CONVENTIONAL PRINTING INKS
For continuous forms printing.
HBL inks for laser printer forms
Introduction
The introduction of laser printers confronted business forms printers with a new technology
requiring certain changes of the usual procedures.
The production of forms for use in laser printers poses certain demands which have to be met
by the printer’s materials, e.g. printing inks and paper, and by the manufacturing conditions.
The study of functional relationships between ink, print, printing process, and laser printers
was particularly important for printing ink manufacturers. Laser imprinting on forms is a
significant example for conditions of use which shape the profile of requirements to be met
by printing inks. In the case discussed here, the printing inks have to meet particularly demanding requirements.
HUBER-GRUPPE formulated the HBL inks for this application.
HBL stands for “HitzeBeständig für Laserdrucker”, that is heat resistant for laser printers.
Critical interactions in laser printers
The question of possible interactions between pre-printed business forms and laser printers
requires a brief explanation of the laser printing principle. Laser printers are composed of
the following components:
Data memory for at least one page of output.
Laser station, modulator, and mirror system to convert the stored information into light pulses.
Electro-photographic printing unit to produce latent charge images on a photoconductor drum.
Developing station to apply toner and generate an electrostatic image on the latent charge image.
Transfer station to transfer the electrostatic image onto paper. The paper with the toner adhering to it is carried
over a preheating plate, heated to about 120 °C, to fix the image thermically. The toner powder is melted onto the paper between burning in
and counter pressure roller.
The burning in roller is heated up to temperatures between 180 and 220 °C, depending on
the type of laser printer. The melting temperatures of toner powders are located between 80
and 150 °C. That is the temperature which the paper has to reach to fix the image perfectly.
Pressure of around 300 kN/m2 may occur in the nip between burning
in and
counter pressure
roller.
Trouble free operation of the laser printer requires a perfect fit of all the components
participating
in the process. This concerns the following parameters:
The layout of the form should avoid, if possible, overprinting of solid areas and laser
imprinting
on pre-printed solids. Wherever possible the inking adjustment should avoid
exceeding
the thickness of ink layer usual in forms printing, around 1.3 grams.
Multicolor
commercial work (mailings) must only be produced with inks for U.V. curing or hot air drying.
Tension length and bending stiffness of the paper have to conform to DIN 6721, and the
paper has to belong to fiber class Z 100 according to DIN 827 (100% cellulose).
Printing process, i.e. appropriate damping fluid for offset printing, minimum damping, printing plates.
Printing ink.
Laser printer troubles become apparent or occur nearly exclusively in the
burning in station.
A comparatively large number of types of disturbance is known where one or several of the
above parameters are inadequate, or are not sufficiently adjusted to each other.
Build up of printing ink particles on the preheating plate and on burning in or counter pressure rollers.
Mechanical damage of the burning in roller, often coated with silicone resin, due to adhering printing ink and toner particles.
Swelling of rollers, caused by volatile components of printing inks, e.g. mineral oils.
Dirt on the burning in roller marking in the printed image of forms.
Smoke and odor caused by evaporating or volatizing components of paper or printing inks.
Insufficient adhesion or repelling of the toner powder on printed areas on the paper.
HBL inks from HUBER-GRUPPE
All HKS®-E inks are HBL special inks containing binders with the required profile of characteristics.
Good printability was a major consideration when developing these systems. Stability and
high tolerance for damping fluids, i.e. wide range between the scumming limit on one hand
and the generation of wash marks on the other, help to lower the waste rate.
Most HBL inks contain only small amounts of volatile ingredients. Disturbances in the laser
printer caused by volatizing or evaporating ink ingredients, and swelling of the
burning in roller
are thus avoided. The fluid components such as vegetable oils and reactive thinner are capable of interlacing
oxidatively, and they are completely incorporated in the ink film. Oxidative drying causes a
phase change from fluid to solid.
The driers, based on organically combined metals, catalyze the oxidative interlacing reaction,
taking place under the influence of the oxygen contained in the air, between suitable vegetable
oils and reactive thinner.
Contrary to inks based exclusively on binders containing only mineral oils, the striking in
capability of HBL inks is lower, i.e. they need more time to strike in.
Striking in was tested on coated paper because on that stock differences show more clearly
than on uncoated paper such as used in business forms printing (without hot
air drying or
radiation curing). The fact that HBL inks need more time not only for striking in but also for drying requires a
sufficient time interval between printing and use in the laser printer. At least three to five days
are necessary, depending on the number of colors and ink coverage.
Otherwise ink may stick to the burning in roller of the laser printer, causing ghosting of the
printed image. Inks for U.V. curing should be used where overprinting is necessary.
The following problems may occur when using HBL inks on self duplicating papers:
The commercially available types of SD papers are not of identical quality. Differences of
interaction with printing inks are therefore possible. Before running the job, tests for contact
yellowing and neutralization are recommended. Special inks from HUBER-GRUPPE should be
used if the problems occur during the test.
Additives
Only special additives must be used with HBL inks:
Printing oil 10 T 1405
It matches the binder system of the inks and may be used to reduce the tack of the inks if stock
of low wet picking resistance has to be printed on. Picking and piling on blankets can thus be
avoided.
Grafo Drier 10 T 5001
Emulsified damping fluid may retard drying if the image requires low inking. The problem can
normally be eliminated with Grafo Drier.
Transparent white 30 IL 1000
This is the only admissible product to brighten color shades, because it is based on the same
binders as those used in HBL inks.
Technical information and Safety Data Sheets for all these products are available.
