US20070289979A1

US20070289979A1 - Double-wall plastic produce container having ventilation holes therein, and mold for the manufacture thereof

Info

Publication number: US20070289979A1
Application number: US11/452,921
Authority: US
Inventors: Neri Jean
Original assignee: Individual
Current assignee: Individual
Priority date: 2006-06-15
Filing date: 2006-06-15
Publication date: 2007-12-20

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

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

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.
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 harvest blueberries must have ventilation holes therein to prevent deterioration of the fruits due to heat and airless confinement. The surface of these containers must be free of crevices and pin holes and must have an overall surface texture that is well adapted to be disinfected with steam or detergent and water for example.
The surface of these containers must also be sealed to prevent moisture, dust, dirt or other impurities from migrating into the plastic material, or from penetrating inside the hollow space of the double-wall structure of the container.
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.
Examples of prior art double-wall plastic articles having holes therein are shown in the following documents:
U.S. Pat. No. 3,506,154 issued to Tracy W. Barnes on Apr. 14, 1970;
U.S. Pat. No. 6,155,580 issued to Ronny Symons on Dec. 5, 2000.
Both examples illustrate common hole structures in double-wall plastic articles made by rotational molding processes. For comparison purposes, the common hole structure 20 as found in the prior art articles is illustrated in the accompanying drawings. In FIGS. 2 and 3, the hole 22 in one wall 24 is larger than the hole 26 in the other wall 28 of a double-wall article, and both holes are joined by a conical section 30. This type of hole structure makes it easy to remove a molded article from a mold, and therefore, it has been widely used in the rotational molding industry.
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. As such it is believed that a need still exists in the agricultural industry for double-wall plastic produce containers having porosity-free ventilation holes therein.

SUMMARY OF THE INVENTION

In the present invention, however, there is provided a double-wall plastic container having porosity-free hole structures therein. There is also provided a mold with hole-forming inserts therein for molding a double-wall ventilated container in a rotational molding process.
In one aspect of the container according to the present invention, each hole structure comprises a central hole surrounded by a flat solid plastic flange extending at right angle from the central hole, and 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 of the container. 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. The thickness of the flange is at least 0.75 times the thickness of one of the walls in the double-wall structure. This hole structure is advantageous as it is moldable without generating porosity around the central hole thereof.
In another aspect of the present invention, the mold for manufacturing the above-mentioned 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 metal wall.
The hole-forming inserts are made of metal and each has a metal pin extending therefrom and against the inside wall. A projecting surface on each of the hole-forming inserts extends from the outside wall toward the inside wall and defines with the inside wall a space of even thickness surrounding the pin. This projecting surface on each of the inserts makes an obtuse angle with the space of even thickness and a right angle with the pin.
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.
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.
This brief summary has been provided so that the nature of the invention may be understood quickly. A more complete understanding of the invention can be obtained by reference to the following detailed description of the preferred embodiment thereof in connection with the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

One embodiment of a double-wall container having ventilation holes therein is illustrated in the accompanying drawings, with three preferred hole structures therefor being illustrated in greater details. In these drawings the same numerals are used to identify the same elements.

FIG. 1 is an isometric view of a stackable, double-wall, plastic produce container according to a preferred embodiment of the present invention;

FIG. 2 is a perspective view of a hole structure of the prior art;

FIG. 3 is a cross-section view of the hole structure of the prior art as seen along line 3-3 in FIG. 2;

FIG. 4 is a perspective view of a first preferred hole structure;

FIG. 5 is a cross-section view of the hole structure illustrated in FIG. 4, as seen along line 5-5 in FIG. 4;

FIG. 6 is a cross-section view of a second preferred hole structure, and a cross-section view of a hole-forming insert that is used for forming this second preferred hole structure;

FIG. 7 is a cross-section view of a third preferred hole structure, and a cross-section view of a hole-forming insert that is used for forming this third preferred hole structure;

FIG. 8 is a perspective view of the hole-forming insert for forming the second preferred hole structure;

FIG. 9 is a perspective view of the hole-forming insert for forming the third preferred hole structure.

DESCRIPTION OF THE PREFERRED EMBODIMENT

While this invention is susceptible of embodiment in many different forms, there are shown in the drawings and will be described in details herein one specific embodiment of a double-wall ventilated container, with three different preferred ventilation hole structures, with the understanding that the present disclosure is to be considered as an example of the principles of the invention and is not intended to limit the invention to the embodiment and preferred hole structures illustrated and described.
For reference purposes, FIG. 1 illustrates a stackable, double-wall plastic produce container 34 with ventilation holes 36 according to one of the preferred hole structures described and illustrated herein.
Referring now to FIGS. 4 and 5, the first preferred hole structure 40 is illustrated therein. The first preferred hole structure 40 is distinguishable from the hole structure 20 of the prior art, as shown in FIGS. 2 and 3, for having a flat disc-like solid flange 42 surrounding the hole 44, and extending at a right angle from the hole 44.
The first preferred hole structure 40 has a large hole 46 in the outside wall 48 of the double-wall structure of the container, and a conical section 50 extending from the outside wall 48 to the flange 42. The hole 44 has a cylindrical shape and extends through the centre of the flange 42. In this preferred hole structure, the flange 42 is integrated with the inside wall 52 of the container and is flush with the inside wall.
Preferably, the diameter ‘A’ of the disc-like flange 42 is about three times the diameter ‘B’ of the hole 44. The flange thickness ‘C’ is preferably equal to or larger than about 0.75 times the wall thickness ‘T’ of one of the walls 48, 52 in the double-wall structure of the container 34.
Preferably, the flange 42 is flush with the inside wall 52 of the container, as mentioned above, but can also be positioned at an intermediate distance between both walls, with two conical sections 50 extending respectively to each wall 48, 52.
Referring now to FIGS. 6-9, the hole-forming inserts 56, 58 for forming two of the preferred hole structures will be explained. In the first hole-forming insert 56, as illustrated in FIGS. 6 and 8, the insert comprises a cup-like member 60 which is adapted to be mounted in an opening 62 through the outside wall 64 of a mold. The cup-like member 60 is preferably welded to the outside wall 64 of the mold, as illustrated, but can also be mounted to the mold with fasteners.
The cup-like member 60 has a threaded hole 66 through its centre. A threaded plug 68 is mounted into the threaded hole 66 and is adjustable relative to the cup-like member 60. A locknut 70 on the threaded plug 68 is used to retain the plug 68 at a desired position relative to the cup-like member 60.
The threaded plug 68 has a hollow core 72. A spring 74 is mounted in the hollow core, and a metal pin 76 is slidably mounted in the hollow core below the spring. In a blueberry container, the metal pin 76 could have a diameter of ¼ inch for example. A head 78 on the pin 76 holds the spring captive against the bottom end of the hollow core 72. In use, the spring 74 pushes the pin 76 against the inside wall 80 of the mold, as illustrated in FIGS. 6 and 7.
It should be understood that the side walls 64, 80 of the mold are made of metal. The hole-forming inserts 56, 58 are also made of metal and are mounted to absorb heat from both side walls 64, 80.
The rate of the spring 74 is selected, and the initial compression of the spring may be adjusted by turning the threaded plug 68 and the locknut 70, to ensure that there is a good contact between the end of the metal pin 76 and the inside wall 80 of the mold when the mold in closed, such that there is good heat transfer coefficient between the inside wall 80 of the mold and the pin 76.
The hole-forming insert 56 is used for forming a ventilation hole that is enclosed by a spherical depression 82, as may be understood from the illustration in FIGS. 6 and 8. The second hole-forming insert 58 has a bar-like, trapezoidal body 90, as illustrated in FIGS. 7 and 9. This second hole-forming insert 58 can be used to form ventilation holes inside a reinforcing rib on a container, such as the rib 92 illustrated in FIG. 1.
It will also be appreciated that the hole-forming insert 56 can also be modified so that the cup-like member has a conical shape. The hole formed with it would have a same cross-section as in the illustration in FIG. 7, and an appearance as illustrated in FIGS. 4 and 5. It will also be appreciated that the spherical cup-like member 60 can also be replaced by a cylindrical shaped member (not shown) to obtain substantially the same advantageous results as those mentioned herein.
For reference purposes the conical section 50 and the spherical section 82 are also referred to herein as the spacer means because these elements are used for retaining both walls of the double-wall construction at a proper distance from each other around a hole 44.
Referring again to FIG. 7, it will be appreciated that the angles of the plastic walls around the third preferred hole structure, at ‘D’, ‘E’, ‘F’ and ‘G’ are obtuse angles or right angles. The same obtuse and right angles can be found in the first and second preferred hole structures as illustrated in FIGS. 5 and 6. The relatively large angles along the preferred hole structures are believe to be a contributing factor for preventing the formation of porosity in the plastic material during the molding process. A good heat transfer between the inside wall 80 of the mold and the pin 76 is also another important contributing factor for preventing the formation of porosity in the preferred hole structures.
While three hole structures for preventing the formation of porosity in the plastic material of a double-wall container, have been illustrated in the accompanying drawings and described herein above, it will be appreciated by those skilled in the art that various modifications, alternate constructions and equivalents may be employed without departing from the spirit and scope of the invention. Therefore, the above description and the illustrations should not be construed as limiting the scope of the invention, which is defined by the appended claims.

Claims

1. A double-wall plastic container having a double-wall structure comprising a first and second spaced-apart walls, and ventilation holes therein;

each of said ventilation holes having a hole structure comprising a central hole surrounded by a flange made of solid plastic, and spacer means connecting said flange to said first wall, wherein segments of said spacer means connected to said flange and to said first wall define angles of 90° or more.

2. The double-wall plastic container as claimed in claim 1, wherein said flange extends perpendicularly from said central hole.

3. The double-wall plastic container as claimed in claim 2, wherein said central hole has a diameter and said flat flange has a width of about three times said diameter.

4. The double-wall plastic container as claimed in claim 3, wherein said first and second walls have a similar wall thickness and said flange has a flange thickness of at least 0.75 times said wall thickness.

5. The double-wall plastic container as claimed in claim 4, wherein said flange extends along and flush with said second wall.

6. The double-wall plastic container as claimed in claim 1, wherein said spacer means has a conical shape.

7. The double-wall plastic container as claimed in claim 1, wherein said spacer means has a spherical shape.

8. The double-wall plastic container as claimed in claim 1, further having ribs therein, and one of said ventilation holes is located in one of said ribs, and said spacer means define sides of said rib.

9. A double-wall plastic container having a double-wall structure comprising a first and second spaced-apart walls, and ventilation holes therein;

each of said ventilation holes having a hole structure comprising a central hole surrounded by a flange made of solid plastic and extending along and flush with said first wall at a right angle from an axis of said central hole, said flange having a width of about three times a diameter of said central hole; and

spacer means connecting said flange to said second wall, wherein segments of said spacer means connected to said flange and to said second wall define obtuse angles.

10. The double-wall plastic container as claimed in claim 9, wherein said first and second walls have a similar wall thickness and said flange has a flange thickness of at least 0.75 times said wall thickness.

11. The double-wall plastic container as claimed in claim 9, wherein said flange has a disc-like shape.

12. A mold for molding a ventilated, double-wall container by a rotational molding process;

said mold comprising spaced-apart inside and outside walls;

an opening is said outside wall;

a hole-forming insert mounted in said opening;

said hole-forming insert having a pin extending therefrom and against said inside wall, and a projecting surface extending toward said inside wall and defining with said inside wall a space of even thickness surrounding said pin.

13. The mold as claimed in claim 12, wherein said space of even thickness extends perpendicularly from said pin.

14. The mold as claimed in claim 12, wherein said hole-forming insert comprises a compression spring mounted therein against an end of said pin for pushing said pin against said inside wall.

15. The mold as claimed in claim 13, wherein said projecting surface has a spherical shape, a conical shape or a cylindrical shape.

16. The mold as claimed in claim 14, wherein said hole-forming insert comprises a threaded hollow plug adjustably mounted therein and said pin and said spring are mounted inside said threaded hollow plug.

17. The mold as claimed in claim 12, wherein said projecting surface makes obtuse angles with said outside wall and with said space of even thickness.

18. The mold as claimed in claim 12, wherein said hole-forming insert comprises a bar-like trapezoidal body defining said projecting surface.

19. The mold as claimed in claim 13, wherein said space of even thickness has a width of about three times a diameter of said pin.

20. The mold as claimed in claim 13, wherein said space of even thickness has a disc-like shape.