JP6256832B2 - Printed wiring board for strain gauge - Google Patents

Description

  The present invention relates to a printed wiring board for a strain gauge.

  Strain gauges are widely applied to strain measurement of an object to be measured and stress measurement using the strain of the object to be measured.

  These strain gauges have a structure in which, for example, a conductive pattern made of a metal foil processed by a technique such as photolithography is stacked on a flexible resin substrate. As this resin, resins such as polyimide and polyester are used (see Japanese Patent Laid-Open No. 2000-146511).

JP 2000-146511 A

  However, strain gauges using resins such as polyimide and polyester have a disadvantage that the measurement error of the strain amount increases due to the springback of the resin at the time of measurement because the elastic modulus of the resins is large. For this reason, it is conceivable to use a fluororesin having a small elastic coefficient. However, since the surface of the fluororesin is inactive, the conductive pattern made of the metal foil may be peeled off from the fluororesin.

  The present invention has been made based on the circumstances as described above, and an object thereof is to provide a printed wiring board for a strain gauge that has a small measurement error of the strain amount and is less likely to peel off the conductive pattern from the base film. Yes.

  The invention made in order to solve the above-mentioned problems comprises a base film mainly composed of a fluororesin, and a conductive pattern laminated on the surface of the base film and including a strain sensitive part, and the base film has a surface A strain gauge printed wiring board having a modified layer in at least a region where a conductive pattern is present, wherein the modified layer contains a siloxane bond and a hydrophilic organic functional group.

  The printed wiring board for strain gauges of the present invention has a small strain measurement error and is less likely to peel off the conductive pattern from the base film.

FIG. 1 is a schematic plan view of a printed wiring board for strain gauges according to a first embodiment of the present invention. FIG. 2 is a schematic sectional view taken along line XX of FIG. FIG. 3 is a schematic cross-sectional view of a printed wiring board for strain gauges according to the second embodiment.

[Description of Embodiment of Present Invention]
The present invention comprises a base film mainly composed of a fluororesin and a conductive pattern laminated on the surface of the base film and including a strain sensitive part, wherein the base film has at least a conductive pattern on the surface. The strain gauge printed wiring board includes a modified layer, and the modified layer includes a siloxane bond and a hydrophilic organic functional group.

  The strain gauge printed wiring board includes a base film containing a fluororesin as a main component. Thus, by using a fluororesin as the main component of the base film, the printed wiring board for strain gauges can have a small elastic coefficient and a small springback, thereby reducing a measurement error. In addition, the surface of the fluororesin is inactive, but the strain gauge printed wiring board has a modified layer having high activity on the surface side of the base film, so that the adhesion between the base film and the conductive pattern is improved. . Thereby, even if distortion occurs in the measurement object to which the printed wiring board for strain gauge is attached, there is little possibility that the conductive pattern is peeled off from the base film. By these things, the said printed wiring board for strain gauges can be used suitably for a strain gauge.

  The contact angle between the surface of the base film and pure water is preferably 90 ° or less. Thus, the adhesiveness of a modified layer and a conductive pattern further improves by making a contact angle with the pure water of the surface of a base film below the said upper limit.

  The average thickness of the modified layer is preferably 400 nm or less. Thus, the followability with respect to the expansion-contraction of a to-be-measured object can further be improved by making the average thickness of a modified layer below the said upper limit.

  The average surface roughness (Ra) of the modified layer surface in the region where the conductive pattern exists is preferably 4 μm or less. Thus, by making the said average surface roughness below the said upper limit, the flatness of the base film surface by which a strain sensitive part is arrange | positioned can be improved, and a measurement precision can further be raised.

  The crush resistance by the loop stiffness test of the base film is preferably 0.1 N / cm or more and 20000 N / cm or less. Thus, by making the crush resistance by the loop stiffness test of a base film into the said range, the said printed wiring board for strain gauges has sufficient flexibility, and can further improve the followable | trackability with respect to the expansion-contraction of a to-be-measured object.

  As the hydrophilic organic functional group, a hydroxyl group, carboxy group, carbonyl group, amino group, amide group, sulfide group, sulfonyl group, sulfo group, sulfonyldioxy group, epoxy group, methacryl group or mercapto group is preferable. Thus, by making a hydrophilic organic functional group into the above thing, the adhesiveness of a base film and a conductive pattern further improves.

  The base film has the modified layer also in a region where the conductive pattern does not exist, and is laminated on at least a part of the surface of the strain sensitive part and at least a part of the surface of the modified layer. It is preferable to further include a cover film mainly composed of a resin. Thus, by further providing a cover film mainly composed of a fluororesin, the strain sensitive part can be protected while suppressing an increase in springback.

  Here, the “main component” is a component having the highest content, for example, a component having a content of 50% by mass or more. Further, the “hydrophilic organic functional group” is a functional group composed of only a nonmetallic element such as a carbon atom, a hydrogen atom, an oxygen atom, a nitrogen atom, or a sulfur atom and has a hydrophilic property. Further, the “contact angle with pure water” is a value of a contact angle measured by the sessile drop method of JIS-R-3257 (1999). “Average surface roughness (Ra)” means arithmetic average roughness measured in accordance with JIS-B-0601 (2013). “Crush resistance by loopness test” means a repulsive force when a cylinder is produced with a predetermined R and a load is applied. Furthermore, “front” and “back” mean the direction in which the conductive pattern side is the front and the opposite side is the back in the thickness direction of the strain gauge printed wiring board, and the strain gauge printed wiring board It does not mean the front and back of the base film or cover film in use. The “chemical bond” used in the present specification is a concept including a hydrogen bond.

[Details of the embodiment of the present invention]
Hereinafter, the printed wiring board for strain gauges according to the present invention will be described in detail.

[First embodiment]
The strain gauge printed wiring board 10 of FIGS. 1 and 2 includes a base film 1 mainly composed of a fluororesin, and a conductive pattern 3 that is laminated on the surface of the base film 1 and includes the strain sensing part 2. .

<Base film>
The base film 1 has a modified layer 4 containing a fluororesin as a main component and including a siloxane bond structure and a hydrophilic organic functional group on the surface side (including a region where the conductive pattern 3 is laminated). Since the base film 1 has a fluororesin as a main component, the elastic modulus is smaller than that of a resin such as polyimide or polyester as a main component.

  Here, the fluororesin is an organic group in which at least one hydrogen atom bonded to the carbon atom constituting the repeating unit of the polymer chain has a fluorine atom or a fluorine atom (hereinafter also referred to as “fluorine atom-containing group”). Refers to the substituted one. The fluorine atom-containing group is a group in which at least one hydrogen atom in a linear or branched organic group is substituted with a fluorine atom, and examples thereof include a fluoroalkyl group, a fluoroalkoxy group, and a fluoropolyether group. .

  The “fluoroalkyl group” means an alkyl group in which at least one hydrogen atom is substituted with a fluorine atom, and includes a “perfluoroalkyl group”. Specifically, a “fluoroalkyl group” is a group in which all hydrogen atoms of an alkyl group are substituted with fluorine atoms, and all hydrogen atoms other than one hydrogen atom at the end of the alkyl group are substituted with fluorine atoms. Group.

  The “fluoroalkoxy group” means an alkoxy group in which at least one hydrogen atom is substituted with a fluorine atom, and includes a “perfluoroalkoxy group”. Specifically, a “fluoroalkoxy group” is a group in which all hydrogen atoms of an alkoxy group are substituted with fluorine atoms, and all hydrogen atoms other than one hydrogen atom at the end of the alkoxy group are substituted with fluorine atoms. Group.

  The “fluoropolyether group” is a monovalent group having an oxyalkylene unit as a repeating unit and having an alkyl group or a hydrogen atom at the terminal, and at least one hydrogen of the alkylene oxide chain or the terminal alkyl group A monovalent group in which an atom is substituted with a fluorine atom. The “fluoropolyether group” includes a “perfluoropolyether group” having a plurality of perfluoroalkylene oxide chains as repeating units.

  Examples of the fluororesin constituting the base film 1 include polytetrafluoroethylene (PTFE), polytetrafluoroethylene / perfluoroalkyl vinyl ether copolymer (PFA), tetrafluoroethylene / hexafluoropropylene copolymer (FEP), Tetrafluoroethylene / hexafluoroethylene copolymer, polyvinylidene fluoride (PVDF), polychlorotrifluoroethylene (PCTFE), chlorotrifluoroethylene / ethylene copolymer (ECTFE), polyvinyl fluoride (PVF), In addition, a thermoplastic fluororesin (THV) composed of three types of monomers such as tetrafluoroethylene, hexafluoropropylene, and vinylidene fluoride, and fluoroelastomer may be mentioned. Further, a mixture or copolymer containing these compounds can also be used as a material constituting the base film 1.

  Among them, the fluororesin constituting the base film 1 includes tetrafluoroethylene / hexapropylene copolymer (FEP), polytetrafluoroethylene / perfluoroalkyl vinyl ether copolymer (PFA), or polytetrafluoroethylene (PTFE). ) Is preferred. By using these fluororesins, the base film 1 has flexibility, light transmittance, heat resistance, and flame retardancy.

  Moreover, the base film 1 can contain, for example, engineering plastics, flame retardants, flame retardant aids, antioxidants, lubricants, processing stabilizers, plasticizers, reinforcing materials and the like as optional components.

  As said engineering plastic, it can select and use from a well-known thing according to the characteristic calculated | required by the base film 1, Typically, aromatic polyetherketone resin can be used.

  This aromatic polyetherketone has a structure in which the benzene rings are bonded to the para position and the benzene rings are connected to each other by a rigid ketone bond (—C (═O) —) or a flexible ether bond (—O—). It is a thermoplastic resin. As the aromatic polyether ketone, for example, ether ether ketone (PEEK) having a structural unit in which an ether bond, a benzene ring, an ether bond, a benzene ring, a ketone bond and a benzene ring are arranged in this order, an ether bond, a benzene ring, Examples include polyether ketone (PEK) having a structural unit in which a ketone bond and a benzene ring are arranged in this order. Among them, PEEK is preferable as the aromatic polyether ketone. Such an aromatic polyether ketone is excellent in wear resistance, heat resistance, insulation, workability and the like.

  A commercially available product can be used as the aromatic polyether ketone such as PEEK. As P aromatic polyether ketones, those of various grades are commercially available, and a single grade of aromatic polyether ketone that is commercially available may be used alone, or multiple grades of aromatic polyketone may be used. Ether ketone may be used in combination, or modified aromatic polyether ketone may be used.

  Although it does not specifically limit as a lower limit of the ratio with respect to the said fluororesin of the total content of the engineering plastic in the base film 1, 10 mass% is preferable, 20 mass% is more preferable, and 35 mass% is further more preferable. When the total content of engineering plastics is less than the above lower limit, the characteristics of the base film 1 may not be sufficiently improved. On the other hand, the upper limit of the ratio of the total content of engineering plastics to the fluororesin is not particularly limited, but is preferably 50% by mass and more preferably 45% by mass. When the content of the engineering plastic exceeds the above upper limit, the advantageous characteristics of the fluororesin may not be sufficiently exhibited.

  Various known flame retardants can be used, and examples thereof include halogen flame retardants such as bromine flame retardants and chlorine flame retardants.

  Various known flame retardant aids can be used, and examples include antimony trioxide.

  Various known antioxidants can be used as the antioxidant, and examples thereof include phenolic antioxidants.

  Examples of the reinforcing material include carbon fiber, glass fiber, and the like, and twisted yarns and cloths formed from these, such as glass cloth, may be used.

  As a minimum of average thickness of base film 1, 3 micrometers is preferred and 6 micrometers is more preferred. When the average thickness of the base film 1 is less than the above lower limit, the strength of the base film 1 becomes insufficient, and the base film 1 may be torn. On the other hand, the upper limit of the average thickness of the base film 1 is preferably 100 μm, and more preferably 55 μm. When the average thickness of the base film 1 exceeds the above upper limit, the elasticity of the base film 1 may increase the springback of the strain gauge printed wiring board 10 and increase the measurement error of the strain amount.

  The modified layer 4 is formed by bonding a modifying agent having a hydrophilic organic functional group and forming a siloxane bond (Si—O—Si) to the fluororesin constituting the base film 1. That is, in the modified layer 4, the hydrophilic organic functional group is bonded to Si atoms constituting the siloxane bond. The hydrophilic organic functional group imparts wettability to the surface of the base film 1. The chemical bond between the fluororesin and the modifier may be composed of only a covalent bond or may include a covalent bond and a hydrogen bond. The modified layer 4 is a region that is considered to have a different molecular structure and abundance of elements from other regions of the fluororesin layer 2 excluding the modified layer 4.

The Si atom constituting the siloxane bond (hereinafter, this atom is referred to as “Si atom of siloxane bond”) is bonded to the fluororesin layer via at least one of N atom, C atom, O atom, and S atom. It is covalently bonded to two C atoms. For example, Si atoms of the siloxane _{bond, -O -, - S -,} - S-S -, - (CH 2) n -, - NH -, - (CH 2) n-NH -, - (CH 2) _{n-O- (CH 2) m-} (n, m is 1 or more is an integer.) binds to the C atom of fluorine resin through an atomic group, and the like.

  The hydrophilic organic functional group is preferably a hydroxyl group, carboxy group, carbonyl group, amino group, amide group, sulfide group, sulfonyl group, sulfo group, sulfonyldioxy group, epoxy group, methacryl group, or mercapto group. Among these, those containing N atoms or S atoms are more preferable. These hydrophilic functional groups improve the adhesion of the surface of the base film 1. The modified layer 4 may include two or more of these hydrophilic functional groups. In this way, by imparting hydrophilic functional groups having different properties to the modified layer 4, the surface reactivity of the base film 1 can be varied. These hydrophilic functional groups are bonded to Si atoms, which are components of siloxane bonds, directly or via one or a plurality of C atoms (for example, a methylene group or a phenylene group).

  As the modifier for forming the modified layer 4 having the above characteristics, a silane coupling agent having a hydrophilic organic functional group in the molecule is preferable, and a hydrolyzable functional group containing Si atoms. A silane coupling agent having a group is more preferable. Such a silane coupling agent is chemically bonded to the fluororesin constituting the base film 1.

  The hydrolyzable functional group containing the Si atom is specifically a group in which an alkoxy group is bonded to the Si atom. Examples of the alkoxy group include a methoxy group, an ethoxy group, a propoxy group, a t-butoxy group, and a pentyloxy group.

  Examples of the hydrophilic organic functional group containing an N atom include an amino group and a ureido group.

  Examples of the silane coupling agent having a hydrophilic organic functional group containing an N atom include aminoalkoxysilane, ureidoalkoxysilane, and the like, and derivatives thereof.

  Examples of the aminoalkoxysilane include 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, N- (2-aminoethyl) -3-aminopropylmethyldimethoxysilane, and N- (2-aminoethyl) -3. -Aminopropyltrimethoxysilane, N- (2-aminoethyl) -3-aminopropyltriethoxysilane, N-phenyl-3-aminopropyltrimethoxysilane and the like.

  Examples of aminoalkoxysilane derivatives include ketimines such as 3-triethoxysilyl-N- (1,3-dimethyl-butylidene) propylamine, and N-vinylbenzyl-2-aminoethyl-3-aminopropyltrimethoxysilane acetic acid. Examples thereof include salts of silane coupling agents such as salts.

  Examples of the ureidoalkoxysilane include 3-ureidopropyltriethoxysilane, 3-ureidopropyltrimethoxysilane, N- (2-ureidoethyl) -3-aminopropyltrimethoxysilane, and the like.

  Examples of the hydrophilic organic functional group containing an S atom include a mercapto group and a sulfide group.

  Examples of the silane coupling agent having a hydrophilic organic functional group containing an S atom include mercaptoalkoxysilane, sulfide alkoxysilane, and derivatives thereof.

  Examples of mercaptoalkoxysilanes include 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, and 3-mercaptopropyl (dimethoxy) methylsilane.

  Examples of the sulfide alkoxysilane include bis (3-triethoxysilylpropyl) tetrasulfide and bis (3-triethoxysilylpropyl) disulfide.

  The silane coupling agent may be one having a modified group introduced. As the modifying group, a phenyl group is preferable.

  Examples of the silane coupling agent include 3-aminopropyltriethoxysilane, N-phenyl-3-aminopropyltrimethoxysilane, 3-ureidopropyltriethoxysilane, 3-mercaptopropyltrimethoxysilane, and bis. (3-Triethoxysilylpropyl) tetrasulfide is preferred.

  As the modifier, other coupling agents can be used in addition to the silane coupling agent. Any other coupling agent may be used as long as it has reactivity with the fluororesin of the base film 1 or a radical thereof. For example, a titanium coupling agent can be used.

  Examples of the titanium coupling agent include isopropyl triisostearoyl titanate, isopropyl tristearoyl titanate, isopropyl trioctanoyl titanate, isopropyl dimethacrylisostearoyl titanate, isopropyl tridodecylbenzenesulfonyl titanate, isopropyl isostearoyl diacryl titanate, isopropyl tri ( Dioctyl phosphate) titanate, isopropyl tricumyl phenyl titanate, isopropyl tris (dioctyl pyrophosphate) titanate, isopropyl tri (N-aminoethyl-aminoethyl) titanate, tetraisopropyl bis (dioctyl phosphite) titanate, tetraoctyl bis (ditridecyl phos) Fight) Titanate, Tetra (2 2-diallyloxymethyl-1-butyl) bis (ditridecylphosphite) titanate, dicumylphenyloxyacetate titanate, bis (dioctylpyrophosphate) oxyacetate titanate, diisostearoylethylene titanate, bis (dioctylpyrophosphate) ethylene titanate Bis (dioctylpyrophosphate) diisopropyl titanate, tetramethyl orthotitanate, tetraethyl orthotitanate, tetrapropyl orthotitanate, tetraisopropyl tetraethyl orthotitanate, tetrabutyl orthotitanate, butyl polytitanate, tetraisobutyl orthotitanate, 2-ethylhexyl titanate, stearyl Titanate, cresyl titanate monomer, cresyl tita Polymers, diisopropoxy-bis (2,4-pentadionate) titanium (IV), diisopropyl-bis (triethanolamino) titanate, octylene glycol titanate, titanium lactate, acetoacetic estiltitanate, diisopropoxybis (Acetylacetonato) titanium, di-n-butoxybis (triethanolaminato) titanium, dihydroxybis (lactato) titanium, titanium-isopropoxyoctylene glycolate, tetra-n-butoxytitanium polymer, tri-n-butoxytitanium Monostearate polymer, butyl titanate dimer, titanium acetylacetonate, poly (titanium acetylacetonate), titanium octylene glycolate, titanium lactate ammonium salt, titanium Examples include lactate ethyl ester, titanium triethanolamate, and polyhydroxytitanium stearate.

  The upper limit of the contact angle with respect to pure water on the surface of the modified layer 4 is preferably 90 °, and more preferably 80 °. When the contact angle with respect to the pure water on the surface of the modified layer 4 exceeds the above upper limit, the adhesion with the conductive pattern 3 may be insufficient. On the other hand, the lower limit of the contact angle with respect to pure water on the surface of the modified layer 4 is not particularly limited. The contact angle of the surface of the modified layer 4 with pure water can be measured using a contact angle measuring device “GI-1000” manufactured by ERMA.

  The lower limit of the surface tension of the base film 1 is preferably 50 mN / m, more preferably 60 mN / m. If the wetting tension is less than the above lower limit, the adhesive force is insufficient and the conductive pattern 3 may be peeled off. The lower limit of the wetting tension is larger than the wetting tension of pure polytetrafluoroethylene (PTFE). That is, the surface of the base film 1 has higher surface adhesion than the ordinary fluororesin by forming the modified layer 4. The “wetting tension” is a value measured according to JIS-K-6768 (1999).

The modified layer 4 preferably has the following etching resistance. That includes iron chloride, density is not more 1.31 g / cm ³ or more 1.33 g / cm ³ or less, free hydrochloric acid concentration using an etchant or less 0.1 mol / L or more 0.2 mol / L Thus, it is preferable that the modified layer 4 is not removed with respect to the etching treatment that is immersed at 45 ° C. or lower for 1 minute to 2 minutes. Here, that the modified layer 4 is not removed means that the hydrophilicity of the surface of the base film 1 is not lost, and for example, the contact angle with respect to pure water on the front and back surfaces of the base film 1 does not exceed 90 °. In some cases, the etching process may cause a small portion of hydrophobicity to appear in the region where the modified layer 4 is formed. However, if the entire region has hydrophilicity, such a state may be hydrophilic. It is assumed that sex is maintained. Thus, since the modified layer 4 has etching resistance, a cover film can be easily laminated on the surface of the modified layer 4 after the conductive pattern 3 is formed by etching as will be described later.

  Although it does not specifically limit as a minimum of the average thickness of the modification layer 4, 10 nm is preferable and 50 nm is more preferable. When the average thickness of the modified layer 4 is less than the lower limit, the surface of the base film 1 cannot be sufficiently modified, and the conductive pattern 3 may not be peeled off. On the other hand, the upper limit of the average thickness of the modified layer 4 is preferably 400 nm, and more preferably 200 nm. If the average thickness of the modified layer 4 exceeds the above upper limit, the strain sensitive part may not sufficiently expand and contract following the expansion and contraction of the object to be measured. The average thickness of the modified layer can be measured using an optical interference type film thickness measuring instrument, an X-ray photoelectron spectroscopy (X-ray photoelectron spectroscopy) analyzer, an electron microscope, or the like.

  The upper limit of the average surface roughness (Ra) of the surface of the modified layer 4 in the region where the conductive pattern is present is preferably 4 μm and more preferably 1 μm. When the average surface roughness (Ra) of the surface of the modified layer 4 exceeds the above upper limit, the flatness of the surface of the base film on which the strain sensitive part is disposed is lowered, and the measurement accuracy may be lowered. On the other hand, the lower limit of the average surface roughness (Ra) of the surface of the modified layer 4 is not particularly limited.

  The lower limit of the crush resistance by the loop stiffness test of the base film 1 is preferably 0.1 N / cm. If the crush resistance is less than the lower limit, the strain gauge printed wiring board 10 may not have sufficient flexibility. On the other hand, the upper limit of the crush resistance is preferably 20000 N / cm, more preferably 5 N / cm, and even more preferably 2 N / cm. If this crushing resistance exceeds the above upper limit, handling of the strain gauge printed wiring board 10 may be difficult, and the base film 1 may be expensive.

<Conductive pattern>
The conductive pattern 3 is composed of, for example, a metal foil laminated on the modified layer 4. This conductive pattern 3 connects the strain sensitive part 2 in which a change in resistance value is measured, a pair of electrode parts 5 that electrically connect the conductive pattern 3 to the outside, and the strain sensitive part 2 and the electrode part 5. A wiring part 6 is provided.

  The strain gauge in which the printed wiring board for strain gauge 10 is used has a cross-sectional area that decreases due to stretching of the metal and increases in length, resulting in an increase in resistance value, and conversely, a cross-sectional area due to compression of the metal. The strain amount of the object to be measured is measured by utilizing the fact that the length decreases as the length increases and the resistance value decreases as a result.

  The strain sensing unit 2 is a single resistor in which a plurality of belt-like parts arranged in parallel at regular intervals are connected by a connecting part extending in the width direction between end parts. That is, the strain sensing unit 2 has a zigzag shape in which a single band-like body is folded back multiple times at regular intervals. Electrode portions 5 are connected to both ends of the strain sensing portion 2 via wiring portions 6. It is preferable that the band-like portion of the strain sensing portion 2 has a small width so that the change rate of the resistance value can be easily detected. On the other hand, the width of the wiring part 6 is preferably large so that the ratio of the resistance value in the wiring part 6 to the resistance value of the entire conductive pattern 3 is small. Moreover, it is preferable that the electrode part 5 is arrange | positioned in the outer periphery vicinity of the base film 1 so that the wiring from the outside can be connected easily. The electrode portion 5 may be plated with nickel, gold or the like in order to facilitate the soldering operation.

  The metal constituting the conductive pattern 3 is not particularly limited as long as it has electrical conductivity. For example, platinum, aluminum, nickel, tungsten, iron, gold, silver, copper, palladium, chromium, copper nickel alloy, nickel Although a chromium alloy, a copper manganese alloy, an iron chromium alloy etc. can be mentioned, A copper nickel alloy, a nickel chromium alloy, a copper manganese alloy, and an iron chromium alloy are preferable from a resistance value, a linear expansion coefficient, etc.

  The lower limit of the average thickness of the conductive pattern 3 is preferably 1 μm and more preferably 3 μm. When the thickness of the conductive pattern 3 is less than the above lower limit, the conductive pattern 3 may be cut. On the other hand, the upper limit of the average thickness of the conductive pattern 3 is preferably 100 μm, and more preferably 50 μm. If the average thickness of the conductive pattern 3 exceeds the above upper limit, the conductive pattern 3 may be too thick to follow the strain change of the object to be measured.

<Method for producing printed wiring board for strain gauge>
Next, a method for producing the strain gauge printed wiring board 10 will be described.

  The strain gauge printed wiring board 10 can be manufactured by a manufacturing method including a modifier attaching step, a base film laminating step, and a conductive pattern forming step.

(Modifier adhesion process)
In the modifier attaching step, the reforming layer 4 is formed by modifying the base film 1 with alcohol, water, and the base film 1 on the back surface of the metal foil forming the conductive pattern 3, that is, the surface of the metal foil facing the base film 1. It is a step of attaching a primer containing a modifier for forming. The method for attaching the primer to the metal foil is not particularly limited, but for example, an immersion method, a spray method, a coating method, or the like can be adopted. Then, the primer alcohol is removed by drying. The alcohol can be removed by natural drying, drying by heating, drying by reduced pressure, or the like. In addition, you may perform this drying continuously in the press machine which performs the thermocompression bonding of the following lamination process. After drying, heating (for example, 120 ° C. for 15 minutes) is performed to form a Si—O—Si bond.

  As a minimum of content in the whole primer of a modifier, 0.1 mass% is preferred and 0.5 mass% is more preferred. When the content of the modifier is less than the above lower limit, the surface of the base film 1 may not be sufficiently modified. On the other hand, the upper limit of the content of the modifier is preferably 5% by mass, and more preferably 3% by mass. When the content of the modifier exceeds the above upper limit, the modifier is aggregated, and there is a possibility that a primer film having a uniform thickness cannot be formed on the back surface of the metal foil.

  Although the amount of water in the primer is sufficient, it is an essential substance for the condensation of the modifier. As content in the whole primer of water, it can be 0.01 mass% or more and 0.1 mass% or less, for example.

(Base film lamination process)
The base film laminating step is a step of laminating a fluororesin sheet constituting the base film 1 on the back surface of the metal foil forming the conductive pattern 3, that is, on the primer adhered in the modifier adhering step. The laminate of the base film 1 and the metal foil is thermocompression bonded by a press machine. This thermocompression bonding is preferably performed under reduced pressure in order to prevent bubbles and voids from being formed between the base film 1 and the metal foil. By this thermocompression bonding, a chemical bond is formed through another atom between the C atom of the fluororesin and the Si—O—Si bond formed from the modifier. In order to suppress oxidation of the metal foil, it is preferable to perform thermocompression bonding under low oxygen conditions such as in a nitrogen atmosphere.

  As the lower limit of the thermocompression bonding temperature, the melting point of the fluororesin constituting the base film 1 is preferable, and the decomposition start temperature of the fluororesin is more preferable. Further, the lower limit of the difference between the thermocompression bonding temperature and the melting point of the fluororesin is preferably 30 ° C, more preferably 50 ° C. When the thermocompression bonding temperature is lower than the above lower limit, the fluororesin is not activated and the reaction with the modifier may be insufficient. Further, by setting the thermocompression bonding temperature to be equal to or higher than the decomposition start temperature of the fluororesin, it is considered that a part of the fluororesin is more likely to be a radical and is further bonded to the modifier via other atoms. On the other hand, the upper limit of the thermocompression bonding temperature is preferably the decomposition temperature of the fluororesin. Here, the decomposition start temperature refers to the temperature at which the fluororesin begins to thermally decompose, and the decomposition temperature refers to the temperature at which the mass of the fluororesin decreases by 10% due to thermal decomposition. When the thermocompression bonding temperature exceeds the above upper limit, the fluororesin is decomposed and the base film 1 may be damaged.

  As an example, when the fluororesin constituting the base film 1 is a tetrafluoroethylene / hexafluoropropylene copolymer (FEP), the melting point of the fluororesin is about 270 ° C. ° C is preferred, and 320 ° C is more preferred. On the other hand, the upper limit of the thermocompression bonding temperature at this time is preferably 600 ° C., more preferably 500 ° C.

  The thermocompression bonding pressure is preferably 0.01 MPa or more and 100 MPa or less. Moreover, as pressurization time of thermocompression bonding, 0.01 minutes or more and 1000 minutes or less are preferable. However, the thermocompression bonding pressure and the pressurizing time are not limited to these, and may be set in consideration of the reactivity of the modifier.

  By such thermocompression bonding, a Si—O—Si bond is formed from the modifier, and a part thereof is bonded to the fluororesin via another atom. These bonds are presumed to include covalent bonds because the modified layer 4 has the above-mentioned etching resistance. In addition, the modified layer 4 is composed of a polymer spread in a film shape, and a large number of hydrogen bonds are formed between the polymer and the fluorine tree, so there is a possibility that both are strongly bonded. The bond is presumed to include a hydrogen bond. On the other hand, since the Si—O—Si bond and the hydrophilic organic functional group exist in the vicinity of the surface of the metal foil, the metal foil is fixed to the surface of the fluororesin.

  In this bonding step, other known radical generation methods such as electron beam irradiation may be used in combination with the pressure heating. Examples of electron beam irradiation include γ-ray irradiation treatment. By using electron beam irradiation or the like in combination, radicals of the fluororesin can be generated more effectively, so that the certainty of adhesion between the base film 1 and the metal foil (conductive pattern 3) can be further increased. it can. Moreover, the electron beam irradiation is not necessarily performed in the bonding step, and may be performed at the same time when the base film 1 is formed, for example, or may be performed after the bonding step.

(Conductive pattern formation process)
In the conductive pattern forming step, the conductive pattern 3 is formed by the same method as the etching method employed in the conventional printed wiring board manufacturing method. For example, a resist film having a shape corresponding to the conductive pattern 3 to be formed is laminated on the surface of the metal foil, and the laminate is immersed in an etching solution to form the conductive pattern 3. Although the metal foil is removed by this etching, the modified layer 4 formed on the base film 1 is not removed.

<Advantages>
The strain gauge printed wiring board 10 includes a base film 1 mainly composed of a fluororesin. As described above, by using a fluororesin as the main component of the base film 1, the strain gauge printed wiring board 10 can have a small elastic coefficient and a small spring back, thereby reducing a measurement error. Further, although the surface of the fluororesin is inactive, the strain gauge printed wiring board 10 has the modified layer 4 having high activity on the surface side of the base film 1, so that the base film 1 and the conductive pattern 3 Adhesion is improved. Thereby, there is little possibility that the conductive pattern 3 will peel from the base film 1 even if distortion arises in the to-be-measured object which the said printed wiring board 10 for strain gauges was affixed. By these things, the said printed wiring board 10 for strain gauges can be used suitably for a strain gauge.

  Moreover, since the modified layer 4 and the conductive pattern 3 are joined by thermocompression bonding, an adhesive is not necessary. Thereby, the printed wiring board 10 for strain gauges can be made thin. In addition, the modified layer 4 and the conductive pattern 3 can be easily joined.

[Second Embodiment]
The strain gauge printed wiring board 11 of FIG. 3 includes a base film 1 mainly composed of a fluororesin, a conductive pattern 3 that is laminated on the surface of the base film 1 and includes the strain sensitive part 2, and a strain sensitive part. 2 and a cover film 7 mainly composed of a fluororesin laminated on at least a part of the surface of the modified layer 4. Since the base film 1, the strain sensing part 2, the conductive pattern 3, and the modified layer 4 are the same as the strain gauge printed wiring board 10 of the first embodiment, the same reference numerals are given and the description thereof is omitted. .

  This cover film 7 protects the strain sensing part 2. Moreover, as a fluororesin which has the main component of the cover film 7, the thing similar to the fluororesin which the base film 1 has as a main component can be used. Moreover, the cover film 7 can contain, for example, engineering plastics, flame retardants, flame retardant aids, antioxidants, lubricants, processing stabilizers, plasticizers, glass cloths, and the like as optional components as in the base film 1.

  The lower limit of the average thickness of the cover film 7 is preferably 1 μm and more preferably 3 μm. When the average thickness of the cover film 7 is less than the above lower limit, the conductive pattern 3 may not be sufficiently protected. On the other hand, the upper limit of the average thickness of the cover film 7 is preferably 100 μm, and more preferably 55 μm. When the average thickness of the cover film 7 exceeds the above upper limit, the springback is increased due to the elasticity of the cover film 7, and the measurement error of the strain amount may be increased.

  The cover film 7 can be laminated on the strain sensitive part 2 and the modified layer 4 by, for example, bonding with an adhesive. It can also be performed by bonding the cover film 7 and the base film 1 by heat melting. This thermal melting can be performed, for example, under conditions of 180 ° C. or more and 400 ° C. or less, 20 minutes or more and 30 minutes or less, 3 MPa or more and 4 MPa or less. In the lamination of these cover films 7, the surface of the modified layer 4 is active, so that the adhesion between the cover film 7 and the modified layer 4 is improved.

[Other Embodiments]
The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is not limited to the configuration of the embodiment described above, but is defined by the scope of the claims, and is intended to include all modifications within the meaning and scope equivalent to the scope of the claims. The

  In the printed wiring board for strain gauges of the above embodiment, one conductive pattern is stacked on the base film, but a plurality of conductive patterns may be stacked. In this case, the amount of strain in a plurality of directions in the object to be measured can be measured by changing the direction of the strain sensing part of each of the plurality of conductive patterns.

  Moreover, the shape of the strain sensing part in the said strain gauge printed wiring board is not limited to the shape shown in FIG. The shape of the strain sensing part may be such that, for example, a plurality of band-like parts are arranged radially around the origin. In this case, the extending portions connecting the plurality of belt-shaped portions form a concentric arc. Such a shape of the strain sensing part can be suitably used for measuring the pressure of the diaphragm.

  Furthermore, in the printed wiring board for strain gauges of the above embodiment, the modified layer is formed on the entire surface of the base film, but the modified layer may be formed at least in a region where the conductive pattern exists, It does not have to be formed on the entire surface of the base film. However, in the printed wiring board for strain gauges of the second embodiment, it is preferable that a modified layer is formed at a position in contact with the cover film from the viewpoint of adhesion to the cover film.

  The printed wiring board for strain gauges of the present invention has a small strain measurement error and is less likely to peel off the conductive pattern from the base film. As a result, it can be used suitably for strain measurement of an object to be measured with large strain.

DESCRIPTION OF SYMBOLS 1 Base film 2 Strain sensitive part 3 Conductive pattern 4 Modified layer 5 Electrode part 6 Wiring part 7 Cover film 10, 11 Printed wiring board for strain gauges

Claims (7)

A base film mainly composed of a fluororesin, and a conductive pattern laminated on the surface of the base film and including a strain sensitive part,
The base film has a modified layer in a region where at least a conductive pattern exists on the surface,
The strain gauge printed wiring board, wherein the modified layer contains a siloxane bond and a hydrophilic organic functional group.   The printed wiring board for strain gauges according to claim 1, wherein a contact angle of the surface of the modified layer with pure water is 90 ° or less.   The printed wiring board for strain gauges according to claim 1 or 2, wherein an average thickness of the modified layer is 400 nm or less.   4. The strain gauge printed wiring board according to claim 1, wherein an average surface roughness (Ra) of the modified layer surface in a region where the conductive pattern is present is 4 μm or less. 5.   The strain gauge printed wiring board according to any one of claims 1 to 4, wherein the crush resistance of the base film by a loop stiffness test is 0.1 N / cm or more and 20000 N / cm or less.   The hydrophilic organic functional group is a hydroxyl group, carboxy group, carbonyl group, amino group, amide group, sulfide group, sulfonyl group, sulfo group, sulfonyldioxy group, epoxy group, methacryl group or mercapto group. The printed wiring board for strain gauges of any one of Claim 5. The base film has the modified layer in a region where the conductive pattern does not exist,
7. The cover film according to claim 1, further comprising a cover film that is laminated on at least a part of the surface of the strain sensitive part and at least a part of the surface of the modified layer and mainly contains a fluororesin. The printed wiring board for strain gauges as described in the item.

Images