Moisture content and performance of wet water kraft paper tape

The moisture content of wet water kraft tape paper has a great influence on printing. If the moisture is too low, the paper will be brittle, and static electricity will easily occur during printing. Today, Baijin wet water kraft paper tape manufacturers will introduce to you what factors affect the moisture content of kraft paper tape.

If the moisture content is too high, it will make it difficult for the ink to dry, and the change of moisture will also have a great impact on the various properties of the paper. With the change of moisture, its basis weight, tensile strength, folding resistance, etc. will change. , The paper size of wet water kraft paper tape will also expand and contract, and even curl, curl, wrinkle, and ruffle.

All kinds of wet water kraft paper tape paper have an optimal moisture content value. Under this value, the various properties of wet water kraft paper tape paper are in a good state. The best moisture content of the cast coated newspaper board is 7% ± 2%, 4%-7% for white cardboard, 8%±2% for single-sided coated white cardboard. This is the moisture content of the wet water kraft tape paper when it leaves the factory.

During storage in the printing plant, wet water kraft tape paper is used as a moisture-absorbing material. He can absorb moisture from the air. The rate of absorption depends on the relative humidity and temperature of the air. It can also transfer ten to the air and lose moisture. The rate depends on the moisture content of the wet water kraft paper tape and the ambient temperature and humidity. When the moisture absorption rate and the wet water rate are the same, the wet water kraft paper tape paper is in equilibrium with the air, and the moisture content in the wet water kraft tape paper remains unchanged. In this case, the moisture content of the wet water kraft tape paper is called equilibrium moisture.

Relative humidity refers to the ratio of the moisture content in the air at a certain temperature to the moisture content that the air can hold when saturated at that temperature. The same wet water kraft paper tape paper has different equilibrium moisture under different relative humidity.

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In addition, the wet water kraft paper tape has the following characteristics:

① Affected by the properties of wet water kraft paper tape

Under the same relative humidity, the more hydrophilic the paper, the higher its equilibrium moisture content; on the contrary, the lower it is. The wet water kraft paper tape without auxiliary materials has higher equilibrium moisture, while the wet water kraft tape paper with filler, sizing, and coating has lower equilibrium moisture. The balance of moisture in thick products of the same variety is higher than that of thin products. This is because the ratio of water-absorbent base paper in thick products is high.

② Affected by temperature

Under the same relative humidity, the temperature change is about 15℃, and the maximum change in the equilibrium moisture of the wet water kraft paper tape is about 0.5%. However, during printing, the moisture content of wet water kraft paper tape should be controlled within ±0.1% for overprinting, otherwise the accuracy of overprinting will be affected. Therefore, the color printing workshop should control the temperature change at ±3 while controlling the relative humidity. ℃.

③ Affected by moisture absorption and dehumidification

The moisture content ofwhen the paper reaches equilibrium by low moisture absorption under a certain relative humidity is lower than the moisture content when it reaches equilibrium when high moisture is dehumidified under the same relative humidity. This is wet water kraft paper tape. Hysteresis effect of paper moisture absorption.

To make the moisture content of the wet water kraft paper tape the same as the original. Corrective measures must be taken. That is, wet water kraft paper tape paper that reaches equilibrium at a certain relative humidity, if it is to be dehumidified to reach the original equilibrium moisture after absorbing moisture in a high humidity environment, it must be placed in an environment with a lower relative humidity than the original, and vice versa.

In addition, the speed of moisture absorption and dehumidification is also different, and the dehumidification speed is much slower. But regardless of moisture absorption or dehumidification, the starting speed is relatively fast, and the closer it is to the equilibrium, the slower it is. This process is also related to paper quality and air mobility. Under standard humidity and temperature, a single cigarette paper can reach 5.8% equilibrium moisture after 35 minutes of treatment.

It takes 2-4 hours for various printing papers to reach 5%-8% equilibrium moisture; it takes longer for packaging cardboard. This hysteresis between the change in relative humidity and the change in the moisture content of the wet water kraft paper tape will bring about a hysteresis effect between the deformation of the wet water kraft paper tape and the change in relative humidity.

④ Affected by the directionality of wet water kraft paper tape

The so-called directionality means that the balance moisture of the wet water kraft paper tape is inconsistent in the vertical and horizontal directions, and the horizontal expansion rate is far greater than the vertical expansion rate. Therefore, the horizontal expansion and contraction deformation of the wet water kraft tape paper is larger than the vertical direction. Tests show that the expansion and contraction of a single fiber in the transverse direction is equivalent to about 20 times that in the longitudinal direction. However, the inner fibers of the wet water kraft paper tape are arranged in a variety of directions, but the number is usually more arranged in the longitudinal direction.

Therefore, the difference in the vertical and horizontal stretch ratio of wet water kraft paper tape paper is not as large as the vertical and horizontal stretch of a single fiber. Taking the relative humidity from 50% to 60% as an example, the ratio of vertical and horizontal expansion is about 3:7, which is about 2.3 times. This ratio varies according to the degree of fiber arrangement and orientation. The stronger the directionality, the greater the ratio. Paper with scattered and irregular fiber arrangement directions is one of the key problems to reduce the transverse expansion and contraction rate and avoid the occurrence of inaccurate registration.

⑤ Affected by both sides of wet water kraft tape paper

A very flat wet water kraft paper tape paper, when the environment changes, the wet water kraft paper tape paper will absorb moisture or dehumidify in the air. If it is moisture absorption, the elongation of the back side is greater than that of the front side, and the wet water kraft paper tape will curl toward the front; if it is dehumidification, the reverse side will shorten more than the front side, and the wet water kraft tape paper will curl toward the reverse side.

No matter which direction it is curled, it always takes the longitudinal direction of the wet water kraft paper tape as the axis. This situation is caused by the different orientation of the front and back sides of the wet water kraft paper tape. Especially cardboard, the performance in this aspect is even greater.