1、 Common problems and solutions of gravure printing
1. Scraper line or ink line appears.
The reasons are as follows: the scraper is worn or there is dirt on the scraper; the ink is mixed with impurities; the ink fineness is not enough; the printing plate is not well polished, too rough, and the ink viscosity is too high.
Treatment method:
a) If the scraper line moves regularly with the left and right swing of the scraper, it can be judged that the scraper is worn or there is dirt on the scraper, and the bamboo stick can be used to remove the dirt at the position of the knife lifting line; if the scraper is worn, the scraper should be polished immediately or replaced with a new one.
b) In printing, all ink must be filtered. Try to use new ink.
c) Ink particles are too thick, fineness is not enough, easy to appear lines, use fineness meter to detect the ink fineness, if the fineness is not enough, you need to change the ink.
d) If the printing plate is not well polished or there are small hard blocks on the printing plate, the fine sandpaper can be used to grind back and forth on the printing plate first. If the problem still can not be solved, chrome stripping and re plating are required.
e) Regular measurement of ink viscosity, to maintain the stability of ink viscosity, conditional manufacturers can use ink automatic viscosity controller.
2. Printing water lines.
The main reasons for the appearance of water marks are: the viscosity of the ink is too low; the engraving of the printing plate is too deep; the fluidity of the ink is poor.
Treatment method:
a) Increase the viscosity of ink properly;
b) Increase printing speed.
c) Adjust the blade angle to sharp angle.
d) Version engraving is too deep to adjust the need to re plate.
e) Improved ink flow.
3. Ink back stick.
The main reasons for printing back sticking are: the solvent is too slow to dry and the ink has poor dryness; the winding pressure is too high during the printing process, and the stacking pressure is too high after printing (especially in high temperature weather); the temperature of cooling water is too high to achieve cooling effect; the temperature of drying oven is too high, and the ink will appear false drying phenomenon; the surface tension of non printing surface of printing film is large (or double-sided Corona) So that the film non printing surface and ink affinity, ink transfer.
Treatment method:
a) Replace with quick drying solvent to dry the ink.
b) Adjust the winding pressure to reduce it as much as possible. The winding diameter should not be too large and the stacking weight should be small.
c) Check whether the cooling water of the printing machine is turned on and whether the water temperature meets the requirements.
d) The temperature and wind power of the oven should be adjusted at 50-65 ℃.
e) Test the surface tension of the film before printing. The surface tension of the printed surface should be greater than that of the non printed surface. The film with double corona should not be used.
4. Printing color difference.
The main reasons for the color difference of printing are as follows: the position, angle and pressure of the squeegee change to cause the printing color difference; the change of ink viscosity causes the printing color difference; the change of ink color concentration causes the printing color difference; the printing plate has become lighter after printing to a certain amount; the printing plate blocking causes the printing brush color difference; when the multi-color mixed configuration spot color, if the proportion of each pigment in the mixed ink is quite different In the printing process, if the ink circulation is not good, it is easy to cause ink precipitation, which will cause printing color difference.
Treatment method:
a) Adjust the position, angle and pressure of the squeegee properly to keep the color of printing consistent.
b) Regular measurement of ink viscosity, to maintain the consistency of ink viscosity, conditional manufacturers can be equipped with ink viscosity automatic controller.
c) Adjust the color density of the ink (add the original ink or diluent in the ink) to keep the color consistency.
d) Chrome removal and re plating of printing plate or plate reprocessing.
e) Clean the plate roller with a plate cleaner.

f) Check the ink circulation system to keep the ink flowing well.

5. Static failure.
Plastic film in printing due to friction will produce static electricity. Static electricity does great harm to the quality of printed matter, and even causes fire. Special attention should be paid in the printing process. The main printing faults caused by film static electricity are as follows: the ink silk in the shape of "whisker" is caused around the printed picture and text; when the field part is printed, it will appear mottled, and the ink can not be transferred, resulting in blank part. Although the film static electricity can not be completely eliminated, it can be properly treated in the printing process to avoid electrostatic failure.
The main treatment methods are as follows:
a) Properly improve the air humidity in the workshop.
b) Increase the printing viscosity of the ink properly.
c) The proportion of alcohol and ketone solvents should be increased appropriately in printing solvent, but not too much, otherwise the composite strength of the subsequent process will be affected.
d) The equipment should be installed with static elimination device and should be maintained and checked regularly.
6. Printing pan color (fog plate).
The phenomenon that the scraper fails to completely clean the ink on the non graphic part of the printing plate causes the ink to transfer to the printing substrate is called pan color, also known as foggy plate. The main causes of printing pan color are: the accuracy of printing plate is insufficient, eccentric, poor chrome plating; scraper pressure is insufficient, angle is not suitable; printing viscosity of ink is too large; the environmental humidity in the workshop is too high, which makes the ink liquidity poor; the alcohol solvent addition proportion is too large, resulting in poor ink solubility.
Treatment method:
a) Improve the manufacturing precision of plate roller.
b) Increase the pressure of the scraper, adjust the angle of the scraper to 60-70 degrees, and the distance between the two tangent points is 50-60cm.
c) Reduce the printing viscosity of the ink properly.
d) Adjust the solvent formula, reduce the proportion of alcohol solvent, and appropriately increase the proportion of ketone solvent.
2、 Common problems and solutions of dry lamination
1. The peeling strength of the composite film is not enough
It can be divided into the following situations:
The glue does not solidify completely. When it is peeled off, it is still sticky on the surface of the glue.
reason:
1) The wrong proportion of adhesive and insufficient curing agent lead to incomplete curing. When preparing the adhesive, it should be prepared according to the proportioning parameters specified by the adhesive manufacturer;
2) The purity of the solvent is not enough, the water or alcohol in the solvent exceeds the standard, the water or alcohol reacts with the curing agent in the glue, and the reduced proportion of the curing agent leads to the incomplete curing of the glue. The solvent used for dry compound is ethyl ester, so each batch of ethyl ester should be sampled and inspected when entering the factory. If the purity is not enough, it can not be used;
3) The high residual solvent of ink in printing film causes insufficient glue curing. Some of the residual solvents in ink (especially PET ink) will react with the curing agent in the glue, thus consuming the curing agent, resulting in insufficient glue curing.
Countermeasures:
① It is better not to composite the film immediately after printing. If time permits, it can be placed for 1-2 days before laminating;
② If the residual solvent is high, the proportion of curing agent can be appropriately increased when compounding;
③ Choose fast curing glue.
4) The curing temperature of the composite membrane is low, the curing time is not enough, the crosslinking is not enough and the curing is not complete.
Countermeasures: increase the ripening temperature or choose fast curing glue.
2. Apparent problems of composite films
1) Small dots.
Generally, it is less likely to appear immediately after laminating, unless it is slag and muddy impurities. After a period of time after coating, this phenomenon may occur because of the corrosion of the ink on aluminum. When the ink presents a certain acid or alkaline, and the amount of glue is small, it can not form a layer of connection.
2) A little gray.
There are two possibilities of small gray spots, one is the uneven roller caused by glue spots, the other is the uneven ink caused by the ink is not compacted spots. Both possibilities are related to the process, which can be solved by adjusting the process to increase the thickness of the glue.
3) Little white dot.
The general surface of the ink discoloration in the case of easy to appear. It often appears in the composite of aluminum coating. There are two reasons: first, the covering power of the ink is not strong or uneven, especially the white oil ink, which makes the aluminum color penetrate, and small white spots are formed where there is no aluminum color penetration; second, due to process reasons, the drying channel temperature (especially the first drying channel) is too high or the amount of glue is too thick, which causes the glue layer surface condensation in the first drying channel, and ethyl ester is flushed out in the second and third drying channels When, squeeze up the glue, showing the ink color. The solution is to improve the covering power of the ink or adjust the suitable temperature of the first, second and third drying channels, and gradually increase the temperature. Avoid over temperature of the first stage.
4) Small crystal point.
There are two kinds of concave and convex, the causes are different: the protruding small crystal points are mostly due to glue mixing, or the machine is not cleaned. The method to eliminate the small crystal point is that the glue must be mixed in strict accordance with the correct glue mixing method, and the machine must be cleaned after use; the concave small crystal point, carefully observed with a magnifying glass, will find that there are small bubbles, which is mainly caused by excessive moisture.
5) Little scar.
It is mainly due to the uneven activation of the film, the same scar appears in the printing process, of course, it may also be caused by the long activation time.
6) Wavy.
Ripple is easy to occur on the white film, mainly because the molecular weight of the glue is not uniform. After passing through the hot drying channel and hot roller, the elastic polymer chain shrinks, and the intramolecular shrinkage of different molecular weights is not consistent. The uneven internal shrinkage causes waviness. In this case, the glue should be considered.

7) The influence of film on surface quality.
Due to the smoothness and uniformity of the film surface, the similar phenomena of the above six phenomena may be caused. To distinguish between the causes of the film or the above-mentioned six cases, you can carefully observe the film without lamination with a magnifying glass. Because the transparent glue is between the two films, it forms a composite film together with the two films. With a magnifying glass, the spots and waves on the original very small film are enlarged. In many cases, problems can only be found through careful observation.
3. Tunnel phenomenon of composite membrane.
Because of the shrinkage of the membrane, the edge or center part of the composite membrane is like earthworm like delamination, which is called composite membrane tunnel phenomenon. The reasons for this phenomenon
It mainly includes the following aspects:
1) In the process of lamination, when the composite substrate shrinks after lamination due to poor tension control and the shrinkage ratio is quite different, the bonding of the adhesive layer of the composite membrane is damaged, and the tunnel phenomenon occurs. The solution is to set the appropriate tension according to the tensile characteristics of different composite substrates.
2) Film wrinkling, uneven thickness, in order to avoid wrinkling the composite film, increase the tension to composite, resulting in composite membrane tunnel. The solution is to check the state of the film during unwinding when laminating, such as wrinkling and edge shaking.
3) The molecular weight of the adhesive is small, which leads to the low initial viscosity of the composite membrane, which leads to the tunnel phenomenon of the composite membrane. The solution is to select high molecular weight, high cohesion, fast curing adhesive.
4) Due to the excessive coating amount of adhesive, the composite film is not completely cooled after the heat sealing roller, and the adhesive layer still has a certain fluidity, resulting in the tunnel phenomenon of the composite film. The solution is to reduce the coating amount of adhesive properly.
4. The smoothness of the composite membrane is poor.
The smooth property of the composite film is poor, and the friction force between the films is large, which reduces the opening performance and operation performance of the composite film. The main reasons for the poor smoothness of the composite film are as follows:
1) The curing temperature of the composite membrane is too high. Treatment method: reduce the curing temperature, the curing temperature should not exceed 50 ℃, if time allows, the natural aging is better.
2) The composite substrate has poor smoothness. Treatment method: composite film powder spraying.
3) The composite membrane absorbs moisture. Treatment method: pay attention not to touch water during storage and transportation, and pay attention to composite membrane protection when indoor humidity is too high.
5. Wrinkle of composite film. The cause of the wrinkle of the composite film.
1) The composite substrate itself is wrinkled. Treatment method: pay attention to check the state of the composite film, such as uneven thickness, lotus leaf edge, wrinkle and other phenomena, do not use.
2) The imbalance of guide roller and composite roll causes the wrinkle of composite film. Treatment method: check and adjust each guide roller and compound roller to make them balanced.
Dongguan Beite packaging materials Co., Ltd. - located in Dongguan City, the world's manufacturing city, is a subsidiary of Beite packaging (China) Co., Ltd., with a plant area of 6000 square meters. It is a flexible packaging enterprise integrating R & D, production and sales. It has a complete set of domestic advanced production equipment, a scientific and humanized management system and a group of experienced technical personnel For backing, to provide customers with quality products and first-class service.
The company produces composite bags, roll film, fruit bags, aluminum foil bags, suction mouth bags, self-supporting bags, zipper bags, anti-static bags, special-shaped bags, etc., which are suitable for the internal and external packaging of food, daily chemicals, electronics, toys, medicine, cosmetics, industrial products and other industries.
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