I. Overview of foamed rubber products
Foam rubber products are produced by physical or chemical foaming method with rubber as the base material to obtain sponge-like rubber porous structure products. This technology has been widely used in various production industries, such as automobile door and window seals, cushioning pads, building construction gaskets, seismic materials, sports protection facilities, etc.
1、The concept of foamed rubber
The so-called foamed rubber is also widely known as rubber foaming technology, is the use of specific foaming agent to treat rubber, so that rubber has a characteristic performance of a processing means. This technology is more widely used in the current production field, is the most common method of production work at this stage.
2、Classification of foamed rubber products
Foamed rubber products are currently one of the most used products in the production field, which can be divided into two kinds of microporous structure and porous structure according to the pores. And the microporous structure can be divided into separate foaming products and continuous foaming products. According to the raw material of rubber can be divided into this product into natural rubber foaming products, isoprene foaming products, SBR foaming products, ethylene propylene rubber foaming products, etc.
Second, foam rubber products with analysis
Foamed rubber products are more and more widely used in the current society, its production and production process and thermoplastic foaming has a world of difference, it has a vulcanization cross-linking speed and the speed of decomposition of the foaming agent to match the problem. That is to say, a rubber material successful foaming in addition to the cross-linking speed there is a close relationship between the vulcanization process of rubber materials and the decomposition of the blowing agent occurs when the principle is basically the same, are an extension of the gas expansion wall to produce the corresponding resistance process.
1、The choice of the main material
In the manufacturing process, usually require the specific objectives of the product to choose the scientific rubber body materials, these materials in the selection of soft, moderate strength, good amount of elasticity of natural rubber products, but also to choose some artificial rubber to meet the needs of the product. For the production of oil-resistant foam products, in addition to the need to choose a reasonable scientific nitrile rubber, but also to analyze the proportion and relationship of neoprene, and even to meet the needs of some special products, you can also use two or more kinds of rubber and the form.
2、The choice of foaming agent
Foaming agent is the most critical link in the entire production of foamed rubber, and its selection is closely related to the efficiency and quality of work. Generally speaking, the good performance of the foaming products must choose a scientific and reasonable foaming agent, and the amount of foaming agent, the use of methods to meet the current social development requirements. At present, the blowing agent mainly contains organic blowing agent and inorganic blowing agent two. Inorganic blowing agent mainly refers to sodium bicarbonate, ammonium bicarbonate, urea, etc. These blowing agents have the advantages of fast decomposition speed and low temperature in the application, theoretically its foaming performance is also better. As the gas produced by this technology in the application is mainly carbon dioxide and ammonia, etc., the presence of these gases makes the rubber structure has a large permeability coefficient, it is difficult to create a closed-hole foam rubber, the production of foam rubber low quality, low strength, shrinkage, easy to deformation, so it is extremely easy to use alone in the work, and generally can be used as an organic foaming agent to use.
The current work, we commonly used foaming agent mainly contains nitrogen dicarbonamide, nitroso, dibenzosulfonyl hydrazide ether, etc.. These materials in the application of its decomposition temperature is about 200 ℃ or more, and in the production process also need to add other auxiliary blowing agent, such as urea, magnesium oxide, zinc oxide, etc., so its decomposition is greatly reduced, thermal decomposition of the gas produced mainly contains nitrogen, carbon dioxide, ammonia, etc., these gases are not only non-toxic, odorless, and even has the advantage of not polluting the environment, not discolored. The pore size of rubber foam products made with foaming agent is larger, and the shrinkage rate is also larger; when using foaming agent, the auxiliary foaming agent has stearic acid, alum, etc., which can significantly reduce the decomposition temperature of foaming agent to 130~150℃ after adding.
3, the choice of vulcanization system
Vulcanization system is very important in the research process of foaming products, first of all, whether the matching of vulcanization system and foaming system is the key to making good performance of foaming products. A rubber can be successfully foamed, the most important thing is the vulcanization process of rubber and the decomposition process of the foaming agent should be basically synchronized, or sulfur time than the foaming time slightly ahead. Therefore, after choosing the vulcanization system, adjust the foaming system to match it, or after choosing the foaming system, adjust the vulcanization system to match it.
4、The choice of reinforcing filler
Carbon black, silica and other reinforcing agents can improve the strength and stiffness of foamed rubber products, the appropriate addition of calcium carbonate, clay and other fillers can improve the processing performance of the rubber and reduce costs. Carbon black should choose semi-reinforced FEF and SRF carbon black, filler should choose light calcium carbonate, clay, etc., the amount should not be too much, preferably 20 to 40 copies.
5、The choice of plasticizer
Plasticizer requirements are: good plasticizing effect, low dosage, fast absorption rate, good compatibility with rubber, small volatility, no migration, non-toxic, odorless, inexpensive and easy to obtain. Plasticizer can improve the degree of dispersion of the compounding agent, the processability and molding of the rubber blend. Foam rubber products that require high foam multiplier, the general amount of plasticizer added is larger, and choose a good compatibility with rubber plasticizer.
6、The choice of antioxidant
Foam rubber products for porous structure, surface area is larger, relatively easier to aging, must be combined with antioxidants. The principle of selecting antioxidant is both good anti-aging effect, but also does not affect the decomposition of the foaming agent. Can choose 4010, 264, MB and other antioxidants, the amount of more than the general rubber products.
7, the principle of rubber foaming
Solid rubber foaming production of rubber sponge, the principle is to add foaming agent in the selected rubber or re-add foaming agent, the decomposition of the foaming agent in the vulcanization temperature to release gas, surrounded by rubber to form a bubble hole 'so that the rubber expansion to form a sponge.
The main factors that determine and influence the structure of the bubble pore are: the amount of blowing agent gas, the gas diffusion rate in the rubber, the viscosity of the rubber and the speed of vulcanization, the most critical of which is the matching of the amount of blowing agent gas, the speed of gas generation and the speed of vulcanization of the rubber.
To make better rubber products, the choice of blowing agent species and rubber vulcanization system is the key. There are two specific methods:
First, according to the vulcanization temperature to choose the decomposition temperature and the appropriate blowing agent, and then according to the decomposition speed of the blowing agent in the vulcanization temperature to adjust the vulcanization speed of the rubber, such as the use of late promoter and other promoters and vulcanization system, can be used to adjust the amount of promoter to adjust the vulcanization speed.
Second, in the case of the vulcanization system to determine the speed of vulcanization, according to the choice of foam varieties and suitable particle size. The particle size of the blowing agent is also one of the most important factors in determining the decomposition speed of the blowing agent. The particle size decreases, the specific surface area of the particles increases, the heat transfer efficiency increases, and the decomposition speed is accelerated, so the balance between the decomposition speed of the blowing agent and the vulcanization speed of the rubber can be adjusted by choosing the suitable particle size of the blowing agent.
Three, processing technology
1、Plasticizing
The essence of plasticizing raw rubber is to break and destroy the macromolecular chain of rubber. Improve the plasticity of rubber, so that the mixing and blending process of the compounding agent is easier to carry out. In the preparation of foam rubber products, the better the plasticity of rubber, the easier it is to make products with uniform bubble holes, small density and small shrinkage rate. Therefore, the raw rubber should be fully plasticized.
2、Storage
After the rubber is mixed, it must be placed for a long enough time, generally 2~4h, so that various additives are fully dispersed in the rubber mix. The more evenly the rubber additives are dispersed, the better the stability of the product size, the smoothness of the surface and the uniformity of the bubbles.
3、Temperature
Rubber foam is very sensitive to temperature. The same rubber material has different foaming effects at different temperatures. Because the foaming system and the vulcanization system are sensitive to temperature differently, changing the vulcanization temperature will readjust the problem of matching the vulcanization system with the foaming system.
4、Forming
The molding methods of foamed rubber products are: extrusion molding, molding, flat molding, etc. EPDM foamed products are commonly used in extrusion molding, and NBR are mostly used in molding.
