JP5257297B2 - Addition-curing silicone rubber composition - Google Patents

Description

  The present invention relates to an addition-curable silicone rubber composition that provides a molded article that has high strength after curing, and even if a minute flaw enters a rubber during molding or use, the flaw is unlikely to become large.

  Silicone rubber has excellent heat resistance, cold resistance, safety, electrical insulation, weather resistance, etc., so it can be used for automobile parts such as connector seals and spark plug boots, and rolls for copiers and packing for microwave ovens. Widely used in various fields such as building parts, sealants and other building parts, baby bottle nipples and diving equipment. However, since the intermolecular force of the siloxane polymer forming the silicone rubber is very small, curing only the polymer results in a rubber with very low strength, which is inappropriate in terms of moldability and practical use. It becomes a material. In order to solve such problems, reinforcing silica such as fumed silica and precipitated silica is usually blended.

  On the other hand, silicone rubber is classified into a rubber-like rubber called a millable rubber or clay rubber called HCR (High Consistency Rubber), and a liquid type rubber having a viscosity called liquid rubber or LSR (Liquid Silicone Rubber). In recent years, liquid rubber has been rapidly increasing in demand because it is suitable for injection molding capable of mass production in a short time.

  In particular, a material in which a cured product is obtained by a cross-linking reaction between an alkenyl group, which is referred to as an addition curing type, and a hydrogen atom directly bonded to a silicon atom, that is, a SiH functional group, has a fast reaction, and hardly produces a by-product. It is used in a wide range of fields.

  However, even if silicone rubber contains reinforcing silica such as fumed silica and precipitated silica, its rubber strength is insufficient compared to natural rubber and other organic rubbers, especially tear strength (crescent type). The difference from organic rubber was obvious. In order to improve these, in JP-A-1-249858, JP-A-6-93185, JP-A-7-3034, and JP-A-7-268218 (Patent Documents 1 to 4), various compositions and Although a manufacturing method is disclosed, it is still very difficult to provide a material having a tear strength (crescent type) exceeding 50 kN / m constantly.

  On the other hand, in rubber applications, there may be a characteristic that the crack does not easily grow over time even when cracked in the rubber, and this characteristic does not necessarily coincide with the tear strength. This property is particularly important for rubber materials used in baby bottle nipples with cuts such as round holes and crosscuts. As such a material having excellent crack growth resistance, a millable type material is introduced in Japanese Patent Application Laid-Open No. 2004-256589 (Patent Document 5), but this is limited to organic peroxide crosslinking. The point which was excellent in the moldability of hardening was not made use of.

JP-A-1-249858 JP-A-6-93185 Japanese Patent Laid-Open No. 7-3034 JP 7-268218 A JP 2004-256589 A JP-A-9-12890

  The present invention has been made in order to improve the above circumstances. The cured rubber has high strength and high tearing, and even if the cured rubber is cracked, the crack is difficult to increase. An object of the present invention is to provide an addition-curable silicone rubber composition suitable for pacifiers.

  As a result of intensive studies to achieve the above object, the present inventor has found that two specific types of crosslinking agents for an addition-curable silicone rubber composition containing an alkenyl group-containing organopolysiloxane that is liquid at room temperature as a base polymer. Combination of organopolysiloxanes having silicon-bonded hydrogen atoms (SiH functional groups), that is, organopolysiloxanes having 3 to 5 SiH functional groups per molecule and organopolysiloxanes having 6 or more SiH functional groups per molecule In combination with siloxane, it has been found that an addition-curable silicone rubber composition that gives a cured product that has high strength, high tearing, and that does not easily become large even if cracked can be obtained. It came.

  JP-A-9-12890 (Patent Document 6) discloses an example of using an organopolysiloxane having 3 to 6 SiH functional groups in one molecule as an organopolysiloxane having a specific SiH functional group. Although it is shown, it is used alone to improve oil resistance. There is no description of organopolysiloxanes with different SiH functional group contents in the text, and they are also used in Examples and Comparative Examples. There is no example.

Accordingly, the present invention provides the following addition-curable silicone rubber composition.
[Claim 1]
(A) Both ends of a molecular chain are blocked with diorganoalkenylsiloxy groups, and do not have an alkenyl group bonded to a silicon atom in the middle of the molecular chain, and have an average degree of polymerization of 100 to 1,000. Part (B) Organopolysiloxane having at least three alkenyl groups in the molecule and different from the component (A) which is liquid at room temperature 0 to 50 parts by mass (C-1) Bonded to the silicon atom at the end of the molecular chain Organohydrogenpolysiloxane (C ) containing 2 hydrogen atoms, 1 to 3 hydrogen atoms bonded to silicon atoms in the middle of the molecular chain, and 3 to 5 hydrogen atoms bonded to silicon atoms in total. -2) A total of 6 or more hydrogen atoms bonded to silicon atoms at the molecular chain end and / or hydrogen atoms bonded to silicon atoms in the middle of the molecular chain per molecule. Ganohydrogenpolysiloxane The molar ratio of each silicon atom-bonded hydrogen atom (SiH group) in the component (C-1) and the component (C-2) is [SiH group (C-1)] / [SiH group (C -2)] = 90/10 to 10/90, and silicon atoms in component (C-1) and component (C-2) relative to the sum of alkenyl groups in component (A) and component (B) Amount in which the total molar ratio of bonded hydrogen atoms (SiH groups) is [SiH group] / [alkenyl group] = 1.1 to 3.0 (D) Fine powder silica 5 to 80 parts by mass (E) Addition reaction catalyst An addition-curable silicone rubber composition containing a catalytic amount.
[Claim 2]
The addition-curable silicone rubber composition according to claim 1, wherein the component (C-1) is a linear organohydrogenpolysiloxane having 4 to 100 silicon atoms in one molecule .
[Claim 3]
The addition curable silicone rubber composition according to claim 1 or 2, wherein the component (C-1) is a dimethylhydrogensiloxy group-blocked dimethylsiloxane / methylhydrogensiloxane copolymer having both molecular chain terminals.
[Claim 4]
(B) The compounding quantity of a component is 2-50 mass parts with respect to 100 mass parts of (A) component, The addition-curable silicone rubber composition of any one of Claims 1-3.
[Claim 5 ]
The addition curable silicone rubber composition according to any one of claims 1 to 4, wherein the fine powder silica of component (D) is fumed silica having a specific surface area of 250 m ² / g or more by BET method.
[Claim 6 ]
The addition-curable silicone rubber composition according to any one of claims 1 to 5 , which is used for baby pacifiers or baby bottle nipples.

  According to the present invention, it is possible to obtain an addition-curable silicone rubber composition in which not only the cured rubber has high strength and high tear, but also when the cured rubber has cracks, the cracks do not progress greatly. .

Hereinafter, the present invention will be described in more detail.
The alkenyl group-containing organopolysiloxane of component (A) is the main component (base polymer) of the silicone rubber composition of the present invention, wherein both ends of the molecular chain are blocked with diorganoalkenylsiloxy groups, and silicon atoms in the middle of the molecular chain An organopolysiloxane which does not have an alkenyl group bonded to the liquid and has an average degree of polymerization of 100 to 1,000 and is liquid at room temperature (25 ° C.). As the component (A), for example, the following average composition formula (I) What is shown by can be used.
R ¹ _a SiO _{(4-a) / 2} (I)
Wherein R ¹ is an unsubstituted or substituted monovalent hydrocarbon group having the same or different carbon number of 1 to 10, preferably 1 to 8, and a is 1.5 to 2.8, preferably 1. (It is a positive number in the range of 8 to 2.5, more preferably 1.95 to 2.05.)

Here, as the unsubstituted or substituted monovalent hydrocarbon group bonded to the silicon atom represented by R ¹ , a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a tert-butyl group, Pentyl group, neopentyl group, hexyl group, cyclohexyl group, octyl group, nonyl group, alkyl group such as decyl group, aryl group such as phenyl group, tolyl group, xylyl group, naphthyl group, benzyl group, phenylethyl group, phenylpropyl Aralkyl groups such as groups, vinyl groups, allyl groups, propenyl groups, isopropenyl groups, butenyl groups, hexenyl groups, cyclohexenyl groups, octenyl groups and other alkenyl groups, and some or all of the hydrogen atoms of these groups are fluorine. Substituted with a halogen atom such as bromine, chlorine, cyano group, etc., such as chloromethyl group, chloro Propyl group, bromoethyl group, trifluoropropyl group, but cyanoethyl group and the like, all R ¹ of 90 mol% or more, and particularly it is preferable that all of R ¹ other than the alkenyl group is a methyl group.

In addition, at least two of R ¹ are alkenyl groups (preferably those having 2 to 8 carbon atoms, more preferably 2 to 6 carbon atoms, and particularly preferably a vinyl group). The alkenyl group in the organoalkenylsiloxy group needs to be located at both ends of the molecular chain as an alkenyl group (that is, an alkenyl group bonded to the silicon atom at the molecular chain end). That is, the component (A) does not contain any other alkenyl group (that is, an alkenyl group bonded to a silicon atom in the middle of the molecular chain) other than the alkenyl group located at the molecular chain end.

Therefore, since the alkenyl group in component (A) exists only at the molecular chain end (that is, only two in the molecule when component (A) has a linear structure), The content of the alkenyl group is determined by the degree of polymerization, but is 6.0 × 10 ⁻⁶ mol / g to 3.0 × 10 ⁻⁴ mol / g, particularly 1.0 × 10 ^{−5 in the} organopolysiloxane. It is preferable to set it as mol / g-2.0 * 10 < ^-4 > mol / g. If the amount of the alkenyl group is less than 6.0 × 10 ⁻⁶ mol / g, the rubber hardness is too low to form a gel, and if it exceeds 3.0 × 10 ⁻⁴ mol / g, the crosslinking density increases. It becomes too hard rubber.

  The structure of this organopolysiloxane basically has a linear structure in which both ends of the molecular chain are blocked with diorganoalkenylsiloxy groups such as dimethylvinylsiloxy groups, and the main chain is composed of repeating diorganosiloxane units. , A partially branched structure, a ring structure or the like may be used. When there is a branch, the end of the branched chain is blocked with a diorganoalkenylsiloxy group such as dimethylvinylsiloxy group, but is blocked with a triorganosiloxy group not containing alkenyl such as trimethylsiloxy group. However, it is desirable that the average number of alkenyl groups in the component (A) is less than 3, usually 2 to 2.2, particularly 2 to 2.1. Regarding the molecular weight, the average degree of polymerization (weight average degree of polymerization in terms of polystyrene in gel permeation chromatography (GPC) analysis, hereinafter the same) is usually 100 to 1,000, preferably 150 to 800. If it is less than 100, sufficient rubber feeling cannot be obtained, and if it is higher than 1,000, the viscosity becomes high and molding becomes difficult.

  Specific examples of the component (A) include, for example, molecular chain both ends diorganoalkenylsiloxy group-capped diorganopolysiloxane such as dimethylvinylsiloxy group-capped dimethylpolysiloxane (in this case, the organo group has an alkenyl group). Is not included).

Next, the alkenyl group-containing organopolysiloxane of the component (B) is an organopolysiloxane having at least three alkenyl groups in the molecule and different from the component (A) which is liquid at room temperature. As this (B) component, what is shown by the following average composition formula (II) can be used, for example.
R ² _b SiO _{(4-b) / 2} (II)
(In the formula, R ² is an unsubstituted or substituted monovalent hydrocarbon group having the same or different carbon number of 1 to 10, preferably 1 to 8, and b is 1.8 to 2.5, preferably 1. (It is a positive number in the range of 9 to 2.1.)

Here, the unsubstituted or substituted monovalent hydrocarbon group bonded to the silicon atom represented by R ² is the same as R ¹ described above, and includes a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, Alkyl group such as isobutyl group, tert-butyl group, pentyl group, neopentyl group, hexyl group, cyclohexyl group, octyl group, nonyl group, decyl group, aryl group such as phenyl group, tolyl group, xylyl group, naphthyl group, benzyl Group, aralkyl group such as phenylethyl group, phenylpropyl group, etc., alkenyl group such as vinyl group, allyl group, propenyl group, isopropenyl group, butenyl group, hexenyl group, cyclohexenyl group, octenyl group, and hydrogen of these groups Some or all of the atoms are substituted with halogen atoms such as fluorine, bromine and chlorine, cyano groups, etc. Romechiru group, chloropropyl group, bromoethyl group, trifluoropropyl group, but cyanoethyl group and the like, 90 mol% of the total R ² or more, and particularly preferably all R ² other than the alkenyl group is a methyl group .

Further, among R ^{2 in} one molecule, the number of alkenyl groups (preferably having 2 to 8 carbon atoms, more preferably 2 to 6 and particularly preferably vinyl groups) is 3 or more, preferably It is essential to have about 3 to 50, more preferably about 4 to 20. The alkenyl group content is preferably in the range of 0.00001 mol / g to 0.002 mol / g, particularly 0.00002 mol / g to 0.001 mol / g. When the amount of the alkenyl group is more than 0.002 mol / g, the rubber hardness is increased and the rubber may be brittle. If it is less than 0.00001 mol / g, sufficient rubber strength may not be obtained. The alkenyl group may be bonded to the silicon atom at the end of the molecular chain, may be bonded to the silicon atom in the middle of the molecular chain, or may be bonded to both. Therefore, when the component (B) has a linear structure, it essentially contains an alkenyl group bonded to a silicon atom in the middle of the molecular chain.

  The structure of this organopolysiloxane is basically a linear structure in which both ends of the molecular chain are blocked with triorganosiloxy groups and the main chain is composed of repeating diorganosiloxane units, as in the case of component (A). However, a partially branched structure, a ring structure, or the like may be used. Regarding the molecular weight, the average degree of polymerization is usually from 50 to 1,000, preferably from 100 to 500, and is preferably liquid at room temperature. If the average degree of polymerization is less than 50, a rubber feeling cannot be obtained, and if it exceeds 1,000, the viscosity is too high and blending and molding may be difficult.

  Specific examples of the component (B) include, for example, molecular chain both ends diorganoalkenylsiloxy group blocked organoalkenylsiloxane / diorganosiloxane copolymer such as molecular chain both ends dimethylvinylsiloxy group blocked methylvinylsiloxane / dimethylsiloxane copolymer. Polymers, molecular chain both ends triorganosiloxy group-blocked triorganosiloxy group-blocked organoalkenylsiloxane / diorganosiloxane copolymer such as methylvinylsiloxane / dimethylsiloxane copolymer Group is not included).

  The compounding quantity of such organopolysiloxane (B) is 0-50 mass parts with respect to 100 mass parts of (A) component, Preferably it is 2-40 mass parts, More preferably, it is the range of 5-30 mass parts. If the amount of component (B) is too large, the cured product will be hard and brittle rubber.

  Next, the combination of the components (C-1) and (C-2) is a combination of hydrogen atoms bonded to silicon atoms in the components (C-1) and (C-2) (that is, hydrosilyl groups represented by SiH). ) Acts as a curing agent (crosslinking agent) for curing the composition by crosslinking with the alkenyl group bonded to the silicon atom in the components (A) and (B) by a hydrosilylation addition reaction. It is essential to achieve the main object of the invention.

(C-1) An organohydrogenpolysiloxane having a total of 3 to 5 hydrogen atoms bonded to silicon atoms at the molecular chain terminals and / or silicon atoms in the middle of the molecular chain, per molecule. Is, for example, the following average composition formula (III)
R ³ _c H _d SiO _{(4-cd) / 2} (III)
Wherein R ³ is an unsubstituted or substituted monovalent hydrocarbon group having 1 to 10 carbon atoms, c is 0.7 to 2.1, d is 0.001 to 1.0, and c + d is a positive number satisfying 0.8 to 3.0.)
It is essential that it has 3 to 5, preferably 4 or 5 silicon-bonded hydrogen atoms (SiH group) in one molecule. When the number of SiH groups in the molecule is 2 or less, the rubber strength is lowered, and when it is 6 or more (that is, when the component (C-2) described later is compounded alone), the crack progress suppressing effect is obtained. It can no longer be obtained. When an organohydrogenpolysiloxane having 3 to 5 SiH groups in one molecule is used, the chain length of the base polymer (component (A)) can be efficiently extended by two-point crosslinking without reducing the rubber strength. Therefore, it is possible to effectively suppress the progress of cracks.

Here, examples of the monovalent hydrocarbon group for R ³ include the same groups as those exemplified for R ¹ , but those having no aliphatic unsaturated group such as an alkenyl group are preferred. Further, c is preferably 0.8 to 2.0, d is preferably 0.01 to 1.0, c + d is preferably 1.0 to 2.5, and (C-1) component organohydrogen The molecular structure of the polysiloxane may be any of linear, cyclic, branched, and three-dimensional network structures. In this case, the number of silicon atoms in one molecule (or the degree of polymerization) is preferably 3 to 300, particularly 4 to 150, and more preferably about 5 to 100 at room temperature (25 ° C.). .

  In addition, the hydrogen atom bonded to the silicon atom may be located at either the molecular chain end or in the middle of the molecular chain, and may be located at both, but 3 to 5, preferably 4 or Of the five SiH groups, two are preferably located at both ends of the molecular chain as hydrogen atoms bonded to the silicon atom at the molecular chain end (for example, a silicon atom-bonded hydrogen atom in a diorganohydrogensiloxy group). In addition, the remaining 1-3, especially 2 or 3, are bonded in the middle of the molecular chain as hydrogen atoms (for example, silicon-bonded hydrogen atoms in the organohydrogensiloxane unit) in the middle of the molecular chain ( It is preferably located at the molecular chain non-terminal.

Examples of the organohydrogenpolysiloxane of component (C-1) include 1,1,3,5,5-pentamethyltrisiloxane, 1,3,5,7-tetramethylcyclotetrasiloxane, and methylhydrogencyclopolysiloxane. Siloxane, methylhydrogensiloxane / dimethylsiloxane cyclic copolymer, tris (dimethylhydrogensiloxy) methylsilane, tris (dimethylhydrogensiloxy) phenylsilane, trimethylsiloxy group-blocked methylhydrogenpolysiloxane, trimethylsiloxy group at both ends Blocked dimethylsiloxane / methylhydrogensiloxane copolymer, both ends dimethylhydrogensiloxy group blocked methylhydrogenpolysiloxane, both ends dimethylhydrogensiloxy group blocked dimethyl Rokisan-methylhydrogensiloxane copolymers, both end trimethylsiloxy-blocked methylhydrogensiloxane-diphenylsiloxane copolymers, both end trimethylsiloxy-blocked methylhydrogensiloxane-diphenylsiloxane-dimethylsiloxane copolymer, (CH ₃ ) Copolymer comprising ₂ HSiO _1/2 units and SiO _4/2 units, comprising (CH ₃ ) ₂ HSiO _1/2 units, (CH ₃ ) ₃ SiO _1/2 units and SiO _4/2 units. And a copolymer comprising (CH ₃ ) ₂ HSiO _1/2 units, SiO _4/2 units, and (C ₆ H ₅ ) ₃ SiO _1/2 units.

Subsequently, an organohydrogenpolysiloxane having a total of 6 or more hydrogen atoms bonded to silicon atoms at the molecular chain terminals and / or silicon atoms in the middle of the molecular chain as a component (C-2). As, for example, the following average composition formula (IV)
R ⁴ _e H _f SiO _{(4-ef) / 2} (IV)
Wherein R ⁴ is an unsubstituted or substituted monovalent hydrocarbon group having 1 to 10 carbon atoms, e is 0.7 to 2.1, f is 0.002 to 1.0, and e + f is a positive number satisfying 0.8 to 3.0.)
It is essential to have 6 or more silicon-bonded hydrogen atoms (SiH groups) in one molecule. When an organohydrogenpolysiloxane having 6 or more SiH groups in one molecule is used, the crosslink points of the polymer are concentrated (localized) in the siloxane matrix, so that the rubber strength, particularly the tear strength, is significantly improved. The effect is obtained.

Here, examples of the monovalent hydrocarbon group for R ⁴ include the same groups as those exemplified for R ¹ , but those having no aliphatic unsaturated group such as an alkenyl group are preferred. Also, e is preferably 0.8 to 2.0, f is preferably 0.02 to 1.0, e + f is preferably 1.0 to 2.5, and (C-2) component organohydrogen The molecular structure of the polysiloxane may be any of linear, cyclic, branched, and three-dimensional network structures. In this case, the number of silicon atoms in one molecule (or the degree of polymerization) is preferably 6 to 300, particularly 8 to 150, and more preferably about 8 to 100 at room temperature (25 ° C.). .

  In addition, it is essential that the number of hydrogen atoms (SiH groups) bonded to the silicon atom is 6 or more, preferably 8 or more, and more preferably 10 or more. The upper limit of the number of silicon atom-bonded hydrogen atoms (SiH groups) is usually about 300 or less, preferably about 150 or less, more preferably about 100 or less. The hydrogen atom bonded to the silicon atom may be located at either the molecular chain end or in the middle of the molecular chain, or may be located at both.

Examples of the organohydrogenpolysiloxane of component (C-2) include methylhydrogencyclopolysiloxane, methylhydrogensiloxane / dimethylsiloxane cyclic copolymer, trimethylsiloxy group-blocked methylhydrogenpolysiloxane at both ends, and trimethyl at both ends. Siloxy group-blocked dimethylsiloxane / methylhydrogensiloxane copolymer, both ends dimethylhydrogensiloxy group-blocked methylhydrogenpolysiloxane, both ends dimethylhydrogensiloxy group-blocked dimethylsiloxane / methylhydrogensiloxane copolymer, both ends trimethyl Siloxy group-blocked methyl hydrogen siloxane / diphenyl siloxane copolymer, trimethylsiloxy group-blocked methyl hydrogen siloxane dip Sulfonyl-dimethylsiloxane copolymer, (CH ₃₎ a copolymer consisting of ₂ HSiO _1/2 units and SiO _4/2 units, (CH _{3) 2} HSiO _1/2 units and (CH _{3) 3} SiO _{1 / 2} unit and a copolymer consisting of SiO _4/2 units, a copolymer consisting of (CH ₃ ) ₂ HSiO _1/2 units, SiO _4/2 units and (C ₆ H ₅ ) ₃ SiO _1/2 units Examples include coalescence.

  The organohydrogenpolysiloxanes of the component (C-1) and the component (C-2) are generally 0.2 to 20 parts by mass, particularly 0.3 to 100 parts by mass of the component (A). It is preferable to mix in the range of about 15 parts by mass, but the silicon atom in the component (C-1) and the component (C-2) with respect to the sum of the alkenyl groups in the component (A) and the component (B) The total molar ratio of bonded hydrogen atoms (SiH groups) is [SiH group] / [alkenyl group] = 1.1 to 3.0, preferably 1.2 to 2.5. If this molar ratio is less than 1.1, crosslinking is insufficient and high strength cannot be obtained or a sticky rubber is obtained. On the other hand, when the molar ratio is larger than 3.0, foaming is observed in the molded product, or release from the mold becomes difficult.

  Moreover, the compounding ratio of (C-1) component and (C-2) component is the molar ratio of each silicon atom bond hydrogen atom (SiH group) in (C-1) component and (C-2) component. [SiH group (C-1)] / [SiH group (C-2)] = 90/10 to 10/90, preferably [SiH group (C-1)] / [SiH group (C -2)] = 80/20 to 20/80, more preferably [SiH group (C-1)] / [SiH group (C-2)] = 70/30 to 30/70. If this ratio is larger than 90/10, sufficient rubber strength cannot be obtained, and if it is smaller than 10/90, the effect of suppressing the progress of cracks cannot be obtained.

Next, the fine powder silica of the component (D) is not particularly limited as long as it is used as a reinforcing material for silicone rubber. As the fine powder silica, those used in conventional silicone rubber compositions can be used, and in particular, fine powder silica having a specific surface area of 50 m ² / g or more by the BET method is used. In particular, 50 to 400 m ² / g precipitated silica, fumed silica or the like is preferably used. In order to improve rubber strength, fumed silica is suitable, and in particular, those having a specific surface area of 250 m ² / g or more by the BET method are preferred.

  Further, the fine powder silica may be surface-treated fine powder silica. In that case, these fine powder silicas may be directly treated in a powder state in advance. It can be processed by a generally well-known technique as a normal processing method. For example, the untreated fine powder silica and the processing agent are put in a mechanical kneading apparatus or a fluidized bed sealed at normal pressure, and an inert gas is present if necessary. Under the mixing treatment at room temperature or heat treatment. In some cases, a catalyst may be used to facilitate the treatment. After kneading, the treated fine powdered silica can be produced by drying. The blending amount of the treatment agent may be equal to or more than the amount calculated from the coating area of the treatment agent.

  Treatment agents are silazanes such as hexamethyldisilazane, methyltrimethoxysilane, ethyltrimethoxysilane, propyltrimethoxysilane, butyltrimethoxysilane, dimethyldimethoxysilane, diethyldimethoxysilane, vinyltriethoxysilane, vinyltrimethoxysilane. Silane coupling agents such as trimethylmethoxysilane, triethylmethoxysilane, vinyltris (methoxyethoxy) silane, trimethylchlorosilane, dimethyldichlorosilane, divinyldimethoxysilane and chloropropyltrimethoxysilane, polymethylsiloxane, organohydrogenpolysiloxane, etc. These organic silicon compounds are surface-treated with these and used as hydrophobic fine powder silica. As the treating agent, silane coupling agents or silazanes are particularly preferable.

  (D) The compounding quantity of a component is 5-80 mass parts with respect to 100 mass parts of (A) component, Preferably it is 10-70 mass parts, More preferably, it is 15-60 mass parts. If the amount is less than 5 parts by mass, the rubber strength may be too low to make it difficult to remove the mold. If the amount exceeds 80 parts by mass, filling becomes difficult, and workability and workability deteriorate.

  (E) Component addition reaction catalyst includes platinum black, platinous chloride, chloroplatinic acid, reaction product of chloroplatinic acid and monohydric alcohol, complex of chloroplatinic acid and olefins, platinum bisacetoacetate, etc. And platinum group metal catalysts such as platinum-based catalysts, palladium-based catalysts, and rhodium-based catalysts. In addition, the compounding quantity of this addition reaction catalyst can be made into a catalyst quantity, and is 0.5-1,000 ppm with respect to (A) component normally in conversion of the mass of a platinum group metal, Especially about 1-500 ppm. .

  Other components include fillers such as quartz powder, diatomaceous earth, calcium carbonate, and aluminum oxide, conductive agents such as carbon black, conductive zinc white, and metal powder, nitrogen-containing compounds, acetylene compounds, and phosphorus as necessary. Compounds, nitrile compounds, carboxylates, tin compounds, mercury compounds, sulfur compounds and other hydrosilylation reaction control agents, heat-resistant agents such as iron oxide, titanium oxide and cerium oxide, internal mold release agents such as dimethyl silicone oil, adhesiveness It is optional to add an imparting agent, a thixotropic imparting agent or the like.

  The addition-curable silicone rubber composition of the present invention can be obtained by simply mixing the above-described components (A) to (E) and, if necessary, optional components evenly at room temperature. It is preferable that the total amount of the component (A) or a part thereof and a planetary mixer, a kneader or the like be heat-treated in a range of 100 to 200 ° C. for 1 to 4 hours in advance, and after cooling to room temperature, other components are added and mixed.

  The molding method can be freely selected depending on the viscosity of the mixture, and any method such as injection molding, compression molding, dispenser molding, injection molding, extrusion molding, or transfer molding may be employed. The curing condition can be usually heated at 60 to 200 ° C. within a range of 10 seconds to 24 hours.

In order to be effectively used for these moldings, the viscosity of the present composition is preferably 50 to 800 Pa · s, more preferably 80 to 80 at a shear rate of 10 s ⁻¹ at 25 ° C. The range is 600 Pa · s, more preferably in the range of 100 to 500 Pa · s. Even if this viscosity is less than 50 Pa · s or more than 800 Pa · s, molding becomes difficult.

  In order to obtain the above viscosity, the viscosity is appropriately adjusted depending on the degree of polymerization of the organopolysiloxane component to be used (particularly the (A) component which is the base polymer) and the type and blending amount of the finely divided silica of the (D) component can do. For example, when the average degree of polymerization of the component (A) is 800 or more, the blending amount of the fine powder silica of the component (D) is 40 parts by weight with respect to 100 parts by mass of the component (A) in the case of dry silica (fumed silica). In the case of wet silica (precipitated silica) having a low surface activity and not more than 50 parts by mass, the content is preferably 50 parts by mass or less with respect to 100 parts by mass of component (A). Moreover, when the average degree of polymerization of (A) component is 300-800, the compounding quantity of (D) component is 60 mass parts or less (especially 20-50 mass parts) with respect to 100 mass parts of (A) component, ( When the average degree of polymerization of component A) is less than 300, the amount of component (D) is preferably 40 parts by mass or more (particularly 40 to 100 parts by mass) with respect to 100 parts by mass of component (A).

  In addition, the curing speed of such an addition-curable silicone rubber composition is not particularly limited as long as it is suitable for the molding method described above. However, if importance is placed on the efficiency, a curing tester [rotorless type disc rheometer, When 10% curing time at 3 minutes measurement at 130 ° C. with a moving die rheometer or MDR] is T10 (seconds), it is preferably in the range of 10 seconds ≦ T10 ≦ 60 seconds, more preferably The range is 15 seconds ≦ T10 ≦ 40 seconds. If it is less than 10 seconds, curing may be too fast and molding may be difficult, and if it exceeds 60 seconds, the molding cycle may be long and uneconomical.

  In order to set the 10% curing time in the above range, in addition to the addition reaction catalyst of component (E), conventionally known addition reaction control for acetylene compounds, phosphorus compounds, nitrogen-containing compounds, nitrile compounds, carboxylates, etc. It is preferable to use an agent, particularly preferably, an acetylene compound (acetylene alcohol) having a hydroxyl group on carbon having a triple bond in combination. The blending amount of the addition reaction control agent can be appropriately selected based on the blending ratio with the component (E) so that the above T10 falls within an appropriate range.

  The addition-curable silicone rubber composition of the present invention is not only high-strength, high-tear, but also hard to progress even if there are cracks. It is useful as a waterproof sealing material for baby bottle nipples and automobiles.

  EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention concretely, this invention is not limited to a following example. In addition, a part shows a mass part by the following example. Moreover, an average polymerization degree shows the weight average polymerization degree in polystyrene conversion in a gel permeation chromatography (GPC) analysis.

[Example 1]
60 parts of dimethylpolysiloxane (1) having an average degree of polymerization of 500 blocked at both ends with dimethylvinylsiloxy groups and a specific surface area of 300 m ² / g by BET method (manufactured by Aerosil Japan, Aerosil 300) ) 40 parts, 8 parts of hexamethyldisilazane, and 2.0 parts of water were mixed at room temperature for 30 minutes, heated to 150 ° C., and stirred for 3 hours. After cooling, 15 parts of dimethylpolysiloxane (1), dimethylpolysiloxane (2) having an average degree of polymerization of 200 having both ends blocked with trimethylsiloxy groups and having 8 vinyl groups per molecule in the side chain [ 15 parts of vinyl group amount 0.00052 mol / g] was added, and stirring was continued for 30 minutes to obtain a silicone rubber base. Methyl hydrogen polysiloxane having 4 SiH groups per molecule as both crosslinks and side chains as a cross-linking agent on 130 parts of this silicone rubber base (that is, dimethylsiloxane siloxy group-blocked dimethylsiloxane / methylhydrogen at both molecular chain ends) Siloxane copolymer) (3) Methyl hydrogen polysiloxane having 2.5 parts of [degree of polymerization 20, SiH group amount 0.0028 mol / g] and 10 SiH groups per molecule only in the side chain (ie, Molecular chain both ends trimethylsiloxy group-blocked dimethylsiloxane / methylhydrogensiloxane copolymer) (4) 2.5 degree of polymerization degree 22, SiH group amount 0.0066 mol / g, ethynylcyclohexanol 0 as reaction control agent 0.07 part was added and stirring was continued for 15 minutes until the silicone rubber composition [ Viscosity of 289Pa · s at a shear rate of 10s ^-1 at 5 ° C., viscosity at 0.9 s ^-1 is 856Pa · s. Measured with a precision rotary viscometer Rotobisco RV1 (Eihiro Seiki), and so on. ] Was obtained.

  At this time, the molar ratio between the alkenyl group and the SiH group is [polysiloxane (3) + polysiloxane (4)] / [polysiloxane (1) + polysiloxane (2)] = 2.0, polysiloxane (3). The molar ratio of SiH groups in the polysiloxane (4) is (3) / (4) = 30/70.

  A cured product obtained by mixing 100 parts of this silicone rubber composition with 0.1 part of a platinum catalyst (Pt concentration of 1% by mass) and performing a press cure at 120 ° C. for 10 minutes is based on JIS-K6249. The strength, elongation at break, tear strength (crescent) and crack elongation test were performed, and the measurement results are shown in Table 1. In the crack extension test, a test piece for measuring the tear strength (crescent) is used, a part 10 mm away from a 1 mm cut is marked, and the whole test piece is extended until the distance between the marks increases from 20 mm to 40 mm. Then, hold the state with a jig (used for permanent elongation measurement), whether or not the test piece breaks after being placed in an oven at 180 ° C, and if it does not break, the length of the cut (when stretched) Was measured.

[Example 2]
60 parts of dimethylpolysiloxane (5) having an average degree of polymerization of 800 having both ends blocked with dimethylvinylsiloxy groups and a hydrophobized surface and a specific surface area of 230 m ² / g by the BET method (Tokuyama) Manufactured by Leoroseal DM-30S), 2 parts of hexamethyldisilazane, and 1 part of water were mixed at room temperature for 30 minutes, heated to 150 ° C., and stirred for 3 hours. After cooling, 20 parts of dimethylpolysiloxane (5) was further added and stirred for 30 minutes to obtain a silicone rubber base. 120 parts of this silicone rubber base is 20 parts of the dimethylpolysiloxane (1) of Example 1, both ends are blocked with vinyldimethylsiloxy groups, and the average degree of polymerization is 150 with 10 vinyl groups per molecule in the side chain. 5 parts of a certain dimethylpolysiloxane (6) [vinyl group amount 0.00094 mol / g] was added, and after stirring for 30 minutes, methyl having 5 SiH groups per molecule at both ends and side chains as a crosslinking agent. 1.6 parts of hydrogen polysiloxane (ie, dimethylhydrogensiloxy group-blocked dimethylsiloxane / methylhydrogensiloxane copolymer with both ends of the molecular chain) (7) [degree of polymerization 17, amount of SiH group 0.0042 mol / g] And 1.0 part of methyl hydrogen polysiloxane (4) of Example (1), ethynyl siku as a reaction control agent Was added 0.06 parts of hexanol, and the stirring was continued for 15 minutes, the silicone rubber composition Viscosity is 228Pa · s at a shear rate of 10s ^-1 at 25 ° C., viscosity at 0.9 s ^-1 is 556Pa · s ] Was obtained.

  At this time, the molar ratio between the alkenyl group and the SiH group is [polysiloxane (7) + polysiloxane (4)] / [polysiloxane (5) + polysiloxane (1) + polysiloxane (6)] = 1.5. The molar ratio of SiH groups of polysiloxane (7) and polysiloxane (4) is (7) / (4) = 50/50.

  About 100 parts of this silicone rubber composition, 0.1 part of a platinum catalyst (Pt concentration 1 mass%) was mixed, and a cured product obtained by performing a press cure at 120 ° C./10 minutes was the same as in Example (1). Based on K6249, hardness, tensile strength, elongation at break, tear strength (crescent) and crack elongation test were performed, and the measurement results are shown in Table 1.

[Example 3]
50 parts of dimethylpolysiloxane (1) of Example 1, 20 parts of dimethylpolysiloxane (2) of Example (1), fumed silica having a specific surface area of 300 m ² / g by BET method (manufactured by Nippon Aerosil Co., Ltd., 35 parts of Aerosil 300) Precipitated silica (manufactured by Nippon Silica Co., Ltd., nip seal SS-30P) having a specific surface area of 125 m ² / g by a BET method with a hydrophobized surface and a DBP oil absorption (dibutyl phthalate oil absorption) of 170 ml / 100 g ) 10 parts, 8 parts of hexamethyldisilazane, and 1.0 part of water were mixed at room temperature for 30 minutes, heated to 150 ° C., and stirred for 3 hours. After cooling, 20 parts of dimethylpolysiloxane (1) of Example 1 was added and stirring was continued for 30 minutes to obtain a silicone rubber base. After adding 25 parts of the dimethylpolysiloxane (5) of Example 2 to 135 parts of this silicone rubber base, stirring was continued for 30 minutes, and methylhydrosilane having three SiH groups per molecule at both ends and side chains as a crosslinking agent. Genpolysiloxane (namely, dimethylhydrogensiloxy group-blocked dimethylsiloxane / methylhydrogensiloxane copolymer with both ends of the molecular chain) (8) [polymerization degree 18, SiH group amount 0.0023 mol / g] 1.2 parts, Further, methylhydrogenpolysiloxane having 20 SiH groups per molecule at both ends and side chains as a crosslinking agent (that is, dimethylsiloxane / methylhydrogensiloxane copolymer blocked with dimethylhydrogensiloxy groups blocked at both ends of the molecular chain) (9 ) [Polymerization degree 30, SiH group amount 0.0102 mol / g] 1.5 parts, It was added 0.07 part of ethynyl cyclohexanol as a response control agent, and the stirring was continued for 15 minutes, the viscosity at a shear rate of 10s ^-1 of the silicone rubber composition [25 ° C. is 289Pa · s, at 0.9 s ^-1 Of 672 Pa · s].

  At this time, the molar ratio between the alkenyl group and the SiH group is [polysiloxane (8) + polysiloxane (9)] / [polysiloxane (1) + polysiloxane (2) + polysiloxane (5)] = 1.2. The molar ratio of SiH groups of polysiloxane (8) and polysiloxane (9) is (8) / (9) = 15/85.

  About 100 parts of this silicone rubber composition, 0.1 part of a platinum catalyst (Pt concentration 1 mass%) was mixed, and a cured product obtained by performing a press cure at 120 ° C./10 minutes was the same as in Example (1). Based on K6249, hardness, tensile strength, elongation at break, tear strength (crescent) and crack elongation test were performed, and the measurement results are shown in Table 1.

[Comparative Example 1]
Instead of 2.5 parts of methylhydrogenpolysiloxane (3) in Example 1, methylhydrogenpolysiloxane having SiH groups only at both ends (namely, dimethylhydrogensiloxy group-blocked dimethylpolysiloxane having molecular ends at both ends) (10) A silicone rubber composition was obtained in the same manner except that 5.2 parts of [degree of polymerization 20, amount of SiH group 0.00136 mol / g] was used.

  At this time, the molar ratio between the alkenyl group and the SiH group was [polysiloxane (10) + polysiloxane (4)] / [polysiloxane (1) + polysiloxane (2)] = 2.0, polysiloxane (10). And the molar ratio of SiH groups in polysiloxane (4) is (10) / (4) = 30/70.

  About 100 parts of this silicone rubber composition, 0.1 part of a platinum catalyst (Pt concentration 1 mass%) was mixed, and a cured product obtained by performing press cure at 120 ° C./10 minutes was applied to JIS-K6249 in the same manner as in Example 1. Based on the results, hardness, tensile strength, elongation at break, tear strength (crescent) and crack elongation test were performed, and the measurement results are shown in Table 1.

[Comparative Example 2]
A silicone rubber composition was obtained in the same manner as in Example 2, except that methyl hydrogen polysiloxane (7) was not used and only 2.1 parts of methyl hydrogen polysiloxane (4) was used. Here, the molar ratio of the alkenyl group and the SiH group is [polysiloxane (4)] / [polysiloxane (5) + polysiloxane (1) + polysiloxane (6)] = 1.5, which is the same as that in Example 2. It is.

  About 100 parts of this silicone rubber composition, 0.1 part of a platinum catalyst (Pt concentration 1 mass%) was mixed, and a cured product obtained by performing press cure at 120 ° C./10 minutes was applied to JIS-K6249 in the same manner as in Example 1. Based on the results, hardness, tensile strength, elongation at break, tear strength (crescent) and crack elongation test were performed, and the measurement results are shown in Table 1.

[Comparative Example 3]
A silicone rubber composition was obtained in the same manner as in Example 3 except that methyl hydrogen polysiloxane (8) was not used and only 1.8 parts of methyl hydrogen polysiloxane (9) was used. Here, the molar ratio of the alkenyl group to the SiH group is [polysiloxane (9)] / [polysiloxane (1) + polysiloxane (2) + polysiloxane (5)] = 1.2, which is the same as that in Example 3. It is.

  About 100 parts of this silicone rubber composition, 0.1 part of a platinum catalyst (Pt concentration 1 mass%) was mixed, and a cured product obtained by performing press cure at 120 ° C./10 minutes was applied to JIS-K6249 in the same manner as in Example 1. Based on the results, hardness, tensile strength, elongation at break, tear strength (crescent) and crack elongation test were performed, and the measurement results are shown in Table 1.

Claims (6)

(A) Both ends of a molecular chain are blocked with diorganoalkenylsiloxy groups, and do not have an alkenyl group bonded to a silicon atom in the middle of the molecular chain, and have an average degree of polymerization of 100 to 1,000. Part (B) Organopolysiloxane having at least three alkenyl groups in the molecule and different from the component (A) which is liquid at room temperature 0 to 50 parts by mass (C-1) Bonded to the silicon atom at the end of the molecular chain Organohydrogenpolysiloxane (C ) containing 2 hydrogen atoms, 1 to 3 hydrogen atoms bonded to silicon atoms in the middle of the molecular chain, and 3 to 5 hydrogen atoms bonded to silicon atoms in total. -2) A total of 6 or more hydrogen atoms bonded to silicon atoms at the molecular chain end and / or hydrogen atoms bonded to silicon atoms in the middle of the molecular chain per molecule. Ganohydrogenpolysiloxane The molar ratio of each silicon atom-bonded hydrogen atom (SiH group) in the component (C-1) and the component (C-2) is [SiH group (C-1)] / [SiH group (C -2)] = 90/10 to 10/90, and silicon atoms in component (C-1) and component (C-2) relative to the sum of alkenyl groups in component (A) and component (B) Amount in which the total molar ratio of bonded hydrogen atoms (SiH groups) is [SiH group] / [alkenyl group] = 1.1 to 3.0 (D) Fine powder silica 5 to 80 parts by mass (E) Addition reaction catalyst An addition-curable silicone rubber composition containing a catalytic amount. The addition-curable silicone rubber composition according to claim 1, wherein the component (C-1) is a linear organohydrogenpolysiloxane having 4 to 100 silicon atoms in one molecule . The addition curable silicone rubber composition according to claim 1 or 2, wherein the component (C-1) is a dimethylhydrogensiloxy group-blocked dimethylsiloxane / methylhydrogensiloxane copolymer having both molecular chain terminals. (B) The compounding quantity of a component is 2-50 mass parts with respect to 100 mass parts of (A) component, The addition-curable silicone rubber composition of any one of Claims 1-3. The addition curable silicone rubber composition according to any one of claims 1 to 4, wherein the fine powder silica of component (D) is fumed silica having a specific surface area of 250 m ² / g or more by BET method. The addition-curable silicone rubber composition according to any one of claims 1 to 5 , which is used for baby pacifiers or baby bottle nipples.