Maxcess International -Fife, MAGPOWR, and Tidland present Converting Blog

« Home » Coating, Laminating, and Printing

Filed under: Coating, Laminating, and Printing --- Tim Walker @ 09:05 AM

Another recent Q and A:

In running a multi-color rotogravure press, if we have different diameters in our impression roller in different printing units, maybe having variation of maximum up to 3mm in the circumference, because some of the impression roller have been ground once after too much wear.
1) Does it effect the tension in the web?
2) Will it lead to registration problems?

Answer:

My expectation is that the impression roller diameter variations will cause some tension variations, but not necessarily cause registration problems. The answer to why I think this is somewhat complicated, but here's my thought process, in brief.

Multi-color presses typically run in draw control with either a mechanical or electronic drive shaft to synchronize the rotation of the variation printed patterns. In draw control, the tension is determined by the incoming tension (from the unwind) and the speed ratios of the other drive points. Impression roller circumference or diameter variations will directly create speed variations. A 3mm circumference variation on a 10" diameter roller (250mm) would have a speed variation of 0.4 percent, which is a large amount for most papers and films and would create a tension variations.

However, in rotogravure, the inking nip is not necessarily a no slip process. The ink-lubricated gravure cylinder is able to slip (on a microscale) relative to the web, but since it is driven with the lineshaft, all the printing pattern stay in synch without any major effect of small variations in tension goes up or down (talking here about tension offsets present in the steady state, not tension oscillations over time).

-tjw

Filed under: Coating, Laminating, and Printing --- Tim Walker @ 08:56 AM

This question came in to me recently regarding nip uniformity in printing nips. My answer applies to any nipped process.

In our operation for 8 color rotogravure presses, sometimes the pressure in the printing unit nip area varies on both sides of impression roller resulting in the wrinkles/misregistration. To eliminate the problem, we balance the impression roller by different mechanical methods and run the machine. However, we only discover the problem once the machine runs.

Is there anyway of checking the balance of nip pressure on both sides at each printing unit nip, maybe with the help of some mechanical guage putting between the cylinder and impression roller on each side and applying the pneumatic pressure?

My answer:

There are simple and complex ways to measure nipping roller uniformity. Almost all are static measurements, so they don’t indicate variations over time or differences through the roller rotations (unless you take multiple measurements).

The first option many people use is to measure nip footprint length (sometimes called width) in the machine direction. You can measure nip width by inserting Post-It ™ notes from either side of the closed nip, then open the nip to measure the gap between the opposing notes. Many people use knurled aluminum foil (called Sto-Foil) from Stowe-Woodward. There are other nip footprint measuring options, including carbon paper, Fuji Prescale film (sold as Pressurex by Sensor Products), and electronic thin film sensor options from Tekscan and Sensor Products.

Force can be measured indirectly with a frictional device (made of a brass-steel sandwich) and a force gauge or with the Tekscan or Sensor Product devices.

You could also consider installing a load cell in your nipping assembly to measure the force exerted by any external air cylinders (and assume roll weight is constant).

I recommend nip sensing products from both Tekscan (www.tekscan.com), and Sensor Products, Inc. (www.sensorprod.com/nip.php)

I would recommend first trying simple nip width measurement (like the Post-It or carbon paper methods) or the frictional brass-steel system.

-tjw

Filed under: Coating, Laminating, and Printing --- Tim Walker @ 08:00 AM

Contributed by Tim Walker-

Question:

I have a three layers product of thin paper/LDPE/thin paper (extrusion laminated product). Our customer complains of sagging or bagginess at the product edges. I expected that PE thickness variation could be the cause, but what about other factors such as: 1) alignment between guide roller and nip roller, 2) temperature variation of cooling roller, and 3) wound roll stiffness.

For any cause of web sagging or bagginess, you must find a cause that fits the shape or location of the bagginess. Whenever I have a suspected cause of a defect, I try an experiment to see if I can make the defect intentionally or make it worse. To test the theory of whether (1), (2), or (3) contribute to bagginess, try making these worse or shifting them from side to side and see if the bagginess follows. If yes, then you have proven these as real bagginess cause.

Answer:

From my experience I don’t expect that guide or nip roller alignment will create bagginess, but it is simple to try an experiment with misaligned rollers and find out. I also don’t suspect that cooling roller temperature variations are the bagginess source. The wound roll stiffness or hardness variations should be directly related to the crossweb thickness variations. I do expect that there will be a strong correlation between thicker lanes and where bagginess forms. Also, tighter rolls will have higher stresses and lead to more yielding (and bagginess), looser winding conditions should reduce bagginess.

Another factor to consider with paper products is moisture. If you dry out paper, wind it, then expose the roll edges to a humid environment, then edges may become baggy relative to the center of the web. Try wrapping you rolls with a moisture barrier during storage and shipping and see if the bagginess is reduced.

Filed under: Coating, Laminating, and Printing --- Tim Walker @ 09:42 AM

Melissa from Cambridge Label stumped me with a simple question:

What is the most accurate proofing method available today?

I'm not in the loop on this technology enough to know.
If anyone has an answer. Please reply here or send a note to Melissa at melissa@cambridgelabel.com.

tjw

Filed under: Coating, Laminating, and Printing --- Tim Walker @ 10:51 AM

ICSTS: International Coating Science and Technology Symposium.

I'm not a coating guy, more of a beam-head (MEs), but I know the who's who of advance coating wet-heads (ChemEs) go to this conference every two years.

The next one is this year, September 9-13 in Denver, CO.

Beside coating experts, these guys are great at acronym confusion. The symposium is the ICSTS. The organization that runs it is the ISCST (Int'l Soc. of CST). ISCST's ICSTS? Whew.

Filed under: Coating, Laminating, and Printing --- Tim Walker @ 12:13 PM

After my last post on EB curable inks, I decided to look in one more place, at the AIMCAL website (www.aimcal.org).

I went to AIMCAL's site. Clicked on SOURCEBOOK on the side menu, then on MATERIALS SUPPLIERS, then COATINGS, finally on RADIATION CURED.

Here's the direct link to bypass these clicks:
http://aimcal.org/sourcebook/results.asp?category=104

After a few clicks to follow the companies lists, it's clear that Cork Industries, Rohm and Haas, and Northwest Coatings may all be able to help with EB curable inks. (The other two listings may also, but it was going to take more time at their websites to confirm this.)

Hope this helps. tjw

Filed under: Coating, Laminating, and Printing --- Tim Walker @ 11:38 AM

A recent post asked:
'I am trying to find anyonw who works with EB curable inks.'

Last week, I attended the AIMCAL Fall Technical Conference in Myrtle Beach. One of the highlights of the conference was a panel discussion between an expert panel representing several types of drying and curing technology (including conventional convection drying, IR, EB, hot can, microwave, and UV).

The panel expert for EB was Rick Sanders of Energy Sciences Inc. Rick also presented a paper 'EB Coating Developments for Graphic Arts'. From his presentation, it's clear that ESI is a equipment supplier of EB curing systems, but I expect he'd be a good resource to find who makes the EB curable inks.

Also on the drying-curing panel was Juliet Midlik of Prime Systems (an equipment manufacturer of UV curing systems). Juliet presented a paper on managing UV curing byproduct heat with a chilled roller. Related to the EB curable ink question, during the panel discussion Juliet mentioned that the chemistry for UV and EB curable inks are quite similar, but that UV inks need a UV activation chemistry added to them. Based on this comments, I'd think she may also be able to steer you to UV or EB curable ink suppliers.

Neither of these contacts will get you the direct link you need, but hopefully, get you one step away (and a chance to talk about equipment options).

Contact info for Rick and Juliet... (continued)

Continue reading"Contacts for EB Curable Inks?"

Filed under: Coating, Laminating, and Printing --- Tim Walker @ 02:00 PM

What's the difference between registering a new patterned feature (print, die cut, laminate) to an upstream integrated pattern vs. registering to a pre-patterned web?

How about putting it another way? If you have a choice of developing a new Excel spreadsheet (or other computer program) or modifying a spreadsheet someone else has written, which is easier?

It is almost always harder to work on something that someone else has started. It was hundreds of years between the beginning of manufacturing processes to the creation of the assembly line. Having to modify someone else's work requires an initial step of figuring out where they left off. When you do a job yourself, you know what's been done (unless you put it on the shelf for too long, then it's like starting over).

Let's get back to registration.

Whenever possible, always integrate multiple printing, die cutting, and laminating steps in a single process. It may seem that creating a complex integrated process will lead to more waste (it often does), but in the case of registration, a great deal of startup and process variation waste is actually reduced by integration.

More...

Continue reading"Registration to Pre-Printed Webs"

Filed under: Coating, Laminating, and Printing --- Tim Walker @ 03:31 PM

Like the song says "I don't know much about chemistry", but what I do know is that these processes, coating, laminating, and printing are all an interesting interaction of chemistry and mechanics. It's the mechanical part I bring to the table.

I don't expect to post much in this section of convertingblog.com, but I thought the blogsite would be lacking without this subtopic. You can only make so much money unwinding, transporting, slitting, and winding (alot of money for some folks), but if you coat, laminate, or print, you can go further.

For all you wet-end converters, please drop in and give us your converting challenges, victories, and oddities.

Thanks tjw+