Resin base material with conductive film, electronic device, electromagnetic wave shield sheet, and planar heat-emitting body

Abstract

A resin base material with a conductive film according to the present invention comprises: a resin base material 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. In a cross section in the thickness direction, an interface between the thermoplastic resin layer and the conductive film is present between the resin base material and the conductive film, and at least one or more isolated particles, including the conductive particles, is in a state of being present inside the thermoplastic resin layer in the vicinity of the interface.

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 a conductive film and a resin substrate can be improved by forming an isolated particle-containing region within the thermoplastic resin layer of a resin substrate, where isolated conductive particles exist. This led to the completion of 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 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 a conductive film, an interface between the thermoplastic resin layer and the conductive film exists between the resin substrate and the conductive film, and at least one or more isolated particles containing the conductive particles exist inside the thermoplastic resin layer near the interface. 2. The resin substrate with a conductive film according to 1, wherein in the cross-section, there are isolated particles whose distance from the interface is 0.1 μm or more and 15 μm or less. 3. The resin substrate with a conductive film according to 1 or 2, wherein in the cross-section, the cross-sectional area is 0.3 μm ２ 200 μm or more ２ A conductive film-coated resin substrate having the isolated particles described below. 4. A conductive film-coated resin substrate according to any one of 1 to 3, wherein the surface modification region is included in at least a part of the vicinity of the surface of the thermoplastic resin layer. 5. A conductive film-coated resin substrate according to 4, wherein the surface modification region includes the amorphous region of the thermoplastic resin layer. 6. A conductive film-coated resin substrate according to any one of 1 to 5, wherein the resin substrate includes one or more selected from the group consisting of polyester, polycarbonate, polyimide, and polyolefin. 7. A conductive film-coated resin substrate according to any one of 1 to 6, wherein the particles included in the conductive particles include dendritic particles. 8. 1 to 7. A conductive film-coated resin substrate as described in any one of the above, 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 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. In at least one cross-section in the thickness direction of the conductive film-coated resin substrate, an interface between the thermoplastic resin layer and the conductive film exists between the resin substrate and the conductive film, and at least one isolated particle containing conductive particles exists inside the thermoplastic resin layer near that interface.

[0014] According to the inventors' findings, by heating a plurality of conductive particles under pressure onto a softened or melted surface-modified portion of a thermoplastic resin layer, an isolated particle-containing region is formed within the thermoplastic resin layer, where isolated particles containing conductive particles exist. This improves the adhesion between the conductive film and the resin substrate. In the isolated particle-containing region, the self-weight of the isolated particles, the pressing action due to the subsequent pressurizing and heating treatment, and the resin flow in the surface-modified portion make it easier for the conductive film to adhere to the surface-modified portion of the thermoplastic resin layer, thus increasing the physical adhesion between the two. It is also presumed that when a conductive paste containing multiple conductive particles is dried, the particles present on the lower side of the dried film sink into the surface-modified portion of the thermoplastic resin layer due to their self-weight and the pressurizing and heating treatment, thereby forming the isolated particle-containing region. Furthermore, the above pressurizing and 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, peeling between the conductive film and the resin substrate is suppressed, and the physical adhesion between the two is presumed to increase.

[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. It is presumed that the heating and pressing treatment presses multiple conductive particles against the surface-modified portion of the thermoplastic resin layer, but 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 isolated particle-containing regions and embedded structures described above. 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 the 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 isolated particle-containing regions or embedded structures described above. Furthermore, the adhesion force due to the 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 one or both of an amorphous thermoplastic resin and a crystalline thermoplastic resin. In the present specification, surface modification is defined as a change in the state of a part of the surface of the thermoplastic resin layer caused by irradiation with xenon flash. Generally, an amorphous thermoplastic resin softens, and a crystalline thermoplastic resin melts. A part of the molten crystalline thermoplastic resin may become amorphous and take on an amorphous state. It should be noted that 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 base material is melted by xenon flash, the melted surface portion is more likely to reflect electron beams and exhibits a slight white color compared to the unmelted interior. That is, the amorphous region can be observed as a relatively white region in a cross-sectional SEM image.

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

[0034] In another preferred embodiment, in the surface modification step, a state in which at least a part of the plurality of conductive particles is embedded near the surface 1A of the thermoplastic resin layer may be formed. At least a part of the plurality of conductive particles may be one single particle, or either or both of a sintered product obtained by sintering a plurality of particles. Although the detailed mechanism is not clear, it is presumed that when the surface 1A is in a softened or molten state, the conductive particles easily penetrate into the surface layer, and the embedded state is formed in combination with the subsequent pressure treatment as necessary.

[0035] The thermoplastic resin layer serves as the base substrate of the resin base material. In this case, the thickness of the thermoplastic resin layer may be 10% to 100% of the thickness of the resin base material, 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 200°C or lower, and more preferably 180°C or lower. By using a thermoplastic resin layer having a heat resistance temperature equal to or higher than the above lower limit, thermal deformation of the entire resin base material caused by the heating and pressing treatment in the sintering step can be suppressed. By using a thermoplastic resin layer having a heat resistance temperature equal to or lower than the above upper limit, surface modification can be promoted. Generally, the heat resistance temperature is calculated as follows: when the product is placed in a machine and the temperature is increased by 10°C starting from 50°C, the temperature at which abnormality (distortion, deformation, discoloration, change in functionality, etc.) occurs in the product is measured, and the heat resistance temperature is obtained by subtracting 10°C from the temperature at which such abnormality occurs in the product. In the present specification, it is preferable to use a heat resistance temperature indexed by distortion and deformation as the abnormality.

[0037] Examples of the material of the thermoplastic resin include polyesters such as PET (polyethylene terephthalate) and PEN (polyethylene naphthalate), polycarbonate, polyimide, polyolefins such as polyethylene and polypropylene, etc. These may be used alone or in combination of two or more. Among the above materials, those having high transparency to xenon flash are preferred as the thermoplastic resin material. This can suppress thermal deformation of the substrate 1 caused by heat generation due to absorption of the xenon flash.

[0038] The substrate 1 is usually in the form of a film, a sheet or a plate. From the viewpoint of industrial productivity, any of these shapes is preferable for the substrate.

[0039] The substrate 1 is preferably flexible. A flexible printed circuit (FPC) can be manufactured by adopting a flexible substrate. Using a flexible substrate is preferable from the viewpoint of mass productivity, for example.

[0040] The thickness of the substrate 1 is not particularly limited and can be set appropriately depending on the final application (electronic device, RF tag, electromagnetic shielding film, planar heating element, etc.) and various circumstances, as described later. The thickness of the substrate 1 is typically 10 to 250 μm, preferably 30 to 100 μm. However, from the viewpoint of suppressing curling during and after the manufacturing of the substrate with the 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 here can be determined by measuring the thickness of the portion of the substrate where the conductive pattern does not exist.

[0041] <Conductive Paste> An example of a conductive paste includes multiple 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 particles mainly composed of silver and particles mainly composed of copper. Here, the expression "mainly composed of silver" means that the ratio of silver elements in the total constituent elements of the particles is preferably 50 mol% or more, more preferably 75 mol% or more, even more preferably 90 mol% or more, and particularly preferably 95 mol% or more. Similarly, the expression "mainly composed of copper" means that the ratio of copper elements in the total constituent elements of the particles is preferably 50 mol% or more, more preferably 75 mol% or more, even more preferably 90 mol% or more, and particularly preferably 95 mol% or more. The conductive particles may also contain elements other than silver and copper, as long as the desired conductivity is obtained. Examples of elements other than silver and copper include gold, aluminum, platinum, palladium, iridium, tungsten, nickel, tantalum, lead, zinc, and the like.

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

[0044] The conductive particles preferably contain dendritic metal particles, and more preferably contain dendritic copper particles. By using dendritic metal particles, adhesion to the thermoplastic resin layer can be further enhanced compared to spherical particles. It is presumed that dendritic metal particles are more likely to be embedded in the thermoplastic resin layer. However, the conductive particles may also contain metal particles of other shapes, such as spherical particles, in addition to dendritic metal particles. "Dendritic" usually refers to a shape having a main trunk that extends in one direction and at least one branch that branches off from the main trunk. Copper particles produced by electrolysis usually become dendrites due to the copper crystal formation mechanism. In the field of copper particles, dendritic copper particles produced by electrolysis are usually referred to as "dendritic copper particles." The meaning of the term "dendritic copper particles" in this specification is the same as the usual meaning of the term "dendritic copper particles" in the field of copper particles.

[0045] The proportion of dendritic copper particles in the total conductive particles is preferably 50% by mass or more, more preferably 75% by mass or more, and even more preferably 90% by mass or more. Of course, all of the copper particles (100% by mass) may be dendritic copper particles. Since dendritic copper particles are relatively inexpensive, a high proportion of dendritic copper particles in a mixture 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 conductive particles are measured by laser diffraction scattering, the particle size D at which the cumulative frequency reaches 50% is... ５０ The particle size is preferably 0.5 to 100 μm, more preferably 0.6 to 50 μm, even more preferably 0.7 to 30 μm, and particularly preferably 0.7 to 20 μm. ５０ A moderately large size allows for a reduction in the number of grain boundaries between conductive particles per unit volume. This is thought to lead to a lower resistivity in the resulting conductive pattern. D ５０ By keeping the size of the conductive particles small, the "gaps" between them are reduced, which is thought to lead to a lower resistivity in the resulting 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] Furthermore, the manufacturing method of the present embodiment may include other steps between the laminating step and the sintering step and / or after the sintering step. For example, between the laminating step and the sintering step, an infiltration step of infiltrating component X, which is capable of removing oxide films on the surfaces of conductive particles, into the conductive particle-containing layer 2 may be performed. From the viewpoints of ease of process implementation and the ease of infiltrating component X into the conductive particle-containing layer 2, in the infiltration step, the conductive particle-containing layer 2 is preferably infiltrated with a liquid in which component X is dissolved or dispersed. In the present specification, the "removal" of an oxide film includes not only the case where the oxide itself present on the surface of the conductive particle is removed, but also the case where the oxide returns to a non-oxide through a chemical change such as reduction of the oxide.

[0058] Component X may include one or two or more selected from the group consisting of carboxylic acids, phosphorus oxoacids, hydrazine-based 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. The carboxylic acid is not limited thereto, and organic acids other than carboxylic acids may also be used. Examples of phosphorus oxoacids include phosphinic acid, phosphonic acid, phosphorous acid, phosphoric acid, diphosphoric acid, triphosphoric acid, and metatriphosphoric acid. Examples of hydrazine-based compounds include hydrazine, and derivatives of hydrazine include hydrazine salts such as hydrazine monohydrochloride, hydrazine dihydrochloride, hydrazine monohydrobromide, and hydrazine sulfate; phenylhydrazine; and other -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 pressurization, 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. The conductive film 3 is made of a base material composed of a sintered body of multiple conductive particles. The conductive film 3 does not contain isolated particles 3B that are separated from the base material and exist without electrical connection. In this specification, isolated particles 3B refer to particles that are not in contact with the conductive film in the observed cross-section and are observed surrounded by a thermoplastic resin layer.

[0066] The conductive film-coated resin substrate 10 has an interface 9 in at least one of its cross-sections in the thickness direction, in which at least a portion exists between the thermoplastic resin layer of the substrate 1 and the conductive film 3. The conductive film-coated resin substrate 10 has an isolated particle-containing region in which isolated particles 3B containing conductive particles exist inside the thermoplastic resin layer near the interface 9. The isolated particles 3B are in a state in which their entire periphery is covered by the thermoplastic resin layer. The isolated particles 3B may include a single unsintered conductive particle (not having a structure in which two or more particles are linked), or they may include a sintered piece of conductive particles in which two or more are linked and there is no interface at the linking portion. In this specification, "in 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, "near the interface" means, for example, a range of 20 μm or less from the interface.

[0067] In a cross-section of the conductive film-coated resin substrate 10 in the thickness direction, the distance from the interface 9 to the isolated particle 3B is, for example, 0.1 μm or more and 15 μm or less, preferably 0.2 μm or more and 12 μm or less, and more preferably 0.5 μm or more and 10 μm or less. The conductive film-coated resin substrate 10 may have one or more isolated particles 3B having the above distance. There may also be isolated particles 3B that do not meet the above distance.

[0068] In a cross-section of the conductive film-coated resin substrate 10 in the thickness direction, the cross-sectional area of ​​the isolated particle 3B is, for example, 0.3 μm. ２ 200 μm or more ２ Preferably 0.6 μm ２ 150 μm or more ２ More preferably 1 μm ２ 100 μm or more ２ The following applies: The conductive film-coated resin substrate 10 may have one or more isolated particles 3B having the above-mentioned cross-sectional area. It is also possible that isolated particles 3B that do not satisfy the above-mentioned cross-sectional area may be present.

[0069] Furthermore, it is preferable that the conductive film-coated resin substrate 10 has an embedded structure in which at least a portion of the conductive film 3 is embedded in a recess 5 formed by the surface 1A of the substrate 1 being recessed in the thickness direction.

[0070] 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.

[0071] 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 melted 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. Furthermore, at least a portion of the isolated particles 3B may be present in the surface-modified region 8, preferably in an amorphous surface-modified region 8.

[0072] In another embodiment, at interface 9, the thermoplastic resin layer other than the surface-modified region 8 may be in contact with the conductive film 3, or the surface-modified region 8 may be in contact with the conductive film 3.

[0073] 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.

[0074] 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.

[0075] 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.

[0076] <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.

[0077] 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.

[0078] 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.

[0079] 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.

[0080] <Method for Manufacturing Electromagnetic Shielding Sheets> As an application other than electronic devices, it is conceivable to manufacture electromagnetic shielding sheets using the manufacturing method of the conductive film-equipped substrate (resin substrate with conductive film) of this embodiment. Specifically, by making the pattern used when printing the conductive paste in the lamination process a pattern specific to electromagnetic shielding sheets (such as a mesh pattern), electromagnetic shielding sheets can be manufactured.

[0081] <Method for Manufacturing a Planar Heating Element> As another application, it is conceivable to manufacture a planar heating element using the method for manufacturing a substrate (resin substrate with conductive film) equipped with the conductive pattern of this embodiment. A planar heating element is a material on which electrical wiring is provided, and heat is generated when an electric current is passed through the wiring. Specific examples of planar heating elements include those used for anti-fogging and cold protection, such as the rear windows of passenger cars.

[0082] Although embodiments of the present invention have been described above, these are merely examples, and various other configurations can be adopted. Furthermore, the present invention is not limited to the embodiments described above, and modifications, improvements, etc., within the scope that can achieve the objectives of the present invention are included in the present invention.

[0083] The present invention will be described in detail below with reference to examples, but the present invention is not limited in any way to the descriptions of these examples.

[0084] <Preparation of conductive paste> (Conductive paste 1) Electrolytic copper powder (manufactured by Fukuda Metal Foil & Powder Industry Co., Ltd., D ５０ 82 parts by mass of (5 μm, dendritic), 2 parts by mass of epoxy resin, and 16 parts by mass of organic solvent were weighed and mixed with a spatula to obtain a mixture. Then, this mixture was stirred using a rotary-orbiting stirrer. In this way, a conductive paste 1 in paste form at 23°C was obtained.

[0085] (Conductive paste 2) Instead of electrolytic copper powder, atomized copper powder (manufactured by Fukuda Metal Foil & Powder Industry Co., Ltd., D ５０ Conductive paste 2 was obtained in the same manner as conductive paste 1, except that a spherical shape (5 μm) was used, at 23°C.

[0086] <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°.

[0087] (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.

[0088] (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.

[0089] (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

[0090] (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.

[0091] (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.

[0092] (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.

[0093] (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.

[0094] <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.

[0095] 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 that appeared relatively white 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 substrate with the conductive film after the sintering process for Example 1. In Example 1, it was confirmed that there were multiple isolated particles located within the PET layer (thermoplastic resin layer) of the substrate, separated from the conductive film. Similarly, in Examples 2 and 3, it was confirmed that there were multiple isolated particles. On the other hand, in Comparative Example 1, the presence of isolated particles was not confirmed. In Example 1, for three particles arbitrarily selected from the isolated particles confirmed in Figure 5, the distance from the interface between the PET layer and the conductive film to the isolated particle was 1.3 μm for the first isolated particle, 2.5 μm for the second isolated particle, and 8.7 μm for the third isolated particle, with an average distance of 4.2 μm for the three points. Furthermore, in the cross-section shown in Figure 5 of Example 1, the cross-sectional area of ​​the isolated particle is 7.5 μm for the first isolated particle. ２ The second isolated particle is 2.3 μm ２ The third isolated particle is 9.8 μm ２ The average cross-sectional area of ​​the three points is 6.5 μm². ２ Figure 6 shows a cross-sectional image of the conductive film-coated substrate of Comparative Example 1, after the conductive film has been peeled off and the surface of the substrate is exposed.

[0096] <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.

[0097] <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.

[0098] <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.

[0099]

[0100] 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.

[0101] This application claims priority based on Japanese Patent Application No. 2025-056697, filed on 28 March 2025, and incorporates all of its disclosures herein.

[0102] 1. Substrate 1A Front surface 1B Back surface 2. Conductive particle-containing layer 3. Conductive film 3B Isolated particles 3A Linear portion 4. Xenon flash 5. Recess 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, an interface between the thermoplastic resin layer and the conductive film exists between the resin substrate and the conductive film, and at least one isolated particle containing the conductive particles is present inside the thermoplastic resin layer near the interface.

2. A resin substrate with a conductive film according to claim 1, wherein, in the cross-section, there are isolated particles whose distance from the interface is 0.1 μm or more and 15 μm or less.

3. A resin substrate with a conductive film according to claim 1 or 2, wherein the cross-section has a cross-sectional area of ​​0.3 μm². ２ 200 μm or more ２ A resin substrate with a conductive film, wherein the following isolated particles are present.

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

5. A resin substrate with a conductive film according to claim 4, wherein the surface modified region includes amorphous material 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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