Millable-type silicone rubber compound, and millable-type silicone rubber composition

Abstract

To provide a millable-type silicone rubber compound that, while being applicable to relatively low-hardness silicone rubbers, is capable of exhibiting high plasticity and realizing silicone rubber with excellent mechanical strength upon curing.SOLUTION: A millable-type silicone rubber compound includes the following constituents (A)-(D):. (A) 100 pts.mass of an organopolysiloxane raw rubber having an average polymerization degree of 1,000-100,000, and two or more alkenyl groups bonded to silicone atom(s) in a molecule; (B) 5-100 pts.mass of a reinforcing silica having a specific surface area by a BET absorption method of 50-450 m2 / g; and (C) 0.1-20 pts.mass of a partial hydrolysate of an organoalkoxysilane; and (D) 0.01-5.0 pts.mass of a silazane compound.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a millable type silicone rubber compound and a silicone rubber composition using said compound. [Background technology]

[0002] To manufacture a millable type silicone rubber compound, it is necessary to knead a reinforcing filler such as fumed silica into the organopolysiloxane. In this case, a surface treatment agent for the reinforcing filler, called a dispersant (wetter), is used. Usually, when dispersing a reinforcing filler such as silica into the organopolysiloxane, an organosilane or siloxane having a silanol group is used as the surface treatment agent. If the amount of the surface treatment agent is too large, the plasticity of the silicone rubber compound decreases, and the plasticity of the silicone rubber composition decreases accordingly. When such a composition is used, depending on the molding method, such as extrusion molding, the uncured molded product cannot withstand its own weight and deforms, resulting in a defective product. In addition, there is a drawback in that a sticky feeling occurs on the surface of the silicone rubber composition, deteriorating the processability. Conversely, if the amount of the surface treatment agent added is insufficient, the plasticity increases, but there is a problem that crepe hardening, called plastic reversion, increases.

[0003] In order to solve the above problems, Patent Document 1 describes the addition of a resin. Patent Document 2 describes the addition of a polycyclic aromatic compound having two or more phenyl groups. Although both methods increase the plasticity, there is no description of the problem of plastic reversion, and the additives are expensive. Patent Document 3 describes that the plastic reversion can be suppressed by heating the silicone rubber compound at 200 to 250°C for 4 to 12 hours, but this is not economical. Patent Document 4 reports that a silicone rubber compound with high plasticity can be obtained by adding a catalyst for condensation reaction of a specific organometallic compound and condensing silanol by heat treatment. However, it has been difficult to stably obtain the desired plasticity of the silicone rubber compound. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 6-256658 [Patent Document 2] Japanese Patent Application Publication No. 5-065415 [Patent Document 3] Japanese Patent Application Publication No. 7-133356 [Patent Document 4] JP 2014-109014 A Summary of the Invention [Problem to be solved by the invention]

[0005] The present invention has been made in view of the above circumstances, and has as its object to provide a millable-type silicone rubber compound which can exhibit high plasticity even when used with silicone rubber of relatively low hardness, and which can produce a silicone rubber with excellent mechanical strength upon curing, and a silicone rubber composition containing said millable-type silicone compound. [Means for solving the problem]

[0006] The present invention provides a millable type silicone rubber compound characterized by containing the following components (A) to (D): (A) organopolysiloxane raw rubber having two or more alkenyl groups bonded to silicon atoms in each molecule and an average degree of polymerization of 1,000 to 100,000: 100 parts by mass, (B) Specific surface area by BET adsorption method is 50 to 450 m 2 / g reinforcing silica: 5 to 100 parts by mass, (C) a partial hydrolysate of an organoalkoxysilane represented by the following formula (1): 0.1 to 20 parts by mass, [ka] (In the formula, R is a monovalent hydrocarbon group having 1 to 12 carbon atoms, and R 1 represents an alkyl group having 1 to 4 carbon atoms; and (D) a silazane compound represented by the following formula (2) and / or (3): 0.01 to 5.0 parts by mass, [ka] (In the formula, R 1 each independently represents an alkyl group having 1 to 4 carbon atoms, and n is an integer of 3 or more and 10 or less.

[0007] The millable silicone rubber compound of the present invention is capable of exhibiting high plasticity, and upon curing can produce a silicone rubber with excellent mechanical strength.

[0008] R and R in the above formula (1) 1 are preferably independently any one of a methyl group, an ethyl group, and a propyl group.

[0009] Such millable silicone rubber compounds can exhibit higher plasticity and can more reliably produce silicone rubber with excellent mechanical strength upon curing.

[0010] The present invention also provides a millable type silicone rubber composition comprising the millable type silicone rubber compound of the present invention and (E) a curing agent.

[0011] The millable silicone rubber composition of the present invention is capable of exhibiting high plasticity, and upon curing can produce a silicone rubber with excellent mechanical strength.

[0012] For example, the (E) curing agent may be an (E1) hydrosilylation reaction type curing agent that contains a combination of an organohydrogenpolysiloxane and a hydrosilylation catalyst.

[0013] Such millable silicone rubber compositions are capable of exhibiting high plasticity, and upon curing can produce silicone rubber with excellent mechanical strength.

[0014] Alternatively, the (E) curing agent may be (E2) an organic peroxide.

[0015] Such millable silicone rubber compositions are capable of exhibiting high plasticity, and upon curing can produce silicone rubber with excellent mechanical strength. Effect of the Invention

[0016] The millable silicone rubber compound of the present invention is capable of exhibiting high plasticity, and upon curing can produce a millable silicone rubber with excellent mechanical strength.

[0017] The millable silicone rubber composition of the present invention is capable of exhibiting high plasticity, and upon curing can produce a silicone rubber with excellent mechanical strength. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] As described above, there has been a need for the development of a millable type silicone rubber compound that can exhibit high plasticity and produce a silicone rubber with excellent mechanical strength upon curing, and a silicone rubber composition containing such a millable type silicone compound.

[0019] As a result of intensive research into the above-mentioned problems, the present inventors have discovered that, in addition to an organopolysiloxane raw rubber (base polymer) having two or more alkenyl groups bonded to silicon atoms in one molecule and an average degree of polymerization of 1,000 to 100,000 and reinforcing silica, a compound represented by the following formula (1): [ka] (In the formula, R is a monovalent hydrocarbon group having 1 to 12 carbon atoms, and R 1 represents an alkyl group having 1 to 4 carbon atoms. and a silazane compound represented by the following formula (2) and / or (3): 0.01 to 5.0 parts by mass, [ka] (In the formula, R 1 each independently represents an alkyl group having 1 to 4 carbon atoms, and n is an integer of 3 or more and 10 or less. The present invention was completed based on the discovery that the silicone rubber compound obtained by using the above has high plasticity and is resistant to plastic reversion, and furthermore, the strength of the silicone rubber obtained by curing this silicone rubber compound is very excellent.

[0020] That is, the present invention is a millable type silicone rubber compound containing the following components (A) to (D): (A) organopolysiloxane raw rubber having two or more alkenyl groups bonded to silicon atoms in each molecule and an average degree of polymerization of 1,000 to 100,000: 100 parts by mass, (B) Specific surface area by BET adsorption method is 50 to 450 m 2 / g reinforcing silica: 5 to 100 parts by mass, (C) a partial hydrolysate of an organoalkoxysilane represented by the following formula (1): 0.1 to 20 parts by mass, [ka] (In the formula, R is a monovalent hydrocarbon group having 1 to 12 carbon atoms, and R 1 represents an alkyl group having 1 to 4 carbon atoms; and (D) a silazane compound represented by the following formula (2) and / or (3): 0.01 to 5.0 parts by mass, [ka] (In the formula, R 1 each independently represents an alkyl group having 1 to 4 carbon atoms, and n is an integer of 3 or more and 10 or less.

[0021] The present invention also relates to a millable type silicone rubber composition comprising the millable type silicone rubber compound of the present invention and (E) a curing agent.

[0022] In the present invention, the mixture of the above (A) to (D) components before the addition of the (E) curing agent is referred to as the silicone rubber compound, and the compound to which the (E) curing agent is added is referred to as the silicone rubber composition.

[0023] The present invention will be described in detail below, but the present invention is not limited thereto.

[0024] [Millable type silicone rubber compound] The millable type silicone rubber compound of the present invention has the following features: (A) organopolysiloxane raw rubber having two or more alkenyl groups bonded to silicon atoms in each molecule and an average degree of polymerization of 1,000 to 100,000: 100 parts by mass, (B) Specific surface area by BET adsorption method is 50 to 450 m 2 / g reinforcing silica: 5 to 100 parts by mass, (C) a partial hydrolysate of an organoalkoxysilane represented by the following formula (1): 0.1 to 20 parts by mass, [ka] (In the formula, R is a monovalent hydrocarbon group having 1 to 12 carbon atoms, and R 1 represents an alkyl group having 1 to 4 carbon atoms, and (D) a silazane compound represented by the following formula (2) and / or (3): 0.01 to 5.0 parts by mass, [ka] (In the formula, R 1 each independently represents an alkyl group having 1 to 4 carbon atoms, and n is an integer of 3 or more and 10 or less. It contains as an essential component.

[0025] Each component of the millable type silicone rubber compound of the present invention will now be described in more detail.

[0026] -(A) Component- In the present invention, component (A) is an organopolysiloxane raw rubber having two or more alkenyl groups bonded to silicon atoms in each molecule and an average degree of polymerization of 1,000 to 100,000. Component (A) is the main component and base polymer of the silicone rubber compound of the present invention.

[0027] The alkenyl group is preferably an alkenyl group having 2 to 8 carbon atoms, and more preferably an alkenyl group having 2 to 6 carbon atoms. Specific examples include a vinyl group, an allyl group, a butenyl group, a pentenyl group, a hexenyl group, and a cyclohexenyl group. Of these, a vinyl group is preferred.

[0028] Examples of the substituent other than the alkenyl group include monovalent hydrocarbon groups having 1 to 12 carbon atoms, particularly 1 to 8 carbon atoms. Specific examples include alkyl groups such as methyl, ethyl, propyl, butyl, hexyl, and octyl groups, cycloalkyl groups such as cyclopentyl and cyclohexyl groups, aryl groups such as phenyl and tolyl groups, and aralkyl groups such as benzyl and 2-phenylethyl groups. Fluoroalkyl groups in which a part of an alkyl group is substituted with a fluorine atom may also be used. Among these, methyl and phenyl groups are preferred, and methyl groups are particularly preferred.

[0029] The component (A) is characterized by having two or more alkenyl groups in one molecule, preferably 2 to 50, more preferably 2 to 20 alkenyl groups. Among them, those having a vinyl group are particularly preferred. In this case, it is preferable that 0.01 to 20 mol %, particularly 0.02 to 10 mol %, of the total siloxane units of the organopolysiloxane are siloxane units having an alkenyl group. The alkenyl group may be bonded to a silicon atom at the molecular chain terminal, or to a silicon atom in the middle of the molecular chain (non-terminal of the molecular chain), or both, but it is preferable that the alkenyl group is bonded to a silicon atom at at least the molecular chain terminal.

[0030] It is also desirable that at least 80 mol %, preferably at least 90 mol %, more preferably at least 95 mol %, of all siloxane units in the organopolysiloxane, and even more preferably all siloxane units except for siloxane units having alkenyl groups, are dialkylsiloxy groups, and particularly dimethylsiloxy groups.

[0031] The molecular structure of the organopolysiloxane, which is the component (A), is preferably linear or partially branched.Specifically, the repeating structure of the diorganosiloxane unit constituting the main chain of the organopolysiloxane is preferably one consisting of repeating dimethylsiloxane units alone, or one in which diorganosiloxane units such as diphenylsiloxane units, methylphenylsiloxane units, methylvinylsiloxane units, or methyl-3,3,3-trifluoropropylsiloxane units are introduced as part of the repeating structure.

[0032] In addition, both molecular chain terminals are preferably capped with a group selected from, for example, a trimethylsiloxy group, a dimethylphenylsiloxy group, a vinyldimethylsiloxy group, a divinylmethylsiloxy group, a trivinylsiloxy group, etc., and are particularly preferably capped with a vinyldimethylsiloxy group.

[0033] Examples of the organopolysiloxane of component (A) include methylvinylpolysiloxane, methylphenylvinylpolysiloxane, methyltrifluoropropylvinylpolysiloxane, and the like.

[0034] Such organopolysiloxanes can be obtained, for example, by (co)hydrolytic condensation of one or more organohalogenosilanes, or by ring-opening polymerization of a cyclic polysiloxane (such as a siloxane trimer or tetramer) using an alkaline or acidic catalyst.

[0035] The average degree of polymerization of the organopolysiloxane is 1,000 to 100,000, preferably 2,000 to 50,000, more preferably 2,500 to 30,000, and particularly preferably 3,000 to 20,000. The organopolysiloxane has no self-flowing property at room temperature (25°C), that is, it is a so-called raw rubber-like (non-liquid) state. If the average degree of polymerization is too small, problems such as roll adhesion occur when compounded, and roll workability deteriorates. If the average degree of polymerization is too large, the viscosity of the raw rubber becomes too high, so that it becomes difficult to knead with the (B) component during the production of a silicone rubber compound, and the physical properties of the resulting rubber deteriorate. The degree of polymerization can be measured as a weight average degree of polymerization in terms of polystyrene by gel permeation chromatography (GPC) analysis.

[0036] The component (A) may be a single type, or a mixture of two or more types differing in molecular weight (degree of polymerization) or molecular structure.

[0037] -(B) Component- The reinforcing silica of component (B) is a filler that is added to obtain a silicone rubber composition with excellent mechanical strength. For this purpose, it is necessary to add a filler having a specific surface area (BET adsorption method) of 50 to 450 m 2 / g, and preferably 100 to 450 m 2 / g, more preferably 100 to 300m 2 / g. The specific surface area is 50m 2 If the specific surface area is less than 450 m / g, the mechanical strength of the cured product will be low. 2 If it is greater than 1 / g, the particle size will be too fine, which will result in poor workability during the production of the silicone rubber compound.

[0038] Examples of such reinforcing silica include fumed silica, precipitated silica, and the like, and also those whose surfaces have been hydrophobized with chlorosilane, hexamethyldisilazane, and the like are preferably used. Among these, fumed silica, which has excellent dynamic fatigue properties, is preferred.

[0039] The component (B) may be used alone or in combination of two or more kinds.

[0040] The amount of the reinforcing silica of the above component (B) is 5 to 100 parts by mass, and preferably 10 to 50 parts by mass, per 100 parts by mass of the organopolysiloxane of the above component (A). If the amount of the above component (B) is too small, the reinforcing effect is not obtained, whereas if the amount is too large, the processability is deteriorated, the mechanical strength is reduced, and the dynamic fatigue durability is also deteriorated.

[0041] -(C) Component- In the present invention, a partial hydrolysate of an organoalkoxysilane represented by the following formula (1) is used as component (C). This component (C) is an essential component that reacts with hydroxyl groups present on the surface of the above-mentioned component (B) and acts as a surface treatment agent for quickly and uniformly dispersing component (B) in component (A). [ka] (In the formula, R is a monovalent hydrocarbon group having 1 to 12 carbon atoms, and R 1 represents an alkyl group having 1 to 4 carbon atoms.

[0042] Specific examples of the organoalkoxysilane include trimethoxy(methyl)silane, trimethoxy(ethyl)silane, trimethoxy(propyl)silane, trimethoxy(butyl)silane, trimethoxy(hexyl)silane, triethoxy(methyl)silane, tripropoxy(methyl)silane, and tributoxy(methyl)silane. Among these, trimethoxy(methyl)silane, trimethoxy(ethyl)silane, and triethoxy(methyl)silane are preferred, and trimethoxy(methyl)silane is more preferred. Partial hydrolysates of these organoalkoxysilanes are used as component (C). Since component (C) is a partial hydrolysate, the monovalent hydrocarbon group derived from the above R and the above R 1 In addition to the alkoxy groups derived from these, some hydroxy groups (hydroxysilyl groups) are also present.

[0043] Here, the degree of polymerization of the partial hydrolyzate of the organoalkoxysilane component (C) is preferably 2 to 100, and among these, it is particularly preferable to use a partial hydrolyzate with a degree of polymerization of 2 to 30 as the main component. If the component (C) is not a partial hydrolyzate, that is, if a monomer is used, it will be easily volatile, and will volatilize during kneading, resulting in an unstable plasticity of the resulting silicone rubber compound. In addition, the amount of volatile components will increase, which will be industrially dangerous, such as inhalation of volatile vapors and ignition. On the other hand, if the degree of polymerization of the component (C) is 100 or less, the viscosity of the component (C) will be appropriate, it will be easy to blend, and the surface treatment ability of the above-mentioned component (B) will be sufficient.

[0044] The kinetic viscosity of component (C) at 25°C is 1.0 to 1,000 mm 2 / s range is preferable, and 1.5 to 500 mm 2 / s is more preferable, and 1.5 to 300 mm 2 / s is particularly preferred. This kinematic viscosity is a value measured by a method using a Cannon-Fenske viscometer described in JIS Z8803: 2011. If it is within this range, it is preferable because it is easy to blend with other components and volatile components are also suppressed.

[0045] The amount of the partial hydrolyzate of organoalkoxysilane (C) is 0.1 to 20 parts by mass, preferably 0.5 to 10.0 parts by mass, per 100 parts by mass of the above-mentioned (A) component. If the amount of the (C) component is 0.1 parts by mass or less, plastic reversion occurs, causing problems in subsequent processability, or in the worst case, the compound cannot be obtained. If the amount of the (C) component is more than 20 parts by mass, the obtained compound may become sticky, causing poor processability, or the mechanical properties of the silicone rubber obtained by curing the compound may decrease.

[0046] -(D) Component- The component (D) is a silazane compound represented by the following formula (2) and / or (3). [ka] (In the formula, R 1each independently represents an alkyl group having 1 to 4 carbon atoms, and n is an integer of 3 or more and 10 or less.

[0047] It acts as a condensation reaction catalyst for causing a mutual condensation reaction between the silanol groups present on the surface of the reinforcing silica of component (B) and the silanol groups of component (C).

[0048] In addition, it is essential that the component (D) uses one or more of the above silazane compounds. Examples of the silazane compounds represented by the above formula (2) include 1,3-bis-(3,3,3-trifluoropropyl)-1,1,3,3-tetramethyldisilazane, 1,3-bis-(3,3,3-trifluoropropyl)-1,3-diethyl-1,3-dimethyldisilazane, and 1,3-bis-(3,3,3-trifluoropropyl)-1,3-dipropyl-1,3-dimethyldisilazane. Examples of the cyclic silazane compounds represented by the above formula (3) include 1,3,5-tri(3,3,3-trifluoropropyl)-1,3,5-trimethylcyclotrisilazane, and 1,3,5,7-tetra(3,3,3-trifluoropropyl)-1,3,5,7-tetramethylcyclotetrasilazane.

[0049] The amount of the (D) component added is 0.01 to 5.0 parts by mass, preferably 0.05 to 3.0 parts by mass, per 100 parts by mass of the (A) component. If the amount of the (D) component used is too small, the time required for surface treatment of the reinforcing silica may be extended, or the degree of surface treatment may be reduced, resulting in failure to obtain a silicone rubber compound. Conversely, if the amount of the (D) component used is too large, the (D) component may remain in the silicone rubber compound, and when attempting to obtain a silicone rubber cured product by addition curing using a platinum catalyst, the physical properties of the cured product may be unstable, or tack (adhesion) may occur on the surface of the cured product due to insufficient curing.

[0050] There is no particular restriction on the method of adding the (D) component, but it is preferable to add the (D) component to the (C) component and then add it promptly to the vessel containing the (B) component. This allows the condensation reaction between the silanol group of the (B) component and the alkoxy group of the (C) component to proceed efficiently. In addition, in order to make it easier to knead the (D) component with a two-roll mill or kneader, the (D) component may be made into a paste with organopolysiloxane or the like beforehand.

[0051] The millable silicone rubber compound of the present invention is preferably produced using a device capable of uniformly kneading the above-mentioned (A) to (D) components in the prescribed amounts. There are no particular limitations on the device capable of uniformly kneading, but considering the reactivity of the (D) component and removal after the reaction is completed, it is preferable to use a device that is likely to generate heat during stirring. Specifically, the millable silicone rubber compound can be obtained by kneading using a kneader, Banbury mixer, roll mill, etc., but it is particularly preferable to produce it using a kneader.

[0052] When the above components (A) to (D) are mixed, the partial hydrolyzate of organoalkoxysilane (C) acts as a wetter for the reinforcing silica (B). To promote the wetting effect, it is effective to add a catalyst for condensation reaction (D). In this case, water may be added as an optional component to further promote wetting. By adding this component, the partial hydrolyzate of organoalkoxysilane (C) quickly acts as a wetter for the reinforcing silica (B). In order to effectively treat the hydroxyl groups present on the surface of the component (B), it is essential that the component (C) contains a reactive group that quickly reacts with the hydroxyl group. For this reason, a partial hydrolyzate of an organosilicon compound that contains many reactive groups with hydroxyl groups in the molecule and hardly causes three-dimensional crosslinking is effective.

[0053] The temperature at which the components (A) to (D) are mixed is preferably in the range of 0 to 200° C., more preferably 10 to 180° C., and even more preferably 20 to 170° C. The time for mixing the components (A) to (D) is not particularly limited, but in consideration of production efficiency, it is desirable to set the mixing time to be preferably 1 to 300 minutes, and more preferably 10 to 120 minutes.

[0054] [Millable type silicone rubber composition] The millable type silicone rubber compound obtained as described above can be blended with a curing agent (E) to obtain a millable type silicone rubber composition.

[0055] That is, the millable type silicone rubber composition of the present invention is characterized in that the millable type silicone rubber compound contains a curing agent (E).

[0056] The component (E) will be described in more detail below.

[0057] -(E) Component- The (E) curing agent is not particularly limited as long as it is capable of curing the above-mentioned (A) component, but addition reaction (hydrosilylation reaction) type curing agents generally known as rubber curing agents, that is, (E1) hydrosilylation reaction curing agents containing a combination of an organohydrogenpolysiloxane (crosslinking agent) and a hydrosilylation catalyst, or (E2) organic peroxides are preferred.

[0058] If such a composition contains (E1) a curing agent for a hydrosilylation reaction or (E2) an organic peroxide, it is possible to exhibit high plasticity and, upon curing, to realize a silicone rubber with excellent mechanical strength.

[0059] The organohydrogenpolysiloxane used as the crosslinking agent of the addition reaction type curing agent (E1) has two or more hydrosilyl groups in one molecule. In particular, the organohydrogenpolysiloxane represented by the following formula (4) is preferred. [ka] (In the formula, R 3 are each independently a hydrogen atom or a group selected from the group consisting of an alkyl group having 1 to 8 carbon atoms, an aryl group having 6 to 10 carbon atoms, and an aralkyl group having 7 to 10 carbon atoms, and two or more R 3 is a hydrogen atom. In addition, two or more hydrogen atoms cannot be present on the same silicon atom. a is an integer of 2≦a≦30, b is an integer of 0≦b≦300, c is an integer of 0≦c≦10, and d is an integer of 0≦d≦30. In addition, the bonds of each siloxane unit may be in blocks or random.

[0060] Here, R 3 are each independently a hydrogen atom, or a group selected from the group consisting of an alkyl group having 1 to 8 carbon atoms, preferably 1 to 6 carbon atoms, an aryl group having 6 to 10 carbon atoms, preferably 6 to 8 carbon atoms, and an aralkyl group having 7 to 10 carbon atoms, preferably 7 to 9 carbon atoms. However, there may be at least 2, preferably 2 to 200, more preferably 2 to 130 R 3 is a hydrogen atom. Examples of the alkyl group include alkyl groups such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, pentyl, and hexyl groups, and cycloalkyl groups such as cyclohexyl. Examples of the aryl group include phenyl and tolyl groups. Examples of the aralkyl group include benzyl and 2-phenylpropyl groups. A fluoroalkyl group in which a part of the alkyl group is substituted with a fluorine atom may be used. Furthermore, a is an integer of 2≦a≦30, preferably 2≦a≦20. b is an integer of 0≦b≦300, preferably 3≦b≦200. c is an integer of 0≦c≦10, preferably 0≦c≦5. and d are integers of 0≦d≦30, preferably 0≦d≦20.

[0061] The molecular structure of the organohydrogenpolysiloxane may be any of linear, cyclic, branched, and three-dimensional network structures. In this case, the number of silicon atoms (or degree of polymerization) in one molecule is preferably 2 to 300, particularly about 4 to 200, and is liquid at 25°C. The hydrosilyl group may be present at the molecular chain terminal, in the side chain (in the middle of the molecular chain), or both.

[0062] Examples of the organohydrogenpolysiloxane include 1,1,3,3-tetramethyldisiloxane, 1,3,5,7-tetramethylcyclotetrasiloxane, methylhydrogencyclopolysiloxane, methylhydrogensiloxane-dimethylsiloxane cyclic copolymer, tris(dimethylhydrogensiloxy)methylsilane, tris(dimethylhydrogensiloxy)phenylsilane, methylhydrogenpolysiloxane capped at both ends with trimethylsiloxy groups, dimethylsiloxane-methylhydrogensiloxane copolymer capped at both ends with trimethylsiloxy groups, and dimethylhydrogenpolysiloxane capped at both ends with dimethylsiloxy groups. Siloxy group-blocked dimethylpolysiloxane, copolymer of dimethylhydrogensiloxane and methylhydrogensiloxane blocked at both ends with dimethylhydrogensiloxane, copolymer of methylhydrogensiloxane and diphenylsiloxane blocked at both ends with trimethylsiloxy groups, copolymer of methylhydrogensiloxane, diphenylsiloxane and dimethylsiloxane blocked at both ends with trimethylsiloxy groups, cyclic methylhydrogenpolysiloxane, copolymer of cyclic methylhydrogensiloxane and dimethylsiloxane, copolymer of cyclic methylhydrogensiloxane, diphenylsiloxane and dimethylsiloxane, (CH3)2HSiO 1 / 2 Units and SiO 4 / 2 A copolymer consisting of (CH3)2HSiO units. 1 / 2 Units and SiO 4 / 2 Units and (C6H5)SiO 3 / 2and copolymers consisting of units, and the above-listed compounds in which some or all of the methyl groups have been substituted with other alkyl groups such as ethyl groups, propyl groups, etc., or aryl groups such as phenyl groups, etc. Specific examples of such organohydrogenpolysiloxanes include compounds of the following structural formula:

[0063] [ka] (In the formula, k is an integer of 2 to 10, and s and t are each an integer of 0 to 10.)

[0064] The organohydrogenpolysiloxane preferably has a viscosity of 0.5 to 10,000 mPa·s, and particularly preferably 1 to 300 mPa·s, at 25° C. The viscosity is a value measured using a rotational viscometer according to the method described in JIS K7117-1:1999.

[0065] It is also desirable to incorporate this organohydrogenpolysiloxane in an amount such that the molar ratio (hydrosilyl groups / alkenyl groups) of hydrogen atoms bonded to silicon atoms in the organohydrogenpolysiloxane to the alkenyl groups bonded to silicon atoms in component (A) is 0.5 to 10, preferably 0.8 to 6, and more preferably 1 to 5. If the ratio is 0.5 or more, crosslinking will proceed sufficiently and sufficient mechanical strength will be obtained, while if it is 10 or less, the physical properties after curing will be good, and in particular the heat resistance and compression set resistance will be appropriate.

[0066] The hydrosilylation catalyst used in the (E1) addition reaction curing agent is a catalyst that promotes the addition reaction between the alkenyl group in the (A) component and the hydrosilyl group in the organohydrogenpolysiloxane as a crosslinking agent. Examples of the hydrosilylation catalyst include platinum group metal catalysts such as ruthenium and platinum. Platinum group metal catalysts include the platinum group metals and their compounds. For this, catalysts that have been known as catalysts for addition reaction curing silicone rubber compositions can be used. For example, fine particle platinum metal adsorbed on a carrier such as silica, alumina, or silica gel, platinic chloride, chloroplatinic acid, reaction products of chloroplatinic acid and monohydric alcohols, complexes of chloroplatinic acid and olefins, complexes of chloroplatinic acid and vinyl group-containing (poly)siloxanes, complexes of chloroplatinic acid and phosphite esters, and complexes of these with vinyl group-containing (poly)siloxanes, palladium catalysts, rhodium catalysts, ruthenium catalysts, etc. are listed. Among these, platinum or platinum compounds are particularly preferred.

[0067] The amount of hydrosilylation catalyst added may be a catalytic amount capable of promoting the addition reaction, and is usually used in the range of 1 ppm to 1 mass % calculated as the mass of platinum group metal relative to the amount of component (A), preferably in the range of 10 to 500 ppm. When the amount added is 1 ppm or more, the addition reaction is sufficiently promoted and sufficient curing can be achieved. On the other hand, when the amount is 1 mass % or less, it is economical.

[0068] In addition to the above catalysts, an addition crosslinking regulator may be used to adjust the curing rate, such as ethynylcyclohexanol or tetramethyltetravinylcyclotetrasiloxane.

[0069] On the other hand, examples of the (E2) organic peroxide include benzoyl peroxide, 2,4-dichlorobenzoyl peroxide, p-methylbenzoyl peroxide, o-methylbenzoyl peroxide, 2,4-dicumyl peroxide, 2,5-dimethyl-2,5-bis(t-butylperoxy)hexane, di-t-butyl peroxide, t-butyl perbenzoate, and 1,6-hexanediol-bis-t-butylperoxycarbonate.

[0070] The amount of organic peroxide added is preferably 0.1 to 15 parts by mass, particularly 0.2 to 10 parts by mass, per 100 parts by mass of component (A). If the amount added is sufficient, the crosslinking reaction proceeds sufficiently, and deterioration of physical properties such as a decrease in hardness, insufficient rubber strength, and an increase in compression set does not occur. In addition, if the amount added does not exceed the above amount, it is economically preferable, and the amount of decomposition product of the curing agent is sufficiently small, and deterioration of physical properties such as an increase in compression set and discoloration of the obtained sheet do not increase.

[0071] In addition to the above-mentioned components, the millable type silicone rubber composition of the present invention may contain additives such as electrical conductivity imparting agents such as carbon black, flame retardant imparting agents such as iron oxides and halogen compounds, antistatic agents, softening agents, antioxidants, ultraviolet absorbers, colorants, etc.

[0072] The millable type silicone rubber composition of the present invention thus obtained can be cured, for example, at 60 to 300°C, particularly 80 to 200°C, for 5 seconds to 1 hour, particularly 30 seconds to 30 minutes, to obtain a silicone rubber cured product. EXAMPLES

[0073] The present invention will be specifically described below using examples and comparative examples, but the present invention is not limited to these.

[0074] The average degree of polymerization was measured as the weight-average degree of polymerization converted into polystyrene by gel permeation chromatography (GPC) analysis, the viscosity was measured using a rotational viscometer according to the method described in JIS K7117-1:1999, the kinetic viscosity was measured using a Cannon-Fenske viscometer according to the method described in JIS Z8803:2011, and the refractive index was measured using an Abbe refractometer according to the method described in JIS K0062:1992.

[0075] Specific examples of each component used in the examples and comparative examples of the present invention are given below.

[0076] (A) Organopolysiloxane rubber (A-1) Organopolysiloxane raw rubber consisting of 99.975 mol % dimethylsiloxane units and 0.025 mol % dimethylvinylsiloxy units, having an average of two vinyl groups bonded to silicon atoms per molecule and an average degree of polymerization of 8,000. (A-2) Organopolysiloxane gum consisting of 99.5 mol % dimethylsiloxane units, 0.475 mol % methylvinylsiloxane units, and 0.025 mol % dimethylvinylsiloxy units, having an average of 40 vinyl groups bonded to silicon atoms per molecule and an average degree of polymerization of 8,000. (A-3) An organopolysiloxane gum consisting of 99.975 mol % fluoropropylmethylsiloxane units and 0.025 mol % dimethylvinylsiloxy units, having an average of two vinyl groups bonded to silicon atoms per molecule and an average degree of polymerization of 4,000.

[0077] (B) Reinforcing Silica (B-1) BET specific surface area is 200m 2 / g of fumed silica (product name: Aerosil 200, manufactured by Nippon Aerosil Co., Ltd.) (B-2) BET specific surface area is 130m 2 / g of surface-treated silica (product name: Aerosil R-972, manufactured by Nippon Aerosil Co., Ltd.)

[0078] (C) Partial hydrolysate of organoalkoxysilane (C-1) Partial hydrolysis product of trimethoxy(methyl)silane (product name: KC-89S, manufactured by Shin-Etsu Chemical Co., Ltd., kinematic viscosity [25°C]: 5 mm 2 / s, refractive index [25℃]: 1.394) (C-2) Partial hydrolysis product of trimethoxy(methyl)silane (product name: X-40-9225, manufactured by Shin-Etsu Chemical Co., Ltd., kinematic viscosity [25°C]: 100 mm 2 / s, refractive index [25℃]: 1.407) (C-3) Trimethoxy(methyl)silane (product name: KBM-13, manufactured by Shin-Etsu Chemical Co., Ltd., kinematic viscosity [25°C]: 0.5 mm 2 / s) [For comparative example] (C-4) Dimethylpolysiloxanediol (product name: X-93-1727, manufactured by Shin-Etsu Chemical Co., Ltd., kinematic viscosity [25°C]: 13 mm 2 / s) [For comparative example]

[0079] (D)Catalyst (D-1) 1,3-bis-(3,3,3-trifluoropropyl)-1,1,3,3-tetramethyldisilazane (Tokyo Chemical Industry Co., Ltd., purity: 94% or more) (D-2) Hexamethyldisilazane (Tokyo Chemical Industry Co., Ltd., purity: 96% or more) [for comparison] (D-3) Isopropylamine (Tokyo Chemical Industry Co., Ltd., purity: 99% or more) [for comparison]

[0080] The above components were mixed in the amounts shown in Table 1, and a silicone rubber compound was obtained through the following steps.

[0081] [Silicone rubber compound manufacturing process] Components (A) and (B) were added to a 3 L kneader along with components (C) and (D) in the amounts shown in Table 1. The mixture was kneaded uniformly and then further kneaded at the temperature and for the time shown in Table 1 to obtain a silicone rubber compound.

[0082] <Plasticity measurement> The silicone rubber compounds prepared in each of Examples 1 to 3 and Comparative Examples 1 to 6 were kneaded 15 times with a triple roll, and the William's plasticity was measured 10 minutes later (initial stage) using the method described in JIS K6249:2003, and then the plasticity was measured after one day at 40°C, and the change in plasticity after one day at 40°C relative to the initial value was calculated to evaluate the change over time. Values ​​for the change over time within ±50 were judged to be acceptable (same or better than the conventional product), and values ​​that deviated from this were judged to be unacceptable (worse than the conventional product).

[0083] <Physical property measurement> For each of 100 parts by mass of the silicone rubber compounds prepared in Examples 1 and 2 and Comparative Examples 1 to 4 and 6, 0.01 parts by mass of a platinum catalyst (manufactured by Shin-Etsu Chemical Co., Ltd.) containing 1% by mass of a chloroplatinic acid-divinyldisiloxane complex calculated as platinum atomic mass and a compound represented by the following formula (E1) were used as an addition reaction type curing agent: [ka] 0.85 parts by mass of organohydrogenpolysiloxane (manufactured by Shin-Etsu Chemical Co., Ltd.) represented by the formula: was added and mixed uniformly to prepare a millable type silicone rubber composition for each example. This composition was press cured at 120°C for 10 minutes, and then post cured at 200°C for 4 hours to prepare a test sheet for each example.

[0084] To 100 parts by mass of the silicone rubber compound prepared in each of Example 3 and Comparative Example 5, 0.8 parts by mass of a paste containing 80% 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane as the organic peroxide (E2) was added and mixed uniformly to prepare a millable type silicone rubber composition for each example. This composition was press-cured at 165°C for 10 minutes, and then post-cured at 200°C for 4 hours to prepare a test sheet for each example.

[0085] The hardness (Durometer A), tensile strength, elongation at break, tear strength (crescent), and compression set (150°C / 22 hours, 25% compression) of the prepared test sheets were measured according to the description of JIS K6249: 2003. Those with a tensile strength of less than 9.0 MPa, a tear strength of less than 40 kN / s, or a compression set of more than 30% were judged to be unacceptable due to poor physical properties.

[0086] [Table 1]

[0087] [Evaluation Results] Each of the silicone rubber compounds obtained in Examples 1 to 3 satisfied the requirements of the present invention, and it was found that the physical properties of each silicone rubber compound, as well as the physical properties of the molding test sheets obtained by curing the millable silicone rubber compositions prepared using them (density, hardness, elongation at break, tensile strength, tear strength, compression set) satisfied the target performance values.

[0088] In contrast, in Comparative Examples 1 and 2, a silazane compound or a simple amine compound that does not satisfy the requirements of the present invention was used as the condensation reaction catalyst for component (D). As a result, the millable type silicone rubber composition produced using this silicone rubber compound was cured to obtain a molding test sheet, and the physical properties of the sheet were lower in tensile strength and tear strength than those of Examples 1 and 2. As a result, the results deviated from the target values.

[0089] In Comparative Example 3, the organoalkoxysilane used as component (C) has the same structure, but is not a partial hydrolyzate. As a result, the organoalkoxysilane blended during kneading and heat treatment mixing is volatilized, which is thought to have reduced the degree of surface treatment of the reinforcing silica (component (B)). As a result, the initial plasticity is high and the plasticity after 24 hours at 40°C is high. In addition, the physical properties of the molding test sheet obtained by curing the millable type silicone rubber composition prepared using the silicone rubber compound of Comparative Example 3 show that the tear strength and compression set are worse than those of Examples 1 and 2. As a result, the results deviate from the target values.

[0090] In Comparative Example 4, dimethylpolysiloxane having hydroxyl groups at both ends was used as component (C). It is believed that this was the reason why the initial plasticity of the resulting silicone rubber compound was low. In addition, the millable type silicone rubber composition produced using this silicone rubber compound was cured to obtain a molding test sheet. In terms of physical properties, the tensile strength was lower than in Examples 1 and 2. This resulted in a deviation from the target value.

[0091] Comparative Example 5 differs from Example 2 in that a silazane compound, which is not a requirement of the present invention, was used as the condensation reaction catalyst for component (D). The millable type silicone rubber composition produced using this silicone rubber compound was cured to obtain a molding test sheet. The physical properties of the tensile strength and tear strength of the molding test sheet were lower than those of Example 2, resulting in deviation from the target values.

[0092] In Comparative Example 6, dimethylpolysiloxane having hydroxyl groups at both ends was used as component (C), and a silazane compound, which is not a requirement of the present invention, was used as the catalyst for the condensation reaction of component (D). As a result, the initial plasticity of the resulting silicone rubber compound was low, and the millable type silicone rubber composition produced using this silicone rubber compound was hardened to obtain a molding test sheet, and the physical properties of the tensile strength and tear strength were lower than those of Examples 1 and 2. As a result, the results deviated from the target values.

[0093] From the above results, it is clear that the silicone rubber compound of the present invention has high plasticity, and that the cured product obtained by curing the silicone rubber composition prepared using the compound exhibits very good mechanical strength, etc. [Industrial Applicability]

[0094] The millable silicone rubber compound of the present invention and the silicone rubber composition obtained by compounding the compound with a curing agent can show high plasticity even in the millable silicone rubber compound with a relatively low hardness. Therefore, it can contribute to the dimensional stability of low hardness extrusion molding materials. In addition, the silicone rubber composition using this silicone rubber compound has very good mechanical strength of the cured product, so it is expected to be applied to building materials and transportation fields that require high durability. In addition, it can be widely applied to electrical equipment, medical care, food fields, etc.

[0095] The present invention is not limited to the above-described embodiment. The above-described embodiment is merely an example, and anything that has substantially the same configuration as the technical idea described in the claims of the present invention and exhibits similar effects is included in the technical scope of the present invention.

Claims

1. A millable type silicone rubber compound characterized by comprising the following components (A) to (D): (A) organopolysiloxane gum having two or more alkenyl groups bonded to silicon atoms in each molecule and an average degree of polymerization of 1,000 to 100,000: 100 parts by mass, (B) A specific surface area measured by the BET adsorption method is 50 to 450 m ２ / g reinforcing silica: 5 to 100 parts by mass, (C) a partial hydrolysate of an organoalkoxysilane represented by the following formula (1): 0.1 to 20 parts by mass, 【Chemistry 1】 (In the formula, R is a monovalent hydrocarbon group having 1 to 12 carbon atoms, R １ represents an alkyl group having 1 to 4 carbon atoms; (D) a silazane compound represented by the following formula (2) and / or (3): 0.01 to 5.0 parts by mass, 【Chemistry 2】 (In the formula, R １ each independently represents an alkyl group having 1 to 4 carbon atoms, and n is an integer of 3 or more and 10 or less.

2. R and R in the formula (1) １ 2. The millable type silicone rubber compound according to claim 1, wherein each of the groups is independently any one of a methyl group, an ethyl group, and a propyl group.

3. 3. A millable type silicone rubber composition comprising the millable type silicone rubber compound according to claim 1 or 2 and (E) a curing agent.

4. 4. The millable silicone rubber composition according to claim 3, wherein the (E) curing agent is (E1) a hydrosilylation reaction type curing agent which contains a combination of an organohydrogenpolysiloxane and a hydrosilylation catalyst.

5. 4. The millable silicone rubber composition according to claim 3, wherein the curing agent (E) is an organic peroxide (E2).

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