Vulcanized rubber refers to rubber (raw rubber) that has undergone vulcanization, forming a three-dimensional spatial structure and becoming vulcanized rubber. Vulcanized rubber possesses characteristics such as non-stickiness and resistance to breaking. Most rubber products are made from this type of rubber (commonly known as rubber or rubber sheet). The general term for rubber materials after vulcanization processing is vulcanized rubber. After vulcanization, a spatial three-dimensional structure forms within the raw rubber, giving it high elasticity, heat resistance, tensile strength, and insolubility in organic solvents.
1. Basic Principles of Rubber Vulcanization
Rubber softens when heated, hardens, becomes brittle when cold, is difficult to shape, wears easily, and is soluble in gasoline and other organic solvents. It contains double bonds within its molecules, making it prone to addition reactions and aging. To improve the performance of rubber, raw rubber undergoes a series of processing steps in production. Under certain conditions, the raw rubber in the compound undergoes a chemical reaction with the vulcanizing agent, transforming from linear macromolecules into three-dimensional network macromolecules. This imparts excellent properties such as high strength, elasticity, wear resistance, and corrosion resistance to the rubber compound. This process is known as rubber vulcanization.
Vulcanization involves the basic process of creating vulcanized rubber by cross-linking raw rubber molecules to form a three-dimensional network structure. Different vulcanization systems are suitable for different raw rubbers. A composite is formed using raw rubber as the main component, supplemented by various auxiliary materials (which include systems for filling and reinforcement, vulcanization, protection, plasticization, and the addition of special substances). Vulcanization is a treatment method applied after coating with an insulating or sheathing layer, intending to activate the vulcanization system within the auxiliary materials, causing permanent cross-linking in the rubber, increasing elasticity, and reducing plasticity.
The vulcanization process is generally divided into four stages: induction, pre-vulcanization, optimal vulcanization, and over-vulcanization. To achieve this reaction, external energy must be applied to reach the necessary vulcanization temperature, and the rubber is then maintained within this temperature range to complete the entire vulcanization reaction.
2. Introduction to Rubber Vulcanization Processes
Rubber vulcanization can be classified into three types based on the vulcanization conditions: cold vulcanization, room temperature vulcanization, and hot vulcanization.
1)Cold Vulcanization
Cold vulcanization can be used for vulcanizing thin film products. The products are immersed in a carbon disulfide solution containing 2% to 5% sulfur chloride, then washed and dried.
2)Room Temperature Vulcanization
During room temperature vulcanization, the vulcanization process occurs at room temperature and normal pressure. For example, room-temperature vulcanized rubber cement (mixed rubber solution) is used for bicycle inner tube joints and repairs.
3)Hot Vulcanization
Hot vulcanization is the primary method for vulcanizing rubber products. Based on different vulcanization media and methods, hot vulcanization can be divided into direct vulcanization, indirect vulcanization, and mixed gas vulcanization.
(1) Direct Vulcanization: The product is directly placed in a hot water or steam medium for vulcanization.
(2) Indirect Vulcanization: The product is vulcanized in hot air. This method is generally used for products with strict appearance requirements, such as rubber shoes.
(3) Mixed Gas Vulcanization: first use air vulcanization and then switch to direct steam vulcanization. This method overcomes the drawbacks of steam vulcanization affecting the appearance of the product, as well as the slow heat transfer long vulcanization time, and aging issues associated with hot air vulcanization.
