Take a Closer Look at Pad Printing
By Michael DeCesare
12 January, 2006
© 2006 Pentex Print Master Industries Inc.
How do you achieve good pad printing results?
With
30 years in the pad printing business we think that it is important to stop and
review the things we think we know as sometimes we can surprise ourselves and
learn that we have developed a few bad habits over the years. Changing
technologies and chemistry have allowed the pad printing process to mature to a
point where it has become an essential part of manufacturing and product
promotion. The pad printing process has evolved to become widely accepted
particularly in the plastics industry due to special features which allow easy
printing on unconventional shapes which are impossible to print with other
printing techniques.
A
good pad printing job can be described as an optimum ink transfer that is
achieved by means of a sharp balance between surface tensions of the
corresponding surfaces; that is pad, ink, cliché (printing plate) and substrate
which turns into high definition printing. In order to achieve a commercially
acceptable print, there are several factors which need to be addressed before
beginning: they are Artwork, Printing Plates, Printing Pads, the Substrate, the
Ink, and the printing environment.
New
Lazex Computer to Matte Film with Lazex Emulsion Enhancer Spray
Good
quality art is the definite starting point because the reproductions you print
can only be as good or as bad as the original artwork. Not only does the
artwork need to be high quality, but it must be printed on the proper film in
the proper format. Use the Lazex Matte
film and a high quality 1200 DPI laser printer to create your film. It is not recommended that you use Vellum or
Clear Glossy film because they do not give you the highest quality image
reproduction on the printing plate.
Using
a glossy film on polymer plates is not recommended for several reasons, glossy
films have a high surface tension which traps air between the film and the
plate, and this will cause marks to be left on the plate when washing out the
plate. Gloss Finish film has a higher
static charge that attracts dust and will create small marks that will transfer
onto the printed part during the print process.
The Lazex Matte Finish Film which is designed for use on polymer plates
does not create a static attraction and will prevent pin-holes and water marks
on your printing plates.
The
film must be printed POSITIVE, EMULSION DOWN. Inspect the film for any marks,
pin holes or unwanted defects before proceeding. If you are satisfied with the
quality of the artwork, you now need to enhance the density of the film. This
is achieved by spraying the matte Lazex film with the Lazex Toner Enhancer
Spray. The side of the film that the laser printer prints onto is called the
EMULSION side; this is the side that needs to be sprayed. After spraying, allow
the film to dry for several minutes before proceeding. The image on the film
should be noticeably darker than it was; it is vitally important that the image
be as dark as possible.
Processing Polymer Printing Plates (Clichés)
Printing plates hold
the “Master Image” in the printing process; all prints are generated from the
printing plate. Using a high quality 
printing
plate is essential. Plates can be from one of two
categories, steel plates or polymer plates. Steel plates are used for print runs
over 100,000 parts, polymer plates are used for shorter runs. Both types of
plate will reproduce
high quality prints. For simplicity, we will use polymer printing plates for our
discussion.
First
and Second Exposures:
Step
One – with Lazex Film Emulsion down. The
printing plate must be exposed to Ultra-Violet Light and the Film Art in order
to create the image on the plate. Place the emulsion side of the plate against
the emulsion side of the film, you now place these face down on your UV
exposure unit and expose the plate to the UV light. The film will mask or
protect the areas of the plate where the image is to be located; the exposed
areas will begin to harden when exposed to the UV light. The longer the
exposure time, the shallower the depth of the relief area of the image. The exposure time is dependant on the type of
film being used, the source of UV light and the distance the plate is from the
UV light source. Using a Pentex PTX-702
UV Exposure unit and the Lazex Matte Film, we recommend an exposure time of 70
seconds.
Step
Two – 300 Line Gravure Screen for Normal Images and 150 Line Gravure Screen for
larger open images. Using a gravure
screen is necessary to prevent ink being pulled out of the relief area of the
plate by the ink cup (or doctor blade).
The gravure screen creates a dot pattern that will act as a bridge for
the ink cup and prevent it from dipping into the relief area. Choosing the right gravure screen depends on
the type of plate and the size of artwork being printed. We recommend that a 300 line gravure screen
is used on a polymer plate for most types of print but a 150 line gravure
screen may be used on prints that have larger open areas. We recommend an exposure time of 35 seconds
using a Pentex PTX-702 Exposure Unit.
After
the exposure is completed the plate is ready for the wash out process. Polymer printing plates can be either WATER
WASH (Pentex PTX-52W) or
Choosing
Your Printing Pads
Printing
pads are made of silicone and are used to “Pick Up” or “Transfer” the print
from the printing plate and “Deposit” the print onto the substrate (part) that
is being printed. Printing pads are available in a variety of shapes and sizes
and are made of different silicone types depending on the characteristics that
are required. Choosing the right shape of printing pad is determined by the
shape of the product being printed and by the image to be printed. For
instance, a radically shaped pad works very well on a flat surface. The hardness (durometer) or type of silicone
is chosen by determining the shape and strength of the surface to be printed
on. For flat and smaller, tighter concave surfaces, a harder pad (60+
durometer) would be required. On rounded objects a softer (less than 60
durometer) pad may be considered. Choosing the correct pad is critical. Using
the wrong pad can cause pinholes or other defects in the print. The printing
pad should be replaced on a regular basis as the pad will age causing the
silicone to loose its effectiveness to release the print, it will suffer wear
and tear as part of the printing process and may even become damaged as a
regular part of printing.
Understanding
the Substrate
The
substrate is the item being printed. Understanding the surface will allow you
to determine how the surface needs to be prepared. Surface preparation consists
of one or both of the following operations: cleaning and pre-treating. All
parts must be cleaned as finger prints, dust, and any other surface contaminant
will not allow the print to be deposited properly onto the surface of the part.
Substrates that have a high surface tension such as Polypropylene, Metals,
Chromed and Lacquered Surfaces need to be pre-treated after they are cleaned.
Pre-treating can be done by one of three methods: Chemical Wiping (InkFlexx
MP2000-104 Pre-Wipe), Flame Treating, and Corona Treating. The method you use
would be determined by the quantity of parts and your budget.
InkFlexx
– One
Ink Formulated for Printing on All Substrates
Once
the parts have been prepared, we can concentrate on our ink. The InkFlexx
MP2000 series printing inks will have the greatest 
impact
on the quality of print and adhesion of ink onto the substrate.
With
the wide variety of
substrates, it is important to know the composition of the material that you are
printing on because the ink will interact differently
with different substrates. Using a premium quality pad printing ink is
essential. Many inks are simply reformulated screen printing inks which do not
have the opacity that is required for pad printing. Remember that pad printing
puts down a print that is approximately 20 microns thin where screen printing
lays down double that thickness. With
only half the amount of ink required for screen printing, pad printing inks
must deliver equally opaque color reproduction. Why would you use an ink that
is not designed for the job?
InkFlexx
inks were the first pad printing inks formulated specifically for pad printing
and for use on a wide range of substrates, (rather than the usual hodge podge
of ink types used for each different substrate). InkFlexx has simplified the
pad printing process by eliminating errors caused by selecting the wrong ink.
It has also meant a reduction in ink costs as only one ink needs to be
inventoried, (not three to four different types of inks as other suppliers
would have you do). Just think… one ink!
Extensive
research has brought forth the InkFlexx line of pad printing inks which doubles
as a superior screen printing ink when high quality detail printing and opacity
are required. It may be used as received or the pigmentation may be reduced
with extenders to produce equally excellent results.
Some
important characteristics of InkFlexx Inks are:
1. Optimum Ink Transfer – Achieved by means of a sharp balance
between surface tensions of the corresponding surfaces: Pad, Ink, Cliché and
Substrate. The result is a high definition print in either spot color or
process color printing.
2. The high opacity of the InkFlexx Inks allows printing of high
relief jobs and printing of light colors on dark substrates with a single hit.
3. Quick drying properties allow for high speed printing of multiple
colors while still maintaining high gloss characteristics.
4. Very good mechanical and chemical resistance exhibited by the
basic ink may be further enhanced by the addition of the available additives.
5. Wide range of standard colors which are also used as mixing
colors.
6. Very good adhesion to a wide variety of materials including, ABS,
Acrylic, PBT, PET, PET G, Polyamides, Polycarbonates, Thermo-rigid Polyester,
Polystyrene, LD-PE, HD-PE, Polypropylene, Rigid and Flexible PVC, SAN, Glass,
Stainless Steel, Aluminum, Chrome Plate, Iron, Tin, Wood, Lacquered, Galvanised
and Powder Coated surfaces.
When
preparing InkFlexx you must know whether or not the ink is to be used as a
single or a two-component ink mixture. A two-component ink mixture is an ink
that is using a hardener (also referred to as a catalyst or an epoxy ink). The
ink mixture should always be measured by weight using a digital scale accurate
to at least 0.1 grams. Always follow the InkFlexx formulation guide
recommendations on the amount of thinners, hardeners, and/or any additives that
are required. Using amounts other that what is recommended may not give the
desired result. When inks are mixed in the wrong proportions, you may
experience problems with transfer, opacity, sharpness, and adhesion. Also,
cross-linking products from other ink lines is not recommended as thinners,
hardeners, and additives are designed to work with the ink in a certain way,
and using another product will affect the chemistry and you may have
undesirable effects.
The
Printing Environment
Where
you do your pad printing is an important consideration. You want to locate your pad printing in an
area that has a controlled temperature environment, is clean, and is well lit.
The
pad printing process works through the evaporation of the thinners from the
time the ink is picked up from the printing plate to the time that it is
deposited onto the substrate. One of the
most important factors in controlling this variable is the ambient temperature
of the print environment. The printing
room should be air conditioned and maintained at a constant temperature year
round.
This
room should be kept clean, you do not want dust to get onto the print. Keeping pad printing machines close to
working machinery such as injection molding machine is not recommended.
Having
a well lit environment is important not just for the operator’s comfort, but is
also used as a quality control tool.
Colors will look different under different lighting conditions; the
ambient lighting should be as close to daylight conditions as possible.
Information about Pentex
With
over 30 years of service to the pad and screen printing industries, Pentex has
the expertise and experience to help you achieve your print production goals.
There are several important reasons why Pentex should be your supplier and a
partner in helping you achieve success. At Pentex, we are always looking for
ways to improve our machines and supplies to make your pad and screen printing
operations more efficient. From our pad printers to our high-tech DiscMaster
series CD screen printers, no idea is too small for our engineers. New ideas
are always being explored to further improve our product line to satisfy our
customers’ growing needs. When an off the shelf solution is not what you are
looking for, our design and engineering experience will allow you to draw on
over 30 years of real world solutions. We will work with your production team
to ensure maximum productivity at every stage of your printing operation. No
detail is too small, no task is too large. At Pentex, we are proud of the reputation
our machines have earned in the last quarter century. We are equally proud of
our reputation for providing great service to our customers.
You
can contact us by email at Pentex@inkflexx.com
or visit our website at www.inkflexx.com.
