Speaking of Underexposure

[DouglasGrigar]

Indy, talked to Richard, have a 21 and will start testing and comparing with the KIWO exposure calculator and will report the results when I have time to go over this (possibly the next class).

Part of our problem could very well be the issue with some (not-so) professional “screen printing experts” who are clearly giving out erroneous information (a testament to doing something for 50 plus years wrong continues to be wrong each and every year and never improves). We have some real drama queens and parasites in this industry.

In a sea of ignorance the island of simple competence is a glowing oasis.

I hope your statements here coming right after my post are a coincidence and not directed my way...

 

Goodness no...

If I lay into someone I will do it directly - you will find that I don’t often lay into someone - actually I almost never. I prefer to have a conversation where both the other person and myself learn something.

I was more explaining how Richard and I were having a short conversation about how the 21 is promoted and is far too often abused and misused. This misuse is promoted and I abandoned the 21 because the directions given by some are very, very, wrong. I have a problem supporting anything that causes problems for the process for others.

Now with Richards updated information I will progress with this and see if we can make things better for others in the industry - simple, yes?

It may well work out that the use of the scale and the exposure calculator both in conjunction my end up as my position - we will see.

[DouglasGrigar]

Doug I have been messing with the TLX emulsion I got. I printed out my own eight step step wedge test for it, I wanted to use a step wedge test from my own printer to get more accurate results with my own printer. The problem I am having even after the step test I cannot get a full exposure no matter what time I advance to, remember I am only using a UV exposure unit. Tho i cannot get a full exposure I still get good actually very good stencils all be it it takes twenty minutes, even tho the stencils are coming out really nice I have to fight the scumming and poor wash out. I am going to retire the emulsion because i am convinced its not viable with a UV light source. Hope fully soon we will have a new MH unit in its place?

When you say UV light source, exactly what unit are we talking about?

What emulsion are you using as your “comparison” to this one?

Humidity?

Are you sure the tub of TLX you received was in date and had a good bottle of diazo?

The biggest problem with any emulsion is the fact that we are dealing with multiple variables and they are all intertwined, identifying the exact problems can get tricky over the phone or internet.

[DouglasGrigar]

Doug, did you say that yer using clear film on an Epson?  If so I really, really want to know how to set this up!

I just use one of the inexpensive clear films and converted my Epson to the “hybrid” inks. Just the other day I had a student switch from his standard Epson ink to this ink and his problems with burn in exposure disappeared.

While underexposure is without a doubt the most widespread and common problem out in the wild, I would say poor quality positives are in the top 5 most common frustrating problems.

Poor positive v. good quality positive is like night and day.

[bimmridder]

Off subject, but Doug, it was nice to meet you. I wish I would have had more time to talk. Vendors think the shows are too long, and the attendees think they're too short!

[ZooCity]

Doug, did you say that yer using clear film on an Epson?  If so I really, really want to know how to set this up!

I just use one of the inexpensive clear films and converted my Epson to the “hybrid” inks. Just the other day I had a student switch from his standard Epson ink to this ink and his problems with burn in exposure disappeared.

While underexposure is without a doubt the most widespread and common problem out in the wild, I would say poor quality positives are in the top 5 most common frustrating problems.

Poor positive v. good quality positive is like night and day.

Details man, details.  What do you mean by a "hybrid" ink, a pigment/dye combo?  I would love to go back to using a truly clear positive film.  These days it's really all close to the same cost, regular v. "wp" but for me it's all about decreasing the light scatter/blocking. 

[Frog]

Perhaps something like this? http://store.inkjetcarts.us/screen-positive-black-hybrid-ink-p4487.aspx

[DouglasGrigar]

Perhaps something like this? http://store.inkjetcarts.us/screen-positive-black-hybrid-ink-p4487.aspx

That is the one...

[DouglasGrigar]

Off subject, but Doug, it was nice to meet you. I wish I would have had more time to talk. Vendors think the shows are too long, and the attendees think they're too short!

Too bad the show got hectic.

Next time we can get together board members for each show for dinner or something.

[ZooCity]

Thanks Doug and thank you Sir Frog for the link.  Nice price on that stuff too.  I think I'm going to start up a new thread about high-line count film positives and contemplate having the time to switch inks and films and do all that fun, aforementioned stuff again. 

[alan802]

I have always known underexposure was very widespread among screen printers but we've never had an issue with it.  I'm not saying we never underexpose, I'm just saying that it's never been one of those variables that has given us problems.  We have used several different types of "exposure calculators" when an emulsion rep would come in and we were trying out a new emulsion, but I've never used one other than those very rare occasions, 3-4 times in 5+ years.  We've never had emulsion locked in a screen during reclaim or any of the other problems that underexposure causes.  I'm sure if we looked at every stencil through a loupe, we would find areas that needed improvement, but out of all the issues we've faced over the years, this hasn't been one that we have dealt with for whatever reason.  We have a seriously badass exposure unit, 10K metal halide so maybe that's one reason it's not an issue for us, or maybe it's something else, but I'm sure it's mostly due to us never having used an inferior light source.  We have had our share of other shops come by and let me burn a tough stencil for them, several dozen times over the past few years but I don't think it's our knowledge of the stencil making process that is superior, I think it's our light source.

[ZooCity]

That is a one bad-ass light source Alan.  10k?  Sounds glorious. 

[DouglasGrigar]

I have always known underexposure was very widespread among screen printers but we've never had an issue with it.  I'm not saying we never underexpose, I'm just saying that it's never been one of those variables that has given us problems.

...I think it's our light source.

No problems with exposure would make you 1 out of 100 shops and I think Richard would back me up on that - for you this is a good thing.

It could be your exposure light, but I have seen problems with big units in shops also - the problem is not exactly the unit used but the lack of information that person may have.

[inkman996]

Sorry Doug I was vague.

We use a Vastex Exposit, i have used it for almost 15 years now and consider my self quite adept at making quality screens from a low end light source.

Normally I am using QLT, with 4 minute average exposure time with very little room for error. The TLX seems like I could expose it for ever and still have a non fully developed screen. Again i blame that on the light source it is just not a good mix of tools. Fortunately I only mixed half the other half should be fine to use again after we get a new exposure unit.

[alan802]

That is a one bad-ass light source Alan.  10k?  Sounds glorious. 

It is glorious, and it's one of those things that I don't appreciate like I should because it's all I've ever known.  I've never had to expose a screen with anything else.  We did jump from a 5K bulb to a 10K a few years ago, but that's the extent of my exposure unit experience.  I know there are lot's of cheaper alternatives for exposure that will produce satisfactory results but I think the $2500 we paid for our unit was worth every penny.  I know from reading the forums for so many years that the light source is usually one of those tools that is somewhat skimped out on.  The shop with the single point metal halide is probably in the minority by a long shot.  I can see how lot's of people can justify going cheap in this area because of the results you can get with some flouro bulbs or halogen work light but I love our unit and I don't think we could ever go backwards or down in our light source.  I can't say for sure since I've never used anything else, but never having to worry about some of the things that are very common problems at other shops is a nice thing, especially when it comes to exposing our screens.  We use a pure photopolymer emulsion and coat heavy for our lower mesh screens and our exposure times are very fast, under a minute for most everything.  305's with a 10% EOM will expose in around 15 seconds with a new bulb.  Our unit also has a light integrator so we use light units instead of time so I can't say exactly what our exposure times are.

[DouglasGrigar]

Sorry Doug I was vague.

We use a Vastex Exposit, i have used it for almost 15 years now and consider my self quite adept at making quality screens from a low end light source.

Normally I am using QLT, with 4 minute average exposure time with very little room for error. The TLX seems like I could expose it for ever and still have a non fully developed screen. Again i blame that on the light source it is just not a good mix of tools. Fortunately I only mixed half the other half should be fine to use again after we get a new exposure unit.

With some additional information...

When was the last time you changed the unfiltered UV bulbs? (they should be the unfiltered BL bulbs). They will put out light in a rather consistent way, but the output drops enough at 700 hours (or less) they should be changed once a year in the average small shop.

With any FL tube unfiltered UV bulb exposure unit with the correct glass to bulb setup I would expect about 15 to 21 min of exposure with TLX and 21-28 with darker dual cure emulsions. This is tested with an exposure calculator for a full and complete exposure (no change) and sounds excessive - well it is the nature of the beast - you want a full and complete exposure it takes time with the low power units.

I would wager that your QLT would show underexposure and that type of unit when tested for a complete full total exposure with an exposure calculator - this btw would be using the “glisten or shine” method of coating screens (high EOM).

It is news that is distressing to many because often they are told that your emulsion will expose in less than 2 min. on units like that - it will not give test results that match even close to that...