Barcode Printing Technology Solutions for Plastic Packaging (4)

Third, bar code plastic gravure in the common faults and solutions

The common faults described below are minor defects if the failure is not serious for packaging printing outside the bar code. However, for bar code printing, even if it is a very slight flaw, it will directly affect the reading effect and must be taken to avoid it. Therefore, in a certain sense, bar code printing can be said to be stricter than the printing requirements of other parts.

1. Knife line

The “knife line” refers to the fact that the ink on the portion of the plate that has no pattern lines is not scraped and is transferred to the object to be printed, and line-like contamination occurs at the place where the ink is not allowed (the appearance of an unsightly silk path). In general, it takes a period of time for printing to take place and a certain number of impressions are printed before this failure occurs. Printing inks, printing plate rollers and doctor blades are the three main factors affecting the printing knife line, and environmental printing conditions also have a certain influence on the printing knife line.

the reason:

(1) It has a lot to do with the fineness and quality of the ink (squeegee fitness). The phenomenon of high-grade ink is lighter, while that of low-grade ink is heavier. Improper substances, coarse particles, and foreign substances in the ink can lift or damage the blade, and can form a knife line.

(2) Roller finish and chrome plating quality are poor.

(3) The accuracy of the platen roll machining is not enough, and the eccentricity of the platen roll causes impact on the blade to become the cause of the blade line. At this point you need to re-install or correct.

(4) Bad doctor scraping state.

(5) The viscosity of the working ink is too large. The ink on the layout is excessively dry, and the friction between the plate roller and the blade is relatively increased. It is difficult for the blade to scrape the ink on the plate. (When drying is too late, a trace amount of ink adhering to the non-line portion of the plate roller will be transferred to the film to form a platen).

(6) Adhesion of hard objects on the roll plate will directly damage the blade. Always check and wipe.

(7) Environmental conditions. When the humidity is too high, the dispersibility of the ink is deteriorated and the printing plate is not easily scratched. When the humidity is too low (dry), the plastic film absorbs dust due to electrostatic charges (dust falling into the ink will directly damage the doctor blade and the plate), both of which will cause knife lines. When the ambient temperature is too high, the volatilization is too fast and the solvent balance is unbalanced; when the ambient temperature is too low, the ink dissolves poorly, resulting in difficulty in scraping the ink.

In short, many factors affecting the printing knife line are related to each other, and can directly hurt the knife, or can first hurt the plate layout and then damage the scraper, or foreign matter enters between the scraper and the plate roller to partially lift the blade, and it is easy to blur with the layout. At the same time, it is difficult to judge when a failure occurs, which is caused by ink, squeegee, or layout factors, and the solution cannot be specified. However, in the case of printing inks, substrates, printing equipment, etc., it is generally considered that the following methods are effective.

Solution:

(1) Reduce the viscosity of the ink as much as possible to make it easier for the scraper to scrape the ink off the non-screen portion.

(2) Prevent foreign matter from being mixed during printing (use metal mesh, fabric filter, etc.).

(3) Try to increase the proportion of fresh ink.

(4) Check whether the roller has eccentricity. The diameter of the printing plate roller should be avoided as much as possible, so as to facilitate the control of the status of the ink in the printing roller mesh.

(5) Adjust the squeegee (grinding, pressing, hardness, thickness, angle, position, etc.) to check if the squeegee installation is even and balanced.

(6) Confirm the surface condition of the chrome plating (when sandpaper is used to erase the plate, replating is also a method).

(7) Use slow-drying solvents when conditions are lighter.

(8) Add an appropriate amount of a slowing agent.

(9) The printing shop maintains proper temperature and humidity.

(10) Clean up ventilation ducts in time to reduce the impact of dust.

(one two three four five six seven)