WO2021100535A1

WO2021100535A1 - Silicone rubber composition for keypad production, and keypad

Info

Publication number: WO2021100535A1
Application number: PCT/JP2020/041810
Authority: WO
Inventors: 大地轟
Original assignee: 信越化学工業株式会社
Priority date: 2019-11-22
Filing date: 2020-11-10
Publication date: 2021-05-27
Also published as: JP2021080415A; JP7484140B2

Abstract

The purpose of the present invention is to provide a silicone rubber composition suitable as a keypad material, said silicone rubber composition having exceptional dynamic fatigue durability (keystroke durability) even in high temperature/high humidity environments, and a keypad obtained by curing molding said silicone rubber composition.　In the present invention, a silicone rubber composition is cured and molded, said silicone rubber composition containing an alkenyl-group-containing organopolysiloxane having a degree of polymerization of 100 or higher, reinforcing silica, an alkenyl-group-containing organosilazane and/or alkenyl-group-containing alkoxysilane, hydrochloric acid, a fatty acid ester and/or an ester of an aliphatic alcohol, a cerium-element-containing organopolysiloxane containing a carboxylate containing elemental cerium, and a curing agent.

Description

Silicone rubber composition for making keypads and keypads

The present invention relates to a silicone rubber composition having excellent dynamic fatigue durability and suitable as a keypad material, and a keypad obtained by curing and molding the composition.

Silicone rubber has excellent weather resistance, electrical properties, low compression permanent strain resistance, heat resistance, cold resistance, etc., so it can be used in various fields such as electrical equipment, automobiles, construction, medical care, and food. Widely used. For example, for remote controllers, typewriters, word processors, computer terminals, keypads used as rubber contacts for musical instruments, building gaskets, anti-vibration rubber for audio equipment, connector seals, automobile parts such as spark plug boots, and computers. Examples include packing for compact discs used, and applications such as bread and cake molds. At present, the demand for silicone rubber is increasing more and more, and the development of silicone rubber having excellent properties is desired.

Among them, the keypad material is widely used for keyboards of mobile phones, personal computers, etc., and as a characteristic required for these keypad materials, it is required that the load change when a key is pressed is small. Normally, when the molding key is repeatedly pressed, the load on the key decreases as the number of keystrokes increases. The smaller the decrease in the peak load, the better the key characteristics, and the material exhibiting such load characteristics is excellent as the keypad material.

Silicone rubber is widely used as such a keypad material. Japanese Unexamined Patent Publication No. 2001-164111 (Patent Document 1) proposes a silicone rubber composition for a keypad.

However, in recent years, as the shape of the key to be molded has become more complicated, the strain itself applied to the key has become larger, and with the miniaturization of the equipment used in recent years, the shape of the material has a larger strain. Things are increasing. Therefore, the dynamic fatigue durability is not sufficiently satisfied in response to the strict demands of recent years.

Japanese Patent Application Laid-Open No. 2009-275158 (Patent Document 2) is for a key pad having excellent dynamic fatigue durability (keying durability) by using a phosphoric acid ester of an alkyl group partially substituted with chlorine. Although a suitable silicone rubber composition has been proposed, it is not preferable because the keystroke durability is not sufficient and the manufacturing apparatus is corroded. In order to solve this problem, Japanese Patent Application Laid-Open No. 2011-105782 (Patent Document 3) uses organodisilazane having an alkenyl group in the molecule and an ester of a fatty acid ester and / or an aliphatic alcohol. A silicone rubber composition suitable for a key pad having excellent fatigue durability has been proposed. In Japanese Unexamined Patent Publication No. 2017-218487 (Patent Document 4), instead of organodisilazane having an alkoxy group in the molecule, a vinyl group that is cheaper and suppresses catalytic poisoning and yellowing of a cured product during additional vulcanization. A silicone rubber composition suitable for a key pad having excellent dynamic fatigue durability using the containing alkoxysilane has been proposed. However, there is no description about the durability under high temperature and high humidity, and the durability may be lowered under the condition of 50 ° C. and 50% RH or more.

Japanese Unexamined Patent Publication No. 2001-164111 Japanese Unexamined Patent Publication No. 2009-275158 Japanese Unexamined Patent Publication No. 2011-105782 JP-A-2017-218487

The present invention has been made in view of the above circumstances, and is excellent in dynamic fatigue durability (keystroke durability) even under high temperature and high humidity, and cures a silicone rubber composition suitable as a keypad material and the composition. It is an object of the present invention to provide a molded keypad.

As a result of diligent studies to achieve the above object, the present inventor has made an alkenyl group-containing organopolysiloxane having a degree of polymerization of 100 or more, a reinforcing silica, an alkenyl group-containing organosilazane and / or an alkenyl group-containing alkoxysilane. To cure and mold a silicone rubber composition containing hydrochloric acid, an ester of a fatty acid ester and / or an aliphatic alcohol, an organopolysiloxane containing a cerium element containing a carboxylate containing a cerium element, and a curing agent. As a result, it has been found that a keypad having excellent dynamic fatigue durability can be obtained even under high temperature and high humidity, and the present invention has been made.

Therefore, the present invention provides a keypad composed of the following silicone rubber composition for producing a keypad and a cured molded product of the composition.
[1]
(A) The following average composition formula (1)
R ¹ _n SiO _{(4-n) / 2} (1)
(In the formula, R ¹ is the same or different unsubstituted or substituted monovalent hydrocarbon group, and n is a positive number from 1.95 to 2.04.)
Organopolysiloxane having at least two alkenyl groups in one molecule and having a degree of polymerization of 100 or more: 100 parts by mass,
(B) Reinforcing silica having a specific surface area of 50 m ² / g or more by the BET method: 10 to 100 parts by mass,
(C) The following (C-1) alkenyl group-containing organosilazane: 0.1 to 10 parts by mass and / or (C-2) alkenyl group-containing alkoxysilane: 0.1 to 10 parts by mass, and hydrochloric acid (however, (C-1) It is not necessary to use it in combination with the component.): 0.0001 to 0.2 parts by mass,
(D) Fatty acid ester and / or aliphatic alcohol ester: 0.01 to 5 parts by mass,
(E) The following (EA) Organopolysiloxane having a viscosity at 25 ° C. of 10 to 10,000 mPa · s: 100 parts by mass,
(Eb) General formula (2)
(R ² COO) _m M ¹ (2)
(In the formula, R ² is the same or different monovalent hydrocarbon group, M ¹ is cerium or a mixture of rare earth elements containing cerium as a main component, and m is a positive number of 3 to 4.)
Carboxylate of cerium represented by: 0.05 to 5 parts by mass with respect to 100 parts by mass of the above (EA) component in terms of mass of cerium atom, and (Ec) general formula (3). )
(R ³ O) ₄ M ² (3)
(In the formula, R ³ is the same or different monovalent hydrocarbon group, and M ² is titanium or zirconium.)
Titanium or zirconium compound represented by and / or its partially hydrolyzed condensate: The mass conversion of titanium atom or zirconium atom is 0.01 to 5 times the mass of cerium atom of the above (Eb) component. Uniform heat treatment reaction product of the mixture consisting of the amount: 0.01 to 5 parts by mass with respect to 100 parts by mass of the total of the components (A) to (D), and (F) curing agent: effective curing amount A silicone rubber composition for producing a key pad, which comprises.
[2]
The silicone rubber composition for producing a keypad according to [1], wherein the reinforcing silica of the component (B) is untreated silica.
[3]
The silicone rubber composition for producing a keypad according to [1] or [2], wherein the curing agent of the component (F) is a combination of an organohydrogenpolysiloxane and a hydrosilylation catalyst or an organic peroxide.
[4]
A keypad made of a cured molded product of the silicone rubber composition according to any one of [1] to [3].

According to the present invention, a silicone rubber composition excellent in dynamic fatigue durability (keying durability) even under high temperature and high humidity and suitable as a keypad material, and a keypad obtained by curing and molding the composition can be obtained. ..

It is a side view of the keypad which concerns on this invention. This is a click pattern of the keypad according to the present invention.

<Silicone rubber composition for making keypads>
The silicone rubber composition for producing a keypad of the present invention contains the following components (A) to (F).
Hereinafter, the present invention will be described in more detail.
[(A) Organopolysiloxane]
The organopolysiloxane of the component (A) is the main component (base polymer) of the present composition, and has an alkenyl group bonded to at least two silicon atoms in one molecule represented by the following average composition formula (1). It contains.
R ¹ _n SiO _{(4-n) / 2} (1)
(In the formula, R ¹ is the same or different unsubstituted or substituted monovalent hydrocarbon group, and n is a positive number from 1.95 to 2.04.)

In the above average composition formula (1), the ^{monovalent hydrocarbon group represented by R 1} is usually a monovalent hydrocarbon group having 1 to 20, preferably 1 to 12, and more preferably 1 to 8 carbon atoms. Is. For example, an alkyl group such as a methyl group, an ethyl group, a propyl group or a butyl group, a cycloalkyl group such as a cyclohexyl group, an alkenyl group such as a vinyl group, an allyl group, a butenyl group or a hexenyl group, an aryl such as a phenyl group or a tolyl group. A group, an aralkyl group such as a β-phenylpropyl group, or a chloromethyl group or a trifluoropropyl group in which a part or all of the hydrogen atom bonded to the carbon atom of these groups is substituted with a halogen atom, a cyano group, etc. Examples thereof include a cyanoethyl group. Among these, a methyl group, a vinyl group, a phenyl group and a trifluoropropyl group are preferable, and a methyl group and a vinyl group are more preferable. Among these, among the ^{monovalent hydrocarbon groups represented by R 1} in the molecule, 50 mol% or more is preferably a methyl group, more preferably 80 mol% or more is a methyl group, and further. preferably, all of R ¹ other than the alkenyl group is a methyl group.

In the above average composition formula (1), n is a positive number of 1.95 to 2.04, preferably a positive number of 1.98 to 2.02. Unless this n value is in the range of 1.95 to 2.04, the obtained cured product may not exhibit sufficient rubber elasticity.

Further, the organopolysiloxane of the component (A) needs to have at least two alkenyl groups in one molecule, and in the above formula (1), 0.001 to 10 mol% of ^{R 1, particularly 0.} It is preferable that 0.01 to 5 mol% is an alkenyl group. The alkenyl group is preferably a vinyl group and an allyl group, and particularly preferably a vinyl group.

The degree of polymerization of the organopolysiloxane of the component (A) is preferably 100 or more (usually 100 to 100,000), particularly preferably in the range of 1,000 to 100,000, and is in the range of 3,000 to 50,000. Is more preferable, and the range is particularly preferably in the range of 4,000 to 20,000. This degree of polymerization is determined as the polystyrene-equivalent weight average degree of polymerization in GPC (gel permeation chromatography) analysis.

The weight average molecular weight referred to in the present invention refers to the weight average molecular weight using polystyrene as a standard substance measured by gel permeation chromatography (GPC) under the following conditions.

[Measurement condition]
-Development solvent: Toluene-Flow rate: 1 mL / min
-Detector: Differential refractometer (RI)
-Column: KF-805L x 2 (manufactured by Shodex)
-Column temperature: 25 ° C
-Sample injection amount: 30 μL (toluene solution with a concentration of 0.2% by mass)

The organopolysiloxane of the component (A) is not particularly limited as long as this condition is satisfied, but usually the main chain is a diorganosiloxane unit (R ¹ ₂ SiO _2/2 , R ¹ is the same as above, and below. consists repetition of the same), both molecular chain terminals are blocked with triorganosiloxy groups (R ¹ ₃ SiO _1/2), is preferably a straight-chain diorganopolysiloxane with both molecular chain ends, It is preferably sealed with a trimethylsiloxy group, a dimethylvinylsiloxy group, a dimethylhydroxysiloxy group, a methyldivinylsiloxy group, a trivinylsiloxy group, etc., and in particular, it is sealed with a siloxy group having at least one vinyl group. Those are suitable. These organopolysiloxanes may be used alone or in combination of two or more having different degrees of polymerization and molecular structure.

[(B) Reinforcing silica]
The reinforcing silica of the component (B) acts as a component that imparts excellent mechanical properties to the obtained 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) present on the surface. In the present invention, the specific surface area of the reinforcing silica of the component (B) by the BET method ^{needs to be 50 m 2} / g or more, preferably 100 to 400 m ² / g. If this specific surface area is ^{less than 50 m 2} / g, the reinforcing effect of the component (B) may be insufficient.

As the reinforcing silica of the component (B), even if it is used in an untreated state, if necessary, a silica that has been surface-treated with an organosilicon compound such as organopolysiloxane, organopolysilazane, chlorosilane, or alkoxysilane is used. However, when untreated silica is used, the dispersibility of the reinforcing silica becomes better when used in combination with the components (C) and (D) described later, and the composition of the present invention can be used as a keypad. It is preferable because the keystroke durability is further improved when used. These reinforcing silicas may be used alone or in combination of two or more.

The blending amount of the reinforcing silica of the component (B) is 10 to 100 parts by mass, preferably 10 to 80 parts by mass, and more preferably 20 to 70 parts by mass with respect to 100 parts by mass of the organopolysiloxane of the component (A). It is a department. If this blending amount deviates from the above range, not only the processability of the obtained silicone rubber composition is lowered, but also a machine such as tensile strength and tear strength of the silicone rubber cured product obtained by curing the silicone rubber composition. The target characteristics are insufficient.

[(C) Alkoxy group-containing organosilazane and / or alkenyl group-containing alkoxysilane, and hydrochloric acid]
The alkenyl group-containing organosilazane of the component (C-1) and / or the alkenyl group-containing alkoxysilane of the component (C-2) and hydrochloric acid are dispersibility improvers for reinforcing silica in the silicone rubber composition of the present invention. It acts as a surface treatment agent), and at the time of curing, the alkenyl groups in the organopolysiloxane which is the base polymer and the alkenyl groups in the alkenyl group-containing organosilazane and / or the alkenyl group-containing alkoxysilane are crosslinked to form the organopolysiloxane. It acts as a cross-linking point with silica. Hydrochloric acid acts as a dispersibility improver for silica in the silicone rubber composition of the present invention.

The alkenyl group-containing organosilazane of the component (C-1) is not particularly limited, but is 1-vinylpentamethyldisilazane, 1,3-divinyl-1,1,3,3-tetramethyldisilazane, 1,3. -Dimethyl-1,1,3,3-tetravinyldisilazane, 1,3-divinyl-1,1,3,3-tetravinyldisilazane and the like are exemplified, but 1,3-divinyl-1,1 , 3,3-Tetramethyldisilazane is suitable.

The amount of the alkenyl group-containing organosilazane of the component (C-1) added is 0.1 to 10 parts by mass, preferably 0.1 to 10 parts by mass, based on 100 parts by mass of the organopolysiloxane of the component (A) when added alone. It is 0.1 to 7 parts by mass, more preferably 0.1 to 5 parts by mass. If the amount added is less than 0.1 parts by mass, the effect of improving the dynamic fatigue durability of the obtained cured product of the silicone rubber composition cannot be obtained, and if it is more than 10 parts by mass, the obtained cured silicone rubber composition is cured. The hardness of the object becomes too high, which is also economically unfavorable.

The alkenyl group-containing alkoxysilane of the component (C-2) is not particularly limited, but vinyltriethoxysilane, vinyltrimethoxysilane, divinyldimethoxysilane, vinyltris (methoxyethoxy) silane and the like are preferable.

The amount of the alkenyl group-containing alkoxysilane added as the component (C-2) is 0.1 to 10 parts by mass, preferably 0.1 to 10 parts by mass, based on 100 parts by mass of the organopolysiloxane of the component (A) when added alone. It is 0.1 to 7 parts by mass, more preferably 0.1 to 5 parts by mass. If the amount added is less than 0.1 parts by mass, the effect of improving the dynamic fatigue durability of the obtained cured product of the silicone rubber composition cannot be obtained, and if it is more than 10 parts by mass, the obtained cured silicone rubber composition is cured. The hardness of the object becomes too high, which is also economically unfavorable.
As described above, both the (C-1) component and the (C-2) component are expected to have the same effect. Therefore, when both the (C-1) component and the (C-2) component are blended, the same effect is expected. The total amount added is 0.1 to 10 parts by mass, preferably 0.1 to 7 parts by mass, and more preferably 0.1 to 5 parts by mass with respect to 100 parts by mass of the organopolysiloxane of the component (A). can do.

Hydrochloric acid is used in combination with the component (C-1) and / or the component (C-2), but may not be used in combination with the component (C-1).
The concentration of hydrochloric acid is preferably 0.05 to 5N, more preferably 0.05 to 2N. If the concentration of hydrochloric acid is lower than 0.05N, the amount of hydrochloric acid added increases, which is not preferable. On the contrary, if the concentration of hydrochloric acid is higher than 5N, handling is dangerous and it is used when blending each component. It is not preferable because it may corrode the device.
Note that hydrochloric acid usually refers to an aqueous hydrogen chloride solution prepared together with water such as deionized water, distilled water, and pure water.

The amount of hydrochloric acid added is 0.0001 to 0.2 parts by mass, preferably 0.0001 to 0.1, as the amount of hydrogen chloride in hydrochloric acid with respect to 100 parts by mass of the organopolysiloxane of the component (A). It is a mass part. If the amount of hydrochloric acid added is less than 0.0001 parts by mass as the amount of hydrogen chloride, the effect of improving dynamic fatigue durability may not be obtained. Further, even if the amount of hydrochloric acid added is more than 0.2 parts by mass as the amount of hydrogen chloride, it is not preferable because it becomes necessary to remove excess water.

[(D) Fatty acid ester and / or aliphatic alcohol ester]
The fatty acid ester and / or the fatty alcohol ester of the component (D) acts as a dynamic fatigue durability improver and a mold peelability improver of the cured product of the silicone rubber composition.
Examples of the fatty acid ester include lower saturated fatty acids having 4 to 9 carbon atoms such as butyric acid, caproic acid, conantic acid, capric acid, and pelargonic acid, and carbons such as capric acid, undecanoic acid, lauric acid, myristyl acid, palmitic acid, and stearic acid. Esters derived from various fatty acids such as higher saturated fatty acids having several tens to 20s, unsaturated fatty acids having 14 to 18 carbon atoms such as myristoleic acid, oleic acid, and linoleic acid, and fatty acids having OH groups such as ricinolic acid and having 18 carbon atoms. Compounds are exemplified.
Examples thereof include ester compounds of these various fatty acids with lower alcohols (for example, lower alcohols having about 1 to 6 carbon atoms such as methanol and ethanol) and ester compounds with polyhydric alcohols such as sorbitan ester and glycerin ester. ..

Examples of the aliphatic alcohol ester include saturated alcohols having 8 to 18 carbon atoms such as caprylyl alcohols, capryl alcohols, lauryl alcohols, myristyl alcohols and stearyl alcohols, and oleyl alcohols, linoleil alcohols and linolene alcohols having 18 carbon atoms. Ester compounds derived from various aliphatic alcohols such as unsaturated alcohols of the above are exemplified.
In particular, glutaric acid esters, dibasic acid esters such as suberic acid esters, and tribasic acid esters such as citric acid esters with these various fatty alcohols are exemplified.

Among these, it is preferable to use a glycerin ester of ricinoleic acid or a citric acid ester of an aliphatic alcohol having 1 to 20 carbon atoms, preferably 10 to 20 carbon atoms.

The blending amount of the component (D) is 0.01 to 5 parts by mass, preferably 0.05 to 3 parts by mass with respect to 100 parts by mass of the organopolysiloxane of the component (A). If the amount of the component (D) is less than 0.01 parts by mass, the mold peelability of the cured silicone rubber product is not improved, and if it is more than 5 parts by mass, discoloration of the cured silicone rubber product, compression set, etc. It is economically unfavorable because the characteristics deteriorate or the plastic return deteriorates.

[(E) component]
The component (E) is a uniform heat treatment reaction product of a mixture consisting of the components (Ea), (Eb) and (Ec) described later.
^{The organopolysiloxane of the component (EA) is one} of the unsubstituted or substituted organopolysiloxanes represented by the above average composition formula (1), in which R 1 has an aliphatic unsaturated bond such as an alkenyl group. Except for those that are valent hydrocarbon groups, it is a linear or branched organopolysiloxane that is liquid at room temperature and is substantially composed of repeating diorganopolysiloxane units (linear structure).
Here, the viscosity of the component (Ea) is 10 to 10,000 mPa · s, preferably 50 to 1,000 mPa · s at 25 ° C. When the viscosity is less than 10 mPa · s, the amount of siloxane evaporated at a high temperature tends to increase, and the mass change may become large. Further, when it exceeds 10,000 mPa · s, it may be difficult to smoothly mix with the cerium compound described later.
The viscosity can be measured by the rotational viscometer described in JIS K 7117-1: 1999.

The cerium carboxylate of the component (Eb) is represented by the general formula (2).
(R ² COO) _m M ¹ (2)
(In the formula, R ² is the same or different monovalent hydrocarbon group, M ¹ is cerium or a mixture of rare earth elements containing cerium as a main component, and m is a positive number of 3 to 4.)
It is represented by.
Here, ^{as the same or different monovalent hydrocarbon group represented by R 2} , specifically, a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group and the like have 1 to 30 carbon atoms. Preferably, an alkyl group having 1 to 20 carbon atoms is exemplified. Further, ^{among the cerium represented by M 1} or the rare earth element mixture containing cerium as the main component, the rare earth element mixture containing cerium as the main component specifically includes cerium, lanthanum, praseodymium, neodymium and the like. A mixture containing rare earth elements is exemplified.
The "main component" means that the mixture of rare earth elements usually contains 50% by mass or more, preferably 60 to 99% by mass, and more preferably 80 to 99% by mass of cerium.
Specific examples of the cerium carboxylic acid salt include salts of carboxylic acids such as 2-ethylhexanoic acid, naphthenic acid, oleic acid, lauric acid, and stearic acid and a mixture of cerium or a rare earth element containing cerium as a main component. Will be done.
The carboxylate of cerium may be used as an organic solvent solution in combination with an organic solvent because of its ease of handling and compatibility with the titanium compound or zirconium compound of the component (Ec) described later. Preferably, examples of the organic solvent include petroleum-based solvents such as standard solvent, mineral spirit, ligroin, tarpen, and petroleum ether, and aromatic solvents such as toluene and xylene.
The amount of the component (Eb) added is 0.05 to 5 parts by mass, preferably 0.1, based on 100 parts by mass of the component (Ea) in terms of mass of cerium atoms in the component. It is an amount of up to 3 parts by mass. If the amount added is less than 0.05 parts by mass, the expected keying durability under high temperature and high humidity may not be obtained. On the other hand, if the amount is more than 5 parts by mass, the cerium compound may become non-uniform in the component (Ea), and the expected keystroke durability may not be obtained.

The titanium compound or zirconium compound of the component (Ec) is represented by the general formula (3).
(R ³ O) ₄ M ² (3)
(In the formula, R ³ is the same or different monovalent hydrocarbon group, and M ² is titanium or zirconium.)
It is represented by.
Here, ^{as the same or different monohydric hydrocarbon group represented by R 3} , the number of carbon atoms such as isopropyl group, n-butyl group, stearyl group and octyl group is preferably 1 to 30, and more preferably the number of carbon atoms. It is an alkyl group of 1 to 20. Examples of such a compound include tetraalkoxytitanium and tetraalkoxyzirconium, but the compound may be a partially hydrolyzed condensate thereof.
The amount of the component (Ec) added is 0.01 to 5 times the mass of the cerium atom in the component (Eb) in terms of the mass of the titanium or zirconium atom in the component. The amount is preferably 0.05 to 3 times. If the amount added is less than 0.01 times, it may be difficult to uniformly introduce the carboxylic acid salt of cerium, which is the component (Eb), into the organopolysiloxane, which is the component (Ea), which is 5 times. If it is more than that, the keystroke durability may decrease.

The component (E) is a uniform heat treatment reaction product of a mixture consisting of the components (Ea), (Eb) and (Ec).
This mixture can be obtained by mixing the components (Ea), (Eb) and (Ec) and then heat-treating at a temperature of 150 ° C. or higher. If the heating temperature is less than 150 ° C, it is difficult to obtain a uniform composition, and if it exceeds 310 ° C, the thermal decomposition rate of the component (Ea) increases, so that it is preferably 150 to 310 ° C, more preferably 200 to 305 ° C. More preferably, the heat treatment is performed at 250 to 300 ° C.
In the mixing of the components (Ea), (Eb) and (Ec), these three components may be mixed at the same time, but the cerium carboxylate of the component (Eb) is used. Since it tends to be agglomerated, it is preferable to mix the component (Eb) and the component (Ec) in advance to obtain a uniform composition, and then mix the component (Ea).
The amount of the component (E) added is 0.01 to 5 parts by mass, preferably 0.05 to 2 parts by mass with respect to 100 parts by mass in total of the components (A) to (D). If the amount of the component (E) added is less than 0.01 parts by mass, the expected keying durability under high temperature and high humidity may not be obtained. Further, even if it exceeds 5 parts by mass, the expected keying durability under high temperature and high humidity may not be obtained.

[(F) Hardener]
The curing agent for the component (F) is not particularly limited as long as it can cure the component (A) described above. For example, the following (F-1) addition reaction curing agent and / or (F-2) organic peroxide can be used. Examples include oxide curing agents. That is, in the silicone rubber composition of the present invention, these curing agents react with the organopolysiloxane of the component (A) to form a crosslinked structure and give a cured product.

(F-1) Addition reaction curing agent The addition reaction curing agent of the component (F-1) can be used in combination with an organohydrogenpolysiloxane and a hydrosilylation catalyst.

The organohydrogenpolysiloxane is linear or cyclic if it contains 2 or more, preferably 3 or more, more preferably 3 to 200, and further preferably about 4 to 100 SiH groups in one molecule. , Branched shape, for example, organohydrogenpolysiloxane represented by the following average composition formula (4) can be used.

R ⁴ _p H _q SiO _{(4-pq) / 2} (4)
In the above average composition formula (4), R ⁴ represents an unsubstituted or substituted monovalent hydrocarbon group, which may be the same or different, and in particular, the one excluding the aliphatic unsaturated bond is preferable. R ⁴ is usually preferably one having 1 to 12 carbon atoms, particularly preferably 1 to 8 carbon atoms, and specifically, an alkyl group such as a methyl group, an ethyl group or a propyl group, a cycloalkyl group such as a cyclohexyl group, or phenyl. Aryl groups such as groups and trill groups, aralkyl groups such as benzyl group, 2-phenylethyl group and 2-phenylpropyl group, and groups in which some or all of the hydrogen atoms of these groups are substituted with halogen atoms or the like, for example. , 3,3,3-trifluoropropyl group and the like. In the average composition formula (4), p is 0 ≦ p <3, preferably 1 ≦ p ≦ 2.2, q is 0 <q ≦ 3, preferably 0.002 ≦ q ≦ 1, and p + q is 0. It is a positive number that satisfies <p + q ≦ 3, preferably 1.002 ≦ p + q ≦ 3.

Organohydrogenpolysiloxane has two or more, preferably three or more SiH groups in one molecule, both at the end of the molecular chain and in the middle of the molecular chain. May be good. Further, the organohydrogenpolysiloxane preferably has a viscosity at 25 ° C. of 0.5 to 10,000 mPa · s, particularly preferably 1 to 300 mPa · s.

Specific examples of such organohydrogenpolysiloxane include 1,1,3,3-tetramethyldisiloxane, 1,3,5,7-tetramethylcyclotetrasiloxane, and tris (hydrogendimethylsiloxy). ) Methylsilane, Tris (hydrogendimethylsiloxy) phenylsilane, methylhydrogencyclopolysiloxane, methylhydrogensiloxane / dimethylsiloxane cyclic copolymer, both-terminal trimethylsiloxy group blockage methylhydrogenpolysiloxane, both-terminal trimethylsiloxy group blockade Dimethylsiloxane / methylhydrogensiloxane copolymer, both-terminal dimethylhydrogensiloxy group-blocking dimethylpolysiloxane, both-terminal dimethylhydrogensiloxy group-blocking dimethylsiloxane / methylhydrogensiloxane copolymer, both-terminal trimethylsiloxy group-blocking methylhydro Gensiloxane / diphenylsiloxane copolymer, both-terminal trimethylsiloxy group-blocked methylhydrogensiloxane / diphenylsiloxane / dimethylsiloxane copolymer, both-terminal trimethylsiloxy group-blocked methylhydrogensiloxane / methylphenylsiloxane / dimethylsiloxane copolymer, Both-terminal dimethylhydrogensiloxy group-blocked methylhydrogensiloxane / dimethylsiloxane / diphenylsiloxane copolymer, both-terminal dimethylhydrogensiloxy group-blocked methylhydrogensiloxane / dimethylsiloxane / methylphenylsiloxane copolymer, (CH ₃ ) ₂ HSiO _1/2 unit and (CH ₃ ) ₃ Siloxane _1/2 unit and SiO _4/2 unit, (CH ₃ ) ₂ HSiO _1/2 unit and SiO _4/2 unit Combined, a _{copolymer consisting of (CH 3} ) ₂ HSiO _1/2 units, SiO _4/2 units and (C ₆ H ₅ ) ₃ SiO _1/2 units, etc., and some of the methyl groups in the above-exemplified compounds. Alternatively, examples thereof include those in which all of them are replaced with other alkyl groups, phenyl groups, etc., and compounds having the following structural formulas can be exemplified.

(In the formula, k is an integer of 2 to 10, and s and t are integers of 0 to 10.)

The blending amount of the organohydrogenpolysiloxane is preferably 0.1 to 40 parts by mass, more preferably 0.3 to 20 parts by mass with respect to 100 parts by mass of the organopolysiloxane of the component (A).

Further, the organohydrogenpolysiloxane was bonded to a silicon atom in the organohydrogenpolysiloxane for an aliphatic unsaturated group such as an alkenyl group or a diene group bonded to a silicon atom in the component (A) and the component (C). It is desirable to mix in an amount such that the molar ratio of hydrogen atoms (that is, SiH groups) is preferably 0.5 to 10 mol / mol, more preferably 0.7 to 5 mol / mol. If it is less than 0.5 mol / mol, cross-linking may not be sufficient and sufficient mechanical strength may not be obtained, and if it exceeds 10 mol / mol, the physical characteristics after curing deteriorate, and particularly heat resistance. The compression set may deteriorate.

The hydrosilylation catalyst is a catalyst in which an alkenyl group bonded to a silicon atom in the components (A) and (C) is subjected to an addition reaction with a silicon atom-bonded hydrogen atom (SiH group) in the organohydrogenpolysiloxane.
Examples of the hydrosilylation catalyst include platinum group metal-based catalysts, which include platinum group metal alone and compounds thereof, and known catalysts for addition reaction curable silicone rubber compositions can be used. Examples thereof include fine particle platinum metal adsorbed on a carrier such as silica gel, alumina or silica gel, secondary platinum chloride, platinum chloride acid, alcohol solution of hexahydrate chloride platinum acid, palladium catalyst, rhodium catalyst and the like. Platinum or platinum compounds are preferred.

The amount of the hydrosilylation catalyst added may be such that the addition reaction can be promoted, and is usually used in the range of 1% by mass to 1% by mass with respect to the organopolysiloxane of the component (A) in terms of mass in terms of the amount of platinum-based metal. However, the range of 10 to 500 mass ppm is preferable. If the addition amount is less than 1% by mass, the addition reaction may not be sufficiently promoted and curing may be insufficient, while if the addition amount exceeds 1% by mass, the reactivity may be increased even if a larger amount is added. It has less impact and can be uneconomical.

A hydrosilylation reaction control agent such as an acetylene compound may be added to the addition reaction curing agent of the component (F-1), if necessary.

(F-2) Organic Peroxide Hardener Examples of the organic peroxide hardener as a component of (F-2) include benzoyl peroxide, 2,4-dichlorobenzoyl peroxide, p-methylbenzoyl peroxide, and o. -Methylbenzoyl peroxide, 2,4-dicumyl peroxide, 2,5-dimethyl-2,5-bis (t-butylperoxy) hexane, di-t-butyl peroxide, t-butylperbenzoate, 1 , 6-Hexanediol-bis-t-butylperoxycarbonate and the like.

The amount of the organic peroxide curing agent added is preferably 0.1 to 10 parts by mass, particularly 0.2 to 5 parts by mass with respect to 100 parts by mass of the organopolysiloxane of the component (A). If the blending amount is less than 0.1 parts by mass, the curing of the silicone rubber composition may be insufficient, and conversely, if the blending amount is more than 10 parts by mass, the decomposition residue of the organic peroxide causes the silicone rubber. The cured product may turn yellow.

In addition, addition reaction curing and organic peroxide curing in which the component (F-1) and the component (F-2) are combined and blended within the above-mentioned blending amount with respect to the component (A). It can also be used as a co-vulcanized type silicone rubber composition in combination.

[Other optional ingredients]
In addition to the above-mentioned components, the silicone rubber composition of the present invention contains, if necessary, non-reinforcing silica such as quartz powder, crystalline silica, and diatomaceous earth, and carbon such as calcium carbonate, acetylene black, furnace black, and channel black. Heat resistance improver such as black, colorant, red iron oxide, cerium oxide, flame retardant improver such as platinum, titanium oxide, triazole compound, thermal conductivity improver such as acid receiver, alumina, boron nitride, mold release agent , Dimethylpolysiloxane having silanol groups at both ends may be added as a dispersant.

<Preparation and molding of silicone rubber composition for making keypads>
The silicone rubber composition for producing a keypad of the present invention can be obtained by uniformly mixing each of the above components using a mixing device such as a two-roll mill, a Banbury mixer, or a dow mixer (kneader). It is desirable that the components (A), (B), (C), (D), (E) (and other optional components) are blended and mixed, and then the component (F) is blended.

The silicone rubber composition of the present invention is used for a keypad. In order to form such a key pad, the silicone rubber composition can be molded at the same time as heat curing to obtain a molded product made of a rubber-like elastic body (silicone rubber cured product).

The method for curing the silicone rubber composition is not particularly limited, but any method may be used as long as sufficient heat is applied to the above-mentioned decomposition of the curing agent and vulcanization of the silicone rubber composition. The temperature condition for curing depends on the curing method, but is usually 80 to 400 ° C. The molding method is not particularly limited, and for example, a molding method such as continuous vulcanization by extrusion molding, press molding (pressure molding), or injection molding can be adopted. Further, if necessary, secondary vulcanization may be carried out at 150 to 250 ° C. for about 1 to 10 hours.

Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples. The viscosity is a value at 25 ° C. measured by a rotational viscometer described in JIS K 7117-1: 1999. The method for measuring physical characteristics and the method for testing dynamic fatigue durability are shown below.

Method for measuring physical characteristics The silicone rubber composition was cured, and the hardness (durometer A) and tensile strength were measured according to JIS K 6249: 2003.

Dynamic Fatigue Durability Test Method Dynamic fatigue durability was measured by the following method.
[Keystroke test method]
The silicone rubber composition is press-molded using a mold to prepare a molding key having the shape shown in FIG. 1, the molding key is fixed, a load of 1,200 g is applied from above, and a speed of 3 times per second is applied. I hit the key with. Keystrokes were made under the conditions of 23 ° C. and 50% RH and 85 ° C. and 85% RH.
[Molding key load measurement method]
The load of the key was measured using a load measuring device (MODEL-1305-DS manufactured by Aiko Engineering Co., Ltd.). When the key is pressed and the displacement is applied, the click pattern shown in FIG. 2 is usually obtained. The click pattern F1 was measured as a peak load.
[Evaluation method of keystroke fatigue durability of molded keys]
By the above keystroke test method, the peak load change before and after 200,000 keystrokes was calculated by the following formula.
Peak load change (%)
= [F1 value before keystroke test-F1 value after keystroke test] / F1 value before keystroke test x 100

[Example 1]
A terpenate solution of 2-ethylhexanoate (rare earth element content 6% by mass) of a mixture of rare earth elements containing cerium as the main component in 100 parts by mass of dimethylpolysiloxane with both ends of trimethylsiloxy group having a viscosity of 100 mPa · s (rare earth element content 6% by mass) 10% by mass A mixture of parts (0.55 parts by mass of cerium) and 2.1 parts by mass of tetra-n-butyl titanate (titanium mass is 0.3 times the mass of cerium in the 2-ethylhexanate) is prepared in advance. When the mixture was added with sufficient stirring, a yellowish white dispersion was obtained. A small amount of nitrogen gas was circulated through the mixture to allow the turpen to flow out, and then the mixture was heated at 300 ° C. for 1 hour to obtain a dark reddish brown, almost transparent composition 1.
The average degree of polymerization is 99.850 mol% of dimethylsiloxane unit and 0.125 mol% of methylvinylsiloxane unit as the diorganosiloxane unit constituting the main chain, and 0.025 mol% of dimethylvinylsiloxy group as the terminal group of the molecular chain. 60 parts by mass of linear organopolysiloxane (raw rubber), which is about 6,000, dimethylsiloxane unit 99.475 mol% and methylvinylsiloxane unit 0.50 mol% as diorganosiloxane units constituting the main chain, molecular chain Fumed silica (raw rubber) containing 0.025 mol% of dimethylvinylsiloxy group as a terminal group and having an average degree of polymerization of about 6,000, having 40 parts by mass of linear organopolysiloxane (raw rubber) and a BET specific surface area of 300 m ² / g. Product name "Aerozil 300" manufactured by Nippon Aerozil Co., Ltd. 32 parts by mass, 6 parts by mass of dimethylpolysiloxane having both-terminal silanol groups as a dispersant and a viscosity of 30 mPa · s at an average degree of polymerization of 15 and 25 ° C. 1 part by mass of vinyltrimethoxysilane and 0.1 part by mass of 1N hydrochloric acid were kneaded with a kneader and heat-treated at 170 ° C. for 2 hours to prepare "Compound 1". For 100 parts by mass of the "compound 1", 0.4 parts by mass of a citrate ester of an aliphatic alcohol having 18 carbon atoms ("Kaowax 220" manufactured by Kao Corporation) and 0.1 parts by mass of composition 1. Add 0.4 parts by mass of 2,5-dimethyl-2,5-bis (t-butylperoxy) hexane as a curing agent, mix uniformly, and then 10 at ^{165 ° C. and 70 kgf / cm 2.} Pre-cure was performed for 1 minute, and then post-cure was performed at 200 ° C. for 4 hours to prepare a test sheet. Table 1 shows the physical characteristics of this sheet and the measurement results of the dynamic fatigue durability test.

[Example 2]
It was produced by the same method as in Example 1 except that the amount of the composition 1 corresponding to the component (E) of the present invention was 0.5 parts by mass. Table 1 shows the physical characteristics and the measurement results of the dynamic fatigue durability test.

[Example 3]
Example 1 except that the glycerin ester of ricinoleic acid (“Kaowax 85P” manufactured by Kao Corporation) was used instead of the citric acid ester of the fatty alcohol having 18 carbon atoms corresponding to the component (D) of the present invention. Manufactured by the same method as above. Table 1 shows the physical characteristics and the measurement results of the dynamic fatigue durability test.

[Example 4]
As a curing agent, not 2,5-dimethyl-2,5-bis (t-butylperoxy) hexane, but methylhydrogenpolysiloxane having a SiH group in the side chain (polymerization degree 38, SiH group 0.0074 mol / mol / 0.8 parts by mass of both-terminal trimethylsiloxy group-blocking dimethylsiloxane / methylhydrogensiloxane copolymer), 0.05 parts by mass of ethynylcyclohexanol as a reaction control agent, 0.1 mass% of platinum catalyst (Pt concentration 1% by mass) After adding parts by mass and mixing uniformly, precure ^{was performed at 120 ° C. and 70 kgf / cm 2} for 10 minutes, and then post-cure was performed at 200 ° C. for 4 hours to prepare a test sheet. Table 1 shows the physical characteristics and the measurement results of the dynamic fatigue durability test.

[Example 5]
Same as in Example 1 except that 1,3-divinyl-1,1,3,3-tetramethyldisilazane was used instead of 1 part by mass of vinyltrimethoxysilane and 0.1 part by mass of 1N hydrochloric acid. Manufactured by the method. Table 1 shows the physical characteristics and the measurement results of the dynamic fatigue durability test.

[Comparative Example 1]
It was produced by the same method as in Example 1 except that the composition 1 corresponding to the component (E) of the present invention was not added. Table 2 shows the physical characteristics and the measurement results of the dynamic fatigue durability test.

[Comparative Example 2]
It was produced by the same method as in Example 1 except that vinyltrimethoxysilane corresponding to the component (C) of the present invention was not added. Table 2 shows the physical characteristics and the measurement results of the dynamic fatigue durability test.

[Comparative Example 3]
It was produced by the same method as in Example 1 except that 1N hydrochloric acid corresponding to the component (C) of the present invention was not added. Table 2 shows the physical characteristics and the measurement results of the dynamic fatigue durability test.

[Comparative Example 4]
It was produced by the same method as in Example 1 except that a citric acid ester of an aliphatic alcohol having 18 carbon atoms corresponding to the component (D) of the present invention (“Kaowax 220” manufactured by Kao Corporation) was not added. .. Table 2 shows the physical characteristics and the measurement results of the dynamic fatigue durability test.

[Comparative Example 5]
It was produced by the same method as in Example 4 except that the composition 1 corresponding to the component (E) of the present invention was not added. Table 2 shows the physical characteristics and the measurement results of the dynamic fatigue durability test.

[Comparative Example 6]
It was produced by the same method as in Example 5 except that the composition 1 corresponding to the component (E) of the present invention was not added. Table 2 shows the physical characteristics and the measurement results of the dynamic fatigue durability test.

Claims

(A) The following average composition formula (1)
R 1 n SiO (4-n) / 2 (1)
(In the formula, R 1 is the same or different unsubstituted or substituted monovalent hydrocarbon group, and n is a positive number from 1.95 to 2.04.)
Organopolysiloxane having at least two alkenyl groups in one molecule and having a degree of polymerization of 100 or more: 100 parts by mass,
(B) Reinforcing silica having a specific surface area of 50 m 2 / g or more by the BET method: 10 to 100 parts by mass,
(C) The following (C-1) alkenyl group-containing organosilazane: 0.1 to 10 parts by mass and / or (C-2) alkenyl group-containing alkoxysilane: 0.1 to 10 parts by mass, and hydrochloric acid (however, (C-1) It is not necessary to use it in combination with the component.): 0.0001 to 0.2 parts by mass,
(D) Fatty acid ester and / or aliphatic alcohol ester: 0.01 to 5 parts by mass,
(E) The following (EA) Organopolysiloxane having a viscosity at 25 ° C. of 10 to 10,000 mPa · s: 100 parts by mass,
(Eb) General formula (2)
(R 2 COO) m M 1 (2)
(In the formula, R 2 is the same or different monovalent hydrocarbon group, M 1 is cerium or a mixture of rare earth elements containing cerium as a main component, and m is a positive number of 3 to 4.)
Carboxylate of cerium represented by: 0.05 to 5 parts by mass with respect to 100 parts by mass of the above (EA) component in terms of mass of cerium atom, and (Ec) general formula (3). )
(R 3 O) 4 M 2 (3)
(In the formula, R 3 is the same or different monovalent hydrocarbon group, and M 2 is titanium or zirconium.)
Titanium or zirconium compound represented by and / or its partially hydrolyzed condensate: The mass conversion of titanium atom or zirconium atom is 0.01 to 5 times the mass of cerium atom of the above (Eb) component. Uniform heat treatment reaction product of the mixture consisting of the amount: 0.01 to 5 parts by mass with respect to 100 parts by mass of the total of the components (A) to (D), and (F) curing agent: effective curing amount A silicone rubber composition for producing a key pad, which comprises.
The silicone rubber composition for producing a keypad according to claim 1, wherein the reinforcing silica of the component (B) is untreated silica.
The silicone rubber composition for producing a keypad according to claim 1 or 2, wherein the curing agent of the component (F) is a combination of an organohydrogenpolysiloxane and a hydrosilylation catalyst or an organic peroxide.
A keypad made of a cured molded product of the silicone rubber composition according to any one of claims 1 to 3.