Physical properties and processing technology of common engineering plastics

Time:2021-06-01 11:58:09 / Popularity: / Source:

1. PS (Polystyrene)

processing technology of common engineering plastics 
1. PS performance: PS is an amorphous polymer with good fluidity and low water absorption (less than 00.2%). It is a transparent plastic that is easy to mold and process. Light transmittance of its products is 88-92%, coloring power is strong, and hardness is high. However, PS products are brittle, prone to internal stress cracking, poor heat resistance (60-80℃), non-toxic, and have a specific gravity of about 1.04g\cm3 (slightly greater than water).
Molding shrinkage rate (value is generally 0.004—0.007in/in), transparent PS—this name only indicates transparency of resin, not crystallinity. (Chemical and physical properties: Most commercial PS are transparent, non-crystalline materials. PS has very good geometric stability, thermal stability, optical transmission characteristics, electrical insulation characteristics and a very small tendency to absorb moisture. It can resist water and diluted inorganic acids, but it can be corroded by strong oxidizing acids such as concentrated sulfuric acid, it can swell and deform in some organic solvents. )
2. Process characteristics of PS: Melting point of PS is 166℃, processing temperature is generally 185-215℃, melting temperature is 180~280℃, for flame-retardant materials, upper limit is 250℃ and decomposition temperature is about 290℃, so processing temperature range is wide. Mold temperature is 40~50℃, injection pressure: 200~600bar, injection speed is recommended to use a fast injection speed, runner and gate can use all conventional types of gates.
Before processing, PS materials usually do not need to be dried unless they are improperly stored. If drying is required, recommended drying conditions are 80C for 2 to 3 hours. Due to low specific heat of PS, some molds made by it can quickly condense and solidify when it dissipates heat. Its cooling rate is faster than that of ordinary raw materials, and mold opening time can be earlier. Its plasticizing time and cooling time are shorter, molding cycle time will be reduced; gloss of PS products will be better with increase of mold temperature.
3. Typical applications: packaging products (containers, covers, bottles), disposable medical supplies, toys, cups, knives, tape reels, windshields, and many foam 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 source diffusers, insulating films, etc.).

2. HIPS (modified polystyrene)

processing technology of common engineering plastics 
1. Performance of HIPS: HIPS is a modified material of PS. Molecule contains 5-15% rubber. Its toughness is about four times higher than that of PS, and its impact strength is greatly improved (high impact polystyrene). There are flame retardant grades, stress cracking resistance grades, high gloss grades, extremely high impact strength grades, glass fiber reinforced grades, and low residual volatilization grades.
Other important properties of standard HIPS: flexural strength 13.8-55.1MPa; tensile strength 13.8-41.4MPa; elongation at break 15-75%; density 1.035-1.04 g/ml; it has advantages of molding processing and strong coloring power of PS. HIPS products are opaque. HIPS has low water absorption and does not need to be pre-dried during processing.
2. Process characteristics of HIPS: Because HIPS molecules contain 5-15% of rubber, which affects its fluidity to a certain extent, injection pressure and molding temperature should be higher. Its cooling rate is slower than PS, so it needs enough holding pressure, holding time and cooling room.
Molding cycle is slightly longer than that of PS, and its processing temperature is generally 190-240℃. HIPS resin absorbs water slowly, so it does not need to be dried under normal circumstances. Sometimes too much moisture on the surface of material will be absorbed, thereby affecting appearance quality of final product.
Drying at 160°F for 2-3 hours will remove excess water. There is a special "white edge" problem in HIPS parts, which can be improved by increasing mold temperature and clamping force, reducing holding pressure and time, etc., and water trapping in product will be more obvious.
3. Typical application range: Main application areas are packaging and disposable products, instrumentation, household appliances, toys and entertainment products, and construction industry. Flame-retardant (UL V-0 and UL 5-V), impact-resistant polystyrene has been produced and widely used in TV housings, commercial machines and electrical products.

3. SA (SAN--styrene-acrylonitrile copolymer/strong glue)

1. SA performance: chemical and physical properties: SA is a hard, transparent material, not easy to produce internal stress cracking. Transparency is very high, its softening temperature and impact strength are higher than that of PS. Styrene component makes SA hard, transparent and easy to process; acrylonitrile component makes SA chemically and thermally stable.
SA has strong load bearing capacity, chemical resistance, thermal deformation resistance and geometric stability. Adding glass fiber additives to SA can increase strength and thermal deformation resistance, reduce thermal expansion coefficient. Vicat softening temperature of SA is about 110℃. Deflection temperature under load is about 100C, and shrinkage rate of SA is about 0.3~0.7%.
2. Technological characteristics of SA: Processing temperature of SA is generally 200-250℃. Material is easy to absorb moisture and needs to be dried for more than one hour before processing. Its fluidity is slightly worse than PS, so injection pressure is also slightly higher (injection pressure: 350~1300bar), injection speed: high-speed injection is recommended. It is better to control mold temperature at 45-75°C. Drying treatment: If stored improperly, SA has some hygroscopic properties. Recommended drying conditions are 80°C, 2~4 hours.
Melting temperature: 200~270℃. If processing thick-walled products, you can use a melting temperature below lower limit. For reinforced materials, mold temperature should not exceed 60℃. Cooling system must be well designed, because mold temperature will directly affect appearance, shrinkage and bending of product. Runners and gates: All conventional gates can be used. Gate size must be appropriate to avoid streaks, freckles and voids.
3. Typical applications: electrical (sockets, housings, etc.), daily commodities (kitchen appliances, refrigerator devices, TV bases, cassette boxes, etc.), automotive industry (headlight boxes, reflective environments, dashboards, etc.), household goods (Tableware, food knives, etc.), cosmetic packaging safety glass, water filter housing and faucet knob, medical products (syringes, blood suction tubes, kidney percolation devices and reactors).
Packaging materials (cosmetic case, lipstick casing, mascara cap bottle, cap, cap sprayer and nozzle, etc.), special products (disposable lighter shells, brush substrates and bristles, fishing gear, dentures, toothbrush handles, penholders, instrument nozzles, and directional monofilaments), etc.

4. ABS (super non-breaking glue)

processing technology of common engineering plastics 
1. ABS performance: ABS is synthesized from three chemical monomers: 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 smoothness and high strength. Polymerization of three monomers produces a terpolymer with two phases, one is continuous phase of styrene-acrylonitrile, the other is dispersed phase of polybutadiene rubber). From 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 general-purpose engineering plastic. It has a variety of varieties and a wide range of uses. It is also called "general plastic" (MBS is called transparent ABS). ABS is easy to absorb moisture, specific gravity is 1.05g/cm3 (slightly heavier than water), shrinkage rate is low (0.60%?), size is stable, it is easy to form and process. Characteristics of ABS mainly depend on ratio of three monomers and molecular structure in two phases. This allows great flexibility in product design, and as a result, hundreds of ABS materials of different qualities have been produced on the market.
These different quality materials provide different characteristics, such as medium to high impact resistance, low to high finish and high temperature distortion characteristics. ABS material has super easy processing, appearance characteristics, low creep, excellent dimensional stability and high impact strength.
ABS is a light yellow granular or bead-like opaque resin, non-toxic, odorless, low water absorption, has good comprehensive physical and mechanical properties, such as excellent electrical properties, abrasion resistance, dimensional stability, chemical resistance and surface gloss, etc., is easy to process and shape. Disadvantages are weather resistance, poor heat resistance, and flammability.
2. Process characteristics of ABS
2.1 ABS has high hygroscopicity and moisture sensitivity. It must be fully dried and preheated (at least 2 hours at 80~90C) before molding, moisture content should be controlled below 0.03%.
2.2 Melt viscosity of ABS resin is less sensitive to temperature (different from other amorphous resins). Although injection temperature of ABS is slightly higher than that of PS, it cannot have a loose heating range like PS, and it cannot be blindly heated to reduce its viscosity. It can be increased by increasing screw speed or injection pressure to improve its fluidity. Generally, processing temperature is 190-235℃.
2.3 Melt viscosity of ABS is medium, higher than that of PS, HIPS, AS, and higher injection pressure (500~1000bar) is required.
2.4 ABS material adopts medium-to-high injection speed and has better effect. (Unless shape is complex and thin-walled parts require a higher injection speed), product nozzle position is prone to produce air lines.
2.5 Molding temperature of ABS is relatively high, and its mold temperature is generally adjusted at 25-70°C. When producing larger products, temperature of fixed mold (front mold) is generally about 5℃ higher than that of movable mold (rear mold). (Mold temperature will affect finish of plastic parts, lower temperature will result in lower finish)
2.6 ABS should not stay in high temperature barrel for too long (should be less than 30 minutes), otherwise it will easily decompose and turn yellow.
3. Typical applications: automobiles (dashboards, tool hatches, wheel covers, mirror boxes, etc.), refrigerators, high-strength tools (hair dryers, blenders, food processors, lawn mowers, etc.), telephone shells, typewriter keyboard, recreational vehicles such as golf carts and jet sleds.

5. BS (K material)

1. Performance of BS BS is a butadiene-styrene copolymer, which has certain toughness and elasticity, low hardness (softer), and good transparency. Specific gravity of BS material is 1.01f\cm3 (similar to water). Material is easy to color, good fluidity, easy to form and process.
2. Process characteristics of BS: Processing temperature range of BS is generally 190-225℃, and mold temperature is preferably 30-50℃. Material should be dried before processing. Because of its good fluidity, injection pressure and injection speed can be lower.

6. PMMA (Acrylic)

1. PMMA is an amorphous polymer, commonly known as plexiglass. Excellent transparency, good heat resistance (heat deformation temperature is 98℃), and good impact resistance. Its products have medium mechanical strength and low surface hardness. They are easily scratched by hard objects and leave traces. It is similar to PS. It is not easy to be brittle, and its specific gravity is 1.18g/cm3. PMMA has excellent optical properties and resistance to weather changes.
Penetrability 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 characteristics. As load increases and time increases, it can lead to stress cracking.
2. Process characteristics of PMMA: PMMA has strict processing requirements. It is very sensitive to moisture and temperature. It must be fully dried before processing (recommended drying conditions are 90℃, 2~4 hours), its melt viscosity is relatively large, it needs to be molded under higher temperature (225-245℃) and pressure. Mold temperature is better at 65-80℃.
Stability of PMMA is not very good, and it will be degraded if exposed to high temperature or staying for too long at a higher temperature. Screw speed should not be too large (about 60% is enough), it is easy to appear in thicker PMMA parts

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