Author Topic: Exposure time for Murakami SP-Pro with M&R Starlight UV LED Screen  (Read 10296 times)

Offline Rubysky

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Re: Exposure time for Murakami SP-Pro with M&R Starlight UV LED Screen
« Reply #30 on: January 26, 2017, 11:03:58 PM »
I just bought exposure calculator and it should be able to help me dial in the expose time. Product ship all the way from UK lol.

I did expose 2 screens today.

Both screens was coated 2;2

110 mesh exposed 75 sec
155 mesh exposed 75 sec

110 mesh couldn't hold fine detail. It washes out with water.
155 mesh hold detail very well. All the hair thickness detail was there.

When the screen couldn't hold detail, this is because under exposed? How do I know if I over exposed? This is really dumb question but I think a lot noob have this in their mind ><

Should I increase the exposure time to 90 sec for 110 mesh?

Thanks.



Offline Frog

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Re: Exposure time for Murakami SP-Pro with M&R Starlight UV LED Screen
« Reply #31 on: January 26, 2017, 11:20:06 PM »
I just bought exposure calculator and it should be able to help me dial in the expose time. Product ship all the way from UK lol.

I did expose 2 screens today.

Both screens was coated 2;2

110 mesh exposed 75 sec
155 mesh exposed 75 sec

110 mesh couldn't hold fine detail. It washes out with water.
155 mesh hold detail very well. All the hair thickness detail was there.

When the screen couldn't hold detail, this is because under exposed? How do I know if I over exposed? This is really dumb question but I think a lot noob have this in their mind ><

Should I increase the exposure time to 90 sec for 110 mesh?

Thanks.


Ruby, if you are experimenting while waiting for your calculator, do a damn step wedge test like I linked to way back! It's the only way to accurately determine the correct times for each of your mesh counts. Why are you resisting this standard procedure, newbie or not? Do exposures from less than 60 seconds to 120 seconds (or more).here's the link again. http://murakamiscreen.com/wp-content/uploads/2012/07/Step-Test-Instructions.pdf
You should see your underexposed areas wash out prematurely and your overexposed closing in and not washing out.
You'll probably see actual stripes showing the "steps", and you should see the sweet spot  that rinsed out fine and also held your detail. You will notice that higher mesh counts usually expose faster, and you will find that white exposes faster than the yellow and orange and other colored meshes you may come across. Make sure to document your findings carefully.

The calculator does these "steps" for you in one long exposure with different tints letting light in in the equivalent of different times.
« Last Edit: January 26, 2017, 11:24:32 PM by Frog »
That rug really tied the room together, did it not?

Offline Rubysky

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Re: Exposure time for Murakami SP-Pro with M&R Starlight UV LED Screen
« Reply #32 on: January 26, 2017, 11:54:34 PM »
I'll give it a try tomorow :)

Thanks for the link.

Offline ABuffington

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Re: Exposure time for Murakami SP-Pro with M&R Starlight UV LED Screen
« Reply #33 on: February 14, 2017, 04:53:21 PM »
Hello Rubsky and all the other great posts here.  We have been doing tests at various facilities using the Starlight or STE and here are some tips that will help>

Coating: Keep coating thin.  1:1 dull maximum, 1:2 sharp a little less emulsion, 1:1 sharp even less emulsion.  This is with an American style coater with a thick 1/8th inch edge and a thin 1/16th inch edge.  In Japan we use much sharper scoop coaters than the US so that is why they recommend more coats.  So the edge profile should be looked at when talking about the number of coats since different coaters, speed and angle can all yield very different emulsion thicknesses.
Exposure: Humidity is the main reason times from one shop to another could be different, along with different thicknesses of emulsion coated, different scoop coaters, etc.  So times can vary shop to shop.  I can shoot faster in SoCal on a hot offshore day when humidity is at 6% than I can on a rainy day with humidity at 100%.  We don't see the differences much on a Metal Halide since it has a wider latitude or window of good exposures.  But on an LED with shorter times, the window for a good strong expsosure and details can be much more narrow.  Humidity or the moisture in the air is absorbed by emulsions, like a sponge, and it affects exposure.  Also dry your screens well before exposure.  Drying overnight, or using a dehumidifier is recommmended in your screen room.  Separate the sink, reclaiming and developing from your screen storage area.  It will be hard to dial in the correct exposure if the humidity jumps up and down due to reclaiming, wet reclaimed screens, or overspray entering your screen room area.
LED vs Metal Halide this is one of user preference.  I have a new appreciation for the productivity of LED and if you don't overcoat the emulsion they work very well and have cost/production benefits. They do produce strong screens, but a pure photopolymer emulsion like HVP or Murakami T9 have an advantage with post exposure.  This really helps with discharge, water base or HSA printing to obtain a 'stronger' screen through post exposure.
Step Test, Hardness Scale, Exposure Calculator for LED the Step test is the way to go.  The 2 pieces of film used in a calculator will block a substantial amount of LED light.  My tests here in the lab gave higher exposure times than my step test.  The step test method did help get details and durability.  Using a hardness scale with the resulting times and hitting 6-7 will validate the time.

Rubsky: Use Murakami MS-Degreaser - this is our go to product for good emulsion adhesion.  If exposed well the emulsion will hold better with a good degreaser.  Dishwashing soap should be avoided due to oils in there to prevent dry hands.

Don't be surprised at the softness of the exposure on an LED. Once dried it will print plastisol fine.  For waterbase and discharge try Murakami T9.  You can post expose in sun, or on a 5k MH, or back on the LED itself for post exposure.  Post expose the squeegee side.  Pure photopolmers and LED allows for post exposure.  M&R's new Gemini LED exposure unit does exposure on one side and post exposure on both sides very efficiently.

Rubsky you mentioned SP emulsion, This is SP-1400?  I have many, many SP emulsions, please clarify.

Admiral's times of
28 seconds for 225S
40 for 150S
for SP1400 match closely to my tests here.  Note he coated 1:1 sharp.  Less coating is better for LED exposure.  If you coat more or use a thick edge your times will go up.  I would use these times on halftone work, for vector I would bump up exposure by 5-10 seconds just to cook it more. 

Bake the Cake, if you dry well, expose as much as you can while still retaining details, dry well in a hot box or the sun, you will have baked the cake and have a durable screen.

I will be presenting at Totally T-shirts in April showing how to use LED with Murakami T9 to print any ink without hardeners.  Contact SGIA for reservations.

Al





Alan Buffington
Murakami Screen USA  - Technical Support and Sales
www.murakamiscreen.com