PVC transparent sheet
DATE：2022/3/12 8:47:51 / READ： / SOURCE：This station
PVC transparent sheet
1. Material selectionThe material used for the extrusion molding of R-PVC transparent plate (sheet) is mainly PVC resin, which is composed of stabilizer, impact enhancer, processing aid, lubricant and other auxiliary materials. The type and quality of main and auxiliary raw materials will directly affect the processing performance and the physical properties of the final product. For example, the average relative molecular weight of PVC resin is inconsistent, which will bring difficulties to molding processing; Adding additives with high refractive index of resin will not produce products with high transparency. Therefore, it is very important to select the best components of the mixture according to the extrusion process and the specific requirements of the production of transparent plate (sheet). Casting film production line www.handern.com com
(1) PVC resin PVC resin is a kind of plastic with strong heat sensitivity, poor heat resistance, and the thermal melting temperature is close to the decomposition temperature. Therefore, the selection of PVC resin should be appropriate. It is best to choose the suspension loose type (XS), which is required to have the advantages of high whiteness, appropriate viscosity, relatively uniform particle size, good thermal stability, basically consistent average relative molecular weight, easy plasticization, short molding time and so on. The specific technical indexes of pvc-xs resin that can meet the production requirements of R-PVC transparent plate (sheet) are shown in table 2-36. The number of domestic manufacturers capable of producing this PVC resin has gradually increased in recent years, especially the resins produced by Beijing No. 2 chemical plant, Tianjin chemical plant, Jinxi Chemical Plant and Shanghai Tianyuan Chemical Plant have high whiteness, less fish eyes and good thermal stability, which are more favorable for extruding R-PVC transparent plates (sheets). Casting film production line www.handern.com com
In the whole cycle of heat stabilizer from material mixing to extrusion molding, PVC has a long heating process, which is easy to decompose hydrogen chloride gas and form conjugated polyene structure. Especially under the action of photooxygen, it will promote and aggravate the decomposition of PVC, make the color of polymer change from light to dark, greatly reduce the physical and mechanical properties and transparency, and lose the use value of products. The purpose of adding heat stabilizer is to stabilize and capture the chlorine atom on the carbon chlorine bond in PVC, reduce the production of compound hydrogen, avoid the formation of CO strangled polyene structure, prevent the further decomposition of PVC, ensure the smooth progress of PVC extrusion processing and prolong the service life of products. For the selection of heat stabilizer for R-PVC transparent plate (sheet) products, in addition to excellent thermal stability of resin, good compatibility and no impact on the physical properties and secondary processing performance of products, it should also pay attention to the same or close to the refractive index of resin (1.52 ~ 1.55). Because only when it is the same or basically consistent with the refractive index of the resin, the refractive index of the mixed materials will tend to be consistent, and the transparency of the transparent plate (sheet) can be improved. Casting film production line www.handern.com com
There are many kinds of heat stabilizers for PVC, including lead salt, calcium zinc, cadmium barium zinc and organotin. Their basic physical properties are shown in table 2-37. It can be seen from table 2-37 that organotin stabilizer should be selected for the production of R-PVC transparent board (sheet). Dibutyltin laurate, dibutyltin maleate and mercaptan di-n-octyl tin are used according to their composition. Mercaptan di-n-octyl tin with comprehensive effect is usually used. Tin mercaptan is a light yellow non-toxic liquid with excellent thermal stability. Its refractive index (1.49-1.5) is close to that of the resin (1.52-1.55). It has good transparency and has a certain plasticizing effect, which is conducive to the plasticization of materials.
Beijing additives General Factory (formerly Beijing No. 3 chemical plant) can produce various brands of organotin stabilizers, among which Beijing M-103 mercaptan tin is more suitable for extruding R-PVC transparent plate (sheet)- Good results can be obtained when the general dosage (mass fraction) is 2 ~ 3.
(3) Impact enhancers improve the impact strength of PVC as a brittle material. Impact enhancers such as CPE, EVA, ABS or MBS often need to be added. Compare with CPE, en and ABS. MIS plays a better role in impact strength, transparency and bending whiteness. The reason why adding MBS can improve the toughening and impact resistance of products is that the ternary copolymer of MBS, methyl methacrylate (m), butadiene (b) and ethylene (s), when the butadiene rubber component is introduced into PNC, the external impact energy is absorbed by the tiny "craze" generated on the surface of rubber particles. There are many brands of MBS. When designing the process formula of PVC transparent plate (sheet), it is better to use MBS with particle size between 0.1 ~ 1qm. Because if the particle size is too different, it will affect the uniform dispersion of MBS in PVC, hinder the extrusion process and degrade the product performance. At the same time, special attention should be paid to the selection of MBS with comprehensive effect. Practice has proved that MBS containing less butadiene can not only achieve the purpose of impact strengthening, but also make the transparency and bending whitening of products ideal. In some MBS varieties, the effects of different butadiene contents on product properties are shown in table 2-38. Generally, 2 ~ 3 phr should be used in the proportioning period. If the dosage exceeds 4 phr, the extrusion and sheet quality will be affected. MBS was developed earlier in China. Shanghai Gaoqiao Chemical Plant and other enterprises have produced MBS of similar quantity and number, which can be used for products. Casting film production line www.handern.com com
Author：admin