JP7659380B2 - Manufacturing method of laminated film and strain sensor - Google Patents

Description

The present invention relates to a method for manufacturing a laminated film and a strain sensor.

Conventionally, a strain gauge has been known that has a substrate made of polyimide and a resistor made of chromium nitride formed on the substrate (see, for example, Patent Document 1 below).

JP 2019-66312 A

Therefore, strain gauges are required to suppress the variation in temperature resistance coefficient caused by storage in a hot and humid environment. However, the strain gauge described in Patent Document 1 has the disadvantage of not being able to fully satisfy the above requirements.

In addition, if a crack occurs in the resistor of the strain gauge, it will be impossible to sense the strain of the test object.

The present invention provides a laminated film and a method for manufacturing a strain sensor in which the variation in temperature resistance coefficient caused by storage in a humid and hot environment is suppressed and the generation of cracks is suppressed.

The present invention (1) is a laminated film having an insulating base film and a resistive layer in that order in the thickness direction, the resistive layer having a thickness of 150 nm or less, the laminated film being cut to have lengths of 15 mm and 5 mm in a first direction and a second direction perpendicular to the thickness direction and perpendicular to each other, and the absolute values of the dimensional change rates in each of the first direction and the second direction after pulling both ends of the sample in the first direction with a force of 49 mN/5 mm for 4 hours in an atmosphere of 85°C and 85% RH are both 0.025% or less.

In the laminate film of the present invention, the absolute values of the dimensional change rates of the laminate film in both the first and second directions are 0.025% or less, so that the fluctuation of the temperature resistance coefficient due to storage in a humid and hot environment is suppressed. In addition, in the laminate film of the present invention, the thickness of the resistance layer is 150 nm or less, so that the generation of cracks can be suppressed.

The present invention (2) includes a laminated film having an insulating base film and a resistive layer in that order in the thickness direction, the resistive layer having a thickness of 150 nm or less, the base film being cut so that the lengths in a first direction and a second direction perpendicular to the thickness direction and perpendicular to each other are 15 mm and 5 mm, respectively, and after both ends of the sample in the first direction are pulled with a force of 49 mN/5 mm for 4 hours in an atmosphere of 85°C and 85% RH, the absolute values of the dimensional change rates in each of the first direction and the second direction are both 0.040% or less.

In the laminated film of the present invention, the absolute values of the dimensional change rate of the base film in each of the first and second directions are 0.040% or less, so that the laminated film is prevented from varying in temperature resistance coefficient due to storage in a humid and hot environment. In addition, in the laminated film of the present invention, the thickness of the resistive layer is 150 nm or less, so that the generation of cracks can be prevented.

The present invention (3) includes the laminate film according to (1) or (2), in which the resistive layer contains chromium nitride.

The present invention (4) includes the laminate film according to any one of (1) to (3), in which the base film is polyimide or polyethylene naphthalate.

The present invention (5) includes a method for manufacturing a strain sensor, which comprises patterning the resistive layer in the laminate film described in (1) or (2) to form a strain sensor portion.

The manufacturing method of the present invention makes it possible to manufacture a strain sensor in which the variation in temperature resistance coefficient caused by storage in a humid and hot environment is suppressed and the generation of cracks is suppressed.

The laminated film and strain sensor manufactured by the strain sensor manufacturing method of the present invention suppress the variation in temperature resistance coefficient due to storage in a humid and hot environment, and suppress the formation of cracks.

FIG. 1 is a cross-sectional view of a laminated film according to one embodiment of the present invention. 2A and 2B show a strain sensor in which the resistive layer shown in FIG. 1 is patterned, with FIG. 2A being a cross-sectional view and FIG. 2B being a plan view. FIG. 3 is a cross-sectional view of a substrate film that is the subject of measurement of the dimensional change rate.

First Embodiment
A first embodiment of the laminated film of the present invention will be described with reference to FIG.

<Laminated film>
The laminated film 1 is a film for a strain sensor used in manufacturing a strain sensor 15 (see FIGS. 2A to 2B) described later. In other words, the laminated film 1 is an intermediate member for producing the strain sensor 15. However, the laminated film 1 is a device that can be distributed as a single component and is industrially applicable. The laminated film 1 extends in a planar direction perpendicular to the thickness direction. Specifically, the laminated film 1 includes a base film 2 and a resistive layer 3 in this order toward one side in the thickness direction.

<Base film>
The base film 2 is insulating. The base film 2 forms the other surface in the thickness direction of the laminate film 1. The base film 2 extends in the planar direction.

The thermal expansion coefficient of the base film 2 at 25°C to 155°C is, for example, 28 ppm/°C or less, preferably 20 ppm/°C or less, more preferably 17 ppm/°C or less, and for example, 1 ppm/°C or more, in both the first direction and the second direction perpendicular to the thickness direction and perpendicular to each other. If the thermal expansion coefficient of the base film 2 is equal to or less than the upper limit mentioned above, the absolute value of the dimensional change rate of the laminate film 1 (described later) can be kept within a predetermined range. In the examples described later, the thermal expansion coefficient is measured, for example, according to the description of JIS K 7197 (1991).

The thermal shrinkage rate of the base film 2 at 200°C is, for example, 0.05% or less, preferably 0.04% or less, more preferably 0.03% or less, particularly preferably 0.02% or less, and is, for example, more than 0%. If the thermal shrinkage rate of the base film 2 is equal to or less than the upper limit described above, the absolute value of the dimensional change rate of the laminate film 1 (described later) can be kept within a specified range. The thermal expansion coefficient is measured according to the description of JIS K 7133 (1999).

The material of the base film 2 is not particularly limited, and specifically, a material having the above-mentioned range of thermal expansion coefficient and/or thermal shrinkage rate is selected. Examples of the material of the base film 2 include resins such as polyimide (PI) and polyethylene naphthalate (PEN). These can be used alone or in combination. From the viewpoint of obtaining a low thermal expansion coefficient and a low thermal shrinkage rate, PI and PEN are preferable. The base film 2 can be a commercially available product, such as Kapton 200V, Kapton 200EN, Kapton 150EN (all polyimide films manufactured by Toray DuPont Co., Ltd.), and the Teonex series (polyethylene naphthalate films manufactured by Teijin Limited).

The thickness of the base film 2 is not particularly limited, and is, for example, 2 μm or more, preferably 10 μm or more, more preferably 20 μm or more, and is, for example, 500 μm or less, preferably 300 μm or less, more preferably 100 μm or less.

One side of the base film 2 in the thickness direction can be subjected to treatments such as corona discharge treatment, ultraviolet irradiation treatment, plasma treatment, and sputter etching treatment to improve adhesion with the resistive layer 3.

<Resistance layer>
The resistive layer 3 is a layer that is patterned when the strain sensor 15 (see FIGS. 2A and 2B) is manufactured from the laminated film 1. The resistive layer 3 is disposed on one surface in the thickness direction of the base film 2. The resistive layer 3 forms one surface in the thickness direction of the laminated film 1. Specifically, the resistive layer 3 is in contact with the entire one surface in the thickness direction of the base film 2.

The resistive layer 3 contains chromium nitride. Specifically, the material of the resistive layer 3 contains chromium nitride as a main component. On the other hand, the material of the resistive layer 3 is allowed to contain, for example, unavoidable impurities. The proportion of unavoidable impurities in the resistive layer 3 is, for example, 1 atomic % or less, preferably 0.1 atomic % or less, and more preferably 0.05 atomic % or less. Preferably, the resistive layer 3 is made of chromium nitride.

In chromium nitride, the molar parts of nitrogen atoms per 100 molar parts of chromium atoms is, for example, 1.0 molar part or more, and, for example, 10.0 molar parts or less. The molar parts of nitrogen atoms per 100 molar parts of chromium atoms are measured by Rutherford backscattering spectrometry (RBS).

The thickness of the resistive layer 3 is 150 nm or less. On the other hand, if the thickness of the resistive layer 3 exceeds 150 nm, cracks are likely to occur in the resistive layer 3.

The thickness of the resistive layer 3 is preferably 100 nm or less, more preferably 90 nm or less, and even more preferably 80 nm or less, and is, for example, 10 nm or more, preferably 20 nm or more. If the thickness of the resistive layer 3 is equal to or greater than the above-mentioned lower limit, a high gauge factor can be ensured.

<Method of manufacturing laminated film>
In the method for producing the laminated film 1, for example, the laminated film 1 is formed by a roll-to-roll method.

First, in this method, for example, a long base film 2 is prepared. In this case, if the long direction is the first direction and the width direction perpendicular to the long direction and the thickness direction is the second direction, the absolute value of the thermal expansion coefficient of the base film 2 from 50 to 200°C in the first direction is, for example, 28 ppm/°C or less, preferably 20 ppm/°C or less, more preferably 15 ppm/°C or less, and for example, 1 ppm/°C or more. The absolute value of the thermal expansion coefficient of the base film 2 from 50 to 200°C in the second direction is, for example, 28 ppm/°C or less, preferably 15 ppm/°C or less, more preferably 10 ppm/°C or less, and for example, 0.5 ppm/°C or more.

Next, in this method, the resistive layer 3 is formed on one side of the substrate film 2 in the thickness direction while the long substrate film 2 is being transported. Examples of the film formation method include sputtering, vacuum deposition, and ion plating. Sputtering is preferred, and reactive sputtering is more preferred.

In reactive sputtering, the target is made of chromium, and the sputtering gas is a mixture of an inert gas such as argon and nitrogen. The volume ratio of nitrogen to 100 volume parts of inert gas is, for example, 0.5 to 15 volume parts.

This produces a laminate film 1 having a base film 2 and a resistive layer 3.

Then, if necessary, the laminated film 1 is heated to increase the crystallinity of the resistance layer 3 and improve its stability. The heating temperature is not particularly limited, and is, for example, 100°C or higher, preferably 125°C or higher, and is, for example, 200°C or lower, preferably 180°C or lower. The heating time is, for example, 1 minute or longer, preferably 5 minutes or longer, and is, for example, 3 hours or shorter, preferably 2 hours or shorter.

This results in a laminated film 1 having a base film 2 and a resistive layer 3.

The absolute values of the dimensional change rate in each of the first and second directions of the laminated film 1 are both 0.025% or less. Since the absolute values of the dimensional change rate in each of the first and second directions of the laminated film 1 are both 0.025% or less, fluctuations in the temperature resistance coefficient due to storage in a humid and hot environment are suppressed.

The absolute value of the dimensional change rate of the laminated film 1 in each of the first and second directions is preferably 0.020% or less, more preferably 0.010% or less, even more preferably 0.005% or less, and particularly preferably 0.003% or less, and is, for example, greater than 0.000%.

To determine the dimensional change rate of the laminated film 1 in each of the first and second directions, first prepare a sample by cutting the laminated film 1 to lengths of 18 mm and 5 mm in the first and second directions, respectively. Next, fix both ends of the sample in the first direction using a chuck jig so that the distance between them is 15 mm, and pull with a force of 49 mN/5 mm for 4 hours in an atmosphere of 85°C and 85% RH. Measure the length of the sample in the first direction after pulling. Then, calculate the dimensional change rate in the first direction using the following formula. Using a similar method, measure the dimensional change rate in the second direction.

Dimensional change rate in the first direction length [%] = (first direction length of sample after pulling - first direction length of sample before pulling) / first direction length of sample before pulling x 100

Dimensional change rate in the second direction length [%] = (second direction length of sample after pulling - second direction length of sample before pulling) / second direction length of sample before pulling x 100

The difference in the temperature coefficient of resistance of the resistive layer 3 before and after storage for 240 hours at 85°C and 85% RH is, for example, 100 ppm/°C or less, preferably 55 ppm/°C or less, more preferably 50 ppm/°C or less, even more preferably 35 ppm/°C or less, particularly preferably 30 ppm/°C or less, and for example, 1 ppm/°C or more. If the difference in the temperature coefficient of resistance before and after storage is equal to or less than the above-mentioned upper limit, the measurement accuracy of the strain sensor 15 is improved.

To determine the difference in the resistance temperature coefficient before and after storage, after patterning the resistive layer 3, one side and the other side in the thickness direction of the laminated film 1 are fixed with glass plates, and they are stored in an atmosphere of 85°C and 85% RH for 240 hours. The difference in the resistance temperature coefficient before and after storage is determined. Details of how to determine the difference in the resistance temperature coefficient before and after storage will be described in the examples below.

<Method of manufacturing strain sensor>
Next, a method for manufacturing the strain sensor 15 will be described with reference to FIGS. 2A and 2B.

As shown in Figures 2A and 2B, in this manufacturing method, the resistive layer 3 in the laminated film 1 described above is patterned to form a resistive pattern 4. Methods for patterning the resistive layer 3 include, for example, etching, specifically dry etching and wet etching, preferably dry etching, and more preferably laser etching.

The resistor pattern 4 integrally includes a strain sensor section 5, a terminal 6, and wiring 7.

As shown in FIG. 2B, the strain sensor unit 5 has a generally zigzag shape in a plan view. Specifically, the strain sensor unit 5 has a plurality of first wires 8, a plurality of first connection wires 9, and a plurality of second connection wires 10.

Each of the multiple first lines 8 extends along a first direction. The multiple first lines 8 are aligned and spaced apart in the second direction.

The multiple first connection lines 9 connect the first-direction ends of adjacent first lines 8 in the second direction.

The multiple second connection lines 10 connect the other ends in the first direction of the first lines 8 adjacent in the second direction. When projected in the first direction, the first connection lines 9 and the second connection lines 10 are arranged alternately.

The terminal 6 is spaced apart from the strain sensor unit 5 in the planar direction. The terminal 6 has, for example, a land shape that is generally rectangular in plan view. Two terminals 6 are provided with a gap between them.

The wiring 7 connects the two terminals 6 to both ends of the strain sensor unit 5.

In the strain sensor section 5, a single conductive path is formed that runs from one terminal 6 through one wiring 7, the strain sensor section 5 and another wiring 7 to the other terminal 6.

The dimensions of the strain sensor section 5 are set appropriately depending on the application and purpose. The widths of the first line 8, the first connection line 9, and the second connection line 10 are, for example, 1 μm or more, preferably 5 μm or more, and more preferably 10 μm or more, and, for example, 150 μm or less, preferably 100 μm or less, and more preferably 70 μm or less.

The shape of the base film 2 is also set appropriately depending on the application and purpose of the strain sensor 15, and is formed to the desired dimensions, for example, by external processing.

<Measurement of strain using a strain sensor>
Next, a method of placing the strain sensor 15 on the test object 20 and measuring the amount of strain (amount of deformation) of the test object 20 will be described.

As shown in FIG. 2A, the laminated film 1 of the strain sensor 15 is attached to the surface of the specimen 20 via an adhesive layer 21. Lead wires 23 are connected to the two terminals 6 via a conductive adhesive layer 22. The lead wires 23 are electrically connected to an external resistance measurement circuit (not shown).

When the specimen 20 is distorted, the resistance value of the strain sensor unit 5 changes. Based on this, the amount of strain is calculated in the resistance measurement circuit.

Specifically, when the specimen 20 expands in the first direction, a tensile strain is applied to the first wire 8, the cross-sectional area of the first wire 8 decreases, and the resistance of the strain sensor unit 5 increases. On the other hand, when the specimen 20 contracts, a compressive strain is applied to the first wire 8, the cross-sectional area of the first wire 8 increases, and the resistance of the strain sensor unit 5 decreases. The amount of strain in the specimen 20 is calculated from the amount of change in resistance.

<Effects of the First Embodiment>
In the laminated film 1, the absolute values of the dimensional change rates of the laminated film 1 in both the first and second directions are 0.025% or less, so that the fluctuation of the temperature resistance coefficient due to storage in a humid and hot environment is suppressed. Also, in the laminated film 1, the thickness of the resistance layer 3 is 150 nm or less, so that the generation of cracks can be suppressed.

In addition, according to the manufacturing method of the first embodiment, it is possible to manufacture a strain sensor 15 in which the variation in the temperature resistance coefficient due to storage in a humid and hot environment is suppressed and the generation of cracks is suppressed.

<Modification of the First Embodiment>
In the first embodiment, the longitudinal direction (MD direction) produced by the roll-to-roll method is defined as the first direction, and the width direction (TD direction) is defined as the second direction, and the dimensional change rates in the first and second directions are obtained, but this is not limited thereto. Specifically, regardless of the production method of the laminated film 1, any one direction perpendicular to the thickness direction can be defined as the first direction, and the direction perpendicular thereto can be defined as the second direction, and the dimensional change rates in these directions can be obtained. The absolute values of the dimensional change rates of the laminated film 1 in each of such first and second directions are also 0.025% or less.

Second Embodiment
In the second embodiment described below, the same reference numerals are used for the same components and steps as those in the first embodiment described above, and detailed descriptions thereof will be omitted. In addition, the second embodiment can achieve the same effects as the first embodiment, unless otherwise specified. Furthermore, the first embodiment and the second embodiment can be appropriately combined.

In the first embodiment, the dimensional change rate of the laminate film 1 is specified, but this is not limited thereto. As shown in FIG. 3, in the second embodiment, the dimensional change rate of the base film 2 can be specified.

The base film 2 that is the subject of the dimensional change rate is, specifically, the long base film 2 that is prepared first, as shown in Figure 3.

After storing this base film 2 in an atmosphere of 85°C and 85% RH for 4 hours, the absolute values of the dimensional change rates in both the first and second directions are 0.040% or less. On the other hand, if the absolute value of the dimensional change rate in at least one of the first and second directions exceeds 0.040%, the fluctuation of the temperature resistance coefficient due to storage in a humid and hot environment is not suppressed.

The absolute value of the dimensional change rate of the base film 2 in each of the first and second directions is preferably 0.020% or less, more preferably 0.010% or less, even more preferably 0.005% or less, and particularly preferably 0.004% or less, and is, for example, more than 0.000%. The method for determining the dimensional change rate of the base film 2 is the same as that of the laminate film 1.

When the base film 2 is prepared as a long base film 2, the long direction of the base film 2 is the first direction, and the width direction is the second direction. The dimensional change rate of the base film 2 in the first direction is, for example, 0.025% or less, more preferably 0.010% or less, even more preferably 0.005% or less, particularly preferably 0.004% or less, and for example, exceeds 0.000%. The dimensional change rate of the base film 2 in the second direction is, for example, 0.040% or less, more preferably 0.010% or less, even more preferably 0.007% or less, particularly preferably 0.005% or less, and for example, exceeds 0.000%.

The base film 2 prepared for the production of the laminated film 1 is not the base film 2 after 4-hour stretching in an atmosphere of 85°C and 85% RH (high-temperature, high-humidity tensile test), but a base film 2 that does not have a history of the above-mentioned wet heat deformation (high-temperature, high-humidity tensile test) (so-called untreated). In other words, the above-mentioned high-temperature, high-humidity tensile test is a process necessary for the measurement to determine the dimensional change rate, and is not a manufacturing process for the base film 2.

In the method for manufacturing the laminated film 1, a resistive layer 3 is formed on one side in the thickness direction of the base film 2 having the above-mentioned specific dimensional change rate in the same manner as in one embodiment, and heated as necessary, thereby obtaining the laminated film 1.

Then, the resistive layer 3 of the laminated film 1 is patterned to form the strain sensor section 5.

<Effects of the Second Embodiment>
In the laminated film 1, the absolute values of the dimensional change rates of the base film 2 in both the first and second directions are 0.040% or less, so that the fluctuation of the temperature resistance coefficient due to storage in a humid and hot environment is suppressed. Also, in the laminated film 1, the thickness of the resistance layer 3 is 150 nm or less, so that the generation of cracks can be suppressed.

In addition, according to the manufacturing method of the second embodiment, it is possible to manufacture a strain sensor 15 in which the variation in the temperature resistance coefficient due to storage in a humid and hot environment is suppressed and the generation of cracks is suppressed.

<Modification of the second embodiment>
In the second embodiment, the dimensional change rate of the base film 2 before the laminate film 1 is manufactured is specified, but the dimensional change rate of the base film 2 after the laminate film 1 is manufactured and the resistance layer 3 in the laminate film 1 is removed may be within the above range.

<Modifications of the First and Second Embodiments>
The laminate film 1 may have a dimensional change rate that satisfies the range of the first embodiment (0.025% or less), and the base film 2 may have a dimensional change rate that satisfies the range of the second embodiment (0.040% or less).

Preferably, the dimensional change rate of the laminate film 1 satisfies the range of the first embodiment, and the dimensional change rate of the base film 2 satisfies the range of the second embodiment. This further suppresses the fluctuation of the temperature resistance coefficient due to storage in a humid and hot environment.

The present invention will be described in more detail below with reference to examples and comparative examples. Note that the present invention is in no way limited to the examples and comparative examples. In addition, the specific numerical values of the blending ratio (content ratio), physical property values, parameters, etc. used in the following description can be replaced with the upper limit values (numerical values defined as "equal to or less than") or lower limit values (numerical values defined as "equal to or more than" or "exceeding") of the corresponding blending ratio (content ratio), physical property values, parameters, etc. described in the above "Form for carrying out the invention".

Example 1
A base film 2 having a thickness of 50 μm and made of a polyimide film (Kapton 200V) manufactured by DuPont-Toray Co., Ltd. was prepared.

The base film 2 was set in a sputtering device. The inside of the sputtering device was evacuated to a vacuum of 1×10 ⁻³ Pa or less, and then a resistive layer 3 made of chromium nitride was formed by reactive pulse DC sputtering (pulse width: 1 μs, frequency: 100 kHz) under the following conditions.

Target: Chromium, 500 mm x 150 mm flat plate shape Power: 5 kW (power density: 6.7 W/cm ² )
Magnetic flux density (target surface): 30 mT
Substrate temperature: 150° C.
Sputtering gas: mixed gas of argon and nitrogen Film formation pressure: 0.085 Pa

The number of parts by volume of nitrogen gas introduced into the sputtering device per 100 parts by volume of argon gas introduced into the sputtering device was adjusted to be as shown in Table 1.

This resulted in the production of a long laminated film 1 comprising a base film 2 and a resistive layer 3.

The laminated film 1 was then heated (annealed) at 155°C for 60 minutes.

Example 2 to Comparative Example 2
A laminate film 1 was produced in the same manner as in Example 1, except that the type of base film 2, the thickness of base film 2, the amount of nitrogen introduced during sputtering, the thickness of resistive layer 3, etc. were changed according to the descriptions in Table 1.

<Evaluation>
The laminated film 1 of each of the Examples and Comparative Examples was measured for the following items. The results are shown in Table 1.

Observation of the Resistive Layer
The resistance layer 3 was visually observed to check for the presence or absence of cracks.

<Thickness of Resistive Layer>
The laminated film 1 was treated by FIB microsampling so as to expose a cross section, and then the cross section was observed by FE-TEM.

FIB device: Hitachi FB2200, Acceleration voltage: 40 kV
FE-TEM equipment: JEOL JEM-2800, accelerating voltage: 200 kV

<Difference in temperature coefficient of resistance before and after storage of resistive layer at 85° C. and 85% RH for 240 hours>
The laminated film 1 was cut to a size of 10 mm × 200 mm, and the resistive layer 3 was patterned by laser patterning into a zigzag shape with a width of 30 μm to produce the strain sensor 15. In this case, the patterning was adjusted so that the resistance of the wiring 7 was about 10 kΩ, and the resistance of the strain sensor part 5 was 30 times the resistance of the wiring 7.

A sample was created by attaching glass plates to both sides of the strain sensor 15 using an adhesive.

The temperature of the strain sensor part 5 of the sample was set to 5°C. A tester was connected to each of the two terminals 6, and the two-terminal resistance at 5°C was measured by passing a constant current and reading the voltage. In the same manner, the two-terminal resistance was measured at 25°C and 45°C.

The resistance temperature coefficient of the strain sensor section 5 (resistance layer 3) was calculated by taking the average of the resistance temperature coefficient calculated from the resistance values at 5°C and 25°C and the resistance temperature coefficient calculated from the resistance values at 25°C and 45°C.

Separately, the above sample was stored at 85°C and 85% RH for 240 hours. The resistance temperature coefficient of the strain sensor part 5 of the sample after storage was determined.

Then, the difference in the resistance temperature coefficient of the strain sensor unit 5 before and after storage was determined.

<Dimensional change rate of laminated film and base film>
A. Dimensional change rate of laminated film A sample was prepared by cutting the long laminated film 1 to a size of 15 mm x 5 mm. The length of the sample, 15 mm, corresponded to the length of the laminated film 1 in the longitudinal direction (first direction) (MD direction). The width of the sample, 5 mm, corresponded to the length of the laminated film 1 in the width direction (second direction) (TD direction).

The sample was placed in a thermomechanical analyzer (TMA 4000SE, manufactured by Netsch Japan). Specifically, one end and the other end of the sample in the longitudinal direction were held with a chuck. The measurement chamber was set to 85°C and 85% RH. The sample was pulled with a force of 49 mN/5 mm for 4 hours.

Then, the dimensional change rate of the laminated film 1 in both the length direction and width direction before and after tension was determined.

B. Dimensional Change Rate of Base Film The dimensional change rate of the base film 2 before the formation of the resistive layer 3 was determined in the same manner as above in both the length direction and width direction of the base film 2 before and after storage.

<Thermal expansion coefficient of base film>
The thermal expansion coefficient of the base film 2 was measured in accordance with JIS K 7197 (1991) using the following device and conditions.

Equipment: SII NanoTechnology TMA/SS7100
Measurement mode: Tensile method Measurement load: 19.6 mN
Temperature range: 25℃ to 155℃
Heating rate: 10° C./min
Measurement atmosphere: Atmosphere (air)

<Thermal shrinkage rate of base film>
The heat shrinkage rate of the base film 2 at 200° C. was measured according to the description in JIS K 7133 (1999).

1 Laminated film 2 Base film 3 Resistance layer 5 Sensor portion 15 Strain sensor

Claims (3)

A laminated film including an insulating base film and a resistive layer in that order in a thickness direction,
the base film is polyimide or polyethylene naphthalate,
the resistive layer is made of chromium nitride or made of chromium nitride and unavoidable impurities;
The thickness of the resistive layer is 150 nm or less,
The laminated film is cut to prepare a sample so that the lengths in a first direction and a second direction which are perpendicular to the thickness direction and perpendicular to each other are 15 mm and 5 mm, respectively, and after pulling both ends of the sample in the first direction with a force of 49 mN/5 mm for 4 hours in an atmosphere of 85°C and 85% RH, the absolute values of the dimensional change rates in each of the first direction and the second direction are both 0.025% or less. The insulating base film and the resistive layer are provided in that order in the thickness direction.
the base film is polyimide or polyethylene naphthalate,
the resistive layer is made of chromium nitride or made of chromium nitride and unavoidable impurities;
The thickness of the resistive layer is 150 nm or less,
A laminated film, characterized in that a sample is prepared by cutting the base film to have lengths of 15 mm and 5 mm in a first direction and a second direction that are perpendicular to the thickness direction and perpendicular to each other, and after pulling both ends of the sample in the first direction with a force of 49 mN/5 mm for 4 hours in an atmosphere of 85°C and 85% RH, the absolute values of the dimensional change rates in each of the first direction and the second direction are both 0.040% or less. A method for producing a strain sensor, comprising patterning the resistive layer in the laminated film according to claim 1 or 2 to form a strain sensor portion.

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