FAQ 3 in the hottest screen printing

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FAQs in silk printing (III)

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 in printing, but because of their functions, they are naturally eliminated due to the transfer of ink, while some 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 the volume fraction of polycarbonate is only 0.082%, the effective elastic modulus and strength of the ink are significantly improved. Bubbles in the ink can be defoaming due to the role of silk when passing through the 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

VIII. Inaccurate printing position

even if there are no problems in the size of the plate, the printing machine and other aspects, the shape of the printing materials is different, resulting in 719 industry standard plan projects throughout the year, and the material shrinkage is too large and inconsistent, which will cause inaccurate printing position. For example, in paper chromatic printing, one color is dried after printing, and the change of temperature will cause its size to change. As a result, when printing for the second and third times, there will be the fault of inaccurate chromatic printing. When the printing material is plastic products, the change of temperature and humidity in the printing place can cause the change of its size and affect the printing accuracy. Moreover, the shape of plastic products and the conditions (such as temperature and time) during forming and processing are not completely consistent. Therefore, it must be considered when printing, and corresponding measures must be taken to make corrections in advance as far as possible

IX. poor overprint

overlapping ink film is called overprint. In multicolor printing, on the ink film of the previous printing, the ink of the next printing cannot be clearly printed. Due to different types of inks, some are easy to produce, and some are not easy to produce. For example, for oxidation polymerization inks, excessive addition of desiccant will promote drying. When the oxidation and hardening of the ink film are excessive, the two-color inks will repel each other. In addition, if too much defoamer is added to the volatile ink, the defoamer will form a film on the surface of the ink strand, preventing overprint. The remedy is to use the ink with good overprint performance, reduce the viscosity of the ink, add additives to the ink, and reduce the drying speed of the ink

X. the size of finished ink strands is expanded.

sometimes the printing size is expanded after silk printing. It is not only an indispensable basic production link for a large number of industrial and agricultural products, but also the main reasons for the expansion of printing size are the low viscosity of ink and excessive fluidity; The size expansion of silk screen printing plate during production is also the reason for the expansion of printing size

in order to prevent the ink from overflowing around after printing due to the excessive fluidity of the ink, resulting in the larger printing size, a certain amount of thickener can be added to the ink with excessive fluidity to reduce the fluidity of the ink. Fast drying ink can also be used to speed up the drying speed of the ink after printing and reduce the flow of the ink. When making silk screen printing plates, we should strictly ensure the quality of silk screen printing plates

Xi. Ink film cracking

ink strand cracking is caused by the action of solvent and large temperature changes. Substrate material itself will also lead to the phenomenon of ink film cracking

in order to prevent the cracking of the ink film, the nature of the ink and the solvent resistance of the substrate should be considered when selecting the solvent. Select the materials with strong solvent resistance and oil resistance as the printing materials, and pay attention to keeping the workshop temperature balanced. When printing multi-color overprint, it should be fully dried in each color, and strictly control the drying temperature, which can effectively prevent the occurrence of ink film cracking

XII. Ink bleeding

ink bleeding refers to the phenomenon of ink overflow on the outside of the printed line. When printing a line, the ink overflows on one side of the moving direction of the scraper, which affects the tidiness of the line. This phenomenon is called ink bleeding. Inking can be solved by adjusting the relationship between the printing plate and the ink, and the relationship between the operation of the scraper and the wire tension angle. The shape of the through-hole part of the screen printing plate varies according to the plate making methods (indirect method, direct method, direct method). The ideal through hole should be close to the substrate during scraping. The printing plate with ideal through-hole shape, the ink film printed is sharp, neat, accurate in size, and does not bleed ink. In order to prevent the occurrence of smoke and ink, the plate film should have appropriate thickness, elasticity and smoothness. For this purpose, soft nylon silk and polyester silk with high dimensional accuracy can be used to make plates. In order to prevent ink drying, it is best to use oblique stretching in the plate making process

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