Printing ink
The ink color is provided by two types of materials, one is a dye and the other is a pigment.
1. Dyes
The characteristics of dyes are transparent, through selective absorption of certain spectral components in the incident light to make the transmitted light change color. Therefore, dye ink can be used not only to print color photos, but also to print transparent light box sheets. In traditional color photos and transparent positive films, dyes are used for color formation.
The raw materials of many kinds of dyes are insoluble in water, so some special solvents are needed to first melt them and then add water to dilute them. Some of these dye-dissolving solvents are harmful to the materials used to make ink heads. When the sample is injected into the ink head, the ink head is quickly damaged. The reason for this is that the solvent causes damage to the ink head.
The durability of ink is basically determined by the original material of the dye. Magenta in EPSON dye ink is a less durable color. Use it to print color cards on matt paper, and found that if exposed to the air, you don't need to see the light. As long as one month, the color will fade a lot, making the gray scale become green. The EPSON ink copied by some manufacturers is even more terrible. After printing tonight, if it is not coated in time, it will fade the next morning.
Ink should be used in different printers and other things must be added to change its viscosity, surface tension, and possibly thermal expansion coefficient or boiling point, etc., so that different printers can be ejected smoothly. These additives should also be safe for the ink head. The solvents and additives used in different printers make different printers have different selectivity for paper. As everyone knows that EPSON dye ink printers are very picky, but if its ink is replaced, it can be used as any paper like HP printers.
In the process of preparing compatible inks from different manufacturers, most of the inks are not formulated with a single dye. The phenomenon is that most of the inks on the market have higher color saturation than original inks. We usually need to mix two to three inks to produce colors close to the original inks.
2. Pigments
Pigment inks used to be made from mineral pigments after grinding. Today's pigments may also have non-mineral materials. Generally speaking, it is made of solid pigments after grinding and emulsification. Its main feature is relatively durable, the coarser the particles, the more durable. It is not very transparent. It can also be seen from the ink bottle, it is a bit like milk. Therefore it cannot be used to print transparencies. Because it is opaque, the saturation of its synthetic colors: red, green, and blue is also relatively low.
No oily ink is used in small printers. Only large outdoor sprayers use oily ink. This kind of ink is similar to printing ink, but printing ink usually uses transparent dyes, and outdoor sprayers use inks formulated with pigments. The spray holes of outdoor sprayers are very large and not easy to block. This ink uses organic solvents and film-forming agents, like paint. The requirements on the material surface are very low. Both water-resistant and light-resistant, but the quality is not very good.
Ink color matching problem
There are three main parameters of ink color similarity: hue, color saturation, and density. We usually use several types of inks to make it consistent with the original ink.
What is more difficult to deal with is another factor
Since human eyes can also cause artifacts in human observation, matching the three primary colors of yellow, magenta, and cyan does not mean that the colors mixed with these inks are consistent with the original ink. The reason is that the color looks the same, and its absorption spectrum may be different. Therefore, the absorption spectrum produced by the mixing of the two types of dyes must be different, and the resulting color may be different. Mainly manifested in the different colors of red, green and blue. Therefore, when choosing the original ink, we must also take care of the matching degree of these three mixed colors. If the six colors match well, the remaining problems are not big. Because in the printing software, the color formation mainly depends on these 6 colors to construct other colors by the additive method.
Printing paper and matching with ink
Let's first discuss reflective printing paper. The main purpose of the printing paper coating is to absorb ink faster and prevent the ink from spreading laterally. The ink absorption capacity of ordinary offset paper is also good, but it cannot prevent the lateral diffusion of ink, so the resulting image is not high in definition, and the color saturation is extremely low.
We may usually notice that the surface of the plaster or whitewashed wall skin can also absorb ink, and the dot spread is relatively small. Therefore, we use something similar to gypsum powder for coating, the print quality will be better. Coated paper is this kind of thing. Of course, it may not be coated with gypsum powder. It is made of some white fine powder mixed with some binder, and there are many small holes in the middle to absorb ink. After the ink drops, it spreads in both depth and horizontal direction. Compared with offset paper, its horizontal spread is smaller, so the clarity and color saturation are better. In addition, its pores are relatively large, no matter what kind of ink can be absorbed. But after the moisture of the ink evaporates, these pores also become a smooth channel for the air to enter, so the photos printed on the coated paper fade faster. Pictures printed with HP printers will fade by more than 30% after one year. The coating of the coated paper is still not strong enough, and the powder can be wiped off with a light stroke, and it cannot be protected by laminating.
Another disadvantage of coated paper is that the diffuse reflection formed by the rough surface structure makes the maximum density of the photo not very high, usually only reaching the level of 1.6, and sometimes reaching 2.0 with special black ink. However, due to the opaque coating, the level of the dark part is not good.
The printing paper developed with coated paper as the basic technology is called powder coated paper by many people. Although the degree of dot spread is different, their defects are common.
High-gloss photo paper for printing is very different from coated paper. Especially for high-gloss photo paper for traditional printers such as Hewlett-Packard and Novajet, if we use a little water droplet on it, the surface coating will become sticky. But it is transparent again, and it makes us feel like animal glue. However, the current coating probably uses high molecular organic compounds, and will not use the bovine bone glue or pig skin glue used in the film. When a drop of ink drops on it, we will find that the coating bulges obviously after absorbing water. Obviously this "glue" absorbs water and dye molecules into its own microstructure and makes itself soft and swell. A good coating does not absorb ink fast, but absorbs ink slowly, and the surface tension of the coating is relatively large, so that the ink droplets do not infiltrate around like water drops on the lotus leaf when they are not drawn into the "glue" Then slowly suck it into the "glue". After the water volatilizes, the "gel" shrinks and wraps the dye tightly. The thick-coated printing paper has strong ink absorption capacity and small horizontal spread. This kind of printing paper can be printed with a relatively large amount of ink. The printed photos are clear and sharp, the density of dark parts is large, and the layers are crystal clear. We once bought a paper that had been coated twice, and the printing effect was excellent. Our recently customized canvas is coated twice.
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