The positive graph PS version of the resistance force analysis of two reasons

Second, the effect of electrolytic roughening

1. Sand effect introduction

The purpose of the roughening process is to form a layer of sand on the surface of the printing plate. An analysis of lithographic quality failures revealed that 90 to 95% of the causes were directly or indirectly caused by sand. Sand spots have the following effects:

1 The specific surface area of ​​the printing plate is enlarged so that the plate base has a wetting condition and a basis for adsorption to the liquid. This is the basis for the adsorption of the photosensitive layer (lipophilic layer) and fountain solution (hydrophilic).

2 The condensation of the capillaries is produced, and it is easy to receive and store the liquid that acts on the surface. That is, with sand, the absorption capacity of the photosensitive layer increases, the ability of the photosensitive layer to resist mechanical friction during use increases, and the resistance to printing increases. At the same time, with sand, the water holding capacity of the printing plate is enhanced. The layout of the clean, more effectively prevent the emergence of dirty fault.

3 Increased number of adsorption centers, so that the aluminum plate fully achieves the goal of being both lipophilic and hydrophilic, so that the basis of the graphic and blank parts is more firmly and more stable, that is, when the printing plate is working, The quality and wear resistance of the plates are maintained throughout.

2. The requirements of the state of the sand

The role of sand, only for the ideal sand, if the state of the sand can not meet the requirements, the sand will not only have the above effect, but will affect the performance and life of the printing plate.

The ideal sand spot should:

1 The peaks are on the same plane and the shape is smooth; while the valley bottoms should be on the same plane and the valleys are deep;

2 The distance between adjacent sands should be kept 3um;

3 layout sand requires the same size, consistent depth and distribution.

In accordance with the first feature, the layout can have sufficient moisture to prevent dirtiness during printing. If it does not meet the second characteristic, the plate grain is too fine and the water storage capacity is too low. The plate is easy to get dirty; if the distance between two adjacent grains is greater than 3um, the plate grain is too coarse, although the water storage capacity is high, but Moisture on the printing plate will be taken away by the high-speed rotating rubber roller, which will reduce the amount of water stored in the plate and cause dirt. Only in accordance with the above three conditions, can we ensure that the layout of the water evenly and stably, the dot reproducibility is good, and the resistance to printing is high.

From the above discussion, it can be seen that the coarse grain formed by electrolytic coarsening will seriously affect the printing plate's resistance to printing. Only the ideal sand spot can help the printing plate and printing force. The grain size of the PS plate is generally 500 to 700 mesh/mm2, and the size is generally about 0.6 μm, and the depth is 1.5 to 7 μm.

3. Factors affecting the quality of the grain

1Electrolyte effect on the quality of sand

Electrolytic roughening uses the following electrolytes: hydrochloric acid solution, nitric acid solution, and nitric acid are mixed solutions supplemented by hydrochloric acid.

Selecting the hydrochloric acid solution as the sand spot of the electrolyte will cause the “edge effect”, that is, the fine grain in the middle part of the plate and the rough grain on the edge.

The nitric acid solution was used as the sand spot formed by the electrolyte, and the depth was lighter, so the resistance to ink was low.

Selection of nitric acid-based, hydrochloric acid supplemented by the electrolyte obtained sand, you can get high-resistant printing plate, is the main electrolyte used.

2 Effect of electrolysis conditions on the quality of sand

A. The effect of current

The use of direct current to roughen the plate, resulting in uneven distribution of the sand, and the serious corrosion of the aluminum plate, so that the wear resistance decreased.

The use of alternating current electro-sanding can obtain evenly-distributed sand and corrosion of aluminum plates.

B. Influence of voltage and power

In the electrolyte, asymmetrical waveform AC power is fed in, and Vyang> Vyang Qyang> Qyang regulates cathode and anode power ratio, ie Qyin/Qyang can change the thickness of the sand. In general, Q Yin / Q Yang should be controlled at 0.4 to 0.8. V yin is generally 10-15V. The alternating current has a frequency of 50-60 Hz. The higher the frequency, the finer the sand. By electrolyzing the aluminum plate according to the above conditions, it is possible to obtain a grain having a moderate thickness and a multilayer structure in a short period of time. This type of sand has good water retention properties, making it difficult for the printing plate to become dirty, and it also enhances the printing plate's resistance to printing forces. (to be continued)