Choosing The Correct Union White
Plastisol
For Underbasing Applications
* Overview
With so many white inks to choose from on the market today, it can become very
confusing and frustrating when trying to choose the correct white plastisol to use as an
underbase for flash curing applications. Is there one "miracle white" that does
it all or is it necessary for printers to inventory more than one white ink? This paper
will honestly answer those questions as well as deal and rate the best choices of Union
Ink products to use as underbase whites. Squeegee, mesh, printing, flash curing and curing
parameters will also be discussed.
* What is Underbasing?
Underbasing is a process where a white ink is printed on a dark colored shirt, placed
underneath a drying unit called a flash cure dryer which brings the ink film to a minimum
gel temperature and allows colors to be printed on top of the white underbase ink. Because
this process basically turns the substrate you are printing on from a dark color to a
white, it allows you to produce vibrant prints while utilizing standard opacity inks such
as Union Ultrasoft, Mixopake, Autoline or Tru-Tone series inks.
* What Union White Inks Are The Best Choices For 100% Cotton Dark Shirts?
The best choice for underbasing 100% cotton dark shirts is PAFC-1020 Fast Flash White.
This ink has been specifically formulated for underbasing. It's creamy,
easy-printing consistency provides a smooth surface for overprint colors.
PAFC-1020 has a low after flash tack which is important if you cannot afford
to sacrifice a print head as a cool down station (see section titled
"Printing Parameters" for more information about cool down stations. Fast
Flash White is not designed as a stand alone white (such as MIXO-1000 or PADM-1057) and will not produce satisfactory results
when used as a standard plastisol or as a mixing white.
MIXO-1000 Mixopake White works well for printers wanting one ink for 100% cotton also. The
only disadvantage of MIXO-1000 is a print head on automatic presses may be needed for a
cool down station because of a slight after flash tack..
* What Inks Are The Best Choices For Polyester or Polyester Blend Garments?
Because shirts containing any amounts of polyester are prone to dye migration
(bleeding) a specially formulated ink must be used on this substrate. This ink is
manufactured with special ingredients to prevent the dyes of the shirt from migrating
through the ink film. Consult the Union Ink Catalog section "General Information
About Plastisol Inks" for more information on the causes and prevention of dye
migration.
The best choice for underbasing polyester blended dark garments is PAFC-1050 Fast Flash
Low-Bleed White. PAFC-1050 is specially formulated to minimize dye migration, provides a
smooth printing surface for overprint colors and flash cures tack free very quickly
helping to eliminate the need for a cool down station. As in the Fast Flast White for
cotton, PAFC-1050 does not provide satisfactory results when used as a standard plastisol
or as a mixing white.
Even though PADM-1057 Maxopake Low-Bleed White may
also be used as underbase whites they are not necessarily the best choice
for this application. Low-bleed whites are typically formulated with special
resins, fillers, and plasticizers designed to stop dye migration. Some even
contain a small amount of blowing agent (commonly used to manufacture puff
inks) in order to increase opacity and maximize their bleed resistance.
These ingredients can cause an uneven printing surface for your subsequent
colors if the ink deposit is too thick and requires a longer flash time.
* Mesh Specifications For Underbase Whites*
MIXO 1000, PAFC-1020, 1050, PADM 1020
Simple block areas: 86T-110T (Manual Press) 125T (Automatic Press).
Detailed images: 110T (Manual Press) 140T (Automatic Press).
Fine line halftones: 125T-140T (Manual Press) 160T-200T (Automatic Press).
* Mesh Specification For Overprint Colors*
Simple block areas: 200T (Manual Press) 260T (Automatic Press).
Detailed images: 230T (Manual Press) 305T (Automatic Press).
Fine line halftones: 260T (Manual Press) 350T (Automatic Press).
*These are guidelines only and may need to be varied depending upon the amount of detail
and the number of colors in the design
* Printing Specifications
Underbase screens on your automatic or manual press should be set off-contact in order
for the ink to clear the screen cleanly. It may be necessary to double stroke the
underbase to clear the ink from the screen cleanly and provide the smoothest surface for
the overprint colors.
Squeegees should be set at a slight angle and with just enough pressure applied to clear
the ink from the screen. It is recommended printers using automatic presses back off the
squeegee pressure until the ink does not print and then slowly increase the pressure until
the desired underbase print is achieved. Remember, you are trying to print the ink on top
of the garment, not drive the ink through the garment. If the print starts appearing on
your platen you are probably using too much pressure.
If possible, overprint colors should be printed from the smallest to largest area of
coverage in order to minimize pick-up on the backs of the screens. Squeegee pressure is
important in this stage because you are now printing on a piece of non-absorbant vinyl
which is not as forgiving as an absorbent garment. Too much pressure will cause the colors
to smear. To alleviate this problem either use a lighter pressure during the print stroke
or utilize finer mesh counts for overprint colors.
* Flash Curing the Underbase
Your flash cure unit must be large enough to not only cover the design but should be at
least 4" larger than the design you are flash curing. Some of the smaller 16 inch
square units can barely cure a 14 inch design much less the oversized prints in demand by
customers today.
The flash cure unit should be positioned above the design so you can get a partially cured
print in a matter of 3-5 seconds while not burning the garment. Plastisols will reach what
is called the gel temperature at approximately 240 degrees Fahrenheit. This can be
measured with either a temperature strip or temperature probe available from Union Ink
Company. Caution: Be careful not to fully cure the underbase ink. An overprint color may
not adhere to a fully cured underbase and flake off after the shirt is washed. Another
indication of overcuring the underbase is if little pinholes of white can be seen through
the overprint color. If so, lower your flash cure temperature or raise the height of the
flash cure unit.
After flash curing the underbase white, the ink may be appear sticky even though it is
fully gelled. This is known as "after flash tack" and usually occurs in inks not
specifically formulated for flash curing. This occurs more frequently on automatic presses
because of the production speeds. This tack goes away in a few seconds but slows down
production in the meantime.
To eliminate this problem a cool down station may be necessary or fans may be needed
between print heads to cool down the underbase print. For example, on a six color press
the underbase would be printed on head #1, flash cured on head #2, head #3 would be empty
and used as the cool down station. The overprint colors would be printed on heads #4, #5,
and 6. Because of the cool down station you will be limited to three colors. This is why
the best choice is to use an ink specifically designed for underbasing where after flash
tack is not a factor.
On manual presses with rotary table platens "after flash tack" is usually not a
factor because the underbase has had sufficient time to cool and lose the "after
flash tack" before the print comes back around for the overprint colors.
For designs with more than two or three colors it will be very difficult to achieve an
acceptable print without adding a second or even a third flash to the printing sequence.
As each new color is printed, a little bit of the previous color is picked up on the backs
of the screens resulting in mottled looking and uneven color intensity.
*Disclaimer
Customer testing is required and should be mandatory with this product or any new
product or process before running production. Our technical advice and recommendations
given verbally, in writing, or by trials are believed to be correct. They are not binding
also with regard to the possible rights of third parties and do not exempt you from your
task of examining the suitability of our products for the intended use. We cannot accept
any responsibility for application and processing methods which are beyond our control,
nor can we accept responsibility for misuse by you of the products or use by you of the
products outside the specified written instructions given with the products. User must
protect sensitive skin, exposed wounds and eyes from contact with products.
* For More Information
This paper was written and produced for your information by the staff of Union Ink
Company. For more information about this product, process or any other Union Ink product
please call 1-800-526-0455.
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