Polyphenylene ether (PPO) is also one of the five tigers of general engineering plastics. It has the advantages of high rigidity, high heat resistance, non-combustibility, high strength and excellent electrical properties. The dielectric constant and dielectric loss of PPO is one of the smallest in engineering plastics and is almost unaffected by temperature and humidity.
Commonly used is the 2,6-dimethylphenol synthesis of polyphenylene ether, has excellent overall performance, the most important feature is under long-term load, has excellent dimensional stability and outstanding electrical insulation, the use of a wide range of temperature, can be in -127 ~ 121 ℃ range of long-term use. It has outstanding resistance to water and steam, and the products have high tensile strength, impact strength and creep resistance. In addition, there are good wear resistance and electrical properties.
I Processing of PPO
PPO processing to injection molding, extrusion, molding, but also foam, blowing plastic, glass fiber reinforced, electroplating, vacuum coating, printing, machining and fusion welding. ppo reusable, generally reused 3 times, its performance is not significantly reduced. ppo melt fluidity is poor, processing and molding difficulties, most of the practical applications for modified ppo.
The following is an introduction to the PPO injection moulding process.
1. PPO baking material
PPO is a non-crystalline polymer, water absorption is very low, but the moisture will make the product surface defects such as silver, bubbles, for this reason, the raw material can be placed in the oven 80 ~ 1OO ℃, dry 1-2h after use.
2. The choice of injection molding machine
For PPO melt should be used screw injection molding machine, nozzle using straight-through type is good, the aperture is 3-6mm. the main flow of the mold should use a larger taper or use the pull material hook, the sprue to short thick is good.
3. Injection temperature
The injection temperature of PPO is 270-290°C. The molding temperature of PPO is 280-330°C and the molding temperature of modified PPO is 260-285°C. The melt temperature of PPO is 270-290°C.
PPO has a very high heat resistance, thermal decomposition temperature up to 350 ℃, no obvious thermal degradation phenomenon within 300 ℃. Usually, the barrel temperature is controlled at 260-290℃, and the nozzle temperature is about 10℃ lower than the barrel temperature.
Due to the high viscosity of the PPO melt, a higher mould temperature should be used when injection moulding. Usually, the mould temperature is controlled at 100~150℃. When the mould temperature is lower than 100℃, thin-walled plastic parts are easy to be filled with insufficient and delamination; while higher than 150℃, bubbles, silver wire, warpage and other defects are easy to appear.
4. Injection pressure
PPO melt viscosity, in the injection molding, it is appropriate to take high pressure, high-speed injection, holding pressure and cooling time can not be too long. Increase the injection pressure, the melt is conducive to filling the mold, the general injection pressure control in 100-140MPa, holding pressure control in 40-80MPa. according to the specific circumstances to make adjustments.
5. Injection speed
Products with long runners need to be injected quickly, but in this case ensure that the film has sufficient aeration.
II Blending modification of PPO
The performance of polyphenylene ether is very good, but poor solvent resistance, products are prone to stress cracking, low notch impact strength, expensive raw materials, the Achilles heel is its melt viscosity is very large, poor fluidity, and softening temperature of 300 ℃ or more, and 330 ℃ high temperature processing and easy to degradation, resulting in processing molding difficulties and energy consumption is too large. In order to overcome these shortcomings and give PPO new properties, it has been modified in a variety of ways.
1.PPO and PS blend modification
PPO and PS are amorphous polymers with good compatibility. By blending into PS, processing costs can be reduced and the processability of PPO can be greatly improved, but the heat resistance is slightly reduced. This is the first generation of polyphenylene ether alloy, so that PPO has been widely used, in order to improve the performance of this type of alloy, people have been doing various improvements to it.
2.PPO and PA blend modification
The blending of the two not only improves the processing performance and solvent resistance of PPO, but also improves the heat resistance and dimensional stability of PA, thus achieving complementary advantages. However, the compatibility of the two is very poor, belonging to a completely incompatible system, and the phase separation of the co-blended gold is serious, resulting in a brittle alloy. Researchers have done a lot of research in the capacitance, toughening and strengthening of PPO/PA alloys, and have achieved many research results and made PPO/PA alloys widely used.
3. Blending modification of PPO and PBT
The blending of the two worthy materials effectively solves the problem of large water absorption of PPO/PA alloy. The toughness and strength of the PPO/PBT alloy cannot meet the requirements of various uses, similar to the PPO/PA blended system, which also needs to be toughened and strengthened.
4.PPO and PPS blending modification
In recent years, in some electronic and electrical components of the surface assembly process, steam welding and VPS method using solder is becoming mainstream, so the resin used is also required to resist high temperatures above 260 ℃, while the glass transition temperature of pure PPO is only about 210 ℃, can not meet such high heat-resistant requirements, so the development of high heat-resistant PPO / PPS alloy. But the two also need to increase the capacity of the treatment.
5. PPO and PTFE blend modification
The two blended materials, both PPO heat resistance, mechanical properties, dimensional stability and PTFE wear resistance, lubrication performance, water absorption is small, high precision products performance. It can meet the comprehensive performance requirements of physical properties and bearing properties close to metal structural parts.
5. PPO and SBS blend modification
PPO and SBS have good compatibility, PPO/SBS alloy improves the deflection and impact performance of PPO, with low water absorption, good toughness, high heat deflection temperature and high dimensional accuracy, mainly used in the electrical industry and automotive industry and other fields.
III Applications of PPO
1. Electrical and electronics
The electrical and electronic industry is widely used in the manufacture of connectors, coil winding spools, mechanical component shields, switches and relays, tuning equipment, large electronic displays, variable capacitors, battery accessories, microphones and other components.
2. Automotive industry
Suitable for instrument panel parts, window frames, shock absorbers, pump filters, radiator grilles, speaker grilles, consoles, fuse boxes, relay boxes, connectors, wheel covers, etc.
3. Household appliances
Used for TV sets, computers, cameras, video cassettes, tape recorders, air conditioners, heaters, rice cookers and other parts. For copiers, computer systems, printers, fax machines and other external parts and components.
4. Industrial machinery
Suitable for making heat-resistant parts, insulating parts, wear-resistant parts, transmission parts; making higher temperature gears, fan blades, valves and other parts, can replace the use of stainless steel; can also be made of screws, fasteners and connecting parts.