Printing Quality Assurance - X-Loupe

Printing Quality Assurance - X-Loupe

Printing Quality Assurance Recently, printing industries have been facing a revolutionary challenge in digital processing, in order to meet clients’ d...

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Printing Quality Assurance Recently, printing industries have been facing a revolutionary challenge in digital processing, in order to meet clients’ different needs, such as enquiring small quantity but of large variety, closing deals as quickly as possible, and undergoing compressed working time. Having to face such strict conditions, emphasis put on the printing quality is thus very crucial. In order to minimize the errors caused by macrography and experienced head staff, it’s been years that the printing industries use scientific tools to test printing quality. However, these tools are not only costly, but also too heavy to be taken out of the laboratory and to be applied in the real production line. With the microphotography development background, our company, Lumos Technology Co., Ltd., has combined Canon’s optical technology to develop a portable microscope, the X-Loupe Portable Microscope Camera, with 60, 150, and 300 magnifications and 8 million pixels of resolution.

5. Examine the printing color control strip. 6. Examine the strip of 3D lenticular print 

To test finished products under microscope: 1. 2. 3. 4. 5.

Examine the surface of the printed products. Examine the rub resistance of surface. Examine the adhesive force. Examine the printing dots. Examine the printing color control strip.

With this advanced development, we provide not only an efficient inspection intrument for the printing process, but also an auxiliary observing tool for the printing related R&D departments, the laboratories and the production line. The excellent optical rendering capacity and large view finder can minimize eye fatigue under long working hours, reduce time for decision making and increase accuracy, so that the work can be more efficient and the process can be reduced. In addition, with the mobility and portability of the X-Loupe, staff is able to directly photograph samples in the production line. The X-Loupe can help cut down the spot-check procedure, and can be used by the sales representatives as a convenient tool to show and discuss the printing matter with the clients.

I. Applying the X-Loupe to test printing processes



To test raw materials under microscope: 1. Examine the fineness of grind. 2. Examine the surface physical property of the raw material. 3. Examine the surface chemical property of the raw material. 4. Examine the coating hardness of the raw material. 5. Examine the surface tension of the plastic raw material.



To test semi-finished products under microscope: 1. 2. 3. 4.

Examine the rub resistance of surface. Examine the adhesive force. Examine the level of dryness. Examine the printing dots.

Illustration: Micro-observation of rub resistance after the test (Photographed with the X-Loupe G20, 150X)

The X-Loupe is able to obtain the actual test data as follows: It can at least observe 0.5% and 99.5% tiny dots of plate control wedge on the printing plate and 0.01mm to 0.02mm dots on the printed material. It can also be combined with various printing testers, such as rubbing resistance tester, grind gauge…etc. to assist the micro-measurement of the tested materials and products. Also by combining with the digital microscope and image processing software, more precise dot area of 0% and 100% can be obtained. The X-Loupe can observe whether the color overlay is within allowable error of ±0.1mm. Combining with a protractor, it can evaluate the angle of the outlets to avoid apparent moiré pattern. For example, the allowable error for black screen is 45 degrees, 75 degrees for magenta screen, and 15 degrees for blue screen. In addition, it can also calculate the screen ruling.

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Printing Quality Assurance II. Applying the X-Loupe to test raw materials The printed materials and ink are the printing raw materials. Their quality is very much connected with the appearance of the printed product. The X-Loupe can be used directly to process the printing test of the raw materials, it can save the trouble of getting samples and having them tested and verified in the laboratories. 1. Examine the fineness of grind If the fineness of grind is too big, the ink might build up in the process. Besides, to get sophisticated printed product, the ink with smaller fineness of grind should be used. This test is using some brand yellow ink. The result shows that there is more rubbing at the end of the grind gauge, which indicates that the fineness of grind is smaller. Using the X-Loupe G20 with 150X magnification power, we can clearly see the rubbing condition.

Illustration 2.5 shows the microphotograph of the plastic surface (Photographed with the X-Loupe G20, 150X)

3.

Examine the surface tension of the plastic material

The surface tension for the printed plastic material is especially crucial when printing. If the surface tension on the printed material is too big, the ink then can not adhere to the surface efficiently.

Illustration 2.6 shows a test done by Dyne Test Pen (Photographed with the X-Loupe G20 150X) Illustration 2.1 – Microphotograph of the rubbing after the test of the fineness of grind (Photographed with the X-Loupe G20, 150X)

2. Examine the surface of printed raw materials (paper, metal and plastic) For special materials such as metal or plastic, the X-Loupe can promptly view the smoothness of the material surface, in order to provide important referential basis when printing.

III. Applying the X-Loupe to test semi-finished products The main purpose of testing semi-finished products is to appraise and maintain the quality during the whole printing process. In the case of printing failure, to test semi-finished products is especially important because the QA (quality control) staff can learn what variables have an influence on the printed products from the manufacturing process. The following is an example of using the X-Loupe to do microscopy for the semi-finished products. 1. Examine the rub resistance of surface Rub resistance test is often used in testing the packaging. If the abrasion resistance is weak, then the printed product is very likely to be rubbed during delivery. The test done here is taking wet semi-finished product as a test object. Illustration 3.1 is the rubbing resistance tester. Illustration 3.2 is the microphotograph of the rub resistance test on the wet semi-finished product.

Illustration 2.4 shows the microphotograph of the metal surface (Photographed with the X-Loupe G20, 150X)

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Printing Quality Assurance drying time determines the time for delivery. An ink drying time tester can be used to measure the dryness of the printed matter. However, it is more difficult to monitor the level of dryness when the ink colors are lighter. In this case, the X-Loupe then can provide assistence to process the monitoring. Illustrations 3.4 and 3.5 show the ink level of dryness. Illustration 3.1 – the Rubbing Resistance Tester.

Illustration 3.4 shows that the ink is still wet (Photographed with the X-Loupe G20, 300X)

Illustration 3.2 shows the microphotograph of the wet semi-finished product after the rub resistance test (Photographed with the X-Loupe G20, 150X)

2. Examine the adhesive force If the adhesive force of the printed image is too weak, the colors might easily come off. Tests on the adhesive force are often used on printed materials such as plastic or metal, as imagaes printed on these kinds of material can come off due to external force. The test done here is using uncut plastic as the printed material. Illustration 3.3 shows the microphotograph of the adhesive force after the test. Printed image did not come off.

Illustration 3.5 shows that the ink is already dry (Photographed with the X-Loupe G20, 300X)

4. Examine the printing dots (on the printing plate) To keep consistent quality of the final printed matter depends on the quality of the printing plate. Therefore, the staff can use the X-Loupe to check if there’s a defect on the printing plate, or observe how the dots are distributed. Illustration 3.6 indicates that the dots on the printing plate are not those of traditional ones.

Illustration 3.6 is photographed with the X-Loupe G20, 150X. Illustration 3.3 shows the microphotograph of the adhesive force (Photographed with the X-Loupe G20, 150X)

3.

Examine the level of dryness

The length of time it requires to dry the printed matter is one of the main concerns of the printing firms because the

5. Examine the printing color control strip (plate control wedge on the printing plate) The distribution of dots on the printing plate can be observed clearly from the Fogra plate control wedge. In general, for better quality products, 5% and 95% of dots should emerge. If not, the finer images printed will not

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Printing Quality Assurance come into view. Illustration 3.7 shows the microphotograph of the 5% dots on the plate control wedge. Illustration 3.8 shows the microphotograph of the 95% dots on the plate control wedge. Both Illustrations show that the 5% and 95% of dots successfully emerge on the printing plate. If finer printed matter is to be printed, then the printing plate should be able to reveal smaller dots.

Illustration 3.9 is Photographed with the X-Loupe G20, 150X.

IV. Applying the X-Loupe to test finished printing products

Illustration 3.7 shows the microphotograph of the 5% dots on the plate control wedge (Photographed with the X-Loupe G20, 300X)

Howsoever the best quality of raw materials has been chosen or the whole printing process is under precise control, if the outcome of the quality of the finished products is not ideal, all these printed matter will be regarded as defects and they are to be returned to the factories. 1. Examine the surface of the finished products

Illustration 3.8 shows the microphotograph of the 95% dots on the plate control wedge (Photographed with the X-Loupe G20, 300X)

6. Examine the stripe of the 3D lenticular print For 3D lenticular printing, it is important to pay attention to the width of the stripe. If the width of the stripe of the printed matter is different from the one on the grating, the finished printed matter may not have the outcome it is supposed to have. The general stripe number for a unit includes 62 stripes per inch and 75 stripes per inch. Illustration 3.9 shows the 3D semi-finished products and the micro ruler. We can tell that the number of stripe on the grating should be 62 per inch.

The X-Loupe can observe sophisticated condition of the printed matter. Illustration 4.1 shows the dots structure of color printing. The results show that it is obviously the AM outlets. Illustration 4.2 shows the defective image with the white spot in the middle. Illustration 4.3 is the microphotograph of the stripes on the printed plastic material. This can be identified as machinery carved intaglio. Illustration 4.4 shows the comparison of the gray area in the printed matter. The upper part of the Illustration shows the gray scale, and the lower part of the Illustration shows the gray area. Illustration 4.4 shows that the gray part has more proportion of blue color, thus the gray balance setting should be adjusted.

Illustration 4.1 shows the microphotograph of color image printing (Photographed with the X-Loupe G20, 300X)

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Printing Quality Assurance

Illustration 4.2 shows image with a defect (Photographed with the X-Loupe G20, 300X)

Illustration 4.5 shows the microphotograph of surface after rubbing resistance test (Photographed with the X-Loupe G20, 150X)

3. Examine the adhesive force

Illustration 4.3 shows the microphotograph of plastic packaging printing (Photographed with the X-Loupe G20, 150X)

Illustration 4.4 shows the gray color comparison of the printed matter (Photographed with the X-Loupe G20, 150X)

2. Examine the rub resistance of surface This test uses a printed product as the testing object and a rubbing resistance tester as the tool. (Please refer to illustration 3.1) Illustration 4.5 is the microphotograph of a printed product after the rub resistance test - the object has been rubbed 1,000 times. From the test result, we can tell that the surface of the printed matter has excellent resistance to rubbing.

If the adhesive force of the printed image is weak, the color will come off easily. The adhesive force is often tested on the printed plastic and metal materials because images printed on these kinds of materials could come off easily due to external force. This test is using plastic material as the object. Illustration 4.6 is the microphotograph of the adhesive force after the test. By rubbing the image from one direction, the color then comes off the printed image.

Illustration 4.6 shows the microphotograph of the adhesive force after the test (Photographed with the X-Loupe G20, 150X)

4. Examine the printing dots The X-Loupe can be used to observe the printing dots, and in combination with image processing software, the dot area can also be calculated. Illustration 4.7 shows that the FDA is 50% (the dot value set by the computer file) on the printed matter. The calculation for the dot area is as follows: A. Using the image processing software, PhotoImpact to capture part of the image in Illustration 4.7. The dot patterns in Illustrations 4.8 and 4.9 show how the captured images are being processed in the image processing software, PhotoImpact – both are of gray scale. The dot pattern shown in illustration 4.9 is the result of processing the dot pattern in Illustration 4.8. The method is to choose the dot pattern shown in Illustration 4.8, and save it as a new image file. The saved new image file is shown in Illustration 4.9 (the dot pattern is being

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Printing Quality Assurance selected) B. Using the ‘distribution’ function of the software, we know that the total number of pixels of the dot pattern in Illustration 4.8 is 184468 (see the image on the bottom right). Illustration 4.9 shows that when the dot pattern is being selected, the total number of pixels is 90730. C. Divide 90730 by 184468, we can get 0.48, which shows that the dot area is 48%.

Illustration 4.7 shows the microphotograph of 50% of FDA (Photographed with the X-Loupe G20, 150X)

Illustration 4.9 shows the microphotograph of the magenta screen angle (Photographed with the X-Loupe G20, 150X)

Illustration 4.10 shows the microphotograph of the yellow screen angle (Photographed with the X-Loupe G20, 150X)

Illustration 4.11 shows the microphotograph of the blue screen angle (Photographed with the X-Loupe G20, 150X)

Illustration 4.8 shows the total pixels number obtained by the software Combining the X-Loupe with a protractor to measure the screen angle. Inappropriate screen angle might produce apparent moiré pattern. Therefore, how to choose the screen angle is a knowledge that the staff must learn about. Illustrations 4.9 to 4.12 show the outlets on the magenta screen, yellow screen, blue screen and black screen The screen angles are 75, 0, 15 and 45 degrees respectively.

Illustration 4.12 shows the microphotograph of the black screen angle (Photographed with the X-Loupe G20, 150X)

Combining the X-Loupe with a micro ruler, we can calculate the screen ruling. Using Illustration 4.13 as an example, there are 7 dots in 1mm, consequently, there are 177.8 dots in 1 inch. We can therefore estimate that the number of dots is 175 ruling / inch.

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Printing Quality Assurance

Illustration 4.16 shows the microphotograph of the blue solid area. The white silky line is the defective area. (Photographed with the X-Loupe G20, 150X)

Illustration 4.13 shows the microphotograph of the micro ruler and yellow dots (Photographed with the X-Loupe G20, 150X)

5. Examine the printing color control strip Combining the X-Loupe with a micro ruler, we can obtain the resolution of the printed lines. Illustration 4.14 shows that the magenta lines are part of the image printed on the resolution strip. The magenta lines are thinner than 0.25mm, and are estimated as 0.1mm.

Illustration 4.14 shows the microphotograph of a micro ruler and magenta lines (Photographed with the X-Loupe G20, 150X)

The register of printed matter is very important. If the color overlprint is inaccurate, it might affect the visual effect which the printed matter tries to present, and the image resolution will be poor, too. Using Illustration 4.17 as an example, the X-Loupe is used to observe the colors. We can find that the blue color has more inaccurate regulation. Also by using the standard magnifier that the Printing and Research Center uses to observe the vertical lines of the overlayed crosshair, we know that the difference between the blue overlay and black overlay is from 0.05mm to 0.006mm, which is lower than the margin of allowable error.

Illustration 4.17 shows the microphotograph of the overprint.

Illustration 4.15 is the well-known ‘Calibration Target’. The Calibration Target is a powerful tool used to process quality control. Illustration 4.16 shows the blue solid area of the Calibration Target. We can find white spots and a white silky line in the image. If the color density measured is based on this solid area, the data obtained may not be accurate. Illustration 4.18 shows the microphotograph of the 2.5% dot of solid area (Photographed with the X-Loupe G20, 150X)

Illustration 4.15 shows the Calibration Target.

Illustration 4.18 shows that the dot area of the magenta outlets scale is 2.5%, which indicates that these are non-traditional dots. If observed by a magnifier, we can find that the dot width is between 0.01mm and 0.02mm, which indicates that the X-Loupe at least can observe the size of dots shown in Illustration 4.18.

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