JPH0439487B2 - - Google Patents

Description

[Detailed description of the invention]

[Technical Field of the Invention] The present invention relates to a method for producing a liquid silicone rubber base with excellent fluidity. [Prior art and its problems] Conventionally, silicone rubber molded products have been produced by kneading organic peroxide into a silicone rubber composition containing organopolysiloxane and an inorganic filler such as reinforcing silica as main ingredients, crosslinking, It is obtained by hardening and molding. However, this method requires complicated steps such as mastication using two rolls and dispensing before molding. For this reason, recently, organopolysiloxanes having silicon-bonded vinyl groups with a relatively low degree of polymerization,
A liquid silicone rubber molding method in which a molded article is obtained by curing organohydrodiene polysiloxane with a platinum-based catalyst is widely used. In the case of this method, it is fluid before curing, the process is simple, and it is easy to apply to injection molding and automate.
It has the advantage of simplifying the entire process from kneading to molding. However, this liquid silicone rubber composition needs to have fluidity while containing a large amount of reinforcing filler, and the conventional method of mixing organopolysiloxane and inorganic filler and then heat-treating the composition is not effective. Therefore, plasticizers such as hexamethyldisilazane, diphenylsilanediol, cyclic dimethylpolysiloxane, polydimethylsiloxane with a polymerization degree of 20 or less with silanol group-blocked ends, and polydimethylpolymer with both ends with alkoxy group-blockers are used as plasticizers. Addition of siloxane etc. was essential. As a result, the composition and process become complicated and the manufacturing cost becomes high. [Object of the Invention] The present invention aims to eliminate these drawbacks, and provides a method for easily producing a liquid silicone rubber base with excellent fluidity without adding a plasticizer and using a conventional batch-type kneading device. The present invention provides a method. [Structure of the Invention] The object of the present invention is to provide an organopolysiloxane having a viscosity of 100 to 100,000 centipoise at 25°C and having at least two silicon-bonded alkenyl groups in one molecule and an inorganic filler as a main ingredient. When producing a liquid silicone rubber base, (1) first, the organopolysiloxane is heated to a temperature in the range of 100 to 300°C, and (2) the inorganic filler is added and mixed. This can be achieved by a silicone rubber-based manufacturing method. To explain this, the organopolysiloxane used in the present invention is the main raw material for the liquid silicone rubber base, and must have at least two silicon-bonded alkenyl groups in one molecule. Examples of the alkenyl group include a vinyl group, an allyl group, and a 1-propenyl group. Groups that bond to silicon atoms other than alkenyl groups in the organopolysiloxane include monovalent organic groups that do not have aliphatic unsaturated bonds, such as methyl groups,
Alkyl groups such as ethyl, propyl, and butyl groups; substituted alkyl groups such as 2-phenylmethyl, 2-phenylethyl, and 3,3,3-trifluoropropyl; and aryl groups such as phenyl and tolyl. Illustrated. Furthermore, a hydroxyl group or an alkoxy group may be present. The viscosity of the organopolysiloxane is in the range of 100 to 100,000 centipoise at 25°C, preferably in the range of 300 to 30,000 centipoise. Two or more kinds of these organopolysiloxanes may be used in combination. In that case, if the viscosity of the mixture falls within the range of 100 to 100,000 centipoise, then less than 100 centipoise,
Viscosities greater than 100,000 centipoise can be used. Inorganic fillers serve as reinforcing agents or reinforcing agents and extenders for liquid silicone rubber, and include wet silica, dry silica, fine quartz powder, fumed titanium dioxide, diatomaceous earth, talc, and hydroxide. Examples include aluminum, particulate alumina, colloidal calcium carbonate, graphite, and carbon black, and one or more of these may be used. Among these, wet silica or a filler containing it is preferable because remarkable fluidity can be obtained when wet silica is used. The amount of the inorganic filler used depends on the properties of the inorganic filler and the desired tensile strength and hardness of the cured silicone rubber product, and is not particularly limited, but in general, the inorganic filler is dry silica, wet silica, or carbon black. When the material is extremely fine and has great reinforcing properties, it is preferably 5 to 100 parts by weight per 100 parts by weight of the organopolysiloxane. When the reinforcing property is small and the reinforcing property is small, or when the reinforcing property is small, the amount is preferably 10 parts by weight to 500 parts by weight. In the method of the present invention, organopolysiloxane is charged into a conventionally used planetary mixer, kneader mixer, etc., and heated at 100 to 300°C, preferably 150 to 250°C, with stirring for 10 minutes to 3 hours. The plasticizer is added by adding any amount of inorganic filler, preferably any amount of wet silica, at once or preferably in portions, and heating and stirring for 30 minutes to 5 hours. It is possible to produce a liquid silicone rubber base with excellent fluidity. By employing the method of the present invention, fluidity is significantly improved compared to the conventional method of mixing organopolysiloxane and inorganic filler and then heat-treating. As the liquid silicone rubber-based curing agent of the present invention, a combination of an organohydrodiene polysiloxane and a platinum-based catalyst is preferably used, but an organic peroxide may be used in some cases. The amount of curing agent added is usually in the range of 0.5 to 30 parts by weight for organohydrodiene polysiloxane, and in the range of 0.5 to 10 parts by weight for organic peroxides, per 100 parts by weight of the liquid silicone rubber base. . In the case of a platinum-based catalyst, it is usually used in an amount of 1 to 300 ppm in terms of platinum based on the weight of the organopolysiloxane. A silicone rubber elastic body can be obtained by adding the above-mentioned curing agent to the liquid silicone rubber base of the present invention and curing it by heating. On this occasion,
Addition reaction retardant, heat resistant agent, flame retardant, as necessary.
Colorants may also be added. Furthermore, various methods such as compression molding, injection molding, transfer molding, and cast molding can be used as the molding method. [Embodiments of the Invention] Next, embodiments of the present invention will be explained. Parts in Examples and Comparative Examples mean parts by weight, and the viscosity is the value at 25°C. Example 1 100 parts of dimethylpolysiloxane having a viscosity of 2000 centipoise and end-blocked with dimethylvinylsilyl groups at both ends was placed in a planetary mixer and heated with stirring until the internal temperature reached 150°C. To this, 40 parts of wet silica (Nipsil LP manufactured by Nippon Silica Kogyo Co., Ltd.) was added and mixed in four portions over about 1 hour.
After the wet silica was added, the mixture was heated and mixed for an additional 2 hours, and then cooled. The initial viscosity of this liquid silicone rubber base and the viscosity after being left at 25° C. for 30 days were measured using a Bismetron BS rotational viscometer (rotor No. 7). In addition, 100 parts of liquid silicone rubber base is added as a crosslinking agent. 2.5 parts of dimethylsiloxane/methylhydrodienesiloxane copolymer shown by , a platinum catalyst of 8 ppm calculated as platinum based on the weight of organopolysiloxane, and 0.05 part of 3-methylbutynol-1 as a reaction inhibitor. Add and mix evenly.
This was press-vulcanized at 150°C for 5 minutes to obtain a silicone rubber sheet with a thickness of 2 mm. The physical properties of this were measured. These results are the first
Shown in the table. Comparative Example 1 Dimethylpolysiloxane used in Example 1
100 parts of the mixture was placed in a planetary mixer, and 40 parts of the wet silica used in Example 1 was added and mixed in four portions at room temperature. After the addition, the temperature was raised to 150°C, heated and mixed for 2 hours, and then cooled. When this initial viscosity was measured, it exceeded 120,000 centipoise and was impossible to measure. Comparative Example 2 Dimethylpolysiloxane used in Example 1
Put 100 parts into a planetary mixer and bring the temperature to 80
When the temperature reached .degree. C., charging and mixing of the wet silica used in Example 1 was started, and after the charging was completed, the temperature was raised to 150.degree. C., heated and mixed for 2 hours, and then cooled. The viscosity and physical properties of this silicone rubber base were measured in the same manner as in Example 1. The results are shown in Table 1.

[Table] Compared to Comparative Examples 1 and 2, by employing the method of the present invention, a silicone rubber base with low initial viscosity and excellent fluidity with little change in viscosity after standing can be obtained. Example 2 100 parts of the dimethylpolysiloxane with a viscosity of 2,000 centipoise and end-blocked with dimethylvinylsilyl groups at both ends used in Example 1 was placed in a planetary mixer.
The mixture was heated with stirring until the internal temperature reached 200°C. 50 parts of the wet silica used in Example 1 was added and mixed in 4 portions over about 1 hour. After the addition was completed, the mixture was further heated and mixed for 2 hours, and then cooled. The viscosity and physical properties of this silicone rubber base were measured in the same manner as in Example 1.
As a result, the initial viscosity was 4300 poise, and the hardness (JIS-A)
55, tensile strength was 70 Kg/cm ² , elongation was 210%, and tear strength was 10 Kg/cm 2 . Example 3 100 parts of dimethylpolysiloxane having a viscosity of 7,000 centipoise and end-blocked with dimethylvinylsilyl groups at both ends was placed in a kneader mixer and heated with stirring until the internal temperature reached 150°C. 40 parts of the wet silica used in Example 1 was added to this for about 1 hour.
Mixed. After the addition was completed, the mixture was further heated and mixed for 2 hours, and then cooled. The viscosity and physical properties of this silicone rubber base were measured in the same manner as in Example 1. However, the physical properties were measured for silicone rubber sheets prepared by changing only the amount of crosslinking agent added to 1.5 parts. The results are shown in Table 2. Comparative Example 3 Dimethylpolysiloxane used in Example 3
100 parts were placed in a kneader mixer, and 40 parts of the wet silica used in Example 1 was added and mixed in four portions at room temperature. After the addition, the temperature was raised to 150°C, heated and mixed for 2 hours, and then cooled. The initial viscosity of this was not measurable. Comparative Example 4 Dimethylpolysiloxane used in Example 3
100 parts were placed in a kneader mixer, and when the temperature reached 80°C, 40 parts of the wet silica used in Example 1 was added and mixed in four portions. 150 after the end of input
The mixture was heated to .degree. C., heated and mixed for 2 hours, and then cooled. The viscosity and physical properties were measured in the same manner as in Example 3.

[Table] Example 4 100 parts of a dimethylsiloxane/methylphenylsiloxane copolymer (methylphenylsiloxane unit 3 mol %) with a viscosity of 40,000 centipoise and end-blocked with dimethylvinylsilyl groups was placed in a kneader mixer, and the inside was stirred. It was heated until the temperature reached 200°C. 50 parts of wet silica (Carplex 80, manufactured by Shionogi & Co., Ltd.) was added and mixed in 4 portions over a period of approximately 1 hour. After the addition was completed, the mixture was further heated and mixed for 2 hours, and then cooled. The viscosity and physical properties of this liquid silicone rubber base were measured in the same manner as in Example 1. However, the physical properties were measured for silicone rubber sheets prepared by changing only the amount of crosslinking agent added to 1.0 part. The results are shown in Table 3. Comparative Example 5 The mixing conditions of Example 4 were changed and the mixture was mixed at room temperature and then heated to 200°C.
Its initial viscosity was not measurable. Comparative Example 6 A test was conducted in which the mixing conditions of Example 4 were changed so that the initial temperature during mixing was 80°C and then the temperature was raised to 200°C, but the initial viscosity could not be measured.

〔Effect of the invention〕

According to the method for producing a liquid silicone rubber base of the present invention, using a conventionally known kneading machine, the organopolysiloxane is first heated to 100 to 300°C, and then the inorganic filler is added and mixed. This makes it possible to easily produce a liquid silicone rubber base with excellent fluidity without using plasticizers, which are essential in conventional methods, simplifying operations and reducing costs compared to conventional methods. It becomes possible.

Claims (1)

[Claims] 1. A liquid silicone rubber base having a viscosity of 100 to 100,000 centipoise at 25°C and containing at least two silicon-bonded alkenyl groups in one molecule and an inorganic filler as main ingredients. A method for producing a liquid silicone rubber base, which comprises: (1) first heating the organopolysiloxane to a temperature in the range of 100 to 300°C, and then (2) adding and mixing the inorganic filler. . 2. The manufacturing method according to claim 1, wherein the inorganic filler is wet silica.