Plastic container having reinforcing depressions

A lightweight plastics bottle (1) having a body wall of substantially constant wall thickness and having a plurality of depressed zones (7) having a floor portion (12) spaced inwardly of and parallel to the general plane of the body wall. The depressed zones (12) are arranged in a series of horizontal rows characterised in that the body is non-cylindrical having a number of body panels and that each of said depressed zones (12) has at least one long dimension (9) lying in a direction which is not parallel to the longitudinal axis (10) of the bottle.

This invention relates to thin wall plastics containers such as lightweight 
plastics bottles having a wall thickness of between about 0.2 mm and 0.6 
mm. 
Plastics bottles can be blow-moulded to have thin side walls but clearly 
the stiffness of the side walls of the bottle is thereby reduced. There is 
a risk that the filled bottles will bulge or sag when stored, particularly 
in warm temperatures and problems can also arise on the filling lines if 
there is any kind of interruption to the passage of the bottles 
therethrough and a row of bottles becomes pushed together in a queue 
compressing the bottles at the head of the queue. If the bottles are to be 
enclosed in e.g. a plastics stretch film sleeve, the bottle must also 
resist any compression forces exerted by the sleeve significantly 
distorting the bottle, and finally the bottle must be sufficiently rigid 
for the user to be able to comfortably handle the bottle without 
compressing it unduly, particularly after the bottle has been opened since 
any compression of a filled bottle can readily lead to accidental 
discharge of some of the contents. 
It has been previously proposed in DE-A-1432253 to provide a one-trip 
plastics bottle having a substantially constant wall thickness and a body 
portion at least a part of which is provided with a plurality of depressed 
zones arranged in a series of horizontal rows. As illustrated in this 
disclosure the depressed zones are of diamond shape having a long 
dimension disposed vertically with the depressed zones in each row being 
vertically aligned and meeting one another. Bulging of the side walls is 
not a problem since the body is cylindrical. The orientation of the 
diamond shape depressed zones with their long dimensions vertical is in 
the direction to improve compression or top load strength of the bottle 
but as shown horizontal lines of weakness exist in the planes passing 
through the points where the depressed zones of one horizontal row 
approach the depressed zones of adjacent rows. 
According to the present invention there is provided a lightweight plastics 
bottle having a body wall of substantially constant wall thickness and 
having a plurality of depressed zones having a floor portion spaced 
inwardly of and parallel to the general plane of the body wall, said 
depressed zones being arranged in a series of horizontal rows 
characterised in that the body is non-cylindrical having a number of body 
panels and that each of said depressed zones has at least one long 
dimension lying in a direction which is not parallel to the longitudinal 
axis of the bottle. The stiffness of the body panels is increased 
primarily about axes which lie at right angles to the long dimensions of 
the depressed zones. 
Preferably the depressed zones have at least one long dimension lying 
normal to the longitudal axis of the bottle so that the stiffness of the 
body panels about a vertical axis, i.e. to provide bulge resistance, is at 
least as great as the stiffness of the body panels about a horizontal 
axis, i.e. in the direction which contributes to the top load strength of 
the bottle. 
The side walls of the depressed zones which connect the floor portion 
thereof to the body wall are preferably inclined to the plane of the body 
wall. 
The depressed zones can be arranged as discrete zones separated from each 
other by areas in the general plane of the body wall, alternate rows of 
depressed zones being arranged in alternate columns, the distance between 
alternate rows and alternate columns being less than the maximum dimension 
of the depressed zones in the direction of the spacing of the rows and 
columns respectively. 
In an alternative arrangement the depressed zones of each row are arranged 
in vertically aligned columns, the depressed zones having a shape to 
adjoin adjacent depressed zones in each row and column with the inclined 
side edges meeting at junctions in a plane other than the plane of the 
floor portion or the plane of the wall and the junctions of each column 
and row being separated from one another by body portions in one of said 
floor or wall planes. 
Secondary depressions can be formed at the junctions between at least some 
of the depressed zones, said secondary depressions having floor portions 
spaced inwardly of the floor portions of the depressed zones and having 
inclined edges merging with the inclined edges of the depressed zones and 
connecting with the body wall. This ensures that the stiffness of the body 
about axes passing through the secondary depression is maximised. 
The depressed zones can be of any convenient shape such as round, oval or 
polygonal but when the depressed zones of each row are arranged in 
vertical columns the depressed zones preferably have a polygonal shape 
such that the corners of the polygons meet one another. 
The floor portions of the depressed zones are preferably spaced from the 
plane of the body wall by between one and eight times the thickness of the 
wall. The wall thickness is preferably between 0.2 mm and 0.5 mm, the long 
dimension of the depressed zone being between 3 mm and 8 mm. The depressed 
zones should not be too deep in relation to their size since stresses may 
be formed in the material in the blow-moulding process. Small and deep 
depressed zones are also likely to lead to undue thinning of the material 
in the blow-moulding.

Referring to FIG. 1 there is shown a lightweight plastics bottle 1 having 
four side walls 2. The top of the bottle has a neck closed by a closure 
cap 3, the neck being connected to the side walls by a shoulder 4. 
As seen from above the side walls 2 are joined by radiused corners 5 and to 
provide rigidity to these corners arcuate grooves 6 are formed at 
intervals therein. 
To stiffen the side walls 2 and minimise bulging i.e. minimising any 
tendency of the bottle to tend towards a circular cross-section, each of 
the side walls is provided with a series of depressed spacing zones 7 
spaced from one another by similarly shaped zones 8 lying in the normal 
plane of the side wall 2. 
As shown more clearly in the enlarged perspective view of FIG. 2 the 
depressed zones 7 have a rhombus shape with the long dimensions 9 
extending at right angles to the vertical axis 10 of the bottle. The edges 
11 of the depressed zones are inclined outwardly from a floor portion 12 
and are joined with the floor portions and the normal plane of the side 
wall by a small radii 13. 
The depressed zones of each horizontal row are arranged in vertically 
aligned columns. 
The polygonal form of the depressed zones is such that the inclined edges 
of the depressed zone meets with the edges of adjacent depressed zones in 
adjacent columns and rows. More particularly, because of the radii 13 the 
intersections are formed at a plane intermediate the planes of the floor 
portions and the normal plane of the side wall. Thus the normal plane of 
the side wall between adjacent spacing zones 8 is curved downwardly at 14 
and the floor portions curve upwardly at 15 at the intersections. It is 
thereby ensured that there are no continuous straight lines extending 
across the side wall in any direction which are not interrupted by a 
change in the plane of the material. The depressed zones thus provide a 
stiffening of the side wall in all directions. 
Because the long dimension 9 of the depressions is normal to the 
longitudinal axis 10 of the bottle the stiffening effect of the series of 
depressed zones 7 is more effective to stiffen the body wall against 
bending about the direction of the axis 10 than against bending about axes 
in the direction of the long dimension 9. The depressed zones are 
therefore particularly effective in stiffening the body wall against bulge 
tending to cause the cross-sectional shape of the bottle to become 
circular. 
In order to further strengthen the body panel at the junctions between the 
spacing zones 8 secondary depressions 16 can be provided at this location 
as shown in FIGS. 3 to 6. These secondary depressions 16 have floor 
portions 17 which as seen in FIG. 5 are spaced inwardly of the floor 
portion 12 of the depressed zones. The depressions have inclined edges 18 
which merge with the spacing zones 8 and the inclined edges 11 of the 
depressed zones with small radii 13. 
It will be understood that these depressions 16 are particularly effective 
in stiffening the side wall against bending along planes 19--19, i.e. in 
resisting bulging by bending along these planes. 
The depressions 16 can however lead to a reduction of the stiffening effect 
of the depressed zones against bending in the horizontal planes passing 
through the depressions in a single row. As shown in FIG. 6 the 
depressions 16 are therefore not provided in rows aligned with the 
recesses 6 in the corners of the bottle since the presence of the recesses 
6 aligned with the depressions 16 can lead to undue reduction in the top 
load strength of the bottle. 
Referring now to FIG. 7, there is shown as alternative arrangement of 
depressed zones 7 in which the depressed zones are again arranged in 
horizontal rows but in which depressed zones in alternate rows are 
arranged in alternate columns with the distance between alternate rows and 
alternate columns being less than the maximum dimensions of the depressed 
zones in the direction of the spacing of the rows and columns 
respectively. 
As shown in FIG. 7 the depressed zones are each a square, arranged to have 
a long dimension 9 aligned with the longitudinal axis 10 of the bottle and 
an identical long dimension 9 at right angles thereto. The spacing between 
adjacent rows is less than the dimension 9 and the spacing between 
adjacent columns is also less than the dimension 9. The depressed zones of 
adjacent rows are thus nested between one another but each of the 
depressed zones are discrete and separated from one another by areas 2 in 
the normal plane of the side wall. 
As before each depressed zone 7 has a floor portion 12 and inclined edges 
11 joining the floor portion 12 to the areas 2 of the side wall, all the 
intersections of the edges with each other and with the floor portions and 
the side wall areas 2 being formed with small radii 13. 
It will be apparent that the nesting of the rows and columns of depressed 
zones ensures that all planes of the wall in the direction of the 
longitudal axis 10 of the bottle, and all planes at right angles thereto, 
are interrupted by depressed zones which stiffen the side wall against 
bending about axes in these directions. Nevertheless it will be apparent 
that the side wall is not stiffened against bending along a line such as 
shown at 20 and 21 in FIG. 7. The side wall is nevertheless considerably 
stiffened against bulging and in respect of top loading. 
The depressed zones can be of any convenient shape and in the arrangement 
of FIG. 8 the depressed zones 7 are circular. As before the depressed 
zones have a floor portion 12 and inclined edges 11, the edges joining the 
floor portion 12 and side wall areas 2 with small radii 13. Whilst this 
arrangement considerably stiffens the side wall in respect of bulge and 
top load strength it allows bending along lines 20 and 21 as in the 
arrangement of FIG. 7. 
Bottles according to each of the embodiments described above can be made by 
blow-moulding of a plastics material such as high density polyethylene to 
have a substantially constant wall thickness in the range of 0.2 to 0.6 
mm, such bottles being generally known as lightweight bottles. Such 
bottles having flat side walls are relatively flexible and can readily be 
deformed out of their predetermined shape. By providing depressed zones as 
described the stiffness of the side walls has been found to be 
considerably increased and problems arising from bulging of the walls, or 
compression of the walls during handling of the bottles both mechanically 
and by the user have been minimised. 
The stiffening effect of the depressed zones is obviously dependant upon 
the depth of the depressed zones and it has been found that this depth 
should be between one and eight times the thickness of the wall. The depth 
of the depressed zones is also governed by the size of the depressed zones 
since otherwise the blow-moulding can lead to undue thinning of the 
plastics material. Preferably the depressed zones should have a long 
dimension of between 3 mm and 12 mm, particularly between 5 mm and 9 mm. 
Lightweight bottles according to the invention can be provided with a 
plastics film sleeve for decoration and labelling, the plastics film being 
stretched to apply to the bottle and subsequently allowed to shrink back 
to conform the bottle side walls without causing the side walls to bend 
inwards. Gaps between the plastics sleeve and the bottle side walls are 
therefore avoided.