Author Topic: The positive and exposure  (Read 4680 times)

Offline DouglasGrigar

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The positive and exposure
« on: May 27, 2011, 11:31:13 AM »
Possibly we need to make sure we are talking about the same thing.

Full and complete exposure - what is it?

(This may be the main reason for some perceived disagreement)

How does the D-min and D-max effect the screen stencil exposure?

(We of course have the new direct-on-stencil print direct without a positive)

What effects can we expect to deal with using various exposure units and how does that change your demands for a positive?

(How can or does a low-power exposure unit make additional demands on positive quality?)
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Offline yorkie

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Re: The positive and exposure
« Reply #1 on: May 27, 2011, 11:45:08 AM »
The first variable to a full exposure is the thickness of the emulsion being exposed. As i run a manual press and never come close to wearing out the emulsion, i like my emulsion as thin as possible.

I do not believe that thicker emulsion gives thicker coatings, because the squeegees i use squeeze the mesh between the squeegee and the shirt.

Multiple coats of emulsion make harms halftone clarity.


Offline tonypep

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Re: The positive and exposure
« Reply #2 on: May 27, 2011, 11:57:55 AM »
The first variable to a full exposure is the thickness of the emulsion being exposed. As i run a manual press and never come close to wearing out the emulsion, i like my emulsion as thin as possible.

I do not believe that thicker emulsion gives thicker coatings, because the squeegees i use squeeze the mesh between the squeegee and the shirt.

Multiple coats of emulsion make harms halftone clarity.
True and not true.......thick stencils will yield higher ink deposits no question (ever print high density?)
But yes thick stencils will result in increased dot gain and har the halftone clarity.
tp

Offline DouglasGrigar

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Re: The positive and exposure
« Reply #3 on: May 27, 2011, 02:05:38 PM »
Multiple coats of emulsion make harms halftone clarity.


Only to a point - as Tony pointed out - there is a point-of-no-return with EOM.

There is a point where not enough EOM harms the clear formation of a gasket for halftones.



Above is printed evidence via SEFAR who was kind enough to provide the better micro photos than I can with my microscope.

The above can be repeated, measured, and tested in any location with just about any emulsion.
When there are no standards, you must make them!

Offline DouglasGrigar

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Re: The positive and exposure
« Reply #4 on: May 27, 2011, 02:30:16 PM »
I do not believe that thicker emulsion gives thicker coatings, because the squeegees i use squeeze the mesh between the squeegee and the shirt.


True, with some additions.

We are talking about dealing with screen printing - that is flexible squeegee, flexible mesh, and flexible stencil...

Now we have the “Rope Bridge Effect (c)”



The more open the print area the more likely the squeegee is to flex down to the substrate and touch the substrate - this is why screen printing always gives us the “smile” or concave layer of ink.

Now consider adding “pillars” of emulsion - what we get with halftones and detailed patterns - now we have the second item come into play - the effects of surface tension and liquids the smaller the area of ink the more likely that this comes into play and we get “droplets” that tend to form a dot or dome shape, if the substrate is absorbent this effect will be negated to some extent particularly with water based inks on fabric less with plastisol.

Viscosity plays a part in this also - smaller dot, higher viscosity, more effect with surface tension. (We also have pressure deformation but that comes later after the transfer of ink.)

Now before I go much further with anything...

I am not attacking you or your posts - please understand this, I am simply pointing out some HS level science applied to the process of screen printing.

I LOVE to be WRONG!...     I LOVE to be WRONG!...     I LOVE to be WRONG!...     I LOVE to be WRONG!...   
I may not be from Missouri but I understand “show me” I am more than happy to be wrong and to change, the value of my material is not in the material or my connection to it but only if it is fact and is applicable - I only care about facts and application the content has to follow that, I don’t care nor do I have an interest in promoting a POV or product unless it fits.

My job is to search answers, study screen printing, fix things for clients and then show that in a form to people so that they can work more effectively and profitably in their business.

When I am wrong, that adds more information I can use to present to more screen printers and make things better for at least one more person - and when I say tears, I am dead serious about that, more than a few times I have come across tears of frustration - and I understand, I have been there myself.

I consider the bad and wrong things in my background the MOST valuable it seems that education works best and is most memorable when some pain is involved.

Where I differ from most is that I simply cannot just take information - it must be fact, it must be testable, it needs to be in a form that can be tested simply and it must be repeatable. Also stacking a test in favor of a result is without value, it may show the same answer but it also shows an agenda, my agenda is simply “the little guy” the advancement of the industry out of the stoner-hippie troglodyte stage into the light of some form of "enlightenment era” where we value facts and results and not pushing a product for profit at the expense of “the little guy.”

Who advocates for “the little guy?"
When there are no standards, you must make them!