【Practical】 Formulation design of rigid PVC drainage pipe
【Practical】 Formulation design of rigid PVC drainage pipeUPVC pipe is also called rigid PVC pipe. It is an amorphous thermoplastic vinyl chloride resin by adding certain additives (such as stabilizers, lubricants, fillers, modifiers, etc.), and then processed into a pipe by an extruder.
Rigid PVC drainage pipe (UPVC)
Advantages: light weight, corrosion resistance, high strength, can be recycled and so on.
Disadvantages: high melt viscosity, poor fluidity and other processing difficulties.
UPVC hard tube formula
PVC (SG-5) + stabilizer (lead salt, metal soaps) + lubricant + processing aid + pigment
Formulation components
1PVC resin
In order to obtain rapid and uniform plasticization, the suspension method should be used to loosen the resin, the resin models are SG-5.
Note: S means that PVC resin is made by suspension method, G means general-purpose resin, and SG-5 is mostly used for transparent products, hard tubes and profiles.
2PVC stabilizer
Pure PVC resin is extremely sensitive to heat. When the heating temperature reaches above 90 ℃, a slight thermal decomposition reaction will occur; when the temperature rises to 120 ℃, the decomposition reaction will increase; at 150 ℃, 10 minutes, the PVC resin will be from the original The white gradually changes to yellow-red-brown-black. The decomposition process of PVC resin is due to a series of chain reactions caused by the de-HCL reaction, which finally leads to the breakage of the macromolecular chain. One of the methods to prevent the thermal decomposition of PVC is to add a stabilizer to capture the HCl produced by the thermal decomposition of PVC to prevent the catalytic degradation of HCl.
PVC commonly used stabilizer
1
Compound stabilizer
1. Liquid barium-zinc composite stabilizers are generally light yellow to yellow-brown oily liquids, with a specific gravity of 1.0-1.1 at room temperature, good heat resistance, and are not contaminated by sulfides. It can improve the stability effect when used in combination with epoxy plasticizer It has an activation effect on the blowing agent.
2. Liquid calcium-zinc compound stabilizer The main components of non-toxic liquid calcium-zinc stabilizer are calcium stearate, calcium ricinoleate, zinc stearate, zinc ricinoleate, epoxy soybean oil, and ultraviolet absorber. Liquid calcium and zinc stabilizers are generally selected from fat and fat calcium and zinc salts that are more soluble in organic solvents and have fewer carbon atoms. Due to different components and different properties, it is generally a pale yellow to yellow clear oily liquid with a specific gravity of 1.0-1.05 at room temperature. It is a non-toxic stabilizer for PVC, and is mainly used as a stabilizer for food packaging films and utensil foam artificial leather.
3. The lead salt compound stabilizer has good thermal stability and has been widely used. However, the powder of lead salt is fine. In the ingredients and mixing, the dust of the lead salt is inhaled by people and will cause lead poisoning. For this reason, scientists have developed a new type of Compound lead salt heat stabilizer. This composite additive uses symbiotic reaction technology to mix tri-salt, di-salt and metal soap in the reaction system with the initial ecological grain size and various lubricants to ensure the full dispersion of the heat stabilizer in the PVC system At the same time, due to co-melting with lubricant to form particles, it also avoids poisoning caused by lead dust. The compound lead salt stabilizer contains the heat stabilizer component and lubricant component required for processing, and is called the full package heat stabilizer
3
Organotin
Good stabilizing effect, transparent, toxic or non-toxic, limited use due to high price.
4
Metal soap
The stabilizing effect is general. It is classified as transparent, toxic or non-toxic. It is rarely used alone. It is often used in combination. It is often used in soft products.
5
Rare earth
The new variety has the advantages of transparency and non-toxicity, and has great development prospects.
3 Lubricant
PVC melts have a strong tendency to adhere to metals, and the friction between the melts and between the melts and the processing equipment is large, and lubricants must be added to overcome frictional resistance. The amount of lubricant added is relatively large. According to the different compatibility of lubricant and PVC resin, it can be divided into internal lubricant (good compatibility) and external lubricant (poor compatibility).
1
Metal soap (external lubricant)
Metal salts of higher fatty acids (commonly known as metal soaps) are one of the commonly used lubricants. In addition to its lubricating effect, it is also a heat stabilizer for PVC. For the saponification of a certain metal, the longer the carbon chain of the combined fatty acid, the better the lubricity. Commonly used are calcium stearate, zinc stearate, lead stearate, etc., among which lead stearate has the best lubricity.
2
Polyethylene wax (internal lubricant)
PE wax is also called polymer wax. As a lubricant, it has stable chemical properties and good electrical properties. Compared with other external lubricants of PVC, polyethylene wax has stronger internal lubrication.
4 filler
Also known as filler, filler. Solid materials added to the material to improve performance or reduce costs. Generally organic, inorganic, metallic or non-metallic powders that do not contain water, are neutral and do not adversely affect the components of the material can be used as fillers.
1. Light calcium carbonate (filler)
English: LightCalcium Carbonate, also known as Precipitated Calcium Carbonate (PCC). It is made by chemical processing methods. Because its sedimentation volume (2.4-2.8mL / g) is larger than that of heavy calcium carbonate produced by mechanical methods (1.1-1.9mL / g), it is called light calcium carbonate.
Characteristics: non-toxic, odorless, non-irritating, usually white.
Calcium carbonate can play a role as a skeleton in plastic products. It has a great effect on the dimensional stability of plastic products, can increase the hardness of products, and can also improve the surface gloss and surface smoothness of products. Adding calcium carbonate to general plastic products can improve the heat resistance. Since the whiteness of calcium carbonate is more than 90%, it can also replace expensive white pigments to play a certain whitening effect.
5 modifier (impact modifier)
1. ACR (Acrylic copolymer) impact modifier is an acrylic copolymer with a core-shell structure, is a PVC impact modifier with excellent comprehensive performance. Its PVC products have excellent impact resistance, low temperature toughness.
ACR processing modifier is a high molecular weight polymer made by emulsion polymerization, which can accelerate the melt plasticization of PVC, improve surface gloss, and improve product quality. Generally, domestic drain pipes often have a high content of calcium powder. High molecular weight ACR has better effect on products, such as HF-100 and 801 of Shandong Hongfu Chemical Co., Ltd. It can obviously improve the fluidity and thermal deformation of PVC melt, promote plasticization, and the surface of the product is smooth and beautiful.
2
CPE Chlorinated Polyethylene
Chlorinated polyethylene is a polymer material made from high-density polyethylene (HDPE) through chlorination substitution reaction. According to different structures and uses, chlorinated polyethylene can be divided into two types: resin-type chlorinated polyethylene (CPE) and elastomer-type chlorinated polyethylene (CM). It is an excellent impact modifier for PVC plastics.
6. Pigment
Typical UPVC formula composition (parts by mass)
PVC 100, light calcium 20, lead salt stabilizer 3.5, PE wax 0.3, stearic acid 0.2, processing aid ACR (HF-100 / 801, etc.) 1.5, paraffin wax 0.35, titanium dioxide 1.5, ultramarine 0.02, brightener 0.02
Extrusion process conditions of PVC hard products
Mix the temperature at a high speed to 115 degrees, and then lower it to 45 degrees at a low speed to discharge the material.
The barrel temperature is 160 ℃ ~ 180 ℃, the head temperature is 180 ℃ ~ 200 ℃, the screw speed depends on the model.
Attention
There are many components in the PVC formula, and they must be mixed thoroughly. Pay attention to the order of addition. Fillers with large oil absorption should be added later to prevent oil absorption. Lubricants are added last to prevent the dispersion of other components. Control the mixing temperature, generally around 115 ℃.
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