Copolymer mixture, multilayer film, packaging or bag and method for producing multilayer films

 

(57) Abstract:

Usage: in food industry for packaging of food products. The inventive copolymer mixture comprising 90 to 50 wt.% copolymer of vinylidene chloride with vinyl chloride and 10 to 50 wt.% copolymer of vinylidene chloride with methyl acrylate, and the amount of vinyl chloride in the mixture is more than 12 wt.%, and of methyl acrylate is less than 2.8 wt.%. The proposed multi-layer film containing a barrier layer above copolymer mixture, the method of obtaining the multilayer film and the package or bag of the multilayer film. 4 C. and 11 C.p. f-crystals, 2 tab.

The invention relates to new compounds vinylidenechloride copolymers suitable for use as a barrier layer in the film for packaging, for example, meat. In addition, the invention relates to a multilayer film containing such a mixture as a barrier layer, and the package containing the film.

Packing of cut raw meat produced in the food industry, the film has become a very important activity in recent years. Many foods, such as meat, including processed meat, poultry, fish and cheese, usually wrapped in foil to prevent espartanos the AI, for example, shrink packaging film having good barrier properties, which protect food from moisture loss and contact with oxygen, which can damage the contents of the package upon oxidation. Such films contain a barrier layer to provide barrier properties, and material used to provide appropriate barrier properties, are the copolymers of vinylidene chloride with vinyl chloride. U.S. patent N 4793751 (Viskase) describes a multilayer heat-shrinkable film which comprises a barrier layer of a mixture of a copolymer of vinylidenechloride and methyl acrylate, and copolymer of vinylidene chloride with vinyl chloride, containing about 2.9 to 13.5 wt.% of methyl acrylate and 2.9-11.6 wt.% vinyl chloride. Irradiated multilayer film containing a layer of copolymer of vinylidene chloride with vinyl chloride, greatly lose color during storage due to the decomposition of this layer. Discoloration also occurs when the layer is subjected to thermal stress above ambient temperature for a long time.

EP 204918 (Union Carbide) describes the use of copolymers of vinylidene chloride with methyl acrylate as a barrier layer in multilayer films, dosiernomo high temperatures.

U.S. patent N 4798751 describes, however, that although the copolymers of vinylidene chloride with methyl acrylate have the advantage, which is to avoid discoloration, however, there are difficulties with their treatment compared with the processing of films, consisting of a copolymer of vinylidene chloride with vinyl chloride. The main problem in the above U.S. patent is that methylacrylate copolymer is very sensitive to temperature and shear stress during extrusion of the film. The extrusion can be carried out only in a narrow temperature region without premature decomposition of the polymer in the extruder or extrusion head. This decomposition leads to the fact that at the exit of the extruder appear particles or gel is decomposed material, which cause defects in the film. Such defects can lead to rupture of the bubbles and the marriage of the film during extrusion and processing.

Since the optimal melting temperature of the various layers in the multilayer film can be significantly different, in U.S. patent describes the need for a wide range of temperatures required for extrusion methylacrylate copolymer. It was found that a certain number of destroyed material Boo is in it is important to keep this material in the extrusion installation in the form of a thin layer on the walls of the extruder and the extrusion head for so long, as possible.

The aim of the invention described in U.S. patent N 4798751 is to provide a mixture which is a barrier layer in multilayer films, compressible, which are not discolored by irradiation or long term ageing at elevated temperatures, when using the mixture avoids the difficulties of processing related to the temperature sensitivity and the sensitivity associated with shear stress during extrusion.

Description of U.S. patent has as one of its goals the elimination of the difficulties of processing related to the temperature sensitivity and the sensitivity associated with shear stress during extrusion. The description says nothing about other features of the extrusion process, particularly temperature, is needed to guarantee high performance extrusion process.

WO 91/08260 refers to the advantageous properties of the mixture, described in U.S. patent N 4798751, but notes that it has certain limitations. Two resin in the mixture is prone to separation: describes that the mixture is most effective when it is prepared immediately prior to extrusion, which requires, for example, the additional gain is to use a single resin, copolymer of vinylidene chloride with methyl acrylate, but but containing at least 0.5 hours to 100 hours weight acrylic polymer as a lubricant. Used acrylic polymer preferably contains at least one ester of acrylic acid or methacrylic acid and provide low adhesion to metal and thermal degradation during extrusion.

It was discovered that certain mixtures of copolymers of vinylidene chloride with vinyl chloride and copolymers of vinylidene chloride with methyl acrylate have significantly improved extrusion properties that are not disclosed and are not proposed as described in U.S. patent N 4798751 and WO 91/08260.

It has been found that certain mixtures of copolymers of vinylidene chloride with vinyl chloride and copolymers of vinylidene chloride with methyl acrylate can be extruded and processed at lower temperatures than those required for pure copolymer of vinylidene chloride with vinyl chloride or of pure copolymer of vinylidene chloride with methyl acrylate. Reducing the temperature required to obtain a film containing such a barrier layer, the opposite of what was expected for a mixture of vinylidenechloride - vinyl chloride and between the needed to clean copolymers.

The invention provides a method of obtaining increased speed of extrusion of a mixture of copolymers of vinylidenechloride compared with extrusion speeds, obtained by extrusion of the copolymer separately.

Low temperature processing has several advantages. First, it leads to economic benefits from the point of view of reduced consumer energy required to obtain packaging films containing such barrier layer, and, therefore, reduce costs. In addition, the use of low temperature treatment reduces the risk of thermal decomposition of packaging film. When using certain mixtures of vinylidenechloride - vinyl chloride and vinylidenechloride - methyl acrylate, the performance of the material in the production of packaging film increases considerably compared to the performance obtained in the production of films containing comparable barrier layer vinylidenechloride - vinyl chloride or vinylidenechloride - methyl acrylate in the same mode process.

In the study of the behavior of new mixes data were obtained to define what redenchilada and methyl acrylate; data do not give information about whether it might be achieved in practice increased performance. The data obtained are not in a relationship with improved extrusion characteristics.

Features of the invention, therefore, provides a mixture of copolymers containing 90-50 wt. % copolymer of vinylidene chloride with vinyl chloride and 10-50 wt.% copolymer of vinylidene chloride with methyl acrylate and preferably 1-5 wt. % relative to the total weight of the mixture of the copolymer plasticizer and/or stabilizator, where the amount of vinyl chloride in the mixture is more than 12 wt.%, and of methyl acrylate is less than 2.8 wt.%.

In accordance with a preferred variant of the invention, the mixture comprises 75-65 wt. % copolymer of vinylidene chloride with vinyl chloride and 25-35 wt.% copolymer of vinylidene chloride with methyl acrylate.

Copolymer of vinylidene chloride with vinyl chloride, used in the invention contains 15 to 30%, preferably 20-24%, more preferably about 22% of vinegared and 85-70%, preferably 80-76%, more preferably about 78% of vinylidenechloride. Copolymer of vinylidene chloride with vinyl chloride preferably has a mole. m 70000-100000, more preferably 90000-140000. The copolymer is typically more preferably 1,50-1,60. Copolymer of vinylidene chloride with vinyl chloride can be obtained by the emulsion polymerization or suspension polymerization, although it is preferable to use the polymerization in emulsion.

Relative viscosity referenced in this description, measured in accordance with ASTM (American standard test method) D using the resin solution in tetrahydrofuran.

Copolymer of vinylidene chloride with methyl acrylate preferably includes a 6.5 to 9.5 wt. %, preferably 7.5 to 8.5 wt.% more preferably about 8 wt. % of methyl acrylate and 93.5-90,5 wt.%, preferably 91,5-of 92.5 wt.%, more preferably about 92 wt.% vinylidenechloride. Copolymer of vinylidene chloride with methyl acrylate preferably is suspension polymerized copolymer preferably has a mole. m 80000-140000, preferably 100000-120000. Preferably the copolymer of vinylidene chloride with methyl acrylate has a melting point of about 155oC and a relative viscosity of about 1.48.

The mixture of the invention preferably contains 1-5 wt.%, preferably 2-3 wt. % plasticizer and/or stabilizer (preferably about 2 wt. %), the plasticizer is usually liquid. Can be used with traditional oil, dibutylsebacate and glycerylmonostearate. Preferably use epoxidizing soybean oil.

The invention also provides a multilayer film containing a barrier layer, which contains the proposed copolymer mixture. Such films are preferably shrink when heated. They preferably contain a layer capable of heat welding, the barrier layer containing a mixture of the present invention, and resistant to damage layer, there may be additional layers.

The invention also provides a method of obtaining such a multilayer film in accordance with the invention, which includes, for example, extrusion layer capable of heat welding, the barrier layer and resistant to damage layer, and preferably orienting the extruded layers.

The multilayer film of the invention contains in addition to the barrier layer capable of heat welding layer and resistant to damage layer additional layers. The film can contain an intermediate layer or between the core layer capable of heat welding, and a barrier layer in order to provide a four-layer structure. In a four-layer structure, the layer capable of heat to swine 15 - 40 microns, preferably about 25 μm, the barrier layer has a thickness of 3 to 10 μm, preferably 5 to 6 μm, and resistant to damage layer has a thickness of 5 to 30 μm, preferably about 16 microns.

In an alternative embodiment, the film of the invention has a six-plane structure. It contains capable of heat welding layer, the first and second intermediate layers or between the core layer capable of heat welding, and a barrier layer, the third intermediate layer or core between the barrier layer and resistant to damage layer and resistant to damage layer. In this embodiment, is able to heat welding layer usually has a thickness of 5 to 30 μm, preferably about 10 microns, the first intermediate layer has a thickness of 5 to 20 μm, preferably about 12 microns, the second intermediate layer has a thickness of 5 to 30 μm, preferably about 15 μm, the barrier layer has a thickness of 3 to 10 μm, preferably 5 to 6 μm, the third intermediate layer has a thickness of 5 to 20 μm, preferably about 11 microns, and resistant to damage layer has a thickness of 3 to 10 μm, preferably about 4 microns.

In General, the film of the present invention will have an overall thickness of 40 to 120 μm, preferably 50 to 90 microns and more preferably about 60 microns.

4-C10--olefins, such as but-1-ene, Oct-1-ene and Gex-1 - ene; polymer molecules contain long chains with multiple branches; specific gravity is usually 0,916 - 0,925 and usually depends on the content of the co monomer;

the term "polyethylene, very low density" (v) belongs to the linear polyethylene polymers such DREUX, but generally have a lower specific weight, for example 0,915 - 0,860 or below;

- the term "copolymer of ethylene and vinyl acetate" (EVA) refers to a copolymer formed from monomers of ethylene and vinyl acetate in which the ethylene units are present in large numbers, and vinyl acetate units are present in small amounts;

- the term "ion meter" refers, for example, a copolymer of ethylene with copolymerizate ethylenedeamine acid monomer, usually ethylenedeamine carboxylic acid, which may be bilateral or monobasic, but usually monobasic, for example acrylic or methacrylic acid, preferably in the ionized form than in the form of the free acid, neutralizing cation is an ion of any suitable metal, such as alkali metal ion, zinc ion or other ion polyvalent metal; Surlyn is factory Marlim means for adhesion of adjacent layers in the films of the present invention, can be any of those known as suitable for adhesion of adjacent layers coextruding films. Suitable adhesive layers include, for example, chemically modified ethylene polymers, for example copolymers of ethylene with esters of ethylenedeamine carboxylic acids, as for example by alkylacrylate and methacrylates, grafted copolymers of maleic acid or anhydride to a copolymer of ethylene with vinyl acetate grafted copolymers molten anhydrides of carboxylic acids with polyethylene, a mixture of resin and mixed with polyethylene, or copolymers of ethylene and alpha-olefin. Such materials include adhesives sold under the brand name Bynel (DuPont) or Admer (Mitsui).

Able to heat welding layer used in the film of the invention may be any standard layer, welded by heating. Such a layer may, for example, be DREUX-polyethylene, very low density, DREUX-linear low density polyethylene, copolymer of ethylene and vinyl acetate or ion meter (for example, Surlyn), a copolymer of ethylene and acrylic acid, a copolymer of ethylene and methacrylic acid, copolymer of ethylene and propylene or a layer of a copolymer of ethylene and butylacrylate. In the preferred embodiment, using the method of the NECS of the invention may be of any standard type such layer, for example, a copolymer of ethylene and f, polyethylene, very low density, copolyamide, linear low density polyethylene, ion meter (for example, Surlyn), or a layer of a copolymer of ethylene and methacrylic acid. In a preferred embodiment, resistant to damage layer is a layer of a copolymer of ethylene and vinyl acetate, preferably having a vinyl acetate content of about 9%.

It is clear that instead of the individual resins in different layers of the layered materials of the invention it is possible to use a mixture of resins, in particular in a layer capable of heat welding, and the layer resistant to damage.

When the core or intermediate layer or layers are present between the layer capable of heat welding, and a barrier layer, it (they) may be, for example, a copolymer of ethylene and vinyl acetate, a copolymer of ethylene and butyl acrylate, or a layer of a copolymer of ethylene and methacrylic acid. In a preferred embodiment, in the four-layer structure is used as the core of a copolymer of ethylene and vinyl acetate having a vinyl acetate content of about 9%.

In the six-plane structure described above, two of the intermediate layer or core, located between the layer capable of heat welding, and a barrier layer, edocfile first intermediate layer, or core, which is adjacent to the layer capable of heat welding, contains 18% vinyl acetate, and the second intermediate layer, or core, which is adjacent to the barrier layer, contains 9% of vinyl acetate. Resistant to damage layer of a copolymer of ethylene and vinyl acetate preferably contains about 9% of vinyl acetate. When the intermediate layer is between the barrier layer and resistant to damage layer, as for example in the six-plane structure described above, the intermediate layer may contain, for example, polyethylene, very low density. It is clear that in some cases, when there is an intermediate layer or core of polyethylene, very low density, it can lead to an unsatisfactory connection with a layer resistant to damage, such as a layer of ionomer if they do not use adhesive or bonding layer. It is clear that in such cases it is necessary to use a separate bonding layer, for example, containing a copolymer of ethylene and vinyl acetate modified with acid, or used in the core or intermediate layer of a mixture of polyethylene, very low density, and such a modified copolymer of ethylene and vinyl acetate. A copolymer of ethylene and vinylacetat what you can create, using standard equipment for extrusion and layer-by-layer formation of a film.

The invention provides a method of producing a film, comprising preparing a mixture in accordance with the invention, extruding the mixture to form a film and, optionally, orientation and/or crosslinking of the film. Multilayer films can be crosslinked by irradiation of the entire film. In a preferred embodiment, one or more layers of the multilayer film (substrate) ekstragiruyut and subsequently sew irradiation; and the barrier layer and other layers then ekstragiruyut on a substrate.

In a separate embodiment, using a tubular extruder, a layer capable of heat welding, and intermediate layers between the layer capable of heat welding, and a barrier layer, coextruded, and these layers are then irradiated with electrons to provide crosslinking and increase strength extruded layers. Typically, the irradiation is carried out with the use of high-energy electrons to provide a dose of 1 to 10 Mrad, preferably 3 to 7, for example about 4.5 Mrad. Crosslinking can also be carried out in a known way, using chemical cross-linking agents.

After irradiation the barrier layer and the remaining layers plait the Orient (for example, with a factor 3 to 5) in the longitudinal and transverse directions.

Orientation can, for example, be accomplished by using the known method of trapping bubbles, which is well known in this field. Extruded tubular film is cooled. Then, the tubular film is fed into the tub with hot water, subsequently remove it from the hot water, inflate and turn into a thin tube. The tubular film is rapidly cooled, and then roll for further processing. Preferably the orientation is carried out at 85 - 100oC, more preferably at 90 - 95oC. In accordance with the invention, the preferred heat-shrinkable film.

Films of the invention can be used to form packaging standard way. For example, when the film get in the form of a tubular film bags can be created by the transverse sealing and cutting aligned tubular film to obtain separate bags. Alternative bags you can get sharp longitudinal tubular film along one edge and then the transverse sealing and cutting the film for production of bags. There are other ways of getting bags and packages that can be easily lighting is in accordance with the invention, can be, for example, used for packing raw meat, poultry, fish, processed meat, and in some cases cheese. Barrier film according to the invention preferably have an oxygen permeability of less than 70 cm3/m2/ 24 h/ATM, measured in accordance with ASTM (American standard test method) D 3985, preferably less than 40 cm3/m2/ 24 h/ATM, while testing is carried out at a relative humidity of 0%, 23oC.

In the following examples, the heat resistance was determined using a Brabender mixer. The test temperature was 160oC. the First rotor speed was 63 rpm, the second rotor speed was 73 rpm Quantity of material within the mixing chamber was 60, the Mixing chamber before use was kondicionirovanie for 60 min at 160oC. After addition of the test sample in the mixing chamber the first sample was collected after 4 min, and subsequent samples were collected with 2-minute intervals until the decomposition of the tested samples. On thermal decomposition to be judged by the blackening of the tested samples.

Example. Used 2.5 inch polyvinylidenechloride extruder (equipped with a screw having a length to d was extrudible mixture, consisting of 68% of a copolymer of vinylidene chloride with vinyl chloride (vinyl chloride 22%, average mol. m 110000), 30% of a copolymer of vinylidene chloride with methyl acrylate (methyl acrylate 8,5%, average mol.m. 110000) and 2% epoxidizing soybean oil as a plasticizer.

During extrusion, the extruder is operated at the following temperatures: zone 1 60oC, zone 2 80oC, zone 3 115oC, the adapter 110oC.

The head of the extruder was maintained at a temperature of 155oC in the first test and 160oC in the second.

Received performance at both temperatures head 79 - 84 kg/h PVDC (polyvinylidenechloride). The mixture showed a thermal stability, as measured by the procedure described above, 7 - 8 minutes

Comparative example. Using the same procedure and equipment as in example I was extrudible mixture of a copolymer of vinylidene chloride with vinyl chloride, used in the example, with 2% epoxidizing soybean oil (A) and the copolymer of vinylidene chloride with methyl acrylate used in the example, with 2% epoxidizing soybean oil (B).

The temperature used in the extruder were as follows:

(A) zone 1 60oC, zone 2 95oC, zone 3 126oC, the holder 122ooC. the Performance obtained in the production of films A and B when using an extruder at a speed of 50 rpm was significantly lower than those obtained in the example. After 12 h of testing the performance of A was 60 kg/h Through 48 h test performance A was 65 kg/h the Performance obtained in the production of B, amounted to 68 kg/h

It is clear that the temperature required for extrusion of the materials A and B in the extruder and the holder between the extruder and head), higher than those needed in the sample, especially in the area of zone 3 of the extruder and the holder.

The mixture showed a thermal stability, as measured by the procedure described above, corresponding to 8 minutes (mixture A) and 6 to 7 minutes (mixture B).

The reasons for higher output when using the mixtures according to the invention is not entirely clear. The rheological data obtained from testing of mixtures A and B and mixtures used in the example shown in table. 1 and 2. The data are not in a relationship with extrusion results of the tests in the example and comparative example and not give instructions that advantageous results can be obtained from the point of view of performance and/or reduce t is CLASS="ptx2">

Conducted a series of experiments on determination of rheological properties using a laboratory Brabender extruder and associated instrumentation. The extruder had a diameter of 19 mm and was equipped with a 3-zone screw with a length to diameter 25:1 and a compression ratio of 4:1. The ratio of the lengths of the following areas: feeding zone 10 D (10 diameters), the pressing zone 3 diameter, area homogenization - 12 diameters.

This extruder is used for processing previously described 3 mixtures using 2 different temperature profile described for simplicity, in accordance with the temperature of the head of the extruder (150oC and 160oC, respectively), the results are shown in table. 1 and 2, respectively.

1. Copolymer mixture comprising 90 to 50 wt.% copolymer of vinylidene chloride with vinyl chloride and 10 to 50 wt.% copolymer of vinylidene chloride with methyl acrylate, wherein the amount of vinyl chloride in the copolymer mixture is more than 12 wt.%, and the number of methyl acrylate is less than 2.8 wt.%.

2. The mixture under item 1, characterized in that it contains 75 to 65 wt.% copolymer of vinylidene chloride with vinyl chloride and 25 to 35 wt.% copolymer of vinylidene chloride with methyl acrylate.

3. The mixture is about 30 wt.% copolymer of vinylidene chloride with methyl acrylate.

4. Mix on PP.1, 2 or 3, characterized in that the copolymer of vinylidene chloride with vinyl chloride contains 20 to 24 wt.% vinyl chloride and 80 76 wt.% vinylidenechloride.

5. The mixture according to any one of the preceding paragraphs, characterized in that the copolymer of vinylidene chloride with vinyl chloride is saying.m. 90000 - 140000.

6. The mixture according to any one of the preceding paragraphs, characterized in that the copolymer is vinylidenechloride and methyl acrylate contains 7.5 to 8.5 wt.% of methyl acrylate and 91.5 - of 92.5 wt.% vinylidenechloride.

7. The mixture according to any one of the preceding paragraphs, characterized in that the copolymer of vinylidene chloride with methyl acrylate has a mol.m. 100000 - 120000.

8. The mixture according to any one of the preceding paragraphs, characterized in that it contains 1 to 5 wt.% plasticizer and/or stabilizer.

9. The mixture under item 8, characterized in that it contains about 2 wt.% plasticizer and/or stabilizer.

10. The mixture according to any one of the preceding paragraphs, characterized in that it contains as a plasticizer and/or stabilizer epoxydecane soybean oil.

11. Multi-layer film, capable of containing the heat welding layer, the barrier layer containing copolymer mixture, and a layer resistant to damage, tragicomic points.

12. Film on p. 11, characterized in that it is heat-shrinkable.

13. The package or bag, characterized in that it is formed of a multilayer film according to p. 11 or 12.

14. A method of obtaining a multilayer film, which contains able to heat welding layer, the barrier layer containing copolymer mixture, and a layer resistant to damage, which includes obtaining the barrier layer, the extrusion of the layers of the multilayer film and, optionally, orientation and/or crosslinking of the film, characterized in that the copolymer mixture in the barrier layer is a copolymer mixture according to any one of paragraphs.1 - 10.

15. The method according to p. 14, wherein the one or more layers of the multilayer film ekstragiruyut for the formation of the substrate, the substrate is irradiated and the barrier layer and the layer resistant to damage, ekstragiruyut irradiated on the substrate.

 

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