GB1575701A - Plastics containers - Google Patents

Description

(54) PLASTICS CONTAINERS (71) We, BLOPAK LIMITED, a British Company of 30 Union Street, Birmingham, do hereby declare the invention for which we pray that a patent may be granted to us and the method by which it is to be performed to be particularly described in and by the following statement: This invention relates to plastics containers of polygonal shape particularly, though not exclusively, for the packaging of foodstuffs for storing in refrigerators or deep freezers.

Such containers are usually injection moulded from thermoplastics materials. It is characteristic of thermoplastics that as they solidify they shrink. In moulding the shrinkage in planes transverse to the axis of the injection nozzle is greater than in planes extending longitudinally of that axis. In the case of thermoplastics, such as high density polythene and polypropylene, which are suitable for use at low temperatures, the difference in shrinkage is especially pronounced, the shrinkage in the transverse planes being about twice as great as the shrinkage in the longitudinal planes.Because of the shrinkage differential one finds that in known containers moulded from thermo-plastics material for use in refrigerators or deep freezers, there is often some bellying of those walls of the container which as are they are formed in the mould extend in directions longitudinal, or generally longitudinal, to the axis of the injection nozzle, even though the walls may be intended to be straight. For convenience walls of a container which extend in the aforesaid directions are hereinafter referred to as "longitudinal walls".

The bellying of the longitudinal walls makes the containers difficult to stack and nest for storage whilst they are empty.

Furthermore during production and filling of the containers the bellying of the longitudinal walls makes handling of the containers by means of mechånìcal hå tling equipment difficult.

It is an object of the present invention to rovide a moulded thermoplastics container in which bellying of its longitudinal walls due to shrinkage is avoided or at least considerably reduced.

The present invention consists in an injection moulded container of thermoplastics material being of polygonal shape having longitudinal walls as hereinbefore defined comprising plain portions of substantially uniform thickness laterally spaced by thicker portions which extend longitudinally of the longitudinal walls and increase in thickness across their widths, away from the plain portions and are wider than their greatest thickness, and the longitudinal walls being joined by corners which are thicker than the plain portions.

The difference in the thickness of material across the longitudinal walls (that is transverse to the direction of the axis of the injection nozzle in the molding of the container) provided by the plain and thicker portions, results in controlled differential solidifying of the longitudinal walls during the moulding process. As they are the thinnest parts of the longitudinal walls the plain portions solidify first. They then tend to resist shrinkage of the thicker portions and the corners as those parts solidify subsequently. The result is a tensioning of the longitudinal walls which counteracts the shrinkage stresses in the plastics material in planes transverse to the axis of the injection nozzle and prevents or reduces bellying of the longitudinal walls.Thus the provision of the plain and thicker portions enables substantially straight longitudinal walls to be provided in the container.

The plain and thicker portions may extend parallel to the longitudinal axis of the longitudinal walls. In such an arrangement each longitudinal wall of the container may, for example, have two plain portions, one adjacent to each of the corners joining the wall to an adjacent longitudinal wall, and just the one thicker portion between the plain portions.

The plain and thicker portions may alternatively extend obliquely in the longitudinal direction of the longitudinal walls. In the oblique arrangement the portions may all slant in the same way, or some of the thicker portions may slant one way and others another way so that a zig-zag or criss-cross pattern of the thicker portions results with the plain portions between and separated by them.

The thickness of the thicker portions may increase continuously across their widths away from the plain portions. Alternatively the thickness may be increased in stages.

Conveniently the latter is achieved by forming the thicker portions with a series of ribs which extend side-by-side longitudinally of the longitudinal walls, the ribs successively increasing in thickness across their widths, away from the plain portions. The widths of the ribs may increase as their thickness increases. The ribs may have convexly rounded surfaces. The radii of curvature of the rounded surfaces may be the same for all the ribs. The ribs have the advantageous effect of breaking up the flow of the plastics material during the mounding of the counter. In addition the ribs are beneficial when the container is adapted to nest with another similar container because the depressions between the ribs provide channels along which air can escape from the lastmentioned container as the container is inserted into it and thereby allow the containers to fit snugly together.They also facilitate separation of nested containers.

The increasing thickness of the thicker portions may be accommodated at the outer or inner surfaces of the longitudinal walls.

The plain and thicker portions may extend for only part of the lengths of the longitudinal walls. It is desirable however in general that they should extend for at least half the lengths of the walls. Parts of the longitudinal walls longitudinally beyond the plain and thicker portions are preferably of a thickness intermediate the thicknesses of the plain portions and the thickest parts of the thicker portions.

An embodiment of a container in accord ance with the invention will now be de scribed by way of example with reference to the accompanying drawings in which, Figures 1 and 2 are plan and side views respectively of the container, Figure 3 is a section on line 3-3 of Figure 1, Figure 4 is an enlarged fragmentary sec tion on line 4-4 of Figure 3, and Figure 5 is a fragmentary view showing a modification.

The container is intended for the packaging of foodstuffs which may be frozen. It is injection moulded from a high density polythene.

As shown, the container is substantially square in plan with rounded corners. It has a base wall 1, side walls 2 which are slightly inclined outwardly away from the base wall, and a continuous, outwardly turned over, rim 3 with which a lid, not shown, sealingly engages in known manner. The base wall 1 has an inset circular central portion 4 but is otherwise flat. In the moulding of the container the plastics material is injected into the mould from the injection nozzle at the centre of the central portion 4 of the base wall.The side walls 2, which constitute longitudinal walls of the container, are each divided in height into three bands, being a shallow bottom band 5 adjacent the base wall, a substantially deeper middle band 6 which is stepped outwardly from the bottom band, and a top band 7 which is stepped outwardly by a similar extent from the middle hand and is of a depth intermediate that of the other two bands. Corresponding bands of the side walls merge with one another. The depth of the middle band 6 of each side wall is equal to approximately half the height of the wall. In a container which is deeper than the container shown in the drawings the middle bands would be deeper in relation to the heights of the side walls.

The middle band 6 of each side wall has a plain portion 8 near each end which is rectangular and extends for the height of the band. Between the two plain portions 8 there is a thicker portion 9 formed with vertical ribs 10. The ribs have convexly rounded surfaces which all have the same radius of curvature. The ribs are all substantially wider than their greatest thickness and they successively increase in thickness and width laterally away from the plain portions 8, as best seen in Figure 4. Thus the thickest part of the thicker portion 9 is half way between the plain portions. That part is approximately 60% thicker than the plan portions. Between the ribs the thickness of the thicker portion reduces to the thickness of the plain portions. In a typical example the plain portions are 0.025" thick, the greatest thickness of the ribs immediately next to the plain portions is 0.028" and from those ribs the greatest thickness of the succeeding ribs increases by 0.004" increments to a maximum of 0.040" for the ribs at the middle of the thicker portion. The changes in thickness of the middle bands are all accommodated at the outside surfaces of the bands so that their inside surfaces are plain, as are the inside surfaces of the bottom and top bands.

The top and bottom bands of the side walls, the base wall 1 and the corners of the container between the side walls 2 and between the side walls and the base wall are all thicker than the plan portions 8 but not thicker than the thickest parts of the thicker portions 9. In the typical example mentioned above the top bands are 0.035" thick, the bottom bands are 0.030" thick, as are the corners joining the side walls to the base wall, the base wal increases from 0.030" thick at those corners to 0.040" thick at the central portion 4, and the corners between the four side walls are 0.040" thick.

Instead of the plain portions and thicker portions extending vertically they may extend obliquely to the vertical. In the modification of Figure 5 the middle band of each side wall of the container has a plurality of plain portions 8 separated by a plurality of thicker portions 9 which are in two series, the one series slanting one way and the other series slanting another way and intersecting the first series. The thicker portions are in the form of ribs having convexly rounded surfaces and they project from the inside surface of the middle band. Accordingly the outside surface of the middle band in this instance is plain.

WHAT WE CLAIM IS: 1. An injection moulded container of thermoplastics material being of polygonal shape having longitudinal walls as hereinbefore defined comprising plain portions of substantially uniform thickness laterally spaced by thicker portions which extend longitudinally of the longitudinal walls, increase in thickness across their widths away from the plain portions and are wider than their greatest thickness, and the longitudinal walls being joined by corners which are thicker than the plain portions.

2. A container according to Claim 1 wherein the thickness of the thicker portions increases continuously across their widths away from the plain portions.

3. A container according to Claim 1 wherein the thickness of the thicker portions increases in stages across their widths away from the plain portions.

4. A container according to Claim 3 wherein the thicker portions are each formed with a series of ribs which extend side-by-side longitudinally of the longitudinal walls and successively increase in thickness across their width away from the plain portions.

5. A container according to Claim 4 wherein the ribs successively increase in widths away from the plain portions.

6. A container according to Claim 4 or Claim 5 wherein the ribs have convexly rounded surfaces.

7. A container according to Claim 6 wherein the rounded surfaces of the ribs all have the same radius of curvature.

8. A container according to any preceding claim wherein the plain and thicker portions extend parallel to the longitudinal axis of the longitudinal walls.

9. A container according to Claim 8 wherein each longitudinal wall has two plain portions, one adjacent to each of the corners joining the wall to the adjacent longitudinal walls, and just one thicker portion between the plain portions.

10. A container according to any of Claims 1 to 7 wherein the plain and thicker portions extend obliquely longitudinally of the longitudinal walls.

11. A container according to Claim 10 wherein some of the thicker portions slant one way and others slant another way so that there is a zig-zag or criss-cross pattern of the thicker portions with the plain portions between and separated by them.

12. A container according to any preceding claim wherein the plain and thicker portions extend for part only of the lengths of the longitudinal walls.

13. A container according to Claim 12 wherein the plain and thicker portions extend for at least half the lengths of the longitudinal walls.

14. A container according to Claim 12 or Claim 13 wherein parts of the longitudinal walls longitudinally beyond the plain and thicker portions are of a thickness intermediate the thickness of the plain portions and the thickest parts of the thicker portions.

15. A container according to any preceding claim wherein a bottom wall is joined to the longitudinal walls by corners which are thicker than the plain portions.

16. A container substantially as described herein with reference to and as illustrated by Figures 1 to 4 of the accompanying drawings.

17. A container substantialy as described herein with reference to and as illustrated by Figures 1 to 4 as modified by Figure 5 of the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (17)

**WARNING** start of CLMS field may overlap end of DESC **. walls, the base wall 1 and the corners of the container between the side walls 2 and between the side walls and the base wall are all thicker than the plan portions 8 but not thicker than the thickest parts of the thicker portions 9. In the typical example mentioned above the top bands are 0.035" thick, the bottom bands are 0.030" thick, as are the corners joining the side walls to the base wall, the base wal increases from 0.030" thick at those corners to 0.040" thick at the central portion 4, and the corners between the four side walls are 0.040" thick. Instead of the plain portions and thicker portions extending vertically they may extend obliquely to the vertical. In the modification of Figure 5 the middle band of each side wall of the container has a plurality of plain portions 8 separated by a plurality of thicker portions 9 which are in two series, the one series slanting one way and the other series slanting another way and intersecting the first series. The thicker portions are in the form of ribs having convexly rounded surfaces and they project from the inside surface of the middle band. Accordingly the outside surface of the middle band in this instance is plain. WHAT WE CLAIM IS:

1. An injection moulded container of thermoplastics material being of polygonal shape having longitudinal walls as hereinbefore defined comprising plain portions of substantially uniform thickness laterally spaced by thicker portions which extend longitudinally of the longitudinal walls, increase in thickness across their widths away from the plain portions and are wider than their greatest thickness, and the longitudinal walls being joined by corners which are thicker than the plain portions.

2. A container according to Claim 1 wherein the thickness of the thicker portions increases continuously across their widths away from the plain portions.

3. A container according to Claim 1 wherein the thickness of the thicker portions increases in stages across their widths away from the plain portions.

4. A container according to Claim 3 wherein the thicker portions are each formed with a series of ribs which extend side-by-side longitudinally of the longitudinal walls and successively increase in thickness across their width away from the plain portions.

5. A container according to Claim 4 wherein the ribs successively increase in widths away from the plain portions.

6. A container according to Claim 4 or Claim 5 wherein the ribs have convexly rounded surfaces.

7. A container according to Claim 6 wherein the rounded surfaces of the ribs all have the same radius of curvature.

8. A container according to any preceding claim wherein the plain and thicker portions extend parallel to the longitudinal axis of the longitudinal walls.

9. A container according to Claim 8 wherein each longitudinal wall has two plain portions, one adjacent to each of the corners joining the wall to the adjacent longitudinal walls, and just one thicker portion between the plain portions.

10. A container according to any of Claims 1 to 7 wherein the plain and thicker portions extend obliquely longitudinally of the longitudinal walls.

11. A container according to Claim 10 wherein some of the thicker portions slant one way and others slant another way so that there is a zig-zag or criss-cross pattern of the thicker portions with the plain portions between and separated by them.

12. A container according to any preceding claim wherein the plain and thicker portions extend for part only of the lengths of the longitudinal walls.

13. A container according to Claim 12 wherein the plain and thicker portions extend for at least half the lengths of the longitudinal walls.

14. A container according to Claim 12 or Claim 13 wherein parts of the longitudinal walls longitudinally beyond the plain and thicker portions are of a thickness intermediate the thickness of the plain portions and the thickest parts of the thicker portions.

15. A container according to any preceding claim wherein a bottom wall is joined to the longitudinal walls by corners which are thicker than the plain portions.

16. A container substantially as described herein with reference to and as illustrated by Figures 1 to 4 of the accompanying drawings.

17. A container substantialy as described herein with reference to and as illustrated by Figures 1 to 4 as modified by Figure 5 of the accompanying drawings.