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Common plastic materials used in toys I. ABS: Acrylonitrile-butadiene-styrene polymer 1. Functions of the three components Acrylonitrile (A) – contributes to higher hardness of the product, as well as improved wear and heat resistance. Butadiene (B) – enhances flexibility while maintaining the material’s toughness, elasticity, and impact resistance. Styrene (S) – maintains good formability (fluidity and colorability) as well as the rigidity of the material (note: various grades are available depending on the components). 2. ABS has good plating properties and is the best among all plastics in terms of platability. 3. ABS has a significantly higher impact strength than GPPS. 4. The ABS raw material is light yellow and opaque, with the products having a high surface finish. 5. ABS has a low shrinkage rate and good dimensional stability. 6. Insensitive to organic solvents: It dissolves in alcohols, aldehydes, esters, and oxidized hydrocarbons to form an emulsive stream (ABS paste). 7. Material blending properties: ABS+PVC~~~improves toughness, flame resistance, and aging resistance. ABS+PC~~~Improves impact strength and heat resistance. Molding process of ABS: 1. It is necessary to thoroughly dry the material before molding, so that the moisture content is less than 0.1%; the drying conditions should be a temperature of 85°C for at least 3 hours. 2. ABS has good fluidity, and it is prone to forming flash; the injection pressure should be between 70 and 100 MPa – it should not be too high. 3. The temperature of the cylinders should not exceed 250°C. The temperature of the front cylinder should be between 160~~~210°C, that of the middle cylinder between 170~~~190°C, and that of the rear cylinder between 160~~~180°C. Excessively high temperatures can cause the plastic components to decompose, thereby reducing their fluidity. 4. The mold temperature should be between 40 and 80°C; high appearance standards require a high mold temperature as well. 5. The injection speed should primarily be at medium or low levels. Injection force: 80~~130 MPa. 6. Inspection of internal stress in ABS: It is considered satisfactory if no cracks appear after immersing the product in kerosene for 2 minutes. II. MBS – Transparent ABS, polymethacrylate – butadiene – styrene copolymer. Key properties: transparent, highly flexible, resistant to acids and alkalis, good fluidity, easy to shape and color, and dimensionally stable. III. SBS—K material (transparent). Butadiene and styrene polymers (KR01, KR03). Main properties: transparent, good elasticity, easy to shape. IV. PS material: Polystyrene (GPPS rigid plastic, HIPS modified polystyrene – GPPS: rigid; HIPS: shatter-resistant). A) Appropriate amounts (5–20%) of butadiene rubber are added to GPPS for modification, thereby improving the impact resistance of the rigid plastic. B) Color: GPPS–high transparency with a brittle texture; HIPS–opaque, milky white or slightly yellow in color. C) HIPS and GPPS can be blended as needed; the higher the proportion of GPPS, the better the surface gloss and flowability of the resulting product. HIPS: GPPS at a ratio of 7:3 or 8:2 can maintain sufficient strength and surface quality. *Molding process of polypropylene: 1. GPPS has a wide range of molding temperatures (the molding temperature is far from the degradation temperature); heating, flow, and curing occur rapidly, resulting in a short molding cycle. As long as the mold cavity can be fully filled, the temperature of the barrel should be kept relatively low – 200°C for the front barrel and 160°C for the rear barrel. 2. GPPS has good fluidity, and high injection pressures (70~~~130 PMa) are not required during molding; excessive pressure instead increases residual internal stresses in the product—especially causing the plastic parts to crack after injection. (Modified PS, namely HIPS, has slightly poorer flowability than GPPS.) 3. The injection speed should be relatively high in order to reduce weld lines (water trapping marks), but it is greatly influenced by the injection pressure; an excessively high speed may result in flash or fragmentation upon mold release. 4. Molding temperature: 30℃~~50℃. 5. Polystyrene (GPPS) requires no drying before molding due to its low hygroscopicity, whereas modified polystyrene (HIPS) needs to be dried at a temperature of 60°C to 80°C for 2 hours. V. Polypropylene (PP) – a type of crystalline plastic; its main properties are as follows: 1. It is semi-transparent, lightweight (with a density of 0.91), and can float on water. 2. Good fluidity and formability, surface gloss, (trace remaining at the colored area on PE). 3. A high molecular weight results in high tensile strength and high yield strength (fatigue resistance). 4. It has high chemical stability, is insoluble in organic solvents, resistant to spraying, heating, and difficult to bond. 5. It exhibits excellent wear resistance, as well as good impact resistance at room temperature. 6. It has a high molding shrinkage rate (1.6%), resulting in unstable dimensions; the molded parts are prone to deformation and shrinkage. *Understanding the molding process of polypropylene (PP material): 1. Polypropylene has good fluidity, allowing the cavity to be filled with relatively low injection pressure. Too high pressure can lead to flash, but too low pressure causes severe shrinkage; the injection pressure is generally in the range of 80~~~90 MPa, with the holding pressure being around 80% of the injection pressure. A longer holding time is advisable to compensate for the shrinkage. 2. Suitable for rapid injection; to improve poor exhaust, the exhaust groove should be made slightly deeper at 0.3 mm. 3. Polypropylene has a high degree of crystallinity; the temperature for the front barrel is 200~~~240°C, 170~~~220°C for the middle barrel, and 160~~190°C for the rear barrel. Due to its wide range of suitable processing temperatures, it is easy to shape. In practice, lower temperatures are used to reduce edge defects and shrinkage. 4. Due to the high shrinkage rate of the material, to accurately control the dimensions of the glued parts, the cooling time should be appropriately extended. 5. The mold temperature can be set at a low level (20~~~40°C). A too high mold temperature leads to higher crystallinity and stronger intermolecular forces, resulting in products with good stiffness and gloss; however, these products have poor flexibility and transparency, as well as significant shrinkage. 6. The back pressure should be set at 0.1 MPa; in the dry powder coloring process, the back pressure should be increased appropriately to improve the mixing effect. VI. Polyvinyl chloride (PVC) Polyvinyl chloride (PVC) is a amorphous plastic, and its raw material is transparent. The main properties are as follows: 1. The range of hardness of the material can be expanded by adding plasticizers. 2. Difficult to ignite and self-extinguishing, with poor thermal stability. 3. PVC dissolves in cyclohexane, benzene, dichloroethane, and soft rubber used for separating oil from water in fuel systems (containing cyclohexane). 4. PVC is mainly used for rubber coating (and for making dolls). *Understanding the molding processes of polyvinyl chloride (PVC): 1. Soft PVC has a high shrinkage rate (1.0~~2.5%). The polar molecules of PVC tend to absorb moisture, so it needs to be dried before molding; the drying temperature is 85~~95°C for 2 hours. 2. During molding, the barrel is subjected to heat repeatedly over a long period, which causes the decomposition of vinyl chloride monomer and HCL (i.e., degradation); therefore, the dead corners inside the mold cavity and the nozzle should be cleaned regularly. 3. Adding ABS to soft PVC can improve its toughness, hardness, and mechanical strength. 4. Since the molding temperature for PVC is close to its decomposition temperature, it is necessary to strictly control the temperature of the barrel, using as low a molding temperature as possible. At the same time, the molding cycle should be shortened as much as possible to reduce the residence time of the melt in the barrel. The temperature parameters for the barrel are: 160~~~170°C for the front barrel, 160~~165°C for the middle barrel, and 140~~150°C for the rear barrel. 5. For materials that are prone to decomposition and have poor fluidity, the mold runners and gates should be as short as possible, and their thickness should be sufficient to reduce pressure losses and enable rapid filling of the cavity. Injection pressure should be high and at low temperatures; the back pressure should range from 0.5 to 1.5 MPa. The wall thickness of PVC products should not be too thin – it should be at least 1.5 mm, otherwise it will be difficult for the material flow to fill the cavity. 6. The injection speed should not be too fast, to avoid intense friction of the molten material as it passes through the gate, which can raise the temperature and lead to shrinkage marks. 7. The mold temperature should be as low as possible (around 30~~~45°C) to shorten the molding cycle and prevent deformation of the molded parts upon removal from the mold (the parts may need to be shaped using a setting mold if necessary). .8. To prevent cold material from blocking the gate or flowing into the mold cavity, a larger cold slug well should be designed to store the cold material. VII. Polyoxymethylene (POM, also known as Acetal) Polyoxymethylene (POM), commonly referred to as Acetal, is a crystalline plastic with the following main properties: 1. Polyoxymethylene is a milky-white, shiny plastic. 2. It possesses comprehensive mechanical properties, high hardness and rigidity, good impact resistance, as well as excellent wear resistance and self-lubricating properties. 3. Good resistance to organic solvents and stable performance. 4. The dimensions remain relatively stable after molding and are less affected by temperature changes. *Understanding the molding process of POM polyoxymethylene: 1. Polyoxymethylene has low hygroscopicity (water absorption rate < 0.5%), so it generally does not need to be dried or only briefly dried before molding. 2. It has a narrow temperature range for molding, poor thermal stability, and decomposes to release formaldehyde at temperatures above 250°C (causing the melt color to darken); therefore, increasing the temperature alone to improve fluidity is harmful and ineffective. For normal plastic injection molding, lower barrel temperatures and shorter residence times are advisable; increasing the injection pressure can improve the flowability of the melt and the surface quality of the product. (Melt flow rate is relatively sensitive to shear velocity.) Temperature parameters: front cylinder 190–210°C, middle cylinder 180–205°C, rear cylinder 150–170°C. Pressure parameters: the injection pressure is around 100 MPa, and the back pressure is 0.5 MPa. 3. Molding temperature: 80–100°C is appropriate (usually heat transfer oil is used). 4. POM has a high cooling shrinkage rate (2–2.5%), which can lead to shrinkage during molding; therefore, the holding time must be extended to compensate for this shrinkage. VIII. Polyethylene (PE) “Patterned Material” Polyethylene (PE), commonly known as “patterned material,” is a crystalline plastic. Its main properties are as follows: 1. Polyethylene is divided into two types – high-density (HPPE) and low-density (LPPE); the higher the density, the lower the transparency. 2. Polyethylene is a translucent particle, giving the rubber product a milky white appearance. 3. Polyethylene possesses flexibility, impact resistance, ductility, and wear resistance, as well as good toughness at low temperatures. 4. It does not melt in any flux at room temperature, and its chemical properties are stable; on the other hand, PE is difficult to bond. 5. It has low mechanical strength, a low heat deformation temperature, and its surface is prone to scratching. 6. Polyethylene (PE) is commonly used in blow-molded products. *Understanding the molding process of polyethylene: 1. It has good fluidity, a wide range of molding temperatures, and is easy to mold. 2. The injection pressure and holding pressure should not be too high, to avoid large stresses within the molded part that could cause deformation or cracking; the injection pressure should be 60~~70 MPa. 3. It has low water absorption, so no drying treatment is required before processing. 4. Increasing the barrel temperature improves the visual quality, but it results in a high molding shrinkage rate (2–2.5%). If the barrel temperature is too low, the products are prone to deformation (this issue is more severe when using a single gate; using multiple gates helps to reduce warping). The appropriate temperature settings are: 200–220°C for the front barrel, 180–190°C for the middle barrel, and 160–170°C for the rear barrel. 5. The mold temperature should remain consistent before and after processing (a mold temperature of 20~~40°C is generally appropriate). The cooling water should not be too close to the surface of the cavity, to avoid excessive local temperature differences that could cause residual internal stresses in the product. Increasing the mold temperature results in good product gloss, but the molding cycle becomes longer. Lowering the mold temperature results in products with good flexibility and high transparency, as well as high impact strength. If the mold temperature is too low, rapid cooling can cause the products to deform or lead to molecular orientation that results in delamination. In short, by adjusting the mold temperature, it is possible to control the hardness and flexibility of the products. 6. Due to its soft texture, it is possible to use forceful demolding instead of a slide when necessary. IX. Polycarbonate (PC) (the most expensive) Polycarbonate (PC), commonly known as “bulletproof glass adhesive,” is a crystalline plastic. Its main properties are: 1. It is transparent in appearance, rigid yet flexible; it burns slowly and extinguishes gradually once removed from the flame. 2. PC material has the best impact resistance among plastics. 3. It has a low shrinkage rate during molding (0.5~~0.7%), resulting in high precision of the finished products and good dimensional stability. 4. It has good chemical stability, but is not resistant to alkalis, metals, aromatic hydrocarbons, and other organic solvents. 5. Poor fatigue strength and sensitivity to notches. *Understanding the molding process of polycarbonate (PC): 1. PC is very sensitive to trace amounts of moisture; therefore, it must be thoroughly dried before molding, with a moisture content of 0.015%, using a drying temperature of 110–120°C for 12 hours. 2. It has poor fluidity and requires high-pressure injection molding; however, too high injection pressure causes significant residual internal stress in the product, leading to cracking. 3. The viscosity of PC material is highly sensitive to temperature; as the temperature rises, the viscosity decreases. The temperature for the front barrel should be 240~~260°C, that for the middle barrel 260~~280°C, and that for the rear barrel 220~~~230°C, with the overall temperature not exceeding 310°C. 4. Mold design requirements: The flow channels should be large and numerous, polished; the cavities and cores must be quenched or coated with hard chromium. 5. Too fast injection speed can cause the melt to break, paste-like spots to appear at the gate, and poor venting (trapped air) can lead to burning of the product. 6. Molding temperature: 80~~100°C. 7. An annealing treatment is applied at 125–135°C for 2 hours, followed by natural cooling to room temperature. X. Polyamides (PA) – Polyamides are commonly known as “nylon”. They are crystalline plastics, and there are various types such as nylon 6, nylon 66, nylon 1010, etc. 1. Nylon possesses good toughness, wear resistance, fatigue resistance, self-lubricating properties, and self-extinguishing properties. 2. It has good low-temperature performance, high impact strength, high tensile strength, and good elasticity. 3. Nylon has high water absorption; after absorbing water, its tensile strength increases to a certain extent, but other strengths (such as tensile strength and stiffness) decrease, with a shrinkage rate of 0.8~~1.4%. 4. It is resistant to weak acids, weak bases, and common solvents; at room temperature it can dissolve in phenol (which can be used as an adhesive), as well as in formic acid and saturated methanol solutions of calcium chloride. *Understanding of nylon molding processes: 1. It is necessary to thoroughly dry the material before injection molding; the drying temperature should be 80–90°C, with a drying time of 24 hours. 2. Nylon has low viscosity and good flowability; it is prone to forming burrs, and the pressure should not be too high, generally ranging from 60 to 90 MPa. 3. As the temperature of the barrel changes, the shrinkage rate fluctuates significantly; excessively high temperatures can cause the molten material to change color and result in brittle silver-colored filaments. Nylon material below its melting temperature is very hard and can damage the mold and screw; the barrel temperature is generally between 220 and 250°C, and it should not exceed 300°C. 4. Mold temperature control: Nylon is a crystalline plastic, and its products are highly affected by the mold temperature; therefore, strict control over the mold temperature is required. High mold temperature: results in higher crystallinity, greater rigidity and hardness, improved wear resistance, and less deformation. Low mold temperature: good flexibility, high elongation rate, and low shrinkage; the mold temperature should be controlled between 20 and 90°C. 5. High-speed injection: Nylon has a high melting point, which means a high solidification temperature (enabling rapid manufacturing and high production efficiency). To ensure proper filling of the mold (preventing the molten material from solidifying before reaching its melting point), high-speed injection is necessary. This is especially true for thin-walled parts or those with long flow distances. In cases where the part walls are thicker or flash occurs, attention should be paid to the exhaust problems caused by high-speed injection. 6. Annealing treatment and temperature adjustment treatment. a Annealing treatment: Annealing increases the crystallinity and improves rigidity, reducing the likelihood of deformation and cracking. The annealing conditions involve a temperature 10~~20°C higher than the operating temperature, with a duration of 10~~60 minutes. b. Temperature adjustment treatment: Helps maintain dimensional stability, improves toughness, and enhances the distribution of internal stresses. The method for temperature adjustment involves immersing in boiling water or a potassium acetate solution. Potassium acetate: water = 1.25:100, time 2~~16 HRS. XI. Polymethyl methacrylate (PMMA), commonly known as Acrylic, is a type of amorphous plastic. 1. It has high transparency, is lightweight and not prone to deformation, and exhibits good light transmission properties. 2. PMMA is difficult to ignite and can slow down combustion. 3. It is intolerant to alcohols, as well as strong bases; it is soluble in aromatic hydrocarbons and chlorinated hydrocarbons (trichloroethane can be used as an adhesive). 4. Easy to shape with stable dimensions. 5. Its impact resistance and surface hardness are slightly poor, making it prone to scuffing; therefore, higher requirements are placed on packaging. *Understanding of the PMM molding process: 1. Acrylic has high transparency, which causes molding defects such as bubbles, flow marks, impurity spots, and silver threads to become clearly visible; as a result, molding is difficult and the yield of qualified products is low. 2. The raw material must be thoroughly dried; insufficient drying can lead to issues such as silver threads and bubbles. Drying conditions: temperature of 95~~~100°C, time of 6 hours. The thickness of the material layer should not exceed 30 mm, and the hopper must be kept warm to prevent re-humidification. 3. Due to its poor fluidity, it is suitable for high-pressure molding; the injection pressure should be between 80 and 100 Mpa. The holding pressure should be around 80% of the injection pressure. The back pressure should not be too high to prevent early cooling of the gate and runner systems. It is necessary to increase the injection time appropriately, and sufficient pressure must be used to ensure proper filling. 4. Injection speed: The injection speed has a significant impact on viscosity; it should not be too fast, as high injection speeds can cause bubbles, burning, and poor transparency in the plastic parts. Low injection pressure, on the other hand, can result in thicker weld lines in the products. 5. Material temperature: Fluidity increases as the temperature of the screw barrel rises, but the temperature should not be too high, provided that the mold cavity can still be filled, in order to reduce defects such as discoloration and silver streaks. The temperature for the front barrel is 200~~~230°C, for the middle barrel it is 215~~235°C, and for the rear barrel it is 140~~~160°C. 6. The mold temperature is high, resulting in high product transparency; it also reduces welding defects. In particular, it helps to minimize internal stresses in the products, and it facilitates full filling of the mold cavity. The mold temperature is generally between 70 and 90°C. 7. The design and flow of the mold should be simple and smooth, allowing for the formation of wide gates. 8. Reduce internal stress: The heat treatment temperature is 70–80°C, and the cooling time using hot air or water is generally 4 hours. 9. Reduce beer plastic black spots: a. Ensure clean raw materials (clean environment). b Clean the mold. c) Clean the machine (clean the front part of the cylinder, the screw, and the nozzle). 10. Keep the mold surface smooth; apply a coating for corrosion resistance. Use release agents as little as possible, or avoid using them altogether, and increase the mold’s draft angle to facilitate demolding.