JPH0515731B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a silicone rubber foam composition and a silicone rubber foam from which a spongy silicone rubber foam with a high expansion ratio can be easily obtained. PRIOR ART AND PROBLEMS TO BE SOLVED BY THE INVENTION Silicone rubber foams have spongy elasticity added to the general characteristics of silicone rubber, such as heat resistance, cold resistance, and electrical properties. Used for a wide range of purposes. 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 any tackiness, 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. Here, 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 hardening agent decomposes before gas is generated from the foaming agent, the foaming ratio will decrease.
The result is a heterogeneous foam with a coarse cell structure. Therefore,
It is necessary to balance the decomposition of the blowing agent with the decomposition of the curing agent (organic peroxide), which requires great care in the manufacture of the foam. For this purpose, it has been proposed to use azobis isobutyronitrile as a blowing agent (Japanese Patent Application Laid-open No. 44-461), but this method sufficiently removes the decomposition products of the blowing agent and is safe. In order to eliminate hygiene problems, it is necessary to perform a long post-cure, which poses a practical problem. In addition, a method using t-alkylhydrazinium salt or carbonylhydrazine as a blowing agent has been proposed (Japanese Patent Application Laid-Open No. 1981-81420), and according to this proposal, the control conditions for obtaining a good foamed product are However, the organic oxide 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 create foams that can be used in a wide range of applications. There are still problems in terms of acquisition. 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. Means and Effects for Solving the Problems The present inventors have made intensive studies to achieve the above object, and as a result, the following general formula (1) is used as the organosiloxane constituting the silicone rubber foam composition. (However, in the formula, R ¹ is an unsubstituted or substituted monovalent hydrocarbon group that does not contain an aliphatic unsaturated group, and R ² has 3 or more carbon atoms and has a carbon-carbon double bond bonded to a silicon atom. A monovalent unsubstituted or substituted hydrocarbon group or a monovalent unsubstituted or substituted hydrocarbon group having 5 or more carbon atoms and having a carbon-carbon double bond via at least one carbon atom from a silicon atom,
a, b are 1.95<a+b<2.01 and b is (a+
b) The number is 2 mol% or less of the amount. ) By using the organopolysiloxane shown in the figure above, when it is foamed and cured with a foaming agent with a decomposition temperature of 40 to 280°C and an organic peroxide, the foaming ratio is high and the foam can be fully expanded from the inside to the surface. It can be cured to form a soft, spongy foam with no tackiness, and there is a wide selection range of blowing agents and organic peroxides, and the control conditions can be greatly relaxed, making foam molding easy. It has been found that the heat resistance, cold resistance, and electrical properties of silicone rubber are not impaired. That is, although vinyl group-containing organopolysiloxanes are usually used for crosslinking silicone rubber, the use of such vinyl group-containing organopolysiloxanes is not preferable for the manufacturing method of silicone rubber foams. The present inventors have discovered that the objects of the present invention can be effectively achieved by using the organopolysiloxane of formula (1) described above that does not have a vinyl group, and have thus completed the present invention. Therefore, the present invention provides (a) an organopolysiloxane represented by the above general formula (1), and (b) a decomposition temperature of 40 to 280°C.
The present invention provides a silicone rubber foam composition comprising a blowing agent and (iii) 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 as the component (a) constituting the silicone rubber composition of the present invention has the following general formula (1). (However, in the formula, R ¹ is an unsubstituted or substituted monovalent hydrocarbon group that does not contain an aliphatic unsaturated group, and R ² is a carbon-carbon double bond that has 3 or more carbon atoms and is bonded to a silicon atom.) or a monovalent unsubstituted or substituted hydrocarbon group having 5 or more carbon atoms and having a carbon-carbon double bond via at least one carbon atom from a silicon atom. , a, b are 1.95<a+b<2.01 and b is (a
+b) is a number that is 2 mol% or less of the amount. ). Here, R ¹ in the above formula (1) specifically includes an alkyl group such as a methyl group, an ethyl group, a propyl group, a butyl group, a cycloalkyl group such as a cyclohexyl group, an aryl group such as a phenyl group, and a tolyl group. , the same or similar aliphatic groups selected from chloromethyl groups, trifluoropropyl groups, cyanoethyl groups, etc. in which some or all of the hydrogen atoms bonded to carbon atoms of these groups are substituted with halogen atoms, cyano groups, etc. Mention may be made of unsubstituted or substituted monovalent hydrocarbon groups that do not contain saturated groups. In addition, examples of monovalent unsubstituted or substituted hydrocarbon groups in which the number of carbon atoms in R ² in the above formula (1) is 3 or more and have a carbon-carbon double bond on the carbon bonded to a silicon atom include 1 -hexenyl group, 1-ethyl-1-
butenyl group, 1-octenyl group, styryl group, 1
-methylene-2-propenyl group, etc., and one or more of these may be present. Among these, 1-ethyl-1-butenyl group is preferred from the viewpoint of easy availability of raw materials and ease of synthesis. Furthermore, examples of monovalent hydrocarbon groups having 5 or more carbon atoms and having a carbon-carbon double bond from a silicon atom through at least one carbon atom include:
Examples include ethylidene norbornyl group, methylene norbornyl group, dicyclopentenyl group, 4-pentenyl group, 4-hexenyl group, cyclooctenyl group, and one or more of these may be present. Among these, ethylidene norbornyl group is preferred from the viewpoint of easy availability of raw materials and ease of synthesis. Note that R ² may contain two or more of the above-mentioned groups. As mentioned above, the present invention uses an organopolysiloxane that does not contain vinyl groups, and if it contains vinyl groups, it will be difficult to form a good foaming state, as shown in the experiment described below. Become. 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 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 R ² group does not have such disadvantages and has excellent surface vulcanizability. In formula (1), a and b are numbers such that 1.95<a+b<2.01 and b is 2 mol% or less of the amount of (a+b), more preferably 0.05 to 1.5 mol%. If the content of b is more than 2 mol %, physical properties such as heat resistance will deteriorate. Furthermore, the organopolysiloxane of formula (1) used in the present invention has dimethylsiloxane units [(CH ₃ ) ₂ SiO units] as a major part, and diphenylsiloxane units [(C ₆ H ₅ ) ₂ SiO units], methylphenylsiloxane units [(CH ₃ )(C ₆ H ₅ )SiO units], etc., and one or more of them are 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, causing the cells to collapse and the cell structure to become non-uniform; if it exceeds 280°C, even if a blowing aid is used, Foaming ratio decreases. Types of such blowing agents include inorganic blowing agents such as ammonium carbonate (decomposition temperature 30-60°C), sodium bicarbonate (decomposition temperature 60-150°C), diazoaminobenzene (decomposition temperature 95-115°C), Azodicarboxylic acid amide (decomposition temperature 190-195℃), barium azodicarboxylate (decomposition temperature 240-250℃), trihydrazine triazine (decomposition temperature 260-280℃),
p-Toluenesulfonyl hydrazide (decomposition temperature
105℃), 4,4-oxybis(benzenesulfonylhydrazide) (decomposition temperature 155-160℃), dinitrosopentamethylenetetramine (decomposition temperature 205℃)
etc., and t-alkylhydrazinium salts such as 5-phenyltetrazole, t-butylhydrazinium chloride, di-t-butylhydrazinium sulfate, and carbonylhydrazine such as 2-propenoic acid hydrazide and acetylhydrazine. Examples include compounds, and these can be used alone or in combination of two or more. The amount of the organopolysiloxane may be selected depending on the purpose of use and the amount of other components.
It is preferably 0.5 to 20 parts by weight per 100 parts by weight.
If it is less than 0.5 part by weight, it will be difficult to form a soft spongy foam with a high expansion ratio. If it exceeds 20 parts by weight, the physical properties of the foam may deteriorate. 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 chloride, 2,4-dichlorobenzoyl peroxide, t-butyl perbenzoate, dicumyl peroxide, 2, 5-bis-(t-butylperoxy)-2,5-dimethylhexane, 2,5-bis-(t-butylperoxy)-2,5-dimethylhexane, dimyristylperoxydicarbonate, dicyclo Dicarbonates such as dodecyl peroxydicarbonate, t-butyl monoperoxycarbonate, the following formula (2) (However, in the formula, R is a monovalent hydrocarbon group having 3 to 10 carbon atoms.) Compounds represented by the following are exemplified, and one or more of these 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 the organopolysiloxane.
If the amount is less than 0.1 part by weight, the surface of the foam will not be sufficiently hardened, causing tackiness and being easily scratched.
Furthermore, the decomposed gas of the blowing agent may escape, making it impossible to form a foam with a high expansion ratio. on the other hand,
If it exceeds 5 parts by weight, the physical properties of the resulting foam may deteriorate. It is preferable to further incorporate a finely powdered silica filler into the composition of the present invention. This fine powder silica filler is added for the purpose of reinforcing, thickening, improving processability, and increasing the amount of silicone rubber foam.For example, fumed silica, wet silica, fumed silica whose surface has been hydrophobically treated, wet silica, etc. One or more types of quartz fine powder, diatomaceous earth, etc. may be used, and among them, those having a specific surface area of 1 m ² /g or more are preferably used. Here, the blending amount of the fine powder silica filler is 5 parts by weight per 100 parts by weight of the organopolysiloxane of component (A).
~500 parts by weight, especially 10-300 parts by weight are preferred. If the amount of fine powder silica filler blended is less than 5 parts by weight, reinforcing properties may be poor, and if it exceeds 500 parts by weight, foaming may be 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, alkoxy Dispersants such as group-containing silane, heat resistance improvers such as iron oxide, cerium oxide, iron octylate, titanium oxide, various pigments for coloring, flame retardant aids such as platinum compounds, palladium compounds, etc., usually silicone rubber. Additives added to the foam composition can be used. Incidentally, these optional components can be added to the silicone rubber foam composition of the present invention in usual amounts. There is no particular restriction on the order of compounding the silicone rubber foam composition of the present invention, and the compounding may be carried out according to a conventional method, and there is no particular restriction on the mixing method such as kneading, for example, using a two-roll, kneader, Banbury mixer, etc. Can be used. The silicone rubber foam composition thus obtained can be made into a silicone rubber foam of any shape depending on the application by normal pressure foaming such as extrusion calendering or mold foaming. In this case, the foam curing conditions are 100
Heat and foam at a temperature of ~300℃ for 5 seconds to 30 minutes, or
Alternatively, a step cure may be performed in which the temperature is divided into two or more stages. In addition, the post-crosslinking conditions are as follows:
Usually, heat treatment is performed at 150 to 250°C for 0 to 10 hours, and the silicone rubber foam composition of the present invention can obtain silicone rubber foam in a good foamed state under a wide range of manufacturing conditions. be. Effects of the Invention As explained above, the silicone rubber foam composition of the present invention does not necessarily use special blowing agents and organic peroxides, but uses commonly used blowing agents and organic peroxides. In addition, by relaxing the control conditions for foam curing, it is possible to obtain a silicone rubber foam that is sufficiently hardened to the surface at a high expansion ratio and is soft without tack. 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 the viscosity is at 25°C.
Shows the measured values at . Examples 1 to 4, Comparative Examples 1 and 2 Both ends of the molecular chain were blocked with trimethylsilyl groups (CH ₃ ) ₂ SiO unit 99.85 mol% and R ² shown in Table 1
After mixing 100 parts of an organopolysiloxane with a viscosity of about 10000000 cs and 0.15 mol% of ^R2 ( _CH3 )SiO _0.5 units having a group and 40 parts of humid silica (trade name Aerosal R-972, manufactured by Tegutsusa),
The mixture was uniformly kneaded using two rolls to form a base compound. 2.4 as peroxide in this base compound
- 0.8 parts of dichlorobenzoyl peroxide 50% paste and 0.9 parts of peroxide, azodicarbonamide as a blowing agent (trade name Cellmic CAP,
5 parts (manufactured by Sankyo Kasei Co., Ltd.) were added and further kneaded to obtain a composition. Next, after sufficiently degassing the above composition, it is molded to obtain a sheet with a thickness of 3 mm, and this sheet is heated in an oven at 200°C for 15 minutes to foam.
It was cured 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.

[Table] From the results in Table 1, the compositions of comparative examples containing dimethylpolysiloxane or methylpolysiloxane containing vinyl groups have poor foaming properties and are not practical, whereas the silicone rubber foam of the present invention The foam obtained from the composition has a good expansion ratio and is soft.
It was observed that the surface was sufficiently cured. Example 5, Comparative Examples 3 and 4 The amount of 1-ethyl-1-butenyl group in R ² is 0 to 7.
A silicone rubber foam was obtained in exactly the same manner as in Example 1 except that the mol% was changed, and its properties were evaluated. The results are shown in Table 2.

[Table] Example 6, Comparative Example 5 A silicone rubber foam was obtained in exactly the same manner as in Example 3, except that the amount of ethylidene norbornyl group was changed in the range of 0 to 7 mol %, and its properties were evaluated. The results are shown in Table 3.

【table】

Claims (1)

[Claims] 1 (a) The following general formula (1) (However, in the formula, R ¹ is an unsubstituted or substituted monovalent hydrocarbon group that does not contain an aliphatic unsaturated group, and R ² is a carbon-carbon double bond that has 3 or more carbon atoms and is bonded to a silicon atom.) or a monovalent unsubstituted or substituted hydrocarbon group having 5 or more carbon atoms and having a carbon-carbon double bond via at least one carbon atom from a silicon atom. , a, b are 1.95<a+b<
2.01 and b is 2 mol% or less of the amount of (a+b). A silicone rubber foam composition comprising: (b) a blowing agent having a decomposition temperature of 40 to 280°C; and (c) an organic peroxide. 2. A silicone rubber foam obtained by foaming and curing the foam composition according to claim 1.