Multi-color printing quality control of offset paper
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In the multi-color printing of offset paper, in order to ensure the quality of printed matter and meet the requirements of customers, we must control all aspects. I think the focus should be on the following aspects.
1. Control of plate quality
(1) When printing, slightly increase the actual exposure so that the dots on the plate are slightly smaller than the dots on the film to compensate for the increase in dots caused by the pressure during printing.
(2) During the baking process, the printing plate will undergo elongation and contraction during the process of cooling from cold to hot. Therefore, in order to ensure accurate overprinting, baking is generally not recommended when performing multicolor printing.
(3) The school edition should be proficient and accurate, minimize the number of proofs, and avoid inaccurate overprinting of the plates due to artificial deformation.
2. Pressure control
(1) Since the surface of the offset paper is rough, the ink absorbing performance is good. Therefore, in order to make the printing ink thick and the dots are clear, the printing pressure should be appropriately increased during printing.
(2) The pressure of the water roller and the ink roller should be appropriate while maintaining good water transfer and ink transfer performance.
3. Selection of printing consumables
(1) Paper. In the multi-color printing process, paper with good sizing degree and good printability should be selected to avoid the phenomenon of pulling and dropping powder. At the same time, pay attention to the impact of paper pH on print quality. The paper should be hanged before printing.
(2) Ink. The fast-drying and bright type ink is an osmotic drying type ink, which can avoid the phenomenon of powdering, matt, sticky, and pulling of the resin type ink, and is more suitable for printing on offset paper, so it is recommended to use a fast-drying and bright type ink.
(3) Blanket. In order to ensure that the dots can be well restored, the blot can be well transferred, and an air cushion blanket should be used.
4. Control of printing conditions
(1) The pH of the dampening solution is controlled at 5.5 to 6.5. If the dampening solution pH is not properly controlled, it will affect the blotting and print quality.
(2) Strictly control the moisture of the printing surface during printing, and maintain the balance of ink and water to achieve the best printing state of “small ink dry water”.
(3) Control of temperature and humidity in the workshop. In the printing process of offset paper, when the humidity of the workshop is large, wrinkles, pulling, falling powder, etc. are easily generated, and when the humidity is small, static electricity is easily generated. In order to achieve the best printing, the temperature of the workshop is controlled at 22 to 25 ° C, and the humidity is controlled at 55% to 65%.