Inkjet ink for decorative sheets, decorative sheets, and decorative boards

Abstract

To provide an inkjet ink for decorative sheet that is excellent in dispersibility of silver nanoparticle, a decorative sheet that has both high brightness feeling and high designability, and a decorative board.SOLUTION: An inkjet ink for decorative sheet comprises a silver nanoparticle, a phosphate ester-based dispersant, and a solvent.SELECTED DRAWING: None

Description

[Technical field]

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

[0002] Conventionally, for the purpose of obtaining a special design effect that reflects illumination light and exhibits brilliance, brilliant printed matter obtained by printing a brilliant pattern or the like on a substrate using a brilliant ink obtained by kneading a brilliant pigment into an appropriate binder resin has been widely used for various purposes (e.g., Patent Documents 1 and 2). Moreover, brilliant pigments generally consist of metal powders such as scaly aluminum powder (aluminum flakes) and pearlescent pigments such as titanium dioxide-coated mica.

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

[0004] By the way, various types of glittering pigments are commercially available with particle sizes ranging from a few μm to over 100 μm. For glittering decorative sheets that use printing techniques, metallic inks such as silver inks (sometimes called mirror inks, regel inks, hologram inks, or stellar inks depending on the powder shape) that contain glittering pigments, and pearl inks, are used, so glittering pigments with an average particle size of approximately 30 μm or less are usually used due to restrictions on the printability of these inks.

[0005] Meanwhile, inkjet printing has now been put to practical use in a wide variety of fields and applications, making it a familiar presence. For example, even in ordinary households, inkjet printing is often used as an output device for personal computers or as a printer for New Year's cards and photos, and in industry, it is often used for commercial printing such as barcode printers, signs, POP, and advertising media.

[0006] The first advantage of inkjet printing is that the printers are relatively inexpensive and high image quality can be obtained. Also, printing does not require printing plates, and the desired printed matter can be obtained using data from a computer or dedicated equipment. This does not simply mean that the cost of printing plates can be saved, but also has many other advantages, such as shortening the time required for printing and simplifying the process of making prototypes and test prints, known as proofs.

[0007] Meanwhile, in conventional decorative sheets, patterns are 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 a small amount of printing is required, and may not be suitable in terms of print quality when the pattern is complex. In response to this, 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 considered to mix a glittering pigment into the inkjet ink to impart glitter to the inkjet-printed layer.

[0008] However, as described 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 in order to eject minute droplets. On the other hand, since most photoluminescent pigments have large particle sizes, when ink in which photoluminescent pigments are dispersed is used, clogging problems can occur within the nozzle, making it difficult to eject the ink stably.

[0009] For this reason, it is generally difficult to print with inkjet inks containing glittering pigments, and the only way to print a glittering layer is to use a solid film by coating as in Patent Documents 1 and 2, or to print it by other methods such as gravure printing, which often results in poor design and complicated printing processes. In other words, there was a problem with conventional decorative sheets that had both high brightness and high design. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Patent No. 4725226 [Patent Document 2] Patent No. 6107180 [Patent Document 3] JP 2001-71447 A [Patent Document 4] JP 2004-299378 A [Patent Document 5] Patent No. 4834981 [Non-patent literature]

[0011] [Non-Patent Document 1] T. Togashi, S. Ojima, I. Sato, K. Kanaizuka, and M. Kurihara, Chem. Lett., 2016, 45, 646-648 Summary of the Invention [Problem to be solved by the invention]

[0012] The present invention has been devised in consideration of the problems and circumstances described above, and its object is to provide an inkjet ink for decorative sheets that has excellent dispersibility of silver nanoparticles, as well as a decorative sheet and decorative board that have both high brightness and high designability. [Means for solving the problem]

[0013] The present invention provides a decorative sheet and decorative board with a high sense of brilliance, as well as an inkjet ink for decorative sheets, which can be stably printed by inkjet printing without the aggregation of silver nanoparticles by using an ink containing silver nanoparticles and a phosphate ester-based dispersant.

[0014] In order to solve the problems, an inkjet ink for decorative sheets according to one embodiment of the present invention comprises silver nanoparticles, a phosphate ester-based dispersant, and a solvent. A decorative sheet according to one aspect of the present invention comprises at least an inkjet printed layer formed on a substrate sheet using an inkjet ink. A decorative board according to one aspect of the present invention includes the decorative sheet described above, and a substrate disposed on the base sheet side of the decorative sheet. Effect of the Invention

[0015] According to an embodiment of the present invention, an inkjet ink containing silver nanoparticles with excellent dispersibility can be obtained, thereby obtaining a decorative sheet and a decorative board with both high brightness and high designability. Specifically, according to the present invention, by using polyoxyethylene alkyl ether phosphate with an HLB value of 7 to 14, an inkjet ink containing silver nanoparticles with excellent dispersibility can be obtained, and a decorative sheet and a decorative board with high brightness can be stably obtained by inkjet printing. [Brief description of the drawings]

[0016] [Figure 1] FIG. 2 is a diagram showing a scanning electron microscope image of silver nanoparticles observed after a dispersion liquid of silver nanoparticles 1 obtained in Example 1 of the present invention was applied to a substrate and dried. [Diagram 2] FIG. 2 is a diagram showing the particle size distribution and cumulative frequency (%) of silver nanoparticles 1 obtained in Example 1 of the present invention. [Diagram 3] FIG. 2 is a diagram showing the chemical structure of a phosphate ester-based dispersant used in the present invention. [Figure 4]1 is a schematic cross-sectional view illustrating the configuration of a decorative sheet according to a first embodiment of the present invention. [Diagram 5] FIG. 4 is a schematic cross-sectional view illustrating the configuration of a decorative sheet according to a second embodiment of the present invention. [Figure 6] FIG. 4 is a schematic cross-sectional view illustrating the configuration of a decorative sheet according to a third embodiment of the present invention. [Figure 7] FIG. 11 is a schematic cross-sectional view illustrating the configuration of a decorative sheet according to a fourth embodiment of the present invention. [Figure 8] FIG. 11 is a schematic cross-sectional view illustrating the configuration of a decorative sheet according to a fifth embodiment of the present invention. [Figure 9] FIG. 13 is a schematic cross-sectional view illustrating the configuration of a decorative sheet according to a sixth embodiment of the present invention. [Figure 10] FIG. 13 is a schematic cross-sectional view illustrating the configuration of a decorative sheet according to a seventh embodiment of the present invention. [Figure 11] 1 is a schematic cross-sectional view illustrating the configuration of a decorative board provided with a decorative sheet according to a first embodiment of the present invention. [Figure 12] FIG. 13 is a diagram showing a scanning electron microscope image of silver nanoparticles observed after a dispersion liquid of silver nanoparticles 2 obtained in Example 5 of the present invention was applied to a substrate and dried. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] Hereinafter, the configurations of the inkjet ink, decorative sheet, and decorative board according to the embodiments of the present invention will be described with reference to the drawings. The same components are designated by the same reference numerals unless there is a reason for convenience. In each drawing, the thickness and ratio 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 of the present invention.

[0018] The inkjet inks according to the embodiments of the present invention have a common feature of containing silver nanoparticles, a phosphate ester-based dispersant, and a solvent. Each decorative sheet has at least an inkjet printing layer formed using an inkjet ink on a substrate sheet. Whether the glittering layer, which is a printing layer imparted glittering by including silver nanoparticles, is produced by an inkjet printing method can be easily determined by observing, for example, a wood grain pattern or other pattern expressed on the printing layer with a magnifying glass or the like, whether it is printed in brown or in multiple colors such as red, blue, yellow, and black.

[0019] In the past, it was difficult to make inkjet ink from large particle size photoluminescent pigments, and although there were devices that could eject them, they were limited in number. In addition, it was difficult to adjust the brightness, making it difficult to print with the desired design. On the other hand, it was relatively easy to make inkjet ink from small particle size metal nanoparticles, but the brightness was often insufficient, making it difficult to print with the desired design. The inventors of the present application discovered that by using an inkjet ink containing silver nanoparticles dispersed with a phosphate ester-based dispersant (hereinafter simply referred to as "silver nanoparticle ink"), the silver nanoparticles do not aggregate, allowing for stable printing, and the silver nanoparticles are smoothly aligned, resulting in high design quality and brilliance even with a small amount of silver nanoparticles. For example, it is possible to print and reproduce fine lines and gradations specific to building materials, and pearlescent designs characterized by a pale luster that is difficult to express with inks that use aluminum.

[0020] The composition of the silver nanoparticle ink used in this embodiment will be described in detail below. The surface of the silver nanoparticles used in this embodiment is covered with protective molecules containing an amine compound as a main component. The "main component" here refers to the component (molecule) that is most abundant among the multiple protective molecules covering the surface of the silver nanoparticles. The silver nanoparticles according to this embodiment have a median diameter (D50) in the range of 1 nm to 250 nm, and can be dispersed in a dispersion medium such as an organic solvent or water. 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. The average primary particle diameter was determined from the particle size distribution measured in a 0.1% by mass dispersion using a Nanotrac UPA-EX150 particle size distribution analyzer (dynamic light scattering method, Nikkiso Co., Ltd.).

[0021] There is no limitation on the shape of the silver nanoparticles, but it is preferable that the silver nanoparticles include any 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 of particles. In addition, if the silver nanoparticles are spherical in shape, the size tends to be uniform, and it is expected that the silver nanoparticles will be arranged without gaps. For this reason, spherical silver nanoparticles are also expected to have good visibility (brilliance). As the source of silver constituting the silver nanoparticles, among silver-containing compounds, a silver compound that is easily decomposed by heating to generate metallic silver is preferably used.

[0022] Examples of such silver compounds include silver carboxylates, which are compounds of silver 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 produces metal by decomposition and is less likely to produce impurities other than silver. Silver oxalate has a high silver content, and when heated, the oxalate ions are decomposed and removed as carbon dioxide. This means that no reducing agent is required, and metallic silver can be obtained by thermal decomposition without leaving any impurities behind, which is an advantage.

[0023] When the silver compound is thermally decomposed, alcohol, fatty acid, polymer, etc. may be added. The addition of these is expected to adjust the particle size, change the dispersion medium, and improve the dispersion stability. Examples of alcohol include methanol, ethanol, 1-propanol, etc., fatty acids include oleic acid, linoleic acid, etc., and polymers include polyvinylpyrrolidone, gelatin, etc. The amine compound that protects the surface of the silver nanoparticles is not particularly limited in structure, but it preferably has a primary amino group RNH2 (R is a hydrocarbon group) because of the ease of coordination with the silver atom. Secondary amino groups can also be coordinated, but their reactivity is lower than that of primary groups.

[0024] A diamine compound having multiple amino groups may also be used. In the case of a diamine compound, if the compound has a primary amino group and a tertiary amino group, the primary amino group is selectively coordinated to the silver atom, and the bulky tertiary amino group faces outward, so that the surface of the silver nanoparticles is easily protected. Examples of the amine 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.

[0025] 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. Also, a plurality of different amines may be used simultaneously.

[0026] Thus, the silver nanoparticles used in this embodiment may be silver nanoparticles produced, for example, by mixing silver oxalate and amine and thermally decomposing them to form a silver oxalate amine complex. Techniques for producing silver nanoparticles by thermally decomposing silver oxalate and amine are described, for example, in JP 2012-162767 A and JP 5574761 A. The above-mentioned method does not require mixing a reducing agent for reducing silver ions, and it is possible to produce silver nanoparticles by a simple method. In addition, the silver nanoparticles obtained by the above-mentioned method have amino groups of amine molecules mainly coordinated to the silver particle surface, and have high dispersibility in a dispersion medium. In addition, since the particle size and dispersibility can be changed depending on the manufacturing conditions, the silver nanoparticle ink using these can express a design in which the brilliance is adjusted depending on the silver nanoparticles used and their concentration.

[0027] There is also a method for producing silver nanoparticles by using polyvinylpyrrolidone as a molecule that coordinates to the surface of the particles when silver oxalate is thermally decomposed (Non-Patent Document 1). The silver nanoparticles synthesized by this method include plate-shaped ones, which are expected to have a high sense of brightness when printed. 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. In addition, since the metallic luster is enhanced, 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 decreases, and if it exceeds 50% by mass, the dispersibility may decrease.

[0028] The phosphate ester dispersant for dispersing the silver nanoparticles according to the present embodiment is preferably polyoxyethylene alkyl ether phosphate with an HLB value of 7 to 14. If the HLB is 7 or less or 14 or more, the silver nanoparticles may not be completely dispersed. The phosphate ester moiety is preferably a polyoxyethylene alkyl chain. Other polyoxyalkylene alkyl chains may not disperse. The amount of addition is preferably 1% to 30% based on the mass of the silver nanoparticles. More preferably, it is 5% to 20%. If it is less than 1%, the silver nanoparticles may not disperse, and if it exceeds 30%, the luster of the silver nanoparticles may be lost. Specific examples of the phosphate ester dispersant that can be added to the present invention include NIKKOL DDP-4, DDP-6, DDP-8, DDP-10 (Nikko Chemicals), Plysurf A212C, A215C, A208F, A210B, A219B (Dai-ichi Kogyo Seiyaku), etc., but are not limited thereto.

[0029] An example of the chemical structure of a phosphate ester dispersant is shown in Figure 3. The silver nanoparticle ink according to this embodiment may contain additives such as a pigment, a defoaming agent, a leveling agent, and a curing agent in addition to the dispersant described above. Examples of the dispersion medium contained in the silver nanoparticle ink according to this embodiment include water, ethanol, 2-propanol, 1-butanol, methyl ethyl ketone, ethyl acetate, toluene, cyclohexanone, terpenes such as terpineol, and the like. A polar solvent such as alcohol is preferable, as it enhances dispersibility with the phosphate ester dispersant. The dispersion medium may be a suitable mixture of the above-mentioned components according to the desired physical properties of the coating liquid.

[0030] The blending ratio of the above components in the coating liquid is not particularly limited, but when it is necessary to prevent the coating liquid from drying in the nozzle, such as in the inkjet printing method, it is more preferable that the inkjet coating liquid (silver nanoparticle ink) contains at least one organic solvent with a boiling point of 110°C or higher, such as glycerin, propylene glycol, 1-butanol, cyclohexanone, and terpineol, in total at 1% by mass or more. If the content of the above components in the coating liquid is less than 1% by mass, the coating liquid is more likely to dry, which may cause clogging of the nozzle. There is no upper limit to the content of the above components, but if the content is too high, the time required for drying the coating liquid may be extended.

[0031] The color of the layer printed with the silver nanoparticle ink according to this embodiment (inkjet printing layer) can be expressed not only in silver derived from silver, but also in blue, green, yellow, red, and other colors derived from localized surface plasmon resonance of silver nanoparticles, but is not limited to these. The size and shape of the silver nanoparticles, surface modification, ink concentration, particle density on the substrate, etc. affect the color. The configuration of the decorative sheet according to each embodiment of the present invention will be described below.

[0032] (First embodiment) FIG. 4 is a schematic cross-sectional view illustrating the configuration of the decorative sheet 10 according to the first embodiment of the present invention. In the decorative sheet 10 according to the first embodiment, a silver pattern printed layer (glossy pattern printed layer) 2 is formed on a substrate sheet 1 by an inkjet printing method using silver nanoparticle ink. The silver pattern printed layer 2 formed using the silver nanoparticle ink simultaneously becomes a glossy layer K1, and has the function of imparting a sense of brilliance to the decorative sheet 10 and enhancing the design. Here, the color of the "silver pattern printed layer 2" according to this embodiment is not limited to silver (silver color). This is because, as described above, the color changes depending on the size and shape of the silver nanoparticles contained, the surface modification, the concentration of the ink, the particle density on the substrate, and the like. In this embodiment, the glossy pattern printed layer formed containing silver nanoparticles is conveniently referred to as a "silver pattern printed layer" in order to distinguish it from the "color pattern printed layer" described later.

[0033] The silver pattern printed layer 2 preferably contains 90% by mass or more of silver nanoparticles, more preferably 95% by mass or more, and even more preferably 98% by mass or more, based on the total mass of the silver pattern printed layer 2. If the content of silver nanoparticles is 90% by mass or more, a sense of brightness can be effectively imparted to the silver pattern printed layer 2. The thickness of the silver pattern printed layer 2 is preferably in the range of 10 nm to 1000 nm, more preferably in the range of 100 nm to 500 nm, and even more preferably in the range of 200 nm to 400 nm. If the thickness of the silver pattern printed layer 2 is within the above numerical range, it can be printed by inkjet printing and effectively impart brilliance to the inkjet printed layer.

[0034] As shown in FIG. 4, the silver pattern printed layer 2 may be formed so as to cover at least a portion of the surface of the base sheet 1, or may be formed so as to cover the entire surface of the base sheet 1. Materials for the base sheet 1 include sheet-shaped polyvinyl chloride (PVC) resin, acrylic resin, polyolefin-based polypropylene resin, polyethylene resin, polycarbonate resin, etc., all of which are flexible, thermoplastic, moldable, and suitable for printing, as well as sheet-shaped paper, steel plate, wood, etc. These can be appropriately selected depending on the application and specifications of the base sheet 1.

[0035] Second embodiment 5 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, a pattern formed with colored ink is used as a color picture printed layer 2', and a silver picture printed layer 2 (glossy layer K2) using silver nanoparticle ink is formed thereon by inkjet printing. Therefore, the decorative sheet 20 according to the second embodiment is a highly designed decorative sheet 20 in which the glittering layer K2 shows a sense of brilliance colored with any color. The color picture printed layer 2' can be formed by a printing method such as gravure printing or inkjet printing.

[0036] The thickness of the color pattern printed layer 2' is preferably in the range of 1 μm to 100 μm, more preferably in the range of 10 μm to 80 μm, and even more preferably in the range of 30 μm to 50 μm. If the thickness of the color pattern printed layer 2' is within the above numerical range, the silver pattern printed layer 2 can be effectively given a brilliance colored with any color. The thickness of the color pattern-printed layer 2' is preferably within a range of 1 to 10 times, more preferably 2 to 8 times, and even more preferably 3 to 5 times, the thickness of the silver pattern-printed layer 2. If the thickness of the color pattern-printed layer 2' is within the above numerical range, the silver pattern-printed layer 2 can be effectively imparted with a sense of brilliance colored in any color.

[0037] The color picture printed layer 2' may be a layer containing silver nanoparticles, but is preferably a layer not containing silver nanoparticles. When the color picture printed layer 2' is a layer not containing silver nanoparticles, the brilliance of the silver picture printed layer 2 tends to be more prominent. If the color picture printed layer 2' is a layer containing silver nanoparticles, it is possible to impart a brilliance to the entire decorative sheet 20. In addition, the silver pattern printed layer 2 (lustrous layer K2) may be formed so as to cover the entire surface of the color pattern printed layer 2', as shown in Figure 5, or may be formed so as to cover only a portion of the surface of the color pattern printed layer 2'.

[0038] Third embodiment FIG. 6 is a schematic cross-sectional view illustrating the configuration of the decorative sheet 30 according to the third embodiment of the present invention. In the decorative sheet 30 according to the third embodiment, the silver pattern printed layer 2 formed using the silver nanoparticle ink included in the decorative sheet 10 according to the first embodiment shown in FIG. 1 and the color pattern printed layer 2' formed using the color ink included in the decorative sheet 20 according to the second embodiment shown in FIG. 5 are formed on the same plane of the base sheet 1 so that they do not overlap. Therefore, only a part of the silver pattern printed layer 2 is made into the glittering layer K1, and a highly designed decorative sheet 30 is obtained in which only that part shows a sense of brilliance. It is to be noted that the order of forming the silver pattern printed layer 2 formed using the silver nanoparticle ink and the color pattern printed layer 2' formed using the color ink may be either first. In other words, the silver pattern printed layer 2 may be formed on the base sheet 1 by the inkjet printing method using the silver nanoparticle ink, and then the color pattern printed layer 2' may be formed using the color ink, or the color pattern printed layer 2' may be formed using the color ink, and then the silver pattern printed layer 2 may be formed by the inkjet printing method using the silver nanoparticle ink. In addition, the silver pattern printed layer 2 (photoluminescent layer K1) and the color pattern printed layer 2' may be formed so that a portion of the surface of the base sheet 1 is exposed, as shown in Figure 6, or the silver pattern printed layer 2 (photoluminescent layer K1) and the color pattern printed layer 2' may be formed so as to cover the entire surface of the base sheet 1.

[0039] (Fourth embodiment) FIG. 7 is a schematic cross-sectional view illustrating the configuration of the decorative sheet 40 according to the fourth embodiment of the present invention. In the decorative sheet 40 according to the fourth embodiment, a colored pattern printed layer 2' formed on a base sheet 1 using a colored ink, a glittering layer K2 which is a silver pattern printed layer 2 formed on the colored pattern printed layer 2' using a silver nanoparticle ink, and a glittering layer K3 which is a silver pattern printed layer 2 formed on the base sheet 1 using a silver nanoparticle ink are formed. In other words, in the decorative sheet 40 according to the fourth embodiment, in addition to the form of the decorative sheet 20 according to the second embodiment shown in FIG. 5, a glittering layer K3 is formed. As a result, the decorative sheet 40 according to the fourth embodiment is a decorative sheet 40 with high designability that is partially colored and shows a sense of brilliance overall. Although not shown, the side surfaces of the color pattern printed layer 2' may also be covered with a glittering layer (silver pattern printed layer 2). In addition, the silver pattern printed layer 2 (lustrous layer K2) may be formed so as to cover the entire surface of the base sheet 1 and the color pattern printed layer 2', as shown in Figure 5, or may be formed so as to cover at least a portion of the surface of the base sheet 1 and the color pattern printed layer 2'.

[0040] Fifth embodiment 8 is a schematic cross-sectional view illustrating the configuration of a decorative sheet 50 according to a first embodiment of the present invention. In the decorative sheet 50 according to the first embodiment, a primer layer 3 is provided on a base sheet 1, and a silver pattern-printed layer (glossy pattern-printed layer) 2 is formed thereon by an inkjet printing method using silver nanoparticle ink. The silver pattern-printed layer 2 formed using silver nanoparticle ink simultaneously becomes a glossy layer K4, and has the function of imparting a sense of brilliance to the decorative sheet 50 and enhancing the design. Although not shown, a color pattern-printed layer 2' may be provided on the primer layer 3 as in the previous embodiments 2 to 4.

[0041] Any material can be used for the primer layer 3 as long as it can produce a smooth surface. Examples of materials for the primer layer 3 include ester resins, urethane resins, acrylic resins, urethane-based acrylic resins (urethane acrylates), vinyl chloride-vinyl acetate copolymers, polyvinyl butyral resins, and the like, but materials that have good adhesion and bonding properties with other layers are preferred. The primer layer may contain, as necessary depending on the intended use, one or more of various conventionally known additives such as antioxidants, ultraviolet absorbers, light stabilizers, heat stabilizers, plasticizers, lubricants, antistatic agents, flame retardants, fillers, etc. In addition, the primer layer may also function as an ink absorbing layer by mixing silica fine particles, or as a color layer by mixing a dye.

[0042] The thickness of the primer layer is not particularly limited and may be appropriately changed depending on the material and application used. However, when the surface of the layer below the primer layer is rough, it is preferable to provide a sufficient thickness so that the surface of the primer layer becomes smooth. Furthermore, the primer layer can be applied by any method, such as gravure, inkjet, screen, bar coating, or the like.

[0043] Sixth embodiment FIG. 9 is a schematic cross-sectional view illustrating the configuration of a decorative sheet 60 according to a sixth embodiment of the present invention. In the decorative sheet 60 according to the sixth embodiment, a pattern formed with colored ink is used as a color picture printed layer 2', a primer layer 3 is applied thereon, and a silver picture printed layer 2 (glossy layer K4) using silver nanoparticle ink is further formed by an inkjet printing method. Therefore, the decorative sheet 60 according to the sixth embodiment is a highly designed decorative sheet 60 in which the glittering layer K4 has a shining part colored with an arbitrary color. The color picture printed layer 2' may be formed to cover only a part of the surface of the base sheet 1 as shown in FIG. 9, or may be formed to cover the entire surface of the base sheet 1. In addition, the silver pattern printed layer 2 (lustrous layer K4) may be formed so as to cover only a portion of the surface of the primer layer 3, or may be formed so as to cover the entire surface of the primer layer 3.

[0044] Seventh embodiment Fig. 10 is a schematic cross-sectional view illustrating the configuration of a decorative sheet 70 according to a seventh embodiment of the present invention. In the decorative sheet 70 according to the seventh embodiment, the surface of the decorative sheet 10 according to the first embodiment shown in Fig. 4 is covered with a surface protective layer 4. In other words, the decorative sheet 70 is a decorative sheet having a surface protective layer 4 on the outermost layer. The material of the surface protection layer 4 may be, for example, a thermosetting resin, an ionizing radiation curing resin, or a mixture of these resins. The thermosetting resin may be, for example, a thermosetting resin having a urethane bond, such as a two-component curing urethane resin. The ionizing radiation curing resin may be, for example, 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. By using these materials, the hardness of the surface protection layer 4 may be improved, and the surface physical properties such as abrasion resistance, scratch resistance, and solvent resistance may be improved.

[0045] In addition, functional additives such as antibacterial agents and antifungal agents may be added to the surface protective layer 4 to impart various functions. In addition, if necessary, an ultraviolet absorber or a light stabilizer may be added to the surface protective layer 4. As the ultraviolet absorber, for example, a benzotriazole-based, benzoate-based, benzophenone-based, or triazine-based agent can be used. As the light stabilizer, for example, a hindered amine-based agent can be used. Furthermore, when anti-staining performance or cellophane tape (registered trademark) releasability is required, a release agent having a silicone skeleton can be added. In this case, the type of release agent is not particularly limited, but by using a silicone release agent having a terminal functional group that is reactive to the resin composition, the durability of the anti-staining performance and the cellophane tape (registered trademark) releasability can be improved.

[0046] The decorative sheet 70 of the seventh embodiment has a surface protective layer 4 covering the surface of the decorative sheet 10 of the first embodiment shown in Figure 4, but similarly, the decorative sheet 70 may have a form in which the surface protective layer 4 covers each of the surfaces of the decorative sheet 20 of the second embodiment to the decorative sheet 60 of the sixth embodiment shown in Figures 5 to 9, respectively. The thickness of the surface protective layer 4 is not particularly limited as long as it can cover the entire silver pattern printed layer 2 (lustrous layer K1), but is preferably in the range of 1 μm to 50 μm, more preferably in the range of 5 μm to 30 μm, and even more preferably in the range of 10 μm to 20 μm. If the thickness of the surface protective layer 4 is within the above numerical range, the silver pattern printed layer 2 can be effectively protected and the flexibility of the decorative sheet 70 can be maintained.

[0047] Fig. 11 is a schematic cross-sectional view illustrating the configuration of a decorative board 100 including a decorative sheet 70 according to a seventh embodiment of the present invention. As shown in Fig. 11, the decorative board 100 according to this embodiment has a laminated structure in which the decorative sheet 70 shown in Fig. 10 is laminated on one surface of a substrate 6. An adhesive layer 5 is provided between the substrate 6 and the decorative sheet 70, and the substrate 6 and the decorative sheet 70 are bonded together by the adhesive layer 5. For example, a wood board such as plywood, particle board, medium density fiberboard (MDF), hardboard, or a metal board can be used as the substrate 6. Furthermore, for example, a thermoplastic resin, a thermosetting resin, or the like can be used as the adhesive layer 5.

[0048] The decorative board 100 shown in Figure 11 has a laminated structure in which the decorative sheet 70 shown in Figure 10 is laminated on one side of a substrate 6, but it may also have a laminated structure in which decorative sheets in which each surface of the first embodiment of the decorative sheet 10 to the sixth embodiment of the decorative sheet 60 shown in Figures 4 to 9, respectively, is covered with a surface protective layer 4 are laminated on a substrate 6. EXAMPLES

[0049] Next, examples of the decorative sheet according to this embodiment will be described. The decorative sheet according to the first embodiment or the sixth embodiment will be described as an example using the material configuration and process shown below, but the present invention is not limited to these.

[0050] <Example 1> [Synthesis of silver oxalate] 9.92g of oxalic acid dihydrate (Kanto Chemical Co., Ltd.) was dissolved in 60mL of distilled water while heating, and 26.7g of silver nitrate (Kanto Chemical Co., Ltd.) was dissolved in 20mL of distilled water while heating while stirring in a 110℃ oil bath, and the mixture was added and heated and stirred for 1 hour. The precipitated silver oxalate was collected by natural filtration, and then filtered and washed with 200mL of hot water and 50mL 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 21.6g (yield 90.4%).

[0051] [Synthesis of silver nanoparticles 1] In the synthesis of silver nanoparticles, 1.43g of n-hexylamine (Tokyo Chemical Industry Co., Ltd.), 1.21g of N,N-diethyl-1,3-diaminopropane (Tokyo Chemical Industry Co., Ltd.), and 0.13g of oleic acid (Kanto Chemical Co., Ltd.) were added to the mixture, which was then heated and stirred in an oil bath at 110°C. Carbon dioxide bubbles began to form within 10 minutes, and after a few minutes the mixture turned into a brown suspension. After heating for 5 minutes, the mixture was cooled, and 30mL of methanol was added. The precipitate obtained by centrifugation was naturally dried to obtain 1.48g of blue solid silver nanoparticles 1 (yield based on silver: 97.0%).

[0052] [Ink preparation] 0.20 g of the obtained silver nanoparticles 1 was added to 2.0 g of n-butanol (Kanto Chemical Co., Ltd.), 0.02 g of phosphate ester dispersant NIKKOL DDP-8 (Nikko Chemical Co., Ltd.) was added, and the mixture was stirred to prepare a dispersion liquid. In this case, since there were 0.2 g of silver nanoparticles per 2.0 g of dispersion solvent, the mass % of the silver nanoparticles was 10%. The dispersant was added at 10% of the mass of the silver nanoparticles. The dispersion liquid was passed through a syringe filter (Whatman Co., 25 mm GD / X syringe filter (GF / B 1.0 μm)) to prepare silver nanoparticle ink 1 for inkjet printing.

[0053] The obtained silver nanoparticles 1 were observed in S-TEM mode (accelerating voltage 30 kV) using a scanning electron microscope (Hitachi High-Technologies Corporation, SEM S-4800), and spherical particles with a particle diameter of about 10 to 30 nm were observed. The results are shown in Figure 1. More specifically, Figure 1 is a scanning electron microscope image of silver nanoparticles 1 observed after the silver nanoparticle dispersion obtained in Example 1 was dropped onto a substrate (copper mesh microgrid) and dried. Next, we performed dynamic light scattering particle size measurement (Nikkiso Co., Ltd., Nanotrac UPA-EX150) on silver nanoparticle ink 1. The results showed that the silver nanoparticles were well dispersed with an average particle diameter of 20 nm. The results are shown in Figure 2.

[0054] [Preparation of decorative sheet 10] A PVC film (FZ manufactured by RIKEN TECHNOS CORPORATION) was used as the base sheet 1. Next, a primer coating liquid was applied as the primer layer 3 using a wire bar #7, and the primer layer was heated for 1 minute in an oven heated to 40°C to remove the solvent. The surface roughness of the primer layer was measured to be Sa 0.463 μm. The surface roughness was measured using a 3D measuring laser microscope (Olympus Corporation, LEXT OLS4000). Next, as the color pattern printing layer 3', inkjet inks (yellow, magenta, cyan) not containing glittering pigment were used to print wood grain images with a resolution of 305 dpi using an inkjet printer. Furthermore, as the glittering pattern printing layer 2, a medium-color wood grain pattern was printed using the above-mentioned silver nanoparticle ink using an inkjet printer. Furthermore, as the surface protection layer 4, a PVC film was attached by thermal lamination. In this way, the decorative sheet of Example 1 was produced.

[0055] <Example 2> The silver nanoparticles 1 obtained in Example 1 were treated in the same manner as in Example 1 except that 0.02 g of phosphate ester dispersant NIKKOL TDP-8 (Nikko Chemical) was added to prepare silver nanoparticle ink 2, and the decorative sheet of Example 2 was prepared.

[0056] <Example 3> The silver nanoparticles 1 obtained in Example 1 were treated in the same manner as in Example 1, except that 0.02 g of phosphate dispersant NIKKOL DDP-10 (Nikko Chemical) was added, to give silver nanoparticle ink 3, which was then used as the decorative sheet of Example 3.

[0057] <Example 4> The silver nanoparticles 1 obtained in Example 1 were treated in the same manner as in Example 1, except that 0.02 g of a phosphate dispersant NIKKOL TDP-2 (Nikko Chemical) was added, to give silver nanoparticle ink 4, which was then used as the decorative sheet of Example 4.

[0058] <Example 5> The synthesis of silver nanoparticles was changed 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, and 1.92 g of silver oxalate was added and heated and stirred in an oil bath at 95 ° C. After heating, the color began to change after a few minutes, and after 18 minutes, carbon dioxide foaming occurred and the suspension changed to 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 naturally dried to obtain 1.29 g of silver nanoparticles (silver-based yield 95.0%), which is a blue solid. A scanning electron microscope image of the obtained silver nanoparticles is shown in FIG. 12. Silver nanoparticles with a particle diameter of 40 to 60 nm were observed. The obtained silver nanoparticles 2 were used in the same manner as in Example 1 to prepare silver nanoparticle ink 5, and the decorative sheet of Example 5 was produced.

[0059] <Example 6> Using the same materials as in Example 1, a color pattern printed layer 2' was printed, a primer layer 3 was applied, a glossy pattern printed layer 2 was printed on top of that, and a surface protective layer 4 was applied to produce a decorative sheet 60 according to the sixth embodiment shown in Figure 9, as Example 6.

[0060] <Comparative Example 1> The silver nanoparticles 1 obtained in Example 1 were treated in the same manner as in Example 1, except that 0.02 g of a phosphate dispersant NIKKOL DDP-2 (Nikko Chemical) was added, to give silver nanoparticle ink 6, which was then used as the decorative sheet of Comparative Example 1.

[0061] <Comparative Example 2> The silver nanoparticles 1 obtained in Example 1 were treated in the same manner as in Example 1, except that 0.02 g of a phosphate dispersant NIKKOL DLP-10 (Nikko Chemical) was added, to give silver nanoparticle ink 7, which was used as the decorative sheet of Comparative Example 2.

[0062] <Comparative Example 3> The silver nanoparticles 1 obtained in Example 1 were treated in the same manner as in Example 1, except that 0.02 g of phosphate ester dispersant Antox-400 (Nippon Nyukazai) was added, to give silver nanoparticle ink 8, which was then used as the decorative sheet of Comparative Example 3.

[0063] <Comparative Example 4> The decorative sheet of Comparative Example 4 was produced in the same manner as in Example 1, except that a wood grain pattern was printed with a gravure printing machine using a gravure ink containing a photochromic pigment (Lamistar (registered trademark) manufactured by Toyo Ink Co., Ltd.) as the photochromic pattern printing layer.

[0064] <Comparative Example 5> The decorative sheet of Comparative Example 5 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 glittering pigment as the picture printed layer.

[0065] <Comparative Example 6> The decorative sheet of Comparative Example 6 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 silver ink (manufactured by Mimaki Engineering Co., Ltd.) that did not contain silver nanoparticles as the picture printed layer.

[0066] [Evaluation method for silver nanoparticle ink] After preparing the silver nanoparticle ink, the ink was left to stand for one day, after which its appearance was evaluated to see if any precipitate was present.

[0067] [Decorative sheet evaluation method] The decorative sheets of the above-prepared Examples and Comparative Examples were evaluated for brilliance and design. Brightness The sense of brilliance was evaluated by a sensory test using human eyes on the surface of the decorative sheet. The evaluation criteria are as follows: The brightness perception was evaluated by 50 or more of 100 subjects based on the same judgment results. In other words, if 50 or more people judged the wood grain to be natural and to have reproduced the natural luster of natural wood, the product was rated as "○". In addition, more than 50 people rated the wood grain as having an unnaturally strong shine and therefore unable to reproduce the natural luster of natural wood, or as having a grain that was too weak and therefore unable to reproduce the natural luster of natural wood, as "X". Since the color varies depending on the ink, the color was not taken into consideration and only the shine was evaluated.

[0068] ·Design The design was evaluated by a visual sensory test of the surface of the decorative sheet. The evaluation criteria are as follows: The design was evaluated by 100 subjects, with more than 50 of them giving the same judgment. In other words, more than 50 people rated the product as "○" when they felt that the contours of the fine lines (a few μm wide) of the wood grain pattern were reproduced properly without any blurring. In addition, more than 50 people rated items where they felt the outlines of the fine lines (a few microns wide) in the wood grain pattern were blurred and not reproduced as "X", and items with partial unevenness in the printing were rated as "△". A microscope with a magnification of 100x was used to confirm the outlines of the fine lines in the wood grain pattern.

[0069] [Evaluation Results] The evaluation results of Examples 1 to 6 and Comparative Examples 1 to 6 are shown in Tables 1 and 2.

[0070] [Table 1]

[0071] [Table 2]

[0072] As shown in Table 1, the one using the phosphoric acid ester dispersant with an HLP value of 7 to 14 did not have any precipitate, and as shown in Table 2, the decorative sheets of Examples 1 to 3, 5, and 6, which satisfy the conditions of the present invention, had good both brilliance and design. In Example 4, the brilliance was sufficient, but unevenness was observed in some parts of the print. On the other hand, the decorative sheets of Comparative Examples 1, 2, and 3 lacked brilliance and some unevenness occurred. In Comparative Example 4, which used a gravure printing machine, the thin lines were blurred and the design was insufficient. In Comparative Example 5, in which UV ink not containing a glittering pigment was inkjet printed, the brilliance was insufficient. In Comparative Example 6, in which UV silver ink not containing silver nanoparticles was inkjet printed, the brilliance was excessive. In Comparative Example 4, in which a primer layer was not provided, the brilliance was improved by increasing the resolution, but the brilliance was not easily expressed compared to when a primer layer was provided. [Explanation of symbols]

[0073] 1 Base sheet 2 Silver pattern printing layer (glossy pattern printing layer) 2' Color pattern printing layer 3 Primer layer 3' Color pattern printing layer 4 Surface protective layer 5 Adhesive layer 6 Substrate

Claims

1. An inkjet ink for decorative sheets for forming a picture print layer using an inkjet printing method, Contains silver nanoparticles, phosphate ester dispersant, and solvent. The phosphate ester-based dispersant has an HLB (Hydrophilic-Lipophilic Balance) value, which indicates the degree of affinity of a surfactant for water and oil (a water-insoluble organic compound), of 7 or more and 14 or less; the solvent is ethanol, 2-propanol, 1-butanol, methyl ethyl ketone, ethyl acetate, toluene, cyclohexanone, terpineol, glycerin, or propylene glycol; An inkjet ink for decorative sheets, comprising only a phosphate triester compound as the phosphate ester-based dispersant.

2. 2. The inkjet ink for decorative sheets according to claim 1, wherein the silver nanoparticles are surface-protected with protective molecules mainly containing an amine compound.

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

4. The inkjet ink for decorative sheets according to any one of claims 1 to 3, characterized in that the solvent is 1-butanol.

5. 5. The inkjet ink for decorative sheets according to claim 1, wherein the phosphate moiety of the phosphate-based dispersant is a polyoxyethylene alkyl chain.

6. The inkjet ink for decorative sheets according to any one of claims 1 to 5, characterized in that the phosphate ester-based dispersant is contained in an amount of 1% to 30% by mass relative to the mass of the silver nanoparticles.

7. A decorative sheet comprising at least an inkjet printed layer formed using the inkjet ink according to any one of claims 1 to 6 on one surface side of a base sheet.

8. 8. The decorative sheet according to claim 7, wherein the inkjet printed layer is a glittering picture printed layer containing the silver nanoparticles.

9. 9. The decorative sheet according to claim 7, further comprising a colored pattern printed layer formed on one surface of the base sheet using colored inks.

10. The decorative sheet according to claim 9, characterized in that the glossy picture printed layer consisting of the inkjet printing layer and the color picture printed layer formed using colored inks have non-overlapping portions in which the two do not overlap when viewed in a plane.

11. 11. The decorative sheet according to claim 9 or 10, further comprising the inkjet print layer formed on the color pattern print layer.

12. The decorative sheet according to any one of claims 7 to 11, characterized in that a color pattern printed layer is formed on one side of the base sheet, and a primer layer and an inkjet printed layer are formed in this order on the base sheet and the color pattern printed layer.

13. The decorative sheet according to any one of claims 7 to 12, further comprising a surface protective layer as an outermost layer.

14. A decorative board comprising the decorative sheet according to any one of claims 7 to 13 and a substrate disposed on the other surface side of the base sheet of the decorative sheet.

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