JPH06107807A - Production of molded silicone rubber article - Google Patents

Abstract

PURPOSE:To produce the title article in a short time at a little man-hour and a low cost. CONSTITUTION:The article is produced by coating the surface of a noncured silicone rubber compsn. mainly comprising an alkenylated organopolysiloxane rubber with an org. peroxide which is liq. at normal temp. and has an activation energy of 25-41kcal/mol, and then molding and curing the compsn. by compression molding at a temp. higher than the decomposition point of the peroxide for obtaining a half-life of 10min.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a silicone rubber molded product which enables simplification of molding process.

[0002]

2. Description of the Related Art Conventionally, compression molding, which is known as a method for molding silicone rubber, uses an uncured silicone rubber composition with two rolls, three rolls, a kneader mixer, etc. Mix the organic peroxide uniformly with a kneading machine, sheet out with two rolls etc. according to the size and shape of the mold, then cut this sheet into a shape that is easy to handle. It is inserted into the mold and compressed under heating. However, this method has a disadvantage that it requires a considerable time and man-hours for mixing the organic peroxide, and that an expensive kneader is required for mixing the organic peroxide and discharging the sheet. It was

[0003]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for producing a silicone rubber molded product which requires a small number of steps, can be obtained in a short time and at low cost. .

[0004]

According to the present invention, the surface of an uncured silicone rubber composition containing an alkenyl group-containing organopolysiloxane raw rubber as a main component is coated with 25 to 41 parts of the surface.
A liquid organic peroxide having an activation energy of Kcal / mol and applied at room temperature is applied, and then the composition is heated to a temperature equal to or higher than the decomposition temperature for obtaining a half-life of 10 minutes of the organic peroxide. The present invention relates to a method for producing a silicone rubber molded article, which is characterized by curing by compression molding under conditions.

To explain this, a typical example of the alkenyl group-containing organopolysiloxane raw rubber used in the present invention is represented by the general formula R ³ ₃ SiO [R ⁴ ₂ SiO] mR ³ ₃ (wherein R ³ is substituted or R ⁴ is an unsubstituted monovalent hydrocarbon group or a hydroxyl group, R ⁴ is a substituted or unsubstituted monovalent hydrocarbon group, 0.1 to 2.0 mol% of which is an alkenyl group, and m is 3000. It is a diorganopolysiloxane represented by the above number) and has a raw rubber-like shape at room temperature. In the above formula, R ³ and R ⁴ may be the same or different from each other, and are alkyl groups such as methyl group, ethyl group, propyl group, cycloalkyl groups such as cyclohexyl group, β-phenylethyl group. The aralkyl group such as, an aryl group such as a phenyl group, a vinyl group, an alkenyl group such as an allyl group, and an alkyl group in which a hydrogen atom is substituted with a cyano group or a fluorine atom are exemplified. Of R ⁴ , 0.1 to 2.0 mol% is preferably an alkenyl group, and among the alkenyl groups, a vinyl group is preferred.

The uncured silicone rubber composition used in the present invention may be any one containing the above alkenyl group-containing organopolysiloxane raw rubber as a main component,
Although not particularly limited, a composition in which the above-mentioned alkenyl group-containing organopolysiloxane raw rubber is mixed with various reinforcing fillers and non-reinforcing fillers as described below is generally used.

The organic peroxide applied to the surface of the uncured silicone rubber composition is 25 to 41 Kcal / mo.
An organic compound having an activation energy of 1 and being liquid at room temperature is used. When the activation energy of this organic peroxide is less than 25 Kcal / mol, it becomes difficult to completely cure the silicone rubber composition obtained by applying the organic peroxide, and the silicone rubber composition is sufficiently cured and has rubber elasticity. −
It is difficult to obtain rubber molded products. If the activation energy exceeds 41 Kcal / mol, the physical properties of the silicone rubber molded product will be impaired. The need for the organic peroxide to be liquid at room temperature is to ensure its permeation rate and diffusion rate when applied to an uncured silicone rubber composition. Unsuitable for invention.

In the present invention, the organic peroxide as described above is applied to the surface of the uncured silicone rubber composition as described above. The shape of the uncured silicone rubber composition is applied during the application. I'm not particular about it. However, the thickness of the uncured silicone rubber composition is preferably 4 mm or less, and more preferably 3 mm or less, from the surface coated with the organic peroxide. The organic peroxide is preferably applied on the entire surface of the uncured silicone rubber composition from the viewpoint of the flow in the mold during compression molding. At the time of compression molding, even if the coating surface of the organic peroxide is between the layers of the unvulcanized composition,
It may be on the surface, and the coating structure is not particularly limited. The amount of the organic peroxide applied is 0.2 with respect to 100 parts by weight of the uncured silicone rubber composition to be molded.
The range is preferably from 2.0 to 2.0 parts by weight, more preferably from 0.5 to 1.5 parts by weight. The coating solution may be an organic peroxide alone, or a linear or cyclic organopolysiloxane may be used as a diluent. Further, a volatile organic solvent such as a rubber swelling agent such as toluene, xylene, or acetone may be used. Examples of the organic peroxide used in the present invention include the following organic compounds. The numerical value in parentheses after the compound name indicates activation energy (Kcal / mol). 1,1-bis (t-butylperoxy) -3,3,5-trimethylcyclohexane (33.2), 1,1-bis (t
-Butylperoxy) -cyclohexane (31.4),
Di-t-butylperoxide (37.3), t-butylcumylperoxide (38.2), 2,5-dimethyl-2,5di (t-butylperoxy) hexane (36.
3) 2,5-Dimethyl-2,5-di (t-butylperoxy) hexyne (36.7). In the present invention, the activation energy of the organic peroxide means ΔE in the following formula. k = A exp (-ΔE / RT) In the above formula, k is a decomposition rate constant, A is a frequency factor, R is a gas constant, and T is temperature (K.). The curing temperature is preferably a decomposition temperature or higher for obtaining a half-life of 10 minutes of the organic peroxide. The half-life is the time until the concentration of organic peroxide is reduced to half the initial concentration.

The uncured silicone rubber composition used in the present invention may optionally contain various reinforcing fillers and non-reinforcing fillers. Examples of such fillers include precipitated silica, fumed silica, fumed titanium dioxide, pyrogenic silica, reinforcing fillers such as carbon black, ground quartz, diatomaceous earth, titanium dioxide, zinc oxide, calcium carbonate, Examples include non-reinforcing fillers such as magnesium oxide, and silica-based fillers surface-treated with organic silicon compounds such as hexamethyldisilazane, trimethylchlorosilane, dimethyldichlorosilane, and cyclic dimethylpolysiloxane. Further, heat-resistant agents, flame retardants, pigments and the like known for silicone rubber can be contained.

[0010]

EXAMPLES The present invention will now be described with reference to examples. In the examples, "parts" means "parts by weight".

[0011]

Example 1 (CH ₃ ) ₂ Si0 unit 99.8 mol%,
(CH ₃ ) (CH ₂ ═CH) Si 0 units consisting of 0.2 mol%, both ends blocked with dimethylvinylsiloxy groups 100 parts of organopolysiloxane raw rubber with an average degree of polymerization of 7,000, average polymerization as a plasticizer 4 parts of silanol-terminated dimethylpolysiloxane oil of degree 3 were placed in a kneader mixer. Next, precipitated silica [Nippon Silica Co., Ltd.]
Manufactured by Nipsil LP] (45 parts) was added and kneaded until uniform. This kneaded material was heat-treated at 150 ° C. for 2 hours to obtain an uncured silicone rubber composition. This composition was formed into a sheet shape (about 145 mm × 210 mm × 2.5 mm). Then, on one side of this, 2,5-dimethyl-2,5
-Di (t-butylperoxy) hexane was added in an amount of 0.3 parts and 0.1 parts, respectively, per 100 parts of the silicone rubber composition.
Apply 6 parts evenly, frame mold (150mm × 2
20 mm × 2 mm), and compression molded under the conditions of a press temperature of 170 ° C., a press pressure of 200 kg / cm ² (gauge pressure), and a curing time of 10 minutes to obtain sheet-like silicone rubber molded products. Obtained. About this silicone rubber sheet JI
Physical properties were measured according to SK6301. For comparison, after adding 0.3 parts and 0.5 parts of the organic peroxide to the uncured silicone rubber composition, respectively,
Mix with two rolls until uniform. Silicone rubber molded articles were produced from the obtained compositions by the same method as described above, and their physical properties were measured. The results are also shown in Table 1.

[Table 1]

[0012]

Example 2 (CH ₃ ) ₂ SiO unit 99.5 mol%,
(CH ₃ ) (CH ₂ ═CH) SiO unit consisting of 0.5 mol%, both ends blocked with dimethylvinylsiloxy groups, and 100 parts of organopolysiloxane raw rubber having an average degree of polymerization of 7,000 was kneaded with a kneader mixer. -I put it in. Next, 65 parts of conductive carbon black [trade name: Denka Black, manufactured by Denki Kagaku Co., Ltd.] was added thereto and kneaded until uniform to obtain an uncured silicone rubber composition. This composition is formed into a sheet (about 148 mm x 218 mm x 1.0 mm)
3 pieces were prepared. Then, 1,1-bis (t-butylperoxy) 3,3,5 on both sides of these sheets.
0.6 parts of trimethylcyclohexane were evenly applied to 100 parts of this silicone rubber composition. Then, this was filled in the same frame mold as in Example 1, and compression molded under the conditions of a press temperature of 150 ° C., a press pressure of 200 kg / cm ² (gauge pressure), and a curing time of 10 minutes, A sheet-shaped silicone rubber molded product was obtained. Physical properties of this silicone rubber sheet were measured in the same manner as in Example 1. For comparison, two parts of 100 parts of the uncured silicone rubber composition and two parts of the organic peroxide of 0.6 part were used.
And mixed until homogeneous. A silicone rubber molded article is produced from the obtained composition by the same method as described above,
Its physical properties were measured. The results are also shown in Table 2.

[Table 2]

[0013]

Example 3 A diorganopolysiloxane composed of 99.67 mol% of 3,3,3-trifluoropropylmethylsiloxane unit and 0.33 mol% of methylvinylsiloxane unit, and both ends of the molecular chain of which were blocked with silanol groups. Raw rubber 1
To 100 parts, 46 parts of fumed silica having a specific surface area of 200 m ² / g, and 12 parts of dimethylpolysiloxane capped with dimethylhydroxy groups at both ends having a viscosity of 20 centipoise as a silica surface treating agent were uniformly kneaded with a kneader mixer. An uncured fluorosilicone rubber composition was prepared. This composition is formed into a sheet (about 120 mm x 120 mm x 1.
5 mm (2 mm) were prepared. Then, on the surface of these sheets, an acetone solution of 2,5-dimethyl-2,5-di (t-butylperoxy) hexane (pure content 50% by weight)
1.2 parts was applied to 100 parts of the uncured fluorosilicone rubber composition, and after air-drying for 5 minutes, 3 sheets were laminated and cured in the same manner as in Example 1. Then, the physical properties of this fluorosilicone rubber sheet were measured. Further, 0.6 part of the above-mentioned organic peroxide was mixed with the uncured fluorosilicone composition in two rolls until uniform.
The resulting composition was cured by the same method as above, and the physical properties were measured. The physical property values (hardness, tensile strength, elongation) were the same in both cases. The results are also shown in Table 3.

[Table 3]

[0014]

Example 4 (CH ₃ ) ₂ SiO unit 99.8 mol%,
(CH ₃ ) (CH ₂ ═CH) SiO unit consisting of 0.2 mol%, 100 parts of diorganopolysiloxane raw rubber having both ends blocked with dimethylvinylsiloxy groups and a specific surface area of 1
An uncured silicone rubber composition was prepared by uniformly kneading 45 parts of 30 m ² / g wet-process silica and silanol group-capped dimethylpolysiloxane having a viscosity of 10 centistokes with a kneader mixer. This composition was formed into a sheet shape (about 80 mm × 80 mm × 2 mm). 0.6 parts of 2,5-dimethyl-2,5-di (t-butylperoxy) hexane was coated on the surface of two sheets of this sheet per 100 parts of the uncured silicone rubber composition. 2 sheets were superposed on each other, and a key pad having 24 key tops having a size of 75 mm × 80 mm and a height of 8 mm was formed by heat compression molding at 170 ° C. This keypad was sufficiently cured and could be used as a keypad.

[0015]

According to the manufacturing method of the present invention, it is possible to obtain a silicone rubber molded product in a small number of steps, in a short time, and at low cost. Further, according to the production method of the present invention, it is possible to grasp the physical properties of the uncured silicone rubber composition after curing in a short time. When applied as a process inspection means at the time of manufacturing, it significantly contributes to speeding up process inspection and reducing man-hours.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location C08L 83/07 LRT 8319-4J // B29K 83:00

Claims (2)

[Claims] 1. An organic peroxide which is liquid at normal temperature and has an activation energy of 25 to 41 Kcal / mol on the surface of an uncured silicone rubber composition containing an alkenyl group-containing organopolysiloxane raw rubber as a main component. After applying, and after applying
A method for producing a silicone rubber molded article, which comprises curing the composition by compression molding under a temperature condition of a decomposition temperature or higher for obtaining a half-life of 10 minutes of the organic peroxide. 2. The method for producing a silicone rubber molded article according to claim 1, wherein the uncured silicone rubber composition has a sheet shape.