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The popular “Heidelberg Learning tips” inputs on Dampening solutions in offset printing is rendered below for the benefit of readers.

Dear readers, next to the printing plate and the offset ink, the dampening solution represents the third significant factor in offset printing. Perfect print output – even during high print runs – results from the optimal interaction of these system components.

The below articles are intended to help you to develop a general understanding of the dampening solution, its composition, and its application in the printing industry.

Contents:

  1. Dampening Solution and Additives
  2. The Basis: Water
  3. Water Hardness
  4. pH-Balance
  5. pH-Balance und Buffer
  6. Conducivity = μS/cm
  7. Wetting the Plates
  8. Testing Alcohol
  9. Araeometer Readings
  10. Alcohol Drawbacks in Dampening Solution
  11. Preparing the Dampening Solution
  12. Dampening Solution and Print Problems

1. Dampening Solutions Additives

  • Ideally, the dampening solution should possess a water hardness of 8° dH to 12° dH and a pH-Balance of 4.8 to 5.5.
  • The typical dampening solution temperature ranges between 10°C to 15°C.

At the same time, a printer must know that at low temperatures condensation water collects on tubes and in the dampening solution vats, and this may lead to the formation of water droplets.

Dampening solution additives are complex material systems with various components included to promote adequate emulgation and wetting (surface tension).

They are important for pH-Balance adjustment and for stabilisation (buffer systems), protection against corrosion, for a cooling effect, and in avoiding slime formation (biocide).

In view of the wide-ranging and variegated quality of water, selecting the appropriate additive is essential.

2. The Basis: Water

Water found in nature is not clean, rather it contains numerous gasses and minerals. A printer uses tap water as the source material for his dampening solution.  The water’s hardness is measured in appraising the quality of the water, which largely depends on the quantities of calcium and magnesium present.

In any case, the hardness of the water must be calculated before any additives are introduced, since hardness is no longer easily determined in a prepared dampening solution. Test-strips are useful in performing a simple determination of the total water hardness.

Determining the carbonate hardness is accomplished by means of an indicator solution (substances helpful in making measurements are available, for example, from Heyl Bros., Myron L, Merck, Neukum…). At the same time, one should always remember that a measurement only represents a momentary “snapshot”, and that the quality of the water can continue to fluctuate quite dramatically.

Nearly all manufacturers of dampening solutions will perform a water analysis on request.

you can buy the pH Meter from Amazon, by clicking the above image.

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Converting raster images from an RGB colorspace into a print CMYK colorspace has two significant impacts:

1) Typically a compression and alteration of colors as the image is transformed from the original RGB gamut to the different gamut used for CMYK presswork.

2) The on-press printability of the imagery in terms of color stability, press performance/runnability, and ink usage (i.e. cost).

Converting images from one CMYK separation condition into a different CMYK separation condition by reseparating files is primarily intended to enhance the printability of the imagery while maintaining the appearance of the original CMYK
imagery. Put another way, reseparating CMYK files is effectively a way to optimize press forms.

Under Color Removal & Grey component Replacement (UCR & GCR)

The principle of RGB to CMYK separation:
In order to go to press, RGB color images must be converted to their process color counterparts; cyan, magenta, and yellow. An achromatic black channel is added because if the color black in presswork is just made from CMY it can often appear “muddy” or “patchy.” Also, making dark colors from the three chromatic process colors can lead to a higher than desirable volume of ink on the press sheet.

Neutral colors made up of three process colors are also more difficult to maintain consistent on press as solid ink densities normally vary through the run compared with a neutral made primarily of a single black ink. The net effect of introducing black ink in process printing is a reduction of ink usage/costs, stabilization of color (especially gray
tones), and and better printability.
The conversion process is done by taking the 3 channel RGB image, passing it through a 3 channel device independent CIEL*a*b* profile connection color space where the RGB is converted to CMY and the black channel added, and finally
outputting the result as a 4 channel CMYK image.