Injection molding is the most efficient production method for large-scale preparation of various UHMWPE wear-resistant profiles. Compared with ordinary plastics, UHMWPE injection molding has the following difficulties: the resin is difficult to feed and plasticize; The melt has large viscosity and is easy to clog. Injection mold filling is difficult to compact; The product is easy to deform when cooled.
Japanese Mitsui Petrochemical Company realized the injection molding and commercialization of UHMWPE in the 1970s. Its injection molding technology is actually a combination of plunger injection and compression molding, which has the defects of poor plastization, slow heat transfer and long molding cycle. Later, the reciprocating screw injection molding technology was developed, and the reciprocating screw was used to shear and stretch the melt, which solved the problem of poor plasticization. In the 1980s, Beijing Plastics Research Institute improved the reciprocating screw to use high pressure and high speed injection technology to complete UHMWPE injection molding, but due to the low clamping force of domestic injection molding machine and backward operating system, the stability of injection molding products is poor. In addition, plunger push injection machine, multi-plunger injection machine and plunger stamping injection machine are used for UHMWPE injection molding, but there are some shortcomings such as poor plasticizing effect, long molding cycle and small melt amount.
In recent years, some enterprises have used reciprocating screw injection molding machines to carry out injection molding production of flow-modified UHMWPE, but so far, injection molding technology has not been applied in the field of UHMWPE on a large scale.
The modification of injection grade resin mainly focuses on improving fluidity, including polymerization modification and blending modification. Such as the use of new catalytic, polymerization process to prepare bimodal polyethylene, oleoresin containing solvent, resin containing lubricant modifier; In addition, the processing properties of UHMWPE materials are improved by blending with components that can improve the matrix fluidity.
HDPE and UHMWPE have good compatibility. UHMWPE/HDPE blending is a convenient and effective method for UHMWPE flow modification. The nanoparticle makes the composite material have the characteristics of organic, inorganic and nanomaterial. By introducing the nanoparticle in situ polymerization, the injection-grade composite material with uniform dispersion can be prepared. The development of a new type of resin with narrow molecular weight distribution, long chain branched structure and low entanglement by using a new catalytic polymerization technology such as single active center can solve the contradiction between machining properties and mechanical properties, and is also a promising research direction.
Improving the fluidity of the resin can avoid problems such as melting glue and injection difficulties, and the filling mode should also solve the problems such as the structure of the product is not tight and the shrinkage is serious. The combination of fluidity modification and injection molding process and equipment can finally form a stable and excellent injection molding product with comprehensive performance.