Printing ink and decorative article

Abstract

This printing ink comprises: (A) a resin having a refractive index of 1.5 or more; (B) carbon black having a primary particle diameter of 10-50 nm; and (C) titanium oxide having a primary particle diameter of 10-100 nm.

Description

Printing Ink and Decorated Articles

[0001] The present disclosure relates to printing ink and decorated articles.

[0002] In all articles such as electrical appliances, electronic devices, building materials, furniture, household goods, etc., various decoration techniques are used to enhance the design quality of the appearance. In order to produce a high-class feeling, a decoration method that generates a special gloss on the surface has attracted attention. For example, by making the surface of an article a directional reflecting surface, it is possible to produce different glosses depending on the way light hits it. One of the conventional techniques is a method of obtaining various glosses due to the difference in refractive index between these layers by laminating a plurality of metal oxide thin films with different refractive indexes on the surface of a substrate. By forming the metal oxide thin film by vapor deposition or the like, a more excellent optical effect can be obtained.

[0003] As a directional reflection, a characteristic one is retroreflection. In Patent Document 1, in the technical fields such as traffic signs and vehicle reflection displays, in order to obtain a coating film having a thick and shiny metallic appearance, exhibiting sufficient retroreflectivity with high brightness at night, and having both a high-class feeling and a thick and designed functionality, a method of forming a multi-layer coating film in which a metallic base coating film layer, a retroreflective coating film layer, and a clear coating film layer are formed in this order as a reflection layer is disclosed.

[0004] In Patent Document 2, regarding an optical member used for road signs and the like applied to a 3D distance sensor, it includes a wavelength conversion part and a first reflection part arranged at a position where light of a first wavelength can be incident from one side in a first direction. The wavelength conversion part converts light of the first wavelength into light of a second wavelength different from the first wavelength and emits it, and the first reflection part reflects light of the first wavelength and retroreflects light incident from one side in the first direction. Patent Document 2 discloses that the first reflection part may be formed as a total reflection surface at the interface between the first part and the second part, but in order to efficiently reflect the incident light, it is disclosed that a metal film is vapor-deposited on the interface between the first part and the second part.

[0005] Japanese Unexamined Patent Application Publication No. 2021-013898, Japanese Unexamined Patent Application Publication No. 2021-110818

[0006] However, forming metal oxide thin films by vapor deposition or other methods requires specialized equipment, and the increased number of lamination steps leads to longer manufacturing times and more steps, making efficient production difficult.

[0007] The technology using a metallic base coating layer disclosed in Patent Document 1 attempts to achieve retroreflectivity by combining a metallic base coating layer containing aluminum pigment and interference pigment with a retroreflective coating layer. However, due to the large particle size of the aluminum pigment and interference pigment, it is not possible to obtain a highly aesthetically pleasing, uniquely directional reflective surface. In the conventional technology for obtaining retroreflectivity disclosed in Patent Document 2, a metal film is formed as the first reflective layer by vapor deposition, making efficient production difficult.

[0008] Therefore, one of the objectives of this disclosure is to provide a decorative method that easily forms a highly aesthetically pleasing surface gloss with a directional reflective surface.

[0009] As a result of diligent research into the above-mentioned problems, the inventors have found that the above-mentioned problems can be solved by using several embodiments described below, and have thus come to fruition with the present invention.

[0010] [1] A printing ink comprising a resin with a refractive index of 1.5 or higher (A), carbon black with a primary particle size of 10 to 50 nm (B), and titanium dioxide with a primary particle size of 10 to 100 nm (C).

[0011] [2] The printing ink described in [1], wherein when an ink surface printed with the printing ink to have a surface roughness Ra of 2.5 μm or less is measured using a goniophotometer with the incident angle fixed at 60°, the half-width of the peak of the reflected light intensity with respect to the receiving angle of the reflected light is 10 or more.

[0012] [3] The printing ink according to [1] or [2], wherein the resin (A) with a refractive index of 1.5 or higher comprises at least one selected from the group consisting of styrene resins, polyester resins, epoxy resins, and acrylic resins.

[0013] [4] The printing ink according to any one of [1] to [3], comprising a resin (A) with a refractive index of 1.5 or higher, wherein the resin has a glass transition temperature of 50 to 100°C.

[0014] [5] A printing ink according to any one of [1] to [4], wherein the mass ratio of carbon black (B) to titanium dioxide (C) is 1:99 to 40:60.

[0015] [6] A printing ink according to any one of [1] to [5], further comprising inorganic particles (D) having a refractive index of 1.3 to 1.7 and a volume-based average particle diameter (D50) of 1 to 20 μm as determined by laser diffraction scattering.

[0016] [7] A printing ink for screen printing, as described in any of [1] to [6].

[0017] [8] A printing ink according to any of [1] to [7], for use on decorative articles.

[0018] [9] A decorated article comprising a decorated article and an ink layer formed on the decorated article using a printing ink described in any of [1] to [8].

[0019]

[10] The decorative article according to [9], wherein the printing ink further comprises inorganic particles (D) having a refractive index of 1.3 to 1.7 and an average particle diameter on a volume basis of 1 to 20 μm as determined by laser diffraction scattering.

[0020] One aspect of this disclosure provides a decorative method for easily forming a highly aesthetically pleasing surface gloss with a directional reflective surface.

[0021] Figure 1 is a graph showing the measurement profiles of the goniophotometers for the examples and comparative examples. Figure 2 is a graph showing the measurement profiles of the goniophotometers for the examples and comparative examples.

[0022] The following describes some embodiments of the present disclosure, but the present invention is not limited by the examples in the following description.

[0023] In the following description, "ink surface" refers to the surface of the printed layer, which consists of printing ink. Printing ink may be abbreviated as "ink" or "ink" in the specification.

[0024] <Printing Ink> The printing ink of this disclosure is characterized by comprising a resin (A) with a refractive index of 1.5 or higher, carbon black (B) with a primary particle size of 10 to 50 nm, and titanium dioxide (C) with a primary particle size of 10 to 100 nm. Hereinafter, the resin (A) with a refractive index of 1.5 or higher will also be referred to simply as resin (A), the carbon black (B) with a primary particle size of 10 to 50 nm will also be referred to simply as carbon black (B), and the titanium dioxide (C) with a primary particle size of 10 to 100 nm will also be referred to simply as titanium dioxide (C). In this disclosure, an article decorated with a printing ink will also be referred to as a decorated article. In a decorated article, the side on which the printing ink is printed will be referred to as the ink side. If the decorated article is a film or sheet, the side opposite the ink side will be referred to as the back side. In a decorated article, the side on which the decoration is visible will be referred to as the decorated side. For example, in applications where the decoration is visible from the ink side, the ink side becomes the decorated side; in applications where the decoration is visible from the back side, the back side becomes the decorated side; and in applications where the decoration is visible from both the ink side and the back side, both sides become the decorated side.

[0025] The printing inks of this disclosure can be used as an alternative to a method that uses multilayer reflective thin films to form a directional reflective surface due to differences in refractive index between layers. The printing inks of this disclosure have small primary particle sizes of carbon black (B) and titanium dioxide (C), which allows for directional reflection in the ink layer due to differences in refractive index between particles. The mechanism is not entirely clear, but when using carbon black and titanium dioxide with large primary particle sizes, incident light is reflected at the particle surface, resulting in a narrower angular width in the direction of reflection. When using carbon black and titanium dioxide with small primary particle sizes, the gaps between the carbon black and titanium dioxide particles are larger, so in addition to reflection at the particle surface, light is also reflected between the particles, resulting in a wider angular width in the direction of reflection.

[0026] Further investigation revealed that in decorative articles with a directional reflective structure, when using printing inks containing carbon black and titanium dioxide with small primary particle sizes, light is reflected even between particles, resulting in a stronger reflection intensity in a direction deviated from the specular reflection direction. Thus, in decorative articles with a directional reflective structure, the printing inks of this disclosure cause reflected light to be reflected in a direction deviated from the specular reflection direction, and the angular width of the direction in which incident light is reflected is widened. Such decorative articles have a directional reflective surface and can achieve a highly aesthetically pleasing surface gloss.

[0027] The printing inks of this disclosure are particularly useful for achieving black surface gloss because they can form directional reflective surfaces using carbon black (B). For example, by forming a black ink layer using the printing inks of this disclosure, a highly aesthetic black surface gloss can be achieved.

[0028] Directional reflective structures can be created using inorganic particles or by utilizing surface irregularities on the decorated object. In all of these methods, the technique is used to cause the reflected light to be reflected in a direction shifted from the specular reflection direction due to the refraction of light as the incident light passes through the directional reflective structure.

[0029] In this disclosure, directional reflection primarily refers to retroreflection. It has the characteristic of reflecting a specified incident light at any angle. On the other hand, the reflection intensity itself tends to be weaker because the light is scattered in all directions.

[0030] By using the printing ink of this disclosure together with a directional reflective structure, a directional reflective surface can be formed in a decorated article that has a wide angular width in the direction of reflection of incident light, without a decrease in reflection intensity in directions deviated from the direction of specular reflection of incident light, thereby obtaining a surface gloss with high aesthetic appeal. For example, such a directional reflective surface can be obtained by forming an ink layer containing inorganic particles further added to the printing ink of this disclosure on the article to be decorated, or by forming the ink of this disclosure on the article to be decorated which has surface irregularities, or by a combination of these.

[0031] The printing inks of this disclosure are preferable to have a half-width of 5 or more at half maximum of the peak of the reflected light intensity with respect to the receiving angle of the reflected light when the ink surface printed using the printing ink to a surface roughness Ra of 2.5 μm or less is measured using a goniophotometer with the incident angle fixed at 60°.

[0032] An ink surface exhibiting such characteristic half-width can possess a highly aesthetic surface gloss with directional reflection. The half-width defined here may be 5 or more, and is preferably 10 or more, 15 or more, or 20 or more. Within these ranges, the range of angles in which the reflected light is visible is widened, and directional reflection with excellent aesthetic appeal can be obtained. The half-width is preferably 60 or less, 50 or less, 40 or less, 30 or less, 25 or less, 22 or less, or 20 or less. Within these ranges, the visibility of the reflected light changes with angle, and directional reflection with excellent aesthetic appeal can be obtained. Here, the half-width is the width between two points that are half the height of the peak (peak of reflection intensity with respect to the receiving angle of the reflected light) (maximum value) of the reflection spectrum. Here, the unit of half-width is expressed in degrees (°).

[0033] Furthermore, in this measurement, the reflectance intensity preferably has a peak at a light reception angle of 70 to 80° of the reflected light. An ink surface exhibiting such a characteristic peak can have a highly aesthetic surface gloss with unique directional reflection. The preferred film thickness in this case is preferably 5 to 20 μm, more preferably 6 to 15 μm, and particularly preferably 7 to 10 μm. In addition, the ink of this disclosure may be used in two or more layers.

[0034] The method for measuring the ink surface using a goniotphotometer follows the conditions below. For details, the measurement can be performed according to the method disclosed in the examples. Apparatus: Goniotphotometer, Murakami Color Technology Laboratory Co., Ltd. "GP-200" Light source: Converging light at an angle of 1.5° Incident angle: 60° Receiver angle: 0 to 100° Measurement surface: Ink surface

[0035] In this disclosure, the surface roughness Ra of the ink surface is a measured value in accordance with JIS B0601:2001.

[0036] The resin (A) will be described below.

[0037] The refractive index of resin (A) is preferably 1.5 or higher. Within this range, the resin film that forms the base of the ink layer exhibits an appropriate refractive index, enabling the creation of a highly reflective decorative surface. Directional reflection occurs on the highly reflective decorative surface, resulting in a highly aesthetically pleasing surface gloss. Since resin (A) typically exhibits a lower refractive index than carbon black (B) and titanium dioxide (C), it exhibits a refractive index that does not affect the reflection of light on the surface of these particles. For example, the refractive index of resin (A) is preferably 1.7 or less, 1.65 or less, 1.6 or less, or 1.55 or less.

[0038] In this disclosure, the refractive index of the resin is a value that follows the Abbe formula of the critical angle method, in accordance with JIS K 7142:2014. The refractive index of the resin can be measured by a measurement method that follows the Abbe formula of the critical angle method.

[0039] The glass transition temperature of resin (A) may be 10 to 200°C, 20 to 180°C, or 30 to 150°C, but is more preferably 50 to 100°C. The glass transition temperature of resin (A) should preferably be 50°C or higher, 55°C or higher, or 58°C or higher. In these ranges, the occurrence of changes in the state of resin (A) is suppressed at the ambient temperature of the article, which is near room temperature, so that the high reflectivity of resin (A) can be obtained more stably. The glass transition temperature of resin (A) should preferably be 100°C or lower, 90°C or lower, or 80°C or lower. In these ranges, the coatability on the decorated article can be further improved, the occurrence of cracks in the ink layer can be suppressed, and directional reflectivity can be further improved. In addition, flexibility is imparted to the ink layer, so adhesion to decorated articles with complex surface shapes can be further improved, and the conformability of the ink layer to flexible decorated articles can be further improved.

[0040] In this disclosure, the glass transition temperature of the resin is a measurement obtained by differential scanning calorimetry (DSC). For details, it can be measured according to the method disclosed in the examples.

[0041] Resin (A) is preferably a resin capable of functioning as a binder in the ink layer, and more preferably a thermoplastic resin. Examples of resin (A) include styrene resins, polyester resins, epoxy resins, acrylic resins, vinyl chloride-vinyl acetate copolymer resins, polyurethane resins, rosin resins, styrene-maleic acid resins, dammar resins, polycarbonate resins, rosin-modified maleic acid resins, rosin ester resins, terpene resins, and other thermoplastic resins. These may be used individually or in combination of two or more. In this disclosure, the styrene resin is a resin containing at least a styrene skeleton, and may be a polystyrene resin, an acrylonitrile-styrene copolymer, an acrylonitrile-butadiene-styrene copolymer, and the like. In this disclosure, the acrylic resin is a resin containing constituent units derived from at least one selected from the group consisting of acrylic acid, methacrylic acid, and derivatives thereof, and may be poly(meth)acrylic acid, poly(meth)acrylate, (meth)acrylic-styrene copolymer, and the like.

[0042] Preferably, the resin (A) contains at least one selected from the group consisting of styrene resins, polyester resins, epoxy resins, and acrylic resins. These resins have a high refractive index while having a relatively high glass transition temperature, which prevents scratching of the ink layer and suppresses diffuse reflection, thus enabling better directional reflection. The polyester resin may be a polyester polyol resin. The acrylic resin may be an acrylic polyol resin, a homopolymer or copolymer of phenoxy(meth)acrylate, a homopolymer or copolymer of benzyl(meth)acrylate, etc.

[0043] In the present disclosure, in order for the resin (A) to satisfy a refractive index of 1.5 or more, it is preferably a resin having a ring structure, more preferably a resin having an aromatic ring structure. Preferred examples of the group having an alicyclic structure include a cyclohexyl group, a norbornane group, an adamantyl group, a cyclopentyl group, a cycloheptyl group, a cyclohexylene group, a fluorene group, a carbazole group, and a tetrahydrofuran group. Preferred examples of the group having an aromatic ring structure include a phenyl group, a phenylene group, a naphthyl group, a pyridyl group, an anthracenyl group, a fluorenyl group, an indenyl group, a naphthylene group, and a biphenyl group. Among them, a phenyl group and a phenylene group are preferable. That is, it is particularly preferable to have a benzene ring structure. The above ring structure is preferably contained in the total amount of the resin at 20% by mass or more, 30% by mass or more, 40% by mass or more, and more preferably 50% by mass or more. Further, it is more preferable that the ring structure is contained in the total amount of the resin at 95% by mass or less, 90% by mass or less, 85% by mass or less, or 80% by mass or less. The resin is preferably a styrene resin, an acrylic resin having a ring structure, an epoxy resin, or a polyester resin.

[0044] The styrene resin preferably has a weight average molecular weight of 1,000 to 50,000. The polyester resin preferably has a weight average molecular weight of 5,000 to 50,000. The epoxy resin preferably has a weight average molecular weight of 100 to 5,000. The acrylic resin preferably has a weight average molecular weight of 20,000 to 100,000.

[0045] Examples of commercially available products of the resin (A) include styrene resins: MS-200 manufactured by Toyo Styrene Co., Ltd. (refractive index 1.57), polyester resins: RX-4800 manufactured by DIC (refractive index 1.58), epoxy resins: JER828 manufactured by Mitsubishi Chemical Corporation (refractive index 1.54), acrylic resins: Tech Polymer (registered trademark) manufactured by Sekisui Chemical Co., Ltd. (adjustable between refractive indices of 1.50 and 1.59), and the like.

[0046] Resin (A) may be contained in an amount of 1 to 60% by mass, 5 to 30% by mass, or 10 to 20% by mass based on the total mass of the printing ink. Within these ranges, resin (A) shows solubility in an organic solvent, improves the uniform dispersibility of carbon black (B) and titanium oxide (C), and also improves the coating property. Therefore, the uniformity of the directional reflection can be further enhanced by the uniformly distributed carbon black (B) and titanium oxide (C) in the ink layer.

[0047] Hereinafter, carbon black (B) will be described.

[0048] Carbon black is particles that exhibit black color and are used as a black pigment. In the present disclosure, a highly reflective decorative surface due to directional reflection can be formed by the small primary particle diameter of carbon black (B) contained in the ink layer.

[0049] The primary particle diameter (B) of carbon black (B) is preferably 50 nm or less, 40 nm or less, 30 nm or less, or 25 nm or less. Within these ranges, the gaps between particles in the ink layer become larger, and light is reflected between carbon black (B) particles or between carbon black (B) and titanium oxide (C), enabling the induction of directional reflection from the decorative surface. The primary particle diameter of carbon black (B) is preferably 10 nm or more, 15 nm or more, or 20 nm or more. Within these ranges, the amount of light passing between particles in the ink layer is reduced, making it possible to make the decorative surface have appropriate high reflectivity. Also, since the aggregation of particles in the printing ink is suppressed, the uniformity of the reflection intensity of the ink layer can be further enhanced.

[0050] As the carbon black, channel black, furnace black, thermal black, lamp black, etc. can be used. Examples of commercially available products of carbon black include "MA100, #23000" of Mitsubishi Chemical Group Corporation, "Seast 5H, Seast NH" of Tokai Carbon Co., Ltd., "SUNBLACK X15, SUNBLACK X25" of Asahi Carbon Co., Ltd., etc.

[0051] Hereinafter, titanium oxide (C) will be described.

[0052] Titanium dioxide is a particle that exhibits a high refractive index and generally has excellent opacity. In this disclosure, the small primary particle size of titanium dioxide (C) contained in the ink layer makes it possible to form a highly reflective decorative surface due to directional reflection.

[0053] The primary particle size (B) of titanium dioxide (C) is preferably 100 nm or less, 80 nm or less, 60 nm or less, or 50 nm or less. Within these ranges, the gaps between particles in the ink layer become larger, allowing light to reflect between titanium dioxide (C) particles or between titanium dioxide (C) particles and carbon black (B), resulting in directional reflection from the decorated surface. Furthermore, if the primary particle size of titanium dioxide (C) is smaller within these ranges, the ink layer will contain minute particles with a high refractive index, causing stronger light scattering between the ink layers and resulting in reflected light having a bluish tint. A bluish-black surface gloss is preferred for the color scheme of items where a sense of luxury is desired. The primary particle size of titanium dioxide (C) is preferably 10 nm or more, 15 nm or more, or 20 nm or more. Within these ranges, the amount of light passing between particles in the ink layer is reduced, making it possible to achieve a moderately high reflectivity on the decorated surface. Furthermore, because particle aggregation in the printing ink is suppressed, the uniformity of the reflectivity of the ink layer can be further improved.

[0054] Titanium dioxide (C) is titanium dioxide (TiO2). ２ It is preferable that the titanium(C) oxide exhibits hydrophobicity through surface treatment.

[0055] Examples of commercially available titanium dioxide (C) products include Teika Co., Ltd.'s "MT-100HD, MT-500HD" and Ishihara Sangyo Co., Ltd.'s "TTO-51(A), TTO-55(A)".

[0056] The primary particle size of carbon black (B) and titanium dioxide (C) is calculated as the arithmetic mean of the major axis of a significant number of particles measured in image observation using a transmission electron microscope (TEM). For details, the measurement can be performed according to the method disclosed in the examples.

[0057] The mass ratio of carbon black (B) to titanium oxide (C) may be 0.1:99.9 to 20:80, or 0.5:99.5 to 30:70, and preferably 1:99 to 40:60, or 2:98 to 50:50. A higher mass ratio of 0.1:99.9 or higher indicates a greater proportion of carbon black (B), which can further enhance directional reflectivity. Conversely, a lower mass ratio of 20:80 or lower indicates a greater proportion of carbon black (B), which can also further enhance directional reflectivity.

[0058] The amount of carbon black (B) may be 0.1 to 80 parts by mass, 0.5 to 60 parts by mass, 3 to 50 parts by mass, or 20 to 40 parts by mass per 100 parts by mass of resin (A). The amount of titanium oxide (C) may be 10 to 95 parts by mass, 30 to 90 parts by mass, 60 to 88 parts by mass, or 80 to 85 parts by mass per 100 parts by mass of resin (A). The total mass of carbon black (B) and titanium oxide (C) may be 1 to 50 parts by mass, 5 to 40 parts by mass, or 10 to 30 parts by mass per 100 parts by mass of resin (A).

[0059] The printing ink may further contain inorganic particles (D) having a refractive index of 1.3 to 1.7 and an average particle size (D50) based on volume measured by laser diffraction scattering method of 1 to 20 μm. Hereinafter, these inorganic particles will also be simply referred to as inorganic particles (D).

[0060] The inorganic particles (D) have a low refractive index of 1.7 or less and a large average particle diameter of 1 μm or more, which allows for the provision of a directional reflective structure in the ink layer. That is, incident light incident on the inorganic particles (D) is refracted at the interface of the inorganic particles (D), creating a structure in which light is reflected in directions other than specular reflection. Since the printing ink of this disclosure contains carbon black (B) and titanium dioxide (C) with small primary particle diameters, directional reflection from the decorated surface can be obtained by utilizing the refractive index difference at the interface of the inorganic particles (D). For example, directional reflection from the decorated surface can be obtained by having a higher intensity of reflected light in a direction slightly shifted from the direction of specular reflection, for example, within plus or minus 20°.

[0061] The refractive index of the inorganic particles (D) should be small compared to that of the resin (A) to prevent excessive light scattering and to obtain more appropriate directional reflection on the decorated surface. For example, the refractive index of the inorganic particles (D) should be within ±15%, ±10%, or ±5% of the refractive index of the resin (A). From this viewpoint, a refractive index of 1.3 or higher is preferable for the inorganic particles (D). Furthermore, a refractive index of 1.7 or lower is preferable, and it is also preferable to have a refractive index of 1.6 or lower, or 1.5 or lower.

[0062] The average particle diameter of the inorganic particles (D) should be 20 μm or less, 15 μm or less, 10 μm or less, or 8 μm or less. The average particle diameter of the inorganic particles (D) should be 1 μm or more, 2 μm or more, or 3 μm or more. By including inorganic particles (D) with average particle diameters within these ranges in the ink layer, more appropriate directional reflectivity can be obtained. For example, the average particle diameter of the inorganic particles (D) should be 1 to 20 μm, 2 to 15 μm, 3 to 10 μm, or 3 to 8 μm.

[0063] In the ink layer of the printing inks of this disclosure, the combination of carbon black (B) and titanium dioxide (C) can induce directional reflection on the decorated surface.

[0064] In this disclosure, the average particle diameter (D50) is the particle diameter at which the volume-based integrated value in the particle size distribution obtained by laser diffraction and scattering method becomes 50%. For example, it can be measured using Microtrac (Microtrac-Bell Co., Ltd. "MT3300EXII"). For details, it can be measured according to the method disclosed in the examples.

[0065] Examples of inorganic particles include silica particles, glass particles, and resin particles. Inorganic particles may be solid or hollow, but hollow particles are preferred because they have a low refractive index.

[0066] The inorganic particles (D) may be in amounts of 10 to 90 parts by mass, 30 to 80 parts by mass, or 50 to 70 parts by mass per 100 parts by mass of resin (A). The total mass of carbon black (B) and titanium dioxide (C) may be in amounts of 1 to 50 parts by mass, 5 to 40 parts by mass, or 10 to 30 parts by mass per 100 parts by mass of inorganic particles (D). Commercially available inorganic particles can be used for inorganic particles (D). There are no particular restrictions on the surface shape, but those sold as spherical particles can be preferably used. In addition, inorganic particles (D) may be surface treated. For example, hydrophobic surface-treated particles such as Fuji Silysia Chemical Co., Ltd.'s "SYLOPHOBIC 200" (product name, average particle size 3.9 μm, refractive index 1.46) can be preferably used.

[0067] Printing inks may further contain organic solvents. Examples of organic solvents include glycol ether-based organic solvents, ester-based organic solvents, aliphatic organic solvents, aromatic organic solvents, alcohol-based organic solvents, and ketone-based organic solvents. Among these, ketone-based organic solvents are preferable from the viewpoint of resin solubility, and glycol ether-based organic solvents, which have good printability, may also be used. Organic solvents may be used individually or in combination of two or more.

[0068] Examples of glycol ether-based organic solvents include ethylene glycol dibutyl ether, ethylene glycol monobutyl ether, ethylene glycol monohexyl ether, ethylene glycol monomethoxymethyl ether, diethylene glycol ethyl methyl ether, diethylene glycol dimethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, diethylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol monobutyl ether, dipropylene glycol monomethyl ether, triethylene glycol dimethyl ether, triethylene glycol monomethyl ether, tripropylene glycol monomethyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, and propylene glycol monobutyl ether.

[0069] Examples of ester-based organic solvents include gamma butyrolactone, cellosolve acetate, propylene glycol monomethyl ether acetate, ethylene glycol diacetate, ethylene glycol monoacetate, ethylene glycol monobutyl ether acetate, diethylene glycol diacetate, diethylene glycol monoethyl ether acetate, diethylene glycol monobutyl ether acetate, and propylene carbonate.

[0070] Aliphatic organic solvents include n-paraffinic solvents, isoparaffinic solvents, and cycloparaffinic solvents.

[0071] Aromatic organic solvents include toluene, xylene, ethylbenzene, naphthalene, tetralin, and solvent naphtha, as well as solvents rich in aromatics such as Swazole (manufactured by Cosmo Oil Co., Ltd. and Maruzen Petrochemical Co., Ltd.), Solvesso (manufactured by ExxonMobil Corporation), and Cactusfine (manufactured by Japan Energy Co., Ltd.).

[0072] Ketone-based organic solvents can be classified into cyclic ketone-based organic solvents, which have a cyclic skeleton, and ketone-based organic solvents, which do not have a cyclic skeleton. Among these, cyclic ketone-based organic solvents are preferred from the viewpoint of printability.

[0073] As cyclic ketone organic solvents, organic solvents containing a cyclic ketone structure of 5 to 7 members in the molecule are preferred. Examples of 5-membered cyclic ketone organic solvents include cyclopentanone, 2-methyl-2-cyclopenten-1-one, 2-methylcyclopentanone, 3-methylcyclopentanone, 2-ethylcyclopentanone, 3-ethylcyclopentanone, 2,2-dimethylcyclopentanone, and 2,4,4-trimethylcyclopentanone. Examples of 6-membered cyclic ketone organic solvents include cyclohexanone, isophorone, 2-cyclohexen-1-one, 2-methylcyclohexanone, 3-methylcyclohexanone, 4-methylcyclohexanone, 4-ethylcyclohexanone, 2,6-dimethylcyclohexanone, and 2,2-dimethylcyclohexanone. Examples of 7-membered cyclic ketone organic solvents include cyclopeptanone and 2-cyclopeptan-1-one.

[0074] Examples of ketone-based organic solvents that do not have a cyclic skeleton include acetone, methyl ethyl ketone, methyl isobutyl ketone, and diisobutyl ketone.

[0075] The organic solvent is preferably present in an amount of 40 to 80% by mass, and more preferably in an amount of 50 to 70% by mass, relative to the total mass of the printing ink.

[0076] The printing ink may further contain an extender pigment. Examples of extender pigments include silica, alumina, talc, calcium carbonate, and precipitated barium. These may be used individually or in combination of two or more. The extender pigment is preferably present in an amount of 0.1 to 50% by mass, and more preferably in an amount of 5 to 20% by mass, relative to the total mass of the printing ink. The inorganic particles (D) described above may also be used as the extender pigment.

[0077] The printing ink may further contain an antifoaming agent. The antifoaming agent is preferably included in an amount of 0.1 to 5% by mass, and more preferably in an amount of 0.3 to 4% by mass, relative to the total mass of the printing ink. Examples of compounds constituting the antifoaming agent include acrylic resins, vinyl ether resins, butadiene resins, silicone resins, fluororesins, and modified resins thereof (however, resin (A) is not included). The antifoaming agent is preferably a non-silicone resin, and acrylic resins, vinyl ether resins, and butadiene resins may be used individually or in combination of two or more. Examples of commercially available antifoaming agents include the "BYK series" from Bic Chemie Japan and the "Florence series" from Kyoeisha Chemical Co., Ltd.

[0078] The printing ink may further contain a leveling agent. The leveling agent is preferably present in an amount of 0.1 to 1% by mass relative to the total mass of the printing ink. The compound constituting the leveling agent is preferably an acrylic resin and / or a silicone resin (however, resin (A) is not included). These may be used individually or in combination of two or more. Examples of commercially available leveling agents include Kyoeisha Chemical's "Polyflow Series."

[0079] The printing ink may, as needed, contain additives such as dispersants, wetting agents, anti-skinning agents, UV absorbers, antioxidants, crosslinking agents, preservatives, fungicides, viscosity modifiers, and pH adjusters, to the extent that they do not hinder the objectives of the present invention.

[0080] Printing inks can be manufactured using any known dispersion method. For example, a resin (A), carbon black (B), titanium dioxide (C), selectively inorganic particles (D), and additives can be mixed with an organic solvent, stirred using a stirrer, and then dispersed using a disperser such as a three-roll machine, paint shaker, attritor, or sand mill to produce a printing ink.

[0081] The articles to be decorated with printing ink are not particularly limited and include inorganic substrates such as glass and ceramics; polyester substrates such as polyethylene terephthalate; polyolefin substrates such as polyethylene, polypropylene, ethylene-vinyl acetate and others; nylon substrates such as polyamide; acrylic substrates; polyvinyl chloride substrates; polycarbonate substrates; polyurethane substrates; epoxy substrates; and metal substrates such as stainless steel plates, aluminum plates, and copper plates. Laminates of these may also be used. Furthermore, vapor-deposited substrates in which inorganic compounds such as silica, alumina, and aluminum are vapor-deposited onto the substrate can also be used, and the vapor-deposited surface may be coated with polyvinyl alcohol or the like. Corona treatment, flame treatment, and stretching treatment may also be applied. The shape of the articles to be decorated is not particularly limited and may be in the form of sheets, plates, films, or three-dimensional structures such as structures.

[0082] By forming an ink layer on a light-impermeable substrate, incident light on the printed surface is reflected in a directional manner, resulting in a highly aesthetically pleasing surface gloss when viewed from the ink surface. A similar effect can be obtained when forming an ink layer on a light-transmitting substrate. For substrates with high light transmittance, it is preferable to increase the amount of printing ink applied to thicken the ink layer in order to enhance the reflectivity of the printing ink according to this disclosure. From the viewpoint of aesthetic appeal and protection of the ink layer, other light-transmitting ink layers, overcoat layers, or combinations thereof may be further provided on the ink layer.

[0083] When an ink layer is formed on a light-transmitting substrate, incident light on the back surface undergoes directional reflection, resulting in a highly aesthetically pleasing surface gloss when viewed from the substrate side (the back surface). One such application is reverse printing. The printing ink of this disclosure has small primary particle sizes of carbon black (B) and titanium dioxide (C), allowing light to pass through easily. Therefore, in the case of reverse printing, it is preferable to form a shielding layer on top of the ink layer of the printing ink of this disclosure. The shielding layer is preferably formed with black ink of the same hue as the printing ink of this disclosure, but other hues may also be used. By forming an ink layer of the printing ink of this disclosure between the transparent substrate and the shielding layer, directional reflection of the hue of the shielding layer is achieved when viewed from the light-transmitting substrate side (the back surface), resulting in a highly aesthetically pleasing surface gloss.

[0084] <Decorated Articles> The decorated articles of this disclosure comprise a to be decorated article and an ink layer formed on the to be decorated article, wherein the ink layer is formed using the printing ink described above. The ink layer may be printed by any printing method, such as screen printing, roll coater, dispenser coating, dip coating, brush coating, etc., with screen printing being preferred. For screen printing, it is preferable to use a cylinder press printing machine or a semi-automatic printing machine as the printing machine and a printing plate made of a resin material such as nylon or polyester, or a metal material such as stainless steel. A drying step may be provided after printing, and the drying temperature after printing is preferably 25 to 120°C, more preferably 40 to 100°C, and even more preferably 60 to 80°C.

[0085] By laminating another light-transmitting ink layer or overcoat layer on top of the ink layer, the ink layer can be protected, and its design can be further enhanced. For applications where visibility from the reverse side is required, the ink layer may be formed by coating a light-transmitting substrate with printing ink. In this case, a shielding layer may be further formed on top of the ink layer, and an uneven surface may be formed on the printed side of the light-transmitting substrate.

[0086] The decorated article may be a decorated laminate, and may have, for example, the following laminated structure. In the following laminated structure, the right side is the decorated surface. In the following, the directional reflective ink layer is formed using the printing ink of this disclosure. Substrate / directional reflective ink layer Substrate / shielding layer / directional reflective ink layer Substrate / directional reflective ink layer / overcoat layer Substrate / shielding layer / directional reflective ink layer / overcoat layer Directional reflective ink layer / light-transmitting substrate Shielding layer / directional reflective ink layer / light-transmitting substrate

[0087] The present invention will be specifically described below using examples, but the present invention is not limited in any way by the following examples. In the present invention, unless otherwise specified, "parts" refers to "parts by mass" and "%" refers to "percentage by mass". The numerical values ​​in the table refer to "parts" unless otherwise specified, and blank spaces indicate that the part was not used.

[0088] The following describes the measurement methods for each physical property used in the examples.

[0089] (Glass transition temperature (Tg) of resin) The glass transition temperature (Tg) was determined by DSC (Differential Scanning Calorimetry). The measuring instrument used was Rigaku Corporation's "DSC8231," with a measurement temperature range of -70 to 250°C, a heating rate of 10°C / min, and the midpoint between the endothermic start temperature and the end temperature based on the glass transition in the DSC curve was defined as the glass transition temperature.

[0090] (Resins with a refractive index of 1.5 or higher) Polystyrene resin: refractive index 1.59, Tg 59°C. Contains approximately 75% by mass of benzene ring structure. Polyester resin: refractive index 1.55, Tg 60°C. Contains 40-50% by mass of benzene ring structure. Polyester resin: refractive index 1.55, Tg 23°C. Contains 40-50% by mass of benzene ring structure. Epoxy resin: refractive index 1.55, Tg 74°C. Contains 30-40% by mass of benzene ring structure. Acrylic resin: refractive index 1.51, Tg 79°C. Contains approximately 15% by mass of benzene ring structure.

[0091] (Resins with a refractive index of less than 1.5) Acrylic resin: refractive index 1.49, Tg 80℃, does not contain ring structures. Urethane resin: refractive index 1.44, Tg 69℃, does not contain ring structures.

[0092] (Primary particle size of carbon black and titanium dioxide) The primary particle size of carbon black and titanium dioxide was determined by measuring the major axis of 100 particles in images observed using a transmission electron microscope (TEM), and the arithmetic mean of these measurements was taken as the primary particle size.

[0093] (Average particle size (D50) of inorganic particles) The average particle size (D50) of inorganic particles was determined as the particle size (D50) at which the cumulative value based on volume in the particle size distribution obtained by laser diffraction scattering method becomes 50%.

[0094] (Surface roughness Ra of the ink surface) Using a Keyence Corporation "Shape Analysis Laser Microscope VK-X100," an image of the ink surface was captured with a 50x objective lens, and the arithmetic mean roughness Ra (μm) of the entire screen area was measured according to the JIS B0601:2001 method.

[0095] (Preparation of Printing Ink) Table 1 shows the component content ratios of the printing ink. The components were weighed according to the formulation in the table, uniformly mixed using a rotary mixer, and then passed through a three-roll disperser twice to prepare screen printing ink (S1). The refractive index and glass transition temperature (Tg) of the resins shown in the table were determined by the above method. The primary particle size of carbon black and titanium dioxide was determined by the above method. The details of the components are as follows.

[0096] Carbon black (primary particle size 24 nm): Mitsubishi Chemical Group Corporation "MA100". Carbon black (primary particle size 15 nm): Mitsubishi Chemical Group Corporation "#2300". Carbon black (primary particle size 55 nm): Mitsubishi Chemical Group Corporation "MA220". Titanium dioxide (primary particle size 15 nm): Teika Co., Ltd. "MT-100HD". Titanium dioxide (primary particle size 30 nm): Teika Co., Ltd. "MT-500HD". Titanium dioxide (primary particle size 250 nm): Ishihara Sangyo Co., Ltd. "CR80". Inorganic particles: Silica particles, average particle size (D50) 3.9 μm, refractive index 1.46. Defoaming agent: Non-silicone defoaming agent, BIC Chemie Japan Co., Ltd. "BYK-057".

[0097] The table shows the mass percentage (mass%) of carbon black and titanium oxide relative to the total mass of carbon black and titanium oxide.

[0098] (Evaluation of angle dependence of optical properties (directional reflection characteristics) of decorated articles) The printing inks of the examples and comparative examples shown in the table were screen printed onto the following substrates using a screen printing plate (NBC Meshtec, L-SCREEN, 100-035 / 255PW), and the decorated articles were heat-treated at 80°C for 0.5 hours. The thickness of the ink layer after drying was 10 μm. Substrate: Transparent substrate made of polyethylene terephthalate (PET).

[0099] Light was shone onto the ink surface of the decorated articles, and the reflected light was measured using a goniotphotometer under the following conditions. Throughout the examples and comparative examples, the amount of incident light was varied so that the maximum peak reflectance was approximately 85%. Furthermore, the surface roughness Ra of the ink surface of the obtained decorated articles was measured using the above method, and in both the examples and comparative examples, it was 2.5 μm or less. Apparatus: Goniotphotometer, Murakami Color Technology Laboratory Co., Ltd. "GP-200" Light source: Converging light at an angle of 1.5° Incident angle: 60° Receiver angle: 0-100° Measurement surface: Ink surface

[0100] From the measurement profile of the goniotograph, the full width at half maximum (FWHM) of the peaks observed between 0° and 90° was calculated. If two or more peaks were observed, the FWHM of the peak with the highest intensity was used. The angle dependence of the optical properties (directional reflection characteristics) of the decorated articles was evaluated from the FWHM values ​​in the following order. The results are shown in the table. Grade A (Excellent): The FWHM of the reflection intensity peak is 20 or more and 60 or less. Grade B (Good): The FWHM of the reflection intensity peak is 10 or more and less than 20. Grade C (Poor): The FWHM of the reflection intensity peak is less than 10. Note that levels A and B are industrially usable.

[0101] Figure 1 shows the measurement profiles of the goniophotometer, with Example 2 shown by a solid line and Comparative Example 4 shown by a dashed line. In this figure, specular reflection was observed in Comparative Example 4, while in Example 2, the peak was broadened with a slight angle shift from specular reflection, indicating that a specific directional reflection was occurring.

[0102] (Evaluation of the strength comparison of optical properties of decorated articles) The printing inks of Example 2 and Comparative Example 4 shown in the table were coated onto the following substrate by screen printing, and the substrate was heat-treated at 80°C for 0.5 hours to obtain decorated articles. The thickness of the ink layer after drying was 10 μm. Substrate: Transparent substrate made of polyethylene terephthalate (PET).

[0103] The ink surface of the decorated articles was irradiated with light of the same incident intensity, and the reflected light was measured using a goniophotometer under the following conditions. Furthermore, the surface roughness Ra of the ink surface of the obtained decorated articles was measured using the above method, and in both Example 2 and Comparative Example 4, it was 2.5 μm or less. Apparatus: Goniophotometer, Murakami Color Technology Laboratory Co., Ltd. "GP-5" Light source: Converging light at an angle of 1.5° Incident angle: 60° Receiver angle: 0 to 100° Measurement surface: Ink surface

[0104] Figure 2 shows the goniophotometer measurement profiles, with Example 2 shown as a solid line and Comparative Example 4 shown as a dashed line. In this figure, when the ink layer thickness is the same, the reflectance intensity of Example 2 was observed to be weaker than that of Comparative Example 4.

[0105]

[0106]

[0107]

[0108] The results shown in the table and figures indicate that the decorative articles obtained using the printing inks of the examples exhibit angle dependence of the optical properties of the articles, and that unique directional reflection occurs with low reflection intensity, resulting in a directional reflective surface and a highly aesthetically pleasing surface gloss.

[0109] Although the present invention has been described with reference to several embodiments described above, the present invention is not limited to these embodiments. Various modifications can be made to the structure and details of the present invention within the scope of the invention. This disclosure is related to the subject matter described in Japanese Patent Application No. 2024-221858, filed on 18 December 2024, all of which are incorporated herein by reference.

Claims

1. A printing ink comprising a resin with a refractive index of 1.5 or higher (A), carbon black with a primary particle size of 10 to 50 nm (B), and titanium dioxide with a primary particle size of 10 to 100 nm (C).

2. The printing ink according to claim 1, wherein when an ink surface printed with the printing ink to have a surface roughness Ra of 2.5 μm or less is measured using a goniophotometer with the incident angle fixed at 60°, the half-width of the peak of the reflected light intensity with respect to the receiving angle of the reflected light is 10 or more.

3. The printing ink according to claim 1 or 2, wherein the resin (A) having a refractive index of 1.5 or higher includes at least one selected from the group consisting of styrene resins, polyester resins, epoxy resins, and acrylic resins.

4. The printing ink according to claim 1 or 2, wherein the resin (A) having a refractive index of 1.5 or higher includes a resin having a glass transition temperature of 50 to 100°C.

5. The printing ink according to claim 1 or 2, wherein the mass ratio of carbon black (B) to titanium dioxide (C) is 1:99 to 40:

60.

6. The printing ink according to claim 1 or 2, further comprising inorganic particles (D) having a refractive index of 1.3 to 1.7 and a volume-based average particle diameter (D50) of 1 to 20 μm as determined by laser diffraction scattering.

7. A printing ink according to claim 1 or 2, for use in screen printing.

8. The printing ink according to claim 1 or 2, for use in decorative articles.

9. A decorated article comprising a decorated article and an ink layer formed on the decorated article using the printing ink described in claim 1 or 2.

10. The decorative article according to claim 9, wherein the printing ink further comprises inorganic particles (D) having a refractive index of 1.3 to 1.7 and a volume-based average particle diameter of 1 to 20 μm as determined by laser diffraction scattering.

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