Manufacturing method for printing sets and conductive components

Abstract

The present invention provides a printing set that exhibits excellent conductivity and abrasion resistance, and reduces deterioration of appearance due to aging, and a method for manufacturing a conductive member using the printing set. [Solution] The printing set includes a recording medium comprising a substrate, an ink-receiving layer containing a nitrate formed on at least one side of the substrate to constitute a printing surface, metal fine particles treated with a carboxylic acid-based dispersant, and polyvinyl resin, and an ink for inkjet printing on the printing surface of the recording medium to form a conductive layer. The nitrate contained in the ink-receiving layer may be at least one selected from the group consisting of sodium nitrate and aluminum nitrate.

Description

Technical Field

[0001] The present invention relates to a printing set including an inkjet ink containing metal fine particles, and a method for manufacturing a conductive member using the printing set.

Background Art

[0002] Conventionally, a technique for forming a conductive layer by inkjet printing silver nanoink (silver colloid ink) is known.

[0003] For example, Patent Document 1 discloses a method for obtaining conductivity on a substrate by reacting silver ultrafine particles dispersed as silver colloid in water and an organic solvent with mucocloric acid having halogen (chlorine) in the molecule by ionic bond.

[0004] Patent Document 2 discloses an ink composition for printing on glossy paper, which includes silver nanoparticles, a polymer dispersant having a carboxyl group, and an aqueous solvent.

[0005] Patent Document 3 discloses a recording liquid that contains a bright pigment including silver particles having a number average particle diameter of less than 200 nm, a modified ethylene vinyl acetate polymer, or a polyamidoamine salt and a fatty acid amide, and has a viscosity of 40 mPa·s or less (20 °C).

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0007] However, as in the invention described in Patent Document 1, ink receiving layers containing halogen salts tend to be avoided in order to meet the demand for halogen-free materials. In particular, conductive layers obtained using silver nanodispersions starting from silver nitrate have the problem of not having high adhesion to ink receiving layers containing halogen salts.

[0008] The invention of Patent Document 2 relates to an ink composition for forming an image with excellent metallic luster (Patent Document 2

[0009] ). Patent Document 2 does not disclose at all the concept of imparting conductivity to a printed image, and does not contain any description or suggestion of a method for imparting conductivity. In the invention of Patent Document 2, the glossy paper includes an ink receiving layer, but there is no disclosure of the details of the ink receiving layer (Reference Document 2,

[0099] ). Referring to Reference Document 2,

[0090] , the ink receiving layer is used to absorb the dispersant and solvent in the ink composition and fix the ink binding resin to the glossy paper, and mainly consists of a pigment and a binder resin (Patent Document 2,

[0087] ). From this, it can be concluded that Patent Document 2 does not disclose at all the concept of imparting conductivity to a solid image printed on an ink receiving layer.

[0009] Similarly, the invention of Patent Document 3 relates to a recording liquid for forming images with excellent metallic luster (see

[0006] and

[0007] of Patent Document 3), and Patent Document 3 does not disclose at all the concept of imparting conductivity to printed materials.

[0010] On the other hand, in recent years, a method has been proposed for forming antennas for IC tags such as RFID using inkjet printing with ink containing metal nanoparticles. However, with conventional methods, in order to impart sufficient conductivity to the conductive layer, the precursor layer of the conductive layer must be subjected to high-temperature treatment (firing) to remove the dispersant interposed between the metal nanoparticles. With such methods, it is difficult to form a conductive layer on substrates such as heat-sensitive plastics.

[0011] Furthermore, in IC tags and the like, there is a consideration to form a thermal recording layer on the opposite side of the substrate from the side where the antenna is formed. This opposite side is used as a thermal recording surface for recording visible information such as barcodes. However, in the above method which involves firing, the thermal recording surface changes color due to the heat during firing, and the recording function is lost. Therefore, it is difficult to manufacture IC tags that maintain conductivity as an antenna while also possessing thermal recording functionality.

[0012] Furthermore, when the printed conductive layer is used for recording identification information such as IC tags, it is required to maintain high accuracy in reading the information, and it is preferable that it has excellent abrasion resistance, taking into account physical contact with the conductive layer. Also, significant deterioration of the appearance of the conductive layer can lead to the conductive layer peeling off from the ink receiving layer and the risk of disconnection, so it is preferable to reduce deterioration of the appearance due to changes over time.

[0013] Therefore, the object of the present invention is to provide a printing set that exhibits excellent conductivity and abrasion resistance, and can reduce deterioration of appearance due to changes over time, and a method for manufacturing a conductive member using the printing set. [Means for solving the problem]

[0014] The printing set of the present invention includes a substrate, a recording medium comprising an ink-receiving layer containing a nitrate formed on at least one side of the substrate to constitute a printing surface, metal fine particles treated with a carboxylic acid-based dispersant, and a polyvinyl resin, and an ink for inkjet printing on the printing surface of the recording medium to form a conductive layer.

[0015] In the printing set of the present invention, the nitrate contained in the ink receiving layer may be at least one selected from the group consisting of sodium nitrate and aluminum nitrate.

[0016] In the printing set of the present invention, the ink may further contain a rust inhibitor.

[0017] In the printing set of the present invention, the ratio of the rust inhibitor to 100 parts by mass of the metal fine particles may be 0.2 parts by mass or more and 4.0 parts by mass or less.

[0018] In the printing set of the present invention, the rust inhibitor may be at least one selected from the group consisting of thiols and chelates.

[0019] In the printing set of the present invention, the polyvinyl resin may be at least one selected from the group consisting of partially saponified polyvinyl alcohol (PVA) and polyvinyl acetal (PVB).

[0020] The method for manufacturing a conductive member of the present invention includes a step of forming a conductive layer by inkjet printing an ink containing metal fine particles treated with a carboxylic acid-based dispersant and a polyvinyl resin on a printing surface of a recording medium including a base material and an ink receiving layer containing nitrate that is formed on at least one side of the base material and constitutes the printing surface.

[0021] In the method for manufacturing a conductive member of the present invention, the ink may further contain a rust inhibitor.

[0022] In the method for manufacturing a conductive member of the present invention, the ratio of the rust inhibitor to 100 parts by mass of the metal fine particles may be 0.2 parts by mass or more and 4.0 parts by mass or less.

[0023] In the method for manufacturing a conductive member of the present invention, the rust inhibitor may be at least one selected from the group consisting of thiols and chelates.

Effect of the Invention

[0024] According to the printing set of the present invention, since nitrate is contained in the ink receiving layer, a metal nanoink printed body using nitrate derived from metal fine particles in the ink as a starting material can be obtained without requiring high-temperature treatment. Thereby, a conductive layer having excellent conductivity can be formed. Further, since the ink receiving layer does not contain a halogen salt, the requirement for halogen-free can also be met.

[0025] Furthermore, because the salt in the ink-receiving layer is a nitrate, it exhibits low volume resistivity and minimal change in appearance over time. This makes it possible to provide a conductive layer that can maintain low resistivity over a long period of time. In addition, because the ink contains polyvinyl resin, the adhesion of the conductive layer to the ink-receiving layer can be improved, and peeling of the conductive layer can be prevented.

[0026] Furthermore, since the metal nanoparticles are treated with a carboxylic acid-based dispersant, good properties can be obtained in terms of both volume resistivity and abrasion resistance, and deterioration of appearance due to aging can be reduced.

[0027] As a result of the above, the printing set of the present invention makes it possible to obtain a conductive layer that achieves both reduced deterioration of appearance due to aging and scratch resistance of the printed material. [Modes for carrying out the invention]

[0028] The printing set of the present invention includes a recording medium which comprises an ink-receiving layer that constitutes a printing surface by being formed on at least one side of the substrate, and an ink that constitutes a conductive layer by being inkjet printed on the printing surface of the recording medium.

[0029] [Recording media] (1) Base material Examples of substrates constituting recording media include paper and resin films. Examples of paper include fine paper, medium-quality paper, art paper, bonded paper, recycled paper, paralyta paper, cast-coated paper, corrugated cardboard, condenser paper, and glassine paper. Examples of resins constituting resin films include polyolefin resins such as polyethylene and polypropylene; vinyl chloride resins such as polyvinyl chloride, vinyl chloride copolymer, and polyvinylidene chloride; polyester resins such as polyethylene terephthalate and polyethylene naphthalate; styrene resins such as polystyrene and ABS resin; acrylic resins such as polymethyl methacrylate; polyamide, polyimide, polycarbonate, triacetate, epoxy resin, polyarylate, polysulfone, polyethersulfone, fluororesin, phenoxy resin, polyphenylene sulfide, cellophane, and nylon. These can be used individually or in combination of two or more.

[0030] In the inkjet printing process using the printing set of the present invention, high-temperature treatment (firing) is not required when forming the conductive layer. Therefore, a plastic film with low heat resistance, such as polypropylene, can be used as the substrate. A laminate made by laminating two or more types of paper or resin film can also be used as the substrate.

[0031] The recording medium is prepared by applying an ink-receiving layer coating to one or both sides of a substrate and drying it to form an ink-receiving layer. This configures one or both sides as a printable surface for forming a conductive layer by inkjet printing.

[0032] The thickness of the substrate can be arbitrarily set depending on the application of the recording medium or conductive component being manufactured, or the type and configuration of the substrate used (single layer or laminate, single-sided or double-sided printing surface), etc. Since high-temperature treatment (firing) is not required when forming the conductive layer, the recording medium may have one side of the substrate as a printing surface with an ink-receiving layer formed thereon, and the opposite side as a thermal recording surface with a thermal recording layer, as described above.

[0033] The thermal recording layer can be composed of, for example, a basic, normally colorless dye (leuco dye) and an acidic color developer. The thickness of the thermal recording layer can be set arbitrarily. Considering the improvement of the thermal responsiveness of the thermal recording layer and the clarity of the print, the thickness of the thermal recording layer is preferably 4 μm or more, particularly 6 μm or more, and preferably 10 μm or less, particularly 8 μm or less. (2) Ink receiving layer The ink-receiving layer comprises a hydrophilic resin, a filler, and a water-soluble nitrate. The ink-receiving layer is formed by applying a coating containing these components to one or both sides of a substrate and allowing it to dry.

[0034] The thickness of the ink receiving layer can be arbitrarily set depending on the application of the recording medium or conductive material being manufactured, or the type and configuration of the substrate used (whether the printing surface is single-sided or double-sided). For example, the thickness of the ink receiving layer is 1 μm or more, preferably 3 μm or more, and more preferably 5 μm or more. For example, the thickness of the ink receiving layer is 40 μm or less, preferably 35 μm or less, and more preferably 30 μm or less.

[0035] If the thickness of the ink-receiving layer is less than this range, the effect of efficiently incorporating the mixing dispersion medium and metal particle dispersant in the ink into the ink-receiving layer and rapidly drying the ink may be insufficient. On the other hand, if the thickness of the ink-receiving layer exceeds the above range, depending on the type and thickness of the substrate, the conformability of the ink-receiving layer to the substrate may decrease, and it may become easier to peel off from the substrate. In contrast, by setting the thickness of the ink-receiving layer within the above range, it is possible to impart appropriate flexibility to the ink-receiving layer, further improving the effect of rapidly drying the ink while maintaining a state that is less likely to peel off from the substrate.

[0036] (hydrophilic resin) The hydrophilic resin functions as a binder to form an ink-receiving layer by binding fillers and nitrates. During inkjet printing on the printing surface, which is the surface of the ink-receiving layer, the hydrophilic resin incorporates the solvent in the ink into the ink-receiving layer, accelerating the drying of the ink. Furthermore, the hydrophilic resin dissolves the nitrates with the incorporated solvent to generate nitrate ions, which react with the dispersant coating the surface of the metal microparticles. This causes the dispersant to detach from the surface of the metal microparticles and be incorporated into the ink-receiving layer along with the solvent.

[0037] As hydrophilic resins, various conventionally known hydrophilic resins can be used, such as polyvinyl acetal resins like polyvinyl butyral; acrylic resins like polyacrylic acid; polyvinyl alcohol resins; urethane resins; starch resins; and carboxymethylcellulose resins. Of these, polyvinyl alcohol resins are preferred.

[0038] Specific examples of polyvinyl alcohol include, but are not limited to, the Kuraray Poval® series of polyvinyl alcohols manufactured by Kuraray Co., Ltd., all of which are supplied as solids with a volatile content of 5% or less for use as binders. Examples include fully saponified polyvinyl alcohols such as PVA-105, PVA-117, and PVA-124, partially saponified polyvinyl alcohols such as PVA-205, PVA-217, and PVA-224, and partially saponified high-purity polyvinyl alcohols such as PVA-205C, PVA-217C, and PVA-224C. One or more of these polyvinyl alcohols can be used.

[0039] The proportion of hydrophilic resin is preferably 5 parts by mass or more, particularly 10 parts by mass or more, and preferably 35 parts by mass or less, particularly 30 parts by mass or less, based on solid content, of 100 parts by mass of the total amount of solids forming the ink receiving layer. If the proportion of hydrophilic resin is below this range, the flexibility and conformability of the ink receiving layer to the substrate will decrease, and it may become more prone to peeling from the substrate.

[0040] On the other hand, if the proportion of hydrophilic resin exceeds the above range, the proportion of filler will relatively decrease. Therefore, the effect of making the ink-receiving layer porous by incorporating filler and improving the absorption of the mixed dispersion medium contained in the ink may not be sufficiently obtained. Also, the proportion of nitrate will relatively decrease. Therefore, the effect of incorporating nitrate, which allows the ink to dry more quickly and forms a conductive layer with excellent conductivity, may not be obtained.

[0041] In contrast, by setting the proportion of hydrophilic resin within the above range, the ink-receiving layer can be given appropriate flexibility, maintaining a state where it is difficult to peel off from the substrate. Furthermore, by making the ink-receiving layer porous, the absorption capacity of the mixed dispersion medium contained in the ink can be improved. In addition, the ink can be dried more quickly in a shorter time, and a conductive layer with excellent conductivity can be formed.

[0042] (filling material) The filler functions to improve the absorption of the mixed dispersion medium contained in the ink by making the ink-receiving layer porous through dispersion in the hydrophilic resin. Various fillers, either inorganic or organic, can be used as the filler.

[0043] Examples of inorganic fillers include porous or non-porous fine particles made from light calcium carbonate, heavy calcium carbonate, magnesium carbonate, kaolin, talc, calcium sulfate, barium sulfate, titanium dioxide, zirconia, cerium, antimony oxide, zinc oxide, zinc sulfide, zinc carbonate, satin white, aluminum silicate, diatomaceous earth, calcium silicate, magnesium silicate, silica (amorphous synthetic silica, colloidal silica, silica sol, etc.), alumina, colloidal alumina, alumina hydrate, lithopone, zeolite, hydrated halloysite, magnesium hydroxide, etc.

[0044] Examples of organic fillers include porous or non-porous fine particles made from polyethylene resins, polystyrene resins, (meth)acrylic resins, vinyl chloride resins, vinyl acetate resins, polyester resins, styrene / acrylic resins, styrene / butadiene resins, styrene / isoprene resins, methyl methacrylate / butyl methacrylate resins, polycarbonate resins, polyacrylate resins, silicone resins, urea resins, melamine resins, epoxy resins, phenolic resins, diallyl phthalate resins, and the like.

[0045] The average particle size of the filler can be appropriately selected depending on the type of filler (inorganic or organic, porous or non-porous), etc. However, as a filler, various types of alumina that are acidic, neutral or alkaline and have a primary particle size of about 1 nm to 100 nm are preferred in terms of their effect on improving the absorbency of the mixed dispersion medium. Note that one type of filler from the above-mentioned fillers, or two or more types with different types or particle sizes, can be used in combination.

[0046] The proportion of the filler can be appropriately selected depending on the type of filler. For example, if the filler is alumina, the proportion of alumina is preferably 40 parts by mass or more, particularly 50 parts by mass or more, and preferably 80 parts by mass or less, and particularly 70 parts by mass or less, out of 100 parts by mass of the total amount of solids forming the ink receiving layer. Furthermore, the proportion of alumina is preferably 200 parts by mass or more, particularly 250 parts by mass or more, and preferably 400 parts by mass or less, and particularly 350 parts by mass or less, per 100 parts by mass of hydrophilic resin.

[0047] If the proportion of alumina is below this range, the effect of making the ink-receiving layer porous by incorporating alumina and improving the absorption of the mixed dispersion medium contained in the ink may not be sufficiently obtained. On the other hand, if the proportion of alumina exceeds the above range, the proportion of hydrophilic resin as a binder becomes relatively smaller. As a result, the flexibility and conformability of the ink-receiving layer to the substrate may decrease, making it easier to peel off from the substrate.

[0048] In contrast, by setting the proportion of alumina within the above range, the ink-receiving layer can be given appropriate flexibility, maintaining a state where it is difficult to peel off from the substrate. Furthermore, by making the ink-receiving layer porous, the absorption capacity of the mixed dispersion medium contained in the ink can be improved.

[0049] (nitrate) As the nitrate, various nitrates that can form hydrates, i.e., are water-soluble, can be used. Examples of water-soluble nitrates include sodium nitrate, aluminum nitrate, and magnesium nitrate. Among these, at least one selected from the group consisting of sodium nitrate and aluminum nitrate is particularly preferred in terms of the effects of incorporating the aforementioned nitrates.

[0050] The proportion of nitrate is preferably 5 parts by mass or more, particularly 10 parts by mass or more, and preferably 35 parts by mass or less, and particularly 30 parts by mass or less, based on anhydrous basis, of 100 parts by mass of the total amount of solids forming the ink receiving layer. Furthermore, the proportion of nitrate is preferably 25 parts by mass or more, particularly 50 parts by mass or more, and preferably 175 parts by mass or less, and particularly 150 parts by mass or less, based on anhydrous basis, per 100 parts by mass of hydrophilic resin.

[0051] If the nitrate ratio is below this range, the effect of incorporating nitrate to rapidly dry the ink in a shorter time and form a conductive layer with excellent conductivity may not be achieved. On the other hand, if the nitrate ratio exceeds the above range, the appearance may deteriorate over time. In contrast, by setting the nitrate ratio within the above range, it is possible to rapidly dry the ink in a shorter time and form a conductive layer with excellent conductivity. Furthermore, deterioration of the appearance over time can be reduced.

[0052] Furthermore, chlorine and bromine contained in halogen salts other than nitric acid have been identified as toxic, such as generating dioxins during incineration, which poses problems during recycling. Therefore, restrictions on their use are necessary. Sulfates also tend to produce sulfide ions, which are said to be one of the causes of silver degradation, and these ions change significantly over time.

[0053] [Printing Set] The printing set of the present invention includes the above-mentioned recording medium and an ink for forming a conductive layer on the printing surface of the recording medium.

[0054] The inks that make up the printing set are prepared using a metal colloid solution as a raw material, in which metal nanoparticles are dispersed in a dispersion medium such as water. Examples of metals that form the metal nanoparticles include gold, silver, copper, platinum, palladium, rhodium, ruthenium, iridium, osmium, nickel, bismuth, aluminum, zinc, tin, cobalt, and iron. One of these metals or an alloy of two or more metals can be used. In particular, silver or an alloy of silver is preferred for use as the antenna of the IC chip in the aforementioned IC tag. Silver or an alloy of silver is resistant to oxidation, so it is resistant to changes over time and does not deteriorate much in terms of conductivity. On the other hand, copper is easily oxidized and its conductivity deteriorates easily, and gold and platinum, which are said to deteriorate less, are more expensive than silver, etc.

[0055] The average particle size of the metal nanoparticles can be arbitrarily set depending on the application of the conductive material to be manufactured, or the pattern of the conductive layer, etc. The average particle size of the metal nanoparticles may be, for example, 10 nm to 60 nm, preferably 20 nm to 50 nm. Since such metal nanoparticles are dispersed in the dispersion medium, the metal colloidal solution may also be called a metal nanodispersion. The average particle size of the metal particles can be measured, for example, by dynamic light scattering, but may also be measured by laser diffraction scattering.

[0056] The proportion of metal nanoparticles (solid content) is preferably 5% by mass or more, particularly 10% by mass or more, of the total amount of ink, and preferably 40% by mass or less, particularly 30% by mass or less. More preferably, the proportion of metal nanoparticles (solid content) is 15% by mass or more and 20% by mass or less of the total amount of ink. The proportion of metal nanoparticles can be appropriately adjusted within the above range depending on the conductivity of the conductive layer to be formed. In the case of an IC chip antenna, where particularly high conductivity is required, the proportion of metal nanoparticles should be set to a higher range within the above range. However, even if the conductivity is low after one print, the conductivity can be improved by printing two or three times in layers.

[0057] Metal colloidal solutions containing metal nanoparticles are produced by adding a dispersant such as a polymer dispersant and a reducing agent to an aqueous solution of a metal salt, or by adding dextrin, which acts as both a dispersant and a reducing agent, thereby reducing and precipitating the metal into fine particles in the solution. The surface of the precipitated metal nanoparticles is treated with a dispersant, i.e., covered with a dispersant, to maintain dispersion stability in the metal colloidal solution. Alternatively, metal colloidal solutions can also be produced by dispersing metal nanoparticles, manufactured by various methods such as gas-phase and liquid-phase methods, together with a dispersant in a dispersion medium such as water.

[0058] The inks that make up the printing set are prepared by adding water and a water-soluble organic solvent as dispersion media, and polyvinyl resin to the above-mentioned metal colloid solution, and further adding rust inhibitors, surfactants, etc., as needed. By using a mixed dispersion media of water and a water-soluble organic solvent as the dispersion medium, the drying properties of the ink can be improved, and the drying time can be shortened even further.

[0059] Examples of organic solvents include dihydric alcohols such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, butylene glycol, pentanediol, and hexanediol; trihydric alcohols such as glycerin and trimethylolpropane; and glycol ethers such as ethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monobutyl ether, diethylene glycol monoethyl ether, diethylene glycol diethyl ether, diethylene glycol monobutyl ether, diethylene glycol dibutyl ether, diethylene glycol methyl ethyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol monobutyl ether, propylene glycol n-propyl ether, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol monobutyl ether, tripropylene glycol monomethyl ether, tetraethylene glycol dimethyl ether, and tetraethylene glycol diethyl ether. One or more of these water-soluble organic solvents can be used. Higher alcohols may also be added to the ink.

[0060] Furthermore, another preferred definition of an organic solvent is that it may be, for example, an alkylene glycol, a glycol ether, or the like.

[0061] The ratio of water to organic solvent in a mixed dispersion medium can be set arbitrarily. However, the proportion of water in the total amount of water and organic solvent is preferably 50% by mass or more, particularly 60% by mass or more, and preferably 80% by mass or less, particularly 90% by mass or less.

[0062] If the proportion of water is below this range, the proportion of organic solvent becomes relatively too high, reducing the solubility of the nitrate contained in the ink-receiving layer of the recording medium. As a result, the mechanism described earlier, which incorporates the dispersant covering the surface of the metal nanoparticles into the ink-receiving layer and imparts excellent conductivity to the conductive layer, may become insufficient.

[0063] On the other hand, if the proportion of water in the mixed solvent exceeds the aforementioned range, the proportion of organic solvent becomes relatively low, resulting in high surface tension and reduced wettability. This can cause dots to not connect sufficiently between print patterns, leading to disconnections. Furthermore, inkjet head clogging may occur. As a result, it becomes difficult to print fine-grained images. Conversely, by keeping the proportion of water within the aforementioned range, the wettability of the mixed solvent increases, suppressing inkjet head clogging as a humectant, and enabling the printing of fine-grained images. Note that the proportion of water in the mixed solvent is the total ratio of water added during ink preparation and water contained in the metal colloid solution.

[0064] Examples of polyvinyl resins include polyvinyl alcohol (PVA) and polyvinyl acetal (PVB). The polyvinyl alcohol may be partially saponified polyvinyl alcohol (e.g., saponification degree of 90 mol% or less), intermediately saponified polyvinyl alcohol (e.g., saponification degree exceeding 90 mol% and 96 mol% or less), or fully saponified polyvinyl alcohol (e.g., saponification degree exceeding 96 mol% and 99 mol% or less).

[0065] Of these, it is preferable to use at least one selected from the group consisting of partially saponified polyvinyl alcohol (PVA) and polyvinyl acetal (PVB) as the polyvinyl resin. If partially saponified PVA and PVB are included in the ink as resin components, the adhesion to the ink receiving layer can be further improved.

[0066] The proportion of polyvinyl resin is preferably 0.5% by mass or more, particularly 1.0% by mass or more, and preferably 25.0% by mass or less, particularly 20.0% by mass or less, of the total amount of ink. If the proportion of polyvinyl resin is less than the above range, its contribution to scratch resistance and other properties may be insufficient. On the other hand, if it exceeds the above range, the conductivity may be poor.

[0067] Rust inhibitors readily form chelates with metal microparticles, leading to stable dispersion and improved contact between metal microparticles after printing, thereby forming a thin metal film and improving adhesion. Rust inhibitors are preferably provided in emulsion form.

[0068] Examples of rust inhibitors include thiols, chelates, and benzotriazoles.

[0069] Examples of thiols include mercaptosilane, thioglycolic acid, thioglycerol, guanylthiourea, and thioureas. Specific examples of thiol rust inhibitors include NEW DAIN SILVER S1 and NEW DAIN SILVER FC from Yamato Kasei Co., Ltd.

[0070] Examples of chelates include chelating ligands that form metal complexes (e.g., ethylenediaminetetraacetic acid (EDTA)). Specific examples of chelating rust inhibitors include Kilescoat® CZ, Kileslight® WZ-7, Kileslight® CW, Kileslight® CWB, Kileslight® WK-5, Kileslight® W-511, Kileslight® G-50, Kileslight® 3N-50, Kileslight® AG-10, Kilesclean® AG-2, and Kileslight® W-1, all manufactured by Kilesto Co., Ltd.

[0071] Examples of benzotriazoles include 1,2,3-benzotriazole, carboxybenzotriazole, methylbenzotriazole, and tolyltriazole. Specific examples of benzotriazole rust inhibitors include VERZONE® C-BTA (carboxybenzotriazole) manufactured by Yamato Kasei Co., Ltd.

[0072] The proportion of the rust inhibitor is preferably, for example, 0.2 parts by mass or more, particularly 0.5 parts by mass or more, and 4.0 parts by mass or less, particularly 3.0 parts by mass or less, per 100 parts by mass of metal fine particles. If the proportion of the rust inhibitor is less than the above range, its contribution to abrasion resistance may be insufficient. On the other hand, if it exceeds the above range, conductivity may be poor.

[0073] Furthermore, the ratio of the rust inhibitor to 100 parts by mass of metal fine particles (solid content) in the metal colloid solution is preferably, for example, 0.2 parts by mass or more, particularly 0.5 parts by mass or more, and preferably 4.0 parts by mass or less, particularly 3.0 parts by mass or less.

[0074] Surfactants function to adjust the wettability of ink to inkjet printer nozzles and other components, thereby optimizing the ejection of ink droplets from those nozzles. Anionic surfactants, cationic surfactants, amphoteric surfactants, and nonionic surfactants can all be used.

[0075] The proportion of surfactant is preferably 0.1% by mass or more, and preferably 0.5% by mass or less, of the total amount of ink.

[0076] The total ratio of water to organic solvent represents the remaining amount of other components. In other words, the proportions of metal particles, dispersants, rust inhibitors, and surfactants contained in the metal colloid solution should be set within the above ranges, and the total amount of ink should be set to 100% by mass.

[0077] [Method for manufacturing conductive materials] The present invention relates to a method for manufacturing a conductive member, characterized by the use of the above-described printing set. Specifically, a conductive layer is patterned by inkjet printing the ink from the printing set onto a printed surface, which is the surface of an ink-receiving layer formed on one or both sides of the recording medium. This results in a conductive member having a conductive layer with a predetermined pattern formed on the recording medium.

[0078] This method allows for the production of metal nano-ink prints using nitrates derived from metal nanoparticles in the ink as the starting material, without requiring high-temperature processing, because the ink-receiving layer contains nitrates. This enables the formation of a conductive layer with excellent conductivity. Furthermore, since the ink-receiving layer does not contain halogen salts, it can meet the requirements for halogen-free materials.

[0079] Furthermore, because the salt in the ink-receiving layer is a nitrate, it exhibits low volume resistivity, has minimal change in appearance over time, and provides a conductive layer that can maintain low resistivity for a long period of time. In addition, because the ink contains polyvinyl resin, the adhesion of the conductive layer to the ink-receiving layer can be improved, and peeling of the conductive layer can be prevented.

[0080] Furthermore, since the metal nanoparticles are treated with a carboxylic acid-based dispersant, good properties can be obtained in terms of both volume resistivity and abrasion resistance, and deterioration of appearance due to aging can be reduced.

[0081] As a result of the above, the printing set of the present invention makes it possible to obtain a conductive layer that achieves both reduced deterioration of appearance due to aging and scratch resistance of the printed material. [Examples]

[0082] The present invention will be further described below based on examples and comparative examples, but the configuration of the present invention is not limited to these examples.

[0083] [Recording media] First, each component was blended to achieve the composition (mass%) shown in Table 1. Then, a mixed dispersion medium of water and ethanol was added, and the mixture was stirred to prepare the coating for the ink receiving layer (receiving layers 1-7).

[0084] The information on the ingredients used in Table 1 is as follows:

[0085] Hydrophilic resin: Polyvinyl alcohol (PVA) [Kuraray Poval (registered trademark) PVA-117, solid, manufactured by Kuraray Co., Ltd.] Filler: Alumina [Alumina sol 520A (AS-520-A) manufactured by Nissan Chemical Corporation] Aluminum nitrate: Aluminum nitrate nonahydrate [manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.] Sodium nitrate: Sodium nitrate [manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.] Aluminum sulfate: Aluminum sulfate [manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.] Next, basis weight 64.0 g / m² 2 A barrier layer coating containing a urethane resin was applied to one side of a substrate made of high-quality paper, and dried to form a barrier layer with a thickness of 3 μm. Next, the ink-receiving layer coating prepared above was applied to the barrier layer, and dried to form an ink-receiving layer with a thickness of 10 μm, thereby creating a recording medium.

[0086] [Table 1]

[0087] [ink] (1) Preparation of silver nanodispersion (Silver nanodispersion 1) To a nitric acidic silver nitrate aqueous solution containing 16.98 parts by mass of silver nitrate, 74.90 parts by mass of water, and 2 parts by mass of 0.1 N nitric acid, 0.52 parts by mass of a carboxylic acid-based polymer dispersant [DISPERBYK (registered trademark) 190, manufactured by BIC Chemie Japan Co., Ltd.] was added and dissolved. Once the polymer dispersant was completely dissolved, 5.6 parts by mass of triethanolamine as a reducing agent was added to reduce and precipitate the silver into fine particles. At this point, the silver concentration was 10.8% by mass. Next, the reaction solution was desalted by ion exchange treatment and further concentrated to prepare silver nanodispersion 1 (silver colloid solution). The proportions of each component in the total amount of silver nanodispersion 1 were 50% by mass of silver, 2% by mass of the carboxylic acid-based polymer dispersant, and 48% by mass of water.

[0088] (Silver nanodispersion 2) Silver nanodispersion 2 (silver colloid solution) was prepared in the same manner as silver nanodispersion 1, except that a phosphoric acid-based polymer dispersant [DISPERBYK (registered trademark) 102, manufactured by BIC Chemie Japan Co., Ltd.] was used instead of a carboxylic acid-based polymer dispersant. The proportions of each component in the total amount of silver nanodispersion 2 were 50% by mass of silver, 2% by mass of the phosphoric acid-based polymer dispersant, and 48% by mass of water.

[0089] (2) Preparation of silver ink) The silver nanodispersion obtained above was mixed with each component in the proportions shown in Tables 2 and 3, stirred and mixed, and then filtered using a 3 μm membrane filter to prepare silver inks 1 to 20 for forming the conductive layer.

[0090] The information on the major components shown in Tables 2 and 3 is as follows:

[0091] The surfactant is an acetylenediol-based surfactant [Orphine E1010 manufactured by Nisshin Chemical Industry Co., Ltd.].

[0092] The resin is • Partially saponified polyvinyl alcohol [Polyvinyl alcohol "JP-05 (saponification degree 87.0-90.0 mol%)" manufactured by Nippon Vivipar Co., Ltd.] • Polyvinyl acetal [Water-based polyvinyl acetal resin "Eslec (registered trademark) KW-M" manufactured by Sekisui Chemical Co., Ltd.] • Polyvinyl acetal [Water-based polyvinyl acetal resin "Eslec (registered trademark) KW-10" manufactured by Sekisui Chemical Co., Ltd.] • Intermediately saponified polyvinyl alcohol [Polyvinyl alcohol "JT-05 (saponification degree 93.5.0~95.0 mol%)" manufactured by Nippon Vivid Vinegar Co., Ltd.] • Fully saponified polyvinyl alcohol [Polyvinyl alcohol "JF-02 (saponification degree 97.8.0~98.8 mol%)" manufactured by Nippon Vinegar Vinegar Co., Ltd.] • Modified EVA [Modified EVA (ethylene-vinyl acetate) copolymer wax emulsion "AQUATIX 8421" manufactured by BIC Chemie Japan Co., Ltd.], and • Contains polyamide [AQ-633E manufactured by Kusumoto Chemical Co., Ltd.].

[0093] Rust inhibitors are • "NEW DAIN SILVER S1," a silver tarnish inhibitor manufactured by Yamato Kasei Co., Ltd. • "NEW DAIN SILVER FC," a silver tarnish inhibitor manufactured by Yamato Kasei Co., Ltd. • Contains "Kireslight® WK-5," a water-soluble rust inhibitor manufactured by Kirest Co., Ltd.

[0094] The wood preservative and fungicide used is "Proxel XL-2" manufactured by Azelis.

[0095] [Table 2]

[0096] [Table 3]

[0097] [Manufacturing of printing sets and conductive components] (Examples 1-21, Comparative Examples 1-5) A recording medium on which the above-mentioned receiving layers 1 to 7 are formed, along with silver inks 1 to 20, is combined to form a printing set as shown in Tables 4 to 6. A conductive layer is then patterned on the printed surface of the recording medium to manufacture a model of an IC tag as a conductive component.

[0098] [Evaluation Test] Evaluation tests were conducted on each conductive material sample to assess the following properties. The evaluation results are shown in Tables 4 to 6.

[0099] (1) Volume resistivity evaluation Using the printing sets of Examples 1-21 and Comparative Examples 1-5, a rectangular conductive layer with a width of 20 mm and a length of 100 mm was formed on the printing surface of each recording medium by inkjet printing with silver inks 1-20 at a resolution of 600 dpi. After standing for 24 hours, the volume resistivity between both ends of the conductive layer was measured using a resistance meter [RM3545 manufactured by HIOKI E.E. CORPORATION] with a four-short-needle probe method. The obtained volume resistivity (conductivity) was evaluated according to the following criteria.

[0100] ○: 1 × 10 -5 Ω·cm order (1×10 -5 Ω·cm~9×10 -5 Ω·cm) △: 1 × 10 -4 Ω·cm order (1×10 -4 Ω·cm~9×10 -4 Ω·cm) ×: Cannot be measured (2) Changes in appearance over time The samples from Examples 1-21 and Comparative Examples 1-5 used in the volume resistivity measurements described above were left to stand in a 60°C environment and removed after 96 hours. The change in appearance over time after standing was evaluated according to the following criteria. Note that deterioration in appearance impairs the reliability of RFID and labels, and changes in surface color make it difficult to use as a display label, etc. Furthermore, deterioration in the adhesion between the printed conductive layer and the ink receiving layer leads to peeling of the surface of the conductive material, resulting in a loss of conductivity.

[0101] ○: No change compared to the sample before standing. △: Changes in color and surface condition are observed compared to the sample before standing. ×: Peeling of the conductive layer or deterioration of the surface is observed. (3) Scratch resistance evaluation Using the printing sets of Examples 1-21 and Comparative Examples 1-5, a conductive layer with silver inks 1-20, 20 mm wide and 20 mm long, was formed on the printing surface of each recording medium by inkjet printing at a resolution of 600 dpi. After standing for 24 hours, the surface of the conductive layer was rubbed once back and forth with a cotton swab, and the surface condition of the conductive layer was observed visually. Scratch resistance was evaluated according to the following criteria.

[0102] ○: No peeling ○△: Scratch marks remain, but the surface has not peeled off. △: Only a portion of the surface has peeled off. ×: Completely detached

[0103] [Table 4]

[0104] [Table 5]

[0105] [Table 6]

[0106] [Evaluation Results] Referring to Table 4, a comparison between Examples 1 and 2 and Comparative Example 1 revealed that when the ink receiving layer contains nitrates such as aluminum nitrate or sodium nitrate, the appearance changes over time are less likely to occur compared to when it contains sulfates such as sodium sulfate. In contrast, sulfates generate sulfide ions, which are said to cause sulfidation, one of the causes of silver degradation, and are therefore thought to cause greater changes in appearance over time.

[0107] Referring to Table 4, a comparison between Examples 1 and 4-6 and Example 3 revealed that when the ink receiving layer contains nitrate, if the nitrate content is 5% by mass or more in terms of solid content, the volume resistivity can be lowered (excellent conductivity). Furthermore, a comparison between Examples 1 and 3-5 and Example 6 revealed that if the nitrate content is 30% by mass or less in terms of solid content, the change in appearance over time can be reduced.

[0108] Referring to Tables 4 and 5, and comparing Examples 1 and 7-10 with Comparative Examples 2-4, it was found that in order to obtain good properties in terms of volume resistivity and abrasion resistance, and to reduce deterioration of appearance over time, the silver nano-ink needs to contain at least polyvinyl resin (PVA) as a resin component.

[0109] In contrast, a modified EVA resin was used in Comparative Example 2, and a polyamide resin was used in Comparative Example 3. When these resins were used, a tendency for the volume resistivity to be very high was observed. Furthermore, it was found that the adhesion of the silver nanoink to the ink receiving layer was low, and the abrasion resistance was also low. In Comparative Example 4, where the silver nanoink did not contain any resin, the volume resistivity was low and good, but the conductive layer peeled off easily in the abrasion resistance evaluation.

[0110] Referring to Tables 4 and 5, and comparing Examples 1 and 7-8 with Examples 9-10, it was found that among the polyvinyl resins contained in silver nanoink, partially saponified polyvinyl alcohol (PVA) and polyvinyl acetal (PVB) are particularly preferred. It was found that if partially saponified PVA and PVB are included as resin components in silver nanoink, the fixation performance can be further improved.

[0111] Referring to Tables 4 to 6, a comparison of Examples 1, 11-12, and 14-17 with Example 13 revealed that the volume resistivity of the silver nanoink can be lowered (resulting in superior conductivity) by including a rust inhibitor. Furthermore, a comparison of Examples 1 and 11-12 showed that good conductivity can be achieved regardless of whether thiols (Examples 1, 11, and 14-17) or chelates (Example 12) are used as rust inhibitors.

[0112] Referring to Tables 4 and 6, and comparing Examples 1 and 15-16 with Examples 14 and 17, it was found that a rust inhibitor blending ratio of 0.1% by mass or more and 0.5% by mass or less is preferable. It was found that when the rust inhibitor blending ratio is less than 0.1% by mass, the abrasion resistance decreases slightly, and when it exceeds 0.5% by mass, the volume resistivity decreases slightly. However, even when the rust inhibitor blending ratio is less than 0.1% by mass or greater than 0.5% by mass, practically sufficient properties in terms of abrasion resistance and volume resistivity can be achieved.

[0113] On the other hand, from another perspective, referring to Table 6, a comparison between Examples 15-16 and Examples 14 and 17 revealed that the blending ratio of the rust inhibitor is preferably 0.5 parts by mass or more and 3.0 parts by mass or less per 100 parts by mass of silver nanoparticles. It was found that when the blending ratio of the rust inhibitor is less than 0.5 parts by mass, the abrasion resistance decreases slightly, and when it exceeds 3.0 parts by mass, the volume resistivity decreases slightly. However, even when the blending ratio of the rust inhibitor is less than 0.5 parts by mass or more than 3.0 parts by mass per 100 parts by mass of silver nanoparticles, practically sufficient properties in terms of abrasion resistance and volume resistivity can be exhibited.

[0114] Referring to Tables 4 and 6, and comparing Examples 1 and 19-20 with Examples 18 and 21, it was found that the blending ratio of the resin component in the silver nano-ink is preferably 1% by mass or more and 20% by mass or less. It was found that when the blending ratio of the resin component is less than 1% by mass, the abrasion resistance decreases slightly, and when it exceeds 20% by mass, the volume resistivity decreases slightly. However, even when the blending ratio of the resin component is less than 1% by mass or more than 20% by mass, practically sufficient properties in terms of abrasion resistance and volume resistivity can be exhibited.

[0115] Referring to Tables 4 and 6, a comparison between Example 1 and Comparative Example 5 revealed that it is preferable for the silver nanodispersion used in the preparation of silver nanoink to contain silver nanoparticles treated with a carboxylic acid-based dispersant. Even when treated with a dispersant, treatment with a phosphate-based dispersant tended to decrease the volume resistivity, and the appearance changed significantly over time, resulting in the conductive layer easily peeling off during abrasion resistance evaluation.

Claims

1. A recording medium comprising a substrate and an ink-receiving layer containing a nitrate, which is formed on at least one side of the substrate and constitutes a printing surface. A printing set comprising metal fine particles treated with a carboxylic acid-based dispersant and a polyvinyl resin, and an ink for inkjet printing on the printing surface of the recording medium to form a conductive layer.

2. The printing set according to claim 1, wherein the nitrate contained in the ink receiving layer is at least one selected from the group consisting of sodium nitrate and aluminum nitrate.

3. The printing set according to claim 1 or 2, wherein the ink further comprises a rust inhibitor.

4. The printing set according to claim 3, wherein the ratio of the rust inhibitor to 100 parts by mass of the metal fine particles is 0.2 parts by mass or more and 4.0 parts by mass or less.

5. The printing set according to claim 4, wherein the rust inhibitor is at least one selected from the group consisting of thiols and chelates.

6. The printing set according to claim 1 or 2, wherein the polyvinyl resin is at least one selected from the group consisting of partially saponified polyvinyl alcohol (PVA) and polyvinyl acetal (PVB).

7. A method for manufacturing a conductive member, comprising the step of inkjet printing an ink containing metal fine particles treated with a carboxylic acid-based dispersant and a polyvinyl resin onto the printing surface of a recording medium which includes a base material and an ink-receiving layer containing a nitrate formed on at least one side of the base material to constitute a printing surface, thereby forming a conductive layer.

8. The method for manufacturing a conductive member according to claim 7, wherein the ink further comprises a rust inhibitor.

9. The method for manufacturing a conductive member according to claim 8, wherein the ratio of the rust inhibitor to 100 parts by mass of the metal fine particles is 0.2 parts by mass or more and 4.0 parts by mass or less.

10. The method for manufacturing a conductive member according to claim 9, wherein the rust inhibitor is at least one selected from the group consisting of thiols and chelates.

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