Figure 2.1 Some of the polymers used for shrink film labels. Source- Klöckner Pentaplast
In addition to substrates, we must also consider certain container characteristics and even;
Figure 2.1 Some of the polymers used for shrink film labels. Source: Klöckner Pentaplast
Figure 2.2 There are many factors to be considered in film selection. Source: Klöckner Pentaplast
environmental settings (Figure 2.2). For instance, we must consider squeezability: is the container squeezable, and which substrate should be chosen to make it easy to squeeze? What about scuffing? How does the material perform when applied to the final product and is transported? Is it going to be packaged as a half tray bundle wrap; or is it going to be surrounded by cardboard protection? How does the shrink force affect the choice of film? These are just a few examples of what must be considered when choosing which substrate to use.
Figure 2.2 There are many factors to be considered in film selection. Source- Klöckner Pentaplast
There are other general considerations as well, like light sensitivity: if the product is sensitive to light, we must factor this variable into the type of substrate we select. Similarly, if the product experiences rough handling from the production facility to the store shelf, we must take this into consideration when selecting the appropriate substrate. In short, there is a range of factors to consider when choosing the appropriate substrate.
The starting point for selecting a shrink film is the container shape and characteristics. The container shown in Figure 2.3 is a trigger bottle, an asymmetric shape with long sides. This type of container can be round, it can be square, or it can be long-sided. Each container type has different characteristics that will determine the shrink sleeve substrate most appropriate for the container.
Figure 2.3 Container shape and the fundamental questions to ask. Source- Klöckner Pentaplast
Determining the appropriate substrate means starting with some fundamental questions, which we will divide into four categories (Figure 2.3).
Maximum shrinkage percentage is critical. The film needs to shrink enough so it does not show ‘flowering’, an effect that occurs when the film does not shrink enough, causing the top or the bottom to ‘flower.’ The substrate must shrink enough to provide complete coverage of the container being decorated. For example, if the sleeve is not required to go to the top of a narrow neck, it will require a lower shrinkage than one that does.
Is a high or low shrink force required? Shrink force is another significant consideration. Shrink force is the force exerted on the container as the film shrinks onto it. Shrink force factor considerations, such as shrink tunnel type and shrink tunnel effects, will be discussed in greater detail later in this article.
Now we will address these four fundamental questions one by one.
Maximum shrinkage. There are several factors to consider regarding maximum shrinkage. One factor is the container shape and the maximum shrinkage required to cover it. Other considerations include the container contours, the container wall thickness, whether the container is full or empty and the tunnel type. Does the container have ribs? Is it a trigger bottle? Is it asymmetric?
The formula for the maximum shrink required is shown in Figure 2.4. Simply take the narrowest circumference (or diameter for a round container), divide by the widest circumference (or diameter), subtract from 1, and change to a percentage. Then add 1%-2% for layflat oversize and safety. This gives the maximum shrink percent required of the substrate.
Figure 2.4 The formula for determining maximum shrinkage. Source- Klöckner Pentaplast
Indeed, what is layflat oversize and why do we need it? The layflat of a shrink sleeve is when a shrink sleeve reel has been made into a tube and then is flattened. Measuring from one side to the other of the flattened tube is called the layflat. If the layflat is exactly the same as the circumference of the container, the sleeve will not fit over the container smoothly and will jam. The machinery application manufacturer will advise what layflat oversize is needed; for instance, it could be 5mm, or 10mm or so.
It depends on the container shape and how the shoulder is formed. For instance, if the container has a sharp shoulder, then the layflat will need to be a little bit larger. We must also consider the speed at which the shrink sleeve label is applied; when running faster, more oversize will be needed. For example, if the speed is 400 bottles per minute, the applicator supplier will advise that a specific layflat oversize is required, and this specific layflat oversize enters our calculus.
The formula then provides the total percent shrink needed, which may be, for instance, 60% shrink. Always purchase a film with slightly more shrinkage than the total percent shrink needed to make sure it completely shrinks over the container. In the example provided, you would purchase a film with a shrinkage of, say, 62%.
Shrink force. How does shrink force affect the choice of substrate? How about ribs or contours? Let’s assume the container has ribs. A weak shrink force won’t pull the film into the ribs; it will just ‘bridge over’ them. When the consumer then handles that container, it will feel cheap and ill-fitted. They will be able to feel the loose film over the ribs. To get a good customer feel, the film should pull into the ribs and be tight on them . So a higher shrink force is required.
However, if the container is empty, particularly a weak container (for instance, a HDPE container that is being sleeved empty), then a high shrink force will distort the bottle in the shrink tunnel. When the film shrinks onto the container, the film will be strong enough to twist and distort the bottle.
This could mean that the bottle cannot be filled, and cannot be capped. In short, container wall thickness, tunnel type, whether the container is being sleeved empty or filled, all matter in the choice of substrate.
Shrink tunnel effects. Relaxation is another important consideration (Figure 2.5). As an empty HDPE container travels through a shrink tunnel, it will be in the shrink tunnel for maybe five or 10 seconds, depending on the length of the tunnel, speed of the line, etc. The container will expand as it goes through the tunnel due to the heat. When the label shrinks onto the expanded container inside the tunnel, the label will fit the container snugly while inside the tunnel. However, when it comes out of the tunnel and returns back to ambient temperature, the container will shrink back.
What then happens to the sleeve? It does not shrink back, and the sleeve does not fit tightly anymore – it becomes loose and can spin on the container; the film does not ‘relax’ back with the container. This loose fit does not provide a good customer feel. What is needed is a film that shrinks back with the container as it cools. As the container reduces in size, the film needs to shrink with it and remain tight. This is referred to as ‘relaxation’ - the film needs to 'relax' with the container.
Now, let’s discuss smiling/frowning. Consider a long-sided oval container, a square container, or a trigger container. If the wrong material is chosen, the shrink sleeve will ‘pull up’ from the bottom on the long side of the container. This effect is called 'frowning'. A similar effect happens at the top of the container – the label will pull down and cause a ‘smile’, which appears unsightly on the retail shelf. The converter does not want a label with this effect, and the brand owners certainly do not like it. There are certain materials that have a tendency not to frown or smile, but there are others that do; choosing the right substrate for these shaped containers is important. If it is a round container, it is not as important, but on a container with a long, straight side, it can be critically important.
Figure 2.5 Some of the key shrink tunnel effects Source- Klöckner Pentaplast
There are also a number of other things to consider and take into account when choosing the right substrate (see Figure 2.6).
Figure 2.6 Some of the fundamental things that need to be considered. Source- Klöckner Pentaplast
Does the brand owner accept PVC? PVC was the first material developed for shrink sleeves. It is considered a great shrink sleeve substrate in a number of ways. However, some brand owners consider PVC a problem due to environmental considerations. Therefore, one of the first considerations will be: ‘What is allowed by the brand owner? Will the brand owner accept PVC?’ This is a fundamental question that affects substrate choice.
Light blocking: Certain drinks require protection from the effects of light, which therefore becomes another consideration when selecting the appropriate substrate. Some examples include dairy beverages, isotonic drinks, and aseptically packaged drinks. In addition, product constituents such as vitamins, particularly riboflavin, also require protection from the effects of light. Finally, taste and flavor attributes require protection from the effects of light. In summary, visible light and/or UV light can destroy or change the nature of the product being decorated, and we must enter these factors into the substrate equation.
Ultraviolet detection: Some application machines use ultraviolet detection to determine whether the
sleeve was applied correctly to the container. For this reason, the sleeves need an optical brightener present in the film. The application machine ‘sees’ if the sleeve is positioned correctly on the container, and if it is not, it will divert the container off the conveyer. It is possible for the printer to print the optical brightener (OB) onto the substrate, but if the print levels of OB fade, there is potential for large rejections of sleeves – so having the OB in the substrate is more reliable.
Transportation: In the United States, for instance, many beverages are transported using half trays with bundle wrap. The containers are packed closely together and often rub against one another during transport. Because of this, the shrink sleeves on the containers can be scuffed or damaged, and the result is an unsightly product. So a consideration in the choice of shrink film substrate is how resistant to scuffing must the film substrate be?
Recyclability: The shrink sleeve itself generally cannot be recycled into clear recycled polymer as they are printed; they can only be recycled into secondary uses. However, the container generally can be recycled. Hence, a consideration in the choice of substrate is how the sleeve will be separated from the container in the recycle system? The sleeve needs to be removed from the container so that the container (and the sleeve separately) can be recycled. This has become an increasingly important consideration recently as ever more containers are sleeved.
LABEL FILM TYPES AND CHARACTERISTICS
Having talked about containers and their characteristics, we will now start looking at the range of films that can be used and their characteristics. What substrates are best used for which applications? We shall look at the key characteristics of each shrink film and their main technical details.
PVC (Polyvinyl Chloride)
PVC is the oldest of the shrink films and a terrific all-around film. This film processes well, it prints well, it shrinks well and it has a great shrink curve. It can be printed with rotogravure, letterpress, offset and flexo, using UV, solvent, or water-based inks. It is a great material. It can be supplied in UV protection grades, as well as with optical brightener grades. It has been around for so long that it is possible to get PVC film in a host of variations. It is available with low shrink, medium shrink and high shrink, but, as mentioned before, the primary concern with using this film is whether the brand owner will accept it.
As can be seen in Figure 2.7, PVC shrink is midrange at 55-65%; not particularly high, though, not low.
Figure 2.7 Characteristics and technical details for PVC film. Source- Klöckner Pentaplast
PVC has a moderate shrink force that will crush empty containers. It will also not ‘relax’ on empty HDPE containers, resulting in a loose sleeve. The scuff resistance is middling – better than OPS, but not as good as PETg. Finally, squeezability is poor; on a squeezable container, the sleeve will crinkle and will have a poor customer ‘feel’.
Another term worthy of mention is natural shrinkage, which is a term that pertains to converters. When a roll of film is purchased it will be stored in the converter’s warehouse, where it will gradually shrink (creep), depending on the warehouse temperature. Usually, the shrink is imperceptible.
PET hardly shrinks at all; OPS will shrink significantly more. Films that have greater levels of natural shrinkage likely will have shrunk by the time they are put on the press. After printing, the film will move into a warehouse, where it may continue to shrink, unless the warehouse is kept very cold. If the converter is in a hot place, OPS can be very difficult to manage. Natural shrinkage for PVC is good, i.e., it has very little natural shrinkage when kept at reasonable warehouse temperatures. Natural shrinkage concerns material that is printed and handled; in other words, once it has been shrunk onto the container, natural shrinkage no longer becomes a concern.
PETg (Polyethylene Terephthalate, Glycol-Modified)
PETg is typically referred to as just PET. However, there is no such thing as a shrink sleeve made from pure PET. Every PET shrink sleeve is made from a PET that has been modified in some way. The general terminology we use for this modified film is PETg. It is a clear film and it has the highest maximum shrinkage of all shrink film substrates. If a converter desires shrink rates of 75% or greater, this is the only substrate option. It will shrink all the way down to the neck of a narrow neck beer bottle or two liter beverage bottle. It is commonly used when PVC is not an option allowed by the brand owner. It handles well and has an excellent printing surface – printing really stands out and has a vibrant look. When comparing PET and PVC side by side, the PVC prints well, but PET will stand out a bit more. PET substrates can also come with UV protection to protect the label or, at a higher level of protection, protect the product contents. It is also possible to get optical brightener versions of PET for sleeve detection. It works well in steam tunnels, which we will discuss later. And if used with care, it can also operate in hot air tunnels.
Maximum shrinkage for PET is 75% or greater. The shrink force, however, is high. It will crush empty containers and distort them. It also will not relax, so if there is an empty HDPE container that has expanded during the shrink tunnel process, then a PET sleeve will not shrink back with the container, and will instead be loose. However, it is a tough, durable material and has the best scuff resistance. When two containers are placed together and rubbed, they will still appear unblemished, even after being shipped over long distances. For glass or metal containers, use PET.
Glass next to glass will scuff – therefore a PET sleeve is required. Natural shrinkage for PET is good, and as mentioned before, PET is excellent for printing.
One thing worthy of mention about PET, however, is concerning smiling and frowning. There are several grades of film available, and some of them are specifically designed not to frown or to smile. The converter therefore has to be a bit careful about which PET to use with long-sided, non-round containers.
White Opaque (non-clear PETg)
There are several versions of white opaque film in the market that are PET films containing various mineral fillers. It is possible to purchase these in both glossy and matte versions. If light protection is needed, white opaque will provide about 70% to 80% light protection. To get 99% - 100% light protection, however, the converter will need to print black on the reverse of the film. Examples of this include products such as Nesquik or Fairlife dairy beverages in the U.S. that, when the label is removed, show a 100% black print on the inside of the sleeve. It is worth mentioning that the printer should not print the black over the seam, though. The black ink is printed to protect the contents from light. If the white opaque has been chosen only for aesthetics, though, there is no need to print the reverse black.
White opaque films offer shrinkage percentages that are very similar to those of clear PET – roughly 75% shrinkage.
New to the market are the ‘bi-color’ films – which are white on one side, and black or grey on the reverse side. These films provide complete light-blocking without requiring the printer to print the 100% black ink reverse print. Examples are the ‘Eklipse’ product from Klöckner Pentaplast.
Reference also needs to be made about the printing of white opaque films. White glossy film prints , much the same as PET – very well. White opaque generally prints well unless it is printed rotogravure. The white opaque surface is not flat, which causes a matte effect. Shrink sleeves are commonly printed rotogravure: Asia, for example, is 100% rotogravure; Europe is maybe 50%; in North America, in the shrink business, it is around 30-45%. When the matte surface connects to a rotogravure cylinder in the printing process, the ink needs to come out of the tiny cells in the cylinder and transfer to the substrate. Any film surface variation will cause a problem with a fine 10% rotogravure halftone – the ink will not come out of the cells cleanly. The capillary action needed to pull the ink out of the gravure cell does not happen, causing a missing dot. So with half tones and highlights of 10%, 15% or 20% dots, there will be printed image problems. Electrostatic Assist (ESA) helps but does not solve the problem entirely. Moreover, many printers are wary of ESA with solvent gravure on safety grounds. Offset or flexo printing typically does not encounter issues of this sort when printing on white opaque film.
OPS (Oriented Polystyrene)
The word ‘oriented’ in OPS simply means it has been stretched. 0PS is a great material. Nevertheless, the converter needs to be familiar with how to process it. It is tricky to print, particularly using rotogravure. It will tend to shrink both in the warehouse and after it has been printed on and is sent to the customer. It is very susceptible to shrinking at even slightly elevated temperatures.
Care needs to be taken with OPS film – it is no match for oil and chemicals. Solvent rotogravure generally uses a mixture of acetates and alcohols, with a high percentage acetate and a low percentage alcohol. Unfortunately, if a drop of ethyl acetate is put on an OPS film, it will melt straight through the film, burning a hole through it. This shows how weak OPS film is against acetates, and yet the solvent rotogravure converter would like to print with them. To print OPS, it is necessary to reverse the percentage and have an alcohol-rich ink system . requiring the ink in the press to be removed and replaced with a special OPS ink. When the converter goes back to a PVC or PET film, then the OPS ink will need to be removed and the press replenished of other inks. There are combination inks that can print both PET and OPS, but using these inks means carefully choosing your substrates.
Figure 2.8 Characteristics and technical details for PET shrink film. Source- Klöckner Pentaplast
Figure 2.9 Characteristics and technical details for white opaque film. Source- Klöckner Pentaplast
OPS provides a medium to reasonably high shrinkage, as noted in Figure 2.10. It is possible to get OPS that goes higher than 65%, but it is a special OPS.
Figure 2.10 Characteristics and technical details for Oriented Polystyrene. Source- Klöckner Pentaplast
elaxation is excellent for an empty HDPE container going through a shrink tunnel decorated with OPS substrate. OPS is very good at relaxing back, so if the bottle has expanded and the OPS shrinks onto it, then as the bottle cools and contracts, the OPS will just shrink back (relax) with it – it remains tight. However, rub two OPS sleeved containers together, and within three or four rubs it will show scuffing. Within 10 rubs, there will be a hole in the film. It is a very weak film, so if the decorated containers are going to be transported over a long distance, it is not advisable to use OPS.
In terms of squeezability, there is no crinkle. Squeeze OPS and it returns to its shape, it takes the form back to that of the expanded bottle. Brand owners love it for this reason, but it requires care when it is handled and printed.
Polyolefin shrink sleeve film is generally a combination of polyethylene (PE) and polypropylene (PP).
The most common labeling technology used to label PET beverage bottles is the polypropylene (PP) wrap-around label. The recycling industry has developed a straightforward technology to separate the PP wrap-around label from the PET container using float tanks, where, after grinding, the PET bottle flakes sink and the PP label floats. In doing so, they separate the valuable, clean PET bottle flakes from the printed PP label, which allows the PET bottle flakes to be recycled. Unfortunately, the specific gravity of PETg, PVC and OPS shrink labels is greater than 1.0, meaning that they will sink in a float tank. The advantage of polyolefin shrink sleeves is that they float, however. The polyolefin shrink sleeve material can therefore be separated from the PET bottle flakes, allowing the PET bottle flakes to be recycled.
PO films are also good on crinkle and relaxation.Their performance rivals that of OPS, and because
of this, brand owners’ interest level in PO is quite high.
OPS film has many drawbacks, particularly in processability and scuff resistance, as detailed in Figure 2.10. However, there is a material available that overcomes these drawbacks. Such film consists of an OPS core with a PET skin on each side. This provides the gentle shrink characteristics of OPS, but adds the printing, robustness and scuff resistance benefits of PET, providing the best of both worlds. This is the Hybrid/Layered multi-polymer film.
Shrinkage of these films is medium to high at 65-70%. It does relax well, similar to OPS. Scuff resistance is excellent and it is straightforward to print. It is the perfect material in many ways. Natural shrinkage is not as bad as OPS but not quite as good as PET; printing with a PET surface is excellent. Hybrid/Layered films comprise the best elements of PET and OPS and are therefore an excellent option.
Figure 2.11 Characteristics and technical details of Polyolefin shrink film. Source- Klöckner Pentaplast
Figure 2.12 Characteristics and technical details of Hybrid/Layer shrink sleeve films. Source- Klöckner Pentaplast
SUMMARIZING THE SHRINK SLEEVE FILM CHARACTERISTICS
Having reviewed the main types of shrink sleeve films, their characteristics and technical details, we may now put all of this together in one simplified summary table (Figure 2.13). It is a great visual in terms of showing the pluses and minuses for each of the materials and their technical considerations. It should be mentioned, however, that these are guidelines – not hard-and-fast rules – and also are not the only considerations.
Figure 2.13 A summary of the characteristics and technical details of shrink sleeve films. Source- Klöckner Pentaplast
UNDERSTANDING THE DECISION-MAKING JOURNEY
To this point in this article, we have discussed the effect of container shapes, shrink process requirements and the characteristics and technical details of the various shrink films. The aim now is to better understand the film selection decision-making process, provide a guide to the decision process itself and then to look at a number of example decision-making journeys.
To begin this journey, it will help to understand further the nature of the choices being made using Figure 2.14. We need to start narrowing down the shrink film options. First, we will start with the top row of the chart: the shrink tunnel. Is it a hot air or radiant heat tunnel? Is it a steam tunnel?
Figure 2.14 The decision making journey. Source- Klöckner Pentaplast
Steam tunnels are very common, and as indicated by the name, they dispense steam through nozzles on each side of the tunnel as the container travels through. The steam creates a two-phase system, condensing on the sleeve while the energy from the latent heat of vaporization goes into the sleeve. The steam envelopes the containers and condenses evenly on the sleeves, creating a very even shrink. As it condenses on the film, it shrinks gradually, but with a controllable shrink. Steam shrink tunnels are very effective, but they are not used in powder plants, in applications where steam cannot be used, or where steam is not available. Brand owners also tend to be wary of using steam tunnels when sleeving empty containers.
Hot air tunnels. Hot air tunnels direct hot air jets at the shrink sleeve to shrink it uniformly but, as can be imagined, a jet of hot air is not distributed evenly, so will tend to shrink the sleeve unevenly. To counteract this, the shrink films are designed with a very smooth, gentle shrink curve characteristic where the material will perform even though it is being impinged with different temperatures and different velocities. In this way, a good shrink result can be created with a hot air tunnel. Radiant tunnels have a more uneven temperature and shrink distribution than do hot air tunnels but are generally used for tamper evident applications only.
The next row down looks at the maximum shrink percentage, which was discussed earlier in the article. This creates another way of narrowing down the field of potential shrink films for a particular application.
The third row down has to do with container type. Is it a glass container? A metal container? An HDPE container that is cold and filled – a milk chug, for instance? Or is it an HDPE container that is empty or hot, i.e., it is going to shrink back and potentially create a loose sleeve? Is the container a PET container, cold and filled, or an empty PET container? This row details the container that is to be sleeved and its condition.
The next row reviews some additional requirements. What about scuffing – is this a concern? Is PVC an option (i.e., allowed by the brand owner) or not? Is floatability required for separation of the sleeve from the container? What about the container shape? Does it have ribs or a tightly contoured container where a high shrink force is needed to pull it in?
The bottom row of the diagram lists out the different substrate options.
Now that the choices have been defined, it becomes possible to work through the following decision-tree examples that will illustrate the process.
We begin with Figure 2.15 and select a hot air tunnel in the top row. The selection of a hot air tunnel results in PET film being removed from the options (note that films taken out are shown in red). Why? It is possible with particular PET films and particular container shapes to make PET work well in a hot air tunnel. Nevertheless, PET struggles to make a good shrink result in a hot air tunnel – the shrink curve is too steep,
However, if the container requires a very high shrink film, then it is possible that PET may have to be used – and getting a good shrink result will be difficult. Therefore, the material needs to be chosen very carefully. What if the max shrink required is less than 60%? A very low shrink film will be needed and all other options remain viable.
Figure 2.15 Shrink film choice for a hot air tunnel with 60% -70% shrinkage, a cold-filled HDPE container, and where scuffing is a concern and PVC is not preferred by the brand owner. Source- Klöckner Pentaplast
At the next level down, assume in this scenario that the container is a HDPE cold filled milk container that needs a medium shrink (i.e., between 60% and 70%). Everything aside from PET (which we lost above) stays in and nothing else drops out. What else can be considered? If we assume that the brand owner doesn’t accept PVC, we highlight that box and PVC drops out. We can also assume that these containers are going to be transported cross-country in half-trays, so scuffing is a consideration. This requirement eliminates PO film and OPS film from the list of viable options. This results in the ideal material being a Hybrid/Layered film. Please note, this decision tree says nothing about price; this decision tree only factors technical considerations.
Other materials can potentially work in this particular scenario; but the most suitable substrate for this particular situation is the Hybrid film (Figure 2.15).
The tunnel is hot air again and the container requires between 60% and 70% shrinkage. The container in this example is a PET container that is cold and filled. PETg will therefore be removed as an option due to the hot air tunnel.
The gentlest shrink curve comes from OPS film, but it is highly susceptible to scuffing. If scuffing is not an issue, OPS is a great option. However, as in the diagram, if scuffing is a concern, then PVC, OPS and PO all will drop out, and again, the ideal solution will end up as a Hybrid film (Figure 2.16).
Figure 2.16 Shrink film choice for a hot air tunnel with less than 60% shrinkage, a cold and filled PET container and where scuffing is a concern. Source- Klöckner Pentaplast
This time we are using a hot air shrink tunnel (therefore, no PET film), the container requires less than 60% shrinkage, and we are shrink labeling an empty PET container. PVC can be discounted because its shrink force is too high and the PVC sleeve will distort the container as it shrinks. We need a sleeve with very low shrink force, which leaves PO, OPS and Hybrid substrates as options. However, in this case the brand owner has requested a floatable shrink sleeve so that the sleeve can be easily separated from the PET bottle in the recycling system using a float tank. In this case, the only substrate that fits this purpose is the polyolefin (PO) shrink sleeve substrate (Figure 2.17).
Figure 2.17 Shrink film choice for a hot air tunnel with less than 60% shrinkage, an empty PET container and where floatability for recycling is required. Source- Klöckner Pentaplast
Once all the factors have been taken into account and the heat shrink film has been carefully chosen, the result will be a beautifully shrink sleeved container. Having said that, the shrink sleeve tree that has been used in this article is still rather basic, and additional questions, queries or issues may arise.
One such question might be that of whether corona treatment is required when printing the substrate. The only sleeve material on which corona treatment is always needed is polyolefin film. Depending on what the printing technology is and depending on the inks, the other substrates do not need corona, however it could be helpful, particularly when printing UV inks on PVC and PET. If, corona treatment is used, it should not be overdone, particularly on PETg. Over-corona can produce some dramatic effects – creating blockages or even blowholes in the substrate.
For polyolefin film, the film manufacturer will normally corona treat with a high corona level. When the converter uses corona during printing, only a little ‘bump’ is required to increase the dyne level of the material so that the ink wets out better.
PETg and PVC accept ink well without surface treatment – when printed UV flexo, solvent- or water-based flexo, solvent rotogravure, UV or EB offset.
Another question that sometimes arises is concerning PLA (Polylactic Acid) shrink films. Polylactic Acid is a plant-based material, generally made from corn. Only one company produces the film, Plastic Suppliers, and the use of PLA is always brand owner driven. If the brand owner needs a PLA sleeve, they should contact Plastic Suppliers. There are pluses and minuses with PLA; contact this company for further information and to determine if this film is an appropriate solution.
What about the shrink film gauge? Shrink films are available in a variety of different thicknesses, but most applications use between a 40-micron and 50-micron film. For some applications, 60-micron or 70-micron is needed, but these are rare.
Much of the thickness determination comes from the application machine. If the brand owner wants to run their plants as fast as possible with a wide process window, then 50-micron is generally most appropriate. If the brand owner wants to save some money, go to a 40- or 45-micron: although this might be a bit more tricky to shrink – the process window of the shrink process will narrow, and the tunnel may be more difficult to set up for a reliable good shrink result.
How does film thickness affect the shrink force? The shrink force varies linearly with caliper; a thinner film has a lower shrink force. However, the shrink force difference between OPS and PET is much larger than the variation from thickness, so moving from 50-micron to 40-micron with a PET film will still be nowhere near as low as a 50-micron OPS. The OPS is a fundamentally softer, gentler material.
It is worthwhile to mention some guidelines regarding the price differential between different shrink films. Firstly, the density of the substrate needs to be considered – the printer and brand owner are more interested in the cost per square meter, than how heavy it is! The density of OPS is about 1.05 g/cm3. The density of PET is about 1.32 g/cm3. The density of PVC is about 1.35 g/cm3. PVC and PET are about the same density, but OPS is much less dense. OPS is more expensive per kg but as the yield is higher, you get more square meters for each kg of film. To compare film costs, it is necessary to calculate back to the square meter by using yield figures provided by the film manufacturer. Hybrid has a density that is in between that of PETg and OPS at about 1.1/1.15. Polyolefin is below 1 (it floats), coming in at around 0.95-0.97 g/cm3.
When comparing film prices, always consider the density/yield of the film. Be particularly careful with white opaque films, which can either be very heavy with low yield due to mineral fillers, or so heavily voided that they have very light densities – some even less than water – resulting in very high yields.
There are many companies globally that supply heat shrink substrates. United States-based suppliers are listed in Figure 2.18.
SUMMARY OF FILM CHARACTERISTICS
PETg (inc. White Opaque)
Depends on Grade