Introduction of LCP engineering materials and injection molding process
LCP is the abbreviation of Liquid Crystal Polymer in English. It is called liquid crystal polymer in China. It is a new type of polymer material. It will generally become a liquid crystal form under certain heating conditions. Therefore, it is named after its characteristics. Decided LCP
The use of plastic raw materials
LCP is the abbreviation of Liquid Crystal Polymer in English. It is called liquid crystal polymer in China. It is a new type of polymer material. It will generally become a liquid crystal form under certain heating conditions. Therefore, it is named after its characteristics. Determined the usefulness of LCP plastic materials.
LCP plastic raw material full name LIQUID CRYSTAL POLYMER, Chinese name liquid crystal polymer. It is a new type of polymer material that generally exhibits liquid crystallinity in the molten state. These materials have excellent heat resistance and molding processability. The polymerization method is mainly composed of melt polycondensation, and the wholly aromatic LCP is assisted by solid phase polycondensation to obtain a high molecular weight product. Non-aromatic LCP plastic materials are often prepared by one-step or two-step melt polymerization. In recent years, continuous melt polycondensation has been developed to produce high molecular weight LCP. Liquid crystal aromatic polyester is oriented in the liquid crystal state due to its macromolecular chain. It has a heterogeneous fiber structure, special properties, and high product strength, which is no less than metal and ceramic. Tensile strength and flexural modulus can be developed over a variety of thermoplastic engineering plastics over the past 10 years. Mechanical properties, dimensional stability, optical properties, electrical properties, chemical resistance, flame retardancy, processability, heat resistance, and low coefficient of thermal expansion. The properties, processability and price of the obtained liquid crystal polyester are different depending on the monomers used. The choice of fillers and the amount of filler added also affect its performance.
1. High liquidity
2, good dimensional stability
3, good solvent resistance
4, high mechanical strength
5, good flame retardancy
1, quick connector, coil, switch, socket
2, pump parts, valve parts
3. Automotive fuel peripheral parts
4, electronic furnace container
A: Liquid crystal can be further classified into a lyotropic liquid crystal polymer and a thermotropic liquid crystal polymer. The former is in a liquid crystal state in a solvent, and the latter is in a liquid crystal state due to a change in temperature.
B: The main chain of the liquid crystal polymer molecule is rigid, the molecules are tightly packed, and are highly oriented during the molding process, so that the linear expansion coefficient is small, the molding shrinkage rate is low, and the strength and elastic modulus are excellent and excellent. The heat resistance has a high load deformation temperature, and some can be as high as 340 ° C or more.
C: LCP has good weather resistance and radiation resistance, has excellent flame retardancy, and can extinguish the flame without continuing to burn. Its combustion level reaches the UL94V-0 level. LCP plastic materials are one of the best special plastics for fire safety.
D: The general thermotropic liquid crystal polymer has a good fluidity and is easy to process. The molded product has a sheath-core structure peculiar to a liquid crystal polymer, and the resin itself has a fiber property and has a high orientation in a molten state, so that it can exert a fiber-reinforced effect. This is also the most striking feature of liquid crystal polymers.
E: Thermotropic liquid crystal polymer can also be made into polymer blending materials with various plastics. The liquid crystal polymer in these blending materials can enhance the strength, rigidity and heat resistance of the material. .
F: The density of LCP plastic raw materials is 1.4~1.7g/cm3. The liquid crystal polymer has high strength, high modulus mechanical properties, and self-reinforcing property due to its structural characteristics, so that the unreinforced liquid crystal plastic can reach or exceed the mechanical engineering of tens of glass fiber reinforced with ordinary engineering plastics. The level of strength and modulus; if enhanced with glass fiber, carbon fiber, etc., far more than other engineering plastics.
G: LCP liquid crystal polymer also has excellent thermal stability, heat resistance and chemical resistance. For the creep defects of most plastics, the liquid crystal material is negligible, and the wear resistance and wear resistance are excellent.
H: LCP plastic raw materials have excellent electrical insulation properties. Its dielectric strength is higher than that of general engineering plastics, and its arc resistance is good. As an electrical application part, its electrical properties are not affected when the continuous use temperature is 200~300 °C. The intermittent use temperature can reach about 316 °C.
I: LCP plastic materials have outstanding corrosion resistance. LCP products will not be corroded in the presence of 90% acid and 50% alkali. For industrial solvents, fuel oil, detergents and hot water, after contact Will not be dissolved, and will not cause stress cracking.
Injection molding process
The molding temperature of LCP is high, and the melting temperature is in the range of 300 to 425 ° C due to its variety. LCP has low melt viscosity and good fluidity, similar to olefin plastics. LCP has a very small coefficient of linear expansion and good dimensional stability. The molding processing conditions are as follows: molding temperature 300~390°C; mold temperature 100~260°C; molding pressure 7~100MPa, compression ratio 2.5~4, molding shrinkage 0.1~0.6.
Generally, the barrel temperature, nozzle temperature, and material melting temperature are shown in the table.
If the life of the screw is taken into account, the temperature difference between the rear part, the middle part and the front part can be reduced. In order to prevent the nozzle from flowing, the nozzle temperature can be 10 ° C lower than the temperature shown in the table. If the fluidity is to be increased, the temperature can be set to 20 ° C higher than the temperature shown in the table, but the following must be noted.
When the temperature of the cylinder is lowered: the residence time is too long, the pellets will not be aged in the cylinder, and corrosive gas will not be generated, so the long residence time generally does not cause any major problems. However, if the molding is interrupted for a long time, lower the temperature of the barrel. When molding again, it is better to throw away the mold.
Barrel temperature (°C) for each grade
2. Mold temperature
The mold temperature of LCP plastic material can be molded between 30 °C and 150 °C. However, we generally set the mold temperature to around 70 °C - 110 °C. In order to shorten the molding cycle, prevent flash and deformation, choose a low mold temperature; if the product size is required to be stable (especially for products under high temperature conditions), reduce the occurrence of weld seams and solve the problem of insufficient filling, etc. Choose a high mold temperature.
The speed of the screw is typically 100 rpm. In the case of glass-containing or carbon-containing glass (eg A130, A230, etc.), in order to prevent the glass fiber from being broken, we must choose a lower speed. In addition, the back pressure is as low as possible. When the barrel temperature is set to 300 ° C, the residence time of the material in the barrel has an effect on the mechanical properties and color of the plastic.
Injection pressure speed
The most suitable injection pressure must depend on the material, the shape of the product, the mold design (especially the sprue, runner, gate) and other molding conditions. However, LCP has no grade and its melt viscosity is very low, so the injection pressure is lower than that of ordinary thermoplastic resins. It is a good method to use low pressure at the beginning of the molding and then slowly increase the pressure. The molded article can be molded under the injection pressure of 15 MPa to 45 MPa. In addition, the curing time of the LCP is relatively fast, so a fast injection speed is easy to obtain good results.
The molding cycle depends on the size, shape, thickness, mold structure and molding conditions of the molded article. As mentioned above, LCP has good fluidity, so its filling time is short and the curing speed is faster, so we can get a shorter molding cycle. A representative molding cycle is from 10 seconds to 30 seconds.
Main use of LCP
1) LCP plastic materials are excellent in high strength, high rigidity, high temperature resistance, electrical insulation, etc., and are used in electronics, electrical, optical fiber, automotive and aerospace.
2) Fiber made of liquid crystal can be used as a fish net, sporting goods, brake pads, optical fiber display materials, etc., and can also be made into a film for soft printed circuits, food packaging, and the like.
3) LCP plastic materials have been used in microwave ovens to withstand high and low temperatures. LCP can also be used for printed circuit boards, satellite electronic components, jet engine parts; for electrical and electronic machinery parts or components; and for medical applications. 4) LCP plastic raw materials can be added with high filler as integrated circuit packaging material, instead of epoxy resin as the encapsulation material of coil bobbin; for fiber optic cable joint sheath and high strength components; instead of ceramic as filling material in chemical separation tower Wait. 5) LCP plastic raw materials can also be blended with polysulfone, PBT, polyamide and other plastics to form alloys. After molding, the mechanical strength is high, which can replace plastics such as glass fiber reinforced polysulfone, which can improve mechanical strength. It can also increase the strength of use and chemical stability. The LCP is currently being studied for panels external to the spacecraft, brake systems for exterior vehicles and so on,
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