| Introduction
The following notes are intended to
guide those printers who may be using UV products for the first time. They
are meant to supplement the already extensive knowledge of printing acquired
through day to day experience with conventional inks and varnishes.
The problems listed are varied, and
though many hopefully may never be experienced, they have been included
to provide a reasonably comprehensive aid to the printer. They have been
arranged in a clear format to enable easy reference. |
| PROBLEM |
POSSIBLE
CAUSES |
SUGGESTED
SOLUTIONS |
| 1.
Ink is solid in the can or is becoming solid from the bottom of the container. |
(a)
Ink storage area is too warm. |
Relocate
inks in a more suitable area. |
|
(b)
Interaction between the pigment and vehicle caused by wrong pigment type. |
Contact
the ink maker. |
|
(c)
Ink has passed its useful life. 6-12 months is usually claimed, but can
be much longer than this. |
Check
the date of manufacture. Practice good storage methods to avoid using new
stock before old. |
|
(d)
Ink may be crystallized. |
This
may occur due to ink being stored at too low a temperature. |
|
(e)
Ink may be affected by stray light. |
Replace
lids of containers when not in use. Screen sunlight from pressroom. Most
UV systems do not allow high energy light to escape. |
|
(f)
Contamination of ink by metal parts or metal left in contact with ink after
mixing. |
Ensure
brass or copper does not remain in close contact with ink, varnishes or
coating as this may cause hardening. |
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| 2.
Ink drying on rollers or blankets; tack increases during run. |
(a)
Rollers and blankets not compatible with ink. |
Contact
suppliers for alternative products. |
|
(b)
Stray light in pressroom. |
Adequately
filter direct sunlight and fluorescent lamps. |
|
(c)
Rollers may not have been primed correctly; still removing low viscosity
components from ink, causing tack to rise. |
Prime
rollers when new, and when replacing several rollers for maintenance purposes. |
|
(d)
Inks may be contaminated by products mistakenly added, i.e. conventional
reducer, or extender (tinting medium). |
Practice
good housekeeping to ensure that all non-UV products are kept off the press
and that a separate storage is kept for UV products. |
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| 3.
Piling of ink on rollers, blankets and plates. |
(a)
Blankets and/or rollers may not be suitable for use with UV cured products. |
Contact
suppliers of appropriate products for suitable alternatives. |
|
(b)
Contamination with spray powder on sheets from previous run on another
press. |
Dry-run
to remove spray, or crush spray. Removal is preferable. |
|
(c)
Ink rheology may be poor due to being of light-fast or light-resistant
type. |
Reduce
ink slightly to improve flow, or contact the ink maker. |
|
(d)
Setting of dampers, rollers, plates or blankets may be causing poor transfer. |
Check
settings of the mentioned items. |
|
(e)
Excess water may make the transfer problem worse, causing some emulsification. |
Reduce
water setting slightly. UV inks, like conventional solvent-based inks,
run better with minimum water. |
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| 4.
Blankets
embossing. |
(a)Wrong
blanket type. |
Consult
with blanket supplier for compatible type. |
|
(b)
Using relief plate to spot coat with UV coating. |
Consider
using blanket specifically made for UV.
Coating is often more aggressive than
ink to the blanket. |
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| 5.
Picking of paper surface. |
(a)
Paper surface is too weak, or stock may be 'green' and lack good surface
strength. |
Change
to better stock. Contact mill or paper supplier if stock has been successfully
used before. |
|
(b)
Ink tack is too high. |
Reduce
the ink with gelled or liquid reducer. PLEASE NOTE: Too much reducer may
retard proper curing. |
|
(c)
Water setting is too high, weakening the coating surface. |
Apply
less dampening water. |
|
(d)
Rollers not primed. |
Prime
rollers with appropriate product or reducer. |
|
(e)
Wrong blanket type. |
Replace
blanket. |
|
(f)
Interstation lamp not curing sufficiently. |
Check
lamp curing; also, press speed may be too high causing poor cure. |
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| 6.
Ink is misting. |
(a)
Rollers set incorrectly. |
Reset
rollers. |
|
(b)
Too much ink is being carried on the rollers, or if ink is a tint. |
Reduce
amount of ink on rollers, or, if ink is a tint, strengthen tint. |
|
(c)
Ink rheology is poor. |
Contact
ink maker to improve flow characteristics. |
|
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| 7.
Ink 'laying-back' in the duct. |
(a)
Ink may be highly pigmented. |
Stir
frequently or use duct agitator if available. |
|
(b)
Ink formulation may be unsuitable. |
Consult
ink maker. |
|
(c)
Ink may be too stiff. |
Use
reducer or ink-duct agitators. |
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| 8.
Halftones 'filling-in'. |
(a)
Too much ink supplied to plate. |
Reduce
amount of ink on rollers. |
|
(b)
Tack too high, preventing good flow. |
Mix
in small quantity of reducer. |
|
(c)
Ink is highly pigmented. |
Reduce
ink with liquid or gelled UV reducer. |
|
(d)
Ink may be partially cured by 'stray light'. |
Ensure
light is not reflected from cylinders onto blankets and plates. Screen
off all direct ambient light shining onto the press rollers and cylinders. |
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| 9.
Ink transferred to impression cylinders on perfecting presses. |
(a)
Interstation lamp not on or insufficient time allowed to warm-up. |
Switch
lamp on or allow lamp to complete 'warm-up' cycle before using it. |
|
(b)
Press speed is too high for the lamp to effect a good cure. |
Slow
press speed slightly until curing is satisfactory or fit more powerful
lamp if possible. (This is often not possible due to press specifications). |
|
(c)
Lamp may be failing. |
Replace
lamp. |
|
(d)
Electrical problems. |
Consult
electrician. |
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| 10.
Ink is not curing, or sheets are sticking together in the stack. |
(a)
UV curing unit is not switched on. |
Switch
on unit, check fuses and circuit breakers. |
|
(b)
Curing
unit has lost efficiency due to lamps or reflectors being soiled. Lamps
may also have reached the end of their useful life. |
Clean
lamps and reflectors, if possible. If not possible, change lamps and reflector
skins if fitted. |
|
(c)
Ink is conventional solvent-based ink, not UV. |
Wash-up
rollers carefully using appropriate solvents and change to UV curing inks. |
|
(d)
Film weight of ink is too heavy, beyond the capability of the lamps. |
Run
less ink if possible or use interstation curing if fitted. |
|
(e)
Press speed too high for lamps. |
Use
more lamps, or increase the power of lamps if applicable. Slow the press
speed. |
|
(f)
Roller contamination, poor wash-up. |
Re-wash
the rollers; flush oily solvent and dry properly so that no residue remains. |
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