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Jan 23, 2004 12:00 AM
What is lamination?
Lamination is a quick and easy way to protect your prints. Lamination protects prints by permanently bonding clear plastic film to one or both sides of the prints, making them tear- and waterproof. It preserves your prints from moisture and environmental damage. In addition, color enhancement and contrast are added to your print images. Glossy-looking prints have a higher quality look to them. Lamination prevents prints from becoming creased, sun damaged, wrinkled, stained, smudged, abraded and/or marked by grease, fingerprints and environmental concerns.
Three types of laminators are used most often in digital imaging:
use a lamination pouch that is usually sealed on one side. The inside of the lamination pouch is coated with a heat-activated film that adheres to the product being laminated as it runs through the laminator. The substrate side of the board contains a heat-activated adhesive that bonds the print to the substrate. This can be any of a number of board products or another sheet of laminate. The pouch containing the print, laminate and substrate is passed through a set of heated rollers under pressure, insuring that all adhesive layers bond to one another.
use one or two large rolls of lamination film. The film used in the roll laminator has a heat-activated glue on one side of the lamination that sticks to the print when it is run through the laminator. In the case of digital prints, the strength of the bond is limited by the adhesion strength of the thermal glue to the ink layer on the printed media. The rolls of lamination film look very similar to a large roll of Saran Wrap. One roll is mounted on top of the machine, while a second is fed simultaneously from the underside. The top roll laminates the top of the print, while the bottom roll laminates the bottom side in a process called encapsulation. You can also use just the print side lamination film, since the bottom of any mounting board does not usually require lamination. There are also hybrid types of laminators that provide only top heat for lamination with thermal material. This type of laminator would not be able to encapsulate. After a print has been laminated, a sharp blade is usually needed to cut the laminated print from the machine. Different types of laminators have different numbers of rollers. Lamination film, as it enters the laminator, passes through the rollers, which help evenly distribute heat and keep the lamination pouch pressed shut during the lamination process.
and cold pouch laminators do not use heat to laminate pouches. The cold roll/pouch lamination film is pressure-sensitive, which means the film has a sticky side that adheres to the product when it is brought into contact. Cold lamination is good for use with products that can be damaged by heat. One example of this would be wax-based ink that can be melted by heat. Another is using pressure-sensitive adhesives with temperature-sensitive media, such as vinyl or other low melt plastics.
Laminate film is generally categorized into these five categories: standard thermal laminating films, low-temperature thermal laminating films, heat-assisted laminating films, pressure-sensitive films and liquid laminates.
Standard thermal laminating films
This is typically a polyester film with a polyethylene (copolymer) adhesive that requires temperatures between 210º-240ºF to bond. These are the most popular films today, largely due to their low price. They can also be the most problematic to work with.
Low-temperature thermal laminating films
These are virtually identical to standard thermal films in that they are constructed of polyester with a polyethylene adhesive. They bond at a lower temperature, 185º-210ºF. It is likely that these laminates will replace standard thermal films at some point in the future.
Heatset (or heat-assisted) laminating films
Usually these films are PVC- or polyester-based films, although there are a few exceptions. The adhesive is thermoplastic and only requires 170º-195ºF to bond to the substrate.
These laminates are frequently PVC (vinyl) or polyester with an acrylic adhesive, with the composition of the adhesive varying from one manufacturer to the next. Sometimes they are referred to as "cold" laminating films, because they don’t require heat to bond with a substrate, just pressure.
Liquid laminates are just that--liquid coatings that require a specific liquid-coating machine or applicator. These coatings are for the most part solvent- or aqueous-based; chemical composition will vary from manufacturer to manufacturer.
Thermal vs. pressure-sensitive laminates
There are a number of differences between thermal laminates and pressure-sensitive laminates (PSAs). PSAs require minimal heat and adhere to a broader range of substrates. They work well on heat-sensitive materials and fragile toners. PSAs can be used for a wide variety of indoor/outdoor applications and many offer UV protection.
Thermal laminating film is typically more cost effective than a PSA, and offers minimal waste. It is proven to be very durable and is used in a wide variety of indoor applications. Thermal laminates provide applications with image enhancement, protection and rigidity. Thermal laminates for the digital print market are almost always made up of a polyester film with a polyethylene adhesive layer. PSAs can be manufactured with anything from polyester to polycarbonate to vinyl.
Laminate description ratio
The ratio indicates the amount of film versus the amount of adhesive. For example, if someone refers to a 4/3, they are talking about a seven mil film that is comprised of four mils film and three mils adhesives. (Mil refers to 1/1000 of an inch, and is not to be confused with millimeter, which is about 4/100 of an inch.)
The thickness of lamination film is known as the mil thickness (thousandths of an inch).
The base or outer protective layer of most thermal laminating film. It does not melt during the thermal laminating process. It is also the base layer of many PSA films.
The adhesive almost always used in thermal films. During hot lamination it liquefies. Lamination takes place in the nip (the space where the pressure rollers meet). Fans or chill rollers in the laminator then help cool the adhesive so it becomes a flexible solid again.
Calendared Vinyl (less expensive)
Calendared film is manufactured through a calendaring process. In simple terms, a molten mass of vinyl is pulled through pairs of polished heated rollers until it is stretched to a thickness of two, three or four mils. The film is then wound into rolls for adhesive coating. Calendaring is a more efficient and cost-effective method of producing films, which brings the price of vinyl down dramatically.
Cast Vinyl (more conformable)
Pouring liquid vinyl onto a very smooth casting sheet produces cast film. As the material moves through heat curing ovens, the solvents are removed to fuse the remaining solids into a film. When the film emerges from the ovens it’s ready for adhesive coating. Cast films are normally rated at an outdoor durability of four to seven years, and are more resistant to fading than calendared film colors because cast films contain better pigments and UV stabilizers. Additionally, cast vinyl is dimensionally stable, very conformable, and resists shrinkage and expansion.