JPH06294692A - Resistor paste and pressure sensor employing the same - Google Patents

Abstract

PURPOSE:To provide a high quality pressure sensor employing a resistor having electric resistance variable with the pressure by employing a resistor paste excellent in TCR characteristics and sensor sensitivity. CONSTITUTION:The pressure sensor comprises a metal base 1, an insulation layer 2 formed on the surface thereof, a resistor 3 formed on the surface of the insulation layer 2 and having electric resistance variable through deformation, and an electrode 4 for detecting resistance variation of the resistor 3, wherein the resistor 3 is formed by firing a resistor paste composed of a ruthenium oxide, an iron compound, glass frit, an organic vehicle, and a diluent.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resistor paste for a pressure sensor in which the electric resistance of a resistor changes in response to a pressure change, and a pressure sensor for detecting pressure by a change in the electric resistance of a resistor in response to pressure change. Regarding

[0002]

2. Description of the Related Art In recent years, sensors for detecting the amount of load and pressure have been widely used to detect the magnitude of stress and load generated in various parts of machines, ships, automobiles and the like. Various sensors of this type have been proposed depending on the type of base material and the type of strain-sensitive material.

As a typical example thereof, polyester,
On a film made of resin such as epoxy or polyimide,
There is a sensor (1) in which a thin film resistor made of a Cu-Ni alloy, a Ni-Cr alloy or the like is formed by vapor deposition or sputtering.

Also, as disclosed in Japanese Patent Publication No. 3-20682, there is a sensor (2) using a glass plate instead of the resin film.

Further, as disclosed in Japanese Patent Application No. 3-282663, a metal substrate, a glass layer made of a crystallized glass material formed on the surface thereof, and further formed on the surface of the glass layer, There has been proposed a pressure sensor 3 including a resistor whose electric resistance changes when strain is applied.

The magnitudes of stress, load and pressure are measured as follows. The pressure of the member generated by an external force or load is transmitted to the resistor through the resin film, the glass plate, and the metal base material. Due to the transmitted pressure, the length and the cross-sectional area of the resistor change, so that the electric resistance changes. By detecting this change in electrical resistance as an electrical signal, the magnitude of stress, load, pressure, etc. applied to the member can be detected.

By the way, one of the applications in which the pressure sensor has a large market is a vehicle suspension used in an automobile or the like. Hereinafter, the vehicle suspension will be described as an example. For example, the pressure sensor (1) is attached to the surface of the shaft with an adhesive resin or the like, and the load applied to the wheel by the vehicle body is detected by this pressure sensor.

[0008]

[Problems to be Solved by the Invention] However, (1)
When used for a long time under severe environmental conditions, such as a vehicle suspension, where the temperature range is -50 ° C to 150 ° C and the maximum load reaches 2 tons, the pressure sensor has a poor adhesive strength. Is peeled off from the member. Particularly, in the pressure sensor of (2), when the glass plate is welded to a member having a curved surface such as a shaft,
Since the glass plate has poor adhesion, strong adhesion is difficult and easy to peel off. However, in the pressure sensor of (3), since the constituent elements of the metal substrate and the crystallized glass layer and between the crystallized glass layer and the resistor layer are mutually diffused, the adhesiveness is very strong, and the pressure sensor can be used under severe environmental conditions. It is the most suitable sensor to use, but it has not been put to practical use. One of the causes of this is that the temperature change rate (TCR) of resistance is 100-
It may be as high as 200 PPm / ° C. An expensive temperature compensating element is required to eliminate the change in the resistance value due to the temperature change, which leads to an increase in the size and cost of the sensor.

An object of the present invention is to solve the above-mentioned problems of the prior art and to provide a resistor paste having excellent temperature characteristics of the resistor and a pressure sensor using the same.

[0010]

In order to achieve this object, a pressure sensor of the present invention comprises a resistor paste and a metal substrate composed of ruthenium oxide, an iron compound, a glass frit, an organic vehicle and a diluent. An insulating layer formed on the surface of the metal substrate, a resistor formed on the surface of the insulating layer, the electric resistance of which changes with the deformation of the resistor, and an electrode for detecting a resistance change of the resistor. ,
The resistor is formed by firing a resistor paste composed of ruthenium oxide, an iron compound, glass frit, an organic vehicle and a diluent.

[0011]

The resistor paste is usually composed of a conductive substance, a glass frit, an organic vehicle and a diluent, and ruthenium oxide is generally used as the conductive substance. The absolute value of the temperature change rate (TCR) of the resistor using such a resistor paste is 100 to 200 PPm.
/ ° C. Using the resistor paste of the present invention,
In addition to the conductive substances, glass frits, organic vehicles and diluents that are the components of general resistor paste, the addition of iron compounds lowers the TCR, and the strain when compression / tensile is applied. The rate of change in resistance (GF) due to increases, and the sensor amplification factor can be reduced.

[0012]

EXAMPLES The pressure sensor of the present invention will be specifically described below. FIG. 1 shows a pressure sensor according to an embodiment of the present invention. In FIGS. 1A and 1B, 1 is a metal substrate, 2 is an insulating layer, 3 is a resistor, and 4 is an electrode.

Next, each component of the sensor of the present invention will be described. (1) Insulating Substrate (a) Metal Substrate The metal substrate used in the present invention includes various alloy materials such as hollow steel, stainless steel, silicon steel, nickel-chromium-iron, nickel-iron, kovar, invar, and the like. Although a clad material or the like is selected, from the viewpoint of adhesion with the insulating layer, S
US430 is most preferred.

Once the material of the metal substrate has been determined, the desired shape processing, hole processing, etc. can be carried out by ordinary mechanical processing, etching processing,
It is applied by laser processing or the like. A cylindrical shape, a plate shape (including a foil shape), or the like is selected as the shape depending on the size of the load applied and the application.

For the purpose of improving the adhesion of the insulating layer, these metal substrates are degreased on the surface and then subjected to sandblasting, various platings of nickel, cobalt, etc., or an oxide coating layer is formed by thermal oxidation treatment. To do

(B) Insulating Layer As the insulating layer formed on the metal substrate of the sensor of the present invention, a crystallized glass layer is selected. From the viewpoint of electrical insulation and heat resistance, the crystallized glass layer is preferably composed of non-alcal crystallized glass (for example, a MgO-based crystal phase is deposited by firing). The glass composition is especially MgO
Of 16 to 50% by weight, SiO ₂ of 7 to 30% by weight, B ₂ O
_{3 to 5} to 34% by weight, BaO to 0 to 50% by weight, La ₂ O
₃ is 0 to 40% by weight, CaO is 0 to 20% by weight, P ₂ O ₅
Is 0 to 5% by weight, MO ₂ is 0 to 5% by weight (where M is Z
At least one element of r, Ti, and Sn) is preferable.

As described above, one of the reasons for selecting the crystallized glass material is to strengthen the adhesion between the metal substrate and the glass layer. In particular, the above composition has very strong adhesion.

As a method for coating the above-mentioned crystallized glass layer on a metal substrate, there are a spray method, a powder electrostatic coating method, an electrophoretic electrodeposition method and the like. The electrophoretic electrodeposition method is the most preferable from the viewpoints of the denseness of the coating, the electric insulation, and the like.

According to this method, alcohol and a small amount of water are added to glass and the mixture is ground and mixed in a ball mill for about 20 hours so that the average particle diameter of glass is about 1 to 5 μm. The obtained slurry is put in an electrolytic cell and the liquid is circulated. Then, the metal substrate is immersed in this slurry to obtain 100 to 400V.
The glass particles are deposited on the surface of the metal substrate by performing negative polarization with. After drying, this is heated at 850-900 ° C for 10
Bake for 1 minute to 1 hour. As a result, the glass fine particles are melted, and the glass component and the metal material component are sufficiently diffused into each other, so that strong adhesion between the glass layer and the metal substrate can be obtained.

In the firing, a method of gradually raising the temperature from room temperature to reach the above temperature causes innumerable fine needle-like crystals to be deposited, so that the anchor effect described later works more strongly and the adhesion with the resistor is improved. preferable.

(2) Resistor As the material for the resistor, it is possible to use a resistance material such as ruthenium oxide, tantalum oxide, thallium oxide, lead ruthenate, etc., which has a property that the electric resistance is changed by various pressure changes. However, ruthenium oxide is selected in terms of coating properties and cost. The resistor paste of the present invention comprises ruthenium oxide, an iron compound glass frit, an organic vehicle and a diluent. Iron compounds include inorganic iron compound crystals such as iron oxide, iron nitrate and iron chloride, and iron citrate,
There are solid-state materials such as organic iron compound crystals such as iron oxalate and iron acetylacetonate, organic acid iron such as iron naphthenate and iron octylate, and liquid materials such as iron sulfamate. When used as a paste material, a liquid material is preferable from the viewpoint of mixability and the like.

Next, a concrete example will be described. (Example 1) In accordance with the above-mentioned insulating layer forming step, SUS43
A 100 μm thick crystallized glass layer having a composition shown in (Table 1) to (Table 5) was electrophoretically electrodeposited on the surface of a 0 substrate (100 mm × 100 mm × 0.5 mm) and baked at 880 ° C. for 10 minutes. Various properties such as surface roughness, waviness, and heat resistance of the sample were investigated. The results are shown in (Table 1) to (Table 5) together with the composition.

The surface roughness was measured by a Talysurf surface roughness meter and indicated by the surface centerline average roughness Ra, and the waviness was evaluated by the peak-valley difference R _max obtained by the Talysurf surface roughness meter.

Regarding the heat resistance, the sample was put in an electric furnace at 850 ° C. for 10 minutes, taken out of the furnace, and allowed to cool naturally for 30 minutes. A spalling test was repeated to examine the state of cracks and peeling of the sample. . The presence of cracks was examined by immersing the cracks in red ink, wiping the surface, and visually observing the cracks. ○, △, × in the table are ○
No abnormalities are observed even after 10 cycles or more,
Δ represents the one generated in 5 to 9 cycles, and × represents the one generated in 4 cycles or less.

For adhesion, a bending test of the substrate was carried out. When the glass layer was peeled off and the metal part was exposed, x was given, Δ when the metal part was partially exposed, and ◯ when the metal part was not exposed.
And

A comprehensive evaluation was carried out based on the above evaluations, and the results are shown by ◯, Δ, and ×. Nos. 1 to 8 are obtained by changing SiO ₂ and B ₂ O ₃ while keeping other components constant. No
In Nos. 9 to 15, SiO ₂ / B ₂ O ₃ was made almost constant and the amount of MgO was changed. No16 ~ 19 is also Ca
The amount of O was changed. No. 20-24 are the same
The amount of CaO was changed. Similarly, Nos. 25 to 29 are those in which the amount of La ₂ O ₃ was changed. No30 ~ 42
Are ZrO ₂ , TiO ₂ , SnO ₂ , P ₂ O ₅ , and Z, respectively.
This is a study of the influence of nO.

As is apparent from the table, if the SiO ₂ content is increased, the heat resistance is improved, but the surface property and the adhesion are deteriorated. On the contrary, when the amount of B ₂ O ₃ is increased, the surface property and the adhesion are improved but the heat resistance is decreased. Therefore, due to the trade-off between the two, SiO ₂ is 7 to 30 in the present invention.
Wt%, B ₂ O ₃ is preferably in the range of 5 to 34 wt%.

The amount of MgO has a correlation with the crystallinity, and if it is less than 16% by weight, the precipitation of crystals is insufficient and the heat resistance is poor. Again 50
If the content is more than 10% by weight, crystals are likely to be precipitated, and when the glass is melted, it is easily crystallized, and it is difficult to obtain a homogeneous glass, and the surface roughness is increased.

If the amount of CaO is 20% by weight or more, the surface property is deteriorated, which is not preferable. When the amount of BaO is 50% by weight or more, heat resistance and adhesion are deteriorated, which is not preferable.

When La ₂ O ₃ is 40% by weight or more, heat resistance is deteriorated, which is not preferable. Other components that can be added are ZrO
₂ , TiO ₂ , SnO ₂ , P ₂ O ₅ , ZnO and the like can be mentioned, but up to 5% by weight can be added.

[0031]

[Table 1]

[0032]

[Table 2]

[0033]

[Table 3]

[0034]

[Table 4]

[0035]

[Table 5]

A pressure sensor having a resistor formed on the basis of the above-described manufacturing method will be described with reference to FIG. Direct 40φ
mm-shaped, 100 μm thick disc-shaped metal substrate (SUS430)
As pretreatment, degreasing, washing with water, pickling, washing with water, nickel plating, and washing with water are performed, and then immersed in a slurry composed of glass particles having the composition shown in No. 7 in (Table 1) to prepare a counter electrode and a metal. By applying a DC voltage between the base materials, the surface of the metal base material is coated with the glass particles, the temperature is raised from room temperature to 880 ° C. over 2 hours, and then the temperature is maintained at this temperature for 10 minutes. The crystallized glass layer of was formed as an insulating layer. Next, an electrode was formed by screen-printing an Ag-Pd-based paste in a predetermined pattern on the surface of the insulating layer and firing at 850 ° C.

The resistor paste is prepared with an average particle size of 0.1.
5 μm ruthenium oxide, PbO-S with an average particle size of 1 μm
100 g of an iO ₂ -B ₂ O ₃ type glass frit and an organic binder containing ethyl cellulose and terpineol as main components were weighed in a ratio of 3: 5: 2, and 6 g of iron naphthenate was added thereto, and these were mortared. After being mixed with, the mixture was further thoroughly mixed with three rollers. On the way, add a diluent containing butyl carbitol acetate as a main component at a suitable time to add 25
Paste viscosity of 200 ± 25 under conditions of ℃, 10rpm
It was prepared to have kcps.

This paste was screen-printed on a base material on which predetermined electrodes were previously formed, leveled at room temperature for 10 minutes, dried in a constant temperature bath at 120 ° C. for 30 minutes, and finally baked at 650 ° C. to a thickness. A resistor having a thickness of 30 μm was formed as a pressure sensor.

Example 2 A paste was prepared by adding 5 g of iron octylate instead of iron naphthenate in Example 1.

Example 3 A paste was prepared by adding 6.5 g of iron sulfamate instead of iron naphthenate in Example 1.

Example 4 In Example 1, instead of lead naphthenate, iron oxide, iron nitrate, iron chloride, iron citrate,
A paste was prepared by adding 3 g of iron oxalate and iron acetylacetonate (abbreviated as Fe-AcAc) in terms of iron oxide.

For the above Examples 1 to 3 and the following Comparative Examples, TC values on the low temperature side (-50 to 25 ° C.) and the high temperature side (25 to 150 ° C.) were determined from the resistance value at -50 ° C. to 150 ° C.
R was measured. Further, the rate of resistance change when a pressure of 0 to 2000 mmH ₂ O was applied was measured, and this was taken as GF ^* , and the results are shown in (Table 6).

[0043]

[Table 6]

As is clear from (Table 6), this embodiment is
It can be seen that the TCR is one digit lower than that of the comparative example, and the GF value is about 1.5 times higher. Therefore, according to the present invention, it is possible to provide a pressure sensor having excellent temperature characteristics and sensor sensitivity.

Although a part of the iron compound has been described in this embodiment, it goes without saying that the same applies to other iron compounds.

Comparative Example Ruthenium oxide having an average particle diameter of 0.15 μm and PbO—SiO ₂ —B ₂ O _{3 having} an average particle diameter of 1 μm
The glass frit of the system and the organic binder containing ethyl cellulose and terpineol as main components were weighed in a ratio of 3: 5: 2, mixed in a mortar, and then mixed by a triple roller. On the way, a diluent containing butyl carbitol acetate as a main component is added at an appropriate time to increase the paste viscosity to 200 ± 25 k.
The resistor paste was prepared so as to have cps (25 ° C., 10 rpm). This paste was screen-printed on the substrate with electrodes and leveled at room temperature for 10 minutes.
Dry in a constant temperature bath at 20 ℃ for 30 minutes and finally at 650 ℃
And a resistor having a thickness of 30 μm was formed to obtain a pressure sensor.

[0047]

As described above, the resistor paste of the present invention and the pressure sensor using the same can provide a high-quality sensor having a low TCR and a high GF by adding an iron compound to the resistor paste. It will be possible.

[Brief description of drawings]

1A and 1B are a plan view and a sectional view of a pressure sensor according to an embodiment of the present invention.

[Explanation of symbols]

 1 Metal Substrate 2 Insulating Layer 3 Resistor 4 Electrode

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Akihiko Yoshida 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (8)

[Claims] 1. A resistor paste comprising a conductive substance or a material which becomes a conductive substance by firing, a glass frit, an organic vehicle and a diluent, and an iron compound. 2. The resistor paste according to claim 1, wherein the iron compound is organic fatty acid iron. 3. The resistor paste according to claim 2, wherein the organic fatty acid iron is iron naphthenate or iron octylate. 4. The resistor paste according to claim 1, wherein the iron compound is iron sulfamate. 5. The iron compound is at least iron oxide, iron nitrate,
2. The resistor paste according to claim 1, containing one or more compounds selected from iron chloride, iron citrate, iron oxalate, and iron acetylacetonate. 6. An insulating substrate, a resistor formed on the surface of the insulating substrate and having an electric resistance that changes with the deformation of the insulating substrate, and an electrode for detecting a resistance change of the resistor, A pressure sensor characterized in that the body is composed of a resistor paste comprising ruthenium oxide, an iron compound, a glass frit, an organic vehicle and a diluent. 7. The pressure sensor according to claim 6, wherein the insulating substrate is a metal substrate having an insulating layer formed on the surface thereof. 8. The metal substrate is SUS430 and the insulating layer is M
gO: 16 to 50 wt%, SiO ₂ : 7 to 30 wt%,
_{B 2 O 3: 5~34wt%,} BaO: 0~50wt%, L
_{a 2 O 3: 0~40wt%,} CaO: 0~20wt%, P
₂ O ₅ : 0-5 wt%, MO ₂ : 0-5 wt% (however, M
The pressure sensor according to claim 7, wherein is a crystallized glass layer made of a composition of at least one element of Zr, Ti, and Sn.