Ink volume during ink transfer

The amount of ink in the print is related to the area of ​​the surface of the printing plate or the surface of the printing material. Usually the amount of ink in the printing can be expressed by the weight of ink per unit area, that is g/m2; also can be expressed by the volume of ink per unit area, ie ml/m2; by calculation, the ink layer thickness (μm) can also be used To represent. The amount of ink on the printing plate before printing is called the printing plate ink volume, denoted by x; the amount of ink transferred to the surface of the paper or other printing material after printing is called the amount of ink transferred, and is represented by y. The unit of x, y can be g/m2, or can be expressed in μm.

The ratio of the amount of ink y transferred to the amount of ink x in the printing plate, expressed as a percentage, called ink transfer rate, denoted as f, ie
f=(y/x)×100%.........(1)

The ratio of the amount of transferred ink y to the remaining amount of ink x-y on the plate after printing, called the ink transfer coefficient, denoted as e, ie
e=y/(xy).........(2)

The amount of ink transferred is related to the amount x of printing ink, that is, y is a function of x. Therefore, the ink transfer rate f and the ink transfer coefficient e are also functions of the plate ink amount x. If the analytical relationship between y and x is known (or the data of x and y is measured), and x is the abscissa, y, f, and e are the ordinates, respectively, and they can be made (or fitted out). ) y-x, f-x, e-x curves; they are called ink transfer amount curve, ink transfer rate curve, and ink transfer coefficient curve, respectively.

The influence of printing materials on ink transfer rate f is very obvious. For example, coated paper and newsprint, their ink transfer rate curves are shown in Figure 4. The two curves obtained under the same experimental conditions are quite different: the surface of the coated paper is smooth and poorly absorbable. With the increase of the ink amount x of the printing plate, the ink transfer rate initially increases rapidly, and after the maximum value is reached, the decline is rapid. The convex peak of the curve is more obvious; the newsprint surface is rough, and the absorption is good. With the increase of x, the increase is slow, and after the maximum value is reached, the decrease is also slow, the curve shape is gentle, and the convex peak is not obvious.

1. Using ink preset parameters must eliminate interference conditions and determine the maximum degree of uncertainty. For example, determine the height of the ink holding capacity, the temperature and humidity of the environment, choose the pH value of the fountain solution, the type of ink, paper, plate, the running speed of the machine, and the condition of the machine.

In the above conditions, the condition control of the machine is the most difficult, so the machine needs to be maintained on a regular basis, and a test is performed after each maintenance. Of course, such a test can sometimes be combined with the actual production for inspection.

2. The current printing equipment's performance is tested with the printing conditions determined. There are two main parameters to test this performance. On the one hand, it is to establish the function of the ink transfer state of each ink zone and the amount of ink required by the JDF process to output the graphic information. On the other hand, it is required to test the stability of printing under this working condition. . The ink transfer state of each ink zone established under the stable working condition will be valid as a function of the required ink output volume of the JDF process output graphic information. Otherwise, the remaining ink and other factors will be tested before starting the printer. The effect of measurement error.

The judgment of the printing quality needs to measure the density of the ground, the dot enlargement rate, the gray balance, the printing contrast, and whether the density of each ink zone is even. However, the judgment of printing stability requires the sampling of multiple proofs to be evaluated by CP and CPK values. CP represents the stability of the printing process, that is, the amount of fluctuation printed between the upper limit USL and the lower limit LSL, by sampling the density of the plurality of proofs, calculating the variance with the standard value, and plotting the curve representing the printing stability ( As shown in Fig. 5, the CP value is obtained by the formula CP = (USL-LSL)/6S. Table 1 shows the stability data of the long printing and the short printing.

CPK=min[(USL-Mean)/3s,(Mean-LSL)/3s]

In this formula, Mean represents the measured actual density of printing. In general, the CP and CPK values ​​for short-run printing are higher than those for long-run printing. CPK greater than 1.33 indicates better stability; CPK indicates acceptable between 1 and 1.33; if less than 1.0, printing stability is not very good.

3. According to the test results of the print job status and the analysis of the print output characteristics, the relationship between the parameter values ​​of the ink transfer amount information such as Ink, InkZoneCalculationParams, and InkZoneProfile output by the JDF and the ink quantity control status is established, and the relational function library is established to realize the printing work. State control and ink presets provide the basis.

After mastering the above debugging methods, it can not only apply the ink amount control information on the printing equipment supporting CIP3, but also can apply the data on the equipment that does not support the CIP3 function before, and achieve a stable working state within the shortest ink regulation time. .

Reprinted from: Guangdong Printing Network