US20040209021A1

US20040209021A1 - Multi-layer laminate structure

Info

Publication number: US20040209021A1
Application number: US10/418,524
Authority: US
Inventors: Keith Shih
Original assignee: Individual
Current assignee: International Paper Co
Priority date: 2003-04-18
Filing date: 2003-04-18
Publication date: 2004-10-21
Also published as: TW200500205A; WO2004092273A1

Abstract

A multi-layer structure for fabricating a beverage container having two or more layers comprising paperboard and at least one barrier layer formed of a blend of polyethylene, nylon and a compatibilizer selected from maleic anhydride modified polyethylene, zinc neutralized ethylene methacrylic acid, sodium neutralized ethylene methacrylic acid, ethylene acrylic acid copolymers, ethylene methacrylic acid copolymers and epoxy functionalized polyethylene. The containers or cartons made from the laminates containing the blend offer substantial heat resistance and exhibit superior abuse resistance. The method and process of making the blend and multi-layer structure are also disclosed.

Description

The present invention relates to multi-layer laminate structures having two or more layers, at least one layer of which comprises a blend of polyethylene, nylon and a compatibilizing agent. More particularly this invention relates to a multi-layer laminated material suitable for forming a beverage container comprising a layer made of paperboard and a layer formed of a blend of polyolefin, polyamide and a compatibilizing agent. The layer comprising the blend may be deposited on one surface of the paperboard or onto another layer preferably composed of a polyester, polypropylene, polyethylene, ethylene vinyl alcohol copolymer (EVOH), polyacrylonitrile, polyvinylidene chloride (PVDC), or foil with or without an adhesive tie layer in between them.

BACKGROUND OF THE INVENTION

Many foods, especially liquids, are susceptible to oxygen or other gases that cause them to spoil, degrade, or change flavor. Therefore, the package or container that is used to store the food should have very good oxygen barrier properties to protect its contents.

It is also very important that the package have very good moisture barrier properties, so that moisture does not get in if dry food is stored inside. In the case for liquid (or water-containing) storage, the excellent moisture barrier properties of the package will minimize the moisture transport out of the package, as well. In paperboard-based packaging systems, the required barrier properties can be provided by polymer resin coatings applied on the paperboard.

The cellulosic materials in the paper based packages such as gable top cartons are susceptible to moisture, which can weaken their internal bonds and leads to bulging of the carton and a perception of a spoiled and obsolete product on the shelf. The weakening of the internal fibrous structure inside a paperboard can happen through any one or any combination of the following three mechanisms: 1) diffusion of moisture through the polymer resin coating into the paperboard, 2) moisture wicking through pinholes or defects generated by coating and the subsequent converting processes, and 3) moisture wicking through unprotected raw edge at the side seam or at the bottom seam.

If the paperboard becomes weakened due to the first mechanism, a thick layer of moisture barrier such as polyethylene or polypropylene can be applied on both sides of the paperboard to overcome it. If the third mechanism causes the paperboard to weaken, one can use the skiving technology to protect the raw edge. Skiving is essentially done by 1) cutting out the outside polymer layer along with a portion or all of the paperboard and 2) folding the remaining polymer layer over and sealing it to the board to protect the paperboard raw edge. Skiving is commonly done in gable top cartons to effectively protect the paperboard raw edge.

Carton defects are often caused by blister or bubble formation on the layer immediately adjacent to the paperboard at the inside of the carton. This happens during heat sealing when intensive heat is applied to the inside of the carton. Since paperboard usually contains some amount of moisture, in equilibrium with the outside environment, this intensive heat can vaporize the moisture inside the paperboard. The outside carton surface is usually coated with a layer of a moisture barrier such as polyethylene. The temperature at the outside surface is not very high so that this outside moisture barrier layer remains rather rigid. Therefore, the vapor cannot escape through the outside barrier layer. Since the inside surface temperature is very high, the polymer layer immediately adjacent to the paperboard may be “softened” enough so that blister or pinhole formation becomes inevitable. Therefore, placing a layer of polymer with good heat resistance and high melting or softening temperatures such as polyamide (nylon) adjacent to the paperboard is a very important and essential structure design to prevent this blister or pinhole formation from happening.

After filling with the food contents, the gable-top cartons or other shape containers made from these paperboard/polymer laminates are generally packed inside corrugated boxes and these boxes are stacked on top of each other in a pallet for transportation. The transportation of milk or juice is usually done in a refrigerated truck maintained at a temperature of approximately 4° C. The food contents, particularly the liquid food such as juice and milk, can create a tremendous dynamic load to the laminate structure and cause damage to the cartons due to vibration or jittering of these boxes during transportation. Typically the damage manifests itself in the form of leakage at the bottom of the cartons. Polyamide or nylon polymers provide abuse resistance to the structure due to their toughness. Other factors such as the coating thickness (coat weight), adhesion of film to paperboard, types of internal or surface sizing on the paperboard can also affect the abuse resistance of the cartons or containers.

Polyolefins such as polyethylene or polypropylene have been used to provide moisture barrier as well as heat sealing properties. Generally speaking, a resin exhibiting excellent moisture barrier properties does not have good oxygen barrier properties and vice versa. Polyolefins are known to have poor oxygen barrier performance. Therefore, multi-layer structures containing both oxygen barrier layers and moisture barrier layers have been developed to address these concerns. Ethylene vinyl alcohol copolymer (EVOH) has excellent oxygen barrier properties and has been used in packaging applications for oxygen sensitive foods, such as orange juice. Other polymers such as polyethylene terephthalate (PET), polyacrylonitrile, and polyvinylidene chloride (PVDC), EVOH nanoclay composite, or polyamide nanoclay composite could be used as the oxygen or aroma barrier. Nylon polymers have also been used in paperboard packaging structures resulting in good oxygen barrier performance for foods that require only moderate protection from oxygen. However, nylon polymers are better known to impart abuse resistance and heat resistance to the paperboard structure. Aluminum foil has also been used in the laminate structure to result in both excellent moisture and oxygen barrier performance.

Paperboard/polymer laminate structures that consist of layers of nylon polymers, polyolefins, and/or ethylene vinyl alcohol copolymers (EVOH) are described in U.S. Pat. Nos. 3,972,467, 4,835,025, 4,888,222, 5,175,036, 5,958,534, 6,110,548, and 6,383,582. While all of the prior arts patents addressed the issues of oxygen and moisture barrier performance, none focused on improving the abuse resistance of the cartons made from these paperboard/polymer laminates.

The toughness of polyamides, particularly at low temperatures, can be modified or improved by rubbers or elastomers. The room temperature toughness of polyamides can also be improved by introducing fillers such as calcium carbonate. Alternatively, one could blend polyamides with another polymer having good toughness properties. However, it may require the addition of a compatibilizer in this blending approach if the polymer chosen is not compatible with the polyamide(s). Polymers with good toughness include but are not limited to linear low density polyethylene (LLDPE), low density polyethylene (LDPE), metallocene polyethylene (m-PE), zinc or sodium salts of ethylene methacrylic acid copolymer (Surlyn®), and maleic anhydride modified polyethylene. It is quite common that additional co-monomers with rubbery properties and low glass transition temperatures are included in the polymerization process of Surlyn® polymers and maleic anhydride modified polyethylene to achieve excellent low temperature toughness.

When blending Surlyn® polymers with polyamides, it may not be necessary to add a compatibilizer because the polymer pairs are compatible between themselves. When blending polyamide with another polymer such as LDPE, it is necessary to add a third component, the compatibilizer, to produce a compatible blend. The role of compatibilizer is to reduce the interfacial surface energy between the phase domains and hence reduce the phase domain sizes of the blend. In an incompatible blend the phase domain sizes are very large and the mechanical properties such as strength and toughness are dramatically reduced.

Generally, blending polyamide with a low melting temperature resin such as polyethylene would have a tendency to reduce the heat resistance of the blend. It is essential that the modified (toughened) polyamides maintain a substantial level of heat resistance so that the paperboard will not blister or forms pinholes during converting operation. The blends of the present invention can be applied to the paperboard to form laminates with substantial heat resistance and improved abuse resistance when the laminates are made into the cartons or containers.

U.S. Pat. No. 3,373,222 discloses a blend of 40-60% by weight of a polyamide and 40-60% by weight of a polyolefin resin, and 2-10% by weight of a carboxylated polyethylene having an acid number from 2.75 to 50. This blend is capable per se of being shaped into various non-pinch crazing forms without any difficulties. This is not what is contemplated by the present invention but rather a blend to be applied to paperboard to form laminates having improved heat and abuse resistance when formed into cartons and containers.

SUMMARY OF THE INVENTION

It is therefore an object of the invention to provide a compatible polyolefin-polyamide blend, which is substantially resistant to heat and has improved toughness to be used in multi-layer laminate structures.

Another object of the invention is to provide a multi-layer laminate structure, particularly suitable for use for beverage packaging purposes which has low permeability to gases, in particular oxygen and vapors, in particular water vapor and at the same time has improved physical properties such as abuse resistance and is substantially resistant to heat.

It is another object of the invention to provide a multi-layer laminate material having two or more layers comprising paperboard and at least one barrier layer formed of a blend of polyolefin, polyamide and a compatibilizer.

It is another object of the invention to provide a multi-layer structure comprising paperboard and at least one barrier layer formed from a blend of polyamide, polyolefin and a compatibilization agent deposited on one surface thereof.

In accordance with the invention, there is provided a blend comprising polyolefin, preferably polyethylene, a polyamide, preferably nylon 6 and a compatibilization agent selected from maleic anhydride modified polyethylene, zinc neutralized ethylene methacrylic acid copolymer, sodium neutralized ethylene methacrylic acid copolymer, ethylene acrylic acid copolymer, ethylene methacrylic acid copolymer and epoxy functionalized polyethylene.

The invention also provides a process for producing the blend and a multi-layer laminate structure including the same which comprises mixing the polyolefin, polyamide and compatibilization agent, heating and blending the mixture to form a melt and extruding the melt onto paperboard or another material by the extrusion coating or extrusion lamination process.

The process can be carried out by, first pre-blending the polyolefin, polyamide with a sufficient amount of a compatibilization agent in a mixer to make a dry blend, and then introducing the dry blend into the extruder hopper. A single screw extruder equipped with a mixing section such as a Maddock mixer is sufficient to make a compatible blend. Alternatively the polyolefin, polyamide and compatibilization agent can be pre-compounded in a twin screw extruder, a single screw extruder equipped with a mixing screw, or an internal mixer and pelletized. These pellets can then be fed directly into the extruder for extrusion coating. In the instance when the pre-compounded blend is used, it is not necessary to equip the single screw extruder on the extrusion coating line with any mixing element.

In both instances, the mixture is heated and the melt blend is extruded as a coating or film onto the paperboard. It is of course possible for the melt blend to be extruded onto another layer of a multi-layer structure other than directly onto the paperboard.

The obtained blend compositions and the multi-layer structures produced therewith may be converted into packaging materials intended for the packaging of beverages which require low water vapor transmission rates and low gas, particularly oxygen and flavor permeabilities, and improved abuse resistance.

DETAILED DESCRIPTION OF THE EMBODIMENTS OF THE INVENTION

The blends of polyolefin, polyamide and compatibilization agent are obtained by a melt blending process using a single screw extruder in a extrusion coating line or co-extrusion coating line, as long as the extruder is equipped with a mixing section. Alternatively the blend can be pre-compounded off-line by a twin-screw extruder, a single screw extruder equipped with a mixing section, or an internal batch mixer. The blend obtained is then palletized. These pellets are then fed into the extruder hopper of the single extruder in the extrusion coating line for the subsequent processing. Polyolefins that may be used are polyethylene homopolymers such as but not limited to low density polyethylene, linear low density polyethylene, metallocene polyethylene, and high density polyethylene; polypropylene homopolymers, copolymer of propylene with ethylene, and rubber modified (impact modified) polypropylene. Most preferred as the polyolefin is low-density polyethylene such as Tenite 1924P from Eastman Chemical Company or MarFlex™ PE 4517 from Chevron Phillips Chemical Company. The polyolefin resin may be used in the form of granules or powders. [0023]
Polyamides that may be used are nylon 6, nylon 7, nylon 8, nylon 11, nylon 12, nylon 6-6, nylon 6-9 and nylon 6-10, copolymers of nylon 6 and nylon 6-6, amorphous nylon such as the one sold by DuPont under the trade name of Selar PA, MXD6 nylon such as sold by Mitsubishi Gas Chemical Company, and polyamide nanoclay composites. The preferred polyamide is nylon 6 such as Capron® B73QP manufactured by Honeywell Plastics The compatibilization agents can be maleic anhydride modified polyethylene, such as Fusabond®, polymers from DuPont or Tymor® resins from Rohm and Haas, zinc or sodium neutralized ethylene-methacrylic acid copolymers such as Surlyn®, ionomers from DuPont, modified Surlyn® ionomers with additional functional groups, ethylene acrylic acid copolymers such as Primacor® polymers from Dow Chemical Company, ethylene methacrylic acid copolymers such as Nucrel® polymers from DuPont, or epoxy functionalized polyethylene such as Lotader® polymers from Atofina. The preferred compatibilizer is maleic anhydride modified polyethylene such as Tymor® 1N06 from Rohm and Haas or Surlyn® ionomer such as Surlyn® 1857 from DuPont for a blend of nylon 6 and LDPE. [0024]
The blend will preferably contain less than 40% by weight of the polyolefin, preferably polyethylene, more than 60% by weight of the polyamide preferably nylon 6 and from about 0.1 weight % to about 15 weight % of the compatibilization agent. A particularly preferred blend contained 90% by weight of the nylon 6, approximately 8.5% by weight of the LDPE, and approximately 1.5% by weight by weight of the compatibilizer. [0025]
The process of the invention is most advantageously performed by the use of an extrusion coating line having at least a single screw extruder equipped with a mixing section. The three components are pre-blended (dry blended) in a mixer before being introduced into the extruder. A single screw extruder equipped with a mixing section, such as a Maddock mixer, is sufficient to melt blend the polyethylene, nylon 6 and compatibilization agent. Alternatively the dry blend can be pre-compounded in a twin-screw extruder, in a single screw extruder equipped with a mixing section, or in an internal mixer. The melt blend formed is then pelletized and the pellets fed directly into a single screw extruder for extrusion coating or film coating operations. In the instance when the pre-compounded blend is used, there is no need to equip the single screw extruder on the extrusion coating or film casting line with any mixing element. [0026]
In order to obtain an optimal mixing of the polyethylene, nylon 6 and compatibilization agent during the extrusion process, they should all be in their molten states. In general, a practical melt processing temperature for polyethylenes is in the range of from about 130° C. and upwards, for the compatibilizers in the range of from about 110° C. and upwards, and for polyamides in the range from about 220° C. and upwards. In order to get good mixing between these components, the temperature of the extruder barrel section at which the mixing section is located should be above 220° C. However, the processing temperatures must not be so high that any substantial degree of degradation of the polymer resins will take place. The temperature of the melt should therefore not exceed about 320-330° C. [0027]
While the present invention is directed to polyamide and polyolefin blend barrier layers for paperboard substrates, the invention is not limited to the extrusion of such layer on cellulosic substrates. Accordingly, the substrate may be comprised of only paperboard, polymer films, aluminum foil, and their combination. The blend of polyamide and polyolefin layer may also be applied to polymeric materials such as thermoplastics and many other materials where there is a desire to reduce the oxygen, moisture, and/or flavor vapor transport through the material. [0028]
Examples of such paperboard include but are not restricted to bleached paperboard, unbleached paperboard, kraft, sulfide, and multi-ply board. The basis weight of paperboard could vary from 20 lbs/3,000 square foot (or 20 lbs/ream) to 500 lbs/ream. [0029]
Various coatings or treatments may be applied to the paperboard before or after co-extrusion coating with the blend of polyamide and polyolefin. These coatings or treatments could include sizing agents, primers and other wet-end and off-line additives. Other methods known to those of ordinary skill may be used to obtain a container such as single or multi-layer polymer structure or plastic container containing the blend of this invention. Examples of such a rigid or flexible container could be plastic bottles, jars, pouches, and bags. [0030]
A particularly preferred substrate for inclusion in the laminate structures of the invention is a bleached paperboard made by International Paper Company with basis weights in the range of 120 lbs/ream to 400 lbs/ream and more preferably in the range of 140 lbs/ream to 290 lbs/ream. [0031]
The method of making a paperboard/polymer laminate structure containing at least a layer of polyamide and polyolefin blend is preferably carried out using the extrusion coating process. The blend can be prepared on-line. In a preferred method, a gravimetric or volumetric blender is used to meter the three components (polyamide, polyolefin, and compatibilizer) to the proper proportions and mix them to form the dry blend. The dry blend is then introduced into the extruder hopper via a conveying device. A single screw extruder equipped with a mixing section, such as a Maddock mixer, serves to melt blend the polyamide, polyolefin, and the compatibilizer to form a stable melt curtain for extrusion coating operation. Alternatively one can use gravimetric or volumetric feeders to directly feed the individual resin in the right proportions to the extruder. [0032]
Alternatively the blend could be prepared off-line. The blend can be compounded or melt blended in a twin screw extruder, a single screw extruder equipped with the mixing section, or in an internal batch mixer such as a Banbury mixer. The melt blend formed is then pelletized. The pellets are then fed into an extruder for extrusion coating or extrusion lamination operations. [0033]
In the extrusion coating process a moving paperboard is coated with single or multi-layer polymer melt fed through the extrusion coating die. The paperboard/polymer melt laminate is then subsequently passed through a nip roll/chill roll in order to cool it down before it is wrapped up in the winding station. If a multi-layer polymer is involved, it may be necessary to place a tie layer or tie between two dissimilar polymer layers. For instance, it may be necessary to place a tie layer between a polyamide layer and a polyolefin layer. Another example is to co-extrude EVOH with LDPE, it is necessary to place a tie layer between these two polymer layers. Depending on the polymer layers used in forming the multi-layer structure, the choice of tie layer may change. For instance, maleic anhydride modified polyethylene is suitable to be used as a tie layer between polyamide and polyolefin. However, maleic anhydride modified polyethylene may not be suitable as the tie layer between polyester and polyethylene. When co-extruding polyamide and EVOH together, one may eliminate the use of a tie layer because the adhesion between polyamide and EVOH is generally good. Generally speaking the tie layer used for polyamide and another resin can also be used as the tie layer between the blend of polyamide and polyolefin and same specific resin. Therefore, maleic anhydride modified polyethylene is suitable for use as a tie layer between the blend of polyamide and polyolefin and polyethylene. The preferred tie layer resin in this case is maleic anhydride modified polyethylene such as Plexar® 5125 from Equistar Chemical Company. [0034]
It may be necessary to apply a treatment to the paperboard surface in order for it to adhere to the hot polymer melt. The usual treatment is flame treatment so that polar species are induced on the paper surface. The flame treatment is usually done on-line. Other surface treatment includes corona discharge, and ozone treatment. These treatments can be done on-line or off-line. [0035]
In the case of a multi-layer co-extrusion coating, various polymer melts from different extruders flow through the heated pipes to a feed block. Each polymer melt is converted into a layered form inside the feed block. Various molten polymer layers are then combined at the exit of the feed block before the combination enters into the extrusion-coating die. An alternative method is to use the multiple manifold die and to allow the layers to combine inside the die. The layers are combined at or close to the final land of the die, and they exit as one integral layer. A third approach combines both the feed block and multiple manifolds to provide even better processing control. [0036]
Another method of making a paperboard/polymer laminate structure containing a least a layer of polyamide and polyolefin blend is to use the extrusion lamination process. In this process, a solid polymer laminate that has been pre-formed elsewhere is fed along with the moving paper web through an extrusion die. A polymer hot melt layer (as an adhesive layer) is directed through the extrusion die and deposited between the paperboard and the laminate. The paperboard/adhesive/laminate is then passed through the nip roll and the chill roll to cool down before it was wound on the roll at the winding station. It may be necessary to apply a surface treatment on the laminate film surface in order for it to stick to the adhesive layer. [0037]
It may also be necessary to apply a surface treatment on the paperboard for the same reason. The surface treatment for the laminate film can be corona discharge or ozone treatment and can be done either on-line or off-line. As for the surface treatment for paperboard, it can be flame, corona discharge, or ozone. [0038]
An alternative method is to use adhesive lamination, where an adhesive, a primer or glue is applied between two adjacent layers or substrates during the lamination process. [0039]
The following structures were prepared and illustrate preferred laminates of the invention: [0040]

Structure #1

12 polyolefin

10 paperboard

14 polyolefin/polyamide blend

(compatibilized)

16 tie

18 polyolefin
12 designates a polyolefin gloss layer for printing (5-20 lbs/ream, preferably 12 lbs/ream). 10 is the paperboard (100-300 lbs/ream, preferably of 125-285 lbs/ream). 14 is a compatibilized blend of polyamide (nylon) and polyolefin with a coat weight of 2-20 lbs/ream, preferably 5 lbs/ream. 16 is a tie layer having a coat weight of 1-5 lbs/ream, preferably 1.5 lbs/ream, and 18 is another polyolefin layer (heat sealing layer) in food contact, having a coat weight of 10-25 lbs/ream, preferable in the range between 12-20 lbs/ream. [0041]

Structure #2

22 polyolefin

20 paperboard

24 polyamide/polyolefin blend

26 tie

28 polyolefin

30 polyolefin

32 tie

34 EVOH*

36 tie

38 polyolefin
22 designates a polyolefin gloss layer for printing (5-20 lbs/ream, preferably 12 lbs/ream). 20 is the paperboard (100-300 lbs/ream, preferably in the range of 125-285 lbs/ream). 24 is a compatibilized blend of polyamide (nylon) and polyolefin having a coat weight of 2-20 lbs/ream, preferable 5 lbs/ream. 26 is a tie layer having a coat weight of 1-5 lbs/ream, preferably 1.5 lbs/ream. 28 is polyolefin layer having a coat weight of 6-30 lbs/ream, preferably 28 lbs/ream, 30 is also a polyolefin layer having a coat weight of 1-7 lbs/ream, preferably 4 lbs/ream. 32 is another tie layer with a coat weight of 1-5 lbs/ream, preferably 1.5 lbs/ream, 34 can be one of the following: 1) ethylene vinyl alcohol copolymer (EVOH) containing 26-44 mol % ethylene, 2) polyamide such as nylon 6, nylon 66, nylon 10, nylon 6-10, amorphous nylon, MXD6 nylon, 3) a compatibilized blend of polyamide and polyolefin. The coat weight of this layer, 34, is between 0.5-7 lbs/ream, preferably 2-4 lbs/ream. 36 is another tie layer having a coat weight of 1-5 lbs/ream, preferably 1.5 lbs/ream and 38 is the food contact polyolefin layer having a coat weight of 1-7 lbs/ream, preferably 4 lbs/ream. [0042]

Structure #3

42 polyolefin

40 paperboard

44 polyamide/polyolefin blend

46 EVOH

48 tie

50 polyolefin

52 tie

54 EVOH

56 tie

58 polyolefin
42 designates a polyolefin gloss layer for printing (5-20 lbs/ream, preferably 12 lbs/ream). 40 is the paperboard (100-300 lbs/ream, preferably 125-285 lbs/ream), 44 is a compatibilized blend of polyamide (nylon) and polyolefin having a coat weight of 2-20 lbs/ream, preferably 5 lbs/ream. 46 is an ethylene vinyl alcohol copolymer (EVOH) having a coat weight of between 0.5-10 lbs/ream, preferably 3-6 lbs/ream. 48 is a tie layer. The coat weight of this tie layer, 48, is between 0.5-15 lbs/ream, preferably 8 lbs/ream. 50 is a polyolefin layer having a coat weight of 1-20 lbs/ream, preferably 4-10 lbs/ream. 52 is another tie layer having a coat weight of 1-5 lbs/ream, preferably 1.5 lbs/ream. 54 is another EVOH layer with a coat weight of 1-10 lbs/ream, preferably 3 lbs/ream. 56 is another tie layer having a coat weight of 1-5 lbs/ream, preferably 1.5 lbs/ream. 58 is the food contact polyolefin layer having a coat weight of 1-20 lbs/ream, preferably 4-10 lbs/ream. [0043]

EXAMPLE 1

Multi-layer paperboard/polymer laminates were produced at the pilot scale co-extrusion line. Two structures were made. The control structure (Run 1) had the following multi-layer construction: [0044]
Run 1—LDPE (gloss finish)/paperboard/nylon 6/tie layer/LDPE [0045]
Run 2 had the following multi-layer construction: [0046]
Run 2—LDPE (gloss finish)/paperboard/blend of nylon 6 and LDPE/tie/LDPE [0047]
In both runs, 12 lbs/ream of the gloss LDPE coating were used. The paperboard basis weight was 265 lbs/ream in both runs. In Run 1, the coat weight of nylon 6 was 5 lbs/ream and in Run 2 the coat weight of the blend of nylon 6 and LDPE was also 5 lbs/ream. The coat weight for the tie layer in both structures was 1.5 lbs/ream. The coat weight for the LDPE on the matte side (also the food contact side) was 14 lbs/ream for both structures. The blend was made up of approximately 90 wt % nylon 6, 1.5 wt % compatibilizer, and 8.5 wt % LDPE. During the co-extrusion coating process, the polymer to paperboard adhesion was checked by the cross cut method. [0048]
1) Using a sharp knife or razor blade, a first light cut of the polymer coating on the paperboard was made. A second similar cut was made so as to form an “X” shape between the two cuts. [0049]
2) the knife edge was used for starting the polymer separation from the paperboard at the center of the “X” cut. [0050]
3) The polymer was grasped and then slowly pulled to cause separation of the coating from the paperboard. [0051]
4) The degree of fiber tear on the polymer film surface was observed and a rating of excellent, good, fair, and poor in descending order was assigned based thereon. [0052]
Excellent adhesion was found for both samples on both the gloss side coating (LDPE to paperboard) and the matte side coating (laminate to paperboard), as we observed 100% fiber tear when we pulled the film away from the paperboard. [0053]
The coated paperboard was converted into blanks using a side seam sealing machine and a skiver. A blue dye (methylene blue) alcohol solution was used to check the side seam quality, particularly the pinhole resistance. The visual examination lead to a ranking of one of the following five in descending order: excellent, very good, good, fair, and poor. These blanks were then fed into the milk filling machine (H-100 filler by Evergreen) for carton conversion and filing. 2% low fat milk was used to fill the half-gallon size cartons with standard J bottom. A red dye (Scarlet Moo) aqueous solution was used to check the pinhole resistance of the board at the bottom of the carton. In this test, unfilled empty carton was filled with the red dye solution and sat for 2 minutes. The red dye solution was then poured out of the carton. The bottom portion of the carton was wiped cleaned with an absorbent tissue and then visually examined for existence of pinholes. The visual examination lead to a ranking of one of the following five in descending order: excellent, very good, good, fair, and poor. Both the side seam pinhole resistance and bottom pinhole resistance tests reveal the heat resistance of the coated boards. [0054]

The cartons filled with the milk were stored in the cold room at approximately 4° C. for two days. Then these cartons were subjected to the distribution abuse resistance test. This is an in-house developed test method to simulate the vibration and jittering of the cartons experienced during transportation. The test is designed to compare the relative bottom durability or distribution abuse resistance of cartons to a control group within a study. Data are not to be used for comparison between studies. A total of 40 cartons are used for each test. The tester essentially consists of a shaker table. The variables in this tester are rpm of the motor and duration of the test. The testing conditions were: 210 rpm for 15 minutes, 225 rpm for 15 minutes, 250 rpm for 15 minutes, and 270 rpm for 15 minutes. After the test, the bottom of each carton was visually examined to detect leakage. The total number of leakage (for a total of 40 cartons) was then recorded as the distribution abuse resistance of the cartons. Table 1 lists all of the test results.

TABLE 1


Results of the adhesion test, pinhole resistance test, and distribution abuse resistance test.

				Abuse
				resistance
Adhesion to	Adhesion to	Pinhole	Pinhole	(# leaks out
paperboard	paperboard	resistance	resistance	of 40
(gloss side)	(matte side)	(side seam)	(bottom)	cartons)

Run 1	excellent	excellent	excellent	very good	17
Run 2	excellent	excellent	excellent	very good	4

EXAMPLE 2

Multi-layer paperboard/polymer laminates were produced at the co-extrusion line. Two structures were made. The control structure (Run 3) had the following multi-layer construction: [0056]
Run 3—LDPE (gloss finish)/paperboard/nylon 6/tie layer/LDPE [0057]
Run 4 had the following multi-layer construction: [0058]
Run 4—LDPE (gloss finish)/paperboard/blend of nylon 6 and LDPE and compatibilizer/tie/LDPE [0059]
In both runs, 12 lbs/ream of the gloss LDPE coating were applied. The paperboard basis weight was 265 lbs/ream in both runs. In Run 3, the coat weight of nylon 6 was 5 lbs/ream and in Run 4 the coat weight of the blend of nylon 6 and LDPE was also 5 lbs/ream. The coat weight for the tie layer in both structures was 1.5 lbs/ream. The coat weight for the LDPE on the matte side (also the food contact side) was 14 lbs/ream for both structures. The blend was made up of approximately 80 wt % nylon 6, 5 wt % compatibilizer, and 15 wt % LDPE. [0060]

The adhesion test, pinhole resistance test, and distribution abuse resistance test for both structures (from Run 3 and Run 4) were carried out as described in Example 1. The results are listed in Table 2.

TABLE 2


Results of the adhesion test, pinhole resistance test, and distribution abuse resistance test.

Run 3	excellent	excellent	excellent	very good	10
Run 4	excellent	excellent	excellent	very good	5

Articles made from the multi-layer laminate structure comprising the compatibilized blends of polyolefin (polyethylene) and polyamide (nylon 6) and paperboard, according to the present invention are possessed of superior distribution abuse resistance and subsantial heat resistance. When combining the compatibilized blend of nylon 6 and LDPE with a high oxygen barrier such as EVOH, polyester, polyacrylonitrile, polyvinylidene chloride, or a foil and a high moisture barrier such as LDPE or a foil, the resultant structure is suitable for use in beverage packaging and particularly for packaging juices and punches that require a high barrier against moisture and gases, such as oxygen and against flavor components. [0062]

Claims

We claim:

1. Process for producing a compatibilized blend of polyethylene and nylon which comprises forming a mixture of polyethylene, nylon, and a compatibilizer which is a member selected from the group consisting of maleic anhydride modified polyethylene, zinc neutralized ethylene methacrylic acid, sodium neutralized ethylene methacrylic acid, ethylene methacrylic acid copolymers, ethylene acrylic acid copolymers and epoxy functionalized polyethylene and heating said mixture in an extruder to a temperature which is sufficient to form a homogeneous melt blend of said polyethylene, nylon and compatibilizer.

2. A process according to claim 1 which comprises forming said blend by separately introducing each of said polyethylene, nylon and compatibilizer into said extruder for forming said mixture in situ.

3. A process according to claim 1 which comprises forming said blend by dry mixing said polyethylene, nylon and compatibilizer prior to introduction into the extruder.

4. A compatibilized blend of polyethylene, nylon and a compatibilizer which is a member selected from the group consisting of maleic anhydride modified polyethylene, zinc neutralized ethylene methacrylic acid, sodium neutralized ethylene methacrylic acid, ethylene methacrylic acid copolymers, ethylene acrylic acid copolymers and epoxy functionalized polyethylene.

5. A compatibilized blend according to claim 4 wherein said polyethylene is a member selected from the group consisting of low density polyethylene, linear low density polyethylene, metallocene polyethylene and mixtures thereof.

6. A compatibilized blend according to claim 4 wherein said nylon is a member selected from the group consisting of nylon 6, nylon 7, nylon 8, nylon 11, nylon 12, nylon 6-6, nylon 6-9, nylon 6-10, copolymer of nylon 6 and nylon 6-6, amorphous nylon, MXD6 nylon, nylon nanoclay composite and mixtures thereof.

7. A compatibilized blend according to claim 4 wherein said nylon is nylon 6.

8. A compatibilized blend according to claim 4 wherein said polyethylene is low density polyethylene and said nylon is nylon 6.

9. A compatibilized blend according to claim 4 wherein said compatibilizer is present in said blend in an amount of about 0.1 wt. % to about 15 wt. %.

10. A compatibilized blend according to claim 4 wherein said blend contains less than about 40 wt. % of said polyethylene.

11. A compatibilized blend according to claim 4 wherein said blend contains more than about 60 wt. % of said nylon.

12. A compatibilized blend according to claim 4 wherein said compatibilizer is present in an amount of about 0.1 wt. % to about 15 wt. % said polyethylene is present in an amount of less than about 40 wt. % and said nylon is present in an amount of more than about 60 wt. %.

13. A multi-layer laminate material having two or more layers comprising at least one layer comprising a compatibilized blend according to claim 4.

14. A laminated material comprising a paperboard substrate and a layer formed of a compatibilized blend according to claim 4 deposited on one surface of the paperboard.

15. A beverage container comprising a multi-layered structure comprising a paperboard substrate and at least one barrier layer formed of a compatibilized blend according to claim 4.

16. A beverage container according to claim 15 wherein said barrier layer is deposited on one surface of said paperboard.