Heat-shrinkable tubing is a device that can change its diameter and shrink under the influence of high temperatures. During the shrinkage process, it will envelop the object placed in it and provide protection: insulation and from mechanical damage. The scope of application of the tubes is radio electronics, automotive, used as a wire insulator, for protection metal pipes against corrosion, as well as for antenna equipment.

Basic statements

If we talk in simple words, then heat shrink tubing (HERE) is a replacement for standard blue electrical tape. The only thing is that they cannot be used in areas with ornate bends and where there is different thickness along the way.

Their main advantage is the ability to shrink when heated, it provides the necessary insulation and mechanical protection. The cost of the tubes is relatively low, they provide ease of use different colors, including the most common ones for cables - red, blue, green, yellow, striped. With their help you can not only insulate, but also mark wires to make it easier to further work with them.

I would like to dwell on labeling in more detail, since this is one of the important areas of use HERE. They are widely used when it is necessary to mark three-phase electrical circuits. They use red, yellow and green colors. By also marking the wires that correspond to a certain phase, you can make the operation process easier. The standard option for grounding is yellow-green striping.

Material characteristics

Before using HERE, you need to choose them correctly, and for this you need to know the main characteristics. These include:

• Shrinkability - this coefficient varies from 1:2 to 1:6.
• Adhesive layer.
• The composition of the tube can be PVC, polyolefin, elastomer, fluorine polymer.
• Color – single-color, combined.

And, also resistance to such influences - temperature, chemical exposure, light stabilization, resistance to petroleum products.

There is also a division according to the strength of the tube walls; according to this indicator, there are thick-, medium- and thin-walled ones. The first two types are combined into one group and are characterized by a wall thickness of 1.5-4.5 mm, which it will become as a result of shrinkage. The ratios vary from 2:1 to 6:1. They have an adhesive inner layer.

Thin-walled ones can be transparent or colored, with a wall thickness of up to 1 mm after shrinkage, the narrowing ratio is from 2:1 to 4:1. Used as insulators and markers. They often have special characteristics, including:

• Self-extinguishing.
• No halogen emissions during fire.
• Heat resistance.
• Reduced heat shrink temperature.
• Improved resistance to ultraviolet rays.
• Resistance to mechanical and chemical influences.

1. When indicating the size of the tube, manufacturers indicate two numbers through the fraction: one is the diameter before shrinkage, the second is after. Additional markings may indicate the color and length of the cut.
2. When you choose HERE, it is important to consider that its diameter should be larger than that of the product for which it will be used. For shrinkage to occur correctly, its diameter after shrinkage should be slightly smaller than the diameter of the product on which it is mounted.
3. Before using HERE, you need to inspect it for damage and burrs. If scratches or burrs are found, it is better to refuse to use such tubes.
4. If you plan to use HERE with an adhesive layer, then the surface on which they will be placed must first be cleaned and degreased. To avoid damage to the tube, there should be no places on the product that could be potentially dangerous for the TUT. If there are sharp edges, they need to be sanded and smoothed.

First you need to prepare your tools. Any sources that provide the required heat flow are suitable for this. Minimum temperature it should be +70 degrees. The required indicators are indicated during labeling. It depends on the type of tube: for a thick-walled tube the temperature should be higher, for a thin-walled one it should be lower. If you plan to use construction hair dryer, then the requirements for it are identification required temperature. If you use gas-burners, then it is important that they have a soft yellow flame. Options for use as a heat source include matches and lighters.

Shrinkage technique:

1. Surface preparation, which includes degreasing, cleaning and heating. To do this, depending on the material, you can use sandpaper or a rag soaked in solvent.
2. Selecting a tube in accordance with the requirements, warming it up, which is especially important for thick-walled tubes. It needs to be warmed up without placing it on its place of “permanent residence” and not until maximum temperature, but by half, that is, if the temperature of complete shrinkage is 120 degrees, then it needs to be heated to 60.
3. Next, the tube is placed on the object to be isolated, the surface. On heating device set the required temperature.
4. Shrinkage should start from the middle. After sitting evenly in the center, you should move to the right and left.
5. It needs to be heated evenly, moving the heat source along it, this will prevent local overheating, and therefore damage HERE.
6. If on inner surface If there is glue, it should leak out as a result of shrinkage. After shrinking, the item must be left alone until it cools completely.

Application HERE is modern and convenient solution. To experience all the benefits of this insulator, you need to use it correctly. We tried to explain in as much detail as possible everything you need to know to successfully use HERE.

Video: how to use heat shrink tubing

Heat-shrinkable tubes are quite simple and easy to use. They can be easily and quickly placed on various objects, resulting in a durable and reliable polymer coating, following the contours of the object, and having good electrical insulating properties. To achieve the best results, you should follow the recommendations below.

Tools:

Shrinkage of heat-shrinkable tubes can be carried out using a variety of heating sources, which can be: a stream of hot air, the flame of a propane-butane gas burner (set to soft yellow flame) or other heat sources capable of heating materials above +120 °C. The given temperatures are approximate, calculated for the most common types of tubes and may differ up or down depending on the type of tube.
At home, shrinkage can be done using matches, a lighter, or by placing (where possible) the tube in boiling water. We recommend using special heat guns for working with heat-shrinkable materials ( industrial hair dryers), which are not only convenient and safe, but also often have a temperature control function and a set of attachments different shapes, facilitating shrinkage of products in hard-to-reach places.

Preparation of heat-shrinkable tube:

1. Select a handset with the required physical properties, and correctly selected internal diameter(the diameter of the tube after complete shrinkage should be smaller than the size of the object on which it shrinks - as a rule, the standard diameter of the tube after shrinkage should be 15 - 20% less than the size of the shrink object). In this case, it is necessary to pay attention to the shrinkage coefficient of the tube; most often it is 2:1, i.e. the tube decreases in diameter by half, but there are tubes with a large shrinkage coefficient.
2. Preheat the pipe to 1/2 the shrinkage temperature (it depends on the type of pipe). This point is especially relevant for thick-walled tubes and large diameters; for thin-walled tubes this step is not necessary.

Shrinkage

1. Place the tube on the object or surface to be coated (Fig. 1)
2. Set the heating temperature to about +120°C, while the shrinkage temperature should not exceed the temperatures specified by the manufacturer in order to avoid overheating of the material from which the tube is made, melting, twisting or wave-like shrinkage of the tube.
3. It is recommended to start shrinking from the middle of the tube (Fig. 2). The pipe needs to be heated around it, trying to get uniform shrinkage. The central part of the tube should shrink and fit tightly to the surface of the insulated object.
4. Seat the pipe in the direction from the middle to its ends (Fig. 3). The tube must be heated evenly, constantly moving the heat source along its surface to prevent local overheating.
5. A properly seated pipe should be smooth, without bumps or bulges. If the inside of the pipe is coated with glue, then after shrinkage the glue should appear along the edges of the tube. (Fig. 4).
6. Leave the insulated item to cool completely.

When working with thick-walled tubes, busbars and high-voltage cables, it is recommended to perform a number of additional operations:
- Clean the cable surface and degrease it, for example using a cloth soaked in a fat-free solvent.
- Clean the surface of cables with a sheath of PCV (Polyvinyl chloride) with fine sandpaper, and preheat the surface of cables with a sheath of PE (Polyethylene).
- Metal surfaces remove burrs with sandpaper.
- Copper or steel objects(cable cores, busbars, etc.) large section must be preheated, since having high thermal conductivity, when shrinking they will actively remove heat from the heating zone, preventing good warm-up and high-quality shrinkage of tubes.

Helpful Tips:

The shrink tube must be selected in such a way that it standard size after shrinkage it should ideally be at least 20% smaller than the diameter of the object to be coated
- When using, cut the tube carefully. Be sure that the ends of the tube are straight and free of burrs. Otherwise, when shrinking, the tube will burst, go in waves or shrink unevenly
- Start shrinking the tube from one end, gradually moving along it as it shrinks. If the tube has thick walls or a large diameter, you can start shrinking it from the middle to the edges
- It is important to choose the optimal temperature for shrinking so that the tube shrinks quickly and without damage. The tube manufacturer always indicates the optimal shrinkage temperature on the packaging or on the tube itself. If the data on optimal temperature There is no shrinkage, use temperatures from +120 °C to +150 °C. In most cases, this will be sufficient to ensure proper shrinkage and minimize the risk of tube damage from overheating.
- Overheating/underheating of the tube during the shrinking process can lead to bubbles, charring, discoloration, incomplete shrinkage and tube damage

It is not difficult to buy heat-shrinkable tubing in Vladivostok, but its quality leaves much to be desired. What bothers me the most is the translucency. The train of thought is simple: if the heat shrink is translucent, like a cover for a school notebook, then its insulation is poor. And to be honest, all these half-pink and half-green tubes in no way harmonize with my wires, which are exclusively red, black, yellow or white.

I prefer to buy heat-shrinkable tubes from the hobbyking online store - the price is more attractive there and the quality of the tubes is much higher. Just don’t consider me an avid buyer of heat shrink: I bought it once and took a meter of each tube from the diameters and colors I needed - there’s enough for now, although some stocks are already running low. If I need more, I'll buy it there. As practice shows, a one-meter set is enough for a year of leisurely use. Heat-shrinkable tubes are marked by their original, primary diameter, that is, by the size before shrinkage. On average, all heat shrinks shrink exactly twice. Some more, some a little less. In any case, it is worth selecting the tube so that the diameter of the wire is slightly larger than half the diameter of the heat shrink. For example, a 14 mm heat shrink tube will shrink to 7 mm - in this case it must be used with a wire of at least 8 mm in diameter.

How to heat and shrink heat shrink tubing?

Most the right tool For similar work will soldering iron. However, this thing is not cheap and it is stupid to buy it just for the heat shrink. If you have a soldering iron with temperature control or Soldering Station, then you can burn the tube with the thick part of the soldering iron. Not a sting, but the place where it hides a heating element. Quite a working option.

Can an open flame be used for heat shrinking?

By open flame I mean any source of fire: a match, a lighter, a candle. In principle, the tube can be shrinked with an open flame, but you need to remember a few points:

1. During sudden shrinkage, the tube may become deformed and slide off.
2. With due diligence, heat shrink tubing can be burned through
3. Colored tube may become smoked

The main problem with using an open flame is that the source is always located below, so the structure must be constantly rotated over the flame so that the tube is compressed evenly. By the way, it is advisable to keep it three to four centimeters from the visible flame: there the temperature is most optimal. There is no need to stick the tube directly into the flame or its base: the temperature is lower there. I don’t recommend using turbo lighters or gas burners - the pipe will ruin in an instant!

How is heat shrink better than classic blue electrical tape?

Firstly, the tube does not unwind over time. Secondly, it does not stick to the material being insulated and does not leave an adhesive layer on it. And when correct selection color and diameter looks more aesthetically pleasing. By the way, removing the tube is much easier: just make a longitudinal cut. Heat shrink is also indispensable when insulating closely spaced contacts, for example, on connectors: there is no need to wrap it, that’s why free space not required.

Why is heat shrink tubing worse than regular blue electrical tape?

Except that it cannot be used to insulate structures of complex shapes whose size varies. If the connector has a diameter of 10 mm, and the wire is only 3 mm, then the tube simply will not reach the wire or will not fit onto the plug.

What sizes are there?

On the hobbyking website there are tubes from 2 to 100 millimeters. I was once in a store with electrical goods and all sorts of powerful things - there were heat-shrinkable tubes with a diameter of 25, and, if I’m not mistaken, even 50 centimeters. Tubes with a diameter of up to one or two centimeters really look like tubes. And the larger ones are flattened into stripes and look like a ribbon. It is important to remember that they are all marked by diameter, and not by the width of the flattened tape. For example, a red tube with a diameter of 14 mm looks like a ribbon with a width of 24 mm.

The diameter of the tube and its width in the flattened state are two different things!

Which ones to take?

I'll tell you about personal experience. So here's what I bought:

• 25 mm, transparent - convenient for isolating ESC and all sorts of USB boards (hubs, modems, wi-fi whistles)
• 16mm, clear - suitable for connectors and some small boards, probes or sensors
• 14 mm, red - I practically didn’t use it because I took it for my ESC, but didn’t calculate the dimensions; most often I cut it into thin rings and mark some cables; it is also indispensable for my Turnigy 4WD Rally car
• 6 mm, blue - for power wires; due to the color not being the most popular for me, it was practically not used, but many electricians will find it useful
• 6 mm, yellow - for power wires; used more often since I actively use the 12-volt line
• 6 mm, black - actively used for wires and connector connectors (3.5 and 4 mm bullet)
• 5 mm, black - the absolute leader in use in its diameter, out of stock
• 5 mm, yellow - used for insulating motor connectors (3.5 mm bullet)
• 5 mm, blue - helps in color differentiation of wires, although not so actively used
• 5 mm, red - the second most used in its diameter, I already have very little of it left
• 4 mm, black - completely out of stock, need to reorder
• 4 mm, red - only a little left and still useful
• 4 mm, yellow - there is quite a lot left, usually 12 volts like this thin wires I don't have any
• 3 mm, black - out of stock because it is very useful for almost all wires
• 2 mm, red - ran out quickly
• 2 mm, black - ran out even faster

Obviously, my most popular sizes are small diameters, but this is understandable: small models are thin wires. Diameters of 5-10 mm will be of interest to electricians and car enthusiasts: the former work with serious wires, and the latter like to seal everything. Larger diameters have even more specific applications, except for one: heat shrink can be stretched onto the handles of the tool and make it more convenient (and electrically safe) to handle. I use large gauges to insulate modules and boards.

When packaging various types food products The main requirement for packaging and packaging method is to protect and preserve the quality of the packaged product for a certain time (until the moment of its consumption).

For these purposes they use various techniques and methods, of which the most widely used are packaging in shrink and stretch films, aseptic packaging, packaging in vacuum and in a gas environment, and a number of others.

Heat shrink called polymer films, capable of contracting under influence of temperature exceeding the softening temperature of the polymer. Such films are obtained by stretching the polymer material in a highly elastic heated state and subsequent cooling.

In engineering practice, shrink films are usually classified as films that have the ability to produce increased (up to 50% or more) shrinkage and are used for packaging various products.

The advantages of packaging in shrink films compared to traditional film packaging include a reduction in packaging volume due to the tight fit of the product, and a relatively lower weight of films. Shrink film packaging is often cheaper and more attractive to look at than a regular cardboard box. This type of packaging provides certain advantages for retail: reducing the amount of packaging material and the space on the sales floor occupied by the product as it is sold. Shrink wrapping protects the product from environmental influences.

Types of shrink film
Shrink films can be classified according to several criteria:

1) depending on the raw material There are such types of shrink film as films made from crystallizing PO (LDPE, HDPE, PP), copolymers of ethylene with vinyl acetate, PVC, VCVD (copolymer of vinyl chloride with vinyl dechloride), polystyrene, rubber hydrochloride, polyamide.

Polyolefin Shrink Film , popular in the European market, has a special, so-called cross-cross molecular structure, due to which the film with minimum thickness able to withstand the highest loads.

Compared with PVC shrink film polyolefin film has a number of advantages: shrinkage is 2 times higher; shrinkage temperature is lower; no turbidity, high gloss; wider range of storage temperatures for goods packaged in film without changing the properties of the film; the presence of a stretch reserve (a higher degree of elasticity) protects the film from bursting; due to the absence of chlorine molecules, there is no smell when sitting down. In addition, PVC can release chlorine not only during disposal, but also when storing the product at temperatures above +25° C, giving specific smell product. Polyolefin films, which do not contain chlorine, are more loyal to the product.

The most widespread Low density polyethylene shrink films , having satisfactory mechanical strength in the temperature range from -50°C to +50°C, easy to weld, elastic and inert in relation to most packaged substances and having a low cost.

The most modern and high quality are shrink films based on linear polyethylene . Possessing excellent strength, they, unlike polypropylene films, do not deform the product at all and are suitable for packaging even newspapers and magazines. Due to their multilayer nature, films based on linear polyethylene have some barrier properties. They are also distinguished by a wide range of possible storage temperatures for goods: from - 80° C to +80° C.

Heat shrink films made of polypropylene Compared to polyethylene, they are characterized by increased rigidity and higher strength indicators. They are less susceptible to cracking under the influence of residual stresses, are transparent, and have reduced permeability to water vapor and various aromatic substances.

Shrink films also receive based on radiation-modified polyethylene . Exposure to ionizing radiation during the manufacturing process of shrink films can increase their heat resistance, shrinkage stress, and improve strength properties.

2) depending on the degree of shrinkage films are distinguished in the longitudinal and transverse directions uniaxial and biaxial.
- uniaxial films shrink predominantly in one direction: for example, longitudinally by 50-70%, and transversely by 10-20%.
- biaxially oriented films shrink in both directions, with the same or different degrees of shrinkage: for example, in the longitudinal direction by 50-60%, and in the transverse direction by 35-45%.

3) depending on consumer requirements shrink films are produced thickness from 20 to 250 microns With maximum deviation in thickness no more than +20% of the specified:
- shrink films with a thickness of 20 to 50 microns are used for single packaging;
- shrink films with a thickness of 50 to 100 microns are used for group packaging;
- shrink films with a thickness of 100 to 250 microns are used for staple packaging;

4) depending on the production method are produced:
- single layer shrink film produced by extrusion.
This method involves pressing a material with high viscosity into liquid state, through the forming tool (head), in order to obtain a product with a cross section the desired shape;
- multilayer shrink film produced by coextrusion method.
In the production of coextruded films, the same types of extruders are used as in the production of homogeneous films (however, with a completely different extruder head solution). The coextrusion process uses at least two, but often more, extruders equipped with a co-head. Jets of various plastics are combined in dies that form the final part of the head, less often - immediately after exiting the head.
Multilayer shrink film includes a first layer of an acid copolymer, an ethylene copolymer with an α-olefin, or a mixture thereof, and a second layer containing an ethylene copolymer with 9-20 wt.% vinyl acetate. The film may have a third layer of barrier polymer, a fourth layer of ethylene copolymer with 9-20 wt.% vinyl acetate and a fifth layer.
The formation of each layer of multilayer shrink film occurs separately. That's why possible defects of each layer do not coincide, and the film turns out to be 15-20% stronger than a single-layer film of similar thickness. Thus, it becomes possible to reduce the thickness (and therefore the cost) of multilayer “heat shrinkage” without deteriorating its performance characteristics. In addition, reducing the film thickness makes it possible to reduce the temperature in the thermal tunnel, which allows the film consumer to save energy.

5) depending on the (co-)extrusion technology shrink films look like:
- sleeves . (Co-)extrusion with blowing is used;
- canvases . It is produced by the flat-slit (co-)extrusion method, or the sleeve produced by the blown (co-)extrusion method is cut lengthwise;
- half sleeves . It is either a rolled web (produced by flat-slot (co-)extrusion) or a cut sleeve (produced by blown (co-)extrusion);
For various methods extrusion, the design of the extruder heads and other devices has fundamental differences, however, the design of the extruder and the operating principle of the forming tool are the same for both methods.

Properties of shrink film

The physical, mechanical and operational properties of the films are determined by the chemical nature of the polymer used and the degree of its orientation.

Important characteristics of shrink films are shrinkage rate (shrinkage factor) and shrinkage stress . The degree of shrinkage is characterized by the ratio of the linear dimensions of the sample before and after shrinkage and is determined by the formula:

Kyс = (Lo - L/Lo)100%, where Lo and L are the length of the sample before and after shrinkage.

Shrinkage stress Sus- this stress that occurs in an oriented material when heated to a certain temperature is determined by the formula:

Sus = P/S, MPa, where P is the force generated during shrinkage; S - cross-sectional area of ​​the sample after shrinkage.

The shrinkage voltage depends on the temperature and duration of heating of the film. The lower the shrink temperature, the longer it takes for the film to shrink. If shrinkage is performed at high temperatures, then the shrinkage time may be insignificant. The strength of the films after shrinkage decreases somewhat, but remains sufficient to ensure the integrity of the package.

For packaging single products of small mass, for example, baked goods, bird carcasses, aerosol cans, souvenir sets, films with a thickness of 20 - 50 microns are used; for group packaging, a film with a thickness of 50 - 100 microns is selected; for packaging on pallets (stack packaging) - a film with a thickness of 100 - 250 microns.

The table shows the main properties of some shrink films

To achieve high physical, mechanical and technological characteristics of shrink film as a packaging material, the following requirements are imposed on it: formulation, high uniformity of properties across the entire field of the film, high quality winding

Packaging options and areas of application of shrink film

Shrink films used for packaging a variety of food products, cans, bottles, haberdashery and household products, newspapers, magazines, stationery, etc.

Possible options for packaging in shrink film can be divided into three main groups: single, group and stack packaging.

Single packaging(it is called piece, or individual) - each individual product is wrapped in film, which, after shrinking, tightly fits the product, repeating its configuration.

Group packaging- a set of several similar or different types of products is pre-packaged, which, as with a single package, are wrapped in film, after shrinkage of which a dense package is obtained. Packaging can only be done in film or using preliminary placement of products on special substrates. This type of packaging can be used as a transport container

Stack packaging- products (bags, boxes, books, bricks, trays with cans, bottles, etc.) are placed on a rigid pallet in several rows, which are covered with a cover of shrink film and fed into a tunnel oven. After shrinking, a compact stack is obtained that can be easily moved by lifting vehicles. Stack packaging is a modern and promising type of transport packaging of goods.

The process of packaging in shrink film includes the following operations: laying the product on a substrate (tray, pallet); wrapping with film; package welding; shrinkage (passage through the shrink chamber); cooling of products.

Shrink film shells design are divided into wrapping, full wrapping and sheathing type.

Obanderolivayuschie packaging shells cover a group of products (packaging units) or a transport package (block package) completely around the perimeter, and have holes on the end sides.

When fully wrapped the film shell completely covers the transport package or group of products (packaging units).

For fastening transport packages with packaging shells sheath type Covers are made from tubular shrink film by joining the upper edges of a section of sleeve with a welded seam.

Printing on shrink film
If we talk about shrink film for group packaging, then it is quite thick and durable material. Printing is usually done on the front surface - unlike shrink labels. The gravure printing method is predominantly used, but flexography is also confidently gaining its space.

Flexographic and gravure printing methods are also used for printing on thin shrink films for small packaging.

Printing on shrink films presents challenges that are not typical for working with paper. Prepress preparation requires a special approach. It is necessary to design the image in such a way that when it shrinks on a product or group of products, for example, the same bottles, it does not turn out to be distorted. Here the “distorting mirror” effect must be calculated in advance. Special software products have already been created for this purpose.

Film shrinkage also affects the paint. The main thing is that the paint film remains flexible enough, otherwise after shrinkage, tears, cracks, and dark stripes will appear in places where pigment accumulates. Almost all quality paint manufacturers have overcome these problems.

Working with paints water based are faced with another problem. The bulk of such orders were traditionally carried out on gravure printing machines, but now more and more flexographic printing houses are offering printing with water-based inks. However, when the finished printed package is cured in a steam tunnel dryer, the ink may pick up moisture again.

Application of shrink film
According to the experience of foreign enterprises, 95% of shrink films are used for non-food products and only 5% for food products (most often for packaging pizza and vegetables). In our country, shrink films are widely used for packaging food products. Areas of application in food industry quite varied, the most common of which are the following:

Packaging of bakery products - used to increase sales time and, in addition, in such packaging bakery products acquire an aesthetic presentation;

Packaging of meat and poultry - to increase shelf life, give an aesthetic appearance and convenience for retail sale;

Packaging of confectionery or semi-finished products using trays of appropriate sizes. Such packaging, thanks to the rigid tray, ensures greater safety of the product compared to conventional packaging in bags and has a packaging volume that is more attractive to the consumer.

Group packaging of cans, bottles, bags of alcoholic and soft drinks, dairy products, etc.

Shrink film is also used in the field of non-food products. In particular, it is used to:

Packaging of paper products - fax paper, printing products. In this case, shrink films with a low degree of shrinkage are used;

Packaging of radio-electronic, metalworking and light industry products;

Packaging of household products;

Packaging of chemical, food, medical, perfumery products;

Packaging building materials: skirting boards, glazing beads, platbands, cornices, blinds, wallpaper and many other long pieces. In this case, heat-shrinkable films with different shrinkage in the longitudinal and transverse directions are used;

Packaging of video cassettes, CDs, DVDs, souvenirs, etc.

Shrink films are also used for packaging products in brick and glass factories.

Heat-shrink films are polymer films that can shrink under the influence of temperatures exceeding the softening temperature of the polymer. Such films are obtained by stretching the polymer material in a highly elastic heated state and subsequent cooling. The consequence of this is the directional orientation of the molecular chains of the polymer and the occurrence of stresses in them. During subsequent cooling and solidification, these deformations and stresses are fixed in the material as a result of the glass transition and crystallization processes. When reheated, relaxation processes occur in such films, and they tend to return to their original sizes. This rebound ability is called "polymer memory" or heat shrinkage.

Shrink films can be made from many crystallizing thermoplastics, including low-density polyethylene and high density, polypropylene, copolymers of ethylene with vinyl acetate, polyvinyl chloride, copolymers of vinylidene chloride and vinyl chloride (povidene), polystyrene, polyisoprene hydrochloride (escaplene) and others. The main characteristics of shrink films are given in Table 1. The most widely used shrink films are made of low-density polyethylene, which have satisfactory mechanical strength in the temperature range from -50 to +50 0 C, are easily welded, elastic and inert in relation to most packaged substances and have a low price.

Table 1. Main characteristics of shrink films.

Heat-shrinkable films made of polypropylene, in comparison with polyethylene, are characterized by increased rigidity and higher strength properties. They are less susceptible to cracking under the influence of residual stresses, are transparent, and have reduced permeability to water vapor and various aromatic substances. For example, shrink film made from povidene is an elastic, highly transparent, physiologically harmless vapor and gas impermeable material, resistant to oils, grease and many other aggressive chemicals, etc. Heat-shrinkable films are also produced on the basis of radiation-modified polyethylene. Exposure to ionizing radiation during the manufacturing process of shrink films can increase their heat resistance, shrinkage stress, and improve strength properties.

Important characteristics of shrink films are the degree of shrinkage (shrinkage ratio) and shrinkage voltage.

The degree of shrinkage is characterized by the ratio of the linear dimensions of the sample before and after shrinkage; it is determined by the formula:
Кус =(1 0 -1) / 1 0 *100%
where 1о and 1 are the length of the sample before and after shrinkage.

As already noted, during the production of shrink films, the tensile stresses (orientation) of the molecular chains of the polymer are fixed in them. When the film is heated to a highly elastic state, these stresses are released and, returning the molecular chains to their original state, shrink the film. If the shrinkage process is prevented by applying an external force, then the shrinkage force developed by the film can be measured. The shrinkage stress, yc, that arises in an oriented material when it is heated is determined by the ratio of the shrinkage force to the cross-section of the film sample before shrinkage and is expressed in MPa. The shrinkage voltage depends on the temperature and duration of heating of the film. At low heating temperatures, it takes longer for the film to shrink, and at high temperatures, the shrinkage time may be insignificant. Depending on the degree of shrinkage in the longitudinal and transverse directions, films are distinguished between uniaxially oriented and biaxially oriented. Uniaxially oriented films shrink predominantly in one direction: for example, in the longitudinal direction by 50 - 70%, and in the transverse direction by 10-20%. Biaxially oriented films shrink in both directions with the same or different degrees of shrinkage: for example, in the longitudinal direction by 50...60%, and in the transverse direction by 35 -45%.

Depending on the production method and consumer requirements, shrink films are produced in thicknesses from 20 to 250 microns with a maximum deviation in thickness of no more than +20% of the specified one. They are supplied in rolls in the form of a sleeve, half-sleeve or sheet. During the production process, these films can be modified with various kinds of additives that give them special properties, including corrosion inhibitors (protect metal products from corrosion), light stabilizers (increase their service life in the open air) , oxidizing agents electoral action and antioxidants (increase the durability of films), coloring pigments and other substances, for example, preventing the film from sticking to polymer bagged products during shrinkage. Shrink film packaging shells are widely used for securing transport packages, either alone or in combination with other packaging means, including flat pallets, backing sheets and frames. Shrink wrapping can accommodate single products, groups of products or packaging units, and shipping bags or block bags, with or without pallets.

In the first case, each individual product is wrapped in film, which, after shrinking, tightly fits its surface, repeating the general configuration of the product.

In the second case, a set (group) of several similar or different types of products (packaging units) is completed, sealed with a shell of shrink film into a tight package. In this case, the products can be placed on special substrates, trays, backing sheets and frames, which, together with the shell, perform the function of transport packaging.

In the third case of piece goods, transport units or packages on a flat pallet or without it, a multi-tiered transport package or block package is formed and secured with a tight-fitting packaging shell made of shrink film. The process of packaging cargo with shrink wrappers includes the following operations:

formation of a multi-tiered transport package, if possible with dressing, on a pallet or without it;

wrapping the package with shrink film;

welding the edges of the film and forming a packaging shell;

heating, shrinking and cooling of the packaging shell.

Shrink film casings, according to their design, are divided into wrap-around, completely wrap-around and sheath-type.

ABOUT parcel wrapping packaging shells cover a group of products (packaging units) or a transport package (block package) completely around the perimeter, and have holes on the end sides. They are made from film material coming from two rolls and joined at the edges by two longitudinal welds (Fig. 1a) or coming from one roll and joined by one longitudinal seam (Fig. 1b).

In this case, the width of the film web is taken to be much larger than the length of the bag and when shrinking, the protruding edges of the film are pulled onto its end walls. As a result, the shell is obtained with holes with an area of ​​0.3 -0.5 from the end surface of the package.

When fully wrapped, the film shell completely covers the transport package or group of products (packaging units). When making such shells from a film web coming from two rolls, the edges of the film are connected to each other by sealed welds made along the perimeter (on four sides) of the package (Fig. 1c). If this shell is made of film material coming from one roll or half-sleeve film, then its edges are connected with sealed welds on three sides of the package (Fig. 1d). And when using tubular film, the edges of the shell are connected to each other by two sealed transverse welds located on opposite sides of the package (Fig. 1e). To fasten transport packages with casing-type packaging shells, covers are made from tubular heat-shrinkable film by connecting the upper edges of a section of the sleeve with a welded seam. Then such a cover is straightened around the perimeter into a rectangle, placed on top of a transport package formed on a rigid base (flat pallet) so that the lower edge of the cover is slightly lower than the pallet, and heated. In this case, the film contracts, bottom edge The cover is pulled under the pallet, and the shell firmly holds the transport package together on all sides (Fig. 1e). In particular, on an automated packaging complex model FSA well-known company"Mollers" (Germany) this process is carried out as follows. In the automatic stacker of the complex, a transport package is formed from packaged unit cargo on a flat pallet and transferred by a conveyor to the sheathing machine. Here, the grippers of the machine frame, which is in the upper position, are inserted into the lower end of the tubular film unwinding from the roll, straighten it into a rectangle according to the size of the package and, feeding it inward through the fingers of the grippers compressed air, inflate the sleeve. Then, by moving the frame down, the film sleeve is placed over the entire package, including the height of the pallet. Next, the film is cut from the top of the roll using an appropriate mechanism, and at the same time the top of the cover is welded with a sealed transverse seam. After this, the grippers release the lower edge of the cover, and the frame, moving upward, heats and shrinks the film using gas or electric beam heaters located along the inner perimeter of the frame. In the upper end position the frame stops and the heaters are switched off. Then the sealed transport package is removed, the next one is installed in its place, and the cycle is repeated with a productivity of 14 to 120 packages per hour.

The same company has created technology and automated complexes of the PKS series, which ensure the palletless formation of transport packages from cargo in bags or other predominantly soft packaging and their fastening with heat-shrinkable casings of the casing type. During the work process, a transport package of packaged cargo is formed on the table of the automatic stacker of this complex, the latter upper layer in which it is not laid completely so that there are recesses on the edges along the length of the package to the width of the forks of the loader. Then the formed package is fed by a conveyor to the automatic covering machine, where a heat-shrinkable cover is put on it, just like in the FSA model complex discussed above. Next, the package is moved to a rotating station, which turns it 180 0 so that the top layer with recesses along the edges is at the bottom. From the station, the package is transferred to the second covering machine, where a back cover made of the same tubular film as the cover is placed on top of it with heat shrinkage, and at the same time, on the lower recesses of the bag, the cover film is thermo-profiled for forks. After this, the finished transport package (Fig. 1g)

The dimensions of the piece of film (length, width) required for fastening the transport package with a shrink wrap are calculated depending on the cargo fastening scheme (Fig. 1) using the formulas given in Table 2.

Table 2. Formulas for calculating the dimensions of the development of a heat-shrinkable packaging shell.

Note: L – package length; B – package width; H – package height; c – allowance for welding joint (c = 20E40 mm); z – pallet height ((z=150E200 mm)

The strength of the packaging shell is determined by the thickness of the shrink film and the strength characteristics of the polymer. When fastening packaged goods only with a heat-shrinkable shell made of polyethylene film its thickness must correspond to that indicated in Table 3.

Table 3. Data for determining the thickness of the polyethylene heat-shrinkable packaging shell.

When fastening packages formed on a rigid base (flat pallet, backing frame), the required film thickness is selected depending on the weight and overall dimensions of the package being fastened, as well as the coefficient of friction between the surfaces of the packaged products according to one of the following graphs obtained empirically. To determine the thickness of polyethylene shrink film using a method that takes into account the mass and overall dimensions of the package being fastened, first calculate average densityРср package according to the formula:
P av =M/LxBxH, kg/m 3
where M is the mass of the formed package, kg;
L, B and H – length, width and height of the package, respectively, m.

Then, according to the graph shown in Fig. 2, depending on the value of Рср, the thickness of the film is determined, which is optimal when transporting a given package by one type of transport. When transporting these packages with transshipment or mixed transport (for example, rail and water), the film thickness determined according to the schedule should be increased by 0.02 -0.03 mm. The required thickness of polyethylene shrink film can also be determined from the graph shown in Fig. 3, based on the mass of the package being fastened M and the coefficient of friction ftr between the mating surfaces of packaged piece products (plates, sheets, bricks, tiles and others) or packaged piece goods ( in bags, packages, boxes, bales, etc.).

Packages with products (with or without packaging) that have mechanical strength sufficient for transporting and stacking the packages are secured with shells made of shrink film. Original dimensions The shells must be such that during the shrinkage of the film the maximum degree of shrinkage is not realized. After shrinking, the shell should tightly fit the transport package and have no mechanical damage. The welded joints contained on it must have a tensile strength of at least 11 MPa (110 kgf/cm2). It is not allowed to use heat-shrinkable casings for products whose surface is coated with lubricant, as well as for products packaged in polymer materials, the melting point of which is lower than or equal to the melting temperature of the shrink film. It is also not allowed to weld the shell to the packaged product or its packaging.