Method of and apparatus for molding multi-layer polymer plastic articles having inner, outer and interior or core layers, with control of relative volumetric flow rates of the inner and outer layers enabling relative shifting of the position of the core layer and control of the relative thickness of the inner and outer layers in the molded articles

Abstract

A novel technique for molding multi-layer polymer plastic articles having inner, outer and interior or core layers by controlling relative volumetric flow rates of the inner and outer layers to enable relative shifting of the position of the core, and also the relative thickness of the inner and outer layers in the molded articles; and with leading, and, where desired, trailing ends of the interior layer flow into the mold cavity substantially positioned on the zero gradient of the velocity profile of the flowing polymer streams.

Description

FIELD[0001] The present invention relates to the co-extrusion of pluralities of flowing polymer plastic streams through nozzle extruders and the like into injection molding and similar apparatus for forming multi-layer plastic articles in which an interior core is encased by inner and outer layers of the article; and, more particularly, to the control of relative volumetric flow rates of the layers for attaining greater flexibility in the properties and relative thickness and positions of the layers in the ultimate article. More specifically, the invention is especially, though not exclusively, useful with co-extrusion processes of the type described in my earlier U.S. Pat. No. 5,914,138, issued Jun. 22, 1999 For Apparatus For Throttle-Valving Control For The Co-Extrusion Of Plastic Materials As Interior Core Streams Encased By Outer And Inner Streams For Molding And The Like.BACKGROUND OF INVENTION[0002] A common problem in multilayer molding is the maintaining of a uniform penetra...

AI Technical Summary

Benefits of technology

This approach enables the production of multi-layer plastic articles with controlled core layer positioning and thickness, reducing molding cycle times and preventing delamination, while enhancing barrier and scavenger layer performance by optimizing the relative humidity and thickness of layers.

Problems solved by technology

A common problem in multilayer molding is the maintaining of a uniform penetration of the leading edge of the interior core layer, when that layer is not near the zero gradient of the velocity profile of the flowing polymer stream as it flows through a hot runner nozzle and / or into the mold cavity forming the molded article.

This problem of maintaining uniform penetration of the leading edge of the interior core layer when it is not close to the zero gradient of the velocity profile becomes particularly severe when there is the requirement to form the multilayer article with the core layer not centered on the midplane of the article.

In three-material, four-layer preform molding, this leading edge problem also occurs, particularly when the volumetric flow rate of one of the interior core layers is greater than that of the other interior core layer.

Another common current problem also arises in using post-consumer recycled plastic (PCR) in a molded article that consists of layers of two other polymers.

With such 5-layer technology, however, the molding cycle times are significantly longer than if the article had been molded of only one material.

Such 5-layer molded articles, moreover, suffer delamination of the layers if the second polymer has low adhesion to the virgin skin layers and to the central PCR layer.

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