JPH0224463B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a fiber-type dew condensation sensing element for attachment between electrodes, which is comprised of a hygroscopic fiber having conductive particles substantially uniformly supported on its surface.

In recent years, as interest in temperature and humidity control has increased, demand for humidity sensing elements has increased. For example, if the interior walls of a house are exposed to high humidity for a long period of time, mold and cracks will form, significantly reducing their durability. High humidity (90-100% RH), especially in places with relatively high humidity such as baths and closets.
Temperature control at the bottom is required. Also, while water is essential when growing plants in greenhouses, leaving plants under high humidity conditions of nearly 100% for long periods of time will hinder plant growth. In addition, it is necessary to distinguish whether it is raining or not, whether there is dew on the dryer or not, whether the windows of buildings and vehicles are fogged or not, and whether there is frost on tea fields or the like. Determining the humidity is a typical example of humidity under high humidity conditions.

Many switching elements (condensation detection elements) are being developed for the purpose of humidity control under such high humidity conditions, but there are very few that are inexpensive, sensitive, and durable.

A resin dispersion type dew condensation detector is known so far. It consists of a mixed moisture-sensitive membrane of a hygroscopic polymeric resin and a conductive powder material.
Since this mixed moisture-sensitive membrane is hygroscopic, when the environmental humidity increases, the amount of moisture absorbed increases, the volume expands, and the contact between the conductive powders dispersed in the moisture-sensitive membrane is broken. The volume change of this mixed moisture-sensitive film is detected as a resistance value change by the electrode substrate. Such a resin dispersion type dew condensation sensing element has a so-called switching characteristic in which the resistance value increases as the relative humidity increases, and the resistance value sharply increases at high humidity.

However, since the resistance value of such a moisture-sensitive film changes due to a change in volume due to the amount of moisture absorbed by the entire film, it is difficult to accurately detect changes in humidity on the film surface. That is, the moisture absorption rate and dehydration rate of the entire moisture sensitive membrane determine its response speed. In addition, in creating this resin dispersion type dew condensation sensing element, we strictly control the types of conductive powder and resin, the uniform dispersion of the resin, conductive powder, and solvent, and the coating and baking conditions of the moisture-sensitive film on the electrode substrate. There must be. For example, a moisture-sensitive film with a non-uniform dispersion state lacks reliability in moisture-sensing properties and cannot provide switching properties.

In order to solve this problem, it is necessary to use a moisture-sensitive membrane that is as thin as possible, has mechanical strength, has a high rate of moisture absorption and dehydration, and has a stable chemical structure. Furthermore, in order to uniformly disperse the conductive powder in the resin, the affinity between the conductive powder and the resin must be maximized. Furthermore, the moisture sensitive membrane must have excellent weather resistance.

As a result of extensive research, the present inventors have discovered that a moisture-sensitive element with excellent mechanical strength, reactivity, and weather resistance can be produced by adhering, adsorbing, or adsorbing conductive particles onto the surface of hygroscopic fibers. The present invention has been completed.

An object of the present invention is to provide a dew condensation sensing element that has excellent reactivity, weather resistance, and mechanical strength, and that can be easily manufactured.

That is, the dew condensation sensing element of the present invention is composed of a hygroscopic fiber whose surface is substantially uniformly supported with conductive particles having a particle size of 5000 Å or less, for use by being attached between electrodes. It is characterized by

In the present invention, the conductive particles have a particle size of 5000
Conductive particles made of carbon fine particles with a size of Å or less are used. These particles may also contain other impurities in amounts that do not significantly affect conductivity. For example, ink particles containing glue and other trace impurities can be used as conductive particles. The particles used usually have a particle size in the range of 30 to 5000 Å, preferably in the range of 100 to 1000 Å.

The hygroscopic fibers may be natural, semi-synthetic or synthetic fibers, but those having a moisture absorption of at least 1%, preferably 5% or more at 20° C. and 95% relative humidity are used. Examples of these include almost all natural cellulose fibers such as cotton, hemp, silk, wool, and rayon; semi-synthetic cellulose fibers such as cellulose nitrate, cellulose acetate, and triacetate; polyamide (nylon) acrylic, polyvinyl alcohol (vinylon), etc. Examples include synthetic fibers. In particular, nylon is preferred because the length and thickness of the fibers can be freely changed, and it is resistant to insects and mold and is durable.

The conductive particles can be placed directly on the hygroscopic fibers or with an adsorbent,
It can be supported using an adhesive or the like. As adsorbent or adhesive, customary adhesives can be used. However, it is preferred if the adsorbent or adhesive itself is hygroscopic, since it will shrink or expand like the hygroscopic fibers to which it is applied. Examples of the hygroscopic adsorption (or adhesive) agent include glue (gelatin) and melamine resin. The manner in which the conductive particles are supported on the hygroscopic fibers may be any manner, such as adhesion, adsorption, or sorption, as long as the particles are retained on the surface of the fibers.

The amount of conductive particles applied to the surface of the hygroscopic fibers varies depending on the conductive particles used and the form of the element constructed from the fibers (e.g. paper, filament, etc.), but is usually 10 ^-5 to ^{10 -2} mg. /mm ² , preferably
10 ^-5 to 10 ^-3 mg/mm ² . If the amount of conductive particles applied is outside the above range, the sensitivity, that is, the rate of change in resistance value will decrease.

The sensing element of the present invention may be a single fiber carrying conductive particles, or a thread made of the fiber. However, a thread-like material in which single fibers are aligned in the same direction is preferred from the viewpoint of sensitivity. The thickness and length of the single fiber or yarn can be changed depending on the usage of the obtained element, and are not particularly limited.

One particularly preferred sensing element is, for example, 10 ^-5 ~
It is a thread-like material composed of single fibers having 10 ^-3 mg/mm ² of carbon fine particles on the surface.

The fiber-type sensing element according to the present invention is produced by immersing a hygroscopic monofilament or a thread made of monofilament in a solution containing conductive particles and optionally an adsorbent or adhesive.
and can be obtained by drying.
When the conductive particles are fine carbon particles, a commercially available Indian ink or ink liquid containing ink particles and glue may be used as the solution. In order to uniformly support the conductive particles on the fibers, the solution may be stirred.

The sensing element of the present invention can be easily attached between the electrodes using, for example, a conductive adhesive such as silver paste.

Next, the present invention will be explained in more detail using Examples and Comparative Examples.

Example 1 Natural cotton threads 60, 50 and 30 were attached using silver paste between each of the three miniature light bulb type electrodes 2 insulated with an insulator 3 as shown in Fig. 1, and these were used for writing. By immersing it in ink liquid for 5 minutes and then drying it, fiber type dew condensation sensing elements A ₁ , A ₂ and A ₃ in which ink particles were attached to the surface of the natural cotton thread were obtained.

As a result of observing each obtained element with an electron microscope,
Each cotton thread consists of many natural cellulose filaments, and it was confirmed that ink was not filled between the cellulose fibers, but that ink particles were adsorbed onto each filament. It was also confirmed using an electron microscope that these ink particles had a diameter of less than 1000 Å and were relatively homogeneously adsorbed onto the single fibers (see Figure 2).

A sensing element _A1 made from natural cotton thread 60 was fixed in a bracket and placed in a temperature-humidity control room.
Measurement was performed at 40° C. using an AC resistance measuring device R whose circuit mode automatically switches to parallel resistance or series resistance depending on the resistance value.

Its moisture sensitivity characteristics are shown in FIG. 3 by curve _A1 . The resistance value of this element is suitable for relative humidity 90-97%, especially 95-97%
It can be seen that the percentage changes significantly.

Example 2 Ink liquid treatment was carried out in the same manner as in Example 1, except that polyamide yarn (nylon 6) was used, which has a hygroscopicity of 3.5 to 5%, which is much higher among synthetic fibers, has high elasticity, and has little strength loss even when wet. Detection element B was obtained, and its moisture sensitivity characteristics at 40°C were measured in the same manner as in Example 1. The results are shown by curve B in FIG.

From the above results, it can be seen that even when polyamide yarn is used, dew condensation switching characteristics equivalent to those obtained when natural cotton yarn is used can be obtained.

Example 3 One cellulose single fiber was taken out from the cotton thread 60 used in Example 1 and treated with India ink in the same manner as in Example 1 to produce a sensing element C made of a single fiber. Similarly, its moisture sensitivity characteristics at 40°C were measured.

The results are shown by curve C in FIG. However, the length of the single fiber was adjusted so that the initial resistance value of this element was approximately the same as that of element _A1 of Example 1.

Since the number of ink particles adsorbed on one single fiber was somewhat large (5×10 ^-3 mg/mm ² ), the resistance change rate was as low as that of Example 1.
Although the dew condensation switching characteristics were lower than those of the device _A1 , it was possible to obtain dew condensation switching characteristics that could be used as a dew condensation sensing element.

Example 4 One cellulose fiber was taken from hemp thread, which has a higher elastic modulus than cotton thread, and treated in the same manner as in Example 1 to produce a sensing element D consisting of a single fiber. The moisture sensitivity characteristics at 0.degree. C. were measured and the results are shown by curve D in FIG.

In this case, dew condensation switching characteristics equivalent to those of element C of Example 3 were obtained.

Comparative Example 1 A cellulose nitrate porous membrane (ultrafiltration membrane) not composed of single fibers was treated with black ink in the same manner as in Example 1 to obtain a sensing element G.

Moisture Sensitive Characteristic Test Sensing elements A ₂ and A ₃ made using cotton threads 50 and 30 in Example 1, and sensing element G made in Comparative Example 1 were each fixed on a glass plate, and silver was placed between the electrodes. Attach using base plate,
Using the resistance measuring device used in Example 1, 30°C, 50°C
Moisture sensitivity characteristics at ℃ and 70℃ were measured.

The results are shown in FIG.

From FIG. 4, it can be seen that the sensing element A ₂ according to the invention and
It can be seen that A ₃ has excellent dew condensation switching characteristics, especially at temperatures below 50° C., but the device G of the comparative example does not have sufficient characteristics.

Responsiveness test For the sensing elements A ₂ and A ₃ described above, relative humidity changes of 95% to 97% at 40°C and 60°C and
Responsiveness was measured from 97% to 80%. The results are shown in FIG.

From FIG. 5, it can be seen that the above-described sensing element according to the present invention has excellent responsiveness, in that when the relative humidity is changed from 95% to 97%, it becomes constant within a few minutes. Since the time required to change the humidity in the test chamber is several minutes, the response time of the device is several seconds.

Durability test The above-mentioned sensing element A ₂ was kept at 40℃ for one day.
They were left near the windshield of a car traveling 30 km, and the reproducibility of their dew condensation switching characteristics was measured. The results are shown in FIG.

It can be seen from FIG. 6 that the dew condensation switching characteristics of the above-mentioned sensing element according to the present invention do not change even after one month.

Overall Characteristics The humidity sensitivity-response characteristics of the sensing element _A1 obtained in Example 1 at 40°C were measured. The results are shown in FIG. This result shows that the dew condensation switching characteristic of the sensing element _A1 is reversible.

The dew condensation switching characteristics of the detection elements of Examples 2 to 4 are also reversible at relative humidity of 90 to 97%, especially 95 to 97%, have short response times (several seconds), can withstand repeated use, and can be stored in a car for one month. We confirmed that there was no change even if we left it alone. Note that when changing from 95% to 97%, it takes several minutes for the resistance value to become constant, but this is because the humidity change in the test chamber takes several minutes, and the response time of the element is several seconds. It is.

As described above, the materials used in the dew condensation sensing element of the present invention can be obtained at low cost, the manufacturing method thereof is simple, and furthermore, it has extremely excellent moisture sensitivity and weather resistance. Furthermore, since the element of the present invention is made of fiber,
It has greater mechanical strength than conventional moisture-sensitive membranes.

[Brief explanation of drawings]

Fig. 1 is a schematic front view of the fiber-type dew condensation sensing element of the present invention attached between miniature light bulb type electrodes, Fig. 2 is an electron micrograph of the sensing element obtained in Example 1, and Fig. 3 is an electron micrograph of the sensing element obtained in Example 1.
The figure is a graph showing the moisture sensitivity characteristics of the sensing elements of Examples 1 to 4, FIG. 4 is a graph showing the humidity sensitivity characteristics of the sensing elements of Example 1 and Comparative Example 1, and FIG. FIG. 6 is a graph showing the responsiveness. FIG. 6 is a graph showing the durability of the sensing element according to the present invention. FIG. 7 is a graph showing the moisture sensitivity-responsiveness of the sensing element according to the present invention. In the figure, 1... fiber type dew condensation sensing element, 2... electrode, 3... insulator, R... resistance measuring device.

Claims (1)

[Scope of Claims] 1. A fiber composed of a hygroscopic fiber whose surface substantially uniformly carries conductive particles consisting of fine carbon particles having a particle size of 5000 Å or less, for use by being attached between electrodes. Type dew condensation detection element. 2. The device according to claim 1, wherein the conductive particles are adsorbed onto the surface of hygroscopic fibers using a hygroscopic adsorbent. 3. The device according to claim 2, wherein the hygroscopic adsorbent is glue. 4. Claims 1 to 4, which are filamentous bodies made of hygroscopic single fibers carrying carbon particles on the surface.
The device according to any one of item 3.