JP3159258B2 - How to store temperature history information - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method of storing ambient temperature history information.

[0002]

2. Description of the Related Art Conventionally, in the case of storing history information of the ambient temperature, a temperature indicating material using a dye or the like that changes color when the temperature exceeds a specific temperature, or a combination of various temperature sensors and a storage device is used. It is used.

[0003] Temperature history information is very important information in storage, distribution, and use of various products and parts. In other words, the state of products and parts can be determined from the temperature history information, and quality assurance and failure cause clarification can be efficiently performed.

[0004] However, in the case of storing the temperature history information due to the discoloration of the conventional temperature indicating material, it is only possible to store whether or not the temperature has reached a specific temperature. That is, time information indicating how much time has elapsed at a specific temperature cannot be recorded. In addition, the temperature indicating material is ultraviolet rays,
Since it is susceptible to electromagnetic waves, humidity and the like other than the external temperature, there is a problem in reliability. Furthermore, the temperature indicating material cannot cope with a low temperature of 0 ° C. or lower or a high temperature of 200 ° C. or higher. Even if it can cope, there is a drawback that the characteristics are degraded or decomposed in minutes or seconds. Note that a temperature indicating material cannot be used for the purpose of giving confidentiality to temperature history information.

On the other hand, when various temperature sensors and a storage device are combined, it is possible to store a wide variety of temperature histories, but it is necessary to supply power to this system, and a space for accommodating the system is secured. There are problems such as the necessity of performing such operations, and the method can be applied only to very limited uses.

Japanese Unexamined Patent Publication No. Hei 3-170036 discloses a method for obtaining information on the temperature history of a certain object. In the method, an irreversible transformation is performed at a high temperature to change the magnetic properties of a ferrite-containing mixed grain stainless steel. Disclosed is a method comprising pre-combining the object with a temperature history indicator that is a piece, developing a temperature history, measuring the magnetic properties of the piece, and estimating the information from changes in the magnetic properties. Have been.

However, according to this method, when the ferrite, which is a ferromagnetic material, is exposed to a high temperature of 400 to 700 ° C., the ferrite is transformed into a non-ferromagnetic carbide, an intermediate metal phase, and austenite, whereby its magnetic properties are increased. Changes are required, and high-temperature conditions are required to cause transformation.

[0008]

SUMMARY OF THE INVENTION As described above, a temperature that is compatible with a wide temperature range, has confidentiality, is hardly affected by external environments other than temperature, and is stable, efficient and has excellent reproducibility. Developing a method of storing the history information has been a major issue.

It is an object of the present invention to provide an efficient and simple method of storing temperature history information.

[0010]

According to the present invention, there is provided a method of storing temperature history information, wherein the history of changes in ambient temperature is stored by irreversible demagnetization due to a change in the magnetic domain structure of a magnetic material. About.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The term "irreversible demagnetization" as defined in the present invention refers to a phenomenon in which the magnetic flux density or magnetization of a magnet material, particularly the residual magnetic flux density or residual magnetization, changes with temperature. Only the magnetic domain structure changes due to temperature changes while maintaining the composition and form, and the magnetic flux that restores the magnetic domain structure is not applied even when the temperature returns to the original temperature. This is a phenomenon that does not return to the state, and the ambient temperature is stored as the amount of change in the residual magnetic flux density or residual magnetization due to the irreversible demagnetization.

In the method described in Japanese Patent Application Laid-Open No. 3-170036, the fact that the magnetic properties change due to the transformation of a material under high temperature conditions is used as the information storage means of the temperature history. Since only the magnetic domain structure changes due to temperature change while maintaining the composition and form, even if the temperature returns to the original temperature, the change in the magnetic domain structure does not return to the original irreversible demagnetization is used as the information storage means of the temperature history, It can be used in a wide temperature range, especially in a temperature range much lower than that of the above-mentioned publication, and can be applied to a wide range of applications, for example, acquisition of temperature history information which is a guide for reusing OA equipment such as a personal computer. Becomes possible.

In the method of the present invention, when the temperature history is complicated or when the history information is grasped in more detail, a temperature indicating material capable of displaying the highest or lowest attained temperature by discoloration can be used together. It is. For example, when the degree of irreversible demagnetization due to a short history at a high temperature and a long history at a low temperature, that is, the amount of change in the residual magnetic flux density or residual magnetization is about the same, both are used by using a temperature indicating material. Can be distinguished.

In the present invention, the amount of change in the residual magnetic flux density or residual magnetization per unit temperature, that is, the sensitivity can be adjusted depending on the shape of the magnetic material used. In other words, when it is desired to set a large amount of change, it is preferable that the distance between the magnetic poles (N, S) is short, that is, the shape is such that the demagnetizing factor N is large.

The magnetic material for storing temperature history information used in the present invention is a ferromagnetic material and a hard material having a coercive force of 10 A / m or more. Since the amount of change in the residual magnetic flux density or residual magnetization depending on the temperature differs depending on the material, it is preferable to use an optimal material as appropriate depending on the temperature range to be used and the required determination accuracy. Also, by combining different materials, history information over a wide temperature range can be stored.

As such a material, particularly, 200 ° C.
In the above, the alloy magnet containing samarium and cobalt is 0 ° C.
Above 200 ° C., alloy magnets containing neodymium, iron, and boron are preferable as materials for storing temperature history information, and below 0 ° C., barium ferrite magnets or strontium ferrite magnets are preferable. The upper limit of the temperature range is not particularly defined, but in the present invention, irreversible demagnetization due to a change in the magnetic domain structure without transformation is used as storage means of temperature history information. Up to.

In addition, since the magnetic properties of the magnetic material can be measured in a state of non-contact and coated with the non-magnetic material, the whole or a part of the magnetic material is coated with the non-magnetic material. Thus, the present invention can be applied to a use in which the information is to be kept secret from a third party. Further, since it is not necessary to supply electric power to the magnetic body, the size can be reduced.

[0018]

Embodiments of the present invention will be described below.
The present invention is not limited to the embodiments described below. In the examples, the ratio of the change amount of the absolute value of the magnetic field strength before and after the processing to the absolute value of the magnetic field strength before the processing is defined as the change rate of the magnetic field strength.

Examples 1 to 6 In Example 1, a cylindrical samarium-cobalt magnet (trade name “REC-32A” (trade name)) having a diameter of 5 mm and a height of 5 mm was used. The magnet was heated in a heating furnace at 200 ° C. for 5 hours, and then kept at room temperature for 7 days. Then, it was similarly heated at 200 ° C. for 5 hours. After keeping at room temperature for further 7 days, it was similarly heated at 200 ° C. for 10 hours. At this time, after each heating step, the magnet was left at room temperature for 1 hour, and the magnetic field strength at the bottom surface of the magnet was measured using a Hall element type magnetic field sensor. Note that the measured magnetic field strength is a physical quantity corresponding to the residual magnetic flux density of the magnet. Further, the ratio of the change amount of the magnetic field strength before and after the heating to the magnetic field strength before the heating was defined as the change rate of the magnetic field strength. The variation width of the rate of change caused by the magnetic field sensor is about ± 0.1%.

In the second embodiment, a cylindrical neodymium / iron / boron magnet having a diameter of 5 mm and a height of 5 mm ("NEO" manufactured by TDK)
REC-50 "(trade name)). The magnet was heated in a heating furnace at 60 ° C. for 5 hours, and then kept at room temperature for 7 days. Then, it was similarly heated at 60 ° C. for 5 hours. After keeping at room temperature for further 7 days, it was similarly heated at 60 ° C. for 10 hours. At this time, after each heating step, the magnet was left at room temperature for 1 hour, and the magnetic field strength at the bottom surface of the magnet was measured using a Hall element type magnetic field sensor.

In the third embodiment, a columnar strontium / ferrite-based magnet having a diameter of 5 mm and a height of 5 mm ("FDK" manufactured by TDK)
B6N "(trade name)). This magnet in a thermostat
After cooling at 20 ° C. for 5 hours, it was kept at room temperature for 7 days. Subsequently, it cooled similarly at -20 degreeC for 5 hours. After keeping at room temperature for further 7 days, it was similarly cooled at -20 ° C for 5 hours. At this time, after each heating step, the magnet was left at room temperature for 1 hour, and the magnetic field strength at the bottom surface of the magnet was measured using a Hall element type magnetic field sensor.

In Example 4, a magnet having the same shape and material as in Example 3 was used. The magnet was heated in a heating furnace at 200 ° C. for 5 hours, and then kept at room temperature for 7 days. Then, similarly,
Heat at 00 ° C. for 5 hours. After keeping at room temperature for further 7 days, it was similarly heated at 200 ° C. for 10 hours. At this time, after each heating step, the magnet was left at room temperature for 1 hour, and the magnetic field strength at the bottom surface of the magnet was measured using a Hall element type magnetic field sensor.

In Example 5, a magnet having the same shape and material as in Example 3 was used. The magnet was heated in a heating furnace at 60 ° C. for 5 hours, and then kept at room temperature for 7 days. Then, as well as 60
Heated at ° C. for 5 hours. After keeping at room temperature for further 7 days, it was similarly heated at 60 ° C. for 10 hours. At this time, after each heating step, the magnet was left at room temperature for 1 hour, and the magnetic field intensity at the bottom surface of the magnet was measured using a Hall element type magnetic field sensor.

FIG. 1 shows the change in the rate of change of the magnetic field strength with respect to the total processing time in Examples 3 to 5. From this figure, it can be seen that the strontium ferrite magnet has a low temperature,
It can be seen that the sensitivity is high for temperatures lower than ℃.

In Example 6, a magnet having the same shape and material as in Example 1 was used. The magnet was cooled in a thermostat at -20 ° C for 5 hours, and then kept at room temperature for 7 days. Then, similarly-
Cooled at 20 ° C. for 5 hours. After keeping at room temperature for further 7 days, it was similarly cooled at -20 ° C for 5 hours. At this time, after each heating step, the magnet was left at room temperature for 1 hour, and the magnetic field strength at the bottom surface of the magnet was measured using a Hall element type magnetic field sensor.

The shape of the magnet may be other than a cylinder.
Any shape, such as a rectangular parallelepiped shape, a donut shape, or a thin film shape, can be applied as long as a change in magnetic properties can be measured. In Examples 1 to 6, various magnets, which are ferromagnetic and hard materials, were used as the magnetic material, but other magnetic materials can also be used in the present invention.

As the magnetic properties to be measured, the rate of change of the magnetic field strength, which is a physical quantity corresponding to the residual magnetic flux density, is measured, but the change of the residual magnetization may be measured.
In addition, other magnetic characteristics such as magnetic permeability and coercive force may be used in combination. The accuracy can be improved by using a plurality of these physical quantities.

Tables 1 and 2 show the results of the above examples.

[0029]

[Table 1] Note) *: Time of heating or cooling

[0030]

[Table 2] Note) *: Time of heating or cooling

As is clear from Table 1, it can be seen that the magnetic field strength of the magnet changes when the temperature history is given to the magnet. That is, by using a magnetic material, temperature history information can be stored as the amount of change in magnetic field strength. In Examples 1 to 6, after all the heating steps were completed,
After a lapse of one month, the magnetic field strength was measured, and showed the same value as the magnetic field strength measured after the completion of the entire heating step.

Comparative Example 1 Temperature indicating material ("LI-200" (trade name) manufactured by NOF Engineering Co., Ltd.)
Was heated in a heating furnace at 200 ° C. for 5 hours, and then kept at room temperature for 7 days. Then, it was heated at 200 ° C. for 5 hours. However, the temperature indicating material decomposed during the first 5 hours of heating. When the heating time was 3 minutes, the temperature indicating material changed from light yellow to black, but remained black until the temperature indicating material was decomposed.

Comparative Example 2 A temperature indicating material ("LI-60" (trade name) manufactured by NOF Engineering Co., Ltd.) was heated in a heating furnace at 60 ° C. for 5 hours, and then kept at room temperature for 7 days. Subsequently, it heated at 60 degreeC for 5 hours. At this time, the temperature indicating material changed from white to green by the first heating for 5 hours.
The remaining 5 hours of heating remained black and did not change.

As described above, in Comparative Examples 1 and 2, it can be determined that the temperature has reached the predetermined temperature, but no information can be obtained on the time. On the other hand, in the first to sixth embodiments, the total time of exposure to the predetermined temperature, that is, the temperature history information can be stored.

[0035]

According to the present invention, it is possible to cope with a wide temperature range,
Efficient and simple storage of temperature history information becomes possible.

[Brief description of the drawings]

FIG. 1 is a graph showing a change in a change rate of a magnetic field intensity with respect to a total of processing times in Examples 3 to 5.

Claims (15)

(57) [Claims] 1. A method for storing temperature history information, wherein a history of ambient temperature changes is stored by irreversible demagnetization due to a change in the magnetic domain structure of the magnetic body. 2. The method according to claim 1, wherein the magnetic material is a ferromagnetic material and has a coercive force of 10.
2. The method of storing temperature history information according to claim 1, wherein the material is a hard material of A / m or more. 3. The method according to claim 1, wherein the irreversible demagnetization is a physical quantity due to a change in magnetic flux density or magnetization. 4. The method according to claim 3, wherein the magnetic flux density is a residual magnetic flux density. 5. The method according to claim 3, wherein the magnetization is a residual magnetization. 6. The method for storing temperature history information according to claim 1, wherein the ambient temperature is 200 ° C. or higher. 7. The method according to claim 1, wherein the magnetic material is an alloy magnet containing samarium and cobalt. 8. The method according to claim 1, wherein said ambient temperature is not lower than 0 ° C. and lower than 200 ° C.
Storage method of temperature history information described in section. 9. The magnetic material according to claim 1, wherein the magnetic material is an alloy magnet containing neodymium, iron, and boron.
9. The method of storing temperature history information according to any one of items 8 to 8. 10. The method according to claim 1, wherein the ambient temperature is lower than 0 ° C. 11. The temperature history information according to claim 1, wherein the magnetic material is a barium ferrite magnet or a strontium ferrite magnet. Memory method. 12. The temperature history information according to claim 1, wherein sensitivity of irreversible demagnetization is adjusted by controlling a demagnetizing factor of the magnetic material. Memory method. 13. The temperature history information according to claim 1, wherein the magnetic material is entirely or partially coated with a nonmagnetic material. Memory method. 14. The method of storing temperature history information according to claim 1, wherein a temperature indicating material capable of displaying the highest or lowest attainable temperature by discoloration is used in combination. 15. The method of storing temperature history information according to claim 1, wherein the history is a total time of exposure to a specific temperature.