Paper substrate with conductive film, electronic device, electromagnetic wave shielding sheet, and planar heating element

Abstract

A paper substrate with a conductive film according to the present invention comprises: a paper substrate including a fiber layer; and a conductive film including a sintered body of a plurality of conductive particles. The paper substrate has a surface in which a recess is formed in a thickness direction. At least a portion of the conductive film is in a state of being embedded in the recess. In a cross-section A in the thickness direction of the paper substrate with a conductive film, at least a portion of the conductive film in the state of being embedded in the recess has a micro-protrusion facing a micro-recess of the fiber layer.

Description

Paper substrates with conductive films, electronic devices, electromagnetic shielding sheets, and planar heating elements.

[0001] The present invention relates to a paper substrate with a conductive film, an electronic device, an electromagnetic 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 5.

[0003] Japanese Patent Publication No. 3597952 (republished) 07-097249 Japanese Patent Publication No. 2013-504864 Japanese Patent Publication No. 2012-129343 Japanese Patent Publication No. 2015-088536

[0004] In the above-mentioned Patent Documents 1 to 5, drying, heating, or light firing are used as methods for forming conductive patterns. As a result of our investigation, we found that there is room for improvement in terms of adhesion between the conductive film and the paper substrate in paper substrates equipped with a conductive film.

[0005] The inventors have discovered that in regions where a conductive film is embedded in recesses formed in a paper substrate, a fine uneven structure is formed by the paper substrate and the conductive film, thereby improving the adhesion between the conductive film and the paper substrate, 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, and planar heating element are provided.

[0007] 1. A conductive film-coated paper substrate comprising a paper substrate containing a fiber layer and a conductive film containing a sintered body of a plurality of conductive particles, wherein the paper substrate has a surface in which recesses are formed in the thickness direction, at least a portion of the conductive film is embedded in the recesses, and in a cross-section A in the thickness direction of the conductive film-coated paper substrate, at least a portion of the conductive film embedded in the recesses has a micro-protrusion facing the micro-recesses of the fiber layer. 2. The conductive film-coated paper substrate according to 1, wherein in cross-section A, at least one of the micro-protrusions has a structure that protrudes in the thickness direction beyond a straight line connecting the two ends of the opposing micro-recesses. 3. The conductive film-coated paper substrate according to 1 or 2, wherein in cross-section A, at least one of the micro-protrusions has a structure that protrudes in a direction intersecting the thickness direction beyond at least one end of the opposing micro-recesses. 4. 3. A conductive film-coated paper substrate as described in 1., wherein in the structure protruding in the intersecting directions, when the maximum length in the direction perpendicular to the thickness direction is L1 and the maximum length in the thickness direction is L2, L1 / L2 is 0.1 or more and 6.0 or less. 5. A conductive film-coated paper substrate as described in any one of 1 to 4, wherein in cross-section A, an interface exists in at least a part between the fiber layer and the conductive film, formed by the arrangement of the micro-recesses and the micro-protrusions so as to mutually fill each other. 6. A conductive film-coated paper substrate as described in any one of 1 to 5, wherein the conductive film has a conductive pattern including linear portions. 7. A conductive film-coated paper substrate as described in 6, wherein in cross-section B passing through the short direction and the thickness direction of the linear portion of the conductive pattern, the width in the short direction of the linear portion is 30 μm or more and 5000 μm or less. 8. A conductive film-coated paper substrate according to any one of the above, wherein the paper substrate includes any of the following selected from the group consisting of kraft paper, glassine paper, acid paper, sulfuric acid paper, fine paper, coated paper obtained by coating these papers with a liquid containing pigment and / or resin, and impregnated paper obtained by impregnating paper with a liquid containing pigment and / or resin.9. A paper substrate with a conductive film as described in any one of 1 to 8, wherein the particle size D is such that the cumulative frequency is 50% in the volume-based cumulative particle size distribution curve obtained when the particle size of the conductive particles is measured by laser diffraction scattering. ５０ A conductive film-coated paper substrate having a thickness of 0.5 μm or more and 100 μm or less. 10. An electronic device comprising a conductive film-coated paper substrate as described in any one of 1 to 9. 11. An electronic device as described in 10, wherein the electronic device is an RF tag. 12. An electromagnetic wave shielding sheet comprising a conductive film-coated paper substrate as described in any one of 1 to 9. 13. A planar heating element comprising a conductive film-coated paper substrate as described in any one of 1 to 9.

[0008] According to the present invention, a conductive film-coated paper substrate with excellent adhesion between the conductive film and the paper substrate, 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 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 shows an SEM image showing a cross-section of the conductive film-coated paper substrate of Example 1. This shows an enlarged view of Figure 4. This shows an SEM image showing a cross-section of the conductive film-coated paper substrate 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 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 including a sintered body of a plurality of conductive particles. The paper substrate has a surface in which recesses are formed in the thickness direction, and at least a portion of the conductive film is embedded in the recesses. In at least one cross-section A in the thickness direction of the conductive film-coated paper substrate, at least a portion of the conductive film embedded in the recesses has a micro-protrusion facing the micro-recesses of the fiber layer.

[0014] According to the inventors' findings, in the region where a conductive film is embedded in a recess formed in the fiber layer of a paper substrate, a fine uneven structure is formed by the surface of the recess in the fiber layer and the embedded portion of the conductive film, thereby improving the adhesion between the conductive film and the paper substrate. It is presumed that this fine uneven structure interlocks with each other and functions as an anchor, suppressing delamination between the conductive film and the paper substrate and increasing the physical adhesion between them.

[0015] Furthermore, it was found that the above-mentioned fine uneven structure can be achieved by forming a film made of conductive paste on a paper substrate and then subjecting the film to heat and pressurize treatment. The detailed mechanism is not clear, but it is presumed to be as follows: The film made of conductive paste contains multiple unsintered conductive particles, and it is presumed that when these multiple conductive particles are pressed against the fiber layer of the paper substrate by the heat and pressurize treatment, depressions are formed in the fiber layer, and within these depressions, a cellulose wall with the original high modulus of elasticity and high heat resistance is generated as the fibers are compressed. The multiple conductive particles that have moved into these depressions are sintered while being compressed by this cellulose wall, and it is thought that a conductive film having micro-protrusions facing the micro-depressions of the fiber layer is formed. General adhesion is exerted by the affinity when the conductive paste is printed on the substrate and by the interaction at the interface when the conductive paste is dried. The adhesion due to the fine uneven structure of this embodiment differs from general adhesion in that it is exerted after heat and pressurization (sintering of conductive particles).

[0016] 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 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).

[0017] 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.

[0018] 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. 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. In Figure 2, the X direction means the orthogonal direction perpendicular to the thickness direction (Z direction).

[0019] 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) to 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), and as shown in Figure 1(C), a sintering step of sintering the plurality of conductive particles in the conductive particle-containing layer 2 by heating and pressurizing to form a conductive film 3.

[0020] 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.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] <Substrate> Substrate 1 may be a paper substrate consisting of a fiber layer, or 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, or inorganic particles such as clay can be used. It is preferable that the paper substrate has heat resistance compared to ordinary resin substrates.

[0027] In Figure 1(B), the surface 1A of the substrate where the conductive paste is formed may consist of a fiber layer, or it may consist of a mixture of a fiber layer and a release layer and / or a coating layer. For example, when a paper substrate having a release layer and / or a coating layer on one side is used, the surface 1A of the substrate 1 may have a portion of the underlying fiber layer exposed from the release layer or coating layer, and may consist of a fine coating in which the fiber layer is exposed in 30% or more, preferably 50% or more, of the total area of ​​the surface 1A. For reasons that are not entirely clear, if an exposed fiber layer is present in the area where the conductive paste is formed, multiple conductive particles can penetrate into the interfiber gaps of the fiber layer during the heat and pressure treatment.

[0028] As a specific base material 1, any known material can be used, but for example, any paper selected from the group consisting of kraft paper, glassine paper, acid paper, sulfuric acid paper, fine paper, coated paper (including lightly coated paper) which is one of these papers coated with a liquid containing pigment and / or resin, or impregnated paper which is one in which a liquid containing pigment and / or resin is impregnated into the paper may be used.

[0029] The base material 1 is typically in the form of a film, sheet, or plate. From the viewpoint of industrial productivity, any of these shapes of the base material is preferred.

[0030] The base material 1 is preferably flexible. By using a flexible base material, a flexible printed circuit board (FPC) can be manufactured. Using a flexible base material is preferable, for example, from the viewpoint of mass production.

[0031] 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.

[0032] <Conductive Paste> An example of a conductive paste includes multiple conductive particles and a solvent.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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. ５０When D is appropriately large, the number of grain boundaries between conductive particles per unit volume can be reduced. This is considered to lead to a lower specific resistance of the obtained conductive pattern. D ５０ When D is not excessively large, the number of "gaps" between conductive particles is reduced, which is considered to lead to a lower specific resistance of the obtained conductive pattern.

[0038] Conductive particles are commercially available, for example, from DOWA Electronics Co., Ltd., Fukuda Metal Foil & Powder Co., Ltd., and the like. Two or more different types of conductive particles may be used in combination for the purpose of adjusting and optimizing the particle size distribution or for other purposes.

[0039] The proportion of the conductive particles in the total non-volatile components of the conductive paste is preferably 95% by mass or more, more preferably 97% by mass or more, still more preferably 98% by mass or more, and particularly preferably 99% by mass or more.

[0040] When the conductive paste contains a solvent, the coatability on a substrate or printability of the conductive paste is improved. The solvent typically includes an organic solvent. The solvent may contain water as long as the conductive particles can be appropriately dispersed. The type of the solvent is not particularly limited. Any solvent may be used as long as it does not substantially alter the properties of each component in the conductive paste. The amount of the solvent used may be appropriately adjusted according to the coating and printing method of the conductive paste, for example. The amount of the solvent used is, based on the total mass of the conductive paste, for example 3 to 30% by mass, preferably 5 to 25% by mass, and more preferably 10 to 20% by mass.

[0041] The conductive paste may optionally contain resin components such as a resin and a binder, and a dispersant for the resin components, but may also be substantially free of the resin components and the dispersant. When the resin component is contained, the amount of the resin component 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, relative to 100 parts by mass of the conductive particles. Preferable examples of the resin component include polyvinylpyrrolidone, polyester, epoxy resin, (meth)acrylic resin, polyvinyl acetal, cellulose resin (e.g., ethyl cellulose), and phenolic resin. Here, the expression "substantially free of" a resin or binder means either containing no resin or binder at all, or containing a resin or binder but in such a small amount that the effect expected from the use of the resin or binder (specifically described below) cannot be obtained (for example, 1% by mass or less, specifically 0.5% by mass or less, based on the total non-volatile components of the conductive paste).

[0042] In addition, the conductive paste may or may not contain various additive components conventionally used in ink compositions and conductive pastes. Examples of the additive components include antioxidants, silane coupling agents, and curing agents. These may be used alone or in combination of two or more thereof.

[0043] In the manufacturing method of the present embodiment, a sintering step is performed after the above-mentioned lamination step. In the sintering step, the plurality of conductive particles contained in the conductive particle-containing layer 2 are sintered by heat and pressure treatment to form the conductive film 3.

[0044] The heat and pressure treatment can be performed, for example, using a flat press device provided with a heating mechanism. That is, by sandwiching a laminate of the base material 1 and the conductive particle-containing layer 2 provided from the conductive paste between two (a pair of) flat plates and pressing while heating, the conductive particles in the conductive particle-containing layer 2 can be sintered.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] Component X may include one or more selected from the group consisting of carboxylic acids, phosphorus oxoacids, hydrazine compounds, inorganic acids, phenols, and other reducing substances. Examples of carboxylic acids include citric acid, formic acid, acetic acid, malonic acid, malic acid, tartaric acid, ascorbic acid, succinic acid, fumaric acid, and propionic acid. However, it is not limited to these, and organic acids other than carboxylic acids may be used. Examples of phosphorus oxoacids include phosphinic acid, phosphonic acid, phosphorous acid, phosphoric acid, diphosphate, triphosphate, and metatriphosphate. Examples of hydrazine compounds include hydrazine, hydrazine derivatives such as hydrazine salts including monohydrazine hydrochloride, hydrazine dihydrazine hydrochloride, monohydrazine hydrobromide, and hydrazine sulfate, phenylhydrazine, and others -NH-NH ２Examples of compounds with a specific structure include those mentioned above. Inorganic acids include, for example, hydrochloric acid, nitric acid, sulfuric acid, and hydrobromic acid. Phenols include, for example, pyrogallol, orthoaminophenol, and hydroquinone. Other reducing substances include, for example, pyrazolidone compounds. Phenidone is an example of a pyrazolidone compound. These may be used individually or in combination of two or more. Among these, component X can be a compound with a small pKa in water. Specifically, a compound with a pKa of -5.0 to 5.0 in water is preferred as component X, and a compound with a pKa of -4.0 to 4.5 is more preferred as component X. Incidentally, if component X is a polybasic acid, it is preferable that the smallest pKa among multiple pKa values ​​is within the above range. The pKa value here can be the value at room temperature (e.g., 25°C). The liquid containing component X is preferably water in which component X is dissolved or dispersed. Using water is preferable from the standpoint of reducing environmental impact and ensuring process safety (non-flammable). Of course, organic solvents in which component X is dissolved or dispersed can also be used. The concentration of component X in the liquid is, for example, 0.05 to 50 mol / L, preferably 0.1 to 40 mol / L, more preferably 0.1 to 30 mol / L, even more preferably 0.1 to 10 mol / L, and particularly preferably 0.15 to 5.0 mol / L. Of course, a liquid containing component X at a lower concentration than those shown herein may be used, or a liquid containing component X at a higher concentration than those shown herein (e.g., saturation concentration) may be used.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] By the above manufacturing method, a paper substrate 10 with a conductive film can be obtained.

[0055] Figure 2 is a schematic cross-sectional view showing an example of a conductive film-coated paper substrate 10. The conductive film-coated paper substrate 10 only needs to include a cross-section A in at least one of its cross-sections, which has a fine uneven structure (micro-recesses 5A and micro-recesses 7A) formed on the conductive film 3 embedded in the recess 5 of the substrate 1 shown in Figure 2. The recess 5 of the substrate 1 is formed in 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 where the surface 1A of the substrate 1 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. In this specification, "at least one cross-section" means that the configuration is confirmed in at least one of a plurality of cross-sections set on the object, and it is not necessary that the configuration be confirmed in all cross-sections. The cross-section may be a cross-section perpendicular to the extending direction of the object, a cross-section along the extending direction, or a cross-section including the thickness direction.

[0056] The conductive film 3 embedded in the recess 5 has a convex structure that is convex in the thickness-down direction from the conductive film 3 toward the substrate 1, so as to follow the surface of the recess 5. A part of the convex structure protrudes to form a micro-protrusion 7A. The conductive film 3 may have one or more micro-protrusions 7A in a single cross section A. Multiple micro-protrusions 7A may exist facing each other micro-recess 5A. Furthermore, the convex structure of the conductive film 3 may be embedded in the recess 5 for, for example, 50% or more of the area of ​​cross section A, preferably 70% or more of the area. Also, in a cross section B passing through the short-side direction and the thickness direction of the line portion 3A of the conductive pattern, the area of ​​the line portion 3A embedded in the recess 5 is, for example, 500 μm. ２ ~50,000 μm ２ This is also possible. The entire conductive film 3 may be embedded in the recess 5, or a portion of the conductive film 3 may be not embedded in the recess 5 and have a portion that protrudes upward in the thickness direction.

[0057] Multiple conductive particles in the conductive film 3 are sintered and connected to one another. Sintering means that, through heating and pressurizing, the particles fuse together at the contact points on the metal surfaces between them, and multiple conductive particles are joined (connected) to form an integrated structure.

[0058] The sintered structure in the conductive film 3 is preferably located not only near the upper surface but also near the lower surface, and preferably has a continuous structure extending from the upper surface to the lower surface. The density of the sintered structure in the conductive film 3 can be defined using the area of ​​conductive particles calculated by cross-sectional image analysis, and while it may differ between the area near the lower surface and the area near the upper surface, it is preferable that they be of similar density.

[0059] In cross-section A, an interface 9 may exist between the fiber layer of the substrate 1 and the conductive film 3, where a micro-recess 5A and a micro-protrusion 7A are arranged to fill each other. At interface 9, the fiber layer and the conductive layer are in contact with each other. This further enhances adhesion.

[0060] In this embodiment, in cross-section A, at least one of the micro-protrusions 7A may have a structure that protrudes in the thickness direction beyond the straight line connecting the two opposing micro-recesses 5A.

[0061] Furthermore, in this embodiment, in cross-section A, at least one of the micro-protrusions 7A may have a structure that protrudes in a direction intersecting the thickness direction from at least one end of the opposing micro-recess 5A. The intersecting direction is not limited to a direction perpendicular to the thickness direction at 90 degrees, but may be any direction that forms an acute angle with respect to the thickness direction in the range of more than 0 degrees to 90 degrees.

[0062] Furthermore, in this embodiment, in the structure protruding in intersecting directions, when the maximum length in the direction perpendicular to the thickness direction, which is at a 90-degree angle to the thickness direction, is defined as L1, and the maximum length in the thickness direction is defined as L2, then L1 / L2 is, for example, 0.1 to 6.0, preferably 0.15 to 5, and more preferably 0.2 to 4. By having a structure in which micro-protrusions protrude in a direction perpendicular to the thickness direction, the protruding structure acts as a catch in the thickness direction, increasing the adhesion force to the substrate 1.

[0063] Figure 3 is a top view of an example of a paper substrate 10 with a conductive film, 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 consist 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.

[0064] 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.

[0065] <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.

[0066] 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.

[0067] 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.

[0068] 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.

[0069] <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.

[0070] <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.

[0071] 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.

[0072] 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.

[0073] <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 polyester resin, and 16 parts by mass of organic solvent were weighed and kneaded 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.

[0074] <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 40 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°.

[0075] (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.

[0076] (Sintering Process) After the drying 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 Industries 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 180°C, upper roll 180°C), pressure: 20 MPa, conveying speed: 1 m / min, no gap

[0077] (Examples 2-5) In the printing process described above, a conductive film-coated substrate was manufactured in the same manner as in Example 1, except that glassine paper (SB Release, manufactured by Nippon Paper Industries Co., Ltd.) was used as the substrate in Example 2, micro-coated paper (EG-X, manufactured by Oji Paper Co., Ltd.) in Example 3, high-quality paper (OK Princess, manufactured by Oji Paper Co., Ltd.) in Example 4, and sulfuric acid paper (Drip W, manufactured by Oji Paper Co., Ltd.) in Example 5.

[0078] [Comparative Example 1] A conductive film-coated substrate was manufactured in the same manner as in Example 1, except that after the drying process, the above sintering process was not performed, and the substrate was heated at 180°C for 10 minutes in a hot air circulating atmospheric oven.

[0079] <Observation of the cross-section> 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.

[0080] In the cross-sectional images of Examples 1 to 5, 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 the convex portions of the conductive film were embedded in the recesses of the fiber layer of the substrate was confirmed. In addition, it was confirmed that there were multiple micro-convex portions on the convex portions of the conductive film embedded in the recesses, facing the micro-recesses of the fiber layer. On the other hand, in Comparative Example 1, no recesses formed in the thickness direction of the fiber layer of the substrate were confirmed. Figure 4 shows a cross-sectional image of the substrate with the conductive film of Example 1, Figure 5 shows an enlarged view of a part of the conductive film in Figure 4 (the part corresponding to the micro-convex portion), and Figure 6 shows a cross-sectional image of the substrate with the conductive film of Comparative Example 1.

[0081] The results of analyzing the cross-sectional SEM images in Figures 4 and 5 are shown below. The width in the short direction of the fine line portion of the conductive pattern was 300 μm. In Figure 5, it was confirmed that the micro-protrusions of the conductive film have a structure that protrudes in a direction intersecting the thickness direction from at least one end of the micro-recess of the opposing fiber layer. In this structure protruding in the intersecting direction of the micro-protrusions, when the maximum length in the direction perpendicular to the thickness direction is L1 and the maximum length in the thickness direction is L2, L1 / L2 was 0.48.

[0082] <Measurement of Resistivity> 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 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 resistivity of Example 1 was 2.0 × 10⁻⁶.－５ Ω·cm. On the other hand, in Comparative Example 1, conduction could not be confirmed, and the specific resistance could not be calculated. It is speculated that the specific resistances of Examples 2 to 5 are also lower than that of Comparative Example 1, similarly to Example 1.

[0083] <Adhesion> The obtained base material with a conductive film was bent by hand and restored to the original flat shape, and this operation was repeated 5 times. Thereafter, the presence or absence of peeling of the conductive pattern was confirmed by visual observation and magnified observation. In Examples 1 to 5, no peeling of the conductive pattern was observed. In Comparative Example 1, the conductive pattern peeled from the base material.

[0084] From the above results, it was shown that the base materials with a conductive film of Examples 1 to 5 have higher adhesion compared to Comparative Example 1. Further, regarding the base material with a conductive film, it was confirmed that the conductive film has lower resistance in Example 1, and the same tendency is expected for Examples 2 to 5.

[0085] This application claims priority based on Japanese Patent Application No. 2025-056590 filed on March 28, 2025, and the entire disclosure thereof is incorporated herein.

[0086] 1 Base material 1A Surface 2 Conductive particle-containing layer 3 Conductive film 3A Line portion 5 Recess 5A Fine recess 7A Fine protrusion 9 Interface 10 Paper base material with conductive film

Claims

1. A conductive film-coated paper substrate comprising a paper substrate containing a fiber layer and a conductive film containing a sintered body of a plurality of conductive particles, wherein the paper substrate has a surface in which recesses are formed in the thickness direction, at least a portion of the conductive film is embedded in the recesses, and in a cross-section A in the thickness direction of the conductive film-coated paper substrate, at least a portion of the conductive film embedded in the recesses has a micro-protrusion facing the micro-recesses of the fiber layer.

2. A conductive film-coated paper substrate according to claim 1, wherein in the cross-section A, at least one of the micro-protrusions protrudes in the thickness direction beyond the straight line connecting the two opposing micro-recesses.

3. A conductive film-coated paper substrate according to claim 1 or 2, wherein in the cross-section A, at least one of the micro-protrusions protrudes in a direction intersecting the thickness direction more than at least one end of the opposing micro-recesses.

4. A conductive film-coated paper substrate according to claim 3, wherein, in the structure protruding in the intersecting directions, when the maximum length in the direction perpendicular to the thickness direction is L1 and the maximum length in the thickness direction is L2, L1 / L2 is 0.1 or more and 6.0 or less.

5. A paper substrate with a conductive film according to claim 1 or 2, wherein in the cross-section A, an interface exists in at least a portion between the fiber layer and the conductive film, formed by the arrangement of the micro-recesses and the micro-protrusions so as to mutually fill each other.

6. A paper substrate with a conductive film according to claim 1 or 2, wherein the conductive film has a conductive pattern including linear portions.

7. A paper substrate with a conductive film according to claim 6, wherein in a cross section B passing through the short direction and the thickness direction of the line portion of the conductive pattern, the width of the line portion in the short direction is 30 μm or more and 5000 μm or less.

8. A conductive film-coated paper substrate according to claim 1 or 2, wherein the paper substrate comprises any of the following selected from the group consisting of kraft paper, glassine paper, acid paper, sulfuric acid paper, fine paper, coated paper obtained by coating these papers with a liquid containing pigment and / or resin, and impregnated paper obtained by impregnating paper with a liquid containing pigment and / or resin.

9. A paper substrate with a conductive film according to claim 1 or 2, wherein the particle size D of the conductive particles is such that the cumulative frequency is 50% in the volume-based cumulative particle size distribution curve obtained when the particle size of the conductive particles is measured by laser diffraction scattering. ５０ A conductive film-coated paper substrate having a thickness of 0.5 μm or more and 100 μm or less.

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

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

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