Unclear graphics are one of the more common faults in gravure printing. They are generally caused by five factors: human, machine, material, law and ring.
Employees' lack of good professional ethics and responsibility is one of the reasons for many major quality accidents. In order to ensure the quality of gravure printing, it is necessary to strengthen the professional ethics education for employees, strengthen the sense of position; require employees to master the use and operation procedures of equipment.
2. Machine factors
In gravure printing, the problem of equipment that causes unclear graphics is that some related devices are not fully equipped or even equipped, and are not well utilized. These devices mainly include the following.
A, ink circulation device. Many companies' printing equipment is not equipped with an ink circulation device, which directly adds ink to the ink tray. As a result, the circulation of the ink is insufficient, and the fluidity is not good, resulting in unclear paste and printed graphics. The ink circulation device includes two types of a motor type ink circulation device and a pneumatic pump type ink circulation device. The motor type is lower in price, but the ink is not on the disc due to the foreign matter in the ink blocking the filter screen of the ink outlet slot, causing deinking. The initial amount of ink is large, which is easy to cause waste of ink. Pneumatic pump type has a small amount of initial ink distribution, which can reduce ink waste, and there is little chance that foreign matter in the ink blocks the filter screen and fire caused by overheating of the motor, and has high safety.
B. The ink scraper swings left and right. In order to extend the service life of the scraper, some companies often remove the left and right swinging device of the scraper. This will not only cause problems such as unclear graphics, but also shorten the service life of the plate cylinder.
C, circulating water cooling device. The main function of the circulating water cooling device is to quickly cool the printed matter out of the oven, so as not to cause the anti-stick phenomenon and the mutual adhesion of the front and back of the printed matter after winding. Because of its high cost, many printing companies often do not have equipment when they introduce equipment. The direct consequences of this are twofold.
First, with the long-term operation of the equipment, the temperature of the first guide roller that passes through the print out of the oven rises rapidly. When the temperature rises to a certain extent, the resin in the ink is burned, resulting in anti-stick phenomenon. The printed graphics are not clear.
Second, the ink or varnish on the printed matter does not completely dry out and enters the winding device. When it is unfolded, it will cause mutual adhesion between the front and the back, which also causes the printed graphic to be unclear. In order to reduce the unclear printing and printing, it is recommended that you install the above devices in time.
3, material factors
The main materials that affect the quality of printed matter are: printing materials, inks, solvents and rubber rollers.
A, printing materials. The printing materials include plastic, paper, aluminized paper and aluminum foil. Our company mainly prints aluminum foil and aluminized paper. The surface treatment of aluminum foil is not good, too much oil will make the transfer performance of the ink worse, resulting in unclear printing graphics; while the aluminum plating paper has a poor aluminum plating effect, the surface is uneven, and the printed matter will produce many bright spots. Not clear.
B, ink. The viscosity, fineness, yield value, thixotropy, fluidity, adhesion and other quality indicators of the ink do not meet the printing requirements, will affect the transfer of ink on the substrate, resulting in unclear prints. In addition, too much impurity in the ink will affect the clarity of the printed image. When the old ink is on the machine, it should be filtered, and a certain amount of new ink should be added, and if necessary, the new ink should be used.
C, solvent. The low purity of the solvent, containing too much fat or moisture, is inevitably detrimental to the full dissolution of the ink, resulting in impure print hue, unclear and unfilled printed graphics.
D, plate cylinder. For gravure printing, the number of screen cylinder lines, the shape and depth of the cells, the quality of the chrome layer, and the surface grinding treatment will directly affect the ink transfer rate in the cells. The ink transfer rate is low and the printed graphics are not clear.
4, method factors
The proficiency of the operation skills, the correctness of the operation method, and whether or not the operation is strictly in accordance with the operating procedures have an important influence on the quality of the printed matter. In summer, the temperature is higher and the solvent volatilization speed is faster. At this time, the blade angle should be minimized, the distance between the ink-scraping point and the embossing point should be shortened, and the evaporation of the ink solvent on the printing plate should be reduced to reduce the occurrence of blocking phenomenon. In the case of slower solvent evaporation in the winter, the opposite adjustment method is adopted to promote the evaporation of the solvent and reduce the occurrence of paste. For example, aluminum foil and aluminized paper have different adsorptivity to ink, and different blade adjustment methods should also be used. In addition, the blade pressure. The adjustment of the pressure of the embossing roller, the tension of the printing material, and the volatility of the solvent are also adjusted according to the seasons and the raw materials.
5. Environmental factors
The environmental sanitation is poor, and the flying dust and other debris will fall into the ink, causing quality problems such as knife wire and blockage, resulting in unclear printed images. If the ambient temperature is too high, the solvent will evaporate too quickly, and blockage will occur, resulting in unclear printed images. If the ambient humidity is too large, excessive moisture will be infiltrated into the ink, which will not only reduce the purity of the ink, but also cause atomization on the surface of the ink, resulting in dull and unclear printed images. Therefore, the environment of the printing workshop should be kept clear and clean, and the temperature and humidity of the environment should be kept as constant as possible.