Silly Putty, Ketchup and syrup... and how that relates to our inks.

[Dottonedan]

There are a number of things I feel I need to learn more about to better understand our printing processes.
[size=78%]Inks are one of them. To learn more, I decided to dig in a little to understand what each of these words are and how they relate to each other.[/size]
For me, I would like a visual of each and where they are (how each affect the other) in the process. At what sage, what affect the play on the outcome.




Rheology:


Shear rate:


Viscosity:      The measure of resistance or the time hit take to become more fluid like. In a nut shell, (Ketchup and Syrup both have a higher viscosity than water).


Thixotropy:

[Sbrem]

I've always been a fan of the whipped cream/syrup theory...

Steve

[tonypep]

Rheolgic, Thixoprate, and body length play into much of this. As mentioned before much has to do with both the manufacture and the practicionare. Different bases are designed to perform certain applications. And pigments can be difficult to understand.
I have seen and been in shops where the automixer was left unattened for a few hours. Guess what? Ink (plastisol) cured  in the bucket.
 Just from over mixing

[blue moon]

Thixotropy: property of inks to change viscosity as it's being sheared. Plastisol flows better as the squeegee travels over it. High thixotrpic index means the change is more drastic.

for screen printing we want inks with high index so they will flow through the mesh as we print. We also want them to be solid once they are printed so they don't spread and we also want the time to change to be short so it maintains the shape. This is all very important for printing halftones as we want the dots to stay the same size and shape as the stencil.

pierre

[blue moon]

There are a number of things I feel I need to learn more about to better understand our printing processes.
[size=78%]Inks are one of them. To learn more, I decided to dig in a little to understand what each of these words are and how they relate to each other.[/size]
For me, I would like a visual of each and where they are (how each affect the other) in the process. At what sage, what affect the play on the outcome.




Rheology:


Shear rate:


Viscosity:      The measure of resistance or the time hit take to become more fluid like. In a nut shell, (Ketchup and Syrup both have a higher viscosity than water).


Thixotropy:

Rheology is a general info on the properties of the fluid. From an article: "Rheology describes the flow properties of a fluid or a flowable substance." It is a pretty broad description of what the ink.

Shear Rate is the speed of your printing stroke. It only applies (or applies properly) if you are relatively perpendicular to the stencil and are shearing the ink. If the angle is low and you are mashing the ink through the openings you might have (theoretically) a shear rate of zero.

pierre

[tonypep]

Exactly. Yellows verses cobalt blues mostly will require different applications. They mostly will need different attention as they have different properties.

[Prince Art]

Thixotropy: property of inks to change viscosity as it's being sheared. Plastisol flows better as the squeegee travels over it. High thixotrpic index means the change is more drastic.

for screen printing we want inks with high index so they will flow through the mesh as we print. We also want them to be solid once they are printed so they don't spread and we also want the time to change to be short so it maintains the shape. This is all very important for printing halftones as we want the dots to stay the same size and shape as the stencil.

pierre

In addition to defining the concept, this post provides a succinct insight into the concerns screen printing ink has to balance. All of this makes obvious sense once considered, but I've never seen it in a simple statement like this. Very helpful - thanks!

...And now I wonder how the differences in pressure & speed available on an auto vs what's possible with manual printing might affect selection of optimal ink formulation for each process...