JP2002265784A - Storage method for silica-containing rubber compounds - Google Patents

Abstract

(57) Abstract: Storage of a silica-containing rubber compound, wherein the silica-containing rubber compound is accommodated in a storage container in a state of being covered with a sheet, and a moisture-absorbing agent is present in the storage container. Method. According to the storage method of the present invention, moisture absorption of the silica-containing rubber compound can be prevented easily and for a long time.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a silica-containing rubber compound for preventing foaming due to moisture absorbed when a silica-containing rubber compound is extruded by hot air vulcanization under normal pressure. It relates to the storage method of the compound.

[0002]

2. Description of the Related Art A silica-containing rubber compound such as a silicone rubber compound containing silica fine particles, when it absorbs moisture,
When this is molded as it is, air bubbles are often generated in the entire molded product. However, when the compound has almost no moisture absorption, no air bubbles are generated in the molded product and the defective rate of the molded product is greatly reduced.

[0003] As one of the causes of the moisture absorption of the silica-containing rubber compound, it is considered that moisture in the air is adsorbed to hydroxyl groups (silanol groups) existing on the silica surface as a filler. Therefore, in order to suppress moisture adsorption,
There are methods of using silica having a small number of hydroxyl groups or using surface-treated silica. However, in the former, the strength is often lowered without obtaining a sufficient reinforcing effect, and it is difficult to obtain the physical properties required as a molded article, and in the latter, the raw material cost is higher than when untreated silica is used. I will. In addition, as a method for preventing the adsorption of moisture to silica, there is a method of storing the moisture in the air in a place such as a controlled temperature and humidity chamber where the moisture in the air is controlled. come.

The present invention has been made in view of the above circumstances, and makes it easier to absorb moisture of a silica-containing rubber compound.
Another object of the present invention is to provide a method for storing a silica-containing rubber compound that can be prevented for a long time.

[0005]

Means for Solving the Problems and Embodiments of the Invention The present inventors have made intensive studies to achieve the above object, and as a result, covered a silica-containing rubber compound with a sheet and accommodated in a storage container. In this case, by enclosing the anti-hygroscopic agent in the storage container, compared to a method of using silica having a small number of hydroxyl groups, a method of using surface-treated silica, or a method of storing in a place such as a thermo-hygrostat. The present inventors have found that moisture absorption of a silica-containing rubber compound can be prevented more easily and for a long time, and the present invention has been accomplished.

Accordingly, the present invention provides a method for storing a silica-containing rubber compound, wherein the silica-containing rubber compound is accommodated in a storage container in a state of being covered with a sheet, and a moisture-absorbing agent is present in the storage container. I will provide a.

Hereinafter, the present invention will be described in detail. In the method for storing a silica-containing rubber compound of the present invention, the silica-containing rubber compound is accommodated in a storage container in a state of being covered with a sheet, and a moisture-absorbing agent is present in the storage container.

The sheet covering the rubber compound containing silica may be a sheet usually used for packing a rubber compound, and may be, for example, a polyolefin resin sheet such as polyethylene or polypropylene. This sheet may be a flat sheet or a bag-shaped sheet, and the whole surface of the silica-containing rubber compound or one or more sheets may be used to shield the silica-containing rubber compound from moisture in the outside air. It is preferable to cover some surfaces.

In the present invention, a conventionally used paper container such as a cardboard box can be used as it is without specially preparing a tightly-sealing type as a storage container.

In the present invention, it is necessary to interpose a moisture absorption inhibitor between the silica-containing rubber compound covered with the sheet and the storage container. As the moisture absorption inhibitor, those containing silica gel as a main component are preferable.
There is no particular limitation on the particle size and the like of the silica gel, and those commercially available can be used.

The amount of the above-mentioned moisture-absorbing agent is not particularly limited as long as it can prevent moisture absorption of the silica-containing rubber compound. However, when silica gel is used as the moisture-absorbing agent, 1 kg of the silica-containing rubber compound is used. It is desirable that the weight is 0.5 g or more, preferably 0.5 to 50 g, more preferably 1 to 10 g. If the amount is less than 0.5 g, the effect of preventing moisture absorption of the silica-containing rubber compound may be insufficient, and bubbles may be generated in a molded article using the compound.

When a moisture-absorbing agent, particularly silica gel, is used, it is preferable to pack it in a bag, and it is preferable to divide the above amount into one or two or more portions.
The position at which the moisture-absorbing agent is interposed is not limited as long as the effect is exhibited. However, when two or more moisture-absorbing agents are used, the moisture-absorbing agents are placed at equal intervals or at appropriate intervals. It is preferable to arrange them in

Examples of the silica-containing rubber compound include silica-containing rubber compounds such as a silicone rubber compound, an EPDM rubber compound, an SBR rubber compound, an NBR rubber compound, a silicone-modified rubber compound and the like. Those which are addition-crosslinked by hydrosilylation are preferred.

Among them, the silica-containing rubber compound stored by the method of the present invention includes (A) an organopolysiloxane represented by the following average composition formula (1): R ¹ _a SiO _{(4-a) / 2} (1) (In the formula, R ¹ is an unsubstituted or substituted monovalent hydrocarbon group, and a is a positive number of 1.8 to 2.3.) (B) A silicone rubber compound containing silica fine powder as a main component is preferable.

(A) of the above silicone rubber compound
The component is an organopolysiloxane represented by the following average composition formula (1). R ¹ _a SiO _{(4-a) / 2} (1) (wherein, R ¹ is an unsubstituted or substituted monovalent hydrocarbon group, and a is a positive number from 1.8 to 2.3.)

Here, R ¹ in the above average composition formula (1) is a methyl group, an ethyl group, a propyl group, a butyl group,
Hexyl group, alkyl group such as dodecyl group, cycloalkyl group such as cyclohexyl group, vinyl group, allyl group, butenyl group, alkenyl group such as hexenyl group, phenyl group,
Aryl groups such as tolyl groups, benzyl groups, aralkyl groups such as β-phenylpropyl group, or chloromethyl groups in which part or all of the hydrogen atoms bonded to carbon atoms of these groups have been substituted with halogen atoms, cyano groups, etc. Or a trifluoropropyl group, a cyanoethyl group or the like, preferably an unsubstituted or substituted monovalent hydrocarbon group having 1 to 12 carbon atoms, more preferably 1 to 8 carbon atoms. A is 1.8 to 2.3, preferably 1.95 to
It is a positive number of 2.04.

In this case, the organopolysiloxane preferably has an alkenyl group bonded to at least two silicon atoms in one molecule, and 0.001 to 5 mol% of R ¹ , particularly 0.1 to 0.1 mol%. 01-0.5 mol%
It is preferred to contain an alkenyl group, especially a vinyl group amount of the above.

The organopolysiloxane is usually obtained by cohydrolyzing and condensing one or more of organohalogenosilanes, or by converting a cyclic polysiloxane (such as a siloxane trimer or tetramer) into an alkaline or acidic solution. It can be obtained by ring-opening polymerization using a catalyst, and is basically a linear diorganopolysiloxane, but may be partially branched. Further, a mixture of two or more kinds having different molecular structures may be used. In addition, it is preferable that the molecular chain end of this organopolysiloxane is blocked with a triorganosilyl group such as a trimethylsilyl group, a dimethylvinylsilyl group, a dimethylhydroxysilyl group, a divinylmethylsilyl group, and a trivinylsilyl group.

The organopolysiloxane preferably has a viscosity at 25 ° C. of 100 cs or more. More preferably, 100,000 to 10,000,
000 cs. The degree of polymerization is 100 or more, especially 3,0
00 or more, and the upper limit is preferably 100,
000, and more preferably 20,000.

Next, the silica fine powder of the component (B) is blended to obtain a silicone rubber compound having excellent mechanical strength. For this purpose, BET is used.
The specific surface area is 50 m ² / g or more, especially 100 to 400 m ²
/ G. Examples of the silica fine powder include fumed silica (dry silica), precipitated silica (wet silica), and the like, and particularly fumed silica (dry silica).
Is preferred. Further, these surfaces may be subjected to hydrophobic treatment with organopolysiloxane, organopolysilazane, chlorosilane, alkoxysilane, or the like. These silicas may be used alone or in combination of two or more.

The addition amount of the silica fine powder is not particularly limited, but preferably less than 5 parts by weight with respect to 100 parts by weight of the organopolysiloxane of the component (A), which is too small to provide a sufficient reinforcing effect. May not be obtained, and if the amount is more than 100 parts by weight, the processability may be deteriorated, and the physical properties of the obtained silicone rubber may be deteriorated. Therefore, 5 to 100 parts by weight, preferably 10 to 10 parts by weight. It is desirable that the amount be 90 parts by weight, particularly preferably 20 to 80 parts by weight.

The silicone rubber compound used in the present invention contains, in addition to the above components, if necessary, ground quartz,
Non-reinforcing silica such as diatomaceous earth, carbon black such as acetylene black, furnace black, channel black, filler such as calcium carbonate, coloring agent, heat resistance improver, flame retardant improver, acid acceptor, thermal conductivity improvement It is optional to add various alkoxysilanes, diphenylsilanediol, carbon functional silane, silanol group-containing low-molecular siloxane, etc. as various additives such as an agent, a release agent or a dispersant for a filler.

The silicone rubber compound used in the present invention can be obtained by uniformly mixing the above-mentioned components using a rubber kneading machine such as a two-roll mill, a Banbury mixer or a dew mixer (kneader).

The silicone rubber compound obtained in this manner can prevent moisture absorption reliably and for a long period of time by the above-mentioned storage method. Further, it is preferable to remove (filter) the foreign matter by using a strainer or the like before storing.

When molding is performed using the silicone rubber compound stored by the method of the present invention, it is preferable to further blend (C) a curing agent with the silicone rubber compound.

The curing agent (C) is appropriately selected depending on the reaction mechanism for obtaining the rubber-like elastic material.
The reaction mechanism includes (1) a crosslinking method using an organic peroxide vulcanizing agent, and (2) a crosslinking reaction using an addition reaction. Further, a cross-linking reaction using the cross-linking reactions (1) and (2) together is also possible.

(1) As organic peroxide vulcanizing agents, benzoyl peroxide, 2,4-dichlorobenzoyl peroxide, p-methylbenzoyl peroxide,
o-methylbenzoyl peroxide, 2,4-methylbenzoyl peroxide, 1,6-bis (para-toluoylperoxycarbonyloxy) butane, 1,6-
Bis (2,4-dimethylbenzoylperoxycarbonyloxy) hexane, 2,4-dicumyl peroxide, 2,5-dimethyl-bis (2,5-t-butylperoxy) hexane, di-t-butylper Oxide, t
-Butylperoxybenzoate, 1,1-bis (t-
(Butylperoxy) -3,3,5-trimethylcyclohexane, 1,6-bis (t-butylperoxycarboxy) hexane, dicumyl peroxide, cumyl-t-
When an organic peroxide such as butyl peroxide is used and hot-air vulcanization is performed under normal pressure, benzoyl peroxide, 2,4-dichlorobenzoyl peroxide,
A diacyl organic peroxide such as methylbenzoyl peroxide is generally used. These organic peroxides may be used alone or in combination of two or more. The amount of the organic peroxide added as a curing agent is 0.05 to 1 based on 100 parts by weight of the organopolysiloxane (A).
5 parts by weight, preferably 0.2 to 5 parts by weight. If the amount is less than 0.05 part by weight, crosslinking may be insufficient. If the amount is more than 15 parts by weight, an improvement in curing speed may not be expected. In addition, a long time is required to remove unreacted substances and decomposition residues. There are cases.

When the crosslinking reaction by the addition reaction (2) is used, at least one of the organic groups bonded to silicon atoms in one molecule is alkenyl as the organopolysiloxane used in the component (A). Organopolysiloxanes which are groups, especially vinyl groups, are used.

The crosslinking reaction by the addition reaction uses an addition reaction catalyst and a crosslinking agent for the addition reaction. As the addition reaction catalyst, any conventionally known addition catalyst may be used, and specifically, a platinum group metal simple substance and its compound can be used. For example, particulate platinum metal adsorbed on a carrier such as silica, alumina or silica gel, platinum (II) chloride, chloroplatinic acid, a complex of chloroplatinic acid hexahydrate with olefin or divinyldimethylpolysiloxane, chloroplatinic acid hexachloride Examples thereof include a water salt alcohol solution, a palladium catalyst, and a rhodium catalyst. The addition amount of the addition reaction catalyst is a catalytic amount, which is usually 1 to 1,000 in terms of a platinum-based metal amount.
Although it is used in the range of 0 ppm, it is preferably 10 to 10 ppm.
A range of 0 ppm is appropriate. If the amount is less than 1 ppm, the crosslinking reaction is not sufficiently promoted, and the curing may be insufficient. On the other hand, if the amount is more than 1,000 ppm, the effect on the reactivity may be small, and it is uneconomical.

As a crosslinking agent for the addition reaction, S
An organohydrogenpolysiloxane having 2 or more, preferably 3 or more iH groups is suitably used, and this organohydrogenpolysiloxane may be any of linear, cyclic and branched. Known organohydrogenpolysiloxane can be used as a curing agent for the reaction-curable silicone rubber composition,
Usually, a compound represented by the following average composition formula (2) can be used. R ² _x H _y SiO _{(4-xy) / 2} (2)

In the above formula, R ² is the same as R ¹ , preferably having 1 to 12 carbon atoms, especially 1 to 8 alkyl, alkenyl, aryl, aralkyl, etc .; It is an unsubstituted or substituted monovalent hydrocarbon group such as a group-substituted product. x and y are 1 ≦ x ≦ 2.2, 0.00
It is a positive number satisfying 2 ≦ y ≦ 1 and satisfying 1.002 ≦ x + y ≦ 3. The above-mentioned SiH group has two or more, preferably three or more in one molecule, which may be at the terminal of the molecular chain or in the middle.

More specifically, methylhydrogenpolysiloxane having trimethylsiloxy groups at both ends, dimethylsiloxane / methylhydrogensiloxane copolymer having trimethylsiloxy groups at both ends, dimethylsiloxane having dimethylhydrogensiloxy groups at both ends, dimethylsiloxane at both ends Hydrogensiloxy group-blocked dimethylsiloxane / methylhydrogensiloxane copolymer, trimethylsiloxy group-blocked methylhydrogensiloxane / diphenylsiloxane copolymer at both ends, trimethylsiloxy group-blocked methylhydrogensiloxane / diphenylsiloxane / dimethylsiloxane at both ends Polymer, (C
Copolymer consisting of H ₃ ) ₂ HSiO _1/2 unit and SiO _4/2 unit, (CH ₃ ) ₂ HSiO _1/2 unit, SiO _4/2 unit and (C ₆ H ₅ ) SiO _3/2 unit And the like.

The organohydrogenpolysiloxane preferably has a viscosity at 25 ° C. of 300 cs or less.

The amount of the organohydrogenpolysiloxane is based on the amount of the organopolysiloxane (A)
0.01 to 10 parts by weight, especially 0.3 to 100 parts by weight
It is preferably from 10 to 10 parts by weight. Preferably,
The ratio of the hydrogen atom bonded to the silicon atom to one alkenyl group in the component (A) is suitably in the range of 0.5 to 10, and particularly in the range of 1 to 4. 0.
If it is less than 5, crosslinking may not be sufficient and sufficient mechanical strength may not be obtained, and if it is more than 10, physical properties after curing are reduced, and particularly heat resistance and compression set are significantly deteriorated. There is. Further, a known platinum catalyst inhibitor such as a polymethylvinylsiloxane cyclic compound, an acetylene group-containing alcohol, or a peroxide is preferably added to the silicone rubber composition.

It is also possible to use an organic peroxide as a curing agent, an addition reaction catalyst used for a crosslinking reaction by an addition reaction, and an organohydrogenpolysiloxane in combination.

The silicone rubber composition using the silicone rubber compound stored by the method of the present invention includes:
In addition to the above components, it is optional to add various additives as necessary.

This silicone rubber composition comprises the above-mentioned silicone rubber compound and the above components in two rolls,
It can be obtained by mixing uniformly using a rubber kneader such as a Banbury mixer or a Dew mixer (kneader).

The silicone rubber composition thus prepared can be easily cured by heating and curing to obtain a silicone rubber. The curing method may be any method that applies sufficient heat to the vulcanization of the silicone rubber, and the molding method is not particularly limited, such as continuous vulcanization by extrusion molding, pressing, and molding by injection. In particular, normal pressure hot air vulcanization is preferably employed. In this case, the heating temperature is 100 to 500 ° C., particularly 2
00 to 400 ° C, time is several seconds to 1 hour, especially 10 seconds to 3 hours
Preferably, it is 0 minutes. Also, if necessary, 180
The secondary vulcanization may be performed at a temperature of about 250 ° C for about 1 to 10 hours.

The silicone rubber molded product obtained by using the silicone rubber compound stored by the method of the present invention is:
Air bubbles are not generated, and the molded article has a low defect rate.
It is particularly suitable to be used for extrusion molding or sponge which is easily affected by the adsorption component of silica, and does not foam when extrusion molding is performed by normal pressure hot air vulcanization, and foam molding for sponge. An excellent molded product having a uniform and fine cell structure without a problem that the cell accuracy becomes non-uniform when performed can be obtained.

[0040]

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.

[Example 1] Silicone rubber compound KE-551-U (manufactured by Shin-Etsu Chemical Co., Ltd.) was packed in a polyethylene sheet, put in a bag of silica gel (trade name: Desikite), and then put in a cardboard box. Stuffed. The amount of silica gel was 5 g per 1 kg of the rubber compound.

[Example 2] Silicone rubber compound KE-571-U (manufactured by Shin-Etsu Chemical Co., Ltd.) was packed in a polyethylene sheet, put in a bag of silica gel (trade name: Desikite), and then put in a cardboard box. Stuffed. The amount of silica gel was 5 g per 1 kg of the rubber compound.

[Comparative Example 1] Silicone rubber compound KE-551-U (manufactured by Shin-Etsu Chemical Co., Ltd.) was packed in a polyethylene sheet and packed in a cardboard box without a bag of silica gel.

[Comparative Example 2] Silicone rubber compound KE-571-U (manufactured by Shin-Etsu Chemical Co., Ltd.) was packed in a polyethylene sheet and packed in a cardboard box without a bag of silica gel.

The materials of the above Examples and Comparative Examples were put together in a thermo-hygrostat set at 80 ° C./90% RH for 7 days together with the cardboard boxes, and an indoor warehouse without temperature control for 60 days from June 10 Table 1 summarizes the water content of the rubber compound measured by the Karl Fischer method and the state of foaming when subjected to hot-air vulcanization (HAV) under normal pressure.

The normal pressure hot air vulcanization is performed by adding 0.5 parts by weight of an additional vulcanizing agent C-25A (manufactured by Shin-Etsu Chemical Co., Ltd.) and C-25B (Shin-Etsu Chemical Co., Ltd.) to 100 parts by weight of the rubber compound. 2.0 parts by weight) were added to a roll, and a sheet piece having a thickness of 5 mm and a size of at least 5 cm × 5 cm was obtained and suspended in a dryer set at 200 ° C. for 5 minutes. went.

[0047]

[Table 1]

[0048]

According to the storage method of the present invention, moisture absorption of the silica-containing rubber compound can be prevented easily and for a long time.

 ────────────────────────────────────────────────── ─── Continued on front page (72) Inventor Makoto Kusama 2-6-1 Otemachi, Chiyoda-ku, Tokyo Shin-Etsu Chemical Co., Ltd. F-term (reference) 3E067 AA11 AB96 BA06C BA15B BB02C BB15B BB16B BC04B BC06C CA05 EA03 EE25 FA04 FC01 GB12 4J002 AC071 AC081 BB151 CP031 DJ016 FD01 FD14

Claims (7)

[Claims] 1. A method for storing a silica-containing rubber compound, wherein the silica-containing rubber compound is accommodated in a storage container in a state of being covered with a sheet, and a moisture-absorbing agent is present in the storage container. 2. The storage method according to claim 1, wherein the sheet is a polyolefin resin sheet. 3. A moisture-absorbing agent comprising silica gel as a main component,
This was added to the silica-containing rubber compound in an amount of 0.1 kg / kg.
3. The storage method according to claim 1, wherein 5 g or more is used. 4. The storage method according to claim 1, wherein the silica-containing rubber compound is an organic peroxide cross-link or an addition cross-linking by hydrosilylation. 5. The silica-containing rubber compound comprises: (A) the following average composition formula (1): R ¹ _a SiO _{(4-a) / 2} (1) (wherein R ¹ is an unsubstituted or substituted monovalent hydrocarbon) The group, a is a positive number of 1.8 to 2.3.) A silicone rubber compound comprising, as a main component, an organopolysiloxane (B) silica fine powder. The storage method described. 6. The storage method according to claim 5, wherein the silica-containing rubber compound is an extruded or sponge silicone rubber compound. 7. The storage method according to claim 1, wherein the storage container is made of paper.