Paper base material equipped with electroconductive film, electronic device, electromagnetic wave shielding sheet, planar heating element, intermediate of paper base material equipped with electroconductive film, and electroconductive paste

Abstract

A paper base material equipped with an electroconductive film according to the present invention comprises a paper base material that includes a fiber layer, and an electroconductive film that is provided on at least part of the surface of the paper base material and has an electroconductive pattern. The electroconductive film includes a sintered body of a plurality of electroconductive particles, and includes a cured product of a thermosetting resin in at least part of the fiber layer and in at least part of the electroconductive film.

Description

Conductive film-coated paper substrates, electronic devices, electromagnetic shielding sheets, planar heating elements, intermediates for conductive film-coated paper substrates, and conductive pastes.

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

[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 3.

[0003] Japanese Patent Publication No. 2003-258420, Japanese Patent Publication No. 2018-160512, Japanese Patent Publication No. 2024-001439

[0004] In the above-mentioned Patent Documents 1 to 3, a conductive ink receiving layer, an adhesive resin layer, or a thermoplastic resin is provided between the paper substrate and the conductive pattern to adhere them. The conductive pattern is formed by heating or light firing. However, sufficient research has not been conducted on the reliability of the connection under high temperature and high humidity conditions. As a result of our research, we have found that there is room for improvement in terms of high temperature and high humidity reliability in paper substrates equipped with a conductive film.

[0005] The inventors have discovered that high-temperature and high-humidity reliability in paper substrates with conductive films can be improved by forming cured thermosetting resin products in both the paper substrate and the conductive film, and have completed the present invention.

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

[0007] 1. A paper substrate with a conductive film, comprising a paper substrate including a fiber layer, and a conductive film having a conductive pattern provided on at least a portion of the surface of the paper substrate, wherein the conductive film includes a sintered body of a plurality of conductive particles, and a cured product of a thermosetting resin is included in at least a portion of the conductive film and at least a portion of the fiber layer. 2. A paper substrate with a conductive film according to 1, wherein in the fiber layer where the conductive film does not overlap, a resin-impregnated region α1 containing the cured product of the thermosetting resin exists on at least a portion of the side surface of the conductive pattern. 3. A paper substrate with a conductive film according to 2, wherein, in a top view, a line segment l is present in the width direction perpendicular to the extending direction of the conductive pattern. １ When the line segment l is drawn, １ Let L1 be the width of the conductive pattern passing through the line segment l １ A conductive film-coated paper substrate, wherein the conductive film is parallel to the surface, and when L2 is the distance from the side surface of the conductive pattern to the outer edge of the resin-impregnated region α1, L2 / L1 × 100 is 30% or more and 70% or less. 4. A conductive film-coated paper substrate according to 2. or 3., wherein, in a top view, the resin-impregnated region α1 exists so as to surround at least a part of the outer edge of the conductive pattern. 5. A conductive film-coated paper substrate according to any one of 1. to 4., wherein a resin-impregnated region α2 containing a cured product of the thermosetting resin exists in at least a part of the fiber layer over which the conductive film overlaps, and in a cross-section of the conductive film-coated paper substrate, a line segment l exists in the thickness direction of the paper substrate. ２ When the line segment l is drawn, ２6. A conductive film-coated paper substrate, wherein the maximum distance L3 of the resin-impregnated region α2 that passes through is 0.1L or more, when the thickness of the fiber layer is L. 6. A conductive film-coated paper substrate according to any one of 1 to 5, wherein a resin-impregnated region α1 containing the cured product of the thermosetting resin exists in the fiber layer where the conductive film does not overlap, and a resin-impregnated region α2 containing the cured product of the thermosetting resin exists in the fiber layer where the conductive film overlaps, and the resin filling rate of the resin-impregnated region α2 is lower than the resin filling rate of the resin-impregnated region α1. 7. A conductive film-coated paper substrate according to any one of 1 to 6, wherein the thermosetting resin (a1) in the cured product contained in the conductive film and the thermosetting resin (a2) in the cured product contained in the fiber layer are of the same type. 8. 1 to 7. A conductive film-coated paper substrate according to any one of the above, wherein the fiber layer has a resin-impregnated region α containing a cured product of the thermosetting resin and a resin-non-impregnated region β not containing a cured product of the thermosetting resin. 9. A conductive film-coated paper substrate according to any one of 1 to 8, wherein the thermosetting resin includes one or more selected from the group consisting of phenolic resin, epoxy resin, (meth)acrylic resin, and urethane resin. 10. A conductive film-coated paper substrate according to any one of 1 to 9, wherein at least a portion of the space between the fiber layer and the conductive film has an uneven interface formed by arrangements that fill each other. 11. A conductive film-coated paper substrate according to any one of 1 to 10, wherein the particles contained in the conductive particles include dendritic particles. 12. A conductive film-coated paper substrate according to any one of the above, wherein, in the volume-based cumulative distribution of particle diameters obtained when the particle diameter of the conductive particles is measured by laser diffraction scattering, the particle diameter D50 at the point where the cumulative volume from the smallest particle side reaches 50% is 0.5 μm or more and 100 μm or less. 13. A conductive film-coated paper substrate according to any one of the above, wherein the conductive particles contain copper. 14. An electronic device comprising a conductive film-coated paper substrate according to any one of the above.15. An electronic device as described in 14, wherein the electronic device is an RF tag. 16. An electromagnetic wave shielding sheet comprising a conductive film-coated paper substrate as described in any one of 1 to 13. 17. A planar heating element comprising a conductive film-coated paper substrate as described in any one of 1 to 13. 18. An intermediate of a conductive film-coated paper substrate comprising a paper substrate including a fiber layer, and a patterned dry film provided on at least a portion of the surface of the paper substrate, wherein the dry film is obtained by drying a conductive paste containing a plurality of conductive particles and a thermosetting resin, and the thermosetting resin in a B-stage state is contained in at least a portion of the fiber layer together with at least a portion of the dry film. 19. A conductive paste used to form a cured product of a thermosetting resin in a paper substrate and a conductive film, comprising a plurality of conductive particles, a thermosetting resin, and a solvent.

[0008] According to the present invention, a conductive film-coated paper substrate with excellent high-temperature and high-humidity reliability is provided, as well as an electronic device using the same, an electromagnetic wave shielding sheet, a planar heating element, an intermediate for the conductive film-coated paper substrate used therein, and a conductive paste are provided.

[0009] This is a schematic cross-sectional view showing an example of the manufacturing process of a conductive film-coated substrate according to this embodiment. This is a schematic cross-sectional view showing an example of a conductive film-coated paper substrate according to this embodiment. This is a schematic top view showing an example of a conductive film-coated paper substrate according to this embodiment. This is an SEM image showing a cross-section of the conductive film-coated paper substrate of Example 1. This is an optical microscope image showing a top view of the conductive film-coated paper substrate of Example 1. This is an optical microscope image showing a cross-section of the conductive film-coated paper substrate of 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 paper substrate of this embodiment will be described.

[0013] The conductive film-coated paper substrate of this embodiment comprises a paper substrate including a fiber layer, and a conductive film having a conductive pattern provided on at least a portion of the surface of the paper substrate, wherein the conductive film includes a sintered body of a plurality of conductive particles, and a cured product of a thermosetting resin is included in at least a portion of the conductive film and at least a portion of the fiber layer.

[0014] According to the inventors' findings, the dimensional stability of the paper substrate can be improved by curing the thermosetting resin, and the adhesion between the paper substrate and the conductive film can be improved, thereby enhancing the high-temperature and high-humidity reliability of the conductive film-coated paper substrate. In other words, the thermosetting resin contained in the conductive paste can function as a modifier for the fiber layer of the paper substrate, as well as as a binder for the conductive film.

[0015] Although the detailed mechanism is not clear, it is presumed to be as follows: In high-temperature and high-humidity tests, when environmental conditions of temperature and humidity fluctuate, the fiber layer in the paper substrate undergoes dimensional changes due to swelling, etc., which causes cracks in the conductive film on the paper substrate, increasing its resistance. In contrast, by using a cured product of thermosetting resin, the dimensional changes of the paper substrate are suppressed and the adhesion between the paper substrate and the conductive film is improved, thereby suppressing the cracks that occur in the conductive film. As a result, it is presumed that the high-temperature and high-humidity reliability of the conductive film-coated paper substrate can be improved.

[0016] It was also found that the above-described structure of a paper substrate with a conductive film can be achieved by forming a film made of a conductive paste containing a thermosetting resin on the paper substrate and then subjecting the film to a heat and pressure treatment.

[0017] Furthermore, the above-described pressurized and heated treatment may create an embedded structure in which at least a portion of the conductive film is embedded in a recess formed in the fiber layer of the paper substrate. Since the embedded structure functions as an anchor, it is presumed that delamination between the conductive film and the paper substrate is suppressed, and the physical adhesion between the two is increased.

[0018] The conductive film-coated paper 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. RFID media incorporate 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. An 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 paper substrate. The inlay may optionally include a meander pattern and / or a capacitor hat. In addition to the inlay, a 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).

[0019] The following describes the manufacturing method of the conductive film-coated paper substrate according to this embodiment, while detailing each component of the conductive film-coated paper substrate.

[0020] Figures 1(A) to 1(C) are cross-sectional views showing an example of a method for manufacturing a paper substrate with a conductive film. Figure 2 is a schematic cross-sectional view showing an example of a paper substrate 10 with a conductive film.

[0021] An example of a method for manufacturing a paper substrate with a conductive film according to this embodiment includes, as shown in Figures 1(A) and 1(B), a lamination step of forming a layer containing a plurality of conductive particles (conductive particle-containing layer 2) on the surface of a paper substrate (substrate 1) using a conductive paste containing a thermosetting resin, and a sintering step of forming a conductive film 3 by sintering the plurality of conductive particles in the conductive particle-containing layer 2 through a heat and pressure treatment, as shown in Figure 1(C). 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 the X-Y plane.

[0022] 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, a thermosetting resin, and a solvent.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] 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 embodiments shown in Figures 1(A) to 1(B), as long as a laminate comprising a base material 1 and a conductive particle-containing layer 2 can be obtained.

[0027] 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.

[0028] <Substrate> Substrate 1 may be a paper substrate consisting of a fiber layer, or it may be a paper substrate having a release layer or a coating layer on one or both sides of the surface of the fiber layer. A laminate layer containing a polymer material such as a thermoplastic resin may be included between the release layer and the fiber layer. Cellulose fibers (natural fibers) or semi-synthetic fibers can be used for the fiber layer included in the paper substrate. Known materials can be used for the release layer, but for example, silicone or non-silicone materials can be used. Known materials can be used for the coating layer, but materials such as thermoplastic resins such as polyethylene and polypropylene, inorganic particles such as clay can be used. It is preferable that the paper substrate has heat resistance compared to ordinary paper substrates.

[0029] On the surface 1A of the base material in FIG. 1(B), the portion where the conductive paste is formed may be composed of a fiber layer, or may be composed of a mixture of a fiber layer and a release layer and / or a coat layer. For example, when a paper base material having a release layer and / or a coat layer on one side is used, the surface 1A of the base material 1 may have a portion where a part of the lower fiber layer is exposed from the release layer or the coat layer, and may be formed of a fine coat in which the fiber layer is exposed on 30% or more, preferably 50% or more of the total area of the surface 1A. Although the reason is not clear, when a fiber layer is present in the portion where the conductive paste is formed, fine wire printability can be improved.

[0030] As the specific base material 1, known materials can be used. For example, any paper selected from the group consisting of kraft paper, glassine paper, acid paper, parchment paper, high-quality paper, coated paper (including lightly coated paper) obtained by coating these papers with a liquid containing a pigment and / or a resin, and impregnated paper obtained by impregnating paper with a liquid containing a pigment and / or a resin may be used.

[0031] The base material 1 is generally in the form of a film, a sheet or a plate. From the viewpoint of industrial productivity, any of these shapes of the base material is preferable.

[0032] The base material 1 preferably has flexibility. A flexible printed circuit (FPC) can be manufactured by employing a flexible base material. Use of a flexible base material is preferable, for example, from the viewpoint of mass productivity.

[0033] The thickness of the base material 1 is not particularly limited, and can be appropriately set according to the end use (electronic devices, RF tags, electromagnetic wave shielding films, planar heating elements, etc.) described later and various circumstances. The thickness of the base material 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 base material provided with a conductive pattern, the thickness of the base material is preferably 100 to 250 µm, more preferably 100 to 150 µm. Incidentally, the thickness of the base material herein can be obtained by measuring the thickness of a portion of the base material where no conductive pattern exists.

[0034] <Conductive Paste> An example of a conductive paste includes a plurality of conductive particles, a thermosetting resin, and a solvent. The conductive paste of this embodiment can be used to form a cured product of the thermosetting resin in a paper substrate (substrate 1) and in a conductive film 3.

[0035] 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.

[0036] 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.

[0037] The conductive particles preferably contain dendritic metal particles, and more preferably contain dendritic copper particles. By using dendritic metal particles, adhesion to the fiber layer can be further enhanced compared to spherical particles. It is presumed that dendritic metal particles are more likely to penetrate the fiber 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.

[0038] 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.

[0039] 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 is 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.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] The thermosetting resin is not particularly limited as long as it hardens by a heating and pressurizing treatment to sinter conductive particles, but examples include phenolic resins, epoxy resins, (meth)acrylic resins, urethane resins, etc. These may be used individually or in combination of two or more. Among these, phenolic resins are preferred from the viewpoint of heat resistance, and resol-type phenolic resins are more preferred from the viewpoint of rapid curing. The conductive paste may also contain a curing agent or curing catalyst for the crosslinking reaction of the thermosetting resin along with the thermosetting resin, but it is preferable to include a self-crosslinking type thermosetting resin. For example, by using a resol-type phenolic resin that can self-crosslink without the addition of a curing agent, a one-component type conductive paste can be made, improving workability. The content of phenolic resin in 100% by mass of thermosetting resin is, for example, 1 to 100% by mass, preferably 80 to 100% by mass, and more preferably 90 to 100% by mass.

[0044] The thermosetting resin is preferably one that hardens when heated to a temperature of approximately 150°C to 220°C. The reaction initiation temperature of the thermosetting resin is, for example, 170 to 220°C, preferably 190 to 210°C.

[0045] The gel time of the thermosetting resin is, for example, 40 to 200 seconds, preferably 40 to 150 seconds, and more preferably 40 to 90 seconds. This allows for adjustment of the curing speed of the thermosetting resin.

[0046] The weight loss of the thermosetting resin when heated to 200°C at a starting temperature of 40°C and a heating rate of 10°C / min, as determined by simultaneous differential thermal and thermogravimetric measurements, is, for example, 1 to 20%, preferably 1 to 10%, and more preferably 1 to 5%. This suppresses the decomposition of the cured thermosetting resin during the sintering process.

[0047] The thermosetting resin content is, for example, 1 to 40% by mass, preferably 5 to 30% by mass, and more preferably 10 to 20% by mass, based on 100% by mass of the conductive paste.

[0048] The conductive paste may, if necessary, contain resin components other than thermosetting resins, such as binders and dispersants for resin components, but may also substantially contain no resin components or 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, polyvinyl acetal, and cellulosic resins (e.g., ethylcellulose). Here, "substantially free" of other resins and binders means that no other resins or binders are included at all, or that other resins or binders are included, but in such small amounts that the effects expected from the use of other resins or binders (explained specifically below) 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).

[0049] 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.

[0050] In the manufacturing method of this embodiment, a sintering step is performed after the lamination step described above. That is, the lamination step yields an intermediate of the conductive film-coated paper substrate. By performing the sintering step on the obtained intermediate, a conductive film-coated paper substrate is obtained.

[0051] An example of an intermediate for a conductive film-coated paper substrate comprises a paper substrate (substrate 1) containing a fiber layer, and a patterned dry film provided on at least a portion of the surface of the paper substrate, wherein the dry film is a conductive paste containing a plurality of conductive particles and a thermosetting resin that has been dried (conductive particle-containing layer 2), and at least a portion of the dry film, as well as at least a portion of the fiber layer, contains a thermosetting resin in a B-stage state (semi-cured state). That is, the B-stage state is a state in which the curing of the thermosetting resin has partially progressed. The thermosetting resin in the B-stage state contains uncured components.

[0052] In the lamination process described above, a portion of the thermosetting resin in the conductive particle-containing layer 2 may penetrate to the fiber layer of the paper substrate (substrate 1). The thermosetting resin may spread to the fiber layer below the conductive particle-containing layer 2, or it may spread to the thermosetting resin in the left-right direction of the conductive particle-containing layer 2. In this case, the cured product of the thermosetting resin contained in the conductive film 3 formed in the next sintering process and the cured product of the thermosetting resin contained in the fiber layer of the substrate 1 will both contain cured products of the same type of thermosetting resin. This allows the thermosetting resin in the conductive particle-containing layer 2 to penetrate to the fiber layer of the substrate 1, eliminating the need to separately impregnate the fiber layer of the substrate 1 with thermosetting resin, thus increasing manufacturing efficiency.

[0053] In the sintering process, multiple conductive particles contained in the conductive particle-containing layer 2 are sintered by heating and pressurizing to form a conductive film 3.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] 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. The method of supplying the liquid in which component X is dissolved or dispersed in the penetration step to at least the surface of the conductive particle-containing layer 2 is not particularly limited. Known methods such as dropping, spraying, and immersion can be used as specific methods. 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.

[0059] As the component X, one or more selected from the group consisting of carboxylic acids, phosphorus oxo acids, hydrazine-based compounds, inorganic acids, phenols, and other reducing substances may be included. Examples of the carboxylic acid include citric acid, formic acid, acetic acid, malonic acid, malic acid, tartaric acid, ascorbic acid, succinic acid, fumaric acid, propionic acid, and the like. The present invention is not limited thereto, and organic acids other than carboxylic acids may be used. Examples of the phosphorus oxo acid include phosphinic acid, phosphonic acid, phosphorous acid, phosphoric acid, diphosphoric acid, triphosphoric acid, metatriphosphoric acid, and the like. Examples of the hydrazine-based compound 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.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] 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.

[0064] By the above manufacturing method, a paper substrate 10 with a conductive film can be obtained.

[0065] Figure 2 is a schematic cross-sectional view showing an example of a conductive film-coated paper substrate 10. Figure 3 is a top view of an example of a conductive film-coated paper substrate 10, viewed from the direction normal to the surface 1A of the substrate 1. 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.

[0066] The conductive film-coated paper substrate 10 shown in Figure 2 comprises a paper substrate (substrate 1) including a fiber layer, and a conductive film 3 having a conductive pattern provided on at least a portion of the surface 1A of the paper substrate. 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.

[0067] At least a portion of the conductive film 3 having a conductive pattern, and at least a portion of the fiber layer of the substrate 1, each contain a cured thermosetting resin. Here, the region of the fiber layer in which the cured thermosetting resin exists is defined as the resin-impregnated region α. ​​The resin-impregnated region α is formed when the thermosetting resin in the conductive paste impregnates the fiber layer of the substrate 1 and hardens. In this case, in the conductive film-coated paper substrate 10, the cured thermosetting resin in the resin-impregnated region α may be in the C stage state (fully cured state).

[0068] In one embodiment, the cured product of the thermosetting resin contained in the conductive film 3 may be present in at least a part of the conductive film 3 (such as the lower part), or it may be present throughout the entire conductive film 3 from the lower to the upper part.

[0069] In one embodiment, as shown in Figure 3, in a fiber layer where the conductive films 3 do not overlap in a top view, a resin-impregnated region α1 containing a cured thermosetting resin may be present in at least a portion of the side surface 3B of the conductive pattern (conductive film 3).

[0070] In another embodiment, as shown in Figure 3, a resin-impregnated region α1 may exist in a top view so as to surround at least a portion of the outer edge of the conductive pattern (conductive film 3). The presence of a resin-impregnated region α1 surrounding the conductive pattern suppresses the direct transmission of shrinkage forces, etc., generated in the substrate 1 during high-temperature and high-humidity testing to the conductive pattern, that is, it effectively suppresses dimensional changes of the substrate 1 from the side direction of the conductive pattern. Furthermore, in a top view, the resin-impregnated region α1 may be located in a position surrounding the side surface 3B or other end faces of the line portion 3A of the conductive pattern, or it may be located in a position surrounding the corner of the conductive pattern. Also, in a top view, the shape of the resin-impregnated region α1 may be configured to be substantially the same as the shape of the outer edge of the conductive pattern. A top view means a view taken from above the surface 1A of the substrate 1, looking down at the surface 1A, using the normal to the surface 1A of the substrate 1.

[0071] In another embodiment, in a top view of the conductive film-coated paper substrate 10, a line segment l is observed in the width direction perpendicular to the extending direction of the conductive pattern (for example, the line portion 3A of the conductive film 3). １When you draw the line segment l, １ Let L1 be the width of the conductive pattern passing through the line segment l １ Let L2 be the distance from the side surface 3B of the conductive pattern, which is parallel to the line segment, to the outer edge of the resin-impregnated region α1. In this case, L2 / L1 × 100 is, for example, 30% to 70%, preferably 40% to 60%. For the distance L2, the line segment l １ It may also be defined as the shortest distance from one side surface 3B of the conductive pattern to the outer edge of the resin-impregnated region α1 on that side, in a direction parallel to the direction. This shortest distance is defined as line segment l. １ The width of the resin-impregnated region α1 parallel to the same line segment l may also be measured. １ The width of the resin-impregnated region α1 through which the object passes may be measured. The distance L2 may be the average value obtained by arithmetic mean-measurement of multiple measurements.

[0072] In another embodiment, as shown in Figure 2, a resin-impregnated region α2 containing a cured thermosetting resin may be present in at least a portion of the fiber layer in which the conductive film 3 overlaps when viewed from above. In the cross-section of the conductive film-coated paper substrate 10, a line segment l is present in the thickness direction of the paper substrate (substrate 1). ２ When you draw the line segment l, ２ Let L3 be the maximum distance of the resin-impregnated region α2 passing through the same line segment l ２ Let L be the thickness of the fiber layer passing through it. That is, in the cross-section, there are multiple line segments l in the thickness direction. ２ When set, each line segment l ２ Let L3 be the maximum length of α2 shown above. In this case, the maximum distance L3 of the resin-impregnated region α2 is, for example, 0.1 L or more, preferably 0.5 L to 1.0 L, and more preferably 0.7 L to 1.0 L.

[0073] In another embodiment, a resin-impregnated region α1 containing a cured thermosetting resin may exist in the fiber layer where the conductive film 3 does not overlap when viewed from above, and a resin-impregnated region α2 containing the cured thermosetting resin may exist within the fiber layer where the conductive film 3 overlaps. In this case, the resin filling rate of the resin-impregnated region α2 may be lower than the resin filling rate of the resin-impregnated region α1 in the cross-section of the conductive film-coated paper substrate 10. That is, a resin-impregnated region α1 with a relatively high resin filling rate is formed on the side surface 3B of the conductive film 3, and a resin-impregnated region α2 with a relatively low resin filling rate is formed on the lower side of the conductive film 3. In this way, a relatively soft resin-impregnated region α2 is formed below the conductive film 3, which can improve the flexibility of the conductive film 3 in the width direction. Preferably, when viewed in the width direction of the conductive film 3, the resin-impregnated regions α1, α2, and α1 may exist in that order, that is, a soft resin-impregnated region α2 may exist between hard resin-impregnated regions α1. The presence of alternating hard and soft areas, resembling stripes, results in better flexibility in the width direction compared to a material that is entirely rigid.

[0074] Although the detailed mechanism is not clear, the heating and pressurizing treatment in the sintering process described above causes the conductive particle-containing layer 2 to compress the fiber layer of the substrate 1 in overlapping regions, making it difficult for the thermosetting resin to penetrate the fiber layer in these regions. Therefore, it is presumed that more thermosetting resin is impregnated on the side 3B of the conductive film 3 than on the lower side of the conductive film 3, resulting in a higher resin filling rate in the resin-impregnated region α1 than in the resin-impregnated region α2. The degree of resin filling rate can be evaluated, for example, by optical microscope images of the cross-section. Regions with high impregnation of thermosetting resin (e.g., phenolic resin) tend to have a higher yellow color concentration.

[0075] In another embodiment, the thermosetting resin (a1) in the cured product of the conductive film 3 and the thermosetting resin (a2) in the cured product of the fiber layer of the substrate 1 may be of the same type. This makes it possible to suppress differences in the degree of dimensional change caused by the resin between the conductive film 3 containing the cured product of the thermosetting resin and the fiber layer of the substrate 1. For thermosetting resin (a1) and thermosetting resin (a2) to be of the same type, it is sufficient if they belong to the same resin classification (for example, the same resin classification as phenolic resin), and preferably their properties such as hygroscopicity and curability are also similar.

[0076] The fiber layer of the substrate 1 may have, in its cross-section, a resin-impregnated region α containing a cured thermosetting resin and a resin-non-impregnated region β that does not contain a cured thermosetting resin. The resin-non-impregnated region β may be located on the side surface 3B of the conductive film 3, at least on the side surface 3B of the resin-impregnated region α1.

[0077] In one embodiment, at least a portion of the space between the fiber layer of the substrate 1 and the conductive film 3 may contain an uneven interface (interface 9) that is arranged to fill in the gaps between them.

[0078] The conductive film-coated paper substrate 10 shown in Figure 2 has an embedded structure in which at least a portion of the conductive film 3 is embedded in a recess 5 formed by the thickness direction of the surface 1A of the substrate 1. The recess 5 of the substrate 1 is formed during the sintering process by heating and pressing the conductive particle-containing layer 2 before firing. That is, 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 recess 5 of the paper substrate 1 is not formed in advance by laser irradiation or punch pressing before the lamination process.

[0079] In a cross-section of the conductive film-coated paper 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. In another embodiment, a fine uneven structure may be formed on at least a part of the surface of the protruding portion in the part embedded in the recess 5.

[0080] As shown in Figure 3, the conductive film 3 may have a conductive pattern including linear portions 3A. The linear portions 3A may consist of straight lines or curves. The conductive pattern of the conductive film 3 is not limited to narrow linear portions 3A, and 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.

[0081] 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.

[0082] <Electronic Devices> Electronic devices can be manufactured using a substrate (paper 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.

[0083] 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.

[0084] 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.

[0085] 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.

[0086] <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 (paper 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.

[0087] <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 (paper substrate with a 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.

[0088] 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.

[0089] 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.

[0090] <Preparation of conductive paste> (Conductive paste 1) Electrolytic copper powder (manufactured by Fukuda Metal Foil & Powder Industry Co., Ltd., D ５０ 73 parts by mass of (5 μm, dendritic), 12 parts by mass of thermosetting resin (resol-type phenolic resin), and 15 parts by mass of organic solvent were weighed and mixed with a spatula to obtain a mixture. This mixture was then stirred using a rotary-orbiting stirrer. In this manner, a conductive paste 1 in paste form at 23°C was obtained.

[0091] The weight loss (%) of the resol-type phenolic resin used in conductive paste 1 was measured using a differential thermal and thermogravimetric analyzer (TG-DTA) under conditions of heating to 200°C at a starting temperature of 40°C and a heating rate of 10°C / min. The reaction initiation temperature (°C) was determined from the obtained TG-DTA measurement results. In addition, the resin was placed on a hot plate set to 160°C, and the time at which fluidity was lost was visually confirmed and determined as the gel time (seconds). As a result, the weight loss of the resol-type phenolic resin was 2.5%, the reaction initiation temperature was 205°C, and the gel time was approximately 70 seconds.

[0092] (Conductive Paste 2) Conductive paste 2 was obtained in the same manner as conductive paste 1, except that a thermoplastic resin (polyvinylpyrrolidone) was used instead of a thermosetting resin, and was prepared at 23°C.

[0093] <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: Paper substrate (coated paper manufactured by Oji Paper Co., Ltd., thickness 70 μm, width 150 mm) was used. ・Printing machine: Screen printing machine (Micro-Tech, Desk Top 38SA model) was used. ・Screen plate: A screen plate with a pattern having fine lines (325 mesh, mesh diameter 16 μm, emulsion thickness 20 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°.

[0094] (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.

[0095] (Sintering Process) After the drying process, a film-like material (polyimide film) was placed on top of the patterned conductive particle-containing layer to obtain a laminated body of the laminate and the film-like material. The laminated body was placed on a metal plate (30 mm x 20 mm) set on the lower plate using a flat press machine (Housen Co., Ltd., HSSP008) equipped with two opposing flat plates (upper plate, lower plate), and hot-pressed 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 hot-pressing, the film-like material was peeled off to produce a conductive film-coated substrate with a conductive film provided on the surface of the substrate. ・Hot-pressing conditions: Heating temperature (pressing temperature): 200°C, pressure: 83 MPa, time: 30 seconds. However, the pressing temperature was not the machine's displayed value but was accurately measured and adjusted using a thermocouple. The pressure was calculated as follows. First, regarding the area of ​​the metal plate placed on the flat press machine (lower plate), 30 x 20 mm = 600 mm ２ This was calculated. The applied pressure was denoted as F. 600 mm ２ Since a force F was applied to this region, F ÷ 600 mm ２ The pressure was calculated using the following method.

[0096] [Comparative Example 1] 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.

[0097] <Observation of Cross-Sections> Both sides of the obtained conductive film-coated substrate were cut 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. This cross-section was photographed with a scanning electron microscope (SEM) to obtain a cross-sectional image. In the cross-sectional image of Example 1, a sintered structure of copper powder was confirmed in the conductive film. In addition, the existence of a structure in which a part of the conductive film is embedded in the fiber layer of the substrate was confirmed. The cross-sectional image of Example 1 is shown in Figure 4. Figure 5 shows the top view of the conductive film-coated substrate of Example 1, and Figure 6 shows the cross-sectional view, both taken using an optical microscope. In Example 1, the presence of cured thermosetting resin was confirmed in the conductive film and in the fiber layer of the substrate. In addition, in the top view of Figure 5, it was confirmed that a resin-impregnated region α1 containing cured thermosetting resin exists in the fiber layer where the conductive film does not overlap, and a resin-impregnated region α2 containing cured thermosetting resin exists in the fiber layer where the conductive film overlaps. In the top view of Figure 5, line segment l is located in the width direction perpendicular to the extension direction of the thin line portion of the conductive pattern. １ When you draw the line segment l, １ Let L1 be the width of the thin wire portion of the conductive pattern passing through, and the line segment l １ When L2 is the distance from the side of the fine line portion of the conductive pattern parallel to the outer edge of the resin-impregnated region α1, L2 / L1 × 100 was 51.8%. At this time, L1 was 282 μm, and L2 was 146 μm, which was obtained from the average width of the five resin-impregnated regions α1 shown in Figure 5. In the cross-sectional view of Figure 6, the line segment l is in the thickness direction of the paper substrate. ２ When you draw the line segment l, ２ The maximum distance L3 of the resin-impregnated region α2 passing through was 1.0 L, where L is the thickness of the fiber layer. Furthermore, from the cross-sectional view in Figure 6, it was confirmed that the resin-impregnated region α1 had a higher resin filling rate than the resin-impregnated region α2, as it was more yellowish.

[0098] <High Temperature and High Humidity Reliability> The obtained conductive film-coated substrates were subjected to a high temperature and high humidity test at 85°C, 85% RH, and for 168 hours. Before and after the high temperature and high humidity test, the resistance value was measured using a four-terminal resistance meter for the fine-line portion (measurement width of 250 μm in the central region) of the conductive pattern of the conductive film on the obtained conductive film-coated substrates, 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. Furthermore, after the high temperature and high humidity test with the test time changed to 16 hours, the conductive film was visually observed and the crack occurrence state was evaluated. In Comparative Example 1, the presence of numerous small cracks and large cracks was confirmed, but in Example 1, it was confirmed that there were few small cracks and no large cracks.

[0099]

[0100] From the results above, it was found that the conductive film-coated substrate of Example 1 exhibited superior high-temperature and high-humidity reliability compared to Comparative Example 1.

[0101] This application claims priority based on Japanese Patent Application No. 2025-056749, filed on 28 March 2025, and incorporates all of its disclosures herein.

[0102] 1 Base material 1A Surface 2 Conductive particle-containing layer 3 Conductive film 3A Line portion 3B Side surface 5 Recessed resin-impregnated area α1 Resin-impregnated area α2 Resin-unimpregnated area β 9 Interface 10 Paper base material with conductive film

Claims

1. A paper substrate with a conductive film, comprising: a paper substrate including a fiber layer; and a conductive film having a conductive pattern provided on at least a portion of the surface of the paper substrate, wherein the conductive film includes a sintered body of a plurality of conductive particles, and a cured product of a thermosetting resin is included in at least a portion of the conductive film and at least a portion of the fiber layer.

2. A conductive film-coated paper substrate according to claim 1, wherein in the fiber layer where the conductive films do not overlap, a resin-impregnated region α1 containing a cured product of the thermosetting resin exists on at least a portion of the side surface of the conductive pattern.

3. A paper substrate with a conductive film according to claim 2, wherein, in a top view, a line segment l is present in the width direction perpendicular to the extending direction of the conductive pattern. １ When the line segment l is drawn, １ Let L1 be the width of the conductive pattern passing through the line segment l １ A paper substrate with a conductive film, wherein the conductive film is parallel to the surface, and when L2 is the distance from the side surface of the conductive pattern to the outer edge of the resin-impregnated region α1, L2 / L1 × 100 is 30% or more and 70% or less.

4. A conductive film-coated paper substrate according to claim 2, wherein, in a top view, the resin-impregnated region α1 is present so as to surround at least a portion of the outer edge of the conductive pattern.

5. A paper substrate with a conductive film according to claim 1 or 2, wherein at least a portion of the fiber layer over which the conductive film overlaps contains a resin-impregnated region α2 containing a cured product of the thermosetting resin, and in a cross-section of the paper substrate with the conductive film, a line segment l exists in the thickness direction of the paper substrate. ２ When the line segment l is drawn, ２ A conductive film-coated paper substrate, wherein the maximum distance L3 of the resin-impregnated region α2 that passes through is 0.1L or more, when L is the thickness of the fiber layer.

6. A conductive film-coated paper substrate according to claim 1 or 2, wherein a resin-impregnated region α1 containing a cured product of the thermosetting resin exists in the fiber layer where the conductive film does not overlap, and a resin-impregnated region α2 containing a cured product of the thermosetting resin exists in the fiber layer where the conductive film overlaps, and the resin filling rate of the resin-impregnated region α2 is lower than the resin filling rate of the resin-impregnated region α1.

7. A paper substrate with a conductive film according to claim 1 or 2, wherein the thermosetting resin (a1) in the cured product containing the conductive film and the thermosetting resin (a2) in the cured product containing the fiber layer are of the same type.

8. A conductive film-coated paper substrate according to claim 1 or 2, wherein the fiber layer comprises a resin-impregnated region α containing a cured product of the thermosetting resin and a resin-non-impregnated region β not containing a cured product of the thermosetting resin.

9. A conductive film-coated paper substrate according to claim 1 or 2, wherein the thermosetting resin comprises one or more selected from the group consisting of phenolic resin, epoxy resin, (meth)acrylic resin, and urethane resin.

10. A paper substrate with a conductive film according to claim 1 or 2, wherein at least a portion of the space between the fiber layer and the conductive film has an uneven interface formed by being arranged to fill each other.

11. A conductive film-coated paper substrate according to claim 1 or 2, wherein the particles contained in the conductive particles include dendritic particles.

12. A paper substrate with a conductive film according to claim 1 or 2, wherein, in the volume-based cumulative distribution of particle diameters obtained when the particle diameter of the conductive particles is measured by laser diffraction scattering, the particle diameter D50 at the point where the cumulative volume from the smallest particle side reaches 50% is 0.5 μm or more and 100 μm or less.

13. A conductive film-coated paper substrate according to claim 1 or 2, wherein the conductive particles contain copper.

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

15. An electronic device according to claim 14, wherein the electronic device is an RF tag.

16. An electromagnetic shielding sheet comprising a paper substrate with a conductive film according to claim 1 or 2.

17. A planar heating element comprising a paper substrate with a conductive film according to claim 1 or 2.

18. An intermediate for a conductive film-coated paper substrate, comprising: a paper substrate including a fiber layer; and a patterned dry film provided on at least a portion of the surface of the paper substrate, wherein the dry film is obtained by drying a conductive paste containing a plurality of conductive particles and a thermosetting resin, and the thermosetting resin in a B-stage state is contained in at least a portion of the dry film and at least a portion of the fiber layer.

19. A conductive paste used for forming a cured thermosetting resin in a paper substrate and a conductive film, comprising a plurality of conductive particles, a thermosetting resin, and a solvent.

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