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

[tonypep]

That's a Joe Clarkism

[mk162]

most of the time the dummy holding the bucket is thinking about a)quittin' time or b)sex or c)both of the above.

[Homer]

most of the time the dummy holding the bucket is thinking about a)quittin' time or b)sex or c)both of the above.

my new guy is thinking about his 4th kid on the way and smoke breaks...but I just broke him of that habit, quit or ....

we have a heated rolling ink cart....somebody turned the heat up a bit too much and fully cooked a brand new bucket of IC yellow gold...it was me.

[ScreenFoo]

so what are the variables that we can control?
so what are some of the things that are preset in the ink and we have no control of?

I was hoping someone else would jump in, but here's my take on it:

I believe there are over 500 of them--the main reason I would pay attention more to those with a large impact on labor or materials.
The SPTF has a rather complete spread broken down by department of what all variables could affect a final print.  Pretty interesting stuff.

IMHO, I don't think of everything as really pre-set in the ink as far as the printing end goes--you can change most of the important printing variables.  Not to say the cheapest white on the market can necessarily print like the most expensive, but you can reduce tack and viscosity with a reducer, reduce tack and keep a similar viscosity with the right base, add opacity with pigment (or whatever other name the ink company gives their product) etc. 

I suppose the things you can't change are the reasons by which you choose or do not choose to buy an ink--color, gloss, gel/cure temps, grind, types of plasticizers, etc.

[ZooCity]

Pigment shape? 

I can't find a micro image of white pigment or titanium dioxide for some reason but I was once told that the white pigment has a spiky shape that is not optimal for getting it to roll around and pass through little square holes. 

[starchild]

Pigment shape? 

I can't find a micro image of white pigment or titanium dioxide for some reason but I was once told that the white pigment has a spiky shape that is not optimal for getting it to roll around and pass through little square holes.

Well whites are made up of a high pigment load which adds weight to it so it's  heavy, it's also actually shaped like (tiny balls) but because of the weight  they settle and clump together making (bigger balls). Both white's heavy balls and color's spiky needle like shape, will benefit from performance meshes..

The spiky colors benefit from wide open meshes along with higher squeege speeds (that aid in aligning the spikes in the direction of the opening)..

The heavy ballsy whites also benefit from wider open areas but that's due to the more open the area of the mesh, the lower the pressure drop will be, so the white experiences less resistance in its travel through the tunnel to get to the other side of the mesh..

Meshes with thinner threads will offer more open areas, as well as lower pressure drop values because of the smaller diameter of the thinner thread.

Sent using Tapatalk

[mk162]

it really makes me wonder how tiny the white particles in digital ink are.  I know they use TO2 as a pigment, but getting that pigment smaller than a human hair is impressive.

I know Xenon came out with a white with a really small particle size.  Prints well too.

[jsheridan]

Pigment shape? 

I can't find a micro image of white pigment or titanium dioxide for some reason but I was once told that the white pigment has a spiky shape that is not optimal for getting it to roll around and pass through little square holes.

Here you go.



The more a white ink is 'ground' the smaller the particles become.
The smaller the grind, the less opaque it becomes so the manufacturer has to find the balance with printability across a WIDE mesh range.

So to answer you question on what makes white so hard to print.. were trying to pass these shapes through a square hole shaped via filament thread that over time begins to fray and increases surface tension trapping those fine dioxide particels in the open mesh area.



Look at that.. printing a white comes down to the screen.. how about that.

Once again, what we do is the most important... SCREENprinting.
Keep your white screens newer and at decent tension for best performance.

[Printficient]

it really makes me wonder how tiny the white particles in digital ink are.  I know they use TO2 as a pigment, but getting that pigment smaller than a human hair is impressive.

I know Xenon came out with a white with a really small particle size.  Prints well too.

We now grind our own white and black pigments.  This gives us more control and consistency.

[RichardGreaves]

the ink's Yield Stress (measured in dynes/cm) is high.

starchild.

How are you measuring the ink's Yield Stress?

[ScreenFoo]

^^I think it IS time for a physics lecture.  I'd love to read a more than a bit about that type of testing. 

JS--Killer pics.  Makes me wonder though, guideline I've gone by is that particle size should be less than a third of your mesh opening--the pic with the clogged opening makes it look as if the pigment particle is bigger than the opening--any background on the how/why?

Dilatant flow is next, right?  Time to get some corn starch and make some oobleck. 

[starchild]

the ink's Yield Stress (measured in dynes/cm) is high.

starchild.

How are you measuring the ink's Yield Stress?

Do you mean short of having my very own hi-tec lab? Well just like everyone else, the spatula pulled across the ink bucket technique.. The thing is I am able to identify and give name to what is being affected when I do this..

The point I am trying to make in these threads, is that the ink manufactures don't use a ladle and pot-stir,  to mix inks like they're cooking moon shine nor do they do something hokey pokey to test it's performance.. Yet that is how it's sold.. well at least to the little guys..

The specs I pointed out, In my opinion, should be available to all and definitions applied to them so that printers can select their inks deliberately.. As soon as something goes contrary in production we start adjusting things with blind confusion and confidence.. The inks behavior is really a complete stranger to us..

But what if we can predict how the ink will behave before we even make the purchase? And what if when the ink does something contrary? we can pinpoint where the f up happened and report back to the manufacture with confidence and not frustration. The ink man wins as well because he can identify exactly where the week points are and fix the problems- making his product better.. And what if anyone of our forum members can ask- "I want a white that I can use as an underbase for a process print, so that I don't experience color shifts" and many can reply/recommend a particular ink of choice, just by reading off the xy chromaticity  value to know where in the color spectrum the hue and saturation of a white ink leans?

Information (quality) is King.. We all make most of our selections based on it anyway..

Any manufacture/supplier that approaches his marketing this way will easily dominate the market..

Someone please tell me why you would not want an ink from a manufacture that offers a Certificate of Analysis?

Sent using Tapatalk

[alan802]

I'd love to have everything that an ink manufacturer could offer us printers that could help us.  My problem is I wouldn't be able to understand most everything on a COA more than likely without Joe explaining it all to me.

I always pull the spatula through an ink to see how it performs and I know what I look for when performing that test but beyond that, the technical points to that test are way over my head.  If the channel collapses right away does that mean "X"?  If the channel stays for 3 seconds does it mean "Y"?  If the spatula bends over backwards almost does it mean that "Y" needs to be adjusted by a certain amount?  All those things I don't understand one bit.  I wish I did though.

[ScreenFoo]

I'm in agreement that it would be wonderful to have all parameters of the ink in hand.  Personally, I have reps that can't tell me if I have blowing agent in my white, or what type of migration blocker they are using, and that makes it seem a little unrealistic to me.  It's a bit out there to expect to pay what we do for ink, and for the ink companies to somehow afford to employ chemists for tech support... but it would be great, I agree.

I'd also point out that every ink I've ever printed puts the responsibility on the printer to test for fitness for a particular purpose before any print run.   Just like any other industry, you can feel free to take a sample from your supplier to any independent lab and get whatever characteristics you want tested and quantified.  If you can't or won't test the characteristics that are important don't cry foul to the manufacturer, they spell it out on just about every bucket that's out there.  The thing that makes me wonder is that people seem to have issues with the SAME ink, which means unless their ink maker is putting out product of poor quality and they are not noticing, then they are having issues they need to look in the mirror to address.

[ScreenPrinter123]

http://m.youtube.com/watch?v=pEQAie8ABLE&feature=kp