Dot gain for hybrid inks

[Non-periodic]

We have a press machine using hybrid UV varnishing technology with hybrid ink. We measured a test print calculating the correct dot gain values but we always get false values. At first we measured the Lab values of each ink and determined the Density. When we use the measured Dot gain curve and make print the Black and Magenta were poor and the Yellow was very much.

We used SpectroEye Bestmach finding the best Lab values and measuring the dot gain, and tried to use Lindbloom's Dotgain from Lab spreadsheet but these methods produce approx. the same wrong dot gain values.

 

[meddington]

We have a press machine using hybrid UV varnishing technology with hybrid ink. We measured a test print calculating the correct dot gain values but we always get false values.

Can you explain what you mean by "false values"?

What are your target dot gain values, and how do these compare with the values your getting?

Calculating dot gain from lab values can result in similar or identical values to that calculated from density, but this is not always the case. Depends on the ink set and sometimes corrective formulae are needed.

 

[gordo]

What are your target dot gain values, and how do these compare with the values your getting?

Just adding to meddington's post: Was this a dedicated test pressrun? Could you post a low resolution picture of the test form? Also, for the purposes of building curves - dot gain is not important. The current response and target values are the important numbers. Could you post the target values you are wanting to hit, as well as the current values you are currently getting?
Also, are you able to use a densitometer to gather the data rather than work with CIEL*a*b* values? If so, could you provide that data?

best, gordon p

my print blog here: Quality In Print

 

[Non-periodic]

Can you explain what you mean by "false values"?

What are your target dot gain values, and how do these compare with the values your getting?

Calculating dot gain from lab values can result in similar or identical values to that calculated from density, but this is not always the case. Depends on the ink set and sometimes corrective formulae are needed.

Our target values are the ISO 12647-2 standard values found in X-Rite Profile Maker because we use 175 lpi and I didn't find the standard values for this screen frequency nor in the ISO standard neither in BVDM website (MedienStandard Druck 2008).

We use Huber hybrid ink. The "false values" mean there will be always an elbow in the dot gain curve and the printed material will poor and must increase the density matching to the proof. The proof machine well calibrated Efi XF with Epson printer.

As I know the formulae in Bruce Lindbloom' spreadsheet use reflectance instead of density and Murray-Davies equation.

 

[Non-periodic]

Could you post the target values you are wanting to hit, as well as the current values you are currently getting?
Also, are you able to use a densitometer to gather the data rather than work with CIEL*a*b* values? If so, could you provide that data?

my print blog here: Quality In Print

I will post the current values on Monday morning and yes we are able to use densitometer. To tell the truth we measured with X-rite SepctroEye' Densitometric functions and the result was the same.

 

[dimitri]

There are many factors that can cause dot gain to vary on press. Do you 'cure' each hybrid ink?
I do not know if that is the case with you, but turning interdeck UV lights on or off has a significant impact on dot gain (plus-minus 5%, maybe more). Also, do you measure the values wet or dry? Hybrid inks will have some dryback.
If by an 'elbow' you mean some uneveness, then something is wrong, either mechanical on the press (check your packing and ink-water balance to begin with...) or with the way you are taking the measurements. Such 'uneveness' would appear either with densitometric or LAB gathered dot gain readings.