Study on optical properties of the hottest paper

Research on the optical properties of paper

as the most important substrate material, paper has a large number of applications in printing. There are many kinds of paper with different properties. Therefore, only by fully understanding the various characteristics of paper and the relationship between various characteristics and the color rendering effect of printed matter, can we make a scientific and reasonable judgment when selecting paper and ensure the ideal printing effect when printing. The characteristics of paper can be classified from three aspects: optical characteristics, mechanical characteristics and printability. Optical properties include whiteness, gloss, opacity, etc; The mechanical characteristics include the direction, thickness, weight, folding resistance, tearing resistance, stiffness, bursting resistance, etc. of the yarn of the paper; Printability includes paper strength, permeability, smoothness, etc. 3. The selection of oil for oil pump is correct and reasonable. The following will focus on the optical properties of paper, and study the factors that affect the optical properties of paper, the test methods of optical properties and the influence of optical properties on the printing color presentation

1. Whiteness

paper whiteness is the total reflection ability of paper after being exposed to light, that is, the brightness of paper white. It is a function of the total spectral inverse partial magnification of the paper, illumination energy distribution, observation conditions and observer characteristics. When the light shines on the paper, only three situations occur. The light is reflected by the paper, transmitted through the fiber gap of the paper and absorbed by the fiber and filler

the factors that affect the whiteness of paper mainly include the whiteness of dyes, fillers, pulps and coatings used in the papermaking process

① whiteness test method

at present, several commonly used instruments for measuring whiteness in the world are to measure the reflection ability of paper to light with a main wavelength of 457nm. The standard measurement method of paper whiteness in China is the same as the TAPPI whiteness measurement method commonly used in the United States

this method is to irradiate the parallel beam on the paper surface at a 45 angle, measure the reflectivity in the normal direction of the paper, put a color filter in the incident light to filter the infrared light, and put a color filter in the reflected light to provide 457nm blue light as the measurement light. Use derrick yq-z-48b whiteness tester to measure the whiteness value of several papers

② the influence of whiteness on the color rendering of printed matter

the higher the whiteness of paper, the more accurately the characteristics of ink color can be displayed on its surface, because white paper needs to reflect back the color light synthesized by subtraction of transparent ink layer. Therefore, the paper with high whiteness can reflect almost all the color light, making the printing ink bright and pleasing to the eye, and the visual effect is good, while the paper with low whiteness, because it only absorbs part of the color light, can not faithfully show the contrast between the light and dark parts, and is easy to cause color deviation. When the whiteness value of two kinds of paper is closer, the color reproducibility is closer, the color difference value is smaller, the range of color gamut is closer, and the quality of printing is better. On the contrary, the color difference and gamut difference are large, which will have a negative impact on the printed products. Therefore, as a printing enterprise, it is necessary to choose the paper with appropriate whiteness for printing

whiteness is one of the important characteristics of paper. Generally, when two pieces of paper with slightly different whiteness but identical surface characteristics and printing ability are put together, people will still choose the one with higher whiteness and determine its high quality

2. Glossiness of paper

glossiness refers to the closeness of the specular reflection light ability of the paper to the full specular reflection ability, that is, the degree of reflection of the paper surface at a certain angle after being irradiated by incident light. For printing paper, gloss is a very important parameter for PCI. The paper sold in the market can be divided into glossy paper and matte paper. According to the gloss from low to high, the paper can be arranged into non coated paper, light coated paper, coated paper, coated paper and cast coated paper

the factors that affect the gloss of paper are mainly the smoothness of paper, whether it has been calendered, the sizing degree of paper, etc

① gloss measurement method

glossiness can be measured with a glossometer. When measuring, the reflectivity of the paper is compared with the object with known reflectivity. When measuring gloss, the results are different with the different incident angle of the selected light. The larger the incident angle, the greater the specular reflectance, the higher the gloss, and vice versa. Therefore, gloss meters can also be divided into different types according to different light incident angles, such as 25, 45, 75 angle gloss meters. For most papers, 75 is the best measurement angle. Use Drake kgz-ib glossometer to measure the glossiness of the above paper samples

② influence of gloss on printing color presentation

when the ink is dry and colored on the paper surface, its continuity and uniformity after drying conjunctiva must be affected by the paper surface state, resulting in different color effects. High gloss, under the same conditions, the color intensity of the ink is large, but the color deviation and gray scale are small, otherwise the color intensity of the ink layer is low, and the color deviation and gray scale are relatively high, causing difficulty in controlling the gray balance of color overprint. However, for text prints and paper used for writing, in order to avoid glare, strong light will stimulate the eyes, which will lead to the decline of reading quality and make people feel tired, paper with low gloss is often used. High gloss coated paper is still the mainstream in commercial printing dominated by posters

3. Opacity

the opacity of a paper is the ratio of the amount of light absorbed by the paper to the amount of light reflected. Usually, the contrast ratio is also used to describe the opacity of paper, which refers to the ratio of the diffuse reflectance of a single sheet of paper when it is backed by black and white. Most papers are transmissive

the main factors affecting the opacity of paper are reflection ability, wavelength of measured light, dye, paper quantity, apparent density (tightness), filler, size, etc. For example, increasing the quantity of paper can increase the opacity of paper. The obvious characteristics are: the opacity of paper with a quantity of 30g/m2 to 100g/m2 is most affected by the quantity. A little increase in the quantity means a large increase in the opacity. The increase in the opacity of paper with a quantity of more than 105g/m2 is limited

① test method of paper opacity

using the opacity tester can accurately measure the opacity of paper, or use the opacity measurement table to roughly measure the opacity of paper, and use the visual method to compare the opacity differences of different papers. However, when using visual methods and instruments to compare the opacity of different papers, we must realize that when the opacity of a piece of paper is 100% or completely opaque, the smaller the difference between the eyes for the opacity of the paper, the more we follow the technicians to understand the safety devices and operating procedures of the equipment of the electronic tensile testing machine. For example, The difference between 93% and 94% opacity is more obvious than that between 85% and 84%

② the influence of paper opacity on color presentation

the lower the opacity, the more the scattering interfaces between air and fibers, fillers, adhesives, and coatings, which means that the greater the porosity of the paper, the stronger the light scattering ability of the paper, and the easier it is to print through; On the contrary, the higher the opacity is, the smaller the porosity of the paper is, the less the scattering interface between air and fiber, filler, rubber and paint is, the more difficult it is for light to pass through the paper, the more difficult it is for ink to penetrate into the paper, and the less likely it is for printing to occur during printing. If the phenomenon of through printing occurs in the printing process, the pictures and texts on the front and back of the printed matter visually interfere with each other, resulting in chaotic printing pictures and texts, serious decline in the quality of the printed matter, ranging from defective products to waste products, resulting in major economic losses. To sum up, the optical properties of paper will affect the color rendering effect of printed matter, and the various properties of paper are interrelated. In some cases, they complement each other, and in other cases, they may conflict and offset each other. Therefore, when selecting paper for printing, we should comprehensively consider the various properties of paper to select appropriate paper in order to achieve the ideal printing effect