"He who marches out of step hears another drum." ~ Ken Kesey
Great question, however I would think a swab test although ideal would only tell you if the swabbed surface was converted. Still have to deal with the full film thickness to insure total conversion.
Quote from: GKitson on February 26, 2016, 01:33:04 PMGreat question, however I would think a swab test although ideal would only tell you if the swabbed surface was converted. Still have to deal with the full film thickness to insure total conversion.if there was such a thing, after exposure, the swab test could be done on the 'inside' of the screen.. if it passed, you'd know if the light source penetrated ALL the way through and completely cross linked the emulsion.due to the directionality of the light, the inside being cured would mean that the outside and middle would have to be as welll.
We recommend the swab test on the inside of a screen being developed. White fabric wiped on the wet area of the screen away from the image should not show emulsion color. We use high powered microscopes, even electron microscopes to see what is going on. Looking at halftones is one way to see how the exposure went, you can visibly see undercutting of overexposure or weak exposure, but the real exposure info on cross linking is molecular in nature and not visible. There are chemists who can explain how many milli joules are needed to excite a molecule of sensitizer to make a handshake, but this is all overkill IMO for the average printer. Keeping a log of every screen with all screen parameters, EOM, Tension, exposure time, etc etc is a cheap method to back track to an issue. The Stouffer scale seems to be the best tool, but as you mention Jason, it doesn't completely tell you if the exposure was complete. If it breaks down, the exposure isn't correct, but the lamp condition, light quality , drying procedure, EOM, and other variables all play a part. Documentation can reveal issues. If 2 different personnel coat and one achieves an EOM at 12% and the other is at 2% and the 2% design has tons of pinholes after 2k then a log would pinpoint the EOM as the difference and one cause of the pinholes. If EOM is the same, then set up, inks, drying, could be the issue. Al
Would it work if you slightly under exposed inorder to get more detail and then re exposed the screen to strengthen it?
Quote from: ABuffington on February 26, 2016, 02:41:05 PMWe recommend the swab test on the inside of a screen being developed. White fabric wiped on the wet area of the screen away from the image should not show emulsion color. We use high powered microscopes, even electron microscopes to see what is going on. Looking at halftones is one way to see how the exposure went, you can visibly see undercutting of overexposure or weak exposure, but the real exposure info on cross linking is molecular in nature and not visible. There are chemists who can explain how many milli joules are needed to excite a molecule of sensitizer to make a handshake, but this is all overkill IMO for the average printer. Keeping a log of every screen with all screen parameters, EOM, Tension, exposure time, etc etc is a cheap method to back track to an issue. The Stouffer scale seems to be the best tool, but as you mention Jason, it doesn't completely tell you if the exposure was complete. If it breaks down, the exposure isn't correct, but the lamp condition, light quality , drying procedure, EOM, and other variables all play a part. Documentation can reveal issues. If 2 different personnel coat and one achieves an EOM at 12% and the other is at 2% and the 2% design has tons of pinholes after 2k then a log would pinpoint the EOM as the difference and one cause of the pinholes. If EOM is the same, then set up, inks, drying, could be the issue. AlDid the swap test this morning on our 150-S mesh screens , coated with Murakami Aquasol TS sharp edge 2/1. At an exposure time of 30 seconds on our LED exposure unit we still managed to get underexposed screens. It`s really baffling to me how the exposure times with that unit can be so long and still not expose a screen proper.
To brush up on the subject of exposure and type of control tools, you can go back to this article from 1999...http://www.screenweb.com/content/calculating-a-good-dose-exposureThis is back in the day when trade mags used to feature some really technical stuff.
Quote from: Orion on February 29, 2016, 11:19:33 AMTo brush up on the subject of exposure and type of control tools, you can go back to this article from 1999...http://www.screenweb.com/content/calculating-a-good-dose-exposureThis is back in the day when trade mags used to feature some really technical stuff.awesome article... now I know what toy Danny was talking about...it's a digital radiometer (light meter) with a uv-transmissive filter...Extech LT300 Precision Digital Light Meter