Low and negitive DOT gain

[REYES1377]

Looking for input on what causes very low and negitive dot gain on press. I tend to experience this quite often and can't seem to figure out how this is happening. When this dose occur I start with the basics: Blanket, packing, roller settings, fountain solution. Is it possible the plate is coming with a curve that is low? Any ino will be appreciated. Thanks!

 

[Kaoticor]

I would also check your measuring instrument. If you are reading low dot gains with a densitometer, it could be that it is out of calibration. I would check with another densitometer if you have one. Also, in answer to your question, if your plate curve is out of whack, yes, it can affect all kinds of readings.

 

[Cornishpastythighs]

Do you have targets on your plates for measuring and checking your platemaking process.I would start there first before you look at anything on the press.

 

[REYES1377]

Do you have targets on your plates for measuring and checking your platemaking process.I would start there first before you look at anything on the press.

Yes the plates are read before coming out to press. Also we have read with different devices and they all show the same reading. It isnt speciffic to one color or all the time. But often enough to be concerned.

 

[gordo]

Looking for input on what causes very low and negitive dot gain on press. I tend to experience this quite often and can't seem to figure out how this is happening. (snip)

As mentioned you start with the plate - and with the press.
Prepress should be applying a tone reproduction curve to the plate so that you get the required tone reproduction in your presswork at the solid ink density standards that you've established for the substrates that you print on.

Most shops have at least three curves sets that they use when making a plate - one for gloss coated, one for matte coated, and one for uncoated.

If your shop only uses one set of curves then your press operator may be adjusting densities to try and compensate for dot gain and match the proof. That can cause variation in your measured dot gains.
It's also possible that the curves you are using aren't appropriate for your required print characteristic or that conditions have changed since they were created.

What you need to do is have documented standards and specifications in prepress and press room. They will allow you to determine if the problem is in prepress or in the press room.

Best, gordo

 

[Bob Peterson]

Reyes1377

First, providing the plates you are receiving are indeed correct, use your loupe and take a look at the dot structure. Make sure it's a good solid dot, not mottled from poor ink/water balance, as this will also show up as low dot gain.

If the first suggestion isn't the case, have you noticed any change in the physical properties of the ink i.e (body/flow)? Do you find yourself having to more or less ink to match previously printed jobs? Have you made any changes to your fountain solution and/or alcohol substitute? Have you changed the roller and/or fountain chiller temperatures?

Any of the above will cause the ink to print too sharp. Take a look at each of these and you should be able to resolve the problem. If you want to discuss further, give me a call, you have my number.

Bob

 

[rajkengeri]

yes first check plate calibration 50-50 then Rip curve and printing

 

[Always Learning]

Hi,

Just a thoght... is your colour bar being produced linier? I'm no repro guy but I think there are options to keep it linier or apply the press curve. This may be why you are chasing your tail a little.

 

[danremaley]

Looking for input on what causes very low and negitive dot gain on press. I tend to experience this quite often and can't seem to figure out how this is happening. When this dose occur I start with the basics: Blanket, packing, roller settings, fountain solution. Is it possible the plate is coming with a curve that is low? Any ino will be appreciated. Thanks!

Some of the "new" process-less plates may have a 'sharpening' on press.
Here's a "HOT" tip - place a measurable patch in the color bar of 3% dot of Y-M-C-K. You now can 1-measure the first spot that will sharpen on the plate and 2-confirm that the plates are correct and 3-if the press is creating a 'double". Few people know that ALL separations created in photoshop have a 20% dot gain allowance, therefore printing "sharper than 20% (i.e. 16%) will result in "lighter" reproduction. A heavier dot gain, say 26% will result in a "darker" reproduction. A long time "secret" is that, at SWOP densities 1.00Y 1.40M 1.30C 1.70K the midtone dot gains create gray balance when the yello is 2% lower than Magenta and Cyan which are the same. It's a sliding scale - Y14 M&C16 Y18 M&C20 Y20 M&C22.
Dan 412.89.7643 Cell

 

[Ozkan Hangisi]

Looking for input on what causes very low and negitive dot gain on press. I tend to experience this quite often and can't seem to figure out how this is happening. When this dose occur I start with the basics: Blanket, packing, roller settings, fountain solution. Is it possible the plate is coming with a curve that is low? Any ino will be appreciated. Thanks!

Could you please give more details for better help.
Does your problem occur always ?
Does sharpening start immeditialy with print or later on ?
Does sharpening happen on same kind and brand paper or with a special brand ?
What type plate are you using ? (Positive,negative,thermal,silver,photopolymer,conv. etc..) ?
Do you check batch number when you open a new plate package ?
Does your CtP room always have stable&ideal temperature and humidity ?
Did you recently check CtP&processor conditions ? (Laser power, focus, dirt on lenses & brushes pressure, replemisment calibration, parameters like speed, temp etc..)