Antibacterial decorative sheets and decorative panels

Abstract

To provide an antibacterial decorative sheet and a decorative laminate, to be used for a wall material, a ceiling material and a floor material in an architectural structure such as housing, an interior material and fittings such as a fixture material, household furniture and fixtures, etc., exterior for residential facilities and home appliances, and vehicle interior, etc. for motor vehicles.SOLUTION: An antibacterial decorative sheet at least includes, on one surface side of a base material sheet, a brilliant pattern printed layer formed using an inkjet ink, and a surface protective layer on the brilliant pattern printed layer. The surface protective layer is transparent and porous, and has a haze of 10% or lower. The inkjet ink contains silver nanoparticles.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to an antibacterial decorative sheet and decorative board. The present invention relates to a technology suitable for antibacterial 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 exterior of housing equipment and home appliances, and the interior of vehicles such as automobiles. [Background technology]

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

[0003] For example, in the surface decoration of building materials, furniture, the housings of home appliances, etc., decorative sheets and decorative boards with a glittering layer added to a wood grain pattern are used for the purpose of reproducing the luster, depth, and wood grain feel that are unique to 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] The decorative sheet has a pattern 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. In response to this, the technology described in Patent Document 3 proposes using inkjet printing for printing the decorative sheet. In this case, for example, in order to improve the design of the decorative sheet, it is possible to mix a glitter pigment into the inkjet ink to impart glitter to the inkjet-printed layer.

[0006] Inkjet printing is now widely used in a variety of fields and applications, making it a familiar presence. For example, in the home, 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 also widely used for commercial printing such as barcode printers, signs, POP displays, 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, known as proofs.

[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, because many photoluminescent pigments have large particle sizes, using ink in which photoluminescent pigments are dispersed can cause problems with clogging inside 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 create a glittering layer is to use a solid coating method as in Patent Documents 1 and 2, or to print it using other methods such as gravure printing, which often results in poor design and a complicated printing process. In other words, there has been a problem with conventional decorative sheets that offer both high brightness and high design.

[0010] In addition, decorative sheets are becoming increasingly sophisticated, resulting in multi-layered sheets and increased manufacturing processes. Given the recent rise in hygiene awareness, antibacterial properties are a particularly sought-after feature. Numerous antibacterial products using silver nanoparticles have been developed, and even minute amounts of silver nanoparticles have been shown to be highly effective. The antibacterial properties of silver nanoparticles result from the oxidation of the particles in the presence of oxygen and protons, releasing silver ions. Silver ions interact with thiol groups in enzymes and proteins essential for bacterial life, affecting cellular respiration and causing cell death. Therefore, for silver nanoparticles to exert their antibacterial properties, it is important to use them in an environment where oxygen and protons are present. However, because oxidation of silver nanoparticles causes discoloration, it has been difficult to create decorative sheets that combine antibacterial and decorative properties using silver nanoparticles alone. [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 consideration of the above-mentioned problems and circumstances, and its purpose is to provide decorative sheets and decorative panels that have high brightness, high design potential, and antibacterial properties. [Means for solving the problem]

[0013] In order to solve the above problems, according to one aspect of the present invention, there is provided an antibacterial decorative sheet comprising at least a glittering picture printed layer formed on one side of a base sheet using inkjet ink, and a surface protective layer on the glittering picture printed layer, wherein the surface protective layer is transparent and porous, the haze of the surface protective layer is 10% or less, and the inkjet ink contains silver nanoparticles. The size of the voids in the surface protection layer is in the range of 10 nm to 1 μm. An antibacterial decorative sheet characterized by:

[0014] The sheet is characterized by further comprising a colored picture printed layer formed using colored ink on one side of the base sheet.

[0015] The glittering picture printed layer and the color picture printed layer formed using colored inks have a non-overlapping portion where they do not overlap in a plan view.

[0016] The photosensitive material is characterized in that it has the glittering picture print layer formed on the color picture print layer.

[0017] A color picture print layer is formed on one side of the base sheet, and a primer layer and a glitter picture print layer are formed in this order on the base sheet and the color picture print layer.

[0018] A decorative board comprising the antibacterial decorative sheet and a substrate disposed on the other side of the decorative sheet. [Effects of the Invention]

[0019] According to an embodiment of the present invention, decorative sheets and decorative boards can be obtained that have high brightness, excellent design, and also antibacterial properties. Specifically, according to an embodiment of the present invention, a glossy pattern printed layer is printed using an inkjet ink containing silver nanoparticles, and then a transparent porous surface protective layer with a haze of 10% or less and a void size of 10 nm to 1 μm is provided on top of that, thereby obtaining antibacterial decorative sheets and decorative boards with high brightness. In other words, it is possible to reproduce prints that have antibacterial properties in addition to pearlescent designs characterized by the fine lines and gradations unique to building materials and a pale luster that is difficult to achieve with inks that use aluminum. [Brief explanation of the drawings]

[0020] [Figure 1] FIG. 1 is a diagram showing a scanning electron microscope image of silver nanoparticles observed after a dispersion of silver nanoparticles 1 obtained in Example 1 of the present invention was applied to a substrate and dried. [Figure 2] FIG. 1 is a diagram showing the particle size distribution and cumulative frequency (%) of silver nanoparticles 1 obtained in Example 1 of the present invention. [Figure 3] 1 is a schematic cross-sectional view illustrating the configuration of a decorative sheet according to a first embodiment of the present invention. [Figure 4] 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 5] 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 6] FIG. 10 is a schematic cross-sectional view illustrating the configuration of a decorative sheet according to a fourth embodiment of the present invention. [Figure 7] FIG. 10 is a schematic cross-sectional view illustrating the configuration of a decorative sheet according to a fifth embodiment of the present invention. [Figure 8] FIG. 10 is a schematic cross-sectional view illustrating the configuration of a decorative sheet according to a sixth embodiment of the present invention. [Figure 9] FIG. 4 is a schematic cross-sectional view illustrating the configuration of a decorative board provided with a decorative sheet according to a second embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0021] Hereinafter, the configurations of the decorative sheet and decorative board according to the embodiments of the present invention will be described with reference to the drawings.

[0022] The same components are designated by the same reference numerals unless there is a reason for convenience. In each drawing, 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 embodiments of the present invention have the common feature of comprising at least a glossy picture printed layer formed on a base sheet using inkjet ink and a transparent porous surface protective layer thereon, the inkjet ink containing silver nanoparticles. Whether the glossy picture printed 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 picture such as a wood grain pattern expressed on the printed layer, and seeing whether it is printed in brown or in multiple colors of red, blue, yellow, and black.

[0024] (First embodiment) FIG. 3 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 glittering pattern-printed layer 2 is formed on a substrate sheet 1 by inkjet printing using silver nanoparticle ink, and is covered with a transparent, porous surface protective layer 3. The glittering pattern-printed layer 2 formed using silver nanoparticle ink imparts a sense of brilliance to the decorative sheet 10 and has the function of enhancing its design. Here, the color of the glittering pattern-printed layer 2 according to this embodiment is not limited to silver (silver color). This is because, as mentioned above, the color changes depending on the size and shape of the silver nanoparticles contained, surface modification, ink concentration, particle density on the substrate, etc.

[0025] The glittering pattern printed layer 2 preferably contains 90% by mass or more, more preferably 95% by mass or more, and even more preferably 98% by mass or more of silver nanoparticles relative to the total mass of the glittering pattern printed layer 2. If the silver nanoparticle content is 90% by mass or more, a sense of brilliance can be effectively imparted to the silver pattern printed layer 2.

[0026] The thickness of the glittering 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 glittering pattern printed layer 2 is within the above numerical range, glitter can be effectively imparted to the glittering pattern printed layer by inkjet printing.

[0027] As shown in Figure 3, the glossy 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.

[0028] Furthermore, the decorative sheet 10 has its outermost surface covered with a porous surface protective layer 3. Because the surface protective layer has nano-sized pores, it is possible to minimize oxidation of the silver nanoparticles and maintain antibacterial properties and design properties. In other words, the decorative sheet 10 is a decorative sheet having a porous surface protective layer 3 on its outermost surface. The embodiments described below also have a porous surface protective layer 3 on its outermost surface.

[0029] (Second embodiment) 4 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 serves as the color picture printed layer 3, on which a glitter picture printed layer 2 using silver nanoparticle ink is formed by inkjet printing, and which is then covered with a transparent, porous surface protective layer 4. As a result, the decorative sheet 20 according to the second embodiment is a highly designable decorative sheet 20 in which the glitter picture printed layer 2 exhibits a sense of brightness colored in any color. The color picture printed layer 3 can be formed by a printing method such as gravure printing or inkjet printing, for example.

[0030] The thickness of the color picture printed layer 3 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 picture printed layer 3 is within the above numerical range, the brilliance of any color can be effectively imparted to the glitter picture printed layer 2.

[0031] The thickness of the color picture printed layer 3 is preferably in the range of 1 to 10 times, more preferably 2 to 8 times, and even more preferably 3 to 5 times the thickness of the glitter picture printed layer 2. If the thickness of the color picture printed layer 3 is within the above numerical range, the glitter picture printed layer 2 can be effectively imparted with the brightness of any color.

[0032] The color picture printed layer 3 may be a layer containing silver nanoparticles, but is preferably a layer that does not contain silver nanoparticles. If the color picture printed layer 3 is a layer that does not contain silver nanoparticles, the brightness of the glittering picture printed layer 2 tends to be more pronounced. If the color picture printed layer 3 is a layer that contains silver nanoparticles, it is possible to impart a brightness to the entire decorative sheet 20.

[0033] In addition, the glossy pattern printing layer 2 may be formed so as to cover the entire surface of the color pattern printing layer 3, as shown in Figure 4, or may be formed so as to cover only a portion of the surface of the color pattern printing layer 3.

[0034] (Third embodiment) FIG. 5 is a schematic cross-sectional view illustrating the configuration of a decorative sheet 30 according to a third embodiment of the present invention. In the decorative sheet 30 according to the third embodiment, the glittering pattern-printed layer 2 formed using the silver nanoparticle ink of the decorative sheet 10 according to the first embodiment shown in FIG. 3 and the colored pattern-printed layer 3 formed using the colored ink of the decorative sheet 20 according to the second embodiment shown in FIG. 4 are formed on the same plane of the base sheet 1 so as not to overlap, and are covered with a transparent, porous surface protective layer 4. This results in a decorative sheet 30 with a highly designable design, in which only a portion of the glittering pattern-printed layer 2 exhibits a sense of brilliance. Note that the order of forming the glittering pattern-printed layer 2 formed using the silver nanoparticle ink and the colored pattern-printed layer 3 formed using the colored ink does not matter. In other words, a glossy pattern printed layer 2 may be formed on a base sheet 1 by inkjet printing using silver nanoparticle ink, and then a colored pattern printed layer 3 may be formed using colored ink, or a colored pattern printed layer 3 may be formed using colored ink, and then a glossy pattern printed layer 2 may be formed by inkjet printing using silver nanoparticle ink.

[0035] As shown in Figure 5, the glossy picture printing layer 2 and the color picture printing layer 3 may be formed directly on the substrate rather than on the color picture printing layer 3, or the glossy picture printing layer 2 and the color picture printing layer 3 may be formed so as to cover the entire surface of the substrate sheet 1.

[0036] (Fourth embodiment) FIG. 6 is a schematic cross-sectional view illustrating the configuration of a decorative sheet 40 according to a fourth embodiment of the present invention. In the decorative sheet 40 according to the fourth embodiment, a color picture-printed layer 3 formed using colored inks is formed on a base sheet 1, a glitter picture-printed layer formed using silver nanoparticle inks is formed on the color picture-printed layer 3, and a glitter picture-printed layer 2 formed using silver nanoparticle inks is formed on the base sheet 1, and these are covered with a transparent porous surface protective layer 4. In other words, in the decorative sheet 40 according to the fourth embodiment, in addition to the configuration of the decorative sheet 20 according to the second embodiment shown in FIG. 4, a glitter picture-printed layer 2 is formed. This results in a decorative sheet 40 according to the fourth embodiment that is partially colored and has a highly designable appearance, exhibiting an overall sense of brilliance. Although not shown, the side surfaces of the color picture-printed layer 3 may also be covered with the glitter picture-printed layer 2.

[0037] As shown in Figure 4, the glossy pattern printing layer 2 may be formed so as to cover the entire surface of the base sheet 1 and the color pattern printing layer 3, or it may be formed so as to cover at least a portion of the surface of the base sheet 1 and the color pattern printing layer 3.

[0038] (Fifth embodiment) 7 is a schematic cross-sectional view illustrating the configuration of a decorative sheet 50 according to a fifth embodiment of the present invention. In the decorative sheet 50 according to the fifth embodiment, a primer layer 5 is provided on a base sheet 1, and a glittering pattern is printed thereon by inkjet printing using silver nanoparticle ink. A printed layer 2 is formed, and is covered with a transparent porous surface protective layer 4. The glittering pattern printed layer 2 formed using silver nanoparticle ink has the function of imparting a sense of brilliance to the decorative sheet 50 and enhancing its design. Although not shown, a color pattern printed layer 3 may be provided on the primer layer 5 as in the above-described embodiments 2 to 4.

[0039] There are no particular limitations on the thickness of the primer layer 5, and it may be changed as appropriate depending on the material used and the application. However, if the surface of the layer below the primer layer 5 is rough, it is preferable to provide a sufficient thickness so that the surface of the primer layer 5 is smooth. Furthermore, the primer layer 5 may be applied by any method, and can be applied by, for example, a gravure method, an inkjet method, a screen method, or even a bar coat method.

[0040] (Sixth embodiment) FIG. 8 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 serves as the color picture printed layer 3, on which a primer layer 5 is applied. Furthermore, a glitter picture printed layer 2 using silver nanoparticle ink is formed by inkjet printing, and this is covered with a transparent porous surface protective layer 4. Therefore, the decorative sheet 60 according to the sixth embodiment is a highly designable decorative sheet 60, in which the glitter picture printed layer 2 has shiny portions colored with any color. The color picture printed layer 3 may be formed to cover only a portion of the surface of the base sheet 1, as shown in FIG. 8, or may be formed to cover the entire surface of the base sheet 1.

[0041] The glittering picture-printed layer 2 may also be formed so as to cover only a part of the surface of the primer layer 5, or may be formed so as to cover the entire surface of the primer layer 5.

[0042] Fig. 9 is a schematic cross-sectional view illustrating the configuration of a decorative board 100 including a decorative sheet 10 according to a first embodiment of the present invention. As shown in Fig. 9, the decorative board 100 according to this embodiment has a laminated structure in which the decorative sheet 10 shown in Fig. 3 is laminated on one surface of a substrate 6. An adhesive layer 5 is provided between the substrate 6 and the decorative sheet 10, and the substrate 6 and the decorative sheet 10 are bonded together by the adhesive layer 5.

[0043] The decorative board 100 shown in Figure 9 has a laminated structure in which the decorative sheet 10 shown in Figure 3 is laminated on one side of the substrate 6, but it may also have a laminated structure in which the decorative sheet 20 of the second embodiment to the decorative sheet 60 of the sixth embodiment shown in Figures 4 to 8, respectively, are laminated.

[0044] The silver nanoparticle ink and the materials and configuration of the decorative sheet used in this embodiment will be described in detail below.

[0045] 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.

[0046] The silver nanoparticles according to this embodiment have a median diameter (D50) of, for example, 1 nm to 250 nm, and are dispersible in a dispersion medium such as an organic solvent or water. If the median diameter (D50) of the silver nanoparticles is less than 1 nm, visibility (brilliance) may decrease, while if the median diameter (D50) of the silver nanoparticles is greater than 250 nm, 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, Nikkiso Co., Ltd.).

[0047] There is no limitation on the shape of the silver nanoparticles, but they may be spherical, flat, polygonal, or the like. It is preferable that the silver nanoparticles have a plurality of shapes. Plate-shaped 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 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).

[0048] 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. Such silver compounds include, for example, 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 the silver compounds, silver oxalate is preferably used because it easily decomposes to produce metal and is less likely to produce impurities other than silver.

[0049] 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 it is advantageous in that impurities are less likely to remain.

[0050] 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, and improve dispersion stability. Examples of alcohols include methanol, ethanol, and 1-propanol. Examples of fatty acids include oleic acid and linoleic acid. Examples of polymers include polyvinylpyrrolidone and gelatin.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] Thus, 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 JP 2012-162767 A and Japanese Patent No. 5574761 A. The above-described method eliminates the need for a reducing agent to reduce silver ions, allowing for the production of silver nanoparticles using a simple method. Furthermore, the silver nanoparticles obtained using this method have amino groups of the amine molecules primarily coordinated to the silver particle surface, resulting in high dispersibility in the dispersion medium. Furthermore, because the particle size and dispersibility can be altered by adjusting the production conditions, silver nanoparticle inks using these inks can create designs with adjustable brilliance depending on the silver nanoparticles used and their concentration.

[0055] 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 (T. Togashi, S. Ojima, I. Sato, K. Kanaizuka, M. Kurihara, Chem. Lett., 2016, 45, 646-648). The silver nanoparticles synthesized using this method include plate-shaped ones, which are expected to have a high brightness when printed.

[0056] 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.

[0057] A dispersant may be used when dispersing the silver nanoparticles according to this embodiment in a solvent or the like used as a dispersion medium. Dispersants can be broadly classified as anionic, cationic, or nonionic, and are selected appropriately depending on the potential of the particle surface and the dispersion medium. Anionic dispersants are typically sulfate esters, phosphate esters, carboxylic acids, and sulfonic acids, with many of them primarily having an ethylene oxide (EO) adduct molecular structure. Cationic dispersants can be classified as quaternary ammonium salts, such as Cl salts, non-Cl salts, and EO adducts. Nonionic dispersants can be broadly classified as alkylene oxide adducts and chalcanolic amides. Because the surface modification of the silver nanoparticles according to this embodiment is an amine complex, anionic dispersants are particularly preferred. Specifically, polyoxyethylene alkyl ether phosphates (salts), polyoxyethylene alkyl ether sulfates, polyoxyethylene alkyl ether acetates, polyoxyethylene alkyl ether succinates, etc. are preferred, with polyoxyethylene alkyl ether phosphates (salts) being particularly preferred.

[0058] Specific examples include, but are not limited to, Phosphanol RB-40, RD-510Y, RD720N, RL-210, RS-410 (Toho Chemical Industry Co., Ltd.), NIKKOL DDP-8NV, DDP-2, DDP-4, DDP-6, DDP-8, DDP-10 (Nikko Chemicals Co., Ltd.), Plysurf A212C, A215C, A208F, M208F, A208A, A208B, A210B, A219B, DB-01, AL, DBS (Dai-ichi Kogyo Seiyaku Co., Ltd.), and the like.

[0059] The silver nanoparticle ink according to this embodiment may contain additives such as a pigment, an antifoaming agent, a leveling agent, a curing agent, etc. in addition to the dispersant described above.

[0060] 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, etc. The dispersion medium may be an appropriate mixture of the above components depending on the desired physical properties of the coating liquid.

[0061] 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 inside the nozzle, as in inkjet printing, it is more preferable that the inkjet coating liquid (silver nanoparticle ink) contains a total of 1 mass % or more of one or more organic solvents with a boiling point of 110°C or higher, such as glycerin, propylene glycol, 1-butanol, cyclohexanone, or terpineol. If the content of the above components in the coating liquid is less than 1 mass %, the coating liquid is more likely to dry, which may cause nozzle clogging. There is no upper limit to the content of the above components, but if it is too high, the coating liquid will not dry out as quickly as needed. There may be a delay.

[0062] The color of the layer printed with the silver nanoparticle ink according to this embodiment (glossy pattern printed layer) 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.

[0063] Materials for the base sheet 1 according to this embodiment include sheet-shaped polyvinyl chloride (PVC) resin, acrylic resin, polyolefin-based polypropylene resin, polyethylene resin, polycarbonate resin, etc., which are flexible, thermoplastic, moldable, and suitable for printing, as well as sheet-shaped paper, steel plate, wood, etc. These can be selected as appropriate depending on the application and specifications of the base sheet 1.

[0064] The material for the transparent porous surface protection layer 4 according to this embodiment can be, for example, a paint using silica nanoparticles with phenyl groups and polysilane, as described in Japanese Patent No. 6379582. This can be applied to produce a transparent porous film, but is not limited to this.

[0065] The thermosetting resin contained in the coating material may be, for example, a thermosetting resin having a urethane bond, such as a two-component curing urethane resin. Furthermore, the ionizing radiation curing resin may be, for example, an ultraviolet curing resin. Examples of ultraviolet curing resins that can be used include (meth)acrylic resins, silicone resins, polyester resins, urethane resins, amide resins, and epoxy resins. By using these materials, the hardness of the surface protection layer 4 can be improved, and surface properties such as abrasion resistance, scratch resistance, and solvent resistance can be improved. The coating material may also contain a surface conditioner that provides surface antifouling properties.

[0066] The transparent, porous surface protection layer 4 may be made of any material, as long as its haze is 10% or less and its pore size is 10 nm to 1 μm. It is sufficient that the appearance of the printed layer containing silver nanoparticles is not impaired; a haze value of 10% or more results in a white appearance and poor visibility. Furthermore, if the pore size is 10 nm or less, antibacterial properties may be reduced, and if it is 1 μm or more, oxidation of the silver nanoparticles may be accelerated, resulting in discoloration.

[0067] The surface protective layer 4 may also contain an ultraviolet absorber. 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 or 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 by using a silicone release agent having a terminal functional group that is reactive with the resin composition, the stain prevention performance and durability of Cellotape® releasability can be improved.

[0068] Any material can be used for the primer layer 5 according to this embodiment 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, and polyvinyl butyral resins, but materials that have good adhesion and bonding properties with other layers are preferred.

[0069] The primer layer 5 may contain one or more of various conventionally known additives such as antioxidants, ultraviolet absorbers, light stabilizers, heat stabilizers, plasticizers, lubricants, antistatic agents, flame retardants, and fillers, depending on the intended use. The ink-absorbing layer may also function as an ink-absorbing layer by mixing the ink or as a color layer by mixing the coloring matter.

[0070] The substrate 7 according to this embodiment may be made of a wood board such as plywood, particle board, medium density fiberboard (MDF), or hardboard, or a metal plate. The adhesive layer 6 may be made of a thermoplastic resin or a thermosetting resin. [Example]

[0071] Next, examples of the decorative sheet according to this embodiment will be described.

[0072] The decorative sheet 50 according to the fifth embodiment will be described using the following material configuration and process as an example, but the present invention is not limited to these.

[0073] [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).

[0074] [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).

[0075] 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 1. More specifically, Figure 1 is a scanning electron microscope image of the silver nanoparticles obtained in Example 1, observed after the toluene dispersion of the silver nanoparticles was dropped onto a substrate (copper mesh microgrid) and dried.

[0076] 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 D50 of 15 nm. The results are shown in Figure 2. The solid line in Figure 2 indicates the cumulative frequency (%).

[0077] [Ink Preparation] 0.20 g of the silver nanoparticles obtained in the above process were added to 1.8 g of toluene (Kanto Chemical Co., Ltd.) and 0.2 g of terpineol (isomer mixture, Fujifilm Wako Pure Chemical Industries, Ltd.) and stirred to form a dispersion. In this case, since 0.2 g of silver nanoparticles were used for 2.0 g of dispersion solvent, the mass percentage of silver nanoparticles was 10%. The dispersion was passed through a syringe filter (Whatman, 25 mm GD / X syringe filter (GF / B 1.0 μm)) to prepare silver nanoparticle ink for inkjet printing.

[0078] [Preparation of Surface Protective Layer Coating 1] Phenyl group surface-modified silica fine particles (product name: PL-2-TOL, particle size around 25 nm, The solid content ratio of polymethylphenylsilane (PMPS; product name: SI-10-10, manufactured by Kuwa Chemical Co., Ltd.) was 50% by mass, the solid content ratio of polymethylphenylsilane (PMPS; product name: SI-10-10, manufactured by Osaka Gas Chemical Co., Ltd.) was 1%, and the solid content ratio of pentaerythritol triacrylate (PETA; solid content concentration 100%) was 49%, and the coating liquid was diluted with toluene so that the ratio of total solids to the weight of the coating liquid was 20% by mass, to prepare surface protective layer coating 1.

[0079] [Evaluation of surface protective layer 4] The haze of the prepared surface protective layer was measured using a haze meter ("NDH2000" manufactured by Nippon Denshoku Industries Co., Ltd.) after applying only the surface protective layer coating material to a PET substrate (Lumirror T60, 75 μm thick, manufactured by Toray Industries, Inc.) using a wire bar #7, heating it for 1 minute in an oven heated to 40°C, removing the solvent, and irradiating it with UV light under a nitrogen purge.

[0080] [Preparation of decorative sheet 50] A PVC film (FZ manufactured by Riken Technos Corporation) was used as the base sheet 1. Next, a wood grain image with a resolution of 610 dpi was printed using inkjet inks (yellow, magenta, and cyan) without glitter pigments as the color picture print layer 3 using an inkjet printer. A primer coating solution was applied to the primer layer 5 using a wire bar #7, and the resulting layer was heated in an oven heated to 40°C for 1 minute to remove the solvent. Furthermore, a wood grain pattern with a resolution of 610 dpi was printed using the silver nanoparticle ink as the glitter picture print layer 2 using an inkjet printer. Furthermore, the surface protection layer 4 was formed by applying the surface protection layer coating 1 using a wire bar #7, heating in an oven heated to 40°C for 1 minute to remove the solvent, and then irradiating with UV light under a nitrogen purge to produce a decorative sheet 50. A schematic cross section is shown in FIG. 7.

[0081] [Example 2] [Preparation of Surface Protective Layer Coating 2] The solid content ratio of phenyl group surface-modified silica microparticles (product name: PL-3-TOL, particle diameter approximately 35 nm, manufactured by Fuso Chemical) was 50 mass%, the solid content ratio of polymethylphenylsilane (PMPS; product name: SI-10-10, manufactured by Osaka Gas Chemical) was 1%, and the solid content ratio of pentaerythritol triacrylate (PETA; solid content concentration 100%) was 49%, and the coating liquid was diluted with toluene so that the ratio of total solids to the weight of the coating liquid was 20 mass%, to prepare coating material 1 for surface protection layer. [Preparation of decorative sheet 50] A decorative sheet 50 was produced in the same manner as in Example 1, except that the surface protective layer coating 2 was applied instead of the surface protective layer coating 1. A schematic cross-sectional view is shown in FIG.

[0082] [Comparative Example 1] [Preparation of Surface Protective Layer Coating 3] The solid content of the phenyl group surface-modified silica microparticles (product name: PL-7-TOL, particle diameter approximately 75 nm, manufactured by Fuso Chemical) was 50 mass %, the solid content of the polymethylphenylsilane (PMPS; product name: SI-10-10, manufactured by Osaka Gas Chemical) was 1%, and the solid content of the pentaerythritol triacrylate (PETA; solid content concentration 100%) was 49%, and the coating solution was diluted with toluene so that the ratio of total solids to the weight of the coating solution was 20 mass %, to prepare coating material 3 for the surface protective layer.

[0083] A decorative sheet 50 was produced in the same manner as in Example 1, except that the surface protective layer coating material 3 was applied instead of the surface protective layer coating material 1. A schematic cross-sectional view is shown in FIG.

[0084] Comparative Example 2 A decorative sheet 50 was produced in the same manner as in Example 1, except that a PVC film was attached by thermal lamination as the surface protective layer 4 of Example 1. A schematic cross-sectional view is shown in FIG.

[0085] [Decorative sheet evaluation method] The decorative sheets of the examples and comparative examples prepared above were evaluated for brightness and design.

[0086] Brightness The sense of brilliance was evaluated by a visual sensory test of the surface of the decorative sheet. The evaluation criteria were as follows: 50 or more of 100 test subjects evaluated the sense of brilliance based on the same evaluation results. That is, if 50 or more test subjects evaluated that the brilliance of the wood grain was natural and that the natural luster of natural wood was reproduced, they were judged as "○". In addition, if 50 or more test subjects evaluated that the brilliance of the wood grain was too strong to be natural, and that the natural luster of natural wood was not reproduced, they were judged as "×". Note that because the color varies depending on the ink, only the brilliance was evaluated, without taking color into consideration.

[0087] ·Design The design was evaluated by a visual sensory test of the surface of the decorative sheet. The evaluation criteria were as follows: 50 or more of the 100 test subjects evaluated the design based on the same results. That is, if 50 or more subjects felt that the outlines of the fine lines (several μm wide) of the wood grain pattern were properly reproduced without blurring, they were rated as "Good." If 50 or more subjects felt that the outlines of the fine lines (several μm wide) of the wood grain pattern were blurred and not reproduced, or if the color was obscured by the protective film, they were rated as "Poor." If there were partial printing irregularities, they were rated as "Good." A microscope with a magnification of 100x was used to check the outlines of the fine lines of the wood grain pattern.

[0088] ·Antibacterial Antibacterial tests were conducted based on JIS Z 2801:2010 (film adhesion method). Specifically, Escherichia coli and Staphylococcus aureus were dropped onto each of the decorative sheets of Example 1 and Comparative Examples 1 and 2 as contaminants, and the sheets were stored in a dark place at 25°C for 24 hours. After that, the number of viable bacteria was counted and the antibacterial activity value was calculated. An antibacterial activity value of 2.0 or higher was considered to have antibacterial properties.

[0089] The evaluation results of Examples 1 and 2 and Comparative Examples 1 and 2 are shown in Table 1.

[0090] [Table 1]

[0091] As described above, it was found that the decorative sheets obtained in Examples 1 and 2 were decorative sheets that achieved both design and antibacterial properties. In Comparative Example 1, the surface protective layer was white and lost transparency, resulting in poor brightness and design. In Comparative Example 2, no antibacterial properties were exhibited. The invention as originally claimed is set forth below. [1] An antibacterial decorative sheet comprising at least a glossy picture printed layer formed on one side of a base sheet using inkjet ink, and a surface protective layer on the glossy picture printed layer, wherein the surface protective layer is transparent and porous; the haze of the surface protective layer is 10% or less; The antibacterial decorative sheet is characterized in that the inkjet ink contains silver nanoparticles. [2] Item 1. The antibacterial decorative sheet according to item 1, further comprising a colored pattern printed layer formed using colored ink on one side of the base sheet. [3] Item 1 or 2. The antibacterial decorative sheet according to either item 1 or 2, characterized in that the glossy picture printed layer and the color picture printed layer formed using colored inks have non-overlapping portions where they do not overlap in a planar view. [4] Item 3. The antibacterial decorative sheet according to either item 1 or 2, characterized in that the glittering picture print layer is formed on the color picture print layer. [5] 5. The antibacterial decorative sheet according to any one of items 1 to 4, characterized in that a color picture printed layer is formed on one side of the base sheet, and a primer layer and a glitter picture printed layer are formed in this order on the base sheet and the color picture printed layer. [6] A decorative board comprising the antibacterial decorative sheet and a substrate disposed on the other side of the decorative sheet. [Explanation of symbols]

[0092] 1 Base sheet 2. Glossy pattern printing layer 3 Color pattern printing layer 4 Surface protective layer 5 Primer layer 6 Adhesive layer 7. Circuit Board 10 Decorative Sheet 20 Decorative Sheet 30 decorative sheets 40 decorative sheets 50 decorative sheets 60 decorative sheets 100 decorative panels

Claims

1. An antibacterial decorative sheet comprising at least a glossy picture printed layer formed on one side of a base sheet using inkjet ink, and a surface protective layer on the glossy picture printed layer, wherein the surface protective layer is transparent and porous; the haze of the surface protective layer is 10% or less; and the inkjet ink contains silver nanoparticles. An antibacterial decorative sheet characterized in that the size of the voids in the surface protective layer is in the range of 10 nm to 1 μm.

2. 2. The antibacterial decorative sheet according to claim 1, further comprising a colored pattern printed layer formed using colored ink on one side of the base sheet.

3. An antibacterial decorative sheet according to either claim 1 or claim 2, characterized in that the glossy pattern printed layer and the color pattern printed layer formed using colored ink have non-overlapping portions in which they do not overlap when viewed in a plane.

4. 3. The antibacterial decorative sheet according to claim 2, wherein the glittering picture print layer is formed on the color picture print layer.

5. An antibacterial decorative sheet according to any one of claims 1 to 4, characterized in that a color picture printed layer is formed on one side of the base sheet, and a primer layer and a glitter picture printed layer are formed in this order on the base sheet and the color picture printed layer.

6. A decorative board comprising the antibacterial decorative sheet described in any one of claims 1 to 5 and a substrate arranged on the other side of the antibacterial decorative sheet.

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