JP3785974B2 - How to prevent coated paper breaks - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a paper coating method. In paper mills, paper made by a paper machine may be used as it is, but depending on the printing application, a coating solution containing resin and inorganic pigment is applied and the surface is smoothed to improve printing suitability. In order to achieve this, calendar processing is often performed. The coating method includes various methods such as blade coating, roll coating, and coating with a curtain flow coater. The present invention is an explanation relating to blade coating.
[0002]
[Prior art]
For blade coating, as in the chamber applicator system shown in FIG. 3, the coating liquid is applied from the applicator portion to the paper surface while the paper S is being run along the backing roll B, and immediately applied to the paper S. The applied coating solution is scraped off by the doctor blade, and the coating solution is made uniform on the paper surface. When applying the coating liquid from the applicator unit to the running paper surface, the paper may meander, so that it cannot be accurately applied only to the paper surface. Therefore, the coating is performed wider than the paper width.
[0003]
As another coating method in blade coating, there is also an apparatus as shown in FIG. The apparatus of FIG. 4 is called a jet fountain system, and can form an uncoated part like the chamber applicator system.
[0004]
In addition to the above, the coating method in blade coating includes a number of methods such as a method using a roll coater. After coating, the coating solution applied by the doctor blade is scraped off and the coating solution is applied. The method is the same in all methods in that it is uniform on the paper surface. However, the roll coater method is not as easy as the jet fountain method or the chamber applicator method for coating width operations such as coating wider or narrower than the paper width.
[0005]
[Problems to be solved by the invention]
If the coating is wider than the paper width, the applied coating solution is pulled in the edge direction at the left and right ends of the paper, and the 2-3 mm portions at both ends are extremely thick compared to the center. become. In the drying process of the next process following the coating, the coating liquid in the thick coating part is delayed in drying, so it separates from the paper surface, adheres to the cylinder and other rolls, and accumulates as a coating liquid soot .
[0006]
If these coating liquids are transferred to the coated surface of the paper or detached from the roll and dropped onto the coated surface, it will not only cause defects on the paper surface, but will also bite into the resin roll of the calendar in the calendar processing process. Damage the resin roll.
[0007]
Further, when coating is performed wider than the paper width, a part of the coating solution is also applied to the backing roll surface at both ends. The coating solution applied to the surface of the backing roll is usually scraped off by a flow clintor (not shown). It accumulates and the doctoring effect decreases. As a result, a part of the coating liquid adheres to the back surface of the paper.
[0008]
Therefore, both ends of the paper are coated on the back surface as well as the front surface. After coating, the paper is dried with the dryer in the next process, but the coating solution applied to the back side does not dry sufficiently, so a part of the coating solution becomes a coating solution on the roll of the dryer. Adhere and deposit. When the coating liquid detaches from the roll and adheres to the paper surface, it may cause a paper surface defect and damage the calendar roll.
[0009]
Therefore, in order to prevent the occurrence of the paper surface defect and prevent damage to the calender resin roll, the coating is usually performed narrower than the paper width, and uncoated portions are provided at both ends. This uncoated part is called dry edge.
[0010]
However, when an uncoated portion is provided, the portion is excessively dried in the next drying step as compared with the central portion where a normal amount of coating solution is applied. As a result, a shrinkage difference occurs between the uncoated portion and the central portion. The uncoated portion is pulled more strongly than the central portion because the shrinkage rate is larger than that of the central portion.
[0011]
The coated paper coated on one side is then coated on the opposite side (back side) and further subjected to calendering. At this time, the surface is rubbed with a doctor blade, or a large pressurizing force is applied by a high linear pressure in the calendar processing step. As a result, a fissure occurs in the uncoated portion that is strongly pulled, and the fissure spreads to the center starting from the fissure, causing a paper break. In addition, due to pulling, the paper is deformed in the vicinity of the uncoated portion, and small wrinkles are generated. The fine lines are rubbed with a doctor blade, or a large pressure is applied, and the paper may be cut off.
[0012]
[Means for Solving the Problems]
As shown in FIG. 1, the present invention provides a blade coating method in which an uncoated portion (dry edge) is provided at both ends of a paper for coating, by supplying a fluid to the uncoated portion after coating. The above problems were solved by making the drying speed substantially equal to that of the central part. When the coating liquid is water-soluble, the fluid to be supplied is usually water. A supply method supplies as a small water droplet by spraying or shower ring. The place suitable for the supply is suitable for a place where the paper is not squeezed by water supply, such as near the turning roll as shown in FIG. 1 or near the blade just after the blade coating as shown in FIG. Since the drying speed of the uncoated part is approximately proportional to the amount of water supplied to the uncoated part, the amount of water supplied should be approximately equal to the amount of water in the coating liquid applied to the center. It is only necessary to supply a predetermined amount of water so that the moisture content of the uncoated part and the central part at both ends is substantially equal. In order to accurately supply a predetermined amount of water, a special device is required at a place where water is supplied, but in the present invention, it is not necessary to measure the amount of water to be supplied so accurately. At the dryer outlet, the amount of water supply should be adjusted so that the difference in moisture content is 1.0% or less, so that the moisture content in the uncoated part of the paper and the central part are almost the same. That's fine.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Next, an example of a preferred embodiment of the invention will be described with reference to the drawings. FIG. 1 shows how paper S is coated with a water-soluble coating solution by a blade coater, then the running direction is changed by a turning roll T, and water is sprayed on an uncoated portion in the vicinity of the direction change point. It is a schematic diagram shown.
[0014]
In the figure, S is paper, T is a turning roll, D is an uncoated part, N is a spray nozzle, and water is made into small water droplets by the jet output using pressure air and sprayed toward the uncoated part. Yes. The smaller the water droplets, the more water can be uniformly contained on the paper surface. However, on the other hand, the spray range is too wide, and spray may reach the central part where spraying is not necessary. In such a case, a shielding plate is provided so that spray water is not applied to the central part. It is desirable to take measures.
[0015]
Although it is desirable to limit the supply of water to the uncoated part, since the uncoated part is in a very narrow range, the water droplets sprayed on the backing roll and other parts are actually applied. If the water droplets to be sprayed contain solids such as pigments or resin, these impurities become traps and accumulate on the backing roll and others, which fall on the paper surface and cause defects in paper quality. Sometimes. Therefore, it is preferable to use clean water as the water to be supplied. In principle, the recycled water is also filtered before use.
[0016]
A schematic diagram of FIG. 2 is given as a second embodiment of the invention. 2, as in FIG. 1, B is a backing roll, P is a blade, and D is an uncoated portion. FIG. 2 shows a state where water droplets are sprayed from the nozzle N to the uncoated portion D at the outlet of the doctor blade P of the blade coater.
[0017]
The amount of water supplied to the uncoated part D needs to be approximately equal to the central part and the drying speed, but while observing the state of the paper after drying at the dryer outlet or at the dryer outlet Since the moisture content of the central portion and the uncoated portion is measured and adjusted to an appropriate supply amount so that the moisture content of both is substantially equal, the drying speed can be adjusted without any particular measurement.
[0018]
【The invention's effect】
According to the present invention, the drying speed of the uncoated portions at both ends is substantially equal to that at the central portion, so that the stress generated at the both ends particularly during the traveling of the paper is eliminated, and the paper break can be prevented.
[Brief description of the drawings]
FIG. 1 is a schematic diagram of an embodiment of the present invention. FIG. 2 is a schematic diagram of an embodiment of the present invention. FIG. 3 is an explanatory diagram of coating by a chamber applicator system. FIG. 4 is an explanatory diagram of coating by a jet fountain system. [Explanation of symbols]
B Backing roll D Uncoated part F Fountain H Blade holder N Spray nozzle P Doctor blade S Paper T Turning roll

Claims (3)

In blade coating, in which both sides of the paper are coated with an uncoated part, fluid is supplied to the uncoated part after coating, and the drying speed between the uncoated part and the center part at both ends is almost the same. A method for preventing paper breakage in the manufacture of coated paper, wherein the amount of fluid supply is adjusted to be equivalent. In blade coating where coating is performed by providing an uncoated part at both ends of paper, after application, water drops are supplied to the uncoated part, and the drying speed or moisture content between the uncoated part and the center part at both ends is applied. A method for preventing paper breakage in the manufacture of coated paper, characterized in that the amount of water supply is adjusted so that the rate is substantially equal. In blade coating, in which both sides of the paper are coated with an uncoated part, after application, water droplets are supplied to the uncoated part, and both ends of the paper at the exit of the next dryer following blade coating A method for preventing paper breakage in the manufacture of coated paper, characterized in that the water supply amount is adjusted so that the difference in water content between the uncoated portion and the central portion is 1.0% or less.

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