The PS plate coated with the photosensitive layer in advance is processed into a printing plate for printing after exposure, development, decontamination, gumming and other processes. In the positive-type PS plate, the exposed photosensitive layer undergoes photolysis reaction and is dissolved by the developer to be removed from the plate surface. After applying the adhesive layer, a stable hydrophilic blank portion is formed; the unexposed photosensitive layer remains in The printing plate is lipophilic and forms part of the image (Figure 1).
Fig. 1 Positive drawing PS plate making process
1. Exposure
The photosensitive layer of the positive version and the PS version are closely placed and placed in a special printing machine. After vacuum extraction, the light source of the printing machine is turned on, and the photosensitive layer of the non-image part generates light under the irradiation of light. Decomposition reaction, this process is called exposure, also known as printing.
1. Original outlet quality
The PS version has fine sand mesh, high resolution, good tone reproducibility and dot reproducibility. In order to make full use of this advantage of the PS version, there are certain requirements for the dot density and dot finish of the original version used for printing.
The original version of the PS version is usually made by electronic scanning, photography or laser phototypesetting. In the production process of the original version, due to the low gamma value of the photographic film, when the exposure, development or thinning is excessive, a soft dot with a low density value or an activity with a small edge density value and a large center density value will be formed Dot; With such original printing, a slight increase or decrease in exposure will cause a large reduction or increase in the area of ​​the dots on the printing plate, thus affecting the reduction of the PS version to the dots (see Figure 2). Therefore, the dots on the original version used for printing should be hard dots with high density, uniform edge and center density, and smooth peripheral edges. Generally, the dot density value is above 3.0 (the density of the field version should be higher). The rigidity of the exposure of the hard dots is relatively large. Even if there is some change in the exposure, the dot area on the printing plate will not change much, and the quality of the printing is relatively stable.
For the original plate used for printing, the surface is also required to be clean, without scratches, pinholes, and no glue marks on the stitched image.
Fig. 2 Reproduction effect of soft and hard dots
2. Exposure principle
Put the emulsion side of the original version of the positive image and the photosensitive layer of the PS version together, vacuum suction to make it close, and then turn on the light source in the printing machine to expose the printing plate. The light passes through the non-image part of the original plate to reach the photosensitive layer, and the visible part of the photosensitive layer decomposes and emits nitrogen gas to form indone compounds and indene acid compounds upon contact with water.
Exposure time of several photosensitive resins
Plate photosensitive resin model
Exposure time (s)
light source
Type 215
15 ～ 20
Iodine gallium lamp
Type 214
20 ～ 30
Iodine gallium lamp
Type 124
40 ～ 75
Iodine gallium lamp
3. Exposure light source
The photosensitive layer of the PS version has a certain spectral sensitivity. Only light with a wavelength in a certain limited range can cause the molecular structure of the photosensitive layer to change. That is, only when the light emission spectrum of the light source matches the spectral sensitivity of the photosensitive layer Only then, the photosensitive layer may undergo a photochemical reaction. According to the measurement, the wavelength range of the light wave that can cause the photochemical reaction of the photosensitive layer is 250-420 urn. Considering the absorption of light by the glass of the printing machine and the original film of the printing plate during printing, this range is actually 300-450 nm. The wavelength of the light wave in the above range is mainly ultraviolet light and blue-violet light with higher energy. Therefore, in order to make the photosensitive layer of the PS plate quickly sensitive, so that the tone of the image can be well reproduced on the printing plate, it is necessary to select a light source that can generate ultraviolet light or blue-violet light of sufficient intensity.
In addition to the light spectrum used for printing, the light emission spectrum should match the spectroscopic sensitivity of the photosensitive layer, and the following conditions should also be met: the light energy distribution is uniform and stable, so it will be used in the digitalization and standardization of the printing process; low power consumption , High printing efficiency; Simple structure, easy operation, easy maintenance; Factors that pollute the environment during use (such as heat, ozone, smoke, etc.) should be reduced as much as possible.
According to the above requirements, currently, as the PS version of the printing light source, there are mainly high-pressure mercury lamps and iodine gallium lamps. The high-pressure mercury lamp is made by encapsulating mercury vapor into the lamp tube, and the emission spectrum is continuous, with a wavelength range of 300-450 nm, which matches the spectral sensitivity of the photosensitive layer of the PS plate very well, and the printing efficiency is very high. The gallium iodide lamp is made by adding bromine of gallium and gallium metal to the lamp tube of the high-pressure mercury lamp. The amount of light in the emitted spectrum near the 400nm wavelength band is significantly increased, which is more in line with the spectral sensitivity of the photosensitive layer of the PS version. , The printing efficiency is higher. Using the iodine gallium lamp as the light source for printing is about 0.5 to 1 times higher than the high-pressure mercury lamp.
The quality of printing is not only related to the spectrum and light intensity of the light source, but also affected by the distance between the plate and the light source. The shorter the distance, the less exposure time is required. However, the light source is close to the plate, and the part of the plate that is vertically irradiated by the light is larger than the surrounding part of the plate that is obliquely illuminated. This will cause the part of the plate that is directly illuminated to be overexposed, and the part that is obliquely illuminated to be underexposed. In order to avoid this phenomenon, the distance between the layout and the light source should be equal to or slightly longer than the length of the diagonal of the layout.
WeeTaach Digital Signage covers a wide series of such as 32, 43, 49, 55, 58 and 65 inches, portrait or landscape, This series of digital signage panels are running with Android OS, and we are happy to accept OEM productions on basis of quantitative orders.
â… . Illustration:
â…¡. Main Features:
- Excellent cost/performance device
- Fashion design, user-friendly UI
- Local and Network service & maintenance
- Easy Ads timing & content control
- Playback of A/V programs, Office files, etc.
- Unified management through server/control center
- Ethernet, WIFI & mobile network services
- Android OS
â…¢. Specification
- Type: Wall-mount
- Color: White, Black, or customized
- Screen: First class LED backlighted
- Screen Proof: 4mm-thick tempered glass
- Screen size: 32 to 65 inches
- Touch Mode: IR or Capacitive (Optional)
- Main Interfaces: 2*USB2.0, SD or TF slot,1*MSATA, 1*RJ45
- Speaker: Embedded 2x10W, stereo
- Definition: 1080x1920
- Brightness: 350cd/m²
- Static Contract: 1200:1
- Visual Angle: 178 degrees (V/H)
- Display Scale: 9:16/16:9
- Power Supply: AC100-240V, 50/60Hz
- Working Condition: 0 to 50 degree C/ 10% to 90% RH
- Storage Condition: -20 to 60 degree C/ 10% to 90% RH
Note: The technical specifications herein are for reference only. We remain the rights to upgrade without prior notice.
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