Troubleshooting of the most popular gravure drawin

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Troubleshooting of gravure printing wire drawing

several positive signals have appeared in the economic operation of China's extruder industry. Wire drawing is one of the problems often encountered in gravure printing, involving gravure printing machine, plate cylinder, doctor blade, printing environment, ink and many other factors. Improper handling will affect production and quality

wiredrawing is also called pulling and stringing. When the ink performance and ink color rendering degree are different, its performance degree is also different. Generally, the wiredrawing phenomenon of black, cyan and magenta is obvious, and generally appears on a large area of shallow

common wire drawing is mainly divided into three types: shallow position wire drawing, field color block wire drawing at the starting position of the doctor blade, and irregular wire drawing in the printing blank

I. wire drawing at shallow position

1 Eliminate wiredrawing from the source of design and plate making

fully consider the printability in the original design and plate making. We must consider the printing direction and try to avoid printing from shallow to deep; The black and magenta versions are most prone to shallow upper drawing, especially the black version. Because the carbon particles in the ink are thick, when the black is very light, there is almost no carbon particles in a point, so it is more prone to wire drawing. Therefore, a large area of black and light should be set as a special gray version as far as possible to reduce the printing difficulty and scrap rate

2. Use the doctor blade correctly to avoid wire drawing

(1) selection of doctor blade. The surface hardness of the chrome plate cylinder is HV850 ~ 1100. The hardness of the doctor blade should be lower than that of the printing plate, about hv600. If the hardness is too low, the ink cannot be scraped clean. If the hardness is too high, the wear of the printing plate will be accelerated, and knife marks will be produced, which will affect the print quality

(2) flatness of doctor blade. When installing the doctor blade, the blade should be flattened first, and the screws should be tightened from the middle to both sides in turn. It should not be done in one step. It needs to be repeated twoorthree times to ensure that the blade is evenly stressed

(3) sharpness of doctor blade. You can use 600 × water sandpaper or 2 × metallographic sandpaper to polish the doctor blade, or use a special grinder to grind the back of the doctor blade into a bevel of about 25 °, even if the new blade is still to be ground

(4) doctor blade angle. The angle of the doctor blade is smaller than that in normal printing, and the distance between the contact point and the embossing point of the doctor blade and the printing plate is shortened at the same time

3. Reasonably select and match the ink to prevent wire drawing

(1) when there is a large area of shallow or layer transition on the layout, the ink with good quality should be selected to prevent wire drawing caused by too thick ink pigment particles. Generally, the fineness of the ink is 15 μ m. Too rough ink particles have great damage to the doctor blade and printing plate

(2) when mixing ink, on the premise that it has no effect on other patterns on the same printing plate, consider using slow drying solvent, and do not add too many auxiliary solvents such as ethyl acetate, so as to prevent the ink from changing and normal printing

(3) ensure that the ink viscosity is moderate and stable. The production of wire drawing is directly related to the viscosity of ink. Generally speaking, the higher the viscosity of ink, the easier it is to produce knife lines in printing. In addition, because the performance of each brand of ink is different, the amount of solvent added is also different. When mixing ink, you can refer to the specific data provided by the ink manufacturer, and carry out specific operations in combination with your own printing conditions and printed products

wire drawing at the starting position of the field color block

wire drawing at the starting position of the field color block is shown as the lifting of the doctor blade at the edge of the field color block, resulting in the dotted line at the edge of the printing color block, which is generally a few millimeters of short wire. The main reason is that the ink viscosity is too large and there is too large pigment particle crystallization in the ink. The solution is as follows

1. Filter the ink and add a certain amount of new ink during use

2. Adjust the angle of the doctor blade smaller, and shorten the distance between the contact point between the doctor blade and the printing plate and the impression point

irregular wire drawing in the printing blank

irregular wire drawing in the printing blank shows irregular ink channels that are sometimes absent, long and short, and usually thick. The causes and solutions are as follows

1. Foreign matters are stuck on the blade of the doctor blade or under the blade. The doctor blade can be moved back and forth and up and down during the printing process, and the adhered foreign matters can be removed or directly removed on the blade of the doctor blade with a bamboo stick (it must be completed by a skilled operator to avoid unnecessary losses due to improper operation). If necessary, it is necessary to stop the machine to thoroughly clean the doctor blade

2. Insufficient ink circulation. At the dead corner of some inks in the ink tank, due to the lack of good circulation, the resin precipitates, forming crystals and lumps of different sizes, or the surface forms ink flakes due to excessive drying (ink flakes are easy to occur in summer, and ink crystals and lumps are more common in spring and Autumn due to the influence of temperature). With the circulation of inks, some ink crystals or ink flakes are brought to the blade by the rotating plate roller, The doctor blade breaks it to form irregular wire drawing. Therefore, we must improve the ink circulation and filtration

(1) cycle improvement. Method 1: tilt the ink tank left and right to ensure that the ink can be injected from the higher end and flow out from the lower end to form a good cycle; Method 2: put the ink tank flat, but the ink must be injected from both ends at the same time and refluxed from the middle, which can also form a good cycle, and the ink cannot be injected from one side

(2) filtration improvement. The ink must be filtered for the first time before use, even if it is new ink. Generally, 140 mesh/inch filter is used to extend sincere greetings and good congratulations to the Mongolian people. The filtration of ink circulating in the ink tank is more important. It can well filter out the resin crystals and foreign impurities formed by the ink in the process of use. The purpose of selection should be finer. The method is like in go-pda. 1. Put a silk stocking under the ink outlet bucket to form a filter bucket. After filtration for a period of time, if the filtration is blocked and the ink flow is not smooth, you can insert some small holes in the top of the bucket with a bamboo stick to increase the ink guiding effect, The lower part of the bucket can also play a good role in depositing impurities, as shown in Figure 3. This method is used by some large printing plants in Shanghai and Guangdong to control the problem of intermittent ink drawing

3. Ink fatigue. This situation often occurs when the inking area of the printing plate is relatively small. During the printing process, the resin in the ink is constantly consumed. If the solvent is continuously added without adding new ink, the resin cannot be supplemented and the sensor device that converts heat into electricity will change the proportion of each component of the ink, resulting in ink fatigue and affecting normal use. Adding new ink properly can solve the problem

other forms of wire drawing

1 Wire drawing caused by printing plate

(1) surface treatment of printing plate. Now gravure is mostly used for electronic engraving. During the engraving process, many small burrs will be formed at the edge of the engraving hole. These small burrs will also damage the doctor blade during the printing process, causing wire drawing. However, this kind of wire drawing is limited to the parts with dots on the printing plate and will not extend to the blank. Generally, the new version is prone to this situation. Within a certain range, with the increase of printing volume, wire drawing will gradually decrease. This requires that in the process of making the plate cylinder, on the one hand, we should ensure that the hardness of the engraved copper layer is moderate, reduce the formation of small burrs in the engraving process, and do a good job in the treatment of the copper layer after engraving; On the other hand, formulate a standardized chromium layer polishing process, including the type of abrasive belt used, the rotation speed of the plate cylinder, the swing frequency and moving speed of the polishing head, and the polishing time. If there is wire drawing in the printing process, you can also polish the surface of the printing plate with 2 # metallographic sandpaper or 600 # water sandpaper or special nylon, which can generally solve the wire drawing problem

(2) installation of printing plate. If the printing plate jumps in the circumferential direction during the printing process, it may also cause wire drawing. It is necessary to check the concentricity of the printing plate and the plate shaft (the top should be checked when installing the plate without shaft), check whether the bearing and transmission parts are deformed and worn, and even whether the base is horizontal

2. Wire drawing caused by environment

the environment of the printing site must be kept clean. If there is dust in the operating environment, it may be mixed into the ink, resulting in wire drawing. Therefore, in the printing operation site, the walking of personnel should be reduced as much as possible, and the sanitation and cleaning work should be done well during the commute. Companies with conditions can isolate the printing unit and install air conditioning facilities and dust removal equipment

reprinted from: Printing Technology

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