JPH0337237A - Production of silicone rubber foam - Google Patents

Abstract

PURPOSE:To produce a silicone rubber foam which is opalescent, translucent and colorable by performing the expansion and curing of a composition comprising a specified diorganopolysiloxane, a finely powdered silica filler, a blowing agent and a vulcanizer by an ultrahigh frequency vulcanization system. CONSTITUTION:An expansible silicone rubber composition is obtained by mixing 100 pts.wt. diorganopolysiloxane having a degree of polymerization of 1000-30000, represented by the formula [wherein R is an (un)substituted monovalent hydrocarbon group; and (a) is 1.95-2.05] and containing at least 14mol%, based on the siloxane units, cyanoethyl- or cyanopropyl-substituted siloxane units with 10-300 pts.wt. finely powdered silica filler (e.g. fumed silica), 1-10 pts.wt. blowing agent (e.g. azobisisobutyronitrile), a vulcanizer (e.g. dicumyl peroxide) and optionally a dispersant, a heat resistance improver, a pigment, etc., This composition is expanded and cured by an ultrahigh frequency vulcanization system.

Description

Detailed Description of the Invention [Industrial Application Field 1] The present invention relates to a method for producing a silicone rubber foam, and in particular a method for producing a silicone rubber foam by foaming and curing a foamable silicone rubber composition using an ultra-high frequency vulcanization method. It relates to a manufacturing method.

[Prior Art] Recently, in the field of manufacturing thick-walled foams such as architectural gaskets and insulating foam rolls, there has been an increasing demand for stable and inexpensive production of these foams by continuous extrusion. As a method to meet such demands, for example, in the case of materials such as ethylene propylene diene rubber (EPDM) and chloroprene rubber (CR), ultrahigh frequency vulcanization (Ultra) If, gh is applied to continuous extrusion molded products of these materials.
FrequencyValcanlzation,
A method of performing a treatment (hereinafter referred to as U) IF vulcanization has been put into practical use.

This UHF vulcanization process usually operates at 2,450±50MHz.
By irradiating the workpiece with microwaves of 915±25MHz in a microwave heating oven, the workpiece absorbs the microwave and generates heat, resulting in foaming and crosslinking of the workpiece. This method is based on the calorific value p (watt/rr?) of the object to be treated.
) is expressed by the following formula.

(Here, f: microwave frequency (H2), E: high frequency electric field (V/m), ε: relative permittivity of the object to be treated, tan
δ: indicates dielectric loss coefficient).

Conventionally, this UHF vulcanization treatment is considered to be suitably applicable to objects having a loss index of ε and tan δ of 0.08 or more, particularly 0.2 or more.

On the other hand, in the field of silicone rubber foams, in order to stably and inexpensively manufacture the above-mentioned thick-walled foams using continuous extrusion molding, studies are being conducted on conventional processes and on the development of new foam curing technologies. Hot air vulcanization (HAV), which is conventionally known.

Continuous vulcanization methods such as continuous steam vulcanization (CV) and molten salt vulcanization (LCM) are unsuitable for producing long foams, and the cells in the resulting foams are not in good condition. Since there is a problem that UHF vulcanization is not possible, the application of UHF vulcanization to silicone rubber is also being considered, but generally silicone rubber has a loss index of about 0.03 at 3GH2, so
It is said that application of F vulcanization is virtually impossible.

Therefore, regarding the method of curing organosiloxane using microwaves, the organosiloxane constituting the organopolysiloxane composition has an aryl group, a fluorinated aliphatic hydrocarbon group, and at least one carbon-bonded mercapto group as an organic group. A method of irradiating microwaves to a material containing 5% or more of silicon-bonded organic groups selected from hydrocarbon groups, hydrocarbon groups having at least one carbinol group, and aliphatic hydrocarbon ether groups It has been proposed (see Japanese Patent Laid-Open No. 52-37963).

[Problems to be Solved by the Invention] However, the method of converting the unbonded organic group in organosiloxane into a special organic group as described above does not require the characteristic properties of silicone rubber such as heat resistance, weather resistance, and electrical properties. There are practical difficulties in that it lowers the vulcanization properties and deteriorates the vulcanization properties.

For this reason, the present inventors previously proposed a method of adding iron oxide powder and ferrite powder to a conventionally known organopolysiloxane composition and performing UHF vulcanization (Patent Application No. 63-22
2057), but this product has a disadvantage in that it cannot be colored in any color because its appearance is close to black, and it lacks adhesiveness.

[Means for Solving the Problems] The present invention relates to a method for producing a silicone rubber foam that overcomes these disadvantages, and includes (i) a method for producing a silicone rubber foam having an average degree of polymerization of 1,000 to 30,000; ,5iO4-
(where R is the same or different unsubstituted or substituted monovalent hydrocarbon group, a is a number from 1.95 to 2.05), and 14 mol% or more of the siloxane units are cyanoethyl 100 parts by weight of diorganopolysiloxane which is a siloxane unit substituted with a group or a cyanopropyl group, 0
) A foamable silicone rubber composition consisting of 10 to 300 parts by weight of ffi powdered silica filler, c) 1 to 10 parts by weight of a blowing agent, and 2) a vulcanizing agent is foamed and cured using an ultra-high frequency vulcanization method. It is characterized by:

That is, as a result of various studies by the present inventors on a method for producing a silicone rubber foam by UHF vulcanization that does not impair the characteristics of silicone rubber, we found that siloxane units substituted with cyanoethyl groups or cyanopropyl groups are present in the siloxane units constituting the organopolysiloxane. They discovered that this silicone rubber composition could be vulcanized by UHF by adding The present invention was completed by conducting research on the siloxane composition of organosiloxane.

This will be explained in further detail below.

[Function] The diorganopolysiloxane as component a) constituting the foamable silicone rubber composition used in the method of the present invention is represented by the formula R, 5IOn-a, where R is a methyl group, an ethyl group, Alkyl groups such as propyl and butyl groups, alkenyl groups such as vinyl, allyl and butenyl groups, aryl groups such as phenyl and tolyl groups, or some or all of the hydrogen atoms bonded to the carbon atoms of these groups. Same or different unsubstituted or substituted 1 selected from chloromethyl group, chloropropyl group, 3,3.3-trifluoropropyl group, 2-cyanoethyl group, cyanopropyl group, etc. substituted with halogen atom, cyano group, etc. This R group is considered to be a valent hydrocarbon group, but in order to UHF vulcanize a foamable silicone rubber composition in which a silica filler, a blowing agent, and a vulcanizing agent as described later are added to this organopolysiloxane, one of the is required to be a cyanoethyl group and /m to be a cyanopropyl group. If the amount of siloxane groups substituted with cyanoethyl groups or cyanopropyl groups is less than 14 mol% of the total siloxane units, the UHF absorption properties of this foamable silicone rubber composition will decrease and a good thick foam can be formed. Therefore, it is necessary to set the content to 14 mol% or more.

Among the unsubstituted or substituted-valent hydrocarbon groups represented by R, those other than the cyanoethyl group and cyanopropyl group include methyl group, vinyl group, phenyl group, 3,3.3-
)-lifluoropropyl group is preferred.

In addition, if the value of a in the general formula representing this organopolysiloxane is less than 1.95, the fluidity of the organopolysiloxane will deteriorate, making it difficult to blend with the silica filler 1 blowing agent and vulcanizing agent described later. If it is larger than 2.05, the degree of polymerization of the organopolysiloxane will not increase and the viscosity will be low, reducing workability.
It is necessary to have a range of 95 to 2.05.

Note that this organopolysiloxane has an average degree of polymerization of 1,
If it is less than 30,000, the viscosity will be low, and the composition containing the silica filler will have low plasticity and poor shape retention. Since the compounding properties of the polymers become extremely difficult, it is necessary to set the average degree of polymerization to 1,000 to 30.0+10.

In addition, the fine powder silica filler as component 0 in the foamable silicone rubber composition used in the method of the present invention is added for the purpose of reinforcing, thickening, improving processability, increasing the weight of the silicone rubber, etc. Examples of the company's products include famed silica, T1-type silica, surface-hydrophobized faded silica, wet silica, fine quartz powder, diatomaceous earth, etc. calcium.

It may contain a small amount of calcium carbonate, carbon black, glass fiber, etc., but these have a specific surface area of so1/
It is preferable that the amount of the above-mentioned organopolysiloxane is 100 m!g or more. If it is less than 10 parts by weight, the desired reinforcing properties will not be obtained and the processability will be insufficient, and if it exceeds 300 parts by weight,
Processing properties such as mold flowability and dischargeability are extremely deteriorated, so it is necessary to use a range of 10 to 300 parts by weight, but the preferred range is 50 to 200 parts by weight.

Next, the foaming agent as the component 8) constituting this composition is used to make the molded product obtained from this composition into a foam, which is stable at room temperature, but when exposed to high temperatures. Any material that emits a foaming gas is sufficient, and this foaming gas is generally considered to be nitrogen gas, but
This may be carbon dioxide or other gases, which are commercially available and include azobisisobutyronitrile, dinitrosopentamethylenetetramine, benzenesulfone hydrazide, N,N'-dinitros Examples include -N,N'-dimethyl terephthalamide and azodicarbonate, but if the blending amount is less than 1 part by weight per 100 parts by weight of diorganopolysiloxane as the first component, foaming gas may occur. Since the amount generated is small, a good foam cannot be obtained, and if the amount is more than tell parts, the processability of the composition will be reduced, and adding more than necessary will be wasteful, so 1 to ton parts, preferably. The amount may be 3 to 7 parts by weight.

In addition, the vulcanizing agent as the second component constituting this composition is a component blended for crosslinking the composition, and this includes a combination of an organic peroxide or a platinum-based compound and an organohydrodiene siloxane. Illustrated. Examples of this organic peroxide include benzoyl peroxide, monochlorobenzoyl peroxide, p-methylbenzoyl chloride, 2,4-dichlorobenzoyl peroxide, and t-
Butyl perbenzoate, dichloromethane, 2
゜5-bis-(t-butylperoxy)-2,5-dimethylhexane, 2,5-bis-(t-butylperoxy)-2,5-dimethylhexane, similystilperoxydicarbonate, dicarbonate, etc. Dicarbonates such as cyclododesilver oxydicarbonate, t-butyl monoperoxycarbonates, compounds represented by the following formula (wherein R is a monovalent hydrocarbon group having 3 to 10 carbon atoms), etc. are exemplified, and these may be used alone or in combination of two or more, but the blending amount is limited to the diorganopolysiloxane as the first component.
If the amount is less than 0.5 parts by weight based on 3i parts, a cured product with sufficient physical properties may not be obtained or the foam may become stiff. If it is more than 5 parts by weight, it may not meet the purpose. Since the foam may become a hard sponge that cannot be put to practical use, the amount may be in the range of 0.5 to 5 parts by weight, but the preferred range is 1 to 3 parts by weight. In addition, regarding this vulcanizing agent, if the organopolysiloxane as the above-mentioned component (a) contains an alkenyl group, it may undergo an addition reaction with this alkenyl group; Siloxane may be added, and a platinum-based addition reaction catalyst such as chloroplatinic acid, a complex acid of chloroplatinic acid and an olefin or vinyl siloxane, or an alcoholic solution of chloroplatinic acid may be added as a curing catalyst. The amount of platinum to be blended is (a) the amount of platinum relative to the diorganopolysiloxane component, and if it is less than 5 ppm, this addition reaction may not proceed sufficiently, and if it is more than 500 ppm, it is meaningless, so it is 5 to 500 ppm. You can do this, but
This preferred range is 2 to 200 ppm.

The foamable silicone rubber composition used in the method of the present invention can be obtained by mixing predetermined amounts of the above-mentioned components 1) to 2) and kneading them uniformly. Low molecular weight siloxane of 100 or less, silanol group-containing silane, alkoxy group-containing silane, iron oxide, cerium oxide.

Heat resistance improvers such as iron octylate, titanium oxide, pigments for coloring, flame retardant aids such as platinum compounds, palladium compounds, and even other additives that are usually added to this extremely foamable silicone rubber composition. Adding additives and the like is optional.

The foamable silicone rubber composition produced in this way can be made into a foamed silicone rubber molded article by tlHF vulcanization, but this UHF vulcanization is carried out in a vent type extruder -> UHF heating section - secondary vulcanization.

This may be carried out using a continuous extrusion vulcanizer consisting of a sulfur section and a take-off machine. Therefore, in this molding process, the foamable silicone rubber composition is first fed into a vent-type extruder, from which a silicone rubber molded body is continuously extruded into the desired shape. 2,450±50MHz or 915±25MHz high frequency oscillator and irradiate this high frequency. The foaming agent and organic peroxide decompose as the foaming agent and organic peroxide decompose, resulting in foaming and vulcanization hardening.This foaming and vulcanization are further In order to increase the speed, it is also possible to incorporate a heater in this tl) IF heating section to accelerate the temperature rise.
The foaming and vulcanization of the silicone rubber molded article is almost completely foamed and cured by this UHF vulcanization, which is then followed by conventionally known atmospheric pressure hot air vulcanization (HAV), fluid bed vulcanization (PCM) vulcanization, etc. It is recommended to carry out secondary vulcanization using UV rays, as this completes the vulcanization and removes the decomposition products generated during UHF vulcanization, making it easier and more stable to produce the desired silicone rubber foam molded product. This gives the advantage of being able to obtain

The silicone rubber foam molded product obtained by such a method constitutes the foamable silicone rubber composition used herein. (a) A siloxane in which the organopolysiloxane as a component is substituted with a cyanoethyl group or a cyanopropyl group. Since it is the same as conventional organopolysiloxane except that it contains units, it has excellent heat resistance, cold resistance, weather resistance,
It has excellent electrical properties and low compression set.This is also because this UHF vulcanization can generate heat not only on the surface layer but also on the inside almost simultaneously, resulting in fine foam cells and a cell shape. It has the advantage of being a well-matched foam molded product, which can also be made in a variety of colors, making it useful for building gaskets, insulation foam rolls, etc. It can be industrially advantageously used as a thick foam molded product.

[Example] Next, Examples of the present invention will be given, and parts in the examples indicate parts by weight.

Examples 1-3. Comparative Example 1 Contains dimethylsiloxane units, cyanopropyl methylsiloxane units, cyanoethyl methylsiloxane units, methylvinylsiloxane units, and dimethylvinylsiloxane units in the amounts shown in Table 1.The average degree of polymerization is about s, ooo. Four types of organopolysiloxanes I
(10 parts of dimethylpolysiloxane (degree of polymerization: 4) whose molecular chain ends are blocked with silanol groups as a dispersant)
and 35 parts of Humid Silica Aerosil 200 (trade name, manufactured by Nippon Aerosil ■) were added, kneaded in a kneader, and heat-treated at 160° C. for 2 hours to prepare a base compound.

Next, 100 parts of this base compound was added with a blowing agent (azobisisobutyronitrile) and an organic peroxide vulcanizing agent (2,4-dichlorobenzoyl peroxide, dicumyl peroxide) in the amounts shown in Table 1. was added and kneaded to obtain a foamable silicone rubber composition.

Supply this foamable silicone rubber composition to an extruder equipped with a die with a cylinder diameter of 40!11/φ and a cylinder length to diameter ratio of L/D 12 and 20-φ/10 mmφ. From now on, room temperature (15-30℃)
A tube-shaped silicone rubber molded body with an outer diameter of 2 (1 + vφ and an inner diameter of IQ mmφ) was continuously extruded and placed in a 1.5 m long UHF heating section that emitted microwaves with a frequency of 2.450 ± 50 MHz. A silicone rubber foam molded product was produced by circulating hot air at 180°C through two units at a conveyance speed of 2 m/min, foaming, and vulcanization and curing.The physical properties of this molded product were examined and are listed in Table 1. The results were as expected.

Table 1 [Effects of the Invention] The present invention relates to a method for producing a silicone rubber foam, which as described above is an organopolysiloxane containing 14 mol% or more of siloxane units substituted with cyanoethyl groups or cyanopropyl groups. A silicone rubber foam is produced by UHF vulcanization of a foamable silicone rubber composition to which a silica filler, a blowing agent, and a vulcanizing agent are added. Or, since it contains a cyanopropyl group-substituted siloxane unit, it can be UHF vulcanized,
This organopolysiloxane is the same as ordinary organosiloxane except that it contains siloxane units substituted with cyanoethyl and cyanopropyl groups, so it has the characteristic properties of silicone rubber such as heat resistance, weather resistance, electrical properties, and vulcanization properties. Since the foam obtained is milky white and translucent and can be colored freely, it is used industrially as a thick foam molded product for construction gaskets, insulation material 9 foam rolls, etc. It has the advantage that it can be used to advantage.

Claims (1)

[Claims] 1. A) Formula R_aSiO_(_4_-_a_)_/_2 (where R is the same or different unsubstituted or substituted monovalent hydrocarbons) having an average degree of polymerization of 1,000 to 30,000 100 parts by weight of a diorganopolysiloxane in which 14 mol% or more of the siloxane units are siloxane units substituted with a cyanoethyl group or a cyanopropyl group, b) fine powder; A foamable silicone rubber composition comprising 10 to 300 parts by weight of a silica filler, c) 1 to 10 parts by weight of a blowing agent, and d) a vulcanizing agent is foamed and cured using an ultra-high frequency vulcanization method. Method for manufacturing silicone rubber foam.