Standards for Handling Common Problems in the Printing Process

. Equipment maintenance standards:

Maintenance of the main drive system: maintenance includes cleaning and lubrication. Every Monday, add oil once to the film guide rollers and to the bearings, sliders, chains and hand wheels that work at normal temperature. Before the start of each month, apply grease (lubricant, once) to the film guide roller bearings and chains inside the drying tunnel.

Maintenance of electrical equipment: this includes the electrical control department and the various actuating electrical devices. Electrical parts should normally be kept clean and dry, and wiring should be safe and reliable; do not dismantle or refit any electrical facility without good reason. If an electrical fault occurs, report it to the technical department in good time.

Before the start of each month, regularly inspect the machine as a whole to see whether any screws are loose, and reinforce any loose parts.

Troubleshooting: (common faults in gravure printing and their solutions)

. Plate scumming (ink dragging)

Symptom: ink that the doctor blade has failed to scrape clean remains on the non-image areas of the gravure cylinder and is transferred to the film during printing, becoming a smudge.

Reduce the printing speed.

Adjust the doctor blade angle to make it steeper.

Reduce ink viscosity.

Adjust the solvent to increase the ink drying speed.

Check whether the doctor blade is mounted straight and whether the pressure is even.

. Doctor blade marks (blade lines)

Symptom; ink not scraped clean by the doctor blade is dragged into linear smears on the non-image areas of the gravure cylinder and transferred to the film; it also refers to the effect caused by nicks in the doctor blade.

Filter the ink to reduce debris and coarse pigment particles in the ink.

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

Check whether the doctor blade edge has small nicks; grind it with sandpaper or replace it.

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

Symptom: the ink of the previous colour offsets onto the plate of the next colour.

Reduce the pressure of the impression cylinder.

Improve the adhesion of the previous colour's ink and increase the ink drying speed.

Reduce the viscosity of the next colour.

Symptom: the ink shows uneven print transfer mottling.

Reduce the depth of the cells on the gravure cylinder.

Increase the printing speed.

Change the angle of the cells on the gravure cylinder.

Increase ink viscosity.

Correct the printing tension.

During printing, the ink transfer rate steadily decreases.

When production restarts after printing has ended, the ink clogged in the plate cannot be dissolved.

Flatten the doctor blade.

Reduce the evaporation rate of the solvent.

Reduce ink viscosity.

At the end of each print run the gravure cylinder should be cleaned thoroughly at once.

Symptom: when the web is wound up immediately after printing, the ink and the film stick to each other, or the ink transfers to the reverse side of another layer of film.

Reduce the winding tension.

Allow the ink to dry thoroughly.

Increase the ink drying speed.

Use an appropriate amount of anti-blocking agent.

Symptom: the printed ink layer exhibits whitening.

Reduce the air temperature in the workshop.

Increase the drying capacity of the printing press so as to dry rapidly and thoroughly.

. Rubber roller debris

Symptom: regular incomplete printing of the image and text occurs during printing.

Check whether there is small debris such as bits of film on the rubber roller.

Check whether the surface of the rubber roller is damaged.

Symptom; colour differences appear between rolls during printing.

Strictly control ink viscosity and keep it stable and consistent.

Ensure that the ink mixing ratio is the same every time so that the colour is stable.

Prevent colour variation caused by plate clogging on halftone plates.

Keep the printing speed stable.

Keep the doctor blade angle stable.

Prevent colour variation caused by improper use of old ink.

Symptom: the printed matter is misaligned lengthwise or crosswise, making the image and text of the printed matter blurry.

Prevent misregistration caused by improper tension setting; make appropriate adjustments according to the actual situation.

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

Make crosswise adjustments at any time.

Check whether the printing cylinder and rubber roller are running out.

If the cause is a film quality problem (such as slack or tight edges or flaring), replace the film.

Symptom: the printed dimensions of the printed matter do not match the actual required size.

Adjust the printing tension appropriately.

Prevent dimensional deviation caused by improper temperature setting.

. Process operation steps:

The coating gravure printing process is operated as follows:

Preparation of raw materials. After receiving the production work order, collect the raw materials according to product specifications and quantity. Prepare inks with matching performance characteristics and an appropriate amount of additives according to the product's colour sample. Before printing begins, the type and quantity of ink should be mixed in advance.

Installation of the cylinder: select the correct cylinder and install it as required by the process sheet. If a multi-colour product is being printed, attention must also be paid to the left and right faces of the cylinder, and the printing cylinders should be installed in each unit according to the printing colour sequence.

The colour sequence for colour printing is generally; white

The colour sequence for colour printing is generally: black

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

Start the machine for a trial print. Run the machine empty at low speed to check whether all parts of the machinery are normal, mount the roll stock on the unwinding shaft, taking care to face the treated surface of the film towards the printing side, and adjust the tension. Check whether the doctor blade scrapes the ink evenly and whether the areas without a pattern are scraped clean.

Adjustment of the drying temperature: apart from the evaporation rate of the solvent itself, how quickly the ink dries is mainly determined by the temperature of the hot air in the oven. Generally speaking, when the machine speed is high, the ink layer is thick, the ambient temperature is low, the humidity is high and the solvent evaporates slowly, the drying temperature should be set slightly higher. The principle for temperature adjustment is to keep the drying temperature as low as possible while ensuring that the printed matter is thoroughly dried.

. 4. 2

Adjustment of printing pressure. Generate printing pressure between the impression cylinder and the printing cylinder, the amount of pressure being governed by what is just sufficient to produce a clear image and text.

. 4. 3

Tension adjustment. The following factors should be considered in tension adjustment:

. 4. 4

The type and stretch rate of the film, for example

if the stretch rate is large, the tension should be smaller;

if the stretch rate is small, the tension should be increased appropriately.

. 4. 5

The thickness and quality of the film. When the film is relatively thick the tension may be increased appropriately; when the two edges of the film are not equally tight, the tension may be increased appropriately.

. 4. 6

Drying oven temperature. When the ambient temperature rises, the film stretches more easily, so the tension may be reduced accordingly.

Winding: the web should not be wound too tightly, so as to prevent the product from deforming or picking up dirt. As a general rule, it is judged acceptable when the product is wound neatly and, placed upright, the core does not slide.

Inspection of product quality. (Against the product quality standard)

Ink that the doctor blade has failed to scrape clean remains on the non-image areas of the gravure cylinder and is transferred to the film during printing, becoming a smudge.

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