UV Coating Problem

[kdw75]

We bought a UV coating machine from China. It was new, the price was right, and we plan to do very low volumes on it. Of course the support is almost non-existent, and we are having a major problem with it. The sheets that come out aren't fully cured, you can leave fingerprints in it. The lamp looks good, and if you hold the sheet under the lamp for 30-40 seconds, it will eventually cure.

The only thing, other than a defective lamp, that we have come up with, is the fact that we have 208-210 voltage, and the machine is designed for 220.

Any thoughts, suggestions or help would be appreciated.

 

[Cornishpastythighs]

Check that your coating cures at the same wavelength as your UV lamp output. You coating supplier should be able to help you determine this.
It may be you have a sub standard Mercury lamp in your machine, does it only have one lamp? Get a new UV lamp.
If you can hold the sheet under a UV lamp for 40 seconds without causing a fire something is certainly wrong, that sheet should burst into flames.
Make sure you are using the correct voltage and amps for the machine.
Try another coating from a different manufacturer.
Does the cure get better if you slow the machine down.
Get yourself some of these to check lamp output, rather crude method but they do work.
http://www.uvprocess.com/product.asp?code=INTS+LBL+B

Good luck

 

[dgerharter]

This brings up an interesting problem that I am going through right now. How do you know when your UV inks and coating are cured "enough" (and what does that really mean)? I am working with my ink and coating supplier to develop some kind of objective, repeatable test (used at press) to let us know when we have achieved the correct amount of cure, without over curing.

What tests do you use? How repeatable, accurate and helpful are they? Do they do a good job of predicting cure levels, or are they just a "looks good to me"? I've heard of the thumb twist, tape pull, scratch test, and MEK rub test (among others), but all of these are manual tests that are affected to some degree by the person performing the test (or other factors). We've purchased the Ink Rub Tester machine from IST and have begun testing and correlating the results of that, but we get different results based on the amount and color of ink under the coating - not to mention it's almost impossible to get MEK in California.

Any insight from the community would be appreciated.

 

[danprtr]

This brings up an interesting problem that I am going through right now. How do you know when your UV inks and coating are cured "enough" (and what does that really mean)? I am working with my ink and coating supplier to develop some kind of objective, repeatable test (used at press) to let us know when we have achieved the correct amount of cure, without over curing.

What tests do you use? How repeatable, accurate and helpful are they? Do they do a good job of predicting cure levels, or are they just a "looks good to me"? I've heard of the thumb twist, tape pull, scratch test, and MEK rub test (among others), but all of these are manual tests that are affected to some degree by the person performing the test (or other factors). We've purchased the Ink Rub Tester machine from IST and have begun testing and correlating the results of that, but we get different results based on the amount and color of ink under the coating - not to mention it's almost impossible to get MEK in California.

Any insight from the community would be appreciated.

Ink / coating manufacturer has the answer to what UV spectrum and qty of light is needed. You can compare those specs. with your machine output using a UV radiometer. One brand is "Power Puck" which you can google. You're asking very good questions as there is such a thing is too much cure as well. UV ink failures are very costly and frustrating if you just use the tests you mentioned.

Good Luck!

 

[MaMaDx]

..

Just few words to what Cornishpastythighs have said - the lamp might be greatly out of focus. In other words it can be mounted too high above the conveyour. UV-systems that I know install UV-lamp in 10 cm distance above the conveyor. Sometimes it's very usefull to have variable distance - when You need to defocus the lamp (on plastic for example).
30-40 seconds is too much for curing - I'll say You need 1 second for the sheet to pass through curing window to be cured well. If the sheet is stucked for 5 seconds - it will burn rapidly (ventilation causes great oxygene supply).

..

All those tests that You're performing relate only to hardness of coating and it's adhesion (or scratch resistance) to the substrate. But they don't answer the main question - is there enough energy supplied to 100% cure the ink? danprtr gave You the clue how to calculate the quantity of energy (Joulies) that sheet receives when it goes through curing window. I'll add one thing - the company is called EIT. But it's also very important what is the peak power level of UV-curing system (Watts). You can have 2 different UV systems that irradiate the sheet with the same energy quantity but one of them can cure better because it has higher peak level that helps UV-proccess to run smoothly (bond all the radicals). BTW this peak level very depends on the lamp reflector installed in Your machine. Reflector actually gathers all the energy emmited by the lamp into one point (or interval if You need). If You don't have reflector or it's incorrectly installed You'll get poor curing. It's like magnifying glass - when You're focusing sun beams into one point over the sheet of paper it will burn. That is equivalent to what I said about peak power level. Though the energy received by the sheet of paper is the same (Joulies) - You're just focusing it (Watt).
There is one test that can tell You curing degree - it's acetone test. You can google for it - it's very simple. I'm workking with UV coat and acetone test shows 13-17 seconds. It's the time needed for acetone to destroy the UV ink layer.
BTW we also have TMI ink rub tester. But we used it for testing UV varnishes. It's also kind of subjective test. It's hard to etimate results with human eye - we use the difference of glossmeter measurements before and after the test. But it's seems to be not so good.

 

[gpollard]

Im coating blank paper for digital and it gums up everything and pain to clean up

 

[akalaray]

Im coating blank paper for digital and it gums up everything and pain to clean up

What machine are you using?

 

[gpollard]

tec lighting uv coater