The PVC plastic profile is mainly composed of PVC resin and additives. The additives are further divided into: heat stabilizer, lubricant, processing modifier, impact modifier, filler, ageing agent, colorant, etc. . Before designing a PVC formulation, you should first understand the properties of PVC resins and various additives.
1. The design principle of PVC profile formulation
1.1. PVC resin selection and use
The resin for producing PVC plastic profiles is polyvinyl chloride resin (PVC). Polyvinyl chloride is a polymer made of vinyl chloride monomer. The output is second only to PE.
The PVC resin can be classified into two types, a loose type (XS) and a compact type (XJ), depending on the dispersing agent in the polymerization. The loose particle size is 0.1-0.2mm, the surface is irregular, porous, cotton-like, easy to absorb plasticizer, compact particle size is less than 0.1mm, surface is regular, solid, table tennis, difficult to absorb plasticizer, At present, more loose types are used. PVC can be divided into ordinary grade (toxic PVC) and sanitary grade (non-toxic PVC). Hygienic grade requires a vinyl chloride (VC) content of less than 10 × 10-6, which can be used in food and medicine. Different synthetic processes, PVC can be divided into suspension PVC and emulsion PVC. According to the national standard GB/T5761-93 "Inspection standard for general-purpose polyvinyl chloride resin for suspension method", the suspension method PVC is divided into PVC-SG1 to PVC-SG8 eight kinds of resins, wherein the smaller the number, the greater the degree of polymerization, the molecular weight is also The larger the strength, the higher the melt flow, and the more difficult the processing. When selecting a soft product, PVC-SG1, PVC-SG2, and PVC-SG3 are generally used, and a large amount of plasticizer needs to be added. For example, a polyvinyl chloride film is made of SG-2 resin, and 50 to 80 parts of a plasticizer is added. When processing hard products, plasticizers are generally not added or added in small amounts, so PVC-SG4, PVC-SG5, PVC-SG6, PVC-SG7, and PVC-SG8 are used. For example, SG-4 resin is used for PVC hard pipe, SG-5 resin is used for plastic door and window profile, SG-6 resin is used for hard transparent film, and SG-7 and SG-8 resin are used for hard foamed profile. The emulsion method PVC paste is mainly used for artificial leather, wallpaper, floor leather and plastic products. Some PVC resin manufacturers ship PVC resin according to the degree of polymerization (degree of polymerization is the number of unit links, the degree of polymerization multiplied by the molecular weight of the chain is equal to the molecular weight of the polymer), such as PVC resin produced by Shandong Qilu Petrochemical Plant, the factory products It is SK-700; SK-800; SK-1000; SK-1100; SK-1200. The SG-5 resin has a degree of polymerization of from 1,000 to 1,100. The physicochemical properties of PVC resin are shown in the fourth chapter.
The PVC powder is a white powder having a density between 1.35 and 1.45 g/cm3 and an apparent density of 0.4 to 0.5 g/cm3. We regard the content of plasticizers in PVC products as soft and hard products. Generally, the plasticizer content is 0~5 parts for hard products, 5~25 parts for semi-hard products, and more than 25 parts for soft products.
PVC is a non-crystalline, polar polymer with high softening temperature and melting temperature. Pure PVC generally needs to be plasticized at 160-210 °C. PVC display due to polar bonds between macromolecules. Hard and brittle performance. In addition, the chlorine-containing group in the PVC molecule easily causes the PVC to de-HCl reaction, thereby causing the PVC degradation reaction. Therefore, PVC is extremely unstable to heat and the temperature rises, which greatly promotes the dehydrochlorination of PVC. When the temperature reaches 12O ° C, pure PVC begins to dehydrogenate, resulting in thermal degradation of PVC. Therefore, in the processing of PVC, various additives must be added to process and modify the PVC and impact modification so that it can be processed into a useful product.
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