Types of self-adhesive film – technology and quality
When it comes to choosing a suitable self-adhesive film, we often have difficulty choosing between a monomeric or polymeric product. We hear that the cast foil is much better than the other, but the price is higher. Which film is best for our needs?
The answer depends on what surface we are installing on and what life we expect from this film.
Mass-produced films differ according to the technology used – calendering or cast – and according to the material from which they are created – monomers or polymers.
1. Monomer or polymer film?
The self-adhesive film has three main layers – a PVC (Polyvinyl Chloride) film, an adhesive layer, and a silicone backing. The film is made of polyvinyl chloride (PVC) and can be monomeric or polymeric, and its thickness varies from 50 to 200 microns. Over the years, a film that does not contain PVC has also been created.
1.1 What are monomers and polymers?
Monomer comes from mono- (one) and -mer (part). It is a type of molecule that has the ability to chemically bond with other molecules in a long chain. A polymer is a chain of an indefinite number of monomers. Essentially, monomers are the building blocks of polymers, which in turn are a more complex type of molecule. The word is derived from poly- (many) and -mer (part). A polymer, as a larger class of molecule, can be natural or synthetic. Since polymers are made up of monomers, they are stronger, more durable and more reliable to operate.
1.2 Monomer PVC film
Uses small molecular size plasticizers. Because the bonds between the molecules are too few, this makes the foil very sensitive to stretching, heating and cooling. An old monomer film can be recognized by its typical cracking, which is due to the weak bonds of the monomer. When stretched, these bonds either break or very quickly try to restore their original size. These foils are absolutely prohibited for application on any type of vehicle, except for very short-term promotional purposes.
1.3 Polymeric PVC film
It uses molecules with many more bonds in all directions. Thus, it is much stronger, stretchable and resistant to temperature fluctuations. It is suitable for both indoor and outdoor advertising and its service life is significantly longer.
1.4 Polyester film
All sun protection, impact protection and decorative glass films are produced on the basis of polyester. This is determined by the purpose of the self-adhesive film. One of 3M’s most high-tech films is the 3M Prestige Sun Control Window Film series, which has over 200 nanolayers in a product thickness of 38 microns.
1.5 Not PVC film
In addition to PVC film, there is already a polyurethane self-adhesive film on the market. 3M created 3M Envision Print Film 48C and 3M Envision Print Film 480 series – PVC-free film. PVC is one of the plastics that pollute the environment the most. More and more countries and companies are banning the use of products from this material. The European Union’s program calls for a complete ban on PVC in the next 10 years.
The biggest advantage of non-PVC film is that it does not have any physical memory. Series 480 allows stretching of the material up to 180%, which is unthinkable even for the flagship of 3M-cast film 3M IJ180mC. More and more companies are covering cars with this self-adhesive film due to two main advantages. The first is that it is very easy to work with, and the second is that it is preferred by companies that aim to optimize their operations so that they are environmentally friendly. (so-called “eco-friendly/green companies.”)
1.6 Masters
Additives called masterbatch are added to all PVC products. They can be for UV resistance, plasticity and flexibility of the material, also stabilizers for temperature fluctuations and against the penetration of microorganisms. The colorists are also masters. Since the PVC raw material is very cheap, the main cost of the self-adhesive film comes from the added masterbatches. In most cases, they determine up to 50% of the price. However, their use significantly increases the quality of the resulting product.
3M films use the highest class masterbatches. The obvious difference is in the colors. If you compare the colors of 3M film with those of any competing company, you will notice that 3M’s are significantly brighter and cleaner. In addition, the company pays special attention to UV stabilizers and plasticizers in PVC. Experience shows that when comparing the same grades of self-adhesive film of 3M and competing manufacturers, the products of the American leader perform better.
2. Calendered or cast film?
There are two types of technology for creating the PVC film from which the foil is produced – calendering (rolling) and cast (casting).
2.1 Monomers and polymers are calendered.
What does that mean? Calendering is a quick and inexpensive process. The material (PVC) is melted and pressed with a series of rollers (in Bulgaria the term rolling is used) to form a sheet of the desired size. After that, it cools and goes to lay the adhesive layer and the silicone pad.
2.1.1 Disadvantage – the presence of physical memory
In the production of self-adhesive film with this technology, internal tension is created thanks to the rollers that press it. This internal tension is known as physical memory or the “pizza effect”. Just as a pizza left unrolled after a while begins to shrink and try to recover the shape from which it was rolled, so the foil tries to recover the original size from which it was pulled.
2.1.2 Applications of calendered film
The resulting monomer or polymer film is mainly suitable for creating advertising and decorative applications on flat surfaces – glass partitions, signs, and others. Calendered monomers are mainly recommended for promotional and indoor applications. Their life is a maximum of one year. Shrinkage, peeling of edges and corners, as well as splitting, are typical for them.
The presence of internal tension (physical memory) in the monomer self-adhesive film makes the application of complex 3D surfaces difficult or even impossible. The calendered monomer film cannot be stretched, and even if we can, it recovers its original shape extremely quickly. Peeling and tearing of the foil begins.
Calendered polymer self-adhesive film has a much longer life and with proper application, you can get a warranty of up to 5 years, and the life of the film can even exceed 10 years. Typical applications are all smooth illuminated and non-luminous signs, stained glass windows, and even automotive film, but applied to smooth details without 3D bumps.
3M’s calendered polymers are further tempered by temperature shock right from their creation. The finished film passes through several cold and hot ovens. This thermal shock shrinks the foil at the factory. In this way, the greatest shrinkage is already a fact, and the physical memory effect of the finished product is minimal.
For this reason, calendered 3M polymer films perform well on slight 3D irregularities. Many applicators report that the 3M IJ40 and 3M Scotchcal 50 series work better than the cast foils of some of the more budget-competitive brands.
2.2 Леене на фолио – каст
Film casting (cast) is the key to achieving ultimate quality. In this technology, PVC is poured in liquid form onto paper, moving at high speed. A long squeegee measuring the width of the roll gives the exact height of the cast material. The resulting combination of paper and liquid PVC enters an oven where it polymerizes. At the exit from the oven, the paper is separated from the foil and it goes for additional application of glue and silicone backing. This technology is extremely complex and precise, and few companies can afford to produce such materials. The high quality created is why the price of this type of film is higher.
2.2.1 Advantages of cast film
With the casting technology, a thin film is obtained – 35-50 microns. It contains no internal tension, is flexible, and has no physical memory whatsoever. Cast self-adhesive film is the only possible PVC film for sticking to 3D surfaces. Due to the lack of physical memory, it can be stretched up to 150% of its size without creating internal effort (physical memory) in the material.
2.2.2 Standard for wrapping vehicles
All over the world, cast foil is the standard for the complete wrapping of all types of vehicles – cars, trucks, buses, trains, even bicycles. A mandatory condition for a quality product is their use with the appropriate cast laminates.
In recent times, it has become popular to fully cover cars, motorcycles, etc. with self-adhesive film. vehicles. A self-adhesive film is produced for complete wrapping of cars with unique colors, textures, even imitation of chrome (silver). This would not have been possible without cast technology.
3. Types of glue used to create self-adhesive film
Most often, adhesives are divided into two types – acrylic or solvent. This depends on the chemical components and the production and application system.
3.1 Acrylic glue
Acrylic adhesives are of two types – solvent or water-based. At their core, acrylic adhesives stick quickly and have high strength, thanks to the cross-links that are formed during the polymerization of acrylic acid. Variations in chemical composition create different types of acrylic adhesive with specific properties, according to the desired application.
They exist in both liquid and paste form and in strip form.
It is often applied in the form of two components. The first is an initiator – a material applied to one part and an adhesive agent – applied to the other part. The two are pressed together until the curing process is complete. This type of adhesive is known as pressure-sensitive.
Pressure-sensitive solvent acrylic adhesives ensure durability in long-term applications. They provide performance, including better heat, chemical, and water resistance, than almost all other adhesive categories.
3.2 Solvent adhesive
Solvent adhesive is a non-reactive, drying adhesive that is created from a variety of ingredients – most commonly polymers. It is also cheaper than acrylic glue.
Cheap glue when combined with cheap paper produces a chemical reaction. This means that the product is unstable, has no plasticity, and is difficult to peel off the protective paper. This makes it extremely difficult to peel small letters from foil and apply them, especially if it’s been a day or two since they were cut. It also has a short shelf life and unsatisfactory shelf life.
Since bulk monomer film is sold at a lower price, it contains a semi-liquid solvent adhesive. When shrinking the monomer film, the solvent adhesive remains at the original size of the sticker and on it the surface starts to get dirty. Thus, around letters and stickers that have shrunk from time, the familiar dirty halos remain. Besides being unsightly, these marks are sticky and hold dirt that is sometimes almost impossible to clean.
The effectiveness of solvent-based adhesives is largely determined by the polymer system in the formulation. The choice of adhesive type depends on the specifics of the materials to be bonded and the desired resistance to temperature and other atmospheric conditions. Most solvent-based adhesives contain flammable solvents that require special safety precautions to be taken when working. In addition, many organic solvent adhesives are banned due to concerns about polluting the environment with harmful emissions.
After the glue is applied, it evaporates relatively quickly, which leads to an increase in viscosity – the internal tension of the adhesive layer. After gluing, it is necessary to wait for the so-called set time, which increases the initial strength of the adhesive bond.
3.3 Adhesive allowing easy removal (removable) and permanent adhesive
The permanent adhesive is a strong bonding component that provides a stable bond. Once glued, the connection between the surface and the adhesive layer takes place quickly and strength is already a fact. If removal is desired, after peeling off the glued material, traces of glue remain, which are often difficult to clean.
According to the definition of 3M, an adhesive that allows easy release means that it provides the ability to remove even by a non-professional with no more than 10% traces.
In many cases, customers need a quick and clean removal of the foil after some time. Because of this, an adhesive has been created that allows for easy peeling. It guarantees easy and quick disassembly even without previous experience.
There is a misconception that release adhesives are weaker than permanent adhesives. In the former, the bond is strongest between the PVC coating and the adhesive layer and weaker between the adhesive layer and the surface. This fact does not make its adhesive strength less than that of permanent glue.
Easy-peel adhesives have a shelf life. It determines the duration of their properties. At 3M, the standard is 2 years after installation.
3.4 Technologies of the adhesive layer
3M has created two undeniably innovative technologies for the application of self-adhesive film with pressure-sensitive adhesive. The Comply system consists of thousands of tiny channels, forming a grid, through which the air is brought out with a slight pressure on the surface. And, with Controltac technology, thanks to the millions of dispersed glass microspheres in the adhesive layer, the initial contact of the film with the surface is limited. This allows multiple repositioning of the film during installation. The final fixing of the self-adhesive film is done by pressure with a spatula and so-called post-heating – “baking” of the already mounted film.
Another very useful technology is the gray opaque back. The adhesive layer is produced in a dark gray color and this allows the self-adhesive film to stand out without the color of the base surface showing through.
4. Silicone pad
Silicone backing is a compacted paper material with a silicone coating. It is used to protect the adhesive of the self-adhesive film.
The backing is applied during the manufacturing process. It is used to prevent premature sticking of the adhesive surface. Protective pads are available in different colors and materials, paper, plastic, without or with printing under the cover or on the back of the liner.
Little known is the fact that “Bubble free” and “Comply” technologies are obtained thanks to the silicone pad. It has an embossed mesh and when the siliconized paper is placed against the foil, powerful shafts press them and thus the embossed mesh creates the channels in the glue through which the air is then pushed.
5. Applications and conclusions
In appearance, all foils look almost the same. This causes most people to decide what type of material to use based solely on price. Knowing the technologies and materials of production, we can also make the right decisions when choosing the self-adhesive film, according to the different possible applications.
5.1 Promotional Applications
All applications lasting up to 6 months on flat surfaces with high surface energy (glass, chipboard, aluminum, powder-coated sheets, etc.) can be made with the cheapest possible monomer films. Naturally, it should be taken into account that in more severe cold or heat it is possible to peel the corners or other parts of the foil. This mainly depends on the manufacturer and the quality of the self-adhesive film produced.
5.2 Medium-term applications on flat surfaces
In these cases, it is recommended to use a medium or high-end polymer self-adhesive film, depending on the required durability.
5.3 Very durable applications on flat surfaces
The use of high-grade cast foil is mandatory for all applications that have an expected life of more than 10 years. The production technology of the cast materials and the high quality of the raw materials used enable a long service life.
5.4 Automotive Applications
It is mandatory to use cast self-adhesive film with cast laminate. Compromises can only be allowed when installing stickers on equal parts and expected durability of no longer than 5-6 years. 3M’s high-end calendered polymer self-adhesive film can be used here. In this case, again all printed stickers must have the corresponding laminate.
5.5 Shelf life
Manufacturers are obliged to write the production date on each product, because after a certain period, under certain conditions, any self-adhesive film can lose its adhesive properties, shrink, and/or start a reaction between the silicone paper and glue. In any case, the qualities of the self-adhesive film are not those declared by the manufacturer.
