Molding silicone rubber composition and silicone rubber mold

Abstract

To provide a molding silicone rubber composition that excels in defoaming performance and the like.SOLUTION: A molding silicone rubber composition comprising: (A) an organopolysiloxane containing a silicon atom-bonded alkenyl group; (B) surface-treated silica particle whose surfaces of fumed silica particles are coated only with 1,3-divinyl-1,1,3,3-tetramethyldisilazane and 1,1,1,3,3,3-hexamethyldisilazane; (C-1) a hydrogenpolysiloxane composed of R12HSiO1 / 2 units and SiO4 / 2 units; (C-2) a hydrogenpolysiloxane composed of R13SiO1 / 2 units, R12SiO2 / 2 units, and R1HSiO2 / 2 units; (D) a dimethylpolysiloxane having both terminal ends blocked with trimethylsiloxy groups and having a viscosity of 20-300 mPa s; (E) a dimethylpolysiloxane having both terminal ends blocked with trimethylsiloxy groups and having a viscosity of 10,000-150,000 mPa s; (F) a dimethylsiloxane-diphenylsiloxane copolymer having both terminal ends blocked with trimethylsiloxy groups and having a viscosity of 10-600 mPa s; and (G) a platinum catalyst, wherein the molding silicone rubber composition is free of a resinous organopolysiloxane having a silicon atom-bonded alkenyl group.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a silicone rubber composition for molding and a silicone rubber mold, and more specifically to an addition-cure silicone rubber composition for molding and a silicone rubber mold (so-called female mold) obtained by curing the composition. [Background technology]

[0002] Using a silicone rubber mold as an inverted master mold, filling it with resin and then curing it to produce multiple products, is widely used in a wide range of applications, from hobbyist miniature models to industrial prototype models. Examples of silicone rubber compositions used in these include addition reaction curing liquid silicone rubber compositions that are liquid before curing, and that can be easily cured at room temperature or by heating after mixing with a curing agent to form an inverted mold. Addition reaction curing silicone rubber compositions have favorable molding properties as molding materials, such as no reaction by-products and an extremely small shrinkage rate when cured, but have the problem that, because they are rubber, the injected resin adheres closely to the rubber mold, making them difficult to release from the mold.

[0003] As a means of improving the releasability of the hardened replica from the mold, Patent Document 1 proposes a silicone rubber composition to which a non-crosslinkable silicone polymer having a chain length equal to or longer than that of the crosslinkable base polymer has been added. However, rubber molds using such silicone rubber compositions have problems such as insufficient releasability from urethane resins and epoxy resins, and the rubber molds are prone to breakage when repeated duplication is performed.

[0004] Patent Document 2 proposes a silicone rubber composition that uses only a linear organopolysiloxane as the base polymer and fumed silica that has been surface-treated with a silazane compound having a vinyl group as the filler. Patent Document 3 also proposes a silicone rubber composition that contains titanium oxide as a filler. However, when these silicone rubber compositions are used, the transparency of the resulting silicone rubber mold is impaired by the filler, making it difficult to check the state of the master mold and the replica inside.

[0005] Patent Document 4 proposes a silicone rubber composition containing an organopolysiloxane resin composed of monofunctional siloxane units and tetrafunctional siloxane units having alkenyl groups. However, materials containing such organopolysiloxane resins have the problem of poor defoaming and fluidity when mixed and poured into a master mold such as a metal mold. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 7-118534 [Patent Document 2] Japanese Patent Application Laid-Open No. 2002-194219 [Patent Document 3] Japanese Patent Application Publication No. 7-033985 [Patent Document 4] Japanese Patent Application Publication No. 2018-95796 Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention has been made to solve these problems, and its object is to provide a silicone rubber composition for molding that has excellent defoaming properties, fluidity, and transparency, and that upon curing gives a silicone rubber mold that is easy to demold when producing a replica. [Means for solving the problem]

[0008] As a result of extensive research aimed at solving the above problems, the present inventors discovered that a specific addition-curable silicone rubber composition provides a silicone rubber mold that is excellent in defoaming properties, fluidity, and transparency, and that produces copies that are easy to demold, and thus completed the present invention.

[0009] That is, the present invention is 1. (A) 100 parts by mass of a linear or branched organopolysiloxane having two or more alkenyl groups bonded to silicon atoms per molecule and having a viscosity at 23°C of 600 to 200,000 mPa·s; (B) Specific surface area by BET method is 180 to 500 m 2 / g of fumed silica particles whose surfaces are coated with only 1,3-divinyl-1,1,3,3-tetramethyldisilazane and 1,1,1,3,3,3-hexamethyldisilazane: 1 to 50 parts by mass; (C)(C-1)R 1 2HSiO 1 / 2 (In the formula, R 1 are each independently a substituted or unsubstituted alkyl group. 4 / 2 Resinous organohydrogenpolysiloxane consisting of units: 1 to 5 parts by mass, (C-2)R 1 3SiO 1 / 2 Units, R 1 2SiO 2 / 2 Units and R 1 HSiO 2 / 2 Units (wherein R 1 are the same as above.) 1 to 5 parts by mass of a linear organohydrogenpolysiloxane, (D) 2 to 10 parts by mass of a dimethylpolysiloxane capped at both molecular chain terminals with trimethylsiloxy groups and having a viscosity at 23°C of 20 to 300 mPa s, (E) 5 to 15 parts by mass of a dimethylpolysiloxane terminated at both molecular chain terminals with trimethylsiloxy groups and having a viscosity at 23°C of 10,000 to 150,000 mPa s, (F) 0.01 to 0.5 parts by mass of a dimethylsiloxane-diphenylsiloxane copolymer capped at both molecular chain ends with trimethylsiloxy groups and having a viscosity at 23°C of 10 to 600 mPa·s, and (G) Platinum catalyst a silicone rubber composition for molding, which does not contain a resinous organopolysiloxane having an alkenyl group bonded to a silicon atom; 2. The silicone rubber composition for molding according to 1, wherein the component (A) comprises (A-1) a dimethylpolysiloxane capped at both molecular chain terminals with dimethylvinylsiloxy groups and (A-2) a dimethylsiloxane-methylvinylsiloxane copolymer capped at both molecular chain terminals with trimethylsiloxy groups. 3. The silicone rubber composition for molding according to 1 or 2, wherein the molar ratio of the total number of hydrogen atoms bonded to silicon atoms to the total number of alkenyl groups bonded to silicon atoms in the composition is 0.5 to 5.0. 4. A mold-making agent comprising the mold-making silicone rubber composition according to any one of 1 to 3. 5. A silicone rubber mold obtained by curing the silicone rubber composition for molding described in any one of 1 to 3. to provide. [Effects of the Invention]

[0010] The silicone rubber composition for molding of the present invention has defoaming properties, fluidity, and transparency that are suitable for work, and the silicone rubber mold obtained by curing the silicone rubber composition for molding of the present invention has a hardness that is suitable for pulling out resin replicas and has excellent demoldability. [Brief explanation of the drawings]

[0011] [Figure 1] 1A and 1B show a method for producing a silicone rubber mold in an embodiment, in which (a) is a schematic plan view showing a state in which a silicone rubber composition is poured into a container with a master mold placed inside, (b) is a schematic longitudinal cross-sectional view taken along line bb in (a), and (c) is a schematic longitudinal cross-sectional view of the silicone rubber mold. [Figure 2] FIG. 1 shows a method for molding a replica using a silicone rubber mold in the evaluation of demoldability in the examples, where (a) is a schematic vertical cross-sectional view showing the state in which liquid urethane resin is poured into the silicone rubber mold, and (b) is a schematic vertical cross-sectional view of a urethane resin replica. DETAILED DESCRIPTION OF THE INVENTION

[0012] The present invention will be specifically described below. In the present invention, the term "silicone rubber composition for molding" refers to an uncured (liquid) composition that has fluidity in an uncured state, is brought into contact with the entire surface or a portion of the surface of a master mold by a method such as casting or application, and is cured in that state to form a mold (mold-making master) for use in duplication using resin or the like.

[0013] The silicone rubber composition for molding according to the present invention comprises: (A) a linear or branched organopolysiloxane having two or more alkenyl groups bonded to silicon atoms per molecule and having a viscosity at 23°C of 600 to 200,000 mPa·s; (B) Specific surface area by BET method is 180 to 500 m 2 / g of fumed silica particles whose surfaces are coated with only 1,3-divinyl-1,1,3,3-tetramethyldisilazane and 1,1,1,3,3,3-hexamethyldisilazane; (C)(C-1)R 1 2HSiO 1 / 2 (In the formula, R 1 are each independently a substituted or unsubstituted alkyl group. 4 / 2 a resinous organohydrogenpolysiloxane comprising units; (C-2)R 1 3SiO 1 / 2 Units, R 1 2SiO 2 / 2 Units and R 1 HSiO 2 / 2 Units (wherein R 1 are the same as above.) a linear organohydrogenpolysiloxane, (D) a dimethylpolysiloxane terminated at both molecular chain ends with trimethylsiloxy groups, having a viscosity at 23°C of 20 to 300 mPa·s; (E) a dimethylpolysiloxane terminated at both molecular chain ends with trimethylsiloxy groups, having a viscosity at 23°C of 10,000 to 150,000 mPa·s; (F) a dimethylsiloxane-diphenylsiloxane copolymer terminated at both ends by trimethylsiloxy groups and having a viscosity at 23°C of 10 to 600 mPa·s, and (G) Platinum catalyst and does not contain a resinous organopolysiloxane having an alkenyl group bonded to a silicon atom.

[0014] [1] Component (A) Component (A) is a linear or branched organopolysiloxane containing two or more silicon-bonded alkenyl groups per molecule, and is the main component that crosslinks the silicone rubber composition for molding of the present invention to form rubber.

[0015] The viscosity of component (A) is 600 to 200,000 mPa·s, preferably 5,000 to 20,000 mPa·s. If the viscosity exceeds 200,000 mPa·s, workability decreases, and if it is less than 600 mPa·s, the cured product will have poor rubber elasticity. The viscosity in this invention is measured at 23°C using a rotational viscometer.

[0016] The molecular structure of component (A) is preferably linear or branched (linear with some branching), with the main chain consisting of repeating diorganosiloxane units and both molecular chain terminals blocked with triorganosiloxy groups.

[0017] The alkenyl group bonded to the silicon atom is not particularly limited, but is preferably an alkenyl group having 2 to 10 carbon atoms, and more preferably an alkenyl group having 2 to 8 carbon atoms. Specific examples thereof include vinyl, allyl, 1-butenyl, 1-hexenyl, etc. Among these, vinyl is preferred from the standpoint of ease of synthesis and cost. The number of alkenyl groups is not particularly limited as long as it is 2 or more, but 2 to 10 is preferred. The alkenyl groups may be present at the ends (both ends or one end) of the molecular chain of the organopolysiloxane, or may be present somewhere in the middle, but from the perspective of the flexibility of the resulting silicone rubber mold, it is preferable that they be present at only both ends.

[0018] The group bonded to the silicon atom other than the alkenyl group is not particularly limited, but is preferably a monovalent hydrocarbon group having 1 to 20 carbon atoms, more preferably a monovalent hydrocarbon group having 1 to 10 carbon atoms. Specific examples thereof include alkyl groups such as methyl, ethyl, n-propyl, n-butyl, n-hexyl, n-octyl, and n-dodecyl; aryl groups such as phenyl; and aralkyl groups such as 2-phenylethyl and 2-phenylpropyl. In addition, some or all of the hydrogen atoms of these hydrocarbon groups may be substituted with halogen atoms such as chlorine, fluorine, or bromine. Specific examples thereof include halogen-substituted monovalent hydrocarbon groups such as fluoromethyl, bromoethyl, chloromethyl, and 3,3,3-trifluoropropyl groups. Among these, alkyl groups having 1 to 4 carbon atoms are preferred, and from the standpoint of ease of synthesis and cost, it is more preferred that 90 mol % or more of these groups are methyl groups.

[0019] Specific examples of component (A) include dimethylpolysiloxanes terminally capped with dimethylvinylsiloxy groups, dimethylsiloxane-diphenylsiloxane copolymers terminally capped with dimethylvinylsiloxy groups, methylvinylpolysiloxanes terminally capped with dimethylvinylsiloxy groups, dimethylsiloxane-methylvinylsiloxane copolymers terminally capped with dimethylvinylsiloxy groups, dimethylsiloxane-methylvinylsiloxane-methylphenylsiloxane copolymers terminally capped with dimethylvinylsiloxy groups, and trimethylsiloxanes terminally capped with trimethylsiloxanes. Examples include dimethylsiloxane-methylvinylsiloxane copolymers capped with hydroxy groups, methylvinylpolysiloxanes capped with trimethylsiloxy groups at both molecular chain terminals, dimethylsiloxane-methylvinylsiloxane-methylphenylsiloxane copolymers capped with trimethylsiloxy groups at both molecular chain terminals, and dimethylpolysiloxanes capped with trivinylsiloxy groups, of which dimethylpolysiloxanes capped with dimethylvinylsiloxy groups at both molecular chain terminals and dimethylsiloxane-methylvinylsiloxane copolymers capped with trimethylsiloxy groups at both molecular chain terminals are particularly preferred. The component (A) may be used alone or in combination of two or more types.

[0020] When two or more types of component (A) are used in combination, it is preferable that they include (A-1) a dimethylpolysiloxane terminally blocked with dimethylvinylsiloxy groups and (A-2) a dimethylsiloxane-methylvinylsiloxane copolymer terminally blocked with trimethylsiloxy groups. In this case, the viscosity of component (A-1) is preferably 600 to 200,000 mPa·s, more preferably 1,000 to 100,000 mPa·s, and even more preferably 1,000 to 50,000 mPa·s.The viscosity of component (A-2) is preferably 600 to 100,000 mPa·s, more preferably 600 to 10,000 mPa·s, and even more preferably 600 to 5,000 mPa·s.

[0021] When the (A-1) component and the (A-2) component are used in combination, it is preferable to use them so that the total of the (A-1) component and the (A-2) component is 100 parts by mass, and the blending ratio thereof, in mass ratio, is preferably (A-1) / (A-2)=70 / 30 to 98 / 2, more preferably 75 / 25 to 98 / 2, and even more preferably 80 / 20 to 98 / 2.

[0022] [2](B) Component (B) Component has a specific surface area of ​​180 to 500 m by the BET method. 2 / g of fumed silica particles are surface-treated silica particles whose surfaces are coated with only 1,3-divinyl-1,1,3,3-tetramethyldisilazane (DVTMDS) and 1,1,1,3,3,3-hexamethyldisilazane (HMDS). DVTMDS and HMDS react with the active hydrogen of the hydroxyl groups on the surface of the fumed silica to generate vinyldimethylsiloxy and trimethylsiloxy groups. This surface treatment improves the dispersibility of the silica particles in component (A), and while maintaining the transparency of the composition, it can impart mechanical properties such as tensile strength, tear strength, and elongation at break to the resulting cured product.

[0023] From the viewpoint of the mechanical properties of the cured product, the mass ratio of DVTMDS to HMDS used in the surface treatment of the fumed silica is preferably DVTMDS / HMDS=1 / 99 to 10 / 90, more preferably 1 / 99 to 5 / 95. If the ratio is 1 / 99 or more, the resulting cured product will have excellent hardness, tensile strength, and tear strength, and if it is 10 / 90 or less, the elongation at break will be excellent.

[0024] The surface treatment method is not particularly limited, but for example, a mixer such as a planetary mixer or kneader can be used to mix 100 parts by mass of component (A) with untreated fumed silica in an amount such that the amount of surface-treated silica particles falls within the range described below, for example, 0.5 parts by mass or more but less than 50 parts by mass, and 4 to 20 parts by mass of 1,3-divinyl-1,1,3,3-tetramethyldisilazane and 1,1,1,3,3,3-hexamethyldisilazane in total, at 20 to 40°C for 1 to 4 hours, and then heat-treated at 120 to 170°C under atmospheric pressure or reduced pressure for 2 to 8 hours to volatilize the unreacted 1,3-divinyl-1,1,3,3-tetramethyldisilazane and 1,1,1,3,3,3-hexamethyldisilazane, thereby obtaining a mixture in which component (B) is dispersed in component (A). To efficiently proceed with the surface treatment, 0.5 to 5.0 parts by mass of water may be added.

[0025] On the other hand, if fumed silica that has been surface-treated in advance with dimethyltetravinyldisilazane, trimethylchlorosilane, octamethylcyclotetrasiloxane, hexamethylcyclotrisiloxane, dichlorodimethylsilane, or the like is used in place of untreated fumed silica in the surface treatment step, the fluidity and transparency of the composition will be impaired.

[0026] The BET specific surface area of ​​the surface-untreated fumed silica particles used in component (B) is 180 to 500 m 2 / g, preferably 190 to 400m 2 / g. BET specific surface area is 180m 2 If the viscosity is less than 500 m / g, the transparency of the composition and the cured product will be insufficient. 2 If the content exceeds 1 / g, the particles tend to aggregate, resulting in a decrease in the flowability of the composition and a decrease in the mechanical properties of the cured product.

[0027] As the surface-untreated fumed silica particles, commercially available products can be used, such as Aerosil 200 and Aerosil 300 (manufactured by Nippon Aerosil Co., Ltd.); Reolosil QS-102, Reolosil QS-30, and Reolosil QS-40 (manufactured by Tokuyama Corporation).

[0028] The blending amount of component (B) is 1 to 50 parts by mass, preferably 15 to 40 parts by mass, per 100 parts by mass of component (A). If the blending amount of component (B) is less than 1 part by mass, the silicone rubber mold will not have sufficient hardness, and large molds will bend under their own weight. On the other hand, if the blending amount of component (B) is more than 50 parts by mass, the hardness of the cured product will be too high, making it difficult to remove the resin replica from the silicone rubber mold.

[0029] [3](C-1) component The component (C-1) is R 1 2HSiO 1 / 2 (In the formula, R 1 are each independently a substituted or unsubstituted alkyl group. 4 / 2 This component is a resinous organohydrogenpolysiloxane consisting of units, and crosslinks through hydrosilylation between the Si-H groups in this component and the alkenyl groups in component (A) and the vinyl groups on the surface of component (B), thereby curing the silicone rubber composition of the present invention.

[0030] R 1 The alkyl group preferably has 1 to 10 carbon atoms, more preferably 1 to 8 carbon atoms, and specific examples thereof include methyl, ethyl, n-propyl, n-butyl, n-hexyl, n-octyl, and n-dodecyl groups. In addition, some or all of the hydrogen atoms of these alkyl groups may be substituted with halogen atoms such as chlorine, fluorine, or bromine, and specific examples thereof include halogen-substituted alkyl groups such as fluoromethyl, bromoethyl, chloromethyl, and 3,3,3-trifluoropropyl groups. Among these, alkyl groups having 1 to 4 carbon atoms are preferred, and methyl groups are more preferred.

[0031] The content of hydrogen atoms bonded to silicon atoms in component (C-1) is preferably 0.7 to 1.7 mass%, more preferably 0.8 to 1.5 mass%, of the total component. If the content of hydrogen atoms bonded to silicon atoms is 0.7 mass% or more, the composition will have excellent curability, and if it is 1.7 mass% or less, a cured product with excellent mechanical properties will be obtained.

[0032] The viscosity of the component (C-1) at 23°C is preferably 1 to 100 mPa·s, and more preferably 1 to 80 mPa·s, from the standpoints of the curability of the composition and the mechanical properties of the cured product.

[0033] The blending amount of component (C-1) is 1 to 5 parts by mass, preferably 2 to 4 parts by mass, per 100 parts by mass of component (A). If it is less than 1 part by mass, the resulting silicone rubber mold will not have sufficient hardness, and the releasability of the silicone rubber mold and the resin replica will be insufficient. If it exceeds 5 parts by mass, the composition will yellow, resulting in a decrease in transparency and an increase in viscosity, and the elongation at break and tear strength of the silicone rubber mold will decrease.

[0034] [4](C-2) component The component (C-2) is R 1 3SiO 1 / 2 Units, R 1 2SiO 2 / 2 Units and R 1 HSiO 2 / 2 Units (wherein R 1 is the same as above.) and crosslinks via hydrosilylation between the Si-H groups in this component and the alkenyl groups in component (A) and the vinyl groups on the surface of component (B), thereby curing the silicone rubber composition of the present invention.

[0035] R 1 Specific examples of the alkyl group include the same as those exemplified for the component (C-1) above, with alkyl groups having 1 to 4 carbon atoms being preferred, and methyl groups being more preferred.

[0036] The content of hydrogen atoms bonded to silicon atoms in component (C-2) is preferably 0.25 to 0.8% by mass, more preferably 0.25 to 0.6% by mass, of the total component. If the content of hydrogen atoms bonded to silicon atoms is 0.25% by mass or more, the composition will have excellent curing properties, and if it is 0.8% by mass or less, the composition will have excellent demoldability between the silicone rubber mold and a resin replica such as a urethane resin.

[0037] The viscosity of the component (C-2) at 23°C is preferably from 1 to 300 mPa·s, and more preferably from 1 to 100 mPa·s, from the standpoints of the curability of the composition and the mechanical properties of the cured product.

[0038] The amount of component (C-2) blended is 1 to 5 parts by mass, preferably 2 to 4 parts by mass, per 100 parts by mass of component (A). Less than 1 part by mass increases the viscosity of the composition, reduces transparency, and reduces the elongation at break and tear strength of the silicone rubber mold. More than 5 parts by mass results in insufficient hardness of the silicone rubber mold and insufficient demoldability between the silicone rubber mold and the resin replica.

[0039] From the viewpoints of the fluidity and transparency of the composition, as well as the mechanical properties and demoldability of the silicone rubber mold, the mass ratio of component (C-1) to component (C-2) [(C-1) / (C-2)] is preferably 0.5 to 2.0, and more preferably 0.7 to 1.8.

[0040] Furthermore, in terms of the curability of the composition and the mechanical properties of the cured product, the ratio of the total number of hydrogen atoms bonded to silicon atoms to the total number of alkenyl groups bonded to silicon atoms in the composition is preferably such that the total number of Si-H groups in components (C-1) and (C-2) is within a range of 0.5 to 5.0 mol per 1 mol of the total number of alkenyl groups in components (A) and (B), and more preferably within a range of 1.0 to 3.0 mol.

[0041] [5](D) component Component (D) is a dimethylpolysiloxane capped at both molecular chain ends with trimethylsiloxy groups, with a viscosity of 20-300 mPa·s at 23°C. Because component (D) does not contain crosslinkable functional groups and has a low viscosity, it bleeds onto the surface of the silicone rubber mold after curing, improving the demoldability of resin replicas made from urethane resins and other materials.

[0042] The viscosity of component (D) at 23°C is 20 to 300 mPa·s, preferably 30 to 200 mPa·s. If it is less than 20 mPa·s, it will be prone to volatilization when transferred to the rubber mold surface, resulting in poor demoldability. On the other hand, if it exceeds 300 mPa·s, bleeding will occur more slowly, resulting in poor initial demoldability.

[0043] The amount of component (D) blended is 2 to 10 parts by mass, preferably 3 to 8 parts by mass, per 100 parts by mass of component (A). If it is less than 2 parts by mass, the viscosity of the composition tends to increase, reducing defoaming properties and failing to improve the demoldability of the silicone rubber mold. On the other hand, if it exceeds 10 parts by mass, the silicone rubber mold will not be hard enough, resulting in an unstable shape.

[0044] [6](E) component Component (E) is a dimethylpolysiloxane capped at both molecular chain ends with trimethylsiloxy groups, with a viscosity of 10,000 to 150,000 mPa·s at 23°C. Like component (D), it bleeds onto the surface of the silicone rubber mold after curing, improving the demoldability of resin replicas. Because this component has a higher viscosity than component (D), it bleeds onto the silicone rubber mold surface more slowly, effectively improving demoldability during repeated duplication.

[0045] The viscosity of component (E) at 23°C is 10,000 to 150,000 mPa·s, preferably 20,000 to 120,000 mPa·s. If it is less than 10,000 mPa·s, it will migrate to the rubber mold surface too quickly, resulting in poor demoldability during repeated duplication. If it exceeds 150,000 mPa·s, the viscosity of the entire composition will increase, resulting in poor defoaming and workability.

[0046] The amount of component (E) blended is 5 to 15 parts by mass, preferably 6 to 15 parts by mass, and more preferably 7 to 13 parts by mass, per 100 parts by mass of component (A). If it is less than 5 parts by mass, it is difficult to obtain the effect of improving the demoldability of the silicone rubber mold, while if it exceeds 15 parts by mass, the viscosity of the entire composition increases, reducing defoaming properties and workability, and the silicone rubber mold will not have enough hardness, resulting in an unstable shape.

[0047] [7] (F) component Component (F) is a dimethylsiloxane-diphenylsiloxane copolymer capped at both molecular chain ends with trimethylsiloxy groups, with a viscosity of 10 to 600 mPa·s at 23°C. Like components (D) and (E), it bleeds onto the silicone rubber mold surface after curing and improves the demoldability of the resin replica. This component has a relatively low viscosity and contains phenyl groups, allowing it to bleed quickly onto the silicone rubber mold surface, effectively improving initial demoldability.

[0048] From the viewpoint of transparency and compatibility of the composition, the ratio of dimethylsiloxane units to diphenylsiloxane units in component (F) is preferably in the range of 1.42 to 1.52 so that the refractive index of component (F) is 1.42 to 1.52. The refractive index is measured at 25°C using the sodium D line (wavelength 589.3 nm) with a digital refractometer RX-9000α manufactured by Atago Co., Ltd.

[0049] The viscosity of component (F) at 23°C is 10 to 600 mPa·s, preferably 50 to 500 mPa·s. If it is less than 10 mPa·s, this component will separate from the composition before curing. If it exceeds 600 mPa·s, bleeding will occur more slowly, resulting in poor initial demoldability.

[0050] The blending amount of component (F) is 0.01 to 0.5 parts by mass, and preferably 0.05 to 0.3 parts by mass, per 100 parts by mass of component (A). Less than 0.01 part by mass will not improve the demoldability of the silicone rubber mold, while more than 0.5 part by mass will cause the composition to become cloudy, reducing transparency and fluidity.

[0051] [8](G) component Component (G) is a platinum catalyst that promotes the addition reaction (hydrosilylation reaction) between the alkenyl groups in components (A) and (B) and the Si-H groups in components (C-1) and (C-2). Specific examples include fine particle platinum, chloroplatinic acid, reaction products of chloroplatinic acid and alcohol, platinum chelate compounds, complexes of platinum and diketones, coordination compounds of chloroplatinic acid and olefins, complexes of chloroplatinic acid and vinylsiloxane, and those supported on carriers such as alumina, silica, and carbon black. Among these, the reaction product of chloroplatinic acid with an alcohol and the complex of chloroplatinic acid with a vinylsiloxane are particularly preferred because of their high catalytic activity.

[0052] The amount of component (G) that can be added is not limited as long as it promotes curing (hydrosilylation reaction) of the composition, but the amount of platinum metal atoms in this component is preferably in the range of 0.01 to 500 ppm by mass, more preferably 1 to 50 ppm, relative to the mass of component (A).Within this range, the reaction rate of the addition reaction is appropriate.

[0053] [9](H) component The silicone rubber composition of the present invention may contain benzotriazole as component (H). Adding this component to the silicone rubber composition prevents the platinum catalyst (component (G)) from oxidizing to platinum black, thereby preventing the silicone rubber mold from turning black.

[0054] When component (H) is used, the blending amount is preferably 1 to 50 ppm by mass, more preferably 3 to 30 ppm by mass, based on the total composition, in order to prevent inhibition of curing.

[0055]

[10] Component (I) The silicone rubber composition of the present invention may contain (I) a cure retarder that inhibits the hydrosilylation reaction in order to ensure the storage stability of the composition and the working time until cure. Specific examples of the cure retarder include vinyl group-containing cyclic organopolysiloxanes such as vinylcyclotetrasiloxane, triallyl isocyanurate, alkyl maleate, acetylene alcohols and their silane or siloxane modified products, hydroperoxide, tetramethylethylenediamine, etc. More specifically, 1,3,5,7-tetramethyl-1,3,5,7-tetravinylcyclotetrasiloxane, ethynylcyclohexanol, dimethylbis(1,1-dimethyl-2-propynyl)silane, 3-methyl-1-tridecyn-3-ol, etc. are preferred.

[0056]

[11] Other ingredients In addition to the above components (A) to (G) and the optional components (H) and (I), the silicone rubber composition for molding of the present invention may contain other components, such as those listed below, as long as they do not impair the effects of the present invention. Specific examples of such other components include plasticizers, flame retardants, thixotropic agents, antibacterial agents, and antifungal agents.

[0057] The silicone rubber composition for molding of the present invention does not contain a resinous organopolysiloxane having alkenyl groups bonded to silicon atoms, as the presence of such a resinous organopolysiloxane would result in poor defoaming and flow properties for the composition. Specific examples of resinous organopolysiloxanes having alkenyl groups bonded to silicon atoms include those represented by the formula: CH2=CH(CH3)2SiO 1 / 2 Siloxane units represented by the formula: (CH3)3SiO 1 / 2 Siloxane units represented by the formula: SiO 4 / 2 Resin-like organopolysiloxanes consisting of siloxane units represented by the formula: CH2=CH(CH3)2SiO 1 / 2 Siloxane units represented by the formula: (CH3)3SiO 1 / 2 Siloxane units represented by the formula: CH3SiO3 / 2 Examples of suitable organopolysiloxanes include resin-like organopolysiloxanes consisting of siloxane units represented by the following formula:

[0058] The silicone rubber composition for molding of the present invention can be prepared by mixing the above-mentioned components (A) to (G), and, if necessary, component (H), component (I), and other components, using a known method such as a kneader or planetary mixer.

[0059] The silicone rubber composition for molding of the present invention can be stored in the same container with all components in the presence of the cure retarder (I). However, it can also be a two-component composition in which a first component containing components (A), (B), and (G) and a second component containing components (C-1) and (C-2) are prepared separately and the first and second components are mixed before use. It is also possible for there to be components that are used in common in both the first and second components. By forming the composition into such a two-component form, storage stability can be further ensured.

[0060] The viscosity of the silicone rubber composition for molding of the present invention is not particularly limited, but is preferably 3,000 to 1,000,000 mPa·s as measured at 23°C using a rotational viscometer. A viscosity of 3,000 mPa·s or higher results in excellent mechanical properties for the cured product, while a viscosity of 1,000,000 mPa·s or lower results in excellent fluidity of the composition. From the perspective of ease of molding (casting), a viscosity of 5,000 to 200,000 mPa·s is more preferred, and 5,000 to 100,000 mPa·s is even more preferred.

[0061] The silicone rubber composition for molding of the present invention can be poured or applied to encase the entire master (mother mold) or to a portion of the surface of the master mold, and after curing, can be removed from the master mold to obtain a silicone rubber mold. Regarding curing conditions, for example, curing proceeds even at room temperature (5 to 35°C), but curing can also be accelerated by heating, and this method is effective when it is desired to improve mass productivity. When heat curing is carried out, it can usually be carried out under conditions of a temperature of 40 to 80° C. for about 2 to 20 hours.

[0062] A molding resin such as urethane resin or epoxy resin is poured into the silicone rubber mold of the present invention, cured at a curing temperature appropriate for the type of molding resin, and then the molded product can be removed from the silicone rubber mold to obtain a resin replica.

[0063] The silicone rubber mold of the present invention preferably has a durometer A hardness according to JIS K 6253-3:2012 of 30 to 50. If the durometer A hardness is 30 or more, deformation of the silicone rubber mold can be suppressed when the resin replica is removed from the silicone rubber mold, and if the hardness is 50 or less, the resin replica can be easily released from the silicone rubber mold. [Example]

[0064] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples. In the examples and comparative examples, the viscosity is measured at 23°C using a rotational viscometer, and the weight-average molecular weight (Mw) is a standard polystyrene-equivalent value measured by gel permeation chromatography (GPC) using a Tosoh HLC-8220 GPC with toluene as the solvent. The refractive index is a value measured at 25°C using the sodium D line (wavelength 589.3 nm) with an Atago RX-9000α digital refractometer. Me represents a methyl group, and Vi represents a vinyl group.

[0065] [1] Production and evaluation of silicone rubber compositions [Example 1-1] (A-1) 95 parts by mass of dimethylpolysiloxane terminated at both molecular chain ends with dimethylvinylsiloxy groups and having a viscosity of 5,000 mPa·s, (A-2) 5 parts by mass of dimethylsiloxane-methylvinylsiloxane copolymer terminated at both molecular chain ends with trimethylsiloxy groups and having a viscosity of 700 mPa·s, BET specific surface area of ​​300 m 225 parts by mass of surface-untreated fumed silica (trade name: Aerosil 300, manufactured by Nippon Aerosil Co., Ltd.) at 1 / g, 0.2 parts by mass of 1,3-divinyl-1,1,3,3-tetramethyldisilazane (DVTMDS), 8 parts by mass of 1,1,1,3,3,3-hexamethyldisilazane (HMDS), and 1 part by mass of water were placed in a kneader and kneaded at 25°C for 2 hours, followed by kneading at 150°C for 2 hours under reduced pressure to remove unreacted DVTMDS and HMDS, thereby obtaining a mixture in which surface-treated silica particles (B) treated with DVTMDS and HMDS were dispersed in the above components (A-1) and (A-2).

[0066] Next, at 25°C, 0.2 parts by mass of (G) chloroplatinic acid-vinylsiloxane complex (platinum concentration 1% by mass), 0.002 parts by mass of (H) benzotriazole, and 0.3 parts by mass of (I) 1,3,5,7-tetramethyl-1,3,5,7-tetravinylcyclotetrasiloxane were added and mixed, and then (C-1) MeHSiO 1 / 2 Units and SiO 4 / 2 1.4 parts by mass of a resin-like methylhydrogenpolysiloxane (viscosity 35 mPa s, Mw 1,700) consisting of units and containing 1.2 mass% hydrogen atoms bonded to silicon atoms, (C-2) Me3SiO 1 / 2 Units, Me2SiO 2 / 2 Units and MeHSiO 2 / 2 A silicone rubber composition was obtained by adding and mixing 1.7 parts by mass of a linear methylhydrogenpolysiloxane (viscosity 100 mPa·s, Mw 6,000) consisting of units and containing 0.33 mass% of hydrogen atoms bonded to silicon atoms, (D) 8 parts by mass of a dimethylpolysiloxane capped at both molecular chain terminals with trimethylsiloxy groups and having a viscosity of 100 mPa·s, (E) 6 parts by mass of a dimethylpolysiloxane capped at both molecular chain terminals with trimethylsiloxy groups and having a viscosity of 100,000 mPa·s, and (F) 0.2 parts by mass of a dimethylsiloxane-diphenylsiloxane copolymer (refractive index 1.425) capped at both molecular chain terminals with trimethylsiloxy groups and having a viscosity of 100 mPa·s.

[0067] [Example 1-2] A silicone rubber composition was obtained in the same manner as in Example 1-1, except that the amount of component (C-1) added was changed to 1.7 parts by mass and the amount of component (C-2) added was changed to 1.4 parts by mass.

[0068] [Examples 1-3] A silicone rubber composition was obtained in the same manner as in Example 1-1, except that the amount of component (D) added was changed to 6 parts by mass and the amount of component (E) added was changed to 8 parts by mass.

[0069] [Examples 1-4] A silicone rubber composition was obtained in the same manner as in Example 1-1, except that (H) benzotriazole was not added.

[0070] [Comparative Example 1-1] A silicone rubber composition was obtained in the same manner as in Example 1-1, except that the component (C-1) was not added and the amount of component (C-2) added was changed to 5.2 parts by mass.

[0071] [Comparative Example 1-2] A silicone rubber composition was obtained in the same manner as in Example 1-1, except that the component (C-2) was not added and the amount of component (C-1) added was changed to 2.1 parts by mass.

[0072] [Comparative Example 1-3] A silicone rubber composition was obtained in the same manner as in Example 1-1, except that component (D) was not added and the amount of component (E) added was changed to 14 parts by mass.

[0073] [Comparative Example 1-4] A silicone rubber composition was obtained in the same manner as in Example 1-1, except that component (E) was not added and the amount of component (D) added was changed to 14 parts by mass.

[0074] [Comparative Example 1-5] A silicone rubber composition was obtained in the same manner as in Example 1-1, except that component (F) was not added.

[0075] [Comparative Examples 1-6] In Example 1-1, the amount of component (C-1) added was changed to 1.6 parts by mass, the amount of component (C-2) added was changed to 2.1 parts by mass, and the structural unit ratio was changed to Me3SiO 1 / 2 Unit: Me2ViSiO 1 / 2 Unit: SiO 4 / 2 A silicone rubber composition was obtained in the same manner as in Example 1-1, except that 25 parts by mass of a resinous methylvinylpolysiloxane having a unit ratio of 5:1:8 (molar ratio) and an Mw of 3,000 was added and mixed.

[0076] [Comparative Example 1-7] In Example 1-1, 25 parts by mass of surface-untreated fumed silica was replaced with fumed silica (R-976S manufactured by Evonic, BET specific surface area 300 m) that had been surface-treated with dichlorodimethylsilane in advance. 2 A silicone rubber composition containing R-976S silica particles that had been further surface-treated with DVTMDS and HMDS was obtained by the same procedure as in Example 1-1, except that the amount of silica particles was changed to 25 parts by mass (1 / g).

[0077] The viscosity, defoaming ability, and transparency of the silicone rubber compositions obtained in Examples 1-1 to 1-4 and Comparative Examples 1-1 to 1-7 were evaluated in an environment of 23°C and 50% RH. The results are shown in Table 1, along with the total molar ratio of Si-H groups to the total number of alkenyl groups (vinyl groups) bonded to silicon atoms in the composition (SiH / SiVi ratio).

[0078] [viscosity] The viscosity of the resulting silicone rubber composition at 23°C was measured using a rotational viscometer. [Defoaming] 110 g of the composition was placed in a polyethylene cup having a diameter of 80 mm and a height of 90 mm, and the time required for defoaming was measured at a reduced pressure of 0.2 kPa. If bubbles reached the top of the cup during defoaming, the measurement of the time was stopped, the pressure was returned to 40 kPa to break the bubbles, and the pressure was reduced to 0.2 kPa again before the measurement of the time was resumed. [Light transmittance] The composition was poured into a glass cell (10 mm x 10 mm x 40 mm) taking care to avoid bubbles, and the light transmittance at a wavelength of 800 nm was measured using a spectrophotometer (U-3310 manufactured by Hitachi, Ltd.) with an empty glass cell as a blank.

[0079] [Table 1]

[0080] [2] Silicone rubber mold manufacturing and evaluation [Examples 2-1 to 2-4, Comparative Examples 2-1 to 2-7] As shown in Figures 1(a) to 1(c), a matrix 3 made of ABS resin with masking tape 2 attached to its bottom was placed in a container 1. (It was a rectangular pillar with a square cross section measuring 10 mm on each side, and a stepped portion 4 was formed at the bottom in the direction perpendicular to the paper surface in Figure 1(a). The stepped portion had a width (height) of 2 mm, and the low bottom portion 41 and the high bottom portion 42 had a height difference of 2 mm.) The silicone rubber compositions 5 obtained in Examples 1-1 to 1-4 and Comparative Examples 1-1 to 1-7 were poured into the container 1 so as to encase the matrix 3. The silicone rubber compositions 5 were then degassed under reduced pressure and then cured by heating at 60°C for 4 hours. The cured product was then cooled to room temperature, and the matrix 3 was then pulled out to obtain a silicone rubber mold 6. The results of the following evaluations are shown in Table 2.

[0081] [Tape release properties] After the silicone rubber mold 6 was produced, the peelability of the masking tape 2 from the pulled-out matrix 3 was evaluated according to the following criteria. 〇: Good peeling ×: The tape is torn and adheres to the matrix. [hardness] The durometer type A hardness of the obtained silicone rubber mold 6 was measured in accordance with JIS K6253-3:2012. [Removability] 2(a) and (b), liquid urethane resin 7 (product name: MU-851A, manufactured by Pelnox) was poured into the silicone rubber mold 6 obtained above and cured by heating at 70°C for 40 minutes. After curing, the resin was cooled to 25°C, and the urethane resin molded product (replica) 8 was extracted from the silicone rubber mold 6. The same process was repeated 20 times, and the demoldability was evaluated according to the following criteria. 〇: Easy to pull out from the 1st to 20th repetitions △: The first repeated pull is difficult ×: The silicone rubber mold was partially destroyed within 20 repetitions (the number in parentheses indicates the number of repetitions until the silicone rubber mold was destroyed).

[0082] [Table 2]

[0083] As shown in Tables 1 and 2, the silicone rubber compositions of Examples 1-1 to 1-4 had excellent defoaming properties and transparency, and the silicone rubber molds obtained by curing the silicone rubber compositions of Examples 1-1 to 1-4 had good demoldability for urethane resin replicas.

[0084] In contrast, when the silicone rubber composition of Comparative Example 1-1, which did not contain the (C-1) component, was used, the tape releasability was poor, and the silicone rubber composition of Comparative Example 1-2, which did not contain the (C-2) component, was poor in transparency. The silicone rubber composition of Comparative Example 1-3, which did not contain component (D), had a high viscosity, poor defoaming properties, and the initial demoldability of the resulting silicone rubber mold was also poor. The silicone rubber mold obtained from the silicone rubber composition of Comparative Example 1-4, which did not contain component (E), was poor in demoldability when repeated duplication was performed, and destruction of the rubber mold was observed after the 17th molding. The silicone rubber mold obtained from the silicone rubber composition of Comparative Example 1-5, which did not contain component (F), was poor in initial demoldability. Furthermore, the silicone rubber composition of Comparative Example 1-6, which contained a resinous methylvinylpolysiloxane, had extremely poor defoaming properties, and the silicone rubber composition of Comparative Example 1-7, in which component (B) was changed to fumed silica that had previously been surface-treated with dichlorodimethylsilane and then further surface-treated with DVTMDS and HMDS, had poor transparency. [Explanation of symbols]

[0085] 1 container 2 masking tape 3. Matrices 4 Step 41 Low bottom 42 High bottom 5. Silicone rubber composition 6 Silicone rubber molds 7 Liquid urethane resin 8 Urethane resin molded products (replicas)

Claims

1. (A) 100 parts by mass of a linear or branched organopolysiloxane having two or more alkenyl groups bonded to silicon atoms per molecule and having a viscosity at 23°C of 600 to 200,000 mPa s; (B) A specific surface area measured by the BET method is 180 to 500 m 2 / g of fumed silica particles whose surfaces are coated with only 1,3-divinyl-1,1,3,3-tetramethyldisilazane and 1,1,1,3,3,3-hexamethyldisilazane: 1 to 50 parts by mass, (C) (C-1) R 1 2 HSiO 1 / 2 (In the formula, R 1 are each independently a substituted or unsubstituted alkyl group. 4 / 2 Resinous organohydrogenpolysiloxane consisting of units: 1 to 5 parts by mass, (C-2)R 1 3 SiO 1 / 2 Unit, R 1 2 SiO 2 / 2 Units and R 1 HSiO 2 / 2 Units (wherein R 1 are the same as above.) 1 to 5 parts by mass of a linear organohydrogenpolysiloxane, (D) 2 to 10 parts by mass of a dimethylpolysiloxane capped at both molecular chain terminals with trimethylsiloxy groups and having a viscosity at 23°C of 20 to 300 mPa s, (E) 5 to 15 parts by mass of a dimethylpolysiloxane capped at both molecular chain terminals with trimethylsiloxy groups and having a viscosity at 23°C of 10,000 to 150,000 mPa s, (F) 0.01 to 0.5 parts by mass of a dimethylsiloxane-diphenylsiloxane copolymer capped at both molecular chain terminals with trimethylsiloxy groups and having a viscosity at 23°C of 10 to 600 mPa s, and (G) Platinum catalyst and does not contain a resinous organopolysiloxane having alkenyl groups bonded to silicon atoms.

2. The silicone rubber composition for molding according to claim 1, wherein component (A) comprises (A-1) a dimethylpolysiloxane capped at both molecular chain terminals with dimethylvinylsiloxy groups and (A-2) a dimethylsiloxane-methylvinylsiloxane copolymer capped at both molecular chain terminals with trimethylsiloxy groups.

3. 2. The silicone rubber composition for molding according to claim 1, wherein the molar ratio of the total number of hydrogen atoms bonded to silicon atoms to the total number of alkenyl groups bonded to silicon atoms in the composition is 0.5 to 5.

0.

4. A molding agent comprising the molding silicone rubber composition according to any one of claims 1 to 3.

5. A silicone rubber mold obtained by curing the silicone rubber composition for molding according to any one of claims 1 to 3.

Images