Factors Affecting Photographic Platen Exposure (1)

Abstract: The factors affecting the quality of the stencil in the stencil photosensitivity of ceramic building products such as printed tiles are described. Among the various factors of screen printing photosensitivity, there are many factors involving the screen, and half of them are related to exposure. The screen quality has a close relationship with the exposure time, and the exposure time is affected by many factors. There are four main aspects: the screen, screen, light source and exposure time, and the humidity of the photosensitive adhesive.

Key words: exposure time; screen; screen; light source; exposure distance; humidity of photoresist

1 Introduction

With the rapid development of building ceramics production, the quality and function of building ceramic products such as printing bricks are more and more inclined to its layout decoration effect. 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 relevant factor is the screen (that is, the printing plate), and half of them are factors.

Related 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 edge-to-edge resolution; 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 Screen Selection

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, tolerance 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 coatings. 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 printing plates.

3 Selection of wire mesh

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 mesh area determines the number of colored ink passes and also determines the area covered by the color ink. At the same time, the thickness of the print 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 be used to calculate its ink consumption.

Ink consumption = mesh size 2 × mesh thickness × specific gravity of ink × mesh number of printing area

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 coated on the surface of the web can be determined according to the printing needs. 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 applied several times (usually 2~3 times) on the surface of the mesh 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. The white mesh barely absorbs ultraviolet light, and scattering occurs as shown in Fig. 1 <. UV-absorbing dyeing screens are light yellow, orange and yellow. The color of the screen reduces the scattering of light and absorbs ultraviolet light as shown in Fig. 2 <, although the exposure time is prolonged, the resolution of the mask and the edge sharpness are improved. Therefore, screen printing of ceramic products should use dyed screens as much as possible to improve the quality of the printing plate.