Sourcing polyester film should not be an exercise to search for the lowest price. Unfortunately, many people make the costly mistake of confusing price with value. While increasing global capacity has given the illusion that polyester film is a commodity, the chemistry and technology required to produce this "high-performance commodity" should be understood if you are to maximize its attributes for your application.
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Polyester film is manufactured when chips are produced from PTA (purified terephthalic acid) and EG (ethylene glycol), extruded, and biaxially oriented to produce an ideal "isotropic" film. The film can be modified in manufacturing to meet the requirements of various applications. Polyester film has many features, but its general properties can be broken down into four major areas: physical, thermal, electrical, and optical.
Be Specific
The most critical point to be considered when purchasing polyester film is the exact application for the film. A general application will not provide the information required to ensure that the right film is used. For example, to say you need a polyester film for coating is like saying you need a vehicle for driving.
The best polyester film to use is application-driven by the specific end use. Many factors can influence purchasing the correct polyester film: gauge; width; core size; roll size; clarity level (haze); coefficient of friction (COF); elongation; tensile strength; shrinkage, both machine direction (MD) and transverse direction (TD); surface treatment and coating type; operating temperature; coating system; and dryer capacity. The same can be said for polyester film that is to be printed, metallized, laminated, die-cut, or converted in any process.
The Checklist
Following are the factors to consider when assessing the application before beginning the search for the correct polyester film.
Is the application low, medium, or high end? Flexible duct polyester film would be considered low end, while medical packaging would be high end.
There are three main categories of film thickness: true, nominal, and shaved gauge. True gauge is when the film is produced to an exact thickness for high specialty application.
Nominal gauge is film that meets the industry standard of ñ5 percent. That would mean a -ga film could be as low as 950 ga or as high as ga based on the average of the production run.
Shaved gauge is where the gauge has a specific targeted gauge that is lower than the nominal gauge, i.e., a 640 ga displacing the nominal 700 ga. The impact of shaved gauge is most dramatic in improved yield (sq units/lb), thus lower area costs. For example, using a shaved 650 ga instead of a true 700 ga would result in a 7% savings with negligible effect on performance.
The width you buy can serve to improve your costs. Different manufacturers have different widths that need to be trimmed out (deckle). The closer you can trim a production line, the better production efficiency and yield will be for the producer, allowing the savings to be passed on. This charting plays an important role in production to maximize the bottom line.
The larger the core size, the more economy of scale can be achieved. Smaller core sizes, such as 1 and 3 in., cannot hold weights and roll lengths that are conducive to efficient production processing. While 6-in. cores are most common, 10-in. cores holding jumbo rolls are gaining in popularity because of the reduced number of changeovers required in post-production.
The larger the O.D. of a roll, the larger the roll length and the greater the efficiency, i.e., more production time and less changeover time. Today, O.D.s of 26-30 in. are targeted for maximum efficiency.
Haze and clarity have a direct impact on the cost of film. The clearer and brighter the film, the costlier the film. This higher cost is compounded in processing the film. Usually a brighter film has to be processed at a slower speed and will require more careful handling and result in lower production yields because of the "filler-free" chemistry of the film. Filled film tends to be hazier, handles better, and is more favored in processing. Haze and clarity also can be influenced by gauge.
Adroit buyers try to maximize the value of the polyester film by purchasing a film that is bright but not ultra-bright, thereby obtaining a major savings in the cost of the film.
How a film handles can have a tremendous impact on profitability. COF can be controlled through internal methods (fillers) and external methods (topical and treatment); surface modifications; or coextrusions. The application will determine which system is best. Internal fillers are the most cost-effective method of controlling COF, but they result in increasing haze.
In general, most polyester film has a range of 90 to 110 percent both in the MD and TD. When modifications are made to tensile strength, usually higher costs can be associated because of the slower production rates and costlier forward draw production units that produce tensilized film for the magnetic and the thermal transfer ribbon industry. However, those applications require this tensile-modified film.
This value can vary in the MD and TD, and generally industry standards are 0.5 to 2.0 percent @150 deg C for 30 min. If balance shrinkage or low shrink is required, the cost of the film rises dramatically, i.e., 0% TD shrinkage at 150 deg C for 30 min. This zero TD shrinkage is marketed in the hot stamping industry, but shrinkage in the MD can increase to 0.5%.
Shrink is a factor that should be considered for all applications that are involved in elevated temperatures.
The latest technology is in the area of in-line treatments that allow polyester to have a wider range of features that didn't exist years ago. The advancement has been profound in treatment for adhesion. This treatment improves adhesion to metal, ink, and coating.
Metallized applications that require surface treatment for adhesion are critical for high-end applications. Extreme caution needs to be exercised for the consideration in this product group. Skips or voids in the treatment that are so thin they are measured in angstroms are virtually impossible to see or detect during processing. Dealing with experienced film producers only can minimize this risk.
As manufacturers all over the world try to move away from commodity grades of polyester film to value-added specialty treatments (especially in ultra-clear films), the risks involved in using treated film from unproven suppliers increase.
Coextrusion or multilayered films can be manufactured to create a custom-designed film for many packaging grades that require different characteristics for each layer.
Where to Go
Today's global marketplace offers exciting opportunities that couldn't be imagined 20 years ago. The Internet is changing forever the way commerce will be conducted in the converting industry. The prudent buyer has more options for purchasing polyester film than ever before. Competition is growing, traditional channels overlap through consolidation, and supply chain management has transitioned from a buzzword to an everyday practice.
Sources confronting material managers include manufacturers (domestic and off-shore), merchant converters, distributors, marketing representatives, resellers, brokers, traders, and even competitors. Which source should you use? The answer may be more difficult than you might think.
Your needs, order by order, will determine the correct source from which to purchase polyester film. Do you need price, quality, consistency, short lead time, small quantity, large quantity, special configuration (I.D./O.D.), samples, technical support, etc? The answer may not be one source but multiple sources, depending on what is most important to you for an individual order.
Each source for polyester film fulfills a need in the supply chain and can be useful to a buyer. Large companies tend to deal with large manufacturers, while small companies tend to deal with merchant converters and distributors. The difference between sources can be described as follows:
Merchant converters: Outsource production, strong manufacturing relationship, convert on-site, warehouse, sell private label and brand names, short turnaround time, wide variety of products.
Manufacturers' Representative: Represents off-shore companies, no converting, sell large quantities.
Traders: Buy and sell film on a global basis, no inventory or converting, and limited variety.
Competitors: Outsourcing to competitors that have better core competencies or excess capacity.
In summary, determine what you need for your applications. And, when choosing a source, your confidence in the source must be based on knowledge, technical support, service, quality, and consistency. An adroit buyer will always recognize value when sourcing film, not simply price.
John Felinski is president of Filmquest, St. Charles, IL. He is a recognized authority in the polyester film industry and has been in the forefront of the converting market for more than 27 years, supplying polyester film for flexible packaging; electrical, graphic, and industrial applications; and other high-performance film technologies. You can reach him at 630/584-; This address is being protected from spambots. You need JavaScript enabled to view it. .
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Metallized PET film: What can PET metal be used for?
PET met is a polyester film metallized with aluminum powder. Polyester film (short: PET film) is inherently characterized by high strength and surface hardness. However, especially in terms of diffusion density, its excellent properties can be increased by the use of aluminum powder.
Aluminum-coated PET film has both advantages and disadvantages compared to conventional aluminum foil. The advantages of PET film are the higher tensile strength and lower production costs. In aluminum-coated composites, the processing speed is significantly higher than that of aluminum foil.
This makes PET met (metallized polyester film) particularly suitable for the following applications:
Packaging, especially for foods that are sensitive to moisture or oxidation, such as coffee or instant soups. PET-met stand-up pouches
Relative vapor barriers in building insulation.
Tapes and labels with relatively high chemical and heat resistance for use in vehicle technology or outdoor areas.
High diffusion density, but not absolute diffusion density
PET met, a composite material made of a thin aluminum layer and PET film, has diffusion values of less than 0.5 cm³/m²/d for oxygen and less than 0.3 g/m²/d for water vapor even at a material thickness of 10 μm. These values are already close to the measurement limits for identifying the absolute diffusion density.
However, in order to obtain the absolute diffusion density, classic aluminum foil or other metal foils must be used.
PET met combines the advantages of aluminum and PET film.
Compared to the laminated composite, the aluminum coating in the PET film only causes changes in the diffusion, optical and electrical properties. However, the excellent strength values and low specific gravity characteristics of the PET film remain almost unchanged.
The thickness of the aluminum layer in the PET film is so small that the unit Ångström, which is derived from the atomic diameter, is often used instead of μm (micrometer).
The measured values in angstroms can therefore be regarded as the corresponding number of atoms stacked directly on top of each other. Of course, this does not reflect the actual physical conditions, but illustrates the very small thickness of the metal support layer.
Metallized PET film layer thickness absolute values and comparison
The thickness of the aluminum layer of metallized PET film is usually about 30 Å – 500 Å, which is about 3 to 50 nm. In comparison, pure gold can be reshaped into a thin gold foil of Å. At this thickness, gold is already slightly transparent and appears green in the light.
PET metal foils are always slightly transparent.
Even metallized PET films are not completely opaque. In the case of incident light, this effect is not visible due to the silvery reflective surface. This effect can be altered by printing, dyeing or varnishing as well as brushing or embossing the PET film.
Effective protection against UV and thermal radiation
The highly reflective surface of metallized PET films can be used to create attractive optical effects in packaging as well as to block electromagnetic radiation.
Aluminum vapor-coated PET foils reflect not only visible and infrared light, but also UV light. Aluminum coatings differ from silver or gold coatings, which are used for similar purposes. In contrast to these metals, the degree of reflection of aluminum is largely independent of wavelength. The minimum value is still above 85%, slightly above 800 nm in the near-infrared range.
Effect of film thickness on the reflectivity of PET films
PET metal packaging industry
Packaging made with metallized PET
The reflectance and optical density of metallized PET films increase in proportion to the thickness of the aluminum coating. The optical density (OD) is measured as the logarithm of the incident optical radiation divided by the energy of the transmitted radiation and for metallized PET films its values are typically between 0.25 and 3.5.
The thicker the aluminum layer, the higher the optical density and the lower the transparency.
The reflectivity is therefore about 66-99%, since according to the logarithmic scaling an optical density of 0.3 corresponds to half the intensity of the transmitted radiation.
Changes in properties due to aging
Just like solid pure aluminum, aluminized PET films also undergo surface oxidation. It prevents further chemical transformation of the metal on the side exposed to air and on the substrate side.
This self-passivation caused by the formation of transparent aluminum oxide leads to a decrease in optical density and conductivity, especially in the first 24 hours after the production of the metallized PET film. This must therefore be taken into account during production if customer specifications for these values are to be adhered to.
PET films become more transparent over time.
Since the maximum thickness of the oxide layer is independent of the thickness of the aluminum coating and can only grow up to 3 to 4 nanometers, the effect of the oxide layer is particularly pronounced for thinner coatings. For an aluminum coating with a thickness of approximately 10 nanometers, the optical density drops from 0.2 to 0.28 within 24 hours and in the long term to about half of the original value.
Typical applications for metallized PET films
Metallized PET as food packaging
Metallized PET films are suitable, for example, as a direct replacement for aluminum foil in packaging technology. At the same film thickness, metallized PET films have a higher tensile strength and bending stiffness, so that composites produced by metal evaporation do not wrinkle like aluminum foil.
PETmet as an aluminum substitute with a front and a bottom.
This results in a more aesthetically pleasing packaging. Nevertheless, individual packaging of sweets can also be achieved with metallized PET films, i.e. sealing by twisting the film ends (twist seal).
But aluminum foil also has advantages in certain packaging areas, because, unlike PET film, it is not transparent and guarantees an absolute diffusion density. Therefore, in general, foods packaged in PET film are not as durable as those packaged in aluminum foil. PET film is therefore more suitable for foods with a shorter shelf life, which remain in the supermarket for a relatively short time until the buyer picks it up.
A further application possibility of metallized PET film in the field of food packaging is that the extremely fine metal coating changes the conductivity of the film surface. This makes the PET metal visible in metal detectors, but can also be used to package microwaves with a low moisture content, so that the food can absorb more energy and heat up quickly.
In terms of building insulation, the positive influence of aluminum vaporization on diffusion resistance as well as on the reflection of thermal radiation is very important. Compared with aluminum foil, PET film does not offer an absolute vapor barrier, but the mechanical resistance and reflectivity are significantly higher.
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