Printing properties of coated paper and coated paper

The name of the coated paper is relative to the non-coated paper. According to the method of paper processing, the surface of the paper coated with the calendered paper is called a coated paper. Fig. 1 and Fig. 2 are cross-sectional structural views of a non-coated paper and a coated paper, respectively. If the paper surface of the two papers is observed under a microscope (as shown in FIGS. 3 and 4 ), it can be clearly seen that the uncoated paper fiber is long and the surface microscopic smoothness is poor. Therefore, the ink absorption is strong, and it is generally used for printing a printed line or a rough wire.

After the paper is coated, the smoothness is significantly increased, creating conditions for fine dot printing. Because the coating micropores are much smaller than the micropores in the fiber layer, the ink absorption of the paper surface is significantly reduced, so that after the ink is printed on the paper surface, the liquid chain material does not penetrate a large amount into the paper, and is cured after being leveled. The film, the paper surface is flat, and the ink film is more flat, which has good printing glossiness, printing density and clear printing dots, making the printed drawing page bright in color, rich in layers and strong in three-dimensionality. Printing gloss, non-coated paper is generally only 25% or less, and coated paper is up to about 95%, so coated paper is most suitable for printing of color and fine-grained network prints. It is a paper that consumes a large amount of printed paper at present. Kind of one.

First, the type and use of coated paper

Coated paper, commonly known as coated paper, is available in a wide variety of types and can be used to print a wide variety of color prints.

Single-sided coated paper

One side is coated with calendering and one side is treated with glue. The properties of the two sides of the paper are different. It is suitable for two sides of different printing. For example, the coated side is used for color printing, and the uncoated side is used for monochrome printing.

2. Double-sided coated paper

For the two sides coated with light treatment, the bottom is shiny, with good dimensional stability, suitable for general color prints.

3 special double-sided coated paper

For the two sides coated with light treatment, compared with ordinary double-sided coated paper has a better luster, the surface is smooth and detailed, suitable for the need to show the metal-like texture of the printing of bright items.

Figure 1 Non-coated paper section structure



Figure 2 coated paper section structure



Figure 3 Non-coated paper surface structure



Figure 4 coated paper surface structure

4. Advanced Snow (Light) Coated Paper

The two sides coated with light, but the paper surface gloss is low, the surface of the silty does not hurt the eyes. It is suitable for the printing of non-reflective articles such as replicas of Chinese paintings and apparel fabrics, giving people a sense of simplicity and elegance.

5. Xinli 2000 Premium Coated Paper

For two-sided double coating and then calendered, with good gloss and smoothness, suitable for printing high-grade color prints.

6. Embossed coated paper

Double-sidedly apply the embossed (see Figure 5, Figure 6) paper. Paper gloss is low, because of the relationship between the convex pressure, the paper has a three-dimensional sense, suitable for copying of oil paintings, art advertising design and other color printing.



Figure 5 Schematic representation of single-sided embossing



Figure 6 Single-sided embossing

7. Lightweight coated paper

The surface is lightly coated and has better surface properties than non-coated papers. The quality is between the coated paper and the non-coated paper. It is produced for different needs of printed materials, such as pictorials, high-quality prints, and ivory. Dolin, Snow White, and magazine paper.

(1) Art Paper

The surface is treated with micro-coating, which has better surface performance than non-coated paper. The paper has high whiteness but low gloss and elegant feel. It is suitable for higher screen color printing than offset paper.

(2) Advanced Art Paper

In addition to the surface of the coating after a slight amount of coating, the other pressure light treatment, smooth and detailed paper. Suitable for thin screen printing. However, due to the reduction of the number of capillary holes in the paper after calendering, it has the characteristics of low ink absorption and high ink holding capacity.

(3) Ivory Road Forest Paper

The surface is micro-coated, the surface of the paper is soft and ivory, the texture is meticulous and smooth, and it has good readability, giving a sense of quality. Suitable for printing books, high-grade thin books and other printed matter.

(4) Snow White Forest Paper

Double-sided micro-coating process, the surface is smooth, high whiteness, can be stored for a hundred years without discoloration. It is suitable for the printing of high-level business and industrial journals, book books, books, magazines and other printed matters.

(5) magazine paper

The surface was lightly coated and calendered. Thin paper and high opacity. The gloss increased significantly after printing. However, due to the fact that it contains groundwood pulp, it is easier to turn yellow paper, which is suitable for print, magazines, books and other printed matter.

Second, ink absorption

Paper is a porous material formed by the interweaving of fibers. The basis for absorbing ink is the pores formed by the fiber network. Therefore, the paper's ability to absorb ink determines the permeability of the paper to the ink. Many print failures are often caused by the inability of the paper to absorb the ink and the printing conditions used. Accurately evaluating the paper's ability to absorb ink and predicting the impact on print quality is important for improving paper quality and controlling print quality.

The most reliable method for evaluating the ink absorption capacity of paper is the K&N ink test method, which has been defined as the standard test method for the paper's ink absorption in China.

The test method is as follows: The excess K&N ink is coated on the surface of the paper being tested (K&N ink is a non-drying ink formed by dispersing the white pigment in a colored oil), and the ink is allowed to remain on the surface of the paper for a certain period of time. Excessive ink is wiped off by the soft skin or absorbent cotton, and the reflectance of the soiled area and the reflectance of the clean paper surface are measured separately. The test results are expressed as K&N values, which can be calculated as follows:

K&N=RF/R∝×100%

In the formula: RF-ink reflectivity of the dirty area;

R∝ — Reflectance of blank paper (ie, clean paper).

Table 1 K&N ink absorbency of coated paper



Paper Properties Whiteness (%) Gloss (%) K&N Value (%)
128g/m2 Japanese coated paper 82.262.116.8
128g/m2 Beijing Coated Paper 81.960.630.8



From Table 1, it can be seen that the same coated paper is quantified. Although the difference in whiteness and gloss is not significant, Japanese coated paper is much less ink-absorbing than Beijing coated paper. If the same viscosity of ink is used to print under the same printing conditions, Beijing 128g/m2 coated paper, due to the absorption capacity of the ink is too large, will cause the imprint gloss to decline, the ink color is dim, and even produce "through the print" failure. For Japanese 128 g/m2 coated paper, the absorption rate of the ink is too small, the drying speed of the ink is slowed down, and the phenomenon of “scratching on the back” occurs. If the ink absorption capacity of the paper is measured in advance, the printing process can be adjusted to avoid this phenomenon.

Each paper must have absorption properties that match the printing method and printing conditions in order to obtain a firm, clear, vivid print. For example, lithographic offset printing uses mostly resin inks. The drying of paper is dependent on the oxidized conjunctiva of the ink binder. Therefore, only the paper has a weak absorption, in order to avoid excessive penetration of the ink binder material and even the pigment, so that the paper surface to obtain a bright and bright ink film. However, if the absorption is too bad, although the printing quality is good, it can easily cause the paper to become dirty when printing, affecting the graphic printing effect. Therefore, the xylene absorption of the control paper is generally 40-50s, and the printing effect is better. (Note: The xylene absorptivity test is a standard test method that has been specified in China. This method involves dropping 1 drop of xylene solution onto the surface of a paper on a special test stand to measure the complete absorption of liquid droplets on the surface of the paper and the luster of droplets. The time required to disappear, in seconds, the result).

Gravure printing uses low-viscosity volatile inks. The inks have low viscosity and rely on the volatilization of solvents. The resin forms an ink film on the paper. Therefore, the gravure printing paper has weak absorption. However, if the ink-absorption speed is too slow, the paper and the printing plate will be in close contact with each other, causing the ink to permeate everywhere to generate spots or unclear gradation, resulting in a sticky phenomenon in multi-color printing.

Copper-zinc plate printing plate on the rise of the picture, the pressure, the ink chain material is composed of non-volatile mineral oil, ink fixation on the paper is mainly dependent on the paper's ink absorption performance. Therefore, paper printed with copper-zinc printing plates should have good ink-absorbing properties so that the ink can quickly adhere to the paper.

Third, the surface efficiency

The surface efficiency of paper is not a single optical property, it is a printability that affects print quality in relation to optical properties.

The same ink is printed on different paper under the same printing conditions, and the color change is mainly manifested in the difference in hue. The hue of the ink on the paper is closely related to the surface efficiency of the paper. The surface efficiencies of the paper can be used to understand the hue shift and determine the quality of the paper for color reproduction.

Surface efficiency (PSE) is a physical quantity that combines paper glossiness and ink absorption ability to assess the quality of paper. It can be calculated as follows:

PSE(%)={100-A(%)+G(%)}/2

In the formula: PSE—paper surface efficiency;

A—paper ink absorption capacity;

G—Gloss of paper.

In the calculation, the ink absorption capacity A is calculated from the ink's K&N value as follows:

A(%)=4/3(100-K&N)

The surface efficiency of the paper can also be viewed from the GATF surface efficiency graph shown in FIG. 7 from the value of the ink absorption ability A and the gloss G value, and the value of the PSE is directly determined from FIG. 7 . For example, if the measured paper's ink absorption capacity A = 10%, gloss G = 10%, from the paper in Figure 7 found PSE = 50%.



Figure 7 GATF paper surface efficiency conversion chart

Table 2



Paper ink hue filter RGB color shift (%) grayscale (%) color efficiency (%) paper efficiency (%)
Beijing coated paper (128g/m2) Y1.68