RFID medium

Abstract

An RFID medium according to the present invention comprises an electroconductive-film-equipped base material that has a base material and an electroconductive film which has a conductive pattern provided to at least part of a surface of the base material, wherein: the electroconductive film includes a sintered body of a plurality of conductive particles; the electroconductive-film-equipped base material is an inlay intermediate product which does not have an IC chip electrically connected to the electroconductive film; and when the inlay intermediate product is used as is as a sample and is subjected to a high-temperature high-humidity test, a thermal shock test, and a bending tolerance test, after at least one of the tests, the resistance value of the conductive pattern is not more than 100 Ω, or the specific resistance of the conductive pattern is not more than 6.0×10-5Ω･cm.

Description

RFID medium

[0001] This invention relates to RFID media.

[0002] Studies have been conducted to date on forming conductive patterns using conductive paste. Patent documents 1 to 3 are examples of this type of technology. Patent documents 1 to 3 describe the manufacture of RFID tags using conductive ink.

[0003] Japanese Patent Publication No. 2019-192159, Japanese Patent Publication No. 2020-46834, Japanese Patent Publication No. 2020-90626

[0004] As a result of our investigation, we found that there is room for improvement in terms of high reliability in RFID media comprising a substrate with a conductive film formed using a conductive paste.

[0005] The inventors have discovered that by using a method of sintering a conductive paste by heating and pressurizing (hot pressing method), the reliability of the resulting conductive film-coated substrate, as evaluated by at least one of the high-temperature and high-humidity test, the thermal shock test, and the bending resistance test, can be improved, and have completed the present invention.

[0006] According to one aspect of the present invention, the following RFID medium is provided.

[0007] 1. An RFID medium comprising a substrate and a conductive film having a conductive pattern provided on at least a portion of the surface of the substrate, wherein the conductive film comprises a sintered body of a plurality of conductive particles, and the RFID medium is one of the following: an inlay intermediate without an IC chip electrically connected to the conductive film, an inlay having an IC chip electrically connected to the conductive film, or an IC chip electrically connected to the conductive film, and a tag having a laminated structure on the IC chip, and when the following reliability tests are performed on the sample described below, the resistance value of the conductive pattern after at least one of the following tests X, Y, and Z satisfies the condition that the resistivity of the conductive pattern is 100 Ω or less, or the resistivity of the conductive pattern is 6.0 × 10 －５RFID medium satisfying Ω·cm or less. (Sample) If the RFID medium is the inlay intermediate, the inlay intermediate shall be used as the sample. If the RFID medium is the inlay, the sample shall be the inlay with the IC chip removed. If the RFID medium is the tag, the sample shall be the tag with the IC chip exposed and then removed. (Conditions for reliability testing) Test X: High temperature and high humidity test held at 85°C and 85% RH for 168 hours. Test Y: Thermal shock test performed 200 cycles, with each cycle being 30 minutes from -40°C to 85°C. Test Z: Bending resistance test performed with a bending speed of 30 times / min, bending radius R = 15 mm, and angle: 45°, bending 100 times each on the front and back sides. 2. An RFID medium comprising a substrate and a conductive film having a conductive pattern provided on at least a portion of the surface of the substrate, wherein the conductive film comprises a sintered body of a plurality of conductive particles, and the substrate with the conductive film is an inlay intermediate that does not have an IC chip electrically connected to the conductive film, and when the inlay intermediate is used as a sample and the following reliability tests are performed on the sample, the resistance value of the conductive pattern after at least one of the following tests X, Y, and Z satisfies the condition that the resistivity of the conductive pattern is 100 Ω or less, or the resistivity of the conductive pattern is 6.0 × 10 －５RFID medium satisfying Ω·cm or less. (Conditions for reliability testing) Test X: High temperature and high humidity test held at 85°C and 85% RH for 168 hours Test Y: Thermal shock test performed in a total of 200 cycles, with each cycle being 30 minutes from -40°C to 85°C Test Z: Bending resistance test performed with bending speed: 30 times / min, bending radius R = 15 mm, angle: 45°, bending 100 times each on the front and back sides 3. RFID medium as described in 1. or 2., wherein the total length of the conductive pattern is 300 mm or more and 4000 mm or less, the thickness of the conductive pattern is 3 μm or more and 50 μm or less, and the width of the conductive pattern is 30 μm or more and 5000 μm or less. 4. RFID medium as described in any one of 1. to 3., wherein the particles contained in the conductive particles include dendritic particles. 5. 1. to 4. An RFID medium as described in any one of the above, wherein the particle diameter D of the particle diameter at the point where the cumulative volume from the smallest particle side reaches 50% in the volume-based cumulative distribution of particle diameter obtained when the particle diameter of the conductive particle is measured by laser diffraction scattering is ５０1. An RFID medium having a diameter of 0.5 μm or more and 100 μm or less. 6. An RFID medium according to any one of 1 to 5, wherein the conductive particles contain copper. 7. An RFID medium according to any one of 1 to 6, wherein at least a portion of the conductive film is embedded in the substrate. 8. An RFID medium according to any one of 1 to 7, wherein the plurality of conductive particles contain at least one of atomized copper powder and electrolytic copper powder. 9. An RFID medium according to any one of 1 to 8, wherein the substrate is a resin substrate containing a thermoplastic resin layer. 10. An RFID medium according to any one of 1 to 9, wherein the conductive film comprises a sintered body of the plurality of conductive particles treated with one or more selected from the group consisting of carboxylic acids, phosphorus oxoacids, and hydrazine compounds. 11. An RFID medium according to any one of the above, wherein the conductive film contains a dispersant Y. 12. An RFID medium according to any one of 1 to 11, wherein the thermal shrinkage rate in the MD direction of the thermoplastic resin layer under the conditions of 150°C for 30 minutes, as measured in accordance with JIS C 2318, is 1.0% or less, and / or the difference in thermal shrinkage rates |MD-TD| between the MD direction and the TD direction of the thermoplastic resin layer under the conditions of 150°C for 30 minutes, as measured in accordance with JIS C 2318, is 0.7% or less. 13. An RFID medium according to any one of 1 to 12, wherein the thermoplastic resin layer contains one or more selected from the group consisting of polyester, polyolefin, polycarbonate, and polyimide. 14. An RFID medium according to any one of 1 to 13, wherein the heat resistance temperature of the thermoplastic resin layer is 80°C or higher. 15. An RFID medium according to any one of 1 to 8, wherein the substrate is a paper substrate containing a fiber layer. 16. An RFID medium according to any one of 1 to 8, or 15, wherein at least a portion of the conductive film and at least a portion of the fiber layer contain a cured product of a thermosetting resin.17. An RFID medium according to any one of 1. to 8., 15., or 16., wherein the substrate is 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.

[0008] According to the present invention, a highly reliable RFID medium is 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 substrate according to this embodiment. This is a schematic cross-sectional view showing an example of a conductive film-coated substrate according to this embodiment. This is a schematic top view showing an example of a conductive film-coated substrate according to this embodiment. This is a top view showing the antenna patterns in the examples and comparative examples. This shows a cross-sectional SEM image of Example A1.

[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 overview of the RFID medium in this embodiment will be described.

[0013] The RFID medium of this embodiment may take the form of an inlay intermediate, an inlay, or a tag. In any form, the RFID medium includes the following conductive film-coated substrate. The conductive film-coated substrate comprises a substrate and a conductive film provided on at least a portion of the surface of the substrate. The conductive film has a conductive pattern and includes a sintered body of a plurality of conductive particles. The substrate also includes at least one of a resin substrate including a thermoplastic resin layer and a paper substrate including a fiber layer.

[0014] (1) Inlay Intermediate The inlay intermediate comprises a conductive film substrate that does not have an IC chip electrically connected to the conductive film. That is, this conductive film substrate is in a state where an IC chip is not mounted. For example, this conductive film substrate may be one in which the antenna pattern and the IC chip are not electrically connected. When reliability testing is performed on the inlay intermediate, the inlay intermediate can be used as is as "Sample A".

[0015] The reliability test for "Sample A" may be one of the following three tests (Test X, Test Y, Test Z), or two or three tests may be performed using multiple Sample A samples. (Conditions for reliability tests) ・Test X: High temperature and high humidity test, held at 85°C and 85% RH for 168 hours. ・Test Y: Thermal shock test, performed for a total of 200 cycles, with each cycle consisting of holding the temperature from -40°C to 85°C for 30 minutes. ・Test Z: Bending resistance test, performed with a bending speed of 30 times / min, bending radius R = 15 mm, and angle: 45°, bending 100 times each on the front and back sides.

[0016] The inlay intermediate product shall include at least one of the following conductivity characteristics 1 to 6 after the reliability test described above: • Conductivity characteristic 1: The resistance value of the conductive pattern after test X is 100 Ω or less. • Conductivity characteristic 2: The resistivity of the conductive pattern after test X is 6.0 × 10⁻⁶. －５ The following conditions must be met: • Conductivity characteristic 3: The resistance of the conductive pattern after test Y is 100 Ω or less. • Conductivity characteristic 4: The resistivity of the conductive pattern after test Y is 6.0 × 10 －５The following conditions must be met: • Conductivity characteristic 5: The resistance of the conductive pattern after test Z is 100 Ω or less. • Conductivity characteristic 6: The resistivity of the conductive pattern after test Z is 6.0 × 10⁻⁶. －５ The condition is less than or equal to Ω·cm.

[0017] (2) The inlay comprises a conductive film substrate having an IC chip electrically connected to the conductive film. That is, the conductive film substrate is in a state with the IC chip mounted on it. For example, the antenna pattern and the IC chip may be electrically connected on this conductive film substrate. When reliability testing is performed on the inlay, the inlay with the IC chip removed can be used as "Sample B". Reliability testing on "Sample B" may be performed on any one of the following three (Test X, Test Y, Test Z), or two or three tests may be performed using multiple Sample B. The inlay includes at least one of the above conductive characteristics 1 to 6 after the above reliability testing.

[0018] (3) The tag comprises an IC chip electrically connected to a conductive film, and a conductive film-coated substrate having a laminated structure on the IC chip. That is, the conductive film-coated substrate is protected by a laminated structure such as a laminate layer or a sealing material when the IC chip is mounted on it. For example, the conductive film-coated substrate may have an antenna pattern and an IC chip electrically connected. When reliability testing is performed on the tag, the IC chip removed from the tag after exposure can be used as "Sample C". Reliability testing on "Sample C" may be performed on any one of the following three (Test X, Test Y, Test Z), or two or three tests may be performed using multiple Sample Cs. The tag has at least one of the above conductive characteristics 1 to 6 after the above reliability testing.

[0019] As described above, the RFID medium of the present embodiment may include one selected from each of the following four sets (a) to (d). (a) Set of forms of RFID medium {inlay intermediate product / inlay / tag} (b) Set of forms of base material in base material with conductive film {resin base material / paper base material} (c) Set of forms of reliability test {test X / test Y / test Z} (d) Set of forms of conductive properties {conductive property 1 / conductive property 2 / conductive property 3 / conductive property 4 / conductive property 5 / conductive property 6}

[0020] Note that the resistance values and specific resistances in the above conductive properties 1 to 6 may be within the following ranges. [In the case of resin base material] In the above conductive property 1, the resistance value is 100 Ω or less, preferably 50 Ω or less, more preferably 30 Ω or less. In the above conductive property 2, the specific resistance is 6.0×10 －５ Ω·cm or less, preferably 3.1×10 －５ Ω·cm or less, more preferably 1.8×10 －５ Ω·cm or less. In the above conductive property 3, the resistance value is 100 Ω or less, preferably 50 Ω or less, more preferably 30 Ω or less. In the above conductive property 4, the specific resistance is 6.0×10 －５ Ω·cm or less, preferably 3.1×10 －５ Ω·cm or less, more preferably 1.8×10 －５ Ω·cm or less. In the above conductive property 5, the resistance value is 100 Ω or less, preferably 50 Ω or less, more preferably 30 Ω or less. In the above conductive property 6, the specific resistance is 6.0×10 －５ Ω·cm or less, preferably 3.1×10 －５ Ω·cm or less, more preferably 1.8×10 －５ Ω·cm or less.

[0021] [In the case of paper base material] In the above conductive property 1, the resistance value is 100 Ω or less, preferably 50 Ω or less, more preferably 30 Ω or less. In the above conductive property 2, the specific resistance is 6.0×10 －５ Ω·cm or less, preferably 3.1×10 －５ Ω·cm or less, more preferably 1.8×10 －５It is Ω·cm or less. In the above conductivity characteristic 3, the above resistance value is 100Ω or less, preferably 50Ω or less, and more preferably 30Ω or less. In the above conductivity characteristic 4, the above resistivity is 6.0 × 10 －５ Ω·cm or less, preferably 3.1 × 10 －５ Ω·cm or less, more preferably 1.8 × 10 －５ It is Ω·cm or less. In the above conductivity characteristic 5, the above resistance value is 100Ω or less, preferably 50Ω or less, and more preferably 30Ω or less. In the above conductivity characteristic 6, the above resistivity is 6.0 × 10 －５ Ω·cm or less, preferably 3.1 × 10 －５ Ω·cm or less, more preferably 1.8 × 10 －５ It is less than or equal to Ω·cm.

[0022] In addition, when creating the above samples, if the tags are attached (a substrate with adhesive is attached to the inlay), the adhesive may be dissolved with an organic solvent to expose the inlay (using a method that minimizes the application of physical force), and the chips may be removed. Alternatively, the entire inlay may be exposed by applying physical force, such as peeling off the substrate with adhesive.

[0023] Furthermore, the length (total length), thickness, and width of the conductive pattern can be as follows: The length of the conductive pattern is, for example, 300 mm to 4000 mm, preferably 400 mm to 3000 mm, and more preferably 500 mm to 2000 mm. The thickness of the conductive pattern is, for example, 3 μm to 50 μm, preferably 5 μm to 40 μm, and more preferably 7 μm to 30 μm. The width of the conductive pattern is, for example, 30 μm to 5000 μm, preferably 70 μm to 3000 μm, and more preferably 100 μm to 1000 μm. The above length, thickness, and width may be used for fine wire patterns or antenna patterns of the conductive pattern. For measuring resistance, the total length of the conductive pattern can be used as the measurement target. The total length of the conductive pattern means the sum of the lengths from the two connection ends, which are the connection parts (planned connection parts) to the IC chip, to the ends of the two patterns that extend from each of them. Furthermore, for resistivity measurement, the measurement target can be the conductive pattern portion in the area where the IC chip is planned to be mounted or a portion of the conductive pattern close to the IC chip mounting area. In this case, the width of the conductive pattern is preferably, for example, 200 μm or more. Note that the thickness and width of the conductive pattern may be the average values ​​at the measurement location.

[0024] According to the inventors' research, the following findings were obtained. In a conductive film formed by sintering a conductive paste, conductive paths are formed by electrical contacts where conductive particles come into contact or fuse with each other. These electrical contacts are prone to degradation due to environmental stress. Although the detailed mechanism is not clear, it is thought that the heat and pressure treatment (hot press method) causes a structure in which a portion of the conductive film formed by sintering of conductive particles in the conductive paste is embedded in the substrate, thereby improving the strength of the electrical contacts. As a result, it is presumed that the reliability of the conductive film-coated substrate, or RFID media using a conductive film-coated substrate, as evaluated by at least one of the high-temperature and high-humidity test, the thermal shock test, and the bending resistance test, can be improved.

[0025] Further, the above pressure and heat treatment may form an embedded structure in which at least a part of the conductive film is embedded in a recess formed in the base material. It is presumed that since the embedded structure functions as an anchor, peeling between the conductive film and the base material is suppressed, and the physical adhesion between the two is enhanced.

[0026] Further, it was found that by including dispersant Y or a cured product of a thermosetting resin in the conductive film formed of a sintered body of conductive particles, stable and high reliability of the conductive film can be obtained even after each test.

[0027] When the base material is a resin base material including a thermoplastic resin layer, the conductive paste may contain dispersant Y. Although the detailed mechanism is not clear, it is understood that dispersant Y favorably disperses the conductive particles and is not dissolved by component X, so that the conductive particles can be sintered together while maintaining the dispersed state until immediately before sintering, and remains in the sintered body as a binder even after sintering. Accordingly, it is presumed that a favorable sintered structure can be realized.

[0028] When the base material is a paper base material including a fiber layer, the conductive paste may contain a thermosetting resin. It is considered that the cured product of the thermosetting resin can improve the dimensional stability of the paper base material and enhance the adhesion between the paper base material and the conductive film, thereby improving the high-temperature and high-humidity reliability of the paper base material with a conductive film. That is, the thermosetting resin contained in the conductive paste can function as a modifier for the fiber layer of the paper base material and also as a binder for the conductive film.

[0029] Further, although the detailed mechanism is not clear, it is presumed as follows. In a high-temperature and high-humidity test, when environmental conditions of temperature and humidity fluctuate, the fiber layer in the paper base material undergoes dimensional change due to swelling or the like, which causes cracks in the conductive film on the paper base material and increases the resistance value. In contrast, the cured product of the thermosetting resin suppresses the dimensional change of the paper base material and enhances the adhesion between the paper base material and the conductive film, thereby suppressing the occurrence of the aforementioned cracks in the conductive film. As a result, it is presumed that the high-temperature and high-humidity reliability of the paper base material with a conductive film can be improved.

[0030] The conductive film-coated substrate of this embodiment can be used for various applications, including, for example, electronic devices, electromagnetic shielding sheets, and planar heating elements. Preferably, as an electronic device, it can be used in RFID media such as inlays (sometimes called inlets) and tags (RF tags). RFID media can be used in inlays, tags, labels, tickets, cards, and other media formed by processing inlays. The RFID media incorporates an RFID-compliant IC chip. Such RFID media have visibly printed information about the object to be attached, the object to be affixed, or the wearer, and the incorporated IC chip can store various information about the object. The inlay comprises a substrate, an electrical circuit (such as an antenna), and an IC chip, and at least a portion of the metal pattern included in the substrate and electrical circuit may be composed of the conductive film-coated substrate. The inlay may optionally include a meander pattern and / or a capacitor hat. In addition to the inlay, the tag may further include a sealing member to protect the IC chip. The inlay within the tag may be molded with a sealing material such as resin on the side where the IC chip is mounted or on both sides. Information (such as barcodes or text) may also be printed on the surface of the tag. In addition to the inlay, the label may further include adhesive for attachment to a substrate and printed information (such as barcodes or text).

[0031] The following describes the manufacturing method of the conductive film-coated substrate according to this embodiment, while detailing each component of the conductive film-coated substrate.

[0032] Figures 1(A) to 1(C) are cross-sectional views showing an example of a method for manufacturing a conductive film-coated substrate. Figure 2 is a schematic cross-sectional view showing an example of a conductive film-coated substrate 10. Figures 1(A) to 1(C) are cross-sectional views of the substrate in the thickness direction. In Figure 2, the Z direction means the same direction as the thickness direction. The Z direction may also be defined as the normal direction to the X-Y plane, when the plane of the surface 1A of the substrate 1 is defined as the X-Y plane.

[0033] An example of a method for manufacturing a conductive film-coated substrate according to the first embodiment is, when the substrate 1 is a resin substrate including a thermoplastic resin layer, a lamination step is to form a layer containing a plurality of conductive particles (conductive particle-containing layer 2) on the surface of the resin substrate (substrate 1) using a conductive paste containing a plurality of conductive particles, as shown in Figure 1(A); an impregnation step is to impregnate the conductive particle-containing layer 2 with a component X capable of removing the oxide film on the surface of the conductive particles, as shown in Figure 1(B); and a sintering step is to form 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).

[0034] Furthermore, an example of a method for manufacturing a conductive film-coated substrate according to the second embodiment is, when the substrate 1 is a paper substrate including a fiber layer, a lamination step is to form a layer containing a plurality of conductive particles (conductive particle-containing layer 2) on the surface of the paper substrate (substrate 1) using a conductive paste containing a plurality of conductive particles, as shown in Figure 1(A); and a sintering step is to form 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).

[0035] In the first and second embodiments, the conductive paste may contain a dispersant Y. In the first embodiment, in the penetration step, the dispersant Y is selected to be insoluble in component X so that at least a portion of the dispersant Y contained in the conductive particle-containing layer 2 remains undissolved.

[0036] The penetration process is preferably carried out in the first embodiment, but may or may not be carried out in the second embodiment.

[0037] In the lamination process, as shown in Figure 1(A), 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.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] In this way, a laminate comprising a base material 1 and a conductive particle-containing layer 2 can be obtained. Note that the lamination process is not limited to the embodiment shown in Figure 1(A), as long as a laminate comprising a base material 1 and a conductive particle-containing layer 2 can be obtained.

[0042] 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.

[0043] In the penetration process, as shown in Figure 1(B), component X capable of removing the oxide film on the surface of the conductive particles is permeated into the conductive particle-containing layer 2. Removing the oxide film on the surface of the conductive particles means, for example, immersing a metal oxide in component X and confirming the removal of the oxide film of the metal oxide. If a copper oxide film is used as the evaluation sample as the metal oxide, the removal of the oxide film may be confirmed by a change in the color of the evaluation sample.

[0044] The penetration step can be carried out between the lamination step described above and the sintering step described later. The method of supplying the liquid in which component X is dissolved or dispersed to at least the surface of the conductive particle-containing layer 2 in the penetration step 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 penetration of component X into the conductive particle-containing layer 2, it is preferable that in the penetration step, the 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.

[0045] 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. Preferably, one or more selected from the group consisting of carboxylic acids, phosphorus oxoacids, and hydrazine compounds can be used. 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 such as 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). As the liquid containing component X, water in which component X is dissolved or dispersed is preferred. 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.

[0046] 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.

[0047] It is presumed that by performing an oxide film removal treatment using component X, which is capable of removing the oxide film on the surface of conductive particles, it is possible to improve the adhesion between the sintered body (conductive film) of conductive particles and the substrate while suppressing the increase in the resistance value of the conductive film.

[0048] Although the detailed mechanism is not clear, it is thought to be as follows: When component X is brought into contact with the copper powder, the oxide film on the surface of the copper particles contained in the copper powder is removed. At this time, component X remains on the copper surface in a state in which it has reacted with the copper to form a compound. During the sintering process, it is thought that at least a portion of the copper compound of component X is thermally decomposed, forming a clean surface on the copper particle surface. This makes it easier for the parts where the clean surfaces come into contact to fuse (sinter), thus enabling a reduction in resistance. Furthermore, heating and pressing (hot pressing) can be used to promote the fusion at the parts where the clean surfaces come into contact.

[0049] Here, the following methods can be used to detect the copper compounds of component X remaining on the surface of the sintered body after the sintering process. Examples of these methods include gas chromatography-mass spectrometry (GC-MS), time-of-flight secondary ion mass spectrometry (TOF-SIMS), and XANES measurement using synchrotron radiation. Even at the temperature during the sintering process, some of the copper compounds of component X may remain without thermal decomposition. An example of a copper compound of component X is the copper formate complex compound obtained when formic acid treatment is performed. One or more types of copper formate complex compounds may be present, and it is presumed that some of them begin to decompose at a low temperature of about 110°C. It should be noted that some of the copper compounds of component X, such as the copper formate complex compound, may not decompose at 200°C.

[0050] 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.

[0051] 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.

[0052] <Substrate> The substrate 1 may be a resin substrate containing a thermoplastic resin layer, or a paper substrate containing a fiber layer. A preferred embodiment of the substrate 1 is a resin substrate containing a thermoplastic resin layer.

[0053] As the resin substrate, a resin substrate containing a thermoplastic resin layer satisfying a thermal shrinkage rate of 1.0% or less in the MD direction and / or a difference in thermal shrinkage rates between the MD and TD directions |MD-TD| of 0.7% or less may be used. The MD direction refers to the machine direction, and the TD direction refers to the transverse direction perpendicular to the machine direction. The thermal shrinkage rate is measured in accordance with JIS C 2318 under the conditions of a predetermined temperature of 150°C for 30 minutes.

[0054] The upper limit of the thermal shrinkage rate in the MD direction of the thermoplastic resin layer at 150°C for 30 minutes is, for example, 1.0% or less, preferably 0.8% or less, and more preferably 0.5% or less. On the other hand, the lower limit of the thermal shrinkage rate in the MD direction is not particularly limited and may be 0% or 0.01% or more.

[0055] In the thermoplastic resin layer, the upper limit of the difference in thermal shrinkage rates between the MD direction and the TD direction |MD-TD| at 150°C for 30 minutes is, for example, 0.7% or less, preferably 0.6% or less, and more preferably 0.4% or less. On the other hand, the lower limit of the difference in thermal shrinkage rates |MD-TD| is not particularly limited and may be 0%, or 0.01% or more.

[0056] Methods for reducing the thermal shrinkage of the thermoplastic resin layer include selecting a material with a high heat resistance temperature and using a stretched film. The thermoplastic resin layer may preferably be composed of a biaxially oriented film. Furthermore, thermal shrinkage can also be reduced by making at least a portion of the surface of the thermoplastic resin layer amorphous (non-crystalline).

[0057] The lower limit of the heat resistance temperature of the thermoplastic resin layer is, for example, 80°C or higher, preferably 90°C or higher, and more preferably 100°C or higher. On the other hand, the upper limit of the heat resistance temperature of the thermoplastic resin layer is, for example, 250°C or lower, preferably 220°C or lower, and more preferably 200°C or lower. By using a thermoplastic resin layer having a heat resistance temperature of the lower limit or higher, it is possible to suppress thermal deformation of the entire resin substrate due to the heating and pressurizing treatment in the sintering process. By using a thermoplastic resin layer having a heat resistance temperature of the upper limit or lower, surface modification can be promoted. The general heat resistance temperature is calculated by placing the product in a machine and raising the temperature by 10°C starting from 50°C, measuring the temperature at which an abnormality (distortion, deformation, discoloration, change in functionality, etc.) occurs in the product, and subtracting 10°C from the temperature at which such an abnormality occurs. In this specification, it is preferable to use the heat resistance temperature with distortion and deformation as indicators of abnormalities.

[0058] In another embodiment, the manufacturing method of this embodiment may include a surface modification step in which, when the base material 1 is a resin base material including a thermoplastic resin layer, at least a portion of the surface side of the thermoplastic resin layer of the base material 1 is softened or melted by energy irradiation such as a xenon flash.

[0059] A surface modification region can be formed by irradiating the surface 1A of the thermoplastic resin layer with a xenon flash, etc. In the surface modification step after the lamination step in which the conductive particle-containing layer 2 is provided on the substrate 1, it is preferable to irradiate with a xenon flash from the back surface 1B side, which is opposite to the surface 1A side. Alternatively, when irradiating from the back surface 1B, the xenon flash may be irradiated through the substrate 1. The conductive particles contained in the conductive particle-containing layer 2 can suppress efficiency reduction due to light diffusion, etc., and can also suppress unintended sintering of conductive particles together.

[0060] The resin substrate may be composed of a thermoplastic resin layer having a surface-modified region in which at least a portion of the surface 1A is softened or melted, or it may be composed of a thermoplastic resin layer in which a heat-softening coating layer is laminated on at least a portion of the surface 1A.

[0061] Examples of energy sources include broadband waves from xenon flash lamps, LEDs, halogen lamps, metal halide lamps, and other UV lamps, as well as YAG lasers and CO2 lasers. ２ While there are various types of narrowband waves (single waves) such as lasers and semiconductor lasers, it is preferable to use xenon flash, which is a pulsed irradiation of broadband waves. By using broadband waves, surface irradiation becomes possible, and variations in the degree of surface modification in the in-plane direction of surface 1A can be suppressed. By using pulsed light emission such as xenon flash lamps, the thermal effects are more easily localized compared to continuous light emission such as halogen lamps and metal halide lamps, making it easier to control surface modification. In addition, by using pulsed light, copper particles near the resin are selectively heated, contributing to the surface modification of the resin. With continuous light, the entire copper particle film is heated, which can lead to oxidation of copper and be unfavorable for subsequent sintering.

[0062] In the surface modification process, the energy of the xenon flash is, for example, 10 to 5000 J, preferably 20 to 2500 J, and more preferably 50 to 2000 J.

[0063] Specifically, the surface modification step may involve the xenon flash described above, which may be applied to the dried film of the conductive particle-containing layer 2. This suppresses the occurrence of damage to the conductive particle-containing layer 2 due to sudden boiling of the solvent caused by xenon flash irradiation before drying. It also suppresses inhibition of modification of the thermoplastic resin layer. The dried film of the conductive particle-containing layer 2 is obtained by performing a heat treatment to dry the conductive particle-containing layer 2 during the lamination process.

[0064] The thermoplastic resin contained in the thermoplastic resin layer includes either an amorphous thermoplastic resin or a crystalline thermoplastic resin, or both. In this specification, surface modification is defined as a change in state of a portion of the surface of the thermoplastic resin layer due to irradiation with a xenon flash. Typically, the amorphous thermoplastic resin softens, and the crystalline thermoplastic resin melts. A portion of the melted crystalline thermoplastic resin may become amorphous and remain in an amorphous state. The amorphous region formed near the surface 1A of the thermoplastic resin layer can be identified using a cross-sectional SEM image. For example, when the surface of a crystalline PET substrate is melted with a xenon flash, the melted surface portion reflects electron beams more easily than the unmelted interior and appears slightly white. That is, the amorphous region can be observed as a region that appears relatively white in a cross-sectional SEM image.

[0065] In a preferred embodiment, the following sintering step may be carried out using a substrate 1 in which an amorphous region is formed on at least a portion of the vicinity of the surface 1A of the thermoplastic resin layer. In the first embodiment, an amorphous region may be formed on the surface 1A of the thermoplastic resin layer in the surface modification step, and preferably, an amorphous layer having a predetermined depth may be formed from the surface 1A. In the second embodiment, a substrate 1 including a thermoplastic resin layer having an amorphous region on at least a portion of the surface 1A can be prepared, and a lamination step can be carried out using this.

[0066] In another preferred embodiment, the surface modification process may create a state in which at least a portion of a plurality of conductive particles are embedded near the surface 1A of the thermoplastic resin layer. At least a portion of the plurality of conductive particles may be a single particle, a sintered product of multiple particles, or both. Although the detailed mechanism is not clear, it is presumed that the softened or molten state of the surface 1A makes it easier for the conductive particles to penetrate into the surface layer, and, if necessary, in combination with subsequent pressurizing treatment, the embedded state is formed.

[0067] The thermoplastic resin layer serves as the base material for the resin substrate. In this case, the thickness of the thermoplastic resin layer may be 10% to 100% of the thickness of the resin substrate, and preferably 20% to 100%.

[0068] Examples of thermoplastic resin materials include polyesters such as PET (polyethylene terephthalate) and PEN (polyethylene naphthalate), polycarbonates, polyimides, and polyolefins such as polyethylene and polypropylene. Among these, polyesters, polycarbonates, and polyimides are preferred from the viewpoint of heat resistance. These may be used individually or in combination of two or more. Among the thermoplastic resin materials mentioned above, those with high permeability to xenon flash are preferred. This suppresses thermal deformation of the substrate 1 caused by absorbing xenon flash and generating heat.

[0069] A paper substrate containing a fiber layer may also 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 in the paper substrate. Known materials can be used for the release layer, such as silicone or non-silicone materials. Known materials can be used for the coating layer, such as thermoplastic resins like polyethylene and polypropylene, or inorganic particles like clay.

[0070] In Figure 1(A), 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, or it 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, the presence of a fiber layer in the area where the conductive paste is formed can improve the printability of fine lines.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] 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.

[0075] <Conductive Paste> An example of a conductive paste includes a plurality of conductive particles and a solvent. The conductive paste used in the first embodiment preferably includes a plurality of conductive particles, a dispersant Y, and a solvent. The conductive paste used in the second embodiment preferably includes a plurality of conductive particles, a thermosetting resin, and a solvent.

[0076] 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.

[0077] 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.

[0078] Multiple conductive particles may include at least one of atomized copper powder and electrolytic copper powder. Of these, the inclusion of electrolytic copper powder is more preferable. Atomized copper powder is produced, for example, by a method of spraying or impacting water or gas onto molten copper that has been melted at a high temperature. Atomized copper powder usually contains spherical particles and amorphous particles. Electrolytic copper powder is produced, for example, by a method of electrochemically depositing copper. Electrolytic copper powder usually contains dendritic particles. On the other hand, wet copper powder is copper powder produced by chemically reducing or substituting copper ions in an aqueous solution, but a relatively large amount of surface treatment agent is used to suppress the aggregation of copper powder. Among such copper powders, atomized copper powder and electrolytic copper powder are preferable because they have a smaller coating of surface treatment agent on the surface of the copper particles compared to wet copper powder.

[0079] Although the detailed mechanism is not clear, atomized copper powder and electrolytic copper powder have less surface treatment agent coating on the copper particle surface, which promotes the removal of oxide film by component X. Therefore, it is presumed that surface cleaning by thermal decomposition of the copper compound of component X is promoted, thereby enabling further reduction of resistance.

[0080] The conductive particles preferably contain dendritic metal particles, and more preferably contain dendritic copper particles. By using dendritic metal particles, adhesion to the thermoplastic resin layer can be further enhanced compared to spherical particles. It is presumed that dendritic metal particles are more likely to be embedded in the thermoplastic resin layer. However, the conductive particles may also contain metal particles of other shapes, such as spherical particles, in addition to dendritic metal particles. "Dendritic" usually refers to a shape having a main trunk that extends in one direction and at least one branch that branches off from the main trunk. Copper particles produced by electrolysis usually become dendrites due to the copper crystal formation mechanism. In the field of copper particles, dendritic copper particles produced by electrolysis are usually referred to as "dendritic copper particles." The meaning of the term "dendritic copper particles" in this specification is the same as the usual meaning of the term "dendritic copper particles" in the field of copper particles.

[0081] 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.

[0082] 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.

[0083] 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.

[0084] 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.

[0085] Dispersant Y may include polyolefin resins, polyvinyl alcohol resins (including polyvinyl acetal resins), polyalkylene glycol resins, polyvinylpyrrolidone resins, polyester resins, polyamide resins (resins containing at least one of a polyamide skeleton and a polyimide skeleton), (meth)acrylic resins, urethane resins, and epoxy resins, but preferably may also include hydrophobic dispersants such as polyester resins having a polyester skeleton. The hydrophobic dispersant may also include polymeric dispersants with a number average molecular weight of about 1,000 to 30,000 in terms of polystyrene. Dispersant Y may also include hydrophilic dispersants such as polyvinylpyrrolidone, polyethyleneimine, mono- or dialkylamines having 2 to 12 carbon atoms, tertiary amines, gum arabic, xanthan gum, polysaccharides, starch, gelatin, and agar. These may be used individually or in combination of two or more.

[0086] When using a hydrophilic component X, it is preferable that the conductive paste contains a hydrophobic dispersant Y, and vice versa. Being hydrophilic means that the molecule contains hydrophilic functional groups or skeletons, such as carboxyl groups, phosphate ester skeletons, or amino groups. Being hydrophobic means that the molecule contains hydrophobic functional groups or skeletons, such as aromatic rings (benzene rings) or long-chain hydrocarbon chains. Furthermore, at least one of component X and dispersant Y may contain both hydrophilic and hydrophobic functional groups or skeletons (for example, polar functional groups and aromatic rings). Here, when one component X and dispersant Y is hydrophobic and the other is hydrophilic, it means that they are relatively hydrophobic or relatively hydrophilic. For example, water solubility (g / 100mL) may be used as an indicator of the relative strength of hydrophobicity and hydrophilicity. By using a combination of a relatively hydrophobic substance and a relatively hydrophilic substance, the dissolution of the dispersant Y in component X during the manufacturing process can be suppressed.

[0087] Furthermore, the dispersant Y is preferably one that does not dissolve in component X. The property of not dissolving in component X can be indicated by the amount remaining after immersion of component X as follows. The amount of dispersant Y remaining after immersion in formic acid, which can be determined according to the measurement method below, is, for example, 90% by mass or more, preferably 95% by mass or more, and more preferably 99% by mass or more. (Measurement method) Dispersant Y is immersed in a 5% by mass aqueous solution of formic acid for 13 hours. When the weights of the dry dispersant Y before and after immersion are W0 (g) and W1 (g), respectively, the amount remaining after immersion in formic acid (mass%) is calculated from [W1 / W0] × 100%.

[0088] The content of dispersant Y in 100% by mass of the total nonvolatile components of the conductive paste is, for example, 0.5 to 15% by mass, preferably 1 to 10% by mass, and more preferably 2 to 5% by mass.

[0089] 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.

[0090] 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.

[0091] 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.

[0092] The conductive paste may, if necessary, contain other resin components and binders other than those exemplified above, as well as other dispersants for resin components, but may also substantially contain no resin components or other 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 other resin components include polyvinylpyrrolidone resin, phenoxy resin, and cellulose-based resin (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).

[0093] 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.

[0094] In the sintering process, as shown in Figure 1(C), multiple conductive particles in the conductive particle-containing layer 2 on the substrate 1 are sintered by heating and pressurizing to form a conductive film 3. Immediately before the sintering process, the conductive particle-containing layer 2 of the laminate includes unsintered portions in which multiple conductive particles have not yet been sintered.

[0095] 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 left and right 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.

[0096] 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.

[0097] 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.

[0098] 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 pressurization is performed using a roll press device, the heating and pressurization time per unit area tends to be shorter compared to heating and pressurization using a flat press device, so care should be taken to appropriately control the heating, pressurization, transport speed (roll bending speed), etc.

[0099] 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.

[0100] 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.

[0101] Furthermore, the manufacturing method of this embodiment may include other steps between the lamination process and the sintering process, and / or after the sintering process.

[0102] 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.

[0103] By the above manufacturing method, a conductive film-coated substrate 10 can be obtained.

[0104] Figures 2 and 3 are schematic cross-sectional views showing examples of conductive film-coated substrates 10, respectively. Figure 2 shows the conductive film-coated substrate 10 of the first embodiment, and Figure 3 shows the conductive film-coated substrate 10 of the second embodiment.

[0105] The conductive film-coated substrate 10 shown in Figures 2 and 3 comprises a substrate 1 and a conductive film 3 formed on at least a portion of the surface 1A of the substrate 1.

[0106] Multiple conductive particles in the conductive film 3 are sintered and connected to one another. Sintering means that, through heating and pressurizing, the particles fuse at the contact points on the metal surfaces between them, and multiple conductive particles are joined (connected) to form an integrated structure.

[0107] In one embodiment, the conductive film-coated substrate 10 may have an embedded structure in which at least a portion of the conductive film 3 is embedded in a recess 5 formed by the surface 1A of the substrate 1 being recessed in the thickness direction.

[0108] In a cross-section of the conductive film-coated 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, preferably 70% or more, of the total area, and the entire conductive film may be embedded in the recess 5. However, a portion of the conductive film 3 may have a raised portion in the thickness direction that is not embedded in the recess 5.

[0109] In one embodiment, if the base material 1 is a resin base material including a thermoplastic resin layer, the thermoplastic resin layer in the base material 1 may have a surface modification region in at least a portion near the surface 1A. The surface modification region may form a layer having a predetermined thickness in the depth direction from the surface 1A. This surface modification region is composed of a softened or melted and solidified portion of the surface 1A of the thermoplastic resin layer, i.e., a softened layer or a melted layer. In one preferred embodiment, the surface modification region may be configured to include part or all of the amorphous portion of the thermoplastic resin layer.

[0110] In one embodiment, when the base material 1 is a resin base material including a thermoplastic resin layer, an interface 9 may exist in at least a portion of the cross-section in the thickness direction of the conductive film-coated base material 10 between the thermoplastic resin layer of the base material 1 and the conductive film 3. At the interface 9, the thermoplastic resin layer other than the surface-modified region may be in contact with the conductive film 3, or the surface-modified region may be in contact with the conductive film 3.

[0111] In another embodiment, if the base material 1 is a paper base material including a fiber layer, as shown in Figure 3, at least a portion of the conductive film 3 having a conductive pattern and at least a portion of the fiber layer of the base material 1 may 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 base material 1 and hardens. That is, in the conductive film-coated base material 10, the cured thermosetting resin in the resin-impregnated region α is in the C stage state. In one other embodiment, the cured thermosetting resin contained in the conductive film 3 may exist in at least a portion of the conductive film 3 (e.g., the lower part), or it may exist throughout the entire conductive film 3 from the lower to the upper part. In one other embodiment, in the fiber layer where the conductive film 3 does not overlap in a top view, a resin-impregnated region α1 containing a cured thermosetting resin may exist on at least a portion of the side surface of the conductive pattern (conductive film 3). In one of the other embodiments, 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 another embodiment, 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.

[0112] Figure 4 is a top view of an example of a conductive film-coated substrate 10, viewed from the direction normal to the surface 1A of the substrate 1. As shown in Figure 4, 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 may be a fine line pattern or an antenna pattern. 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 4. When the plane of the surface 1A of the substrate 1 is defined as the X-Y plane, the X direction in Figure 4 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.

[0113] In Figure 4, 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 substrate 1 can be provided to such fine line portions 3A.

[0114] <Electronic Devices> Electronic devices can be manufactured using a substrate equipped with the conductive film of this embodiment (a substrate with a conductive film). 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.

[0115] 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.

[0116] 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.

[0117] 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.

[0118] 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.

[0119] 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.

[0120] <Preparation of conductive paste> (Conductive paste A1) Electrolytic copper powder (manufactured by Fukuda Metal Foil & Powder Industry Co., Ltd., D ５０82 parts by mass of (5 μm, dendritic), 2 parts by mass of dispersant Y (polyester resin), and 16 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 way, conductive paste A1, which is paste-like at 23°C, was obtained. Here, the amount of dispersant Y used, and as a reference example, phosphate ester (DISPERBY K-111), remaining after formic acid immersion was evaluated according to the following procedure. First, the dispersant immediately before use was weighed and placed in a glass container. The weight of the dispersant at this time was taken as W0 (g). Next, 1 mL of 5% by mass formic acid aqueous solution was weighed and placed in the glass container. Then, the dispersant was left standing at room temperature for 13 hours while immersed in the formic acid aqueous solution. Only the dispersant was transferred to another glass container and dried in a hot air drying oven at 120°C for 10 minutes, and the weight of the dried dispersant Y was measured. The weight of the dispersant at this time was denoted as W1 (g). Using the W0 and W1 obtained above, the amount of dispersant remaining after immersion in the formic acid aqueous solution was calculated from the formula [W1 / W0] × 100%. As a result, the amount remaining after immersion in the formic acid aqueous solution was 98% of the polyester resin used. On the other hand, the phosphate ester dissolved or dispersed completely immediately after being added to the 5% by mass formic acid aqueous solution, resulting in a cloudy liquid, and could not be transferred to another glass container. Therefore, the amount remaining was considered to be 0%. (Conductive paste A2) Conductive paste A2 was obtained in the same manner as conductive paste A1 above, except that the amount of electrolytic copper powder was changed to 81 parts by mass, 2 parts by mass of polyvinyl acetal resin was added as dispersant Y instead of 2 parts by mass of polyester resin, and the amount of organic solvent was changed to 17 parts by mass. At 23°C, conductive paste A2 was obtained.

[0121] (Conductive paste B1) Electrolytic copper powder (manufactured by Fukuda Metal Foil & Powder Industry Co., Ltd., D ５０73 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 compound. Then, this compound was stirred using a rotary-orbiting agitator. Conductive paste B1, which is paste-like at 23°C, was obtained in the same manner as conductive paste B1 above. (Conductive paste B2) Conductive paste B2, which is paste-like at 23°C, was obtained in the same manner as conductive paste B1 above, except that the amount of electrolytic copper powder was changed to 77 parts by mass, 0.3 parts by mass of polyvinylpyrrolidone resin was added as another resin component in place of 12 parts by mass of thermosetting resin (resol-type phenolic resin), and the amount of organic solvent was changed to 22.7 parts by mass. (Conductive Paste B3) Conductive paste B3 was obtained in the same manner as conductive paste B2, except that the amount of electrolytic copper powder was changed to 75 parts by mass, the amount of polyvinylpyrrolidone resin was changed to 4 parts by mass, and the amount of organic solvent was changed to 21 parts by mass. Conductive paste B3 was obtained in the same manner as conductive paste B1, except that the amount of electrolytic copper powder was changed to 81 parts by mass, phenoxy resin was added as another resin component in place of 12 parts by mass of thermosetting resin (resol-type phenolic resin), and the amount of organic solvent was changed to 16 parts by mass. Conductive paste B4 was obtained in the same manner as conductive paste B1, except that the amount of electrolytic copper powder was changed to 81 parts by mass, phenoxy resin was added as another resin component in place of 12 parts by mass, and organic solvent was changed to 16 parts by mass.

[0122] <Manufacturing of conductive film-coated substrates> [Example A1] (Printing process) The conductive paste A1 described above was screen printed onto the surface of the substrate to form a patterned coating (conductive particle-containing layer) and obtain a laminate. The printing process was carried out according to the following specific conditions. ・Substrate: Biaxially oriented PET film (thickness 50 μm, width 150 mm, heat resistance temperature 160°C) was used. ・Printing machine: Screen printing machine (Micro-Tec, Desk Top 38SA model) was used. ・Screen plate: A screen plate (325 mesh, mesh diameter 16 μm, emulsion thickness 40 μm) with a pattern having fine lines (aperture pattern corresponding to the antenna pattern shown in Figure 5) 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°.

[0123] (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.

[0124] (Surface modification process) After the drying process, the substrate, which did not have a patterned dried film formed on its back side, was irradiated with xenon flash using a xenon flash device (XENON Corporation, X-1100) under the conditions of applied voltage of 3000V, applied energy of 1300J, and irradiation time of 680μs.

[0125] (Immersion Process) After the surface modification process, the entire laminate was immersed in a formic acid aqueous solution (an aqueous solution containing formic acid as component X) for 10 seconds. Subsequently, the laminate was washed and drained.

[0126] (Sintering Process) After the penetration 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 laminated body and the film-like material. The laminated body was placed on a metal plate (30 mm x 20 mm) set on the lower plate of a flat press machine (manufactured by AS ONE Corporation, HC300-15K) 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 having a conductive film with the antenna pattern shown in Figure 5. ・Hot-pressing conditions: Heating temperature (pressing temperature): 140°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.

[0127] [Example A2] A conductive film-coated substrate was manufactured in the same manner as in Example A1, except that conductive paste A2 was used instead of conductive paste A1. [Example B1] A conductive film-coated substrate was manufactured in the same manner as in Example A1, except that conductive paste B1 was used instead of conductive paste A1, a paper substrate (coated paper manufactured by Oji Paper Co., Ltd., thickness 70 μm, width 150 mm) was used as the substrate in the printing process, the surface modification process and the penetration process were not performed, the sintering process was performed after the drying process, and the following conditions were adopted for the hot press in the sintering process: heating temperature (press temperature): 200°C, pressure: 83 MPa, time: 30 seconds. [Reference Examples B2 to B4] A conductive film-coated substrate was manufactured in the same manner as in Example B1, except that conductive pastes B2 to B4 were used instead of conductive paste B1, respectively.

[0128] [Comparative Example A1] A conductive film-coated substrate was manufactured in the same manner as in Example A1, except that the above penetration step was not performed, and the above sintering step was not performed after the above surface modification step, and the substrate was heated at 140°C for 5 minutes in a hot air circulating atmospheric oven.

[0129] [Comparative Example B1] A conductive film-coated substrate was manufactured in the same manner as in Example B1, except that after the drying step described above, the substrate was heated at 150°C for 5 minutes in a hot air circulating atmospheric oven without performing the sintering step described above.

[0130] <Observation of Cross-Sections> Samples of the conductive film-coated substrate, molded on both sides with epoxy resin, were cut using ion milling to expose the cross-section of the fine-line portion of the conductive pattern of the conductive film, perpendicular to the direction in which the conductive pattern extends. These cross-sections were photographed with a scanning electron microscope (SEM) to obtain cross-sectional images. In the cross-sectional images of Examples A1-A2 and Example B1, 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, in Examples A1-A2, the existence of a structure in which a portion of the conductive film was embedded in the PET layer of the substrate was confirmed, while in Example B1, the existence of a structure in which a portion of the conductive film was embedded in the fiber layer of the substrate was confirmed. As a representative example, a cross-sectional SEM image of Example A1 is shown in Figure 6.

[0131] <Measurement of Resistance After Reliability Testing> After performing the following test X as a reliability test on the obtained conductive film substrate, the total resistance (Ω) of the antenna pattern (total length 1230 mm) shown in Figure 5 was measured using a four-terminal resistance meter. Specifically, the "resistance between measurement points P1 and P2" and the "resistance between measurement points P3 and P4" shown in Figure 5 were measured, and the total resistance (Ω) of the antenna pattern was calculated from the sum of the "resistance between measurement points P1 and P2" and the "resistance between measurement points P3 and P4". In addition, the resistance of the fine line portion at measurement point P2, which is close to the area where the IC chip is to be mounted, was measured using a four-terminal resistance meter, and the film thickness was measured using a film thickness gauge. The resistivity ρ was calculated using the formula ρ = R × W × t / L, where L is the length of the measurement section, W is the width of the conductive pattern in that section, t is the film thickness of the conductive pattern in that section, and R is the resistance value. Note that the width W and film thickness t were calculated using the average value of multiple measurements taken at the measurement location. • Test X: A high-temperature and high-humidity test was conducted using an environmental testing machine (ESPEC SH-642) at 85°C and 85% RH for 168 hours.

[0132] The resistance values ​​of each example after Test X (high temperature and high humidity test) were as follows: Example A1: 25Ω Example B1: 52Ω Comparative Example A1: Over 100Ω Comparative Example B1: Over 100Ω Furthermore, the resistivity of each example after Test X (high temperature and high humidity test) was as follows: Example A1: 1.5 × 10 －５ Ω・cm Example B1: 3.2 × 10 －５ Ω・cm Comparative example A1: 6.1×10 －５ Ω・cm Note that the resistivity of Comparative Example B1 has not yet been determined.

[0133] Furthermore, for Examples A1, B1, and Reference Examples B2 to B4, the initial resistance values ​​before Test X (high temperature and high humidity test) were measured using the method described above. Example A1: 23Ω Example B1: 37Ω Reference Example B2: 21Ω Reference Example B3: 41Ω Reference Example B4: 27Ω For Reference Examples B2 to B4, as a screening evaluation, the resistance values ​​after holding at 85°C, 85% RH for 3 hours may also be measured.

[0134] Furthermore, the resistance of the entire antenna pattern after performing the following test Y was determined using the same resistance measurement method as in test X above. • Test Y: A thermal shock test using a thermal shock device (TSE-12-A, manufactured by ESPEC). Each cycle consists of holding the temperature from -40°C to 85°C for 30 minutes, for a total of 200 cycles.

[0135] The resistance values ​​for each example after Test Y (thermal shock test) were as follows: Example A1: 24Ω Example B1: 42Ω

[0136] Furthermore, the resistance of the entire antenna pattern after performing the following test Z was determined using the same resistance measurement method as in test X above. • Test Z: A bending test using a bending test machine (DMLHP-CS, manufactured by Yuasa System Equipment Co., Ltd.), bending speed: 30 times / min, bending radius R = 15 mm, angle: 45°, bending 100 times each on the front and back sides. However, in test Z, as shown in Figure 5, the bending point was defined as the straight line C passing between measurement points P2 and P4, where the IC chip is mounted.

[0137] The resistance values ​​for each example after Test Z (bending test) were as follows: Example A1: 24Ω Example B1: 69Ω In addition, in Example A2, the initial resistance value before Test Z was 45Ω, while the resistance value after Test Z was 84Ω.

[0138] <Communication Characteristics (Communication Distance Before and After Reliability Testing)> Tag samples were prepared by sandwiching the obtained conductive film-coated substrate (dry inlay) between adhesive substrates and laminating them. The communication distance (mm) was measured using an RFID reader with the obtained tag samples. The communication distance before and after the reliability test were measured, and the decrease rate (%) of the communication distance was calculated from [(Communication distance before test - Communication distance after test) / Communication distance before test]. For the reliability test, tests X, Y, and Z were performed, and the decrease rate of the communication distance for each tag sample was determined for each test. The decrease rate of the communication distance for Example A1 was smaller than that for Comparative Example A1 in all tests X, Y, and Z. Also, the decrease rate of the communication distance for Example B1 was smaller than that for Comparative Example B1 in all tests X, Y, and Z. Furthermore, the rate of decrease in communication distance in Example A1 was smaller than that in Example B1 in all of the tests X, Y, and Z.

[0139] The conductive film-coated substrates of Examples A1 and B1 exhibited better communication characteristics after reliability tests such as high-temperature and high-humidity tests compared to Comparative Examples A1 and B1, respectively, demonstrating their suitability as RFID media.

[0140] This application claims priority based on Japanese Patent Application No. 2025-056745, filed on 28 March 2025, and incorporates all of its disclosures herein.

[0141] 1. Substrate 1A Front surface 1B Back surface 2. Conductive particle-containing layer 3. Conductive film 3A Line portion 5. Recess 9. Interface 10. Substrate with conductive film

Claims

1. An RFID medium comprising a substrate and a conductive film having a conductive pattern provided on at least a portion of the surface of the substrate, wherein the conductive film comprises a sintered body of a plurality of conductive particles, and the RFID medium is one of the following: an inlay intermediate without an IC chip electrically connected to the conductive film, an inlay having an IC chip electrically connected to the conductive film, or an IC chip electrically connected to the conductive film, and a tag having a laminated structure on the IC chip, and when the following reliability tests are performed on the sample described below, the resistance value of the conductive pattern after at least one of the following tests X, Y, and Z satisfies the condition that the resistivity of the conductive pattern is 100 Ω or less, or the resistivity of the conductive pattern is 6.0 × 10 －５ RFID medium satisfying Ω·cm or less. (Sample) If the RFID medium is the inlay intermediate, the inlay intermediate shall be used as the sample. If the RFID medium is the inlay, the sample shall be the inlay with the IC chip removed. If the RFID medium is the tag, the sample shall be the tag with the IC chip exposed and then removed. (Conditions for reliability testing) Test X: High temperature and high humidity test held at 85°C and 85% RH for 168 hours. Test Y: Thermal shock test performed 200 cycles, with each cycle being 30 minutes from -40°C to 85°C. Test Z: Bending resistance test performed with a bending speed of 30 times / min, bending radius R = 15 mm, and angle: 45°, bending 100 times each on the front and back sides.

2. An RFID medium comprising a substrate with a conductive film, wherein the conductive film comprises a substrate and a conductive film having a conductive pattern provided on at least a portion of the surface of the substrate, wherein the conductive film comprises a sintered body of a plurality of conductive particles, and the substrate with the conductive film is an inlay intermediate that does not have an IC chip electrically connected to the conductive film, and when the inlay intermediate is used as a sample and the following reliability tests are performed on the sample, the resistance value of the conductive pattern after at least one of the following tests X, Y, and Z satisfies the condition that the resistivity of the conductive pattern is 100 Ω or less, or the resistivity of the conductive pattern is 6.0 × 10⁻⁶. －５ RFID media that meets the requirement of Ω·cm or less. (Conditions for reliability testing) Test X: High temperature and high humidity test held at 85°C and 85% RH for 168 hours. Test Y: Thermal shock test performed for a total of 200 cycles, with each cycle being 30 minutes from -40°C to 85°C. Test Z: Bending resistance test performed with a bending speed of 30 times / min, bending radius R = 15 mm, and angle of 45°, bending 100 times each on the front and back sides.

3. An RFID medium according to claim 1 or 2, wherein the total length of the conductive pattern is 300 mm or more and 4000 mm or less, the thickness of the conductive pattern is 3 μm or more and 50 μm or less, and the width of the conductive pattern is 30 μm or more and 5000 μm or less.

4. An RFID medium according to claim 1 or 2, wherein the particles contained in the conductive particles include dendritic particles.

5. The RFID medium according to claim 1 or 2, wherein the particle diameter D at the point where the cumulative volume from the smallest particle side reaches 50% in the volume-based cumulative distribution of particle diameters obtained when the particle diameter of the conductive particles is measured by laser diffraction scattering is the particle diameter D ５０ However, the RFID medium has a thickness of 0.5 μm or more and 100 μm or less.

6. An RFID medium according to claim 1 or 2, wherein the conductive particles include copper.

7. An RFID medium according to claim 1 or 2, wherein at least a portion of the conductive film is embedded in the substrate.

8. An RFID medium according to claim 1 or 2, wherein the plurality of conductive particles include at least one of atomized copper powder and electrolytic copper powder.

9. An RFID medium according to claim 1 or 2, wherein the substrate is a resin substrate containing a thermoplastic resin layer.

10. An RFID medium according to claim 9, wherein the conductive film comprises a sintered body of a plurality of conductive particles treated with one or more selected from the group consisting of carboxylic acids, phosphorus oxoacids, and hydrazine compounds.

11. An RFID medium according to claim 9, wherein the conductive film contains a dispersant Y.

12. An RFID medium according to claim 9, wherein the thermal shrinkage rate in the MD direction of the thermoplastic resin layer under the conditions of 150°C for 30 minutes, as measured in accordance with JIS C 2318, is 1.0% or less, and / or the difference in thermal shrinkage rates |MD-TD| between the MD direction and the TD direction of the thermoplastic resin layer under the conditions of 150°C for 30 minutes, as measured in accordance with JIS C 2318, is 0.7% or less.

13. An RFID medium according to claim 9, wherein the thermoplastic resin layer comprises one or more selected from the group consisting of polyester, polyolefin, polycarbonate, and polyimide.

14. An RFID medium according to claim 9, wherein the heat resistance temperature of the thermoplastic resin layer is 80°C or higher.

15. An RFID medium according to claim 1 or 2, wherein the substrate is a paper substrate containing a fiber layer.

16. An RFID medium according to claim 15, wherein at least a portion of the conductive film and at least a portion of the fiber layer contain a cured product of a thermosetting resin.

17. An RFID medium according to claim 15, wherein the substrate is 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.

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