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screen printing => Ink and Chemicals => Topic started by: Joe Clarke on April 12, 2016, 10:31:01 AM
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White ink seems to be 50% of the consumption but at times 95% of the issues on press.
Here are a few generic suggestions about managing your whites prior to & during production.
White ink:
Never intermix brands or series.
High fabric-mass-easier to bridge.
Longer staple lengths-easier matte.
When using a barrel pump, don’t stir.
If print 100 matches print two, don’t stir.
The slippery slope is 115°F, DON’T EXCEED.
Summertime in Nashville, mosdef don’t stir!
Ink thins during press run, wait it out … ouch!
Hand stir quarts, for gallons & fivers; automate.
Helix mixing paddles raise the lower ink to the top.
5 - gallon paddle types don’t, and they run ~ 60 RPM.
Helix type, 3/8” drill 600 RPM >100x shear-rate vs paddle.
The cheap, meat thermometer works well to monitor temp.
2-min. helix cooler than ~ 2-hrs. on paddle, same shear-rate.
If helix ink doesn’t clear well the problem is tack, not viscosity.
Peanut Butter, Honey, Suntan Oil are high tack, Cold Cream isn’t.
Stirring can break-up weak, temporary bonds, tack is permanent.
No amount of stirring, warming or pumping will reduce the ink tack.
Stirring is meant to redistribute the particles, heating is a by-product.
Warming is short lived, increases tack but doesn’t redistribute particles.
The warming process can be prior to production or during from the flash.
Higher tack ink is directly proportional to overheating and increasing tack.
When we flash curing, NEVER return used white ink to the virgin container.
Ink thickens during press run, reduce flash distance first then its temperature.
Proper high-shear, high-speed ink transfer runs cooler than traditional transfer.
Shear thinning white inks w/ >5.0:1 ratio can be printed at top print stroke speeds.
Inks w/ tack level greater than 35% should be stirred and printed at very slow speeds.
Curable Reducer will increase flash time, causes after tack and compromises durability.
After proper stirring print #5 won’t clear, wrong; ink, mesh, blade, stencil, press settings.
Low tack white [<35%] on high ink transfer mesh, fitted blades & press; clears on first pass.
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Interesting list.
I have never seen tack expressed as a percentage, or shear thinning as a ratio like that.
How does one go about measuring them?
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This, my friend, is why we love white discharge and colors. My printers don't like dealing with dealing with plastisol, especially white. Its also why we were referred to for large volume contract continuous business by an ink manufacturer ;)
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Both tack and shear-thinning properties require lab equipment to quantify but it is equipment every ink maker should have. It is most certainly "the hard way" but we gauge tack [~how the white adheres to iteslf VS how it adheres to something else] every day on press. Ink which has excessive tack won't bridge or matte-down easily, it requires a lot of squeegee angle and / or pressure, doesn't clear the mesh well and tends to leave a rough surface. Shear thinning is a ratio of two viscosities [~the friction between two fluid layers of ink]; flooded viscosity and transferring viscosity. We want the tack ratio to be low as possible and to a limit we want the shear-thinnning ratio to be as high as possible.
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Interesting list.
I have never seen tack expressed as a percentage, or shear thinning as a ratio like that.
How does one go about measuring them?
Both tack and shear-thinning properties require lab equipment to quantify but it is equipment every ink maker should have. It is most certainly "the hard way" but we gauge tack [~how the white adheres to iteslf VS how it adheres to something else] every day on press. Ink which has excessive tack won't bridge or matte-down easily, it requires a lot of squeegee angle and / or pressure, doesn't clear the mesh well and tends to leave a rough surface. Shear thinning is a ratio of two viscosities [~the friction between two fluid layers of ink]; flooded viscosity and transferring viscosity. We want the tack ratio to be low as possible and to a limit we want the shear-thinnning ratio to be as high as possible.
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This, my friend, is why we love white discharge and colors. My printers don't like dealing with dealing with plastisol, especially white. Its also why we were referred to for large volume contract continuous business by an ink manufacturer ;)
Yeah Tpep, but you can't discharge everything or cannnnnnn you LOL, using discharge white is very nice if I could I would use it on everything and not use plastisol white at all.
darryl
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Pretty much everything except performance wear which we don't do. We have several DC/UB formulas for the stubborn ones. Also expanding the DC color offering to accommodate new business.
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So you're saying I can use cold cream to reduce tack...sweet!! ;-)
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So you're saying I can use cold cream to reduce tack...sweet!! ;-)
Only if you first warm the cold cream in a hot oven or preferably a ceramic kiln then gently stir.
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So you're saying I can use cold cream to reduce tack...sweet!! ;-)
Only if you first warm the cold cream in a hot oven or preferably a ceramic kiln then gently stir.
Well I now have cold cream all over the bottom of my kiln and it stinks to high hell in here. Should I have used one of the glass jars? Dang!
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Both tack and shear-thinning properties require lab equipment to quantify but it is equipment every ink maker should have. It is most certainly "the hard way" but we gauge tack [~how the white adheres to iteslf VS how it adheres to something else] every day on press. Ink which has excessive tack won't bridge or matte-down easily, it requires a lot of squeegee angle and / or pressure, doesn't clear the mesh well and tends to leave a rough surface. Shear thinning is a ratio of two viscosities [~the friction between two fluid layers of ink]; flooded viscosity and transferring viscosity. We want the tack ratio to be low as possible and to a limit we want the shear-thinnning ratio to be as high as possible.
So share thinning, is how easily the ink inside the mesh funnel, separates from the top layer of itself, as the squeegee's edge passes over the mesh opening? If this is interpreted this way, if the ink tack ratio is low, one of the attributes of the ink would be that the shear-thinning ratio would be (on the positive side of things) high? So one measurement does not work independently of the other- right? Like you said a high tack ink won't separate from itself well.
And what causes the ink to be high tack in the first place?
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Certain liquid components and resin choices.
One example is Mineral Spirits. Its a filler liquid.
I personally hate it....
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I know of one 3rd wld op that siphoned gasoline from a jeep to thin ink for..............get this......................kids wear
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Tony;
I'm not surprised at all by that. I know I've seen some crazy stuff in my earlier years working for people (Flat Stock and graphic printers are the worse). Also, bet that people in this country are oblivious to how some of their kids apparel is produced and more than likely paid double for it.
Joe;
I'm bowing through your ink like crazy so I hope your making a crap ton if that stuff cause I'm averaging a gallon to two gallons a day of that stuff (Good Ink)
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Reminds me of the shop that cleaned screens with gas. Gallon container under the press...paper towels soaked in it...and they smoked in the shop as well.
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OMG that just reminded me a shop I helped at for a couple days. They did the same crap and smoked. I remember running a 20k order for them and the 2 stackers fell a sleep on the ground at the end of the dryer. LOL
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Both tack and shear-thinning properties require lab equipment to quantify but it is equipment every ink maker should have. It is most certainly "the hard way" but we gauge tack [~how the white adheres to iteslf VS how it adheres to something else] every day on press. Ink which has excessive tack won't bridge or matte-down easily, it requires a lot of squeegee angle and / or pressure, doesn't clear the mesh well and tends to leave a rough surface. Shear thinning is a ratio of two viscosities [~the friction between two fluid layers of ink]; flooded viscosity and transferring viscosity. We want the tack ratio to be low as possible and to a limit we want the shear-thinnning ratio to be as high as possible.
So share thinning, is how easily the ink inside the mesh funnel, separates from the top layer of itself, as the squeegee's edge passes over the mesh opening? If this is interpreted this way, if the ink tack ratio is low, one of the attributes of the ink would be that the shear-thinning ratio would be (on the positive side of things) high? So one measurement does not work independently of the other- right? Like you said a high tack ink won't separate from itself well.
And what causes the ink to be high tack in the first place?
Your conclusion is absolutely correct! The “splitting” you refer to is a result of several interrelated factors; 1) the lower limit or “plastic viscosity” of the shear-thinning in [how thin does it get when placed under a shearing force] 2) the tack level at that lower viscosity limit 3) the [fluid] pressure differential created by the blade and 4) the fluid momentum of the ink as it leaves the blade to enter the cells of the mesh.
The relationship between shear-thinning and tack is not conspicuous on press. However an ink that is not highly shear-thinning and / or high tack will not clear or clean at elevated print stroke speeds. We use a calibrated test image on press to gauge the speed limit, in the lab it is easier to isolate the two attributes of a white ink.
We use different pieces of equipment to analyze the shear-thinning nature of an ink independent of its tack level. The goal is to offer an ink which responds favorably to both low and high shear forces [specifically shear-stress which is perpendicular to the screen and shear-rate which is parallel to the screen]. The target is to achieve the widest latitude possible so the product works under the widest range of conditions—highly shear-thinning AND low tack. In practice, press one to press two, side one to side two, first shift to second shift ETC.
The “speed limit” is a result of the transfer-rate of the mesh divided by the tack level of the ink multiplied by the [fluid] pressure differential caused by the blade. So a shear-thinning ink will offer the widest latitude but if the mesh and blade don’t restrict it too much it will allow printing at top speed with superior bridging and matte-down. This is how Alan802 can run at 30”/second [as fast as his press will stroke] with merely 18 PSI of pressure on the blade and get exceptional matte-down at top speed.
As for “why is it tacky” Colin is correct. When the two primary ingredients of an ink are intermixed the liquid phase has an affinity for and will alter the solid phase. The moment this happens “tack” occurs as a result. We screen-printers need tack for one reason; if there was no tack the phases would separate during the press run. Any more tack than this requisite level only gets in the way of transfer and quality. With white ink there are some formulators who build tack into the ink to keep it from penetrating the garment, their ink tends to be high viscosity AND high tack requiring a lot of blade “pressure” [downward force]. Others take the same approach to stop penetration but then the set up a delicate structure in the ink which is subject to “thinning out” during a longer press run which incorporates flashing. There are others who try not to build tack into the mix and rely on shear-thinning properties to avoid penetration.
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Tony;
I'm not surprised at all by that. I know I've seen some crazy stuff in my earlier years working for people (Flat Stock and graphic printers are the worse). Also, bet that people in this country are oblivious to how some of their kids apparel is produced and more than likely paid double for it.
Joe;
I'm bowing through your ink like crazy so I hope your making a crap ton if that stuff cause I'm averaging a gallon to two gallons a day of that stuff (Good Ink)
Thanks for the kind words but there is nothing like printing more shirts Ross!
I am looking for another application for your skills. Ross have you noticed those white lines on the streets in Newton Falls? Must be miles of them...let's talk next week? Meanwhile we're in good shape on inventory; Colleen is becoming a real master at throwing those 40 pound bags of resin around the plant! Her birthday isn't until January but I have promised to get her a forklift.
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Excellent talk soon
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Got a backdoor request for clarification last night about warming the ink.
When an ink sits motionless for an extended perior of time, its components form temporary bonds. The goal of stirring the ink is to break-up these bonds, not to heat the ink. In the process of breaking these bonds we will see a slight reduction in viscosity but as stated above, stirring to reduce "tack" is a fools errand. To attempt to reduce tack with stirring would overheat the product and ruin it.
Overheating whether from excessive stirring, flash units or pre-warming the ink causes the plasticizer to thin at about 115F. At this point the free plasticizer begins to flux the resin and the resin absorbs more of the free-plasticizer. For a short time the ink will become more fluid and flow more readily but then as it cools it will finish with a higher tack than it started with due to the reduction in free plasticizer.
Case in point, like a rookie I unwittingly left a fiver of white in the trunk overnight prior to a call at first light, it was 25F. I pulled the five from the trunk, walked to the press, dumped some ink in the 156/64 and with a flood and a single print stroke with a 60/90/60 blade at 1/2 maximum speed, the white cleared the dry screen and looked pretty darn good. On the third pass ONCE WE HAD BROKEN THE TEMPORARY BONDS the print looked pristine because it was a low tack white. At which point we increased the stroke speed.
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I will say that with a little adjustment this ink will print any parameters you wish. Fast. Slow. Middle. This ink would run great with an IR flash as the true flash temp is very low for what has the appearance of what in the old days, would be a finish white. There was a time when we had flash whites and finish whites. The flash white flashed at a low temp and the finish white looked white. A low flash temp helps keep following colors from "gelling" which causes bad wow printing. All inks have a flash temp. The object is to not reach the flash temps of colors but dry the underlay. Joe's white also feels correct when flashed. A flashed white should feel like paper and not be sticky or tacky.