JPH08296190A - Drying of formed web - Google Patents

Abstract

PURPOSE: To extremely shorten a drying time and to enable drying at a low temperature. CONSTITUTION: A forming solution containing at least a fiber material in a dispersed state is separated from a liquid component by a scooping net by removal of the solution to give a formed web in a hydrous state. Hot air is sent from the top of the formed web in a hydrous state and the lower space under the scooping wet is made into an evacuated state. The formed web is dried by passing the hot air through it. A thick and a heavy formed webs can be readily dried to an absolute dry state and a formed web in a hydrous state can be dried with slight heat history.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for drying a papermaking web, and more particularly to a method for drying a water-containing web obtained by a batch type papermaking method.

[0002]

2. Description of the Related Art Generally, when a web is manufactured by a papermaking method, the water-containing papermaking web obtained by scraping with a plow net is squeezed by a press part to remove liquid, and then repeatedly pressed on a heating roller by a dryer part. And it is continuously dried. However, in the case of a web having a large basis weight, drying by the continuous method as described above is not preferable because it takes a long time to dry, and a batch type method using a heating press or a box dryer is used. It is generally dried.

However, the water-containing papermaking web has a low strength, and a large papermaking web has a risk of being deformed or broken when being moved to the drying step. In addition, when the papermaking web is a composite of synthetic resin, there is a problem that the synthetic resin undergoes a thermal history and is deteriorated by heating for a long time.

Conventionally, as a method for shortening the drying time of a water-containing papermaking web, a method described in JP-A-6-41900 is known. In this method, a high frequency is applied to the hydrous web to heat the inside thereof and dry the remaining water. However, when the papermaking web is made of a conductive material such as carbon fiber, the above method cannot be put into practice because discharge occurs when a high frequency is applied.

[0005]

The inventors of the present invention have completed the present invention as a result of earnest research in view of the above problems, and the object of the present invention is to include at least a fiber material in a dispersed state. The papermaking liquid is dewatered with a plow net,
It is an object of the present invention to provide a method for drying a papermaking web, which can efficiently dry the obtained water-containing papermaking web and can also dry a thick papermaking web in a short time.

[0006]

An object of the present invention is to dry a papermaking liquid containing at least a fibrous material in a dispersed state, and a water-containing papermaking web obtained by deliquoring a liquid component with a scouring net, While heating air is sent from above the papermaking web, the space below the plow net is depressurized, and the heating air is passed through the papermaking web to dry the papermaking web. It

The water-containing papermaking web in the present invention is obtained by a batch-type papermaking method, and the papermaking liquid used may be a dispersion of only the fiber material, other than the fiber material and resin powder or the like. The material may be mixed and dispersed. That is, examples of the water-containing papermaking web obtained include a web composed only of a fiber material, a composite web composed of a fiber material and a resin powder, and the like.

The method for removing the papermaking liquid by means of a sieve is not particularly limited, and examples thereof include a natural flow-down type and a forced flow-down type by reducing pressure.

In the method of the present invention, the space below the mesh is maintained under reduced pressure so that heated air can quickly pass through the papermaking web. The size of the reduced pressure may be appropriately set as necessary, and is preferably 500 Torr or less. The degree of pressure reduction is usually high at the start of drying and low at the end of drying. The method for maintaining the depressurized state is not particularly limited, and a known appropriate method may be used. As such a depressurizing method, there can be mentioned, for example, a method using a vacuum pump such as an oil rotary type or a water ring type. However, since the method using the water ring type vacuum pump may suck liquid or vapor, it is necessary to provide a trap. It is preferable because it can be used even when liquid is removed during papermaking.

In the method of the present invention, heated air is sent from above the papermaking web, and the space below the mesh is depressurized. The temperature of the heated air may be appropriately set within a range that does not denature them, depending on the types of materials constituting the papermaking web. The temperature of the heated air is, for example, 3
It is about 0 to 150 ° C.

In the method of the present invention, unnecessary heating is avoided and the drying operation is completed promptly, so that the heat history of the web can be reduced, and at the same time, thermal energy can be saved. Therefore, in the method of the present invention, it is preferable to measure the temperature of the heated air sent to the papermaking web and the temperature of the heated air that has passed through the papermaking web to determine the temperature difference between the two. That is, the dry state can be sequentially confirmed by determining the temperature difference between the temperature of the heated air passing near the upper surface of the papermaking web and the temperature of the air passing near the lower surface of the papermaking web. When this happens, the drying operation may be terminated.

The temperature of the heated air that has passed through the papermaking web is
While the water content of the papermaking web is high, the temperature difference is relatively low and the temperature difference is large. However, the water content increases as the water content decreases, and when the water content reaches a dry state, the temperature difference almost disappears. The above-mentioned predetermined temperature difference in the present invention can be appropriately set according to the required dry state, for example, 0.5 to 1.5 ° C,
Usually, it becomes almost dry at about 1.0 ° C.

If the temperature of the heated air sent to the papermaking web is known in advance, the drying operation can be terminated when the temperature of the heated air passing through the papermaking web reaches a predetermined temperature. In this method, the drying operation can be terminated when the temperature of the air passing through the lower surface of the papermaking web reaches a temperature lower than the temperature of the heated air sent to the papermaking web by the above-mentioned predetermined temperature difference.

[0014]

EXAMPLES The present invention will now be described in more detail with reference to its examples.

Example 1 3.37 kg of carbon fiber having a fiber length of 50 mm and powdery phenolic resin (trade name: Bell Pearl, manufactured by Kanebo) 3.37
A fiber / resin dispersion liquid prepared by dispersing 1 kg and an aqueous medium was prepared as a papermaking liquid. This papermaking liquid is provided with a sieve mesh (500φ, 80
It was poured onto the mesh and drained to obtain a water-containing papermaking web having a thickness of 10 cm. The temperature sensor A was installed on the upper surface of the obtained papermaking web, and the temperature sensor B was installed between the lower surface of the papermaking web and the plow net.

Next, while keeping the space below the plow net in a depressurized state, air heated to 60 ° C. was sent from above the obtained paper making web to pass through the inside of the paper making web for drying. Twenty-five hours after the start of drying, the temperature difference between the temperature sensor A and the temperature sensor B became 1.0 ° C., and the drying operation was terminated at this point. The results are as shown in Table 1.

Example 2 The water-containing papermaking web obtained in the same manner as in Example 1 was carried out except that the drying operation was terminated at the time when the temperature indicated by the temperature sensor B in Example 1 reached 59 ° C. It was dried as in Example 1. Drying was completed 24 hours after the start of drying. The results are shown in Table 1.
Was about the same.

Comparative Example 1 The water-containing papermaking web obtained in the same manner as in Example 1 was carefully taken out, transferred to a box dryer, and dried at 110 ° C. for 50 hours by the box dryer. The results are as shown in Table 1.

[0019]

[Table 1]

[0020]

EFFECTS OF THE INVENTION According to the method of the present invention, since heated air is forced to pass through the water-containing papermaking web after papermaking, the inside of the papermaking web is rapidly dried, and the drying time is significantly shortened. be able to. Therefore, it is possible to easily dry a water-containing paper web having a large thickness and a water-containing paper web having a large basis weight to an absolutely dry state.

Further, according to the method of the present invention, it is possible to perform drying at a low temperature in a short time, and it is possible to perform drying with a small heat history. Therefore, the method of the present invention is extremely suitable for drying a papermaking web for molding, which is composed of a fiber material and a resin powder.

Claims (3)

[Claims] 1. When drying a water-containing papermaking web obtained by draining a papermaking liquid containing at least a fibrous material in a dispersed state by a drainage, heated air is sent from above the papermaking web. At the same time, the space below the sieve net is depressurized, and the heated air is passed through the papermaking web to dry the papermaking web. 2. A temperature difference between the temperature of heated air passing near the upper surface of the papermaking web and the temperature of air passing near the lower surface of the papermaking web is measured, and the temperature difference reaches a predetermined temperature or less. The method for drying a papermaking web according to claim 1, wherein the drying is finished at that point. 3. The papermaking process according to claim 1, wherein the temperature of the heated air fed from above the papermaking web is kept constant, and the drying is terminated when the temperature of the air passing near the lower surface of the papermaking web reaches a predetermined temperature. How to dry the web.