Manufacturing method for millimeter-wave transmitted printed materials

Abstract

To provide a manufacturing method of a millimeter wave transmission printed matter which is excellent in high luminance designability and millimeter wave transmission, and has less environmental loads.SOLUTION: A manufacturing method of a millimeter wave transmission printed matter includes a step of forming a print layer on a plastic base material by gravure printing using a gravure plate and printing ink, wherein the printing ink contains an aluminum thin piece and a binder resin, a mass ratio of the aluminum thin piece to the binder resin solid content is 80 / 20 to 40 / 60, a screen line number of the gravure plate is 100-350 lines / inch, and a millimeter wave transmission attenuation amount of the millimeter wave transmission printed matter is -1.5 dB or less.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a millimeter-wave transmissive printed matter.

Background Art

[0002] Today, for automobile painting, since purchasers have come to prefer painted colors with luster, paints containing a luster material (such as mica, aluminum flakes, etc.) are often used. Therefore, resin products for the exterior of automobiles, such as bumpers that make up an automobile, are also often painted with paints containing a luster material in order to maintain harmony with other parts of the automobile. On the other hand, in order to improve the safety of automobiles, a distance measuring radar device that warns the driver that the automobile is approaching surrounding objects may be provided behind each part of the automobile, such as behind the radiator grill, back panel, etc. Since such a radar device measures the distance by irradiating electromagnetic waves onto an object, if there is something (such as metal) that blocks the electromagnetic waves between the radar device and the object, its function cannot be fulfilled. Therefore, resin products for the exterior of automobiles, such as the radiator grill, etc. (the cover part of the radar device) located in front of the radar device, require electromagnetic wave transmissibility, and particularly millimeter-wave transmissibility with a frequency of about 30 to 300 GHz is required. For a component having a metal film, such as a decorative emblem, to have high millimeter-wave transmissibility, it is necessary for the metal film to have a so-called sea-island structure composed of discontinuous independent islands. On the other hand, since the radiator grill, decorative emblems, etc. constitute the appearance of the vehicle, from the perspective of design, it is also required that the metal film has sufficient metallic luster.

[0003] Indium and tin are known metals that can maintain a certain degree of sea-island structure even when the thickness of the metal film is sufficient to obtain metallic luster. However, indium is expensive, and there was a problem that the manufacturing cost was high when metal films were formed using indium. To reduce this manufacturing cost, for example, Patent Document 1 describes a resin product in which a metal film is formed by sputtering indium and aluminum or palladium, which readily alloy with indium, in that order onto a resin substrate. However, although the resin product described in Patent Document 1 reduces the amount of indium used, the majority of the metal film is still indium, so it was not sufficient to reduce the manufacturing cost.

[0004] Patent Document 2 describes a method for achieving glossiness without using indium, which involves spray-painting a paint containing aluminum flakes onto a transparent substrate. However, the method described in Patent Document 2 requires diluting the paint to a low viscosity, which leads to environmental problems such as the emission of large amounts of VOCs during painting, and other methods for forming coatings are desired. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2019-188806 [Patent Document 2] Japanese Patent Publication No. 2019-123819 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] The present invention aims to provide a method for manufacturing millimeter-wave transparent printed materials that exhibit high brightness design and excellent millimeter-wave transmittance, while also having a low environmental impact. [Means for solving the problem]

[0007] In light of the above problems, the inventors conducted thorough research and found that these problems can be solved by using the manufacturing method described below, thus concluding the present invention.

[0008] In other words, the present invention relates to a method for manufacturing a millimeter-wave-transmitting printed material, comprising the step of forming a printed layer on a plastic substrate by gravure printing using a gravure plate and printing ink, wherein the printing ink contains aluminum flakes and a binder resin, the mass ratio of aluminum flakes to binder resin solids is 80 / 20 to 40 / 60, the screen ruling of the gravure plate is 100 to 350 lines / inch, and the millimeter-wave transmission attenuation of the millimeter-wave-transmitting printed material is -1.5 dB or less.

[0009] The present invention also relates to a method for manufacturing the above-mentioned millimeter-wave transmitting printed material, wherein the film thickness of the millimeter-wave transmitting printed material is 50 to 250 nm.

[0010] The present invention also relates to a method for producing the above-mentioned millimeter-wave transmitted printed material, wherein the aluminum flakes are vapor-deposited aluminum with an average particle diameter of 1 to 15 μm and an average thickness of 50 nm or less.

[0011] The present invention also relates to a method for manufacturing the above-mentioned millimeter-wave transmitted printed material, wherein the screen ruling of the gravure plate is 180 to 350 lines / inch.

[0012] The present invention also relates to a method for manufacturing the above-mentioned millimeter-wave transmitted printed material, wherein the stylus angle of the gravure plate is 110 to 150°.

[0013] The present invention also relates to a method for manufacturing the above-mentioned millimeter-wave transmitted printed material, wherein the gravure plate type is compressed, normal, elongated, coarse, or fine.

[0014] The present invention also relates to a method for manufacturing the above-mentioned millimeter-wave transmitting printed material, wherein the plastic substrate is an acrylic substrate.

[0015] The present invention also relates to a method for producing the above-mentioned millimeter-wave-transmitting printed material, wherein the binder resin comprises at least one selected from the group consisting of vinyl chloride-vinyl acetate copolymer resin, urethane resin, and acrylic resin. [Effects of the Invention]

[0016] This invention makes it possible to provide a method for manufacturing millimeter-wave transparent printed materials that have excellent high-brightness design and millimeter-wave transmittance properties, as well as low environmental impact. [Modes for carrying out the invention]

[0017] The embodiments of the present invention will be described in detail below, but the matters described below are merely examples of embodiments of the present invention, and the present invention is not limited to these matters unless it exceeds the gist of the invention.

[0018] The present invention relates to a method for manufacturing a millimeter-wave-transmitting printed material, comprising the step of forming a printed layer on a plastic substrate by gravure printing using a gravure plate and printing ink, wherein the printing ink contains aluminum flakes and a binder resin, the mass ratio of aluminum flakes to binder resin solids is 80 / 20 to 40 / 60, and the screen ruling of the gravure plate is 100 to 350 lines / inch, thereby enabling the production of a millimeter-wave-transmitting printed material with a millimeter-wave transmission attenuation of -1.5 dB or less.

[0019] When the screen ruling of the gravure plate is within the above range, and at the same time the mass ratio of the aluminum flakes in the printing ink to the binder ink is within the above range, the printed layer forms a sea-island structure, enabling both high brightness and millimeter-wave transmission.

[0020] Gravure printing The manufacturing method of the present invention includes a step of forming a printed layer on a plastic substrate by gravure printing using a gravure plate and printing ink. By diluting the printing ink described later with a diluting solvent to a viscosity and concentration suitable for gravure printing, supplying it to a printing unit, and printing with a gravure printing machine, a millimeter-wave transmissive printed matter can be obtained. By appropriately selecting the layout of the gravure plate, the stylus angle, the screen line number, etc., the film thickness of the printed matter and the state of the printed surface can be adjusted. In addition, the printing speed is preferably 100 to 300 m / min, and more preferably 100 to 150 m / min from the viewpoint of design.

[0021] <Gravure plate> The gravure plate is not particularly limited as long as the screen line number is 100 to 350 lines / inch. The printed layer printed with this plate forms an island structure derived from the cells of the gravure plate, thereby improving the millimeter-wave transmissivity of the printed matter.

[0022] The screen line number is the number of dot patterns arranged within 1 inch. In the gravure plate of the present invention, the screen line number is preferably 180 to 350 lines / inch or less, more preferably 200 to 300 lines / inch, and particularly preferably 250 to 300 lines / inch. This is because the millimeter-wave transmissivity of the printed matter is further improved.

[0023] As the method for forming the cells of the gravure plate, there are an engraving method and an etching method. When the engraving method is used, the cells are formed into quadrangular pyramids, so the transferability of the printing ink described later is good. On the other hand, when the etching method is used, although the cells are small, recesses with a constant depth are formed, so it is suitable for printing extremely small characters, complex figures, and fine patterns. From the above characteristics, the engraving method is preferred in the present invention.

[0024] <Method for making a plate by etching method> One method for creating gravure plates using the aforementioned etching method involves forming cell recesses on the surface of a metal cylinder, which is made of an iron core roll plated with copper. This method consists of processes such as surface treatment, coating with photosensitive solution, printing, developing, etching, and chrome plating. In the etching process, first, the surface of the metal cylinder is degreased and the oxide film removed to improve adhesion during the coating of the photosensitive solution. Then, a photosensitive solution such as polyvinyl polysinate is coated and dried, and the design data is printed onto it using a laser or the like to form latent images of image and non-image areas. The image areas are removed with developing chemicals to form a resist pattern. The metal cylinder with this resist pattern is then etched using an etching solution of ferric chloride (copper) to form recesses of the desired depth. After etching is complete, the resist pattern is removed, the cylinder surface is cleaned, and chrome plating or the like is performed to improve print durability. In this case, the depth of the recesses created by etching is usually formed to about several tens of micrometers.

[0025] Gravure plates in etching are preferably made by copper plating or chromium plating, and can be made by conventional, screen gravure, or laser methods, but screen gravure and laser plates are preferred. A rectangular cell shape is preferred, and a plate depth of 40 μm or less is preferred.

[0026] <Method for creating plates using the engraving method> One method of creating gravure plates using engraving involves driving an engraving needle (part of the engraving head) onto a copper-plated cylinder to form cells. By controlling the speed at which the engraving needle is driven (amplitude) and the speed at which it moves (width feed speed), various plate types such as compressed, normal, elongated, coarse, and fine can be produced. Afterwards, the surface is cleaned and chrome plating or other treatments are applied to improve print durability.

[0027] A diamond needle (stylus) is preferably used as the engraving needle. By changing the tip angle of the needle (stylus angle), the depth and volume of the cell can be changed without changing the diameter, thus allowing for adjustment of the density. In this invention, the stylus angle is preferably 110° to 150°, more preferably 120° to 150°, and particularly preferably 130° to 150°. This is because forming an appropriate sea-island structure improves millimeter-wave transmission.

[0028] The type of gravure printing plate can be appropriately selected depending on the printing ink and the condition of the printed material, but in the case of engraving, it is preferable to use compressed, normal, elongated, coarse, or fine.

[0029] <Printing Ink> The printing ink used in this invention contains aluminum flakes and a binder resin, with a mass ratio of aluminum flakes to binder resin of 80 / 20 to 40 / 60. The inclusion of aluminum flakes gives the printed material a glossy sheen (luster), and the inclusion of binder resin improves the ink's adhesion to the substrate. The mass ratio of aluminum flakes to binder resin is preferably 70 / 30 to 15 / 85, and more preferably 70 / 30 to 30 / 70. When the ratio of aluminum flakes is 80 or less, the ink's adhesion to the substrate improves, and when the ratio of aluminum flakes is greater than 40, high gloss is achieved, and luster is more easily exhibited.

[0030] <Aluminum flakes> The printing ink used in this invention contains aluminum flakes. In this invention, aluminum flakes refer to aluminum pigment shaped into flakes. Aluminum pigments are generally produced by melting a lump of aluminum, extracting it in flake or solid form, and then milling it in a solvent to shape its particle size, thickness, and surface condition (milling method). On the other hand, aluminum pigment in flake form can also be produced by vapor deposition. Specifically, a release layer is uniformly applied to a film, an aluminum layer is vacuum-deposited onto it, and then the release layer is dissolved to obtain a thin film of aluminum pigment. Subsequently, the obtained thin film of aluminum pigment is stirred and milled to adjust its particle size. The aluminum pigment formed by the above method can be dispersed in a solvent and used as an aluminum paste.

[0031] The aluminum flakes used in this invention are not limited by their manufacturing method, but vapor-deposited aluminum obtained by vapor deposition is preferred because it is an extremely thin film with a uniform film thickness, allowing for good glossiness in ink-printed materials.

[0032] The average particle size of the aluminum flakes is preferably 1 to 15 μm, more preferably 3 to 15 μm, and even more preferably 5 to 10 μm. If the average particle size of the aluminum flakes is 1 μm or more, sufficient glossiness can be obtained in the ink coating film, and if it is 15 μm or less, millimeter-wave transmittance of the ink printed material is easily achieved.

[0033] The average film thickness of the aluminum flakes is preferably 5 to 50 nm, more preferably 8 to 40 nm, and even more preferably 10 to 30 nm. When the film thickness is 5 nm or more, it is easier to achieve both glossiness and millimeter-wave transmittance in the coating film, and when it is 50 nm or less, the orientation of the aluminum in the coating film is more aligned, resulting in better glossiness.

[0034] <Binder resin> The printing ink used in this invention contains a binder resin. The binder resin refers to the binding resin in the ink, and is preferably a thermoplastic resin soluble in an organic solvent. The inclusion of a binder resin in the ink not only makes it easier to hold aluminum flakes in the coating film, but also improves the adhesion between the ink and the substrate.

[0035] Examples of binder resins, but not limited to those listed below, include urethane resins, cellulose resins, polyamide resins, vinyl chloride-vinyl acetate copolymer resins, vinyl chloride-acrylic copolymer resins, rosin resins, ethylene-vinyl acetate copolymer resins, vinyl acetate resins, acrylic resins, styrene resins, styrene-maleic acid copolymer resins, polyester resins, alkyd resins, ketone resins, cycloplastic rubbers, chlorinated rubbers, butyral, polyacetal resins, petroleum resins, and modified resins thereof. These resins can be used individually or in combination of two or more. In particular, it is preferable to include one or more selected from the group consisting of urethane resins, vinyl chloride-vinyl acetate copolymer resins, and acrylic resins.

[0036] <urethane resin> The urethane resin can be any resin having a urethane bond, and examples include a urethane resin composed of a polyol and a polyisocyanate; and a urethane urea resin obtained by reacting a urethane prepolymer of terminal isocyanates composed of a polyol and a polyisocyanate with a chain extender such as a polyamine; and these are preferably used. Examples of methods for producing such a urethane resin include the methods described in Japanese Patent Publication No. 2013-256551, Japanese Patent Publication No. 2018-127545, and Japanese Patent Publication No. 2013-213109.

[0037] The weight-average molecular weight of the urethane resin is preferably between 10,000 and 100,000, and more preferably between 20,000 and 80,000. A weight-average molecular weight of 10,000 or more is expected to result in good resistance to humid heat, blocking, and lamination strength, while a weight-average molecular weight of 100,000 or less is expected to result in good plate coverage and ink stability over time.

[0038] The urethane resin has a hydroxyl value of 1 to 40 mgKOH / g and / or an amine value of 1 to 20 mgKOH / g, preferably a hydroxyl value of 3 to 30 mgKOH / g and / or an amine value of 3 to 15 mgKOH / g. If the hydroxyl value is 1 mgKOH / g and / or the amine value is 1 mgKOH / g or higher, adhesion to the substrate is good, and if the hydroxyl value is 40 mgKOH / g or less and / or the amine value is 20 mgKOH / g or less, the ink's long-term stability is good.

[0039] Examples of polyols used in the synthesis of urethane resins include polyester polyols, polyether polyols, polylactone polyols, polycarbonate polyols, polyolefin polyols, castor oil polyols, hydrogenated castor oil polyols, dimer diols, and hydrogenated dimer diols. Among these, polyether polyols and polylactone polyols are preferred.

[0040] Examples of the polyether polyols include polyether polyols of polymers or copolymers of ethylene oxide, propylene oxide, tetrahydrofuran, etc. Among these, polytetramethylene glycol, polypropylene glycol, and polyethylene glycol are preferred, and the number average molecular weight is preferably 500 to 10,000, and more preferably 500 to 3,000. The number average molecular weight is calculated from the hydroxyl value with hydroxyl groups at the ends, and is determined by (Formula 1). (Equation 1) Number-average molecular weight of polyol = 1000 × 56.1 × valence of hydroxyl groups / hydroxyl value

[0041] The aforementioned polylactone polyol refers to a polyol having a hydroxyl group at the ring-opened polymerized end of a lactone. Polylactone polyols are often synthesized by ring-opening polymerization of a lactone in the presence of a polyol, and at least one of α-acetolactone, β-propiolactone, γ-butyrolactone, δ-valerolactone, and ε-caprolactone is preferred as the lactone constituting the polylactone polyol. Furthermore, the polyol constituting the polylactone polyol is preferably a diol, and suitable examples include ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,3-butanediol, 1,6-hexanediol, 1,8-octanediol, 1,9-nonanediol, neopentyl glycol, 3-methyl-1,5-pentanediol, 2-methyl-1,3-propanediol, 3,3,5-trimethylpentanediol, 2,4-diethyl-1,5-pentanediol, 1,12-octadecanediol, 1,2-alkanediol, 1,3-alkanediol, 1-monoglyceride, 2-monoglyceride, 1-monoglycerin ether, and 2-monoglycerin ether.

[0042] Furthermore, when synthesizing polylactone polyols, dibasic acids may be used in combination with the lactones and polyols mentioned above. Examples of dibasic acids include adipic acid, phthalic anhydride, isophthalic acid, terephthalic acid, maleic acid, fumaric acid, succinic acid, oxalic acid, malonic acid, pimelic acid, azelaic acid, sebacic acid, suberic acid, glutaric acid, 1,4-cyclohexyldicarboxylic acid, dimer acids, and hydrogenated dimer acids.

[0043] The polylactone polyol preferably has a number average molecular weight of 500 to 10,000, and more preferably 500 to 3,000. Furthermore, it is preferable to contain 5 to 50% by mass of structural units consisting of polylactone polyol in the urethane resin, more preferably 5 to 35% by mass, and even more preferably 10 to 35% by mass. This is because it improves resistance to moisture and heat, as well as resistance to hydrolysis.

[0044] Examples of the aforementioned polyisocyanates include various known aromatic diisocyanates, aliphatic diisocyanates, and alicyclic diisocyanates commonly used in the production of urethane resins. For example, 1,5-naphthylene diisocyanate, 4,4'-diphenylmethane diisocyanate (MDI), 4,4'-diphenyldimethylmethane diisocyanate, 4,4'-dibenzyli isocyanate, dialkyldiphenylmethane diisocyanate, tetraalkyldiphenylmethane diisocyanate, 1,3-phenylenediisocyanate, 1,4-phenylenediisocyanate, tolylene diisocyanate, butane-1,4-diisocyanate, hexamethylene diisocyanate, isopropyl diisocyanate, methylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, lysine diisocyanate, Examples include cyclohexane-1,4-diisocyanate, xylylene diisocyanate, isophorone diisocyanate, dimeryl diisocyanate, dicyclohexylmethane-4,4'-diisocyanate, 1,3-bis(isocyanate-methyl)cyclohexane, methylcyclohexane diisocyanate, norbornane diisocyanate, m-tetramethylxylylene diisocyanate, 4,4-diphenylmethane diisocyanate, bis-chloromethyl-diphenylmethane diisocyanate, 2,6-diisocyanate-benzyl chloride, and dimer isocyanates obtained by converting the carboxyl groups of dimer acids to isocyanate groups. These may also exist as trimers forming an isocyanurate ring structure. These polyisocyanates can be used individually or in combination of two or more. Preferably, the materials are tolylene diisocyanate, isophorone diisocyanate, xylylene diisocyanate, hydrogenated xylylene diisocyanate, hexamethylene diisocyanate, and isocyanurate derivatives of hexamethylene diisocyanate.

[0045] The polyamines that make up the urethane resin are not limited as long as they function as chain extenders and form urea bonds. In addition to ethylenediamine, propylenediamine, hexamethylenediamine, diethylenetriamine, triethylenetetramine, isophoronediamine, and dicyclohexylmethane-4,4'-diamine, amines having hydroxyl groups in their molecules, such as 2-hydroxyethylethylenediamine, 2-hydroxyethylpropyldiamine, 2-hydroxyethylpropylenediamine, di-2-hydroxyethylethylenediamine, di-2-hydroxyethylenediamine, di-2-hydroxyethylpropylenediamine, 2-hydroxypyropyrethylenediamine, di-2-hydroxypyropyrethylenediamine, and di-2-hydroxypropylethylenediamine, can also be used. These chain extenders can be used individually or in combination of two or more. Furthermore, polyfunctional polyamines can be used as needed, specifically diethylenetriamine, iminobispropylamine (IBPA, 3,3'-diaminodipropylamine), N-(3-aminopropyl)butane-1,4-diamine (spermidine), 6,6-iminodihexylamine, 3,7-diazanonane-1,9-diamine, and N,N'-bis(3-aminopropyl)ethylenediamine. Among these, isophoronediamine, hexamethylenediamine, and iminobispropylamine are preferred.

[0046] <Vinyl chloride-vinyl acetate copolymer resin> The vinyl chloride-vinyl acetate copolymer resin is obtained by copolymerizing vinyl chloride and vinyl acetate. The vinyl chloride-vinyl acetate copolymer resin preferably has a weight-average molecular weight of 5,000 to 100,000, and more preferably 20,000 to 70,000. The structure derived from vinyl acetate monomer is preferably 1 to 30% by mass of the solid content of the vinyl chloride-vinyl acetate copolymer resin, and the structure derived from vinyl chloride monomer is preferably 60 to 95% by mass. In this case, solubility in organic solvents is improved, and adhesion to the substrate and film properties are also improved.

[0047] <Acrylic resin> The aforementioned acrylic resin refers to a polymer having acrylic monomers as constituent units. Furthermore, "acrylic monomer" refers to a monomer having an acrylic group or a methacrylic group, and "methacrylic and acrylic" are sometimes collectively abbreviated as "(meth)acrylic". Furthermore, "methacrylate and acrylate" are sometimes collectively abbreviated as "(meth)acrylate".

[0048] The acrylic resin is not particularly limited and may have an acid value, but the acid value is preferably 20 mg KOH / g or less, and more preferably 10 mg KOH / g or less. An acid value of 20 mg KOH / g or less can further improve the durability of the ink film and laminate. The acrylic resin having an acid value is obtained by copolymerizing an acrylic monomer having an acid value with another acrylic monomer. Examples of acrylic monomers having an acid value include (meth)acrylic acid, maleic anhydride, 2-(meth)acryloyloxyethyl succinic acid, 2-(meth)acryloyloxyethyl hexahydrophthalic acid, 2-(meth)acryloyloxyethyl phthalic acid, and 2-(meth)acryloyloxyethyl acid phosphate, among which (meth)acrylic acid is preferred.

[0049] The weight-average molecular weight (Mw) of the acrylic resin is preferably between 20,000 and 300,000. A weight-average molecular weight of 20,000 or higher allows for a combination of moldability and surface hardness. A weight-average molecular weight of 300,000 or lower results in good resistance to chemicals and other substances.

[0050] The degree of dispersion (Mw / Mn), which is the ratio of the weight-average molecular weight (Mw) to the number-average molecular weight (Mn) of the acrylic resin, is preferably 1.5 to 10, more preferably 2 to 9, and even more preferably 2.5 to 8. The weight-average molecular weight and number-average molecular weight can be determined by GPC measurement.

[0051] <Organic solvents> The printing ink used in the present invention may contain an organic solvent. Known organic solvents can be used, including aromatic organic solvents such as toluene and xylene, ketone organic solvents such as methyl ethyl ketone and methyl isobutyl ketone, ester organic solvents such as ethyl acetate, n-propyl acetate, isopropyl acetate, isobutyl acetate, methanol, ethanol, n-propanol, isopropanol, n-butanol, ethylene glycol monopropyl ether, and propylene glycol monomethyl ether. These can also be used in mixtures. Among these, organic solvents that do not contain aromatic organic solvents such as toluene and xylene (non-toluene organic solvents) are preferred from an environmental perspective.

[0052] <Additives> The printing ink used in the present invention may appropriately contain known additives, such as pigment derivatives, dispersants, wetting agents, adhesion aids, leveling agents, defoaming agents, antistatic agents, trapping agents, antiblocking agents, wax components, isocyanate-based curing agents, and silane coupling agents.

[0053] <Manufacturing of printing inks> The printing ink used in the present invention can be produced by dispersing / mixing aluminum flakes or a dispersion of aluminum flakes in a mixture of a binder resin and an organic solvent. Specifically, for example, a printing ink can be produced by mixing a binder resin, a dispersion of aluminum flakes, an organic solvent, and, if necessary, the aforementioned dispersant.

[0054] The viscosity of the printing ink produced by the above method is preferably in the range of 40 to 500 mPa·s at 25°C as measured by a B-type viscometer, more preferably 50 to 350 mPa·s, in order to accommodate gravure printing. This viscosity range corresponds to a viscosity of approximately 9 to 40 seconds in a Zahn cup #4. The viscosity of the printing ink can be adjusted by appropriately selecting the type and amount of raw materials used, such as binder resin and organic solvent.

[0055] When gravure printing with printing ink, it is preferable to dilute the ink to a viscosity suitable for printing using a diluent solvent. The above-mentioned organic solvent is used as the diluent solvent. The viscosity of the diluted ink is preferably 13 to 20 seconds on a Zahn cup #3 and 30 to 250 mPa·s on a B-type viscometer. Furthermore, the ink solids content after dilution is preferably 5% or more, and more preferably 8% or more, because this reduces VOC emissions during printing.

[0056] <Plastic substrate> The substrates that can be used in the printed materials of the present invention are not particularly limited as long as they are plastic substrates, and examples include polyolefins such as polyethylene and polypropylene, polyesters such as polyethylene terephthalate, polycarbonate, and polylactic acid, polystyrene resins such as polystyrene, acrylonitrile-styrene copolymer (AS) resin, acrylonitrile-butadiene-styrene copolymer (ABS) resin, and acrylonitrile-ethylene-styrene copolymer (AES), acrylic, nylon, polyamide, polyvinyl chloride, polyvinylidene chloride, or film-like substrates made of these composite materials. Among these, it is preferable to use acrylic film or other acrylic substrates from the viewpoint of substrate adhesion and millimeter-wave transmission. Furthermore, the substrate may be coated with polyvinyl alcohol or the like, or subjected to surface treatment such as corona discharge treatment.

[0057] <Millimeter-wave transparent printed material> The millimeter-wave permeable printed material produced by the manufacturing method of the present invention has a millimeter-wave transmission attenuation of -1.5 dB or less. Preferably, the millimeter-wave transmission attenuation is -1.0 dB or less.

[0058] In millimeter-wave transparent printed materials, the thickness of the printing ink layer is preferably between 50 nm and 250 nm. A thickness of 50 nm or more tends to produce a glossy appearance, while a thickness of 250 nm or less tends to achieve millimeter-wave transparency. [Examples]

[0059] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. It is not. In this invention, parts and percent refer to parts by weight and weight percent, respectively, unless otherwise noted.

[0060] (Hydroxyl value) The hydroxyl value is calculated by esterifying or acetylating the hydroxyl groups in the resin with excess acid anhydride, and then back-titrating the remaining acid with an alkali. The amount of hydroxyl groups per gram of resin is then converted to the number of milligrams of potassium hydroxide, according to JIS K0070.

[0061] (Amine value) The amine value is the equivalent amount of hydrochloric acid and the amount of potassium hydroxide required to neutralize the amino groups contained in 1 g of resin. The acid value is the equivalent amount of potassium hydroxide and the amount of acid groups required to neutralize the acid groups contained in 1 g of resin. The measurement method may be a known method, and was performed in accordance with JIS K0070, using the following method. • Method for measuring amine value The sample was weighed accurately to 0.5-2 g (sample amount: Sg). 30 mL of neutral ethanol (BDG neutral) was added to the weighed sample and dissolved. The resulting solution was titrated with a 0.2 mol / l ethanolic hydrochloric acid solution (titer: f). The endpoint was defined as the point where the solution changed color from green to yellow. The amine value was determined using the titration volume (A mL) at this point and the following formula. (Formula) Amine value = (A × f × 0.2 × 56.108) / S

[0062] (Weight average molecular weight) The weight-average molecular weight was determined by measuring the molecular weight distribution using a GPC (gel permeation chromatography) instrument (Shodex GPC System-21, manufactured by Showa Denko Corporation) and calculating the molecular weight in terms of polystyrene equivalent.

[0063] (Average particle size and average thickness of aluminum flakes) The average particle size and thickness of the aluminum pigment were observed using a scanning electron microscope (JSM-6390LA) manufactured by JEOL Ltd. The average particle size and film thickness of the aluminum pigment were measured at four locations in the obtained images, and their average values ​​were calculated.

[0064] (Synthesis Example 1) [Preparation of vinyl chloride-vinyl acetate copolymer resin solution] Vinol H30 / 48M (a copolymer resin manufactured by Wacker, consisting of vinyl chloride / vinyl acetate / acid monomer = 70 / 29 / 1 (mass ratio), with a weight-average molecular weight of 70,000) was dissolved in methyl ethyl ketone (hereinafter referred to as "MEK") to obtain a vinyl chloride-vinyl acetate copolymer resin solution with a solid content of 25%.

[0065] (Synthesis Example 2) [Preparation of Polyurethane Resin Solution] A mixture consisting of 50 parts of polycaprolactone diol with a number-average molecular weight of 1250, which is a ring-opened polymer of ε-caprolactone; 50 parts of polytetramethylene glycol (hereinafter referred to as "PTG") with a number-average molecular weight of 2000; 19 parts of neopentyl glycol; 99 parts of isophorone diisocyanate (hereinafter referred to as "IPDI"); and 54.5 parts of ethyl acetate was reacted at 80°C under a nitrogen stream for 4 hours to obtain a solvent solution of the terminal isocyanate prepolymer. Next, the above-mentioned terminal isocyanate prepolymer solution was gradually added at 40°C to a mixture consisting of 17.5 parts isophorone diamine (hereinafter "IPDA"), 2.6 parts dibutylamine (hereinafter "DBA"), 10.2 parts 2-hydroxyethylethylenediamine (hereinafter "AEA"), 303.3 parts ethyl acetate, and isopropanol, and the reaction was further carried out at 80°C for 1 hour to obtain a polyurethane resin solution with a solid content of 30%, an amine value of 7.0 mg KOH / g, a hydroxyl value of 22.1 mg KOH / g, and a weight-average molecular weight of 40,000 (the solvent composition in the solution was ethyl acetate / 2-propanol (IPA) = 60 / 40 (mass ratio)).

[0066] (Manufacturing Example 1) [Manufacturing of Printing Ink S1] Printing ink S1 was obtained by mixing 19 parts of vinyl chloride-vinyl acetate copolymer resin solution, 75 parts of aluminum paste A (deposited aluminum: average particle size 8 μm, average thickness 25 nm, medium: n-propyl acetate, solid content 10%), and 6 parts of MEK.

[0067] (Manufacturing Examples 2-9) [Manufacturing of Printing Inks S2-S9] Printing inks S2 to S9 were obtained using the same method as for the production of printing ink S1, except that the raw materials and mixing ratios were changed as shown in Table 1.

[0068] [Table 1]

[0069] The details of the raw materials in Table 1 are shown below. • Acrylic resin solution: Acrit 6AN-5000 (manufactured by Taisei Fine Chemical Co., Ltd., solids content 40.5%) • Aluminum paste B (vapor-deposited aluminum: average particle size 11 μm, average thickness 23 nm, medium: n-propyl acetate, solids content 10%) • Aluminum paste C (vapor-deposited aluminum: average particle size 13 μm, average thickness 52 nm, medium: n-propyl acetate, solids content 60%) • Aluminum paste D (pulverized aluminum: average particle size 15 μm, average thickness 123 nm, medium: n-propyl acetate, solids content 60%)

[0070] <Creating printed materials> (Example 1) The printing ink S1 obtained above was diluted with methyl ethyl ketone (MEK) to a viscosity of 200 mPa·s (Zaan Cup No. 3, 16 seconds). This was then printed onto a 75 μm thick acrylic film (manufactured by Kaneka, Sanduren) at a printing speed of 120 m / min using a gravure printing plate (fine) with a stylus angle of 140 degrees and a screen ruling of 250 lines / inch to obtain printed material G1.

[0071] (Examples 2-19) Printed materials G2 to G19 were obtained by producing printed materials in the same manner as in Example 1, except that the printing and platemaking conditions described in Tables 2 and 3 were changed.

[0072] (Comparative Examples 1-5) Printed materials H1 to H5 were obtained by the same method as in Example 1, except that the printing conditions listed in Table 4 were changed.

[0073] (Comparative Example 6) The printing ink S1 obtained above was diluted with methyl ethyl ketone (MEK) to a viscosity of 30 mPa·s, and spray-coated onto the surface of a 75 μm thick acrylic film (manufactured by Kaneka, Sanduren) using a spray gun. The coating and drying process was repeated to obtain a printed material H6 with a print layer thickness of approximately 200 nm after drying.

[0074] The following evaluation was performed using the printed materials obtained above. The results are shown in Tables 2-4.

[0075] <Adhesion to substrate> 12mm wide cellophane tape manufactured by Nichiban was applied to the ink coating of printed materials, and the amount of ink removed upon peeling was visually evaluated. A: Only the tape peels off (good adhesion to the substrate). B: Part of the ink film is removed from the adhesive surface of the tape (poor adhesion to the substrate). The rating for practical usability is A.

[0076] <Millimeter-wave transmission attenuation> Using a millimeter-wave transmitter (E8257D) and receiver (N9030A) manufactured by Keysight Technologies, a 77 GHz millimeter wave was incident on the sample from the transmitter at an incidence angle of 0° at room temperature. The millimeter wave transmitted through the sample was received by the receiver, which was positioned opposite the transmitter with the sample in between, and the millimeter-wave transmission attenuation was measured. A: 1dB or less B: Greater than 1dB and less than or equal to 1.5dB C: Greater than 1.5dB The ratings for practical usability are A and B.

[0077] <Gloss value> From the substrate side of the printed matter produced in the above Examples and Comparative Examples, using a surface analyzer RA-532H manufactured by Canon, the gloss values under the conditions of an incident angle of 20 degrees and a light-receiving angle of 20 degrees, and an incident angle of 60 degrees and a light-receiving angle of 60 degrees were measured. A: 400 or more B: 300 or more and less than 400 C: Less than 300 Practically usable evaluations are A and B.

[0078] <VOC emission> Evaluation ink was diluted with a solvent (MEK) to the viscosity during gravure printing or spray coating, and evaluated in three stages according to the solid content of the diluted ink (the higher the solid content of the diluted ink, the less VOC is emitted during drying, which is preferable). The above viscosity is 200 mPa·s for gravure printing and 30 mPa·s for spray coating. A: 8% or more B: 5% or more and less than 8% C: Less than 5% Practically preferable evaluations are A and B.

[0079]

Table 2

[0080]

Table 3

[0081]

Table 4

[0082] Based on the above results, we were able to achieve the objective of providing a method for creating printed materials with excellent gloss and millimeter-wave transmittance using gravure printing. When the printing ink contained aluminum flakes and binder resin with a mass ratio of aluminum flakes / binder resin solids of 80 / 20 to 40 / 60, and the screen ruling of the gravure plate was 100 to 350 lines / inch, we were able to achieve gloss and millimeter-wave transmittance in the printed materials. In contrast, in Comparative Examples 3, 4, and 6, the millimeter-wave transmittance attenuation did not fall below -1.5 dB, and in Comparative Examples 2 and 5, sufficient gloss (gloss value) was not achieved. Furthermore, Comparative Example 1 resulted in poor ink adhesion to the substrate, and Comparative Example 6 resulted in high VOC emissions.

Claims

1. A method for manufacturing a millimeter-wave-transmitting printed material, comprising the step of forming a printed layer on a plastic substrate by gravure printing using a gravure plate and printing ink, The printing ink comprises aluminum flakes and a binder resin. The aluminum flakes are vapor-deposited aluminum with an average particle diameter of 1 to 15 μm and an average thickness of 52 nm or less. The mass ratio of the aluminum flakes to the binder resin solids is 80 / 20 to 40 / 60. The screen ruling of the aforementioned gravure plate is 100 to 350 lines / inch. A method for manufacturing a millimeter-wave transmitting printed material, wherein the millimeter-wave transmission attenuation of the millimeter-wave transmitting printed material is -1.5 dB or less.

2. A method for manufacturing a millimeter-wave-transmitting printed material according to claim 1, wherein the film thickness of the millimeter-wave-transmitting printed material is 50 to 250 nm.

3. A method for manufacturing a millimeter-wave transmitted printed material according to claim 1 or 2, wherein the screen ruling of the gravure plate is 180 to 350 lines / inch.

4. A method for manufacturing a millimeter-wave transmitted printed material according to claim 1 or 2, wherein the stylus angle of the gravure plate is 110 to 150°.

5. A method for manufacturing a millimeter-wave transmitted printed material according to claim 1 or 2, wherein the gravure plate type is compressed, normal, elongated, coarse, or fine.

6. A method for manufacturing a millimeter-wave-transmitting printed material according to claim 1 or 2, wherein the plastic substrate is an acrylic substrate.

7. A method for producing a millimeter-wave-transmitting printed material according to claim 1 or 2, wherein the binder resin comprises at least one selected from the group consisting of vinyl chloride-vinyl acetate copolymer resin, urethane resin, and acrylic resin.

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