Conductive film-equipped substrate, electronic device, electromagnetic wave shielding sheet, planar heating element, and method for manufacturing conductive film-equipped substrate

Abstract

This conductive film-equipped substrate (10) comprises: a substrate (1); and a conductive film (3) that is provided on at least a part of a surface (1A) of the substrate (1). The conductive film (3) contains: a sintered body of a plurality of conductive particles that have been treated with a component X capable of removing an oxide film on the surfaces of the conductive particles; and a dispersant Y. One of the component X and the dispersant Y has hydrophobicity, and the other has hydrophilicity.

Description

A conductive film-coated substrate, an electronic device, an electromagnetic wave shielding sheet, a planar heating element, and a method for manufacturing a conductive film-coated substrate.

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

[0002] Studies have been conducted to date on forming conductive patterns using conductive pastes. Patent documents 1 and 2 are examples of this type of technology. Patent document 1 describes a conductive paste containing copper powder, polyester resin, and a solvent. Patent document 2 describes a dispersion of metal nanoparticles containing metal nanoparticles and a dispersant having a polyester skeleton.

[0003] Japanese Patent Publication No. 5723283, Japanese Unexamined Patent Publication No. 2020-035718

[0004] Dispersants can adsorb to metal particles and suppress the aggregation of fine particles, but using a large amount of dispersant may hinder the improvement of conductivity in the sintered metal particle body. The inventors have found that when a conductive paste containing a dispersant is used, there is a trade-off relationship between the adhesion between the conductive film and the substrate and the reduction of the conductive film's resistance. In other words, the use of a dispersant can improve the adhesion between the conductive film and the substrate, but conversely, it may increase the resistance of the conductive film.

[0005] Based on the above circumstances, the inventors investigated whether the above trade-off could be resolved by performing an oxide film removal treatment on the conductive particles before the sintering process. They found that depending on the combination of component X and dispersant Y used in the oxide film removal treatment, the dispersant Y may dissolve, and the effect of improving adhesion by the dispersant Y may not be obtained. As a result of diligent investigation based on this finding, they discovered that by performing an oxide film removal treatment and adopting a combination of component X and dispersant Y that suppresses the dissolution of the dispersant Y, it is possible to improve the adhesion between the conductive film and the substrate, as well as reduce the resistance of the conductive film, thus completing the present invention.

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

[0007] 1. A conductive film-coated substrate comprising a substrate and a conductive film 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 treated with a component X capable of removing the oxide film on the surface of the conductive particles, and a dispersant Y, wherein one of the component X and the dispersant Y is hydrophobic and the other is hydrophilic. 2. A conductive film-coated substrate comprising a substrate and a conductive film 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 treated with one or more selected from the group consisting of carboxylic acids, phosphorus oxoacids, and hydrazine compounds, and a hydrophobic dispersant Y. 3. A conductive film-coated substrate according to 1. or 2., wherein the dispersant Y satisfies the requirement of 90% by mass or more of the remaining amount after formic acid immersion, as determined according to the following measurement method. (Measurement method) Immerse the dispersant Y in a 5% by mass aqueous solution of formic acid for 13 hours. When the weights of the dispersant Y in the dry state before and after immersion are W0 (g) and W1 (g), respectively, the remaining amount (mass%) after formic acid immersion is calculated from [W1 / W0] × 100%. 4. A conductive film-coated substrate according to any one of 1 to 3, wherein the dispersant Y contains a resin having a polyester skeleton. 5. A conductive film-coated substrate according to any one of 1 to 4, wherein the conductive film contains a sintered body of a plurality of conductive particles treated with a carboxylic acid, and the carboxylic acid contains a carboxylic acid with 7 or fewer carbon atoms in the molecule. 6. A conductive film-coated substrate according to any one of 1 to 5, wherein the substrate contains a thermoplastic resin layer. 7. 6. A conductive film-coated substrate as described above, 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.8. A conductive film-coated substrate according to 6. or 7. wherein the thermoplastic resin layer comprises one or more selected from the group consisting of polyester, polyolefin, polycarbonate, and polyimide. 9. A conductive film-coated substrate according to any one of 1. to 8. wherein the particles contained in the conductive particles include dendritic particles. 10. A conductive film-coated substrate according to any one of 1. to 9. wherein the particle diameter D is the point in the volume-based cumulative distribution of particle diameters obtained when the particle diameter of the conductive particles is measured by laser diffraction scattering, where the cumulative volume from the small particle side reaches 50%. ５０ A conductive film-coated substrate having a thickness of 0.5 μm or more and 100 μm or less. 11. A conductive film-coated substrate according to any one of 1 to 10, wherein the conductive particles contain copper. 12. A conductive film-coated substrate according to any one of 1 to 11, wherein at least a portion of the conductive film is embedded within the substrate. 13. An electronic device comprising a conductive film-coated substrate according to any one of 1 to 12. 14. An electronic device according to 13, wherein the electronic device is an RF tag. 15. An electromagnetic wave shielding sheet comprising a conductive film-coated substrate according to any one of 1 to 12. 16. A planar heating element comprising a conductive film-coated substrate according to any one of 1 to 12. 17. A method for manufacturing a substrate with a conductive film, comprising the steps of: forming a conductive particle-containing layer on at least a portion of the surface of a substrate using a conductive paste containing a plurality of conductive particles and a dispersant Y; impregnating the conductive particle-containing layer with a component X capable of removing the oxide film on the surface of the conductive particles; and sintering the plurality of conductive particles to form a conductive film, wherein in the impregnation step, the dispersant Y contained in the conductive particle-containing layer remains undissolved.

[0008] According to the present invention, a conductive film-coated substrate having a conductive film with low resistance and good adhesion is provided, as well as an electronic device using the same, an electromagnetic wave shielding sheet, a planar heating element, and a method for manufacturing the conductive film-coated substrate.

[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 top view showing an example of a conductive film-coated substrate according to this embodiment.

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

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

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

[0013] The conductive film-coated substrate of the first embodiment comprises a substrate and a conductive film 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 treated with component X capable of removing the oxide film on the surface of the conductive particles and a dispersant Y, wherein one of component X and the dispersant Y is hydrophobic and the other is hydrophilic.

[0014] The conductive film-coated substrate of the second embodiment comprises a substrate and a conductive film 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 treated with one or more selected from the group consisting of carboxylic acids, phosphorus oxoacids, and hydrazine compounds, and a hydrophobic dispersant Y.

[0015] According to the inventors' findings, it has been found that by using a conductive paste containing a dispersant Y and combining it with an oxide film removal treatment using component X, it is possible to improve the adhesion between the sintered body of conductive particles (conductive film) and the substrate while suppressing the increase in the resistance value of the conductive film. By using a combination of a hydrophobic dispersant Y and a hydrophilic component X, or by using a combination of a hydrophilic dispersant Y and a hydrophobic component X, it is possible to leave the dispersant Y almost undissolved by component X.

[0016] Although the detailed mechanism is not clear, it can be understood that the dispersant Y effectively disperses the conductive particles and, because it is not dissolved by component X, maintains its dispersed state until just before sintering, allowing the conductive particles to be sintered together. After sintering, it remains in the sintered body as a binder, and it is presumed that this enables the realization of a desirable sintered structure.

[0017] Component X can be any substance capable of removing copper oxide films. Specific examples of hydrophilic component X that is soluble in water include carboxylic acids, phosphorus oxoacids, and hydrazine compounds.

[0018] Although the detailed mechanism is not clear, it is presumed 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.

[0019] 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.

[0020] Furthermore, the above-described pressurized heating treatment may form an embedded structure in which at least a portion of the conductive film is embedded in a recess formed in the substrate. Since the embedded structure functions as an anchor, it is presumed that delamination between the conductive film and the substrate is suppressed, and the physical adhesion between the two is increased.

[0021] 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).

[0022] 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.

[0023] 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.

[0024] An example of a method for manufacturing a conductive film-coated substrate according to the first embodiment includes, as shown in Figure 1(A), a lamination step of forming a layer containing a plurality of conductive particles (conductive particle-containing layer 2) on the surface of a substrate 1 using a conductive paste containing a plurality of conductive particles and a dispersant Y; as shown in Figure 1(B), an impregnation step of impregnating the conductive particle-containing layer 2 with a component X capable of removing the oxide film on the surface of the conductive particles; and as shown in Figure 1(C), a sintering step of sintering the plurality of conductive particles in the conductive particle-containing layer 2 by heating and pressurizing treatment to form a conductive film 3. In the impregnation step, the dispersant contained in the conductive particle-containing layer 2 remains almost undissolved.

[0025] In the second embodiment, the method for manufacturing a conductive film-coated substrate involves using one or more components selected from the group consisting of carboxylic acids, phosphorus oxoacids, and hydrazine compounds as component X in the penetration step described above.

[0026] 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.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] Component X may include one or more selected from the group consisting of carboxylic acids, phosphorus oxoacids, hydrazine compounds, inorganic acids, phenols, and other reducing substances. Examples of carboxylic acids include citric acid, formic acid, acetic acid, malonic acid, malic acid, tartaric acid, ascorbic acid, succinic acid, fumaric acid, and propionic acid. However, it is not limited to these, and organic acids other than carboxylic acids may be used. Examples of phosphorus oxoacids include phosphinic acid, phosphonic acid, phosphorous acid, phosphoric acid, diphosphate, triphosphate, and metatriphosphate. Examples of hydrazine compounds include hydrazine, hydrazine derivatives such as hydrazine salts including monohydrazine hydrochloride, hydrazine dihydrazine hydrochloride, monohydrazine hydrobromide, and hydrazine sulfate, phenylhydrazine, and others -NH-NH ２Examples of compounds with a specific structure include those mentioned above. Inorganic acids include, for example, hydrochloric acid, nitric acid, sulfuric acid, and hydrobromic acid. Phenols include, for example, pyrogallol, orthoaminophenol, and hydroquinone. Other reducing substances include, for example, pyrazolidone compounds. Phenidone is an example of a pyrazolidone compound. These may be used individually or in combination of two or more. Among these, component X can be a compound with a small pKa in water. Specifically, a compound with a pKa of -5.0 to 5.0 in water is preferred as component X, and a compound with a pKa of -4.0 to 4.5 is more preferred as component X. Incidentally, if component X is a polybasic acid, it is preferable that the smallest pKa among multiple pKa values ​​is within the above range. The pKa value here can be the value at room temperature (e.g., 25°C). The liquid containing component X is preferably water in which component X is dissolved or dispersed. Using water is preferable from the standpoint of reducing environmental impact and ensuring process safety (non-flammable). Of course, organic solvents in which component X is dissolved or dispersed can also be used. The concentration of component X in the liquid is, for example, 0.05 to 50 mol / L, preferably 0.1 to 40 mol / L, more preferably 0.1 to 30 mol / L, even more preferably 0.1 to 10 mol / L, and particularly preferably 0.15 to 5.0 mol / L. Of course, a liquid containing component X at a lower concentration than those shown herein may be used, or a liquid containing component X at a higher concentration than those shown herein (e.g., saturation concentration) may be used.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] <Substrate> Substrate 1 may be a resin substrate containing a thermoplastic resin layer, or a paper substrate containing a fiber layer. The preferred form of substrate 1 is a resin substrate containing a thermoplastic resin layer.

[0039] As the resin base material, a resin base material including a thermoplastic resin layer that satisfies a requirement that the heat shrinkage rate in the MD direction is 1.0% or less and / or the difference in heat shrinkage rate between the MD direction and the TD direction |MD-TD| is 0.7% or less may be used. The MD direction refers to the Machine Direction, and the TD direction refers to the Transverse Direction orthogonal to the machine direction. The heat shrinkage rate is measured in accordance with JIS C 2318 under the conditions of a predetermined temperature of 150°C and a duration of 30 minutes.

[0040] In the thermoplastic resin layer, the upper limit of the heat shrinkage rate in the MD direction at 150°C after 30 minutes is, for example, 1.0% or less, preferably 0.8% or less, more preferably 0.5% or less. On the other hand, the lower limit of the heat shrinkage rate in the MD direction is not particularly limited, and may be 0%, or may be 0.01% or more.

[0041] In the thermoplastic resin layer, the upper limit of the difference in heat shrinkage rate between the MD direction and the TD direction |MD-TD| at 150°C after 30 minutes is, for example, 0.7% or less, preferably 0.6% or less, more preferably 0.4% or less. On the other hand, the lower limit of the heat shrinkage rate difference |MD-TD| is not particularly limited, and may be 0%, or may be 0.01% or more.

[0042] Methods for reducing the heat shrinkage of the thermoplastic resin layer include selecting a material with a high heat resistance temperature, using a stretched film, and the like. The thermoplastic resin layer may preferably be composed of a biaxially stretched film. Furthermore, heat shrinkage can also be reduced by making at least a part of the surface of the thermoplastic resin layer amorphous (non-crystalline).

[0043] The lower limit of the heat resistance temperature in the thermoplastic resin layer is, for example, 80°C or higher, preferably 90°C or higher, more preferably 100°C or higher. On the other hand, the upper limit of the heat resistance temperature in the thermoplastic resin layer is, for example, 250°C or lower, preferably 220°C or lower, more preferably 200°C or lower. By using a thermoplastic resin layer having a heat resistance temperature equal to or higher than the above lower limit, it is possible to suppress thermal deformation of the entire resin base material caused by the heating and pressing treatment in the sintering step. By using a thermoplastic resin layer having a heat resistance temperature equal to or lower than the above upper limit, surface modification can be promoted. General heat resistance temperature is calculated as follows: when a product is placed in a machine and the temperature is increased by 10°C starting from 50°C, the temperature at which an abnormality (distortion, deformation, discoloration, change in functionality, etc.) occurs in the product is measured, and the temperature obtained by subtracting 10°C from the temperature at which the abnormality occurs in the product is defined as the heat resistance temperature. In the present specification, it is preferable to use a heat resistance temperature that uses distortion and deformation as indicators of abnormality.

[0044] In another aspect, when the base material 1 is a resin base material including a thermoplastic resin layer, the production method of the present embodiment may include a surface modification step of softening or melting at least a part of the surface side of the thermoplastic resin layer of the base material 1 by energy irradiation such as xenon flash.

[0045] A surface modified region can be formed by a method such as irradiating a xenon flash onto the surface 1A of the thermoplastic resin layer. In the surface modification step after the laminating step in which the conductive particle-containing layer 2 is provided on the base material 1, it is preferable to irradiate the xenon flash from the back surface 1B side opposite to the front surface 1A side. Furthermore, when irradiating from the back surface 1B, the xenon flash may be irradiated after passing through the base material 1. The conductive particles contained in the conductive particle-containing layer 2 can suppress efficiency reduction caused by factors such as light diffusion, and can also suppress unintended sintering between conductive particles.

[0046] The resin base material may be composed of a thermoplastic resin layer having a surface modified region in which at least a part of the surface 1A is softened or melted, or may be composed of a thermoplastic resin layer in which a heat-softened coating layer is laminated on at least a part of the surface 1A.

[0047] 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.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] 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%.

[0054] 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.

[0055] 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.

[0056] In Figure 1(B), the surface 1A of the substrate where the conductive paste is formed may consist of a fiber layer, or it may consist of a mixture of a fiber layer and a release layer and / or a coating layer. For example, when a paper substrate having a release layer and / or a coating layer on one side is used, the surface 1A of the substrate 1 may have a portion of the underlying fiber layer exposed from the release layer or coating layer, 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.

[0057] 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.

[0058] 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.

[0059] 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.

[0060] 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.

[0061] <Conductive Paste> An example of a conductive paste includes multiple conductive particles, a dispersant Y, and a solvent.

[0062] 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.

[0063] 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.

[0064] 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.

[0065] 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.

[0066] 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.

[0067] 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.

[0068] 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.

[0069] The conductive paste contains a dispersant Y. When a hydrophilic component X is used, the conductive paste contains a hydrophobic dispersant Y, and when a hydrophobic component X is used, the conductive paste contains a hydrophilic dispersant Y. 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, a polar functional group and an aromatic ring). 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 into component X during the manufacturing process can be suppressed. In this specification, hydrophilicity / hydrophobicity is used as a concept to indicate the ability of the dispersant Y to dissolve in component X.

[0070] 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%.

[0071] Dispersant Y can include polyolefin resins, polyvinyl alcohol 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 it may also include hydrophobic dispersants such as polyester resins having a polyester skeleton. The hydrophobic dispersant may also include polymer 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.

[0072] 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.

[0073] 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.

[0074] The conductive paste may, if necessary, contain other resin components such as other resins and binders, as well as other dispersants for resin components, in addition to the components exemplified above, but may also substantially not contain other resin components and other dispersants. If other 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 epoxy resin, polyvinyl acetal, cellulosic resin (e.g., ethylcellulose), and phenolic resin. Here, "substantially not containing" other resins or binders means either not containing any other resins or binders at all, or containing other resins or binders, but in such small amounts that the effects expected from the use of other resins or binders (specifically described 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).

[0075] 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.

[0076] 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 pressing 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. In the sintering process, multiple conductive particles contained in the conductive particle-containing layer 2 are sintered by heating and pressing to form a conductive film 3.

[0077] 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.

[0078] In addition to a flat press device, heating and pressurization can also be performed using a roll press device or other devices. For example, a method may be employed in which a laminate comprising a base material 1 and a conductive particle-containing layer 2 is sandwiched between two opposing rolls and transported between these two rolls. Alternatively, a method may be employed in which the laminate is placed on a flat plate or on the flat surface of a table having a flat surface, a roll is brought into contact with it from above, and pressure is applied to the laminate while the roll is rotated. However, when heating and pressurizing using a roll press device, the heating and pressurizing time per unit area tends to be shorter compared to heating and pressurizing using a flat press device, so care should be taken to appropriately control the heating, pressurizing, transport speed (roll rotation speed), etc.

[0079] 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.

[0080] 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.

[0081] 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.

[0082] 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.

[0083] By the above manufacturing method, a conductive film-coated substrate 10 can be obtained.

[0084] Figure 2 is a schematic cross-sectional view showing an example of a conductive film-coated substrate 10. The conductive film-coated substrate 10 comprises a substrate 1 and a conductive film 3 formed on at least a portion of the surface 1A of the substrate 1.

[0085] 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.

[0086] 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.

[0087] 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 of the total area, preferably 70% or more, and the entire conductive film may be embedded in the recess 5. However, a portion of the conductive film 3 may have a portion that is not embedded in the recess 5 and protrudes upward in the thickness direction.

[0088] 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.

[0089] In another embodiment, in the cross-section in the thickness direction of the conductive film-coated substrate 10, an interface 9 may exist in at least a portion between the thermoplastic resin layer of the substrate 1 and the conductive film 3, and at the interface 9, the thermoplastic resin layer other than the surface-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.

[0090] Figure 3 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 3, the conductive film 3 may have a conductive pattern including linear portions 3A. The linear portions 3A may consist of straight lines or curves. The conductive pattern of the conductive film 3 is not limited to narrow linear portions 3A, but may also have pads or capacitor hats with a relatively large area. For example, circular, elliptical, square, or other polygonal shapes can be used as top views of the pads or capacitor hats. Note that the cross-sectional view in Figure 2 may be a cross-section of the linear portion 3A of the conductive film 3 shown in Figure 3. When the plane of the surface 1A of the substrate 1 is defined as the X-Y plane, the X direction in Figure 3 may be defined as the short direction of the linear portion 3A, and the Y direction may be defined as the long direction of the linear portion 3A.

[0091] In Figure 3, the direction in which the line portion 3A of the conductive pattern extends is defined as the longitudinal direction, and the width direction of the line portion 3A is defined as the short direction. In this embodiment, in at least one of the cross-sections B that pass through the short direction and the thickness direction of the line portion 3A of the conductive pattern, the width of the line portion 3A in the short direction is, for example, 30 μm or more and 5000 μm or less, preferably 70 μm or more and 3000 μm or less, and more preferably 100 μm or more and 1000 μm or less. Even fine lines with a width of 500 μm or less, which are usually difficult to punch out, can be formed by the printing described above, and adhesion to the base material 1 can be provided to such fine line portions 3A.

[0092] <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.

[0093] 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.

[0094] 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.

[0095] 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.

[0096] <Method for Manufacturing Electromagnetic Shielding Sheets> As an application other than electronic devices, it is conceivable to manufacture electromagnetic shielding sheets using the manufacturing method of the conductive film-equipped substrate (conductive film-coated substrate) of this embodiment. Specifically, by making the pattern used when printing the conductive paste in the lamination process a pattern specific to electromagnetic shielding sheets (such as a mesh pattern), electromagnetic shielding sheets can be manufactured.

[0097] <Method for Manufacturing a Planar Heating Element> As another application, it is conceivable to manufacture a planar heating element using the method for manufacturing a substrate (substrate with a conductive film) equipped with the conductive pattern of this embodiment. A planar heating element is a material on which electrical wiring is provided, and heat is generated when an electric current is passed through the wiring. Specific examples of planar heating elements include those used for anti-fogging and cold protection, such as the rear windows of passenger cars.

[0098] 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.

[0099] 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.

[0100] <Preparation of conductive paste> (Conductive paste 1) Electrolytic copper powder (manufactured by Fukuda Metal Foil & Powder Industry Co., Ltd., D ５０ 82 parts by mass of (5 μm, dendritic), 2 parts by mass of dispersant Y (polyester resin), and 16 parts by mass of organic solvent were weighed and mixed with a spatula to obtain a mixture. Then, this mixture was stirred using a rotary-orbiting stirrer. In this way, a conductive paste 1 in paste form at 23°C was obtained.

[0101] (Conductive Paste 2) Conductive paste 2 was obtained in the same manner as conductive paste 1, except that the content ratio of dispersant Y was changed to 0 parts by mass and the content ratio of organic solvent was changed to 18 parts by mass, at 23°C.

[0102] (Conductive paste 3) Conductive paste 3 was obtained in the same manner as conductive paste 1, except that 8 parts by mass of phosphate ester (DISPERBY K-111) was mixed as another dispersant, and the content ratio of dispersant Y was changed to 0 parts by mass and the content ratio of organic solvent to 12 parts by mass. The paste was heated to 23°C.

[0103] The remaining amounts of dispersant Y and other dispersants used in each conductive paste after immersion in formic acid were evaluated according to the following procedure. For conductive paste 1, the above-mentioned polyester resin was used as dispersant Y, while for conductive paste 3, the above-mentioned phosphate ester was used as the other dispersant. Hereafter, dispersant Y and other dispersants will be collectively referred to simply as "dispersant." The dispersant was weighed immediately before use and placed in a glass container. The weight of the dispersant at this time was defined as W0 (g). Next, 1 mL of a 5% by mass formic acid aqueous solution was weighed and placed in the glass container. The dispersant was then 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 120°C hot air drying oven for 10 minutes. The weight of the dried dispersant Y was then measured. The weight of the dispersant at this time was defined as W1 (g). Using W0 and W1 obtained above, the amount of dispersant remaining after immersion in the formic acid aqueous solution was calculated using the formula [W1 / W0] × 100%. As a result, the amount remaining after immersion in the formic acid aqueous solution was 98% for the polyester resin used in conductive paste 1. On the other hand, the phosphate ester used in conductive paste 3 dissolved or dispersed completely immediately after being added to the 5% by mass formic acid aqueous solution, resulting in a cloudy liquid, and therefore could not be transferred to another glass container. For this reason, the remaining amount was considered to be 0%.

[0104] <Manufacturing of conductive film-coated substrates> [Example 1] (Printing process) The conductive paste 1 described above was screen printed onto the surface of the substrate to form a patterned coating (conductive particle-containing layer) and obtain a laminate. The printing process was carried out according to the following specific conditions. ・Substrate: Biaxially oriented PET film (thickness 50 μm, width 150 mm, heat resistance temperature 160°C) was used. ・Printing machine: Screen printing machine (Micro-Tech, Desk Top 38SA model) was used. ・Screen plate: A screen plate with a pattern having fine lines (325 mesh, mesh diameter 16 μm, emulsion thickness 40 μm) was used. ・Printing conditions: Printing pressure 0.18 MPa, squeegee speed 30 mm / sec, clearance (distance between screen plate and substrate) 2.0 mm, attack angle 80°.

[0105] (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.

[0106] (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.

[0107] (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.

[0108] (Sintering step) After the infiltration step, a film-like material (polyimide film) was stacked so as to be in contact with the patterned conductive particle-containing layer, to obtain a laminated body of the laminate and the film-like material. The laminated body was placed on a metal plate (30 mm×20 mm) installed on the lower plate using a flat press (HC300-15K, manufactured by AS ONE Corporation) equipped with two opposing flat plates (upper plate, lower plate), and hot-pressed under the following conditions to sinter copper powder (a plurality of conductive particles) in the conductive particle-containing layer, thereby forming a sintered body (conductive film). After hot pressing, the film-like material was peeled off to produce a base material with a conductive film comprising the conductive film provided on the surface of the base material. ・Hot pressing conditions: Heating temperature (pressing temperature): 140°C, pressure: 83 MPa, time: 30 seconds. However, the pressing temperature was adjusted by accurately measuring the temperature with a thermocouple, not based on the indicated value of the machine. The pressure was obtained by the following calculation. First, for the area of the metal plate installed on the flat press (lower plate), 30×20 mm=600 mm ２ was calculated. Further, the pressing force was defined as F. Since a force F was applied to the area of 600 mm ２ , the pressure was calculated by the calculation of F÷600 mm ２ .

[0109] [Example 2] A base material with a conductive film was produced in the same manner as in Example 1, except that in the infiltration step described above, a phosphorus oxo acid aqueous solution containing phosphinic acid as component X was used instead of the formic acid aqueous solution. [Example 3] A base material with a conductive film was produced in the same manner as in Example 1, except that in the infiltration step described above, a hydrazine aqueous solution containing hydrazine as component X was used instead of the formic acid aqueous solution.

[0110] [Comparative Example 1] A base material with a conductive film was produced in the same manner as in Example 1, except that in the printing step described above, conductive paste 2 was used instead of conductive paste 1. [Comparative Example 2] A base material with a conductive film was produced in the same manner as in Example 1, except that the infiltration step described above was not performed, and the sintering step described above was performed after the surface modification step. [Comparative Example 3] A base material with a conductive film was produced in the same manner as in Example 1, except that in the printing step described above, conductive paste 3 was used instead of conductive paste 1.

[0111] <Observation of Cross-Sections> Samples of the conductive film-coated substrate, molded on both sides with epoxy resin, were cut using ion milling to expose the cross-section of the fine-line portion of the conductive pattern of the conductive film, perpendicular to the direction in which the conductive pattern extends. These cross-sections were photographed with a scanning electron microscope (SEM) to obtain cross-sectional images. In the cross-sectional images of Examples 1 to 3, although boundaries between copper particles were partially visible, it was confirmed that the particles were in close contact with each other and that electrical connections were formed. Furthermore, it was confirmed that a structure in which a part of the conductive film was embedded in the resin layer of the substrate was observed.

[0112] <Measurement of Resistivity> The resistance value was measured using a four-terminal resistance meter for the fine-line portion (measurement width 250 μm in the central region) of the conductive pattern of the conductive film on the obtained conductive film-coated substrate, and the film thickness was measured using a film thickness gauge. The resistivity was calculated from the measured resistance value and film thickness. The results are shown in Table 1. In Table 1, the resistivity value is listed as a relative value with Comparative Example 3 as the reference (1.00 times). A resistivity smaller than that of Comparative Example 3 was judged to be good. It is presumed that Example 3 will also have a resistivity value smaller than that of Comparative Example 3, similar to the other examples.

[0113] <Adhesion> The conductive film on the obtained conductive film-coated substrate was subjected to commercially available Nichiban cellophane tape (registered trademark). Then, the cellophane tape (registered trademark) was quickly peeled off in a direction perpendicular to the substrate surface, and the adhesion was evaluated as to whether or not the conductive film peeled off. If the conductive film did not peel off, the adhesion was judged as "good," and if the conductive film peeled off, the adhesion was judged as "poor."

[0114]

[0115] Based on the above results, the conductive film-coated substrates of each example showed lower resistance of the conductive film compared to Comparative Examples 2 and 3, and higher adhesion of the conductive film compared to Comparative Examples 1 and 3.

[0116] This application claims priority based on Japanese Patent Application No. 2025-056746, filed on 28 March 2025, and incorporates all of its disclosures herein.

[0117] 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 X Component X

Claims

1. A conductive film-coated substrate comprising: a substrate; a conductive film 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 treated with a component X capable of removing an oxide film from the surface of the conductive particles; and a dispersant Y, wherein one of the component X and the dispersant Y is hydrophobic and the other is hydrophilic.

2. A conductive film-coated substrate comprising: a substrate; and a conductive film 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 treated with one or more selected from the group consisting of carboxylic acids, phosphorus oxoacids, and hydrazine compounds; and a hydrophobic dispersant Y.

3. A conductive film-coated substrate according to claim 1 or 2, wherein the dispersant Y satisfies the requirement that the amount remaining after formic acid immersion, determined according to the following measurement method, is 90% by mass or more. (Measurement method) The dispersant Y is immersed in a 5% by mass aqueous solution of formic acid for 13 hours. When the weights of the dispersant Y in a dry state before and after immersion are W0 (g) and W1 (g), respectively, the amount remaining after formic acid immersion (mass%) is calculated from [W1 / W0] × 100%.

4. A conductive film-coated substrate according to claim 1 or 2, wherein the dispersant Y comprises a resin having a polyester skeleton.

5. A conductive film-coated substrate according to claim 1 or 2, wherein the conductive film comprises a sintered body of a plurality of conductive particles treated with a carboxylic acid, and the carboxylic acid comprises a carboxylic acid having seven or fewer carbon atoms in the molecule.

6. A conductive film-coated substrate according to claim 1 or 2, wherein the substrate includes a thermoplastic resin layer.

7. A conductive film-coated substrate according to claim 6, 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.

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

9. A conductive film-coated substrate according to claim 1 or 2, wherein the conductive particles include dendritic particles.

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

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

12. A conductive film-coated substrate according to claim 1 or 2, wherein at least a portion of the conductive film is embedded within the substrate.

13. An electronic device comprising a conductive film-coated substrate according to claim 1 or 2.

14. An electronic device according to claim 13, wherein the electronic device is an RF tag.

15. An electromagnetic shielding sheet comprising a conductive film-coated substrate according to claim 1 or 2.

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

17. A method for manufacturing a substrate with a conductive film, comprising the steps of: forming a conductive particle-containing layer on at least a portion of the surface of a substrate using a conductive paste containing a plurality of conductive particles and a dispersant Y; impregnating the conductive particle-containing layer with a component X capable of removing the oxide film on the surface of the conductive particles; and sintering the plurality of conductive particles to form a conductive film, wherein in the impregnation step, the dispersant Y contained in the conductive particle-containing layer remains undissolved.

Images