JPH1192207A - Production of gypsum thin-formed board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an inexpensive thin-formed board high in mechanical strength by incorporating α-gypsum hemihydrate as a byproduct from the wet phosphoric acid production process with a fibrous material, water, and, as necessary, an admixture and a setting regulator to prepare a mixed slurry at a specific temperature which, in turn, is subjected to filtration and drying. SOLUTION: This gypsum thin-formed board is obtained through the following process: first, α-gypsum hemihydrate 15-35 wt.% in adhered water content produced as a byproduct in manufacturing wet phosphoric acid by decomposing igneous phosphate rock with sulfuric acid is dried and ground; next, the resulting α-gypsum hemihydrate is incorporated with a fibrous material (e.g. pulp fiber), hot water, and, as necessary, an admixture (e.g. wollastonite powder) and a setting regulator (an alkaline substance such as NaOH or a hardenable alkaline inorganic matter like cement) to prepare a slurry at a temp. of 40-80 deg.C; wherein the setting regulator is intended for the pH adjustment of the resulting slurry, its amount to be added being 0.1-5 pts.wt. based on 100 pts.wt. of the α-gypsum hemihydrate; the resultant slurry is then dehydrated using a vacuum filter, molded and then dried.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a gypsum sheet.

[0002]

2. Description of the Related Art Conventionally, a gypsum sheet is prepared by adding powdered hemihydrate gypsum (mainly β-hemihydrate gypsum), a fibrous substance, a hardening regulator for hemihydrate gypsum and / or other admixtures, and adding water. The slurry is mixed to form a mixed slurry, the slurry is formed into a film by solid-state rotating drum, the obtained films are laminated, dewatered, pressed, and dried. Also, using α hemihydrate gypsum, the slurry temperature condition was 85
It has also been proposed that the temperature be set to a temperature of at least ℃.
No. 42).

According to the conventional method described above, gypsum hemihydrate gypsum is used as a gypsum raw material, but α-hemihydrate gypsum is not actually used because the production cost of α-hemihydrate gypsum powder is high. When β-hemihydrate gypsum is used, the β-hemihydrate gypsum is generally obtained by calcining in a gas phase at 120 to 170 ° C. in a Celtic kiln, so that gypsum dihydrate, type III or type II anhydrous gypsum is mixed, The stability of the setting and hardening time is poor, and the strength is also negative. Therefore β compared to α hemihydrate gypsum
In addition to the rapid setting and hardening of gypsum hemihydrate, there is a problem that a large amount of setting regulator is required in the paper making process to perform industrial continuous production in the paper making process, and it is difficult to control the setting and hardening. As a result, the quality of the product is degraded, and the cost burden is large.

[0004] Further, in the case of β-hemihydrate gypsum, since the filterability is poor, in order to obtain an ordinary gypsum sheet, it is necessary to prepare β-hemihydrate gypsum, a fiber substance, a filter aid, a setting regulator and / or other admixtures. Is added to water, and the slurry mixed with water is formed on the surface of a rotating drum to form a film of about 0.5 mm, and several films are combined to obtain a product having a predetermined thickness. Done. This method is inferior in productivity to a long knitting method in which the slurry is supplied onto a belt conveyor surface having a dewatering mechanism to obtain a product having a predetermined thickness in a single papermaking operation, and the method for producing a thick material is not suitable. Not suitable.

Further, a gypsum paper making machine characterized by adding a fibrous material or the like to a gypsum slurry obtained by pregelatinizing dihydrate gypsum by a pressurized aqueous solution method as disclosed in Japanese Patent Application Laid-Open No. 4-139042, wherein the slurry temperature is 85 ° C. or higher. Although a plate manufacturing method has been proposed, the manufacturing process is complicated, and the slurry temperature is as high as 85 ° C. or higher, so there are problems such as quality and cost.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a production method in which, when β-hemihydrate gypsum is used, the slurry has poor filterability and low productivity. Further, it is difficult to control the setting and hardening time, and a setting regulator is required. On the other hand, when α-hemihydrate gypsum disclosed in Japanese Patent Application Laid-Open No. 4-19042 is used, the production process is complicated, and the slurry temperature is 8
Since the temperature is as high as 5 ° C. or more, there are problems such as quality and cost.

[0007]

According to the present invention, α-hemihydrate gypsum obtained as a by-product when phosphoric acid is produced by a wet phosphoric acid production method is used, and a specific additive is added thereto to form a mixed slurry. It has been found that the slurry temperature is produced at a low temperature.

That is, the present invention provides a mixed slurry by adding a fibrous substance, water, and, if necessary, an admixture and a setting modifier to α-hemihydrate gypsum obtained when phosphoric acid is produced by a wet phosphoric acid production method. The present invention relates to a method for producing a gypsum paperboard, wherein the temperature is 40 to 80 ° C.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.
The present invention is characterized in that α-hemihydrate gypsum obtained as a by-product when phosphoric acid is produced by a wet phosphoric acid production method is used, and the mixed slurry temperature is as low as 40 to 80 ° C.
The phosphoric acid obtained by the wet phosphoric acid production method is phosphoric acid obtained by reacting a phosphate rock with an inorganic acid in a liquid phase, and is also called wet phosphoric acid.

The wet phosphoric acid production method includes a sulfuric acid method, a hydrochloric acid method, and a silicic acid method. Among the sulfuric acid methods, there are a dihydrate hemihydrate method, a hemihydrate dihydrate method, and an anhydrous method. The wet phosphoric acid production method used in the present invention,
It is the dihydrate / hemihydrate method of the sulfuric acid method. Examples of the type of phosphate rock used include igneous phosphate rock, aqueous phosphate rock, buried phosphate rock, and the like, but are not particularly limited, but igneous phosphate rock with less impurities is preferably used. Igneous phosphate rock is
Coal ore (former Soviet Union), farabora ore (South Africa) and the like are used, and the wet phosphoric acid production method (diwater-hemihydrate method) using these decomposes igneous rock phosphate rock with sulfuric acid to obtain wet phosphoric acid. At that time, the α-hemihydrate gypsum containing 15 to 35% of by-product adhering water is immediately dried and pulverized, and can be used as a product as it is. It is also possible to add a setting regulator as needed and use it for each application.

The setting modifier added to α-hemihydrate gypsum is used for adjusting the pH of the mixed slurry of α-hemihydrate gypsum. The setting regulator is not particularly limited as long as it is an organic or inorganic substance exhibiting alkalinity. Preferably, inorganic compounds such as hydroxides such as NaOH, KOH and Ca (OH) ₂ , carbonates such as CaCO ₃ and K ₂ CO ₃ and Na ₂ O, CaO and MgO which form hydroxides in an aqueous solution And an ammonia gas / solution, and two or more kinds may be used in combination.

Naturally, as an inorganic alkali,
A hardening inorganic substance having alkalinity such as cement may be added and mixed. The amount of alkali to be added is α hemihydrate gypsum 10
0.1 parts by weight (based on α-hemihydrate gypsum), alkali 0.1 to
5 parts by weight, more preferably 0.2 to 1 part by weight.

[0013] The α-hemihydrate gypsum thus obtained is mixed with water to form a mixed slurry. It is preferable to use warm water for adjusting the temperature of the water used so that the temperature of the mixed slurry is 40 to 80 ° C. In the present invention, it is important to adjust the temperature of the mixed slurry to 40 to 80 ° C. When the temperature of the mixed slurry is lower than 40 ° C., the progress rate of the hydration reaction is increased, and apparent coagulation is accelerated. On the other hand, if the temperature exceeds 80 ° C., the hydration rate becomes slow, and it is difficult to mold within a predetermined time. Therefore, the temperature of the mixed slurry is preferably from 40 to 80 ° C, more preferably from 45 to 60 ° C.

The concentration of the mixed slurry is preferably 2 to 40%. The slurry concentration referred to here is α hemihydrate gypsum weight /
(Α hemihydrate gypsum weight + mixed water weight), and the same applies hereinafter. It is necessary to adjust the setting time as needed, and a retarder or an accelerator may be added to the mixed slurry.

Examples of the retarder include hydroxycarboxylic acids. Examples include malic acid, sodium malate, potassium malate, lithium malate, tartaric acid, sodium tartrate, potassium tartrate, lithium tartrate, citric acid, sodium citrate, potassium citrate, lithium citrate, and the like. Among them, particularly preferred are citric acid and salts thereof. or,
The amount of addition is 0.01 to 2 parts by weight, preferably 0.05 to 1 part by weight, per 100 parts by weight of α-hemihydrate gypsum (based on α-hemihydrate gypsum).
0 parts by weight is preferred. If the amount is less than 0.01 part by weight, a substantial retarding effect cannot be obtained, which is not preferable. On the other hand, if it exceeds 2 parts by weight, the setting time becomes extremely long, and the strength is also deteriorated.

The amount of the alkali metal carbonate or the like added as an accelerator is 0.01 to 1 part by weight, preferably 0.05 to 0.1 part by weight, based on 100 parts by weight of α-hemihydrate gypsum (based on α-hemihydrate gypsum).
3 parts by weight are preferred. If the amount is less than 0.01 part by weight, the effect of accelerating the setting is small, and if it exceeds 1 part by weight, the setting speed is too high and the workability is deteriorated. Examples of the alkali metal of carbonate or bicarbonate include lithium, sodium, and potassium.

The concentration of the α-hemihydrate gypsum slurry at 40 to 80 ° C. obtained by adding water or warm water to a mixture containing α-hemihydrate gypsum and, if necessary, a retarder or an accelerator is 2 to 40% by weight. Preferably, the content is more preferably 10 to 30% by weight.

On the other hand, in the present invention, pulp fibers are used as the fibrous substance, wollastonite powder, calcium carbonate powder and the like are used as the admixture. These are added and mixed to produce an additive slurry at a temperature of 40 to 80 ° C. The composition of the additive slurry is 0.2 to 1.5 parts by weight of pulp fiber and 0.3 to 2 parts of wollastonite powder with respect to 100 parts by weight of hot water.
Parts by weight, preferably from 0.5 to 3 parts by weight of calcium carbonate powder.

The α-hemihydrate gypsum slurry at 40 to 80 ° C. obtained as described above and the additive slurry are mixed and stirred.
Produce a mixed slurry at ８０80 ° C. The mixed slurry was poured onto an endless belt conveyor having a reduced pressure filter, and dewatered while moving through the reduced pressure filter.
The primary board becomes 0% by weight. At that time, the board is cooled down to 30-35 ° C by air cooling, and the hydration of α-hemihydrate gypsum (dihydrate)
Temperature condition. This primary board is cut to a predetermined size by a cutter, and is cut into 20 to 40 kg / cm ^2.
To form a secondary board. The time required from the start of mixing the mixed slurry to obtaining the secondary board is about 10 minutes. After curing this secondary board at room temperature for about 24 hours, it can be dried with a dryer at a drying temperature of 40 to 60 ° C. to obtain a gypsum papermaking board.

[0020]

The present invention will be described more specifically with reference to examples and comparative examples, but the present invention is not limited to the following examples unless it exceeds the gist. Parts by weight or% by weight are indicated by parts or% unless otherwise specified. Example 1 A gypsum papermaking plate was produced as follows using igneous phosphate rock and sulfuric acid and α-hemihydrate gypsum by-produced by a wet phosphoric acid production method. To 100 parts of dried α hemihydrate gypsum,
0.4 parts of slaked lime and 1000 parts of warm water were mixed as alkali to obtain an α-hemihydrate gypsum slurry having a slurry temperature of 45 ° C. On the other hand, pulp fiber 8 parts, wollastonite powder 10
Parts, 14 parts of calcium carbonate powder and 1000 parts of hot water at a temperature of 45 ° C. 1100 parts of this α hemihydrate gypsum slurry and additive slurry 412
0 parts were kneaded for 5 minutes to obtain a mixed slurry. The mixed slurry was poured into a reduced pressure filter having a filtration area of 180 mmφ and filtered under a reduced pressure of 300 mmHg.
Was obtained. At that time, it was air-cooled to 30 ° C., and the temperature condition was such that hydration (dihydrate) of α-hemihydrate gypsum proceeded. This primary board was cut and molded under pressure with a pressing force of 30 kg / cm ² to obtain a molded body 10 minutes after the start of mixing the α-hemihydrate gypsum slurry and the additive slurry. After it was cured at room temperature for 24 hours, it was dried with a dryer at 45 ° C. to obtain a gypsum paperboard having the following physical properties.

Specific gravity 1.51 Flexural strength (kg / cm ² ) 215 Thickness (mm) 10.2

The obtained gypsum sheet was evaluated by the following method. Gypsum-made board evaluation method 1) Specific gravity of board After the test piece was prepared (50 mm x 50 mm), it was measured in a room with good ventilation for 7 days or more. 2) Bending strength This was performed in accordance with JIS R 9112. Test piece (30
0 × 400 mm) is placed on the support (350 mm in width) of a bending strength tester (Marubishi Scientific Machinery Co., Ltd. GBL-500), the suspension is aligned with the center of the board, and the suspension is 250 mm.
Pressurize at N / min. The force when the board was broken was defined as the bending strength.

Comparative Example 1 The same operation was performed as in Example 1 except that the temperature of the mixed slurry was changed to 35 ° C., but the coagulation speed was too high to produce.

Comparative Example 2 The same operation as in Example 1 was carried out except that the temperature of the mixed slurry was 90 ° C., however, the coagulation speed was low and the production could not be carried out within a predetermined time.

Comparative Example 3 The procedure of Example 1 was repeated except that the α-hemihydrate gypsum slurry of Example 1 was changed to β-hemihydrate gypsum slurry. as a result,
The coagulation rate was high, and the filterability was poor, and production was not possible.

[0026]

According to the gypsum of the gypsum papermaking board, α-hemihydrate gypsum is not actually used but β-hemihydrate gypsum is used because the production cost of α-type hemihydrate gypsum is high. Due to the properties of β-hemihydrate gypsum, the setting hardening time is poor in stability, a large amount of hardening modifier is required in the papermaking process for continuous production, and there is a problem that it is difficult to control the setting hardening. The present invention relates to an inexpensive α obtained as a by-product from the wet phosphoric acid production method.
Use hemihydrate gypsum and adjust the mixed slurry temperature to 40-80.
By finding conditions as low as ℃, we have established a method for producing gypsum paperboard with low cost and high strength.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI C04B 16:02 14:28 14:04) 103: 12 103: 22 111: 20 (72) Inventor Tadashi Yoshino Hikoshima, Shimonoseki City, Yamaguchi Prefecture. 7-1-1, Sakomachi Mitsui Toatsu Chemicals Co., Ltd.

Claims (5)

[Claims] 1. A mixed slurry is prepared by adding a fibrous substance, water, and, if necessary, an admixture and a setting agent to α-hemihydrate gypsum obtained when phosphoric acid is produced by a wet phosphoric acid production method. A method for producing a gypsum sheet, wherein the temperature is from 80 to 80 ° C. 2. The method for producing a gypsum sheet according to claim 1, wherein the α-hemihydrate gypsum is obtained by a wet phosphoric acid production method using igneous phosphate rock. 3. The method for producing a gypsum sheet according to claim 2, wherein Na ₂ O contained in the igneous phosphate rock is 0.05 to 0.15%. 4. The setting modifier added to α-hemihydrate gypsum is α-hemihydrate gypsum.
0.1 per 100 parts by weight of hemihydrate gypsum (based on α-hemihydrate gypsum)
The method for producing a gypsum sheet according to claim 3, wherein the amount is from 5 to 5 parts by weight. 5. The method for producing a gypsum sheet according to claim 4, wherein the setting modifier added to the α-hemihydrate gypsum is a curable inorganic substance exhibiting alkalinity.