Analysis of the reasons for poor photolithographic exposure

1 Introduction

With the rapid development of building ceramics production, the quality and function of building ceramic products such as printing tiles are more and more inclined to the effect of layout decoration. Product design, color effects and exquisite printing directly affect the quality of the product and market competitiveness. The screen plate is the key to ensure the quality of ceramic printing and product quality. In screen printing photosensitivity, the factors that affect the exposure quality may come from various aspects. There are many factors related to ink, equipment, substrates, and manuscripts. Among the various factors of screen printing photosensitivity, the most involved are the screen (ie, the printing plate), and half of the factors relate to exposure. A good-quality screen needs to achieve two goals: the image should be completely resolved, and at the same time, it should have good print edge definition; non-images should be completely cross-linked and cured. In short, a good printing plate should faithfully reproduce the original and have a good resistance to printing. Both of these goals are closely related to the correct exposure time, and the exposure time is affected by many factors.

Poorly exposed screens are most likely to fail. If you put it into the workshop without being aware of it, it will cause problems such as downtime, waste of printed materials, poor print quality, and difficulty in recycling. Overexposure is rarely seen but it affects the printed edge definition and resolution of the screen. There are four main factors that affect exposure quality and various factors; but manuscripts are not one of them. Photoresists react to light exposure and geometric conditions, but they have no effect on resolution of fine copies and accelerated exposure. The four factors related to exposure affect the time required for full screen curing and the quality of the finished screen. The effect of these four factors on the quality of photolithographic plates is discussed below.

2. The choice of screen

The selected screen should meet the requirements for the number of prints, the used ink, the quality of the print, and the selection of the screen. Photosensitive adhesives have a wide range of applications, but none of them are suitable for all applications. Consult suppliers and manufacturers to listen to their suggestions.

Exposure latitude is a problem that must be considered. Because the latitude relaxes the use requirements of the film material, it is very much in line with the needs of users. Underexposure, latitude allows you to choose slightly less than the exposure time and get excellent print quality, printability and recyclability; overexposure, latitude to avoid sidewall corrosion and avoid longer than optimal exposure During the time "blocked version." The screen stencil thickness and the stencil cross-sectional size play separate roles in exposure control. The total thickness of the photoresist affects the exposure time, while the size of the cross section of the template (the thickness of the photoresist on the screen printing surface) affects the sharpness of the printed edge. The open area of ​​the screen, the required cross-sectional area of ​​the stencil, the content of solid particles in the sensitized adhesive, and the type of sensitized adhesive determine the number of sensitized adhesives to be coated. Currently used in a large number of photosensitive adhesive, domestic tolerance than the imported photosensitive adhesive is worse. However, its cost is much lower than imported photosensitive adhesives; in terms of the author's long-term use, domestically produced photosensitive adhesives, as long as they can accurately determine the exposure time, can be reasonably selected to obtain a good screen. The key lies in the control of exposure. Of course, imported photosensitive adhesives are indeed more able to guarantee the quality of the prints.

3. Selection of screen

The selection of the screen should pay attention to the relationship between the printing area of ​​the mesh and the area of ​​the wire diameter. If the printing area of ​​the mesh is 45%, then the area of ​​the network wire will occupy 55%, the network wire is fine, the mesh is large, and the printing area is also large. Based on this, we can choose the screen according to the size of the screen. The area of ​​the mesh determines the number of colored ink passes, and also determines the area covered by the colored ink. At the same time, the thickness of the printed layer is determined by the mesh thickness. In practice, the thickness of the printed layer is determined not only by the thickness, aperture, and wire diameter, but also by the viscosity of the ink, the surface printability of the substrate, the hardness, edge, pressure, and printing speed of the blade. The ink thickness of the screen printing can be calculated using the following formula:

(2* diameter) /3

Because the thickness of the printed ink layer is not likely to remain constant, especially due to the viscosity of the color ink and the surface properties of the substrate, its thickness after the leveling is only about 1/3 of the thickness of the web.

At the same time, with the aperture and thickness of the net, the following formula can also be used to calculate its ink consumption.

Ink consumption = mesh size 2x mesh thickness x specific gravity of the ink x mesh area of ​​the printing area, and the thickness of the ink layer of the screen printing is directly determined by the thickness of the photosensitive resin. The thickness of the photosensitive layer coating on the mesh surface can be According to the needs of printing decisions. However, in general, a thicker coating will make the outline of the printed pattern clearer. This is due to the fact that the coating is too thin to create a concave slope between the screens. This will make the printing ink in the printing content is too large and flow, resulting in unclear or deformed pattern edge, while too thin a photosensitive layer will reduce the plate printing rate.

In order to achieve the desired printing effect, it can be coated several times (usually 2-3 times) on the mesh surface that is in contact with the substrate. It should be noted that after each coating must be dried and then coated again.

In addition, the template determines the image, and the screen is the carrier of the image. As such, screens play an important role in every component of the screen printing process. In general, the screen wire diameter is relatively coarse, the mesh is low, or the screen is dyed, and the exposure time needs to be lengthened. The percentage of open area varies with the number of meshes, the size of the mesh, and the diameter of the mesh, and determines the amount of sensitized coating and the desired cross-sectional area of ​​the pellicle. Mesh with a high percentage of open area has a lower percentage of area than open area. The total thickness of the photoresist increases, and the exposure time will increase.

Screen color affects exposure time, film resolution, and print clarity. White silk screens absorb almost no UV light and scatter. UV-absorbing dyeing screens are light yellow, orange and yellow. The color of the screen reduces the scattering of light, and although it extends the exposure time, it increases the resolution and edge definition of the film. Therefore, screen printing of building ceramic products should use dyeing screens as much as possible to improve the quality of printing plates. (to be continued)