Stretchable wiring material and stretchable device

Abstract

To provide a stretchable wiring material which has high conductivity and high stretchability, and has a small change of conductivity in stretching.SOLUTION: A stretchable wiring material contains a resin and metal powder, and has a breaking elongation rate of 130% or more and a resistance rate (ρ0) before stretching of 2×10-2 [Ωmm] or less, wherein the metal powder contains scale-like powder, and a ratio of the resin is 8 wt.% or more and 20 wt.% or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a stretchable wiring material and a stretchable device. [Background technology]

[0002] In recent years, with the development of flexible sensors, wearable devices capable of managing physical condition have been attracting attention. Wearable devices are expected to be used in a wide range of applications in the fields of sports science and healthcare, such as those embedded in clothing or attached directly to the skin, to measure and monitor specific body parts. Because human skin expands and contracts repeatedly on a daily basis, if a wearable device is required to be worn without stress, it is desirable for the device to have stretchability corresponding to the object being worn. Furthermore, it is desirable for wearable devices to have a certain level of strength to withstand stresses generated when bending or rolling, taking into account handling and human movement. In this specification, devices with such characteristics are referred to as stretchable devices, regardless of their intended use.

[0003] Stretchable devices are expected to include electrodes, wiring, devices, electronic components, thin-film sensors, and the like within a stretchable element, and their quality must be maintained even in environments where they are repeatedly stretched and contracted. However, it is difficult to realize such stretchable devices using polyimide sheets, which are used in conventional thin-film resin substrates. For these reasons, it is expected that the element and electrodes of stretchable devices will be primarily made of resins that are suitable for stretchability, such as urethane resin, silicone resin, acrylic resin, epoxy resin, polycarbonate, polystyrene, or polyolefin. In particular, a stretchable film that is a cured product of a composition containing a (meth)acrylate compound having a siloxane bond, a (meth)acrylate compound other than the (meth)acrylate compound having a urethane bond, and an organic solvent with a boiling point in the range of 115 to 200°C at atmospheric pressure, in which the (meth)acrylate compound having a siloxane bond is unevenly distributed on the surface side of the film, is said to have excellent stretchability and strength comparable to polyurethane, and the film surface has excellent water repellency comparable to silicone (see Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-206626 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the case of a resin sheet (resin film) whose main constituent material is a cured product of a resin composition as described in Patent Document 1, if the curing reaction does not proceed uniformly, variations in composition and degree of curing occur within the resin sheet, resulting in a problem that the resin sheet does not have the desired elasticity, strength, and resistance to deterioration over time. Furthermore, in order to realize stretchable devices, wiring that is highly conductive and stretchable, and furthermore, that exhibits minimal change in conductivity when stretched, is desired.

[0006] The present invention has been made in consideration of the above circumstances, and aims to provide a stretchable wiring material and a stretchable device that are highly conductive and highly stretchable, and further have small changes in conductivity when stretched. [Means for solving the problem]

[0007] In order to solve the above problems, the present invention provides the following means.

[0008] The stretchable wiring material according to the first aspect of the present invention contains resin and metal powder, has a breaking elongation of 130% or more, and a resistivity (ρ0) before stretching of 2×10 -2 [Ωmm] or less, the metal powder contains flaky powder, and the ratio of the resin is 8 wt% or more and 20 wt% or less.

[0009] The stretchable wiring material according to the second aspect of the present invention contains resin and metal powder, has a breaking elongation rate of 130% or more, and a resistivity (ρ ) at a stretch rate of 50% relative to the resistivity (ρ ) before stretching. 50 ) ratio (ρ 50 / ρ0) is 7 or less, the metal powder contains flaky powder, and the ratio of the resin is 8 wt % or more and 20 wt % or less.

[0010] In the stretchable wiring material according to the above aspect, the resistivity (ρ 50 ) at 100% stretching ratio (ρ 100 ) ratio (ρ 100 / ρ 50 ) may be 8 or less.

[0011] The stretchable wiring material according to a third aspect of the present invention contains resin and metal powder, has a breaking elongation rate of 130% or more, and a resistivity (ρ ) at a stretch rate of 50% relative to the resistivity (ρ ) before stretching. 50 ) ratio (ρ 50 / ρ0) at a stretch rate of 50% (ρ 50 ) at 100% stretching ratio (ρ 100 ) ratio (ρ 100 / ρ 50) is 140% or less, the metal powder contains scale-shaped powder, and the proportion of the resin is 8 wt% or more and 20 wt% or less.

[0012] In the stretchable wiring material according to the above aspect, the resin may be solidified by drying.

[0013] In the stretchable wiring material according to the above aspect, the proportion of the scale-shaped powder in the metal powder may be 2.5 wt % or more and 50 wt % or less.

[0014] In the stretchable wiring material according to the above aspect, the average maximum particle size of the scale-shaped powder may be 3 μm or more and 10 μm or less.

[0015] A stretchable device according to a third aspect of the present invention uses the stretchable wiring material according to the above aspect. [Effects of the Invention]

[0016] According to the present invention, it is possible to provide an expandable wiring material that is highly conductive and highly stretchable, and further, exhibits little change in conductivity when stretched. DETAILED DESCRIPTION OF THE INVENTION

[0017] The present invention will be described in detail below. The materials, dimensions, etc. exemplified in the following description are merely examples, and the present invention is not limited thereto and can be appropriately changed within the scope of the present invention.

[0018] (Stretchable wiring material (first embodiment)) The stretchable wiring material of the first embodiment contains resin and metal powder, has a breaking elongation rate of 130% or more, and a resistivity before stretching of 2×10 -3 The metal powder contains scale-shaped powder, and the resin ratio is 4 wt% or more and 20 wt% or less.

[0019] (resin) The resin contained in the stretchable wiring material of the first embodiment is not particularly limited, and any known stretchable resin can be used. Examples include urethane-based resins, acrylic-based resins, epoxy-based resins, urea-based resins, polyurethane-urea-based resins, methacrylic acid-based resins, polyacrylic resins, silicone-based resins, diene-based resins, polyester-based resins, polyether-based resins, polyamide-based resins, polystyrene-based resins, and polyimide-based resins. These may be used alone or in combination of two or more.

[0020] The resin is preferably soluble in one or more solvents selected from diethylene glycol monobutyl ether acetate (BCA), butyl carbitol (BC), ethyl cyanoacrylate (ECA), α-terpineol, diethylene glycol monobutyl ether, and diethylene glycol monoethyl ether acetate.

[0021] The stretchable wiring material of the first embodiment can be formed by applying and solidifying a resin composition containing the resin to be used, metal powder, and a solvent. Among the above resins, a dry-solidification type resin is preferred, which can be molded and solidified by simply coating and drying the resin composition without undergoing a curing reaction. An example of a dry-solidification type resin is a urethane-based resin. In this case, the stretchable wiring material according to the present invention can be called a dry-solidification type stretchable wiring material. This is because, in the case of resins that require a curing reaction, if the curing reaction does not proceed uniformly, variations in composition and degree of curing will occur within the wiring material sheet, and the resulting sheet may not have the desired elasticity, strength, and resistance to deterioration over time. Furthermore, when a urethane resin is used, it is preferable that the resin component contains a siloxane bond, because in this case the resin composition has appropriate water repellency and hydrolysis of the urethane bond is suppressed.

[0022] The proportion of resin in the stretchable wiring material of the first embodiment is 8 wt % or more and 20 wt % or less. The stretchable wiring material of the first embodiment is a wiring material with small changes in conductivity when stretched, and the resin proportion is set to 8 wt% or more to ensure high stretchability (high elongation at break) as a prerequisite. On the other hand, the stretchable wiring material of the first embodiment is a wiring material with high conductivity before and during stretching, and the resin proportion is set to 20 wt% or less to ensure high conductivity (low resistivity). The proportion of resin in the stretchable wiring material is preferably 10 wt % or more, and 18 wt % or less.

[0023] When the resin in the stretchable wiring material of the first embodiment contains a urethane-based resin, the proportion of urethane bonds in the resin is preferably 15 wt % or more, and more preferably 17 wt % or more. The proportion of urethane bonds in the resin is, for example, C 13 It can be calculated by calculating the peak area corresponding to the urethane bond in an NMR (Nuclear Magnetic Resonance) spectrum. Furthermore, in examples where the proportion of urethane bonds in the resin is high, as will be described later, the elongation at break may be low. The reason for this is not clear at present, but based on the examples, the proportion of urethane bonds in the resin is preferably 30 wt% or less, more preferably 25 wt% or less, and even more preferably 22 mol% or less.

[0024] (metal powder) The metal powder is not particularly limited, and known metal powders can be used. Examples include silver (Ag) powder, carbon (C), copper (Cu) powder, palladium (Pd) powder, gold (Au) powder, and platinum (Pt) powder. Among these, silver powder or an alloy powder containing silver as the main component is preferred because of its low resistance. Here, an alloy powder containing silver as the main component means that the proportion of silver is greater than 50 wt%, preferably 70 wt% or more, more preferably 80 wt% or more, and even more preferably 90 wt% or more.

[0025] The metal powder to be used may be either a suitably manufactured product or a commercially available product. For example, a method for producing silver powder includes adding an aqueous solution containing a reducing agent to an aqueous reaction system containing silver ions to reduce and precipitate silver particles. Alternatively, the silver powder may be silver powder having a silver surface and a metal other than silver inside, such as silver-coated copper powder.

[0026] Metal powders include scaly powders. In this specification, "scaly powder" refers to powder (metal powder) whose thickness is 1 / 10 or less of the maximum particle diameter. The maximum particle diameter of scaly powders is defined as follows: The length from end to end of each powder varies depending on the direction when viewed from above, and the longest of these lengths is taken as the maximum particle diameter. The maximum particle diameter can be determined by observation with an optical microscope or a scanning electron microscope (SEM) (for example, a 5000x field of view). When the metal powder is shaped like a scale, the metal powder particles have upper and lower surfaces that extend in the planar direction, and therefore the metal powder particles tend to be in planar contact with each other, leading to high conductivity (low resistivity).

[0027] Furthermore, the scale-shaped (flake-shaped) metal powder to be used may be an appropriately manufactured product or a commercially available product. For example, flake-shaped metal powder can be produced by forming a thin film of the desired metal and then pulverizing the thin film. Since this method is used to produce the powder by pulverizing the thin film, the individual crushed metal pieces are also flat. The thickness relative to the particle size (i.e., the degree of flatness) can be adjusted by adjusting the thickness of the thin film and the degree of pulverization.

[0028] The proportion of the scaly powder contained in the metal powder is preferably 2.5 wt% or more, more preferably 5 wt% or more, and even more preferably 7.5 wt% or more, and preferably 50 wt% or less, more preferably 40 wt% or less, even more preferably 30 wt% or less, and even more preferably 25 wt% or less. From the viewpoint of high conductivity (low resistivity), a high proportion of flake-shaped powder in the metal powder is preferable, but if it is too high, stretchability decreases and the breaking elongation rate drops. In order for the stretchable wiring material to stretch smoothly when it stretches, the metal powder needs to have freedom of movement, but if the proportion of flake-shaped powder exceeds 50 wt%, it is thought that this is due to the fact that the flake shape itself creates high resistance to movement.

[0029] The average maximum particle size of the scale-shaped powder is preferably 3 μm or more and 10 μm or less. If the particle size is 3 μm or more, sufficiently high conductivity (low resistivity) can be obtained due to the effect of surface contact between the metal powder particles, and if the particle size is 10 μm or less, a decrease in sufficient elasticity can be prevented, preventing a decrease in the breaking elongation.

[0030] (Elongation at break) The breaking elongation of the stretchable wiring material is 130% or more. The breaking elongation is preferably 150% or more, more preferably 200% or more, even more preferably 250% or more, and even more preferably 300% or more. The breaking elongation of the stretchable wiring material can be increased by increasing the proportion of resin contained in the stretchable wiring material, but an increase in the proportion of resin leads to an increase in resistivity. Therefore, the breaking elongation is appropriately adjusted by adjusting the proportion of resin depending on the breaking elongation and resistivity required for the stretchable device in which the stretchable wiring material is used.

[0031] In this specification, "elongation at break" is defined as {(length at break - length before stretching) / length before stretching} x 100. The elongation at break can be measured in each predetermined direction, but in this specification, "elongation at break of 150% or more" defines the elongation at break in the direction in which the elongation at break is the greatest. If there is no anisotropy in the elongation at break, the elongation at break will be the same in all directions, and if the anisotropy in the elongation at break is small, the elongation at break will be close in all directions.

[0032] (Method for measuring elongation at break) First, an example of a method for preparing a sample will be described below. A glass plate with a clean surface is prepared. Next, a PET film is placed on the glass plate and the top is secured with tape. Next, an applicator (e.g., YOSHIMITSU, YA type, 75 mm, 152 μm) is prepared and set. Next, the stretchable wiring paste in the container is stirred without air being introduced. Next, the stretchable wiring paste is applied to the PET film. Next, the applicator is slid to spread the stretchable wiring paste. Next, after spreading the stretchable wiring paste, the PET film and the glass plate are secured with tape. Next, after leaving it for 3 to 5 minutes, it is placed in a dryer preheated to 90 to 100°C and dried for 1 hour. Through these steps, a sheet sample of stretchable wiring material with a thickness of approximately 30 to 70 μm is obtained. The combined thickness of the PET film and the sheet sample of stretchable wiring material is approximately 150 μm.

[0033] The elongation at break can be measured as follows. Six strip-shaped measurement samples, each 10 mm wide and 30 mm long, are cut out from a sheet sample of the stretchable wiring material. The elongation at break is calculated for each measurement sample using the method described below, and the average value is taken as the elongation at break. A metal substrate is clamped between the upper and lower grips of the measuring device, and the measurement sample is fixed to the metal substrate with double-sided tape so that the measurement point is 10 mm wide and 10 mm long. The measurement sample is then pulled at a pulling rate of 10 mm / min using a tensile tester (for example, Autograph AGS-5kNX, manufactured by Shimadzu Corporation). The length of the measurement sample at break is then measured, and the length before pulling (10 mm) is subtracted from this length to calculate the elongation at break for each measurement sample. The average value is taken as the elongation at break, and the elongation at break is calculated according to the above definition.

[0034] (Resistivity before stretching) The resistivity of the stretchable wiring material before stretching (normal resistivity) is 2×10 -2 [Ωmm] or less. 7×10 -3 [Ωmm] or less is preferable, and 6 × 10 -3 [Ωmm] or less is more preferable, and 4×10-3 It is more preferable that the hardness is [Ωmm] or less. The resistivity before stretching of the stretchable wiring material can be reduced by increasing the proportion of metal powder contained in the stretchable wiring material, but a decrease in the resin proportion accompanying an increase in the metal powder proportion leads to a decrease in the breaking elongation. Therefore, the resistivity before stretching is appropriately adjusted by adjusting the proportion of metal powder according to the breaking elongation and resistivity required for the stretchable device in which the stretchable wiring material is used.

[0035] (Method for measuring resistance and resistivity) First, a sheet-shaped sample of the stretchable wiring material is prepared by the method described above. The resistivity before stretching can be measured as follows. As with the measurement of the elongation at break, six strip-shaped measurement samples, each 10 mm wide and 30 mm long, are cut out from a sheet sample of the stretchable wiring material. A metal substrate is clamped between the upper and lower grips of the measuring device, and the measurement sample is fixed to the metal substrate with double-sided tape so that the measurement point is 10 mm wide and 10 mm long. The resistance value of each measurement sample is measured in this state. The average value is taken as the resistance value before stretching R0. Note that the resistance value for each elongation is determined by moving the metal substrate by 1 mm at a time to stretch the sample, measuring the resistance value at each elongation, and the average value of the six samples is taken as the resistance value R at that elongation. Next, the thickness of a sheet sample of the stretchable wiring material is measured as follows. A sheet sample of the stretchable wiring material is punched into a circle. Next, the sample is placed on a flat table, and a rectangular PET film with one side larger than the diameter of the circular sample is placed on top of the sample. The thicknesses of the four corners of the rectangular PET film are measured using, for example, a Digimicro ZC-101 (manufactured by Nikon Corporation), and the average is taken as the thickness of the PET film. Next, the combined thickness of the sample and the PET film is measured at five points: top, bottom, left, right, and center, and the thickness of the PET film is subtracted from the average thickness to calculate the thickness t of the sample. Next, the resistivity ρ0 (=R0×(cross-sectional area / length)) is calculated from the above-mentioned pre-stretch resistance value R0 and the thickness t, width, and length of the sheet-like sample of the stretchable wiring material. Similarly, the resistivity at each elongation rate is calculated from the resistance value at each elongation rate and the thickness t, width, and length of the sheet-like sample of the elastic wiring material: resistivity ρ (= R × (cross-sectional area / length)).

[0036] In the stretchable wiring material according to the first embodiment, the resistivity (ρ ) at a stretch rate of 50% relative to the resistivity (ρ ) before stretching is 50 ) ratio (ρ 50 / ρ0) is preferably 7 or less, more preferably 6 or less, and even more preferably 5 or less. 50 ) at 100% stretching ratio (ρ 100 ) ratio (ρ 100 / ρ 50 ) is preferably 8 or less, more preferably 7 or less, even more preferably 6 or less, and most preferably 5 or less. In addition, the resistivity at a stretch rate of 50% (ρ 50 ) ratio (ρ 50 / ρ0), and the resistivity at 50% stretching (ρ 50 ) at 100% stretching ratio (ρ 100 ) ratio (ρ 100 / ρ 50 ) is preferably 7 or less, more preferably 6 or less, and even more preferably 5 or less.

[0037] In the stretchable wiring material according to the first embodiment, the resistivity (ρ ) at a stretch rate of 50% relative to the resistivity (ρ ) before stretching is 50 ) ratio (ρ 50 / ρ0) at a stretch rate of 50% (ρ 50 ) at 100% stretching ratio (ρ 100 ) ratio (ρ 100 / ρ 50 ) is preferably 140% or less, more preferably 80% or less, even more preferably 70% or less, even more preferably 60% or less, and even more preferably 50% or less.

[0038] In the stretchable wiring material according to the first embodiment, the resistivity (ρ ) at a stretch rate of 50% relative to the resistivity (ρ ) before stretching is 50 ) ratio (ρ 50 / ρ0), and the resistivity at 50% stretching (ρ 50 ) at 100% stretching ratio (ρ 100 ) ratio (ρ 100 / ρ 50 ) are all 7 or less, and the resistivity (ρ 50 ) ratio (ρ 50 / ρ0) at a stretch rate of 50% (ρ 50 ) at 100% stretching ratio (ρ 100 ) ratio (ρ 100 / ρ 50 ) is more preferably 140% or less.

[0039] (Stretchable wiring material (second embodiment)) The stretchable wiring material according to the second embodiment contains resin and metal powder, has a breaking elongation rate of 130% or more, and a resistivity (ρ ) at a stretch rate of 50% relative to the resistivity (ρ ) before stretching. 50 ) ratio (ρ 50 / ρ0) is 7 or less, the metal powder contains scale-shaped powder, and the proportion of resin is 8 wt% or more and 20 wt% or less. Explanation of the configuration common to the stretchable wiring material according to the first embodiment will be omitted. Furthermore, the resistivity (ρ 50 ) at 100% stretching ratio (ρ 100 ) ratio (ρ 100 / ρ 50 ) is preferably 8 or less. The proportion of resin in the stretchable wiring material is preferably 10 wt % or more, and 18 wt % or less.

[0040] The smaller the change in resistivity when the elastic wiring material is stretched, the more preferable it is. Resistivity ratio before stretching and after stretching at 50% (ρ 50 / ρ0) is preferably 6 or less, more preferably 5 or less.50 ) at 100% stretching ratio (ρ 100 ) ratio (ρ 100 / ρ 50 ) is more preferably 7 or less, even more preferably 6 or less, and even more preferably 5 or less.

[0041] In the stretchable wiring material according to the second embodiment, it is preferable that the rate of change (ρ100 / ρ50) of the ratio of the resistivity (ρ100) at a stretch rate of 100% to the resistivity (ρ50) at a stretch rate of 50% to the resistivity (ρ0) before stretching is 140% or less.

[0042] (Stretchable wiring material (third embodiment)) The stretchable wiring material of the third embodiment contains resin and metal powder, has a breaking elongation rate of 130% or more, and a resistivity (ρ ) at a stretch rate of 50% relative to the resistivity (ρ ) before stretching. 50 ) ratio (ρ 50 / ρ0) at a stretch rate of 50% (ρ 50 ) at 100% stretching ratio (ρ 100 ) ratio (ρ 100 / ρ 50 ) is 140% or less, the metal powder contains scale-shaped powder, and the proportion of resin is 8 wt% or more and 20 wt% or less. Explanation of the configuration common to the stretchable wiring material according to the first embodiment will be omitted. The proportion of resin in the stretchable wiring material is preferably 10 wt % or more, and 18 wt % or less.

[0043] The resistivity of the stretchable wiring material decreases as it stretches, but the smaller the rate of this decrease, the more preferable it is. 100 / ρ 50 ) / ratio(ρ 50 / ρ0)) is preferably 80% or less, more preferably 70% or less, even more preferably 60% or less, and most preferably 50% or less.

[0044] (Method for producing stretchable wiring material) The stretchable wiring materials of the first to third embodiments can be produced through the following main steps: (1) a stretchable wiring paste production step, (2) a stretchable wiring paste application step, and (3) a drying and solidification step. That is, in the (1) stretchable wiring paste preparation step, a resin composition containing the above-mentioned resin and solvent is mixed with metal powder to prepare a stretchable wiring paste. Next, in the (2) stretchable wiring paste application step, the stretchable wiring paste is applied to a substrate (e.g., a PET film). After that, in the (3) drying and solidification step, the solvent is removed and the resulting material is dried and solidified to prepare a stretchable wiring material.

[0045] Hereinafter, the characteristics of the stretchable wiring material will be described while giving specific examples of resin compositions (resin and solvent) for producing the stretchable wiring material. A specific example is a resin composition containing a resin component (sometimes referred to in this specification as "resin component (II)"), in which the resin component has a group represented by the following general formula (11), (21), or (31) and a urethane bond.

[0046] [ka] (In the formula, Z1 is an alkyl group, and one or more hydrogen atoms in the alkyl group may be substituted with a cyano group, a carboxy group, or a methoxycarbonyl group, and the two or more substituents may be the same or different. Z2 is an alkyl group. Z3 is an aryl group. R4 is a hydrogen atom or a halogen atom. The bond marked with an * is formed between the bond recipient of the group represented by general formula (11), (21), or (31).)

[0047] The resin component (II) contained in this resin composition has a urethane bond, and therefore has high flexibility. Resin component (II) is obtained by polymerization using a resin having a urethane bond and a polymerizable unsaturated bond and a RAFT agent for reversible addition-fragmentation chain transfer polymerization (hereinafter sometimes abbreviated as "RAFT polymerization"), from which the group represented by general formula (11), (21), or (31) is derived. By carrying out the polymerization reaction in this manner, gelation of the polymerized resin during the process of forming a crosslinked structure can be avoided, and a resin component with the desired degree of polymerization and crosslinked state can be obtained. In other words, resin component (II) having a group represented by general formula (11), (21), or (31) exhibits little variation in degree of polymerization and crosslinked state. Furthermore, the resin component (II) may have a siloxane bond, and in this case, the resin composition has appropriate water repellency and the hydrolysis of the urethane bond in the resin component (II) is suppressed. Such a resin component (II) can be obtained by carrying out a polymerization reaction using a resin having a siloxane bond and a polymerizable unsaturated bond. The method for producing the resin component (II) by RAFT polymerization will be described in detail separately.

[0048] The resin having a urethane bond and a polymerizable unsaturated bond used in producing the resin component (II) is an oligomer, and may be referred to as "resin (a)." The resin having a siloxane bond and a polymerizable unsaturated bond used in producing the resin component (II) is an oligomer, and in this embodiment may be referred to as "resin (b)." Resin component (II) is a polymer formed by polymerizing resins (a) together at their polymerizable unsaturated bonds. When resin (b) is used, resin component (II) is a polymer formed by polymerizing resins (a) and (b) at their polymerizable unsaturated bonds.

[0049] When resin (b) is used, the resin component (II) preferably has both a urethane bond and a siloxane bond in one molecule.

[0050] The resin (a) is not particularly limited as long as it has a urethane bond and a polymerizable unsaturated bond. Examples of the resin (a) include those having a urethane bond and a (meth)acryloyl group as the group having a polymerizable unsaturated bond, and more specifically, urethane (meth)acrylates and the like. In this specification, the term "(meth)acrylate" is a concept that encompasses both "acrylate" and "methacrylate." The same applies to terms similar to (meth)acrylate; for example, the term "(meth)acryloyl group" is a concept that encompasses both "acryloyl group" and "methacryloyl group."

[0051] The resin (b) is not particularly limited as long as it has a siloxane bond and a polymerizable unsaturated bond. Examples of the resin (b) include various known silicone resins having a (meth)acryloyl group as a group having a polymerizable unsaturated bond, and more specifically, examples thereof include modified polydialkylsiloxanes in which a (meth)acryloyl group is bonded to one or both ends of a polydialkylsiloxane such as polydimethylsiloxane.

[0052] Due to its composition, resin component (II) has high solubility in solvents, and therefore the resin composition containing resin component (II) also has high solubility in solvents. Such a highly soluble resin composition can be easily formed into a resin composition layer by, for example, printing it onto an object to be applied using various printing methods. Then, by solidifying the resin composition layer by drying without curing, a layer (resin layer, wiring material sheet) similar to the wiring material sheet can be produced. This method is suitable for forming electrodes or wiring using the resin composition containing a conductive component.

[0053] Such a highly soluble resin composition is used to form a wiring sheet having stretchability, and a stretchable device constructed using this wiring sheet has the great advantage of being able to suppress breakage during stretching. From a materials perspective, possible causes of breakage in conventional stretchable devices during stretching include (i) structural defects such as voids and interfacial peeling caused by shrinkage due to heat or curing reactions, (ii) uneven hardness caused by uneven composition, and (iii) deterioration of materials over time caused by light exposure, oxidation, etc. Therefore, by suppressing structural defects such as voids, interfacial peeling, compositional irregularities, and deterioration of materials over time, it is possible to suppress breakage of stretchable devices when they are stretched. Although stretchable substrates are typically processed by thermal melting or crosslinking by thermal or photocuring, there are concerns that the reliability of stretchable devices may be reduced when considering microfabrication due to the reasons (i) to (iii) above. In contrast, if there were a resin that could be molded by simply coating and drying the resin composition, compatible with lamination methods, it would be expected to produce good results.

[0054] The stretchable wiring material can be produced by adding metal powder to the resin composition of the above specific example to produce a stretchable wiring paste, applying the stretchable wiring paste to a substrate, and then drying and solidifying it to obtain a wiring sheet-like stretchable wiring material (hereinafter sometimes referred to as a "wiring material sheet"). A plurality of wiring material sheets can also be stacked to produce a stretchable wiring material. The wiring sheet contains resin component (II) as a main component and therefore has good stretchability. When resin (b) is used, the wiring sheet also has moderate water repellency, which suppresses deterioration over time due to hydrolysis. The wiring sheet with these properties is particularly suitable for constructing various stretchable devices, including wearable devices.

[0055] The wiring material sheet can be formed by simply solidifying the resin composition by drying, as described above, without carrying out a curing reaction of the resin composition, and therefore does not have the drawbacks associated with carrying out a curing reaction.

[0056] For example, it is extremely difficult to uniformly cure a material that is not transparent to ultraviolet light in a photocurable wiring material sheet. For example, when ultraviolet light is irradiated around a mounted device or electronic component in a photocurable wiring material sheet, the transmittance of ultraviolet light varies, resulting in areas with different degrees of cure. In areas with low cross-linking density, the wiring material sheet is prone to breakage. Furthermore, non-cross-linked areas are prone to deterioration due to oxidation. On the other hand, the thermal curing reaction tends to cause differential shrinkage in the wiring material sheet due to heat distribution during curing. Such differential shrinkage can easily cause separation at the interface between different constituent materials, such as between a device and a sealant. Furthermore, if regions with different degrees of cure occur in the wiring material sheet due to heat distribution, repeated expansion and contraction can easily cause deterioration. Furthermore, in both the photocuring reaction and the thermosetting reaction, it is difficult for the reaction to proceed uniformly within the wiring material sheet, resulting in variations in the composition and degree of cure within the wiring material sheet, and the wiring material sheet after curing may not have the desired elasticity and strength. Furthermore, since the wiring material contains a curing agent, it is prone to deterioration over time due to heat and light. In contrast, the wiring material sheet obtained by drying and solidifying the stretchable wiring paste containing the resin composition of the above specific example does not have such a problem.

[0057] The wiring material sheet can be produced, for example, by applying the stretchable wiring paste to a target location and solidifying it by drying, without carrying out a curing reaction.

[0058] The stretchable wiring paste can be applied by a known method using various coaters or wire bars, or by various printing methods including inkjet printing.

[0059] When producing the wiring sheet, the drying temperature of the stretchable wiring paste is preferably 25 to 150°C, and more preferably 25 to 120°C. When the drying temperature is 25°C or higher, the wiring sheet can be produced more efficiently. When the drying temperature is 150°C or lower, the drying temperature is prevented from becoming excessively high, which makes it less likely that deformation of the release sheet or damage to the wiring sheet will occur, and prevents deterioration of the wiring sheet.

[0060] In producing the wiring sheet, the drying time of the stretchable wiring paste may be appropriately set depending on the drying temperature, but is preferably 10 to 120 minutes, more preferably 30 to 90 minutes. When the drying time is within this range, a wiring sheet with good properties can be efficiently produced.

[0061] Completion of solidification by drying of the stretchable wiring paste (formation of a wiring material sheet) can be confirmed, for example, by the fact that no clear change in the mass of the resin composition being dried is observed.

[0062] The thickness of the stretchable wiring material is not particularly limited, but for example, a thickness of 10 to 5000 μm can be used.

[0063] (Application) The stretchable wiring material according to the present invention can be used as wiring in a stretchable device. [Example]

[0064] The present invention will be described in more detail below with reference to specific examples, although the present invention is not limited to the examples shown below.

[0065] The raw materials used to prepare the stretchable wiring paste are shown below. Resin (a) (a)-1: Urethane acrylate oligomer (product name: UN-5500, manufactured by Negami Chemical Industrial Co., Ltd.) ·Resin (b) (b)-1: Methacrylate-modified polydimethylsiloxane in which one end is modified with a methacryloyl group (product name: Silaplane (registered trademark) FM-0721, manufactured by JNC Corporation) Polymerization initiator (c) (c)-1: Dimethyl 2,2'-azobis(2-methylpropionate), azo polymerization initiator (product name: V601, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) RAFT agents (1)-1: RAFT agent represented by the following formula (1)-1 (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) (3)-1: RAFT agent represented by the following formula (3)-1 (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) Other polymerizable components MMA: methyl methacrylate ·solvent BCA: butyl carbitol acetate ·Metal powder Silver powder (ratio of scale-shaped powder: 12.5 [wt%], average maximum particle size: 3 μm)

[0066] [ka]

[0067] [Example 1] Resin (a)-1, polymerization initiator (c)-1, RAFT agent (1)-1, silver powder, and BCA were weighed into a flask and mixed at room temperature using a stirrer to obtain a stretchable wiring paste. The amounts of resin (b), polymerization initiator (c), and RAFT agent were determined so that the proportion of urethane bonds in the resin of the resulting stretchable wiring material would be 20 wt% based on 100 parts by mass of resin (a). The amount of silver powder was also determined so that the proportion of resin in the resulting stretchable wiring material would be 5 wt%. In other words, the amount of silver powder was determined so that the ratio of resin to silver powder would be 8 wt%:92 wt%.

[0068] Next, a sheet-shaped sample of the stretchable wiring material was prepared by the method described above, and the breaking elongation, resistivity before stretching (ρ0), and resistivity at a stretching rate of 50% (ρ 50), resistivity at 100% stretching (ρ 100 The results are shown in Table 1.

[0069] [Table 1]

[0070] (Examples 2 to 5, Comparative Examples 1 and 2) In Examples 2 to 5 and Comparative Examples 1 and 2, sheet samples of the stretchable wiring material were prepared in the same manner as in Example 1, except that the amount of silver powder blended was adjusted so that the resin proportions of the resulting stretchable wiring material were 10 wt%, 15 wt%, 18 wt%, 20 wt%, 6 wt%, and 22 wt%, respectively. The obtained samples were measured for the same properties. The results are shown in Table 1.

[0071] (Examples 6 to 9, Comparative Examples 3 to 5) In all of Examples 6 to 9 and Comparative Examples 3 to 5, the resin proportion of the resulting stretchable wiring material was 15 wt%, and the proportions of urethane bonds in the resin of the resulting stretchable wiring material were adjusted to 17.5 wt%, 20 wt%, 22 wt%, 25 wt%, 30 wt%, 0 wt%, 10 wt%, and 15 wt%, respectively. Sheet samples of stretchable wiring material were produced in the same manner as in Example 1. The obtained samples were measured for the same properties. The results are shown in Table 1.

[0072] (Comparative Examples 6 and 7) In Comparative Examples 6 and 7, the stretchable wiring paste was applied and then subjected to a curing reaction rather than being dried and solidified. In Comparative Example 6, the stretchable wiring paste was obtained in the same manner as in Comparative Example 5, except that the silver powder did not contain flake-shaped silver powder. In Comparative Example 7, the same stretchable wiring paste as in Example 9 was used. The obtained samples were subjected to similar measurements of properties. The results are shown in Table 1.

[0073] (Examples 10 to 16) In Examples 10 to 16, the resin proportion of the resulting stretchable wiring material was 15 wt%, and the proportion of urethane bonds in the resin of the resulting stretchable wiring material was 20 mol%, and sheet samples of stretchable wiring material were prepared in the same manner as Example 1, except that the proportions of scale-shaped powder in the silver powder were 2.5 wt%, 7.5 wt%, 12.5 wt%, 30 wt%, 40 wt%, and 50 wt%, respectively. The obtained samples were subjected to the same measurements, and the results are shown in Table 1.

[0074] The findings from the results in Table 1 are shown below. Values ​​without a value in Table 1 were either not measurable or not measured.

[0075] First, Examples 1 to 6 are compared with Comparative Examples 1 and 2. When the proportion of urethane bonds in the resin and the proportion of scaly powder were fixed at the proportions shown in Table 1, the following findings were obtained. When the resin content in the wiring material was 8 wt% or more (resin:silver powder = 8:92), the breaking elongation was 130% or more, and the higher the resin content, the higher the breaking elongation value. On the other hand, when the resin content was 20 wt% or more, the pre-stretch resistivity was 1 × 10 -2 [Ωcm] or more. Higher elongation at break (150% or more) and lower pre-stretch resistivity (5 × 10 -3 From the viewpoint of achieving both a high dielectric strength (Ωcm or less), the proportion of resin in the wiring material is preferably 10 wt % or more and 18 wt % or less. Furthermore, when the resin ratio was 20 wt% (resin:silver powder = 20:80) (Example 5), the resistivity before expansion and contraction was 1.53 × 10 -2 [Ωcm], which is slightly high, reflects the high breaking elongation rate, and the resistivity at a stretch rate of 50% (ρ 50 ) ratio (ρ 50 / ρ0) is a low change rate of 1.7, and the resistivity (ρ 50 ) at 100% stretching ratio (ρ 100 ) ratio (ρ 100 / ρ 50 ) was 4.0, which was a sufficiently low rate of change.50 / ρ0) and the ratio (ρ 100 / ρ 50 ), the proportion of resin in the wiring material is preferably 10 wt % or more and 20 wt % or less. In addition, it has a high breaking elongation rate (over 150%) and a low ratio (ρ 50 / ρ0) to 100 / ρ 50 From the viewpoint of achieving both the rate of change of the resistance and the temperature, the proportion of the resin in the wiring material is preferably 10 wt % or more and 15 wt % or less. Furthermore, it has a high breaking elongation (over 150%), a low pre-stretch resistivity, and a low ratio (ρ 50 / ρ0) and the ratio (ρ 100 / ρ 50 ), and low ratio (ρ 50 / ρ0) to 100 / ρ 50 From the viewpoint of satisfying all of the change rates of the above items, the proportion of resin in the wiring material is preferably 10 wt % or more and 15 wt % or less.

[0076] Next, Examples 3, 6 to 9 are compared with Comparative Examples 3 and 4. When the proportions of resin and scale-shaped powder in the wiring material were fixed at the proportions shown in Table 1, the following findings were obtained. When the proportion of urethane bonds in the resin was 15 wt% or less, the breaking elongation was 40% or less. On the other hand, when the proportion of urethane bonds was 25 wt% (Example 8), the breaking elongation was 245.5%, but when it was 30 wt% (Example 9), the breaking elongation was 130.4%. From the viewpoint of a high breaking elongation (150% or more), it is preferable that the proportion of urethane bonds in the resin be 17.5 wt% or more and 25 wt% or less. Furthermore, a higher breaking elongation (150% or more) and a lower pre-stretch resistivity (7 x 10 -3 From the viewpoint of achieving both a high elastic modulus (viscosity [Ωcm] or less), the proportion of urethane bonds in the resin is preferably 20 wt % or more and 25 wt % or less. In addition, it has a high breaking elongation rate (over 150%) and a low ratio (ρ 50 / ρ0) and the ratio (ρ 100 / ρ 50), the proportion of urethane bonds in the resin is preferably 17.5 wt % or more and 25 wt % or less. In addition, it has a high breaking elongation rate (over 150%) and a low ratio (ρ 50 / ρ0) to 100 / ρ 50 From the viewpoint of achieving both the rate of change of the urethane bond content and the viscosity of the resin, the proportion of the urethane bond in the resin is preferably 17.5 wt % or more and 22 wt % or less. Furthermore, it has a high breaking elongation (over 150%), a low pre-stretch resistivity, and a low ratio (ρ 50 / ρ0) and the ratio (ρ 100 / ρ 50 ), and low ratio (ρ 50 / ρ0) to 100 / ρ 50 From the viewpoint of satisfying all of the above mentioned change rates of urethane bonds, the proportion of urethane bonds in the resin is preferably 17.5 wt % or more and 22 wt % or less.

[0077] In Comparative Examples 6 and 7, the stretchable wiring paste was applied, and then subjected to a hardening reaction rather than being dried and solidified. In Comparative Example 6, which does not contain scale-shaped silver powder, the resistivity before stretching was 5×10 -1 The elongation at break was 10% or less in Comparative Example 7, which has the same composition as Example 9, and is therefore not suitable for application to stretchable devices.

[0078] Next, Examples 3 and 10 to 14 are compared. When the proportion of resin in the wiring material and the proportion of urethane bonds in the resin were fixed at the proportions shown in Table 1, the following findings were obtained. When the ratio of the scale-shaped powder in the silver powder reached 40 wt% and 50 wt%, the breaking elongation was negatively affected, and the breaking elongation gradually decreased. Furthermore, when the ratio was 40 wt% (Example 13), the ratio (ρ 50 / ρ0) to 100 / ρ 50 ) change rate becomes 130% or more, and in the case of 50 wt% (Example 14), the ratio (ρ 50 / ρ0) is 51 times larger. From this viewpoint, when the ratio of scale-shaped powder in the silver powder is in the range of 2.5 wt% or more and 50 wt% or less, a higher breaking elongation rate (150% or more) and a lower pre-stretch resistivity (7 × 10 -3 [Ωcm] or less). High elongation at break (over 150%) and low ratio (ρ 50 / ρ0) and the ratio (ρ 100 / ρ 50 ), the proportion of the scale-shaped powder in the silver powder is preferably 2.5 wt % or more and 40 wt % or less. In addition, it has a high breaking elongation rate (over 150%) and a low ratio (ρ 50 / ρ0) to 100 / ρ 50 From the viewpoint of achieving both the rate of change of the particle diameter and the particle size, the proportion of the scale-shaped powder in the silver powder is preferably 2.5 wt % or more and 12.5 wt % or less. Furthermore, it has a high breaking elongation (over 150%), a low pre-stretch resistivity, and a low ratio (ρ 50 / ρ0) and the ratio (ρ 100 / ρ 50 ), and low ratio (ρ 50 / ρ0) to 100 / ρ 50 From the viewpoint of satisfying all of the above-mentioned change rates, the proportion of the scale-shaped powder in the silver powder is preferably 2.5 wt % or more and 12.5 wt % or less.

[0079] High flexibility can be achieved by including urethane bonds in the resin. Furthermore, when the resin includes either urethane bonds or siloxane bonds, the dispersion and aggregation of silver powder are improved, resulting in both high elasticity and low resistance. Furthermore, when the resin includes both urethane bonds and siloxane bonds, even greater improvements can be achieved.

Claims

1. Contains resin and metal powder, The breaking elongation is 130% or more, Resistivity before stretching (ρ ０ ) at a stretch rate of 50% (ρ ５０ ) ratio (ρ ５０ / ρ ０ ) is 7 or less, the ratio (ρ 100 / ρ 50 ) of the resistivity (ρ 100 ) at a stretch rate of 100% to the resistivity (ρ 50 ) at a stretch rate of 50% is 8 or less; The metal powder includes a scale-shaped powder, The proportion of urethane bonds in the resin is 17 wt % or more and 30 wt % or less, a ratio of the resin to the total of the resin and the metal powder is 8 wt % or more and 20 wt % or less, The ratio of scale-shaped powder in the metal powder is 2.5 wt % or more and 50 wt % or less, The stretchable wiring material, wherein the resin is solidified by drying without undergoing a curing reaction.

2. Contains resin and metal powder, The breaking elongation is 130% or more, Resistivity before stretching (ρ ０ ) at a stretch rate of 50% (ρ ５０ ) ratio (ρ ５０ / ρ ０ ) at a stretch rate of 50% (ρ ５０ ) at a stretch rate of 100% (ρ １００ ) ratio (ρ １００ / ρ ５０ ) is 140% or less, The metal powder includes a scale-shaped powder, The proportion of urethane bonds in the resin is 17 wt % or more and 30 wt % or less, a ratio of the resin to the total of the resin and the metal powder is 8 wt % or more and 20 wt % or less, The ratio of scale-shaped powder in the metal powder is 2.5 wt % or more and 50 wt % or less, The stretchable wiring material, wherein the resin is solidified by drying without undergoing a curing reaction.

3. The stretchable wiring material according to claim 1 or 2, wherein the average maximum particle diameter of the scale-shaped powder is 3 μm or more and 10 μm or less.

4. A stretchable device using the stretchable wiring material according to any one of claims 1 to 3.

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