[WWI] Screen printing decals

[Dave Calhoun]

Regarding Dave's question on screen printing, I have a good knowledge on this process (although not current industrial methods) I took a class on screen printing 20 years ago at rochester Institute of Technology as part of the Printing management program.  There is some industrial equipment needed to do this, such as a exposure frame and UV light.  The process is pretty simple, you take a metal or wooden frame and apply a fine fabric "screen" to it, the finer the mesh of the screen the smaller and finer the printed image will be.  A photosensitive coating is applied to the screen, then a film positive of your image (not sure if you can even find film positives any more since the graphics industry has switched to direct to plate technology the last 10 years or so) is applied to the screen, and it is put into a vacuum frame that draws the film tightly against the screen.  A UV light is used to expose the photosensitive coating, and whereever the light hits will harden, but the area under the film remains unexposed.  Then a high pressure water hose is used to spray out the unexposed material from the screen.  When dry the screen is ready to print, screen printing ink is put inside the frame and a rubber squeegee is used to pull the ink down the image and this presses the ink onto the decal paper under the screen.  This allows a image to be printed in any color that you can get the ink for. (there are tons of colors available, black, white and all colors in between can be mixed by a good ink company)  Each color has a seperate screen, and they must be printe 1 color at a time, register is tough for each consecutive layer.  That is the reason that Americal may have had some register problems, unlike offset printing where all colors are printed in one pass through the press, each color is printed seperately and overlayed for correct register.
So it is a pretty complex process and although simple methods such as hand cut T shirt logos are easily made at home, for scale white serial #'s you would need a professional shop to make the film, expose the frame, etc. so I do not see that as a feasable alternative for short run low cost images.
Any questions let me have it!
Dave Calhoun "printing Estimator"
 Message: 14
Date: Wed, 16 Jan 2008 08:33:50 -0000
From: "Hooper, Dave" <Dave.Hooper at Clarks.com>
Subject: Re: [WWI] Americal-Gryphon
To: "World War I Modeling Mailing List" <wwi at wwi-models.org>
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<530179FB663F734185432AE18EAE6398010FDCE3 at COR-STR-EX04.CORP.CJCLARK.COM>

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Hi all

 

It's been interesting reading all the responces from my 'off the cuff' comment. 

 

>From my point of view the one thing that stops me from attempting a project is a lack of suitable decals. This is not such a problem as it used to be as thanks to computer technology as I have a limited ability to create my own decals as long as the don't require a complex white background. 

 

In my attempts I perhaps surfer from a lack of knowledge (ie; I might take a profile as inspiration which is inaccurate) and I lack the resources and technical know-how to create perfect decals (as above). There must be other modellers out there who have the knowledge, but lack the know-how etc, or members how have the resources but not the know how.................etc, etc, etc. It sounds fanciful but if we could somehow pull these resources in to one we could have the capability to produce some good material.

 

There have been a few e-mails going around concerning the technical aspects of decal printing and I was particularly interested to learn that you can no longer get white ink for ALPS printers. What about screen printing? Does anybody out there know what that requires? I wasn't thinking of complete full colour screen prints, but if you had the capability to screen print in white you could effectively print a white background decal or lettering and place a second lazer printed colour decal on top. That way you could have the best of both worlds.

 

I'm not sure if I completely like the idea of having a central bank of images that any Tom, Dick and Harry can access. For my own material, I am happy for people have free access to it as long as they are making non profit making use of it. I would perhaps prefer to have small unusable thumbs to be available with the complete full size image available on request. That way I have some control over the distribution of my work.

 

One final comment, I'm sure we could arrange to send one of Diego's friendly finger chopping friends around to anybody who complains.

 

Regards

 

Dave   
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