The factors that ink layer control should consider in screen printing

Before we begin to discuss with everyone about how the ink layer is controlled, we should first review some of the problems we have experienced in printing:
1. There are dark and light colors when printing color patches.
2. Mesh expansion (printed with moire) when screen printing is adjusted.
3, the difference in color changes in batch printing. When these problems are serious, they will affect the progress of production and batch returns, which will inconvenience our normal work. So how to control and prevent these problems from happening is a question worthy of our screen printers. The following are the variables we should understand in printing.

First, analysis of theory through the ink:

There are two methods to analyze the amount of ink transmitted through the screen. One is to calculate the amount of ink through the screen theory, and the other is the actual amount of ink printed. Calculating the theoretical ink penetration has the following formula:

Open hole rate: L

Screen thickness: D

Theoretical ink penetration: M=L×D÷100%

The above formula is only a theoretical calculation of the amount of ink through the screen, once applied to the practice of printing, the data will change, but in direct proportion. Let's look at the following factors:

1. The mesh number of the screen (directly determines the hole width and hole opening rate). The higher the mesh number of the screen, the smaller the hole width, and the lower the hole opening rate, for example, the mesh width of the 355 mesh is 31 μm, the opening ratio is 26%, and the theoretical ink penetration is 14.3 cm 3 /m 2 . The aperture width of the screen is 45 μm, and the opening rate is 35%. The theoretical ink penetration is 16.3 cm3/m2.

2. The wire diameter of the screen (directly affects the thickness of the wire, the opening rate, and the size of the mesh). It refers to the diameter of the unwoven thread diameter, and the braided thread diameter becomes oval. Will affect the size of the cell. Different screen mesh diameters of the same mesh size will also affect the size of the opening and the opening rate.

For example: 305 mesh wire diameter 31um hole rate is 35%, hole width is 49um, mesh thickness is 49um, the theoretical amount of ink is 17. 2cm3/m2.

305 mesh wire diameter 34um hole rate is 29.6%, hole width is 45um, mesh thickness is 55um, the theoretical amount of ink is 16. 3cm3/m2.

305 mesh screen diameter 40um hole rate is 20. 1%, hole width is 37um, mesh thickness is 65um theoretical ink penetration 13cm3/m2.

3, the thickness of the screen (directly affects the ink layer). We can use the thickness gauge to test the screen thickness of the stretched screen. Since the screens produced by various manufacturers have their own weaving techniques, the curvature of the warp and weft lines is not the same. The greater the degree of bending, the thinner the screen becomes, and vice versa. During the stretching process, due to the influence of external forces, the wire diameter is stretched, which ultimately affects the thickness of the wire mesh.

4, the hole width of the screen (directly affect the amount of ink). We know that the wider the mesh, the greater the amount of ink under the screen. In the process of stretching, the higher the tension, the lower the mesh number, and the wider the mesh opening, the greater the amount of ink penetration.

5, the open hole rate of the screen (directly affect the amount of ink). The so-called open rate refers to the area ratio of the ink-permeated area per unit area of ​​the screen to the total area. For example, for a screen with an aperture ratio of 35%, the ink-permeable portion is 35%, and the portion where the thread is not blocked is 65%. The screen with the higher aperture ratio has a larger amount of ink.

Calculation formula:

Hole width: K

The mesh number is: M

Inches are: Y

Open rate: L=K×M÷Y2×100%

6, the pressure plane of the screen (directly affect the thickness of the network, hole width).

More than 355 mesh imported screens are flattened. The flattened mesh will obviously become thinner and the mesh will become smaller. Flattened wire mesh When stretching the net, we look at the following example: When the pressure plane is stretched towards the squeegee, the ink can be saved by 10% to 15%, and the pressure plane can be stretched toward the substrate surface to save ink by 15%. ~25%.
Second, the actual printing through the ink:

1, the tension of the screen (influence the size of the opening, screen mesh, wire diameter, thickness). As the tension increases, the screen's own technical parameters will change accordingly. The mesh number of the screen is affected first, and the higher the tension is, the greater the number of meshes decreases (until plastic deformation of the screen occurs). Next, the width of the mesh will be affected, the mesh will become larger, the wire diameter will become thinner, and the mesh will become thinner. These factors will eventually lead to changes in the amount of ink.

2, the thickness of the film (decided under the ink). If we use sensitized adhesive to make screens, we must also consider the solid content of the sensitized adhesive itself. After the photographic paste with low solids content, the film will evaporate and the film will be thinned. So we can only use the thickness gauge to check the overall thickness of the screen.

3, ink type (indirectly affect the ink layer thickness). We know that after the solvent ink is printed, the solvent will evaporate, and the ink layer will eventually thin. After the photocurable ink is printed, the resin is cured immediately after being exposed to ultraviolet light, so the ink layer remains unchanged.

4, ink viscosity (indirectly affect the ink layer thickness). The lower the viscosity of the ink in the printing process, the thicker the ink layer, because the ink itself contains less solvent, the thinner the opposite.

5. The hardness of the squeegee (indirectly affects the thickness of the ink layer). In the printing process, the higher the hardness of the squeegee, the less likely it is to deform, and the lower the amount of ink is, the larger is the opposite.

6, the mouth of the blade (directly affect the amount of ink). If the edge of the blade is at a right angle, the amount of ink is small. If the ink is obtuse, the amount of ink is large.

7, the angle of the blade. (Indirectly affects the ink thickness). When printing, the smaller the angle between the doctor blade and the screen, the greater the amount of ink under the printer, because the doctor blade is in surface contact with the screen. The opposite is small.

8, scraper pressure (directly affect the amount of ink). During printing, the greater the pressure applied to the blade, the lower the ink is, because the ink has been driven before it is completely squeezed out of the mesh. The opposite is small.

9, ink knife pressure (directly under the ink). The greater the pressure applied to the ink-returning blade, the greater the amount of ink under the ink is due to the fact that a small amount of ink has been pushed out of the mesh by the ink-returning blade before it is not scratched. The opposite is small.

10, the speed of squeegee (indirectly affect the ink layer thickness). The faster the printing speed is, the smaller the ink is. Because the ink has not been completely filled with the mesh, the ink has been squeezed out, causing the ink supply to be interrupted.

11, printing materials. (Directly affect the ink layer thickness). The surface roughness of the substrate will also affect the thickness of the ink layer, and the rough surface ink will penetrate (such as woven, leather, wood). On the contrary, it is large.

12, the printing environment (indirectly affect the ink layer thickness). One issue that we have always overlooked is the change in the temperature and humidity of the printing shop environment. If the temperature of the printing environment changes too much, it will affect the ink itself (such as ink viscosity, fluidity, etc.).

Third, how to calculate the ink layer thickness?

Through the above discussion, we know that if there is a change in one part of the printing process, which will ultimately lead to inconsistent ink output, then how should we calculate the thickness of the ink layer? One method is to weigh the weight of wet ink. First, try to control every link in the printing process to remain unchanged. After printing, the weight of the substrate is weighed. After subtracting the original weight of the substrate, the data obtained is wet ink. Weight, another method is to measure the thickness of the ink layer, using a thickness gauge to measure the thickness of the substrate after the ink, and then subtract the original thickness of the substrate, the data obtained is the thickness of the ink layer.

Fourth, how to control the thickness of the ink layer?

How to control the thickness of the ink layer has become a problem faced by screen printers. The first thing we need to do is to use existing measuring equipment to ensure the accuracy and objectivity of the measured data; conditional factories can use automatic The coating machine completes the sizing process and ensures the thickness of the adhesive layer. The next thing to do is to ensure that every aspect of plate making and printing is kept as constant as possible, and that each printing parameter should be properly documented to provide the ideal data for finding the proper ink layer thickness.

Reproduced from: China and Hong Kong silk screen network

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