Highly efficient kneading of extruders
Generally, synthetic resin compounds, prepared by mixing great quantities (for example, equivalent to a resin) of extenders such as gypsum or calcium carbonate in thermoplastic resin such as polyethylene, or polypropyrene are incombustible or produce less noxious gas even when these compounds burn and therefore the compounds are widely used as various types of molded products, packing materials and architechtural materials. Furthermore, the resin can be saved by using the materials in this type of composition and the demands for these synthetic resin compounds will increase in the future.
In case of producing the pellets of synthetic resin compounds which are thus greatly extended, the thermoplastic resin and extenders should be kneaded while being melted and the mixture should be homogenized.If the kneading efficiency of the twin screw extruder is low, great quantities of extender cannot be added, the compound cannot be homogenized and the producing speed becomes slow.The principal object of the present invention is to provide an extruder capable of highly efficient kneading of the resin compounds, in view of the problems described above.This principal object can be applied to the cases other than production of extended resin compounds.
That is, it is applied to production of a compounded resin by mixing a plurality of different kinds of resin materials and production of bonding agents and paints by blending the resin and specific materials.With respect to the bonding agents, since the conventional solvent-type, emulsion-type or water-soluble bonding agents provides its adhering force to objective materials through evaporation of single screw extruderand drying and solidifying of the bonding agent, the industrial use of this type of the bonding agent is confronted with various problems such as the necessity of large-capacity drying equipment, deterioration of the productivity and environmental pollution and danger of fire due to production of a great volume of solvent vapor when the solvent type bonding agent is dried.
Instead of using bonding agents with the accompanying various problems, the hot-melt type bonding agents have recently been developed and their use is spreading.This hot-melt type bonding agent is a solid bonding material containing no water or solvent and readily becomes a low-viscosity fluid when it is heated.When this hot-melt type bonding agent is used, it is melted to a fluid by heating and applied to objective materials, and the materials are instantaneously bonded after spontaneous cooling.Accordingly, the hot-melt type bonding agent requires a shorter time for the bonding work than other bonding agents for which the drying equipment is required, and this bonding agent is economical because the drying equipment is unnecessary and therefore provides high productivity and does not produce a solvent vapor as in case of a solvent type bonding agent. Thus it is forecast that the demands for the sheet production extruder will increase more and more in the future.The blending of materials for the hot-melt type bonding agent can be varied in accordance with the applications. Generally it contains the base polymer (for example, EVA, polyethylene with low molecular weight, APP, polyisobutylene, styrenebutadiene, etc.) as the principal component, viscous resin (for example, rosin, terpene resins, petrochemical resins, cumarone, indene resins, etc.), various waxes and stabilizing agent.