JP7128159B2 - Transparent liquid silicone rubber composition and cured product - Google Patents

Description

TECHNICAL FIELD The present invention relates to a transparent liquid silicone rubber composition containing organopolysiloxane as a main component and cured by a hydrosilylation reaction.

For the purpose of improving weather resistance and guiding light in LED lights and various liquid crystal monitor screens, the use of silicone resins with high hardness and high transparency (Patent Documents 1 to 3) has attracted attention. In particular, a cured product of a hydrosilylation-curable liquid silicone rubber composition has come into use, which is highly transparent because it does not contain silica, does not impair its elasticity even at low temperatures, and is relatively easy to mold by heat curing.

However, in order to increase the hardness of silicone rubber that does not contain any silica as a reinforcing material, a large amount of silicone resin is blended, which causes problems in rubber physical properties and heat resistance. Moreover, when silica is blended as a reinforcing material, there is a problem that high transparency is not achieved.

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

SUMMARY OF THE INVENTION It is an object of the present invention to provide a silicone rubber composition having excellent tear strength while sufficiently maintaining hardness and high transparency.

In order to achieve the above problems, in the present invention,
(A) 100 parts by mass of a linear or branched organopolysiloxane containing at least two silicon-bonded alkenyl groups per molecule;
(B) a silicone resin containing R ₃ SiO _1/2 units and SiO _4/2 units (where R is a monovalent hydrocarbon group having 1 to 6 carbon atoms and at least two are alkenyl groups) 5 to 50 parts by mass,
(C) 10 to 150 parts by mass of sol-gel silica containing an alkenyl group,
(D) Organohydrogenpolysiloxane containing at least two silicon-bonded hydrogen atoms per molecule (the number of silicon-bonded hydrogen atoms per silicon-bonded alkenyl group in the composition is number is 1.0 to 3.0) and (E) a hydrosilylation reaction catalyst.

With such a transparent liquid silicone rubber composition, a silicone rubber composition having excellent tear strength while sufficiently maintaining hardness and high transparency can be obtained.

The present invention also provides a cured product obtained by curing the above transparent liquid silicone rubber composition.

At this time, it is preferable that the hardness is 55 or more with a type A durometer measured by the method described in JIS K 6249:2003.

At this time, it is preferable that the total light transmittance of the 1 mm-thick cured sheet measured by a method conforming to JIS K 7361-1:1997 is 93% or more.

Such a cured product is suitable for various optical uses.

According to the transparent liquid silicone rubber composition of the present invention, it is possible to obtain cured products having high transparency and high hardness as well as excellent tear strength. optimal.

As described above, there has been a demand for the development of silicone rubber compositions that have excellent tear strength while sufficiently maintaining hardness and high transparency.

As a result of intensive studies to achieve the above object, the present inventors found that by blending an organopolysiloxane that is liquid at room temperature together with an inorganic filler of sol-gel silica having an alkenyl group into a silicone rubber composition, silicone The inventors have found that the cured product can exhibit sufficient hardness and high transparency, and that the tear strength is excellent, and have completed the present invention.

That is, the present invention
(A) 100 parts by mass of a linear or branched organopolysiloxane containing at least two silicon-bonded alkenyl groups per molecule;
(B) a silicone resin containing R ₃ SiO _1/2 units and SiO _4/2 units (where R is a monovalent hydrocarbon group having 1 to 6 carbon atoms and at least two are alkenyl groups) 5 to 50 parts by mass,
(C) 10 to 150 parts by mass of sol-gel silica containing an alkenyl group,
(D) Organohydrogenpolysiloxane containing at least two silicon-bonded hydrogen atoms per molecule (the number of silicon-bonded hydrogen atoms per silicon-bonded alkenyl group in the composition is and (E) a hydrosilylation reaction catalyst: a transparent liquid silicone rubber composition.

Although the present invention will be described in detail below, the present invention is not limited thereto.

<Transparent liquid silicone rubber composition>
The transparent liquid silicone rubber composition of the present invention contains the above components (A) to (E). Each component will be described in more detail below.

(A) Alkenyl Group-Containing Organopolysiloxane Component (A) is a linear or branched organopolysiloxane containing at least two silicon-bonded alkenyl groups per molecule. The organopolysiloxane of component (A) is not particularly limited in its average degree of polymerization, and may contain at least two silicon-bonded alkenyl groups in one molecule. A known polymer used as a base polymer for liquid silicone rubber can be employed.

Component (A) may be in the form of oil or raw rubber at room temperature (25°C), and more preferably has a polystyrene-equivalent weight average molecular weight of 5,000 to 1,000 by gel permeation chromatography (GPC). ,000, particularly 20,000 to 800,000, and mixtures thereof.

In the present invention, the weight average molecular weight refers to the weight average molecular weight measured by gel permeation chromatography (GPC) under the following conditions using polystyrene as a standard substance.

[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)
(These are all 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)

These are usually the following average composition formula (I)
R ¹ _a SiO _(4-a)/2 (I)
It is preferably linear, and may contain a partial branch.

Here, R ¹ in the average composition formula (I) is a monovalent hydrocarbon group having 1 to 6 carbon atoms. Specific examples of R ¹ 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; group, cyclohexenyl group, phenyl group, and other unsubstituted monovalent hydrocarbon groups. The plurality of substituents (R ¹ ) may be different or the same, but it is necessary that they contain two or more alkenyl groups in the molecule.

Further, in the average composition formula (I), a is a positive number of 1.9 to 2.4, preferably a positive number of 1.95 to 2.05.

Examples of component (A) include linear organopolysiloxanes whose main chain consists of repeating diorganopolysiloxane units (D units) and whose molecular chain ends are blocked with triorganosiloxy groups (M units). and it is preferred that the substituents attached to the silicon atoms are methyl or phenyl groups. Examples of alkenyl groups bonded to silicon atoms which must be contained in one molecule at least two times include vinyl, allyl, butenyl, pentenyl, and hexenyl groups, with vinyl groups being particularly preferred. , which may be at the chain ends or side chains.

(B) Alkenyl group-containing silicone resin Component (B) is a 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, per molecule are alkenyl groups.

Specific examples of the monovalent hydrocarbon group R having 1 to 6 carbon atoms in the silicone resin include alkyl groups such as methyl group, ethyl group, propyl group, butyl group, pentyl group and hexyl group, vinyl group, allyl group, Examples include alkenyl groups such as butenyl group, pentenyl group and hexenyl group, cyclohexyl groups, cyclohexenyl groups, and unsubstituted monovalent hydrocarbon groups such as phenyl group. The plurality of Rs contained in the silicone resin (B) component may be the same or different, but from the viewpoint of compatibility with other components, 80 mol% or more of R is a methyl group. and it is preferred to employ a vinyl group as the alkenyl group.

In this case, the ratio of M units to Q units is preferably 0.6 to 1.2 mol, more preferably 0.8 to 1.0 mol, per 1 mol of Q units. If the M unit is 0.6 mol or more with respect to 1 mol of the Q unit, there is no fear of gelation, and if the M unit is 1.2 mol or less with respect to 1 mol of the Q unit, a resin structure develops. , sufficient hardness improvement effect can be obtained.

Regarding the 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 R 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 the hydrosilylation-curable liquid silicone rubber composition, it is preferable that the proportion of the above-mentioned M units and Q units in all structural units is 80 mol % or more. , more preferably 90 mol % or more.

Specific examples of the silicone resin of component (B) include a copolymer of a vinyldimethylsiloxy group and a Q unit, a copolymer of a vinyldimethylsiloxy group/trimethylsiloxy group and a Q unit, and a vinyldimethylsiloxy group/dimethyl Copolymers of siloxane and Q units, copolymers of vinyldimethylsiloxy groups/phenylsilsesquioxane and Q units, copolymers of vinyldimethylsiloxy groups/dimethylsiloxane/phenylsilsesquioxane and Q units , and copolymers of trimethylsiloxy group/vinylmethylsiloxane and Q units.

Regarding the molecular weight of the silicone resin as the component (B), the weight average molecular weight determined by GPC using polystyrene as a standard substance is preferably 2,000 to 8,000, particularly 2,000 to 6,000. , which is normally solid at room temperature.

The amount of component (B) in the present invention is 5 to 50 parts by mass per 100 parts by mass of component (A),
It is preferably 10 to 35 parts by mass. From the viewpoint of the viscosity of the composition, this range is suitable for molding. If it exceeds 50 parts by mass, the cured product becomes brittle and cracks occur in a long-term heat resistance test at 150°C. On the other hand, if it is less than 5 parts by mass, the hardened product becomes soft and sticky on the surface, making it unsuitable for molding.

(C) Alkenyl Group-Containing Sol-Gel Silica Component (C), alkenyl group-containing sol-gel silica, is essential for imparting sufficient strength and transparency to silicone rubber and improving tear strength.

In the sol-gel silica production method, based on the conventionally known Japanese Patent No. 3756339, reactive groups remaining on the surface of hydrophobic silica fine particles are triorganosilylated with a silazane compound or a monofunctional silane compound (hereinafter referred to as a silazane compound, etc.) to form a silane. This is a production method for obtaining surface-treated silica fine particles. The alkenyl group-containing sol-gel silica used in the present invention is used in combination with a silica surface treatment agent containing an alkenyl group when reacting a silazane compound or the like with the reactive groups remaining on the surface of the hydrophobic silica fine particles during the sol-gel silica production method. It is obtained by reacting It can also be obtained by mixing the component (A) polymer, sol-gel silica, and a silica surface treating agent containing an alkenyl group, and treating the silica surface in situ with the polymer.

Component (C) preferably has an average particle size of 20 to 700 nm, more preferably 20 to 500 nm, particularly preferably 20 to 400 nm. If the particle diameter is 20 nm or more, there is no risk of loss of transparency due to strong aggregation. Further, when the thickness is 700 nm or less, the transparency is improved and a sufficient effect of improving the mechanical strength of the rubber is obtained.

Alkenyl group-containing silica surface treatment agents include 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 ratio of surface treatment with a silica surface treatment agent containing an alkenyl group is, for example, the ratio of coating with a silica surface treatment agent containing an alkenyl group to the sol-gel silica specific surface area, that is, of the sol-gel silica specific surface area, It can be defined as the proportion of the portion (area) covered by the silica surface treatment agent containing alkenyl groups. This proportion is preferably 1-80%, more preferably 2-70%, particularly preferably 5-40%, very preferably 10-30%. If the proportion is 1% or more, a sufficient rubber strength can be obtained, and if it is 80% or less, there is no possibility that the hardness will become too high.

The amount of sol-gel silica containing an alkenyl group as component (C) is 10 to 150 parts by mass, preferably 15 to 100 parts by mass, per 100 parts by mass of component (A). If the amount is less than 10 parts by mass, the obtained cured product of the composition containing component (C) will not have sufficient rubber strength, and if it is more than 150 parts by mass, the hardness will be too high.

Component (D) organohydrogenpolysiloxane (D) contains at least two silicon-bonded hydrogen atoms per molecule and has the following average compositional formula (II):
R ² _b H _c SiO _(4-bc)/2 (II)
A conventionally known organohydrogenpolysiloxane represented by can be applied.

Here, R ² in the average composition formula (II) is a monovalent hydrocarbon group having 1 to 6 carbon atoms, and specific examples thereof include methyl group, ethyl group, propyl group, butyl group and pentyl group. , an alkyl group such as a hexyl group, an unsubstituted monovalent hydrocarbon group such as a cyclohexyl group, a cyclohexenyl group, and a phenyl group. Among them, a methyl group and a phenyl group are preferred. 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 0.8 and 3.0, preferably between 1.0 and 2.5.

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

Specific examples of the organohydrogenpolysiloxane of component (D) include methylhydrogenpolysiloxane with both ends trimethylsiloxy group-blocked, dimethylsiloxane-methylhydrogensiloxane copolymer with both ends trimethylsiloxy group-blocked, and dimethylhydrogen at both ends. Siloxy group-blocked dimethylpolysiloxane, both ends dimethylhydrogensiloxy group-blocked dimethylsiloxane/methylhydrogensiloxane copolymer, both ends trimethylsiloxy group-blocked methylhydrogensiloxane/diphenylsiloxane copolymer, both ends trimethylsiloxy group-blocked methyl Hydrogensiloxane/diphenylsiloxane/dimethylsiloxane copolymer, cyclic methylhydrogenpolysiloxane, cyclic methylhydrogensiloxane/dimethylsiloxane copolymer, cyclic methylhydrogensiloxane/diphenylsiloxane/dimethylsiloxane copolymer, ( _CH3 ) ₂ HSiO _1/2 units and SiO _4/2 units, from (CH ₃ ) ₂ HSiO _1/2 units, SiO _4/2 units and (C ₆ H ₅ )SiO _3/2 units can be exemplified by copolymers consisting of

In order to ensure the hardness of the cured product of the liquid silicone rubber composition, the present invention provides a (C) so that the number of silicon-bonded hydrogen atoms per alkenyl group is in the range of 1.0 to 3.0, preferably in the range of 1.5 to 2.5 The amounts of ingredients are to be adjusted. If the number of hydrogen atoms bonded to the silicon atoms is less than 1.0, the cured product may be soft and have surface tackiness. Conversely, if the number of hydrogen atoms bonded to silicon atoms exceeds 3.0, the cured product may lose flexibility and become brittle.

The transparent liquid silicone rubber composition of the present invention can be obtained by adjusting the components (A), (B), (C), and (D) above, with a type A durometer measured by the method described in JIS K 6249:2003. gives a cured product with a hardness of 55 or more. In order to increase the hardness of the silicone rubber cured product, generally, an organopolysiloxane containing more alkenyl groups and an organohydrogenpolysiloxane containing more silicon-bonded hydrogen atoms are used. A method of adding siloxane to the composition to increase the crosslink density is used.

Hydrogen bonded to a silicon atom in component (D) per silicon-bonded alkenyl group in the composition (e.g., in components (A), (B), and (C)), among others Desired hardness can be easily obtained when the ratio of the number of atoms is large. However, if this ratio is too large, adhesion to the mold during molding is likely to occur, and mold releasability may deteriorate, and mold cleaning may become complicated. As a result, it may become impossible to ensure sufficient quality as a silicone cured product, or productivity may decrease.

(E) Hydrosilylation reaction catalyst Component (E) is a hydrosilylation reaction catalyst, and known hydrosilylation reaction catalysts can be applied. Examples thereof include platinum black, platinic chloride, chloroplatinic acid, reaction products of chloroplatinic acid and monohydric alcohols, complexes of chloroplatinic acid and olefins, palladium-based catalysts, and rhodium-based catalysts. Among these, it is preferable to use a complex of chloroplatinic acid and an olefin. The amount of the hydrosilylation reaction catalyst compounded is the amount of the catalyst. Specifically, in the total of components (A) to (E), the mass of platinum group metal atoms is 0.1 to 200 ppm, preferably 1 to 50 ppm. If the blending amount of the above catalyst is 200 ppm or less, there is no possibility that the resulting cured product will turn yellow and lose its transparency.

Other Additive Components The transparent liquid silicone rubber composition of the present invention contains an organopolysiloxane containing silicon-bonded alkenyl groups and alkoxysilyl groups other than the components (A) and (B) described above. An alkoxysilane-based compound, a silane coupling agent, a titanium-based or zirconium-based condensation catalyst, or the like may be blended as a cross-linking aid.

Further, the transparent liquid 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, Polyethylenes such as 5,7-tetravinylcyclotetrasiloxane and 1,3,5-triallyl-1,3,5-triazine-2,4,6-(1H,3H,5H)-trione (triallyl isocyanurate) Acetylenes such as functional alkenyl compounds, 1-ethynylcyclohexanol, 3-methyl-1-butyn-3-ol, 3-methyl-1-pentyn-3-ol, 3,5-dimethyl-1-hexyn-3-ol A hydrosilylation reaction inhibitor such as an alcohol derivative may be added to ensure pot life.

Furthermore, the transparent liquid silicone rubber composition of the present invention can be blended with various dyes, flame retardants, and the like. Further, the present invention is characterized in that it does not contain silica or the like, which impairs transparency. These optional components may be used singly or in combination of two or more.

The transparent liquid silicone rubber composition of the present invention can be prepared by uniformly mixing the above components using a conventional mixing stirrer, kneader or the like.

<Cured Product of Transparent Liquid Silicone Rubber Composition>
The present invention also provides a cured product obtained by curing the transparent liquid silicone rubber composition described above. A cured product of the transparent liquid silicone rubber composition can be obtained by heating and curing the above silicone rubber composition in which each component is uniformly mixed, for example, at 80 to 350°C, preferably 100 to 200°C, more preferably 120 to 150°C. can get. When heat curing is performed at 120 to 150° C., the heating time is preferably 10 seconds to 120 minutes, more preferably 30 seconds to 70 minutes.

The cured product of the present invention preferably has a hardness of 55 or more, more preferably 55 to 90, as measured by a type A durometer according to JIS K 6249:2003.

The cured product of the present invention preferably has a total light transmittance of 93% or more as measured by a method conforming to JIS K 7361-1:1997 for a cured product sheet having a thickness of 1 mm. If the cured product sheet has a total light transmittance of 93% or more, it is advantageous for use in optical applications such as lamp exterior materials and resin lenses.

As for the method of molding the cured product, any known thermosetting resin molding method can be used. and pressurized vulcanization under predetermined molds and conditions. Alternatively, a two-liquid mixing type liquid injection molding machine can obtain a cured product having a desired shape using an arbitrary mold, and for example, a molded product suitable for optical applications can be obtained.

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, the transparent liquid silicone rubber composition of the present invention is supplied between two continuous resin films, 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.

EXAMPLES Hereinafter, the present invention will be specifically described by showing examples and comparative examples, but the present invention is not limited to the following examples. In addition, the unit of the compounding amount is a mass part.

[Example 1]
(A) 60 parts of dimethylpolysiloxane (1) (weight average molecular weight = 56,000) whose both ends are blocked with dimethylvinylsiloxy groups and has an average degree of polymerization of 750; Sol-gel silica (average particle size 115 nm) surface treated with 1,3-divinyl-1,1,3,3-tetramethyldisilazane at 27.7% coverage (2) 40 parts, water 2.0 parts were mixed at room temperature for 30 minutes, the temperature was raised to 150° C., stirring was continued for 3 hours, and the mixture was cooled. After that, 24 parts of the above dimethylpolysiloxane (1), (A) a dimethylpolysiloxane silicone (3) having an average degree of polymerization of about 230 and having 5 mol of vinyl groups in side chains, both ends of which are blocked with trimethylsiloxy groups. ) (weight average molecular weight = 17,000) were mixed at room temperature for 30 minutes to obtain a silicone rubber base (I).

To 100 parts of this silicone rubber base (I), 32 parts of the above dimethylpolysiloxane (1), (B) (CH ₃ ) ₃ SiO _1/2 units, (CH ₂ =CH) (CH ₃ ) ₂ SiO _1/2 Unit, SiO _4/2 unit copolymer (silicone resin) (4) (M unit/Q unit (molar ratio) = 0.85, number of alkenyl groups per molecule: 4.3, weight average molecular weight = 3 ,000) was added, and the stirring was continued for 30 minutes. Amount 0.00759 mol/g) 11.0 parts [SiH groups in methylhydrogenpolysiloxane (5)/(dimethylpolysiloxane (1), sol-gel silica (2), dimethylpolysiloxane silicone (3), silicone resin (4) total of alkenyl groups) = 2.2 (mol/mol)], 0.04 parts of ethynylcyclohexanol as a reaction controller, and 0.1 part of a platinum catalyst (Pt concentration of 1% by mass) were added, and 15 Stirring was continued for a minute to obtain a silicone rubber composition.

After press-curing this silicone rubber composition at 120°C for 10 minutes, the cured product was post-cured at 150°C for 1 hour in an oven. Time elongation and tear strength (angle) were measured. The results are shown in Table 1.

A polyethylene terephthalate (PET) liner and a frame with a thickness of 1.1 mm are superimposed on the press plate, the above hydrosilylation-curable liquid silicone rubber composition is poured into this frame, and a PET liner and press plate are further placed thereon. 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 silicone rubber transparent sheet with a thickness of about 1 mm.

The total light transmittance and haze (turbidity) of a sheet having 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]
(A) 16 parts of the dimethylpolysiloxane (1) and (B) 16 parts of the silicone resin (4) were added to 100 parts of the silicone rubber base (I) obtained in the same manner as in Example 1, and stirring was continued for 30 minutes. After that, (D) 7.9 parts of the methylhydrogenpolysiloxane (5) [SiH groups in methylhydrogenpolysiloxane (5)/(dimethylpolysiloxane (1), sol-gel silica (2), and silicone resin (4) total alkenyl groups) = 2.5 (mol/mol)], 0.04 parts of ethynylcyclohexanol as a reaction controller, and 0.1 part of a platinum catalyst (Pt concentration of 1% by mass) were added, and 15 Stirring was continued for a minute to obtain a silicone rubber composition.

[Example 3]
In Example 1, sol-gel silica 40 surface-treated with 1,3-divinyl-1,1,3,3-tetramethyldisilazane in an amount that covers 27.7% of the specific surface area of (C) sol-gel silica part is changed to 40 parts of sol-gel silica surface-treated with 1,3-divinyl-1,1,3,3-tetramethyldisilazane in an amount that covers 13.1% of the specific surface area of sol-gel silica, ( D) A silicone rubber composition was prepared in the same manner, except that the amount of methylhydrogenpolysiloxane (5) was changed from 11.0 parts to 8.4 parts [SiH group/alkenyl group total = 1.8 (mol/mol)]. got stuff

[Comparative Example 1]
In Example 1, 40 parts of sol-gel silica surface-treated with 1,3-divinyl-1,1,3,3-tetramethyldisilazane in an amount covering 27.7% of the specific surface area of sol-gel silica was added to hexagonal 40 parts of methyldisilazane-treated sol-gel silica (average particle size: 115 nm) was used, and 11.0 to 9.3 parts of (D) methylhydrogenpolysiloxane (5) [total of SiH groups/alkenyl groups=2. 2 (mol/mol)], to obtain a silicone rubber composition in the same manner.

[Comparative Example 2]
In Example 2, 40 parts of sol-gel silica surface-treated with 1,3-divinyl-1,1,3,3-tetramethyldisilazane in an amount covering 27.7% of the specific surface area of sol-gel silica was added to hexagonal Changed to 40 parts of methyldisilazane-treated sol-gel silica, (D) methylhydrogenpolysiloxane (5) from 11.0 parts to 6.0 parts [total of SiH groups/alkenyl groups = 2.5 (mol/mol) ] to obtain a silicone rubber composition.

The silicone rubber compositions obtained in Examples 2 and 3, and Comparative Examples 1 and 2 were also cured in the same manner as in Example 1. Elongation and tear strength (angle) were measured. A silicone rubber transparent sheet having a thickness of about 1 mm was prepared in the same manner as in Example 1, and the total light transmittance and haze (turbidity) were measured. Table 1 shows the measurement results.

From the results of Examples 1 to 3, the transparent liquid silicone rubber composition of the present invention having component (C), sol-gel silica containing an alkenyl group, exhibited excellent hardness, tensile strength, tear strength, transmittance, and haze. showed good performance in terms of In addition, the value of elongation at break also showed performance sufficient for practical use.

On the other hand, in Comparative Example 1 using a composition having sol-gel silica having no alkenyl group instead of the component (C), the elongation at break showed a high value, but in Comparative Examples 1 and 2, the tensile strength was low. , did not show sufficient performance in terms of tear strength. In addition, from the measurement results of transmittance and haze, the transparency was inferior to that of the transparent liquid silicone rubber composition of the present invention.

From the above, it has been clarified that the transparent liquid silicone rubber composition of the present invention is a silicone rubber composition having excellent tear strength while sufficiently maintaining hardness and high transparency.

It should be noted that the present invention is not limited to the above embodiments. The above-described embodiment is an example, and any device having substantially the same configuration as the technical idea described in the claims of the present invention and exhibiting the same effect is the present invention. included in the technical scope of

Claims (4)

(A) 100 parts by mass of a linear or branched organopolysiloxane containing at least two silicon-bonded alkenyl groups per molecule;
(B) a silicone resin containing R ₃ SiO _1/2 units and SiO _4/2 units (where R is a monovalent hydrocarbon group having 1 to 6 carbon atoms and at least two are alkenyl groups) 5 to 50 parts by mass,
(C) 10 to 150 parts by mass of sol-gel silica containing an alkenyl group,
(D) Organohydrogenpolysiloxane containing at least two silicon-bonded hydrogen atoms per molecule (the number of silicon-bonded hydrogen atoms per silicon-bonded alkenyl group in the composition is number is 1.0 to 3.0), and (E) a hydrosilylation reaction catalyst catalyst amount , and
In the component (B) , the ratio of the R ₃ SiO _1/2 units to the SiO _4/2 units is 0.6 to 0.6 to ₁ mol of the SiO _4/2 units _. A transparent liquid silicone rubber composition characterized by being 1.2 mol and solid at room temperature . A cured product obtained by curing the transparent liquid silicone rubber composition according to claim 1 . 3. The cured product according to claim 2, which has a hardness of 55 or more with a type A durometer measured by the method described in JIS K 6249:2003. The curing according to claim 2 or 3, wherein the total light transmittance of the cured product sheet having a thickness of 1 mm measured by a method conforming to JIS K 7361-1: 1997 is 93% or more. thing.