PROCESS FOR OBTAINING A METAL-FREE COEXTRUDED BI-ORIENTED OF 7 LAYERS FILM FOR PACKAGING BY TRIPLE-BUBBLE PROCESS USED FOR STERILIZATION PROCESSES UP TO 135°C

Abstract

The invention provides a process of obtaining a bi-oriented co-extruded film of 7 layers by triple bubble process for autoclave sterilization processes, which unlike the current existing materials for food sterilization, the invention does not require an individual manufacturing process of each sheet and subsequent lamination, but it is manufactured in a single step, in addition no metal compound is included in its composition, and provides a shelf life of more than a year in food products that are packaged in the process of sterilization (retort) inside the film.

Claims

1. A process of obtaining a metal-free 7-layer co-extruded bi-oriented film for packaging by triple bubble process, the process comprising the steps of: a) co-extruding at a temperature between 5-15° C. a tubular strip of 7 layers with a tubular central head, in a first bubble, where said tubular strip has a dimension of 20 to 350 mm to obtain a co-extruded tubular strip; b) cooling the co-extruded tubular strip in stage a) by immersing it in water until the strip reaches between 5° and 12° C., to obtain an amorphous multilayer strip; c) heating the amorphous tubular multilayer strip obtained in stage b) to a temperature of 70 to 75° C.; d) biaxially orienting the tubular multilayer strip heated in stage c) in a second expansion bubble at a temperature of 68 to 75° C. to obtain an amorphous bi-oriented primary film; and e) heating the amorphous bi-oriented primary film obtained in stage d) until reaching 140 to 150° C. to stabilize it and eliminate thermal shrinkage and possible elongation to obtain a metal-free film for packaging.

2. The process in accordance with claim 1, wherein in step a) the 7 layers are individually extruded by extruders that feed each of the materials, where these materials comprise three layers of 30 to 40% polypropylene (1)(2)(3), a first layer of 5 to 7% of adhesives and additives (4), a first layer of 20 to 25% of polyamide (5), a layer of 8 to 10% of ethylene-vinyl-alcohol (6) and a second layer of 20 to 25% polyamide (7).

3. The process in accordance with claim 2, wherein the adhesive has a flux index of between 2.0 and 4.0 and is chosen from the group that includes those obtained from n-butane.

4. The process in accordance with claim 2, wherein the adhesive is selected from: maleic anhydride; or polypropylene with density between 0.8 to 0.95 g/cm.sup.3 and specific gravity up to 1.05 g/cm.sup.3 as a vehicle, said additive is chosen from the group comprising of cristobalites.

5. (canceled)

6. The process in accordance with claim 4, wherein the additive comprises 1 to 3% Cristobalite Flux.

7. The process in accordance with claim 1, wherein in step e) the film is tubular.

8. The process in accordance with claim 1, wherein steps c) and d) are optional.

9. A metal-free 7-layer co-extruded bi-oriented film for packaging comprising: 40 to 50% polyamide, 30 to 40% polypropylene, 8 to 10% ethylene-vinyl-alcohol (EVOH), and 5% to 7% of at least one adhesive and at least one additive.

10. The metal-free 7-layer co-extruded bi-oriented film for packaging; according to claim 9, wherein the adhesive is chosen from; adhesives having the group that has a flux index of between 2.0 and 4.0; the adhesive is obtained from n-butane; 1 to 3% maleic anhydride; or the group of cristobalites.

11. (canceled)

12. (canceled)

13. The metal-free 7-layer co-extruded bi-oriented film for packaging, according to claim 9, wherein the additive has polypropylene with a density of between 0.8 to 0.95 g/cm.sup.3 and specific gravity up to 1.05 g/cm3 as a vehicle.

14. (canceled)

15. The metal-free 7-layer co-extruded bi-oriented film for packaging, according to claim 10, wherein the adhesive comprises 1 to 3% of cristobalite flux.

16. The metal-free 7-layer co-extruded bi-oriented film for packaging according to claim 9, wherein the film has a thermal resistance of up to 135° C.

17. The metal-free 7-layer co-extruded bi-oriented film for packaging according to claim 16, wherein the film has a thermal resistance of 121° C.

18. A metal-free 7-layer co-extruded bi-oriented film for packaging according to claim 9, wherein the film has a caliber of 3 to 7 thousandths of an inch.

19. Metal-free 7-layer co-extruded bi-oriented film for packaging according to claim 9, wherein the film has an oxygen permeability of less than 0.05 cm.sup.3/m.sup.2 per day.

20. The metal-free 7-layer co-extruded bi-oriented film for packaging according to claim 9, wherein the film has a water vapor transmission of 0.930946 g/m.sup.2.Math.day.

21. The metal-free 7-layer co-extruded bi-oriented film for packaging according to claim 9, wherein the film has a water vapor transmission of 0.060065 g/100 in.sup.2.Math.day.

22. The metal-free 7-layer co-extruded bi-oriented film for packaging; according to claim 9, wherein the film has a shelf life greater than or equal to one year to the food that is packed within said film by the retort process.

23. The metal-free 7-layer co-extruded bi-oriented film for packaging: according to claim 9, wherein the film has a seal force of 16 to 22 lb/in.sup.2.

24. The metal-free 7-layer co-extruded bi-oriented film for packaging according to claim 9, wherein the film is a food packaging film use for sterilization processes.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0020] FIG. 1 shows a top view where the flow of the materials is detailed, the heads of the extruders are observed until the exit in the winder.

[0021] FIG. 2 shows a schematic side view of one of the preferred modalities of the invention, balloon co-extrusion, where the workstations are reduced, and where the location of the feeding hoppers is shown (17).

[0022] FIG. 3 shows a front view of the co-extrusion dice, where it is observed how the resins of each extruder are fed and joined at the bottom, which is the outlet opening; where PP: Polypropylene, PA: Polyamide, ADH: Adhesives and additives and EVOH: Ethylene-Vinyl-Alcohol.

[0023] FIG. 4 shows a side view of a bag formed by the film object of the present invention.

[0024] FIG. 5 shows a schematic view of the distribution of layers of the film object of the present invention.

[0025] FIG. 6 shows the process object of the invention.

[0026] FIG. 7 shows a photograph of an isometric side view of the film object of the invention with food inside (sausages).

[0027] FIG. 8 shows a diagram of the method used for measuring the seal force of the film according to ASTM F88. Where A) is the unsupported technique, B) is supported 90° C. by hand and C) is the technique supported at 180° C., the arrows indicate the fastening element (grip) within each technique.

[0028] FIG. 9 shows a graph with the optimum operating temperature.

DETAILED DESCRIPTION OF THE INVENTION

[0029] The present invention provides a process for obtaining a bi-oriented co-extruded film of 7 layers by triple bubble process for autoclave sterilization processes. Currently, the materials (films) for food sterilization are laminated packaging of different materials, which are extruded individually and in caliber of 3 to 7 thousandths total, using multilayer lamination processes, and therefore more complex processes.

[0030] The present invention does not require the individual manufacturing process of each sheet and subsequent lamination, so the process is shorter and with less risks.

[0031] The risks that are avoided with the process of the present invention are: delamination, use of adhesives, space and time for rest or curing, contamination in all these subprocesses. By having the process in line and obtaining the material in tubular form the inner part is not in direct contact with any material surface where it can be contaminated, unlike what happens in a flat lamination, in addition, it grants shelf lives of at least one year to the food products that are packed inside said film in the process of sterilization (retort), these products include but are not limited to meat foods, vegetables, legumes, among others, so their main application is in food packaging where refrigeration or freezing is not required for preservation.

[0032] In addition, the film object of the present invention, contributes to reduce food waste since it can keep food in appropriate conditions during a long shelf life, and provides a transparent material, without printing, which is ideal for use with label.

[0033] This film allows to have a first layer of contact with food, a second layer of barrier and a third outer layer; where the first layer of contact with food has an excellent sealing strength so that its structure allows the film of the present invention, to form packages or bags (16), as shown in FIG. 4, said packaging (16) comprises a body (14) that in its upper part has an opening or mouth and a seal (15) in its lower part, in addition, this first layer of contact with food is resistant to the thermal process and abrasion, provides flexibility, strength, structure and mechanical resistance; on the other hand, the second layer of barrier allows to extend its utility life, and its third outer layer provides high mechanical resistance, strength and shine and is resistant to high temperatures.

[0034] Therefore, the present invention provides a film with a wall thickness of 3 to 7 thousandths of an inch, with a very low oxygen permeability, lower than 0.05 cm.sup.3/m.sup.2 per day, and a high thermal resistance of up to 135° C., preferably 121° C. for cooking and sterilization processes in autoclave.

[0035] This film is manufactured by a co-extrusion of 7 layers with bi-orientation in triple bubble process, as shown schematically in FIG. 5, it is composed of three layers of polypropylene (1, 2 and 3), a first layer of adhesives and additives (4), a first layer of polyamide (5), a layer of ethylene-vinyl-alcohol (6) and a second layer of polyamide (7), these layers are completely merged in the film object of the present invention.

[0036] The film comprises 40 to 50% polyamide, 30 to 40% polypropylene, 8 to 10% ethylene-vinyl-alcohol (EVOH), and 5% to 7% of at least one adhesive and at least one additive, where the adhesive has a flow index of between 2.0 and 4.0, and is chosen from the group comprising those obtained from n-butane, preferably the adhesive is between 1 to 3% maleic anhydride; and the additive has polypropylene with a density of between 0.8 to 0.95 g/cm.sup.3 and specific gravity of up to 1.05 g/cm.sup.3 as a vehicle, said additive is chosen from the group of cristobalites and preferably the additive comprises 1 to 3% of Cristobalite Flux.

[0037] It should be noted that co-extrusion is a process that allows combining the properties of different polymers into a single structure or product that has improved properties. Thus, it is possible to improve or combine properties such as puncture resistance of the packaging, heat sealing, appearance, permeability, etc., and material consumption is optimized by using recycled material or lower cost materials for the internal layer(s).

[0038] Co-extrusion is applied in the extrusion of sheets and films, mainly for food packaging, pharmaceuticals, etc., as well as in the extrusion of tubes, and in some cases for extrusion of profiles.

[0039] The process of retorting or sterilization is a physical technique of preserving food hermetically packaged in a container and subjected to high temperatures for a period to completely destroy its microorganisms, pathogens or not, and spores. In this process temperatures above 100° C. are applied, in the order of 115 to 121° C. for varied periods of time and its objective is the destruction of all viable organisms that can be counted by a proper counting or cultivation technique and their spores, as well as those that can deteriorate the food, providing a shelf life of more than 6 months. The speed of heat penetration into a food influences the treatment time and is defined as the amount of heat transferred per unit of time.

[0040] As shown in FIG. 6, the process of the present invention comprises the stages of:

[0041] a) Co-extrude (8) at a temperature of between 5-15° C. a 7-layer tubular strip with a tubular central head, as shown in FIG. 1, in a first bubble, where said tubular strip has a dimension of 20 to 350 mm. The 7 layers are individually extruded by extruders that feed each of the materials, where these materials comprise three layers of polypropylene (1)(2)(3), a first layer of adhesives and additives (4), a first layer of polyamide (5), a layer of ethylene-vinyl-alcohol (6) and a second layer of polyamide (7), and where the adhesive has a flux index of between 2.0 and 4.0, preferably the adhesive is maleic anhydride, and the additive has as a vehicle polypropylene with density between 0.8-0.95 g/cm.sup.3 and specific gravity of up to 1.05 g/cm.sup.3, said additive is chosen from the group of cristobalites, preferably the additive comprises 1 to 3% of Cristobalite Flux, to obtain a co-extruded tubular strip.

[0042] b) Cool (9) the co-extruded tubular strip in stage a) by immersing it in water until said strip reaches between 5° to 12° C., to obtain an amorphous multilayer strip, that is not crystalline.

[0043] c) Heat (10) the amorphous tubular multilayer strip obtained in stage b) to a temperature of 70 to 75° C.

[0044] d) Orient (11) biaxially the tubular multilayer strip heated in stage c) in a second expansion bubble at a temperature of 68 to 75° C. to obtain an amorphous bi-oriented primary film.

[0045] e) Heat (12) the amorphous bi-oriented primary film obtained in stage d) until reaching 140 to 150° C. to stabilize it and eliminate thermal shrinkage and possible elongation to obtain a metal-free film for packaging, where said film is tubular.

[0046] In a preferred modality of the invention, stage c) and d) are optional in the process, as shown in FIG. 2, after stage a), cools b) and passes to stage e), having a balloon co-extrusion process like the “alternate” process of this same document.

[0047] Once the tubular film is obtained at the end of stage e), the user places the product inside the bag, closes it and seals it with temperature and pressure, and places it inside an autoclave for processing, obtaining food products such as the one shown in FIG. 7.

Example 1. Barrier Studies of the Film Object of the Present Invention

[0048] According to the Report/Service Number 903-19 of the Center for Research and Applied Chemistry, where the oxygen and water vapor permeability of the material is evaluated, the following results are observed:

[0049] Oxygen transmission, according to ASTM-D-3985-2017 (using CEF-60/CCQ-028-1 coulometric sensor:

[0050] cm.sup.3/m.sup.2.Math.day=Values below the limit of the equipment, which is 0.05 cm.sup.3/m.sup.2.Math.day

[0051] g/100 in2.Math.day=Not reported for being below the equipment limit.

[0052] Water vapor, according to ASTM-F-1249-13 (using CEF-60/CCQ-038 infrared sensor):

[0053] Transmission in g/m.sup.2.Math.day=0.93094

[0054] Transmission in g/100 in.sup.2.Math.dia=0.060065

[0055] This proves a very high oxygen barrier, comparable to an ALOX PET (12)/NY (25)/W-RCPP (100) laminated material that offers a value only specified as less than 1.0.

Example 2. Shelf-Life Studies of the Film of the Present Invention

[0056] According to the report number MB-20-097 of the PIT Technology Center, in the Microbiology Laboratory, of Sigma Foods, when samples with 1 year of life are analyzed, it gives a real shelf in extreme conditions (T>50° C./RH Environment/397 days).

[0057] In table 1, different samples are shown, those marked as “key 3, 4 and 5” correspond to the present invention, without observing any difference vs the samples that do not have this key, and that correspond to products in regular laminated containers.

TABLE-US-00001 TABLE 1 Shelf-life assessment of various samples. Listeria Internal MA CT E. coli BAL Fungus Yeasts Salmonella spp monocytogenes Code UFC/g Presence/Absence in 25 g NTR 708 09-249 <10 <10 <10 <10 <10 <10 Absence Absence CAATA9.18.19 Bean NTR 708 09-250 <10 <10 <10 <10 <10 <10 Absence Absence CAATA9.18.19 Bean Code 1 pork 09-252 <10 <10 <10 <10 <10 <10 Absence Absence meat test Code 2 pork 09-253 <10 <10 <10 <10 <10 <10 Absence Absence meat test Code 3 Aug/23.sup.rd 09-254 <10 <10 <10 <10 <10 <10 Absence Absence pork meat bag test Code 4 Aug/23.sup.rd 09-255 <10 <10 <10 <10 <10 <10 Absence Absence pork meat bag test Code 5 July/5.sup.th 09-256 <10 <10 <10 <10 <10 <10 Absence Absence standard sample pork meat test Methodology B C C H G G M O

Example 3. Physical-Mechanical Evaluation of the Film of the Present INVENTION

[0058] Tests are performed to determine the seal strength of the present invention, in a GBPI brand fixed bar sealing equipment, where it has a temperature of 220° C., for 1 sec and with a pressure of 35 pounds per square inch.

[0059] The method used for the measurement of the seal force is ASTM F88, in which the test tubes are placed on a dynamometer and a force is exerted at 180°, measuring the force required to separate the adhered films, according to FIG. 7.

[0060] With this technique the results of these tests are between 16 and 22 lb/in.sup.2, with an average of 19 lb/in.sup.2.

[0061] Tests were done to determine the optimal operating temperature, a curve like the one shown in FIG. 8 was generated:

[0062] With which it is verified that the material resists 121° C. for a period of 30 min, approximately, and with which the sterilization of the food is achieved. The conditions also include a back pressure in the autoclave that is 2.0 kgf.

[0063] Having sufficiently described my invention, I consider as a novelty and therefore claim as my exclusive property, what is contained in the following claims: