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April 19, 2013
We have recently installed a Flexo press but my prepress department is telling me I cannot use our existing gravure separations to make Flexo plates from. Why not?
This is a common dilemma for many companies and designers
alike wanting to move into the flexographic field. There is no doubt that Flexo has come a long
way and is capable of producing some very high quality print but it does have
certain limitations that have to be taken into account at the design and color
Unlike gravure Flexo does have some dot gain that can create
problems in creating soft gradients, vignettes and it does have a limit to the
size of dot it can hold. This means that an allowance has to be built into the
screening of artwork separations for a Flexo plate to be able to hold it up and
to allow for the dot gain that is inevitable even with the best press and
Registration is another challenge, and inevitably means more trapping
is needed than for the same gravure printed image. All this said, Flexo’s
ability to print on any substrate, its speed of interchangeability of plates
and variety of ink systems, all at an acceptable price even with short runs, is
what I am sure led you to add Flexo to your
April 3, 2013
How essential is daily/weekly cleaning of a press and how much does it really affect our bottom line?
It is this sort of question that probably answers why I see so many presses
in such a run down and poorly functional condition. If you are running your
equipment continuously, as most companies do, the gradual build-up of ink, paper
dust, grease and other contaminates will eventually overwhelm most key
components on your press such as gears, bearings, drive shafts, belts, and pulleys. The problem is this can take a while and causes the operator to have to
make daily adjusts to the operation of your machine. This will lead to slower speeds,
more make ready, reduced print quality and higher waste, all of which will affect
your bottom line.
It is vital to make time each day and every week for proper
maintenance and cleaning of your equipment and its key components. It is the
responsibility of management to understand that good housekeeping practice is
essential to maintaining a consistly profitable business and is not something
that can be overlooked or ignored. Sooner or later it will, as they say, “stop
the press” and instead of a few minutes or hours to make a repair it could take
several hours or even days if the fatigue and wear is serious enough. So, how
much does it affect your bottom line? In every way and then some!
March 24, 2013
What is the most effective way to improve our bottom line that doesn't entail a huge capital investment?
| In my opinion if you were to improve your general housekeeping of your press room but in particular your anilox, you would be able to :
Reduce Down time
Reduce Set up time
Reduce set up material
Reduce ink costs
Reduce roll replacement costs
Improve print quality
All of which will lead to an improved bottom line, but it takes a real commitment and the use of the right cleaning solution and equipment to achieve more consistent ink transfer from the anilox to the plate to the substrate. Whenever I do plant evaluations I invariably find that housekeeping is a low priority and is not taken seriously by many management teams. They claim that it is important but there seems to be little or no real accountability other than to blame the press operator. So please do take a look at your cleaning procedures and if you are not sure what to use, ask your vendors as they will be pleased to help.
March 11, 2013
We are plagued with scoring on our anilox, what are we doing wrong?
After plugging of the anilox cell, scoring of the anilox surface has to be the most common issue that all printers have with their anilox rolls. Unlike plugged cells however, which can be cleaned and in so doing regain their volume, a score line in the surface of an anilox cannot be removed and in effect requires the roll to be reworked.
With this said, it is therefore paramount that everything possible must be done to reduce the possibility of scoring the engraved surface of your anilox. Notice I said "reduce the possibility", this is because a great deal of scoring comes from contamination within your ink or coating. Even if you have filters and rare earth magnets in your ink lines, it is difficult if not impossible to remove all metal, pigment/resin clumping and paper dust particles all of which can and do get trapped between the anilox and doctor blade. This will drag the particle around the surface of the roll, which can and will cause score lines of varying degrees. The irony is that you do not have to dig a groove into the surface coating to have it show up on your print, just dragging a hard particle across the surface of the anilox will change its surface characteristic, which in turn will be reflected in a different color density in the form of a light or dark line.
Doctor blade pressure and angle are also very critical. Too much pressure and too acute an angle will cause the blade to begin to wipe from the back of the blade, which increases its surface area, compounding the issue of potential scoring of contamination digging into the roll surface. You need to make sure that the blade is parallel to the anilox surface at set up, that there is no dried ink on its edge, and that the roll is inked up adequately before the blade is presented to the roll.
Too much pressure on the doctor blade, particularly plastic blades, can lead to the blade softening, which can trap hardened particles in it that, in turn, can and will lead to scoring of the roll surface. I strongly recommend that on receipt of your newly engraved anilox that you wash it thoroughly to help remove any remaining ceramic particles, and that if you chip the edge of the roll you fill it immediately to help reduce further ceramic particles getting into the ink and again getting dragged around the surface of the roll.
Remember ceramic is inert, cannot be pulled out with magnets and is very difficult to filter out, and other than diamond can cause dramatic damage to the engraved surface of your roll. So, as you can see, there are a lot of potential causes of scoring and while difficult to eliminate can be significantly reduced with a better understanding of its root causes.
February 26, 2013
Is XG really the answer to Flexo finally being recognized as an equal to offset and gravure printing?
far, flexo has tried simply adding more colors to extend its spot color range
and for a while has had some success with 7-color printing. This has now been
extended into 4-color process printing by running higher density CMYK and has
shown some remarkable results for the few that have tried it.
ink transfer from many photopolymer plates has proved such an issue that
texturization of solid plate surfaces has been used to help it achieve greater
densities. Special software programs and new plate
materials are helping the process significantly and can be very productive on
press with fewer color changes, wash-ups and reduced ink costs. That said, it does
not appear so far to replace all spot colors but is producing gamut ranges that
are challenging offset and gravure. Will it ever be seen as an equal? It
really depends on the buyer and ultimately the consumer's expectations.
January 2, 2013
What are the benefits of LED technology; can they cure my existing UV inks?
(light-emitting diodes) emit light when subjected to an electric current. The
light that is generated consumes very
little energy, and the diodes have an extremely long working
life. One major benefit is they do not generate any ozone, unlike conventional UV lamps
with mercury tubes. A typical LED-UV lamp system consists of numerous LED
panels across a given press width and have multiple rows. The substrate can be
very close to the LED panels since very
little direct heat is generated.
Conventional UV lamps requires
a warm-up phase before they can operate; LED-UV lamps has no waiting time and
are ready to use immediately when they are switched on. LED-UV lamps only produce a small
range of the conventional spectrum of UV lamps and have no high-energy IR radiation or hazardous UV-B and UV-C radiation. LED UV cannot cure conventional UV inks due to the narrow
wave length window of the LED-UV lamp, which peaks at 395 nm. It should be
noted that being a new technology you will find the LED lamps and inks more
expensive than your conventional UV technology. That said, the lower energy consumption
(claimed at up to 80%), reduced need for sophisticated air exhaustion systems and
their perceived safer operation for the operator and others around the printing press makes it a technology
very well worth while considering.
December 3, 2012
How many types of print cylinders are there, and which is the most accurate?
Probably the best know print cylinder is the integral shafted cylinder.
While the most rigid and most accurate over the years has the journal shaft, running completely through the tubular core, it is also much heavier as a result when compared to the stub shafted design. The stub shafted integral roll journals are heat shrunk and often welded for added strength but are more susceptble to deflection, which in turn can lead to a lot more plate bounce. Its major benefit however is that the roll is much lighter and cheaper to build, which makes it more popular.
The next type of plate cylinder is a tubular core with a shaft that it can be mounted on and off. Original designs used tapered cones and lock nuts but have been largely replaced with more modern expandable shafts that use hydraulic or pneumatic expansion of the shaft to lock it to the inner bore of the core.
Finally there is probably the most popular which is the air cylinder. In most cases it looks just like a normal plate cylinder but has a hole drilled usually in the header on one side of the cylinder and 3-4 smaller holes drilled through the outer shell of the core with perhaps one other in the center. Plates are mounted on a sleeve consisting of polyester, fiberglass, carbon fiber or a combination of these materials and is slid onto the outside of the cylinder after air has been pumped into the cylinder from the header air valve. The air escaping from the smaller surface holes on the cylinder creates a cushion of air that the sleeve can slide over and locks into place once the air supply is stopped. Due to the action of sliding the sleeves on and off the cylinder, and the likelihood that dirty, moist air very often is put through unfiltered air lines, these cylinders are prone to scratching and corrosion and as a result will usually need refurishment and even replacement after several years of regular use.
The tubular demountable cylinders can be very accurate but great care needs to be taken to ensure that the shafts are not bent or scratched during installation and removal. Of the two shafted integral designs, the straight through shafted is the most durable and accurate but this often gets overlooked in today's rush to reduce weight and cost but if you are willing to make the initial investment as well as the right lifting equipment, they will last you a lifetime if properly maintained and looked after.
November 5, 2012
Could you give any further explanation of what type of ink measuring cups are best to use in the flexo process?
| It seems that viscocity measurement is once again a popular subject, as it should be considering the impact it can have on print quality and ink consumption. There are a number of measuring cups used today dependent on the application, although they are all known as efflux cups. All are metal cups that contain a given amount of ink or other solution and each has a hole at the bottom. The ink or coating is measured in seconds in regard to how long it will take to drain through the hole, which in turn gives a viscosity reading. Two types of cups are most popular in the flexo industry: the Zahn and the Shell cup. Both have a hole at the bottom but the shell cup has a 1-inch tube attached to the drain hole. Maintaining the size of the cup and holes are critical to achieving accurate measurements so keeping them clean is fundemental to this. Both cups are made in a variety of sizes but generally you should use one that measures between 20-40 seconds. The most common types used is the No. 2 Zahn and the No. 3 Shell cup although as mentioned in a previous answer the DIN No. 4 cup is also gaining in popularity with some printers.
October 24, 2012
What is (ITR) technology, and how can it benefit my company?
“ITR”, otherwise known as “In the round” is the generic term
that has been used for a long time to describe any image that has been produced
around the circumference of a plate cylinder or sleeve in either a photopolymer
or elastomer covering. The technology has been used primarily in Europe for more than thirty years with elastomer coatings being vulcanized, ground and directly
laser engraved onto sleeves and integral rolls. While plate material has and
still can be exposed in the round and is classified by some as “ITR” , I
personally only classify it as true “ITR” if the material has been bonded or
vulcanized to the sleeve or roll circumference and engraved or washed out while in a continuous format. As to the benefits of true “ITR”
there are many ranging from dramatically increased press speeds, improved print quality, improved
registration, more uniform densities, less dot gain, less bounce, reduced
waste, improved productivity, improved profitability, less set up time and less
October 11, 2012
We hear so much about best practice being necessary for good quality print but how do we define what is best practice?
This is a
very big subject but for me best practice is about eliminating as many
variables as possible on and around the press. You need to look at each aspect
of the print process and determine what you believe to be the most effective in
helping you to achieve consistent results.
This usually starts by measuring and
recording what is being done to help to determine if it is repeatable and if
the results are acceptable. Generally the use of measuring devices such as
spectrophotometers, densitometers, video web inspection, interferometers,
viscometers are necessary to help capture the necessary data in an accurate
form that can then be repeated and measured accurately each time a job is run.
Always try to get your suppliers involved at the earliest stage possible as
they will then be able to assist you in achieving what is best practice for you
and your company and more to the point, how to define it.
September 24, 2012
We seem to always be damaging our anilox. What can we do to reduce this and is there any way of repairing the edges of the anilox without a full replacement?
Considering how long anilox
have been around, you would think that this topic would be long since over but
unfortunately it continues to be the bane of every print shop. I will also
assume that you are referring to laser-engraved ceramic anilox. Damage to
anilox falls into three main categories: Impact, scoring & chipping.
damage is usually caused by the roll surface coming into a hard usually sharp
surface or having a nut, bolt or other foreign object run through the print
Scoring is a little more complex and although it can also be caused by
contamination in the ink such as metal particles and other larger hard objects
it more often comes from running blades dry, running blades out of alignment,
applying too much pressure, running at the wrong angle or simply choosing the
wrong material, thickness or just not changing it soon enough.
generally occurs on the edge of the anilox, which is the most fragile area of
any ceramic anilox. It is critical if a anilox is chipped that it be filled
immediately with an epoxy filler or two part filler such as JB weld as quickly
after the damage has occurred. Although it will never be a permanent fix, it
will slow the rate of break down, and help reduce further damage to the blade and
leakage from the edge of the roll. If you do not repair the chip immediately it
will migrate around the circumference of the entire edge of the roll, making
replacement the only option. One thing many printers do not take into account
is where the ceramic particles go when they chip off the roll, which is
into the ink and how much these ceramic particles actually contribute to
scoring of the roll face so it can have to major visible effects on the anilox
and not just on the edge of the roll. In my experience, if the repair is carried
out speedily and with some care, the repair can hold up for several months or
longer if it is monitored and perhaps even repaired again.
August 27, 2012
Why is trapping so important in Flexography, and how do we determine what will work best for us?
Trapping generally refers to overlapping
colors that are adjacent to one another and occurs with all designs. Even with
the best presses, there tends to be some movement from color to color when
trying to register them without leaving a white gap between them. While newer
presses may claim to be able to register color to color with very little trap
being applied, it is just good sense to make some allowance to help make the
printers job easier and the customers' satisfaction greater. Having said this, if
you apply too much trap between medium hue colors they can create a darker line
where they meet. The trick to what works best for you and your equipment is to
carry out regular finger printing to help determine the sort of registration
that can be held and is particularly important on older equipment as bearings
and gears begin to wear.
Having an experienced prepress operator that has
plenty of separation experience can make the art of trapping look easy, but
even with newer software that can be used to apply trapping between colors
automatically there is a great skill to being able to help make any job either
easy to print, or a nightmare if care is not taken when applying trapping.
Always try to explain to your prepress house/customer what you need to
produce a good print for them and do not be afraid to adjust your files to what
you need and not what someone else thinks you need. This can be particularly
difficult when a customer is more
accustomed to offset printing where little or no trapping is often the norm.
August 6, 2012
What images can we print using a variable data inkjet printer, and can we print on any substrate?
It should first be understood
that all VDP (Variable Data Printers) are not all capable of producing the same
images at the same speed. That said, most systems are capable of producing
sequential numbering, 1 and 2 D bar codes, random numbering, harvest marks and
graphics. Speed and resolution of print can and does vary a lot from machine to
machine. Again, although most substrates can be printed on including absorbent
and non-absorbent materials, not all VDP systems offer the variety of inks to
be able to do this. Most systems only print in one color — that being black — but
more advanced systems can print in other colors and other specialty inks.
July 12, 2012
Why is it necessary to corona treat different substrates, and when is best to treat a material?
It is necessary to treat any material when you want to
improve the adhesion of inks, coatings or adhesives. Most commonly plastic
films are treated but it is also necessary to treat foils, paper and synthetic
materials. Treating generally works best for films when they are being extruded
or in-line just prior to printing. Treating basically increases the surface
energy of a material and in so doing improves its wettability, which is what
helps the adhesion of your inks and coatings to it. It is worth noting that all
treatments diminish over time so you should run as soon as a material has
been treated or at least be able to retreat it in line just
prior to printing.
July 2, 2012
How do we decide what type of mounting tape to use with our plates to help minimize dot gain at the higher speeds we are now able to achieve?
new press designs, higher press speeds are indeed setting a new challenge for
printers and mounting tape manufacturers alike. Conventional hard vinyl cheaper
tapes may have been suitable for some at lower speeds but higher press speeds
present a new set of dynamic issues that demand consistent compression and
rebound capability of the tape to last through the entire run.
Foam sticky back
materials seem to struggle at higher speeds and new elastomer cushion and
higher temp resistant adhesives appear to be able to cope better. There are
obviously a wide variety of tapes each with their own features and with the
many other variables on press it really means some due diligence on you and
your supplier’s part to try out a variety of tapes to help determine what works
best for you with each plate material that you may be using.
even plate cylinders all have a profound impact on the eventual dot gain you
will see, not forgetting the operators skill at setting the optimum pressure
between the plate to substrate, anilox to plate, blade to anilox and even
doctor roll to anilox. This evaluation all takes time, patience and
perseverance as it is rare that you will be able to get the right combination
from the outset. There is no doubt that the more experience your supplier has
the better your chance of finding what will work best for you. Do bear in mind that your prepress can have a profound impact on
also helping to minimize your doubt gain by making the necessary allowances at
the file separation and screening stage, not forgetting your anilox and ink
supplier, so you must involve all of your suppliers inside and out if you what
to achieve the best result and help you decide what is right for you.