CN110869558A

CN110869558A - Paperboard, paperboard container and method for using paperboard product

Info

Publication number: CN110869558A
Application number: CN201880046471.2A
Authority: CN
Inventors: C.C.杨; R.巴瓦伊; C.E.阿尔基维奇
Original assignee: WestRock MWV LLC
Current assignee: WestRock MWV LLC
Priority date: 2017-07-10
Filing date: 2018-06-29
Publication date: 2020-03-06
Also published as: WO2019014000A1; KR20200028900A; EP3652380A1; US20190009970A1; JP2020526421A; CA3067595A1; BR112019025570A2

Abstract

A method for using a paperboard product includes heating the paperboard product by microwave radiation. A paperboard product comprising: a paperboard substrate having a first major side and a second major side; and one or more layers of high density polyethylene on at least one of the first and second major sides of the paperboard substrate.

Description

Paperboard, paperboard container and method for using paperboard product

Technical Field

The present application relates to polymer coated paperboard, and more particularly, to polymer coated paperboard that can be converted into a container suitable for heating or cooking of food by microwave radiation.

Background

In the 1950 s, extrusion coating of low density polyethylene was first used to coat meat wrapping paper, and low density polyethylene was widely used as a barrier coating for hot and cold drinking cups, as well as in a variety of other applications.

Polypropylene resins have been used in all plastic containers for microwave heating of food. The polypropylene coated paperboard can be converted into a container or cup suitable for heating or cooking of food by microwave radiation. However, extrusion coating polypropylene onto paperboard and converting the polypropylene coated paperboard into containers and cups has created challenges for the paperboard industry. To address the challenges of extrusion coating polypropylene onto paperboard and converting polypropylene coated paperboard, a mixture of polypropylene and 20% low density polyethylene is coated onto paperboard to make a polymer coated paperboard that can be converted into a container suitable for food heating or cooking by microwave radiation.

Those skilled in the art continue to make research and development efforts in the field of polymer coated paperboard.

Disclosure of Invention

In one aspect, the disclosed method for using a paperboard product includes heating the paperboard product by microwave radiation. A paperboard product comprising: a paperboard substrate having a first major side and a second major side; and one or more layers of high density polyethylene on at least one of the first and second major sides of the paperboard substrate.

In another aspect, a paperboard container is disclosed that includes: a paperboard substrate having a first major side facing an interior of the paperboard container and a second major side facing an exterior of the paperboard container; and one or more layers of high density polyethylene directly on the first main side of the paperboard substrate.

In another aspect, a paperboard is disclosed that is comprised of: a paperboard substrate having a first major side and a second major side; one or more layers of high density polyethylene on one or both of the first and second major sides of the paperboard substrate; and optionally a clay coating layer between the one or more high density polyethylene layers on one or both of the first major side and the second major side of the paperboard substrate.

Other aspects of the disclosed paperboard, paperboard container, and method for using a paperboard product will become apparent from the following description, the accompanying drawings, and the appended claims.

Drawings

FIG. 1 is a cross-section of a paperboard according to a first embodiment;

FIG. 2 is a cross-section of a paperboard according to a second embodiment;

FIG. 3 is a cross-section of a paperboard according to a third embodiment;

FIG. 4 is a cross-section of a paperboard according to a fourth embodiment;

FIG. 5 is a cross-section of a paperboard according to a fifth embodiment;

FIG. 6 is a cross-section of a paperboard according to a sixth embodiment;

FIG. 7 is a cross-section of a paperboard according to a seventh embodiment;

FIG. 8 is a cross-section of a paperboard according to an eighth embodiment;

FIG. 9 is a schematic view of an extrusion coating system for coating a high density polyethylene layer onto a paperboard substrate;

FIG. 10 is a top view of an unprinted sidewall blank;

FIG. 11 is a top plan view of a printed side wall blank having indicia printed on a major side thereof;

FIG. 12 is a perspective view of an embodiment of an exemplary paperboard container;

FIG. 13 is a cross-sectional side view of the paperboard container of FIG. 12;

FIG. 14 is a perspective view of the lid of the paperboard container of FIG. 12;

FIG. 15 is a perspective view of another embodiment of an exemplary paperboard container;

FIG. 16 is a cross-sectional side view of the paperboard container of FIG. 15;

FIG. 17 is a graph relating to a polymer extrusion coating test showing melt curtain neck-in of paperboard with a high density polyethylene coating compared to melt curtain neck-in of paperboard with a polypropylene/low density polyethylene coating;

figure 18 is a graph relating to polymer extrusion coating tests showing the level of corona treatment of paperboard with a high density polyethylene coating compared to the level of corona treatment of paperboard with a polypropylene/low density polyethylene coating;

FIG. 19 is a graph relating to polymer extrusion coating tests showing the coefficient of friction (CoF) of paperboard with a high density polyethylene coating compared to the coefficient of friction (CoF) of paperboard with a polypropylene/low density polyethylene coating;

FIG. 20 is a graph relating to polymer extrusion coating tests showing the abrasion resistance of paperboard with a high density polyethylene coating compared to the abrasion resistance of paperboard with a polypropylene/low density polyethylene coating;

figure 21 is a graph relating to polymer extrusion coating tests showing the Water Vapor Transmission Rate (WVTR) of paperboard with a high density polyethylene coating compared to the Water Vapor Transmission Rate (WVTR) of paperboard with a polypropylene/low density polyethylene coating; and

figure 22 is a graph relating to polymer extrusion coating tests showing the cup form heat seal curve for paperboard with a high density polyethylene coating compared to the cup form heat seal curve (profile) for paperboard with a polypropylene/low density polyethylene coating.

Detailed Description

A paperboard comprising: a paperboard substrate having a first major side and a second major side; and one or more layers of high density polyethylene on at least one of the first and second major sides of the paperboard substrate. The paperboard may further include a clay coating layer between the one or more high density polyethylene layers on one or both of the first major side and the second major side of the paperboard substrate.

Fig. 1 is a cross-section of a paperboard 10 according to a first embodiment. The paperboard 10 comprises a paperboard substrate 11 having a first major side 12 and a second major side 13; and a layer 15 of high density polyethylene on the first main side 12 of the paperboard substrate 11. The high density polyethylene layer 15 may be disposed directly (i.e., without an intervening layer) on the first major side 12 of the paperboard substrate 11. A layer 15 of high density polyethylene may be disposed at the outermost surface of the paperboard 10 at the first major side 12. The paperboard substrate 11 may be disposed at the outermost surface of the paperboard 10 at the second major side 13.

Fig. 2 is a cross-section of a paperboard 20 according to a second embodiment. The paperboard 20 includes a paperboard substrate 21 having a first major side 22 and a second major side 23; a clay coating layer 24 on the first major side 22 of the paperboard substrate 21; and a high density polyethylene layer 25 on the clay coating layer 24. The clay coating layer 24 may be disposed directly (i.e., without an intervening layer) on the first major side 22 of the paperboard substrate 21. The high density polyethylene layer 25 can be disposed directly (i.e., without an intervening layer) on the clay coating layer 24. A high density polyethylene layer 25 may be disposed at the outermost surface of the paperboard 20 at the first major side 22. The paperboard substrate 21 may be disposed at the outermost surface of the paperboard 20 at the second major side 23.

Fig. 3 is a cross-section of a paperboard 30 according to a third embodiment. The paperboard 30 includes: a paperboard substrate 31 having a first major side 32 and a second major side 33; a high density polyethylene layer 35 on the first major side 32 of the paperboard substrate 31; and a clay coating layer 36 on the second major side 33 of the paperboard substrate 31. The high density polyethylene layer 35 may be disposed directly (i.e., without an intervening layer) on the first major side 32 of the paperboard substrate 31. The clay coating layer 36 may be disposed directly (i.e., without an intervening layer) on the second major side 33 of the paperboard substrate 31. A high density polyethylene layer 35 may be arranged at the outermost surface of the paperboard 30 at the first main side 32. The clay coating layer 36 may be disposed at the outermost surface of the paperboard 30 at the second major side 33.

Fig. 4 is a cross-section of a paperboard 40 according to a fourth embodiment. The paperboard 40 includes: a paperboard substrate 41 having a first major side 42 and a second major side 43; a first clay coating layer 44 on the first major side 42 of the paperboard substrate 41; a high density polyethylene layer 45 on the first clay coating layer 44; and a second clay coating layer 46 on the second major side 43 of the paperboard substrate 41. The first clay coating layer 44 may be disposed directly (i.e., without an intervening layer) on the first major side 42 of the paperboard substrate 41. The high density polyethylene layer 45 can be disposed directly (i.e., without an intervening layer) on the first clay coating layer 44. The second clay coating layer 46 may be disposed directly (i.e., without an intervening layer) on the second major side 43 of the paperboard substrate 41. A high density polyethylene layer 45 may be arranged at the outermost surface of the paperboard 40 at the first main side 42. A second clay coating layer 46 may be disposed at the outermost surface of the paperboard 40 at the second major side 43.

Fig. 5 is a cross-section of a paperboard 50 according to a fifth embodiment. The paperboard 50 includes: a paperboard substrate 51 having a first major side 52 and a second major side 53; a first high density polyethylene layer 55 on the first main side 52 of the paperboard substrate 51; and a second high density polyethylene layer 57 on the second major side 53 of the paperboard substrate 51. The first high density polyethylene layer 55 may be disposed directly (i.e., without an interposer) on the first major side 52 of the paperboard substrate 51. The second high density polyethylene layer 57 may be disposed directly (i.e., without an intervening layer) on the second major side 53 of the paperboard substrate 51. A first high density polyethylene layer 55 may be arranged at the outermost surface of the paperboard 50 at the first main side 52. A second high density polyethylene layer 57 may be arranged at the outermost surface of the paperboard 50 at the second main side 53.

Fig. 6 is a cross-section of a paperboard 60 according to a sixth embodiment. The paperboard 60 includes: a paperboard substrate 61 having a first major side 62 and a second major side 63; a clay coating layer 64 on the first major side 62 of the paperboard substrate 61; a first high density polyethylene layer 65 on the clay coating layer 64; and a second high density polyethylene layer 67 on the second major side 63 of the paperboard substrate 61. The clay coating layer 64 may be disposed directly (i.e., without an intervening layer) on the first major side 62 of the paperboard substrate 61. The first high density polyethylene layer 65 can be disposed directly (i.e., without an intervening layer) on the clay coating layer 64. The second high density polyethylene layer 67 may be disposed directly (i.e., without an intervening layer) on the second major side 63 of the paperboard substrate 61. A first high density polyethylene layer 65 may be arranged at the outermost surface of the paperboard 60 at the first main side 62. A second high density polyethylene layer 67 may be disposed at the outermost surface of the paperboard 60 at the second major side 63.

Fig. 7 is a cross-section of a paperboard 70 according to a seventh embodiment. The paperboard 70 includes: a paperboard substrate 71 having a first major side 72 and a second major side 73; a first high density polyethylene layer 75 on the first major side 72 of the paperboard substrate 71; a clay coating layer 76 on the second major side 73 of the paperboard substrate 71; and a second high density polyethylene layer 77 on the clay coating layer 76. The first high density polyethylene layer 75 may be disposed directly (i.e., without an intervening layer) on the first major side 72 of the paperboard substrate 71. The clay coating layer 76 may be disposed directly (i.e., without an intervening layer) on the second major side 73 of the paperboard substrate 71. The second high density polyethylene layer 77 can be disposed directly (i.e., without an intervening layer) on the clay coating layer 76. A first high density polyethylene layer 75 may be disposed at the outermost surface of the paperboard 70 at the first major side 72. A second high density polyethylene layer 77 may be disposed at the outermost surface of the paperboard 70 at the second major side 73.

Fig. 8 is a cross-section of a cardboard 80 according to an eighth embodiment. The paperboard 80 includes: a paperboard substrate 81 having a first major side 82 and a second major side 83; a first clay coating layer 84 on the first major side 82 of the paperboard substrate 81; a first high density polyethylene layer 85 on the first clay coating layer 84; a second clay coating layer 86 on the second major side 83 of the paperboard substrate 81; and a second high density polyethylene layer 87 on the second clay coating layer 86. The first clay coating layer 84 may be disposed directly (i.e., without an intervening layer) on the first major side 82 of the paperboard substrate 81. The first high density polyethylene layer 85 can be disposed directly (i.e., without an intervening layer) on the first clay coating layer 84. The second clay coating layer 86 may be disposed directly (i.e., without an intervening layer) on the second major side 83 of the paperboard substrate 81. The second high density polyethylene layer 87 can be disposed directly (i.e., without an intervening layer) on the second clay coating layer 86. A first high density polyethylene layer 85 may be disposed at the outermost surface of the paperboard 80 at the first major side 82. A second high density polyethylene layer 87 may be arranged at the outermost surface of the cardboard 80 at the second main side 83.

While various embodiments of the paperboard have been described above with reference to fig. 1-8, modifications will occur to those skilled in the art upon reading the specification. For example, in any of the above figures 1-8, any of the high density polyethylene layers may be replaced with a plurality of high density polyethylene layers. The present application includes such modifications and is limited only by the scope of the claims.

The paperboard substrate may comprise any web of fibrous material capable of having a high density polyethylene layer applied thereto. The paperboard substrate may be bleached or unbleached. For example, the paperboard substrate may comprise coated natural kraft board, full sulfate bleached pulp board (white core white card), full unbleached sulfate pulp board (solid unbleached pulp board), coated recycled board, coated white lined chip board (grey board), or folding box board (yellow core white card).

The thickness of the paperboard substrate may depend on various factors, such as the density of the paperboard substrate. For example, the paperboard substrate may have a paperboard thickness (caliper thickness) in the range of 6 points to 36 points (1 point equals 0.001 inches). As one particular example, the paperboard substrate may have a paperboard thickness of 7 points to 30 points. As another specific example, the paperboard substrate may have a paperboard thickness in the range of 14 points to 20 points. As yet another specific example, the paperboard substrate may have a paperboard thickness in the range of 16 points to 18 points. As used herein, a 1 point is equal to 0.001 inches, and 0.001 inches is equal to 25.4 micrometers (μm).

The weight of the paperboard substrate may depend on various factors. For example, the paperboard substrate may have a basis weight ranging from 60 to 350 pounds per 3,000 square feet(basis weight). As one particular example, the paperboard substrate may have every 3000ft²A basis weight of 100 to 150 pounds. As another specific example, the paperboard substrate may have every 3000ft²A basis weight of 150 to 180 pounds. As yet another specific example, the paperboard substrate may have every 3000ft²A basis weight of 180 to 220 pounds.

A clay coating layer may be applied to the paperboard substrate to improve the print quality of the surface of the paperboard. The clay coating layer may include a mixture of inorganic pigments and one or more other materials such as binders (e.g., emulsion polymer binders) and dispersants. In a particular example, the clay coating layer may include kaolin clay.

The clay coating layer may be applied in any manner that enables the clay coating layer to be applied to the paperboard substrate. In a specific example, a clay coating layer may be applied to a paperboard substrate. Examples of coaters that may be used include air knife coaters, rod coaters, multi-head coaters, roll/knife coaters, cast coaters, lab coaters, gravure coaters, kiss coaters, liquid application systems, reverse roll coaters, curtain coaters, spray coaters, and extrusion coaters.

The inventors have surprisingly found that the high density polyethylene protects the paperboard substrate from moisture even after heating the paperboard substrate by microwave radiation.

The density of the high density polyethylene of the one or more high density polyethylene layers may vary from 0.93 to 0.97g/cm³. In one example, the density of the high density polyethylene varies from 0.95 to 0.96 g/cm³. In one aspect, the high density polyethylene can have a melt index greater than 0.3 g/10min (190 ℃/2.16 kg). In another aspect, the high density polyethylene can have a melt index greater than 4 g/10min (190 ℃/2.16 kg). In yet another aspect, the high density polyethylene can have a melt index greater than 8 g/10min (190 ℃/2.16 kg). In one aspect, a first layer of the one or more high density polyethylene layers may have a first density and a first melt index, and the one or more high density polyethylene layersA second of the ene layers may have a second density and a second melt index different from the first density and the first melt index.

An exemplary high density polyethylene layer is a single layer of 100% high density polyethylene resin extrusion coated on either or both sides of a paperboard substrate, wherein the high density polyethylene has 0.950 g/cm according to ASTM D792³And a Melt Index (MI) of 12 g/10min at 190 ℃ under a 2.16 kg load according to ASTM D1238.

The one or more high density polyethylene layers may be applied to the paperboard substrate using any available technique. Examples of suitable techniques for applying the one or more high density polyethylene layers include extrusion coating, extrusion lamination, curtain coating, and adhesive lamination. In one example, multiple high density polyethylene layers may be coextruded onto a paperboard substrate. In another example, a first high density polyethylene layer may be laminated to paperboard, and then a second high density polyethylene layer may be extruded onto the paperboard. In yet another example, a first high density polyethylene layer may be extruded onto paperboard, and then a second high density polyethylene layer may be laminated onto the paperboard.

Fig. 9 illustrates an exemplary extrusion coating system 90 for coating a high density polyethylene layer onto a paperboard substrate. As shown, the paperboard substrate 91 may be unwound from an unwind roll 92 and passed between a gloss roll 93 and a chill roll 94 and wound onto a rewind roll 95. At the same time, resin 96 may be extruded from slot die 97 at elevated temperature onto a moving paperboard substrate. The resin coated paperboard substrate 91 may then be passed through a gloss roll 93 and a chill roll 94 to cool the resin 96 and impart the desired finish. The thickness of the coating can be controlled by controlling the ratio of the speed of the moving paperboard substrate 91 to the speed of the resin 96 extruded from the slot die 97.

The composition of the one or more high density polyethylene layers may be a pure high density polyethylene layer or may be a mixture of high density polyethylene and one or more other materials that do not inhibit the ability of the high density polyethylene layer to protect the paperboard substrate from moisture even after the paperboard substrate is heated by microwave radiation. For example, the one or more high density polyethylene layers can comprise high density polyethylene in an amount of 50% or more (such as 60% or more, 70% or more, 80% or more, 90% or more, 95% or more, 99% or more, or 100%) of the high density polyethylene layers. In an example, the first high density polyethylene layer may comprise a first percentage of high density polyethylene and the second high density polyethylene layer may comprise a second percentage of high density polyethylene different from the first percentage of high density polyethylene.

The disclosed paperboard can be made into paperboard products using any available technique. While various operations for making the paperboard product are described below, modifications will occur to those skilled in the art upon reading the specification. The present application includes such modifications and is limited only by the scope of the claims.

The disclosed paperboard may be printed with indicia, such as high quality advertising text and graphics, on one or both major sides by a printing operation. The printing operation may include any device or system capable of identifying the paperboard with indicia. For example, the printing operation may include a printer capable of printing high quality text and/or graphics (e.g., advertising text and graphics) onto cardboard. Specific examples of printing techniques include offset printing, gravure printing, flexographic printing, and digital printing.

The disclosed paperboard may be cut into blanks by a cutting operation. The cutting operation may include any device or system capable of cutting a blank from a paperboard. For example, the cutting operation may comprise a die cutter. The cutting operation may provide a blank having a desired shape. The shape of the blank may depend on the intended shape and configuration of the paperboard product. Further, where the cutting is performed after the printing operation, the cutting operation may cut the blank such that the printed indicia is positioned at a desired location.

The blank may be formed into a paperboard product by a forming operation. The forming operation may shape and assemble one or more blanks into a paperboard product having a desired shape and configuration. The forming operation may include any apparatus or system capable of forming one or more blanks into a paperboard product having a desired shape and configuration. The forming operation may, for example, comprise a stamping die or a thermoforming die.

Although the various operations of making the paperboard product are described above in a particular order, and as separate operations performed by separate machines or systems, it should be understood that one or more of the operations may be performed in a different order, combined into a single operation, divided into multiple operations, or performed by a single machine or system.

Embodiments of methods for using paperboard products can include heating the disclosed paperboard products by microwave radiation. For example, a paperboard product can be heated by microwave radiation (such as by heating the paperboard product in a microwave oven), wherein the paperboard product comprises: a paperboard substrate having a first major side and a second major side; and one or more layers of high density polyethylene on at least one of the first and second major sides of the paperboard substrate. During heating of the paperboard product, the food product (e.g., soup, oatmeal, coffee, water, etc.) may be on the surface of the paperboard product.

In an example, the paperboard product may be a paperboard container (e.g., cup, bowl). The paperboard container can have any desired container configuration.

It will be understood that paperboard containers can be made from the disclosed paperboard using any available technique. While various operations for making paperboard containers are described below, modifications will occur to those skilled in the art upon reading the specification.

A roll of the disclosed paperboard can be printed with indicia on one or both major sides by a printing operation, such as by offset, gravure, flexographic, or digital printing. The printed or unprinted paperboard may be cut into container blanks, such as side wall blanks, bottom blanks, or lid blanks, by a cutting operation, such as by a die cutter. Fig. 10 and 11 illustrate

exemplary sidewall blanks

100, 110 that may be used in the manufacture of paperboard containers. Fig. 10 shows an unprinted sidewall blank 100 and fig. 11 shows a printed sidewall blank 110 having indicia 112 printed on major sides thereof.

The printed or unprinted container blank is then formed into a paperboard container by a forming operation. For example, the

sidewall blanks

100, 110 of fig. 10 or 11 may be shaped in the following manner: the

sidewall blanks

100, 110 are wrapped around a mandrel to form a frustoconical sidewall. In one example, the side wall blank may have a 16 point paperboard thickness. The sidewalls may be completed by: longitudinal ends of the shaped sidewall blanks are overlapped and sealed to form an overlapped and sealed seam. The seam may be sealed using any available technique. In one example, the seam may be sealed by heating and joining the first high density polyethylene layer and the second high density polyethylene layer at the overlap. In another example, the seam may be sealed by: the first longitudinal end is folded and the first high density polyethylene layer at the first longitudinal end and the first high density polyethylene layer at the second longitudinal end are heated and joined.

In a non-limiting embodiment, the container may include a bottom. The bottom may be made of the disclosed paperboard, different paperboard or non-paperboard materials. In one example, the bottom blank may have a 13 point paperboard thickness. Any available technique may be used to seal the bottom to the sidewall. In an example, a lower end of the sidewall may be shaped to form a circumferential recess. The bottom portion may be placed into the circumferential recess and sealed to the sidewall. In a particular example, at least one of the side wall and the bottom has a high density polyethylene layer, which facilitates excellent sealing.

In a non-limiting embodiment, the container may include a lid. The lid may be made from the disclosed paperboard, different paperboard, or non-paperboard materials such as film materials (e.g., polymers; metals; metal-polymer combinations), pressed-on lids (e.g., molded plastic lids), and the like. The lid may be sealed to the sidewall or may remain an unsealed lid. The lid may be sealed to the side wall using any available technique and may depend on the type of lid used, among other possible factors. In a particular example, at least one of the sidewall and the lid has a high density polyethylene layer, which facilitates excellent sealing.

During packaging, a food product (e.g., soup, oatmeal, etc.) may be placed into the interior volume of the paperboard container, and the lid may be sealed to the sidewall of the paperboard container, such as with a heat seal, adhesive, or interference fit.

In an example, the upper end of the sidewall can be rolled over to form a flange, and the lid can be sealed to the flange.

In another example, the film material may be sealed (such as by lamination) to the sidewalls to seal the paperboard container. A second non-sealing cover may be provided to cover the membrane material.

While various embodiments of paperboard containers are described below, modifications will occur to those skilled in the art upon reading the specification.

An embodiment of an exemplary paperboard container 120 is illustrated in fig. 12-14. A paperboard container 120 formed from the disclosed paperboard can include a sidewall 122, a bottom 124, and a lid 126. The side wall 122 may be formed by, for example, die cutting a side wall blank from a sheet of the disclosed paperboard into a desired configuration (e.g., trapezoidal), such as the

side wall blanks

100, 110 of fig. 10 and 11. The sidewall blank may include a first longitudinal end and a second longitudinal end. The sidewall 122 may be formed by overlapping two longitudinal ends to enclose the interior cavity of the container, thereby forming an overlapped seam 128 in which the first longitudinal end is positioned inward of the second longitudinal end. The seam 128 may be sealed by, for example, joining a high density polyethylene layer at the first longitudinal end to a high density polyethylene layer at the second longitudinal end.

The bottom 124 may be formed from the disclosed paperboard. The bottom 124 may be sealed to the sidewall 122 using various techniques. As one example, a lower end of the sidewall 122 may be shaped to form the circumferential recess 130. The bottom 124 may be placed into the recess 130 and sealed to the sidewall 122. Suitable techniques for sealing the bottom 124 to the sidewall 122 include hot air heat sealing and ultrasonic sealing.

The lid 126 may be an unsealed plastic lid 126. The cover 126 may be attached to the sidewall 122 by, for example, an interference fit. The upper end of the sidewall 122 may be rolled to form a bead 132. The lid 126 may be brought into an interference fit with the bead 132 at the upper end of the side wall 122 so that the lid 126 may be repeatedly removed and attached to cover the paperboard container 120.

Another embodiment of an exemplary paperboard container 140 is illustrated in fig. 15 and 16. A paperboard container 140 formed from the disclosed paperboard can include sidewalls 142, a bottom 144, and a lid 146. The side wall 142, such as the

side wall blanks

100, 110 of fig. 10 and 11, may be formed by, for example, die cutting the side wall blank into a desired configuration (e.g., trapezoidal) from a sheet of the disclosed paperboard. The sidewall blank may include a first longitudinal end and a second longitudinal end. The sidewall 142 may be formed by stacking two longitudinal ends to enclose the interior cavity of the container, thereby forming a stacked seam (not shown) in which the first longitudinal end is positioned inwardly of the second longitudinal end. The seam may be sealed, for example, by joining the high density polyethylene layer of the first longitudinal end to the high density polyethylene layer of the second longitudinal end and heating.

The bottom 144 may be formed from the disclosed paperboard. The bottom 144 may be sealed to the sidewall 142 using various techniques. As one example, a lower end of the sidewall 142 may be shaped to form a circumferential recess 150. The bottom 144 may be placed into the recess 150 and sealed to the sidewall 142. Suitable techniques for sealing the bottom 144 to the sidewall 142 include hot air heat sealing and ultrasonic sealing.

The cover may be sealed to the sidewall 142. The paperboard cover 146 can be made of the disclosed paperboard, different paperboard, or different materials, such as film materials (e.g., polymers; metals; metal-polymer combinations). The lid 146 may be sealed to the sidewall 142 using various techniques. As one example, the upper end of the sidewall may be rolled to form the flange 152, and the cover 146 may be sealed to the flange 152. The cover 146 may be sealed to the flange 152 by, for example, attaching a high density polyethylene layer of the cardboard cover 146 to a high density polyethylene layer of the flange 152 and heating. As another example, the film cover 146 may be sealed to the flange 152 by, for example, heat sealing or an adhesive, and a second cover may be provided to cover the film cover 146.

Another embodiment of an exemplary paperboard container can include a food product contained within an interior volume of the paperboard container and a lid sealing the interior volume of the paperboard container. The lid may be sealed using any available technique and may depend on the type of lid used, among other possible factors. The indicia may include instructions for heating the food product by microwave radiation. The guide may be included with the paperboard container in any manner, such as by printing on the exterior of the paperboard container or by additional packaging material attached to the paperboard container. Accordingly, a paperboard container containing a food product may be purchased by a consumer, and the food product may be heated by microwave radiation according to guidelines when the food product is contained in the paperboard container. Additional steps may be included without departing from the scope of the present disclosure.

Fig. 17-22 show the results of a High Density Polyethylene (HDPE) coating on a paperboard substrate compared to a conventional polypropylene and 20% low density polyethylene (PP/LDPE) coating on a paperboard substrate.

Figure 17 relates to polymer extrusion coating tests performed on a fully sulfate bleached pulp paperboard substrate. The die width for the polymer extrusion coating test was 19 inches. After the extrusion coating process, the width of the polymer coating on the paperboard was measured. The difference between the die width (19 inches) and the width of the polymer coating on the paperboard is referred to as the total neck-in. For polymer extrusion processes, reduced neck-in is beneficial for improving material utilization by reducing trim waste (trim waste). In the tests, HDPE extrusion coating showed a total neck-in (1.5 inches) much less than the total neck-in (3.6 inches) of PP/LDPE. HDPE extrusion coating shows better process performance than PP/LDPE extrusion coating by improving material utilization.

Figure 18 relates to polymer extrusion coating tests performed on a full sulfate bleached pulp paperboard substrate. After extrusion, a corona treatment is imparted on the polymer coating surface. The polymer surface energy as measured by dyne levels was monitored over a period of 28 days (4 weeks). For polymer coated surfaces, higher dyne levels are advantageous to ensure easy printability on polymer surfaces. In this example, the HDPE surface can be initially corona treated at a higher dyne level than the PP/LDPE surface. Dyne levels also decay more slowly for HDPE surfaces than for PP/LDPE surfaces. HDPE coatings show better printability characteristics than PP/LDPE coatings.

Figure 19 relates to polymer extrusion coating tests performed on a full sulfate bleached pulp paperboard substrate. The coefficient of friction (CoF) was measured as the friction force that caused two surfaces (i.e., the same type of polymer coating and polymer coating) to slide. A lower CoF is beneficial in reducing the force required to promote sliding of two polymer surfaces against each other. The static CoF is a measure of the initial force required to initiate the sliding motion. Kinetic CoF is a measure of the force required to maintain motion. In this example, the HDPE surface shows a lower static CoF and a lower kinetic CoF than the PP/LDPE surface. This suggests that HDPE surfaces would be more advantageous in converting and packaging processes.

Figure 20 relates to polymer extrusion coating tests performed on a full sulfate bleached pulp paperboard substrate. The abrasion resistance of the polymer coated surface was tested by subjecting the polymer surface to 2 pound weight sled sliding (sliding) and rubbing back and forth 999 times. In this test, the high density polyethylene surface showed better wear resistance than the polypropylene/low density polyethylene surface, since there was less material lost due to friction.

Figure 21 relates to polymer extrusion coating tests performed on a fully sulfate bleached pulp paperboard substrate. The Water Vapor Transmission Rate (WVTR), also known as the Moisture Vapor Transmission Rate (MVTR), of the polymer coated paperboard was measured at 100 ° F (37.8 ℃) and 90% RH (relative humidity). WVTR is a measure of water vapor transmission through a substrate. In this example, the high density polyethylene shows a lower WVTR than the polypropylene/low density polyethylene. This suggests that high density polyethylene has better moisture resistance or water vapor barrier properties than polypropylene/low density polyethylene.

Figure 22 relates to polymer extrusion coating tests performed on a fully sulfate bleached pulp paperboard substrate. The polymer coated paperboard was then cut into side wall blanks and bottom blanks suitable for a 16 ounce beverage cup form. Cup conversion tests were conducted on a PMC-1250 cup forming machine at a speed of 165 cups per minute. The sidewall temperature setting is varied. Fiber tear of the cup side seam seal was measured as an indicator of side seam heat seal performance. In this example, paperboard coated with high density polyethylene was able to be heat sealed at lower temperatures at the same cup transition speed and showed better fiber tear than paperboard coated with polypropylene/low density polyethylene.

Tables 1 and 2 relate to polymer extrusion coating tests performed on paperboard coated on one side with kaolin clay for sidewall stock and fully sulphate bleached pulp paperboard for bottom stock. The side wall stock rolls and bottom stock rolls were cut to the appropriate size for forming 12 ounce and 17 ounce cups. In both examples, high density polyethylene coated paperboard was formed and sealed at lower sidewall temperatures and faster converting speeds.

TABLE 1

Conditions for Heat sealing of cup-shaped article (12 ounce cup)

Settings/conditions	PP/LDPE Condition	HDPE Condition
			Cup speed (cup number/minute)	180	210
Side wall temperature (F)	1075	1025

TABLE 2

Conditions for Heat sealing of cup-shaped article (17 ounce cup)

Settings/conditions	PP/LDPE Condition	HDPE Condition
			Cup speed (cup number/minute)	125	135
Side wall temperature (F)	950	900

While various embodiments of the disclosed paperboard, paperboard containers, and methods for using the same have been shown and described, modifications will occur to those skilled in the art upon reading the specification. The present application includes such modifications and is limited only by the scope of the claims.

Claims

1. A method for using a paperboard product, the method comprising:

heating a paperboard product by microwave radiation, the paperboard product comprising:

a paperboard substrate having a first major side and a second major side; and

one or more layers of high density polyethylene on at least one of the first major side and the second major side of the paperboard substrate.

2. The method of claim 1, wherein the paperboard substrate comprises at least one of coated natural kraft paperboard, full sulfate bleached pulp paperboard, full unbleached sulfate pulp paperboard, coated recycled paperboard, coated white lined chip board, and folding box board.

3. The method of claim 1, wherein the paperboard substrate has a paperboard thickness in the range of 7 points to 30 points.

4. The method of claim 1, wherein at least one high density polyethylene layer has a thickness between 0.93 and 0.97g/cm³A density in the range of (a) to (b).

5. The method of claim 1 wherein at least one high density polyethylene layer has a melt index greater than 0.3 g/10min (190 ℃/2.16 kg).

6. The method of claim 1 wherein during the heating of the paperboard product, a food product is on a surface of the paperboard product.

7. The method of claim 1, wherein the paperboard product is in the configuration of a container.

8. A paperboard container, comprising:

a paperboard substrate having a first major side facing an interior of the paperboard container and a second major side facing an exterior of the paperboard container; and

one or more layers of high density polyethylene directly on the first major side of the paperboard substrate.

9. The paperboard container of claim 8, wherein the paperboard substrate is disposed at an outermost surface of the second major side of the paperboard.

10. The paperboard container of claim 8, further comprising one or more layers of high density polyethylene on the second major side of the paperboard substrate.

11. The paperboard container of claim 8, further comprising a clay coating layer on the second major side of the paperboard substrate.

12. The paperboard container of claim 11, further comprising one or more layers of high density polyethylene on the clay coating layer.

13. The paperboard container of claim 8, wherein said paperboard substrate has a paperboard thickness in the range of 7 to 30 points.

14. The paperboard container of claim 8, wherein at least one high density polyethylene layer has a thickness in the range of 0.93 and 0.97g/cm³A density in the range of (a) to (b).

15. The paperboard container of claim 8, wherein at least one high density polyethylene layer has a melt index greater than 0.3 g/10min (190 ℃/2.16 kg).

16. The paperboard container of claim 8, wherein said paperboard container is in a cup or bowl configuration.

17. The paperboard container of claim 8, wherein the paperboard container comprises a food product contained within an interior volume of the paperboard container and a lid sealing the interior volume of the paperboard container.

18. The paperboard container of claim 17, wherein the indicia on the exterior of the paperboard container or on packaging material attached to the paperboard container comprises guidelines for heating the food product by microwave radiation.

19. A paperboard, consisting of:

a paperboard substrate having a first major side and a second major side;

one or more layers of high density polyethylene on one or both of the first and second major sides of the paperboard substrate; and

optionally a clay coating layer between the paperboard substrate and the one or more high density polyethylene layers on one or both of the first major side and the second major side of the paperboard substrate.

20. The paperboard of claim 19, wherein the paperboard substrate has a paperboard thickness in the range of 7 points to 30 points.

21. The paperboard of claim 19 wherein at least one high density polyethylene layer has a thickness in the range of 0.93 and 0.97g/cm³A density in the range of (a) to (b).

22. The paperboard of claim 19, wherein at least one high density polyethylene layer has a melt index greater than 0.3 g/10min (190 ℃/2.16 kg).