Formulation design (1) Selection of NBR and PVC The content of polar gene acrylonitrile in NBR is different, and the polarity is different, which has an impact on the compatibility of the blend and the performance of the product. This formula uses NBR-40 produced by Lanzhou Chemical Plant. Both suspension method and emulsion method can produce PVC. Suspension method PVC is cheap, but the melting temperature is higher during the processing process, and high temperature plasticization and mixing are required; emulsion method PVC The price is more expensive, but plasticizers can be used for pre-impregnation and swelling, and high-temperature plasticizing equipment is not required during processing. The degree of polymerization of PVC also has a great influence on the properties of the blend. The high degree of polymerization of PVC can improve the strength, constant elongation strength and aging resistance of the blend, and at the same time, its own viscosity and plasticizing temperature also increase, which makes processing difficult. This formula selects PVC-RH.
(2) The performance of PVC blends with different dosages of PVC and NBR is different, although PVC and NBR can be blended and blended in any proportion to make thermoplastic plastic characteristics or nitrile rubber rubber characteristics. Various blends of the product, but the ratio must also be selected according to the actual use requirements of the product. The amount of NBR is small, and the dispersibility of NBR in PVC is poor. When the amount of NBR is increased to NBR/PVC=20/80 or more, NBR will be more evenly dispersed in PVC, and the compression set of the product will be reduced; while the amount of PVC Increased, tensile strength and aging resistance are improved, and the appearance quality of the product is improved. According to the performance requirements of automobile sealing strips, this formula uses a blend of NBR/PVC=40/60.
(3) Softening and plasticizing system The main function of softening and plasticizing system is to reduce the intermolecular force of the polymer, increase the mobility of the polymer molecular chain, that is, reduce the softening temperature of the polymer. According to the actual performance requirements of the product, use phthalic acid (DOP) and dioctyl sebacate (DOS) together with a ratio of DOP/DOS=5/1.
(4) The reinforcement system usually selects medium and super wear-resistant carbon black, high wear-resistant carbon black, fast extrusion carbon black, etc. as the reinforcing agent, supplemented by appropriate amounts of clay, calcium carbonate, and talc as fillers to improve processing performance. At the same time reduce production costs.
(5) The anti-aging system can use a substituted phenol anti-aging agent. The antioxidant can produce complexation with PVC stabilizers to prevent the aging of PVC molecular chains from breaking bonds.
(6) PVC stabilizing system PVC is degraded due to heat and mechanical shear during processing, and its products are easily damaged by heat, light and oxygen during use. The selection of stabilizers must be based on the requirements of processing technology and final product performance Come to consider. We use lead stabilizers, which have good stability and weather resistance.
(7) The degree of unsaturation of NBR in the vulcanization system is small, and the amount of sulfur can be reduced. When a high amount of thiurams and sulfenamides are used in combination or a low-sulfur system in which thiurams are used in combination with thiazoles, the PVC/NBR blend has excellent physical and mechanical properties. This formula uses a low-sulfur system that combines thiurams and thiazoles, and the vulcanization accelerator dose is 23 parts.
Indoor small formulation test (1) PVC plasticizing and NBR plasticizing firstly mix PVC with plasticizers and stabilizers, stir evenly with a mixer, and plasticize NBR on an open mill to a plasticity of 0.29 or more, and leave it for 8 hours. . The stirred PVC is plasticized on a hot rubber mixer. The roller temperature is generally controlled at about 160e and the roller distance is 0.51mm. Under the action of the roller heat and shear, the PVC forms a molten state and is wrapped in the roller. (2) Rubber-plastic co-rolling process: After the PVC is wrapped in the roller, add NBR plastic compounding rubber, heat it evenly, cut off the heating power, pass the cooling water, add zinc oxide, antioxidant, stearic acid and carbon black in sequence to adjust To the proper roll distance, cool down the next piece, separate each piece with a little release agent, and leave it for 8 hours to make a blend masterbatch. According to the NBR mixing process, control the roll temperature at about 60e, add a vulcanization accelerator, mix for about 10 minutes, and adjust the roll distance to form a blend. If the mixing time is too long, scorching will occur, and the structure of the extruded product will be incomplete if the time is too short. (3) Physical and mechanical properties The physical and mechanical properties of the blends in the indoor small formulation test are shown in the table. The results show that the physical and mechanical properties at room temperature meet the requirements of GB7526) 87 standard. When the total amount of vulcanization accelerator reaches 3 parts, the tear strength decreases, which is lower than GB7526) 87 standard requirements. When the total amount of vulcanization accelerator reaches 2 parts, the elongation at break of 10[email protected] hot air aging is lower than the standard requirement. The compression set of formulations 2 and 3 meet the standard requirements. The brittleness temperature of the three formulas all meet the standard requirements.
Conclusion Compared with the traditional single rubber compound and plastic modified materials, the physical and mechanical properties and surface appearance quality of PVC/NBR rubber-plastic blends are improved; Hot air is aging, and the surface appearance quality is good; compared with the plastic modified sealing strip, the compression set is small, the surface appearance quality is similar, and the texture is fine and tough. It is easy to produce with the general equipment of rubber manufacturers and has better elasticity. Therefore, the use of PVC/NBR blends is an effective way to improve automotive weather strip materials.
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