JP6237456B2 - Strain-sensitive resistance paste and mechanical quantity sensor element - Google Patents

Description

  The present invention relates to a strain-sensitive resistance paste and a mechanical quantity sensor element that can be used for measuring mechanical quantities (strain, stress, etc.).

In order to measure various mechanical quantities, a mechanical quantity sensor element having a strain sensitive body whose electric resistance value (simply referred to simply as “resistance value”) changes according to the strain quantity is used. As such a mechanical quantity sensor element, a metal strain gauge is representative, but in addition to this, a paste (strain sensitive resistance paste) made of a composite of ruthenium oxide (RuO ₂ ) and glass is used as a strain generating body. The mechanical quantity is also measured by measuring the resistance value of the strain sensitive layer formed by baking on a measurement object or an insulating plate. The description regarding such a strain sensitive resistance paste or a mechanical quantity sensor element exists in the following patent document, for example.

JP 2005-172793 A JP 2007-107963 A

  Patent Document 1 proposes a mechanical quantity sensor element in which a strain sensitive layer (pressure sensitive body) is formed between two insulating plates. When this mechanical quantity sensor element is used, the strain sensitive layer is uniformly distorted through the insulating plate, and the mechanical quantity acting can be accurately measured. However, Patent Document 1 does not mention anything about the durability and reliability of the mechanical quantity sensor element.

Patent Document 2 describes the durability of a mechanical sensor element by suppressing the creep phenomenon of glass as a viscoelastic body by dispersing inorganic crystalline reinforcing particles larger than RuO ₂ particles in glass as a matrix. It is proposed to improve the reliability and reliability. Specifically, the reinforcing particles are alumina particles having an average particle diameter of 4.5 to 53 μm or aluminum borate whiskers having an average fiber length of 10 to 30 μm and a fiber diameter of 0.5 to 1 μm. Although the creep characteristics of a pressure sensitive body containing RuO ₂ particles can be improved by these reinforcing particles, the mechanical quantity sensor element having the pressure sensitive body does not necessarily have load characteristics (linearity, hysteresis characteristics, etc.), durability, It was not excellent in reliability (to ensure desired characteristics over a long period of time).

  The present invention has been made in view of such circumstances, and has excellent sensor characteristics (load characteristics) and can stably perform accurate measurement of mechanical quantities while ensuring high reliability and durability. It is an object of the present invention to provide a strain sensitive resistance paste suitable for producing a strain sensitive layer and a mechanical quantity sensor element having the strain sensitive layer.

As a result of extensive research and trial and error, the present inventor has conducted a trial and error, and as a result, by using a strain sensitive resistance paste capable of dispersing fine fibers of a specific shape in a glass holding RuO ₂ , It was newly found that a mechanical sensor element having excellent characteristics and capable of increasing the breaking load can be obtained. By developing this result, the present invention described below has been completed.

《Strain-sensitive resistance paste》
(1) The strain sensitive resistance paste of the present invention comprises conductive particles comprising ruthenium oxide (RuO ₂ ) and having conductivity, a matrix forming material comprising glass holding the conductive particles, and the matrix forming material A reinforcing fiber made of an electrical insulating material that is dispersed in the matrix forming material to reinforce the matrix-forming material and a dispersion medium that disperses the conductive particles, the matrix-forming material, and the reinforcing fiber are mixed and adhered. A strain-sensitive resistance paste used for forming a strain-sensitive layer (strain-sensitive body) that changes an electric resistance value in accordance with a strain amount of a strain body, wherein the reinforcing fibers have an average fiber diameter of 4 μm or less. In addition, the average fiber length is 8 μm or less.

(2) When the strain-sensitive resistance paste of the present invention (appropriately, simply referred to as “paste”) is used, a resistance change characteristic (corresponding simply to “sensor characteristics”) that appears corresponding to the strain (or stress, etc.) that acts. ) Is very good, and it is easy to form a strain-sensitive layer having high strength and durability and reliability, and in turn, to manufacture a mechanical quantity sensor element having the strain-sensitive layer.

  The reason why the paste of the present invention exhibits such excellent characteristics is not necessarily clear, but at present it is considered as follows. Usually, the strain sensitive layer bends under stress (load), and compressive stress (compressive strain) is generated inside the neutral surface of the flexure, and tensile stress (tensile strain) is generated outside thereof. In any case, a stress is applied to the strain sensitive layer in a direction along the formation surface, and the strain is caused in the strain sensitive layer by the stress, thereby changing the resistance value of the strain sensitive layer. Here, when the strain-sensitive layer is formed using the paste of the present invention, the fine reinforcing fibers contained in the paste extend along the formation surface of the strain-sensitive layer, that is, the state oriented on the formation surface. (See FIG. 1). That is, the reinforcing fibers according to the present invention are oriented and distributed along the direction of the formation surface of the strain sensitive layer where stress is easily applied. Therefore, even if the reinforcing fiber according to the present invention is fine or even in a small amount, the strain sensitive layer can be effectively reinforced. In addition, the reinforcing fibers according to the present invention extending along the formation surface of the strain-sensitive layer are very fine, so that the reinforcing fibers themselves are less likely to be a starting point for fracture.

  Thus, the strain sensitive layer formed using the paste of the present invention is reinforced with fine reinforcing fibers extending in the direction of the formation surface, so even if a slight load (stress) or impact is applied. In addition, microcracks and the like are less likely to occur in the matrix-forming material (glass) that holds the conductive particles, can exhibit stable output characteristics over a long period of time, and can exhibit extremely excellent durability and reliability.

  In addition, the reinforcing fibers according to the present invention are very fine and long and extend along the formation surface of the strain sensitive layer, so that coarse fibers and particles are dispersed in the matrix forming material as in the past. Unlike the case where it is made, the strain distribution (stress distribution) around the reinforcing fiber tends to be uniform, and the fluctuation range of the strain (stress) around the reinforcing fiber is small. As a result, the strain (stress) acting on the strain-sensitive layer is uniformly dispersed and acts on each conductive particle dispersed therein, and within the measurement range (range), the stress (stress) The relationship between the distortion and the resistance value (linearity) is good, and excellent sensor characteristics with a small output difference (hysteresis) between loading and unloading are exhibited.

  By using the paste of the present invention in this way, it becomes possible to obtain a strain sensitive layer capable of achieving both sensor characteristics and durability / reliability at a high level, and further a mechanical quantity sensor element including the strain sensitive layer. It is thought.

<Mechanical sensor element>
The present invention can be grasped not only as the above-mentioned paste but also as a mechanical quantity sensor element having a strain sensitive layer formed using the paste. That is, the present invention includes an insulator and a strain-sensitive layer formed on the insulator using the above-described strain-sensitive resistance paste, and a measurement object (straining body) to which the insulator is attached. It can also be grasped as a mechanical quantity sensor element characterized in that the acting mechanical quantity can be detected based on a change in electric resistance value generated in the strain sensitive layer. The mechanical quantity sensor element appropriately includes an electrode connected to the strain sensitive layer.

<Others>
(1) The strain sensitive layer according to the present invention (the same applies to the mechanical quantity sensor element) enables detection or measurement of various mechanical quantities generated in the measurement object by measuring a resistance value that changes due to the generated strain. Is. The mechanical quantity here is not limited as long as it is a physical quantity that causes strain in the strain sensitive layer. For example, any of force, pressure (stress), torque, speed, acceleration, position, displacement, impact force, weight, mass, vacuum, rotational force, vibration, noise, and the like may be used.

(2) Unless otherwise specified, “x to y” in this specification includes a lower limit value x and an upper limit value y. A range such as “a to b” can be newly established with any numerical value included in various numerical values or numerical ranges described in the present specification as a new lower limit value or upper limit value.

It is a schematic diagram of the strain sensitive layer formed with the strain sensitive resistance paste of this invention. It is a schematic diagram which shows a mode that stress is applied to a mechanical quantity sensor element. 6 is a graph showing the relationship between the stress of the mechanical quantity sensor element according to Sample 1 and the rate of change in resistance. 5 is a graph showing the relationship between the stress of the mechanical quantity sensor element according to Sample 2 and the rate of change in resistance. 6 is a graph showing the relationship between the stress of the mechanical quantity sensor element according to Sample 3 and the rate of change in resistance. 6 is a graph showing the relationship between the stress of the mechanical quantity sensor element according to Sample 4 and the rate of change in resistance. 6 is a graph showing the relationship between the stress of the mechanical quantity sensor element according to Sample 5 and the rate of change in resistance. It is a schematic diagram which shows a mode that a 3 point | piece bending test is performed with respect to the strain sensitive layer formed in the surface of a strain generating body. It is a graph which shows the relationship between the load obtained by the 3 point | piece bending test, and resistance change rate.

  The contents described in this specification can be applied not only to the paste of the present invention but also to a mechanical sensor element having a strain-sensitive layer obtained thereby. In addition, a component related to a manufacturing method can be a component related to an object if understood as a product-by-process claim. One or two or more components arbitrarily selected from the present specification may be added to the above-described components of the present invention. Which embodiment is the best depends on the target, required performance, and the like.

《Reinforcing fiber》
(1) The reinforcing fiber according to the present invention preferably has an average fiber diameter of 4 μm or less, 3 μm or less, and further 2 μm or less. Further, the average fiber length is preferably 8 μm or less, 6 μm or less, and more preferably 5 μm or less. If the average fiber diameter or the average fiber length is excessive, it is not preferable because the sensor characteristics, durability, reliability, etc. are deteriorated.

  The average fiber diameter may be 2 nm or more, 10 nm or more, or 100 nm or more, regardless of the lower limit. Moreover, although the average fiber length does not ask | require the lower limit, it can usually be 400 nm or more, 800 nm or more, or 1 micrometer or more. If the average fiber diameter or the average fiber length is too small, the effect is poor and it is difficult to produce or obtain.

The average fiber diameter referred to in the present specification is a value obtained by randomly selecting 20 fibers from an enlarged photograph of fibers taken with an electron microscope and measuring their maximum outer diameters (fiber diameters). Average value.
The average fiber length is an average value of values obtained by randomly selecting 20 fibers from an enlarged photograph of fibers taken with an electron microscope and measuring their maximum fiber lengths.

(2) Reinforcing fiber is 1-15 parts by mass, 5-10, with 100 parts by mass of the total amount of conductive particles, matrix-forming material, and dispersion medium (including solvent) (in other words, the whole excluding reinforcing fibers). It is preferable that it is contained by mass part and further 6-9 mass parts. If there are too few reinforcing fibers, the effect will be poor, and if there are too many reinforcing fibers, the total amount of conductive particles and matrix-forming material (especially the amount of conductive particles) will be relatively lowered, and the sensitivity of the strain-sensitive layer (to stress or strain) The change rate of the resistance value) may be reduced.

(3) The reinforcing fiber may be any material as long as it does not substantially deteriorate the characteristics of the strain-sensitive layer that changes the resistance value according to the strain amount and reinforces the matrix-forming material or the strain-sensitive layer. . Such reinforcing fibers are usually made of an electrical insulating material such as ceramics. More specifically, the reinforcing fibers are made of inorganic crystalline fibers (including whiskers) such as alumina, zirconia, silica, and aluminum borate.

《Conductive particles》
Conductive particles according to the present invention consists of RuO _2. The particle size is not particularly limited, but it is preferable that the particle size is equal to or larger than that of the reinforcing fiber because deterioration of sensor characteristics, a decrease in breaking load, and the like due to the reinforcing fiber can be suppressed.

《Matrix forming material》
The matrix forming material according to the present invention is a glass that holds conductive particles (RuO ₂ particles) and reinforcing fibers while dispersing them, and uniformly reflects the strain generated in the strain sensitive layer or applied stress to the conductive particles. Consists of. The glass used as the matrix forming material is not limited to the kind thereof, for example, borosilicate glass such as lead borosilicate glass, alkali borosilicate glass, lead silicate glass such as alkali lead silicate glass, aluminosilicate glass, Alkali / alkaline earth silicate glass such as soda lime glass, phosphate glass and the like, and further, a mixed composition glass thereof can be used. In addition, the electroconductive particle and the matrix formation material may use the strain sensitive resistance paste marketed as it is.

<Mechanical sensor element>
(1) If the paste of this invention is used, it is possible to form a strain sensitive layer directly on a measuring object (straining body) and to measure the mechanical quantity. However, in order to produce uniform and average distortion in the strain sensitive layer (especially conductive particles) and to perform highly accurate measurement stably, the electrical insulator (simply referred to as “insulator”) is sensitive. It is preferable to use a mechanical quantity sensor element in which a strain layer is formed and an electrode is provided on the strain sensitive layer. At this time, if the insulating layer is composed of two insulating plates facing each other and the strain sensitive layer is sandwiched between these insulating plates, the stress or strain is more uniformly or averaged in the strain sensitive layer. It is suitable for improving the handleability.

The insulator may be of any material. For example, ZrO ₂ (zirconia), Al ₂ O ₃ (alumina), MgAl ₂ O ₄ , SiO ₂ , 3Al ₂ O ₃ .2SiO ₂ , Y ₂ O ₃ , CeO ₂ , La ₂ O ₃ , Si ₃ N _{4 and the} like. The insulator need only be insulated from the portion that contacts the strain sensitive layer, and does not need to be entirely made of an insulating material. For example, the insulator according to the present invention may be a metal body coated with ceramic as described above.

(2) There may be various methods for forming the strain sensitive layer on the insulator (manufacturing method of the mechanical quantity sensor element). For example, a mechanical quantity sensor element in which a strain sensitive layer is formed on an insulator can be obtained by applying (printing) the paste of the present invention on the insulator and then baking it. The thickness of the strain sensitive layer is not limited, but is preferably 1 to 200 μm, 5 to 100 μm, and more preferably 10 to 50 μm, for example. If the thickness of the strain sensitive layer is too small, the resistance value becomes excessive and the sensitivity to strain can be reduced. On the contrary, if the thickness is excessive, the resistance value is excessively decreased, and the sensitivity to distortion can be lowered.

  Examples 1 and 2 are shown below to describe the present invention more specifically.

[Example 1]
A plurality of mechanical quantity sensor elements (samples) were manufactured using strain-sensitive resistance pastes to which various reinforcing materials (reinforcing fibers and reinforcing particles) were added, and the sensor characteristics were measured and evaluated.

"Overview"
As shown in FIGS. 1 and 2, the mechanical quantity sensor element of each sample is coupled to the strain sensitive layer, _two insulating plates (ZrO ₂ plates) sandwiching the strain sensitive layer, and the strain sensitive layer. It consists of a silver electrode. As will be described later, each sample is first bonded by screen printing various pastes on one side of each insulating plate, followed by firing, and firing in a state where the treated surfaces of both insulating plates are in contact with each other. The stress (load) was applied while changing the stress (load) from one of the insulating plates of the mechanical quantity sensor element thus obtained, and the resistance change rate of the strain-sensitive layer generated at that time was measured.

<Production of sample>
Commercially available resistance paste (Rheus Co., R 8235DGV / hereinafter referred to as “raw material paste”) in which RuO ₂ particles, glass and their dispersion medium (organic solvent) are combined, and the reinforcement shown in Table 1 A material (alumina fiber or alumina particle) was prepared. The reinforcing materials of Sample 1 and Sample 3 are alumina fibers (Denka Alsene) manufactured by Denki Kagaku Kogyo Co., Ltd. The reinforcing material of Sample 2 is an alumina whisker manufactured by Sigma Aldrich. In Sample 4, alumina particles from Kojundo Chemical Laboratory Co., Ltd. were used as the reinforcing material instead of these reinforcing fibers.

  Each reinforcing material was added to the raw material paste in the ratio shown in Table 1, and mixed with a rotation / revolution mixer. Thus, a strain-sensitive resistance paste (referred to as “sample paste” as appropriate) containing reinforcing fibers or reinforcing particles was prepared (paste preparation step). In Sample 5, the raw material paste was used as it was without adding the reinforcing material.

  Two insulating plates (25 mm × 25 mm × 1.5 mm / Kyocera Corporation zirconia plate) were prepared for each sample, and each sample paste was screen-printed on each side. These insulating plates were heated in the atmosphere at 850 ° C. for 10 minutes, and the sample paste was baked on the insulating plates (first firing step). Thereby, the organic component was evaporated from the sample paste, the inorganic component was baked, and a strain sensitive layer was formed on the surface of the insulating plate made of zirconia. The thickness of the strain sensitive layer formed on the surface of each insulating plate was about 15 μm.

  The two insulating plates having the strain-sensitive layer formed on one side thereof were further heated in the atmosphere at 850 ° C. for 30 minutes (second firing step) with the strain-sensitive layer side being in contact with each other. As a result, a combined body in which the two insulating plates and the strain sensitive layer were integrated was obtained. An element having a predetermined size (4 mm × 4 mm × 3 mm) was cut out from each combined body. The thickness of the strain sensitive layer of each element thus obtained was about 25 μm.

  A silver paste (H-4566N manufactured by Shoei Chemical Industry Co., Ltd.) was applied to the opposing side surface of each element in which the strain sensitive layer was exposed. This was heated in the atmosphere at 850 ° C. for 10 minutes to form a silver electrode on each element (electrode formation step). In this way, a sample comprising a mechanical sensor element (see FIG. 2) having a sandwich structure in which the strain sensitive layer was sandwiched between insulators was obtained.

<Measurement>
As shown in FIG. 2, a stress f in the stacking direction is applied from one insulating plate to the mechanical quantity sensor element of each sample. The stress f was gradually changed in the range of 0 to 100 MPa, and the change in resistance value of the strain sensitive layer at that time was measured at room temperature (25 ° C.).

Specifically, the stress f is increased from 0 MPa to 100 MPa and then decreased from 100 MPa to 0 MPa. At this time, the change rate (resistance change rate) ρf = 100 × (Rf) of the resistance value (Rf) when stress is applied to the resistance value (R0) at the start of measurement (0 MPa) when no stress is applied. -R0) / R0 (%) is calculated. 3A to 3E show the relationship between the stress and the resistance change rate for each sample thus obtained. In the following, the resistance change rate when the stress is 0 MPa is represented by ρ ₀ , the resistance change rate when the stress is 50 MPa is represented by ρ ₅₀ , and the resistance change rate when the stress is 100 MPa is represented by ρ ₁₀₀ .

Further, the nonlinearity and hysteresis for each sample were calculated as follows, and the obtained results are also shown in Table 1. Nonlinearity, and [rho ₅₀ based on the measured value, 'absolute value difference between | ρ _50' ρ ₀ and [rho ₅₀ obtained when linear approximation two points when ρ ₁₀₀ -ρ ₅₀ | the FS ( The value divided by Full Scale was expressed as a percentage (% FS). Hysteresis is the percentage (%) obtained by dividing the absolute value difference | ρ _50i −ρ _50d | by FS (Full Scale) between ρ _50i when stress is increased and ρ _50d when stress is decreased. FS). Incidentally, FS sensitivity when the f = 100 MPa, that is, [rho _100.

<Evaluation>
The following can be understood from Table 1 and FIGS. 3A to 3E (these are simply referred to as “FIG. 3”). First, when using a sample paste to which a reinforcing fiber within the scope of the present invention is added, each of the mechanical quantity sensor elements (Samples 1 and 2) has sufficient sensitivity, and when the stress increases and At the time of decrease, the resistance change rate changed linearly with respect to the stress, and the hysteresis was also small. The sensor characteristics of these samples are equivalent to the mechanical quantity sensor element of Sample 5 using the raw material paste without adding the reinforcing material as it is.

  On the other hand, when a sample paste to which a reinforcing material that is outside the scope of the present invention is added is used, any of the mechanical quantity sensor elements (samples 3 and 4) has a curve in which the rate of change in resistance is convex downward with respect to stress. It became clear that linearity and hysteresis deteriorated greatly. As described above, when coarse reinforcing fibers deviating from the range defined in the present invention are used (in the case of Sample 3), as well as in the case of using isotropic reinforcing particles even in the case of fine particles (in the case of Sample 4) However, it has been clarified that the same level of sensor characteristics as in the case of not adding them (in the case of Sample 5) cannot be obtained.

[Example 2]
"Overview"
Using the sample paste according to Sample 1 and the raw material paste according to Sample 5 described above, a test piece having a strain sensitive layer formed on the surface of the insulating plate is manufactured, and the three-point bending strength of the strain sensitive layer is measured and evaluated. did. The former test piece is designated as sample 21, and the latter test piece is designated as sample 25. The formation of each strain sensitive layer was basically performed in the same manner as in Example 1, and the details are as follows.

<Production of sample>
Each paste was screen-printed on one side of an alumina plate (25 mm × 5 mm × 0.65 mm) to be a strain generating body, dried (150 ° C. × 30 minutes) and then fired (850 ° C. × 10 minutes) (strain sensitive) Layer forming step, firing step). In addition, drying was performed in air | atmosphere and baking was performed in air | atmosphere.

  The silver paste described above was applied to both ends of the strain-sensitive layer (20 mm × 5 mm × 15 μm) thus obtained and baked to form silver electrodes in the same manner (electrode formation step). A lead wire for resistance value measurement was attached to the silver electrode with solder to obtain each sample for a three-point bending test.

<Measurement>
Using Sample 21 and Sample 25, a three-point bending test as shown in FIG. 4 was performed with a precision load tester, and the change in resistance value of each strain sensitive layer was measured. The results thus obtained are shown in FIG.

<Evaluation>
(1) As is clear from FIG. 5, the sample 21 containing the reinforcing fiber according to the present invention exhibits excellent sensor characteristics (linearity and low hysteresis) similar to the sample 25 not containing the reinforcing fiber. It can also be seen that the change in the resistance change rate with respect to the load of Sample 21 is more gradual than that of Sample 25, and that the rigidity is increased by the reinforcing fibers, and thus the strain of the strain sensitive layer is suppressed. It can also be seen that Sample 21 has a higher breaking strength than Sample 25 and is about 7 to 10% stronger.

  For these reasons, the strain-sensitive layer formed using the strain-sensitive resistance paste of the present invention exhibits excellent sensor characteristics, and has improved durability and reliability by increasing strength and suppressing strain (high rigidity). It was confirmed that

(2) Incidentally, when the breakdown load of each sample (load when the strain sensitive layer breaks) was examined in detail, the sample 21 was 3.24 kgf and the sample 25 was 3.04 kgf. These breaking loads are arithmetic average values of the breaking loads obtained when the above-described three-point bending test is performed three times. In the case of this three-point bending test, tensile stress acts on each strain sensitive layer, and its resistance value increases. Therefore, when the resistance value of each strain sensitive layer became infinite, it was determined that the strain sensitive layer was broken, and the load at that time was defined as the fracture load. In any case, it has been found that the strength is sufficiently increased when the reinforcing fiber according to the present invention is contained in the strain-sensitive layer.

Claims (5)

Conductive particles comprising ruthenium oxide (RuO ₂ ) and having conductivity;
A matrix-forming material made of glass holding the conductive particles;
Reinforcing fibers made of an electrical insulating material that is dispersed in the matrix-forming material and reinforces the matrix-forming material;
The conductive particles, the matrix-forming material, and a dispersion medium for dispersing the reinforcing fibers are mixed,
A strain-sensitive resistance paste used to form a strain-sensitive layer that changes an electric resistance value according to the amount of strain of an attached strain generating body,
The reinforcing fiber has an average fiber diameter of 4 μm or less and an average fiber length of 8 μm or less.   The strain-sensitive resistance paste according to claim 1, wherein the reinforcing fiber is contained in an amount of 1 to 15 parts by mass, where the total amount of the conductive particles, the matrix forming material, and the dispersion medium is 100 parts by mass.   2. The strain-sensitive resistance paste according to claim 1, wherein the reinforcing fiber has an average fiber diameter of 2 nm to 3 μm and an average fiber length of 400 nm to 5 μm. An insulator;
A strain sensitive layer formed on the insulator using the strain sensitive resistance paste according to any one of claims 1 to 3,
A mechanical quantity sensor element characterized in that a mechanical quantity acting on a measurement object to which the insulator is attached can be detected based on a change in an electric resistance value generated in the strain sensitive layer. The insulator comprises two insulating plates facing each other,
The mechanical sensor element according to claim 4, wherein the strain-sensitive layer is sandwiched between the insulating plates.

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