Paper making and fiber liberation – Processes and products – Multi-layer waterlaid webs or sheets
Reexamination Certificate
1999-05-19
2002-04-30
Chin, Peter (Department: 1731)
Paper making and fiber liberation
Processes and products
Multi-layer waterlaid webs or sheets
C162S125000, C162S127000, C162S129000, C162S130000, C162S135000, C162S137000, C162S158000
Reexamination Certificate
active
06379497
ABSTRACT:
BACKGROUND OF THE INVENTION
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 paperboard has to have good thermal resistance, improved formability, and, to be economical, reduced board weight, or, for premium applications, increased container rigidity. The fiber weight (hereinafter “w”) of the paperboard should be at least about forty pounds 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 of this invention is in the range of about 3 to 9 pounds per 3000 square foot ream at a fiberboard thickness of 0.001 inch. The preferred fiber mat density is in the range of about 4.5 to 8.3 pounds per 3000 square foot ream at a fiberboard thickness of 0.001 inch. To achieve the superior properties of our novel cellulosic paperboard, it has been discovered that the board at a fiber mat density of 3, 4.5, 6.5, 7, 8.3, and 9 pounds per 3000 square foot ream at a fiberboard thickness of 0.001 inch, should have a GM Taber stiffness of at least 0.00716 w
2.63
grams-centimeters/fiber mat density
1.63
pounds per 3000 square foot ream at a fiberboard thickness of 0.001 inch, and a GM tensile stiffness of at least about 1890+24.2 w pounds per inch. The preferred GM Taber stiffness value for paperboards having the fiber mat density given above is 0.00501 w
2.63
grams-centimeter/fiber mat density
1.63
pounds per 3000 square foot ream at a fiberboard thickness of 0.001 inch, and the GM tensile stiffness is 1323+24.2 w pounds per inch. The high GM Taber stiffness values listed are desired to facilitate the bending of the paperboard into the aforementioned articles of manufacture and to provide these articles with greater rigidity. Likewise the high GM Taber and GM tensile stiffness prevents the plates, cups, and other articles of manufacture from collapsing when used by the consumer. The articles of manufacture can suitably be prepared from either one-ply or multi-ply paperboard as disclosed herein. The present invention provides one-ply and multi-ply paperboard comprising (a) predominantly cellulosic fibers, (b) bulk and porosity enhancing additive interspersed with the cellulosic fibers in a controlled distribution throughout the thickness of the paperboard, and (c) size press applied binder coating optionally including a pigment adjacent both surfaces of the paperboard and penetrating into the board to a controlled extent. The amount of size press applied is at least one pound for each three thousand square foot ream of paperboard having a fiber mat density of about 3 to below 9 pounds per 3000 square foot ream at a fiberboard thickness of 0.001 inch. For boards having a fiber mat density of 9 pounds per 3000 square foot ream at a fiberboard thickness of 0.001 inch or a greater density, the amount of size press applied should be at least six pounds for each three thousand square foot ream. The overall fiber weight of the paperboard is at least 40 lbs. per 3000 square foot ream, suitably 60 to 320 lbs. per 3000 square foot ream, preferably 70 to 240 lbs. per 3000 square foot ream, most preferably 80 to 220 lbs. per 3000 square foot ream, and the distribution of the bulk and porosity enhancing additive is controlled so that at least twenty percent of the additive is distributed in the central layer and not more than 75 percent of the additive is distributed on the periphery of the paperboard with no periphery having more than twice the percent of the additive distributed in the central layer of the paperboard. The penetration of the size press applied binder and optionally pigment coating into board is controlled to produce a cellulosic fiber board web having at a fiber mat density of 3, 4.5, 6.5, 7, 8.3, and 9 pounds per 3000 square foot ream at a fiberboard thickness of 0.001 inch, a GM Taber stiffness respectively of at least 0.00716 w
2.63
grams-centimeter/fiber mat density
1.63
pounds per 3000 square foot ream at a fiberboard thickness of 0.001 inch, and GM tensile stiffness of about 1890+24.2 w pounds per inch. The preferred GM Taber stiffness for the paperboard of this invention having a fiber mat density of 3, 4.5, 6.5, 7, 8.3, and 9 pounds per 3000 square foot ream at a fiberboard thickness of 0.001 inch is 0.00501 w
2.63
grams-centimeter/fiber mat density
1.63
pounds per 3000 square foot ream at a fiberboard thickness of 0.001 inch, and the preferred GM tensile stiffness is 1323+24.2 w pounds per inch. The GM tensile and GM Taber values for the web and one-ply board are the same. For multi-ply board the overall paperboard GM Taber stiffness and GM tensile stiffness are the same as for a one-ply paperboard. The aforementioned combination of GM Taber stiffness and GM tensile stiffness provides a paperboard which can readily be converted to useful high quality cups, plates, compartmented plates, bowls, canisters, French fry sleeves, hamburger clam shells, rectangular take-out containers, food buckets, and other consumer products and useful articles of manufacture including cartons and folding paper boxes. This paperboard is also particularly suitable for the manufacture of heat insulating paperboard containers having on their wall surfaces a foamed layer of a thermoplastic film such as a polyethylene.
FIELD OF INVENTION
This invention relates to an improved paperboard, to improved shaped paperboard products, and to methods of making such paperboard and shaped paperboard products including heat insulating paperboard containers such as cups having as their wall surface a foamed layer of a thermoplastic film. More particularly, this invention is directed to an improved bulk-enhanced paperboard, to methods of making such an improved paperboard, and to shaped paperboard products made from such improved paperboard.
DESCRIPTION OF BACKGROUND ART
Prior art has not been able to produce a paperboard having the GM Taber stiffness and GM tensile of the board of this invention. 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.
The void volume provided by the microspheres reduces the rate of thermal transfer within the paper, which is desirable in
Sandstrom Erland
Shanton Kenneth J.
Swoboda Dean
Chin Peter
Finnegan, Henderson & Farabow, Garrett & Dunner, L.L.P
Fort James Corporation
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