Envelopes – wrappers – and paperboard boxes – Paperboard box – Box material includes a coating or a nonpaperboard...
Patent
1995-05-20
1997-01-28
Elkins, Gary E.
Envelopes, wrappers, and paperboard boxes
Paperboard box
Box material includes a coating or a nonpaperboard...
220443, 220445, 229919, 229939, B65D 520, B65D 542
Patent
active
055971113
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to a corrugated thermoplastic blank for producing a container.
BACKGROUND OF THE INVENTION
Corrugated thermoplastic sheet has proved to be unsuitable for the construction of boxes especially where relatively heavy loads are to be carried in such boxes. These relatively heavy loads may comprise fish or vegetables which weigh in the order of 4 to 15 kilograms. Boxes constructed from the corrugated thermoplastic sheet have been too weak for these loads. Such corrugated thermoplastic sheet has traditionally been 3 to 4 mm thick and has had a weight of approximately 600 grams per m.sup.2 with a buckling load resistance index of about 100. This sheet could simply be made thicker and heavier to increase its strength. However by increasing the thickness and the weight of the sheet, more material is used and consequently it is not cost effective to increase the thickness and the weight of the sheet to increase the strength of the sheet.
SUMMARY OF THE INVENTION
It is an object of this invention to provide a lightweight yet sufficiently strong blank made of corrugated thermoplastic sheet.
The applicant has addressed the above objective by increasing the overall thickness of the sheet whilst using substantially the same amount of material as used in prior an sheets. The skins and flutes of this sheet are thus thinner than the prior art sheets. However such sheet is unsuitable for the construction of the required boxes since the flutes can collapse as the skins move relative to one another.
It is accordingly a further object of this invention to provide a reinforced lightweight, corrugated thermoplastic blank which can be used to produce a box of sufficient strength.
Corrugated thermoplastic boxes have suffered from the disadvantage that water can be trapped between the two skins of the corrugated sheet. Such water, besides adding to the weight of a box, can promote the growth of bacteria which is obviously undesirable especially in food applications.
The thermoplastic material, especially polypropylene, has a memory which is not destroyed by the creation of fold lines which are created in the same manner in which fold lines are created in corrugated cardboard blanks. Thus even after a fold line has been created on a sheet of polypropylene in the traditional corrugated cardboard manner, the sheet is not easily folded along that line because it tends to return to its original unfolded planar shape because of its memory. It is important that the walls of a box erected from the blank be perpendicular to the base of the box. If the original memory of the thermoplastic sheet is not destroyed the sidewalls of the box will tend to move out of their perpendicular orientation and thus decrease the stacking strength of the box.
It is accordingly a further object of this invention to provide a corrugated thermoplastic blank for a box in which water cannot become trapped within the corrugated sheet and wherein the original memory of the thermoplastic material is substantially reduced or destroyed along the fold lines of the blank.
According to the invention a container blank made of corrugated thermoplastic sheet having two skins spaced from one another by flutes includes a base panel connected to wall panels by fold lines each comprising a weld line welding the two skim together and substantially reducing or destroying the original memory of the thermoplastic along the length of the weld line, and wherein the free edges of the blank are sealed to prevent liquid from entering the blank with the weld lines and the sealed free edges and/or the weld lines surrounding and reinforcing each panel thereby increasing the strength of each panel of the blank and thereby the strength of a container erected from the blank.
The sheet is preferably at least 5 mm thick but not thicker than 10 mm and may be between 6,0 mm and 7,5 mm thick.
The sheet may weigh between 400 and 850 grams/m.sup.2. Preferably the sheet weighs between about 500 grams/m.sup.2 and about 700 grams/m.sup.2.
The panels of the b
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The Wiley Encyclopedia of Packaging Technology, John Wiley & Sons (1986), pp. 226-228.
Grobler Ronald
Mackinnon Malcolm R.
Elkins Gary E.
Korpak Limited
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