How to measure paper moisture
The moisture content of paper refers to the ratio of the reduced mass of the paper sample when it reaches "constant weight" at the specified drying temperature (105 ± 2) ℃ to the original mass, expressed as a percentage.
The method for determining moisture content is to take two samples of a certain mass (accurate to 0.0001g), put them into "weighing bottles" that have already been weighed, and dry them in a hot air drying oven for several hours (generally 4 hours). After cooling for 30 minutes, weigh them. If the requirements cannot be met, dry repeatedly until the weight remains constant. Then, divide the difference in mass before and after drying by the mass before drying, and through simple calculation, obtain the moisture content of the paper.
Air generally contains a certain amount of moisture. When the moisture in the air exceeds that 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 desorb and transfer to the air until a moisture balance is reached between the two. It should be pointed out that the adsorption and desorption effects are manifested as two isotherms, and the desorption curve is located above the adsorption curve (known as hysteresis phenomenon). So, the moisture content of paper changes with the dry temperature of the climate. Usually, the moisture content in the air is about 7%, and the moisture content of ordinary printing paper is 7% ± 2%. If it exceeds this limit, it means that the moisture content in the paper is not qualified, and you can request compensation from the merchant.
The moisture content of paper can affect many of its properties. From a printing perspective, moisture almost has an impact on paper size, stretch rate, tensile strength, surface strength, etc., which cannot be underestimated. Excessive moisture in paper can make overprinting difficult, delay ink drying, and reduce tensile and surface strength; The moisture content of paper is too low, which can make the paper surface brittle and easily generate static electricity, leading to quality problems such as "double sheets" and "blank sheets" during printing.
