Printer Operation Guide

Advances in equipment, processes, and control technology have enabled the rapid development of print quality. However, the final printing product depends on the perfect combination of many variables, including the operating conditions of the material and printing press. The SNAP guide hopes to achieve the best print quality by standardizing the printing operation. These guides are based on a large number of experiments and numerous devices that have been proven to produce quality prints through these settings.

After preparing proofs according to SNAP's parameter descriptions, printing according to the following guidelines is stable, and high-quality prints will surely be obtained. Due to differences in measurement methods, materials and equipment, the tolerance range in the table was generated.

For information on test sheets, see the section "Observation Conditions and Densitometer Measurements."

Solid ink density Printing field colors and measuring solids with equipment such as densitometers determine the density of solid inks. The measured value indicates the relative amount of ink on the substrate. The following table lists the color reproduction to be balanced, solid ink density values ​​recommended by SNAP.

Solid ink density (SID) recommendation

Dry Solid Ink Density (SID) Offset (Newspaper) Offset (Commercial Print) Flexo Embossing 0.90 0.95 0.95 0.90
Magenta 0.90 0.95 0.97 0.90
Yellow 0.85 0.90 0.79 0.85
Black 1.05 1.10 1.05 1.00
Tolerance range +/- 0.05 +/- 0.10 +/- 0.04 +/- 0.05

Ink Density Keys All density values ​​are dry transmission (T) density values ​​in the SID state, absolute density values, and paper density.

The difference between the ink density value measured immediately after printing and the ink density value measured after drying after printing for a certain period of time is called "dryback". Usually the ink density value measured immediately after printing is higher than the density value after drying over a certain period of time, so the dryback value should be added to the above printer measurement value. For dryback values ​​in offset and flexo, the industry experience is generally 0.02 to 0.05. With the change of printing machine and color, dryback value is also different. For information on the dryback test, see the "Observation and Measurement" section.

Since commercial printing always hopes to achieve the proof effect, and newspaper printing only matches the density value of ink, the target value of cold solid density for commercial printing is always slightly higher than that of newspaper printing, and its variable is also slightly larger than the variation of newspaper printing.

For more information on color balance, see the section "Grey Balance and Color Scale in Process Control".

Dot enlargement/tone value increase (TVI)

Dot enlargement/TVI refers to halftone dot gain due to different stages of the replication process. Each stage of the process, from film to platemaking to final printing, will result in dot gain/TVI.

Total dot gain = mechanical (physical) dot gain + optical (visual) dot gain

The total dot gain/TVI consists of mechanical (physical) and optical (visual) halftone dot gain values. When the dots are transferred from the film to the printing plate, and then transferred from the printing plate to the paper, the dot size increases. In addition, when dots were printed on newsprint, the dot gain values ​​perceived by the eye and the densitometer were greater than the physical expansion of a single dot. This is because light scatters inside the paper, and some light is not only absorbed by the ink but also penetrates halftone dots. This visual enlargement of the halftone size is referred to as optical dot enlargement/TVI. If the surface properties of the substrate result in more light scattering and reflection, the optical dot gain/TVI value will also increase.

The dot gain/TVI value is measured with a reflection densitometer and the like. It must be ensured that the Marray-Davirs equation is used in the instrument used, because the measurement result of this equation integrates both mechanical and optical dot gains.

The dot gain/TVI values ​​provided by SNAP assume the use of the Marray-Davirs equation.

Dot Extend/TVI is expressed as a percentage. This percentage is an additional term and is not mathematically derived. For example, if the film dot area or gradation value is 50%, and the image area of ​​the printed document is 80%, then we say that the dot gain/TVI value is 30%. This percentage is only the difference between two percentages (80%-50%=30%), not the original gradation value.

The following table lists the dot gain/TVI values ​​for different tone values ​​(measured by the densitometer). For example, the initial gradation of a cyan on film or in a document is 25%, and the cyan may reach a 53% gradation on the final print. (Initial dot 25% +28% dot gain = 53%) With these values ​​in mind, film, documents, and other materials can be reasonably adjusted at the prepress stage for proper print reproduction. Therefore, the optimal tone reproduction curve can be generated for the film, document, or RIP process, and an appropriate parameter table can be created using the electronic prepress application software.

The print operator should use the following table as the target value or tolerance range.

If the measured value does not always meet the values ​​in the table below, relevant investigations should be conducted. For special dot-up values ​​for certain specific print or newsprint, consult with film or document providers.

Dot gain/TVI for different tone values

Dot gain/TVI (25%) Offset (85lpi) Offset (100lpi) Flexo (85lpi) Flexo (72-85lpi)
Green 28% 32% 25% 15%
Magenta 28% 32% 25% 15%
Yellow 28% 32% 25% 15%
Black 28% 32% 25% 15%
Tolerance +/- 3% +/- 3% +/- 3% +/- 3%
Dot gain / TVI (50% tone) Offset (85lpi) Offset (100lpi) Flexo (85lpi) Flexo (72-85lpi)
Green 30% 32% 27% 18%
Magenta 30% 32% 27% 18%
Yellow 30% 32% 27% 18%
Black 30% 32% 27% 18%
Tolerance +/- 4% +/- 4% +/- 4% +/- 4%
Dot gain/TVI (75% tone) Offset (85lpi) Offset (100lpi) Flexo (85lpi) Flexo (72-85lpi)
Green 20% 20% 16% 18%
Magenta 20% 20% 16% 18%
Yellow 20% 20% 16% 18%
Black 20% 20% 16% 18%
Tolerance +/- 3% +/- 3% +/- 3% +/- 3%

Note: Offset and printing plates are used for ordinary offset printing. The principle of image transfer from plate to blanket is used to obtain the corresponding dot gain/TVI, ink overprint, and print contrast. The CTP process eliminates the need for film, and the printing plate transfers images directly to the paper. Therefore, the dot extension/TVI, ink overprint, and contrast of the CTP process are different from ordinary offset printing.

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