JPH0784562B2 - Room temperature curable polyorganosiloxane composition - Google Patents

Description

Description: TECHNICAL FIELD OF THE INVENTION The present invention forms an ultra-low hardness rubber-like elastic body which is rapidly cured at room temperature and has a non-adhesive surface after curing and excellent wear resistance. Polyorganosiloxane composition.

[Technical background of the invention and its problems]

Condensation of polyorganosiloxane having hydroxyl groups at both ends of the molecular chain, an alkoxysilane having at least three alkoxy groups in the molecule as a cross-linking agent, and / or a partial hydrolysis condensate thereof and an organotin compound catalyst Room temperature curable liquid silicone rubber compositions are well known and widely used in various fields as room temperature curable silicone rubbers.

When the condensation type room temperature curable liquid silicone rubber composition has an extremely low hardness (hardness JIS A is 5 or less), the amount of the crosslinking agent is reduced or both ends of the molecular chain are blocked with triorganosilyl groups. It is known to add polyorganosiloxane (silicone oil).

However, in any of these cases, surface tack (a phenomenon in which the rubber surface becomes sticky and sticky) occurs on the cured rubber surface, and the abrasion resistance is deteriorated.

That is, when a conventional condensation type room temperature curable liquid silicone rubber having a low hardness is used, for example, in a printing pad, the surface thereof is sticky, so that the printability such as the transferability of the ink is poor, and the relatively short period. As a result, the rubber surface becomes worn and it is no longer possible to fulfill its function. In addition, when it is formed into a roll shape on a metal core bar and is rotated in contact with another substance,
Since the surface is sticky, the two stick to each other, and due to the large abrasion of the rubber, a gap is created between the rolls, not only the function as the roll cannot be fulfilled, but also the worn rubber is in contact. There is a disadvantage that the quality of the contact substance is impaired by transfer to a substance, and in order to solve these disadvantages, it is necessary to coat the surface portion of the rubber with another material.

[Object of the Invention]

An object of the present invention is to provide a room temperature curable polyorganosiloxane composition which solves such drawbacks and provides a low hardness silicone rubber having a non-adhesive surface and excellent abrasion resistance.

[Structure of Invention]

The present inventors have conducted various studies on the reduction of the hardness of the condensation-type room temperature curable liquid silicone rubber, and further on the surface tack and abrasion resistance improvement measures of the condensation-type room temperature-curable liquid silicone rubber. The present inventors have found that it is effective to blend a room temperature curable liquid silicone rubber composition with a copolymer of a polyoxyalkylene compound and a polyorganosiloxane, and completed the present invention.

That is, according to the present invention, (A) both ends of a molecular chain are blocked with silanol groups,
10 to 40% by weight of linear polydiorganosiloxane having a viscosity of 100 to 100,000 cP at 0 ° C, one end of the molecular chain is blocked with a silanol group, the other end is blocked with a triorganosilyl group, and the viscosity at 25 ° C is 100. To 100,000 cP linear polydiorganosiloxane 90-60% by weight 100 parts by weight (B) Polyoxyalkylene compound and polyorganosiloxane copolymer 0.5-50 parts by weight (C) General formula R ¹ Si (OR ² ) ₃ (wherein R ¹ represents a monovalent hydrocarbon group or OR ² and R ² represents a monovalent hydrocarbon group) and / or a partial hydrolysis-condensation product thereof. Provided is a room temperature curable polyorganosiloxane composition comprising 0.5 to 20 parts by weight (D) 0.5 to 100 parts by weight of fumed silica having a hydrophobic surface and (E) 0.01 to 5 parts by weight of a curing catalyst. Do Than it is.

Of the component (A) used in the present invention, a linear polydiorganosiloxane in which both ends of the molecular chain are capped with silanol groups has the general formula (In the formula, R ³ and R ⁴ are the same or different, substituted or unsubstituted monovalent hydrocarbon groups, and m is an integer which makes the viscosity of this compound at 25 ° C. 100-100,000 cP). There are things.

Here, R ³ and R ⁴ are methyl group, ethyl group, propyl group, alkyl group such as butyl group, aryl group such as phenyl group,
Preferable examples are aralkyl groups such as β-phenylethyl group and β-phenylpropyl group, and further preferable examples are substituted hydrocarbon groups such as chloromethyl group and 3,3,3-trifluoropropyl group. . Of these, a methyl group is most preferable because it is easy to synthesize, maintains good physical properties after curing, and has a low viscosity before curing.

Further, in order for the composition of the present invention to exhibit good fluidity, and the cured silicone rubber obtained therefrom to exhibit good rubber elasticity and to have excellent mechanical strength, the linear polydiene Organosiloxane is 100 to 100,000 cP (25
It is required to have a viscosity in the range of (° C.).

A linear polydiorganosiloxane in which both ends of this molecular chain are used in combination with a linear polydiorganosiloxane blocked with silanol groups. One end of the molecular chain is blocked with a silanol group and the other end is blocked with a triorganosilyl group. As the general formula (In the formulas, R ⁵ , R ⁶ , and R ⁷ are the same or different from each other, substituted or unsubstituted monovalent hydrocarbon groups, and n is an integer that makes the viscosity of this compound at 25 ° C. 100 to 10,000 cP.) The items shown in are listed. These R ⁵ , R ⁶ and R ⁷ are the above R ³ and R
^{The same as 4} is exemplified as a preferable example, and among these, the methyl group is the most preferable because it is easy to synthesize, and has good physical properties after curing and has a low viscosity before curing. preferable.

Further, in order for the composition of the present invention to exhibit good fluidity, and the cured silicone rubber obtained therefrom to exhibit good rubber elasticity and to have excellent mechanical strength, the linear polydiene Organosiloxane is 100 to 10,000 cP (25
It is necessary to have a viscosity in the range of (° C.). In order for the cured silicone rubber obtained from the composition of the present invention to have an appropriately low hardness, the mixing ratio of the two kinds of polysiloxane used in (A) is set to a linear polydiene having silanol groups at both molecular chain terminals. Organosiloxane 10-40% by weight
In contrast, the other linear polydiorganosiloxane 90-
It should be 60% by weight.

If the compounding amount of the former polysiloxane is too small, the hardness of the rubber obtained from such a composition will be too low and it will become brittle. On the other hand, if the amount is too large, the hardness of the rubber becomes high, making it unsuitable for printing.

The component (B) used in the present invention is a copolymer of a polyoxyalkylene compound and polyorganosiloxane.
The component (B) is hydrophilic, has good compatibility with printing ink, and plays a role of improving printability when the cured silicone rubber obtained from the composition of the present invention is used in a printing pad. Examples of the organic group bonded to the silicon atom of the polyorganosiloxane include a methyl group, an ethyl group, an alkyl group such as a propyl group, and an aryl group such as a phenyl group, except for the junction with the polyoxyalkylene moiety. A methyl group is preferred for ease of synthesis. Examples of polyoxyalkylenes include polyoxyethylene, polyoxypropylene, and copolymers of oxyethylene units and oxypropylene units.

The end of the molecular chain of the polyoxyalkylene moiety is a hydroxyl group,
Either a methoxy group or a butoxy group may be used. The junction of polyoxyalkylene and polyorganosiloxane is
From the viewpoint of long-term hydrolysis resistance, it is preferable that at least 3 carbon atoms are present between the silicon atom and the first oxygen atom of the polyoxyalkylene moiety. As an example of such a bond, a chain propylene chain is used. Examples thereof include a group, a chain butylene group, and a γ- (β-hydroxypropylene) oxypropyl group. In the molecular structure of such a polyoxyalkylene-polyorganosiloxane copolymer, the polysiloxane skeleton may be linear or branched, and the polyoxyalkylene may be grafted at the end of the polyorganosiloxane or as a side chain. It may be either.

Specifically preferred component (B) is (B) a copolymer of a polyoxyalkylene compound represented by the following general formula and a polyorganosiloxane.

(In the formula, R ⁸ is the same or different alkyl group or aryl group, R ⁹ is H, CH ₃ or (CH ₂ ) ₂ CH ₃ , p, q
Is an integer of 1 or more, and generally about 1 to 10 is preferable. x is an integer of 3 or more, and generally about 3 to 10 is preferable. y is 2 or 3, z is an integer of 3 or more,
Generally, about 3 to 10 is preferable. ) The amount of the component (B) used is 0.5 to 100 parts by weight of the component (A).
It is 50 parts by weight. If it is less than 0.5 parts by weight, the sufficient effect intended by the present invention cannot be obtained, and if it exceeds 50 parts by weight, the rubber obtained becomes brittle, and neither is practical.

The alkoxysilane and / or its partial hydrolysis-condensation product as the component (C) used in the present invention is necessary for the composition of the present invention to cure to a good elastic body, This is the general formula R ¹ Si (OR ² ) ₃ (where R
¹ represents a monovalent hydrocarbon group or OR ² and R ² represents a monovalent hydrocarbon group. ).

R ¹ is the same or different monovalent hydrocarbon group selected from an alkyl group such as a methyl group, an ethyl group, a propyl group and a butyl group, an alkenyl group such as a vinyl group and an aryl group such as a phenyl group, or Is an OR ² group that is a
A propoxy group is preferred.

R ² is also a monovalent hydrocarbon group, particularly preferably a methyl group, an ethyl group, a propyl group and a butyl group, which are alkyl groups having 1 to 4 carbon atoms.

Typical examples of the component (C) include methyltrimethoxysilane, phenyltrimethoxysilane, vinyltrimethoxysilane, methyltriethoxysilane, methyltripropoxysilane, ethylorthosilicate, propylorthosilicate and partial hydrolysis thereof. An example is a decomposition condensate. Note that these examples do not limit the scope of the claims of the present invention.

The amount of component (C) used is 0.5 with respect to 100 parts by weight of component (A).
~ 20 parts by weight. If it is less than 0.5 part by weight, the cured rubber will not have sufficient strength, and if it exceeds 20 parts by weight, the obtained rubber will be brittle, and neither will be practical.

The component (D) used in the present invention is fumed silica having a hydrophobic surface, and the amount thereof is 0.5 to 100 parts by weight, preferably 1 to 50 parts by weight, relative to 100 parts by weight of the component (A). . If it is less than 0.5 part by weight, the rubber after curing will not have sufficient abrasion resistance, and if it exceeds 100 parts by weight, a rubber having a low hardness cannot be obtained.

Further, examples of the hydrophobizing agent for fumed silica include organosilicon compounds such as trimethylchlorosilane, dimethyldichlorosilane, hexamethyldisilazane, cyclic polydimethylsiloxane, and chain polydimethylsiloxane.

Examples of the curing catalyst (E) used in the present invention include organic tin compounds such as tin naphthenate, dimethyltin dilaurate, dibutyltin diacetate, dibutyltin dioctoate, dibutyltin dimethoxide, and dioctyltin dilaurate. It is preferable to use a diorganotin dicarboxylic acid salt having good curability or a derivative thereof because it has a large catalytic activity.
The amount of the curing catalyst (E) added is 0.0 with respect to 100 parts by weight of (A).
1 to 5 parts by weight. If the amount added is less than this, it will be insufficient as a curing catalyst, and it will take a long time to cure, and the curing inside the surface far from the contact surface with air will be poor. On the other hand, if the amount is larger than this, the storage stability decreases, which is not suitable. The more preferable range of addition is 0.1 to 3 parts by weight.

The composition of the present invention may optionally further contain a filler in addition to the components (A) to (E), and other polyorganosiloxane within a range not impairing the effects of the present invention. You may use together. Such additional additives include:
Examples thereof include quartz powder, diatomaceous earth, titanium oxide, iron oxide, polydimethylsiloxane, and alkenyl group-containing polysiloxane.

〔The invention's effect〕

When the low-hardness silicone rubber obtained from the composition of the present invention is used for a printing pad, the effect of greatly increasing the printing life can be obtained due to its surface non-adhesiveness and excellent abrasion resistance.

〔Example〕

Next, examples of the present invention will be given, but the present invention is not limited to these examples. All parts in the examples are parts by weight, Me represents a methyl group, and Bu represents a butyl group.

Example 1 20 parts of polydimethylsiloxane in which both ends of a molecular chain having a viscosity of 10,000 cP at 25 ° C. are blocked with silanol groups, and one end of a molecular chain having a viscosity of 2,000 cP at 25 ° C. has a silanol group and the other end has trimethylsilyl. 80 parts polydimethylsiloxane blocked with a group, average molecular formula 10 parts of a polyoxyalkylene-polysiloxane copolymer represented by 4 parts, 4 parts of propyl orthosilicate, a fumed silica surface-hydrophobized with dimethyldichlorosilane: 5 parts of Aerosil R972 (trade name, manufactured by Degussa) and dibutyltin dilaurate After mixing 1.0 parts and curing at 25 ℃ for 24 hours, the hardness of the obtained rubber-like elastic body, surface tack by touch with fingers and I went. The results are shown in Table 1.

Comparative Example 1 50 parts of polydimethylsiloxane in which both ends of a molecular chain having a viscosity of 10,000 cP at 25 ° C. were capped with silanol groups and 50 parts of polydimethylsiloxane in which both ends of a molecular chain having a viscosity of 100 cP at 25 ° C. were capped with trimethylsilyl groups 50 , 3 parts of propyl orthosilicate, 5 parts of Aerosil R972 and 1.0 part of dibutyltin dilaurate were mixed and cured at 25 ° C for 24 hours. Hardness of rubber-like elastic body obtained, surface tack by touch and abrasion resistance The test was evaluated. The results are shown in Table 1.

Comparative Example 2 At 25 ° C., 100 parts of polydimethylsiloxane in which both ends of a molecular chain having a viscosity of 10,000 cP were blocked with silanol groups were mixed with 0.3 part of propyl orthosilicate, 5 parts of Aerosil R972 and 1.0 part of dibutyltin dilaurate and mixed at 25 ° C. twenty four
The rubber-like elastic body obtained after being cured for a period of time was evaluated for hardness, surface tack by touch with fingers, and abrasion resistance test.
The results are shown in Table 1.

(Note 1) The abrasion resistance test was performed by the following method.

(Abrasion resistance test conditions) Rotary suppressor Standard wear test wheel manufactured by Toyo Seiki Seisakusho H22 Test rotation speed 60 rpm, 500 rotations Load 1kg (Method) Apply the silicone rubber test piece surface to a rotary presser with a load of 1kg. Ratio of test piece volume and test piece volume after wear under the above conditions Was measured.

Example 2 35 parts of polydimethylsiloxane in which both ends of a molecular chain having a viscosity of 5,000 cP at 25 ° C. were capped with silanol groups, and 25 ° C.
The viscosity is 800 cp, and one end of the molecular chain has a silanol group and the other end has a trimethylsilyl group blocked polydimethylsiloxane 65 parts, average molecular formula 20 parts of polyoxyalkylene-polysiloxane copolymer represented by, 8 parts of phenyltriethoxysilane, fumed silica: Aerosil 200 (manufactured by Nippon Aerosil Co., Ltd., trade name)
Fumed silica 40 hydrophobized with hexamethyldisilazane
25 parts by weight and 0.5 parts of dibutyltin diacetate
The hardness of the rubber-like elastic body obtained after curing at 24 ° C. for 24 hours, the surface tack by finger touch, and the abrasion resistance test were evaluated. The results are shown in Table 2.

Comparative Example 3 In Example 2, instead of the fumed silica hydrophobized with hexamethyldisilazane, crystallite was used as quartz powder.
A rubber-like elastic body was prepared in the same manner except that 40 parts of VX-S (trade name, manufactured by Tatsumori Co., Ltd.) was blended, and the hardness, surface tack, and abrasion resistance test were evaluated. The results are shown in Table 2.

Comparative Example 4 The same as Example 2 except that 20 parts of polydimethylsiloxane having both ends of the molecular chain blocked with trimethylsilyl groups and a viscosity at 25 ° C. of 50 cP was blended in place of the polyoxyalkylene-polysiloxane copolymer. A rubber-like elastic body was prepared by the method, and the hardness, surface tack and abrasion resistance test were evaluated. The results are shown in Table 2.

Comparative Example 5 In Example 2, the compounding ratio of polydimethylsiloxane having silanol groups at both ends of the molecular chain and polydimethylsiloxane having one end of the molecular chain blocked with a silanol group and the other end blocked with a trimethylsilyl group was 35. A rubber-like elastic body was prepared in the same manner except that the number of parts was changed from 65 parts and 65 parts to 50 parts and 50 parts, and the hardness, surface tack, and abrasion resistance tests were evaluated. The results are shown in Table 2.

Example 3 30 parts by weight of polydimethylsiloxane in which both ends of a molecular chain having a viscosity of 20,000 cP at 25 ° C. were capped with silanol groups,
Polydimethylsiloxane with a silanol group at one end and a trimethylsilyl group at the other end, with a viscosity of 3,500 cp at 25 ℃ 70 parts, average molecular formula 2 parts of a polyoxyalkylene-polysiloxane copolymer represented by: 4 parts of ethyl orthosilicate, Aerosil R9
72 3 parts, 5 parts titanium oxide and 0.5 parts dibutyltin dilaurate were mixed and cured for 24 hours at 25 ° C. The hardness of the rubber-like elastic body, the surface tack and the abrasion resistance test by finger touch were evaluated. went. The results are shown in Table 3.

Example 4 A rubber-like elastic body was prepared in the same manner as in Example 3 except that the compounding amount of the polyoxyalkylene-polysiloxane copolymer was 40 parts, and the hardness, surface tack and abrasion resistance test were conducted. Was evaluated. The results are shown in Table 3.

Example 5 A rubber-like elastic body was prepared in the same manner as in Example 3 except that the blending amount of Aerosil R972 was changed to 40 parts, and the evaluation results of hardness, surface tack and abrasion resistance test were conducted. The results are shown in Table 3.

Comparative Example 6 A rubber-like elastic body was prepared in the same manner as in Example 3 except that the compounding amount of the polyoxyalkylene-polysiloxane copolymer was 80 parts, and the hardness, surface tack and abrasion resistance test were conducted. Was evaluated. The results are shown in Table 3.

Comparative Example 7 The same procedure as in Example 3 was repeated except that the viscosity (25 ° C.) of polydimethylsiloxane having silanol groups at both ends of the molecular chain was changed to 500 cP and the blending amount of Aerosil R972 was changed to 150 parts. A rubber-like elastic body was prepared and evaluated for hardness, surface tack and abrasion resistance test. The results are shown in Table 3.

Claims (4)

[Claims] 1. (A) 10 to 40% by weight of a linear polydiorganosiloxane represented by the following general formula, (In the formula, R ³ and R ⁴ are substituted or unsubstituted monovalent hydrocarbon groups which are the same or different from each other, and m is an integer which makes the viscosity of this compound at 25 ° C. 100 to 100,000 cP.) A linear polydiorganosiloxane represented by
90-60% by weight (In the formula, R ⁵ , R ⁶ and R ⁷ are substituted or unsubstituted monovalent hydrocarbon groups which are the same or different from each other, and n is an integer which makes the viscosity of this compound at 25 ° C. 100 to 10,000 cP). (B) Copolymer of polyoxyalkylene compound represented by the following general formula and polyorganosiloxane 0.5 to 50 parts by weight (In the formula, R ⁸ is the same or different alkyl group or aryl group, R ⁹ is H, CH ₃ or (CH ₂ ) ₂ CH ₃ , p, q
Is an integer of 1 or more, x is an integer of 3 or more, y is 2 or 3,
z represents an integer of 3 or more. ) (C) An alkoxysilane represented by the general formula R ¹ Si (OR ² ) ₃ (in the formula, R ¹ represents a monovalent hydrocarbon group or OR ² , and R ² represents a monovalent hydrocarbon group) and / or Or 0.5 to 20 parts by weight of a partial hydrolyzed condensate thereof (D) 0.5 to 100 parts by weight of fumed silica having a hydrophobized surface, and (E) 0.01 to 5 parts by weight of a curing catalyst at room temperature. Polyorganosiloxane composition. 2. The composition according to claim 1, wherein R ^{1 of} (C) is a monovalent hydrocarbon group selected from a methyl group, a phenyl group and a vinyl group. 3. The composition according to claim 1, wherein R ^{2 in} (C) is an alkyl group having 1 to 4 carbon atoms. 4. The composition according to claim 1, wherein the component (E) is an organotin compound.