1. Properties of PS
PS is an amorphous polymer with good fluidity and low water absorption (less than 0.2%). It is a transparent plastic that is easy to mold and process. Its products have a light transmittance of 88-92%, strong coloring ability, and high hardness. However, PS products are brittle, prone to internal stress cracking, and have poor heat resistance (60-80℃). It is non-toxic and has a specific gravity of approximately 1.04 g/cm³ (slightly greater than water).
2. Processing Characteristics of PS
Melting point of PS is 166℃, and processing temperature is generally 185-215℃. Decomposition temperature is approximately 290℃, so its processing temperature range is relatively wide. PS material does not need to be dried before processing. Due to its high MI and good fluidity, injection pressure can be lower. Because PS has a low specific heat, its products can quickly condense and solidify with some mold cooling, and its cooling speed is faster than that of general raw materials, allowing for earlier mold opening. Both plasticization time and cooling time are shorter, reducing molding cycle time; gloss of PS products improves with increasing mold temperature.

 

1. Properties of HIPS
HIPS is a modified material of PS, containing 5-15% rubber components. Its toughness is about four times higher than that of PS, and its impact strength is greatly improved. It has advantages of PS in terms of molding and strong coloring ability. HIPS products are opaque. HIPS has low water absorption and does not require pre-drying during processing.
2. Processing Characteristics of HIPS
Because HIPS molecules contain 5-15% rubber, this affects its fluidity to a certain extent, so higher injection pressure and molding temperature are recommended. Its cooling speed is slower than that of PS, so sufficient holding pressure, holding time, and cooling time are required. Molding cycle will be slightly longer than that of PS, and processing temperature is generally 190-240℃. HIPS parts often exhibit a specific "white edge" problem. This can be improved by increasing mold temperature and clamping force, reducing holding pressure and time, but this may result in more noticeable flow marks in product.

1. Properties of AS
AS is a styrene-acrylonitrile copolymer, which is less prone to internal stress cracking. It has high transparency, its softening temperature and impact strength are higher than PS.
2. Processing Characteristics of AS
Processing temperature of AS is generally 200-250℃. This material is hygroscopic 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. A mold temperature of 45-75℃ is preferred.

1. Properties of ABS
ABS is an acrylonitrile-butadiene-styrene terpolymer, possessing high mechanical strength and excellent overall "toughness, rigidity, and strength" properties. It is an amorphous polymer. ABS is a general-purpose engineering plastic with diverse varieties and wide applications, also known as "general-purpose plastic" (MBS is called transparent ABS). ABS is hygroscopic, with a specific gravity of 1.05 g/cm³ (slightly heavier than water), low shrinkage (0.60%), dimensional stability, easy molding and processing.
2. Processing Characteristics of ABS
2.1 ABS has high hygroscopicity and moisture sensitivity. It must be thoroughly dried and preheated before molding and processing, controlling moisture content to below 0.03%.
2.2 Melt viscosity of ABS resin is less sensitive to temperature (unlike other amorphous resins). Although injection temperature of ABS is slightly higher than PS, it does not have same wide temperature range as PS.  Blindly increasing temperature to reduce viscosity is not effective; instead, increasing screw speed or injection pressure can improve its fluidity. A general processing temperature of 190-235℃ is preferred.
2.3 Melt viscosity of ABS is moderate, higher than PS, HIPS, and AS, requiring higher injection pressure for molding.
2.4 Using a medium injection speed for ABS material generally yields better results. (Unless shape is complex or thin-walled parts require a higher injection speed), air bubbles are prone to appear at the gate of product.
2.5 ABS molding temperature is relatively high, and mold temperature is generally adjusted to 45-80℃. When producing larger products, temperature of fixed mold (front mold) is generally about 5℃ higher than that of moving mold (rear mold).
2.6 ABS should not remain in high-temperature barrel for too long (should be less than 30 minutes), otherwise it will easily decompose and turn yellow.

1. Properties of BS
BS is a butadiene-styrene copolymer. It has certain toughness and elasticity, low hardness (relatively soft), and good transparency. Specific gravity of BS material is 1.01 g/cm³ (similar to water). This material is easy to color, has good fluidity, is easy to mold and process.
2. Process characteristics of BS
Processing temperature range of BS is generally 190-225℃, and mold temperature is preferably 30-50℃. This material should be dried before processing. Due to its good fluidity, injection pressure and injection speed can be lower.

1. Properties of PMMA
PMMA is an amorphous polymer, commonly known as plexiglass. It has excellent transparency and good heat resistance (heat distortion temperature is 98℃). Its products have medium mechanical strength and low surface hardness, and are easily scratched by hard objects. Compared with PS, it is less prone to brittle fracture, and its specific gravity is 1.18 g/cm³.
2. Process characteristics of PMMA
PMMA processing requirements are relatively strict. It is very sensitive to moisture and temperature. It must be thoroughly dried before processing. Its melt viscosity is relatively high, requiring molding at higher temperatures (225-245℃) and pressure. Mold temperature is preferably 65-80℃. PMMA has poor stability, and high temperature or prolonged exposure to high temperatures will cause degradation. Screw speed should not be too high (about 60% is sufficient). "Voids" are prone to appear in thicker PMMA parts, requiring a large gate and processing methods such as "low material temperature, high mold temperature, and slow injection".

1. PE Properties
PE is the most widely produced plastic, characterized by its softness, non-toxicity, low cost, and ease of processing. PE is a typical crystalline polymer. It comes in many types, with LDPE and HDPE being the most common. It is a translucent plastic with low strength and a specific gravity of 0.94 g/cm³ (less than water). LDPE is softer (commonly known as soft plastic), while HDPE is commonly known as hard soft plastic; it is harder than LDPE, has poor light transmission, and a higher degree of crystallinity. PE has good chemical resistance, is not easily corroded, and is difficult to print on.
2. PE Processing Characteristics
The most significant characteristic of PE parts is their large molding shrinkage rate, which easily leads to shrinkage and deformation. PE has low water absorption and does not require drying. PE has a wide processing temperature range and is not easily decomposed (decomposition temperature is 320℃). Higher pressure results in higher density and lower shrinkage. PE has medium fluidity, requiring strict control of processing conditions and maintaining a constant mold temperature (40-60℃). Degree of crystallinity of PE is related to molding process conditions; it has a high cold solidification temperature, and lower mold temperatures result in lower crystallinity. During crystallization process, anisotropic shrinkage causes internal stress concentration, making PE parts prone to deformation and cracking. Placing product in an 80℃ water bath can relieve some of stress. During molding, slightly higher material and mold temperatures are preferable, and injection pressure should be kept as low as possible while ensuring product quality. Mold cooling requires rapid and uniform cooling, and product is quite hot when demolded.

 

1. PP Properties
PP is a crystalline polymer. Among common plastics, PP is the lightest, with a density of only 0.91 g/cm³ (less than water). Among general-purpose plastics, PP has the best heat resistance, with a heat distortion temperature of 80-100℃, and can be boiled in water. PP has good stress crack resistance and a very high bending fatigue life, commonly known as "hundred-fold plastic." The overall performance of PP is superior to that of PE. PP products are lightweight, tough, and have good chemical resistance. PP's disadvantages: low dimensional accuracy, insufficient rigidity, poor weather resistance, and susceptibility to "copper damage." It exhibits post-molding shrinkage, and after demolding, it is prone to aging, becoming brittle, and deforming.
2. PP's Processing Characteristics
PP has good fluidity at its melting temperature and good molding performance. PP has two characteristics in processing: First, viscosity of the PP melt decreases significantly with increasing shear rate (less affected by temperature); second, it exhibits a high degree of molecular orientation, resulting in a larger shrinkage rate.
Processing temperature of PP is best around 200-300℃. It has good thermal stability (decomposition temperature is 310℃), but at high temperatures (270-300℃), prolonged residence in barrel may lead to degradation. Because viscosity of PP decreases significantly with increasing shear rate, increasing injection pressure and injection speed will improve its fluidity, reduce shrinkage deformation and sink marks. Mold temperature should be controlled within range of 30-50℃. PP melt can penetrate very narrow mold gaps, resulting in flash. During melting process, PP absorbs a large amount of heat of fusion (high specific heat), so product is quite hot after demolding. PP material does not require drying during processing. PP has a lower shrinkage rate and crystallinity than PE.

1. PA's Properties
PA is also a crystalline plastic, with many varieties. Commonly used nylons for injection molding include nylon 6, nylon 66, nylon 1010, and nylon 610. Nylon has toughness, wear resistance, and self-lubrication. Its main advantages include high mechanical strength, good toughness, fatigue resistance, smooth surface, low friction coefficient, wear resistance, heat resistance (can be used for a long time within 100℃), corrosion resistance, lightweight parts, easy dyeing, and easy molding. Main disadvantages of PA are: easy water absorption, strict injection molding technical requirements, and poor dimensional stability. Due to its high specific heat, product is quite hot.
PA66 is variety with the highest mechanical strength and widest application in PA series. It has high crystallinity, so its rigidity, hardness, and heat resistance are all high. PA1010 was first developed in my country in 1958.
It is translucent, has a low specific gravity, high elasticity and flexibility, lower water absorption than PA66, and reliable dimensional stability.
2. Processing Characteristics of PA
PA is highly hygroscopic and must be thoroughly dried before processing. Moisture content should be controlled below 0.3%. Well-dried raw materials result in high-gloss products; otherwise, surface will be rough. PA does not gradually soften with increasing temperature, but rather softens within a narrow temperature range near melting point. Melting point is very distinct; once temperature is reached, flow occurs (unlike PS, PE, PP, etc.).
Viscosity of PA is much lower than other thermoplastics, and its melting temperature range is narrow (only about 5℃). PA has good fluidity and is easy to mold, but it is also prone to flashing. Nozzle drooling is common, requiring a larger suck-back. PA has a high melting point and solidification point; molten material can solidify in mold at any time if temperature drops below melting point, hindering complete mold filling. Therefore, high-speed injection must be used (especially for thin-walled or long-flow parts). Nylon molds require adequate venting.
PA has poor thermal stability in molten state and is prone to degradation. Barrel temperature should not exceed 300℃, and heating time of molten material in barrel should not exceed 30 minutes. PA requires a relatively high mold temperature; mold temperature can be used to control its crystallinity to obtain desired properties.
Optimal mold temperature for PA is 50-90℃. Processing temperature for PA1010 is preferably 220-240℃, and for PA66, it is 270-290℃. PA products sometimes require "annealing" or "moisture conditioning" depending on quality requirements.

1. Properties of POM
POM is a crystalline plastic with excellent rigidity, commonly known as "acetal resin." It possesses excellent fatigue resistance, creep resistance, wear resistance, and heat resistance. POM does not easily absorb moisture, has a specific gravity of 1.42 g/cm³, a shrinkage rate of 2.1% (relatively high), making dimensional control difficult, and a heat distortion temperature of 172℃.
2. Processing Characteristics of POM
POM does not require drying before processing, but preheating during processing (around 100℃) is recommended for better dimensional stability. POM has a narrow processing temperature range (195-215℃); prolonged residence time in barrel or temperatures exceeding 220℃ will cause decomposition. Screw speed should not be too high, residual material should be minimized. POM products have high shrinkage and are prone to shrinkage or deformation.
POM has a high specific heat, requiring high mold temperatures (80-100℃). Product is very hot after demolding, so care must be taken to prevent burns. POM is best molded under medium pressure, medium speed, and high mold temperature conditions.

1. Properties of PC
PC is an amorphous plastic with good transparency. It possesses excellent overall properties, including high mechanical strength, good toughness, good heat and weather resistance, high dimensional stability, easy coloring, and low water absorption. PC has a heat distortion temperature of 135-143℃ and can be used for extended periods at working temperatures of 120-130℃. Disadvantages of PC are: poor chemical resistance, high melt viscosity, poor fluidity, and extreme sensitivity to moisture, easily leading to internal stress cracking.
2. Processing Characteristics of PC
PC material is sensitive to temperature; its melt viscosity decreases significantly with increasing temperature, leading to faster flow. It is not sensitive to pressure; to improve fluidity, increasing temperature is necessary. PC material must be thoroughly dried before processing (around 120℃), with moisture content controlled to within 0.02%. PC material is best molded under high material temperature, high mold temperature, and high pressure, slow speed conditions. A mold temperature of 80-110℃ is ideal, and molding temperature should be 280-320℃. PC products are prone to surface defects, gate marks, and significant internal residual stress, leading to cracking. Therefore, PC molding requires high precision. PC material has a low shrinkage rate (0.5%), resulting in minimal dimensional changes. Products molded from PC material can have their internal stress relieved by annealing.

1. Properties of EVA
EVA is an amorphous plastic, non-toxic, with a specific gravity of 0.95 g/cm³ (lighter than water). Its products have poor surface gloss, good elasticity, are soft and lightweight, have low mechanical strength, good fluidity, are easy to process and mold. It has a relatively large shrinkage rate (2%). EVA can be used as a carrier for color masterbatches.
2. Processing Characteristics of EVA
EVA has a low molding processing temperature (160-200℃), with a wide range. Its mold temperature is low (20-45℃). This material needs to be dried before processing (drying temperature 65℃). During EVA processing, mold temperature and material temperature should not be too high, otherwise surface will be rough (not smooth). EVA products tend to stick to the front mold, so it is better to make cold slug well at main runner of gate in a pull-out style. It easily decomposes at temperatures above 250℃. EVA is best processed using "low temperature, medium pressure, and medium speed" process conditions.

1. Properties of PVC
PVC is an amorphous plastic with poor thermal stability and is easily decomposed by heat. PVC is difficult to burn (good flame retardancy), has high viscosity, and poor fluidity. There are many types of PVC, divided into soft, semi-rigid, and rigid PVC. Density is 1.1-1.3 g/cm³ (heavier than water), and shrinkage rate is large (1.5-2.5%). PVC products have poor surface gloss (US has recently developed a transparent rigid PVC that can rival PC).
2. Processing Characteristics of PVC
PVC has a narrow processing temperature range (160-185℃), making processing more difficult and requiring high process control. Drying is generally not required during processing (if drying is needed, it should be done at 60-70℃). Mold temperature is relatively low (20-40℃). PVC processing is prone to producing air bubbles and black streaks, so processing temperature must be strictly controlled. Screw speed should be low (below 50%), residual material should be minimal, and back pressure should not be too high. Mold venting must be good. PVC material should not remain in high-temperature barrel for more than 15 minutes. For PVC, it is better to use a large gate size, and molding under "medium pressure, slow speed, and low temperature" conditions is preferred. PVC products tend to stick to the front mold; mold opening speed (first stage) should not be too fast. Gate should be designed with a pull-out type at cold slug well of runner. Before stopping machine when processing PVC, barrel should be cleaned promptly with PS sprue material (or PE material) to prevent PVC decomposition and generation of HCl, which corrodes screw and inner wall of barrel.

 

1. Properties of PPO
PPO (NORLY) is an engineering plastic with excellent overall performance. It has higher hardness than PA, POM, and PC, high mechanical strength, good rigidity, good heat resistance (heat distortion temperature of 126℃), high dimensional stability (shrinkage rate of 0.6%), and low water absorption (less than 0.1%). Disadvantages include instability to ultraviolet light, high price, and low usage.
2. Processing Characteristics of PPO
PPO has high melt viscosity, poor fluidity, and requires high processing conditions. Before processing, it needs to be dried at 100-120℃ for 1-2 hours. Molding temperature is 270-320℃, and mold temperature should be controlled at 75-95℃. Molding should be carried out under "high temperature, high pressure, and high speed" conditions. During injection molding process of this plastic, jetting flow marks (snake patterns) are prone to occur in front of gate; a larger gate size is preferable.