Double-wall plastic produce container having ventilation holes therein, and mold for the manufacture thereof

Abstract

In this ventilated double-wall plastic container, each hole structure has a central hole surrounded by a solid flange extending along the inside wall of the double-wall structure. The hole structure also has a spacer portion connecting the solid flange to the outside wall of the double-wall structure. The wall segments of the hole structure between the spacer portion and the flange and between the spacer portion and the outside wall of the container define angles that are either obtuse angles or right angles. In another aspect, the mold for manufacturing the double-wall container has spaced-apart inside and outside metal walls, a plurality of openings in the outside metal wall, and hole-forming inserts mounted in the openings and projecting toward the inside wall. A projecting surface on each of the hole-forming inserts defines with the inside wall a space of even thickness surrounding a pin at the centre of the insert.

Description

FIELD OF THE INVENTION[0001]This invention pertains to double-wall produce containers having ventilation holes therein, and more particularly it pertains to double-wall plastic produce containers having porosity-free hole structures therein. This invention also pertains to molds having hole-forming inserts therein for manufacturing ventilated double-wall plastic containers using a rotational molding process.BACKGROUND OF THE INVENTION[0002]Fruits and vegetables are commonly harvested in plastic containers that are stacked on a harvesting machine and transported to a storage facility. These containers are generally made with a double-wall structure for increased sturdiness, to better resist stacking and handling stresses. These double-wall plastic containers are generally manufactured using rotational molding processes.[0003]Fruits such as blueberries are harvested at the end of the summer when ambient temperatures are relatively high. Therefore, the containers that are used to harve...

AI Technical Summary

Benefits of technology

[0013]When a container is formed therein, the hole-forming insert, the pin and the space of even thickness define a region inside the mold that is surrounded by hot metal and wherein plastic pellets or plastic powder can easily penetrate and be evenly melted, for preventing the occurrence of porosity in the molten plastic around the hole.

[0014]In yet another aspect of the present invention, each hole-forming insert has a spring mounted therein and this spring acts against the metal pin for pushing the pin against the inside wall of the mold. The force of the spring ensures a good contact between the pin and the inside wall of the mold, and a better heat transfer coefficient between the metal pin and the inside wall of the mold.

Problems solved by technology

It has always been a challenge in the rotational molding industry to form ventilation holes in a double-wall plastic container without causing porosity to occur around these holes.

It has also been found that it is very difficult to eliminate porosity from this type of hole structure, and especially from the region identified by the detail circle 32 in FIG. 3.

For this reason, this type of hole structure has been found unsuitable for application in a double-wall plastic container that is used for carrying blueberries for example.

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