Calcium silicate board manufacturing method

Abstract

To provide a calcium silicate board which can recycle waste calcium silicate boards without using an additive having extremely high reactivity, which can increase the blending ratio of the waste boards, which can absorb a larger amount of carbon dioxide in the manufacturing process, and which can suppress a decrease in strength without significantly increasing the specific gravity after molding. [Solution] A calcium silicate board is characterized by being produced by mixing a slurry containing pulverized calcium silicate board powder obtained by carbonating pulverized calcium silicate board waste, a siliceous raw material, a calcareous raw material, and a fibrous material, molding the mixture, and curing it in an autoclave.

Description

[Technical Field]

[0001] The present invention relates to calcium silicate boards. [Background technology]

[0002] Calcium silicate boards are manufactured by kneading a slurry containing calcareous raw materials, siliceous raw materials, fibrous materials, aggregates, additives, etc., then forming it into the desired shape and curing it in an autoclave. This manufacturing process generates a large amount of waste materials, such as abrasive powder, offcuts, and defective products, which have been disposed of as industrial waste, causing a major problem.

[0003] Therefore, a method has been used in which these waste materials are finely crushed and mixed again with slurry for recycling. However, because the crushed powder of the waste materials is almost non-reactive, it can function as a filler if it is mixed in at about 10% by weight of the total raw materials, but if more is mixed in, the strength of the calcium silicate board tends to decrease, and there is a limit to the amount that can be recycled.

[0004] Various research and development efforts have been conducted on the effective recycling of calcium silicate board waste. For example, a method for producing a calcium silicate molded body has been developed, which involves adding water to powdered calcium silicate waste to form a slurry, adding sulfuric acid to the slurry so that the H2SO4 / CaO molar ratio relative to the CaO in the calcium silicate waste is 0.1 to 0.9, and then adding the slurry to a calcium silicate molded body raw material, forming it into a desired shape, and curing it in an autoclave (Patent Document 1). In this manufacturing method, the calcium silicate waste, whose blending ratio had previously been limited due to the problem of reduced strength, is treated with sulfuric acid, making it possible to significantly increase the blending ratio without reducing the strength of the calcium silicate molded body. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2000-203924

[0006] However, the manufacturing method of calcium silicate molded bodies described in Patent Document 1 uses sulfuric acid, which is a strong acid, and therefore there is a possibility that it may damage piping in the factory. Furthermore, since a large amount of sulfuric acid is consumed during mass production, it is essential to ensure the safety of workers, so there is room for improvement.

[0007] Furthermore, in response to the issue of global warming, various industries are working towards decarbonization. The production of calcium silicate boards requires autoclave curing, which requires a large amount of water vapor, making it a process that emits a lot of carbon dioxide, and reducing carbon dioxide emissions has become a major issue. In the concrete and cement industry, progress is being made in the development of environmentally friendly concrete that uses materials that absorb carbon dioxide, and similar technology was also needed for calcium silicate boards. Summary of the Invention [Problem to be solved by the invention]

[0008] The problem to be solved by the present invention is to provide a calcium silicate board that can recycle waste calcium silicate board without using highly reactive additives, that can increase the blending ratio of the waste board, that can absorb more carbon dioxide during the manufacturing process, and that can suppress the decrease in strength without significantly increasing the specific gravity after molding. [Means for solving the problem]

[0009] The present invention provides a calcium silicate board characterized by being produced by mixing a slurry containing pulverized calcium silicate board powder obtained by carbonating pulverized waste calcium silicate board, a siliceous raw material, a calcareous raw material, and a fibrous material, molding the mixture, and curing it in an autoclave. [Effects of the Invention]

[0010] The calcium silicate board of the present invention has the advantages of being able to recycle waste calcium silicate board without using highly reactive additives, allowing the mixing ratio of the waste material to be increased, absorbing more carbon dioxide during the manufacturing process, and suppressing a decrease in strength without significantly increasing the specific gravity after molding. DETAILED DESCRIPTION OF THE INVENTION

[0011] The calcium silicate board according to the present invention is, for example, one that meets the calcium silicate board type 2 standard in JIS A 5430 (fiber reinforced cement board). Calcium silicate boards according to this standard are mainly made from siliceous raw materials, calcareous raw materials, admixtures, etc., and are manufactured by a papermaking method. The main component is calcium silicate hydrate (e.g., tobermorite), and they are used for interior decoration and soffits. The standard defines 0.8 calcium silicate boards as having a bulk density of 0.60 g / cm. 3 More than 0.90g / cm 3 Less than 10.0N / mm bending strength 2 As a 1.0 calcium silicate board, bulk density: 0.90 g / cm 3 More than 1.20g / cm 3 Less than 13.0N / mm bending strength 2 It is stipulated that the above is true.

[0012] First, the present invention is characterized by using pulverized calcium silicate board powder obtained by subjecting pulverized waste calcium silicate board material to a carbonation treatment.

[0013] Examples of calcium silicate board waste include abrasive dust generated during the calcium silicate board polishing process, offcuts generated to adjust dimensions after calcium silicate board molding, defective products that do not meet the above standards and cannot be sold, and used calcium silicate board generated when demolishing buildings.

[0014] In the present invention, these waste materials are finely pulverized to produce pulverized powder for use. The particle size of the pulverized 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 greater the effect of the carbonation treatment. In the present invention, the particle size refers to the average particle size, which is the arithmetic mean diameter calculated from the particle size distribution (volume distribution) detected by laser diffraction / scattering (Microtrac) method.

[0015] After calcium silicate board waste is pulverized into powder, it is subjected to a carbonation treatment. Known carbonation methods can be used, such as injecting a certain amount of carbon dioxide gas with a concentration of approximately 99% into a slurry containing powdered calcium silicate board waste. The carbon dioxide gas can be of any concentration, and can be exhaust gas from boilers or other equipment involved in the calcium silicate board manufacturing process, or a carbon dioxide gas cylinder. However, it is preferable to use a high-concentration carbon dioxide gas for reaction efficiency reasons. The carbon dioxide gas can be injected using either a liquid-phase method or a gas-phase method. 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 pulverized calcium silicate board powder is mixed and dispersed in 100 parts by weight of water to obtain a slurry containing pulverized calcium silicate board powder, and carbon dioxide gas is then injected into the slurry. In the case of the gas phase method, for example, crushed powder of calcium silicate plate is sealed in a Tedlar bag, and carbon dioxide gas is blown directly into the Tedlar bag.

[0016] When calcium silicate hydrate contained in ground powder of calcium silicate board is subjected to carbonation treatment, calcium carbonate and silicon dioxide are produced, which makes it reactive again and it is thought that it can be reused to manufacture calcium silicate board.

[0017] The carbonation treatment is carried out by appropriately adjusting the carbonation degree. In the present invention, the carbonation degree is preferably 50% or more, more preferably 60% or more, even more preferably 70% or more, and particularly preferably 80% or more. The higher the carbonation degree, the higher the reactivity, and it is possible to produce calcium silicate boards with a level similar to that obtained when virgin raw materials are used.

[0018] Various measuring instruments are used to analyze the carbonation degree. For example, to confirm that the carbonation degree is nearly 100%, powder X-ray diffraction can be used to determine whether the peak of tobermorite, a calcium silicate hydrate, has completely disappeared. If the carbonation degree is other than this, the amount of decarbonation of calcium carbonate can be measured using differential thermogravimetric analysis (TG-DTA analysis), and the amount of decarbonation can be calculated proportionally, taking the amount of decarbonation of a ground calcium silicate plate with a carbonation degree of 100% as the standard.

[0019] In the present invention, in addition to the ground calcium silicate board powder obtained by carbonating ground calcium silicate board waste, raw materials such as siliceous raw materials, calcareous raw materials, fibrous materials, aggregates, and additives can be used.

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

[0021] Examples of the calcareous raw material include slaked lime, cement, quicklime, etc., which can be used alone or in combination.

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

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

[0024] The calcium silicate board powder obtained by the carbonation treatment is preferably blended in an amount of 1 to 60 parts by weight, more preferably 3 to 50 parts by weight, even more preferably 5 to 45 parts by weight, and particularly preferably 8 to 40 parts by weight, based on 100 parts by weight of all raw materials. Blending within this range makes it possible to produce calcium silicate boards that meet the above-mentioned specifications, and also tends to enable effective use of waste materials.

[0025] The amount of CO2 fixed in the produced calcium silicate board can be expressed as the amount of CO2 fixed per kg of calcium silicate board (g-CO2 / kg) by measuring the amount of decarbonation of calcium carbonate using differential thermogravimetric analysis (TG-DTA analysis). The amount of CO2 fixed in the calcium silicate board 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. By keeping the amount within this range, it tends to be possible to produce calcium silicate boards that meet the above standards while ensuring a certain level of CO2 fixation.

[0026] A slurry is produced by adding several times the weight of the raw materials to water, and then the slurry is molded into calcium silicate boards by known methods, such as papermaking, dehydration pressing, and pouring, depending on the concentration of the slurry and the degree of carbonation.

[0027] After the calcium silicate board is formed, it is cured in an autoclave. The curing temperature is preferably 100 to 250° C., and particularly preferably 150 to 200° C. 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 values ​​calculated as solid content. [Example]

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

[0030] (Experimental Example 2) 15 parts by weight of ground calcium silicate board powder (abrasive powder: average particle size 0.8 μm) was mixed and dispersed in 100 parts by weight of water to obtain a slurry of ground calcium silicate board powder. Carbon dioxide gas with a concentration of 99.5% or more was blown into the slurry until the carbonation level reached 75%, and a slurry of ground calcium silicate board powder carbonated to 75% was obtained by the liquid phase method. The degree of carbonation was calculated by measuring the amount of decarbonation of calcium carbonate by differential thermogravimetry (TG-DTA analysis) and proportionally converting the amount of decarbonation of the 100% carbonated pulverized calcium silicate powder described in Experimental Example 1 to 100%.

[0031] (Experimental Example 3) 15 parts by weight of ground calcium silicate board powder (abrasive powder: average particle size 0.8 μm) was mixed and dispersed in 100 parts by weight of water to obtain a slurry of ground calcium silicate board powder. Carbon dioxide gas with a concentration of 99.5% or more was blown into the slurry until the carbonation level reached 50%, and a slurry of ground calcium silicate board powder carbonated to 50% was obtained by the liquid phase method. The degree of carbonation was calculated by measuring the amount of decarbonation of calcium carbonate by differential thermogravimetry (TG-DTA analysis) and proportionally converting the amount of decarbonation of the 100% carbonated pulverized calcium silicate powder described in Experimental Example 1 to 100%.

[0032] (Experimental Example 4) Ground calcium silicate board powder (ground powder: average particle size 0.8 μm) was sealed in a Tedlar bag, and carbon dioxide gas with a concentration of 99.5% or more was blown in until the carbonation reaction was complete, obtaining 100% carbonated ground calcium silicate board powder by the gas phase method. The completion of the carbonation reaction was judged by the complete disappearance of the peak of tobermorite, a calcium silicate hydrate, by powder X-ray diffraction.

[0033] <Manufacturing calcium silicate boards> Example 1 The slurry of 100% carbonated calcium silicate board crushed powder obtained in Experimental Example 1 was mixed with 20% by weight of solid content, silica sand 21% by weight, diatomaceous earth 10% by weight, slaked lime 25% by weight, gypsum 8% by weight, wollastonite 11% by weight, and pulp 5% by weight, and five times the amount of water was added and mixed and dispersed to obtain a slurry. This slurry was made into a sheet with a thickness of 6 mm and a bulk density of 0.80 g / cm by a papermaking method. 3 The mixture was cured in an autoclave at saturated vapor pressure at 180° C. for 5.5 hours, and then removed from the autoclave to produce a calcium silicate board according to Example 1.

[0034] Examples 2 to 16 According to the mixing ratio in the mixing table shown below, the slurry of carbonated calcium silicate plate powder obtained in Experimental Examples 1 to 4 and other raw materials were mixed, and five times the amount of water was added and mixed to obtain a slurry. This slurry was made into sheets by a papermaking method to have the thickness and bulk density shown in the table below, and after curing in an autoclave at the curing temperature and time shown in the table below, the sheets were removed from the autoclave to produce calcium silicate boards according to Examples 2 to 16.

[0035] (Examples 17 to 20) According to the blending ratios in the blending table shown below, the slurry of carbonated calcium silicate board powder obtained in Experimental Examples 1 to 4, the untreated calcium silicate board powder that had not been carbonated (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 made into sheets by a papermaking method to have the thickness and bulk density shown in the table below, and after curing in an autoclave at the curing temperature and time shown in the table below, the sheets were removed from the autoclave to produce calcium silicate boards according to Examples 17 to 20.

[0036] (Comparative Examples 1 to 5) According to the mixing ratio in the recipe below, uncarbonated ground calcium silicate board powder (abrasive powder: average particle size 0.8 μm) and other raw materials were mixed, and five times the amount of water was added and mixed to obtain a slurry. This slurry was made into sheets by a papermaking method to have the thickness and bulk density shown in the table below, and after curing in an autoclave at the curing temperature and time shown in the table below, the sheets were removed from the autoclave to produce calcium silicate boards according to Comparative Examples 1 to 5.

[0037] (Comparative Example 6) According to the mixing ratio in the recipe below, uncarbonated ground calcium silicate board powder (abrasive powder: average particle size 0.8 μm) and other raw materials were mixed, and five times the amount of water was added and mixed to obtain a slurry. This slurry was made into sheets using a papermaking method to the thickness and bulk density shown in the table below, and after curing in an autoclave at the curing temperature and time shown in the table below, the sheets were removed from the autoclave to produce calcium silicate boards. The calcium silicate plate was then sealed in a Tedlar bag, and carbon dioxide gas with a concentration of 99.5% or more was blown into it until the carbonation reaction stopped proceeding, yielding a calcium silicate plate carbonated 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, no longer decreased.

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

[0039] <Specific gravity · 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 of the Examples were able to recycle calcium silicate board waste without using highly reactive additives, allowing for an increased blending ratio of the waste material, allowing for greater carbon dioxide absorption during the manufacturing process, and also suppressing strength loss without significantly increasing the specific gravity after molding. On the other hand, the calcium silicate boards of Comparative Examples 1 to 5 used crushed powder of untreated calcium silicate board, and although they appear to have absorbed some carbon dioxide from the air, the amount of absorption was very low, and some of the boards had inferior bending strength to the Examples. The calcium silicate board of Comparative Example 6 used crushed powder of untreated calcium silicate board and was carbonation-treated after autoclave curing, but it absorbed less carbon dioxide and had inferior bending strength to the Examples.

Claims

1. A method for producing calcium silicate boards, characterized by mixing a slurry containing pulverized calcium silicate board powder obtained by carbonating pulverized calcium silicate board waste, a siliceous raw material, a calcareous raw material, and a fibrous material, molding the mixture, and curing it in an autoclave.

2. 2. The method for manufacturing a calcium silicate board according to claim 1, which complies with the calcium silicate board type 2 standard in JIS A 5430 (fiber reinforced cement board).

3. 2. The method for producing calcium silicate boards according to claim 1, wherein the ground powder of calcium silicate boards is carbonated by a liquid phase method to a degree of carbonation of 50% or more.

4. 2. The method for producing calcium silicate boards according to claim 1, wherein the ground powder of calcium silicate boards is carbonated by a gas phase method to a degree of carbonation of 50% or more.

5. 2. The method for producing calcium silicate boards according to claim 1, wherein the average particle size of the ground calcium silicate board powder is 200 μm or less.

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