JPH03122504A - Strain gage - Google Patents

Abstract

PURPOSE:To obtain excellent dimensional stability in relation to temperature and humidity by a method wherein a para-orientation type aromatic polyamide having specific values of logarithmic viscosity, a thermal expansion coefficient, a heat shrinkage rate and an absorption coefficient is used as a material of polyamide resin constituting a film. CONSTITUTION:A gage pattern 2 made up of a resistance grid made of an alloy is formed on a film 1 constituted of a material of polyamide resin and lead wires 3 are connected to the opposite end parts of this pattern 2, so as to construct a strain gage. In this strain gage, the material of polyamide resin constituting the film is a para-orientation type aromatic polyamide having logarithmic viscosity of 3.5 or above, substantially, and the film has a thermal expansion coefficient of (0-15) X 10<-6> mm/mm/ deg.C at a temperature of 25 to 250 deg.C, a heat shrinkage rate of 0.2 % or below at 250 deg.C, a hygroscopic expansion coefficient of 30 X 10<-6> mm/mm/%RH or below at 25 deg.C and an absorption rate of 2.5 wt.% or below at 25 deg.C and at 65 %RH. According to this constitution, high reliability can be obtained for the strain gage even in a harsh environment.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an improved strain gauge, and more specifically, it has excellent dimensional stability against temperature and humidity, has low moisture absorption, and is resistant to tearing. This invention relates to a strain gauge using a film substantially made of para-oriented aromatic polyamide, which is difficult to use and has excellent chemical resistance and heat resistance.

(Prior Art) A strain gauge is a strain gauge that has a gauge pattern formed by arranging resistance wires (resistance grid) on a sheet (film) made of paper, felt, or resin. There are many problems when using resins.

First, the temperature coefficient of resistance of the electrical resistor of a conventional strain gauge is determined by heat treatment, which takes into account the thermal expansion coefficient of the structural material and the thermal expansion coefficient of the strain gauge, and minimizes the apparent strain due to the thermal expansion of the structural material to be measured. I had adjusted it accordingly. This means that in order to meet the requirements for strain gauges with limited size and high electrical resistance, it is necessary to reduce the grid width of the resistor, and the base material (film) relative to the resistor has to be reduced. This increases the effect of thermal expansion. This makes it difficult to minimize the apparent distortion of the structure due to temperature changes by controlling the temperature coefficient of resistance of the resistor.

In addition, when the thickness of the structural material to be measured is thin, if a conventional strain gauge is bonded under pressure with a thermosetting adhesive,
The thin structural material bends due to the difference in thermal expansion with the base material of the strain gauge.

When forming an alloy resistor on a polymer sheet by sputtering, etc., the temperature of the film serving as the substrate is 100 to 3
It is necessary to control the temperature coefficient of resistance of the alloy film by maintaining it at an appropriate temperature of 00°C and adjusting the size of the crystal grains of the alloy film formed on the sheet, but conventional base materials have poor heat resistance. However, there were no known measures to deal with this problem.

Furthermore, strain gauges have been required to have improved creep performance, prevention of changes in adhesive strength over time, and improved chemical resistance.

JP-A-61-176803 is an example of using polyimide resin to solve these problems, but even if this polyimide resin is used, it still has the above problems, especially chemical resistance (resistance to chemicals). alkalinity) and creep properties are not sufficiently improved. In addition, polyimide resins are very expensive, so their use has been avoided.

(Problem B to be Solved by the Invention) An object of the present invention is to provide a highly reliable strain gauge that solves the above-mentioned conventional drawbacks at a low cost.

(Means for Solving the Problems) In the present invention, a gauge pattern consisting of an alloy resistor grid is formed on a film made of a polyamide resin material, and lead wires are connected to both ends of the gauge pattern. In the strain gauge, the polyamide resin material is a film made of substantially para-configured aromatic polyamide having a logarithmic viscosity of 3.5 or more, and
The coefficient of thermal expansion at °C is (0~l5) XIO-6
+nm/nu++/'C12 Thermal contraction rate at 50℃ is o, i% or less, hygroscopic expansion coefficient at 25℃ is 30
X 10-hIIn/nun/%RH or less, and 25
This strain gauge is characterized in that the film has a moisture absorption rate of 2.5% by weight or less at 65% RH.

The aromatic polyamide used in the present invention is substantially composed of units selected from the group consisting of the following structural units.

NH-Ar+-NH-(1) CO-8rt-GO-(2) Nll-Ar+-CO-(3) Here, Arl, Arz, and Ar are each divalent aromatic groups. , (1) and (2) are substantially equimolar when present in the polymer.

In the present invention, in order to ensure good heat resistance, each of 8r2, Arz, and Ar3 needs to be a so-called linearly oriented group.

Here, linear orientation means that the bonds that grow the molecular chain are coaxially or parallel to the opposite direction of the aromatic group. Specific examples of such divalent aromatic groups include paraphenylene, 4,4'-biphenylene, 1,4-naphthylene, 1,5-naphthylene, 2.5-
Examples include pyridazine. They may be substituted one or more with non-reactive groups such as halogen, lower alkyl, nitro, methoxy, cyano groups. Also these 2
A special example of a valent aromatic group is a divalent group represented by the general formula %. Here, X is 4
A divalent group composed of a chain of the following even number of atoms -
Ar, -X-Ar, - as a whole have substantially conjugated double bond properties. Specifically, X is trans-C11=CH-, -! t, N-, -CH=N-.

etc. Ar, , Ar2 and Ar= may each be two or more types, and may be the same or different.

The polymer used in the present invention can be produced from diamines, dicarboxylic acids, and aminocarboxylic acids corresponding to each unit by a method known so far. Specifically, a method is used in which a carboxylic acid group is first induced into an acid halide, an acid imidabride, an ester, etc., and then reacted with an amino group. A solid phase polymerization method or the like can be used.

The aromatic polyamide used in the present invention may be copolymerized with groups other than those mentioned above in an amount of about 10 mol % or less, or may be blended with other polymers.

The most typical aromatic polyamide of the present invention is
Poly-p-phenylene terephthalamide (hereinafter referred to as PPTA)
It is abbreviated as. ) and poly-P-benzamide.

If the degree of polymerization of the polymer of the present invention is too low, it will not be possible to obtain a film with good mechanical properties.
A polymer with a degree of polymerization that gives a value measured at 30° C. by dissolving 0.5 g of polymer in all is selected.

The film used in the present invention should meet the requirements described below.

First of all, the coefficient of thermal expansion of the film used in the present invention is measured in the range of 25 to 250°C and is (0 to 15) x 1O.
-611ITIl/IIl [within the range of 117°C. The thermal expansion coefficient of general organic polymer is 30X
10-"+nm/mm/"C or more, for metals it is (10-20) x 10-bmm/mm/'C, for ceramics it is (1-10) x 10-bmm/m
There is m/"C7'.

As described above, although the coefficient of thermal expansion of organic polymers is larger than that of metals and ceramics, the coefficient of thermal expansion of the film used in the present invention is close to that of ceramics and is almost the same as that of metals. If the coefficient of thermal expansion is as small as that of inorganic materials such as metals and ceramics, when these inorganic materials and organic materials are combined, dimensional changes will occur in response to temperature changes, so thermal stress and warping will not occur, making it suitable for industrial use. It is extremely useful. A film with such excellent dimensional stability against heat was achieved for the first time by preventing shrinkage during drying, maintaining the planar orientation of the molecular chains, and by drying or heat treatment at 350° C. or higher.

Second, the film used in the present invention should have a heat shrinkage rate of 0.2% or less at 250°C. As described above, the heat shrinkage rate of the film used in the present invention is extremely small, and is superior to polyimide, which currently occupies a large position as a heat-resistant film. The heat shrinkage rate is preferably 0.05% or less. The film used in the present invention has an extremely low heat shrinkage rate of 250°C, which is slightly lower than that of drying or heat treatment, without substantially reducing the orientation and crystallinity enhanced by drying or heat treatment.
It can only be obtained by heat-setting the film at the above temperature under no tension or under low tension.

As described above, in the present invention, since a film with a low thermal shrinkage rate is used, even if a temperature change occurs when using a strain gauge, warpage, peeling, or change in resistance value does not occur.

Thirdly, the film used in the present invention has a hygroscopic expansion coefficient of 30 x 10-htmn/mm/ at 25°C.
%RH or less. Hygroscopic expansion coefficient is preferably 20X
10-' decoration/rrm/%RH or less. This characteristic of small dimensional changes due to moisture absorption is important for strain gauges to maintain a certain level of performance and function regardless of whether the lid is opened during the hot and humid summer or the low humidity and dry winter. This is achieved by ensuring high crystallinity and orientation through drying or heat treatment.

Fourth, the film used in the present invention has unique high crystallinity due to high temperature drying or heat treatment, and has a 25°C65%R
The moisture absorption rate in H is 2.5% by weight or less. If the moisture absorption rate is greater than 2.5% by weight, there will be disadvantages such as a significant change in the resistance value of the strain gauge and a decrease in the adhesion between the gauge pattern and the film over time.

Furthermore, the film used in the present invention is heated at 23°C, 65% R
10 when applying a load of 10 kg/sleep 2 at H
It is desirable that the elongation rate after 0 hr is 3% or less. Polyimide and P currently used as base films
When compared with the ET film which shows an elongation rate of 7% or more, it can be seen that it shows good creep resistance properties. Such good creep properties indicate that accurate values can always be obtained even when the strain gauge is used for a long time.

In order to obtain such a film used in the present invention, it is first necessary to adjust the optical anisotropic dope of the para-oriented aromatic polyamide.

A suitable solvent for preparing the dope used for forming the film is sulfuric acid at a concentration of 95% by weight or more. The dope of the present invention, in which it is difficult to dissolve with less than 95% sulfuric acid or the dope becomes extremely viscous after being dissolved, contains chlorosulfuric acid,
A small amount of fluorosulfuric acid, phosphorus pentoxide, trihalogenated acetic acid, etc. may be mixed. Although sulfuric acid can have a concentration of 100% by weight or more, a concentration of 98 to 100% by weight is preferably used due to problems such as stability and solubility of the polymer.

The polymer concentration in the dope is at least a concentration that exhibits optical anisotropy at room temperature (approximately 20 to 30° C.) or higher, and specifically is used at approximately 10% by weight or more. At polymer concentrations below this, ie, polymer concentrations that do not exhibit optical anisotropy at room temperature or higher, the formed film often does not have desirable mechanical properties. The upper limit of the polymer concentration in the dope is not particularly limited, but it is usually 20% by weight or less, especially at high ηi.
For the para-oriented aromatic polyamide of nh, 18% by weight or less is preferably used, more preferably 16% by weight.
It is as follows.

The dope may contain conventional additives such as fillers, light removers, UV stabilizers, heat stabilizers, antioxidants, pigments, solubilizing agents, etc.

Whether the dope is optically anisotropic or optically isotropic can be determined by a known method, such as the method described in Japanese Patent Publication No. 50-8474, but the critical point depends on the type of solvent, temperature, polymer It depends on the concentration, degree of polymerization of the polymer, content of non-solvent, etc., so by investigating these relationships in advance, you can create an optically anisotropic dope and change the conditions to make it an optically isotropic dope. It is possible to change from tropic to optically isotropic.

Prior to molding and solidifying the dope, it is preferable to remove as much insoluble dust, foreign matter, etc. as possible by filtration, etc., and to remove gases such as air generated or involved during melting. Deaeration can be performed after the dope is prepared, or can be achieved by performing it under vacuum (reduced pressure) from the stage of charging raw materials for preparation. Preparation of the dope can be carried out continuously or batchwise.

The dope thus prepared is cast from a die, for example a slit die, onto a moving support surface while maintaining its optical anisotropy. In the present invention, steps such as casting and subsequent conversion to optical isotropy, coagulation, washing, stretching, and drying are preferably performed continuously, but if necessary, all or part of these steps may be performed. It may be carried out intermittently, that is, batchwise.

The method for obtaining the transparent film used in the present invention is to cast the dope onto a supporting surface and then convert the dope from optically anisotropic to optically isotropic prior to solidification.

To change optical anisotropy to optical isotropy, specifically, before solidifying an optically anisotropic dope cast on a support surface, the concentration of the solvent forming the dope is lowered by absorbing moisture. Transform the dope into an optically isotropic region by changing the solubility and polymer concentration, or increase the temperature of the dope by heating to transform the dope phase into an optically isotropic region, or simultaneously or sequentially absorb moisture and heat. This can be achieved by using it in combination with

In particular, methods using moisture absorption, including methods that use heating in combination, are useful because the optical isopotency ratio of optical anisotropy can be achieved efficiently and without causing decomposition of the polymer.

To make the dope absorb moisture, air at normal temperature and humidity may be used, but humidified or heated and humidified air is preferably used. The humidified air may contain mist-like moisture exceeding the saturated vapor pressure, and may be so-called water vapor. However, supersaturated steam at a temperature of about 45° C. or lower is not preferred because it often contains large particles of condensed water. Moisture absorption is carried out by humidified air at room temperature to about 180°C, preferably 50°C to 150''C.

In the case of a heating method, the heating means is not particularly limited;
A method of applying humidified air such as steam to the casting dope,
Methods include irradiation with an infrared lamp and dielectric heating.

The optically cast dope on the supporting surface is then subjected to solidification. For example, water, dilute sulfuric acid of about 70% by weight or less, sodium hydroxide aqueous solution of about 20% or less, and ammonium water, about 10% by weight can be used as the dope coagulating liquid.
These include the following sodium sulfate, sodium chloride aqueous solutions, and calcium chloride aqueous solutions. The temperature of the coagulating liquid is preferably 15°C or lower, more preferably 5°C or lower. This is because, in general, it has been found that the lower the temperature of the coagulating liquid, the less voids are included in the film.

Since the coagulated film as it is contains acid, it is necessary to wash and remove the acid as much as possible in order to produce a film whose mechanical properties are less likely to deteriorate due to heating. Specifically, it is desirable to remove the acid content to about 500 ppm or less. Water is usually used as the cleaning liquid, but if necessary, hot water may be used, or washing may be performed by neutralizing with an alkaline aqueous solution and then using water or the like. Cleaning is carried out, for example, by running the film in a cleaning liquid, spraying a cleaning liquid, or the like.

The cleaned film is then subjected to drying. When a film is placed under no tension as it dries, that is, the moisture content decreases, the film generally shrinks, but when obtaining the film used in the present invention, it is important that the film does not shrink during the drying process. Here, the expression "without shrinkage" should be understood to include drying while maintaining a constant length and drying while stretching.

For example, an embodiment in which the film is stretched only in one direction and the length remains constant in the other direction is also allowed. Selection of the drying temperature is also important; drying should be carried out at a temperature of 350°C or higher (TI"c > 350°C, or dried at an arbitrary temperature first and then dried at 350°C).
It is carried out by heat treatment at a temperature (TloC) of 0° C. or higher without shrinkage. Here, drying means removing moisture from the film, and changing the physical structure (eg, crystalline state) of the film thereafter is called heat treatment.

In any case, it is necessary to fix the structure under tension at Tl('C) of 350° C. or higher, thereby reducing the hygroscopic expansion coefficient and suppressing moisture absorption.

After drying or heat-treating at a temperature Tl ("C) of 350°C or higher, then 250<72<Tl-30
It is also important to perform the heat treatment under no tension or low tension of 0 to 0.8 kg/cm2 at a T2 ("C) that satisfies the requirements. This means performing so-called heat fixation under virtually no tension. However, this heat setting can reduce the thermal shrinkage rate and improve the tear resistance as a side effect.

To perform drying or heat treatment without causing the above-mentioned shrinkage, for example, use a method such as placing it in a tenter or metal frame and placing it in an oven.Also, drying under relaxed or low tension can be done with the free end open. How to insert the tenter into the tenter
2>50 ("C)) method, or by slightly narrowing the gripping interval of the tenter.Other conditions related to drying and heat treatment are not particularly limited, and heated gas (
You can freely choose from methods such as air, nitrogen, argon, etc.), methods using room temperature gas, methods using side radiation heat such as electric heaters and infrared lamps, and dielectric heating methods. In the method of the present invention, one of the preferred embodiments is to manufacture the film while running it continuously throughout the entire process, but if desired, it may be carried out partially in a batch manner. Further, an oil agent, an identification dye, etc. may be added to the film in any step.

In addition, in order to obtain a film with excellent transparency, that is, extremely high light transmittance, the dope is a heat source, moisture absorbing gas, heating gas, support surface, coagulation liquid, cleaning liquid, drying gas, etc., and dirt and dust. It is preferable to keep the content as low as possible, and in this respect, one preferred embodiment is to manufacture the film in a so-called clean room or with clean water.

In the present invention, when integrating the individually oriented aromatic polyamide film and the alloy that will become the resistor, adhesiveness is important. The resistor grid and the film may be integrated by bonding with a thermosetting adhesive, or by forming an alloy film on the film by sputtering, vapor deposition, or the like. At this time, there are six ways to further increase the adhesive strength: roughening the surface of the resistor material, or surface treatment with a silane coupling agent, titanate coupling agent, aluminum alcoholate, aluminum chelate, zirconium chelate, aluminum acetylacetone, etc. Alternatively, the surface of the film may be treated by corona discharge or the like. By using the para-oriented aromatic polyamide film with special characteristics obtained by the above method as an insulating substrate, it is possible to achieve the object of the present invention for the first time without deterioration, deterioration, warping, etc. even in harsh environments. This results in a highly reliable strain gauge that does not cause strain.

(Example) Examples are shown below, but these Examples are intended to explain the present invention, and are not intended to limit the present invention.

FIG. 1 is a plan view of a strain gauge according to an embodiment of the present invention, and FIG. 2 is a plan view of the actual height measurement according to FIG. 1.
FIG. In the figure, reference numeral 1 indicates a characteristic rose-oriented aromatic polyamide film according to the present invention. film 1
A gauge pattern 2 is formed on the surface. The film 1 may be made of only the resin, or may be made of the same or other polymer material with the gauge pattern sandwiched therebetween. The thickness of the film material (that is, the base material) is, for example, about 7.5 to 25 μm. When viewed in cross section, the gauge pattern 2 is composed of a resistor grid 4 as shown in FIG. The thickness of the resistor grid 4 is, for example, 0.3 to 1.0.
It is μm. Note that numeral 3 indicates a lead wire. This example includes, for example, a step of forming a film of CuNi or NiCr alloy on a film by sputtering or vapor deposition, and then fabricating a strain gauge pattern by photo-etching, and a step of manufacturing a strain gauge using a lithography method, a sputtering method, or It is obtained by a process of manufacturing a strain gauge by manufacturing a gauge pattern of CuNi or NiCr alloy film on a film by vapor deposition. Next, a more detailed example will be given regarding the method for producing the individually oriented aromatic polyamide film used in the present invention. In the examples, parts by weight or weight % are shown unless otherwise specified. Logarithmic viscosity ηinh is 98% sulfuric acid 100 m
0.5 g of polymer was dissolved in 1 liter of water and measured at 30° C. in a conventional manner.

A thermomechanical analyzer was used to measure the expansion coefficient.
Length between grips: 15I! 0.05kg/m2 for 1m sample
The load was applied. For thermal expansion coefficient, 25 to 25
The dimensional change of the sample was measured at 0°C, and the change rate between 25 and 250°C was divided by 225 to calculate the change.

On the other hand, in the case of the hygroscopic expansion coefficient, the temperature is first kept in a 20% relative humidity atmosphere at 25°C, and then the
Humidification was performed until the relative humidity rose to 0%, and the dimensional change rate during this period was calculated by dividing by 60. The moisture absorption rate is the weight measured by leaving the film at 25°C and 65% relative humidity for 48 hours, and
This was then calculated from the weight of the film obtained by drying in a vacuum dryer at 120° C. until a constant weight was reached. The heat shrinkage rate at 250°C was calculated from the dimensional change at room temperature (25°C) before and after the oven treatment by applying a tension of 0.05 kg/mm and leaving it in an oven at 250°C for 30 minutes. .

Example 1 A PPTA polymer having an ηinh of 5.5 was dissolved in 99.7% sulfuric acid at a polymer concentration of 11.5% to obtain an optically anisotropic dope at 60°C. The viscosity of this dope was measured at room temperature and was found to be 10,600 poise.

In order to facilitate film formation, this dope was degassed under vacuum while being maintained at 70°C. This case also had optical anisotropy and a viscosity of 4,400 voids as described above. A 1.5m curved pipe from the tank, through the filter, through the gear pump, to the die is kept at 70°C and heated to 0. lX300m
Cast from a gou with a slit of m to a tantalum belt polished to a mirror surface, at a relative humidity of about 12%.
The cast dope was made optically isotropic by blowing air at 5°C, and then introduced together with the belt into water at 5°C to solidify. The coagulated film was then peeled off from the belt and washed by running it in warm water at about 40°C. Without drying the washed film, use a tenter to reduce the length and width by 15% each.
Stretch at a constant length using a second tenter.
It was dried with hot air at 70°C.

Furthermore, the film was introduced into a third tenter, the clip-shaped gripping portion was adjusted so that the gripping length in the width direction and the length direction was decreased by 5% each, and the film was heat-set at 340'C. At this time, the tension in the third tenter was almost O.

The obtained film has a thickness of 20 μm, η1nh=5,1
, strength 28kg/mm", elongation 23%, Young's modulus 760
kg/mn”, thermal expansion coefficient 11 x 10 mm-h
/mm/'C1 thermal contraction rate was less than 0.01%, hygroscopic expansion coefficient 21 x 10 tmth-h/lrrm/%RH1 moisture absorption rate 1.5%.

Also, at 23'C65%RH, 10kg/11
The elongation rate after 100 hours when a load of 1111'' was applied was 2.4%.

Example 2 A PPTA film was produced in the same manner and under the same conditions as in Example 1, except that the third tenter temperature was set to 320°C. The obtained film had a thickness of 20 μm, 7
71nh=5.2, strength 29kg/mm", elongation 25
%, Young's modulus 890 kg/mm2, thermal expansion coefficient 10
10 mm-'/mm/''C1 heat shrinkage rate 0.01
%, hygroscopic expansion coefficient 13 x 10 H-b/mn/
%RH1 moisture absorption rate was 1.6%. Also, 23℃65%
1 when applying a load of 10 kg/w at RH
The elongation rate after 00 hours was 2.2%.

Example 3 A PPTA polymer having an ηinh of 4.8 was dissolved in 99.5% sulfuric acid at a polymer concentration of 12% to obtain a 3,600 poise dope with optical anisotropy at 45°C. After degassing and filtration, the dope was cast onto a tantalum belt through a gouie with a 0.08 mm x 300 rrrm slit. The cast dope was converted into an optically isotropic dope by blowing air at about 75°C with a relative humidity of 80%, and then coagulated with an aqueous sulfuric acid solution at 0°C.

After peeling off the coagulated film from the belt, soak it in room temperature water,
It was washed successively with a 2% caustic soda aqueous solution and with water at about 30 to 40°C. The washed wet film containing approximately 250-350% water was dried at constant length in a tenter with circulating hot air at 180°C. Next, the film was heat-treated from above and below for a fixed length using a 410°C hot plate attached to the exit of the tenter, and the holding length was reduced by about 8% in the width and length directions in a third tenter kept at 300°C. It was heat fixed while The obtained film had a thickness of 25 μm and a thickness of ηinh·4.
4. Strength 32kg/mm", elongation 19%, Young's modulus 80
0kg/mm", thermal expansion coefficient 14X10-6/kaku/'
C1 thermal contraction rate less than 0.01%, hygroscopic expansion coefficient 10X
It was an isotropic film with a moisture absorption rate of 10 mm-'/mm/%RH1 of 0.9%. Further, the elongation rate after 100 hours when a load of 10 kg/mm'' was applied at 23° C. and 65% RH was 2.5%.

The strain gauge using the film shown in the example is
Since the coefficient of thermal expansion is low, the adhesive strength is more stable against temperature changes than when the coefficient of thermal expansion is large.

Furthermore, this strain gauge had improved creep performance, so it continued to provide accurate values even after long-term use.

(Effects of the Invention) The film used in the present invention has extremely excellent dimensional stability against temperature and humidity. It also has a low moisture absorption rate and excellent creep resistance. Furthermore, it also has the excellent heat resistance and chemical resistance that the disjointed aromatic polyamide itself has. Especially when compared with polyimide, which is a conventional heat-resistant base material, it has excellent alkali resistance.

For this reason, the strain gauge of the present invention has high reliability without deformation, warping, peeling, etc., and without failure, even in harsh environments such as high temperatures, high temperatures, and cold temperatures. It also exhibits excellent properties in many respects, such as heat resistance and chemical resistance.

Furthermore, there is an advantage that the aromatic polyamide film can be supplied at a lower cost than polyimide, which is a conventional heat-resistant base material.

[Brief explanation of drawings]

FIG. 1 is a plan view of a strain gauge according to an embodiment of the present invention, and FIG. 2 is a sectional view taken along line AA' in FIG. 1... Film 2... Gauge pattern (including resistor grid) 3.
...Lead wire 4...Resistor grid

Claims (1)

[Claims] In a strain gauge in which a gauge pattern consisting of an alloy resistor grid is formed on a film made of a polyamide resin material, and lead wires are connected to both ends of the gauge pattern, the polyamide resin material has a logarithmic viscosity. is a film made of substantially para-oriented aromatic polyamide with a coefficient of 3.5 or more, and a thermal expansion coefficient of (0 to 15) x 10^-^6 mm/mm/°C at 25 to 250 °C,
Thermal contraction rate at 250℃ is 0.2% or less, and the hygroscopic expansion coefficient at 25℃ is 30 x 10^-^6mm/mm/%.
Moisture absorption rate below RH and at 25°C and 65%RH is 2.
A strain gauge characterized by being a film of 5% by weight or less.