[theory] What makes white ink so hard to print?

[blue moon]

We recently bought some lab equipment and will start some seriously geeky tests on the inks. Richard Greaves is the mastermind behind it, but I am keeping up with him (yes, holding on for dear life, but still with him for now). We are talking testing beyond even what the ink manufacturers can or do, waay beyond! As I expect to see some eye opening results it would be interesting to see what the current thoughts are on some of the subjects and how that relates to what we are about to find out.

With that in mind, what do ppl think is making the white ink so difficult to print with?
What does it take to make it print better?
What are the parameters that need to be controlled in order to get the best print?
How much are we falling short of what the inks can really deliver by either not following the manufacturer's recommendations or not putting in the time to figure how to print better? Is the difference in results negligible or is it significant?

please answer some or all of the questions!

pierre

[tonypep]

Negligible for us but then again we only use white plas when we have to which is rare

[Colin]

oh oh..... I need a lot more time to respond to that question Pierre.

Let's start with printing the ink at optimal temperatures.  Remember all lab testing is done with the ink at 72-75 degrees.  Also, right from the mixer.  A retain is kept from every batch for at least a year.  All ink will body up over time but it usually will follow a curve reaching max body within a few days to a few weeks.  But the labs only test the retain if someone has a complaint about the ink.  Of course long term testing is always done when a new ink is created.

So, one big issue is trying to print white ink is: Printing when it is not at optimal printing temperatures.

There are more and I will try to get to them later.

Good post to follow!

[brandon]

We are talking testing beyond even what the ink manufacturers can or do, waay beyond!

After the awesome experience that the nice folk at Rutland gave me on the factory tour I can safely say you are going to be buying a lot of very expensive testing equipment! Make some room haha.

I would also say with regards to plastisol printing a lot of shops don't tension their mesh often as they should (or at all) or just use the wrong ink for the wrong application. Why read the date sheets? It's just white ink and the cheapest one. It will work!

[alan802]

I think when it comes to printing white ink the most important factor besides the ink itself is the mesh count.  Thinner thread equals better percentage open area and that leads to printing with very little pressure and high speed.  Just test print the same image through a 156/64 and a 150/48 and you'll see the benefits to thin thread.  We rarely print white through standard thread counts anymore.  Squeegee blade can play a small role that will be noticeable to good eye and also will help with print speed.

[abchung]

For me (manual printer):
1. Brand of Ink, I prefer Wilflex over Rutland.
2. Thread diameter. I find thin thread is easier to print as long as I can easily keep the tension above 25 N so the image can remain sharp. So I would prefer a 34 micron over a 31 micron of a 305mesh.
3. Emulsion thickness, if I feel a small step over the mesh. It is good enough for me.
4. Squeegee sharpness. I fill stroke, then I angle the squeegee so I can cut the ink.

Fabric: Fabric that are knitted by German machines are the best to print on.

[kirkage]

Trying to cover a colored surface with white ink breaks some unwritten law of nature. It should not be done. But we do it anyway.

[mimosatexas]

The only issues I have with white plastisol:

1. Gumming up and climbing the squeegee, even on the creamiest inks, more than any other color.
2. The way it reacts to static electricity and flings off little strings that pull away from the mesh.

The actual printing is pretty straightforward with the right variables.

[tonypep]

Proper mesh selection/tension+squeegee parameters+off contact+decent ink=no problem

[ebscreen]

Trying to cover a colored surface with white ink breaks some unwritten law of nature. It should not be done. But we do it anyway.

This.

[ScreenFoo]

1: Lack of understanding/control of variables. 
2. Understanding and controlling ALL the variables which seriously impact labor and materials costs.
3. What's the most important variable when printing white ink?  The same as any other ink--all of them.
4: I'd rephrase--how much are we falling short of what inks can deliver by not understanding and controlling the variables?
That depends--on what variables you understand and control.  Tough to know what you don't know you don't know, however.

The tough thing about this is--Tony makes a great point that with decent ink you won't have problems--but what quantifies a bucket of white being 'decent', 'good', or 'crappy'?  If you read the forums, it's quantified mostly by the user's understanding and control of variables, which is often poor, and leads people to say one ink is good and another is bad, when they are in reality both fine inks, and the problem is in the process, or in the users lack of understanding the process...

[starchild]

I'm not sure about counting on the information and  suggestions of the suppliers/tecnical support/manufacturers as they have no knowledge of the specifications of the tools used in your operations. (All shops have the same tools but all sepc/combination to build the pump are not identical from shop to shop)

What the ink manufacturers should be providing the printers is the Inks analysis data.. These test are done and then technical support sells the ink as- awsome, creamy, good coverage, nice hand, low flash and a bunch of other adjectives and platitudes..

An ink should be selected based on our constructed pump's ability or our pump should be constructed to match the inks personality.. In any case it must be orchestrated..

To understand the personality of the ink we need to Know it's properties:

Optical Sepcifications-
L, a, B
Delta E
Peak Spectral
Gloss percentage
Opacity Per Mil
Bleed Resist
xy Chromaticity Coordinates

Rheological Specifications-
Relative Viscosity
Yield Stress
Plastic Viscosity
Shortness Ratio
Thixotropic Index
Tack Percent
Servers Viscosity

Thermal Specifications-
Low Viscosity
Gel Point
Fusion
Remelt
Hot Tack (after flash)

Physical Properties-
Grind
Emissivity
Specific Gravity
Surface Tension
Critical Surface Tension
Percent Plasticizer
Shore A

Having this relatively short list of properties made available and technical support (job should be) making sure that printers understand what effect each spec have on the ink, then printers will not have a problem choosing the right ink to match their unique setup.

[tonypep]

Great points to understand if you are an ink chemist but will not necessarily make you a better printer. Maybe, maybe not. Some struggle with plastisol, others choose a few whites for different applications and move on. This indicates that the press and pre-press parameters are under control. I applaud Pierre for this undertaking, please don't take this the wrong way. BTW a lot of those properties do not apply to waterbased products. And that plastisol stuff is just too darn expensive!

[Screened Gear]

White ink prints like crap because it has high pigment loads. Why do people have such a hard time printing it? Its because inks are not designed to print 24 shirts. They are designed to print thousands of shirts at a time with out ink viscosity/opacity break down. That is why we add reducer to inks so they perform like they should at lower print runs. The chemical make up and testing of the properties of the ink is really a step in the wrong direction IMO. Unless your doing it to know what inks are closer to what you want to start with. You need to modify inks for your shop. Have short run inks and long run inks. Inks for whites and inks for darks. Being a small shop I modify inks by the job. I am no expert but I have got good at knowing how to modify them for my shop. Everyone wants to use inks straight out of the bucket but on small runs (24-100) that is not always the best ink for the job. Over 100 shirts ink out of the bucket work fine.

I have been using Quick white for a long time and I just got a few new whites and they all printed like crap. It took me about a week to figure out how to print them. Every white ink needs testing and modifications to your printing style. Now those crappy white inks print as well as quick. I didn't modify the inks (long run printing) just the way that I print them.

[starchild]

That list of specs should be laid out just like the mesh manufacturers make their mesh specs partially available and you should not have to be a.. weaver to interpret thier values.. That's the technical support job.. They damn well do it for large operations and shock and jive the major portion of the industry small and medium shops.. It's called a Certificate of Analysis.. Exactly what Pierre is paying to acquire for his small shop.. We don't know better so we don't hold the hustlers feet to the fire.

If your white ink is not transferring but climbing and we know that the mesh specs has a high flow rate to support high squegee speeds and a low pressure drop- that allows the white whose tack percent is spec'd as low, then we need to know if the ink's shortness ratio is beyond say 3.5 and if that's the case then we need a temporary fix for the current press run but the issue should be addressed by the ink supplier or move on to the next ink that specs matches what you need for your print production setup.. Variables are never dialed in, with out known specifications for each part/tool used in the process they're more like hammered in-based on guesses and historical-experience/recorded info and will fall apart as soon as another unknown is switched out and or added to the setup.. There is a reason why one bangin supa dupa ink works for some and a horror for others.. Specs.. And we are all dialed in and variables controlled.. The thing is all variables have one thing in common- values..



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