UV ink printing process and analysis of common problems
We are a big printing company in Shenzhen China . We offer all book publications, hardcover book printing, papercover book printing, hardcover notebook, sprial book printing, saddle stiching book printing, booklet printing,packaging box, calendars, all kinds of PVC, product brochures, notes, Children's book, stickers, all kinds of special paper color printing products, game cardand so on.
For more information please visit
http://www.joyful-printing.com. ENG only
http://www.joyful-printing.net
http://www.joyful-printing.org
email: info@joyful-printing.net
The main components of the UV ink include pigments, oligomers, monomers (reactive diluents), photoinitiators, and various auxiliaries. Among them, the resin and the reactive diluent act to fix the pigment and provide film-forming properties; the pigment imparts a moderate color to the ink and the hiding power to the substrate; and the photoinitiator requires absorption of the photon-initiated polymerization under the interference of the pigment.
UV printing application market from the printing process, UV ink fixation speed, good conjunctival performance, good adhesion to all kinds of printing materials, and scratch resistance, wear resistance, acid and alkali resistance are more common The ink is good, so although its price is much more expensive than ordinary ink, it is still widely used.
The current fields of printing with UV inks are as follows:
1. Non-absorbent materials such as polyethylene (PE) film, polyvinyl chloride (PVC) film, polypropylene (PP) film, metal foil and non-absorbent special materials. If these printing materials are printed by ordinary solvent-based inks, a certain drying time is required, and it is usually necessary to use a dusting, a drying device or other additives in the ink, and the UV ink has no such trouble.
2. When the metal material is printed on the surface of the metal material with UV ink, the curing process can be shortened and the original curing device can be simplified. At the same time, the good curability and conjunctival properties of the UV ink surface not only improve the post-press processing characteristics, but also improve the appearance quality of the product.
3. Commercial paper printing Commercial paper printing uses special printing materials and inks, such as carbonless copy paper, thermal paper, magnetic ink, anti-counterfeiting ink, etc., and requires ink to have certain resistance to discoloration, heat resistance and stability. It is therefore preferred to use UV ink or UV varnish. At the same time, due to the high speed of the printing equipment and the low ink consumption, it also has the favorable conditions for printing with UV ink.
Process adaptability of UV printing
UV offset printing
Offset printing can be divided into sheet-fed offset printing and web-wound offset printing according to the state of the substrate. Sheet-fed offset printing is suitable for printing on paper, cardboard, plastic sheet and metal foil; rotary offset printing is fast, suitable for large-volume books and newspapers. , business forms and self-adhesive printing. UV ink is used in offset printing, mainly considering the following aspects: ink curing of non-absorbent printing materials; ink emulsification may hinder the adhesion of ink and substrate; rotary printing machine is fast, requiring ink curing speed and printing speed Matching, especially for self-adhesive printing and security printing with special inks, UV ink printing is better than resin-based offset inks.
Offset printing is mostly used for fine product printing. UV curing can reduce the loss of fine dots and improve the ink transfer rate of overprinting. When selecting ink materials, the effects of each component on UV inks should be considered to ensure the best printing results. Since the offset ink film is generally 2 to 3 μm, although it is advantageous for photocuring, the ink film is thin, and the hiding power of the pigment on the printing surface is affected to some extent, so generally the pigment content in the formulation is increased; and the pigment content is increased, and the ink film is increased. The light transmission performance is lowered, which is not conducive to UV curing; and the ink film itself is thin. If the wettability of the pigment is not good, the pigment and the filler are easily exposed to the surface of the ink film, which affects the gloss of the ink film, so the dispersion is selected. Good pigments.
The following points should also be noted when using UV offset printing:
(1) Different inks should be selected for different substrates. The light transmittance, curing rate, ink hiding property and gloss of the printed surface should be considered comprehensively.
(2) In color printing, various pigments have different abilities to absorb UV photons, and their transmittances are M, Y, C, and BK from high to low, so the degree of curing of each color ink is also different. The transmittance directly affects the excitation energy of the photon to the photoinitiator. Therefore, it is preferable to arrange the printing color sequence as BK, C, Y, and M, so that the ink having poor light transmittance absorbs photons as much as possible and enhances the curing effect.
(3) The use of alcohol dampening system can reduce the surface tension of the ink and promote the curing effect. In the printing process, the plate oleophobic area (blank part) can be reinforced with dampening solution to ensure sufficient lipophilic area. Ink-friendly, the hydrophilic area is not inked. Improving the ink formulation and adding the corresponding additives can increase the hydrophobicity of the ink, but too much hydrophobicity will cause the ink at the edge of the image to shrink, the fine layer is lost, the dot boundary is not clear, etc., which affects the quality of the printed product.
(4) UV printing has high requirements on the surface strength of the paper, and the surface strength is not enough to cause the pulling failure. When printing with gold or silver cardboard, the surface of the paper is smooth, the affinity for the ink is small, and the second color is easy to overprint. Pull the first color ink off. Therefore, in UV printing, paper with a large surface tension should be selected, and the color sequence should be arranged reasonably, and the relevant process parameters in the printing process should be adjusted to avoid and reduce the occurrence of the above phenomenon.
UV flexographic printing
Flexographic printing is a printing process that has developed rapidly in recent years. The graphic part of the printing plate is higher than the non-image part, and has elasticity, which can better express the subtle level and contour of the graphic part. In addition, it is suitable for a wide range of substrates, in addition to traditional paper, some non-absorbent substrates, such as plastic film, aluminum foil composite paper, cellophane, etc. can also be flexographic printing. Flexographic printing using UV ink, in addition to attention to coloring, curing and adhesion problems, must also pay attention to the effect of ink composition on ink viscosity, rheology, in order to obtain better printability and stability.
The flexographic printing process determines that the UV ink used should not have a high viscosity. Conventional flexographic printing inks are solvent-based and water-based. A large amount of solvent or water is required to adjust the viscosity. Due to the use of a large amount of solvent, most flexographic printing inks approximate Newtonian fluid in terms of rheology, which causes ink to settle and become unstable. Therefore, proper thixotropy imparted to the flexographic printing ink prevents the pigment from flocculation and sedimentation.
UV flexographic printing inks use reactive diluents to reduce the viscosity of the system, so their viscosity may be higher than solvent-based flexographic printing inks. Although the viscosity of UV flexographic printing inks is lower than that of screen printing and offset printing inks, the addition of pigments increases the viscosity, especially when the pigments are wet, dispersed, and stable. In addition, the influence of pigment on the rheology of the ink is more important, and proper thixotropy is beneficial because when the molecular crosslinking inside the ink reaches a certain degree and pseudoplasticity occurs, the ink system without the pigment dispersion stabilizer is On the high-speed running ink roller, the viscosity will drop sharply, but when the ink roller enters the printing portion with a relatively low rate of entry, the viscosity will rise rapidly, and the wetting effect on the surface of the substrate is too poor to be suitable for printing. The ink containing a suitable dispersion stabilizer has a certain stability, and its viscosity is not high. After high shear, the viscosity rises slowly and the printing adaptability is good.
UV screen printing
The UV screen printing ink has a solid content of 100%, no component volatilization, and the thickness of the ink film is basically unchanged after curing, which is favorable for obtaining a high film thickness, and the printing and curing process is easy to control, and can avoid blocking, spotting, etc. Failure, reducing downtime. Although UV screen printing has many advantages, the determination of the photoinitiating conditions affects the curing quality of the ink layer. If it is improperly selected, it only cures quickly on the surface of the ink film. On the other hand, UV screen printing has the advantage that although the ink film is thick, the lower pigment content can achieve high hiding power, which is a favorable condition for the underlying curing. Under the premise of not impeding the pigment saturation and hiding power, appropriately adding a light-transmitting filler with better refractive index, increasing the concentration of the light-transmitting medium in the ink layer, also helps to increase the light-absorbing amount of the underlying initiator. Due to the thickness of the screen printing ink film, the printing precision is not very high, and the pigment particle size can be larger. Therefore, the pigment particle size can be appropriately increased without sacrificing the pigment dispersibility, so that the actual light transmittance of the ink is increased to facilitate the The bottom layer is cured.
UV printing problems
Compared with traditional ink printing, UV printing does have great advantages, but popular applications still face some problems that must be solved and improved.
Price
Although UV inks have the advantages of instant curing and good conjunctival properties, they are relatively expensive, and special UV blankets and UV ink rollers must be used to greatly increase product cost.
Adhesion
During the curing of the UV ink, the internal components are cross-linked and polymerized, and the instantaneous change in volume produces a large internal stress, which affects the adhesion of the ink to the printing material. Although this problem can be improved by surface treatment or modification of the substrate, the fundamental solution is to seek and develop a UV ink that has good adsorptivity, low shrinkage stress, and low cost.
Suitable fountain solution
UV inks are mainly used for non-absorbent substrates, and inks are formulated differently for different substrates. Therefore, the dampening solution is required to have a wide adaptability to ensure the required printing quality. Despite the above problems in UV printing, with the maturity of related technologies and the expansion of application fields, its rapid development is inevitable. In the near future, UV printing will certainly be more widely used and popularized.