JP2010018662A - Liquid silicone rubber composition for optical waveguide plate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hydrosilylated curable liquid silicone rubber composition for an optical waveguide plate, the composition obtained by compounding a predetermined amount of silica as a light diffusing agent into a hydrosilylated curable liquid silicone rubber composition having high transparency, the composition having appropriate light diffusing property though it has high transparency, imparting strength and flexibility to a molded optical waveguide plate since the silica also has an effect of reinforcing the hydrosilylated curable liquid silicone rubber composition, and particularly, the composition suitable for a backlight device. <P>SOLUTION: The hydrosilylated curable liquid silicone rubber composition for an optical waveguide plate comprises, as essential components: (A) a silicone resin having an alkenyl group, comprising units selected from M, Q, D and T units, and having the total amount of M and Q units of not less than 80 mol% and a molar ratio of the M unit with respect to Q unit ranging from 0.5 to 1.5; (B) an organopolysiloxane having an alkenyl group; (C) an organohydrogen polysiloxane containing a hydrogen atom bonded to a silicon atom; (D) a hydrosilylation reaction catalyst; and (E) silica. Since the cured film of the above composition has appropriate light diffusing property though it has high transparency, the film is optimal as the optical waveguide plate of a backlight device for illuminating the keypad of a mobile phone. Since the silica as a light diffusing agent also has an effect of reinforcing the silicone rubber composition, strength or flexibility of the composition is not spoiled. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a liquid silicone rubber composition for an optical waveguide plate that is mainly composed of an organopolysiloxane and is cured by a hydrosilylation (addition) reaction. In particular, a highly transparent and high-hardness molded product can be obtained. The present invention relates to a liquid silicone rubber composition for an optical waveguide plate that is suitably used for an optical waveguide plate of a backlight device for pad illumination.

  Many keypads are equipped with a backlight device for illumination for night use of mobile phones. Conventionally, a large number of light emitting diodes (LEDs) are arranged on the back side of the keypad. However, along with the recent enhancement of functions of mobile phones, there are increasing demands for thinner, lighter, higher brightness, and lower cost lighting backlight devices, and the light used in liquid crystal displays (LCDs). A backlight device for illuminating with corrugated plates has been proposed. This is from an LED light source and an optical waveguide plate that diffuses light by introducing it into the inside from the end face facing the light source, and reflects the light at the reflecting surface installed at the key part to be illuminated and projects the reflected light to the outside. (See Patent Document 1: Japanese Patent Laid-Open No. 2003-59321). The feature of this device is that it can be thinned by installing LEDs in the horizontal direction, and even if the number of LEDs is reduced compared to the conventional type with LEDs installed on the back side, the entire keypad is uniformly brightened. It became possible to illuminate. In addition, the power consumption has been reduced, so the battery has become smaller and lighter, contributing to lower costs.

  The optical waveguide plate of the LCD backlight device is required only for optical characteristics, but the optical waveguide plate of the backlight device for keypad illumination also plays a role of transmitting displacement (click) of key input to the switching element. In addition to being highly transparent, it is also necessary that the elasticity and its temperature dependence are small, and that a thin film with a uniform surface thickness can be formed. In general, acrylic resins and polycarbonate resins are highly transparent and have good film moldability, but cracking may occur during key input due to temperature dependence of elasticity, particularly embrittlement in a low temperature region. Therefore, highly transparent silicone resins that are also applied to optical materials such as LED sealing materials (Patent Document 2: Japanese Patent Laid-Open No. 2002-265787, Patent Document 3: Japanese Patent Laid-Open No. 2006-202952, Patent Document) 4: Japanese Patent Laid-Open No. 2006-342200) was noted because of its excellent low-temperature characteristics. Among them, a cured product of a hydrosilylation-curable liquid silicone rubber composition that is highly transparent because it does not contain silica at all, does not impair elasticity even at low temperatures, and is relatively easy to form by heat curing, is a backlight device for keypad illumination. As an optical waveguide plate, it has been adopted.

Here, in an optical waveguide plate made of a cured product of a highly transparent hydrosilylation-curable liquid silicone rubber composition that does not contain silica at all, incident light from the end face is transmitted as it is, and is reflected at a key portion to be illuminated. In some cases, light did not collect on the surface.
In order to solve this problem, it is common to disperse and contain extraneous fine particles as a light diffusing agent in a highly transparent resin to control the light diffusion in the optical waveguide plate (Patent Document 5: JP-A-4-161448). Has been done. However, it is extremely difficult to disperse the extraordinary fine particles highly uniformly, and the adverse effect that the strength and flexibility of the resin itself are impaired by mixing the extraneous fine particles.

JP 2003-59321 A JP 2002-265787 A JP 2006-202952 A JP 2006-342200 A JP-A-4-161448

  The present invention has been made in view of the above circumstances, and is a highly transparent hydrosilylation-curable liquid silicone rubber composition containing a predetermined amount of silica as a light diffusing agent. Since it has diffusibility and silica also has the effect of reinforcing the hydrosilylation-curable liquid silicone rubber composition, it is possible to give strength and flexibility to the molded optical waveguide plate, especially for backlight devices. An object of the present invention is to provide a hydrosilylation-curable liquid silicone rubber composition suitable for an optical waveguide plate.

  As a result of intensive studies to achieve the above object, the present inventors impart an appropriate light diffusion effect without impairing the strength and flexibility of the highly transparent hydrosilylation-curable liquid silicone rubber composition. For this purpose, the present inventors have found that it is optimal to mix and disperse a small amount of silica within a predetermined range, and have reached the present invention.

That is, the present invention
(A) selected from R ₃ SiO _1/2 unit (M unit), SiO _4/2 unit (Q unit), R ₂ SiO _2/2 unit (D unit), and RSiO _3/2 unit (T unit) The total amount of M units and Q units among these structural units is 80 mol% or more, and the molar ratio of M units to Q units (M / Q) is 0.5 to 1.5. 100 parts by mass of the silicone resin in the range (wherein R is a monovalent hydrocarbon group having 1 to 6 carbon atoms, and at least two of the R groups are alkenyl groups).
(B) 50 to 250 parts by mass of an organopolysiloxane which is liquid at room temperature containing an alkenyl group bonded to at least two silicon atoms in one molecule (C) hydrogen bonded to at least two silicon atoms in one molecule Organohydrogenpolysiloxane containing atoms
Bonded to silicon atom in component (A) and component (B)
Bonded to silicon atom per alkenyl group
Amount of hydrogen atoms to be 1.0 to 10.0 (D) Hydrosilylation reaction catalyst Catalytic amount (E) Silica 0.1 to 10 parts by mass as an essential component A hydrosilylation (addition) curable liquid silicone rubber composition is provided.

  In this case, the component (B) is preferably a linear diorganopolysiloxane. Moreover, the surface-treated silica can be used as the component (E). In blending silica of component (E), it is kneaded with organopolysiloxane of component (B) in advance to make a paste, or added in advance, or organopolysiloxane of component (B), Silica and (F) a silica surface treating agent can be kneaded under heating to form a paste, which can be added. Further, the rubber hardness of the cured product of the composition of the present invention is preferably 70 degrees or more with a durometer A, the total light transmittance of a cured product sheet having a thickness of 2 mm is 90 to 98%, and a thickness of 2 mm. The cured product film preferably has a haze value of 2 to 10.

  The cured product film of the hydrosilylation-curable liquid silicone rubber composition of the present invention has an appropriate light diffusion effect and does not deteriorate the strength and flexibility of the film itself. It is optimal as an optical waveguide plate.

Hereinafter, the present invention will be described in more detail.
The silicone resin of component (A) of the hydrosilylation curable liquid silicone rubber composition of the present invention is composed of R ₃ SiO _1/2 units (M units), SiO _4/2 units (Q units), R ₂ SiO _2/2. A unit selected from a unit (D unit) and an RSiO _3/2 unit (T unit), and the total amount of M units and Q units among these structural units is 80 mol% or more, and is based on Q units It has a branched or three-dimensional network structure in which the molar ratio of M units is in the range of 0.5 to 1.5. Here, R is a monovalent hydrocarbon group having 1 to 6 carbon atoms, and at least two of all R groups in one molecule are alkenyl groups.

  Specific examples of the monovalent hydrocarbon group R having 1 to 6 carbon atoms of the silicone resin include methyl group, ethyl group, propyl group, isopropyl group, butyl group, isobutyl group, tert-butyl group, pentyl group, and hexyl group. Alkyl groups such as vinyl groups, allyl groups, propenyl groups, butenyl groups, pentenyl groups, hexenyl groups, etc., cycloalkyl groups such as cyclohexyl groups, cycloalkenyl groups such as cyclohexenyl groups, and aryls such as phenyl groups At least a part of the hydrogen atoms of the monovalent hydrocarbon group such as an unsubstituted monovalent hydrocarbon group such as a group, 3,3,3-trifluoropropyl group or cyanomethyl group is substituted with a halogen atom or a cyano group And a substituted monovalent hydrocarbon group such as a substituted alkyl group. A plurality of R contained in the silicone resin of the component (A) may be the same or different. However, from the viewpoint of compatibility with the other components of the hydrosilylation-curable liquid silicone rubber composition, 80 mol% or more of R, in particular, all R groups other than alkenyl groups may be methyl groups. preferable. This is because when the compatibility of each component deteriorates, the transparency of the cured product of the hydrosilylation-curable liquid silicone rubber composition decreases. The alkenyl group is preferably a vinyl group, which is also because it maintains compatibility with other components.

In the silicone resin of component (A), R ₃ SiO _1/2 unit (M unit) and SiO _4/2 unit (Q unit) are essential among the above four types of structural units, and hydrosilylation-curable liquid In order to improve the hardness of the cured product of the silicone rubber composition, it is necessary that the proportion of these two types of structural units in the total structural units is 80 mol% or more, preferably 90 mol% or more, more preferably Is 100 mol%. R ₂ SiO _2/2 units (D units) and RSiO _3/2 units (T units) may or may not be included.

When the molar ratio (M / Q) of R ₃ SiO _1/2 unit (M unit) to SiO _4/2 unit (Q unit) is less than 0.5, the hydrosilylation-curable liquid silicone rubber composition The compatibility with this component deteriorates, and if it is greater than 1.5, the hardness of the cured product of the hydrosilylation-curable liquid silicone rubber composition is lowered. Therefore, the molar ratio of M unit to Q unit is required to be in the range of 0.5 to 1.5, and preferably in the range of 0.7 to 1.2.

  Specific examples of the silicone resin as the component (A) include a copolymer of M units and Q units having a vinyldimethylsiloxy group, M units having a vinyldimethylsiloxy group, M units having a trimethylsiloxy group, and Q units. A copolymer of M unit, dimethylsiloxane unit and Q unit having vinyldimethylsiloxy group, copolymer of M unit, phenylsilsesquioxane unit and Q unit having vinyldimethylsiloxy group, vinyldimethyl Examples thereof include a copolymer of an M unit having a siloxy group, a dimethylsiloxane unit, a phenylsilsesquioxane unit and a Q unit, and a copolymer of an M unit having a trimethylsiloxy group, a vinylmethylsiloxane unit and a Q unit.

  The organopolysiloxane of component (B) of the hydrosilylation-curable liquid silicone rubber composition of the present invention contains an alkenyl group bonded to at least two silicon atoms in one molecule, and is usually hydrosilylation-curable. It is a known polymer used as a base polymer of a liquid silicone rubber composition, and has a viscosity at 25 ° C. of 1 to 100 Pa · s, preferably 5 to 100 Pa · s. In addition, the viscosity here is based on a rotational viscometer.

  Further, the component (B) may be a raw rubber-like organopolysiloxane having an average degree of polymerization of 2,000 or more and containing an alkenyl group bonded to at least two silicon atoms in one molecule. This is a known one that is usually used as a base polymer for millable type silicone rubber compounds. The average degree of polymerization is preferably 2,100 to 100,000, more preferably 3,000 to 10,000.

  As the average degree of polymerization of the component (B), for example, an average value (weight average degree of polymerization) calculated from a weight average molecular weight in terms of polystyrene in gel permeation chromatography (GPC) analysis can be applied.

The component (B) is an alkenyl group-containing organopolysiloxane, which is usually represented by the following average composition formula (I)
R ¹ _a SiO _{(4-a) / 2} (I)
(Here, R ¹ is a substituted or unsubstituted monovalent hydrocarbon group having 1 to 6 carbon atoms, and specific examples include alkyl groups such as methyl, ethyl, propyl, butyl, pentyl, and hexyl groups. , Vinyl groups, allyl groups, butenyl groups, pentenyl groups, hexenyl groups and other alkenyl groups, cyclohexyl groups, cyclohexenyl groups, phenyl groups and other unsubstituted monovalent hydrocarbon groups, 3,3,3-trifluoropropyl groups A substituted monovalent hydrocarbon group such as a substituted alkyl group in which at least a part of the hydrogen atoms of the monovalent hydrocarbon group such as a cyanomethyl group is substituted with a halogen atom or a cyano group. However, it is necessary that the molecule contains two or more alkenyl groups, and a is from 1.9 to 2.4, preferably from 1.95 to 2.05. Number of ranges .)
It may be linear or branched. Preferably, the main chain is a linear organopolysiloxane composed of repeating diorganopolysiloxane units (D units) and having both ends of the molecular chain blocked with triorganosiloxy groups (M units). The substituent bonded to the atom is preferably a methyl group or a phenyl group. Further, the alkenyl group bonded to the silicon atom, which is essential to be contained in two or more in one molecule, is preferably a vinyl group, which may be at the molecular chain end or at the side chain, Those containing two (ie, one at each end) are preferred.

  In order to achieve both the hardness and flexibility of the molded film after curing of the hydrosilylation-curable liquid silicone rubber composition of the present invention, (B) component is 50 to 250 parts by mass with respect to (A) component 100 parts by mass. Is preferred. If the component (B) is less than this range, the resulting film is not pliable and brittle. On the other hand, if the component exceeds this range, the film is soft and has a surface tackiness, which is not suitable. Preferably, (B) component is 80-150 mass parts with respect to 100 mass parts of (A) component.

The organohydrogenpolysiloxane of component (C) of the hydrosilylation-curable liquid silicone rubber composition of the present invention contains hydrogen atoms (SiH groups) bonded to at least two silicon atoms in one molecule. The following average composition formula (II)
R ² _b H _c SiO _{(4-bc) / 2} (II)
(Here, R ² is a substituted or unsubstituted monovalent hydrocarbon group having 1 to 6 carbon atoms, and preferably has no aliphatic unsaturated bond. Specific examples include a methyl group, an ethyl group, Alkyl groups such as propyl group, butyl group, pentyl group and hexyl group, unsubstituted monovalent hydrocarbon groups such as cyclohexyl group, cyclohexenyl group and phenyl group, 3,3,3-trifluoropropyl group, cyanomethyl group, etc. And b is a substituted monovalent hydrocarbon group such as a substituted alkyl group in which at least a part of the hydrogen atoms of the monovalent hydrocarbon group is substituted with a halogen atom or a cyano group. Is 0.18 to 1.0, and b + c is 0.8 to 3.0, preferably b is 0.8 to 2.0, c is 0.2 to 1.0, and b + c is 1.0 to 2. It is indicated by a positive number satisfying .5.)
A conventionally known organohydrogenpolysiloxane represented by the formula is applicable. Further, the molecular structure of the organohydrogenpolysiloxane may be any of linear, cyclic, branched, and three-dimensional network structures. In this case, the number of silicon atoms in one molecule (or the degree of polymerization) is preferably 2 to 300, particularly about 4 to 200 at room temperature. In addition, the hydrogen atom (SiH group) bonded to the silicon atom may be at the end of the molecular chain, at the side chain, or both, and at least two (usually 2 to 300) per molecule. Preferably, those containing 3 or more (for example, 3 to 200), more preferably about 4 to 150 are used.

Specific examples of the organohydrogenpolysiloxane of component (C) include 1,1,3,3-tetramethyldisiloxane, 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, dimethylhydrogensiloxy group-blocked dimethylpolysiloxane at both ends, dimethylhydrogensiloxy group-blocked dimethylsiloxane at both ends Tyrhydrogensiloxane copolymer, trimethylsiloxy group-capped methylhydrogensiloxane / diphenylsiloxane copolymer, trimethylsiloxy group-capped methylhydrogensiloxane / diphenylsiloxane / dimethylsiloxane copolymer, cyclic methylhydrogenpolypropylene Siloxane, Cyclic methylhydrogensiloxane / dimethylsiloxane copolymer, Cyclic methylhydrogensiloxane / Diphenylsiloxane / Dimethylsiloxane copolymer, Copolymer consisting of (CH ₃ ) ₂ HSiO _1/2 units and SiO _4/2 units In a copolymer, a copolymer comprising (CH ₃ ) ₂ HSiO _1/2 units, SiO _4/2 units, and (C ₆ H ₅ ) SiO _3/2 units, etc. All other groups such as ethyl and propyl Examples thereof include those substituted with an aryl group such as a kill group and a phenyl group.

  About the compounding quantity of (C) component, in order to make the hardness and flexibility of the molding film after hardening of the hydrosilylation curable liquid silicone rubber composition of this invention compatible, (A) component and (B) component The amount of component (C) so that the number of hydrogen atoms bonded to silicon atoms is 1.0 to 10.0, preferably 1.5 to 5.0, per alkenyl group bonded to silicon atoms. Need to be adjusted. If it is less than this range, it will become a soft and surface-adhesive film, and if it exceeds this range, it will become a non-flexible film.

  As the hydrosilylation reaction catalyst of the component (D) of the hydrosilylation-curable liquid silicone rubber composition of the present invention, a known catalyst can be applied, for example, platinum black, platinum chloride, chloroplatinic acid, chloroplatinic acid, and the like. Examples include reactants with monohydric alcohols, complexes of chloroplatinic acid and olefins, platinum-based catalysts such as platinum bisacetoacetate, palladium-based catalysts, and rhodium-based catalysts. In addition, the compounding quantity of this hydrosilylation reaction catalyst can be made into a catalyst quantity, and is 0.5-1,000 ppm with respect to (A) component and (B) component normally as a mass of a platinum group metal, Preferably it is 1 About 200 ppm.

As the silica of the component (E) of the hydrosilylation curable liquid silicone rubber composition of the present invention, known silica can be applied, for example, dry silica obtained by burning hydrogen tetragonal chloride while supplying hydrogen and oxygen. Examples thereof include wet silica obtained by neutralizing sodium silicate (water glass) with hydrochloric acid or sulfuric acid. Among these, dry silica is preferable because it has a light diffusion effect smaller than that of wet silica and can be incorporated in a relatively large amount, and the reinforcing effect on the hydrosilylation-curable liquid silicone rubber composition is increased. In particular, the specific surface area by BET method of 150 meters ² / g or more, preferably 200 to 400 m ² / g, more preferably is suitable dry silica 150~350m ² / g.

  Moreover, the silica of (E) component which has been surface-treated with a surface treating agent in advance may be used. The surface treatment agent is also used as the component (F) described below.

  (E) component silica is 0.1 to 10 parts by weight, preferably 0.2 to 8 parts by weight, more preferably 0.3 to 6 parts by weight, based on 100 parts by weight of the silicone resin of component (A). More preferably, it is necessary to blend in the range of 0.5 to 5 parts by mass. If the blending amount is too small, a desired haze value as an optical waveguide plate cannot be obtained, and if the blending amount is too large, light transmittance (transparency) suitable for the optical waveguide plate cannot be obtained.

  As the silica surface treating agent of the component (F) of the hydrosilylation curable liquid silicone rubber composition of the present invention, those generally known as silica surface treating agents can be used. For example, alkyl alkoxysilanes, alkylchlorosilanes, alkylsilazanes, silane coupling agents, titanate treatment agents, fatty acid esters, and the like are exemplified. These can be used alone or in combination of two or more.

  As a method of blending the silica of the component (E) into the hydrosilylation-curable liquid silicone rubber composition of the present invention, powdered silica may be added as it is and mixed and dispersed. In order to improve the dispersibility of silica, it is preferable to add polysiloxane and silica after kneading them into a paste. In that case, it is a more preferable aspect to add the silica surface treating agent of (F) component together and / or to heat to 100-180 degreeC during kneading | mixing. In addition, the addition of a general hydrosilylation-curable liquid silicone rubber composition that is highly filled with silica as compared with the composition of the present invention is expected to have the same effect as the addition of silica as a paste. Therefore, it is a preferable method. Here, “a general hydrosilylation curable liquid silicone rubber composition” refers to a commercially available hydrosilylation room temperature curable liquid silicone rubber composition or a hydrosilylation thermosetting liquid silicone rubber composition for injection molding. Point to. In these and the composition of the present invention, the role of silica is different, and therefore the content is also greatly different. That is, since the silica compounding in the general hydrosilylation curable liquid silicone rubber composition is intended to reinforce the siloxane polymer and impart rubber strength and hardness, the silica compounding amount is generally 10 to 50% by mass. In contrast, the silica of the composition of the present invention plays a role of appropriately diffusing light transmission, has no reinforcing effect on the siloxane polymer, and the silica content is the total amount of the components (A) to (E). About 0.03 to 6% by mass.

  The hydrosilylation curable liquid silicone rubber composition of the present invention includes an alkoxysilane-based compound containing an alkoxysilyl group, a silane coupling agent, a titanium-based or zirconium-based condensation catalyst as long as the effects of the present invention are not impaired. Etc. may be blended as a crosslinking aid.

Also, for example, 1,3,5,7-tetramethyl-1,3,5,7-tetravinylcyclotetrasiloxane and 1,3,5-triallyl-1,3,5-triazine-2,4,6 Hydrosilyl such as polyfunctional alkenyl compounds such as-(1H, 3H, 5H) -trione (triallyl isocyanurate), acetylene alcohol derivatives such as 1-ethynylcyclohexanol and 3,5-dimethyl-1-hexyn-3-ol For example, an inorganic filler such as treated silica surface-treated with trimethylchlorosilane or octamethyltetracyclosiloxane can be used to increase the hardness and strength of the cured product. You may mix | blend in order to improve. Furthermore, it is possible to add dyes, pigments, flame retardants, release agents and the like as long as the effects of the present invention are not impaired.
Each of these optional components may be used alone or in combination of two or more.

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

  An optical waveguide plate made of a cured product of the hydrosilylation-curable liquid silicone rubber composition of the present invention, particularly an optical waveguide plate for a backlight device, comprises the above-mentioned hydrosilylation-curable liquid silicone rubber composition in which the respective components are uniformly mixed. It is obtained by heat curing at 80 to 350 ° C, preferably 100 to 200 ° C, more preferably 120 to 150 ° C. As the molding method, a known film molding method using a thermosetting resin can be used. For example, in the case of a press molding method, the hydrosilylation-curable liquid silicone rubber composition of the present invention is poured between two resin films (liners). The pressure vulcanization may be performed under a predetermined mold and conditions. As an example of the stretch molding method, while supplying the hydrosilylation curable liquid silicone rubber composition of the present invention between two continuous resin films, the film is stretched to a certain thickness by a roll and continuously supplied to a heating furnace. And normal pressure hot air vulcanization. If the liner is peeled off after cooling after curing, an optical waveguide plate can be obtained.

  In this case, the cured product of the hydrosilylation curable liquid silicone rubber composition of the present invention preferably has a rubber hardness of 70 degrees or more, particularly 75 to 85 degrees in terms of durometer A, which is tacked from the surface of the optical waveguide plate. It is important to remove the property (stickiness). An optical waveguide plate of a backlight device for keypad illumination of a cellular phone is sandwiched between a light-shielding sheet having a key top on the upper surface and a metal dome on the lower surface. This is because the corrugated plate and / or the optical waveguide plate and the light shielding sheet are brought into close contact with each other, and light is diffused therefrom, resulting in a problem that the luminance of the entire surface of the optical waveguide plate is lowered. As a means for obtaining the rubber hardness, in order to improve the hardness, in particular, (1) the content of the component (A) is increased, and (2) a hydrogen atom (SiH group bonded to a silicon atom in one molecule). ) There are methods such as using the component (C) having a large number, (3) adding a polyfunctional alkenyl compound, etc., and adjusting the hardness by combining these appropriately.

  The total light transmittance of the cured sheet having a thickness of 2 mm is preferably 90 to 98%, particularly 94 to 96%, as measured with a direct reading haze computer HGM-2 manufactured by Suga Test Instruments Co., Ltd. If the total light transmittance is less than 90%, light diffusion in the optical waveguide plate is too strong, and incident light does not reach the farthest portion of the optical waveguide plate, resulting in uneven brightness. On the other hand, when the total light transmittance exceeds 98%, the incident light is transmitted as it is, and it becomes difficult to collect the light at the portion to be illuminated. As a means for obtaining the total light transmittance, there is a method of adjusting the blending ratio of the component (A), the component (B), and the component (C). The smaller the difference in refractive index between the components (A), (B), and (C), the higher the light transmittance. However, since these components actually differ in refractive index, the total light transmittance decreases. Although tending, the desired total light transmission can be achieved by proper combination.

  Furthermore, it is preferable that the haze value of the cured sheet having a thickness of 2 mm is 2 to 10, particularly 3 to 5, as measured by a direct reading haze computer HGM-2 manufactured by Suga Test Instruments Co., Ltd. When the haze value is less than 2, incident light is transmitted as it is, and it becomes difficult to collect light at a portion to be illuminated. On the other hand, when the haze value exceeds 10, light diffusion in the optical waveguide plate is too strong, and incident light does not reach the farthest part of the optical waveguide plate, resulting in uneven brightness. Examples of the means for setting the haze value include adjusting the amount of component (E). Since the haze value increases as the amount of the component (E) is increased, it may be determined by the blending amount that provides the desired haze value.

  EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention concretely, this invention is not limited to a following example. In addition, the unit of a compounding quantity is a mass part. Moreover, a weight average molecular weight and a weight average polymerization degree are the polystyrene conversion values in a gel permeation chromatography (GPC) analysis. The viscosity is a value measured by a rotational viscometer.

[Examples 1-9, Comparative Examples 1-6]
For each example of the hydrosilylation-curable liquid silicone rubber composition, (A) silicone resin, (B) alkenyl group-containing organopolysiloxane, (C) organohydrogenpolysiloxane, (D) hydrosilylation reaction catalyst, (E) Tables 1 and 2 show the blending amounts of silica, (G) hydrosilylation reaction control agent, (H) silica-containing paste, (I) silica-containing hydrosilylation addition reaction curable liquid silicone rubber composition. Each composition was uniformly mixed and stirred and degassed under reduced pressure. In addition, the amount of SiH groups in the table indicates the number of hydrogen atoms bonded to the silicon atom of the component (C) per one alkenyl group bonded to the silicon atom in the components (A) and (B). Here, the silica-containing hydrosilylation addition reaction curable liquid silicone rubber of component (I) refers to a commercially available room temperature curable liquid silicone rubber or a thermosetting liquid silicone rubber for injection molding.

  A polyethylene terephthalate (PET) liner and a 2.2 mm-thick frame are stacked on the press plate, and the hydrosilylation-curable liquid silicone rubber composition is poured into the frame, and a PET liner and a press plate are further added thereto. Laminated and press molded at 120 ° C. for 10 minutes. Thereafter, the entire PET liner was taken out, cooled, the PET liner was peeled off, and post-cured in a 150 ° C. oven for 1 hour to obtain a silicone rubber transparent sheet having a thickness of about 2 mm.

The following physical properties were evaluated for these.
・ Rubber hardness: JIS-K6249 (2mm sheet), durometer A
-Transparency: The total light transmittance and haze value of a 2 mm sheet were measured.
-Comprehensive evaluation: When the rubber hardness is 70 or more with durometer A, transparency is 90 to 98% of total light transmittance, and all three items of haze value 2 to 10 are satisfied, ◯, otherwise.

Materials Used (A) Silicone Resin A-1 Copolymer of (CH ₃ ) ₃ SiO _1/2 Unit, (CH ₂ ═CH) (CH ₃ ) ₂ SiO _1/2 Unit, SiO _4/2 Unit Molar ratio _{: (CH 3) 3 SiO 1/2} / (CH 2 = CH) (CH 3) 2 SiO 1/2 / SiO 4/2 = 40/10/50
Number of alkenyl groups per molecule: 4.2 (weight average molecular weight = 3,000)
Copolymer of A-2 (CH ₃ ) ₃ SiO _1/2 unit, (CH ₂ ═CH) (CH ₃ ) ₂ SiO _1/2 unit, SiO _4/2 unit Molar ratio: (CH ₃ ) ₃ SiO _{1 / 2} / (CH ₂ ═CH) (CH ₃ ) ₂ SiO _1/2 / SiO _4/2 = _40/5/55
Number of alkenyl groups per molecule: 3.5 (weight average molecular weight = 5,000)

(B) Alkenyl group-containing organopolysiloxane B-1 Both end dimethylvinylsiloxy group-blocked dimethylpolysiloxane Weight average degree of polymerization: about 450 (weight average molecular weight = about 33,000)
Viscosity: about 5 Pa · s
B-2 Dimethylpolysiloxane blocked with dimethylvinylsiloxy groups at both ends Weight average polymerization degree: about 1,100 (weight average molecular weight = about 80,000)
Viscosity: about 100 Pa · s
B-3 Both end dimethylvinylsiloxy group-capped dimethylpolysiloxane Weight average degree of polymerization: about 8,000 (weight average molecular weight = about 600,000)

(C) Organohydrogenpolysiloxane C-1 Both end trimethylsiloxy group-blocked methylhydrogenpolysiloxane Viscosity: 20 mPa · s
Number of SiH groups per molecule: 40 (SiH group content 0.016 mol / g)
C-2 Both-end dimethylhydrogensiloxy group-blocked dimethylpolysiloxane / methylhydrogenpolysiloxane copolymer Viscosity: 40 mPa · s
Number of SiH groups per molecule: 45 (SiH group content 0.011 mol / g)

(D) Hydrosilylation reaction catalyst D-1 Platinum catalyst Pt concentration: 1% by weight

(E) Silica E-1 Dry silica Specific surface area (BET method): 300 m ² / g
E-2 Dry silica Specific surface area (BET method): 200 m ² / g
E-3 Wet silica Specific surface area (BET method): 190 m ² / g
E-4 Surface treatment dry silica Specific surface area (BET method): 170 m ² / g, Surface treatment agent: Dimethyldichlorosilane E-5 Surface treatment dry silica Specific surface area (BET method): 300 m ² / g, Surface treatment agent: Hexa Methyl disilazane

(F) Silica surface treatment agent F-1 Hexamethyldisilazane

(G) Hydrosilylation reaction control agent G-1 1-ethynylcyclohexanol

(H) Silica-containing paste H-1 30 parts by mass of E-1 and 70 parts by mass of B-1 paste H-2 100 parts by mass of H-1 and 5 parts by mass of hexamethyldisilazane (F- 1) and paste kneaded at 150 ° C. for 1 hour

(I) Silica-containing hydrosilylation addition reaction curable liquid silicone rubber composition I-1 KE-2000-60A manufactured by Shin-Etsu Chemical Co., Ltd. Thermosetting liquid silicone rubber A liquid for injection molding (silica content: about 25% by mass )
I-2 KE-2000-60B manufactured by Shin-Etsu Chemical Co., Ltd. Thermosetting liquid silicone rubber B for injection molding (silica content: about 25% by mass)
Note: KE-2000-60A and KE-2000-60B are 50:50 (equal weight) mixed type liquid silicone rubber.

Claims (8)

(A) selected from R ₃ SiO _1/2 unit (M unit), SiO _4/2 unit (Q unit), R ₂ SiO _2/2 unit (D unit), and RSiO _3/2 unit (T unit) Among these all structural units, the total amount of M units and Q units is 80 mol% or more, and the molar ratio of M units to Q units (M / Q) is 0.5 to 1.5. Silicone resin that is in the range
100 parts by mass (wherein R is a monovalent hydrocarbon group having 1 to 6 carbon atoms, and at least two of all R groups in one molecule are alkenyl groups.)
(B) Organopolysiloxane containing an alkenyl group bonded to at least two silicon atoms in one molecule
50-250 parts by mass (C) Organohydrogenpolysiloxane containing hydrogen atoms bonded to at least two silicon atoms in one molecule
Bonded to silicon atom in component (A) and component (B)
Bonded to silicon atom per alkenyl group
Amount of hydrogen atoms to be 1.0 to 10.0 (D) Hydrosilylation reaction catalyst Catalytic amount (E) Silica 0.1 to 10 parts by mass as an essential component Hydrosilylation-curable liquid silicone rubber composition.   The hydrosilylation-curable liquid silicone rubber composition for an optical waveguide plate according to claim 1, wherein the component (B) is a linear diorganopolysiloxane.   The hydrosilylation-curable liquid silicone rubber composition for an optical waveguide plate according to claim 1 or 2, wherein the component (E) is a surface-treated silica.   4. The optical waveguide plate according to claim 1, wherein the component (E) component silica is kneaded in advance with the component (B) organopolysiloxane to form a paste and added. Hydrosilylation-curable liquid silicone rubber composition.   (B) Organopolysiloxane, (E) silica, (F) Silica surface treatment agent is kneaded under heating to form a paste, and added to the component (E). The hydrosilylation-curable liquid silicone rubber composition for an optical waveguide plate according to claim 1, 2, or 3.   The hydrosilylation-curable liquid silicone rubber composition for an optical waveguide plate according to any one of claims 1 to 5, wherein the rubber hardness of the cured product is 70 degrees or more by durometer A.   The hydrosilylation-curable liquid silicone rubber composition for optical waveguide plates according to any one of claims 1 to 6, wherein the cured product sheet having a thickness of 2 mm has a total light transmittance of 90 to 98%.   The hydrosilylation-curable liquid silicone rubber composition for optical waveguide plates according to any one of claims 1 to 6, wherein the cured product film having a thickness of 2 mm has a haze value of 2 to 10.