Compared with ordinary inks, UV inks have the advantages of fast curing speed, good ink film performance, scratch resistance, abrasion resistance, acid and alkali resistance, etc. In addition, UV inks are suitable for various soft and hard substrates, such as films (such as PE , PP, PVC), metal and other non-absorbent printing materials, laying a good foundation for the post-press processing of printed products. Therefore, in recent years, UV inks have been favored by the printing industry and have been widely used in many fields. However, there are also some problems in the application of UV inks, such as curing problems, cross-color problems, adhesion problems, etc.
Below, we will analyze and discuss the four common problems in the use of UV ink, hoping to provide valuable help.
Question 1: How to ensure the curing quality of UV ink?
UV ink can be applied to offset printing, gravure printing, flexo printing and other printing methods. No matter which printing method is adopted, I believe that the fundamental issue that everyone is most concerned about is the curing quality of UV ink. UV ink can undergo photochemical reaction under the radiation of ultraviolet light, so as to achieve the purpose of curing. It can be seen from this curing principle that UV inks have different properties before and after exposure to ultraviolet light, that is, UV inks can maintain stable rheology before exposure to ultraviolet light radiation, and will rapidly cure after exposure to ultraviolet light radiation. It is conceivable that the factors that affect the effect of ultraviolet radiation will also affect the curing quality of UV inks. Therefore, in order to ensure the radiation effect of ultraviolet light, the following three aspects must be in place.
1. Do a good job of ink balance control
In the process of offset printing, UV ink is of weak polarity. If the balance of ink and water is not well controlled, emulsification will easily occur, resulting in the ink film becoming opaque, which directly affects the transmittance of UV light, thereby slowing down the curing speed of UV ink. , causing the ink film to remain incompletely cured after the formation of the ink film. If the printed product in this situation is rubbed or rubbed with tape, the surface of the printed product will be scratched or drawn. Therefore, controlling the ink-water balance in the printing process is one of the important factors to ensure the curing quality of UV ink. Since the adhesion between molecules of UV ink is larger when the viscosity is larger, the water resistance of UV ink will become stronger. Therefore, in order to reduce the emulsification value of UV ink, the principle of small amount of water must be grasped in the printing process, so that the water resistance of UV ink will become stronger. To ensure bright colors, thick ink layer, clear and full dots.
2. Keep the workshop temperature and humidity suitable
During the printing process, changes in the temperature and humidity of the workshop will affect the performance of UV inks and substrates. For example, when the workshop temperature is low and the humidity is high, the light-curing reaction of UV inks is slow, and its binding ability to the substrate will also decrease. Therefore, when printing with UV ink, the temperature and humidity of the workshop must be controlled within a suitable range. Generally, the temperature of the workshop should be controlled at 20-25 degree , and the relative humidity should be controlled at 50 percent -65 percent .
3. Ensure the UV light intensity of the UV lamp
First of all, it is an important prerequisite to select and install UV lamps with suitable power according to the printing speed and product type. The ultraviolet light intensity of the UV lamp directly affects the curing time of the UV ink, which is also a key factor affecting the internal hardening of the ink film. In order to ensure the curing quality of UV ink, the UV lamp should be replaced in time after reaching the actual service life.
Secondly, if the ink contains impurities or the dust in the production process adheres to the surface of the UV lamp, the intensity of ultraviolet light will be weakened, thereby greatly reducing the curing quality of the UV ink. Therefore, the lamp box should be disassembled after the UV lamp has been used for a period of time. Down, use a clean and soft cotton cloth dipped in absolute ethanol to gently wipe the surface of the UV lamp to ensure that it is clean and bright.
Finally, the reflector located inside the UV light box can concentrate 80 percent of the ultraviolet light on the printed product. If paper powder or dust adheres to the reflector, it will affect its reflection effect on ultraviolet light. Therefore, in daily production, the reflector must be cleaned and maintained in time to maintain its best reflection angle and reflection ability. This work can be done at the same time as cleaning the UV lamp, that is, use a clean and soft cotton cloth dipped in absolute ethanol for cleaning. During cleaning and maintenance, the reflector should be closed manually to check whether its closed state is intact, and if necessary, the integrity of its closing device should also be checked. Generally, the closing device adopts pneumatic components, and electric eyes or electromagnetics can be used to detect its working state. In addition, check the condition of the launch plate. Once the surface of the reflector is black or uneven, it should be replaced in time.
In addition, the purity and amount of pigments in the UV ink system, the arrangement of the printing color sequence, and the printing speed will all have a certain impact on the curing of the UV ink.
Question 2: How to solve the problem of cross color in UV ink application?
In the process of UV ink printing, the most troublesome problem for operators is color smearing. This problem is generally caused by the improper arrangement of the printing color sequence, the printing pressure is not adjusted to the best state, and the fluidity of the UV ink is too large. In order to solve the problem of UV ink cross color, it is recommended to start from the following two aspects.
1. Reasonable arrangement of printing color sequence
When the proportion of each color in the printed pattern is quite different, the phenomenon of cross color is most likely to occur. In this case, the color sequence should be appropriately changed according to the actual amount of printing ink. The color with a smaller amount of ink can be printed first, and then the color with a larger amount of ink can be printed last, which can not only effectively avoid the phenomenon of cross color, but also make the The ink volume is maximized, and the color is fuller.
2. Reasonably adjust the printing pressure
The adjustment of printing pressure is also critical to solve the problem of color crossover during UV ink printing. For example, the pressure between the blanket cylinder and the plate cylinder must be adjusted within the standard pressure; the blanket should preferably be a blanket for UV printing; the key color group should use an independent UV curing device, etc.
Question 3: How to solve the problem of insufficient UV ink adhesion?
When printing on some non-absorbent substrates such as gold and silver cardboard, due to the short curing time of UV ink, sometimes the problem of low adhesion of UV ink to the substrate occurs. Insufficient UV ink adhesion will have a greater impact on the printing quality and subsequent processing of the product.
To solve the problem of insufficient UV ink adhesion, the usual measure is to corona treatment of the printing material, thereby changing its polarity and increasing the binding ability of the UV ink to its surface, thereby improving the adhesion of the UV ink. In addition, the curing effect of UV ink directly affects its adhesion. If it is verified that the problem of insufficient adhesion of UV ink is not caused by the quality of the printing material and the curing quality of UV ink, then it can be considered whether it is the quality of the UV ink itself.
In this regard, printing companies need to strengthen communication with UV ink suppliers and try to add an appropriate amount of adhesion promoter to improve it.
Question 4: What are the special requirements for applying UV ink?
1. Requirements for printing equipment
Compared with ordinary ink, the application of UV ink has certain requirements on printing equipment. For example, at present, many printing companies realize UV printing by adding UV curing devices to ordinary offset presses, but there are many problems in this equipment transformation method. For example, UV ink is highly corrosive, which may cause ordinary rubber rollers and blankets to expand. , affecting the stability of the printing pressure, and even lead to peeling or surface cracking of the rubber roller in severe cases. Therefore, UV ink printing has extremely high requirements on cots and blankets, and generally requires the use of special cots and blankets for UV printing.
Under the irradiation of ultraviolet light, the common gripper will be heated and deformed, which will affect the overprinting accuracy. Therefore, the gripper on the printing unit must be replaced with a special gripper for UV printing.
UV ink has high viscosity and strong corrosiveness, which not only easily cracks the ordinary ink fountain, causes UV ink to flow into the ink tooth transmission mechanism, causes the ink tooth drive motor to fail due to excessive resistance, and the rubber roller adjustment mechanism and the ink series roller swing. Mechanisms are also vulnerable to damage. Once these faults occur, it will be more troublesome to deal with. When the UV ink flows into the ink tooth transmission mechanism, it must be stopped immediately and the ink tooth transmission mechanism must be disassembled, otherwise it is difficult to clean it. However, because the internal parts of the ink tooth transmission mechanism are designed very closely, disassembly is more troublesome, especially the inner cylinder The elastic pin is very small in size and is easily damaged during the disassembly process, which will cause secondary damage to the printing equipment. Therefore, in order to avoid the occurrence of the above failures, the most important premise is to use the ink fountain film with reliable quality. In addition, the operator is also required to strengthen the daily maintenance of the printing equipment, clean it thoroughly, and use qualified accessories and raw materials consumables.
2. Requirements for storage conditions
The above-mentioned UV ink curing problems, printing stability, etc. all require an important premise, that is, good ink storage conditions.
From experience, the best storage temperature of UV ink should be controlled at 20-25 degree , avoid sunlight, the best relative humidity should be controlled at 55 percent -65 percent , sealed storage, avoid dust mixing, and UV ink storage warehouse It is best to maintain a constant temperature and humidity. At the same time, it should also be noted that the UV ink storage warehouse should be kept away from fire and heat sources to prevent accidents.
The storage and use management of UV ink should also follow the principle of "first in, first out", that is, the UV ink purchased first should be used first to prevent the UV ink from being stored for too long and affecting its quality of use. UV ink remaining after printing must be sealed and stored in a dark place. UV ink should not be stored for a long time. It should be used before its shelf life. The longest shelf life should not exceed one year. Otherwise, once the UV ink deteriorates, it will not only affect the printing quality, but even cause printing failure in severe cases.
In a word, the factors that affect the use of UV ink are closely related and affect each other. Printing companies must consider multiple angles in the process of applying UV ink, eliminate difficult problems, and give full play to the advantages of UV ink.
