PET plastic is the abbreviation of polyethylene terephthalate, abbreviated to pet or PETP. Polyterephthalate plastics, mainly including polyethylene terephthalate pet and polybutylene terephthalate PBT. Polyethylene terephthalate is also known as polyester resin. It is a condensation polymer of terephthalic acid and ethylene glycol, together with PBT, collectively known as thermoplastic polyester, or saturated polyester.
The molecular structure of pet plastics is highly symmetrical, and it has a certain ability of crystal orientation, so it has high film-forming and forming properties. Pet has good optical properties and good weather resistance.
In addition, pet plastics have excellent wear resistance, friction, dimensional stability and electrical insulation. PET bottles are widely used because of their high strength, good transparency, non-toxic, impermeable, light weight and high production efficiency. The molecular chain structure of PBT is similar to that of pet, and most of its properties are the same. However, the main chain of PBT is changed from two methylene groups to four, so the molecules are more flexible and the processability is better.
Pet is an opalescent or light yellow highly crystalline polymer with smooth and glossy surface. It has good creep resistance, fatigue resistance, friction resistance, low wear and high hardness, and has the largest toughness in thermoplastic plastics; it has good electrical insulation performance, little influence by temperature, but poor corona resistance. Non toxic, weather resistant, chemical resistant, good stability, high moisture absorption, drying before molding is necessary. It is resistant to weak acids and organic solvents, but not to hot water immersion and alkali.
PET resin has high glass transition temperature, slow crystallization rate, long molding cycle, large molding shrinkage, poor dimensional stability, brittle molding and low heat resistance.
With the improvement of nucleating agent, crystallizer and glass fiber, pet has the following characteristics besides PBT
1. The hot deformation temperature and long-term service temperature are the highest among the general engineering thermoplastics;
2. Because of its high heat resistance, the Reinforced PET can be immersed in 250 ℃ solder bath for 10s, which can hardly deform or change color, so it is especially suitable for the preparation of electronic and electrical parts for tin soldering;
3. The bending strength is 200MPa, the elastic modulus is 4000mpa, the creep and fatigue resistance are also very good, the surface hardness is high, and the mechanical properties are similar to those of thermosetting plastics;
4. Because the price of ethylene glycol used in PET production is almost half as much as that of butanediol used in PBT production, the price of PET resin and Reinforced PET are the lowest among engineering plastics, and have high cost performance ratio.
5. Bonding of PET resin: sili-1706 one component room temperature vulcanizate is an elastomer after curing. It has excellent waterproof and shockproof adhesive. It can resist high and low temperature. Because of the research on molecular structure of resin, sili-1706 is specially used to bond engineering plastics.
Glass fiber reinforced pet is suitable for the electronic, electrical and automotive industries. It is used in various coil frameworks, transformers, TV sets, recorder parts and shells, automobile lamp holders, lampshades, white heat lamp holders, relays, selenium rectifiers, etc. At present, the consumption ratio of PET engineering plastics in several application fields is: Electrical and electronic 26%, automobile 22%, machinery 19%, appliances 10%, consumer goods 10%, others 13%. At present, the total consumption of PET engineering plastics is still small, accounting for only 1.6% of the total pet.
1. Film materials: all kinds of food, medicine, non-toxic and aseptic packaging materials; high-grade packaging materials for textiles, precision instruments and electrical components; substrates for recording tapes, video tapes, film films, computer floppy disks, metal coating and photosensitive films; electronic and mechanical fields such as electrical insulating materials, capacitor films, flexible printed circuit boards and membrane switches.
2. Application of packaging bottle: its application has developed from the original carbonated beverage to beer bottle, edible oil bottle, condiment bottle, medicine bottle, cosmetic bottle, etc.
3. Electronic and electrical appliances: manufacturing connector, coil winding tube, integrated circuit shell, capacitor shell, transformer shell, TV accessories, tuner, switch, timer shell, automatic fuse, motor bracket and relay, etc.
4. Automobile accessories: such as switchboard cover, ignition coil, various valves, exhaust parts, distributor cover, metering instrument cover, small motor cover, etc., and can also use pet's excellent coating property, surface gloss and rigidity to make automobile external parts.
5. Mechanical equipment: manufacturing gear, cam, pump housing, belt pulley, motor frame and watch parts, also used as microwave oven, baking tray, various ceiling, outdoor billboard and model, etc. .
6. The molding process of pet plastics can be injection molding, extrusion, blow molding, coating, bonding, machining, electroplating, vacuum metal plating and printing.
the way to distinguish
1. First smell the smell. The smell of pet is different from that of ordinary plastics. If you burn it with a lighter, you will smell a very fragrant and comfortable smell (burn a bottle at random). If there are other ingredients in pet, the taste will be very pungent. Some bottles containing SEBS cannot be used.
2. If the burning part is too black or the oil drops quickly, most melting points are abnormal, which is often found in PET film.
3. Wire drawing: when burning, pull the wire on the lighter to see whether it is long or not, and then break the drawn wire to see if the broken point in the middle is rolled into a small circle. The more the coil is, the higher the melting point is.
But generally, if it is a bottle piece, there should be no big problem. The most important point is to distinguish whether it contains PVC, which is the fatal injury of pet. First, take more samples, and then spread them in sunny places. PVC is light blue in the sun. If you fold in half, there will be a white crease. The above is the naked eye identification, the accuracy is limited, mainly depends on experience.
There is a more practical and better way, buy an oven, adjust the temperature to 250 degrees and bake there for half an hour. If the goods contain PVC, there will be a lot of yellow spots on the surface; if the melting point is not enough, it will melt quickly.
In fact, there are many kinds of pet to be made, such as pet crushing film from foreign factories, pulp block material, roll film with length less than 30 cm, which have different customer groups.
For the identification of these goods, oven inspection is strongly required. In particular, pet reels are very scarce in the whole market. The price of films with a length of 80-120 cm and a thickness of 3-5 wires is very high (white and transparent).