How to detect and control the PS plate surface treatment solution (top)

The PS version is an abbreviation of Presensitized Offset Plates, which is an offset printing plate formed by preliminarily coating a photosensitive liquid on the surface of a plate base.

According to statistics, the total demand for PS plates in China has reached 100 million square meters each year, and the total production capacity of domestic PS plates has approached 200 million square meters. China's PS version of the manufacturing industry has become one of the important industries in the current printing equipment manufacturing industry. It has formed a fully equipped, large-scale, serialized PS version of the R&D, production, sales, and service systems that have become rare in China and are truly One of the leading printing equipment in the domestic market.

At present, the aluminum-based positive-type PS plate is widely used in China. It is a 0.1-0.5-mm-thick aluminum plate base used as a support, and a sand-like oxide film layer is formed by electrolysis, oxidation, and other surface roughening treatments. The cloth is made of a diazo photosensitive layer.

The Importance of Testing and Control of Surface Treatment Fluids for PS Plate Production Line

The key to the PS version technology is the photo-resist performance and surface treatment effect of the plate. The role of the surface roughening treatment technology of the printing plate base is to change the processing conditions of the surface treatment of the printing plate, and to improve the state of the sand grains so as to obtain a better printability, so that the printing (graphics) part has a good foundation. The specific surface area of ​​the layout is enlarged, and the ability to adsorb the photosensitive resin is enhanced. For the blank portion, it is advantageous for storing moisture and reducing the surface tension, effectively preventing the surface of the plate from being dirty. Thus, the process section of the PS plate base surface treatment occupies a very important position in the entire production line.

The focus of the surface treatment of the plate is to establish a sand spot, which plays an important role in the performance of the PS plate. For example, the resolution, sharpness, and printing rate of the PS plate have a direct relationship with the state of the sand. The method of setting up the sand on the surface of the aluminum plate includes a mechanical graining method, an electrolytic graining method, a sand blasting method, an etching method, and the like. Nowadays, the electrolytic plate method is commonly used for medium and large PS plate production lines. In order to better establish the coarse grained plate base, the aluminum plate is generally subjected to degreasing treatment before electrolysis, followed by oxidation treatment after electrolysis, and a plurality of water washing and neutralization steps are also included between these steps.

In the entire process flow of the surface treatment section of the PS plate production line, a variety of different acid and alkali solutions are used as the surface treatment solution, and the aluminum plate base is subjected to a series of treatments such as degreasing, electrolytic roughening, dust removal, and oxidation. .

1) Alkaline washing (degreasing) process section

In addition to the oil from the NaOH, slow-scale additives and other components. The concentration of lye in the degreasing process section is slightly different depending on the plate version of the manufacturer of the PS plate, the speed of the production line, and the treatment process. The control range of the processing temperature is approximately the same. The addition of the slow-scale additive is to prevent the lye from binding on the rubber roller to harden the dirt and destroy the substrate. The temperature of the deoiling is controlled so that the oil is saponified and emulsified more quickly, thereby completely removing the grease on the surface of the substrate. Will cause serious corrosion of the layout.

If the lye concentration is too low, the oil on the surface of the printing plate will be dirty, resulting in poor electrolyzed grit, or no sand. If the concentration of lye is too high, the plate base will corrode seriously, resulting in waste of raw materials. And easy to foul. If the temperature is too low, the deoiling effect will be poor; if the temperature is too high, the material and energy will be wasted.

2) Electrolytic process section

The electrolyte composition is mainly HCl. The aluminum plate adopts alternating current when electrolyzing sand, and the electrolyte uses dilute hydrochloric acid. When the aluminum plate is a cathode, hydrogen ions in the solution receive electrons on the aluminum plate to generate hydrogen gas and escape; when the aluminum plate is an anode, aluminum atoms emit electrons. Generates aluminum ions into the electrolytic solution. Under the repeated action of the alternating current, the reaction proceeds alternately, and fine and uniform sand is generated.

In addition to electrolyte concentration, electrolysis processes also involve a series of important parameters such as current density, voltage, polar distance, and electrolysis time. If the concentration of the acid is too low, the conductivity will be reduced, the electrolysis effect will be poor, and the coarse and fine state of the sand will be affected. If the concentration of the acid is too high, it will affect the state of the sand and electrolysis. If the temperature is too low, the conductivity of the electrolyte will be deteriorated, and after the electrolysis, fog will appear on the surface of the substrate; if the temperature is too high, the sand will become coarse and affect the electrolytic effect.

Under certain conditions of the electrolyte concentration, the current, voltage, and other process parameters must be matched to produce the desired electrolytic sanding effect. In the actual production process, with the progress of electrochemical reaction, the electrolyte concentration will inevitably change, but the current and voltage and other parameters are fixed. As a result, the mismatch between process parameters will inevitably result, affecting the effect of electrolysis.

3) Oxidation process section

The main component of the oxidizing solution is H2SO4. Oxidation film formation mechanism is very complex, there are many influencing factors, in actual production should be based on production experience, at any time to adjust the temperature, voltage, current, oxidation time and other process parameters, so as to obtain the ideal oxide film thickness.

The formation quality of the oxide film requires dense and high hardness. In the oxidation stage, the concentration and temperature of the oxidizing solution together determine the rate of oxide film formation, and the oxide film formation rate directly determines the quality of the oxide film. If the oxide film is generated too quickly, the oxide film will be loose, rough, brittle, and not wear-resistant; if the production rate is too slow, it will inevitably lead to low production efficiency. Therefore, a dense and hard oxide film layer can be obtained only by controlling the proper rate of oxide film formation. It can be seen that in the oxidation process section, controlling the concentration and temperature of the oxidizing solution is a very important task within a certain range of process conditions.

If the concentration of the acid is too low, the conductivity of the oxidizing solution will be deteriorated, resulting in a small current reaching the surface of the plate, affecting the formation of the oxide film; if the concentration of the acid is too high, the oxide film will be generated too quickly. If the temperature is too low, the oxide film will be generated too slowly; if the temperature is too high, the oxide film will be generated too quickly.

In summary, the concentration and temperature of various surface treatment liquids are very important process parameters in the PS plate production process, which directly determine the effect of the surface treatment of the plate base and the quality of the final PS plate. Therefore, real-time detection and control of the concentration and temperature of various acid and alkali solutions ensures stable process conditions are particularly important.

Current status of detection and control of acid-base solution in PS plate production line

At present, the status quo of surface treatment fluids detection and control in domestic PS plate manufacturing enterprises can be roughly divided into manual control, semi-automatic control and automatic control.

1) Manual control

This is the common practice of most small and medium-sized PS plate manufacturers in China. Mainly in the entire production line of data management system has not yet formed, the degree of automation is low, the surface treatment process for a variety of acid-base treatment liquid detection is often only the instrument display, and no automatic real-time control. The concentration test is completed by artificial laboratory titration. The supplement fluid is also artificially performed by experience. Therefore, it is greatly influenced by human factors.

1 Regular inspection. In the production line, each acid-base solution tank in the surface treatment process section is equipped with a corresponding acid-base concentration detection device, a cassette-type or wall-mounted display panel, and shows the acid or alkali in the tank. The real-time concentration of the liquid. In the normal production process, as the reaction progresses, the concentration of various acid-base solutions will be reduced or changed in varying degrees. Therefore, workers will regularly inspect the indications of various instruments according to certain shifts. After a regular inspection, the worker informs the inspector to sample and test the actual concentration of the treatment fluid. In addition, if there are problems in the production process that affect the quality of the finished media, the workers will also sample the surface treatment fluid.

2 laboratory titration test. The concentration of the solution is measured in the laboratory through titration. The inspector determines the endpoint of the titration according to the color change of the indicator, and then calculates the analytical result based on the volume consumed by the standard solution to obtain the exact concentration of the treatment solution.

3 artificially added. The worker who is responsible for supplementing the stock solution shall, after receiving the notification from the inspector, add a certain amount of stock solution to the treatment box according to the corresponding concentration difference to restore the concentration of the solution required by the process. The amount of specific supplement fluid is often based on the practical experience of workers for many years, gradually explored a certain amount of experience.