CHANGLONGXING SCIENCE & TECHNOLOGY (SHENZHEN) CO.,LTD
1.LLDPE
1.1 Application of LLDPE
LLDPE is suitable to be used for the production of film, molding, pipe, wire and cable, bags, hollow products, drinking water pipes, daily use transparent containers, composite wire, and etc.
1.2 Property of LLDPE
Chemical and Physical Properties
LLDPE is a kind of copolymer produced by Ethylene and a small number of high alpha olefins(Such as Butene-1,Hexene-1,Octenes-1,4-methyl-1-pentene,and etc.) after the process of high or low pressure polymerization with the function of Catalyzer.The density is 0.915 ~ 0.940 g / cm3. However, according to the D-1248-84 ASTM, the LLDPE with density 0.926 ~ 0.940 g /cm3 is in the range of density for polyethylene (MDPE). The new generation of LLDPE increased its density range to the plastic body (0.890 ~ 0.915 g /cm3 ) and elastomer (<0.890 g /cm3). But the United States Plastics Industry Association (SPI) and the United States plastics industry committee (APC) only expanded the scope of LLDPE to plastic body but not elastomers.
Advantage of LLDPE
Better low temperature toughness, low temperature impact resistance, environmental stress cracking resistance, puncture resistance, etc.
MLDPE, a new type of LLDPE, enjoys a better mechanical properties, puncture resistance, and environmental stress cracking resistance and flexibility.
Disadvantage of LLDPE
Poor optical performance;performance ranges greatly when the density, molecular weight and the molecular weight distribution are ranging.
Processing: Good process forming ability. LLDPE for extrusion blow molding enjoys wide molecular weight distribution,low melt flow rate (1g/10min);LLDPE for injection molding enjoys narrow molecular weight distribution, higher melt flow rate (more than 2g/10min) and high gloss product.
Usage :It could be used for blow molding barrel liner and also suitable for producing large parts of blow molding, such as the isolation shed for road traffic. And also,it is widely used to produce blow molded container with other olefin resin to improve the performance of the hollow article.
2. LDPE
2.1 Application of LDPE
LDPE is always used to produce the bowl, cabinet, pipe couplings, daily necessities, food packaging, food containers, bags, plumbing pipes, wires and etc.
2.2 Property of LDPE
Chemical and physical properties
The density of LDPE material for commercial use is 0.91~0.94 g/cm3. LDPE could be penetrated by gas and water vapor.LDPE high coefficient of thermal expansion is not suitable for long-term use of products.
If the density of LDPE is 0.91~0.925g/cm3 , then its shrinkage rate is 2%~5%; if the density is 0.926~0.94g/cm3,then its shrinkage rate is1.5%~4%. But the current actual shrinkage rate still depends on the parameter of injection molding.LDPE can resist various kinds of solvents at room temperature, but will expand in aromatic hydrocarbon and chlorinated hydrocarbon solvents.Like HDPE, LDPE is prone to get into the trouble of environmental stress cracking
2.3 Injection Molding Processing Conditions of LDPE
Dry: No need generally Melting temperature: 180~280℃
Mold temperature: 20~40℃ to achieve a uniform cooling and more economical heating.It is recommended that the diameter of cooling cavity should be at least 8mm. And the distance from the cooling cavity to the surface of the mold should not be larger than the 1.5 times diameter of the cooling chamber.
Injection pressure: maximum to 1500bar.
Holding pressure: maximum to 750bar.
Injection speed: Fast injection speed is recommended.
Runner and gate: Various types of runners and gates are available. LDPE is particularly suitable to be used in hot runner molds.
Typical use: bowl, cabinet, pipe couplings, daily necessities.
3.HDPE
3.1 Application of HDPE
HDPE is always used to produce caps, food storage containers, automotive fuel tanks, electrical and duct boxes, safety caps, coaxial cable insulation, daily-used transparent containers, wires, tubing, and etc.
3.2 Property of HDPE
Chemical and physical properties
The high crystallinity of HDPE leads to its high density, high tensile strength, high distortion temperature, high viscosity and high chemical stability.
HDPE enjoys stronger anti-permeability than LDPE while the strength of anti-impact is comparatively lower. The characteristics of PH-HD are mainly controlled by the density and weight distribution of molecular. The molecular weight distribution of HDPE for injection mold is very narrow. The HDPE is classified into three types according to the different density.For the density of 0.91~0.925g/cm3, we call it the first type HDPE; for the density of 0.926~0.94g/cm3 , we call it the second type HDPE; for the density of 0.94~0.965g/cm3 , we call it the third type HDPE.
HDPE is prone to get into the trouble of environmental stress cracking but it can be relieved by using a material with very low flow characteristic which reduces the internal stress. HDPE tend to be very easy to dissolve in hydrocarbon solvents when the temperature is higher than 60℃ its solubility is better than that of LDPE.
3.3 Injection Molding Processing Conditions of HDPE
Drying: if stored properly, then no need to dry.
Melting temperature: 220~260℃. For larger molecules,200~250℃ is recommended.
Mold temperature: 50~95℃. Wall thickness of plastic parts below 6mm requires higher mold temperature,more than 6mmrequires lower mold temperature. The cooling temperature of plastic parts should be uniform in order to reduce the difference of shrinkage rate. Within the optimal machining cycle time, the diameter of cooling channel should be not less than 8mm, and the distance to mold surface should be within 1.3d (Here "d" refers to the diameter of the cooling cavity).
Injection pressure: 700~1050bar.
Injection speed: High speed injection is recommended.
Runner and gate: The diameter of the runner is between 4 and 7.5mm, the length of the runner should be as short as possible. Various types of gate is available while the gate length should be no more than 0.75mm. It is particularly suitable to be used in hot runner molds.
Typical usage: refrigerator containers, storage containers, household utensils, sealing cover, etc.
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