17 basic properties of paper you should know
February 16, 2023
Are you worrying about your paper quality?
Do you know how many basic properties can determine the quality of your paper？
In this article, a total of 17 basic properties will be divided.
- Physical properties: quantitative; thickness; tightness; smoothness; stretch; permeability.
- Mechanical properties: tensile strength; folding resistance; tearing degree.
- Optical properties: whiteness; opacity.
- Others: moisture; elongation; sizing; absorbency; ash; longitudinal and transverse orientation of paper and cardboard.
Quantitative, commonly known as gram weight, refers to the weight of paper per unit area, which is generally expressed in terms of how many grams per square meter..
It is the most basic physical index of paper. Its level and uniformity affect all physical, mechanical, optical and printing properties of paper.
Quantitative is the most basic quality indicators of paper and paperboard. Because most paper is sold by weight. Quantitative refers to the weight per unit area, generally expressed in grams per square meter of paper. The paper we use in our life generally refers to the area of the paper.
Thickness indicates how thick or thin the paper is.
The micrometer is used to measure the thickness of the paper under a certain area and pressure. The general pressure is 980 kPa.
Thickness of a batch of paper or cardboard is usually required to be the same, otherwise the thickness of the manufactured items will not be consistent.
Tightness refers to the weight of paper and cardboard per cubic centimeter. Its result is expressed in Gram/Cube centimeter. Tightness = Quantitative/Thickness
The tightness means that the weight of the paper and cardboard of each cubic centimeter, it is expressed in gram/cubic centimeter.
Tightness is a measure of the degree of tightness of the paper or cardboard structure, and it is the basic nature of paper and cardboard.
It has a close relationship with the porosity, absorbency, rigidity and intensity of the paper. Also affects the optical properties of paper and paperboard, printing properties, physical properties.
Smoothness refers to the time, expressed in seconds, required for a certain volume of air to pass through the gap between the sample surface and the glass surface under a certain pressure under a certain vacuum.
The smoothness depends on the surface condition of the paper. If the paper surface is uneven, the smoothness of the paper is very poor.
The size change of paper caused by water immersion or air drying after water immersion is called paper stretch.
Represents the percentage of the original size of the sample size with the size of the increase or decrease.
Paper permeability is in a certain area, a certain vacuum, the amount of air per minute through the paper or through 100 ml of air required time, expressed in ml / minutes.
It is used to identify the degree of air gap in the middle of the paper layer, and is also one of the indicators to test the moisture resistance of the paper.
Permeability is with the size of the tightness of the paper and the increase or decrease. Fibers interweave closely, the permeability of paper is small, and vice versa, the greater the paper's moisture resistance is also lower.
To reduce the permeability and improve the moisture resistance of the paper, the first step is to increase the bond and uniformity between the fibers, which requires providing the pulping degree of the paper stock in the pulping.
Permeability is the main physical characteristic of cement bag paper, paper bag paper, cigarette paper, cable paper, copy paper and industrial filter paper, etc., all need to determine the size of its permeability.
Tensile strength is the tension to which the paper or board is subjected.
Usually expressed in absolute tension: that is, the tension of a specimen of a certain width (Newton).
Or with the breaking length expressed: that is, the length of paper required for a strip of paper of a certain width to be pulled off under its own gravity (m).
Or with the transverse section of the tension resistance expressed: that is, the unit cross-sectional tension resistance of the specimen (Newton / square meter).
Tensile strength is one of the important parameters of physical properties. It is also a basic test.
Folding resistance refers to the paper and cardboard under a certain tension, the number of times the reciprocal folding can withstand 180 °.
Fold resistance indicates the paper's ability to resist soft folding.
Tearing degree is the force required to tear a pre-cut specimen to a certain length, expressed in mN (tons).
The tearing degree of paper is the ability of paper and cardboard to resist the balance crack.
The whiteness of paper or cardboard is the reflectivity of white or near-white paper or cardboard surface to blue light, to be expressed relative to the reflectivity of blue light irradiation magnesium oxide standard plate surface.
Whiteness is a necessary condition for all white paper and partially processed light-colored paper. It is specified according to the requirements of use, especially important for printing paper and writing paper. But with the different uses, the requirements for whiteness are different. In particular, gravure paper, white cardboard, special thin paper and other paper requirements whiteness in more than 90%, offset printing paper, securities paper, senior writing paper, drawing paper, senior typing paper and other paper requirements whiteness in more than 80%, letterpress paper, general writing paper, glossy paper requirements whiteness between 60 to 70%, newsprint requirements whiteness of 45 to 50%.
For printing pictorials, art pictures and other paper, a higher whiteness is required, while for printing books and magazines, the whiteness of the paper should not be too high.
Opacity is an optical property of paper. The opacity of paper refers to the ratio of the reflectivity of green light to
the corresponding reflectivity of several completely opaque samples when a single sample is padded with a fully absorbed black pad.
The opacity of the paper is very important for printing paper. Only paper with a certain degree of opacity to ensure the quality of printing. For writing paper, also requires a certain opacity, in order to facilitate the writing of both sides of the paper.
The moisture in the paper sheet is the most significant factor affecting the main properties of the paper.
Moisture is the ratio of the reduced weight of paper and cardboard to the original weight when dried to constant weight at 100-150°C, expressed as a percentage.
It is an important indicator for testing paper. Any paper product standards have moisture percentage regulations, this is because the main component of the composition of paper is cellulose. The relationship between fiber and water is the most important relationship in paper manufacturing.
The moisture content of a single fiber affects the fiber strength, cotton toughness and paper formability.
The moisture content of single-rooted fiber affects the fiber strength, sheep toughness and sheet forming properties.
Paper moisture affects paper weight, strength, durability, gauge stability, ink receptivity, finish, softness and overall printing and electrical properties of the paper, etc.
Therefore, moisture is an important indicator of paper.
The elongation rate refers to the percentage of the length of the extension of paper or cardboard after a certain tension to cracking to the length of the original test.
Elongation is an important index to measure the strength and toughness of paper, which is actually the limit strain of paper when it is broken.
The greater the elongation, the more elastic the paper, the more difficult it is to break the paper. It is cable, paper bag paper, packaging paper and its similar paper varieties of important properties.
The sizing degree of paper and cardboard is indicated by the maximum width of the lines that do not spread nor penetrate when scribed with standard ink in millimeters; or expressed in terms of the weight (g/m2) that can be added after the surface absorbs water when one side of the paper and cardboard is in contact with water for a certain period of time.
Absorbency refers to the absorption properties of paper and board to water or other organic solutions.
The absorption of paper depends on the nature of the fiber, the slurry degree of the slurry, and the structure of the paper.
In the printing process, the absorption performance of the paper is too high, which will lead to a large amount of ink, or even through the print. If the paper absorption performance is too small, and will make the paper printed unclear, in the use of flat paper, due to the refresh speed, but also easy to stain other paper.
Paper absorbency to some extent with the paper's breathability, tightness, smoothness, sizing has a close relationship.
The ash refers to the ratio of the weight of the residue after the paper or cardboard is burned to the weight of the bonedry sample, which is expressed at a percentage.
The ash content of paper and paperboard mainly depends on the amount of impurities such as the filler in the paper, generally 0.1-0.9%. The ash content of sizing substances and mineral color is only a small part of the total ash content of paper.
6.Longitudinal and transverse orientation of paper and cardboard
Paper has a certain orientation.
The longitudinal direction is the direction parallel to the paper machine run. Since most of the fiber arrangement follows the direction of paper machine operation, and in this direction the paper is subjected to greater traction.
The horizontal direction is the same as the direction in which the paper runs perpendicular to the paper machine.