flexo printing troubleshooting guide

Flexo printing troubleshooting guide

Common problems in printing :

There are many reasons for affecting the quality of gravure printing. The most important ones are: the environment of the workshop, the pressure of the impression cylinder, the pressure and angle of the doctor blade, the printing speed, the viscosity of the ink, the tension control, the drying system, the quality of the cylinder, etc.

It must be strictly controlled the above work,that can printing better .

a. Determine the appropriate temperature and humidity of the printing workshop:

If the temperature in the printing workshop is too high and the temperature is too high, the printed matter may be back-adhesive, discolored, color-shifted, stuck, and poorly adhered. In severe cases, the ink will be decomposed and printed. If the printing shop is too dry, in the case of fast printing speed, static electricity will be generated, which will cause the pattern to be partially embossed, and in the case of slow printing speed, the print will be dull and dry, paste and so on. Generally, the temperature of the printing workshop is controlled at 20-25 ° C, and the relative humidity is controlled at 55%-75%.

b. The pressure of the impression cylinder should be appropriate

If the impression cylinder is not flat, there will be leakage and uneven coloring; if the pressure of the impression cylinder is too large, the printed pattern will be ghosted, unclear, dull, etc.; if the pressure of the impression cylinder is too small, it will appear shallow. The part of the net is lost or plugged, and the text is broken and unclear. A high-quality impression cylinder with a smooth surface and moderate hardness should be used, and the pressure of the impression cylinder should be adjusted during printing. The choice of pressure should be based on different printing methods (printing, printing), different substrates (paper, aluminum platinum, plastic), and the same thickness of the same substrate.

c. The blade pressure and angle should be adjusted well.

The angle between the scraper and the cylinder is generally controlled at 45-65°. Further adjustment is made according to the depth of the layer and the printing speed. When adjusting, the distance between the blade and the offset roller should be adjusted to match the printing speed. The appropriate pressure of the scraper can be adjusted according to the depth of the plate.

d. Control printing speed

The printing speeds provided by the different presses will be different, and the printing speed cannot be exceeded when printing. In addition, the choice of printing speed depends on different printing methods, different workshop environments, different printing methods, different printing materials, different patterns to determine the appropriate printing speed, to ensure the final best printing quality.

e. Choose the right ink viscosity

To adjust the working viscosity of the ink, on the one hand, the printing speed should be considered, the printing speed should be fast, and the fast drying solvent should be selected; if the printing speed is slow, the slow drying solvent should be selected. On the other hand, in the printing process, the volatile solvent is replenished in time, preferably mixed with the ink and added to the ink fountain to ensure the consistency of the color of the printed matter. In order to ensure that the spot color version is thick and bright in color, the ink viscosity of the general spot color ink is higher than that of the four color ink.

f. Drying system must be matched

The drying system affects the speed of the gravure press. Its main function is to improve the adhesion fastness of the ink on the surface of the printing material, so that the solvent in the ink is completely dried to prevent undue, resulting in odor after back-sticking or bag-making. Therefore, the drying system should match the speed of the printing press, and then adjust the oven temperature and air volume according to the size of the pattern on the printed matter.

g. Cylinder quality

The impact of the plate quality problem on print quality is very large. Such as: cylinder accuracy is not good: dynamic balance difference, size head, ovality and concentricity deviation will affect the overprint; plate too deep will affect the ink drying, hair and other issues; the plate is too shallow will lead to the field color Not thick, some parts of the field appear drawing; the poor polishing of the plate will cause problems such as smudges, swarf, etc.; insufficient chromium hardness or insufficient thickness of the chrome layer will affect the amount of printing of the cylinder and so on.

Some common problems in printing due to improper control of the above work are: smudges, field drawing, stenciling, overprinting, inaccurate in-situ ink, and multiple colors.

 

Common problems and solutions ：

 

1 , the version of the pollution:

It refers to the phenomenon that the ink that has passed through the blade is transferred to the printing paper or film, which is a malfunction unique to gravure printing.

Produce a version of the phenomenon:

1. Scraper line: Unrelated long lines appear in the printed and non-lined parts.

2. Version fog: The scraper scrapes the ink on the plate when printing, causing a very shallow layer of ink in the blank portion.

The main factors that produce the scraper line are:

1. There is foreign matter between the scraper and the platen roller, or the scraper is poorly ground and damaged. Fine line: There are hard inclusions that cause damage to the blade. Thick thick lines: There are soft inclusions, and the double lines appear in the center of the pattern.

2. Printing speed is too fast, ink viscosity is too high;

3. The scraper is in a wave state, the blade is excessively detected, the blade pressure is too large, and the blade angle is not accurate;

4. The plate is poorly polished and the polishing is not thorough, resulting in residual chrome thorns on the edge of the cell, causing the swarf to damage the blade during printing;

5. The hardness of the chrome is low, causing the squeegee to damage the layout during printing.

Solution:

1. Remove debris: ink filtration and cleaning of the inside of the scraper;

2. Properly reduce the printing speed and reduce the viscosity of the ink;

3. Adjust the scraper, pay attention to the length of the soft scraper, avoid the blade is too hard or too soft, and pay attention to the level of the blade. The angle between the scraper and the cylinder should be standard;

4. Once the plate is damaged, it must be deplated or re-polished.

Reasons for producing a version of fog:

1. The old scraper knife is not worn.

2. The blade is too hard during printing, the printing speed is too fast, and the viscosity of the ink is too high.

3. The chrome is not completely polished, the small burrs on the surface of the chrome layer are not polished, or the layout is too smooth and the roughness is not enough.

4. The hardness of chrome is not enough. When printing, the scraper damages the layout and the full version of the scraper is injured.

Solution:

1. The grinding blade is tough and removes the tough edges or small gaps of the knife. New soft blades can also be replaced.

2. Adjust the blade angle, properly reduce the printing speed and properly reduce the viscosity of the ink.

3. After the above adjustment, the fog phenomenon still does not improve, and only the chrome layer polishing can be performed again.

4. After the printing, the blade scraping is very serious, and only the chrome re-polishing can be performed.

2, the field drawing:

It refers to a phenomenon in which the ink in the solid part of the pattern is poorly transferred.

The phenomenon of drawing in the field: the white line and the solid line of different lengths are formed in the direction of the blade edge of the pattern.

Cause:

1. The angle of the scraper is not suitable when printing. Under normal circumstances, the scraper is too hard, and the toughness of the knife directly contacts the layout.

2. The printing speed is too fast and the ink viscosity is high.

3. The pressure of the embossing roller is insufficient and the ink transfer is poor.

4. Cylinder polishing problem, the chrome burr on the edge of the ground is not thrown away.

5. The quality of the cylinder is too thick, the mesh wall is too thick, the ground is not real, or the dot is worn after printing.

Solution:

1. Adjust the angle of contact between the scraper and the plate to prevent the blade from directly contacting the plate.

2. Appropriately reduce printing speed and ink viscosity.

3. Appropriately increase the pressure of the embossing roller.

4. After the above work adjustment, the drawing phenomenon has not been improved, in order to consider the quality of the cylinder, the measurement of the dot is normal, the dot is small and the wall is very thick and needs to be re-plate. The dot is normal and needs to be re-polished.

5. Start printing without the phenomenon of drawing in the field, after printing for a period of time, in order to consider the problem of dot wear, it needs to be re-plated.

 

3,  the blocked version:

Generally, in the gravure printing process, only 1/3-2/3 of the ink in the plate pocket is transferred to the printing material, and if the residual ink solidifies immediately before leaving the printing material to enter the ink tank, it is re-entered. The transfer rate of the ink squeegee and the ink before the solvent is dissolved in the ink tank will gradually decrease, eventually resulting in blockage, and the amount of transferred ink can not cover the performance of the printing material and cause spots on the printed product.

The reason for the plug version:

1. In the workshop environment, the temperature is too high, causing the ink to dry too fast, which causes the problem of the plate.

2. The ink viscosity is too high and the printing speed is too slow, causing the ink to dry too fast, resulting in a plate.

3. The problem of embossing rubber roller, dirt on the surface of the embossing roller (such as dust, ink, etc.) or damage and wear on the surface of the embossing roller can lead to poor ink transfer during printing, which causes the printing plate to have a plate problem.

4. Poor surface tension treatment of plastic film leads to ink transfer failure during printing.

5. In shallow-layer plugs, the angle of the doctor blade is too hard, which may cause poor ink transfer in shallow layers.

6. The problem of the quality of the cylinder: the high-light level of the electric part or the hanging part is shallow, especially the part of the electric part and the net part of the printed product is not deep enough.

7. During the cylinder-making process, defects may occur in the inner wall of the cell due to the process or the like, surface defects may be left in the chrome plating, or burrs may be generated during the grinding. These factors will lead to blockage, and eventually the ink is lost and the dot is lost. Not completely waiting for a fault.

Solution:

1. Control the environment of the printing workshop, requiring indoor temperature: 18-25 degrees, relative humidity: 55%-75%. In the case where the indoor temperature cannot be improved, a slow drying agent may be appropriately added to the solvent to reduce the drying speed of the ink.

2. Appropriately reduce the viscosity of the ink. If the viscosity is too high, the solvent content in the ink is relatively small, and it is more volatile and the ink is dried on the cylinder. Therefore, the viscosity of the ink must be appropriately lowered.

3. The effect of printing speed: the speed is too slow, which prolongs the evaporation time of the solvent in the ink, so that the ink is easily dried in the mesh cavity, and the drying speed is slowed down by appropriately increasing the printing speed.

4. The embossed rubber roll surface is cleaned to remove surface dust and ink, and the damaged embossing roll can be replaced.

5. If the surface tension of the printed material is not well handled, the material may be corona treated or replaced with a printed material.

6. According to the actual situation, the angle between the small scraper and the cylinder is adjusted. The pressure of the squeegee and the angle of the squeegee are determined according to the depth of the printing plate and the ink inking.

7. For the plate plate with high gloss level, after adjusting the blade pressure and angle and reducing the ink and adding slow-drying agent, it can be considered as the quality problem of the cylinder, and the shallow level is properly raised.

8. For the middle and dark level of the plug version, if the adjustment is not improved, check the dot, whether there is a defect in the inner wall of the cell or whether there is a burr at the edge of the dot after chrome plating.

4,  poor overprinting:

The phenomenon of poor overprinting occurs: the mark line quasi-pattern is not accurate or the mark line pattern is not accurate, and it is difficult to overprint, sometimes sometimes not allowed. The conditions of overprinting are not allowed: the left and right overprinting is not allowed, and the upper and lower overprinting is not allowed.

Reasons for inaccurate overprinting:

1. There is a problem in the installation of the front plate of the printing plate. The cylinder keyway is not locked, and the dirt in the hole is not cleaned, resulting in poor concentricity.

2. The biggest problem in the left and right overprinting of the pattern is that the air volume and temperature control in the printing and drying system are not good. The problem of inaccurate printing in the paper plate is a problem in the printing and drying system.

3. Improper control of the material tension during printing can cause difficulties in overprinting the pattern.

4. Plate quality: cylinder accuracy is not good, such as: concentricity difference, large dynamic balance deviation, cylinder size and ovality, incremental problem (incremental too large or inverted increment), keyway size is too large, keyway edge There are burrs.

5. The set of rolls in the plate has different weights, which can also cause difficult overprinting during printing.

6. There is a problem with the increase of the cylinder, and the more the number of cylinders, the faster the printing speed is, the higher the accuracy and increment requirement of the cylinder.

7. Another problem with the quality of the cylinder is that the overprinting is inaccurate due to imposition problems or equipment problems. The main phenomenon is that there is a certain joint or multiple joints in the multi-joint product and other joint printing.

Solution:

1. In the case of inaccurate overprinting, first check the assembly problem of the cylinder, adjust the keyway cutter to lock, and clean the cylinder to block the hole.

2. In view of the problem of inaccurate left and right overprinting, if there is no problem with the overprinting of the proof paper, it is necessary to adjust the control of the air volume and temperature in the printing and drying system.

3. In the case of difficult overprinting, it is necessary to adjust the tension control of the printing material, especially the equipment without the automatic tension control system.

4. In the case where the above work has been adjusted, it is necessary to consider the problem of the quality of the cylinder. It is difficult to overprint up and down, often running the plate, in order to check the accuracy of the cylinder. In the accuracy of the cylinder, the problem that is most likely to cause the upper and lower overprinting problems is that the dynamic balance problem and the cylinder increment have problems, and the same size head and ellipticity deviation is too large. Therefore, after determining the accuracy of the cylinder, it is necessary to adjust the above work.

5. In the case where the number of individual joints in the multi-piece product is not accurate, it can be determined that the quality of the roll is a problem.

 

5,  the field is not true:

It means that the solid part of the pattern is not thick, the ink brightness is not enough, it is not bright, and the ink layer is gray.

Reasons for the inaccuracy of the field:

1. If the viscosity of the ink is too low during printing or the ink dilution ratio is too high, the brightness of the ink layer may be insufficient and the ink layer may not be bright.

2. In a certain place on the ground, there is a case where the ink is not in the real place. If the quality of the cylinder is not problematic, there may be a problem of the plate in the plate or the stamping roller here.

3. The pressure of the embossing rubber roller during printing is not enough, resulting in less ink consumption in the cell, resulting in false ink on the ground.

4. The on-line ink caused by the quality problem of the cylinder is not true: the depth of the engraving is not enough, the field is light, the field is light, and it is not resistant to printing.

Solution:

1. Appropriately increase the viscosity of the ink, reduce the proportion of ink dilution, and ensure that the ink layer on the ground is bright.

2. For some parts of the field where the ink is not true, check whether the layout is shallow and the plate is in use. After checking the above problems, check the stamping roller for damage. Handle the checked problems one by one.

3. Increase the pressure of the stamping roller to increase the amount of ink in the cell.

4. After printing for a period of time, there is a situation where the field is not inked, either in the field or in the field. The field plug can be solved by cleaning, and the actual wear can be deplated or reworked.

5. On-machine printing is not true on the spot, except that the pressure of the embossing roller is not enough, that is, the depth of the engraving is not enough or the field is sloppy. Insufficient depth of engraving can be improved by changing the electro-engraving process and increasing the depth of engraving. The field smear can be detected by measuring the dots, and indeed the fading can be deplated or reworked.

 

6,  Multi-printing color has a shade:

Multi-blocking products, the color difference between each unit.

The reason why the color of the multi-ply imposition product has a depth:

1. The surface of the embossing rubber roller is damaged or the surface has ink, which causes the surface of the embossing rubber roller to be uneven. In addition, the plastic surface of the embossing rubber roller has different elasticity after being aged, which causes the ink volume of the mesh to be different during printing, thereby causing a shallow depth.

2. The printing blade is unevenly placed in a wave state; in addition, the blade is not on the same horizontal line as the surface of the cylinder.

3. In the quality problem of the cylinder: the change of the dot point causes the left and right sides to have a shallow depth, one is the change of the left and right net value caused by the electric carving device, and the other is the change of the left and right net value caused by the uneven pressure during the chrome polishing.

4. For products with rich multi-color overlay and electric sub-graphs, using the same-line same-angle process will also create the problem of depth between left and right.

Solution:

1. Clean dust and ink from the surface of the embossing roller or replace the embossing roller.

2. Reassemble the squeegee to ensure that the soft blade is parallel to the hard blade; and that the squeegee is on the same level as the cylinder surface.

3. If there is a network change in the quality problem of the cylinder, it must be re-made to ensure that there is no change before and after the dot.

4. The problem of the depth of the same network cable with the same network angle can only be solved by the adjustment of the electric carving process.