- December 01, 2000, John Felinski, Filmquest
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.
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.
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.
Following are the factors to consider when assessing the application before beginning the search for the correct polyester film.
- End Use:
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 1000-ga film could be as low as 950 ga or as high as 1050 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.
- Inner Diameter (I.D.):
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.
- Outer Diameter (O.D.):
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.
- Coefficient of Friction:
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:
- Manufacturers: Domestic production in the US, with monthly production schedules. Off-shore manufacturers produce film around the world and sell large containers directly to customers or use public warehouses to improve lead time (letters of credit are not uncommon).
Merchant converters: Outsource production, strong manufacturing relationship, convert on-site, warehouse, sell private label and brand names, short turnaround time, wide variety of products.
- Distributor: Stock certain film, buy large units, resell small units, no converting.
Manufacturers' Representative: Represents off-shore companies, no converting, sell large quantities.
- Resellers: Buy film and only resell "as is" with no converting.
Traders: Buy and sell film on a global basis, no inventory or converting, and limited variety.
- Broker: Buy off-spec and customer returns with 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 630/584-0101; firstname.lastname@example.org.
The views and opinions expressed in Technical Reports are those of the author(s), not those of the editors of PFFC. Please address comments to the author(s).