“Engineering plastics: analysis of types and application characteristics to help modern industrial development”

Engineering plastics are of various types and widely used. Their excellent performance is often used to replace metal materials. Many friends in the injection molding industry and terminal design industry are often troubled by the inability to correctly distinguish the characteristics of different types of plastics when choosing raw materials. This article will introduce you to the various types of engineering plastics in detail from four aspects: the basic properties of plastics, material properties, molding characteristics and uses.

1. PA​

1. Basic properties

(1) Specific gravity: PA6-1.14g/cm³, PA66-1.15g/cm³, PA1010-1.05g/cm³ (2) Molding shrinkage: PA6-0.8-2.5%, PA66-1.5-2.2% (3) Molding temperature: 220-300℃ (4) Drying conditions: 100-110℃, 12 hours

2. Material properties

Tough, wear-resistant, oil-resistant, water-resistant, and mildew-resistant, but absorbs a lot of water. Nylon 6 has good elasticity, high impact strength, and absorbs a lot of water; nylon 66 has better performance than nylon 6, high strength, and good wear resistance; nylon 610 is similar to nylon 66, but absorbs less water and has low rigidity; nylon 1010 is translucent, absorbs less water, and has good cold resistance.

3. Molding characteristics

(1) The crystal material has a high melting point, a narrow melting temperature range, and poor thermal stability. It will decompose when the material temperature exceeds 300 degrees and the retention time exceeds 30 minutes. It is easy to absorb moisture and needs to be dried. The water content should not exceed 0.3%;

(2) Good fluidity and easy to overflow. It is advisable to use a self-locking nozzle and it should be heated;

(3) The molding shrinkage range and shrinkage rate are large, the directionality is obvious, and shrinkage holes and deformation are prone to occur;

(4) The mold temperature is selected in the range of 20-90 degrees according to the wall thickness of the plastic part. The injection pressure is selected according to the type of injection machine, material temperature, shape and size of the plastic part, and mold pouring system. The molding cycle is selected according to the wall thickness of the plastic part. When the resin viscosity is low, the injection and cooling time should be extended, and white oil should be used as a release agent;

(5) The form and size of the mold casting system. Increasing the runner and gate size can reduce shrinkage.

4.Scope of application

Mechanical parts, gears, bearings, electrical components

2. PC

1. Basic properties

(1) Specific gravity: 1.18-1.20g/cm³ (2) Molding shrinkage: 0.5-0.8% (3) Molding temperature: 230-320℃ (4) Drying conditions: 110-120℃, 8 hours

2. Material properties

It has high impact strength, good dimensional stability, is colorless and transparent, has good colorability, good electrical insulation, corrosion resistance and wear resistance, but has poor self-lubrication, a tendency to stress cracking, is easily hydrolyzed at high temperatures, and has poor solubility with other resins.

3. Molding characteristics

(1) Amorphous material, good thermal stability, wide molding temperature range, poor fluidity. Low hygroscopicity, but sensitive to water, must be dried. Small molding shrinkage, prone to melt cracking and stress concentration, so the molding conditions should be strictly controlled, plastic parts must be annealed;

(2) For plastic parts with high melting temperature, high viscosity and weight greater than 200g, it is advisable to use a heated extension nozzle;

(3) The cooling speed is fast, the mold pouring system is based on the principle of being thick and short, a cold well should be set, the gate should be large, and the mold should be heated;

(4) If the material temperature is too low, it will cause material shortage and dull plastic parts. If the material temperature is too high, it will easily overflow and cause foaming of plastic parts. When the mold temperature is low, the shrinkage rate, elongation rate and impact strength are high, while the bending, compression and tensile strength are low. When the mold temperature exceeds 120 degrees, the plastic parts cool slowly and are prone to deformation and sticking to the mold.

4. Scope of application

Used to make small instrument parts, insulating transparent parts and impact-resistant parts, optical lenses, transparent screens, car windows, and electronic housings.

3.POM

1. Basic properties

(1) Specific gravity: 1.41-1.43g/cm³ (2) Molding shrinkage: 1.2-3.0% (3) Molding temperature: 170-200℃ (4) Drying conditions: 80-90℃, 2 hours

2. Material properties

It has good overall performance, high strength and stiffness, good wear resistance, low water absorption, and good dimensional stability, but poor thermal stability, easy to burn, and prone to aging when exposed to the atmosphere.

3. Molding characteristics

(1) Crystallization material, with a narrow melting range, fast melting and solidification, and crystallization occurs when the material temperature is slightly lower than the melting temperature. It has medium fluidity. It absorbs little moisture and can be dried without treatment;

(2) Low friction coefficient, good elasticity, and surface defects such as wrinkles are easy to occur on the surface of plastic parts;

(3) It is very easy to decompose, and the decomposition temperature is 240 degrees. During decomposition, irritating and corrosive gases are generated. Therefore, the mold steel should be made of corrosion-resistant materials.

4、Scope of application

It is used to produce wear-reducing and wear-resistant parts, transmission parts, as well as parts for chemicals, instruments , gears, bearings, automobile parts, electrical components, etc.

4. PPO

1. Basic properties

(1) Specific gravity: 1.07g/cm³ (2) Molding shrinkage: 0.3-0.8% (3) Molding temperature: 260-290℃ (4) Drying conditions: 130℃, 4 hours

2. Material properties

(1) White particles. Good overall performance, can be used in 120-degree steam, good electrical insulation, low water absorption, but has a tendency to stress cracking. Modified polyphenylene ether can eliminate stress cracking;

(2) It has outstanding electrical insulation, excellent water resistance and good dimensional stability. Its dielectric properties rank first among plastics;

(3) MPPO is a modified material made by blending PPO and HIPS. Currently, all materials on the market are of this type;

(4) It has high heat resistance, with a glass transition temperature of 211 degrees and a melting point of 268 degrees. It tends to decompose when heated to 330 degrees. The higher the PPO content, the better the heat resistance. The heat deformation temperature can reach 190 degrees.

(5) Good flame retardancy, self-extinguishing, and moderate flammability when mixed with HIPS. Lightweight, non-toxic, and can be used in the food and pharmaceutical industries. Poor light resistance, and will discolor if used in sunlight for a long time;

(6) It can be blended and modified with ABS, HDPE, PPS, PA, HIPS, glass fiber, etc.

3. Molding characteristics

(1) Non-crystalline material, low moisture absorption;

(2) Poor fluidity, similar to Newtonian fluid, viscosity is sensitive to temperature, and product thickness is generally above 0.8mm. It is very easy to decompose, and corrosive gas is produced during decomposition. The molding temperature should be strictly controlled, the mold should be heated, and the gating system should have little resistance to material flow;

(3) The water absorption rate of polyphenylene ether is very low, about 0.06%, but a small amount of water will cause silver threads and other roughness on the surface of the product. It is best to dry it. The temperature should not exceed 150 degrees, otherwise the color will change;

(4) The molding temperature of polyphenylene ether is 280-330 degrees, and the molding temperature of modified polyphenylene ether is 260-285 degrees.

4. Scope of application

It can be used to make heat-resistant parts, insulating parts, wear-resistant parts, transmission parts, medical and electronic parts; it can be used to make gears, fan blades, valves and other parts used at higher temperatures, and can replace stainless steel; it can be used to make screws, fasteners and connectors; electrical parts of motors, rotors, casings and transformers.

5.PBT

1. Basic properties

PBT used as engineering plastics has two types: unmodified and modified. The unmodified grade has a large molding shrinkage rate and its mechanical properties are not as good as other engineering plastics, so it is rarely used alone. Nearly 80% of PBT is modified.
2. Material properties

(1)It is a milky white crystalline solid, tasteless, odorless, non-toxic, and the surface of the product is glossy. It has better flexibility than PET, and its melting temperature and rigidity are relatively lower;

(2)It has excellent electrical insulation properties. It can be maintained even in humid and harsh environments;

(3)Has good weather resistance;

(4) Can resist corrosion from general chemicals, such as weak acids.

3. Scope of application

(1) Manufacturing various automotive parts, such as door handles, bumpers, rearview mirror housings, etc.;

(2) Manufacturing of electronic and electrical parts, such as connectors, sockets, plugs, fuse boxes, etc.;

(3) Production of various electrical appliance housings and components, such as telephones, indoor and outdoor lighting housings, hair dryer components, etc.

6. ABS-King of General Plastics

1. Basic properties

(1) Specific gravity: 1.05g/cm³

(2) Molding shrinkage: 0.4-0.7%

(3) Molding temperature: 200-240℃

(4) Drying conditions: 80-90℃, 2 hours

2. Material properties

(1) Good comprehensive performance, high impact strength, chemical stability, and good electrical properties;

(2) Good welding properties with 372 organic glass, can be made into two-color plastic parts, and can be chrome-plated and painted on the surface;

(3) There are high impact resistance, high heat resistance, flame retardant, reinforced, transparent and other grades;

(4) The fluidity is slightly worse than HIPS, but better than PMMA, PC, etc., and has good flexibility.

3. Molding characteristics

(1) Amorphous materials have medium fluidity and high moisture absorption, so they must be fully dried. Plastic parts that require glossy surfaces must be preheated and dried at 80-90 degrees for a long time, for 3 hours.

(2) High material temperature and high mold temperature are recommended, but the material temperature is too high and it is easy to decompose (the decomposition temperature is >270 degrees). For plastic parts with higher precision, the mold temperature should be 50-60 degrees, and for high gloss and heat-resistant plastic parts, the mold temperature should be 60-80 degrees.

(3) If you need to solve the problem of water lines, you need to improve the fluidity of the material, adopt high material temperature, high mold temperature, or change the water entry level.

(4) If heat-resistant or flame-retardant materials are used, plastic decomposition products will remain on the mold surface 3-7 days after production, causing the mold surface to become shiny. The mold needs to be cleaned in time, and venting positions need to be added to the mold surface.

4. Scope of application

Manufacture of general mechanical parts, wear-resistant parts, transmission parts and telecommunication parts.