Latest Processing technology of fluororubber
The fluororubber synthesis technology of polymer synthetic materials is not the most difficult, and the most important point is the modification and processing technology of fluororubber. With the development of science and technology, various types of fluororubbers have been developed at home and abroad, mainly by changing the polymerization monomers to achieve different compositions and properties of fluororubbers. In addition to the monomer composition, the vulcanization system during processing is one of the key factors determining the physical properties of the fluororubber. There are currently three types of vulcanization systems that have been developed: diamine compounds containing two amino groups in the molecule, polyol compounds containing two hydroxyl groups, peroxides, and polyfunctional compounds. Among them, the most widely used is a polyol vulcanization system, and the polyol used is limited to bisphenol AF. Compared with the traditional diamine vulcanization system, the polyol system has two advantages of small compression set and high anti-scorch safety. The cross-linking point in the peroxide vulcanization system contains a more stable C-C bond, so the chemical resistance of the vulcanizate is superior. Further, the ether-containing monomer cold-resistant fluororubber must be vulcanized by using a peroxide because the hydrogen fluoride is removed from the vinylidene fluoride bond.
(1) The formulation of fluororubber is generally composed of raw rubber, acid acceptor, vulcanizing agent, accelerator, reinforcing filler, processing aid and the like. The performance of domestic fluororubber and foreign fluororubber is basically the same, but the processing performance is somewhat different. The processing performance of domestic glue is poor, mainly because the Mooney viscosity is high, which affects the processing fluidity of the rubber compound. Domestic fluororubber 26 is equivalent to VitonA of DuPont, USA, and fluororubber 246 is equivalent to VitonB. Many foreign fluororubber raw rubbers have been added with vulcanizing agents. Fluorine rubbers supplied by 3M Company of the United States and Daikin Corporation of Japan have already added vulcanizing agents.
(2) Vulcanization is to make the fluororubber a certain degree of cross-linking, so that it has good performance. The fluororubber vulcanization can be carried out by an ionic addition mechanism of a nucleophilic reagent, or by a radical mechanism by a peroxide or a ray. Amine compounds (No. 1 and No. 3 vulcanizing agents) vulcanized fluororubber can solve the requirements of general products; using No. 2 vulcanizing agent can solve the processing of the glue. In the sealing article, in order to have a small compression deformation value, a phenol compound should preferably be used as a vulcanizing agent. Such as hydroquinone, bisphenol A, bisphenol AF, etc., with the appropriate accelerator to suit high-level performance requirements. In solving the resistance of corrosive media, it is recommended to use peroxide-vulcanized fluororubber.
(3) The acid-absorbing agent, also known as the stabilizer, is to solve the corrosion and pollution of the metal by the hydrogen fluoride generated during the processing of the fluorine rubber, so that the sulfurization reaction proceeds smoothly. Ca(OH)2 and the like. Generally, MgO, CaO, ZnO, PbO, and dibasic lead phosphite are used, and the amount thereof is generally 5 to 10 parts. Their addition has its own characteristics: MgO has good heat resistance; PbO has good acid resistance; CaO has small compression deformation; it is advantageous for eliminating bubbles; ZnO and dibasic lead phosphite, the fluidity of the rubber is improved, and the water resistance is good; OH)2 has small compression deformation, and Ca(OH)2 and active MgO are added. In the phenolic vulcanization system, a low compression deformation compound can be obtained. In short, choose the right acid absorber to meet the actual performance requirements.
(4) Fluororubber is a self-reinforcing rubber. Due to different performance requirements and uses, it needs to be adjusted through the reinforcement and filling system to make the function and cost meet the needs of users. The general dosage is between 10 and 30 parts. At present, the commonly used reinforcing fillers are generally thermal black, spray carbon black, white carbon black, calcium sulfate, barium sulfate, calcium oxide, carbon fiber and the like. With N990 carbon black or spray carbon black imported from Canada, good processing technology and corresponding physical properties are obtained in black products. Adding 20 parts of carbon fiber fluororubber, the compound has good fluidity, and after processing the vulcanized complex shape product, its appearance is better than N-990 and spray carbon black, and the surface is smooth. Due to the high thermal conductivity of the carbon fiber rubber compound, it is suitable for the use of high-speed moving rubber parts. It should be noted that the cost of adding carbon fibers is high and the elongation is low. Color fluororubber products can use white carbon black, titanium white, calcium fluoride, calcium carbonate, etc., and the corresponding pigments can be used to obtain the corresponding rubber compound. However, when processing a compression type sealing product, when selecting a color material, it is necessary to pay attention to the reasonable matching of the pigment and the high temperature, and also to control the compression deformation value of the rubber material, so that the product can adapt to the work under compression.
(5) Processing aids are a major advance in the processing of fluororubbers in recent years. It can improve the mixing process of fluororubber, prevent scorch, improve the fluidity and extrusion performance of the rubber compound, and prevent sticking and sticking in the processing without affecting the performance of the rubber compound. The role of the external release agent. In the processing of fluororubber, new processing aids such as fluororubber, low molecular weight polyethylene, zinc stearate, Ws280, palm wax, and model 935P have emerged, providing a new means for processing and application of fluororubber. . It is usually added in an amount of 1 to 2 servings.
The amount of vulcanizing agent added and its effect vary depending on the type of vulcanization system and fluororubber. Currently, polyhydric alcohol vulcanization systems are mainly used at home and abroad. For plasticizers, stearates or low molecular weight fluororubbers are commonly used in China. When the amount of rubber is large, the degree of automation is high, or the process of extrusion or injection molding is prone to scorch, and a certain amount of scorch retarder needs to be added. P-nitrophenol, p-nitrobenzoic acid, o-hydroxybenzoic acid and scorch inhibitor NA are usually used. Promoters, the use of polyol vulcanization systems require accelerators to have better scorch performance during the mixing and processing stages, but also have a faster vulcanization rate.
(6) Modification. Although fluororubber has many excellent properties, it also has disadvantages such as poor mold flowability, easy compression deformation, raw rubber processing performance, and poor physical properties of vulcanized rubber. In order to solve the fluidity of the fluororubber, a high relative molecular mass and a low molecular weight fluororubber may be used in combination, and a fluororubber having a wide relative molecular mass distribution may be produced by process adjustment. In order to solve the compression set property of the fluororubber, the fluororubber can obtain low compression set by adding a vulcanized cross-linking agent, a promoter and a heat-resistant auxiliary, thereby solving and improving the physical and mechanical properties of the fluororubber. In addition, the addition of an inorganic filler is also used to modify the fluororubber.
Acrylate rubber is a new thermoplastic elastomer formed by blending fluororubber or acrylate rubber with acrylate plastic. Acrylate rubber is mainly used in the automotive industry and is called "automotive rubber". Fluororubber is also mainly used in automobiles. Therefore, blending fluororubber with a relatively low-priced acrylate rubber can significantly reduce production costs without sacrificing performance. The acrylate rubber containing epoxide vulcanization point forms a miscible blend with the fluororubber through dipole-dipole interaction, thereby improving the mechanical properties of the blend.