JPH04203960A - Humidity responsive material and element - Google Patents

Abstract

PURPOSE:To achieve an improved temperature detection property without any hysteresis when temperature is increased or decreased by forming with a porous titanium dioxide sintered body where a non-porous titanium dioxide sphere is aggregated and sintered. CONSTITUTION:A resin-coated porous titanium dioxide sphere is aggregated and it is heated and sintered at a temperature where the porous titanium dioxide sphere is converted to a non-porous property, thus obtaining a porous titanium dioxide sintered body with a high mechanical strength where a non-porous titanium dioxide sphere is aggregated and sintered with a uniform porosity. A temperature-responsive element with it as a moisture-responsive material shows an improved and sensitive temperature-responsive characteristic without any hysteresis when temperature is increased or decreased.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application This invention relates to moisture-sensitive materials and axensor. More specifically, the present invention relates to a moisture-sensitive material and a moisture-sensitive element that can sensitively and accurately detect changes in relative humidity and are suitable for use in sensors for controlling air humidity.

(B) Prior Art Moisture-sensitive materials that detect changes in the humidity of the air by detecting changes in physical properties that change in response to changes in the humidity of the air have been known for a long time.

Among such moisture-sensitive materials, MgCrtO& -TiO, system, ZnOLiz
Ceramics such as OVtOs, Ti0t-SnOts, and hydroxide apatite are known.

In addition to the above ceramics, titanium dioxide (T
A humidity sensor using a porous titanium dioxide sintered body obtained by firing a mixture of (iOz) powder and a resin (binder) to remove the resin component is known.

(c) Problems to be Solved by the Invention However, the porous titanium dioxide sintered body, which is the above-mentioned known moisture-sensitive material, is a mixture of titanium dioxide powder and resin on the sintered surface (referred to as a green body). Since a non-uniform state occurs between a portion with a large amount of water and a portion with a small amount of water, many of them have non-uniform pores.

When a moisture-sensitive material having such uneven pore diameters is used as a moisture-sensitive material, its resistance value tends to fluctuate, making it difficult to obtain a linear resistance value characteristic. This is not preferable in terms of the design of the humidity sensor, and the resulting humidity sensor has low accuracy.

Regarding this point, the present inventors first discovered that resin-coated porous titanium dioxide spheres individually coated with resin (binder) were aggregated and sintered to produce a porous titanium dioxide sintered body with uniform pore diameters. They discovered that the material acts as a moisture-sensitive material with excellent sensitivity, and have filed a patent application (Japanese Patent Application No. 1-242808).

This invention was made by roughly developing this knowledge, and in particular, it not only has excellent detection sensitivity, but also allows accurate humidity detection without hysteresis, and has mechanical strength. It is an object of the present invention to provide a moisture-sensitive material and a moisture-sensitive element that are excellent in terms of temperature and temperature.

(D) Second Means and Effects for Solving the Problems Thus, according to the present invention, there is provided a moisture-sensitive material comprising a porous titanium dioxide sintered body formed by aggregating and sintering non-porous titanium dioxide spheres. Ru. Furthermore, a moisture sensitive element made of such a moisture sensitive material is provided.

In this invention, resin-coated porous titanium dioxide spheres are assembled and heated and sintered at a temperature that converts the porous titanium dioxide spheres into non-porous, thereby forming uniform non-porous titanium dioxide spheres. The fact that a porous titanium dioxide sintered body with high mechanical strength can be obtained by aggregating and sintering with a porosity of This is based on the discovery of the fact that it exhibits excellent and sensitive moisture-sensing characteristics without hysteresis in temperature and temperature drops.

The moisture-sensitive material of this invention consists of resin-coated (composite) porous titanium dioxide spheres that are once produced from titanium dioxide powder.
It consists of a porous titanium dioxide sintered body that is assembled as components and then further pressurized and sintered. Such a specific sintered body can be manufactured, for example, by the method described below. That is, a mixture of titanium dioxide powder surface-treated with a lipophilic agent and a polymerizable vinyl monomer is prepared, and in some cases, an organic material that is compatible with the above monomer and is substantially incompatible with water is prepared. Adding a solvent to the above mixture suppresses the increase in viscosity due to an increase in the amount of titanium dioxide powder in the above mixture, expands the range of addition amount of titanium dioxide powder, and in oil droplet dispersion of the above mixture in an aqueous system, This makes it possible to disperse and hold individual oil droplets in a spherical shape, and as a result, the titanium dioxide powder (secondary particles) dispersed within each oil droplet is aggregated into a spherical shape, and then the resin coating (
Composite) A method in which porous titanium dioxide spheres are manufactured, which are then assembled into a predetermined shape, pressure molded, and then heated at a predetermined temperature to remove the coating resin and sintered to become a porous body. be.

In the above method, the surface-treated titanium dioxide powder means that the (titanium dioxide) powder only needs to be surface-treated before polymerization of the polymerizable vinyl monomer used. Therefore, the titanium dioxide powder may be surface-treated in advance before being added to the polymerizable vinyl monomer or a mixture of the monomer and a predetermined organic solvent. The surface treatment may be performed by adding titanium dioxide powder to a mixture of a predetermined organic solvent and a lipophilic agent used for surface treatment.

The above-mentioned surface treatment refers to a treatment in which the titanium dioxide powder is brought into contact with the above-mentioned lipophilic agent and the lipophilic agent is adsorbed or bonded to the surface of the powder. This treatment is accomplished by conventional mechanical methods and the like. That is, a mixture of a lipophilic agent and titanium dioxide powder, or a mixture of a lipophilic agent, titanium dioxide powder, and a polymerizable vinyl monomer is heated at room temperature or under cooling using, for example, a propeller blade or a homogenizer. This is achieved by stirring at high speed.

As the titanium dioxide powder used for this removal, normal titanium dioxide powder can be used, and its particle size is 001 to 2.
．． Preferably between 0 μm and 0.1 to 15 μm
is preferred.

The lipophilic agent has a functional group that strongly adsorbs or binds to the titanium dioxide powder and has a high affinity for the polymerizable vinyl monomer, or a functional group that can bind to the monomer. It is possible to use a substance that has Examples of such substances include higher fatty acids such as oleic acid, stearic acid, and palmitic acid, unsaturated carboxylic acids such as acrylic acid and methacrylic acid, and polar groups such as aminoethyl acrylate, hydroquine ethyl acrylate, and cyanoethyl acrylate. acrylic ester having
Coupling agents such as titanate coupling agents and silane coupling agents can be mentioned. Among these,
Preferably, the agent has a functional group that strongly binds to titanium dioxide powder, such as a titanate coupling agent or a silane coupling agent. For example, titanate coupling agents include isopropyl tris (dioctyl pyrophosphate) and bis(dioctyl pyrophosphate) titanate, which have a pyrophosphate type lipophilic group, and examples of titanate having a phosphate type lipophilic group include tetraoctyl tris(dioctyl pyrophosphate) and bis(dioctyl pyrophosphate) titanate. Examples include bis(ditrideneruphosphate) titanate, and examples of silane coupling agents include those having a vinyl group, such as vinyltrichlorosilane, vinyltrimethoxinelan, and γ-methacryloquinebrobyltrimethoxysilane. It will be done.

Note: Any known polymerizable vinyl monomer can be used as is, as long as it can exist as spherical oil droplets when dispersed in an aqueous system and can form a polymer under polymerization conditions. can. Such monomers may be used alone or in combination of two or more, or may be used in combination with a known crosslinking agent. Suitable monomers include acrylic esters such as methyl acrylate and ethyl acrylate, methacrylic esters such as methyl methacrylate and ethyl methacrylate, and aromatic vinyl compounds such as styrene. Suitable examples of the crosslinking agent include methacrylic acid esters of polyhydric alcohols such as ethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate, and trimethylolpropane trimethacrylate, divinylbenzene, and the like. The polymerization initiator may be any initiator as long as it is soluble in the polymerizable vinyl monomer used, such as commonly used peroxides such as benzoyl peroxide, lauroyl peroxide, and diacetyl peroxide; Examples include azo compounds such as isobutyronitrile and azobisdimethylvaleronitrile.

The organic solvent used is one that is compatible with the polymerizable vinyl monomer and is substantially incompatible with water. "Substantially incompatible with water" means insoluble or slightly soluble in water. Further, this organic solvent is used to adjust the viscosity of a mixture consisting of titanium dioxide powder and a polymerizable vinyl monomer as described below, and therefore, it preferably has a viscosity of 3.0 centipoise (CP) or less at room temperature. Furthermore, those having affinity with the polymerizable vinyl monomer used are preferable. Examples of such organic solvents include acetic acid esters such as methyl acetate and ethyl acetate, hydrocarbons such as hexane and heptane, ketones such as methyl ethyl ketone and methyl isobutyl ketone, and aromatic hydrocarbons such as benzene and toluene. - In the above manufacturing method, a slurry-like mixture is first prepared from titanium dioxide powder surface-treated with the above-mentioned lipophilic agent, a polymerizable vinyl monomer, an organic solvent added as necessary, and the like. When preparing this slurry, titanium dioxide powder is usually used in an amount of 150 to 1,300 parts by weight based on 100 parts by weight of the polymerizable vinyl monomer, and the porosity and sphericity of the titanium dioxide particles obtained are It is preferable to use it in a range of 230 to 1000 parts by weight. The lipophilic agent is determined by the minimum covering area of the lipophilic agent and the specific surface area of the titanium dioxide powder used, but it is usually 0.2 to 30% of the titanium dioxide powder.
Used in parts by weight. The organic solvent is used in an amount necessary to adjust the viscosity of the slurry mixture to a level that allows it to maintain spherical oil droplets during dispersion in an aqueous system as described below. This amount is 10% of the polymerizable vinyl monomer.
It is suitable to use in a range of 1 to 200 parts by weight, and preferably in a range of 1 to 150 parts by weight, relative to 0 parts by weight.

If the above amount is 200 parts by weight or more, it is not preferable because it becomes difficult to obtain substantial strength of the polymer that binds the titanium dioxide powders together. The polymerization initiator is preferably used in an amount of 0.1 to 2.0% by weight of the polymerizable vinyl monomer. The above-mentioned slurry-like mixture is prepared into a uniform slurry by a mechanical method similar to the above-mentioned surface treatment.

The slurry mixture prepared as described above is dispersed in an aqueous system and subjected to polymerization conditions for the polymerizable vinyl monomer in the mixture. The dispersion is accomplished by mechanical methods similar to those described above. At this time, the dispersion conditions are set so that resin-coated titanium dioxide spheres having a particle size range described below are dispersed in a size of oil droplets. The above-mentioned polymerization is achieved by adjusting according to the type of polymerizable vinyl monomer used, but the conditions for usual @turbidity polymerization can be applied as is.

Through the above dispersion and polymerization, a spherical resin having a particle size of 1 μm to lzx, which is an aggregate of titanium dioxide powder coated and composited with a resin made of a polymer of a polymerizable vinyl monomer, is produced in an aqueous system. Coated titanium dioxide spheres are obtained. The titanium dioxide spheres are separated and dried by a conventional method. Among these, it is more preferable to select and use spheres having a particle size of 15 μl to 50 μl in terms of the mechanical strength of the sintered body.

In this invention, the resin-coated porous titanium dioxide spheres obtained as described above are pressure-molded into a predetermined shape.

Pressurizing conditions at this time vary depending on the size of the resin-coated porous titanium dioxide sphere used, but a pressure sufficient to maintain the desired shape of the molded product is applied. Usually 0.5~
A pressure of about L, Ot/am2 is preferred.

The aggregate of resin-coated titanium dioxide spheres held in the desired shape by the pressure molding is then subjected to heat treatment. This heat treatment allows the resin in the titanium dioxide sphere to be smoothly removed without being carbonized, and the titanium dioxide particles in the titanium dioxide sphere to be fused together (substantially point contact fusion) while maintaining their spherical shape. ), ie under conditions in which the porous titanium dioxide spheres constituting the aggregate are converted into substantially non-porous titanium dioxide spheres. The heating temperature in this heat treatment is 1150 to 155
The temperature is set at around 0°C. If the temperature is below 1150°C, the density of the sintered body is too low and it is not suitable, and if it exceeds 1550°C, not only the inside of the titanium dioxide spheres but also the spaces between the titanium dioxide spheres will fuse, making it impossible to secure the desired porosity of the sintered body. Undesirable. A particularly preferable heating temperature is 1250 to 1400.
It is ℃. However, as for the heating state to the above heating temperature, t
It is necessary to take a long time (for example, 5 hours) to raise the temperature to OOO'C in order to avoid carbonization of the resin. On the other hand, the heating and holding time is usually about 1 to 6 hours.

Through such treatment, a porous titanium dioxide sintered body as a moisture-sensitive material in the present invention can be obtained, and its density is preferably 2.59/cm'' or more.

Such a porous titanium dioxide sintered body is a non-porous titanium dioxide sphere (usually 1 to 50 μm, preferably 15 to 50 μm).
It is made of a porous body in which micrometers (μm) are aggregated and integrated, and has a uniform pore distribution and excellent mechanical strength. In addition to exhibiting sensitive moisture-sensing properties, it is possible to assemble conventional ceramic moisture-sensitive materials and titanium dioxide spheres in a porous state.
Compared to moisture-sensitive materials made of co-porous titanium dioxide sintered bodies, there is no hysteresis in temperature rise and fall for humidity detection.
The stability, reproducibility, and accuracy of detection output have been significantly improved. The porosity of the pores and the density of the sintered body are
By adjusting the content of titanium dioxide powder, the particle size of titanium dioxide spheres, etc., it can be easily controlled within a range that does not impair the above characteristics. However, the bending titanium dioxide spheres contain additives that can adjust the conductivity (for example, N
b t Os, 5btOS, etc.) may be mixed.

By using such a moisture-sensitive material, the moisture-sensitive element of the present invention can be obtained. In such a moisture-sensitive element, the moisture-sensitive material used is preferably of a thick film type. The form of the element applied in this case is as shown in FIG.
A pair of electrodes (2) on both the front and back sides of the thick film-like moisture-sensitive material (1)
(2) and the impedance (Z
) In order to detect the fluctuation of
A configuration in which it is connected to the meter (4) is preferable. When using the above humidity sensing element, by measuring the relationship between the relative humidity in the air and the corresponding impedance (Z) in advance, fluctuations in impedance measured by placing the humidity sensing element in the atmosphere to be measured can be avoided. , the relative humidity in the atmosphere (
%RH) can be determined. Specifically, reference is made to the description of Examples described later.

EXAMPLES The present invention will be explained below with reference to Examples, but the present invention is not limited thereby.

(e) Example [Preparation of resin composite titanium dioxide spherical particles] Example, 1 In a 2Q beaker, methyl methacrylate 2799, silane coupling agent [γ-methacryloxypropyltrimethoxysilane, 5Z- manufactured by Toshi Silicone Co., Ltd.] 603
0121,09, azobisisobutyronitrile 0°60
After adding 9 and melting, add titanium dioxide (rutile type 1 particle size 0.24u++, manufactured by Teikoku Kako Co., Ltd. JR-600λ)
Add 700g and mix with a stirrer equipped with propeller blades for 20
The surface was treated at 00 rpm for 2 hours.

Magnesium birophosphate 6 metathetically decomposed in a 5Q autoclave
2.6 kg of water containing 0 g of sodium dodecylbenzenesulfonate and 269 g of sodium dodecylbenzenesulfonate were added thereto, and then the above slurry was added and emulsified. After purging with nitrogen, the stirring speed was set to 50 orpm, and polymerization was carried out at 60°C. After the polymerization was completed, the mixture was cooled to room temperature and the dispersant was decomposed with hydrochloric acid, followed by filtration. When the obtained particles were observed with a scanning electron microscope (SEM), they were found to be approximately 8.
They were spherical particles with a center diameter of μm, and formed titanium dioxide spherical particles composited with polymethyl methacrylate (PM!l!A) resin.

Example 2 In a 212 beaker, 279 g of methyl methacrylate,
Silane bubbling agent [γ-methacryloxypropyltrimethoxysilane, manufactured by Toshi Silicone Co., Ltd. S5Z
-6030121,09, 060 g of azobisisobutyronitrile was added, dissolved, and then titanium dioxide (rutile type 7 particle size 0, 2 μm, manufactured by Teikoku Kako Co., Ltd. JR-600A
) 700g and stirred with a stirring device equipped with propeller blades.
The surface was treated at 00 rpm for 2 hours.

Magnenium pyrophosphate metathesis 6 in a 5Q autoclave
2.6 kg of water containing 0 g of sodium dodecylbenzenesulfonate and 2.6 g of sodium dodecylbenzenesulfonate were added thereto, and the slurry was then added and emulsified. After purging with nitrogen, the stirring speed was set to 40 Orpm, and polymerization was carried out at 60°C. After the polymerization was completed, the mixture was cooled to room temperature and the dispersant was decomposed with hydrochloric acid, followed by filtration. When the obtained particles were observed with a scanning electron microscope (SEM), they were found to be spherical particles with a center diameter of about 20 μm, forming titanium dioxide spherical particles composited with polymethyl methacrylate (PMMA) resin.

Example 3 In a beaker of 212, methyl methacrylate 2499,
Ethylene glycol dimethacrylate 30g, butyl acetate 3009, titanate coupling agent [bis(dioctylpyrophosphate) oxyacetate titanate,
Plain Act KR-138S (manufactured by Ajinomoto Co., Inc.) 21.
0g, azobisisobutyronitrile 0.149,
After dissolving, titanium dioxide (rutile type 1 particle size 0.2 μm)
, JR-600A) 7009 manufactured by Teikoku Kako Co., Ltd., was added thereto, and surface treatment was carried out at 200 rpm for 2 hours using a stirring device equipped with a propeller blade.

Magnesium pyrophosphate metathesis in 5Q autoclave 5
09 and sodium dodecylbenzenesulfonate 0759 were added, and then the above slurry was added and emulsified. After purging with nitrogen, the stirring speed was set to 40 Orpm, and polymerization was carried out at 60°C. After the polymerization was completed, the mixture was cooled to room temperature and the dispersant was decomposed with hydrochloric acid, followed by filtration. When the obtained particles were observed with a scanning electron microscope (SEM11), they were found to be spherical particles with a center diameter of approximately 50 μm, forming methane dioxide spherical particles composited with polymethyl methacrylate (PMMA) resin. child.

[Preparation of sintered titanium dioxide spherical particles and moisture-sensitive element] Example 4 The PMMA composite titanium dioxide spherical particles obtained as in Example 1 were weighed by 0.59, and were placed in a mold for molding ( 1
2,5sul'X27.5xxh). Pressure molding was carried out for 15 seconds at a molding pressure of 1 ton and 7 cm" to obtain a molded product with an apparent density of 879/c and an amount of 3. Then, the above PM
Five IA composite titanium dioxide spherical particle molded bodies were stacked and placed in an electric furnace, and fired at TAOO°C for 3 hours to obtain a sintered body. The apparent density of this sintered body was 31319/am' and the strength was 1220 Kg/am''.

A silver electrode (manufactured by Degussa) was coated on the disk surface of this tablet-shaped sintered body, and baked at a temperature of 560° C. for 5 minutes to obtain a moisture-sensitive element.

Example 5 The PMMA composite titanium dioxide spherical particles obtained as in Example 2 were weighed and placed in a mold C12.
, 5xxeX21.5xxh]. Molding pressure 1
Pressure molding was performed for 15 seconds at ton/cm t to obtain a molded product with an apparent density of 1.849/Cl113. Next, five of the PMMA composite titanium dioxide spherical particle molded bodies were stacked and placed in an electric furnace, and fired at 1300°C for 3 hours to obtain a sintered body.

The apparent density of this sintered body was 3.019/cm3, and the strength was 420 Kg/cm'.

A silver electrode (manufactured by Degussa) was coated on the disk surface of this tablet-shaped sintered body, and baked at a temperature of 560° C. for 5 minutes to obtain a moisture-sensitive element.

Example 6 0.59 of the PMMA composite titanium dioxide spherical particles obtained as in Example 3 were weighed and placed in a mold for molding (1
2,5ix#X27.5xih). Molding pressure 1
ton/am" for 15 seconds, and the apparent density is 1.
．． A molded article of 929/cI113 was obtained. Next, the above P
Five MMAI-combined titanium dioxide spherical particle molded bodies were stacked and placed in an electric furnace, and fired at 1300° C. for 3 hours to obtain a sintered body. The apparent density of this sintered body is 3.209/cm'
The strength was 298 kg/am''.

A silver electrode (manufactured by Degussa) was coated on the disk surface of this tablet-shaped sintered body, and baked at a temperature of 560° C. for 5 minutes to obtain a moisture-sensitive element.

It was confirmed by an electron microscope that the sintered bodies of Examples 4 to 6 were all porous bodies in which non-porous titanium dioxide spherical particles were sintered by point contact bonding.

[Measurement of Moisture Sensitive Characteristics] The moisture sensitive characteristics of the moisture sensitive elements obtained as in the above examples were measured as follows.

Impedance measurements were performed in a humid atmosphere.

The humidity sensing element to be measured was fixed to a holder and loaded into a constant temperature and humidity chamber (manufactured by Tabai Seisakusho, PSL-2E) at 20°C. Changes in impedance can be measured using an LCZ meter (Y
(manufactured by HP, 4276A), and the measurement was performed at a frequency of 1 kHz and with an AC voltage applied.

The humid atmosphere is 10%RH-10QRH in the above constant temperature and humidity chamber.
Changes in characteristics due to temperature rise and temperature fall were measured in the range of %R1 (%R1).
12).

[Measurement results of humidity-sensitive characteristics] As for the humidity-sensitive characteristics, for the humidity-sensitive element of Example 2.5,
Figure 3 shows the results of measuring changes in impedance with respect to changes in relative humidity. From this, it can be seen that when the temperature is raised and lowered at a frequency of 1 kHz, the change in impedance follows the same trajectory and is extremely excellent without hysteresis. Note that the moisture-sensitive elements of other Examples had similar history characteristics.

(f) Effects of the Invention According to the moisture-sensitive material of the present invention, it is possible to obtain a moisture-sensitive element that is sensitive and has excellent humidity sensing performance without hysteresis in temperature rise and temperature drop. The mechanical strength of the material itself is also sufficient to provide a practical device, making it possible to realize a high-performance moisture-sensitive device.

[Brief explanation of the drawing]

Figure 1 is a perspective view of an example of a moisture-sensitive element made of the moisture-sensitive material of the present invention, Figure 2 is an explanatory diagram of the structure of the humidity-sensitive element shown in Figure 1, and Figure 3 is a diagram illustrating the use of the humidity-sensitive element of Figure 1. It is a graph showing the history characteristics of 1g wet material. l...moisture sensitive material, 2...electrode, 3...
...Lead, 4...LCZ meter. Shikaori 1. P-! lI 1 Figure 21! F 3m H(”/, RH)

Claims (3)

[Claims] 1. A moisture-sensitive material made of a porous titanium dioxide sintered body made by aggregating and sintering non-porous titanium dioxide spheres. 2. Porous titanium dioxide sintered body is 2.5g/cm^3
The moisture-sensitive material according to claim 1, having a density of at least 100%. 3. A humidity sensing element comprising a humidity sensing material according to claim 1 electrically interposed between a pair of electrodes.