Gravure Printing Maintenance and Troubleshooting Guide for Flexible Packaging Converters

Equipment maintenance standard

Main drive maintenance: clean and lubricate the system. Every Monday, add oil once to film guide rollers and to bearings, sliders, chains, and handwheels working at room temperature. Before the start of each month, apply grease once to the film guide roller bearings and chains in the drying tunnel.

Electrical equipment: the electrical control department and all actuating devices must stay clean and dry, with safe, reliable wiring. Do not dismantle or reassemble electrical facilities without authorization; report any electrical incident immediately to the technical department.

Before each month begins, inspect the whole machine to see if any screws are loose, and tighten any loose points.

Troubleshooting: common gravure printing faults and solutions

Plate scumming (ink dragging)

Symptom: ink not fully removed by the doctor blade remains on the non-image area of the gravure cylinder and transfers to the film, creating a stain.

Lower the printing speed.

Set the doctor blade at a steeper angle.

Reduce ink viscosity.

Adjust the solvent to accelerate ink drying.

Verify the doctor blade is mounted straight and pressure is even.

Doctor blade marks (blade lines)

Symptom: ink not cleaned by the doctor blade is dragged into linear marks on the non-image area of the gravure cylinder and transfers to the film; it also covers defects caused by nicks on the blade.

Filter the ink to remove debris and oversized pigment particles.

Lift the doctor blade or use a chopstick to clear debris or coarse pigment particles trapped under it.

Check the blade edge for small nicks; grind it with sandpaper or replace it.

If the cylinder surface is rough, polish it with sandpaper.

Symptom: ink from the previous color offsets onto the next color's plate.

Reduce impression cylinder pressure.

Improve the adhesion of the previous color ink and increase its drying speed.

Reduce the viscosity of the next color.

Symptom: ink transfer appears uneven and mottled.

Reduce the cell depth of the gravure cylinder.

Increase the printing speed.

Change the cell angle on the gravure cylinder.

Increase ink viscosity.

Correct the printing tension.

During printing, the ink transfer rate keeps falling.

When production resumes after printing stops, ink clogged in the plate cannot dissolve.

Flatten the doctor blade.

Slow down solvent evaporation.

Reduce ink viscosity.

Clean the gravure cylinder immediately after every print run.

Symptom: if rewinding starts immediately after printing, ink and film stick together, or ink transfers to the reverse side of another film layer.

Reduce winding tension.

Ensure the ink dries completely.

Increase the ink drying speed.

Use an appropriate amount of anti-blocking agent.

Symptom: the printed ink layer whitens.

Lower the workshop air temperature.

Increase the dryer capacity of the printing press for fast, thorough drying.

Rubber roller debris

Symptom: regular incomplete printing of graphics and text.

Check the rubber roller for small debris such as bits of film.

Check whether the rubber roller surface is damaged.

Symptom: color variation appears between rolls during printing.

Tightly control ink viscosity and keep it stable and consistent.

Keep the ink mixing ratio identical each time for stable color.

Prevent color variation caused by plate clogging on halftone plates.

Keep printing speed stable.

Keep the doctor blade angle stable.

Prevent color variation caused by improper use of old ink.

Symptom: printed matter is misaligned in the machine or cross direction, making graphics and text blurry.

Prevent misregistration caused by incorrect tension settings, and adjust appropriately based on actual conditions.

Prevent misregistration caused by dirty guide rollers; clean the guide rollers of each unit.

Make cross-direction adjustments at any time.

Check whether the printing cylinder and rubber roller run out.

If the issue comes from film quality (such as slack/tight edges or flaring), replace the film.

Symptom: the printed size does not match the required size.

Adjust printing tension appropriately.

Prevent dimensional deviation caused by improper temperature settings.

Process operation steps

Coating gravure printing is operated as follows:

Raw material preparation: after receiving the production work order, collect materials by product specification and quantity. Based on the color sample, prepare matching ink and the right amount of additives. Mix the ink type and quantity before printing starts.

Cylinder installation: select and install the correct cylinder according to the process sheet. For multicolor work, pay attention to the left and right faces of the cylinder and load printing cylinders into each unit in the correct color sequence.

The color sequence for color printing is generally: white

The color sequence for color printing is generally: black

Select a rubber roller compatible with the cylinder and install the doctor blade.

Trial printing: run the machine empty at low speed and check all mechanical parts. Load roll stock onto the unwinding shaft, face the treated side of the film toward the printing side, and adjust tension. Check whether the doctor blade scrapes ink evenly and cleans non-image areas.

Drying temperature adjustment: ink drying speed depends not only on solvent evaporation but mainly on hot-air temperature in the oven. Generally, when machine speed is high, ink layer is thick, ambient temperature is low, humidity is high, and solvent evaporates slowly, set drying temperature slightly higher. The principle is to keep drying temperature as low as possible while ensuring full drying.

4.2

Printing pressure adjustment: create printing pressure between the impression cylinder and the printing cylinder; pressure should be just enough to produce clear graphics and text.

4.3

Tension adjustment: consider the following factors:

4.4

Film type and stretch rate, for example

If stretch rate is high, use lower tension;

If stretch rate is low, increase tension appropriately.

4.5

Film thickness and quality: for thicker film, tension may be increased appropriately; if the two edges are not equally tight, tension may also be increased appropriately.

4.6

Drying oven temperature: when ambient temperature rises, film stretches more easily, so tension can be reduced accordingly.

Winding: do not wind too tightly, to avoid product deformation or ink transfer. A common standard is that the roll is neatly wound and, when stood upright, the core does not slide.

Product quality inspection: check against the product quality standard.

Ink not fully removed by the doctor blade remains on the non-image area of the gravure cylinder and transfers to the film during printing, creating a stain.

This article is reprinted from China Packaging Network (pack.cn); original link: http://news.pack.cn/show-362251.html