WO1999056953A1

WO1999056953A1 - Laminated carton package and method of manufacture

Info

Publication number: WO1999056953A1
Application number: PCT/US1999/009992
Authority: WO
Inventors: Roger P. Hoffman
Original assignee: The Hoffman Group Ltd.
Priority date: 1998-05-06
Filing date: 1999-05-06
Publication date: 1999-11-11

Abstract

A laminated paperboard package is produced by initially printing graphics by high speed web printing on a sheet of clay-coated unbleached cellulosic fiber material such as kraft paper. The printed paper is then continuously applied to a surface of a web cellulosic substrate, and laminated to the substrate through use of an adhesive, which may be waterproof, to provide a laminated product. The laminated product is then die cut to the desired shape, folded and glued into the configuration of a box or container. A layer of water absorbent, cellulosic fiber material can be bonded to the inner surface of the substrate to prevent moisture from the contained product from seeping outwardly through the substrate to the printed paper.

Description

LAMINATED CARTON PACKAGE AND METHOD OF MANUFACTURE

BACKGROUND OF THE INVENTION In recent years with the advent of mega-retailers and mass merchandizing, packaging has rapidly evolved. Today, more than ever, packaging is an extension of the marketing effort and product differentiation is often more important than the product itself. Thus product differentiation through enhanced printed graphics on the packaging is critical. In the paper industry, the terms "paperboard" or "fiberboard" are generally considered to fall into two broad categories: 1) Containerboard - these boards are used to make corrugated containers and include corrugating medium and linerboard; and 2) Boxboard - which is used to make folding cartons such as boxes, and the like. It has been recognized that sharp, precise graphics cannot be obtained when printing directly on paperboard products, due to the fact that the paperboard printing surface is relatively rough or uneven, as compared with clay coated paper. Further, paperboard normally has a grey or brown color, and printing directly on the darker color of the paperboard will tend to distract from the resolution of the graphs.

To meet the demand for improved graphics, clay-coating may be applied directly to the paperboard substrate to improve the printing surface. In some cases, the base material is bleached and in other cases it is multi-layer recycled or unbleached board. However, the clay- coated paperboard is relatively thick and rough as compared to publication grade paper and though modern web printing processes can be employed, the quality of the graphic images achieved cannot approach those printed on publication grade paper.

There have been attempts to use white packaging substrates produced from bleached pulp. While the white substrates provide a brighter printing surface, as compared with the normal brown and grey paperboard, the white paperboard is considerably more costly to produce and lacks the strength of an unbleached pulp substrate. 2

The preponderance of white packaging has a surface made with bleached pulp or clay- coated bleached pulp. Examples of these packages include an uncoated solid bleached kraft folding carton or a white top or mottled white corrugated container where the exterior linerboard is made with multi-ply paperboard having an exterior ply of bleached fibers, virgin fibers from virgin bleached pulp or deinked recycled bleached fiber. A white package surface may also be created by using clay-coated bleached paper labels affixed or laminated to folding cartons and corrugated containers. These typically virgin bleached fiber labels may cover the entire surface of the package, or in the case of "spot" labels, they may only be applied on the major panels of the package. Unfortunately when it comes to packaging, bleached fibers are a detriment for several reasons. First, it costs more to make bleached pulp. In order to bleach wood fibers, the great majority of the lignin must be removed. The cooking process in removing lignin also removes cellulose and hemicellulose. The lower the yield the more the desirable material (cellulose and hemicellulose) is cooked away. Second, bleached pulps are weaker than unbleached pulps. This loss of strength is a result of the cellulose being damaged by the more severe pulping conditions necessary for bleaching. Additionally, hemicellulose contributes to pulp stiffness, yet is nearly completely absent in bleached pulp. Third, bleached pulps are more dense. Therefore, they have a lower caliper for a given basis weight. Package caliper is important in obtaining stiffness, and the stiffer the board the better its stacking performance will be. Finally, bleaching pulp has significant environmental consequences. The production of chlorine bleached pulp has been shown to produce dioxins and other undesirable air and water emissions.

A beverage carrier, which is a type of carton, is designed to contain beverage bottles and cans in six-packs, twelve-packs, 24-packs, cubes, or the like. As the beverage cans and bottles have considerable weight, it is important that the beverage carrier have high tear strength and, because the product is often stored in cold, damp environments, the beverage carrier board must have sufficient wet strength, the typical beverage carrier is a two-ply product. It generally consists of a base ply of virgin kraft formed from long soft wood fibers, which provide the increased tear strength, and an outer or top ply, generally formed of shorter fibers made from softwoods and hardwoods. These two plies are simultaneously bonded together on the papermaking machine. The top ply side typically receives a clay coating and graphics are then 3 subsequently printed on the clay coat. The printed sheet is then die-cut into sections and each section is folded and glued into the shape of a box or container that subsequently receives the beverage cans.

It is expensive to produce and transport the clay coated paperboard from which beverage carriers are made. Due to the relatively rough surface of the coated paperboard, the printed graphics do not have the fine or sharp resolution compared to graphics printed on publication grade paper. A problem in printing of the beverage carrier is that although it can be done on web presses, it cannot be done at high speed. Thus, cost per carton is expensive and the quality moderate by comparison to publication grade paper. Finally, the logistics of handling heavy boards through the printing process and commerce means moving greater tonnage to create the final product.

Thus, there exists a distinct market for competitively priced paperboard packaging that is environmentally friendly and has enhanced graphics, stiffness and strength.

SUMMARY OF THE INVENTION

The invention is directed to a laminated fiberboard package, particularly a folding carton or a corrugated container, having enhanced graphics and to a method of producing the same. In accordance with the invention, an outer sheet or top ply composed of a clay-coated, unbleached cellulosic fiber material such as unbleached kraft paper is printed with graphics, preferably by a high speed web printing method. The printed web is then rewound in roll form and stored for subsequent application to a cellulosic substrate. When producing beverage carriers, the cellulosic substrate preferably consists of one or more plies of predominately unbleached virgin kraft linerboard, while when producing a product such as a cereal box, the cellulosic substrate can be formed of one or more plies of predominately recycled fibers. At the box manufacturing site, the rolled, printed, clay-coated, unbleached kraft paper is unwound and continuously applied to a surface of the moving web of cellulosic substrate and bonded to the substrate by an adhesive, to thereby provide a laminated substrate to be used for packaging material, particularly for a folding carton. The adhesive continuously bonds the entire inner surface of the printed paper to the outer surface of the cellulosic substrate. An overprint varnish may be applied to the printed surface to prevent scuffing or rubbing off of the printed graphics and to increase the coefficient of friction of this surface. The 4 printed paper is then laminated to the cellulosic substrate. The laminated product is then die cut into a plurality of sections, units, or segments of desired shape and each section is then folded and glued to form the configuration of a box. The boxes, in a flat folded state, are shipped to the manufacturer of the product, the boxes are then opened, the product inserted and the end flaps are then glued or secured to provide the final packaged product for distribution.

In certain instances, e.g. when dealing with a beverage carrier, the beverage cans may be introduced into the laminated box in a refrigerated state. Subsequently moisture may condense on the refrigerated cans, which may run off the can and be deposited and absorbed by the carrier material causing warping or disfiguration of the laminated box. To overcome this problem, a layer of water absorbent, cellulosic material, such as kraft paper, corrugated medium, or newsprint can be applied to the inner surface of the laminated substrate prior to die cutting, and folding and gluing. The water absorbent cellulosic layer is applied to the inner surface of the laminated substrate through use of a waterproof adhesive such as a hot melt adhesive. The water absorbent layer will absorb any moisture which may be present within the package to prevent warping of the laminated package.

The invention provides enhanced graphics for paperboard packaging by use of high speed printing on unbleached cellulosic fiber material comprised of unbleached virgin kraft pulp and/or recycled pulp, which is then bonded to the cellulosic substrate by means of an adhesive. It is preferred to construct laminated packaging having an outer layer made from clay-coated unbleached kraft paper. This paper has a basis weight of 20 to 150#/ream (ream is

3,000 ft.²). The advantages are these:

1. The unbleached backside of the label is not visible since it is affixed to the unbleached portion of the package, and thus the unbleached fibers do not show.

2. Clay-coated unbleached kraft paper is less costly to produce than clay-coated bleached paper.

3. In the process of printing or when laminating sheets to folding cartons or corrugated containers - either spot labels or full surface labels - the minimum basis weight of the sheets that can be handled without wrinkles relates to the inherent stiffness of the fiber. Unbleached fibers are inherently stiffer than bleached, and at the same time have a higher bulk. It is possible that sheets made of the stiffer, bulkier fibers in clay-coated unbleached kraft may allow the printing and/or laminating of lower basis weight paper. 5

4. The clay-coated kraft paper is smooth, and is typically manufactured on a fourdrinier machine at relatively high speeds. The fibers are refined for smoothness and the forming consistency is low to reduce flocculation. Prior to coating, the sheet of unbleached kraft is calendered to further enhance smoothness. The paper may be coated on the paper machine after calendering, or alternately, it may be coated in a separate, off-line operation.

5. The unbleached fibers contribute more strength per pound of weight to the strength of the packaging than bleached fibers. This means less packaging and therefore less solid waste to dispose of.

6. With this invention, high graphics white packages can be inexpensively made without the need for bleaching and the associated negative environmental impact.

7. Since unbleached fiber is produced at a higher yield, less trees are needed to make a ton of packaging and since the packaging is stronger, fewer tons of packaging are required. The combined impact - higher yield and higher strength packages will result in a significant reduction in the number of acres of timber than must be harvested annually for packaging needs.

8. Paper is lighter than board. Thus, shipping the lighter weight paper to and from the printing locations improves logistics and reduces freight costs.

9. More printed images can be stored, transported, and processed if the images are imparted on a thinner substrate.

DESCRIPTION OF THE PREFERRED EMBODIMENT The invention is directed in general to a laminated printed package consisting of a cellulosic substrate or base layer of unbleached virgin kraft linerboard, preferably with wet strength characteristics, or alternately of recycled pulp fibers, being laminated through use of an adhesive, which may have waterproof properties, to a corresponding outer or top sheet of paper printed with graphics.

The outer layer or top paper sheet to be used in the invention, may be clay coated paper which has a thickness generally in the range of 0.00125 inch to 0.01000 inch. The outer or top paper sheet is a clay coated unbleached kraft paper because of all the advantages previously noted herein. 6 The outer or top paper in roll form is unwound and printed by conventional techniques, preferably by any variety of high speed web printing methods, operating at a speed generally in the range of 500 to 3200 ft. per minute. One to multiple color printing can be utilized to print the graphics on the clay-coated or smooth surface of the paper. As an in-line process with the printing or as an off-line process, an overprint varnish or other similar protective coating may be applied over the printed graphic image. After printing, the paper may be rewound into roll form and stored for subsequent application to a cellulosic substrate at the location of the box manufacturer. Alternatively, the paper may be immediately laminated to the substrate.

The cellulosic substrate can be produced by conventional methods and can consist of unbleached virgin kraft pulp, recycled cellulosic pulp produced from old corrugated containers, newsprint, white office waste, and the like, or mixtures of virgin kraft pulp and recycled cellulosic pulp. Preferably, the substrate is produced in one or more plies on the forming section of the paper machine and generally has a basis weight of 25 lbs. to 90 lbs. per 1,000 sq. ft., and a thickness of 0.009 to 0.035 inches. However, it is contemplated that the substrate could be a single-, double-, or triple-walled corrugated board. When producing a beverage carrier, where high tear strength is required in the laminated product, long fiber, virgin soft wood pulp is preferred as the base layer of the substrate, and an outer or top ply of finer fiber hardwood pulp can be applied to the base ply on the forming section of the paper machine. When producing a laminated product that is designed to contain products of lesser weight, such as cereal boxes, milk cartons, or the like, the substrate can be formed of one or more plies of recycled pulp, produced from old corrugated cartons, newsprint, office waste, and the like.

When there is need for producing a high strength product such as a beverage carrier, cellulosic substrates can be produced by a typical kraft process, in which wood chips are cooked at a temperature of approximately 340°F with the addition of sodium hydroxide and sodium hydrosulfide (conventional kraft white liquor) for a period of about 20 to 60 minutes to dissolve the lignin. After cooking, the pulp is washed which acts to remove up to 98% of the residual cooking chemicals. The pulp is then diluted with water to a solids content of about 4% and treated with sulfuric acid and alum to obtain the desired pH. The pulp stock is then delivered to the headbox of the forming section of the papermaking machine in the form of a slurry, and the pulp slurry is fed from the headbox onto the forming fabric to provide a pulp mat. 7 On the forming fabric, water is removed from the pulp mat by both gravity and mechanical induced vacuum, and the partially dewatered pulp then passes through the press section and drying section of the papermaking machine, in a conventional manner, to produce the dry cellulosic substrate. If the substrate consists of multiple plies, the pulp for each additional ply is fed from a second headbox located downstream of the first headbox onto the base ply to provide the composite structure in a conventional manner.

When producing paperboard packaging such as cereal boxes, the cellulosic substrate will generally consist of multiple plies of recycled fibers. The pulping of the recycled fibers is carried out in a conventional manner, in which the recycled cellulosic waste is mixed with water and chemical dispersants, such as sodium hydroxide. The mixture is then subjected to a shear type of pulping agitation to break down the cellulosic waste into individual fibers and to liberate inks and toners. During pulping, dispersant chemicals act to dissociate the ink from the fibers, and disperse the ink particles in the aqueous pulp slurry. Following the dispersion, the pulp can then be subjected to conventional ink removal operations which can be accomplished either by froth floatation or dilution washing.

When utilizing virgin unbleached kraft pulp, the cellulosic substrate will be brown in color, while the substrate formed from recycled materials will generally be brown or grey in color, depending upon the nature of the paper being recycled. At the site of the box manufacturer, the printed paper is unwound, and then continuously laminated by means of an adhesive to a corresponding moving web of the cellulosic substrate. Preferably, the moving web is continuous. However, corrugated sheets may be substituted for the moving web and the printed paper may be laminated thereon in a discontinuous lamination process. An adhesive layer is applied to cover and bond the entire inner surface of the printed paper to the outer surface of the cellulosic substrate. Selection of the adhesive used should be influenced by the product contained within the box. For example, products that contain oils require the use of adhesives that prevent migration of the oils to the outer layer of the box. Alternatively, moist products require the use of waterproof or water-resistant adhesives, such as an epoxy resin, urea formaldehyde resin or a hot melt adhesive. The preferred adhesive to prevent moisture migration is a hot melt adhesive applied in liquid form (available from Ato 8 Findley, Inc.), a liquid polymer or solvent based adhesive (available from H.B. Fuller Co.) or in a dry non-tacky, solid film form (available from Dow Chemical Co.).

In practice, the laminating process may require that the substrates be heated to a temperature in the range of 150°F to 200°F and the adhesive is preferably applied to the undersurface of one of the substrates by a gate roll size press, or a metering blade. The substrate with the adhesive on its undersurface is then applied to the upper surface of the corresponding substrate to provide a laminated product which is passed through compression rolls to firmly bond the printed paper to the substrate. If a hot melt adhesive film is used, the film is merely fed between the cellulosic substrate and top paper and then passed through heated compression rolls to form the laminated printed package.

In the laminated beverage carrier product, the printed paper extends over the entire surface area of the substrate with exception of the flap area immediately below the handle portion of the carrier, which when folded, will not be visible. The laminated product is then die "cut into a plurality of sections or segments of the desired shape or configuration. Each section is then folded and glued to form the carrier. The flat boxes are then shipped to the manufacturer of the product to be packaged. At the site of the product manufacturer, the flat boxes are opened, the product inserted, and the end flaps are then glued to provide the final packaged product that can be sent for distribution.

In certain instances, the items, such as beverage cans, inserted into the laminated package may be cold or refrigerated, and in this case, moisture may condense on the cans. It has been found that the condensed moisture from the cans and transferred to the carrier material may tend to cause warping or disfigurement of the laminated package. To overcome this problem, a layer of water absorbent cellulosic material such as kraft paper, corrugated medium or newsprint, can be applied to the inner surface of the carrier, through use of a waterproof adhesive, which can take the form of an epoxy resin, urea formaldehyde resin, hot melt or the like. Any moisture condensing on the refrigerated cans will be absorbed in the inner layer of cellulosic material and will not migrate through the laminated package due to the barrier created by the waterproof adhesive, thus eliminating warping or other disfigurement of the package interior and exterior. It is also contemplated that in certain instances, a layer or film of waterproof material, such as polyethylene film, can be applied to the inner face of the laminated material prior to die 9 cutting and folding. The waterproof film will prevent migration of water or moisture through the laminated package to aid in minimizing any warpage or disfigurement of the package.

The invention maximizes the technology of current high speed web printing processes for enhanced graphics in packaging by laminating printed rolls of unbleached, clay-coated kraft paper to a heavier weight cellulosic substrate immediately preceding the die cutting, folding and gluing process.

Claims

10 CLAIMS I claim:

1. A laminated carton comprising a laminated composite sheet folded and glued in the configuration of a box, said sheet composed of a fiberboard base layer of unbleached cellulosic fibers selected from the group consisting of unbleached virgin kraft pulp and recycled pulp, said base layer having an inner surface and an outer surface; an outer layer of unbleached cellulosic fiber material selected from the group consisting of unbleached kraft pulp and recycled pulp having an inner surface and an outer surface, with printed graphics disposed on the outer surface of the outer layer; and a separate layer of adhesive disposed between the inner surface of the outer layer and the outer surface of the base layer and serving to bond the outer layer to said base layer, the inner surface of said outer layer being bonded continuously to the entire outer surface of said base layer.

2. The carton of claim 1 , and further including a first clay coating on the outer surface of the outer layer, said printed graphics disposed on said first clay coating.

3. The carton of claim 1, wherein said adhesive is waterproof.

4. The carton of claim 1, wherein said base layer is single-wall corrugated board.

5. The carton of claim 1, wherein said base layer is multi-wall corrugated board.

6. The carton of claim 1, wherein said base layer is paperboard selected from the group consisting of linerboard, corrugating medium and boxboard.

7. The carton of claim 1, and further including a layer of water absorbent material disposed on the inner surface of said base layer, and a layer of waterproof adhesive bonding said absorbent material to said base layer.

8. The carton of claim 1, and including a layer of waterproof material disposed on the inner surface of said base layer.

9. A laminated carton, comprising a laminated composite sheet folded and glued in the configuration of a box, said sheet including a fiberboard base layer of unbleached cellulosic fiber material selected from the group consisting of unbleached virgin kraft pulp and recycled pulp, said base layer having an inner surface and an outer surface; an outer layer of unbleached cellulosic fiber material selected from the group consisting of unbleached kraft pulp and recycled pulp disposed on the outer surface of said base layer and extending continuously over the entire outer surface of said base layer, said outer layer having an inner surface and an outer 11 surface; a separate layer of waterproof adhesive disposed between the outer surface of said base layer and the inner surface of said outer layer and serving to continuously bond the inner surface of said outer layer to the outer surface of said base layer, a clay coating on the outer surface of said outer layer, and printed graphics on said clay coating.

10. The carton of claim 9, wherein said base layer is single wall corrugated board.

11. The carton of claim 9, wherein said base layer is paperboard selected from the group consisting of linerboard, corrugating medium and boxboard.

12. The carton of claim 9, wherein said base layer is multiple-wall corrugated board.

13. A laminated carton to contain containers, comprising a laminated composite sheet folded and secured in the configuration of a box, said sheet including a fiberboard base layer of unbleached cellulosic fibers selected from the group consisting of unbleached virgin kraft pulp and recycled pulp, said base layer having a thickness of 0.009 inch to 0.035 inch, said base layer having an inner surface and an outer surface; said sheet further including an outer layer of unbleached cellulosic fiber material selected from the group consisting of unbleached kraft pulp and recycled pulp having a thickness in the range of 0.00125 inch to 0.01000 inch and extending continuously over the entire outer surface of said base layer, said outer layer having an inner face and an outer face; a separate layer of waterproof adhesive disposed between the outer surface of said base layer and the inner face of said outer layer to bond said outer layer to said base layer, a clay coating on the outer face of said unbleached cellulosic fiber outer layer, printed graphics disposed on the outer face of said outer layer, a layer of water absorbent material disposed on the inner surface of said base layer, a layer of waterproof adhesive bonding said water absorbent material to the inner surface of said base layer, and a plurality of containers disposed within said box.

14. In a method of producing a laminated carton, the steps comprising the production of a fiberboard base layer of unbleached cellulosic fibers, producing a sheet of unbleached cellulosic fiber material having a clay coating on a first surface thereof, printing graphics on the clay coated first surface of said paper sheet, coating the printed surface with an overprint varnish or other type of protection coating, continuously applying the printed unbleached cellulosic fiber sheet to a first surface of said base layer, applying adhesive between contiguous surfaces of said base layer and said printed unbleached cellulosic fiber sheet to bond the printed paper to the base layer and produce a laminated structure with said printed 12 unbleached cellulosic fiber sheet disposed over substantially the entire surface area of the base layer.

15. The method of claim 13, and further including the steps of cutting the laminated structure into segments, and forming each segment into the configuration of a box with said printed unbleached cellulosic fiber sheet constituting an outer face of the box.

16. The method of claim 13, wherein said base layer is produced from unbleached virgin kraft pulp.

17. The method of claim 13, wherein said base layer is produced from recycled pulp.

18. The method of claim 13, wherein said base layer is unbleached kraft linerboard.

19. The method of claim 13, and further including the step of applying a waterproof coating to the inner surface of said base layer.