The present invention relates to a bottom structure of a paper box for storage of liquid, and more particularly, relates to a paper box for storage of liquids such as milk, juice, sake, soy sauce and the like.
Recently, various paper boxes made of thermoplastic synthetic resin laminate plate-like paper have been used instead of conventional metal cans or glass bottles as containers for storing liquid such as milk, juice or sake. The reason for this is that the paper boxes have the following advantages;
(a) Since the paper boxes have generally a regular parallelepiped shape, any dead space can be removed and they may be laid one on another in carriage or storage; PA1 (b) The paper boxes are light in weight and thin in thickness in comparison with glass bottles; PA1 (c) The value of goods may be enhanced by applying decorative printing on their outside surface; PA1 (d) The paper boxes may readily be collapsed flat after consuming contents therein; PA1 (e) The paper boxes may be disposed of by burning after use; and PA1 (f) The content contained therein may be protected securely.
Conventionally, as such a paper box, there has been a container developed, manufactured for sale by Ex-Cello-O Corporation (Japanese Utility Model Publication No. 4661/71) for milk containers. As shown in FIG. 1, its bottom structure has a plate-like paper structure as indicated by folding lines, i.e., dot-and-dash lines and folding-back lines, i.e., by two-dot-one-dash lines. After a connecting portion G formed along one edge of the plate-like paper is connected with corresponding portion opposite thereto to form a rectangular tube as shown in FIG. 2A, the paper is folded along the folding lines and the folding-back lines as shown in FIGS. 2B to 2D to thereby form the bottom structure. In the container disclosed in the above-mentioned Japanese Utility Model Publication No. 4661/71, one bottom plate A among the two bottom plates A and B forming outermost bottom surface is inserted between the confronting bottom plate B and the folded inside portions as shown in FIGS. 2A to 2D. Since the edges of the folded portions C and D, E and F are intimately contacted with each other by a precise arrangement for folding, the container has the above-described advantages that the liquid contained therein will not leak, however there has been a fear that, when the end of the bottom plate is inserted into an extremely narrow gap between bottom plate B and folded portions D, E as shown in FIG. 2C, the end of the bottom plate A may be folded back midway in the process.
In order to overcome these defects, a paper box having the end portion of the bottom plate A removed as shown in FIG. 3 has been manufactured and available in the market. However, the bottom structure of the paper box is made up of a half-size bottom plate which is overlapped in part only by the other half-size bottom plate when folded, and, in association with the folding-back portions C, D, E and F, each edge thereof does not always abut precisely with the others unlike the preferred paper box illustrated by FIG. 4A, but poor overlapping is likely to be caused as in the case of sub-standard boxes illustrated by FIG. 4C in which case liquid contained therein is threatened to leak through gaps therebetween and the boxes of such structure have eventually led to a deteriorated quality of box.