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Choosing the Right Film

Choosing the correct laminating films for a particular job is not always as simple as it may first appear. Just using what is on the shelf or thinking any type of film will work can end up causing challenges once the laminating process begins. This Q&A article will cover several of the issues that should be considered closely when laminating printed material.

Q:  Is dyne level an important element when utilizing laminating film on a particular job?

The surface tension of the substrate becomes important when working with processes
such as UV coatings, overprint varnishes, ink jet applications, adhesives and foil stamping.
A low dyne level on the surface (less than 38) will mean a marginal to unsuccessful bond
to the substrate. In the case of laminated surfaces, dyne is used as a predictive tool for the
degree of adhesion to the product during the process application.
The most common type of dyne measurement tools in the print market today is dyne
solutions, which come in pen format or solutions in jars. The pens are easily acquired,
simple to use and come in different dyne indication levels.
Most laminating films can be corona-treated to increase the dyne level, which is always
recommended due to the gradual decay of the surface charge. Any film roll that has
been corona-treated should never be stood up on its end on the floor. This can provide a
discharge path for the static charge captured on the film surface.
Typical dyne levels for film is standardized by a minimum of 40 dyne on a wide variety of
films. The typical dyne level is usually 42 on the surface and much greater on the adhesive
side. Minimum requirements for UV coatings and foil stamping applications are preferred
to be at a dyne level of around 40.

Factors Affecting Dyne Levels

Ionized Sprayers
. These devices are used to reduce static electricity in stacked paper.
They are used primarily in conditions of low humidity at the feeder sections of presses,
laminators, folders and coaters. Ionized sprayers spray out ionized air that reduces static
and also reduces the dyne level, especially in areas closest to the nozzle. If a localized
area of dyne failure exists, this may be the root cause.

Paper
. Paper is a variable that, at times, will disguise itself as a film problem. Some
papers have a pH difference between the wire side and the felt side (print side). It is not
uncommon to find a neutral pH on the felt side and a high alkaline pH on the wire side.
This is not a problem for lamination, but for applications such as presentation folders,
overlay boxing and case bound book covers, it does create a problem. A high pH has the
same effect on adhesive binding applications as it does in many litho-print applications.
The ink, as well as the glue, do not dry. Emulsification results with a high alkaline condition
where ink or glue absorbency is required. An alkaline condition inhibits ink drying and
curing; the same is true for an adhesive that would be used to adhere a laminated surface
to the unlaminated surface with water-based glue. The recommendation here is to check
both sides of the paper stock and make a note of the findings in the job folder. There are
pH pens that indicate neutral, acid or alkaline conditions in paper.

Humidity
. High humidity and very low humidity will affect the interpretation of a dyne
reading so all readings would be best served at pressroom environment, which should be
maintained at roughly 50 percent RH.

Time
. Not using the corona-treated film within the manufacturer’s suggested timeframe
might cause a less than desirable performance. There is a bleed-off of charge over a
period of time known as dark decay – even though the film still may be wrapped and
packaged.

Poor Handling. As mentioned earlier, a corona-treated roll never should be stacked on its
end, which will provide a discharge path for the corona treatment.
Glue recommendations and additional information about other finishing applications should
be obtained from the film supplier.


Q:  What is the best type of film for my particular application?


Several films are available on the market today, each has its own unique set
of characteristics for certain applications.

Oriented Polypropylene (OPP) Films (sometimes referred to as BOPP)
Description: Oriented Polypropylene (OPP) is a very clear and flexible film
used in several applications from dust jackets on case bound books to food
wrap applications.
Clarity: OPP is probably the clearest of laminate films available today. Clarity
becomes an issue especially in applications involved in print because the
clearer the film the less apparent color shift. All films and other coating
applications will shift or enrich the colors on a printed piece, especially in the
pastel color renditions of the print.
Durability: Another key characteristic of OPP is its flexibility. It is used
primarily for dust jackets on case bound books and gives the book a “sparkle”
for shelf appeal.
Versatility: OPP has limited versatility because it is difficult to overprint, glue,
UV coat and foil stamp. Sometimes you will see dust jackets that include foil
stamping on the cover but this is usually done prior to the application of the
OPP film. However, OPP does emboss very well.
Unique Characteristic: OPP is a flexible film that is very soft and scratches
easily. Additionally, it is FDA-approved right off the shelf so it is suitable for
some food packaging applications. It is the most cost-effective film on the
market.
Typical Application: Due to the cost effectiveness and the extreme flexibility
of OPP, it is used for direct mail pieces, advertising magnets, dust jackets
and most anything that has a dated life that most likely will be discarded.

PET or Polyester (PET) Films (sometimes referred to as Mylar® – trade
name of DuPont)
Description: PET has the largest family of thicknesses for laminating films.
Thicknesses range from 1.2 mil to 15 mil thick in conventional, day-to-day
applications.
Clarity: The clarity is just a little less than OPP but also is dependent upon
the thickness of the PET film. The thicker the PET the less clear a product
will appear. This fall-off in clarity is virtually impossible to notice by the human
eye and will only render a difference in a side-by-side comparison of OPP
and PET laminates.
Durability: PET is extremely durable and has a hard surface and structure
that is more rigid than flexible.
Versatility: PET is more versatile than OPP and can be glued, foil stamped
and UV coated. It has a limited range for embossing due to the rigidity
factor, so thickness will be a key issue if embossing is required as a finishing
application.
Unique Characteristics: Since it is highly durable, PET is used for
identification applications such as security cards, ID cards and menu
applications. The durability factor also ensures the product will be usable
over extended periods – especially long timeframe demands requiring years
of use.
Typical Application: Case bound book covers, menus, credit cards, loyalty
cards and gift cards. PET with a special coating makes it ideal for write-on/
wipe-off dry erase boards as well.

Nylon Films
Description: Nylon is the first commercially successful synthesized product
and is used on a wide range of products from balloons to books covers to
food packaging applications.
Clarity: Nylon is consistent with the clarity of PET film.
Durability: Extremely durable, nylon is not susceptible to mildew so it ages
very well and continually protects the surface to which it is adhered.
Versatility: Probably the best and most versatile film available today, nylon
typically has a good dyne level so spot UV, gluing, foil stamping, printing and
embossing all work well with nylon films.
Unique Characteristics: There are many misconceptions regarding nylon and
the book component industry. Perhaps the most popular is the concept that
nylon is porous and allows moisture to pass through the film structure. This
is simply not true and is misleading. Nylon, however, is wickable, meaning
that it allows moisture to be drawn off. This also means that it can absorb
moisture. Hence, it is good for gluing applications such as presentation
folders, franking and inkjet addressing. The flexibility aspect of nylon makes
it ideal for perfect bound books. Nylon eliminates the curled cover situation in
environments of variable humidity. Nylon does allow for the expansion of the
book cover caused by humidity and also allows for the cover to return to a flat
condition once it has equalized the humidity, provided that the nylon film has
been applied correctly.
Typical Application: Perfect bound book covers, presentation folders and any
single-sided application requiring lamination.

Cellulous Acetate Films (biodegradable films)
Description: Cellulous acetate films are essentially derived from wood and
are a biodegradable film that is a sustainable option. It is being used for book
covers, presentation folders and gift cards.
Clarity: It has excellent clarity, equivalent or better than OPP film.
Durability: Currently, cellulous acetates are being used in the gift card market
and have not come into high demand in the book component industry.
However, it would have the durability properties for these applications as
well. It is a very durable film for a variety of applications.
Versatility: Cellulous acetate film has many of the same characteristics as
nylon and surpasses nylon in clarity and run-ability.
Unique Characteristic: Cellulous acetate is a biodegradable film made from
wood and wood by-products. There has been much curiosity regarding
biodegradable films and as environmental concerns continue, the use of
these films is sure to grow. Price is the major obstacle due to the current low
volume of production. If volume continues to grow the overall price will come
down. Additionally, cellulous acetate is a brittle film, which means that it will
snap easier and not have film roll-up on the trailing edge of the sheet.
Typical Application: Gift cards, presentation folders and book covers.

Q: What should be considered when gluing to a laminated surface?

Many applications exist that require a laminated sheet to be glued. Case or
hard bound books are a common example of where the laminated sheet is
flood coated with glue and the two book boards and spine are set on the glue
side and then folded over. Another application is a laminated presentation
folder where a laminated tab is folded over onto itself as the glue tab for one
or more pockets on the folder. This is a critical application because the glue
needs to adhere to the laminated face of the tab and the inside cover all
within a suitable amount of time. Typically, for production runs on a folder-
gluer, a combination of a hot melt glue to hold the flap and a water-based
glue for long-term adherence is used. Compatibility is the key focal point.
Glue that works with nylon film may not work with PET or OPP films.
A recommended test for the glue on a laminated product once it is set and
cured is to place the sample in a freezer for 12 hours and then test the bond
again. What works and responds at room temperature may fail after it has
been exposed and/or stored in a cold warehouse or transported in a truck in
the winter.
Another concern with glue is the compatibility with paper surface pH. Many
C1S sheets are neutral pH on the surface and are high alkaline on the wire
side. As mentioned earlier, a high pH tends to emulsify when an acidic
solution is placed in contact with it, which can result in failing adhesion.

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