Commonly Used Plastic Properties
- AS
1. AS performance
AS is a propylene-styrene copolymer, also called SAN, with a density of about 1.07g/cm3. It is not prone to internal stress cracking. It has higher transparency, higher softening temperature and impact strength than PS, and poorer fatigue resistance.
2. Application of AS
Trays, cups, tableware, refrigerator compartments, knobs, lighting accessories, ornaments, instrument mirrors, packaging boxes, stationery, gas lighters, toothbrush handles, etc.
3. AS processing conditions
The processing temperature of AS is generally 210~250℃. This 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 the injection pressure is also slightly higher, and the mold temperature is controlled at 45~75 ℃ is better.
- ABS
1. ABS performance
ABS is acrylonitrile-butadiene-styrene terpolymer. It is an amorphous polymer with a density of about 1.05g/cm3. It has high mechanical strength and good comprehensive properties of “vertical, tough and steel”. ABS is a widely used engineering plastic with various varieties and wide uses. It is also called “general engineering plastic” (MBS is called transparent ABS). It is easy to shape and process, has poor chemical resistance, and the products are easy to be electroplated.
2. Application of ABS
Pump impellers, bearings, handles, pipes, electrical appliance casings, electronic product parts, toys, watch cases, instrument cases, water tank casings, cold storage and refrigerator inner casings.
3. ABS process characteristics
(1) ABS has high hygroscopicity and poor temperature resistance. It must be fully dried and preheated before molding and processing to control the moisture content below 0.03%.
(2) The melt viscosity of ABS resin is less sensitive to temperature (different from other amorphous resins). Although the injection temperature of ABS is slightly higher than that of PS, it does not have a looser temperature rising range like PS, and blind heating cannot be used. To reduce its viscosity, you can increase the screw speed or increase the injection pressure/speed to improve its fluidity. The general processing temperature is 190~235℃.
(3) The melt viscosity of ABS is medium, higher than that of PS, HIPS, and AS, and its fluidity is poorer, so higher injection pressure is required.
(4) ABS has a good effect with medium to medium injection speeds (unless complex shapes and thin parts require higher injection speeds), the nozzle of the product is prone to air marks.
(5) ABS molding temperature is relatively high, and its mold temperature is generally adjusted between 45 and 80°C. When producing larger products, the temperature of the fixed mold (front mold) is generally about 5°C higher than that of the movable mold (rear mold).
(6) ABS should not stay in the high-temperature barrel for too long (should be less than 30 minutes), otherwise it will easily decompose and turn yellow.
- PMMA
1. Performance of PMMA
PMMA is an amorphous polymer, commonly known as plexiglass (sub-acrylic), with a density of about 1.18g/cm3. It has excellent transparency and a light transmittance of 92%. It is a good optical material; it has good heat resistance (heat resistance). The deformation temperature is 98°C). Its product has medium mechanical strength and low surface hardness. It is easily scratched by hard objects and leaves traces. Compared with PS, it is not easy to be brittle.
2. Application of PMMA
Instrument lenses, optical products, electrical appliances, medical equipment, transparent models, decorations, sun lenses, dentures, billboards, clock panels, car taillights, windshields, etc.
3. Process characteristics of PMMA
The processing requirements of PMMA are strict. It is very sensitive to moisture and temperature. It must be fully dried before processing. Its melt viscosity is relatively high, so it needs to be molded at a higher temperature (219~240℃) and pressure. The mold temperature is between 65~ 80℃ is better. The thermal stability of PMMA is not very good. It will be degraded by high temperature or staying at a higher temperature for too long. The screw speed should not be too high (about 60rpm), as it is easy to occur in thicker PMMA parts. The “void” phenomenon requires large gates and “high material temperature, high mold temperature, slow speed” injection conditions to process.
4. What is acrylic (PMMA)?
Acrylic (PMMA) is a clear, hard plastic often used in place of glass in products such as shatterproof windows, illuminated signs, skylights and aircraft canopies. PMMA belongs to the important family of acrylic resins. The chemical name of acrylic is polymethyl methacrylate (PMMA), which is a synthetic resin polymerized from methyl methacrylate.
Polymethylmethacrylate (PMMA) is also known as acrylic, acrylic glass, and is available under trade names and brands such as Crylux, Plexiglas, Acrylite, Perclax, Astariglas, Lucite, and Perspex, among others. Polymethylmethacrylate (PMMA) is often used in sheet form as a lightweight or shatterproof alternative to glass. PMMA is also used as a casting resin, ink, and coating. PMMA is part of the engineering plastic materials group.
5. How is acrylic made?
Polymethyl methacrylate is made through polymerization as it is one of the synthetic polymers. First, methyl methacrylate is placed into the mold and a catalyst is added to speed up the process. Due to this polymerization process, PMMA can be shaped into various forms such as sheets, resins, blocks, and beads. Acrylic glue can also help soften the PMMA pieces and weld them together.
PMMA is easy to manipulate in different ways. It can be bonded with other materials to help enhance its properties. With thermoforming, it becomes flexible when heated and solidifies when cooled. It can be sized appropriately using a saw or laser cutting. If polished, you can remove scratches from the surface and help maintain its integrity.
6. What are the different types of acrylic?
The two main types of acrylic plastic are cast acrylic and extruded acrylic. Cast acrylic is more expensive to produce but has better strength, durability, clarity, thermoforming range and stability than extruded acrylic. Cast acrylic offers excellent chemical resistance and durability, and is easy to color and shape during the manufacturing process. Cast acrylic is also available in a variety of thicknesses. Extruded acrylic is more economical than cast acrylic and provides more consistent, workable acrylic than cast acrylic (at the expense of reduced strength). Extruded acrylic is easy to process and machine, making it an excellent alternative to glass sheets in applications.
7. Why is acrylic so commonly used?
Acrylic is often used because it has the same beneficial qualities as glass, but without the brittleness issues. Acrylic glass has excellent optical properties and has the same refractive index as glass in the solid state. Because of its shatterproof properties, designers can use acrylics in places where glass would be too dangerous or would otherwise fail (such as submarine periscopes, aircraft windows, etc.). For example, the most common form of bulletproof glass is a 1/4-inch-thick piece of acrylic, called solid acrylic. Acrylic also performs well in injection molding and can be formed into almost any shape that a mold maker can create. The strength of acrylic glass combined with its ease of processing and machining make it an excellent material, which explains why it is widely used in consumer and commercial industries.
