The history of this material began abroad in the middle of the last century. It was used for packaging food products. The technical film was the result of numerous modifications of the chemical composition and production technologies, which provided it with a wide range and a high level of use.
Composition
The properties that a technical polyethylene film possesses, and its purpose depend on the composition:
- High density low density polyethylene (LDPE).
- Dense structure low density polyethylene (HDPE).
- Linear LDPE with a modified composition.
- Compound variations: for example, LDPE and HDPE, with polypropylene.
Technical requirements
Polyethylene is not toxic; it consists of a group of flammable, non-toxic materials with an ignition temperature of 300 ° C; other characteristics depend on the composition:
Low pressure polyethylene film:
- Mechanically strong material (0.94 ÷ 0.96 g / cm 2 ).
- Resistant to high temperatures (yield at 112 ° C).
- Resistant to food fats, oils. Neutral to acidic and alkaline substances.
- The disadvantage is a high level of permeability, almost 6 times higher than the VD film. Contact with hydrocarbons is unacceptable and undesirable - with easily oxidizing substances.
- Technical film based on low-pressure polyethylene is indispensable for packaging products undergoing sterilization and a certain range of food products.
High pressure polyethylene film:
- It has a density of 0.91 ÷ 093 g / cm 2 .
- Moderate tensile strength.
- Low yield allows you to weld pieces of material.
- Frost-resistant: up to - 60 °.
- Paint is easily applied to the surface.
Linear LDPE: The basis for creating stretch multilayer films.
Each type of material produced must comply with the requirements of state regulatory documents:
- Technical plastic film - GOST 10354 - 82.
- Shrink polyethylene - GOST 25951 - 83.
- HDPE GOST 16338 - 85.
- HDPE GOST 16337 - 77.
Production
The technical film is produced by extrusion technology in several stages:
- Melting and blowing semi-liquid composition, passed at the exit through different types of nozzles:
- The ring giving a sleeve type of packaging. At the exit of the nozzle, the material is blown up and dried along its entire length, followed by pulling it onto the rollers and winding full rolls. A laborious process that allows you to get a canvas up to 2400 mm long.
- Flat, allowing you to get a straight film sheet. After extrusion, the material is dried, stretched and cut. This is a faster technology, but polyethylene sheets do not exceed 1.5 m.
- Polyethylene is being modified to obtain the material with the desired properties:
- Chemical, with the addition of certain elements.
- Mechanical, by stretching.
- "Crosslinking" using ion radiation
- Thermostabilization. After heat treatment, the structure of the material becomes more resistant to mechanical damage.
Technical film: characteristics and types of finished products
Depending on the modifications of the feedstock, the following types of technical polyethylene can be seen on sale:
- Light stabilized: it is highly resistant to solar radiation, the service life depends on the concentration of stabilizers. It has bright colors: yellow, green and so on.
- Shrink: when heated, it changes its size by tightening the object inside. Web width up to 150 mm, sleeves up to 2500 mm.
Shrinkage:
- Longitudinal: from 40 to 80%.
- Transverse: 10 ÷ 50%.
- Composite heat-shrink: various types of coating with the addition of reagents that change the property of the material to the required characteristics.
- Reinforced: technical film with a mesh of polypropylene or polyethylene.
- Transparent: the starting material is LDPE. The copolymer ethylene vinyl acetate hydrophilic film has increased transparency.
- Color: material - LDPE, dyes, stabilizers.
Technical polyethylene film: fields of application
The variety of species allows the use of polyethylene in almost all spheres of human activity:
- Construction: in the form of a sleeve or canvas, thickness 60 ÷ 200 microns. It is used for packing and shelving pallets with materials and protecting surfaces from contamination.
- Technical film with black pigment: various types of work, including covering the shoots “under the steam” (thickness from 60 microns), mulching, density 10 ÷ 60 microns.
- Hydrophilic with increased transparency: for greenhouses.
- Shrink film (sleeve, web) from primary and secondary, cheaper raw materials.
- In the form of bags: for packing garbage and waste.
Technical polyethylene film has a large assortment that allows you to satisfy any customer wishes. The main disadvantage is the high decomposition time of the material and the low level of its processing.