HK1016539B - A container laminate structure - Google Patents

Description

Laminated board structure for container

Background

1. Field of the invention

The present invention relates to a metal foil-free carton construction that provides extended shelf life for juice flow. More particularly, the present invention relates to a container having a low oxygen permeability, which remains sealed for at least 90 days, which retains a high level of flavor, protects vitamin C, resists swelling and durability, without losing the ability to slice the side seams of the carton blank or sterilize the interior of the carton with hydrogen peroxide. The container structure includes a polyamide polymer, an ethylene vinyl alcohol copolymer high quality barrier layer, and a thin polyolefin layer on the matte side of the laminate.

2. Description of the prior art

It is well known that heat sealable polyolefin polymers such as low density polyethylene are currently used as elements in food and/or non-food cardboard packaging but have a very low resistance to oxygen transmission. Air holes, scratches, cracks or grooves formed by score lines, present on conventional packaging materials and cartons, create additional leak sites. It is well known that sealing materials such as aluminum foil, and polar brittle materials such as polyacrylonitrile, polyvinylidene chloride, polyvinyl chloride, etc., can act as barriers to varying degrees to prevent oxygen transmission. However, all of these materials lack the strength necessary under high-speed press processing conditions, i.e., the stress crack resistance required to form a comprehensive low-permeability structure during scoring, package forming, and misdispensing. In addition, leakage from unsealed slots in the top, bottom and side seams of the carton has also resulted in poor performance of the carton.

Existing mass-produced carton structures for storing liquid and solid, food and non-food products have employed readily heat-sealable barrier laminates consisting of both a cardboard base layer and a metal foil oxygen barrier layer sandwiched between two thick layers of a polyolefin polymer coating such as Low Density Polyethylene (LDPE). The polyolefin polymer is made of a relatively inexpensive heat-sealable moisture barrier material. One problem with conventional structures is that the metal foil layer, which acts as an oxygen barrier to prevent oxygen transfer into and out of the carton, can rupture during blank conversion, carton forming, and package dispensing stages.

During the formation of a closed chevron "top, flat" top, or other folded heat-sealed top, as well as during the formation of a fin-type sealed bottom, or other conventional folded bottom, the flexing and folding that occurs can place excessive localized stresses on the thin metal foil or other oxygen barrier layer, which often results in cracks and pinholes.

To date, there have been no economically attractive metal-foil-free cardboard packages on the market that consistently maintain oxygen impermeability similar to glass or metal containers. The object of the present invention is to produce a shelf-life-prolonging, low-oxygen-permeability, laminate structure for sealed containers, such as a package or carton based on cardboard, which prevents the permeation of gases and, in addition, the escape of aroma components or the ingress of microbial contamination. It is a further object of the present invention to produce a package which is economical per unit cost, substantially compatible with existing converting methods, and capable of being formed, filled and sealed economically at various high speeds, various temperatures, various pressures and dwell times using conventional packaging machinery.

It is another object of the present invention to produce a laminate structure for containers, such as a gable-top carton structure, that extends the shelf life (ELL) of food packages such as juice.

It is yet another object of the present invention to produce a laminate structure for a metal foil-free container having a long shelf life, which can utilize hydrogen peroxide (H)₂O₂) To pairIt is sterilized, absorbs a very small amount of odorous oils, can be cut into sheets and sealed on the sides, and has extremely high durability and swelling resistance. Such a structure will have a low oxygen permeability and will prevent the ingress of microbial contamination.

Summary of The Invention

These and other drawbacks of the prior art are addressed by the present invention, which is directed to extending the life of a package or carton and a method of making such a carton, which has a polyolefin polymer coating, such as polyethylene polymer, on the matte side, or product side, to allow sterilization with hydrogen peroxide. The package contains a high quality barrier layer of ethylene vinyl alcohol copolymer containing about 29 mole% of ethylene comonomer in its copolymer, as well as a thin tie layer and a thin coating of polyolefin polymer, such as low density polyethylene, to reduce the amount of scented oil absorbed to less than 10%. The provision of such a thin tie layer and polyolefin polymer coating on the matte side of the present structure ensures that the side seam of the structure can be skived using standard skiving equipment.

Brief Description of Drawings

These and other attributes of the present invention will be described using the following figures wherein

FIG. 1 is a cross-sectional view of a preferred embodiment of the laminate of the present invention;

FIG. 2 is a cross-sectional view of a preferred embodiment of the laminate shown in FIG. 1, illustrating a possible sequence of construction of such a laminate; and

figure 3 is a cross-sectional view of the laminate shown in figure 1, shown in a skived state.

Detailed Description

The preferred embodiment of the present invention is a shelf-life, low oxygen permeability sealed laminate structure, as shown in figure 1. All weights are expressed in grams per square meter. Preferably, the structure 5 comprises a cardboard substrate having a weight of 163-652g coated on one side with a coating 12 of a polyolefin polymer such as low density polyethylene, papery low density polyethylene, or mixtures thereof, the coating having a weight of 8.2-32.6g, and preferably about 19.6 g. The coating 12 is a "smooth" layer that is in contact with the atmosphere. On or in the bottom surface of the base layer 10 is a polyamide polymer coating 14 having a weight of 3.3 to 32.6g, preferably about 8.2 g. The polyamide polymer coating can be, but is not limited to, nylon 6, nylon 66, nylon 10, nylon 6-12, nylon 12, amorphous nylon, and other suitable polyamides. A tie layer 16 is applied to the underside or inner layer of the polyamide polymer coating 14. The bond coat has a coat weight of 0.8 to 11.4g, with a preferred value of about 2.4 g. The polyolefin polymer coating 18 is applied to the bottom or inner layer of the tie layer 16 at a coating weight of 9.8 to 48.9 grams, with a preferred value of approximately 29.3 grams.

On the underside or inner layer of the polyolefin polymer coating 18 is a further polyolefin polymer coating 20 having a weight of 1.6 to 11.4g, preferably about 6.5 g. Disposed on the underside of the polyolefin polymer coating 20 is a second tie layer 22 having a coating weight of 0.8 to 8.2g, with a preferred value of approximately 2.4 g. The high quality barrier layer 24 of ethylene vinyl alcohol copolymer is disposed on the bottom surface or inner layer of the second tie layer 22 at a coat weight of 0.8 to 6.5 grams, with a preferred value of approximately 3.3 grams. A third tie layer 26 is provided on the bottom or inner layer of the high quality barrier layer of ethylene vinyl alcohol copolymer and has a coat weight of 0.8 to 8.2g, with a preferred value of approximately 2.4 g. A final layer of polyolefin polymer 28 is disposed on the bottom surface of tie layer 26, on the matte or product contacting side. The matte polyolefin polymer 28 has a coating weight of 1.6-11.4g, with a preferred value of approximately 6.2 g.

The laminate, which has a smooth exterior and a matte interior, is provided with two polyolefin polymer coatings 12 and 28, respectively. Because the use of polyolefin polymers for the matte finish 28 and the lubricious finish 12 prevents contact between the antimicrobial hydrogen peroxide and the ethylene vinyl alcohol, the polyolefin polymers do not react deleteriously with the hydrogen peroxide, thus allowing the laminate 5 to meet FDA requirements. Because hydrogen peroxide is the disinfectant of choice, the configuration of the present invention is desirable over conventional configurations. Hydrogen peroxide is the most effective germicidal substance and eliminates microbial contamination, thereby meeting FDA requirements.

The use of the high-quality barrier layer 24 of ethylene vinyl alcohol copolymer, along with the tie layer 26 and the polyolefin polymer coating 28, minimizes the loss of scented oil. Experiments with this laminate structure showed that this structure 5 caused less than 10% of the flavor loss over a cycle time of at least 90 days, which is considered a long shelf life, in the case of orange juice, more nearly 6% of the total flavor loss. Conventional ethylene vinyl alcohol copolymer coatings contain 44 mole% of ethylene comonomer in their copolymer. The high quality barrier layer 24 of ethylene vinyl alcohol of the present invention contains ethylene comonomer in an amount of 27 to 32 mole%, with a preferred value of approximately 29 mole%.

Conventional cartons are coated with an ethylene vinyl alcohol copolymer at a level of 44 mole% ethylene comonomer and provide a shelf life of about 5 to 6 weeks. In order to achieve oxygen permeability comparable to that of the present invention, the thickness of the ethylene vinyl alcohol copolymer coating must be increased by at least 2 to 3 times for the carton. Accordingly, the cost of the above-described paperboard sheet increases and in many instances makes such cartons economically unfeasible.

The present invention uses an extruded laminate coated with a high quality barrier layer of ethylene vinyl alcohol copolymer having an ethylene comonomer content of 29 mole%. The result of adding the high quality barrier layer 24 of ethylene vinyl alcohol copolymer to the laminate 5 is that the container has the desired extended shelf life of at least 90 days. In addition, the thickness of the coating 24 is about half the thickness of a conventional ethylene vinyl alcohol copolymer coating having an ethylene comonomer content of 44 mole%. Thus the laminate of the present invention has a longer shelf life of at least 90 days and is less expensive than conventional laminates. In order to obtain a conventional ethylene vinyl alcohol copolymer coating of comparable oxygen permeability, it must have a thickness of 2-3 times. Such a configuration is not economically feasible.

In forming a preferred container from the laminate 5, the side seams are skived. Skiving is a method of attaching side seams of a carton which prevents the cardboard edge structure from being exposed to liquid contents and thus prevents liquid from being drawn into the laminate. The laminate is used such that it overlaps itself at different locations. The laminate is folded as shown in figure 3 so that the edges of the cardboard do not touch the contents of the container. At the inner side 50 near the end of the laminate 5, approximately half of its thickness is cut away so that it is foldable on itself. This ensures that only the polyolefin polymer contacts the contents and the outer side 60. In order to successfully cut the laminate into sheets, one must also realize that the polar polymer will not seal to itself, but only the non-polar polymer, when heated by direct impingement with a flame. Polyolefin polymers, such as low density polyethylene, low linear polyethylene, or mixtures thereof, are non-polar and can be processed well from a sheeting standpoint.

For this reason, tie layer 26 and polyolefin polymer coating 28 are used in matte applications. Both coatings 26 and 28 are relatively thin. For example, polyolefin polymer coatings typically have a coating weight of 16.3 to 19.6 g. With the coatings 26 and 28 provided, the side seams of the laminate 5 can be skived, since the polyolefin polymer seals by itself with flame impact heating.

The polyolefin polymer coating 14 is primarily used to provide mechanical strength and thermal resistance, thereby improving the durability and expansion resistance of the laminate 5. The polyolefin polymer coating 18 acts as a caulking layer so that during heating the coating 18 "melts" somewhat so that it fills the channels created in the laminate when folded to form the package. It is envisioned that adhesive layers 16 and 22 may be eliminated without departing from the spirit of the present invention.

Referring to fig. 2, a polyolefin polymer coating 12 is disposed on a base layer 10. While the polyamide polymer coating 14, tie layer 16 and polyolefin polymer are formed into a coextruded laminate 30 and placed on the other side of the substrate 10. Next, the polyolefin polymer coating 20, the tie layer 22, the ethylene vinyl alcohol copolymer coating 24, the tie layer 26, and the polyolefin polymer coating 28 are formed into a coextruded laminate 40 and placed on the hybrid extruded laminate 30, thus forming the laminate 5. Although the above is one method of producing the laminate 5, other methods may be employed. The adjacent polyolefin polymer coatings 18 and 20 may be a single polyolefin polymer coating. The key coatings required to achieve the performance characteristics required by the present invention have been discussed earlier. The remaining tie layers and polyolefin polymer coatings are used to aid in processing and producing the coextruded laminate and to provide the laminate 5 with the desired amount of material. These coatings may be replaced or deleted as needed so long as the laminate retains the proper amount of material to maintain the desired performance characteristics.

Although several embodiments of the carton structure have been described 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 foregoing description. It is, therefore, to be understood that all such variations, modifications and changes are believed to fall within the scope of the present invention as defined by the appended claims.

Claims (12)

1. A laminate structure for a container, comprising:

a substrate having an inner surface and an outer surface;

an outer heat-sealable polymeric material coating on the outer surface of the base layer;

a polyamide polymer layer disposed on the inner surface of the base layer to provide mechanical strength and thermal resistance to the laminate and to improve durability thereof;

a high quality barrier layer of ethylene vinyl alcohol copolymer disposed within said polyamide polymer layer for protection against moistureThe coating weight of the high-quality barrier layer of ethylene vinyl alcohol copolymer is 0.8-6.5g/m²；

A thin tie layer coated on the inside surface of said high quality barrier layer of ethylene vinyl alcohol copolymer and a thin coating of heat sealable polymer material coated on said thin tie layer to form the inside surface of said container and to enable the cutting of the side seams of said container into sheets and the sterilization of said laminate with hydrogen peroxide, wherein said high quality barrier layer of ethylene vinyl alcohol copolymer contains 27 to 32 mole% of ethylene comonomer.

2. A container laminate structure as set forth in claim 1 wherein said base layer is paperboard.

3. A container laminate structure as recited in claim 1, wherein said outer layer of heat sealable polymer material and said thin layer of heat sealable polymer material comprise one of low density polyethylene, linear low density polyethylene, or mixtures thereof.

4. A container laminate structure as set forth in claim 1 further comprising a tie layer disposed on an inner surface of said polyamide polymer layer.

5. A laminate structure for a container as set forth in claim 4 further comprising at least one polyolefin polymer layer disposed on an inner surface of said tie layer.

6. A container laminate structure as recited in claim 5, further comprising a second tie layer disposed on an interior surface of said at least one polyolefin polymer layer, and wherein said ethylene vinyl alcohol copolymer high quality barrier layer is disposed on an interior surface of said second tie layer.

7. A laminate structure for a container comprising:

a paperboard substrate having an inner surface and an outer surface;

a layer of linear low density polyethylene or a mixture thereof coated on the outer surface of said base layer;

a layer of polyamide polymer disposed on the inner surface of the base layer to provide mechanical strength and thermal resistance to the laminate and to improve its durability;

a high quality barrier layer of ethylene vinyl alcohol copolymer disposed on the inside of said polyamide polymer layer to prevent the absorption of flavor oils from the contents of said container, said high quality barrier layer of ethylene vinyl alcohol copolymer having a coating weight of 0.8 to 6.5g/m²；

A thin tie layer coated on the inside surface of said high quality barrier layer of ethylene vinyl alcohol copolymer and a thin polyolefin polymer layer coated on said thin tie layer to form the inside surface of said container and to enable the skiving of the side seams of said container and the sterilization of said laminate with hydrogen peroxide, wherein said high quality barrier layer of ethylene vinyl alcohol copolymer contains 27 to 32 mole% of ethylene comonomer.

8. A laminate structure for a container as set forth in claim 7 further comprising substantially a tie layer disposed on an inner surface of said polyamide polymer layer.

9. A container laminate structure as set forth in claim 7 further comprising substantially at least one polyolefin polymer layer disposed on an inner surface of said adhesive layer; and

a second tie layer disposed on an inner surface of said at least one polyolefin polymer layer, and wherein said high quality barrier layer of ethylene vinyl alcohol copolymer is disposed on an inner surface of said second tie layer.

10. A container laminate structure as recited in claim 7, wherein said at least one polyolefin polymer layer is a first outer layer and a second inner layer.

11. A laminate structure for a container comprising:

a paperboard substrate having an inner surface and an outer surface;

a layer of linear low density polyethylene or a mixture thereof coated on the outer surface of said base layer;

a polyamide polymer layer disposed on the inner surface of the base layer to provide mechanical strength and thermal resistance to the laminate and to improve durability thereof;

a high quality barrier layer of ethylene vinyl alcohol copolymer containing 29 mole% of ethylene comonomer disposed within said polyamide polymer layer to prevent the uptake of scented oil from the contents of said container and to provide a low permeability oxygen barrier, said high quality barrier layer of ethylene vinyl alcohol copolymer having a coat weight of 0.8 to 6.5g/m²。

A tie layer disposed on an inner surface of said polyamide polymer layer;

a first outer polyolefin polymer layer and a second inner polyolefin polymer layer disposed on the inner surface of said tie layer;

a second tie layer disposed on an inner surface of said second inner layer, wherein said high quality barrier layer of ethylene vinyl alcohol copolymer is disposed on an inner surface of said second tie layer; and

a thin tie layer coated on the inside surface of said high quality barrier layer of ethylene vinyl alcohol copolymer and a thin polyolefin polymer layer coated on said thin tie layer to form the inside surface of said container and to enable the skiving of the side seams of said container and the sterilization of said container with hydrogen peroxide.

12. A container laminate structure as recited in claim 1, wherein said polyamide polymer is selected from the group consisting of nylon 6, nylon 66, nylon 6-12, nylon 10, nylon 12, and amorphous nylon.