Silicone rubber composition with low mold contamination

Abstract

To provide an addition-curable silicone rubber composition that minimizes mold contamination even subsequent to continuous molding of primary vulcanization.SOLUTION: A low-mold-contamination silicone rubber composition is an addition-curable silicone rubber composition that includes (A) a 3D network-structured organopolysiloxane resin containing an alkenyl group, with R13SiO1 / 2 units and SiO4 / 2 units, the molar ratio of R13SiO1 / 2 units to SiO4 / 2 units being 0.5-1.5, (B) a linear organopolysiloxane having two or more alkenyl groups binding to silicon atoms in one molecule, (C) a linear organohydrogenpolysiloxane represented by the general formula (1) (where R2 is an alkyl group and R3 is an alkyl group or a hydrogen atom), (D) an organohydrogenpolysiloxane having two or more hydrosilyl groups in one molecule and one to three phenyl groups in one molecule, and (E) an addition reaction catalyst.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a silicone rubber composition that produces little mold contamination. [Background technology]

[0002] Silicone-based resins with high hardness and transparency have attracted attention in order to improve the weather resistance and optical waveguides of LED lights and various liquid crystal monitor screens, and 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 thermosetting (Patent Documents 1 to 4).

[0003] Generally, silicone rubber used as a condenser 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 mold contamination occurs 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 contamination. 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. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2010-174233 A [Patent Document 2] JP 2010-174234 A [Patent Document 3] International Publication No. 2016 / 098883 [Patent Document 4] International Publication No. 2016 / 098884 Summary of the Invention [Problem to be solved by the invention]

[0005] The present invention has been made to improve the above circumstances, and has an object to provide an addition curing silicone rubber composition that suppresses mold contamination even after continuous molding of the primary vulcanization. Another object is 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 cured product with high transparency. [Means for solving the problem]

[0006] In order to solve the above problems, the present invention provides An addition curable silicone rubber composition comprising: (A)R 1 3SiO 1 / 2 Units (wherein R 1 are independently monovalent hydrocarbon groups having 1 to 10 carbon atoms) and SiO 4 / 2 It has the unit SiO 4 / 2 R to unit (Q unit) 1 3SiO 1 / 2 The molar ratio [M / Q] of units (M units) is 0.5 to 1.5, and the alkenyl group content is 1×10 -4 ~5×10 -3 mol / g three-dimensional network structure organopolysiloxane resin: 100 parts by mass (B) a linear organopolysiloxane that is liquid at 23° C. and has two or more alkenyl groups bonded to silicon atoms in each molecule: 50 to 250 parts by mass, (C) A linear organohydrogenpolysiloxane represented by the following general formula (1): [ka] (In the formula, R 2 are independently alkyl groups having 1 to 10 carbon atoms; R 3 are 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. : an amount corresponding to a 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 of 1.0 to 1.5 (D) an organohydrogenpolysiloxane having two or more hydrosilyl groups and 1 to 3 phenyl groups per molecule: 0.1 to 5 parts by mass per 100 parts by mass of component (A), (E) Addition reaction catalyst: catalytic amount The present invention provides a silicone rubber composition with low mold contamination, which contains

[0007] Such a silicone rubber composition can maintain an average surface roughness of 0.15 μm or less even after multiple moldings of the cured product, and therefore can provide a cured product with high transparency and little loss of brightness even when molded continuously. Effect of the Invention

[0008] According to the present invention, an addition curable 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 continuously molded, 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 cured product with high transparency can be obtained. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] As a result of intensive research by the present inventors in order to achieve the above-mentioned object, it was 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 appropriate ratios, it is possible to obtain a silicone rubber composition which gives a cured product having an elongation at break of 200% or more after primary vulcanization, which inhibits mold contamination after continuous molding of the primary vulcanization, and which gives a highly transparent cured product having an average surface roughness of 0.15 μm or less when removed from the mold, thereby completing the present invention.

[0010] The above findings were obtained from the investigation of various materials, which revealed that when the elongation at break of the cured product after primary vulcanization is 200% or more, it is easy to remove from the mold, and when the average surface roughness of the cured product is 0.15 μm or less, light diffusion and leakage can be prevented, resulting in a cured product with high transparency and little change in luminance.

[0011] That is, the present invention provides: An addition curable silicone rubber composition comprising: (A)R 1 3SiO 1 / 2 Units (wherein R 1 are independently monovalent hydrocarbon groups having 1 to 10 carbon atoms) and SiO 4 / 2 It has the unit SiO 4 / 2 R to unit (Q unit) 1 3SiO 1 / 2 The molar ratio [M / Q] of units (M units) is 0.5 to 1.5, and the alkenyl group content is 1×10 -4 ~5×10 -3 mol / g three-dimensional network structure organopolysiloxane resin: 100 parts by mass (B) a linear organopolysiloxane that is liquid at 23° C. and has two or more alkenyl groups bonded to silicon atoms in each molecule: 50 to 250 parts by mass, (C) A linear organohydrogenpolysiloxane represented by the following general formula (1): [ka] (In the formula, R 2 are independently alkyl groups having 1 to 10 carbon atoms; R 3 are 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. : an amount corresponding to a 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 of 1.0 to 1.5 (D) an organohydrogenpolysiloxane having two or more hydrosilyl groups and 1 to 3 phenyl groups per molecule: 0.1 to 5 parts by mass per 100 parts by mass of component (A), (E) Addition reaction catalyst: catalytic amount The silicone rubber composition has low mold-staining properties and contains

[0012] The present invention will be described in detail below, but the present invention is not limited thereto.

[0013] <Addition-curing 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 liquid.

[0014] (A) Alkenyl group-containing silicone resin (organopolysiloxane resin with a three-dimensional network structure) The alkenyl-containing organopolysiloxane resin of component (A) (organopolysiloxane resin with a three-dimensional network structure, resin copolymer) is R 1 3SiO 1 / 2 Units and SiO 4 / 2 It is an organopolysiloxane resin having a three-dimensional network structure that contains units as a main component. It is preferable that the component (A) is a solid at 25°C.

[0015] R 1are 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.

[0016] The alkenyl-containing three-dimensional network-structured organopolysiloxane resin (resin copolymer) of the component (A) is 1 3SiO 1 / 2 Units and SiO 4 / 2 units, and optionally R 1 2SiO 2 / 2 Units and R 1 SiO 3 / 2 Units (R 1 may include the above.

[0017] SiO 4 / 2 R to unit (Q unit) 1 3SiO 1 / 2 The molar ratio [M / Q] of units (M units) is 0.5 to 1.5, and 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.

[0018] Above R 1 2SiO 2 / 2 Units and above R 1 SiO 3 / 2 The total amount of the units may be 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. 1 / 2 Unit: (CH2=CH)(CH3)2SiO 1 / 2Units, SiO 4 / 2 Copolymers of the units are preferred.

[0019] Furthermore, the alkenyl-containing organopolysiloxane resin of component (A) has an alkenyl group content of 1×10 -4 ~5×10 -3 moles / g, preferably 2×10 -4 ~3×10 -3 moles / g, more preferably 3×10 -4 ~2×10 -3 mol / g vinyl group. Alkenyl group content is 5×10 -3 More than 1×10 moles / g makes the rubber hard and brittle. -4 Less than mol / g will make the rubber softer and weaker.

[0020] The resin copolymer is usually prepared by a suitable method (i.e., hydrolysis and condensation to obtain R 1 3SiO 1 / 2 Units and SiO 4 / 2 The copolymers can be prepared by co-hydrolytic condensation of mono- and tetra-functional chlorosilanes and alkoxysilanes (which form the copolymer units) by methods well known in the art.

[0021] (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.

[0022] The viscosity of the component (B) is preferably in the range of 1 to 100 Pa·s at 23° C., as measured using a rotational viscometer described in JIS K7117-1:1999, more preferably 5 to 100 Pa·s, and even more preferably 10 to 100 Pa·s.

[0023] The number of the alkenyl groups is 2 or more, preferably 2-50, and more preferably 2-20.

[0024] The alkenyl group preferably has a carbon number of 2 to 10, and more preferably 2 to 8. Specific examples include a vinyl group, an allyl group, a propenyl group, an isopropenyl group, and a butenyl group, with a vinyl group being preferred.

[0025] The group other than the alkenyl group is preferably a monovalent hydrocarbon group having 1 to 10 carbon atoms, more preferably a monovalent hydrocarbon group having 1 to 8 carbon atoms. Examples include alkyl groups such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, hexyl, and cyclohexyl groups, aryl groups such as phenyl, tolyl, and xylyl groups, and aralkyl groups such as benzyl groups. Of these, methyl and phenyl groups are preferred.

[0026] The alkenyl-containing organopolysiloxane of component (B) is linear, and its main chain is made up of diorganosiloxane units (R 1 2SiO 2 / 2 ) repeating units, and both ends of the molecular chain are triorganosiloxy groups (R 1 3SiO 1 / 2 Preferably, the diorganopolysiloxane is a linear diorganopolysiloxane terminated with

[0027] The organopolysiloxane of the component (B) is preferably 1.0×10 -5 ~2.0×10 -4 mol / g of alkenyl groups. -5 ~1.3×10 -4 It is preferable that the alkenyl group content is 100 moles / g. If the alkenyl group content is sufficient, the crosslink density is sufficiently high and the practical rubber strength is not reduced, and if the alkenyl group 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 1 This was measured by H-NMR spectroscopy.

[0028] The average degree of polymerization (or the number of silicon atoms in the molecule) of the organopolysiloxane of component (B) 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 a standard substance.

[0029] [Measurement conditions] Developing solvent: toluene Flow rate: 1mL / min Detector: Refractive index detector (RI) Column: KF-805L x 2 (Shodex) Column temperature: 25℃ Sample injection volume: 30 μL (toluene solution with a concentration of 0.2% by mass)

[0030] The blending amount of the (B) component 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 the (A) component. If the blending amount is less than the above range, the cured product may be brittle, whereas if the blending amount exceeds the above range, the cured product may be soft and unsuitable for lens applications.

[0031] (C) Linear organohydrogenpolysiloxane Component (C) is a linear organohydrogenpolysiloxane having hydrogen atoms bonded to silicon atoms (hydrosilyl groups). The hydrosilyl groups in the molecule crosslink via a hydrosilylation addition reaction with alkenyl groups bonded to silicon atoms in components (A) and (B) above, and act as a curing agent for curing the composition.

[0032] The component (C) is represented by the following general formula (1). [ka] (In the formula, R 2 are independently alkyl groups having 1 to 10 carbon atoms; R 3are 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.

[0033] Here, R 2 Examples of the alkyl group having 1 to 10 carbon atoms represented by the formula (I) include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a tert-butyl group, a pentyl group, a neopentyl group, a hexyl group, a cyclohexyl group, an octyl group, a nonyl group, and a decyl group. 2 90 mol % or more of R 2 Preferably, the R group is a methyl group. 3 is R 2 In addition to those represented by the formula:

[0034] 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, z / (y+z), is 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 a 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.

[0035] 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, dimethylsiloxane-methylhydrogensiloxane copolymer capped at both ends with dimethylhydrogensiloxy groups, etc. These may be used alone or in combination of two or more.

[0036] (D) Organohydrogenpolysiloxane having a phenyl group The organohydrogenpolysiloxane of component (D) has two or more hydrogen atoms (hydrosilyl groups) bonded to silicon atoms in each molecule, and one to three phenyl groups in each molecule. Since component (C) does not have a phenyl group, the organohydrogenpolysiloxanes of components (C) and (D) are essentially different.

[0037] The hydrosilyl groups in the above component (D) crosslink with the silicon-bonded alkenyl groups in 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.

[0038] 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 an aliphatic unsaturated group 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 molecular chain terminals.

[0039] Examples of the organohydrogenpolysiloxane of component (D) above include tris(dimethylhydrogensiloxy)phenylsilane, copolymer of methylhydrogensiloxane / diphenylsiloxane capped at both ends with trimethylsiloxy groups, copolymer of methylhydrogensiloxane / methylphenylsiloxane capped at both ends with trimethylsiloxy groups, copolymer of dimethylsiloxane / methylhydrogensiloxane / diphenylsiloxane capped at both ends with trimethylsiloxy groups, copolymer of dimethylsiloxane / methylhydrogensiloxane / methylphenylsiloxane capped at both ends with trimethylsiloxy groups, copolymer of methylsiloxane / methylhydrogensiloxane / diphenylsiloxane capped at both ends with dimethylhydrogensiloxane / diphenylsiloxane capped at both ends with dimethylhydrogensiloxane / methylhydrogensiloxane capped at both ends with dimethylhydrogensiloxane / methylphenylsiloxane dihydrogensiloxane-diphenylsiloxane copolymer, dihydrogensiloxane-methylphenylsiloxane copolymer with both ends blocked by dimethylhydrogensiloxane, dihydrogensiloxane-methylhydrogensiloxane copolymer with both ends blocked by dimethylhydrogensiloxane, dihydrogensiloxane copolymer with both ends blocked by dimethylhydrogensiloxane, methylhydrogensiloxane-methylphenylsiloxane copolymer, methylhydrogensiloxane-diphenylsiloxane cyclic copolymer, methylhydrogensiloxane-methylphenylsiloxane cyclic copolymer, dimethylsiloxane-methylhydrogensiloxane-diphenylsiloxane cyclic copolymer, dimethylsiloxane-methylhydrogensiloxane-diphenylsiloxane cyclic copolymer, dimethylsiloxane-methylhydrogensiloxane-methylphenylsiloxane cyclic copolymer, (CH3)2HSiO 1 / 2 Units and SiO 4 / 2 Units and (C6H5)SiO 3 / 2 A copolymer consisting of (CH3)2HSiO units. 1 / 2 Units and SiO 4 / 2 Units and (C6H5)2SiO 2 / 2 A copolymer consisting of (CH3)2HSiO units. 1 / 2 Units and SiO 4 / 2 Units and (C6H5)3SiO 1 / 2 A copolymer consisting of (CH3)3SiO units.1 / 2 Units and (CH3)2HSiO 1 / 2 Units and SiO 4 / 2 Units and (C6H5)SiO 3 / 2 A copolymer consisting of (CH3)3SiO units. 1 / 2 Units and (CH3)2HSiO 1 / 2 Units and SiO 4 / 2 Units and (C6H5)2SiO 2 / 2 A copolymer consisting of (CH3)3SiO units. 1 / 2 Units and (CH3)2HSiO 1 / 2 Units and SiO 4 / 2 Units and (C6H5)3SiO 1 / 2 and copolymers consisting of units.

[0040] The blending amount of the above component (D) is 0.1 to 5 parts by mass per 100 parts by mass of the above component (A).

[0041] In addition, the amount of the (C) component and the (D) component in the addition curable silicone rubber composition is 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 it 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 the mold contamination prevention effect is poor. On the other hand, if it is higher than 1.5, the hardness and elongation at break of the cured product after primary vulcanization become too high, and the cured product is damaged.

[0042] (E) Addition reaction catalyst The addition reaction catalyst for component (E) is not particularly limited so long as it is for use in hydrosilylation addition reactions, and examples of such catalysts include platinum-based catalysts such as platinum black, platinic chloride, chloroplatinic acid, reaction products of chloroplatinic acid with monohydric alcohols, complexes of chloroplatinic acid with olefins, platinum bisacetoacetate, and the like, palladium-based catalysts, and rhodium-based catalysts.

[0043] The amount of the addition reaction catalyst (E) can be a catalytic amount, preferably 0.1 to 10 ppm, particularly preferably 0.5 to 10 ppm, of platinum group metal (by mass) relative to the total mass of the composition. If the amount of the (E) component is less than 0.1 ppm, curing will be difficult to proceed, and if it is more than 10 ppm, the cured product may become discolored.

[0044] Other Ingredients 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).

[0045] <Preparation of Addition-Curable Silicone Rubber Composition> An addition-curable silicone rubber composition can be prepared by adding and uniformly mixing the above components (A) to (E), and, if necessary, other optional components. This mixing can be performed 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.

[0046] <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 or injection molding is preferably used as the molding method. In addition, in order to reduce the roughness of the cured surface and increase 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.

[0047] <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 / 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 2mm thick silicone rubber cured product obtained by post curing at 150°C / 1 hour (secondary vulcanization) after press curing has a total light transmittance of 90% or more, particularly 92% or more, for D65 light as described in JIS K 7361-1:1997, and a 2mm 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 it from the mold.

[0048] Furthermore, if the average surface roughness of the cured product removed from the mold after the primary vulcanization and continuous molding is 0.15 μm or less, diffusion and leakage of light can be prevented, and a decrease in brightness can be suppressed.

[0049] 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 in luminance because it is able to prevent light diffusion or leakage, and is therefore suitable for optical applications such as LEDs. EXAMPLES

[0050] 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 indicate parts by mass. The average degree of polymerization indicates 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: 1mL / min Detector: Refractive index detector (RI) Column: KF-805L x 2 (Shodex) Column temperature: 25℃ Sample injection volume: 30 μL (toluene solution with a concentration of 0.2% by mass)

[0051] [Materials used] (A) Organopolysiloxane resin (silicone resin) with a three-dimensional network structure "A-1": (CH3)3SiO 1 / 2 Unit: (CH2=CH)(CH3)2SiO 1 / 2 Units, SiO 4 / 2 Copolymer of 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

[0052] (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: 30Pa s Number of alkenyl groups per molecule: 2

[0053] (C) Linear organohydrogenpolysiloxane

[0054] "C-1": Methylhydrogenpolysiloxane with both ends blocked by trimethylsiloxy groups according to the formula below Number of SiH groups per molecule: 50 (SiH group content: 0.0076 mol / g) [ka]

[0055] "C-2": Methylhydrogenpolysiloxane with both ends blocked by trimethylsiloxy groups according to the formula below Number of SiH groups per molecule: 70 (SiH group content: 0.0104 mol / g) [ka]

[0056] "C-3": Methylhydrogenpolysiloxane with both ends blocked by trimethylsiloxy groups as shown below Number of SiH groups per molecule: 20 (SiH group content: 0.0074 mol / g) [ka]

[0057] (D) Organohydrogenpolysiloxane having a phenyl group (phenyl group-containing organopolysiloxane) "D-1": Tris(dimethylhydrogensiloxy)phenylsilane Number of SiH groups per molecule: 3 (SiH group content: 0.0091 mol / g) Number of phenyl groups per molecule: 1 [ka]

[0058] "D-2": Methylhydrogensiloxane-diphenylsiloxane copolymer with both ends blocked by trimethylsiloxy groups, as shown below Number of SiH groups per molecule: 6 (SiH group content: 0.0063 mol / g) Number of phenyl groups per molecule: 4 [ka]

[0059] (E) Addition reaction catalyst (hydrosilylation reaction catalyst) · "E-1": Platinum catalyst (Pt concentration: 1% by mass)

[0060] (F) Hydrosilylation reaction inhibitor "F-1": 1-ethynylcyclohexanol

[0061] [Examples 1-2 and Comparative Examples 1-4] For each example of the low mold-staining silicone rubber composition, the respective amounts of (A) organopolysiloxane resin with 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, then degassed under reduced pressure.

[0062] A polyethylene terephthalate (PET) liner and a 2.2 mm thick frame were placed on a press plate, and the mold-low-contamination silicone rubber composition was poured into the frame. A PET liner and a press plate were then placed on top of the mold-low-contamination silicone rubber composition, and press-molded at 120°C for 10 minutes. The two PET liners were removed and cooled, and the PET liner was peeled off to obtain a silicone rubber transparent sheet of approximately 2 mm thickness. 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. 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 in accordance with JIS K 6253-3:2012, and the elongation at break was measured in accordance with JIS K 6251:2017. Furthermore, the total light transmittance was measured for D65 light as described in JIS K 7361-1:1997, and the haze was measured using D65 light as described in JIS K 7136:2000. The results are shown in Table 1.

[0063] - Method for evaluating releasability from compression molding mold: The above low mold-staining silicone rubber composition was press-vulcanized at 120℃ for 10 minutes using a chrome-plated compression molding mold, and a cured sheet measuring 13cm x 17cm x 2mm thick was molded, and the releasability of the molded product from the mold was examined. The results are shown in Table 1.

[0064] Average surface roughness and brightness of cured products: 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 the average surface roughness and brightness of the cured products were not evaluated. The low mold-staining silicone rubber compositions of Examples 1 and 2 and the comparative silicone rubber compositions of Comparative Examples 1 and 2 were used to mold at 150°C / 20 seconds curing, and the average surface roughness of the cured products at each number of shots was measured using an Olympus laser microscope, and the results are shown in Table 1. The brightness of the cured products at each number of shots was also measured using a high-sensitivity spectral radiance device, and the results are shown in Table 1.

[0065] [Table 1]

[0066] 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.

[0067] 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 the average surface roughness was 0.20 μm, which was inferior to the examples, and the brightness was also reduced.

[0068] 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 in the technical scope of the present invention.

Claims

[Claim 1] An addition curable silicone rubber composition comprising: (A) R １ ３ SiO １／２ Units (wherein R １ are independently monovalent hydrocarbon groups having 1 to 10 carbon atoms) and SiO ４／２ having units, SiO ４／２ R to unit (Q unit) １ ３ SiO １／２ The molar ratio [M / Q] of the unit (M unit) is 0.5 to 1.5, and the alkenyl group content is 1×10 －４ ~5×10 －３ mol / g three-dimensional network structure organopolysiloxane resin: 100 parts by mass (B) a linear organopolysiloxane that is liquid at 23° C. and has two or more alkenyl groups bonded to silicon atoms in each molecule: 50 to 250 parts by mass, (C) A linear organohydrogenpolysiloxane represented by the following general formula (1): 【Chemistry 1】 (In the formula, R ２ are independently alkyl groups having 1 to 10 carbon atoms; R ３ are 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. : an amount corresponding to a 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 of 1.0 to 1.5 (D) an organohydrogenpolysiloxane having two or more hydrosilyl groups and 1 to 3 phenyl groups per molecule: 0.1 to 5 parts by mass per 100 parts by mass of component (A); (E) Addition reaction catalyst: catalytic amount 1. A silicone rubber composition with low mold contamination, comprising:

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