Knowledge about LCP injection molding

The knowledge related to LCP injection molding is as follows.
1. Processing of LCP material (liquid crystal polymer)
Key point. LCP material should be dried before use. The temperature is about 150℃ and the time is about 4~6 hours. The residual moisture content of the dehumidified LCP should be less than 0.02% and the dew point should be kept at -35℃.
Note: It is recommended to use a vacuum dehumidifier dryer for drying. Do not use a general dryer. Because the vacuum dehumidification dryer can extract the moisture from LCP material, the general dryer can not completely extract the moisture from the material, and it is difficult to achieve the quality requirement of the product.
2. Injection molding process of LCP material
The following issues should be noted when forming.
1 Proportional back pressure makes the feeding more accurate and stable.
2 Large back pressure can be used for large products and small back pressure for small products.
3 Large products will have less density and poor surface gloss if the back pressure is small.
4 High sensitivity injection system and automatic VP (V injection pressure, P holding pressure) conversion function make the product precise and stable. If necessary (if the product is very precise), it is recommended to install a pressure sensor at the cavity door. Make VP switching closer to reality.
6 The holding time of beer flat products should not be too long, otherwise it will easily cause warping of the products and generate stress.
7 The LCP material stays in the material tube too long or the residual amount is too large, which makes the LCP material overfire and bubbles will appear on the product surface. In general, open the mold within 3 seconds after the material melting is finished, and the residual amount is guaranteed to be within 5mm.
8 If the machine is opened again, the scrap must be injected.
9 The molding cycle depends on the size, shape, thickness, mold structure and molding conditions of the product. the LCP material has good fluidity, so the filling time is relatively short and the crystal molding speed is fast, so the molding cycle is relatively short.
3. Selection of injection molding machine for LCP material
Special injection molding machine for LCP material must be selected.
The screw needs to be made of material with better wear resistance.
The screw head should have a structure that prevents backflow.
More accurate temperature control system is required.
The nozzle part needs to be specially designed.
The feeding and injection system should be sensitive.
The capacity of the injection tube should pay attention to the weight of the product and should not be too big or too small.
4. Process focus of special molds for LCP material
1 The mold design for LCP products is very important. The glue inlet of the mold should use a normal opening rather than a hot nozzle. If hot nozzle is used the product is easy to foam and the temperature is too high and the product may overheat.
2 General mold temperature is about 140 ℃, the upper (before) mold temperature should be higher than the lower (after) mold, because the upper (before) mold temperature is high, the melting nature of the melt is not easy to cause cold glue, while the lower (after) mold temperature is low. The product is easy to crystallize, the upper (before) lower (after) mold temperature difference is not more than 15 ℃.
3 In the choice of mold temperature, in order to shorten the molding cycle and prevent shrinkage, a lower mold temperature should be chosen; if there are high requirements for the dimensional stability of the product, the occurrence of seams and underfilling, then a higher Mold temperature.
5. Pressure and speed
The most suitable pressure must depend on the material, the shape of the product, the mold design (especially the gates, runners, sprue) and other molding conditions. However, LCP is not graded and its melt viscosity is very low, so the pressure is lower than that of ordinary thermoplastic resins.
Using low pressure at the beginning of molding and then slowly increasing the pressure is a good way to go. The finished product can be molded at pressures ranging from 15 MPa to 45 MPa. In addition, the curing time of LCP is relatively fast, so it is easy to get good results when the speed is fast.
6. Molding cycle time
The molding cycle depends on the size, shape, thickness, mold structure and molding conditions of the molded product. As mentioned above, LCP has good flowability, so its filling time is short and curing speed is fast, so we can get a short molding cycle. A representative molding cycle is 10 seconds to 30 seconds.