JP7287335B2 - Liquid addition-curable silicone rubber composition and cured product thereof - Google Patents

Description

TECHNICAL FIELD The present invention relates to a liquid addition-curable silicone rubber composition and a silicone rubber cured product which provide a cured product having high transparency, high hardness, and excellent flexibility and tear strength.

In order to improve the weather resistance and optical waveguide of LED light parts and various LCD monitor screens, silicone resins with high hardness and high transparency (Patent Document 1: JP-A-2002-265787, Patent Document 2: JP-A-2006- No. 202952, Patent Document 3: JP-A-2006-342200, Patent Document 4: JP-A-2008-101056) have attracted attention, and among them, it does not contain silica at all, is highly transparent, does not impair elasticity even at low temperatures, Cured products of addition curing type liquid silicone rubber, which are relatively easy to mold by heat curing, have come into use. Cured products of silicone rubber having good heat retention, high hardness and high transparency are also used for food and beverage containers.

However, the above-mentioned cured product has a low tear strength and has a problem of breakage in actual use. In general, cured silicone rubber with high tear strength contains a large amount of fumed silica (dry silica), and in this case, transparency (especially haze) is not always sufficient, so silica is not necessarily used. There is a demand to improve transparency to the level of silicone rubber cured products that do not contain any silicone rubber.

JP-A-2002-265787 JP 2006-202952 A Japanese Patent Application Laid-Open No. 2006-342200 JP 2008-101056 A

The present invention has been made in view of the above circumstances, and provides a liquid addition-curable silicone rubber composition and a silicone rubber cured product that provide a cured product having high transparency, high hardness, flexibility and excellent tear strength. intended to provide

As a result of intensive studies to achieve the above object, the inventors of the present invention have found that when only fumed silica is normally used in a liquid addition-curable silicone rubber composition, light is scattered by the silica, resulting in transparency. (especially haze) is reduced, but by adding a predetermined amount of (E) a silica surface treatment agent containing an alkenyl group (vinylsilazane, etc.) to (D) fumed silica, transparency is improved. The present inventors have found that a composition can be obtained which gives a cured product having a high hardness and excellent flexibility and tear strength, thereby completing the present invention.

Accordingly, the present invention provides the following liquid addition-curable silicone rubber composition and cured silicone rubber.
[1]
(A) At least two silicon-bonded alkenyl groups per molecule, at least one of which is an alkenyl group bonded to a silicon atom at the end of the molecular chain, with an average degree of polymerization of 1,500 or less at room temperature Liquid alkenyl group-containing organopolysiloxane: 100 parts by mass,
(B) R ₃ SiO _1/2 units (M units) and SiO _4/2 units (Q units) (wherein R is a monovalent hydrocarbon group having 1 to 6 carbon atoms and at least two of which are alkenyl groups) as an essential structural unit: 10 to 40 parts by mass of an alkenyl group-containing silicone resin,
(C) Organohydrogenpolysiloxane containing at least two silicon-bonded hydrogen atoms in one molecule: The number of silicon-bonded hydrogen atoms in component (C) is ) and component (E) in an amount of 1.0 to 3.0 per silicon-bonded alkenyl group in total,
(D) fumed silica having a BET specific surface area of 150 m ² /g or more: 10 to 40 parts by mass;
(E) a silica surface treatment agent containing an alkenyl group: 0.1 to 5 parts by mass per 100 parts by mass of component (D); Silicone rubber composition.
[2]
The liquid addition-curable silicone rubber composition of [1], wherein component (E) is a hydrolyzable organosilicon compound containing an alkenyl group.
[3]
Total light transmittance of a sheet with a thickness of 1 mm measured by a method in accordance with JIS K 7361-1: 1997 is 93% or more, haze (cloudiness) is 3% or less, and tearing based on JIS K 6249: 2003 The liquid addition-curable silicone rubber composition according to [1] or [2], which gives a cured product having a strength (angle) of 25 kN/m or more.
[4]
A cured silicone rubber obtained by curing the liquid addition-curable silicone rubber composition according to [1] or [2].
[5]
A cured product sheet with a thickness of 1 mm has a total light transmittance of 93% or more and a haze (cloudiness) of 3% or less, as measured by a method conforming to JIS K 7361-1: 1997, and conforms to JIS K 6249: 2003. The silicone rubber cured product according to [4], which has a base tear strength (angle) of 25 kN/m or more.

INDUSTRIAL APPLICABILITY According to the present invention, it is possible to provide a liquid addition-curable silicone rubber composition that gives a cured product having high transparency, high hardness, flexibility and excellent tear strength, and the cured product thereof. is particularly suitable for parts for various optical applications and for containers.

The present invention will be described in more detail below.
<Liquid addition-curable silicone rubber composition>
The liquid addition-curable silicone rubber composition of the present invention comprises the following components (A) to (F).

(A) Alkenyl group-containing organopolysiloxane (A) component is the main ingredient (base polymer) of the present composition, contains an alkenyl group bonded to a silicon atom at the molecular chain end, and has a silicon atom in one molecule It is an alkenyl group-containing organopolysiloxane that is liquid at room temperature and has an average degree of polymerization of 1,500 or less, which contains at least two alkenyl groups bonded to .

As such an alkenyl group-containing organopolysiloxane that is liquid at room temperature, one represented by the following average compositional formula (I) can be used.
^R1aSiO _{( 4-a)/2} (I)
(In the formula, R ¹ is the same or different unsubstituted or substituted monovalent hydrocarbon group having 1 to 10 carbon atoms, preferably 1 to 8 carbon atoms, and a is 1.5 to 2.8, preferably 1. 8 to 2.5, more preferably a positive number in the range of 1.95 to 2.05.)

Here, R ¹ specifically includes a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a tert-butyl group, a pentyl group, a neopentyl group, a hexyl group, a cyclohexyl group and an octyl group. , nonyl, decyl, and other alkyl groups; phenyl, tolyl, xylyl, naphthyl, and other aryl groups; benzyl, phenylethyl, phenylpropyl, and other aralkyl groups; vinyl, allyl, and propenyl groups , isopropenyl group, butenyl group, hexenyl group, cyclohexenyl group, octenyl group and other alkenyl groups, and some or all of the hydrogen atoms of these groups are substituted with fluorine, bromine, chlorine and other halogen atoms, cyano groups, etc. Examples include chloromethyl group, chloropropyl group, bromoethyl group, trifluoropropyl group, cyanoethyl group and the like, but preferably 90 mol % or more of all R ¹ are methyl groups.

At least two of R ¹ must be alkenyl groups (preferably those having 2 to 8 carbon atoms, more preferably 2 to 6 carbon atoms, and most preferably vinyl groups).

The alkenyl group content in the organopolysiloxane is 1.0×10 ⁻⁵ to 8.0×10 ⁻⁴ mol/g, particularly 2.0×10 ⁻⁵ to 6.0×10 ⁻⁴ mol/g. preferably. If the amount of alkenyl groups is less than 1.0×10 ⁻⁵ mol/g, the rubber hardness of the resulting cured product is low, and the resulting cured product may pose problems in practical use ^. If it is more than ⁴ mol/g, the resulting cured product may have too high a crosslink density, resulting in a brittle rubber.

This alkenyl group may be bonded to a silicon atom at the terminal of the molecular chain or bonded to a silicon atom in the middle of the molecular chain (non-terminal of the molecular chain). At least one, preferably two or more alkenyl groups bonded to the silicon atom at the chain end (that is, the silicon atom in the triorganosiloxy group) is contained in the molecule, and particularly at the silicon atom at the end of the molecular chain When two or more bonded alkenyl groups are contained in the molecule, the alkenyl group bonded to the silicon atom in the middle of the molecular chain (that is, the silicon atom in the diorganosiloxane unit or the monoorganosilsesquioxane unit) is It may or may not be contained, but if the molecule contains only one alkenyl group bonded to a silicon atom at the end of the molecular chain, an alkenyl group bonded to a silicon atom in the middle of the molecular chain must contain at least one.
Unless at least one, preferably two or more, alkenyl groups are bonded to silicon atoms at the ends of the molecular chains, a cured silicone rubber having high tear strength cannot be obtained.

In the present invention, the base polymer contains only alkenyl groups bonded to silicon atoms in the middle of the molecular chain (i.e., does not contain alkenyl groups bonded to silicon atoms at the ends of the molecular chain) liquid alkenyl groups at room temperature When the containing organopolysiloxane is used alone as the main ingredient, a cured rubber product with low hardness and high tear strength cannot be obtained, and the component (A) containing alkenyl groups bonded to the silicon atoms at the ends of the molecular chains. An alkenyl group-containing organopolysiloxane that is liquid at room temperature and contains only alkenyl groups bonded to silicon atoms in the middle of the molecular chain as alkenyl groups (i.e., does not contain alkenyl groups bonded to silicon atoms at the ends of the molecular chain) Even when polysiloxane is used in combination, a cured rubber product with good transparency cannot be obtained.
Therefore, in the present invention, the alkenyl group-containing organopolysiloxane of component (A) contains an alkenyl group bonded to a silicon atom at the terminal of a molecular chain and has at least two silicon-bonded alkenyl groups in one molecule. It is required to use only organopolysiloxanes having groups.

Specific examples of such alkenyl group-containing organopolysiloxanes include diorganopolysiloxanes blocked at both molecular chain ends with diorganoalkenylsiloxy groups, diorganopolysiloxanes blocked at both molecular chain ends with organodialkenylsiloxy groups, and diorganopolysiloxanes blocked at both molecular chain ends. Diorganopolysiloxane endblocked with trialkenylsiloxy groups, diorganosiloxane-organoalkenylsiloxane copolymer endblocked with diorganoalkenylsiloxy groups at both ends of the molecular chain, one end of the molecular chain endblocked with diorganoalkenylsiloxy groups and the other end triorganosiloxy group-blocked diorganosiloxane/organoalkenylsiloxane copolymers, etc., preferably diorganopolysiloxanes blocked with diorganoalkenylsiloxy groups at both molecular chain terminals and/or diorganoalkenylsiloxy groups at both molecular chain terminals It is a blocked diorganosiloxane/organoalkenylsiloxane copolymer.
The "organo group" in each of the above siloxanes means the same unsubstituted or substituted monovalent hydrocarbon group other than an alkenyl group among R ¹ in formula (I).

Component (A) contains at least two silicon-bonded alkenyl groups in one molecule, at least one of which is an alkenyl group bonded to a silicon atom at the end of the molecular chain. Alkenyl group-containing organopolysiloxanes that are liquid at a room temperature of 1,500 or less can be used singly or in combination of two or more having different molecular structures and degrees of polymerization.

The structure of the component (A) organopolysiloxane is particularly preferred to be a linear diorganopolysiloxane whose molecular chain ends are blocked with triorganosiloxy groups and whose main chain consists of repeating diorganosiloxane units. Preferably, it may partially contain a small amount of a branched structure (monoorganosilsesquioxane unit).

As for the molecular weight, the average degree of polymerization is 1,500 or less, usually 100 to 1,500, preferably 150 to 1,100. If it is less than 100, a sufficient rubbery feel may not be obtained, and if it is more than 1,500, the viscosity may become high and molding may become difficult.
In the present invention, the average degree of polymerization and weight average molecular weight are determined by gel permeation chromatography (GPC) using water, dimethylformamide (DMF), tetrahydrofuran (THF), and toluene as solvents, polyethylene oxide, polyethylene glycol, or It can be calculated as a polystyrene equivalent measurement value.

(B) Alkenyl group-containing silicone resin Component (B) is an alkenyl group-containing silicone resin having R ₃ SiO _1/2 units (M units) and SiO _4/2 units (Q units) as essential structural units.
Here, R is a monovalent hydrocarbon group having 1 to 6 carbon atoms, and at least 2, preferably 3 to 8 in one molecule (all structural units) are alkenyl groups.

Specific examples of R include alkyl groups such as methyl group, ethyl group, propyl group, butyl group, pentyl group and hexyl group; alkenyl groups such as vinyl group, allyl group, butenyl group, pentenyl group and hexenyl group; and cyclohexyl group. cycloalkyl groups such as cycloalkyl groups, cycloalkenyl groups such as cyclohexenyl groups, and unsubstituted monovalent hydrocarbon groups such as aryl groups such as phenyl groups.

The plurality of Rs contained in the alkenyl group-containing silicone resin of component (B) may be the same or different. It is preferable to have Moreover, from the viewpoint of maintaining compatibility with other components, it is preferable to employ a vinyl group as the alkenyl group.

In this case, the ratio of M units to Q units (M units/Q units) is 0.6 to 1.2 mol, preferably 0.8 to 1.0 mol, of M units per 1 mol of Q units. be. If the M units are too small, gelation may tend to occur.

Regarding component (B), as described above, R ₃ SiO _1/2 units (M units) and SiO _4/2 units (Q units) are essential. It may contain units selected from ₂ SiO _2/2 units (D units) and RSiO _3/2 units (T units). In order to improve the hardness of the cured product of a hydrosilylation-curable (addition-curable) liquid silicone rubber composition, the ratio of the above-mentioned M units and Q units to all structural units should be 80 mol% or more. and more preferably 90 mol % or more.

Specific examples of alkenyl group-containing silicone resins as component (B) include copolymers of vinyldimethylsiloxy groups and Q units, copolymers of vinyldimethylsiloxy groups/trimethylsiloxy groups and Q units, and vinyldimethylsiloxy. Copolymer of group/dimethylsiloxane and Q unit, copolymer of vinyldimethylsiloxy group/phenylsilsesquioxane and Q unit, vinyldimethylsiloxy group/dimethylsiloxane/phenylsilsesquioxane and Q unit Examples include copolymers, and copolymers of trimethylsiloxy group/vinylmethylsiloxane and Q units.

Regarding the molecular weight of the alkenyl group-containing silicone resin of component (B), the weight average molecular weight measured by gel permeation chromatography (GPC) using polystyrene as a standard substance is 2,000 to 8,000, particularly 4,000 to 6. ,000, which is normally a solid at room temperature.

In the present invention, the weight-average molecular weight of the silicone resin refers to the weight-average molecular weight measured by gel permeation chromatography (GPC) under the following conditions, using polystyrene as a standard (hereinafter the same applies to alkenyl group-containing silicone resins).
[Measurement condition]
Measuring device: TOSOH EcoSEC HLC-8320GPC
Detector: Combined use of differential refractive index detector (RI) and UV detector Column: TSKgel Super Multipore HZ-H (4.6 mm ID × 15 cm × 2) or TSKgel Super Multipore HZ2000 (6.0 mm ID × 15 cm × 2) (both manufactured by Tosoh Corporation)
Developing solvent: tetrahydrofuran (THF)
Flow rate: 0.35mL/min
Column temperature: 40°C
Sample injection volume: 10 μL (THF solution with a concentration of 0.1% by mass)

Component (B) is added in an amount of 10 to 40 parts by mass, preferably 10 to 35 parts by mass, per 100 parts by mass of component (A). Molding is suitable if the blending amount is within this range. On the other hand, if the blending amount is out of this range, the tear strength may decrease in the 150° C. long-term heat resistance test, the cured product may become brittle, and cracks may occur. Moreover, transparency may fall.

Component (C) organohydrogenpolysiloxane (C) contains at least two silicon-bonded hydrogen atoms (SiH groups) per molecule and has the following average compositional formula (II):
^R2bHcSiO _{( 4-bc)/2 (} II)
A conventionally known organohydrogenpolysiloxane represented by can be applied.

Here, each R ² is independently a monovalent hydrocarbon group having 1 to 6 carbon atoms, specifically, an alkyl group such as methyl group, ethyl group, propyl group, butyl group, pentyl group and hexyl group. groups, cyclohexyl groups, cyclohexenyl groups, and unsubstituted monovalent hydrocarbon groups such as phenyl groups. Among them, a methyl group and a phenyl group are preferable. b is a positive number of 0.7 to 2.1, preferably a positive number of 0.8 to 2.0, c is a positive number of 0.18 to 1.0, preferably a positive number of 0.2 to 1.0 and b+c is a positive number between 0.88 and 3.0, preferably between 1.0 and 2.5.

The molecular structure of the component (C) organohydrogenpolysiloxane may be linear, cyclic, branched or three-dimensional network. In this case, the number of silicon atoms in one molecule (or the degree of polymerization) is 2 to 300, particularly about 4 to 200, which is liquid at room temperature (25 ° C.) is preferably used, and the weight in terms of polystyrene by GPC Those having an average molecular weight of 500 to 20,000, especially 800 to 5,000 are preferred. Hydrogen atoms bonded to silicon atoms may be present at the ends of the molecular chains, at the side chains, or at both.

Specific examples of the organohydrogenpolysiloxane of component (C) include methylhydrogenpolysiloxane with both ends trimethylsiloxy group-blocked, dimethylsiloxane-methylhydrogensiloxane copolymer with both ends trimethylsiloxy group-blocked, and dimethylhydrogensiloxane at both ends. Gensiloxy group-blocked dimethylpolysiloxane, both ends dimethylhydrogensiloxy group-blocked dimethylsiloxane/methylhydrogensiloxane copolymer, both ends trimethylsiloxy group-blocked methylhydrogensiloxane/diphenylsiloxane copolymer, both ends trimethylsiloxy group-blocked Methylhydrogensiloxane/diphenylsiloxane/dimethylsiloxane copolymer, cyclic methylhydrogenpolysiloxane, cyclic methylhydrogensiloxane/dimethylsiloxane copolymer, cyclic methylhydrogensiloxane/diphenylsiloxane/dimethylsiloxane copolymer, (CH ₃ ) Copolymers of ₂ HSiO _1/2 units and SiO _4/2 units, (CH ₃ ) ₂ HSiO _1/2 units, SiO _4/2 units and (C ₆ H ₅ )SiO _3/2 units. A copolymer consisting of can be exemplified.

The amount of component (C), organohydrogenpolysiloxane, is determined in order to ensure the hardness of the cured product of the liquid addition-curable silicone rubber composition of the present invention. The total number of silicon-bonded hydrogen atoms (SiH groups) in component (C), particularly alkenyls bonded to silicon atoms in component (A), component (B) and component (E) described later The number of silicon-bonded hydrogen atoms (SiH groups) in component (C) per total group (i.e., the molar ratio of silicon-bonded hydrogen atoms (SiH groups)/alkenyl groups) is The amount is 1.0 to 3.0, preferably 1.5 to 2.5.
If the number of silicon-bonded hydrogen atoms in the component (C) per total alkenyl group is smaller than the above range, the cured product may be soft and have surface tackiness. Conversely, if the number of silicon-bonded hydrogen atoms in the component (C) per total alkenyl group exceeds the above range, the cured product may lose flexibility and become brittle.

In addition to the above components (A), (B), and (C), the method described in JIS K 6249: 2003 for the cured product obtained by adjusting the components (D), (E), and (F) described later. A hardness of 55 or more, more preferably 55 to 90, as measured by a type A durometer.
In order to increase the hardness of the silicone rubber cured product, generally, more alkenyl group-containing organopolysiloxane or the like and more organohydrogenpolysiloxane containing hydrogen atoms bonded to silicon atoms are used. is blended into the composition to increase the crosslink density. Among them, the number of hydrogen atoms (SiH groups) bonded to silicon atoms per total number of alkenyl groups bonded to silicon atoms in components (A), (B), and (E), which will be described later, is (SiH Group)/(alkenyl group) is easier to obtain the desired hardness. However, when this ratio is large, the adhesive tends to adhere to the mold during molding, which may lead to a decrease in mold releasability and complication in cleaning the mold. As a result, the quality of the cured silicone rubber cannot be sufficiently ensured, and the productivity may decrease. Therefore, in order to prevent this, the amount of component (C) to be blended is such that the molar ratio of (SiH group)/(alkenyl group) is 1.0 to 3.0, preferably 1.5 to 2.5. and the amount to be

(D) Fumed silica Component (D), fumed silica, is essential for imparting sufficient strength to the silicone rubber. The specific surface area of fumed silica by the BET method is 150 m ² /g or more, usually 150 to 400 m ² /g, preferably 150 to 350 m ² /g, and if it is less than 150 m ² /g, sufficient strength cannot be obtained. Not only that, the transparency of the cured product is also lowered, and if it is more than 400 m ² /g, there is a possibility that it will become difficult to mix or cause discoloration.

The fumed silica of the component (D) includes Aerosil 130, 200, 300 (manufactured by Nippon Aerosil Co., Ltd., manufactured by Degussa), Cabosil MS-5, MS-7 as hydrophilic silica (that is, surface-untreated silica). (manufactured by Cabot), Rheorosil QS-102, 103 (manufactured by Tokuyama) and the like. Fumed silica is a silica surface-treating agent containing an alkenyl group as component (E), which will be described later, when kneaded with a silicone oil (i.e., component (A), an alkenyl group-containing organopolysiloxane) when preparing a composition. and optionally mixed in the presence of a small amount of water for surface treatment in the composition.

The blending amount of fumed silica is 10 to 40 parts by mass, preferably 15 to 40 parts by mass, per 100 parts by mass of component (A).
If the amount is less than 10 parts by mass, sufficient tear strength cannot be obtained, and if it is more than 40 parts by mass, the transparency may deteriorate.

(E) Alkenyl group-containing silica surface-treating agent As component (E), an alkenyl group-containing silica surface-treating agent, a hydrolyzable silica surface-treating agent containing at least one, preferably two or more alkenyl groups per molecule. Organosilicon compounds are preferred. At this time, the alkenyl group is preferably a vinyl group, an allyl group, a propenyl group, an isopropenyl group, a butenyl group, a hexenyl group, a cyclohexenyl group or an octenyl group, and particularly preferably a vinyl group. Component (E) specifically includes 1,3-divinyl-1,1,3,3-tetramethyldisilazane, 1,1,3,3-tetravinyl-1,3-dimethyldisilazane, vinyl group-containing organosilazanes such as 1-vinyl-1,1,3,3,3-pentamethyldisilazane, 1,1,1,3,5,5,5-heptamethyl-3-vinyltrisilazane; , N-dimethylaminodimethylvinylsilane and other vinyl group-containing aminosilanes, and vinyl group-containing alkoxysilanes such as trimethoxyvinylsilane, triethoxyvinylsilane, methyldimethoxyvinylsilane, and methoxydimethylvinylsilane. -divinyl-1,1,3,3-tetramethyldisilazane and trimethoxyvinylsilane are preferred.

The amount of the alkenyl group-containing silica surface treatment agent to be blended is preferably 0.1 to 5 parts by mass, particularly 0.1 to 3 parts by mass, per 100 parts by mass of fumed silica as component (D).
If the amount is less than 0.1 parts by mass, the transparency will be lowered, and if it is more than 5 parts by mass, the hardness will be too high and the physical properties of the rubber including tear strength will be lowered.

(F) Hydrosilylation reaction catalyst Component (F) is a hydrosilylation reaction catalyst, and known hydrosilylation reaction catalysts can be used. A reactant of platinic acid and a monohydric alcohol, a complex of chloroplatinic acid and olefins, a palladium-based catalyst, a rhodium-based catalyst, and the like can be mentioned. Among these, it is preferable to use a complex of chloroplatinic acid and an olefin.

The blending amount of the hydrosilylation reaction catalyst is a catalytic amount. Specifically, it is about 0.1 to 200 ppm, preferably about 1 to 50 ppm as a platinum group metal (in terms of mass), relative to the total mass of the essential components (components (A) to (E)).
If the amount of the hydrosilylation reaction catalyst is less than 0.1 ppm, curability will be reduced, and if it is more than 200 ppm, the resulting cured product may turn yellow, possibly impairing transparency. .

Other Components The liquid addition-curable silicone rubber composition of the present invention contains silicon-bonded alkenyl groups other than the components (A) to (F) described above, as long as they do not impair the effects of the present invention. Organopolysiloxane, alkoxysilane-based compounds containing alkoxysilyl groups (excluding component (E)), silane coupling agents (excluding component (E)), condensation catalysts such as titanium and zirconium to aid cross-linking It may be blended as an agent.

Further, the liquid addition-curable silicone rubber composition of the present invention includes, for example, 1,3-divinyl-1,1,3,3-tetramethyldisiloxane, 1,3,5,7-tetramethyl-1, 3,5,7-tetravinylcyclotetrasiloxane, 1,3,5-triallyl-1,3,5-triazine-2,4,6-(1H,3H,5H)-trione (triallyl isocyanurate), etc. polyfunctional alkenyl compounds, 1-ethynylcyclohexanol, 3-methyl-1-butyn-3-ol, 3-methyl-1-pentyn-3-ol, 3,5-dimethyl-1-hexyn-3-ol, etc. A hydrosilylation reaction inhibitor such as an acetylene alcohol derivative of may be added to ensure pot life.

Furthermore, the liquid addition-curable silicone rubber composition of the present invention can be blended with various dyes, flame retardants, etc. within limits not impairing the effects of the present invention.
These optional components may be used singly or in combination of two or more.

According to the liquid addition-curable silicone rubber composition of the present invention, a cured product having high transparency, high hardness, and excellent flexibility and tear strength can be obtained. The total light transmittance of a sheet with a thickness of 1 mm measured by the method in accordance with 93% or more, the haze (cloudiness) is 3% or less, and the tear strength (angle) based on JIS K 6249 is 25 kN / m or more. It gives a cured product.

<Preparation and molding of liquid addition-curable silicone rubber composition>
The liquid addition-curable silicone rubber composition of the present invention is prepared by adding other components, if necessary, in addition to the above components (A) to (F) using a conventional mixing stirrer, kneader, etc. It can be prepared by mixing uniformly. Preferably, part of component (A), components (D), (E) and water are first mixed (heated and mixed at about 150° C. if necessary) to prepare a silicone rubber base, and then ( The remainder of component A), components (B), (C), (F) and other components may be added and mixed.

In the present invention, a silicone rubber cured product can be obtained by heat-curing (molding) the liquid addition-curable silicone rubber composition of the present invention by a molding method such as press molding, injection molding, or transfer molding. At this time, the silicone rubber cured product of the liquid addition-curable silicone rubber composition is obtained by heating and curing the above composition at 80 to 350°C, preferably 100 to 200°C, more preferably 120 to 150°C. For example, the curing conditions (primary curing) for liquid addition-curable silicone rubber compositions are preferably 100 to 200° C., particularly 120 to 180° C., for 30 seconds to 30 minutes, particularly 1 to 15 minutes. Further, the obtained silicone rubber may be post-cured (secondary curing) at, for example, 150 to 220° C., particularly 150 to 200° C., for 30 minutes to 6 hours, particularly 1 to 4 hours, if necessary. good.

As for the molding method, a known thermosetting resin molding method can be used. For example, in the case of a press molding method, a liquid addition-curable silicone rubber composition is poured between two liners and molded into a predetermined mold. , under the conditions of vulcanization under pressure. Alternatively, with a two-liquid mixing type liquid injection molding machine, it is possible to obtain a cured product having a desired shape using an arbitrary mold, and to obtain a molded product suitable for optical applications, for example. Furthermore, two-color molding with other resins is also possible. As other means, compression molding, transfer molding, injection molding, etc. can be applied. Further, as an example of the stretching molding method, while supplying the liquid addition-curable silicone rubber composition between two continuous resin films, it is stretched to a constant thickness by rolls and continuously supplied to a heating furnace. A desired transparent cured product in the form of a sheet can also be obtained by performing atmospheric hot air vulcanization, curing, cooling, and peeling off the liner.

The silicone rubber cured product of the present invention obtained in this way has a total light transmittance of 93% or more as measured on a 1 mm thick cured product sheet according to JIS K 7361-1:1997, and a haze (cloudiness ) is preferably 3% or less. This is because if the cured product sheet is out of this range, it is disadvantageous in the use for optical applications such as lamp exterior materials and resin lenses, which is not preferable.
The cured silicone rubber of the present invention preferably has a tear strength (angle) of 25 kN/m or more according to JIS K 6249. If it is less than 25 kN/m, there is a problem in practical strength, and there is a possibility of crushing when removing the cured silicone rubber from the mold.

EXAMPLES The present invention will be specifically described below with reference to examples and comparative examples, but the present invention is not limited to the following examples. In the following examples, "parts" means "mass parts". Moreover, an average degree of polymerization shows a weight average degree of polymerization.

[Example 1]
60 parts of dimethylpolysiloxane (A1), which is liquid at room temperature and has an average degree of polymerization of 750, ^both ends of which are blocked with dimethylvinylsiloxy groups, and fumed silica (Aerosil 300) 40 parts of (D1), 8 parts of hexamethyldisilazane, 0.1 part of 1,3-divinyl-1,1,3,3-tetramethyldisilazane (E1), and 2.0 parts of water at room temperature. After mixing for 30 minutes, the temperature was raised to 150° C., stirring was continued for 3 hours, cooling was continued, 30 parts of the above dimethylpolysiloxane (A1) was added, and the mixture was mixed at room temperature for 30 minutes to obtain a silicone rubber base.
To 100 parts of this silicone rubber base, 32 parts of the dimethylpolysiloxane (A1), (CH ₃ ) ₃ SiO _1/2 units, (CH ₂ =CH) (CH ₃ ) ₂ SiO _1/2 units, SiO _4/2 Unit copolymer (B1) (M unit / Q unit (molar ratio) = 0.85, number of alkenyl groups per molecule: 4.3 (weight average molecular weight = 3,000)) 32 parts, 30 After continuing stirring for 1 minute, 6.75 parts of methylhydrogenpolysiloxane (C1) (number of SiH groups per molecule: 50 (SiH group content: 0.00759 mol/g)) with both ends trimethylsiloxy-blocked as a cross-linking agent [ (SiH groups (mol) in component (C1))/(total (mol) of alkenyl groups in components (A1), (B1), and (E1)) = 1.7 (mol/mol)], reaction control 0.04 part of ethynylcyclohexanol and 0.1 part of a platinum catalyst (Pt concentration of 1% by mass) (F1) were added as agents, and stirring was continued for 15 minutes to obtain a silicone rubber composition.
After press-curing this silicone rubber composition at 120°C/10 minutes, it was post-cured in an oven at 150°C/1 hour. Table 1 shows the results of measurement of elongation and tear strength (angle).
A polyethylene terephthalate (PET) liner and a frame with a thickness of 1.1 mm were placed on the press plate, the liquid addition-curable silicone rubber composition was poured into the frame, and the PET liner and press plate were further placed on top of this. It was laminated and press-molded at 120° C. for 10 minutes. After the two PET liners were taken out and cooled, the PET liners were peeled off and post-cured in an oven at 150° C. for 1 hour to obtain a transparent sheet of cured silicone rubber having a thickness of about 1 mm.
The total light transmittance and haze (turbidity) of a sheet with a thickness of 1 mm were measured using a haze meter (device name: HGM-2, manufactured by Suga Test Instruments Co., Ltd.) in accordance with JIS K 7361-1:1997. Table 1 shows the measurement results.

[Example 2]
60 parts of dimethylpolysiloxane (A1), which is liquid at room temperature and has an average degree of polymerization of 750, ^both ends of which are blocked with dimethylvinylsiloxy groups, and fumed silica (Aerosil 300) 40 parts of (D1), 8 parts of hexamethyldisilazane, 0.1 part of 1,3-divinyl-1,1,3,3-tetramethyldisilazane (E1), and 2.0 parts of water at room temperature. After mixing for 30 minutes, the temperature was raised to 150° C., stirring was continued for 3 hours, cooling was continued, 30 parts of the above dimethylpolysiloxane (A1) was added, and the mixture was mixed at room temperature for 30 minutes to obtain a silicone rubber base.
To 100 parts of this silicone rubber base, 16 parts of the dimethylpolysiloxane (A1), (CH ₃ ) ₃ SiO _1/2 units, (CH ₂ =CH) (CH ₃ ) ₂ SiO _1/2 units, SiO _4/2 Unit copolymer (B1) (M unit / Q unit (molar ratio) = 0.85, number of alkenyl groups per molecule: 4.3 (weight average molecular weight = 3,000)) 16 parts, 30 After continuing stirring for 1 minute, 3.70 parts of methylhydrogenpolysiloxane (C1) (number of SiH groups per molecule: 50 (SiH group content: 0.00759 mol/g)) with both ends trimethylsiloxy-blocked as a cross-linking agent [ (SiH groups (mol) in component (C1))/(total (mol) of alkenyl groups in components (A1), (B1), and (E1)) = 1.7 (mol/mol)], reaction control 0.04 part of ethynylcyclohexanol and 0.1 part of a platinum catalyst (Pt concentration of 1% by mass) (F1) were added as agents, and stirring was continued for 15 minutes to obtain a silicone rubber composition.
After press-curing this silicone rubber composition at 120°C/10 minutes, it was post-cured in an oven at 150°C/1 hour. Table 1 shows the results of measurement of elongation and tear strength (angle).
A polyethylene terephthalate (PET) liner and a frame with a thickness of 1.1 mm were placed on the press plate, the liquid addition-curable silicone rubber composition was poured into the frame, and the PET liner and press plate were further placed on top of this. It was laminated and press-molded at 120° C. for 10 minutes. After the two PET liners were taken out and cooled, the PET liners were peeled off and post-cured in an oven at 150° C. for 1 hour to obtain a transparent sheet of cured silicone rubber having a thickness of about 1 mm.
The total light transmittance and haze (turbidity) of a sheet with a thickness of 1 mm were measured using a haze meter (device name: HGM-2, manufactured by Suga Test Instruments Co., Ltd.) in accordance with JIS K 7361-1:1997. Table 1 shows the measurement results.

[Example 3]
In Example 1, 0.1 part of 1,3-divinyl-1,1,3,3-tetramethyldisilazane (E1) was changed from 0.1 part to 0.2 part. 6.75 to 6.90 parts of Genpolysiloxane (C1) [(SiH groups (moles) in component (C1))/(total alkenyl groups in components (A1), (B1), and (E1) (mol))=1.7 mol/mol)], to obtain a silicone rubber composition in the same manner.
After press-curing this silicone rubber composition at 120°C/10 minutes, it was post-cured in an oven at 150°C/1 hour. Table 1 shows the results of measurement of elongation and tear strength (angle).
A polyethylene terephthalate (PET) liner and a frame with a thickness of 1.1 mm were placed on the press plate, the liquid addition-curable silicone rubber composition was poured into the frame, and the PET liner and press plate were further placed on top of this. It was laminated and press-molded at 120° C. for 10 minutes. After the two PET liners were taken out and cooled, the PET liners were peeled off and post-cured in an oven at 150° C. for 1 hour to obtain a transparent sheet of cured silicone rubber having a thickness of about 1 mm.
The total light transmittance and haze (turbidity) of a sheet with a thickness of 1 mm were measured using a haze meter (device name: HGM-2, manufactured by Suga Test Instruments Co., Ltd.) in accordance with JIS K 7361-1:1997. Table 1 shows the measurement results.

[Comparative Example 1]
In Example 1, 1,3-divinyl-1,1,3,3-tetramethyldisilazane (E1) was not added during the preparation of the silicone rubber base, and both terminal trimethylsiloxy-blocked methylhydrogenpolysiloxane (E1) was used as a cross-linking agent. 6.75 to 6.55 parts of C1) [(SiH groups (mol) in component (C1))/(total (mol) of alkenyl groups in components (A1) and (B1)) = 1.7 (mol/mol)] was changed to obtain a silicone rubber composition in the same manner.
After press-curing this silicone rubber composition at 120°C/10 minutes, it was post-cured in an oven at 150°C/1 hour. Table 1 shows the results of measurement of elongation and tear strength (angle).
A polyethylene terephthalate (PET) liner and a frame with a thickness of 1.1 mm were placed on the press plate, the liquid addition-curable silicone rubber composition was poured into the frame, and the PET liner and press plate were further placed on top of this. It was laminated and press-molded at 120° C. for 10 minutes. After the two PET liners were taken out and cooled, the PET liners were peeled off and post-cured in an oven at 150° C. for 1 hour to obtain a transparent sheet of cured silicone rubber having a thickness of about 1 mm.
The total light transmittance and haze (turbidity) of a sheet with a thickness of 1 mm were measured using a haze meter (device name: HGM-2, manufactured by Suga Test Instruments Co., Ltd.) in accordance with JIS K 7361-1:1997. Table 1 shows the measurement results.

[Comparative Example 2]
In Example 1, 6 parts of 1,3-divinyl-1,1,3,3-tetramethyldisilazane (E1) and 3.5 parts of water, which were added during the preparation of the silicone rubber base, were changed to 3.5 parts. 6.75 to 17.70 parts of methylhydrogenpolysiloxane (C1) endblocked with trimethylsiloxy at both ends [(SiH groups (mol) in component (C1))/((A1), (B1), (E1) A silicone rubber composition was obtained in the same manner, except that the total (mol) of alkenyl groups in the components was changed to 1.7 (mol/mol)].
After press-curing this silicone rubber composition at 120°C/10 minutes, it was post-cured in an oven at 150°C/1 hour. Table 1 shows the results of measurement of elongation and tear strength (angle).
A polyethylene terephthalate (PET) liner and a frame with a thickness of 1.1 mm were placed on the press plate, the liquid addition-curable silicone rubber composition was poured into the frame, and the PET liner and press plate were further placed on top of this. It was laminated and press-molded at 120° C. for 10 minutes. After the two PET liners were taken out and cooled, the PET liners were peeled off and post-cured in an oven at 150° C. for 1 hour to obtain a transparent sheet of cured silicone rubber having a thickness of about 1 mm.
The total light transmittance and haze (turbidity) of a sheet with a thickness of 1 mm were measured using a haze meter (device name: HGM-2, manufactured by Suga Test Instruments Co., Ltd.) in accordance with JIS K 7361-1:1997. Table 1 shows the measurement results.

[Comparative Example 3]
109 parts of room temperature liquid dimethylpolysiloxane (A1) having an average degree of polymerization of 750, (CH ₃ ) ₃ SiO _1/2 units, (CH ₂ ═CH)(CH ₃ ) ₂ SiO _1/2 unit, SiO _4/2 unit copolymer (B1) (M unit/Q unit (molar ratio) = 0.85, number of alkenyl groups per molecule: 4.3 (weight average 32 parts of molecular weight = 3,000)) were added and mixed at room temperature for 30 minutes. 0.00759 mol/g))) 6.62 parts [(SiH groups (mol) in component (C1))/(sum of alkenyl groups in components (A1) and (B1) (mol)) = 1.7 ( mol/mol)], 0.04 part of ethynylcyclohexanol as a reaction control agent, and 0.1 part of a platinum catalyst (Pt concentration of 1% by mass) (F1) were added, and stirring was continued for 15 minutes to obtain a silicone rubber composition. Obtained.
After press-curing this silicone rubber composition at 120°C/10 minutes, it was post-cured in an oven at 150°C/1 hour. Table 1 shows the results of measurement of elongation and tear strength (angle).
A polyethylene terephthalate (PET) liner and a frame with a thickness of 1.1 mm were placed on the press plate, the liquid addition-curable silicone rubber composition was poured into the frame, and the PET liner and press plate were further placed on top of this. It was laminated and press-molded at 120° C. for 10 minutes. After the two PET liners were taken out and cooled, the PET liners were peeled off and post-cured in an oven at 150° C. for 1 hour to obtain a transparent sheet of cured silicone rubber having a thickness of about 1 mm.
The total light transmittance and haze (turbidity) of a sheet with a thickness of 1 mm were measured using a haze meter (device name: HGM-2, manufactured by Suga Test Instruments Co., Ltd.) in accordance with JIS K 7361-1:1997. Table 1 shows the measurement results.

Claims (5)

(A) At least two silicon-bonded alkenyl groups per molecule, at least one of which is an alkenyl group bonded to a silicon atom at the end of the molecular chain, with an average degree of polymerization of 1,500 or less at room temperature Liquid alkenyl group-containing organopolysiloxane: 100 parts by mass,
(B) R ₃ SiO _1/2 units (M units) and SiO _4/2 units (Q units) (wherein R is a monovalent hydrocarbon group having 1 to 6 carbon atoms and at least two of which are alkenyl groups) as an essential structural unit: 10 to 40 parts by mass of an alkenyl group-containing silicone resin,
(C) Organohydrogenpolysiloxane containing at least two silicon-bonded hydrogen atoms in one molecule: The number of silicon-bonded hydrogen atoms in component (C) is ) and component (E) in an amount of 1.0 to 3.0 per silicon-bonded alkenyl group in total,
(D) fumed silica having a BET specific surface area of 150 m ² /g or more: 10 to 40 parts by mass;
(E) a silica surface treatment agent containing an alkenyl group: 0.1 to 5 parts by mass per 100 parts by mass of component (D); Silicone rubber composition. 2. The liquid addition-curable silicone rubber composition according to claim 1, wherein component (E) is a hydrolyzable organosilicon compound containing alkenyl groups. Total light transmittance of a sheet with a thickness of 1 mm measured by a method in accordance with JIS K 7361-1: 1997 is 93% or more, haze (cloudiness) is 3% or less, and tearing based on JIS K 6249: 2003 3. The liquid addition-curable silicone rubber composition according to claim 1 or 2, which gives a cured product having a strength (angle) of 25 kN/m or more. A cured silicone rubber obtained by curing the liquid addition-curable silicone rubber composition according to claim 1 or 2. A cured product sheet with a thickness of 1 mm has a total light transmittance of 93% or more and a haze (cloudiness) of 3% or less, as measured by a method conforming to JIS K 7361-1: 1997, and conforms to JIS K 6249: 2003. 5. The silicone rubber cured product according to claim 4, wherein the base tear strength (angle) is 25 kN/m or more.