Top 10 Precautions for UV Coating on Offset Printing Machines

Installing LED UV on offset printing machines not only achieves good offset printing and inkjet coding effects but also features low energy consumption and is environmentally friendly. Many companies have adopted this measure. However, it should be noted that, offset printing machine LED UV after a period of use, unclear phenomena will occur. This requires regular polishing, which not only improves printing efficiency but also extends the service life. When polishing the offset printing machine LED UV, the following 10 requirements should be noted:

The following are the noteworthy precautions for partial UV coating:

(1) Requirements for printing ink additives.

If directly applying offset printing machine LED UV coating to the surface of the printed matter, do not add or minimize the addition of various additives to the ink during printing, such as detackifying agents and ink oils, to avoid affecting the surface polarity of the ink layer, resulting in poor adhesion between the coating and the ink layer, easy peeling of the coating layer, and thus seriously affecting the coating effect.

(2) Requirements for printing powder spraying.

The amount of powder spraying should be small. A large amount of powder spraying will form a layer of powder on the surface of the printed matter, causing the UV coating layer to not adhere firmly to the ink layer, easily peeling off, and presenting a cloudy appearance in patches, seriously affecting the coating effect. If the amount of powder spraying is not well controlled during printing, it is necessary to remove the powder by hand if necessary.

(3) Requirements for the surface tension of laminated products.

For products that need partial UV coating after lamination, it is required to use a film that has been corona treated on both sides, that is, the surface tension of both sides of the film must reach 38 mN/m or more to ensure that the UV coating can firmly adhere to the film. At the same time, it is necessary to check whether the surface tension of the film used is uniform to prevent local peeling of the coating layer.

(4) Requirements for the surface tension of the coating.

The surface tension of the coating must be less than the surface tension of the ink so that the coating can wet, adhere, and penetrate the graphic parts of the printed matter well. Otherwise, after applying the coating, the coating layer will shrink, and even abnormal phenomena such as pinholes may occur.

(5) Requirements for the viscosity of the coating.

Adjust the viscosity and thickness of the coating to ensure good coating properties. Avoid a coating layer that is too thin, resulting in poor surface gloss, or a coating layer that is too thick, resulting in an orange peel effect or difficulty in curing. The viscosity of the coating can be adjusted by adjusting the temperature of UV curing, and a small amount of alcohol can be added for adjustment if necessary.

(6) Requirements for UV lamps.

Adjust the intensity of UV irradiation according to the characteristics of the printing paper and the size of the UV coating pattern. Generally, curing equipment is equipped with 1-3 sets of UV lamps for adjustment. By selecting the number of UV lamps used, the corresponding light intensity can be achieved, so that the coating layer is easy to cure and not easy to become brittle or break.

(7) Application of UV base oil.

For full-area coating products, a water-based base oil is often used to improve the smoothness of the paper surface and the gloss of the UV coating. This method is also applicable to partial UV coating processes.

(8) Design requirements.

During embossing and die-cutting, the coating layer is prone to cracking and peeling, resulting in white marks at the embossed or cut edges, making the product unsightly. It is recommended to avoid designing UV coating patterns at the embossed or cut edges during design, or the colors of the patterns in the above positions should be designed as light as possible to avoid unsightly effects due to coating peeling.

(9) Consideration of paper deformation.

Because paper is easily affected by ambient temperature and humidity and expands and contracts, for products with high requirements for register accuracy, the expansion and contraction of the paper size must be considered before plate making, the deformation rate must be calculated, and the register accuracy of the partial UV coating pattern and the printing pattern must be ensured.

(10) Testing method for the firmness of the coating layer.

Use a transparent adhesive tape with good viscosity to stick and pull the coating layer or scrape the coating layer with a fingernail. The standard for testing whether the coating layer is firm is that the coating layer does not fall off after sticking and pulling or scraping.

The above are the 10 precautions for offset printing machine LED UV coating. During operation, be sure to follow the specifications strictly, otherwise, the offset printing machine equipment will be damaged. Guangdong Qingda Photoelectric Energy Saving Technology Co., Ltd. A high-end manufacturer specializing in the design, research and development, and production of high-end UV curing equipment for offset printing machines, gravure printing machines, flexographic printing machines, label machines, tin printing machines, and coating machines. It brings unprecedented innovation to the UV curing industry. Welcome to call for inquiries if needed. We look forward to cooperating with you.