The effect of paper on the gloss of printed matter
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The gloss of the paper is determined by the flatness of the surface of the paper, which is related to the type of fiber, the degree of beating and calendering, the proportion of filler, the content of the compound, and the method of sizing. The main factors affecting the gloss of printed matter are the surface smoothness, ink absorption and gloss of the paper.
1. Surface smoothness of the paper
The surface smoothness of the paper, which is the time required to pass a certain amount of air in a gap between the paper and the glass under a certain pressure, in seconds (S). . The surface smoothness of various papers is different. Ordinary paper smoothness is low smoothness paper below 80S, medium smoothness paper above 80S, high smoothness paper from 300 to 600S, such as smoothness of coated paper at 800S, and paper surface clearance of about 2.5μm. The smoothness of domestic 150g/m2 special double-sided coated paper is 500S, while the foreign equivalent weight of coated paper has a smoothness of more than 1000S. The domestically produced 150g/m2 high-grade art paint paper has a smoothness of 1000 to 1500S, which is the paper with the highest standard of smoothness in China.
The smoothness of the paper actually appears as the size of the gap on the surface of the paper. Therefore, the smoothness of the paper has a great influence on the gloss of the finished product. The paper with high smoothness has good contact with the ink, which can ensure the complete reproduction of the dots and make the finished product have better gloss. After the ink is transferred to the surface of the paper. The flatness of the surface of the ink film formed on the paper is also relatively high. After the light is irradiated, a certain "specular reflection" is formed, which shows a certain brightness. On the contrary, the smoothness of the paper, the rough surface of the paper, the imprinted ink film is uneven, the light can only form a diffuse reflection, and the finished product lacks luster.
2. Paper absorbency
The ink absorbing property of paper refers to the absorption property of paper to ink binder. The coarser the paper, the larger the fiber gap and the stronger the absorption capacity of the binder. The ink absorption of different types of paper is different.
When the ink absorbing property of the paper is too large, when the ink layer is dried on the paper surface, the ink material is absorbed in a large amount, and particles such as pigments float on the surface of the blot to form a diffuse reflection, so that gloss cannot be generated. The ink absorption of the paper is too small, and the penetration of the binder is small, and the printed matter with high color and high gloss can be obtained, but at the same time, the phenomenon of slow drying, easy sticking, crystallization and the like is easily generated.
For coated paper (coated paper), there are two main reasons for affecting ink absorption: the first is the variety and dosage of the adhesive used in the coating, and the lower the ratio of the adhesive to the pigment, the absorption of the ink by the paper. The higher the coating concentration, the easier the adhesive and water in the coating penetrate into the thick paper, reducing the amount of adhesive in the coating and increasing the absorbency of the ink. Second, the pigment type and particle fineness in the paint are also related to the ink absorption. The lower the pigment particles, the easier the rubber in the coating is 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 ink absorbing property of the paper is measured by using a graduated ink absorbing tube, and the quantitative test ink sheet is coated on the test sample sheet. After reaching the specified time, the remaining ink on the paper is quickly wiped off with cotton or a clean soft cloth. Thus, the depth of the ink differs depending on the strength of the paper absorption, and then the ink on the paper is measured by a reflectometer. The reflectivity is low and the absorption is strong; otherwise, it is weak. Usually expressed as a percentage A.
3. Paper gloss
The glossiness of the paper itself also determines the gloss of the print. The gloss of the surface of the coated paper depends mainly on the glossing material used in the papermaking and the processing precision of the paper. The light-increasing materials are aluminum stearate, paraffin, and the like. The finishing method is super calendering. The paper processed by the above method has a smooth plane.
The combined effect of the gloss and ink absorbency of the paper is manifested by the surface efficiency of the paper. Specifically, the surface efficiency of the paper can be expressed by the average of the gloss and ink absorbency. which is:
Surface efficiency: [(100-A)]+G/2
Among them: A is the paper absorbency, C is the paper gloss. Using the above formula, the surface efficiency of the paper can be calculated. As shown in the table. Different papers have different surface efficiencies. Coated paper is larger than offset paper, imported coated paper Dagan domestic coated paper. The absorption of the coated paper is smaller, so that the imprint can be dried on the paper surface by means of oxidized conjunctiva, and the binder is prevented from infiltrating into the paper in a large amount, and the adverse effects such as poor gloss, pulverization and imprinting are caused. When using paper with high absorption, it is necessary to increase the amount of ink appropriately when printing, and increase the pressure to increase the density value, so it is easy to cause the compression of the tone and the level of the level. The four-color machine is slightly more absorbent than the one-color machine, because wet-wet printing requires the ink to penetrate slightly faster, which is beneficial to improve the viscosity of the ink layer on the paper (especially the first ink). The overprint rate is increased. In general, to obtain a glossy, colorful picture, it is necessary to use paper with high surface efficiency.