[Q] UV Curable Clear Hardcoat Wavy

jdelgadoc1300

New Member
Dear all,

Beforehand, thank you everyone for your amazing contributions, I've reading the forum for a while and I've learned a lot from you guys.
Today I came to you with a professional question. First of all, I do expect not to violate any forum rules, because the product I'm asking is not from SPI.

I am a Coatings Engineer for an Automotive Tier 1 manufacturer. I'm in charge of two coating processes, one of them involving a Clear Hardcoat which is cured with UV energy, which is applied to a transparent polycarbonate part (so clear on clear), with a paint robot and automatic spray gun.

On my current parts I'm not getting a good surface finishing. Reading from this forum I can relate this condition to high solids, resulting in urethane wave effect.

My original mix is with 60% solids, I added IPA to the mix and got to 44% solids. This improved the finishing but it is still not okay.

Controlling temperature and humidity in the room at 25°C and 50% r.H., 1 minute ambient flash-off, then 2 minutes hot flash-off (compliant to coating datasheet).

I've changed my air cap from HVLP to Conventional, and right now using 4 bar for atomization air and 1.5 bar for shape air, dosing at 98 cc/min. This also improved but slightly.

For this kind of coating and process I can't do any cutting, buffing, re-working.

So do you have any ideas on how to improve the waviness on the surface for the end result?

Thank you in advance!
 
You are making progress with the bar adjustment.
I would look at increasing the atomization a half bar at a time and, at the same time, do the same for the shaping.

I'm not an expert with UV-cured products, but when an OEM built a new plant in the USA, I saw the paint gun manufacturer test every paint with different needle size sets on the robots.
For this application worst case, you may need a different size set, but you can get there with bar adjustment and IPA adding.
 
Do the guns on your robot have a fluid adjustment? It's been 25 years for me, so I had to ask as things change.
If so, start turning in a 1/4 turn at a time, and you may not need to mess with the bar adjustment.
 
Do the guns on your robot have a fluid adjustment? It's been 25 years for me, so I had to ask as things change.
If so, start turning in a 1/4 turn at a time, and you may not need to mess with the bar adjustment.
Hello Mr. Barry! Thanks for your reply!
I will definitely see the option of changing the needle size and try, currently using 0.5 mm.
For the spray gun mounted on the robot, the fluid adjustment is through a PLC, when I first wrote the post I was using 98 ml/min, I did some trials on the week-end and reduced the dosing to 42 ml/min, this gave a better result, the problem was the layer thickness, I slowed down the robot speed to try to compensate this, but then it resulted in some spots with paint accumulation.
Still in a "try and fail" phase, so I do appreciate your input!
Regards!
 
Two things to maybe consider??
The year's ago, when I fooled with Radtec, it was all volunteer, and they would jump on something like this and fix no charge.
Just as a way to promote the UV-cured paints.
Not even sure if they are still in business or in your country.
Option number two, robot guns are state of the art, and usually, the gun manufacturer will send a guy out to help at no charge.
 
I suppose it's not practical to do a two-step application, but on a quick read it seems like 2 thinner coats would achieve the best result, like we do with our 3100 Speed Clear.
Typically UV coatings are production lines, and one coat the 5 secs to 60 seconds cure rate spending how the line is set up.
 
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