Coated paperboards and paperboard containers having improved tactile and bulk insulation properties

Abstract

An improved paperboard has been bulk enhanced by retaining a substantial portion microspheres in a suitable distribution within the paperboard. As in one embodiment, the high retention of the bulk enhancing additives is believed to result from the incorporation of suitable retention aids. The paperboard is able to be formed into suitable paperboard containers without loss of integrity. The resulting containers have increased hold times when they contain hot or cold food or drink.

Description

[0001] This is a continuation of application Ser. No. 10 / 801,825, filed Mar. 17, 2004, now co-pending, which is a continuation of application Ser. No. 09 / 018,563, filed Feb. 4, 1998, now U.S. Pat. No. 6,740,373 B1, which is a continuation-in-part of application Ser. No. 08 / 806,947, filed Feb. 26, 1997, now abandoned, all of which are incorporated herein by reference in their entireties.BACKGROUND OF THE INVENTION [0002] Disposable paper containers, such as plates, trays, bowls, airline meal containers and cafeteria containers, are commonly produced by pressing flat paperboard blanks into the desired shape between appropriately shaped and heated forming dies. Various protective coatings are typically applied to the blanks before forming to make the resulting paperboard containers moisture-resistant, grease-resistant, more readily printable, etc. Often, printing is also applied to the top surface for decoration. A large number of paper products are produced by this method every year. ...

AI Technical Summary

Benefits of technology

[0029] The texture coated cellulosic paperboard must reconcile several conflicting properties to be useful for the manufacture of plates, cups, bowls, canisters, French fry sleeves, hamburger clam shells, rectangular take-out containers, and related articles of manufacture. The coated paperboard should have improved thermal resistance, improved formability, and, to improve economics, the whole board need not be covered with the coating. Additionally the coated paperboard may have reduced board weight and, for premium applications, increased container rigidity. All of the conventional paperboards can be utilized; but for enhanced insulation properties, the fiber weight (hereinafter “w”) of the paperboard should be at least about forty pounds for each three thousand square foot ream. However, for some applications, enhanced properties are achieved for paperboards having a fiber weight of about 10 pounds or less for each three thousand square foot ream. Fiber weight is the weight of fiber in pounds for each three thousand square foot ream. The fiber weight is measured at standard TAPPI conditions which provide that the measurements take place at a fifty percent relative humidity at seventy degrees Fahrenheit. In general, the fiber weight of a 3000 square foot ream is equal to the basis weight of such a ream minus the weight of any coating and / or size press. The fiber mat density of the paperboard utilized in the manufacture of textured containers may be in the range of from at least about 3 to at least about 9 pounds per 3000 square foot ream at a thickness of 0.001 inches. The fiber mat density of the paperboard can be greater that 9 pounds per 3000 square foot ream at a thickness of 0.001 inches. In one embodiment, the fiber mat density is in the range of at least about 4.5 to at least about 8.3 pounds per 3000 square foot ream at a fiberboard thickness of 0.001 inches.

[0035] Sizing agents may also be employed. In one embodiment, about 1 to about 30 pounds of sizing agent for a three thousand square foot ream may be used for paperboards having fiber mat densities of from about 3 to at least about 8.3 pounds per 3000 square foot ream at a fiberboard thickness of 0.001 inches. In another embodiment, 6-30 pounds of sizing agent may be used for a three thousand square foot ream of paperboard having a fiber mat density greater than about 8.3 pounds per 3000 square foot ream at a fiberboard thickness of 0.001 inches. In still yet another embodiment, 0 to about 6 pounds of sizing agent is used for paperboards having fiber mat densities of from about 3 to at least about 9 pounds per 3000 square foot ream at a fiberboard thickness of 0.001 inches. In another embodiment, about 15 to about 30 pounds of the sizing agent is utilized. In still yet another embodiment, about 16 about 19 pounds of the sizing agent is used for each three thousand square foot ream. By controlling the amount of sizing agent added, the GM tensile stiffness of the board may also be controlled.

[0037] The bulk enhanced paperboard of the present invention may be pressed into high quality articles of manufacture having a high GM Taber stiffness and GM tensile stiffness. Useful articles made from the bulk enhanced paperboard include cartons, folding paper boxes, cups, plates, compartmented plates, bowls, canisters, French fry sleeves, hamburger clam shells, rectangular take-out containers, food buckets, heat insulating containers coated or laminated with a polyolefin and foamed with the water contained in the fiberboard, and food containers with a microwave susceptor layer. The articles of manufacture of the present invention are characterized by having excellent insulation properties. These properties enhance the hot and cold containers of this invention. The GM Taber stiffness and GM tensile stiffness for the one-ply web may be the same as for the one-ply paperboard. For multi-ply boards, the GM Taber stiffness and GM tensile stiffness may be the same as for the one-ply paperboard.

Problems solved by technology

While a sense of bulkiness may be provided to some extent in styrofoam and thick pulp-molded containers, such containers suffer a number of drawbacks.

For example, unlike pressed paperboard containers, styrofoam containers are often brittle and they are environmentally unfriendly because they are not biodegradable.

Also, styrofoam containers are not cut-resistant and it is difficult to apply printing to the surface of styrofoam containers.

Additionally, because of their bulkiness, styrofoam containers take up large amounts of shelf space and are costly to ship.

Pulp-molded containers similarly are not cut-resistant and have poor printability characteristics.

Additionally, pulp-molded containers typically have weak bottoms.

It should be noted that prior art extrusion foamed coatings cannot be pattern applied, and therefore have to cover the whole side of the board.

Prior art bulk-enhanced paper products, such as those disclosed in U.S. Pat. Nos. 3,941,634 and 3,293,114, resulting from the addition of expandable microspheres and other bulk enhancing additives and methods for making such paper, suffer from a number of drawbacks.

For example, one persistent problem in such papers is poor retention of the expandable microspheres or other bulk enhancing additives on the embryonic paper web made in the course of manufacturing the paperboard.

This poor retention results in relatively low bulk enhancement of the resulting paperboard per unit weight of bulk enhancing additive added, making the enhancement process unnecessarily costly.

A further problem resulting from the poor retention of microspheres and other bulk enhancers experienced in prior art bulk enhancement methods is fouling of the papermaking apparatus with unretained microspheres and other bulk enhancing additives.

A related problem associated with the addition of microspheres and other bulk enhancing additives in the papermaking process is their uneven distribution within the resulting paperboard.

Paperboards prepared using prior art enhancement techniques have exhibited a decided asymmetry, with microspheres and other bulk enhancing additives migrating to one of the outer surfaces of the paper web and causing undesired roughness in the surface of the finished paper and hence interference with the smooth and efficient operation of the papermaking apparatus.

However, the asymmetric distribution of microspheres experienced in the prior art produces uneven thermal insulating characteristics.

In addition, prior art techniques have not created a satisfactory bulk-enhanced paperboard.

Prior art products tend to have low thermal insulative properties.

The excessive concentration of microspheres at the paper surface creates dusting, which interferes with the operation of printing presses in which the paperboard is used.

The printability of the paperboard itself, that is, the satisfactory retention of printed matter on the paperboard, is also adversely affected by such dusting.

Prior art attempts at addressing the above and other drawbacks and disadvantages of paper containing microspheres and other bulk enhancing additives have been unsatisfactory and have had their own drawbacks and disadvantages.

The introduction of the second paper web adds complexity and expense to the papermaking process.

Furthermore, the Nisser process generally does not optimize thermal insulation characteristics because it does not produce a sufficiently even distribution of microspheres within the resulting paper.

The same problems are encountered in U.S. Pat. No. 3,293,114 and make the use of current bulk-enhanced papers in thermal insulation applications problematic.

This approach, again, has failed to achieve the desired distribution and retention of microspheres, as well as other desirable paper characteristics.

In addition to the expensive film forming materials described in the George Treier article, the Treier process increases the complexity and cost of manufacturing paperboard.

This reduced deformability interferes particularly with top curl forming in rolled brim containers made from bulk-enhanced paperboard.

It also interferes with the drawing of cups, plates, bowls, canisters, French fry sleeves, hamburger clam shells, rectangular take-out containers, and food buckets, the reduced deformability in forming dies, and all other applications requiring deformation of bulk-enhanced paper generally and bulk-enhanced paperboard in particular.

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