LED Bulbs Already Failing

[jvanick]

this is probably a better discussion for a new thread... however I think it's relevant as to how LEDs generate light.

SBQ's like wavelengths in the 385-405nm light range (most sensitive around 395nm, but due to the 'searing' vs 'roasting' argument, prefers to be 'cured' in the areas around each size).

Diazo's like wavelengths down in the 360nm range.

When you're exposing an emulsion such as a diazo which is slower anyways, with a light source that's not in the optimal range, you're looking at much longer exposure times, etc.

I have successfully developed (and do so every day) some extremely fine detail 65+lpi 3% and up with LEDs on the newer SBQs without loss of detail, and in fact would say that my SBQ screens hold better detail than our older Dual Cure emulsions.  I believe this to be more due to the fact that the light source is better suited to the SBQ emulsion wavelengths. 

[Vastex]

this is probably a better discussion for a new thread... however I think it's relevant as to how LEDs generate light.

SBQ's like wavelengths in the 385-405nm light range (most sensitive around 395nm, but due to the 'searing' vs 'roasting' argument, prefers to be 'cured' in the areas around each size).

Diazo's like wavelengths down in the 360nm range.

When you're exposing an emulsion such as a diazo which is slower anyways, with a light source that's not in the optimal range, you're looking at much longer exposure times, etc.

I have successfully developed (and do so every day) some extremely fine detail 65+lpi 3% and up with LEDs on the newer SBQs without loss of detail, and in fact would say that my SBQ screens hold better detail than our older Dual Cure emulsions.  I believe this to be more due to the fact that the light source is better suited to the SBQ emulsion wavelengths.

That is great information and we have noticed that the LED could hold detail on the SBQ that we didn't think we could hold. We are continuing to perform tests and getting some new emulsions that we haven't tried yet. Now that emulsion companies are beginning to make LED specific emulsions, we will probably notice quite a few new emulsions in the coming years. We may need to create a new thread specifically to chat about LED and what emulsions everybody is having great results or issues with.

[DouglasGrigar]

in fact would say that my SBQ screens hold better detail than our older Dual Cure emulsions.

Just to be clear we are comparing old performance with new SBQ to DC not SBQ to DC new performance tested side by side same (tested measured) new vs. new as well?

[jvanick]

in fact would say that my SBQ screens hold better detail than our older Dual Cure emulsions.

Just to be clear we are comparing old performance with new SBQ to DC not SBQ to DC new performance tested side by side same (tested measured) new vs. new as well?

Comparing properly exposed sp1400 to saati phu2 on both my starlight and saati 300w "multisource" led unit.

For reference:
160/48S 20% eom on both emulsions. Screen tension 22nm.

Both were exposed to a solid 7, both run on our i-image with the same file.

Exposed to a solid 7 on the stouffer strip.

Starlight times (no glass)
Sp1400 - 48 seconds
Phu2 - 12 seconds

Saati 300w times
sp1400 - 1 minute 50 seconds
Phu2 - 26 seconds.

The difference between the screens was very slight, up in the 90% and above (which honestly was not really printable as the dot gain fills in everything),  the dots fell off the screen on the sp1400.  Down in the 3 to 4 percent range both looked fine.

I may have some 200x microscope pics of the dots floating around, I'll see if I can dig them up.

[DouglasGrigar]

Comparing properly exposed sp1400 to saati phu2 on both my starlight and saati 300w "multisource" led unit.

Both were exposed to a solid 7, both run on our i-image with the same file.

Exposed to a solid 7 on the stouffer strip.

I was going to ask about what is “properly exposed” then I continued and did see the “solid 7” bit.

That brings up how do we know then we are being proportional with each emulsion using the “solid step” level when the “solid step” always changes from emulsion to emulsion?

[jvanick]

Comparing properly exposed sp1400 to saati phu2 on both my starlight and saati 300w "multisource" led unit.

Both were exposed to a solid 7, both run on our i-image with the same file.

Exposed to a solid 7 on the stouffer strip.

I was going to ask about what is “properly exposed” then I continued and did see the “solid 7” bit.

That brings up how do we know then we are being proportional with each emulsion using the “solid step” level when the “solid step” always changes from emulsion to emulsion?

I've been told solid 7 from both Murakami and Saati.

What do you mean regarding solid step changing?

[DouglasGrigar]

The linking of the chemicals and speed of each emulsion and reaction to exposure changes, that much is obvious, the “step/strip method” to get the same linking depth from emulsion to emulsion has to have the “step/strip method” calibrated for each emulsion.

Doing this with the strip is not the same as using an exposure calculator.

(I think I fixed it, been a while with the tags on-line).

[jvanick]

Understood.. you also have to take into stencil durability into the equation as well...

So "getting detail" at say a 4 or 5 on the strip isn't good either.

On both of the previous examples, those stencils were durable... (sp1400 moreso, but with post expose, the phu2 was just as good)

[DouglasGrigar]

Understood.. you also have to take into stencil durability into the equation as well...

So "getting detail" at say a 4 or 5 on the strip isn't good either.

On both of the previous examples, those stencils were durable... (sp1400 moreso, but with post expose, the phu2 was just as good)

The problem is we then start to compare apples to oranges, it is one of the reasons I have such a problem with the strip because it is easier to just say “hit a solid (insert a random number that will print 150 shirts without delamination) and you are good” it continues the problem of not having a standard definition of... of well anything in this industry in particular emulsion and subsequent screen exposure.

Going the route of using an exposure calculator in the same way (eliminating the issue of the subjective nature) same linking percentage to same the DC will always hold a shocking amount more high and low end resolution as the very nature of the chemicals indicate.

[jvanick]

  it continues the problem of not having a standard definition of... of well anything in this industry

1000% agree!

[DouglasGrigar]

  it continues the problem of not having a standard definition of... of well anything in this industry

1000% agree!

Try this one on for size...

A Full and Complete Exposure: Where the entire depth of the coated emulsion from face to well side is linked completely as measured with a transmission density scale (exposure calculator).

Note the word “correct” is not in there... but trying to get in a conversation with folks in this industry and have them define the terms “correct” anything (this issue in particular) is maddening.

Without the elimination of the subjective, without repeatable objective testing procedures - how can we continue?

[jvanick]

My use of the strip test had been to pressure wash from both sides... does that count for exposure calculation.

[DouglasGrigar]

My use of the strip test had been to pressure wash from both sides... does that count for exposure calculation.

If I could figure out how to use the strips as an exposure calculator and get repeatable results across all of the emulsions I would be writing an article for the magazines about how and shouting it out everywhere.

Why? because the strip is inexpensive and that would make the use of that helpful across the industry (because screen printers are a notorious bunch of superstitious cheep tight-wads).

I have not so no the strip will not be able to give you objective results in the same way a good quality exposure calculator will - I recommend the most expensive one - the one with ten steps on the large background.

[jvanick]

I have one of those...

When exposing for best resolution,  I was FAR under cured.

[DouglasGrigar]

I have one of those...

When exposing for best resolution,  I was FAR under cured.

And then delamination!

Resolution excellence is nothing if it all falls off at 10 impressions!

Mesh count and thread thickness also play a part in useable resolution, you have to have threads to hold the dots in place and the emulsion stencil has to survive the required number of impressions or... well fail and that costs money.