PS version and offset printing plate production

A. PS version (plate) classification, structure and performance
1. Classification of PS plates:
——Pattern version of positive type PS: The PS version of printing with positive color separation sheet,
The photosensitive film produces a photodecomposition reaction under ultraviolet irradiation.

——Graphic PS version: PS version of negatives using color chart
Its photosensitive film produces photopolymerization under ultraviolet irradiation.
Divided into plate base, oxide layer, photosensitive layer
2. PS plate structure:
- Edition base: aluminum metal base. There are usually two thicknesses of 0.25mm and 0.15mm.
——Oxide layer: ie hydrophilic layer, through anodizing and sealing process
A porous, hard oxide layer forms on the side of the plate. Has strong wear resistance, corrosion resistance, water absorption.
- Photosensitive layer: the oleophilic layer, by the photosensitizer (nitrogen compound),
Film-forming resin, dye, solvent and other components.
3. PS version of the main performance indicators:
- Surface roughness: 0.40≤Ra≤0.90(um)
- Plate base oxide quality: 1.50 ~ 3.50 (g/m2)
- Base substrate photosensitive layer quality: 1.60~2.50 (g/m2)
- Resolution: ≤ 10.0 (um)
——Reproducing range of outlets: 2%~98% Complete outlets - Version base color density: ≤ 0.03
- Sensitivity: ≤300 (mj/cm2)
——Retaining film rate: ≥90%
- Thickness of printing plate: 0.15~0.40mm (thickness deviation? 0.01mm)
- Printing plate size: in line with GB/T 17155-1997
——Resistance to Indian Force: Undecided Note: The main factors affecting the printing plate's resistance to printing force 1PS version Photosensitive film adhesion 2 Separation film Solid density in the field 3 Printing pressure 4 Paper with impurities (grit) amount 5 Fountain solution Ph value II. Offset Printing plate production (printing) process color separation sheet output → exposure → development → revision → post-processing → printing - exposure: is the color separation film and the PS plate film surface close contact with UV light source (such as iodine Lamp) (spectral range approx.

360-430 nm) exposure.
——Development: Photosensitive film (non-printing area) that produces photolysis reaction (exposure) and dissolves in dilute alkali solution to expose

Oxidation (hydrophilic) layer.
——Revision: Cleaning the washed plate with dirt removing agent (consisting of related solvents, thickeners, dyes, wetting agents, etc.)

Edition except dirty operation.

Post-processing: including drying, baking version, ink extraction, and eraser.

• Baking: Mainly to improve the printing plate's resistance to printing. Bake at 5 to 8 minutes at 230°C to 250°C.
·Ink extraction: In order to improve the contrast of the graphic part of the layout (for ease of inspection), the photosensitive film of the printed part of the image is protected from light damage.

, Increase the ink absorption of the printing plate, and apply the ink removing agent on the plate.
• Eraser: To protect the prepared plate and prevent oxidation and dust contamination, apply rubbing paste (such as gum arabic) to the plate.

III. Requirements for the quality of color separation films

- Film base fog density ≤ 0.15
- Solid density ≥ 3.50
- Permeability: Density of the transparent part of the dot (excluding the film base) ≤ 0.10
- The edge width of the network ≤ the width of the network line / 40 (um)
- Film linearization error ≤ ± 2%
- Registration error (diagonal) ≤ 0.02%
- layout clean, no scratches, creases, etc.

Source: Chinese Printing Community