JP2904949B2 - Condensation sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dew condensation sensor suitable for detecting dew condensation on a drum of a rotary head of a video tape recorder, for example.

[0002]

2. Description of the Related Art A dew sensor is used for detecting dew condensation on electronic devices which do not like dew condensation, for example, a head portion of a VTR. It helps prevent accidents caused by damage.

Conventionally, as an electric resistance type dew sensor, as shown in FIGS. 5 (a), 5 (b) and 6, for example, a sensor prepared by blending an electrolyte such as sodium acetate with a hygroscopic polymer material is used. A resistor was placed between the comb electrodes
Dunmore type, other materials using carbon powder as conductive particles for hygroscopic polymer material as moisture sensitive resistor (see FIGS. 7 (a), (b) and 8), and porous materials such as aluminum oxide The resistance value is changed by filling the porous body with water at the time of dew condensation using a porous membrane, and the resistance value is changed by water droplets formed between the electrodes at the time of dew condensation using only comb-shaped electrodes Things are being developed.

[0004] In the case of a comb-shaped electrode alone, the change in resistance value during dew condensation is small and various agings (65 ° C, -40 ° C, 40 ° C 90% R)
H) Since the reliability afterwards is very low, malfunctions are likely to occur. The response speed of the aluminum oxide type is slow,
It has disadvantages such as a large change with time. These points have been improved by the Dunmore type and the carbon film type, and the carbon film type is superior in terms of long-term reliability. This is because the carbon film type is not affected by surface contamination such as adhesion of dust and dirt due to internal conduction.

[0005] As the hygroscopic polymer material used for the carbon film type, there are various materials such as polyvinyl alcohol, acrylic resin, epoxy resin, cellulose resin and polyamide resin. It is desired that these hygroscopic polymer materials are insoluble in water having a high hygroscopic response speed and have low hysteresis at high humidity. In general, since a hygroscopic polymer has a hydrophilic group in the molecule, if the polymer is placed in a high-humidity atmosphere for a long time, the polymer substance is eluted and the resistance at the time of dew condensation hardly increases. Polyvinyl alcohol (P
In the case of using a material obtained by dispersing conductive particles in VA) and drying by heating (for example, refer to JP-A-62-21052), simply heating and drying water-soluble PVA as it is does not have water resistance. It has drawbacks such as elution at high humidity and has a problem in durability.

Accordingly, an object of the present invention is to provide a dew condensation sensor which does not elute even if it absorbs moisture and has durability for long-term use.

[0007]

As shown in FIG. 1 (b), for example, as shown in FIG. 1 (b), the dew condensation sensor according to the present invention comprises an isocyanate And a film formed by dispersing conductive particles in the base material of polyvinyl alcohol crosslinked by the above.

[0008]

According to the present invention, the moisture sensitive resistor 1 of the dew sensor is provided.
Has at least conductive particles in addition to a cross-linking agent in polyvinyl alcohol, and by generating a cross-linking reaction under heating this moisture-sensitive resistor, the dew condensation sensor becomes insoluble even if it absorbs moisture, and has excellent durability. Become.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a dew sensor according to the present invention will be described below with reference to FIGS.

In this embodiment, as shown in FIG. 1A, a pair of interdigital electrodes 2 are formed on a flexible printed circuit board (FPC) 3 by etching a copper foil.
As shown in (b), the moisture-sensitive resistor 1 is provided so as to cover each end of the comb-shaped electrode. This moisture-sensitive resistor 1 according to the present example is made of polyvinyl alcohol (PVA) 10
1.5 parts by weight of blocked isocyanate to 0 parts by weight
7.0 parts by weight, conductive particles and an antifoaming agent were blended to form a film, and polyvinyl alcohol (PV A ) was crosslinked by heating.

Next, regarding the reason why the moisture-sensitive resistor 1 is configured as described above, the electric characteristics, water resistance and durability of the dry-humidity resistor 1 when the components of the moisture-sensitive resistor 1 are set under various conditions. A specific description will be given based on the measurement results.

First, the results of electrical characteristics and water resistance of a dew sensor when various cross-linking agents are used will be described.

The composition used for preparing the sample is as follows. A. 100 parts of polyvinyl alcohol (PVA217 manufactured by Kuraray Co., Ltd.) Crosslinking agent 1, 2.5 for any one of the following crosslinking agents,
5, 10, 20 parts Melamine J-820 (butyl etherified melamine, manufactured by Dainippon Ink Co., Ltd.) Melamine M-3 (methyl etherified melamine, manufactured by Sumitomo Chemical Co., Ltd.) Glioxal NS-19 (Sumitomo Chemical Co., Ltd. Block Isocyanate BN-08 (Sodium bisulfite blocked triisocyanate, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) Block Isocyanate BN-69 (Same as above) Block Isocyanate BN-05 (Same as above) C.I. Acetylene black (Denka Black, manufactured by Denka Corporation) 20 parts

A method for manufacturing a sample will be described. 100 parts of the polyvinyl alcohol, crosslinking agent 1, 2.5, 5,
10 or 20 parts and 20 parts of acetylene black are dissolved and dispersed in distilled water to obtain a uniform coating. This paint is applied on the comb-shaped electrode by a screen printing method, and finally applied so as to have a dry film thickness of 2 μm. Thereafter, the coating film of the comb-shaped electrode is heated at a temperature of 160 ° C. for 30 minutes to cause a crosslinking reaction of polyvinyl alcohol and to evaporate water in the coating film, thereby drying the film (see FIG. 1). .

The method of measuring the resistance value and measuring the water resistance in this example is as follows. A. Resistance value measurement The conduction resistance value of each of the various comb-shaped electrodes prepared by the above method was measured under two conditions, that is, a dry condition and a condition in which water droplets were left on the sample surface to form a dewdrop. The differences were compared. B. Water resistance A test film (dry film thickness: 2 μm) was separately prepared from the paint prepared by the above method, and this film was immersed in water for 1 hour to test the water resistance.

The results are as shown in Table 1, where:
The horizontal column shows various cross-linking agents, and the vertical column shows the amount of the cross-linking agent, and the evaluation of the resistance value during drying and dew condensation and the water resistance at each amount. The evaluation of water resistance was represented by ○ and ×, and when the film state was maintained, ○, and when the film was broken and melted, ×. As can be seen from the results in Table 1, only the blocked isocyanate-based crosslinking agent shows a high resistance value during dew condensation while maintaining water resistance, and the melamine- and glyoxal-based crosslinking agents have resistance values during dew condensation. Was found to be low.

[Table 1]

Next, the optimum blending amount of the crosslinking agent-blocked isocyanate having excellent sensor sensitivity and water resistance will be described.

A method for preparing a sample will be described. 100 parts of polyvinyl alcohol, 36 parts of acetylene black,
A coating material is prepared by dissolving and dispersing 8 parts of an antifoaming agent and 10 parts of blocked isocyanate BN-69 in addition to 0 to 36 parts in distilled water. Making specimen for testing by heating the coating material is applied onto comb electrodes at 160 ° C. 30 min.

The methods of measuring the resistance value and the response speed and measuring the dissolution rate in this example are as follows. A. Measured for each sample of the resistance value and response speed, initially 25 ° C., relative humidity (hereinafter "R
H ". ) Measure the resistance value while keeping it at 75%. Next, this sample is placed in an atmosphere of 60 ° C. and 100% RH to cause dew condensation, and the resistance value in the dew state is measured. At this time, each sample was kept at 60 ° C. and 100%
The response time was measured for how long the resistance value reached 1 MΩ after the RH dew condensation state was reached, and the response speed as a dew sensor was evaluated. B. Next, the film produced in the same manner was immersed in water for 1 hour,
The dissolution rate of the film was measured.

The results are as shown in Table 2 and FIG.
As can be seen from Table 2, the resistance value was from 1.8 KΩ to 2.9 KΩ at 25 ° C. and 75% RH.
At% RH, the value changed to a remarkably high value of 3.3 MΩ to 11 MΩ, and the results were satisfactory for each sample. Next, with respect to the response speed, those having a resistance value as fast as 2 seconds or less to reach 1 MΩ have a compounding amount of the crosslinking agent in the range of 0 to 7 parts. Table 2 shows the results of the elution rate.
As can be seen from FIG. 2 and FIG. 2, the dissolution rate is small and stable when the amount of the crosslinking agent is 1.5 parts or more.

[Table 2] From the above results, it is best to mix 1.5 to 7.0 parts of blocked isocyanate BN-69 with respect to 100 parts of polyvinyl alcohol as the range where the response speed is high, the dissolution rate is small and the water resistance is good. It is.

Next, the durability performance when the sample is kept under high temperature and high humidity conditions for a long time will be described.

The measuring method will be described. Block isocyanate B and system without blended isocyanate
A sample was prepared using a system containing 3 parts of N-69 , and 60
60 hours when left in a bath at 95 ° C and 95% RH for 1000 hours.
100% RH at 25 ° C, 93% RH at 25 ° C, and 75% at 25 ° C
The durability was compared based on the change in resistance value at RH.

The results are shown in Table 3, FIG. 3 and FIG. As shown in Table 3, it can be seen that in the initial state, the same properties are obtained regardless of the presence or absence of the blocked isocyanate. However, the sample without the blocked isocyanate showed a very low increase in resistance after dew condensation after 500 hours, which is the rated specification of a general dew sensor.
The condition of 100 KΩ or more at 0 ° C. and 100% RH is not satisfied. Further, after 1000 hours, the difference in resistance between the dry state and the dew state becomes smaller than that of the cross-linked state, and the switching operation as a dew sensor cannot be performed properly (see FIG. 4).

[Table 3] In contrast, the sample cross-linked with blocked isocyanate still shows 10 ⁵ Ω after dew condensation even after aging for 1000 hours.
The resistance value has risen to the order of, and it can be sufficiently used as a condensation sensor (see FIG. 3). That is, PVA
Can be the the water resistance by crosslinking with blocked isocyanate improved to improve the durability while maintaining high sensitivity.

From the above results, the moisture-sensitive resistor 1 was prepared by mixing 1.5 to 7.0 parts by weight of a blocked isocyanate, conductive particles and an antifoaming agent with respect to 100 parts by weight of polyvinyl alcohol (PVA). By forming a film and cross-linking polyvinyl alcohol (PVA) by heating, a dew condensation sensor which did not elute even when absorbed moisture and had excellent durability even for long-term use was obtained.

It should be noted that the present invention is not limited to the above-described embodiment, but can adopt various other configurations without departing from the gist of the present invention.

[0026]

According to the present invention, there is obtained an advantage that the moisture-sensitive resistor of the dew sensor does not elute even if it absorbs moisture, and exhibits excellent durability even for long-term use.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing an example of a dew sensor.

FIG. 2 is a diagram showing a difference in elution rate depending on a blending amount of a crosslinking agent.

FIG. 3 is a diagram for explanation of the present invention.

FIG. 4 is a diagram used for comparison with the present invention.

FIG. 5 is a diagram for explaining a conventional example.

FIG. 6 is a diagram for explaining a conventional example.

FIG. 7 is a diagram for explaining a conventional example.

FIG. 8 is a diagram for explaining a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Moisture sensitive resistor 2 Comb electrode 3 FPC

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G01N 27/12

Claims (6)

(57) [Claims] 1. A dew condensation sensor provided with a moisture-sensitive resistor between electrodes, wherein the moisture-sensitive resistor is made of polyvinyl alcohol crosslinked with isocyanate as a base material, and conductive particles are dispersed in the base material. A dew condensation sensor characterized by using a membrane. 2. A dew condensation sensor provided with a moisture-sensitive resistor between electrodes, wherein the moisture-sensitive resistor is made of a polyvinyl alcohol cross-linked by a blocked isocyanate as a base material.
A dew sensor comprising a film in which conductive particles are dispersed. 3. A dew condensation sensor provided with a moisture-sensitive resistor between electrodes, wherein the moisture-sensitive resistor is 100 weight polyvinyl alcohol.
1.5 to 7 parts by weight of block isocyanate
The substrate of polyvinyl alcohol crosslinked by Aneto
And a film formed by dispersing conductive particles in the substrate . 4. A dew condensation sensor provided with a moisture-sensitive resistor between electrodes, wherein the moisture-sensitive resistor is polyvinyl alcohol 100 weight.
The blending amount is more than 2 parts by weight and not more than 7 parts by weight based on the
A dew sensor comprising a base material made of polyvinyl alcohol cross-linked by lock isocyanate, and a film formed by dispersing conductive particles in the base material . 5. A dew condensation sensor provided with a moisture-sensitive resistor between electrodes, wherein the moisture-sensitive resistor is made of 100% polyvinyl alcohol.
The blending amount is more than 3 parts by weight and not more than 7 parts by weight based on the
A dew sensor comprising a base material made of polyvinyl alcohol cross-linked by lock isocyanate, and a film formed by dispersing conductive particles in the base material . 6. A dew condensation sensor provided with a moisture-sensitive resistor between electrodes, wherein the moisture-sensitive resistor is made of 100% polyvinyl alcohol.
The blending amount is more than 3 parts by weight and not more than 7 parts by weight based on the
A dew sensor comprising a base material made of polyvinyl alcohol cross-linked by lock isocyanate, and a film having a thickness of about 2 μm formed by dispersing conductive particles in the base material .