Room temperature curable silicone rubber composition

Abstract

[Problem] To provide a room-temperature curable silicone rubber composition that imparts a cured product with significantly reduced yellowing or bubble curling and small change in hardness. [Solution] (A) Linear organopolysiloxane having vinyl groups at both ends of the molecular chain (B) Linear organohydrogenpolysiloxane having SiH groups at both ends of the molecular chain (C) Linear organohydrogenpolysiloxane with both ends of the molecular chain blocked by triorganosilyl groups (D) Hydrosilylation reaction catalyst A room temperature curable silicone rubber composition containing, wherein the total number of SiH groups in components (B) and (C) relative to the SiVi groups in component (A) is 0.7 to 2.5, and the ratio of the number of SiH groups in component (B) to the total number of SiH groups in components (B) and (C) is 0.05 to 0.6.

Description

Technology Field

[0001] The present invention relates to an addition-curing silicone rubber composition that cures at room temperature and imparts a highly transparent cured product. Background Technology

[0002] Highly transparent silicone rubber materials are used in a wide range of applications, such as optical device materials, 3D printer materials, and nanoimprint materials. Additionally, due to their excellent durability, ornamental molded articles containing dried flowers or three-dimensional models encapsulated within silicone gel or silicone rubber have been proposed (Patent Documents 1 and 2). The silicone rubber used for such potting is in a liquid state before curing, and by mixing it with a curing agent, it is simply cured at room temperature or by heating to become a highly transparent rubber material.

[0003] However, such silicone rubber materials had problems such as trapped air bubbles generated during mixing remaining after curing, the material yellowing due to discoloration caused by metal catalysts if left unattended for a long time, or delamination occurring at the interface between the silicone rubber and the container or encapsulation due to shrinkage after curing. Prior art literature

[0004] Japanese Patent Publication No. Hei 8-92002 Japanese Patent Publication No. 2000-336269 The problem to be solved

[0005] The present invention has been made in consideration of the above circumstances and aims to provide a room-temperature curing silicone rubber composition that imparts a cured product with significantly reduced yellowing or bubble curling and small changes in hardness. means of solving the problem

[0006] As a result of conducting careful examinations to achieve the above objective, the inventors discovered that the following specific addition-curing silicone rubber composition reduces the occurrence of bubble curling during mixing, thereby providing a silicone rubber that is highly transparent and has a small change in hardness, and thus completed the present invention.

[0007] That is, the present invention

[0008] 1. (A) Organopolysiloxane represented by the following average formula (1)

[0009] Vi (3-a) R 1 a Si(OR 1 2Si) m OSiR 1 a Vi (3-a) (1)

[0010] (during food, R 1 is an unsubstituted or substituted monovalent hydrocarbon group that does not independently contain an alkenyl group, Vi is a vinyl group, m is a number from 13 to 200, and a is a number from 0 to 2.)

[0011] (B) Organohydrogenpolysiloxane represented by the following average formula (2)

[0012] (HR 1 2SiO 1 / 2 )2(R 1 2SiO 2 / 2 ) n (2)

[0013] (during food, R 1 ...is the same as above, and n is a number from 10 to 80.)

[0014] (C) Organohydrogenpolysiloxane represented by the following average formula (3)

[0015] (R 1 3SiO 1 / 2 )2(HR 1 1SiO 2 / 2 ) s (R 1 2SiO 2 / 2 ) t (3)

[0016] (during food, R 1 ...is the same as above, and s and t are numbers satisfying s≥2 and t≥0, respectively, and 8≤s+t≤100 and 0.05≤s / (s+t)≤1.0.

[0017] (D) Hydrosilylation reaction catalyst

[0018] Contains,

[0019] A room temperature curable silicone rubber composition wherein the total number of SiH groups in components (B) and (C) per vinyl group in component (A) is 0.7 to 2.5, the ratio of the number of SiH groups in component (B) to the total number of SiH groups in components (B) and (C) is 0.05 to 0.6, and the content of metal atoms derived from the hydrosilylation reaction catalyst of component (D) is 15 mass ppm or less relative to the total amount of components (A) to (C).

[0020] 2. (A) A room temperature curing silicone rubber composition as described in 1, wherein the viscosity of the component at 23°C is 10 to 700 mPa·s,

[0021] 3. A room temperature curable silicone rubber composition as described in 1 or 2, wherein the total number of SiH groups in components (B) and (C) per vinyl group in component (A) is 1.0 to 2.0,

[0022] 4. A silicone rubber formed by curing a room temperature curing silicone rubber composition described in any one of 1 to 3,

[0023] 5. Silicone rubber described in 4, wherein the difference between the durometer A hardness of a cured product cured at 23°C for 24 hours and the durometer A hardness of a cured product cured at 23°C for 72 hours is 1 or less.

[0024] 6. Silicone rubber described in 4 or 5 having a transmittance of 90% or more for a wavelength of 400 nm at a thickness of 2 mm.

[0025] It provides. Effects of the invention

[0026] The room-temperature curable silicone rubber composition of the present invention is suitable for sealing specimens, three-dimensional models, decorative items, etc., such as those in plant specimen rooms, because it imparts a silicone rubber with excellent bubble-releasing properties, high transparency, and small change in hardness. Specific details for implementing the invention

[0027] The present invention will be described in more detail below.

[0028] The room temperature curable silicone rubber composition of the present invention contains the following components (A) to (D).

[0029] (A) Organopolysiloxane containing vinyl groups at both ends of the molecular chain

[0030] (B) Organohydrogenpolysiloxane containing SiH groups at both ends of the molecular chain

[0031] (C) Organohydrogenpolysiloxane blocking triorganosilyl groups at both ends of the molecular chain

[0032] (D) Hydrosilylation reaction catalyst

[0033] [1] (A) Component

[0034] (A) The component is a straight-chain organopolysiloxane having vinyl groups at both ends of the molecular chain, represented by the following average formula (1).

[0035] Vi (3-a) R 1 a Si(OR 1 2Si) m OSiR 1 a Vi (3-a) (1)

[0036] R 1 is independently an unsubstituted or substituted monovalent hydrocarbon group other than an alkenyl group, and Vi represents a vinyl group (the same applies hereinafter). R 1As long as it does not have an alkenyl group, there are no particular limitations, and it may be a straight chain, branched, or cyclic chain, but a monovalent hydrocarbon group having 1 to 20 carbon atoms is preferred, a monovalent hydrocarbon group having 1 to 10 carbon atoms is more preferred, and a monovalent hydrocarbon group having 1 to 5 carbon atoms is even more preferred.

[0037] Specific examples thereof include straight-chain or branched alkyl groups such as methyl, ethyl, n-propyl, isopropyl, n-butyl, tert-butyl, and n-hexyl groups; cyclic alkyl groups such as cyclohexyl groups; aryl groups such as phenyl and tolyl groups; and aralkyl groups such as benzyl and phenylethyl groups.

[0038] In addition, some or all of the hydrogen atoms of these monovalent hydrocarbon groups may be substituted with halogen atoms such as F, Cl, Br, cyano groups, etc. Specific examples of such groups include halogen-substituted hydrocarbon groups such as 3,3,3-trifluoropropyl groups; cyano-substituted hydrocarbon groups such as 2-cyanoethyl groups, etc.

[0039] Among these, a methyl group is preferred.

[0040] a is a number from 0 to 2, preferably a number from 0 to 1.8.

[0041] m is a number from 13 to 200, preferably from 30 to 190, and more preferably from 70 to 180. If m is less than 13, it volatilizes during curing, and if m is greater than 200, the bubble removal during mixing of the composition is poor, and workability is also deteriorated.

[0042] (A) The viscosity of the component at 23°C is preferably 10 to 700 mPa·s and more preferably 20 to 500 mPa·s, in that it allows air bubbles generated when mixing the composition to escape easily and imparts a liquid composition that hardens to become a rubbery elastomer. Additionally, the viscosity in the present invention is a value measured using a rotational viscometer.

[0043] Examples of such (A) components include organopolysiloxanes represented by the following average formula. (A) components may be used as a single type or in combination of two or more types.

[0044]

[0045] [2] (B) Component

[0046] (B) is a straight-chain organohydrogenpolysiloxane having hydrogen atoms (i.e., SiH groups) bonded to silicon atoms at both ends of the molecular chain, represented by the following average formula (2), and is a component that imparts rubber properties to the cured product by extending the siloxane chain through a hydrosilylation reaction with the vinyl groups at the ends of the molecular chain of component (A).

[0047] (HR 1 2SiO 1 / 2 )2(R 1 2SiO 2 / 2 ) n (2)

[0048] R 1 The above is identical to the above, and specifically, it may be identical to an unsubstituted or substituted monovalent hydrocarbon group other than the alkenyl group exemplified in the above average formula (1), and a methyl group is particularly preferred.

[0049] n is a number from 10 to 80, preferably from 10 to 50, and more preferably from 10 to 30. If n is less than 10, the component volatilizes during curing, and if n is greater than 80, the viscosity of the composition increases, making it difficult to remove bubbles and also worsening workability.

[0050] (B) Specific examples of the component include, for instance, those represented by the following average formula. Additionally, the component (B) may be used as a single type or in combination of two or more types.

[0051]

[0052] [3] (C) component

[0053] (C) is a straight-chain organohydrogenpolysiloxane with both ends of the molecular chain blocked by triorganosilyl groups, represented by the average formula (3) below, and acts as a crosslinking agent by reacting with the vinyl groups in (A) through hydrosilylation.

[0054] (R 1 3SiO 1 / 2 )2(HR 1 1SiO 2 / 2 ) s (R 1 2SiO 2 / 2 ) t (3)

[0055] R 1 The above is identical to the above, and specifically, it may be identical to an unsubstituted or substituted monovalent hydrocarbon group other than the alkenyl group exemplified in the above average formula (1), and a methyl group is particularly preferred.

[0056] s and t are numbers satisfying s≥2 and t≥0, respectively, and also 8≤s+t≤100 and 0.05≤s / (s+t)≤1.0.

[0057] s is preferably s≥5, more preferably s≥10, s≤100, more preferably s≤50.

[0058] t is preferably t≥5, more preferably t≥10, t≤100, more preferably t≤70.

[0059] s+t is preferably a number of 12≤s+t≤80, and more preferably a number of 15≤s+t≤60. If s+t is less than 8, it volatilizes during curing, and if it exceeds 100, the viscosity of the composition increases, making it difficult to remove bubbles and also worsening workability.

[0060] s / (s+t) is 0.05 ≤ s / (s+t) ≤ 1.0, and preferably 0.2 ≤ s / (s+t) ≤ 0.8. If it is less than 0.05, the rubber properties of the resulting cured product are insufficient.

[0061] (C) Specific examples of the organohydrogenpolysiloxane of the component include dimethylsiloxane-methylhydrogensiloxane copolymer with trimethylsiloxy groups blocked at both ends of the molecular chain represented by the following average formula, and methylhydrogenpolysiloxane with trimethylsiloxy groups blocked at both ends of the molecular chain.

[0062] In addition, (C) ingredient may be used as a single type or in combination with two or more types.

[0063]

[0064] (In the formula, the arrangement of siloxane units is arbitrary.)

[0065] In the room temperature curing silicone rubber composition of the present invention, the total number of SiH groups in components (B) and (C) for one vinyl group in component (A) is 0.7 to 2.5, preferably 1.0 to 2.0. If it is less than 0.7, crosslinking becomes insufficient, and if it exceeds 2.5, foaming due to the generation of hydrogen gas during curing is likely to occur, and transparency or rubber strength is reduced due to the occurrence of voids inside the cured product.

[0066] In addition, the ratio of the number of SiH groups in component (B) to the sum of the number of SiH groups in components (B) and (C) is 0.05 to 0.6, and preferably 0.08 to 0.55. If it is less than 0.05, the rubber properties after curing become brittle, and if it exceeds 0.6, the tackiness becomes strong and workability deteriorates.

[0067] [4] (D) component

[0068] Component (D) is a hydrosilylation catalyst for promoting the hydrosilylation reaction between the alkenyl groups in component (A) and the SiH groups in components (B) and (C).

[0069] (D) As a catalyst for the hydrosilylation reaction component, a platinum group metal catalyst is preferred, and specific examples thereof include platinum black, platinum chloride, chloroplatinic acid, a reaction product of chloroplatinic acid and a monohydric alcohol, a complex of chloroplatinic acid and an olefin, platinum-bisacetoacetate, etc., platinum-based catalysts such as tetrakis(triphenylphosphine)palladium, dichlorobis(triphenylphosphine)palladium, etc., rhodium-based catalysts such as chlorotris(triphenylphosphine)rhodium, tetrakis(triphenylphosphine)rhodium, etc.

[0070] (D) The amount of component (D) is 15 ppm or less in terms of mass of platinum group metal atoms in the component with respect to the total of components (A) to (C), preferably 10 ppm or less, and 0.1 ppm or more, particularly 0.5 ppm or more. Within this range, the reaction rate of the addition reaction becomes appropriate, and the discoloration of the cured product by metal atoms derived from the catalyst can be suppressed.

[0071] [5] (E) component

[0072] In the room temperature curable silicone rubber composition of the present invention, (E) a reaction control agent may be added as needed for the purpose of controlling the reactivity of the hydrosilylation reaction catalyst so as not to cause thickening or gelation when preparing the composition or before heat curing.

[0073] Specific examples of reaction control agents include 3-methyl-1-butyn-3-ol, 3-methyl-1-pentyn-3-ol, 3,5-dimethyl-1-hexine-3-ol, 1-ethynylcyclohexanol, ethinylmethyldecylcarbinol, 3-methyl-3-trimethylsiloxy-1-butyn, 3-methyl-3-trimethylsiloxy-1-pentyn, 3,5-dimethyl-3-trimethylsiloxy-1-hexine, 1-ethynyl-1-trimethylsiloxycyclohexane, bis(2,2-dimethyl-3-butynoxy)dimethylsilane, 1,3,5-trimethyl-1,3,5-trivinylcyclotetrasiloxane, 1,3,5,7-tetramethyl-1,3,5,7-tetravinylcyclotetrasiloxane, Examples include 1,1,3,3-tetramethyl-1,3-divinyldisiloxane, etc., and these may be used as a single type or in combination of two or more types.

[0074] Among these, 1,3,5,7-tetramethyl-1,3,5,7-tetravinylcyclotetrasiloxane is preferred.

[0075] When using component (E), the amount added is preferably 0.001 to 2 parts by mass and more preferably 0.006 to 1.5 parts by mass per 100 parts by mass of the total of components (A) to (C). Within this range, the effect of reaction control is sufficiently exhibited.

[0076] [6] Other ingredients

[0077] In addition to the components (A) to (E) above, other components exemplified below may be incorporated into the room temperature curing silicone rubber composition of the present invention, provided that the purpose of the present invention is not impaired.

[0078] Other components include fillers such as fumed silica, crystalline silica (quartz powder), precipitated silica, and silica with their surfaces hydrophobically treated; conductive agents such as iron oxide, carbon black, conductive zinc oxide, and metal powder; heat-resistant agents such as titanium oxide and cerium oxide; internal release agents such as dimethyl silicone oil; adhesion promoters; thixotropic agents; and coloring agents.

[0079] The room temperature curable silicone rubber composition of the present invention can be prepared by mixing the above components (A) to (D), component (E) used as needed, and other components using a known method with a kneader, a planetary mixer, etc.

[0080] The room temperature curing silicone rubber composition of the present invention may be a two-part composition in which a first part comprising component (A), component (D), and other components as needed, and a second part comprising component (A), component (B), component (C), and other components as needed, are prepared separately, and the first part and the second part are mixed before use. Additionally, there may be components that are commonly used in both the first part and the second part. By making the composition such a two-part composition, storage stability can be further ensured.

[0081] The curing of the room temperature curable silicone rubber composition of the present invention may employ known curing methods and conditions. For example, it may be cured by leaving it at 10 to 40°C for 24 hours or more.

[0082] It is preferable that the difference between the durometer A hardness of a cured product cured at 23°C for 24 hours and the durometer A hardness of a cured product cured at 23°C for 72 hours of the room temperature curable silicone rubber composition of the present invention is 1 or less.

[0083] In addition, the cured product obtained by curing the room temperature curable silicone rubber composition of the present invention under conditions of 23°C and 24 hours preferably has a transmittance of 90% or more of light with a wavelength of 400 nm at a thickness of 2 mm.

[0084] [Example]

[0085] The present invention will be explained more specifically below with reference to examples and comparative examples, but the present invention is not limited to these examples.

[0086] [Examples 1-1 to 1-4, Comparative Examples 1-1 to 1-4]

[0087] A silicone rubber composition was prepared by mixing the following components in the mixing ratio (parts by mass) shown in Table 1. Additionally, the viscosity is the value at 23°C measured by a rotational viscometer.

[0088] (A) Ingredients:

[0089] (A-1) Organopolysiloxane represented by the following average formula (viscosity: 600 mPa·s)

[0090]

[0091] (A-2) Organopolysiloxane represented by the following average formula (viscosity: 100 mPa·s)

[0092]

[0093] (A-3: Comparative component) Organopolysiloxane represented by the following average formula (viscosity: 1,200 mPa·s)

[0094]

[0095] (B) Ingredients:

[0096] (B-1) Organohydrogenpolysiloxane represented by the following average formula

[0097]

[0098] (C) Ingredient:

[0099] (C-1) Organohydrogenpolysiloxane represented by the following average formula

[0100]

[0101] (In the formula, the arrangement of siloxane units is random or block.)

[0102] (C-2) Organohydrogenpolysiloxane represented by the following average formula

[0103]

[0104] (In the formula, the arrangement of siloxane units is random or block.)

[0105] (D) Ingredient:

[0106] (D-1) Toluene solution of platinum chloride-divinyltetramethyldisiloxane complex (mass concentration of platinum 1%)

[0107] (E) Ingredients:

[0108] (E-1) 1,3,5,7-tetramethyl-1,3,5,7-tetravinylcyclotetrasiloxane

[0109]

[0110] 1) Ratio of the number of SiH groups in components (B) and (C) to the number of vinyl groups in component (A)

[0111] 2) Ratio of the number of SiH groups in component (B) to the sum of the number of SiH groups in components (B) and (C)

[0112] [Examples 2-1 to 2-4, Comparative Examples 2-1 to 2-3]

[0113] Each of the following characteristics was evaluated using the silicone rubber compositions prepared in Examples 1-1 to 1-4 and Comparative Examples 1-1 to 1-3.

[0114] [Air wicking]

[0115] The composition, immediately after mixing until the height reached 50 mm, was poured into a glass bottle with an inner diameter of 40 mm and a height of 60 mm, and cured at 23°C for 10 hours. The cured product was visually observed and evaluated as ○ if bubbles were removed and × if bubbles remained. The results are shown in Table 2.

[0116] [Light transmittance]

[0117] For a sheet in which the composition was poured into a mold to a thickness of 2 mm and cured at 23°C for 24 hours, the light transmittance at a wavelength of 400 nm was measured using a spectrophotometer U-3900 (manufactured by Hitachi High-Tech Science Corp.). The results are shown in Table 2.

[0118] [Tensile strength, elongation at break]

[0119] For dumbbell specimen No. 2, which was poured into a mold to a thickness of 2 mm and cured at 23°C for 24 hours, the tensile strength (MPa) and elongation at break (%) were measured in accordance with JIS K 6249:2003. The results are shown in Table 2.

[0120] [hardness]

[0121] The composition was poured into a mold to a thickness of 2 mm, and the hardness (Durometer A) of the cured product, cured at 23°C for 24 hours, was measured in accordance with JIS K 6253-3:2012. In addition, the hardness of the cured product, cured at 23°C for 72 hours, was measured in the same manner. The results are shown in Table 3.

[0122]

[0123]

[0124] As shown in Tables 2 and 3, it can be seen that the room temperature curable silicone rubber compositions of Examples 2-1 to 2-4 are room temperature curable silicone rubber compositions that provide excellent bubble wicking properties and physical properties after curing, as well as highly transparent cured products with small changes in hardness.

[0125] Meanwhile, in Comparative Example 2-1, where the ratio of the number of SiH groups in components (B) and (C) to the number of vinyl groups in component (A) did not satisfy the scope of the present invention, the change in hardness of the cured product was large.

[0126] (D) In ​​Comparative Example 2-2, where the amount of added component exceeds the upper limit of the scope of the present invention, a decrease in light transmittance due to discoloration occurred.

[0127] In addition, in Comparative Example 2-3, which used a vinyl group-containing organopolysiloxane with high viscosity (m greater than 200) instead of component (A), the bubble-repelling ability was poor.

Claims

Claim 1 (A) Organopolysiloxane Vi represented by the following average formula (1), having a viscosity of 10 to 500 mPa·s at 23°C. (3-a) R 1 a Si(OR 1 2Si) m OSiR 1 a Vi (3-a) (1)(In the food, R 1 is an unsubstituted or substituted monovalent hydrocarbon group that does not independently contain an alkenyl group, Vi is a vinyl group, m is a number from 13 to 200, and a is a number from 0 to 2.)(B) Organohydrogenpolysiloxane represented by the following average formula (2) (HR 1 2SiO 1 / 2 )2(R 1 2SiO 2 / 2 ) n (2)(In the food, R 1 ...is the same as above, and n is a number from 10 to 80.)(C) Organohydrogenpolysiloxane (R) represented by the following average formula (3). 1 3SiO 1 / 2 )2(HR 1 1SiO 2 / 2 ) s (R 1 2SiO 2 / 2 ) t (3)(In food, R 1 (D) A room temperature curing silicone rubber composition for sealing ornamental specimens, three-dimensional models, or decorative items, containing a hydrosilylation reaction catalyst, wherein the total number of SiH groups in components (B) and (C) per vinyl group in component (A) is 0.7 to 2.5, the ratio of the number of SiH groups in component (B) to the total number of SiH groups in components (B) and (C) is 0.05 to 0.6, and the content of metal atoms derived from the hydrosilylation reaction catalyst in component (D) is 15 mass ppm or less relative to the total amount of components (A) to (C). Claim 2 A room temperature curing silicone rubber composition according to claim 1, wherein the viscosity of component (A) at 23°C is 10 to 100 mPa·s. Claim 3 A room temperature curable silicone rubber composition according to claim 1 or 2, wherein the total number of SiH groups in components (B) and (C) per vinyl group in component (A) is 1.0 to 2.

0. Claim 4 A silicone rubber formed by curing a room-temperature curing silicone rubber composition described in claim 1 or 2, and used for sealing ornamental specimens, three-dimensional models, or decorative items. Claim 5 In claim 4, silicone rubber in which the difference between the durometer A hardness of a cured product cured at 23°C for 24 hours and the durometer A hardness of a cured product cured at 23°C for 72 hours is 1 or less. Claim 6 In paragraph 4, silicone rubber having a transmittance of 90% or more of light with a wavelength of 400 nm at a thickness of 2 mm.

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