JPS6344706B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing a gypsum board, and more specifically to a method for manufacturing a gypsum board, which is accompanied by a phenomenon in which wrinkles form on the surface of the product, making it look like an elephant skin, which significantly deteriorates the appearance and properties of the product (hereinafter referred to as elephant skin phenomenon). The present invention relates to a method for manufacturing a gypsum board without any gypsum using a round netting method. In order to manufacture gypsum board using the round netting method, a slurry containing gypsum, fibers and water is made into paper using a round netting machine, but the gypsum conventionally used in the round netting method is manufactured by Gypsum Lime Journal No. 144 (1976). As shown on page 19, its fineness is Blaine value 7000 ~
It was about 8000cm ² /g. However, the conventional round-mesh papermaking method has the disadvantage that elephant skin phenomenon tends to occur on the surface of the obtained product, and the mechanical strength is significantly reduced. As a countermeasure to this problem, it is possible to suppress the occurrence to some extent by reducing the speed of papermaking, but it is not perfect and has the drawback that productivity is significantly reduced. The present inventors sought a method for manufacturing gypsum board using a circular mesh paper manufacturing method that eliminates the drawbacks of the conventional round mesh paper manufacturing method, does not involve the occurrence of the elephant skin phenomenon, and does not reduce productivity compared to the conventional method. As a result of research, the β
-The fineness of hemihydrate gypsum is 1000 cm ² /g in Blaine value.
The present invention was completed based on the knowledge that these problems can be solved by reducing the density to less than 6000 cm ² /g. That is, the gist of the present invention is that β-hemihydrate gypsum,
When manufacturing a gypsum board by making a slurry containing fibers, a setting retarder, and water using a circular mesh papermaking machine, the fineness must be 1000 cm ² /g or more in Blaine value 5000.
A slurry with a concentration of 7 to 15% is made using β-hemihydrate gypsum with a density of less than cm ² /g or a raw material in which 50% by weight or less of a filter aid with a Blaine value of 2000 to 5000 cm ² /g is added to the gypsum. This is a method for producing a gypsum board, which is characterized in that it is processed using a belt conveyor equipped with a vacuum dewatering device at a speed of 40 to 65 m/min. By the source of β-hemihydrate gypsum, naturally produced gypsum and by-product gypsum from exhaust gas desulfurization and phosphoric acid production are used. The fibers used include inorganic fibers such as asbestos, glass fiber, and rock wool, and organic fibers such as pulp, nylon, polypropylene, and acrylic. The fineness of β-hemihydrate gypsum is 1000 in Blaine value.
If it is less than cm ² /g, the solid content of the slurry will tend to settle, making it difficult to scoop out, and the resulting product will have less flexibility and strength. Moreover, if it is 5000 cm ² /g or more, the occurrence of elephant skin phenomenon will be observed in the gypsum board obtained by the round net papermaking method, which will significantly reduce the strength. In addition, the β-hemihydrate gypsum component in the slurry tends to migrate into the superhydrate, and the yield of gypsum decreases accordingly. Furthermore, the moisture content of the paper-formed raw board also increases. The optimal time from the time of slurry preparation to the time of papermaking varies depending on the raw materials used and the specifications of the final product, and correspondingly, conventional setting retarders such as citric acid, its salts, amino acids, its salts and proteins, A modified product thereof can be used. In the method for manufacturing a gypsum board of the present invention, a conventional circular mesh machine is used. That is, from a slurry obtained by kneading β-hemihydrate gypsum, fibers, water, and a gypsum setting retarder, a plurality of solids are extracted using a plurality of circular mesh rotating drums. A film of the solid slurry is laminated on the surface of a belt conveyor equipped with a vacuum dewatering device, and then this laminated film is further rolled together while applying roll pressure with a making roll to obtain a primary gypsum board, so as to have a predetermined thickness. Further, this primary gypsum board is molded with or without pressure and dried to obtain a gypsum board product. The thickness of the product is approximately 4 to 10 mm. In this case, the elephant skin phenomenon of the gypsum board occurs at the stage where the laminated film is roll-pressed by the making roll. Further, powders such as limestone, silica, talc, pearlite, vermiyukilite, mica, slag, fly ash, etc. can be used in combination as a supplementary material. The powder degree at this time is preferably 2000 to 5000 cm ² /g. The amount added is 50% by weight or less based on the gypsum. In addition, the pH of the slurry during papermaking is 5.5 to 110.
If so, the strength of the gypsum board produced by the method of the invention is further increased. The speed of the belt conveyor with vacuum device is 40
~65 m/min is preferred. If it is less than 40 m/min, the dehydration and pressure properties of the film can be improved to some extent and elephant skin can be reduced, but if it is dehydrated too much and the water content is lowered too much, the adhesion between the layers will decrease when laminated. Along with the quality deterioration, fiber orientation and productivity are significantly reduced. Further, if the speed exceeds 65 m/min, elephant skin phenomenon occurs even if the raw material composition, operating conditions, etc. are changed, and a homogeneous flat plate cannot be obtained, resulting in a decrease in quality, which is not preferable. In addition, in the present invention, the slurry concentration is approximately 10% from the viewpoint of normal fiber dispersibility, film homogeneity, and productivity (thickness of sheeting into a circular screen), and 7 to 7%.
A range of 15% is preferred. If the slurry concentration is higher than 15%, fiber dispersibility, film homogeneity, and papermaking properties will deteriorate, as well as film dehydration and pressure properties will deteriorate, resulting in frequent occurrence of elephant skin phenomenon. Also, when the slurry concentration becomes thinner than 7%,
This is not preferable because the paper thickness decreases, the water content of the film decreases too much, and this causes poor adhesion between laminated layers and a decrease in productivity. In addition, increasing the vacuum dehydration pressure improves the dehydration properties, lowers the water content, and reduces the elephant skin phenomenon. Vacuum dehydration draws water from the film through a belt conveyor (felt cloth), so there may be some leakage, and if the vacuum pressure is lowered too much, it will put too much load on the belt conveyor, causing problems such as belt conveyor slipping and stopping. occurs. Furthermore, if the water content of the film is reduced too much, the same problem of poor adhesion between layers as described above will occur. Therefore, the vacuum dehydration pressure is 10 to 76cmHg using the Bourdon tube gauge pressure (scale 0 to 76cmHg, minO, max76cmHg).
It is preferable to set it to 50cmHg. According to the present invention, a gypsum board having a beautiful surface without the elephantine phenomenon on the surface of the product can be manufactured by the round-mesh papermaking method without reducing productivity and increasing the strength of the product. Furthermore, according to the present invention, there is less gypsum flowing out into water. As a result, less gypsum dihydrate is produced in the recycled water, and the promoting effect of gypsum dihydrate on setting of gypsum is significantly reduced, making stable operation possible over a long period of time. Next, the embodiments of the present invention will be described with reference to Examples, but the present invention is not limited thereto. Note that % and parts in the text indicate weight % and parts by weight, respectively, unless otherwise specified. Examples 1 to 4, Comparative Examples 1 to 5 β-hemihydrate gypsum having the fineness shown in Table 1
67.5% with 10% pulp, 10% asbestos, 2.5% glass fiber and 10% limestone powder. In addition, 0.3% of modified amino acid salts, which are denatured by hydrolyzing proteins, were added to each blended composition as a gypsum setting retardant, based on the amount of gypsum.
10 parts of water is added to 1 part of each blended composition and stirred with a pulper to form a slurry, and this slurry is made into paper using a circular mesh paper machine having four cylinders equipped with wire mesh. Body 100Kg/
Pressure was applied using a cm ² surface pressure press to obtain each gypsum board. The setting time, bending strength, and moisture content of each gypsum board were measured, and the results are shown in Table 1.

[Table] As is clear from Table 1, the Blaine value is 1000cm ² /g
In the example products using gypsum having a fineness of less than 5000 cm ² /g, no elephantine phenomenon was observed on the surface, and the bulk specific gravity and bending strength were also high, and the green plate obtained in the manufacturing process was It was found that the water content was low and the setting time was long, resulting in good workability. It was also observed that productivity was improved by 30% compared to the conventional method.

Claims (1)

[Claims] 1 When manufacturing gypsum board by making a slurry containing β-hemihydrate gypsum, fibers, setting retardant, and water using a circular mesh machine, the fineness is the Blaine value.
β-hemihydrate gypsum that is 1000 cm ² /g or more and less than 5000 cm ² /g or 2000 to 2000 in Blaine value for the gypsum
A slurry with a concentration of 7 to 15% is made using raw materials to which 50% by weight or less of a filter aid of 5000 cm ² /g is added,
A method for producing a gypsum board, which is characterized in that it is processed by a belt conveyor equipped with a vacuum dewatering device at a speed of 40 to 65 m/min.