Spot Coating Type and Difference
Apr 24, 2024
Spot UV Coating Type and Difference
According to the needs of product varnishing, spot coating is applied to the parts that need to be highlighted in trademarks and packaging prints. Compared with the surrounding patterns, the varnishing pattern appears brighter, brighter and more three-dimensional, which can produce a unique artistic effect.
UV spot coating is a type of surface finishing technology for printed materials. It is so named because it uses UV varnish with high gloss, transparency and wear resistance to selectively varnish printed graphics and text. While highlighting the layout theme, it also improves the surface decoration effect of the printed materials. Partial or spot UV is mainly used in post-printing finishing of book covers and packaging products to achieve the purpose of making printed products more beautiful.
UV varnishing effect
At present, common spot UV effects include:gloss spot varnishing, full matt coating, skin coating, partial reserved coating, blister coating ,reverse UV , etc.
Spot UV can be implemented after lamination, or it can be coated directly on the printed matter, but in order to highlight the effect of spot coating. Generally, it is done after the printed matter is coated, and most of them are covered with matte film, which accounts for about 80% of spot UV varnishing products. The biggest difference between partial varnishing and full varnishing is that firstly, a printing plate needs to be made, and secondly, there are certain registration requirements for the varnishing equipment. There are three major elements in spot UV coating, namely coating plate, equipment registration and curing equipment. In order to ensure that the spot UV varnishing area is consistent with the size of the printed graphics and text, the photosensitive imaging method should be used when making the coating plate.
1. Partial coating by screen printing
Screen printing has the characteristics of high ink transferability, thick ink layer and strong three-dimensional effect. The screen for glazing should generally be 200-300 mesh (for partial frosting, partial colorful and other glazing effects, the mesh number is lower), and the tension of the mesh should be 20-25N/cm. Since the equipment investment is not large. Many books, periodicals and packaging factories prefer screen printing when increasing their local glazing business. Some professional printing and coating companies improve coating accuracy and production efficiency. Already using a fully automatic drum screen printing machine. The production speed can reach 3000 sheets/hour. However, screen printing partial varnishing basically adopts offline production mode. Online rotary screen printing units are rarely used.
2. Spot varnishing of flexographic plates
Flexographic printing is characterized by the ability to form thicker coatings with a simpler process. Therefore, it is very popular in spot UV coating. Partial varnishing for flexographic printing is divided into ordinary flexographic printing varnishing and special flexographic printing glazing. Some simple graphics and texts still use engraving rubber letterpress plates. Partial varnishing of flexographic printing is suitable for offline spot varnishing and can also be achieved online varnishing. Using the flexographic printing and glazing method, combined with anilox rollers and chamber doctor, the amount of varnish can be accurately controlled and the varnishing quality is stable.
3. Spot coating for gravure printing
Gravure printing also has advantages in local UV glazing due to its thicker printing ink layer and high printing resistance of the gravure cylinder. In particular, the emergence of sheet-fed gravure printing machines has contributed to the development of gravure local glazing. However, due to its high plate making cost, it is mainly used for long-run glazing business.
4. Other spot coating methods
Before the advent of UV varnish, no one would use offset printing for varnishing because its printing ink layer was too thin. UV varnish also has some applications in local UV glazing due to its thicker film layer, higher gloss and high overprint accuracy, but it is mainly used for online glazing.
In terms of production methods, local UV glazing machines can also be divided into offline glazing and online glazing. Offline varnishing refers to printing, and glazing is performed on special equipment, requiring the use of a special glazing machine or calender. When offline varnishing, because the printed matter can be fully dried, a higher gloss can be obtained than with online varnishing. In addition, offline glazing production has great flexibility. Equipment investment is small. Online varnishing means that printing and varnishing are completed on a production line, that is, glazing and UV curing devices are added to the printing press. Allow the print to be varnished directly after printing.
New local UV technology
1. Mixed ink technology
Since UV printing or UV glazing is not suitable for application on the surface of highly absorbent printing materials, and the adhesion of the printing ink surface is poor, most of them require online UV glazing. If all printing is done with UV ink, the cost will inevitably increase. : If ordinary ink is used for printing, lamination or full glazing is required before glazing, which undoubtedly hinders the application of offset printing online glazing. The mixed ink technology effectively solves this bottleneck problem. It combines the advantages of UV inks and traditional inks in terms of performance, that is, the advantages of light curing and oxidative polymerization and drying. It improves the synergistic effect of the ink surface and UV varnish, paving the way for online glazing of offset printing.
2. Reverse upward varnishing
Reverse varnishing (Pro-Cure) is compared to traditional spot coating. The traditional coating method (flexographic printing, screen printing or gravure printing) is used for spot coating. Finally, a spot coating plate must be used for printing to achieve a high-contrast effect of partial graphics and text. Therefore, the overprint accuracy of glazing and printing becomes glazing. The reverse glazing process breaks through the above laws and solves the registration problem.
3. Online UV coating
For flexographic printing and gravure printing, online varnishing is no longer a new technology. However, for offset printing, which has a wide range of applications and high printing accuracy and speed, it is launched under the call for differentiation and value-added services. glazing technology with innovative ideas. There are four main forms of online UV glazing methods that have been applied: ordinary ink + double glazing (water-based glazing + UV glazing); mixed ink + UV glazing; UV ink + UV glazing; UV ink + OP oil + UV glazing (reverse glazing).
4.Digital UV varnishing
No plate is needed,the UV varnishing is processed by the UV Inkjet printhead with LED UV curing.
