Determination and index of the whiteness of the ho

The measurement and index of paper whiteness

the problem of paper whiteness is generally encountered in the production and marketing process of the printing industry. Because the whiteness problem will directly affect the color rendering effect of the product, which is the most important appearance performance quality in the paper properties. Whiteness refers to the whiteness of paper, which is the reflection ability of light waves in the full wavelength range. The whole application range of light includes electromagnetic amplitude radiation, such as X-ray, ultraviolet, infrared and microwave. Light is just a carrier. The whole image can be produced by tensile test or point by point scanning before the shoelace leaves the factory at the same time. However, the final receiver is the human eye. Therefore, whether it is an imaging or a fast scanning imaging, according to the observer's vision, the scanning should be fast enough to make people feel that a complete image appears in a certain field of vision. To achieve this effect, the speed of the image passing through the human eye must reach at least 40 times per second, so that the human eye can feel the continuity of the image. Here we need to introduce several concepts related to this. The law of linear propagation of light; Light travels in a straight line in a uniform medium. Reflection law; The incident ray, reflection ray and normal are in the same plane, and the incident angle is equal to the reflection angle. The optical path difference (POD) of the wave to the ideal spherical surface can be expressed by the formula:

opd=s1 (x02+y02) + s2y0{(x02+y02) h0`+s3 (x02+3y02) h0`2+s4 (x02+y02) h0`2+s5y0h0`3. The coefficients S1, S2... S5 are called sader, representing spherical aberration, smart aberration, astigmatism, Tangqu and domain change respectively.

then, how to measure the whiteness (also known as brightness) of paper And? At present, the whiteness of paper is mostly determined by measurement in China. However, due to the continuous development of the paper industry, various fillers, dyes, oba and other papermaking chemical additives are added to the paper, so the measured whiteness can not accurately reflect the whiteness of visual acceptance. Therefore, the whiteness of paper has long been measured by visual whiteness in the world

whiteness measures the whiteness of paper by the reflection value of light wave with the measurement wavelength of 457mm (about 380 ~ 510mm) on the sample. It is commonly used in measuring the whiteness of pulp. At present, there are mainly two different measurement methods in the world, namely, ISO brightness and tappl brightness of paper brightness specified by the international organization for standardization. The main difference between the two lies in the angle of light, the size of the sample and the accuracy of the instrument, while the whiteness is measured only by the reflection of the paper on the light wave, and the visual characteristics of the eyes are not always considered, so it is not objective. Generally speaking, color is the impression generated by the light emitted and reflected by objects through vision. For example, sunlight has seven colors (red, orange, yellow, green, green, blue, purple), which are all objective, and are all colors reflected in human vision through light wave reflection. The measurement of whiteness is based on the visual characteristics of human eyes. Therefore, a negative value can be generated more accurately to reflect the whiteness of the paper. It is based on the visual characteristics of human eyes. Through a large number of experiments to calibrate the wavelength and intensity of the three primary colors (red, green, blue), and then determine the three primary color quantities x, y, Z of a specific color through the additive method, and establish the three color phase diagram, so as to correspond the color with the three stimulus values one by one. Different colors can be described by different numbers. When we measure the whiteness of paper, we can get different secondary tristimulus values, and thus get the visual whiteness

to sum up, whiteness and visual whiteness are both indicators to reflect the whiteness of paper. The two are closely related. Generally speaking, the whiteness is high, and the visual whiteness is also high, but sometimes the whiteness is high, and the visual whiteness is not necessarily high. For example, high-end cultural paper, with many dyes, additives, brighteners, enhancers, wet strength agents, emulsifiers, fluorescent agents and other chemicals, has a high apparent whiteness, but the whiteness changes little

therefore, in real life, it is common for the printing industry to mix whiteness and visual whiteness. It can be seen that the measurement and indicators of whiteness and visual whiteness must be constantly explored and summarized through practice. When there is too much oxide skin, we must improve our understanding. In this way, it will bring ideal results to the products and sales of the printing industry, which is greatly beneficial

source: Printed today