Summary of PVC models and applications

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Summary of PVC models and applications. PVC (Polyvinyl Chloride) – Injection molding process conditions: Drying treatment: Generally, no drying treatment is required. Melting temperature: 185–205°C. Molding temperature: 20–50°C. Injection pressure: can reach up to 1500 bar. Holding pressure: can reach up to 1000 bar. Injection speed: A suitable injection speed should be used to avoid material degradation. Flow channels and gates: All conventional gates can be used. When machining smaller parts, it is best to use a needle-point gate or a submersion gate ； For thicker parts, it is best to use a fan gate. The minimum diameter of a needle-point gate or submersion gate should be 1 mm ； The thickness of the fan-shaped gate must not be less than 1 mm. Chemical and physical properties Rigid PVC is one of the most widely used plastic materials. PVC material is an amorphous material. In actual use, stabilizers, lubricants, processing aids, colorants, impact modifiers, and other additives are frequently added to PVC materials. PVC material features non-flammability, high strength, resistance to weathering, and excellent geometric stability. PVC has strong resistance to oxidizers, reducers, and strong acids. However, it can be corroded by strong oxidizing acids such as concentrated sulfuric acid and concentrated nitric acid, and it is not suitable for use in situations involving contact with aromatic hydrocarbons or chlorinated hydrocarbons. The melting temperature of PVC during processing is a very important process parameter; if this parameter is not properly set, it can lead to material decomposition. PVC has quite poor flow properties, and its process window is very narrow. In particular, PVC materials with high molecular weights are more difficult to process (lubricants are usually added to such materials to improve their flow properties); therefore, PVC materials with low molecular weights are generally used. The shrinkage rate of PVC is quite low, generally ranging from 0.2 to 0.6%. PVC tends to release toxic gases during the molding process. Its typical applications include water supply pipes, household plumbing pipes, wall panels for buildings, casings for commercial machinery, packaging for electronic products, medical devices, and food packaging, among others. PVC stands for polyvinyl chloride, and genuine polyvinyl chloride is non-toxic. Chloroethylene is the toxic component; polymers all have an issue related to their degree of polymerization. When the degree of polymerization is high enough and the content of chloroethylene drops to a certain level, the result is non-toxic PVC! PVC is non-toxic; it becomes toxic only when various toxic additives such as heat stabilizers and plasticizers are added! Some PVCs experience a significant shrinkage of up to 2%! Over time, PVC material tends to change color. PVC is sensitive to light, oxygen, and heat; it degrades easily, leading to changes in the color of PVC products. The sequence of color changes is as follows: white --> pink --> light ** --> brown --> reddish-brown --> blackish-red --> black. After being processed into finished products, PVC emits a very unpleasant odor. Indeed, the smell of PVC that I’ve encountered is always unpleasant, and it tends to attract dust due to its static electricity properties. PVC is also extremely widely used in wires, cables, plugs, and various transparent packaging products! PVC (polyvinyl chloride) has the structure -(CH2-CH2)-|CH3. Generally, PVC with less than 15% plasticizer content is considered hard PVC, while that with more than 15% plasticizer content is classified as soft PVC. The PVC used in toys is usually soft PVC. At temperatures of 35–90 degrees Celsius, the main properties of PVC are as follows: a) It is an amorphous plastic, transparent, and easy to color; b) The amount of plasticizer in the material determines its hardness (usually between 55–90 degrees Celsius) as well as its mechanical properties. Key points regarding the injection molding process: a) The raw materials must be dry, as vinyl chloride molecules are prone to absorbing moisture. The drying temperature should be around 85°C, with a drying time of at least 2 hours; b) The molding temperature is close to the decomposition temperature, so it’s necessary to use the lowest possible temperature for injection. Additionally, the molding cycle should be shortened as much as possible to reduce the time the molten material stays in the barrel. Temperature parameters: 160–170°C at the beginning, 160–165°C in the middle, and 140–150°C at the end. Due to PVC’s poor heat resistance, prolonged heating in the barrel can cause hydrogen chloride (HCl) to be released, leading to yellowing or even black spots on the molded parts. Hydrogen chloride also corrodes the mold cavities, so it’s important to clean these areas regularly. c) PVC has poor flow properties, so the gates and runners in the injection mold should be as wide, short, and thick as possible. The wall thickness of the molded parts should be at least 1.5 mm to minimize pressure losses and allow the molten material to fill the cavity quickly. In general, high pressure and low temperature are preferred (injection pressure above 200 Mpa, back pressure of 0.5–1.5 Mpa, and holding pressure at 20–30% of the injection pressure). d) The mold temperature should be kept as low as possible (usually using chilled water to maintain a temperature of 30–45°C) to shorten the molding cycle and reduce deformation after the parts are removed from the mold. If necessary, shaping molds or shrinkage molds can be used to correct any deformations. e) The sprue material: Well-cleaned sprue material can be reused 100%. f) Shutting down the machine: Turn off the power before starting production, and use PE to clean the machine after shutdown. PVC is used in records, bottles, synthetic leather, flooring materials, thin sheets, plastic films, heat-shrinkable sleeves, shoes, wires, water supply and drainage pipes (UPVC), and adhesives. Blended modified plastics: a) PVC + EVA → increases impact strength (provides long-lasting plasticization); b) PVC + ABS → improves toughness and increases impact strength. This post was last edited by wivern on 2008-7-6 at 19:51