WO1996018544A1

WO1996018544A1 - Packages with protected raw edges and method of manufacture

Info

Publication number: WO1996018544A1
Application number: PCT/US1995/015620
Authority: WO
Inventors: Charles E. Gibbons; Dawson G. Wilkerson; Joe L. Kinsey, Jr.; Robert L. Lanham
Original assignee: International Paper Company
Priority date: 1994-12-14
Filing date: 1995-12-14
Publication date: 1996-06-20
Also published as: AU4506196A

Abstract

A paperboard polymer coated carton having impregnated raw edge seams is provided. The raw edge (10) of the side seam is sealed by applying a sealant (40) directly to the paperboard raw edge (10), with the sealant (40) achieving sufficient penetration into the raw edge (10) to maintain the integrity of the sealant (40) during end use. The sealant (40) can be solvent borne, water borne, or hot melt. The sealant (40) is applied to the side seam raw edge (10) prior to the side seam operation, and the method of applying the sealant (40) is selected so that a continuous film of the sealant (40) can be applied to the side seam raw edge. The sealant (40) is one of wax, wax blend, saran emulsion, EVOH solution, polyvinyl alcohol solution, liquid adhesive, and hot melt adhesive.

Description

"PACKAGES WITH PROTECTED RAW EDGES AND METHOD OF MANUFACTURE"

BACKGROUND OF THE INVENTION

1. Field of the Invention The present invention relates to paperboard polymer coated cartons having protected board raw edge seams and a method of manufacturing such cartons. More particularly, the present invention relates to a carton in which the raw edge is impregnat¬ ed with a sealant to improve the integrity of the carton by preventing slow leaking or excessive oxidation of the product contained therein, and a corresponding method of manufacturing such a carton.

2. Description of the Prior Art Paperboard containers are widely used for the packaging of foodstuffs such as powdered mixes, cereals, corn chips, and the like and are suitable for packaging liquids in general and many food substances, particularly those which are moisture- sensitive. Such containers are often formed from precut blanks comprising paperboard covered on both sides with a thermoplastic material such as polyethylene. Polyethylene inhibits the passage through the material of bacteria and other microorganisms, moisture, and the contents of the container. In addition, the thermoplastic coating serves as an adhesive when subjected to heat and pressure. As a result, seams or joints between overlapped edges of the blank may be made by applying heat and pressure to the overlapped edges.

During the manufacturing of these cartons, the blank is formed and seamed into a tube. One edge of the blank at the seam, is located inside of the container, hereinafter the inside seam. If the inside raw edge is exposed, the paperboard layer will come into contact with the contents of the container. Such contact is undesirable, since any liquid in the container will wick into the cut or raw edge of the blank, and enter the paperboard component of the laminate. Furthermore, if a raw edge of the blank is on the outside of the container, the paperboard may absorb moisture or bacteria and other microorganisms at the raw edge. Polymer coated or laminated paperboard has been used for many years for various packaging applications, especially in cartons for containing liquids. The gable top milk carton is a classic example. The uses of such paperboard cartons have expanded to include the packaging of juices, drinks, non-food liquids and dry products. Customer demands for increasing shelf life have been increasing. Improved fill product processing techniques, and improved barrier composite structures have achieved increased shelf life. However, most classic carton designs share a common weakness; the side seam raw edge. Various methods have been developed to eliminate or protect the side seam raw edge from contact with the fill product. Skiving is one technique that has been used to protect the side seam raw edge, for many years. Skiving effectively eliminates the side seam raw edge, but results in a narrower, weaker side seam seal, with narrow product containment seal width. The skiving process requires the side seam sealer be run at reduced line speeds. Because a more complex seal, with reduced seal width is being produced, scrap rates increase.

SUMMARY OF THE INVENTION

These and other deficiencies of the prior art are addressed by the present invention which is directed to a paperboard polymer coated carton having a paraffin impregnated in the raw edge seams.

An object of the present invention is to seal the raw edge of the side seam by applying a sealant directly to the paperboard raw edge, with the sealant achieving sufficient penetration into the raw edge to maintain the integrity of the sealant during end use. The sealant can be solvent borne, water borne, or hot melt. A specific example is wax or wax blend impregnation of the raw edge.

Another object of the present invention is to apply the sealant to the side seam raw edge prior to the side seaming operation, and the choosing the application method so that a continuous film of the sealant can be applied to the side seam raw edge.

Another object of the present invention is to apply the sealant to the raw edge at normal side seam sealer speeds, up to 2000 cartons per minute, so that the applicator can be incorpo¬ rated into the side seam sealer line, or alternatively, a separate applicator line could be employed as an intermediate manufacturing step.

BRIEF DESCRIPTION OF THE DRAWINCS

These and other attributes of the present invention will be described with respect to the following drawings in which:

FIG. 1 is a side view of a conventional side seam;

FIG. 2 is a side view of a skived side seam; and

FIG. 3 is a side view of a sealed edge side seam of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring to Figs. 1 and 2, a convention side seam and a skived side seam are illustrated. During the manufacturing of paperboard cartons, a blank is formed and seamed into a tube. In the conventional side seam shown in Fig.l, one edge 10 of the blank at the seam, is located inside (or on the matte side) of the container, hereinafter the inside seam. When the inside raw edge 10 is exposed, the paperboard layer will come into contact with the contents of the container. Scoring on the raw edge become the avenue of penetration for liquid inside the container into the paperboard. Liquid in the container wicking into the raw edge 10 of the blank, and thus the paperboard component of the laminate will corrupt the integrity of the container.

Fig. 2 shows a skived side seam 20 developed to prevent the wicking which occurs in the convention side seam of Fig. 1. Skiving is achieved by modifying the standard seam by removing a narrow layer of the gloss raw edge, which includes the paperboard 22 and outer coating 24, from the inner panel 28, creating a side seam flap. The flap is then bent back on itself to the carton outside or gloss side, and flame sealed to the opposite carton edge 30 to create a matte/gloss and a matte/matte seal.

While the skived side seam of Fig. 2 has better resistance to wicking than the conventional side seam of Fig. 1, the skiving process creates a narrower, weaker side seam due to the removal of the narrow layer on the gloss raw edge, and therefore creates a narrow product containment seal.

In order to overcome the drawbacks of the seals of Figs. 1 and 2, the present invention, as shown in Fig. 3, impregnates the raw edge 10 of a conventional side seam with a sealant 40. For high barrier packaging applications, or for packages containing aggressive fill products, the formation of a continuous film to seal the side seam raw edge 10 would be required. The sealant 40 must be sufficiently flexible to withstand carton formation on form fill machinery. The sealant 40 may be, but is not limited to one of the following substances: waxes, wax blends, saran emulsion, EVOH solution, polyvinyl alcohol solution, liquid adhesives, and hot melt adhesives.

The choice of a particular sealant 40 depend on a number of factors, including: the degree of penetration into the raw edge, contamination of side seam surfaces, raw edge sealing quality, flexibility of the material so that it will not fracture during transportation of filled cartons, the application technique, and compatibility with the fill material.

The sealant 40 is applied to the side seam raw edge 10, and may be applied to other critical raw edges or a carton blank as need arises. The sealant 40 can be applied in numerous ways, including but not limited to by nozzle, immersion, spray, or other appropriate methods for solvent or water borne sealants, or by hot melt nozzle, immersion or other appropriate methods for application of hot melt materials.

Solvent or water borne adhesives may be cured by applying heat, either by a dedicated heat source, or by the action of the existing seal burners on the side seam sealer. The hot melt may require some cooling time prior to the side seam seal being created.

In testing, three wax blends were tested against a straight microcrystalline wax. The three blends were chosen to have low viscosity at 190 degrees F, and to achieve sufficient penetration and flexibility/toughness at room temperature and lower. The waxes were heated to 190 degrees F, and manually applied with brush to the bottom side seam raw edges of stacks of flat blanks. A large hot air gun was used to preheat the raw edges to minimize crystallization and facilitate penetration. Hot air knives appear to be preferable to the hot air gun. Cartons were side seamed and then filled with shelf- stable grape drink. The filled cartons were stored at 73 degrees F for two weeks and then subjected to vibratory abuse at 150 cycles per minute for 30 minutes. The bottom side seam corners were then graded for leaks, with the following results: CARTON TYPE LEAKS,/10 AVG. DIFF. FROM CONTROL

Untreated 4.8

Paraffin wax 1.5 97.5% confidence

Wax blend 5320 2.3 95.0% confidence

Wax blend 5321 1.0 99.0% confidence

Wax blend 5322 2.1 97.5% confidence

Microcrystalline 3.1 less than 90.0% wax confidence

While the paraffin wax showed good results it ap¬ pears to be too brittle for use in the paperboard context.

Having described several embodiments of the in accordance with the present invention, it is believed that other modifications, variations and changes will be suggested to those skilled in the art in view of the description set forth above. It is therefor to be understood that all such variations, modifications and changes are believed to fall within the scope of the invention as defined in the appended claims.

Claims

8WHAT IS CLAIMED IS:

1. A method of sealing a side seam of a paperboard container comprising the steps of: applying a sealant to said side seam, applying heat to seal overlapping sides of said container.

2. A method as recited in claim 1, further compris¬ ing the step of heating said sealant to cure said sealant.

3. A method as recited in claim 1, wherein said sealant is one of wax, wax blend, saran emulsion, EVOH solu¬ tion, polyvinyl alcohol solution, liquid adhesive, and hot me11 adhesive.

4. A method as recited in claim 1, wherein said sealant is a wax blend and said wax blend is heated to cure said sealant.

5. A method as recited in claim 4, wherein said sealant is applied to said side seam and other critical raw edges.

6. A method as recited in claim 1, wherein said step of applying sealant is performed by using one of a roll, nozzle, immersion method, and spray method.

7. A method as recited in claim 1, wherein said sealant is applied to said side seam raw edge prior to a side seaming operation.

8. A method as recited in claim 1, wherein said step of applying sealant is performed so that a continuous film of said sealant can be applied to said side seam raw edge.

9. A blank for a container, comprising: inner and outer surfaces; a raw edge side seam; a sealant applied to said side seam and pene¬ trating said side seam to resist deterioration of container integrity.

10. A blank for a container as recited in claim 9, wherein said sealant is one of wax, wax blend, saran emulsion, EVOH solution, polyvinyl alcohol solution, liquid adhesive, and hot melt adhesive.

11. A blank for a container as recited in claim 9, wherein said sealant is a wax blend which is heated to cure said sealant.

12. A blank for a container as recited in claim 9, wherein said sealant is applied to said side seam and other critical raw edges.

13. A blank for a container as recited in claim 9, wherein said sealant is applied to said side seam raw edge prior to a side seaming operation.

14. A blank for a container as recited in claim 9, wherein said sealant is applied so that a continuous film of said sealant can be applied to said side seam raw edge.