Printing ink layer thickness control
Some printing products have higher requirements on the ink layer thickness, and some manufacturers also use the ink layer thickness as one of the important indicators for the quality inspection of printed products. In order to reasonably control the ink layer thickness, we should focus on the following two links.
(1) Analyze the intrinsic relationship between the thickness of the ink layer and theoretical ink penetration, and convert the thickness of the ink layer (known) into the theoretical ink penetration of the screen.
(2) The printing conditions are limited to a certain range in response to the influence of changes in printing conditions on the amount of ink transferred.
In order to unify these two points, a combination of printing test and calculation is used to solve this problem. Since the dot diameters of the printed dots are relatively large, the ink layer thickness will be greatly different, so it is discussed in two cases.
1. Calculate the amount of ink printed in large dots (dot diameter D>2.5mm)
Due to the large dot area, the thickness of the photosensitive emulsion on the screen is negligible. Therefore, the required thickness of the ink layer should be ensured by the number of screen meshes. In this case, the following steps can be used to determine the required screen mesh number. To meet the basic requirements of ink thickness.
(1) Test printing. Select one kind of screen mesh number, and find the corresponding theoretical ink permeability from the technical manual provided by the wire mesh manufacturer, and use X (unit cm3/m2) as the test mark.
In the trial printing, in order to reduce the influence of the printing conditions on the amount of ink penetration, the printing conditions that are consistent with the actual printing should be adopted, that is, the printing conditions are limited within a reasonable range.
(2) Testing. The thickness of the ink layer of the test print was measured after the test and expressed in y (unit μm).
(3) Assuming that the required ink layer thickness is x (unit cm3/m2), the required theoretical ink penetration Thv is obtained. The following relationships exist between the parameters:
Thv/X=x/y (3)
which is:
Thv=X(x/y) (4)
(4) Determine the number of screen meshes required. From the desired theoretical ink penetration Thv, the required screen mesh number is retrieved from the screen technology data.
2. Calculate the amount of ink printed in small dots (dot diameter D≤2.5mm)
Because the printing dots are smaller and the thickness of the ink layer of the printed product is thinner, the effect of the thickness of the emulsion on the thickness of the ink layer cannot be ignored. Therefore, the ink layer thickness of the printing product should be controlled by the mesh size and the thickness of the emulsion. . Therefore, when calculating the required theoretical ink permeability, the necessary corrections to equation (4) must be made:
Thv=X[(xg)/(yg)] (5)
That is, in calculating the theoretical amount of ink penetration, the thickness g of the emulsion should be subtracted from the thickness y of the ink layer of the test print and the thickness x of the desired ink layer of the printing ink. In general, the thickness of the emulsion is usually 5 to 7 μm.
3. Experiment
In order to verify the rationality of the trial printing method, the actual printing was taken as an example to conduct a trial printing.
(1) Thickness of printed ink layer: x=70μm
(2) Experimental conditions
1 laboratory equipment: manual screen printing machine, pneumatic stretching machine
2 Experimental Materials: * Cardboard, * Monofilament Polyester Wire Mesh, * Scraper: Hardness HV60, Scraper Angle 45°, * Ink: Viscosity 80 Pa·s
3 printing speed: 3 meters / minute
4 Ambient temperature: 15°C at room temperature
(3) Experimental procedure
1 Select a mesh with a mesh size of 110 mesh/inch (optional) and check the theoretical ink penetration X of the material supplied by the wire mesh manufacturer to 56 cm3/m2.
2 Use the silk screen selected above to conduct trial printing. After the quality of the printed product is stable, take 10 sheets and measure the ink layer thickness separately. Then calculate the average value to obtain the average ink layer thickness y=43 μm.
3 According to formula (4), calculate the theoretical ink-permeation amount Thv of the desired screen=56×(70/43)=91(cm3/m2).
4 check the theoretical transmission Thv (for 91cm3/m2) corresponds to the number of screen mesh L = 71 mesh / inch.
5 Use screen mesh with a mesh size of 71 mesh/inch for printing. After the quality of the printed product is stable, take 10 sheets and measure the ink layer thickness. Then calculate the average value to obtain the average ink layer thickness x'=66μm. .
6 test results analysis and conclusion
The thickness of the ink layer requiring printing x = 70 μm was compared with the actual printing ink layer thickness x' = 66 μm obtained by the test printing method, and the relative error was [(70-66)/70] × 100% = 5.7%. In the printing, due to the use of a manual screen printing machine, it is difficult to keep the angle of the squeegee and the printing speed consistent, and it is inevitable that this error occurs. If the printing conditions can be more strictly controlled, the ink layer thickness error will be smaller.
From this, it can be concluded that the proposed method is reasonable.
Conclusion
This paper starts from the screen ink penetration and briefly analyzes the various factors affecting the ink penetration. It derives the intrinsic link between the theoretical ink penetration amount and the screen technical parameters and ink thickness, and uses the combination of printing test and calculation. Methods: The theoretical ink penetration, ink layer thickness, screen mesh number, and printing conditions are organically linked to form a working system that controls the thickness of the ink layer of the printed product. In order to strictly control the ink layer thickness of the printed product, a reasonable selection is made. The screen mesh number provides a reliable basis.
Source: "Printing Technology - Packaging Printing"