U.S. patent application number 10/546635 was filed with the patent office on 2006-10-12 for container, method and apparatus for making the same.
Invention is credited to Charles Jonathan Britton.
Application Number | 20060226158 10/546635 |
Document ID | / |
Family ID | 9952871 |
Filed Date | 2006-10-12 |
United States Patent
Application |
20060226158 |
Kind Code |
A1 |
Britton; Charles Jonathan |
October 12, 2006 |
Container, method and apparatus for making the same
Abstract
A container (1) having a body and a rim (3) defining an opening
for the container, the container being made of a material such as
PET or PEN, is manufactured in a two-stage process. The first stage
comprises injection moulding a preform (15) which has a rim (3)
formed at its mouth and a continuous body-forming portion (32)
extending across the preform from the inner periphery (19) of the
rim, the rim having an outwardly-directed extent and including a
downwardly-extending portion (21) spaced outwardly from the inner
periphery and an outwardly-extending portion (5,6,29) located
outwardly of the downwardly extending portion. In the second stage
the preform is placed in a moulding cavity (56) of a blow moulding
apparatus (7) at an elevated temperature with the preform being
located by means of the rim (3). The body-forming portion expands
in the cavity to form the container side wall (20) and bottom wall
(2). The upper region (18) of the side wall contacts the
downwardly-extending portion (21) of the rim such as to form a box
section (25). The side wall (20) has at its upper side region a
step (23) above which the diameter of the cavity is substantially
equal to or approaches the diameter of the downwardly-extending
portion (21) of the rim. Below the step (23) the diameter is less
than the diameter of the inner periphery of the rim and tapers
therefrom inward downwardly to the bottom wall (2) at an acute
angle, whereby the containers can internest.
Inventors: |
Britton; Charles Jonathan;
(Tewkesbury, GB) |
Correspondence
Address: |
PROSKAUER ROSE LLP
ONE INTERNATIONAL PLACE 14TH FL
BOSTON
MA
02110
US
|
Family ID: |
9952871 |
Appl. No.: |
10/546635 |
Filed: |
February 12, 2004 |
PCT Filed: |
February 12, 2004 |
PCT NO: |
PCT/GB04/00549 |
371 Date: |
May 22, 2006 |
Current U.S.
Class: |
220/659 |
Current CPC
Class: |
B65D 2401/00 20200501;
B65D 2543/00555 20130101; B29B 2911/14331 20150501; B65D 2543/0062
20130101; B65D 2543/00296 20130101; B29C 51/04 20130101; B29B
2911/14026 20130101; B65D 2543/00796 20130101; B65D 2543/00509
20130101; B29B 2911/14033 20130101; B65D 2543/00537 20130101; B29B
2911/1402 20130101; B29B 2911/14335 20150501; B29B 2911/14333
20130101; B65D 43/0212 20130101; B29B 2911/14426 20130101; B29C
49/06 20130101; B65D 2543/00092 20130101; B29B 2911/1404 20130101;
B29B 2911/1442 20130101; B29B 2911/14366 20130101; B29B 2911/14337
20150501; B29B 2911/14433 20130101; B29C 45/00 20130101; B29K
2067/00 20130101; B29B 2911/14486 20130101; B65D 1/46 20130101;
B65D 21/0233 20130101; B29C 49/0073 20130101; B65D 2543/0074
20130101; B65D 2543/00472 20130101; B65D 2543/00685 20130101; B29L
2031/7132 20130101; B29L 2031/716 20130101; B65D 55/06 20130101;
B65D 2543/00731 20130101; B29B 2911/14326 20130101 |
Class at
Publication: |
220/659 |
International
Class: |
B65D 1/42 20060101
B65D001/42 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 12, 2003 |
GB |
0303174.7 |
Claims
1. A container having a body and a rim defining an opening for the
container, the container being made of a material which is
susceptible to deformation when heated, the container comprising: a
rim formed at the mouth of the container, the rim having an
outwardly-directed extent and including a downwardly-extending
portion spaced outwardly from the inner periphery and an
outwardly-extending portion located outwardly of the
downwardly-extending portion; a container side wall and bottom
wall, the upper region of the side wall contacting the
downwardly-extending portion of the rim; characterized in that: the
upper region of the side wall contacts the downwardly-extending
portion of the rim such as to form a box section; and the side wall
of the container has at its upper side region a narrowing side wall
section above which the diameter of the side wall is substantially
equal to or approaches the diameter of the downwardly-extending
portion of the rim and below which the diameter is less than the
diameter of the inner periphery of the rim and tapers therefrom
inward downwardly to the bottom wall at an acute angle, whereby
like containers can internest.
2. A container according to claim 1, in which the container
material comprises polyethylene terephthalate (PET), polyethylene
naphthalate (PEN), or a PET and PEN blend.
3. A container according to claim 1, in which the rim has an
outwardly-extending portion radially beyond the
downwardly-extending portion.
4. A container according to claim 3, in which the
outwardly-extending portion has a peripheral flange to assist in
manual grasping of the container when nested with another like
container.
5. A container according to claim 1, in which the rim has a
radially inner inverted U section, then a V shaped groove, and
finally an inverted V section.
6. A container according to claim 5, in which the
downwardly-extending portion extends downwardly from the V shaped
groove.
7. A container according to claim 1, in which said acute angle is
between 7 and 11 degrees.
8. A container according to claim 1, further including
radially-extending reinforcing ribs spaced around the periphery of
the rim of the container.
9. A container according to claim 1, in which the narrowing side
region comprises a step above which the side wall is of
substantially constant diameter.
10. A container according to claim 1, in which above the narrowing
side region the container is formed with outwardly extending
external ribs, the diameter of the container widening relatively
rapidly in the region of the external ribs to approach the diameter
of the downward extension.
11. A container according to claim 1, further comprising a lid for
the container, the lid conforming with the upper surface of the
rim.
12. A container according to claim 11, in which the lid sealingly
engages the rim of the container and comprises two sealing elements
one on the top and the other at the side of the portion of the lid
engaging the rim.
13. A container according to claim 11, including a flap at the side
of the lid to assist removal thereof.
14. A method of manufacturing a container having a body and a rim
defining an opening for the container, the container being made of
a material which is susceptible to deformation when heated, the
method comprising the steps of: injection moulding in an
injection-moulding apparatus a preform which has a rim formed at
its mouth and a continuous body-forming portion extending across
the preform from the inner periphery of the rim, the rim having an
outwardly-directed extent and including a downwardly-extending
portion spaced outwardly from the inner periphery and an
outwardly-extending portion located outwardly of the
downwardly-extending portion; placing the preform in a moulding
cavity of a pressure moulding apparatus at an elevated temperature
with the preform being located by means of the rim; and moving the
body-forming portion in the pressure moulding apparatus downwardly
and outwardly whereby the body-forming portion expands in the
cavity to form the container side and bottom walls, the upper
region of the side wall contacting the downwardly-extending portion
of the rim, and the rest of the body-forming portion contacting the
sides of the cavity to form a shape defined by the interior shape
of the cavity; characterized in that: the upper region of the side
wall contacts the downwardly-extending portion of the rim such as
to form a box section; and the interior of the moulding cavity of
the pressure moulding apparatus is shaped to define the side and
bottom walls of the container with the cavity having at its upper
side region a narrowing side wall section above which the diameter
of the cavity is substantially equal to or approaches the diameter
of the downwardly-extending portion of the rim and below which the
diameter is less than the diameter of the inner periphery of the
rim and tapers therefrom inward downwardly to the bottom wall at an
acute angle, whereby the resultant containers can internest.
15. A method according to claim 14, in which the container material
comprises polyethylene terephthalate (PET), polyethylene
naphthalate (PEN), or a PET and PEN blend.
16. A method according to claim 14, in which the injection moulding
step forms the rim with an outwardly-extending portion radially
beyond the downwardly-extending portion.
17. A method according to claim 16, in which the
outwardly-extending portion has a peripheral flange to assist in
manual grasping of the container when nested with another like
container.
18. A method according to claim 14, in which the injection moulding
step forms the rim with a radially inner inverted U section, then a
V shaped groove, and finally an inverted V section.
19. A method according to claim 18, in which the
downwardly-extending portion extends downwardly from the V shaped
groove.
20. A method according to claim 14, in which said acute angle is
between 7 and 11 degrees.
21. A method according to claim 14, further including
radially-extending reinforcing ribs spaced around the periphery of
the rim of the container.
22. A method according to claim 14, in which the cavity of the
pressure moulding apparatus is shaped such that the narrowing side
region comprises a step above which the cavity is of substantially
constant diameter.
23. A method according to claim 14, in which the cavity of the
pressure moulding apparatus is shaped such that above the narrowing
side region the container is formed with outwardly extending
external ribs, the diameter of the container widening relatively
rapidly in the region of the external ribs to approach the diameter
of the downward extension.
24. A method according to claim 14, in which the pressure moulding
apparatus is blow moulding apparatus.
25. A method according to claim 14, in which the step of moving the
body-forming portion is assisted by mechanical stretching of the
body-forming portion in the pressure moulding apparatus.
26. A method according to claim 14, further comprising the step of
providing a lid for the container, the lid conforming with the
upper surface of the rim.
27. A method according to claim 26, in which the lid sealingly
engages the rim of the container and comprises two sealing elements
one on the top and the other at the side of the portion of the lid
engaging the rim.
28. A method according to claim 26, including a flap at the side of
the lid to assist removal thereof.
29. Apparatus for manufacturing a container having a body and a rim
defining an opening for the container, the container being made of
a material which is susceptible to deformation when heated, the
apparatus comprising: an injection-moulding apparatus adapted to
injection-mould a preform which has a rim formed at its mouth and a
continuous body-forming portion extending across the preform from
the inner periphery of the rim, the rim having an
outwardly-directed extent and including a downwardly-extending
portion spaced outwardly from the inner periphery and an
outwardly-extending portion located outwardly of the
downwardly-extending portion; a pressure moulding apparatus having
a moulding cavity; means for placing the preform in the moulding
cavity of the pressure moulding apparatus at an elevated
temperature with the preform being located by means of the rim; and
means in the pressure moulding apparatus for moving the
body-forming portion downwardly and outwardly whereby the
body-forming portion expands in the cavity to form the container
side and bottom walls, the upper region of the side wall contacting
the downwardly-extending portion of the rim, and the rest of the
body-forming portion contacting the sides of the cavity to form a
shape defined by the interior shape of the cavity; characterized in
that: the cavity is so shaped that the upper region of the side
wall contacts the downwardly-extending portion of the rim such as
to form a box section; and the interior of the cavity in the
pressure moulding apparatus is shaped to define the side and bottom
walls of the container with the cavity having at its upper side
region a narrowing side wall section above which the diameter of
the cavity is substantially equal to or approaches the diameter of
the downwardly-extending portion of the rim and below which the
diameter is less than the diameter of the inner periphery of the
rim and tapers therefrom inward downwardly to the bottom wall at an
acute angle, whereby containers formed by the apparatus can
internest.
30. Apparatus according to claim 29, in which the injection
moulding apparatus forms the rim with an outwardly-extending
portion radially beyond the downwardly-extending portion.
31. Apparatus according to claim 30, in which the
outwardly-extending portion comprises a peripheral flange to assist
in manual grasping of the container when nested with another like
container.
32. Apparatus according to claim 29, in which the injection
moulding apparatus forms the rim with a radially inner inverted U
section, then a V shaped groove, and finally an inverted V
section.
33. Apparatus according to claim 32, in which the
downwardly-extending portion extends downwardly from the V shaped
groove.
34. Apparatus according to claim 29, in which said acute angle is
between 7 and 11 degrees.
35. Apparatus according to claim 29, in which the injection
moulding apparatus is further shaped to form radially-extending
reinforcing ribs spaced around the periphery of the rim of the
container.
36. Apparatus according to claim 29, in which the cavity of the
pressure moulding apparatus is shaped such that the narrowing side
region comprises a step above which the cavity is of substantially
constant diameter.
37. Apparatus according to claim 29, in which the cavity of the
pressure moulding apparatus is shaped such that above the narrowing
side region the container is formed with outwardly extending
external ribs, the diameter of the container widening relatively
rapidly in the region of the external ribs to approach the diameter
of the downward extension.
38. Apparatus according to claim 29, in which the pressure moulding
apparatus is blow moulding apparatus.
39. Apparatus according to claim 29, in which the pressure moulding
apparatus includes means for mechanical stretching of the
body-forming portion.
40. Apparatus according to claim 29, further comprising means for
forming a lid for the container, the lid conforming with the upper
surface of the rim.
41. Apparatus according to claim 40, in which the lid sealingly
engages the rim of the container and comprises two sealing elements
one on the top and the other at the side of the portion of the lid
engaging the rim.
42. Apparatus according to claim 40, including a flap at the side
of the lid to assist removal thereof.
43. A container manufactured using the method of claim 14.
Description
BACKGROUND OF THE INVENTION
[0001] This invention relates to containers moulded from plastics
materials and to a method of and apparatus for making such
containers.
[0002] The invention is particularly suitable for the manufacture
of containers in the nature of cans or pots, preferably with lids,
from polyethylene terephthalate (PET), though it is not limited to
such manufacture. PET is particularly suitable for storing
solvent-based contents, but is a difficult material to use in
manufacture.
[0003] We have appreciated that it would be desirable to produce
PET containers which use a minimum of plastics material, and yet
were sufficiently strong for normal use, which occupied a minimum
of space when empty for transporting, and yet which were easy to
handle and use individually. When fitted with a lid the containers
should stack readily and be easy to open. Such containers could be
manufactured in a variety of sizes particularly in the range 250 ml
to 5 litres or 1/2 pint to 1 gallon.
[0004] The present inventor's International Patent Application
WO97/19801 describes a method of making a container using a
two-stage process. In the first stage an embryo container is formed
by injection moulding. In this stage the rim is essentially fully
formed, but the body is not yet formed, and instead the embryo
container walling takes the form of a central tube extending
inwardly from the inner periphery of the rim. The embryo container
is then transferred to a blow moulding machine and the walling is
expanded outwardly to form the container body. The present
inventor's International Patent Application WO0/46118 describes a
container-with a more complex rim construction.
[0005] Other prior proposals for the manufacture of containers
include Japanese Laid-Open Patent Application Sho 57-77439 (U.S.
Pat. No. 4,367,821 to Holt) and International Patent Application
WO99/28196 (U.S. Pat. No. 6,179,158 to Koda).
SUMMARY OF THE INVENTION
[0006] The invention in its various aspects is defined in the
independent claims below, to which reference may now be made.
Advantageous features are set forth in the appendant claims.
[0007] Preferred embodiments of the invention are described in more
detail below with reference to the drawings. The preferred
embodiments take the form of a container having a body and a rim
defining an opening for the container, the container being made of
a material which is susceptible to deformation when heated. The
container is manufactured in a two-stage process. The first stage
comprises injection moulding in an injection-moulding apparatus a
preform which has a rim formed at its mouth and a continuous
body-forming portion extending across the preform from the inner
periphery of the rim, the rim having an outwardly-directed extent
and including a downwardly-extending portion spaced outwardly from
the inner periphery and an outwardly-extending portion located
outwardly of the downwardly-extending portion.
[0008] In the second stage the preform is placed in a moulding
cavity of a blow moulding apparatus at an elevated temperature with
the preform being located by means of the rim. The body-forming
portion expands in the cavity to form the container side and bottom
walls. The upper region of the side wall contacts the
downwardly-extending portion of the rim such as to form a box
section. The rest of the body-forming portion contacts the sides of
the cavity to form the side and bottom walls of the container.
[0009] In a first embodiment, the side wall has at its upper side
region a narrowing side region in the form of a step above which
the diameter of the cavity is substantially equal to or approaches
the diameter of the downwardly-extending portion of the rim. Below
the step the diameter is less than the diameter of the inner
periphery of the rim and tapers therefrom inward downwardly to the
bottom wall at an acute angle, whereby the containers can
internest.
[0010] In a second embodiment, above the narrowing side region the
container is formed with outwardly extending external ribs, the
diameter of the container widening relatively rapidly in the region
of the external ribs to approach the diameter of the downward
extension.
[0011] The container is preferably provided with a lid which
conforms with the upper surface of the rim. The lid sealingly
engages the rim of the container and comprises two sealing elements
one on the top and the other at the side of the portion of the lid
engaging the rim. A flap may be provided at the side of the lid to
assist removal thereof.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] The invention will now be described in more detail, by way
of example, with reference to the drawings, in which:
[0013] FIG. 1 is a side sectional view through a first container
embodying the present invention;
[0014] FIG. 2 is a sectional detail through the rim of the
container of FIG. 1;
[0015] FIG. 3 shows three nested containers, with the left-hand
part of the figure in section and the right-hand part in side
view;
[0016] FIG. 4 is a side sectional view through an injection moulded
preform used in the manufacture of the container of FIG. 1;
[0017] FIG. 5 is a sectional view through an injection moulding
machine illustrating the manufacture of the preform;
[0018] FIG. 6 is a sectional view through a blow moulding machine
illustrating the initial stage in the formation of the container
from the preform;
[0019] FIG. 7 is a view similar to FIG. 6 showing the end of the
blow moulding operation;
[0020] FIG. 8 is a sectional view similar to FIG. 1 of the
container of FIG. 1 when fitted with a lid;
[0021] FIG. 9 is a sectional detail through the rim of the
container and lid in FIG. 8;
[0022] FIG. 10 is a side sectional view of the lid;
[0023] FIG. 11 is a sectional detail of the rim of the lid;
[0024] FIG. 12 is a side sectional detail showing an optional catch
having a downwardly extending flap;
[0025] FIG. 13 is a side view of the region of the flap;
[0026] FIG. 14 is a detail in plan of the lidded container showing
an optional rib;
[0027] FIG. 15 illustrates an alternative construction where the
flap is received in a recess in the container wall;
[0028] FIG. 16 is a side view of a second container embodying the
invention with a lid;
[0029] FIG. 17 is a plan view of the container lid of FIG. 16;
and
[0030] FIG. 18 is a side sectional view through the container and
lid of FIG. 16.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0031] A first embodiment of the invention will now be described
with reference to the drawings. FIG. 1 is a side sectional view
through the finished container 1. The container is of generally
cylindrical shape with sides 20 and a base 2. The base has a
concave central portion to provide additional strength. The rim 3
of the container which defines its mouth has, proceeding from its
inner periphery 19, an inverted U section 4, then a V shaped groove
5, and finally an inverted V section 6. Thus the rim extends
generally outwardly from the inner periphery 19. All this is shown
more clearly in FIG. 2. The V shaped groove 5 together with a
downward extension 21 from the bottom of that groove form a
downwardly-extending portion. The upper region 22 of the side wall
20 of the container contacts this downward extension 21, so as to
form a box section 25. This substantially increases the strength of
the rim. The inverted V section 6 then extends further outwardly of
the downward extension 21, culminating in a depending flange
29.
[0032] About 15-20% of the way down the side wall 20 of the
container is a step 23, where the diameter of the side wall narrows
abruptly. The side wall region 18 above the step is cylindrical and
has a diameter which is substantially the same as the diameter of
the downward extension 21. The side wall region 24 below the step
is slightly less than the diameter of the inner periphery 19 of the
rim, and tapers from the step inward downwardly at a acute angle of
7 to 11 degrees. With this structure the container shown in FIG. 1
can internest with a like container. When nested, as shown in FIG.
3, the step 23 of one container rests on the rim 3 of the container
below. However, the containers are easy to separate. This arises
because the flanges 29 extend clear of the side wall sections 18,
enabling individual containers to be grasped easily, and because
the step 23 abuts the rim 3 of the container below and thus the
containers cannot be forced into too tight an engagement of their
tapering parts.
[0033] Nevertheless the containers are of relatively strong
construction for the thickness of the material being used. The
strength comes from the rim construction, which includes the box
section 25, and from the existence of the step region 23 which
gives strength to the upper part of the side wall of the
container.
[0034] The strength may be enhanced by the use of vertical
reinforcing ribs. Typically eight ribs 32 may be included,
equi-spaced around the container. The presence of such ribs is
indicated by cross-hatching an FIGS. 1 and 2. The ribs can be
across the box section 25 and/or fill the inverted V 6.
[0035] The method of manufacturing the container of FIG. 1 will now
be described. The manufacturing method is based on that described
in the present inventor's International Patent Application
WO97/19801. The shape of the rim is a further development of the
rim described in the present inventor's International Patent
Application WO00/46118. Reference may be made to both these
applications for further details and variations concerning the
design.
[0036] The first stage in the method is to form a preform 15.as
shown in FIG. 4. The preform has the rim 3 in its final form, with
the inner periphery 19, inverted U 4, V shaped groove 5, downward
extension 21, inverted V 6, and flange 29. The ribs 32, if present,
are also formed at this time. The wall 20 of the body of the
container is not however formed at this time, but instead the
preform includes a continuous dished or bowl-shaped body-forming
member 32 which extends across the preform from the inner periphery
19 of the rim but which is of reduced size compared with its final
form. The shape of this member 32 can be anything from approaching
a flat membrane to a substantially tubular shape. In the section
seen in FIG. 4, the shape adopted by the member 32 is approximately
an arc of one-third of a circle.
[0037] The preform 15 is formed by injection moulding on an
injection moulding machine 40, as illustrated in FIG. 5. The
injection moulding machine has two main sections, namely a lower
section formed by a cavity insert 42 and an upper section formed by
an inner preform pin 44 and an outer preform section 46. Neck
splits 48 are also provided, carried by neck split carrier plates
50, on the machine carousel 52. Plastics material is injected
through an injection orifice 54 in the cavity insert 42 at the
bottom centre of the preform 15. Injection moulding apparatus is
very well known and thus a detailed description of such apparatus
need not be given here. It should be noted however that the rim of
the preform is fully formed in this operation and adopts the shape
required in the final container. The body-forming portion 32 of the
preform depends from the inner periphery of the rim. The preform is
designed in such a manner that a straightforward vertical movement
of the central mould core (preform pin 44 and section 46) will
allow removal of the preform from the mould. There are no undercuts
or slides in the construction of either the core or the cavity. The
use of injection moulding allows the rim to be formed with high
accuracy, which is necessary for good sealing of the lid.
[0038] It should be noted that in this description the preform and
eventual container are assumed to be in conventional orientation,
that is with the mouth at the top and the base at the bottom. The
terms "up" and "down" and their derivatives should therefore be
construed in this sense although in actual fact the orientation of
the preform or container may be different from this.
[0039] The preform is now moved from the injection moulding machine
to a blow moulding machine. A blow moulding machine is one type of
pressure moulding machine; a less preferred alternative would be to
employ a machine that uses suction rather than blowing. The preform
is transferred to the blow moulding machine 7, shown in FIG. 6,
while still hot and pliable. If it has cooled down, then it is
reheated so as to be pliable. The blow moulding machine 7 has a
cavity 56 defined at the sides by two movable mould halves 11 and
12 and at the bottom by a moveable base or punt 13. The top of the
cavity is defined by a circular top plate 8 which carries an
axially vertically moveable rod 9. The rod 9 can be lowered into
the open top of the preform 15 such that it engages the sides 10 of
the preform. As it descends it causes mechanical downward
stretching of the container wall. The rod 9 has a hollow centre 58
which allows compressed air to travel into the cavity above the
preform through angled holes 17 near the bottom of the rod. The rod
9 also has peripheral channels 60 which allow compressed air into
radial channels 16 which open right at the top of the cavity near
the top of the side wall 20 of the container.
[0040] The rim 3 is held fast in the blow mould. More particularly,
the V groove 5 and the inverted V groove 6 are supported by the
mould halves, though in the case of the outermost groove 6 only
partially so. The remainder of the groove 6 is fitted into a
continuous metal ring 14, split into two, such that it can
subsequently lift the finished moulding clear of the blow mould 7.
The metal ring 14, or neck splits, are carried on neck split
carrier plates 64.
[0041] Thus the sequence is that first the two blow mould halves
11,12 close around the pliable preform 15, at an elevated
temperature, and the metal ring 14. The circular top plate 8 is
lowered onto the mould, which it touches at the outside face of the
inner U groove 4. Then the stretch rod 9 is lowered to force the
material 32 which is to constitute the container walls towards the
base 13 of the mould cavity 56. Simultaneously, compressed air is
introduced into the hollow centre 58 and the channels 60 of the
stretch rod 9. It emerges both from the holes 16 at the top and the
angled holes 17 at the bottom. The holes 16 at the top are larger
than those 17 at the bottom and also nearer the source of the
compressed air. This causes the plastics material at the top of the
preform to move outwardly until it contacts the side of the blow
mould cavity, covering the base of the inverted U 4 as it does so.
This thus forms the larger diameter portion 18, as well as the box
section 25, the latter being formed by the side wall of the
container bearing against the downward extension 21 to complete the
box section shape.
[0042] As the compressed air continues to blow, it also emerges
from the holes 17 at the lower end of the rod 9, and now forms the
remainder of the container by compressing the still-soft plastics
material of the preform hard against the metal sides of the blow
mould. This continues to be assisted by the mechanical
strengthening caused by the stretch rod 9. The fully-formed
container in the blow moulding machine is shown in FIG. 7.
[0043] The shape of the mould cavity 56 is such as to impart the
desired shape to the container walls 20. Thus the cavity 56 has a
narrow side wall section or step 66 about one-fifth or one-sixth of
the way down the side wall. Above the step 66 the diameter of the
cavity is approximately the same as the downward extension 21 of
the rim 3 of the preform 15 when located in position in the mould
cavity. Below the step 66 the diameter is less than the diameter of
the inner periphery 19 of the rim 3 of the preform when located in
position in the mould cavity. Descending further down the cavity,
the cavity well tapers inwardly at an acute angle of 7 to 11
degrees, until it reaches the bottom wall of the cavity.
[0044] Once the material has cooled and solidified, the blow mould
opens and the container is lifted out. The container is lifted out
by the rim 3, and this can be facilitated by mould rings which form
and engage with an undercut 28 (see FIG. 2) on the outer face of
the rim 3, these rings themselves splitting into two to release the
product.
[0045] The container 1 is preferably fitted with a lid 26 as shown
in FIGS. 8 and 9. The lid 26 is flat across the main central part
but is shaped in the region of its periphery to conform with the
upper surface of the rim 3 of the container 1. To this end the lid
26 first has a ridge 70 which conforms over the top of the U
section 4, now forming the box section 25, and then has a
downwardly extending wedge shape 27 which mates with the V-groove
5. Because of the rigid nature of the material, however, the two
interlocking tapers between the wedge shape 27 and the V-groove 5
will not retain the closure or lid 26, which, due to the radial
compressive force of the V groove, will gradually lift out from the
sealing faces.
[0046] Thus, as shown in FIG. 9, the lid 26 is retained on the
container 1 by a downwardly extending flange 72 depending from the
periphery of the lid and conforming to the upper and outer faces of
the rim in the region of the inverted V groove 6. The flange 72
thus fits around the flange 29. The flange 72 furthermore carries a
detent in the form of an inwardly-facing rib 74 on its inner face.
This inwardly-facing rib 74 engages with the undercut 28 which was
formed on the injection moulding machine forming a mating detent.
The inside diameter of the lid outer flange 72 is smaller than the
outside diameter of the flange 29 just above the undercut 28.
[0047] The sealing is thus provided by the combination of two
sealing structures at an angle of 90 degrees to each other, namely
the wedge shape 27 and the V-groove 5 on the one hand, and the rib
74 and the undercut 28 on the other.
[0048] Sectional views of the lid alone are shown in FIGS. 10 and
11.
[0049] In order to facilitate release and removal of the lid, a
flap 35 may be provided as shown in FIGS. 12 to 15. As best seen in
FIG. 12, the flap extends downwardly from the periphery of the
flange 72 at selected points identified by an external rib 37. The
flap hinges at 36. The lower outwardly-curved portion of the flap
is accessed by inserting the user's finger beneath it, and pulling
in an upward direction, at which point the flap becomes a hinged
lever. It is restrained from travelling beyond 90 degrees to the
container, i.e. upwardly of the horizontal, by the rib 37. Further
upward movement of the flap 35 causes the outer flange 72 of the
lid to become detached from the underside of the flange 29 of the
rim. This permits removal of the lid by peeling the flange 72 from
the flange 29 of the container 1. FIG. 13 shows a side view and
FIG. 14 a top view of the region of the flap 35.
[0050] An alternative arrangement is shown in FIG. 15, where the
flap or handle 35 is larger and has a portion 38 which fits in a
recess 39 near the top of the container.
[0051] The flap may be configured to have a "tamper evident"
membrane, visually indicating that it has already been used
previously to open a container.
[0052] The container of FIG. 1 is formed with the box section 25 at
the top inner face which provides structural strength and permits
large hoop stresses to be developed between the wedge shape 27 and
the V-groove on the container. The strength is further aided by the
step 23 and by the taper below the step to the bottom of the
container.
[0053] The container can internest as shown in FIG. 3 which
illustrates three internesting containers. Each container sits with
its step 23 sitting on the upper surface of the rim 3 of the
container below it. Thus the outer part of the tapering section
cannot become too firmly wedged in the inner part of the tapering
section of the container below it. Separation of the containers is
further facilitated by the fact that the outer part of the rim
extends outwardly of the container wall, making it easy for the
user to grab hold of two adjacently stacked containers so as to
separate them.
[0054] Thus the advantageous features of adequate strength, ability
to nest, and ease of separation, while using a minimum of plastics
material, are provided by the co-operative effects of the box
structure giving strength to the ring, and the step and taper
giving strength to the body while the step allows one container to
rest on the rim of another. Ease of separation is assisted by the
outwardly-extending portion of the rim with its
downwardly-extending peripheral flange which facilitates manual
gripping on the containers for separation.
[0055] The container is preferably made from polyethylene
terephthalate (PET), for which the process is particularly
suitable. Other thermoplastic resins may however be used, including
polyethylene naphthalate (PEN), and also PET and PEN blends, in
both the crystalline and amorphous structures of these two
materials. Also, other rigid plastics including polyvinyl chloride
(PVC), polycarbonate, acrylics, and various polyolefins including
polypropylene and high density and low density polythene. In
principle any material susceptible to deformation when heated may
be used, but the method is particularly advantageous with PET
etc.
[0056] The containers can be formed as pails, buckets, or cans and
are particularly suitable for enclosing solvent-based contents for
storage for long period without solvent loss. They may, in
particular, be used as cans for paints and other coating materials.
The container itself is made as a unitary element without the need
for welds, which are costly and can be unreliable. The containers
can be formed accurately of PET, which requires blow moulding to
give the biaxial stretching necessary for optimum strength. Despite
having a reasonably narrow taper, the containers can be nested
without jamming. Finally, the container can be repeatedly resealed
and yet can be opened again without the need for special tools.
[0057] A second embodiment of the invention is illustrated in FIGS.
16 to 18. This embodiment is similar to the first embodiment and
thus only the differences will be described.
[0058] In the second embodiment the step 23 and the upper section
18 of the container side wall of the first embodiment are replaced
by a strongly tapering section 80 with external ribs 82. Thus in
the region of the ribs, the diameter of the container widens
relatively rapidly to approach the diameter of the downward
extension. The external ribs have horizontal lower peripheries so
that, when nested, the ribs sit on the top of the rim of the
container below, again stopping jamming from taking place. In other
respects the container is the same as the container of the first
embodiment.
[0059] Although preferred embodiments of the invention have been
described and illustrated, by way of example, many modifications
may be made to the method, apparatus and containers described.
* * * * *