Preliminary study on the resistance of the PS version
We are a big printing company in Shenzhen China . We offer all book publications, hardcover book printing, papercover book printing, hardcover notebook, sprial book printing, saddle stiching book printing, booklet printing,packaging box, calendars, all kinds of PVC, product brochures, notes, Children's book, stickers, all kinds of special paper color printing products, game cardand so on.
For more information please visit
http://www.joyful-printing.com. ENG only
http://www.joyful-printing.net
http://www.joyful-printing.org
email: info@joyful-printing.net
Pre-coated photosensitive lithography (also known as PS version) has been applied since the 1950s. With its high resolution, smooth dot and high printing durability, it has gradually replaced the plates of protein and multi-layer metal plates, becoming a modern fast printing. New plate. At present, under normal circumstances, the PS version of the printing durability is generally around 100,000 impressions, the baked PS version of the printing durability can be increased by 3-5 times, reaching 300,000 to 500,000 impressions, but now many manufacturers reflect PS The printing capacity of the printing plate is not high, generally only 21,000 prints, even after printing thousands of copies, it begins to lose version. Here, I only discuss and analyze the plate production and plate making process of the PS version of the printing force according to the personal experience and the PS version production process.
First, the choice of plate
The base of the PS version is aluminum. The aluminum material used for the PS plate belongs to the general industrial grade pure aluminum, the thickness is generally 0.3mm, and the content is 99.5%. The main impurities are iron and silicon, followed by copper, magnesium, zinc, manganese, titanium and the like. The presence of a small amount of impurities in the aluminum plate can increase the tensile strength and hardness of the pure aluminum, reduce the elongation, and lower the electrical conductivity of the aluminum.
Second, the composition and coating of the sensitizer
The PS plate photosensitive agent is composed of a photosensitive material, a film-forming polymer resin, a dye, and an organic solvent. For the photosensitive layer coated with the photosensitizer alone, it has strong alkali resistance, poor film forming property, and difficulty in development; and an appropriate amount of phenol resin is added to the photosensitizer. Although the alkali resistance is poor, the film forming property and the adsorptivity are improved. The ratio of the two is 0.5:1 or 0.62:1. If the photosensitizer is small, the film forming resin is more, the alkali resistance is lowered, and the dot is easily lost. The residual film rate is low, which directly reduces the printing durability of the printing plate.
The coating of the PS plate sensitizer requires a special coater to ensure uniform thickness of the photosensitive layer after coating. The coater is generally divided into two types, a single plate and a roll plate. In the coating method, there are paving type, roll coating type, extrusion type and electrostatic coating type. We do not advocate the use of centrifugal coating. In China, the roll coating type is commonly used. In order to ensure the coating quality, the solid content of the negative-type photosensitive layer is about 1g/m2. The positive pattern is 2-2.5 g/m2 and the thickness is generally (20 ± 1.0) mg/dm2. When the coating produces a lateral stripe or other failure, it should be removed in time.
Third, the PS version of the plate making
The key to PS platemaking is to maximize the reproduction of the dots and tones of the film, creating a strong lipophilic base and a stable hydrophilic base on the surface of the plate. Otherwise, not only is the time wasted, but the more serious is that the printing plate is resistant to printing and the plate is wasted. A number of factors that directly affect the quality of the platemaking include the original plate making. PS version of dot reproducibility, plate making equipment and conditions. Plate making process and operation, especially exposure, development conditions, etc.
1. Original version
The original version of the PS version of the positive or negative image can be made by conventional photolithography, electronic color separation and photo-alignment. In addition to the tone reproduction curve should be adjusted, you must also pay attention to the original density contrast and dot finish. Because the original Y value is too low, exposure, lack of development or excessive thinning. It is easy to form a soft dot with low density or an active dot with a large intermediate density and a small edge density. The drying stability of these two types of dots is poor, and the exposure and development changes slightly, which will make the printing plate different in depth, which will directly affect the printing durability of the printing plate. The original version of the hard dot is high in density, and the dot is smooth, and the tolerance of exposure and development is large. Therefore, the quality is stable. Therefore, the original version of the handwriting pattern must be clear and dense, and the contrast is large. Take Huaguang brand YZ-600 11 type film as an example. The original maximum density should be above 4.0. The minimum density is below 0.05 and the gamma is above 8.0. The layout is cleaned to reduce fog and collage.
2. Printing light source
For the light source. Since the sensitizer is a redox reaction. Only the sensitizer can absorb enough light energy to generate T, and its decomposition, cross-linking and bonding degree are proportional to the required light intensity and illumination time. Therefore, the emission spectrum of the plate-type light source and the photosensitive agent photosensitive curve Sensitive areas should be matched as much as possible. Experiments have shown that the spectroscopic sensitivity of the positive-type photosensitive thorn is within the range of 300 nm to 460 nm, and the pattern is within the range of 200 nm to 500 nm. Consider the effects of the original plate and the printing plate. The spectral design is suitable in the 350nm-460nm region, so the ideal light source for the current PS plate is the iodine gallium lamp.
3. Exposure
In the normal plate making process. Exposure is the most important factor affecting dot changes and layout depth. We know that the exposure of the printing plate = illumination × printing time. Because the commonly used PS version of the positive pattern belongs to the photodecomposition type. Therefore, when the exposure exceeds the critical amount of light, that is, when the exposure is excessive, the dots are reduced, and the thin strokes and small dots are difficult to reproduce; when the exposure is less than the critical amount, that is, when the exposure is insufficient. The outlets will expand correspondingly and become thicker. Make the layout dirty and affect the depth of the layout. Therefore, during the printing process, the amount of exposure is controlled. It should be monitored by continuous adjustment of the scale or Brunel test strip. The effect is to check the exposure after development. Generally, the proof plate is controlled at 3-4 grades (density 0.4-0.55), and the printing plate is controlled at 4.5-5.5 grade (density 0.625-0.775). In the case of a sun-printed version, such a plate can be qualified if it can be dried in pairs with 0.5% of small dots and 99.5% of hollow dots.
4. Development
The development of the PS plate consists in removing the photosensitive layer of the blank portion to maintain the hydrophilic property of the surface of the PS plate. It is an important part of the PS plate making process, and is not only affected by the properties of the sensitizer and the original state, but also by the development conditions such as the concentration of the developer, the temperature, the degree of fatigue, and the development time.
(1) Influence of concentration
The concentration of the developer. Generally speaking, it refers to the content of the developing main agent. Insufficient developer concentration not only increases development time, but also tends to cause incomplete development. When the concentration is too large, the development time is accelerated, the whole process is difficult to control, the development is excessive, the dots are reduced or damaged, the unexposed photosensitive layer is dissolved, and the printing plate is reduced in fat sensitivity and printing durability. Therefore, in order to accurately control the concentration, after the plate is developed through 30-60 s, it is observed whether the hollow point of the Brunel test strip is 98%-99% clear and whether the small black point of 1%-2% is firm, if A clear and solid point indicates that the concentration is appropriate.
(2) The effect of temperature
In the case where other development conditions are relatively stable. The higher the development temperature, the faster the development speed, and vice versa. The general development temperature should be controlled at around 20 °C. The automatic developing machine should be controlled at 25 ° C. If it exceeds 30 ° C, the dots will dissolve. The intermolecular bonding force between the photosensitive material and the film-forming substance in the photosensitive layer is weakened, the alkali resistance is lowered, the percentage of the dot area of the plate is reduced, and the tone reproduction of the printing plate is destroyed.
(3) Influence of developer fatigue
The fatigue of the developer refers to a decrease in the developing ability of the developer. If it is developed by manual development, since the developer is exposed to the air, the absorbed moisture and CO2 accelerate the deterioration of the developer and affect the developing performance. Another reason for the fatigue of the developer is that the photodecomposition substance is dissolved therein, and the developing ability is remarkably lowered. Therefore, the alkaline developer currently used should minimize contact with air during storage and use, reduce the influence of moisture and CO2 on it, and regularly replace and quantify the addition of syrup.
(4) Influence of development time
Since the development time is affected by factors such as the exposure amount of the printing plate, the performance of the sensitizer, the development mode, and the state of the developer, it is necessary to control and stabilize the above-mentioned variability factors, and then perform the test with a gray scale. To determine the development conditions and the correct development time, the development time is generally about 1 minute.
Fourth, baked version
After the printing plate is baked, the photosensitive groups in the photosensitive layer disappear, and the phenolic resin undergoes thermal crosslinking reaction by heat, and the linear molecules become large mesh molecules. At this time, the solvent resistance, corrosion resistance, abrasion resistance of the printing plate and the adsorption property of the photosensitive layer to the plate surface are greatly improved. However, at the time of baking, in addition to the change of the photosensitive layer in the image portion, the surface of the anodized aluminum plate base is sealed by the closed pores, which may increase the water flow due to water loss, causing the plate to be dirty. Therefore, before baking, the layer must be evenly coated with a layer of protective agent to protect the blanks from dirt. Generally, the coating amount is from 20 ml to 30 ml in one open coating. The baking temperature is controlled at 230 °C - 250 °C. The time is 5-8 minutes. It must be noted that the special baking machine used for the baking plate should have a constant temperature control device with a temperature difference between ±2 °C. If the baking temperature is too high or the time is too long, the photosensitive layer will be carbonized and deteriorated, and the deformation and mechanical strength of the aluminum plate will be affected. Decrease, affect the printing durability of the printing plate and the life of the plate; if the temperature is too low or the time is too short, the photosensitive layer will not be cured by heat, which will also affect the printing durability. After baking, it must be naturally cooled, and it is not necessary to use forced cooling with water to avoid deformation of the plate base. After cooling, the protective agent is washed away with a waste developer, neutralized with 3% phosphoric acid, and washed with water. If it is not applied to the machine, it should be coated with gum arabic for protection.
The production and drying of the PS version plays a decisive role in improving the printing durability of the printing plate. When the printing process is carried out according to data, standardization and standardization, the production and drying of the printing plate is particularly important. therefore. We only deal with the above problems carefully, eliminate the external and human factors in the production and printing process, vigorously promote data, standardization, standardization and drying, maximize the quality of plate making, and improve the printing durability of printing plates. Implement it in practice.