The hottest printing paper and printing quality 1

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Printing paper and printing quality

physical properties of paper

I. basis weight

quantitative is commonly known as gram weight, which refers to the weight of paper per unit area, expressed in grams per square meter. Generally, paper with a ration below 250 g/m2 is called paper; Those with a ration of more than 250 g/m2 are called paperboard or paperboard. Quantitative is the most basic physical index of paper. Its level and uniformity affect all physical and printing properties of paper

II. Thickness and tightness

thickness refers to the thickness of paper or paperboard directly measured under a certain pressure between two measuring plates, in mm or μ M meter. Generally, the thickness directly affects the opacity of the paper, and the greater the thickness, the better the opacity. The uniformity of thickness has great influence on the paper, especially the energy measurement range of the heavy drop hammer impact testing machine 300j. Three experiments can be carried out: a method, B method and C method. The uneven thickness will affect the decline of gloss and whiteness and the instability of harmonic color reproduction

tightness refers to the weight per unit volume of paper, also known as density, which is calculated by dividing the quantity by the thickness

tightness is a physical index to measure the density of the paper structure. For the paper with the same paper fiber, the greater the tightness, the denser the paper is. On the contrary, the looser the paper is. The tightness of paper is in direct proportion to its tensile strength

III. tensile strength

tensile strength is the maximum tensile force that the operator can bear before breaking the paper or paperboard of unit width under the conditions specified in the standard test method. When the paper is stretched by tension, the paper will stretch in the direction of the force. When the tension increases to make the spline break, the elongation reaches the limit. At this time, the ratio of the length of elongation to the original length is called elongation, which is expressed in percentage

for web printing, the tensile strength and elongation of paper are important indicators. Because the paper roll is driven by the rotary press, the paper will be under great tension. If the tensile strength is too small, it will cause paper breakage; If the elongation is too large, it will change the size of the paper and increase the overprint error. Therefore, the use of paper with high tensile strength and low elongation can effectively prevent and reduce paper breakage in printing and reduce overprint error

IV. folding resistance

the folding resistance of paper refers to the number of folds that the sample can withstand before breaking in a special instrument under the specified test conditions, expressed in double folds

folding resistance is one of the important indexes indicating the mechanical strength of paper and paperboard, and it is a comprehensive measure of paper strength and flexibility. This index is necessary for many kinds of paper and paperboard, especially for newspapers, banknote paper, map paper and book cover paper, because they have to undergo repeated folding in use. In order to prolong their service life, they must have such a high number of folding resistance

v. surface strength of paper

the surface strength of paper refers to the combination of fibers, fillers, pigments, etc. of the operation layer with the paper when the experimental force is applied to the sample, and the firmness of the connection, that is, the strength of the mutual bonding of the surface materials of the paper

generally speaking, it is difficult to achieve complete smoothness. The surface strength of paper is relatively low, while the surface strength of coated paper is high. The phenomenon of falling powder and hair often occurs in printing is closely related to the surface strength of the paper. In newspaper printing, the surface of the paper is often peeled off by the ink film and left on the ink roller, resulting in no inking of the printed matter, white spots, and the fine fibers of the falling filler material will also block the graphic part on the printing plate, making the printed graphic more and more unclear

VI. smoothness

generally speaking, smoothness refers to the time required for the lower volume of air to pass through the gap between the sample surface and the glass surface under a certain pressure and area under a certain vacuum, expressed in seconds

the smoothness of the paper surface has a direct impact on the impact resistance of the printing brush. The paper with high smoothness is easy to be evenly covered by the ink film during printing, so the printing effect of coated paper is better than offset paper. The paper with higher smoothness can be used for more detailed and precise printing points to produce higher quality prints. We require paper with uniform smoothness, followed by paper with high smoothness. The unit of smoothness is the time of air flow. The test principle is to apply a quantitative amount of air pressure on the paper surface with an area of about one square inch, so as to calculate the time of air flowing along the surface. The longer the time, the higher the smoothness

VII. Absorbency

paper absorbency refers to the paper's ability to absorb water or solvents. For ink, it is the absorption ability of ink, which can also be said to be the penetration ability of ink to paper. It is not only related to the degree of looseness and capillary state of paper, but also related to the surface properties of paper fibers, the content of fillers, pigments and adhesives, the composition and characteristics of ink, as well as the printing method and printing pressure

paper needs to have certain absorbency to promote the transfer of ink. However, if the absorption is too high, the ink binder will be too much penetrated into the interior of the paper, and the pigment material will accumulate on the surface of the paper, making it difficult to form a film, resulting in the lack of gloss of the print and even the chalking of the ink layer. Generally, the greater the absorption, the more obvious the dot expansion. When the absorption is too strong, it will also lead to ink penetration, which will seriously affect the quality of prints

VIII. Brightness

the whiteness of paper refers to the whiteness of paper, which is the total reflection of uniform diffuse reflection of visible light in all wavelength ranges. The factors that affect the whiteness are mainly the lignin content and bleaching degree in the paper paddle. Because the lignin is yellow, in order to obtain high whiteness paper, it is necessary to reduce the lignin content in the paper as much as possible

the whiteness of the paper has a great influence on the color range of the final print. The higher the whiteness of the paper, the more it can reproduce the true color of the ink. The brighter the color of the final print, the wider the color gamut. Generally, the whiteness of paper is low, yellow, and the whiteness of offset paper and coated paper is relatively high

IX. opacity

this feature means that when printed words and pictures are printed on one side of the paper, and words or pictures are also printed on the other side, they will not reflect. Good paper has a high opacity, so that the books made can enable readers to focus on the contents of their own pages when reading, so as not to be affected by the faint visibility on both sides of the image and make their eyes tired. The factors that affect the opacity are: I. the thickness of the paper itself; ii. Whether glue is applied; III. smoothness and roughness of paper surface; IV. plant fiber ingredients, etc. The test method is to measure how much light can penetrate the paper itself, and the unit is percentage rate

X. gloss

gloss is the closeness of the paper surface to the full mirror reverse ability in terms of the reverse incident light ability. It is expressed by the ratio of the mirror reverse rate of the paper at a certain angle to the mirror reverse rate of the standard black glass at the same angle

paper mills usually measure the reflection of light on the surface of white paper, and express the reflection rate in percentage. The industry will use this number rate to grade the paper, and the paper with high number rate is the finished product with high quality. When the gloss of paper is large, the color of its printed matter appears more bright. Some publicity posters and magazines will use high brightness paper to highlight their contents and pictures to attract attention, but books will be made of low brightness paper to reduce the fatigue of the eyes affected by too much reflected light

it can be seen from the above that the properties of paper are related to its printability, which is known by all printers. However, it is not clear to everyone which quantity has the greatest impact on Printing Reproduction and the difference between each quantity and printing reproduction. If the influence of each quantity on printing performance can be described by a certain value, it will undoubtedly be of great help to the printing industry in guiding production

Xi. Surface efficiency

surface efficiency is a non-optical characteristic that affects the reproduction of paper color gradients

pse (%) =100-a (%) +g (%)/2

pse - paper surface efficiency

a - ink absorption capacity of paper

g - gloss of paper

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