What should be paid attention to in screen exposure and photosensitive coating

In the mass production process of screen printing, if a specific link is not noticed, it will bring a series of troubles to the production, and this situation will not be resolved one day, it will always trouble the production.

The editor of Bisheng.com mainly discusses several problems that are often encountered in production and are easily overlooked.

—, The color of the wire mesh

The colors of the wire mesh are white, yellow, amber, red, etc., among which the yellow wire mesh is preferred. In our production, we usually use 270 ~ 280T yellow silk screen imported from Japan or Germany. For particularly delicate printed products, we usually use 350T imported yellow silk screen.

Why use yellow wire mesh? We know that the brilliant colors in nature are all due to the effect of light. Without light, there is no color. The color of light is determined by the frequency of light waves. Red, orange, yellow, green, blue, basket, and purple are the light that people's visual nerves can feel, called visible light. Different colors are obtained by the selective absorption and reflection of light on the surface of an object. In short, any color we can see is the color of light. That is, when a beam of light hits the surface of a yellow object, only the yellow light is reflected, stimulating our optic nerves to appear colored, and other colored light is absorbed, so we see the color of the object is yellow.

Because screen printing uses ultraviolet light during exposure, purple light is a mixed reflection of cyan and magenta hues in color, that is, the lack of yellow hues in black. During the exposure, the yellow of the purple plus silk screen is superimposed into black, so the surface of the yellow silk screen (ie, the bottom of the emulsion layer) is not light-sensitive or lightly exposed, so there will be no "back exposure" phenomenon, and the resulting image has high definition , No vignetting.

What is backfat? That is, when light passes through the transparent part of the film and reaches the emulsion layer, reflections, refractions, and slow shots are generated on the surface of the white screen located in the middle or bottom of the coating layer, which is just exposed from the bottom and inside of the coating surface. This phenomenon is called "back exposure". It will cause a virtual halo during exposure and affect the reproduction of tones.

2. Coating of photosensitive emulsion

Put the prepared photosensitive liquid into the stainless steel tank, and the photosensitive liquid will occupy about half of the tank. The coating tank is in contact with the lower end of the inclined screen, and while the tank is inclined to flow out the photosensitive solution, the tank is slowly and uniformly lifted up to apply along the surface of the screen. The coating speed should not be too fast, too fast will cause blistering of the photosensitive emulsion, and pinholes will occur on the film surface; too slow will cause uneven coating of the photosensitive emulsion. In order to obtain the best coating effect, it is best to apply from the side that is in contact with the substrate when printing. The coating area should be slightly smaller than the screen frame, and then apply the screen upside down and apply again. After coating the reverse side of the screen, it is dried so that the photosensitive emulsion fills the mesh. It is best to use hot air drying at 30 ~ 35 ℃, which can shorten the drying time. If the temperature is higher than 40 ℃, the screen will produce hot fog.

The sensitivity of the emulsion in the liquid stage is low, and the sensitivity increases with the drying of the coating film, and the specified sensitivity can be reached after complete drying. .

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