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The general process of plastic injection molding
1. PS (polystyrene)
Performance of 1.PS
PS is an amorphous polymer with good fluidity and low water absorption (less than 0.2%). It is a transparent plastic which is easy to be processed. Its product has a transmittance of 88-92%, strong coloring power and high hardness. However, PS products are brittle, easy to produce internal stress cracking, poor heat resistance (60-80 C), non-toxic, specific gravity of about 1.04 g/cm 3 (slightly greater than water).
Forming shrinkage (usually 0.004-0.007), the name transparent PS only indicates the transparency of the resin, not the crystallinity. (chemical and physical properties: most commercial PS are transparent, amorphous materials. PS has very good geometric stability, thermal stability, optical transmission characteristics, electrical insulation characteristics and very small moisture absorption tendency. It is resistant to water and diluted inorganic acids, but can be corroded by strong oxidizing acids such as concentrated sulfuric acid, and can expand and deform in some organic solvents. )
Technological characteristics of 2.PS
PS melting point is 166, processing temperature is generally 185-215, melting temperature is 180-280, for flame retardant materials upper limit is 250, decomposition temperature is about 290, so the processing temperature range is wide.
Mold temperature 40 ~ 50 C, injection pressure: 200 ~ 600bar, injection speed is recommended to use a rapid injection rate, runner and gate can use all conventional types of gate. PS material is usually not dry unless it is stored properly. If it is dry, the recommended drying conditions are 80C and 2~3 hours.
Because of the low specific heat of PS, some of its molds can be quickly condensed and solidified by heat dissipation. Its cooling rate is faster than that of ordinary raw materials, and the mold opening time can be earlier. Its plasticizing time and cooling time are shorter, molding cycle time will be reduced; PS products gloss with the mold temperature increases.
3. typical application area
Packaging products (containers, caps, bottles), disposable medical supplies, toys, cups, knives, tape shafts, windbreaks and many foaming products - egg boxes. Meat and poultry packaging trays, bottle labels and foamed PS cushioning materials, product packaging, household goods (tableware, trays, etc.), electrical (transparent containers, light scatterers, insulation film, etc.).
Two, HIPS (modified polystyrene)
The performance of 1.HIPS:
HIPS is a modified PS material, which contains 5-15% rubber. Its toughness is about four times higher than PS, and its impact strength is greatly improved (high impact polystyrene). There are flame retardant grade, stress cracking resistance grade, high gloss grade, high impact strength grade, glass fiber reinforced grade and low residual volatile grade.
Other important properties of standard HIPS: bending strength 13.8-55.1 MPa; tensile strength 13.8-41.4 MPa; elongation at break 15-75%; density 1.035-1.04 g/ml; PS has the advantages of molding and strong coloring force. HIPS products are opaque. HIPS has low water absorbency and does not require pre drying when processing.
Technological characteristics of 2.HIPS
HIPS contains 5-15% rubber, which affects its fluidity to a certain extent. The injection pressure and molding temperature should be higher. Its cooling speed is slower than that of PS, so sufficient pressure, holding time and cooling inlet are needed. The forming cycle will be slightly longer than that of PS, and its processing temperature is generally 190-240 degrees.
HIPS resin absorbs water slowly, so in general, it does not need drying. Sometimes too much moisture on the surface of the material will be absorbed, which will affect the appearance quality of the final product. Drying 2-3H at 160 degrees F can remove excess moisture. There is a special "white edge" problem in HIPS parts, which can be improved by increasing mold temperature and clamping force, reducing packing pressure and time, and so on.
3. typical application area
The main application areas are packaging and disposable goods, instrumentation, household appliances, toys and entertainment products and construction industry. Flame retardant (ULV-0 and UL5-V), impact resistant polystyrene has been produced and widely used in television housing, commercial machinery and electrical products.
Three, SA (SAN-- styrene acrylonitrile copolymer / energized glue)
Performance of 1.SA
Chemical and physical properties: SA is a hard and transparent material that does not cause internal stress cracking. The transparency is very high, and its softening temperature and impact strength are higher than PS. Styrene makes SA hard, transparent and easy to process; acrylonitrile makes SA chemical and thermal stable. SA has strong load-bearing capacity, chemical reaction resistance, thermal deformation resistance and geometric stability.
Adding glass fiber additives in SA can increase the strength and thermal deformation resistance and reduce the thermal expansion coefficient. The softening temperature of VEKA SA is about 110 C. The deflection temperature under load is about 100C, and the shrinkage rate of SA is about 0.3~0.7%.
Five, BS (K material)
Performance of 1.BS
BS is a butadiene-styrene copolymer, it has a certain degree of toughness and elasticity, low hardness (soft), good transparency. The specific gravity of BS is 1.01f\cm3 (similar to water). The material is easy to stain, fluidity and easy to form.
Technological characteristics of 2.BS
The processing temperature range of BS is generally at 190-225 C, and the mold temperature is better at 30-50 C. The material should be dried before processing. Because of its good fluidity, the injection pressure and injection speed can be lower.
Six, PMMA (Asia plus)
Performance of 1.PMMA
PMMA is amorphous polymer, commonly known as plexiglass. The product has excellent transparency, good heat resistance (hot deformation temperature is 98 C), good impact resistance, medium mechanical strength, low surface hardness, easy to be scratched by hard objects and leave traces, compared with PS, not easy to brittle crack, specific gravity is 1.18g/cm 3.
PMMA has excellent optical properties and weather resistance. The penetration of white light is as high as 92%. PMMA products have very low birefringence and are especially suitable for making DVDs. PMMA has room temperature creep properties. As load increases and time increases, stress cracking can occur.
Technological characteristics of 2.PMMA
PMMA is very sensitive to moisture and temperature. It should be fully dried before processing (recommended drying conditions are 90, 2 ~ 4 hours), and its melt viscosity is relatively high. It needs to be molded under higher (225-245) and pressure. The mold temperature is better at 65-80.
The stability of PMMA is not very good. Degradation will be caused by high temperature or longer residence time. Screw speed should not be too large (about 60%). The thick PMMA parts are prone to appear "holes" and need to be processed by large gate, "low material temperature, high mold temperature, slow" injection method.
3. typical application area
Automotive industry (signal lamp equipment, dashboard, etc.), pharmaceutical industry (blood container, etc.), industrial applications (DVD, light scatterer), consumer goods (beverage cups, stationery, etc.).
Technological characteristics of 2.SA
The processing temperature of SA is generally at 200-250 C. The material is easy to absorb moisture and needs to be dried for more than an hour before processing. Its fluidity is slightly worse than PS, so the injection pressure is slightly higher (injection pressure: 350 ~ 1300bar). The injection speed is recommended to use high-speed injection. The mold temperature control is better at 45-75 degrees centigrade. Drying: if the storage is not proper, SA has some hygroscopic properties.
The recommended drying conditions are 80 C and 2~4 hours. The melting temperature is 200~270 C. If thick wall products are processed, the melting temperature below the lower limit can be used. For reinforced materials, the mold temperature should not exceed 60 degrees. The cooling system must be well designed because the mold temperature will directly affect the appearance, shrinkage and bending of the product. Runner and gate: all conventional gates can be used. The gate must be properly sized to avoid striations, spots and gaps.
3. typical application area
Electrical (sockets, shells, etc.), daily commodities (kitchen appliances, refrigerators, TV base, cassette boxes, etc.), automotive industry (headlight boxes, reflective conditions, dashboards, etc.), household goods (tableware, food knives, etc.), cosmetic packaging safety glass, water filter shell and faucet twisting.
Medical products (syringe, blood suction tube, renal percolation device and reactor). Packaging materials (cosmetic box, lipstick sleeve, Mascara cap bottle, cover, cap sprayer and nozzle, etc.), special products (disposable lighter shell, brush base material and hard wool, fishing gear, denture, toothbrush handle, penholder, instrument nozzle and directional monofilament).
Four, ABS (super unbroken glue)
Performance of 1.ABS
ABS is synthesized from three chemical monomers of acrylonitrile, butadiene and styrene. (Each monomer has different characteristics: acrylonitrile has high strength, thermal stability and chemical stability; butadiene has toughness and impact resistance; styrene has easy processing, high finish and high strength. The polymerization of the three monomers produces a terpolymer with two phases, one is the continuous phase of styrene-acrylonitrile and the other is the dispersion phase of polybutadiene rubber. )
From the morphological point of view, ABS is a non-crystalline material with high mechanical strength and good comprehensive properties of "toughness, toughness and steel". It is an amorphous polymer, ABS is a versatile engineering plastics, its variety, wide range of uses, also known as "general plastics" (MBS called transparent ABS), ABS easy to absorb moisture, specific gravity of 1.05g/cm 3 (slightly heavier than water), low shrinkage (0.60%), size stability, easy to molding.
The properties of ABS depend mainly on the ratio of three monomers and the molecular structure in the two phases. This allows for great flexibility in product design, resulting in hundreds of different quality ABS materials on the market. These materials of different qualities provide different properties, such as medium to high impact resistance, low to high finish and high temperature distortion. ABS material has super machinability, appearance characteristics, low creep, excellent dimensional stability and high impact strength.
ABS is light yellow granular or bead opaque resin, non-toxic, tasteless, low water absorption, has good comprehensive physical and mechanical properties, such as excellent electrical properties, wear resistance, dimensional stability, chemical resistance and surface gloss, and easy to process and molding. The disadvantages are weatherability, poor heat resistance and flammability.
Technological characteristics of 2.ABS
(1) ABS has high hygroscopicity and humidity sensitivity. It must be fully dried and preheated before molding (drying for at least 2 hours at 80-90C), and the moisture content should be controlled below 0.03%.
(2) the melt viscosity of ABS resin is less sensitive to temperature (unlike other amorphous resins).
Although the injection temperature of ABS is slightly higher than that of PS, it can not have a wide range of temperature rise as PS does, and can not be blindly heated to reduce its viscosity. It can be used to increase the screw speed or injection pressure to improve its fluidity. The general processing temperature is 190-235 degrees.
(3) The melt viscosity of ABS is moderate, higher than PS, HIPS and AS, and higher injection pressure (500-1000 bar) beer is needed.
(4) ABS material is better at medium speed and higher injection speed. (Unless the shape is complex and the thin-walled parts require a higher injection rate), the nozzle position of the product is prone to air marks.
(5) the molding temperature of ABS is higher, and the mold temperature is generally adjusted at 25-70 C. When producing larger products, the temperature of fixed die (front mold) is generally about 5 degrees higher than that of moving die (Hou Mo). (mold temperature will affect the smoothness of plastic parts, and lower temperature will result in lower finish).
(6) ABS should not stay in the high temperature barrel for too long (less than 30 minutes), otherwise it is easy to decompose and yellowing.
3. typical application area
Automobiles (dashboards, tool hatches, wheel covers, reflective mirror boxes, etc.), refrigerators, powerful tools (hair dryers, stirrers, food processors, mowers, etc.), telephone shells, typewriter keyboards, recreational vehicles such as golf carts and jet skis.
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