NL9200292A - Polymer film composed of a plurality of layers and essentially impermeable to gases - Google Patents

Abstract

The applications of such a polymer film are in the field of agriculture for crop protection and decontamination of crops and soil; in industry and for personal protection against toxic vapours and gases. Also provided is a method for fabricating such films from a plurality of layers by coextrusion.

Description

Title: Multi-layer polymer film that is substantially impermeable to gases.

The invention relates to a three-layer coextruded film for use in agriculture and the household. This film has a low permeability to gases used for soil disinfection such as methyl bromide.

The films of the invention make it possible to efficiently decontaminate the soil with reduced amounts of toxic gas compared to conventional decontamination films used today, thereby reducing the risk of environmental pollution.

Polyethylene (PE) is a favorite plastic film for agricultural use because it is inexpensive, mechanically strong, flexible and easy to manufacture. It can be obtained in a variety of thicknesses and widths. It is known in a low density form (LDPE), in a linear low density form (LLDPE) and in a high density form (HDPE). All PE films can be stabilized against ultraviolet radiation using hindered amine light stabilizers (HALS), by adding hydroxy benzophenones (BFn). PE permeability for gas is low.

Polyamide (nylon) is a suitable polymer as a food packaging film because of its low gas permeability, strength, and low tear resistance. The price of nylon is relatively high. These qualities make nylon unsuitable for agricultural applications.

Using a new method for the tri-extruder blown film line, a three-layer thin film is composed of a very thin layer of nylon adhered to thicker PE layers. The films produced combine the strength of PE with the low gas permeability of nylon, while keeping costs relatively low. The total investment in soil decontamination using this invention will not be higher due to the use of reduced amounts of gas. By reducing the use of toxic gas, a further positive environmental effect occurs.

The practice consists of spreading plastic layers over the surface of the soil, and at the same time or later by introducing toxic irrigation gas (usually methyl bromide) into existing irrigation pipes. Because of the high permeability of the commonly used PE disinfection film, much of the gas introduced penetrates upward through the film, and only a portion of it dissipates through the soil thereby disinfecting the soil.

Since gas cannot penetrate through the film of the invention, most of it will be dissipated through the bottom, making it possible to use smaller amounts.

In many places, disinfection films are left on the fields as a cover film for a season. In this aspect lies a further advantage of the invention: the low gas permeability lowers the concentration of CO2 (an essential gas for photosynthesis) and increases the concentration of alcoholic fermentation products (which takes place in the soil) which prevents weed growth compared to normal clear PE cover films.

According to the present invention, new, improved fumigation and cover films are provided. These have a low permeability to gases compared to commonly used PE films.

According to a preferred embodiment, a multi-layered coextruded film is comprised of one layer of a substantially gas impermeable material and one layer of polyethylene, and a choice of an adhesive layer therebetween.

Such films can have any desired thickness, the preferred range being from about 30 to 100 µm.

UV stabilizers can be used to prevent degradation by solar radiation. The use of UV stabilizers is done according to the. instructions from the supplier, usually about 5% by weight. Such new films can be applied in several ways: 1. In open fields for decontamination:

Films are spread on the bottom, overlapping a previous one. Gas is passed through the soil for disinfection during or after spreading the film. Such films remain on the field for at least 72 hours before being removed and disposed of.

2. In open field for decontamination and covering:

The film is spread on the bottom, overlapping an earlier one. Gas is passed through the soil for disinfection during spreading of the film. At least 72 hours after the disinfection, the film is punctured systematically, and the soil is sown or planted through the holes. Such films will remain in place for the duration of the renovation.

3. In open fields for flower bed disinfection:

Films are spread on a flower bed, being held in place by soil at the corners. Gas is passed through the soil for disinfection while the film is being spread, or later through the irrigation system. Such films remain on the field for at least 72 hours, and are then removed and disposed of.

4. In an open field for the disinfection and covering of a flower bed:

Films are spread on the flower bed, and held in place by laying soil on the corners. Gas is passed through the soil for disinfection during the spreading of the film, or later through the irrigation system. At least 72 hours after decontamination, the film is systematically punctured, and the soil is sown or planted through the holes. Such films will remain in place for the entire duration of the renovation.

5. At home and in open spaces, the films of the invention can provide additional protection against chemical warfare agents, giving people extra time to organize and put on gas masks.

6. In chemical laboratories, public buildings, schools, hospitals and the like, the films can be prepared to cover and seal an entire house in the event of unexpected exposure to a hazardous gas environment, giving the staff sufficient time to organizing and protecting the inhabitants.

7. In the food industry as food packaging material which increases the shelf life of the products.

Example 1 - comparative example:

A three layer film was coextruded containing three layers of LDPE, 10 µm each. All these layers were stabilized against UV radiation in a conventional manner. The extrudate was blown in a tube shape of 3.2 m circumference and of 30 µm thickness. The tube shape was cut lengthwise to form a flat film.

Example 2:

A three-layer film was coextruded containing one layer of a copolymer nylon 6-12 of 10 µl thick and two layers of LDPE, each 20 µl thick. All layers were stabilized against UV radiation in a conventional manner. The extrudate was blown into a tube shape with a circumference of 3.2 m and a thickness of 30 µl. The tube shape was cut longitudinally to form a flat film.

Example 3:

A three-layer film was coextruded to contain one layer of a copolymer nylon 6-12 of 20 µl thick and two layers of LDPE, each 40 µl thick. All layers were stabilized against UV radiation in a conventional manner. The extrudate was blown into a tube shape with a circumference of 2.0 m and a thickness of 100 µm. The tube shape was cut longitudinally to form a flat film.

Example 4:

A three-layer film was coextruded, comprising a 70 µl thick layer of LDPE, a 20 µl thick layer of copolymer nylon 6-12, and a 10 µl thick intermediate layer of EAA resin. The extrudate was blown into a tube shape with a circumference of 2 m, which had a thickness of 100 μπι. The tube shape was then cut into bags.

Example 5:

A three-layer film was coextruded, comprising a 10 µl thick layer of LDPE, a 10 µl thick layer of HDPE, and a 10 µl thick intermediate layer of homopolymer nylon 6. The extrudate was blown into a tube shape with a circumference of 3.2 m. The tube shape was cut longitudinally to form a flat film.

Example 6:

A three-layer film was coextruded containing a 10 µl thick layer of LDPE, a 10 µl thick layer of HDPE, and a 10 µl thick intermediate layer of a homopolymer nylon 6-12. The extrudate was blown in a tube shape with a circumference of 3.2 m and a thickness of 30 μπι. The tube shape was cut longitudinally to form a flat film.

Example 7:

A three-layer film was coextruded containing a 20 µl thick layer of LDPE, a 40 µl thick layer of LLPE, and a 20 µl thick intermediate layer of a copolymer EVOH. The extrudate was blown into a tube shape with a circumference of 2 m and a thickness of 100 μπι.

The decontamination effectiveness was tested in the southern part of Israel. Soil mushrooms of two species were planted for the experiment at a depth of 10 and 30 cm. The soil was then divided into garden beds, which were covered with the films of Example 1 and Example 2, and disinfected with different amounts of methyl bromide: 50 g / m2 (the recommended dose) and 25 g / m2. 4 reps were performed for each bed.

The gas permeability of the film according to Example 3 was tested by an independent institute:

Israel Rubber Research Association.

TABLE

From the table above, it can be seen that when the amount of the fumigant gas is reduced by half, the film of the invention maintains the fumigation effectiveness at both depths, while under normal LDPE films the fumigation effectiveness decreases 30 cm below the surface. It is possible that later experiments will show that a further decrease in the amount of fumigant gas is possible while maintaining the same total parasite eradication.

The film of Example 3 was tested for permeability using the so-called "Finabell test". The standard here is to keep the gas inside for at least 240 minutes.

The films of Example 3 retained the gas even after 420 minutes when the test was stopped.

When the film according to the invention is used as a cover for soil fumigation in agricultural fields, it is possible to use half the amount of fumigation gas (methyl bromide) and obtain the same amount of pest removal.

The gas permeability of the films is low enough to make them suitable as a self-defense aid in the event of a chemical weapons attack.

Claims (11)

A multilayer coextruded polymer film that is substantially gas impermeable for use in agriculture, industry, or for personal protection, comprising a layer of a gas barrier resin, a layer of polyethylene, and optionally an intermediate adhesive layer. The two-layer polymeric film of claim 1, wherein one layer of PE and the second is selected from PA, PET, EVOH and polyurethane. The multilayer polymer film of claim 1, wherein the adhesive layer is selected from EAA, EVA, PIB and other commercially available adhesive polymers. The multilayer polymer film of claim 1 or 2, wherein each of the layers has a thickness in the range from 5 to about 100 μτη. A two-layer polymeric film according to claim 3, wherein the PE layer has a thickness of about 30 to about 100 μπι and the barrier layer has a thickness of about 5 to about 50 μτη. A process for the manufacture of multilayer polymer sheets according to claims 1 to 5, which comprises co-extruding film from two or three layers using film blowing or casting methods. A soil fumigation method, wherein the volatile effective substance is passed under a layer according to any one of claims 1 to 5, which layer covers the land where pests are to be eradicated. The method according to claim 7, wherein the active ingredient is methyl bromide, and the layer remains for a sufficiently long period of time. A method according to claim 7 or 8, wherein after the plague eradication the film is pierced where necessary and seedlings are planted through such holes with the polymer layer serving as a cover film. A method according to claim 7 or 8, wherein the polymer layer is spread over a flower bed and the gaseous active materials are introduced under the layer. A protective agent for humans in the event of an unexpected exposure to a toxic gas environment, comprising a protective layer or cloth made of a multilayer polymer layer according to any one of claims 1 to 4.