[Basic characteristics] High-density polyethylene is an opaque white wax-like material with a specific gravity lighter than water and a specific gravity of 0.941~0.960. It is soft and tough, but slightly harder than LDPE, and slightly stretchable, non-toxic and tasteless.
[Combustion characteristics] It is flammable and can continue to burn after leaving the fire. The upper end of the flame is yellow and the lower end is blue. It will melt when burning, with liquid dripping and no black smoke. At the same time, it emits the smell of paraffin wax.
[Main advantages] Acid and alkali resistance, organic solvent resistance, excellent electrical insulation, and still maintain a certain degree of toughness at low temperatures. Surface hardness, tensile strength, rigidity and other mechanical strength are higher than LDPE, close to PP, tougher than PP, but the surface finish is not as good as PP.
[Main Disadvantages] Poor mechanical properties, poor air permeability, easy deformation, easy aging, easy to be brittle, less brittle than PP, easy to stress cracking, low surface hardness, easy to scratch. It is difficult to print. When printing, surface discharge treatment is required, no electroplating, and the surface is dull.
[Applications] Used for extruding packaging films, ropes, woven bags, fishing nets, water pipes; injection molding low-grade daily necessities and shells, non-load-bearing components, plastic boxes, turnover boxes; extrusion blow molding containers, hollow products, bottles.
[Injection molding process] HDPE has countless applications, ranging from reusable thin-walled beverage cups to 5-gsl cans, which consume 1/5 of domestic HDPE. Injection molding grades generally have a melt index of 5-10. There are grades with toughness and lower fluidity and higher fluidity grades with processability. Uses include daily necessities and food thin-walled packaging; tough, durable food and paint cans; high resistance to environmental stress cracking applications, such as small engine fuel tanks and 90-gal garbage cans.
Generally, the melting point of HDPE is 142°C, and the decomposition temperature is 300°C; the adjustable range of injection temperature is relatively large. When injection molding, the general use temperature is 180℃-230℃; because it is olefin plastic, it does not absorb water, so it does not need to be dried during production, but for product quality, it can be dried at 60℃ for 1hr to discharge floating water; polyethylene The melt viscosity is high, the flow length ratio is small, and thin-walled products may lack glue. Therefore, the gate and runner are relatively large; the product is easy to be charged with static electricity, and the surface is easy to attract. The shrinkage rate is 16‰, and the overflow value is 0.05mm.