AN INTRODUCTION TO LAMINATION SYSTEMS AND MATERIALS
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:
Pouch laminators
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.
Heated roll laminators
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.
Cold roll laminators
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.
Film types
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.
Pressure-sensitive films
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
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.)
Mil Thickness
The thickness of lamination film is known as the mil thickness
(thousandths of an inch).
Polyester
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.
Polyethylene
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.
