5. Gloss
The concept of gloss includes paper gloss and print gloss. The print glossiness of a paper refers to the fact that, under the specified conditions, the solid gloss ink is used to perform solid printing on a paper sample, and after drying, the glossiness of the blot area is measured and expressed as a percentage.
Gloss is a unique index of coated paper, which has a great influence on the aesthetic and three-dimensional impression of the printing effect. There is a very important relationship between the amount of coating and the integrity of the base paper coverage and gloss. The minimum requirements for paper gloss and print gloss for offset printing coated papers were 60% and 88%, respectively.
6. Absorptivity
Absorption of paper refers to the paper's ability to absorb the binder and its solvent in the ink, which is usually expressed as a percentage. Absorption of paper is also called ink absorption. Its strength is very obvious on the printing hue and the gloss of the ink layer. In paper with strong ink absorption, the hue of printed ink tends to fade, and the ink layer also lacks gloss. In addition, since the binder in the ink is mostly absorbed by the fibrous tissue of the paper, the pigment particles are not sufficiently protected, the ink film on the print is not firm, and the phenomenon of “powdering†of the print is likely to occur. Conversely, if the ink absorption property of the paper is too weak, the ink layer of the print product will not be adhered securely, and the print will not be easily dried, which may cause the back of the print product to become dirty.
7. Smoothness
The smoothness of the paper is a technical indicator for evaluating the degree of surface roughness of the paper, and is a physical quantity indicating the level, smoothness, and uniformity of the surface of the paper. That is, under certain vacuum conditions, the volume of air, measured in seconds, is measured as the time it takes for the air to flow between the surface of the paper test specimen under a certain pressure and the smooth glass surface. The higher the number of seconds, the better the smoothness. The better the paper smoothness, the more uniform and complete the contact between the paper and the printing plate at the time of printing. The more the ink layer on the layout (topography) or blanket is transferred, the better the color rendering of the print. On the other hand, paper with poor smoothness has uneven ink transfer, and the paper has a strong penetrability with respect to the amount of ink, and the color rendering effect is also poor, and the ink of the printed product tends to be faded or faded. The smoothness of the paper directly determines the print quality of the printed matter.
Third, improve the suitability of coated paper printing
As a high-grade printing paper, coated paper not only needs to be able to adapt to the printing requirements of various advanced printing machines, but also has bright colors, clear and vivid images after printing, and requires suitable prices, accurate product positioning, and high cost performance. The improvement of the printability of coated paper is not simply achievable from a certain point of improvement. It is necessary to work hard from the three aspects of the base paper, coating formulation, and on-site production management, from the raw materials (including the physical indicators of the base paper), the control of the coating formulation (including the improvement of the coating properties), to the subsequent sequence of finishing and a series of processes. There is a need for strict requirements, and only in this way is it possible to obtain coated paper with good quality and good printing performance.
Base paper
The non-coated paper used to produce coated paper is called base paper. The base paper has a great influence on the production and quality of coated paper. Therefore, there are special requirements for the composition, strength, surface properties and absorbency of the base paper.
1 raw paper composition
The coated paper base paper generally contains about 70% hardwood pulp, and the remainder is softwood pulp. It is generally required that the original paper has high tensile strength and surface strength. In order to increase the strength of the base paper, in addition to improving the composition of the slurry, it is sometimes possible to appropriately increase the degree of beating and surface sizing.
2 surface properties
The surface properties of coated paper base paper are relatively strict. The base paper must not be too rough or too smooth. Too rough raw paper can not meet the printing requirements even if the surface smoothness after coating is too smooth, the effective bonding area between the coating and the base paper is small, and the bond strength between the coating layer and the paper surface after coating is insufficient.
3 Absorption and uniformity
The attractiveness of the base paper is moderate, the absorption is too large, and the powder dropping phenomenon easily occurs after coating: Absorption is poor, and the base paper is not bonded to the coating layer after coating. The uniformity of the base paper is better to facilitate the uniform coating.
2. Control of coating properties
1 Coating
Coated paper must first have two major characteristics: that is, coating adaptability and printability. Coating adaptability means that a uniform coating amount can be achieved at the time of coating. The printability of printing is the effect of smooth printing quality.
The coating has a wide range of concentrations and can be between 30 and 70%. In general, the higher the concentration, the greater the viscosity and the poorer the flowability, which will affect the uniformity of the coating.
2 coating amount
When the coating amount becomes larger within a certain range, the smoothness of the paper is improved, the dot appearance effect is good, the ink absorption is uniform, and the ink receiving performance is good, and the ink is easily transferred to the coating surface uniformly, thereby achieving improved coating. The purpose of printing paper adaptability.
3. Development of new printing paper special printability improver
Combining the production process of coated paper, research and development of printability improver for coated paper is one of the important ways to improve the printability of coated paper in the future. For example, the “Printability Improvement Aid for Coated Paper†once developed by the Hangzhou Chemical Research Institute showed good results in use, resulting in a significant improvement in the printability of coated paper and a significant increase in the quality of coated paper products. Moreover, the product has a reasonable production process and low cost, meets environmental protection requirements, and has good economic benefits.
Source: Guangdong Printing