TWI883011B - Room temperature curing silicone rubber composition - Google Patents

Abstract

The subject of the present invention is to provide a room temperature curing silicone rubber composition that significantly reduces yellowing or bubble inclusions and provides a cured product with little hardness variation. The solution of the present invention is a room temperature curing type silicone rubber composition, which contains (A) a linear organic polysiloxane having vinyl groups at both ends of the molecular chain, (B) a linear organic hydropolysiloxane having SiH groups at both ends of the molecular chain, (C) a linear organic hydropolysiloxane capped with triorganosilyl groups at both ends of the molecular chain, and (D) a hydrosilylation reaction catalyst, wherein the total number of SiH groups in the components (B) and (C) relative to the SiVi groups in the component (A) is 0.7 to 2.5, and the ratio of the number of SiH groups in the component (B) to the total number of SiH groups in the components (B) and (C) is 0.05 to 0.6.

Description

Room temperature curing silicone rubber composition

The present invention relates to an addition-curing polysilicone rubber composition which cures at room temperature and gives a highly transparent cured product.

Highly transparent silicone rubber materials are widely used in optical device materials, 3D printer materials, nano-printing materials, etc. In addition, due to its excellent durability, it is proposed to seal dried flowers or three-dimensional models in silicone gel or silicone rubber to form ornamental moldings (patent documents 1, 2). The silicone rubber used for such potting is liquid before hardening, and is mixed with a hardener and simply hardened at room temperature or by heating to become a highly transparent rubber material.

However, such silicone rubber materials have the problem that bubbles generated during mixing remain after hardening, or the material turns yellow due to coloring by metal catalysts after long-term storage, and the shrinkage after hardening causes peeling at the interface between the silicone rubber and the container or enclosure. [Prior Art Literature] [Patent Literature]

[Patent document 1] Japanese Patent Publication No. 8-92002 [Patent document 2] Japanese Patent Publication No. 2000-336269

[Problems to be solved by the invention]

The present invention was completed in view of the above situation, and aims to provide a room temperature curing silicone rubber composition that greatly reduces yellowing or bubble rolling and provides a cured product with little hardness change. [Means for solving the problem]

As a result of intensive research to achieve the above-mentioned object, the inventors have found that the following specific addition-curing silicone rubber composition reduces the occurrence of air bubble entrainment during mixing, and provides a silicone rubber with high transparency and little hardness change, thereby completing the present invention.

That is, the present invention provides: 1. A room temperature curing polysilicone rubber composition, characterized by containing: (A) an organic polysiloxane represented by the following average formula (1): (wherein, ^R1 is an independent unsubstituted or substituted monovalent alkyl group not including 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) an organohydropolysiloxane represented by the following average formula (2): (wherein, ^R1 is the same as above, and n is a number from 10 to 80) (C) an organohydropolysiloxane represented by the following average formula (3): (wherein, ^R1 is the same as above, s and t satisfy s≧2 and t≧0 respectively, are 8≦s+t≦100, and satisfy 0.05≦s/(s+t)≦1.0) (D) Hydrosilylation reaction catalyst, 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), 2. A room temperature curing polysilicone rubber composition as described in 1, wherein the viscosity of component (A) at 23°C is 10 to 700 mPa•s. 3. A room temperature curing polysilicone 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. 4. A polysilicone rubber obtained by curing the room temperature curing polysilicone rubber composition as described in any one of 1 to 3. 5. A polysilicone rubber as described in 4, wherein the difference between the durometer A hardness of the cured product cured at 23°C for 24 hours and the durometer A hardness of the cured product cured at 23°C for 72 hours is 1 or less. 6. The polysilicone rubber as described in 4 or 5, wherein the transmittance of light with a wavelength of 400 nm at a thickness of 2 mm is 90% or more. [Effect of the invention]

The room temperature curing silicone rubber composition of the present invention is suitable for sealing specimens, three-dimensional models, decorations, etc. in herbariums, etc., because it provides a silicone rubber with excellent bubble removal, high transparency and little hardness change.

The present invention is described in more detail below. The room temperature curing type silicone rubber composition of the present invention contains the following components (A) to (D). (A) Organic polysiloxane containing vinyl groups at both ends of the molecular chain (B) Organic hydropolysiloxane containing SiH groups at both ends of the molecular chain (C) Organic hydropolysiloxane capped with triorganosilyl groups at both ends of the molecular chain (D) Hydrosilylation reaction catalyst

[1] Component (A) Component (A) is a linear organic polysiloxane having vinyl groups at both ends of the molecular chain represented by the following average formula (1).

R ¹ is independently an unsubstituted or substituted monovalent alkyl group other than an alkenyl group, and Vi represents a vinyl group (hereinafter the same). R ¹ is not particularly limited as long as it does not have an alkenyl group, and may be any of a linear, branched, or cyclic type, but is preferably a monovalent alkyl group having 1 to 20 carbon atoms, more preferably a monovalent alkyl group having 1 to 10 carbon atoms, and still more preferably a monovalent alkyl group having 1 to 5 carbon atoms. Specific examples thereof include linear or branched alkyl groups such as methyl, ethyl, n-propyl, isopropyl, n-butyl, tert-butyl, and n-hexyl; cyclic alkyl groups such as cyclohexyl; aryl groups such as phenyl and tolyl; and aralkyl groups such as benzyl and phenylethyl. Furthermore, part or all of the hydrogen atoms of these monovalent alkyl groups may be substituted by halogen atoms such as F, Cl, Br, cyano groups, etc. Specific examples of such groups include halogen-substituted alkyl groups such as 3,3,3-trifluoropropyl, and cyano-substituted alkyl groups such as 2-cyanoethyl. Among these, methyl groups are preferred.

a is a number between 0 and 2, preferably between 0 and 1.8. m is a number between 13 and 200, preferably between 30 and 190, and more preferably between 70 and 180. When m is smaller than 13, it causes volatility during hardening, and when it is larger than 200, the air bubble removal during mixing of the composition is deteriorated, and the workability is deteriorated.

The viscosity of component (A) at 23°C is preferably 10 to 700 mPa•s, more preferably 20 to 500 mPa•s, from the viewpoint of easily removing bubbles generated when mixing the composition and hardening the composition into a rubbery elastic body. In addition, the viscosity in the present invention is a value measured using a rotary viscometer.

Examples of such component (A) include organic polysiloxane represented by the following average formula. Component (A) may be used alone or in combination of two or more.

[2] Component (B) Component (B) is a linear organic hydropolysiloxane having hydrogen atoms (i.e., SiH groups) bonded to silicon atoms at both ends of the molecular chain represented by the average formula (2) below. It is a component that extends the siloxane chain by a hydrosilylation reaction with the vinyl groups at the ends of the molecular chain of component (A), thereby imparting rubber properties to the cured product.

R ¹ is the same as described above. Specifically, it includes the same unsubstituted or substituted monovalent hydrocarbon groups as those exemplified in the above average formula (1) except for the alkenyl groups. Among them, methyl group is particularly preferred.

n is 10 to 80, preferably 10 to 50, and more preferably 10 to 30. When n is less than 10, the components may volatilize during hardening, and when n is greater than 80, the viscosity of the composition increases, making it difficult to remove bubbles and deteriorating the workability.

Specific examples of the component (B) include those represented by the following average formula. In addition, the component (B) may be used alone or in combination of two or more.

[3] Component (C) Component (C) is a linear organic hydropolysiloxane represented by the following average formula (3) in which both ends of the molecular chain are capped with triorganosilyl groups, and is used as a crosslinking agent by undergoing a hydrosilylation reaction with the vinyl groups in component (A).

R ¹ is the same as described above. Specifically, it includes the same unsubstituted or substituted monovalent hydrocarbon groups as those exemplified in the above average formula (1) except for the alkenyl groups. Among them, methyl group is particularly preferred.

s and t satisfy s≧2, t≧0, respectively, and satisfy 8≦s+t≦100, 0.05≦s/(s+t)≦1.0. s is preferably s≧5, more preferably s≧10, more preferably s≦100, more preferably s≦50. t is preferably t≧5, more preferably t≧10, more preferably t≦100, more preferably t≦70. s+t is preferably 12≦s+t≦80, more preferably 15≦s+t≦60. When s+t is less than 8, it will volatilize during hardening. When it exceeds 100, the viscosity of the composition will increase, making it difficult to remove bubbles and deteriorating the workability. s/(s+t) is 0.05≦s/(s+t)≦1.0, preferably 0.2≦s/(s+t)≦0.8. When it is less than 0.05, the rubber properties of the hardened product will be insufficient.

Specific examples of the organohydropolysiloxane as component (C) include dimethylsiloxane·methylhydrosiloxane copolymers with trimethylsiloxy groups at both ends of the molecular chain represented by the following average formula, and methylhydropolysiloxane with trimethylsiloxy groups at both ends of the molecular chain. Component (C) may be used alone or in combination of two or more.

(wherein the arrangement of the siloxane units is arbitrary).

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

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, preferably 0.08 to 0.55. If it is less than 0.05, the rubber will become brittle after curing, and if it exceeds 0.6, the adhesiveness will increase and the workability will deteriorate.

[4] Component (D) Component (D) is a hydrosilylation reaction catalyst for promoting the hydrosilylation reaction between the alkenyl group in component (A) and the SiH group in components (B) and (C). The catalyst for the hydrosilylation reaction as component (D) is preferably a platinum group metal catalyst. Specific examples thereof include platinum black, secondary platinum chloride, chloroplatinic acid, a reaction product of chloroplatinic acid and a monohydric alcohol, a complex of chloroplatinic acid and an olefin, a platinum-based catalyst such as diacetylacetate, a palladium-based catalyst such as tetrakis(triphenylphosphine)palladium, dichlorobis(triphenylphosphine)palladium, and a rhodium-based catalyst such as chlorotris(triphenylphosphine)rhodium and tetrakis(triphenylphosphine)rhodium.

The amount of component (D) added is 15 ppm or less, preferably 10 ppm or less, 0.1 ppm or more, and particularly preferably 0.5 ppm or more, based on the mass of platinum group metal atoms in the component relative to the total amount of components (A) to (C). Within this range, the reaction rate of the addition reaction becomes appropriate, and the coloring of the cured product caused by the metal atoms from the catalyst can be suppressed.

[5] (E) Component In the room temperature curing type silicone rubber composition of the present invention, a reaction control agent (E) may be added if necessary for the purpose of controlling the reactivity of the catalyst for the hydrosilylation reaction in a manner that does not cause viscosity increase or gelation during preparation of the composition or before heat curing.

Specific examples of the reaction control agent include 3-methyl-1-butyne-3-ol, 3-methyl-1-pentyne-3-ol, 3,5-dimethyl-1-hexyne-3-ol, 1-ethynylcyclohexanol, ethynylmethyldecylmethanol (Carbinol), 3-methyl-3-trimethylsilyloxy-1-butyne, 3-methyl-3-trimethylsilyloxy-1-pentyne, 3,5-dimethyl-3-trimethylsilyloxy-1-hexyne, 1- Ethylene-1-trimethylsiloxycyclohexane, bis(2,2-dimethyl-3-butynyloxy)dimethylsilane, 1,3,5-trimethyl-1,3,5-trivinylcyclotetrasiloxane, 1,3,5,7-tetramethyl-1,3,5,7-tetravinylcyclotetrasiloxane, 1,1,3,3-tetramethyl-1,3-divinyldisiloxane, etc. These can be used alone or in combination of two or more. Among these, 1,3,5,7-tetramethyl-1,3,5,7-tetravinylcyclotetrasiloxane is preferred.

When component (E) is used, its addition amount is preferably 0.001 to 2 parts by mass, more preferably 0.006 to 1.5 parts by mass, based on 100 parts by mass of the total of components (A) to (C). Within this range, the effect of reaction control is fully exerted.

[6] Other components In addition to the above-mentioned components (A) to (E), the room temperature curing silicone rubber composition of the present invention may also contain other components as listed below, as long as they do not impair the purpose of the present invention. As other components, fillers such as fumed silica, crystalline silica (quartz powder), precipitated silica, silica having a hydrophobic surface, conductive agents such as iron oxide, carbon black, conductive zinc oxide, and metal powder; heat resistant agents such as titanium oxide and calcium oxide; internal mold release agents such as dimethyl polysilicone oil; adhesion imparting agents; thixotropic imparting agents; coloring agents, etc. can be listed.

The room temperature curing polysilicone rubber composition of the present invention can be prepared by mixing the above-mentioned (A) to (D) components, the (E) component used if necessary, and other components using a known method such as a kneader, a planetary mixer, etc. The room temperature curing polysilicone rubber composition of the present invention can be prepared by separately preparing a first agent comprising the (A) component, the (D) component, and other components if necessary, and a second agent comprising the (A) component, the (B) component, the (C) component, and other components if necessary, and can be a two-part composition in which the first agent and the second agent are mixed before use. In addition, it can be a component commonly used in the first agent and the second agent. By setting the composition as such a two-part composition, storage stability can be further ensured.

The room temperature curing type silicone rubber composition of the present invention can be cured by known curing methods and conditions. For example, it can be cured by standing at 10-40°C for more than 24 hours.

The difference between the durometer A hardness of the room temperature curing polysilicone rubber composition of the present invention cured at 23°C for 24 hours and the durometer A hardness of the cured product cured at 23°C for 72 hours is preferably 1 or less. In addition, the room temperature curing polysilicone rubber composition of the present invention cured at 23°C for 24 hours preferably has a transmittance of 90% or more at a wavelength of 400nm at a thickness of 2mm. [Example]

Although the present invention is described below with reference to embodiments and comparative examples, the present invention is not limited to these embodiments.

[Examples 1-1 to 1-4, Comparative Examples 1-1 to 1-4] The following components were mixed in the blending ratio (mass parts) shown in Table 1 to prepare a silicone rubber composition. The viscosity is the value measured at 23°C using a rotary viscometer.

(A) Components: (A-1) Organic polysiloxane represented by the following average formula (viscosity: 600 mPa•s) (A-2) Organic polysiloxane represented by the following average formula (viscosity: 100 mPa•s) (A-3: Comparative component) Organic polysiloxane represented by the following average formula (viscosity: 1,200 mPa•s)

(B) Component: (B-1) an organohydropolysiloxane represented by the following average formula

(C) Component: (C-1) an organohydropolysiloxane represented by the following average formula (In the formula, the arrangement of the siloxane units is random or blocky.) (C-2) An organohydropolysiloxane represented by the following average formula: (wherein the arrangement of the siloxane units is random or block).

(D) Ingredients: (D-1) Toluene solution of chloroplatinic acid-divinyltetramethyldisiloxane complex (concentration based on mass of platinum: 1%)

(E) Ingredients: (E-1) 1,3,5,7-Tetramethyl-1,3,5,7-tetravinylcyclotetrasiloxane

1) Ratio of the number of SiH groups in components (B) and (C) to the number of vinyl groups in component (A) 2) Ratio of the number of SiH groups in component (B) to the total number of SiH groups in components (B) and (C)

[Examples 2-1 to 2-4, Comparative Examples 2-1 to 2-3] The following properties were evaluated using the silicone rubber compositions prepared in Examples 1-1 to 1-4 and Comparative Examples 1-1 to 1-3. [Bubble Removal] The composition was poured into a glass bottle with an inner diameter of 40 mm and a height of 60 mm until the height just reached 50 mm, and hardened at 23°C for 10 hours. The hardened product was visually observed, and the one with bubble removal was evaluated as 0, and the one with bubble residue was evaluated as ×. The results are shown in Table 2. [Light transmittance] For a plate in which the composition was poured into a mold having 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-Technologies Co., Ltd.). The results are shown in Table 2. [Tensile strength, elongation at break] For a No. 2 dumbbell test piece in which the composition was poured into a mold having 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. [Hardness] The composition was poured into a 2mm thick mold and hardened at 23°C for 24 hours. The hardness (durometer A) of the hardened product was measured in accordance with JIS K 6253-3:2012. The hardness of the hardened product was also measured at 23°C for 72 hours. The results are shown in Table 3.

As shown in Table 2 and Table 3, it is understood that the room temperature curing type silicone rubber compositions of Examples 2-1 to 2-4 are room temperature curing type silicone rubber compositions that eliminate bubbles or have excellent physical properties after curing, and provide highly transparent cured products with little hardness change. On the other hand, in Comparative Example 2-1, in which the ratio of the number of SiH groups in the (B) and (C) components to the number of vinyl groups in the (A) component does not meet the range of the present invention, the hardness change of the cured product is large. In Comparative Example 2-2, in which the addition amount of the (D) component exceeds the upper limit of the range of the present invention, a decrease in light transmittance occurs due to discoloration. In Comparative Example 2-3, in which a high-viscosity (m exceeding 200) vinyl-containing organopolysiloxane is used instead of component (A), the deterioration of the bubble property is eliminated.

Claims (4)

A room temperature curing silicone rubber composition is characterized by comprising: (A) an organic polysiloxane Vi (3-a) R ¹ _a Si(OR ¹ 2 Si) m OSiR 1 a Vi _{(3-a) ( 1} ) having a viscosity of ¹⁰ to 100 _mPa‧s at ₂₃ °C and represented by _the following average formula (1) (wherein R ¹ is an independent non-substituted or substituted monovalent hydrocarbon group not including an alkenyl group, Vi is a vinyl group, m is a number of 13 to 200, and a is a number of 0 to 2) (B) an organic hydrogen polysiloxane (HR ¹ ₂ SiO _1/2 ) ₂ (R ¹ ₂ SiO _2/2 ) _n (2) having an average formula (2) (wherein R ¹ is the same as above, and n is a number between 10 and 80) (C) an organohydropolysiloxane represented by the following average formula (3): (R ¹ ₃ SiO _1/2 ) ₂ (HR ¹ ₁ SiO _2/2 ) _s (R ¹ ₂ SiO _2/2 ) _t (3) (wherein R ¹ is the same as above, s and t satisfy s≧2, t≧0 respectively, are 8≦s+t≦100, and satisfy 0.05≦s/(s+t)≦1.0) (D) hydrosilylation reaction catalyst, the total number of SiH groups in components (B) and (C) per vinyl group in component (A) is 1.0-2.0, the ratio of the number of SiH groups in component (B) to the total number of SiH groups in components (B) and (C) is 0.05-0.6, and the content of metal atoms in the hydrosilylation reaction catalyst derived from component (D) is 15 mass ppm or less relative to the total amount of components (A) to (C). A polysilicone rubber, which is obtained by hardening the room temperature curing polysilicone rubber composition described in claim 1. For example, the silicone rubber of claim 2, wherein the difference between the durometer A hardness of the cured product cured at 23°C for 24 hours and the durometer A hardness of the cured product cured at 23°C for 72 hours is 1 or less. For example, the silicone rubber of claim 2 or 3, wherein the transmittance of light with a wavelength of 400 nm at a thickness of 2 mm is greater than 90%.