1、 Recoiling
After printing on plastic film or cellophane, the impression of dryness appears. However, during the storage period after the drum or bag is printed, the back is sticky and dirty. In serious cases, the printing pieces cannot be torn apart, and the ink layer of the picture and text is transferred and dyed, resulting in the scrapping of the product. This phenomenon is more likely to occur in high temperature season, but high temperature is not the only reason for sticking back, it is also closely related to a series of factors such as plastic, ink, solvent, air volume, light, speed and so on.
1. The solvent in gravure ink can not be completely volatilized after printing.
(1) Plastic film printing ink is dried by solvent evaporation. The volatilization rate is an important factor to determine the drying condition of ink layer and the printing quality. The slower the solvent volatilizes, the better the reproduction of the plate is, the more beautiful the printing color is, but it is easy to adhere; on the contrary, the impression of white imprinting will be produced. Therefore, it is the key to choose the solvent with appropriate evaporation speed for gravure printing of plastic film. In continuous register printing, the solvent must be completely volatilized within the running time between two printing stations, otherwise, the roller will stick when printing in the next station. (2) After film printing, the organic solvent in the ink is not completely volatilized in the drying system, and there is still residual heat after the film is rolled up, which brings the solvent remaining in the ink layer with the conditions of continuous volatilization and adhesion. (3) High temperature wet plum section, after printing, film winding is too tight or pressure.
Countermeasures: the volatilization rate of solvent in ink depends not only on the boiling point of solvent, vapor pressure, latent heat of vapor, but also on the temperature, humidity, air volume, solute and ink thickness of the operating environment. Therefore, according to the change of conditions, the volatile speed of solvent in the ink should be adjusted at any time. In general temperature, if the ink layer dries too fast, the solvent with slow evaporation (such as Shanghai 74-92 type plastic film slow drying thinner) should be added; otherwise, the solvent with fast evaporation (such as 74-91 plastic film fast drying thinner) should be added. It can also be diluted with mixed solvents of xylene, ethanol and isopropanol (the three solvents are mixed at 1 / 3 ratio, and it is better to use single solvent than mixed solvent). If you feel that the drying is too fast, you can use a little butanol instead of ethanol (butanol can increase the ink luster). But you must pay attention to the appropriate amount, so as not to affect the drying of the printing.
The solvents used in gravure printing of plastic film are mainly alcohol and benzene. Ethanol and isopropanol are used for alcohols, toluene and xylene are used for benzene. Due to the need of nitrocellulose, esters, such as ethyl acetate and butyl acetate, should be added.
In short, strive to ink in the organic solvent before winding up to be completely volatile. Appropriately slow down the speed and increase the air volume. After the film is printed, it is loosely placed in the wire woven basket, so that the ink layer can continue to ventilate and dry. After curing, it is cut, bagged and printed with film. After that, it is bound and placed vertically in the carton to reduce the pressure between the film surfaces.
2. Plastic gravure ink poor ink. Some plastic gravure inks have low melting point and are easy to stick when operating at high temperature and high relative humidity.
Countermeasures: ① when conditions permit, install air conditioner in the operation workshop, control the smothering temperature between 18 ℃ and 20 ℃ and control the relative humidity below 65%; ② replace the ink with good ink property.
3. Poor suitability of plastic film printing and packaging. Reasons: ① plastic film processed by non packaging resin; ② insufficient opening agent in resin. Countermeasures: replace plastic film.
4. Electrostatic effect: cause: the plastic film produces static electricity, forming the adhesion between the film. Countermeasure: add antistatic stab in plastic.
2、 Poor register accuracy
There are several reasons why the color of plastic film is not allowed:
1. Vertical direction (shipping direction) printing registration change.
(1) The tension changes when the film is pulled. Causes: improper adjustment of drum brake of Uncoiler device; too much reel material or too large diameter of drum material; improper setting of three roller speed; decrease of surface friction of three rolls; tension change of rewinder. Countermeasures: check and adjust the control devices.
(2) Plate cylinder diameter difference bad reason: plate making diameter difference growth is not accurate. Countermeasures: measure the diameter difference (method: see plate making section).
(3) The rule line is abnormal. Reasons: insufficient density, printing offset, etc. Countermeasures: adjust the sensitivity of the photocell, manual elimination of printing plate paste and other defects.

(4) Plate cylinder diameter is small. Cause: it is difficult to control the overprint accuracy with small roll diameter. Countermeasures: if the length of the printing bag is short, mosaic method can be used, that is, more than two bags are printed on one printing roller.

2. The horizontal registration is unstable. The reasons are: (1) the film side is loose, and the film guide roller is not parallel; (2) the printing pressure is uneven on the left and right; (3) the plate cylinder and the imprint cylinder form taper; (4) the film tension changes, forming the film left and right swing. Countermeasures: check and adjust each element one by one, and repair if the lateral registration device is loose.
3、 Poor printing fastness
The reasons for poor printing fastness of plastic film are as follows:
1. Poor corona treatment of polyolefin film. Countermeasures: test whether the surface tension of PE and PP is more than 40 dyne / cm.
2. The affinity between the printing ink and the printed material is poor. The ratio of mixed solvent is poor. Countermeasures: change the ink, adjust the solvent ratio.
3. The temperature and relative humidity of printing workshop change greatly. Countermeasures: try to control the relative humidity of the workshop between 50% and 60%, but not too low. When it is lower than 40%, it is easy to generate static electricity. The best temperature control is 18 ℃ ~ 23 ℃, and keep the environment clean and air circulation.
4. The printability of plastic film itself is very poor, and it still does not meet the requirements after corona treatment. Countermeasures: replace the printed materials.
4、 Pattern size shift
1. When printing, the size of the longitudinal pattern shrinks. Cause: insufficient shrinkage allowance. Due to the influence of plastic film tension and heating and drying, the longitudinal size of the film is larger than that of the printed text. Countermeasures: plate making to appropriate size of shrinkage; film tension to the minimum.
2. When printing, the pattern size in the longitudinal direction is extended. Cause: gravure size on shrinkage allowance left too much. Countermeasures: increase the film tension.
5、 The reproduction of printing level is poor
1. The highlight is too deep. Cause: printing plate too deep, too much ink. Countermeasures: (1) increase the mesh; (2) reduce the pigment in the ink; (3) properly increase the angle between the scraper and the plate surface.
2. The highlight is too shallow. Reason: the depth of the plate is not enough. Countermeasures: (1) use deep tone ink; (2) reduce the angle between the doctor blade and the plate surface.
3. The dark tone is too deep. Cause: the printing plate is too deep. Countermeasures: due to insufficient ink drying, the ink layer may agglomerate, if necessary, to replace the version.
4. The dark density is not enough. Reason: not enough depth. Countermeasures: use deep tone ink.
5. In the middle of the ink depth junction is obvious.
Cause: poor ink. Countermeasures: change the ink with good characteristics.
6、 Dry ink layer and poor conjunctiva after printing
Reasons: 1. Hot air temperature, wind speed, air volume, exhaust volume is insufficient. Countermeasures: adjust the drying device.
2. After printing, the ink layer has the false appearance of dry conjunctiva, and the ink layer still contains residual solvents. The residual heat of about 40 ℃ is still left after the film is rewinding, which is suitable for the solvent to continue to move. In addition, there is a certain pressure when the film is rewinding, which results in the harm of sticking back. Countermeasures: (1) the ink layer should be completely dried after printing; (2) the film should be put in the wire basket loosely in order to cool the film, and then rewinding, slitting and bag making after the film is cooled.
7、 The luster of printed matter is weak
Cause: excessive ink dilution.
Countermeasures: control the amount of diluent.
8、 The edge of the imprint is not smooth and the background color has spots
Cause: the viscosity of the ink is too low and the solvent is used excessively.
Countermeasures: add new ink, improve viscosity.
9、 There are orange peel marks on the printing layer
Cause: ink drying too fast, concentration too light, leveling poor, thixotropy, static electricity, printing speed is too slow.
Countermeasures: find out the causes and take corresponding measures.
10、 There are scratches on the printing layer
Cause: guide roller scratch, ink mixed with sand, scraper uneven, scraper and plate angle is not appropriate.
Countermeasures: corresponding treatment.
11、 The tone is thin
Reasons: (1) ink color thin: (2) poor color reflection.
Countermeasures: (1) adjust the ink property; (2) first lay the base color with white ink, and then register in sequence. Inside printing, the hierarchical version first overprint three primary colors, and finally lay the background color.
12、 Biting color
In overprint, the second color ink sticks off the first color ink.
Reasons: the ink layer after the first color printing is not completely dry, the second color pressure is high, or the machine speed is too fast, or the cold and hot air is poor, and the substrate printing suitability is poor, all can cause color biting.
Countermeasures: find out the causes and take corresponding measures. ① The results show that: 1) adding proper amount of quick drying agent; 2) slowing down the speed; 3) reducing the pressure of imprinting cylinder; 4) increasing the amount of cold and hot air.
13、 Printing rough, blank point more than full version, field has cloud pattern, tone is not full
Reasons: ① too much solvent; ② thick ink; ③ too thin ink; ④ too fast volatilization; ⑤ poor ink fluidity.
Countermeasures: ① reduce the amount of solvent; ② change the ink or regrind; ③ adjust the ink consistency; ④ add slow drying solvent appropriately; ⑤ change the ink.
In addition to the ink itself caused by chemical reaction blocking phenomenon (not common), the other factors are summarized as five points:
(1) In the printing ink, in time, it will cause a large amount of ink drying, such as printing ink.
(2) In the printing process, when the scraper is far away from the printing roller or the angle is unreasonable, the diameter of the plate roller is large, or the depth of the plate roller into the ink tank is not enough, the hot air blown out from the dryer affects the surface of the plate cylinder, which is easy to cause serious block.
(3) Impurities are mixed into the ink.
(4) The engraving depth of cylinder wire (or etching depth of gravure) is not suitable.
(5) When printing, the temperature is too high to make the solvent in the ink volatilize too fast, and it is easy to block the page.
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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