JP7628940B2 - Silicone rubber composition and method for producing same - Google Patents

Description

The present invention relates to a millable silicone rubber composition, its manufacturing method, and its cured product.

Silicone rubber has excellent weather resistance, electrical properties, low compression set, heat resistance, cold resistance, etc., and is therefore widely used in a variety of fields, including electrical equipment, automobiles, construction, medicine, and food. Examples of applications include rubber contacts used as rubber contacts in remote controllers, typewriters, word processors, computer terminals, musical instruments, etc.; construction gaskets; various rolls such as copier rolls, developing rolls, transfer rolls, charging rolls, and paper feed rolls; vibration-proof rubber for audio equipment, etc.; and packing for compact discs used in computers. Currently, the demand for silicone rubber is increasing, and the development of silicone rubber with excellent properties is desired.

Silicone rubber usually has a high coefficient of friction and is used in various products as a non-slip material. On the other hand, there is also a high demand for silicone rubber with good surface slipperiness. A known method for lowering the coefficient of friction on the surface of silicone rubber is to add a low-compatible oil. For example, when the silicone rubber is dimethyl silicone, adding a low-viscosity oil with an introduced phenyl group causes the poorly compatible phenyl oil to seep out from within the molded product to the surface after molding, lowering the surface friction coefficient. These materials are widely used in oil-bleed materials for automobiles, etc. (Patent Document 1, Patent Document 2).

However, these oil-bleeding materials tend to exude oil components onto the surface, which can transfer to other materials and cause stains. One method for providing slipperiness without adding phenyl oil is to add a polymer that does not contain alkenyl groups (Patent Document 3), but further improvements are needed.

A composition containing a two-liquid addition-curing silicone composition and a sodium polyacrylate-based superabsorbent polymer is exemplified as an adhesive for wet tissues (Patent Document 4), but since it is an adhesive, there is no description regarding its slipperiness.

There is a description of an elastomer composition in which a hydrophilic polymer such as sodium polyacrylate and an inorganic salt are added to a base elastomer (Patent Document 5). After vulcanizing the elastomer composition, it is brought into contact with water for 2 to 6 hours, whereby the inorganic salt reacts with the water absorbed via the hydrophilic polymer and crystallizes. It is described that this results in high tensile strength and high hardness, but there is no description of slipperiness, and no examples of silicone rubber.

International Publication No. 2006/070947 JP 2009-185254 A JP 2008-195939 A Special table 2018-510675 publication JP 2017-222848 A

The present invention was made in consideration of the above circumstances, and aims to provide a silicone rubber composition that becomes a silicone rubber (cured product) that exhibits excellent slipperiness when wetted with water and loses its slipperiness when dried.

In order to solve the above problems, the present invention provides
(A) 100 parts by mass of an organopolysiloxane represented by the following average composition formula (1) having two or more alkenyl groups in one molecule and an average degree of polymerization of 100 or more:
R ¹ _a SiO _(4-a)/2 (1)
(In the formula, R ¹ is independently a monovalent hydrocarbon group having 1 to 12 carbon atoms, and a is a positive number of 1.95 to 2.05.)
(B) reinforcing silica having a specific surface area of 50 m ² /g or more as measured by the BET method: 10 to 100 parts by mass;
(C) sodium polyacrylate; 0.3 to 15 parts by mass per 100 parts by mass of the total of the (A) component and the (B) component;
(D) a curing agent; a silicone rubber composition containing an effective amount of the curing agent.

With such a silicone rubber composition, it is possible to obtain a silicone rubber (cured product) that exhibits excellent slipperiness when wetted with water and loses its slipperiness when dried.

It is also preferable that the molecular weight of component (C) is 10,000 to 7,000,000.

Such a silicone rubber composition has a sufficiently low dynamic friction coefficient, exhibits high slip properties, and does not deteriorate the physical properties of the cured product.

It is also preferable that the silicone rubber composition is an organic peroxide curing type silicone rubber composition.

The silicone rubber composition of the present invention can be of this type.

It is also preferable that the silicone rubber composition is an addition reaction curing type silicone rubber composition.

The silicone rubber composition of the present invention can be of this type.

The present invention also provides a method for producing the above silicone rubber composition, comprising the steps of:
A step of mixing the component (C) with a part of the component (A) to obtain a sodium polyacrylate paste;
mixing the sodium polyacrylate paste with the remaining components (A), (B) and (D) to obtain the silicone rubber composition;
The present invention provides a method for producing a silicone rubber composition comprising the steps of:

This method of manufacturing a silicone rubber composition makes it easier to mix component (C) with other components.

According to the present invention, it is possible to provide a silicone rubber composition (millable type silicone rubber composition) that can provide a silicone rubber with an effectively reduced surface friction coefficient by wetting the cured product (molded product) with water, a method for producing the same, and the cured product thereof.

As mentioned above, there was a demand for a silicone rubber composition that would develop excellent slipperiness when wetted with water, and turn into a silicone rubber (cured product) that would lose that slipperiness when dried.

As a result of extensive research into achieving the above object, the inventors have discovered that adding a specific amount of sodium polyacrylate to a heat-curable silicone rubber composition results in a silicone rubber composition that has sufficient slip properties when the surface of the cured product is wetted with water.

That is, the present invention provides:
(A) 100 parts by mass of an organopolysiloxane represented by the following average composition formula (1) having two or more alkenyl groups in one molecule and an average degree of polymerization of 100 or more:
R ¹ _a SiO _(4-a)/2 (1)
(In the formula, R ¹ is independently a monovalent hydrocarbon group having 1 to 12 carbon atoms, and a is a positive number of 1.95 to 2.05.)
(B) reinforcing silica having a specific surface area of 50 m ² /g or more as measured by the BET method: 10 to 100 parts by mass;
(C) sodium polyacrylate; 0.3 to 15 parts by mass per 100 parts by mass of the total of the (A) component and the (B) component;
(D) A curing agent; the silicone rubber composition contains an effective amount of the curing agent.

The present invention will now be described in more detail.
In this specification, the specific surface area is a value measured by the BET method. The millable composition generally means a composition that is high-viscosity and non-liquid and does not have self-flowing properties at room temperature (25°C), and can be uniformly kneaded under shear stress with a kneader such as a roll mill (e.g., two-roll or three-roll). The organopolysiloxane raw rubber generally means a non-liquid organopolysiloxane component that has a high degree of polymerization (high viscosity) and does not have self-flowing properties at room temperature (25°C).

[Silicone rubber composition]
[(A) Organopolysiloxane]
In the present invention, component (A) is an organopolysiloxane represented by the following average composition formula (1), which has two or more alkenyl groups in one molecule and has an average degree of polymerization of 100 or more.
R ¹ _a SiO _(4-a)/2 (1)
(In the formula, R ¹ is independently a monovalent hydrocarbon group having 1 to 12 carbon atoms, and a is a positive number of 1.95 to 2.05.)

In the above average composition formula (1), R ¹ is independently a monovalent hydrocarbon group having 1 to 12 carbon atoms, preferably 1 to 8 carbon atoms, and specifically includes alkyl groups such as methyl, ethyl, propyl, butyl, hexyl, and octyl groups, cycloalkyl groups such as cyclopentyl and cyclohexyl groups, alkenyl groups such as vinyl, allyl, propenyl, butenyl, and hexenyl groups, cycloalkenyl groups such as cyclohexenyl groups, aryl groups such as phenyl and tolyl groups, aralkyl groups such as benzyl and 2-phenylethyl groups, and groups in which some or all of the hydrogen atoms of these groups have been replaced with halogen atoms such as fluorine and chlorine, such as chloromethyl and trifluoropropyl groups. Among the above, methyl, vinyl, phenyl, and trifluoropropyl groups are preferred, and methyl and vinyl groups are particularly preferred.

In particular, the organopolysiloxane as component (A) is characterized by having two or more alkenyl groups in one molecule, preferably 2 to 50 alkenyl groups, and particularly preferably 2 to 20 alkenyl groups. The alkenyl group may be a cyclic aliphatic unsaturated group such as a cycloalkenyl group. As the alkenyl group, vinyl groups and allyl groups are preferred, with vinyl groups being particularly preferred.

It is also preferred that 0.01 to 20 mol %, and particularly 0.02 to 10 mol %, of all R ¹ 's are alkenyl groups. This alkenyl group may be bonded to a silicon atom at a 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 preferred that at least one of the alkenyl groups is bonded to a silicon atom at a molecular chain terminal.

It is also desirable that 80 mol % or more, preferably 90 mol % or more, more preferably 95 mol % or more, of all R 1 ^s , and further preferably all R ^{1 s} other than alkenyl groups are alkyl groups, particularly methyl groups.

a is a positive number between 1.95 and 2.05, preferably between 1.98 and 2.02, and more preferably between 1.99 and 2.01.

The molecular structure of the organopolysiloxane of component (A) is preferably linear or partially branched. Specifically, the repeating structure of the diorganosiloxane unit (R ¹ ₂ SiO _2/2 , R ¹ is the same as above, and the same applies below) constituting the main chain of the organopolysiloxane is preferably one consisting of repeating dimethylsiloxane units alone, or one in which a diorganosiloxane unit having a phenyl group, vinyl group, 3,3,3-trifluoropropyl group or the like as a substituent, such as a diphenylsiloxane unit, a methylphenylsiloxane unit, a methylvinylsiloxane unit, or a methyl-3,3,3-trifluoropropylsiloxane unit, has been introduced as part of the dimethylpolysiloxane structure consisting of repeating dimethylsiloxane units constituting the main chain.

In addition, both molecular chain terminals are preferably blocked with a triorganosiloxy group (R ¹ ₃ SiO _1/2 ) such as a trimethylsiloxy group, a dimethylphenylsiloxy group, a vinyldimethylsiloxy group, a divinylmethylsiloxy group, or a trivinylsiloxy group.

Such organopolysiloxanes can be obtained, for example, by cohydrolytic condensation or 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 100 or more (usually 100 to 100,000), preferably 1,000 to 100,000, more preferably 2,000 to 50,000, and particularly preferably 3,000 to 20,000. It is preferable that the organopolysiloxane has no self-flowability at room temperature (25°C), and is in a so-called raw rubber state (non-liquid state). If the average degree of polymerization is less than 100, problems such as roll adhesion will occur when the compound is made, and roll workability will deteriorate. The average degree of polymerization is determined as the average degree of polymerization from the weight average molecular weight in terms of polystyrene by gel permeation chromatography (GPC) analysis measured under the following conditions.
[Measurement conditions]
Developing solvent: tetrahydrofuran (THF)
Flow rate: 0.6mL/min
Detector: Refractive index detector (RI)
Column: TSK Guard column Super H-L
TSKgel SuperH4000 (6.0mm I.D. x 15cm x 1)
TSKgel SuperH3000 (6.0mm I.D. x 15cm x 1)
TSKgel SuperH2000 (6.0mm I.D. x 15cm x 2)
(Both manufactured by Tosoh Corporation)
Column temperature: 40°C
Sample injection volume: 20 μL (THF solution with a concentration of 0.5% by mass)

Component (A) may be used alone or as a mixture of two or more types differing in molecular weight, degree of polymerization, or molecular structure.

[(B) Reinforcing Silica]
The reinforcing silica of component (B) acts as a component that imparts excellent mechanical properties to the resulting silicone rubber composition. The reinforcing silica may be precipitated silica (wet silica) or fumed silica (dry silica), and has a large number of silanol groups (SiOH) on its surface. In the present invention, the specific surface area of the reinforcing silica of component (B) must be 50 m ² /g or more, as measured by the BET method, and is preferably 100 to 400 m ² /g. If the specific surface area is less than 50 m ² /g, the reinforcing effect of component (B) will be insufficient.

The reinforcing silica of component (B) may be used in an untreated state, or may be surface-treated with an organosilicon compound such as organopolysiloxane, organopolysilazane, chlorosilane, or alkoxysilane, as necessary. These reinforcing silicas may be used alone or in combination of two or more types.

The amount of reinforcing silica (B) is 10 to 100 parts by mass, preferably 10 to 80 parts by mass, and more preferably 20 to 70 parts by mass, per 100 parts by mass of the organopolysiloxane (A). If the amount of (B) is less than 10 parts by mass per 100 parts by mass of the organopolysiloxane (A), the mechanical properties of the silicone rubber cured product obtained by curing the silicone rubber composition, such as tensile strength and tear strength, will be insufficient, and if the amount of (B) is more than 100 parts by mass, the processability of the resulting silicone rubber composition will decrease.

[(C) Sodium polyacrylate]
The sodium polyacrylate of the component (C) absorbs water and expands when it comes into contact with water. It then seeps out onto the surface of the silicone rubber cured product, and exhibits slipperiness. If the molecular weight is 10,000 to 7,000,000, the silicone rubber cured product exhibits good slipperiness when wetted with water, so this is preferred, with 100,000 to 7,000,000 being more preferred, and 1,000,000 to 6,600,000 being even more preferred. If the molecular weight is 10,000 or more, the dynamic friction coefficient is sufficiently reduced, and high slipperiness is exhibited. If the molecular weight is 7,000,000 or less, the physical properties of the cured product are not reduced.
When the molecular weight of the sodium polyacrylate used has a distribution, it is preferable that both the upper and lower limits are within the above ranges.

The amount of component (C) added is 0.3 to 15 parts by mass, preferably 0.3 to 10 parts by mass, and more preferably 0.5 to 5 parts by mass, per 100 parts by mass of the total of components (A) and (B). If it is less than 0.3 parts by mass, good slip properties will not be obtained, and if it exceeds 15 parts by mass, the physical properties of the cured product may deteriorate.

[(D) Curing Agent]
The curing agent for component (D) is not particularly limited as long as it can cure the silicone rubber composition, but the following (D-1) organic peroxide curing agent and/or (D-2) addition reaction curing agent can be used.

(D-1) Organic Peroxide Curing Agent Examples of the (D-1) organic peroxide curing agent 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, and 1,6-hexanediol-bis-t-butylperoxycarbonate.

By adding an organic peroxide curing agent to a silicone rubber compound, which is a composition containing components (A), (B), and (C), an organic peroxide curing type silicone rubber composition can be obtained. The amount of organic peroxide curing agent added is preferably 0.1 to 10 parts by mass, and more preferably 0.2 to 5 parts by mass, per 100 parts by mass of component (A). If the amount is 0.1 part by mass or more, curing will not be insufficient, and if it is 10 parts by mass or less, the cured silicone rubber will not yellow due to decomposition residues of the organic peroxide curing agent.

(D-2) Addition reaction curing agent As the addition reaction curing agent (D-2), a combination of an organohydrogenpolysiloxane and a hydrosilylation catalyst can be used. By adding the addition reaction curing agent to a silicone rubber compound, an addition reaction curing type silicone rubber composition can be obtained.

The organohydrogenpolysiloxane may have a linear, cyclic, branched, or three-dimensional network structure, so long as it contains preferably two or more, more preferably three or more, even more preferably about 3 to 200, and still more preferably about 4 to 100 hydrogen atoms bonded to silicon atoms in one molecule (i.e., hydrosilyl groups). Any organohydrogenpolysiloxane known as a curing agent for addition reaction curing silicone rubber compositions can be used, and for example, an organohydrogenpolysiloxane represented by the following average composition formula (2) can be used.
R ² _r H _s SiO _(4-rs)/2 (2)

In the above average composition formula (2), R ² independently represents a monovalent hydrocarbon group, preferably excluding an aliphatic unsaturated bond. The carbon number of the monovalent hydrocarbon group of R ² is preferably 1 to 12, more preferably 1 to 8. Specific examples of R ² include alkyl groups such as methyl, ethyl, and propyl groups, cycloalkyl groups such as cyclohexyl groups, aryl groups such as phenyl and tolyl groups, aralkyl groups such as benzyl, 2-phenylethyl, and 2-phenylpropyl groups, and groups in which some or all of the hydrogen atoms of these groups have been substituted with halogen atoms or the like, for example, 3,3,3-trifluoropropyl groups.

Note that r is preferably 0<r<3, more preferably 0.5≦r≦2.2, and even more preferably 1.0≦r≦2.0. s is preferably 0<s≦3, more preferably 0.002≦s≦1.1, and even more preferably 0.005≦s≦1. Furthermore, 0<r+s≦3 is preferably, more preferably 1≦r+s≦3, and even more preferably 1.002≦r+s≦2.7.

The organohydrogenpolysiloxane preferably has two or more hydrosilyl groups in one molecule, more preferably three or more, which may be at the molecular chain terminals, in the middle of the molecular chain, or both. In addition, it is preferable that this organohydrogenpolysiloxane has a viscosity at 25°C of 0.5 to 10,000 mPa·s, and particularly 1 to 300 mPa·s. In the present invention, the viscosity is a value measured using a rotational viscometer at 25°C as described in JIS K7117-1:1999.

Specific examples of such organohydrogenpolysiloxanes include 1,1,3,3-tetramethyldisiloxane, 1,3,5,7-tetramethylcyclotetrasiloxane, tris(hydrogendimethylsiloxy)methylsilane, tris(hydrogendimethylsiloxy)phenylsilane, methylhydrogencyclopolysiloxane, methylhydrogensiloxane-dimethylsiloxane cyclic copolymers, methylhydrogenpolysiloxanes capped at both ends with trimethylsiloxy groups, dimethylsiloxane-methylhydrogensiloxane copolymers capped at both ends with trimethylsiloxy groups, dimethylpolysiloxanes capped at both ends with dimethylhydrogensiloxy groups, dimethylsiloxanes capped at both ends with dimethylhydrogensiloxy groups, end-blocked dimethylsiloxane-methylhydrogensiloxane copolymer, end-blocked methylhydrogensiloxane-diphenylsiloxane copolymer with trimethylsiloxy groups at both ends, end-blocked methylhydrogensiloxane-diphenylsiloxane-dimethylsiloxane copolymer with trimethylsiloxy groups at both ends, end-blocked methylhydrogensiloxane-methylphenylsiloxane-dimethylsiloxane copolymer with trimethylsiloxy groups at both ends, end-blocked methylhydrogensiloxane-dimethylsiloxane-diphenylsiloxane copolymer with dimethylhydrogensiloxy groups at both ends, end-blocked methylhydrogensiloxane-dimethylsiloxane-methylphenylsiloxane copolymer with dimethylhydrogensiloxy groups at both ends, (CH Examples _of the copolymer include a copolymer consisting of ( _CH3 )2HSiO1 _/2 units, ( _{CH3 )} 3SiO1 _{/2 units} , and SiO4 _{/2 units} , a copolymer consisting of ( _CH3 ) _{2HSiO1 /2} units, SiO4 _/2 units, and _{( C6H5} ) _{3SiO1 /2} units, and copolymers in which part or _all of the methyl groups in the above _exemplary compounds have been substituted with other alkyl groups, phenyl groups, or the like.

The amount of the organohydrogenpolysiloxane is preferably 0.1 to 40 parts by mass per 100 parts by mass of the total amount of the silicone rubber compound (containing components (A), (B), and (C)). The ratio of hydrogen atoms bonded to silicon atoms (hydrosilyl groups) per alkenyl group in component (A) is preferably in the range of 0.5 to 10, and more preferably in the range of 0.7 to 5. If the number is 0.5 or more, crosslinking is sufficient and sufficient mechanical strength is obtained, and if the number is 10 or less, the physical properties after curing will not decrease, and in particular there will be no deterioration in heat resistance or large compression set.

The hydrosilylation catalyst is a catalyst that causes a hydrosilylation addition reaction between the alkenyl group of component (A) and the silicon-bonded hydrogen atom (hydrosilyl group) of the organohydrogenpolysiloxane. Examples of hydrosilylation catalysts include platinum group metal catalysts, which include simple platinum group metals and their compounds, and which are conventionally known as catalysts for addition reaction curing silicone rubber compositions. Examples of such catalysts include particulate platinum metal adsorbed on a carrier such as silica, alumina, or silica gel, platinum catalysts such as platinic chloride, chloroplatinic acid, and alcohol solutions of chloroplatinic acid hexahydrate, palladium catalysts, and rhodium catalysts, but platinum or platinum compounds (platinum catalysts) are preferred.

The amount of hydrosilylation catalyst added should be sufficient to promote the addition reaction, and is usually used in the range of 1 ppm to 1% by mass, calculated as the amount of platinum group metal relative to component (A), with a range of 5 to 500 ppm by mass being preferable. If the amount added is 1 ppm by mass or more, the addition reaction is sufficiently promoted and curing is sufficient, while if it is 1% by mass or less, sufficient reactivity is maintained and it is not uneconomical.

In addition to the hydrosilylation catalyst, an addition reaction inhibitor may be used according to the purpose of the present invention in order to adjust the curing rate. Specific examples include acetylene alcohol-based inhibitors such as ethynylcyclohexanol, and organosilicon compound-based inhibitors such as 1,3,5,7-tetramethyl-1,3,5,7-tetravinylcyclotetrasiloxane, 1,3-divinyl-1,1,3,3-tetramethyldisiloxane, and bis[(1,1-dimethyl-2-propyn-1-yl)oxy]dimethylsilane. The addition reaction inhibitors may be used alone or in combination of two or more.

In addition, the silicone rubber compound can be mixed with the (D-1) and (D-2) components in the above-mentioned ranges to produce a co-vulcanization type silicone rubber composition (millable type silicone rubber composition) that uses both addition reaction curing and organic peroxide curing.

[Other ingredients]
In addition to the above-mentioned components, the silicone rubber composition of the present invention (millable type silicone rubber composition) can contain, as necessary, fillers such as crushed quartz, crystalline silica, diatomaceous earth, calcium carbonate, etc., colorants, tear strength improvers, acid acceptors, thermal conductivity improvers such as alumina, boron nitride, etc., release agents, various alkoxysilanes as dispersants for fillers, in particular phenyl group-containing alkoxysilanes and their hydrolysates, diphenylsilanediol, carbon functional silane, dimethylpolysiloxane having silanol groups at both ends, 3,3,3-trifluoropropylmethylpolysiloxane having silanol groups at both ends, and other fillers and additives known in the art for use in thermosetting type silicone rubber compositions.

[Method of manufacturing silicone rubber composition]
The silicone rubber composition of the present invention can be produced by mixing a composition containing 100 parts by mass of component (A) and 10 to 100 parts by mass of component (B), heat treating the mixture to obtain a base compound, and then adding an effective amount of component (D) within the above-mentioned blending amount range to 100 parts by mass of the silicone rubber compound obtained by adding 0.3 to 15 parts by mass of component (C) to 100 parts by mass of the base compound.

The method for obtaining the silicone rubber composition of the present invention is not limited to the above. For example, there are cases where no heat treatment is performed when the components (A) and (B) are mixed to obtain the base compound, and cases where the component (C) is mixed with the components (A) and (B) when the base compound is formulated, instead of adding the component (C) to the obtained base compound.

In addition, in the above method for producing a silicone rubber composition, instead of adding component (C) alone, a sodium polyacrylate paste is prepared by mixing component (C) with a part of component (A), and the sodium polyacrylate paste is added to the base compound so that the amount of component (C) falls within the above range to prepare a silicone rubber compound, and an effective amount of component (D) within the above range can be added to produce a silicone rubber composition.

<Curing conditions>
The silicone rubber composition of the present invention can be cured under known curing conditions by a known curing method to obtain a cured product. Specifically, the composition can be cured by heating at preferably 25 to 200°C, more preferably 80 to 160°C. The heating time is preferably 0.5 minutes to 5 hours, more preferably 1 minute to 3 hours. Furthermore, secondary vulcanization at 150 to 250°C for 1 to 10 hours is expected to remove the decomposition residue of the organic peroxide curing agent and stabilize the physical properties.

The silicone rubber cured product obtained by curing the silicone rubber composition of the present invention has excellent slip properties when the sheet surface is wetted with water.

The present invention will be specifically explained below with examples and comparative examples, but the present invention is not limited to the following examples.

Physical property measurement method [Measurement method]
In the present examples and comparative examples, the prepared cured products (test sheets) were evaluated as follows.

[Various physical properties]
The resulting silicone rubber cured product was measured for various physical properties (hardness (Durometer A hardness meter), tensile strength, and elongation at break) in accordance with JIS K 6249:2003.

[Kinematic friction coefficient]
The dynamic friction coefficient of the test sheet was measured by using an automatic friction and wear analyzer TSf-503 (manufactured by Kyowa Interface Science Co., Ltd.) under the conditions of a load of 1 kg, a tensile speed of 10 mm/s, and a point contact (steel ball), and the dynamic friction coefficient was measured when the same location was slid 10 times (initial). In addition, the dynamic friction coefficient was also measured when a drop of water was dropped on the dynamic friction coefficient measurement location (water drop), and then the water was dried at room temperature (25°C) for 48 hours, and the dynamic friction coefficient was measured (dry). Note that, since the initial dynamic friction coefficients of Example 8 and Comparative Example 5 were too large compared to the other Examples, the load was changed from 1 kg to 500 g and the measurements were performed.

[Finger touch test]
The slipperiness was evaluated when the test sheet was rubbed with a finger moistened with water.
◎: Very slippery (slippery)
〇: Slippery (not slippery)
×: Not slippery

[Preparation of sodium polyacrylate paste]
A sodium polyacrylate paste was prepared by kneading 100 parts by mass of organopolysiloxane gum composed of 99.850 mol % dimethylsiloxane units, 0.125 mol % methylvinylsiloxane units, and 0.025 mol % dimethylvinylsiloxane units and having an average degree of polymerization of about 8,000 with 100 parts by mass of sodium polyacrylate (1) (manufactured by Wako Pure Chemical Industries, Ltd., degree of polymerization: 22,000 to 70,000 (molecular weight: 2,069,000 to 6,583,000)) using a two-roll mill and then a three-roll mill.

[Example 1]
As component (A), 100 parts by mass of organopolysiloxane raw rubber consisting of 99.850 mol% dimethylsiloxane units, 0.125 mol% methylvinylsiloxane units, and 0.025 mol% dimethylvinylsiloxane units and having an average degree of polymerization of about 8,000, as component (B) 40 parts by mass of fumed silica (product name: Aerosil 200, manufactured by Nippon Aerosil Co., Ltd., specific surface area measured by BET method: 200 ^m2 /g) and 6 parts by mass of dimethylpolysiloxane having silanol groups at both ends, an average degree of polymerization of 4, and a viscosity at 25°C of 15 mPa·s were added, and then mixed in a kneader and heat-treated at 170°C for 2 hours to prepare base compound (1).

0.5 parts by mass of sodium polyacrylate (1) (manufactured by Wako Pure Chemical Industries, Ltd., polymerization degree: 22,000 to 70,000 (molecular weight: 2,069,000 to 6,583,000)) was added to 100 parts by mass of base compound (1) to prepare silicone rubber compound (1). 0.4 parts by mass of 2,5-dimethyl-2,5-bis(t-butylperoxy)hexane as a curing agent was mixed with 100 parts by mass of silicone rubber compound (1) to prepare a silicone rubber composition, which was press-cured for 10 minutes under conditions of 165°C and 70 kgf/ ^cm2 , and then post-cured for 4 hours at 200°C to prepare a test sheet (1), and various physical properties, dynamic friction coefficient, and slipperiness were measured.

[Example 2]
A test sheet (2) was prepared in the same manner as in Example 1, except that the amount of sodium polyacrylate (1) was 5.0 parts by mass, and various physical properties, dynamic friction coefficient, and slipperiness were measured.

[Example 3]
A test sheet (3) was prepared in the same manner as in Example 1, except that sodium polyacrylate (1) was replaced with sodium polyacrylate (2) (product name: AQUALIC FH-S, manufactured by Nippon Shokubai Co., Ltd., molecular weight: 3,000,000 to 5,000,000), and various physical properties, dynamic friction coefficient, and slipperiness were measured.

[Example 4]
A test sheet (4) was prepared in the same manner as in Example 1, except that sodium polyacrylate (1) was replaced with sodium polyacrylate (3) (product name: AQUALIC DL-100, manufactured by Nippon Shokubai Co., Ltd., molecular weight: 3,500), and various physical properties, dynamic friction coefficient, and slipperiness were measured.

[Example 5]
A test sheet (5) was prepared in the same manner as in Example 1, except that the sodium polyacrylate paste prepared above was used as 1 part by mass instead of the sodium polyacrylate (1), and various physical properties, dynamic friction coefficient, and slipperiness were measured.

[Example 6]
As component (A), 100 parts by mass of organopolysiloxane raw rubber consisting of 99.850 mol% dimethylsiloxane units, 0.125 mol% methylvinylsiloxane units, and 0.025 mol% dimethylvinylsiloxane units and having an average degree of polymerization of about 8,000, as component (B) 60 parts by mass of fumed silica (product name: Aerosil 200, manufactured by Nippon Aerosil Co., Ltd., specific surface area measured by BET method: 200 ^m2 /g) and 10 parts by mass of dimethylpolysiloxane having silanol groups at both ends, an average degree of polymerization of 4, and a viscosity at 25°C of 15 mPa·s were added, and then mixed in a kneader and heat-treated at 170°C for 2 hours to prepare base compound (2).

To 100 parts by mass of the base compound (2), 0.5 parts by mass of sodium polyacrylate (2) (product name: AQUALIC FH-S, manufactured by Nippon Shokubai Co., Ltd., molecular weight: 3,000,000 to 5,000,000) was added to prepare a silicone rubber compound (2). A silicone rubber composition was prepared by mixing 100 parts by mass of the silicone rubber compound (2) with 0.9 parts by mass of methylhydrogenpolysiloxane (degree of polymerization: 38, hydrosilyl group: 0.00725 mol/g) having hydrosilyl groups on the side chains as a curing agent, 0.04 parts by mass of ethynylcyclohexanol as an addition reaction inhibitor, and 0.05 parts by mass of a platinum catalyst (Pt concentration: 1% by mass). The silicone rubber composition was press-cured for 10 minutes under conditions of 120°C and 70 kgf/ ^cm2 , and then post-cured for 4 hours at 200°C to prepare a test sheet (6). Various physical properties, dynamic friction coefficient, and slipperiness were measured.

[Example 7]
100 parts by mass of organopolysiloxane raw rubber consisting of 99.850 mol % dimethylsiloxane units, 0.125 mol % methylvinylsiloxane units, and 0.025 mol % dimethylvinylsiloxane units and having an average degree of polymerization of approximately 8,000 as component (A) and 20 parts by mass of fumed silica (product name: Aerosil R972, manufactured by Nippon Aerosil Co., Ltd., specific surface area measured by BET method: 110 ^m2 /g) as component (B) were added and mixed in a kneader to prepare base compound (3).

0.5 parts by mass of sodium polyacrylate (2) (trade name: AQUALIC FH-S, manufactured by Nippon Shokubai Co., Ltd., molecular weight: 3,000,000 to 5,000,000) was added to 100 parts by mass of base compound (3) to prepare silicone rubber compound (3). 0.4 parts by mass of 2,5-dimethyl-2,5-bis(t-butylperoxy)hexane as a curing agent was mixed with 100 parts by mass of silicone rubber compound (3) to prepare a silicone rubber composition, which was press-cured for 10 minutes under conditions of 165°C and 70 kgf/ ^cm2 , and then post-cured for 4 hours at 200°C to prepare a test sheet (7). Various physical properties, dynamic friction coefficient, and slipperiness were measured.

[Example 8]
As component (A), 100 parts by mass of organopolysiloxane raw rubber consisting of 99.825 mol% 3,3,3-trifluoropropylmethylsiloxane units, 0.125 mol% methylvinylsiloxane units, and 0.05 mol% dimethylvinylsiloxane units and having an average degree of polymerization of about 4,000, as component (B) 40 parts by mass of fumed silica (product name: Aerosil 200, manufactured by Nippon Aerosil Co., Ltd., specific surface area measured by BET method: 200 ^m2 /g), 1 part by mass of 3,3,3-trifluoropropylmethylsiloxane having silanol groups at both ends, an average degree of polymerization of 4, and a viscosity of 15 mPa·s at 25°C, and 5 parts by mass of diphenylsilanediol were added, and the mixture was mixed in a kneader and heat-treated at 150°C for 2 hours to prepare base compound (4).

0.5 parts by mass of sodium polyacrylate (2) (trade name: AQUALIC FH-S, manufactured by Nippon Shokubai Co., Ltd., molecular weight: 3,000,000 to 5,000,000) was added to 100 parts by mass of base compound (4) to prepare silicone rubber compound (4). 0.6 parts by mass of 2,5-dimethyl-2,5-bis(t-butylperoxy)hexane was mixed with 100 parts by mass of silicone rubber compound (4) as a curing agent to prepare a silicone rubber composition, which was press-cured for 10 minutes under conditions of 165°C and 70 kgf/ ^cm2 , and then post-cured for 4 hours at 200°C to prepare a test sheet (8), and various physical properties, dynamic friction coefficient, and slipperiness were measured.

[Example 9]
As component (A), 100 parts by mass of organopolysiloxane raw rubber consisting of 99.850 mol% dimethylsiloxane units, 0.125 mol% methylvinylsiloxane units, and 0.025 mol% dimethylvinylsiloxane units and having an average degree of polymerization of about 8,000, and as component (B), fumed silica (product name: Aerosil 200, manufactured by Nippon Aerosil Co., Ltd., specific surface area measured by the BET method: 200 ^m2 40 parts by mass of dimethylpolysiloxane having silanol groups at both ends, an average degree of polymerization of 4, and a viscosity of 15 mPa·s at 25° C., and 0.52 parts by mass of sodium polyacrylate (2) (product name: AQUALIC FH-S, manufactured by Nippon Shokubai Co., Ltd., molecular weight: 3,000,000 to 5,000,000) as component (C) were added, and the mixture was mixed in a kneader and heat-treated at 170° C. for 2 hours to prepare a base compound (5) (silicone rubber compound (5)).

100 parts by mass of the base compound (5) was mixed with 0.4 parts by mass of 2,5-dimethyl-2,5-bis(t-butylperoxy)hexane as a curing agent to prepare a silicone rubber composition, which was press-cured for 10 minutes under conditions of 165°C and 70 kgf/ ^cm2 , and then post-cured for 4 hours at 200°C to prepare a test sheet (9). Various physical properties, dynamic friction coefficient, and slipperiness were measured.

[Comparative Example 1]
A test sheet (10) was prepared in the same manner as in Example 1, except that sodium polyacrylate (1) was not added, and various physical properties, dynamic friction coefficient, and slipperiness were measured.

[Comparative Example 2]
A test sheet (11) was prepared in the same manner as in Example 1, except that the amount of sodium polyacrylate (1) was 0.1 parts by mass, and various physical properties, dynamic friction coefficient, and slipperiness were measured.

[Comparative Example 3]
A test sheet (12) was prepared in the same manner as in Example 6, except that sodium polyacrylate (2) was not added, and various physical properties, dynamic friction coefficient, and slipperiness were measured.

[Comparative Example 4]
A test sheet (13) was prepared in the same manner as in Example 7, except that sodium polyacrylate (2) was not added, and various physical properties, dynamic friction coefficient, and slipperiness were measured.

[Comparative Example 5]
A test sheet (14) was prepared in the same manner as in Example 8, except that sodium polyacrylate (2) was not added, and various physical properties, dynamic friction coefficient, and slipperiness were measured.

The results are shown in Tables 1 to 5. The units of values in the tables are parts by mass.

<Evaluation Results>
Regarding the dynamic friction coefficient when water was dropped onto the test sheet made from the silicone rubber composition of the present invention, the dynamic friction coefficient when water was dropped onto the test sheet of the Example tended to be significantly lower than that of the Comparative Example measured under the same conditions. In addition, the results of the finger touch test showed that all of the Examples were rated as ◎ or ◯, whereas all of the Comparative Examples were rated as ×, confirming that the test sheet using the present invention exhibits slipperiness when wetted with water.

In addition, when water was dripped onto the test sheets of the examples and then the sheets were dried for 48 hours, the dynamic friction coefficients were all similar to the initial values. This confirmed that the slipperiness exhibited by wetting the test sheets using the present invention disappeared when the sheets were dried.

The hardness, tensile strength, and elongation at break of the test sheets produced were comparable in both the examples and the comparative examples when measured under the same conditions.

The present invention is not limited to the above-described embodiment. The above-described embodiment is merely an example, and anything that has substantially the same configuration as the technical idea described in the claims of the present invention and exhibits similar effects is included within the technical scope of the present invention.

Claims (5)

(A) 100 parts by mass of an organopolysiloxane represented by the following average composition formula (1) having two or more alkenyl groups in one molecule and an average degree of polymerization of 100 or more:
R ¹ _a SiO _(4-a)/2 (1)
(In the formula, R ¹ is independently a monovalent hydrocarbon group having 1 to 12 carbon atoms, and a is a positive number of 1.95 to 2.05.)
(B) reinforcing silica having a specific surface area of 50 m ² /g or more as measured by the BET method: 10 to 100 parts by mass;
(C) sodium polyacrylate; 0.3 to 5 parts by mass per 100 parts by mass of the total of the (A) component and the (B) component;
(D) a curing agent; a silicone rubber composition comprising an effective amount of the curing agent. The silicone rubber composition according to claim 1, characterized in that the molecular weight of component (C) is 10,000 to 7,000,000. The silicone rubber composition according to claim 1 or 2, characterized in that the silicone rubber composition is an organic peroxide curing type. The silicone rubber composition according to claim 1 or 2, characterized in that the silicone rubber composition is an addition reaction curing type. A method for producing the silicone rubber composition according to any one of claims 1 to 4, comprising the steps of:
A step of mixing the component (C) with a part of the component (A) to obtain a sodium polyacrylate paste;
mixing the sodium polyacrylate paste with the remaining components (A), (B) and (D) to obtain the silicone rubber composition;
2. A method for producing a silicone rubber composition comprising the steps of: