Application principle of flexo printing photosensitive resin plate

In the past 30 years, the photosensitive resin plate has indeed greatly improved the quality of printed products and contributed to the promotion of the vigorous development of flexo printing.

The photohardenable resin was used as part of the mummy production process from the era of ancient Egypt in the 15th century. In the modern science, it was in the early 1820s that natural resin was used to cover the metal objects to produce extremely primitive images by exposure to sunlight.

By the 20th century MR. Louis Plambeck, Mr. Panbek used the photohardenable principle to guide the application of images. Mr. Pan’s first patent application was approved in 1950. In the field of electronics and printing, there have been hundreds or even several. More than a thousand patents are widely used in the formation of images. In the printing industry, there are also many types of ultraviolet photo-curing technology used. For the reader, the most common ones are the sensation, photo-resin and UV ink.

In the past 30 years, the photosensitive resin plate has indeed greatly improved the quality of printed products and contributed to the promotion of the vigorous development of flexo printing.

The basic structure of the photohardening makes the application of UV images to the application of resin printing plates, which is the subject of this article.

※ Photo hardening process

The resin plate used for flexo printing may be either one piece or it may be liquid. These materials basically include several elements, that is, a binder, a monomer resin, and a photosensitizer. <a binder, a monomer and a photoinitiator> may be a mixture of various forms of material. The resin sheet is now a solid-state binder, a liquid monomer resin, and a photosensitizer. However, liquid resin systems use only liquid components. The relatively hard or soft nature of the material can be controlled by the nature of these main ingredients and plasticizers. The use of a solid-state binding agent in combination with a liquid component can be more extensive than the use of a liquid component, and the control range is also larger, so that a sheet-form resin plate can be applied more widely than a liquid resin. The solid binder can be used for various purposes. The most important thing is to stabilize the mixture of the monomer resin and the photosensitizer in the plate, and serve as the backbone of the printed image. The photosensitive starter is borrowed from the plate. A molecule that causes a chain reaction by irradiation with light.

This chain reaction, also known as photopolymerization, promotes the polymerization of the monomeric resin molecules and the binding agent to form a staggered network of three-dimensional spaces in portions exposed to ultraviolet (UV) light.

<Main components in a photosensitive resin plate>

Figure 1 shows a schematic diagram of the composition of the resin plate material. The pink part represents a polyester binder, the yellow oval represents a photosensitive initiator (abbreviated as I), and the orange molecule (abbreviated as M) is a monomeric resin molecule. In the process of plate making, when UV light is mainly exposed at a wavelength of 365 nm, the photopolymerization starts when it is moved through the film to the resin plate.

Figure 1a shows that the photosensitive initiator absorbs UV light and thus breaks down to produce drastic changes. The fierce and unrestrained reaction of the ruptured egg shells with the R resin molecules causes them to interact with other monomers (such as 1b in Fig. 2).

This part of the chain reaction is also known as the starting effect. This active monomer molecule reacts with other molecules and the binder polymerizes to form a staggered network chain, and the physical properties of the material of the plate itself also change, and the chain reaction of this part is called a reproductive effect. (Figure 2 of 2) When two active molecules (monomer M or radiant molecule R) interact with each other, an extremely inactive chain is formed or becomes part of a staggered network. This type of reaction is called termination (stabilization). <Figure 2 of 3>

<Figure II: Process of Photopolymer Resin Polymerization>

(to be continued)