First, the moisture content and relative humidity of paper

First of all, we first understand the moisture content of paper in order to know how to solve the cause and solution of crumpled paper.

The so-called moisture content refers to the loss of water at a high temperature of 105 degrees Celsius for a long time. According to this result called "slow drying method" test. Freshly made plain paper has a water content of about 4 to 6 percent and powdered paper has 5 to 7 percent.

For information on the moisture content of ordinary non-powdered paper, it can be known whether those papers are suitable for printing purposes. However, we cannot measure the degree of suitability of printed paper for the same information. There are several reasons.

1. The first is because there are two kinds of moisture content in the paper. One is the moisture in the wood fiber. Since these waters and fibers are not closely connected, it is easy to increase or decrease.
2. As for another crystal such as rosin (added during the manufacture of paper), there is a strong dependence on paper and it is not easy to increase or decrease.

As far as these two kinds of water are concerned, the latter has nothing to do with the retractability of the paper, but the former has a direct impact.

The paper mill uses the “slow drying method” for testing, and in addition to calculating those free-floating waters, the water molecules can also increase the pulling force. If we want to accurately calculate the amount of water flowing on the painted paper, we must accurately calculate the water that is dependent on the paper. When calculating, we must consider the quality of the paper. Because the quality of the paper is different, the quantity can be different. Affect this amount of water.

Relative humidity

There are two ways to calculate air humidity. One is absolute humidity and the other is relative humidity.

The so-called absolute humidity is not commonly used in general, it refers to the content of water in the air.

Relative humidity refers to the relative percentage of moisture at a given temperature and the ability to hold moisture.

A variety of hygrometers can be used to measure relative humidity. One hygrometer called hygrometer is extremely accurate, but if you do not blow the air around the wet table before reading the reading, the resulting reading will be higher than the standard. .

In addition, the relative humidity of the paper may also be calculated by a long-sword type hygrometer as long as the relative humidity between the air and the relative humidity between the papers are equal.

Paper moisture content balance

Absorption of moisture or loss of moisture from the paper to the air is important for correcting adverse effects. The change in the moisture content of the paper, if the relative humidity of the paper is lower than the ambient air, the paper will absorb the moisture of the air and extend to the four sides until the relative humidity of the air and the paper is equal.
Wherever paper contains free-flowing moisture, the relative humidity of the paper also changes at any time. The relationship between the moisture content of paper and relative humidity is limited by the conditions at the time of manufacture, such as the degree of pressure on the paper fibers, the high clay content of the paper, and the amount of powder applied. It also has an impact. The ratio of the powder and the amount of backing paper on the coated paper also has its effect.

Whether or not the paper absorbs air moisture is not determined by the moisture content of the paper. The real decisive factor depends on the relative humidity of the paper. The relative humidity of the paper can be calculated directly with a sword-type hygrometer or indirectly based on the ratio of moisture content and relative humidity of the paper.

Paper absorbs air moisture faster than it releases moisture. If the same type of paper is placed in a place with high humidity and low humidity, and then put back to a place with moderate humidity, it will be placed on a low-humidity paper and will absorb water at a faster rate, and another Paper will release water at a slower rate. But for a long time, the two will maintain a balance of equal relative humidity.

As for the wrinkled paper problem, it can be said that it is closely related to positive worries, because the two often appear together. Severe overprinting, if not bad, may occur with creased paper. It may also be caused by machine malfunctions, tooth nozzle pressure adjustments, excessive pressure on the paper, the size of the paper being different from the standard, or the unevenness of the paper.

In general, the problem of overprinting and wrinkling is very complicated. If the causes are to be separated, we must clearly understand the following factors:

1, paper quality
2, the degree of smoothness of the paper before printing
3, a variety of printing presses: monochrome, two-color and four-color printing presses and different models (such as Roland, Heidelberg) presses.
4, color order
5, relative humidity of printing workshop and paper
6, the paper's clenched edges, pull rules and paper patterns caused by the impact:
1 The degree of misprinting on the corner of the paper (edge ​​portion of the tail of the paper)
2 The degree of paper crease caused by water absorption and moisture elongation after evaporation of paper 3 Paper size and paper angle
7. The pressure of the rubber cloth cylinder and the impression cylinder of the printing press, and how much the fountain solution is controlled.

Second, crumpled paper solution

1. The logistics center controls the quality of purchased paper, must pass the test before the formal production, do not just replace the brand of paper, do not purchase poor quality paper in order to reduce costs and cause trouble in the production process, in turn, a waste of time, gains and losses customers.

2. Where conditions permit, the paper can be used to handle the paper. Not sure. The empty car can press a white paper (that is, no ink to leave it empty, to give the paper a stable tension, and temperature).

3. In the production of single and double color printers, the paper is cut (especially in rain and wet weather), and after each last printing press, plastic film or shrink film must be used. Not windy, but to ensure that the paper deformation.

4. Appropriately adjust the printing color sequence. If there is a large solid surface area, adjust it to the last color sequence printing, but pay attention to the control of ink hue.

5. The printing shop is best equipped with air conditioning to ensure the relative temperature and relative humidity of the workshop. If the conditions are not mature, you can use another method to make a small room to put printing paper in a small room to get wet or use a small air conditioner to solve the problem.

If the printing paper is 157 g or less, the paper can be used to generate a fan-shaped streak to enhance the stiffness of the paper. 80g or less can be folded in the paper to one or two stripes, in order to maintain a smooth paper, without affecting pull rules.

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