Gravure plate failure analysis and troubleshooting: overprinting is not allowed
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There are many factors affecting overprinting accuracy in gravure printing, such as the stability and reliability of the main motor and its control system, the transmission form and accuracy of the gearbox, the dynamic and static balance of the paper guide roller, the sensitivity of the electrical system and Reliability, the illegal operation of the equipment during use, the wear and tear caused by the maintenance of the mechanical system, local deformation, etc. are all factors of overprinting. Here is a summary of some of the factors associated with the plate roll.
(1) Mechanical precision of the plate roll
At present, the plate roller mechanical precision of the plate-making factory is generally required to meet the following requirements:
Length limit deviation roller length ± 0.2%
Diameter limit deviation ± 0.02mm
Wall thickness range 6mm-12mm
Keyway width depth limit deviation +0.3mm
Cone hole taper limit deviation ±1°
Cylindricity is not more than 0.03mm
Flange rounded corner 7mm ~ 11mm
Dynamic balance below 80g (1200r/m)
The accuracy of the plate roll is one of the reasons for the inaccuracy of overprinting. The single recess machine currently has two forms of a shaft version, a hollow version.
Axis version
The shaft version has a high cost, but the machining accuracy is also high. Because the shaft plate version is processed by the imported MDC car, the precision of the car mill is high. On the other hand, the reference point of the car grinding is the same as the reference point during printing, so the mechanical precision of the plate roll during printing high.
2. Hollow version
The cost of the hollow version is slightly lower, but the processing standard is difficult to be the same as the printing standard, and even if the plate making is consistent with the printing standard, there is still a problem in the printing when the operator wears the shaft or the long-term disassembly of the shaft, especially the brutal disassembly. The shaft damage is caused, so that after the actual thread is worn, the left and right jumps of the plate roll are out of tolerance, and the out-of-roundness is the main reason for overprinting.
(2) The influence of the direction of the silk thread on the overprint
In general, the lateral expansion of the paper fibers is much larger than the longitudinal expansion of the paper fibers, typically 2 to 8 times. Therefore, the transverse elongation of the paper fibers is much larger than the longitudinal elongation. Straight silk paper printing means that the direction of the printed paper fibers coincides with the direction of rotation of the drum. Horizontal silk paper printing means that the paper fiber direction is consistent with the drum axis direction. The straight-lined paper is changed from the start-up to the printing. The expansion and contraction of the paper is horizontally larger than the longitudinal direction. After printing, the paper graphic is prone to lateral misregistration. After the horizontal silk paper is printed, the expansion and contraction of the paper is longitudinally larger than the horizontal direction, and the printed image is prone to longitudinal misregistration. Therefore, what kind of silk paper is used for printing, the amount of expansion and contraction of the silk paper is provided to the plate making company.
(3) The plate making company has an overall zooming function in the electric engraving section
The lateral overall scaling or the longitudinal overall scaling can be used to compensate for the changes caused by the paper thread according to the fixed amount of change of the paper thread.
(4) Using trapping (covering) to compensate for overprinting errors
Fundamentally, the purpose of the capping technology is mainly to compensate for the overprinting error of the printing press (because there is a mechanical error in the precise printing machine), and the covering method is divided into a contraction and an expansion.
1. Indentation (printing print color sequence is generally from light to deep)
The capping retraction is to narrow the upper color evenly to the next color of 0.05mm to 0.1mm. For example, the big red will shrink the yellow line. Under the deep purple, the red will be reduced to a line. However, the indentation is generally applicable to a pattern in which two colors overlap on a large area, and a small pattern is not suitable.
2. External expansion (printing and printing color sequence is generally from shallow to deep)
The external expansion type cover is widely used in practice. Where the adjacent colors are generally expanded by shallow depth 0.15mm~0.3mm, the quality defects of the adjacent two-color white joints are compensated by the overprinting error, and the yield is greatly improved.