Some Discussions on Increasing Printing Rate of Printing Plates (I)

Under the premise of guaranteeing the quality of printed matter, the highest number of printing plates can withstand is called the printing rate of printing plates. The printing rate of printing plates directly affects the level of printing costs. Therefore, for printing companies, it is of practical significance to study how to improve the printing rate of printing plates.

Before we discuss how to improve the printing plate printing rate, we must first clarify the following questions: What structure on the plate determines the printing plate's printing rate? What are the factors that affect the printing rate of printing plates? As the saying goes, it is necessary to catch the cow's nose. Only by grasping the main factors that affect the printing rate of the printing plate, we can improve the process more effectively by improving the printing plate printing rate. Here we discuss separately:

First, determine the printing plate printing rate and plate properties:

1. The PS version is based on aluminum

The aluminum plate material is widely used due to its advantages of light weight (2.7 g/cm density), ease of processing, and good flexibility. However, aluminum is a relatively active metal and is easily oxidized by oxygen in the air and many substances such as acids, alkalis, and salts, thereby changing the printability; in addition, aluminum has high ductility (tensile strength is 14kg/mm2, and the degree of stretching is 3 to 4%), poor resistance to mechanical forces (Rockwell hardness 15 to 19), the above can also be said to be the chemical and physical defects of the aluminum plate as a base plate.

2. The thickness of aluminum base is between 0.2 and 0.4mm

This further determines the aluminum plate's ability to withstand mechanical forces (bending, stretching, knocking, etc.). If the mechanical strength of the aluminum plate exceeds the tolerance of the aluminum plate, it will definitely affect the normal use or even discard of the plate.

3. PS plate surface microporous structure

This microporous structure can effectively improve the hydrophilicity of the blank part of the printing plate in the printing process, but is relatively easy to be damaged under the action of friction. As shown in the figure, the microporous structure on the printing plate can be divided into four grades of ABCDE. The closer it is to the top (AB), the more susceptible it is to abrasion. When the degree of abrasion reaches E, the microporous structure on the printing plate is basically If it is smoothed out, it loses its ability to contain water, and it cannot effectively resist ink. In other words, the printing plate at this time is basically scrapped.

4. Hydrophilic salt layer on the plate surface

There is a relatively dense hydrophilic salt layer (sodium aluminosilicate) on the surface of the PS plate. This hydrophilic salt layer has a porous structure, high hardness (similar to that of chromium), and strong hydrophilicity, so it has a strong reservoir. Water and abrasion resistance. The hydrophilic salt layer on the surface of the printing plate is equivalent to a protective layer on the surface of the printing plate. The protection and timely restoration of the hydrophilic salt layer will directly affect the printing rate and the use quality of the printing plate.

5. Photosensitive resin layer on the plate surface

This layer of photosensitive resin is the graphic basis of the surface of the printing plate. It is hydrophobic and hydrophobic, and the abrasion resistance is relatively good to the blank. However, due to the influence of chemical components (diazonium compounds), the alkali resistance is relatively poor. Since the surface layer is only 1.5 to 2.0 μm, slight scratches can cause damage to the layout and it is difficult to repair. Therefore, the protection of the graphic part (photosensitive resin layer) is more important.

Second, we can put the factors that affect the printing plate's printing rate into several aspects: raw material selection; plate making and printing process; mechanical damage to the printing plate; electronic corrosion and chemical corrosion of the printing plate. Below we discuss separately.

1. Selection of raw materials:

i. Choosing a good PS original is the primary prerequisite for the life of the printing plate in the printing process. A good PS must have a uniform surface and a smooth surface, and the photosensitive surface of the printing plate should be smooth and smooth, and the dots should be well reproduced.
Ii. Paper: It requires high surface strength, light powder removal, and less surface degumming. Ink: Fine pigment particles are required. The choice of paper and ink directly affects the wear of the printing plate during the printing process.
2. Platemaking and printing process

i. Improper storage or handling, running before exposure or development; overexposure; over development. The results of these three are the same, and all have an effect on the photosensitive resin adhesive on the surface of the PS plate (the direct result is that the photosensitive film is thinned and the ability to withstand friction is reduced). When making the PS plate, strictly follow the procedures and meet the printing needs. Follow the principle of "strong exposure and weak development" in the printing process. Test the light source diligently, test the developer concentration and diligently record, and make the exposure time accurate and develop. The speed is right.

Ii. Roasting the developed PS plate is a very effective way to increase the printing plate's printing rate. Here we give a more detailed description: After the printing plate is baked, the photosensitive base in the photosensitive layer disappears, and the phenolic resin undergoes thermal crosslinking reaction by heat, and turns from linear molecules to large-scale network molecules. At this time, the solvent resistance, corrosion resistance, and abrasion resistance of the printing plate and the adsorption of the photosensitive layer to the plate surface are greatly improved. However, during baking, in addition to the change in the photosensitive layer of the graphic part, the surface of the anodized aluminum plate base is closed by the pore sealing treatment, and the flowability may be increased due to the loss of water, causing the plate to be dirty. Therefore, before baking, it is necessary to evenly apply a layer of protective agent to the plate with absorbent cotton to protect the blank from dirt. The general coating amount is one pair of open coating 20ml-30ml. Baking plate temperature control at 230 °C -250 °C. The time is 5-8 minutes. It must be noted that the special roasting machine used in the roasting plate must have a constant temperature control device with a temperature difference of ±2°C. The baking temperature is too high or the time is too long can cause carbonization of the photosensitive layer, aluminum plate deformation and mechanical strength. Reducing affects the printing plate's resistance to printing force and the life of the plate base; the temperature is too low or the time is too short, and the thermal curing degree of the photosensitive layer is not enough, which will also affect the printing resistance. After baking, it must be cooled naturally, and it should not be cooled by water to avoid deformation of the plate base. After cooling, the protective agent was washed off with a waste developer, neutralized with 3% phosphoric acid, and washed with water and dried, and gum arabic was applied to protect it.