How to Perform Start-up Operations in Flexible Packaging Printing?

1. Start-up Conditions

Start-up work may begin only after the start-up preparation work has been completed.

1. Start-up

The machine operator starts the main motor to make the plate cylinder run at low speed, and at the same time starts the burner, oven temperature and fans.

1. Taping

The ink mixer and the unwinding/winding workers wrap the plate cylinder end caps and the threaded parts of the plate shaft with adhesive tape, so as to prevent ink from adhering to them during operation and affecting the next plate mounting.

1. Raising the Ink Trough

The three people act separately: raise the ink trough so that the plate cylinder is immersed 3-4 cm into the ink trough.

1. Adjusting the Doctor Blade

The three people act separately: lower the doctor blade until it lightly touches the plate surface, preliminarily set the printing distance according to the characteristics of the screen pattern, and adjust it until the blade face is balanced so that ink scraping is basically good, then press the pneumatic switch. If the ink scraping effect is still not good at this time, the feed distance at both ends of the doctor blade should be adjusted in a balanced manner until ink scraping is good. Note: when ink is not scraped clean, the pneumatic pressure of the doctor blade should be appropriately increased; mechanical pressure must not be used, so as to avoid shortening the service life of the doctor blade or the plate cylinder.

1. Setting Process Parameters

The machine operator sets the unwinding tension, winding tension, feed tension, take-up tension and the pressure of the front and rear traction rollers.

1. Lowering the Pressure Rollers

The ink mixer and the unwinding/winding workers start from the first color and press down the printing pressure rollers in sequence, controlling the pressure within the specified range.

1. Preliminary Registration

The three people carry out the work simultaneously and operate separately, performing registration in the longitudinal and transverse directions manually. After it is basically accurate, switch to automatic mode.

1. Coarse Ink Adjustment

As soon as the ink color appears, the ink mixer must immediately carry out color matching and ink adjustment. There is no need to wait until registration is completely accurate and the machine is stopped before adjusting the ink.

When the ink color differs greatly, even if the film is still running, coarse color matching can be carried out without stopping the machine (both spot colors and gradation effects are acceptable). At this time, the ink should be adjusted as quickly as possible; the film can be cut and sampled for color comparison while the machine is running, without stopping. Only after the newly adjusted ink color comes out and the hue is basically close may the machine be stopped for color matching when registration is basically accurate. Before coarse ink adjustment, the required ink must be placed within easy reach in advance, and the phenomenon of looking for ink everywhere when ink is needed should be avoided.

1. Color Matching (Color Comparison)

① After registration is basically accurate, the machine operator stops the machine, and the ink mixer compares colors. Color matching work should be carried out only after ensuring that the adjusted ink is mixed evenly.

② According to the requirements of printing standards or printing standard samples, compare colors carefully. The hue of each color block of the entire pattern should be carefully compared at one time; it is not permitted to compare the hue of only some of the color blocks in one sampling.

③ When comparing colors, according to the requirements of the product structure, corresponding materials (such as pearl film, metallized film, white cardboard, etc.) should be laid under the substrate for the comparison.

1. Fine Ink Adjustment

① The ink mixer carefully adjusts the ink according to the color comparison results and stirs the ink evenly as quickly as possible.

② At this time, the machine operator should adjust the balance bar according to the registration effect.

③ The ink mixer's task is to complete the ink adjustment work as much as possible at the same time as the machine operator completes color registration.

1. Preliminary Inspection

① While the ink mixer is comparing and adjusting colors, the machine operator should carry out preliminary inspection work and check whether the product has defects other than hue, such as: wrong printing of the product, poor transfer in light screen areas, plate blocking, blade lines, incomplete ink scraping, mottled ink color, pressure marks, etc.

② While the ink mixer is comparing and adjusting colors, the machine operator should make handling decisions as quickly as possible based on the preliminary inspection results. It should be ensured that all problems that appeared before the next sampling are resolved.

③ While the ink mixer is adjusting colors, the unwinding/winding workers carry out auxiliary color adjustment and registration work.

1. Sampling

① After fine ink adjustment, begin sampling.

② If the hue fails to meet the standard, the color comparison and color adjustment process need to be repeated.