UV lamp wavelength, power and ink adhesion

UV ink is a type of ink that uses ultraviolet light as an energy source, and the photoinitiator in the ink generates free radicals or cations to initiate polymer curing after being irradiated with ultraviolet light. With the rapid development of UV inks in recent years, the application of UV inks in screen printing is becoming more and more extensive. However, in the process of using UV ink, some problems are prone to occur, such as poor curing, surface anti-sticking, and poor adhesion after curing. Therefore, it is necessary to master UV curing principles in practical applications, factors affecting curing, and countermeasures to solve these problems . The performance of printing ink directly affects the quality of the printed matter, and the two important physical indicators of ink performance are the hardness and adhesion of the film.

Adhesion refers to the bonding force between the ink film layer and the printing substrate. It has a significant impact on the performance of UV-curable inks. If the adhesion of the ink is not good, other properties are difficult to achieve. Hardness refers to the sufficiency of the crosslinking polymerization reaction after the ink is cured by UV light. The surface of the ink film layer that is fully cured is smooth, shiny, and high in hardness. The ink film layer that is not completely cured has a rough surface, powdery, and The gloss and surface hardness are low, so the hardness of the film layer is an important indicator to measure the performance of the ink. The following is some discussion on some problems in the use of UV ink.

1. The wavelength of the UV lamp and the wavelength of the power UV lamp should meet the wavelength range sensitive to UV ink. UV inks of various brands require different UV wavelengths. If the wavelength emitted by the UV lamp is within the wavelength range of the ink sensitivity, the UV ink can be cured, otherwise it will affect the curing to a certain extent.

The energy of the UV light determines the penetration ability of the UV ink ink layer when the light is crosslinked, especially the deep penetration ability of the UV ink. When the UV energy is insufficient, the ultraviolet light does not provide enough polymerization energy to make the curing insufficient. Even if it is irradiated under UV light for more time, it cannot be fully cured, and the ink layer cannot be cross-linked deep, which affects the hardness and Adhesion performance. If the UV energy is too large, the surface of the ink layer will be rapidly cured, the surface hardness will increase, the brittleness of the ink layer will increase, and the flexibility will decrease. Under the action of external force, such as the ink layer, the ink layer at the edge of the ink layer will peel off from the substrate and fall off.

The UV lamp power of the general UV light curing machine is about 80 ~ 120W / cm.

2. Surface treatment of the substrate If there are oil stains, solvents, untreated low molecular weight or other impurities on the surface of the substrate, it will affect the adhesion of the UV-curable ink to the substrate, so the substrate must be cleaned before printing. Generally, ethanol can be used to wipe the surface of the substrate. After the oil surface is treated, the surface can be treated with sandpaper, etc. to increase the surface roughness and increase the adhesion.

3. The surface tension of the UV-curable ink on the substrate has an important relationship with the wetting of the UV ink on the substrate, and the wetting of the UV ink on the substrate is mainly determined by the surface tension of the UV ink and the substrate. When the surface tension of the UV ink is less than the surface tension of the substrate, good wetting can be achieved, while good wetting may achieve good adhesion. Therefore, in order to make the UV ink adhere well to the substrate, the surface tension of the UV ink must be reduced as much as possible while increasing the surface tension of the substrate. One method that can be used is to reduce the surface tension of the UV ink by adding a surfactant; another method is to wipe the surface of the substrate with cyclohexanone to increase the surface tension of the substrate, or according to the different surface tension of the substrate Perform chemical oxidation treatment, corona treatment and light treatment to increase the polarity of the substrate, thereby increasing the surface tension of the substrate and achieving the purpose of improving the adhesion between the substrate and the ink.

4. The thickness of the film layer The thickness of the film layer has a great influence on the adhesion and the hardness index. The film thickness of the ink is too thick or too thick, making ultraviolet light difficult to penetrate, the ink cannot be completely cured or only the surface ink is cured, and the internal ink is not completely cured, which will directly reduce the various resistance characteristics of the ink. Focus and film forming hardness. If the film thickness of the ink is too thin, pinholes and trachoma are likely to occur, and the hiding power is reduced accordingly. Therefore, the film thickness of the ink must be strictly controlled. In screen printing, the control of ink thickness is mainly achieved through the selection of different screens. Generally, colored inks should be as thin as possible due to the pigment's covering effect on UV light. A 350-mesh screen is used; the available mesh of transparent ink is relatively low Screen printing; and some special inks such as luminous inks, etc., because of the particle size of the filler, a smaller mesh screen is required for printing.

5. The curing time is the same as the thickness of the film layer, and the curing time has a great influence on the hardness. If the curing time is too short, the cross-linking reaction of the film layer is insufficient, and only a powdery, rough, and matte film layer can be formed. Generally speaking, it is beneficial to ensure the film forming hardness of the ink by appropriately extending the curing time. Of course, when the curing time is too long, due to excessive UV light irradiation, the surface hardness is increased and the surface tension is reduced, which also causes poor adhesion between the ink and the substrate.

The method to determine the appropriate curing time is to pass through the UV curing machine at a certain speed under a certain power of UV lamp, wipe the surface of the ink layer with cotton cloth soaked in absolute ethanol 50 times, observe the cotton cloth and substrate to see if there is UV ink If it is wiped off, the curing speed is reduced and the curing time is extended until the UV ink on the substrate cannot be wiped off. This is the appropriate curing time.

6. Addition of adhesion promoter Adding adhesion promoter in the UV ink formulation can significantly improve the adhesion of the ink, but different adhesion promoters have different effects on different substrates, and need to be determined by experiment. Variety of adhesion promoter.

7. Curing temperature Because the UV lamp will emit a lot of heat when the UV curing machine is in use, when the printed substrate is sensitive to temperature, the UV lamp will emit a lot of heat and will have a negative impact on the substrate. The distance between the large substrate and the UV lamp can be solved by increasing the cooling method, but increasing the distance between the substrate and the UV lamp is equivalent to reducing the power of the UV lamp, and curing will be affected. You can reduce the solidification temperature by increasing the cooling method. The cooling methods are air cooling and water cooling. The method of air cooling is more common, but the common problem is that the effect of air cooling is not ideal.

The use of water cooling is a relatively effective method. Many of the UV curing machines currently on the market are water-cooled UV curing machines.

Here you can find the related products in Lexmark, Canon and more brand Printer Parts, If you want to know more about Lexmark, Canon printer parts, please click the product details to view models, pictures, prices and other information. Whatever you are a group or individual, we will do our best to provide you with accurate and comprehensive message about Lexmark, Canon printer parts!

More Printer Parts

Printer Parts,More Printer Parts,Hp Printer Parts,Part Print

Dunhua Office Equipment Co., Ltd. , https://www.dunhuaparts.com