Screen printing printing materials--paper and cardboard (2)

March 14, 2019

In the papermaking process, in order to achieve better results, the moisture content in the paper must be accurately adjusted. The humidity of the paper is the weight ratio between water and fiber in the paper. The moisture content in paper depends on the composition and relative humidity of the paper. The amount of water vapor in the air is called air humidity. Absolute humidity refers to the amount of water in a state where 1 cubic meter of air is in the state of water vapor. The maximum amount of water vapor that can be absorbed by 1 cubic meter of air is called the maximum humidity or saturation point, and the maximum humidity depends largely on the temperature. The ratio of absolute humidity to maximum humidity is called relative humidity and expressed as a percentage:

For example, a screen printing factory has a temperature of 20 degrees, and every cubic meter of air in the room can absorb up to 17.3 grams of water vapor. If it is assumed that there are 10.4 grams of water vapor per cubic meter of air in a screen printing plant, the relative humidity will be:

In general, paper producers produce stored paper at temperatures of 50-55% relative humidity and 18 degrees Celsius, which is also the most favorable climatic conditions for screen printing paper. Relative humidity can be measured with a hygrometer. A general hygrometer can measure the relative humidity in a room, and a rod or sword hygrometer can measure the relative humidity of a paper pile. Hygrometers should always be calibrated with a wet-dry meter. If the paper and paper room are too moist, the two edges that are at right angles to the fiber direction of the paper will be wavy. If wet paper is used or stored in a room with high temperature, the so-called pay-off “disc” paper may be caused by evaporation of water.

As a general guideline, it can be assumed that a piece of paper capable of absorbing 10% humidity will be stretched by 0.1%, ie, 1 mm per stretch. This figure cannot be ignored for screen printers engaged in large format printing. .

Other criteria commonly used for paper identification are that the paper should be able to absorb the proper amount of ink, and that the dry time value should not adversely affect the ink; the impact of the paper on ink durability should be as small as possible; the paper should be rectangular when cut and Flattening; Paper should not be prone to static electricity and should not contain any easily peeling ingredients or substances. Also note that the paper has long and short grained paper. The fiber direction of the long grain paper erodes to the long side of the paper. The fiber direction of the short grain paper is parallel to the short side of the paper. If the two papers are mixed together, There must be a large deviation in press pressure.

Paper size

At present, the standard paper size used abroad is derived from the German standard, that is, based on the AO size based on the new size, so that all the various sizes of paper shapes

Paper management

Paper is a sensitive material and should be handled with special care. The following important rules should be followed:

1. The temperature of the paper store should be kept at 18-20 degrees, and the relative humidity should be kept at 55-60%.
2. Light is the enemy of paper, so the paper should have opaque packaging and be stored in a dark room.
3. If the air in the paper warehouse and printing room cannot be adjusted, the paper is sealed with polyethylene film.
4. When the paper is transported, it should be flat.
5. Before printing, the paper must first adapt to the new environment. Before screen printing begins, small-size paper must be placed in the screen printing shop for several days, and large-sized paper should be placed for at least one week.
6. Paper should be shipped as flat as possible.
7. If the paper needs to be folded, fold it parallel to the fiber direction.
8. When stacking paper, size the paper first.
9. Each order should be marked with the order number or delivery date. If not, at least the type, quality and quantity of the paper should be indicated.
10. In order to monitor the paper in the paper bank, a card index should be established.

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