JPH0665504A - Method for crosslinking silicone rubber - Google Patents

Abstract

PURPOSE:To obtain from a heat-curable silicone rubber a rubber product free from blooming and good in evenness of material properties and in dimensional accuracy by using a specific compound as a vulcanizing agent. CONSTITUTION:A heat-curable silicone rubber (e.g., DY32-421U, manufactured by Dow Corning Toray Silicone Co., L+d.) is vulcanized with desirably 0.1-1.0 pt.wt., preferably 0.25-0.75 pt.wt., t-butyl peroxy-3,5,5-hexanoate per 100 pts.wt. the rubber.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to an electronic copying machine and an LBP.
Platen rollers and fixing rollers used in (laser beam printers), full keyboard covers for computers and word processors, shaft seals and -O rings in the automobile industry, packing and diaphragms for general industries, gaskets and electric kettles in the electric industry. The present invention relates to a method for cross-linking a silicone rubber used for a silicone rubber product such as a round packing or a belt for a conveyor heater, which requires particularly dimensional accuracy.

[0002]

2. Description of the Related Art Generally, silicone rubber is excellent in heat resistance and cold resistance, exhibits good compression-restoration property over a wide temperature range, and has weather resistance, ozone resistance, corona resistance, electrical characteristics, heat resistant oil resistance,
It is a material having excellent chemical resistance and hot water resistance, and is used in various industrial fields by utilizing these characteristics.

There are various grades of silicone rubber depending on its form and curing mechanism, but they are roughly classified into millable silicone rubber and liquid silicone rubber.

The millable type silicone rubber is mainly composed of straight-chain polyorganosiloxane (raw rubber) having a high degree of polymerization, to which a silica-based reinforcing filler and various additives for imparting various properties are added. It is a type of rubber in which the base compound is adjusted and then a vulcanizing agent is added and the mixture is heated and cured.

This type of silicone rubber is
It is widely used industrially because it can be handled like ordinary organic rubber because it is molded and processed after roll processing such as vulcanizing agent mixing and sheeting, and is also called thermosetting silicone rubber or heat vulcanizing silicone rubber. To be done.

In the thermosetting silicone rubber, an organic peroxide is generally used as a vulcanizing agent, and the type and amount of the organic peroxide is appropriately used depending on the molding method and molding temperature. ing.

Organic peroxides used in thermosetting silicone rubbers are roughly classified into four types: diacyl peroxides, peroxyesters, peroxyketals, and dialkyl peroxides.

As the diacyl peroxide, benzoyl peroxide, 2,4-dichlorobenzoyl peroxide, bis (P-chlorobenzoyl) peroxide, bis (orthomethylbenzoyl) peroxide, etc. are used for thermosetting silicone rubber. ing.

As the peroxyester, t-butylperoxybenzoate, 2,5-dimethyl-2,5-di (benzoylperoxy) hexane, t-butylperoxyisopropyl carbonate, etc. are used in the thermosetting silicone rubber. Has been done.

Peroxyketals include 1,1-bis (t-butylperoxy) 3,3,5-trimethylcyclohexane, 1,1-bis (t-butylperoxy) cyclohexane and 2,2-bis ( t-Butylperoxy) octane, n-butyl 4,4-bis (t-butylperoxy) valerate and the like are used in thermosetting silicone rubbers.

As the dialkyl peroxide,
Di-t-butyl peroxide, t-butyl cumyl peroxide, di-cumyl peroxide, α, α-bis (t
-Butylperoxy-m-isopropyl) benzene,
2,5-Dimethyl-2,5-di (t-butylperoxy) hexane, 2,5-dimethyl-2,5-di (t-butylperoxy) hexyne-3, etc. are used for thermosetting silicone rubber Has been done.

These organic peroxides include thermosetting silicone rubbers which are industrial pure products, paste-like products using silicone gum or silicone oil as a binder, and powder-like products sprinkled with powder such as calcium carbonate. It is used.

In the thermosetting type silicone rubber using such organic peroxide, dicumyl peroxide (trade name Perk Mill D, manufactured by NOF Corporation) or 2,5- Dimethyl-2,5-
Di (t-butylperoxy) hexane (trade name Perhexa 25B, manufactured by NOF CORPORATION), but the thermosetting silicone rubber blended with these organic peroxides has a fairly high compression molding temperature of 160-180 ° C. Therefore, in products requiring dimensional accuracy with silicone rubber, dicumyl peroxide and 2,5-dimethyl-2,5-di (t-butylperoxy) are used to suppress dimensional variation due to linear shrinkage. )
Using an organic peroxide that has a lower decomposition temperature than hexane
Molded at a relatively low temperature of 110-140 ℃.

As such an organic peroxide for low temperature vulcanization, 2,4-dichloroperoxide (trade name: Nybar C
S, manufactured by NOF CORPORATION, diacyl peroxide and peroxyester, t-butylperoxypropyl carbonate (trade name: Perbutyl I, manufactured by NOF CORPORATION), and peroxyketal 1,1-bis (t). -Butylperoxy) 3,3,5-trimethylcyclohexane (trade name Perhexa 3M, manufactured by NOF CORPORATION) is generally used.

[0015]

However, when 2,4-dichloroperoxide is used as the organic peroxide for low temperature vulcanization, there is a problem that blooming occurs on the surface of the molded silicone rubber product.

Blooming is a phenomenon in which a compounding agent precipitates from the rubber and is crystallized on the surface, and in the case of 2,4-dichloroperoxide, its decomposition products gradually exude, and the rubber surface There is a phenomenon of whitening.

Further, as an organic peroxide for low temperature vulcanization
When 2,4-dichloroperoxide is used, it induces deterioration of compression set and also causes the molding of thick moldings and KE95.
Silicone rubber using a high-moisture filler such as wet silica exemplified by 1U (trade name, manufactured by Shin-Etsu Chemical Co., Ltd.)
This causes a problem that cracking (depolymerization) due to the decomposition residue of 2,4-dichloroperoxide occurs extremely remarkably.

When 1,1-bis (t-butylperoxy) 3,3,5-trimethylcyclohexane is used as an organic peroxide for low temperature vulcanization, a silicone containing a large amount of wet silica such as KE951U is used. Although there is no problem with rubber,
Low compression set silicone rubber such as DY32-421U (trade name, manufactured by Toray Dow Corning Silicone Co., Ltd.) induces vulcanization inhibition, resulting in insufficient vulcanization and adhesion on the product surface. At the same time, a problem occurs that the rubber hardness cannot be maintained.

This problem cannot be solved even if the amount of 1,1-bis (t-butylperoxy) 3,3,5-trimethylcyclohexane added is increased, and the organic peroxide has a similar structure. A similar tendency was observed with 1,1-bis (t-butylperoxy) cyclohexane.

A similar phenomenon was observed with t-butyl peroxyisopropyl carbonate, which is a peroxy ester, and there was a problem that the rubber hardness could not be maintained.

[0021]

Means for Solving the Problems As a result of intensive studies to solve the above conventional problems, the present invention has revealed that in a thermosetting silicone rubber, tert-butylperoxy 3,5,5-hexanoate was used as a vulcanizing agent. The present invention has been completed by finding out that the above problems can be solved and vulcanization molding can be carried out at a relatively low temperature around 140 ° C. by using it.

Tertiary butyl peroxy 3,5,5-hexanoate in the present invention is classified as a peroxy ester, and sold under the trade name of perbutyl 355 (manufactured by NOF Corporation) or Trigonox 42 (manufactured by Kayaku Akzo). It is a colorless liquid.

The molding temperature in the present invention varies depending on the type and composition of the thermosetting silicone rubber, the shape of the product, etc., but is 130 to 160 ° C., preferably 140 to 150 ° C.

The thermosetting silicone rubber that can be used in the present invention is not particularly limited, and dimethyl silicone rubber, methyl vinyl silicone rubber, methylphenyl vinyl silicone rubber and fluorosilicone rubber can be applied.

The kind of the filler is not particularly limited, but an inorganic reinforcing agent, an inorganic filler or the like is used in a timely manner, and the amount of the filler used is 100 parts by weight of the base gum and the total amount of the filler is 20.
〜200 parts, preferably 40〜120 parts.

As the inorganic reinforcing agent, dry silica such as Aerosil 200, Carplex 1120, Shilton R-2, Tokseal U, Nipseal VN3, wet silica such as Ultrasil VN3, Hisil 223, activated calcium carbonate such as Hakutan CC, Examples include special calcium carbonate such as white luster A, magnesium silicate such as mistron vapor, and aluminum silicate such as hard clay.

As the inorganic filler, light calcium carbonate, heavy calcium carbonate, clay such as kaolin, silane-modified clay such as Nuke 321, quartz powder such as talc, crystallite and minusyl, celite and radiolite can be used. Diatomaceous earth, alumina, chromium oxide, aluminum sulfate, barium sulfate, calcium sulfate, mica,
Examples include silica sand, and usually several types are used in combination. In addition, a wetting agent (wetting agent) can be added to prevent secondary bonding due to the activity of the silica surface, and as a result, the reinforcing effect is increased and the storage stability of the rubber compound is improved.

Examples of these wetting agents include silicone resins, alkoxysilanes and roxanes, hydroxysilanes and siloxanes, silazanes such as hexamethyldisilazane, organic acid esters and polyhydric alcohols. Silanes and siloxanes are generally used from the viewpoints of compatibility with silicone gum and heat resistance of the wetting agent itself.

Further, a metal oxide such as cerium oxide or red iron oxide or a metal organic hydrochloric acid may be used as the heat resistance improver, and further barium oxide, barium dioxide or calcium oxide may be used as a reversion inhibitor. Acid acceptors such as magnesium oxide and zinc oxide may be used.

In addition, processing aids, flame retardants, conductive carbon, and the like may be added if necessary.

[0031]

[Function] Generally, the standard of the molding temperature of thermosetting silicone rubber is measured by the 2-minute half-life temperature of the organic peroxide used (half-life is the time when the peroxide concentration is reduced to half the initial concentration due to decomposition). I know empirically what I can do.

Considering that 90% or more of the cross-linking is usually completed within just a few minutes during the primary vulcanization of the thermosetting silicone rubber, the 2-minute half-life temperature is used as a guide for the molding temperature. It is a reasonable choice to do.

Table 1 shows the half-life temperatures of various organic peroxides for thermosetting silicone rubber.

[0034]

[Table 1]

Molding at a mold temperature higher than the one-minute half-life temperature is generally referred to as high temperature shortening time vulcanization, and since the vulcanization time can be shortened, it is a well-known manufacturing method in the rubber industry. In the case of a product having a large rubber thickness, it takes a long time to be heated to a deep portion due to the thermal conductivity of rubber, so that it is not very effective in reducing the vulcanization time.

Further, in vulcanization at high temperature, it is necessary to pay attention to problems such as rubber scorch starting before the mold is closed.

Molding at a mold temperature lower than the 6-minute half-life temperature is generally not practical because the vulcanization time becomes extremely long.

Therefore, by using an organic peroxide having a low half-life temperature as a vulcanizing agent for thermosetting silicone rubber, the vulcanizing temperature can be lowered even when molding is carried out for a certain vulcanizing time. , Silicone rubber products with excellent dimensional accuracy can be supplied without a polishing step, and the temperature of the press heating platen is low, which saves energy.

Although the present invention is mainly intended for thermosetting silicone rubber, it can be applied to other elastomers capable of peroxide vulcanization, such as EPDM and fluororubber.

[0040]

[Examples] DY32-421U made by Toray Dow Corning Silicone Co., Ltd. was used as a thermosetting silicone rubber, and tert-butyl peroxy 3,5,5-hexanoate, an organic peroxide, was used as a base in Japan. A sample was obtained by kneading 0.5 parts by weight of perfume 355 made of oil and fat into a base rubber with a test roll.

Then, as shown in Table 2, various samples (comparative example 1) obtained by adding a known organic peroxide vulcanizing agent to thermosetting silicone rubber (Toray DY32-421U)
As a result of various experiments compared with the above-mentioned 4), the following results were obtained.

[0042]

[Table 2]

First, the time (seconds) to reach 90% vulcanization degree at each temperature was measured with Curastometer III type (manufactured by Japan Synthetic Rubber Co., Ltd.), and the results in Table 3 were obtained.

[0044]

[Table 3]

From these results, when 1,1-bis (t-butylperoxy) 3,3,5-trimethylcyclohexane was used as a vulcanizing agent in Toray DY32-421U (Comparative Example 3), 90% was obtained. It was found that the temperature at which the vulcanization degree was reached was higher than that in the case of using 2,5-dimethyl-2,5-di (t-butylperoxy) hexane in Comparative Example 1 (Comparative Example 1).

This phenomenon was not improved even if the amount of 1,1-bis (t-butylperoxy) 3,3,5-trimethylcyclohexane was increased.

This phenomenon is the same for 1,1-bis (t-butylperoxy) 3,3,5-trimethylcyclohexane and 1,1-bis (t-butylperoxy) cyclohexane, which have a similar chemical structure. there were.

Further, even with t-butylperoxyisopropyl carbonate (Comparative Example 4), the temperature at which the degree of vulcanization reaches 90% is higher than that of tertiary butylperoxy 3,5,5-hexanoate used in the present invention. Then, a phenomenon was observed in which the half-life temperature of the organic peroxide was reversed from that of 2 minutes.

Then, the rubber physical properties of each sample were measured according to JIS K6301, and the results shown in Table 4 were obtained. From these results, it was found that in Comparative Examples 3 and 4, the rubber hardness was particularly lower than that of the other samples, and sufficient cross-linking was not performed.

[0050]

[Table 4]

The reason why this phenomenon occurs in a silicone base such as Torre DY32-421U is not critical, but the radicals generated from dry silica in the base, or acid or alkali catalyst residues of some organic peroxides are generated. It is thought to be for trapping.

2,5-Dimethyl-2,5-shown in Comparative Example 1
When di (t-butylperoxy) dichlorohexane is used, stable rubber properties can be obtained without such a problem, but it is necessary to raise the vulcanization temperature, and the shrinkage rate is 4.0% due to the effect. Since it is considerably large, it is not possible to obtain a product with small dimensional variations.

As an organic peroxide for low temperature vulcanization, 2,4
-When dichloroperoxide is used (Comparative Example 2)
In that case, stable cross-linking is obtained and rubber hardness is not a problem, but it causes deterioration of compression set.

Further, a bloom generation test was conducted on each sample, and the results shown in Table 5 were obtained.

[0055]

[Table 5]

In Comparative Example 2, there is a problem that bloom is generated in the product as the compression set is deteriorated.

On the other hand, as shown in the examples, in the sample using tert-butylperoxy 3,5,5-hexanoate as the vulcanizing agent, no vulcanization failure occurred and good compression set was obtained. It was found that a silicone rubber cross-linked product having the same was obtained.

By using tertiary butyl peroxy 3,5,5-hexanoate as the vulcanizing agent, the temperature during the primary vulcanization can be lowered by 20 to 30 ° C., and as a result, the thermal expansion coefficient of the rubber can be reduced. Since the shrinkage ratio due to the influence of 1) can be reduced, a product with stable dimensional accuracy can be molded without a polishing step.

The amount of the vulcanizing agent tert-butyl peroxy 3,5,5-hexanoate used in the present invention varies depending on the thermosetting silicone rubber to be applied.
The amount is generally 0.1 to 1.0 part by weight, preferably 0.25 to 0.75 part by weight.

Organic peroxides generally used in thermosetting silicone rubbers are, for example, RC-4 manufactured by Toray Dow Corning Silicone Co., Ltd. for the purpose of preventing scattering and improving dispersibility.
Most of the silicone paste has a content of about 50%, but the silicone paste type may also be applied in the present invention, and in that case, it is necessary to increase the amount according to the content rate.

Further, the shaft seal, the rubber roller, etc. need to be vulcanized and adhered to an adherend such as a metal fitting or a core metal. In this case, the adhesive is a conventional thermosetting silicone rubber primer, For example, Chemrock 607 and 608 manufactured by Road, Sixson AN-187 and Sixon 304 manufactured by Sixson Incorporated, and Dow Corning Toray.
SH2260 primer and DY32-012 manufactured by Silicone Co., Ltd., Primer No. 16 and No. 18B manufactured by Shin-Etsu Chemical Co., Ltd. can be applied, and if necessary, they are diluted with an organic solvent such as alcohol, MEK or toluene and used.

[0062]

As described above, according to the present invention, a silicone rubber product having stable physical properties and good dimensional accuracy can be obtained.

Claims (1)

[Claims] 1. A method for crosslinking silicone rubber, characterized in that, in a thermosetting silicone rubber, tertiary butyl peroxy 3,5,5-hexanoate is used as a vulcanizing material.