JP2004315343A - Silica-dispersed liquid - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of preparing a silica-dispersed liquid having an excellent film-formability and giving an excellent water-resistant coating film. <P>SOLUTION: The silica-dispersed liquid has SiO<SB>2</SB>/M<SB>2</SB>O mole ratio (SiO<SB>2</SB>/M<SB>2</SB>O) of 3-10, the total content of SiO<SB>2</SB>and M<SB>2</SB>O of 1-60 wt.%, and the area ratio of Q<SB>3</SB>structure signal vs. Q<SB>2</SB>structure signal in the<SP>29</SP>Si-NMR spectrum of 1.5≤Q<SB>3</SB>/Q<SB>2</SB>≤10 and is prepared by dealkalizing an alkali silicate solution. The silica component of the silica-dispersed liquid comprises Si forming an Si-C bond and Si not forming an Si-C bond, where the mole ratio of SiO<SB>2</SB>in the SiO<SB>2</SB>component vs. M<SB>2</SB>O (SiO<SB>2</SB>/M<SB>2</SB>O) is 3-10, the content of Si forming the Si-C bond in the total Si is 0.1-30 mol%, and the total content of SiO<SB>2</SB>and M<SB>2</SB>O is 1-60 wt.%. The silica-dispersed liquid is prepared by mixing a condensation reaction product of an alkylsilane and/or an alkylsiliconate and an alkali silicate and then dealkalizing. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a silica dispersion used for a coating agent for various substrate surfaces.

  Various types of coating agents have been applied to the exposed surface or mortar-finished surface of concrete because it has a property of easily absorbing water, being easily stained, or being easily weathered when exposed to sunlight or wind and rain. In addition, a concrete coating agent is used for the purpose of preventing carbonation of concrete due to carbon dioxide gas or acid rain in the air. For example, acrylic, urethane, silicon, and fluorine resin coating agents are on the market, but there are problems such as peeling due to poor adhesion to concrete surfaces and deterioration due to rainwater such as acid rain. .

  In recent years, a system for recycling concrete waste has been actively developed. Conventionally, most of the waste concrete materials are used for roadbed materials and backfill materials, but demand for roadbed materials is not expected to grow in the future. Therefore, a method of crushing waste concrete to obtain recycled aggregate and regenerating it into concrete has been studied. However, such recycled aggregate has a large water absorption rate, and concrete using the aggregate has low quality such as strength, deformation characteristics, shrinkage characteristics, and durability. Therefore, a treatment method for improving the quality of the recycled aggregate has begun to be studied. As one of them, a treatment method using a heated milling method has been proposed, but is not versatile in view of the construction and operation cost of a large-scale treatment plant (for example, see Non-Patent Document 1).

  Since water glass forms a vitreous coating film when dried, it has been used as an inorganic paint, an adhesive, a binder, and the like. However, the coating film has a problem in water resistance such as being water-soluble and not resistant to moisture. In order to cope with such a problem, various methods of treating the surface of the coating film with an acid or an alkali have been proposed. However, the coating film surface is easily damaged at the time of work, and the workability and performance are required such as washing with water. There was a problem. Attempts have also been made to add hardeners such as metals, metal oxides, and metal hydroxides to water glass, but they cause rapid gelation and have problems in workability and practicality (for example, And Patent Document 1).

  In order to improve the quality of the recycled aggregate, it is conceivable to use a treatment agent capable of forming a coating film on the surface of the concrete or mortar as well as the protection and reinforcement of the surface. According to such a treating agent, it is considered that the quality of the recycled aggregate can be easily and inexpensively increased. As such a treating agent, the use of the above-mentioned water glass or other colloidal silica dispersion is conceivable, but as described above, it has poor water resistance and also has a drawback that film formability on the aggregate surface is poor. , The effect of a practical level cannot be obtained.

  In addition, a ground injection material comprising a silica solution obtained by subjecting water glass to a dealkalization treatment has been proposed. Usually, a silica solution used for this purpose is excellent in water resistance, but has a film forming property and an aggregate. It was inadequate as a coating agent or a treating agent for recycled aggregate, for example, because of poor permeability and not suitable for long-term storage (for example, see Patent Documents 2 and 3).

On the other hand, it is widely known that silanes, particularly alkoxysilanes, are useful as a water repellent and a waterproofing agent for treating stones, masonry, concrete and the like. As a technique using such a silane, for example, a treatment agent obtained by dissolving silane in alcohol or the like, a method using an aqueous solution of hydrolyzed silane, a method using an aqueous silane compound, and the like are known (for example, Patent Document 4). However, in these methods, it is difficult to increase the thickness of the film, and the adhesiveness to concrete is insufficient. Therefore, there is a problem that the water repellency and the waterproofness of the base material are not maintained.
Patent No. 2705756 Patent No. 3216878 Japanese Patent No. 2987620 JP-A-6-248259 Fumino Tomitsu, "Ceramics", The Ceramic Society of Japan, 2002, Vol. 37, No. 12, p946-951

  The present invention relates to a silica dispersion which is preferably used as a coating agent for various substrate surfaces and has excellent film-forming properties and excellent water resistance (hereinafter, simply referred to as water resistance) of the formed coating film, and the silica dispersion. It is an object to provide a method for producing a dispersion.

That is, the present invention
[1] A silica dispersion obtained by dispersing at least a silica component and an alkali metal-containing component in water, wherein the silica component is represented by SiO ₂ and the alkali metal-containing component is represented by M ₂₀ (M is an alkali metal atom). when expressed, the molar ratio of SiO ₂ and _{M 2 0 (SiO 2 / M} 2 0) from 3 to 10, and the total content of SiO ₂ and M ₂ 0 is 1 to 60 wt%, and In the assignment of the spectrum of the silica component by ²⁹ Si-NMR, the ratio of the area of the signal showing the Q ₃ structure to the area of the signal showing the Q ₂ structure in the signal showing the Q _n (n = O to 4) structure was 1.5. ≦ Q ₃ / Q ₂ ≦ 10, silica dispersion,
(2) The method for producing a silica dispersion according to the above (1), which comprises a step of dealkalizing the alkali silicic acid solution,
(3) a method for producing a silica dispersion according to the above (1), comprising hydrothermally treating a mixture comprising silica sand, water and an alkali metal-containing compound, and dissolving the silica sand.
(4) a silica dispersion obtained by dispersing at least a silica component and an alkali metal-containing component in water, wherein the silica component contains Si that forms a Si-C bond and Si that does not form a Si-C bond. When the alkali metal-containing component is represented by M ₂ O (M is an alkali metal atom), the molar ratio of the component represented by SiO ₂ in the silica component to M ₂ O (SiO ₂ / M ₂ 0) is 3 to 10, the content of Si to form a Si-C bond is 0.1 to 30 mol% of the total Si, and the total content of SiO ₂ and M ₂ 0 1 to 60 weight % Silica dispersion,
[5] In the assignment of the spectrum of the silica component by ²⁹ Si-NMR, the ratio of the area of the signal showing the Q ₃ structure to the area of the signal showing the Q ₂ structure in the signal showing the Q _n (n = O to 4) structure Is 1.5 ≦ Q ₃ / Q ₂ ≦ 10, the silica dispersion according to the above [4],
[6] a method for producing a silica dispersion comprising a step of mixing an alkylsilane condensation reaction product and / or an alkylsiliconate with an alkali silicic acid solution and then subjecting the mixture to a dealkalization treatment;
(7) The coating agent comprising the silica dispersion according to (1), (4) or (5),
[8] The concrete surface coating agent comprising the silica dispersion according to [1], [4] or [5], and [9] the silica dispersion according to [1], [4] or [5]. Aggregate treatment agent containing liquid,
About.

  According to the present invention, a silica dispersion having excellent film-forming properties and water resistance is provided. The silica dispersion is suitably used as a coating agent for various substrate surfaces. The coating film formed by the coating agent contributes to improving the water resistance of the substrate.

  The silica dispersion of the present invention is a silica dispersion obtained by dispersing at least a silica component and an alkali metal-containing component in water, and has two major modes.

Silica dispersion of the first aspect is made from components which silica component is represented by SiO _2, when (the M an alkali metal atom) M ₂ 0 an alkali metal-containing component expressed in, SiO ₂ and M ₂ 0 (In the present specification, sometimes simply referred to as SiO ₂ / M ₂₀ ratio), the total content of SiO ₂ and M ₂₀ , and the assignment of the spectrum of the silica component by ²⁹ Si-NMR, Q _n (in this specification, simply referred to _{Q 3 / Q 2) (n} = 0~4) the ratio of the area of the signal indicative of the area of the signal, Q ₂ structure showing Q ₃ structure in the signal showing the structure One particular feature is that it is in a specific range.

The silica dispersion of the second embodiment is one in which the silica component contains Si that forms a Si—C bond and Si that does not form a Si—C bond, and the alkali metal-containing component is M ₂₀ (M is When represented by an alkali metal atom), the molar ratio of the component represented by SiO ₂ in the silica component to M ₂ O (in this specification, sometimes simply referred to as SiO ₂ / M ₂₀ ratio), silica dispersion One of the major features is that the content of Si forming the Si—C bond in the total Si contained in the liquid and the total content of SiO ₂ and M ₂₀ are in specific ranges.

  Since the silica dispersion of the present invention has the above constitution, it is possible to form a film on various substrate surfaces such as an inorganic substrate, an organic substrate, and a metal material, and water resistance of the film formed on the surface. (In this specification, simply referred to as water resistance). Further, in the silica dispersion of the second aspect, the formed film can exhibit water repellency at an early stage after the film is formed. Therefore, in this specification, “water resistance” may include the water repellency in some cases.

  In this specification, the term “alkali metal atom, alkaline earth metal atom and metal atom belonging to Group 3B” means an element belonging to Group 1A, IIA and IIIB in the periodic table, respectively.

  Hereinafter, the silica dispersions of the first embodiment and the second embodiment will be described respectively.

In the first embodiment, when describing the SiO ₂ / M ₂₀ ratio and the total content of SiO ₂ and M _20, as described above, SiO ₂ represents a silica component and M ₂₀ represents an alkali metal-containing component. .

The silica component refers to a component containing Si that can be represented by SiO ₂ irrespective of the state of silicon. The component may be in the form of a salt. Examples of the silica component include silicate, silicic acid, and silicon dioxide. The silica component may be composed of a single component, or may be composed of two or more components.

  As used herein, the term “alkali metal-containing component” refers to a component containing an alkali metal atom (M). M is, for example, a lithium atom, a sodium atom, a potassium atom, or the like. From the viewpoint of versatility, a sodium atom is preferred. Examples of the alkali metal-containing component include sodium oxide, lithium oxide, potassium oxide, and the like. The alkali metal-containing component may be composed of a single component, or may be composed of two or more components.

The SiO ₂ / M ₂₀ ratio in the silica dispersion of the present invention is 3 to 10, preferably 3.2 to 8, more preferably 4.2 to 6.6. When the SiO ₂ / M ₂₀ ratio is less than 3, the water resistance is poor, and when it exceeds 10, the film formability is poor.

However, as described below, when colloidal silica is used in the production of a silica dispersion, the silica dispersion can exhibit sufficient film-forming properties even when the SiO ₂ / M ₂₀ ratio exceeds 10. That is, the upper limit of the SiO ₂ / M ₂₀ ratio in the silica dispersion of the present invention is 10 from the viewpoint of satisfying both the expression of sufficient film-forming properties and the cost reduction by not using colloidal silica. From the viewpoint of satisfying only the expression of sufficient film-forming properties, it may be 100 as described later.

The total content of SiO ₂ and M _{20 in} the silica dispersion of the present invention is 1 to 60% by weight, preferably 5 to 40% by weight, and more preferably 10 to 30% by weight. When the total content of SiO ₂ and M ₂ O is less than 1% by weight, for example, when the aggregate is coated with such a silica dispersion, a decrease in the water absorption of the coated aggregate is not expected. If it exceeds, the permeability to the aggregate decreases.

The silica component contained in the silica dispersion of the present invention has a specific chemical structure. It is also necessary to include such a silica component in order to impart excellent film formability and water resistance to the silica dispersion of the present invention. Specifically, when ²⁹ Si-NMR measurement is performed, in the assignment of the spectrum of the silica component by ²⁹ Si-NMR, the area of the signal indicating the Q ₃ structure in the signal indicating the Q _n (n = O to 4) structure and Q ₂ area signal showing the structure (however, when the part of both signals overlap, both the area of the signal by a technique for approximating the two signals in linear sum of Gaussian functions and Lorentz functions) ratio of 1.5 ≦ Q ₃ / Q ₂ ≦ 10, preferably 1.5 ≦ Q ₃ / Q ₂ ≦ 9.0, and more preferably 2.0 ≦ Q ₃ / Q ₂ ≦ 5.5. The ²⁹ Si-NMR measurement is performed using a dried product of the silica dispersion (water removed at 25 ° C. for 72 hours).

Here, Q and _{n-structural,} chemical structure depends on the number of bridging oxygen atoms of the oxygen atom of the SiO ₄ tetrahedral units is a structural unit of the silica (oxygen atom bonded to two Si) Wherein _n of Qn is the degree of bonding of SiO ₄ units and is the number of bridging oxygen atoms. Chemical shifts of the signal indicating such a structure by ²⁹ Si-NMR measurements are known to vary with the degree of coupling Q _n. Q _n chemical shift (TMS standard) of the signal indicative of the structure a liquid and a solid, "Fundamentals and Applications of glass science" [There is wide by compound classes are assigned roughly as follows Sumio Sakka al, published Company: Uchida Lao Tsuru Farm, 1997].

Structure chemical shift
Q ₀ : -65 to -75ppm
Q ₁ : -76 to -84ppm
Q ₂ : -85 to -90ppm
Q ₃ : -92 to -100ppm
Q ₄ : -105 to -115ppm

In order to obtain good film forming properties and water resistance, it is necessary that SiO ₂ forms an appropriate network structure. The Q ₀ , Q ₁ , and Q ₂ structures are point or linear bonds and do not contribute to the formation of a network structure, but serve as a binder for weakly connecting the network structures, and are related to the formation of a film. Therefore, these are parameters of the film forming property. Also, as the ratio of these structures increases, the structure tends to be dissolved in water. The Q ₃ and Q ₄ structures form a network structure and are parameters of water resistance. Only the Q ₃ and Q ₄ structures tend to be rigid, and the balance between the former structure and the latter structure becomes important from the viewpoint of both improving film forming properties and water resistance.

That is, from the viewpoint of improving the water resistance by forming a network structure by the silica component, it is preferable that the Q ₀ , Q ₁ and Q ₂ structures are small. Further, from the viewpoint of improving the film-forming property by forming a long-distance network structure between the silica components, it is preferable that the Q ₃ and Q ₄ structures do not exist in an excessive ratio. In the silica dispersion of the present invention, among the Q ₀ , Q ₁ , and Q ₂ structures, there are generally many Q ₂ structures, and thus the main structures are Q ₂ , Q _3, and Q ₄ structures. From the viewpoint of improving both the film formability and the water resistance of the silica dispersion of the present invention, the amount of change with respect to the SiO ₂ / M ₂₀ ratio is particularly large compared to the combination of Q ₃ / Q ₂ and Q ₄ / Q _{2. 3} / Q ₂ was selected, and the optimum conditions of Q ₃ / Q ₂ were found.

  The pH of the silica dispersion of the present invention is preferably 9 to 11.5 from the viewpoints of both storage stability and improvement of the water resistance of the dried solid.

  The silica dispersion of the present invention is preferably composed of a sol in which solid particles are uniformly dispersed in water. However, even if fine particles are present to such an extent that the particles become cloudy, the dispersion may be uniform. Water serving as a medium may contain another solvent such as an organic solvent as long as the effect of the present invention is not affected. Here, the term “dispersion” refers to a state in which a gel-like substance derived from the aggregation of solid particles does not exist in a medium. A silica dispersion is subjected to a 1 mm mesh sieve, and 90% by weight or more of the dispersion is sieved. If it has passed, it is determined that the dispersion is in a dispersed state.

  Further, the silica dispersion of the present invention may further contain other components such as an alkoxysilane such as ethyl silicate and methyl silicate.

  The silica dispersion of the present invention can be obtained, for example, by (1) dealkalizing an alkali silicic acid solution (aqueous alkali silicic acid solution), or (2) a mixture containing silica sand, water and an alkali metal-containing compound. Can be obtained by hydrothermal treatment to dissolve the silica sand.

  Examples of the method for producing the silica dispersion of the present invention according to the aspect (1) include a production method including a step of subjecting an alkali silicic acid solution to a dealkalization treatment.

  The alkali silicate solution referred to in this specification mainly refers to a concentrated aqueous solution of alkali-silicate glass. Examples of the alkali ions in the concentrated aqueous solution of alkali-silicate glass include cations such as lithium ions, sodium ions, and potassium ions.

  The alkali silicic acid solution before the dealkalization treatment used in the present invention is not particularly limited, and may be a commercially available product or a product produced by a known method.

  Specifically, for example, sodium silicate solution (JIS standard No. 1 water glass, No. 2 water glass, No. 3 water glass or No. 4 water glass), lithium silicate solution (lithium silicate 35, lithium silicate 45 or Lithium silicate 75), potassium silicate solution (1K potassium silicate, C silicate, B silicate, A silicate or 2K potassium silicate) and the like.

  The dealkalization treatment referred to in this specification refers to a treatment for removing alkali ions (particularly sodium ions) in an alkali silicic acid solution. The treatment can be performed by, for example, treatment with a cation exchange resin or electrolytic dialysis treatment. From the viewpoint of simplicity, treatment with a cation exchange resin is preferable.

  The treatment with the cation exchange resin is performed, for example, by adding the cation exchange resin to the alkali silicic acid solution while stirring the alkali silicic acid solution to remove alkali ions, and bringing the alkali silicic acid solution into contact with the resin. The removal can be performed by removing alkali ions in the alkali silicic acid solution. In addition, a method in which a column is filled with a cation exchange resin and a solution is passed through the column, or a method in which contact with the resin is promoted by press-in of pressurized air or the like can be adopted.

  In the electrodialysis treatment, an alkali silicate solution is filled in an electrodialysis layer in which a pair of electrodes are inserted at both ends, in which an anion and a cation exchange membrane are alternately arranged, and a direct current is applied to the electrolytic dialysis treatment. Refers to a treatment for removing alkali ions. The treatment can be performed using, for example, a commercially available electrolytic dialysis treatment device.

  For example, in the case of performing a dealkalization treatment of an alkali silicate solution by a treatment with a cation exchange resin, the quantitative ratio of the cation exchange resin and the alkali silicate solution to be treated is determined by the composition of the alkali silicate solution to be treated. In general, the amount is preferably 50 to 400 parts by weight, more preferably 80 to 320 parts by weight, based on 100 parts by weight of the cation exchange resin. The contact time between the alkali silicic acid solution and the cation exchange resin is preferably about 1 to 60 minutes. The contact between the two can be terminated, for example, by filtering the alkali silicic acid solution containing the resin to remove the resin.

On the other hand, when the alkali silicate solution is subjected to a dealkalization treatment by electrolytic dialysis treatment, after the treatment is started, a part of the treated silica dispersion is taken with time, and the SiO ₂ / M ₂ O ratio is measured to obtain the desired value. The processing may be ended when the value of.

In the above production method, the ratio of SiO ₂ / M ₂ O is 3 to 10, preferably 3.2 to 8, more preferably 4.2 to 6.6, and the total content of SiO ₂ and M ₂₀ and Q ₃ It is suitable for producing a silica dispersion wherein / Q ₂ is in the above range.

In addition, the SiO ₂ / M ₂₀ ratio of the silica dispersion liquid produced as described above can be appropriately adjusted by the hydroxide of the alkali ion or the like.

  The method for producing the silica dispersion of the present invention according to the above aspect (2) includes a step of hydrothermally treating a mixture containing silica sand, water and an alkali metal-containing compound to dissolve the silica sand. Is mentioned. The silica dispersion of the present invention, for example, after mixing silica sand, an alkali metal-containing compound and water, by dissolving the silica sand by hydrothermal treatment, or, after mixing the silica sand, the alkali metal-containing compound and water, It can be obtained by dissolving the silica sand by hydrothermal treatment, after pulverizing the anhydrous alkali silicate obtained by hydrothermal treatment and then calcining as required. The amount of silica sand, water and alkali metal-containing compound used is not particularly limited, but water is 300 to 2800 parts by weight, alkali metal-containing compound (in terms of oxide) per 100 parts by weight of silica sand. But 5 to 40 parts by weight is preferred.

The SiO ₂ content of the silica sand is preferably at least 90% by weight, more preferably at least 95% by weight, particularly preferably at least 97% by weight. The shape and average particle size of the silica sand are not particularly limited. Examples of the silica sand include pearl sand and flattery sand from Australia, Sarawak sand from Indonesia, and silica sand obtained by grinding silica stone.

  Examples of the alkali metal-containing compound include hydroxides, carbonates, nitrates and sulfates of alkali metal atoms, and sodium is preferred as the alkali metal atom. Preferred examples of the alkali metal-containing compound include sodium hydroxide, sodium carbonate, sodium nitrate, and sodium sulfate.

  The hydrothermal treatment referred to in this specification means, for example, in a nickel crucible, an operation of dissolving silica sand under pressure in an aqueous alkali solution, and the pressure condition is preferably 0.5 to 1.8 MPa, more preferably 0.7 to 1.8 MPa. It is 1.7 MPa, particularly preferably 0.9 to 1.7 MPa. The treatment temperature is preferably from 150 to 220 ° C, more preferably from 160 to 200 ° C, particularly preferably from 170 to 200 ° C, and the treatment time is not particularly limited, but is preferably from 1 to 24 hours.

  As a firing method, a known method is generally used, and a method of firing at a temperature of preferably 300 to 1500 ° C, more preferably 500 to 1300 ° C is exemplified. The heating time is usually 0.1 to 24 hours. Such firing can be usually performed in a heating furnace such as an electric furnace or a gas furnace.

  After the calcination, the obtained alkali silicate is optionally pulverized and adjusted to a predetermined particle size. For the pulverization, for example, a pulverizer such as a ball mill and a roller mill is used.

In the above production method, the ratio of SiO ₂ / M ₂ O is 3 to 10, preferably 3.2 to 8, more preferably 4.2 to 6.6, and the total content of SiO ₂ and M ₂₀ and Q ₃ It is suitable for producing a silica dispersion wherein / Q ₂ is in the above range.

In addition, the SiO ₂ / M ₂₀ ratio of the silica dispersion liquid produced as described above can be appropriately adjusted by the hydroxide of the alkali ion or the like.

Furthermore, by mixing the silica dispersion of the present invention and colloidal silica, or by mixing a silica component other than colloidal silica such as silicate, silicic acid, silicon dioxide and colloidal silica, and then performing a dealkalization treatment, A silica dispersion having the same film formability and water resistance as the silica dispersion of the present invention but having a SiO ₂ / M ₂₀ ratio of 3 to 100 (hereinafter referred to as silica dispersion (2)) is obtained. be able to. When the silica dispersion (2) is prepared by mixing the silica dispersion of the present invention and colloidal silica, colloidal silica is added to the silica dispersion of the present invention and mixed, or colloidal silica is mixed. Can be obtained by adding and mixing the silica dispersion.

As the colloidal silica, water-dispersible or non-aqueous organic solvent-dispersible colloidal silica such as alcohol can be used. Such colloidal silica is generally silica (SiO ₂₎ containing 20 to 50% by weight solids.

  Water-dispersible colloidal silica is usually prepared from an alkali silicic acid solution, and such a colloidal silica can be easily obtained as a commercial product. The organic solvent-dispersible colloidal silica can be easily prepared by substituting the water of the water-dispersible colloidal silica with an organic solvent. Such an organic solvent-dispersible colloidal silica can be easily obtained as a commercial product similarly to the water-dispersible colloidal silica.

  Examples of the organic solvent include lower aliphatic alcohols such as methanol, ethanol, isopropanol, n-butanol and isobutanol; ethylene glycol derivatives such as ethylene glycol, ethylene glycol monobutyl ether and ethylene glycol monoethyl ether acetate; diethylene glycol, diethylene glycol Examples thereof include diethylene glycol derivatives such as monobutyl ether and hydrophilic organic solvents such as diacetone alcohol. Further, toluene, xylene, ethyl acetate, butyl acetate, methyl ethyl ketone, methyl isobutyl ketone, methyl ethyl ketoxime and the like may be used together with these organic solvents.

  The mixing ratio of the silica dispersion and the colloidal silica produced by the production method is usually preferably 50 to 1000 parts by weight of colloidal silica with respect to 100 parts by weight of the silica dispersion.

In addition, the silica dispersion of the present invention and the silica dispersion (2) containing colloidal silica, the SiO ₂ / M ₂ O ratio is 3 to 100, preferably 10 to 100, more preferably 18 to 100. it is 90, particularly preferably 20 to 80, the total content and Q ₃ / Q ₂ of SiO ₂ and M ₂ 0, which is the same range as the silica dispersion of the present invention.

  The silica dispersion (2) can also be obtained by subjecting colloidal silica to a dealkalization treatment in the same manner as described above.

In addition, the SiO ₂ / M ₂₀ ratio of the silica dispersion liquid produced as described above can be appropriately adjusted by the hydroxide of the alkali ion or the like.

  The silica dispersion of the second embodiment is obtained by introducing Si that forms a Si—C bond into the silica component of the silica dispersion of the first embodiment. Therefore, the silica component in the silica dispersion of the present embodiment contains Si that forms a Si—C bond and Si that does not form a Si—C bond. The introduction of Si that forms a Si—C bond further imparts water repellency to the film formed by the silica dispersion.

The “SiO ₂ / M ₂₀ ratio” and the “total content of SiO ₂ and M ₂₀ ” in this embodiment have the same meanings as those in the first embodiment.

  On the other hand, the content of Si that forms a Si-C bond is 0.1 to 30 mol% of the total Si contained in the silica dispersion from the viewpoint of imparting sufficient water repellency to the formed film, and is preferably Is 1 to 20 mol%, more preferably 3 to 15 mol%.

  The content of Si forming a Si—C bond in all Si can be measured, for example, by a method described in Examples described later.

In the silica dispersion of this embodiment, in the assignment of the spectrum of the silica component by ²⁹ Si-NMR, the area of the signal showing the Q ₃ structure and the Q ₂ structure in the signal showing the Q _n (n = 0 to 4) structure Is preferably the same as that of the dispersion from the same viewpoint as that of the silica dispersion of the first embodiment.

  The silica dispersion of the present embodiment is obtained by adding, to the silica dispersion of the first embodiment, for example, one kind of a compound having a hydrophilic group and an alkyl group imparting appropriate hydrophobicity (a compound having a Si—C bond). Alternatively, it is preferable to produce by adding two or more kinds. In the method (1) of the method for producing a silica dispersion liquid according to the first embodiment, the alkali silicic acid solution is mixed with one or more compounds having a Si—C bond, and then subjected to a dealkalization treatment. During the treatment, a condensation reaction may be simultaneously performed between the alkali silicic acid and the compound to produce the silica dispersion of this embodiment. The latter method is more suitable as a method for producing the silica dispersion of this embodiment because the production process can be simplified and the cost is low.

  Examples of the compound having a Si-C bond include alkyl siliconates and alkyl silanes.

For example, as the alkylsiliconate, a compound represented by the following general formula is preferably used.
R _n -Si- (OM) _4-n
In the formula, n represents the number of bonds of R to Si, and is 1, 2 or 3. R represents an alkyl group, and the alkyl group preferably has 1 to 2 carbon atoms. M represents a hydrogen atom or an alkali metal atom. Specific examples of the compound include sodium methylsiliconate [CH ₃ Si (OH) ₂ (ONa)] and potassium ethyl siliconate [C ₂ H ₅ Si (OH) ₂ (OK)].

Further, as the alkylsilane, a compound represented by the following general formula is preferably used.
R ¹ -Si (OR ² ) ₃
In the formula, R ¹ and R ² represent the same or different alkyl groups. Specific examples of the compound include methyltrimethoxysilane, ethyltrimethoxysilane, hexyltrimethoxysilane, decyltrimethoxysilane, methyltriethoxysilane, propyltriethoxysilane, hexyltriethoxysilane, and decyltriethoxysilane. Is mentioned. The carbon number of R ¹ is preferably 1-3, and the carbon number of R ² is preferably 1-2.

  Specifically, the silica dispersion of this embodiment can be produced through a process of mixing a condensation reaction product of an alkylsilane and / or an alkylsiliconate with an alkali silicic acid solution, followed by a dealkalization treatment. Further, the silica dispersion of this embodiment can also be produced by mixing the above-mentioned alkylsiliconate or the above-mentioned condensation reaction product with a commercially available water glass and then subjecting the mixture to a dealkalization treatment. The addition amount of the alkylsiliconate or the condensation reaction product is preferably 0.1 to 20 parts by weight, more preferably 1 to 10 parts by weight, based on 100 parts by weight of water glass. When the alkylsiliconate and the condensation reaction product are used in combination, the amount thereof is preferably such that the addition amount of both compounds falls within a suitable addition amount range of one of the compounds. The dealkalization treatment may be performed by a method similar to that for preparing the silica dispersion of the first embodiment.

  In addition, for example, at the time of or after the preparation of the silica dispersion of the first embodiment, an alkylsiliconate is added and uniformly mixed to produce the silica dispersion of the present embodiment. The addition amount of the alkyl siliconate is preferably 0.1 to 20 parts by weight, more preferably 1 to 10 parts by weight, based on 100 parts by weight of the silica component in the silica dispersion at the time of the preparation before or after the addition of the alkyl siliconate. Department. Further, for example, after the alkylsilane is subjected to a condensation reaction using an acid (for example, in a 0.005N hydrochloric acid solution) or an alkali (for example, in a 0.02 (v / v)% aqueous ammonia solution) as a catalyst, the obtained condensation reaction product is subjected to a second reaction. The silica dispersion of the present embodiment can be produced by mixing uniformly during or after the preparation of the silica dispersion of the first embodiment. The addition amount of the condensation reactant is preferably 0.1 to 20 parts by weight, more preferably 1 to 10 parts by weight, based on 100 parts by weight of the silica component in the silica dispersion during the preparation before or after the addition of the condensation reaction product. Department.

  As the compound having a Si-C bond, the above-mentioned compounds specifically exemplified in the present specification are preferable. Therefore, the method for producing the silica dispersion of this embodiment includes a condensation reaction product of alkylsilane and / or an alkylsiliconate. And an alkali silicic acid solution (for example, the above-mentioned water glass), and then a method including a step of performing a dealkalization treatment is preferable.

It should be noted that it is not possible to impart water repellency by using a condensation reaction product of alkoxysilanes [general formula: Si- (OR) ₄ ; R represents an alkyl group] as disclosed in Japanese Patent No. 2705756. Can not. The reason for this is not clear, but it is probably because all or most of the alkyl groups bonded to Si have been eliminated by the condensation reaction.

  The film formed by the silica dispersion liquid of the present embodiment is, for example, by the water repellency exerted by an alkyl group derived from an alkyl siliconate or the like, on the surface of the object on which it is formed, in the initial stage after film formation. Provides water repellency at one time. Although the water repellency is probably due to the fact that the alkyl group responsible for the water repellency on the film surface is oriented to the outside of the film at the time of film formation, it gradually aligns with the large amount of water to the inside of the film. And finally, the surface of the object to be treated becomes hydrophilic.

  Various applications are conceivable utilizing the effect exerted by the silica dispersion of this embodiment. For example, the silica dispersion of this embodiment is effective as a concrete aggregate treating agent. The surface of the concrete aggregate is treated with the dispersion, for example, by dipping the aggregate in the silica dispersion of the present invention and then performing a drying treatment, a water-repellent coating film is formed on the surface of the aggregate, The surface of the material becomes water repellent. As a result, the water absorption of the aggregate decreases. If such an aggregate is used, for example, when kneading with mortar, it can be sufficiently kneaded with a small amount of water, and workability is improved. In addition, strong adhesion (reactivity) with the mortar paste is realized on the aggregate. Therefore, even if an aggregate having a high water absorption rate is used, a low-viscosity fresh concrete with high operability can be realized with a small amount of water, and a high-strength, low-shrinkage concrete body can be molded. . Particularly, there is an advantage in that a low-viscosity fresh concrete having a high slump value can be realized even when using low-quality aggregate. Examples of the low-quality aggregate include an aggregate having many micropores and a high water absorption, and, for example, a recycled aggregate.

  Further, by applying the silica dispersion of this embodiment to the concrete surface, a water absorption preventing effect can be imparted to the concrete, and excellent effects such as salt damage, freezing damage, prevention of deterioration due to neutralization, and prevention of bleaching can be exhibited.

  By further adding an arbitrary surfactant to the above silica dispersion of the present invention (hereinafter, including the silica dispersion (2)), the permeability of the dispersion to a substrate (for example, concrete) is increased. An improved composition (hereinafter, referred to as a surfactant-containing composition) is obtained.

  Examples of the surfactant include a cationic surfactant, an anionic surfactant, an amphoteric surfactant, and a nonionic surfactant. Among these, a nonionic surfactant is particularly used. Is preferred.

  Examples of the cationic surfactant include a linear alkylbenzene sulfonate, a polyoxyethylene addition alcohol sulfate, and an alkyl sulfate.

  Examples of the anionic surfactant include sodium alkyl ether sulfate, alkyltrimethylammonium salt, and alkylpyridinium salt.

  Examples of the amphoteric surfactant include alkyl carboxy betaine, alkyl sulfo betaine and the like.

  Examples of the nonionic surfactant include polyoxyethylene alkyl ether, polyoxyethylene alkyl phenyl ether, and fatty acid diethanolamide.

  The alkyl group preferably has 6 to 22 carbon atoms, and more preferably has 8 to 14 carbon atoms. Further, the alkyl group may be linear or branched.

  The surfactant content in the surfactant-containing composition is preferably from 0.01 to 10% by weight, more preferably from 0.1 to 5% by weight.

  Examples of the method for preparing the surfactant-containing composition include a method of adding and mixing a surfactant when preparing the silica dispersion or after the preparation.

  Further, the silica dispersion of the present invention, or the surfactant-containing composition, by further adding an optional thickener, can also exhibit excellent carbon dioxide shielding properties, a thicker coating film substrate A composition that can be formed on the surface (hereinafter, referred to as a thickener-containing composition) is obtained.

  Examples of the thickener include nonionic thickeners such as polyoxyethylene glycol fatty acid ester (for example, Emanone 3299R manufactured by Kao Corporation) and quaternary ammonium-type copolymers (for example, GAFQUART (registered trademark) series manufactured by ISP) ), Acrylic resins (for example, Acronal (registered trademark) series manufactured by BASF) and the like.

  The content of the thickener in the thickener-containing composition is preferably 0.01 to 10% by weight, more preferably 0.1 to 5% by weight.

  As a method for preparing the thickener-containing composition, for example, a method of adding and mixing a thickener when preparing the silica dispersion of the present invention or the surfactant-containing composition or after the preparation. Is mentioned.

  Further, a composition having improved stability by adding a compound having a chelating ability to metal ions as a stabilizer to the silica dispersion of the present invention, the surfactant-containing composition or the thickener-containing composition. (Hereinafter referred to as a stabilizer-containing composition).

  Examples of the stabilizer include ethylenediaminetetraacetic acid, nitrilotriacetic acid, diethylenetriaminepentaacetic acid, hydroxyethylethylenediaminetriacetic acid, propylenediaminetetraacetic acid, bis (2-hydroxyphenylacetic acid) ethylenediamine, and salts thereof, and aliphatic oxycarboxylic acids. And condensed phosphates. Examples of the aliphatic oxycarboxylic acid include tartaric acid, citric acid, succinic acid, gluconic acid, dihydroxyethylglycine and the like. Examples of the condensed phosphate include salts of polyphosphoric acid such as pyrophosphoric acid, triphosphoric acid, trimetaphosphoric acid, and tetrametaphosphoric acid. Specific examples thereof include sodium pyrophosphate, sodium acid pyrophosphate, sodium tripolyphosphate, and sodium tetrapolyphosphate. , Sodium hexametaphosphate, sodium acid hexametaphosphate or potassium salts thereof.

  The content of the stabilizer in the stabilizer-containing composition is preferably 0.01 to 5% by weight, more preferably 0.5 to 1% by weight.

  Further, the silica dispersion of the present invention, the surfactant-containing composition, the thickener-containing composition or the stabilizer-containing composition, as a curing accelerator, an alkaline earth metal or a metal atom belonging to Group 3B. A compound (hereinafter, referred to as a curing accelerator-containing composition) having an improved curing rate by adding a contained compound (hereinafter, referred to as an alkaline earth metal-containing compound or a group 3B metal-containing compound, respectively) is obtained.

  Examples of the alkaline earth metal-containing compound include calcium carbonate, magnesium carbonate, calcium hydroxide, magnesium hydroxide, magnesium oxide, calcium chloride, magnesium chloride, calcium nitrate, magnesium nitrate, calcium sulfate, magnesium sulfate, and the like. Examples of the metal-containing compound include aluminum chloride, aluminum hydroxide, aluminum nitrate, aluminum phosphate, and aluminum borate.

  The content of the curing accelerator in the composition containing the curing accelerator is preferably 0.01 to 10% by weight, more preferably 0.1 to 1% by weight.

  The silica dispersion provided in the present invention, and the surfactant-containing composition, the thickener-containing composition, the stabilizer-containing composition and the curing accelerator-containing composition are extremely excellent in film formability and water resistance. It is suitably used as a coating agent for various substrate surfaces. All of these contain the silica dispersion of the present invention as a main component. Accordingly, the present invention further provides a coating agent comprising the silica dispersion of the present invention.

  The coating agent of the present invention may be the silica dispersion of the present invention, or a surfactant-containing composition, a thickener-containing composition, a stabilizer-containing composition or a curing accelerator-containing composition itself, By mixing the silica dispersion of the present invention, or a surfactant-containing composition, a thickener-containing composition, a stabilizer-containing composition, or a curing accelerator-containing composition with other additional components as required. Can be prepared. Other components include, for example, alkylsilane compounds, and the amount thereof is not particularly limited as long as the desired effects of the present invention are not inhibited.

  The coating agent of the present invention is excellent as a surface coating agent or an immersion agent for coating various substrate surfaces such as an inorganic base material, an organic base material, and a metal material. It can be used to prevent deterioration. The coating agent of the present invention is used by coating on the surface of a substrate or immersing the substrate in the agent. As the inorganic base material, for example, concrete or glass, for the organic base material, for example, acrylic resin, urethane resin, epoxy resin, polyester resin or silicone resin, and as the metal material, for example, a plated steel plate Can be

  Examples of the method for coating the surface of the substrate with the coating agent of the present invention include known methods such as a brush coating method, a roller method, a spray method, a spraying method, a dipping method, and a filling method. The coating can be applied by a suitable method according to the application. After the application, by appropriately drying and curing, a good coating film can be formed on the substrate surface. The formation of the coating film is caused by the development of a network structure mainly formed by a silica component formed on the surface of the substrate and / or as the coating agent partially impregnated in the substrate is dried.

  The silica dispersion of the present invention used in the coating agent of the present invention has excellent film-forming properties and water resistance. Therefore, for example, a coating film formed by the coating agent of the present invention can exhibit high water resistance, and can prevent, for example, sulfation and salt damage of concrete having a coating film formed on the surface. In addition, the coating film can also exhibit a gas barrier function. For example, when a coating film is formed on the concrete surface, the concrete can be prevented from being neutralized by a gas-proof effect of carbon dioxide or the like. Accordingly, as one embodiment of the coating agent of the present invention, a concrete surface coating agent capable of forming a coating film exhibiting the above-described effects is provided.

  Further, the coating film formed by the coating agent of the present invention also exhibits an effect of suppressing the water absorption of the inorganic porous material due to its water resistance. That is, the formation of the coating film on the surface of the inorganic porous body can prevent the permeation of water into the inorganic porous body. Examples of the inorganic porous body include concrete, mortar, aggregate, and the like. Among them, the use of aggregates, particularly recycled aggregates, is effective, and from the viewpoint of simplicity, it is preferable to coat by an immersion method or a spraying method. The formation of the coating film reduces the water absorption of the aggregate. Therefore, as one embodiment of the coating agent of the present invention, an aggregate treating agent capable of forming a coating film exhibiting the above-described effects is provided.

  Since the coating film formed by the coating agent of the present invention can exhibit the above-described excellent effects, the formation of the coating film contributes to the improvement of the water resistance of the base material. Therefore, the substrate (eg, aggregate) coated with the coating agent of the present invention exhibits excellent water resistance.

  The elemental analysis methods in Examples, Reference Examples and Comparative Examples, the method for quantifying Si forming Si—C bonds in all Si, and the methods for evaluating film formability and water resistance are summarized below.

Elemental analysis The abundance of silicon atoms and alkali (eg, sodium) ions in the silica dispersion was determined in accordance with JIS R2216 ("Advancement in X-ray analysis 21", Agne Technology Center, March 31, 1990, first edition, p93), glass After pretreatment of the measurement sample by the bead method, measurement was performed using a fluorescent X-ray analyzer (manufactured by Rigaku Corporation, model number: ZSX-100e). By comparing the intensity of the SiKα peak and the MKα peak corresponding to silicon atoms and alkali ions with the intensity obtained when measuring a standard sample containing the corresponding element at a known concentration, the silicon atom concentration in the silica dispersion liquid and The alkali ion concentration was determined. In addition, silicon atoms and alkali ions were converted to oxides to represent their contents, and the SiO ₂ / M ₂ O ratio in the silica dispersion was determined.

Determination of Si forming Si—C bond in all Si The silica dispersion was maintained at 25 ° C. for 72 hours, and the dried product from which the medium was removed was subjected to ²⁹ Si-NMR measurement. Here, in the assignment of spectra by ²⁹ Si-NMR, the chemical shift of Si (R—SiO ₃ ; R represents an alkyl group) forming a Si—C bond is in the range of −40 to −70 ppm, The chemical shift of Si (SiO ₄ ) forming only O bonds is in the range of −65 to −115 ppm, and both peaks can be assigned separately [Encyclopedia of nuclear magnetic resonance, Vol. 7, pp. 4386-4398. John Wiley & Sons Ltd. (1996)]. Therefore, the ratio (P) of the area of the signal belonging to Si forming the Si-C bond to the total area of the signal belonging to both Sis (the area of the signal belonging to all Si) is as follows. formula:

Determined by Since the value of P corresponds to the value of the proportion (mol%) of Si forming the Si-C bond in the total Si when the total Si is 100 mol%, the P in the total Si The content (mol%) of Si forming the Si-C bond is obtained.

Film formation test 100 ml of silica dispersion was put into a beaker and about 100 ml of a glass plate of 76 mm x 26 mm x 1.5 mm (slide glass S-1214 manufactured by Matsunami Co., Ltd.) was cut in a length of 1/2 to 2/3. After immersion for 3 seconds, the substrate was lifted up, and left to dry at room temperature for 1 day with the surface of 76 mm × 26 mm inclined at about 45 ° from the horizontal plane. Thereafter, the formed coating film was visually observed under an optical microscope (50 ×) (manufactured by Nikon Corporation, model number: OPTIHOT-100) to evaluate the film formation state according to the following evaluation criteria, and formed a silica dispersion liquid. The sex was evaluated.

(Evaluation criteria)
◎: Sufficient film-forming properties, no cracks ○: Film-forming properties, but cracks △: No film-forming properties

Water resistance test 5 g of a silica dispersion liquid was placed in a glass Petri dish (flat petri dish, product number: 70, diameter: 75 mm), and dried at 50 ° C for 1 day in a drier (ADVANTEC, model number: FC-410). A dried cured product was obtained. The weight (g) of the cured product was measured (W1) using an electronic balance (manufactured by METTLER, model number: AB204-S), and then immersed in 50 ml of ion-exchanged water for 12 hours. Thereafter, the ion-exchanged water was removed with a spoid, dried again at 50 ° C. for 1 day in a drier (manufactured by ADVANTEC, model number: FC-410), and the weight of the cured product was measured (W2). Thereafter, the residual dissolution rate (%) [(W2 / W1) × 100] was calculated, and the water resistance of the silica dispersion was evaluated according to the following evaluation criteria.

(Evaluation criteria)
◎: Residual dissolution rate exceeding 50% ○: Dissolution residual rate 10% to 50% △: Dissolution residual rate less than 10%

Example 1
A solution obtained by mixing and stirring 250 g of commercially available No. 3 water glass (manufactured by Nippon Chemical Industry Co., Ltd.) and 750 g of ion-exchanged water was added to a cation exchange resin (manufactured by Organo Corporation, product number: Amberlite IR120B (H)). 160 g was gradually added while stirring little by little. After addition of the whole amount, stirring was continued for another 10 minutes. The cation exchange resin was separated by filtration from the mixed solution through a SUS mesh (mesh size: 0.075 mm) to obtain a dealkalized silica dispersion. When the pH of the obtained silica dispersion was measured at 20 ° C. using a pH meter (manufactured by METTLER, model number: MP-100), it was 10.94. Table 1 shows the evaluation results of the SiO ₂ / M ₂₀ ratio, pH, the total content of SiO ₂ and M ₂₀ , Q ₃ / Q _2, and film formability and water resistance. FIG. 1 shows an optical electron micrograph (× 50) of a coating film formed on a sheet glass using the silica dispersion liquid of this example.

Examples 2 to 6
Using No. 3 water glass or No. 1 water glass (manufactured by Nippon Kagaku Kogyo Co., Ltd.), the alkali removal treatment was performed in the same manner as in Example 1 except that the amounts of ion exchange water and cation exchange resin were changed. A silica dispersion was prepared. Table 1 shows the amounts used, the SiO ₂ / M ₂₀ ratio of the silica dispersion, the pH, the total content of SiO ₂ and M ₂₀ , Q ₃ / Q _2, and the evaluation results of film formability and water resistance. . FIG. 2 shows an optical electron micrograph (× 50) of a coating film formed on a plate glass using the silica dispersion liquid of Example 3.

Comparative Examples 1-4
Using a No. 3 water glass or a No. 1 water glass, a dealkalized silica dispersion was prepared in the same manner as in Example 1, except that the amounts of ion-exchanged water and cation-exchange resin were changed. Table 1 shows the amounts used, the SiO ₂ / M ₂₀ ratio of the silica dispersion, the pH, the total content of SiO ₂ and M ₂₀ , Q ₃ / Q _2, and the evaluation results of film formability and water resistance. . FIGS. 3 and 4 show optical electron micrographs (× 50) of the coating films formed on the plate glass using the silica dispersions of Comparative Examples 1 and 2, respectively.

As can be seen from the results in Table 1, the silica dispersions of Examples 1 to 6 had a SiO ₂ / M ₂₀ ratio of 3 to 10, and the total content of SiO ₂ and M ₂₀ was 1 to 60% by weight. And Q ₃ / Q ₂ satisfies 1.5 ≦ Q ₃ / Q ₂ ≦ 10, which is excellent in both film formability and water resistance. On the other hand, the silica dispersions of Comparative Examples 1 to 4, which deviate even one from such a range, are inferior in either film formability or water resistance.

Example 7
After mixing 22.0 g of silica sand (Australia's flattery sand, SiO ₂ content 99.8 wt%, average particle size 150 μm), 14.4 g of NaOH aqueous solution (48 wt% concentration), and 293.3 g of ion-exchanged water, the mixture was mixed in a nickel crucible to 1.4 g. Hydrothermal treatment was performed at 180 ° C. for 4 hours at MPa to prepare a silica dispersion. Table 2 shows the SiO ₂ / M ₂ O ratio, the pH, the total content of SiO ₂ and M ₂₀ , the Q ₃ / Q _2, and the evaluation results of film formability and water resistance of this silica dispersion.

Example 8
After mixing 44.0 g of the above silica sand, 23.3 g of the above NaOH aqueous solution, and 339.0 g of ion-exchanged water, the mixture was subjected to hydrothermal treatment at 1.7 MPa and 200 ° C. for 8 hours in a nickel crucible to prepare a silica dispersion. Table 2 shows the evaluation results of the SiO ₂ / M ₂₀ ratio, pH, total content of SiO ₂ and M ₂₀ , Q ₃ / Q _2, film formability and water resistance of this silica dispersion.

  As can be seen from the results in Table 2, the silica dispersions of Examples 7 and 8 are excellent in both film formability and water resistance.

Reference Example 1
While stirring 900 g of colloidal silica (Snowtec 20L (manufactured by Nissan Chemical Industries, Ltd., SiO ₂ content 20% by weight)), 200 g of the alkali-treated silica dispersion of Example 4 was added to this colloidal silica at room temperature. The mixture was gradually added and mixed to prepare a silica dispersion (silica dispersion (2)).

The film formability of the obtained silica dispersion (2) was equivalent to that of the dealkalized silica dispersion of Example 4 before mixing with colloidal silica. On the other hand, in the water resistance test, assuming that the immersion time is 96 hours, the dissolution residual ratio of the dealkalized silica dispersion of Example 4 is about 50%, but the silica dispersion (2) of Reference Example 1 The residual dissolution rate exceeded 90%. The SiO ₂ / M ₂₀ ratio of the silica dispersion liquid (2) of Reference Example 1 was 37.7, the pH was 11.07, the total content of SiO ₂ and M ₂₀ was 19.5% by weight, and Q ₃ / Q ₂ was 8.3. there were.

Example 9
The water absorption of the regenerated fine aggregate (particle size: 5 mm or less) coated with each of the silica dispersions of Examples 1 to 8, Reference Example 1, and Comparative Example 1 was examined.

  Put 2000 ml of silica dispersion in a container (240 mm diameter x 230 mm height), immerse 2 kg of recycled fine aggregate at room temperature for 1 hour, pass through a sieve (opening 0.25 mm), and mix silica dispersion and recycled fine aggregate. Was isolated. The regenerated fine aggregate in a wet state was dried at room temperature for 24 hours. The water absorption of the dried fine aggregate and the fine aggregate not immersed in the silica dispersion (untreated fine aggregate) was determined in accordance with JIS A1109. Table 3 shows the results.

  From the results in Table 3, it was confirmed that the water absorption of the aggregates treated with the silica dispersions of Examples 1 to 8 and Reference Example 1 was reduced.

Example 10
Sodium methylsiliconate (chemical formula: CH ₅ NaO ₃ Si) was used as a compound having a Si—C bond. To a mixed solution of 250 g of No. 3 water glass (manufactured by Nippon Chemical Industry Co., Ltd.) and 250 g of ion-exchanged water, 15.5 g of a 30 (w / v)% aqueous solution of the compound was added with stirring. Next, 100 g of a cation exchange resin [manufactured by Organo Corporation, product number: Amberlite IR120B (H)] 100 g was gradually added to the mixed solution little by little while stirring. After addition of the whole amount, stirring was continued for another 10 minutes. The cation exchange resin was separated by filtration through a SUS mesh (mesh opening: 0.075 mm) from the mixture, and a silica dispersion obtained by subjecting a mixture of sodium methylsiliconate and water glass to a dealkalization treatment was obtained. The pH of the obtained silica dispersion was measured using a pH meter (manufactured by METTLER, model number: MP-100) at 20 ° C. and found to be 11.10. The ratio of SiO ₂ / M ₂ O is 5.5, the total content of SiO ₂ and M ₂ O is 16.2% by weight, Q ₃ / Q ₂ is 4.3, and the amount of Si forming a Si—C bond in all Si is 3 mol%. Furthermore, the film-forming property on a glass plate and the water resistance were also good. In addition, as shown in Table 4 (time-dependent changes in the contact angle between the coating film and water immediately after the film formation), the coating film shows water repellency continuously in the early stage (about 60 minutes) after the film formation. Was. The water repellency was evaluated by measuring a contact angle between a coating film on a glass plate and water obtained under the same conditions as in the film-forming property test using a contact angle measuring device (manufactured by Kyowa Interface Science Co., Ltd.). The larger the contact angle, the better the water repellency. The contact angle was also measured for a coating film formed in the same manner using the silica dispersion of Comparative Example 4. The results are shown in Table 4.

Example 11
3 g of 0.1 N hydrochloric acid was added dropwise while stirring 50 g of propyltriethoxysilane and 50 g of water, and stirring was further continued for 60 minutes to obtain a uniform transparent solution. 12.5 g of the above solution was gradually added to a mixed solution of 250 g of No. 3 water glass (manufactured by Nippon Chemical Industry Co., Ltd.) and 250 g of ion-exchanged water while stirring little by little. Thereafter, 100 g of a cation exchange resin (manufactured by Organo Co., Ltd., product number: Amberlite IR120B (H)) was gradually added while stirring little by little. After addition of the whole amount, stirring was continued for another 10 minutes. The cation exchange resin was separated by filtration from the mixed solution through a SUS mesh (mesh opening: 0.075 mm) to obtain a silica dispersion obtained by dealkalization. When the pH of the obtained silica dispersion was measured at 20 ° C. using a pH meter (manufactured by METTLER, model number: MP-100), it was 10.98. Further, the SiO ₂ / M ₂ O ratio is 5.5, the total content of SiO ₂ and M ₂ O is 17% by weight, Q ₃ / Q ₂ is 4.4, and the amount of Si forming a Si—C bond in all Si is 3 mol%. Furthermore, the film-forming property on a glass plate and the water resistance were also good. Further, as shown in Table 4, the coating film exhibited water repellency continuously in the initial stage (about 60 minutes) after the film formation. The water repellency was evaluated in the same manner as in Example 10.

  From the results in Table 4, it can be seen that the coating films formed by the silica dispersions of Examples 10 and 11 each exhibit the water repellency as described above. According to this result, due to the water repellency of the coating film, in the initial stage immediately after the film formation, the portion where the film was formed has a clear hydrophobic property, but the hydrophobic effect gradually weakens over time and gradually becomes hydrophilic. It was confirmed that it took on a characteristic.

Mortar kneading test After the aggregate (average particle size: 5 mm or less) was immersed in the silica dispersion of Example 10 for 1 hour, the silica dispersion and the aggregate were separated through a sieve (opening 0.25 mm), and the aggregate was separated. Dry for 1 day at room temperature (treated aggregate). For comparison, the same operation was performed on the aggregate using water instead of the silica dispersion (untreated aggregate).

  1000 g of dried aggregate, 665 g of ordinary Portland cement (manufactured by Taiheiyo Cement Co.), 6.3 g of water reducing agent (manufactured by Kao Corporation, trade name "Mighty") and 300 g of water are kneaded with a mortar mixer for 3 minutes, and the slump value is obtained. Was measured. Mortar was formed (4cm x 4cm x 16cm square pillar), and after 24 hours aerial curing, bending strength test after 28 days in water curing, 24 hours aerial curing, 7 days to 30 days after water curing, The length change rate was measured under the conditions of a temperature of 20 ° C. and a humidity of 60%. The slump value was measured by a mortar cone (upper inner diameter 70φmm, lower inner diameter 100φmm, height 60mm) and JIS R5201. The bending strength test was performed using an Autograph DCS-5000 (manufactured by Shimadzu Corporation). The length change rate was measured by a contact gauge method (JIS A1129). Table 5 shows the results.

From the results shown in Table 5, it can be seen that the viscosity reduction (slump value) of fresh concrete can be realized by the aggregate treatment using the silica dispersion of the present invention. In addition, it can be seen that the treatment is effective for improving the strength and reducing shrinkage of concrete. A similar test was separately performed using a 20% (v / v)% solution (solvent: isopropyl alcohol) of methyltrimethoxysilane known as a water repellent as a treatment liquid. Was 5.66 N / mm ² , which was remarkably reduced.

  According to the present invention, a silica dispersion having excellent film-forming properties and water resistance is provided. The silica dispersion is suitably used as a coating agent for various substrate surfaces.

FIG. 1 is an optical electron micrograph (× 50) of a coating film formed on a plate glass using the silica dispersion liquid of Example 1. FIG. 2 is an optical electron micrograph (× 50) of a coating film formed on a glass sheet using the silica dispersion liquid of Example 3. FIG. 3 is an optical electron micrograph (× 50) of a coating film formed on a plate glass using the silica dispersion liquid of Comparative Example 1. FIG. 4 is an optical electron micrograph (× 50) of a coating film formed on a plate glass using the silica dispersion liquid of Comparative Example 2.

Claims (9)

A silica dispersion obtained by dispersing at least a silica component and an alkali metal-containing component in water, wherein the silica component is represented by SiO ₂ and the alkali metal-containing component is represented by M ₂₀ (M is an alkali metal atom). The molar ratio of SiO ₂ to M ₂ O (SiO ₂ / M ₂ O) is 3 to 10 and the total content of SiO ₂ and M ₂ O is 1 to 60% by weight; In the assignment of spectra by ²⁹ Si-NMR, the ratio of the area of the signal showing the Q ₃ structure to the area of the signal showing the Q ₂ structure in the signal showing the Q _n (n = 0 to 4) structure was 1.5 ≦ Q ₃ A silica dispersion wherein / Q ₂ ≦ 10.   The method for producing a silica dispersion according to claim 1, comprising a step of subjecting the alkali silicic acid solution to a dealkalization treatment.   The method for producing a silica dispersion according to claim 1, further comprising a step of hydrothermally treating a mixture containing silica sand, water and an alkali metal-containing compound to dissolve the silica sand. A silica dispersion obtained by dispersing at least a silica component and an alkali metal-containing component in water, wherein the silica component contains Si forming a Si-C bond and Si not forming a Si-C bond. When the alkali metal-containing component is represented by M ₂₀ (M is an alkali metal atom), the molar ratio (SiO ₂ / M ₂₀ ) of the component represented by SiO ₂ in the silica component to M ₂₀ is 3 to 10, 0.1 to 30 mol% content in the whole Si of Si to form a Si-C bond, and the total content of SiO ₂ and M ₂ 0 is 1 to 60 wt% , Silica dispersion. In the assignment of the spectrum by ²⁹ Si-NMR of the silica component, the ratio of the area of the signal showing the Q ₃ structure to the area of the signal showing the Q ₂ structure in the signal showing the Q _n (n = 0 to 4) structure was 1.5 ≦. The silica dispersion according to claim 4, wherein Q ₃ / Q ₂ ≦ 10.   A method for producing a silica dispersion, comprising a step of mixing a condensation reaction product of an alkylsilane and / or an alkylsiliconate with an alkali silicic acid solution, followed by a dealkalization treatment.   A coating agent comprising the silica dispersion according to claim 1, 4 or 5.   A concrete surface coating agent comprising the silica dispersion according to claim 1, 4 or 5. An aggregate treating agent comprising the silica dispersion according to claim 1, 4 or 5.

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