The full name is Polyvinylchlorid, the main ingredient is polyvinyl chloride, bright color, corrosion-resistant, strong and durable, due to the increase in the manufacturing process of plasticizers, anti-aging agents, and other toxic auxiliary materials to enhance its heat resistance, toughness, ductility, etc., so its products are not generally stored food and medicine. Generally do not store food and medicine. It is a favorite, popular and widely used synthetic material in the world today. Its global usage is the second highest among all kinds of synthetic materials. According to statistics, in 1995 alone, PVC was produced in Europe in the amount of about 5 million tons and consumed in the amount of 5.3 million tons. In Germany, PVC production and consumption of an average of 1.4 million tons. PVC is with a growth rate of 4% in the world-wide production and application. In recent years, the growth rate of PVC has been particularly significant in Southeast Asia, where there is an urgent need for infrastructure development. PVC is the most suitable material for the production of three-dimensional surface films.
PVC (Polyvinyl Chloride), the monomer of which has the structural formula CH2=CHCl
Chemical and Physical Properties:
Rigid PVC is one of the most widely used plastics materials. PVC is actually a polymerized substance of vinyl, and the material is amorphous in nature. processing agents, colorants, anti-impact agents and other additives. PVC is non-flammable, high strength, resistant to weathering, and has excellent geometric stability. PVC is highly resistant to oxidizing agents, reducing agents and strong acids. However, it can be corroded by concentrated oxidizing acids such as concentrated sulfuric acid and concentrated nitric acid and is not suitable for contact with aromatic hydrocarbons and chlorinated hydrocarbons.
The melting temperature of PVC during processing is a very important process parameter, and if this parameter is not correct, it will lead to problems of material decomposition. The flow characteristics of PVC are quite poor and its process range is very narrow. Especially large molecular weight PVC materials are more difficult to process (such materials usually need to add lubricants to improve the flow characteristics), so usually use small molecular weight PVC materials. The shrinkage of PVC is quite low, generally 0.2 to 0.6%.
Injection molding process conditions
Drying treatment: usually do not need to dry treatment.
Melting temperature: 185~205℃ Mold temperature: 20~50℃
Injection pressure: up to 1500bar Holding pressure: up to 1000bar Injection speed: to avoid material degradation, generally use a fairly high injection speed.
Runners and Gates: All conventional gates can be used. For smaller parts, it is best to use a pinpoint or dive-in gate; for thicker parts, it is best to use a fan gate. The minimum diameter of the pin-tip or submerged gate should be 1mm; the thickness of the fan gate should not be less than 1mm.
Typical use: PVC has the outstanding characteristics of abundant raw materials (petroleum, limestone, coke, salt and natural gas), mature manufacturing process, low price, wide range of uses, etc., and has now become the world's second largest general-purpose resin after polyethylene resin, accounting for 29% of the total consumption of synthetic resins in the world. It has become the second largest general-purpose resin in the world after polyethylene resin, accounting for 29% of the world's total consumption of synthetic resin. PVC is easy to process and can be processed by molding, laminating, injection molding, extruding, calendering, blow molding hollow and so on. PVC is mainly used in the production of artificial leather, film, wire sheathing and other plastic soft products, water supply pipes, household pipes, housing wall panels, commercial machine shells, electronic packaging, medical equipment, food packaging, speedboat fenders, but also the production of plates, doors, windows and valves and other plastic hard products.
PVC can be divided into soft PVC and hard PVC, of which hard PVC accounts for about 2/3 of the market, soft PVC accounts for 1/3. soft PVC is generally used for flooring, ceilings, and the surface layer of leather, but due to the soft PVC contains softeners (which is also the difference between soft and hard PVC), easy to become brittle, not easy to save, so its scope of use has been limited. Hard PVC does not contain softener, so it is flexible, easy to mold, not easy to brittle, non-toxic and non-polluting, long preservation time, so it has great development and application value. Below are referred to as PVC. soft PVC is mostly used to make vacuum blister film, used for all kinds of panels of the surface layer of the packaging, so it is also known as decorative film, adhesive film, used in building materials, packaging, medicine and many other industries. The building materials industry accounted for the largest proportion of 60%, followed by the packaging industry, there are a number of other small-scale application of the industry.
Simply put, an aqueous solution of salt undergoes chemical decomposition by the action of an electric current. This process produces chlorine, caustic soda and hydrogen. Refining and cracking oil or gasoline produces ethylene. When chlorine and ethylene are mixed, vinyl dichloride is produced; vinyl dichloride can be converted to produce chlorinated vinyl, which is the basic component of polyvinyl chloride. The polymerization process joins the chlorinated vinyl molecules together to form the PVC chain. Polyvinyl chloride produced in this way is in the form of a white powder. It cannot be used alone, but can be mixed with other components to produce many products.
Vinyl chloride was first synthesized in 1835 in the laboratory of Justus von Liebig. And polyvinyl chloride was synthesized by Baumann in 1872. But it wasn't until the 1920s that the first commercial product of PVC was produced in the United States, and it was only within the next 20 years that large-scale production began in Europe.
Polyvinyl chloride has the advantages of flame retardant (flame retardant value of more than 40), high chemical resistance (resistant to concentrated hydrochloric acid, concentration of 90% sulfuric acid, concentration of 60% of nitric acid and concentration of 20% of sodium hydroxide), mechanical strength and good electrical insulation. However, its heat resistance is poor, the softening point of 80 ℃, at 130 ℃ began to decompose and discoloration, and precipitation of HCI.
[Edit]
PVC features and molding characteristics
Specific gravity: 1.38 g / cm3, molding shrinkage: 0.6-1.5%, molding temperature: 160-190 ℃.
Characteristics: mechanical properties, excellent electrical properties, acid and alkali resistance, chemical stability, but the softening point is low. It is suitable for the production of sheet, wire and cable insulation, seals and so on.
Molding characteristics:
1. Amorphous material, small moisture absorption, poor fluidity. In order to improve the fluidity and prevent the occurrence of air bubbles, the plastic can be pre-dried. The mold casting system should be thick and short, the gate cross-section should be large, there should be no dead ends. The mold should be cooled and the surface should be chrome plated.
2. Because of its corrosive and fluidity characteristics, it is best to use special equipment and molds. All products should be added with different kinds and quantities of additives according to the needs.
3. Very easy to decompose, at a temperature of 200 degrees with steel. In contact with steel and copper at 200 degrees Celsius, it is easier to decompose, and corrosive and irritating gases will be released when it decomposes. Irritating gases. Small molding temperature range.
4. Screw injection machine nozzle, the aperture should be large, to prevent dead-end stagnant material. Good not to bring the inserts, if there are inserts should be preheated.
What is the pollution of PVC?
PVC Pollution Causes:
Some toxic additives and plasticizers in PVC, may leak or gasification; some additives will interfere with the biological endocrine (affecting reproductive function), some can increase the risk of cancer; incineration of PVC waste will produce carcinogenic dioxin and pollution of the atmosphere.
Conventional PVC materials, such as wires and cables, are a serious source of pollution. In the manufacture, use and disposal, will produce a large number of dioxin, chlorohydrochloric acid, lead and other harmful substances; PVC material combustion will occur when a lot of smoke, and produce harmful HCL gas; and most of the PVC material contains Pb (lead), Cd (cadmium), etc. (used as cable stabilizers) a variety of harmful heavy metals, which will cause some harm to human health; incineration or burial, will cause Pollution of soil and water.
Since most disposable medical devices are made of medical-grade polyvinyl chloride (PVC) or polycarbonate (PC), the thermal decomposition of PVC during processing has a strong corrosive effect on steel, and PC has high hardness and high viscosity, thus the material requirements for the parts of the plasticizing part must be corrosion-resistant, anti-abrasive, and have a high degree of polished performance. At present, most of the medical injection molding machine using barrel screw hard chrome plating method or stainless steel as the material to produce machine screw to achieve the above special requirements. In addition, in order to prevent the thermal decomposition of PVC processing gas, the requirements of the dynamic fixed template surface aluminizing treatment, but also on the periphery of the plate gold aluminizing treatment or stainless steel plate production of plate gold, plate gold seams using non-toxic silicone sealing, in order to prevent the plastic processing of gas to the outside (plastic processing of gas can be centralized through a special device and then after purification and treatment can be released into the atmosphere). (Gases generated during plastic processing can be collected centrally by special equipment and then purified before being discharged into the atmosphere).
Hazards of DEHP, a common additive to PVC: Because DEHP (di-phthalate) is easily atomized, other vinyl products, including automotive interiors, shower curtains, or floor coverings, can release toxic gases into the atmosphere, and DEHP is easily soluble in oily liquids. There are also emerging safety concerns about additives leaking out of these soft plastic toys if children chew on them. Some studies suggest that this additive may complicate health issues, but further research is needed. According to some medical studies, PVC plasticizers may cause chronic diseases such as scleroderma, cholangiocarcinoma, angiosarcoma, brain cancer, and acrosteolysis. 2004, a team of Swedish and Danish academics found that the phthalates DEHP and BBzP, commonly used in PVC, were associated with allergies in children. In 2004, a team of Swedish and Danish researchers found that the phthalates DEHP and BBzP, commonly used in PVC, were strongly associated with childhood allergies.
For unplasticized polyvinyl chloride (U-PVC), since it does not contain plasticizers, there is no DEHP leakage, but the process usually adds stabilizers, most of which are lead salt stabilizers, and lead is a toxic substance that can leach out during use, endangering human health, and should not be ignored. Currently there are non-lead salt stabilizers, but the cost is high, not yet popularized.
[Edit]
The development of China's PVC market
In recent years, China's polyvinyl chloride (PVC) development speed is amazing, new construction, expansion projects have been on the ground, rapid expansion of production capacity, production has increased dramatically. 1997-2006, China's PVC production capacity, production average annual growth rate of up to 22.2% and 20.0% respectively.
In 2006, the cumulative output of PVC resin was 8,238,583.86 tons; in 2007, the cumulative output of PVC resin reached 9,716,783.63 tons; in 2008, the cumulative output of PVC resin from January to May was 4,028,666.03 tons.
2008-2012, the global market demand for polyvinyl chloride (PVC) is expected to grow rapidly at an average annual rate of 4%, especially in some developing countries, the market demand will show rapid growth. China's demand for PVC resin will also maintain rapid growth, especially in building materials, in recent years is in a period of rapid growth. With the increasing pace of internationalization of the Chinese market, PVC resin packaging materials and pipes in the cement, fertilizers, food, food, beverages, pharmaceuticals, detergents, cosmetics and other fields will have a broad space for development, and its demand for a corresponding substantial increase; in addition, automobiles, communications, transportation field of PVC resin demand is also a high-speed growth in China's PVC resin industry is still a large space for development.