Second, the normative requirements of the proofing process 1. Environmental conditions - room temperature range 18 °C ~ 25 °C.
- Indoor humidity range: relative humidity 60% to 80%.
——Lighting conditions: Refer to “CY3-91 Color Evaluation Lighting and Observation Conditionsâ€
Color temperature: 6500K (D65 light source);
Color rendering coefficient: ≥ 90%;
Illumination: Look at the sample table and paper table about 500 ~ 1500lx (that is, four 36W fluorescent lamps, irradiation distance 1.2m).
- Dust and ventilation: Proofing room must consider both dust and ventilation, that is, when cleaning the blanket and ink roller should be appropriate exhaust, usually not suitable for ventilation, so as not to affect the control of temperature and humidity.
2. Raw Materials - Ink: One or two sets of inks (one set for quality proofing and one set for general product proofing to reduce costs) are selected after hue and coupling testing.
- Paper: In principle, one type of coated paper (128g/m2 or 157g/m2), or two types of paper (one for coated paper and one for offset paper) should be fixed. When you need to use printing paper to proof, you must measure the thickness of the paper to ensure that the paper pressure is accurate.
- Blankets and liners: Air rubber and hard liners (such as coated paper or white film base) are in principle used. The thickness of the blanket and pad must be calibrated to ensure that the roller pressure is accurate.
——Cleaning roller: When cleaning the ink roller and blanket, use the roller cleaning liquid with good cleaning effect, rapid and effective, and less stimulation to personnel.
3. Equipment condition - leveling of the proofer: The leveling error of the long side of the machine is measured with a 0.02 mm/m scale level meter to be ±0.04 mm, and the short side is ±0.02 mm.
- The pressure of the blanket cylinder (indicated by the height of the blanket surface relative to the roller) is: (0 ± 0.03mm), measured once every 120°, and averaged, ie: blanket thickness + spacer thickness = (2.286 ± 0.03) mm. If the blanket is used for a long time (eg 3 months or more), the thickness of the liner should be adjusted in time if it exceeds this range.
- The pressure of the platen (including the thickness of the PS plate) is: +0.12 to +0.15mm (that is, the surface of the PS plate is higher than the height of the guide rail).
- Paper table pressure (including paper thickness) is: +0.15 ~ +0.18mm (that is, the surface of the paper is higher than the height of the guide rail).
——There are two rollers on both sides of the active rack. When the rack is moved to the side of the ink-sharing system and the rack is not pressurized at the same time, the pressure on the roller and the lower rail surface can be turned by hand to rotate. Yes, too tight or too loose must be adjusted.
- Ink system: The ink roller print width of the ink roller on the platen or paper should be uniform and the error is less than 1mm.
- The distance between the velvety roller and the plate is 0.01mm (measured with feeler gauge).
- Tracks, gears, racks, bearings, etc. are lubricated in accordance with the maintenance regulations. The principle is to provide less oil and diligent fuel.
- Periodically check and calibrate the reflection densitometer.
4. Process conditions - control of field density: The method is determined by the relative contrast K value on the premise that the raw materials are fixed, the machine condition is normal, and the environmental control is normal. The actual field density corresponding to the maximum K value of each color version is the actual field density that needs to be controlled under the current conditions. The maximum relative contrast K value means that the maximum amount of ink can be applied under the premise of the dot gain rate.
K = D in the field - D75% of outlets D. The actual field density of each site is not the same. Is a factory (company), under different environmental conditions, paper, ink and different printability conditions, the field density value is also not. It is recommended that a relative contrast K value be measured each summer and winter to determine the different field densities.
- Quality of outlets: Mainly through the sampling control signal strips. Therefore, the proofing version must be affixed with the control strips for proofing in order to measure the density of the field, the enlargement ratio of the outlets, the reduction quality of the outlets, and ghosting. The outlets should be dense, non-tailed, and empty. In general, the fact that outlets are not true is mainly caused by unbalanced water and water (excessive water volume). Other reasons may be due to insufficient pressure and the excessively coarse sand of the PS version (especially the regenerated version).
The amount of dampening water should be controlled to the minimum, dampening should rely mainly on the automatic water supply device and plate condensing water.
- Choice of ink and ink: The type of proof ink should be consistent with the printing ink in principle. In addition to hue, the viscosity of the four proofing inks should be basically the same. The ambient temperature should be controlled normally. The ink should be fully pressed and blended on the ink adjustment table. After the ink reaches the ink-equalizing system, it should have more than 20s of ink-inking time to fully emulsify the ink. Plate condensing temperature can not be too low, otherwise it will cause ink viscosity is too high, resulting in pull paper phenomenon. The ink must be packed in small bottles (1kg or 2kg). After use, the lid must be tightly closed to prevent drying and crusting.
- Ink uniformity: The blackness of several proofs is even. Similarly, it is required that the ink color (solid density) in the horizontal direction of each same sheet be consistent, and the error should be smaller than the error allowed in the solid density.
- Four-color version of the standard: In accordance with industry standards, four-color version under normal circumstances, the cross-line register error should be less than the required requirements (see CY/T4-91). The main reason for overprinting is the paper quality, ambient temperature, improper control of dampening water volume, and improper operation.