MXPA99003088A - Plastic food wrapper resistant to perforce - Google Patents

Abstract

A tubular food wrap comprising a layered film structure in the form of a tube having a plurality of layers. At least one of these layers contains a metallocene polyolefin resin. The invention also includes the capaunica film from which the tubular food wrap is made and the method for making the film and the tubular film. The metallocene polyolefin resin-containing layer can include a mixture containing from about 60 to about 90% by weight of low density polyethylene and from about 10 to about 40% by weight of metallocene polyethylene. The tubular food wrap may further include at least one layer of nylon and at least one layer of polyalkylvinyl alcohol. The food wrap may also include at least one tie layer between the metallocene-containing layer and the nylon layer for laminating the metallocene-containing layer and the nylon layer together. The layers can be coextruded or laminated layers

Description

WRAPPING ALI MENTO PLASTIC RESISTANT TO PERFORATION Background of the Invention This invention relates to food wraps, and more particularly relates to food wraps made of plastic film materials. According to the invention, such food wraps are generally tubular in shape and the food is stuffed into the tubular film. The first tubular food casings were intestinal materials that were cleaned and then stuffed with the food product, for example meats to form sausages. However, the use of intestinal materials was not adequate for fast and current manufacturing methods since the cleaning of the intestinal product was labor intensive, time-consuming and expensive. Furthermore, such products did not have a uniform diameter and the source of supply of such materials could not meet the current demand for sausages and other food products stuffed in tubular casings. Artificial tubular food casings were then made to overcome deficiencies of intestinal materials. The first commercially successful artificial tubular food casings were made from regenerated cellulose.

Such casings were made by extruding viscose in the form of a tube and then regenerating the cellulose from the viscose or by folding a fiber mat, for example paper into a tube and then impregnating the paper with the viscose followed by the regeneration to form a tube comprising a regenerated cellulose reinforced with fiber. Regenerated cellulose tubes are still used in the activity due to the desirable properties for most food sausage operations. Such tubes are generally permeable to water, gases and smoke vapors making the casing ideal for the subsequent treatment, for example smoked, of the contained food product. However, such wrappings were not edible, which led to the development of edible wrappings made from collagen which simulated the edible nature of the original intestinal material. However, in certain applications, there is a need for a tubular food wrap having properties not covered by regenerated cellulose or collagen. There are situations in which permeability is not desired and where high strength, flexibility and puncture resistance are required than those normally available with regenerated cellulose or collagen casings. For this purpose, laminated plastic tubular films have been developed. Such films have been commonly made of low density polyethylenes (either linear or branched chain or mixtures thereof) alone or in the form of a layer, i.e. the form laminated or co-extruded with polyamide film, for example nylon (usually nylon 6 or nylon 66). Such tubular films have also been made that incorporate a layer of a polyvinyl alcohol (such as ethylvinyl alcohol, EVOH) as an oxygen barrier layer. While such laminated plastic films have been successful, they do not yet have the performance that is desired. Thin plastic film wrappers (usually less than 0.0076 cm thick) should be stiff enough to mold the emulsion of meat contained within the uniform tubular shape (called "chub" in the industry); even this film must be thin and foldable enough to be grouped and folded under a metal end fastener without being cut or twisted by the fastener or allowing air and moisture to escape through the folded ends of the package. In addition, the hulk usually contains a semifluid mixture of ground meat, ingredients and water and the wrapper must maintain the tubular shape, resist dripping, sharp blows and impacts through processing, packing, shipping and the rigors of handling. retail In addition, a variety of other characteristics are required for machining capability, sealing capability, oxygen barrier, heat hot and cold filling operations, fresh, frozen freezing bark applications, and so on. The film must be functional and have good clarity, brightness and printing capacity for consumer appearance. Several films and film laminates are available which serve for this packaging market; however none of them offers the optimal properties at competitive prices. For example, as previously mentioned, nylon can be used in those applications in combination with other film layers to provide structural strength to a thin film. Films such as EVOH can be used to provide the necessary oxygen barrier. The properties of nylon and EVOH are altered with any exposure to moisture. Also, both films have little resistance to drilling and fluid impact in those applications, as the tests have shown. Therefore, those films are kept at the minimum layer values in the structure to obtain their respective beneficial properties. Polyethylene is generally more foldable, provides structural strength and moisture barrier properties. However, conventional polyethylene blends such as LDPE (branched low density polyethylene) and LLDPE (linear low density polyethylene) (and derivatives) influence the folding capacity of the overall structure at higher percentages of the structure. This increases the thickness total structure that contributes to the previously described problems, and reduces performance and clarity. If a more easily foldable, thinner collapsible and puncture-resistant oxygen barrier film layer were available, (1) the total thickness would be reduced, (2) the clarity would be improved, (3) the survival of the package, (4) the manufacturing methods (film extrusion) could be expanded, (5) the yield could be improved, and (6) the use of the envelope in the sausage location could be increased since it could be placed on a roll. Metallocene catalyzed polymers, or metallocene plastomers, were introduced by the plastics industry about seven or eight years ago. These plastomer products offer significant performance benefits, in this case for low density polyethylene. The main disadvantage of the metallocene has been and still is the cost, and the processing capacity of the resin in extrusion operations.

Brief Description of the Drawings Figure 1 shows a tubular food wrapper of the invention. Figure 2 shows a cross section of a tubular food casing of the invention.

Figure 3 shows a cross section of the laminated film used to make a tubular food wrapper of the invention.

Brief Description of the Invention The invention is a tubular food wrap that includes a laminated film structure in the shape of a tube having a plurality of laminated layers. At least one of the layers contains a metallocene polyolefin resin. The invention includes the single laminated film from which the tubular food wrap is made and the method makes the film and the tubular film. The metallocene polyolefin resin-containing layer may include a mixture containing from about 60 to about 90 weight percent low density polyethylene and from about 10 to about 40 weight percent metallocene polyethylene. The tubular food wrap may further include at least one layer of nylon and at least one layer of polyalkyl vinyl alcohol. The food wrap may also include at least one tie layer between the metallocene-containing layer and the nylon layer for laminating the metallocene-containing layer and the nylon layer together.

Detailed description of the invention The tubular food casing of the invention may include numerous layers while at least one of the layers contains a metallocene resin. For example, at least in a preferred embodiment, the film has at least seven layers that can be described as follows: a) a first layer which is a film that includes a mixture of between about 15 and about 25 weight percent of metallocene polyethylene, and between about 75 and about 85 weight percent of a low density polyethylene, b) a second layer which is a tie layer including an adhesive polymer, c) a third layer including nylon, d) a fourth layer including a polyvinyl alcohol, e) a fifth layer including nylon, f) a sixth layer which is a tie layer including an adhesive polymer, and g) a seventh layer which is a film including a mixture of between about 15 and about 20 weight percent of metallocene polyethylene and, between about 75 and about 85 weight percent of a low density polyethylene. The low density polyethylene, for example of molecular weight 5000 to 50000, can be a mixture of linear polyethylene (LLDPE) and branched chain polyethylene (LDPE) made using traditional Ziegler-Natta type catalysts. The preferred metallocene polymer has a narrow molecular weight distribution which may be indicated by the ratio of the weight average molecular weight to the number average molecular weight. Such resins preferably have a weight average molecular weight ratio to the number average molecular weight of between about 2 and about 2.25. The metallocene polymer has a weight average molecular weight of between about 5000 and 50000. The metallocene polymers are olefin and vinyl type polymers using metallocene catalysts. Examples of such polymers suitable for use in accordance with the present invention are metallocene polyethylenes and metallocene polypropylenes. The metallocene polyolefin is preferably a polyethylene metallocene polymer. An especially preferred metallocene polymer is sold under the trademark EXACT 3132 from Exxon Corporation. Exact 3132 has an index of 1.2 g / 10 min, a density of 0.9, a peak melting temperature of 96 ° C, a tensile strength of 65.2 MPa (669.25 kg / cm2) in the direction of machine and 62.3; MPa (639.73 kg / cm2 and a force of drilling resistance of 8 Ibs / thousand. In the preferred embodiment, the metallocene polymer is mixed with standard low density polyethylene polymers at a temperature above the softening point of the polymers to form the preferred mixture. The mixture is then extruded into the desired metallocene containing the film layer. The bonding layer between the metallocene layer and the nylon layer contains an adhesive polymer that is approved for food. Examples of the preferred resins for inclusion in the bonding layer are acrylate polymers having adhesive properties, adhesive properties and linear low density polyethylenes modified with anhydride. An especially preferred resin for use in the tie layer is the linear low density polyethylene modified with coextrudable rubber anhydride BYN EL CXA 4125 available from The Dupont Corporation. Such resins have a melt index of 2.5 dg / min, a density of 0.926, a melting point of 126 ° C and a freezing point of 1 10 ° C. The nylon barrier can be made from any suitable polyamide type polymer although preferably it is nylon 6 or nylon 6-6 or mixtures thereof. A vapor barrier usually comprises a polyvinyl alcohol is also preferably present. The preferred polyvinyl alcohol is polyethylvinyl alcohol (EVOH).

The tubular food casing of the invention can be extruded as a tube in the form of multiple layers or can be a tubular food wrap with a sealed seam made from a flat laminated film structure having a plurality of laminated layers, at least one of the layers containing a metallocene polyolefin resin. The tubular film of the invention preferably has a total thickness, i.e., the total laminate structure, from about 0.0025 to about 0.0050 cm. A stitched tubular food wrapper of the invention can be made by winding a flat film having opposite edges in the shape of a cylinder so that the edges are close together and the sealing surfaces of the film together near the edges. , wherein the flat film is a laminated film structure having a plurality of laminated layers and at least one of the layers contains a metallocene polyolefin resin. A preferred form of the invention comprises: a) a coextruded 7-layer barrier film structure of approximately 1.25 mils in thickness consisting of (1) two outer coating layers, each approximately 33% of the total thickness, Extruded with a mixture of 20% Exxon Exact 3132 metallocene resin with 80% of a 90% blend of low density polyethylene and low density polyethylene. slip and anti blocking additives; 82) two intermediate tie layers, each approximately 5% of the total thickness, extruded with acrylate resin; (3) two additional inner layers, each approximately 8% of the total thickness, extruded with a mixture of nylon 60% nylon 6 and 40% nylon 66 (amorphous nylon) and (4) a core layer approximately 8% of the total thickness, extruded with an EVOH barrier resin b) (a) above, treated on one side to accept printing; c) (b) above, printed as required; d) (c) above, dry-bonded adhesive laminated with white adhesive ink for a monolayer film sealer sheet, approximately 1.0 mils thick. The monolayer film was extruded with a mixture of 20% Exxon Exact 3132 metallocene resin with 80% of a 90% / 10% low density polyethylene and a low density polyethylene plus slip, antiblock and dye additives. The above food wrap was compared to an identical control wrap except that the linear low density polyethylene resin was used without mixing with metallocene resin. The results are shown in the Table.

TABLE Control Wrap Containing Metallocene Caliber 2.5 2.25 Stress Resistance Machine Direction 337.9 kg / cm2 282.6 kg / cm2 Transverse Direction 234.3 kg / cm2 237.1 kg / cm2 Elongation at Breakdown Machine Direction 364% 356% Cross Direction 437% 459% Machine Direction Module 3031 .3 kg / cm2 3024.6 kg / cm2 Cross Direction 3206.3 kg / cm2 3743.4 kg / cm2 Oxygen Transfer 1 .4 cc / m2 / day 2.1 cc / m2 / day Dact Impact ASTM D1709 125 g / thousand 153 g / thousand Final Dart Test 5 correct / 15 failed 20 correct / 0 failed In the final dart test, the casing is stuffed with sausage meat and deposited at the end from a standard height. Laboratory and field tests showed that the puncture resistance of a 7-layer structure with as little as 20% metallocene in the coating layers is comparable to or better than the LDPE / LLDPE mixture prior to a measurement thinner general of 17%. Packing tests indicate that other attributes of the envelope are not compromised ((ie, uniformity, machinability) and even other attributes are improved such as the ability to sealing (speed, resistance), clarity, clamping, etc. In addition, this 7-layer structure laminated to a monolayer sealer sheet, approximately 0.0025 cm, of the same metallocene mixture further improves the puncture resistance and impact of the total film envelope. Figure 1 shows an embodiment of the invention wherein a coextruded film 10 is curved to the shape of a tube 12 and sewn into the seam 14 to form the food wrap 16.1a. Figure 2 shows the inner metallocene layer 18 followed by the tie layer 20, nylon layer 22, EVOH layer 24, nylon layer 26, tie layer 28 and outer metallocene layer 30. Figure 3 shows a cross section of coextruded film 32 used to make a food wrapper as shown in Figure 1, showing layers 18, 20, 22, 24, 26, 28 and 30 as shown in Figure 2.

Claims (10)

1 . A tubular food wrapper comprising a layered film structure in the form of a tube having a plurality of layers, characterized in that at least one of those layers contains a metallocene polyolefin resin. The wrapping of claim 1, characterized in that at least one of said layers are co-extruded layers.

3. The casing of claim 1, characterized in that at least one of the layers is a laminated layer.

The tubular food casing of claim 1, characterized in that the metallocene polyolefin resin containing layer comprises a blend of from about 60 to about 90 weight percent low density polyethylene and from about 10 to about 40 weight percent. 100 percent by weight of metallocene polyethylene.

5. The tubular food casing of claim 4, characterized in that the tubular food casing further comprises at least one layer of nylon.

The tubular food casing of claim 5, characterized in that the food casing comprises at least one intermediate joining layer to said at least one metallocene-containing layer and the nylon layer to adhere the metallocene-containing layer and the nylon layer together.

7. The tubular food casing of claim 6, characterized in that the film comprises at least seven coextruded layers: a) a first layer which is a film including a mixture of between about 15 and about 25 weight percent polyethylene of metallocene, and between about 75 and about 85 weight percent of a low density polyethylene, b) a second layer which is a tie layer including an adhesive polymer, c) a third layer including nylon, d) a fourth layer layer including a polyvinyl alcohol, e) a fifth layer including nylon, f) a sixth layer which is a tie layer including an adhesive polymer, and g) a seventh layer which is a film including a mixture of approximately 15 and about 20 weight percent of metallocene polyethylene and, between about 75 and about 85 weight percent of a low density polyethylene. The food casing of claim 7, characterized in that it further comprises an eighth layer comprising a mixture of between about 15 and about 25 weight percent polyethylene of

metallocene, and between about 75 and about 85 weight percent of a low density polyethylene, the eighth layer being laminated to said seventh layer by means of an adhesive. 9. The tubular food casing of claim 7, characterized in that the low density polyethylene is a mixture of linear and branched chain polyethylenes. 10. The food casing of claim 1, characterized in that the metallocene polyolefin is a polyethylene metallocene polymer. eleven . The tubular film of claim 1, characterized in that the metallocene polymer has a weight average molecular weight ratio to number average molecular weight of between about 2 and about 2.25. 12. The tubular film of claim 2, characterized in that the metallocene polymer has a weight average molecular weight ratio to number average molecular weight of between about 2 and about 2.25. The tubular film of claim 5, characterized in that the metallocene polymer has a weight average molecular weight ratio to number average molecular weight of between about 2 and about 2.25. 14. The tubular film of claim 6, characterized in that the metallocene polymer has a weight-average molecular weight ratio to number-average molecular weight.

approximately 2 and approximately 2.25. 15. The tubular film of claim 7, characterized in that the metallocene polymer has a weight average molecular weight ratio to number average molecular weight of between about 2 and about 2.25. 16. The tubular film of claim 8, characterized in that the metallocene polymer has a weight average molecular weight ratio to number average molecular weight of between about 2 and about 2.25. 17. The tubular film of claim 9, characterized in that the metallocene polymer has a weight average molecular weight ratio to number average molecular weight of between about 2 and about 2.25. 18. The tubular film of claim 10, characterized in that the metallocene polymer has a weight average molecular weight ratio to number average molecular weight of between about 2 and about 2.25. 19. The tubular film of claim 1, characterized in that the metallocene polymer has a weight average molecular weight of between about 5000 and 50000. The tubular film of claim 1, characterized in that the laminated structure has a thickness from about 0.0025 to about 0.0050 cm. twenty-one . The tubular film of claim 7, characterized in

that the laminated structure has a thickness from about 0.0025 to about 0.0050 cm. 22. The tubular film of claim 6, characterized in that the tie layer comprises a linear low density polyethylene modified with anhydride. 23. The tubular film of claim 7, characterized in that the tie layer comprises a linear low density polyethylene modified with anhydride. 24. The tubular food casing of claim 1, characterized in that the food casing is a sealed seam tubular food casing comprising a co-extruded film structure having a plurality of co-extruded layers, at least one of the layers which contains a metallocene polyolefin resin. 25. A method for making the stitched tubular food wrap of claim 24, which comprises winding a flat film having opposite edges in the shape of a cylinder so that the edges are close to each other and the sealing surfaces of the film together near the edges wherein the flat film comprises a coextruded film structure having a plurality of coextruded layers, characterized in that at least one of the layers contains metallocene polyolefin resin.