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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.

If you have a new question to ask, just CLICK HERE to post your question.  Questions and comments will be reviewed by our staff and posted as quickly as possible.  All questions should be non-commercial in nature

As always, thanks for visiting www.nvpublications.com.


 

January 22, 2015

Can you please explain why many people seem to prefer LED lighting over incandescent lighting with regard to their use in densitometers and spectrophotometers?

Probably the most compelling reason for choosing LEDs is their longevity in that they can last up to 10 times longer than incandescent lighting ; in many cases up to 50,000 hours or longer.

They are also very rugged and can withstand a significant amount of vibration and impact that is often found in most industrial applications. LEDs are also much cooler and do not as a result suffer from the thermal expansion of the glass cover as found with incandescent lights. LEDs are also much more efficient by converting electrical energy directly to photons and can be manufactured to cope with many different measuring conditions by mixing multiple LEDs together to provide a wide spectrum of coverage. Finally LEDs have much greater stability, turn on very quickly and provide a constant output over along time.

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November 20, 2014

Is there an alternative material to steel or aluminum construction chamber systems and if so what are its benefits?

One of the most exciting innovations in flexo today is the carbon fiber chamber blade system. Carbon fiber is extremely strong and much stiffer than aluminum by as much as 300%. Not being steel or aluminum, carbon fiber will not corrode and is resistant to all types of inks, solvents and adhesives.

They are generally easier to clean up and require much less water to rinse clean than conventional materials. Newer designs with carbon fiber systems usually mean the chamber does not need removing to replace the doctor and retaining blade. They can be up to 70% lighter than aluminum and even greater when compared with steel. This makes them much easier to handle and can often be lifted in and out of a machine if needed by one operator.

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October 20, 2014

We use a variety of Dyne pens to measure the Dyne level of our films. What are the pros and cons of using this method of measurement?

Most companies use dyne pens as a method to evaluate the treatment ( dyne ) levels of their materials because they are relatively cheap and easy for most operators to use. This does mean that the results can be very subjective dependent on the interpretation of each peron’s observations and can vary dependent on the application rate and pressure that is applied.

Great care must be taken not to contaminate the substrate to be tested or the pen itself with such elements as dust, wax finger prints, water and plasticizers. Water is a particular problem as every surface will have absorbed some water and like all of the other contaminents mentioned will cause incorrect readings.

All pens have a mix of two liquids to give the different dyne levels so once opened the liquids will begin to evaporate and as one usually evaporates faster
than another if the top is not kept on the pen when not in use it will quickly become inaccurate. On plastic film static electricity can also be a problem as this will also
affect the wettability of the dyne fluid and as a result can result in inaccurate results.

Surface roughness of a material can and will affect the de-wetting of the pen fluids.

The truth is all dyne levels are approximations so at least three test lines should be drawn down on the material with the first two usually being ignored to ensure that any contaminants have been flushed from the prior use of the pen.

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September 25, 2014

What matters more — the material that a doctor blade is made from or its thickness?

There is no doubt that choosing the correct blade material to suit your specific print application is very critical. Choose a material that is too soft and you will have to replace it almost every shift, too hard and it may damage your anilox. And if the material is not resistant to the ink or coatings that you are using then it may be chemically attacked and simply corrode.

All that said, if your blade is not rigid enough it will fold over the first time your operator applies too much pressure between the blade and the anilox. Blades that are too thin will also have a tendency to develop a wave in them even with careful installation so will be unable to wipe your anilox evenly across the full face of your roll. This is particularly prevelant in wider web machines. Even when the recommended blade thickness is used many need a back-up material to give it further rigidity and support. If a blade bends to the point that you are no longer wiping with its edge but the back of the blade then you have really lost all control of your wiping action and will potentially cause serious damage to your anilox.

So to some extent blade thickness may initially have it over the material but if you want consistent wiping of your anilox throughout your entire print run you had better make sure you have the right material as well.

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August 18, 2014

What is the best method to analyze our anilox cells to determine their condition and current volume capacity?

A quick visual inspection can give you a very good idea of the general condition of any anilox. Look for score lines, dings, chipping around the edge of the roll and of course general contamination.

Any roll with a significant number of score lines, mechanical impact damage or chipping around its edge is likely to need relacement sooner rather than later. In regard to cell condition and current volume capacity this cannot be done with the naked eye and requires some form of magnification in the form of a roll scope or interferometry device.

The roll scope is the most common but is dependent very much on the operator skill and can be very subjective. That said, in the hands of an experienced operator it can be reasonably consistent provided the scope is well maintained and calibrated on a  regular basis. It does allow for pictures to be taken of the cells but requires a manual calculation by the operator to determine the cell count and to calculate a theoretical volume.

There are also a number of liquid volume test methods to help determine volume but they again require considerable operator expertise and can have quite a wide range of accuracy. Interferometry is probably the most accurate but again requires significant operator training, regular calibration and is a significant investment but is capable of providing very accurate data and pictures in 3D showing the exact cell structuure, line count and volume. It is up to each printer to determine how much information they require, which will determine the level of investment necessary.

You can of course ask your roll supplier to carry out a regular inspection of your anilox and provide you with the same information but there is always likely to be some bias in regard to the information given so you should always review the data provided and apply some common sense yourself, particularly when it comes time to replacing your rolls.

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May 20, 2014

Digital printing appears to be making some inroads into short print runs. Is there any way we can combat this with Flexo?

One of the most interesting developments in Flexo is the use of process colors to create spot colors. While not a new concept, it has really only been the relatively recent introduction of new software packages that can convert spot colors into process files that allow for brand spot colors to be reproduced as a process set instead of the conventional
special spot colors.

Of particular interest is that of creating seven instead of four process colors that gives the printer the ability to reproduce a vast number of pantone colors, which reduces the number of colors needed, the number of plates required, the amount of ink required, and the amount of time required to set up and run. All of this makes for a more affordable, quicker way of producing even very short runs, making flexo just as competitive if not more competitive than digitally printed short runs.

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April 22, 2014

How do we reduce vibration and bounce when printing multiple images across our wide web press?

This can be a challenge for most printers if you are using a pin registration system or are producing plates with a straight cut across the width of your plate. The solution, while simple, can be a challenge for printers using the above methods of mounting their plates as it entails stepping the image either up and down or stepping the image progressively down as you step and repeat it across the width of your web. This will then require you to cut your plates in the same stepped manner and can make mounting quite a challenge and eliminates the option of using a conventional pinned system.

The reason for the stepping of the image is to minimize the possibility of a continous gap occuring on any or all of the colors across the web. This means that some part of the image should be in contact with the web, which in turn will be pressed against the impression roll. This in turn will reduce the bounce and hence vibration that can often be seen and even heard at press side when the printed edge finishes in a straight line.

One method of overcoming these mounting challenges is to have the design engraved as a continous engraving, i.e. ITR, which can be produced in elastomer by direct laser ablation or as thermally ablated or chemically washed continous polymer sleeves.

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March 20, 2014

Our plate supplier has expressed that he is concerned about the amount of ozone in our plant but did not explain why. Can you tell me what this has to do with the plates that he supplies us?

Ozone is generated by electrical motors and corona treater equipment and is a form of oxygen. The reason your plate supplier is concerned is that ozone will attack all forms of plates and will eventually cause cracking in the plate surface, which will obviously make them unusable. For this reason you should store plates well away from areas that ozone may be generated as well as away from any direct UV such as sunlight, which will have a similar effect.

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February 27, 2014

Our anilox supplier has offered to audit our anilox. What information should we expect from this?

The first thing to remember about any anilox audit is that it’s a “snapshot” in time, in that the moment it is done it is already out of date assuming that you continue to use your anilox.

Fundamental information that you would expect from any audit would be anilox engraving, volume, and any obvious damage such as scoring, mechanical impact damage, chipping, general cell condition, and overall cleanliness. You will be surprised how many rolls are sent out for refurbishment when they are simply plugged with ink or coatings so if you are advised to replace an anilox that does not have any obvious damage,scoring or chipping please make sure it has been mechanically cleaned and its volume rechecked before making the final decision to have it reworked.

Remember about the “snapshot” in time comment so you need to act on the audit information immediately. Failure to do so really minimizes the benefit of the audit.

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February 10, 2014

We have recently purchased a new press that uses anilox and plate sleeves, what do we need to do to keep them in good condition?

The first thing to do is to make sure that every manager, supervisor and operator understands how much they cost to purchase and the cost of replacement. In my experience most personnel at all levels view sleeves as a disposable items, which ultimately they may be, but if properly cared for can give many years of
service.

You mentioned both types of sleeves, that being anilox and plate sleeve. Both, however, cannot function without the appropriate air mandrel that you will apply compressed air into via an air inlet nipple either through the header of the mandrel or through the journal. The air escapes through a series of small holes that are drilled around the circumference of the mandrel usually at the end nearest the inlet and also in the center of the mandrel face. This will create an air layer that allows the sleeves to be slid onto the mandrel core before being locked in place when the air is stopped and the sleeve contracts back to its original diameter.

So just as you have recognized the importance keeping the sleeves in good condition it is just as important, if not more, to protect your air mandrel from any form of surface scratches, dings, or contamination. Failure to protect the surface of the mandrel will result in sleeves sticking to the core resulting in the operators inability to push them along the full face of the mandrel or indeed to be able to easily remove them.

Never use greater air pressure than recommended by the supplier as this can distort thinner walled sleeves and can result in catastrophic failure of the air mandrel. Always ensure the compressed air is dry and oil free as any contamination can cause rusting of the inside of the mandrel, which can leak onto the surface of the mandrel and the inside of the sleeve.This can make removal of the sleeve very difficult if not impossible if moisture or staining does build up on the end of the mandrel.

Each sleeve type has its own unique features and weaknesses but both are prone to premature failure due to mis-handling and lack of good housekeeping. In the case of the anilox sleeve they are generally the more complex structure with an inner composite tube, flexible inner core and an outer aluminum shell. It is the outer shell that is ceramic coated and laser engraved. The key to remember is that while ceramic is very abrasive resistant, they are very susceptable to impact damage. For this reason great care must be taken not to bump the sleeve into anything or to drop any heavy or sharp objects onto it as the ceramic will invariably crack and come away from the sleeve’s outer core.

You must store the anilox sleeve carefully at all times and take great care never to allow them to be dropped on the ends or knocked over, which will result in distortion of the sleeve and make it impossible to be slid onto its mandrel. The inside must be kept clean at all times and again great care must be taken to prevent scratching, scoring or any cuts to the inside of the sleeve. This applies to plate sleeves equally as much. You can store both types of sleeves vertically or horizontally but they must not be allowed to rest against another sleeve or rack support and when stored horizontally plastic tubing should be used if you choose to support them through the middle. If you prefer to store them in boxes, you shoud use cones placed in both ends if you choose to so that they again do not rest on the face of the sleeve.

In the case of plate sleeves, try to minimze the amount of cutting of the backing tape to help reduce cutting of the sleeve outer face, which can case them to split if cut too deeply or at least present a very rough surface to mount future plates onto.
While plate sleeves are a much simpler construction than an anilox sleeve they should always be treated with great care and kept as clean as possible at all times

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