The effect of paper on the gloss of prints

The gloss of paper is determined by the degree of flatness of the paper surface, which is related to the type of fiber, the degree of beating and calendering, the content ratio of the filler, the rubber, and the sizing method. The main factor affecting the glossiness of printed paper is the surface smoothness, ink absorption, and gloss of the paper.

Paper surface smoothness

The surface smoothness of paper, which represents the time required for a certain amount of air to pass through the gap between paper and glass when a certain area of ​​paper is under certain pressure, in seconds (S) . The surface smoothness of various papers is different. Ordinary paper smoothness below 80S is a low smoothness paper, 80S or more is a medium smoothness paper, 300~600S is a high smoothness paper, if the coated paper has a smoothness of 800S, the paper surface gap is about 2.5μm. The smoothness of domestic 150g/m2 premium double-sided coated paper is 500S, while the same gram of coated paper abroad, the smoothness of more than 1000S. Domestically produced 150g/m2 advanced fine arts coating paper with a smoothness of 1000 to 1500S is the highest grade paper in China.

The level of smoothness of paper is actually represented by the size of the gap on the surface of the paper. Therefore, the level of smoothness has a great influence on the gloss of the finished product. The paper with high smoothness has good contact with the ink and can ensure that the dots are completely reproduced and the finished product has a good gloss. After the ink is transferred to the surface of the paper. The surface roughness of the ink film formed on the paper is also relatively high. After the light is irradiated, a certain "mirror reflection" is formed, showing a certain brightness. On the other hand, poor smoothness, rough surfaced paper, and uneven imprinted ink film can only form diffuse reflections on light, and the finished product lacks luster.

2. Ink absorption of paper

The absorbency of paper refers to the absorption performance of the paper to the ink binder. The more rough the paper, the larger the fiber gap, and the stronger the absorption ability of the binder. The ink absorption of different types of paper is different.

When the ink absorption of the paper is too large, and the ink layer is dried on the paper surface, the ink binder material is absorbed in a large amount, and the pigment and other particles float on the surface of the print to form a diffuse reflection, so that no gloss can be produced. The ink absorption of the paper is too small, the penetration of the linking material is small, and a printed product with a vivid color and high gloss can be obtained, but at the same time, it is prone to phenomena such as slow drying, easy adhesion, and crystallization.

For coated paper (coated paper), there are two main factors affecting ink absorption: The first is the type and amount of adhesive used in the coating. The lower the ratio of adhesive to the pigment, the lower the ink absorption of the paper. The higher; the lower the coating concentration, the easier the adhesive and water in the coating can penetrate into the thick paper, reducing the amount of adhesive in the coating and increasing the ink absorption. Second, pigments in the paint and fineness of the particles are also related to ink absorption. The lower the pigment particles are, the less likely the rubber in the coating is to be transferred to the paper base: the coarser the pigment particles, the larger the particle gap. The greater the absorbency of the ink, the worse the gloss effect of the print.

The determination of the ink absorption of the paper is the use of a calibrated ink-absorbing tube. The quantitative test ink is coated on the test sample sheet. After reaching the prescribed time, the remaining ink on the paper is quickly wiped off with cotton or a clean soft cloth. In this way, the depth of the ink varies with the absorption of the paper, and then the reflectance of the paper is measured using a reflectometer. The reflectivity is low and the absorption is strong; otherwise, it is weak. Usually expressed as a percentage of A.

3. Gloss of paper

The quality of the gloss of the paper itself also determines the glossiness of the print. How the gloss of the coated paper surface depends on the light-enhancing materials used in papermaking and the precision of the paper. Lightening materials include aluminum stearate and paraffin wax. The finishing method is super calendering. Paper produced by the above method has a smooth surface.

The combined effect of glossiness and ink absorption of the paper is expressed as the surface efficiency of the paper. Specifically, the surface efficiency of the paper can be represented by the average value of gloss and ink absorbency. which is:

Surface efficiency: [(100-A)] + G/2

Among them: A is the paper absorbs the ink, C is the paper glossiness Uses the above-mentioned formula to be able to calculate the surface efficiency of the paper. As shown in the table. Different papers have different surface efficiencies. Coated paper is larger than offset paper, and imported copperplate paper is made into dried copperplate paper. The absorption of coated paper is smaller, so that the print can be dried on the surface of the paper by means of an oxidized conjunctiva, avoiding a large amount of the binder material penetrating into the paper, and having undesirable effects such as poor gloss, chalking, and imprinting. The use of high-absorbency paper, printing should increase the amount of ink, and increase the pressure to increase the density value, it is easy to cause tone compression, hierarchical and parallel. Four-color printing machine than the monochrome machine printing paper suction slightly larger, because wet-wet printing hope that the ink penetration speed is slightly faster, help to improve the paper ink layer viscosity (especially the first printing of ink), so that after printing Overprint rate increased. In general, to obtain a glossy, colorful picture, it is necessary to use paper with high surface efficiency.

Reprinted from: China LED Advertising Lighting Network