Quantitative: the weight per square meter, expressed in g/㎡. For example, the basis weight of cultural printing paper is generally 32-80g/㎡, and the basis weight of cardboard is generally 200-400g/㎡.
②Thickness: The thickness measured directly between the two measuring plates under the pressure of 100kPa, expressed in mm.
③Tightness: Indicates the degree of tightness of the paper structure, the weight of paper per cubic centimeter, expressed in g/c㎥. For the same amount of paper, the thicker paper is looser.
④Porosity and air permeability: General paper contains 70% pores. Air permeability is the amount of air per minute or the time for a certain amount of air to pass through a certain area of paper under a certain degree of vacuum, expressed in ml/min or s/100ml, respectively.
⑤ Stretch ratio: the relative change of paper size after paper soaking in water or after humidification or dehumidification at different temperatures, expressed as a percentage of the size increase or decrease to the original sample size. Offset printing paper has higher requirements for stretch rate.
⑥Strength: The paper is affected by external force and reaches some specific values reflected by the failure point. Mainly include tensile strength and elongation at break, bursting resistance, folding resistance, tearing degree, stiffness, and so on. Various strength indicators are particularly important for packaging paper.
⑦ Fire point: generally 130 ~ 255.5 ℃.
Optical performance index
①Whiteness: The reflectance of white or nearly white paper surface to blue light, expressed as a percentage relative to the reflectance of standard magnesium oxide board.
②Opacity: expressed as the percentage ratio of the reflectivity of a single sample on the “full absorption” black liner to the reflectivity of several completely opaque samples.
③Transparency: The degree to which light penetrates through the paper. It is expressed by the maximum number of layers that the sample can see the ink lines clearly. Optical performance indicators are more important for printing paper and tracing.
Chemical performance index
①Moisture: The weight of water that can be evaporated in the paper at 100～105℃ is expressed as a percentage of the weight of the paper.
② Ash content: expressed as a percentage of the weight of the residue after burning of the paper to the weight of the absolute dry sample of the paper sample.
③pH value: the pH value of the water extract after soaking the paper sample in distilled water at 95～100℃ for 1 hour. These chemical properties are particularly important for electrical and technical papers.
①Sizing degree (water resistance): The performance of the paper surface to prevent the penetration and diffusion of ink during writing is very important for writing paper. Use a duckbill pen dipped in special ink to draw a line on the paper, expressed as the maximum width (mm) of the non-diffusion and non-penetrating line.
②Smoothness: Under a certain degree of vacuum, the time required for a certain volume of air to pass through the gap between the sample surface and the glass surface under a certain pressure, is expressed in seconds.
③Surface strength: Offset printing paper is required to have good surface strength in order to prevent the paper from falling off the lint. The number of wax sticks that press the paper with the wax stick until the fibers are drawn can also be expressed by measuring the drawing speed with a printing applicator. For drawing paper and tracing paper, the rubbing resistance is measured, which is a test of the bonding strength of the surface tissue of the paper. The time required for the gap between the sample surface and the glass surface of the mica paper under a certain pressure is expressed in seconds.
In addition to the above properties, there are many testing requirements for special properties in other technical papers. For example, the dielectric constant, dielectric strength, and dielectric loss of electrical industrial paper, the burning speed of cigarette paper, the thermal conductivity of thermal insulation paper, the resistance coefficient of filter paper to fluid and the retention coefficient of filters, and the Softness, absorbency, etc. are all important performance indicators of quality, and they need to be tested according to specified standards to evaluate their performance.