JPH0547573B2 - - Google Patents

Description

[Detailed description of the invention]

≪Industrial Application Field≫ The present invention relates to a method for producing silicone rubber foam, and in particular, to a silicone rubber foam that provides a good finish at corners, edges, etc. even when a mold with a complicated shape is used. Concerning a method of manufacturing a body. <<Prior art>> Silicone rubber foams are widely used in various applications because they have spongy elasticity in addition to the general properties of silicone rubber such as safety and hygiene, heat resistance, cold resistance, and electrical properties. . In this case, the silicone rubber foam not only has a high expansion ratio, but also has the characteristics of silicone rubber: it is sufficiently hardened to the surface, has no tackiness, and has a thin, soft, spongy surface skin. It is required that safety and hygiene, heat resistance, cold resistance, electrical properties, etc. are not impaired. In this case, it is known that it is important to maintain a balance between foaming and curing when heating and foaming a silicone rubber foam composition in order to obtain a silicone rubber foam with a good foaming state. That is,
The composition for obtaining the silicone rubber foam contains an organopolysiloxane, a blowing agent, and a curing agent (organic peroxide) for forming the silicone rubber foam, and this composition is heated. As a result, the foaming agent decomposes and foams, and at the same time, curing starts due to the action of the curing agent. At this time, if the blowing agent decomposes first, the cells tend to collapse and the cell structure becomes non-uniform; on the other hand, if the blowing agent decomposes later and a considerable degree of curing progresses before gas is generated from the blowing agent, foaming occurs. The magnification decreases, resulting in a non-uniform foam with a rough cell structure. Furthermore, the progress of curing depends on the decomposition of the curing agent. Therefore, it is necessary to balance the decomposition of the blowing agent and the decomposition of the curing agent (organic peroxide) and at the same time balance the vulcanization rate of the organopolysiloxane. However, this is complicated as it requires careful attention to the manufacture of the foam. Therefore, it has been proposed to use azobisisobutyronitrile, which functions not only as a blowing agent but also as a curing agent (Japanese Patent Publication No. 44-
461 Publication), the decomposition products generated here are a health and safety problem, so it is necessary to perform a long post-cure in order to sufficiently remove these decomposition products and eliminate health and safety problems. There was a practical problem. A method using azodicarbonamide as a blowing agent is also known. However, in this case, the decomposition temperature was as high as 210°C, so it was not suitable as a silicone rubber foam. This drawback has been solved by adding various decomposition temperature lowering agents that lower the decomposition temperature of azodicarbonamide, such as the one disclosed in U.S. Pat. No. 2,806,073, but the foam vulcanization conditions are still delicate. The disadvantage was that it was difficult to obtain a consistent foam. Therefore, in the past, it has not been possible to improve the finish of the corners and edges of foams with complex shapes. <<Problems to be Solved by the Invention>> As a result of intensive studies to solve these conventional drawbacks, the inventors of the present invention have found that foaming can be achieved by combining a certain type of organopolysiloxane, an azodicarbonamide blowing agent, and a dialkyl peroxide. It is possible to easily balance the curing process, and by adding a certain amount of finely powdered silica as a filler and using this composition to perform mold foaming in which the pressure is removed after press vulcanization, corner The inventors have discovered that it is possible to produce a silicone rubber foam with extremely good finish in the edges and edges, and have arrived at the present invention. SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a method for producing a silicone rubber foam with a good finish at the corners and edges of the foam and no tackiness even when a complicated mold is used. <Means for Solving the Problems> The above objects of the present invention are as follows: (1) Organopolysiloxane represented by the general formula R _a SiO _(4-a)/2 100 parts by weight Fine powder silica filler 3 to 50 parts by weight Part Azodicarbonamide foaming agent with a decomposition temperature of 160°C or less 2 to 10 parts by weight An azodicarbonamide blowing agent with a decomposition temperature that gives a half-life of 10 hours or more
Dialkyl peroxide above 110℃
A mold is filled with a silicone rubber foam composition containing 0.1 to 10 parts by weight, and press vulcanization is performed at a temperature of 150 to 200°C for 2 to 10 minutes, followed by depressurization.
This was achieved by a method for producing silicone rubber foam characterized by heat treatment at a temperature of 250°C for 0 to 8 hours. The above components will be explained in detail below. Organopolysiloxane as the above component
In R _a SiO _(4-a)/2 , R is a methyl group, an ethyl group,
Alkyl groups such as propyl groups and butyl groups, alkenyl groups such as vinyl groups and allyl groups, aryl groups such as phenyl groups and tolyl groups, and some or all of the hydrogen atoms bonded to the atoms of these groups are replaced by halogen atoms, cyano Same or different unsubstituted or substituted monovalent hydrocarbon groups selected from chloromethyl group, chloropropyl group, 3,3,3-trifluoropropyl group, 2-cyanoethyl group, etc. substituted with groups, a is a positive number from 1.95 to 2.05, and the organopolysiloxane preferably contains 0.2 mol% or less of vinyl groups. Generally, if the amount of vinyl groups in the silicone rubber exceeds 0.2 mol %, the foam becomes hard, making it impossible to obtain a foam that is good enough for practical use. In the present invention, it is particularly preferable that the vinyl group content is 0.025 to 0.07 mol%. The organopolysiloxane desirably has a linear molecular structure, but may have a partially branched structure. Further, it is preferable that the molecular chain terminals are blocked with a triorganosilyl group or a hydroxyl group. Examples of the triorganosilyl group include a trimethylsilyl group and a dimethylvinylsilyl group. The above-mentioned organopolysiloxane may have a viscosity of 100,000 cs or more at 25°C, and the degree of polymerization is not particularly limited. The fine powder silica filler as a component is added for the purpose of reinforcing silicone rubber, thickening it, improving processability, increasing its weight, etc. Examples include humid silica, wet silica, quartz powder, diatomaceous earth, etc. I can do it. It is preferable that these fine powder silica fillers have a specific surface area of 1 m ² /g or more. If the amount of the finely divided silica filler added is less than 3 parts by weight per 100 parts by weight of the organopolysiloxane, not only will the desired reinforcing properties not be obtained, but also the workability will be insufficient, which is not preferred. On the other hand, if it exceeds 50 parts by weight, processability such as mold flowability will be extremely reduced. A particularly preferred range of the amount of finely divided silica filler added is 3 to 30 parts by weight. Azodicarbonamide-based blowing agents whose components have a decomposition temperature of 160°C or less can generally be easily obtained by adding urea, urea-based compounds, zinc oxide, zinc stearate, polyethylene glycol, etc. as additives to azodicarbonamide. However, from the viewpoint of safety and hygiene in particular, it is preferable to use urea or a urea-based compound as an additive. Examples of such azodicarbonamide foaming agents include Cellmic CAP-250 and Cellmic
Examples include CAP (both product names manufactured by Sankyo Kasei Co., Ltd.). The dialkyl peroxide component, which has a decomposition temperature (τ) of 110°C or higher to obtain a half-life of 10 hours, is used to accelerate heat curing of silicone rubber, and examples thereof include 2,
5-bis-(t-butylperoxy)-2,5-dimethylhexane (τ=118°C), dicumyl peroxide (τ=116°C), 2,5-bis-(t-butylperoxy)- 2,5-dimethylhexyne (τ
= 135°C), ditertiary butyl peroxide (τ = 124°C), and the like. The amount of the dialkyl peroxide to be blended can be appropriately selected depending on the type thereof, the amount of other components, etc., and is generally 0.1 to 10 parts by weight per 100 parts by weight of the organopolysiloxane. Note that diacyl peroxides (e.g., 2,4,-dichlorobenzoyl peroxide, benzoyl peroxide, etc.) or peroxyketals (e.g., 1,1,-bis( t-butylperoxy-
3,3,5-trimethylcyclohexane) etc. have a half-life of 10 hours at a temperature below 110°C, so they decompose before the blowing agent and accelerate vulcanization, making it possible to obtain a good foam. It is difficult. The silicone composition of the present invention comprising the above components may further contain a dispersant such as a low molecular weight siloxane with a degree of polymerization of 100 or less, a silanol group-containing silane, an alkoxy group-containing silane, iron oxide, oxidized iron, etc. Heat resistance improvers such as cerium, iron octylate, titanium oxide, pigments for coloring, platinum compounds,
Flame retardant aids such as palladium compounds and other additives that are usually added to silicone rubber compositions can be added. In the present invention, the silicone rubber composition thus obtained is filled into a mold, and the temperature is 150-150°C.
Press vulcanization is performed at 200°C for 2 to 10 minutes, followed by mold foaming by removing pressure. By employing the above-mentioned temperature, the silicone rubber foam composition of the present invention has a good and uniform balance between foaming and curing, and the pressure applied during press vulcanization allows it to be molded into molds with complex shapes. Even if you use
Since the composition is evenly distributed to all corners, the corners and edges of the finished molded product are sharp. In the present invention, after obtaining the above foam molded product, in order to complete vulcanization and decomposition of the foaming agent,
Furthermore, it is also effective to perform post-curing at 150-220°C for 0-8 hours. <<Effects of the Invention>> As detailed above, in the method for producing a silicone rubber foam of the present invention, a composition in which a blowing agent, an organopolysiloxane, a filler, and an organic peroxide are optimally combined is used. , by setting the foaming temperature in mold foaming to 150-200℃,
Not only can a high foaming ratio be achieved,
Since the foaming is carried out under pressure, corners, edges, etc. can be sharpened, and there is no tacky feeling on the surface, so the quality of the foamed molded product obtained is extremely good. ≪Example≫ The present invention will be explained in more detail with reference to Examples below.
The present invention is not limited thereby. In addition, parts in each example indicate parts by weight, and viscosity indicates a value measured at 25°C. Examples 1 and 2 and Comparative Example 1 As shown in Table 1, (CH ₃ ) ₂ SiO units, (CH ₂ =
100 parts of an organopolysiloxane with a viscosity of approximately 1,000,000 cs at 25°C, consisting of CH) CH ₃ SiO units and (CH ₃ ) ₃ SiO _1/2 units, and humid silica (Erosil R-972: trade name manufactured by Degutsusa Co., Ltd.) 20 After mixing these parts, they were uniformly kneaded using two rolls to obtain a basic composition. 100 parts of this basic composition was added with an azodicarbonamide foaming agent (Celmic®) as a foaming agent.
5 parts of CAP-250 (manufactured by Sankyo Kasei Co., Ltd.) and 2,5-bis(t-butylperoxy)-2, as a vulcanizing agent.
0.5 part of 5-dimethylhexane was added and further kneaded to obtain a composition for a foam molded body. After sufficiently deaerating the obtained composition, 6 mm
The mixture was filled into a press mold having a space of 50 mm x 140 mm, vulcanized at a press pressure of 30 Kgf/cm ² and a temperature of 165° C. for 5 minutes, and then the pressure was removed to obtain a foam. The specific gravity and hardness of the foam thus obtained are as shown in Table 1.

[Table] Example 3, Comparative Example 2, and Comparative Example 3 To 100 parts of the basic composition of Example 1, 2,5-bis(t-butylperoxy)-2,5 was added as a vulcanizing agent.
- 0.5 part of dimethylhexane and 5 parts of various azodicarbonamide foaming agents shown in Table 2 were added, and the composition for a foamed molded body was thoroughly mixed and degassed and foamed in the same manner as in Example 1. The results were obtained.

[Table] Examples 4, 5 and Comparative Example 4 The basic composition of Example 1 was used and the effects of the type of vulcanizing agent were investigated using the formulations shown in Table 3. .

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Claims (1)

[Claims] 1 General formula R _a SiO _(4-a)/2 (wherein R represents an unsubstituted or substituted monovalent hydrocarbon group containing 0 to 0.2 mol% of vinyl group, a is 1.95 to 2.05)
100 parts by weight Fine powder silica filler with a specific surface area of 1 m ² /g or more 3 to 50 parts by weight Azodicarbonamide blowing agent with a decomposition temperature of 160°C or less 2 to 10 parts by weight Decomposition agent that gives a half-life of 10 hours or more temperature is 110
Dialkyl peroxide above ℃
A mold is filled with a silicone rubber foam composition containing 0.1 to 10 parts by weight, and press vulcanization is performed at a temperature of 150 to 200°C for 2 to 10 minutes, followed by depressurization, and then vulcanization at 150 to 250°C.
A method for producing a silicone rubber foam, the method comprising heat treating at a temperature of 0 to 8 hours.