JPH0129518B2 - - Google Patents

Description

[Detailed description of the invention]

<Technical Field of the Invention> The present invention relates to a reversible temperature indicating material, which is a type of temperature control material containing a substance whose hue changes depending on temperature changes. <Technical background of the invention and its problems> As conventional technology, there are temperature control materials called thermopaint and thermocrayon (registered trademarks of NOF Corporation) that change color at a certain temperature.
Because this type of material is extremely useful and easy to use, research has progressed significantly in recent years, expanding the range of color change temperatures and improving temperature accuracy, allowing users to freely select a specific temperature indicator material depending on the application. It has become possible to choose. Most of these materials exhibit irreversible changes, but some of them also have properties called reversible or quasi-irreversible. However, its heat resistance limit temperature is said to be around 250℃ at the highest. The reason for this is that there are restrictions due to the thermal instability of the color-changing material itself and the binder required when preparing it as a pigment. However, the use of temperature display using color-changing temperature indicator material is currently expanding greatly, and it is stable up to higher temperatures.
There is a need for long-lasting materials that can be processed in a variety of ways. In addition, the addition of color-changing temperature-indicating materials to various home appliances such as cooking and heating products is being considered, but in addition to the heat resistance issues mentioned above, the chemical stability of color-changing materials, processability, repeated lifespan, cost, and damage to the human body are also being considered. The reality is that materials that fully meet various requirements, such as whether or not they are toxic, are not available. <Objective of the Invention> Taking these circumstances into consideration, the present invention provides a metal oxide that is chemically stable even if the lower limit temperature at which the hue changes is slightly higher than that of conventionally proposed materials. In addition to using it as a temperature-indicating material, we also aim to use it in a wider range of applications by combining it with a processing method that takes advantage of its advantages. <Example> First, the progress up to the present invention will be explained. Cobalt green, also known as Linman green, is a very stable compound that has been used for a long time as an inorganic green pigment.
[nZnO−1CoO] system or [nZnO−1CoO−
(0.5 to 1.5) MgO] system, and usually has a composition of n=3 to 10. Regarding the former cobalt green [nZnO-1CoO], the composition ratio,
The color tone and phase were confirmed by X-ray diffraction, and the results shown in Table 1 were obtained.

[Table] In this X-ray analysis, ZnO is present throughout the area.
As the n value decreased, the ZnCo ₂ O ₄ (spinel structure) phase increased. The color tone was slightly yellowish green in the range of n=1.6 to about 17. On the other hand, the latter cobalt green [nZnO―1CoO―
0.5MgO] system, there was a tendency for the overall color to appear bluish green. The n value is 1.6 for both systems.
When the value is less than 1, the influence of ZnCo ₂ O ₄ becomes strong, and as the n value decreases, the color tone gradually darkens, making it unsuitable as a basic material for green pigments. The above cobalt green does not depend on its composition (n value),
When the temperature rose above room temperature, the color became slightly blackish and no particularly noticeable change in color tone occurred. The present inventor conducted an experiment in which the above-mentioned n value was varied in order to investigate in detail the relationship between ZnO contained in excess in this system and the green color tone. At the same time, I was interested in how the color tone would change if we incorporated another system in which all of the ZnO present in the system was changed to other compounds. So ZnO
A substance that reacts with a substance to form a new compound, and the color of the polycrystalline form of that compound is white.
- I decided to try adding an amount equivalent to 0.5 or n. As a preliminary step, we first investigated various compounds that seemed likely to form stable formation phases with ZnO. The results shown in Table 2 were obtained by firing an additive compound having an equimolar composition with ZnO.

[Table] Next, the above [nZnO-1CoO] and [nZnO-1CoO
WO ₃ , MoO ₃ and Nb ₂ O ₅ were added to cobalt green with n = 6.7 in two systems of 0.5MgO] in the ratio of n-0.5 mol for the former system and n mol for the latter system. When each was added and fired, bright blue polycrystals were obtained. According to X-ray analysis, it is inferred that the latter system contains a trace amount of MgCo ₂ O ₄ (spinel structure), but since there is no clear difference from the former system, we will consider it as the basic component here. Table 3 shows the results of adding the above metal oxides to the [nZnO-1CoO] system.

[Table] These products exhibited a unique phenomenon in which the blue color tone faded to gray when the temperature was increased, and the color returned to normal when the temperature was returned to room temperature. Next, for WO ₃ , MoO ₃ and Nb ₂ O ₅ , the relationship between the amount of each additive added and the phase and color tone formed was investigated. Here, [nZnO―
Table 4 shows the results regarding the amount of WO ₃ added to 1CoO]. The amount added in the table is for cobalt green consisting of 6.7 mol of ZnO and 1 mol of CoO.
This is the number of moles of WO ₃ added.

[Table] The minimum temperature at which the color tone changes in this table depends on the amount of additive added. 170℃ when 0.7,
When it is 56.0, it is 120℃. As can be seen from the formed phase and color tone, as the amount added decreased from 6.2 mol, the influence of cobalt green gradually became stronger, and as the amount increased, the influence of WO ₃ became more prominent. In other words, it is assumed that n = 6.2, where the generated phase is close to the ZnWO ₄ single phase, is suitable for a material exhibiting a blue color tone. On the other hand, [nZnO―
1CoO−0.5MgO], a similar trend was also observed. In this case, the optimal value is slightly shifted to 6.7.
Located near Mole. These quantities were reconfirmed through experiments conducted based on the results in Table 4, with the range of addition amounts narrowed further. This is the reason why n-0.5 or n is considered good. The reversible temperature indicating material according to the present invention uses a polycrystalline material made of the above-mentioned cobalt green to which a tungsten oxide compound, a molybdenum oxide compound, or a niobium oxide compound is added. The composition ratio of cobalt green is [nZnO-1CoO] system,
The system [nZnO-1CoO-(0.5-1.5)MgO] is also n
is 1.6 to 17. Additives are WO ₃ , H ₂ WO ₄ ,
There are five types: MoO ₃ , H ₂ MoO ₄ , and Nb ₂ O ₅ . The addition ratio is n-0.5 for [nZnO-1CoO],
In the case of [nZnO-1CoO-(0.5-1.5)MgO], it is n. These additive mixtures include WO ₃ , H ₂ WO ₄ ,
From 850℃ to 950℃ for Nb ₂ O ₅ , MoO ₃ ,
In the case of H ₂ MoO ₄ , calcination and firing were repeated at 650°C to 750°C. In the former case, when the firing temperature exceeded 950°C, there was a tendency for CoO to remain intact. Further, in the latter case, a part of the sintered body sometimes becomes a semi-molten state at temperatures above 750°C, and in that case, a uniform polycrystalline body cannot be obtained. The generated phase obtained by the above firing, its color tone, and the minimum change temperature are as shown in Table 3. The temperature dependence of the reflection spectrum of the produced substance will be described in the specific example below, but the basic component cobalt green (nZnO-1CoO)
The temperature dependence of the reflection spectrum of WO ₃ with n=6.7 as a representative example of the additive is shown in FIGS. 2 and 3, respectively. Next, the thermal stability and various properties of these products will be described. The products of the cobalt green tungsten monoxide compound system and the cobalt green-niobium oxide compound system were stable up to a minimum of 950°C. The cobalt green-molybdenum oxide compound system was stable up to at least 750°C.
These temperatures were determined from the results of repeated heating and cooling thermal cycle tests, X-ray diffraction, and measurements of the temperature dependence of the reflection spectrum. The product was almost insoluble in water and was not attacked by dilute acids or dilute alkalis. Furthermore, no signs of deterioration were observed even after long-term ultraviolet irradiation. Unlike conventional temperature-indicating materials, the reversible temperature-indicating material according to the present invention has stable properties, and therefore can be processed in various ways. For example, taking advantage of its thermal stability, it can be mixed and dispersed as is into porous glass, ceramics, asbestos plates, etc. and heated and processed, or it can be uniformly dispersed in glass frit and heat treated to form a film. Also good. It is also possible to mix and disperse it directly into cement materials, taking advantage of its chemical stability. In addition, it is also possible to form a coating film by uniformly dispersing it in a water-soluble glass coating agent or a ceramic dispersion coating agent and applying it to the surface of various temperature-measuring objects. Next, a specific example according to the present invention will be described. (1) Cobalt green...Synthesis of [nZnO-1CoO] and [nZnO-1CoO-(0.5-1.5)MgO] and measurement of temperature dependence of reflection spectra. All reagent grade ZnO, Co ₃ O ₄ , Mg(OH) ₂
Cobalt green n=1.6 to n=
Eight types of compounds up to 17 were synthesized by calcination. In this case, Co ₃ O ₄ has an atomic ratio of Co
Converted to CoO. Calcining temperature 850℃, firing temperature 950℃
The main firing was repeated twice to obtain a desired cobalt green compound. This was applied to a spectrophotometer to measure the temperature dependence of the reflection spectrum in the visible range (400 nm to 800 nm). As a representative example of the cobalt green mentioned above, [6.7ZnO]
1CoO] is shown in Figure 2. (2) Calcination of cobalt green and metal oxides and measurement of the reflection spectra of the products. Among the cobalt greens obtained by firing in the previous section, [6.7ZnO-1CoO] and [6.7ZnO-1CoO-
0.5MgO] and reagent grade WO ₃ , H ₂ WO ₄ ,
MoO ₃ , H ₂ MoO ₄ and Nb ₂ O ₅ were each weighed by weight as listed in Table 5 below. 1 sample 50g
It is. For convenience of description [6.7ZnO―1CoO]
CG, [6.7ZnO−1CoO−0.5MgO]
It is written as In addition, the amount of each specific metal oxide is
It has a composition ratio of 6.2 moles to CG and 6.7 moles to CG.

[Table] Among the above starting materials, H ₂ WO ₄ and H ₂ MoO ₄
Although it is a well-known fact that WO ₃ and MoO ₃ are released by releasing one water molecule at 100°C and 70°C, respectively, these are used as starting materials for experiments and descriptions. Next, the manufacturing process will be explained according to the process diagram shown in FIG. First, each sample mixture was thoroughly ground in an automatic mortar and then uniformly mixed in a ball mill for 12 hours. Then, it was transferred to a porcelain crucible and heated to Table 6 in a Matsufuru furnace.
Heat treatment was carried out under the conditions shown below. After each sample is calcined, it is crushed in an automatic mortar and fired.

Moved to [Table]. After firing, it was slowly cooled to 400°C and left to cool to room temperature. Then, regarding the obtained powder
The formed phase was confirmed by line diffraction. The produced phases of Samples 1 and 2, 3 and 4, 5 and 6, and 7 and 8 are the same. Regarding CG, the products shown in Table 3 were confirmed, but CG contained an extremely small amount of a product presumed to be MgCo ₂ O ₄ on the edge of the detection limit. The obtained powder was adjusted to have a particle size in the range of 25 μm to 37 μm, and then subjected to a spectrophotometer to measure the temperature dependence of the reflection spectrum. Temperature is room temperature and 70℃ from 70℃ to 350℃
There are a total of 6 points at intervals of ℃. Table 3 shows the color tone of the product due to the addition of the above additives and the changes upon temperature rise.
As outlined in . As a representative example, the measurement results for Sample 1 in Table 5 are shown in FIG. Second
Comparison with Figure 3 and Figure 3 shows that these are different materials that exhibit clearly different reflections. In Figure 4, the reflectance overall shifts toward longer wavelengths as the temperature rises, and at the same time becomes broader, but if you look closely, the peak around 470 nm decreases, and the reflectance from 620 nm to 720 nm decreases. The rise of is shifted to the long wavelength side. There is a strong possibility that the small peak near 530 nm is related to reflection of WO ₃ for some reason. Visually, it changed from a beautiful sky blue to gray at about 150 degrees Celsius. In addition, during the measurement, we repeatedly considered the thermal followability of reflection, the presence or absence of thermal history, etc., and the results were satisfactory. Next, Samples 1, 3, 5, 7, 9, and 10 in Table 5 were processed to have grain sizes of 37 μm or less as described below. (1) First, each sample was added to 25% by weight glass frit (particle size: approximately 6 μm) and mixed thoroughly to obtain a pale blue mixed fine powder. Ethanol was appropriately added to this and kneaded to form a paste. This was applied uniformly to ordinary glass, unglazed ceramic plates, and asbestos plates using a sepature. After air drying or heat treatment, baking was performed at 480°C for 3 hours to form a porous film with a thickness of about 80 μm. The surface condition and color tone can be controlled to some extent by adjusting the baking temperature and the mixing ratio of glass frit. The change in hue of these films is basically the same as that of powder. (2) Next, a small amount of a water-soluble glass coating agent containing an SiO ₂ component was added to each of the above powder samples and thoroughly kneaded to form a paste. This was applied to a glass substrate, an aluminum plate, a polyimide film, an unglazed ceramic plate, and an asbestos plate, which had been previously subjected to a satin finish. This operation was performed using a spatula, glass rod, etc.
The roll method is suitable for mass production. This was heated at 150℃ for 1 hour and the thickness was 60μm.
A hard film of 80 μm was formed. The film is resistant to heat shock and mechanical peeling forces, and has excellent durability. In a long-term thermal cycle test of the film formed by this processing method, the inherent discoloration and temperature characteristics of the material were not influenced, reduced, or deteriorated. (3) Using a ceramic dispersion coating agent, each of the powder samples described above was formed into a film on the substrate described in the previous section. This coating agent is made by adding and dispersing fine powders of ZrO ₂ and Al ₂ O ₃ to the water-soluble glass coating agent described above. The methods of kneading, coating and drying are exactly the same as those described above. The resulting film (approximately 80 μm thick) is hard and highly heat resistant. In this case, the film contains ZrO ₂ and Al ₂ O ₃ and therefore has a white color, and although the contrast is somewhat weak at room temperature, it is clearly visible as a pale blue color. When the temperature rises, the color inherent to the material is gray, but the film becomes almost white. Although the thermal cycle of heating and cooling was repeated many times in these cases, there was no sign of deterioration in the color change and temperature indicating function. Incidentally, the temperature indicating material may be directly mixed into the substrate by mixing and dispersing a base material such as porous glass, ceramic, asbestos, cement, or plastic, or by press molding. The embodiments of the reversible temperature indicating material according to the present invention described above have the characteristics summarized below. (1) Matters related to color change temperature characteristics. (a) The visual color tone of this type of substance changes reversibly from blue to gray at approximately 150°C. (b) Has no thermal history, good temperature followability, and sufficient repeated life. (2) Matters regarding stability, safety and production benefits. (a) Virtually insoluble in water and not attacked by dilute acids and dilute alkalis. It does not deteriorate even when exposed to ultraviolet light. (b) The system with the addition of tungsten oxide compounds and niobium oxide compounds is stable up to 950°C, and the system with the addition of molybdenum oxide compounds is stable up to 750°C. (c) Does not contain substances harmful to the human body. (d) The materials are relatively inexpensive and the manufacturing method is simple. (3) Matters regarding the diversity of processing based on the stability of this system of substances. (a) It is stable and insoluble in water and organic solvents, so it can be dispersed in various solvents. (b) Since it does not change or deteriorate due to ultraviolet rays, it can be applied to outdoor objects. (c) It is stable up to relatively high temperatures, so processing that involves heating is possible. <Effects of the Invention> According to the present invention described above, a reversible temperature indicating material that is chemically stable and can be used in a wide range of applications can be obtained.

[Brief explanation of drawings]

FIG. 1 is a process diagram of the manufacturing process of one embodiment of the reversible temperature indicating material according to the present invention, and FIGS. 2 to 4 are graphs of the temperature dependence of the reflection spectrum of substances related to the reversible temperature indicating material measured by a spectrophotometer. It is a diagram.

Claims (1)

[Scope of Claims] 1. A compound represented by [nZnO-1CoO] or a compound represented by [nZnO-1CoO-(0.5-1.5)MgO] (where n is 1.6-17 and represents a molar ratio)
WO ₃ , H ₂ WO ₄ , MoO ₃ , H ₂ MoO ₄ , in a ratio of n mol (n-0.5) to the above compound, respectively.
It is composed of a zinc cobalt oxide-zinc metal oxide system polycrystal obtained by heat treating a composition mixture to which a metal oxide consisting of any one of Nb ₂ O ₅ is added. Characteristic reversible temperature indicating material. 2 The metal oxide is WO ₃ , H ₂ WO ₃ , or
When Nb ₂ O ₅ is below 950℃, MoO ₃ or
2. The reversible temperature indicating material according to claim 1, which is a substance obtained by heat-treating H ₂ MoO ₄ at 750° C. or lower. 3. The reversible temperature indicating material according to claim 1, wherein the polycrystalline material is dispersed and mixed in a water-soluble glass coating agent, a ceramic dispersion coating agent, or a glass frit.