PLASTIC PACKAGING MATERIAL

Abstract: This invention discloses a method of preserving horticultural products (10) by providing a plastic packaging material (12) having a thickness of up to about 500 microns and a permeability to water vapor exceeding about 1.5g mm/m<-2> per day at 38 degrees C and 85 - 95 % relative humidity, whereby when the material (12) is used to package produce and other horticultural products (10) no condensation appears on a surface of the material.

Description: 1 PLASTIC PACKAGING MATERIAL FIELD OF THE INVENTION The present invention relates to plastic pack¬ aging materials generally and more particularly plastic packaging materials for food and horticultural products such as produce, as well as packaging techniques and packaged products. BACKGROUND OF THE INVENTION A great variety of plastic packaging materials is known in the patent literature. The following patents and published patent applications are thought to be representative of the state of the art, particularly in the field of nylon-6 packaging materials, packaging for produce and control of humidity in packaging: U.S. Patents: 5,037,459; 4,842,741; 3,876,738 Japanese Abstracts: 05-329,947; 06-071,766; 05-316,943; 01-148,144; 57-167,331; 01-167062; 03-059,196; 06- 062,728; 04-074,529; 01-309,621; 05-230,235 European Patents: 358,038; 566,097 WO Published PCT Application 8,404,529; 9,302,130 Australian Patent 636,284 SUMMARY OF THE INVENTION The present invention seeks to provide an improved plastic packaging material which has a relative¬ ly high permeability to water vapor. There is thus provided in accordance with a preferred embodiment of the present invention a plastic packaging material having a thickness of up to about 500 microns and a permeability to water vapor exceeding about 1.5g mm m -2 per day at 38 degree C and 85 - 90% relative humidity. The material allows for minimal or no condensa¬ tion on its surface when used to package produce or flowers. There is also provided in accordance with a preferred embodiment of the present invention a packaged produce product including a plastic packaging material having a relatively high permeability to water vapor and providing an atmosphere for the packaged produce which comprises approximately 4 - 12% 0 2 , 2 - 20% C0 2 , and has a relative humidity of 85 - 100%. There is additionally provided in accordance with a preferred embodiment of the present invention a method of preserving food products comprising: providing a plastic packaging material of the type described hereinabove; and at least partially enclosing the food product using the plastic packaging material, thereby to provide an environment for the food product which comprises approximately 4 - 12% 0 2 , 2 - 20% C0 , and has a relative humidity of 85 - 100%. Preferably, the plastic packaging material is based on a polyamide such as nylon-6 or nylon-66. For example, the material may be manufactured from a polymer¬ ic material that comprises a blend of nylon-6 or nylon-66 with other polymeric and/or non-polymeric components. In accordance with a preferred embodiment of the present invention, the raw material may be manipulat¬ ed to increase the 0 2 and C0 2 permeability of the film. For example, blends of nylon-6 and other components may be manufactured into a material having a porous charac¬ ter. Additionally or alternatively, the plastic packaging material may be manipulated after the film is formed. Thus the plastic packaging material may be perforated to have holes of approximately 1 - 10 mm diameter covering up to about 0.5% of the surface area of the material, or the plastic packaging material may be microperforated to have holes of approximately 0.05 - 1 mm diameter in a density of up to about 2000 holes per square meter of the material . Microperforation or perforation may take place either in a continuous or in a batch process. For exam¬ ple, the perforation may be effected by contacting the material with one or more rollers, plates or other de¬ vices studded with appropriately sized and positioned pins or needles. Alternatively, the perforation or micro- perforation may be effected by use of laser technology. Perforation may occur during extrusion of the material downstream of a bubble collapsing frame or m tandem with a subsequent processing step such as printing or package forming. In accordance with a preferred embodiment of the present invention, the raw material may be manipulat¬ ed to tailor its permeability to water vapor. For exam¬ ple, blends of nylon-6 and other raw materials may be processed to produce a film with a lower water vapor permeability than a film processed from nylon-6 alone. Additionally or alternatively, the packaging material may be manipulated by heat treatment or orienta¬ tion processes to reduce its water vapor permeability. In accordance with a preferred embodiment of the present invention, the raw material may be manipulat¬ ed to absorb or degrade ethylene gas. For example, blends of polyamides with other compounds which absorb or de¬ grade ethylene may be employed in the manufacture of the packaging material. BRIEF DESCRIPTION OF THE DRAWINGS The present invention will be understood and appreciated more fully from the following detailed de¬ scription, taken in conjunction with the drawing in which: Fig. 1 is a simplified illustration of produce packaging in accordance with a preferred embodiment of the present invention. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Reference is now made to Fig. 1, which illus¬ trates produce packaging in accordance with a preferred embodiment of the present invention. In the illustrated embodiment, produce 10, such as bean sprouts, is enclosed within a bag 12 preferably composed of nylon-6 or a blend containing nylon-6. Alternatively a package or wrap other than a bag may be provided. The nylon-6 film may be extrusion blown or produced in any other conventional manner from raw materials which are commercially avail¬ able, inter alia, under the trade name Capron 8209 from Allied Signal or under the trade name Ultramid B4 from BASF. In accordance with a preferred embodiment of the present invention the nylon-6 material may be extru¬ sion blended with nylon-6I/6T (for example SELAR PA 3426 commercially available from Dupont) to produce films of 20 and 30 micron thickness. The ratios may be between 80 - 99% nylon-6 and 1 - 20% nylon-6I/6T. The resulting films have reduced water vapor permeability relative to nylon-6 alone and retain the ability to minimize conden¬ sation. Additionally in accordance with a preferred embodiment of the present invention the material may be a blend of nylon-6 and polyolefins and compatibilizers (for example Orgalloy LE 6000, commercially available from Elf Atochem) . Such blends can be employed to produce films having reduced water vapor permeability relative to that of nylon-6 alone and are characterized by minimal mois¬ ture condensation on the film surface when used to pack¬ age produce or other horticultural products. Further in accordance with a preferred embodi¬ ment of the present invention the nylon-6 material may be extrusion blended with nylon-11 or nylon-12 to produce films having reduced water vapor permeability relative to that of nylon-6 alone and are characterized by minimal moisture condensation on the film surface when used to package produce or other horticultural products. Additionally in accordance with a preferred embodiment of the present invention the polyamide materi¬ al may be extrusion blended with porous additives, such as silica or diatomaceous earth to produce films having reduced water vapor permeability relative to that of polyamide alone and are characterized by ethylene sorp- tion and by minimal moisture condensation on the film surface when used to package produce or other horticul¬ tural products. The ratios may be between 88 - 99% polya¬ mide and 0.5 - 12% porous additive. Additionally in accordance with a preferred embodiment of the present invention, the films may be oriented during manufacture or in a subsequent processing step to provide films having reduced water vapor perme¬ ability relative to unoriented films produced of the same raw materials. The oriented material is characterized by minimal moisture condensation on the material surface when used to package produce or other horticultural products. Further in accordance with a preferred embodi¬ ment of the invention, films of polyamide with or without the above described additives and compositions and having thicknesses of 5 - 100 microns may be passed through a heating tunnel to heat the film to temperatures of 100 200 degrees centigrade to provide films having reduced water permeability relative to polyamide that is not heat-treated and are characterized by minimal moisture condensation on the film surface when used to package produce or other horticultural products. Additionally in accordance with a preferred embodiment of the present invention a polyamide material may be extrusion blended with soluble starch or salt additives and then passed through a water bath at 4 - 100 degree C to extract the soluble additive in order to produce films having increased 0 2 and C0 2 permeability relative to the base polyamide alone. The ratios may be between 88 - 99% polyamide and 1 - 12% soluble starch or salt additive. The bath water preferably is circulated, filtered and reintroduced to the bath on a continuous basis. Excess water is preferably removed from the film by passing it through a heating tunnel as described in the preceding paragraph. Trays, baskets, containers, holders, bags, films or any other packaging material formed from films having a thickness generally m excess of 100 micron of nylon-6 or any other suitable polymer having water per e- ability exceeding 1.5 g mm per day at 38 degrees C with or without the additives or compositions described above may be provided by extrusion or any other suitable manufacturing process. Film and sheets manufactured from any of the materials listed above and/or by any of the techniques listed above may be unperforated, or they may be perfo¬ rated or microperforated to increase the permeability of the film to 0 2 and C0 2 . For the purposes of the specification and claims, perforation refers to holes of approximately 1 10 mm diameter covering up to about 0.5% of the surface area of the material. For the purposes of the specification and claims, microperforation refers to holes of approximately 0.05 - 1 mm diameter in a density of up to about 2000 holes per square meter of the material. Reference is now made to the following exam¬ ples which provide an indication of the scope of the present invention. EXAMPLE I Nylon-6 extrusion blown film having a thickness of 40 microns was employed to package bean sprouts, mushroom, tarragon, chive and chickory lettuce. After 8 days of storage at 4 degrees C and a relative humidity of 90 - 97%, the sprouts were inspected and their weight loss was measured and compared with a control package of sprouts which had been stored under identical conditions in PVC film packaging. The weight loss of the nylon-6 packaged sprouts was found to be less than of the control packaged sprouts. The nylon-6 packaged sprouts had a white color and were crisp, while the PVC packaged sprouts were brown and were not crisp. The mushrooms were white and fresh after 18 days of storage in nylon-6 packaging. Visual observations of the tarragon, chive and chickory lettuce indicated that they stayed fresher longer in the nylon-6 packaging as compared to polyethylene packaging. EXAMPLE II Nylon-6 extrusion blown film having a thickness of 20 microns and perforations 6 - 8 mm in diameter was used to package grapes. After 12 days of storage at 0 degrees C and 7 days storage at 20 degrees C, the condi¬ tion of the grapes was compared with control packages packaged in both perforated and non-perforated polyethyl¬ ene. The grapes packaged in nylon-6 showed a higher percentage of healthy clusters and lower levels of decay than the control packages. EXAMPLE III Nylon-6 extrusion blown film having a thickness of 20 microns and microperforations 0.8 mm in diameter was used to package snap beans (green beans) . After 5 days of storage at 5 degrees C and 3 days storage at 20 degrees C, the condition of the beans was compared with control packages packaged in micro-perforated polyethyl¬ ene. The beans packaged in nylon-6 showed less weight loss, less rusty spots and substantially no mold growth as compared with the control packages. EXAMPLE IV Nylon-6 extrusion blown film having a thickness of 20 microns in both perforated and microperforated forms was used to package cucumbers. After 6 days of storage at 8 degrees C and 3 days storage at 20 degrees C, the condition of the cucumbers was evaluated and was found to be very good. The cucumbers packed in microper- forated packages showed no chilling injury, while those in perforated packages showed very low chilling injury. EXAMPLE V A blend of 20% nylon 6I/6T and 80% nylon-6 was extrusion blown into a film 20 microns thick, microperfo- rated, and used to package cherry tomatoes. After a number of days, there was no condensation in the packages and the tomato quality was better than that of tomatoes packaged in alternative materials. EXAMPLE VI A blend of 10% nylon 6I/6T and 90% nylon-6 was extrusion blown into a film 30 microns thick, perforated, and used to package lettuce. EXAMPLE VII 25 micron thick nylon-6 film, manufactured by a chill-roll cast process and then biaxially oriented by means of tenter frame orientation equipment was used to wrap cut flowers. EXAMPLE VIII 30 micron thick nylon-66 film, manufactured by an extrusion blown film process, was perforated and then passed through a heating tunnel at 200 degrees C and was used to package carrots. EXAMPLE IX 15 micron thick nylon-12 film, manufactured by extrusion in a chill-roll cast process and microperforat¬ ed was used to package berries. EXAMPLE X A copolymer of nylon-6 and nylon-66 is extruded into a film 20 microns thick via a blown film double- bubble process that imparts a high degree of orientation to the film. The film is then microperforated and used to package lettuce. EXAMPLE XI A blend of nylon 610 and 8% soluble starch is extruded into a 30 micron thick film by a water quench cast film process. The soluble starch is extracted during the water quenching stage, leaving a porous film which is then passed through a heating tunnel and ultimately used to package green and red peppers. EXAMPLE XII A blend of 95% nylon-1 and 5% nylon 6I/6T is extruded in a chill-roll cast process to produce a sheet 150 microns thick. This material is then perforated and thermoformed into trays to package corn. It will be appreciated by persons skilled in the art that the present invention is not limited by what has been particularly shown and described hereinabove. Rather the scope of the invention is defined only by the claims which follow:

Claims: C L A I M S 1. A plastic packaging material having a thickness of up to about 500 microns and a permeability to water vapor exceeding about 1.5g mm m -2 per day at 38 degree C and 85 - 90% relative humidity, whereby when the material is used to package produce and other horticultural products no condensation or minimal condensation appears on a surface of the material. 2. A packaging material according to claim 1 and wherein the plastic packaging material is based on a polyamide formulation. 3. A packaging material according to claim 1 or claim 2 and wherein the plastic packaging material is perforated to have holes of approximately 1 - 10 mm diameter covering up to about 0.5% of the surface area of the material. 4. A packaging material according to any of the preceding claims and wherein said plastic packaging material is microperforated to have holes of approximate¬ ly 0.05 - 1 mm diameter in a density of up to about 2000 holes per square meter of the material. 5. A packaged produce product including a plastic packaging material having a relatively high permeability to water vapor, and that allows the package produce to be contained m an atmosphere which comprises approximately 4 - 12% 0 2 , 2 - 20% C0 2 , and has a relative humidity of 85 - 100%, whereby no condensation or minimal condensa¬ tion appears on a surface of the material. 6. A packaged product according to claim 5 and wherein the plastic packaging material is based on a polyamide formulation. 7. A packaged product according to claim 5 or claim 6 and wherein the plastic packaging material is perforated to have holes of approximately 1 - 10 mm diameter covering up to about 0.5% of the surface area of the material. 8. A packaged product according to any of the preceding claims 5 - 7 and wherein said plastic packaging material is microperforated to have holes of approximate¬ ly 0.05 - 1 mm diameter in a density of up to about 2000 holes per square meter of the material. 9. A packaged product according to any of claims 5 8 and wherein said product comprises horticultural products . 10. A method of preserving horticultural products comprising: providing a plastic packaging material of the type described hereinabove; and at least partially enclosing the horticultural product using the plastic packaging material, thereby to provide an environment for the horticultural product which comprises approximately 4 - 12% 0 2 , 2 - 20% C0 , and has a relative humidity of 85 - 100%. 11. A method according to claim 10 and wherein the plastic packaging material is based on a polyamide formulation. 12. A method according to claim 10 or claim 11 and wherein the plastic packaging material is perforated to have holes of approximately 1 - 10 mm diameter covering up to about 0.5% of the surface area of the material. 13. A method according to any of the preceding claims 10 - 12 and wherein said plastic packaging materi¬ al is microperforated to have holes of approximately 0.05 1 mm diameter in a density of up to about 2000 holes per square meter of the material. 14. A method according to any of claims 10 - 13 and wherein said product comprises horticultural products. 15. A method according to claim 12 or claim 13 and wherein the perforation takes place in a continuous process. 16. A method according to claim 12 or claim 13 and wherein the perforation takes place in a batch process. 17. A method according to any of claims 12, 13, 15 and 16 and wherein perforation occurs during extrusion of the material. 18. A method according to any of claims 12, 13, 15 and 16 and wherein perforation occurs during a subsequent processing step.

Inventors: AHARONI NEHEMIA, MARX NIR MOIRA, NEHORAY NERY, AHARONI, NEHEMIA, MARX NIR, MOIRA, NEHORAY, NERY
Applicants: AHARONI NEHEMIA, BEN TZUR ISRAEL, ISRAEL STATE, MARX NIR MOIRA, NEHORAY NERY, STEPAC L A THE STERILIZING PAC, AHARONI, NEHEMIA, BEN-TZUR, ISRAEL, MARX NIR, MOIRA, NEHORAY, NERY, STATE OF ISRAEL - MINISTRY OF AGRICULTURE, STEPAC L.A., THE STERILIZING PACKAGING COMPANY OF
Application year: 1996
Main classification: B65D85
IPC codes: A22C13, A23L3, B65D81, B65D85