JPH08259720A - Production of silicone foam - Google Patents

Abstract

PURPOSE: To obtain a process for producing a silicone foam in which the cells are extremely small and uniform in size, and to obtain a process for producing silicone foams with a mold which have excellent performance and are uniform in dimensions. CONSTITUTION: A two-pack type curable liquid organopolysiloxane which consists of a main agent and a hardener and does not generate any foaming gas upon curing reaction is fed separately. The two ingredients are mixed by means of a stirrer rotating at 100rpm or higher, during which a gas is kept being forced into the mixture at a pressure of 2-100kgf/cm<2> . The resulting homogeneous mixture is discharged and hardened.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a silicone foam, and more particularly to a method for producing a uniform silicone foam having fine cells.

[0002]

2. Description of the Related Art Silicone foams have the following properties: rubber strength, heat resistance,
Since it has good cold resistance and rubber elasticity, it is used as a sealant and heat insulating material provided around the automobile engine, a sealant for electric / electronic parts, a gasket material, various roll materials for printers, building gasket materials, etc. in use. As a method for obtaining such a foam of a silicone polymer, a method of adding an organic peroxide and a foaming agent to a silicone polymer and heating to foam and cure, and a two-component type silicone foam composition comprising a main agent and a curing agent is used. A method of mixing and utilizing hydrogen gas generated by the reaction is known. The former is easy to obtain a strong foaming agent, but it is difficult to use in a liquid composition, and there is a limitation in workability and application.

The latter can be worked efficiently by using a device, but the foaming in the silicone foam thus obtained is difficult to control because it is due to hydrogen gas generated by a chemical reaction, and the foaming is difficult. Cell diameter is 200
Since it becomes coarse to about 2,000 μm and its size varies, the performance as a foam such as heat insulation and cushioning property is insufficient, and in the case of a foam obtained by foaming in a mold, However, there is a drawback that the dimensions also vary.

Therefore, in order to improve such drawbacks, recently, a method has been proposed in which a gas is pressed into a silicone foam composition to form fine and uniform foam cells (JP-A-6-200066). Gazette). However, even in the above method, since hydrogen gas generated by a chemical reaction is basically used, it is not possible to form a foam cell having a sufficiently fine and uniform size, and the performance of the foam is not sufficient. However, there is a drawback in that it is not possible to obtain a foam having a uniform size by die molding.

[0005]

The inventors of the present invention have made extensive studies in order to solve the above-mentioned drawbacks, and as a result, did not utilize the gas generated by the reaction but used a forced stirrer to produce a gas at a specific pressure. When dispersed in a curable liquid organopolysiloxane composition, an extremely fine and uniform foam cell can be obtained, and therefore, the performance of the resulting foam is excellent, and when it is obtained by die molding. Also found that a foam having a uniform size was obtained, and arrived at the present invention.

[0006] Therefore, a first object of the present invention is to provide a method for producing a silicone foam in which the foam cells can be made extremely fine and uniform in size. A second object of the present invention is to have excellent performance as a foam,
It is an object of the present invention to provide a method for producing a silicone foam that can obtain a foam having a uniform size by molding.

[0007]

The above objects of the present invention are to provide a curable liquid organopolysiloxane composition comprising a curable liquid organopolysiloxane composition and a curative which do not generate a gas that reacts with foaming. The curing agent was separately transported and both liquids were mixed, and at the same time, the gas was injected at a pressure of ² to 100 kgf / cm ² while mixing with a forced agitator having a rotor rotation speed of 100 rpm or more, and then uniformly dispersed. It has been achieved by a method for producing a silicone foam, characterized in that the mixture is discharged and cured.

The curable liquid organopolysiloxane composition used in the present invention is a composition composed of two liquids of a main component and a curing agent, and is a liquid organopolysiloxane composition which is cured by mixing the two liquids. is there. The curable organopolysiloxane composition used in the present invention is simply a mixture,
It is necessary that it does not become a foam when cured. This is because it is difficult to control the cells of the foam if the gas generated by the chemical reaction is used for foaming. Also, the pot life is short when the one-pack type is used,
Workability deteriorates significantly.

The composition used in the present invention is not particularly limited as long as it satisfies the above conditions, but it is an addition reaction curable liquid comprising the following components (A), (B), (C) and (D). It is preferable to use an organopolysiloxane composition, and it is particularly preferable that the component (B) and the component (C) are separate from the viewpoint of foaming and curing during mixing. Therefore, a mixture obtained by mixing the component (A) and the component (D) with the component (C) is used as the main component, and the component (A) and the component (D) are optionally mixed with the component (B) or the component (B). It is preferable to use the mixture as a curing agent.

(A) It has at least two alkenyl groups in one molecule and has a viscosity at 25 ° C. of 100 to 200,
Organopolysiloxane having a molecular weight of 000 cSt: 100 parts by weight (B) Organohydrogenpolysiloxane having two or more hydrogen atoms bonded to silicon atoms in one molecule: Silicon per alkenyl group contained in the component (A) Sufficient amount to supply 0.6 to 6.0 hydrogen atoms bonded to atoms (C) Platinum group metal-based catalyst: catalytic amount (D) Fine powder silica having a BET specific surface area of at least 50 m ² / g : 5 to 70 parts by weight

The organopolysiloxane as the component (A) must have at least two alkenyl groups in one molecule, and compounds represented by the following chemical formulas 1 and / or 2 are preferable.

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R ₁ in the above chemical formulas ₁ and 2 is a methyl group,
Number of carbon atoms is 1 such as ethyl, propyl, butyl, etc.
An alkyl group having from 6 to 6; an aryl group such as a phenyl group and a tolyl group; a hydrogen atom bonded to a carbon atom of an alkyl group having from 1 to 6 carbon atoms, such as a chloromethyl group, a trifluoropropyl group, and a cyanoethyl group. Substituted or unsubstituted monovalent hydrocarbon groups which may be the same or different and are selected from groups in which all or a part of them are substituted with halogen atoms or cyano groups (provided that they are aliphatic unsaturated hydrocarbon groups). (Excluding hydrogen group), a methyl group, a phenyl group and a trifluoropropyl group are preferable, and a methyl group is particularly preferable.

R ₂ is an alkenyl group such as a vinyl group or an allyl group, and a vinyl group is particularly preferable. 1 alkenyl group
At least two are contained in the molecule. m is 50 to 2,0
00, and n is a number from 0 to 0.1. The viscosity of such an organopolysiloxane at 25 ° C. is
As described above, it is preferably 100 to 200,000 cSt. If it is less than 100 cSt, the mechanical strength of the obtained foam is insufficient, and if it exceeds 200,000 cSt, it becomes difficult to disperse the gas in the mixed composition.

The organohydrogenpolysiloxane which is the component (B) is required to have at least two hydrogen atoms directly bonded to silicon atoms, and it has the general formula R _3a
H _b SiO 2 _{(4- (a + b) / 2)} R ₃ in the above general formula
Is a substituted or unsubstituted monovalent hydrocarbon group which may be the same or different (excluding an aliphatic unsaturated hydrocarbon group), a is a number of 0 to 2 and b is 1 Number of 3 and a +
b is any number from 1 to 3.

Specific examples of R ₃ include alkyl groups such as methyl group, ethyl group, propyl group, butyl group, pentyl group and hexyl group. Among these groups, it is particularly preferable to use an organohydrogenpolysiloxane in which R ₃ is a methyl group from the viewpoint of easy availability.

The platinum group metal-based catalyst which is the component (C) has a function of promoting the addition reaction between the component (A) and the component (B). Examples of platinum group metal-based catalysts include platinum, platinum-based compounds, platinum complexes, and the like. Specific examples include platinum black or platinum supported on silica or carbon black, chloroplatinic acid, an alcohol solution of chloroplatinic acid, and a platinum compound such as a complex of chloroplatinic acid and olefin or vinylsiloxane. To be

The addition amount of the component (C) is 0.1 as platinum metal based on the total weight of the components (A), (B) and (C).
To 200 ppm is preferable, and especially 1 to 50 p
It is preferably pm. If it is less than 0.1 ppm, the addition reaction will be slow, and if it exceeds 200 ppm, the reaction promoting effect will be small, which is rather uneconomical. The differentially-divided silica, which is the component (D), is a filler and has a function to reinforce the foam, but depending on the amount contained, it greatly influences the foaming state.

Specific examples of the fine powder silica include fine powder silica such as fumed silica (Erosil 200: trade name of Nippon Aerosil Co., Ltd.), wet silica, or halogenated silane, silazane or low molecular siloxane. Examples of the silica include a surface-treated silica. Among these, from the viewpoint of increasing the strength of the foam obtained, as described above, the BET specific surface area is at least 50 m ² / g,
Preference is given to using finely divided silica, which is preferably 100 to 400 m ² / g.

As other fillers, inorganic fillers such as zinc oxide, magnesium oxide, calcium carbonate, precipitated silica, titanium dioxide, aluminum oxide, quartz powder, talc, bentonite, asbestos and glass fiber, and / or
Alternatively, an organic filler such as an organic fiber may be added. Furthermore,
If necessary, alcohol compounds for controlling the addition reaction of the components (A) and (B), low molecular weight siloxane containing vinyl groups, colorants such as pigments and dyes, red iron oxide, cerium oxide, etc. A heat resistance improver, a thixotropy imparting agent such as polyether, a rust preventive, and a viscosity modifier may be added to the composition.

The viscosity of the curable liquid organopolysiloxane composition used in the present invention at 25 ° C. is preferably 1,000 cp to 10,000,000 cp,
More preferably 5,000 cp to 5,000,000 c
p. If the viscosity is lower than 1,000 cp, the strength of the resulting foam may be impaired, and 10,000,
When the viscosity is higher than 000 cp, it becomes difficult to press the gas under pressure and a foam may not be obtained.

The forced agitator used in the present invention has at least holes for introducing the main agent, the curing agent and the compressed gas separately, and holes for discharging the mixed / dispersed composition, and the gas is dispersed in the composition. It is an apparatus having a rotor for stirring the introduced composition and gas in an airtight tank having a mixing chamber for mixing (see FIG. 1). This forced agitator acts to disperse the main agent and the curing agent, which are separately transported from the main agent tank and the curing agent tank, and the introduced compressed gas in the composition by stirring and mixing in a closed or semi-closed state. .

Next, the manufacturing method of the present invention will be described in more detail with reference to the drawings. FIG. 1 is a schematic sectional view showing an example of a forced stirring mixer used in the production method of the present invention. FIG. 2 is a schematic configuration diagram showing the overall configuration of the manufacturing method of the present invention. In the figure, reference numeral 7 is a curing agent tank for storing the curing agent, 8 is a curing agent tank for storing the curing agent, 9 is a metering pump for transporting the curing agent or the curing agent, 1 is a mixing agent for the curing agent and the curing agent.
A forced stirring mixer that stirs and evenly disperses the gas.
Reference numeral 2 denotes a rotor which is incorporated in a forced mixing stirrer and which has a plurality of blades around it and rotates to mix the main agent and the curing agent and to uniformly disperse the gas in the mixture. Also, 10
Is a compressor or gas cylinder for sending gas under pressure to the forced agitation mixer 1.

In producing a silicone foam, first, a curing agent and a main agent (raw material) are charged into the curing agent tank 7 and the main agent tank 8, respectively, and then the pressure inside the tanks 7 and 8 is reduced by a pressure reducing pump (not shown). Then defoam the raw material. Forced stirrer 1 for defoamed curing agent and main agent
Then, it is quantitatively transported by the metering pump 9. The curing agent and the main agent transported into the forced agitator 1 are forcibly agitated and mixed by the rotor 2.

At this time, the gas is forced into the forced agitator 1 from the compressor or the gas cylinder 10 and uniformly dispersed in the mixture of the curing agent and the main agent. The gas used is not particularly limited as long as it does not react with the curing agent or the main agent, and can be appropriately selected. Examples of such a gas include air, nitrogen gas, carbon dioxide,
Helium, argon and the like can be mentioned, but among these, it is preferable to use air from the viewpoint of economy.

The amount of the gas dispersed in the mixture is 1:10 to 10: 1 in volume ratio with respect to the volume of the solution at the time of mixing.
Is preferable, and more preferably 5:10 to 1
It is 0: 1. If the volume ratio of gas exceeds 1:10, the mechanical strength of the obtained foam will be reduced, and if it is less than 10: 1, the performance such as heat insulating property, metering property, cushioning property as the foam will be reduced. is there.

The number of rotations of the rotor 2 during the stirring and mixing is 10
It is necessary to be 0 rpm or more, preferably 10
0 to 6,000 rpm, more preferably 500 to 5,0
It is 00 rpm. If it is less than 100 rpm, mixing and dispersion will be insufficient and a good foam cannot be obtained. 6,0
Even if it exceeds 00 rpm, the effect of improving mixing / dispersion does not change, and it may be uneconomical.

The pressure in the agitating mixer at the time of agitating and mixing is 2
-100 kgf / cm ² , preferably 10-50 kgf
/ M ² . If it is less than 2 kgf / cm ² , the solution ratio of the gas to be dispersed tends to be less than 10: 1 with respect to the mixed liquid, and if it exceeds 100 kgf / cm ² , it tends to exceed 1:10.

In this way, the mixed composition in which the gas is uniformly mixed is discharged into the atmosphere or the mold (see FIG. 3),
Although it may be left standing at room temperature for curing and foaming, it is preferably heated to 80 to 200 ° C. from the viewpoint of accelerating the curing reaction. It should be noted that it is preferable that the injection amount in the case of discharging into the mold be the same as the internal volume of the mold. By doing the above, it is possible to obtain a foam having good performance, which has fine and uniform foam cells and can be made into a uniform size corresponding to the mold (see FIG. 4).

[0029]

According to the production method of the present invention, gas is forced into a mixture of a curable liquid organopolysiloxane composition at a specific volume ratio and pressure and mixed by a forced stirrer, so that an extremely fine and uniform size is obtained. Silicone foams having foam cells can be produced. Therefore, the obtained foam not only has good performance, but also becomes a foam having a uniform size corresponding to the mold when used as a mold-molded product.

[0030]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, but it should not be construed that the invention is limited thereto. Example 1. The main agent and the curing agent shown in Table 1 are put into the curing agent tank 7 and the main agent tank 8, respectively, and after depressurizing the inside of the tank with a vacuum pump to defoam the main agent and the curing agent, the mono pump 9 (Hyojin equipment stock (Manufactured by the company) were separately transported into the mixing chamber 19 of the forced agitation mixer 1 at a transportation speed of 50 g / min, and the mixture was stirred and mixed for 1 minute with the rotation speed of the rotor 5 being 5,000 rpm.

During this stirring, the compressors 10 to 3
After introducing 0 kg / cm ² of compressed air into the mixing chamber 19 and sealing the mixture, the compressed air supply was stopped and the lower valve was opened, and the obtained mixture was placed in a mold with deaeration holes. The liquid was discharged from the injection hole to the inside thereof, and the degassing hole and the injection hole were closed after the injection was completed. Next, heat the mold 12
After heating at 0 ° C. for 30 minutes, the mold was removed to obtain a roll of silicone foam (see FIG. 4).

When the hardness (Asker C) of the foam roll thus obtained was measured, it was 50 and the specific gravity was 0.3. Moreover, when the cross section of the obtained roll was measured with an optical microscope, the diameter of the foamed cells in the roll was about 50 μm, which was uniform. The roll of the obtained foam had a uniform size corresponding to the mold.

[0033]

[Table 1]

Embodiment 2 FIG. The main agent and the hardener shown in Table 1 were respectively charged into the hardener tank 7 and the main agent tank 8, and the inside of the tank was decompressed by depressurizing with a vacuum pump, and then the Mono pump 9 (manufactured by Hyojin Equipment Co., Ltd.) Then, they were separately transported into the mixing chamber of the forced agitation mixer 1 at a transportation speed of 30 g / min, and the mixture was stirred and mixed for 1 minute with the rotation speed of the rotor 5 being 500 rpm. 20 kg / cm from the high pressure nitrogen cylinder during this stirring
The compressed nitrogen gas of No. ² was introduced into the mixing chamber to make the latter half closed state.

Next, after the supply of compressed air was stopped, the lower valve was opened and the resulting mixture was discharged into the container (see FIG. 5). Put this container in the oven,
A silicone foam sheet was obtained by heating at 30 ° C. for 30 minutes. When the hardness (Asker C) of the obtained foamed sheet was measured, it was 40, the tensile strength was 15 kg / cm ² , and the elongation was 2
The specific gravity was 00% and 0.5. Further, when the cross section of the obtained foamed sheet was measured by an optical microscope, the diameter of the foamed cells in the foamed sheet was about 50 μm, which was uniform. Further, the obtained foamed sheet had a uniform size corresponding to the container.

Comparative Example 1. When a sheet was molded in exactly the same manner as in Example 2 except that the number of revolutions of the rotor was changed to 50 rpm and the pressure of nitrogen gas was changed to 1 kg / cm ² , a foamable sheet was not obtained.

Example 3. The base material and the curing agent having the compositions shown in Table 2 were placed in the material tank shown in FIG. 2 and defoamed under reduced pressure by a vacuum pump. Next, a forced stirrer 1 (developed by Auto Machine Co., Ltd.) shown in FIG. 1 was used with a Mono pump (Hyojin Equipment Co., Ltd.) at a transport speed of 50 g / min for each.
And rotate the rotor 5 at 3,500 rpm,
Stir-mix for 1 minute. At this time, by the compressor,
Pressing compressed air into the mixing chamber at a pressure of 30 kg / cm ² ,
The valve 6 was closed.

Next, after the supply of compressed air was stopped and the valve 6 was opened, the mixture was injected through the injection hole into the mold shown in FIG. 3 (at this time, the deaeration hole valve 16 was previously opened. Every other time and closed after the injection). The silicone foam roll shown in FIG. 4 was obtained by removing the mold 10 minutes after the injection hole valve 13 was closed. Roll hardness is 4
It was 0 (Asker C) and the specific gravity was 0.3. The foam cells were fine and uniform with a diameter of about 50 μm.

[0039]

[Table 2]

Example 4. The main agent and effect agent having the compositions shown in Table 2 were placed in the material tank shown in FIG. 2 and defoamed under reduced pressure by a vacuum pump. Next, each was transported to the forced agitation mixer 1 shown in FIG. 1 at a transportation speed of 30 g / min, and the rotor 5 was rotated at 2,000 rpm for stirring and mixing. At this time, pressurized nitrogen was supplied to the mixing chamber by a high pressure nitrogen cylinder.
The valve 6 was pressed in at a pressure of kg / cm ² and the valve 6 was slightly opened. Next, the mixture was discharged into the container shown in FIG. When the mold was removed after 30 minutes, a silicone foam sheet was obtained. The obtained sheet has a hardness of 30 (Asker C), a tensile strength of 15 kg / cm ² , and an elongation of 300%.
And the specific gravity was 0.5.

Example 5. Rotational speed of rotor 5 3,500r
A silicone foam roll was obtained in exactly the same manner as in Example 3 except that pm was set to 7,000 rpm. The obtained roll had a hardness of 40 (Asker) and a specific gravity of 0.3. The foam cells were fine and uniform with a diameter of about 50 μm.

Comparative Example 2. The same main agent and curing agent as those used in Example 3 were used, and each was transported to the forced agitation mixer 1 shown in FIG. 1 at a transportation rate of 30 g / min, and the rotor 5 was rotated at 50 rpm and stirred. Mixed. At this time, pressurizing nitrogen into the mixing chamber by a high pressure nitrogen cylinder 20k.
The valve 6 was press-fitted with a pressure of g / cm ² , and the valve 6 was slightly opened. Next, the mixture was discharged into the container shown in FIG. When the mold was removed after 30 minutes, a silicone sheet containing a slight amount of bubbles was obtained, but no foam was obtained.

Comparative Example 3. Rotor speed of rotor 5 2,000r
Except for setting pm to 80 rpm, the same procedure as in Example 4 was carried out. As a result, a silicone sheet containing a few bubbles was obtained, but no foam was obtained.

[Brief description of drawings]

FIG. 1 is a schematic sectional view showing an example of a forced agitator used in the present invention.

FIG. 2 is a schematic configuration diagram showing an overall configuration of a manufacturing method of the present invention.

FIG. 3 is a schematic cross-sectional view of a mold for molding the silicone foam roll used in Example 1.

4 is a schematic cross-sectional view of the silicone foam roll obtained in Example 1. FIG.

5 is a schematic cross-sectional view of a molded container for a silicone foam sheet used in Example 2 and a sheet molded with the container. FIG.

[Explanation of symbols]

 1 Forced Stirring Mixer 2 Main Agent Introducing Hole 3 Hardener Introducing Hole 4 Compressed Gas Introducing Hole 5 Rotor 6 Mixed Composition Discharge Valve 7 Curing Agent Tank 8 Main Agent Tank 9 Metering Pump 10 Compressor or Gas Cylinder 11 Mandrel 12 Mold 13 injection hole 14 deaeration hole 15 injection hole valve 16 deaeration valve 15 silicone foam roll 17 container 18 silicone foam sheet 19 mixing chamber

Front page continuation (72) Inventor Ryuichi Handa 1 Hitomi, Oita, Matsuida-cho, Usui-gun, Gunma 10 Shin-Etsu Chemical Co., Ltd. Silicone Electronic Materials Research Laboratory

Claims (3)

[Claims] 1. A main component of a curable liquid organopolysiloxane composition consisting of two liquids, a main component which does not react to generate a gas involved in foaming and a curing agent, and the curing agent are separately transported and both liquids are mixed. At the same time, ^{2 to} 100 kgf / cm ²
Rotation speed of the rotor is 100
A method for producing a silicone foam, which comprises mixing with a forced stirrer at rpm or more, and then discharging and curing the uniformly dispersed mixture. 2. The method for producing a silicone foam according to claim 1, wherein the discharging is performed in a mold. 3. A curable liquid organopolysiloxane composition having (A) at least two alkenyl groups in one molecule and a viscosity at 25 ° C. of 100 to 200,000 cS.
organopolysiloxane of t: 100 parts by weight, (B) an organohydrogenpolysiloxane having two or more hydrogen atoms bonded to silicon atoms in one molecule: per alkenyl group contained in the component (A), An amount sufficient to supply 0.6 to 6.0 hydrogen atoms bonded to silicon atoms, (C) platinum group metal-based catalyst: catalytic amount, and (D) BET specific surface area of at least 50 m ² / g. A method for producing a silicone foam according to claim 1 or 2, which comprises 5 to 70 parts by weight of finely divided silica.