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With China Plastic Machinery
With China Plastic Machinery
Polystyrene (PS) is one of the five general-purpose plastic, which can be mainly divided into general-purpose polystyrene (GPPS), high-impact polystyrene (HIPS) and expandable polystyrene (EPS).
Polystyrene (PS) is a thermoplastic resin polymerized with styrene as the main raw material. It is a type of synthetic resin that can be repeatedly heated to soften and cooled to solidify. It has extremely high transparency, with a light transmittance of more than 90%. It has the advantages of good electrical insulation, easy coloring, good processing fluidity, good rigidity and good chemical corrosion resistance. The PS plastic industry chain mainly includes petrochemical production industries such as styrene, mineral oil, ethylbenzene, zinc stearate, and polybutadiene rubber, and is mainly used in electronic appliances, daily necessities and toys, building materials, packaging materials and other fields. Among them, electronic appliances are the largest application field of the polystyrene industry. In the electronic appliances industry, ordinary materials of general-purpose polystyrene are mainly used to manufacture injection molded parts, audio-visual products, lighting products and other products.
On October 27, 2017, the World Health Organization's International Agency for Research on Cancer published a preliminary list of carcinogens for reference, and polystyrene is on the list of Class 3 carcinogens.
General-purpose polystyrene is a thermoplastic resin, a glossy, transparent beaded or granular solid. Density 1.04-1.09, transparency 88%-92%, refractive index 1.59-1.60. Under stress, birefringence occurs, the so-called stress-optical effect. The melting temperature of the product is 150-180¡æ, the thermal decomposition temperature is 300¡æ, the heat deformation temperature is 70-100¡æ, and the long-term use temperature is 60-80¡æ. At 5-6¡æ lower than the heat deformation temperature, after annealing, the stress can be eliminated and the heat deformation temperature can be increased. If a small amount of ¦Á-methylstyrene is added during the production process, the heat resistance grade of general-purpose polystyrene can be improved.
It is soluble in aromatic hydrocarbons, chlorinated hydrocarbons, aliphatic ketones and esters, but can only swell in acetone. It is resistant to the effects of certain mineral oils, organic acids, alkalis, salts, lower alcohols and their aqueous solutions. It has low water absorption and can still maintain its mechanical properties and dimensional stability in a humid environment. Its optical properties are second only to acrylic resins. It has excellent electrical properties, high volume resistivity and surface resistivity, and is not affected by changes in temperature and humidity, nor by corona discharge. It also has good radiation resistance. Its main disadvantages are that it is brittle and easy to crack, has low impact strength, poor heat resistance, cannot withstand boiling water, and can only be used at lower temperatures and lower loads. It has poor sunlight resistance and is flammable. It emits black smoke and a special odor when burning.
General-purpose polystyrene is made by free radical polymerization or ionic polymerization of styrene as a monomer. The production methods include bulk polymerization, solution polymerization, suspension polymerization and emulsion polymerization. The main methods used in industrial production today are suspension polymerization and bulk polymerization.
1. Bulk polymerization method: Styrene monomer is fed into a prepolymerization kettle, and then a small amount of additives and initiators are added. Prepolymerization is carried out by heating and stirring at 95-115¡ãC. After the conversion rate reaches 20%-35%, it is fed into a tower reactor with a stirrer for continuous polymerization. The polymerization temperature is gradually increased to about 170¡ãC to achieve complete conversion. A small amount of unreacted styrene is released from the top of the tower and can be recycled and reused. The polymer is continuously discharged from the bottom of the tower, and the finished product is obtained by extrusion granulation, and then shipped after packaging. The process is as follows.
2. Suspension polymerization method: Styrene is used as monomer, water is used as medium, gelatin or starch, polyvinyl alcohol, hydroxyethyl cellulose and other protective colloids or insoluble inorganic salts such as magnesium carbonate, magnesium silicate, calcium phosphate and the like are used as dispersants, maleic anhydride-styrene copolymer sodium salt is used as a dispersant, and benzoyl peroxide is used as an initiator to initiate polymerization at about 85¡ãC. It is also possible to carry out high-temperature polymerization at a high temperature of more than 100¡ãC in a high-pressure polymerization kettle without an initiator. The polymer is washed, separated and dried to obtain a colorless and transparent fine bead resin.
Polystyrene has good fluidity, good processing performance, easy coloring and good dimensional stability. It can be processed into various parts by injection molding, extrusion, blow molding, foaming, thermoforming, bonding, coating, welding, machining, printing and other methods, and is particularly suitable for injection molding.
During injection molding, the material can generally be used directly without drying. However, in order to improve the quality of the product, it can be pre-dried in a blast oven at 55-70¡ãC for 1-2 hours. The specific processing conditions are roughly: barrel temperature of about 200¡ãC, mold temperature of 60-80¡ãC, injection temperature of 170-220¡ãC, 60-150MPa, and compression ratio of 1.6-4.0. In order to eliminate internal stress, the molded product can be treated at a constant temperature of 70¡ãC in an infrared lamp or blast oven for 2-4 hours.
During extrusion molding, the screw length-to-diameter ratio L/D is generally 17-24, air cooling is used, and the extrusion temperature is 150-200¡ãC.
During blow molding, the blanks obtained by injection molding and extrusion can be blow molded to obtain the desired products. The blow molding pressure is generally 0.1-0.3MPa.
PS plastic (polystyrene)
English name: Polystyrene
Specific gravity: 1.05 g/cm3
Molding shrinkage: 0.6-0.8%
Molding temperature: 170-250¡æ
Drying conditions: ---
a. Mechanical properties: high strength, fatigue resistance, dimensional stability, small creep (little change under high temperature conditions);
b. Heat aging resistance: enhanced After UL temperature index reaches 120~140¡æ (long-term outdoor aging is also very good);
c. Solvent resistance: no stress cracking;
d. Water stability: easy to decompose in water (use with caution in high temperature and high humidity environment);
e. Electrical properties:
1. Insulation performance: excellent (it can maintain stable electrical properties even in humidity and high temperature, and is an ideal material for manufacturing electronic and electrical parts);
2. Dielectric coefficient: 3.0-3.2;
3. Arc resistance: 120s
f. Molding processability: injection molding or extrusion molding with ordinary equipment. Due to the fast crystallization speed and good fluidity, the mold temperature is also lower than that of other engineering plastic. When processing thin-walled parts, it only takes a few seconds, and for large parts, it only takes 40-60s.
a. Electronic appliances: connectors, switch parts, household appliances, accessory parts, small electric covers or (heat resistance, flame retardancy, electrical insulation, molding processability);
b. Automobiles:
1. Exterior parts: mainly corner grilles, engine heat release hole covers, etc.;
2. Internal parts: mainly mirror stays, wiper brackets and control system valves;
3. Automotive electrical parts: automotive ignition coil twisted tubes and various electrical connectors, etc.
c. Mechanical equipment: video tape recorder belt drive shaft, computer cover, mercury lamp cover, electric iron cover, baking machine parts and a large number of gears, cams, buttons, electronic watch shells, camera parts (heat-resistant and flame-retardant requirements)
According to different needs, you can choose the following adhesives:
1.G-955: single-component room temperature curing soft elastic shockproof adhesive, high and low temperature resistant, but slow bonding speed, the glue usually takes 1 day or several days to cure.
2. KD-833 instant adhesive, can quickly bond PS plastic in a few seconds or tens of seconds, but the adhesive layer is hard and brittle and cannot withstand soaking in hot water above 60 degrees.
3. QN-505, two-component adhesive, soft adhesive layer, suitable for large-area bonding or compounding of PS. But the high temperature resistance is poor.
4.QN-906: two-component adhesive, high temperature resistance.
5.G-988: Single component room temperature vulcanized adhesive, after curing, it is an elastomer with excellent waterproof and shockproof adhesive, high and low temperature resistance, 1-2mm thickness, 5-6 hours basic curing, with certain strength. It takes at least 24 hours to fully cure. Single component, no need to mix, just apply it after extrusion and let it stand, no need to heat.
6.KD-5600: UV ultraviolet curing adhesive, bonding transparent PS sheets and plates, can achieve a traceless effect, need to be cured by ultraviolet light. The effect after bonding is beautiful. But the high temperature resistance is poor.
Electrical insulation (especially high frequency insulation) is excellent, colorless and transparent, light transmittance is second only to organic glass, coloring and water resistance, good chemical stability, general strength, but brittle, prone to stress brittle cracking, not resistant to organic solvents such as benzene and gasoline. Suitable for making insulating transparent parts. Decorative parts and chemical instruments. Optical instruments and other parts.
Molding performance
¢± Amorphous material, low moisture absorption, no need for full drying, not easy to decompose, but large thermal expansion coefficient, easy to produce internal stress. Good fluidity, can be molded by screw or plunger injection molding machine.
¢² High material temperature, high mold temperature, low injection pressure, extended injection time is conducive to reducing internal stress and preventing shrinkage. Deformation.
¢³ Various forms of gates can be used, the gate is connected to the arc of the plastic part to avoid damaging the plastic part when removing the gate. The demoulding slope is large and the ejection is uniform. The wall thickness of the plastic part is uniform, preferably without inserts. If there are inserts, they should be preheated.
PS is widely used in the optical industry because it has good light transmittance. It can be used to manufacture optical glass and optical instruments, as well as transparent or brightly colored ones, such as lampshades, lighting fixtures, etc. PS can also be used to manufacture many electrical components and instruments that work in high-frequency environments. Since PS plastic is a difficult-to-inert surface material, it needs to be bonded with professional PS glue in industry.
PS alone is very brittle when used to make products, but adding a small amount of other substances, such as butadiene, to PS can significantly reduce the brittleness and improve the impact toughness. This plastic is called impact-resistant PS, and its mechanical properties are greatly improved. This plastic can be used to make many mechanical parts and components with excellent performance.
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