Low density paperboard articles

Abstract

The invention provides a low density paperboard material and associated method for use in producing an insulated container, and is especially well-suited for making cups. The paperboard material comprises a paperboard web including wood fibers and expanded microspheres, and has a relatively low density ranging from about 6 to about 10 lb / 3MSF / mil, a relatively high caliper ranging from about 24 to about 35 mil, and an internal bond strength of at least about 80×10−3 ft−lbf., preferably at least 100×10−3 lft−lbf. For applications such as cups the material is also coated on one or both sides with a barrier coating, preferably low density polyethylene, to limit liquid penetration into the web. The low density paperboard material of the invention is convertible for manufacture of containers, particularly cups, and exhibits insulative properties comparable to higher cost materials conventionally used to make cups. Also, the surface of the low density board may have a Sheffield smoothness of 300 SU or greater compared with the surface smoothness of 160 to 200 SU for conventional cupstock, the latter having been thought necessary for adequate print quality. However, it has been found that the low density board exhibits good printability on flexo printing machines despite its relatively rough surface, which is surprising and bonus effect realized along with the insulative and other properties of the board.

Description

FIELD OF THE INVENTION [0001] This application is a continuation-in-part of copending provisional application Ser. No. 60 / 178,214, filed Jan. 26, 2000. [0002] This invention relates generally to the production of articles from low density paper and paperboard and to insulated articles made therefrom, and in particular, relates to cups made of low density paper and paperboard. BACKGROUND AND SUMMARY OF THE INVENTION [0003] Insulated cups and containers are widely used for serving hot and cold beverages and other food items. Such articles may be made from a variety of materials including polystyrene foam, double-walled containers, and multi-layered paper-based containers such as paperboard containers containing an outer foamed layer. Paper-based containers are often more desirable than containers made from styrene-based materials because paper-based materials are generally more amenable to recycling, are biodegradable and have a surface more acceptable to printing. However, multi-laye...

AI Technical Summary

Benefits of technology

[0006] The present invention is directed to a low density paperboard material for use in producing insulated containers such as paper cups. In general, the paperboard material comprises a paperboard web that includes expanded microspheres and has a basis weight suitable for manufacturing an insulated container such as a paper cup, in which case the board preferably has a basis weight ranging from about 200 to about 220 lbs / 3000 ft.2 (3MSF). Low density paperboard according to the invention incorporates from about 0.25 to 10 wt. % (on a dry basis) expanded micropheres and has a relatively low apparent density ranging from about 6.0 to about 10 lb. / 3MSF / mil and a relatively high caliper ranging from about 24 to about 35 mil. These properties are especially well-suited for board products used to manufacture cups, particularly cups dimensioned to contain 16 ounces of fluid (Internal base diameter=2 ¼ inches). However, it is to be appreciated that low density paperboard according to the invention may find utility in a wide range of applications and product dimensions where properties of low density / thermal insulation are desirable.

[0012] The low density board of the invention is contrasted with conventional cupstock which is calendered to provide, among other things, a much higher density in the order of 11-12 lb / 3MSF / mil, a much lower caliper in the range of 20 mil, and an associated relatively smooth surface in the range of from about 160 to about 200 SU believed necessary for acceptable print quality. This higher density / lower caliper board has the effect of increasing the thermal conductivity of the board (i.e., decreased insulation).

[0015] Paperboard webs made according to the invention exhibit increased insulative properties compared to conventional single ply paperboard webs and are significantly less expensive to produce than multi-layered paperboard products or paperboard products containing a foamed outer coating. The low density paperboard material may therefore be converted into cups and other insulated containers on conventional processing equipment with minimal loss in machine speed, and a reduced tendency to form buckles and other irregularities in the converting operations.

[0016] A key feature of the invention is the use of expandable microspheres in the papermaking furnish and a resulting relatively low density / high caliper board containing the expanded spheres. Although the presence of microspheres in the papermaking furnish had been thought to adversely effect physical properties of the resulting materials for certain end use applications, it has now been found that by producing the materials according to the invention, the resulting board may be readily converted into containers such as insulated cups. Without desiring to be bound by theory, it is believed that suitable insulative paperboard products having strength properties required for cup converting operations may be produced by significantly increasing the caliper of the material and decreasing the density (compared to conventional board products) while maintaining a relatively high internal bond.

Problems solved by technology

However, multi-layered and multi-walled paper-based containers are relatively expensive to manufacture compared to polystyrene foam-based articles and often do not exhibit comparable insulative properties.

Paperboard containers having an outer foam insulation layer are generally less expensive to produce than double-walled containers, but the outer surface is less compatible with printing.

However, the '934 patent deals with relatively low basis weight paper not suitable for insulated container manufacture, makes no mention of use of the product in the manufacture of paperboard containers having insulative properties, and gives no teaching as to how such a product could be produced so as to enable use of the product in fabricating insulative containers such as cups and the like.

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