JP3113187B2 - Thermosetting silicone rubber composition and keypad 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 thermosetting silicone rubber composition and a keypad using the same, and more particularly to a thermosetting silicone rubber composition having excellent durability, low hysteresis, The present invention relates to a thermosetting silicone rubber composition which can provide a keypad with less decrease in low hysteresis, has excellent roll workability, has little plasticization return, and has excellent storage stability, and a keypad using the same.

[0002]

Technical background of the invention and its problems Silicone rubber is
Due to its excellent moldability, dimensional stability after molding, elastic properties, etc., it is widely used in electric desk calculators, switches for television and audio products, and keypad switches as input devices for computers. It is well known that durability, load value, and low hysteresis are important as characteristics of a keypad, and various studies have been made so far. As a result, the durability and initial hysteresis before the keypad breaks have been improved, but the load value gradually decreases while using the keypad, and the hysteresis also increases at the same time, There was a problem that it could not be used practically long before the keypad was destroyed. To solve such problems, no fundamental solution has been studied so far. Further, the silicone rubber compound is generally blended with a finely divided silica-based filler such as fumed silica or wet silica in order to impart reinforcement. However, because of the temporal hygroscopic effect of these fillers, hard silicone rubber compound called plasticizing return, a phenomenon which becomes brittle, which since the need of plasticizing occurs, reducing the productivity of the silicone rubber molding Therefore, there is a demand for a silicone rubber compound having little storage reversion and excellent storage stability. In order to solve such problems, various methods for surface treatment of finely powdered silica-based fillers have been proposed. However, the viscosity of the silicone rubber compound is reduced, causing the compound to become sticky and the roll workability to be reduced. There is a problem of doing.

[0003]

SUMMARY OF THE INVENTION The present invention has been made to solve such problems. That is, the present invention relates to a thermosetting silicone rubber composition and a keypad using the same. More specifically, the present invention is excellent in durability, has low hysteresis, and further decreases load value and low hysteresis with time. It is an object of the present invention to provide a thermosetting silicone rubber composition capable of obtaining a keypad having a small amount of heat and a keypad using the same.

[0004]

The present inventors have conducted intensive studies to achieve the above object. As a result, 10-50% by weight of the base polyorganosiloxane was closed with a silanol group at the end, and the viscosity at 25 ° C was reduced. Using a polydiorganosiloxane of 10,000 to 100,000 cSt, and further having a terminal closed with a silanol group and having a viscosity at 25 ° C. of 5 to 500 cSt, a fine silica powder filler,
The inventors have found that a keypad made of a thermosetting silicone rubber compound mixed with a catalytic amount of a curing agent is effective, and have completed the present invention. That is, the present invention provides: (A) an average unit formula: R _a SiO _{(4-a) / 2} (where R is a substituted or unsubstituted monovalent hydrocarbon group,
a represents a number in the range of 1.98 to 2.02), having an average degree of polymerization of 4000 to 20000, and a triorganosilyl group at the molecular chain end.
Closed polyorganosiloxane (B) terminal silanol groups is, 100 parts by weight of the base polymer consisting of polydiorganosiloxane viscosity at 25 ° C. is 10000～100000CSt (however, the proportion of the component (B) in the base polymer is (C) a polydiorganosiloxane having a terminal closed with a silanol group and having a viscosity at 25 ° C. of 5 to 500 cSt.
Parts by weight (D) 5 to 200 parts by weight of finely divided silica-based filler (E) a thermosetting silicone rubber composition containing a catalytic amount of a curing agent, and heat curing of the silicone rubber composition It is a keypad made of things.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail. The average unit formula of the component (A) used in the present invention: R _a SiO _{(4-a) / 2} (where R is a substituted or unsubstituted monovalent hydrocarbon group,
a represents a number in the range of 1.98 to 2.02), the polyorganosiloxane having an average degree of polymerization of 4000 to 20000 is one of the base polymers of the curable silicone composition, and is mainly a linear one. Is used, a part of which may form a branched or three-dimensional structure, or a homopolymer, a copolymer or a mixture thereof. The substituted or unsubstituted monovalent hydrocarbon group bonded to the silicon atom of the polyorganosiloxane includes, for example, an alkyl group such as a methyl group, an ethyl group and a propyl group; a vinyl group, an allyl group and a butadienyl group. An alkenyl group; an aryl group such as a phenyl group, a xenyl group, and a naphthyl group; a cycloalkyl group such as a cyclohexyl group; a cycloarenyl group such as a cyclohexenyl group; an aralkyl group such as a benzyl group; Alkylaryl group and the like. As the monovalent hydrocarbon group bonded to these silicon atoms, a methyl group is mainly used. For example, in the case of a vinyl group, 0 to 5 relative to the total number of organic groups from the viewpoint of mechanical strength and crosslinkability. %, And particularly preferably in the range of 0.05 to 3%. The terminal of the molecular chain of the polyorganosiloxane is a triorganosilyl group. Examples of the triorganosilyl group include a trimethylsilyl group, a dimethylvinylsilyl group, a methylphenylvinylsilyl group, and a methyldiphenylsilyl group. The average degree of polymerization of the component (A) is in the range of 4000 to 20000, preferably 50.
It is preferably from 100 to 10,000, particularly preferably from 6000 to 7000. If this degree of polymerization is too small, it is difficult to obtain sufficient mechanical strength,
On the other hand, if it is too large, it becomes difficult to incorporate the compound into the system.

The polydiorganosiloxane used in the present invention, in which the components (B) and (C) are terminated with silanol groups, acts synergistically, has excellent roll workability, and has little plasticization reversion. Excellent stability, excellent durability,
It is essential for achieving the object of the present invention to obtain a silicone rubber keypad having low hysteresis, less decrease in load value and hysteresis over time, and excellent in practical durability. The viscosity of the component (B) at 25 ° C. is from 10,000 to 100,000 cSt, and if the viscosity is less than 10,000 cSt, the mechanical strength of the silicone rubber is reduced.If the viscosity is more than 100,000 cSt, the load value and the low hysteresis over time are reduced. Significant drop is large. The component (B) is one of the base polymers of the curable silicone composition of the present invention, and its compounding amount is 10 to 50 parts by weight based on 100 parts by weight of the total amount of the components (A) and (B). Department. The amount of component (B) is 10% of the total 100 parts by weight of component (A) and component (B).
If the amount is less than 10 parts by weight, the desired effect of the present invention is not sufficient, and if it is more than 50 parts by weight, the mechanical strength is reduced.

The viscosity of the component (C) at 25 ° C. is 5 to 500 cSt.
If the viscosity is less than 5 cSt, the plasticity of the silicone rubber composition is reduced, and the roll workability is deteriorated.
If it is larger, the plasticization return becomes large, and the storage stability decreases. The amount of the component (C) is 0.1 to 10 parts by weight based on 100 parts by weight of the total of the components (A) and (B). If the compounding amount of the component (C) is less than 0.1 part by weight with respect to 100 parts by weight of the total of the components (A) and (B), the load value and the low hysteresis property decrease with time. When the amount is more than the weight part, the mechanical strength is reduced and the effect aimed at by the present invention cannot be obtained.

The finely divided silica-based filler as the component (D) in the present invention includes well-known silica fillers such as fumed silica, wet silica, quartz, and diatomaceous earth which are generally used for compounding silicone rubber and the like. Is used. The preferred particle size of these silica fillers is 20 μm or less. These silica-based fillers are preferably those that have not been surface-treated, but may be those that have been surface-treated with an organosilane, organosiloxane, organosilazane, or the like to such an extent that the roll workability is not reduced, or You may make it react with these processing agents in process. If the compounding amount of the component (D) is too large, the mechanical properties of the silicone elastomer obtained by vulcanization decrease, and if too small, mechanical properties such as tensile strength cannot be added. 5 to 100 parts by weight of the total amount of component and component (B)
Used in the range of 200 parts by weight. The curing agent of the component (E) cures the composition consisting essentially of the components (A) to (D) to form 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 (tercia) L-butylperoxy) hexane and the like. These are 0.1 parts per 100 parts by weight of the total of components (A) and (B).
Used in the range of ~ 5 parts by weight. Further, as a curing agent for the addition-type reaction, a polyorganosiloxane having a hydrogen atom bonded to an average of two or more silicon atoms in one molecule is used as a crosslinking agent, and a platinum-based catalyst is used as a curing catalyst. The compounding amount of the polyorganosiloxane having a hydrogen atom is such that one alkenyl group bonded to a silicon atom in the polyorganosiloxane in the component (A) and the component (C) is 0.5 hydrogen atom bonded to a silicon molecule.
The platinum catalyst is generally used in an amount of about 1 to 1000 ppm with respect to the total amount of the component (A) and the component (C).

[0009] The rubber composition for a keyboard according to the present invention is obtained by mixing the above-mentioned components (A) to (D) by kneading with a roll and the like. Iron, glass fiber, etc.
Known additives such as fillers, heat-resistant agents, and pigments used in the production of ordinary silicone rubber compounds may be blended. Further, a specific shape such as a keypad can be obtained by subjecting the above-described composition to heat molding by a known molding method such as press molding using a mold or injection molding.

[0010]

Industrial Applicability The silicone rubber composition of the present invention has excellent roll workability, low plasticization reversion, excellent storage stability, excellent durability, low hysteresis,
Further, it is possible to obtain a keypad in which the load value and the low hysteresis property with the passage of time are hardly reduced.

[0011]

EXAMPLES Next, examples of the present invention will be described, but the present invention is not limited to the following examples. Also,
Parts in the examples represent parts by weight. Further, the load value and the hysteresis show measurement results by the following methods. <Method of Measuring Load Value and Hysteresis> The keypad shown in FIG. 1 was prepared, and after restoring the keypad after applying a load as shown in FIG. 2 and measuring the stress at that time. The load value was used. Using this value, hysteresis was determined by the following equation. Hysteresis (%) = (Pressing load value-Return load value) / Pressing load value x 100 Example 1 (CH ₃ ) ₂ SiO unit 99.88 mol%, (CH ₃ ) (CH ₂ = CH) SiO unit 0.
70 parts of a polyorganosiloxane having a polymerization degree of 6000, composed of 12 mol% and capped with a dimethylvinylsilyl group, and 30 parts of a polydiorganosiloxane capped with a silanol group and having a viscosity of 45,000 cSt at 25 ° C. Terminal closed with silanol group, viscosity at 25 ° C is 90cSt
2.5 parts of polydiorganosiloxane, wet silica (N
(ipsil LP) 45 parts and zinc stearate 0.05 part are kneaded with a kneader mixer until uniform, and 150 ° C x
After the heat treatment for 3 hours, 0.2 part of 2,5-dimethyl 2,5-di (tert-butylperoxy) hexane was added and uniformly mixed to obtain a silicone rubber composition. At this time, the roll workability was evaluated. Further, 500 g of this silicone rubber compound was left in an air heating dryer at 90 ° C. for 72 hours, taken out, allowed to cool, and then put into a 16-inch roll to observe the degree of plasticization return. Next, the composition was subjected to primary vulcanization with a press at a temperature of 170 ° C. under a pressure of 100 kgf / cm ² for 10 minutes to produce a keypad shown in FIG.
Using this keypad, the load value and hysteresis are measured, and a key test is performed 10800 times per minute.
The load value and the hysteresis at 100,000, 200,000, 300,000 and 400,000 times were measured, and the rate of change from the initial value was calculated. Table 1 shows the results.

Example 2 99.88 mol% of (CH ₃ ) ₂ SiO unit, 0.9% of (CH ₃ ) (CH ₂ = CH) SiO unit
60 parts of a polyorganosiloxane having a polymerization degree of 6000, which is composed of 12 mol% and terminated with a dimethylvinylsilyl group, and 40 parts of a polydiorganosiloxane which is terminated with a silanol group and has a viscosity of 60,000 cSt at 25 ° C. , End closed with silanol group, viscosity at 25 ° C is 90c
St polydiorganosiloxane 2.0 parts, wet silica
(Nipsil LP) 45 parts and 0.05 part of zinc stearate are kneaded with a kneader mixer until uniform, and 150 ° C while kneading.
After heat treatment for 3 hours, 0.2 part of 2,5-dimethyl 2,5-di (tert-butylperoxy) hexane was added and uniformly mixed to obtain a silicone rubber composition. Evaluation was performed in the same manner as in Example 1 using this silicone rubber compound. Table 1 shows the results.

Example 3 99.88 mol% of (CH ₃ ) ₂ SiO units, (CH ₃ ) (CH ₂ CHCH) SiO units
75 parts of a polyorganosiloxane having a polymerization degree of 6000, composed of 12 mol% and capped with a dimethylvinylsilyl group, and 25 parts of a polydiorganosiloxane capped with a silanol group and having a viscosity of 60000 cSt at 25 ° C. Terminal closed with silanol group, viscosity at 25 ° C is 90 cSt
1.0 part polydiorganosiloxane, wet silica (N
(ipsil LP) 45 parts, dimethyldimethoxysilane 2.0 parts and zinc stearate 0.05 parts were kneaded with a kneader mixer until uniform, and heat-treated at 150 ° C. for 3 hours while kneading, followed by 2,5-dimethyl 2,5- 0.2 parts of di (tert-butylperoxy) hexane was added and mixed uniformly to obtain a silicone rubber composition. Evaluation was performed in the same manner as in Example 1 using this silicone rubber compound. Table 1 shows the results.

COMPARATIVE EXAMPLE 1 99.88 mol% of (CH ₃ ) ₂ SiO units, (CH ₃ ) (CH ₂ CHCH) SiO units
It consists of 12 mol%, 100 parts of polyorganosiloxane with a polymerization degree of 6000, the end of which is blocked with dimethylvinylsilyl group, and the end is closed with a silanol group.
Knead 4.0 parts of 90 cSt polydiorganosiloxane, 45 parts of wet silica (Nipsil LP) and 0.05 parts of zinc stearate with a kneader mixer until uniform, and knead 1
After heat treatment at 50 ° C for 3 hours, 0.2 part of 2,5-dimethyl 2,5-di (tert-butylperoxy) hexane was added and uniformly mixed to obtain a silicone rubber composition.
Evaluation was performed in the same manner as in Example 1 using this silicone rubber compound. Table 1 shows the results.

Comparative Example 2 99.88 mol% of (CH ₃ ) ₂ SiO units, (CH ₃ ) (CH ₂ = CH) SiO units
40 parts of a polyorganosiloxane having a polymerization degree of 6000, which is composed of 12 mol% and is capped with a dimethylvinylsilyl group, and 60 parts of a polydiorganosiloxane capped with a silanol group and having a viscosity of 45,000 cSt at 25 ° C. Terminal closed with silanol group, viscosity at 25 ° C is 90cSt
2.5 parts of polydiorganosiloxane, 45 parts of wet silica (Nipsil LP) and 0.05 part of zinc stearate are kneaded with a kneader mixer until uniform, and 150 ° C. while kneading.
After heat treatment for 3 hours, 0.2 part of 2,5-dimethyl 2,5-di (tert-butylperoxy) hexane was added and uniformly mixed to obtain a silicone rubber composition. Evaluation was performed in the same manner as in Example 1 using this silicone rubber compound. Table 1 shows the results.

COMPARATIVE EXAMPLE 3 99.88 mol% of (CH ₃ ) ₂ SiO units, (CH ₃ ) (CH ₂ = CH) SiO units
70 parts of a polyorganosiloxane having a polymerization degree of 6000 and consisting of 12 mol% and capped with a dimethylvinylsilyl group, and polydiorganosiloxane 30 capped at a terminal with a trimethylsilyl group and having a viscosity of 45,000 cSt at 25 ° C.
And 2.5 parts of polydiorganosiloxane having a viscosity of 90 cSt at 25 ° C, 45 parts of wet silica (Nipsil LP) and 0.05 parts of zinc stearate are kneaded with a kneader mixer until the parts are uniformly closed. while doing
After heating at 150 ° C for 3 hours, 2,5-dimethyl 2,5-
0.2 parts of di (tert-butylperoxy) hexane was added and mixed uniformly to obtain a silicone rubber composition. Evaluation was performed in the same manner as in Example 1 using this silicone rubber compound. Table 1 shows the results.

COMPARATIVE EXAMPLE 4 99.88 mol% of (CH ₃ ) ₂ SiO units, (CH ₃ ) (CH ₂ = CH) SiO units
70 parts of a polyorganosiloxane having a polymerization degree of 6000, composed of 12 mol% and capped with a dimethylvinylsilyl group, and 30 parts of a polydiorganosiloxane capped with a silanol group and having a viscosity of 45,000 cSt at 25 ° C. Knead 45 parts of wet silica (Nipsil LP) and 0.05 part of zinc stearate with a kneader mixer until uniform, and knead
After heating at 150 ° C for 3 hours, 2,5-dimethyl 2,5-
0.2 parts of di (tert-butylperoxy) hexane was added and mixed uniformly to obtain a silicone rubber composition. Evaluation was performed in the same manner as in Example 1 using this silicone rubber compound. Table 1 shows the results.

[0018]

[Table 1]

As is evident from the results shown in Table 1, the thermosetting silicone rubber composition of the present invention has excellent roll workability, low plasticization reversion, and a keypad using the same has excellent durability. Comparative Example 1, which has low hysteresis and has little decrease in load value and low hysteresis over time, has a significant decrease in load value and low hysteresis over time. Similarly, Comparative Example 2 in which the component (B) was blended beyond the scope of the present invention, and Comparative Example 3 in which a polydiorganosiloxane terminated with a trimethylsilyl group was used as the component (B), exhibited roll workability and plasticization return. In addition, the load value and the low hysteresis property with the passage of time are remarkably reduced. Furthermore, in Comparative Example 4 having no (C), in addition to extremely poor plasticization return, the load value and the low hysteresis property with the passage of time are remarkably reduced.

[Brief description of the drawings]

FIG. 1 is a view showing a keypad manufactured for a load value and hysteresis measurement test in an example.

FIG. 2 is a graph showing a relationship between a pressing load value and a return load value for a load value and hysteresis measurement test of an example.

Claims (2)

(57) [Claims] (A) Average unit formula: R _a SiO _{(4-a) / 2} (where R is a substituted or unsubstituted monovalent hydrocarbon group,
a represents a number in the range of 1.98 to 2.02), having an average degree of polymerization of 4000 to 20000, and a triorganosilyl group at the molecular chain end.
Closed polyorganosiloxane (B) terminal silanol groups is, 100 parts by weight of the base polymer consisting of polydiorganosiloxane viscosity at 25 ° C. is 10000～100000CSt (however, the proportion of the component (B) in the base polymer is (C) a polydiorganosiloxane having a terminal closed with a silanol group and having a viscosity at 25 ° C. of 5 to 500 cSt.
(C) A thermosetting silicone rubber composition containing 5 to 200 parts by weight (D) a fine powdery silica filler and (E) a catalytic amount of a curing agent. 2. A keypad comprising a heat-cured product of the silicone rubber composition according to claim 1.