Vulcanization condition

The main factors affecting the vulcanization process are the amount of sulfur, the vulcanization temperature and the vulcanization time.

1 sulfur dosage. The larger the amount, the faster the vulcanization rate and the higher the degree of vulcanization that can be achieved. The solubility of sulfur in rubber is limited, and excessive sulfur will be precipitated from the surface of the rubber compound, commonly known as "sulphur spray". In order to reduce the phenomenon of sulfur spurting, it is required to add sulfur at a temperature as low as possible, or at least below the melting point of sulfur. According to the requirements of the rubber products, the amount of sulfur in the soft rubber is generally not more than 3%, the amount in the semi-hard rubber is generally about 20%, and the amount in the hard rubber vulcanization condition can be as high as 40% or more.

2 vulcanization temperature. If the temperature is 10 ° C higher, the curing time is shortened by about half. Since rubber is a poor thermal conductor, the vulcanization process of the product differs due to the difference in temperature of its various parts. In order to ensure a relatively uniform degree of vulcanization, thick rubber products are generally gradually heated, low temperature and long time vulcanization.

3 vulcanization time. This is an important part of the vulcanization process. The time is too short and the degree of vulcanization is insufficient (also known as under-sulphur). The time is too long and the degree of vulcanization is too high (commonly known as sulfur). Only the proper degree of vulcanization (commonly known as vulcanization) can guarantee the best overall performance.

Silicone rubber vulcanization principle

How many vulcanizations do silicone rubber have? Silicone rubbers are generally highly saturated structures with low vulcanization activity, so they cannot usually be vulcanized with sulfur. The most common vulcanizing agents are organic peroxides. Silicone rubber can also be irradiated and vulcanized by high-energy radiation. The vulcanization mechanism of radiation vulcanization is the same as that of peroxide, and both are reactive and cross-linked. Below Qingshan New Materials Xiaobian share the principle of silicone rubber vulcanization.

Dimethyl silicone rubber does not contain vinyl in the molecule. It is a saturated rubber. Usually, a highly active peroxide is used as a vulcanizing agent. The peroxide free radical takes hydrogen from the methyl rubber methyl group to form a macromolecular radical. The recombination of the macromolecular radical forms a crosslink bond, such as dibenzoyl peroxide as a vulcanizing agent.

It can be seen from the above reaction that the vinyl rubber containing vinyl group can regenerate the radical which can continue the reaction in the vulcanization, and therefore, the introduction of a small amount of vinyl group into the silicone rubber can greatly improve the vulcanization activity and improve Vulcanizing agent cross-linking efficiency, reducing the amount of peroxide and improving the performance of the product. Since the initial radical which initiates the crosslinking reaction is decomposed by the peroxide, increasing the amount of the peroxide in a certain range can significantly increase the degree of crosslinking of the silicone rubber vulcanizate, which leads to an increase in the strength of the rubber compound. And can improve dynamic performance and compression deformation, but tear resistance is reduced.

According to the level of peroxide vulcanization activity, the commonly used peroxides are classified into general-purpose and vinyl-specific types. It has high activity and can sulphurize various silicone rubbers, such as dibenzoyl peroxide (BP), 2?4-dichloroperoxybenzoyl (DCBP), tert-butyl peroxybenzoate. Ester (TBPB), which belongs to this type. Vinyl-specific type has low activity and can only vulcanize vinyl-containing silicone rubber, such as di-tert-butyl peroxide (DTBP), dicumyl peroxide (DCP and odorless DCP), 2?5-2 Methyl-2?5-di-tert-butylperoxyhexane (DBPMH) and the like belong to this type. Dibenzoyl peroxide is often formulated as a 50% active silicone grease to ensure safe production and improved dispersion in the compound. The decomposition products are benzene, benzoic acid and carbon dioxide, which are volatile. They must be pressurized during a period of vulcanization, and since the decomposition products contain acidic substances, the amount should not be too much to avoid reducing the heat resistance of the product. This product is not suitable for manufacturing. Thick-walled model products. Generally, 100 parts of dimethyl silicone rubber is used in the form of 4-6 parts of dibenzoyl silicone oil paste, and the amount of vinyl silicone rubber is 0.5-2 parts.

Compared with dibenzoyl peroxide, the decomposition temperature of 2.4-dichloroperoxydibenzoyl peroxide is lower than that of dibenzoyl peroxide, and the decomposition rate is higher. Because of the low decomposition temperature, the scorch performance is not Ok, therefore, the amount of this substance should be as small as possible. The decomposition products are 2.4-dichlorobenzoic acid and 2.4-dichlorobenzene, which are relatively non-volatile, so that bubbles can be avoided without pressurization during vulcanization, and it is particularly suitable for continuous vulcanization of atmospheric hot air of the extruded product. The amount is similar to that of dibenzoyl peroxide.

Dibenzoyl peroxide, 2.4-dichloroperoxybenzoyl peroxide belongs to aroyl peroxide and cannot be used in carbon black-containing compounds because carbon black interferes with the vulcanization of peroxides. Light-colored compounds have a strong tendency to burn, and the acid in the decomposition products can impair the heat resistance of the silicone rubber products of the sealing system.

Di-tert-butyl peroxide is effective for vinyl-containing silicone rubber, is not easily scorched, and has less compression deformation and good physical and mechanical properties. The disadvantage is that the vapor pressure is high, so the volatilization is also high, and it is highly volatile during the storage of the rubber compound. This product can be used in model products. It can also be used to mold thick products and carbon black-containing compounds. The dosage is generally 0.5-1 part.

Dicumyl peroxide DCP and odorless DCP, and 2.5-dimethyl-2.5-di-tert-butylperoxyhexane are not volatile, easy to use, low compression deformation of vulcanizate, and no decomposition of products with carboxyl groups Therefore, it is particularly stable in the vulcanizate of the sealed article. They are suitable for molded thick products, metal-bonded products and injection products, as well as carbon black-containing compounds for a wide range of applications. When 2.5-dimethyl-2.5-di-tert-butylperoxyhexane is used, the vulcanizate has a high elongation. When dicumyl peroxide is used, the decomposition product has an odor, and this odor is stored in the product for a long time, and when 2.5-dimethyl-2.5-di-tert-butylperoxyhexane is used, it can be avoided. This drawback. The vulcanizates obtained from these two peroxides have a lower tear strength. The amount is generally 0.5 - 1 part.

The amount of peroxide should not be too large, and when it exceeds the appropriate amount, the elongation and tear strength of the vulcanized rubber are degraded. This downward trend is particularly the case of using 2.4-dichloroperoxybenzoyl peroxide or dibenzoyl peroxide.

How many vulcanizations do silicone rubber have?

The vinyl-containing silicone rubber raw rubber can be subjected to addition vulcanization in addition to vulcanization and vulcanization using a peroxide. The vulcanization vulcanizing agent used today is mainly a hydrosilyl-containing peroxide or polymer. The Si-H group is added to the vinyl group to effect vulcanization. In this reaction, a platinum complex is usually used as a catalyst.

Vulcanization accelerator

   The vulcanization accelerator is a kind of auxiliary agent which can accelerate the vulcanization reaction rate, shorten the vulcanization time, lower the vulcanization temperature, reduce the amount of the vulcanizing agent, and can improve or improve the physical and mechanical properties of the vulcanizate. According to its nature and chemical composition, it can be divided into two categories: inorganic accelerators and organic accelerators. The inorganic accelerator is the earliest used, but the vulcanized rubber has poor performance due to the small promotion effect. It is now basically replaced by organic accelerators. With the continuous development of synthetic rubber varieties and uses, the existing accelerators are complicated, and they are usually classified into thiazoles, thiurams, sulfenamides, anthraquinones, dithiocarbamic acids according to the chemical structure of the accelerator. Salts, aldehydes, xanthates and thioureas.

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