HUT62625A - Foil suitable for packing fresh food - Google Patents

Abstract

A packaging film consisting essentially of a terpolymer of ethylene, unsaturated monocarboxylic acid, an alkyl acrylate or methacrylate, and 0.1 to 2 weight percent of at least one sorbitan fatty acid ester, upon exposure to corona treatment exhibits good sealing properties and improved resistance to fogging.

Description

The present invention relates to olefin-based polymeric films suitable for packaging fresh meat, vegetables and cheeses.

The requirement for foils for packaging fresh meat, vegetables and cheeses is that such foils provide health protection for the product under wide-ranging circumstances, and are aesthetically pleasing and manageable. The film must be strong, tough, shiny, and transparent. It must be resistant to the formation of water droplets on its inner surface during application (hereinafter referred to as fog formation). During the packaging process, the film is stretched and must follow the shape of the product to be packaged. It must be sufficiently adhesive to remain on the food until the hot glue is applied, without hindering unwinding from the roll. It is also important that the film is clearly ruptured and highly puncture resistant. Adequate bonding must be obtained in industrial packaging processes under widely varying conditions. The oxygen permeability must be such that the carcasses remain attractive in color for three to four days.

Currently used fresh meat wrapping films are generally made from highly plasticized polyvinyl chloride. It is highly desirable in the food industry to replace these films with materials which are free of halogens and plasticizers. Although many polyolefin-based formulations have been proposed for this purpose, none of them are fully suited to meet the wide variety of market needs. · · · · · · · · · · · · · · · · · · · · · ·

Japanese Patent Application No. 53-134591-A discloses a packaging film consisting of (a) ethylene, (b) 9.7-2.0 mol% of unsaturated carboxylic acid alkyl ester, (c) 0-2.5 mol% of unsaturated carboxylic acid, and d. 0.3 to 2.5 mol% of unsaturated carboxylic acid metal salt. The film has good mechanical, thermal and optical properties, including vapor resistance.

U.S. Patent No. 3,048,266 discloses a fog-proof polyolefin film which is an anti-fog agent such as sorbitol fatty acid mono- or diester, which is an ethylene oxide or polyoxyethylene ester or ether. contain. Copolymerized ethylene or propylene polyolefin polymers are suitable for film production.

U.S. Patent No. 3,048,263 discloses a fog-proof polyolefin film similar to that described above.

U.S. Patent No. 4,189,420 discloses a polyolefin resin mixture comprising a low molecular weight polybutene, a glyceride mixture, and preferably a surface wetting agent such as a sorbitol fatty acid ester.

U.S. Pat. No. 4,486,552 discloses a fog-resistant ethylene polymer film, particularly a linear low density ethylene polymer-based polyolefin film, which comprises an alkylphenol alkoxylate containing an anti-fog agent such as 1) poly (alkylene fatty acid ester) or 3) a combination of component 2) and any of the components of component 1).

U.S. Patent 3,541,040 discloses a fog-proof polyolefin film consisting of a blend comprising a polyolefin resin, sodium dioctylsulfosuccinate, glycerol monostearate, and a reaction product of lauryl alcohol and ethylene oxide.

U.S. Patent 3,498,962 discloses an olefin polymer containing a sarcosine derivative as an anti-fog agent.

British Patent No. 1,206,089 discloses a composition comprising an olefin polymer such as polyethylene; The product from the reaction of 0.25-4% ethylene oxide with a C8-C18 alcohol; 0.1% to 2% fatty acid esterified polyhydroxy alcohol; and 0.05-0.75% by weight of an alcohol diester alkali metal salt of sulfobuccinic acid. It is claimed that the film produced from the composition is resistant to fog formation.

French Patent No. 2,117,386 discloses a film for wrapping fresh meat comprising an ethylene-vinyl acetate copolymer and 0.5 to 6% of an anti-blocking agent consisting of a partial ester of a polyol and an aliphatic monocarboxylic acid or an ester thereof. consists of a poly (alkyleneoxy) derivative.

Japanese Patent Application Serial No. 53-108145-A discloses a resin composition which is partially soluble. hydrolyzed vinyl acetate copolymer and a small amount of low molecular weight polyolefin and sorbitol fatty acid ester. The resin can be used to produce a transparent, shiny, and fog-proof film.

The present invention relates to a packaging film comprising the components

(a) at least 80% by weight of a terpolymer consisting of at least 50% by weight of ethylene, 2 to 20% by weight of C 3-8 unsaturated monocarboxylic acid and 2 to 20% by weight of a group consisting of at least one alkyl acrylate, alkyl methacrylate or mixtures thereof is derived, contains a C 2 -C 12 alkyl group and the acyl moiety is neutralized with 0 to 10% by weight of at least one metal ion, and

b) 0.1% to 2% by weight of at least one sorbitol fatty acid ester, and at least one side of the film is treated with crown light to prevent fogging of the film used for packaging the wet food product.

The present invention also relates to a process for making a wrapping film in which

a) mixing a terpolymer consisting of at least 50% by weight of ethylene, 2-20% by weight of C 3-8 unsaturated monocarboxylic acid and 2-20% by weight of a group consisting of at least one alkyl acrylate, alkyl methacrylate or components thereof a mixture of 2 to 12 carbon atoms from the mixture and neutralized with 0 to 10% by weight of the acyl moiety with at least one metal ion; 0.1 to 2% by weight with at least one sorbitol fatty acid ester;

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b) processing the mixture into a film; and

c) subjecting the foil to at least one side of the foil to such an extent that no foil is formed on the foil used to package the wet food.

The present invention also relates to a food packaging method implemented with the above packaging films.

The films of the present invention are prepared primarily from an ethylene terpolymer prepared by a well-known, high-temperature, stirred-constant reactor as described in the well-known free radical polymerization process such as U.S. Patent 4,351,931. The chemical composition of the polymer, as is well known, is monomeric feed! can be controlled by selecting the right speed.

The ethylene terpolymer is 2-20% by weight of ethylene

Contains C3-C8 unsaturated monocarboxylic acid and 2-20% by weight of at least one mixture of alkyl acrylate, alkyl methacrylate, or components thereof having alkyl groups having 1 to 12 carbon atoms. The monocarboxylic acid is preferably acrylic or methacrylic acid or a mixture thereof, and this component is preferably present in an amount of 4 to 12% by weight, more preferably 5 to 10% by weight, most preferably 6 to 8% by weight. The carboxylic acid component of the polymer provides an appropriate combination of transparency, strength and puncture resistance of the film.

Suitable C 2 -C 12 alkyl groups such as propyl, isopropyl, η-butyl, isobutyl, η-pentyl, n-hexyl, η-octyl, 2-ethylhexyl and n-dodecyl are suitable. alkyl acrylates or methacrylates. Such compounds containing the methyl group are not preferred. Isobutyl and n-butyl acrylate are most preferred. These ester groups are preferably present in an amount of from 4 to 12% by weight, more preferably from 5 to 10% by weight, most preferably from 6 to 8% by weight. The alkyl acrylate or methacrylate component of the polymer provides the desired high extensibility and elasticity of the film.

Terpolymers containing ethylene, methacrylic acid and isobutyl acrylate are most preferred for general acceptance in food applications.

The polymeric component of the film according to the invention may be used in the form of a non-neutralized acidic terpolymer or of a terpolymer containing a small amount of, for example, up to 10% by weight of metal ions. Suitable metals include those in Sections I, II, III, IVA and VII of the Periodic Table. (as described in Handbook of Chemistry and Physics, Chemical Rubber Publishing Co., 37th Edition, page 392). Such metals include, in particular, sodium, potassium, lithium, cesium, silver-mercury, copper, beryllium-magnesium, calcium, strontium-barium-copper, cadmium, mercury, tin, lead, iron, cobalt, nickel, zinc and aluminum; however, non-toxic metals are preferred for food applications. Of these, zinc and sodium are the most preferred.

In general, non-neutralized polymers are preferred, however, for example, slight neutralization may be desirable to improve melt stability. The amount of the neutralizing metal ion, if used, should not fall below an undesirably lower melt index. The quality grade of the foil, determined according to ASTMD-1238, has a tensile index of 190 ° C, 1-15, 190 ° C. preferably 5 to 12, more preferably 7 to 10 dg / min. Such an advantageous melt index polymer can be processed at high speed into high-quality film at about 180 ° C to avoid evaporation of the anti-fog agent.

The terpolymer may also be a component of the entire polymer of the film, but other polymers of up to 18% by weight or even 19.9% by weight may be used without impairing the advantageous properties of the film of the invention. In particular, a small amount of at least one second polymer, such as an ethylene-based homopolymer or copolymer, may be used as a carrier resin to facilitate the addition of the sorbitol fatty acid ester described below. The amount of carrier resin is generally 10% by weight or less of the composition; experience has shown that about 5% by weight (binary) acid copolymer is suitable for this purpose. The terpolymer generally comprises at least 80% by weight of the film, preferably at least 90% by weight.

A small amount of at least one sorbitol fatty acid ester is added to the polymer. Sorbitol and anhydride esters of sorbitol fatty acid esters with fatty acids, i.e. C8-20 fatty acids. Sorbitol monolaurate is preferred. The amount of ester in the polymer is about 0.1 to 2% by weight, preferably 0.3 to 0.8% by weight. The optimum concentration is 0.5% by weight. The presence of the sorbitol fatty acid ester improves the film's anti-fog properties while at the same time blocking and providing good transparency.

A composition comprising a terpolymer and a sorbitol fatty acid ester is prepared by mixing the two components. The mixing * ·· »* ·

9 is usually carried out in the melt phase. Generally, the additive concentrate is prepared in a suitable olefin copolymer or terpolymer, and the pellets made from the concentrate are dry mixed with the terpolymer pellets prior to feeding into the film extruder. Other methods may be used if desired, but the addition of the sorbitol fatty acid ester is always carried out before the terpolymer is melted and converted into a film. The preparation of the composition into a film is preferably accomplished by the well-known bubble blowing and orientation process (i.e., blown film process) followed by the bubble lowering, slicing, treatment and winding.

The sorbitol ester used for the terpolymer film alone is not sufficient to prevent fog formation because it obviously does not migrate to the surface of the film to cause the formation of a continuous water coating instead of a discrete droplet of water. However, treating one side of the film with crown light greatly improves the anti-fog and other properties of the film.

Crown light treatment devices are well known in the art and are described, for example, in U.S. Patent No. 3,133,1993. The apparatus comprises an earthed metal cylinder with an insulated housing and an electrode mounted parallel to the axis of the metal cylinder. The foil passes through the insulated cylinder and crown discharge occurs between the electrode and the foil. The measured control parameter, the distance between the electrode and the insulated cylinder cover to the extent necessary to achieve the desired wetting voltage

- 10 adjustable as defined in ASTM D-2578. It is impossible to determine universally and specifically the parameters of the crown light treatment because they are a function of linear velocity, film width, electrode layout and purity, film additives, film temperature, and other factors. However, the determination of the wetting voltage and the setting of the appropriate parameters to achieve the desired wetting voltage can be accomplished by one skilled in the art. The treatment is suitable when the wetting stress is (40-50) x 10 ^-5 N / cm, preferably (42-48) x ^{10 5} N / cm.

The amount of energy used is important because a certain amount of energy is required to improve the film surface to the desired degree. The film is treated with crown light only on the side of the material to be packaged. Accordingly, the foil blowing line, the crown light treatment unit, the foil shredder and the winding means are arranged so that the foil fed into the packaging machine is in the desired orientation. Of course, both sides of the film can be treated. Dual treatment has a detrimental effect on hot glue, but in some circumstances very little crown light treatment on the second side is effective. It is known to one skilled in the art that proper handling can be accomplished by a variety of devices and geometric arrangements.

EXAMPLE 1 Pelletized ethylene terpolymer consisting of ethylene, 6% by weight isobutyl acrylate and 6% by weight methacrylic acid, having a melt flow index of 9 dg / min (190 ° C). · ♦ ··· · * · »« «· · · · · · · · · · · · · ···

- 11 mixed with 5 parts by weight of pelletized concentrate containing 10 parts by weight of sorbitol monolaurate and 90 parts by weight of ethylene-methacrylic acid copolymer resin. The dry mixture was extruded with a 50 mm single screw extruder with 100 mm diameter circular die at a melt temperature of 180 ° C to obtain a film of 16 mm. The film is subjected to a film blowing process at a speed of 27 m / min in which the blown bubble has a diameter of 4.5: 1 relative to the die. The film thickness is 16 mm.

One surface of the foil is subjected to a crown light treatment with a Kalwar® apparatus. The electrode slot and power are adjusted so that the film surface has a wetting voltage of 44Ί0 ⁵ N / cm measured in accordance with ASTM D-2578. The flow rate of the film at the discharge point is 27 m / min.

The resulting film is clear, glossy (105% gloss as determined by ASTM D-2454), and has very good adhesion and elasticity. The latter properties are examined by placing the foil by hand over the mouth of a wide-mouthed jug, and pressing with the finger to observe its recovery.

The resulting foil is used to wrap fresh meat in a tray. Packaging was performed using a commercially available Delford brand (Delford Co., Japan). The machine stretches the foil, slides the tray with its contents onto the grid, wraps the foil on the tray, and then glues the foil under the tray with hot glue. Heat sealing is used to seal the inner and outer surfaces of the film. The packing speed is 50 packs per minute; the packages are very rooftop and have a smooth surface.

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The packaging of simulated food units was subjected to a similar test with the Ilapak Targa Model 50 A brand Ilapak SA. Similarly, the results of the study are very satisfactory.

By changing the temperature setting of the hot melt adhesive plate of the Delford apparatus, it is found that the film of the present invention can be hot-melted over a wide temperature range of 115-150 ° C and allows permanent bonding. The temperature range that can be used to heat ordinary foils used in food packaging is always very narrow, usually

5-10 ° C (e.g. 110-120 ° C for ethylene-vinyl acetate copolymer). Polyvinyl chloride films have an adhesive range of about 124 ° C to about 140 ° C, but under these conditions, there is no proper bonding and therefore regular fluid leakage.

2-6. Examples

The process of Example 1 was used to prepare additional films, except that the composition of the terpolymer was varied as described in Table I. In each case, the extruded composition contains 0.5% by weight of sorbitol monolaurate and is subjected to crown treatment on one side.

Table I

Example isobutyl Metakri l- flow Drop ³ brightness Blur ⁰ number acrylate acid index number (%] l%] Second 8 8 7 200 112 3.3 Third 5 10 7 190 121 2.6 4. 10 5 7 160 97 5.7 5th 5 5 7 150 88 6.4 6th 6 6 7 260 118 2 ^ 5

^a According to ASTM D-1709, in [g] b According to ASTM D-2454 ^c According to ASTM D-1003

1-6. Each of the films produced in Examples 1 to 4 is subjected to a fog test. The test is performed by placing the foil samples on the mouth of two glass half-filled beakers, and placing the beakers in a refrigerator at 8.8 ° C and in an oven at 35 ° C for 5 days. Beakers are often inspected to determine if a drop or water film is formed on the bottom surface of the foil. If, in any of the tests, droplets of water which interfere with transparency are produced, the film shall be considered inappropriate.

The films of Examples 2, 3 and 6 show excellent optical properties and resistance to drop-induced puncture compared to other films.

The packaging test described in Example 1 is carried out according to Examples 2-5. For example, the films of the examples are Mini and W18 and W40 (Automatic Industria SRL, Italy). The Mini equipment is a semi-automatic, manual-powered and hot-plate adhesive system. The W18 and W40 are high speed heated conveyor adhesive equipment. Each of the films studied yielded attractive functional packages at the speeds generally obtainable with the equipment.

The film of Example 3 is particularly strong, transparent and shiny.

- 14 The performance characteristics of the Automac brand used to test the film of Example 6 are very balanced, the packages produced are attractive, and the production speed is as designed for the machine.

A. Comparative Example

The procedure of Example 4 is repeated, but no crown light treatment is performed. The film's resistance to fog formation is inadequate because after a few hours, droplet formation on the film surface is observed.

B. Comparative Example

The procedure of Example 4 is repeated by applying a crown light treatment on both surfaces of the film, which results in a wetting stress of about 45 to 10 ~ ⁵ N / cm. The heat sealing of the film thus obtained at 110-150 ° C is not satisfactory.

C. Comparative Example

The procedure of Example 4 is repeated by replacing sorbitol monolaurate with glycerol monooleate. The film has a poor behavior against fog formation.

D. Comparative Example

The procedure of Example 4 is repeated without the use of an anti-fog agent, but one side of the film is subjected to crown light treatment to achieve a wetting voltage of 44 x 10 ⁵ N / cm. The foil shows very poor results in the fog formation test, with rapid formation of droplets.

Example 7

The procedure of Example 6 is repeated, except that

15 by neutralizing the terpolymer to about 5% by weight with zinc ions, thereby reducing the melt index to about 5. The film thus obtained has exactly the same properties as the film of Example 6, showing good results in fog formation tests, and can therefore be classified as excellent.

The above examples show that the polymer films of the present invention are excellent in packaging equipment designed for soft polyvinyl chloride films and are preferred in all areas where halogen-free packaging material is desired.

Claims (20)

Claims 1. Packaging film, characterized in that it comprises its components (a) at least 80% by weight of a terpolymer consisting of at least 50% by weight of ethylene, 2 to 20% by weight of C 3-8 unsaturated monocarboxylic acid and 2 to 20% by weight of a group consisting of at least one alkyl acrylate, alkyl methacrylate or mixtures thereof derived from a group having 2 to 12 carbon atoms and the acyl moiety being neutralized with 0 to 10% by weight of at least one metal ion, and b) 0.1-2% by weight of at least one sorbitol fatty acid ester and at least one side of the film treated with crown light such that the wetted surface of the treated surface is (40-50) x 10 ^-5 N / cm. 2. Packaging film according to claim 1, characterized in that in order to achieve the proper corona treatment (42-48) xlO ^-5 N / cm wetting power level. Packaging film according to claim 1 or 2, characterized in that the terpolymer comprises units derived from ethylene, methacrylic or acrylic acid and n-butyl acrylate or isobutyl acrylate. Packaging film according to claim 3, characterized in that the terpolymer comprises 4 to 12% by weight of a unit derived from methacrylic or acrylic acid and 4 to 12% by weight of n-butyl acrylate or isobutyl acrylate. Packaging film according to Claim 4, characterized in that the terpolymer comprises 5-10% by weight of a unit derived from methacrylic or acrylic acid and 5-10% by weight of n-butyl acrylate or isobutyl acrylate. Packaging film according to claim 4, characterized in that the terpolymer comprises from 6 to 8% by weight of a unit derived from methacrylic or acrylic acid and from 6 to 8% by weight of n-butyl acrylate or isobutyl acrylate. 7. Packaging film according to any one of claims 1 to 3, characterized in that it contains a terpolymer containing non-neutralized acid groups. 8. Packaging film according to any one of claims 1 to 3, characterized in that 1-6% by weight of the acid groups of the terpolymer are neutralized with sodium or zinc ions. 9. Packaging film according to any one of Claims 1 to 3, characterized in that the terpolymer has a melt index of 4-12 dg / min at 190 ° C. 10. Packaging film according to any one of claims 1 to 3, characterized in that it contains sorbitol monolaurate as the sorbitol fatty acid ester. Packaging film according to claim 10, characterized in that the amount of sorbitol monolaurate is 0.3-0.8% by weight. 12. Method 1-11. The packaging film according to any one of claims 1 to 3, characterized in that: a) we mix it up · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · i) at least 80% by weight of a terpolymer consisting of at least 50% by weight of ethylene, 2 to 20% by weight of C 3-8 unsaturated monocarboxylic acid and 2 to 20% by weight of a group consisting of at least one alkyl acrylate, alkyl methacrylate or a mixture of components having from 2 to 12 carbon atoms and neutralized with from 0 to 10% by weight of the acyl moiety with at least one metal ion; ii) 0.1 to 2% by weight with at least one sorbitol fatty acid ester; b) processing the mixture into a film; and c) subjecting the film to at least one side (40-50) x 10 ^-5 N / cm to a crown light treatment. 13. The method of claim 12, wherein the crown light treatment is performed to such an extent that the wetted stress (42-45) x 10 ^-5 N / cm is applied to the treated surface. 14. A process according to claim 12 or 13, wherein the terpolymer is used It contains 4-12% by weight of a unit derived from methacrylic acid or acrylic acid and 4-12% by weight of n-butyl acrylate or isobutyl acrylate. 15. The process according to any one of claims 1 to 3, wherein the sorbitol fatty acid ester is used in an amount of 0.3-0.8% by weight of the bit monolaurate, based on the amount of the mixture. 16. A film-wrapped space according to claim 1 *. · · · · · · · 99 99 · ··· »····· *» · 4 · ··· - 19 4 * characterized in that the food containing moisture is packaged. 17. A process for producing a foil wrapped product according to claim 2, characterized in that the food containing moisture is packaged. 18. A process for producing a foil wrapped product according to claim 4, characterized in that the food containing moisture is packaged. 19. A process for producing a foil wrapped product according to claim 11, characterized in that the food containing moisture is packaged. 20. The packaging film of claim 1, wherein: 95% by weight of a terpolymer consisting of 88% by weight of ethylene, 6% by weight of isobutyl acrylate and 6% by weight of methacrylic acid and having a melt flow index of 9 dg / min; 0.5% by weight of sorbitol monolaurate as sorbitol fatty acid ester; - 4.5% by weight of ethylene-methacrylic acid copolymer resin; and, on one side of the film, treated with crown light to an extent that the wetting stress of the treated surface is 44 · 10 ^-5 N / cm.