Gravure plate fault analysis and troubleshooting: overprinting is not allowed

There are many factors that affect overlay 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 balance of the dynamic and static balance of the paper guide roller, and the sensitivity of the electrical system. Reliability, illegal operation of the equipment during use, wear of the mechanical system without maintenance, local deformation, etc. This mainly analyzes some factors related to the printing roller.

(A) mechanical precision of the roller

At present, the mechanical precision of the printing roller manufactured by the plate makers generally meets the following requirements:
Length limit deviation ±0.2% of roll length
Diameter limit deviation ±0.02mm
Wall thickness range 6mm-12mm
Keyway width depth limit deviation +0.3mm
Taper taper limit deviation ±1°
The cylindricity is not more than 0.03mm
Flange fillet 7mm～11mm
Dynamic balance below 80g (1200r/m)
One of the reasons for overprinting accuracy is the poor accuracy of the roll. The single-chamfer machine currently has two forms of a plate with a shaft version, a hollow version.
1. Axis version with shaft version is expensive, but machining accuracy is also high. Because the plate-shaping platemakers have to go through an imported MDC grinding machine during machining, on the one hand, the precision of the grinding machine is high. On the other hand, the reference point for grinding is the same as the reference point for printing, so the mechanical accuracy of the printing roller high.
2. The hollow version of the hollow version is slightly less expensive, but because the processing standard at the time of plate making is difficult to be the same as the printing standard, secondly, even if the plate making is consistent with the printing standard, there are cases where the operator does not regulate the wear of the shaft or the long-term demolition of the wearer's shaft at the time of printing. In particular, brute demolition caused shaft damage, making the actual roller wear out of the shaft, the deviation of the roller around the roller is poor, and out-of-roundness is the main reason for overprinting.

(b) Impact of the direction of paper strands on overprinting

In general, the lateral expansion of paper fibers is much larger than the longitudinal expansion of paper fibers, which is generally 2-8 times. Therefore, the transverse elongation of the paper fibers is also much greater than the longitudinal elongation. Straight silk 缕 paper printing refers to the direction of the printed paper fiber and the drum rotation direction. Cross-hitch paper printing refers to the direction of the paper fiber and the roller axis. Straight silk 缕 paper from the boot to the end of printing, the paper's expansion and contraction is more horizontal than the vertical, after the printing of paper images appear prone to horizontal overprint is not allowed. After the horizontal silk file is printed, the paper's expansion and contraction changes are greater in the longitudinal direction than in the horizontal direction. After the printing, the vertical and horizontal images are liable to be misprinted. Therefore, what type of silk paper is used for printing, and the amount of change in the shrinkage of this silk paper must be provided to the platemaking company.

(III) The plate-making company has an overall zoom function in the electric carving station

Depending on the fixed variation of the paper web, the overall horizontal or vertical scale can be used to compensate for the changes caused by the paper strands.

(4) Use trapping (Mida) to make up for overlay error

Fundamentally speaking, the purpose of the capping technology is mainly to compensate for overprint errors in the printing press (because there are mechanical errors in the precise printing presses), and the contraction mode is divided into inward shrinkage and outward expansion.
1. Retraction (color printing process is generally from shallow to dark)
The shrinkage of the neck is to shrink the uniform color within the next color to the next color of 0.05mm to 0.1mm. For example: Under the big red, shrink the yellow line. Under dark purple, narrow the red line. However, the internal shrinkage is generally applicable to a pattern with a large area of ​​two colors, and a small pattern is not applicable.
2. External enlargement (color sequence for surface printing is generally from shallow to deep)
In the practical application of external expansion of the cover a lot, where the adjacent color is generally used to expand the shallow depth 0.15mm ~ 0.3mm, make up the overlay error caused by adjacent two color dew white seam quality defects, so that greatly improved yield.