JPH0568337B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for molding a liquid silicone rubber composition.
The present invention relates to a method for molding a liquid silicone rubber composition, in which a silicone rubber molded article is obtained by discharging it into water at a temperature of 25° C. or higher and curing it.

[Prior Art] Conventionally, in order to obtain a molded article from a liquid silicone rubber composition, the constituent components of the liquid silicone rubber composition are mixed at room temperature or higher to form a liquid silicone rubber composition, and the composition of the liquid silicone rubber composition is mixed. An object is placed in a mold and cured at a temperature of 120°C or higher (for example, Japanese Patent Application Laid-open No. 149354/1983,
17428), and the composition is discharged into hot air at 200 to 400°C to cure it.

[Problems to be solved by the invention] However, in these conventional molding methods,
In both cases, the liquid silicone rubber composition is made at room temperature or higher, and the molded product is obtained by curing the liquid silicone rubber composition in a mold at high temperatures or in hot air, which causes several problems. has been found.

In other words, the liquid silicone rubber composition expands during curing, making it difficult for the obtained molded product to separate from the mold, and the liquid silicone rubber composition comes into contact with the high-temperature inner surface of the mold, resulting in a temporary decrease in viscosity. As a result, there are many disadvantageous problems in molding, such as the tendency for burrs to occur in the molded product, and air bubbles are likely to occur inside the molded product, making it particularly difficult to obtain thin-walled molded products or thin thread-like molded products. It was difficult.

Therefore, the present inventors investigated a molding method that does not have such problems, and found that the above problems can be largely solved by discharging a liquid silicone rubber composition into water at a temperature of +25°C or higher and curing it. We have confirmed that this is the case and have completed the present invention.

An object of the present invention is to provide a method for molding a liquid silicone rubber composition, which can produce thin-walled molded products or thin thread-like molded products, and can yield uniform molded products with less air bubbles and a low molding shrinkage rate. be.

[Means for solving the problems and their effects] The above purpose is to prepare a liquid silicone rubber composition by mixing the constituent components of the liquid silicone rubber composition at a temperature in the range of -60 to +5°C, and then to This is accomplished by discharging it into water at a temperature of +25°C or higher and curing it to obtain a molded product.

To explain this, the liquid silicone rubber composition used in the present invention is a liquid or paste-like composition at room temperature that contains a liquid organopolysiloxane having a reactive group, a crosslinking agent, and/or a curing catalyst as the main ingredients. It hardens into a rubber-like elastic body when left at room temperature or heated, and may be either a sag type or a non-sag type. As for the curing mechanism, examples include an addition reaction type, a radical reaction curing type using an organic peroxide, and a condensation reaction type, but the addition reaction type is preferable because it has a fast curing rate and is excellent in curing uniformity. Particularly preferred in the present invention as such an addition reaction type liquid silicone rubber composition are (A) an organopolysiloxane having at least two lower alkenyl groups in one molecule; (B) an organopolysiloxane having at least two lower alkenyl groups in one molecule; Organopolysiloxane (C) having a silicon-bonded hydrogen atom Platinum-based catalyst 0.1 to 1000 parts by weight of platinum-based metal per 1 million parts by weight of the total amount of components (A) to (B) [However, component (A) 1 The total number of alkenyl groups per molecule and hydrogen atoms per molecule of component (B) is at least 5.
A liquid silicone rubber composition comprising:

To explain this, component (A) is the main component of organopolysiloxane that provides silicone rubber,
This is a component that undergoes an addition reaction with component (B) and hardens due to the catalytic action of component (C). Component (A) must have at least two lower alkenyl groups bonded to silicon atoms in one molecule; if the number of lower alkenyl groups is less than two, a network structure will not be formed, resulting in good curing. I can't get things. Examples of such lower alkenyl groups include vinyl, allyl, and propenyl groups. Further, such a lower alkenyl group may be present anywhere in the molecule, but is preferably present at least at the terminal end of the molecule. Furthermore, the molecular structure of this component may be linear, linear with branches, cyclic, or network-like, but preferably linear with or without a small amount of branching. . The molecular weight of this component is not particularly limited and can range from a liquid with a low viscosity to a raw rubber with a very high viscosity.
Preferably, the viscosity at 25°C is 100 centipoise or more. Examples of such organopolysiloxanes include methylvinylpolysiloxane, a copolymer of methylvinylsiloxane and dimethylsiloxane, dimethylpolysiloxane with dimethylvinylsiloxy groups blocked at both ends, and dimethylsiloxane-methyl siloxane with both ends blocked with dimethylvinylsiloxy groups. enylsiloxane copolymer, dimethylsiloxane-diphenylsiloxane-methylvinylsiloxane copolymer with both ends blocked with dimethylvinylsiloxy groups,
Dimethylsiloxane-methylvinylsiloxane copolymer with both ends blocked with trimethylsiloxy groups, dimethylsiloxane-methylphenylsiloxane-methylvinylsiloxane copolymer with both ends blocked with trimethylsiloxy groups, methyl with both ends blocked with dimethylvinylsiloxy groups (3 , 3,3-trifluoropropyl)polysiloxane, dimethylsiloxane-methyl(3,3,3-trifluoropropyl)siloxane copolymer with both ends capped with dimethylvinylsiloxy groups, _CH2 =CH( _CH3 ) _2SiO ^1/2 unit and ( _{CH 3} ) _{3 SiO} ^1/2
Examples include polysiloxane consisting of SiO ⁴ / ₂ units and SiO 4 /2 units. In the present invention, the above organopolysiloxanes may be used in combination.

Component (B) used in the present invention is a crosslinking agent for component (A), and due to the catalytic action of component (C), silicon-bonded hydrogen atoms in this component connect with lower alkenyl groups in component (A). It is cured by addition reaction. Component (B) must have at least two silicon-bonded hydrogen atoms in one molecule in order to function as a crosslinking agent.

The total number of alkenyl groups in one molecule of component (A) and silicon-bonded hydrogen atoms in one molecule of component (B) is at least 5. If it is less than 5, a network structure is not substantially formed and a good molded product cannot be obtained, which is not preferable.

There are no particular limitations on the molecular structure of this component,
It may be linear, linear including branched, cyclic, etc. There is no particular limitation on the molecular weight of this component, but (A)
In order to improve the compatibility with the components, the viscosity at 25°C is preferably 1 to 50,000 centipoise.

The amount of this component added is such that the molar ratio of the total amount of silicon-bonded hydrogen atoms in this component to the total amount of all lower alkenyl groups in component (A) is (0.5:1) to (20:1).
It is preferable to use an amount such that the molar ratio is
If it is less than 0.5:1, it will be difficult to obtain good curing properties.
This is because when the ratio is greater than 20:1, the hardness tends to increase when the cured product is heated. In addition, when organosiloxanes containing a large amount of alkenyl groups are separately added for reinforcement etc., it is preferable to add this component containing silicon-bonded hydrogen atoms in an amount corresponding to the alkenyl groups.

Specific examples of this component include methylhydrodiene polysiloxane with trimethylsiloxy groups blocked at both ends, dimethylsiloxane-methylhydrodiene polysiloxane copolymer with both ends blocked with trimethylsiloxy groups, and dimethylhydrodienepolysiloxane copolymer with both ends blocked with trimethylsiloxy groups. Dimethylsiloxane-methylhydrodienesiloxane copolymer, dimethylsiloxane-methylhydrodienesiloxane cyclic copolymer, ( _CH3 ) ₂ copolymer consisting of ^HSiO1 / ₂ units and ^SiO4 / ₂ units, ( _CH3 ) ₂ HSiO ^1/2 _units and
Examples include copolymers consisting of SiO ⁴ / ₂ units.

Component (C) is a catalyst that causes an addition reaction between a silicon-bonded hydrogen atom and an alkenyl group. Specific examples include chloroplatinic acid, a solution of this in alcohol or ketones, and an aged solution of the same. , complex compounds of chloroplatinic acid and olefins,
These include complex compounds of chloroplatinic acid and alkenylsiloxane, complex compounds of chloroplatinic acid and diketone, platinum black, and those in which platinum is supported on a carrier.

The amount of this component added is the total amount of component (A) and component (B).
0.1 to 1000 as platinum metal per 1 million parts by weight
This is because if the amount is less than 0.1 part by weight, the crosslinking reaction will not proceed sufficiently, and if it is more than 1000 parts by weight, it is uneconomical. When normally used, the amount of platinum-based metal added is preferably about 1 to 100 parts by weight.

The liquid silicone rubber composition used in the present invention may contain a filler in order to adjust the fluidity and improve the mechanical strength of the molded product. Such fillers include reinforcing fillers such as precipitated silica, fumed silica, pyrogenic silica, fumed titanium oxide, ground quartz, diatomaceous earth, asbestos, aluminosilicate, iron oxide, zinc oxide, calcium carbonate, etc. Examples include non-reinforcing fillers, which may be used as is or may be surface-treated with an organosilicon compound such as hexamethylsilazane, trimethylchlorosilane, or polymethylsiloxane. In addition, it is possible to add trace amounts or small amounts of acetylene compounds, hydrazines, triazoles, phosphines, mercaptans, etc. to the organopolysiloxane composition used in the present invention as additives for suppressing the curing reaction. There is no problem as long as it does not impair the purpose of the present invention. In addition, pigments, heat resistant agents, flame retardants, plasticizers, and organopolysiloxanes having one alkenyl group per molecule for low modulus may be added as necessary.

Next, as a preferred liquid silicone rubber composition, there is a radical reaction-curable liquid silicone rubber composition using an organic peroxide. If necessary, inorganic fillers such as fumed silica, precipitated silica, heat resistant agents, pigments, etc. are added. It is preferable to select an organic peroxide having a decomposition temperature in the range of +25°C to +100°C.

In the present invention, it is preferable to prepare the liquid silicone rubber composition by mixing the constituent components of the liquid silicone rubber composition at low temperature. This mixing temperature is preferably within the range of -60℃ to +5℃,
More preferably, the temperature is in the range of -30°C to 0°C. This is because when the temperature is below -60°C, the organopolysiloxane used in the present invention tends to become gel-like and cannot be discharged, and when the temperature exceeds +5°C, a curing reaction progresses during mixing, making it difficult to discharge. This is because the mechanical strength of the resulting cured product is greatly reduced.

Then, the liquid silicone rubber composition thus obtained is discharged into water at a temperature of +25° C. or higher and cured. If the curing temperature is less than 25°C, the curing speed of the liquid silicone rubber composition used in the present invention will decrease, resulting in a decrease in productivity, which is not preferable. As for the method of discharging into water, the liquid silicone rubber composition may be once discharged into the air and then immediately introduced into water, or it may be directly discharged into water.

The molding method of the present invention includes, for example, combining a cooling device with a well-known kneading molding machine for liquid silicone rubber,
The components of the liquid silicone rubber composition are mixed in this molding machine to produce a liquid silicone rubber composition, and then the composition is passed through a die or nozzle for the intended molded product and preset at a temperature of +25°C or higher. It can be carried out by discharging it into a heated water bath and curing it.

By using the molding method of the present invention, not only thick molded products but also thin molded products such as films and thin molded products such as filaments can be efficiently produced.

[Example] Next, the present invention will be explained with reference to Examples. The middle part of the example indicates parts by weight, and the viscosity is the value at 25°C.

Example 1 100 parts of dimethylpolysiloxane (vinyl group content: 0.25% by weight) with a viscosity of 2000 centipoise, with both molecular chain ends capped with dimethylvinylsiloxy groups, 30 parts of dry silica with a specific surface area of 200 m ² /g, and both molecular chains Viscosity 10 with end capped with trimethylsiloxy group
Add 2 parts of centipoise methylhydrodiene polysiloxane [containing 1% by weight of hydrogen atoms bonded to silicon atoms] and mix at a shear rate of 10 sec ^-1.
A mixture with a viscosity of 5000 poise was obtained (mixture A). Next, the same dimethylpolysiloxane 100 as above
100 parts of the same dimel polysiloxane as above, 30 parts of the same dry silica as above, and an isopropyl alcohol solution of chloroplatinic acid [platinum content: 3% by weight]
0.1 part was added and mixed to obtain a mixture similar to the above (mixture B).

This mixture A was placed in tank 1 for liquid silicone rubber composition, and mixture B was similarly placed in tank 2 for liquid silicone rubber composition and set. Next, these are fed into a screw type kneading extruder 8 which has been cooled in advance to -5°C in a refrigerant circulation device 10 using pressure pumps 4 and 5, and mixture A and mixture B are mixed.
were mixed in a 1:1 ratio.

This mixture was continuously extruded into hot water at a temperature of 60° C. filled in a hot water tank 17 at a linear speed of 3 m/min through a nozzle 19 having a diameter of 0.3 mm and cured. This cured product was wound onto a take-up roll 26 via support rolls 21, 22 and guide rolls 23, 24, 25 to obtain a thread-like filament 20. When the physical properties of this thread-like filament were measured, it was found to have a tensile breaking stress of 42 Kg/cm ² and a tensile elongation of 60%. Further, when this thread-like filament was cut with a knife and the cut surface was observed, no air bubbles were found anywhere.

For comparison, when the mixture obtained above was extruded into hot water adjusted to 5° C., the organopolysiloxane composition was insufficiently cured and no thread-like filaments were obtained.

The mixture obtained in the same manner as above except that the passage of the refrigerant through the jacket 9 of the screw type kneading extruder 8 was stopped and the temperature was kept at room temperature (20°C) was extruded into hot water adjusted to 60°C. However, it could not be discharged uniformly, and the cured product could not be obtained as a uniform thread-like filament. Moreover, the surface condition was uneven. Furthermore, when this thread-like filament was cut with a knife and the cut surface was observed, fine air bubbles were found.

Example 2 100 parts by weight of dimethylpolysiloxane (vinyl group content 0.15% by weight) with a viscosity of 10,000 centipoise and whose molecular chain ends are blocked with dimethylvinylsiloxy groups, and 40 parts of dry silica with a surface area of 200 m ² /g and both ends of the molecular chain. was capped with trimethylsiloxy groups and had a viscosity of 12 centistokes [content of hydrogen atoms bonded to silicon atoms: 0.9% ^by weight]. A viscous mixture was obtained (mixture A). Next, 20 parts of the same dry silica as above and 0.1 part of an isopropyl alcohol solution of chloroplatinic acid [platinum content 3% by weight] were added to 100 parts of the same dimethylpolysiloxane as above and mixed to obtain a mixture as above. (Mixture B).

This mixture A was placed in a raw material tank 1 for a liquid silicone rubber composition, and the mixture B was similarly placed in a raw material tank 2 for a liquid silicone rubber composition. Next, these are preheated to -20℃ in the refrigerant circulation device 10.
Mixture A and Mixture B were fed into a screw-type kneading extruder 8, which had been cooled to 100 degrees, using pressure pumps 4 and 5, and mixed at a ratio of 1:1. When this mixture was continuously extruded through the nozzle 19 (a film molding nozzle with a discharge port hole diameter of 0.2 mm x 10 mm) at a linear speed of 6 m/min into hot water at a temperature of 40°C filled in the hot water tank 17, A transparent film with a thickness of 0.15 mm and a glossy surface was obtained. When the physical properties of this film were measured, the tensile stress was 60Kg/cm ² and the tensile elongation was 600.
It was %. Moreover, no air bubbles were found on the surface or inside.

Example 3 100 parts of dimethylpolysiloxane (vinyl group content: 0.12% by weight) with a viscosity of 1000 centipoise, both molecular chain ends blocked with dimethylvinylsiloxy groups, 25 parts of dry silica with a specific surface area of 300 m ² /g, and both molecular chains Viscosity 10 with end capped with trimethylsiloxy group
Add 1 part of centipoise methylhydrodiene polysiloxane [containing 1% by weight of hydrogen atoms bonded to silicon atoms] and mix at a shear rate of 10 sec ^-1.
A mixture with a viscosity of 12000 poise was obtained (mixture A). Next, the same dimethylpolysiloxane as above
To 100 parts, 30 parts of the same dry silica as above and 0.1 part of isopropyl alcohol solution of chloroplatinic acid [platinum content: 3% by weight] were added and mixed to obtain the same mixture as above (mixture B).

This mixture A was placed in tank 1 for liquid silicone rubber composition, and mixture B was similarly placed in tank 2 for liquid silicone rubber composition and set. Next, these are fed into a screw type kneading extruder 8 which has been cooled in advance to -5°C in a refrigerant circulation device 10 using pressure pumps 4 and 5, and mixture A and mixture B are mixed.
were mixed in a 1:1 ratio.

This mixture was continuously extruded into hot water at a temperature of 60° C. through the mouthpiece 19 of a tube-forming die (outer diameter of the discharge port: 3.0 mm, inner diameter (nipple diameter): 2.0 mm) and hardened. This cured product is passed through support rolls 21, 22 and guide rolls 23, 24, 25 at a linear speed of 30 m/min to a winding roll 2.
6 to obtain a 1000 m hollow filament 20. When the physical properties of this filament were measured, it was found to have a tensile breaking stress of 100 Kg/cm ² , a tensile elongation of 700%, an outer diameter of 1.0 mm, and a wall thickness of 0.25 mm. Also,
When this hollow filament was cut with a knife and the cut surface was observed, no air bubbles were found anywhere.

[Effects of the Invention] In the present invention, a liquid silicone rubber composition is prepared by mixing the constituent components of a liquid silicone rubber composition at a temperature of -60°C to +5°C, and then the composition is mixed with water at a temperature of +25°C or higher. As the silicone rubber molded product is obtained by discharging it into a mold and curing it, thin-walled molded products that cannot be obtained with conventional molding methods can be obtained.In particular, silicone rubber filaments, which are thin thread-like molded products, silicone rubber hollow filaments, and silicone rubber molded products can be obtained. A rubber film can be obtained, and the obtained silicone rubber molded product has few air bubbles and has a small molding shrinkage rate, so it has the characteristics that a homogeneous molded product with excellent withstand voltage can be obtained.

[Brief explanation of drawings]

FIG. 1 is a schematic process diagram for carrying out the present invention. 1, 2... Raw material tank for liquid silicone rubber composition, 3a... Raw material for liquid silicone rubber composition, 3b... Raw material for liquid silicone rubber composition,
4, 5... Pressure pump, 6, 7... Raw material supply pipe for liquid silicone rubber composition, 8... Screw type kneading extruder, 9... Screw type kneading extruder cooling jacket, 10... Screw type kneading Extruder cooling refrigerant circulation device, 11, 12... Screw-type kneading extruder cooling refrigerant supply pipe, 13... Pressurized steam circulation device, 14, 15... Pressurized steam supply pipe, 16... Temperature Water tank jacket, 17... Hot water tank, 18... Liquid silicone rubber composition supply curved tube, 19... Mouthpiece, 20... Silicone rubber molded product, 21, 22... Support roll, 23, 24, 2
5... Guide roll, 26... Winding roll,
27...Hollow part.

Claims (1)

[Claims] 1. A liquid silicone rubber composition is prepared by mixing the constituent components of the liquid silicone rubber composition at a temperature in the range of -60 to +5°C, and then the composition is heated to a temperature of +5°C.
A method for molding a liquid silicone rubber composition, which comprises discharging it into water at 25°C or higher and curing it to obtain a molded product. 2. The molding method according to claim 1, wherein the liquid silicone rubber composition is of an addition reaction curing type. 3. The liquid silicone rubber composition comprises (A) an organopolysiloxane having at least two lower alkenyl groups in one molecule, (B) an organopolysiloxane having at least two silicon-bonded hydrogen atoms in one molecule, and (C) Platinum-based catalyst 0.1 to 1000 parts by weight of platinum-based metal per 1 million parts by weight of the total amount of components (A) to (B) [however, alkenyl group per molecule of component (A) and component (B)] The total number of hydrogen atoms per molecule is at least 5.
The molding method according to claim 1, which comprises: 4. The molding method according to claim 1, wherein the molded product is a rubber filament. 5. The molding method according to claim 1, wherein the molded product is a rubber hollow filament. 6. The molding method according to claim 1, wherein the molded product is a rubber film.