Let's talk thixotropic

[Printficient]

Being one of the main characteristics of ink I think that a lack of understanding what it is and what it has to do with that crappy print that we all have had (me excluded of course  ) It would be beneficial to know some generalities.  So how about some input from the ink gurus that are out there.

[mooseman]

An ink discussion dealing with thixotropic properties is only half the story without also addressing shear-thinning.
why not  show us the product you have in mind  then explain why it is better / different that other ink products.
mooseman

[Joe Clarke]

Being one of the main characteristics of ink I think that a lack of understanding what it is and what it has to do with that crappy print that we all have had (me excluded of course  ) It would be beneficial to know some generalities.  So how about some input from the ink gurus that are out there.

.

Mooseman makes a good point, a preface on the basics of shear-thinning will help simply a discussion on Thixotropic. I am going there now and will return, probably this evening.

[pwalsh]

Being one of the main characteristics of ink I think that a lack of understanding what it is and what it has to do with that crappy print that we all have had (me excluded of course  ) It would be beneficial to know some generalities.  So how about some input from the ink gurus that are out there.

Sonny, I'm about as far away from being an Ink Guru as there is, but here's my take on Thixotropic Inks.  When it comes to screen inks this property refers to an inks ability to reduce viscosity under shear, to promote flow though the screen mesh to affect a transfer at the substrate interface. A highly desirable quality of the ink is that it will immediately body-up after transfer from the screen to the garment to avoid wicking and dot gain.

An example of how this property can impact screen-printing is when a screen-printer is trying to get a good first down white, the most popular "fixes" are to grab a softer squeegee, increase squeegee angle and/or pressure, select a more open mesh, or to slow down the squeegee stroke. The unfortunate fact is that almost all of these fixes ignore or are working directly against the thixotopic properties of the ink. 

In many case the best print results are obtained with a more vertical squeegee blade, with a lower pressure, operating at a much faster squeegee stroke speed.  At the risk of attracting a real guru I'd suggest watching this video on Joe Clarke's Smilin' Jack Squeegee  https://youtu.be/lDLA-kk42vQ

[starchild]

Being one of the main characteristics of ink I think that a lack of understanding what it is and what it has to do with that crappy print that we all have had (me excluded of course  ) It would be beneficial to know some generalities.  So how about some input from the ink gurus that are out there.

Sonny, I'm about as far away from being an Ink Guru as there is, but here's my take on Thixotropic Inks.  When it comes to screen inks this property refers to an inks ability to reduce viscosity under shear, to promote flow though the screen mesh to affect a transfer at the substrate interface. A highly desirable quality of the ink is that it will immediately body-up after transfer from the screen to the garment to avoid wicking and dot gain.

An example of how this property can impact screen-printing is when a screen-printer is trying to get a good first down white, the most popular "fixes" are to grab a softer squeegee, increase squeegee angle and/or pressure, select a more open mesh, or to slow down the squeegee stroke. The unfortunate fact is that almost all of these fixes ignore or are working directly against the thixotopic properties of the ink. 

In many case the best print results are obtained with a more vertical squeegee blade, with a lower pressure, operating at a much faster squeegee stroke speed.  At the risk of attracting a real guru I'd suggest watching this video on Joe Clarke's Smilin' Jack Squeegee  https://youtu.be/lDLA-kk42vQ

What is needed is a comprehensive understanding of an link's rheological properties in order to truly troubleshoot that part of the ink.. You want an ink to move easily when a minimum force is applied, thin enough to transfer through the mesh opening and regain it's body to hold the image shape when it touches the substrate and also stay put.. All these wants and needs have named measurable attributes (properties can contain attributes) I've mentioned the yield stress, plastic viscosity, shortness ratio and surface tension although surface tension- wet and critical surface tension- dry is more a thermal property..

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[tonypep]

This is all new to me

[starchild]

This is all new to me

I think in the early years of this community you were doing right by us- Then your company decided to be party poop'rs.. There's a lot we can learn from you but can't.. I personaly enjoyed your retail line tidbits

[tonypep]

Well you can really blame "The One Who Shall Not Be Named" on that. Had one of his then cronies drop an anonymous letter. Seriously though all that stuff is not new to me. More than a decade ago I decided to steer away from plastisol almost completely so its more like an "Oh yeah forgot about" that thing. The discharge pioneering has driven and grown our business tremendously. Of course its not for everyone and we like it that way. Can't blame the company for keeping things close to the vest.
Back on topic.............Joe? 

[Joe Clarke]

An ink discussion dealing with thixotropic properties is only half the story without also addressing shear-thinning.
why not  show us the product you have in mind  then explain why it is better / different that other ink products.
mooseman

Agreed Mooseman.
I will restrict my comments to white inks.

"Shear thinning" is a catch-all phrase for the nature of how the white ink flows on and through the screen mesh but specifically if said ink is placed under a "shearing force". "Shearing" is a DIRECTION of the applied force and there are three types of shearing force; shear-stress which is perpendicular to the mesh, shear-rate which is parallel to the mesh and some combination of shear-stress & shear-rate.

Textbook shear-stress [perpendicular] is the traditional method of T-Shirt ink transfer which involves; a white ink which is not shear-thinning or barely shear-thinning intended to keep it from penetrating the garment, a minimum of FLUID pressure, a mesh with a low transfer rate, an excessive EOM [based on the fabric thickness], tons of blade angle, even more blade pressure, aluminum winged flood-bar and a very slow stroke speed. This rig "squeezees" and does NOT cause the ink to thin during transfer, as a result, bridging and mattedown are difficult to achieve, the white tends to require post-flash smoothing and sometimes there is a need for a double-stroke.

Textbook shear-rate [parallel to the plane of the mesh] demands a white ink which is highly shear-thinning, high viscosity in the flooded state, that thins significantly as the squeegee hits it but has low enough tack to transfer with minimum pressure at maximum speed. High speed causes the ink to thin and low squeegee pressure allows proper off-contact. Then the fluidized ink preforms the image the instant  before it transfers, this facilitates the white bridging the knit, fiber matte-down and tends to create a smooth, imprintable surface.

By their very nature, high-shear whites have a lot of latitude on-press. As Sonny stated they can print with slow, medium, fast or maximum speed. They do well with low count / thick threads or high count / thinner threads, they will forgive an excessive EOM, allow a winged flood and darn near any blade - angle & pressure, they do a good job against fibrillation and are by their nature very over-printable.

The wide latitude of a high-shear white allows us to "plug 'n play" for improved quality and increased throughput. The best environment for a high-shear white is a mesh with a high fill-rate and low capacity, constant dynamic tension irrespective of count, a minimum RzS1, EOM and RzS2 stencil, an optimal gap to allow "image pre-formation" and fill-blade and a squeegee with a dynamic edge which fits the mesh and a dynamic profile which fits the low tack level of the white ink. When we incorporate some of these conditions a high-shear white will run as fast as the press can stroke [around 40"/second at a speed of "10" for 700 to 900 shirts per hour] with minimal pressure and allow us to control our ink deposit simply by adjusting blade speed.

JC

 

[Joe Clarke]

Being one of the main characteristics of ink I think that a lack of understanding what it is and what it has to do with that crappy print that we all have had (me excluded of course  ) It would be beneficial to know some generalities.  So how about some input from the ink gurus that are out there.

Hi Sonny!

Peter's comments are spot-on and I attempeted to resond to Mooseman's post only a moment ago [you might look at it first] but if I may add just a bit of geek to Peter's guidance; the two major types of shear-thinning are psuedoplastic and thixotropic.

Psuedoplastic is better suited to a toothpaste tube wherein the "pump" is a sealed, collapsible container with a small, single point of exit for the paste. As we squeezee the tube the tacky paste thins a bit, then it exits the small opening while the squeezing continues only to return to its initial viscosity at the same rate it originally thinned. With psuedoplasticity the rate of "thinning" matches the rate of "recovery" it's memory is virtually 100% elastic.

Thixotropic is better suited for screen-printing wherein our "pump" is a completely open, fixed container with a multitude of various sized points of exit for the white ink. If we treat the transfer process like a toothpaste tube and "squeeze" [with high angle, high pressure and slow speed] it won't thin the ink much at all and we have the "typical" issues on press. But if we use high-shear [rate] and stroke faster, the ink will thin as designed, pre-form the image, whistles through the mesh, limits fibrillation and creates a smooth surface. These attributes are due to the "shortness" of thixotrpoic flow, specifically how long does the white remain thin AFTER it leaves the blade. A short ink recovers faster, a long ink recovers shorter but the rate of recovery is slower than the rate of thinning. This flow property creates the widest window of opportunity to flood, fill, clear, transfer, wet, release [the mesh] and level without penetrating the shirt. 

A psuedoplastic ink would force us to squeeze in which case DEPOSIT [fluid volume] and PRESSURE [downward force] are each two ends of a see-saw--one goes up the otehr goes down. Squeezing is what causes theinevitable lost time between 'in-register" and "ready for approval" An ink with targeted thixotropy allows printing so that DEPOSIT [fluid volume] runs a parallel path to PRESSURE [downward force] which gives us latitude on press and shortens the time-to-color.

JC

PS: It is yet to be corroberated but it has been widely rumored for years now that the Walsh Family have exchanged viscometers and high-end rheometers for Brithdays and major holidays--don't be fooled; this guy really knows his stuff!

[GaryG]

Lovin' some of that lingo!
Smiling Jack on the way. 

Been printing for a long time and going to do some
in house R&D. Fun, fun, thanks for getting me on my horse Joe!