Improved non-foil composite structures for packaging juice

Abstract: The present invention relates to a non-foil composite barrier for an improved container for citrus juices and other liquids. The container utilizes a paperboard barrier laminate for the containment of essential oils and the prevention of losses of vitamin C. Also disclosed is a process of making the laminate. The laminate makes use of an inner barrier layer of a heat-sealable ethylene vinyl alcohol copolymer to enhance the barrier properties of the laminate. The invention provides a container for liquids containing essential oils and/or flavors constructed from a laminated characterized by the fact that it comprises: a) a paperboard substrate (36); b) a thin outer layer (34) of a heat sealable low density polyethylene polymer coated on said outer surface of said paperboard substrate; c) an ethylene vinyl alcohol copolymer layer (44); and d) a heat sealable layer of a low density polyethylene layer (46).

Description: The invention relates to heat-sealable barrier laminates for the containment of essential oils and the prevention of loss of vitamin C in paperboard cartons, as well as to a process for making such laminates. More particularly, this invention relates to containers for liquids which are comprised of an improved heat-sealable non-foil composite structure which retains the vitamin C in juice at nutritional-claims levels throughout the normal expected shelf life when the carton/package is made as well as improving the retention of citrus juice flavor oils therein. Heat-sealable low-density polyethylenes are well known to be components of current paperboard citrus juice cartons which provide little barrier to absorption and/or transmission of citrus juice essential flavor/aroma oils. Additionally, it is well known that impermeable materials such as aluminum foil, polar materials such as, e.g., polyamides, polyethylene terephthalates, polyvinylidene chlorides and polyvinyl chlorides , and highly crystalline non-polar materials such as high-density polyethylene and polypropylene provide varying degrees of barrier to the absorption and/or transmission of non-polar citrus juice flavor oils such as e.g. d-Limonene . However, these materials require a thick liquid contact low density polyethylene layer for heat sealability as well as an expensive tie layer to provide consistent adhesion between the LDPE and the barrier material. The thick LDPE liquid contact layer 0.037mm (1.5 mil) generally required in such cartons also absorbs citrus flavor/aroma oils, with resultant deleterious effects on product quality. JP-A-108549/86 describes a laminate which is intended to prevent diffusion of odor or taste from the package into the contents of the container. A gas barrier resin which could be the ethylene vinyl alcohol copolymer is coextruded with a polyolefin which could be e.g., LDPE, HDPE, polypropylene and ethylene-propylene copolymer to form the two layer laminate, called the BS layer, in contact with the liquid food. The thickness of the ethylene vinyl alcohol copolymer is stated to be 1-30 µm that is up to 0.03 mm and the polyolefin thickness ranges between 10 - 200 µm (0.01 mm - 0.2 mm). The two layer laminate is laminated onto a substrate, which may be paper, by means of an adhesive, such as a polyurethane, or an isocyanate. In Example 1, the laminate consists from the exterior to the interior of LDPE/paper/LDPE/AC/EVOH/LDPE that is with three layers of LDPE. Both the outer and intermediate LDPE layer have a thickness of 15 µm (0.015 mm). Also the EVOH layer is 15 µm thick and the innermost LDPE layer in contact with the food is 30 µm thick (0.03 mm; 1.17 mil). In Example 2 of JP-A-108549/86, a maleic anhydride-modified low density polyethylene is used in addition to LDPE with a total of three layers of LDPE and one layer of modified polyethylene. Examples 3 and 8 are similar to Example 2. Three layers of LDPE and one layer of modified polyethylene are used in Example 4. Two layers of HDPE (high density polyethylene) in addition to one layer of LDPE and one layer of modified polyethylene are used in Example 5. The method of preparation in JP-A-108549/86 consists of preparing first the BS layer, which is the two layer laminate of EVOH and LDPE, which constitutes the inner layer. Blow molding is used. JP-A-108549/86 reports results of tests of odor and taste carried out by injecting odorless air into the package, heating to 40°C for two hours, cooling, followed by evaluation. The retention of essential oils in citrus juices and the loss of vitamin C are not determined. The existing commercial structure for a paperboard carton for juice and similar products has utilized an easily heat-sealable barrier laminate composed of paperboard sandwiched between two layers of low density polyethylene (LDPE). The LDPE is an inexpensive heat-sealable moisture barrier. The conventional structure falters in that the thick LDPE layer absorbs the essential oils of the juice after short periods of time causing integrity decay of heat seals, stress cracking of the layer and allows transmission of the essential oils into the paperboard and to the atmosphere. Additionally, the conventional structure provides virtually no barrier resistance to oxygen causing the juice to lose vitamin C in large amounts. One other conventional structure adds two additional layers to the structure identified above, namely a foil layer and an additional LDPE layer. The expensive foil layer increases barrier resistance to the flow of oxygen, while the additional LDPE allows for ultimate heat-sealability of the laminate. The improved conventional structure has poor barrier properties relating to the absorption of essential oils and aromas, since the interior contacting layer is still a thick layer of LDPE. The object of the present invention is to produce an improved juice packaging heat-sealable juice carton which does not transmit flavor/odor ingredients of citrus and other juices and exhibits an improved cost-to-performance ratio relative to foil-lined cartons. According to the present invention this object is attained with a container for liquids containing essential oils and/or flavours obtainable by: (a) flame treating a paperboard substrate on both sides; (b) placing on one side of the thus treated paperboard substrate a layer of molten LDPE by extrusion coating; (c) extruding or coextruding onto the uncoated side of the paperboard substrate a sandwich layer of EVOH surrounded by tie layers, or one tie layer and EVOH, or EVOH alone, and corona discharge treating or flame treating the newly placed layer; (d) extruding onto the tie layer-EVOH-tie layer sandwich layer, or the tie layer-EVOH layer, or the EVOH layer thus treated a very thin layer of LDPE; and (e) heat sealing the thus obtained laminate from front to back (LDPE to LDPE) at conventional temperatures of 122°C to 260°C (250°F to 500°F). Further, the present invention provides a process for forming a container according to claim 1 which comprises the steps of: (a) flame treating a paperboard substrate on both sides; (b) placing on one side of the thus treated paperboard substrate a layer of molten LDPE by extrusion coating; (c) extruding or coextruding onto the uncoated side of the paperboard substrate a sandwich layer of EVOH surrounded by tie layers, or one tie layer and EVOH, or EVOH alone, and corona discharge treating or flame treating the newly placed layer; (d) extruding onto the tie layer-EVOH-tie layer sandwich layer, or the tie layer-EVOH layer, or the EVOH layer thus treated a very thin layer of LDPE; and (e) heat sealing the thus obtained laminate from front to back (LDPE to LDPE) at conventional temperatures of 122 to 260°C (250°F to 500°F). Preferred embodiments are set forth in the dependent claims. The container of the present invention reveals an improved non-foil composite structure providing a substantial barrier to the loss of vitamin C and an almost complete barrier to the loss of essential flavor oils over the shelf life period of the carton (six weeks) and far beyond the six week period as well. A preferred embodiment comprises from the outer atmosphere exposed surface to the inner surface contacting the essential oils and/or flavors (liquid juice): a first exterior layer of a low density polyethylene polymer; a paperboard substrate; an interior laminate coating comprising a Plexar® tie layer, an ethylene vinyl alcohol copolymer (EVOH) layer, and another Plexar® tie layer and a second layer of a low density polyethylene polymer coated onto the laminate coating layer of Plexar® /EVOH/ Plexar® in contact with the juice rendering the laminate heat-sealable. A second embodiment of the present invention comprises from the outer atmosphere exposed surface to the inner surface contacting the essential oils and/or flavors (liquid juice); a thin layer of a low density polyethylene polymer, a paperboard substrate, a tie layer of Plexar® or ethylene acrylic acid, an interior layer of an ethylene vinyl alcohol copolymer (EVOH) and a chin layer of a low density polyethylene polymer coated onto the interior layer of EVOH, in direct contact with the juice, rendering the laminate heat-sealable. A third embodiment of the present invention comprises a thin layer of a low density polyethylene polymer, a paperboard substrate, an interior layer of an ethylene vinyl alcohol copolymer (EVOH) and a thin layer of a low density polyethylene polymer coated onto the interior layer of EVOH, in direct contact with the liquid, rendering the laminate heat-sealable. The containers of the present invention enable significant flavor oil retention of the citrus juice contained, and also significant prevention of loss of vitamin C, resulting in a substantial extension of the shelf life thereof and permits replacement of the costly aluminum foil barrier. The preferred ethylene vinyl alcohol copolymer is sold under the product name EVAL EP® resins and is available from EVAL Company of America. The preferred tie layer is a Plexar 177® and is available from USI Corporation. The present invention has produced a suitable container which has excellent barrier properties utilizing a laminate which can be heat-sealed with its exterior and interior layers being a non-polar constituent (LDPE) and a like non-polar constituent (LDPE) from front to back. The liquid juice components are insoluble in the polar EVOH material, preventing flavor oil absorption and resulting swelling, stress cracking, plasticization and heat seal degradation as occurs with a thick LDPE as the contact layer. The preferred containers of the present invention not only exhibit significant barrier properties to extend the shelf life of the juice, but the laminates for the containers can be produced using conventional extrusion equipment. The process according to the present invention is preferably carried out as follows: Stepwise, the paperboard is flame treated on both sides. Second, a layer of molten LDPE is then placed onto the paperboard substrate by extrusion coating. Thirdly, the web is turned over and a sandwich layer of EVOH surrounded by Plexar® tie layers, or one Plexar® tie layer and EVOH, or EVOH alone is coextruded onto the uncoated exposed side of the paperboard substrate. This newly placed layer is corona discharge treated or flame treated to facilitate adhesion of a subsequent food contact layer of LDPE. Lastly, a layer of LDPE is extruded onto the interior sandwich layer of Plexar® -EVOH- Plexar®, or Plexar® -EVOH layer or EVOH layer. The completed laminate can now be heat-sealed from front to back (LDPE to LDPE) at conventional temperatures of 122°C to 260°C (250°F to 500°F). The newly formed laminate can then be scored, cut into blanks, folded and side-seam heat-sealed thereon for transport. Once transported, the prepared blanks can be filled onto conventional equipment, such as a PurePak® machine made by Ex-Cell-O. The blanks are formed heat-sealed at the bottom, filled and heat-sealed at the top by the PurePak® machine to complete the filled carton. The barrier laminates produced by the present invention not only exhibit excellent barrier properties and can be easily constructed but also meet FDA approval for use in food packaging. EVAL Company of America's EVAL EP® is FDA approved for direct food contact and the preferred ethylene vinyl alcohol copolymer according to the invention. Other EVOH's which heat seal at low temperatures of 122°C - 260°C (250°F to 500°F) and which can be cut on conventional machinery could also be used as the barrier material. Thus, until the advent of the present invention few suitable containers for the containment of citrus juices have been developed which retain the advantages of using paperboard as the base material as well as have a relatively inexpensive barrier layer (EVOH) which can be fabricated using conventional extrusion coating equipment. The present containers make use of heat-seals for seaming and closing, for example, cartons, folding square or rectangular containers or boxes, and/or even fabricating cylindrical tubes. The packaging material is printed, converted into flat blanks, side seamed, and then formed, filled, and sealed using conventional carton filling machines. Specifically, the preferred embodiment of the new packaging material, as used to produce (280 g , 0.94 l , 1.89 l , 0.31 l (10-ounce, quart, half-gallon and three-quart) PurePak® cartons, comprises an exterior coating of 5.4 kg (12 lbs) LDPE, paperboards of varying thickness (depending on carton size), a coextruded sandwich layer of 1.665 kg (4.5 lbs ) of an adhesive tie material Plexar 177® , 1.48 kg (4.0 lbs ) EVOH EVAL® , 1.665 kg (4.5 lbs ) of a tie layer material Plexar 177 , and a product contact coating layer of 3.7 kg (10 lbs ) LDPE. The second embodiment of the present invention comprises an exterior coating of 0.020 mm (0.8 mil) LDPE, paperboards of varying thickness (depending on carton size), 0.012 mm to 0.020 mm (0.5-0.8 mil) adhesive tie layer, 0.005 mm to 0.018 mm (0.2 to 0.7 mil) EVOH, and 0.018 mm (0.7 mil) LDPE (product-contact). The third embodiment of the present invention comprises an exterior coating of 0.020 mm (0.8 mil) LDPE, paperboards of varying thickness (depending on carton size), 0.005 to 0.018 mm (0.2 to 0.7 mil) EVOH, and 0.018 mm (0.7 mil) LDPE (product-contact). Prior cartons containing aluminum foil are often expensive relative to the performance problems they present when being form-fill-sealed by the juice packager. Also, the usual thick 8.1 kg (22 lb) or 0.037 mm LDPE (1.5 mil) product-contact layer generally required in such cartons absorbs citrus flavor/aroma oils, with subsequent deleterious effects on product quality. The present invention makes use of a relatively inexpensive layer of EVOH, reducing loss of essential oils and vitamin C, while functioning as an excellent barrier. Provided is a very thin 0.018 mm (0.7 mil) product-contact layer of LDPE thereby reducing juice absorption in the product-contact layer and resultant degradation of the contact layer. FIG. 1 is a cross-sectional elevation of an existing commercial structure of a laminate; FIG. 2 is a cross-sectional elevation of an existing commercial structure of a laminate; FIG. 3 is a cross-sectional elevation of an existing commercial structure of a laminate; FIG. 4 is a cross-sectional elevation of an existing commercial structure of a laminate; FIG. 5 is a cross-sectional elevation of the preferred embodiment of the laminate of the present invention; FIG. 6 is a cross-sectional elevation of an alternate embodiment of the laminate of the present invention; FIG. 7 is a cross-sectional elevation of an alternate embodiment of the laminate of the present invention; FIG. 8 is a block diagram representing the process for making the preferred embodiment of the laminate of the present invention; FIG. 9 is a block diagram representing the process for making the alternate embodiment of the laminate of the present invention; and FIG. 10 is a block diagram representing the process for making the alternate embodiment of the laminate of the present invention. The existing commercial structure for a paperboard carton for juice and similar products has made use of an easily heat-sealed barrier laminate composed of paperboard 4 (FIG. 1) sandwiched between two thick layers of low density polyethylene (LDPE) 2,6 .037 mm (1.5 mil). The LDPE is an inexpensive heat-sealable material which acts to a limited extent as a moisture barrier to prevent loss of essential oils (flavor) and aroma. The problem encountered with the conventional laminate structure has been that the essential oils of the juice (namely - d-Limonene) have, after short periods of time, been absorbed into the thick 0.037 mm (1.5 mil) LDPE layer causing heat seal decay, stress cracking, and swelling while stripping the juice of essential oils. Additionally, the conventional structure (FIG. 1) provides virtually no barrier resistance to oxygen which causes the juice to lose vitamin C in great quantities after a relatively short period of time. To illustrate, the conventional paperboard 1.89 l (1/2 gallon) juice carton will lose 60.5% of its essential oil (d-Limonene) and 84% of its vitamin C content in a storage period of six weeks (SEE TABLE 1). One conventional existing paperboard carton (FIG. 2) utilizes two extra layers in addition to the layers disclosed in FIG. 1 to add greater barrier resistance to the passage of oxygen and resultant loss of vitamin C. Expensive aluminum foil 14 has been added to the laminate structure to increase the barrier's resistance to the flow of oxygen. An additional thick layer of LDPE 16 is needed to allow the laminate to be heat-sealed from front to back with the exterior LDPE 8 layer. The structure of the barrier laminate (FIG. 2) has poor barrier properties relating to the absorption of essential oils and aromas, since the heat-sealable contacting layer is a thick layer of low density polyethylene. The shelf storage life of the juice carton made up of the barrier laminate of FIG. 2 still exhibits a percentage loss of essential oils (d-Limonene) of 35.5%, while greatly improving its barrier properties with respect to the percentage loss of vitamin C, 24% (See Table 1). The addition of the foil layer allows the laminate to exhibit excellent O₂ barrier properties. Although the use of a foil layer is extremely beneficial, the enormous increased expense makes the use of foil economically less desirable. FIGS. 3 and 4 disclose structures or barrier laminates described in US-A- 4,513,036. FIG. 3 discloses a barrier laminate comprising a sandwich of LDPE 18-paperboard 20-High Density Polyethylene (HDPE) 22-LDPE 24. The laminate disclosed exhibits large losses of essential oils during its shelf life of six weeks, namely 60.5%, while also exhibiting large losses of vitamin C during the six week period, namely 87% (see Table 1). The economics and ease of fabrication of the laminates of FIG. 3 are outweighed by the poor barrier properties exhibited. FIG. 4 discloses the preferred embodiment of US-A- 4,513,036, namely a barrier laminate comprising LDPE 26-Paperboard 28-Polypropylene 30-LDPE 32. The additional polypropylene layer 30 adds to the barrier properties at relatively low additional costs. The barrier properties still are extremely deficient in resistance to the passage of oxygen and loss of vitamin C, namely 71% after six weeks. The polypropylene laminate structure loses 39.5% of its essential oils (d-Limonene) after six weeks (see Table 1). Both embodiments disclosed in the patent cited above do not adequately preserve the flavor/aroma and vitamin C content of the juice. The structure of the existing commercial constructions have all faced the same problem due to the necessity for heat sealing the seams and closures while forming the carton blank and while filling the cartons with, e.g., juice. The necessity of forming a heat seal from the front to the back of the laminate has resulted in the use of a thick exterior layer of LDPE and a thick interior layer of LDPE, both non-polar compounds which exhibit excellent heat-sealing characteristics to one another (see FIGS. 1-4). Referring to FIG. 5, the preferred embodiment of the laminate according to the present invention is shown as comprising a paperboard substrate 36 of varying thickness which is most suitably high-grade paperboard stock, for example, 128 kg (282 lb.) Milk Carton Board, to which is applied on one side a coating of low density polyethylene (LDPE) 34, in a coating weight ranging from about 4 to about 6.7 kg (about 9 to about 15 pounds) per ream. Any commercial extrusion coating grade LDPE is suitable for use herein. On the back or interior portion of the laminate, namely onto the paperboard layer 36, is coextruded a sandwich 44 of a 2.03 kg (4.5 lb.) tie material (Plexar 177® , 1.8 kg (38/4.0 lb.) EVAL® , 2.03 kg (40/4.5 lb.) tie material (Plexar 177® 42. The EVOH being a barrier layer composed of EVAL Company of America's EVAL EP® resins. Extruded thereon is a coating of 4.5 kg (10 lbs.) LDPE 46. Referring to FIG. 6, the alternate embodiment of the laminate according to the present invention is shown as comprising a paperboard substrate 54 of varying thickness which is suitably high grade paperboard stock, i.e., 128 kg (282 lb.) milk carton board, to which is applied on one side a very thin 0.020 mm (0.8 mil) coating of low density polyethylene (LDPE) 52, in a coating weight range averaging 5.4 kg (12 lbs.) per 276 m² (3000 square feet). Any commercial extrusion coating grade LDPE is suitable for use herein. On the back or interior portion of the laminate, namely onto the paperboard layer 54, a Plexar 177® tie layer 56 and a layer of 0.005 mm (0.2 mil) to 0.018 mm (0.7 mil) of EVOH 58 are applied by coextrusion. The EVOH being a barrier layer composed of EVAL Company of America's EVAL EP® resins. Extrusion coated thereon is a very thin 0.018 mm (0.7 mil) layer 62 of a non-polar LDPE. Referring to FIG. 7, a third embodiment of the laminate according to the present invention is shown as comprising a paperboard substrate 66 of varying thickness which is suitably high grade paperboard stock, i.e. 282 lb. milk carton board, to which is applied on one side a very thin 0.020 mm (0.8 mil) coating of LDPE 64, a 0.0050 mm to 0.018 mm (0.2 to 0.7 mil) layer of EVOH 68 is applied by extrusion coating. Extrusion coated thereon is a thin layer 70 of a non-polar LDPE. Referring now to FIG. 8, wherein a block diagram discloses the method of forming the heat-sealable barrier laminate of FIG. 5. The laminate can be easily fabricated. In Step A, the paperboard is flame treated two sides. Step B, a molten layer of the LDPE 34 is extrusion coated onto the paperboard substrate 36. Step C, the LDPE layer 34 is corona discharge or flame treated in preparation for subsequent printing. Step D, the web is turned over to facilitate Step E, which has a sandwich layer 44 of Plexar® 38/ EVAL® 40/ Plexar® 42 coextruded onto the paperboard substrate 36. In Step F, extrusion coating of a layer of LDPE 46 onto the sandwich layer 44 completes the laminate. Referring now to FIG. 9, wherein a block diagram discloses the method of forming the heat sealable barrier laminate of FIG. 6. In Step A, the paperboard is flame treated on two sides. Step B, a molten layer of LDPE 52 is extrusion coated onto the paperboard substrate 54. Step C, the LDPE layer 52 is corona discharge or flame treated to provide subsequent inner layer adhesion. Step D, the web is turned over to facilitate Step E, which has a layer of molten tie layer 56 and EVOH 58 coextruded onto the paperboard substrate 54. Step F, the tie/EVOH layer 60 has its surface corona discharge treated or flame treated to facilitate the adhesion of a subsequent interior product-contact thin LDPE coating 62 to complete the laminate. Referring now to FIG. 10, wherein a block diagram discloses the method of forming the heat-sealable barrier laminate of FIG. 7. In Step A, the paperboard 66 is flame treated on two sides. Step B, a molten layer of LDPE 64 is extrusion coated onto the paperboard substrate 66. Step C, the LDPE layer 64 is corona discharge or flame treated to provide subsequent inner layer adhesion. Step D, the web is turned over to facilitate Step E, which has a layer of molten EVOH 68 extrusion coated onto the paperboard substrate 66. Step F, EVOH layer 68 is corona discharge treated or flame treated to facilitate the adhesion of a subsequent interior product-contact thin LDPE coating to complete the laminate. The unique barrier effect provided by the carton of the present invention to the % loss of essential oils and to the % loss of vitamin C is clearly demonstrated by the following example outlined in Table 1. Standard 1.89 l (1/2 gallon) juice containers were prepared and filled with juice. A typical essential oil in the juice was d-Limonene. The filled cartons were stored for a test period of six weeks after which the juice was analyzed to determine the percentage loss by weight of the essential oil d-Limonene and the percentage loss by weight of vitamin C. All weights in kg (lbs.) are given in kgs. (lbs.) per 276 m² (3000 square feet). Test Sample,1.89 (½ Gallon) Juice Container % Loss of Essential Oil % Loss of Vitamin C LDPE/BOARD/LDPE (FIG. 1) 60.5 84 LDPE/BOARD/LDPE/FOIL/LDPE (FIG. 2) 35.5 24 LDPE/BOARD/HDPE/LDPE (FIG. 3) 60.5 87 LDPE/BOARD/POLYPROPYLENE/LDPE (FIG. 4) 39.5 71 LDPE/BOARD/PLEXAR-EVOH-PLEXAR/LDPE (FIG. 5) 16.5 46 It can be clearly seen that the container prepared according to the present invention provides an almost complete barrier to the loss of essential oils far greater than has been present in existing structures. Additionally, the oxygen passage or percentage loss of vitamin C has been greatly reduced over all prior laminates not containing aluminum foil. The effectiveness of the container of the present invention as a barrier to migration of essential oils and flavors, as well as a barrier to a loss of vitamin C permits a significant extension of shelf life thereof.

Claims: A container for liquids containing essential oils and/or flavours obtainable by : (a) flame treating a paperboard substrate on both sides; (b) placing on one side of the thus treated paperboard substrate a layer of molten LDPE by extrusion coating; (c) extruding or coextruding onto the uncoated side of the paperboard substrate a sandwich layer of EVOH surrounded by tie layers, or one tie layer and EVOH, or EVOH alone, and corona discharge treating or flame treating the newly placed layer; (d) extruding onto the tie layer-EVOH-tie layer sandwich layer, or the tie layer-EVOH layer, or the EVOH layer thus treated a very thin layer of LDPE; and (e) heat sealing the thus obtained laminate from front to back (LDPE to LDPE) at conventional temperatures of 122°C to 260°C (250°F to 500°F). The container according to claim 1 wherein the layer of molten LDPE has a thickness of 0.020 mm (0.8 mil), one tie layer and EVOH are coextruded onto said uncoated side of the paperboard substrate, the thickness of the EVOH being 0.005 to 0.018 mm (0.2 to 0.7 mil), and the very thin layer of LDPE has a thickness of 0.018 mm (0.7 mil). The container according to claim 2 wherein the layer of molten LDPE is corona discharge treated to enhance the printability of the laminate. The container according to claim 2 wherein the layer of molten LDPE is flame treated to enhance the printability of said laminate. The container according to claim 2 wherein the tie layer is a layer of ethylene acrylic acid. The container according to claim 5 wherein the layer of molten LDPE is corona discharge treated to enhance the printability of said laminate. The container according to claim 5 wherein the layer of molten LDPE is flame treated to enhance the printability of said laminate. The container according to claim 1 wherein the layer of molten LDPE is a 5.4 kg (12 lb) layer, a tie layer-EVOH-tie layer sandwich layer is coextruded onto the uncoated side of the paperboard substrate, each of the tie layers being a 1.665 kg (4.5 lb) layer and the EVOH layer being a 1.48 kg (4.0 lb) layer, and the very thin layer of LDPE is 3.7 kg (10 lb) layer. The container according to claim 8 wherein the layer of molten LDPE is corona discharge treated to enhance the printability of the laminate. The container according to claim 8 wherein the layer of molten LDPE is flame treated to enhace the printability of the laminate. The container according to claim 8 wherein said tie layers are Plexar® type tie materials. A process for forming a container according to claim 1 which comprises the steps of: (a) flame treating a paperboard substrate on both sides; (b) placing on one side of the thus treated paperboard substrate a layer of molten LDPE by extrusion coating; (c) extruding or coextruding onto the uncoated side of the paperboard substrate a sandwich layer of EVOH surrounded by tie layers, or one tie layer and EVOH, or EVOH alone, and corona discharge treating or flame treating the newly placed layer; (d) extruding onto the tie layer-EVOH-tie layer sandwich layer, or the tie layer-EVOH layer, or the EVOH layer thus treated a very thin layer of LDPE; and (e) heat sealing the thus obtained laminate from front to back (LDPE to LDPE) at conventional temperatures of 122 to 260°C (250°F to 500°F). The process according to claim 12 wherein the layer of molten LDPE is a 5.4 kg (12 lb) layer which is subjected to corona discharge treatment or flame treatment, a tie layer-EVOH-tie layer sandwich layer is coextruded onto the uncoated side of the paperboard substrate, each of the tie layers being a 1.665 kg (4.5 lb) layer and the EVOH layer being a 1.48 kg (4.0 lb) layer, and the very thin layer of LDPE is a 3.7 kg (10 lb) layer. The process according to claim 12 wherein the layer of molten LDPE is extruded with a thickness of 0.020 mm (0.8 mil) and subjected to corona discharge treatment, a tie layer and a EVOH layer are coextruded onto the uncoated side of the paperboard substrate, the EVOH layer having a thickness of 0.005 to 0.018 mm (0.2 to 0.7 mil) and being subjected to corona discharge treatment, and the very thin layer of LDPE is extruded with a thickness of 0.018 mm (0.7 mil). The process according to claim 12 wherein the layer of molten LDPE is extruded with a thickness of 0.020 mm (0.8 mil) and subjected to flame treatment, a tie layer and a EVOH layer are coextruded onto the uncoated side of the paperboard substrate, the EVOH layer having a thickness of 0.005 to 0.018 mm (0.2 to 0.7 mil) and being subjected to flame treatment, and the very thin layer of LDPE is extruded with a thickness of 0.018 mm (0.7 mil). The process according to claim 12 wherein the layer of molten LDPE is extruded with a thickness of 0.020 mm (0.8 mil) and corona discharge treated, an EVOH layer is extruded onto the uncoated side of the paperboard substrate with a thickness of 0.005 to 0.018 mm (0.2 to 0.7 mil) and corona discharge treated, and the very thin layer of LDPE is extruded onto the corona discharge treated EVOH layer with a thickness of 0.018 mm (0.7 mil). The process according to claim 12 wherein the layer of molten LDPE is extruded with a thickness of 0.020 mm (0.8 mil) and flame treated, an EVOH layer is extruded onto the uncoated side of the paperboard substrate with a thickness of 0.005 to 0.018 mm (0.2 to 0.7 mil) and flame treated, and the very thin layer of LDPE is extruded onto the flame treated EVOH layer with a thickness of 0.018 mm (0.7 mil).

Inventors: GIBBONS CHARLES E, TANNER CYNTHIA L, WHILLOCK ALLAN A, GIBBONS, CHARLES E., TANNER, CYNTHIA L., WHILLOCK, ALLAN A.
Applicants: INT PAPER CO, INTERNATIONAL PAPER COMPANY
Application year: 1988
Main classification: B32B27
IPC codes: B32B27, B65D65