Aspects of CTP Quality Control

The development and popularization of CTP and digital workflow have promoted a printing revolution on a global scale. CTP makes the printing process change from the cumbersome traditional printing simulation operation process to the high-quality, high-efficiency digital printing operation process. CTP technology has been developed rapidly under the close attention of people. In 2011, the sales of the CTP version surpassed the PS version for the first time, and the CTP version will basically replace the PS version in the future. CTP technology is the fastest-growing part of the printing field, especially its technological innovation speed is very fast. Every innovation brings new vitality to the printing industry and will effectively promote the process of digital printing.

Since the development of CTP technology, no one has doubted its market viability. In order to make full use of the value of CTP, printing companies must fully consider multiple quality parameters such as exposure conditions, printing plate uniformity, and printing plate output stability.

CTP quality control

1. Determine the best exposure conditions
The control of exposure parameters can keep the mechanical system and optical system of CTP in good condition. The direct factors that affect the CTP exposure quality include the focal length of the laser head, the zoom distance, the exposure intensity, the luminous power, the rotation speed of the drum, etc.

2. Environmental control of CTP
Environmental control is crucial to the dot reproduction of CTP output. A suitable environment can not only ensure the normal operation of the machine but also ensure the output quality of the printing plate. CTP environment control mainly includes the temperature, humidity, and air quality control of the printing room. The checkerboard formed by light exposure points, and the checkerboard formed by 8×8 laser exposure points constitute the background area, both of which are 50% of the dotted area. During the experiment, the control variable method can be used to find the best conditions, that is to say, one of the conditions is changed, and the other conditions are kept unchanged for the experiment.
For example, to find the best exposure intensity, you can set different exposure intensities through CTP, control the roller speed and other factors to remain unchanged, and then usually require the temperature of the printing room to be 20°C±2°C. If the temperature of the printing room is too high, it is easy to Accelerate the aging of the thermal laser head. The humidity in the printing room needs to be controlled at a relative humidity of 50% ± 10%. If the humidity is too high, the cleaning of the plate and the inside of the machine is equivalent to the output of the printing plate. First, visually observe the exposure control area of the measurement and control strip on the output printing plate. From right to left, the more invisible circular marks, the better the exposure intensity. If the visible circular mark appears black, the exposure is underexposed; if the visible circular mark appears white, the exposure is overexposed. In this way, the optimal exposure intensity can be found, and other optimal exposure conditions can be found in the same way. unfavorable. In addition, the CTP workshop needs to set up dust removal facilities to keep the indoor air clean. If the particulate matter in the air is not up to standard, on the one hand, it will affect the smooth flow of the air path, and on the other hand, it will also have a great impact on the normal operation of the laser head.

3. Developer control
In the process of CTP development, to complete the development correctly, it is a crucial step to control the temperature, concentration, and conductivity of the developer. Low temperature or low concentration of the developer will cause the printing plate to stay at the bottom, making the CTP printing plate not rinsed clean, and there will be coating residue in the blank area; The coating loss is more, and the small dots are lost. Similarly, the pH value and conductivity of the developer also need to be controlled within a certain range, otherwise, the development will also appear to leave a bottom or overdevelop. There are no fixed values for the setting of parameters such as temperature, concentration, and conductivity of different developers. Developers from different manufacturers have different parameters. If you use the developer recommended by the CTP manufacturer, you can use the manufacturer’s set value; if it is not recommended by the manufacturer If the developer is used, a matching test between the plate material and the developer is required.

4. Plate output uniformity
At present, the output uniformity of the CTP printing plate has been widely recognized by everyone, but in the actual production process, there will be problems such as the uneven output of the printing plate due to various factors such as the aging of the laser head and the change of the CTP developer. At this time, it is necessary to The CTP is regularly tested for uniformity.

The output uniformity of the CTP printing plate can be detected by measuring the dot area ratio of the ladder. If the dot value of the printing plate changes very little, it means that the uniformity of the CTP system is very good; but if it is found that the dot value changes significantly, it is necessary to check the developer and the laser light source, and take corresponding measures.

5. Plate output stability
Not only the exposure accuracy and output uniformity of CTP are very important, but also the output stability of CTP printing plate is also very important, which is mainly affected by exposure conditions, developing conditions and machine stability.

6. Linearization control of CTP

Because the CTP dot output is affected by a series of factors such as temperature, humidity, developing speed, and exposure intensity, it is difficult to guarantee the linearization of the dot output of the printing plate. Therefore, in the digital printing workflow, there is generally a corresponding linearization of the CTP printing plate. module. The accuracy of the output CTP dots can be ensured through CTP linearization. The process of plate linearization is roughly as follows:

① Output the dot ladder printing plate under standard exposure and development conditions, and measure the area of each gradient dot on the printing plate;

②Open the CTP linearization module in the process, put the measured data into the corresponding module, and the linearization calibration curve will be automatically generated;

③Invoke the linearization correction curve to output the printing plate during CTP output;

④ Check the linearization of the printing plate again and perform linearization correction.

7. Plate inspection
After the CTP plate making is completed, the printing plate must be inspected. The main inspection contents are as follows:
① Check the tone and dots of the printing plate, and 1% to 99% of the dots are well reproduced;
② Check the color of the printing plate: avoid confusion of color and color sequence;
③ Check the relevant dimensions: bite-size, finished product size, bleeding size; check whether the center of the plate is centered;
④ Check that the finished line is clear, the position of the needle line is correct, and the folding line is clear and accurate;
⑤Compared with the blue paper and digital samples, check whether there are missing colors, missing text blocks, missing changes, or dirty spots;
⑥ Check whether there are mottlings and scratches on the CTP plate, whether there is a screen drop on the plate, whether the white area on the plate has been washed clean, and whether the protective glue covering the whole plate is even.

In the process of using CTP, printing companies should not just think about producing a large number of printing plates, thinking that the more they publish, the more profits they will make. If there are a large number of waste plates, the loss outweighs the gain. Enterprises should not only ensure the quantity of publications but also ensure the quality in order to maximize profits.