Starlight 3140 LED - Issues with Breakdown

[ben]

We have a Starlight and we use Murakami T9 emulsion with either Murakami MS hardener for jobs of 150-299 pcs or Murakami A&B hardener for anything over 300 pcs. On top of that, we post-harden the squeegee side too. The hardeners + post-hardening gets us by, but I'm in the camp of firmly believing that they're band-aids. I only take those measures because, before I got to this shop, there were constant issues with breakdown, even under 150 pcs.

This exposure unit isn't even fully exposing a 156Y coated 2:1 dull at 30 seconds. I even exposed it for 120 seconds just as a test and saw little to no difference. Regardless, if we don't use hardener, we see breakdown on press. I don't know if anyone else does this, but a test I've used in the past is to rub the white sleeve of a shirt against the squeegee side directly after the screen is developed. If I see emulsion coming off on the fabric, I know the emulsion wasn't exposed fully.

I know I coat slower than most (about 7-10 seconds per coat) to get a high EOM because I hate double-stroking jobs. I don't have an EOM meter, unfortunately, but I coat consistently and it has been working enough to get us by.

Anyway, I'm starting to hate the Starlight because it just doesn't seem to have the multi-spectral wavelengths necessary to fully "bake the cake" as Lon Winters says. I know Murakami specifically changed the color of T9 a few months back to allow it to work with LED units better. It didn't seem to change anything for us though. I called Murakami and was blown away that they told me my EOM is probably too high. In my experience with them, they've always pushed a high EOM ratio.

I'm debating buying different LED's, Jerry-rigging them to the bed of current LED's and doing some R&D to see if it changes anything.

Sorry for the novel. I'm just at wit's end trying to improve this set up. Any help is appreciated.

[kingscreen]

We use our Starlight everyday for discharge screens without issue.  Post exposed.  Hardener only on runs above 250.
Saati Textil PHU; 1/1 with a ProCoat.   I'd put my bet on the emulsion and not the Starlight.

[ben]

We've used Saati's PHU2, CCI's WR14, Murakami's Aquasol HVP, and have settled on T9 because it worked the best. I'd still like to find a solution so we don't have to use a hardener whatsoever though.

[ABuffington]

Hello,  Al here from Murakami,

Ok, lets check a few things here to help you out.

1. Coating:  Switch to 1:1 sharp edge coating, 1:2 sharp edge at the most.  1:1 sharp coating yields a 12% EOM in my tests on a 180/54 mesh and similar mesh. Speed, angle and mesh count all play a roll in the EOM you will achieve.  1:1 coating on an M&R uni-coater yields about 6%, 1:2 10%., but this is on mesh above 125 tpi and will vary depending on mesh count and thread type.  S mesh coats thicker, HD mesh coats thinner.

2. Drying the screen - humidity controlled rooms are more predictable.  35% at 80 degrees F yields great results.  If you don not have a dehumidifier dry overnight with a fan that is off the floor to circulate air.  If you are in a very humid area a dehumidifier in the screen storage area can help create dry screens that expose easier.  Screens with excessive moisture content reduces the exposure quality.  Screens are like sponges, they absorb humidity from the air, from a wash out sink, reclaimed screens, or lots of coated screens.  Humidity lowers the durability of an emulsion.  Dry screens in a room at 35% humidity work well.  It's what you can't see that matters in screen making.  Dry to they touch is a common issue.  Give the screen time to dry in the correct environment.  Separate water sources like sinks and reclaimed screens from your coating drying area for easier control.  Use a door or plastic vapor barrier strips to keep moisture out of the storage area.

3. Bake the Cake, a phrase Lon and I both use to obtain max exposure times. Discharge screens need all the light energy they can take up to over exposure.  An image is not an indicator that you are exposing it well.  Use an exposure calculator to obtain good emulsion exposure where the emulsion is cured on the inside of the screen during image wash out.  If you are after good halftones then use an appropriate mesh count to obtain all tonal values  The inside of the best panel should show no emulsion color, sharp straight edges, and good halftones on higher mesh counts.  IF you underexpose to see easy washout your screen will break down.  Use a pressure washer for development. Under exposure is like undercooked bread, gooey on the inside and not fully baked.  When well exposed it will take pressure washer development to get out all details and fine openings.  If you do not have an exposure calculator then do a step test: http://murakamiscreen.com/step-test-to-determine-proper-exposure-times/ download entire article for graphics showing how to do it.  (Use ten seconds for the individual panel time in the step test for LED light)

4. Dry well afterward in a hot box or drying cabinet.  If not available use a space heater behind the fan and dry completely.  Post expose on the starlight when dry at 2x the exposure time.  In the south and southwest you can use the sun, but in the north the UV of the sun is pretty weak in winter, so dry well and post expose on the starlight.

5. The basic recipe is:  1:1 sharp coat, dry well, expose completely, dry well and you can achieve durable screens.

6. Post exposure does help increase strength, but should be used only on well exposed screens.  Post exposing an underexposed screen won't reach the durability of a well exposed screen with post exposure. 

T9 was formulated to work well with LED and the Starlight is a good LED unit in our tests.  Just need a thinner coat, good drying process and full exposure.

PM me or call if you still have issues
Alan 323.697.4334

[ZooCity]

140-160s here for our Starlight to expose a 150/48 and hit a solid 6-7 on the stouffer strip. 

Crank the time up if you want to keep the eom you have.   If using film ensure you have very good d-min : d-max.   

Also if using film, ventilate around the Starlight.  It will get hot enough to warp the panel the leds are mounted to at this exposure length over a production day.  Ours is typically ran without glass and was at over 107˚F on the outside of the blanket in an air conditioned screen room last I put the gun on it.   The ventilation system in the unit just can't keep it cool enough for full expo on some emulsion/screen/coating combos.  M&R will warranty warped boards but, at a minimum, you will be paying shipping both ways to replace the board which will cost more than the components on that board do from the oem.

If you want to explore other LEDs you should go for it provided you have some electronics savvy.  The LEDs in the Starlight have a narrow histogram, almost all the power is in the 405nm range.  The starlight array is more/less stock uv output LEDs (quite cheap and available online) glued with no particular precision to a panel which isn't particularly flat.  So if you don't mind losing the warranty you have little to lose and could possibly upgrade things by installing a more thoughtful LED array.  Not that I'm encouraging that as a first approach to your issue. 

Another option is to switch to an emulsion that really likes 405nm. 

[Colin]

Like Chris, we use the starlight 3140.

We use the Murakami T9 - with the Diazo added.

Smart Mesh panels from sure lock on M3 frames stretched on average to 27+- newtons:
150/48
180/48
225/40
270/34
330/34

http://www.murakamiscreen.com/documents/MeshGuidefromCatalogweb.pdf

I use the monster max scoop coater.  One coat shirt side 2 on squeegee side on my 150s.  Slow scoop coats as stated above.  I will have in the neighborhood of 50% EOM.

For my 180 and above its one over one.

My exposure times on 150S mesh are between 40 and 50 seconds.  I prefer to expose on the harder/over cured side of things.  But detail resolution trumps all and I will go as low as 35.

180: 20-30 seconds.  For fine halftones 50-55 lpi I will shoot from 18-20 seconds (this is for full tonal resolution).
225: 12 seconds to hold 60 lpi 15 seconds for spot color work.
270: 8 seconds for 60 lpi
330: 6.5 seconds for 60 lpi.

We have an iImage DTS set to maximum resolution.  We keep far more detail than we ever have before with the above equipment.  As long as my screen are under 40% humidity from the beginning, I can spray out everything that the iImage gives me.

Recently we did a run of 1000 tanks, discharge.  I "overexposed" my first exposure, thoroughly dried the screen to under 40% humidity, then post exposed squeegee side for 3 minutes.  Zero breakdown.  No hardeners added.  180s mesh.

With this set up, my only real variable I have to watch out for is the moisture content of my emulsion.  If my screens are to wet - I am doomed from the beginning.

Hope this helps

[ben]

Thanks for all the input, everyone!

Al, here's what we have set up at our shop:

1. We did try coating 1:1 on any S-mesh in the past and still had similar issues. We were coating plastisol screens heavier than water-based, but the wb screens still broke down, so we just went back to coating everything the same way and adding hardener to wb screens. Granted, those test were done on low-tension (18n or less) 156-64, 196-55, 150-48 S, 180-48 S, and 225-40 S. Screen tension is definitely an issue I've been trying to get in order from the day I started here, but it's an ongoing process. We have to use 50+ PSI for most jobs on our Diamondback S to get our screens to clear. Obviously, this plays a part in breakdown as well, but I've been trying to increase EOM so we can get a larger deposit with a single stroke. Regardless, we have some new s-threads on the way so I'll give those a shot when they come in.

2. We have a Vastex drying cabinet that usually sits around <30% humidity and 90 degrees F. We also have a homemade drying rack, which I have set to about the same settings. I'll see about bringing that temp down to 80F though. Our darkroom is usually at about 50%+ humidity and 70 degrees F so I try to keep all our screens in the drying cabinets for at least 2 hours to dry (sometimes overnight if I have the time) and I always put them in there for 15 minutes prior to exposing.

3. We used CCI's exposure calculator and I thought I had it as dialed in as it could be, but clearly something was wrong in that process. I just downloaded the step test article, so I will give that a shot as well.

4. We always completely dry the screens before we post expose. I'll make sure this process keeps up.

Thanks again for all the help. I will try these new steps and see if we can achieve a better screen.

It's also good to know that you guys have had success with a Starlight and T9 without using hardener.

Colin, I will use your exposure times as a reference point.

ZooCity, thanks for the tip on cooling the exposure unit! How exactly do you operate the exposure unit without the glass? Do you have a Tri-loc set up in the exposure unit?

Thanks again, everybody! 

[ABuffington]

T9 can be dried at 104 degrees, if you add diazo then 80 degrees helps preserve the diazo sensitivity.  Diazo is not needed, but it will increase already good resolution and make wash out of 5-20% dots easier.  Push the exposure upwards.  The step test should show you what exposure your films are capable of.  Good solid black imagery allows for longer exposures.  It's not how fast we expose, but how well we expose the emulsion to achieve durability.  Resolution of details can be had with full exposure with good black film imagery.  You should have difficulty seeing through a 3x3 square of black ink.  If it is very transparent the exposure light will get through as well.  Power washer spray is recommended for pure photopolymers at full exposure.

Al

[ben]

Perfect. We're not currently adding diazo and I don't want to necessarily add another variable to the equation just yet, but it's good to know we can. We do a decent amount of sim process, stochastic, and 4CP so that may come in handy.

We have good films. We use CCI's Max Blackout ink and run all our seps through FilmMaker v4, so we definitely have the dmax opacity and we have dot linearization going on too. I'm in the midst of the step test now, so I will report back here with my findings. Thanks again!

[ZooCity]

We are CTS, except for right now.  Right now we're film so the glass is back on. 

[ben]

Ah, that makes sense. Thanks, ZooCity!