JP3527376B2 - Crosslinking agent for silicone rubber and crosslinking method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cross-linking agent suitable for cross-linking silicone rubber used in electronic equipment, automobile parts, electric wire coating materials, copying machine rolls, medical products and the like.

[0002]

2. Description of the Related Art Silicone rubber is generally cross-linked and molded under heating using an organic peroxide as a cross-linking agent. As the silicone rubber, dimethyl silicone rubber, methyl vinyl silicone rubber, methylphenyl silicone rubber, fluorosilicone rubber and the like are generally used, and these have characteristics such as crosslinking property, low temperature property and good oil resistance. is doing. These rubbers are rarely molded using only a cross-linking agent. In many cases, these rubbers are used as reinforcing materials such as dry silica and wet silica, plasticizers such as silicone oil, and for the purpose of improving various physical properties. To the silicone rubber compound obtained by blending various additives to be added, etc., after adding and mixing the required amount of organic peroxide as a crosslinking agent, the required temperature in a mold or hot air oven,
It is heated for the required time to obtain a silicone rubber molded product.

Generally, bis (2,4-dichlorobenzoyl) peroxide, dibenzoylperoxide, bis (4-chlorobenzoyl) peroxide, t-butylperoxybenzoate, and the like are used for crosslinking the silicone rubber compound as described above. Dicumyl peroxide,
Organic peroxides such as 2,5-di (t-butylperoxy) hexane, t-butylcumyl peroxide, and di-t-butylperoxide are used in liquid, solid (powder) form or paste form. The type and amount of the cross-linking agent are selected and used depending on the conditions such as the molding method, the molding temperature, the type of silicone rubber, and the type of additives. Among these various crosslinking agents, bis (2,4-dichlorobenzoyl) peroxide is an excellent crosslinking agent, and is most industrially used. That is, it has the advantages that the crosslinking rate is the fastest among the above-mentioned crosslinking agents, the productivity is good, and hot air crosslinking (HAV) can be efficiently performed.

Hot air crosslinking is, for example, a method of continuously crosslinking an extruded product, and a silicone rubber tube extruded from an extruder, a silicone rubber-coated electric wire or the like is 200-400.
This is a molding method in which crosslinking is carried out by passing through a hot air oven at about ℃. Usually, bis (2,4-dichlorobenzoyl) peroxide or bis (4-chlorobenzoyl) peroxide is used as a crosslinking agent for hot air crosslinking.
Although these cross-linking agents are characterized in that they do not cause foaming in the molded product, bis (4-chlorobenzoyl) peroxide has a slow cross-linking speed, so it is used for hot-air cross-linking except in special cases. That is not the case. Therefore, the crosslinking agent that can be used for hot-air crosslinking is essentially only bis (2,4-dichlorobenzoyl) peroxide. However, a silicone rubber molded product obtained by crosslinking molding using this crosslinking agent by a hot air crosslinking method or a pressure molding method has a problem that blooming occurs. Blooming is a phenomenon in which the decomposition products of the cross-linking agent gradually exude and the surface becomes white. To prevent this, a silicone rubber molded product cross-linked with bis (2,4-dichlorobenzoyl) peroxide is molded. It is necessary to carry out a secondary crosslinking treatment at a high temperature for a long time afterward. Screw (2,
4-dichlorobenzoyl) peroxide has the lowest crosslinking temperature and the highest crosslinking efficiency among the crosslinking agents for various silicone rubbers, and is the only crosslinking agent that can be used for hot air crosslinking. There is a problem that treatment must be performed, and there is a strong demand for solving this problem. Further, this compound has a chlorine atom in its molecular structure, and it has been pointed out that this compound may adversely affect the environment.

[0005]

We have already obtained the same crosslinking properties as the former by using bis (2-methylbenzoyl) peroxide as a crosslinking agent instead of bis (2,4-dichlorobenzoyl) peroxide. It has been found that a silicone rubber molded product having no blooming can be obtained (Japanese Patent Laid-Open No. 59-1875).
8). In addition, there is a patent using bis (4-methylbenzoyl) peroxide (Japanese Patent Publication No. 4-50327), but bis (4-methylbenzoyl) peroxide has a low melting point of about 53 ° C. and thus has a drawback of lacking storage stability. There is. Further, bis (4-methylbenzoyl) peroxide has a high decomposition temperature and requires a high temperature for crosslinking, and it takes time to crosslink at the same crosslinking temperature as bis (2-methylbenzoyl) peroxide. There is a drawback to say.

In the production of a crosslinking agent composed of a peroxide, if it is synthesized as a pure product, there is a high risk of explosion due to impact or friction. Therefore, it is usually synthesized as a wet body diluted with silicone oil to reduce its purity. The product is then made into a paste and dehydrated by adding the required amount of silicone oil. Hydrated products containing water whose purity has been reduced with silicone oil of bis (4-methylbenzoyl) peroxide were subjected to a risk evaluation reference value (10 times test with an orifice diameter of 9 mm in a pressure vessel test (PVT) related to the manufacturing process. In case of rupture 4 times or less, handling under the Fire Service Law can be cleared as a dangerous goods 5th class 2nd class).
-In the case of wet products whose purity has been reduced using silicone oil of (methylbenzoyl) peroxide, it is very important to clear the standard value of the risk evaluation in the PVT under the PVT during the manufacturing process. difficult.

By mixing bis (2-methylbenzoyl) peroxide and bis (4-methylbenzoyl) peroxide in a wet state or in a paste state, both defects (the former is stable in storage due to its low melting point) Inferior properties, the latter has a high melting point but must be crosslinked at high temperature when used because it has a high decomposition temperature), and they can complement each other. However, in the method in which the peroxide is manufactured and then mixed, the purity of each peroxide is often different depending on the manufacturing lot, so it is difficult to keep the ratio of the two kinds of peroxide constant or to make the product quality uniform. Often accompanied.

[0008]

As a result of intensive studies to solve the above-mentioned problems, the present inventors have found that 2-methylbenzoyl 4'-methylbenzoyl peroxide (Aime BPO).
), A benzoyl peroxide mixture consisting of bis (2-methylbenzoyl) peroxide and bis (4-methylbenzoyl) peroxide (Aime BPO).
The present invention has been completed based on the finding that "containing mixed peroxide" is more stable and safer than bis (2-methylbenzoyl) peroxide, and has a higher crosslinking rate.

That is, the present invention provides (1) a benzoyl peroxide mixture consisting of 2-methylbenzoyl 4'-methylbenzoyl peroxide, bis (2-methylbenzoyl) peroxide and bis (4-methylbenzoyl) peroxide. (2) A cross-linking method for silicone rubber, which comprises using the benzoyl peroxide mixture described in (1).

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below.
The method for synthesizing the silicone rubber crosslinking agent of the present invention includes:
A mixture of 2-methylbenzoyl chloride and 4-methylbenzoyl chloride is reacted with hydrogen peroxide in the presence of alkali. The obtained mixed peroxide (containing Asime BPO) is made into a paste and used as a crosslinking agent for silicone rubber.

In the synthesis of the crosslinking agent for silicone rubber of the present invention, the ratio of 2-methylbenzoyl chloride and 4-methylbenzoyl chloride is 50:50 to 1: 1.
99, an alkaline substance selected from sodium hydroxide, potassium hydroxide and the like is used in a molar ratio of 1 to 1.5 times that of benzoyl chloride. The reaction temperature is 0 to 30 ° C., and the reaction is performed for 1 to 4 hours. This ratio is 5
The one near 0:50 does not have much effect of raising the melting point,
If it is closer to 1:99, the effect of lowering the decomposition temperature is small, so
It is preferably in the range of 20:80 to 5:95. In the risk evaluation with PVT of the intermediate product in the manufacturing process, the numerical value was 4/10 or less even at 50:50 with the orifice diameter of 9 mm, and it is safer if the bis (2-methylbenzoyl) peroxide decreases. Head to the side.

The cross-linking of silicone rubber is carried out by a conventional method, but usually, a plasticizer or an additive for imparting the required performance to the product is added to and mixed with the silicone rubber, and the mixture is used in the present invention for silicone rubber (Acime (BPO-containing) mixed peroxide is added in an amount of about 0.5 to 10 millimoles, preferably about 1 to 10 millimoles, per 100 g of silicone rubber. Good.

Specific examples of the silicone rubber which can be crosslinked by the crosslinking agent of the present invention include dimethylsilicone rubber, methylphenylsilicone rubber, fluorosilicone rubber and the like. These silicone rubbers are mixed with necessary additives, further mixed with a cross-linking agent, and then poured into a target mold or the like, and the cross-linking temperature is usually 100 to 400 ° C. and the cross-linking time is 5 minutes to 4 hours. It is cured under conditions selected from.

Synthetic Example 1 is the Assist BP of the present invention.
Although a method for synthesizing a silicone oil paste having an O-containing mixed peroxide content of 50% by weight has been shown, it can be synthesized by various methods, and the silicone oil used for safety may be the whole or the same. Even if some of them are replaced with phthalic acid esters, there is no problem in the performance. Although it can be used in the form of a pure product, it is preferable to paste it with silicone oil or phthalic acid for safety and finer particles.

The cross-linking agent of the present invention has excellent safety in the production process, has good storage stability, and when used for cross-linking silicone rubber, can give a cross-linked product at a relatively low temperature in a short time. The obtained crosslinked product has no foaming and the crosslink density is high. Further, the silicone rubber cross-linked molded article obtained by the cross-linking method of the present invention does not cause blooming even after a long time.

[0016]

The present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to these.

Synthesis Example 1 In a 1 liter beaker equipped with a stirrer, a thermometer and a dropping funnel, 100 g of water, 352 g (2.2 mol) of 25 wt% sodium hydroxide aqueous solution, 10 wt% Neogen R (trade name, nonionic type) 10 g of an aqueous solution of a surfactant and manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd. was charged and cooled to 0 ° C. under external cooling. 68 g (1.2 g) of hydrogen peroxide containing 60% by weight of hydrogen peroxide was added to this solution.
(Mol) was maintained at 0 to 5 ° C. and added dropwise with stirring. 311 g (2.0 mol) of a mixture of 2-methylbenzoyl chloride and 4-methylbenzoyl chloride in a ratio of 10:90 was gradually added to the obtained mixture at 0 to 5 ° C with vigorous stirring over 60 minutes. It was Further, the reaction mixture was kept at 0 to 5 ° C and stirred for 60 minutes. After completion of the reaction, the reaction mixture is suction filtered on a Nutsche, washed with water until the filtrate shows no alkalinity, and mixed with bis (2-methylbenzoyl) peroxide, bis (4-methylbenzoyl) peroxide and Asime BPO. 351 g of a wet body of peroxide was obtained. The wet body was dried under reduced pressure at room temperature to obtain the above-mentioned Asime BP having a peroxide purity of 99.3% by weight.
247 g of O-containing mixed peroxide (yield 91.0%)
Got

200 g of dimethyl silicone oil was added to 200 g of the mixed peroxide (dry product) thus obtained, and the mixture was thoroughly mixed and homogenized by passing through a three-roll mill, and a peroxide having a peroxide content of about 50% by weight was added. 360 g of silicone paste (Peroxide purity 4
9.8% by weight) was obtained.

Comparative Synthesis Example 1 In Synthesis Example 1, 2-methylbenzoyl chloride and 4 were used.
4 instead of a mixture of methylbenzoyl chloride
A bis (4-methylbenzoyl) peroxide silicone paste having a peroxide content of 50% by weight was obtained by the same treatment as in Synthesis Example 1 except that only -methylbenzoyl chloride was used.

Examples 1 and 2 To the methyl vinyl silicone rubber, 1.1 parts by weight of the peroxide silicone paste containing 50% by weight of the peroxide obtained in Synthesis Example 1 was added to 100 parts by weight of the methyl vinyl silicone rubber. In the case of doing,
Example 2 was the case where 5 parts by weight was added, and the respective blends were thoroughly mixed on a two-roll mill, and pressure molding was carried out at 120 ° C. for 10 minutes using a mold having a thickness of 2 mm. The tensile strength, elongation, and hardness (A type) of the obtained sheet were measured according to JIS-K-6301 "Pulverized Rubber Physical Test Method". Blooming was determined by visually observing the appearance of the sheet surface one day and seven days after pressure molding.

Comparative Examples 1 and 2 Instead of the peroxide silicone paste used in Examples 1 and 2, in Comparative Example 1, a commercially available bis (2,4-dichlorobenzoyl) peroxide silicone paste having a peroxide content of 50% by weight was used. 1.5 parts by weight were used, except that in Comparative Example 2, 1.1 parts by weight of the bis (4-methylbenzoyl) peroxide silicone paste having a peroxide content of 50% by weight obtained in Comparative Synthesis Example 1 was used. The same process as in Example 1 or Example 2 was carried out to obtain a sheet by pressure molding.

Table 1 shows various physical properties of the sheets obtained in Examples 1 and 2 and Comparative Examples 1 and 2, respectively.

[0023]

[Table 1] Table 1 Examples Press conditions Physical properties of crosslinked material Blooming Tensile strength Elongation Hardness 1 day 7 days later kg / cm ² % 1 120 ° C × 10 minutes 92 590 53 None None 2 Same as above 90 570 54 None None Comparative example 1 Same as above 89 580 53 Ali Ali 2 130 ℃ × 10 minutes 84 620 50 None

From Table 1, assimilated BPO of Examples 1 and 2
The contained mixed peroxide shows the same or good results as the physical properties of the crosslinked product of bis (2,4-dichlorobenzoyl) peroxide, and no blooming is observed,
Moreover, since the physical properties of the crosslinked product are superior to those of bis (4-methylbenzoyl) peroxide, it is clear that the peroxide of the present invention is an excellent crosslinking agent as compared with known crosslinking agents.

Examples 3 and 4 In the same manner as in Examples 1 and 2, the ascime BPO-mixed peroxide silicone paste obtained in Synthesis Example 1 was thoroughly kneaded in methyl vinyl silicone rubber to obtain Examples 3 and 4, respectively. did. This is about 2mm thick when cold
To mold. This uncrosslinked sheet was put in a gear oven at 200 ° C for 15 minutes to be hot air crosslinked, and the surface became sticky,
The foaming of the cross section of the molded product was observed. Blooming is a bridge 1
It was judged by visually observing the appearance of the sheet surface after one day and after seven days, and these results are summarized in Table 2.

Comparative Example 3 A crosslinked sheet was obtained in the same manner as in Example 4, except that the same crosslinking agent as used in Comparative Example 1 was used in Example 4. The conditions of stickiness, foaming and blooming on the surface at that time are summarized in Table 2.

[0027]

[Table 2]                           Table 2   Example Cross-linked product blooming                   Sticky foaming 1 day later 7 days later     3 None Pear None     4 None Pear None   Comparative example     3 pear pear ant ant

The molecular weight of the asymmetric BPO-containing mixed peroxide of the present invention is 270.3, and the molecular weight of bis (2,4-dichlorobenzoyl) peroxide is 380.0.
Since the weight per mol is 29% by weight smaller than that of Comparative Example 3, the amount of peroxide added in Example 3 is reduced by about 30% compared to Comparative Example 3, but the state of the crosslinked product by the crosslinking agent of the present invention is still good. It can be seen that a crosslinked product without blooming can be obtained.

Synthetic Example 2 In the same manner as in Synthetic Example 1, except that 64 g of dimethyl silicone oil was added after the water was first added, the content of the silicone oil-containing peroxide in the mixed peroxide of the asime BPO was the same as in Synthetic Example 1. 380 g of an intermediate wet body product of 65% by weight was obtained.

Comparative Synthetic Example 2 In the same manner as in Synthetic Example 1, the mixed acid chloride raw material of Synthetic Example 1 was replaced with 2-methylbenzoyl chloride, and bis (2
-Methylbenzoyl) peroxide content 65% by weight
To obtain an intermediate wet body product.

Reference Example The PVT of the intermediate wet body product under the manufacturing process was measured and is shown in Table 3.

[0032]

Table 3 Synthetic examples Crosslinking agent PVT (orifice diameter 9 mm) 2 D 1/10 rupture Comparative synthetic example 2 E 6/10 rupture D: mixed peroxide content in synthetic example 2 65% by weight intermediate humidity Body product E: Bis (2-methylbenzoyl) peroxide content of Comparative Synthesis Example 2 65% by weight Intermediate product

From Table 3, it is clear that the safety of the peroxide intermediate wet body product used in the present invention under the manufacturing process is higher than that of the comparative example.

[0034]

The cross-linking agent of the present invention has excellent safety in the manufacturing process. When the silicone rubber is cross-linked using this cross-linking agent, the cross-linking speed is high and a cross-linked product without blooming can be obtained. Further, since the peroxide of the present invention does not have a chlorine atom, the obtained crosslinked product has a characteristic that there is no danger of releasing a chlorine atom.

Claims (2)

(57) [Claims] 1. 2-Methylbenzoyl 4′-methylbenzoyl peroxide, bis (2-methylbenzoyl) peroxide and bis (4-methylbenzoyl)
A cross-linking agent for silicone rubber, which comprises a benzoyl peroxide mixture comprising peroxide. 2. A method for crosslinking silicone rubber, which comprises using the benzoyl peroxide mixture according to claim 1.