IN THE UNITED STATES PATENT AND TRADEMARK OFFICE International Patent Application For

SELECTIVELY REINFORCED PAPERBOARD CARTONS

This non-provisional application relies on the filing date of provisional U.S. Application Serial No. 60/807286, filed on July 13, 2006, having been filed within twelve (12) months thereof, which is incorporated herein by reference, and priority thereto is claimed under 35 USC § 1.19(e).

BACKGROUND OF THE INVENTION

[0001] In the manufacture of certain paperboard cartons, specific areas of the cartons may require greater strength properties than other areas. For example, when a carton containing beverage cans or bottles is lifted through its handle, a considerable stress is introduced into the paperboard which the carton is formed. The areas around the handle of the carton especially require greater strength because of the downward force exerted by the beverage cans or bottles. The beverage cartons must withstand stress of cyclic loading during transportation, as well as during storage under high moisture condition like in the refrigerator.

[0002] To prevent tearing of the paperboard and failure of the carton, several designs of carton handle are developed to support various stress-relieving/distributing arrangements. (U.S. Patent Nos. 4,558,816; 4,785,991; 5,307,932; and 5,480,091) This is often accomplished by providing fold lines or slits in the carton wall where the handle slots are provided. (Figure 1 and Figure 2) Although the handle design may eliminate the complete strength failure of paperboard carton, it has still been difficult to eliminate minor cracks and tears from the handle slot area.

[0003] One method of achieving the strength requirements is to manufacture the entire carton from a paperboard which has the necessary thickness to provide the strength requirements for the handle area. One drawback of this method is the waste of paperboard in

the areas that do not require additional strength. Additionally, the shipping and handling costs of the paperboard carton increase when a thicker board is used.

[0004] Reinforced materials may be incorporated to the paperboard to enhance the strength properties. U.S. Patent No. 7,195,804 describes a method of producing paperboard composite structure having improved wet tear strength suitable for use in packaging bottles of beverages. The paperboard structure has a backing structure adhered to a paperboard layer, wherein the backing structure includes an oriented polymer film layer and a reinforcing scrim polymer layer bonded together by a thermal bonding polymer layer. The oriented polymer film layer, the thermal bonding layer, and the reinforcing scrim polymer layer each individually comprise a synthetic condensation polymer. This reinforcement method typically uses high cost polymeric or composite reinforcing materials. Furthermore, the plastic coating or laminating to a paperboard substrate is commonly performed off-line from the papermaking process through a multiple-step process, thereby increasing the manufacturing cost.

[0005] To reduce production cost, the reinforcement may be selectively introduced to only the areas of paperboard bearing exerted stress when lifting. U.S. Patent Application No. 2006/0,000,544 describes a method of producing cartons having one or more reinforcing strips laminated or adhered to a carton material using foamed adhesive. The adhesive such as a water-based emulsion is applied in strips in either a continuous or non-continuous manner onto the paperboard substrates. However, adhering bands of selective reinforcement at only the selected areas generally requires special equipments.

[0006] U.S. Patent No. 5,335,774 discloses a can carrier made of paperboard having the areas around cutout of the upper surface coated with waterproof coating to enhance water resistance property and thereby increasing the strength for the can carrier. Additionally, a reinforced thread, formed of a synthetic water resistant material, is bonded to the under surface of the paperboard to strengthen the can carrier. The method is quite complicated, since different modifications must be performed on each side of the paperboard to ensure sufficient strength requirement.

[0007] U.S. Patent No. 4,617,223 discloses a method of selectively reinforcing paperboard only in the critical areas, allowing thinner paperboard to be used for the remaining areas of the article. The critical areas of the uncoated paperboard carton blank are impregnated with a polyisocyanate material, which reacts with hydroxyl groups within the paperboard to form a cured polyurethane reinforcement. To ensure that the curing process of polyurethane is completed in short period, heat may be introduced to reduce the cured time; therefore, additional capital and operation costs are required.

[0008] EP Patent Application No. 0,478,177 teaches a process for reinforcing paperboard to enhance strength properties by impregnating one side of the paperboard with a liquid reinforcing composition such as latex so that the reinforcing composition partially penetrates into the paperboard. A vacuum force is used to allow a penetration to a depth of about 5-25% of the paperboard thickness. For a selective reinforcement, the vacuum force and the reinforcing composition are applied only in those selected areas where such reinforcement is desired. While this process provides a paperboard carton with improved strength, a higher strength level is desired in order to minimize, if not eliminate, the carton failure due to an intensive stress exerted throughout the life cycle of the packaged goods. Additionally, it is desirable to reduce minor cracks and tears which detract from the carton appearance.

[0009] Accordingly, there is still a need for an improved process that is cost effective to selectively reinforce the paperboard cartons so as to minimize the carton mechanical failure. Furthermore, this is a need for the paperboard carton having sufficient strength to minimize such failure that is made from lower basic weight (i.e., thinner) paperboard than the conventional boards used for the current paperboard carton, so as to reduce a raw material cost for manufacturing of paperboard cartons.

[0010] It is an object of this invention is to provide a process for reinforcing paperboard cartons that is cost effective and uses simple process.

[0011] It is another object of this invention is to provide a composition suitable for imparting a selective reinforcement to the paperboard carton treated with such composition.

[0012] It is yet another object of this invention is to provide a reinforced paperboard carton having reinforced strength at the selected areas.

[0013] It is a further object of this invention is to provide a reinforced paperboard carton having reinforcement around the areas where a greater force is exerted when the carton is lifted and/or carried.

[0014] It is yet a further object of this invention is to provide a reinforced paperboard carton having minimized mechanical failure during shipping and handling throughout the life cycle of its packaged goods.

[0015] It is still a further object of this invention is to provide a reinforced paperboard carton having reduced minor cracks and tears during shipping and handling throughout the life cycle of its packaged goods.

[0016] It is yet still a further object of this invention is to provide a carton made of paperboard having lower basis weight (i.e., lighter and sometimes thinner) than that of the board used in the conventional paperboard cartons, yet the invention carton still has sufficient tensile strength and tensile energy adsorption to minimize carton mechanical failure.

[0017] Other objects, features and advantages of the present invention will be set forth in part in the description which follows, and in part will be obvious from the description or may be learned by practice of the invention.

SUMMARY OF THE INVENTION

[0018] The present invention relates to a paperboard carton for packaging application, such as carrier for cans or bottle beverages, having a selective reinforcement to enhance

strength properties. The selected areas of the paperboard carton are reinforced by coating with a water-based formulation containing a water-based polymer and fibers having a dimension of about 50 micron to about 2,000 micron in length and about 20 micron to about 1,000 micron in diameter.

DESCRIPTION OF THE DRAWING

[0019] FIG.l is a pictorial representation of a sleeve-type carrier prior to being lifted and while being lifted by its handle (U.S. Patent No. 4,785,991);

[0020] FIG.2 is a pictorial representation of a carrier having stress relieving arrangement at its handles (U.S. Patent No. 5,480,091);

[0021] FIG. 3 is a plan view of a plank for forming carrier, showing the selected areas to which the chemicals are applied;

[0022] FIG. 4 is a pictorial representation of a carrier, showing the selected areas to which the chemicals are applied;

[0023] FIG.5 is a graph showing the tensile energy adsorption of the paperboards coated, at different coat weights, with the invention water-based reinforced formulations containing polyvinyl alcohol polymer and different levels of the unbleached softwood fibers: 0.25% weight ( Formula A) and 0.50% weight (Formula B) based on the weight of the polymeric solution;

[0024] FIG.6 is a graph showing the strain property of the paperboards coated, at different coat weights, with the invention water-based reinforced formulations containing polyvinyl alcohol polymer and different levels of the unbleached softwood fibers: 0.25% weight ( Formula A) and 0.50% weight (Formula B) based on the weight of the polymeric solution;

[0025] FIG.7 is a graph showing the maximum loading values of the paperboards

coated, at different coat weights, with the invention water-based reinforced formulations containing polyvinyl alcohol polymer and different levels of the unbleached softwood fibers: 0.25% weight ( Formula A) and 0.50% weight (Formula B) based on the weight of the polymeric solution;

[0026] FIG.8 is a graph showing stiffness of the paperboards, at different coating weights, coated with different coating compositions: conventional clay coating composition and the invention water-based reinforced formulation containing 1.5% by weight of MPC particles.

DETAILED DESCRIPTION OF THE INVENTION

[0027] The present inventions now will be described more fully hereinafter, but not all embodiments of the invention are shown. Indeed, these inventions may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. The detailed description is not intended to limit the scope of the appended claims in any manner.

[0028] The reinforced paperboard carton of the present invention is obtained by applying a water-based reinforced formulation to the selected areas. Often these areas are the areas of the paperboard carton subjected to a high exerted stress during shipping and handling throughout a life cycle of the packaged goods inside the cartons.

[0029] The reinforced water-based formulation suitable for use in the present invention comprises:

(a) a water-based polymer, and

(b) a fiber having a dimension of about 50 micron to about 2,000 micron in length and about 20 micron to about 1,000 micron in diameter.

[0030] Suitable water-based polymers for use in the present invention include, but are not limited to, polyurethane, poly(styrene -butadiene), poly(styrene- acrylic), polyacrylic, polyvinyl acetate, poly(acrylic-vinyl acetate), poly(acrylic-vinyl acetate), polyvinyl alcohol, epoxy, polyester, and combinations thereof.

[0031] Suitable fibers may include, but are not limited to, cellulosic fibers, synthetic fibers, and combinations thereof. Cellulosic fibers of various natural origins may be used for use in the present invention. These include, but are not limited to, softwood, hardwood, cotton linter, vegetables, Esparto grass, bagasse, hemp, flax, sugar beet, citrus pulp, linen, jute, ramie, sisal, and combinations thereof. Suitable synthetic fibers for use in the present invention include, but are not limited to, rayon, nylon, polyacetate, polyacrylic, polypropylene, polyethylene, polyester, polyvinyl alcohol, and combinations thereof.

[0032] Fibrillated fibers may also be used in the present invention. Example of these fibrillated fiber include, but are not limited to, microcrystalline cellulose (MCC), micro fibrillate cellulose (MFC), microplatelet cellulose (MPC), and combinations thereof. These fibrillated fibers may be obtained by any method known in art. Examples of the production processes for MCC are reported in U.S. Patent No. 7,037,405; U.S. Patent Application No. 2005/2,39,744; and PCT Patent Application No. 2006/034,837. Examples of the production processes for MFC are reported in PCT Patent Application NO. 2004/055,267 and U.S. Patent No. 4,761,203. Example of the production process for MPC includes the process reported in U.S. Patent No. 4,474,949. Additionally, the MPC fiber may be obtained by passing a suspension of fiber pulp through a high- friction grinder at about 2O ⁰ C to about 9O ⁰ C at atmospheric pressure. [0033] In one embodiment of the present invention, the reinforced water-based formulation contains 80-99% by dry weight of water-based polymer and 1-20 % by dry weight of fibers.

[0034] In one embodiment of the present invention, the reinforced water-based formulation further includes starch to reduce the formulation cost and/or modify the viscosity of the formulation to achieve the most reliable and uniform application to the board surface.

The amount of starch in the invention reinforced water-based formulation may range from about 10% to about 60% by weight based on total weight of the formulation.

[0035] The reinforced water-based formulation of the present invention may further include additives such as surfactants, coalescence agents, buffers, neutralizers, thickeners or rheology modifiers, humectants, wetting agents, biocides, plasticizers, antifoaming agents, colorants, pigments, fillers, waxes, water repellants, slip or mar aids, anti-oxidants, and the like.

[0036] It is well within the ability of one skilled in the art to determine the appropriate pH range, solids level, and film- forming characteristics for the reinforced water- based formulation for the desired applications.

[0037] In one embodiment of the present invention, the reinforced water-based formulation is applied only to the selected areas of the paperboard cartons where the acting stresses are more than 70% of the fatigue limit that causes fracture of board.

[0038] In one embodiment of the present invention, the areas applied with the reinforced water-based formulation is about 10% to about 30% greater than the predetermined area where the stress is about 70% to about 80% more than the critical stress level.

[0039] In one embodiment of the present invention, the distance between the point of maximum stress and the border of the areas applied with the reinforced water-based formulation is about 5% to about 20% greater than the areas where the stress is about 70% to about 80% more than the fatigue limit.

[0040] FEA analyses technique and related software packages may be used to determine the stress concentration area. For example, FIG. 3 and FIG. 4 showed that the paperboard beverage carton have high concentration of stress around the triangle areas located near handle slots.

[0041] The invention reinforced water-based formulation may be applied only on the topside or the backside of the paperboard board on the carton. Additionally, the reinforced water-based formulation may be applied to both side of the paperboard on the carton.

[0042] The reinforced water-based formulation of the present invention may be applied to substrate using known surface coating techniques. These include, not are not limited to, size press, air knife coating, roll coating, blade coating, curtain coating, spraying, and combinations thereof.

[0043] In one embodiment of the present invention, spray coating is used to apply the reinforced water-based formulation to the selected areas of the substrate. For example, a spray gun providing air-open, spring-close actuation that exceed 3,000 cycles per minute and applying a portion of the reinforced water-based formulation with frequency of about 1 millisecond may be used in the present invention. The high frequency application of a portion of the reinforced water-based formulation allows the treated paperboard to be coated only in the targeted areas.

EXAMPLES

[0044] EXAMPLE 1

[0045] The reinforced water-based formulations consisted of an aqueous solution of polyvinyl alcohol SNP S-1514-L commercially available from SNP, Inc.; a non-ionic surfactant Surfynol 440 available from Air Products and Chemicals, Inc.; glycerin plasticizer; and unbleached softwood fibers. The reinforced water-based formulations having two different amounts of unbleached fibers were produced.

[0046] Surfynol 440 surfactant and glycerin were mixed into the aqueous solution of polyvinyl alcohol at an amount, based on the weight of the polyvinyl alcohol solution, of 0.5% by weight and 7% by weight, respectively. The selected amount of unbleached softwood fibers was then added into the resulting aqueous solutions as shown in TABLE 1.

TABLE 1

[0047] The reinforced water-based formulations were spray coated onto the paperboard substrates at different coat weights: 2, 4, 6, and 8 lb/MSF. The strength properties of the coated boards were determined and compared to those of the uncoated paperboard (i.e., coat weight of zero).

[0048] The standard TAPPI methods were used to test the paperboards in both machine direction and cross direction. Tensile energy absorption (TEA) strain and loading properties were determined using the TAPPI standard procedure No. T-494.

[0049] The boards coated with the water-based reinforced formulations A and B had higher tensile energy adsorption (TEA) than the uncoated board for both the machine direction and cross direction. (FIGURE 5, Table 2)

TABLE 2

[0050] The boards coated with the water-based reinforced formulations A and B had improves strain property to that of the uncoated board for both the machine direction and cross direction. (FIGURE 6, Table 3)

TABLE 3

[0051] The boards coated with the water-based reinforced formulations A and B had greater maximum loading values than the uncoated board for both the machine direction and cross direction. (FIGURE 7, Table 4)

TABLE 4

[0052] The paperboard selectively coated with the water-based reinforcement

formulation containing polyvinyl alcohol polymer and unbleached softwood fibers, showed an improvement of 20-60% in tensile properties compared to untreated board.

[0053] EXAMPLE 2 [0054] The water-based reinforced formulation consisted of microplatelet cellulosic particles (MPC) and a standard aqueous clay coating of styrene-butadiene polymeric binder and titanium dioxide pigment. The amount range of MPC in the reinforced formulation was about 1.5% weight based on total weight of the formulation.

[0055] The MPC particles had a volume average particle size range of about 20 microns to about 100 microns. They were produced by passing a suspension of fiber pulp through a high-friction grinder at about 2O ⁰ C to about 9O ⁰ C at atmospheric pressure. The high-friction grinder SupermasscolloiderfS) commercially available from Masuko Sangyo Co.

Ltd. was used to grind fiber pulp into microplatelet particles. The SupcrmasscolloidertJS ⁾ grinder featured two ceramic nonporous plates with an adjustable gap. The upper plate was fixed, while the lower one was rotated at a high adjustable speed. The gap between plates was set at about 40 microns to about HO microns, and the rotation speed υf the lower plate at about 1.200 rpm to about 1.800 rpm. The fiber suspension was repeatedly subjected to grinding until the desired size of MPC particles is achieved. The particle size of MPC was determined using laser light diffraction Microtrac X-100 Tri-Laser-System.

[0056] It is to be understood that similar MPC particles may be produced using other high- friction grinder devices and, if so, would also be suitable for producing the MPC particles. Additionally, the pigment used in the invention water-based reinforced formulation may be any other pigment types known in the arts.

[0057] The water-based reinforced formulation containing MPC particles was applied to a KRAFTP AK® an unbleached folding carton board available from MeadWestvaco Corp., at different coat weight. The GM stiffness of the coated boards was determined and compared to those of paperboard coated with the standard clay coating (i.e., containing no MPC) at the same coat weights. The folding carton board coated with the water-based

reinforced formulation containing MPC particles showed significantly improved stiffness compared to the folding carton coated with a convention clay coating formulation (FIGURE

8).

[0058] It is to be understood that the foregoing description relates to embodiments are exemplary and explanatory only and are not restrictive of the invention. Any changes and modifications may be made therein as will be apparent to those skilled in the art. Such variations are to be considered within the scope of the invention as defined in the following claims.