JPS61264244A - Production of humidity sensor - Google Patents

Abstract

PURPOSE:To decrease the evaporation of a dispersion by ambient temp. and humidity and to improve the sensitivity of a humidity sensor by adding benzyl alcohol to the dispersion, preparing the mixture into a paste state, coating the paste on an insulating base plate provided with two electrodes and baking the coating. CONSTITUTION:The silver electrodes 2a, 2b for soldering lead wires 5, 6 are formed stop the alumina insulating base plate 1 and the carbon electrodes 3a, 3b are connected to and formed on the electrode 2a, 2b. The paste prepd. by adding the benzyl alcohol to the dispersion is coated on the base plate 1 formed with the carbon electrodes 3a, 3b and is baking to form a humidity sensitive resistance film 4. The material for said film 4 is prepd. by 0.2-1pt.wt. diaminodiphenyl methane as a curing agent, 10-40pts.wt. acetylene black as conductive pwoder and 10-40pts.wt. benzyl alcohol as a dissolving liquid to 100pts.wt. hygroscopic resin which is the copolymer of 2-hydroxyethyl methacrylate, glydicyl methacrylate and azobisisobutylonitrile.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for manufacturing a humidity sensor that is used to detect humidity, dew condensation, etc. and has high reproducibility, high sensitivity, and excellent longevity characteristics.

BACKGROUND OF THE INVENTION Many methods of manufacturing humidity sensors of this type are known. For example, Japanese Patent Application No. Sho 62-151890, Japanese Patent Publication No. Sho 56-13362, Japanese Patent Publication No. Sho 60-845.
As shown in Japanese Patent No. 8, a pair of comb-shaped electrodes made of carbon or metal are provided on an insulating substrate such as a glass substrate or an alumina substrate. Next, as a hygroscopic resin, a copolymer of 2-hydroxyethyl methacrylate and glycidyl methacrylate is dissolved in a solvent such as methyl cellosolve or ethyl cellosolve, and this is mixed with a conductive powder such as natural graphite powder ASP or carbon black and a hardening agent diaminodiphenylmethane. Add methyl cellosolve and ethyl cellosolve and mix with a ball mill to disperse well. A humidity sensor was manufactured by applying this dispersion onto an insulating substrate provided with the electrodes described above to form a humidity-sensitive resistive film, and heating the film at 100° C. for 1 hour.

Problems to be Solved by the Invention In such a conventional method, when forming a moisture-sensitive resistive film, there are problems such as evaporation of the solvent in the dispersion caused by ambient temperature and humidity, stability between conductive powder particles, and hygroscopic resin and conductive properties. There were changes in the dispersion state of the powder, and the dispersion liquid could not be stored and there were problems with reproducibility. Further, there is a problem in that when heated at 120'C or higher, the sensitivity of humidity characteristics decreases, and when left at high temperatures, life characteristics deteriorate.

The present invention solves these problems by using a high boiling point solvent that causes less evaporation of the dispersion due to ambient temperature and humidity, and by reducing the amount of curing agent added, and thereby forming a mixture of hygroscopic resin and conductive powder. The object of the present invention is to provide a method for manufacturing a humidity sensor with high reproducibility, high sensitivity, and excellent lifetime characteristics by manufacturing a dispersion liquid that has a stable dispersion state and can be stored for a long period of time.

Means for Solving All Problems In order to solve these problems, the present invention uses diaminodiphenylmethane as a curing agent for a copolymer hygroscopic resin of 2-hydroxyethyl methacrylate, glycidyl methacrylate, and azobisisobutyronitrile. By adding a small amount of acetylene black as a conductive powder to produce a dispersion, and then adding benzyl alcohol, a high boiling point solvent, to produce a paste dispersion, we have created a humidity sensor with excellent reproducibility and long life characteristics. It is characterized by manufacturing.

Function: By using this method, the paste-like dispersion liquid has a stable dispersion state of the hygroscopic resin and conductive powder even under changes in ambient temperature and humidity, can be stored for a long period of time, and has a stable and highly reproducible sensation. A moisture resistant film can be formed. Furthermore, since the amount of curing agent added is small, it is possible to heat the product at high temperatures, which reduces the sensitivity of humidity characteristics and the deterioration of life characteristics when left at high temperatures.

Embodiment FIG. 1 shows an example of a humidity sensor produced by a manufacturing method according to an embodiment of the present invention, FIG. 1 is a plan view, and FIG. 1B is a
It is a sectional view along the -x' line. In FIG. 1, reference numeral 1 denotes an alumina insulating substrate, and silver electrodes 22L and 2bi for soldering lead wires 6, 6 are formed on the upper surface of this alumina insulating substrate 1. Next, the comb-shaped carbon electrodes 32L, 3b are completely soldered and connected to the silver electrodes 2a, 2b.

Next, a method for producing a dispersion liquid for forming the entire moisture-sensitive resistive film 4 will be described. 2-hydroxyethyl methacrylate 1
43g and 10.49g of glycidyl methacrylate (molar ratio 1S:1) were dissolved in 380g of ethyl cellosolve,
1.079 f of azobisisobutyronitrile was added as an initiator and copolymerized by heating at 80"C for 16 hours under a nitrogen stream. For 100 da of this copolymer, 2 g to 1 g of diaminodiphenylmethane o, a curing agent, Conductive powder 49-6
In addition to g', benzyl alcohol '610y~4
0y and mixed on a three-roll machine to produce a paste-like dispersion for printing.

The paste-like dispersion liquid produced in this manner was screen printed on the upper surface of the alumina insulating substrate 1 on which the comb-shaped carbon electrodes 3f & 3b were formed, to form a moisture-sensitive resistive film 4, and the temperature was increased to 100°C. Heat at 180'C for 1 hour to react. After that, solder the lead wires 6, 6 to the silver electrode 21.
A humidity sensor was produced by soldering to L and 2b.

The samples of the above examples were evaluated by the following method.

The evaluation results are shown in FIGS. 2 to 7.

The resistance value was measured at S25°C, 160%RH, 75%RH,
94%RH and 100%RH were measured.

Figure 2 shows copolymer 10o9. Conductive powder 69° 20g of benzyl alcohol, hardening agent iA: 0, 2fl.

The relative humidity-resistance characteristics of a sample obtained by adding 0.5 j7 of B and 1 g of C to prepare a dispersion and heating it for 100° Ct' to form a moisture-sensitive resistive film are shown.

Figure 3 shows copolymer 10ofl, curing agent o, ts9. 20g of benzyl alcohol and 4g of conductive powder for people.

Add sg of B and 6g of C to prepare a dispersion, and heat at 100°C.
The relative humidity-resistance value characteristics of a sample formed by heating for 21 hours to form a humidity-sensitive resistive film are shown.

Figure 4 shows 10 oy of copolymer, o curing agent, tsp, 5 g of conductive powder, and 10 f of benzyl alcohol kAH.

B is 2o9, C is 309, and D is 40y to prepare a dispersion, and the sample is heated for 10o'Cp' to form a moisture-sensitive film.

Figure 5a shows a dispersion prepared by adding benzyl alcohol e1010 to 5g of copolymer 1009, curing agent ○''!p conductive powder, and Figure 5a shows copolymer 100f,
A dispersion was prepared by adding a total of 3 ml of benzyl alcohol to 0.5 g of a curing agent and 5 g of conductive powder. Firing temperature iA is 100'C, B is 150'C+C is 1
The relative humidity-resistance value characteristic diagram of a sample formed by heating at 80° C. for 91 hours to form a humidity-sensitive resistive film is shown.

Figure 6 confirms the storage stability of the dispersion prepared in Figure 2B.
was left in a cool, dark place for 6 days, then screen printed at 100°C.
Relative humidity of sample heated for 1 hour to form moisture sensitive resistive film -
Indicates resistance value characteristics.

FIG. 7 shows the relative humidity-resistance characteristics after the sample in FIG. 2B was left at 85°C.

As shown in FIGS. 2 to 5, the relative humidity-resistance characteristics can be greatly varied by controlling the amount of curing agent and the amount of benzyl alcohol. The amount of curing agent appears to affect the moisture absorption rate of the hygroscopic resin. The amount of benzyl alcohol affects the dispersion state of the hygroscopic resin and the conductive powder and the interparticle stability of the conductive powder. The reason why the sensitivity of humidity characteristics does not decrease even after heat treatment at high temperatures is thought to be because the amount of curing agent added is small and the copolymer hygroscopic resin is not completely cured due to the use of all high boiling point solvents. It will be done. As shown in FIG. 6, it was confirmed that the dispersion was reproducible even if it was left in a cool, dark place for a long period of time. As shown in FIG. 7, it is stable even when left at high temperatures.

In a dew condensation sensor, the resistance value range at room temperature and 94% RH is 2Ω to 100Ω in general usage specifications. Therefore, the curing agent diaminodiphenylmethane is 3111-10.29 ~ 1 da, the conductive powder acetylene black is 4 g ~ 6 g, and the benzyl alcohol is 10 g ~
409 (when the copolymer resin is 10 og).

The amount of benzyl alcohol also affects the workability when screen printing a paste-like dispersion; if it is less than 101, an uneven film will be formed, and if it is more than 4 oy, the pattern will bleed.

Effects of the Invention As described above, according to the present invention, the dispersion state of the hygroscopic resin and conductive powder in a paste-like dispersion can be stabilized, the conductive powder particles can be stabilized, and furthermore, long-term storage is possible. Therefore, it is possible to form a stable and highly reproducible moisture-sensitive resistive film, and the hygroscopic resin does not completely cure even when heated at high temperatures.
It has the advantages of not decreasing the sensitivity of humidity characteristics after being left at high temperatures and reducing the deterioration of life characteristics, and is therefore of great industrial value.

[Brief explanation of drawings]

FIG. 1 shows a humidity sensor manufactured by a manufacturing method according to an embodiment of the present invention, and FIG. 1 is a plan view, FIG. Figures 5 and 6 are relative humidity-resistance characteristic diagrams for each sample, and Figure 7 is Figure 2B.
01... Alumina insulating substrate, 2N, 2b...
...Silver electrode, 32L, 3b...Carbon electrode, 4...Moisture-sensitive resistance film, 5,6...Lead wire. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Fig. 2 Fig. 3 Fig. 4 Relative humidity (γ,) Fig. 5 ct b Fig. 6 4ro7t 11 boats ('/・) Fig. 7 n 藺 (/11-)

Claims (2)

[Claims] (1) A humidity sensor characterized in that benzyl alcohol is added to a dispersion liquid to form a paste, which is coated on an insulating substrate provided with at least two electrodes, and then baked to form a moisture-sensitive resistive film. Production method. (2) 100 parts by weight of a copolymer hygroscopic resin of 2-hydroxyethyl methacrylate, glycidyl methacrylate, and azobisisobutyronitrile as a material for the moisture-sensitive resistance film, and 0.2 to 1 part by weight of diaminodiphenylmethane as a hardening agent. 4 to 6 parts by weight of conductive powder acetylene black,
2. The method for manufacturing a humidity sensor according to claim 1, wherein the dissolving liquid contains 10 to 40 parts by weight of benzyl alcohol.