CTP equipment accuracy detection and solution
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Reasons for detecting the accuracy of CTP equipment
With the widespread use of CTP equipment, many printing companies have two or more CTP devices, and the brands or models of these CTP devices may be different, so there are differences in performance. For example, a printing company in Dongguan introduced its first Creo brand (now acquired by Kodak) CTP equipment in 2003. So far, it has 6-7 CTP equipment, including Creo, love. Different brands such as Kefa, Heidelberg and Kodak. Even CTP equipment of the same brand of the same brand, if the degree of old and new is different, its performance will be biased. These deviations are small, but it is unacceptable for color printing with high accuracy. Therefore, when using multiple CTP devices for plate making, the printed plates cannot be confused. For example, the same set of four-color plates cannot be made on two CTP devices with deviations, especially when the printing process requires a patch. , must use the original CTP equipment plate making, otherwise, it is easy to produce the problem of overprinting.
Therefore, only by eliminating the performance deviation between CTP devices, multiple CTP devices can be used at the same time to maximize production efficiency. The key to eliminating the deviation is to measure the exact value of the deviation, and then use the internal settings to make up and correct it in the CTP device, so that different CTP devices can be aligned to an accurate intermediate value, thus ensuring the accuracy of multiple CTP devices. Consistency.
CTP device accuracy detection method
In the long-term production practice, the author explored a method for detecting the accuracy of CTP equipment, namely the yin and yang exposure elimination method. This method is only suitable for CTP equipment using positive printing plates. The detection principle is: using the yin and yang complementary pattern to expose the same printing plate on two CTP devices successively, first positive image and negative image, after rinsing, observe the printing plate and By detecting the degree of elimination of the pattern, the exact value of the deviation of the CTP device can be measured.
1. Make yin and yang complementary patterns
First, create a file with a flat design software (such as Illustrator). The layout size is the same as the plate size to be used for testing. A set of lines is created in the upper, middle and lower sections of the layout, from 0.05mm to 0.1mm. 0.2mm, 0.3mm, 0.4mm, 0.5mm and 1.0mm are composed of straight lines of different thicknesses, with an interval of 1.5 to 2.0 mm (refer to the distance of the center line of the line), and this set of thin lines contains another The thin line group is composed of a number of 0.05 mm thick lines separated by 0.1 mm (the distance of the straight center line). The values of these line thicknesses are not fixed and depend on the accuracy of the visual inspection requirements.
Then, the AI file created by Illustrator software will output a positive 1-bit tiff file and a negative 1-bittiff file in the CTP process, and then use the Photoshop software to slightly modify the negative 1-bit tiff file. The head and tail of all the lines are neatly wiped to 1~2cm, and the 0.05mm thick line group is erased. The purpose is to artificially leave a part of the pattern for reference analysis after the yin and yang exposure is eliminated. A part of the 1-bit tiff file of the positive image, and Figure 3 shows the corresponding part of the modified 1-bit tiff file.
It should be noted that some CTP processes (such as Kodak) do not output the 1-bit tiff file. In this case, you can use the Illustrator software to create two PDF files with complementary yin and yang.
2. Exposure
Determine the two CTP devices to be tested, one for the A and the other for the B. Firstly, the plate is exposed to the positive image on the A machine once, and then the exposed plate is placed in the B machine to re-exposure the negative image. The direction of the plate must be the same when the two exposures are made. Finally, two The plate after the exposure is rinsed for the next step of data analysis.
3. Data analysis and calculation
The plate layout after two exposures can be roughly divided into two categories: First, the layout is completely blank, indicating that the registration accuracy of the two CTP devices is high, and the yin and yang patterns can completely overlap and cancel each other out. Second, there are many small lines left on the layout, indicating that the registration of the two CTP devices is biased, and the yin and yang patterns are not completely coincident and cannot be completely offset. In fact, the probability of occurrence of the first case is almost zero. This is only possible if exposure is performed on the same CTP device. Therefore, the second case is the basis for data analysis.
From the thickness of the lines left on the second plate layout, the accuracy of the CTP device can be roughly judged: the finer the line, the higher the accuracy, and the lower the accuracy. At the same time, according to the specific width of the lines left on the layout, the exact value of the deviation can be measured.
A partial map of a situation that occurs after the elimination of yin and yang (the horizontal portion of the upper left corner of the layout) is analyzed as a partial map of the other situation that occurs after the elimination of yin and yang (the horizontal portion of the upper left corner of the layout).
The above is a data analysis of the two situations that may occur in the horizontal part of the upper left corner of the plate layout, and other parts of the plate layout will also produce similar effects, so the entire plate layout should be vertical and horizontal. The data generated by each part is comprehensively calculated, and finally the accuracy of the CTP device is obtained.
The calculation of the accuracy of the so-called CTP equipment is essentially the calculation of the lateral deviation value and the longitudinal deviation value measured on the same plate of the two CTP devices. The calculation expression is as follows.
Ph=1/2[(Ltv+Rtv)+(Lbv+Rbv)]
Pv=1/2[(Lth+Lbh)+(Rth+Rbh)]
Where, Ph is the accuracy lateral deviation value; Pv is the precision longitudinal deviation value; Ltv is the upper left longitudinal deviation value; Rtv is the upper right longitudinal deviation value; Lbv is the lower left longitudinal deviation value; Rbv is the lower right longitudinal deviation value; Lth is the upper left longitudinal deviation value; Lateral deviation value; Lbh is the lower left lateral deviation value; Rth is the upper right lateral deviation value; Rbh is the lower right lateral deviation value.
The method for detecting the accuracy of CTP equipment introduced in this paper is simple and intuitive, and the data is accurate and practical. According to the results of the test, fine-tuning can be performed on the CTP device with deviation, or it can be used as a reference for the accuracy evaluation of the CTP device. Generally, for CTP equipment with small deviation value (below 0.5mm), the measured value can be returned to the CTP equipment and corrected by relevant settings. It is recommended to adjust the two CTP devices with deviation to the intermediate value instead of Unilateral adjustment. For CTP equipment with a deviation value of 0.5mm or more, it is necessary to make careful adjustment or no adjustment. If the deviation value of the CTP equipment is too large, the CTP equipment supplier is required to adjust the standard value of the CTP equipment itself.