Common problems of the most popular self-adhesive

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Common problems in self-adhesive label printing

plate cracking

at present, photosensitive resin letterpress is mostly used in self-adhesive label printing in China, and this kind of plate often has the problem of plate cracking. The reasons are analyzed below, and the corresponding solutions are put forward

1. the diameter of the plate roller is too small

the smaller the diameter of the plate roller, the greater the tensile force on the printing plate, and the greater the outward tensile force at the plate interface, so that the plate interface is tilted upward, making it not stick firmly on the plate roller. After printing on the machine, the pressure here is greater than that in other places, which is easy to cause the plate to break. For this, use double-sided adhesive tape with strong adhesion to paste the plate, and seal the non graphic part at the plate interface with adhesive tape

2. the plate is too hard

the plate is too hard, which will cause the plate surface to be too brittle, resulting in plate cracking. For this, you can choose a softer plate. Our factory once printed a full plate live part. At first, we used the Japanese Toyo textile kf-9bgc plate. After a short time of printing, the plate cracked. Later, we used the softer ef-95gc plate. The trouble was eliminated

in addition, dry weather and low temperature in winter also tend to harden the plate. In this regard, the printing plate should be used and made as soon as possible; The temperature of the plate making room shall be kept at about 25oC and equipped with humidification equipment; The prepared printing plate is sealed and stored in a plastic bag; Keep a certain temperature and humidity in the printing workshop. If the printing plate becomes hard after being left unused for a long time, wash the back of the printing plate with hot water to make it soft. However, if the resin version is used, because it can be dissolved in water, it must be avoided that the water contacts the image and text on the front of the printing plate, otherwise it is easy to damage the image and text

3. too much printing pressure

too much printing pressure is also easy to cause the printing plate to break. This phenomenon is particularly easy to occur when there are field pictures and texts at the printing plate interface. Therefore, in the printing process, the printing pressure should be reduced as far as possible on the premise of ensuring the authenticity of pictures and texts

4. unreasonable layout

some layouts are on the spot from beginning to end. In addition, the diameter of the plate roller is too small, so the plate mouth is easy to be cocked up when printing, and it is easy to crack when printing. If you choose a plate roller that is a little larger than the actual step distance, and leave a small plate base at the edge of the plate during plate making, the plate can be attached to the plate roller more easily, which greatly reduces the occurrence of plate cracking

return shadow

in the relief printing process, the graphic part of the printing plate is higher than the non graphic part. When the ink on the plate roller is transferred to the plate, the non graphic part of the printing plate is not inked, and the ink on the plate roller relative to the non graphic part has no place to transfer. Due to the small number of ink rollers in the relief press, the residual ink on the plate roller could not be opened in time, resulting in a year-on-year drop of 5.4%; It is estimated in the industry that the ink volume in 2016 (2) and 2020 is partially unbalanced, and the local ink volume is greater than the ink volume required for printing, which makes the color of local graphics and text darker than that of other parts of the printed product and produces back glue shadow

it can be seen that the generation of adhesive return shadow is closely related to the rationality of ink path design of self-adhesive printing machine

there are several methods to solve the glue back shadow

1. increase the number of ink leveling rollers in the unit

study the rheological properties, multi-level structure and evolution law of polymer matrix nanocomposites under extreme conditions of micro machining. Add several ink leveling rollers in the printing unit to make the ink layer on the plate backup roller more evenly transmitted to the printing plate, so as to greatly reduce the depth of adhesive return

2. change the master roller

for some long version activities, change the diameter of the master roller to be as thick as the master roller, which can also greatly reduce the depth of the glue back shadow. The principle is: the ink area on the plate roller is consistent with the relative position of the ink area on the plate roller, and the ink layer thickness is relatively stable. This method is suitable for satellite self-adhesive label printing machine

3. adjust the ink feeding method

the specific method is to release the ink teeth and adjust the ink nails to control the amount of ink. In this way, the ink can be transferred to the inking roller as evenly as possible while ensuring the amount of ink required for printing, so as to facilitate the ink to be more evenly transferred to the plate roller, so as to reduce the glue back shadow

the ink does not dry

there are many reasons for the ink to dry, which are mainly reflected in the following aspects: according to the different types of test pieces to be tested (plastic, metal, etc.) and the different types of test methods (stretching and tightening), the fixture needs to be replaced for experiments

1. too much ink supply

too much ink supply leads to too thick ink layer and the UV lamp cannot dry the ink in time. This phenomenon mainly occurs when printing live parts. In this case, the ink feeding amount can be minimized without affecting the printing quality. If you can't get good results, you can consider moving the field to the first few groups of printing units for printing. In this way, after baking by multiple UV lamps, the fault will be reduced

2.insufficient power of UV lamp

insufficient power of UV lamp caused by aging of UV lamp or other reasons will also lead to ink drying. In this regard, adjust the power of the UV lamp to the maximum gear. If it is not dry, replace the UV lamp tube to solve the problem

3. too fast printing speed

too fast printing speed will cause the UV lamp too late to dry the ink. This can be solved by changing the printing unit or reducing the printing speed. When printing live parts, the printing speed should be kept at about 20 m/min

printing is dirty.

there are often some indistinct dirty phenomena in the printing process. The following is an analysis of this problem

1. fixed hanging dirty

this situation is mainly caused by dirty things on the surface of the printing plate or the edge of the plate is upturned, which shows that there are dirty spots at the fixed position of the printed image and text. If it is caused by the warping of the plate, there is a line in the image and text part, and its color is consistent with the printing color of the warped plate. The problem can be solved by cleaning the plate or pressing the warped part of the plate edge

2. unfixed dirt hanging

this situation is mainly caused by dirt or hard injuries on the plate roller, which is manifested as periodic unfixed dirt hanging. The solution is to carefully check and replace the damaged cots or clean up the dirt on the master roll

3. paper rubbing causes a similar phenomenon of dirty hanging

in the process of paper feeding, the paper rubs against the edge of the UV lamp, or the paper pressing roller of the machine has foreign matter rubbing against the paper, which will cause the paper surface to be scratched, and the ink printed on it will produce a similar dirty hanging effect. In particular, when printing thick film self-adhesive labels, due to the irradiation of UV lamp, the material will deform and bulge when heated, which is more likely to occur. In this regard, you should carefully observe to find out where the paper is rubbed, and eliminate the dirt by adjusting the angle of the UV lamp or cleaning the paper pressing roller

4. large amount of ink may cause dirty or paste up phenomenon

letterpress printing is a water-free printing method, and large amount of ink may easily cause dirty or paste up of graphics and text. Polymer suppliers and dealers believe that. In addition, too thin ink is also easy to paste the version and cause the image and text to paste. The solution is to reduce the ink volume or increase the viscosity of the ink according to the requirements of the live parts

above, we have analyzed several common problems in self-adhesive label printing, hoping to help you in your daily work. Of course, in addition to the reasons I mentioned, there are many factors that cause the poor printing quality of self-adhesive labels. I hope you can carefully summarize them in your future work, draw lessons and continuously improve the product quality

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