Printing Directly on Photopolymer Plate

To my knowledge, there’s no way to print something UV opaque directly onto unexposed polymer. It’s gelatinous and quite soft when uncured. It’s also water soluble (this is how it can be washed away when finishing the plate) so your average inkjet ink would likely damage the polymer.

The way many photopolymer plates for flexographic printing are now produced is by way of direct laser imaging. This is similar to “Computer-to-Plate” (CTP) platemaking for offset. Unexposed polymer is struck by a moving, ultraviolet laser. The computer controlling the laser turns it on and off as needed to image the plate. There are no negatives involved. I’ve wondered before if it would be possible to hack the imager of a laser printer to make a semi-homebrew one of these, but it wouldn’t be for the faint of heart.
—
Michael Hurley
Titivilus Press
Memphis, TN

This project isn’t far off:

http://hackaday.com/2014/02/03/laser-based-pcb-printer/

They’re using a UV laser to cure the photoresist used on printed circuit boards.

trmartin, what is it you’re trying to do? You want to print directly to the plate, for what reason? james

This one seems a bit more practical:

https://www.youtube.com/watch?v=4SNkzoOvoD8

There is already equipment on the market for direct exposure of Polymerplate via Laser.

You just need the few bucks they charge to afford the stuff.)

trmartin, 1. negatives are good for this process. They can hold 10 times more detail than an inkjet printer. 2.printing on the plate as a resist? how is the polymer plate going to navigate the “printer” as you call it? and then, how would you wash out the plate? 3. Vacuum frames are a good tool to have around. You can even cut a rubylith to make plate
sans négative. best james

I’m aware of the commercial direct-to-plate stuff; I’m intrigued by the potential of home-brewing something for a fraction of the cost of a commercial machine.

It seems to me that there could also be another possibility: print a positive the desired size on acetate using a high-resolution laser printer, then contact-print the positive onto lith film to obtain a sufficiently dense negative with which to expose the photopolymer. Lith film and chemicals are still available from a few sources. You’d need a vacuum frame for exposure to get the best results but possibly a foam-backed exposure frame would give enough contact for lith film exposure using a distant point light source.

Bob

the acetate should work fine but you need to mirror the image so the toner fixes in the back of the acetate there are also some sprays that you apply to the toner for darkening even more.
i have seen several exposure units home made done with old refrigerator compressors even with electromagnets wired so that the vacum starts when you close the window and as exposure light source best option is uv lights also more expensive .should work with other light sources as well with longer exposure times

the acetate should work fine but you need to mirror the image so the toner fixes in the back of the acetate there are also some sprays that you apply to the toner for darkening even more.
i have seen several exposure units home made done with old refrigerator compressors even with electromagnets wired so that the vacum starts when you close the window and as exposure light source best option is uv lights also more expensive .should work with other light sources as well with longer exposure times

Hey guys:

https://www.youtube.com/watch?v=0n5Q5n1wV84

Also:
https://www.youtube.com/watch?v=XyNdcn3W1s4

What you’re talking about is some kind of variation on “CTP” technology; Computer to plate.

The core concept is the removal of the intermediate step of a film- thus discounting a step in the process, reduction of process interpolation, and reduction in exposure contaminants.

(meaning that less compatibility issues between imaging and substrate occur, and you don’t end up with as many things like dust between film and plate, etc etc because you’re ‘removing’ a step in the process.)

It exists commercially, and some printmakers (less commercial realm, more “how can I do this to make art” realm) have looked into it/seen some good results. I’ll see if I can scare up some of my sources, but a few conferences back there was a demo on something like this at SGC if I recall correctly.

Really, photopolymer dissolves with water when you’re using our typical letterpress plate type; most inkjet printers use a combination of ISOPAR-G and PIGMENT to print images, and so since there is a small amount of water in this mixture it could slightly affect the polymer- but really, since you’re putting the ink where you want the polymer to dissolve, and using a UV source to harden the polymer where you didn’t put the ink (water), you shouldn’t really see an issue there.

The problem is going to be in calibrating an inkjet printer to deliver the opacity and clarity you desire. Most of the higher end printers have quite a bit of control you can exert over their output; you can manipulate sophisticated details like amount of ink put out VS time between head passes and even platen distance (the distance between the print head and the substrate). For this to be successful I would think you’d need a fairly high end printer and a cursory knowledge of the software/some trial and error before you could begin to see results that would be in the same building as a film negative.

I would say that you would probably be better off heeding where the industry went- with the CTP laser ablation plates and with the direct laser engraving plates. Look at what WinkingCat was doing (still is doing?) with laser engravers and think about the fact that cheap little desktop laser engravers cost about as much as a nice high quality epson desktop inkjet printer does these days and do the math for yourself.

A bit of nerdy technical detail on a similar subject!

http://e-collection.library.ethz.ch/eserv/eth:25819/eth-25819-01.pdf

Havenpress, I was trying to look up WinkingCat and what it is that they are going with plates, but couldn’t find any info. I’m intrigued by the prospect of using a laser though.

Small offset printers are going out of business left-right-centre. There is not much need for film any more. My film-guy is complaining a lot about the slow business. I am afraid that one day he will follow the fate of the other film output shops and close the film section of his shop.

So, my slow-printing-season-project parts are already in my shop; HP-7550A pen plotter, a microscope objective and a 365nm laser diode. I am planning to make an experimental CPT machine out of these parts. The plotter has 1000 DPI resolution. I have to fit the objective and the diode in to the pen holder and replace the pen-up-down movement with an electronic switch. The plate carrier would be an offset plate with the polymer plate stuck to it somehow.
Using the HPGL printer language, I could print line-by-line with UV light at 1000 DPI. This plotter has servo motors with encoders, it won’t skip a step, won’t get lost like the stepper motor driven units. Capable of 6G acceleration.
Very experimental, but curious about the results, and it does not require a lot of modifications ( I think/hope ).
LOL … the plotter can be driven even with the good old GW Basic.

So I assume you are going to use the CTP photopolymer plate material with the black carbon surface, which you are going to “ablate” (as the plate makers and suppliers call it), with your laser setup. (Most of the flexo photopolymer plates are made like that now).

That is exciting, and will be an impressive accomplishment when you can, for all practical purposes, achieve the same thing that the following can do, but at a much lower cost:

http://www.esko.com/en/Products/overview/cdi/models/

I have faith in you, Louie! Please keep us posted!

Actually I was thinking of using my regular plates. The laser diode is 365nm, the proper wavelength to harden the photo-polymer. With the combination of printing speed and diode power output, I should be able to harden the polymer all the way to the base and get the right shoulder angle too. The beam should be focused on to the surface of the plate.

Just “pen-plotting” with a very narrow laser beam instead of a pen to harden the polymer and not ablating any special masking surface. The plates do have an anti-halation layer on the bottom to prevent the UV light from scattering and hopefully the microscope lens will produce a clean, scatter free beam.
“plotting”, wash, dry and post expose.

By the way, I built my own exposure, washing and drying unit from hardware store items, cannibalised parts and plywood. Plate sales reps don’t want to get close to it, but it works great for MY purposes. The bulbs were those novelty/party black light fluorescent units. It cost me at the time $12 per unit, and I bolted 8 of those together. When I got busier, I replaced the bulbs with the “pro” ones. So my exposure time is now down to 3 minutes instead of 12.

I tried to hand write on a plate with the UV pen, without a lens, but with a pin-hole diaphragm taped to it. When I did it very slow, it did produce a usable plate. I had to go very slow because the laser beam was not concentrated with a lens.

The diode is part of a money-checking UV pen ( flash-light ), so the beam is not focused. The seller claims 5W-365nm.

Very interesting! Your way sounds a lot simpler than using “ablatable” plates. I will be interested to hear more, as you progress……

Best, Geoff

Indeed. Please keep us posted.

I don’t know if you’ll be able to modify a wide-angle UV diode into being anything close to a true laser, but it might work. Also, are you sure the diode you’re getting is 5W? That’s really high for most LEDs. a 200mW laser diode is often powerful enough to light matches or burn paper.
—
Michael Hurley
Titivilus Press
Memphis, TN

As I said: ” the seller claims “

That usually means, when the smoke clears the lab, they check what was the maximum current going trough the item. Then they round it up, and that is the published value. Standard practice these days … unfortunately.
( the 2 x 50W stereo is advertised as a 100W stereo )

The real value is the fraction of the quoted one.

I do have an adjustable constant current power supply I can use to fine tune it’s output as required.

I did not take the pen apart yet. Probably I will have to devise some kind of a “gear puller” to pull the original diffusing lens out. That will be like an open hearth surgery!

Michael Hurley, thanks for the input. It is appreciated, because I really don’t know what am I getting myself in to.
But is looks like an interesting project to tackle during the slow winter season.

Louie: I’ve been making photopolymer rubber stamps for years and on occasion have used it to make printing plates to print shopping bags on my C&P. My results are mixed so I opted for a mag plate from Owosso in size 6x10. I use a Hercules exposure unit and a process camera to shoot film negatives on matte litho film. I think the problem I’ve had is the durometer of the liquid resin I use for stamps vs. printing plates. Your experimental data on this stuff is really cool. I’ve converted the bathroom in my garage print shop to photopolymer and laser with extra ventilation to handle the stink of a laser, however any advice on using liquid resin for letterpress is always appreciated…

Gil

I don’t think I can help you with the liquid polymer. I have no experience with it. In the past, my plate supplier gave me a tour of their shop. They were making huge floor-mat like printing plates for the packaging industry. They were just as soft as the rubber floor-mats. I don’t think that you can increase the hardness of those resins.

What are you using the laser for?

Louie
http://eagleprint.ca

late to this discussion but…

There are “inkjet” machines that do not use water based ink, but instead use a solvent based ink. More like a paint really. They are meant for outdoor signage so the “ink” is very UV resistant. They also tend to print directly onto things like 1/2” plywood, so they are meant to accommodate thick rigid substrates. The problem here is the smallest ones are like 60” wide and the pricing is fairly high.

Hello, I’m still looking for years for an alternative. Is there any news about it?
Louie Dudas is there any progress in your project?

Though it is a product directed at the screenprinting market, this is relevant:

https://www.youtube.com/watch?v=f342NfijEc8

M&R also has a similar product for imaging screens, but instead of imaging with a laser it passes through a hot-wax or water-based inkjet head, and then under a bridge of high-output UV LED’s:

https://www.youtube.com/watch?v=m7yq8cL7u0I

Jusr for interest, there used to be a firm in Bromley, Kent, UK
who made their living printing on the back of small pieces of glass. Real Glass, not plastic. in the 1950s They were to be used as dials in radio sets of that period. With a scale and the names of various stations etc. A Thompson platen was I think used and rubber stereo plates, with special inks subsequently heated hard dry no suprises there. The son of the firm was with me at printing college, amiable fellow, but I always thought but not too bright! That college had photo-etched onto glass various scales required during Ww2, for sub periscopes etc. but no connection with Fullers.

Jusr for interest, there used to be a firm in Bromley, Kent, UK
who made their living printing on the back of small pieces of glass. Real Glass, not plastic. in the 1950s They were to be used as dials in radio sets of that period. With a scale and the names of various stations etc. A Thompson platen was I think used and rubber stereo plates, with special inks subsequently heated hard dry - no suprises there. The son of the firm was with me at printing college, amiable fellow, but I always thought not too bright! That college had photo-etched onto glass various scales required during Ww2, for sub periscopes etc. but no connection with Fullers.

Now there is something that wasn’t thought of.

We’re all thinking of a way to replace film, photosensitive emulsion on a plastic carrier.

Quite some time ago, before rubylith was a thing, shops were pouring a liquid onto plates of glass to let dry then cut away for masks. (I think this where the terms stripping/stripper came from)

So why not find a way to print onto plates of glass with a UV ink, most likely already developed in the Inkjet world. Or possibly even etch a plate of glass with a laser and fill the etch with black paint?

I’m sure the extra layer of even thin glass would make a difference in exposure but it seems a possibility.

Coat polymer plate with an opaque wax..coat or afhere a film of sorts..CNC off where you want it washed away….washout..post harden etc..remove wax with solvent?

Jonathan, with respect your idea won’t work.

Water will undercut the polymer layer wherever the mask is to be left- creating an inverse shoulder.

The process you are describing is known as “Ablation” style direct to plate imaging. Usually it is done as a positive, meaning the removed area is then exposed for effect; in this case, the removed area becomes the raised area of the plate in the end through the means of an exposure.
This can be done with a laser to remove the ‘film/mask’, and then an exposure. Sometimes it’s thermal ablation- meaning there is a coating on the top of the polymer that is thermally responsive and removable as such. Thermally ablate through protective film, peel film, ablated material comes off with film. Expose, remove leftover material, washout.

In the case of laser imaged ablation, I believe the laser removes only the wax, then there’s UV exposure prior to washout. The exposure goes through the ablated areas and those are what remain because the UV passes through the ‘openings’ and exposes/cures the plate emulsion..

After this, the wax is removed from the surface by other means (different means for different systems), and the plate is washed out with water. There may be some systems where the water wash removes the ‘wax’ layer, but I haven’t any first hand experience here so don’t know.

The ablation imaging was developed as a clearer imaging device (lasers expose to a plate that is made in a clean-room setting; thus, no pinholes- no dust in between neg and plate- no dust in between Keene and film); this negates the need for a vacuum suction during exposure and the careful cleaning process that takes part during the exposure prep process- which is something that takes up time.

The ablation process happens about as fast as a film can be printed, but in saving the vacuum time you achieve a reduction in processing time and mistakes, thus net more perfect plates in slightly less time.

There are some issues related to it like your laser must be focused perfectly and calibrated to take off only the image, I heard the plates have a lifespan shorter, and I’ve heard they tend to be sensitive to other factors like humidity.

Ok thanks for the thoughts Haven!

Ok thanks for the thoughts Haven!