In the transparent plastic box printing process, because the surface smoothness of the film is higher than that of the paper, and a layer of primer oil is usually printed at the time of printing, the surface of the film is less adsorbed on the ink, the gradient mesh printing effect is poor, and the ladder is prone to appear. Fault phenomenon. If the prepress design or plate output is not good, it will further affect the gradient net printing effect. In the following, the author analyzes and discusses the precautions to reduce the occurrence of step faults in the printing process of the transparent plastic box gradient mesh from three aspects of the computer design process, the plate making process, and the printing process.
Computer design process
(1) Gradient nets are usually designed using “computer presets”. Gradient strips should not be pulled when designing, otherwise it will easily lead to a stepped fault during printing.
(2) Since PostScript only allows 256 gray levels at most, the larger the gradation step, the more likely it is to have a staircase fault, so the gradual step size should be controlled within a reasonable range.
(3) Minimize the length of the gradation. For the effect of the first field and the second gradation, design the field and the gradient part separately, and then connect them again to reduce the chance of occurrence of a stepped fault.
(4) Gradient meshes for scanning or color separation can use the "Gaussian blur + noise processing" method to reduce the appearance of a stepped fault.
In the actual work, especially in the proofing stage, our company will examine and analyze the design part of the gradient mesh in the manuscript of the customer, and if necessary, will carry out design revision on the computer to ensure the printing effect of the gradient mesh.
Plate making process
(1) The highest output accuracy is used during plate making to reduce the occurrence of step faults. Usually, the maximum output accuracy of CTF plate making is 3657dpi, and the maximum output accuracy of CTP plate making is 2400dpi (up to 4800dpi for configuration).
(2) The lower the number of screen lines, the less likely it is that there will be a staircase fault. For example, the number of screens is usually 175 lines per inch. When a stepped fault occurs in gradient screen printing, the number of screens can be reduced to 150 lines per inch to improve the printing effect.
(3) From the visual analysis, the printing effect when the screening angle is 45° is the most smooth and natural. Therefore, the gradient mesh of the spot color should be designed with a 45° screening angle to reduce the stepped fault.
(4) For the problem of increased printing dots, usually use the dot gain compensation curve to adjust. However, straight line publishing will be used when designing drafting manuscripts to achieve the best gradient effect.
(5) If the concentration and temperature of the liquid in the plate processor are too high, it is likely to cause the loss of fine dots and increase the risk of step faults when the gradient web is printed. Therefore, our company will appropriately reduce the concentration and temperature of the solution of the plater during the plate making process, and use the method of increasing the development time to make up for the lack of potion concentration, which can significantly improve the phenomenon of the stepped fault.
(1) In the printing process, the gradient direction of the gradient mesh and the ink path direction should not be the same.
(2) The pressure of the ink roller should not be too large, otherwise the gradient bar can easily generate ink bars when printing. Therefore, the ink roller pressure must be adjusted strictly according to the specified value.
(3) The fourth root of the printing roller is used to collect the ink. The pressure can be adjusted to be larger. Otherwise, the ink collection will be incomplete and the ink bars will be produced.
(4) The pressure of the water roller should not be too large, otherwise, the gradient web print site is prone to white bars.
(5) The pH of the fountain solution is not easy to be low, otherwise it will cause the loss of fine dots when printing, resulting in a staircase fault.
(6) After the blanket is aged, the ink cannot be transferred normally, resulting in poor transfer of the fine dots, resulting in a stepped fault. Therefore, you should regularly check the condition of the blanket and replace the aging blanket in time.
The reasons for the occurrence of the staircase fault phenomenon in the transparent plastic box gradient web printing are relatively complex. Operators should carefully analyze each process, carefully search for the cause of the problem, and ensure that each operation is strictly performed in accordance with the regulations. The problem can be resolved quickly.