JPH02251542A - Composition for foamed silicon rubber and foamed silicone rubber produced therefrom - Google Patents

Abstract

PURPOSE:To obtain a composition having remarkably extended freedom of the combination of a foaming agent and an organic peroxide and expanded allowable range of the controlling condition and capable of giving a foamed material having high expansion ratio and suitable for various uses by using a specific organopolysiloxane free from vinyl groups as a component. CONSTITUTION:The objective composition is produced by compounding (A) an organopolysiloxane of formula [R<1> is univalent hydrocarbon group free from aliphatic unsaturated group; R<2> is cycloalkyl having a ring containing >=5 constituent carbon atoms; a and b are numbers satisfying the formulas 1.95<(a)+(b)<2.01 and 0<(b)/(a)+(b)<=-0.02, (B) a foaming agent having a decomposition temperature of 40 to 280 deg.C and (C) an organic peroxide. The group R<2> of the component A is preferably cyclohexyl and the numbers (a) and (b) preferably satisfy the formula 0.0005<(b)/(a)+(b)<0.015. The amounts of the components B and C are preferably 0.5 to 20 pts.wt. and 0.5 to 5 pts.wt. per 100 pts.wt. of the component A, respectively.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a silicone rubber foam composition and a silicone rubber foam that can easily produce a spongy silicone rubber foam with a high expansion ratio.

Silicone rubber foam is a material that combines the general characteristics of silicone rubber, such as heat resistance, cold resistance, and electrical properties, with spongy elasticity. It's being used.

In this case, in order to be used more effectively in these applications, silicone rubber foam must have a high expansion ratio, be sufficiently hardened to the surface without tack, be soft and spongy, and have the characteristics of silicone rubber. It is necessary that the material does not impair its heat resistance, cold resistance, electrical properties, etc.

In order to obtain a silicone rubber foam with a good foaming state, it is important to maintain a balance between foaming and curing when heating and foaming the silicone rubber foam composition. That is, the composition for obtaining such a silicone rubber foam contains an organopolysiloxane, a blowing agent, and a curing agent (organic peroxide) for forming the silicone rubber foam. When an object is heated, the foaming agent decomposes and foams, and at the same time hardening begins due to the action of the hardening agent.At this time, if the foaming agent decomposes first, the cells collapse and the cell structure becomes uneven, which in turn causes foaming. If the decomposition of the agent is delayed and a considerable amount of the curing agent decomposes before gas is generated from the blowing agent, the expansion ratio will decrease and a non-uniform foam with a rough cell structure will result. It is therefore necessary to balance the decomposition of the blowing agent and the decomposition of the curing agent (organic peroxide), which requires careful attention in the manufacture of the foam.

For this purpose, it has been proposed to use azobis isobutyronitrile as a blowing agent (Japanese Patent Publication No. 44-4
However, this method requires a long post cure to sufficiently remove the decomposition products of the blowing agent and eliminate health and safety problems, which poses a practical problem.

Furthermore, a method using t-alkylhydrazinium salt or carbonylhydrazine as a blowing agent has been proposed (Japanese Patent Laid-Open No. 62-81420), and according to this proposal, the control conditions for obtaining a good foamed product are However, the organic peroxide to be combined with the blowing agent must be selected in consideration of its half-life temperature, curing time, scorch time, etc., and there is still room for improvement.

In this way, conventional proposals rely on a combination of a specific blowing agent and an organic peroxide, and therefore the heating temperature and time for foaming and curing are limited, making it possible to obtain a foam that can be used in a wide range of applications. There are still problems in this respect.

The present invention was made in view of the above circumstances, and provides a silicone rubber foam with a high expansion ratio that can expand the degree of freedom and control conditions for the combination of blowing agents and organic peroxides, and can be adapted to a wide range of applications. An object of the present invention is to provide a silicone rubber foam composition and a silicone rubber foam that can be obtained.

In order to achieve the above object, the inventors of the present invention have made extensive studies and found that the following general formula (1) % formula % (1 (However, in the formula, R1 is an unsubstituted or substituted-valent hydrocarbon group containing no aliphatic unsaturated group, " is a cycloalkyl group whose cyclic body has 5 or more carbon atoms, a.

This is the number. ) By using the organopolysiloxane shown in the formula, when it is foamed and cured with a foaming agent having a decomposition temperature of 40 to 280°C and an organic peroxide, the foaming ratio is high,
It is sufficiently cured from the inside to the surface, has no tack, and can form a soft, sponge-like foam. Furthermore, the selection range of blowing agents and organic peroxides is wide, and the control conditions can be greatly relaxed. This makes foam molding easier,
Furthermore, it has been found that the heat resistance, cold resistance, and electrical properties of silicone rubber are not impaired.

That is, although organopolysiloxanes containing vinyl groups are usually used for crosslinking silicone rubber, the use of organopolysiloxanes containing vinyl groups is not preferable for the production process of silicone rubber foams; The present invention has been completed based on the discovery that the object of the present invention can be effectively achieved by using the organopolysiloxane of the above-mentioned formula (1) which does not have any of the following.

Therefore, the present invention provides (a) an organopolysiloxane represented by the above general formula (11), (b) a decomposition temperature of 40 to 280°C.
The present invention provides a silicone rubber foam composition comprising a blowing agent and (c) an organic peroxide, and a silicone rubber foam obtained by foaming and curing the composition.

The present invention will be explained in more detail below.

As mentioned above, the organopolysiloxane component (a) constituting the silicone rubber composition of the present invention has the following general formula (1) % formula % (1) (wherein R1 represents an aliphatic unsaturated group). R1 is an unsubstituted or substituted-valent hydrocarbon group that does not contain 5 carbon atoms in the cyclic body.
The above cycloalkyl group, a.

This is shown in .

Here, R1 in the above formula (1) specifically includes an alkyl group such as a methyl group, an ethyl group, a propyl group, a butyl group,
Selected from aryl groups such as phenyl group and tolyl group, chloromethyl group, trifluoropropyl group, cyanoethyl group, etc. in which some or all of the hydrogen atoms bonded to the carbon atoms of these groups are substituted with halogen atoms, cyano groups, etc. unsubstituted or substituted which does not contain the same or different aliphatic unsaturated groups
and valence hydrocarbon groups.

Further, examples of the cycloalkyl group in which the cyclic body of R2 in the above formula (1) has 5 or more carbon atoms include a cyclopentyl group, a cyclohexyl group, and a cycloheptyl group.

Examples include cyclooctyl group, and one or more of these may be present. Among these, cyclohexyl group is preferred in view of easy availability of raw materials and ease of synthesis.

The present invention uses an organopolysiloxane that does not contain vinyl groups, and if it contains vinyl groups, it becomes difficult to form a good foamed state, as shown in the experiments described below. This is considered to be because the crosslinking reaction of the vinyl groups due to the decomposition of the organic peroxide is so fast that most of the crosslinking reaction ends before the blowing agent starts decomposing. In this case, if you reduce the amount of peroxide added in an attempt to slow down crosslinking, the surface of the foam will not be sufficiently vulcanized, causing tackiness and being easily scratched, as well as causing outgassing, making it impossible to obtain a good foam. It turns out. On the other hand, the above-mentioned organopolysiloxane using the R2 group does not have such disadvantages and has excellent surface vulcanizability.

In addition, (in formula 11, a and b are 1.95<a+b<2.01
Furthermore, the organopolysiloxane of formula (1) used in the present invention has dimethylsiloxane units ((CH
:+)zsiO) units as the majority, and diphenylsiloxane units ((C,)l,)zsjO) units,
Methylphenylsiloxane unit ((CHi) (CJs
) 5in) units and the like is preferably contained within 20 mol %.

Further, as the blowing agent to be added as component (b) to the composition of the present invention, any compound having a decomposition temperature of 40 to 280°C can be used. In this case, if the decomposition temperature of the blowing agent is lower than 40'C, the decomposition of the blowing agent will precede curing, the cells will collapse, and the cell structure will become non-uniform.
When the temperature exceeds 0°C, the foaming ratio decreases even if a foaming aid is used in combination.

Examples of such blowing agents include ammonium carbonate (
decomposition temperature 30-60°C), inorganic blowing agents such as sodium bicarbonate (decomposition temperature 60-150°C), diazoaminobenzene (decomposition temperature 95-115°C), azodicarboxylic acid amide (decomposition temperature 190-195°C), Barium azodicarboxylate (decomposition temperature 240-250°C), trihydrazine triazine (decomposition temperature 260-280°C), p-1 luenesulfonyl hydrazide (decomposition temperature 105°C), 4
．． 4-oxybis(benzenesulfonylhydrazide)
(decomposition temperature: 155-160°C), dinitrosopentamethylenetetramine (decomposition temperature: 205°C), and furthermore, 5-phenyltetrazole, t-butylhydrazinium chloride, di-t-butylhydrazinium sulfate, etc. Examples include carbonylhydrazine compounds such as alkylhydrazinium salts, 2-propenoic acid hydrazide, and acetylhydrazine, and one or more of these can be used in combination.

The blending amount can be appropriately selected depending on the purpose of use and the blending amount of other components, but organopolysiloxane 100,! The amount is preferably 0.5 to 20 parts by weight based on the placing part. If it is less than 0.5 parts by weight, it will be difficult to form a soft spongy foam with a high expansion ratio, and if it exceeds 20 parts by weight, the physical properties of the foam will deteriorate. may decrease.

Furthermore, the organic peroxide as component (iii) is commonly used as a catalyst to promote heat curing of silicone rubber foam compositions.

Here, specific examples of the organic peroxide include benzoyl peroxide, monochlorobenzoyl peroxide, p-methylbenzoyl peroxide, 2,4-dichlorobenzoyl peroxide, t-butyl perbenzoate, dicumyl peroxide, .5-bis-(t
-butylperoxy)-2,5-dimethylhexane, 2
．． Dicarbonates such as 5-bis-(t-butylperoxy)-2,5-dimethylhexyne, cimilistyl peroxydicarbonate, dicyclododesilyl oxydicarbonate, t-butyl monoperoxycarbonates, and the following: Examples include compounds represented by formula (2) (wherein R is a monovalent hydrocarbon group having 3 to 10 carbon atoms);
More than one species can be used.

The blending amount can be appropriately selected depending on the type of component, the blending amount of other components, etc., but it is preferably 0.1 to 5 parts by weight per 100 parts by weight of organopolysiloxane. If the amount is less than 0.1 part by weight, the surface of the foam will be insufficiently hardened, causing tackiness and being easily scratched, and furthermore, the decomposition gas of the blowing agent will escape, making it impossible to form a foam with a high expansion ratio. There is. On the other hand, if it exceeds 5 parts by weight, the physical properties of the resulting foam may deteriorate.

It is preferred that the composition of the present invention further contains a finely powdered silica filler. This fine powder silica filler is added for the purpose of reinforcing, thickening, improving processability, and increasing the amount of silicone rubber foam. Examples include fumed silica, wet silica, fumed silica with a hydrophobic surface treatment, and wet silica. One or more types of silica, quartz fine powder, diatomaceous earth, etc. may be used, and among them, those having a specific surface area of 1 rrf/g or more are preferably used.

Here, the blending amount of the fine powder silica filler is 5 to 500 parts by weight per 100 parts by weight of the organopolysiloxane of component (A).
Parts by weight are preferred, especially 10 to 300 parts by weight. If the amount of the fine powder silica filler is less than 5 parts by weight, reinforcing properties may be poor, and if it exceeds 500 parts by weight, foaming may become insufficient.

Furthermore, in addition to the above components, the silicone rubber foam composition of the present invention may contain other optional components depending on the purpose, use, etc., such as low molecular weight siloxane with a degree of polymerization of 100 or less, silanol group-containing silane, alkoxysilane, etc. Dispersants such as group-containing silane, heat resistance improvers such as iron oxide, cerium oxide, iron octylate, titanium oxide, various pigments for coloring,
Additives that are normally added to silicone rubber foam compositions can be used, such as flame retardant aids such as platinum compounds and palladium compounds. Incidentally, these optional components may be added to the silicone rubber foam composition of the present invention in usual amounts.

There is no particular restriction on the order in which the silicone rubber foam composition of the present invention is blended, and it can be blended in accordance with a conventional method.There is also no particular limitation on the mixing method such as kneading, for example, by using two rolls, a kneader, etc.
, Banbury mixer, etc. may be used.

The silicone rubber foam composition thus obtained can be made into a silicone rubber foam of any shape depending on the intended use by normal pressure foaming such as extrusion calendering or mold foaming.

In this case, the foam curing conditions are 100 to 300
The foaming may be carried out by heating at a temperature of 50° C. for 5 seconds to 30 minutes, or stenbucuring may be carried out in which the temperature is divided into two or more stages. In addition, post-vulcanization conditions are usually 150 to 250°C.
The silicone rubber foam composition of the present invention allows silicone rubber foams in a good foamed state to be obtained under a wide range of manufacturing conditions.

EXAMPLES Hereinafter, the present invention will be specifically explained with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples.

In each example, parts indicate parts by weight, and viscosity indicates a value measured at 25°C.

[Example 1. Comparative Example 1] Both ends of the molecular chain were blocked with trimethylsilyl groups (C)
1i) 99.85 mol% of tslO units and R shown in Table 1
R”(CHs)SiOo with 1 group, unit 0.15
100 parts of organopolysiloxane with a viscosity of about 10.000.0OOcs and fumed silica (
Product name Aerosol R...972. (manufactured by Tegussa) and then kneaded uniformly with two rolls to obtain a base compound.

This base compound contains 2.4- as an organic peroxide.
0.8 parts of a 50% paste of silicone oil 800cs of dichlorobenzoyl peroxide and 5 parts of azodicarbonamide as a blowing agent were added and further kneaded to obtain a composition.

Next, after sufficiently degassing the above composition, it was molded to obtain a sheet with a thickness of 3 dragons, and this sheet was heated in an oven at 200°C.
It was foamed and cured by heat treatment for 15 minutes to obtain a silicone rubber foam.

The foaming state, color tone, and surface state of the silicone rubber foam thus obtained were observed, and the foaming ratio was also measured. The results are shown in Table 1.

[Example 2] Actual tlE, 1.2 parts of p-methylbenzoyl peroxide 50% paste as a peroxide and 5 parts of azodicarbonamide as a blowing agent were added to the base compound used in Example 1.
1 part and further kneaded to obtain a composition.

Next, after sufficiently degassing the above composition, it was molded to obtain a sheet with a thickness of 3 dragons, and this sheet was heated in an oven at 200°C.
The foam was cured by heat treatment for 15 minutes to obtain a silicone rubber foam.

The foaming state, color tone, and surface state of the silicone rubber foam thus obtained were observed, and the foaming ratio was measured.

The results are shown in Table 1.

The composition for silicone rubber foam of the present invention does not necessarily use special blowing agents and organic peroxides, but uses commonly used blowing agents and organic peroxides. By simply doing this, it is possible to obtain a silicone rubber foam that is sufficiently cured to the surface at a high expansion ratio by relaxing the control conditions for foam curing, and is soft without tack.

Patent applicant: Shin-Etsu Chemical Co., Ltd.

Claims (1)

[Claims] 1. (a) The following general formula (1) R^1aR^2bSiO_[_4_-_(_a_+_b
_)]_/_2(1) (However, in the formula, R^1 is an unsubstituted or substituted monovalent hydrocarbon group that does not contain an aliphatic unsaturated group, R^2
is a cycloalkyl group whose cyclic body has 5 or more carbon atoms, a
, b is 1.95<a+b<2.01 and b is 0<b/
This is a number satisfying (a+b)≦−0.02. ) an organopolysiloxane represented by (b) a blowing agent having a decomposition temperature of 40 to 280°C; (c)
A composition for silicone rubber foam, characterized by containing an organic peroxide. 2. A silicone rubber foam obtained by foaming and curing the foam composition according to claim 1.