Compared with traditional letterpress printing equipment, PS printing equipment has fast printing speed, high dot quality and exquisite printing patterns. Based on the reasons of equipment upgrading and improving production efficiency, many self-adhesive label printing companies have intermittent PS plate printing equipment. However, in the process of visiting enterprises, the author found that intermittent PS plate printing equipment often has some problems in the actual production process, which brings troubles to enterprises. In this paper, the author on the intermittent PS plate printing equipment often encountered some difficult problems to analyze and give guidance suggestions, hoping to bring some help to the enterprise.
 
 
Infirm ink
 
01 Low surface tension of the material
 
The surface tension of the material will directly affect the adhesion of the ink. If the surface tension value of the material is lower than 38, then the ink is difficult to firmly adhere to the surface of the material, it can be seen that the material with low surface tension is easy to lose ink after repeated friction or 3M tape test. Therefore, it is recommended that Indian companies always have a sound pen (a tool used to test the surface tension of the material), test the surface tension of the material before printing, if the surface tension of the material is less than 38 sound, it is necessary to perform surface treatment of the material before printing. Common surface treatment has two ways of corona and primer, generally speaking, PE, PVC and other soft materials, the use of corona treatment will have a better effect, and PET, BOPP and other hard materials, it is recommended to use primer treatment.
 
In particular, it should be noted that some materials are already coated when they leave the factory, and this material is not suitable for testing with a sound pen. Therefore, when purchasing materials, we must fully communicate with the material supplier, if the material itself is coated, it does not need to be tested for surface tension, nor does it need to be pre-treated, and it can be printed directly. In this case, if the ink adhesion is poor after printing, then it may be that the coating is not done well when the material leaves the factory, then it is necessary to find a material supplier to solve, the coating is not strong resulting in poor ink adhesion just like the foundation is not solid, and then how to perform surface treatment, the effect will not be good.
 
 
02 Ink matching is low
 
Ink and material need to have a certain degree of matching, such as some inks are more suitable for printing paper materials, some inks are more suitable for printing film materials, and some inks are especially suitable for materials with low surface tension. At present, most of the inks used by Indian companies are universal models, such as Hanghua UV161 series, this series of ink performance is moderate, can be applied to most of the materials, but if you encounter low surface tension materials may not be suitable, so you can choose a more suitable VP series ink for printing. In addition, before printing a new material, unless you have a good understanding of the properties of the material, it is best to do ink matching tests. For those who do not have conditions, the easiest way is to send the material to the ink supplier, and the ink supplier will give the most suitable recommendation after testing.
 
03 over-additive
 
In the daily production process, we often add some additives to the ink, such as adding some ink oil or viscosity withdrawal agent when the ink viscosity is too high, these additives can reduce the viscosity of the ink and increase the fluidity of the ink, but we must pay attention to the proportion of additives. If the proportion of additives is too high, it will affect the drying performance of the ink, ink drying will be poor, and the ink will fall off when the tape is tested after the printing is completed, so we must strictly control the proportion of such additives, generally not more than 5%. In addition, it is necessary to know that the ink itself has thixotropy, that is, the viscosity of the ink will decrease during the continuous agitation process, the ink will be added to the ink hopper when printing, the viscosity of the ink will naturally decrease with the continuous agitation of the ink hopper roller, then if the proportion of additives is too high, then the ink will become thinner and more unfavorable to printing.
 
 
04 UV drying problem
 
At present, the mainstream ink drying method of self-adhesive printing is to use UV drying, and the power of UV lamp directly affects the drying effect. Generally speaking, the service life of the lamp is 800h ~ 1000h, but in order to save costs, many Indian companies do not replace the lamp in time when it exceeds the service life, until it can not be used. In this case, if the UV lamp is not replaced in time, even if the power of the UV lamp is turned on to the maximum, it is easy to have poor ink drying phenomenon, and this poor drying problem is sometimes not easy to be found, the main performance is that the ink surface is dry, but the following part of the ink is not completely dry, and the adhesive ink will fall off when using 3M tape test. Therefore, it is recommended that Indian enterprises must strictly do a good job of lamp replacement records, try not to use more than the life of the lamp, and at the same time learn to deep ink printing, that is, when printing a large area of field patterns, the color of the spot color ink is darker, and the ink layer is thin when printing, which is conducive to the complete drying of the ink.
 
 
 Color deviation
 
01 Large dot difference
 
In the daily production process, we often encounter the problem that the color of the printed product cannot catch up with the color of the customer's sample. At this time, we can compare the color difference between the printed product and the customer's sample. The specific method is: print a monochrome sample, and then observe the dot, compare their printed products and samples before the dot size is there is a big difference, if the dot difference is more than 5%, you need to adjust the dot size as far as possible to keep consistent with the sample, so that the color of the printed product should be very close to the color of the sample.
 
02 Spot color ink color difference
 
Self-adhesive printing often encounters spot color printing, if the spot color ink and customer sample color difference is large. Sometimes the pantone color number given by the customer and the sample provided by the customer also have a large color difference, then it is necessary to confirm with the customer which color prevails, and then carry out spot color ink deployment after confirming the color standard with the customer. The previous deployment of spot color ink mainly rely on the experience of the printer, now you can test the color ratio of the ink through the spectrophotometer, and then use the electronic scale according to the test results, after the deployment of spot color ink need to record the weight ratio of various colors of ink, in order to consult the next production. According to the above method, the spot color ink can be quickly and accurately deployed, and the stability of the later spot color ink color production can be ensured.
 
03 There is color difference on the surface of the material
 
There are color differences on the surface of the material, such as the surface of some materials is white, and the surface of some materials is yellow, and the same ink printed in different batches of the surface color of the material may be biased. This deviation is usually not large, but for some customers with strict color requirements, this color difference may not be accepted. In order to solve this problem, you can try to choose some suppliers with relatively stable material properties, and ensure that the color difference between batches is not too obvious as far as possible. At the same time, you can pay attention to this problem when deploying spot color ink, and use spot color ink to compensate for the material color difference. Generally speaking, when we sign samples with customers, there will be upper and lower limits for customers with high color requirements, as long as the color error is within this range, it is acceptable. If no matter how to adjust can not solve, then can only replace the material.
 
The above is the author's analysis of some problems often encountered in the daily production process of intermittent PS printing equipment, in fact, there are many problems encountered in the actual production process, due to limited space, the author can not list all, while the author believes that there are many problems that have not been encountered, I hope this article will bring you some inspiration at the same time, It also allows more colleagues to share their valuable experience with you.

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