Release time：2021-11-19
General purpose plastics refer to those mainly used for mass production of a large number of industrial products, such as films, pipes, shoes, pots, barrels, packaging, etc.
There are three kinds of PE commonly used, namely LDPE, HDPE and LLDPE. The monomers of the three kinds of polyethylene are the same, but the process conditions used to synthesize these polyethylene are different. Therefore, three different polyethylene varieties have been produced, and the properties of these three materials are very different.
LDPE
Abbreviation: LDPE
Commonly known as: flower material or barrel material
Scientific name: low density polyethylene / high pressure polyethylene
English Name: lowdensity polyethlene
Polyethylene natural color is a translucent white waxy material, which is lighter than water, soft, tough, slightly malleable, non-toxic and tasteless.
Combustion characteristics: flammable. It can continue to burn after leaving the fire. The upper end of the flame is yellow and the lower end is blue. When burning, it will melt, there will be liquid dripping, no black smoke, and it will emit the smell of burning paraffin.
Advantages: acid and alkali resistance, organic solvent resistance, good electrical insulation, and certain toughness at low temperature.
Disadvantages: poor mechanical properties, poor air permeability, easy deformation, easy aging, easy brittleness, easy stress cracking, low surface hardness, easy scratching. It is difficult to print. Surface discharge treatment is required during printing. The surface cannot be electroplated and the surface is Matt.
Usage: used for extruding packaging film, film and hose;
Used for injection molding of low-grade daily necessities and shells;
Used for extruding blow molding containers.
Injection molding performance
Low molecular weight polyethylene, melting point 120 ℃, very similar to paraffin; Generally speaking, the melting point of polyethylene is 140 ℃, and the decomposition temperature is 300 ℃. The injection temperature can be adjusted in a wide range, which is commonly used for the refueling washing machine of other raw materials. During injection molding, the general operating temperature is 170 ℃ -220 ℃; As it is an olefin plastic, it does not absorb water, so it does not need to be dried during production, but for the sake of product quality, it can be dried at 60 ℃ for 1 hour to discharge floating water; Polyethylene melt has high viscosity and small flow length ratio, and thin-walled products may lack glue, so the gate and runner are relatively large; The product is easy to carry static electricity, and the surface is easy to absorb dust. The shrinkage rate is 16 ‰; The overflow value is 0.05 mm.
HDPE
Abbreviation: HDPE
Commonly known as: hard soft glue
Scientific name: high density polyethylene / low pressure polyethylene
English Name: highdensity polyethlene
HDPE natural color is an opaque white waxy material, which is lighter than water, soft and tough, but slightly harder than LDPE, and slightly malleable, non-toxic and tasteless.
Combustion characteristics: flammable. It can continue to burn after leaving the fire. The upper end of the flame is yellow and the lower end is blue. When burning, it will melt, with liquid dripping, no black smoke, and the smell of burning paraffin.
Advantages: acid and alkali resistance, organic solvent resistance, good electrical insulation, and certain toughness at low temperature. The surface hardness, tensile strength, rigidity and other mechanical strength are higher than LDPE, close to PP, and tougher than PP, but the surface finish is not as good as PP.
Disadvantages: poor mechanical properties, poor air permeability, easy deformation, easy aging, easy brittleness, brittleness lower than PP, easy stress cracking, low surface hardness, easy scratching. It is difficult to print. Surface discharge treatment is required during printing. The surface cannot be electroplated and the surface is Matt.
Usage: used for extruding and packaging films, ropes, woven bags, fishing nets, water pipes.
It is used for injection molding of low-grade daily necessities, shells, plastic boxes and turnover boxes.
Used for extruding blow molded containers, hollow products and bottles.
Injection molding performance
The melting point of HDPE is generally 142 ℃, and the decomposition temperature is 300 ℃; The injection temperature can be adjusted in a wide range. During injection molding, the general operating temperature is 180 ℃ -230 ℃; As it is an olefin plastic, it does not absorb water, so it does not need to be dried in production, but for the sake of product quality, it can be dried at 60 ℃ for 1 hour to discharge floating water.
Polyethylene melt has high viscosity and small flow length ratio, and thin-walled products may lack glue, so the gate and runner are relatively large; The product is easy to carry static electricity, and the surface is easy to absorb dust. The shrinkage rate is 16 ‰; The overflow value is 0.05 mm.
LLDPE
Abbreviation: LLDPE
Scientific name: linear low density polyethylene / low pressure low density polyethylene
The natural color of linear high-density polyethylene is an opaque white waxy material, which is lighter than water, soft and tough, but slightly harder than LDPE, slightly malleable, non-toxic and tasteless.
Combustion characteristics: flammable. It can continue to burn after leaving the fire. The upper end of the flame is yellow and the lower end is blue. When burning, it will melt, with liquid dripping, no black smoke, and the smell of burning paraffin.
The difference between LDPE, HDPE and LLDPE: the difference between LDPE and HDPE is mainly the difference in density, which leads to the difference in mechanical properties, one is rigid, the other is flexible. The main difference between LLDPE and them is that there are many branched chains in the molecular structure of LLDPE, so this material is both flexible and rigid.
Advantages: acid and alkali resistance, organic solvent resistance, good electrical insulation, and certain toughness at low temperature. The surface hardness, tensile strength, rigidity and other mechanical strength are higher than LDPE, but lower than HDPE.
LLDPE has the best puncture resistance and tear resistance, and is especially suitable for producing films thinner than LDPE but with high strength.
Disadvantages: poor mechanical properties, poor air permeability, easy deformation, easy aging, easy brittleness, brittleness lower than PP, easy stress cracking, low surface hardness, easy scratching. Difficult to print, printing requires surface discharge treatment, no electroplating, and the surface is Matt.
Usage: used for extruding packaging film, tape and cable; The film produced is also called pseudo paper film;
Used for injection molding of low-grade daily necessities and shells;
Used for extruding blow molded containers, hollow products and bottles.
Injection molding performance
The melting point of LLDPE is generally 170 ℃, and the decomposition temperature is 300 ℃. The injection temperature can be adjusted in a wide range. During injection molding, the general operating temperature is 200 ℃ -260 ℃; It has high apparent viscosity and poor fluidity, so it is difficult to inject LLDPE alone. Therefore, it is necessary to increase the power of the injection molding machine or add other low molecular weight plastics to increase its fluidity; Because it is an olefin plastic, it does not absorb water and does not need to be dried during production. However, for the sake of product quality, it can be dried at 60 ℃ for 1 hour to discharge floating water.
The melt viscosity of linear low-density polyethylene is high, the flow length ratio is small, and the fluidity is lower than LDPE and HDPE. Thin walled products may lack glue, so the gate and runner are relatively large; The product is easy to carry static electricity, and the surface is easy to absorb dust. The shrinkage rate is 16 ‰; The overflow value is 0.05 mm.
