JPS58211643A - Humidity sensor - Google Patents

Abstract

PURPOSE:To elevate the sensitivity of a humidity sensor by adding a deliquescent salt to the mixture of an organic fiber adapted to swell by moisture absorption and a conductive fiber after they are mixed and manufactured into a paper to form a moisture sensing section. CONSTITUTION:A cellulose fiber 1a as an organic fiber adapted to swell by moisture absorption and a carbon fiber 1b as conductive fiber are mixed and manufactured into a paper which is impregnated with lithium chloride 1c as deliquescent salt to form a moisture sensing section 1. The cellulose fiber 1a is almost the same as the normally used for material of paper with the beating level of SR35 in terms of freeness. The carbon fiber 1b shall be 5mm. in the length and 35% in the ratio thereof 1b to paper and the moisture sensing section 35-40gr/m<2> in the weight per unit area. The weight of the lithium chloride impregnated in the cellulose fiber 1a shall be 6-18% considering the sensitivity and the impregnation rate of an adhesive 1d (the mixture of polyvinyl butyral and phthalic acid-n-butyl) shall be 6-15% to be added to compensate for joining force of fibril of the cellulose fiber 1a.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a humidity sensor that detects humidity in the air.

One of the applicants of the present application has already filed a patent application No. 142007 (1982) for a humidity sensor that detects humidity using a moisture sensing section made of a paper made from a mixture of organic fibers that swell upon absorption of moisture and conductive fibers.

The present invention aims to provide a humidity sensor that can improve the sensitivity of the humidity sensing section in the humidity sensor.

The present invention will be explained below with reference to specific examples.

In FIG. 1, 1 is a moisture sensitive part made of carbon fiber paper, 2 is a conductive adhesive (for example, made of silver paste), 3 is an electrode, 4 is an insulator (for example, a substrate made of plastic),
4a is a through hole provided in the substrate 4. Conductive adhesive 2
(for example, silver paste) electrically connects one end of the moisture sensitive part l and the electrode 3, and at the same time adheres them.

(2) FIG. 2 schematically shows the internal structure of the humidity sensing section 1. In the figure, la is cellulose fiber, 1b is carbon fiber, and t is paper thickness, and the broken line in the figure indicates the surface of the moisture sensitive part 1. Cellulose fiber 1a is almost the same as that normally used as a raw material for paper, but its degree of beating was 5R35 in terms of freeness. The wire diameter of carbon fiber 1b is 10I
Jm and a fiber length of 51 were used, and the proportion of carbon fiber 1b in the paper was 35% (the remaining 65% was cellulose fiber). The basis weight of the humidity sensing part 1 is 35 to 40 g r / m,
Paper thickness t is 0.2m, size and width) is corner 5fi to corner 1
It can be manufactured arbitrarily up to about 00fi, but here 1
It was about 0 Tsuru x 20W.

FIG. 3 is a diagram showing the detailed internal structure of the humidity sensing section 1, and 1c
is lithium chloride (L') impregnated into cellulose fiber 1a
1C1), and its impregnated weight is about 12
%. ld is an adhesive, which is made of a mixture of polyvinyl butyral (PVB) and n-butyl phthalate (DBP), the mixing ratio of which is 2:1, and its weight is equal to (3) in the moisture sensitive part 1. It is about 9%.

Next, the manufacturing method will be described. The manufacturing method is exactly the same as that of the kingship, which makes washi paper by cutting cellulose fibers (paper making). That is, in the present invention, it can be manufactured very easily by mixing cellulose fibers 1a and carbon fibers 1b and making paper from the mixture.

In this case, the moisture sensing section 1 of a predetermined size may be made by making a large sheet of paper (for example, 1 m square) and cutting it into pieces.

Furthermore, the paper-made moisture sensitive section 1 is impregnated with LiCN. To achieve the above impregnation ratio, a 2% aqueous or 2% ethyl alcohol solution of LiCff1 was used. Next, the glue is impregnated through the process. , :, h d4
; L, impregnated with an ethyl alcohol solution containing 1% PVB and 0.5% DBP. Furthermore, LiC&! ,PVB,
DBP may be simultaneously impregnated with ethyl alcohol solution.

FIG. 4 shows the characteristics of this humidity sensor. Line A shows the performance in the case of not impregnating LiCβ, and line B shows the performance of the example of the present invention in which LiCβ was impregnated. In either case, the resistance value is determined by DC voltage, and the resistance is lower than ever before. Furthermore, Li
Cj! It can be seen that the sensitivity is improved by the impregnation treatment.

Hereinafter, sensitivity will be expressed as the ratio of sensor resistance R90 at 90% humidity to sensor resistance R20 at 20% humidity, that is, R90/R20.

Figure 5 is LiCj! The relationship between impregnation rate and sensitivity is shown.

The preferred range is 6% to 18%.

FIG. 6 shows the relationship between the impregnation rate of adhesive (PVB+DBP ratio 2:1) and sensitivity. Line C is the initial performance, and line C is the performance after the durability test. In addition, the durability test was conducted at 35℃20%R.
H and 35° C. and 85% RH were repeated for 1000 cycles. The preferred range is 6% to 15%.

Figure 7 shows the plasticizer (DB) in the adhesive (PVB+DBP).
The relationship between the mixing ratio of P) and the sensitivity is shown.

Line E is the initial performance, and line F is the performance after the durability test (same as above). The preferred range is 0.2 to 0.45 □(
5) Yes.

The reason why the humidity sensing section 1 of the present invention operates is as follows. First, cellulose fiber 1a can be considered an insulator. Although the carbon fiber 1b is a conductor, it has a slight resistance.

On the other hand, a large number of carbon fibers 1b are intertwined and connected between both ends of the moisture sensitive part 1. Therefore, contact resistance exists between two consecutive carbon fibers.

Therefore, the resistance between both ends of the moisture sensitive part 1, that is, the resistance between the electrodes 3 is reduced by the resistance of the carbon fiber itself and the contact resistance. To be more specific, the overall resistance value is determined in a state where these resistors are connected in series and also in parallel. As described above, since the resistance value of the humidity sensing section 1 of the present invention is different from that of the conventionally known one using ion conduction, a very small resistance value can be easily obtained.

Next, the operation of the humidity sensing section 1 when exposed to moisture will be described.

It has been well known that cellulose fibers or paper made from cellulose fibers absorb (adsorb) humidity (6) in the air.

It is also well known that the amount of moisture adsorbed depends on the humidity of the air, and that the amount of adsorption increases as the humidity increases. Furthermore, the thickness of cellulose fibers that have absorbed moisture is 20 to 3
It is also well known that it can expand by as much as 0% or undergo deformation such as twisting, that is, it has the property of swelling and deforming.

By the way, when the humidity sensitive section 1 of the present invention is exposed to moisture, the cellulose fibers 1a adsorb the moisture in the air, causing the cellulose fibers 1a to swell and deform.

Then, the cellulose fibers that had been in contact with each other until now swell and deform, making it impossible for them to contact each other at various locations. Therefore, the number of carbon fibers that are connected at both ends of the moisture sensitive part 1 decreases, and the resistance value increases. In addition, the increase in resistance value depends on the swelling and deformation of the cellulose fibers, which in turn depends on the humidity in the air. In other words, the resistance value of the humidity sensing section 1 is uniquely determined by the humidity in the air.

On the other hand, when the humidity changes from high humidity to low humidity (7), moisture is removed from the cellulose fibers, the cellulose fibers contract, and as a result, the contact between the carbon fibers is restored and the resistance value decreases again to its original value. do.

The characteristics of the humidity sensor based on the above operating principle are shown in Figure 4, line A.
It will be as shown below. However, this still does not have a sufficiently high sensitivity, making it difficult to use as a humidity sensor. Therefore, if LiC# is impregnated as shown by line B, the sensitivity will be improved. The reason for this is that the impregnated L
As shown in FIG. 3, iCf is contained in cellulose fiber 1a. Since LiCf has deliquescent properties, it has a large ability to take in moisture from the air. LiCf that has taken in water becomes an aqueous solution by itself, and swells and deforms the cellulose fibers 1a. In other words, the degree of swelling and deformation of the cellulose fibers 1a itself can be further increased, and therefore the sensitivity is also improved.

Further, as is clear from FIG. 5, the healing effect of LiCf becomes remarkable when the amount of LiCjl impregnated is 6% or more by weight. The sensitivity decreases again above 18% because of the ion conduction phenomenon of LiCN (8). If ionic conduction occurs, the stability and reproducibility of performance deteriorates, so ionic conduction rarely occurs18
% or less is preferable. From the above, the LiCρ impregnation rate is 6% to 1
8% is good.

In the above explanation, it was stated that the carbon fibers 1b move due to the swelling and deformation of the cellulose fibers 1a, but in order to do so, the cellulose fibers 1a and the carbon fibers 1b must be bonded with a certain degree of bonding force. be.

It is the fibrils of the cellulose fibers 1a that exert this bonding force. In other words, the fibrils are entangled with carbon 1b to maintain bonding with cellulose fiber mla.

However, the bonding force of the fibrils alone is insufficient, and as shown in Figure 6, the initial performance could not be maintained without treatment with the adhesive 1d, and the sensitivity significantly decreased after the durability test. ing. Therefore, durability can be improved by supplementing the bonding force of the fibrils with the adhesive force of the adhesive. As an adhesive, polyvinyl alcohol (
PVA), polyvinyl butyral (PVB), ethyl cellulose, etc. are commonly used (9), but in the inventors' experiments, PVB was able to exhibit the most stable adhesive force. As for the required amount of this adhesive (PVB+DBP), from a comparison between the line C and the line in FIG. 6, it was found that almost durability can be ensured at an impregnation rate of 6% or more. However, if there is too much adhesive, the movement of swelling and deformation of the cellulose fibers 1a is inhibited, resulting in a decrease in sensitivity. As is clear from FIG. 6, the sensitivity decreases significantly when the impregnation rate is 15% or more. From the above, the impregnation rate of the adhesive is preferably 6% to 15%.

Next, consider the possible Wi(D) occupied in the adhesive (pvB+DBP).
BP) ratio will be described below. D B P 7! When l is insufficient, the adhesive becomes significantly solidified and becomes difficult to deform. At this time, it is preferable that the adhesive force acts to strengthen the bonding point between the cellulose fibers 1a and the carbon fibers 1b (Id in Figure 3), but since the adhesive has also penetrated into the inside of the cellulose fibers 1a, Solidification of the agent inhibits the swelling and deformation of cellulose fibers, resulting in a decrease in sensitivity. From FIG. 7, this tendency is remarkable when the DBP ratio is 0.2 or less. on the other hand,
If there is too much DBP, the fluidity of the adhesive will become significant (
10) The adhesive strength at the junction between the cellulose fibers 14 and the carbon fibers 1b decreases, resulting in a decrease in durability. From FIG. 7, this tendency is remarkable when the DBP ratio is 0.45 or more.

From the above, the ratio of DBP in the adhesive is 0.2 to 0.
．． 45 is preferred.

As described above, the humidity sensor of the present invention has a low resistance value (unlike conventional sensors that use ion conduction), and can be measured using direct current resistance, so it can be measured and controlled using a very simple circuit. can do.

Furthermore, the moisture sensing section 1 of the present invention does not utilize the conventionally well-known surface ion conduction, but uses the entire moisture sensing section 1, so it is resistant to dirt, and the moisture sensing section 1 is resistant to dirt. Since it has sufficient pores inside, it is easy for air to pass in and out of the outside air, and it has the characteristic that it is essentially excellent for measuring the humidity of the air.

Note that the present invention can also be used as a dew condensation sensor. This is because cellulose fibers have the ability to absorb moisture and also perform similar swelling and deforming actions. Therefore, it goes without saying that it can also be used as a water sensor (a sensor that detects the presence or absence of water).

In addition, although the moisture sensitive part 1 is made of cellulose fibers and carbon fibers, in addition to cellulose fibers, polyvinyl alcohol fibers, rayon, cotton, and wool may also be used, as long as they are organic fibers that swell with moisture absorption. good. In addition to carbon fibers, activated carbon fibers may be used, metal fibers with a diameter of 10 μm or less may be used, and in short, conductive fibers may be used. Also, if activated carbon fiber is used instead of carbon fiber, adhesive (P
VB+DBP) has better conformability, increases adhesive strength, and further improves durability. The same thing can be said even if carbon fiber and activated carbon fiber are mixed.

Also, instead of LiCβ, other deliquescent salts such as calcium chloride CaCβ, potassium carbonate 2CO3, magnesium nitrate Mg (NO3)2, sodium chloride NaC7! etc. may also be used. Among the above, the one that achieved stable sensitization with the smallest amount was LiCj! Met.

Further, although a plastic substrate is used as the substrate 4, any insulating material such as Bakelite or porous ceramic may be used. Further, although the conductive adhesive 2 is used for electrically connecting the moisture sensitive part 1 and the electrode 3, the electrode 3 may of course be crimped onto the humidity sensitive part using a spring steel clip.

As described above, according to the present invention, sensitivity to humidity is improved.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing an embodiment of the present invention, and FIG. 2 is an 81
3 is a perspective view schematically showing an enlarged part of FIG. 2, and FIGS. 4 to 7 are characteristic diagrams for explaining the operation of the present invention. It is. DESCRIPTION OF SYMBOLS 1... Moisture sensing part, 3... Electrode, 4... Substrate. Representative Patent Attorney Takashi Okabe (13) No. 1.2゜1 degree Figure 2 Attorney 7' ＼ 1b 1a Figure 3 F 4 Figure 20 40 60 80i degree
R1-1 ￥ 5 Figure 6 χ Multi a standard

Claims (4)

[Claims] (1) A moisture-sensitive part made of a paper made by mixing organic fibers that swell when absorbed with moisture and conductive fibers, and to which a deliquescent salt is added;
A humidity sensor comprising: a pair of electrodes provided on the humidity sensing section; and an electrically insulating substrate on which the electrodes and the humidity sensing section are disposed. (2) The humidity sensor according to claim 1, wherein the organic fibers and the conductive fibers of the humidity sensing section are bonded together with an adhesive. (3) The deliquescent salt is lithium chloride, and the proportion of the deliquescent salt in the moisture sensitive section is 6% to 18%. Humidity sensor described in. (4) The adhesive is polyvinyl butyral and phthalic acid.
A mixture with n-butyl, the proportion of which is 6% to 15% in the paper-like material, and the proportion of n-butyl phthalate in the adhesive is 0. 2. The humidity sensor according to claim 2, wherein the humidity is .2 to 0.45.