2. Ink layer thickness

The effect of ink layer thickness on ink volume is also one of the decisive factors. Due to the complexity and variability of printing conditions and substrate conditions, the uncertainty and inhomogeneity of the ink layer thickness are caused. However, most offset presses used today have the characteristics of high accuracy and high reliability. In the case of substrates that are coated paper, the maximum ink layer thickness error will not exceed 0.05 μm in the printing process, and the impact on the total amount of ink is relatively small. . The range of ink layer thickness is not arbitrary. In a particular printing environment, there will always be an optimal ink layer thickness. On the one hand, the ink on the print sheet will be full and the density and contrast in the field will be maximized; On the other hand, it can minimize the value of network points, achieve the best level of reduction, and make the quality of batch prints stable. The specific printing environment here refers to the determination of major factors such as the temperature, humidity, and the like of printing machinery, substrates, inks, and printing shops.

Two methods can be used to measure the thickness of the ink layer: One is the more common weight measurement method, which is to compare the weight difference before and after the ink layer on a substrate sheet, and then divide the ink block area to get the ink layer thickness value. This method is simple and easy to implement, but there are many influencing factors and the accuracy is not enough. It can only be used to verify the nature of the measurement. The other is the density difference method, which compares the difference in density between solid and blank substrates, combined with the characteristics of the test ink itself, based on the relationship between the density difference and the thickness of the ink layer: d=ds(1-e-kf) (In the formula, d is the density of the test area, ds is the density of the solid, k is a constant related to the characteristics of the paper, and f is the thickness of the ink layer in the test area), and the required thickness of the ink layer can be obtained. In the latter method, the determination of the k value is a difficult point. The printer can determine exactly which method should be used for its own reality.

3. Ink specific gravity

That is, the density of ink, commonly used g / cm3 as a unit. This parameter can be calculated using an ink meter or ink distributor. Some ink suppliers can directly provide this parameter. This is a relatively easy parameter to determine.

4. Number of printed sheets

That is, the total amount of printed matter that needs to be printed, which is obviously a very easy parameter to determine.

5. Substrate properties

If substrates only consider paper, they can be roughly divided into coated paper and uncoated paper. They are based on their own ink absorption, surface smoothness, and structural strength, thereby affecting the ink layer thickness and dot gain of printed products, and ultimately indirectly affecting ink usage. However, the specific influence of these factors on the amount of ink is difficult to accurately determine, and it is suitable for qualitative analysis and gives representative or practical significance of the value, which can also be given in addition to other factors.

6. Printing machine characteristics

The influence of printing machinery characteristics on the amount of ink is mainly reflected in two aspects: First, the influence of printing pressure and printing speed on the thickness of the ink layer and the increased value of the dot; on the other hand, the printing machine system directly determines the minimum of the system itself. Ink volume. The minimum amount of ink on the printing press refers to the ink that is lost on the printing press in the form of covering the various mechanical rollers and roller surfaces in the actual printing process, and a certain amount of ink reserved in the ink fountain is used to stabilize the ink supply.

With regard to the analysis of the influence of printing pressure and printing speed on the amount of ink, reference can be made to the analysis of the influence of the characteristics of the substrate on the amount of ink. The minimum amount of ink on the machine varies with different brands and models of presses. If the machine itself provides the best data, if not, it can only be obtained through experiments.

7. Ink loss rate

In the general printing process, in addition to some of the ink will be lost on the drum, some of the ink will be lost during the test, so we must consider the impact of this factor on the overall use of ink. This parameter can be quantitatively analyzed based on actual printing conditions.

8. Pre-stored ink

Due to the existence of a variety of unknown factors, the general printing factory will be equipped with some spot color inks that have already been used, so that they can be pre-stored. This parameter is determined by the printing house itself.

Although the influence values ​​of the following four influencing factors cannot be accurately determined, the accuracy of the calculation of the overall ink volume will not have much impact. Together with our detailed analysis, the possible errors are limited to Small range. The impact on the overall amount of ink is relatively small. This error should be acceptable to the printing house.

Assuming now that we know the relevant parameters of the above various influencing factors, we can obtain the required spot color ink volume. The total amount of ink can be calculated in two steps. In the first step, the amount of ink used in a print is first calculated using the following formula:

The amount of ink used for a print (g) = print area × ink layer thickness × ink specific gravity;
The second step is to find the ink volume for the entire print order;

Total Ink (g) = amount of ink used for a print * ink loss rate × number of prints + minimum amount of ink on the press.

If the entire process is based on rigorous experimental validation and theoretical analysis, it is believed that the resulting total ink volume should be within acceptable accuracy. In fact, the influencing factors such as substrate characteristics, printing machinery characteristics, ink loss rate, and pre-stored ink are all obvious individualities. Each printing factory may change the data when processing different printing work orders. Therefore, it is necessary to use actual conditions according to actual conditions. When these parameters are determined, it is also conceivable to combine these four factors together into one overall influencing factor. This not only simplifies the factors considered, but also simplifies the algorithm, but it may not be feasible to be discussed and actually verified.
(Author/Luo Guanglin Wu Chunming)

Source: "Printing Technology" 2005.1

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