Application of photosensitive materials for printing plates (1)

I. Introduction

The photopolymerization of photosensitive polymers can be mainly used in optical process technologies such as small objects, video discs, etc.; used in printing techniques such as flat, convex (elastic), gravure and color proofing, laser plate making, holographic printing, etc.; Electronic materials such as wire plates, printed circuit boards, solder masks, and dielectric layers. In the case of printing plates, mainly photosensitive resins (resists) or photoresists are mainly used. With the advancement of photochemical synthesis technology, photosensitive substances such as dichromated starches used in the early 1800s were used. Natural substances such as dichromated gelatin have been replaced by synthetic polymers such as poly (vinyl alcohol), poly (vinyl pyrrolidone), poly (vinyl butyral), etc. These photosensitive materials are negative photoresists. Agent. During the booming of micro-process technology in the 1900s, the main purpose of photosensitive polymers was to produce printed circuit boards and metal plates, to carry and connect electronic components with different functional units. Early printed circuit boards used screen printing and were later dried. With the advent of dry resist, this photopolymer has played an important role in the design and manufacture of semiconductor integrated circuits. Although the amount of photoresist used in the process is small, it is an indispensable component. This article will introduce the application of photosensitive polymers in printing related fields and provide reference for future researchers engaged in printing related media to improve their own research and development capabilities.

Second, lithographic plate material photosensitive polymer 1. Negative film version (Negative-working Lithographic plate)
Photopolymer is coated on the anodized aluminum plate, photopolymerized after curing by exposure to negative film to harden the developer, and the photosensitive polymer in the non-imprinted area is not removed during the development process due to exposure without exposure. . The photosensitive polymer used for this type of plate is called a negative photoresist, and the early negative photoresist is a dichromated gelatin, but this photosensitive material has the following serious disadvantages: (1) Within a few hours in a dark room Because of the interaction, it cannot be made by pre-coating; (2) the image loaded by gelatin is not good in corrosion resistance; (3) the carbonization of the plate-making process will damage the quality of the imprint.

As a result of the chemical synthesis technology exhibition, Eastman Kodak Company for the first time on the insoluble polymer: poly (vinyl cinnamate), the polymer has no dark reaction and the coating has a longer shelf life. (shelf time), high photosensitivity and corrosion resistance, hardened by a photocycloaddition.
After long study to improve the exposure sensitivity, Eastman Kodak Company also issued a series of pphenylenediacrylicacid (PPDA) polyester photosensitive compounds. This material is a photosensitive coating of a presensitive (PS) lithographic plate with a maximum absorption wavelength of (365 mm).

Another type of pre-coated type is to coat a thin layer of diazoresin, which belongs to low molecular weight diazonium ion. To make this type of water-soluble photosensitive azo resin, it is made of 4- Diazonium-1,1′-diphenylammine chloride (chemical formula is shown below) and formaldehyde (HCHO) are catalyzed by ZnCl2/H2SO4 to form an azo resin.
Such azo ions generate chlorinated resin and release nitrogen (N2) at the same time under exposure light. The resulting chlorinated resin is insoluble in water, making the print area of ​​the plate partially oleophilic. Such photoresists have been widely used in negative editions. The darkroom reaction of precoated azo PS coatings is very slow and can be stored at room temperature for 6 months to 2 years. The phenomenon of emulsification of the liquid in the bath and the ink during printing occurs. This phenomenon disappears when the whole surface is contacted, and the resin and pigment particles in the ink (lipophilic phase) are deposited on the hardened ink-printed area, while the bath liquid (hydrophilic phase) The gum arabic is adhered to the non-print area, and the ink in the print area is transferred to the object to be printed via the blanket. The printing tolerance of the printing plate is a concern of the industry. This problem is related to the adhesion of the azo resin coating film. The current problem faced by the manufacturer is to find a formulation for high speed and good adhesion.

2. Positive-working Lithographic plate
Exposure to light through a positive film exposure on a metal plate, the light will decompose the coating material in the non-printed area, and the uncoated coating material will not dissolve in the alkaline developer and become an acceptable printing area for the ink. Photosensitive coating materials are called positive photoresists, such as diazonaphtho-quinone-phenolic resin (phenolic resin). The system photoresist has been used in masks used in the semiconductor industry or printed in the printing industry. Edition, the recent development of positive photoresists is mainly attributed to changes in functionality and molecular weight. Diazonaphtho-quinone was published by Kalle in the 1950 edition with =N2 (diazide group) and =O attached to the ortho or meta position, and therefore can be called azo-oxide. This substance, in the presence of trace amounts of water or other polar substances, will convert to indenecarboxylic acid upon irradiation with UV light and will release nitrogen (N2).

Diazonaphthoquinone itself is insoluble in the developer and can be dissolved in the alkaline developer after being converted into indenecarboxylic acid. Therefore, the coating in the non-printed area is developed and removed, and the uncoated printed area coating becomes acceptable in the ink. The final area is to make the plate gelatinized with a finisher to deactivate the non-printed area to prevent contamination during printing. A disadvantage of Kalle's positive film is that it is somewhat fragile and its abrasion resistance is poor, because it must be sintered for 5 minutes (about 230°C) after the plate has been developed and dried so that the coating of the pattern area (positive resist) is more Hardened and anti-friction, the printing of the printing capacity increased. The pre-sintered plate requires careful inspection and removal of grease with detergent. Diazonaphthoquinone-phenolic resin series coating phenolic resin itself is soluble in alkaline solution, adding diazonaphthoquinone component, the dissolution rate of phenolic resin will be reduced, non-ionic and water repellent diazonaphthoquinone as an inhibitor of dissolution Diazonaphthoquinone is converted into acid under exposure to radiation and is soluble in alkaline solution. Therefore, it is no longer a dissolution inhibitor but is converted into a dissolution promoter. That is, indenecarboxylic acid can accelerate the dissolution rate of phenolic resin. According to research, this acceleration effect is Due to the release of N2 in the reaction, the escape of N2 generates an extra free volume, which facilitates the penetration of the developer into the matrix of the polymer. The average exposure time of the positive film is about 1.5-2 times the exposure time of the negative plate. The main reason is that the exposure image of the positive film coating system belongs to a kinetic effect, Diazonaphthoquinone accounts for 20% ( For the weight ratio), the dissolution rate of the coating film subjected to the exposure irradiation is approximately 200 times the dissolution rate of the uncoated coating film. It is worth mentioning that the dissolution rate of the non-irradiated resin coating film is not 0, so the image is developed. The imaging should be stopped immediately after the radiation area is completely dissolved during the process.