and there will be sufficiently little decomposition product of the curing agent, so there will be no deterioration in physical properties such as an increase in compression set, or increased discoloration of the obtained sheet.

-Other ingredients-
In addition to the above-mentioned components, the millable type silicone rubber composition of the present invention may optionally contain electrical conductivity imparting agents such as carbon black, flame retardant imparting agents such as iron oxides and halogen compounds, antistatic agents, softeners, antioxidants, ultraviolet absorbers, colorants, etc., within the scope of the invention not impairing its effects.

(4) Method for Producing and Curing the Composition The method for producing the silicone rubber composition according to the present invention is not particularly limited, but it can be obtained, for example, by the same method as the method for producing the silicone rubber compound described above. In this case, for example, it is preferable to previously mix (A) organopolysiloxane, (B) fine powder silica-based filler as reinforcing silica, (C) silanol oligomer, etc. to prepare a base compound, and then add and mix (D) a curing agent to this.

The millable silicone rubber composition of the present invention thus obtained can be cured at preferably 80 to 300°C, more preferably 100 to 200°C, for preferably 1 minute to 10 hours, more preferably 5 minutes to 5 hours, to obtain a cured silicone rubber.

The present invention will be specifically explained below using synthesis examples, comparative synthesis examples, examples, and comparative examples, but the present invention is not limited to these. In the following examples, unless otherwise specified, "parts" and "%" mean "parts by mass" and "% by mass", respectively. The devices and measurement conditions used in the examples are as follows.

(1) GPC Measurement Conditions (Measurement of Weight Average Molecular Weight)
Apparatus: Tosoh Corporation HLC-8320GPC
Developing solvent: tetrahydrofuran (THF)
Flow rate: 0.6mL/min
Detector: Refractive index detector (RI)
Column: TSK Guard column Super H-H
TSKgel SuperHM-N (6.0mm I.D. x 15cm x 1)
TSKgel SuperH2500 (6.0mm I.D. x 15cm x 1)
(All manufactured by Tosoh Corporation)
Column temperature: 40°C
Sample injection volume: 50 μL (THF solution with a concentration of 2.0% by mass)
Standard: Monodisperse polystyrene (2) Proton nuclear magnetic resonance spectrum ( ¹ H-NMR spectrum) measurement conditions Apparatus: AVANCE III 400 manufactured by BURKER
Solvent: CDCl ₃ (deuterated chloroform)
Internal standard: tetramethylsilane (TMS)
(3) Kinematic viscosity: Measured at 25°C using a Cannon-Fenske viscometer according to the method described in JIS Z8803:2011.

(4) Measurement of plasticity: The silicone rubber compound was kneaded 15 times with a triple roll mill, and the plasticity was measured 10 minutes later (initial) using the method described in JIS K6249:2003. The plasticity after aging at 40°C for 24 hours (accelerated at 40°C) was also measured in the same manner to investigate the storage stability of the silicone rubber compound. If the difference between the initial plasticity and the plasticity after aging at 40°C was 50 or more, it was determined that the long-term storage stability had deteriorated, and if the difference in plasticity was less than 50, it was determined that the compound had passed the test.

(5) Measurement of physical properties of silicone rubber cured product: A predetermined amount of the curing agent (D) was added to 100 parts of the silicone rubber compound described below, and the mixture was mixed uniformly using a two-roll mill. The composition was then heated at 120°C for 10 minutes (Example 5, Comparative Example 6) or at 165°C for 10 minutes (
(Examples 1 to 4, Comparative Examples 1 to 5) were subjected to press curing. Then, post curing was performed at 200° C. for 4 hours, and the 2 mm thick test sheets, 6 mm thick and 29.5 mm thick test sheets,
A cylindrical rubber molding of Φ was prepared. The density, hardness (Durometer A), and compression set (180°C/22 hours, 25% compression) of the prepared test sheet molding or cylindrical rubber molding were measured based on the description in JIS K6249:2003. The resilience modulus was also measured by the method described in JIS K6255:2013. A rubber having a high resilience modulus and a low compression set was judged to have good rubber properties.

[1] Synthesis of 3-glycidyloxypropylsilanol oligomer [Synthesis Example 1] Synthesis of component (C-1) 472 g (2.0 mol) of 3-glycidyloxypropyltrimethoxysilane was placed in a 1 L three-neck flask equipped with a stirrer, a cooling tube, a dropping funnel and a thermometer. 108 g (6.0 mol as the amount of water) of 0.2% hydrochloric acid was dropped into this. During the dropping, the temperature was controlled by appropriately cooling so that the internal temperature was in the range of 20 to 40 ° C. After the dropping was completed, the mixture was heated and stirred at 70 ° C. for 1 hour to proceed with the hydrolysis and condensation reaction of the methoxysilyl group, and then the by-product methanol and excess water were distilled off under reduced pressure at 70 ° C. to obtain a colorless and transparent liquid.
This liquid was compatible and soluble in water at will, and the resulting oligomer had a kinetic viscosity of 726 ^mm2 /s, an epoxy functional group amount of 189 g/mol, and a weight average molecular weight of 830. Analysis of the above by ^1H -NMR, GPC, etc. revealed that it had the average composition structure shown in formula (3) below. The ^1H -NMR spectrum chart is shown in Figure 1.

[Synthesis Example 2] Synthesis of component (C-2) The target 3-glycidyloxypropyl group-containing silanol oligomer was obtained in the same manner as in Synthesis Example 1, except that the amount of 3-glycidyloxypropyltrimethoxysilane was 236 g (1.0 mol), the amount of dimethyldimethoxysilane was 120 g (1.0 mol), and the amount of 0.2% hydrochloric acid was 90 g (5.0 mol as water).
The resulting oligomer had a kinetic viscosity of 218 mm ² /s, an epoxy functional group amount of 258 g/mol, and a weight average molecular weight of 700. Analysis by ¹ H-NMR and GPC measurements revealed that the product had a structure represented by the following formula (4).

[Synthesis Example 3] Synthesis of component (C-3) The target 3-glycidyloxypropyl group-containing silanol oligomer was obtained in the same manner as in Synthesis Example 1, except that the amounts of 3-glycidyloxypropyltrimethoxysilane and 3-glycidyloxypropylmethyldimethoxysilane were 425 g (1.8 mol), 44 g (0.2 mol), and 104.4 g of 0.2% hydrochloric acid (5.8 mol as water) were used.
The resulting oligomer had a kinetic viscosity of 361 mm ² /s, an epoxy functional group amount of 200 g/mol, and a weight average molecular weight of 510. Analysis by ¹ H-NMR and GPC measurements revealed that the product had a structure represented by the following formula (5).

Comparative Synthesis Example 4 Synthesis of Component (Comparative to C-4) A silanol group-containing oligomer not containing 3-glycidyloxypropyl groups was obtained in the same manner as in Synthesis Example 1, except that 31.2 g (0.3 mol) of trimethylmethoxysilane, 48.0 g (0.4 mol) of dimethyldimethoxysilane, and 40.8 g (0.3 mol) of methyltrimethoxysilane were used instead of 3-glycidyloxypropyltrimethoxysilane.
The resulting oligomer had a kinetic viscosity of 15 mm ² /s and a weight average molecular weight of 1,150. Analysis by ¹ H-NMR and GPC measurements revealed that the product had the structure shown in formula (6) below.

Comparative Synthesis Example 5 Synthesis of Component (Comparative to C-5) A linear polymer having silanol ends not containing 3-glycidyloxypropyl groups was obtained in the same manner as in Synthesis Example 1, except that 120 g (1.0 mol) of dimethyldimethoxysilane was used instead of 3-glycidyloxypropyltrimethoxysilane, and the amount of 0.2% hydrochloric acid was 90 g (5.0 mol as water).
The resulting polymer had a kinetic viscosity of 13 mm ² /s and a weight average molecular weight of 270. Analysis by ¹ H-NMR and GPC measurements revealed that the polymer had the structure shown in formula (7) below.

[2] Components The components used in the examples and comparative examples of the present invention are shown below.
(A) Organopolysiloxane raw rubber: Organopolysiloxane raw rubber consisting of 99.825 mol % dimethylsiloxane units, 0.15 mol % methylvinylsiloxane units, and 0.025 mol % dimethylvinylsiloxy units, having one vinyl group bonded to a silicon atom at each end of the molecular chain and 10 vinyl groups at the molecular chain side chains, and having an average degree of polymerization of 8,000. (B) Reinforcing silica: (B-1) As a reinforcing silica, a fumed silica having a BET specific surface area of 200 ^m2 /g that has not been surface-treated (product name: Aerosil 200, manufactured by Nippon Aerosil Co., Ltd.)
(B-2) As reinforcing silica, fumed silica (trade name: R-972, manufactured by Nippon Aerosil Co., Ltd.) having a BET specific surface area of 110 m ² /g and a carbon content of 0.9% and surface-treated with dimethyldichlorosilane was used.
(C) 3-glycidyloxypropylsilanol oligomer (C-1): Oligomer synthesized in Synthesis Example 1 (C-2): Oligomer synthesized in Synthesis Example 2 (C-3): Oligomer synthesized in Synthesis Example 3 (Comparative component)
(Comparative C-4): Oligomer synthesized in Comparative Synthesis Example 4 (Comparative C-5): Polymer synthesized in Comparative Synthesis Example 5 (Comparative C-6): 3-glycidyloxypropyltrimethoxysilane (trade name: KBM-403, manufactured by Shin-Etsu Chemical Co., Ltd., kinematic viscosity 3.0 mm ² /s, molecular weight 236)
(D) Curing Agent (D-1) Addition reaction type curing agent: (a) 0.85 parts of an organohydrogenpolysiloxane represented by the following formula (8) (manufactured by Shin-Etsu Chemical Co., Ltd., kinematic viscosity 17 mm ² /s),
(b) 0.01 parts of a platinum catalyst (manufactured by Shin-Etsu Chemical Co., Ltd.) containing 1% platinum atomic mass of chloroplatinic acid-divinyldisiloxane complex as a hydrosilylation catalyst;
Also, 0.05 parts of ethynylcyclohexanol was added as an addition reaction inhibitor to 100 parts of the silicone rubber compound.

（Ｄ－２）有機過酸化物硬化剤：２，５－ジメチル－２，５－ジ－（ｔ－ブチルパーオキシ）ヘキサン０．５部をシリコーンゴムコンパウンド１００部に添加した。

(D-2) Organic peroxide curing agent: 0.5 parts of 2,5-dimethyl-2,5-di-(t-butylperoxy)hexane was added to 100 parts of the silicone rubber compound.

[3] Production and evaluation of silicone rubber compound [Example 1-1]
100 parts of organopolysiloxane raw rubber (A), 25 parts of reinforcing silica (B-1), and 3 parts of 3-glycidyloxypropylsilanol oligomer (C-1) were charged into a kneader equipped with a heating function, and the above components were mixed at room temperature until uniformly mixed, and then cold blended for 30 minutes. Thereafter, the temperature was raised to 170°C using the heating temperature control function of the kneader, and the mixture was heated and kneaded for 2 hours to obtain silicone rubber compound 1. The plasticity of the obtained compound 1 was measured. The results are shown in Table 1.

[Examples 1-2 to 1-4, Comparative Examples 1-1 to 1-5]
Silicone rubber compounds 2 to 4 and comparative silicone rubber compounds 1 to 5 were obtained in the same manner as in Example 1-1, except that 3 parts of component (C-1) were replaced with components (C-2), (C-3), and (C-4 ratio) to (C-6 ratio) in the proportions shown in Table 1. The plasticity of the obtained silicone rubber compounds was measured. The results are shown in Table 1.

[Examples 1 to 5, Comparative Examples 1 to 6]
100 parts of organopolysiloxane raw rubber (A) were charged with 40 parts of reinforcing silica (B-2), and 5 parts of 3-glycidyloxypropylsilanol oligomer (C-2) (Example 1-5) or 5 parts (comparison with C-4) (Comparative Example 1-6) in a kneader, and simple mixing was carried out for 2 hours until the above components were uniformly mixed, to obtain silicone rubber compound 5 (Example 1-5) or comparative silicone rubber compound 6 (Comparative Example 1-6). The maximum temperature reached was 76°C. The plasticity of the obtained compound was measured. The results are shown in Table 1.

[4] Production of silicone rubber composition, production and evaluation of cured product [Example 2-1]
100 parts of the silicone rubber compound 1 was mixed with 0.5 parts of the curing agent (D-2) using a two-roll mill to homogeneously mix. The mixture was then molded at 165°C for 10 minutes and post-cured at 200°C for 4 hours to produce a 2 mm thick test sheet and a 6 mm thick, 29.5 mm diameter cylindrical rubber molded product.
The obtained sheets or cylindrical rubber moldings were used to evaluate the rubber properties shown in Table 1. The results are also shown in Table 1.

[Examples 2-2 to 2-4, Comparative Examples 2-1 to 2-5]
Silicone rubber compositions were prepared in the same manner as in Example 2-1, except that silicone rubber compounds 2 to 4 and comparative silicone rubber compounds 1 to 5 were used instead of silicone rubber compound 1, and rubber sheets and cylindrical rubber molded products were produced in the same manner as in Example 1, and various rubber properties were evaluated. The results are shown in Table 1.

[Examples 2-5 and Comparative Examples 2-6]
A predetermined amount of curing agent (D-1) was added to 100 parts of the above silicone compound 5 (Example 2-5) or comparative silicone rubber compound 6 (Comparative Example 2-6), and the mixture was uniformly mixed using a two-roll mill. The mixture was then molded at 120°C for 10 minutes and post-cured at 200°C for 4 hours to produce a 2 mm thick test sheet and a 6 mm thick, 29.5 mm diameter cylindrical rubber molded product.
The rubber properties shown in Table 1 were evaluated using the obtained rubber sheets or cylindrical rubber moldings. The results are also shown in Table 1.

[Evaluation Results]
Each of the silicone rubber compounds obtained in Examples 1-1 to 1-5 satisfied the requirements of the present invention, and as shown in Table 1, the initial plasticity of each of the millable type silicone rubber compounds of the Examples to which the 3-glycidyloxypropyl silanol oligomer of component (C) was added was high, and the increase in plasticity after 40°C/24h was also kept low, indicating that they had excellent long-term storage properties.

In contrast, in Comparative Example 1-1, component (C) was a silanol oligomer that did not contain 3-glycidyloxypropyl groups, and the initial plasticity was low and the long-term storage stability was also unacceptable.

In Comparative Example 1-2, a linear silanol polymer not containing 3-glycidyloxypropyl groups is used in component (C), and although the silica surface is well treated and the long-term storage stability is good, the plasticity is significantly lower. Comparative Example 1-4 is an example in which the amount of wetter in Comparative Example 1-2 is reduced by half, and although the initial plasticity is high and good, the silica surface is not treated, and the plasticity increases significantly after 40°C/24h, showing that high plasticity and long-term storage stability cannot be achieved at the same time.

Comparative Example 1-3 is a compound to which 3-glycidyloxypropyltrimethoxysilane (KBM-403), the starting material for the 3-glycidyloxypropylsilanol oligomer of component (C-1), has been added. However, the initial plasticity is low, and the change in plasticity after 24 hours at 40°C is large, failing the test. In addition, the compression set of the cured product of the composition of Comparative Example 2-3 is significantly worse than that of the cured product of the composition of Comparative Example 2-1, indicating that it does not function as a surface treatment agent for silica.

Example 1-4 and Comparative Example 1-5 are comparative studies of a combination of a linear silanol polymer and a silanol oligomer having a 3-glycidyloxypropyl group, and a combination of a linear silanol polymer and a silanol oligomer not containing a 3-glycidyloxypropyl group. It can be seen that even when a linear silanol polymer is used in combination, high plasticity and long-term storage stability are maintained by adding 3-glycidyloxypropyl silanol oligomer.

Example 1-5 and Comparative Example 1-6 were used to verify the effect of 3-glycidyloxypropylsilanol oligomer in a simple blend system that used treated silica and did not undergo heat treatment. It was confirmed that the addition of 3-glycidyloxypropylsilanol oligomer resulted in high plasticity and good long-term storage stability even in a simple blend system.

The above results show that the silicone rubber compounds of Examples 1-1 to 1-5 to which 3-glycidyloxypropylsilanol oligomer was added have high plasticity and excellent long-term storage stability.

Claims (6)

(A) organopolysiloxane gum having two or more alkenyl groups bonded to silicon atoms in each molecule and an average degree of polymerization of 3,000 to 100,000: 100 parts by mass,
(B) reinforcing silica having a specific surface area of 50 to 450 m ² /g as measured by the BET adsorption method: 5 to 50 parts by mass,
(C) 3-glycidyloxypropylsilanol oligomer represented by the following formula (1): 0.1 to 15 parts by mass

(In the formula, R ¹ is a monovalent hydrocarbon group having 1 to 10 carbon atoms, R ² are each independently a monovalent hydrocarbon group having 1 to 10 carbon atoms which may be substituted with a glycidyloxy group, R ³ is a monovalent aliphatic hydrocarbon group having 1 to 10 carbon atoms, a, b, c, and d are numbers which satisfy a ≧ 0.5, b ≧ 0, c ≧ 0, d ≧ 0 and a + b + c + d = 1, and x and y are numbers which satisfy x ≧ 1.0 and y ≦ 0.5.)
A millable type silicone rubber compound comprising: The millable type silicone rubber compound according to claim 1, wherein the weight average molecular weight of component (C) is 500 to 10,000. The millable type silicone rubber compound according to claim 1, wherein in the above formula (1), b, c, and d are numbers that satisfy b=0, 0≦c≦0.5, and 0≦d≦0.2. 100 parts by mass of the millable type silicone rubber compound according to any one of claims 1 to 3,
(D) Curing agent: A millable type silicone rubber composition containing an effective curing amount. The component (D) is an addition reaction type curing agent (D1), and the component (D1) is
(a) an organohydrogenpolysiloxane having two or more hydrosilyl groups per molecule: an amount such that the molar ratio of hydrosilyl groups in the organohydrogenpolysiloxane (a) to alkenyl groups bonded to silicon atoms in the component (A) (hydrosilyl groups/alkenyl groups) is 0.5 to 10; and (b) a hydrosilylation catalyst: 1 ppm to 1% by mass, calculated as the mass of platinum group metal relative to the mass of component (A).
The millable silicone rubber composition according to claim 4, which comprises The millable silicone rubber composition according to claim 4, wherein the (D) component is (D2) an organic peroxide curing agent, and the millable silicone rubber composition contains 0.1 to 8 parts by mass of the (D2) component per 100 parts by mass of the millable silicone compound.

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