UV inkjet ink for decorative sheets, decorative sheets, and decorative boards

Abstract

To provide a decorative sheet having both high brightness feeling and designability, and a decorative plate, as well as an ink jet ink for a decorative sheet friendly to an environment used for manufacturing the decorative sheet and the decorative plate.SOLUTION: A UV inkjet ink for a decorative sheet characterized in that in a decorative sheet 20 having a glitter pattern printed layer 2 in a printed layer coated on a base sheet 1, an ink used for the glitter pattern printed layer 2 contains a UV-curable resin having at least one or more cyclic alkyl ether structures and one or more polymerizable unsaturated bonds, silver nanoparticles, and phosphoric acid based dispersant.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to an inkjet ink for decorative sheets, decorative sheets, and decorative boards for use in interior materials and fittings such as wall materials, ceiling materials, floor materials, and fixtures in buildings such as houses, furniture and fixtures, the exteriors of housing equipment and home appliances, and the interiors of vehicles such as automobiles. [Background technology]

[0002] Conventionally, in order to obtain a special design effect that reflects illumination light and exhibits brilliance, brilliance printed matter has been widely used for various applications, in which brilliance patterns or the like are printed on a substrate using brilliance ink made by kneading brilliance pigments, such as metal powders such as scaly aluminum powder (aluminum flakes) or pearlescent pigments (pearl pigments) such as titanium dioxide-coated mica, into an appropriate binder resin (for example, Patent Documents 1 and 2).

[0003] For example, in the surface decoration of building materials, furniture, the housings of home appliances, etc., a glittering layer is added to a wood grain pattern in order to reproduce the luster, depth, and texture of natural wood using printing technology. In addition to wood grain patterns, various glittering decorative sheets and decorative boards (hereinafter simply referred to as "decorative sheets") that express glittering designs such as silk, pearl, and metallic tones in stone patterns, abstract patterns, etc. are used in a wide range of fields.

[0004] Various types of glitter pigments are commercially available, with particle sizes ranging from a few microns to over 100 microns. For glitter decorative sheets that use printing techniques, metallic inks such as silver inks (sometimes called mirror inks, regel inks, hologram inks, or stere inks depending on the powder shape) that incorporate glitter pigments, and pearl inks, typically use glitter pigments with an average particle size of approximately 30 microns or less due to limitations on their printability.

[0005] In conventional decorative sheets, patterns have been printed by gravure printing. Gravure printing has the advantage of being able to print large quantities at high speed. However, gravure printing is not economical when only small quantities are to be printed, and may not be suitable in terms of print quality when the pattern is complex.

[0006] On the other hand, inkjet printing has now become a familiar presence in a wide range of fields and applications. For example, it is often used in homes as an output device for personal computers or as a printer for New Year's cards and photos, and in industry as a barcode printer or for commercial printing such as signs, POPs, and advertising media.

[0007] The primary advantage of inkjet printing is that the printers are relatively inexpensive and produce high-quality images. Furthermore, printing does not require printing plates; the desired print can be obtained using data from a computer or dedicated equipment. This not only saves on the cost of printing plates, but also has many other advantages, such as shortening the time required for printing and simplifying the process of making prototypes and test prints, also known as proofs.

[0008] For this reason, the technology described in Patent Document 3 proposes using inkjet printing for printing on decorative sheets. In this case, for example, in order to improve the design of the decorative sheet, it is conceivable to mix a glitter pigment into the inkjet ink to impart glitter to the inkjet printed layer.

[0009] However, as seen in Patent Documents 4 and 5, a problem with inkjet printing is that the nozzle inner diameter needs to be reduced to the order of 10 μm to eject minute droplets. Meanwhile, because many photoluminescent pigments have large particle sizes, inks containing dispersed photoluminescent pigments can experience clogging issues within the nozzle, making stable ejection difficult. Furthermore, when photoluminescent pigments with small particle sizes are used, it can be difficult to achieve photoluminescence when printing on coarse substrates such as paper. For these reasons, there has been a problem in that it is generally difficult to print with inkjet inks containing photoluminescent pigments.

[0010] Furthermore, from the perspective of addressing environmental issues, inkjet printing using environmentally friendly inks that do not contain highly toxic organic solvents is attracting attention. For this reason, the use of inks that use water or UV-curable resins as dispersion media is desirable, but in order to disperse the photoluminescent pigments well, it is necessary to select an appropriate dispersant. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] Patent No. 4725226 [Patent Document 2] Patent No. 6107180 [Patent Document 3] Japanese Patent Application Laid-Open No. 2001-71447 [Patent Document 4] Japanese Patent Application Laid-Open No. 2004-299378 [Patent Document 5] Patent No. 4834981 Summary of the Invention [Problem to be solved by the invention]

[0012] The present invention was devised in view of the above-mentioned problems and circumstances, and its object is to provide a decorative sheet and decorative board that have both high brightness and high designability, as well as an environmentally friendly inkjet ink for decorative sheets that is used to produce the decorative sheet and decorative board. [Means for solving the problem]

[0013] In order to solve the above-mentioned problems, an inkjet ink for decorative sheets according to one embodiment of the present invention is a decorative sheet having a glittering picture print layer as a print layer applied to a substrate sheet, wherein the ink used for the glittering picture print layer contains a UV-curable resin having at least one or more cyclic alkyl ether structures and one or more polymerizable unsaturated bonds, silver nanoparticles, and a phosphate ester-based dispersant. The silver nanoparticles are characterized in that the surfaces of the silver nanoparticles are protected by protective molecules mainly containing an amine compound.

[0014] The silver nanoparticles are characterized in that their median diameter (D50) is in the range of 1 nm to 250 nm.

[0015] The phosphate moiety of the phosphate ester-based dispersant is characterized by having a polyoxyethylene chain.

[0016] The substrate sheet is characterized in that it is made of paper.

[0017] The present invention is characterized in that it further comprises a color picture print layer formed using colored inks on the base sheet.

[0018] The decorative sheet is characterized in that a surface protective layer is provided on the outermost surface of the color picture printed layer or the glitter picture printed layer.

[0019] The decorative board is characterized by comprising the decorative sheet and a substrate disposed on the base sheet side of the decorative sheet. [Effects of the Invention]

[0020] According to the present invention, decorative sheets and decorative boards having both high brightness and high designability can be obtained, as well as environmentally friendly inkjet inks for decorative sheets used to produce such decorative sheets and decorative boards. Specifically, by using an inkjet ink for decorative sheets containing a UV-curable resin having at least one cyclic alkyl ether structure and one or more polymerizable unsaturated bonds, silver nanoparticles, and a phosphate ester-based dispersant, a glossy picture print layer can be printed using an inkjet printing method, and decorative sheets and decorative boards having high brightness can be obtained without the need for a printing plate. By using an ink in which silver nanoparticles are dispersed in a UV-curable resin, no solvent is used, making it environmentally friendly and easy to impart gloss to hard, coarse-grained paper substrates and the like. [Brief explanation of the drawings]

[0021] [Figure 1] 1 is a structural example of a dispersant. [Figure 2] 1 is a schematic cross-sectional view illustrating the configuration of a decorative sheet according to a first embodiment of the present invention. [Figure 3] FIG. 3 is a schematic cross-sectional view illustrating the configuration of a decorative sheet according to a second embodiment of the present invention. [Figure 4] 1 is a schematic cross-sectional view illustrating the configuration of a decorative board including a decorative sheet according to a first embodiment of the present invention. [Figure 5] FIG. 1 is a diagram showing a scanning electron microscope image of silver nanoparticles observed after a toluene dispersion of silver nanoparticles obtained in Example 1 of the present invention was applied to a substrate and dried. [Figure 6] FIG. 1 is a diagram showing the particle size distribution and cumulative frequency (%) of the silver nanoparticles obtained in Example 1 of the present invention. [Figure 7] FIG. 1 shows a scanning electron microscope image of silver nanoparticles observed after a 1-butanol dispersion of silver nanoparticles obtained in Example 2 of the present invention was applied to a substrate and dried. [Figure 8]FIG. 10 is a scanning electron microscope image of silver nanoparticles observed after a 1-butanol dispersion of silver nanoparticles obtained in Example 3 of the present invention was applied to a substrate and dried. [Figure 9] FIG. 10 is a diagram showing a scanning electron microscope image of silver nanoparticles observed after a 1-butanol dispersion of silver nanoparticles obtained in Example 4 of the present invention was applied to a substrate and dried. [Figure 10] FIG. 10 is a scanning electron microscope image of silver nanoparticles obtained in Example 5 of the present invention, observed after a 1-butanol dispersion of the silver nanoparticles was applied to a substrate and dried. DETAILED DESCRIPTION OF THE INVENTION

[0022] The following describes the configurations of the decorative sheet and decorative board according to the embodiments of the present invention with reference to the drawings. The same components are designated by the same reference numerals unless otherwise specified for convenience. In the drawings, the thickness and proportions of the components may be exaggerated for clarity, and the number of components may be reduced. Furthermore, the present invention is not limited to the following embodiments as they are, and can be embodied by appropriate combinations and modifications without departing from the spirit and scope of the present invention.

[0023] All decorative sheets according to the present invention have the common feature of comprising an inkjet-printed layer formed on a substrate sheet using an inkjet ink, the inkjet ink containing a UV-curable resin having at least one cyclic alkyl ether structure and one or more polymerizable unsaturated bonds, silver nanoparticles, and a phosphate ester-based dispersant. Whether the glossy layer, which is a printed layer imparted with glossiness by the inclusion of silver nanoparticles, was produced by inkjet printing can be easily determined by observing, with a magnifying glass or the like, a pattern such as a wood grain pattern expressed on the printed layer, whether it is printed in brown or in multiple colors of red, blue, yellow, and black.

[0024] The inventors of the present application have discovered that by using an inkjet ink containing a UV-curable resin, silver nanoparticles, and a phosphate ester-based dispersant (hereinafter simply referred to as "silver nanoparticle ink") to print a glittering layer and by appropriately selecting the particle size and concentration of the silver nanoparticles, it is possible to adjust the sense of brightness, thereby enhancing both the design and glittering properties, and to print and reproduce, for example, the fine lines and gradations that are unique to building materials, and pearlescent designs characterized by a pale luster that is difficult to achieve with inks that use aluminum.

[0025] Hereinafter, embodiments of the decorative sheet according to each embodiment of the present invention will be described.

[0026] (First embodiment) FIG. 2 is a schematic cross-sectional view illustrating the configuration of a decorative sheet 10 according to a first embodiment of the present invention. In the decorative sheet 10 according to the first embodiment, a pattern formed with colored inks constitutes a color pattern printed layer 2' on a substrate sheet 1, and a silver pattern printed layer (glossy pattern printed layer) 2 is formed by inkjet printing using silver nanoparticle ink. The silver pattern printed layer 2 formed using silver nanoparticle ink also serves as a glossy layer K1, imparting a sense of brilliance to the decorative sheet 10 and enhancing its design. The color of the "silver pattern printed layer 2" according to this embodiment is not limited to silver (silver color). This is because, as mentioned above, the color varies depending on the size and shape of the silver nanoparticles contained, surface modification, ink concentration, particle density on the substrate, etc. In this embodiment, the glossy pattern printed layer formed by incorporating silver nanoparticles will be referred to as the "silver pattern printed layer" for convenience in order to distinguish it from the "color pattern printed layer."

[0027] As shown in Figure 2, the silver pattern printing layer 2 may be formed so as to cover at least a portion of the surface of the color pattern printing layer 2', or may be formed so as to cover the entire surface of the color pattern printing layer 2'.

[0028] (Second embodiment) Figure 3 is a schematic cross-sectional view illustrating the configuration of a decorative sheet 20 according to a second embodiment of the present invention. In the decorative sheet 20 according to the second embodiment, the surface of the decorative sheet 10 according to the first embodiment shown in Figure 2 is covered with a surface protective layer 3. In other words, the decorative sheet 20 is a decorative sheet having a surface protective layer 3 as the outermost layer.

[0029] Fig. 4 is a schematic cross-sectional view illustrating the configuration of a decorative board 100 including a decorative sheet 20 according to a second embodiment of the present invention. As shown in Fig. 4, the decorative board 100 according to this embodiment has a laminated structure in which the decorative sheet 20 shown in Fig. 3 is laminated on one surface of a substrate 5. An adhesive layer 4 is provided between the substrate 5 and the decorative sheet 20, and the substrate 5 and the decorative sheet 20 are bonded together by the adhesive layer 4.

[0030] The silver nanoparticle ink and the materials and configuration of the decorative sheet used in this embodiment will be described in detail below.

[0031] The surfaces of the silver nanoparticles used in this embodiment are covered with protective molecules containing an amine compound as the main component. The "main component" here refers to the component (molecule) that is most abundant among the multiple protective molecules covering the surfaces of the silver nanoparticles.

[0032] The silver nanoparticles according to this embodiment have a median diameter (D50) of, for example, 1 nm or more and 250 nm or less. If the median diameter (D50) of the silver nanoparticles is smaller than 1 nm, the visibility (brilliance) may decrease, and if the median diameter (D50) of the silver nanoparticles is larger than 250 nm, the dispersibility may decrease. In addition, the average primary particle diameter is determined by Nanotrac UPA- The particle size distribution was determined from the particle size distribution measured in a 0.1% by mass dispersion using an EX150 particle size distribution analyzer (dynamic light scattering method, Nikkiso Co., Ltd.).

[0033] There are no limitations on the shape of the silver nanoparticles, but they preferably include one or more of spherical, flat, polygonal, etc. Flat silver nanoparticles have a large surface area and are expected to have good visibility (brilliance) even in small amounts. Furthermore, if the silver nanoparticles are spherical, they tend to be uniform in size, and it can be expected that the silver nanoparticles will be arranged without gaps. For this reason, spherical silver nanoparticles are also expected to have good visibility (brilliance).

[0034] As the raw material of silver constituting the silver nanoparticles, among silver-containing compounds, silver compounds that easily decompose upon heating to produce metallic silver are preferably used. Examples of such silver compounds include silver carboxylates in which silver is combined with carboxylic acids such as formic acid, acetic acid, oxalic acid, malonic acid, benzoic acid, and phthalic acid, as well as silver chloride, silver nitrate, and silver carbonate. Among these silver compounds, silver oxalate is preferably used because it easily decomposes to produce metal and is less likely to produce impurities other than silver.

[0035] Silver oxalate has a high silver content, and when heated, the oxalate ions are decomposed and removed as carbon dioxide. This means that metallic silver can be obtained directly by thermal decomposition without the need for a reducing agent, and impurities are less likely to remain, which is an advantage.

[0036] When thermally decomposing a silver compound, alcohol, fatty acid, polymer, etc. may be added. The addition of these is expected to adjust particle size, change the dispersion medium, improve dispersion stability, etc. Examples of alcohols include ethanol, 1-propanol, and 2-propanol. Examples of fatty acids include oleic acid and linoleic acid. Examples of polymers include polyvinylpyrrolidone and gelatin.

[0037] The amine compound that protects the surface of silver nanoparticles is not particularly limited in structure, but preferably has a primary amino group RNH2 (R is a hydrocarbon group) for ease of coordination with silver atoms. Secondary amino groups can also be coordinated, but their reactivity is lower than that of primary amino groups. Diamine compounds having multiple amino groups may also be used. In the case of diamine compounds, if they have primary and tertiary amino groups, the primary amino groups will selectively coordinate with silver atoms, and the bulky tertiary amino groups will face outward, making it easier to protect the surface of silver nanoparticles. Examples of amines include ethylamine, n-propylamine, isopropylamine, 1,2-dimethylpropylamine, n-butylamine, isobutylamine, n-nonylamine, n-aminodecane, n-aminoundecane, n-hexadecylamine, n-heptadecylamine, n-octadecylamine, and n-oleylamine.

[0038] Further, examples of diamines include, but are not limited to, N,N-dimethylethylenediamine, N,N-diethylethylenediamine, N,N-dimethyl-1,3-propanediamine, N,N-diethyl-1,3-propanediamine, N,N-dimethyl-1,5-diamino-2-methylpentane, N,N-dimethyl-1,6-hexanediamine, N,N-dibutylaminopropane, N,N-diisobutyl-1,3-diaminopropane, etc. Furthermore, multiple different amines may be used simultaneously.

[0039] As described above, the silver nanoparticles used in this embodiment may be silver nanoparticles produced, for example, by mixing silver oxalate and an amine and thermally decomposing the mixture to form a silver oxalate-amine complex. Techniques for producing silver nanoparticles by thermally decomposing silver oxalate and an amine are described, for example, in Japanese Patent Application Laid-Open No. 2012-162767 and Japanese Patent No. 5574761. The above-mentioned methods do not require the addition of a reducing agent to reduce silver ions, and can be produced simply. It is possible to produce silver nanoparticles using this method. Furthermore, the silver nanoparticles obtained using the above method have high dispersibility in the dispersion medium, as the amino groups of the amine molecules are primarily coordinated to the surface of the silver particles. Furthermore, since the particle size and dispersibility can be changed by adjusting the manufacturing conditions, silver nanoparticle inks using these can express designs with adjusted brilliance by changing the silver nanoparticles used and their concentration.

[0040] Another method for producing silver nanoparticles involves thermally decomposing silver oxalate and using polyvinylpyrrolidone as a molecule that coordinates with the particle surface (T. Togashi, S. Ojima, I. Sato, K. Kanaizuka, M. Kurihara, Chem. Lett., 2016, 45, 646-648). The silver nanoparticles synthesized by this method include plate-shaped ones, which are expected to produce a high level of brightness when printed.

[0041] The amount of silver nanoparticles added to the coating liquid is preferably, for example, in the range of 1% by mass to 50% by mass relative to the dispersion medium. Since this enhances metallic luster, the amount of silver nanoparticles added is particularly preferably 15% by mass or more. If the amount of silver nanoparticles added is less than 1% by mass, the visibility (brilliance) of the printed matter may decrease, and if it exceeds 50% by mass, dispersibility may decrease.

[0042] The UV-curable resin according to this embodiment has at least one cyclic alkyl ether structure and one or more polymerizable unsaturated bonds. Examples of cyclic alkyl ether structures include epoxide, tetrahydrofuran, tetrahydropyran, dioxolane, and dioxane. While the reason why a cyclic alkyl ether structure is suitable is unclear, it is believed to improve the dispersibility of silver nanoparticles by interacting with the dispersant. Furthermore, since the resin is used in inkjet inks, a viscosity of 20 mPa·s or less is preferred, with 10 mPa·s or less being particularly preferred. Viscosities greater than 20 mPa·s may result in poor ink ejection during printing.

[0043] Specific examples of UV-curable resins include Viscoat #150, #200, MEDOL-10 (Osaka Organic Chemical Industry Co., Ltd.), Light Acrylate THF-A (Kyoeisha Chemical Co., Ltd.), SR-203, 285 (Tomoe Kogyo Co., Ltd.), etc., but are not limited to these, and multiple combinations of these may also be used.

[0044] In this embodiment, the composition may contain a compound that generates a polymerization initiating species upon exposure to ionizing radiation, i.e., a polymerization initiator. When using a compound (photopolymerization initiator) that polymerizes upon exposure to ultraviolet radiation, which is one of ionizing radiation, the photopolymerization initiator may be, for example, acetophenones, benzophenones, α-hydroxyketones, benzyl methyl ketal, α-aminoketones, monoacylphosphine oxides, bisacylphosphine oxides, or the like, used alone or in combination. Specific examples of the photopolymerization initiator include, but are not limited to, Irgacure 184, Irgacure 651, Irgacure 1173, Irgacure 907, Irgacure 369, Irgacure 819, Irgacure TPO (BASF), Esacure KIP-150, and Esacure ONE (Lamberti).

[0045] The phosphate ester-based dispersant for dispersing silver nanoparticles according to this embodiment preferably has a polyoxyethylene polyoxyethylene chain. Other polyoxyalkylene chains may result in inability to disperse. Solubility in resin can be adjusted by changing the chain length of the polyoxyethylene chain. The amount added is preferably 1% or more and 30% or less of the mass of the silver nanoparticles, more preferably 5% to 20%. If it is less than 1%, the silver nanoparticles may not disperse, and if it exceeds 30%, the brilliance of the silver nanoparticles may be lost. Furthermore, since it is added to UV resin, the HLB (Hydrophilic-Lipophilic Balance) value, which represents the degree of affinity of the surfactant for water and oil (organic compounds insoluble in water), is used. The balance is preferably 8 or less.

[0046] Specific examples of phosphate ester dispersants that can be added to the present invention include, but are not limited to, NIKKOL DDP-2, 4, DDP-6 (Nikko Chemicals Co., Ltd.), Plysurf AL, A207H, A208B, A208F, A208N, A208S, A210D (Dai-ichi Kogyo Seiyaku Co., Ltd.), etc. An example of the chemical structure of a phosphate ester dispersant is shown in Figure 1.

[0047] The silver nanoparticle ink according to this embodiment may contain additives such as a pigment, an antifoaming agent, and a leveling agent in addition to the dispersant described above.

[0048] The base sheet 1 according to this embodiment is preferably a paper base, and titanium paper, which is often used for decorative sheets, is particularly preferred, but may be selected appropriately depending on the application. Base materials other than paper may not absorb ink well, making it difficult to impart brilliance.

[0049] The surface protection layer 3 according to this embodiment may be made of a material such as a thermosetting resin, an ionizing radiation curing resin, or a mixture of these resins. The thermosetting resin may be a thermosetting resin having a urethane bond, such as a two-component curing urethane resin. The ionizing radiation curing resin may be an ultraviolet curing resin. The ultraviolet curing resin may be, for example, a (meth)acrylic resin, a silicone resin, a polyester resin, a urethane resin, an amide resin, or an epoxy resin. The use of these materials can improve the hardness of the surface protection layer 3, as well as improve surface properties such as abrasion resistance, scratch resistance, and solvent resistance.

[0050] In addition, functional additives such as antibacterial agents and antifungal agents may be added to the surface protective layer 3 to impart various functions. Furthermore, if necessary, an ultraviolet absorber or a light stabilizer may be added to the surface protective layer 3. Examples of ultraviolet absorbers that can be used include benzotriazoles, benzoates, benzophenones, and triazines. Examples of light stabilizers that can be used include hindered amines. Furthermore, if stain prevention performance and Cellotape® releasability are required, a release agent having a silicone skeleton can be added. In this case, the type of release agent is not particularly limited, but using a silicone release agent having a terminal functional group reactive with the resin composition can improve the stain prevention performance and durability of Cellotape® releasability.

[0051] The thickness of the surface protective layer 3 is not particularly limited as long as it can cover the entire silver pattern printed layer 2 (glossy layer K1), but is preferably in the range of 1 μm to 100 μm, and more preferably in the range of 10 μm to 80 μm. If the thickness of the surface protective layer 3 is within the above numerical range, the silver pattern printed layer 2 can be effectively protected and the flexibility of the decorative sheet 20 can be maintained.

[0052] In addition to the above-mentioned configurations, the decorative sheet according to this embodiment may also be provided with a primer layer, adhesive layer, etc., which improve the adhesion of the protective layer.

[0053] The substrate 5 of the decorative board according to this embodiment can be made of, for example, a wood board such as plywood, particle board, medium density fiberboard (MDF), or hardboard, or a metal plate. The adhesive layer 4 can be made of, for example, a thermoplastic resin or a thermosetting resin.

[0054] The color of the layer (inkjet printed layer) printed with the silver nanoparticle ink according to this embodiment can be expressed not only in silver derived from silver but also in colors derived from localized surface plasmon resonance of silver nanoparticles, such as blue, green, yellow, and red, but is not limited to these. The color is affected by factors such as the size and shape of the silver nanoparticles, surface modification, ink concentration, and particle density on the substrate.

[0055] Traditionally, it has been difficult to create inkjet inks using photoluminescent pigments, and although there are devices capable of discharging them, they are limited in their availability. Furthermore, the brightness is often insufficient or excessive, making it difficult to print with the desired design.

[0056] The inventors of the present application have discovered that by using an inkjet ink containing a UV-curable resin, silver nanoparticles, and a phosphate ester-based dispersant (hereinafter simply referred to as "silver nanoparticle ink") to print a glittering layer and by appropriately selecting the particle size and concentration of the silver nanoparticles, it is possible to adjust the brightness and improve both the design and glittering, making it possible to print and reproduce, for example, the fine lines and gradations characteristic of building materials, and pearlescent designs characterized by a soft luster that is difficult to achieve with inks that use aluminum. Furthermore, the silver nanoparticle ink is an ink in which silver nanoparticles are dispersed in a UV-curable resin that has at least one cyclic ether structure and one or more polymerizable unsaturated bonds using a phosphate ester-based dispersant, making it a solvent-free, environmentally friendly ink, and it is also easy to impart glittering properties to coarse paper substrates, etc. [Example]

[0057] The decorative sheet 20 according to the second embodiment shown in FIG. 3 was produced using the materials and steps described below, but the present invention is not limited to these.

[0058] [Example 1] [Synthesis of silver oxalate] 9.92 g of oxalic acid dihydrate (Kanto Chemical Co., Ltd.) was dissolved in 60 mL of distilled water while heating, and then 26.7 g of silver nitrate (Kanto Chemical Co., Ltd.) was dissolved in 20 mL of distilled water while heating in a 110 °C oil bath while stirring. The solution was added and heated and stirred for 1 hour. The precipitated silver oxalate was collected by gravity filtration, further filtered and washed with 200 mL of hot water and 50 mL of methanol (Kanto Chemical Co., Ltd.), and then dried at room temperature under reduced pressure in a light-shielding desiccator. The yield of silver oxalate thus obtained was 21.6 g (90.4% yield).

[0059] [Synthesis of silver nanoparticles] 3.26 g of N,N-diethyl-1,3-diaminopropane (Tokyo Chemical Industry Co., Ltd.) was added to 0.13 g of oleic acid (Kanto Chemical Co., Ltd.), and 1.90 g of the silver oxalate obtained in the above process was added and stirred in a 110°C oil bath. Carbon dioxide bubbles began to form within 1 minute, and after a few minutes the mixture turned into a brown suspension. After heating for 5 minutes, the mixture was cooled, and 30 mL of methanol was added. The precipitate obtained by centrifugation was air-dried to yield 1.48 g of blue solid silver nanoparticles (97.0% yield based on silver).

[0060] The obtained silver nanoparticles were observed in S-TEM mode (accelerating voltage 30 kV) using a scanning electron microscope (Hitachi High-Technologies Corporation, SEM S-4800), revealing spherical particles with diameters of approximately 5 to 20 nm. The results are shown in Figure 5. More specifically, Figure 5 is a scanning electron microscope image of the silver nanoparticles observed after the toluene dispersion of the silver nanoparticles obtained in Example 1 was dropped onto a substrate (copper mesh microgrid) and dried.

[0061] Next, since the obtained silver nanoparticles were dispersed in toluene, the toluene dispersion was subjected to dynamic light scattering particle size measurement (Nikkiso Co., Ltd., Nanotrac UPA-EX150). The results showed that the silver nanoparticles were well dispersed with a median diameter of 15 nm. The results are shown in Figure 6. The solid line in Figure 6 indicates the cumulative frequency (%).

[0062] [Ink Preparation] 0.20 g of the silver nanoparticles obtained in the above process and Viscoat #150 (Osaka Organic Chemical Industry Co., Ltd.) 2.0g of silver nanoparticles were mixed with 0.2g of silver nanoparticles per 2.0g of dispersion solvent, resulting in a silver nanoparticle mass percentage of 8.5%. The dispersion was passed through a syringe filter (Whatman, 25mm GD / X syringe filter (GF / B 1.0μm)) to produce a silver nanoparticle ink for inkjet printing.

[0063] [Preparation of decorative sheet 20] Titanium paper was used as the base sheet 1. Next, a wood grain pattern was printed using an inkjet printer with inkjet inks (yellow, magenta, cyan) that did not contain glittering pigments to form the color picture printed layer 2'. Subsequently, a wood grain pattern in a neutral color was printed using the above-mentioned silver nanoparticle ink with an inkjet printer to form the glittering picture printed layer 2, and then cured by UV irradiation. Furthermore, a thermosetting multifunctional acrylic urethane resin and Acrydic (manufactured by DIC Graphics Corporation) containing silica was applied to a thickness of 1 μm after drying to form the surface protective layer 3, thereby producing the decorative sheet of Example 1. A schematic cross section is shown in FIG. 3.

[0064] [Example 2] Silver nanoparticles were obtained in the same manner as in Example 1, except that a mixture of 1.43 g of n-hexylamine (Tokyo Chemical Industry Co., Ltd.) and 1.21 g of N,N-diethyl-1,3-diaminopropane (Tokyo Chemical Industry Co., Ltd.) was used instead of 3.26 g of N,N-diethyl-1,3-diaminopropane (Tokyo Chemical Industry Co., Ltd.). A scanning electron microscope image of the obtained silver nanoparticles is shown in Figure 7. The decorative sheet of Example 2 was produced in the same manner as in Example 1, except that the obtained silver nanoparticles were used with Viscoat #200 (Osaka Organic Chemical Industry Co., Ltd.) as the dispersion medium instead of Viscoat #150.

[0065] [Example 3] The synthesis of silver nanoparticles was modified as follows. 6.51 g of N,N-diethyl-1,3-diaminopropane (Tokyo Chemical Industry Co., Ltd.), 0.25 g of oleic acid (Kanto Chemical Co., Ltd.), and 9.60 g of n-butanol (Kanto Chemical Co., Ltd.) were added, followed by 1.92 g of silver oxalate, and the mixture was heated and stirred in a 95°C oil bath. After heating, the color began to change within a few minutes, and after 18 minutes, carbon dioxide began to bubble, turning the mixture into a brown suspension. After heating for 5 minutes, the mixture was cooled, and 30 mL of methanol was added. The precipitate obtained by centrifugation was air-dried, yielding 1.29 g of blue solid silver nanoparticles (95.0% yield based on silver). A scanning electron microscope image of the resulting silver nanoparticles is shown in Figure 8. Using the resulting silver nanoparticles, the decorative sheet of Example 3 was produced using the same procedures as in Example 1.

[0066] [Example 4] Silver nanoparticles were obtained in the same manner as in Example 3, except that a mixture of 1.47 g of 1-hexylamine (Tokyo Chemical Industry Co., Ltd.) and 1.24 g of N,N-diethyl-1,3-diaminopropane (Tokyo Chemical Industry Co., Ltd.) was used instead of 6.51 g of N,N-diethyl-1,3-diaminopropane (Tokyo Chemical Industry Co., Ltd.). A scanning electron microscope image of the obtained silver nanoparticles is shown in Figure 9. The decorative sheet of Example 4 was produced using the obtained silver nanoparticles in the same manner as in Example 1.

[0067] [Example 5] Silver nanoparticles were obtained in the same manner as in Example 3, except that 1-hexanol (Kanto Chemical Co., Ltd.) was used instead of 1-butanol (Kanto Chemical Co., Ltd.) in the synthesis of silver nanoparticles. A scanning electron microscope image of the obtained silver nanoparticles is shown in Figure 10. The decorative sheet of Example 5 was produced using the obtained silver nanoparticles in the same manner as in Example 2.

[0068] [Example 6] A decorative sheet of Example 6 was produced in the same manner as in Example 1, except that silver nanoparticles manufactured by Osaka Soda Co., Ltd. (D50=70 nm) were used as the silver nanoparticles.

[0069] [Example 7] A decorative sheet of Example 7 was produced in the same manner as in Example 1, except that silver nanoparticles (D50=265 nm) manufactured by Osaka Soda Co., Ltd. were used as the silver nanoparticles.

[0070] [Example 8] A decorative sheet of Example 8 was produced in the same manner as in Example 1, except that a vinyl chloride sheet was used as the substrate.

[0071] [Comparative Example 1] The decorative sheet of Comparative Example 1 was produced in the same manner as in Example 1, except that a wood grain pattern was printed with an inkjet printer using a UV ink (manufactured by Konica Minolta) that did not contain a glitter pigment as the picture printed layer.

[0072] Comparative Example 2 The decorative sheet of Comparative Example 2 was produced in the same manner as in Example 1, except that a wood grain pattern was printed with an inkjet printer using UV silver ink (manufactured by Mimaki Engineering Co., Ltd.) that did not contain silver nanoparticles as the pattern printing layer.

[0073] Comparative Example 3 The decorative sheet of Comparative Example 3 was produced in the same manner as in Example 1, except that when preparing the silver nanoparticle ink, Hitenol 18E (Dai-ichi Kogyo Seiyaku Co., Ltd.), a polyoxyethylene alkyl ether sulfate, was used instead of Plysurf AL as the dispersant.

[0074] Comparative Example 4 The decorative sheet of Comparative Example 4 was produced in the same manner as in Example 1, except that when preparing the silver nanoparticle ink, Viscoat #196 (Osaka Organic Chemical Industry Co., Ltd.), which does not have a cyclic alkyl ether structure, was used as the UV-curable resin.

[0075] Comparative Example 5 The decorative sheet of Comparative Example 5 was produced in the same manner as in Example 1, except that when preparing the silver nanoparticle ink, Hitenol 18E was used instead of Plysurf AL as the dispersant and Viscoat #196 was used as the UV-curable resin.

[0076] [Evaluation method] In terms of brightness, items that 50 or more out of 100 test subjects rated as having a natural shine as the wood grain and reproducing the natural luster of natural wood were rated as "○", while items that were rated as having an unnaturally strong shine as the wood grain and therefore not reproducing the natural luster of natural wood, or items that were rated as having a too weak shine as the wood grain and therefore not reproducing the natural luster of natural wood, were rated as "×".

[0077] In terms of design, designs that 50 or more of the 100 test subjects felt were properly reproduced without blurring the outlines of the fine lines (several μm wide) of the wood grain pattern were rated as "○", designs that felt the outlines of the fine lines (several μm wide) of the wood grain pattern were blurred and not reproduced were rated as "×", and designs with partial printing unevenness were rated as "△". A microscope with a magnification of 100x was used to check the outlines of the fine lines of the wood grain pattern.

[0078] [Evaluation results] The evaluation results of Examples 1 to 8 and Comparative Examples 1 to 5 are shown in Table 1.

[0079] [Table 1]

[0080] As shown in Table 1, the decorative sheets of Examples 1 to 6, which satisfied the requirements of the present invention, exhibited both excellent brightness and design. Example 7 exhibited sufficient brightness, but some unevenness in the print was observed, resulting in a fair rating for design. Example 8 exhibited sufficient design but insufficient brightness. This was due to the use of a PVC sheet as the substrate, which tends to produce less brightness than a paper substrate. On the other hand, Comparative Example 1, in which a UV ink containing no photoluminescent pigment was used for inkjet printing, resulted in insufficient brightness. Comparative Example 2, in which a UV silver ink containing no silver nanoparticles was used for inkjet printing, resulted in excessive brightness. Comparative Example 3, in which the dispersant was not a phosphate ester, Comparative Example 4, in which the UV-curable resin did not have a cyclic alkyl ether structure, and Comparative Example 5, in which both were used, exhibited insufficient brightness and insufficient design. This was due to the silver nanoparticles not dispersing in the ink. [Explanation of symbols]

[0081] 1 Base sheet 2 Silver pattern printing layer (glossy pattern printing layer) 2' color picture printing layer 3 Surface protective layer 4 Adhesive layer 5. Substrate 10 Decorative Sheet 20 Decorative Sheet 100 decorative panels K1 photoluminescent layer

Claims

1. A decorative sheet comprising a substrate sheet and a printed layer applied thereon, the printed layer being a glittering pattern printed layer, the UV inkjet ink for the decorative sheet being an ink used for the glittering pattern printed layer, the ink comprising a UV-curable resin having at least one cyclic alkyl ether structure and one or more polymerizable unsaturated bonds, silver nanoparticles, and a phosphate ester-based dispersant.

2. 2. The UV inkjet ink for decorative sheets according to claim 1, wherein the silver nanoparticles are silver nanoparticles whose surfaces are protected by protective molecules mainly containing an amine compound.

3. 3. The UV inkjet ink for decorative sheets according to claim 1, wherein the silver nanoparticles have a median diameter (D50) in the range of 1 nm to 250 nm.

4. 4. The UV inkjet ink for decorative sheets according to claim 1, wherein the phosphate moiety of the phosphate ester-based dispersant has a polyoxyethylene chain.

5. 5. The UV inkjet ink for decorative sheets according to claim 1, wherein the substrate sheet is paper.

6. A decorative sheet comprising a base sheet and a printing layer applied thereon, the printing layer comprising a photoluminescent pattern printing layer, the photoluminescent pattern printing layer comprising a UV inkjet ink for decorative sheets as described in any one of claims 1 to 5.

7. A decorative sheet as described in Claim 6, characterized in that the printed layer further comprises a colored pattern printed layer formed using colored ink.

8. 8. The decorative sheet according to claim 7, further comprising a surface protection layer on the outermost surface of said color picture printed layer or said glitter picture printed layer.

9. A decorative board comprising a decorative sheet according to any one of claims 6 to 8 and a substrate arranged on the base sheet side of the decorative sheet.

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