The screen printing process of glass is prone to faults, some of which are caused by a single reason, but most of which are the result of the cross influence of various reasons.This is what operators should pay special attention to when judging the fault cause of glass screen printing and taking corresponding countermeasures:
Paste version
1.Paste plate, also known as block plate, refers to the screen plate image hole part of the printing ink cannot be transferred to the substrate.The appearance of this phenomenon will affect the printing quality, or even the normal printing.The causes of the paste phenomenon during screen printing are complex.Paste version of the reason can be analyzed from the following aspects: (1) the reason of the glass: the surface of the glass is not clean, there is a watermark, paper, mimeograph, fingerprint, dust particles and other dirt.Thus resulting in paste plate;(2) workshop temperature, humidity and ink properties.Screen printing workshop is required to maintain a certain temperature of about 20℃ and relative humidity of about 50%, if the temperature is high, low relative humidity, the volatile solvent in the ink will quickly volatilize, screen ink viscosity becomes high, thus blocking the mesh.Another point should be noted, if the downtime is too long, will also produce paste version of the phenomenon, the longer the paste version of the more serious.Secondly, if the ambient temperature is low, ink fluidity is also easy to produce paste version;The reason of screen printing plate.The finished screen printing plate should be washed with water and dried before use.If the finished version is left too long to print in time.In the preservation process more or less will adhere to the dust, if not cleaned when printing, will cause paste plate.The reason of printing pressure.In the printing process, too much embossing force will make the scraper bend, the scraper and screen printing plate and glass is not line contact, but a surface contact, so each scraping can clean the ink, leaving residual ink, after a certain period of time will conjunctiva caused by paste plate.(5) Screen plate and glass gap improper reasons.Screen plate and the gap between the glass should not be too small, the gap is too small after the screen can not be timely from the glass, screen plate lifting, printing plate at the bottom of a certain amount of ink, which is also easy to cause paste plate.Ink, in screen printing ink pigments and other solid particles larger, it is easy to plug the phenomenon of mesh.In addition, the selection of mesh mesh and hole area and ink particle size compared to some small, so that the coarser particles of ink is not easy to pass through the mesh and the phenomenon is one of the reasons.For larger ink particles caused by the paste version, can be started from the manufacturing of ink, the main method is to strictly control the ink fineness.
In the printing process, the increase in ink viscosity resulting in paste plate, the main reason is, screen printing plate on the ink solvent evaporation, resulting in increased ink viscosity, and the phenomenon of closure.If the printing image and text area is relatively large, screen printing ink consumption, paste version less.If the image area is small, screen printing ink consumption is less, it is easy to cause paste version, the solution is to use a small number of times the inking principle.Poor ink fluidity, will make ink in the screen will not produce paste version, this situation can be solved by reducing ink viscosity to improve ink fluidity on the premise of not affecting the quality of printing.Paste version of the fault, can be based on the nature of the ink, using the appropriate solvent to scrub.The main point of the scrub is to start from the printing surface and gently wipe from the middle to the periphery.After wiping, check the printing plate, if there is a defect should be timely repair, repair can start printing again.It should be noted that each time the film is swabbed, it will become thinner, such as wipe caused a major defect in the film, then had to change the new printing.2.The ink on the glass is not firmly fixed when the glass is printed, it is important that the glass should be degreased and pre-treated before printing.When the surface of the glass with grease, binder, dust and other substances, it will cause ink and glass bonding.(2) the ink itself adhesion is not enough to cause ink film fixation is not strong, it is best to replace other types of ink for printing.Diluting solvent improper selection will also appear ink film adhesion phenomenon, in the choice of diluting solvent to consider the nature of ink, in order to avoid ink and substrate bond phenomenon.3.Ink uneven ink film thickness, the reason is a variety of ink, ink allocation is bad, or the normal allocation of ink mixed with the ink, printing, due to the role of the solvent expansion, softening, should be through the ink mesh, played the role of the film, so that the ink can not pass.In order to prevent this fault, after the deployment of ink (especially old ink), before use to use a screen to filter again.When reusing used plates, the old ink must be completely removed from the frame.After printing, take care of the printing plate, to be fully washed (including scraper).If the back of the ink front of the tip of the damage, will be along the direction of the scraper movement a trace.When printing glass, there are obvious inks.Therefore, it is necessary to protect the front end of the scraper, so that it does not occur damage, if the damage, it is necessary to use the grinding machine seriously grinding.Moreover, the concave and convex of the printing table will also affect the uniformity of the ink.Convex ink layer is thin, concave ink layer is thick, this phenomenon is also known as uneven ink.In addition, the substrate on the back or printing table if there is dust, will also produce the above fault.
Pinhole phenomenon
Pinhole phenomenon is the biggest headache for glass screen printing workers.There are also various reasons for pinholes, some of which cannot be explained, and some are quality management problems.Pinhole is one of the most important inspection items in the inspection of printed products.Dust and foreign matter attached to the plate.When making a plate, water development will have some sol mixed in.In addition, when emulsion coating, there is dust mixed, attached to the screen will produce pinholes.These, if examined carefully, can be discovered during the test and can be repaired in time.If dust and foreign matter attached to the screen, blocking the screen opening will also cause pinhole phenomenon.Before the formal printing, to carefully check the screen plate, eliminate the dirt on the plate;(2) Glass surface cleaning.The glass plate should be pretreated to make its surface clean before printing.If the glass is not printed immediately after processing, it will be contaminated again.After pretreatment, the dirt such as grease can be removed, at the same time, also can remove the dust attached to the surface.Special attention should be paid to the hand when moving glass, hand fingerprints will also adhere to the printing surface, printing pinholes.
A bubble
Bubble glass in the ink after printing, sometimes there will be bubbles, the main reason for the bubble has the following aspects: substrate prepress treatment is bad.Substrate surface adhesion dust and oil stains and other substances;The bubble in the ink.To adjust the ink, add solvents, additives for mixing, ink will be mixed with some bubbles, if placed regardless, low viscosity ink will naturally defoaming, high viscosity ink some can not naturally defoaming.Some of these bubbles disappear naturally in printing due to the transfer of ink, while others become larger and larger.In order to remove these bubbles, to use the defoamer, ink defoamer addition is generally 0.1 ~ 1% or so, if more than the specified quantity will play the role of foaming.Ink transfer even foam, as long as the substrate wettability and ink mobility is good, its printing ink film surface bubbles will gradually eliminate, the ink to form a flat printing ink film.If the ink bubble is not eliminated, the ink film will form a ring of uneven film surface.In general ink bubbles through the screen, also due to the role of the screen can be defoaming;(3) printing speed too fast or printing speed is not uniform will also produce bubbles.Printing speed should be reduced to maintain the uniformity of printing speed.6.Electrostatic fault Electrostatic current is generally very small, but the potential difference is very large, together with attraction, repulsion, conduction, discharge and other phenomena.(1) To the screen printing of the negative impact.Printing screen, due to the squeegees rubber pressure squeegees make the rubber part and wire mesh electrified.Wire mesh itself is charged, will affect the normal ink, blocking version of the fault;At the moment of substrate output will be screen suction;(2) Methods to prevent static electricity.The methods to prevent the generation of static electricity are as follows: adjust the ambient temperature and increase the air humidity. The appropriate temperature is generally about 20℃, and the relative humidity is about 60%.The transmission of static electricity in wet air;Reduce screen spacing and printing speed.
Finished ink film size expansion screen printing, sometimes appear
Printing size enlargement
The main reason for printing size expansion is low ink viscosity and liquidity;Screen printing plate in the production of the expanded size, also caused by the expansion of the printing size.In order to avoid ink liquidity is too large and cause the printing ink to flow around, resulting in a larger printing size, you can consider to increase the ink viscosity, to reduce ink mobility.In the production of screen plate, to strictly ensure the screen quality, to ensure the tension screen.8.A part of the ink leakage plate film, known as the ink leakage fault, the cause is: a part of the scraper;High scraping pressure;The gap between the plate and the glass is too large;Large deformation, local printing and pressing: ink is not uniform;Overfine wire mesh;Printing too fast, etc.If the glass and ink mixed with dust, do not add treatment on the printing, because of the scraper pressure will make the film damaged;Underexposure in plate making, such as pinhole, will make the film leakage ink phenomenon.At this time, tape can be used from the back of the plate to do emergency treatment.This operation, if not very quickly, will make the layout of the ink dry, have to wipe the whole version of the solvent.Wipe version is also the cause of film stripping, so it is best to avoid.Version of the ink leakage in the part of the ink often occurs, so it is best to strengthen this part of the plate.
A spot
Smear-blotting refers to the appearance of blot-like marks on the graphic and dark parts of the glass surface, which damages the printing effect.Glass screen printing is easy to produce this phenomenon.The reasons are as follows: printing speed and ink drying too slow;The ink is too thin;Ink thixotropy;Effects of static electricity;Poor pigment dispersion in ink, due to the polarity effect of pigment particles, particles mutually agglutinate, color blots appear.Improved methods are: to improve ink mobility;Use quick-drying flux;Printing ink with high viscosity: to increase the thickness of the ink wet film, try to use inks with low oil absorption pigments: to minimize the effects of static electricity.10.Image deformation printing by the squeegees added to the plate, so that the plate and printed between the line contact can be, do not exceed.Too much printing, printing plate and substrate inside contact, screen will be telescopic, resulting in the distortion of the printed image.Screen printing is the least pressure of all printing methods, if we forget this point is not a good print.If you can’t print without increasing the pressure, the gap between the plate and the glass surface should be reduced, so that the pressure of the scraper can be reduced.