Four Color Made Easy

Screen Printing 26 Agustus 2011 Loading..
Screen Printing



I will be the first to say that 4-color process printing (referred to as "process color" in this article) is not for everyone. I also feel that if you just follow the rules, 

printing process color doesn´t have to be any harder than a detailed tight registration job.

This article is written in a quick step-by-step "print-by-numbers" style so you could follow along and print 80% of the process jobs you encounter.

The other 20% may present a few problems with matching customers logo colors and reference colors (faces, products, foods, etc.). These also can be done with a little experimentation.

What is process color?
Let´s make sure we are talking the same language. 4-color process printing is where you start with finished full-color artwork and have a color separator separate out the three subtractive primary colors of yellow, cyan (process blue), and magenta (process red) - plus black. He gives you back the films already halftoned (converted to dots) and you put them on high mesh counts, print them with special process inks and the print looks like the original - or at least it should.

Process color printing is not the same as basic 4-color printing where you cut overlays for the colors and use halftone dots from sheets of dots to create other colors, patterns, etc. Some of you think you are printing process color when you are just printing 4-color. Confused yet?

Why use process color?
The answer is simple. The prints look great when done correctly! Where else can you print with just 4-colors (process colors) and get hundreds of shades and colors and come very close to matching the original artwork?

Also, with computer graphics and inks getting better and better I really think that in a year or so - process color printing will be done by everyone - just like printing with puff ink, jacket printing, caps and any other commodity item.

Why is process printing so hard?
The problem is one of misconceptions. When I consult companies on process printing it is ALWAYS the same scenario. The prints look muddy and out-of-focus and the colors aren´t right. The prints always have this amazingly "heavy" hand (feel) to them too.

The comments are ALWAYS the same. "I had a terrific local separator do the job. He does it for all the big offset printers in town and really knows his stuff" and "I learned somewhere that if I took 3 to 4 times my line count to get my mesh count that I could print good halftones. We always use 230 for our process prints."

Get the picture? There is a misconception that just because a separator has a million dollars worth of equipment he can do T-shirt separations. Plus somewhere people get confused with the "rule" for getting the minimum mesh count to minimize the moire effect when printing halftones with the mesh needed to print process color.

What are the basic rules?
These are actually quite simple. If you talk to the great process printers there is always a common theme. Proper artwork, separations, mesh, frames, tension, inks, press and technique make for great process prints.

Rule #1 - Start off with a GREAT piece of artwork.
With this type of printing you MUST start off with a great piece of artwork because the design is only going to look worse when printed. You just can´t take a small photo, enlarge it and hope that it will BETTER on the shirt.

The artwork should have good contrast and avoid fine subtleties that can get lost in this process. Artists should also avoid fluorescent colors that do not reproduce as accurate.

Rule #2 - ALWAYS use the right separator and NEVER use customer supplied seps!
OK, some of you will be saying that you use your local separator and get good results. I would rather have you get GREAT results!

There are three ways to go here.

Do the separations your self.
You can do the separations in-house using techniques taught on this site.

Use industry specific software for the separations.
The trend is to use industry specific software like FastFilms to do the separations for you in Adobe Photoshop. This is really the way to go

Have the separations done outside.
You will pay between $300 and $500 for outside separations. Check the Buyer´s Guide for separation services.

Rule #3 - Use retensionable frames with the correct mesh and tension.
This one is not too hard. In order to reproduce the halftones exactly you need a perfect printing "plate." You simply cannot print correctly with hand stretched screens at low tension.

In our example we are using one of the popular retensionable screen frames that have been used on a number of jobs in order to "work harden" the fabric. After each job we re-tension in order to get the fabric tighter and tighter. Our sample screens have 305 dyed monofilament fabric tensioned to 30 newtons. We choose 305 because we are hand printing this sample. If using an automatic press you should be up to 350 at 30 newtons - if possible (did you ever try to get 350´s to 30 newtons?).

Rule #4 - Use a dual-cure or pure photopolymer emulsion.
For best results use a dual-cure or pure photopolymer direct emulsion. Use a nick-free scoop coater and coat the screen one time on the outside and one time on the inside. Thin coats allow you to hold finer detail and the photopolymers provide excellent edge definition.

Use an exposure calculator to determine the correct time and DO NOT overexpose the screen. Make sure to compare the film to the screen during wash-out so you can see if you held all the dots. I usually coat up an extra screen so I can determine the correct time from my first exposure.

Rule #5 - Print with a good printing press.
None of the above matters if you press won´t hold registration. I prefer a side-clamp press with lots of adjustments for off-contact, level pallets, etc. but there are excellent rear-clamp presses on the market. If printing with an automatic press, the heavier the press with a center-arm support the better to minimize pallet deflection.

Obviously you can get a more consistent print with an automatic press. Don´t let this stop you though. There are lots of quality process prints coming off manual equipment.

Rule #6 - Spend time on the set-up.
Take extra time on press set-up. Keep the off-contact VERY LOW. This is not like printing athletic numbers. Less than 1/16" and keep the screens parallel to the pallets. Any out-of-register will make the print appear soft or out-of-focus.

Rule #7 - Use the correct inks.
You just can´t take your standard colors out of the can and use them. This process is designed around using the "process colors" of yellow, cyan, magenta and black (if printing white don´t use a high opacity).

Until recently there has been no standardization in this industry. You can now get "ink values" from the ink companies and use them with your own in-house separations. You can now (almost) take the inks right out of the can and use them without any modification. This is quite a change from the days of having to spend hours adjusting the inks. On some jobs you will still have to do this but in order to make process printing easy the industry has to continue the develop standards.

Rule #8 - Use the correct squeegee and printing technique.
When hand printing process color you need to have a good feel and great technique. Keep the strokes consistent and try to make one good stroke do the job. I like to use a medium squeegee with a sharp edge.

If printing with an automatic press keep an eye on squeegee pressure. Use a triple durometer 70/90/70 for good results.

Rule #9 - Print on a good heavyweight shirt.
If you print on a loosely knitted shirt you are just trying to print on air for half the print.

I always try to use a heavyweight, 100% cotton shirt such as a Hanes Beefy-T or Hanes Heavyweight. The better the printing surface the better the print.

Rule #10 - ALWAYS tell the customer of the limitations of the process!
Customers will expect miracles unless you talk to them BEFORE you do the job. The artwork will NEVER look better (unless you use additional spot colors, puffs, metallics and other embellishments). They need to be told that the print will look a little different on a knitted shirt than it does on a poster or paper. With this process you can come within 80% to 90% of the original.

If the job has reference colors you need to be VERY CAREFUL. Have the customer approve the print before a production run is made. If there is a special logo color you may need to print this as a fifth or sixth color all by itself (this is called a "touch plate").

Rule #11 - Don´t ignore rules 1 through 10!
These are the rules. They are really quite simple. If you follow them you too could be doing award winning process color AND getting those larger jobs you dreamed of. If you choose to break them you may do one or two jobs and then just give up because you just can´t get it right.