Calculate accurate exposure - solve exposure problems

Tina Scarpelli's contribution “What is the correct exposure time for this emulsion?” I don’t know how many people ask if Bill Gates asks you for a dollar if you answer this question every time. Some people say that the so-called correct exposure time is only an estimate, and it is true that they absolutely do not lie to you. Due to the instability of the operation process, it is difficult for people to find a series of integrated plate-accurate accurate exposure times. Therefore, taking the exposure time suggested by the manufacturer as a starting point, and then calculating the number of screen printing shops that are suitable for your family, it is simply terrible. One emulsion manufacturer said that 50% of the technical calls they received were related to exposure. When screens are overexposed, they must be remade before printing. Underexposure is a very common problem that has caused the entire production process to stop. On screens, underexposure is mainly due to pinholes, rough edges, or stencil delamination. In the printing, the appearance of jaggies, uneven strokes, and inconsistent colors of halftone dot reproductions. What is even worse is that the screen is damaged due to insufficient exposure, it cannot be regenerated, and the template cannot be removed (in general, the template can be delaminated and then used). This article mainly analyzes several basic exposure problems. The following begins with the most common problems in the screen shop. 1. When exposure and fineness conflict, screens should be able to produce durable, high-quality images that can be recycled. The material used to make the screen is only an influencing factor. The key factors determining the quality of the screen are the quality of the equipment, the correctness of the selected materials, and the control of the screen manufacturing process. A poor light source is enough to cause exposure problems, and emulsions and meshes that do not match the picture requirements are also sources of problems. But the main reason for the exposure problem is to reduce the exposure in order to deal with the details. Did the source of the above problems appear in your work? Yes, it all happened. It was a disastrous consequence. Do not think that when you emphasize a lot of details, you can get images suitable for printing. The fact is the opposite. Today's light source performance and the huge selectability of screens and image screens can almost guarantee fine detail with optimal exposure. Yes, you can really avoid underexposure, especially when your emulsion has a latitude. Post-exposure is a commonly used method for making exposures to underexposed screens. Some emulsion manufacturers say that this method does not benefit, but some manufacturers say it helps to improve the edge of the firm. But one thing that is generally accepted is that it does not have a repair effect on dot loss caused by underexposure. They also agree that only a slight underexposure can be seen. The first step in solving the exposure problem is to properly expose the screen. They also stated that one or more of these parameters should be adjusted frequently during the exposure process. Below we describe the exposure parameters. 2. The effect of the "deep cure" parameter, which affects the exposure, on the UV curable ink is as important as the screen exposure. This is also true for other inks. The screen is sensitive to actinic light, ultraviolet light, and blue-violet light in the spectrum. A good screen needs to be well cured, properly combined with the mesh, and able to withstand the use of printing. The complete cure of screens should be considered in the same way as the complete curing of inks. It is mainly influenced by the following parameters: Light intensity The quality and quantity of light have the same importance for fast and effective curing. The image screen is sensitive to the light in the 365-420 nm band of the UV spectrum. Each time it requires a certain amount of energy to make it completely hardened. Some people call this “spectrum appetite”. Incandescent and floodlights cannot emit energy at these wavelengths. Metal halide lamps, mercury lamps, and some fluorescent lamps emit actinic light to meet the requirements. The screen can also use ultraviolet light or blue-violet light (except for a small amount), but you can see that they differ in exposure time and image quality, which is mainly related to the emitted light. Light intensity does not mean the brightness of light in the human eye. Don't forget that ultraviolet light is invisible light. The light intensity is obtained by measuring the light reaching the screen. Since the use time of the lamp, the power of the exposure unit, and the distance between the lamp and the screen have an influence on the measurement of the light intensity, the conditions must be the same when measuring. The inverse square law of the distance between the lamp and the screen is used to calculate the exposure time at different distances. The formula is as follows: Original exposure time × (square of the new distance ÷ squared of original distance) = new exposure time Example: When the distance doubles, the exposure time It becomes 4 times the original to compensate for the light intensity. On the contrary, when the distance is reduced by a factor of two, the exposure time becomes 1/4 of the original. The type of emulsion that affects imaging speed and resolution and the thickness of the coating also affect the exposure time. The screen material is designed to make the product better, but no one product reaches the perfect level. The thickness of the screen affects the depth of cure, just as ink thickness affects the drying and curing time. The moisture-sensitive layer contained in the exposed emulsion layer can keep the emulsion dry, but the residual moisture-proof agent inhibits the cross-linking process, so if the exposure time is not taken into account, the screen may be underexposed. The number of meshes and color blank areas and the density of the silk fabric produced by the number of meshes and the thickness of the screen determine the amount of emulsion deposited on the mesh. The white mesh will produce halos or light scattering, which will shorten the exposure time. Any silk fabric will produce varying degrees of halos. Halo may be a problem for different image characteristics or it may not be a problem. Sunscreen density This is not a screen parameter, but it may damage the screen if the background density is too high or the image density is too low. Rees film has a transparent background and opaque image area, which is what everyone wants. Another type of positive film is parchment paper, which has a translucent bottom and an image density that blocks light transmission.