Method for manufacturing calcium silicate boards

Abstract

The present invention provides a calcium silicate board that allows for the recycling of waste calcium silicate boards without the use of highly reactive additives, enables an increase in the proportion of waste material in the formulation, allows for the absorption of more carbon dioxide during the manufacturing process, and suppresses a decrease in strength without significantly increasing the specific gravity after molding. [Solution] A calcium silicate board characterized by mixing a slurry containing crushed calcium silicate board powder, obtained by carbonizing crushed calcium silicate board waste, a siliceous raw material, a calcareous raw material, and a fibrous material, molding it, and curing it in an autoclave.

Description

Technical Field

[0001] The present invention relates to calcium silicate plates.

Background Art

[0002] Calcium silicate plates are manufactured by kneading a slurry containing calcareous raw materials, siliceous raw materials, fiber materials, aggregates, additives, etc., then molding into a desired shape, and curing by autoclave curing. And in this manufacturing process, a large amount of waste materials such as polishing powder, cut end materials, defective products, etc. are generated, and since these are treated as industrial waste, it has been a major problem.

[0003] Therefore, a method of finely pulverizing these waste materials, mixing them again with the slurry, and recycling them is used. However, since the pulverized powder of the waste materials has almost no reactivity, it functions as a filler if blended at about 10% by weight of the whole raw materials. However, if blended more than that, the strength of the calcium silicate plate tends to decrease, and there is also a limit to the amount that can be recycled.

[0004] Regarding the effective recycling of calcium silicate plate waste materials, various research and developments have been carried out conventionally. For example, water is added to powdery calcium silicate waste materials to form a slurry, sulfuric acid is added to the slurry so that the H2SO4 / CaO molar ratio becomes 0.1 to 0.9 with respect to CaO in the calcium silicate waste materials, and then the slurry is added to the raw materials of the calcium silicate molded body, molded into a desired shape, and autoclave cured. A method for producing a calcium silicate molded body has been developed (Patent Document 1). In this production method, by subjecting calcium silicate waste materials, whose blending ratio has been restricted due to the problem of strength reduction conventionally, to sulfuric acid treatment, it has been possible to significantly increase the blending ratio without causing a decrease in the strength of the calcium silicate molded body.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

[0006] However, the method for producing calcium silicate molded articles described in Patent Document 1 uses sulfuric acid, a strong acid, which could potentially damage piping within the factory. Furthermore, mass production would require the consumption of large quantities of sulfuric acid, making worker safety essential, thus leaving room for improvement.

[0007] Furthermore, in response to the global warming problem, efforts toward decarbonization are being advanced in various industries. The manufacturing of calcium silicate boards requires autoclave curing, which requires a large amount of water vapor and is a process that emits a lot of carbon dioxide, making the reduction of carbon dioxide emissions a major challenge. In the concrete and cement sector, the development of environmentally friendly concrete using carbon dioxide-absorbing materials is progressing, and similar technology was needed for calcium silicate boards as well. [Overview of the project] [Problems that the invention aims to solve]

[0008] The problem that this invention aims to solve is to provide a calcium silicate board that can recycle waste calcium silicate board material without using highly reactive additives, allows for an increase in the proportion of waste material used in the formulation, can absorb more carbon dioxide during the manufacturing process, and suppresses a decrease in strength without significantly increasing the specific gravity after molding. [Means for solving the problem]

[0009] The present invention relates to a calcium silicate board characterized by being made by mixing a slurry containing calcium silicate board powder obtained by carbonizing crushed calcium silicate board waste, a siliceous raw material, a calcareous raw material, and a fibrous material, molding it, and curing it in an autoclave. [Effects of the Invention]

[0010] The calcium silicate board according to the present invention has the effect of being able to recycle calcium silicate board waste without using highly reactive additives, increasing the proportion of waste material in the blend, absorbing more carbon dioxide during the manufacturing process, and suppressing a decrease in strength without significantly increasing the specific gravity after molding. [Modes for carrying out the invention]

[0011] Examples of calcium silicate boards according to the present invention include those conforming to the Type 2 standard for calcium silicate boards in JIS A 5430 (Fiber-reinforced cement boards). Calcium silicate boards conforming to this standard are mainly manufactured using silicate raw materials, calcareous raw materials, and admixtures as primary raw materials, and are produced by a papermaking method. Calcium silicate hydrate (e.g., tobermorite) is the main component, and they are used for interior finishes and eaves ceilings. In this standard, a 0.8 calcium silicate board has a bulk density of 0.60 g / cm³. 3 More than 0.90g / cm 3 Less than 10.0 N / mm², bending strength 10.0 N / mm² 2 The above is for a 1.0 calcium silicate board, with a bulk density of 0.90 g / cm³. 3 More than 1.20g / cm 3 Less than 13.0 N / mm², bending strength 13.0 N / mm² 2 The above is stipulated.

[0012] First, the present invention is characterized by using calcium silicate board powder obtained by carbonating crushed calcium silicate board waste material.

[0013] Examples of calcium silicate board waste include polishing dust generated during the polishing process of calcium silicate boards, cut-off pieces generated for dimensional adjustment after the molding of calcium silicate boards, defective products that do not meet the above standards and cannot be sold, and used calcium silicate boards generated when buildings are demolished.

[0014] In this invention, these waste materials are finely crushed into a powder before being used. The particle size of the powder is preferably 200 μm or less, more preferably 50 μm or less, and particularly preferably 1 μm or less. The finer the particle size, the greater the surface area, and therefore the more dramatically the effect of the carbonation treatment tends to increase. In this invention, particle size refers to the average particle size, which is the arithmetic mean diameter calculated from the particle size distribution (volume distribution) detected by the laser diffraction / scattering method (microtrac method).

[0015] After crushing the waste calcium silicate board material into powder, these are subjected to a carbonation treatment. Known methods can be used for the carbonation treatment; for example, a method involves blowing a certain amount of carbon dioxide gas with a concentration of approximately 99% into a slurry containing the powdered waste calcium silicate board material. The concentration of carbon dioxide gas can be any desired concentration; exhaust gas from boiler equipment involved in the calcium silicate board manufacturing process can be used, or a carbon dioxide gas cylinder can be used, but it is preferable to use a high concentration for better reaction efficiency. When blowing in the carbon dioxide gas, either a liquid-phase or gas-phase method is acceptable. In the liquid-phase method, for example, 1 to 100 parts by weight, preferably 3 to 60 parts by weight, and particularly preferably 5 to 40 parts by weight, of crushed calcium silicate board powder are mixed and dispersed with 100 parts by weight of water to obtain a slurry containing the crushed calcium silicate board powder, and then carbon dioxide gas is blown into this slurry. In the case of the gas phase method, for example, crushed calcium silicate powder is sealed inside a Tedlar bag, and carbon dioxide gas is blown directly into the Tedlar bag.

[0016] When calcium silicate hydrate contained in crushed calcium silicate board powder is subjected to carbonation treatment, calcium carbonate and silicon dioxide are produced, making it reactive again and potentially reusable in the manufacture of calcium silicate boards.

[0017] The carbonation treatment is carried out by appropriately adjusting the degree of carbonation. In the present invention, the degree of carbonation is preferably 50% or more, more preferably 60% or more, still more preferably 70% or more, and particularly preferably 80% or more. The higher the degree of carbonation, the higher the reactivity, and it is also possible to manufacture calcium silicate plates at a level close to that when virgin raw materials are used.

[0018] For the analysis of the degree of carbonation, various measuring instruments are used. For example, to confirm that the degree of carbonation is approximately 100%, it can be determined by the powder X-ray diffraction method when the peak of tobermorite, which is calcium silicate hydrate, completely disappears. In other cases of the degree of carbonation, the decarbonation amount of calcium carbonate is measured by differential thermal gravimetric analysis (TG-DTA analysis), and based on the decarbonation amount of 100% of the crushed powder of calcium silicate plates with a carbonation degree of 100% as 100%, it can be obtained by calculating through proportional conversion.

[0019] In the present invention, in addition to the crushed powder of calcium silicate plates obtained by carbonation-treating the crushed waste calcium silicate plates, raw materials such as siliceous raw materials, calcareous raw materials, fiber materials, aggregates, and additives can be used.

[0020] Examples of siliceous raw materials include silica sand, silica stone, diatomaceous earth, fly ash, silica fume, white carbon, etc., and these can be used alone or in combination.

[0021] Examples of calcareous raw materials include slaked lime, cement, quicklime, etc., and these can be used alone or in combination.

[0022] Examples of fiber materials include pulp, glass fiber, carbon fiber, rock wool, polyethylene, polypropylene, rayon, polyacrylonitrile, polyamide, polyester, etc., and these can be used alone or in combination.

[0023] As the aggregate, those usually used as fillers can be employed.

[0024] When the total raw materials are 100 parts by weight, the calcium silicate plate pulverized powder obtained by carbonation treatment is preferably blended in an amount of 1 to 60 parts by weight, more preferably 3 to 50 parts by weight, still more preferably 5 to 45 parts by weight, and particularly preferably 8 to 40 parts by weight. Within this range, by blending, calcium silicate plates meeting the above specifications can be produced, and there is a tendency to effectively utilize waste materials.

[0025] Regarding the CO₂ fixation amount in the produced calcium silicate plate, by measuring the decarbonation amount of calcium carbonate by differential thermal gravimetric analysis (TG-DTA analysis), it can be expressed as the CO₂ fixation amount (g-CO₂ / kg) per 1 kg of calcium silicate plate. The CO₂ fixation amount in the calcium silicate plate is preferably, for example, 7.25 g-CO₂ / kg or more and 145 g-CO₂ / kg or less, and particularly preferably 14.5 g-CO₂ / kg or more and 58 g-CO₂ / kg or less. Being within this range tends to enable the production of calcium silicate plates meeting the above specifications while ensuring a CO₂ fixation amount of a certain level or more.

[0026] For the raw materials, several times the amount of water by weight is added to produce a slurry, and a calcium silicate plate is formed by a known method. Examples of the forming method include a paper-making method, a dehydration press method, a pouring method, etc., which are appropriately selected according to the slurry concentration and the degree of carbonation treatment.

[0027] After forming the calcium silicate plate, autoclave curing is carried out. The curing temperature is preferably 100 to 250 °C, and particularly preferably 150 to 200 °C. Also, the curing time is preferably 1 to 10 hours, and particularly preferably 3 to 8 hours.

[0028] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to these descriptions. In these examples, parts by weight are calculated on a solid content basis. [Examples]

[0029] <Carbonation treatment of crushed calcium silicate waste boards> (Experimental Example 1) To obtain a slurry of calcium silicate powder, 15 parts by weight were mixed and dispersed with 100 parts by weight of water and 15 parts by weight of pulverized calcium silicate board powder (abrasive powder: average particle size 0.8 μm). Carbon dioxide gas with a concentration of 99.5% or higher was blown into the slurry until the carbonation reaction was completed, and a slurry of 100% carbonated calcium silicate powder was obtained by the liquid phase method. The completion of the carbonation reaction was determined by powder X-ray diffraction, specifically by the complete disappearance of the peak for tobermorite, which is calcium silicate hydrate.

[0030] (Experimental Example 2) To obtain a slurry of calcium silicate powder, 15 parts by weight were mixed and dispersed with 100 parts by weight of water and 15 parts by weight of pulverized calcium silicate board powder (abrasive powder: average particle size 0.8 μm). Carbon dioxide gas with a concentration of 99.5% or higher was blown into the slurry until the degree of carbonation reached 75%, and a slurry of calcium silicate powder powder with 75% carbonation was obtained by the liquid phase method. Regarding the degree of carbonation, the amount of decarboxylation of calcium carbonate was measured by differential thermogravimetric analysis (TG-DTA analysis), and the degree of carbonation was calculated proportionally using the amount of decarboxylation of the 100% carbonated calcium silicate pulverized powder described in Experimental Example 1 as 100%.

[0031] (Experimental Example 3) To obtain a slurry of calcium silicate powder, 15 parts by weight were mixed and dispersed with 100 parts by weight of water and 15 parts by weight of pulverized calcium silicate board (abrasive powder: average particle size 0.8 μm). Carbon dioxide gas with a concentration of 99.5% or higher was blown into the slurry until the degree of carbonation reached 50%, and a slurry of calcium silicate powder with 50% carbonation was obtained by the liquid phase method. Regarding the degree of carbonation, the amount of decarboxylation of calcium carbonate was measured by differential thermogravimetric analysis (TG-DTA analysis), and the degree of carbonation was calculated proportionally using the amount of decarboxylation of the 100% carbonated calcium silicate pulverized powder described in Experimental Example 1 as 100%.

[0032] (Experimental Example 4) Calcium silicate plate pulverized powder (abrasive powder: average particle size 0.8 μm) was sealed in a Tedlar bag, and carbon dioxide gas with a concentration of 99.5% or higher was blown in until the carbonation reaction was completed, obtaining 100% carbonated calcium silicate plate pulverized powder by the gas phase method. The completion of the carbonation reaction was determined by powder X-ray diffraction, specifically by the complete disappearance of the peak for tobermorite, which is calcium silicate hydrate.

[0033] <Manufacturing of calcium silicate boards> (Example 1) The slurry of 100% carbonated calcium silicate board pulverized powder obtained in Experimental Example 1 was mixed with 20% by weight of solids, 21% by weight of silica sand, 10% by weight of diatomaceous earth, 25% by weight of slaked lime, 8% by weight of gypsum, 11% by weight of wollastonite, and 5% by weight of pulp. Five times the amount of water was added and the mixture was mixed and dispersed to obtain a slurry. This slurry is then processed using a papermaking method to produce a product with a thickness of 6 mm and a bulk density of 0.80 g / cm³. 3 The material was formed in this manner, cured in an autoclave at a saturated vapor pressure of 180°C for 5.5 hours, and then removed from the autoclave to produce the calcium silicate board according to Example 1.

[0034] (Examples 2-16) According to the mixing ratios shown in the following formulation table, the slurry of carbonated calcium silicate plate pulverized powder obtained in Experimental Examples 1-4 and other raw materials were mixed and dispersed with five times the amount of water to obtain a slurry. This slurry was formed by papermaking to achieve the thickness and bulk density shown in the table below. After curing in an autoclave at the curing temperature and time shown in the table below, it was removed from the autoclave to produce the calcium silicate boards described in Examples 2 to 16.

[0035] (Examples 17-20) According to the mixing ratios shown in the following formulation table, the slurry of carbonated calcium silicate plate pulverized powder obtained in Experimental Examples 1-4, untreated calcium silicate plate pulverized powder (abrasive powder: average particle size 0.8 μm), and other raw materials were mixed and dispersed with five times the amount of water to obtain a slurry. This slurry was formed by papermaking to achieve the thickness and bulk density shown in the table below. After curing in an autoclave at the curing temperature and time shown in the table below, it was removed from the autoclave to produce the calcium silicate boards described in Examples 17-20.

[0036] (Comparative Examples 1-5) According to the proportions shown in the formulation table below, untreated calcium silicate plate pulverized powder (abrasive powder: average particle size 0.8 μm) and other raw materials were blended, and five times the amount of water was added and mixed and dispersed to obtain a slurry. This slurry was formed by papermaking to achieve the thickness and bulk density shown in the table below. After curing in an autoclave at the curing temperature and time shown in the table below, it was removed from the autoclave to produce calcium silicate boards according to Comparative Examples 1 to 5.

[0037] (Comparative Example 6) According to the proportions shown in the formulation table below, untreated calcium silicate plate pulverized powder (abrasive powder: average particle size 0.8 μm) and other raw materials were blended, and five times the amount of water was added and mixed and dispersed to obtain a slurry. This slurry was formed using a papermaking method to achieve the thickness and bulk density shown in the table below. After curing in an autoclave at the curing temperature and time shown in the table below, it was removed from the autoclave to produce calcium silicate boards. Then, this calcium silicate plate was sealed in a Tedlar bag, and carbon dioxide gas with a concentration of 99.5% or higher was blown in until the carbonation reaction stopped, thereby obtaining a carbonated calcium silicate plate by the gas phase method. Regarding the completion of the carbonation reaction, it was determined by powder X-ray diffraction that the peak intensity of tobermorite, which is calcium silicate hydrate, did not decrease any further.

[0038] For the calcium silicate plates according to the above examples, etc., the following physical property evaluations were performed. The evaluation results are shown in the following table.

[0039] <Specific Gravity and Flexural Strength> The specific gravity and flexural strength were measured in accordance with JIS A 5430.

[0040] <CO2 Fixation Amount> The CO2 fixation amount was measured by differential thermal gravimetric analysis (TG-DTA analysis) for the decarbonation amount of calcium carbonate, and expressed as the CO2 fixation amount (g-CO2 / kg) per 1 kg of the calcium silicate plate.

[0041]

Table 1

[0042]

Table 2

[0043]

Table 3

[0044] The calcium silicate boards in the examples could recycle calcium silicate waste without using highly reactive additives, and it was possible to increase the proportion of waste material in the blend. This allowed for greater carbon dioxide absorption during the manufacturing process, and also suppressed a decrease in strength without significantly increasing the specific gravity after molding. On the other hand, the calcium silicate boards in Comparative Examples 1 to 5 used untreated calcium silicate powder. While it is thought that they absorbed some carbon dioxide from the air, the amount absorbed was very low, and some exhibited inferior bending strength compared to the examples. The calcium silicate board in Comparative Example 6 used untreated calcium silicate powder and underwent carbonation treatment after autoclave curing, but it still absorbed a small amount of carbon dioxide, and its bending strength was inferior to that of the examples.

Claims

1. A calcium silicate board characterized by being made by mixing a slurry containing calcium silicate board powder, which is obtained by carbonizing crushed calcium silicate board waste, a siliceous raw material, a calcareous raw material, and a fibrous material, molding the slurry, and curing it in an autoclave.

2. The calcium silicate board according to claim 1, characterized in that it conforms to the calcium silicate board type 2 standard in JIS A 5430 (fiber-reinforced cement board).

3. The calcium silicate board according to claim 1, characterized in that the pulverized calcium silicate board powder is subjected to carbonation treatment by a liquid phase method, and the degree of carbonation is 50% or more.

4. The calcium silicate board according to claim 1, characterized in that the pulverized calcium silicate board powder is subjected to carbonation treatment by a gas phase method, and the degree of carbonation is 50% or more.

5. The calcium silicate board according to claim 1, characterized in that the average particle size of the calcium silicate board pulverized powder is 200 μm or less.

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