How to determine the moisture content of paper
The moisture content of paper refers to the ratio of the reduced mass to the original mass when the sample reaches "constant weight" at the specified drying temperature (105 2)℃, expressed in%.
The method of moisture determination is to take two samples of a certain quality (accurate to 0.0001g), put them into the weighing bottle with constant weight, bake them in a hot air drying box for several hours (generally 4 hours), take them out and cool them for 30 minutes, then weigh them. If it can't meet the requirements, dry it repeatedly until the weight is constant. Then, divide the difference between the mass before and after drying and the mass before drying, and get the moisture of the paper through simple calculation.
Generally, air contains a certain amount of moisture. When the moisture in the air is greater than that contained in paper, that is, when the climate is humid, paper will absorb the moisture in the air. On the contrary, when the climate is dry, the moisture in the paper will be desorbed and transferred to the air until the moisture balance between them is reached. It should be pointed out that the adsorption and desorption in this way show two isotherms, and the desorption curve is above the adsorption curve (called hysteresis phenomenon). Therefore, the moisture content of paper changes with the change of dry temperature of climate. Usually, the moisture in the air is about 7%, and the moisture in ordinary printing paper is 7% 2%. If it exceeds this limit, it means that the moisture in the paper is unqualified and you can claim compensation from the merchant.
The moisture content of paper will affect many of its properties. From the point of view of printing, moisture has almost all effects on paper size, expansion rate, tensile strength and surface strength, which can not be underestimated. Excessive moisture in paper will make overprinter difficult, delay ink drying, and reduce tensile strength and surface strength; If the moisture content of paper is too small, the paper will be brittle and prone to static electricity, which will lead to quality problems such as "double sheets" and "blank sheets" when printing.
