JP2007308372A - Method for producing silica gel - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide silica gel for a moisture adjusting agent, which adjusts the humidity of an ambient atmosphere to a prescribed value by adsorbing moisture contained in the atmosphere, can efficiently and highly accurately adjust humidity and can be produced inexpensively. <P>SOLUTION: The silica gel for a moisture adjusting agent, adjusting the humidity of an ambient atmosphere to a prescribed value by adsorbing moisture contained in the atmosphere, is characterized in that (a) the pore volume is 0.6-2.0 ml/g, (b) the specific surface area is 300-1,000 m<SP>2</SP>/g, (c) the modal diameter (D<SB>max</SB>) of pores is <20 nm, (d) the total volume of pores each having a diameter within the range of D<SB>max</SB>±20% is ≥50% of the total volume of the whole pores, (e) it is amorphous, (f) the total content of metal impurities except alkali metals and alkaline earth metals is ≤500 ppm, and (g) the chemical shift δ(ppm) of Q<SP>4</SP>-peak in the solid Si-NMR satisfies following expression (I): -0.0705×(D<SB>max</SB>)-110.36>δ. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

The present invention relates to a silica gel for a humidity control agent that adsorbs moisture contained in an ambient atmosphere and adjusts the atmosphere to a predetermined humidity.

  In recent years, particularly comfortable spaces have been required for residential spaces such as houses and vehicle interiors. In addition, there is a need for a storage technique for maintaining the freshness of foodstuffs and a technique for storing books and paintings for a long period of time. In achieving such a requirement, it is important to appropriately adjust the humidity in addition to the temperature.

Conventionally, the humidity has been adjusted to a comfortable humidity by using a dehumidifier by an air conditioner, a humidifier by a humidifier, or a dehumidifier and a humidifier and electrically controlling them.
On the other hand, in the above technique, the apparatus is complicated and expensive, and since electric power is consumed, the running cost is increased. Therefore, humidity control using a porous material is also performed.

Such porous material includes silica gel. Conventionally, silica gel mainly has A-type silica gel having micropores with an average pore diameter of about 2 nm and a broad pore distribution, and B-type having a distinct pore distribution peak in a meso-macropore region of 2 nm or more. There are two types of silica gel.
In general, the smaller the silica gel pore diameter, the easier the gas such as nitrogen and water vapor is adsorbed by the silica gel. Therefore, when you want to completely dehumidify the system to extremely low humidity (for example, store food and water-free chemicals) A type silica gel is used as a humidity control agent. On the other hand, if you want to adjust the humidity by leaving a certain amount of humidity, as described above, for example, to make your living space more comfortable (for example, when storing recording materials such as photographs and videos, when storing historical materials, documents, and artwork) , When storing cloth / leather products, adding humidity control function to residential building materials and wallpaper, packing silica gel and installing under the floor of the house to adjust the humidity inside the house) Used as a humidity control agent.

  By the way, as in the case of the above-described humidity adjustment using B-type silica gel, when it is desired to control humidity while leaving a certain level of humidity, that is, when it is desired to maintain the inside of the system at a predetermined humidity, the sharper the pore distribution of silica gel (the pore diameter The higher the response, the higher the moisture absorption and release response to subtle changes in environmental humidity, and the higher the ability to adjust the humidity to a certain level.

  However, B-type silica gel, which is widely manufactured in general, has a pore distribution that is not sufficiently sharp, and an advanced humidity control function that adjusts the humidity to a constant humidity cannot be expected. For example, in order to adjust the humidity to a comfortable humidity (relative humidity of 40 to 60%) in a living environment or the like, B-type silica gel having a sufficiently sharp pore distribution centering on a pore diameter of 3 to 5 nm is desired. However, it was difficult to produce silica gel with such a fine pore diameter controlled with high precision with conventional silica gel derived from water glass.

  However, since 1992, when the micelle template silica capable of controlling the pore diameter with high accuracy in the range of 1 to 10 nm has appeared as a silica gel having a desired sharp pore size distribution, the humidity control as described above of the silica gel has occurred. Applications are attracting attention again, and various techniques for controlling humidity using the above micelle template silica (for example, techniques disclosed in Japanese Patent Laid-Open Nos. 6-304437 and 2000-43179) have been proposed.

  Furthermore, research on adsorption heat pumps that apply such humidity control performance of silica gel is being actively conducted. In this technique, a silica gel having a pore diameter of 2 to 4 nm and a very sharp pore distribution is required. The adsorption heat pump uses water as a refrigerant and a porous material such as silica gel as an adsorbent, and is expected to be used as a next-generation air conditioner.

In this adsorption heat pump, when water is adsorbed on silica gel in a vacuum-sealed system, the internal pressure of the system decreases and the water in the system evaporates, cooling is performed by this latent heat, and when the water is desorbed from the silica gel, the internal pressure increases and the system pressure increases. Excess water condenses inside and can be heated by the heat of condensation at this time.
However, although the micelle template silica has a sharp pore distribution of the resulting silica gel, it is manufactured using an organic template, and this organic template is expensive, so it is expensive to manufacture and unnecessary because the manufacturing process is complicated. There is a problem that various impurity metals are easily mixed. In addition, since the pore walls are very thin, the structural strength is weak, physical properties are likely to change, and poor productivity is also a problem.

  By the way, it is well known that alkali metal and alkaline earth metal salts have a very high affinity for water vapor. For example, sodium chloride and potassium chloride are deliquescent salts, calcium chloride is used as a desiccant for preserving food and clothing, and sodium sulfate is used as a solvent desiccant for organic synthesis. In addition, lithium salts such as lithium bromide, lithium chloride, and lithium iodide have the highest moisture absorption performance among alkali metal and alkaline earth metal salts, and the aqueous solution exhibits absorption / release characteristics against water vapor. It is used as an absorption liquid for refrigerators and an adsorbent for humidity adjustment.

  Since these lithium salts are usually dissolved in water and used in a liquid state, they are difficult to handle. For this reason, moisture absorbing materials supported in the pores of various porous materials such as silica gel have been developed. This moisture absorbing material has a water vapor absorption and release characteristic like the above aqueous solution, and is used as a humidity control material for dry dehumidifiers and desiccant air conditioners.

  In this case, the lithium salt is in a solid state in the supported pores under low humidity conditions, but exists as an aqueous solution under high humidity conditions. For the correlation diagram of absorption isotherm and temperature / concentration / water vapor partial pressure of lithium salt, see the Refrigeration Mechanical Engineering Handbook. 1001-1003 (Asakura Shoten), Refrigeration and Air Conditioning Handbook-Basics 376 (Japan Refrigeration Association), Refrigeration and Air Conditioning Handbook-Application 360-361 (Japan Refrigeration Association) and the like, and theoretical absorption capacity under each humidity condition can be known from these materials.

  However, conventional silica gel cannot keep lithium salt highly dispersed (uniformly) in the pores. For this reason, the lithium salt exists in a solid state in the pores under low humidity conditions, but its surface area is insufficient and the original moisture absorption capacity of the lithium salt cannot be exhibited. On the other hand, under high humidity conditions, the lithium salt exists in the form of an aqueous solution in the pores, but the aqueous solution of the lithium salt originally has a relatively high viscosity and is held unevenly in the pores. The thickness of the membrane is biased, and in particular, the high-viscosity part and the thick part of the liquid film are insufficient in the pore diffusion rate of the moisture absorbed, and often fail to exhibit the original moisture absorption capacity of lithium chloride. It was. Therefore, a porous material that can carry lithium salt in a highly dispersed state has been desired.

  As a technique related to this, Japanese Patent Laid-Open No. 11-114410 discloses a technique in which, for example, NaCl is supported on silica gel as an antihypertensive agent. In this technique, the use of a hypotensive agent makes it possible to control the vapor pressure at which moisture is absorbed and released by silica gel. However, since this technique uses the micelle template silica described above, in addition to the above-mentioned problems, production costs are high, the content of impurity metals is large, structural strength is weak, and physical property changes are likely to occur. There are issues such as poor nature.

  The present invention has been made in view of the above-described problems. That is, an object of the present invention is to provide a silica gel for a humidity control agent that can realize highly efficient and highly accurate humidity control and can be manufactured at low cost.

  Therefore, as a result of intensive studies to solve the above problems, the present inventors have a high specific surface area, a high pore volume, a high purity and a homogeneous and stable structure with little structural distortion, The present inventors have succeeded in producing a silica gel for a humidity control agent having a sharp pore distribution, and found that this effectively meets the above-mentioned demand, thereby completing the present invention.

That is, the gist of the present invention is that the silica gel for a humidity control agent has (a) a pore volume of 0.6 to 2.0 ml / g, (b) a specific surface area of 300 to 1000 m ² / g, c) The mode diameter (D _max ) of the pores is less than 20 nm, and (d) the total volume of the pores having a diameter in the range of D _max ± 20% is 50% or more of the total volume of all the pores. Yes, (e) Amorphous, (f) Total content of metal impurities excluding alkali metals and alkaline earth metals is 500 ppm or less, (g) Chemical shift of Q ⁴ peak in solid-state Si-NMR Is that δ satisfies the following formula (I).

−0.0705 × (D _max ) −11.36> δ Formula (I)
Another gist of the present invention is that the silica gel for the humidity control agent has (a) a pore volume of 0.3 to 1.6 ml / g, and (b) a specific surface area of 200 to 900 m ² / g. ,
(C) The mode diameter (D _max ) of the pores is less than 20 nm, and (d) the total volume of the pores whose diameter is in the range of D _max ± 20% is 30% of the total volume of all the pores (E) Amorphous, (f) The total content of impurity metals excluding alkali metals and alkaline earth metals is 500 ppm or less, and (g) humidity control with high affinity to the moisture When containing an auxiliary agent, the content of the humidity adjusting auxiliary agent is in the range of 1 to 80% by weight, and (h) the chemical shift of the Q ⁴ peak in solid Si-NMR is δ (ppm), δ is to satisfy the above formula (I).

According to the silica gel for a humidity control agent of the present invention, the pore diameter of the silica gel can be accurately controlled with a sharp pore distribution centering on the most frequent pore diameter. It is possible to adjust the humidity quickly and accurately.
Furthermore, in the silica gel for a humidity control agent of the present invention, the pore diameter can be accurately controlled to an arbitrary diameter, so that the surrounding relative humidity can be accurately adjusted to an arbitrary humidity in correspondence with such pore diameter control. There are advantages.

In addition, the silica gel for a humidity control agent of the present invention has a very low content of impurities, and further has a homogeneous and stable structure with little distortion of the siloxane bond angle. There is an advantage that there is little change in physical properties.
Furthermore, since the silica gel for a humidity control agent of the present invention has a relatively high pore volume and a high specific surface area as compared with a conventional silica gel having a comparable pore diameter, the conventional silica gel having a comparable pore diameter, Since the water vapor adsorption capacity is excellent and the adsorption capacity is large, there is an advantage that the humidity can be adjusted efficiently.

And since a pore can be controlled with high precision, without using an organic template, there exists an advantage that it can manufacture at low cost.
Moreover, humidity control can be quickly performed with a small amount of use by including a humidity control auxiliary. Further, the silica gel for a humidity control agent of the present invention has a very sharp pore size distribution, a high purity, and a homogeneous structure with little distortion of the bond angle of the siloxane bond. Can be uniformly supported in the pores, and there is an advantage that the humidity control with the humidity control auxiliary can be performed more efficiently than in the past.

Hereinafter, embodiments of the present invention will be described.
The silica gel for the humidity control agent of the present invention (hereinafter also simply referred to as silica gel) is a porous body having a large number of pores as in the case of conventional silica gel, and moisture (water vapor) in the ambient atmosphere is placed in the pores. By adsorbing, the ambient atmosphere is adjusted to a predetermined humidity.

First, the humidity-controlling silica gel according to the first embodiment of the present invention will be described in detail. In the humidity-controlling silica gel of the present invention, the pore volume and specific surface area are in a range larger than usual. Features. Specifically, the value of the pore volume is usually in the range of 0.6 to 2.0 ml / g, preferably in the range of 0.8 to 1.6 ml / g, and the value of the specific surface area is usually 300 to range of 1000 m ² / g, preferably in the range of 300~900m ² / g, further preferably in the range of 400~900m ² / g. These pore volume and specific surface area values are measured by the BET method by nitrogen gas adsorption / desorption.

Further, the silica gel for a humidity control agent of the present embodiment is characterized in that the mode diameter (D _max ) of the pores is less than 20 nm. The mode diameter (D _max ) is a characteristic relating to adsorption and absorption of gas and liquid, and the adsorption and absorption performance is higher as the mode diameter (D _max ) is smaller. The preferred mode diameter ( _Dmax ) of the present silica gel is 17 nm or less, more preferably 15 nm or less. The lower limit is not particularly limited, but is preferably 2 nm or more. The silica gel for a humidity control agent of the present embodiment is hydrothermally treated during production as will be described later. By adjusting the temperature condition of the hydrothermal treatment, the pore diameter can be arbitrarily adjusted in the range of 2 nm to 20 nm. Therefore, each relative humidity can be adjusted at an arbitrary humidity within a range of 35 to 90% (as will be described later, the humidity adjusted by silica gel depends on the pore diameter).

The mode diameter (D _max ) is calculated from the isothermal desorption curve measured by the BET method by nitrogen gas adsorption / desorption from E.E. P. Barrett, L.M. G. Joyner, P.M. H. Hacklenda, J.H. Amer. Chem. Soc. , Vol. 73, 373 (1951), the pore distribution curve calculated by the BJH method is plotted. Here, the pore distribution curve refers to the differential pore volume, that is, the differential nitrogen gas adsorption amount (ΔV / Δ (logd)) with respect to the pore diameter d (nm). Said V represents nitrogen gas adsorption volume.

Furthermore, in the silica gel for a humidity control agent of the present embodiment, the total volume of pores in the range of ± 20% centering on the value of the mode diameter (D _max ) is usually 50% of the total volume of all pores. % Or more, preferably 60% or more. This means that the diameters of the pores of the present silica gel for the humidity control agent are uniform in the pores near the mode diameter (D _max ). The total volume of the pores in the range of ± 20% of the mode diameter (D _max ) is not particularly limited, but is usually 90% or less of the total volume of all the pores.

In relation to this feature, the silica gel for a humidity control agent of the present embodiment has a differential pore volume ΔV / Δ (logd) at the mode diameter (D _max ) calculated by the BJH method, usually 2 to 20 ml. / G, particularly 5 to 12 ml / g (wherein d is the pore diameter (nm) and V is the nitrogen gas adsorption volume). When the differential pore volume ΔV / Δ (logd) is included in the above range, it can be said that the absolute amount of pores arranged in the vicinity of the most frequent diameter (D _max ) is extremely large.

  In addition, the silica gel is characterized in that it is amorphous, that is, no crystalline structure is observed in view of its three-dimensional structure. This means that when the silica gel for a humidity control agent is analyzed by X-ray diffraction, a crystalline peak is not substantially observed. In the present specification, crystalline silica gel refers to a material having a peak of at least one crystal structure at a position exceeding 6 angstroms (Å Units d-spacing) in the X-ray diffraction pattern. Examples of such silica gel include micelle template silica that forms pores using an organic template. Amorphous silica gel is extremely excellent in productivity as compared with crystalline silica gel.

  Further, the present silica gel is characterized in that the content of metal impurities is very low and the purity is extremely high. Specifically, metal elements (metal impurities) belonging to the group consisting of 3A group, 4A group and 5A group of the periodic table and transition metals, which are known to affect the physical properties by existing in silica gel. Is generally 500 ppm or less, preferably 100 ppm or less, more preferably 50 ppm or less, and most preferably 30 ppm or less. Such a small influence of impurities is one of the major factors that enable the silica gel for a humidity control agent of the present embodiment to exhibit excellent properties such as high heat resistance and water resistance.

Here, although the silica gel for a humidity control agent of the present embodiment may contain a trace amount of alkali metal and alkaline earth metal derived from the production process, the alkali metal and alkaline earth metal are very compatible with water vapor. High, leading to enhanced moisture absorption performance. Therefore, the metal impurities here do not include alkali metals or alkaline earth metals.
Furthermore, the present silica gel is characterized in that the bond angle of the siloxane bond forming the skeleton is less distorted. Here, the structural strain of silica gel can be expressed by the value of the chemical shift of the Q ⁴ peak in the solid-state Si-NMR measurement. Hereinafter, the relationship between the structural distortion of silica gel and the chemical shift value of the Q ⁴ peak will be described in detail.

This silica gel is a hydrate of amorphous silicic acid and is represented by the SiO ₂ · nH ₂ O formula, but structurally, O is bonded to each vertex of the Si tetrahedron, Further, Si is further bonded to O and has a structure spread in a net shape. In some repeating units of Si—O—Si—O—, some of O is substituted with other members (for example, —H, —CH _3, etc.). As shown in the following formula (A), there are Si (Q ⁴ ) having ⁴ —OSi, Si (Q ³ ) having 3 —OSi as shown in the following formula (B), etc. In the formulas (A) and (B), the tetrahedral structure is ignored and the Si—O net structure is represented in a plane. In the solid Si-NMR measurement, the peaks based on the respective Si are called Q ⁴ peak, Q ³ peak,.

In the present silica gel, when the chemical shift of the Q ⁴ peak is δ (ppm), δ is represented by the following formula (I):
−0.0705 × (D _max ) −11.36> δ Formula (I)
[That is, the value of δ is smaller than the value (−0.0705 × (D _max ) −11.36) represented by the left side of the above formula (I) (is present on the more negative side)]. Features. In the conventional silica gel, the chemical shift value δ of the Q ⁴ peak is generally larger (existing on the plus side) than the value calculated based on the left side of the formula (I). Therefore, the silica gel for a humidity control agent of the present invention has a smaller value of the chemical shift of the Q ⁴ peak as compared with the conventional silica gel. This is nothing but the fact that the chemical shift of the Q ⁴ peak exists in a higher magnetic field in the silica gel for a humidity control agent of the present invention, and consequently, the bond angle represented by two —OSi with respect to Si. Is more homogeneous and means less structural distortion.

In the silica gel for a humidity control agent of the present invention, the chemical shift δ of the Q ⁴ peak is more than the value calculated based on the left side (−0.0705 × (D _max ) −11.36) of the above formula (I). The value is preferably 0.05% or less, more preferably 0.1%, and particularly preferably 0.15% or less. Usually, the minimum value of the Q ⁴ peak of silica gel is −113 ppm.

The present silica gel has excellent heat resistance, water resistance, and the like, and hardly changes in physical properties. Therefore, the humidity control function is maintained for a long time even under high temperature and high humidity. The relationship between such points and the structural strain as described above is not necessarily clear, but is estimated as follows. In other words, silica gel is composed of aggregates of spherical particles of different sizes, but in a state where there is little structural distortion as described above, high microstructural homogeneity of the entire spherical particles is maintained. Therefore, as a result, it is considered that excellent heat resistance, water resistance and the like are expressed. Note that the peak of Q ³ or less is not easily affected by the structural distortion of silica gel because the expansion of the Si—O net structure is limited.

In relation to the above characteristics, the present silica gel preferably has a Q ⁴ / Q ³ value of 1.3 or more, particularly 1.5 or more, as measured by solid-state Si-NMR. Here, the value of Q ⁴ / Q ³ is the mole of Si (Q ⁴ ) in which four —OSi are bonded to Si (Q ³ ) in which three —OSi are bonded in the above-described repeating unit of silica gel. Means ratio. In general, it is known that the higher this value, the higher the thermal stability of the silica gel. From this, it can be seen that the present silica gel is extremely excellent in thermal stability. On the other hand, micelle template silica often has a Q ⁴ / Q ³ of less than 1.3 and has low thermal stability.

The value of chemical shift and Q ⁴ / Q ³ of Q ⁴ peak, performs solid Si-NMR measurement using the method described later in the description of embodiments, can be calculated based on the result. Further, analysis of measurement data (determination of peak position) is performed by a method of dividing and extracting each peak by, for example, waveform separation analysis using a Gaussian function.

  Unlike the conventional sol-gel method, the present silica gel includes a hydrolysis / condensation step for forming a silica hydrogel through a condensation step for condensing the silica hydrosol obtained together with a hydrolysis step for hydrolyzing silicon alkoxide. Then, following the hydrolysis / condensation step, it can be produced by a method including both a physical property adjusting step for obtaining a silica gel having a desired physical property range by hydrothermal treatment without aging the silica hydrogel.

  The silicon alkoxide used as a raw material for the silica gel for the humidity control agent of the present invention has 1 to 4 carbon atoms such as trimethoxysilane, tetramethoxysilane, triethoxysilane, tetraethoxysilane, tetrapropoxysilane, and tetrabutoxysilane. Examples thereof include tri- or tetraalkoxysilanes having a lower alkyl group or oligomers thereof, and tetramethoxysilane, tetraethoxysilane and oligomers thereof are preferred. Since the above silicon alkoxide can be easily purified by distillation, it is suitable as a raw material for high-purity silica gel.

  Hydrolysis of the silicon alkoxide is usually performed using 2 to 20 mol, preferably 3 to 10 mol, particularly preferably 4 to 8 mol, of water with respect to 1 mol of the silicon alkoxide. Hydrolysis of silicon alkoxide produces silica hydrogel and alcohol. This hydrolysis reaction is usually from room temperature to about 100 ° C., but it can also be performed at a higher temperature by maintaining the liquid phase under pressure. Moreover, you may add solvents, such as alcohol compatible with water, as needed at the time of a hydrolysis. Specifically, lower alcohols having 1 to 3 carbon atoms, dimethylformamide, dimethyl sulfoxide, acetone, tetrahydrofuran, methyl cellolbu, ethyl cellolb, methyl ethyl ketone, and other organic solvents that can be arbitrarily mixed with water can be arbitrarily used. Among them, those that do not exhibit strong acidity or basicity are preferable because a uniform silica hydrogel can be produced.

  When these solvents are not used, the stirring speed at the time of hydrolysis is particularly important for the production of the silica gel for the humidity control agent of the present embodiment. That is, since silicon alkoxide and water for hydrolysis are separated at the initial stage, they are emulsified by stirring to promote the reaction. The stirring speed at this time is usually 30 rpm or more, preferably 50 rpm or more. When such a condition is not satisfied, it becomes difficult to obtain the silica gel for the humidity control agent of the present embodiment. In addition, after alcohol produces | generates by hydrolysis and a liquid turns into a uniform liquid and heat_generation | fever stops, it is preferable to stop stirring in order to form a uniform hydrogel.

  Silica gel with a crystal structure tends to have poor thermal stability in water, and gels are easy to hydrolyze silicon alkoxide in the presence of a template such as a surfactant used to form pores in the gel. Includes a crystal structure. Therefore, in the present embodiment, it is preferable to perform the hydrolysis in the absence of a template such as a surfactant, that is, in a condition where there is no such an amount that it functions as a template.

  The reaction time depends on the reaction solution composition (type of silicon alkoxide and molar ratio with water) and the reaction temperature, and the time until gelation differs, so it is not unconditionally specified. In addition, hydrolysis can be accelerated | stimulated by adding an acid, an alkali, etc. to a reaction system as a catalyst. However, the use of such an additive is not preferable in the production of the present silica gel because it causes aging of the produced hydrogel, as will be described later.

  In the above silicon alkoxide hydrolysis reaction, the silicon alkoxide is hydrolyzed to produce a silicate. Subsequently, a condensation reaction of the silicate occurs, the viscosity of the reaction solution rises, and finally gelates to form a silica hydrogel. Become. In order to produce the silica gel for a humidity control agent of the present invention, it is important to immediately perform a hydrothermal treatment without substantially aging so that the hardness of the hydrogel of silica generated by the above hydrolysis does not increase. It is. Hydrolysis of silicon alkoxide produces a soft silica hydrogel. This hydrogel is stably aged or dried, and then hydrothermally treated, finally resulting in silica gel with controlled pore properties. In this method, silica gel having the physical property range defined in the present invention cannot be produced.

  The hydrothermal treatment of the silica hydrogel formed by hydrolysis, as described above, is performed immediately without substantially aging. This means that the soft state immediately after the formation of the silica hydrogel is maintained and the following conditions are maintained. It means to be subjected to hydrothermal treatment. It is not preferable to add acid, alkali, salt, or the like to the silicon alkoxide hydrolysis reaction system, or to make the temperature of the hydrolysis reaction too strict, since the aging of the hydrogel proceeds. In addition, the temperature and time should not be increased more than necessary in washing, drying, and leaving in post-treatment after hydrolysis.

  The aging state of the hydrogel can be specifically confirmed by referring to the hardness of the hydrogel. The fracture stress, which is a parameter correlated with the hardness of the hydrogel, is usually 6 MPa or less, preferably 3 MPa or less, more preferably 2 MPa or less. By subjecting the hydrogel in a soft state to hydrothermal treatment, silica gel having a physical property range defined in the present invention can be obtained.

  As conditions for this hydrothermal treatment, the state of water may be either liquid or gas, and it may be diluted with a solvent or other gas, but preferably liquid water is used. 0.1 to 10 times by weight, preferably 0.5 to 5 times by weight, particularly preferably 1 to 3 times by weight water is added to the silica hydrogel to form a slurry, usually 40 to 250 ° C., preferably Is carried out at a temperature of 50 to 200 ° C. for usually 0.1 to 100 hours, preferably 1 to 10 hours. The water used for hydrothermal treatment may contain lower alcohols, methanol, ethanol, propanol, dimethylformamide (DMF), dimethyl sulfoxide (DMSO), and other organic solvents.

Although it is possible to perform hydrothermal treatment by changing the temperature condition using a hydrolysis reaction reactor, the optimum conditions are usually different between the hydrolysis reaction and the subsequent hydrothermal treatment. In general, it is difficult to obtain silica gel for the present humidity control agent.
When the temperature is increased under the hydrothermal treatment conditions described above, the pore diameter and pore volume of the resulting silica gel tend to increase. The hydrothermal treatment temperature is preferably in the range of 100 to 200 ° C. Further, with the treatment time, the specific surface area of the silica gel obtained tends to decrease gradually after reaching the maximum once. Based on the above tendency, it is necessary to appropriately select the conditions according to the desired physical property values, but since hydrothermal treatment is intended to change the physical properties of silica gel, it is usually at a higher temperature than the hydrolysis reaction conditions described above. It is preferable to do.

If the hydrothermal treatment temperature and time are set out of the above ranges, it will be difficult to obtain the present silica gel for a humectant. For example, if the hydrothermal treatment temperature is too high, the pore diameter and pore volume of the silica gel become too large, and the pore distribution is also widened. On the other hand, if the hydrothermal treatment temperature is too low, the resulting silica gel has a low degree of crosslinking, poor thermal stability, no peaks in the pore distribution, or Q ⁴ / Q ³ value may become extremely small.

  When the hydrothermal treatment is performed in ammonia water, the same effect can be obtained at a lower temperature than in pure water. In addition, when hydrothermal treatment is performed in ammonia water, the silica gel finally obtained is generally hydrophobic as compared with the case of treatment in pure water, but is usually 30 to 250 ° C, preferably 40 to 200 ° C. When hydrothermal treatment is performed at a high temperature, the hydrophobicity becomes particularly high. The ammonia concentration here is preferably 0.001 to 10%, particularly preferably 0.005 to 5%.

  The hydrothermally treated silica hydrogel is usually dried at 40 to 200 ° C, preferably 60 to 120 ° C. The drying method is not particularly limited, and it may be a batch type or a continuous type, and can be dried under normal pressure or reduced pressure. If necessary, when a carbon component derived from the raw material silicon alkoxide is contained, it can be usually removed by baking at 400 to 600 ° C. Moreover, in order to control a surface state, you may bake at the temperature of a maximum of 900 degreeC. Further, a surface treatment for adjusting hydrophilicity / hydrophobicity may be performed with a silane coupling agent, an inorganic salt, various organic compounds, or the like.

Then, the raw silica gel is pulverized and classified as necessary to finally obtain the intended silica gel for a humidity control agent.
Although the manufacturing method of the silica gel for a humidity control agent of the present invention has been described above, the manufacturing method should be substantially limited except that the silica hydrogel is not aged before hydrothermal treatment for pore control. is not.

  The shape of the silica gel is not limited, and may be spherical, may be other lumps whose shape is not specified, or may be crushed into a fine shape (crushed) as described later. Furthermore, the crushed material may be collected and granulated. In terms of cost, a crushed shape in which the particle size is easily controlled or a granulated product thereof is preferable. Further, silica gel may be formed into a honeycomb shape (this will be described later).

Moreover, the particle diameter of the present silica gel for a humidity control agent is appropriately set depending on the use conditions, and is adjusted to particles of 150 μm or less, for example.
Silica gel classification is performed using, for example, a sieve, a gravity classifier, a centrifugal classifier or the like. The pulverization is performed as follows.
As a method of pulverizing the raw material silica gel, any known apparatus or instrument may be used. For example, ball mills (rolling mills, vibrating ball mills, planetary mills, etc.), agitation mills (tower pulverizers, agitation tank type mills, flow tube type mills, annular (annular) mills, etc.), high-speed rotary pulverizers (screen mills) , Turbo type mill, centrifugal classification type mill), jet crusher (circulation jet mill, collision type mill, fluidized bed jet mill), shear mill (disintegrator, ong mill), colloid mill, mortar, etc. be able to. Among these, when the silica gel has a relatively small diameter (for example, 2 μm or less), a ball mill and a stirring mill are more preferable. Moreover, as a state at the time of pulverization, there are a wet method and a dry method, both of which can be selected, but when the silica gel has a relatively small diameter, the wet method is more preferable. In the case of the wet method, the dispersion medium to be used may be any of organic solvents such as water and alcohol, or may be a mixed solvent of two or more types, and is used properly according to the purpose. It is not preferable to apply an unnecessarily strong pressure or shearing force for a long time during pulverization because the pore characteristics of the raw silica gel may be impaired.

  In addition, as mentioned above, the pulverized silica gel particles (primary particles) may be granulated by a known method to form a granular shape (for example, a spherical shape) or an aggregated shape. In general, when silica gel has a primary particle size of 2 μm or less, agglomerated particles can be obtained by simply drying the slurry as a water slurry without adding a binder, but in the case of particles exceeding 2 μm, Is often necessary. Any substance can be used as the binder. For example, when dissolved in water, sugar, dextrose, corn syrup, gelatin, carboxymethylcellulose (CMC), polyvinyl alcohol (PVA), and other water-soluble polymers , Water glass, silicon alkoxide hydrolyzed liquid (which can also be used in a solvent system), etc. can be used. When dissolved in a solvent, various waxes, lacquers, syrac, oil-soluble polymers, etc. are used. Can do. In order to form aggregates without impairing the porous performance of the raw silica gel, it is desirable not to use a binder. When it is unavoidable, use a minimum amount, and a metal that induces changes in the physical properties of the raw silica gel It is preferable to use a high-purity material with a small amount of impurities.

  Any known method may be used for granulating the silica gel fine particles, but representative methods include rolling method, fluidized bed method, stirring method, crushing method, compression method, extrusion method, injection method, etc. Can be mentioned. Among these, in order to obtain silica gel fine particle aggregates with controlled pore characteristics according to the present invention, pay attention to the selection of the type, amount and purity of the binder, and apply unnecessary pressure when granulating the silica gel fine particles. It is important that there is no such thing.

  Now, as described above, the present silica gel can be formed into a honeycomb shape so as to be incorporated into an air conditioner or the like, and this can be performed by mixing silica gel with a binder and forming this. Moreover, a molded object can also be created using only silica gel. Moreover, a molded object can also be obtained using the thing which mixed silica gel with the binder and water, and was made into the slurry. The slurry containing the silica gel is, for example, silica gel, 2 to 20 parts by weight of an organic binder, 10 to 50 parts by weight of an inorganic binder, and 150 to 200 parts by weight of water with respect to 100 parts by weight of the silica gel. Consists of. As the organic binder, methyl cellulose or the like is used. Silica sol or the like is used as the inorganic binder.

  The silica gel can be applied to a honeycomb body made of ceramic or the like. In this case, for example, a necessary binder is mixed with silica gel, and this is coated on the honeycomb body. As the honeycomb body, for example, cordierite can be used. Silica gel can be used by filling it into a column after it is made into a particle form such as a spherical body or a columnar body. In this case, the particle size is 0.1 to 30 mm in diameter for a spherical body and 0.1 to 30 mm in diameter for a columnar body in consideration of ensuring air permeability of a packed portion of the column and ensuring a contact area with water vapor. The length is preferably about 1 to 30 mm at 10 mm.

  A power machine (pump, fan, etc.) that circulates the air if necessary, with an inlet for introducing air in the space to be conditioned and an outlet for blowing out the conditioned air to the column or honeycomb provided with the silica gel May be attached. The column or honeycomb body allows more air to come into contact with the humidity adjusting agent by actively passing air in a space to be conditioned. Therefore, the humidity of the space can be kept constant in a short time.

  Silica gel can also be used with cellulose fibers. That is, silica gel, cellulose fiber, and an organic binder can be mixed and molded to form a humidity control agent. In this case, the above-mentioned cellulose fiber is mixed with the silica gel and the organic binder to prepare a slurry. Next, the slurry is dehydrated and formed into a semi-humid filter. Thereafter, the semi-humid filter body is dried and solidified to obtain a solidified product. Thereby, humidity control paper is obtained.

  Hereinafter, the humidity control paper will be described in detail. The humidity control paper is preferably composed of 100 parts (parts by weight) of cellulose fibers, 100 to 3000 parts of silica gel, and 1 to 20 parts of an organic binder in solid content with respect to 100 parts of the silica gel. . Thereby, it is possible to obtain a humidity control paper having good moldability and excellent humidity control ability.

  The humidity control paper manufacturing method includes, for example, a first mixing step in which cellulose fibers, silica gel, and water are mixed to form a slurry, and the slurry and an organic binder are mixed to form a mixed slurry. 2 mixing steps, a forming step of dehydrating and forming the mixed slurry to form a semi-humid filter body, and a drying step of drying and solidifying the semi-humid filter body to form an integral solid.

  The cellulose fiber is a fiber fiber mainly composed of cellulose, which is a main component of a plant cell membrane. These include natural cellulose fibers such as cotton, Bombax surfaces (Kiwata), Kabok and other seed hair fibers, hemp, flax, burlap, ramie, mulberry, mitsumata and other gin skin fibers, Manila hemp and New Zealand hemp, etc. Leaf fibers, coniferous trees (pine, fir, spruce, eel, cedar), hardwood (beech, hippopotamus, bopra, maple, etc.) wood fibers.

The artificial cellulose fibers include viscose artificial silk, copper ammonia rayon, fortisan, regenerated cellulose fibers such as nitrate human silk, and semisynthetic fibers such as acetate human silk. Furthermore, this cellulose fiber may be obtained from recycled resources such as old newspapers, Chile papers, old magazines and the like.
This cellulose fiber preferably has a fiber length in the range of 0.1 mm to several tens of mm. When the fiber length is less than 0.1 mm, the fiber entanglement is insufficient and the moldability is poor. On the other hand, if it exceeds several tens of millimeters, the fiber and silica gel are difficult to disperse uniformly, and the specific surface area becomes small, which may reduce the humidity control performance.

Next, it is preferable to add 100 to 3000 parts of silica gel with respect to 100 parts of cellulose fiber. This is because if the amount is less than 100 parts, sufficient ability to absorb moisture in the air may not be obtained. If it exceeds 3000 parts, it may be difficult to maintain a certain shape as a humidity control agent.
The organic binder is preferably 1 to 20 parts with respect to 100 parts of silica gel. In the case of less than 1 part, there is a possibility that a material having sufficient water resistance cannot be obtained. On the other hand, when it exceeds 20 parts, it is difficult to expect sufficient humidity control.

  Moreover, in the said humidity control paper, another additive can be added to such an extent that the outstanding performance is not impaired. Specifically, there are polyvinyl alcohol (PVA), CMC (carboxymethylcellulose), alumina sol, silica sol and the like as a dispersant for improving dispersibility. Examples of the fibrous material include inorganic fibers such as glass fibers and ceramic fibers, or synthetic fibers such as nylon fibers and rayon fibers. Further, there are pigments and dyes as additive aids. Further, there are water glass, cement, plaster and the like as binders for improving the strength.

  Next, the manufacturing method of the humidity control paper will be exemplified. First, the cellulose fiber, silica gel, and water are mixed to form a slurry (first mixing step). The order of mixing these raw materials is not particularly limited. First, an aqueous slurry of cellulose fibers is prepared by beating cellulose fibers with a beater or the like. Next, the cellulose fiber slurry is added to and mixed with silica gel that has been dry pulverized or wet pulverized into an appropriate size and shape. The above mixing is performed using a propeller mixer, a Henschel mixer, a ball mill, a vibration mill, a disper mill, or the like.

  Next, the obtained slurry and the organic binder are mixed to form a mixed slurry (second mixing step). The mixing ratio of the cellulose fiber, silica gel and organic binder is the same as described above. In the first or second mixing step, an aggregating agent such as bangsulphate, acrylamide polymer, and acrylamide-modified polymer may be added and mixed as appropriate for the purpose of improving drainage. Moreover, you may add additives, such as dye and a pigment, suitably.

Next, the obtained mixed slurry is dehydrated and molded into a desired shape using a papermaking method, a filter press method, a slip cast method, or the like to obtain a semi-humid filter body (molding step). Moreover, it is preferable that the moisture content of the semi-humid filter body obtained by this dehydration and shaping | molding is 50-80 wt%.
This is because when the amount of water exceeds 80 wt%, molding in the molding process is difficult, and the shrinkage rate becomes large, and there is a possibility that cracks, cracks, etc. occur in the drying process, resulting in a decrease in strength. is there. Further, if it is less than 50 wt%, the bonding force is weak, which is not preferable. In addition, when this moisture content is 55 to 70 wt%, it is more preferable.

Next, the semi-humid filter body is heated and solidified to obtain an integrally solidified product (drying step). In this drying step, the semi-humid filter is dried by a room temperature drying method, a vacuum drying method, a pressure drying method, a pressure / heat drying method, a vacuum heat drying method, a vacuum freeze drying method, or the like. In this case, the drying may be performed simultaneously with the molding in the molding process.
In the above production method, a filler may be appropriately added as an additive for the purpose of improving the strength and improving the appearance. Examples of the additive include kaolin and silica sand. Moreover, you may add suitably various additives, such as a fungicide, a fragrance | flavor, a pigment, and dye.

The above humidity control paper has an excellent humidity control function. Therefore, for example, it is used by blending into building materials, wall materials, wallpaper, packaging paper for packaging food, corrugated paper used for transporting food, interior materials for automobiles, wall materials for storage of books and paintings, etc. be able to.
The silica gel for a humidity control agent as one embodiment of the present invention is formed as described above and has an excellent humidity control function for the following reasons.

  Silica gel absorbs excess water vapor at high humidity, but releases moisture that has been absorbed at low humidity. If the average pore diameter is set to 3-5 nm, the system is comfortable to accommodate the average pore diameter. The humidity can be adjusted to a high humidity (40% to 60%). This humidity conditioning function is evaluated by the adsorption isotherm of water vapor on silica gel, but the sharper the pore size distribution, the more rapidly the amount of water vapor adsorbed in the vicinity of the relative humidity corresponding to the most frequent pore size. (Hygroscopic capacity) tends to increase. However, in the conventional silica gel, since the pore size distribution is broad, the change in the amount of adsorbed water vapor with respect to the change in humidity becomes slow, and the humidity adjustment becomes slow.

Relative vapor pressure (P / P ₀ ) where the adsorbate (here, water vapor) starts capillary condensation and begins to be rapidly adsorbed on the silica gel [here, since the adsorbate is water vapor, (P / P ₀ × 100) is relative humidity ( %) And the pore radius r (nm) can be expressed by the following Kelvin equation (1).
ln (P / P ₀ ) = − (2V _m γcos θ) / (rRT) (1)
In the above equation (1), V _m is the molar volume of the adsorbate, γ is the surface tension of the adsorbate, θ is the contact angle of the adsorbate, R is the gas constant, and T is the absolute temperature (K) of the adsorbate.

Here, when the adsorbate is water vapor and the temperature T is 298 K (= 25 ° C.), the molar volume V _m = 18.05 × 10 ⁻⁶ m ³ / mol, the surface tension γ = 72.59 × 10 ⁻³ N / m, and further assuming that the gas constant R = 8.3143 J / deg · mol and the contact angle θ = 0, the above equation (1) becomes the following equation (2).
ln (P / P ₀ ) = − 1.058 / r (2)
From the above formula (2), in the silica gel having a pore radius r (nm), when the relative vapor pressure (P / P ₀ ) becomes exp (−1.058 / r), the water vapor is condensed into capillaries and the pores of the silica gel It can be seen that it is adsorbed rapidly.

Thus, the relative vapor pressure (P / P ₀ ) and the relative humidity at which water vapor is adsorbed by the silica gel pores are determined mainly by the pore diameter 2r (nm). Therefore, as described above, in silica gel having a sharp pore size distribution, when the surrounding humidity exceeds a predetermined humidity corresponding to the most frequent pore diameter, moisture absorption is suddenly performed. If it falls below, dehumidification will be carried out rapidly. As a result, the silica gel having a sharp pore size distribution exhibits an excellent humidity control action that allows the ambient humidity to be controlled quickly and accurately to the predetermined humidity.

In this silica gel, the total volume of pores whose diameter is within the range of D _max ± 20% is 50% or more of the total volume of all pores, and the pore distribution is sharper than that of conventional silica gel. Therefore, it is possible to control the pore diameter more precisely than before. And in this silica gel, since the pore diameter can be controlled to an arbitrary diameter in the range of 2 to 20 nm, the relative humidity of the surroundings can be arbitrarily set in a wide range of 35 to 90% corresponding to such a pore diameter control. There is an advantage that humidity can be adjusted with high accuracy.

In addition, producing silica gel having a pore size of 3 to 5 nm and a sharp pore size distribution that can be adjusted to a relative humidity of 40% to 60%, which is a comfortable humidity in a living environment, with high reproducibility, Although it was difficult for the conventional silica gel, the present silica gel can precisely control the pores even in the pore diameter region.
In general, silica gel tends to deteriorate when heated in the presence of moisture, whereas the silica gel for a humidity control agent has a very low impurity content, and further satisfies the above formula (I) and has a siloxane bond angle. Since it is a homogeneous and stable structure with little distortion, it has characteristics such that there is little change in physical properties such as pore characteristics even in harsh environments (for example, high temperature and high humidity). Therefore, even if it is used for a long time or repeatedly accompanied by a regeneration process by heating, there is an advantage that the pore characteristics and thus the humidity control characteristics are hardly deteriorated.

And this silica gel for moisture conditioners is manufactured without using an organic template, and there is an advantage that silica gel having the above-mentioned advantages can be manufactured at low cost by highly accurate pore control.
Furthermore, the silica gel of the present invention is characterized by a relatively high pore volume and a high specific surface area as compared with conventional silica gel having the same pore diameter, and therefore has the same pore diameter. Compared to conventional silica gel, it has better water vapor adsorption capacity and larger adsorption capacity. Therefore, if the moisture absorption capacity of the silica gel is saturated due to high humidity, the silica gel will condense, making it impossible to adjust the humidity with the silica gel. There is an advantage that it can do moisture.

Furthermore, since the silica gel for a humidity control agent is amorphous, it has an advantage of extremely excellent productivity.
Next, a silica gel for a humidity control agent (hereinafter also simply referred to as silica gel) as a second embodiment of the present invention will be described in detail. The silica gel of the present embodiment contains a humidity conditioning aid having a high affinity for moisture with respect to the silica gel for the humidity conditioning agent of the first embodiment described above. In addition, it has a moisture adsorption effect by the humidity control aid.

Hereinafter, the silica gel of the present embodiment will be described in detail. The silica gel for a humidity control agent of the present invention is characterized in that the pore volume and the specific surface area are in a range larger than a normal one. The value of the pore volume is usually in the range of 0.3 to 1.6 ml / g, preferably in the range of 0.4 to 1.5 ml / g, more preferably in the range of 0.5 to 1.3 ml / g. Is preferred. The value of specific surface area in the range of usually 200~900m ² / g, preferably in the range of 200~800m ² / g, further preferably in the range of 200-700 ² / g. These pore volume and specific surface area values are measured by the BET method by nitrogen gas adsorption / desorption, as in the first embodiment.

Each setting of the pore volume and the specific surface area is slightly different from the first embodiment because of the following reasons.
That is, since the humidity conditioning aid is contained in the pores, the lower limit values such as the pore volume and the specific surface area are set to a lower value as compared with the silica gel of the first embodiment.

Further, in the silica gel for a humidity control agent of the present embodiment, the total volume of pores in the range of ± 20% centering on the value of the mode diameter (D _max ) is usually 30% of the total volume of all pores. characterized in that at least% is, this is, the diameter of the pores having the humidity agent for silica gel of the present embodiment, similarly to the silica gel first embodiment, information on nearby modal diameter (D _max) It means that the holes are aligned. The total volume of the pores in the range of ± 20% of the mode diameter (D _max ) is not particularly limited, but is usually 90% or less of the total volume of all the pores.

The setting of the total volume of the pores in the range of ± 20% centering on the value of the mode diameter (D _max ) is slightly different from the first embodiment because of the following reason.
That is, some of the humidity control aids contained in the pores may form a secondary pore structure in the pores. As a result, the mode diameter (D _This is because the total volume of pores in the range of ± 20% around the value of _max ) may be slightly lower than that of the silica gel of the first embodiment. Also, the silica gel of the first embodiment since similar to, the detailed description thereof is omitted, humidity agent for silica gel in the present embodiment, the modal diameter (D _max) calculated by the BJH method, differential pore volume in the modal diameter (D _max) ΔV / Δ (logd), three-dimensional structure, total content of metal elements (metal impurities), chemical shift δ (ppm) of Q ⁴ peak, and Q ⁴ / Q ³ values measured by solid-state Si-NMR It has the following features.

In other words, the mode diameter (D _max ) of the pores is less than 20 nm. The preferred mode diameter ( _Dmax ) of the present silica gel is 17 nm or less, more preferably 15 nm or less. The lower limit is not particularly limited, but is preferably 2 nm or more.
Further, the silica gel for a humidity control agent of the present embodiment has a differential pore volume ΔV / Δ (logd) at the mode diameter (D _max ) calculated by the BJH method, usually 2 to 20 ml / g, particularly 3 to 12 ml. / G is preferable. Further, the silica gel for the humidity control agent of the present embodiment is characterized in that it is amorphous, that is, no crystalline structure is observed in view of its three-dimensional structure.

  Further, the total content of metal elements (metal impurities) is usually 500 ppm or less, preferably 100 ppm or less, more preferably 50 ppm or less, and most preferably 30 ppm or less. Note that, as in the first embodiment, the metal impurities do not include metals that can function as humidity control aids, such as alkali metals and alkaline earth metals, as will be described later.

Furthermore, in the silica gel for a humidity control agent of the present embodiment, when the chemical shift of the Q ⁴ peak is δ (ppm), δ is [−0.0705 × (D _max ) −11.36> δ]. Δ is preferably 0.05% or more smaller than the value calculated based on this formula, more preferably 0.1%, particularly preferably 0.15% or less. Value.

Further, in the humidity control agent for silica gel of the present embodiment, the value of Q ⁴ / Q ³ by the solid Si-NMR measurement is usually 1.3 or more, preferably among them 1.5 or more.
Here, the humidity control aid, which is a major feature of the silica gel of the present embodiment, will be described. As described above, the humidity control auxiliary agent is for inclusion in silica gel in order to give a highly functional humidity control effect, as long as it has a high affinity for moisture, such as organic compounds, inorganic compounds, metal salts, etc. Various substances belonging to the group can be selected, and among the substances belonging to such a group, the content of at least one kind is in the range of 1 to 80% by weight, preferably in the range of 3 to 60% by weight, More preferably, it is in the range of 5 to 50% by weight. Moreover, these substances may be used independently and may be used in combination of 2 or more types.

  In particular, when the humidity conditioning aid is a metal salt and the metal salt is contained in the pores, the metal salt is present in the pores as an aqueous solution under high humidity conditions. The content is such an amount that the volume of the aqueous solution of the humidity control agent stored in the pores due to moisture absorption is equal to or less than the total pore volume of the silica gel at the maximum humidity under the use conditions.

  In other words, if the amount of the aqueous solution consisting of the metal salt and moisture adsorbed on the metal salt exceeds the pore volume, the aqueous solution overflows from the pores. When dried, the metal salt contained in the aqueous solution and discharged from the pores will unnecessarily adhere to the outside of the pores. As a result, the moisture absorption characteristics of the silica gel may be deteriorated. For this reason, when the content of the metal salt increases, the moisture absorption capacity increases, but for the above reasons, there is a possibility that it cannot be used in a high humidity region, and the usable humidity range must be limited.

However, if device-like devices such as providing ancillary equipment are allowed, a static cycle can be established by regenerating silica gel before the amount of aqueous solution in the pores exceeds the pore volume. It can be used even in a high humidity region that cannot be used on the adsorption data.
As the above-mentioned humidity control aid, when an alkali metal salt and an alkaline earth metal salt are contained in silica gel, the water vapor adsorption amount by silica gel becomes very high. For this reason, it is preferable to contain at least one metal salt as a humidity control agent in silica gel among metal salts belonging to the group consisting of alkali metal salts and alkaline earth metal salts.

Here, the alkali metal salt and alkaline earth metal salt to be contained may be any, but since the affinity with water vapor is particularly strong, for example, LiF, NaF, KF, CaF ₂ , MgF ₂ , Li ₂ SO ₄ , Na ₂ SO ₄ , K ₂ SO ₄ , CaSO ₄ , MgSO ₄ , LiNO ₃ , NaNO ₃ , KNO ₃ , Ca (NO ₃ ) ₂ , Mg (NO ₃ ) ₂ , NaCl, LiCl, CaCl ₂ , MgCl ₂ , LiBr , LiI, KBr, and preferably at least one selected from two or more. Of these, lithium salts are particularly preferable because of their most excellent hygroscopicity, and lithium chloride is particularly preferable because of its high moisture absorption per unit weight.

  The presence condition of the above-mentioned humidity control auxiliary agent is arbitrary, for example, even if it is uniformly dispersed in the form of molecules, clusters, particles, or any other state in silica gel, or they are attached and adhered to the silica gel surface. You may do it. Further, at least a part of the humidity conditioning aid may be bonded to a silicon atom directly or via oxygen. Further, these humidity conditioning aids may be solid or liquid. Further, these humidity conditioning aids may be in the form of hydrates, and some of them may be aqueous solutions in the pores.

  Specifically, the metal salt belonging to the group consisting of alkali metal salt and alkaline earth metal salt is a metal salt belonging to the group consisting of alkali metal salt and alkaline earth metal salt contained in the silica gel of the present embodiment. Among them, in order from the one with the highest content, usually 4 types, preferably 3 types, more preferably 2 types, particularly preferably 1 type. Here, when there are two or more metal salts belonging to the group consisting of alkali metal salts and alkaline earth metal salts, the total metal salt content is usually 1 to 80% or more, preferably 3 to 60. % Or more, particularly preferably 5 to 50% or more.

  The humidity control silica gel of the present embodiment is subjected to a condensation step of condensing a silica hydrosol obtained together with a hydrolysis step of hydrolyzing silicon alkoxide, as in the case of the humidity control silica gel of the first embodiment. Includes both the hydrolysis / condensation step for forming the silica hydrogel and the physical property adjustment step for obtaining silica gel in the desired physical property range by hydrothermal treatment without aging the silica hydrogel following the hydrolysis / condensation step. It can be manufactured by the method.

  Hereinafter, although the manufacturing method of the silica gel of the present embodiment will be further described, a point different from the manufacturing method of the silica gel of the first embodiment, that is, a method of adding an auxiliary humidity conditioner to the silica gel will be described. Since it is substantially the same as 1st Embodiment, description is abbreviate | omitted. An example in which a metal salt such as an alkali metal salt or an alkaline earth metal salt is contained as a humidity conditioning aid will be described.

  First, when the present silica gel is produced by doping the humidity conditioning aid before hydrothermal treatment, the moisture conditioning aid is added after the alkali silicate or silicon alkoxide is hydrolyzed and then gelled. The silica hydrogel obtained can be produced by applying a hydrothermal treatment method. As an application example of the method by hydrothermal treatment, preferably, a method of hydrolyzing silicon alkoxide and a humidity control auxiliary agent can be mentioned.

  In the process of hydrolyzing silicon alkoxide to obtain silica hydrogel, one or more humidity conditioning aids are added to the system. About the form etc., if it is a range which does not prevent formation of a homogeneous silica hydrogel, it will not specifically limit, The thing which does not express strong catalytic activity with respect to a hydrolysis of a silicon alkoxide is preferable. Further, from the viewpoint of obtaining high-purity silica gel, it is preferable to use a high-purity humidity conditioning aid.

  The method of adding the humidity conditioning aid is not particularly limited as long as it does not prevent the formation of a homogeneous silica hydrogel. Even if the moisture conditioning aid is added to water for hydrolyzing the silicon alkoxide, it is added to the silicon alkoxide. Alternatively, it may be added to the hydrosol that has become a homogeneous solution immediately after hydrolysis, and is appropriately selected according to operability. Further, if necessary, the humidity conditioning aid may be added to the above-mentioned system after hydrolysis in advance, or conversely, the moisture conditioning aid may be added after partial hydrolysis of the silicon alkoxide. .

  Moreover, the silica gel of this embodiment can be manufactured also by the method of carrying | supporting a humidity control adjuvant on the high purity silica gel after pore control. In this case, first, a humidity conditioning aid is introduced into the silica gel pores. As the method, any known method may be used. For example, an impregnation method well known as a catalyst preparation method <absorption method, pore-filling method, “incipient wetness” method, evaporation drying Examples thereof include an evaporation to dryness method and a spraying method. When a moisture conditioning aid is carried, if the moisture conditioning aid adheres outside the pores, the moisture conditioning aid becomes large particles and the moisture absorption properties deteriorate, so an aqueous solution of the humidity conditioning aid, particularly as in the pore filling method. A method in which does not overflow outside the pores is preferred.

  The humidity conditioning aid can be supported by the above method on silica gel obtained by hydrothermal treatment without hydrolyzing and aging the silicon alkoxide. If it is the range which expresses sex, it will not specifically limit. Further, from the viewpoint of obtaining high-purity silica gel, it is preferable to use a high-purity humidity conditioning aid. When the moisture conditioning aid is post-supported, pretreatment may be performed on the high-purity silica gel serving as a carrier. In addition, when the carbon content derived from the silicon alkoxide etc. which are the raw materials of the silica gel used as a support | carrier is contained, you may bake and remove normally at 400-600 degreeC as needed. Furthermore, in order to control a surface state, you may bake at the temperature of a maximum of 900 degreeC.

Moreover, you may perform the surface treatment for changing states, such as hydrophilicity / hydrophobicity of the support silica gel surface, surface activity, and acidity, as needed.
Although any method described above may be used as a method of incorporating the humidity conditioning aid, the method by loading is more preferred because the pore control can be performed reliably and the moisture conditioning aid to be contained can be selected widely.

Since the silica gel for a humidity control agent as the second embodiment of the present invention contains a humidity control auxiliary agent having a high affinity for water vapor as described above, the humidity control silica gel for the humidity control agent of the first embodiment is higher. There is an advantage that the effect is high.
Further, when the humidity conditioning aid is supported in the pores and the humidity conditioning aid is a metal salt, there are the following advantages.

That is, this silica gel can carry a metal salt in a highly dispersed state compared with conventional silica gel, and can maintain excellent pore characteristics even after carrying. As a result, the supported metal salt can exhibit highly efficient moisture absorption performance close to the theoretical moisture absorption amount. The reason seems to be due to various complex factors, and details are unknown, but are estimated as follows.
(1) Since the support (silica gel) has a very high purity and a homogeneous structure with little distortion of the bond angle of the siloxane bond, the surface state of the support is homogeneous and the metal salt specifically adsorbs. There are few points. Therefore, although the metal salt supported in the pores exists in a solid state at low humidity, it is supported in a highly dispersed (that is, uniformly) in the pores and has a high surface area, thereby exhibiting a high adsorption ability. can do. On the other hand, the metal salt exists as an aqueous solution in the pores under high humidity, but is supported in the pores in a highly dispersed (ie, uniformly) manner as in the low humidity. When the metal salt is, for example, a lithium salt, the aqueous solution has a relatively high viscosity. In particular, when the aqueous solution is unevenly supported in the pores, a highly viscous part or a thick part of the liquid film is locally generated. In such high-viscosity areas or thick areas of the liquid film, the diffusion rate of moisture absorbed in the pores (ie, in the lithium salt aqueous solution with high viscosity) becomes insufficient, All lithium salts tend to be in a state where they do not contribute effectively to moisture absorption (only a part of the lithium salt in the pores contributes to moisture absorption). Since it comes to carry uniformly, this is suppressed.
(2) Since the pore size distribution is very sharp (the pore size is uniform), the supported salt does not precipitate in the pores under different conditions depending on the pore distribution, and the particle size is uniform. Supported. In other words, if the pore size distribution is broad (if the pore sizes are not uniform), the amount of metal salt carried in the pores will be uneven, and the contact efficiency with water vapor will be reduced with a coarse metal particle size. For this reason, it becomes difficult to contribute to moisture absorption, or the moisture absorption speed decreases, so that a sufficient humidity control function cannot be exhibited. On the other hand, if the pore diameters are uniform, many metal salts in the pores can be supported with a uniform fine particle size, and there are fewer coarse particles that do not contribute to moisture absorption. Can be expressed.

EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not restrict | limited to a following example, unless the summary is exceeded. In addition, as an example, when (A) a humidity control aid is not contained in silica gel (corresponding to the first embodiment above), (B) a humidity control aid is contained in silica gel (second implementation above) (Corresponding to the form) will be described.
(A) In the case of not containing a humidity conditioning aid (1) Analysis method of silica gel 1-1) Pore volume, specific surface area BET nitrogen adsorption isotherm was measured with AS-1 manufactured by Cantachrome, The specific surface area was determined. Specifically, the pore volume adopts a value when the relative pressure P / P ₀ = 0.98, and the specific surface area is nitrogen at three points of P / P ₀ = 0.1, 0.2, 0.3. It calculated using the BET multipoint method from the adsorption amount. Further, the pore distribution curve and the differential pore volume at the mode diameter (D _max ) were determined by the BJH method. The interval between each point of the relative pressure to be measured was 0.025.

1-2) Powder X-ray diffraction Using a RAD-RB apparatus manufactured by Rigaku Corporation, measurement was performed using CuKα as a radiation source. The divergence slit was ½ deg, the scattering slit was ½ deg, and the light receiving slit was 0.15 mm.
1-3) Content of metal impurities Fluoric acid was added to 2.5 g of the sample and heated to dryness, and then water was added to 50 ml. ICP emission analysis was performed using this aqueous solution. Sodium and potassium were analyzed by flame flame light method.

1-4) Solid-state Si-NMR Measurement Using a Bruker solid-state NMR apparatus (“MSL300”), a resonance frequency of 59.2 MHz (7.05 Tesla), and a 7 mm sample tube, CP / MAS (Cross) The measurement was performed under the conditions of a Polarization / Magic Angle Spinning probe. Specific measurement conditions are shown in Table 1 below.

Analysis of measured data (Q ⁴ Determination of the peak position) is performed by a method of extracting each peak by the peak division. Specifically, waveform separation analysis using a Gaussian function is performed. For this analysis, waveform processing software “GRAMS386” manufactured by Thermogalatech can be used.
(2) Manufacture and evaluation of silica gel Examples 1-3
1000 g of pure water was charged into a 5 L separable flask (with a jacket) made of glass and fitted with a water-cooled condenser open to the atmosphere at the top. While stirring at 100 rpm, 1400 g of tetramethoxysilane was charged into this over 3 minutes. The water / tetramethoxysilane molar ratio is about 6. Warm water at 50 ° C. was passed through the jacket of the separable flask. Stirring was continued, and the stirring was stopped when the contents reached the boiling point. Subsequently, hot water of 50 ° C. was passed through the jacket for about 0.5 hour to gel the sol produced. Thereafter, the gel was quickly taken out and pulverized through a nylon net having an opening of 600 microns to obtain a powdery wet gel (silica hydrogel).

  450 g of this hydrogel and 450 g of pure water were charged into a 1 L glass autoclave. The conditions were 130 ° C. × 3 Hr for Example 1, 150 ° C. × 3 Hr for Example 2, and 200 ° C. × 3 Hr for Example 3. Hydrothermal treatment was performed. After hydrothermal treatment for a predetermined time, no. It filtered with 5A filter paper, and it dried under reduced pressure until it became constant weight at 100 degreeC, without washing with water, and obtained the raw material silica gel of Examples 1-3, respectively.

  Then, each raw material silica gel was pulverized in a mortar and classified by a sieve to obtain a powder (silica gel of Examples 1 to 3) having an average particle diameter of 20 μm. The physical properties of the silica gels of Examples 1 to 3 are shown in Tables 2 and 3 below.

As shown in Table 2, each of Examples 1 to 3 of the silica gel for a humidity control agent has a total volume of pores in the range of ± 20% centering on the value of the mode diameter (D _max ). It is as high as 60% or more of the total pore volume and has a sharp pore distribution. Therefore, according to the silica gel for a humidity control agent of this invention, it turns out that the pore diameter can be finely controlled by adjusting the hydrothermal treatment temperature.

Further, although Examples 1 to 3 of the present silica gel for a humectant were not shown, no peak on the low angle side (2θ ≦ 5 deg) due to the periodic structure was observed in the powder X-ray diffraction diagram.
Furthermore, as shown in Table 3, in each of Examples 1 to 3 of the silica gel for a humidity control agent, the value of the chemical shift of the Q ⁴ peak of the solid Si-NMR is larger than the value calculated by the above formula (I). Smaller (more on the negative side). On the other hand, in the silica gel of Comparative Example 1 described later, the chemical shift value of the Q ⁴ peak of solid Si-NMR is larger than the value calculated by the above formula (I) (more on the positive side). This means that each of Examples 1 to 3 of the present silica gel for a humidity control agent has less structural distortion than the conventional silica gel as in Comparative Example 1, and the physical properties change even under severe use conditions. It is difficult to do (that is, it is difficult to deteriorate).

The following were prepared as comparative examples.
Comparative Example 1
Silica gel CARIACT G-3 for catalyst carrier manufactured by Fuji Silysia Chemical Ltd. was used.
Comparative Example 2
Silica gel CARIACT G-6 for catalyst carrier manufactured by Fuji Silysia Chemical Ltd. was used.
The various physical properties of Comparative Examples 1 and 2 are shown in Tables 2 and 3 above. In addition, since the silica gel of Comparative Example 1 did not express a clear peak in the pore distribution curve, the average pore diameter was determined as the mode diameter (D _max ).

In any of the silica gels of Comparative Examples 1 and 2, the low angle side peak due to the periodic structure is not observed in the powder X-ray diffraction diagram. Further, when the impurity metal content was measured, it was as shown in the above table, and the silica gels of Comparative Examples 1 and 2 had a higher impurity metal content than the silica gels of Examples 1 to 3. Further, as is apparent from Table 3, the silica gels of Comparative Examples 1 and 2 have a chemical shift value of the Q ⁴ peak of solid Si-NMR compared with the value calculated from the left side of the above formula (I). Since it is a larger value (a value on the positive side), the structure is more distorted than the silica gels of Examples 1 to 3, and the physical properties are likely to change.

Silica gel thermal stability test in water Pure water was added to each of the silica gels of Examples 1 to 3 and Comparative Examples 1 and 2 to prepare a 40 wt% slurry. About 40 ml of the slurry prepared above was sealed in a stainless steel microbomb having a volume of 60 ml, and immersed in an oil bath at 280 ± 1 ° C. for 3 days. A part of the slurry was extracted from the microbomb and filtered through 5A filter paper. The filter cake was vacuum-dried at 100 ° C. for 5 hours. The results of measuring the specific surface area of this sample are shown in Tables 2 and 3. The silica gels of Examples 1 to 3 were less reduced in specific surface area than the silica gels of Comparative Examples 1 and 2, and were excellent in hydrothermal stability.
(3) Performance Evaluation of Humidity Conditioning The humidity conditioning performance of the examples and comparative examples can be evaluated by the following method, for example.
<Static moisture absorption performance evaluation>
It is a method to know the amount of water vapor adsorbed on silica gel by increasing the weight of silica gel or changing the pressure in the system after the dried silica gel is placed in a constant humidity environment to absorb moisture and the moisture absorption reaches saturation. .

The water vapor adsorption isotherm can be obtained by obtaining the water vapor adsorption amount at each relative pressure (relative humidity) and plotting it as the horizontal axis relative pressure and the adsorption amount per 1 g of the vertical silica gel. It can be said that silica gel whose adsorption amount suddenly rises at a constant humidity and has a large amount of change is excellent in humidity control performance for this humidity.
Note that the measurement method based on weight change is called a weight method, and the measurement method based on pressure change is called a volume method.

  As a simple measurement example of the gravimetric method, for example, a hygroscopic test described in JIS Z0701 Testing method for silica gel desiccant for packaging can be given. In the hygroscopicity test, the silica gel placed in a weighing bottle is placed in a glass sealed container containing a sulfuric acid aqueous solution for a predetermined time at a predetermined temperature, and the moisture absorption rate of the silica gel is measured by the change in weight of the silica gel. In this test method, by setting the sulfuric acid aqueous solution to a predetermined concentration / specific gravity, the inside of the glass sealer is set to the relative humidity, and the sulfuric acid aqueous solution for setting the relative humidity to 20%, 50%, and 90%. The concentration / specific gravity is specifically specified.

The relationship between the concentration of sulfuric acid aqueous solution and relative humidity is described in more detail as the total pressure of sulfuric acid aqueous solution in the section of the three-component system vapor-liquid equilibrium in Chapter II, Chapter 8 of Chemical Handbook. In addition, by preparing a sulfuric acid aqueous solution corresponding to an arbitrary humidity, the moisture absorption rate under an arbitrary humidity condition can be obtained in accordance with the above test method.
As a measurement example of the capacity method, a method using a general gas adsorption / desorption device can be mentioned. For example, by using a device such as a water vapor adsorption device BELSORP18 manufactured by Nippon Bell, water vapor absorption / desorption isotherms can be easily measured.
<Dynamic humidity control performance evaluation>
When silica gel is used as a humidity control agent, it is also important that the water vapor absorption and release rate and the humidity control response rate are sufficiently fast. In order to evaluate such performance, a certain amount of humidity control agent is placed in a humidity variable container with a humidity sensor, and the ambient humidity is swung between two conditions of high humidity and low humidity at regular intervals. The container is sealed each time, and the response speed at which the environmental humidity changes due to the moisture absorption and release action of the humidity control agent and the humidity when the change value becomes constant are examined. Silica gel, which has a fast humidity control response to changes in environmental humidity and can be adjusted to a constant humidity even during repeated cycles, is an excellent humidity control agent. In addition to the performance of silica gel itself, the dynamic performance varies greatly depending on the silica gel filling state and molding method.
<Durability evaluation>
Analyze the pore characteristics and moisture absorption characteristics of the repetitively used humectant over time and check for deterioration. If necessary, conduct a deterioration acceleration test and check for deterioration.

Considering the physical property evaluation of the examples of the present silica gel described above, it is expected that the high performance of the present silica gel as a humidity control agent can be confirmed by performing such an evaluation method.
(B) When containing a humidity conditioning aid in silica gel (1) Example 4
The silica gel of Example 4 was produced by supporting lithium chloride as a humidity conditioning aid on the silica gel (raw material silica gel) produced by the same method as in Example 1 above by the pore filling method.

  Specifically, the raw material silica gel was charged into a polyethylene container having an open top and fixed obliquely. A low-speed rotation motor is attached to the bottom of the container, and the motor is operated to rotate the container at 50 rpm to cause the silica gel inside to flow, and a 30 wt% lithium chloride aqueous solution on the powder (silica gel). After spraying 13.3 g and rotating the container for 3 minutes, the powder was taken out from the container.

The volume of the lithium chloride aqueous solution used was set so as not to exceed the total pore volume of the support (silica gel) so that the total amount of the added aqueous solution was absorbed into the pores. This powder was dried in a vacuum dryer at 100 ° C. for 5 hours to obtain a humidity-conditioning silica gel carrying 20.0% by weight of lithium chloride as Example 4.
Various physical properties of Example 4 are shown in Table 4. Further, Table 5 shows the results of moisture absorption measured by the method according to JISZ0701 described above. The silica gel of Example 4 maintains a sharp pore distribution, a high pore volume, and a specific surface area even after supporting lithium chloride. Moreover, in the powder X kneading diffraction diagram, a peak on the low angle side (2θ ≦ 5 deg) due to the periodic structure was not recognized. Furthermore, the metal content excluding alkali metal and alkaline earth metal (that is, impurity metal content) was 0.1 ppm, which was very high purity.

Moreover, the value of the chemical shift of the Q ⁴ peak of solid Si · NMR was smaller than [−0.0705 × (D _max ) −11.36] (existed more on the minus side). That is, it is considered that the silica gel carrier itself maintained a structure with little distortion even after lithium chloride was supported, and maintained a property that was homogeneous, highly stable, and hardly changed in physical properties.

(2) Comparative Example 3
As Comparative Example 3, various physical properties of NIPGELCX-200 manufactured by Nippon Silica Industrial Co., Ltd. having the most frequent pore size similar to Example 4 are shown in Table 4, and the moisture absorption measured in the same manner as Example 4 is shown in Table 5. (However, Comparative Example 3 does not carry lithium chloride). In the powder X kneading diffraction diagram of the silica gel of Comparative Example 3, no peak on the low angle side (2θ ≦ 5 deg) due to the periodic structure was observed. Further, the metal content excluding alkali metal and alkaline earth metal (that is, impurity metal content) was 732 ppm, which was much higher than that of the silica gel of Example 4.

Further, the value of the chemical shift of the Q ⁴ peak of the solid Si · NMlR was larger than [−0.0705 × (D _max ) −11.36] (existed on the plus side). That is, it is considered that the silica gel of Comparative Example 3 is more distorted than the silica gel of Example 4 and the physical properties are likely to change during repeated use. As described above, the silica gel of Comparative Example 3 does not support lithium chloride (humidity control aid), but the silica gel of Comparative Example 3 supported by lithium chloride has pores as compared with Example 4. Since the distribution characteristics are broad and there are many structural strains as described above, it is clear that the pore characteristics are inferior, and it is considered that the moisture absorption characteristics of the supported lithium chloride cannot be fully exhibited.

(3) Comparison of moisture absorption rate The silica gel carrying lithium chloride of Example 4 has a significantly higher moisture absorption rate over the entire humidity range than the silica gel of Comparative Example 3, and has high moisture absorption performance not found in conventional solid moisture absorbents. Indicated. The moisture absorption rate of the silica gel of Example 4 is close to the theoretical moisture absorption curve of lithium chloride, and it is considered that lithium chloride can absorb water vapor very efficiently by being supported on this silica gel.

  Further, the amount of change in moisture absorption (absorption rate difference) between the relative humidity of 8% and the relative humidity of 20% of the silica gel of Example 4 was much larger than that of Comparative Example 3. This indicates that a large amount of moisture can be absorbed and released in a low humidity range with a slight humidity difference. This indicates that the silica gel of Example 4 is very useful as the above-mentioned hygroscopic agent of the heat pump using the moisture absorption and desorption of the hygroscopic agent. Is effective.

Claims (5)

Hydrolysis step of hydrolyzing silicon alkoxide to obtain silica hydrosol;
A condensation step of condensing the silica hydrosol to obtain a silica hydrogel;
And a physical property adjusting step of performing hydrothermal treatment without substantially aging the silica hydrogel. 2. The method for producing silica gel according to claim 1, wherein the hydrolysis step hydrolyzes using 2 mol or more and 20 mol or less of water with respect to 1 mol of silicon alkoxide. The method for producing silica gel according to claim 1 or 2, wherein in the hydrolysis step, stirring is performed at a stirring speed of 30 rpm or more. The method for producing silica gel according to claim 3, wherein in the hydrolysis step, stirring is stopped when the silicon alkoxide and water become a uniform liquid. The method for producing silica gel according to any one of claims 1 to 4, wherein in the physical property adjustment step, hydrothermal treatment of the silica hydrogel having a fracture stress of 6 Mpa or less is performed.