Analysis of Surface Glossiness of Prints (4)
3. Paper properties.
1 Due to the formation of a capillary network due to the interweaving of fibers, the paper has a large number of pores and serves as the basis for ink absorption. The balance between the absorption time of the ink binder and the bonding time of the binder by the paper capillary network determines the degree of penetration of the binder during gloss formation. The gloss of general prints decreases with the increase of paper absorption capacity. Tollenaar conducted many years of research in this area. He pointed out that the greatest impact on the gloss of printed paper is not the average size of the paper pores, but the distribution and number of pores.
However, from the current paper quality control methods, the correlation between the measurement of the number of pores or absorption capacity and the gloss of prints is poor. As shown in Table 4-8, this table is the correlation coefficient between the measurement results of several absorption capacity measurement methods and the gloss of prints. As can be seen from the table, the K&N ink test and Vanceometer's measurement of the heavy oil reflectance method at 20 s have the best correlation with the print gloss, and it can be considered that these two methods are the best methods for measuring the paper absorptivity.
Table 4-8 Correlation coefficient between absorbency measurement and print gloss (r)
1. Vanceometer
Light oil
5s
20s
2s
0.846
0.678
0.452
0.824
0.726
0.657
0.838
0.569
0.486
0.899
0.667
0.518
0.852
0.660
0.531
heavy oil
5s
20s
1s
0.722
0.942
0.878
0.636
0.925
0.889
0.829
0.822
0.87O
0.771
0.905
0.870
0.740
0.899
0.858
Blue ink
2min
10min
0.615
0.772
0.483
0.451
0.766
0.742
0.672
0.836
0.634
0.701
2. Ink contamination test
Hull black ink
Hull Red ink
K&N ink 0.890
0.875
0.860 0.880
0.880
0.835 0.880
0.892
0.920 0.921
0.912
0.962 0.893
0.890
0.894
3. Drop test 0.690 0.690 0.625 0.664 0.686
4. Porosity -0.597 -0.573 -0.684 -0.661 -0.629
Smoothness and luster. Paper smoothness and its own gloss also affect the gloss of the printed matter. High smoothness is conducive to the formation of a uniform and smooth ink film, thereby improving the gloss of prints. This has been confirmed in many researchers' studies. The good gloss of the paper itself can increase the reflectance of the ink film, especially for transparent inks. Figure 4-36 shows the results of two inks printed on four different gloss coated papers. It can be seen from the figure that the gloss of the two inks increases with the improvement of the gloss of the paper itself. Borchers' study also found that there is an excellent correlation between the gloss of the printed matter and the gloss of the paper itself, which is better than the correlation between the gloss of the printed matter and the absorptive capacity of the paper.
From the above discussion, it can be found that there is also a correlation between paper smoothness, gloss, and absorptive capacity. This is easily explained from the papermaking process. For example, calendering can improve the smoothness and gloss of the paper while also reducing the amount of paper porosity, thereby reducing the paper's ability to absorb. In addition, the paper surface pH is also a non-negligible factor in the formation of print gloss. The high pH value is good for the drying of the ink, which helps to improve the gloss of the print.
4. The relationship between paper and ink. More and more studies have found that the relationship between paper and ink has the greatest influence on the gloss of prints. The results of the same group of studies by Feskp et al. are presented below to illustrate this issue. Figure 4-37 shows the relationship between five kinds of blue inks printed on four kinds of paperboards with different absorption capacities. The absorptive capacity of the four kinds of paperboards was measured using a Vanceometer instrument: a heavy oil was rolled on the surface of the cardboard for 20s. The specular reflectance was measured. As can be seen from the figure, a kind of cardboard is printed with different inks, and the gloss of the obtained prints is different. The order of the luster of printed matter formed by printing on the four kinds of paperboards with 5 inks is also different. Paperboard A is printed with 5 inks to form a print with a gloss level of 1, 2, 3, 4, and 5. Paperboard D printed with 5 kinds of ink to form the print gloss order: 4,2,1,5,3. It can be seen that the gloss of prints formed by printing with certain inks (such as inks 2, 4 and 5) is significantly affected by the variety of paperboards. The smaller the absorbent capacity of the cardboard (ie, the greater the reading of the Vanceometer instrument), the higher the gloss of the print; while printing of another ink (such as ink 1, 3) is almost unaffected by the variety of cardboard. This shows that the use of only one type of paper cannot predict the effect of the gloss of the prints formed by ink printing.
Figure 4-38 shows another set of test results. This group of experiments is to print the gloss of different papers on different papers in Figure 4-38. Two different colors of ink (magenta black and cyan ink) are printed on four kinds of cardboard respectively, and the gloss of the print is measured at an angle of 60°. As can be seen from Figure 4-38, the order of the gloss of the printed matter formed by printing four types of paperboard with red ink is: B, C, A, D. The print gloss of the cardboard B is much higher than the other three; the printed matter formed by printing with the blue ink. The order of gloss is: A, D, C, B. We have noticed that when the cardboard B product is printed with red ink, the gloss of the printed matter formed is the highest, and the gloss of the printed matter formed when printing with the blue ink is the lowest. This shows that the use of only one type of ink cannot accurately predict the effect of the gloss of the print formed by the paper printing.
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