UV luminescent ink is a kind of special functional ink prepared by adding luminescent material in transparent ink, which has been widely used. General luminescent ink is made of heat-curing ink doped with luminescent materials, the use of heat curing way to prepare luminescent products, UV ink in the use of a certain degree of difficulty, which is determined by the specificity of the luminescent material. Luminescent material that is long afterglow light-emitting materials is a particle size of 10 ~ 60μm inorganic powder materials, in special conditions and even larger particle size, this powder material has a certain body color and opaque, in practice, you need to print a certain thickness in order to reflect a better light-emitting effect, these problems to the use of UV-cured luminescent inks bring certain difficulties.
Luminescent powder into the ink is a common method of preparing luminescent inks, in the past are heat-curing ink and luminescent powder mixed preparation of luminescent inks. With the development of UV technology, the combination of luminescent powder and UV ink to prepare UV light-emitting ink has been gradually adopted by the majority of printing manufacturers, especially in the production of light-emitting signs with UV light-emitting ink instead of heat-setting light-emitting ink has considerable advantages. The printing of UV light-emitting ink by screen printing technology is a common method for preparing light-emitting signs.
① Luminous Powder Selection: UV luminescent ink should consider the selection of luminescent powder in screen printing, the basic requirement of luminescent powder is high brightness and moderate particle size. Large particle size can not be missed from the screen, small particle size printing thickness is not enough, you need to increase the number of prints to achieve the thickness requirements, labor and time consuming, generally 50 ~ 80μm of the luminescent powder is more appropriate. Rare earth luminescent powder is light yellow-green, so choose to make the signage substrate to blue or green is appropriate.
② stencil production. Light-emitting signs generally require light-emitting layer printed thicker, so the usual 80 mesh polyester monofilament screen, so that the light-emitting powder can pass through the screen, while printing the light-emitting layer is also thicker. In the plate should be considered in general signage products such as some place name signs often the same pattern will not be printed many times in a row, in this case, you can choose a low-grade oil-resistant photopolymer, can save costs.
③ pre-coated primer. In the printing of light-emitting layer before the need to print a white substrate, light-emitting layer printed on the white substrate. Printing substrate layer is one of the necessary steps for printing luminescent ink, pre-coating substrate layer on the surface of the substrate will help to improve the luminous performance of luminescent ink. The use of different pigments of the substrate layer on the ink luminescent performance of the impact is not the same, adding titanium dioxide white substrate layer is most conducive to improving the luminescent performance of luminescent inks, this is because the white substrate layer can be through the ink layer of the incident light as well as emitted fluorescence more fully reflected, maximize the role of the luminescent inks.
It should be noted that UV light-emitting ink needs to have good adhesion on the white substrate, otherwise the light-emitting ink layer will be easy to come off after curing, and white PVC ink is generally used because most of the UV inks have good adhesion on the PVC ink layer, thus avoiding the phenomenon of the light-emitting layer coming off from the signage.
④ Pay attention to the adhesion between layers when printing and curing for several times. The use of UV light-emitting ink should pay attention to a very important issue, the production of signs often need to light-emitting layer to reach a certain thickness, which requires a number of printing to achieve the thickness requirements. As the UV ink is printed once immediately after curing, cured surface smooth, in the next printing is carried out on the basis of the previous layer, this time the need for UV ink between each layer has a good adhesion, can not appear delamination phenomenon. Therefore, in the selection of UV ink should pay special attention to the problem of interlayer adhesion.
Long afterglow light-emitting materials and UV inks used in combination with printing need to pay attention to the following issues.
① long afterglow light-emitting material is a kind of inorganic powder material, light-emitting material density is easy to precipitate, so you need to stir before use, at the same time, light-emitting material is easy to react with rust, heavy metals, etc., so it is not appropriate to use metal rods in the dispersing and grinding process, and it is not suitable to be stored in metal containers, otherwise it will lead to the material to become black, affecting the effect of the use of the material. Container selection of glass, ceramic, enamel lining, plastic containers are appropriate.
② Luminescent ink into a film, light-emitting light-absorbing function is realized by the particles of light-emitting materials. Due to the requirements of the light through the light-emitting materials bonded together in the resin should have good light transmission, no hiding power, so the selection of resin, varnish should be colorless or light-colored transparency is appropriate.
③ The higher the content of luminescent material, the brighter the luminosity, but in order to make the luminescent material have proper adhesion with the coated products, the proportion of resin should not be less than 10% at least. Of course, the higher the proportion of resin, the higher the smoothness and finish of the luminescent coating. Therefore, the amount of luminescent material is generally 20% to 60% of the total mass, or 10% to 35% of the volume, or the amount of luminescent material is determined according to the requirements of luminous brightness.
④UV Luminescent Ink in screen printing to consider the choice of luminescent materials, luminescent materials, the basic requirements of high brightness, particle size moderate. Large particle size can not be missed from the screen, small particle size printing thickness is not enough, need to increase the number of prints to achieve the thickness requirements, waste of time, the use of 20 ~ 80μm of luminescent powder is more appropriate. Luminescent materials are more colorful, the production of sign products generally choose light yellow-green luminescent materials.
⑤ production process, light-emitting materials can not be ground, can not use the three-roller mill, the preparation of light-emitting ink, can only use high-speed disperser or mixer. Specific method is to put the resin or varnish into the container, add add additives, turn on the stirrer, add anti-sinking agent, light-emitting materials in turn under the slow stirring state. After adding the luminous material, increase the speed until the luminous material is uniformly dispersed in the material, and then filter to get the product.
⑥ Heavy metal compounds should not be used as additives.
Pay attention to the choice of mesh size. General light-emitting materials due to the larger particle size, the need for a smaller mesh screen, usually using 100 mesh screen printing is better. The degree of curing of the product after printing also has an impact on the final quality of the product, test whether the curing is complete in the following four ways. One is to test with a pencil hardness meter, generally up to 3 ~ 4H, can be considered that the ink has been fully cured. The second is to test the method of dropping solvent, but also to test the solvent resistance, the propionic acid drops on the surface of the print after 20min, such as no change to prove that it has been fully cured. Third, the compression method test, that is, the cotton fiber placed on the surface of the print, with a smooth bottom 500g weights pressed on the surface of the cotton fiber 2 ~ 3min, and then remove the weights, if the cotton fiber does not stick to the surface of the print to prove that it has been fully cured. Fourth, the grid test method, the use of the grid force in the print surface cross, and then use the tape to stick to the surface of the cross, if there is no sticky ink, indicating that the curing is complete and the adhesion of the ink layer after curing is relatively good.
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