As natural rubber and rubber contract the most common and most important curing agent - sulfur, this product is widely used, it is an integral part of industrial rubber products, despite its very wide application, but few really know its purpose and use points Here I simply elaborate for everyone.
Sulfur alias sulfur, colloidal sulfur, sulfur block. Appearance is light yellow brittle crystal or powder with special smell. A molecular weight of 32.06, the vapor pressure is 0.13kPa, flash point of 207 ℃, a melting point of 119 ℃, boiling point 444.6 ℃, relative density (water = 1) 2.0. Sulfur is insoluble in water, slightly soluble in alcohol, ether, soluble in carbon disulfide. As flammable solids, sulfur is mainly used in the manufacture of dyes, pesticides, matches, gunpowder, rubber, rayon and the like.

Sulfur species on terms, can be divided into ordinary sulfur and insoluble sulfur.

Common sulfur solubility in rubber is 1%, the amount exceeding the solubility of sulfur in the general part of the compound will be discharged cooling surface, that is blooming. Blooming will affect the adhesive between the semi-finished parts, and adversely affect the uniformity of the vulcanized product, so the need to use high sulfur should adopt insoluble sulfur.

Insoluble sulfur polymer sulfur is not soluble in carbon disulfide and taxes, unstable nature, easily converted to insoluble sulfur. Temperature increases, the conversion speed. Adding a small amount to prevent the conversion of chlorine, bromine, iodine monochloride, sulfur, hydrocarbon dienes. The α- sulfur is heated to a high temperature (near boiling), after becoming dark brown viscous oily liquid that is rapidly cooled aggregate into insoluble sulfur. It can also be superheated steam sulfur spray cooled rapidly in cold water to 90 degrees or less to prepare.
Insoluble sulfur product is commonly used in special rubber curing agent, relative to the normal sulfur, which also has the following advantages:

1 insoluble sulfur in rubber dispersed state of existence, so that the compound is not blooming, good viscosity, while ensuring the quality of the appearance of light-colored products.

2, insoluble sulfur in the rubber compound dispersed uniformly, effectively resist gathered sulfur to reduce scorch tendency compound storage process.

3, insoluble sulfur to make plastic material in the storage period is not blooming, keep the rubber component performance uniform. Prevent contamination of products and molds, and removed to overcome blooming increased during the paste process, provide the conditions for the production of the linkage.

4, insoluble sulfur rubber no migration phenomenon in the adjacent layer. Especially in Dingding Ji Shun gum and gum rubber compound, and a high rate of migration of ordinary sulfur, with addition of insoluble sulfur can be avoided later.

5, it can maintain the stickiness between the semi-finished parts, is conducive to forming operations, and ensure uniformity of vulcanized products to ensure product quality.

Insoluble sulfur can be used in the manufacture of tires, belts, hoses, rubber, latex products, and industrial products, and has been widely used in the rubber and wire bonding.

As a curing agent, insoluble sulfur can be added directly at the mixing rubber compounds, sulfur should be in common open cold roll mill was added, preferably added after the other ingredients together. Insoluble sulfur can be added to the mixer, but should be added before the latex at a temperature lower than 90 degrees. When used in soft rubber, generally in an amount of 0.2 to 5.0 parts by weight, in the amount of hard rubber, the amount of up to 25 to 40 parts by mass.

Thiazole accelerators will increase the general risk of sulfur blooming. At temperatures above 90 degrees, for too long can cause insoluble sulfur to the general sulfur conversion.