RU2608027C2 - Method of reducing oxygen penetrability of films made from polyethylene terephthalate used for storage of different food products - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to surface modification of polymer materials and a method of reducing oxygen penetrability of films made from polyethylene terephthalate, used for storage of different food products. Film surface is treated with gaseous mixture containing fluorine 10–15 vol%, nitrogen 68–72 vol%, oxygen 13–22 vol%, processing time 10–15 minutes, pressure 0 kg/cm². Invention provides effectiveness of process of reducing oxygen permeability of polyester film, while maintaining colour, transparency and strength.

EFFECT: invention also provides for development of multilayer package for products with a long and medium storage life.

1 cl, 1 dwg, 1 tbl, 2 ex

Description

The invention relates to the field of surface modification of films made of polyethylene terephthalate (PET) to reduce the oxygen permeability of composites obtained by lamination and containing a barrier layer that prevents the penetration of oxygen, which makes it possible to use them for storage of various food products.

An important operational characteristic of multilayer packaging materials, namely the film, which is used for packaging perishable food products is the presence of a barrier layer that prevents the penetration of oxygen through the packaging to the product. It is the barrier layer that provides long-term storage of meat, fish, cheeses and other perishable products. The less oxygen penetrates through the packaging to the product, the less oxygen will enter the bacteria that poison the product with their waste products, the longer the product will be stored.

Multilayer barrier films in terms of oxygen permeability are conventionally divided into three groups:

- high barrier (permeability 0.1-50 cm ³ / m ² / 24h / 1 kg / cm ^2),

- srednebarernye (permeability of 51-100 cm ³ / m ² / 24h / 1 kg / cm ^2),

- nizkobarernye (101-1400 permeability cm ³ / m ² / 24h / 1 kg / cm ^2).

At the moment, no material is known that would simultaneously possess all the necessary properties: low permeability, transparency, weldability, and strength. Therefore, a multilayer packaging is created in which each layer is responsible for its function (strength, weldability, barrier).

To create multilayer films, two main methods are used: coextrusion and lamination.

The coextrusion method is most often used for the barrier material EVOH (copolymer of polyethylene and vinyl alcohol), because it cannot be used in its pure form. Under the influence of moisture, the material begins to lose its barrier properties and allow oxygen to pass through. Thus, EVOH cannot be an outer layer. Therefore, it is isolated from moisture by layers of a hydrophobizing material - polyethylene (PE) or polypropylene (PP). The oxygen permeability of EVOH is an average of 2 cm ³ / m ² / 24h / 1 kg / cm ^2.

According to the known method [patent RU No. 2430835, published 10.10.2011], the film is made by the method of air drawing along two axes by the method of triple blowing. A multilayer film contains at least nine layers, counting from the outside to the inside, while the layers contain as a component: the first layer from the outside is a material selected from the group consisting of polyethylene terephthalate (PET), polyamide (PA), modified polyamide (MXD6 ), polystyrene (PS), polymethyl methacrylate (PMMA), polycarbonate (PC), cycloolefin copolymer (COC), polypropylene (PP) and high density polyethylene (HDPE) or mixtures of COC, PP or HDPE with polyolefin (PO); the second layer is an adhesion promoter; the third layer is a polyolefin, preferably polyethylene; the fourth layer is an adhesion promoter; the fifth layer is polyamide and, optionally, EVOH, PVA or MXD6; the sixth layer is a polymer providing a barrier to oxygen, selected from a copolymer of ethylene and vinyl alcohol (EVOH), MXD6 and PVA (polyvinyl alcohol), and, optionally, polyamide; the seventh layer is polyamide and, optionally, EVOH, PVA or MXD6; the eighth layer is an adhesion promoter; and the ninth layer is a polyolefin, preferably polyethylene. The method is distinguished by complexity, the resulting package has significant weight.

The lamination method consists in bonding materials. It is used for medium barrier materials based on polyterephthalate. Its price below EVOH, but the oxygen permeability is also lower at 100 cm ³ / m ² / 24h / 1 kg / cm ^2. The scope of the known method is limited, since plastic made of polyethylene phthalate cannot be processed by coextrusion due to its physicochemical characteristics - low adhesion. Therefore, create 3-5-layer materials from PET, polyethylene (PE), polypropylene (PP).

Known works in which to reduce oxygen permeability increase the number of barrier layers, but you can not increase the number of layers, but treat the surface of one layer and give it the barrier of several layers at once, because the diffusion of gases is determined by the surface properties [Nazarov V.G. Surface modification of polymers, Moscow, MGUP, 2008].

Closest to the proposed is a method of manufacturing a polyester container with improved gas barrier properties, suitable for storing packaged carbonated soft drink [patent RU No. 2394681, publ. 07/20/2010]. In the known method, it is proposed to add to the entire initial mass an additive of the composition R100C-AR-COOR2, where AR is selected from the group consisting of phenylene and naphtapene, and R1 and R2 are selected from the group consisting of C1-C10 alkyl groups, phenyl group and naphthyl group .

The disadvantages of this method are:

- The entire volume of the product is subjected to modifications, although only the surface layer is responsible for the barrier properties;

- A complex chemical is used;

- During the production process, chemically active waste is generated.

A new technical result is the simplification of the method, increasing its availability for small industries, reducing the weight of the packaging made of PET plastic while obtaining a sufficient degree of reduction in the oxygen permeability of the processed film.

To achieve a new technical result in a method for reducing the oxygen permeability of polyethylene terephthalate films used to store various food products by modifying a film, the surface of the film is modified by treating it with a gaseous mixture containing 10-15 vol.% Fluorine, 68-72 vol.% nitrogen, 13-22 vol.% oxygen, for 10-15 minutes at a total pressure of the gas mixture of 0 kg / cm ² .

New in the proposed method is the processing of the surface of one layer by a gaseous mixture of the specified composition in order to give it the barrier of several layers simultaneously, because the diffusion of gases is determined by the properties of the surface.

The method can be implemented, for example, using an installation for processing a film including a fluorine electrolyzer, a system for purifying anode gas from electrolyte particles 2, a continuous fluorination chamber 1, a tape system representing a system of shafts with a sealing mechanism from film inlet and outlet gases 3, and exhaust gas utilization system 4. The installation diagram is shown in Fig 1.

The method is as follows.

The gas containing 95% fluorine, 3% HF (the rest of the impurity) obtained in the electrolyzer, after cleaning, goes directly to the fluorination chamber, where it is diluted with atmospheric air to a fluorine content of 10-15 vol.%, 68-72 vol.% Nitrogen and 13-22 vol.% Oxygen.

The film is fed into the chamber through a system of shafts, the processing time, that is, the time spent by the film in the fluorination chamber, is controlled by an electric drive on a winding drum.

At the same time, diluted fluorine forms a layer of a new polymer on the film surface, which gives the whole product unique properties, one of which is a decrease in oxygen permeability.

The invention is further illustrated by examples.

The concentration of the components of the gas mixture, the exposure time and pressure were selected empirically.

A decrease in the amount of fluorine less than 10 vol.% Led to an insufficient decrease in oxygen permeability, an increase in the amount of fluorine above 15 vol.% Led to the destruction of the polymer. The pressure of the gas mixture is selected from those considerations that the process is quite difficult to carry out and control at reduced or increased pressure. The reaction time of 10-15 minutes is sufficient for the complete reaction to form on the surface of the polymer film. The increase in processing time is impractical.

Table 1 shows the processing conditions and the resulting decrease in oxygen permeability.

Example 1

A piece of PET film with dimensions of 210 × 297 mm and a thickness of 12 μm was treated with a gaseous mixture of fluorine, nitrogen and oxygen (fluorine 10 vol.%, Nitrogen 68 vol.%, Oxygen 22 vol.%) For 10 min. At a total pressure of the gas mixture of 0 kg / cm ² . Source and the oxygen permeability of the treated sample was measured, the initial permeability of the sample was 100 cm ³ / m ^2/24 hours, treated - 28 cm ³ / m ^2/24 hours.

Example 2

A piece of PET film with dimensions of 210 × 297 mm and a thickness of 10 μm was treated with a gaseous mixture of fluorine, nitrogen, and oxygen (fluorine 15 vol.%, Nitrogen 72 vol.%, Oxygen 13 vol.%) For 15 min. At a total pressure of the gas mixture of 0 kg / cm ² . Source and the oxygen permeability of the treated sample was measured, the initial permeability of the sample was 100 cm ³ / m ^2/24 hours, treated - 31 cm ³ / m ^2/24 hours.

The PET film thus treated, having increased adhesion, low oxygen permeability, can also be used as a barrier layer in multilayer packaging.

The advantage of this type of processing is that it is possible to obtain a high-barrier film at a medium-barrier price without loss of other properties.

Claims (1)

A method of reducing the oxygen permeability of films made of polyethylene terephthalate used to store various food products by modifying a film, characterized in that the surface layer of the film is modified by treating it with a gaseous mixture containing 10-15 vol.% Fluorine, 68-72 vol.% Nitrogen and 13-22 vol.% oxygen, for 10-15 minutes at a pressure of 0 kg / cm ² .

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