The UV lamp impact on ink adhesion
Time:2016-04-14 09:43Source:sankunClick: Number
The wavelength of the UV lamp and power impact on ink adhesion
UV ink is a kind of using ultraviolet light as an energy source, printing ink light initiator produce free radicals or cationic polymer after exposure to the UV light curing ink varieties.In recent years as the rapid development of UV ink, UV ink has been widely used in the application of screen printing. But in the process of using UV ink is easy to appear some problems, such as curing, surface glue, the phenomenon such as poor adhesion after curing, so need to master the principle of the UV curing in practical application, the influencing factors of solidified, and the countermeasures to solve these problems.Printing ink performance directly affects the quality of the printing quality, two important physical indexes and the performance of ink is the membrane layer hardness and adhesion.
Refers to the film and printing ink adhesion the adhesion strength of the base material, it has a significant influence to the performance of the UV curing ink, if ink adhesion is not good, other properties, it is hard to achieve it.Hardness is refers to the printing ink after UV light curing the crosslinking degree of polymerization of fully, completely full curing ink film surface smooth, glossy, hardness, and not completely curing ink film, rough surface, powder, lacklustre, surface hardness is low, so the film hardness is an important index to measure the performance of ink. Below is the UV ink in the use of some of the problems of some discussion.
1. The wavelength of the UV lamp and the wavelength of the UV lamp power should satisfy the UV ink sensitive wavelength range. Various brands of UV ink for UV wavelength is not the same, if the wavelength of the UV light in ink sensitive wavelength range, UV ink can cure, otherwise you will to a certain extent affect the curing.
UV light energy determines the UV printing ink ink film when light crosslinking UV light penetration, especially for the deeper penetration of UV ink. When UV energy shortage, UV light does not provide enough energy of polymerization, the inadequate curing, no amount of even under UV light irradiation time cannot achieve full curing, ink layer depths cannot crosslinking, thus affecting hardness and adhesion performance. While UV energy is too large will make the ink layer surface rapid solidification, improve surface hardness, ink layer increased brittleness, softness is reduced. This ink layer under the action of external force, such as cutting, the cutting edge part of the ink layer will peel and fall off with the base material. General UV light curing machine configuration of the UV lamp power in 80 ~ 120 w/cm.
2. Surface treatment of base material if there is oil, solvent base material surface, untreated low molecular or other impurities, etc., will affect the UV curing ink in substrate adhesion, so must to clean the base material before printing. Generally available ethanol wipe base material surface, the metal surface after get rid of the oil can be used sand paper processing surface, such as increasing the surface roughness, increase the adhesion.
3. The surface tension of the UV curing ink in substrate adhesion with UV ink on substrate wetting has important relation, and UV ink on substrate wetting is mainly determined by the surface tension of the UV ink and substrate, when the surface tension of the UV ink is smaller than the surface tension of the base material, can achieve good wetting, and good wetting is likely to achieve good adhesion. So if you want to make UV ink on the substrate well, you must try to reduce the surface tension of the UV ink, at the same time increase the surface tension of the substrate. Can use the one way is by adding the surface active agent to reduce the surface tension of the UV printing ink; Another way is to use cyclohexanone wipes substrate surface in order to improve the surface tension of the substrate, or according to the different surface tension of substrates extremely polarity for chemical oxidation treatment, corona treatment and illumination, etc., in order to increase the polarity of the base material, thereby improving the surface tension of the substrate, achieve the goal of improve the base material and the printing ink adhesion.
4. The film layer thickness of the film thickness had a great influence on adhesion and hardness index. Ink film thickness is too thick thick or local, make ultraviolet difficult to penetrate, ink curing ink cannot be completely cured or only surface, internal printing ink is not completely cured, this will directly reduce the ink resistance, adhesion and film hardness features. Ink film thickness too thin, easy to produce pinhole and sand holes, covering power is also reduced. So, it is necessary to strictly control the ink film thickness. Control in screen printing ink thickness is mainly accomplished by choose different screen, usually colored ink due to the effect of cover of the pigment to UV light, ink layer thickness as far as possible some thin requirements, silk screen with 350 goals; Transparent ink printing can be used in the lower screen mesh; While some special ink such as ink, as a result of the filler particle size problem need to use a komoku for silk screen printing.
5. Cure time, like membrane layer thickness, has a great influence on the hardness and curing time. If the curing time is too short, inadequate film crosslinking reaction, can only form powder, rough, matte film layer, in general, the appropriate prolong the curing time on the ink film hardness is good. Curing time is too long, of course, due to excessive UV light irradiation, to improve the surface hardness, surface tension decreases, and can also cause ink and poor adhesion between substrate.
The method to determine the appropriate curing time is in a certain power of UV lamp, with a certain speed through UV curing machine, use cotton with anhydrous ethanol, 50 times wipe ink layer surface, observation of cotton and base material, erased for UV ink, if removed, will decrease the curing speed, longer cure time, until the UV ink on the substrate cannot be erased, at this time for the proper cure time.
6. The adhesion promoter adding adhesion promoter is added in the UV printing ink formula can significantly improve the ink adhesion, but different adhesion promoter for different base material has different effect, need through the experiment to determine the specific varieties of adhesion promoter.
7. In the use of UV curing temperature due to the UV curing machine will emit a lot of heat, in the printing of the base material is more sensitive to temperature, UV lamp emit a lot of heat will have negative effect on the backing material, then can increase the distance between the substrate and UV lamp or increase the cooling way to solve, but increase the distance between the substrate and UV lamp is equal to the reduced the UV lamp power, curing would be affected. Increase cooling method can be used to reduce the curing temperature, cooling air cooling and water cooling, with the method of air cooling are common, but a common problem is air cooling effect is not ideal.
Use effect of the water, is a good method, UV curing machine sells on the market at present many of them are water cooled UV curing machine. To make the UV offset printing work better, to solve main problems are as follows.
1. The design of plate production UV printing design draft must be decided according to the repair order output formats, such as membrane surface is sweep or sweep, the output Angle of number of cables, cables, etc. Some special up higher requirements, such as 3 d printing resolution to high, cable Angle must be compatible with the substrate, avoiding collision mesh; Transparent plastic sheets and aluminized paper often need white ink printing, printing materials should be paid attention to the influence of scale, through the modification of film in order to achieve the best quality in advance.
2. The adhesion substrates such as plastic sheets or gold and silver cardboard permeability is very poor, the ink absorption ability is very weak, so even if the UV printing ink, ink adhesion is very poor, also print quality is not high. Can be based on the material surface treatment to solve.
3. The ink emulsification UV ink, ink balance tolerance is very narrow, easy to cause the ink emulsification, dirty version printing, affect the printing quality. The solution: reduce the printing speed, the printing speed control in 5000 ~ 8000 / hour.
4. In order to improve the printing quality color saturation, curing degree in substrates such as plastic sheet surface of UV printing, printing pressure, ink layer thick, branches increasing serious, which makes the ink is not easy to cure. In order to ensure the quality of printing, printing pressure can't be a big adjustment. Solution is to first moderately reduce the printing speed, make the UV lamp irradiation time lengthened appropriately, let the ink completely curing; Followed by adjusting the UV lamp and the distance between the substrates, increase the intensity of UV light, make the ink curing. UV cure effective wavelength range is 200 ~ 400 nm, printing workshop in some light wavelength in the range, also can cause slight curing ink surface, so we should pay attention to the ambient light for the influence of UV ink.
5. Color sequence arrangement UV offset printing color sequence arrangement problem is more complex. Because of the limitation of lis principle of substrates on the ink layer thinner, when you need to compare the thick ink film, printing quality is difficult to achieve the desired print effect. Such as four-color overprint, we usually use black, green, magenta, yellow color series, because black fill nearly all space, green, magenta, yellow ink forme force is lower, total quantity of ink is not enough, it will cause the color is not full. Solution: a more natural order, the color of the printing ink is smaller, the last ink quantity larger black, so that it reached the highest amount of inking colour more full.
6. Printing alignment UV offset printing for ink using UV light curing, curing of the main problem is to make the substrates under the heat expansion, resulting in misregister. The inconsistent with the UV curing ink, because the ink curing need UV lamp irradiation time longer, and printing set of guidelines need UV lamp irradiation time shorter. Solution: at the end of the reentry after color printed the UV curing, this time even if the substrates, placed by lower temperature for a period of time, can also be made to minimize the deformation of substrates. Under special circumstances, demitint group can also open the UV light, but the shorter the irradiation time, the better. Or it can be cold UV technology.
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UVlamp(2)
