JP2897039B2 - Infrared detector - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an infrared detecting element for detecting an amount of infrared rays by a change in electric resistance according to the temperature of infrared irradiation, and more particularly to an infrared detecting element from a relatively low temperature infrared source emitted from a human body or the like. The present invention relates to a detection element having an excellent infrared detection ability.

[Prior Art] Conventionally, as infrared detecting elements, those using a pyroelectric element utilizing a pyroelectric effect, a thermopile in which thermocouples are integrated, and the like are well known.

However, these infrared detecting elements have drawbacks in response time in applications where a high response speed is required, and inevitably limit the position detection of the infrared source to be detected.
In addition, these arrangements are disadvantageous in terms of price.

The present inventors have previously proposed an infrared detecting element using a semiconductor fiber whose electric resistance changes with temperature (Japanese Utility Model Application No. 63-22).
No. 2506), and an infrared detecting element (Japanese Patent Application No. 1-131435) in which the above-mentioned response is remarkably improved by using a fiber monofilament mainly containing silicon carbide having a specific resistance value and / or a composition specified as the semiconductor fiber. No. 1) and a high-sensitivity infrared detecting element (Japanese Patent Application No. 1-2232888) constituted by a fiber monofilament obtained by heat-treating a carbon fiber precursor and having a specific resistivity and a thermistor constant. Was.

The infrared detecting elements proposed by the inventors have the above-mentioned characteristics, are preferable ones which can solve the disadvantages of the conventional infrared detecting elements, and have achieved great results.

[Problems to be solved by the invention]

However, when such an infrared detecting element is used for detecting infrared rays from a low-temperature (high-wavelength) infrared ray source such as a human body, it is desired to further improve the response speed and sensitivity thereof. .

In general, floors in rooms such as buildings under normal temperature atmosphere,
The surface temperature of walls and ceilings is about 15 ° C,
The surface temperature of the human body is about 20-23 ° C.

Infrared detectors are used as passive detectors, and detectors that check for unexpected intruders, that is, when applied to crime prevention, etc., the above human body temperature, 20-23 ° C (infrared peak wavelength 9.8-9.9 μm) It is desirable to use an infrared detecting element having an excellent detection ability to detect the object clearly and accurately.

It is an object of the present invention to provide a high-sensitivity, low-thermal-time-constant infrared detecting element which is excellent in the ability to detect infrared light of a limited wavelength using the above-mentioned human body as a source.

[Means for solving the problem]

The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, in the detection of infrared light having an infrared peak wavelength of about 9.8 to 9.9 μm, in particular, variations in the type of semiconductor fiber, fiber diameter, and the like affect their detection capabilities. The inventors have found that this is a very important factor and completed the present invention.

The present invention provides a polyacrylonitrile spun fiber filaments obtained by heat treatment after the infusibilized, specific resistance at room temperature is 10 ⁰ ~10 ⁴ Ω · cm, more preferably 10 ² ~10 ⁴ Ω · cm fiber filaments An infrared detecting element in which a fiber monofilament having an average diameter of 7 to 9 μm and a variation of the average diameter in the range of the average diameter ± 1 μm is arranged between the electrodes.

The polyacrylrotrile used in the present invention is spun by a wet spinning method and stretched, whereby variation in the diameter of the fiber filament can be suppressed to a low level.
Further, in the infusible step, when heating under tension by applying tension, the above-mentioned variation in the diameter of the fiber filament was maintained at a low level, the orientation of the carbon atoms was aligned, and limited in the next heat treatment (firing) step. Fiber filaments having variations in specific resistance and diameter can be obtained relatively easily.

Therefore, in the infrared detecting element of the present invention, it is preferable to employ a spun fiber filament of polyacrylonitrile.

Also, spin polyacrylonitrile as described above,
For example, when a fiber filament having an average diameter of 12 to 15 μm and a dispersion of ± 0.8 μm is obtained, it is infused under the following conditions and then heat-treated (fired) to obtain an average diameter of 7 to 9 μm.
A fiber filament having a variation of ± 1 μm can be obtained.

Thus, the fiber filament having the above-mentioned average diameter and variation has good heat dissipation, and is preferable as the infrared detecting element of the present invention. When the polyacrylonitrile spun fiber filament is made infusible, the temperature is raised to 10 to 50 ° C./hr at a temperature of 300 to 350 ° C. under an oxidizing atmosphere (usually air may be used) under a tension of 1.2 to 1.3 under a tension.
It is better to do within the range. If the rate of temperature rise in the infusibilization treatment exceeds 50 ° C./hr or the infusibilization temperature is less than 300 ° C., carbonization while maintaining the fiber shape is impossible, which is not preferable.

In addition, the temperature rise temperature is less than 10 ° C / hr, or the
If the temperature exceeds 50 ° C., it is not preferable because the fibers become brittle. The infusibilized fiber filament is then heat-treated under an inert gas atmosphere such as N ₂ or Ar gas or in a vacuum or under tension.

The heat treatment condition is to raise the temperature at a rate of 5 to 200 ° C / hr, 600 to 8
The reaction is carried out up to a temperature of 00 ° C., but it is more preferable to maintain the temperature at the above temperature for 30 to 60 minutes as needed.

The change in the electric resistance value in this temperature range is rapid, and strict temperature-time control is necessary to obtain an appropriate resistance value.

That is, if the heat treatment temperature is less than the lower limit or the holding time is less than the lower limit, the heat treatment is insufficient and the electrical resistivity is too high to exceed 10 ⁴ Ωcm, which is suitable as the infrared detecting element of the present invention. In addition, the thermal time constant becomes too large, and there is no merit as compared with the conventional pyroelectric element or thermopile.

Also, or the heat treatment temperature exceeds the upper limit, if the retention time exceeds the upper limit, the heat treatment becomes excessive, too electric specific resistance is low, 10 ⁰ Ω · cm less than the result output voltage change small, and the infrared receiver Although infrared rays emitted from a blackbody furnace with a large amount of energy can be detected, infrared rays emitted from a human body or the like cannot be sufficiently detected and cannot be used for the infrared detecting element of the present invention.

In addition, the average diameter and variation of the fiber filaments are 7
The reason why the diameter is limited to ９9 ± 1 μm is that in order to keep the variation of the fiber diameter within the range of ± 1 μm outside the range of the average diameter, it is very difficult to control each condition from spinning to firing. Further, when the variation range exceeds ± 1 μm, the variation of the electric resistivity of each fiber filament becomes large, and as a result, the thermal time constant becomes large, the noise is further amplified, and the SN ratio (signal / noise) becomes poor. The infrared peak wavelength of 9.8 to 9.9 μm which is the object of the present invention
The reason for this is that the detection capability cannot be sufficiently exhibited.

Next, regarding the arrangement of the fiber monofilaments, if the filaments are in contact with or intertwined with each other, the infrared ray receiving area is reduced and the heat radiation is deteriorated, and the fiber monofilaments are arranged without contacting each other because they cause noise. Is more preferred.

 A specific example of such an arrangement is shown in the figure.

FIG. 1 (a) is a view in which a monofilament (F) is stretched between electrodes (A) and (A), and the arrangement is as shown in (1) and (2) of FIG. 1 (b). Those which avoid mutual contact are more preferred.

FIG. 2 shows an example in which monofilaments (F) are similarly crossed and stretched between electrodes (A) and (A) and between electrodes (B) and (B).

In this case, similarly, the combination of (1) (4) and (2) (3) in FIG. 6B, and further (1) (2) and (3)
The combination of (4) may be performed.

[Action]

In the present invention, polyacrylonitrile spun fiber filaments are made infusible and heat-treated, and by using fiber filaments having limited specific resistance and variation in diameter, the detection ability at an infrared peak wavelength of 9.8 to 9.9 μm is improved. It exhibits particularly excellent infrared detection characteristics.

This detection element is most suitable for detecting infrared rays generated from a human body or the like, and can be suitably used for a passive detector for crime prevention or the like.

〔Example〕

 Hereinafter, the present invention will be described specifically with reference to examples.

Examples 1 to 3 Polyacrylonitrile was wet-spun and stretched in a glycerin bath at 150 ° C. to have an average diameter of 13 μm, variation, and maximum diameter.
A spun fiber filament having a minimum diameter of 0.7 μm was obtained. This was heated to 30 ° C./hr, 300 ° C. in air under tension of a draw ratio of 1.3 to make it infusible. Next, heat treatment was performed in an N ₂ gas atmosphere under the conditions shown in Table 1 to obtain fiber filaments having specific resistance values, fiber diameters and variations shown in the same table. Each of the 200 obtained fiber filaments was arranged approximately in parallel between the electrodes at intervals of 2.5 mm.
Then, using a black body furnace at 600 ゜ K and a human body (surface temperature of 23 ° C) as an infrared source, the device to which a DC voltage of 8V was applied was intermittently irradiated with infrared rays using a camera shutter (opening / closing speed: 290μsec). The waveform of the output voltage change due to the change in the electrical resistance of the fiber filament was detected and recorded by a storage scope and an XY plotter to determine the thermal time constant and the output voltage change.

The thermal time constant was the time required to reach 63% of the saturation output value.

 The results are shown in the same table.

Comparative Examples 1 to 3 Infusible fiber filaments were heat-treated in an N ₂ gas atmosphere under the conditions shown in Table 1 in the same manner as in Example 1 to obtain fiber filaments having the specific resistance, fiber diameter and variation shown in the table.
The thermal time constant and the output voltage change were determined by the same method as in Example 1 and the results are shown in the same table.

Comparative Example 4 Specific resistance value of 2.5 × 1 obtained by infusifying and heat-treating coal pitch
0 ³ Ω · cm average fiber diameter 7.1 [mu] m, the variation (maximum diameter - minimum diameter): about fiber filaments of 2.2 .mu.m, the thermal time constant in the same manner as in Example 1 to obtain output voltage variations. As a result, the thermal time constant of the black body furnace was 55 msec and the output voltage change was 16 mV, but it could not be detected by the human body.

According to the results shown in Table 1 above, in particular, it is clear that the product of the example, that is, the present invention, is remarkably excellent in the thermal time constant, that is, the response speed, and the output voltage change is remarkably high as compared with the comparative example.

〔The invention's effect〕

As is clear from the above description and the results of the examples, the infrared detecting element of the present invention has remarkably excellent characteristics with respect to a low-temperature infrared source, particularly, a response speed and a change in output voltage, and can meet the demand for the above-described crime prevention purpose. Things,
Its industrial utilization effect is remarkably large.

[Brief description of the drawings]

FIG. 1 and FIG. 2 are schematic explanatory views of the arrangement of filaments in the embodiment of the present invention, and FIG. 3 is a graph showing the state of infrared detection in the embodiment of the present invention. A, B: electrodes, F: filaments.

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Norio Muto 1-5-18 Miyashita Honmachi, Sagamihara City, Kanagawa Prefecture (72) Inventor Teijiro Kajiwara 1-6-6 Moto-Akasaka, Minato-ku, Tokyo Inside Sogo Security Service Co., Ltd. (72) Inventor Norihisa Mori 1-6-6 Moto-Akasaka, Minato-ku, Tokyo Sogo Security Service Co., Ltd. (72) Inventor Hiroshi Ichikawa 2-5-16 Shodo, Sakae-ku, Yokohama-shi, Kanagawa Prefecture (72) Inventor Hirofumi Harada 1-16-26 Tsudaido Taiheidai, Fujisawa City, Kanagawa Prefecture (56) References JP-A-3-96824 (JP, A) JP-A-2-310430 (JP, A) JP-A-2-71121 (JP, A) JP-A-63-116312 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G01J 1/02

Claims (1)

(57) [Claims] 1. A polyacrylonitrile spun fiber filaments obtained by heat treatment after the infusibilized, specific resistance at room temperature is 10 ⁰ ~10 ⁴ Ω · cm, the fiber filaments an average diameter 7~9μm and the average diameter, An infrared detecting element comprising a fiber monofilament having a variation in the average diameter ± 1 μm, which is arranged between electrodes.