JP3235437B2 - Molding method of silicone rubber foam - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is suitable for use as a protective agent for various important parts such as corners and sensors of building gaskets, cushioning materials, various sponge rolls used for PPC or printers, heat insulating packings, spacers and the like. The molding method of the silicone rubber foam to be formed is described in more detail. Even when a mold having a complicated shape is used, the silicone rubber has a good finish at corners and edges and has excellent creep resistance. The present invention relates to a method for molding a silicone rubber foam from which a foam is obtained.

[0002]

2. Description of the Related Art Conventionally, silicone rubber foams have excellent elasticity in addition to the general properties of silicone rubber such as safety and hygiene, heat resistance, cold resistance and electrical properties. Is used for various purposes. In this case, the silicone rubber foam has a high expansion ratio, is sufficiently cured to the surface, has no tackiness, has a thin and soft spongy surface skin, and further has a loss of properties of the silicone rubber. It is necessary that it is not done.

[0003] In order to obtain a silicone rubber foam having a good foaming state, it is important to maintain a balance between foaming and curing when the silicone rubber foam composition is heated and foamed.

That is, the composition for a silicone rubber foam contains an organopolysiloxane for forming a silicone rubber foam, a foaming agent and a curing agent (organic peroxide). At the same time as the foaming agent is decomposed and foamed by heating the body composition,
Curing is initiated by the curing agent. In this case, if the decomposition of the foaming agent precedes, the bubbles are easily collapsed, so that the cell structure becomes uneven. Conversely, if the decomposition of the foaming agent is delayed, the progress of curing becomes large before gas is generated from the foaming agent. , Resulting in a non-uniform foam with a coarse cell structure. In this case, the progress of curing depends on the decomposition of the curing agent, so that the decomposition of the foaming agent and the curing agent (organic peroxide)
It is necessary to consider the balance with decomposition. However, this is complicated by the need to pay close attention to the production of silicone rubber foam.

In order to solve the above problem, use of azobisisobutyronitrile which functions not only as a foaming agent but also as a curing agent (Japanese Patent Publication No. 44-461).
However, the decomposition products generated in this case have safety and health problems, and in order to eliminate these safety and health problems, the decomposition products are sufficiently removed by long post-curing. And it is disadvantageous in manufacturing.

A method using azodicarbonamide as a foaming agent has also been proposed. In this case, the decomposition temperature of the azodicarbonamide is as high as 210 ° C., so that it is suitable as a foaming agent for silicone rubber. Absent. This can be solved by adding various decomposition temperature lowering agents that lower the decomposition temperature of azodicarbonamide as disclosed in U.S. Pat. No. 2,806,073. It has the disadvantage that the foam vulcanization conditions are delicate and it is difficult to obtain a constant foam.

Further, Japanese Patent Publication No. 5-47573 discloses that
The composition for silicone rubber foam using an azodicarbonamide-based foaming agent to solve the above-mentioned drawbacks is optimized for the composition, including the organic peroxide, and the molding conditions are optimized. A method of molding a silicone rubber foam having a good finish at the corners and edges of the silicone rubber foam has been proposed.In this case, the foamed state of the obtained molded article is good, but the compression state is good. There is still room for improvement in the creep resistance properties as represented by permanent set.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method of molding a silicone rubber foam which has excellent compression set characteristics and creep resistance characteristics and is excellent in safety and health.

The present inventors have conducted intensive studies to achieve the above object, and as a result, the following average composition formula (1) R _a SiO _{(4-a) / 2} (1) R is the same or different unsubstituted or substituted monovalent hydrocarbon group, but more than 0 mol% and not more than 0.2 mol% of R is an alkenyl group, and a is a positive number of 1.95 to 2.05. The organopolysiloxane, finely divided silica filler, an azodicarbonamide-based blowing agent having a decomposition temperature of 160 ° C. or less, and a decomposition temperature giving a half-life of 10 hours or more are 11
After foaming and vulcanizing the composition for silicone rubber foam containing a dialkyl peroxide at 0 ° C. or higher, the composition is irradiated with an electron beam. More preferably, the composition for silicone rubber foam is filled in a mold. At a temperature of 100-250 ° C.
After performing press vulcanization for foaming and vulcanization for 30 minutes, depressurizing, and then performing electron beam irradiation, the obtained silicone rubber foam realizes a high expansion ratio, and the corners and edges are The inventors of the present invention have found that they are sharp and have less tackiness, and have low creep properties that are excellent in compression set characteristics, and have accomplished the present invention.

That is, the present invention provides: (A) the following average composition formula (1): R _a SiO _{(4-a) / 2} (1) wherein R is the same or different unsubstituted or substituted An organoalkoxysiloxane represented by the formula: ## STR1 ## wherein R is more than 0 mol% and not more than 0.2 mol% is an alkenyl group, and a is a positive number from 1.95 to 2.05. (B) 3 to 70 parts by weight of a finely divided silica filler having a specific surface area of 1 m ² / g or more; (C) 2 to 10 parts by weight of an azodicarbonamide-based blowing agent having a decomposition temperature of 160 ° C. or less; D) Foaming and vulcanizing a composition for a silicone rubber foam containing 0.1 to 10 parts by weight of a dialkyl peroxide having a decomposition temperature giving a half life of 10 hours or more and 110 ° C. or more, and then irradiating with an electron beam. Provided is a method for molding a silicone rubber foam characterized by the following:

Hereinafter, the present invention will be described in further detail. The composition for a silicone rubber foam used in the method of molding a silicone rubber foam of the present invention comprises (A) an organopolysiloxane, (B) a finely divided silica filler, It contains (C) an azodicarbonamide-based blowing agent and (D) a dialkyl peroxide.

Here, as the organopolysiloxane of the component (A), those represented by the following average composition formula (1) R _a SiO _{(4-a) / 2} ... (1) are used.

In the above formula, R Are the same or different
Or unsubstituted or substituted C 1-10, especially 1-8 carbon atoms
A hydrocarbon group, specifically, a methyl group, an ethyl group,
Alkyl group such as propyl group, butyl group, vinyl group, allyl
Aryl such as alkenyl group, phenyl group and tolyl group
And some of the hydrogen atoms bonded to the carbon atoms of these groups
Or all of them are substituted with halogen atoms, cyano groups, etc.
Loromethyl group, chloropropyl group, 3,3,3-trif
A fluoropropyl group, a 2-cyanoethyl group and the like,
Among them, methyl group, phenyl group, 3,3,3-to
A trifluoropropyl group is preferred, and a methyl group is particularly preferred.
New

In this case, it is necessary that more than 0 mol% and not more than 0.2 mol%, preferably 0.025 to 0.07 mol% of R is an alkenyl group. The alkenyl group content is R
If the content exceeds 0.2 mol%, the obtained silicone rubber foam becomes hard and the durability is reduced. Incidentally, a vinyl group is preferred as the alkenyl group.

A is a positive number from 1.95 to 2.05, and the organopolysiloxane preferably has a linear molecular structure, but has a partially branched structure. No problem. Further, it is preferable that the molecular chain terminal is blocked with a triorganosilyl group or a hydroxyl group. Examples of the triorganosilyl group include, for example, a trimethyl group,
Examples thereof include a dimethylvinylsilyl group and a trivinylsilyl group. This organopolysiloxane preferably has a viscosity at 25 ° C. of 100,000 cs or more, particularly preferably 100,000 to 10,000,000 cs.

The finely divided silica filler of the component (B) is
It is added for the purpose of reinforcing, thickening, improving processability, and increasing the amount of silicone rubber, and examples thereof include fumed silica, wet silica, quartz powder, and diatomaceous earth. The finely divided silica filler has a specific surface area of 1 m ² / g or more,
In particular, those having 100 to 400 m ² / g are used. The compounding amount is 3 to 70 parts by weight with respect to 100 parts by weight of the organopolysiloxane, and especially 3 to 30 parts by weight.
Parts by weight are preferred. If the amount is less than 3 parts by weight, not only the desired reinforcing property cannot be obtained, but also the workability becomes insufficient. If the amount exceeds 70 parts by weight, the workability such as mold flowability may be extremely reduced. .

Further, as the azodicarbonamide-based blowing agent as the component (C), those having a decomposition temperature of 160 ° C. or lower are used. This is generally obtained by adding urea, a urea compound, zinc oxide, zinc stearate, polyethylene glycol or the like as an additive to azodicarbonamide, and particularly in terms of safety and health, urea or urea. It is preferred to use compounds as additives. As such azodicarbonamide-based foaming agents, commercially available products such as CellMike CAP-250 and CellMike CAP (both products are manufactured by Sankyo Chemical Co., Ltd.) can be used.

The compounding amount of the azodicarbonamide-based foaming agent is 2 to 10 parts by weight, preferably 3 to 8 parts by weight, based on 100 parts by weight of the organopolysiloxane. If the amount is less than 2 parts by weight, foaming may be insufficient. If the amount is more than 10 parts by weight, foaming may be excessive and the properties of the foam may be deteriorated.

Further, as the dialkyl peroxide of the component (D), a dialkyl peroxide having a decomposition temperature (τ) giving a half life of 10 hours or more of 110 ° C. or more is used.
This is used to promote heat curing of silicone rubber. Such dialkyl peroxides include, for example, 2,5-bis- (t-butylperoxy) -2,5-dimethylhexane (τ = 118 ° C.), dicumyl peroxide (τ = 116 ° C.), 2,5 -Bis- (t-butylperoxy) -2,5-dimethylhexine ([tau] = 135 [deg.] C.), di-t-butyl peroxide ([tau] = 124 [deg.] C.) and the like.

The amount of the above-mentioned alkyl peroxide can be appropriately selected according to the kind and the amount of other components.
0.1 parts by weight based on 100 parts by weight of the organopolysiloxane.
It is 1 to 10 parts by weight, preferably 0.2 to 5 parts by weight.

A diacyl peroxide (eg, 2,4-dichlorobenzoyl peroxide, benzoyl peroxide) or a peroxyketal (eg, 1,1-bis (t- Butylperoxy) -3,3,5-trimethylcyclohexane) and the like are preferable because the temperature for obtaining a half-life of 10 hours is lower than 110 ° C., so that they decompose before the blowing agent and promote vulcanization. Although it is difficult to obtain a suitable foam and cannot be used alone in the present invention, it may be used in combination with the component (D) as long as the object of the present invention is not impaired.

The silicone rubber foaming composition containing the above components (A) to (D) may have a degree of polymerization of 1 if necessary.
Dispersant such as low molecular weight siloxane of 00 or less, silanol group-containing silane or siloxane, alkoxy group-containing silane,
Heat resistance improvers such as iron oxide, cerium oxide, iron octylate, titanium oxide, carbon black, conductive metal oxide,
Conductivity imparting agents such as metal powder, pigments for coloring, flame retardant imparting agents such as platinum compounds and palladium compounds, and additives such as calcium carbonate, glass powder, and nylon fibers can be used.

The method for molding a silicone rubber foam of the present invention comprises foaming and vulcanizing a composition for a silicone rubber foam containing the above components (A) to (D). The above-mentioned composition for silicone rubber foam is filled in a mold, and the temperature is in the range of 100 to 250 ° C.
After press vulcanization for 30 minutes, it is preferable to perform mold foaming for removing pressure. In this case, the press pressure is 10-200k
gf / cm ² is preferred. The composition for silicone rubber foam used in the present invention has a good and uniform balance between foaming and curing by adopting the above-mentioned temperature, and has a complicated shape as a mold due to the pressure applied during press vulcanization. Even when the composition is used, since the composition spreads all over the corners, the corners and edges of the completed molded article become sharp.

Further, the present invention further comprises subjecting the silicone rubber foam obtained by foaming and vulcanization to an irradiation treatment with an electron beam, whereby the crosslinking is further promoted and the desired compression set is obtained. A low creep silicone rubber foam having excellent properties can be obtained. If the irradiation treatment with the electron beam is not performed, the molded silicone rubber foam remains in a state of large compression set. Before the electron beam irradiation treatment, 0-150 ° C. at 150-220 ° C. for the purpose of removing the decomposition products of the vulcanizing agent and the foaming agent.
Post-curing for ~ 8 hours is optional.

In this case, it is essential that the electron beam irradiation is performed after the mold foaming. If electron beam irradiation is performed before or at the same time as mold foaming as primary molding, sufficient foaming cannot be achieved, and the object of the present invention cannot be achieved.

The irradiation amount of the electron beam may be determined according to the required physical properties of the target foam, and is arbitrary, but is typically 1 to 300 kGy. If the irradiation amount is less than 1 kGy, the desired low compression set cannot be achieved, and if it exceeds 300 kGy, the foam becomes hard or brittle, and it is economically disadvantageous.

The thickness of the silicone rubber foam obtained according to the present invention depends on the expansion ratio, but is preferably at most about 10 mm or less in view of the cross-linking property during electron beam irradiation. If the thickness of the silicone rubber foam is too thick,
In some cases, crosslinking in the deep part is not sufficiently achieved, and low compression set cannot be obtained. Furthermore, when the applied voltage is increased to pass the electron beam to the deep part, the energy level is different between the surface of the foam and the deep part, so that the cross-linked structure becomes unbalanced, and it is impossible to obtain a uniform silicone rubber foam. Cases arise.

[0028]

As described above, according to the method for molding a silicone rubber foam of the present invention, even a silicone rubber foam having a complicated shape has sharp corners and edges, little surface tack, and further compression. A low creep silicone rubber foam having excellent permanent set characteristics can be obtained, and it is excellent in terms of safety and hygiene.

[0029]

EXAMPLES The present invention will be described below in detail with reference to examples and comparative examples, but the present invention is not limited to the following examples. In the following examples, parts by weight represent parts by weight, and viscosities are measured at 25 ° C.

Examples 1 to 5, Comparative Examples 1 to 5
As shown in FIGS. 1 and 2, (CH_Three)_TwoSiO unit, (CH_Two
= CH) CH_ThreeSiO units and (CH_Three)_ThreeSiO_1/2unit
Having a viscosity at 25 ° C. of about 10,000,000
100 parts of organopolysiloxane of cs and fume dosi
Rica (Aerosil R972; trade name, manufactured by Degussa Co., Ltd.)
After mixing with 20 parts, the mixture is kneaded evenly with two rolls.
A silicone rubber foam base was obtained. 100 parts of this base
Azodicarbonamide blowing agent (Selmy
CAP-250 and Cell Mike 172-C; Sankyo Chemical
5 parts and 2,5-bis (t) as a vulcanizing agent
-Butylperoxy) -2,5-dimethylhexane (addition
Sulfurizing agent A) 0.5 part or 2,5-bis (t-butylperoxide)
Xy) -2,5-dimethylhexyne (vulcanizing agent B) 0.5
Part, and further kneaded to obtain a composition for silicone rubber foam.
I got After sufficiently degassing the obtained composition, 6 m
Press mold with space of mx 50mm x 140mm
Fill, press pressure 30kgf / cm^TwoAt a temperature of 165 ° C
After vulcanizing for 5 minutes, depressurize and remove silicone rubber foam
Obtained. Electron beam irradiation on the obtained silicone rubber foam
Was done. In this case, the electron beam irradiation is performed with an applied voltage of 5 MV,
Electron beam irradiation of 10 to 50 kGy under the condition of 1 mA
(Performed by Radiage Industrial Co., Ltd.). Obtained departure
The physical properties and properties of the foam are shown in Tables 1 and 2.

In Comparative Example 5, secondary vulcanization was performed in a dryer at 200 ° C. for 4 hours in place of electron beam irradiation in Example 1. Further, in Example 1, 2,4-dichlorobenzoyl peroxide 0.6 was used instead of the vulcanizing agent A.
When the portion was used, the sheet hardly foamed and became a hard sheet.

[0032]

[Table 1]

[0033]

[Table 2]

As shown in Table 1, with regard to the silicone rubber foams of Examples 1 to 5, the sponge has no sagging while maintaining a dense structure due to electron beam irradiation. The difference between the silicone rubber foam of the present example and the comparative example is particularly apparent in the compression set characteristics,
In the comparative example, the compression set characteristic exceeds 50%, whereas in the present embodiment, the compression set characteristic is remarkably improved to 20% or less.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-2-107645 (JP, A) JP-A-58-84736 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C08J 9/00-9/42 C08K 3/00-13/08 C08L 1/00-101/16

Claims (2)

(57) [Claims] (A) The following average composition formula (1): R _a SiO _{(4-a) / 2} (1) (wherein, R represents the same or different unsubstituted or substituted monovalent hydrocarbon group) Wherein more than 0 mol% and not more than 0.2 mol% of R are alkenyl groups, and a is a positive number of 1.95 to 2.05.) 100 parts by weight of an organopolysiloxane represented by the following formula: B) 3 to 70 parts by weight of a finely divided silica filler having a specific surface area of 1 m ² / g or more, (C) 2 to 10 parts by weight of an azodicarbonamide-based blowing agent having a decomposition temperature of 160 ° C. or less, (D) 10 hours The composition for foaming and vulcanizing a composition for a silicone rubber foam containing 0.1 to 10 parts by weight of a dialkyl peroxide having a decomposition temperature that gives the above half-life of 110 ° C. or more is irradiated with an electron beam. Molding method of silicone rubber foam. 2. The composition for silicone rubber foam is filled in a mold, press-vulcanized at a temperature of 100 to 250 ° C. for 1 to 30 minutes, foamed and vulcanized, depressurized, and then electron beam. The molding method according to claim 1, wherein the irradiation is performed.