Common problems and Countermeasures in the hottest

2022-08-20
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Common problems and Countermeasures in silk printing (III)

v. pinhole

pinhole phenomenon is the most headache for staff engaged in silk printing. If it is the printing of opaque objects such as billboards and thick paper, such unobservable holes are generally not a problem. However, pinholes are not allowed when precise printing is carried out on aluminum, glass and propylene plates, which need post-processing and corrosion processing. In addition, there are many reasons for pinholes, many of which cannot be explained at present, and some of which are problems of quality management. Pinhole is one of the most important inspection items in the inspection of printing products

① dust and foreign matters attached to the plate. During plate making, some sol will be mixed in when the water washing and developing machine is refitted for model flight test and identification. In addition, when the emulsion is coated, dust is also mixed, and pinholes will be generated when it is attached to the silk. These can be found and repaired in time if you pay attention to inspection during the test. If dust and foreign matters adhere to the plate, blocking the opening of the plate will also cause pinholes. Before formal printing, if you use ink absorbent paper, after several sheets of printing, you can remove these dust from the plate

② after too long-term development, the cleaning of the printing surface. Aluminum plates, glass plates, propylene plates, etc. should be pretreated to make their surfaces clean before printing. After the substrate is pretreated, it should be printed immediately. In multicolor printing, the method of rubbing with alcohol before printing is generally adopted. In addition, semi-automatic and full-automatic ultrasonic cleaning machines can also be used. After pretreatment, dirt such as grease can be removed, and dust attached to the surface can also be removed

the detergent used in the cleaning machine is often mixed with broken fibers. This detergent is dissolved in alcohol. When cleaning the surface of the substrate, it often forms a thin surfactant film, and pinholes will occur when printing ink on the film. Therefore, pay special attention when using detergent and alcohol. When handling the substrate by hand, the fingerprint of the hand will also be attached to the printing surface, also known as the electronic tensile testing machine, and pinholes will be formed during printing. Use limitations

VI. bubbles

the substrate sometimes has bubbles on the ink after printing. The main reasons for bubbles are as follows:

① poor prepress treatment of the substrate. Dust and oil stains are attached to the surface of the substrate

② bubbles in ink. In order to adjust the ink, when adding solvents and additives for mixing, some bubbles will be mixed in the ink. If it is left unattended, the ink with low viscosity will naturally defoaming, while some ink with high viscosity will not naturally defoaming. Some of these bubbles are naturally eliminated due to the transfer of ink during printing, while others become larger and larger. In order to remove these bubbles, defoamer should be used. The addition amount of defoamer in the ink is generally about 0.1 ~ 1%. If it exceeds the specified amount, it will play a foaming role

even if the ink foams after transfer, as long as the wettability of the substrate and the fluidity of the ink are good, the bubbles on the surface of the printing ink film will gradually disappear, and the ink will form a flat printing ink film. If the ink bubbles are not eliminated, the ink film will form a circular uneven film surface. Generally, when bubbles in ink pass through silk, they can be defoaming due to the role of silk. In addition, when mixing the ink, using hot water or boiling water will have a better defoaming effect

for transparent inks such as red, blue and green, the binder of these inks is easy to foam due to the small proportion of organic pigments in the particles. If the corresponding diluent, tackifier or adhesive remover is added, the ink can also be transformed into a stable ink with good printability

③ printing speed is too fast or uneven. Reduce the printing speed appropriately and maintain the uniformity of the printing speed

if the above measures cannot eliminate bubbles in the printed matter, other types of inks can be considered

VII. Marks

silk marks sometimes appear on the ink film surface of silk screen brushes. The main reason for silk marks is the poor fluidity of the ink. In the process of silk screen printing, when the printing plate is lifted, the ink transferred to the substrate fills the trace by its own flow, making the surface of the ink film smooth and neat. If the ink fluidity is poor, when the screen printing plate is lifted, the ink flow is relatively small, and the silk trace cannot be filled, so the ink film with smooth surface cannot be obtained. In order to prevent silk marks on printed matter, the following methods can be adopted

① printing with ink with high fluidity

② consider printing with ink with slow drying speed, increase the flow time of the ink, and gradually expand and solidify the ink

③ try to use thin single silk in plate making

(to be continued)

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