The article covers a specific introduction to transparent plastic injection molding process and transparent plastic raw materials characteristics.
There are various of transparent materials on the market including Polycarbonate, Polyethylene Terephthalate, Polymethyl Methacrylate, Transparent Nylon, Acrylonitrile-styrene Copolymer and Polysulfone, etc., of which PMMA, PC and PET are the 3 most commonly used materials. Today, we will discuss the characteristics and the injection molding process of transparent plastics based on the 3 transparent plastic materials.
● Due to the high light transmittance of transparent plastics, it is necessary to strictly require the surface quality of plastic products, without any defects such as streaks, blowholes, whitening, haze, black spots, discoloration and poor gloss. Therefore, in the whole injection molding process, we should pay attention to and put forward strict and even special requirements for the design of raw materials, equipment, molds and even products.
● Secondly, due to the high melting point and poor fluidity of transparent plastics, in order to ensure the surface quality of products, the process parameters such as higher temperature, injection pressure and injection speed should be adjusted slightly, so that the injection molding can not only fill the mold, but also produce no internal stress, which will cause deformation and cracking of the product.
● Due to the high melting point and poor fluidity of transparent plastics, in order to ensure the surface quality of products, the process parameters such as higher temperature, injection pressure and injection speed should be adjusted slightly, so that the injection molding can not only fill the mold, but also produce no internal stress to cause deformation and cracking of the product.
Before or after using a machine, we should clean every part with PE, PS and other washing agents, makes it clean. When the temporary shutdown, to prevent the material at high temperatures to stay a long time, causing solution drop, and barrel dryer should lower the temperature, such as PC, PMMA, PS other barrel temperature should be reduced to below 160 ℃.
1.The injection temperature should be higher than the injection humidity on the premise that the plastic resin does not decompose.
2.Injection pressure: Generally, we use high injection pressure, to overcome the shortcomings of high melt viscosity. but high pressure may cause internal stress, it makes stripping and deformation difficultly.
3.Injection speed: i should be low under the condition of mold filling, and it is better to adopt slow fast slow multistage injection.
4.Holding time and molding cycle: It should be as short as possible to minimize the residence time of molten materials in the barrel under the condition that the product filling is satisfied and no depression and bubbles are generated.
5.Screw speed and back pressure: On the premise of meeting the plasticizing quality, it should be as low as possible to prevent the possibility of falling off.
6.Mold temperature: The cooling quality of the products has a great impact on the quality of the product, so the mold temperature must be able to accurately control the process. If possible, higher mold temperature should be good.
7.In order to prevent the deterioration of the upper surface quality, the release agent should be used as little as possible during injection molding; when the recycled material is used, it should not be more than 20%.
1. PMMA has high viscosity and poor fluidity, so it is necessary to inject at high material temperature and high injection pressure. The influence of injection temperature is greater than that of injection pressure, but the increase of injection pressure is conducive to improving the shrinkage of products.
2. PC has high viscosity, high melting temperature and poor fluidity, so it must be injected at a higher temperature (270-320t). Relatively speaking, the range of material temperature adjustment is relatively narrow, and the processability is not as good as that of PMMA. The injection pressure has little effect on the fluidity, but the injection pressure should be increased due to the high viscosity. Accordingly, the holding time should be as short as possible in order to prevent the internal stress.
3.Pet molding temperature is high, and the range of material temperature adjustment is narrow (260-300 ℃), but after melting, the fluidity is good, so the processability is poor, and the anti flow device is often added in the nozzle. The mechanical strength and properties are not high after injection, so it is necessary to improve the properties through stretching process and modification. Mold temperature accurate control, is to prevent warpage. Therefore, hot runner mold is recommended. Mold temperature is high, otherwise it will cause poor surface gloss and demoulding difficulty.
Check the performance of transparent plastic materials
1.Bubble: Because the water vapor and other gases in the resin can not be discharged, or due to insufficient mold filling, the condensation surface condenses too fast and forms a “vacuum bubble”.
2. Poor surface gloss: Mainly due to the large roughness of the mold, on the other hand, premature condensation, so that the resin can not copy the mold surface state, all of these make its surface produce small uneven, and make the product lose luster.
4. Chatter mark: It refers to the dense ripple formed from the center of the gate. Because of the excessive viscosity of the melt, the front-end material has condensed in the mold cavity, and then the material breaks through the condensation surface, resulting in the appearance of chatter marks on the surface.
5. Whitening, fog halo: Mainly caused by dust falling into the raw material in the air or the moisture content of raw material is too large.
6. Black spots: Mainly due to the plastic in the barrel, due to local overheating and barrel resin decomposition or deterioration.