Archive for the ‘Printing’ Category

Printing on Hot Corrugated

March 3, 2015

Jason asks,

Could you explain why it’s not recommended to print on hot corrugate fresh from the corrugator?
I know this isn’t common practice, but there are times when it is necessary when a rush order comes in.

Once corrugated sheets come off the corrugator they should be allowed a bit of time to cure. This will allow the sheet time to stabilize and adjust to the relative humidity of the environment, etc. Slight size changes can take place during this time. If you go straight from the corrugator to the converting process, it is possible that you could end up with a finished product that doesn’t meet the customer’s specification.

Basically ink dries by absorption and evaporation. The chemical characteristics of the ink, mainly pH levels, and temperature, greatly influence drying as well. When you induce significant temperature change to the equation, such as hot board, you change the entire drying process. This will most likely result in ink drying before it has time to absorb into the fibres of the sheet, or it may cause the ink to dry on the plate. Both situations can result in poor coverage/print quality and excessive build up on the plates.

Hot sheets can also cause “baking” of the printing plates which will significantly reduce the plates’ ability to properly transfer ink as well as the overall life of the printing plates.

A hot sheet could also possibly experience more crush as it goes through the converting process than a cured sheet would, and therefore result in a degradation of product quality. A sheet that isn’t properly cured may also be more likely to create rolled scores.

Converting equipment can also be affected by hot sheets. The functional characteristics of urethane components such as feed belts or wheels, transfer belts, pull collars, and in some cases even cutting die rubber can be decreased by hot sheets. The coefficient of friction of feed belts and wheels can be reduced causing registration and skew issues. Die cutting rubber can be overheated causing reduced ejection rates and rubber life.

There are probably other issues that we’ve overlooked here, but I hope this gives you some idea of why running hot corrugated is not a good practice.

— Ralph

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Does Flexo Printing Affect Gamma Ray Sterilization

February 10, 2014

Steve asks:

Well, I’ve got an interesting one for you.
We have a major customer who is a global leader in medical device manufacturing. We have a 55” long x 4 x 1 catheter package we do for them. 100% flexo printed. Their question is… “Do we have any documentation, or data on whether flexo print on corrugated affects the characteristics and performance of Gamma Ray sterilization?” We are quite comfortable with data we have on ETO (ethylene oxide) but Gamma is sketchy territory.

Would you or perhaps Clemson have any input for us? The engineers are looking to provide a rationale in their proposal for FDA etc.

I can honestly say that is a question I’ve never been asked before! For insight to this question I reached out to our friends at BCM Inks for some input. Ted Vernardakis, Ph.D., R&D Director/QA Manager for BCM Inks offers this explanation.

“Gamma rays are the most energetic, most powerful and most penetrating radiation of the electromagnetic spectrum. They are more powerful and penetrating than X-rays. They travel through just about everything except lead. Therefore they pass through corrugated board and flexo printing unobstructed, like a hot knife cutting through butter. Corrugated board and/or flexo ink has no effect on Gamma Ray sterilization, whatsoever.”

Hope this helps.

—Ralph

Disposing of Ink Buckets and Cutting Dies

March 7, 2013

Chase asks:

Our plant uses a lot of ink and are constantly obsoleting cutting dies. Both of these process leave us with a waste stream that I cannot find a buyer for. The ink is in standard 5 gallon buckets and we have switched to all plastic handles to make it easier to recycle and take a step of removing metal handles form the process so the whole bucket can be recycled, but i cannot find anyone who wants to fool with the recycling of these buckets even thought the ink residue is water soluble and non-toxic.

We wash these out, but are not in the business of cleaning ink buckets we are a corrugated converter, so there is still some ink that is not washed off. On the other hand is our cutting die situation. Do you know of a good way to recycle or otherwise use these dies without just tossing them out? It is costing us quite a bit of money for extra dumpsters to handle the buckets and dies.

In the January/February 2013 issue of Paperboard Packaging Magazine’s Products & Services section (page 22) there was mention of a Die Recycling Program developed by Triangle Dies & Supplies. They may also have an option for your ink buckets.

You may want to contact them. http://www.tridies.com
-Ralph

Print Striping/Banding Issues

January 17, 2013

Victor asks:

We have been experiencing print variations when we print full coverage. The best way to describe this is that it looks like bands of light then dark print that run horizontally, across the entire width of the press. Similar to when an anilox is hitting the plate too hard, but is not. Sometimes it’s not as obvious at the beginning of the run, but becomes more noticeable after 200 to 300 sheets. Other times it’s obvious from the start. Have you heard of this happening and/or do you have any suggestions?

I reached out to Jack Fulton at Printron and through his sources he offers this info.

There are a number of variables that can create banding or striping when printing.

If the plate is larger than the sheet you will not transfer all of the ink from the plate to the sheet. So the remaining ink will cause uneven printing on subsequent sheets.

Banding or bumping can be caused by several things in combination with each other. If pH or viscosity is out of control it can make the problem worse. If using plastic doctor blades and 60 degree cell anilox rolls you can get a phenomenon like stripping a screw. If you put a screw into a piece of wood and turn it too tight you can strip it. It feels tight then all at once slips. The same thing happens here, the blade is tight against the roll, then slips and re-seats which causes the uneven inking or banding. Ink with more lubrication works best in this situation.

Some converters have reported experiencing banding on diecutters when the doctor blade angle was set at 60 degrees. When changing to a new doctor blade system with the blade angle at 32 degrees the problem went away. If you measure the opening between the two blades in chamber and it’s the same as the distance between the bands you are printing, then this may be the issue.

Also if your chamber moves laterally, or oscillates, stopping the chamber from moving laterally may help this issue.

You may also want to make sure the anilox roll pressure, not the impression but the pressure engaging the roll, is correct. If this is too low it can cause bouncing even with very light impression. You may want to contact your OEM for the correct specs and test procedures.