Resin substrate with conductive film, electronic device, electromagnetic wave shield sheet, and planar heating element

Abstract

A resin substrate with a conductive film according to the present invention comprises: a resin substrate including a thermoplastic resin layer having a heat resistance temperature of 80°C or higher; and a conductive film including a sintered body of a plurality of conductive particles, wherein in one cross-section in the thickness direction, there is a transition region between the resin substrate and the conductive film in which at least a portion of each coexist.

Description

Conductive film-coated resin substrates, electronic devices, electromagnetic shielding sheets, and planar heating elements.

[0001] The present invention relates to a resin substrate with a conductive film, an electronic device, an electromagnetic wave shielding sheet, and a planar heating element.

[0002] Studies have been conducted on forming conductive patterns, such as circuit patterns, on substrates using conductive compositions containing conductive particles. Conductive compositions containing conductive particles are sometimes referred to as conductive pastes, conductive inks, etc. Prior art relating to conductive pattern formation techniques using conductive compositions containing conductive particles can be found in the following patent documents 1 to 4.

[0003] Japanese Unexamined Patent Publication No. 2006-165467 Japanese Unexamined Patent Publication No. 2001-015893 Japanese Patent No. 6491032 Japanese Unexamined Patent Publication No. 11-289149

[0004] In the above-mentioned Patent Documents 1 to 4, a conductive paste containing conductive nanoparticles formed on a resin substrate is subjected to laser light, metal halide lamp, light irradiation, and YAG / CO2. ２ Techniques are used to sinter or dry conductive paste by irradiating it with a laser or the like. As a result of the inventors' investigations, it was found that there is room for improvement in terms of adhesion between the conductive film and the resin substrate in resin substrates equipped with a conductive film.

[0005] The inventors of the present invention have discovered that the adhesion between the conductive film and the resin substrate can be improved by forming a transition region between the resin substrate and the conductive film in which both coexist, and have completed the present invention.

[0006] According to one aspect of the present invention, the following conductive film-coated resin substrate, electronic device, electromagnetic wave shielding sheet, and planar heating element are provided.

[0007] 1. A conductive film-coated resin substrate comprising a resin substrate containing a thermoplastic resin layer having a heat resistance temperature of 80°C or higher, and a conductive film containing a sintered body of a plurality of conductive particles, wherein in a cross-section in the thickness direction of the conductive film-coated resin substrate, there is a transition region between the resin substrate and the conductive film in which at least a portion of each coexist. 2. The conductive film-coated resin substrate according to 1, wherein the transition region has a structure in which at least a portion of the conductive film is embedded in a recess formed in the thermoplastic resin layer. 3. The conductive film-coated resin substrate according to 1 or 2, wherein at least a portion of the surface near the surface of the thermoplastic resin layer includes a surface modification region. 4. The conductive film-coated resin substrate according to 3, wherein at least a portion of the transition region is located within the surface modification region. 5. 3 or 4. A conductive film-coated resin substrate as described in (1), wherein the surface-modified region includes the amorphous region of the thermoplastic resin layer. 6. A conductive film-coated resin substrate as described in any one of (1) to (5), wherein the resin substrate contains one or more selected from the group consisting of polyester, polycarbonate, polyimide, and polyolefin. 7. A conductive film-coated resin substrate as described in any one of (1) to (6), wherein the particles contained in the conductive particles include dendritic particles. 8. A conductive film-coated resin substrate as described in any one of (1) to (7), wherein the particle diameter D at the point where the cumulative volume from the small particle side reaches 50% in the volume-based cumulative distribution of particle diameters obtained when the particle diameter of the conductive particles is measured by laser diffraction scattering is ５０A conductive film-coated resin substrate having a thickness of 0.5 μm or more and 100 μm or less. 9. A conductive film-coated resin substrate according to any one of 1 to 8, wherein the conductive particles contain copper. 10. An electronic device comprising a conductive film-coated resin substrate according to any one of 1 to 9. 11. An electronic device according to 10, wherein the electronic device is an RF tag. 12. An electromagnetic wave shielding sheet comprising a conductive film-coated resin substrate according to any one of 1 to 9. 13. A planar heating element comprising a conductive film-coated resin substrate according to any one of 1 to 9.

[0008] According to the present invention, a resin substrate with a conductive film that has low resistance and good adhesion, an electronic device using the same, an electromagnetic wave shielding sheet, and a planar heating element are provided.

[0009] This is a schematic cross-sectional view showing an example of the manufacturing process for a conductive film-coated substrate according to this embodiment. This is a schematic cross-sectional view showing an example of a conductive film-coated resin substrate according to this embodiment. This is a schematic top view showing an example of a conductive film-coated resin substrate according to this embodiment. This is an SEM image of Example 1. This is an SEM image of Example 1. This is an SEM image of Comparative Example 1.

[0010] Embodiments of the present invention will be described below with reference to the drawings. In all drawings, similar components are denoted by the same reference numerals, and their descriptions are omitted as appropriate. Also, the drawings are schematic diagrams and do not correspond to the actual dimensional ratios.

[0011] In this specification, the notation "X to Y" in descriptions of numerical ranges means X or more and Y or less, unless otherwise specified. For example, "1 to 5 mass%" means "1 mass% or more and 5 mass% or less." In this specification, the notation "(meth)acrylic" represents a concept that encompasses both acrylic and methacrylic. The same applies to similar notations such as "(meth)acrylate." In this specification, the term "electronic device" is used to mean elements, devices, and final products to which electronic engineering technology is applied, such as semiconductor chips, semiconductor elements, printed circuit boards, electrical circuit display devices, information and communication terminals, light-emitting diodes, physical batteries, and chemical batteries.

[0012] The outline of the conductive film-coated resin substrate in this embodiment will be described.

[0013] The conductive film-coated resin substrate of this embodiment comprises a resin substrate including a thermoplastic resin layer having a heat resistance temperature of 80°C or higher, and a conductive film including a sintered body of a plurality of conductive particles, wherein at least one of the cross-sections in the thickness direction of the conductive film-coated resin substrate includes a transition region between the resin substrate and the conductive film in which at least a portion of each coexists.

[0014] According to the inventors' findings, by applying pressure and heating to a softened or melted surface-modified portion of a thermoplastic resin layer, a transition region is formed between the resin substrate and the conductive film where the thermoplastic resin layer and the sintered conductive film of the resin substrate coexist. This improves the adhesion between the conductive film and the resin substrate. In the transition region, a entangled structure is formed in which the thermoplastic resin layer and the conductive film are intertwined, and it is presumed that the physical adhesion between the two is increased. Furthermore, the above pressurized heating treatment forms an embedded structure in which at least a portion of the conductive film is embedded in a recess formed in the thermoplastic resin layer. Since the embedded structure functions as an anchor, it is presumed that peeling between the conductive film and the resin substrate is suppressed, and the physical adhesion between the two is increased.

[0015] Although the detailed mechanism is not clear, it is presumed to be as follows: The conductive particle-containing layer made of conductive paste contains multiple conductive particles in an unsintered state. On the other hand, the surface-modified portion of the thermoplastic resin layer of the resin substrate is in a state where it has undergone a surface modification treatment that softens or melts. When multiple conductive particles are pressed against the surface-modified portion of the thermoplastic resin layer by the heating and pressing treatment, it is presumed that because the resin in the surface-modified portion is easily deformed and moved, multiple conductive particles can penetrate into the interior of the thermoplastic resin layer, thus forming the above-mentioned entangled structure or embedded structure. In contrast, the inventors have found that even if a dried film made of conductive paste is heated and pressed against a thermoplastic resin layer that has not undergone a surface modification treatment that softens or melts, the entirety of multiple conductive particles in the dried film presses against the surface of the thermoplastic resin layer, but it does not result in the formation of the above-mentioned entangled structure or embedded structure. Furthermore, the adhesion force due to the entangled structure or embedded structure in this embodiment differs from general adhesion force in that it is exhibited after heating and pressing (sintering of conductive particles). Typical adhesion is achieved through the affinity between the conductive paste and the substrate when the conductive paste is printed, and through the interaction at the interface when the conductive paste dries.

[0016] The conductive film-coated resin substrate of this embodiment can be used for various applications, including, for example, electronic devices, electromagnetic shielding sheets, and planar heating elements. Preferably, as an electronic device, it can be used in RFID media such as inlays (sometimes called inlets) and tags (RF tags). RFID media can be used in inlays, tags, labels, tickets, cards, and other media formed by processing inlays. The RFID media incorporates an RFID-compliant IC chip. Such RFID media have visibly printed information about the object to be attached, the object to be affixed, or the wearer, and the incorporated IC chip can store various information about the object. The inlay comprises a substrate, an electrical circuit (such as an antenna), and an IC chip, and at least a portion of the metal pattern included in the substrate and electrical circuit may be made of the conductive film-coated resin substrate. The inlay may optionally include a meander pattern and / or a capacitor hat. In addition to the inlay, the tag may further include a sealing member to protect the IC chip. The inlay within the tag may be molded with a sealing material such as resin on the side where the IC chip is mounted or on both sides. Information (such as barcodes or text) may also be printed on the surface of the tag. In addition to the inlay, the label may further include adhesive for attachment to a substrate and printed information (such as barcodes or text).

[0017] The following describes the manufacturing method of the conductive film-coated resin substrate according to this embodiment, while detailing each component of the conductive film-coated resin substrate.

[0018] Figures 1(A) to 1(C) are cross-sectional views showing an example of a method for manufacturing a conductive film-coated resin substrate. Figure 2 is a schematic cross-sectional view showing an example of a conductive film-coated resin substrate 10. Figures 1(A) to 1(C) are cross-sectional views of the substrate in the thickness direction. In Figure 2, the Z direction means the same direction as the thickness direction. The Z direction may also be defined as the normal direction to the X-Y plane, when the plane of the surface 1A of the substrate 1 is defined as the X-Y plane.

[0019] An example of a method for manufacturing a conductive film-coated resin substrate according to this embodiment includes, as shown in Figure 1(A), a lamination step of forming a layer containing a plurality of conductive particles (conductive particle-containing layer 2) on the surface of a resin substrate (substrate 1); as shown in Figure 1(B), a surface modification step of softening or melting at least a portion of the surface side of the thermoplastic resin layer of the substrate 1 with a xenon flash 4; and as shown in Figure 1(C), a sintering step of sintering a plurality of conductive particles in the conductive particle-containing layer 2 by heating and pressurizing treatment to form a conductive film 3.

[0020] In the above manufacturing method, the surface modification step may be performed after the lamination step, or the lamination step may be performed after the surface modification step.

[0021] In the lamination process, a conductive particle-containing layer 2 can be formed on the surface 1A of the substrate 1 using a conductive paste containing multiple conductive particles and a solvent.

[0022] As a method for forming the conductive particle-containing layer 2, for example, a method can be used in which a film is formed using a conductive paste and the solvent contained in the film is dried, but this method is not limited to this.

[0023] Various coating and printing techniques can be applied as methods for forming the film. The conductive particle-containing layer 2 may be provided on the entire surface of the substrate 1, or only on a part of the surface of the substrate 1. In the former case, coating methods using devices such as blade coaters, air knife coaters, doctor coaters, roll coaters, bar coaters (rod coaters), and curtain coaters can be used. In the latter case, various printing methods can be used, such as screen printing, gravure printing, letterpress printing, planar printing (offset printing), inkjet printing, and transfer printing. By appropriately designing the "pattern" during printing, it is possible to manufacture substrates with patterned structures, such as conductive films (circuit patterns) that can function as circuits, or mesh patterns that have electromagnetic wave shielding capabilities. When the conductive paste is provided on only a part of the surface of the substrate 1, it is preferable that the "pattern" of the print be appropriately designed according to the intended use of the final conductive film. To prevent the film from forming in locations other than the desired location on the substrate 1, for example, a film with holes cut out may be placed on the substrate 1, the conductive paste may be applied or printed on top of it, and then the film may be removed.

[0024] It is preferable to perform a heat treatment to dry the solvent contained in the conductive paste, thereby forming a dry film of the conductive particle-containing layer 2. The conditions for the heat treatment are not particularly limited as long as the solvent is sufficiently dried, but are adjusted from the viewpoint of sufficient drying of the solvent and suppression of deterioration of the conductive particles due to excessive heating. The temperature of the heat treatment is preferably 50 to 150°C, more preferably 80 to 120°C. The time of the heat treatment is preferably 30 seconds to 60 minutes, more preferably 1 minute to 30 minutes. The heat treatment to dry the solvent can be performed, for example, by applying hot air to the film. Of course, the heat treatment can be performed by other methods as well. It is preferable that the conductive particle-containing layer 2, which is the dry film, contains a plurality of conductive particles that are substantially unsintered. Furthermore, if the conductive paste contains a curable resin or a crosslinking agent, it is preferable that the curable resin and crosslinking agent in the dry film are substantially unreacted.

[0025] In this way, a laminate comprising a base material 1 and a conductive particle-containing layer 2 can be obtained. Note that the lamination process is not limited to the embodiment shown in Figure 1(A), as long as a laminate comprising a base material 1 and a conductive particle-containing layer 2 can be obtained.

[0026] As another lamination process, for example, a provisional layer formed on the surface of an easily peelable substrate using a conductive paste containing conductive particles may be brought into contact with the surface of a substrate different from the easily peelable substrate, and the provisional layer may be transferred to the surface of the substrate to obtain the above-mentioned laminate. It is preferable to dry the provisional layer before transfer to form a dry film. Another lamination process may involve removing a portion of the conductive particle-containing layer 2 formed on the substrate 1 to obtain a desired shape. That is, a portion of the conductive particle-containing layer 2 may be removed to eliminate excess conductive paste printed on the surface, so-called pattern thickening, such as by printing conductive paste. The removal method is not particularly limited and known methods can be used, but examples include ultraviolet laser etching. This can improve the accuracy and stability of the final conductor pattern.

[0027] <Substrate> Substrate 1 is a resin substrate containing a thermoplastic resin layer with a heat resistance temperature of 80°C or higher. The resin substrate may consist of a thermoplastic resin layer having a surface modification region in which at least a part of the surface 1A is softened or melted, or it may consist of a thermoplastic resin layer in which a heat-softening coating layer is laminated on at least a part of the surface 1A.

[0028] The surface modification region can be formed by irradiating the surface 1A of the thermoplastic resin layer with a xenon flash, or by other means. As shown in Figure 1(B), in the surface modification step after the lamination step in which the conductive particle-containing layer 2 is provided on the substrate 1, it is preferable to irradiate with a xenon flash from the back surface 1B, which is opposite to the surface 1A side. Alternatively, when irradiating from the back surface 1B, the xenon flash may be transmitted through the substrate 1. The conductive particles contained in the conductive particle-containing layer 2 can suppress efficiency reduction due to light diffusion, etc., and can also suppress unintended sintering of conductive particles together.

[0029] Examples of energy sources include broadband waves from xenon flash lamps, LEDs, halogen lamps, metal halide lamps, and other UV lamps, as well as YAG lasers and CO2 lasers. ２ While there are various types of narrowband waves (single waves) such as lasers and semiconductor lasers, it is preferable to use xenon flash, which is a pulsed irradiation of broadband waves. By using broadband waves, surface irradiation becomes possible, and variations in the degree of surface modification in the in-plane direction of surface 1A can be suppressed. By using pulsed light emission such as xenon flash lamps, the thermal effects are more easily localized compared to continuous light emission such as halogen lamps and metal halide lamps, making it easier to control surface modification. In addition, by using pulsed light, copper particles near the resin are selectively heated, contributing to the surface modification of the resin. With continuous light, the entire copper particle film is heated, which can lead to oxidation of copper and be unfavorable for subsequent sintering.

[0030] In the surface modification process, the energy of the xenon flash is, for example, 10 to 5000 J, preferably 20 to 2500 J, and more preferably 50 to 2000 J.

[0031] Specifically, the surface modification step may involve the xenon flash described above, which may be applied to the dried film of the conductive particle-containing layer 2. This suppresses the occurrence of damage to the conductive particle-containing layer 2 due to sudden boiling of the solvent caused by xenon flash irradiation before drying. It also suppresses inhibition of modification of the thermoplastic resin layer. The dried film of the conductive particle-containing layer 2 is obtained by performing a heat treatment to dry the conductive particle-containing layer 2 during the lamination process.

[0032] The thermoplastic resin contained in the thermoplastic resin layer includes either an amorphous thermoplastic resin or a crystalline thermoplastic resin, or both. In this specification, surface modification is defined as a change in state of a portion of the surface of the thermoplastic resin layer due to irradiation with a xenon flash. Typically, the amorphous thermoplastic resin softens, and the crystalline thermoplastic resin melts. A portion of the melted crystalline thermoplastic resin may become amorphous and remain in an amorphous state. The amorphous region formed near the surface 1A of the thermoplastic resin layer can be identified using a cross-sectional SEM image. For example, when the surface of a crystalline PET substrate is melted with a xenon flash, the melted surface portion reflects electron beams more easily than the unmelted interior and appears slightly white. That is, the amorphous region can be observed as a region that appears relatively white in a cross-sectional SEM image.

[0033] In a preferred embodiment, the following sintering step may be carried out using a substrate 1 in which an amorphous region is formed on at least a portion of the vicinity of the surface 1A of the thermoplastic resin layer. In the first embodiment, an amorphous region may be formed on the surface 1A of the thermoplastic resin layer in the surface modification step, and preferably, an amorphous layer having a predetermined depth may be formed from the surface 1A. In the second embodiment, a substrate 1 including a thermoplastic resin layer having an amorphous region on at least a portion of the surface 1A can be prepared, and a lamination step can be carried out using this.

[0034] In another preferred embodiment, the surface modification process may create a state in which at least a portion of a plurality of conductive particles are embedded near the surface 1A of the thermoplastic resin layer. At least a portion of the plurality of conductive particles may be a single particle, a sintered product of multiple particles, or both. Although the detailed mechanism is not clear, it is presumed that the softened or molten state of the surface 1A makes it easier for the conductive particles to penetrate into the surface layer, and, if necessary, in combination with subsequent pressurizing treatment, the embedded state is formed.

[0035] The thermoplastic resin layer serves as the base material for the resin substrate. In this case, the thickness of the thermoplastic resin layer may be 10% to 100% of the thickness of the resin substrate, and preferably 20% to 100%.

[0036] The lower limit of the heat resistance temperature of the thermoplastic resin layer is 80°C or higher, preferably 90°C or higher, and more preferably 100°C or higher. On the other hand, the upper limit of the heat resistance temperature of the thermoplastic resin layer is, for example, 250°C or lower, preferably 220°C or lower, and more preferably 200°C or lower. By using a thermoplastic resin layer having a heat resistance temperature of the lower limit or higher, it is possible to suppress thermal deformation of the entire resin substrate due to the heating and pressurizing treatment in the sintering process. By using a thermoplastic resin layer having a heat resistance temperature of the upper limit or lower, surface modification can be promoted. The general heat resistance temperature is calculated by placing the product in a machine and raising the temperature by 10°C starting from 50°C, measuring the temperature at which an abnormality (distortion, deformation, discoloration, change in functionality, etc.) occurs in the product, and subtracting 10°C from the temperature at which such an abnormality occurs. In this specification, it is preferable to use the heat resistance temperature with distortion and deformation as indicators of abnormality.

[0037] Examples of thermoplastic resin materials include polyesters such as PET (polyethylene terephthalate) and PEN (polyethylene naphthalate), polycarbonates, polyimides, and polyolefins such as polyethylene and polypropylene. These may be used individually or in combination of two or more. Among the above, thermoplastic resin materials with high permeability to xenon flash are preferred. This suppresses thermal deformation of the substrate 1 caused by absorption of xenon flash and subsequent heat generation.

[0038] The base material 1 is typically in the form of a film, sheet, or plate. From the viewpoint of industrial productivity, any of these shapes of the base material is preferred.

[0039] The base material 1 is preferably flexible. By using a flexible base material, a flexible printed circuit board (FPC) can be manufactured. Using a flexible base material is preferable, for example, from the viewpoint of mass production.

[0040] The thickness of the substrate 1 is not particularly limited, and can be appropriately set according to the end use described later (electronic devices, RF tags, electromagnetic wave shielding films, sheet heating elements, etc.) and various circumstances. The thickness of the substrate 1 is typically 10 to 250 µm, preferably 30 to 100 µm. However, from the viewpoint of suppressing the occurrence of curling during and after the production of a substrate provided with a conductive pattern, the thickness of the substrate is preferably 100 to 250 µm, more preferably 100 to 150 µm. Incidentally, the thickness of the substrate herein can be obtained by measuring the thickness of a portion of the substrate where no conductive pattern is present.

[0041] <Conductive Paste> An example of the conductive paste contains a plurality of conductive particles and a solvent.

[0042] The conductive particles preferably contain at least one element selected from the group consisting of silver and copper. Specifically, the conductive particles preferably contain at least one selected from the group consisting of silver-based particles and copper-based particles. Here, the expression "based on silver" means that the proportion of silver element among all constituent elements in the particles is preferably 50 mol% or more, more preferably 75 mol% or more, still more preferably 90 mol% or more, and particularly preferably 95 mol% or more. Similarly, the expression "based on copper" means that the proportion of copper element among all constituent elements in the particles is preferably 50 mol% or more, more preferably 75 mol% or more, still more preferably 90 mol% or more, and particularly preferably 95 mol% or more. The conductive particles may contain elements other than silver and copper as long as desired conductivity can be obtained. Examples of elements other than silver and copper include gold, aluminum, platinum, palladium, iridium, tungsten, nickel, tantalum, lead, and zinc.

[0043] The conductive particles may contain two or more elements. For example, conductive particles in which silver plating is applied to the surface of copper particles (silver-coated copper particles) may be used. Silver-coated copper particles are particles based on copper, and silver is plated on the surfaces of the copper particles in an amount of up to 35% by mass based on the total mass of the particles, for example.

[0044] Preferably, the conductive particles contain dendritic metal particles, and more preferably contain dendritic copper particles. The use of dendritic metal particles can further improve adhesion to the thermoplastic resin layer compared to spherical particles. It is presumed that dendritic metal particles are more likely to be embedded into the thermoplastic resin layer. However, the conductive particles may include metal particles of other shapes such as spherical in addition to dendritic metal particles. The term "dendritic" generally refers to a shape having a trunk extending in one direction and at least one branch branching off from the trunk. Copper particles produced by electrolysis usually form dendrites due to the copper crystal formation mechanism. In the technical field of copper particles, dendritic copper particles produced by electrolysis are generally referred to as "dendritic copper particles". The meaning of the term "dendritic copper particles" in the present specification is the same as the ordinary meaning of the term "dendritic copper particles" in the technical field of copper particles.

[0045] The proportion of dendritic copper particles in all conductive particles is preferably 50% by mass or more, more preferably 75% by mass or more, and still more preferably 90% by mass or more. Of course, all (100% by mass) of the copper particles may be dendritic copper particles. Since dendritic copper particles are relatively inexpensive, a high proportion of dendritic copper particles in a plurality of copper particles (copper powder) leads to a reduction in the manufacturing cost of the conductive film.

[0046] In the volume-based cumulative particle size distribution curve obtained when measuring the particle size of conductive particles by laser diffraction scattering method, the particle diameter D at which the cumulative frequency is 50% ５０ is preferably 0.5 to 100 µm, more preferably 0.6 to 50 µm, still more preferably 0.7 to 30 µm, and particularly preferably 0.7 to 20 µm. D ５０ having an appropriate size can reduce the number of grain boundaries between conductive particles per unit volume. This is considered to lead to a lower specific resistance of the obtained conductive pattern. D ５０ not being excessively large reduces "gaps" between conductive particles, which is considered to lead to a lower specific resistance of the obtained conductive pattern.

[0047] Conductive particles can be purchased from companies such as DOWA Electronics and Fukuda Metal Foil & Powder Industry. Two or more different conductive particles may be used in combination for adjusting and optimizing the particle size distribution or for other purposes.

[0048] The ratio of conductive particles to the total nonvolatile components of the conductive paste is preferably 80% by mass or more, more preferably 85% by mass or more, even more preferably 90% by mass or more, and particularly preferably 95% by mass or more.

[0049] The inclusion of a solvent in the conductive paste improves its applicability or printability on the substrate. The solvent typically includes an organic solvent. The solvent may also include water, as long as it can adequately disperse the conductive particles. The type of solvent is not particularly limited. The solvent should not substantially alter any of the components in the conductive paste. The amount of solvent used can be adjusted as appropriate depending on the application or printing method of the conductive paste. The amount of solvent used is, for example, 3 to 30% by mass, preferably 5 to 25% by mass, and more preferably 10 to 20% by mass, of the total conductive paste.

[0050] The conductive paste may, if necessary, contain resin components such as resins and binders, or dispersants for resin components, but may also substantially not contain resin components and dispersants. When resin components are included, the amount of resin components in the conductive paste is preferably 1 to 15 parts by mass, more preferably 1 to 10 parts by mass, and even more preferably 1 to 5 parts by mass, per 100 parts by mass of conductive particles. Examples of resin components include polyvinylpyrrolidone, polyester, epoxy resin, (meth)acrylic resin, polyvinyl acetal, cellulosic resin (e.g., ethylcellulose), and phenolic resin. Here, "substantially not containing resin or binder" means either not containing any resin or binder at all, or containing resin or binder in amounts so small that the expected effects (specifically described below) from the use of resin or binder cannot be obtained (for example, 1% by mass or less, specifically 0.5% by mass or less, of the total nonvolatile components of the conductive paste).

[0051] The conductive paste may or may not contain various additive components found in conventional ink compositions and conductive pastes. Examples of additive components include antioxidants, silane coupling agents, and curing agents. These may be used individually or in combination of two or more.

[0052] In the manufacturing method of this embodiment, a laminate is used in which a conductive particle-containing layer 2 is laminated on the surface 1A of a softened or melted thermoplastic resin layer, and a sintering process is carried out. Immediately before the sintering process, the conductive particle-containing layer 2 of the laminate includes unsintered portions in which multiple conductive particles have not been sintered. In the sintering process, the multiple conductive particles contained in the conductive particle-containing layer 2 are sintered by heating and pressurizing treatment to form a conductive film 3.

[0053] The heating and pressing process can be carried out, for example, using a flat press device equipped with a heating mechanism. In other words, the laminate of the base material 1 and the conductive particle-containing layer 2 provided by conductive paste can be sandwiched between two (a pair of) flat plates and pressed while heating, thereby sintering the conductive particles in the conductive particle-containing layer 2.

[0054] In addition to a flat press device, heating and pressurization can also be performed using a roll press device or other devices. For example, a method may be employed in which a laminate comprising a base material 1 and a conductive particle-containing layer 2 is sandwiched between two opposing rolls and transported between these two rolls. Alternatively, a method may be employed in which the laminate is placed on a flat plate or on the flat surface of a table having a flat surface, a roll is brought into contact with it from above, and pressure is applied to the laminate while the roll is rotated. However, when heating and pressurizing using a roll press device, the heating and pressurizing time per unit area tends to be shorter compared to heating and pressurizing using a flat press device, so care should be taken to appropriately control the heating, pressurizing, transport speed (roll rotation speed), etc.

[0055] The heating temperature can be set appropriately depending on the heat resistance of the base material 1 and the type of conductive particles used, but for example, it is 50°C to 200°C, preferably 60°C to 180°C, and more preferably 80°C to 150°C. The pressurization is, for example, 5 MPa to 100 MPa, preferably 5 MPa to 80 MPa, and more preferably 10 MPa to 60 MPa. The processing time is, for example, 0.003 seconds to 10 seconds, preferably 0.006 seconds to 3 seconds, and more preferably 0.01 seconds to 1 second. When using a flat press device, the heating temperature is preferably 50°C to 200°C, more preferably 80°C to 160°C, the pressurization pressure is preferably 5 MPa to 80 MPa, more preferably 5 MPa to 75 MPa, and the heating and pressurization time is preferably 0.1 seconds to 60 seconds, and more preferably 0.5 seconds to 40 seconds.

[0056] Furthermore, it is preferable to cover part or all of the surface of the laminate on which the conductive particle-containing layer 2 is provided with a film-like material and then pressurize the conductive particle-containing layer 2 at least. The material of the film-like material can be a polyester film such as a PET film. From another viewpoint, in order to suppress peeling or damage to the conductive particle-containing layer 2, a release film can preferably be used as the film-like material. A release film is usually a resin film with a release agent coated on at least one side, and examples of release agents include silicone-based, fluorine-based, and non-silicone-based types. Release films are available, for example, from Fujimori Kogyo Co., Ltd. From yet another viewpoint, the film-like material may be a non-resin material such as paper or aluminum foil.

[0057] The manufacturing method of this embodiment may include other steps between the lamination step and the sintering step, and / or after the sintering step. For example, between the lamination step and the sintering step, a penetration step may be performed in which a component X capable of removing the oxide film on the surface of the conductive particles is permeated into the conductive particle-containing layer 2. In terms of ease of process implementation and ease of permeating component X into the conductive particle-containing layer 2, it is preferable that in the penetration step, a liquid in which component X is dissolved or dispersed is permeated into the conductive particle-containing layer 2. In this specification, "removal" of the oxide film includes not only cases where the oxide itself present on the surface of the conductive particles is removed, but also cases where the oxide returns to a non-oxide state through chemical changes such as reduction.

[0058] Component X may include one or more selected from the group consisting of carboxylic acids, phosphorus oxoacids, hydrazine compounds, inorganic acids, phenols, and other reducing substances. Examples of carboxylic acids include citric acid, formic acid, acetic acid, malonic acid, malic acid, tartaric acid, ascorbic acid, succinic acid, fumaric acid, and propionic acid. However, it is not limited to these, and organic acids other than carboxylic acids may be used. Examples of phosphorus oxoacids include phosphinic acid, phosphonic acid, phosphorous acid, phosphoric acid, diphosphate, triphosphate, and metatriphosphate. Examples of hydrazine compounds include hydrazine, hydrazine derivatives such as hydrazine salts including monohydrazine hydrochloride, hydrazine dihydrazine hydrochloride, monohydrazine hydrobromide, and hydrazine sulfate, phenylhydrazine, and others -NH-NH ２Examples of compounds with a specific structure include those mentioned above. Inorganic acids include, for example, hydrochloric acid, nitric acid, sulfuric acid, and hydrobromic acid. Phenols include, for example, pyrogallol, orthoaminophenol, and hydroquinone. Other reducing substances include, for example, pyrazolidone compounds. Phenidone is an example of a pyrazolidone compound. These may be used individually or in combination of two or more. Among these, component X can be a compound with a small pKa in water. Specifically, a compound with a pKa of -5.0 to 5.0 in water is preferred as component X, and a compound with a pKa of -4.0 to 4.5 is more preferred as component X. Incidentally, if component X is a polybasic acid, it is preferable that the smallest pKa among multiple pKa values ​​is within the above range. The pKa value here can be the value at room temperature (e.g., 25°C). The liquid containing component X is preferably water in which component X is dissolved or dispersed. Using water is preferable from the standpoint of reducing environmental impact and ensuring process safety (non-flammable). Of course, organic solvents in which component X is dissolved or dispersed can also be used. The concentration of component X in the liquid is, for example, 0.05 to 50 mol / L, preferably 0.1 to 40 mol / L, more preferably 0.1 to 30 mol / L, even more preferably 0.1 to 10 mol / L, and particularly preferably 0.15 to 5.0 mol / L. Of course, a liquid containing component X at a lower concentration than those shown herein may be used, or a liquid containing component X at a higher concentration than those shown herein (e.g., saturation concentration) may be used.

[0059] In the penetration process, it is preferable to treat the conductive particle-containing layer 2 with a carboxylic acid. In this case, component X preferably contains a carboxylic acid, preferably a carboxylic acid with 7 or fewer carbon atoms in the molecule, and more preferably contains formic acid.

[0060] When a sintering process is performed after the penetration process, component X that did not penetrate the conductive particle-containing layer 2 during the penetration process may or may not be removed before the sintering process. To prevent the formation of an oxide film again on the surface of the conductive particles from which the oxide film was removed during the penetration process, it is preferable that the time between the penetration process and the sintering process be short. Specifically, when a sintering process is performed after the penetration process, the time from the end of the penetration process to the start of the sintering process is preferably 1 hour or less, more preferably 30 minutes or less, even more preferably 10 minutes or less, and particularly preferably 1 minute or less. Alternatively, to prevent the formation of an oxide film again on the surface of the conductive particles from which the oxide film was removed during the penetration process, the laminate after the penetration process and before the sintering process may be temporarily stored in an inert gas atmosphere such as a rare gas or nitrogen gas, temporarily stored in a reducing atmosphere, or temporarily stored under vacuum or reduced pressure. After the sintering process, a removal process may be performed to remove any component X remaining on or inside the surface of the obtained conductive film.

[0061] The removal step for removing component X is not particularly limited, as long as it includes a process to reduce the amount of component X remaining in the conductive particle-containing layer 2. This can further reduce the resistivity of the final conductive film 3. For example, if component X has the property of volatilizing when heated, it is conceivable to perform a process to volatilize the component X remaining in the conductive particle-containing layer 2 by heating the conductive particle-containing layer 2 to an appropriate temperature. Another example is to perform a process to dissolve the component X remaining in the conductive particle-containing layer 2 by bringing the conductive particle-containing layer 2 into contact with a liquid such as water. More specifically, the following methods (i) to (v) can be used as processes to reduce the amount of component X remaining in the conductive particle-containing layer 2: (i) Applying an airflow to the conductive particle-containing layer 2. (ii) Injecting an inert gas such as nitrogen gas towards the conductive particle-containing layer 2. (iii) Pressing a liquid-absorbing material such as a sponge against the conductive particle-containing layer 2 to absorb a solution or dispersion containing component X. In a continuous process, it is preferable to use a roll-shaped sponge as the material that can absorb liquid. After absorbing the solution or dispersion, the conductive particle-containing layer 2 may be brought into contact with a liquid such as water (washing), and then the material that can absorb liquid may be pressed against the conductive particle-containing layer 2 again. (iv) The solution or dispersion containing component X is "squeezed" by applying pressure to the conductive particle-containing layer 2 using a roll. After that, the conductive particle-containing layer 2 may be brought into contact with a liquid such as water (washing), and then the liquid may be squeezed out again using a roll. Incidentally, by appropriately controlling the pressure and not heating when applying pressure, the solution or dispersion containing component X can be squeezed out without sintering the conductive particles in the conductive particle-containing layer 2. (v) A combination of two or more of the above (i) to (iv). For example, a combination of (i) and (ii), a combination of (iii) and (iv), etc.

[0062] Furthermore, a pre-pressure step may be included between the lamination step and the penetration step, in which the conductive particle-containing layer 2 is pressurized at least. Performing the pre-pressure step is optional, but performing this step makes it easier to maintain the shape of the conductive particle-containing layer 2 in the subsequent steps (especially the penetration step). When the pressure applied to the conductive particle-containing layer 2 in the pre-pressure step is P1, and the pressure applied to the conductive particle-containing layer 2 in the sintering step is P2, it is preferable that P1 < P2. More specifically, it is preferable that P1 is 0.9 times or less of P2, more preferably 0.75 times or less, and even more preferably 0.6 times or less. In other words, it is preferable that the pressure in the pre-pressure step is sufficiently smaller than the pressure required to compress or sinter the conductive particles in the sintering step.

[0063] By the above manufacturing method, a resin substrate 10 with a conductive film can be obtained.

[0064] Figure 2 is a schematic cross-sectional view showing an example of a conductive film-coated resin substrate 10. The conductive film-coated resin substrate 10 comprises a resin substrate (substrate 1) containing a thermoplastic resin layer with a heat resistance temperature of 80°C or higher, and a conductive film 3 formed on at least a part of the surface 1A of the substrate 1.

[0065] Multiple conductive particles in the conductive film 3 are sintered and connected to one another. Sintering means that, through heating and pressurizing, the particles fuse at the contact points on the metal surfaces between them, and multiple conductive particles are joined (connected) to form an integrated structure.

[0066] The conductive film-coated resin substrate 10 has a transition region 6 in at least one of its cross-sections in the thickness direction, where at least a portion of each coexists between the thermoplastic resin layer of the substrate 1 and the conductive film 3. The transition region 6 is formed between the thermoplastic resin layer of the substrate 1 and the conductive film 3 when viewed in the thickness direction of the conductive film-coated resin substrate 10. In the transition region 6, a portion of the thermoplastic resin in the thermoplastic resin layer and a portion of the sintered body in the conductive film 3 coexist, but the proportion of thermoplastic resin gradually increases on average from the surface 1A toward the depth direction. In this specification, "at least one cross-section" means that the configuration is confirmed in at least one of a plurality of cross-sections set on the object, and it is not necessary that the configuration be confirmed in all cross-sections. The cross-section may be a cross-section perpendicular to the extending direction of the object, a cross-section along the extending direction, or a cross-section including the thickness direction. In this specification, the transition region is the region in which the thermoplastic resin layer of the substrate 1 and the conductive film 3 are observed to be coexisting in a cross-sectional SEM image or the like.

[0067] Furthermore, in the embedded structure of the conductive film-coated resin substrate 10, it is preferable that at least a portion of the conductive film 3 has a convex portion of the conductive film 3 that is embedded in a recess 5 formed by the surface 1A of the substrate 1 being recessed in the thickness direction. The recess 5 of the substrate 1 is composed of a portion of the surface 1A of the substrate 1 that is recessed in the thickness-down direction from the conductive film 3 toward the substrate 1. The convex portion of the conductive film 3 has a convex structure that is convex in the thickness-down direction from the conductive film 3 toward the substrate 1 so as to follow the surface of the recess 5. One or more convex structures may be present on the convex portion. In another embodiment, a fine uneven structure may be formed on at least a portion of the surface of the convex portion of the conductive film 3 embedded in the recess 5. This further enhances the adhesion between the substrate 1 and the conductive film 3.

[0068] In one embodiment, the thermoplastic resin layer in the substrate 1 may have a surface modification region 8 in at least a portion near the surface 1A. The surface modification region 8 may form a layer having a predetermined thickness in the depth direction from the surface 1A.

[0069] In another configuration, at least a portion of the transition region 6 may be located within the surface modification region 8.

[0070] In another embodiment, the surface-modified region 8 is composed of a softened or melted and solidified portion of the surface 1A of the thermoplastic resin layer, i.e., a softened layer or a molten layer. In one preferred embodiment, the surface-modified region 8 may be configured to include part or all of the amorphous portion of the thermoplastic resin layer.

[0071] In another embodiment, in the cross-section in the thickness direction of the conductive film-coated resin substrate 10, an interface 9 may exist in at least a portion between the thermoplastic resin layer of the substrate 1 and the conductive film 3, and at the interface 9, the thermoplastic resin layer other than the surface modification region 8 may be in contact with the conductive film 3, and the surface modification region 8 may be in contact with the conductive film 3.

[0072] In a cross-section of the conductive film-coated resin substrate 10 in the thickness direction, the conductive film 3 embedded in the recess 5 of the substrate 1 may occupy, for example, 50% or more of the total area, preferably 70% or more, and the entire conductive film may be embedded in the recess 5. However, a portion of the conductive film 3 may have a portion that is not embedded in the recess 5 and protrudes upward in the thickness direction.

[0073] Figure 3 is a top view of an example of a conductive film-coated resin substrate 10, viewed from the direction normal to the surface 1A of the substrate 1. As shown in Figure 3, the conductive film 3 may have a conductive pattern including linear portions 3A. The linear portions 3A may be composed of straight lines or curves. The conductive pattern of the conductive film 3 is not limited to narrow linear portions 3A, but may also have pads or capacitor hats with a relatively large area. For example, the top view of the pads or capacitor hats may be circular, elliptical, square, or other polygonal shapes. Note that the cross-sectional view in Figure 2 may be a cross-section of the linear portion 3A of the conductive film 3 shown in Figure 3. When the plane of the surface 1A of the substrate 1 is defined as the X-Y plane, the X direction in Figure 3 may be defined as the short direction of the linear portion 3A, and the Y direction may be defined as the long direction of the linear portion 3A.

[0074] In Figure 3, the direction in which the line portion 3A of the conductive pattern extends is defined as the longitudinal direction, and the width direction of the line portion 3A is defined as the short direction. In this embodiment, in at least one of the cross-sections B that pass through the short direction and the thickness direction of the line portion 3A of the conductive pattern, the width of the line portion 3A in the short direction is, for example, 30 μm or more and 5000 μm or less, preferably 70 μm or more and 3000 μm or less, and more preferably 100 μm or more and 1000 μm or less. Even fine lines with a width of 500 μm or less, which are usually difficult to punch out, can be formed by the printing described above, and adhesion to the base material 1 can be provided to such fine line portions 3A.

[0075] <Electronic Devices> Electronic devices can be manufactured using a substrate (resin substrate with conductive film) equipped with the conductive film of this embodiment. By appropriately designing the pattern of the conductive film, a substrate equipped with a conductive film that can function as a circuit can be manufactured. Then, by combining this substrate with other electronic elements, an electronic device can be manufactured.

[0076] Here are some examples of electronic devices. It should be noted that electronic devices are, of course, not limited to these. • Sensors: For example, the conductive material with the conductive pattern of this embodiment can be applied to conductive members / circuits in sensors such as pressure sensors and vital signs sensors. • Solar cells: For example, the conductive material with the conductive pattern of this embodiment can be applied to the current collection wiring of solar cells. • Membrane switches: A membrane switch is a thin sheet-like switch made by printing circuits and contacts onto a film and then layering them. The conductive material with the conductive pattern of this embodiment can be applied to form the circuits and contacts of such switches. • Touch sensors / touch panels: For example, the conductive material with the conductive pattern of this embodiment can be applied to form lead wiring in touch sensors and touch panels. It is also conceivable to apply the manufacturing method of the conductive material with the conductive pattern of this embodiment to form transparent electrodes in touch sensors and touch panels. • Flexible substrates: Conventionally, circuits are formed by first coating the entire surface of a flexible film with a metal film, and then removing unnecessary parts of the metal film using chemicals. Instead of this conventional method, it is conceivable to form circuits using the manufacturing method of the conductive material with the conductive pattern of this embodiment.

[0077] In particular, in electronic devices where circuits were conventionally formed using conductive paste, using the manufacturing method of this embodiment for circuit formation can reduce the resistivity of the circuit, which can lead to improved performance of the electronic device.

[0078] A particularly preferred electronic device is the RF tag. Specifically, the substrate equipped with the conductive pattern of this embodiment is preferably used to manufacture conductive circuits such as the antenna portion of the RF tag. For the specific structure of the RF tag, refer to, for example, Japanese Patent Publication No. 2003-332714 and Japanese Patent Publication No. 2020-46834.

[0079] <Method for Manufacturing Electromagnetic Wave Shield Sheet> As an application different from electronic devices, it is conceivable to manufacture an electromagnetic wave shield sheet by the method for manufacturing a base material provided with the conductive film (resin base material with conductive film) of the present embodiment. Specifically, in the lamination step, an electromagnetic wave shield sheet can be manufactured by setting a pattern for printing the conductive paste to a pattern specific to an electromagnetic wave shield sheet (such as a mesh pattern).

[0080] <Method for Manufacturing Planar Heating Element> As still another application, it is conceivable to manufacture a planar heating element by the method for manufacturing a base material provided with the conductive pattern (resin base material with conductive film) of the present embodiment. A planar heating element refers to an element in which electric wiring is provided on a base material, and generates heat when current is passed through the wiring. Specific examples of planar heating elements include planar heating elements for anti-fogging and cold protection, such as those used for rear glasses of passenger cars.

[0081] The embodiments of the present invention have been described above. These are merely examples of the present invention, and various configurations other than those described above can be adopted. Furthermore, the present invention is not limited to the above-described embodiments, and modifications, improvements, and the like within the scope that can achieve the object of the present invention are included in the present invention.

[0082] Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited in any way by the description of these examples.

[0083] <Preparation of Conductive Paste> (Conductive Paste 1) Electrolytic copper powder (manufactured by Fukuda Metal Foil & Powder Co., Ltd., D ５０ = 5 µm, dendritic) 82 parts by mass, 2 parts by mass of epoxy resin, and 16 parts by mass of organic solvent were weighed and kneaded with a spatula to obtain a kneaded product. Thereafter, this kneaded product was stirred using a rotation-revolution stirrer. As described above, paste-like Conductive Paste 1 was obtained at 23°C.

[0084] (Conductive Paste 2) Instead of electrolytic copper powder, atomized copper powder (manufactured by Fukuda Metal Foil & Powder Co., Ltd., D ５０ = 5 µm, spherical) was used, and otherwise in the same manner as Conductive Paste 1, paste-like Conductive Paste 2 was obtained at 23°C.

[0085] <Manufacturing of conductive film-coated substrates> [Example 1] (Printing process) The conductive paste 1 described above was screen printed onto the surface of the substrate to form a patterned coating (conductive particle-containing layer) and obtain a laminate. The printing process was carried out according to the following specific conditions. ・Substrate: Biaxially oriented PET film (thickness 50 μm, width 150 mm, heat resistance temperature 160°C) was used. ・Printing machine: Screen printing machine (Micro-Tech, Desk Top 38SA model) was used. ・Screen plate: A screen plate (325 mesh, mesh diameter 16 μm, emulsion thickness 40 μm) with a pattern having fine lines (wire diameter 16 μm) was used. ・Printing conditions: Printing pressure 0.18 MPa, squeegee speed 30 mm / sec, clearance (distance between screen plate and substrate) 2.0 mm, attack angle 80°.

[0086] (Drying process) The laminate obtained in the printing process was placed in a hot air circulating atmospheric oven and heated at 100°C for 5 minutes to evaporate the solvent and obtain a dried film of the conductive particle-containing layer. This formed a patterned dried film with a thickness of approximately 30 μm on the surface of the substrate.

[0087] (Surface modification process) After the drying process, the substrate, which did not have a patterned dried film formed on its back side, was irradiated with xenon flash using a xenon flash device (XENON Corporation, X-1100) under the conditions of applied voltage of 3000V, applied energy of 1300J, and irradiation time of 680μs.

[0088] (Sintering Process) After the surface modification process, a film-like material (biaxially oriented PET film, 12 μm thick) was placed in contact with the patterned conductive particle-containing layer. The laminate and the film-like material were then roll-pressed together using a load-adjustable roll press machine (SA-602, manufactured by Tester Sangyo Co., Ltd.) equipped with two opposing rolls, under the following conditions to sinter the copper powder (multiple conductive particles) in the conductive particle-containing layer and form a sintered body (conductive film). After roll pressing, the film-like material was peeled off to produce a conductive film-coated substrate with the conductive film provided on the surface of the substrate. Roll press conditions: Roll temperature (lower roll 110°C, upper roll 100°C), pressure: 10 MPa, conveying speed: 4 m / min, no gap

[0089] (Example 2) A conductive film-coated substrate was manufactured in the same manner as in Example 1, except that the following penetration step was performed after the surface modification step and the above sintering step was performed after the penetration step. In the penetration step, the entire laminate was immersed in a formic acid aqueous solution (an aqueous solution containing formic acid as component X) for 10 seconds, and then the laminate was washed with water and drained.

[0090] (Example 3) A substrate with a conductive film was manufactured in the same manner as in Example 1, except that conductive paste 2 was used instead of conductive paste 1 in the printing process described above.

[0091] (Comparative Example 1) A substrate with a conductive film was manufactured in the same manner as in Example 1, except that the above surface modification step was omitted and the above sintering step was performed after the above drying step.

[0092] (Comparative Example 2) A conductive film-coated substrate was manufactured in the same manner as in Example 1, except that an A-PET film (amorphous polyethylene terephthalate, 200 μm thick, heat resistance temperature 67°C) was used instead of a biaxially oriented PET film in the printing process described above.

[0093] <Observation of Cross-Sections> Samples of the conductive film-coated substrate, molded on both sides with epoxy resin, were cut using ion milling to expose the cross-section of the fine-line portion of the conductive pattern of the conductive film, perpendicular to the direction in which the conductive pattern extends. These cross-sections were photographed with a scanning electron microscope (SEM) to obtain cross-sectional images. In the cross-sectional images of Examples 1 to 3, although boundaries between copper particles were partially visible, it was confirmed that the particles were in close contact with each other and that electrical connections were formed. Furthermore, the existence of a structure in which a portion of the conductive film was embedded in the PET layer of the substrate was confirmed. On the other hand, in Comparative Example 1, the existence of a structure in which a portion of the conductive film was embedded in the PET layer of the substrate could not be confirmed. In Comparative Example 1, hard copper particles were pressed onto the PET surface, leaving indentations, but the surface as a whole was considered to be almost flat.

[0094] Figure 4 shows a cross-sectional image of Example 1 after the surface modification process and before the sintering process. Near the surface of the substrate, a region exhibiting a relatively white color compared to the interior of the substrate was observed. It is presumed that this region contains an amorphous region formed by the melting of the thermoplastic resin layer (PET) of the substrate. Figure 5 shows a cross-sectional image of the conductive film-coated substrate of Example 1 after the sintering process. From the cross-sectional image of the conductive film-coated substrate of Example 1, it was confirmed that a transition region exists between the PET layer of the substrate and the conductive film, where they coexist. In the transition region, the proportion of thermoplastic resin gradually increases on average compared to the proportion of sintered body, compared to the vicinity of the surface of the conductive film. In Examples 2 and 3, the transition region was also confirmed in the same way as in Example 1. On the other hand, the transition region could not be confirmed in Comparative Example 1. Figure 6 shows a cross-sectional image of the conductive film-coated substrate of Comparative Example 1 with the conductive film peeled off, exposing the surface of the substrate.

[0095] <Measurement of Resistivity> The resistance value was measured using a four-terminal resistance meter for the fine-line portion (measurement width 250 μm in the central region) of the conductive pattern of the conductive film on the obtained conductive film-coated substrate, and the film thickness was measured using a film thickness gauge. The resistivity was calculated from the measured resistance value and film thickness. A smaller resistivity value is preferable. The results are shown in Table 1. In Table 1, "unmeasurable" indicates that there was no conductivity and the resistance value could not be measured.

[0096] <Deformation of Substrate> The obtained conductive film-coated substrates were visually inspected for any deformation of the substrate. The presence or absence of substrate deformation was determined based on whether or not "significant distortion or curvature occurred in part or the entire substrate." The results are shown in Table 1. In Examples 1 to 3, it was confirmed that the surface of the PET layer of the substrate after the sintering process was almost flat, similar to before the sintering process. In Comparative Example 2, it was confirmed that the surface of the PET layer of the substrate after the sintering process was significantly deformed in a wavy pattern.

[0097] <Adhesion> The obtained conductive film-coated substrates were bent by hand and returned to their original flat shape, a process repeated five times. After that, the presence or absence of delamination of the conductive pattern from the PET layer of the substrate was checked visually and under magnification. In Examples 1 to 3, delamination of the conductive pattern could not be confirmed by either visual inspection or under magnification. In Comparative Example 1, delamination of the conductive pattern from the substrate was visually confirmed.

[0098]

[0099] Based on the above results, the conductive film-coated substrates of Examples 1 to 3 showed lower resistance of the conductive film compared to Comparative Examples 1 and 2. Furthermore, the conductive film-coated substrates of Examples 1 to 3 showed better adhesion compared to Comparative Example 1, and showed no thermal deformation of the substrate compared to Comparative Example 2.

[0100] This application claims priority based on Japanese Patent Application No. 2025-056696, filed on 28 March 2025, and incorporates all of its disclosures herein.

[0101] 1. Substrate 1A Front surface 1B Back surface 2. Conductive particle-containing layer 3. Conductive film 3A Line portion 4. Xenon flash 5. Recess 6. Transition region 8. Surface modification region 9. Interface 10. Resin substrate with conductive film

Claims

1. A resin substrate with a conductive film, comprising a resin substrate containing a thermoplastic resin layer having a heat resistance temperature of 80°C or higher, and a conductive film containing a sintered body of a plurality of conductive particles, wherein in a cross-section in the thickness direction of the resin substrate with the conductive film, there is a transition region between the resin substrate and the conductive film in which at least a portion of each coexist.

2. A resin substrate with a conductive film according to claim 1, wherein the transition region has a structure in which at least a portion of the conductive film is embedded in a recess formed in the thermoplastic resin layer.

3. A resin substrate with a conductive film according to claim 1 or 2, wherein the resin substrate with a conductive film includes a surface modification region in at least a portion of the vicinity of the surface of the thermoplastic resin layer.

4. A conductive film-coated resin substrate according to claim 3, wherein at least a portion of the transition region is present in the surface-modified region.

5. A resin substrate with a conductive film according to claim 3, wherein the surface modified region includes an amorphous region of the thermoplastic resin layer.

6. A conductive film-coated resin substrate according to claim 1 or 2, wherein the resin substrate comprises one or more selected from the group consisting of polyester, polycarbonate, polyimide, and polyolefin.

7. A resin substrate with a conductive film according to claim 1 or 2, wherein the particles contained in the conductive particles include dendritic particles.

8. A resin substrate with a conductive film according to claim 1 or 2, wherein the particle diameter D at the point where the cumulative volume from the smallest particle side reaches 50% in the volume-based cumulative distribution of particle diameters obtained when the particle diameter of the conductive particles is measured by laser diffraction scattering is defined as the particle diameter D ５０ However, the conductive film-coated resin substrate is between 0.5 μm and 100 μm in thickness.

9. A resin substrate with a conductive film according to claim 1 or 2, wherein the conductive particles contain copper.

10. An electronic device comprising a resin substrate with a conductive film according to claim 1 or 2.

11. An electronic device according to claim 10, wherein the electronic device is an RF tag.

12. An electromagnetic wave shielding sheet comprising a resin substrate with a conductive film according to claim 1 or 2.

13. A planar heating element comprising a conductive film-coated resin substrate according to claim 1 or 2.

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