How to do printing onto Anodized Aluminum

"The Surface
Treatment &
Finishing of
Aluminium and
Its Alloys"
by Wernick, Pinner
& Sheasby

(note: this book is two volumes)

on eBay or

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A. Hi Chris. Yes, after anodizing, the lettering ink or image is put onto the aluminum article and absorbed into the pores of the anodizing; then the article is sealed by immersion in boiling water or other sealing chemical. I've seen and worked with many aluminum electronic panels with black lettering on them, and have a good understanding of the anodizing process, but I do not have the hands-on experience you are looking for with lettering let alone images. Hopefully another reader will.

If you are a hobbyist, the descriptions here may be enough for you to start experimenting. But if you are considering installing a production facility I think you need to get to a library for access to Wernick, Pinner, & Sheasby, which is the authority on all aluminum finishing issues and has many pages describing the details of the several alternate approaches, and make a preliminary decision which of those approaches you will follow. But I think you should find a consultant with experience in it before committing to installation because it sounds very easy to pick a path which is theoretically workable but which, depending on precisely what you have in mind, is far less practical than others :-)

Luck & Regards,

"The Surface
Treatment &
Finishing of
Aluminium and
Its Alloys"
by Wernick, Pinner
& Sheasby

(note: this book is two volumes)

on eBay or

AbeBooks

or Amazon

(affil links)

A. Absolutely!

I don't have 'hands-on' experience in this, so I can't give you the process step-by-step, but I do know that anodizers commonly anodize aluminum plates, silk-screen the legend onto the plates, then seal the inks into the anodized film.

A. Regarding putting pictures on aluminum, there has been a process for doing this for at least 20 years. I don't have the article I read about this anymore. You would have to go to a technical library and look it up. As I remember, it involves absorbing the photographic silver salt chemicals into the porous anodizing coating. This would have to be done in a light-tight room with only dark room red lights. Sorry I can't help you more.

A. The process the writer is referring to was developed by Peter Laakmann of Synrad Corporation (CO2 lasers) and first published in the early '90s. Basically it involves laser etching the desired information into the anodized plate, then using the remaining anodization as a sort of resist. Dye is applied to the etched areas, given a few moments to be absorbed, the excess wiped off the resist area, and the whole is sealed. Synrad is in a northern suburb of Seattle, I'm sure they can supply a copy of the article. Problems are: a) its labor intensive; secondary and then *tertiary* operations, and b)frankly, we've never had particularly good success with it, although I can't say we've really applied ourselves to getting it right either. Laakmann claims it works great.

Q. What about re-anodizing plates which have been selectively laser-etched back down to bare metal? Has anybody had any experience with this or similar processes?

Try www.se.shibaura-it.ac.jp/~sato/, this is the address of Anodizer's Plaza. You might want to leave a message for Dr. Sato. I know that he is interested in the subject of anodized nameplates.

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Ed. note 11/27/06: Sorry readers, that page is no longer functional

A. You are making a lot of assumptions in thinking that you can do it better than the vendor. That presupposes that your vendor is not much good. Try another vendor first while you do the homework for setting it up in house. Far too many people think that the process is a "just dip it" which is far from the truth. For books, take a look at the gotta have it books in the library at this site.
Do not forget that you need a laboratory for maintaining control of the tanks.

"The Surface
Treatment &
Finishing of
Aluminium and
Its Alloys"
by Wernick, Pinner
& Sheasby

(note: this book is two volumes)

on eBay or

AbeBooks

or Amazon

(affil links)

Aluminum How-To
"Chromating - Anodizing - Hardcoating"
by Robert Probert

Also available in Spanish

You'll love this book. Finishing.com has sold almost a thousand copies without a single return request :-)

A. Hi, Tyler. The general idea involved in coloring or printing onto aluminum is that anodizing the aluminum builds sort of a honeycomb pattern on the aluminum surface, with billions of tiny "drill holes" extending into the anodized layer that can absorb dyes; after exposing this honeycomb to dyes or inks which are absorbed into the drill holes, the aluminum is put into boiling hot water or other agents which swells the aluminum oxide and "seals" it, closing off the tops of the holes.

Thus, aluminum is often colored by dipping into a vat of dye after anodizing and before sealing. Or lettering is put on aluminum by silk screening it with inks after anodizing and before sealing.
----

When it comes to more complicated patterns, "splash anodizing" is common. Exactly how it is done by different companies is usually still trade secret info, but may involve masking before dyeing, and/or overpainting. However, this process probably applies mostly to one-of-a-kind patterns, like fades, rather than intricate repeatable patterns.

When we look at a repeatable intricate pattern, like dollar bills, you have to start thinking to yourself that the manufacturer probably started by printing that pattern onto paper and then transferring it to the parts. Two ways of doing such a transfer are "sublimation printing" and "water transfer printing".

In sublimation printing onto anodized aluminum (although I can't pretend to have seen it done or to know the trade secrets involved in doing it well), the pattern is printed onto paper with inks that turn to gasses when heated. The paper is pressed against the aluminum, heated to cause the dyes to sublimate, absorbed into the anodized pores, then sealed.

In water transfer printing, the pattern floats off from the paper onto the surface of a tank of water, sort of like a stretchable decal. the part is dipped into the water and pulled up through it, and the "decal" wraps around it. Again, although I've seen this done on metals in general as sort of a paint, whether it works as an absorbable dye into the anodized film is not something I actually know. Good luck.

A. Hi Zane.

Although I have a good understanding of anodizing, I think you know a lot more about these imaging processes than I do. Maybe thinking out loud to bring myself up to speed will help bring others up to speed, especially if you correct me where my thinking is wrong.

Robust anodizing is a process not a single step. The aluminum is caustic cleaned, etched, and de-smutted before the anodizing step. The etching and desmutting parameters depend upon the alloy and exactly what is sought. You can see our "Introduction to Anodizing" for a better understanding of the process.

Dry ice going directly from solid to carbon dioxide is a well known example of sublimation -- the process of a material going directly from solid to gas without the intermediate step of liquid phase. Sublimation printing, as I understand it, starts with printing an image onto paper with an inkjet printer, but using special sublimation inks in the cartridges rather than conventional inks. When the paper with the image is sandwiched with another item and heated, the ink sublimates, which transfers the image to the T-shirt, coffee cup, or whatever. I have not seen sublimation printing on aluminum, but I suppose that after anodizing and before sealing, the aluminum is sandwiched with an image printed onto paper, and heated so the image sublimates into the anodized aluminum pores, which are then sealed.

This seems to me like it would be an ideal process for high resolution graphics or multi-color printing, but it wouldn't seem to be as simple, quick, and inexpensive as silk screening or other older technologies for simple black lettering.

Something to recognize about anodizing is that it is an EPA categorically regulated metal finishing process -- CFR 433 (Code of Federal Regulations). That doesn't mean you can't do it in house, but metal finishing was the first operation that most large manufacturers like automobile and appliance manufacturers outsourced, and not without reason. It is frankly a pain to operate these wet process lines with their acids & alkalies, exhaust & fume scrubbing, wastewater treatment, and hazardous waste accumulation headaches if you can outsource it to anodizing jobshops. But I understand that you may not be able to. Good luck.

Regards,

A. Hi Nick. We appended your inquiry to a related thread. Depending on how complex the three dimensional shape is, I'd bet that the pattern is transferred to the aluminum either by sublimation printing or water transfer. Look at "water transfer printing" on youtube and see if it looks promising for what you are envisioning. Good luck.

Regards,

A. Why not directly print onto the anodized aluminum using a normal inkjet printer that has a CD / DVD printing tray, assuming the parts are small enough? Just tape the part to the tray and print as normal. Any high-quality, waterproof, fade-resistant ink should work.

Note that the anodizing must be unsealed, so the pores are still open and can absorb ink. After printing (and the ink dries fully), submerge the part in boiling water to seal the pores.

? Hi Mayank. Sorry but I am not understanding what you mean by "image is split automatically". Can you try some additional words? Are you working with anodized but unsealed aluminum, or have you coated the aluminum with a polyester coating, or what? Thanks.

Regards,

A. Hi Satish. You may wish to start with our Intro to Anodizing Aluminum, and then move on to the two previously mentioned anodizing books. After you have an understanding of the overall process, it will be easier to visualize what people are talking about regarding dyeing while the pores are open, then sealing in the dye. You can have as many colors as you want, but each will need a vat of that color dye and one or more rinse stations, or a silk screen printing station. Good luck.

Regards,

A. Screen printing into the anodize but still unsealed pores is done with DYE based inks. The unsealed pores tend to vary in diameter from 10-100nm depending on the chemistry used to create the anodic coating. The pores are 100-1000 times smaller than the diameter of human hair. Solvent dye molecules in solution will easily fit into these pores. Pigment particles may also be used if they are milled down to under the pore diameter. Solvent dyes and pigments that are dispersed in a solvent medium or vehicle will resist the water based sealing bath and remain in the pores.

The same is true for inkjet printing into the unsealed anodize pores for high resolution multi-color images. Pigment inkjet inks typically have particle sizes too large to fit into the unsealed pores. The same is true for UV inks. UV inks contain monomers and oligomers that are polymerized or crosslinked using UV light that act as a binder or adhesive for the pigments. These binders will just adhere to the anodic surface.

Dye sublimation also transfers the dye into the anodic pores before sealing. Dye sublimation films may be wrapped around non-planar parts to transfer images into the pores.

A. Readers, you may wish to search the site for related topics, or review the following closely related topics:

Luck & Regards,