JP7634501B2 - Silicone rubber composition with low mold contamination - Google Patents

Description

The present invention relates to a silicone rubber composition that causes little mold contamination.

In order to improve the weather resistance and optical waveguides of LED lights and various LCD monitor screens, attention has been focused on silicone resins with high hardness and transparency. Among them, addition-curing silicone rubber cured products have come to be used because they contain no silica, are highly transparent, do not lose elasticity even at low temperatures, and are relatively easy to mold by heat curing (Patent Documents 1 to 4).

Generally, silicone rubber used as a focusing lens for LED lights and the like is required to have high hardness. In the molding method of such silicone rubber, first, primary vulcanization is performed using a mold, and then secondary vulcanization is performed using a high-temperature dryer (oven) for the purpose of stabilizing the physical properties and removing volatile components in the cured product. However, in the case of high-hardness silicone rubber that does not contain reinforcing silica, there is a problem that the mold is soiled when the cured product is removed from the mold after continuous molding of the primary vulcanization, and the average surface roughness of the cured product increases due to the soiling. If the average surface roughness of the cured product exceeds a certain standard value, light diffusion or light leakage occurs, resulting in a problem of reduced brightness.

JP 2010-174233 A JP 2010-174234 A International Publication No. 2016/098883 International Publication No. 2016/098884

The present invention has been made to improve the above situation, and aims to provide an addition-curing silicone rubber composition that suppresses mold contamination even after continuous molding of the primary vulcanization. It also aims to provide a silicone rubber composition that maintains a reduced average surface roughness of the cured product even after multiple pieces are continuously molded, and gives a highly transparent cured product.

（式中、Ｒ^２は独立して炭素数１から１０のアルキル基であり、Ｒ^３は独立して炭素数１から１０のアルキル基もしくは水素原子であり、ｚは８以上の整数であり、ｙは０～１５０の整数であり、０．４０≦ｚ／（ｙ＋ｚ）≦１．０であり、かつ１分子中のヒドロシリル基の数が１０個以上である）
：組成物中の、全アルケニル基のモル数（Ｖｉ）に対する全ヒドロシリル基のモル数（Ｈ）の比（Ｈ／Ｖｉ）が１．０～１．５に相当する量
（Ｄ）１分子中にヒドロシリル基を２個以上有し、１分子中に１～３個のフェニル基を有するオルガノハイドロジェンポリシロキサン：（Ａ）成分１００質量部に対し０．１～５質量部、
（Ｅ）付加反応触媒：触媒量
を含有するものである金型低汚染性シリコーンゴム組成物を提供する。 In order to solve the above problems, the present invention provides
An addition curable silicone rubber composition comprising:
(A) 100 parts by mass _of an organopolysiloxane resin having a three-dimensional network structure, which has R ¹ ₃ SiO _1/2 units (wherein R ¹ is independently a monovalent hydrocarbon group having 1 to 10 carbon atoms) and SiO _4/2 units, in which the molar ratio [M/Q] of R ¹ ₃ SiO _1/2 units (M units) to SiO 4/2 units (Q units) is 0.5 to 1.5 and the alkenyl group content is 1×10 ^-4 to 5×10 ^-3 mol/g; (B) 50 to 250 parts by mass of a linear organopolysiloxane which has two or more alkenyl groups bonded to silicon atoms in each molecule and is liquid at 23° C.;
(C) A linear organohydrogenpolysiloxane represented by the following general formula (1):

(In the formula, ^R2 is independently an alkyl group having 1 to 10 carbon atoms, ^R3 is independently an alkyl group having 1 to 10 carbon atoms or a hydrogen atom, z is an integer of 8 or more, y is an integer of 0 to 150, 0.40≦z/(y+z)≦1.0, and the number of hydrosilyl groups in one molecule is 10 or more.)
(D) an organohydrogenpolysiloxane having two or more hydrosilyl groups and 1 to 3 phenyl groups per molecule in an amount of 0.1 to 5 parts by mass per 100 parts by mass of component (A),
(E) Addition reaction catalyst: The present invention provides a silicone rubber composition with low mold contamination, which contains a catalytic amount of the addition reaction catalyst.

With this type of silicone rubber composition, the average surface roughness of the cured product can be maintained at 0.15 μm or less even after multiple moldings. Therefore, even with continuous molding, there is little loss in brightness, and a highly transparent cured product can be obtained.

According to the present invention, an addition-curing silicone rubber composition is obtained that has an elongation at break of 200% or more after primary vulcanization and suppresses mold contamination even after continuous molding of the primary vulcanization. Therefore, even after multiple pieces are molded continuously, the average surface roughness of the cured product can be maintained at 0.15 μm or less. Therefore, even when continuously molded, there is little loss in brightness, and a highly transparent cured product can be obtained.

As a result of intensive research conducted by the present inventors to achieve the above object, they discovered that by using a specific alkenyl group-containing silicone resin, an alkenyl group-containing linear organopolysiloxane, an organohydrogensiloxane with a high hydrosilyl group content, and a specific organohydrogensiloxane containing a phenyl group in an appropriate ratio, it is possible to obtain a silicone rubber composition that can achieve an elongation at break of 200% or more for the cured product after primary vulcanization, suppresses mold contamination after continuous molding of the primary vulcanization, and gives a highly transparent cured product with an average surface roughness of 0.15 μm or less when removed from the mold. This led to the creation of the present invention.

The above findings were obtained from the examination of various materials, which revealed that if the elongation at break of the cured product after primary vulcanization is 200% or more, it is easy to remove from the mold, and if the average surface roughness of the cured product is 0.15 μm or less, light diffusion and leakage can be prevented, resulting in a highly transparent cured product with little change in brightness.

（式中、Ｒ^２は独立して炭素数１から１０のアルキル基であり、Ｒ^３は独立して炭素数１から１０のアルキル基もしくは水素原子であり、ｚは８以上の整数であり、ｙは０～１５０の整数であり、０．４０≦ｚ／（ｙ＋ｚ）≦１．０であり、かつ１分子中のヒドロシリル基の数が１０個以上である）
：組成物中の、全アルケニル基のモル数（Ｖｉ）に対する全ヒドロシリル基のモル数（Ｈ）の比（Ｈ／Ｖｉ）が１．０～１．５に相当する量
（Ｄ）１分子中にヒドロシリル基を２個以上有し、１分子中に１～３個のフェニル基を有するオルガノハイドロジェンポリシロキサン：（Ａ）成分１００質量部に対し０．１～５質量部、
（Ｅ）付加反応触媒：触媒量
を含有するものである金型低汚染性シリコーンゴム組成物である。 That is, the present invention provides:
An addition curable silicone rubber composition comprising:
(A) 100 parts by mass _of an organopolysiloxane resin having a three-dimensional network structure, which has R ¹ ₃ SiO _1/2 units (wherein R ¹ is independently a monovalent hydrocarbon group having 1 to 10 carbon atoms) and SiO _4/2 units, in which the molar ratio [M/Q] of R ¹ ₃ SiO _1/2 units (M units) to SiO 4/2 units (Q units) is 0.5 to 1.5 and the alkenyl group content is 1×10 ^-4 to 5×10 ^-3 mol/g; (B) 50 to 250 parts by mass of a linear organopolysiloxane which has two or more alkenyl groups bonded to silicon atoms in each molecule and is liquid at 23° C.;
(C) A linear organohydrogenpolysiloxane represented by the following general formula (1):

(In the formula, ^R2 is independently an alkyl group having 1 to 10 carbon atoms, ^R3 is independently an alkyl group having 1 to 10 carbon atoms or a hydrogen atom, z is an integer of 8 or more, y is an integer of 0 to 150, 0.40≦z/(y+z)≦1.0, and the number of hydrosilyl groups in one molecule is 10 or more.)
(D) an organohydrogenpolysiloxane having two or more hydrosilyl groups and 1 to 3 phenyl groups per molecule in an amount of 0.1 to 5 parts by mass per 100 parts by mass of component (A),
(E) Addition reaction catalyst: the silicone rubber composition with low mold staining contains a catalytic amount of the addition reaction catalyst.

The present invention is described in detail below, but is not limited to these.

<Addition-curable silicone rubber composition (low-mold-contamination silicone rubber composition)>
The low mold-staining silicone rubber composition of the present invention is an addition-curable silicone rubber composition. The addition-curable silicone rubber composition of the present invention is characterized by comprising the following components (A) to (E). The addition-curable silicone rubber composition is preferably in a liquid state.

(A) Alkenyl group-containing silicone resin (organopolysiloxane resin with a three-dimensional network structure)
The alkenyl-containing organopolysiloxane resin (three-dimensional network-structured organopolysiloxane resin, resinous copolymer) of component (A) is an organopolysiloxane resin having a three-dimensional network structure containing R ¹ ₃ SiO _1/2 units and SiO _4/2 units as main components. It is preferable that the component (A) is a solid at 25°C.

R ¹ 's are each independently a monovalent hydrocarbon group having 1 to 10 carbon atoms, preferably 1 to 8 carbon atoms. Examples include alkyl groups such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, pentyl, neopentyl, hexyl, cyclohexyl, octyl, nonyl, and decyl groups, aryl groups such as phenyl, tolyl, xylyl, and naphthyl groups, aralkyl groups such as benzyl, phenylethyl, and phenylpropyl groups, and alkenyl groups such as vinyl, allyl, propenyl, isopropenyl, butenyl, hexenyl, cyclohexenyl, and octenyl groups.

The alkenyl group-containing three-dimensional network organopolysiloxane resin (resinous copolymer) of component (A) may be composed of the above-mentioned R ¹ ₃ SiO _1/2 units and SiO _4/2 units, and may also contain R ¹ ₂ SiO _2/2 units or R ¹ SiO _3/2 units (R ¹ is as defined above) as necessary.

The molar ratio [M/Q] of R ¹ ₃ SiO _1/2 units (M units) to SiO _4/2 units (Q units) is 0.5 to 1.5, preferably 0.5 to 1.3. If this molar ratio is less than 0.5, the tackiness of the rubber increases, and if it is more than 1.5, the compatibility decreases, making compounding difficult.

The total amount of the R ¹ ₂ SiO _2/2 units and the R ¹ SiO _3/2 units may be within the range of 50% by mass or less (0 to 50% by mass), preferably 40% by mass or less (0 to 40% by mass), and more preferably 30% by mass or less (0 to 30% by mass) based on the entire copolymer. Among these, copolymers of (CH ₃ ) ₃ SiO _1/2 units, (CH ₂ ═CH)(CH ₃ ) ₂ SiO _1/2 units, and SiO _4/2 units are preferred.

Furthermore, the alkenyl-containing organopolysiloxane resin of component (A) contains vinyl groups in an amount of alkenyl groups of 1×10 ^-4 to 5×10 ^-3 mol/g, preferably 2×10 ^-4 to 3×10 ^-3 mol/g, and more preferably 3×10 ^-4 to 2×10 ^-3 mol/g. If the alkenyl group content is more than 5×10 ^-3 mol/g, the rubber will be hard and brittle, whereas if it is less than 1×10 ^-4 mol/g, the rubber will be soft and weak.

The resinous copolymer can usually be produced by co-hydrolytic condensation of suitable mono- and tetra-functional chlorosilanes and alkoxysilanes (i.e., those which undergo hydrolytic condensation to produce R ¹ ₃ SiO _1/2 units and SiO _4/2 units) by methods well known in the art.

(B) Linear organopolysiloxane (alkenyl group-containing organopolysiloxane)
Component (B) of the present invention is a linear organopolysiloxane that is liquid at 23° C. and has two or more silicon-bonded alkenyl groups per molecule.

The viscosity of the above component (B) is preferably in the range of 1 to 100 Pa·s at 23°C, as measured using a rotational viscometer as described in JIS K7117-1:1999. It is more preferably 5 to 100 Pa·s, and even more preferably 10 to 100 Pa·s.

The number of the alkenyl groups is 2 or more, preferably 2 to 50, and more preferably 2 to 20.

The alkenyl group preferably has 2 to 10 carbon atoms, more preferably 2 to 8. Specific examples include vinyl groups, allyl groups, propenyl groups, isopropenyl groups, and butenyl groups, with vinyl groups being preferred.

As the group other than the alkenyl group, a monovalent hydrocarbon group having 1 to 10 carbon atoms is preferable, and a monovalent hydrocarbon group having 1 to 8 carbon atoms is more preferable. Examples include alkyl groups such as methyl group, ethyl group, propyl group, isopropyl group, butyl group, isobutyl group, tert-butyl group, hexyl group, and cyclohexyl group, aryl groups such as phenyl group, tolyl group, and xylyl group, and aralkyl groups such as benzyl group. Of these, methyl group and phenyl group are preferable.

The alkenyl-containing organopolysiloxane of component (B) is preferably a linear diorganopolysiloxane whose main chain is composed of repeating diorganosiloxane units (R ¹ ₂ SiO _2/2 ) and whose molecular chain is terminally blocked with triorganosiloxy groups (R ¹ ₃ SiO _1/2 ).

The organopolysiloxane of component (B) preferably contains 1.0×10 ⁻⁵ to 2.0×10 ⁻⁴ mol/g of alkenyl groups. It is particularly preferable that it contains 1.3×10 ⁻⁵ to 1.3×10 ⁻⁴ mol/g of alkenyl groups. If the alkenyl group content is sufficient, the crosslink density is sufficiently high and practical rubber strength is not reduced, and if the content is not excessive, the crosslink density is not too high and the elongation at break of the cured rubber is not reduced. The amount of alkenyl groups is measured by ¹ H-NMR spectroscopy.

The average degree of polymerization (or the number of silicon atoms in the molecule) of the organopolysiloxane of component (B) above is preferably 100 to 1,500, and particularly preferably 150 to 1,000. This average degree of polymerization (or average molecular weight) refers to the average degree of polymerization measured by gel permeation chromatography (GPC) under the following conditions, using polystyrene as the standard substance.

[Measurement conditions]
Developing solvent: toluene Flow rate: 1 mL/min
Detector: Refractive index detector (RI)
Column: KF-805L x 2 (Shodex)
Column temperature: 25°C
Sample injection volume: 30 μL (toluene solution with a concentration of 0.2% by mass)

The amount of component (B) blended is in the range of 50 to 250 parts by mass, and preferably 100 to 180 parts by mass, per 100 parts by mass of component (A). If the blended amount is less than the above range, the cured product may be brittle, and conversely, if the blended amount exceeds the above range, the cured product may be soft and may not be suitable for lens applications, etc.

Component (C) is a linear organohydrogenpolysiloxane having hydrogen atoms bonded to silicon atoms (hydrosilyl groups). The hydrosilyl groups in the molecule crosslink with alkenyl groups bonded to silicon atoms in components (A) and (B) above via a hydrosilylation addition reaction, and act as a curing agent for curing the composition.

（式中、Ｒ^２は独立して炭素数１から１０のアルキル基であり、Ｒ^３は独立して炭素数１から１０のアルキル基もしくは水素原子であり、ｚは８以上の整数であり、ｙは０～１５０の整数であり、０．４０≦ｚ／（ｙ＋ｚ）≦１．０であり、かつ１分子中のヒドロシリル基の数が１０個以上である） As the component (C), a compound represented by the following general formula (1) is used.

(In the formula, ^R2 is independently an alkyl group having 1 to 10 carbon atoms, ^R3 is independently an alkyl group having 1 to 10 carbon atoms or a hydrogen atom, z is an integer of 8 or more, y is an integer of 0 to 150, 0.40≦z/(y+z)≦1.0, and the number of hydrosilyl groups in one molecule is 10 or more.)

Examples of the alkyl group having 1 to 10 carbon atoms represented by ^R2 include methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, pentyl, neopentyl, hexyl, cyclohexyl, octyl, nonyl, and decyl groups, and it is preferable that 90 mol% or more of all ^R2 , and particularly all ^R2 groups, are methyl groups. In addition to those represented by ^R2 , ^R3 can be a hydrogen atom.

Furthermore, z in the above general formula (1) is an integer of 8 or more, preferably 10 to 200, more preferably 12 to 100. If z is less than 8, the hardness may be lower than the target (for example, 65 or more) even after secondary vulcanization. y is an integer of 0 to 150, preferably an integer of 0 to 100. Also, 0.40≦z/(y+z)≦1.0. That is, the molar ratio (ratio) of z units to the total of y units and z units is z/(y+z) 40 mol% (0.4) or more, preferably 45 mol% (0.45) or more. If z/(y+z) is less than 40 mol%, the elongation at break after primary vulcanization is low, and the ease of removal from the mold is poor. Also, the number of silicon atom-bonded hydrogen groups (hydrosilyl groups) in one molecule is 10 or more, preferably 12 or more.

Specific examples of the linear organohydrogenpolysiloxane of component (C) include methylhydrogenpolysiloxane capped at both ends with trimethylsiloxy groups, dimethylsiloxane-methylhydrogensiloxane copolymer capped at both ends with trimethylsiloxy groups, and dimethylsiloxane-methylhydrogensiloxane copolymer capped at both ends with dimethylhydrogensiloxy groups. These may be used alone or in combination of two or more.

(D) Organohydrogenpolysiloxane having a phenyl group The organohydrogenpolysiloxane of component (D) has two or more hydrogen atoms bonded to silicon atoms (hydrosilyl groups) per molecule and has one to three phenyl groups per molecule. Since component (C) does not have a phenyl group, the organohydrogenpolysiloxanes of components (C) and (D) are essentially different.

The hydrosilyl groups in the above component (D) crosslink with the silicon-bonded alkenyl groups of the above components (A) and (B) through a hydrosilyl addition reaction, and act as a curing agent for curing the composition. The organohydrogenpolysiloxane of the above component (D) has 2 or more, preferably 3 or more, and preferably 3 to 5 silicon-bonded hydrogen atoms (hydrosilyl groups) per molecule, and 1 to 3, preferably 1 to 2 phenyl groups per molecule.

Here, examples of the substituent other than the phenyl group include aliphatic hydrocarbon groups having 1 to 10 carbon atoms, preferably 1 to 8 carbon atoms. Specific examples include alkyl groups such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, hexyl, and cyclohexyl. Among these, methyl is preferred. Furthermore, those that do not have aliphatic unsaturated groups are preferred. 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 is preferably 3 to 9, more preferably 3 to 8, and even more preferably 4 to 8, and those that are liquid at 25°C are preferably used. It is preferable that the hydrogen atoms bonded to the silicon atoms are located at the ends of the molecular chain.

Examples of the organohydrogenpolysiloxane of component (D) include tris(dimethylhydrogensiloxy)phenylsilane, a methylhydrogensiloxane-diphenylsiloxane copolymer capped at both ends with trimethylsiloxy groups, a methylhydrogensiloxane-methylphenylsiloxane copolymer capped at both ends with trimethylsiloxy groups, a dimethylsiloxane-methylhydrogensiloxane-diphenylsiloxane copolymer capped at both ends with trimethylsiloxy groups, a dimethylsiloxane-methylhydrogensiloxane-methylphenylsiloxane copolymer capped at both ends with trimethylsiloxy groups, a methylhydrogensiloxane-diphenylsiloxane copolymer capped at both ends with dimethylhydrogensiloxy groups, a methylhydrogensiloxane-diphenylsiloxane copolymer capped at both ends with dimethylhydrogensiloxy groups, a methylhydrogensiloxane-methylphenylsiloxane copolymer capped at both ends with dimethylhydrogensiloxy groups, Dimethylhydrogensiloxane-diphenylsiloxane copolymer blocked with dimethylhydrogensiloxane at both ends, dimethylsiloxane-methylphenylsiloxane copolymer blocked with dimethylhydrogensiloxane at both ends, dimethylsiloxane-methylhydrogensiloxane-diphenylsiloxane copolymer blocked with dimethylhydrogensiloxane at both ends, dimethylsiloxane-methylhydrogensiloxane-methylphenylsiloxane copolymer blocked with dimethylhydrogensiloxane at both ends, methylhydrogensiloxane-diphenylsiloxane cyclic copolymer, methylhydrogensiloxane-methylphenylsiloxane cyclic copolymer, dimethylsiloxane-methylhydrogensiloxane-diphenylsiloxane cyclic copolymer, dimethylsiloxane-methylhydrogensiloxane-diphenylsiloxane cyclic copolymer, dimethylsiloxane-methylhydrogensiloxane-methylphenylsiloxane cyclic copolymer, (CH a copolymer consisting of _{(CH 3} ) ₂ HSiO _1/2 units, SiO _4/2 units and (C ₆ H ₅ ) 2 SiO _2/2 units, a copolymer consisting of (CH ₃ ) ₂ HSiO _1/2 units, SiO _4/2 units and (C ₆ H ₅ ) ₂ SiO _2/2 units, a copolymer consisting of (CH ₃ ) ₂ HSiO _1/2 units, SiO _4/2 units and (C ₆ H ₅ ) ₃ SiO _1/2 units, a copolymer consisting of (CH ₃ ) ₃ SiO _1/2 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 (CH ₃ ) ₃ SiO _1/2 units, (CH ₃ ) ₂ HSiO _1/2 units, SiO Examples of _{the copolymer include a copolymer consisting of (CH 3 ) 3 SiO 1/2 units , (} CH ₃ ) ₂ HSiO _1/2 units, SiO _4/2 units and ₍ C ₆ H ₅ ) ₃ SiO _1/2 units _.

The amount of the above component (D) is 0.1 to 5 parts by mass per 100 parts by mass of the above component (A).

The amounts of the (C) and (D) components in the addition-curable silicone rubber composition are such that the ratio (H/Vi) of the total number of moles of hydrosilyl groups (H) to the total number of moles of alkenyl groups (Vi) in the composition is 1.0 to 1.5, and preferably 1.1 to 1.5. If the ratio is less than 1.0, crosslinking is insufficient, the cured product has strong tack, and the rubber has low hardness even after secondary vulcanization, and is poor at preventing mold contamination. On the other hand, if the ratio is higher than 1.5, the hardness and elongation at break of the cured product after primary vulcanization become too high, causing the cured product to break.

(E) Addition reaction catalyst The addition reaction catalyst for component (E) is not particularly limited so long as it is for hydrosilylation addition reactions, and examples thereof include platinum-based catalysts such as platinum black, platinic chloride, chloroplatinic acid, reaction products of chloroplatinic acid and monohydric alcohols, complexes of chloroplatinic acid and olefins, platinum bisacetoacetate, and the like, palladium-based catalysts, and rhodium-based catalysts.

The amount of the addition reaction catalyst component (E) can be a catalytic amount, preferably 0.1 to 10 ppm, and more preferably 0.5 to 10 ppm, of platinum group metal (by mass) relative to the total mass of the composition. If the amount of component (E) is less than 0.1 ppm, curing will not proceed easily, and if it is more than 10 ppm, the cured product may become discolored.

Other Components The addition-curable silicone rubber composition of the present invention can optionally contain other components, such as hydrosilylation reaction inhibitors such as nitrogen-containing compounds, acetylene compounds, phosphorus compounds, nitrile compounds, carboxylates, tin compounds, mercury compounds and sulfur compounds, internal release agents such as dimethylsilicone oil, and adhesion promoters (particularly organosilicon compounds such as alkoxysilanes which contain in their molecule one or more reactive functional groups selected from alkenyl groups, epoxy groups, amino groups, (meth)acryloxy groups, mercapto groups, and the like, but which do not contain hydrosilyl groups in their molecule).

Preparation of Addition-Curable Silicone Rubber Composition
An addition-curable silicone rubber composition can be prepared by uniformly mixing the above components (A) through (E), and, if necessary, other optional components. This mixing can be carried out using a mixer that is generally used in compounding silicone rubber, such as a kneader, gate mixer, Shinagawa mixer, pressure mixer, three-roll mill, or two-roll mill.

<Molding of addition curable silicone rubber composition>
The molding and curing method of the addition curable silicone rubber composition is not particularly limited and may be a conventional method, but compression molding and injection molding are preferably used as the molding method. In addition, in order to reduce the roughness of the cured surface and increase the transparency during molding, a liner with high flatness may be used. As for the curing conditions, for example, primary vulcanization is performed using a mold at 100 to 180°C for 5 seconds to 30 minutes, preferably at 110 to 180°C for 10 seconds to 20 minutes, and particularly at 120 to 160°C for 30 seconds to 10 minutes, and after removing the cured product from the mold, secondary vulcanization is performed in an oven or the like at 80 to 200°C, particularly at 100 to 200°C for 10 minutes to 24 hours, particularly at 30 minutes to 10 hours, to obtain a molded product with a predetermined hardness.

<Cured silicone rubber>
The addition curable silicone rubber composition of the present invention can provide a silicone rubber cured product (elastomer) obtained by press curing at 120°C for 10 minutes (primary vulcanization) has an elongation at break of 200% or more in a tensile test based on JIS K 6251:2017, and a 2 mm thick silicone rubber cured product obtained by post curing at 150°C for 1 hour (secondary vulcanization) after the press cure has a total light transmittance of 90% or more, particularly 92% or more, to D65 light as described in JIS K 7361-1:1997, and a 2 mm thick molded product after the post cure has a haze value of 3% or less in a haze test using D65 light as described in JIS K 7136:2000. If the elongation at break of the cured product after primary vulcanization is 200% or more, it becomes easy to remove from a mold.

Furthermore, if the average surface roughness of the cured product removed from the mold after the primary vulcanization continuous molding is 0.15 μm or less, light diffusion and leakage can be prevented, and a decrease in brightness can be suppressed.

In this way, the addition-curable silicone rubber composition of the present invention provides silicone rubber that is easy to remove from a mold and has high transparency with little loss of brightness, preventing light diffusion and leakage, and can be used favorably in optical applications such as LEDs.

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" refers to "parts by mass." The average degree of polymerization refers to the number-average degree of polymerization. The average degree of polymerization was measured by gel permeation chromatography (GPC) using polystyrene as a standard substance.
[Measurement conditions]
Developing solvent: toluene Flow rate: 1 mL/min
Detector: Refractive index detector (RI)
Column: KF-805L x 2 (Shodex)
Column temperature: 25°C
Sample injection volume: 30 μL (toluene solution with a concentration of 0.2% by mass)

[Materials used]
(A) Three-dimensional network structure organopolysiloxane resin (silicone resin)
"A-1": a copolymer of (CH ₃ ) ₃ SiO _1/2 units, (CH ₂ ═CH)(CH ₃ ) ₂ SiO _1/2 units, and SiO _4/2 units, M units/Q units (molar ratio)=0.90, number of alkenyl groups per molecule: 4.2 (number average molecular weight=3,000), alkenyl group content: 1.4×10 ^-3 mol/g

(B) Liquid Linear Organopolysiloxane (Alkenyl Group-Containing Organopolysiloxane)
"B-1": Dimethylpolysiloxane capped at both ends with dimethylvinylsiloxy groups Average degree of polymerization: 750 (number average molecular weight = 56,000), viscosity: 30 Pa·s
Number of alkenyl groups per molecule: 2

(C) Linear organohydrogenpolysiloxane

"C-1": Methylhydrogenpolysiloxane terminated at both ends with trimethylsiloxy groups, as shown below. Number of SiH groups per molecule: 50 (SiH group content: 0.0076 mol/g)

"C-2": Methylhydrogenpolysiloxane terminated at both ends with trimethylsiloxy groups according to the following formula Number of SiH groups per molecule: 70 (SiH group content: 0.0104 mol/g)

"C-3": Methylhydrogenpolysiloxane terminated at both ends with trimethylsiloxy groups, as shown below. Number of SiH groups per molecule: 20 (SiH group content: 0.0074 mol/g)

(D) Organohydrogenpolysiloxane having a phenyl group (phenyl group-containing organopolysiloxane)
"D-1": tris(dimethylhydrogensiloxy)phenylsilane of the following formula Number of SiH groups per molecule: 3 (SiH group content 0.0091 mol/g)
Number of phenyl groups per molecule: 1

"D-2": Methylhydrogensiloxane-diphenylsiloxane copolymer terminated at both ends with trimethylsiloxy groups according to the following formula Number of SiH groups per molecule: 6 (SiH group content: 0.0063 mol/g)
Number of phenyl groups per molecule: 4

(E) Addition reaction catalyst (hydrosilylation reaction catalyst)
・“E-1”: Platinum catalyst (Pt concentration: 1% by mass)

(F) Hydrosilylation reaction inhibitor "F-1": 1-ethynylcyclohexanol

[Examples 1 to 2 and Comparative Examples 1 to 4]
For each example of the low mold-staining silicone rubber composition, the respective amounts of (A) organopolysiloxane resin having a three-dimensional network structure (silicone resin), (B) linear organopolysiloxane (alkenyl group-containing organopolysiloxane), (C) linear organohydrogenpolysiloxane, (D) organohydrogenpolysiloxane having a phenyl group (phenyl group-containing organohydrogenpolysiloxane), (E) addition reaction catalyst (hydrosilylation reaction catalyst), and (F) hydrosilylation reaction inhibitor are shown in Table 1. Each composition was mixed uniformly and stirred, followed by degassing under reduced pressure.

A polyethylene terephthalate (PET) liner and a 2.2 mm thick frame were placed on top of the press plate, the above-mentioned mold-low-contamination silicone rubber composition was poured into the frame, and a PET liner and press plate were further laminated on top of this and press molded at 120°C for 10 minutes. The two PET liners were removed and cooled, and then the PET liners were peeled off to obtain a silicone rubber transparent sheet with a thickness of approximately 2 mm. The 2 mm thick cured product obtained after 120°C/10 minutes of press curing (primary vulcanization) was measured for hardness in durometer type A according to JIS K 6253-3:2012 and elongation at break according to JIS K 6251:2017, and the results are shown in Table 1. In addition, for a 2 mm thick cured product that was post-cured (secondary vulcanization) in an oven at 150°C for 1 hour after press curing, the hardness using a durometer type A was measured according to JIS K 6253-3:2012, and the elongation at break was measured according to JIS K 6251:2017. Furthermore, the total light transmittance was measured for D65 light according to JIS K 7361-1:1997, and the haze was measured using D65 light according to JIS K 7136:2000. The results are shown in Table 1.

- Method for evaluating releasability from compression molding mold: The above low mold-staining silicone rubber composition was press-vulcanized at 120°C for 10 minutes using a chrome-plated compression molding mold to mold a cured sheet with dimensions of 13 cm x 17 cm x 2 mm thick, and the releasability of the molded product from the mold was examined. The results are shown in Table 1.

- Average surface roughness and brightness of the cured product: An "ARBURG 420C/Allrounder 1000-150" injection molding machine was used. Comparative Example 3 had an elongation at break of 200% or less, and Comparative Example 4 had poor releasability from the compression molding mold, so further evaluation of the average surface roughness and brightness of the cured product was not performed. Using the low mold-staining silicone rubber compositions of Examples 1 and 2 and the comparative silicone rubber compositions of Comparative Examples 1 and 2, molding was performed at 150°C/20 seconds curing, and the average surface roughness of the cured product at each number of shots was measured using an Olympus laser microscope, and the results are shown in Table 1. Additionally, the brightness of the cured product at each number of shots was measured using a high-sensitivity spectral radiance device, and the results are shown in Table 1.

The silicone rubber composition of the present invention, which has low mold contamination, has sufficient elongation at break after primary vulcanization, is easy to remove from the mold, and does not contaminate the mold, resulting in an average surface roughness of the cured product of 0.15 μm or less. In addition, even when continuously molded, it is possible to obtain a cured product with high transparency and little loss in brightness.

On the other hand, the comparative silicone rubber composition used in Comparative Examples 1 and 2, which did not contain component (D), had good elongation at break, but had an average surface roughness of 0.20 μm, which was inferior to the examples, and also had reduced brightness.

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

Claims (1)

An addition curable silicone rubber composition comprising:
(A) 100 parts by mass _of an organopolysiloxane resin having a three-dimensional network structure, which has R ¹ ₃ SiO _1/2 units (wherein R ¹ is independently a monovalent hydrocarbon group having 1 to 10 carbon atoms) and SiO _4/2 units, in which the molar ratio [M/Q] of R ¹ ₃ SiO _1/2 units (M units) to SiO 4/2 units (Q units) is 0.5 to 1.5 and the alkenyl group content is 1×10 ^-4 to 5×10 ^-3 mol/g; (B) 50 to 250 parts by mass of a linear organopolysiloxane which has two or more alkenyl groups bonded to silicon atoms in each molecule and is liquid at 23° C.;
(C) A linear organohydrogenpolysiloxane represented by the following general formula (1):

(In the formula, ^R2 is independently an alkyl group having 1 to 10 carbon atoms, ^R3 is independently an alkyl group having 1 to 10 carbon atoms or a hydrogen atom, z is an integer of 8 or more, y is an integer of 0 to 150, 0.40≦z/(y+z)≦1.0, and the number of hydrosilyl groups in one molecule is 10 or more.)
(D) an organohydrogenpolysiloxane having two or more hydrosilyl groups and 1 to 3 phenyl groups per molecule in an amount of 0.1 to 5 parts by mass per 100 parts by mass of component (A),
(E) An addition reaction catalyst: a silicone rubber composition with low mold contamination, which contains a catalytic amount of the catalyst.