JP2019026772A - Silicone rubber composition - Google Patents

Abstract

To provide a silicone rubber composition which gives a silicone rubber small in a physical characteristic change even if exposed to a high temperature, and excellent in heat resistance.SOLUTION: A silicone rubber composition comprises: (A) 100 pts.mass of organopolysiloxane having a polymerization degree of 100 or more, and having 2 or more of alkenyl groups in one molecule; (B) 10-100 pts.mass of reinforcing silica having a specific surface area by a BET method of 50 m/g or more; (C) 0.01-10 pts.mass of a lanthanum oxide-cerium oxide solid solution; and (D) 0.1-10 pts.mass of a curing catalyst.SELECTED DRAWING: None

Description

  The present invention relates to a silicone rubber composition.

  Silicone rubber has excellent weather resistance, electrical properties, low compression set, heat resistance, cold resistance, etc., so it is widely used in various fields such as electrical equipment, automobiles, architecture, medical care, foods, etc. Has been. For example, remote controllers, rubber contacts used as rubber contacts for musical instruments, architectural gaskets, fixing rolls, developing rolls, transfer rolls, charging rolls, paper rolls, and other office equipment rolls, anti-vibration rubber for audio devices, Used for packing for compact discs, wire covering materials, etc.

  In order to further improve the heat resistance of silicone rubber, it is known to add additives such as cerium oxide, cerium hydroxide, iron oxide, and carbon black (Patent Documents 1 to 5). However, the demand for heat resistance of silicone rubber has been increasing year by year, and these conventional techniques cannot sufficiently meet the demand.

JP 2000-212444 A JP 2002-179917 A JP 2013-035890 A Japanese Patent No. 5174270 JP, 2006-030774, A

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a silicone rubber composition that gives a silicone rubber excellent in heat resistance with little change in physical properties even when exposed to high temperatures. .

In order to achieve the above object, in the present invention, (A) organopolysiloxane having a degree of polymerization of 100 or more and having two or more alkenyl groups bonded to silicon atoms in one molecule: 100 parts by mass, (B ) Reinforcing silica having a specific surface area of 50 m ² / g or more by BET method: 10 to 100 parts by mass, (C) Lanthanum oxide-cerium oxide solid solution: 0.01 to 10 parts by mass, and (D) Curing catalyst: 0 A silicone rubber composition containing 1 to 10 parts by mass is provided.

  With such a silicone rubber composition, it becomes a silicone rubber composition that gives a silicone rubber excellent in heat resistance with little change in physical properties even when exposed to high temperatures.

  Moreover, it is preferable that the content rate of the cerium oxide in the said (C) component is 60 mass%-97 mass%.

  With such a component (C), it is possible to suppress the occurrence of softening deterioration and curing deterioration of the silicone rubber, so that the silicone rubber is further improved in heat resistance.

  The component (C) preferably has an average particle size of 5.0 μm or less.

  If it is such (C) component, since a contact area with siloxane increases, it will give still more favorable heat resistance to silicone rubber.

  The component (D) is preferably an organic peroxide.

  With such a component (D), since there are few factors that inhibit the curing, the handleability is good.

  As described above, the silicone rubber composition of the present invention has excellent heat resistance with little change in physical properties such as hardness, tensile strength and elongation at break even when exposed to high temperatures. A silicone rubber composition giving

  As described above, there has been a demand for the development of a silicone rubber composition that provides a silicone rubber excellent in heat resistance with little change in physical properties even when exposed to high temperatures.

As a result of intensive investigations to achieve the above object, the present inventors have found that (A) an organopolysiloxane having a degree of polymerization of 100 or more and having two or more alkenyl groups bonded to silicon atoms in one molecule, ( B) A silicone rubber composition containing a reinforcing silica having a specific surface area of 50 m ² / g or more according to the BET method, (C) a lanthanum oxide-cerium oxide solid solution, and (D) a curing catalyst in a predetermined mass ratio. The inventors have found that physical properties are not easily deteriorated even when exposed to high temperatures (that is, excellent in heat resistance), and the present invention has been made.

That is, the present invention is (A) organopolysiloxane having a degree of polymerization of 100 or more and having 2 or more alkenyl groups bonded to silicon atoms in one molecule: (B) specific surface area by BET method Reinforcing silica having an A of 50 m ² / g or more: 10 to 100 parts by mass, (C) Lanthanum oxide-cerium oxide solid solution: 0.01 to 10 parts by mass, and (D) Curing catalyst: 0.1 to 10 parts by mass , A silicone rubber composition containing

  Hereinafter, the present invention will be described in detail, but the present invention is not limited thereto.

[(A) Alkenyl group-containing organopolysiloxane]
The component (A) in the silicone rubber composition of the present invention is an organopolysiloxane having a degree of polymerization of 100 or more and having two or more alkenyl groups bonded to silicon atoms in one molecule. Although it does not specifically limit as organopolysiloxane of (A) component, For example, what is represented by the following average compositional formula (1) is mentioned.
R _a SiO _{(4-a) / 2} (1)
(In the formula, R is the same or different unsubstituted or substituted monovalent hydrocarbon group, and a is a positive number of 1.95 to 2.05. However, two or more of R in one molecule. Is an alkenyl group.)

  In the above average composition formula (1), R is the same or different unsubstituted or substituted monovalent hydrocarbon group, usually having 1 to 12 carbon atoms, particularly preferably 1 to 8 carbon atoms, specifically, Alkyl group such as methyl group, ethyl group, propyl group, butyl group, hexyl group and octyl group, cycloalkyl group such as cyclopentyl group and cyclohexyl group, alkenyl group such as vinyl group, allyl group and propenyl group, cycloalkenyl group, An aryl group such as a phenyl group or a tolyl group, an aralkyl group such as a benzyl group or a 2-phenylethyl group, or a trifluoropropyl group in which part or all of the hydrogen atoms of these groups are substituted with a halogen atom or a cyano group In particular, a methyl group, a vinyl group, a phenyl group, and a trifluoropropyl group are preferable. Specifically, the main chain of the organopolysiloxane is composed of dimethylsiloxane units, or a part of the main chain of the dimethylpolysiloxane has a phenyl group, a vinyl group, a 3,3,3-trifluoropropyl group, or the like. Those having a diphenylsiloxane unit, a methylvinylsiloxane unit, a methyl-3,3,3-trifluoropropylsiloxane unit or the like introduced therein are preferred.

  The organopolysiloxane of the component (A) has an alkenyl group (preferably a vinyl group) bonded to two or more silicon atoms in one molecule, and among the groups bonded to the silicon atom, 0.01 to It is preferable that 10 mol%, especially 0.02 to 5 mol% is an alkenyl group.

  The alkenyl group may be bonded to the silicon atom at the molecular chain terminal, or may be bonded to the silicon atom on the side chain, or both, but at least bonded to the silicon atom at the molecular chain terminal. It is preferable. That is, as the organopolysiloxane of component (A), specifically, those having molecular chain ends blocked with dimethylvinylsilyl groups, methyldivinylsilyl groups, trivinylsilyl groups, and the like are preferable.

  a is a positive number of 1.95 to 2.05 and is basically a straight chain, but may be branched within a range not impairing rubber elasticity.

  The degree of polymerization of the organopolysiloxane (A) is 100 or more, preferably 3,000 to 100,000, particularly preferably 4,000 to 20,000. If the degree of polymerization is less than 100, sufficient rubber strength cannot be obtained.

  Moreover, the organopolysiloxane of the component (A) may be used alone or in combination of two or more having different molecular structures and polymerization degrees.

  Such organopolysiloxane of component (A) can be obtained by a known method, for example, by (co) hydrolytic condensation of one or more of organohalogenosilanes, or by using a cyclic polysiloxane with an alkaline or acidic catalyst. Can be obtained by ring-opening polymerization.

[(B) Reinforcing silica]
The component (B) in the silicone rubber composition of the present invention is reinforcing silica having a specific surface area of 50 m ² / g or more according to the BET method.

  The reinforcing silica as the component (B) is not particularly limited, and examples thereof include fumed silica, calcined silica, precipitated silica, and the like, and fumed silica is preferable from the viewpoint of heat resistance.

(B) The specific surface area by BET method of reinforcing silica component is ^{50 m} 2 / g or more, preferably 100 m ² / g or more, particularly preferably 100 to 400 m ² / g. If the specific surface area by BET method is less than 50 m < ² > / g, provision of mechanical strength will become inadequate.

  (B) Reinforcing silica of the component has a surface of chlorosilanes such as trimethylchlorosilane, dimethyldichlorosilane and methyltrichlorosilane, or hexamethyldisilazane, 1,3-divinyl-1,1,3,3 as required. -What hydrophobized with well-known processing agents, such as silazanes, such as tetramethyldisilazane, may be used.

  The amount of the reinforcing silica (B) added is 10 to 100 parts by weight, preferably 20 to 70 parts by weight, particularly preferably 30 to 60 parts by weight, based on 100 parts by weight of the organopolysiloxane (A). It is. When the amount is less than 10 parts by mass, the amount added is too small to obtain a sufficient reinforcing effect. When the amount exceeds 100 parts by mass, the workability is deteriorated and the mechanical strength is lowered.

[(C) Lanthanum oxide-cerium oxide solid solution]
The component (C) in the silicone rubber composition of the present invention is a lanthanum oxide-cerium oxide solid solution, and is a component that remarkably improves the heat resistance of the silicone rubber. Cerium oxide is known as a heat resistance improver for silicone rubber, but in the present invention, it has been found that by forming a solid solution with lanthanum oxide, it is possible to give the silicone rubber heat resistance equal to or higher than that of cerium oxide alone. It was.

  The content of cerium oxide in the lanthanum oxide-cerium oxide solid solution of component (C) is desirably 60% by mass to 97% by mass. If it is 97 mass% or less, since there is not too much content of cerium oxide, generation | occurrence | production of the softening deterioration of 200 degreeC or more of silicone rubber can be suppressed, and more favorable heat resistance can be given to silicone rubber. Moreover, if it is 60 mass% or more, generation | occurrence | production of hardening deterioration of a silicone rubber can be suppressed and a further favorable heat resistance can be given to a silicone rubber.

  The lanthanum oxide-cerium oxide solid solution of component (C) preferably has an average particle size of 5.0 μm or less. The average particle size referred to here refers to the volume average particle size, and is a value measured with Microtrac Model No. MT-3300 (product of Microtrac Bell Co., Ltd.) using water as a measurement solvent. If the average particle size is 5.0 μm or less, the contact area with the siloxane increases, so that the silicone rubber is further improved in heat resistance.

  The addition amount of the lanthanum oxide-cerium oxide solid solution as the component (C) is 0.01 to 10 parts by mass, preferably 0.05 to 5 parts by mass with respect to 100 parts by mass of the organopolysiloxane as the component (A). If it is less than 0.01 part by mass, the effect of improving the heat resistance is insufficient, and if it exceeds 10 parts by mass, physical properties such as strength and elongation of the silicone rubber are deteriorated.

[(D) Curing catalyst]
Component (D) in the silicone rubber composition of the present invention is a curing catalyst. The curing catalyst for component (D) is not particularly limited as long as it can cure the silicone rubber composition of the present invention. Accordingly, it is possible to use an addition curing type curing catalyst in which an organic peroxide or hydrosilyl group-containing organopolysiloxane, which is a known vulcanizing agent for silicone rubber, and a hydrosilylation catalyst are combined. Among these, organic peroxides are preferable in terms of handling and the like because they have fewer curing inhibiting factors than addition curing catalysts.

  Examples of the organic peroxide 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-butylperoxide, t-butylperbenzoate, 1,6-hexanediol-bis-t-butylperoxycarbonate and the like can be mentioned. These may be used individually by 1 type and may use 2 or more types together.

  The amount of the component (D) curing catalyst added is sufficient to cure the silicone rubber composition. Specifically, the amount is 0.1 to 100 parts by weight of the component (A) organopolysiloxane. 10 parts by mass, preferably 0.2-5 parts by mass.

[(E) Organosilane / siloxane]
In addition to the above components, the silicone rubber composition of the present invention preferably further contains an organosilane or siloxane represented by the following general formula (2) as the component (E). By blending the component (E), workability, extrusion characteristics and the like of the silicone rubber composition of the present invention are improved.
R ¹ O (Si (R ² ) ₂ O) _m R ¹ (2)
Wherein R ¹ is the same or different alkyl group or hydrogen atom, R ² is the same or different unsubstituted or substituted monovalent hydrocarbon group, and m is a positive number of 1 to 50. )

Here, R ¹ is the same or different alkyl group or hydrogen atom, and the organosilane or siloxane represented by the general formula (2) has an alkoxy group or a hydroxyl group at the molecular chain end. Examples of R ¹ include a hydrogen atom or an alkyl group having 1 to 4 carbon atoms such as a methyl group, an ethyl group, a propyl group, and a butyl group, and a methyl group, an ethyl group, and a hydrogen atom are preferable. R ² usually has preferably 1 to 12 carbon atoms, particularly 1 to 8 carbon atoms. Specifically, alkyl groups such as a methyl group, an ethyl group, a propyl group and a butyl group, and a cycloalkyl group such as a cyclohexyl group. , An alkenyl group such as a vinyl group, an allyl group, a butenyl group and a hexenyl group, an aryl group such as a phenyl group and a tolyl group, an aralkyl group such as a β-phenylpropyl group, or a hydrogen atom bonded to a carbon atom of these groups For example, a chloromethyl group, a trifluoropropyl group, a cyanoethyl group, etc., in which a part or all of them are substituted with a halogen atom, a cyano group, etc. are mentioned, and a methyl group, a vinyl group, a phenyl group, a trifluoropropyl group are preferable, a methyl group, A vinyl group and a trifluoropropyl group are particularly preferred.

  m is a positive number of 1-50, preferably a positive number of 1-30, particularly preferably a positive number of 1-20. If m is 50 or less, a sufficient addition effect can be obtained without blending in a large amount, and there is no possibility of deterioration in rubber properties due to blending in a large amount.

  The amount of the organosilane / siloxane added as the component (E) is preferably 0.1 to 50 parts by mass, particularly preferably 0.5 to 30 parts by mass with respect to 100 parts by mass of the organopolysiloxane of the component (A). If it is 0.1 parts by mass or more, the effect of addition is sufficiently obtained, and if it is 50 parts by mass or less, there is no fear that the resulting silicone rubber composition will become sticky, so the workability is reduced, There is no risk that the physical properties of the resulting rubber will be degraded.

[Other ingredients]
In addition to the above components, the silicone rubber composition of the present invention includes, as an optional component, a flame retardant imparting agent such as a platinum compound, iron oxide or a halogen compound, or a heat resistance improver other than the component (C) as necessary. Well-known additives in the silicone rubber composition such as an anti-aging agent, an ultraviolet absorber, a colorant, and a release agent can be added.

  Although the manufacturing method of the silicone rubber composition of this invention is not specifically limited, It can obtain by knead | mixing the predetermined amount of the component mentioned above with well-known kneaders, such as a 2 roll, a kneader, a Banbury mixer. If necessary, heat treatment (kneading under heating) may be performed. Specifically, a method in which the components (A) and (B) are kneaded and heat-treated as necessary, and then the component (D) is added at room temperature is preferable. In this case, the component (C) may be blended before or after the heat treatment. In the case of heat treatment, the heat treatment temperature and time are not particularly limited, but it is preferably 100 to 250 ° C, particularly 140 to 180 ° C for 30 minutes to 5 hours.

  When the silicone rubber composition of the present invention is molded, a molding method may be appropriately selected according to the required use (molded product). Specific examples include compression molding, injection molding, transfer molding, normal pressure hot air vulcanization, steam vulcanization, and the like. Curing conditions are not particularly limited and may be appropriately selected depending on a curing method and a molded product. Generally, the curing is performed at 80 to 600 ° C., particularly 100 to 450 ° C. for several seconds to several days, particularly about 5 seconds to 1 hour. Can do. Further, secondary vulcanization may be performed as necessary. The secondary vulcanization can be usually performed at 180 to 250 ° C. for about 1 to 10 hours.

  As described above, the silicone rubber composition of the present invention has excellent heat resistance with little change in physical properties such as hardness, tensile strength and elongation at break even when exposed to high temperatures. A silicone rubber composition giving

  EXAMPLES Hereinafter, although this invention is demonstrated concretely using an Example and a comparative example, this invention is not limited to these.

[Example 1]
100 parts by mass of an organopolysiloxane comprising 99.750 mol% of trifluoropropyl methylsiloxane units, 0.20 mol% of methylvinylsiloxane units and 0.050 mol% of dimethylvinylsiloxane units and having an average degree of polymerization of about 4,000 , 45 parts by mass of fumed silica (Aerosil 130 (manufactured by Nippon Aerosil Co., Ltd.)) with a specific surface area of 130 m ² / g by BET method, trifluoropropyl methylpolysiloxane having silanol groups at both ends and a polymerization degree of 10 10 parts by mass of siloxane was blended with a kneader and heat-treated at 150 ° C. for 2 hours to produce a silicone rubber compound. To the resulting rubber compound, 0.8 parts by mass of lanthanum oxide-cerium oxide solid solution A (average particle size 0.8 μm, lanthanum oxide / cerium oxide ratio = 40/60) was added with two rolls, and then 2,5- 0.5 parts by mass of dimethyl-bis (2,5-t-butylperoxy) hexane was added to obtain a silicone rubber composition. This composition was press-molded under conditions of primary vulcanization 170 ° C./10 minutes and secondary vulcanization 200 ° C./2 hours to produce a 2 mm-thick silicone rubber. The hardness (based on JIS K 6249: 2003) Durometer A), tensile strength, elongation at break (ie, initial rubber properties) were measured. Further, the physical properties of a rubber after a heat resistance test placed in a dryer at 225 ° C. for 7 days were also measured, and the rate of change was calculated. The results are shown in Table 1.

[Comparative Example 1]
Example except that commercially available cerium oxide (manufactured by Anan Kasei Co., Ltd., trade name: cerium oxide S, purity 99.9% or more, average particle size 0.18 μm) is added instead of lanthanum oxide-cerium oxide solid solution A The same operation as in No. 1 was performed to obtain a silicone rubber composition. Using the obtained silicone rubber composition, the physical properties of the rubber after the initial stage and after the heat resistance test were measured in the same manner as in Example 1, and the rate of change was calculated. The results are shown in Table 1.

[Comparative Example 2]
A silicone rubber composition was obtained in the same manner as in Example 1 except that no lanthanum oxide-cerium oxide solid solution A was added. Using the obtained silicone rubber composition, the physical properties of the rubber after the initial stage and after the heat resistance test were measured in the same manner as in Example 1, and the rate of change was calculated. The results are shown in Table 1.

  As shown in Table 1, in Example 1 using a lanthanum oxide-cerium oxide solid solution as a heat resistance improver, the rubber physical properties after the heat resistance test were compared with Comparative Example 1 using cerium oxide as a heat resistance improver. The change rate was small and the heat resistance was good. In Comparative Example 2 in which no heat resistance improver was added, after the heat resistance test, the silicone rubber was severely deteriorated by curing, and the measurement of rubber physical properties was impossible.

[Example 2]
100 masses of methyl vinyl polysiloxane raw rubber having 99.85 mol% of dimethylsiloxane units and 0.15 mol% of methyl-vinylsiloxane units and having a degree of polymerization of about 7,000 with molecular chain ends blocked with dimethylvinylsiloxane units. Part, 45 parts by mass of a fumed silica (Aerosil 300 (manufactured by Nippon Aerosil Co., Ltd.)) having a specific surface area of 300 m ² / g by the BET method, and 8 parts by mass of hexamethyldisilazane were mixed in a kneader mixer and uniformly mixed. Further, the mixture was heated and mixed at 150 ° C. for 1 hour to obtain a silicone rubber base. To the obtained rubber compound, 1.0 part by mass of lanthanum oxide-cerium oxide solid solution B (average particle size 0.8 μm, lanthanum oxide / cerium oxide ratio = 30/70) was added with two rolls, and then 2,5- 0.5 parts by mass of dimethyl-bis (2,5-t-butylperoxy) hexane was added to obtain a silicone rubber composition. This composition was press-molded under conditions of primary vulcanization 170 ° C./10 minutes and secondary vulcanization 200 ° C./2 hours to produce a 2 mm-thick silicone rubber. The hardness (based on JIS K 6249: 2003) Durometer A), tensile strength, elongation at break (ie, initial rubber properties) were measured. Further, the physical properties of a rubber after a heat resistance test placed in a 250 ° C. dryer for 3 days were also measured, and the rate of change was calculated. The results are shown in Table 2.

[Comparative Example 3]
A silicone rubber composition was obtained in the same manner as in Example 2 except that the addition amount of the lanthanum oxide-cerium oxide solid solution B was 0.001 part by mass. Using the obtained silicone rubber composition, the physical properties of the rubber after the initial stage and after the heat resistance test were measured in the same manner as in Example 2, and the rate of change was calculated. The results are shown in Table 2.

  As shown in Table 2, in Example 2 in which an appropriate amount of lanthanum oxide-cerium oxide solid solution was blended, the heat resistance was higher than that in Comparative Example 3 in which the blending amount of lanthanum oxide-cerium oxide solid solution was 0.001 part by mass. The rate of change in rubber physical properties after the test was small, and the heat resistance was good.

  From the above, the silicone rubber composition of the present invention has excellent heat resistance and little change in physical properties such as hardness, tensile strength and elongation at break even when exposed to high temperatures. It became clear that the silicone rubber composition giving

  The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and the present invention has any configuration that has substantially the same configuration as the technical idea described in the claims of the present invention and that exhibits the same effects. Are included in the technical scope.

Claims (4)

(A) Organopolysiloxane having a degree of polymerization of 100 or more and having two or more alkenyl groups bonded to silicon atoms in one molecule: 100 parts by mass
(B) Reinforcing silica having a specific surface area of 50 m ² / g or more by BET method: 10 to 100 parts by mass,
(C) Lanthanum oxide-cerium oxide solid solution: 0.01 to 10 parts by mass, and (D) curing catalyst: 0.1 to 10 parts by mass,
A silicone rubber composition comprising:   2. The silicone rubber composition according to claim 1, wherein the content of cerium oxide in the component (C) is 60% by mass to 97% by mass.   The silicone rubber composition according to claim 1, wherein the component (C) has an average particle size of 5.0 μm or less.   The said (D) component is an organic peroxide, The silicone rubber composition as described in any one of Claims 1-3 characterized by the above-mentioned.