Nowadays, the requirements for the quality of printed matter are higher and higher, especially for packaging and printing, and the appearance quality is more prominent. Moreover, due to different occasions, the requirements for the wear resistance of the ink layer are also different. It directly affects the customer's satisfaction with the print quality. Therefore, many printing plants, especially packaging and printing plants, have generally adopted some inspection instruments, such as densitometers and friction testing machines, to inspect the printing quality in order to ensure the stability of printing colors and the abrasion resistance of ink layers.
In the printing of cartons and cigarette packs, the control of the abrasion resistance of the ink layer is particularly important. If the control is improper, the product will cause the ink layer to fall off due to storage, transportation, removal, etc., which will seriously affect the appearance of the printed product and ultimately affect the interests of users. It is understood that there are several methods for controlling the abrasion resistance of ink layers in printing production:
1) Adopt the friction tester and spectrodensitometer and strictly implement the national standard. Most of these manufacturers are powerful manufacturers that can control the wear resistance of the ink layer.
2) Use a friction tester to test the wear resistance based on the change of the specimen before and after the friction, but it is impossible to quantify the wear resistance. At present, such manufacturers account for the majority, and most of their customers can accept it.
3) Without using test equipment, the wear resistance can be mastered by experience in production, that is, through visual inspection, hand touch, it can also make the wear resistance controlled within the specified range, but it has a great dependence on people. Such manufacturers also account for a certain number.
In order to promote more rigorous and quantitative printing quality control, special test instruments should be used as far as possible. The following is a brief introduction to the detection technology and testing methods of ink layer wear resistance.
Detection of the abrasion resistance of the ink in the test instrument requires the use of a friction tester and a color densitometer.
1. Requirements for the friction tester 1 Friction body: 2 pieces of rubber having a hardness of HS 50 to 53, an area of ​​25 mm x 50 mm, a thickness of 8 mm, and a distance of approximately 45 mm. 2 Friction speed: 43±2 times per minute, stroke 60mm. 3 Load: 20±0.2N.
2. The color densitometer densitometer test error should be ≤ ± 0.02D, can use X-rite series 500-type spectrophotometer, which can measure CMYK four-color density, the precision up to 0.001D.
Test conditions 1 The friction paper is 80 g/m 2 clean offset paper with a width of 50 mm. According to experience, office A4 printing paper can also meet this requirement.
2 The standard of friction frequency is 40 times back and forth, and the friction testing machine of Xinli Company is set 0-999 times, and different times can be set according to user requirements.
3. Test procedure 1 The sample cut to a certain size is fixed on the friction table. The area of ​​the ink layer to be measured is larger than the area of ​​the friction body. Generally, the area is 300 mm×55 mm, and as far as possible, the sample with uniform color is adopted to facilitate measurement.
2 Measure the color density of the ink layer to be tested on the sample, and measure the average value at 3 points. The maximum density of four-color medium density should be taken as the measured value.
3 Fix the friction paper on the friction body, and gently place the friction body on the sample to be rubbed.
4 Set the number of frictions (40 times), turn the friction tester on and off 40 times, and stop to remove the sample.
5 Measure color density on the most heavily rubbed ink layer. Measure 3 points and average.
4. Test results and standard print ink abrasion resistance is calculated as follows: Ink resistance = D/D0×100%; where D0: average density before rubbing; D: average density after rubbing .
The national standard (GB7706-87) stipulates that the wear resistance of decorating printed matter should be ≥70%. This standard is applicable to printed decorative prints that are printed using a flexographic printing process. It does not apply to plastic film prints. This indicator can effectively guide the printing plant to control the ink layer. When the wear resistance is low, the production process can be adjusted as soon as possible to reduce the number of non-conforming products; at the same time, the quality of the product can be graded based on this parameter. .