Beyond the Densitometer

Improve Pressroom Efficiencies – Part I

While handheld densitometers have already been adopted in many flexographic pressrooms, it’s important to remember that these devices do not actually measure color and are therefore incapable of reporting the accuracy of brand or spot colors on press.  The best that desitometers can do is to measure and report the densities (ink film thickness) of solid color patches and the tone value increase (TVI) of halftone dot areas.  While these are both very important print metrics and can absolutely be used to establish some level of process control in the pressroom, the problem is that many brand customers have begun to specify color accuracy using measured CIELab values along with deltaE values as the acceptable tolerances regarding color accuracy.  Therefore, press operators armed with only densitometers cannot know if brand color specifications have been achieved or the precise color changes that are necessary to get within these specifications.  In these situations, with only with a densitometer, operators must still rely on their eyes both during make-ready to match colors and during the production run to ensure color consistency.  The danger here is longer make-ready times, color that does not ever hit the specification, and inconsistent color throughout the run which can all lead to customer rejections, job re-makes, increased waste, and, ultimately, lower profitability for the printer.  
 
So, what can a printer do to improve their efficiencies in the pressroom and reclaim their profitability?  Well, the answer is no different than how printers have increased their productivity & profitability in other parts of their workflow over the last few decades.  Simply put, packaging printers must adopt newer tools that employ the use of science & technology to remove the color “guesswork” for press operators to ensure a much more predictable, accurate, and repeatable color print manufacturing process.  This is exactly the subject of this 3-part blog series that will look at “Good”, “Better” and “Best” technology options that are being deployed today in packaging pressrooms:
    • Good: Replacing densitometers with spectrophotometers
    • Better: Adding press-side color quality software
    • Best: Automating color measurements with an inline spectrophotometer
 
This week, we look at the “Good” solution to increase color accuracy, shorten make-ready times, and allow packaging printers to reclaim their profitability.  
 
Good: Replacing Densitometers with Spectrophotometers  
Overview:  
Quite simply, densitometers do not measure color and are incapable of reporting a color’s CIELab values.  This also means densitometers cannot objectively describe how a color is perceived by the human visual system or quantify the perceived differences between two shades of colors using a ∆E formula.  For this reason, switching from densitometers to spectrophotometers is an absolute must for packaging printers.  Otherwise, press operators cannot know when contractual brand specifications have been achieved or what color changes are required to meet them.  
 
Making this shift is relatively easy for press operators because spectrophotometers can still report all of the familiar densitometric functions like solid ink density and TVI, which are important process control metrics, and the instruments are operated and handled in the same way as densitometers.  However, in addition to reporting densitometric and colorimetric values for measured samples, spectrophotometers have many more features and functions that can help guide operators to faster and more accurate color matches.  
 
Workflow:  
The workflow using a spectrophotometer to check color accuracy is extremely similar to that of using a densitometer.  On a flexo press, the press is stopped and a sample is cut from the roll while on a sheetfed press, a sample is simply pulled from the output stack.  The printed sample is then placed on a flat surface where it can be measured with the spectrophotometer.  Now the press operator selects the measurement mode on the instrument (Density, TVI, CIELab Opacity, etc.), aligns the measurement aperture over the sample to be measured, initiates the measurement, and the results will be shown on the instrument display.  If the user wishes to see other measurement information from this same sample, they will then need to change the display mode on the instrument.  
 
Key Benefits:  
  • Spectrophotometers can store thousands of reference colors (including Pantone libraries) inside the instrument and color differences (∆E’s) between a printed sample and a reference or brand color can be automatically displayed
  • Spectrophotometers can recommend precise density adjustments to achieve the lowest ∆E on press for a particular color. This is a valuable feature that can dramatically reduce pressroom make-ready times because the operator is shown the precise density value that is required for each color in the job to achieve the lowest ∆E.  In some cases, this may indicate that an anilox roll must be changed and in other cases it may indicate ink problems that cannot be fully overcome with density adjustments alone.  In either case, this is valuable information for the operator and can save considerable time and materials.  Consider the example below where the instrument is indicating a 0.18 density increase will greatly reduce the current ∆E of 10.2 down to a ∆E of only 0.9 for this match to Pantone 647 C:
 

Techkon SpectroDens illustrating required density change to achieve the lowest ∆E match

 

  • Spectrophotometers typically have a graphical display of color differences indicating if the printed sample is too red, too blue, too yellow, etc. which can be very helpful if the press operator decides they need to modify or “tone” the ink on press.
  • G7 & ISO reference print conditions are stored within most press-side spectrophotometers which can provide PASS/FAIL indication according to these references and recommended changes to comply with these standards
  • The calculation of ink Opacity is included and invaluable when printing white ink on clear substrates where accurate process and spot color matches are required
  • While still relatively new, SCTV, otherwise known as Spot Color Tone Value (ISO 20654:2017), is a new formula that spectrophotometers can use to calculate the tone value (TV) or dot percentage of any spot color ink based on color measurements instead of CMYK density values. The end result is more accurate TV or TVI measurements that allow for more visually linear tone curves for spot colors with vastly improved predictability on press.
 
Next week, we will pick up where we left off and examine the “Better” solution for press-side color quality control with the advantages of integrating color quality software which is used in conjunction with a pressroom spectrophotometer.  If anyone has any questions or would like to learn more about Techkons products, please feel free to call us anytime.  In addition, for those readers that will be attending FTA’s Infoflex conference in March, please either schedule a time with time us for a one on one live product demonstration or just stop on by the both to say hello!  Talk to you all next week…
You can read the other two parts of this blog here:

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