Analysis and troubleshooting of common faults in t

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Analysis and troubleshooting of common faults in glass fiber printing

the causes of glass fiber printing faults are various, involving many factors such as screen printing plate, screen scraping plate, screen printing ink, screen printing equipment, screen printing materials and operation technology. There is a single reason for the silk screen printing fault, but it is more the result of the cross influence of various reasons. This is what the operator should pay special attention to when determining the cause of the fault and taking corresponding countermeasures

I. paste plate

paste plate is also called blocking plate, which refers to the phenomenon that the ink cannot be transferred to the substrate in the through-hole part of the silk printing plate during printing. The appearance of this phenomenon will affect the printing quality, and even fail to print normally in serious cases

The reasons for the paste phenomenon in the process of silk printing are complex. The reasons for paste can be analyzed from the following aspects

① reasons for substrate. The glass surface is not cleaned, and there are still watermarks, paper prints, mimeographs, fingerprints, dust particles and other dirt. Thus causing paste

② reasons for workshop temperature, humidity and ink properties. The silk printing workshop requires to maintain a certain temperature of about 20 ℃ and relative humidity of about 50%. If the temperature is high and the relative humidity is low, the volatile solvent in the ink will evaporate quickly, and the viscosity of the upper ink will become high, thus blocking the hole. Another point that should be noted is that if the downtime is too long, there will also be a paste phenomenon. The longer the time, the more serious the paste. Secondly, if the ambient temperature is low, the ink fluidity is poor, and it is easy to produce paste

③ reasons for silk screen printing. The prepared screen printing plate can be used only after it is washed with water and dried before use. If the plate is placed too long after making and not printed in time, dust will adhere to it more or less during the storage process. If it is not cleaned during printing, it will cause paste

④ causes of printing pressure. During the printing process, too much embossing force will bend the scraper. The scraper is not in line contact with the screen printing plate and the substrate, but in face contact. In this way, the ink can be scraped clean every time, leaving residual ink. After a certain period of time, the film will form a paste

⑤ reasons for improper clearance between screen printing plate and substrate. The gap between the screen printing plate and the substrate should not be too small. If the gap is too small, the screen printing plate cannot be separated from the substrate in time after scraping. When the screen printing plate is lifted, a certain amount of ink is stuck on the bottom of the printing plate, which is also easy to cause board pasting

⑥ causes of ink. When the pigment and other solid particles in silk printing ink are large, it is easy to block the hole

in addition, the selected wire mesh and through-hole area are smaller than the particle size of the ink, which makes it difficult for the ink with coarser particles to pass through the hole and seal. The paste caused by the larger particles of ink can be solved from the time of manufacturing ink. The main method is to strictly control the fineness of ink

in the printing process, the increase of ink viscosity causes plate pasting. The main reason is that the ink solvent on the screen printing plate evaporates, resulting in the increase of ink viscosity and sealing. If the printing area is relatively large, the ink consumption on the screen printing plate is more, and the paste phenomenon is less. If the image and text area is small and the ink consumption on the screen printing plate is small, it is easy to cause paste. The countermeasure is to adopt the principle of adding ink a few times. The poor fluidity of the ink will cause the ink to paste when it does not pass through the silk. This situation can be solved by reducing the viscosity of the ink and improving the fluidity of the ink without affecting the printing quality

in case of paste failure, appropriate solvent can be used for scrubbing according to the nature of the ink on the plate. The key of scrubbing is to start from the printing surface and wipe gently from the middle to the periphery. Check the printing plate after wiping. If there is any defect, it should be repaired in time. After repairing, the printing can be restarted. It should be noted that the plate film becomes thinner every time it is wiped. If there is a major defect in the plate film during wiping, it has to be printed with a new version

II. The ink is not firmly fixed on the substrate

1. When printing glass, it is very important to strictly degrease and pre-treatment the glass before printing. When the glass surface is attached with grease, adhesives, dust and other substances, it will cause poor adhesion between ink and glass

2. The ink itself has insufficient adhesion, which causes the ink film to be unstable. It is best to replace other kinds of inks for printing. Improper selection of dilution solvent will also lead to the phenomenon of weak ink film indolence. When selecting dilution solvent, we should consider the nature of the ink to avoid the phenomenon of weak adhesion between the ink and the substrate

III. ink film edge defects

in glass fiber printing products, the common problem is serrated burrs (including incomplete or broken lines) on the edge of the printing ink film. There are many reasons for burrs, but the main reason is the quality problem of the silk screen version

① the resolution of photosensitive glue is not high, resulting in the broken red or incomplete fine lines

② using the speed converter of the gear, the exposure time is insufficient or too long, and the development is insufficient, so the edges of the silk printing text and text are not neat and jagged. For a good screen printing version, the edges of the pictures and texts should be smooth and neat

③ when the photosensitive adhesive on the surface of the screen printing plate is not evenly coated, there is still a gap between the screen printing plate and the substrate during printing, and burrs appear on the edge of the printing ink due to the suspended penetration of the ink

④ during the printing process, due to the expansion of the plate film after contacting the solvent, and the degree of warp and weft expansion is different, the surface of the plate film appears uneven. During printing, there is a gap between the silk plate and the substrate, the ink is suspended and penetrated, and the ink film will appear burrs

in order to prevent the occurrence of jagged haircuts, solutions can be considered from the following aspects:

① select high mesh silk plate making

② choose photosensitive materials with high resolution for plate making; We should choose the photosensitive glue with bridge type and good image resolving property

③ make a silk screen printing plate with a certain thickness of photosensitive film to reduce expansion and deformation

④ diagonal tension can also be used, and the best angle is 22.5

⑤ fine line printing can also adopt indirect plate making method, because the possibility of burrs in the indirect plate making method is small:

⑥ with the progress of science and technology in the plate making and printing process, try to control the temperature expansion factor, and use photosensitive materials with small expansion coefficient:

⑦ improve the plate making quality, ensure that the surface of the screen printing plate is flat and smooth, and the edges of the plate lines should be neat

⑧ spray the screen printing plate with a water spray gun to improve the development effect

⑨ the distance between the plate and the substrate, the angle of the scraper, and the printing pressure should be appropriate

IV. uneven inking

the uneven thickness of the ink film is due to various reasons. In terms of ink, it is the poor allocation of ink, or the normally allocated ink is mixed with the ink skin. During printing, due to the effect of solvent, it expands and softens, blocking the holes that should be through the ink, playing the role of the plate film, making the ink unable to pass through

in order to prevent this kind of failure, the blended ink (especially the old ink) should be filtered once before use. When reusing the used printing plate, the old ink attached to the plate frame must be completely removed. When storing the printing plate after printing, it should be fully washed (including scraper)

if the above requirements are followed, the accident of uneven inking will not happen

if the tip of the front end of the ink return plate is damaged, marks will appear along the moving direction of the scraper. When printing glass, there will be obvious uneven inking. Therefore, the front end of the scraper must be well protected from damage. If it is damaged, it must be carefully ground with a grinder

the unevenness of the printing table will also affect the uniformity of inking. The ink layer in the convex part is thin, and the ink layer in the concave part is thick. This phenomenon is also known as uneven inking. In addition, if there is dust on the back of the substrate or on the printing table, the above fault will also occur

v. pinhole

pinhole phenomenon is the most headache for staff engaged in glass fiber printing. There are many reasons for pinholes, many of which are unexplained at present, and some are quality management problems. 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 during water washing and development. 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 the official printing, the edition should be carefully checked to remove the dirt on it

② cleaning of substrate surface. The glass plate shall be printed immediately after its surface is cleaned by pretreatment before printing. If the glass is not printed immediately after treatment, it will be polluted again. After pretreatment, dirt such as grease can be removed, and dust attached to the surface can also be removed

special attention should be paid to that when moving the cloud glass by hand, the fingerprint of the hand will also adhere to the printing surface, and pinholes will be formed during printing

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 J 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 also be defoaming due to the lack of a strong national research support system

③ bubbles will also be generated if the printing speed is too fast or uneven. The printing speed should be reduced appropriately to 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 use ink with good leveling property for printing

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

⑨ try to use thin single silk in plate making

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