The gloss of a print is the closeness of the print surface’s ability to reflect incident light to that of a complete mirror reflection. The paint gloss meter is the most commonly used instrument to measure gloss level. The higher the gloss of a print, the more its surface can reflect light like a mirror, and the more it can cause a brighter appearance characteristic. The gloss level presented by the paper after printing determines whether the print is aesthetically pleasing or not. The main factors affecting the gloss of printed materials are paper, ink, printing pressure and post-press processing methods. The following describes the impact of paper, ink, printing pressure and other factors on the gloss of printed materials.
The performance of the paper on the impact of printed gloss
Printed gloss and the type of paper are highly relevant. Specifically with the paper’s surface smoothness, shine, ink absorption, strength, pH and other five aspects.
1. The smoothness of the paper on the impact of the gloss of the print
The ink film on the paper gloss determines whether the incident light can be a specular reflection. Only high smoothness of the paper produces specular reflection; if the paper’s smoothness is poor, the surface of the paper is rough, the gloss of the print will be very poor. After the paper is coated, the fine particles of the coating fill the depressions on the surface of the original paper. The paper is then supercalendered to improve the smoothness of the paper. Paper with high smoothness facilitates the formation of a uniform and smooth ink film, and the printing gloss is improved. Therefore, to obtain high gloss printing, we must use a high degree of smoothness of the paper, such as coating paper, coated paper.
2. The gloss of the paper on the impact of printed gloss
The paper itself has a good correlation between the luster and the luster of the print; the gloss of the paper determines the brightness of the print. In actual printing, to print high gloss prints, often need to use high gloss paper. The paper gloss from low to high for non-coated paper, light coated paper, coated paper, waxed paper. Coating paper surface gloss depends mainly on the paper used to lighten the material and the precision of paper processing. Lightening materials are paraffin wax, worm wax, aluminum stearate, etc. The finishing method is super calendering.
3. The paper’s ink absorption on the impact of luster
Paper is interwoven by the fiber and the formation of capillary network structure, with a large number of pores, printing is to rely on these pores to absorb ink. Paper absorption actually refers to the absorption performance of the paper on the ink. The rougher the paper, the larger the fiber gap, the stronger the absorption capacity of the linking material. The link material is the ink in the paper surface fixation of the film-forming agent, the excessive absorption of the linked material will make the ink lose leveling performance, ink pigment particles scattered on the surface of the paper can not be formed into a smooth ink film layer, so that the printed surface dull. Only the paper has a weak ink absorption to avoid excessive penetration of the ink linking material or even pigments so that the paper surface gets a bright and shiny ink film. But also can not be too poorly absorbed; otherwise, although the printing luster is good but easy to cause printing paper sticky dirt and other phenomena.
4. Paper surface strength on the impact of printed gloss
Paper surface strength is not high, printing will produce hair, powder phenomenon, the ink film of the print will be uneven, the formation of diffuse reflection of light, when the gloss of the print will decline, or even no luster.
5. The pH of the paper surface on the impact of printed gloss
The acid paper has a delayed drying effect; this is because the inorganic acid in the paper reacts with the desiccant in ink, which will reduce the activity of the desiccant, so acidic paper printing to increase the desiccant appropriately. Neutral or alkaline paper is conducive to the drying of ink. If the paper surface pH value is high (alkaline), the ink in the paper surface drying is fast, conducive to the formation of printed materials with high gloss.
Ink on the impact of printed gloss
Ink factors affecting the luster of printed matter are mainly the smoothness of the ink film, which is determined by the nature of the linked material and the number of decisions. Ink should contain a uniform dispersion of fine pigments and has sufficient viscosity and faster-drying speed to avoid excessive penetration of the linking 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. The nature of the ink on the impact of the printed gloss is mainly in the following areas.
1. the impact of ink film thickness on the printed gloss
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 gloss of printed materials. The thicker the ink film, the more the remaining linking material is, the more conducive to enhancing the luster of the printed material. Gloss increases with the thickness of the ink film and varies from paper to paper. Although the ink is the same, different paper formed by the print gloss with the ink film thickness and the trend is different. High gloss coating paper in the ink film is thin, its printed gloss with the increase in ink film thickness and reduce, this is due to the ink film to cover the paper itself original higher gloss, and the ink film itself formed gloss and due to paper absorption and reduce; With the gradual increase in ink film thickness, the paper on the absorption of the linked material after the basic saturation, its surface to retain the link material increase, gloss also continue to improve. Coating cardboard prints gloss with the increase in ink film thickness quickly, in the ink film thickness increased to 3.8μm later, the gloss will no longer increase with the increase in ink film thickness.
2. The fluidity of the ink
Ink fluidity is too large, the network increases, the size of the imprint expands, the ink layer becomes thin, poor printing gloss; ink fluidity is too small, high gloss, but poor ink transferability, is also not conducive to printing. Therefore, in order to get a better gloss, you should control the fluidity of the ink, not too big and not too small.
3. The leveling of the ink
In the printing process, the ink leveling is good, the gloss is good; poor leveling, easy to pull, the gloss is poor.
4. The content of pigments in the ink.
Generally in the printing press embossing moment, the ink is pressed into the paper as a whole within the larger pores; in a period of time after the embossing, the connecting material began to separate from the ink, was absorbed into the paper within the gap. If the pigment content of the ink is high, the ink film can form a large number of tiny capillaries. And these large numbers of tiny capillaries retain the ability to link material, then the paper surface of the fiber gap to absorb the ability to relate material is much larger. Therefore, compared with inks with low pigment content, inks with high pigment content can make the ink film retain more linkage material. Prints using inks with high pigment content have a higher gloss than those with inks with low pigment content. Therefore, the capillary network structure formed between the pigment particles of the ink is the main factor affecting the gloss of the print. In actual printing, there is another method to increase the shine of printed materials by using the method of glossy oil, which is entirely different from the method of increasing the pigment content of the ink. These two methods of increasing the luster of printed matter in the application, according to the components of the ink and printing ink film thickness to choose. The method of increasing the pigment content is limited by the need for color reproduction in color printing. Small particles of pigment formulated ink, when the pigment content decreases when the print gloss is subsequently reduced, only when the ink film is quite thick to produce a higher gloss. Therefore, this case can be used to increase the pigment content of the method to improve the luster of the print. However, the amount of pigment can only be increased to a certain limit, otherwise, the pigment particles can not be completely covered by the linked material, so that the ink film surface light scattering phenomenon intensifies instead of leading to a reduction in the gloss of the printed material.
5. The size of pigment particles and their degree of dispersion
The capillary effect of the ink film is the main reason for the formation of the printed gloss. The size of the pigment particles in the dispersion state directly determines the state of the ink film capillary, if the ink particles are small, they can form more small capillary. This increases the ability of the ink film to retain the linking material and improves the gloss of the print. At the same time, if the pigment particles are well dispersed, it also helps to form a smooth ink film, which can improve the gloss of the printed material. The limiting factors affecting the degree of pigment particle dispersion are the pH of the pigment particles and the content of volatile substances in the ink. The pH value of the pigment is low, the content of volatile substances in the ink is high, and the dispersion of pigment particles is good.
6. The transparency of the ink
High transparency of the ink formed after the ink film, part of the incident light is reflected by the surface of the ink film, and the other part reaches the surface of the paper, and then reflected out, forming two filter color, this complex reflection enriched the effect of color; and opaque pigment formed ink film, its luster is only reflected by the surface, the luster effect is certainly not as good as transparent ink.
7. The gloss of the link material
The luster of the connecting material is the main factor of whether the ink print can produce luster, the early ink connecting material to flaxseed oil, tung oil, catalpa oil and other vegetable oils, the surface of the film after the smoothness is not high, only present fatty film surface, the incident light to form a diffuse reflection, the gloss of the print is poor. And now the ink linking material to resin as the main component, the smoothness of the surface after the film of the print, the incident light diffuse reflection is reduced, and thus the luster of the print is several times higher than the early ink.
8. The speed of solvent penetration
Printing is just over, because the drying and fixation of ink has not yet been fully completed, therefore, the printing surface of the gloss is very high, such as coated paper, it is often printed on the field part of the gloss than the white paper surface 15 to 20 degrees higher, and the surface is also wet and shiny. But with the further drying and fixation of the ink, the gloss will slowly decline. This is because, when the solvent in the ink still stays on the paper surface, the ink maintains a certain degree of fluidity and has a high degree of smoothness. However, as the solvent penetrates into the paper, the smoothness of the surface is determined by the pigment particles, which are much larger than the molecules of the solvent, so the smoothness of the printing surface is forced to decline with the penetration of the solvent. In this process, the speed of solvent penetration directly affects the smoothness and gloss of the printed surface. If the penetration proceeds slowly and the oxidative polymerization of the resin proceeds at an appropriate rate, the ink surface can harden while maintaining a fairly high level of smoothness. In this way, the printing gloss can be maintained at a high level. On the contrary, if the penetration of the solvent is carried out quickly, then the polymerization of resin hardening, only in the case of printing surface smoothness has been greatly reduced to complete, so that the print gloss is significantly reduced.
Therefore, in the case of the same paper gloss, the slower the penetration rate of the ink, the higher the printing gloss. Even in the case of white paper gloss and ink penetration speed are the same, printing gloss will be different depending on the state of ink penetration on the paper surface. In general, at the same penetration speed, dense and fine penetration state is more conducive to printing gloss than thin and coarse penetration state. But reduce the ink penetration and film speed to improve the printing gloss will cause back sticky ink failure. Therefore, the improvement of paper technology alone is not able to improve the printing gloss and prevent sticky ink failure at the same time, the solution to this problem is still waiting for the improvement of ink manufacturing technology.
9. The drying form of ink
The same amount of ink using different forms of drying, the gloss is not the same, the general oxidation film drying than permeation drying gloss, because the oxidation film drying ink in the film-forming link material more.
The impact of printing pressure on the gloss of the print
Printing pressure is the key to good transfer of the print, the pressure is too large, the print expands, the gloss becomes poor; pressure is too small, the print is not clear, resulting in prints without gloss. Therefore, offset printing to ensure the correct transfer of ink on the blanket to the premise of the paper, should try to use a smaller printing pressure, relying mainly on the ink penetration and oxidation film effect drying, in order to print a good glossy prints.
Improve the glossy method
In the same paper, ink conditions, due to problems in the process operation, often resulting in a large difference in the gloss of the finished product after printing.
a. according to the different grades of printed materials to choose different glossy paper, such as for color promotional printing, in order to increase the contrast, to capture the human vision, still with high gloss coating paper. For text-based printed publications using low gloss paper, such as non-coated paper or non-glossy coated paper.
b. Increase the pH value of the fountain solution
Because the stronger the acidity of the fountain solution, the stronger the decomposition of the ink linkage and pigments, the greater the corrosive force, resulting in roughness of the film surface of the print, reducing the luster of the print. Only to improve the pH value of the fountain solution to ensure the luster of the print.
c. Add glossy pulp. Glossy pulp is processed by the high gloss raw materials, can increase the gloss of the ink, but the amount should not be too large, otherwise it will reduce the drying speed of the ink, sticky dirty, pulling phenomenon.
d. Add the withdrawal of light agent. When some ink color is too dark, does not meet the requirements of spot-color printing, it needs to be lighter. Adding lightening agent can not only make the ink lighter, but also improve the luster of the print.
e. Add 01-94 resin bright toning ink oil (also called No. 19 resin oil). When the ink flow and transferability is not good, can be directly transferred into, not only can improve the ink gloss, but also does not affect the multi-color overprint.