JPH0566895B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a fiber-reinforced anhydrous gypsum board (hereinafter simply referred to as gypsum board) and a method for manufacturing the same. More specifically, the present invention relates to a plate material and an industrial continuous manufacturing method thereof, which comprises forming a sheet from a slurry containing molded anhydrous gypsum, short fibers, and a hardening accelerator, and press-forming this sheet. (Prior Art) Gypsum board is a noncombustible material with excellent bending strength, dimensional stability, fire resistance, and heat insulation properties. In addition, since it has similar processability to plywood in terms of sawing, nailing, and curved surface processing, it is widely used as a material for fireproofing and fire protection manufacturing. Regarding the manufacturing method of this gypsum board,
There are inventions disclosed in No. 253639, No. 57-49004, No. 55-36628, Japanese Unexamined Patent Publication No. 60-42267, and No. 60-171261, etc., but the gypsum plates of these inventions are Hemihydrate gypsum is used for the matrix. However, since the hydration reaction of hemihydrate gypsum is rapid, there have been many problems in paper forming using a round net or fourdrinier machine. That is, the production process from kneading raw materials and water to papermaking and pressurization requires a considerable amount of time. During this period, it is necessary to delay the hydration reaction of hemihydrate gypsum, and a setting retarder is used. There are many disturbance factors to the setting retardation effect of hemihydrate gypsum, which has had a serious adverse effect on process control and quality control. The first disturbance factor is that during the papermaking process, part of the hemihydrate gypsum flows through the mesh into the manufacturing water, and while passing through the circulation system, the hemihydrate gypsum turns into dihydrate gypsum, causing the manufacturing water to be reused. In some cases, dihydrate gypsum is mixed in. This dihydrate gypsum acts as a setting accelerator for hemihydrate gypsum even if it is present in small amounts, so
This causes fluctuations in the coagulation time of the raw materials, hindering the stability of the process. The second disturbance factor is that when cut scraps of raw sheets and raw defective products are reused as raw materials, the dihydration reaction is in progress, so the quantity and
The temporal variation is a variation in the amount of gypsum dihydrate, which affects the setting. The third disturbance factor is a variation in the residence time of the raw material slurry due to equipment malfunction or failure, which also causes a variation in the dihydration reaction before molding, and has a significant impact on the process. Furthermore, when the cured product is cut into predetermined dimensions, chips, damaged products, and defective products are generated. Since the scrap powder that has been pulverized for recovery and use is in the form of dihydrate gypsum, this also results in fluctuations in the dihydration reaction. However, it is also possible to calcinate the material after pulverization to make it semi-hydrated, but this requires equipment. In this way, when performing paper forming using hemihydrate gypsum as a matrix, there were many problems in stabilizing the setting. The above-mentioned Japanese Patent Publication No. 57-49004 is an invention by the present inventors, which improves the above-mentioned drawbacks of papermaking using hemihydrate gypsum, and improves the contact time and residence time between hemihydrate gypsum and water. This is to ensure stable operation by reducing the amount of These require new paper making machines and scrap burning equipment. In addition, a method of blending dihydrate gypsum as it is without installing scrap firing equipment was published in 1983.
Part of this is disclosed in Publication No. 171261. There are the above-mentioned problems when mixing dihydrate gypsum with hemihydrate gypsum, and even if production is possible by using a large amount of setting retarder, product properties such as bending strength and dimensional changes may be affected. New problems arise, such as a decrease in peel strength, interlayer peel strength, etc. On the other hand, molded anhydrous gypsum cures slowly, so it is a raw material that is rarely used other than in small quantities as plaster. (Problems to be Solved by the Invention) In the conventional method for manufacturing gypsum plates using hemihydrate gypsum, there are too many factors that change the setting time, making process management complicated and difficult. In addition, in order to solve these difficulties, large amounts of setting retarders were added, but as a result, setting fluctuated over a long period of time, resulting in uncured particles remaining uncured for several days after production. The situation continued and the product properties deteriorated. Since one-type anhydrous gypsum has a slow hydration rate, a curing accelerator is usually added to it, and curing is almost completed in four weeks or more. However, when paper molding is performed using molded anhydrous gypsum as a raw material, the hydration rate fluctuates greatly even with the addition of hardening accelerators, making it difficult to obtain constant values for product strength, delamination strength, dimensional change rate, etc. In addition, there were also drawbacks such as the occurrence of efflorescence and powderiness, and the performance as an industrial product could not be obtained. The objects of the present invention are (1) to obtain a gypsum board with a high hydration rate and high quality using type anhydrous gypsum as a raw material, and (2) to solve the problems of stability and ease of production in the papermaking process. (Means for Solving the Problems) The present inventors have completed the present invention by conducting intensive research on manufacturing and property improvement using various types of gypsum. The gist of the present invention is to
98-60% by weight, short fibers 2-40% by weight anhydrous gypsum and 100 parts by weight of short fibers, 5-80% inorganic powder
Parts by weight and gypsum hardening accelerator (0.5 to 3.5 parts by weight based on type anhydrous gypsum), and the hydration rate
Anhydrous gypsum paper making with a content of 45% or more and slurry mainly composed of these raw materials are made into sheets,
The present invention relates to a method for producing a fiber-reinforced anhydrous gypsum paper board, which comprises press-forming this sheet at a pressure of 1 to 300 kg/cm ² . Short fibers consist of asbestos or a combination of asbestos and other fibers, or of pulp or a combination of pulp and other non-asbestos fibers. For pressure molding, the pressure ranges from a low pressure of 1 to 10Kg/ ^cm2 to 10Kg/cm2.
It is carried out in the low to medium pressure range of ~300Kg/ ^cm2 . In addition, 5 to 80 parts by weight of inorganic powder is added to 100 parts by weight of the molded anhydrous gypsum and short fibers. The steps of the manufacturing method according to the present invention are as follows. That is, 5 to 15 times as much circulating water is added to the raw material to form a slurry, which is retained in a chiest to homogenize the kneaded material, and this slurry is formed into a sheet using a circular wire or Fourdrinier machine. Cut the edge of this raw sheet and use a roll press or surface press to produce 1 to 10 kg/cm ^{2 (roll press pressure is a value calculated from the specific gravity of the product) or surface press to produce 10 to 300 kg/cm 2}
Perform pressure molding of Kg/cm ² . This pressing force is selected within the range of 20 to 90% of the material composition, product strength, and moisture content of the green sheet (referred to as green sheet moisture content). This pressurized green sheet is cured until hydrated and hardened. At this time, it is necessary to cure the edges of the board so that they do not dry out. The curing period is 2 days or more, preferably 3 days or more and about 2 to 3 weeks. After curing, it is dried if necessary and cut into standard dimensions to be manufactured into products. If pressure molding is not performed here, the product will not have good surface smoothness and will also have low strength. Furthermore, if the pressing force exceeds 300Kg/cm ² , the moisture content of the raw sheet will not be secured, and accordingly, the water necessary for hydration and the specified amount of curing accelerator will not be secured in the sheet. . Therefore, the hydration of the product does not proceed and the properties of the product deteriorate. In papermaking, the kneaded slurry is used to form a film mainly composed of solids in the slurry using the suction force of a rotating drum whose surface is formed with a net.A suitable number of films are laminated on a making roll to form a sheet. do. Paper making is carried out using a circular mesh machine or a Fourdrinier machine that supplies slurry onto a belt conveyor surface with a dewatering function to form a gypsum board. Roll press in pressure forming also includes pressurization of a circular mesh making roll. The temperature of the circulating water during papermaking is 10℃ from the viewpoint of manufacturing efficiency.
The temperature is preferably 20°C or higher. The upper limit is around 35℃ due to the curing effect. The material-related configuration of the present invention is as follows. As the molded anhydrous gypsum, general-purpose ones such as natural dihydrate gypsum, calcined dihydrate gypsum produced as a by-product during the production or removal of phosphoric acid or titanium, or molded anhydrous gypsum produced as a by-product during the production of hydrofluoric acid are used. In addition, the fineness of molded anhydrous gypsum is Blaine value 2000 ~
It is about 9000cm ² /g. This range is selected from the viewpoints of permanence and hydration reactivity. The amount of mold anhydrous gypsum is 98-60% by weight. The amount of molded anhydrous gypsum is determined in relation to 2 to 40% by weight short fibers. If the fiber content is less than 2%, a large amount of solid content flows out through the wire gauze during papermaking, making papermaking impossible. Furthermore, if the fiber content exceeds 40%, it will no longer be a gypsum board but a fibrous board. As a result, the strength of the product and the adhesion between the layers deteriorate, making it unusable as a gypsum board. 5 to 80 parts by weight of inorganic powder is mixed with 100 parts by weight of molded anhydrous gypsum and short fibers. The amount of short fibers is between 2 and 40% by weight. Asbestos or a combination of asbestos and other fibers is used as the short fiber. If asbestos is not used, pulp or a combination of pulp and other non-asbestos fibers is used. The short fibers used are asbestos and cellulose (pulp).
natural fibers such as glass fibers, carbon fibers, glass wool, rock wool, ceramic wool, and other general-purpose fibers, as well as synthetic fibers such as polyamide, polypropylene, polyvinyl alcohol, polyester, polyethylene, and acrylic. , can be used alone or in combination depending on the moisture content of the green board, product strength, etc. Asbestos is used to improve the strength of the product and the moisture content of the green board, but due to regulations, the amount of asbestos is 10% or less, preferably 5% or less. When non-asbestos fibers are used, the amount of pulp is 1% or more, preferably 2-10%. If the pulp content is 1% or less in a non-asbestos type, the dispersion and yield of raw materials during papermaking will be poor, making production extremely difficult. Moreover, if it exceeds 10%, the dispersion of pulp will be poor during paper making, it will be difficult to obtain homogeneity of the material, and non-combustibility will not be obtained as a building material. The pulp is beaten to a predetermined degree of beating, if necessary. The degree of freeness is 800 to 30ml in terms of Canadian Standard Freeness (CSF), and the degree of freedom varies depending on the blending amount and the combination of fibers. In the case of a non-asbestos type, the amount is preferably about 500 to 50 ml from the viewpoint of dispersion during papermaking, yield, product strength, delamination strength, and moisture content of green board. Beating is carried out using a general-purpose machine such as a pulper, disk-cliff reiner, or cone-type refiner. As a hardening accelerator for molded anhydrous gypsum,
H ₂ SO ₄ , K ₂ SO ₄ , Na ₂ SO ₄ , (NH ₄ ) ₂ SO ₄ ,
MgSO ₄ , ZnSO ₄ , FeSO ₄ , CuSO ₄ , Al ₂ (SO ₄ ) ₃ and their double salts such as KAl (so ₄ ) ₂ 12H ₂ O,
Alums such as NaAl(SO ₄ ) ₂・12H ₂ O, NH ₄ Al(so ₄ ) ₂・12H ₂ O, chlorides such as NaCl, CaCl ₂ , MgCl _{2 ,} acid hydrogen salts such as NaHSO ₄ , KHSO ₄ , NaNO ₃ ,
General-purpose nitrates such as NH ₄ NO ₃ and KNO ₃ can be used alone or in combination. The amount of hardening accelerator is the amount retained in the plate and is 0.3 to 4.0%, preferably 0.5 to 3.5%, based on the molded anhydrous gypsum.
If this amount is less than 0.3%, the hydration rate and bending strength will be extremely low even after curing for more than 4 weeks.
Practical materials cannot be obtained. Addition of more than 4.0% has no effect on improving bending strength, etc., and on the contrary increases the rate of dimensional change, causing efflorescence. In addition, filtration performance during production also deteriorates. In addition to the hardening agents mentioned above, CaO, Ca(OH) ₂ , Mg
(OH) ₂ Cement, chlorine in basic slag, silica gel, etc. also have the effect of accelerating hardening, and are sometimes used in combination. In this case, since there is no risk of efflorescence, it is added up to about 10%. Inorganic powders can be divided into three types based on their usage functions. Fine powder with a first fineness of about 7000 cm ² /g or more, such as bentonite, activated clay, sepiolite, attapulgite, other clay minerals,
Examples include silicon dust and diatomaceous earth. This fine powder is used as an auxiliary material during papermaking to obtain homogeneity of the raw material by improving the dispersibility of the raw material and adjusting the elapsed time. It is also used to improve the delamination strength and moisture content of green boards. The amount is 0-20%, preferably 3
~10%. If it exceeds 20%, a large amount of raw material escapes into the waste water, making operation difficult and causing a decline in product properties. These materials are particularly effective in non-asbestos formulations, but can also be used in asbestos formulations. As the second inorganic powder, pulverized products (scraps) of cut products made of dihydrate gypsum are used.
This scrap is reused as part of the raw material. The amount is about 5-35%. The scrap of dihydrate gypsum does not affect the setting of molded anhydrous gypsum, so it is reused in its unfired state. Scrap is a mixture of crushed gypsum and fine fibers and has the effect of improving the yield of raw materials. It is also used as an auxiliary material during papermaking to improve the dispersibility of raw materials, the delamination strength of boards, and the moisture content of green boards. Examples of the third inorganic powder include fillers or lightening materials such as limestone, slaked lime, silica stone, slag, fly ash, wollastonite, mica, pearlite, vermiculite, and shirasu balloon. The total amount of these inorganic powders is 0 to 50 when the molded anhydrous gypsum and staple fibers are 100 parts by weight.
Parts by weight are blended. It is expected to have the same effects as other inorganic powders. A polymer flocculant is sometimes added to improve the yield of raw materials. It is particularly used for non-asbestos materials, but it can also be used for asbestos materials. As the polymer flocculant, general-purpose products such as anionic sodium polyacrylate, polyacrylamide, nonionic polyacrylamide, and polyethylene oxide are used alone or in combination. The amount added is about 1 to 10 ppm. According to the method of the present invention, by using molded anhydrous gypsum and a hardening accelerator instead of hemihydrate gypsum and a setting retarder, there is no possibility that the setting reaction of gypsum will proceed during the papermaking process, and it will last for a long time. Continuous stable continuous operation over time is now facilitated. In addition, cutting waste or product scraps during the process do not affect the hydration reaction of molded anhydrous gypsum, so there is no need to add a setting retarder and they can be reused as raw materials as they are. For this reason, there is no need for new papermaking or firing equipment, and mass production is possible because the paper is manufactured using existing equipment. One type of anhydrous gypsum has a slow hardening speed, and for this reason hardening accelerators are added. However, during the papermaking process, the curing accelerator flowed out together with water and was not effectively captured in the plate. For this reason, a large amount of fiber was blended, and asbestos was used as the fiber, and when non-asbestos fiber was blended, beaten pulp was used, and the pressure was set in the range of 1 to 300 kg/cm ² . As a result, the moisture content of the raw board was increased, and hydration water and hardening accelerator were effectively secured in the board. From these reasons, the hydration rate is 45% as a gypsum board.
In addition, a product was obtained which had excellent properties such as bending strength, interlayer peeling strength, and dimensional change rate, and was free from phenomena such as efflorescence. (Example) The present invention will be explained in further detail with reference to the following examples. In the following Examples and Comparative Examples, slurries were prepared by kneading with a pulper using 5 times the weight of water relative to the total amount of raw materials. At this time, the raw materials were homogenized by adding a hardening accelerator, each fiber, fine powder such as bentonite, scrap, molded anhydrous gypsum, and other inorganic powder to water in this order. The slurry is passed through CHEST and the solid content concentration is 1/10.
diluted to
It was rolled up into a sheet using a making roll to a predetermined thickness. This sheet was pressure-formed using a press to have a thickness of about 6 mm. After pressure molding, curing was performed, and after curing, drying and cutting were performed. Note that Comparative Examples were also produced in the same manner. The formulations, manufacturing conditions, and property test results for each example and comparative example are shown in Tables 1 to 6.

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[Table] Examples 1 to 7 Tables 1 and 2 show changes in the mixing ratio of gypsum and short fibers and the results. Examples 8 to 12 Table 3 shows the formulations and results when the Canadian standard freeness (CSF) of short fibers and pulp was changed. Examples 13 to 19 and Comparative Examples 1 to 2 Table 4 shows the formulations and results obtained by changing the pressurization method and pressure. Examples 20 to 26 and Comparative Examples 3 to 7 Table 5 shows the formulations and results when potassium sulfate and sodium chloride were added as gypsum hardening accelerators. Examples 27 to 30 and Comparative Example 8 Table 6 shows the formulations and results when bentonite was blended as an inorganic powder. The test methods in Tables 1 to 6 showing the results of Examples 1 to 30 and Comparative Examples 1 to 8 are as follows. Test method Specific gravity: Based on JISA5418 asbestos cement calcium silicate plate Bending strength: Based on JISA5418 asbestos cement calcium silicate plate (bending strength) Dimensional change rate: Based on JISA5418 asbestos cement calcium silicate plate (length change rate) Board moisture content: Compliant with JISA5418 asbestos cement calcium silicate board (water content) (drying at 60℃ for 24 hours) Peel strength: Pull a 5 x 5 cm board in the thickness direction and measure the interlayer strength between the boards . Hydration rate: Dry the ground sample at 45℃,
The temperature was raised to ℃ and the amount of dehydration of crystal water from dihydrate gypsum was measured. The hydration rate was determined from the amount of gypsum mixed. Efflorescence test: Immerse the bottom 5 cm of the test specimen width 5 x length 20 cm in water and store it in a constant temperature room at a temperature of 20°C and humidity of 60%.
Visually observe the condition after 2 weeks. ◎ Not at all ○ Hardly any △ Partial cracking × Significant part cracking Surface smoothness: Determined by visual observation of a 50 x 40 cm test piece. ◎ Good ○ Almost good △ Some unevenness × Some unevenness (Effects of the invention) (1) Type anhydrous gypsum is used, and the gypsum board has a high hydration rate, high bending strength, small dimensional change rate, and no interlayer A noncombustible building material with high peel strength, no efflorescence, and excellent workability such as sawing, nailing, and bending workability was obtained. (2) Compared to using conventional hemihydrate gypsum, when molded anhydrous gypsum is used, manufacturing stability can be easily obtained and products with stable quality can be obtained, making industrial production easier. I was able to do it. (3) By using molded anhydrous gypsum, when recovering materials during the manufacturing process and product scrap, the recovered material does not affect the hydration reaction of molded anhydrous gypsum, so it can be reused as part of the raw material. be done. Therefore, no new manufacturing or scrap firing equipment is required, resulting in greater resource and energy savings. (4) By improving the amount of anhydrous gypsum in the mold, the blend of short fibers, and the pressure of pressurization, it was possible to effectively trap hydration water and hardening accelerator in the board. These improvements have improved the hydration rate, making it possible to use type anhydrous gypsum with low utility value, such as type anhydrous gypsum produced as a by-product from the hydrofluoric acid production process, in its original form.

Claims (1)

[Claims] 1 Type anhydrous gypsum 98-60% by weight and short fibers 2
5 to 80 parts by weight of an inorganic powder and a gypsum hardening accelerator are added to 100 parts by weight of a ~40% by weight mixture to form a slurry, and the slurry is made into a paper.
Pressure molded at 1 to 300 kg/ ^cm2 , the amount of hardening accelerator in the molded body is 0.5 to 3.5 parts by weight based on the mold anhydrous gypsum, and the moisture content of the green board is 20 to 90%, A method for producing an anhydrous gypsum paper board, characterized in that the hydration rate after drying is 45% or more. 2. The manufacturing method according to claim 1, wherein the short fibers are pulp with a Canadian standard freeness of 600 to 50 ml.