Solution to Traces on Surface of TPE Injection Molding Products
Time：2020-04-20Hits：2069
Many friends and friends who have touched the TPE injection molding and manufacturing industry have encountered such difficulties. The TPE secondary injection molding process adheres to the condition that the PP surface cloth has air marks and silver lines or the TPE fully transparent goods have air marks on the surface during processing. The main reason is that the main product channel of abrasive tools is quite large. The glue inlet method is deep dipping glue inlet, and the wear-resistant material flows to the periphery of the glue inlet. Because the speed is too fast and the surface layer of the abrasive tools is very smooth, the high shear is the rapid temperature rise of the wear-resistant material in an instant, which causes the TPE raw material to dissolve to form vapor and leave marks. How can we solve this problem?
Injection molding cladding forming is a unique cladding forming. To put it bluntly, cladding forming can be soft plastic cladding hard plastic or soft plastic cladding soft plastic.
First, there are two key ways to keep the package forming:
1. One is secondary injection molding or two-color injection molding, which is maintained on the two-color injection molding machine. A raw material is injected into a commodity, and then the commodity is transferred to a female die matched with another injection cylinder in a two-color machine according to a rotating grinding tool. The part is used as an insert, and another raw material is introduced into the insert to produce an integrated dual-material commodity. The plastic machine is a two-cylinder and dual-mode cavity, and the whole process of injection molding is the production and manufacture of the two raw materials separately. Only the handicraft of one female die will be used as an insert to enter the next female die.
2. The other is two-step injection molding, in which a part of one of the raw materials is molded on an injection machine. Put the parts into another grinding tool as mold guide posts, and then inject the second raw material. The way to keep cladding (including cladding) can be physical locking and organic chemistry. For example, in the former one, with the aid of buckle design scheme, surface roller and external thread of surface tapping, the second layer of raw material is applied to keep the coating (glue). The characteristic of using this method to carry out linear fitting of raw materials is that part of physical connection has strong adhesion, while part of physical connection has small adhesion.
Organic chemistry is based on the molecular structural infectivity and ionic bond binding between the two raw materials. These two kinds of raw materials fuse together to produce a single component, two kinds or even many kinds.
Although the physical loop and the organic chemical bonding method are often applied together in specific applications, it is obvious that the organic chemical fusion between the two raw materials is a more reliable and design-preferred method with greater playability. Such strong ionic bonds include transmission, dissolution, entanglement and transmission of molecular structure or molecular structure chain.
Second, in order to maintain the segment bonding of TPE hard plastic molecular structure, the key is to do a good job in the following three levels of work:
1. The optical activity of TPE raw materials is similar to that of hard plastics (otherwise they cannot be melted, infiltrated and infiltrated in the molten state).
2. The interfacial tension of TPE raw material is lower than that of hard plastic (otherwise TPE solution cannot diffuse outside the surface layer of hard plastic insert); At the interface tension level, mercury is felt to gather into a ball on the surface layer of laminated glass, while water droplets diffuse outside the surface layer of laminated glass.
3. When the thermoplastic polyurethane elastomer solution flows along the hard plastic deformation surface layer in the mold core, the heating value is released in the whole refrigeration process, so that the hard plastic deformation surface layer is quickly and reasonably melted, and a layer of chromatography which can penetrate into each other is generated.
4. The first reason why the plastic wrap cannot be covered is the poor sealing of TPE raw materials. Therefore, the reason why the plastic wrap cannot be deeply covered must be analyzed from the perspective of injection molding.
Third, second, from a technical point of view, you should refer to the following:
1. In order to prevent moisture absorption or dirt on the hard plastic surface layer, this is more likely to occur in the whole process of two-step injection molding, termination and transfer of hard plastic. Optically hard plastics such as PC, PBT, PET, POM are very optically hard plastics such as PA6, PA66. Surface moisture absorption results in the generation and absorption of hydrogen bonds between water molecules. Thermosetting plastic polyurethane elastomer cannot reasonably bond with hard plastic deformation surface molecular structure to produce molecular structure, of course, the guaranteed bonds are reduced together.
2. The actual effect of two-color injection molding is better than two-step injection molding.
Reason: To put it succinctly, the first step of hard plastic injection is hot. Immediately enter the second chamber of 2K plastic machine. During the whole process of positive intermediate migration, water is not digested and absorbed. The high-temperature thermosetting plastic polyurethane elastomer solution is very easy to corrode in the surface cracks, and the surface layer does not have the effect of water vapor absorption.
3. In the second step of plastic wrapping, try to use hard plastic as the core of the insert and choose a higher grinding tool temperature. When the temperature of the hard plastic is higher, the TPE solution cools slowly at high temperature, with sufficient heat generation and sufficient time for crevice corrosion of the hard plastic, resulting in soluble ultra-chromatography.
4. In the second step of plastic wrapping, TPE solution is poured out as far as possible without TPE burrs.
5. Within the allowable scope of production and processing of thermosetting plastic polyurethane elastomer raw materials, choose a higher barrel (dissolved body) temperature as much as possible, otherwise thermosetting plastic polyurethane elastomer is very easy to have sufficient heat generation to crack and corrode hard plastic surface layer.
6. Pay attention to the difficult problem of washing cylinder in the early stage of debugging.
Four, TPE two-color injection molding surface liquidity label solution
1, spewing rate. Reducing the gushing rate depends on the actual effect, which can reduce the craze caused by air pressure.
2. Circulation of chemical substances. When the circulation of raw materials is insufficient, this kind of situation is very easy to occur, which can be handled according to the secret recipe of TPE raw materials (such as the content of board, the uniformity of mixing and the ductility level of raw materials).
3. Surface specifications of plastic-covered goods. You can slightly adjust the surface layer, then try it and adjust the plastic coated abrasive tool again.
4:, When TPE raw materials are dry, the coating is generally a thin commodity. Injection rate is faster, sometimes the plastic bag covers a large area. If there is water in the raw materials, the surface of the commodity will crack under high temperature and high speed.
Sprayed liquid from metal surface treatment of TPE raw material: according to spraying a layer of TPE modifier between TPE raw material and paint, the adhesive force between the plate and the building paint layer is improved, and the spraying problem is solved.
5. Injection temperature. You can try to raise the temperature a little. The injection temperature is proposed to be 180-220 degrees and the grinding tool temperature is proposed to be 40-55 degrees.
The above content is a detailed introduction to the processing technology of TPE plastic-covered injection molding process and the solution to the surface mark. In case of any abnormality found during the injection molding process of TPE and TPR materials, timely seek help from skilled TPE manufacturers. Dechuang Chemical Co., Ltd. will provide you with the most comprehensive TPE technical services or solutions for the application of raw materials free of charge. The masses are warmly welcomed to call for information.
德创化工 (edit：dechuang)
