UV coating scratches

[Mstrkey]

I bought a PP&E-480 offline UV coating machine about two years ago. A very simple machine to run and I was pleased with it. I don't use it terribly often but lately I've noticed when I attempt to coat two sides of a project I'm getting a lot of scratches on the first side I coated(bottom). The funny thing is, the scratches can be rubbed away using a cloth or the sleeve of my shirt, if I push firmly. When I look inside the machine as I run a sheet through, I notice the conveyor belt is running slightly faster than the coating rollers..........which could be the source of the scratching. Unfortunately there is no way to adjust any roller or belt speeds on the machine.

The crazy thing is, this didn't happen before. I've also tried slowing things down to lessen the scratching effect of the conveyor belt and noticed the uv coating getting fuzzy with a checker pattern that directly matches the pattern on the conveyor belt. Has anyone else had this problem on this machine? I'm wondering if my UV lamp is just not up to par? I'm well under the suggested life span of the bulb(even though I've had the machine for a couple of years) but of course that came from china as well so I'm not sure what to think. If I only coat one side of a project everything seems fine, other than finger prints seem to show a little more than they used to, which again makes me suspect the UV coating isn't curing hard enough.

I've never owned another UV coating machine so any help would be appreciated.

 

[dgerharter]

I bought a PP&E-480 offline UV coating machine about two years ago. A very simple machine to run and I was pleased with it. I don't use it terribly often but lately I've noticed when I attempt to coat two sides of a project I'm getting a lot of scratches on the first side I coated(bottom). The funny thing is, the scratches can be rubbed away using a cloth or the sleeve of my shirt, if I push firmly. When I look inside the machine as I run a sheet through, I notice the conveyor belt is running slightly faster than the coating rollers..........which could be the source of the scratching. Unfortunately there is no way to adjust any roller or belt speeds on the machine.

The crazy thing is, this didn't happen before. I've also tried slowing things down to lessen the scratching effect of the conveyor belt and noticed the uv coating getting fuzzy with a checker pattern that directly matches the pattern on the conveyor belt. Has anyone else had this problem on this machine? I'm wondering if my UV lamp is just not up to par? I'm well under the suggested life span of the bulb(even though I've had the machine for a couple of years) but of course that came from china as well so I'm not sure what to think. If I only coat one side of a project everything seems fine, other than finger prints seem to show a little more than they used to, which again makes me suspect the UV coating isn't curing hard enough.

I've never owned another UV coating machine so any help would be appreciated.

Talk to your UV coating supplier about testing methods to analyze the curing of your system. Usual culprits are aging lamps and dirty reflectors.

 

[halmac]

I didn't think it was possible to coat both sides on a single side UV coater. Those "scratches" are UV coating toner streaks.

 

[HRoss]

It sounds more like marking than scratching in light of your ability to "buff" them away. Clearly the coating is cured sufficiently at the surface to prevent permanent scratching. You may have a contaminant on the belt surface. One way to test that theory is to place the sheet on a carrier of some sort to keep the first side coating off the belt and run as usual.

The pattern (a secondary issue) is common when the belt gets too warm (slower speed operation) and causes ink oil, or other plasticizer-like materials to leach out thru the coating. This should also be non-perminanet and "buff-able."

The comment about lamp and reflector maintenance is a good one. Cleaner reflectors and newer lamps deliver better UV to IR ratio thus reducing heat.

 

[pwo]

I have had this problem before. When coating the second pass the applicator roller pressure is too much on the sheet and the scraper blade is not cleaning the excess coating off the chrome roller. We use a 18in Gala coater. When we back off the pressure Those scratches go away. I hope this helps.

 

[Mstrkey]

Thanks for the replies guys. I'm going to try a few of these things on my next job and get back to you.

 

[Mstrkey]

Well I have a new issue. I can UV coat one side of any stock without issue. The reverse side is perfectly clean, no problems. However, when I coat the second side.....the first side is now partially wet again and not fully hardened. This seems impossible to me. At first I thought I was getting more liquid on the bottom of the sheets due to a faulty cleaning blade, but that doesn't make sense because when I run the first side through there is no residue on the other side. I've changed my UV bulb thinking it may not be curing 100% and that hasn't solved the issue. The ONLY thing I've found that helps partially is so run my machine at blisteringly slow speed for the second side. Like one sheet every 30 seconds speed. If I do this, the issue goes away. I don't get it.

 

[kansasquaker]

=However, when I coat the second side.....the first side is now partially wet again and not fully hardened. This seems impossible to me.

You're initial assumption is correct. That wet coating MUST becoming from somewhere else. Have you tried the carrier sheet idea HRoss suggested? Put your piece that has been coated on one side coated side down on a blank sheet of paper and run it through that way. That will tell us, pretty definitively, where the wet stuff is coming from.

 

[D Ink Man]

Change your UV coating to another brand. Have the new vendor prove their coating has faster curing ability. Coater side technical help is recommended. D

 

[Cergei]

Hi. I am familiar with this machine and have been working with such China made u.v. laminating units for 4 years now. This is a fairly small unit and as you have described, quite simple. There is a wash blade that is engaged to wipe the metal roller that presses your substrate on to the rubber roller. This is where your problem lies. Have you changed this squeegee like wash blade since you purchased the unit? Over time, this softens to the point that it does not completely wipe the u.v. varnish off of the metal roller. Minute particles of varnish slip through (very thin layer of varnish). This is what you feel on the back side of the substrate. For the first side, you will not see any wetting on the back, though i guarantee you, it is there. The layer of varnish is so thin, the substrate actually absorbs the varnish and you do not see or feel any wetness on the back. Since your problem starts when you begin to laminate the back side, the previously laminated side is now facing down. The substrate can no longer absorb the minute particles of varnish since it had already been laminated. Either replace the squeegee or flip it and use the opposite side (side inside the aluminum case that holds the squeegee).

As for slowing down the speed and the problem goes away, this is because the roller is turning slow enough that the squeegee can still clean off the residual varnish on the roller. At a faster speed, varnish slips through the squeegee.
Hope this helps