Preliminary exploration on the sealing process of positive thermal CTP plate
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The positive thermal CTP plate material needs to block the pores of the anodized film before use, so that it loses some or all of the adsorption capacity, thereby improving the anti-pollution and anti-corrosion ability of the anodized film. Such a process is called sealing treatment. . If the photosensitive liquid is directly applied without treatment, the plate will firmly adsorb the photosensitive liquid. Even if the plate is exposed, developed or washed with a solvent, the photosensitive liquid cannot be completely detached and is adsorbed on the plate. The blank part is easily contaminated, and the printing plate will be dirty when it is inked or printed. The sealing treatment can reduce the tension of the surface of the plate, reduce the adsorption, enhance the hydrophilicity and stability of the plate, and require the plate base after sealing to be colorless, and has good corrosion resistance and high wear resistance.
The sealing mechanism is complicated, because the sealing treatment is carried out in different media, the reaction speed, the color of the surface of the aluminum plate after sealing, the content of the medium entering the micropores, the hydrophilicity, etc. are different, simple That is to say, the aluminum oxide on the surface of the film layer produces crystal water, and the volume is increased to block a part of the micropores. After the sealing treatment, the volume of the anodized film was increased by about 33%.
General sealing process and materials
The sealing effect plays a key role in the performance of the positive thermal CTP plate. The sealing process is currently commonly used in chemical sealing methods, and the sealing treatment methods include immersion, spray or extrusion coating. The concentration, temperature and sealing time of the sealing solution will have a great influence on the sealing result. There are many kinds of chemical substances used for sealing, such as PVPA, sodium fluoride, sodium fluorosilicate, etc., and their common characteristics are mainly as follows.
(1) Forming a nano-thickness hydrophilic layer on the surface of the oxide layer, increasing the surface area, enhancing the water retention and hydrophilicity of the non-image portion, and facilitating ink-water balance during printing.
(2) The non-image part after development is not easy to leave the bottom, the trace does not leave any trace, and the plate base has better leveling property, which can improve the leveling property of the photosensitive adhesive coating.
(3) The contact reaction between the photosensitive layer and the metal ions of the oxide layer is avoided, and the storage period is prolonged.
(4) Work fluid preparation and production monitoring are convenient.
The process control problems that are likely to occur during the use of the above materials are as follows.
(1) Sealing holes with sodium fluoride and sodium fluorosilicate sealing liquid will cause scaling on the drum of the sealing part due to high sealing temperature and high concentration of sealing liquid, so it is necessary to stop the drum frequently. Cleaning, and this scaling is difficult to wipe off with a rag, must be scraped off with a blade, but scratching with a blade can easily damage the roller.
(2) Using sodium fluoride and sodium fluorosilicate sealing liquid, after each time the sealing liquid in the sealing tank is renewed, after a few days, a large amount of white precipitate will be generated at the bottom of the tank, and the production speed is faster. In this case, after the plate material produced is developed and processed, the image portion often has a phenomenon of missing or small white spots.
(3) PVPA sealing liquid is easy to breed bacteria, has short storage time, short service life and high production cost.
It can be seen that different kinds of sealing liquids have different advantages and disadvantages. The author will elaborate on the use characteristics and process conditions of different sealing liquids for reference by readers.
Exploring the sealing process of different sealing liquids
1. Experimental purpose
The effects of different types of sealing liquids and different sealing conditions on the performance of positive thermal CTP plates were investigated under different types of sealing liquids and the same aluminum-based materials.
2. Scheme design
(1) Under the same conditions of the aluminum-based material treatment process and the thermosensitive photosensitive liquid, the performance of different sealing liquids was examined.
(2) Because fluoride and PVPA are relatively easy to use and low in cost, this experiment involves 1 type of fluoride sealing solution, 1 type of fluorinated derivative compound and 1 type of PVPA sealing solution, numbered I#～III. #.
(3) The positive thermal CTP plates produced by different kinds of sealing liquid and sealing process conditions were compared and compared with online performance, alcohol resistance and aging attenuation performance. Among them, 0# positive thermal CTP plate is not sealed, 1-1#, 1-2#, 2-1#, 2-2#, 2-3#, 2-4#, 3-1 #,3-2# are the positive thermal CTP plates under the conditions of the same kind of sealing liquid and different sealing process.
3. Experimental process
(1) In a domestic production line centralized production test, using a production process with a production speed of 17 m / min for aluminum-based treatment.
(2) Coating photosensitive liquid PK-2-15B.
(3) Adopting the screen 8600Z thermal CTP plate making mechanism version.
(4) Development treatment is carried out using Kodak and a company's self-produced developer.
4. Experimental results
On-line performance, alcohol-resistant adaptability and aging decay performance of positive thermal CTP plates using three different sealing solutions
5. Data analysis
(1) From the results of online performance, the comprehensive performance of I# sealing solution and III# sealing solution is better than that of II# sealing solution.
(2) From the data of alcohol resistance adaptability test, the plate material under the test conditions of 1-2#, 2-4#, 3-2# is better in alcohol resistance.
(3) From the aging attenuation performance test data, the plate under 1-2# experimental conditions has better aging stability than the plate under other conditions, except for the small mesh point reduction, there is no other attenuation performance such as bottoming.
Preliminary exploration conclusion
It can be seen from the preliminary experimental exploration results that the sealing effect of the I# sealing liquid, that is, the fluoride sealing agent, is more remarkable than that of the PVPA and other fluorinated derivative compounds, and the fluoride sealing liquid is simple to prepare. The concentration detection and consumption replenishment operation is simple and easy, and the material cost is low. After a certain precision temperature control and concentration control design, it can be applied to most domestic plate production and processing processes.
Regarding the detection of concentration of sealing liquid and the supplementary control of concentration, this article will not discuss this article. I would like to discuss the exchanges with colleagues in the field of printing and plate manufacturing for reference.