Analysis of the surface gloss of the hottest print

Analysis of surface gloss of printed matter (III)

② other printing conditions. The influence of other printing conditions on the gloss of printed matter is lack of systematic research. The printing pressure has little effect on the gloss of printed matter formed by the printing of coated paper with small absorption capacity; For non coated paper, increasing the printing pressure will reduce the gloss of the printed matter; When the change of printing speed does not lead to the change of printing ink film thickness, its effect on the gloss of printed matter is not very significant. Relevant information points out that the working conditions of the printing workshop are also related factors. The increase of relative humidity in the workshop will reduce the gloss of printed matter. The American College of Paper Chemistry (IPC) studied and explained that this is the result of the increase of paper pores due to the increase of relative humidity. In addition, the increase of workshop temperature will lead to the decrease of ink viscosity, which will also reduce the gloss of printed matter

2. Ink properties. From the previous discussion, I laid the foundation for the stable growth and momentum of Jiaozuo City. We noticed that the gloss of printed matter depends not only on the printing conditions, but also on the properties of ink and paper. In order to further clarify the mechanism of the gloss formation of printed matter, it is necessary to discuss the influence of ink properties on the gloss of printed matter and clarify the relationship between the two. The gloss of printed matter depends on the smoothness of the ink film of the fatigue tester, and the retention of binder in the ink film is conducive to the improvement of smoothness. Therefore, the ink should contain fine pigments that are evenly dispersed, and have sufficient viscosity and fast drying speed to avoid excessive penetration of binder into the paper pores. In addition, the ink should also have good fluidity, so that the ink after printing can flow flat and form a smooth ink film. The composition of ink determines the properties of ink, and various properties of ink interact with each other. It is difficult to understand the impact of a certain property on the gloss of printed matter by studying it in isolation, so it needs to be studied comprehensively

① viscosity of binder and content of pigment. According to the principle of interfacial chemistry, the capillary penetration rate decreases with the increase of liquid viscosity. Therefore, it is generally believed that the gloss of printed matter will increase with the viscosity of ink and binder. However, the actual research has reached the opposite conclusion. Figure 4-35 shows the experimental results of printing a group of binders with different viscosities and inks with different pigment contents on the same coated paper. The pigment is a kind of carbon black pigment. It can be seen from the figure that although the binder content of ink C is not high and the viscosity of binder is low, the gloss of printed matter is very high. However, the gloss of printed matter formed by printing with ink B with high binder content and high viscosity is low. This is because the high pigment content of ink C makes more small capillaries form in the ink film. Compared with the ink with low pigment content, ink C can make the ink film retain more binder. On the contrary, for inks with low pigment content (such as ink b), although the viscosity and content of the binder are high, and the instant penetration of the impression is small, the capillary penetration is slow after leaving the impression area. Finally, due to the low pigment content and the large capillary formed by the ink film, the binder penetrating into the pores of the paper increases. It can be seen from here that the capillary complex structure formed between ink and pigment particles is an important aspect to determine the gloss of printed matter. At the moment of imprinting, the ink is pressed into the larger pores of the paper as a whole; After embossing, the binder 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 binder separation. The effect of capillary retaining binder is much greater than that of printing pressure pressing binder into paper pores

in actual printing, the method of brightening oil is often used to increase the gloss of printed matter, which is completely different from increasing the pigment content of ink. These two methods of increasing the gloss of printed matter should be selected according to the composition of ink and the thickness of printing ink film. Due to the need of color restoration in color printing, the method of increasing pigment content is limited. It can be seen from figure 4-34 that when the pigment content of the ink prepared with small particle pigments decreases, the gloss of the printed matter decreases. Only when the ink film is quite thick can it produce a higher gloss in the modern history of 100 years. Therefore, with regard to the error and shortcomings of the fatigue testing machine when it works, the method of increasing the pigment content can be used to improve the gloss of the printed matter. However, the amount of pigment can only be increased to a certain limit, otherwise the pigment particles will not be completely covered by the binder, which will aggravate the light scattering phenomenon on the surface of the ink film and lead to the decrease of the gloss of the print. The situation of inks prepared with larger pigment particles is different. When the pigment content is reduced from 20% to 15%, although the color intensity is reduced, the gloss of printed matter is not greatly affected; When the pigment content is reduced to 10% and 5%, except for the low thickness of the ink film, the gloss is significantly improved, which is due to the need for a large amount of binder to cover large pigment particles

② the size and dispersion of pigment particles. As mentioned earlier, the capillary effect of ink strands is an important factor in the formation of print gloss. Small ink particles can form more small capillaries, which is conducive to improving the gloss of printed matter. However, the performance size of pigment particles in the dispersed state is more important, which directly determines the state of ink film capillary. Therefore, the pigment particles are well dispersed in the ink, reducing the flocculation phenomenon, which is conducive to improving the gloss of the print. In addition, the pigment particles are small and well dispersed, which is conducive to the formation of a smooth ink film, and is also very beneficial to improving gloss. The research of Hammel et al. Confirmed that these effects exist, pointing out that the pH value of pigment particles and the content of volatile substances in ink directly affect the dispersion of pigment particles. The low pH value of the pigment and the high content of volatile substances in the ink are conducive to the dispersion of pigment particles. This effect is very obvious on coated paper, and has little effect on non coated paper. This shows that paper is also very important to the formation of print gloss. On non coated paper with strong absorption capacity, the retention of binder in the ink film increases with the increase of pigment content, and different trends may occur only when the size of pigment particles themselves varies greatly; On coated paper with weak absorption capacity, the gloss of the printed matter is quite sensitive to the pigment condition. At this time, the gloss of the printed matter can be affected from two aspects: one is to increase the pigment content to retain the binder in the ink film; the other is to improve the dispersion of particles and use small particles to retain more binder to form a smooth ink film

③ drying time. The influence of ink drying on the gloss of printed matter is very obvious. The rapid drying of the ink film on the paper can reduce the amount of binder penetrating into the paper pores, thereby improving the gloss of the printed matter. It can be seen from table 4-7 that no matter what kind of paper, dry oil is added to the binder in the gellable ink film to reduce the penetration of binder in the pores of the paper. It can be seen that the curing of binder is also very important in the formation of print gloss

Table 4-7 changes in 7O ° angular gloss (%) of printed matter after adding dry oil to ink

paper type without dry oil and adding 2% dry oil

coated paperboard 8090

sizing paperboard 5080

non coated paperboard 3050

to sum up, it is quite complicated to adjust a certain property of ink without affecting other properties. It is necessary to comprehensively analyze the ink components and their possible changes after printing in order to adjust them

(I) (II) (III) (IV)