Problems and Solutions Encountered in the Use of Plate Exposure Machines

Posted on 05-13-2024 by Administrator

Correct exposure requires proper development to match. Development conditions include the chemical composition of the developer, temperature, development time, and mechanical agitation.

Currently, plate exposure machines tend to use processes with relatively high power, short exposure times with high intensity, and weak alkaline development (main developer being sodium silicate). This process results in good plate exposure quality, fast development speed, long lifespan, and also enhances the hydrophilicity and ink resistance of the plate surface.

1. Proper configuration of developer: Some PS plate manufacturers provide powder instead of pre-mixed developer with the plates. These powders, containing main and supplementary agents, might not be evenly mixed in the bottle. When preparing the developer, don't pour half each time; instead, follow the manufacturer's instructions to mix the powder with water in the correct proportions. Additionally, replenish the developer quantitatively and replace it when needed. It's also advisable to wipe the plate with a dampening powder before printing.

2. Determination of development time: The correct determination of development time requires the use of PS plate development control strips or UGRA signal strips for analysis.

3. Power supply voltage of the exposure machine: Low voltage during peak electricity consumption periods can cause a decrease in lamp power and insufficient exposure, while voltage might rise during low consumption periods. It's recommended to install a power stabilizer in the plate room to stabilize light source intensity. Each printing enterprise may have different electricity loads and supply situations. If voltage fluctuations exceed 10%, consider installing a voltage stabilizer when problems arise during peak and off-peak electricity usage.

4. Insufficient development: Reasons may include insufficient developer concentration, leading to residual photosensitive emulsion in blank areas, resulting in dirty printing. Follow the correct developer and supplementary agent configurations as per regulations and manufacturer requirements.

5. Decomposition of the photosensitive agent due to various reasons: In such cases, increase exposure or development time to ensure thorough decomposition of the photosensitive emulsion during exposure and complete removal during development.

6. Uneven gumming: Insufficient surface treatment before high-temperature baking leads to gradual hardening of the photosensitive film on PS plates after baking, making it difficult to remove. Some enterprises neglect surface cleaning before printing, even with baking equipment available. Improper handling of splicing transparent tapes can leave technical traces, making it difficult to detect after development. After baking, on-machine corrections become time-consuming and challenging.

7. Application of image-developing ink (dirty removal): Many printing enterprises have eliminated this step. However, it's crucial to analyze the actual role of this process: a. After applying image-developing ink, the inked parts of the plate turn black, revealing hidden dirty spots similar to highlight dots for removal before baking. b. Ink adheres more easily to images after ink application, increasing the hydrophobicity of image areas. c. The ink film formed after ink application can block UV rays from the natural environment, protecting images from secondary exposure and enhancing the ink resistance of highlight dots. Strict control of dirty spots on PS plates should occur in preceding processes to avoid extensive on-machine corrections in subsequent processes.

8. Inadequate original film density: This leads to insufficient Dmax (maximum density), causing light leakage on the plate. Reasons for overdevelopment include too concentrated developer, excessive development time, and high temperature. Excessive exposure can result from low power or low intensity. Prolonged storage of PS plates after exposure without ink application can also lead to overdevelopment.

9. Overdevelopment and overexposure result in image saturation, affecting ink absorption. Unsuitable cushioning, excessive pressure from water or ink rollers, exposure to strong light after PS plate development, and immediate plate dropping after contact with organic solvents can also cause plate detachment.

10. Overexposure and overdevelopment: a. Original film density is low. b. Poor adhesion between the original film and PS plate, low vacuum degree, causing small dot images to be washed away due to light scattering. c. Inadequate printing pressure and cushioning. d. Coarse sand grains on the PS plate (dot areas become blurred). Underexposure and underdevelopment: a. Insufficient exposure. b. Poor transparency of the original film base (high soft film fog density). c. Gumming of the plate. d. Inadequate printing pressure and cushioning. e. Inappropriate printing dampening solution. f. Ink used for printing is too thin.

11. Quality control content for PS plate making stations must be strictly standardized. Inspection should cover specifications, guidelines, color marks, signal strips, text verification, plate cleanliness, dot quality, and image depth.

12. Water used in the plate-making process should be filtered to avoid scratching the plate surface during development.

13. After development, PS plates must be fixed with a 2%-3% concentration of phosphoric acid to neutralize the alkali solution, enhancing the stability of the plate image. When using acidic liquids for neutralization, ensure thorough rinsing of developed plates before treatment.

14. Cleaning: It's easier to remove dirt when plates are wet, but this might lead to additional dirt due to inadequacies during development. Before cleaning, apply a layer of gum solution to the developed PS plates, then dry and remove dirt or apply image-developing ink for better results. Quality control at the plate-making stage is crucial for ensuring printing quality and efficiency. Regular inspections should cover specifications, guidelines, color marks, signal strips, text verification, plate cleanliness, dot quality, and image depth.