Common Issues in Screen Printing and Their Solutions
1. Causes of Pinholes due to Dust and Debris on Screen:
- Dust mixed with photoresist during screen plate coating can lead to pinholes.
- Dust or debris on the screen during the printing process can block mesh holes, resulting in pinholes. To prevent this, regularly check and repair pinholes on the screen, and ensure proper cleaning to remove any dust or debris.
2. Pinholes Caused by Surface Contamination on Printed Board:
- Residue of cleaning agents on the board surface can cause thin film formation and “ink injection,” leading to pinholes.
- Surface contamination from handling with bare hands can also cause “ink injection” and pinholes. To avoid this, thoroughly clean the board surface to remove any residue, and handle boards with gloves to prevent contamination.
3. Appearance of Bubbles in the Printing Material:
- Bubbles may form due to the addition of solvent to adjust the viscosity of the printing material.
- If some bubbles do not disappear naturally, a defoamer may be necessary. To address this issue, allow the material to sit for a period of time to let bubbles dissipate, and use a defoamer as needed to remove any remaining bubbles.
4. Zigzag Screen Printed Wires:
- Thin mask on the screen can cause gaps in the screen image, resulting in jagged wires.
- To maintain optimal wire direction and angle during screen making and stretching, use appropriate thickness and elasticity for the mask, high-mesh polyester filaments for high-size requirements, and adjust screen tension, spacing, and printing pressure as needed.
5. Screen Pattern on Screen Printing Graphics:
- Issues like screen patterns can occur due to the selection of a low-mesh screen, poor thixotropy of the printing material, and fast drying of the material. To overcome this, use a high-mesh screen, materials with good thixotropic properties, and ensure slow-drying materials are used.
6. Speckled Appearance and Spots on Screen Printing Graphics:
- Various causes, including slow printing speed and drying, low solid content, excessive thixotropy, influence of static electricity, and pigment dispersion, can lead to a speckled appearance. Improve fluidity of the printing material, use solvents with faster volatilization speed, select high-viscosity materials, and minimize static electricity with an elimination device to address this issue.
7. Uneven Color in Screen Printing Graphics:
- Uneven dispersion of colorant and high fineness can cause ink bleeding and result in uneven color. To address this, filter the printing material before printing and ensure thorough stirring to prevent uneven coloration.