The purpose of coating bright oil after sheet printing is to protect the image and text imprinting and enhance the decorative effect. Coating wrinkle oil is a special polishing process. Its basic process is: coating wrinkle oil – heat preservation, baking and wrinkling – high temperature drying and forming.
After polishing and baking by the above special polishing process, the surface of the sheet printing is wrinkled and shaped, showing a crystal transparent scale shape. The reflection of light makes the exquisite pictures and texts printed on the sheet have a three-dimensional feeling, forming a special decorative effect.
Four roller coater is generally used to apply wrinkle oil. A layer of wrinkle oil with uniform thickness is coated on the sheet printing by means of axial coating, and the working viscosity of wrinkle oil is controlled within 25 ~ 30s. The coating amount is about 15g / ㎡, and the thickness of the film layer after drying is about 10 ‰. The characteristics of wrinkle oil itself play a decisive role in the quality of products. At the same time, the thickness of desert layer also has an important impact on its quality. Excessive or too thin can not achieve the ideal decorative effect. The film layer is too thick and only has large cracks without wrinkling; The coating layer is too thin, the pattern is unclear or the surface is smooth (the wrinkle effect cannot be achieved). Generally speaking, the color of ink has little effect on the wrinkle effect of wrinkle oil, but the wrinkle effect of some darker dark colors is not very good; The effect of applying wrinkle oil on gold or silver (natural color of tinplate) is better.
Low temperature baking wrinkling is the key process of this process. The quality of products mainly depends on the control of baking temperature and time. Special oven (such as tunnel oven) is used for baking to ensure uniform temperature distribution in the oven; It is generally used to burn LPG or kerosene, blow hot air and dry it through convective heat transfer of air. At present, the more advanced low-temperature baking system has adopted automatic ignition and constant temperature control technology. Which baking process is used is not only related to the oven structure, but also related to the printing speed of the offset press. Due to the compensation relationship between drying time and temperature in a certain range, the printing speed is fast, the drying time is relatively short, and the drying temperature can be higher; The printing speed is slow, the drying time is relatively long, and the drying temperature can be lower. In the actual production process, the baking temperature must be properly controlled. If the temperature is too high, the wrinkle oil will not wrinkle at all, and the effect is the same as that of ordinary glazing, which can not achieve the expected purpose; The temperature is too low, although it can wrinkle, it is easy to bruise the film layer, and it is difficult to feed automatically when drying at high temperature.
After low-temperature baking and wrinkling, the product has been basically finalized, but it is not completely dried at this time. It needs to be dried at 140 ~ 150 ℃ and can only be dried after high-temperature drying for 10 ~ 15min. Only when the product is completely dried can it have excellent physical and chemical properties and excellent mechanical properties, and adapt to later stamping and other molding processing.