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Welcome to  ‘Ask The Expert’.  This page is moderated by industry consultant, Steve Wilkinson.  This page features the answers to your questions. Our visitors can also post comments to these questions/answers as well.  You can learn more about Steve’s background and our ‘Ask The Expert’ page by Clicking Here.

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January 2, 2013

What are the benefits of LED technology; can they cure my existing UV inks?

LEDs (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.

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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.

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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 make ready.

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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.

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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 acustomer is more accustomed to offset printing where little or no trapping is often the norm.

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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.

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