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Moisture content&performance of writable kraft paper tape!

Article provenance:未知 Popularity:Time:2020-08-12 10:21
 
The moisture content of Eco friendly  kraft paper tape has a great influence on printing.
If the moisture content is too low, the paper will be brittle and static electricity will be easily generated in printing;
if the moisture content is too high, the ink will be difficult to dry. The change of moisture has a great influence on various properties of paper.
With the change of moisture content, its quantitative, tensile strength, flexibility and folding resistance will change.
The paper size of writable kraft paper tape will also expand and shrink, and even curl, warping, wrinkling, lotus leaf edge and other phenomena will occur.
 
All kinds of writable kraft paper tape paper have an optimal moisture content value. Under this value, the various properties of writable kraft paper tape paper are in good condition. The best moisture content of cast coated paper and cast coated white board is 7% ± 2%, that of white cardboard is 4% - 7%, and that of single coated white board is 8% ± 2%. This is the moisture content of the kraft paper when it leaves the factory.
 
During the storage in the printing plant, as a kind of hygroscopic material, the writable kraft paper can absorb moisture from the air, and the absorption rate depends on the relative humidity and temperature of the air; it can also transfer moisture to the air and lose moisture, and the rate depends on the moisture content of the paper and the ambient temperature and humidity. When the moisture absorption rate and water loss rate are the same, the paper and air are in balance, and the water content in the paper is unchanged. In this case, the moisture content in the paper is called equilibrium moisture.
 
The so-called relative humidity refers to the ratio of the moisture content in the air at a certain temperature to the moisture content that can be contained when the air reaches saturation at that temperature. The equilibrium moisture of the same kind of writing kraft tape paper is different under different relative humidity.
 
Balance moisture
 
In addition, the change of equilibrium moisture has the following characteristics:
 
① It is affected by the properties of writing kraft paper tape
 
At the same relative humidity, the more hydrophilic the paper, the higher the equilibrium moisture; otherwise, the lower the equilibrium moisture. The equilibrium moisture content of the paper without auxiliary materials is higher than that of the paper with filler, sizing and coating. For the same variety, the balance moisture of thick products is higher than that of thin products, because the ratio of base paper rich in water absorption in thick products is high.
 
② Affected by temperature
 
Under the same relative humidity, the change of temperature is about 15 ℃, the maximum change of equilibrium moisture is about 0.5%. However, in printing, the change of moisture content of kraft paper should be controlled within ± 0.1%, otherwise the accuracy of overprint will be affected. Therefore, the color printing workshop should control the temperature change within ± 3 ℃ while controlling the relative humidity.
 
③ Affected by the stroke to reach equilibrium - hygroscopicity or dehumidification
 
Under a certain relative humidity, the moisture content of the writable kraft paper is lower when the moisture content reaches equilibrium from low moisture absorption, which is the moisture absorption lag effect of the paper. In order to make the water content of the kraft paper adhesive tape consistent with the original. We must adopt the way of "overcorrecting". That is to say, when the relative humidity reaches the balance, if the kraft paper is to be dehumidified to reach the original equilibrium moisture after moisture absorption in a high humidity environment, it must be placed in an environment lower than the original relative humidity, and vice versa.
 
In addition, the speed of moisture absorption and dehumidification is also different, and the dehumidification speed is much slower. However, no matter the moisture absorption or dehumidification, the starting speed is relatively fast, and the closer it is to the equilibrium, the slower it will be. This process is also related to paper and air mobility. Under the standard humidity and temperature, the equilibrium moisture content of single cigarette paper can reach 5.8% after being treated for 35 min, and it takes 2-4 h for all kinds of printing paper to reach the equilibrium moisture of 5% - 8%, and the packing paperboard takes longer time. This change in relative humidity with writable kraft paper tape

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