JPH03165247A - Moisture sensitive device - Google Patents

Abstract

PURPOSE:To prevent the inflow of an org. solvent and corrosive gas by mounting a hydrophobic filter having <=0.5mum hole size in the aperture of a body case. CONSTITUTION:The cap-shaped body case 20 housing a moisture sensitive ele ment 10 is bored with the circular aperture 21 on the surface facing the moisture sensitive element 10 and a tetrafluoroethylene resin filter 30 having, for example, <=0.5mum pore size is coated with an adhesive agent and is mounted into this aperture 21. The vapors of org. and inorg. compds. larger than the water molecules to become the noises of the output of the moisture sensitive device are removed by a 'molecular sieve effect' or the diffusion of the molecules is limited to prevent the molecules from arriving at the moisture sensitive membrane 13 as the tetrafluoroethylene resin filter 30 having <=0.5mum pore size is used.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a humidity sensing device, and particularly to the structure of a filter that is adhesively disposed in an opening communicating with a humidity sensing element housed in a main body case. It is.

[Conventional technology]

FIG. 5 shows an example of this type of humidity sensing device, for example,
FIG. 2 is an exploded view showing the configuration of a conventional gas detector disclosed in Japanese Patent No. 69153. In the figure, a sensor section 4, which is constructed by attaching a gas detection element 3 to the tips of two lead wires 2 inserted through a base 1, is connected to an opening 6 of a main body case 5 leading to the sensor section 4. A porous filter T made of a water-repellent material is attached to prevent water and dust from adhering to the surface of the sensor section 4, particularly the gas detection element 3.

[Problem to be solved by the invention]

Since the gas detection element 3 detects water molecules in the air, it is susceptible to corrosive gases, organic solvents, dust, etc. present in the air. Therefore, conventionally, in order to eliminate such influences other than water as much as possible, sintered bodies or porous resins are used as filter materials. For example, a gas detector that uses tetrafluoroethylene as the porous resin for the filter 7 and has a pore diameter of approximately 1 μm in the opening 6 of the main body case 5 is effective against dust in the air such as cigarette smoke. has been confirmed. However, acetone,
For organic solvents such as methanol and corrosive gases, there is a problem in that the output value of the gas detection element 3 has a large drift and a sufficient filter function cannot be obtained. This is due to the fact that the pores of the tetrafluoroethylene resin are large and that organic solvents and corrosive gases can pass through the pores of the tetrafluoroethylene resin in the same way as water molecules in the air.

[Means to solve the problem]

In order to solve these problems, the present invention provides at least one opening in the main body case in which the humidity sensing element is housed, and a hydrophobic filter having a pore diameter of 0.5 μm or less is attached to this opening. It is something that

[Effect]

In the present invention, a hydrophobic filter having a pore diameter of 0.5 μm or less is attached to the opening of the main body case, thereby preventing the inflow of organic solvents and corrosive gases.

〔Example〕

FIG. 1 is a partially cutaway view showing the structure of an embodiment of the humidity sensing device according to the present invention, and the same parts as in the previous figures are given the same reference numerals. In the same figure, a cap-shaped main body case 20 that houses the humidity sensing element 10 has a circular opening 21 on the surface facing the humidity sensing element 10, and this opening 21 has a hydrophobic filter, for example. A polytetrafluoroethylene resin (PTFE: Teflon) filter 30 having a pore diameter of 0.5 μm or less is installed and coated with adhesive.

Further, as the adhesive for the main body case 20, an epoxy adhesive or a cyanoacrylate adhesive is used.

Silicone adhesives, urethane adhesives, ultraviolet curing adhesives, etc. are applicable. Further, as the humidity sensing element 11, for example, Pt (platinum) is used on an alumina substrate, a glass substrate, or an insulating substrate 11 on which an oxide film is formed.
A lower electrode 12 is formed by forming a film of , Or (chromium), etc. by sputtering or vacuum evaporation, and a moisture-sensitive film 13 is formed by coating a polymer resin on the lower electrode 12 by dipping or a spinner method. After forming the upper electrode 14 by sputtering or vacuum evaporating a film of Au (gold) or the like on the moisture sensitive film 13, the upper electrode 14 is formed, and then two lead wires are formed by breaking each sensor chip. 2m, 2
b respectively the lower electrodes 12.b. An electrical connection is made by adhering to the electrode terminal of the upper electrode 14 with a conductive resin 15.

The moisture sensing element 10 configured in this way has a base 1 and two lead wires 2&.

2b is inserted and fixed, an opening 21 is bored, the nine body case 20 is covered and fixed, and then the tetrafluoroethylene resin filter 30 is adhered to the opening 21 to complete the process.

The humidity sensing device thus configured was subjected to a test in which two types of tetrafluoroethylene resin filters 30 with pore diameters of 1.0 μm and 0.45 μm were exposed to acetone saturated steam for about 20 minutes, and the humidity sensing device was tested before and after the test. After the test, the humidity sensing device was left indoors and the state of recovery of the characteristics was investigated. As a result, as shown in FIG. 2 (pore diameter: 1.0 μm) and FIG. 3 (pore diameter: 0.45 μm), a moisture sensing device (3 It was found that the amount of triad in the case of (Fig.) was small after being left for about 20 minutes, and the properties recovered quickly. In Figures 2 and 3, elapsed time 0 is the time immediately after being exposed to acetone saturated steam for about 20 minutes and taken out, and subsequent elapsed times indicate the time left indoors, and , the plots in these figures are set at the measurement humidity of 10%RH, 30%R.
The maximum drift measured among H, 50% RH, 70% RH, and 90% RH is shown.

FIG. 4 shows an investigation of changes in the amount of drift immediately after being left in acetone saturated steam for about 20 minutes when the pore diameter of the tetrafluoroethylene resin filter 30 of the humidity sensing device having the above-described structure was varied.

In the same figure, by reducing the pore diameter of the tetrafluoroethylene resin filter 30 from the conventional 1.0 μm to 0.5 μm or less, the drift amount is reduced from the conventional approximately 17% RH to approximately 12% RH.
It is small enough to provide sufficient filtering function against organic solvents such as acetone and methanol and corrosive gases. Furthermore, if the pore diameter of the tetrafluoroethylene resin filter 30 is set to less than 0.1 μm, the amount of drift will be further reduced, but in this case, the tetrafluoroethylene resin filter 30 will become eye-catching due to cigarette smoke, oil mist, dust, etc. This may cause clogging, and the diffusion speed of the water molecules themselves decreases, resulting in increased hysteresis of the moisture-sensitive element 10 and a slow response speed at 90% RH. By forming the film into a shape, 002, H2O, etc. can be dissolved and diffused in the bulk film even if the pore size is zero. Further, even in the tetrafluoroethylene resin filter 30 having a pore diameter of 0.1 μm, H2O can easily pass through because the molecule is small and the tetrafluoroethylene resin is hydrophobic, and there is no problem in terms of characteristics. Therefore, the pore diameter of this tetrafluoroethylene resin filter 30 is 0.5 μm.
The following is preferable, and a range of 0.1 to 0.5 μm is most preferable.

By using the tetrafluoroethylene resin filter 30 with a pore size of 0.5 μm or less, the humidity sensing device configured as described above is able to filter out organic matter, which is larger than water molecules that cause noise in the output of the humidity sensing device.
The inorganic compound vapor is removed by the "molecular sieving effect" or the diffusion of molecules is restricted, so that it does not reach the moisture sensitive film 13, and therefore drift can be suppressed.

In addition, in the above-described embodiment, a case was explained in which a tetrafluoroethylene resin filter was used as the hydrophobic filter, but the present invention is not limited to this, and for example, polyethylene, polyether sulfon, etc. may be used. Needless to say, the same effect can be obtained. However, tetrafluoroethylene resin is the most chemically stable.

〔Effect of the invention〕

As explained above, according to the present invention, the pore diameter is 0°5 μm.
By using the following hydrophobic filter, water molecules in the air can pass through with the same pore size of 1.0 μm, but it is difficult for organic solvents and corrosive gases to pass through. Since the damage caused is reduced, it has the extremely excellent effect of providing a moisture sensing device with excellent long-term stability compared to conventional methods.

[Brief explanation of the drawing]

Fig. 1 is a partially cutaway plan view showing an embodiment of the humidity sensing device according to the present invention, and Figs. 2 and 3 show the amount of drift of the humidity sensing device before and after the test, and the humidity sensing device left indoors after the test. Fig. 4 shows the correlation between the pore diameter of the tetrafluoroethylene resin filter and the data immediately after leaving the humidity sensing device in acetone saturated steam for 20 minutes, and Fig. 5 shows the recovery state of the characteristics when FIG. 2 is an exploded view showing the configuration of a conventional humidity sensing device. -...Pace, 2m + 2 b...Leet line,...
...Moisture sensitive element, 11... Insulating substrate, ... Lower electrode, 13... Moisture sensitive film, 14. Upper electrode, 15...
・Conductive resin, 20φ main body case, 21@...opening, 30・tetrafluoroethylene resin filter.

Claims (1)

[Claims] A main body case housing a humidity sensing element using a polymer resin as a humidity sensing membrane is provided with at least one opening, and a hydrophobic filter with a pore diameter of 0.5 μm or less is attached to the opening. Moisture sensing device.