1. Printing conditions

Both the printing machine and its consumables should be properly adjusted, including the viscosity of the ink, blanket, liner, pressure, fountain solution, ambient temperature, humidity, etc. The recommended color sequence for printing is KCMY. It is best not to use the machine's drying system.

2. Field density SID

Start up and print according to the color value (L * a * b *) or density value of standard solid ink. The black version can also use higher values ​​as usual.

3. TVI expanded curve TVI

Measure the TVI value of each CMYK color version. The difference between each TVI curve of CMY should be within ± 3%, and the black version is slightly higher by 3% to 6%, as shown in Figure 6.

(Image 6)

The TVI value is not important at this time. What is important is that all ink curves must be smooth and smooth.

4. Gray balance

Set the spectrophotometer at D50, 2 °, and measure the gray balance value of several HR (50C, 40M, 40Y) blocks on the printed sheet. The standard gray balance value should be:

a * = 0.0 (± 1.0) b * =-1 (± 2.0)
Note: The L * value at this time is not very important.
Within the tolerance range, adjust the solid ink density of CMY to obtain the ideal chroma value.

(Figure 7)

Figure 7 shows how to adjust the solid density of CMY ink for L * a * b * error combinations. Use this table to find the appropriate a * and b * changes in the horizontal row, and then find the appropriate L * column to find the recommended CMY changes. The up and down arrows indicate the increase or decrease. No arrow means no change.

If the gray balance cannot be close to the target a *, b * values, or can not be corrected by a small amount of field density adjustment, then please check whether the value of one or more TVI is too large, whether the hue of the ink is wrong, and whether the overprint is bad It may be due to the ink sticky TACK, or poor emulsification), or the ink color sequence is wrong.

5. Adjust printing uniformity

This is probably the most difficult part of the press calibration. Adjust the printing press keys to minimize the deviation of the solid density on the printed sheet. It is best that the deviation of each ink on the printing surface is not greater than ± 0.05 in order to make the deviation of the gray balance as small as possible. It is not more than ± 1.0a * or ± 2.0b * at the drum.

6. Printing speed

Start the machine (preheating machine) with a production speed of more than 1,000 sheets and check the field density, ash balance and uniformity again. If the change in solid density, gray balance or uniformity of the ink exceeds the value, adjust the printing machine to ensure that the desired printing requirements are obtained, and then increase the speed again as needed to print at the normal production speed to ensure uniform and stable printing quality.

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