Using Primer paint

[Mike Chance in Iowa]

It seems I have read somewhere on this forum or another that our lasers cannot engrave through primer paint. While discussing another topic on this forum, I tried using Rust-oleum Painter's Touch Ultra Cover White Primer and was able to engrave through that. I then picked up a spray can of PlastiKote Sandable Automotive Primer (white) and was able to engrave through that too.

Has anyone had success in using primer on an item and not being able to engrave through it? If so, what name & brand of primer are you using? It appears there are many different types of primer out there in the automotive and home decorating world...

[Lee DeRaud]

Short of embedding actual metal particles in the pigment, I can't imagine why a laser would have much trouble with any paint.

[Richard Rumancik]

Dee posted on this forum that she was able to get a two-toned effect by lasering through paint over primer. She mentioned in in this thread but maybe there is another:

http://www.sawmillcreek.org/showthre...ghlight=primer

It is possible that the primer Dee was using had iron oxide particles in it.

[jason harris]

It seems that she did not want to go through the primer and set up the speed/feed to go through the first layer of paint only, giving the desired effect.

[Lee DeRaud]

Not wanting to laser through a layer of paint and not being able to laser through a layer of paint aren't really the same thing.

[Dee Gallo]

I did not WANT to go through the primer layer, so I could get the desired effect. If the primer was too thin, you could go through it, but a second coat ensured success. This is my test piece, using a patchwork of no primer, red, white and black primers, blue and black top coats. All Automotive paints. The brand I used is Dupli-Color primer, and then either Rustoleum or Dupli-Color paints. Any spray paint will work, you just have to find one you like.

You can see here the different effects from varying powers, speed was 100 on all. The mid-point is 40 speed, where you go through the paint completely but leave the primer. Using two layers of paint gave the different color (brown - based on mixing copper and black) I wanted instead of straight primer color.

hope this helps someone, dee

[Neal Schlee]

Some of the newer Primers (and paints for that matter) are made with microscopic ceramic particals as fillers, this may be why some have issiues.

Neal

[Ernie Balch]

Ever notice how it is impossible to mark aluminum tape with a low power 80W CO2 laser?

A CO2 laser sees any conductive surface (such as Aluminum) as a mirror, highly conductive surfaces distort the electric field of the beam causing a standing wave node of 0 energy to form at the surface. This helps protect the paint coating on the Aluminum cake pan. Aluminum is also very thermally conductive so that helps to rapidly remove the heat as well.

The CO2 laser beam has a very long wavelength of 10.6 um. So the reflection caused standing wave gives you zones of canceled energy and doubled energy at 1/2 wavelength intervals. This effect lets you adjust the laser to leave a thin layer of paint on the Aluminum surface. It is best to use highly pigmented paints because the remaining layer will be very thin.

I expect that Dee's 2 color trick will not work very well on wood. In my experiments it worked great on aluminum tape with pink and green krylon paint, and it not at all on birch plywood.

Paints with real metallic pigments might have interesting properties, metal oxides probably not.

ernie

[Dee Gallo]

Not so, Ernie. I tested it on wood and it worked as well. I was going for a more rustic look, so this sign had 2 coats of spray black primer and a white wash coat (acrylic + water). After the laser, I hand painted the match parts. All the black you see is from the laser removing the white. Afterwards, I sanded the white away at the edges a little.

cheers, dee

[Mike Null]

Ernie

I'm with Dee. I have no technical standing but my practical experience doesn't support your position in this instance.

[Ernie Balch]

Dee, It looks great.

I will have to do some more testing. Thanks for the info.

ernie

[Dan Hintz]

A CO2 laser sees any conductive surface (such as Aluminum) as a mirror, highly conductive surfaces distort the electric field of the beam causing a standing wave node of 0 energy to form at the surface. This helps protect the paint coating on the Aluminum cake pan. Aluminum is also very thermally conductive so that helps to rapidly remove the heat as well.

The CO2 laser beam has a very long wavelength of 10.6 um. So the reflection caused standing wave gives you zones of canceled energy and doubled energy at 1/2 wavelength intervals. This effect lets you adjust the laser to leave a thin layer of paint on the Aluminum surface. It is best to use highly pigmented paints because the remaining layer will be very thin.

Going back through the old threads, but had to comment on this one for future reference...

Metals don't cut easily because the wavelength of the laser imparts too little of its energy to the substrate (think on the order of 0.1%)... that's the explanation in a nutshell, with the mirror analogy and heat distribution being most apt. There's no electric field to distort, there's no standing wave node of 0 energy forming at the surface. I'm not even sure where such an explanation came from. The fact that the there are nodes and anti-nodes within a stream of photons also has zero to do with the depth at which you can engrave a layer of anything, and pigments have no effect on anything other than the amount of energy absorbed within a unit area.

Just don't want the newbies heading down a path of experimentation that will lead to nothing of use...

[Ernie Balch]

Dan,

A laser is a coherent source that has both an electric field and a magnetic field, (electro-magnetic waves). I have 40 years of experience with microlithography and I can assure you that solving the standing wave problem on reflective surfaces has been a major topic since the '70s. Billions of dollars have been spent on methods to reduce this effect.

The effect is also an issue in laser micro machining, it has caused me a lot of problems when laser ablating polymers down to aluminum or gold IC pads that were only 70 microns across.

My experience in micromachining using UV wavelengths and 30 nanosecond pulsed lasers where thermal issues are minimized led me to get carried away with my excitement of knowing the topic. Thinking about Dee's experience, I realized that the effect is washed out by the excess thermal diffusion seen with CO2 laser ablation. A CW infrared laser imparts a great deal of heat that diffuses distances greater that the 5 micron half wavelength during the long times that our substrates are being irradiated.

So in summary, you don't need to worry about the physics in the gross world of laser engraving with CW lasers.
(For more information you can search standing waves and coherent light)