JPH0552857B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention provides a steam-resistant silicone rubber composition,
In particular, the present invention relates to a steam-resistant silicone rubber composition suitable for use in O-rings, gaskets, etc., which has both low compression set and oil resistance. (Prior art) Silicone rubber has excellent electrical properties, heat resistance, cold resistance, weather resistance, and mold release properties, and is also physiologically inert. Although it is used in an extremely wide range of industries, it has a skeletal structure mainly composed of siloxane bonds, so it is not suitable for hot water,
It has a disadvantage that it has low steam resistance, and its siloxane bonds are cleaved especially when it is accompanied by ions such as acids and alkalis. Therefore, for silicone rubber molded products used in applications that are exposed to high-temperature steam or high-temperature hot water, the silicone rubber composition used as the raw material must be formulated with a special vulcanizing agent, or the silicone rubber molded product must be filled with a special vulcanizing agent. Consideration has been taken to use especially high-purity silica as the agent, but in severe conditions this may not be sufficient and the use of silicone rubber may have to be abandoned. Yes, this measure is required. (Structure of the Invention) The present invention relates to a silicone rubber which solves such disadvantages and has particularly excellent steam resistance.

[Formula] (Here, R ¹ is a group selected from a methyl group, 3,3,3-trifluoropropyl group, phenyl group, and a vinyl group, of which 0.1 to 1 mol% is a vinyl group, and a is 1.98 ~
2.02) 100 parts by weight of organopolysiloxane raw rubber, (B) general formula (Here, R ² is an aliphatic unsaturated monovalent hydrocarbon group, R ³
is a substituted or unsubstituted saturated monovalent hydrocarbon group, R ⁴
is a hydrogen atom or a monovalent hydrocarbon group having 1 to 4 carbon atoms, b = 0.05 to 1, c = 0 to 2, d = 0.04 to 2,
b + c + d = 1 to 3, m = 2 to 50) 0.1 to 20 parts by weight of organopolysiloxane, (C) general formula

[Formula] (where R ⁵ is a substituted or unsubstituted monovalent hydrocarbon group having 1 to 6 carbon atoms, e = 1 to 2.5) The specific surface area of the surface treated with organosiloxane is 50 m ² /g or more Reinforcing inorganic filler 10~
It is characterized by consisting of 100 parts by weight and (D) a curing agent. To explain this, the present inventors have conducted various studies on the modification of silicone rubber, particularly on silicone rubber compositions for obtaining silicone rubber molded articles with excellent steam resistance. Polysiloxane raw rubber is surface-treated with an organosiloxane containing an aliphatic unsaturated monovalent hydrocarbon group such as a vinyl group, an allyl group, an acrylic group, and a hydroxyl group or an alkoxy group in its molecule, and an organosiloxane as a filler. It was discovered that a composition to which a silica-based filler was added produces a silicone rubber molded product exhibiting excellent steam resistance, and by further research on this, the present invention was completed. The organopolysiloxane raw rubber as component (A) constituting the composition of the present invention has the general formula shown above.

[Formula] This organic group R ¹ is selected from a methyl group, a 3,3,3-trifluoropropyl group, a phenyl group, and a vinyl ^group . In addition to the generally known effects of reducing sulfur properties, mechanical strength, and compression set, the objective of the present invention is to improve steam resistance (prevention of siloxane cracking and reversion due to steam).
% vinyl groups is required. This organopolysiloxane is synthesized by a well-known method, for example. It can be obtained by ring-opening copolymerization of a mixture of low-molecular cyclic oligomers such as in the presence of an alkali or acid catalyst, equilibration, neutralization and deactivation of the catalyst, and stripping. The ratio of organic groups in the organopolysiloxane thus produced can be varied over a wide range by varying the blending ratio of the above-mentioned cyclic bodies depending on the properties required for this polymer. The terminal of this molecular chain is (CH ₃ ) ₃ SiO _1/2 , (CH ₂ =CH)
(CH ₃ ) ₂ SiO _1/2 , (C ₆ H ₅ ) (CH ₃ ) (CH ₂ = CH)
It may be any of SiO _1/2 , ≡SiOH, ≡SiC ₂ H ₅ and the like, and there are no particular restrictions on this, but it is preferable that it contains a vinyl group. Also, since this organopolysiloxane is a raw rubber-like material, its degree of polymerization is said to be at least 1000 or higher, but this means that if it is too high, the processability of compositions using it as a base material will deteriorate. So this is
It is preferably in the range of 5,000 to 10,000. The organopolysiloxane as component (B) constituting this composition has the above formula. R ² is an aliphatic unsaturated monovalent hydrocarbon group selected from a vinyl group, an allyl group, an acrylic group, a methacryl group, etc., R ³ is a methyl group,
A monovalent hydrocarbon group such as ethyl group, 3,3,3-trifluoropropyl group, phenyl group, or a substituted hydrocarbon group in which the hydrogen atom bonded to the carbon is replaced with another group, R ⁴ is a hydrogen atom or methyl This refers to an alkyl group having 1 to 4 carbon atoms selected from ethyl, propyl, and butyl groups, and which has a hydroxyl group represented by ( ^OR4 ) in the above formula in its molecule or It must have an alkoxy group and be strongly bonded to the inorganic filler described below, which is an essential requirement from the viewpoint of maintaining the initial rubber physical properties of the composition of the present invention and improving the steam resistance of this composition. be done. This organopolysiloxane is produced by co-hydrolysis, partial co-hydrolysis of various organosilanes,
Alternatively, it can be produced by ring-opening copolymerization of a low-molecular cyclic oligomer similar to the method for producing component (A) above, and the molecular structure may be either linear or molecular; If it is a high polymer, the initial rubber physical properties and heat resistance of the composition of the present invention will be deteriorated, so it is preferable to use a polymer with a degree of polymerization of 50 or less.
Note that if the amount of component (B) added to component (A) is too excessive, the initial rubber properties of the composition will deteriorate, making it difficult to mold, and in some cases, the molded product may become deformed. If the amount is too small, the effect of the addition will be insufficient, so the amount is preferably 0.1 to 20 parts by weight per 100 parts by weight of component (A). Next, the reinforcing inorganic filler as component (C) constituting the composition of the present invention is atomized silica, precipitated silica, silica aerogel, etc., which are well known as reinforcing fillers for silicone rubber, etc. If the specific surface area of these is too small, the effect of reinforcing properties and imparting steam resistance will be lost.
It must have a specific surface area of 50 m ³ /g or more. In addition, this filler has the above-mentioned general formula

It is said to be treated with an organopolysiloxane represented by the formula, but the hydrophobized filler permeates from the outside and greatly reduces the amount of water adsorbed on its surface. Moisture-based cracking is significantly reduced. The organosiloxanes used here are (CH ₃ ) ₂ SiO, (CH ₃ ) (CH ₂ =CH)SiO, (CH ₃ )
(C ₆ H ₅ )SiO, CH ₃ SiO _3/2 , and (CH ₂ =CH)SiO _3/2 have organosiloxy groups, and these processing agents can be used in combination of two or more of them. However, this includes R ₃ SiO _1/2 where e in the formula is 3.
are excluded. In addition, the treatment of this inorganic filler with the organosiloxane described above can be carried out in the gas phase,
Although it can be carried out in any liquid phase, it is effective to use a fatty salt of Fe or Sn as a catalyst if necessary. In addition, (A) of this inorganic filler
The amount added to the ingredients is 10 per 100 parts by weight of component (A).
If less than 100 parts by weight, the desired strength of the rubber composition will be insufficient, and if more than 100 parts by weight is added, kneading will become impossible and the strength will decrease as a result.
The amount is preferably 10 to 100 parts by weight per 100 parts by weight of component (A). The curing agent as component (D) constituting the composition of the present invention may be any known curing agent, including organic peroxides,
Examples include organohydrodiene polysiloxanes having three or more ≡SiH groups in one molecule, which is known as so-called addition reaction crosslinking, and platinum-based catalysts. As this organic peroxide, in order to impart excellent steam resistance to the silicone rubber cured by this organic peroxide, an alkyl peroxide is preferred because its decomposition residue is easily removed. Examples include di-t-butyl peroxide, 2,5-dimethyl-2,5-(t-butylperoxy)hexane, and cumyl-t-butyl peroxide. In addition, the organohydrodiene polysiloxane and platinum-based catalyst as the addition reaction crosslinking agent described above may be conventionally known ones, and therefore there is no reason to specifically limit them. Since no decomposition residue of the sulfurizing agent is produced, the cured silicone rubber molded article is given excellent steam resistance. However, this addition reaction type silicone rubber molded product has the disadvantage of being prone to scorch, so when this molding is performed by molding, it is vulcanized with the alkyl peroxide described above, and when it is extrusion molded, it is vulcanized with the above-mentioned alkyl peroxide. Reactive vulcanization is preferred. To prepare the composition of the present invention, first, the above-mentioned (A) to
(C) Ingredients are mixed uniformly, and this is done by mixing a predetermined amount of each ingredient using two rolls, a bread parry mixer,
All you have to do is mix it in a kneader or other kneader, and if necessary, use various softeners (wetters), etc.
Pigments, mold release agents, flame retardants, heat resistance improvers, acid acceptors,
Furthermore, various known additives such as extender fillers are added, but these are carefully controlled to ensure their purity, especially water-soluble components such as acids and alkalis, so as not to adversely affect the steam resistance of the desired silicone rubber molded product. It is preferable that it does not include. Note that as this softener, a low-molecular siloxane containing a silanol group, such as diphenylsilanediol, is usually used, but in the composition of the present invention, the inorganic filler as component (C) is pre-organized. Since the surface is treated with siloxy groups, it is not necessary to add this softener especially if the amount added is relatively low. The composition of the present invention is made by adding the above-mentioned curing agent as the component (D) to this homogeneous mixture of components (A) to (C), and this curing agent is the component of this composition. The composition can be selected depending on the molding method, and the composition obtained in this way can be made into a silicone rubber molded product by compression mode, transfer molding, injection molding, extrusion molding, impregnation, or other molding methods. Ru. Molded articles made from the composition of the present invention can be used for various purposes in the same way as conventional silicone rubber molded articles, but they have particularly excellent steam resistance and are resistant to high-pressure steam and hot water. Since it can be used in places that are exposed to long-term exposure, it can be put to practical use in O-rings, gaskets, boots, etc. for automobile parts, aircraft parts, and various household appliance parts. Furthermore, this molded body is
By adding components (B) and (C), it exhibits low compression set properties and excellent oil resistance, so it can be used in fields that require this type of property. If a platinum compound is added to impart excellent flame retardancy, the added value can be further increased. Next, examples of the present invention will be given. In the examples, parts are parts by weight, Me is a methyl group, and Vi is a vinyl group. The steam resistance shown as the experimental results was measured by the following method. This shows the results. (Steam resistance) Pure water 5 was charged in an autoclave with an internal volume of 20 mm, and a No. 2 dumbbell for tensile strength measurement conforming to JIS K6301 was placed in the autoclave with the lower part of the dumbbell approximately 5 cm above the water surface and heated. , keep the steam temperature at 175℃ and leave it. In addition, regarding this compression set, JIS
Compressed by 25% in accordance with K6301 and then left compressed while steaming this dumbbell to 175%
Measurements were made while keeping the temperature at ℃. Example 100 parts of methyl vinyl raw rubber with an average degree of polymerization of 10,000 and consisting of 99.48 mol% of Me ₂ SiO units, 0.50 mol% of MeViSiO units, and 0.02 mol% of ViMe ₂ SiO _1/2 units was added with an average compositional formula of

Three parts of α,ω-dihydroxymethylvinylpolysiloxane oil represented by the formula were uniformly mixed in a kneader. This mixture is then given the formula

Gradually add 50 parts of fumed silica whose surface has been treated with an organosiloxane having a dimethylsiloxy group represented by the formula and have a specific surface area of 150 m ² /g to form a uniform compound. Heat treated at 150℃ for 1 hour, added 0.5 part of di-t-butyl peroxide per 100 parts of this compound, kneaded with two rolls, and heated for 10 minutes at 170℃ and 50Kg/ ^cm2. Pressure Now create a sheet with a thickness of 2 mm, and press 200
After 4 hours at ℃, vulcanization was performed (hereinafter referred to as sample A).
). For comparison, a sheet (hereinafter referred to as sample B) was prepared in the same manner as above without adding α,ω-dihydroxymethylvinylpolysiloxane oil as component (B). A sheet ( A sample (hereinafter referred to as sample C) was prepared. Next, after measuring the initial properties of the three types of sheets made in this way, their steam resistance was tested using the method described above, in which they were treated in steam at 175°C for 72 hours.
A sample was molded according to JIS K6301 and the compression set in steam was measured under the same conditions.
The results shown in the table were obtained.

【table】

【table】

Claims (1)

[Claims] 1 (A) General formula R ¹ _a SiO _4-a/2 (where R ¹ is a group selected from methyl group, 3,3,3-trifluoropropyl group, phenyl group, and vinyl group) and 0.1 to 1 mol% of it is vinyl group, a is 1.98
(B) General formula (Here, R ² is an aliphatic unsaturated monovalent hydrocarbon, R ³
is a substituted or unsubstituted saturated monovalent hydrocarbon group,
R ⁴ is a hydrogen atom or a monovalent hydrocarbon group having 1 to 4 carbon atoms, b = 0.05 to 1, c = 0 to 2, d = 0.04
-2, b+c+d=1-3, m=2-50)
0.1 to 20 parts by weight, (C) General formula R ⁵ _e SiO _4-e/2 (where R ⁵ is carbon number 1 to
6 substituted or unsubstituted monovalent hydrocarbon group, e=
1 to 2.5) A reinforcing inorganic filler having a specific surface area of 50 m ² /g or more and 10 to 100 parts by weight (D) of a hardening agent. Silicone rubber composition.