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BY
DAVID LEVY - PRESIDENT
BROOKLINE CHEMICAL CORPORATION
BETHESDA, MARYLAND, USA
Rotary screen printing was introduced to the textile
world in 1966. It revolutionized textile printing by improving
production parameters. At the same time it also provided a new
dimension in textile print designs.
Long print runs at relatively high speeds as compared
to flat screen printing techniques have become common. Rotary screen
printing reduced production overhead costs to a lower level, when
applied to large print lots.
Automation, direct drives, automatic screen
positioning, computer command operations, laser engraving, automatic
dispensing of color and chemicals, among others, have contributed to
still higher efficiency in rotary screen printing operations.
Rotary screen printing machines were designed for and
expected to provide mass production quantities, avoiding short runs
and specialty effects which require difficult application techniques
and higher-cost chemical components.
Pigment printing operations constitute the majority
of textile printing worldwide, particularly in the United States.
Pigment printing provides a simplified application of print-dry-cure
and this application was ideal for the rotary screens.
Pigment printing traditionally has been associated
with a harsh hand and poor crock fastness when compared to dyestuff
printing. Pigment prints with very soft hand, upgraded fastness and
special novelty effects have not been expected of rotary screen
printing. Until now.
Since its inception, Brookline Chemical Corporation
has devoted its resources, experience and manpower to developing
unique chemicals and whole systems for the pigment printing and
related segments of the textile industry, creating very special
print effects.
Many of these systems have been produced worldwide
with great commercial success and this success was even further
magnified as these systems were also adopted in rotogravure, flat
printing as well as piece printing. However, their major application
has been in the rotary screen printing field. The purpose of this
paper is to provide details of a few of these specialty systems.
I.SOFT PIGMENT PRINTS WITH HIGH
FASTNESS PROPERTIES:
I.A. SUPERPRINT 101 - SOFT
BINDER:
Pigment print systems include thickeners, binders, cross linking
agents and additives such as softeners, humectants, emulsifiers and
antifoams. While most of these traditional components may affect the
final fabric hand and fastness, the most important component which
affects the fabric hand is the binder system.
Acrylic binders, butadiene SBR and their mixture
combinations have been known for a while.
Acrylic emulsions are expected to resist yellowing
upon exposure to light, heat, and cyclically ageing with oxides of
nitrogen. They usually are attractively priced. However, they render
a fairly harsh hand especially at high concentrations in the print
paste.
Recent developments in acrylic emulsion chemistry
have rendered printing binders with a much softer hand, yet
maintaining reasonable price levels and fastness.
Butadiene SBR emulsions provide a softer handle, but
they are susceptible to yellowing.
Mixtures of both acrylic and butadiene SBR types have
been common in many pigment printing formulations.
Acrylonitrile-based polymers
were a more recent development. The original film produced with
acrylonitrile was tough and fairly rigid and was softened with the
aid of selected plasticizer. The resultant emulsions rendered
excellent printability and fastness to dry crock, dry cleaning and
wash. The wet crock fastness properties were good but needed
improvement.
Modified versions of the acrylonitrile latex were
then developed by adding special modifying components. These
specialty components contributed to an improved wet crock fastness
and hand. Brookline's SUPERPRINT is a specialty latex based on this
chemistry.
Pigment printing requires higher additions of binders
for deep shades. Higher amounts of binder are expected to improve
fastness results, particularly to crock and wash. However, the
amounts of binder usually level-off at 18-20% in print paste
formulations for deep shades, particularly due to a resulting harsh
hand.
The most important feature of the latter type of the
modified acrylonitrile binders, i.e. SUPERPRINT is that the addition
of higher amounts of binder to the print formulation, as required
for deep shades, does not adversely affect fabric hand. It is
therefore possible to arrive at higher pigment print fastness
results by increasing the amounts of the SUPERPRINT binder in the
print system without materially affecting fabric hand.
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