JP5581764B2 - Silicone rubber composition and method for improving compression set resistance of cured antistatic silicone rubber - Google Patents

Description

  The present invention relates to a silicone rubber composition that provides a cured product having excellent antistatic performance not only at room temperature but also at a high temperature without deteriorating compression set, and antistatic silicone rubber curing using the composition. The present invention relates to a method for improving the compression set resistance of an object.

  Silicone rubber has excellent weather resistance, electrical properties, low compression set, heat resistance, cold resistance, and other properties, so it can be used in various fields including electrical equipment, automobiles, architecture, medical care, and foods. Widely used. For example, keypads used as rubber contacts for remote controllers, typewriters, word processors, computer terminals, musical instruments, etc .; gaskets for construction; anti-vibration rubber for audio devices, etc .; automotive parts such as connector seals, spark plug boots, etc. Uses such as packing for compact discs, bread and cake molds to be used. At present, the demand for silicone rubber is increasing, and it is desired to develop a silicone rubber having excellent characteristics.

  These silicone rubbers are generally supplied in the form of a composition containing a highly polymerized organopolysiloxane and a reinforcing filler. This composition is prepared by mixing a reinforcing filler and various dispersants with a raw material polymer using a mixing apparatus such as a dough mixer and a two-roller. Reinforcing fillers such as organopolysiloxane and silica are electrically insulating materials, and the silicone rubber composition obtained by blending them and the cured silicone rubber are charged by contact with various substances, resulting in static electricity. There are problems such as generation of dust and adsorption of dust in the air.

  Conventionally, antistatic rubbers are polyether-based as an antistatic agent (see Patent Document 1: JP-T-2002-500237) or carbon black (Patent Document 2: JP-T-2002-507240, Patent Document 3: JP-T No. 2002-327122). When a polyether type is used, there is a problem that the polyether is decomposed at a high temperature and a sufficient antistatic effect is not exhibited. In particular, it has been the actual situation that the antistatic effect is almost lost even by performing a known post-cure with a thermosetting silicone rubber. When carbon black is used, there is a problem that it is difficult to maintain electrical insulation or it is limited to black. Japanese Patent Laying-Open No. 2003-82232 (Patent Document 4) proposes a silicone rubber composition for a semiconductive roller to which a lithium salt is added. In the semiconductive region, an electric wire that can be used only by an insulating material. There was a problem that it could not be applied to the coating or keypad. In addition, when lithium salt is added, there is a problem that compression set is deteriorated when cured with an organic peroxide.

Special Table 2002-500237 Special table 2002-507240 gazette JP 2002-327122 A JP 2003-82232 A

  The present invention has been made in view of the above circumstances, and provides a silicone rubber composition that provides a cured product having excellent antistatic performance not only at room temperature but also at high temperature without deteriorating compression set and the composition. An object of the present invention is to provide a method for improving the compression set resistance of an antistatic silicone rubber cured product using the above.

  As a result of intensive studies to achieve the above object, the present inventors have found that an organic peroxide curable silicone rubber composition, an ion conductive antistatic agent such as a lithium salt, an alkali metal hydroxide, By using an alkaline substance selected from alkali metal oxides, alkali metal fatty acid salts, alkali metal alcoholates, and alkali metal siliconates in combination, compression set is not deteriorated and compression set resistance is improved at the same time. It was found that a cured product (silicone rubber) that can be maintained and has sufficient antistatic properties even at high temperatures was obtained, and the present invention was made.

Accordingly, the present invention provides the following silicone rubber composition and a method for improving the compression set resistance of the cured antistatic silicone rubber using the composition.
Claim 1:
(A) The following average composition formula (1):
R _n SiO _{(4-n) / 2} (1)
(In the formula, R is the same or different and is an unsubstituted or substituted monovalent hydrocarbon group, and n is a positive number of 1.95 to 2.04.)
And an organopolysiloxane having at least two alkenyl groups in one molecule
100 parts by mass,
(B) 10 to 100 parts by mass of reinforcing silica having a specific surface area of 50 m ² / g or more,
(C) LiBF ₄ , LiClO ₄ , LiPF ₆ , LiAsF ₆ , LiSbF ₆ , LiSO ₃ CF ₃ , LiN (SO ₂ CF ₃ ) ₂ , LiSO ₃ C ₄ F ₉ , LiC (SO ₂ CF ₃ ) ₃ , LiB ( C ₆ H ₅ ) One or more ion conductive antistatic agents selected from ₄
0.0001-5 parts by mass,
(D) Alkali metal siliconate
For the total amount of component (A) and component (B)
5 to 5,000 ppm as an alkali metal,
(E) Organic peroxide curing agent A silicone rubber composition comprising an effective amount.
Claim 2 :
(D) an alkali metal in the component, the silicone rubber composition of claim 1 Symbol placement sodium or potassium.
Claim 3 :
A method for improving the compression set resistance of an antistatic silicone rubber cured product comprising heating and curing the silicone rubber composition according to claim 1 or 2 to obtain a cured silicone rubber.
Claim 4 :
The method for improving the compression set resistance of the cured antistatic silicone rubber according to claim 3, which is formed by heating at 80 to 400 ° C.
Claim 5 :
The method for improving the compression set resistance of the cured antistatic silicone rubber according to claim 3 or 4 , further comprising secondary vulcanization at 150 to 250 ° C.
Claim 6 :
The method for improving the compression set resistance of the cured antistatic silicone rubber according to any one of claims 3 to 5 , which is formed by any one of extrusion molding, press molding, and injection molding.

  According to the present invention, it is possible to obtain a silicone rubber composition that gives a cured product having excellent antistatic performance not only at room temperature but also at high temperature without deteriorating compression set. Also provided is a method for satisfactorily maintaining and improving the compression set resistance of the cured antistatic silicone rubber using the composition.

  Hereinafter, the present invention will be described in more detail. In the present specification, the specific surface area is a value measured by the BET method.

The silicone rubber composition of the present invention is
(A) an organopolysiloxane having an alkenyl group,
(B) reinforcing silica,
(C) an ion conductive antistatic agent,
(D) alkaline substance,
(E) Contains an organic peroxide curing agent.

[(A) Organopolysiloxane]
The (A) component organopolysiloxane is the main component (base polymer) of the present composition, and is represented by the following average composition formula (1): an alkenyl group having at least two silicon atoms bonded to one molecule. It contains.
R _n SiO _{(4-n) / 2} (1)
(In the formula, R is the same or different and is an unsubstituted or substituted monovalent hydrocarbon group, and n is a positive number of 1.95 to 2.04.)

  In said formula (1), R is a C1-C20 normally, Preferably it is 1-12, More preferably, it is a 1-8 monovalent hydrocarbon group. Examples of the monovalent hydrocarbon group represented by R include alkyl groups such as methyl group, ethyl group, propyl group, and butyl group, cycloalkyl groups such as cyclohexyl group, vinyl group, allyl group, butenyl group, and hexenyl group. Alkenyl groups such as phenyl groups, tolyl groups, aralkyl groups such as β-phenylpropyl groups, or some or all of hydrogen atoms bonded to carbon atoms of these groups are halogen atoms, cyano groups, etc. And a chloromethyl group, a trifluoropropyl group, a cyanoethyl group and the like substituted with a methyl group, a vinyl group, a phenyl group and a trifluoropropyl group are preferable, and a methyl group and a vinyl group are more preferable. Among them, among the monovalent hydrocarbon groups represented by R in the molecule, 50 mol% or more is preferably a methyl group, more preferably 80 mol% or more is a methyl group, and all except alkenyl groups. More preferably, R in the formula is a methyl group.

  In the above formula (1), n is a positive number of 1.95 to 2.04, preferably 1.98 to 2.02. If this n is not in the range of 1.95 to 2.04, the resulting cured product may not exhibit sufficient rubber elasticity.

  Further, the organopolysiloxane of the component (A) needs to have at least two alkenyl groups in one molecule, and in the above formula (1), 0.001 to 10 mol% of R, particularly 0.8. It is preferable that 01-5 mol% is an alkenyl group. The alkenyl group is preferably a vinyl group or an allyl group, and particularly preferably a vinyl group.

  The degree of polymerization of the organopolysiloxane is 100 or more (usually 100 to 100,000), particularly preferably in the range of 1,000 to 100,000, and more preferably in the range of 3,000 to 50,000. A range of 4,000 to 20,000 is particularly preferable. In addition, this polymerization degree is calculated | required as a number average polymerization degree of polystyrene conversion in GPC (gel permeation chromatography) analysis.

The organopolysiloxane is not particularly limited as long as this condition is satisfied. Usually, the main chain is composed of repeating diorganosiloxane units (R ₂ SiO _2/2 ), and both ends of the molecular chain are triorganosiloxy. It is preferably a linear diorganopolysiloxane blocked with a group (R ₃ SiO _1/2 ), and both ends of the molecular chain are trimethylsiloxy group, dimethylvinylsiloxy group, dimethylhydroxysiloxy group, methyldivinylsiloxy. Those blocked with a group, a trivinylsiloxy group or the like are preferable, and those blocked with a siloxy group having at least one vinyl group are particularly preferable. These organopolysiloxanes may be used alone or in combination of two or more having different degrees of polymerization and molecular structures.

[(B) Reinforcing silica]
Component (B) reinforcing silica acts as a component that imparts excellent mechanical properties to the resulting silicone rubber. The reinforcing silica may be precipitated silica (wet silica) or fumed silica (dry silica), and has many silanol groups (SiOH) on the surface. The specific surface area of the reinforcing silica according to the BET method needs to be 50 m ² / g or more, preferably 100 to 400 m ² / g. When this specific surface area is less than 50 m ² / g, the reinforcing effect becomes insufficient.

  The reinforcing silica may be surface-treated with organopolysiloxane, organopolysilazane, chlorosilane, alkoxysilane, or the like, if necessary. These reinforcing silicas may be used alone or in combination of two or more.

  (B) The compounding quantity of a component is 10-100 mass parts with respect to 100 mass parts of (A) component, Preferably it is 10-80 mass parts, Most preferably, it is 20-70 mass parts. If the blending amount does not satisfy the range of 10 to 100 parts by mass, not only the workability of the resulting silicone rubber composition is lowered, but also the tensile strength of the cured silicone rubber obtained by curing the silicone rubber composition. Further, mechanical properties such as tear strength are insufficient.

[(C) ion conductive antistatic agent]
The ion conductive antistatic agent of component (C) is not particularly limited as long as it is not an electronic conductive material such as carbon black and is an ion conductive material, but a lithium salt is preferable.
Specifically, LiBF ₄ , LiClO ₄ , LiPF ₆ , LiAsF ₆ , LiSbF ₆ , LiSO ₃ CF ₃ , LiN (SO ₂ CF ₃ ) ₂ , LiSO ₃ C ₄ F ₉ , LiC (SO ₂ CF ₃ ) ₃ , Examples include LiB (C ₆ H ₅ ) ₄ . These may be used alone or in combination of two or more.
The addition amount of the ion conductive antistatic agent is 0.0001 to 5 parts by mass, preferably 0.0005 to 3 parts by mass, more preferably 0.005 to 100 parts by mass of the organopolysiloxane of the component (A). 001 to 1 part by mass, particularly preferably 0.001 to 0.5 part by mass. When the amount is less than 0.0001 part by mass, the antistatic effect is insufficient. When the amount is more than 5 parts by mass, the physical properties and heat resistance of the silicone rubber are adversely affected.

[(D) Alkaline substance selected from alkali metal hydroxide, alkali metal oxide, alkali metal fatty acid salt, alkali metal alcoholate and alkali metal siliconate]
(D) component suppresses deterioration of compression set resistance due to the addition of component (C), and has the effect of maintaining and improving compression set resistance of the cured rubber (molded product). An alkaline substance selected from hydroxides, alkali metal oxides, alkali metal fatty acid salts, alkali metal alcoholates and alkali metal siliconates, specifically, alkali metal oxides such as LiOH, NaOH, KOH, CsOH, etc. Alkali metal oxides such as Li ₂ O, Na ₂ O, K ₂ O, potassium acetate, sodium acetate, lithium acetate, potassium octylate, sodium octylate, lithium octylate, etc., CH ₃ OLi, _{CH 3 ONa, CH 3 OK,} C 2 H 5 OLi, C 2 H 5 ONa, C 2 H 5 OK, C 3 H 7 ONa, C 3 H 7 OK etc. Alkali metal alcoholates such as, those selected from alkali metal siliconate as described below.

（式中、ｐは１〜１，０００、好ましくは１〜２００の正の整数である。）

(In the formula, p is a positive integer of 1 to 1,000, preferably 1 to 200.)

  (D) The compounding quantity of a component is 5-5,000 ppm as an alkali metal with respect to the total mass of (A) component and (B) component, Preferably it is 10-1,000 ppm. When the blending amount of the component (D) is too small, the compression set cannot be improved, and when it is too large, the siloxane bond is ring-opened and the heat resistance is deteriorated.

[(E) Organic peroxide curing agent]
The component (E) is an organic peroxide curing agent and is not particularly limited as long as it can cure the silicone rubber composition of the present invention. (E) A component may be used individually by 1 type, or may use 2 or more types together. Specific examples of the organic peroxide used as the component (E) include benzoyl peroxide, 2,4-dichlorobenzoyl peroxide, p-methylbenzoyl peroxide, o-methylbenzoyl peroxide, 2,4- Dicumyl peroxide, 2,5-dimethyl-bis (2,5-t-butylperoxy) hexane, di-t-butyl peroxide, t-butylperbenzoate, 1,6-hexanediol-bis-t- Examples include butyl peroxycarbonate.

  The addition amount of the organic peroxide is an effective amount for curing the component (A), and is preferably 0.1 to 10 parts by mass, particularly preferably 0.2 to 5 parts by mass with respect to 100 parts by mass of the component (A). If the amount added is too small, it may be difficult to cure, and if it is too large, there will be no further effect, it will not be economical, and the decomposition residue may increase.

[Other optional ingredients]
In addition to the above-described components, the silicone rubber composition of the present invention includes, as necessary, non-reinforcing silica such as quartz powder, crystalline silica, diatomaceous earth, and calcium carbonate, carbon such as acetylene black, furnace black, and channel black. Heat resistance improver such as black, colorant, bengara, cerium oxide, flame retardant improver such as platinum, titanium oxide, triazole compound, heat conductivity improver such as acid acceptor, alumina, boron nitride, release agent Carbon functional silane, dimethylpolysiloxane having silanol groups at both ends, or the like may be added.

  The silicone rubber composition of the present invention can be obtained by uniformly mixing the above components using a mixing apparatus such as a two-roll mill, a Banbury mixer, or a dow mixer (kneader). ), (C) and (D) components are mixed, and then the (E) component is preferably blended.

  The silicone rubber composition thus obtained can be molded simultaneously with heat curing to obtain a molded body made of a rubber-like elastic body (silicone rubber cured product).

  The curing method may be a method in which sufficient heat is applied to decompose the curing agent and vulcanize the silicone rubber. The curing temperature is usually 80 to 400 ° C., although it depends on the curing method. Also, the molding method is not particularly limited, and for example, a molding method such as continuous vulcanization by extrusion molding, press molding (pressure molding), injection molding or the like can be employed. Furthermore, you may carry out secondary vulcanization at 150-250 degreeC for about 1 to 10 hours as needed.

  In addition, as an antistatic performance, a static one meter (manufactured by Sisid Electric Co., Ltd.) was used to charge the surface of a silicone rubber molded product with 6 kV of static electricity by corona discharge, and then the time when the charged voltage was halved. (Half-life) is preferably within 2 minutes, particularly preferably within 1 minute.

  EXAMPLES Hereinafter, although an Example and a comparative example are shown and this invention is demonstrated concretely, this invention is not restrict | limited to a following example.

[Example 1]
100 parts by mass of an organopolysiloxane comprising 99.825 mol% of dimethylsiloxane units, 0.15 mol% of methylvinylsiloxane units, 0.025 mol% of dimethylvinylsiloxy units and having an average degree of polymerization of about 6,000, BET method 45 parts by mass of fumed silica having a specific surface area of 200 m ² / g (Aerosil 200 manufactured by Nippon Aerosil Co., Ltd.), having a silanol group at both ends as a dispersant, an average polymerization degree of 15 and a viscosity at 25 ° C. of 30 mPa · s Dimethylpolysiliconate containing 10 parts by mass of a certain dimethylpolysiloxane, 0.04 parts by mass of adipic acid ester containing 20% by mass of LiN (SO ₂ CF ₃ ) ₂ , and 3% by mass of KOH in terms of potassium atoms (ie , Dimethylpolysiloxane blocked at both ends of molecular chain with potassium salt of hydroxy group Degrees: about 25) was added 0.2 part by weight, and kneaded in a kneader to prepare a base compound (1) was heated for 2 hours at 170 ° C..

To 100 parts by mass of this base compound (1), 0.4 parts by mass of 2,5-dimethyl-2,5-bis (t-butylperoxy) hexane as a cross-linking agent is added with a two-roll mill and mixed uniformly. After that, press curing was performed for 10 minutes under the conditions of 165 ° C. and 70 kgf / cm ² to prepare a 2 mm thick sheet. Subsequently, post-cure was performed in an oven at 200 ° C. for 4 hours to prepare a test sheet and a test piece for measuring compression set and rebound resilience. The test sheet and the test piece were returned to room temperature, and various properties were measured according to the following measurement methods. Similarly, the amount of charge was measured in the same manner for a sample placed in an oven at 200 ° C. for 50 hours. The results are shown in Table 1.

[Measuring method]
[Density, hardness, tensile strength, elongation at break, compression set]
Density, hardness, tensile strength, elongation at break, and compression set were measured by a method according to JIS K6249 using a test sheet and a test piece for compression set measurement prepared according to JIS K6249. The results are shown in Table 1.

[Charge measurement]
Using a static ones meter (manufactured by Sicid Electrostatic Co., Ltd.), the surface of the molded product was charged with static electricity by corona discharge, and then the time during which the charged voltage was halved was measured.

[Example 2]
100 parts by mass of an organopolysiloxane comprising 99.825 mol% of dimethylsiloxane units, 0.15 mol% of methylvinylsiloxane units, 0.025 mol% of dimethylvinylsiloxy units and having an average degree of polymerization of about 6,000, BET method 40 parts by mass of precipitated silica (NIPSIL-LP, manufactured by Tosoh Silica Co., Ltd.) having a specific surface area of 201 m ² / g, having both terminal silanol groups as a dispersant, an average polymerization degree of 15 and a viscosity at 25 ° C. of 30 mPa · dimethylpolysiloxane 4.4 parts by mass is s, examples include LiN (SO ₂ CF ₃₎ 0.08 parts by mass of adipic acid esters containing 20 wt% of _2, 3 mass% of KOH potassium atoms terms Add 0.2 parts by mass of dimethylpolysiliconate similar to 1, knead with a kneader, heat treatment at 170 ° C. for 2 hours To prepare a base compound (2) Te.
A test sheet was prepared in the same manner as in Example 1 using this base compound (2), and various characteristics were measured. The results are shown in Table 1.

[Example 3]
100 parts by mass of an organopolysiloxane comprising 99.825 mol% of dimethylsiloxane units, 0.15 mol% of methylvinylsiloxane units, 0.025 mol% of dimethylvinylsiloxy units and having an average degree of polymerization of about 6,000, BET method 40 parts by mass of precipitated silica (NIPSIL-LP, manufactured by Tosoh Silica Co., Ltd.) having a specific surface area of 201 m ² / g, having both terminal silanol groups as a dispersant, an average polymerization degree of 15 and a viscosity at 25 ° C. of 30 mPa · 0.08 parts by mass of adipic acid ester containing 4.4 parts by mass of dimethylpolysiloxane which is s and 20% by mass of LiN (SO ₂ CF ₃ ) ₂ was added and kneaded with a kneader at 170 ° C. A base compound (3) was prepared by heat treatment for 2 hours.

0.1 part by mass of dimethylpolysiliconate similar to Example 1 containing 3% by mass of KOH in terms of potassium atom with respect to 100 parts by mass of this base compound (3), 2,5-dimethyl-2, After adding 0.4 parts by mass of 5-bis (t-butylperoxy) hexane with a two-roll mill and uniformly mixing, press curing is performed for 10 minutes under the conditions of 165 ° C. and 70 kgf / cm ² . A sheet was produced. Using this sheet, various characteristics were measured in the same manner as in Example 1. The results are shown in Table 1.

[Comparative Example 1]
A base compound (4) was prepared in the same manner as in Example 1 except that the KOH dimethylpolysiliconate used in Example 1 was not added, and the silicone rubber composition (4) thus obtained was tested. The sheet characteristics were measured. The results are shown in Table 1.

[Comparative Example 2]
A base compound (5) was prepared in the same manner as in Example 2 except that the dimethylpolysiliconate of KOH used in Example 2 was not added, and the silicone rubber composition (5) thus obtained was tested. The sheet characteristics were measured. The results are shown in Table 1.

[Comparative Example 3]
A base compound (6) was prepared in the same manner as in Example 2 except that the adipic acid ester containing 20% by mass of LiN (SO ₂ CF ₃ ) ₂ used in Example 2 was not added. The characteristics of the test sheet of the obtained silicone rubber composition (6) were measured. The results are shown in Table 1.

[Comparative Example 4]
Instead of adipic acid ester containing 20% by mass of LiN (SO ₂ CF ₃ ) ₂ used in Example 2, a polyether-modified silicone oil having a viscosity of 75 mPa · s at 25 ° C. (KF351F Shin-Etsu Chemical Co., Ltd.) The base compound (7) was prepared in the same manner as in Example 1 except that 0.4 part by mass of the product was added, and the properties of the test sheet of the silicone rubber composition (7) obtained thereby were measured. Went. The results are shown in Table 1.

（半減期において「ｓ」は秒を、「ｍｉｎ」は分をそれぞれ示す。）

(In the half-life, “s” represents seconds and “min” represents minutes.)

[Evaluation]
Examples 1 to 3 are silicone rubber compositions that meet the conditions of the present invention and have good antistatic properties and compression set. In Comparative Examples 1 and 2, the antistatic property is good, but the compression set is deteriorated. Comparative Example 3 has poor antistatic properties. In Comparative Example 4, the antistatic property deteriorates when exposed to a high temperature for a long time.

Claims (6)

(A) The following average composition formula (1):
R _n SiO _{(4-n) / 2} (1)
(In the formula, R is the same or different and is an unsubstituted or substituted monovalent hydrocarbon group, and n is a positive number of 1.95 to 2.04.)
And an organopolysiloxane having at least two alkenyl groups in one molecule
100 parts by mass,
(B) 10 to 100 parts by mass of reinforcing silica having a specific surface area of 50 m ² / g or more,
(C) LiBF ₄ , LiClO ₄ , LiPF ₆ , LiAsF ₆ , LiSbF ₆ , LiSO ₃ CF ₃ , LiN (SO ₂ CF ₃ ) ₂ , LiSO ₃ C ₄ F ₉ , LiC (SO ₂ CF ₃ ) ₃ , LiB ( C ₆ H ₅ ) One or more ion conductive antistatic agents selected from ₄
0.0001-5 parts by mass,
(D) Alkali metal siliconate
For the total amount of component (A) and component (B)
5 to 5,000 ppm as an alkali metal,
(E) Organic peroxide curing agent A silicone rubber composition comprising an effective amount. (D) an alkali metal in the component, the silicone rubber composition of claim 1 Symbol placement sodium or potassium. A method for improving the compression set resistance of an antistatic silicone rubber cured product comprising heating and curing the silicone rubber composition according to claim 1 or 2 to obtain a cured silicone rubber. The method for improving the compression set resistance of the cured antistatic silicone rubber according to claim 3, which is formed by heating at 80 to 400 ° C. The method for improving the compression set resistance of the cured antistatic silicone rubber according to claim 3 or 4 , further comprising secondary vulcanization at 150 to 250 ° C. The method for improving the compression set resistance of the cured antistatic silicone rubber according to any one of claims 3 to 5 , which is formed by any one of extrusion molding, press molding, and injection molding.