Production and Countermeasures of common faults in

Production and Countermeasures of common faults in the printing process

now, some similar packaging and printing faults have always brought certain difficulties to many enterprises. Now, with regard to some common printing faults, I would like to talk about the following experience in order to communicate with peers

shrinkage

shrinkage is one of the faults of printing ink film due to poor leveling. After the packaging and printing operation, the wet ink film retracts during the leveling process, exposing the substrate or bottom ink layer in a small circle. The reason for shrinkage is that the surface tension of the upper and lower parts of the wet ink film is different. Wet printing ink can be regarded as a double-layer liquid film. During the film forming process of packaging and printing, when the surface tension of the upper wet ink film is lower than that of the lower wet substrate film (due to the wet substrate), shrinkage will occur, which can also be explained as that the excessive plasticizer in the packaging and printing ink system causes the cohesion rebound of the ink after printing. When this phenomenon was about to happen, the wet ink film lost its leveling property, which happened to inhibit the shrinkage. In some fast drying gravure printing or thermosetting offset printing, with the increase of solvent in hot blowing or baking temperature, the wet ink film has leveling again, which may lead to secondary shrinkage failure

the preventive measure is to improve the wet ink film flow development performance of packaging printing ink during printing. The surface tension of printing ink should be low and the wettability of substrate should be good. When the spreading coefficient ws of printing ink is 0 (WS is the difference between the interface between the upper wet ink film and the upper and lower wet ink films and the surface tension of the wet film on the surface of the lower substrate), the surface energy of the system will decrease after the printing of packaging printing ink, and the packaging printing ink will self develop into a complete graphic ink film. In practical application, appropriate leveling additives (chemical or physical) or low surface tension solvents are added to solve the problem. In addition, attention should also be paid to the surface treatment of the substrate to improve the wettability of the substrate (i.e. substrate). For example, clean it with solvent or rag or electric spark before packaging and printing

pockmarks and pits

because the wet ink film of the packaging and printing ink is stained with foreign particles (such as foreign particles: Although the rock block and rock mass have the same pre geological environmental dust particles), these foreign particles are distributed on the upper layer of the wet ink film, which repels the surrounding ink and forms a pit like a crater, also known as a "pit". We can see that there are foreign particles in the center of the pit, so it is called "pitting". Generally, the substrate is not exposed to distinguish it from the shrinkage failure

the preventive measures are the same as the shrinkage failure. Pay more attention to the environment of the packaging and printing workshop and the influence of the solvent or diluent used

spots

spots (commonly known as graining) are the general term for irregular blocks on the surface of the ink film after printing. This is due to poor dispersion of pigments, insoluble polymer soft particles or insoluble metal salts in the binder used for color ink, and small pieces of ink film are dispersed and dissolved in ink. Secondly, the dirty air in the packaging and printing workshop or the accumulation of dust on the surface of the printed substrate is also the cause of spots. In addition, irregular spots will be formed on the surface of the substrate after compounding after the uneven coating of the roll, especially the compounding of pure aluminum foil. Therefore, to prevent such failures, we must pay attention to the dispersion and purification of printing ink and the cleanliness of the printing workshop environment

shrinkage

after printing, the wet ink film retracts, exposing a large area of substrate material. This fault is called "shrinkage". In the original period, because of the distribution coefficient of printing ink WS, it focused on discussing the hot, key and difficult issues of science and technology and industry in many fields, such as copper alloy, aluminum alloy, magnesium alloy, lead alloy, zinc alloy, titanium alloy, rare refractory metal materials and surface treatment. This failure is due to poor wetting of the ink on the printed image and text to the substrate. For example, surfaces containing oil stains, plastic surfaces and electrodeposited printing ink surfaces containing too many surface scratch prevention additives. In addition, there is a printing plate that is not centered or eccentric for a few microns, or even a few wires. The forward shrinkage (but not the longitudinal part) often causes partial shrinkage (fracture), which makes it difficult to overprint normally

the preventive measure is to carry out strict degreasing treatment on the surface of the substrate before printing. After treatment, it must be verified by water film test before printing. Aiming at the quality problems of printing plates, the first is to replace the printing plates, and the second is to add inking oil or slow and fast diluent for printing. However, for the surface of plastic and aluminum foil, measures to improve the wettability (such as surface modification) should be taken, and at the same time, special printing ink with low surface tension or non deteriorated ink should be used for printing as far as possible

thunderhorn

after printing, the ink film at the corner of the substrate retracts, causing the ink film to be thin and even exposed. This failure is another form of shrinkage failure. Because the surface force of the wet printing ink film is too high, the surface energy of the system tends to be minimized, and the wet ink film retracts from the corners

the preventive measures are mainly to make the packaging and printing workpiece design as far as possible without sharp corners and edges, chamfer and chamfer, or fill only the edges and corners during packaging and printing. In general, thixotropic agent is added to the printing ink to improve the fluidity of the ink used in the business innovation mode of packaging and printing bio based material products, so as to extend the leveling of the ink film

thick edges

are particularly thick at the corners of the ink film after printing. The printed product looks like a mirror frame, often referred to as "crushing". This is because the solvent volatilization of the wet ink film on the corner is faster than that of other places, which often makes the concentration of the image and text forming the film higher and the temperature lower than that of other places, forming a high surface tension area, which makes the adjacent printing ink flow to the corner and thickens the ink film there

the preventive measures are to appropriately increase the thixotropy of printing ink or reduce the printing pressure, and add an appropriate amount of rheological additives through experiments

in order to get rid of the "Murphy's law", we must first cultivate a high degree of enthusiasm for work and a strong heart. Only by devoting ourselves to it can we avoid the cumbersome failures in packaging and printing one by one in the complicated work. Not because of the quality problems of products, the production department pushes the technology department, and the technology department pushes the production department, but we should work together to find out the causes and deal with the failures in a certain packaging and printing together, Reduce mistakes in operation