EVA plastics, resins have good flexibility, rubber-like elasticity, can still have good flexibility at -50 °C, good transparency and surface gloss, good chemical stability, good anti-aging and ozone resistance No toxicity. Good blending with filler, good coloring and molding processability. Its use is also very wide. Under normal circumstances, EVA with vinyl acetate content below 5%, its main products are films, wire and cable, LDPE modifiers, adhesives, etc.; EVA products with vinyl acetate content of 5% to 10%. It is an elastic film; EVA with a vinyl acetate content of 20-28% is mainly used for hot-melt adhesives and coated products; vinyl acetate content is 5%-45%; the main products are films (including agricultural films) and films. Materials, injection molding, molded products, foam products, hot melt adhesives, etc. Such as:
(1) Films, sheets, and laminates: Sealed, adhesive, flexible, tough, and tight, suitable for elastic packaging film, heat shrinkable film, agricultural film, food packaging film, laminated film, can be used For the middle layer of polyolefin laminated film.
(2) General supplies: It has the advantages of flexibility, resistance to environmental stress cracking, and good weather resistance. It is suitable for industrial materials such as electric wire insulation bags, household appliance accessories, and window sealing materials.
(3) Daily groceries include sporting goods, toys, seat cushions, drawstrings, sealed container covers, EVA rubber football, etc.
(4) Automobile accessories include shock absorbers, fenders, and interior and exterior trim accessories.
(5) Foaming products: foamed foamed plastic slippers, sandals, building materials, etc. Injection foam has a variety of industrial components, female soles, hot melt adhesives and so on.
Ethylene-vinyl acetate copolymer molding process
EVA can be injection molded, extruded, blown, calendered, rotomolded vacuum thermoformed, foamed, coated, heat sealed, welded, and molded.
Ethylene-vinyl acetate copolymer (EVA)
The EVA resin is an ethylene-vinyl acetate copolymer and generally has a vinyl acetate (VA) content of 5% to 40%. Compared with polyethylene, EVA is widely used in foaming shoes because of the introduction of vinyl acetate monomer in the molecular chain, which reduces high crystallinity, improves flexibility, impact resistance, filler compatibility, and heat-sealing properties. Materials, functional shed films, packaging films, hot melt adhesives, wire and cable, and toys.
The use of EVA resin
EVA resin is an ethylene-vinyl acetate copolymer, generally 5% to 40% vinyl acetate (VA) content. Compared with polyethylene, EVA is widely used in foaming shoes because of the introduction of vinyl acetate monomer in the molecular chain, which reduces high crystallinity, improves flexibility, impact resistance, filler compatibility, and heat-sealing properties. Materials, functional shed films, packaging films, hot melt adhesives, wire and cable, and toys. In general, the performance of EVA resin is mainly determined by the content of vinyl acetate in the molecular chain. In 2001, the market consumption of EVA resin in China was approximately 290 kt. With the development of China's footwear industry and the increase in the use of functional film, China's demand for EVA resin will increase year by year.
(1) Foam Shoes The shoe material is the most important application field of EVA resin in China. In the EVA resin used in shoe materials, the vinyl acetate content is generally 15% to 22%. EVA resin blended foam products are widely used in the soles and interior materials of mid-to-high-end travel shoes, hiking shoes, slippers, and sandals because of their softness, good elasticity, and chemical resistance. In addition, this material is also used in the field of acoustic panels, gymnastics mats and sealing materials. China's Guangdong Shunde, Zhongshan, Jinjiang, Quanzhou, and Wenzhou, Zhejiang are the major production bases of China's footwear industry, and consume a large amount of EVA resin products each year. In 1999, China's foaming shoe materials and shock absorption areas consumed about 150 kt of EVA resin.
(2) Thin Film
The main purpose of EVA film is to produce functional film. The functional shed film has high weather resistance, anti-fog drop and heat preservation performance. Since polyethylene does not have polarity, even if a certain amount of anti-fog drops is added, its anti-fog performance can only be maintained for about 2 months; The film made of a certain amount of EVA resin added not only has a high light transmittance, but also has a great improvement in anti-droplet performance, which can generally exceed 4 months. In addition, EVA can also be used to produce packaging films, medical films, laminated films, casting films, and the like.
In 1999, there were more than 50 companies that used EVA resin to process films in China. In 1999, a total of 800 kt of greenhouse films were produced in China, including 220 kt of functional shed films and about 30 kt of EVA resin. Together with packaging films and medical films, China consumed a total of 37 kt of EVA resin in the film industry.
(3) Wire and Cable With the continuous development of computers and network engineering, people are increasingly using halogen-free flame-retardant cables and silane cross-linked cables for the consideration of the safety of computer rooms. Because EVA resin has good filler inclusion compatibility, it is used in halogen-free flame-retardant cables, semi-conductor shielded cables and two-step silane cross-linked cables. In addition, EVA resin is also used to make some special cable jacket. EVA resin used in wire and cable, vinyl acetate content is generally 12% to 24%. In 1999, the wire and cable industry consumed about 6 000 tons of EVA.
(4) Toys
EVA resin also has many applications in toys, such as child wheels, seat cushions and so on. In recent years, China's toy processing industry has developed rapidly. Production is mostly concentrated in the coastal areas of Dongguan, Shenzhen, Shantou and other places, mainly based on exports and external processing. According to the analysis, these manufacturers consume about 5 000 tons of EVA resin each year, and the use of grades is basically the same as that of shoe materials.
(5) Hot-melt adhesives EVA resin as the main component of the hot melt adhesive, because it does not contain solvents, does not pollute the environment and high security, very suitable for automated assembly line production, it is widely used in books wireless binding, furniture sealing Edge, automotive and home appliance assembly, footwear, carpet coatings and metal anti-corrosion coatings.
Hot melt adhesives mainly use vinyl acetate content of 25% to 40%. Although there are products of this grade in China, they have not been scheduled for production for a long time, and therefore they are all occupied by imported materials. In 1999, China's hot melt adhesive sector was estimated to consume 17 kt of EVA resin.
(6) Others
EVA resin is also widely used in inks, bags, bottle covers, etc. It is estimated that these aspects consume EVA resin no less than 15 kt.
BAKELITE
Polycondensation products of phenols and aldehydes are commonly referred to as phenolic resins, and generally refer to synthetic resins obtained by the polycondensation reaction of phenol and formaldehyde. It is the earliest synthesis of a class of thermosetting resins.
Although phenolic resin is the oldest type of thermosetting resin, due to its easy availability of raw materials, convenient synthesis, and phenolic resin has good mechanical strength and heat resistance, especially with outstanding instantaneous high temperature ablation resistance, and the resin itself There is room for extensive modification, so phenolic resins are still widely used in the manufacture of composite materials such as glass fiber reinforced plastics and carbon fiber reinforced plastics. Phenolic resin composites, in particular in the aerospace industry (spacecraft, rockets, missiles, etc.) have very important uses as structural materials for transient high temperature and ablation.
The synthesis and curing process of the phenolic resin completely follows the law of body-type polycondensation reaction. Controlling different synthesis conditions (such as the ratio of phenols and aldehydes, the type of catalyst used, etc.), two different types of phenolic resins can be obtained: a class called thermosetting phenolic resin, which is a methylolase with further reaction The resin of the group, if the synthetic melon is not controlled, will cause the body type polycondensation reaction to proceed until an infusible and insoluble cured resin having a three-direction network structure is formed. Therefore, this type of resin is also called a first-order resin; It is called a thermoplastic phenolic resin. It is a linear resin. It will not form a three-way network structure during the synthesis process. In the further curing process, a curing agent must be added. This type of resin is also called a second-order resin. The principle of synthesis and curing of these two types of resins is not the same, and the molecular structure of the resins is also different.
The purpose of modification of the modified phenolic resin phenolic resin is mainly to improve its brittleness or other physical properties, improve its adhesion to the fiber-reinforced material and improve the molding process conditions of the composite material.