Quantitative commonly known weight, is the weight of paper per unit area, expressed in grams per square meter. Generally, the basis weight is below 250 g / m2, which is called paper; the basis weight is above 250 g / m2, which is called cardboard or paperboard. Quantitative is the most basic physical indicators of paper, its level and its uniformity, affecting all physical and printing paper performance.
2. Thickness and tightness
Thickness indicates the degree of paper thickness, it refers to the thickness of the paper or cardboard in a direct measurement of pressure between the two measuring plates, in mm or μm. In general, the thickness of a direct impact on the opacity of the paper, the greater the thickness of the opacity the better. Thickness uniformity is especially important for paper, unevenness in thickness affects the reduction in gloss and whiteness, and the tone and color reproduction instability.
Tightness refers to the weight of paper unit volume, also known as density, is calculated by dividing the thickness calculated.
Tightness is a physical measure of the degree of density of the paper structure, the same paper fiber paper, the greater the tightness, the paper the more dense, on the contrary, the more loose paper. The tightness of the paper is proportional to the tensile strength.
3. Tensile strength and elongation
Tensile strength is the maximum pull that can be sustained by the operator before breaking of the unit width paper or cardboard under the conditions specified by the standard test methods. When the paper is stretched by tension, the paper will be stretched in the direction of force. When the pulling force is increased so that the spline is pulled off, the elongation reaches the limit. At this time, the ratio of the length of elongation to the original length is called the elongation, Expressed as a percentage.
For web printing, the tensile strength and elongation of the paper is an important indicator. Because the paper roll in the rotary press, the paper will be under great tension. If the tensile strength is too small, it will cause broken paper; and if the elongation is too large, it will change the size of the paper to increase the overlay error. Therefore, the use of paper with high tensile strength and low elongation can effectively prevent and reduce the occurrence of breakage of paper during printing, and reduce overprint error.
4. Endurance folding
Paper folding endurance refers to the specified test conditions, in specialized equipment, the sample can be folded before breaking the number of times, expressed in double folding.
Friction resistance is one of the most important indicators of the mechanical strength of paper and paperboard. It is a comprehensive measure of the strength and flexibility of paper. This index is necessary for a wide range of paper and board, but for newspapers, bank notes, maps Paper, book cover paper is particularly important, because they are in use to withstand repeated folding, in order to extend its life, you must require them to have such a high number of folding.
5. Paper surface strength
The surface strength of the paper refers to the surface of the paper fibers, fillers, pigments, etc. combined with the paper, the connection firm solid degree, which refers to the strength of the paper surface material combined with each other.
In general, newsprint surface strength is relatively low, while the coated paper surface strength is higher. Often appear in the printing powder off the phenomenon of hair loss and the surface of the paper is closely related to the intensity. In the newspaper printing, the surface of the paper is often stripped off the ink film and left on the ink roller, resulting in inadvertently printed products, white spots appear, the fine fibers of the falling filler material will block the graphic part of the printing plate, so that printing The picture is getting less clear.
The so-called smoothness, under a certain degree of vacuum, a volume of air, by a certain pressure, a sample of the area under the surface area between the glass surface and the time required, expressed in seconds.
The smoothness of the surface of the paper has a direct impact on the printing. When the paper with high smoothness is easy to be covered by the ink film, the printing effect of the coated paper is better than that of the offset paper. The higher the smoothness of the paper, for more sophisticated printing dot use, the production of higher quality print. We are asking for paper with smoothness, followed by high-smoothness paper. The unit of smoothness is the air flow time. The test principle is to use a fixed amount of air pressure on the surface of the paper about a square inch area of the surface of the paper to calculate the air flow along the surface of the time. The longer the time, the higher its smoothness.
The absorbency of the paper refers to the ability of the paper to absorb water or solvents. The ink is on the ink absorption capacity, it can be said that the ink on the paper's ability to penetrate. It is not only related to looseness and capillary state of the paper, but also relates to the surface properties of the paper fiber, the content of the filler, the pigment and the rubber compound, the composition and characteristics of the ink, and also relates to the printing method and the printing pressure.
Paper needs to be absorbent to promote ink transfer. However, if the absorbency is too high, the ink binders will be infiltrated into the interior of the paper too much, and the pigment material accumulates on the surface of the paper, making it difficult to form a film, resulting in a lack of gloss on the printed product and even pulverization of the ink layer. In general, the greater the absorbency, the more obvious network expansion, when the absorptivity is too strong, but also lead to offset printing ink, seriously affecting the quality of printed materials.
Paper whiteness refers to the degree of whiteness of the paper is the total reflection of visible light in all wavelength ranges uniform reflection. The main factors that influence the whiteness are the lignin content and the bleaching degree in paper pulp. Due to the yellow process of lignin, it is necessary to minimize the lignin content in the paper to obtain the paper with high whiteness.
The whiteness of the paper has a greater impact on the color range of the last printed product. The higher the whiteness of the paper, the more realistic the color of the ink is. The more bright the color of the printed product is, the wider the color gamut is. The whiteness of newsprint paper is generally low, yellow, and the whiteness of offset paper and coated paper is relatively high.
This feature refers to the words and pictures printed on one side of the paper, while the other side is also printed with text or pictures, they will not appear transparent phenomenon. Good opacity of the paper is high, so that made of the book so that readers can focus on reading the contents of the page, will not be stamped on both sides of the effect of dim so that the eyes tired. The factors that affect the opacity are: i. The thickness of the paper itself; ii) whether or not the glue has been applied; iii. The smoothness and roughness of the paper surface; iv. The test method is to measure how much light penetrates the paper itself, the unit is the percentage rate.
Gloss is the paper surface in the reverse incident light capacity and full mirror reverse ability close to the paper is the paper at a certain angle of the mirror reverse rate and the standard black glass at the same angle of the mirror reverse ratio Said.
Paper mills usually measure the amount of light reflected from the surface of white paper and the percentage of reflectance. The industry will use this rate to grade the paper, the high rate of paper for the higher quality finished product. Paper luster, the print color appears more vivid. Some posters and magazines use high-gloss paper to draw attention to their text and pictures to attract attention, but books are made with lower-brightness paper to reduce the effects of too much reflected light on the eyes Easy to wear.
From the above, it can be seen that the properties of the paper are related to the printability of the paper, which is known to all printers. However, the amount of the greatest impact on the printing and reproduction, the amount and the size of the relationship between printing and reproduction but not everyone knows. If the amount of the impact on the printing performance can be a certain value to describe the size, then the printing industry to guide the production will undoubtedly be of great help.
11. Surface efficiency
Surface efficiency is a non-optical characteristic that affects the tone reproduction of the paper.
- paper surface efficiency (surface efficiency)
Ink absorption capacity of paper
- Glossiness of the paper.