- Hard PVC formula design
UPVC pipe, also known as rigid PVC pipe, it is amorphous thermoplastic vinyl chloride resin by adding a certain amount of additives (such as stabilizers, lubricants, fillers, modifiers, etc.), and then through the extruder processing into a pipe.
Advantages: light weight, corrosion resistance, high strength, can be recycled and so on.
Disadvantages: high melt viscosity, poor mobility and other processing difficulties.
UPVC hard tube recipe:PVC (SG-5) + stabilizer (lead salt, metal soap) + lubricant + processing aid + pigment
In order to obtain rapid and uniform plasticization, should be used in the suspension of loose resin, resin models are SG-5.
Note: S said PVC resin by the suspension method, G said general-purpose resin, SG-5 for transparent products, hard tube, profiles.
Pure PVC resin is extremely sensitive to heat, when the heating temperature reaches 90 ℃ above, it will occur a slight thermal decomposition reaction; when the temperature rose to 120 ℃ after the decomposition reaction intensified; at 150 ℃, 10 minutes, PVC resin from the original The white gradually turns yellow - red - brown - black. PVC resin decomposition process is due to the HCL reaction caused by a series of chain reaction, and finally lead to macromolecular chain breaks. One way to prevent the thermal decomposition of PVC is to add a stabilizer therein to prevent the catalytic degradation of HCl by capturing HCl produced by thermal decomposition of PVC.
Lead salt composite stabilizer has good thermal stability, has been widely used, but the lead salt powder is small, ingredients and mixed, the dust is inhaled lead to lead poisoning, for which the scientific and technical personnel have developed a new Of the composite lead salt heat stabilizer. This combination of additives using a symbiotic reaction technology will be three salt, two salt and metal soap in the reaction system to the initial ecological grain size and a variety of lubricants mixed to ensure that the heat stabilizer in the PVC system in the full dispersion , And because of the co-melting with the lubricant to form particles, but also to avoid the lead dust caused by poisoning. The composite lead salt stabilizer contains the heat stabilizer components and lubricant components required for processing, and is referred to as a fully packaged heat stabilizer.Stable effect is good, transparent, toxic or non-toxic, due to high price limit use.
New varieties, with a transparent, non-toxic and other advantages, great development prospects.
PVC melt adhesion metal tendency, between the melt and the friction between the melt and processing equipment, need to add lubricant to overcome the friction resistance. The amount of lubricant added is relatively large. According to the compatibility of lubricants and PVC resin different size, can be divided into internal lubricants (good compatibility) and external lubricant (poor compatibility).
Metal soap (external lubricant)
Metal salts of higher fatty acids (commonly known as metal soap), is one of the commonly used lubricants. In addition to lubrication, but also with PVC heat stabilizer. For a certain kind of metal saponification, the longer the carbon chain of the fatty acid, the better the lubricity. Commonly used calcium stearate, zinc stearate, lead stearate, etc., of which the best stearate lead lubrication
Polyethylene wax (internal lubricant)
PE wax, also known as polymer wax, as a lubricant, its chemical stability, good electrical properties. Compared to other PVC external lubricants, polyethylene wax has a stronger internal lubrication.
Also known as filler, filler. Add solid materials that improve performance or reduce costs in the material. Organic, inorganic, metallic or non-metallic powders that are normally non-aqueous, neutral, and undesirable with the ingredients of the material can be used as fillers.
Light calcium carbonate (filler)
English: LightCalcium Carbonate, also known as Precipitated Calcium Carbonate (PCC). Is made by chemical processing methods. Because of its settling volume (2.4-2.8 mL / g) than the heavy calcium carbonate sedimentation volume (1.1-1.9 mL / g) produced by mechanical methods, it is called light calcium carbonate.
Features: non-toxic, odorless, non-irritating, usually white.
Calcium carbonate in the plastic products can play a role in the size of plastic products on the stability of the size of a great role, can improve the hardness of the product, but also can improve the product surface gloss and surface smoothness. In the general plastic products to add calcium carbonate heat resistance can be increased, because the calcium carbonate whiteness of more than 90%, can also replace the expensive white pigment to play a certain whitening effect.
5.Modifier (impact modifier)
ACR (Acrylic copolymer) is a core-shell structure of the acrylic copolymer, is a comprehensive performance of the PVC impact modifier.ACR is a combination of impact resistance and processing and modification of the dual function of plastic additives, because of its core / shell structure, so that its PVC products with excellent impact resistance, low temperature toughness, compatibility with PVC, weather resistance, Stability, processing, and the performance and price ratio is moderate, can significantly improve the melt flow of PVC, thermal deformation, and promote plastics, products, smooth and beautiful surface.
2.Chlorinated polyethylene is a high molecular weight polyethylene (HDPE) by chlorination of the reaction of the polymer material. Depending on the structure and use, chlorinated polyethylene can be divided into resin type chlorinated polyethylene (CPE) and elastomer type chlorinated polyethylene (CM) two categories. PVC plastic is excellent anti-impact modifier.
Typical UPVC Formulation (parts by mass)
PVC 100, light calcium 20, lead salt stabilizer 3.5, PE wax 0.3, stearic acid 0.2, processing aid ACR 1.5, paraffin 0.35, titanium dioxide 1.5, group of youth 0.02, brightener 0.02
Extrusion process conditions of PVC hard products
Mix high speed up to 115 degrees, then put the low speed down to 45 degrees, put the material.
Barrel temperature 160 ℃ ~ 180 ℃, head temperature 180 ℃ ~ 200 ℃, screw speed to see models.
PVC ingredients in the formula is very much, to fully mix evenly. Pay attention to the order of feeding, oil absorption of the filler to be added to prevent oil absorption. The lubricant is finally added to prevent the dispersion of the other components. Control the mixing temperature, usually around 115 ℃.
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