During the printing process, the ink film is transferred to the paper surface and fills the unevenness of the paper surface, making the surface of the print quite smooth. Printed ink film surface of the mirror reflection of light determines the size of the print gloss. And ink film surface with the printing conditions, paper, ink properties and the cooperation between the two.
1. Printing conditions.
① ink film thickness. Ink film thickness is the main factor affecting the luster of the printed material. After the maximum absorption of ink linkage material in the paper, the remaining linkage material is still retained in the ink film, it can effectively improve the luster of the printed material. The thicker the ink film, the more remaining linkage material, the more conducive to improving the gloss of the printed material. It was found that the tendency of gloss to increase with ink film thickness varies with different papers and different inks. Regardless of what kind of paper, gloss with the ink film thickness increases and the amount of improvement have a certain limit.
Printing with different pigment content of the ink formed by the print gloss appears very different. Obviously this difference is due to the different diameter of the ink pigment. To get accurate print gloss with the trend of ink film thickness changes, we must compare the size of the gloss formed under different ink film thickness.
② other printing conditions. Other printing conditions on the impact of printed gloss, the lack of systematic research. Printing pressure on the absorption capacity of small coating paper printing formed by the print gloss less; for non-coating paper, increase the printing pressure will reduce the print gloss; when the printing speed changes did not lead to printing ink film thickness changes, its impact on the print gloss is not very significant. Relevant information points out that the operating conditions of the printing shop is also a relevant factor. Relative humidity in the workshop to increase, will make the print gloss reduced. American Institute of Paper Chemistry (IPC) research and explanation, which is due to the increase in relative humidity led to an increase in paper porosity results. In addition, the increase in shop temperature will lead to a decrease in ink viscosity, which will also reduce the gloss of the print.
2. Ink properties.
From the previous discussion we note that the print gloss not only depends on the printing conditions, but also depends on the nature of the ink and paper. In order to further clarify the mechanism of the formation of printed gloss, it is necessary to specifically discuss the impact of ink properties on the printed gloss, to clarify the link between the two. Print gloss depends on the smoothness of the ink film, and in the ink film of the link material retained in favor of smoothness. Thus, the ink should contain a uniform dispersion of fine pigments, and has sufficient viscosity and faster drying speed, in order to avoid excessive penetration of the link material into the paper pores. In addition, the ink should also have good fluidity, in order to make the printing of the ink flow flat, the formation of a smooth ink film. Ink components determine the nature of the ink, and ink between the various properties are affected by each other, isolated study of a property, it is difficult to figure out its impact on the printed gloss, the need for a comprehensive study.
① Viscosity of the link material and the content of the pigment. According to the principle of interfacial chemistry, capillary penetration rate decreases with the increase in liquid viscosity. Therefore, it is generally believed that the print gloss will increase with the viscosity of the ink and linking material and improve. However, practical studies have come to the opposite conclusion with a group of inks with different viscosities and pigment contents printed on the same type of coated paper. The pigment is the same carbon black pigment. It can be seen that, although the linking material content of ink C is not high, the viscosity of the linking material is also low, but the print gloss is very high. While the link material content is high, the viscosity is also high ink B printing formed by the print gloss is low. This is due to the high pigment content of ink C, so that the ink film to form more small capillaries, compared with the low pigment content of the ink, ink C can make the ink film to retain more link material. On the contrary, the low pigment content of the ink (such as ink B), although the high viscosity of the link material, high content, embossing instant permeation smaller, but after leaving the embossing area capillary permeation slowly, the end because of the pigment content, the ink film formed capillary large, so that the permeation to the paper pores of the link material increased. As can be seen here, the formation of capillary network structure between the ink pigment particles is an important aspect of determining the gloss of the print. At the moment of embossing, the ink is pressed into the larger pores of the paper as a whole; after the embossing, the link material begins to separate from the ink and penetrate into the smaller pores of the paper. The size of the ink film capillary determines the amount of linkage separation. Capillary retention of the role of the link material than the printing pressure to link the material into the paper pores is much larger.
In the actual printing, often used on the glossy oil method to increase the luster of the print, this method is completely different from increasing the pigment content of the ink. These two methods of increasing the luster of the print in the application, according to the components of the ink and printing ink film thickness and choose. The need for color printing color reproduction limits the method of increasing pigment content. The ink film thickness is lower outside the gloss is significantly higher, which is due to cover the large pigment particles need a larger amount of link material.
②The size of the pigment particles and their degree of dispersion. As mentioned earlier, the capillary action of the ink strand is an important factor in the formation of the print gloss. Ink particles can form more small capillaries, thus helping to improve the luster of the print. However, the size of the pigment particles in the dispersed state is more important, which directly determines the state of the ink film capillaries. Therefore, the pigment particles are well dispersed in the ink, reducing the flocculation phenomenon, which is conducive to improving the luster of the printed matter. In addition, the pigment particles are small, well dispersed, and conducive to the formation of a smooth ink film, which is also very beneficial to improve the gloss. Hammel et al.’s study confirmed that these effects exist, pointing out that the pH of the pigment particles and the content of volatile substances in the ink directly affect the degree of dispersion of the pigment particles. The low pH of the pigment and the high content of volatile substances in the ink favor the dispersion of the pigment particles. This effect is very obvious in the coating paper, almost nothing in the non-coating paper. This shows that the paper is also very important for the formation of the gloss of the print. In the absorption capacity of the non-coating paper, the ink film in the retention of the link material with the increase in pigment content, only in the pigment particles themselves when the size of a large difference may appear different trends; in the absorption capacity of weak coating paper, the luster of the print on the pigment condition is quite sensitive, which can be affected from two aspects of the print luster: one is to increase the pigment content to retain the link material in the ink film, the second is to improve the The degree of dispersion of particles and the use of small particles to retain more linkage material to form a smooth ink film.
③Drying time. When the ink dries, the impact on the gloss of the print is very obvious. Ink film in the paper surface to dry quickly can reduce the amount of link material penetration into the pores of the paper, thereby improving the gloss of the printed material. In the process of forming the gloss of the print, the curing of the linking material is also important.
In summary, to adjust the ink without affecting the other properties of a particular property, is a rather complex matter. Need a comprehensive analysis of the ink components and their possible changes after printing, in order to adjust well.
3. Paper properties.
① due to the interweaving of fibers and the formation of capillary network structure, so that the paper has a large number of pores, which becomes the basis for its absorption of ink. Paper capillary network of ink link material absorption time and link material fixation time between the balance determines the formation of printed gloss when the link material penetration degree. Tollenaar has conducted research in this area for many years. He pointed out that the greatest impact on the printed gloss is not the average size of the paper pores, but the size distribution and number of pores.
However, from the current paper quality control methods, the number of pores or absorption capacity measurement and print gloss between the correlation is poor.
Smoothness and luster. Paper smoothness and its own luster also affects the print gloss. High smoothness is conducive to the formation of uniform and smooth ink film, thereby improving the print gloss. This has been confirmed by many researchers in the study. The paper itself is good luster can improve the reflectivity of the ink film, especially for transparent ink is more so. There is an excellent correlation between print gloss and paper itself gloss, better than the correlation between print gloss and paper absorption capacity.
From the above discussion, it can be found that there is also a correlation between paper smoothness, gloss and absorbency. It is easy to explain this from the papermaking process. For example, calendering improves the smoothness and gloss of the paper, while also reducing the amount of pore space in the paper and thus the paper’s absorptive capacity. In addition, the paper surface pH is also a non-negligible factor in the formation of printed gloss. pH is high, which is conducive to ink drying, and thus conducive to improving the gloss of printed materials.
4. The interrelationship between paper and ink.
More and more research has found that the interrelationship between paper and ink has the greatest impact on the luster of printed materials. According to the findings of Feskp et al. The higher the gloss of the print; and another certain ink printing is almost unaffected by the variety of paperboard. This shows that the effect of gloss on the print formed by ink printing cannot be predicted by using only one type of paper.