Discussion on Correct Exposure of Screen Stencil (Part 2)
item :3-way concealed adjustable hinge
material :zinc
capacity :40kgs/60kgs/80kgs/100kgs/120kgs/200kgs
Fourth, light source screen printing plate exposure light source mainly uses metal halide lamps and high-pressure mercury lamps, pulse xenon lamps and carbon arc lamps have been rarely used. The spectral illuminance between them and the light source splitting energy distribution (ie, the peak wavelength) are different. For example, a high-pressure mercury lamp is an ion device that utilizes arc discharge under high voltage conditions to generate strong electron radiation, and its radiation energy is continuous from the near-ultraviolet region to visible light. Therefore, the exposure time used for different exposure light sources is not the same. The aforementioned photosensitive materials of different sensitizers also have different wavelength absorbances for ultraviolet light, so the spectral sensitivity of the photosensitive material is the coincidence degree between the wavelength range and the light energy distribution of the light source, that is, the matching determines the exposure process. The amount of energy absorbed is reflected in the exposure time, such as good matching, the energy of the light source is mostly absorbed by the photosensitive material, and the exposure time is short, whereas the exposure time is longer.
In order to make the emulsion evenly exposed, the screen must be uniformly irradiated. For the point source, the distance between the exposure source and the screen will affect the exposure performance. In general, the middle part of the screen is 100% acceptable for exposure. The edge exposure intensity is weakened, and the larger the screen area is, the more the intensity is weakened; in addition, when the point light source is transmitted to the screen frame with different network spacings, the light energy received from the A plane of the light source 1 m away from the light source The light energy received by the B-plane at 2m is equal, but the illuminance of light energy in the A-plane and B-plane per unit area is not equal, and the latter is 1/4 of the former. This is because the light emitted by the point light source is spread by the square of the irradiated distance. Therefore, the light energy per unit area gradually decreases as the distance increases. This is called the inverse of the illuminance method. Because the point light source has the above-mentioned defects, a “parallel light source†should be used to achieve a good exposure effect. The so-called “parallel light source†converts the diffuse light of the point light source into parallel light through the light source reflection cover of the exposure machine. The light energy reaching the surface in the exposure frame is substantially uniform. In order to reach the light-sensing area with the same intensity as the light source, there is an ideal exposure distance. Based on the actual operation experience, the following formula can be used:
Minimum exposure distance (H) = diagonal distance of the frame (D) + 1/3 diagonal distance of the frame (D) There is also a simple calculation method, namely:
Minimum exposure distance (H) ≥ 1.5 template diagonal distance (D)
From the above empirical formula, it can be seen that the larger the frame area, the farther the exposure distance is, and the longer the exposure time will be.
V. Exposure management Two important parameters need to be controlled during the exposure of the template: the quality of the light source and the uniform distribution within the screen printing plate, ie the distribution of the irradiation light and the density state value of the UV radiation, when the exposure frame The center and the four corners reach the ideal state when the optical density is at the same level.
Normally, the proper exposure of photosensitive materials is calculated by using some simple and practical test tools, such as a 21 grade gray scale card. It is a graded scale made of a grade of solubility (D) on a slender transparent polyester film. The density of the film is from 1~21 levels increase in turn. The screen stencil was exposed with 21 levels of gray grading cards with different exposure parameters. After the development under the same conditions, the resolution of the stencil was observed and the exposure parameters were determined. The other is an exposure calculator, which is composed of five clear circular target columns of 1, 0.7, 0.5, 0.33, and 0.25. After the first column, there is no filter packet and the exposure coefficient is 1. The remaining four have a neutral density filter, which reduces the light reaching the template to 0.7, 0.5, 0.33, and 0.25, respectively, so that five exposures can be performed simultaneously. Use this tool to first estimate the exposure time that you think is correct, then double up and choose one of the five target rows to get the best result, and then multiply the trial time by the selection factor. In both methods, the exposure time covers the entire exposure latitude, from severe underexposure to overexposure.
However, due to changes in external factors such as voltage fluctuations, stained lamp surfaces, and lamp aging, the use of time management methods cannot avoid underexposure. The resulting exposure time is therefore best converted to management with a cumulative light meter, which prevents exposure errors. The cumulative light meter has nothing to do with changes in external factors or the intensity of light, and calculates the energy of the irradiated light until the photosensitive material reaches the photochemical reaction in a cumulative manner. Once the desired light energy value is satisfied, the power will be automatically cut off, and therefore Plate exposure can always be accurately controlled, and the peak value of the photosensitive wavelength range of the cumulative light meter must be consistent with the spectral sensitivity characteristics of the photosensitive material used, and the installation location should be appropriate.
In addition, a ray detector can be used to measure the energy value of light radiation in the ultraviolet range and use the data provided by the emulsion manufacturer to perform the correct screen exposure test on the sensitivity of the emulsion. The instrument can also be used for the new light source The radiation density is recorded, and the intensity of the comparative light source is tested periodically every month under the same light source.
VI. Precautions during operation In actual operation, the stencil illumination received by the screen stencil is also affected by other factors. For example, when ultraviolet light passes through the exposure machine glass and polyester photographic negative film, these materials also absorb part of the light energy, so that the irradiation Energy is weakened, and the type and thickness of different materials are different for UV absorption. This will affect the correctness of the exposure time and compensation must be considered. At the same time, the optical density of polygraphic film should also be considered. If black-and-white silver salt film is used, the contrast should meet the requirements. The density of the black part should be greater than 3, and the transparent part should be less than 0.2.
Do not store too much time after the application of the emulsion or the film on the photosensitive film. Perform exposure immediately after exposure.
Do not use emulsions that have exceeded the shelf life. When using emulsions that have exceeded the shelf life, the following phenomenon will occur: Even if the exposure time is correct, the screen cleaning operation is normal, and the other conditions are not changed. It can be very difficult. The shape of the image can be seen on the layout, but the mesh that forms the image is not transparent and is closed by a layer of mist-like photosensitive film. When using a poor exposure light to expose the elbow, even underexposure may show signs of overexposure.
VII. Concluding remarks From the above analysis and discussion, it can be seen that the exposure of the printing plate of the template is influenced by many process factors, such as process variables such as emulsions, screens, light sources and their matching, and the main factors affecting the tariff control. Testing tools and instruments can do the right exposure. Avoiding many quality problems such as pinholes on the screen, sawtooth, stencil is not strong, difficult to recover, and the typical phenomenon of poor exposure such as stencil development difficulties, so as to achieve the ideal plate-making effect.
Door Hinges,Cabinet Hinges,Cabinet Door Hinges,Concealed Door Hinges
Wenzhou Zhaoxia Hardware Co.,Ltd , https://www.zxcabinethardware.com