Biaxially stretched oriented heat-shrinkable multilayer film

 

(57) Abstract:

Describes biaxially stretched oriented heat-shrinkable multilayer film comprising the oxygen barrier of the Central layer made of a mixture containing a copolymer of ethylene and vinyl alcohol and polyamide intermediate adhesive layer made of adhesive-based polyethylene modified with maleic anhydride, and outer layers of polyolefin having a density < 0,914 g/cm3, characterized in that the Central layer is made from a mixture containing 70-85 wt.% copolymer of ethylene and vinyl alcohol with a melting point of 162 - 178oC and a content of ethylene 36-44 wt.% and 15-30 wt.% polyamide constituting the copolymer poly-caprolactam from nylon, obtained from adipic acid and a diamine, the content of poly-caprolactam in the copolymer of 85 mole%, moreover, the thickness of the Central layer is of 1.27-2,54 µm and the permeability of oxygen through the layer of < 35 cm3/m2/24 h, each intermediate adhesive layer is made of a mixture containing 35-80 wt.% copolymer of ethylene c - olefin, having a density of < 0,914 g/cm3, 20-40 wt.% adhesive polyethylene-based, modified what Etat, modified maleic anhydride, melt index < 0.5 g/10 min and not more than 40 wt.% copolymer of ethylene and vinyl acetate with a melt index not > 1 and a vinyl acetate content of 7-15 wt.%, the mixture has an average melt index and the average melting temperature below the melting temperature of the polymer mixture of the Central layer, and the thickness of each adhesive layer is 2.5-5 % of the film thickness, the first outer layer is slotermeerlaan and made of polyolefin having a density < 0,914 g/cm3with additional content of a copolymer of ethylene with vinyl acetate is not more than 45 wt.%, having a melt index not > 1 and a melting point below the melting temperature of the polymer mixture of the Central layer, with a thickness of 40-70 % of the film thickness, and the second operational resistant outer layer made from a polyolefin having a density < 0,914 g/cm3with additional content of a copolymer of ethylene with vinyl acetate is not more than 45 wt.%, having a melt index not > 1 and a melting point below the melting temperature of the polymer mixture of the Central layer, with a thickness of 20-35 % of the film thickness, and at least one of the outer layers has a temperature of PCR>With in the transverse direction and the total film thickness of 38.1-88,9 mm. The technical result - receiving film having a heat shrinkage and physical properties equivalent to the properties of the films with a barrier layer based on vinylidenechloride copolymer used in the packaging of fresh red meat. 17 C.p. f-crystals, 2 ill., 14 table.

The invention relates to a biaxially stretched multilayer film having a thermal shrinkage and a Central layer of a copolymer of ethylene with vinyl alcohol (EVOH) having a protective oxygen of the property, such as, for example, which are used for food packaging.

Thermoplastic film used for many years for packaging various products, including food products such as fresh red meat. The latter often in the form of large pieces /varietal cuts/ that are placed in bags made of thermoplastic films, which vacuum and sealed, for example, by heating the opposite surfaces of the package with the open end and pressing the inner surfaces together for welding.

Received packages containing food products shipped from meat processing enterprises of the major pieces for the roving package. These packages containing food products must ensure anoxic conditions in turning a sufficient period of time such as 4 to 6 weeks, so the technique of film packaging provides the multilayer film with the Central layer, which is a protective oxygen material. The most commonly used protective oxygen materials are copolymers of vinylidenechloride with various comonomers, such as vinyl chloride /copolymer VC - VDC /or methacrylate/ MA copolymer - VDC/. Other well-known materials that are protective oxygen materials include polyamides and copolymers of ethylene with vinyl alcohol /EVH/.

In addition to the protective oxygen function, thermoplastic film meets a number of other requirements, such as operational stability and voltage in the process of packaging and processing, attractive uniform appearance with no streaks and good optical properties to a valuable food product, such as high-grade cuts of fresh red meat, could be periodically visually inspected to ensure that the packaging is not lost integrity. Therefore, good optical properties include low turbidity and high gloss.

Another physical quality of suitable thermoplastic films for packaging the oxygen-sensitive products, such as fresh red meat, is that the strap must have a heat shrinkage in the direction of processing (/MD/ in the longitudinal direction and in the transverse direction of /th/.

It is necessary that the film package containing a food product, could be vacuumed on the inside of the film, falling along the outer surface of the food product, and is then heated, for example by a stream of hot water in tunnel apparatus for heat shrinkage of the fallen film and to provide a sealed package.

Because of these numerous requirements, thermoplastic films usually contain p is illenium on one side of the Central layer, and termoskleivaniya (welded) layer on the other side of the Central layer.

Still commonly used multi-layer film for packaging fresh red meat was a three-layer film comprising a barrier layer of a copolymer of vinylidenechloride and polyolefin layers from opposite sides, most typically, the layer of the operating mixture of polyethylene-ethylene vinyl acetate /EVA/ and heat-sealed layers. The preferred polyethylene is a polyethylene, very low density /VLD PE/, which is also referred to as polyethylene, ultra low density /ULD PE/, and linear low-density polyethylene /LLD PE/.

In part, because of increased requirements for placement of incinerated waste without generating a chlorine-containing gases, we need to search the oxygen barrier film nejarenogo type.

Another reason why you need to replace the oxygen barrier layers copolymers vinylidenechloride type is their well-known tendency to partial degradation and yellowing while keeping them at sufficient doses. Crosslinking by irradiation is usually carried out to improve the puncture resistance of polyethylene in the inner and outer layers or improve PR is adowanie stable bubbles of the primary tube to expand the field of welding of the inner layer, or a combination of the above possibilities. If the copolymer VC-VDC be irradiated with a dose of 5 Mrad material partially destructively and appears yellow tint which is undesirable.

A copolymer of ethylene with vinyl alcohol /EVOH/ known for many years as suitable protective oxygen material, and in fact is commercially used material for packaging food products, such as, for example, in the systems of heat treatment, where fresh product is placed into a package that vacuum and sealed. The package is then placed in hot water and the food product is cooked in a block /cooked in situ/. After cooking package cooled down and stored at low temperature until the moment when it is ready for use. In General, these subjected to heat treatment packing does not require thermal shrinkage to a condition which is required on the market of fresh red meat and not subject to physical operation of the packaging of fresh red meat.

It is known that film with a protective oxygen layer on the basis of EVOH, was not widely used in industry for packaging, storage and transportation of fresh red meat. One of the reasons is that EVOH is much more sensitive to contact with moisture than vinylidenechloride in conditions of high humidity. This means that the EVOH layer must be extremely well protected against the penetration of moisture from the stored product through the inner layer/and/ and also from the atmosphere through the outer layer of/and/.

Another reason why EVOH is not widely used as a protective oxygen layer in thermoplastic bags for packaging fresh red meat, is that its adhesive properties to the mixtures of polyethylene-EVA essentially inferior vinylidenechloride the copolymers. While the latter may be directly attached to the mixtures of polyethylene-EVA with sufficient strength by keeping the forces of separation in the process of shrinking, it is impossible with oxygen barrier layers on the basis of EVOH. Instead, you must add an additional layer between the barrier layer and the operational or heat-sealable layers. These additional layers are known to act as an adhesive or bonding layer and the function layer of adhesive between the layer of EVOH and /external/ layer with operational resistance or /internal/ heat-sealable layer in the package made from the laminated thermoplastic film. The materials forming these adhesive layers, is is therefore expensive. In addition, they increase the complexity and cost of the manufacturing process.

Another reason why EVOH multilayer films do not replace vinylidenechloride copolymer film, is that the former are much more sensitive to the conditions of biaxial orientation and scope satisfactory conditions of processing much already.

Another reason why the oxygen-barrier layers on the basis of EVOH not replace vinylidenechloride layers, is that the cost of the EVOH resin is much higher. Typically, the layer of EVOH in now known multilayer films comprises about 8 to 20% of the total film thickness and is the most expensive material in the film.

U.S. patent N 4407897 describes a multilayer film comprising EVOH Central layer, the intermediate modified polyolefin adhesive layers and polyolefin outer layers.

U.S. patent N 4495897 describes biaxially stretched, heat-shrinkable multilayer film comprising a mixed Central layer based on EVOH-nylon, intermediate adhesive layers obtained from polyethylene, a modified carboxylic acid, and the outer layers from a mixture of EVA-LLDPE.

U.S. patent N 4557780 describes D50 - 100% EVOH in the form of a Central layer, an intermediate adhesive layers obtained from polyolefins modified with carboxyl groups, and outer layers, comprising 40 to 100% EVA and 0 - 60% LLDPE.

U.S. patent N 4615926 describes a multilayer film, comprising a Central EVOH-nylon layer, an adhesive intermediate layers based on olefins, ionomer resin inner layer and the outer plastic layer.

U.S. patent N 4758463 describes a three-layer biaxially stretched heat-shrinkable film suitable for thermal processing of meat and contains the Central EVOH-nylon layer and outer layers comprising a blend of EVA and EVA with functional anhydrite group as an adhesive connection. This type of film is not suitable for use in the packaging of fresh red meat because of its relatively low resistance to puncture and relatively high cost of VOH Central layer.

U.S. patent N 4851290 discloses a three-layer irradiated film for keeping food filled while hot and then cooled with cold water in the cooling drum and the further stages of cooling, comprising a Central layer of nylon 6,12 or nylon 6,66 and outer layers, consisting of his.

U.S. patent N 4857399 describes a four-layer biaxially stretched heat-shrinkable film suitable for the non-adhesive thermal processing of meat, containing as a Central barrier layer of EVOH-polyamide, a mixture of EVA and ethylene copolymer modified with anhydride as an adhesive for external operational layer on one side of the barrier layer, EVA-anhydride-modified ethylene copolymer mixture as a layer on the other side of the Central barrier layer, and the inner or contact with the meat layer, including a statistical copolymer of ethylene with propylene.

U.S. patent N 5075143 describes deviational film containing as a Central EVOH layer, an intermediate EVA layers, adhesive layers based on chemically modified polyolefin and water-resistant layers on the basis of ionomer or VLDPE. The outer layers are VLDPE welding layer inside and a heat resistant HDPE layer from the outside.

Known biaxially stretched oriented heat-shrinkable multilayer film comprising the oxygen barrier of the Central layer made of a mixture containing a copolymer of ethylene and vinyl alcohol and polyamide intermediate adgezivnuu polyolefin, having a density of < 0,914 g/cm3(U.S. patent N 5004647, CL 32 In 7/12, 1991).

This type of film is not suitable for use in the packaging of fresh red meat because of its poor optical properties and relatively low shrinkage.

An object of the invention is the provision of biaxially stretched multilayer film having a shrink with the oxygen barrier layer on the basis of EVOH and having physical properties at least equivalent properties of films with a barrier layer based on vinylidenechloride copolymer, currently accepted for packaging fresh red meat.

Another objective is the provision of such a film with a barrier layer on the base with EVOH barrier layer, essentially thinner than the well-known multilayer films of EVOH type proposed for the packaging of fresh red meat.

Another objective is the provision of such a film with a barrier layer of EVOH containing less than six layers.

Another objective is the provision of such a film with a barrier layer of EVOH with optical properties at least equivalent properties of multilayer films with a barrier layer based on vinylidenes fact, in biaxial oriented heat-shrinkable multilayer film obtained by the method of extrusion with dual blown and consisting of an oxygen-barrier Central layer made of a mixture containing a copolymer of ethylene and vinyl alcohol and polyamide intermediate adhesive layer made of adhesive-based polyethylene modified with maleic anhydride, and outer layers of polyolefin having a density < 0,914 g/cm3the Central layer is made from a mixture containing 70-85 wt.% copolymer of ethylene and vinyl alcohol with a melting point of 162oC to 178oC and a content of ethylene 36-44 wt.% and 15-30 wt.% polyamide constituting the copolymer poly-caprolactam from nylon, obtained from adipic acid and a diamine, the content of poly-caprolactam in the copolymer of 85 mole%, moreover, the thickness of the Central layer is of 1.27-2,54 µm and the permeability of oxygen through the layer of < 35 cm3/m2/24 h, each intermediate adhesive layer is made of a mixture containing 35-80 wt. % of copolymer of ethylene-olefin, having a density of < 0,914 g/cm3, 20-40 wt. % adhesive on the basis of polyethylene modified with maleic anhydride, with index RA anhydride, with melt index < 0.5 g/10 min and not more than 40 wt.% copolymer of ethylene and vinyl acetate with a melt index not > 1 and a vinyl acetate content of 7-15 wt. %, the mixture has an average melt index and the average melting temperature below the melting temperature of the polymer mixture of the Central layer, and the thickness of each adhesive layer is 2.5-5% of the film thickness, the first outer layer is slotermeerlaan and made of polyolefin having a density < 0,914 g/cm3with additional content of a copolymer of ethylene with vinyl acetate is not more than 45 wt.%, having a melt index not > 1 and a melting point below the melting temperature of the polymer mixture of the Central layer, with a thickness of 40-70% of the film thickness, and the second operating-resistant outer layer made from a polyolefin having a density < 0,914 g/cm3with additional content of a copolymer of ethylene with vinyl acetate is not more than 45 wt.%, having a melt index not > 1 and a melting point below the melting temperature of the polymer mixture of the Central layer, with a thickness of 20-35% of the film thickness, and at least one of the outer layers has a melting point of at least 105oC, and the film microns.

Both the outer layer chemical composition can be identical to each other.

Each outer layer may be made of a mixture containing 60-75 wt.% the copolymer of ethylene-olefin, having a density of < 0,914 g/cm3and 25-40 wt.% copolymer of ethylene with vinyl acetate.

At least one of the outer layers may be made of a mixture containing 40-60 wt. % of copolymer of ethylene-olefin, having a density of < 0,914 g/cm3, 50-20 wt. % plastomeric copolymer of ethylene with a-olefins and 20-40 wt. % of a copolymer of ethylene and vinyl acetate having a vinyl acetate content of 7-15 wt.%.

A copolymer of ethylene and vinyl alcohol may contain 38 wt.% ethylene and having a melt index of 0.8 g/10 min.

The adhesive may be a linear low density polyethylene, modified maleic anhydride.

A copolymer of ethylene - olefin, having a density of < 0,914 g/cm3may be 45-60 wt.% the intermediate adhesive layers.

Adhesive modified with anhydride may be 25-35 wt.% the intermediate adhesive layers.

The copolymer of ethylene and vinyl acetate may be 10-20 wt.% the intermediate adhesive layers.

In the film otnesti < 0,914 g/cm3and a melt index < 1, 15-22 wt.% copolymer of ethylene and vinyl acetate with a melt index of 0.25 g/10 min and a vinyl acetate content of 10 wt.% and 25-35 wt. % adhesive based on low density polyethylene modified with maleic anhydride.

Adhesive modified with anhydride, an intermediate adhesive layer may be a copolymer based on ethylene and vinyl acetate having a melt index of 0.25 g/10 min and a vinyl acetate content amounts to 10 wt.%.

The adhesive may have a melt index < 1.

The film can be irradiated at doses of 1-10 Mrad.

The Central layer can be formed from mixtures containing 78-82 wt.% copolymer of ethylene and vinyl alcohol and 18-22 wt.% copolymer of nylon 6 and nylon 66.

Each outer layer may be made of a mixture containing 65-72 wt.% copolymer of ethylene with alpha-olefin, having a density below 0,914 g/cm3and the melt index is 0.19 g/10 min, and 28-35 wt.% copolymer of ethylene and vinyl acetate with a vinyl acetate content of 10%.

Each outer layer may be made of a mixture containing 42-46 wt.% copolymer of ethylene with alpha-olefin, having a density below 0,914 g/cm3and 34-38 wt. % ACPs the density 0,80, melt index of 1.4 g/10 min and a melting point 71oC.

The first outer layer may include ion meter.

The film may have at least 20% of the free shrinkage at 90oC in the longitudinal direction of processing.

The film may have at least 35% free shrinkage in both directions, longitudinal and transverse.

The film according to the invention meets all the above requirements. For example, its physical properties are at least equivalent to films with a barrier layer of vinylidenechloride copolymer, currently used for packaging fresh red meat. In addition, this film contains a barrier layer based on EVOH, which is essentially thinner than the known multilayer films are known EVOH type proposed for the packaging of fresh red meat.

This film requires no more than five layers and has optical properties at least equivalent to the properties of multilayer films with a barrier layer based on PVDC, currently used for packaging fresh red meat. In addition, this film has a relatively high thermal shrinkage and resistance to puncture required for packaging of svezhego description.

Fig. 1 and 2 represent logarithmic graphs melt index depending on the percentage of polymer with a higher melt index in mixtures.

Thus, the multi-layer film according to the invention is biaxially stretched heat-shrinkable film. In other words, the film has unlimited shrinkage with nezadelannyh ends (unterstrained shrinkage) at least thirty /30/ percentage in the transverse direction, measured at 90oC /194oF/, and preferably at least twenty /20/ percentage shrinkage with nezadelannyh ends in the direction of processing. Most preferably the film has a shrinkage with nezadelannyh ends at least thirty /30/ percent in both directions.

To measure the magnitude of the shrinkage of thermoplastic film and comparing it with these definitions shrinkage film nezadelannyh ends measured way, taken from ASTM D 2732 after immersion in a water bath at 90oC for five seconds. Four of the test specimen cut from this sample film for testing. Samples cut to 10 cm in the process direction and 10 cm in the transverse direction. Each sample is completely immersed for 5 seconds in a water bath at 90oC. Polresta, praterinsel shrinkage, and the original 10 cm make multiples of 10 to get the percentage of shrinkage of the sample. Shrinkage for the four sample average to estimate the shrinkage of the sample film in the MD /in the machine direction and the shrinkage for the four samples is the average for the magnitude of shrinkage in TD /cross/.

When using the polymer mixture in any listed five layers of film and the melt index is an important physical characteristic of the layer, it is defined in terms of "average melt index". For this polymer mixture, this average index was determined from Fig. 1 and 2, which represent the logarithmic graphs of melt index on one axis (for example, y/ and the percentage of polymer with a higher melt index in the mix on another axis /for example, x/. The melt index of component parts of the polymer measured according to the procedure given in ASTM d 1238 at 190oC, unless otherwise noted, and in grams per 10 minutes, the stage in this way to determine the average melt index of two-component mixtures are the following:

1. Be plotted on the chart the value of the melt index of the component with a lower melt index, respectively, 0% on-axis percentage of whom the KSA melt component with a higher melt index, respectively, 100% on-axis the percentage of the component with a higher melt index in the mix /point/.

3. To connect two points with a straight line.

4. The average melt index of the mixture is determined by finding the point on the straight line, which corresponds to the percentage of the component with a higher melt index in the mixture.

If the mixture contains three components, the average melt index of the two components is defined as described above. The average melt index of these two components is then applied on the graph relative to the third component as described in stages 1 and 2 above. From a straight line connecting two points, the average melt index of the third component of the mixture can be determined by the point on the line that corresponds to the percentage content of component/tov/ highest index in the mixture. If the average melt index drugcompanies mixture is higher than that of the third component, the average melt index of the two components used in the form of percentage most of vysokoplavkogo component in the mixture, and represent graphically, respectively.

Determining an average melt index for a binary mixture, using Fig. 1, is illustrated as follows.

The mixture contains 40 wt.% EVA having a melt index of 0.25 and 60% of the adhesive on the left side of the scale of the ordinate, corresponding to 0% of the adhesive. The melt index of the adhesive is applied in the form of dots on the right side of the scale of the ordinate corresponding to 100% of the adhesive. Two points connected by a straight line. The average melt index of the mixture is determined by finding the point on this line, which corresponds to 60 wt.% adhesive on the abscissa, i.e., about 0.88 g/10 min.

Determination of melt index for the three-component mixture using Fig. 2, is illustrated as follows.

The mixture contains 52,5% VLDPE having a melt index of 0.5, 17.5 wt.% EVA having a melt index of 0.25, and 30% of the adhesive on the basis of LLDPE modified with anhydride, having an index of 0.8. The melt index of the EVA put the dot on the left side of the scale of the ordinate corresponding to 0% of the adhesive. The melt index VLDPE is applied in the form of dots on the right side of the scale of the ordinate corresponding to 100% VLDPE. Two points connected by a straight line. The average melt index for a mixture of EVA - LLDPE is determined by finding the point on this line, which corresponds to 79% VLDPE on the abscissa, i.e. approx 0.42 g/10 min This value is applied in the form of a point on the left side of the scale of the ordinate corresponding to 0% of the adhesive. The melt index of the adhesive is applied in the form of a point on Prava side of the scale of the ordinate corresponding to 100% adhesive /0,8/the points on this line, which corresponds to 30% of the adhesive on the abscissa, i.e., 0.50 g/10 min.

When the polymer mixture used in any listed five layers of film, and the melting temperature is an important physical characteristic of the layer, it is defined in terms of "average melting point". For this polymer mixture this value is calculated by adding the individual works of the melting temperature of the polymers and their proportion in the mixture, i.e., the melting point of the polymer 1, multiplied by its share in the mix, plus the melting point of the polymer 2, multiplied by its share in the mix, plus the appropriate factor for any of the other components in the mixture.

The phrase "fractional" means that the melt index of the polymer alone or the average melt index of the polymer mixture does not exceed about 1.

The terms "barrier" or "barrier layer" as used here means a layer of a multilayer film, which acts as a physical barrier to gaseous oxygen molecules. Physically, the material of the barrier layer will reduce the oxygen permeability of the film used to produce the package to less than 70 cm3per square meter in 24 hours at one atmosphere 73oF /2 CLASS="ptx2">

The expression "ethylene-vinyl acetate copolymer" /EVA/ as it is used here, refers to a copolymer obtained from ethylene and vinyl acetate monomers, in which the units derived from ethylene /monomer units, the copolymer are present in large quantities /bulk/ and units derived from vinyl acetate /monomer units, the copolymer are present in smaller bulk quantities.

The expression polyethylene, very low density VLDPE /sometimes referred to as a polyethylene, ultra low density /"ULDPE"/ refers to linear and replacement the polyethylene having a density below about 0,914 g/cm3and according to at least one manufacturer, possibly as low as 0,86 g/cm3. This expression does not include copolymers of ethylene with alpha-olefins with densities below about 0,90 g/cm3with elastomeric properties and is at least one manufacturer to "plastomers of ethylene with alpha-olefins". However, as explained later, blastomere of ethylene with alpha-olefins can be advantageously used in the practice of this invention in the form of the minimum component of some of the layers of this multilayer film. VLDPE does not include linear low density polyethylene /LLDPE/, the specific copolymer/ ethylene with alpha-olefins, usually 1-butene, 1-hexene or 1-octene, and in some cases triple copolymers, such as ethylene, 1-butene and 1-hexene. A method of obtaining a VLDPE /polyethylene/ described in the European patent N 120503.

As for example, described in U.S. patent 4640856 and in U.S. patent 4863769, VLDPE /polyethylene/ capable of being used for biaxial oriented films, which have better properties compared to films of LLDPE /polyethylene/. These best properties include higher shrinkage, higher ultimate tensile strength and great resistance to puncture.

Appropriate VLDPE /polyethylene/ include polyethylene, produced by Dow Chemical Company, Exxon Chemical Company and Union Carbide Corporation and has the following physical properties in the form of resins according to the manufacturers, are summarized in table A.

EVOH is obtained by hydrolysis or saponification/ copolymer of ethylene and vinyl acetate and the copolymer has, as is well known, an effective oxygen barrier properties, hydrolysis-saponification should be almost full, i.e., at least 97%. EVOH is commercially available in the form of resin with different ethylene content and there is a direct relationship between the ethylene content and temperaturemonitor melting between 162oC and 178oC. This is true for EVOH materials having the ethylene content from about 38 mol.% up to about 44 mol. %. It was found that when using the Central layer of a polymeric mixture of EVOH materials with melting points below this area, in the Central layers will not have sufficient oxygen barrier properties to obtain a product with satisfactory heat shrink thin Central layer. For this reason, EVOH materials with ethylene content of about 48 mol.% and above /resulting in melting point below about 162oF/ is not suitable for practical use of this invention as will be demonstrated in the sample 1 /sample 1/.

On the other hand, it was found that the EVOH materials with melting temperatures higher than the above areas are also hard and difficult to stretch in the process of double orientation of the multilayer films according to the invention. Thus, EVOH with an ethylene content of about 32 mol.% and below is not suitable for the present invention. For this reason, it is preferable EVOH with 38 mol.% of ethylene.

EVOH materials vary by melt index, even with the same ethylene content. For example, EVOH mainname at 190oC according to ASTM D 1238/. Although the melt index is not limiting in selecting the appropriate EVOH materials, preferred are the most high melt indexes, because the ending of the film is softer and easier to stretch under biaxial orientation. For this reason, preferred for use in the polymer mixture are EVH materials with melt index of 8.4 with ethylene content of 38 mol.% for multilayer films of the Central layer.

Typical EVOH materials for use in this invention are presented in table Century.

It was found that the film according to the invention as polyamide can be applied only nylon 6,66 in the polymer mixture as an oxygen barrier layer. Nylon 6,66 is a copolymer of nylon 6 and nylon 66. Nylon 6 is polyaminopropyl. Nylon 66 polymer is derived from adipic acid and a diamine. Nylon 6,66 produced by different companies, in some cases, with different percentages of the two monomers, possibly in different ways and mostly with various operating parameters. Thus, the properties of the various copolymers of nylon 6,66 can significantly replicates the AK will be illustrated in example 2, if you use other nylon, such as nylon type 6,12 as polyamide in the polymer mixture for oxygen barrier layer, the Central layer, five-layer film develops the gel and in some cases cracks. The formation of gels may be due to incompatibility or chemical reaction between the two polymers EVOH-nylon 6,12. Cracks are likely to develop because the polymer mixture is stretched unevenly during orientation. Physical properties typical Nasonov are summarized in table C.

It must be borne in mind that the Central oxygen barrier layer film according to the invention includes a polymer mixture consisting of about 70 to 85 wt.% EVOH and from about 15 to about 30 wt.% nylon 6,66. If you use less than 15 wt. % nylon 6,66, the Central layer tends to crack /sometimes explained as "linear extension" /"line-drawing"/ greater than under uniform tension during biaxial orientation. This is partly because EVOH is relatively fragile. In addition, the EVOH may be extended only in a relatively narrow temperature region. In the polymer mixture of the Central layer should not be used more than about 30 wt.% nesetsja polymer mixture, containing from about 78 to 82% EVOH and about 18-22% nylon.

Can be used a variety of copolymers of ethylene with vinyl acetate, having a fractional melt indexes of at least the second and third intermediate adhesive layers and having a vinyl acetate content from about 7 to about 15% of the total weight of the copolymer. Lower vinyl acetate content than in this area gives rigidity and lack of elasticity of the copolymer. Increasing the VA content leads to excessive softness of the copolymer. The vinyl acetate content in the region of 8 to 12 wt.% is preferable from the viewpoint of processing AIDS and strength. Appropriate include EVA copolymers listed in table D. because at least five-layer film of this invention requires that at least one of the fourth and fifth outer layers had a melting point of at least 105oC, it will be apparent from table D and demonstrated in example 2, /G/, that both of these layers may not include 100% of these EVA.

As mentioned previously, the second and third intermediate adhesive layers in contact with the opposite sides of the oxygen barrier of the Central layer, and each includes mainly a mixture of two components: 35 - 80 is idream with melt index below about 1.7, or b/ adhesive based on EVA modified with anhydride with a melt index below about 0.5. The content of the third optional component is from 0 to about 40 wt.% EVA with a fractional melt index, containing from about 7 to about 15 wt.% vinyl acetate. Two or three-component mixture comprising the second and third intermediate adhesive layers have a fractional melt index, as well as the average melting temperature below the melting temperature of the polymer mixture of the Central layer.

Table E is a partial list of the used adhesives based on copolymers of ethylene-modified anhydride in the above examples.

Five-layer film according to the invention can be manufactured by extrusion of all layers simultaneously, i.e. coextruding as, for example, described in U.S. patent N 4448792 or Paladino, i.e., the method of layering with a preliminary coating described in U.S. patent N 3741253, with the formation of a relatively thick primary film or in the form of a flat sheet or in the form of a tube, the most widely used of the latter. This primary and a relatively thick film of biaxially oriented well-known way of capturing injection blow or double injection blow to the extrusion head is cooled, flatten and then preferably oriented re-heating and re-inflate with the formation of secondary bubbles. The evaluation is preferably biaxially oriented, with a transverse orientation /TD/ accompanied by inflating with the radial expansion of the heated film. Orientation towards treatment /MD/ preferably accompanied by the use of clamping rollers rotating at different speeds, for separation and pulling of the film tube in the direction of processing.

The ratio of stretching in the biaxial orientation for the formation of the packaging material is sufficient to provide the film with a total thickness of from about 1.5 to 3.5 mils /38,2 - 89,1 mcm/. The stretch factor MD is usually 3 - 5 and the stretch factor AP also is usually 3 - 5. The overall stretch factor /MD tensile multiplied by the TD stretching/ about 9ץ - 25x is appropriate.

The preferred method for obtaining the multilayer film is coextruded primary tube, which is then biaxially oriented by the method described in the aforementioned U.S. patent N 3456044. In the following examples, all five layers have coextrudable and the main pipe has cooled. biaxial orientation of the air bag /air cushion/, which itself was heated cross flow through a heated porous tube located concentrically around the moving core tube.

It was determined that in the process of biaxial orientation relative to the low degree of the bulge provides a higher magnitude of shrinkage than the relatively high degree of the bulge, when you get a five-layer film of this invention. For example, using basic flat tube width of about 8 cm /3 and 1/8 inches/ in each example, the ratio of the blown 4.6 get the film shrinkage of 21% MD /32% TD/. With a blowing ratio of 3.3, the same film has a shrinkage 31% MD /39% TD/ 90oC.

Although insignificant, it is preferable to complete the stitching of the whole film to expand the scope of welding the inner and outer layers. This is preferably achieved by electron beam irradiation with the dose levels at least about 1 Mrad /MR/ and preferably in the region of 3 - 5 MR, but can be applied to higher doses. The irradiation may be performed on the main tube or after biaxial orientation. The last named post-irradiation, is preferred and is described in U.S. patent N 4737391. The advantage of post-irradiation is that the relatively thin square is level processing. A possible advantage of the pre-irradiation oriented tubes is that if the technologist uses the material for the protective layer, which has a tendency to yellowing when exposed, as for example, a copolymer of vinylidenechloride-vinyl chloride, then this problem can be avoided by irradiation of only the substrate layer.

Or crosslinking can be achieved by adding agent, reinforcing the stitching, to one or more layers, such as described in U.S. patent N 4055328. The most commonly used agents, reinforcing stitching, are organic peroxides, such as trimethylpropane and trimethylacetate.

From the following description it will be seen that five-layer film according to the invention has a very thin Central layer from a mixture of EVOH-nylon 6,66, with a thickness of about 0.05 to 0.1 mil /1,27 - 2,54 µm/, which still provides the oxygen permeability of less than 35 cm2/m2/the Last 24 hours is a characteristic required for shrink packaging of fresh red meat. This is achieved essentially a thinner protective layer containing relatively expensive EVOH than previously proposed film of this type. However, the total film thickness is from about 1.5 to about 3.5 Mirena for packaging fresh red meat.

The second and third adhesive layers of this film are the most expensive components and each of them is only from about 2.5 to 5% of the film thickness.

The fourth and outermost layer of the film becomes the inner layer of a packet received from a film, and is in direct contact with the Packed food product. This layer is from about 40% to about 70% of the film thickness and, as the most thick layer, provides the bulk of the film is required shrinkage properties. The inner surface of the fourth layer is also slovaryami, i.e., the inner surface of the welded together after degassing containing meat package. The thickness of the inner layer of the package should be at least about 40% of the total film thickness to prevent burning during the welding process. On the other hand, the fourth layer should not contain more than about 70% of the film thickness, because the fifth layer /which becomes the outer layer of the package/ must have sufficient mass for operational durability and resistance to puncture from external contacts. As such, the fifth layer contains from about 20% to about 35% of the film thickness. On the contrary, if the thickness of the fifth layer exceeds 35% of the it layer of the package.

The Central barrier layer based on a mixture of EVOH-nylon 6,66 this film has a relatively high average melting temperature. In this context, is relatively high to a relatively low average temperature/frames/ melting a mixture of/this/ that include the second and third intermediate adhesive layers, as well as to the relatively low melting temperature of the fourth and fifth outer layers. These relatively low melting temperature should be low enough for film shrinkage of at least 30% at the 90oC in the transverse direction and preferably at least 20% in the process direction. This is a requirement for shrinkable package, vacuum and sealed, containing meat in relation to the outer surface of the meat, due to the motion through the usual tunneling apparatus for shrink-heated hot water.

Example 1

This series of tests demonstrates the importance of using EVOH having a melting point of about 162oC to about 178oC and the ethylene content from about 36 to about 44 mole% in the polymer mixture of the Central layer, five-layer film. A mixture of six different Central layers each comprising 80% EVOH and 20% nylon 6,66, such key layers and identical to the fourth and fifth outer layers. Thickness in mils / or percentage of the total film thickness / 1 - 5 layers were as follows: 0,08 /3/; 0,08 /32/; 0,08 /3/; 1,72 /65/; 0,69 /26/. Sample 1 had a somewhat different intermediate and outer layers from samples 2 to 6. For sample 1 the second and third intermediate layers were 53% DEFD 1192 type VLDPE, 30% Plexar 3741 adhesive and 17% DQDA 6833 type EVA, and the average melting temperature was 116oC. Fourth outer layer was 100% DQDA 6833 type EVA and fifth outer layer was 76,5% DQDA 6833 type EVA, 19.1% of DFFD 1192 type VLDPE and 4.4% processing additives. For samples 2 to 6 the second and third intermediate layers were 52,5% Attane XU61509.32 type VLDPE 30% Plexar adhesive 3779 and 17.5% DQDA 6833 type EVA and their average melting temperature was 116oC. the Fourth and fifth outer layers were 70,6% DEFD 1192 type VLDPE, 25% DQDA 6833 type EVA and 4.4% processing additive. Their average melt index was 0.25 g/10 min and their weighted average melting temperature was 115oC.

Observed optical properties and some examples were measured gloss. Measured physical properties, i.e.,% shrinkage and dynamic puncture resistance. The results of these tests are summarized in table F.

Sample 2 with 80% EVOH containing 38% of ethylene and 20% nylon 6,66 as a Central layer,WA EVOH from the same manufacturer /8,4 against 3.8/, provided the best view and a bit more shrinkage. This illustrates the advantage of material such as EVOH with 38% ethylene content and melt index 8 in the Central layer of the multilayer film. Samples 4 and 5 were included EVOH with 38% ethylene content from different manufacturers and have good properties. The melting temperature of these copolymers was 173oC. These data confirmed that the melting point of about 178oC is the upper limit for EVOH oxygen barrier of the Central layer in the multilayer film of the present invention. If the melting point of EVOH exceeds a temperature of about 178oC and the ethylene content in it is lower than about 36 wt.%, the hard material is stretched at temperatures orientation suitable for the second to fifth layers with a much lower melting temperature. The result is that the heat shrinkage of the film is unexpectedly low for packaging fresh meat.

Sample 6 was included type EVOH with 44% of ethylene, a variant of the EVOH of the invention with a relatively low melting point, i.e., 164oC.

Sample 1 type EVOH with 48% of ethylene and melting point 158oC provided satisfactory optical, shrinkage and strength Swain and a higher melting temperature, and was unacceptably expensive for commercial use. Differences between the second-fifth layers of sample 1 and sample 2 - 6 does not affect the relative rate of transmission of oxygen in these samples. These data confirm that the ethylene content of 44% is the upper limit of the melting point of 162oC is the lower grandfather to EVOH in Central oxygen barrier layer of the multilayer film of the present invention.

Summarizing, we can say that the samples 2 to 6 are variants of the invention, in which the average melting temperature of the Central layer is higher than in other layers, and the fourth and fifth outer layers have approximately the same melting temperature as the second and third intermediate adhesive layers. These values are as follows: 179oC /Central layer/, 116oC /adhesive layers/ and 115oC /external layers/. The adhesive and the outer layers have a fractional melt indexes.

The region of the melting point of EVOH 162 - 178oC is essentially higher than the melting point of PVDC, the most commonly used as an oxygen barrier layer in multilayer films for packaging fresh meat; vinylidenechloride copolymers melt at about 148 - 150

Example 2

This series of tests with a five-layer film illustrates the importance of using nylon 6,66 as the polyamide component of the oxygen barrier of the Central layer of EVOH. In General it was found that when the gels in this type of film, they are present in the Central layer. For this reason, the presence or absence of gels is a direct indication of the compatibility of the special design of EVOH and nylon in the Central layer. Eight different samples include various polymer combinations in shows what none of Nasonov 6,12 contained in the films Central layer, does not have satisfactory optical properties /samples 7, 8, and 10/. This is possibly due to partial reaction between the nylon and EVOH, or the phenomenon of mixing or incompatibilities that cause intense amounts of gels.

In contrast, samples 3 and 6 with nylon 6,66 were optically superior without gels that does not deny the possibility of using different types of EVOH in the Central layer /38 and 44 mol. % ethylene, respectively/. Samples 2 and 3 each included the same type of nylon 6.66, but the first was only good from the optical point of view, because it contains small quantities of gels. On the contrary, the sample 3 did not contain gels and was optically excellent probably because the EVOH melt index that is included in it, was of 8.4 compared with sample 2, in which the amount of melt index EVOH was a 3.8. Thickness in mils /and the percent of the total film thickness/ layers from the first to fifth samples 2, 3 and 6 variants of the invention were as follows:

Sample:

2 - 0,079 /3/, 0,079 /3/, 0,079 /3/, 1,716 /65/, 0,686 /26/

3 - 0,086 /3/, 0,086 /3/, 0,086 /3/, 1,866 /65/, 0,746 /26/

6 - 0,086 /3/, 0,086 /3/, 0,086 /3/, 1,372 /65/, 0,749 /26/

The second and third intermediate adhesive layers of samples t.32, 17,5% DQDA 6833 type EVA and 30% Plexar adhesive 3779 /samples 2 and 3/ or 30% Plexar 3741 /sample 6/, and 30% Plexar 169 adhesive and 70% DQDA 6633 type EVA /sample 11/. Their average indices of melt /g/ /10 min/ were: 0,51 /samples 7 to 9/, 0,86 /sample 10/ a, 0,46 /samples 2, 3/, 0,54 /sample 6/ and 0.51 /sample 11/. Their average melting point /inoC/ were: 100 /samples 7 to 9/, 111 /sample 10/, 116 /samples 2, 3 and 6/ 101 /sample 11/. Table G illustrates that the nylon in the oxygen barrier layer, five-layer film of the invention should be nylon 6.66.

It is advisable to note that the optical properties of the five-layer films of this invention with oxygen barrier of the Central layers, having the same percentage of a copolymer of ethylene type EVOH and nylon 6,66, are not necessarily identical. For example, samples 2, 9 and 11 have the same type EVOH, constituting 80% of the Central layer and 20% nylon 6,66, but samples 9 and 11 have 100% EVA without VLDPE in their outer layers. On the contrary, the outer layers of the sample 2 comprises 75% VLDPE and 23% EVA. The optical properties of the sample 2 are much better than the samples 9 and 11. The reasons for this difference are not fully understood, but may be associated with a higher extrusion temperatures and biorientation required when more viscoplastic VLDPE blend in their melting temperatures of the Central layer and improves their compatibility. For this reason, or fourth and fifth, or both layers of the film of the invention should have a melting point of at least about 105oC, so that both layers may not include 100% EVA.

Another difference between the samples of the films 2, 9 and 11 is that the adhesive material of sample 2 has a fractional melt index /Plexar 3779/, while the adhesive material samples 9 and 11 /Plexar 169/ has a melt index of 2.5. As discussed later in more detail, for films of this invention with adhesives based on polyethylene, anhydride modified, the melt index of the adhesive should be less than about 1.7. This ensures that the adhesive layer with sufficient strength to withstand tensile forces during the orientation process.

As a result, the samples 2, 3 and 6 are variants of the invention, in which the average melting temperature of the Central /first/ layer, second and third intermediate adhesive layers and the fourth and fifth outer layers are lower, i.e., for samples 2 and 3 they are 180oC, 116oC and 115oWith, and for sample 6 they are 171oC, 116oC and 115oC. the Second and third intermediate adhesive layers and the fourth and fifth outer layers have fractional indices is sowen in the Central layer. Film samples 9 and 11 are optically unsatisfactory, partly because none of them are fourth and fifth outer layers has a melting point of at least about 105oC.

Example 3

A series of tests was conducted with six different concentrations EVA /10% vinyl acetate/ mixed with VLDPE for the two outer layers. Thus, each of the outer layers separate film had the same mixture and they contained EVA ranging from 29% to 63%. The VLDPE content was different between 100% and sum of the content of EVA and 4.4% processing additives. Were used two types of VLDPE, the only significant difference was their indexes melt, i.e., 0.5 for Attane type 61509.32 and 1.0 for Attane type 4001. The percentage of the total film thickness for the first to fifth layers of samples 12 to 17 was as follows: 3, 3, 3, 65 and 26%. The total thickness /mils/ for these samples were: 2,45 /sample 12/, 2,49 /sample 13/, 2,88 /sample 14/, 2,49 /sample 15/, of 2.51 /sample 16 and/ 2,84 /sample 19/. In this sample, the thickness of the Central layer was in the field 0,07-0,09 mil. The Central layer for all samples of the films contained 80% EVOH n and 20% nylon 1539, having a high melting point 116oC. the Second and third intermediate adhesive layers for all of the films consisted of 52.5% of mperature melting was 116oC. in Addition to the optical properties were measured some physical properties. The data are summarized in table H.

If the measurements were carried out under equivalent conditions, biaxial oriented EVA film provides higher shrinkage in the transverse and longitudinal directions /on-Board processing/ than biaxial oriented VLDPE film, although VLDPE has a significantly higher heat shrinkage than the linear low density polyethylene /LLDPE/ with comonomers containing the same number of carbon atoms. These ratios are described, for example, in the aforementioned U.S. patent N 4863769. The dependence of thermal shrinkage also exists in mixtures EVA-VLDPE, i.e. the increase in the content of the EVA provides a higher biaxial thermal shrinkage than lower content of EVA in a mixture with VLDPE. This dependence is illustrated by comparison of samples 12 to 14 with each other or samples 15 to 17 with each other. It was determined that to provide biaxial oriented teplosetevaya film according to this invention, if the fourth and/or fifth outer layers contain EVA, he should not be in excess of 45 wt.%, or optical properties of the film are unacceptable. It probably is because A level, when developing an incompatibility in the extrusion process and/or biaxial orientation, with a much higher melting temperature of the Central layer.

Table H shows that the optical properties of the film /turbidity and gloss/ become worse with increasing concentration of EVA in the outer layer /layers/. This was also demonstrated in table G through a preliminary comparison between samples 2 /100% EVA/ and the sample 11 /75% LLDPE - 25% EVA)/. Thus, % turbidity tends to increase, % luster - to decrease. Moreover, the trend toward dynamic puncture resistance decreases with increasing concentration of EVA in the outer layer /layers/. Because of these opposite trends, the preferred balance of properties with a mixture of EVA-VLDPE fourth and fifth outer layers is the content of the EVA from about 25% to about 40% VLDPE content from about 60% to about 75%. In a further preferred variant of the fourth and fifth outer layers each comprise a blend containing from about 65 to about 72 wt.% VLDPE with a density of about 0,912 and a melt index of about 0,19 /DEFD type 1192/ and from about 22 to about 28 wt.% EVA containing about 10% vinyl acetate.

As a result, the samples 12 to 17 are variants of the invention, in which the average temperature has been melted down is mperature melting than the second and third intermediate adhesive layers. In each example, the melting temperature of the Central layer and the adhesive layer were 179oC and 116oC, respectively. The outer layers of these samples had a fractional melt indexes. The maximum concentration of 45% EVA in the outer layers is demonstrated by comparison of the optical properties of the samples 14 and 16.

Example 4

Another series of tests was conducted to demonstrate that can be used in different types of VLDPE materials in the fourth and fifth outer layers of five-layer film of this invention. In these tests were used six different materials VLDPE in the fourth and fifth outer layers of samples 18 to 23 in a mixture with 25% EVA /10% vinyl acetate/ and 4.4% processing additives. As the adhesive and protective oxygen of the Central layers were essentially identical to significantly change the type VLDPE. We measured some of the pharmacological properties of the films and the results are summarized in table I.

Table I shows that four types of VLDPE gave the same results in respect of physical properties, i.e., samples 19 and 21 - 23. Sample 20 was a mixture of 80% Attane 61590.32 /includes only VLDPE in a good sample 19/ and Attane 61512.21. Although the shrinkage was fair, sample 18, which contained only Attane 61512.21 as its external VLDPE layer, can not be made due to the low melt strength at 400oF temperature head /extruder/. There may not be supported stable bubbles. Thus, this special VLDPE material is unsuitable for use in the outer layers of the considered film with this special composition for the manufacture of teplosetevaya film by extrusion with a double blow with biaxial orientation. However, it is possible that such a film can be made with other equipment for a double blow.

For example, 16 of the oxygen barrier of the Central layer consisted of 80% EVAI H101 type EVOH and 20% nylon 1539; the second and third adhesive layers consisted of 52,5% Attane XU 61509.32 VLDPE, 30% Plexar adhesive 3779 and 17,59% DQDA 6833 type EVA.

Samples 19 to 23 are variants of the invention. Thickness in mils /or percentage of the total film thickness for the first to fifth layers were as follows:

Sample

19 - 0,079 /3/, 0,079 /3/, 0,079 /3/, 1,719 /65,1/, 0,676 /25,9/

20 - 0,095 /3/, 0,095 /3/, 0,095 /3/, 2,064 /65,1/, 0,821 /25,9/

21 - 0,078 /3/, 0,078 /3/, 0,078 /3/, 1,680 /65,1/, 0,668 /25,9/

22 - 0,077 /3/, 0,077 /3/, 0,077 /3/, 1,660 /65,1/, 0,660 /25,9/

23 - 0,082 /3/, 0,082 /3/, 0,082 /3/, 1,77 /65,1/, 0,704 /25,9/

Oxygen Baria EVOH /sample 23/, and each had an average melting point of 179oC /340oF/.

The second and third intermediate adhesive layers contained 52,5% VLDPE, 30% of the adhesive and 17.5% EVA. VLDPE was Attane XU61509.32 /samples 19 to 21/, DEFD 1192 /sample 22/ and Attane XU 61520.01 /sample 23/. The adhesive was Plexar 3779 /samples 19 to 21/ and Plexar 3741 /samples 22 and 23/. EVA was DQDA 6833 all samples. The average indexes of the melt /in g/10 min were as follows: 0,46 /samples 19 to 21/, 0,62 /sample 22 and/ 0,89 /sample 23/. The average melting point /inoC/ 116oC for each of the samples 19 to 23.

For the fourth and fifth outer layers of the test series in this example 4, the average index of the melt /in g/10 min were as follows: 0,4 /sample 19/, 0,55 /sample 20/, 0,71 /sample 21/, 0,21 /sample 22/ and 0.71 /sample 23/. The average melting point /inoC/ for each of the samples 19 to 23 was 115oC.

As you can see from the above, samples 19 to 21 and 23 variants of the invention have the second and third intermediate adhesive layers, and the fourth and fifth outer layers with substantially the same average melting temperature below the melting temperature /first/ Central layer.

As explained earlier, the second and third adhesive layers include two or three compacity adhesive layer with sufficient strength to resist stretching of the film during the biaxial orientation at elevated temperatures. For the same reason, the second and third layers should have an average fractional melt index. As VLDPE is a typical strongest component of the adhesive layers, at least about 35% VLDPE for this component to perform its prescribed functions. On the other hand, the content is more than 80% VLDPE means that the adhesive component is less than 20% of the whole mixture, and it is insufficient for performing an adhesive function between the Central layer and outer layers. In a preferred embodiment, the reflecting these considerations, VLDPE is from about 45% to about 60% of the second and third intermediate adhesive layers.

The second and third intermediate layers include a mixture containing from about 20 to about 40 wt.% the adhesive component. Less than 20% do not provide the required adhesion between adjacent layers of film. More than 40% of the adhesive will increase the average melt index of these layers to the level where they do not have sufficient strength during the orientation process for maintaining the film. In a preferred embodiment, the reflecting these considerations, the adhesive component is about 25 - 38% of the second and third intermediate adhesive layers.

The second and third about the element increases shrinkage properties of the film compared with the two-component mixture. On the other hand, EVA has a lower strength at a temperature of orientation than VLDPE, and for this reason should not exceed about 40 wt.% the layers. As a preferred balance of EVA is present in a concentration of from about 10 to about 20 wt.%.

Example 5

Were conducted a series of tests that demonstrate the importance of using the adhesive on the basis of polyethylene modified with anhydride with a melt index below about 1.7 in the second and third intermediate adhesive layers of this film. The tests also demonstrate the unsuitability of some adhesives based on EVA. Were prepared nine films, each with five layers and is essentially identical to the outer layers, including 70,6% VLDPE, 25% EVA /10% vinyl acetate/ and 4.4% processing additives with an average melt index of 0.25 and an average melting point 115oC. Oxygen Central protective layers were identical and consisted of 80% EVOH /EVAL H 103/ 20% nylon 6,66 /Allied type 1539/. Different substance between samples 24 - 32 was only the adhesive layer. With the exception of sample 24 all samples consisted of 30 wt.% the adhesive component in the second and third layers. Optical properties were visually observed and measured shrinkage. The results of these tests of summerof risovannyh in samples 24 / 32. As explained above, the film according to the invention is suitable for packaging fresh red meat, because it has good optical properties, i.e., a little visual line voltage, low turbidity and high gloss.

It was found that in these five-layer films may appear optically unacceptable line voltage. Their presence /absence/ is directly related to the type used in these layers of adhesive. Sample 28 was close to the acceptable limit with a few lines of tension and adhesive layers comprised 30% Plexar 3779, which consisted of a copolymer based on LLDPE modified maleic anhydride /melt index 0,81/. Sample 29 was similar to the sample 28, the only difference was in the use of VLDPE type Dow 61509.32 in the adhesive and the outer layers instead of VLDPE type of Union Carbide 1192. In the sample 29 was not the visual line voltage, so that its optical properties were excellent in comparison with the sample 28. With one exception /sample 32/ sample 31 was the only film that was without line voltage and its adhesive component consisted of Plexar 3741-based low-density polyethylene modified with maleic anhydride. The adhesive layers of samples 28, 29 and 31 Like they were variants of the invention in table J. Thus, in a preferred embodiment, the second and third adhesive layers consisted of a mixture of from about 48 to about 55 wt.% polyethylene, very low density with a fractional melt index from about 15 to about 22 wt.% copolymer of ethylene and vinyl acetate with a melt index of about 0.25 and a vinyl acetate content of 10% and from about 25 to about 35 wt.% adhesive-based low-density polyethylene modified with maleic anhydride. Thickness in mils /or percentage of the total film thickness for the first to fifth layers of samples 28, 29 and 31 were as follows:

Samples

28 - 0,085/3,0/, 0,085/3,0/, 0,085/3,0/, 1,933/65,1/, 0,730/25,9/

29 - 0,077/3,0/, 0,077/3,0/, 0,077/3,0/, 1,673/65,1/, 0,665/25,9/

30 - 0,089/3,0/, 0,089/3,0/, 0,089/3,0/, 1,933/65,1/, 0,769/25,9/

The oxygen barrier of the Central layer for samples 24 - 32 was from 80% EVAL type H 101 EVOH and 20% nylon 1539 with an average melting point of 179oC.

Sample 24 included Admer 500 as adhesive. Table E identifies the substance as a copolymer based on LLDPE, modified maleic anhydride, with a relatively high melt index of 2.0. Because of this high value, the film had a significant number of tension lines and was optically unsuitable for its intended use captive is about anhydride /melt index of 1.5/, for example, the sample 31 had good optical properties. Thus, in order to be useful in this invention, such adhesives based on polyethylene should have a melt index below about 1.7 g/10 minutes This ensures that the adhesive layer has sufficient strength during the orientation process to maintain (to support) film. Higher melt indexes cannot withstand voltage under these conditions. For this reason, the mixture for the adhesive layer of the film of the invention must have an average melt index, which is fractional.

A sample of 25 included 70% Syrlyn 1650-30% Plexar 106 as an adhesive layer; the latter is a copolymer based on EVA, modified maleic anhydride, 1.2 MI. The film had a significant number of tension lines, probably due to the relatively high index melt adhesive based on EVA and the adhesive layer, so it must be optically unsuitable for packaging fresh red meat. Sample 26 also contained 30% Plexar 106 as an adhesive component and had a relatively high melt index based on EVA /1,2/. This sample showed the number of unwanted tension lines.

Sample 27 contained 30% Bynel CXA 3048 as is the low value of M and a fractional melt index adhesive layer, the film contained a significant number of tension lines in the machine direction /longitudinal/.

The sample contained 30 30% Plexar 169 as adhesive; this copolymer is a copolymer based on low density polyethylene modified with maleic anhydride, with a melt index of 2.5 (see table E/. The sample showed a significant number of the line voltage, so is unsuitable for the purposes of the present invention. This was due to the relatively high melt index, so that the Central layer is not stretched uniformly in the orientation process.

Sample 32 contained 30% Overacc 18302 as adhesive; this ternary copolymer based on EVA with a melt index of 0.6 (see table E/. Despite this relatively low melt index, expressed in fractional average melt index of the second and third adhesive layers, and good optical properties, the film was unsatisfactory due to poor interlayer adhesion. As demonstrated later in example 38 to solve this problem, the index melt adhesives based on EVA, suitable in this invention must be extremely low, i.e. below about 0.5 g/10 min.

In a variant of the invention, the sample 31, the average of them, fourth-fifth outer layers. Each of these examples has a fractional melt index adhesive layers and each has at least 30% of the free shrinkage at 90oC in the transverse direction.

Example 6

In the previously described embodiments of the invention, levels of shrinkage usually amounted to about 31% in the longitudinal direction /direction processing/ and about 39% in the transverse direction, both measured at the 90oC. This is satisfactory for most applications in the packaging of fresh red meat, but it would be desirable to provide even higher levels of shrinkage for some of the final uses of the specified five-layer film.

This can be achieved by the use of different thermoplastic polymers, one or both of the outer layers was demonstrated in two versions with a higher shrinkage of the film according to the invention. In these tests, summarized in table K, were used four films. Samples 33 to 35 are variants of the invention with identical oxygen Central protective layers: 80% EVAL type H 103 EVOH and 20% nylon type 1539. The average melting temperature of the polymer mixture of the Central layer was 164oC. Intermediate the second and the CEN melt was 0,61 g /10 min and the average melting temperature was 116oC.

The outer layers of the sample, 33 were above mixture VLDPE-EVA with an average melting point 115oC and this film provides the average shrinkage properties for packaging fresh red meat. The outer layers of the sample 34 contained three-component blend of VLDPE, EVA and plastomeric type copolymer of ethylene with an alpha olefin, which was Mitsui Tafmer 1085 /melting point 71oC/. Table K shows this film with essentially higher shrinkage properties than the average shrinkage of the sample 33. Moreover, other physical properties of the film and the optical properties were more excellent in comparison with the sample 33. The melt index of the outer layers was of 0.25, below the corresponding value of 0.61 for the adjacent intermediate layers. The average melting temperature of the outer layers 100oC was lower than the corresponding value 116oC for interconnecting the intermediate layers. Thickness in mils /or percentage of the total thickness of the film for the first to fifth layers were as follows: 0,08/3/, /0,08/3/, /1,64/63/ /0,73/28/. Thus, in a preferred embodiment, the high shrinkage at least one of the fourth and fifth outer layers comprises a blend of from about 40 to about 60% VLDPE and from about 5 to about 20 wt.% blastomeres of the copolymer ethyl is Colo 15 wt.% vinyl acetate.

For sample 35 fourth outer layer /which is the inner layer of a packet received from a film/ contains 100% Syrlyn 1706 of ionomer made by the company and DuPont Co., and the fifth outer layer /which is the outermost layer of the package is/ was identical to the outer film layers with regular shrinkage /average melting point 110oC/. Table K shows that this film is essentially also has a higher shrinkage properties than the sample with 33 regular shrinkage. Its optical properties were even better than for sample 34, but dynamic puncture resistance is lower. Since the average melting point of the fourth outer layer was 81oC, it was lower than the corresponding value 103oC for the second intermediate layer. Film thickness in mils /and the percentage of the total thickness of the film for the first to fifth layers were as follows: 0,09/3/, /0,09/3/, /0,09/3/, /1,83/63/, /0,81/28/. The total film thickness was of 2.9 mil.

In order to compare the sample 36 was competing six-plane heat-shrinkable film with a Central layer of EVOH. The film was W. R. Grace type W-E, which was proposed for the packaging of fresh red meat. Table K shows that thermal shrinkage variant of the invention samples 34 and 35 is STI puncture.

One of the preferred variants of the invention with a high shrinkage had the fourth and fifth outer layers each containing a mixture of from about 42 to about 46 wt. % polyethylene, very low density, with a density of about 0,912, from about 34 to about 38 wt.% copolymer of ethylene with vinyl acetate and from about 13 to about 17 wt.% elastomer of ethylene with alpha-olefin, having a density of about 0.88 to, a melt index of about 1.4 g/10 min and a melting point of about 71oC.

Another preferred variant of the invention with a high shrinkage contained the ion meter as at least one fourth component of the outer layer. The latter could, for example, include a mixture of EVA and ionomer, or as in example 36, a fourth outer layer could contain 100% ionomer.

Example 7

In this example, the physical properties of the two versions of the film of the invention /uniform shrinkage and high shrinkage/ compared with two commercially used protective type three-layer films based on vinylidene chloride methyl acrylate /high strength MA Saran and high shrinkage MA Saran/. In addition, variants of this invention is compared with two commercially used protective type of films based on EVOH. Comparisons are summarized in Timoti oxygen five-layer film of the invention is at least comparable with biaxial oriented heat-shrinkable three-layer films vinylidenechloride type, currently used for packaging fresh red meat. Similarly, they are at least comparable with commercially suitable multilayer films of EVOH type.

Example 8

In this example, five-layer film was prepared using a copolymer of ethylene with vinyl acetate, 10 wt.% vinyl acetate /EVA/ modified with anhydride as an adhesive having a melt index of about 0.25 g /10 min /Quantum PPX 5075/ second and the third adhesive layer of the mixture only with VLDPE as another component of the mixture /sample 39/ or three-component mixture with EVA /as a separate component and/ VLDPE /the sample 38/. Optical and physical properties of these films are determined and compared with a five-layer film, differing only by the use of adhesive-based LLDPE modified with anhydride /sample 37/. All these films had adhesive layers with a fractional melt index.

More specifically, examples 37, 38 and 39 were each about the thickness of 66 μm /2,6 Mila/ and each included a protective oxygen of the Central layer containing 80% EVAL H 103 type EVOH and 20% nylon 6,66 type 1539. The fourth and outermost layer of these samples contained 75% DEFD type VLDPE 1192 and 25% DQDA 6833 type EVA. The fifth outer layer of these samples contained 70,6% DEFD type VLDPE 1192, 25% DQDA 6833 type EVA and 4.4% feathers,5% DQDA 6833 type EVA. The adhesive sample 37 was above Plexar 3779 with a melt index of 0.8 (see table E/. The adhesive sample 38 was Quantum-based EVA Plexar type PPX 5075 /with melt index of 0.25/. The adhesive layers of the sample 39 included a two-component mixture of 75% VLDPE type 61509.32 and 25% of the above adhesive Quantum type PPX 5075. The Central layer of these samples was about 3% of the film thickness, and the second and third adhesive layers each also accounted for about 3% of the film thickness. The fourth inner layer was about 63% and the fifth /external/ layer constituted about 28% of the film thickness.

Physical characteristics of these films are summarized in table M and their physical properties are summarized in table n

Sample 38 demonstrates that the five-layer film of this invention include adhesive layers, where the adhesive is a copolymer on the basis of EVA modified with anhydride, with a very low melt index, i.e., below 0.5 g/10 min. in Addition, samples 38 and 39 include a third adhesive layer, which contains either two-component blend of VLDPE and adhesive, or three-component blend of VLDPE and EVA and adhesive EVA, comprising up to about 25 wt.% just an adhesive layer and having a fractional melt index. The content of the EVA in the three-component mixture should not accepts the LOI sufficient strength to maintain the film in terms of orientation.

Tables M and N indicate that adhesives based on EVA samples 38 and 39 were equivalent adhesive image 37 in terms of physical strength, shrinkage and permeability of oxygen and their optical properties were considered good. Optical characterization of these samples with an adhesive having a melt index of 0.25, was essentially excellent in comparison with feature films with an adhesive based on EVA with a higher melt index, such as the samples 25 and 26 /EVA adhesives with a melt index of 1.2/ sample 27 /adhesive based on triple EVA copolymer with melt index of 0.9/. Each of these films had a line. A possible explanation is that as the adhesive based on EVA weaker than on the basis of polyethylene and has a lower melting point, so you have a lower melt index adhesive based on EVA /less than up to about 0.5/ to ensure the same strength, which is supported for tensile forces in the film than with adhesives based on polyethylene /melt index less than about 1/.

Thus, the preferred adhesive based on EVA had a melt index of about 0.25 g/10 min and a vinyl acetate content of about 10 wt.%.

The present invention is not limited wiseana extruded oriented heat-shrinkable multilayer film, consisting of an oxygen-barrier Central layer made of a mixture containing a copolymer of ethylene and vinyl alcohol and polyamide intermediate adhesive layer made of adhesive-based polyethylene modified with maleic anhydride, and outer layers of polyolefin having a density < 0,914 g/cm3, characterized in that the Central layer is made of a mixture containing 70 to 85 wt.% copolymer of ethylene and vinyl alcohol with a melting point of 162 - 178oC and ethylene content of 36 to 44 wt. % and 15 to 30 wt.% polyamide constituting the copolymer poly-caprolactam from nylon, obtained from adipic acid and a diamine, the content of poly-caprolactam in the copolymer of 85 mole%, moreover, the thickness of the Central layer is of 1.27 - 2,54 µm and the permeability of oxygen through the layer of < 35 cm3/m2/24 h, each intermediate adhesive layer is made of a mixture containing 35 to 80 wt.% the copolymer of ethylene-olefin, having a density of < 0,914 g/cm3, 20 to 40 wt.% adhesives based on polyethylene modified with maleic anhydride, with a melt index < 1.7 g/10 min, or adhesive based on a copolymer of ethylene with vinyl acetate, modified malinowy is aspreva not > 1 and a vinyl acetate content of 7 to 15 wt.%, the mixture has an average melt index and the average melting temperature below the melting temperature of the polymer mixture of the Central layer, the thickness of each adhesive layer is 2.5 - 5% of the film thickness, the first outer layer is slotermeerlaan and made of polyolefin having a density < 0,914 g/cm3with additional content of a copolymer of ethylene with vinyl acetate is not more than 45 wt.%, having a melt index not > 1 and a melting point below the melting temperature of the polymer mixture of the Central layer, with a thickness of 40 - 70% of the film thickness, and the second operating-resistant outer layer made from a polyolefin having a density < 0,914 g/cm3with additional content of a copolymer of ethylene with vinyl acetate is not more than 45 wt.%, having a melt index not > 1 and a melting point below the melting temperature of the polymer mixture of the Central layer, with a thickness of 20 - 35% of the film thickness, and at least one of the outer layers has a melting point of at least 105oC, and the film has at least at least 30% of the free shrinkage at 90oC in the transverse direction and the total thickness is antigny each other.

3. The film on the PP. 1 and 2, characterized in that each outer layer is made of a mixture containing 60 to 75 wt.% the copolymer of ethylene-olefin, having a density of < 0,914 g/cm3and 25 to 40 wt.% copolymer of ethylene with vinyl acetate.

4. Film under item 1, characterized in that at least one of the outer layers is made of a mixture containing 40 to 60 wt.% the copolymer of ethylene-olefin, having a density of < 0,914 g/cm3, 5 to 20 wt.% plastomeric copolymer of ethylene with a-olefins and 20 to 40 wt.% copolymer of ethylene and vinyl acetate having a vinyl acetate content of 7 to 15 wt.%.

5. Film under item 1, characterized in that the copolymer of ethylene and vinyl alcohol contains 38 wt.% ethylene and has a melt index of 0.8 g/10 min.

6. Film under item 1, characterized in that the adhesive is a linear low density polyethylene, modified maleic anhydride.

7. Film under item 1, characterized in that the copolymer of ethylene-olefin, having a density of < 0,914 g/cm3is 45 - 60 wt.% the intermediate adhesive layers.

8. Film under item 1, characterized in that the adhesive modified with anhydride, 25 to 35 wt.% the intermediate adhesive layers.

9. Film under item 1, CLASS="ptx2">

10. Film under item 1, characterized in that the adhesive layers are made of a mixture containing 48 - 55 wt.% the copolymer of ethylene-olefin, having a density of < 0,914 g/cm3and a melt index < 1, 15 to 22 wt.% copolymer of ethylene and vinyl acetate with a melt index of 0.25 g/10 min and a vinyl acetate content of 10 wt.% and 25 to 35 wt.% adhesive-based low-density polyethylene modified with maleic anhydride.

11. Film under item 1, characterized in that the anhydride modified adhesive intermediate adhesive layers is a copolymer based on ethylene and vinyl acetate having a melt index of 0.25 g/10 min and a vinyl acetate content amounts to 10 wt.%.

12. The film on the PP. 1 and 5, characterized in that the adhesive has a melt index < 1.

13. Film under item 1, characterized in that the film is irradiated at doses of 1 to 10 Mrad.

14. Film under item 1, characterized in that the Central layer is made from a mixture containing 78 - 82 wt.% copolymer of ethylene and vinyl alcohol, and 18 to 22 wt.% copolymer of nylon 6 and nylon 66.

15. Film under item 1, characterized in that each outer layer is made of a mixture containing 65 to 72 wt.% copolymer of ethylene with alpha-olefin, having a density of below 0.9 racette 10%.

16. Film under item 1, characterized in that each outer layer is made of a mixture containing 42 - 46 wt.% copolymer of ethylene with alpha-olefin, having a density below 0,914 g/cm3and 34 to 38 wt.% copolymer of ethylene and vinyl acetate containing 10 wt.% vinyl acetate, 13 - 17 wt.% elastomer of ethylene with alpha-olefin with a density of 0.80 g/cm3, a melt index of 1.4 g/10 min and a melting point 71oC.

17. Film under item 1, characterized in that it has at least 20% of the free shrinkage at 90oC in the longitudinal direction of processing.

18. Film under item 1, characterized in that it has at least 35% free shrinkage in both directions - longitudinal and transverse.

 

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