Abstract:
A container is made in two stages from thermoplastics material. In the first stage a preform ( 1 ) is injection moulded, the mould parts easily releasing a tubular body ( 2 ) with a closed end and an outwardly projecting rim ( 3 ) at the open end. In the second stage the still heated preform ( 1 ) is blow moulded, possibly with some preliminary mechanical stretching, with the blow pin ( 13 ) seated in the open end of the body ( 2 ) and the preform ( 1 ) held by the other part ( 7 ) of its rim. The wall of the body ( 2 ) is expanded, and immediately below the open end it is stretched outwardly to meld with the underside of the inner part ( 5 ) of the rim. The resultant container thus has a mouth defined by an inset lip. It may be of paint tin form, with a drip groove ( 9 ) around the mouth.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   This is a continuation of application Ser. No. 09/077,528, filed Nov. 29, 1996, now U.S. Pat. No. 6,413,468. 

   FIELD OF THE INVENTION 
   This invention relates to containers, and is particularly concerned with a method of manufacture of containers that resemble tins with press-in lids which can be levered off using the rim of the container as a fulcrum. 
   BACKGROUND OF THE INVENTION 
   Containers of the above type have traditionally been produced in metal, and have been widely used for such contents as paint, drinking chocolate and cornflour. 
   Versions in plastics material have been manufactured, and hitherto they have been produced by welding together two discrete mouldings. The reason for this two-piece construction is the inward overhang of the top flange or rim. If known injection moulding methods are employed, it has been considered impossible to arrange it so that the inside male core can be extracted. The opening is too small to permit any form of collapsible insert. Blow moulding might offer a solution, but the problem with the rim has not been solved. 
   It is the aim of this invention to overcome this difficulty and to enable such a container to be made by blow moulding. 
   SUMMARY OF THE INVENTION 
   According to one aspect of the present invention there is provided a method of making a container to which entry is via an opening inset from adjacent container walling, the material of the container being susceptible to deformation when heated, wherein in a first stage an embryo container is formed with a rim defining an opening projecting outwardly from what is to become the container walling, and wherein in a second stage that embryo container walling, at an elevated temperature, is urged outwardly while the rim is held, whereby the walling expands to leave the inner part of the rim inset therefrom. 
   It will be assumed hereafter that both the embryo and finished container are in an upright attitude with the opening uppermost. 
   The formation of the embryo container in the first stage is conveniently by injection moulding using an inner mould core which is subsequently extractable through said opening, while the transformation from embryo to finished container in the second stage is preferably by blow moulding via the opening, although at least some of the distortion or stretching inherent in the process could be achieved mechanically. 
   In the preferred form, the opening of the embryo container widens towards the mouth, locally thinning the container walling. The rim may then include a lateral flange projecting outwardly from the portion of thinned walling, this thinned portion being deformed in the second stage to co-operate with the underside of the flange. The embryo container also preferably has a further flange on the lateral flange, projecting downwardly to surround the opening end of the container, and the deformation of the thinned portion extends to it being forced against the inside of the further flange and to step out below its free edge. 
   With this arrangement, and if the material of the container is transparent, a data band can be provided on the inside of the further flange of the embryo container to be legible therethrough, the band being made captive by the deformed thinned portion. 
   Conveniently, at the root of the lateral flange there is an upstanding rib which internally smoothly continues the contour of the mouth of the opening. Also, at the outer edge of the lateral flange there may be, on the upper side, a stepped extension forming with said rib an upwardly open channel around the opening. The stepped extension may project laterally beyond the flange, its underside providing means for locating the embryo container during the blow moulding. 
   According to another aspect of the present invention there is provided a container having improved construction, a container made by the method outlined above, and an apparatus for making a container. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a better understanding of the invention, one embodiment will now be described, by way of example, with reference to the accompanying drawing, in which: 
       FIG. 1  is an axial section of a preform of a container prior to blow moulding, 
       FIG. 2  is an axial section of a container in a mould having been expanded by blow moulding from the preform of  FIG. 1 , and 
       FIG. 3  is an axial section of the finished released container. 
   

   DETAILED DESCRIPTION 
   A preform or embryo container  1  has a flat bottomed, bowl shaped body  2  with an outwardly projecting ring or rim portion  3  at the mouth of the body  2 . It is of plastics material formed by injection moulding, and its shape is such that the mould can be of just two parts which, when the plastics has set, can be separated by movement in the axial direction to release the preform  1 . There are no undercuts to complicate the mould. 
   Towards the top of the body  2 , its cylindrical wall becomes thinner, tapering in a smooth concave curve  4  on the inside to about half the thickness of the rest of the body  2 . Projecting radially outwards from this the ring  3  has a flange  5 , and at the outer periphery of this flange there is a further flange  6  projecting downwardly as a co-axial cylindrical skirt. The ring  3  also has a stepped extension  7  projecting above the flange  5  and radially beyond the flange  6 . At the root of the flange  5 , there is an upstanding annular rib  8  which internally smoothly merges into the curved surface  4 . Externally, it slopes down into a channel  9  whose outer side is defined by the extension  7 . 
   For blow moulding, the preform  1  is transferred from an injection mold to a blow mould while still hot. The blow mould comprises two halves  10  and  11  with a base insert or punt  12 . The preform  1  rests by its extension  7  on the edge of the mould cavity and the flange  6  fits snugly in the mouth of that cavity. These parts are cooled quicker than the rest and so solidify enough to provide firm support and location. A blow pin  13  is shaped to snugly fit the groove  9 , the rib  8  and the upper part of the curved surface  4  which defines the opening into the preform. This contact of the blow pin  13  with the plastics material of the rim portion  3  contributes to the local cooling and solidification thereof. 
   Air under pressure is then introduced into the preform  1  through the blow pin  13 . With the rest of the plastics material of the preform still soft and pliable, the pressurized air in the preform  1  causes the thinned portion of its wall near the top to be stretched and expanded radially, so that it is forced against the underside of the flange  5  and the inside of the flange  6 . It then flows around the underside of that flange  6  to meet the wall of the blow mould cavity. The pressurized air inside the body  2  causes the rest of the body  2  to expand and eventually, with blowing complete, the container is as shown in FIG.  2 . The heat is such that where two plastics surfaces have been urged together they become effectively homogeneous. The finished container is therefore as shown in FIG.  3 . As soon as the material is cooled and set, the blow mould halves  10  and  11  are opened and the blow pin  13  is retracted to free the complete moulding. 
   It will be seen that the finished container resembles a conventional paint tin with the channel  9  for drips, and the extension  7  providing a fulcrum for levering off a lid pressed into the opening whose mouth is defined by the rib  8 . 
   The most common shape of the finished container will be cylindrical. However, it would be possible to apply this technique to other shapes, for example elliptical in cross-section or even polygonal. 
   Various plastics materials are suitable, including polyvinyl chloride, high density polythene, polypropylene, acrylic or polycarbonate. Since the one-piece construction offers savings, more expensive materials such as polyethylene terepthalate (P.E.T.), polyethylene napthalate (P.E.N.) and copolymers and blends of these two materials in both crystalline and amorphous forms could be viable. 
   While blow moulding is expected to be the preferred method of expansion, aided by mechanical stretching for large containers, it may be possible to achieve the same effect by suction moulding. 
   In a first embodiment of the disclosed invention, there is a method of making a container to which entry is via an opening inset from adjacent container walling, the material of the container being susceptible to deformation when heated, wherein in a first stage an embryo container  1  is formed with a ring  3  defining the opening substantially in its final form and with the remaining portion, which is to become the container walling, of reduced size compared with its final form, and wherein in a second stage that embryo container walling  2 , at an elevated temperature, is urged outwardly by blow moulding while the ring  3  is held, whereby the walling  2  expands laterally in relation to the opening, wherein the ring  3  provides a seat for a press-in lid and projects outwardly from the embryo container walling, and wherein a blow pin enters closely into the opening to blow the embryo container walling to its final shape. 
   In a second embodiment of the disclosed invention, there is a method of making a container as in the first embodiment described above, wherein the formation of the embryo container  1  in the first stage is by moulding in a two part mould one part of which has a core subsequently extractable through said opening. 
   In a third embodiment of the disclosed invention, there is a method of making a container as described in the second embodiment described above, wherein the formation of the embryo container  1  is by injection moulding. 
   In a fourth embodiment of the disclosed invention, there is a method of making a container as described in any of the embodiments described above, the opening of the embryo container widens towards the mouth, locally thinning the container walling  4 , this thinned portion being deformed in the second stage to co-operate with the underside of said ring. 
   In a fifth embodiment of the disclosed invention, there is a method of making a container as described in any of the embodiments described above, wherein the ring  3  has a flange  6  projecting down to surround the opening end of the container. 
   In a sixth embodiment of the disclosed invention, there is a method of making a container as described in the fifth embodiment described above, wherein the deformation of an upper end section  4  of the embryo container causes it to be forced against the inside of said flange  6  and to step out below its free edge. 
   In a seventh embodiment of the disclosed invention, there is a method of making a container as described in the sixth embodiment described above, wherein the material of the container is transparent and a data band is provided on the inside of said flange  6  of the embryo container  1  to be legible therethrough, the band being made captive by the deformed portion  4 . 
   In an eighth embodiment of the disclosed invention, there is a method of making a container as described in any of the embodiments described above, wherein the upper side of the ring  3  has a peripheral channel  9  defined on the inside by an upstanding rib  8  and on the outside by an outer zone  7  which is upwardly stepped. 
   In a ninth embodiment of the disclosed invention, there is a method of making a container as described in the eighth embodiment described above, wherein the blow pin is shaped to mate with the rib  8  and the peripheral channel  9 . 
   In an tenth embodiment of the disclosed invention, there is a container made by the method of any of the embodiments described herein. 
   In an eleventh embodiment there is an apparatus for making a container having the features described herein. 
   In a further embodiment of the invention, there is a method of making a container in which entry is via an opening inset from adjacent container walling of said container, said opening being in a rim of said container, said method comprising the steps of: injection molding an embryo container in a heated condition from a material susceptible to deformation when heated, said embryo container comprising a bowl-like container-walling-forming portion integrally and monolithically joined at one end thereof to an outwardly protruding annular rim portion, said rim portion defining an opening therethrough which opens into the interior of said container-walling-forming portion, said embryo container being molded in an injection mold including an inner mold core which is extractable through said opening, and said injection mold defining exterior surfaces of said annular rim portion of said embryo container in substantially the final form thereof; removing the embryo container in its entirety from the injection mold and transferring the embryo container at an elevated temperature to a further mold, preferably a blow mold, which has mold cavity walls defining the required final external shape of said container walling to be formed by said container-walling-forming portion; positioning said embryo container on said further mold so that the annular rim portion is supportingly engaged by an upper portion of the further mold and the container-walling-forming portion of the embryo container is suspended downwardly from the annular rim portion into a mold cavity defined by said walls; inserting a mold pin into said opening, and snugly engaging said annular rim portion between said further mold and said mold pin, thereby cooling said rim portion of said embryo container, with said container-walling-forming portion of said embryo container being spaced from said mold cavity walls of said further mold; stretching and expanding said container-walling-forming portion of said embryo container into contact with said mold cavity walls of said further mold by pressure differential between the interior and exterior of said container-walling-forming portion, while maintaining said annular rim portion snugly engaged by and between said further mold and said mold pin; and allowing said container to set and removing said container from said further mold.