JP2019031600A - Addition-curable liquid silicone rubber composition and sealing material for cooling liquid - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an addition curable liquid silicone rubber composition and a sealant for a coolant which give a cured product having excellent low compression permanent strain to a coolant. (A) At least 2 in one molecule. An alkenyl group-containing organopolysiloxane having an alkenyl group bonded to individual silicon atoms, having an average degree of polymerization of 1,500 or less, and being liquid at 25 ° C.: 100 parts by mass, (B) Silicon atom in one molecule Organohydrogenpolysiloxane containing at least two hydrogen atoms bonded to: 0.2 to 20 parts by mass, (C) the specific surface area according to the BET method is 50 to 150 m2 / g, and an alkenyl group-containing silyl group is formed on the surface. Humed silica: 10 to 40 parts by mass, (D) Addition reaction catalyst: Addition curable liquid silicone containing a catalytic amount as a platinum group metal (mass equivalent) with respect to the total mass of the components (A) to (C). Rubber composition. [Selection diagram] None

Description

  The present invention relates to an addition-curable liquid silicone rubber composition and a sealing material for cooling liquid, and in particular, addition-curing that gives a cured product (silicone rubber) having an excellent low compression set to a cooling liquid such as an ethylene glycol aqueous solution. The present invention relates to a heat-resistant liquid silicone rubber composition and a coolant sealing material comprising a cured product of the composition.

  Silicone rubber is heat-resistant, cold-resistant, safe, good in appearance (transparency), soft to the touch, and durable. It is used in a wide range of fields such as gasket materials, building materials, and fiber coating materials.

  When silicone rubber is used as a gasket such as an O-ring or packing, a low compression set is required to prevent seal leakage. However, general silicone rubber has a large compression set, and there is a problem that the shape of the rubber changes for a long period of time when used at a high temperature. Usually, in order to reduce the compression set, it has been necessary to secondary vulcanize a rubber molded by heating and curing at a higher temperature for a longer time.

  In order to solve the above problems, a method has been proposed in which a triazole-based compound is added to an addition-curable silicone rubber composition to reduce compression set without secondary vulcanization (Patent Document 1: Japanese Patent Application Laid-Open No. Hei 11 (1994)). No. 2-24854, Patent Document 2: JP-A-2017-2165).

  However, the above-described method is effective in reducing compression set in air, but is not limited thereto when used in a special environment. For example, in recent automobiles, in order to cool electronic components, a coolant (ethylene glycol aqueous solution) is passed through various parts, and a sealant for coolant must be disposed. In the state in which the coolant is always touched, the above-described method has a problem that the compression set is greatly deteriorated and the sealing property cannot be maintained.

JP-A-2-242854 JP 2017-2165 A

  The present invention has been made in order to improve the above circumstances, and is an addition-curable liquid silicone rubber composition that gives a cured product (silicone rubber) having an excellent low compression set to a cooling liquid such as an ethylene glycol aqueous solution. And a coolant sealing material comprising a cured product of the composition.

As a result of intensive studies to achieve the above object, the present inventors have (A) an alkenyl group bonded to at least two silicon atoms in one molecule, and an average degree of polymerization of 1,500 or less. An alkenyl group-containing organopolysiloxane which is liquid at 25 ° C., (B) an organohydrogenpolysiloxane containing at least two hydrogen atoms bonded to silicon atoms in one molecule, and (C) a ratio according to the BET method. Addition-curable liquid silicone rubber composition comprising a fumed silica having a surface area of 50 to 150 m ² / g and having an alkenyl group-containing silyl group on the surface and (D) an addition reaction catalyst in specific amounts. The present invention finds that a cured product obtained by curing a product has an excellent low compression set against a cooling liquid such as an aqueous ethylene glycol solution. It led to the eggplant.

（式中、Ｒ¹は炭素数１〜３の１価炭化水素基であり、少なくとも１つのＲ¹はアルケニル基であり、Ｘは−Ｃｌ、−ＯＲ²、又は−ＮＲ² ₂、Ｒ²は炭素数１〜６の１価炭化水素基、ｎは１〜３の整数である。）
及び下記一般式（ＩＩ）

（式中、Ｒ¹は上記と同じであり、ｍは１〜６の整数である。）
から選ばれる少なくとも１種のアルケニル基含有有機ケイ素化合物で表面処理したものである〔１〕又は〔２〕記載の付加硬化性液状シリコーンゴム組成物。
〔４〕
（Ａ）、（Ｂ）、及び（Ｃ）成分を含有するシリコーンゴム混合物において、常温下、せん断速度０．９ｓ^-1の時のせん断粘度η¹とせん断速度１０ｓ^-1の時のせん断粘度η²の比（η¹／η²）が２．０以下である〔１〕〜〔３〕のいずれかに記載の付加硬化性液状シリコーンゴム組成物。
〔５〕
せん断粘度の比（η¹／η²）が１．０〜１．８である〔４〕記載の付加硬化性液状シリコーンゴム組成物。
〔６〕
〔１〕〜〔５〕のいずれかに記載の付加硬化性液状シリコーンゴム組成物の硬化物からなる冷却液用シール材。 Accordingly, the present invention provides the following addition-curable liquid silicone rubber composition and coolant sealing material.
[1]
(A) Alkenyl group-containing organopolysiloxane having an alkenyl group bonded to at least two silicon atoms in one molecule, an average degree of polymerization of 1,500 or less, and liquid at 25 ° C .: 100 parts by mass
(B) Organohydrogenpolysiloxane containing at least two hydrogen atoms bonded to silicon atoms in one molecule: 0.2 to 20 parts by mass,
(C) Fumed silica having a specific surface area by the BET method of 50 to 150 m ² / g and having an alkenyl group-containing silyl group on the surface: 10 to 40 parts by mass,
(D) Addition reaction catalyst: an addition-curable liquid silicone rubber composition containing a catalytic amount as a platinum group metal (in terms of mass) with respect to the total mass of the components (A) to (C).
[2]
The addition curable liquid silicone rubber composition according to [1], wherein the component (C) is fumed silica having both an alkenyl group-containing silyl group and an alkyl group-containing silyl group on the surface.
[3]
Component (C) is fumed silica represented by the following general formula (I)

(Wherein R ¹ is a monovalent hydrocarbon group having 1 to 3 carbon atoms, at least one R ¹ is an alkenyl group, X is —Cl, —OR ² , or —NR ² ₂ , R ² is C1-C6 monovalent hydrocarbon group, n is an integer of 1-3.)
And the following general formula (II)

(In the formula, R ¹ is the same as above, and m is an integer of 1 to 6.)
The addition-curable liquid silicone rubber composition according to [1] or [2], which is surface-treated with at least one alkenyl group-containing organosilicon compound selected from:
[4]
In the silicone rubber mixture containing the components (A), (B), and (C), the shear viscosity η ¹ when the shear rate is 0.9 s ⁻¹ and the shear viscosity η when the shear rate is 10 s ⁻¹ at room temperature. ² ratio (η ¹ / η ²⁾ is 2.0 or less (1) to addition curable liquid silicone rubber composition according to any one of [3].
[5]
The addition-curable liquid silicone rubber composition according to [4], wherein the shear viscosity ratio (η ¹ / η ² ) is 1.0 to 1.8.
[6]
[1] to [5] A coolant sealing material comprising a cured product of the addition-curable liquid silicone rubber composition according to any one of [5].

  According to the present invention, an addition-curable liquid silicone rubber composition that gives a cured product (silicone rubber) having an excellent low compression set to a coolant such as an ethylene glycol aqueous solution, and a cooling comprising the cured product of the composition. A liquid sealing material can be provided.

Hereinafter, the addition-curable liquid silicone rubber composition and the coolant sealing material of the present invention will be described in more detail.
[Additionally curable liquid silicone rubber composition]
The addition-curable liquid silicone rubber composition of the present invention comprises (A) an alkenyl group-containing organopolysiloxane, (B) an organohydrogenpolysiloxane, (C) a fumed silica surface-treated with an alkenyl group-containing silyl group, and ( D) It is characterized by containing an addition reaction catalyst.
(A) The alkenyl group-containing organopolysiloxane (A) component is the main component (base polymer) of the composition of the present invention, has an alkenyl group bonded to at least two silicon atoms in one molecule, and has an average polymerization It is an alkenyl group-containing organopolysiloxane having a degree of 1,500 or less and being liquid at 25 ° C. (that is, having self-fluidity). Preferably, the alkenyl group is contained at the molecular chain end. Such an alkenyl group-containing organopolysiloxane comprises only this organopolysiloxane (component (A)).

（式中、Ｒ³は互いに同一又は異種の炭素数１〜１０、好ましくは１〜８の非置換又は置換の１価炭化水素基であり、ａは１．５〜２．８、好ましくは１．８〜２．５、より好ましくは１．９５〜２．０５の正数である。） As the organopolysiloxane having an alkenyl group bonded to at least two silicon atoms in one molecule, a liquid at 25 ° C. represented by the following average composition formula (III) can be used.

Wherein R ³ is an unsubstituted or substituted 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 1 .8 to 2.5, more preferably a positive number of 1.95 to 2.05.)

In the formula (III), R ³ is methyl group, ethyl group, propyl group, isopropyl group, butyl group, isobutyl group, tert-butyl group, pentyl group, neopentyl group, hexyl group, cyclohexyl group, octyl group, nonyl group. , Alkyl groups such as decyl group, aryl groups such as phenyl group, tolyl group, xylyl group, naphthyl group, aralkyl groups such as benzyl group, phenylethyl group, phenylpropyl group, vinyl group, allyl group, propenyl group, isopropenyl An alkenyl group such as a group, a butenyl group, a hexenyl group, a cyclohexenyl group, and an octenyl group, or a group in which some or all of the hydrogen atoms are substituted with a halogen atom such as fluorine, bromine, or chlorine, a cyano group, or the like, For example, chloromethyl group, chloropropyl group, bromoethyl group, trifluoropropyl group, cyanoethyl group Although the like, Preferably, at least 90 mole% of all R ³ is a methyl group.

Of R ³ , at least two must be alkenyl groups (preferably having 2 to 8 carbon atoms, more preferably 2 to 6 carbon atoms, and particularly preferably a vinyl group).
The alkenyl group content in the organopolysiloxane is 1.0 × 10 ^{−6 to} 3.0 × 10 ⁻³ mol / g, especially 1.0 × 10 ^{−5 to} 2.0 × 10 ⁻³ mol. / G is preferable. If the amount of the alkenyl group is less than 1.0 × 10 ⁻⁶ mol / g, the rubber hardness may be too low to form a gel, and if it exceeds 3.0 × 10 ⁻³ mol / g, the crosslinking density Becomes too high, the hardness becomes extremely high, and the elasticity of the rubber may be lost.
In addition, content of the alkenyl group in this invention shall point out the value calculated from the iodine value of the said alkenyl group containing organopolysiloxane measured by the Hanus method.

  The structure of the organopolysiloxane basically has a linear structure in which both ends of the molecular chain are capped with triorganosiloxy groups and the main chain is composed of repeating diorganosiloxane units. It may be a branched structure having a silsesquioxane unit, a cyclic structure, or the like.

  The alkenyl group may be bonded to the silicon atom at the end of the molecular chain or may be bonded to the silicon atom in the middle of the molecular chain (non-terminal of the molecular chain). In the component (A) of the present invention, the molecular chain It is preferable that the molecule contains at least one, preferably two or more alkenyl groups bonded to the terminal silicon atom (that is, the silicon atom in the triorganosiloxy group). The alkenyl group bonded to the silicon atom in the organosiloxane unit or the monoorganosilsesquioxane unit may or may not be contained. If at least one, preferably two or more alkenyl groups bonded to the silicon atom at the molecular chain terminal are not contained, curing may be delayed.

The average degree of polymerization of the organopolysiloxane needs to be 1,500 or less, preferably 100 to 1,500, and more preferably 150 to 1,100. If it is less than 100, sufficient rubber feeling may not be obtained, and if it exceeds 1,500, the viscosity becomes high and molding becomes difficult.
The average degree of polymerization referred to in the present invention refers to the number average degree of polymerization, and refers to the number average degree of polymerization using polystyrene as a standard substance by gel permeation chromatography (GPC) measured under the following conditions. To do.
[Measurement condition]
Developing solvent: Toluene flow rate: 1 mL / min
Detector: Differential refractive index detector (RI)
Column: KF-805L × 2 (manufactured by Shodex)
Column temperature: 25 ° C
Sample injection volume: 30 μL (toluene solution with a concentration of 0.2% by mass)

Specifically, as the organopolysiloxane of component (A), molecular chain both ends diorganoalkenylsiloxy group-blocked diorganopolysiloxane, molecular chain both ends organodialkenylsiloxy group-blocked diorganopolysiloxane, molecular chain Both ends trialkenylsiloxy group-blocked diorganopolysiloxane, molecular chain both ends triorganosiloxy group-blocked diorganosiloxane / organoalkenylsiloxane copolymer, both ends chain diorganoalkenylsiloxy group-blocked diorganosiloxane / organoalkenylsiloxane Examples of the polymer include a diorganosiloxane / organoalkenylsiloxane copolymer in which one end of a molecular chain is blocked with a diorganoalkenylsiloxy group and the other end is a triorganosiloxy group blocked. Diorganoalkenylsiloxy group-capped diorganopolysiloxane, diorganoalkoxysiloxy group-capped diorganopolysiloxane, diorganosiloxane / organoalkenylsiloxane copolymer, and / or diorganoalkenylsiloxy group-capped diorganosiloxane with molecular chain both ends -An organoalkenylsiloxane copolymer. As used herein, “organo” refers to an organic group that does not contain an aliphatic unsaturated group, typically an alkyl group, an aryl group, or an aralkyl group.
(A) A component may be used individually by 1 type, or may use 2 or more types together.

(B) The organohydrogenpolysiloxane (B) component is an organohydrogenpolysiloxane containing at least two hydrogen atoms (Si—H groups) bonded to silicon atoms in one molecule, and Si— The H group is crosslinked with the alkenyl group bonded to the silicon atom in the component (A) by a hydrosilylation addition reaction, and acts as a curing agent for curing the composition.

（式中、Ｒ⁴は互いに同一又は異種の炭素数１〜１０、好ましくは１〜８の非置換又は置換の１価炭化水素基である。また、ｂは０．７〜２．１、ｃは０．００１〜１．０で、かつｂ＋ｃは０．８〜３．０を満足する正数である。） The organohydrogenpolysiloxane of component (B) is represented by the following average composition formula (IV), and is at least 2, preferably 3 or more, more preferably 3 to 100, still more preferably 3 in one molecule. Those having ˜50 silicon atom-bonded hydrogen atoms (Si—H groups) are preferably used.

(In the formula, R ⁴ is an unsubstituted or substituted monovalent hydrocarbon group having 1 to 10 carbon atoms, preferably 1 to 8 carbon atoms, which are the same or different from each other. 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.)

In the formula (IV), R ⁴ is methyl group, ethyl group, propyl group, isopropyl group, butyl group, isobutyl group, tert-butyl group, pentyl group, neopentyl group, hexyl group, cyclohexyl group, octyl group, nonyl group. Alkyl groups such as decyl group, vinyl groups, allyl groups, propenyl groups, isopropenyl groups, butenyl groups, hexenyl groups, cyclohexenyl groups, alkenyl groups such as octenyl groups, aryl groups such as phenyl groups, tolyl groups, naphthyl groups, etc. Or a group in which some or all of the hydrogen atoms of these groups are substituted with halogen atoms such as fluorine, bromine, chlorine, cyano groups, etc., such as chloromethyl group, chloropropyl group, bromoethyl group, trifluoropropyl group, cyanoethyl Although a group etc. can be mentioned, what does not have an aliphatic unsaturated group is preferable.
Further, b is 0.7 to 2.1, preferably 0.8 to 2.0, c is 0.001 to 1.0, preferably 0.01 to 1.0, and b + c is 0.00. It is a positive number satisfying 8-3.0, preferably 1.0-2.5, and the molecular structure of organohydrogenpolysiloxane is any of linear, cyclic, branched, and three-dimensional network structures. It may be. 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.

The content of the Si-H group as the component (B) is 5.0 × 10 ^{−4 to} 1.7 × 10 ⁻² mol / g, particularly 1.0 × 10 ⁻³ to 1 in the organohydrogenpolysiloxane. 0.7 × 10 ⁻² mol / g is preferable. When the amount is less than 5.0 × 10 ⁻⁴ mol / g, the crosslinking density is low and gelation may occur. When the amount is more than 1.7 × 10 ⁻² mol / g, an unstable compound may be formed.

Specific examples of the organohydrogenpolysiloxane of component (B) include methylhydrogencyclopolysiloxane, methylhydrogensiloxane / dimethylsiloxane cyclic copolymer, and trimethylsiloxy group-blocked methylhydrogenpolysiloxane at both ends. , Both ends trimethylsiloxy group-blocked dimethylsiloxane / methylhydrogensiloxane copolymer, both ends dimethylhydrogensiloxy group-blocked dimethylpolysiloxane, both ends dimethylhydrogensiloxy group-blocked dimethylsiloxane / methylhydrogensiloxane copolymer, ( A copolymer comprising CH ₃ ) ₂ HSiO _1/2 units, (CH ₃ ) ₃ SiO _1/2 units and SiO _4/2 units, (CH ₃ ) ₂ HSiO _1/2 units and SiO _4/2 units Copolymers of these and these Such as those obtained by substituting such other alkyl groups some or all of the methyl groups in the shown compounds.

  (B) The compounding quantity of the organohydrogenpolysiloxane of a component is 0.2-20 mass parts with respect to 100 mass parts of (A) component, Preferably it is 0.3-10 mass parts. In addition, the molar ratio (Si) of hydrogen atoms bonded to silicon atoms (Si—H groups) in the organohydrogenpolysiloxane of component (B) and the total amount of alkenyl groups bonded to silicon atoms in component (A). -H group / alkenyl group) is preferably in an amount of 1.0 to 2.0, particularly 1.1 to 1.8. If this ratio is less than 1.0, curing (crosslinking density) may be insufficient, resulting in a sticky rubber. If it is greater than 2.0, the compression set of the cured product may be deteriorated. There is.

(C) The fumed silica (C) component having an alkenyl group-containing silyl group on the surface is indispensable for imparting sufficient rubber strength to the silicone rubber, and has a specific surface area of 50 to 150 m ² / g by the BET method. The fumed silica having an alkenyl group-containing silyl group on the surface, preferably 90 to 150 m ² / g (hereinafter sometimes simply referred to as “silica”). If the specific surface area by the BET method is less than 50 m ² / g, sufficient rubber strength cannot be obtained, and if it is greater than 150 m ² / g, there is a possibility that significant deterioration occurs in the coolant (particularly in an ethylene glycol aqueous solution).

As the component (C), silica having an alkenyl group-containing silyl group on the silica surface is used. As such silica, one that has been surface-treated with an alkenyl group-containing organosilicon compound is used. When silica having no alkenyl group-containing silyl group is used, the compression set in the cooling liquid (particularly in the aqueous ethylene glycol solution) is remarkably deteriorated.
In addition, the silica having an alkenyl group-containing silyl group may be a commercially available one, and when the silicone rubber base is prepared by kneading with the component (A) by the method described later, the surface treatment is simultaneously performed. You may go.
Examples of the alkenyl group-containing silyl group include alkenyldialkylsilyl groups such as vinyldimethylsilyl group and allyldimethylsilyl group, dialkenylalkylsilyl groups such as methyldivinylsilyl group and ethyldivinylsilyl group, and trivinylsilyl groups. And trialkenylsilyl groups such as methylvinylsilyl group and ethylvinylsilyl group, dialkenylsilyl groups such as divinylsilyl group, and alkenylsilyl groups such as vinylsilyl group.

  Examples of the alkenyl group-containing organosilicon compound include divinyltetraalkyldisilazane, 1,1,1,3,5,5,5-heptamethyl-3-vinyltrisilazane, 2,4,6-trimethyl-2,4. , 6-Trivinylcyclotrisilazane and other vinylsilazanes, dialkylaminovinyldialkylsilanes, vinyltrialkoxysilanes, vinylalkyldialkoxysilanes, vinyldialkylalkoxysilanes and other vinylalkoxysilanes, vinyltrichlorosilanes, alkylvinyldichlorosilanes, dialkyls Vinyl group-containing silane coupling agents such as vinylchlorosilane such as vinylchlorosilane are used. Of these, divinyltetraalkyldisilazane is preferable, and 1,3-divinyl-1,1,3,3-tetramethyldisilazane and vinyltrimethoxysilane are particularly preferable from the viewpoint of availability and efficient surface treatment. Used for.

Furthermore, as the component (C), it is preferable to use silica having both an alkyl group-containing silyl group on the surface in addition to the alkenyl group-containing silyl group. Compared with the case where there is no alkyl group-containing silyl group, the resistance to an aqueous solution is further improved.
Here, the alkyl group-containing silyl group refers to a silyl group having no alkenyl group and having an alkyl group, unlike the above-described alkenyl group-containing silyl group. Examples thereof include trialkylsilyl groups such as trimethylsilyl group and butyldimethylsilyl group, dialkylsilyl groups such as dimethylsilyl group and methylethylsilyl group, and alkylsilyl groups such as methylsilyl group.
Silica surface-modified with both an alkenyl group-containing silyl group and an alkyl group-containing silyl group may be surface-treated with an organosilicon compound having an alkyl group on silica that has been surface-modified with an alkenyl group-containing silyl group in advance. The surface treatment may be performed simultaneously with the alkenyl group-containing organosilicon compound and the alkyl group-containing organosilicon compound. Moreover, you may surface-treat with the organosilicon compound containing an alkenyl group to the silica surface-treated with the commercially available alkyl group containing silyl group.
For the surface treatment of silica with an organosilicon compound, a known technique can be used. For example, an untreated silica fine powder and the above organosilicon compound are placed in a mechanical kneader or a fluidized bed sealed at normal pressure. If necessary, mixing treatment is performed at room temperature or heat treatment in the presence of an inert gas. In some cases, a catalyst may be used to facilitate the treatment. After kneading, the treated silica fine powder can be produced by drying. In preparing the composition, these organosilicon compounds are added at the time of kneading with silicone oil (that is, organopolysiloxane of component (A)) and mixed in the presence of a small amount of water if necessary. It is also possible to carry out a surface treatment in the composition.
In this case, particularly when preparing a silicone rubber base by mixing part or all of the component (A) and fumed silica at room temperature (room temperature) or under heating, preferably at 30 to 200 ° C. for 30 to 600 minutes. By adding an alkenyl group-containing organosilicon compound and mixing together with the above components, a fumed silica having an alkenyl group-containing silyl group on the surface is obtained by surface-treating the fumed silica with the alkenyl group-containing organosilicon compound. be able to. In addition, the quantity of the alkenyl group containing organosilicon compound mix | blended at this time is 0.1-10 mass parts with respect to 100 mass parts of whole quantity of fumed silica, It is especially 0.1-5.0 mass parts. preferable.

（式中、Ｒ¹は炭素数１〜３の１価炭化水素基であり、少なくとも１つのＲ¹はアルケニル基であり、Ｘは−Ｃｌ、−ＯＲ²、又は−ＮＲ² ₂、Ｒ²は炭素数１〜６の１価炭化水素基、ｎは１〜３の整数である。）
及び下記一般式（ＩＩ）

（式中、Ｒ¹は上記と同じであり、ｍは１〜６の整数である。）
から選ばれる少なくとも１種の有機ケイ素化合物が用いられる。 As the alkenyl group-containing organosilicon compound, the following general formula (I)

(Wherein R ¹ is a monovalent hydrocarbon group having 1 to 3 carbon atoms, at least one R ¹ is an alkenyl group, X is —Cl, —OR ² , or —NR ² ₂ , R ² is C1-C6 monovalent hydrocarbon group, n is an integer of 1-3.)
And the following general formula (II)

(In the formula, R ¹ is the same as above, and m is an integer of 1 to 6.)
At least one organic silicon compound selected from the group consisting of:

In formula (I), R ¹ is a monovalent hydrocarbon group having 1 to 3 carbon atoms, an alkyl group such as a methyl group, an ethyl group or a propyl group, and an alkenyl group such as a vinyl group, an allyl group or a propenyl group. Is mentioned.
R ¹ is a hydrophobic group when n is 1, and when n is 2 or 3, at least one of them is a hydrophobic group.
X is a hydrolyzable group and is —Cl, —OR ² , or —NR ² ₂ .
R ² is a monovalent hydrocarbon group having 1 to 6 carbon atoms, an alkyl group such as a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, a pentyl group or a hexyl group, an aryl group such as a phenyl group, And alkenyl groups such as vinyl group, allyl group, propenyl group, butenyl group and hexenyl group.
The organosilicon compounds of the formulas (I) and (II) can contain, as R ¹ , an alkyl group as an essential component in addition to the alkenyl group.
The organosilicon compounds of the formulas (I) and (II) may be used alone or in combination of two or more.

  Examples of the alkyl group-containing organosilicon compound include alkyl alkoxysilanes, alkylchlorosilanes, alkylsilazanes, alkylhydroxysilanes, and condensates thereof. Among these, alkylalkoxysilane, alkylchlorosilane, and alkylsilazane are preferable because they easily treat the hydroxyl group on the surface of the silica particles. The alkyl group-containing organosilicon compound is a component that is clearly different from the alkenyl group-containing organosilicon compound in that it does not contain an alkenyl group.

The alkenyl group-containing organosilicon compounds and alkyl group-containing organosilicon compounds represented by formulas (I) and (II) have hydrolyzable groups [X in formula (I) and silazane groups in formula (II)]. This hydrolyzable group directly reacts with the hydroxyl group on the surface of the silica particles or is hydrolyzed with water to form a hydroxyl group, and this hydroxyl group undergoes a dehydration condensation reaction with the hydroxyl group on the surface of the silica particle. The particle surface is modified.
In this way, hydrophobic groups are imparted to the surface of the silica particles, so that the cohesive force of the silica particles in the silicone rubber composition is reduced (aggregation due to hydrogen bonding with silanol groups is reduced), and as a result, silica The dispersibility of the particles is improved. Thereby, the interface of a silica particle and a rubber matrix increases, and the reinforcement effect of a silica particle increases. Furthermore, since the degree of hydrophobicity of the silica particles is improved, an ethylene glycol aqueous solution or the like generally used as a cooling liquid can be prevented from entering the rubber, and the resistance to these aqueous solutions can be increased.

  In addition, the alkenyl group-containing organosilicon compound represented by the formulas (I) and (II) has an alkenyl group as an essential component, whereby the alkenyl group is introduced onto the surface of the silica particles. Therefore, when the silicone rubber composition is cured, the alkenyl group of the alkenyl group-containing organopolysiloxane and the hydride group of the organohydrogenpolysiloxane undergo a hydrosilylation addition reaction to form a network (crosslinked structure). At this time, since the alkenyl group of the silica particle also participates in the hydrosilylation addition reaction with the hydride group of the organohydrogenpolysiloxane, the silica particle is also taken into the network. Thereby, it is possible to increase the hardness and modulus of the formed silicone rubber. Furthermore, when the normally cured rubber comes into contact with a coolant such as an ethylene glycol aqueous solution, ethylene glycol or water penetrates into the rubber, and the interaction between the polymer matrix and silica is cut off, resulting in silica displacement. In the case of having an alkenyl group on the upper side, since silica is fixed on the polymer network, deviation hardly occurs and compression set and the like are improved.

Silica particles are obtained by surface treatment with an alkenyl group-containing organosilicon compound represented by formula (I) and / or formula (II) and an alkyl group-containing organosilicon compound, but hydroxyl groups on the surface of the silica particles remain as much as possible. It is preferable not to do so. If the hydroxyl group concentration on the surface of silica particles in the composition is high, when the cured rubber is used in contact with a cooling liquid such as an ethylene glycol aqueous solution at all times, ethylene glycol and water are absorbed inside the rubber, resulting in significant deterioration of the rubber. May occur.
Although it is difficult to directly determine the amount of hydroxyl groups on the silica surface in the composition, the degree of treatment can be estimated by evaluating the thixotropic properties of the composition. The thixotropy is a ratio of the shear viscosity of the shear viscosity η ¹ at the low shear rate to the shear viscosity η ² at the high shear rate (η ¹ / η ² ) represented by the following formula (A) at a normal temperature. It is possible to evaluate by.
Thixotropic ratio = shear viscosity η ¹ / shear viscosity η ² (A)

When the thixotropy ratio is large, the silica surface treatment degree is low, indicating that there are many hydroxyl groups on the silica surface in the composition. Conversely, when the thixotropy ratio is small, the silica surface treatment degree is high and the hydroxyl group on the silica surface in the composition is high. It shows that there are few.
The shear viscosity is normal temperature (usually 20 to 25 ° C., preferably 22 to 24 ° C.), usually 0.1 to 2.0 s ⁻¹ , preferably 0.5 to 1.5 s ^{−1 at} a low shear rate. η ¹ is measured, and the shear viscosity η ² is measured at a high shear rate of usually 5.0 to 100 s ⁻¹ , preferably 8.0 to 20 s ⁻¹ .
The shear viscosity can be measured using, for example, HAAKE MARS-40 or HAAKE Rheo Stress 6000 manufactured by Thermo Fisher Scientific Co., Ltd.
In the present invention, in particular, the thixotropy ratio (η ¹ / η ² ) of the silicone rubber mixture containing the components (A), (B), and (C) is 23 ° C. and the low shear rate is 0.9 s ^{−. 1 When} the high shear rate is 10 s ⁻¹ , it is 2.0 or less, preferably 1.0 to 2.0, and more preferably 1.0 to 1.8. When the thixotropy ratio (η ¹ / η ² ) is larger than 2.0, the surface treatment degree of silica is lowered and resistance to an ethylene glycol aqueous solution or the like is lost.

  (C) The compounding quantity of the fumed silica of a component 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 exceeds 40 parts by mass, deterioration may easily occur in the cooling liquid (particularly in an ethylene glycol aqueous solution).

(D) Addition reaction catalyst As an addition reaction catalyst of component (D), platinum black, chloroplatinum chloride, chloroplatinic acid, a reaction product of chloroplatinic acid and a monohydric alcohol, a complex of chloroplatinic acid and olefins Platinum catalyst such as platinum bisacetoacetate, palladium catalyst, rhodium catalyst, and the like.
The compounding quantity of an addition reaction catalyst is 0.5-1,000 ppm as platinum group metal (mass conversion) with respect to the total mass of (A)-(C) component, Preferably it is 1-500 ppm.

Other components In the addition-curable liquid silicone rubber composition of the present invention, as long as the effects of the invention are not impaired, as other components, if necessary, a filler such as precipitated silica, quartz powder, diatomaceous earth, calcium carbonate, Conductive agents such as carbon black, conductive zinc white, metal powder, nitrogen-containing compounds and acetylene compounds, phosphorus compounds, nitrile compounds, carboxylates, tin compounds, mercury compounds, sulfur compounds, etc., hydrosilylation reaction control agents, iron oxide , Heat release agents such as cerium oxide, internal mold release agents such as dimethyl silicone oil, and adhesion-imparting agents (particularly selected from alkenyl groups, epoxy groups, amino groups, (meth) acryloxy groups, mercapto groups, etc. in the molecule) Organosilicon such as alkoxysilane which contains at least one functional group and does not contain Si-H group in the molecule Such compounds), and it is optional to formulate the thixotropic agent.

[Molding and curing method]
As a molding / curing method for the addition-curable silicone rubber composition, a conventional method can be adopted. However, as the molding method, an optimal means suitable for the purpose is selected from injection molding, transfer molding, injection molding, compression molding, and the like. Is possible. As curing conditions, heat treatment (primary vulcanization) conditions at 40 to 230 ° C. for about 3 seconds to 160 minutes may be employed. Moreover, you may perform secondary vulcanization (post-cure) for about 10 minutes-24 hours arbitrarily at 40-230 degreeC as needed.

[Sealant for coolant]
A cured product (silicone rubber) obtained by curing the addition-curable silicone rubber composition is based on JIS K 6249: 2003 with ethylene glycol 50 in a state where the cured product is compressed at a compression rate of 25% (including the holder). When the compression set is measured at 120 ° C. and after 1,000 hours, the compression set is 50% or less, particularly 40% or less, especially 35% or less. . In the above test, when the compression set is 50% or less, it is preferable as an O-ring or packing material that always comes into contact with the coolant. In order to achieve the compression set, fumed silica as a filler is treated with an organosilicon compound having an alkenyl group and an alkyl group-containing silicon compound, and a BET specific surface area of 50 to 150 m ² / This can be achieved by using the component (C) which is g.

  Thus, the hardened | cured material of the addition curable silicone rubber composition of this invention can be used suitably as a sealing material for cooling fluid used for the place which always contacts a cooling fluid.

  EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention concretely, this invention is not limited to a following example. In addition, a part shows a mass part by the following example. Moreover, an average degree of polymerization shows a number average degree of polymerization.

[Example 1]
60 parts of dimethylpolysiloxane (A1, vinyl group content 1.2 × 10 ⁻⁴ mol / g) having an average degree of polymerization of 220 blocked at both ends with dimethylvinylsiloxy groups and a specific surface area by BET method of 110 m ² / g and dimethyldichlorosilane-treated fumed silica (C1) (Aerosil R972, manufactured by Nippon Aerosil Co., Ltd.), 30 parts, 1,3-divinyl-1,1,3,3-tetramethyldisilazane 0.2 part, After mixing 2.0 parts of water at 25 ° C. for 30 minutes, the temperature was raised to 150 ° C., stirring was continued for 3 hours, and cooling was performed to obtain a silicone rubber base.
To 90 parts of this silicone rubber base, 50 parts of dimethylpolysiloxane (A2, vinyl group content 3.8 × 10 ⁻⁵ mol / g) having an average degree of polymerization of 750 blocked at both ends with dimethylvinylsiloxy groups was added. After stirring for 30 minutes, methylhydrogen dimethylpolysiloxane (B1, average polymerization degree of 18 having both ends blocked with dimethylhydrogensiloxy groups and having an average of 5 Si—H groups in the side chain as a crosslinking agent 1.95 parts of Si-H group amount 5.6 × 10 ⁻³ mol / g) and 0.025 part of ethynylcyclohexanol as a reaction control agent were added and stirring was continued for 15 minutes to obtain a silicone rubber mixture. It was.
In this mixture, the molar ratio (Si—H group / vinyl group) of the amount of Si—H groups and the total amount of vinyl groups in all the components (A) is 1.2.
The mixture under 23 ℃, HAAKE MARS-40 shear viscosity eta ¹ measured at low shear rate 0.9 s ^-1 using a shear viscosity eta ² were measured at high shear rates 10s ^-1, and its thixotropic ratio Table 1 shows (= shear viscosity η ¹ / shear viscosity η ² ).

  Into this silicone rubber mixture, 0.05 part of a 1,3-divinyl-1,1,3,3-tetramethyldisiloxane platinum complex dimethylsiloxane solution (Pt concentration 1 mass%) was mixed to obtain a silicone rubber composition. It was. About the hardened | cured material obtained by carrying out the press cure of this composition for 120 degreeC / 15 minutes, based on JISK6253-3-3: 2012, based on the hardness in durometer type A, JISK6249: 2003, and compression set. (Test specimen 29 mmφ × 12.5 mm, compression rate 25%, in air, temperature 150 ° C., test time 22 hours) As a result of measurement, compression under immersion in 50% aqueous solution of ethylene glycol based on JIS K6249: 2003 Table 1 shows the results of measuring the permanent set (test piece 29 mmφ × 12.5 mm, compression rate 25%, temperature 120 ° C., test time 1,000 hours).

[Example 2]
60 parts of dimethylpolysiloxane (A1) capped with dimethylvinylsiloxy groups at both ends described in Example 1, fumed silica (C1) treated with dimethyldichlorosilane having a specific surface area of 110 m ² / g by BET method ( Nippon Aerosil Co., Ltd., Aerosil R972) 30 parts, hexamethyldisilazane 3.0 parts, 1,3-divinyl-1,1,3,3-tetramethyldisilazane 0.2 parts, water 2.0 parts 25 parts After mixing at 30 ° C. for 30 minutes, the temperature was raised to 150 ° C., and stirring was continued for 3 hours, followed by cooling to obtain a silicone rubber base.
To 90 parts of this silicone rubber base, 50 parts of dimethylpolysiloxane (A2) having both ends blocked with dimethylvinylsiloxy groups as described in Example 1 was added, and stirring was continued for 30 minutes. 1.95 parts of methylhydrogen-dimethylpolysiloxane (B1) whose both ends are blocked with dimethylhydrogensiloxy groups and 0.025 part of ethynylcyclohexanol as a reaction control agent are added and stirring is continued for 15 minutes. Thus, a silicone rubber mixture was obtained.
In this mixture, the molar ratio (Si—H group / vinyl group) of the amount of Si—H groups and the total amount of vinyl groups in all the components (A) is 1.2.
The mixture under 23 ℃, HAAKE MARS-40 shear viscosity eta ¹ measured at low shear rate 0.9 s ^-1 using a shear viscosity eta ² were measured at high shear rates 10s ^-1, and its thixotropic ratio Table 1 shows (= shear viscosity η ¹ / shear viscosity η ² ).

  Into this silicone rubber mixture, 0.05 part of a 1,3-divinyl-1,1,3,3-tetramethyldisiloxane platinum complex dimethylsiloxane solution (Pt concentration 1 mass%) was mixed to obtain a silicone rubber composition. It was. About the hardened | cured material obtained by carrying out the press cure of this composition for 120 degreeC / 15 minutes, based on JISK6253-3-3: 2012, based on the hardness in durometer type A, JISK6249: 2003, and compression set. (Test specimen 29 mmφ × 12.5 mm, compression rate 25%, in air, temperature 150 ° C., test time 22 hours) As a result, based on JIS K 6249: 2003, it was immersed in a 50% aqueous solution of ethylene glycol. Table 1 shows the results of measurement of compression set (test piece 29 mmφ × 12.5 mm, compression rate 25%, temperature 120 ° C., test time 1,000 hours).

[Example 3]
60 parts of dimethylpolysiloxane (A3, vinyl group amount 2.5 × 10 ⁻⁵ mol / g) having an average degree of polymerization of 1,100 blocked at both ends with dimethylvinylsiloxy groups, and a specific surface area by BET method of 50 m ² / g of fumed silica (C2) (Aerosil 50, manufactured by Nippon Aerosil Co., Ltd.), 1.0 part of hexamethyldisilazane, 1.0 part of 1,3-divinyl-1,1,3,3-tetramethyldisilazane After mixing 0.2 part and 1.0 part of water at 25 ° C. for 30 minutes, 1.0 part of hexamethyldisilazane was further added and mixed at 25 ° C. for 30 minutes. Subsequently, the temperature was raised to 150 ° C., stirred for 3 hours, and then cooled to obtain a silicone rubber base.
To 90 parts of this silicone rubber base, 45 parts of dimethylpolysiloxane (A3) blocked at both ends with dimethylvinylsiloxy groups, and dimethylmethylvinylpolyvinyl having both ends blocked with trimethylsiloxy groups and an average polymerization degree of 200 After adding 5 parts of siloxane (A4, vinyl group amount 6.5 × 10 ⁻⁴ mol / g) and continuing stirring for 30 minutes, methylhydrogen dimethyl having both ends blocked with trimethylsiloxy groups as a crosslinking agent 1.90 parts of polysiloxane (B2, average degree of polymerization 100, Si—H group amount 5.5 × 10 ⁻³ mol / g) and 0.05 part of ethynylcyclohexanol as a reaction control agent are added and stirred for 15 minutes. To obtain a silicone rubber mixture.
In this mixture, the molar ratio (Si—H group / vinyl group) of the amount of Si—H groups and the total amount of vinyl groups in all the components (A) is 1.8.
The mixture under 23 ℃, HAAKE MARS-40 shear viscosity eta ¹ measured at low shear rate 0.9 s ^-1 using a shear viscosity eta ² were measured at high shear rates 10s ^-1, and its thixotropic ratio Table 1 shows (= shear viscosity η ¹ / shear viscosity η ² ).

  Into this silicone rubber mixture, 0.10 parts of a dimethylsiloxane solution of 1,3-divinyl-1,1,3,3-tetramethyldisiloxane platinum complex (Pt concentration 1 mass%) is mixed to obtain a silicone rubber composition. It was. A cured product obtained by subjecting the composition to a press cure at 120 ° C./15 minutes for a post cure at 200 ° C. for 4 hours was further measured according to JIS K 6253-3: 2012, durometer type A As a result of measuring compression set (test piece 29 mmφ × 12.5 mm, compression rate 25%, in air, temperature 150 ° C., test time 22 hours) based on JIS K 6249: 2003, JIS K 6249: Table 1 shows the results of measurement of compression set (test piece 29 mmφ × 12.5 mm, compression rate 25%, temperature 120 ° C., test time 1,000 hours) under immersion in a 50% aqueous solution of ethylene glycol based on 2003. It was shown to.

[Comparative Example 1]
60 parts of dimethylpolysiloxane (A1) capped with dimethylvinylsiloxy groups at both ends described in Example 1, fumed silica (C1) treated with dimethyldichlorosilane having a specific surface area of 110 m ² / g by BET method ( Nippon Aerosil Co., Ltd., Aerosil R972) 30 parts, hexamethyldisilazane 3.0 parts and water 2.0 parts were mixed at 25 ° C. for 30 minutes, heated to 150 ° C., stirred for 3 hours, cooled, A silicone rubber base was obtained.
To 90 parts of this silicone rubber base, 50 parts of dimethylpolysiloxane (A2) having both ends blocked with dimethylvinylsiloxy groups as described in Example 1 was added, and stirring was continued for 30 minutes. 1.95 parts of methylhydrogen-dimethylpolysiloxane (B1) whose both ends are blocked with dimethylhydrogensiloxy groups and 0.025 part of ethynylcyclohexanol as a reaction control agent are added and stirring is continued for 15 minutes. Thus, a silicone rubber mixture was obtained.
In this mixture, the molar ratio (Si—H group / vinyl group) of the amount of Si—H groups and the total amount of vinyl groups in all the components (A) is 1.2.
The mixture under 23 ℃, HAAKE MARS-40 shear viscosity eta ¹ measured at low shear rate 0.9 s ^-1 using a shear viscosity eta ² were measured at high shear rates 10s ^-1, and its thixotropic ratio Table 1 shows (= shear viscosity η ¹ / shear viscosity η ² ).

  Into this silicone rubber mixture, 0.05 part of a 1,3-divinyl-1,1,3,3-tetramethyldisiloxane platinum complex dimethylsiloxane solution (Pt concentration 1 mass%) was mixed to obtain a silicone rubber composition. It was. About the hardened | cured material obtained by carrying out the press cure of this composition for 120 degreeC / 15 minutes, based on JISK6253-3-3: 2012, based on the hardness in durometer type A, JISK6249: 2003, and compression set. (Test specimen 29 mmφ × 12.5 mm, compression rate 25%, in air, temperature 150 ° C., test time 22 hours) As a result, based on JIS K 6249: 2003, it was immersed in a 50% aqueous solution of ethylene glycol. Table 1 shows the results of measurement of compression set (test piece 29 mmφ × 12.5 mm, compression rate 25%, temperature 120 ° C., test time 1,000 hours).

[Comparative Example 2]
60 parts of dimethylpolysiloxane (A2) capped with dimethylvinylsiloxy groups at both ends described in Example 1, fumed silica (C3) having a specific surface area of 300 m ² / g by BET method (manufactured by Aerosil Japan, Aerosil) 300) 40 parts, 8 parts of hexamethyldisilazane, 0.5 part of 1,3-divinyl-1,1,3,3-tetramethyldisilazane, 2.0 parts of water at 25 ° C. for 30 minutes, 160 The temperature was raised to 0 ° C., and stirring was continued for 3 hours, followed by cooling to obtain a silicone rubber base.
To 100 parts of this silicone rubber base, 30 parts of dimethylpolysiloxane (A1) described in Example 1 and 40 parts of dimethylpolysiloxane (A2) described in Example 1 were added and stirring was continued for 30 minutes. 3.30 parts of methylhydrogen-dimethylpolysiloxane (B1) having both ends blocked with dimethylhydrogensiloxy groups described in Example 1 and 0.025 part of ethynylcyclohexanol as a reaction control agent were added, and 15 minutes Stirring was continued to obtain a silicone rubber mixture.
In this mixture, the molar ratio (Si—H group / vinyl group) between the amount of Si—H groups and the total amount of vinyl groups in all components (A) is 2.5.
The mixture under 23 ℃, HAAKE MARS-40 shear viscosity eta ¹ measured at low shear rate 0.9 s ^-1 using a shear viscosity eta ² were measured at high shear rates 10s ^-1, and its thixotropic ratio Table 1 shows (= shear viscosity η ¹ / shear viscosity η ² ).

  Into this silicone rubber mixture, 0.05 part of a 1,3-divinyl-1,1,3,3-tetramethyldisiloxane platinum complex dimethylsiloxane solution (Pt concentration 1 mass%) was mixed to obtain a silicone rubber composition. It was. About the hardened | cured material obtained by carrying out the press cure of this composition for 120 degreeC / 15 minutes, based on JISK6253-3-3: 2012, based on the hardness in durometer type A, JISK6249: 2003, and compression set. (Test specimen 29 mmφ × 12.5 mm, compression rate 25%, in air, temperature 150 ° C., test time 22 hours) As a result, based on JIS K 6249: 2003, it was immersed in a 50% aqueous solution of ethylene glycol. Table 1 shows the results of measurement of compression set (test piece 29 mmφ × 12.5 mm, compression rate 25%, temperature 120 ° C., test time 1,000 hours).

[Comparative Example 3]
About the cured product obtained by further post-curing the cured product obtained in Comparative Example 2 at 200 ° C. for 4 hours, based on JIS K 6253-3: 2012, based on hardness in durometer type A, JIS K 6249: 2003, As a result of measuring compression set (test piece 29 mmφ × 12.5 mm, compression rate 25%, in air, temperature 150 ° C., test time 22 hours), it was immersed in 50% aqueous solution of ethylene glycol based on JIS K 6249: 2003 Table 1 shows the results obtained by measuring the compression set below (test piece 29 mmφ × 12.5 mm, compression rate 25%, temperature 120 ° C., test time 1000 hours).

[Comparative Example 4]
60 parts of dimethylpolysiloxane (A2) capped with dimethylvinylsiloxy groups at both ends described in Example 1, fumed silica (C3) having a specific surface area of 300 m ² / g by BET method (manufactured by Aerosil Japan, Aerosil) 300) 40 parts, 8 parts of hexamethyldisilazane, 0.5 part of 1,3-divinyl-1,1,3,3-tetramethyldisilazane, 2.0 parts of water at 25 ° C. for 30 minutes, 160 The temperature was raised to 0 ° C., and stirring was continued for 3 hours, followed by cooling to obtain a silicone rubber base.
After adding 50 parts of dimethylpolysiloxane (A2) described in Example 1 to 100 parts of this silicone rubber base and continuing stirring for 30 minutes, both ends described in Example 1 are dimethylhydrogensiloxy groups as a crosslinking agent. 1.12 parts of blocked methylhydrogen-dimethylpolysiloxane (B1), 0.005 part of 1,2,3-benzotriazole (manufactured by Tokyo Chemical Industry Co., Ltd.) as a compression set reducing agent, and ethynylcyclo as a reaction control agent 0.025 part of hexanol was added and stirring was continued for 15 minutes to obtain a silicone rubber mixture.
In this mixture, the molar ratio (Si—H group / vinyl group) of the amount of Si—H groups and the total amount of vinyl groups in all components (A) is 1.5.
The mixture under 23 ℃, HAAKE MARS-40 shear viscosity eta ¹ measured at low shear rate 0.9 s ^-1 using a shear viscosity eta ² were measured at high shear rates 10s ^-1, and its thixotropic ratio Table 1 shows (= shear viscosity η ¹ / shear viscosity η ² ).

  Into this silicone rubber mixture, 0.05 part of a 1,3-divinyl-1,1,3,3-tetramethyldisiloxane platinum complex dimethylsiloxane solution (Pt concentration 1 mass%) was mixed to obtain a silicone rubber composition. It was. About the hardened | cured material obtained by carrying out the press cure of this composition for 120 degreeC / 15 minutes, based on JISK6253-3-3: 2012, based on the hardness in durometer type A, JISK6249: 2003, and compression set. (Test specimen 29 mmφ × 12.5 mm, compression rate 25%, in air, temperature 150 ° C., test time 22 hours) As a result, based on JIS K 6249: 2003, it was immersed in a 50% aqueous solution of ethylene glycol. Table 1 shows the results of measurement of compression set (test piece 29 mmφ × 12.5 mm, compression rate 25%, temperature 120 ° C., test time 1,000 hours).

[Comparative Example 5]
60 parts of dimethylpolysiloxane having both ends blocked with dimethylvinylsiloxy groups (A5, average polymerization degree 2,000, vinyl group content 1.3 × 10 ⁻⁵ mol / g), specific surface area by BET method is 110 m ² / 30 parts of fumed silica (C1) (produced by Nippon Aerosil Co., Ltd., Aerosil R972), 3.0 parts of hexamethyldisilazane, 1,3-divinyl-1,1,3,3- After mixing 0.2 parts of tetramethyldisilazane and 2.0 parts of water at 25 ° C. for 30 minutes, the temperature was raised to 150 ° C., stirring was continued for 3 hours, and cooling was performed to obtain a silicone rubber base. However, since this silicone rubber base had a very high viscosity and was difficult to handle, further investigation was stopped.

Claims (6)

(A) Alkenyl group-containing organopolysiloxane having an alkenyl group bonded to at least two silicon atoms in one molecule, an average degree of polymerization of 1,500 or less, and liquid at 25 ° C .: 100 parts by mass
(B) Organohydrogenpolysiloxane containing at least two hydrogen atoms bonded to silicon atoms in one molecule: 0.2 to 20 parts by mass,
(C) Fumed silica having a specific surface area by the BET method of 50 to 150 m ² / g and having an alkenyl group-containing silyl group on the surface: 10 to 40 parts by mass,
(D) Addition reaction catalyst: 0.5 to 1,000 ppm as platinum group metal (in terms of mass) with respect to the total mass of components (A) to (C).
An addition-curable liquid silicone rubber composition containing   The addition curable liquid silicone rubber composition according to claim 1, wherein the component (C) is fumed silica having both an alkenyl group-containing silyl group and an alkyl group-containing silyl group on the surface. Component (C) is fumed silica represented by the following general formula (I)

(Wherein R ¹ is a monovalent hydrocarbon group having 1 to 3 carbon atoms, at least one R ¹ is an alkenyl group, X is —Cl, —OR ² , or —NR ² ₂ , R ² is C1-C6 monovalent hydrocarbon group, n is an integer of 1-3.)
And the following general formula (II)

(In the formula, R ¹ is the same as above, and m is an integer of 1 to 6.)
The addition-curable liquid silicone rubber composition according to claim 1 or 2, which is surface-treated with at least one alkenyl group-containing organosilicon compound selected from the group consisting of: In the silicone rubber mixture containing the components (A), (B), and (C), the shear viscosity η ¹ when the shear rate is 0.9 s ⁻¹ and the shear viscosity η when the shear rate is 10 s ⁻¹ at room temperature. ² ratio (η ¹ / η ²⁾ is 2.0 or less is any one addition curable liquid silicone rubber composition according to claims 1-3. The addition-curable liquid silicone rubber composition according to claim 4, wherein the shear viscosity ratio (η ¹ / η ² ) is 1.0 to 1.8.   A sealing material for cooling liquid comprising a cured product of the addition-curable liquid silicone rubber composition according to any one of claims 1 to 5.