JP2686503B2 - Silicone rubber composition - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[Object of the Invention]

[0002]

FIELD OF THE INVENTION The present invention relates to a silicone rubber composition, and more particularly to a silicone rubber composition having improved workability and processability in a low hardness type silicone rubber composition.

[0003]

2. Description of the Related Art A silicone rubber composition is obtained by blending various fillers with a siloxane base polymer. By selecting the type and amount of the filler, the rubber properties after curing such as mechanical properties can be changed. It is known.

In order to obtain a rubber having a low hardness in such a silicone rubber composition, for example, the compounding amount of the filler is reduced. However, since the siloxane-based polymer has a lower polymer molecular weight than other organic elastomers, if the amount of the filler is small, there is a problem that the composition becomes sticky.

For example, in a silicone rubber composition containing carbon black for the purpose of imparting electroconductivity or non-electrostatic property or coloring, there are some cases where the adhesiveness is remarkable depending on the type of carbon black. In such a rubber compound, there are problems that handling of unvulcanized dough and workability on rolls are poor, and molding work is deteriorated.

As a countermeasure against this, the stickiness can be suppressed by replacing the carbon black with a filler such as diatomaceous earth or zeolite which hardly causes an increase in hardness even if added. However, such fillers
When a small amount is compounded, the effect is not sufficiently obtained, and when a large amount is compounded, rubber properties may be unfavorably affected. That is, not only the desired rubber characteristics cannot be sufficiently obtained, but conversely, the conductivity and the coloring property to be obtained are lowered. Therefore, the method using a filler such as diatomaceous earth or zeolite has not been practical.

[0007]

As described above, in order to obtain a low hardness type silicone rubber, it is generally necessary to suppress the amount of the filler compounded. However, when the compounding amount of the filler is small, required rubber properties are reduced,
There is a problem that workability is reduced due to the development of tackiness.

From the above, even when the amount of the filler compounded in the silicone rubber composition is small, the imparting properties such as conductivity, antistatic property, heat resistance, weather resistance, heat transfer property, and coloring property and It is strongly desired to suppress tackiness and improve workability and processability while maintaining the original properties of rubber.

The present invention has been made in order to solve such a problem, and it has a predetermined characteristic and can suppress the tackiness regardless of the compounding amount of the filler, and the good work can be achieved. It is an object of the present invention to provide a silicone rubber composition that maintains its workability and processability.

[Structure of the Invention]

[0011]

Means and operation for solving the problems] Shi Ricoh <br/> Ngomu composition of the present invention, the polyorganosiloxane the organic radicals bonded to the silicon atom is an alkyl group and / or aryl group as a base polymer, In a silicone rubber composition containing a filler containing a reinforcing filler, 70% by weight or more of the filler is a silica-based filler, and 100 parts by weight of the filler contains magnesium carbonate in an amount of 0.
It is characterized by being mixed in the range of 1 to 20 parts by weight.

The silicone rubber composition of the present invention is a so-called millable type silicone rubber composition, which basically comprises (a) a polyorganosiloxane base polymer and (b) a curing agent, and (c) a component for reinforcement. Various fillers including a filler are uniformly dispersed. Further, in the present invention, magnesium carbonate is further blended as the component (d), and this component (d) is a characteristic component in the present invention.

Among various components used in the basic silicone rubber composition, the polyorganosiloxane base polymer as the component (a) and the curing agent as the component (b) depend on the reaction mechanism for obtaining the rubber elastic body. It is selected appropriately. As the reaction mechanism, (1) a crosslinking method using an organic peroxide vulcanizing agent, (2) a method using an addition reaction, etc. are known. Depending on the reaction mechanism, (a) component and (b) component, that is, curing It is well known that the preferred combination with the catalyst or cross-linking agent will be determined.

That is, when the crosslinking method (1) is applied, the base polymer of the component (a) usually contains a vinyl group among the organic groups bonded to silicon atoms in one molecule. A polydiorganosiloxane having a degree of polymerization of 1000 or more is used. Further, as the curing agent of the component (b), benzoyl peroxide, 2,4-dichlorobenzoyl peroxide, dicumyl peroxide, cumyl
-T-butyl peroxide, 2,5-dimethyl-2,5-di-t-butylperoxyhexane, di-t-butyl peroxide, and other organic peroxide vulcanizing agents are used, and especially low compression set To give dicumyl peroxide, cumyl-t-butyl peroxide, 2,5-dimethyl-2,5-di-
t-Butylperoxyhexane and di-t-butylperoxide are preferred. Incidentally, these organic peroxide vulcanizing agents,
Used as one kind or as a mixture of two or more kinds.

The blending amount of the above-mentioned component (b) organic peroxide is 100 parts by weight of the base polymer (a).
A range of 0.05 to 15 parts by weight is preferred. If the amount of the organic peroxide is less than 0.05 parts by weight, the vulcanization is not sufficiently performed, and
Even if it is compounded in an amount of more than parts by weight, not only is there no particular effect, but also the physical properties of the silicone rubber obtained may be adversely affected.

As the base polymer (a) in the case of applying the addition reaction of the above (2), the same base polymer as in the above (1) is used. Also,
The curing agent of the component (b) is, as a curing catalyst, chloroplatinic acid, a platinum olefin complex, a platinum vinyl siloxane complex,
A platinum-based catalyst such as platinum black or platinum triphenylphosphine complex is used, and a polydiorganosiloxane having an average of at least more than 2 hydrogen atoms bonded to silicon atoms in one molecule is used as a crosslinking agent.

In the curing agent of the above component (b), the amount of the curing catalyst blended is the amount of platinum atom relative to the amount of the component (a).
An amount in the range of 1 to 100 ppm is preferable. If the compounding amount of the curing catalyst is less than 1 ppm as the amount of platinum atom, curing does not proceed sufficiently, and if it exceeds 100 ppm, no particular improvement in the curing rate can be expected. The amount of the cross-linking agent to be added is preferably such that 0.5 to 4.0 hydrogen atoms bonded to silicon atoms in the cross-linking agent are present with respect to one alkenyl group in the component (a), and more preferably The amount is 1.0 to 3.0. When the amount of hydrogen atoms is less than 0.5, curing of the composition does not proceed sufficiently and the hardness of the composition after curing becomes low, and when the amount of hydrogen atoms exceeds 4.0, after curing. The physical properties and heat resistance of the composition are deteriorated.

The organic group of the polyorganosiloxane base polymer of the component (a) used in the above various reaction mechanisms is an alkyl group such as methyl group, ethyl group, propyl group, butyl group, hexyl group and dodecyl group. Base,
Or is exemplified an aryl group such as phenyl group, typically a methyl group is frequently used from ease of synthesis.

As the component (c) in the silicone rubber composition of the present invention, various fillers including a reinforcing filler are applied. As these fillers, silica-based powder which is generally blended with silicone rubber and imparts mechanical properties such as fumed silica, wet silica, and calcined silica, and mechanical properties such as carbon black, as well as electrical conductivity. Examples of the powder include a powder that imparts properties such as coloring property and coloring property. Also silica
Examples of diatomaceous earth containing silica as a silica filler
Shown . Carbon blacks made from natural gas, heavy oil, creosote oil, etc. by endothermic decomposition method, furnace black by furnace type incomplete combustion method, lamp black, channel black and acetylene by contact type incomplete combustion method. It contains a pyrolytic acetylene black obtained from the above as a raw material, and imparts a wide range of properties such as hardness, conductivity, and black colorability to the silicone rubber composition due to the respective properties.
Further, the component (c) in the present invention includes, in addition to those described above, a filler that imparts various properties such as heat conductivity, heat resistance, and weather resistance, and includes titanium oxide, aluminum oxide, and oxide. Examples thereof include zinc, iron oxide, cerium oxide, mica, clay, zinc carbonate, manganese carbonate, cerium hydroxide and glass beads.

However, generally 70% by weight of the component (c)
The above is the silica-based filler, and the present invention is also particularly effective in such a case. Further, the blending amount of the component (c) is
It is arbitrarily selected according to the properties to be obtained, the degree of polymerization of the base polymer of the component (a), etc., and is not particularly limited, and generally the base polymer of the component (a) is used.
It is used in the range of about 1 to 500 parts by weight with respect to 100 parts by weight. However, in the present invention, as will be described later, a low hardness type silicone rubber composition having a small amount of the filler is used, such that the component (c) is 30 parts by weight or less with respect to 100 parts by weight of the component (a). On the other hand, it is particularly effective.

The magnesium carbonate as the component (d) in the present invention is used when the component (c) is mixed in a relatively small amount relative to the base polymer as the component (a), for example, the base polymer.
Even when the amount of the component (c) is about 30 parts by weight or less with respect to 100 parts by weight, the development of tackiness is effectively suppressed without causing an increase in hardness or deterioration of the original properties of rubber. It is a characteristic component in the present invention. That is,
By adding magnesium carbonate together with the component (c), the occurrence of stickiness can be effectively reduced.

As the above-mentioned magnesium carbonate, for example, a so-called basic magnesium carbonate which is industrially produced can be used, and its molecular formula is, for example, 4MgCO ₃ ·.
It is represented by Mg (OH) ₂ .4H ₂ O. Characteristically,
Specific gravity, particle size, specific surface area, pH, oil absorption, impurity metal content,
Various magnesium carbonates can be obtained depending on factors such as ignition loss. In the present invention, these various magnesium carbonates can be used.

The amount of component (d) used in the present invention is preferably in the range of 0.1 to 20 parts by weight per 100 parts by weight of component (c) described above. This is because if the amount is within this range, other physical properties (tensile strength, compression set, heat resistance, etc.) are hardly affected. If it exceeds 20 parts by weight, the physical properties and workability may be adversely affected. A more preferable compounding amount of the component (d) is in the range of 1 to 10 parts by weight.

[0024]

Embodiments of the present invention will be described below. In the following text, all “parts” indicate “parts by weight”.

Example 1 100 parts of polydimethylsiloxane (polymerization degree of about 6000) having 0.15 mol% of methylvinylsiloxane units blocked at the ends with trimethylsilyl groups, 5 parts of silicon dioxide,
10 parts of diatomaceous earth and 1 part of magnesium carbonate were put into a kneader, kneaded, and then the compound was collected, and then taken out. To this, 2,5-dimethyl-2,5-di-t-
A silicone rubber composition was prepared by uniformly mixing 1 part of butylperoxyhexane.

Further, as a comparison with the present invention, a silicone rubber composition (Comparative Example 1) was prepared in the same manner as in Example 1 except that magnesium carbonate was blended at a ratio of 25 parts.
Further, a silicone rubber composition (Comparative Example 2) was prepared without adding magnesium carbonate.

Each of the silicone rubber compositions thus obtained was subjected to press vulcanization at 170 ° C. for 10 minutes as a 2 mm thick sheet, and then as secondary vulcanization at 200 ° C. for 4 hours. Then, vulcanization was performed, and the temperature was returned to room temperature to obtain silicone rubber sheets. The physical properties of the obtained rubber sheet are JIS K 6
It investigated according to 301 (vulcanized rubber physical test method). The roll workability was evaluated by using an 8-inch test roll with a roll gap of 1 mm and 5 mm and a rubber gathering plate spacing of 20 cm. Those that can be cut with a knife or the like and that can be seated were rated as good, and those that could not be sheeted (that is, those that could stick to the roll without being seated due to the development of tackiness) were rated as poor.

Furthermore, 1 mm and 5 mm obtained at this time
The thick sheets were made 100 mm x 100 mm in size, and the surface condition of these sheets was observed to evaluate the workability. The evaluation results of these properties are shown in Table 1 together with the compounding ratio of each composition.

[0029]

[Table 1]

Example 2 100 parts of polydimethylsiloxane (polymerization degree of about 6000) having 0.15 mol% of methylvinylsiloxane units at its ends blocked with trimethylsilyl groups, and 5 parts of silicon dioxide,
10 parts of diatomaceous earth and 1 part of magnesium carbonate were put into a kneader, kneaded, and then the compound was collected, and then taken out. Platinum octanol complex was added to this so that the amount of platinum would be 15 ppm. Both ends were blocked with trimethylsilyl groups, and the viscosity at 25 ° C was 20 cS.
t methyl hydrogen polysiloxane (crosslinking agent) 2
The parts were mixed and uniformly dispersed to prepare a silicone rubber composition.

Further, as Comparative Example 3, one containing magnesium carbonate in a ratio of 30 parts and Comparative Example 4 containing no magnesium carbonate were prepared in the same manner as in Example 2.

The characteristics of each silicone rubber composition thus obtained were evaluated in the same manner as in Example 1. Table 2 shows the results.

[0033]

[Table 2]

As is clear from the measurement results shown in Tables 1 and 2, the silicone rubber compositions obtained in each of the above Examples can significantly improve workability without reducing necessary properties. did it.

The present invention can be widely applied not only to the silicone rubber which imparts the reinforcing property, but also to the system in which it is necessary to reduce the blending amount of various fillers.

[0036]

As described above, according to the silicone rubber composition of the present invention, the workability and processability of the silicone rubber composition having a low hardness, that is, a small amount of the filler can be improved by the original rubber characteristics of the silicone rubber. It is possible to improve the properties imparted by various fillers without sacrificing them.

[0037]

Claims (1)

(57) [Claims] 1. A silicone rubber composition comprising a polyorganosiloxane in which an organic group bonded to a silicon atom is an alkyl group and / or an aryl group as a base polymer, and a filler containing a reinforcing filler is compounded in the silicone rubber composition. 70% by weight or more of the agent is a silica-based filler, and magnesium carbonate is added in an amount of 0.1% by weight to 100 parts by weight of the filler.
Shi Rico <br/> Ngomu composition characterized in that blended in the range of 20 parts by weight.