plate readings and tolerances

[Whitaker]

Hello everyone,

My question is: What are your tolerances for plate readings?

We output a step wedge on all plates and measure every plate, charting the readings for reference. We have a Fuji Saber using the new LP-NV2 plates. Obviously some jobs are more critical than others, so we aren't critical on type only jobs or spot color jobs, but process jobs and repeat jobs we watch and keep within tolerance.

Here is what is on our step wedge and our tolerances.
2% +- .5%
5% +- 1%
10% +- 1%
20% +- 1.5%
30% +- 1.5%
40% +- 2%
50% +- 2%
60% +- 2%
70% +- 2%
80% +- 2%
90% +- 1.5%
95% +- 1%
97% +- 1%

With the violet plates they seem to be consistent for a while then all of a sudden there is a shift. It could be chemistry, although we change the chemistry about every 300 plate, or it could be something else like humidity.

Let me know what you think is acceptable.

Thanks!

Mike

[disbellj]

We have a reflective densitometer with plate reading add-on, and we calibrate each time we use it. Our tolerance is +/- 2. We haven't had a problem with this setup for the years we've been using it, but we don't print to GRACoL2006_Coated1 yet, so I don't know if it would be affected by this tolerance or if we'd need a tighter tolerance then.

Don

[gordo]

Mike, what halftone screen ruling are you using? (the finer the screen the greater the potential variation)

thx, gordo

[Jan Verdonck]

Normrally I Think there exist a Fogra tolerance of +- 1,5% on each patch and a difference of 1% on the same value over the whole plate.

I can suggest to use a special platereader as the x-rite IC plate 2, to become reliable results.

[Whitaker]

We are using 175 line screen, and we are using the Xrite CCdot plate scanner to check the step wedge.

[pmhapp]

Fuji LHPJ plates.
IC Plate II plate reader.
+/- 1% almost every time.

[Whitaker]

Is the Fuji LHPJ plate a thermal plate? We're using the Fuji Saber which is not. Would a thermal device would be more stable?

Fuji is talking about a processor-less violet plate coming out toward the end of next year, but who knows if that will be more stable.

[rich apollo]

> {quote:title=Whitaker wrote:}{quote}
> Here is what is on our step wedge and our tolerances.
> 2% +- .5%
> 5% +- 1%
> 10% +- 1%
> 20% +- 1.5%
> 30% +- 1.5%
> 40% +- 2%
> 50% +- 2%
> 60% +- 2%
> 70% +- 2%
> 80% +- 2%
> 90% +- 1.5%
> 95% +- 1%
> 97% +- 1%


Wow! I wouldn't have thought that the reader could be demonstrated to be that repeatable.

rich

[David Watson]

I was hoping that the LP-NV2 plates would be more stable. We have been using LP-NV Plates for about 4 years, but I am expecting LP-NV2 to be here next week.

I have battled the dot shift problem since the Saber was first installed. We run 900-1500 plates between chemistry changes (4 to 6 weeks). We use a Beta Ultra Dottie 2 plate reader, which is very repeatable. There is ABSOLUTELY a dot shift that occurs, but after all this time I still can't pinpoint exactly why. We keep our Saber and processor very well maintained. I can produce the same dot shift at 150 LPI, 175 LPI, and 200 LPI (200 is our standard). I read the 1%, 2%, and 50% on every black plate (45 degree angle). I monitor temperature, pH, humidity, plate lot numbers, emulsion numbers, etc.

The dot shift we see here is across the whole scale almost like an exposure issue. The 1% dot sometimes disappears, (which is not too surprising), but sometimes it will be holding steady between 0.5% and 1.5% for a week or two or three, and then all of the sudden the 1% reads 2.5 or 3%. The rest of the scale follows (50% which is normally reading 56% with my plate curve applied is reading 58%)

I could explain this away if the lot number changed, or we did a chem change, or changed the scrub rollers or whatever. But more times than not, this will happen without much warning in a batch of plates with the same lot number that has been running perfectly for some time. Sometimes a new box of plates will be different, sometimes not. Sometimes the top 2 or 3 plates in a box will be different than the rest, sometimes not. It is very unpredictable, and very frustrating. Sometimes I will re-linearize to fix the issue only to have to re-linearize again in a few days when the dots mysteriously change back.

A couple of theories I have:

There is a neutral density filter wheel in the Saber that can get loose and shift, although I ask the tech to make sure it is ok at every PM call.
Transportation- I think temperature during shipping may have something to do with it.
Plate age- Plates that are too new seem to be more prone to shifting.
Developer Temperature fluctuations

Anybody else willing to speculate??

Dave Watson
Edwards Printing Co.

www.edwardsprinting.com

[jlind]

Dave:
Very impressive, all the care you have taken in studying the variations. I would suggest two possibilities, without much or any proof. Plate readings change with color, so there might be slight variations in the color of the emulsion. Another possibility is a change, even within a lot, of emulsion thickness. These emulsions are a couple of microns thick applied across a wide web of aluminum at fast pace, on a grain that also has some variation. I think the source of your variation can be found in these factors that are process variation, outside your control.
Just a thought.
John Lind
Cranberry Township, PA
724-776-4718