JP3642890B2 - Method for producing silicone rubber foam - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a silicone rubber foam used for heat insulation, rolls for OA equipment, cushioning materials, cosmetic puffs, weight reduction of various molded articles, and the like.
[0002]
[Prior art]
As a method for producing a thermoplastic resin foam, chemical foaming in which bubbles are generated by a chemical reaction using a foaming agent and physical foaming in which a gas is directly mixed with a resin are generally known. Silicone rubber In the field, a method of performing chemical foaming simultaneously with the curing reaction has been employed. The bubble diameter obtained by this method is, for example, as shown in JP-A-7-241934, by mixing silicone rubber powder, a foam having uniform and fine dispersibility is obtained. Although the device has been devised, the bubble diameter is about 300 to 700 μm even by this method, and according to the study of the present inventor, by controlling the curing method of the silicone rubber composition by various methods, 100 A bubble diameter of ultra-300 μm was obtained, but it was not less than this.
[0003]
[Problems to be solved by the invention]
However, in the above conventional rubber foam production method, particularly the silicone rubber foam production method, foaming and curing proceed simultaneously under one control condition of heating, and the foaming temperature and the curing temperature are close to each other. It is difficult to stably obtain a foam having a fine and uniform bubble diameter and a uniform dispersibility of bubbles [hereinafter simply referred to as (uniform)], and to obtain a uniform foam stably. However, it was necessary to control the curing rate and the foaming rate to a high degree. Even in this case, the bubble diameter is limited to the above range, and it was impossible to obtain a foam having a finer bubble diameter.
That is, the present invention provides a method for producing a silicone rubber foam, which can stably obtain a uniform foam having a cell diameter of 100 μm or less and high productivity without highly controlling the curing rate and the foaming rate. Is.
[0004]
[Means for Solving the Problems]
The present invention relates to a method for producing a silicone rubber foam that solves the above-mentioned conventional problems, and an extruder is used to apply a gas at normal temperature and pressure to an uncured or semi-cured silicone rubber composition. A silicone rubber foam that is molded and cured by infiltrating and diffusing a substance (hereinafter simply referred to as a gaseous substance) above its critical pressure and above its critical temperature, and then reducing the pressure to foam it in an uncured or semi-cured state. In the manufacturing method, the absolute value S of the contact area S (cm ² ) between the gas substance and the silicone rubber composition in the injection part of the gas substance and the extrusion rate V (cm ³ / min. Of the silicone rubber composition). ) In relation to the absolute value V is S ≧ 2 V, and the pressure reducing speed is 10 kgf / cm ² / sec. Or more.
[0005]
DETAILED DESCRIPTION OF THE INVENTION
That is, the present inventor noticed that fine bubbles need only be continuously generated by physical foaming in order to stably obtain a uniform silicone rubber foam with good productivity. As a result of various studies on conditions and raw materials, the present invention has been achieved. The present invention is described in detail below.
[0006]
In the present invention, the gaseous substance is permeated and diffused into the silicone rubber composition at a critical temperature or higher and a critical pressure or higher in order to permeate and diffuse the gaseous substance into the silicone rubber composition quickly and with high density.
In addition, the absolute value S of the contact area S (cm ² ) between the gaseous substance and the silicone rubber composition in the injection part of the gaseous substance and the absolute value of the extrusion rate V (cm ³ / min.) Of the silicone rubber composition The relationship with V is set to S ≧ 2V in order to uniformly and sufficiently permeate and diffuse a gas substance having a temperature above the critical temperature and above the critical pressure into the silicone rubber composition. If the pressure is lower, the number of foamed bubbles decreases when the pressure is lowered, and a foam having sufficient performance cannot be obtained. In other words, the purpose of foaming the silicone rubber is to obtain a molded product having a low hardness, specifically 20 to 40 when a foam having a hardness of 50 before foaming ^. In order to achieve this, it is necessary to set the expansion ratio to 1.5 or more, but such foam cannot be obtained with S <2V.
[0007]
Further, in the present invention, the pressure is decreased at a rate of 10 kgf / cm ² / sec. Or more in order to form fine bubbles of 100 μm or less, specifically 100 μm, and less than 10 kgf / cm ² / sec. The bubble diameter becomes over 100 μm, remarkably over 500 μm, and the desired foam cannot be obtained. In addition, the upper limit of the speed at which the pressure is reduced is not particularly limited, but industrially it is practical to design at 500 kgf / cm ² / sec.
[0008]
As the silicone rubber composition used in the present invention, a conventionally known material may be used, which is composed of a polymer compound having a siloxane bond and a peroxide, a polymer compound having a siloxane bond, and a silicon atom. Examples thereof include those comprising an organohydrogenpolysiloxane having at least two hydrogen atoms in one molecule and a platinum catalyst.
The polymer compound having a siloxane bond and the organohydrogenpolysiloxane may contain an epoxy group, an acrylic group, a halogen atom, or the like.
[0009]
Furthermore, in the present invention, two or more types of curing agents having different curing temperatures are used in combination as the curing agent for the silicone rubber composition, and at least one of the curing agents is left as the curing agent. After semi-curing the material, injecting and diffusing the gaseous substance, reducing the pressure, foaming in the semi-cured state, and performing heat curing using the remaining curing agent, the composition of the foamed composition The viscosity can be adjusted arbitrarily, and the foaming state can be easily controlled and molded. In addition, various additives such as flame retardants, anti-aging agents, weather resistance improvers, impact resistance improvers, reinforcing agents, colorants, and conductivity imparting agents are added to the silicone rubber composition as necessary. There is no problem. In addition, the uncured or semi-cured state in the present invention indicates a state in which it can be plastically flowed in an extruder and a die, and molded and cured into a desired shape.
[0010]
The gaseous substance used in the present invention is not particularly limited, but is selected from hydrogen, helium, nitrogen, oxygen, neon, argon, carbon dioxide, methane, ethane, propane, butane, ethylene, propylene, and the like and mixtures thereof. In particular, carbon dioxide is preferable because it is chemically stable and has a critical temperature close to room temperature.
[0011]
As an apparatus used in the present invention, a known extruder as shown in FIG. 1 can be used. At this time, as described above, the absolute value S of the contact area S (cm ² ) between the gaseous substance 5 and the silicone rubber composition 1 and the silicone rubber composition in the injection portion of the gaseous substance 5 (CO ₂ 5 in FIG. 1). In order to obtain a uniform silicone rubber foam 6, it is necessary that the relationship between the extrusion rate V (cm ³ / min.) Of the product 1 and the absolute value V is S ≧ 2 V, and this gas substance injection portion Is provided after the compression part provided in at least one place in the extruder, or after the part where the pressure of the silicone rubber composition 1 is raised to a certain value or more by the gear pump 3 as shown in FIG. If it does in this way, the backflow in the extruder of the gaseous substance 5 can be prevented.
Further, as means for satisfying the relationship between S and 2V in the present invention, a space is provided in the injection part of the gaseous substance 5 and the porous object 4 is filled therewith, and the gaseous substance 5 is filled through the porous object 4. By injecting, the desired contact area can be easily obtained and the silicone rubber composition 1 can be prevented from flowing back to the gas substance injection portion.
[0012]
Examples of the method for curing the silicone rubber composition include heating, electron beam irradiation, UV irradiation, radiation irradiation and the like, and can be appropriately selected depending on the type of the silicone rubber composition. In view of the properties, a method by heating or electron beam irradiation is preferable. Further, in the present invention, since the silicone rubber composition is foamed and then cured, the foamed uncured or semi-cured silicone rubber composition is used. Therefore, it is most preferable to use a method of uniformly curing to the inside without affecting the thermal conductivity, such as a method using high-frequency heating or a method using electron beam irradiation.
[0013]
【Example】
Next, an Example is given and this invention is demonstrated.
(Example 1)
A silicone rubber compound “KE151-U” was placed in a 50 mm single-screw rubber extruder provided with a gas material injection part after a gear pump filled with porous ceramics having a contact area S of 250 cm ² between the gas material and the composition. "(Shin-Etsu Chemical, trade name) 100 parts by weight and vulcanizing agent, bis-2,4-dichlorobenzoyl peroxide," C-2 "(Shin-Etsu Chemical, trade name) 3 parts by weight A specific gravity of 1.15) was supplied.
The kneaded product pressure is increased to 150 kgf / cm ² by a gear pump, the temperature is increased to 50 ° C., carbon dioxide is supplied at 50 ° C. and 152 kgf / cm ² through the porous ceramic, and extruded from a φ2 mm round die. At the same time, the pressure was released in 2 seconds to obtain a foamed silicone rubber composition. The extrusion rate V of the composition at this time was 43.5 cm ³ / min. This was treated by high frequency heating at 180 ° C. for 2 minutes, and then after-cured in an oven at 200 ° C. for 4 hours to obtain a silicone rubber foam.
At this time, the expansion ratio was 2.6 times, the average bubble size was 42 μm, and the standard deviation of the bubble size was 3.1 μm.
[0014]
(Comparative Example 1)
In the gas substance injection portion at the same position in the extruder used in Example 1, porous ceramics having a contact area S between the gas substance and the kneaded material of 50 cm ² is filled, and the silicone rubber compound “KE151-U” is filled. (Supra) 100 parts by weight and a vulcanizing agent, bis-2,4-dichlorobenzoyl peroxide and "C-2" (supra) 3 parts by weight were fed.
The kneaded material pressure is increased to 150 kgf / cm ² by a gear pump, the temperature is increased to 50 ° C., carbon dioxide is supplied at 50 ° C. and 152 kgf / cm ² through the porous ceramic, and extruded from a φ2 mm round die. At the same time, the pressure was released in 2 seconds. The kneaded product extrusion speed V at this time was 43.5 cm ³ / min.
This was treated by high frequency heating at 180 ° C. for 2 minutes and then aftercured in an oven at 200 ° C. for 4 hours to obtain a silicone rubber composition foam. The foaming ratio at this time was 1.2 times, and the number of bubbles was small, so it was not a foam.
[0015]
【The invention's effect】
According to the present invention, a silicone rubber foam having a uniform and fine cell diameter and uniform cell dispersibility with a cell size of less than 100 μm can be stabilized without highly controlling the curing rate and the foaming rate. Therefore, the manufacturing cost can be reduced and application to various uses becomes possible.
[Brief description of the drawings]
FIG. 1 is a longitudinal sectional view of an example of an extruder used in the present invention.
[Explanation of symbols]
1 silicone rubber composition, 6 silicone rubber foam.
2 screws,
3 Gear pump,
4 porous objects,
5 CO ₂ (gas substance),

Claims (1)

Using an extruder, in a silicone rubber composition in an uncured or semi-cured state, infiltrate and diffuse a gaseous substance at room temperature and normal pressure above its critical pressure and above its critical temperature, and then reduce the pressure. In a method for producing a silicone rubber foam, which is foamed in an uncured or semi-cured state and cured by molding, a gas substance at normal temperature and pressure and a silicone rubber composition in an injection part of the gas substance at normal temperature and pressure The relationship between the absolute value S of the contact area S (cm ² ) and the absolute value V of the extrusion rate V (cm ³ / min.) Of the silicone rubber composition is S ≧ 2V, and the pressure is reduced. Of 10 kgf / cm ² / sec. Or more, a method for producing a silicone rubber foam, wherein

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