JP3413224B2 - Silicone rubber composition and keyboard using the same - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a silicone rubber composition in which a component exuded from a rubber after molding is extremely small, and by utilizing its characteristics, a silicone rubber keyboard in which contact failure and deterioration of keyboard characteristics are prevented. Regarding

[0002]

TECHNICAL BACKGROUND AND PROBLEMS OF THE INVENTION Silicone rubber is
Due to its excellent moldability, dimensional stability after molding, elasticity, etc., it is widely used in electric desk calculators, television / audio product switches and remote control switches, and keyboard switches which are input devices for computers.

However, in the commonly used silicone rubber, when the switch is turned on and off repeatedly, the unreacted silicone component existing in the cured rubber exudes and adheres to the contact portion to cause a current conduction failure. However, there are drawbacks such as the fact that when the switch is pressed, it becomes sticky and the restoring force becomes dull.

[0004]

An object of the present invention is to solve the above-mentioned problems and to provide a silicone rubber composition in which a component exuded from rubber after molding is extremely small, and a silicone rubber keyboard using the same which prevents contact failure and deterioration of keyboard characteristics. The purpose is to provide.

[0005]

The present inventors have conducted extensive studies to achieve the above object, and as a result, have blended a fine powder silica filler having an oil absorption of 200 cc / 100 g or more and a metal salt of a fatty acid having 10 or more carbon atoms. The inventors have found that it is effective to complete the present invention. That is, the present invention is the following components (A), (B)
A keyboard comprising a silicone rubber composition comprising (C), (D) and (E) and a cured product of the composition.

(A) Average unit formula R _a SiO _{(4-a) / 2} (wherein each R represents a substituted or unsubstituted monovalent hydrocarbon group, and a represents a number from 1.98 to 2.02) Polyorganosiloxane 100 parts by weight (B) Oil absorption 200cc / 100g or more fine powder silica filler 3 to 100 parts by weight (C) C10 or more fatty acid metal salt 0.03 to 5 parts by weight (D) Having silanol group, alkoxy group or vinyl group
Organosilanes, organosiloxanes, organosilanes
0.5 to 30% by weight of the processing aid (B) component selected from Razan (E) Catalytic amount of curing agent The present invention will be described in detail below. The polyorganosiloxane as the component (A) is mainly a linear one, but a part thereof may form a branched or three-dimensional structure, and a homopolymer, a copolymer or a mixture thereof. May be Examples of the substituted or unsubstituted monovalent hydrocarbon group R 1 of this polyorganosiloxane include alkyl groups such as methyl, ethyl and propyl; alkenyl groups such as vinyl, allyl and butenyl; aryl such as phenyl, xenyl and naphthyl. Groups; cycloalkyl groups such as cyclohexyl; cycloalkenyl groups such as cyclohexenyl;
Examples thereof include aralkyl groups such as benzyl; alkylaryl groups such as tolyl and xylyl. Monovalent hydrocarbon group directly bonded to silicon atom of this polyorganosiloxane
It is preferable that R 2 is mainly a methyl group, and generally contains 3% or less of an alkenyl group based on the total number of organic groups.

As the finely powdered silica type filler of the component (B), fumed silica, wet silica, quartz, diatomaceous earth and the like which are usually used for compounding silicone rubber and the like are used and surface-treated. Any of those that have not been surface-treated with organosilane, organosiloxane, organosilazane, etc. may be used, but in order to prevent exudation of unreacted components from the rubber after molding which is a feature of the present invention. In order to comply with JIS K 5101, the oil absorption must be 200cc / 100g or more. Also,
If the content of this component (B) is too small, the exudation of unreacted components cannot be prevented, and if it is too large, the mechanical properties of the silicone elastic body obtained by curing this will deteriorate.
(A) Used in the range of 3 to 100 parts by weight with respect to 100 parts by weight.

The metal salt of a fatty acid having 10 or more carbon atoms, which is the component (C), is a so-called metallic soap, and the fatty acid portion thereof may be normal, as well as having an isomer and a substituent. Examples of the metal portion include magnesium, calcium, aluminum, lithium, barium, strontium, zinc, cadmium, and lead, but are not particularly limited. These metal soaps include magnesium stearate, aluminum stearate, calcium stearate, lithium stearate,
Zinc stearate, strontium stearate, lead stearate, barium stearate, cadmium stearate, calcium chlorostearate, barium chlorostearate, cadmium chlorostearate, zinc laurate, barium laurate, cadmium laurate, magnesium laurate, Examples thereof include zinc myristate, aluminum myristate, barium ricinoleate, zinc ricinoleate, and cadmium ricinoleate. Fatty acid salts of lead, cadmium, and barium are toxic, so it is better to avoid using them. Examples of these metallic soaps include Al (OH) (C ₁₇ H ₃₅ COO) ₂ and Al (OH) ₂ (C
Basic salts such as ₁₇ H ₃₅ COO) can also be used. Further, two or more kinds of these metal soaps may be mixed and used. If the compounding amount of this component (C) is too small, the exudation of unreacted components cannot be prevented from the rubber after curing, and if it is too large, the heat resistance of the silicone elastic body obtained by curing will be reduced. It is used in the range of 0.03 to 5 parts by weight based on 100 parts by weight of the component (A).

The processing aid of the component (D) is a treating agent which facilitates the kneading of the finely powdered silica filler and stabilizes the aging of the obtained compound, such as silanol group, alkoxy group and vinyl group. Examples of the organosilane, organosiloxane, organosilazane, and the like. When the amount of the component (D) is too small, the kneading time is shortened and the effect of suppressing the change over time cannot be obtained, and when the amount is too large, the exudation of unreacted components from the rubber after curing is promoted. ) Is used in the range of 0.5 to 30% by weight based on the compounding weight.

The hardener of component (E) is the above-mentioned component.
The composition basically consisting of (A) to (D) is cured to give a rubber-like elastic body. Examples of the curing method include a curing method using an organic peroxide and a curing method using an addition type crosslinking agent and a catalyst. As a curing agent using an organic peroxide, conventionally known benzoyl peroxide, 2,4-dichlorobenzoyl peroxide, ditertiary butyl peroxide, dicumyl peroxide, 2,5-dimethyl-2,5-di (tertiary) Libutyl peroxy) hexane and the like are exemplified. These are generally used in the range of 0.1 to 5 parts by weight based on 100 parts by weight of the component (A). As the curing agent by the addition type reaction, a polyorganosiloxane having an average of two or more hydrogen atoms bonded to silicon atoms in one molecule is used as a crosslinking agent, and a platinum catalyst is used as a curable catalyst. . The amount of the above polyorganosiloxane having a hydrogen atom is such that one alkenyl group bonded to a silicon atom in the polyorganosiloxane, organosilane and organosilazane in the component (A) and the component (D) is added to the silicon molecule. The amount is equivalent to 0.5 to 5 hydrogen atoms to be bonded, and the platinum-based catalyst is generally about 1 to 1000 ppm with respect to the total amount of the component (A) and the component (D).

The silicone rubber composition for a keyboard according to the present invention is obtained by mixing the above components (A) to (E) by roll kneading and the like, and if necessary, titanium oxide, carbon black, iron oxide. Additives such as known fillers, heat-resistant agents and pigments used in the production of ordinary silicone rubber compounds, such as glass fiber, may be added. Further, a specific shaped article such as a keypad can be obtained by heat-molding the above-mentioned composition by a known molding method such as press molding with a mold or injection molding.

[0012]

EXAMPLES The present invention will be described below with reference to examples.
In the examples, all parts are parts by weight. Example 1 (CH _{3) 2} SiO units 99.9 mol% and _{(CH 3) (CH 2 =} CH) SiO units
Consisting of 0.1 mol%, 100 parts of polyorganosiloxane raw rubber blocked at the ends with dimethylvinylsilyl groups, 0.05 parts of magnesium stearate, hydroxyl groups at both ends
Polydimethylsiloxane with a viscosity of 60 cSt at 25 ° C 1.
75 parts and 17.5 parts of fine powder silica filler Nipsil HD (manufactured by Nippon Silica Industry Co., Ltd.) having an oil absorption of 250 cc / 100 g were kneaded with a kneader mixer until uniform, and at 150 ° C. for 2 hours while kneading. After heat treatment to remove volatile siloxane components and water, 2,5-dimethyl-2,5-
0.3 part of di (tert-butylperoxy) hexane was added and uniformly mixed with a two-roll to obtain a silicone rubber composition. This composition is a 200 mm x 200 mm x 2 mm surface chrome-plated iron mold, temperature 170 ℃, pressure
After pressing for 10 minutes under the condition of 100 kg / cm ² , primary vulcanization was performed, and after demolding, secondary vulcanization was performed for 4 hours in an oven set at 200 ° C. JIS C 21 for the obtained rubber sheet
The hardness, tensile strength, elongation and tear strength according to 23 were measured.
Furthermore, after molding the keypad under the same conditions as this and conducting a keystroke test for 500,000 times at a cycle of 5 times per second, the extruding of unreacted components at the part contacting the lower plate when pressing the molded product is checked. Examined. The results of these characteristic determinations are also shown in Table 1.

Example 2 Instead of Nipsil HD in Example 1, oil absorption of 235 cc /
About Example 2 using 100 g of fine powder silica filler Nipsil HD-2 (manufactured by Nippon Silica Industry Co., Ltd.),
The silicone rubber composition obtained was evaluated in the same manner as in Example 1. The results are shown in Table 1.

Comparative Examples 1 and 2 Instead of Nipsil HD in Example 1, oil absorption 190cc /
Comparative Example 1 and Example 1 using 100 g of fine powder silica filler Nipsil LP (manufactured by Nippon Silica Industry Co., Ltd.)
Comparative Example 2 was carried out in the same manner as in Example 1 except that the fine powder silica filler Tokusil US (manufactured by Tokuyama Soda Co., Ltd.) having an oil absorption amount of 190 cc / 100 g was used in place of Nipsil HD. Each silicone rubber composition was evaluated. The results are shown in Table 1.

[0015]

[Table 1]

As shown in Table 1, oil absorption is 200cc / 100g
It can be seen that the silicone rubber composition of the present invention containing the above-mentioned fine powder silica filler has a remarkable improving effect in preventing the exudation of unreacted components.

Example 3 The same procedure as in Example 1 was repeated except that the amount of Nipsil HD was changed to 4 parts and the amount of polydimethylsiloxane was changed to 0.4 part. 5
After conducting a keystroke test for 500,000 times in one cycle, it was examined whether or not the unreacted component oozes out in the portion contacting the lower plate when the molded product is pressed. The results are shown in Table 2.

Comparative Examples 3 and 4 In Comparative Example 3 in which the compounding amount of Nipsil HD and polydimethylsiloxane was 0 part in Example 3, and in Example 3 the compounding amount of Nipsil HD was 2 parts and polydimethylsiloxane was 0.2 part. Comparative Example 4 was carried out in the same manner as in Example 3, and the obtained keypads were evaluated, and the results are shown in Table 2.

[0019]

[Table 2]

As shown in Table 2, the oil absorption is 200cc / 100g.
It can be seen that the use of 3 parts or more of the above-mentioned fine powdery silica-based filler exhibits a remarkable improving effect in preventing the unreacted components from seeping out.

Example 4 The procedure of Example 1 was repeated except that the amount of magnesium stearate was changed to 0.1 part. The obtained keypad was evaluated in the same manner as in Example 1 and the results were obtained. Is shown in Table 3.

Comparative Example 5 In Example 4, the same procedure as in Example 1 was carried out except that magnesium stearate was not added. The obtained keypad was evaluated in the same manner as in Example 4, and the results are shown in Table 3. It was shown to.

[0023]

[Table 3]

As shown in Table 3, it can be seen that the use of 0.03 part or more of magnesium stearate has a remarkable improving effect in preventing the exudation of unreacted components.

Examples 5 and 6 Example 5 in which polydimethylsiloxane was changed to 0.1 part in Example 1 and polydimethylsiloxane was changed to 5
For Example 6 in which the composition was changed to parts, the roll workability after 1 week of production was evaluated in addition to the exudation of unreacted components after the keystroke test, and the results are shown in Table 4.

Comparative Examples 6 and 7 Comparative Example 6 containing no polydimethylsiloxane in Example 1 and Comparative Example 7 containing 7 parts of polydimethylsiloxane were evaluated in the same manner as in Example 5, respectively. The results are shown in Table 4.

[0027]

[Table 4]

As shown in Table 4, it can be seen that the use of 0.1 to 5 parts of polydimethylsiloxane has a remarkable effect of suppressing the change over time and preventing the exudation of unreacted components.

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Claims (2)

(57) [Claims] 1. The following components (A), (B), (C), (D) and
A silicone rubber composition comprising (E). (A) average unit formula R _a SiO _{(4-a) / 2} (wherein each R represents a substituted or unsubstituted monovalent hydrocarbon group, and a represents a number from 1.98 to 2.02) Polyorganosiloxane 100 parts by weight (B) Fine powder silica filler with oil absorption of 200cc / 100g or more 3 to 100 parts by weight (C) Metal salt of fatty acid having 10 or more carbon atoms 0.03 to 5 parts by weight (D) Has a silanol group, alkoxy group or vinyl group
Organosilanes, organosiloxanes, organosilanes
Processing aid selected from lazane (B) 0.5 to 30% by weight relative to the blending weight of component (E) Catalytic amount of curing agent 2. A keyboard comprising a cured product of the silicone rubber composition according to claim 1.