JP2007015886A - Porous molding and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a porous molding which can be hardened without heating and has high strength and excellent heat resistance and water resistance. <P>SOLUTION: The porous molding is a porous molding prepared by molding a raw material containing amorphous silicic acid, reinforcing fibers, and a filler and hardening the molding, wherein a pH8-13 aqueous solution or dispersion containing an alkali metal compound is added, and the hardening is performed without heating. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a porous formed body having high strength and excellent heat resistance, and useful as a building material and a heat insulating material, and a method for producing the same.

As a porous molded body excellent in heat insulation, a fine porous body based on a highly dispersed oxide of silicon and / or aluminum element (Patent Document 1), _{2 to} 4.5 (SiO ₂ ; M ₂ O) ) Molded body based on alkali metal silicate expanded particles composed of silicon dioxide (SiO ₂ ) and alkali metal oxide (M ₂ O) in molar ratio (Patent Document 2) and expanded vermiculite in an amount of 30 to 70% by weight, inorganic bond 15 to 40% by weight of the agent, 0 to 20% by weight of the infrared opaque agent, 15 to 59% by weight of the microporous material, up to 15 to 40% by weight of B ₂ O _{3 with} respect to the weight of the reinforcing fiber, and alkali metal A heat insulating molded body containing 0.5 to 8% by weight of reinforcing fiber containing 2% by weight of oxide at the highest (Patent Document 3) is known.

However, these molded products have low thermal conductivity and excellent heat insulation properties, but must be fired at high temperatures, which requires energy costs in production. Moreover, since the obtained material is brittle, the processability is not sufficient, and since it is powdery, there is a problem that dust is easily generated. Furthermore, since this material does not have water resistance, it will crack when absorbed. Therefore, when used as a heat insulating material, there is a problem that the condensed moisture is absorbed and cracks are generated, and the heat insulating property is greatly reduced.
In addition, examples of porous molded bodies in which alkali is interposed in amorphous silicic acid include high-purity ground glass foam (Patent Document 4) and heat-resistant siliceous foam (Patent Document 5), both of which are silica. It is a (glass) foam and needs to be foamed at a high temperature.

  Moreover, the binder which has water resistance and heat resistance which adjusted the mixing ratio of sodium and potassium in alkali metal silicate is known (patent document 6). When the binder is used in a porous molded body, it is considered possible to have water resistance by mixing and curing the porous formed body, but contains a large amount of alkali metal with respect to silicic acid. In addition, a large amount of alkali metal remains in the porous formed body, and there is a problem that the shrinkage rate when heated is increased and the heat resistance is lowered.

  In addition, a porous formed body (patent document 7) that heats and cures a mixture in the presence of water at a weight ratio of sodium / silicic acid of 0.05 or more and 0.20 or less. There are porous formed bodies (Non-patent Document 1) formed by mixing an alkaline aqueous solution such as sodium hydroxide with a powder of a simple amorphous silica-based material. There is a problem that it is necessary to mold and lacks simplicity.

Japanese Patent Laid-Open No. 7-10651 Japanese Patent Laid-Open No. 7-69752 JP 2000-513693 A JP-A-5-345636 Japanese Patent Laid-Open No. 7-144934 JP-A-5-311091 JP 2001-181018 A Hokkaido Industrial Experiment Station Technical Information Vol. 24, NO. 2, p. 6

  An object of the present invention is to provide a porous molded body that can be cured without requiring heating, and has high strength and excellent heat resistance.

  Thus, as a result of various studies, the present inventors surprisingly added an aqueous solution or aqueous dispersion having a pH of 8 to 13 containing an alkali metal compound to a raw material containing amorphous silicic acid, reinforcing fibers, and a filler. The present invention has been completed by finding that it has high strength, excellent heat resistance and water resistance simply by curing without heating.

  That is, the present invention is a porous molded body obtained by molding and curing a raw material containing amorphous silicic acid, reinforcing fibers and a filler, and an aqueous solution having a pH of 8 to 13 containing an alkali metal compound in the raw material. Alternatively, the present invention provides a porous molded article obtained by adding an aqueous dispersion and curing without heating, and a method for producing the same.

  Since the porous molded body of the present invention can be cured without the need for heating, the energy cost in production can be kept low, and since it has high strength and excellent heat resistance and water resistance, it can be used as a heat insulating material or building material. Is suitable.

  The raw material of the porous molded body of the present invention includes amorphous silicic acid, reinforcing fibers, and a filler. Here, amorphous silicic acid is a raw material for molding a matrix as a porous molded body, and is not particularly limited as long as it has a form of amorphous silicic acid. For example, hydrous silicic acid and white carbon obtained by a precipitation method, silica gel and gel-like silica obtained by a gel method, and dry silica obtained by a combustion method are suitable. Fly ash and silica fume can also be used.

  The particle size and the like of the amorphous silicic acid are not particularly limited, but if a fine particle size is used, a high-strength porous molded body can be easily obtained. For example, the average particle diameter of the primary particles is 2 to 50 mm, particularly 2 to 10 mm, and particulate amorphous silicic acid in which the primary particles are aggregated to form secondary particles is particularly preferable.

  The ratio of the amorphous silicic acid to the whole raw material is preferably 30 to 80% as a mass ratio in a dry state from the viewpoint of thermal conductivity and strength development, and more preferably 35 to 75% when used as a heat insulating material. When used as a building material, 40 to 60% is preferable.

  The reinforcing fiber is a raw material mainly used for improving the strength of the porous molded body, and fibers conventionally used for building materials and heat insulating materials can be used. For example, wood fiber such as cellulose pulp, PAN (polyacrylonitrile) fiber, PVA (polyvinyl alcohol) fiber, synthetic organic fiber such as PP (polypropylene) fiber, glass fiber, carbon fiber or ceramic fiber as necessary be able to.

  The ratio of the reinforcing fibers to the entire raw material is preferably 1 to 20%, and more preferably 5 to 15% as a mass ratio in a dry state from the viewpoint of strength development and moldability during production.

A filler is a raw material used in order to improve the performance required by the use for the obtained porous molded body, and as a filler in the case of using a heat insulating material as a main use, an infrared shielding agent (TiO ₂ , FeTiO ₃ , ZrO ₂ , ZrSiO ₄ , Fe ₂ O ₃ , MnO _{2 and} other metal oxides and SiC) are good. On the other hand, as a filler when using general building materials as the main application, aggregates for reducing the heat shrinkage rate of wollastonite, mica, etc., aggregates for improving the fire resistance performance of calcium carbonate, dolomite, gypsum, etc. Is preferred.

  The ratio of the filler to the whole raw material is preferably 5 to 50% as a mass ratio in the dry state from the viewpoint of thermal conductivity and strength reproducibility, and preferably 20 to 40% when used as a heat insulating material. When using, 10 to 20% is preferable.

  In addition to the essential raw materials, for example, waste materials of the porous molded body according to the present invention, residual cutting materials, and powders such as abrasive powders may be reused as raw materials. However, the amount of the whole raw material is preferably 50% or less in terms of mass ratio in a dry state. If it exceeds 50%, the strength of the resulting porous molded body may be insufficient.

  The porous molded body of the present invention is a dehydration molding of a slurry in which an aqueous solution or aqueous dispersion containing pH 8-13 containing an alkali metal compound is mixed with a raw material containing amorphous silicic acid, reinforcing fibers and fillers, It is characterized in that it is obtained by curing without heating.

  Examples of the aqueous solution of the alkali metal compound include aqueous solutions of alkali metal salts such as sodium hydroxide, potassium hydroxide, and lithium hydroxide. Among these, an aqueous solution of sodium hydroxide is preferable.

  An aqueous dispersion of an alkali metal compound is an alkali metal-treated non-aqueous solution in which hydrogen atoms (H) of all or part of silanol groups (SiOH) on the surface in contact with water are substituted with Si-OM (M: alkali metal). Although it is an aqueous dispersion of crystalline silicic acid, examples of the alkali metal M include sodium, potassium, and lithium. Alkali metal-treated amorphous silicic acid is preferable because it can be stored, transported and operated more easily and handled than alkali metal hydroxide, alkali metal oxide, ammonia and the like.

  The pH of these aqueous solutions or aqueous dispersions must be pH 8-13, more preferably pH 11-13, and still more preferably pH 11-12.

  Among these aqueous solutions or aqueous dispersions, the case of the aqueous dispersion will be described as an example. The porous molded body of the present invention is a Si—O of silanol groups (SiOH) of general amorphous silicic acid. Comparing the distance between (H) and the distance between Si-O (M) of SiOM substituted with alkali metal M contained in the aqueous dispersion, Si-O ( Since the distance between M) becomes long, it becomes rich in reactivity, and can be obtained by curing without heating.

  In addition, when alkaline water such as sodium hydroxide or lithium hydroxide exceeding pH 13 is used in combination with the above raw materials, the shrinkage rate when heated so that a large amount of alkali metal such as sodium or lithium remains in the porous molded body. Can be prevented by using the aqueous solution or aqueous dispersion having a pH of 8 to 13 according to the present invention mixed with the above raw materials.

  The alkali metal-treated amorphous silicic acid contained in the aqueous dispersion of pH 8 to 13 of the present invention is easy to mix with the raw material and suppresses a decrease in strength due to the addition of excess water. %, More preferably 0.01 to 10% by mass, and further preferably 0.1 to 8% by mass.

  The mass ratio of amorphous silicic acid / alkali metal-treated amorphous silicic acid in the porous molded body of the present invention is 100 / 0.001 to 0.10, more 100 / 0.001 to 0. .05 is preferable, and 100 / 0.01 to 0.02 is more preferable.

  The ratio of the raw material amorphous silicic acid to the aqueous solution or aqueous dispersion is a mass ratio with respect to the amorphous silicic acid, amorphous silicic acid / the aqueous solution or aqueous dispersion = 100/1 to 100/50, 100/5 to 100/25 is preferred. This is because if the ratio of the aqueous solution or the aqueous dispersion is lower than the above, the amorphous silicic acid cannot be sufficiently cured and sufficient performance as a porous molded body cannot be obtained. This is because when the ratio of the aqueous solution or the aqueous dispersion exceeds the above, volume reduction is large and compression molding at a constant specific gravity value becomes difficult.

  The aqueous solution or aqueous dispersion may be added to the raw material while mixing the raw materials, or may be added after mixing the raw materials first and then mixed again. In addition, when using a papermaking method as a forming method, the raw material slurry mixed with water added to the raw material is made into a thin film, wound up on a making (forming) roll until it reaches a predetermined thickness, and taken out from the making roll. The aqueous solution or aqueous dispersion may be sprayed on the thin film before winding it on a making roll.

The molding method is not particularly limited, and a known method such as a mold pressing method, a papermaking method (above), or an extrusion molding method may be used.
After molding, no heating or the like is required, and it can be cured by simply leaving it in a greenhouse. In the case of a molding method that does not require much water, such as a mold press method or an extrusion molding method, the minimum strength as a product can be obtained when the molding is completed. In the case of a molding method that requires a large amount of water, such as a papermaking method, the minimum strength as a product can be obtained by performing dehydration after molding. In addition, if a curing time is provided, the strength can be further increased, and the strength is also increased during the steps after the molding step without particularly providing the curing time.

  Here, “no heating or the like is required” means that no special heating is performed, and a raw material slurry (raw material) for the purpose of improving the production efficiency when forming by a manufacturing method such as a normal papermaking method. Are mixed with water), and heat drying treatment for adjusting the moisture content at the time of shipment after curing is included. Therefore, the curing temperature in the present invention is preferably 5 to 40 ° C, particularly 10 to 30 ° C.

  The cured porous molded body is dried in order to keep the moisture content constant and to remove moisture. The drying method is not particularly limited, but usually heat drying at about 105 ° C. is used.

Although the obtained porous molded body is porous and lightweight, it has little heat shrinkage, excellent heat insulation, and excellent strength. When used as a heat insulating material, the preferred density is 250 to 400 kg / m ³ and the bending strength is 20 to 50 N / cm ² . Moreover, when using as a building material, a preferable density is 650-750 kg / m < ³ > and bending strength is 10-15 N / mm < ² >.

EXAMPLES Next, although an Example is given and this invention is demonstrated further in detail, this invention is not limited to these Examples.
<Example 1>
The raw materials listed in Table 1 were weighed and dry mixed with a Henschel mixer at 1500 rpm for 3 minutes. Subsequently, 5 mass% nip seal NA aqueous dispersion (henceforth%) was sprinkled in the Henschel mixer, and also mixed for 1 minute. The mixed raw material was put into a mold, subjected to pressure molding at a pressing pressure of 1.5 to 2.5 MPa, and cured and cured under predetermined curing conditions to produce a porous molded body. This was done 5 times.
The 5% nip seal NA aqueous dispersion was previously mixed with sodium metal-treated silica partially mixed with sodium oxide (Tosoh Silica Co., Ltd.) and had a pH of about 12-13.
At this time, the raw materials and blending ratio (mass%) were 59% by mass of finely divided amorphous silicic acid (Tokuyama Corp., Leoroseal), 30% by mass of infrared shielding agent (Pacific Randum Corp., silicon carbide GMF6S), glass fiber (Unitika Glass). 1% by mass of FIBER, UPDE1 / 4ZA508) and 10% by mass of ceramic fiber (IBIDEN, Bulk 115), and nip seal NA aqueous dispersion was added to the outer portion thereof. Further, the obtained porous back molded body was cured at a curing temperature of 20 ° C. and a curing time of 3 hours, and subsequently at a drying temperature of 24 ° C. and a drying time of 24 hours.
<Examples 2 to 4>
In Examples 2 to 3, the 5% nip seal NA aqueous dispersion was added 10% by mass and 20% by mass (externally divided) in the same procedure as in Example 1, and each was performed once.
In Example 4, in place of the 5% nip seal NA aqueous dispersion, 5% by mass (outside split) of 10% nip seal NA aqueous dispersion shown in Table 1 was added, and the process was performed once.

<Comparative Examples 1-2>
A 20% nip seal NA aqueous dispersion and a 40% nip seal NA aqueous dispersion were prepared, but could not be mixed well with the raw materials.
<Comparative Examples 3-6>
In Comparative Example 3, in place of the 5% nip seal NA aqueous dispersion of Example 1, 5% by mass (external ratio) of 0.12% sodium hydroxide aqueous solution (more than pH 13) was added in the same procedure. went. The number of sodium atoms was adjusted to be about the same as the 5% nip seal NA aqueous dispersion.
In Comparative Examples 4 to 6, the 0.12% sodium hydroxide aqueous solution was added in an amount of 10% by mass, 20% by mass, and 40% by mass (external split) in the same procedure as Comparative Example 3, and each was performed once.
<Comparative Examples 7 to 10>.
In Comparative Examples 7 to 10, instead of the 5% nip seal NA aqueous dispersion of Example, 0% by mass, 5% by mass, 10% by mass, and 20% by mass (external ratio) of water were added in the same procedure. 0% by mass was performed 5 times and the other was performed once. 0% by mass of water is also referred to as no addition of curing agent.

The density (kg / m ³ ), bending strength (N / cm ² ), thermal conductivity (W / m · k), and linear shrinkage rate (%) of the obtained porous molded body were measured.
(Density) Based on JIS A 9510 6.6.
(Bending strength) Based on 6.7 of JIS A 9510.
(Thermal conductivity) Based on the hot wire method of JIS R 2616 (equipment in section 3.5, test piece in section 4.2, operation in section 5.3).
(Linear shrinkage rate) Based on 6.9 of JIS A 9510.

5% nip seal NA aqueous dispersion with an average strength of 48 (N / cm ² ) with a standard deviation of 1.1 (N / cm ² ) and 0.12% sodium hydroxide aqueous solution with an average strength of 34 (N / cm ² ) The deviation was 1.1 (N / cm ² ). When no curing agent was added, the average strength was 30 (N / cm ² ) and the standard deviation was 3.8 (N / cm ² ).

  From Tables 1 to 3, the porous molded bodies of Examples 1 to 4 using aqueous dispersions of alkali metal-treated amorphous silicic acid (pH 11 to 12) were excellent despite being cured without heating. It has a high hardness and thermal conductivity, has a small thermal shrinkage, and is useful as a heat insulating material. Furthermore, handling was easy. On the other hand, Comparative Examples 3 to 6 using a 0.12% sodium hydroxide aqueous solution (greater than pH 13) exhibit strength from a porous molded body to which only water is added, but there is a risk of chemical burns during handling, It is more difficult to handle than alkali metal-treated amorphous silicic acid.

Claims (8)

  A porous molded body obtained by forming and curing a raw material containing amorphous silicic acid, reinforcing fibers and a filler, and adding an aqueous solution or aqueous dispersion having a pH of 8 to 13 containing an alkali metal compound to the raw material And a porous molded body which is cured without heating.   In the aqueous solution or aqueous dispersion containing the alkali metal compound, part or all of the surface in contact with the alkali metal hydroxide aqueous solution or water is replaced with Si-OM (M: alkali metal) amorphous metal-treated amorphous. The porous molded body according to claim 1, which is an aqueous dispersion containing porous silicic acid.   The porous molded body according to claim 2, wherein a mass ratio of amorphous silicic acid / alkali metal-treated amorphous silicic acid in the porous molded body is 100 / 0.001 to 0.05.   The porous molded body according to any one of claims 1 to 3, wherein a temperature for curing the porous formation is 5 to 40 ° C.   A porous material characterized by dehydrating and curing a slurry in which an aqueous solution or aqueous dispersion of pH 8 to 13 containing amorphous silicic acid, reinforcing fibers, a filler, and an alkali metal compound is mixed and not heated. Manufacturing method of a molded object.   In the aqueous solution or aqueous dispersion containing the alkali metal compound, part or all of the surface in contact with the alkali metal hydroxide aqueous solution or water is replaced with Si-OM (M: alkali metal) amorphous metal-treated amorphous. The method for producing a porous molded body according to claim 5, which is an aqueous dispersion containing porous silicic acid.   The method for producing a porous molded body according to claim 6, wherein the mass ratio of amorphous silicic acid / alkali metal-treated amorphous silicic acid in the porous molded body is 100 / 0.001 to 0.05.   The method for producing a porous molded body according to any one of claims 5 to 7, wherein a temperature for curing the porous formation is 5 to 40 ° C.