Influence factors on the calculation of spot color

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Influencing factors of offset spot color ink consumption calculation (Part 2)

2 Ink layer thickness

the influence 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 ink layer thickness is uncertain and uneven. However, most of the offset printing machines used today have the characteristics of high precision and high reliability. When the substrate is coated paper, the maximum error of ink layer thickness in the printing process will not exceed 0.05 μ m. The effect on the total ink amount is quite small. The value range of ink layer thickness is not random. In a specific printing environment, there will always be an optimal ink layer thickness. On the one hand, it can make the ink on the printing sheet full, and maximize the field density and contrast value; On the other hand, it can minimize the value of point increase, realize the best restoration of layers, and stabilize the quality of batch printing. The specific printing environment here refers to that the main factors such as printing machinery, substrate, ink and temperature and humidity in the printing workshop have been determined

two methods can be used to measure the thickness of the ink layer: one is a common weight measurement method, that is, comparing the weight difference between the front and back of the ink layer on a substrate sheet, and then dividing it by the area of the ink block to obtain the thickness of the ink layer. This method is simple and feasible, but it has many influencing factors and is not accurate enough. It can only be used to verify the measurement of properties. The other is the density difference method. By comparing the density difference between the field and blank substrate sheets, combined with the characteristics of the test ink itself, and according to the relationship formula between the density difference and the ink layer thickness: D = DS (1-e-kf) (where D is the density of the test area, DS is the field density, K is a constant related to the paper characteristics, and F is the ink layer thickness value of the test area), the required ink layer thickness value can be obtained. In the latter method, the determination of K value is a difficult point. The printing factory can determine which method to use according to its actual situation

3. Ink specific gravity

refers to the density of ink, usually in g/cm3. This parameter can be determined by using the ink qualitative tester or the ink developing machine "At present, most Chinese enterprises are not equipped with friction and wear testing machines, and some ink suppliers can directly provide this parameter. This is a relatively easy parameter to determine.

4. the number of printed sheets

is the total amount of printed matter to be printed. Obviously, this is an extremely easy parameter to determine.

5. substrate characteristics

if the substrate only considers paper, it can be roughly divided into coated paper and uncoated paper. They are based on their own ink absorption, surface smoothness and structural strength, which affect the ink layer thickness and dot increment of printed matter, and ultimately indirectly affect the ink usage. However, it is difficult to accurately determine the specific impact of these factors on the ink volume. It is suitable to make qualitative analysis and give a representative or practical impact value. This value can also be given by adding the negative value of experimental force to other factors

6. The influence of printing mechanical characteristics on ink volume is mainly reflected in two aspects: one is the influence of printing pressure and printing speed on ink layer thickness and dot increment; On the other hand, the printing mechanical system directly determines the minimum inking amount of the system itself. The minimum inking amount of the printing machine refers to the ink consumed on the printing machine in the form of covering the surface of various mechanical rollers and rollers in the actual printing process, plus a certain amount of ink reserved in the ink bucket to stabilize the ink supply

for the analysis of the influence of printing pressure and printing speed on ink volume, please refer to the analysis of the influence of substrate characteristics on ink volume. The minimum inking amount of the machine varies with different brands and models of printing machines. 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 part of the ink will be lost on the drum, some ink will be lost during the trial printing, so the impact of this factor on the overall ink consumption should also be considered. This parameter can be obtained by quantitative analysis based on the actual printing situation

8. Pre stored ink

due to the existence of various unknowable factors, general printing plants will be equipped with more used spot color inks so that some can be pre stored. This parameter is determined by the printing plant itself

although the influence values of the following four influencing factors cannot be accurately determined, they will not have much impact on the calculation accuracy of the overall ink volume. In addition, our detailed analysis of them makes the possible error limited to a very small range. The influence on the overall ink quantity is relatively small. This error should be acceptable to the printing plant

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

a printed matter - ink volume in may2014 (g) = printing area × Ink layer thickness × Ink specific gravity

step 2: calculate the ink consumption of the whole printing order

total ink volume (g) = ink volume of a printed matter × Ink loss rate × Printing quantity + minimum inking quantity of the printer

if the whole process is based on strict experimental verification and theoretical analysis, it can be believed that the total ink volume obtained should be within the acceptable accuracy range. In fact, the characteristics of substrate, printing machinery, ink loss rate, pre stored ink and other influencing factors are obviously individual. These data may change when each printing plant processes different printing work orders, so it is necessary to determine these parameters according to its own actual situation. It is also conceivable to convert these four factors into an overall influencing factor, which not only simplifies the factors to be considered, but also simplifies the algorithm, But whether it is feasible or not remains to be discussed and verified

(author/luoguanglin, wuchunming)

source: printing technology, January 2005

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