JP7835128B2 - Manufacturing method for millimeter-wave transmitted printed materials - Google Patents

Description

This invention relates to a method for manufacturing millimeter-wave transmitted printed materials.

Today, because car buyers prefer glossy paint colors, paints containing gloss-enhancing agents (such as mica and aluminum flakes) are frequently used in automobile painting. Consequently, exterior plastic products such as bumpers are also increasingly being painted with gloss-enhancing agents to maintain harmony with other parts of the vehicle.
On the other hand, to improve safety, automobiles are sometimes equipped with radar devices for distance measurement that warn the driver when the vehicle approaches an object, located behind various parts of the vehicle, such as the radiator grille or back panel. Since such radar devices measure distance by irradiating an object with electromagnetic waves, if there is something (such as metal) between the radar device and the object that blocks electromagnetic waves, the device will not be able to perform its function. Therefore, the resin exterior products of automobiles, such as the radiator grille (the cover part of the radar device) located in front of the radar device, need to be electromagnetic wave permeable, and in particular, millimeter wave permeability at frequencies of approximately 30 to 300 GHz is required. In order for parts with a metal coating, such as decorative emblems, to have high millimeter wave permeability, it is necessary that the metal coating has a so-called sea-island structure, consisting of discontinuous, independent islands. On the other hand, since radiator grilles and decorative emblems constitute the exterior appearance of the vehicle, from the standpoint of design, it is also required that the metal coating have sufficient metallic luster.

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 using indium to form metal films results in high manufacturing costs. To reduce these manufacturing costs, 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, and therefore, it does not sufficiently reduce manufacturing costs.

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, leading to environmental problems such as the emission of large amounts of VOCs during painting. Therefore, other methods for forming coatings are desired.

Japanese Patent Publication No. 2019-188806 Japanese Patent Publication No. 2019-123819

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.

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

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.

Furthermore, the present invention 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.

Furthermore, the present invention 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.

Furthermore, this invention 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.

Furthermore, the present invention 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°.

Furthermore, the present invention relates to a method for manufacturing the above-mentioned millimeter-wave transmitted printed material, wherein the gravure plate format is one of compressed, normal, elongated, coarse, or fine.

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

Furthermore, the present invention 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.

This invention makes it possible to provide a method for manufacturing millimeter-wave transparent printed materials that exhibit high brightness design, excellent millimeter-wave transmittance, and low environmental impact.

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 essence of the invention.

The present invention relates to a method for manufacturing millimeter-wave-transmitting printed materials, comprising the step of forming a printed layer on a plastic substrate by gravure printing using a gravure plate and printing ink. The method is characterized in that 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 millimeter-wave-transmitting printed materials with a millimeter-wave transmission attenuation of -1.5 dB or less.

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

<Gravure Printing>
The manufacturing method of the present invention includes the 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 diluent 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 transmitting printed material can be obtained. The film thickness and surface condition of the printed material can be adjusted by appropriately selecting the gravure plate type, stylus angle, screen ruling, etc.
Furthermore, the printing speed is preferably 100 to 300 m/min, and more preferably 100 to 150 m/min from the viewpoint of design aesthetics.

<Gravure version>
Gravure printing plates have no particular limitations as long as the screen ruling is between 100 and 350 lines per inch. The printed layer produced by this plate forms a sea-island structure derived from the cells of the gravure plate, thereby improving the millimeter-wave transmittance of the printed material.

The screen ruling is the number of dots per inch. In the gravure printing plates of this invention, the screen ruling 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 it improves the millimeter-wave transmittance of the printed material.

Two methods exist for forming the cells of the gravure printing plate: engraving and etching. Engraving forms the cells in a square pyramidal shape, resulting in good ink transfer properties for the printing inks described later. On the other hand, etching creates small cells with a consistent depth, making it suitable for printing very small characters, complex shapes, and fine designs. Based on these characteristics, engraving is preferred in this invention.

<Method for creating plates using the etching method>
One method for creating gravure plates using the aforementioned etching method involves forming cell recesses on the surface of a metal cylinder 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.

Gravure plates in etching are preferably made by copper plating and chromium plating, and can be produced using 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.

<Method for creating a plate 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.

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 change 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 the millimeter-wave transmission is improved by appropriately forming a sea-island structure.

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

<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.

<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.

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 thickness, allowing for excellent glossiness in ink-printed materials.

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; if it is 15 μm or less, millimeter-wave transmittance of the ink-printed material is easily achieved.

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. A film thickness of 5 nm or more facilitates both the glossy appearance and millimeter-wave transmittance of the coating film, while a film thickness of 50 nm or less allows for more uniform orientation of the aluminum in the coating film, resulting in better glossy appearance.

<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.

Examples of binder resins, though 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 mixtures of two or more. In particular, it is preferable to include one or more resins selected from the group consisting of urethane resins, vinyl chloride-vinyl acetate copolymer resins, and acrylic resins.

<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. Such resins 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.

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 higher is expected to result in good resistance to humid heat, blocking, and lamination strength. A weight-average molecular weight of 100,000 or lower results in good plate coverage and ink stability over time.

The urethane resin has a hydroxyl value of 1 to 40 mg KOH/g and/or an amine value of 1 to 20 mg KOH/g, preferably a hydroxyl value of 3 to 30 mg KOH/g and/or an amine value of 3 to 15 mg KOH/g. A hydroxyl value of 1 mg KOH/g and/or an amine value of 1 mg KOH/g or higher results in good adhesion to the substrate, while a hydroxyl value of 40 mg KOH/g or less and/or an amine value of 20 mg KOH/g or less results in good long-term stability of the ink.

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.

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).
(Formula 1) Number average molecular weight of polyol = 1000 × 56.1 × valence of hydroxyl group / hydroxyl value

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, but at least one selected from 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.

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.

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 hydrolysis resistance.

Examples of the 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-phenylenedi isocyanate, 1,4-phenylenedi isocyanate, 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 group of a dimer acid to an isocyanate group. These may also exist as trimers forming an isocyanurate ring structure. These polyisocyanates can be used individually or in combination of two or more. Among these, tolylene diisocyanate, isophorone diisocyanate, xylylene diisocyanate, hydrogenated xylylene diisocyanate, hexamethylene diisocyanate, and isocyanurate derivatives of hexamethylene diisocyanate are preferred.

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 including 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.

<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 100% by mass 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, film properties, etc., are also improved.

<Acrylic resin>
The term "acrylic resin" refers to a polymer having acrylic monomers as constituent units. "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." Similarly, "methacrylate and acrylate" are sometimes collectively abbreviated as "(meth)acrylate."

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. Having an acid value of 20 mg KOH/g or less further improves the durability of the ink film and laminate. Acrylic resins having an acid value are 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.

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.

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.

<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.

<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.

<Manufacturing of printing inks>
The printing ink used in the present invention can be manufactured 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 manufactured by mixing a binder resin, a dispersion of aluminum flakes, an organic solvent, and, if necessary, the aforementioned dispersant.

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 using a B-type viscometer, in order to accommodate gravure printing. More preferably, it is in the range of 50 to 350 mPa·s. This viscosity range corresponds to a viscosity of approximately 9 to 40 seconds using 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.

When printing inks using gravure printing, 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 using a Zahn cup #3 and 30 to 250 mPa·s using 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.

<Plastic substrates>
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.

<Millimeter-wave transparent printed materials>
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.

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 facilitates the development of glossiness, while a thickness of 250 nm or less facilitates the achievement of millimeter-wave transparency.

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

(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.

(Amine value)
The amine value is the number of milligrams of potassium hydroxide required to neutralize the amino groups contained in 1 g of resin, equivalent to the amount of hydrochloric acid needed. The acid value is the number of milligrams of potassium hydroxide required to neutralize the acid groups contained in 1 g of resin. The measurement method can be a known method, and was performed in accordance with JIS K0070, using the following method.
• Method for measuring amine value: Weigh 0.5 to 2 g of the sample accurately. (Sample amount: S g) Add 30 mL of neutral ethanol (BDG neutral) to the weighed sample and dissolve it. Titrate the resulting solution with a 0.2 mol/l ethanolic hydrochloric acid solution (titer: f). The endpoint is the point where the color of the solution changes from green to yellow, and the amine value is determined using the following formula based on the titration volume (A mL) at this point.
(Formula) Amine value = (A × f × 0.2 × 56.108) / S

(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.

(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.

(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%.

(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-opening 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 mixture was further reacted 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)).

(Manufacturing Example 1) [Manufacturing of Printing Ink S1]
Printing ink S1 was obtained by mixing 19 parts of a 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.

(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.

The details of the raw materials in Table 1 are shown below.
• Acrylic resin solution: Acrylit 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, solid content 10%)
- Aluminum paste C (vapor-deposited aluminum: average particle size 13 μm, average thickness 52 nm, medium: n-propyl acetate, solid content 60%)
- Aluminum paste D (pulverized aluminum: average particle size 15 μm, average thickness 123 nm, medium: n-propyl acetate, solids content 60%)

<Production of 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 plate (fine) with a stylus angle of 140 degrees and a screen ruling of 250 lines/inch to obtain printed material G1.

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

(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.

(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 Corporation, 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.

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

<Adhesion to substrate>
A 12mm wide cellophane tape manufactured by Nichiban was applied to the ink coating of a printed material, 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.

<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: 1 dB or less B: Greater than 1 dB and 1.5 dB or less C: Greater than 1.5 dB The evaluations that are practically usable are A and B.

<Glossiness Value>
The gloss values of the printed materials prepared in the above examples and comparative examples were measured from the substrate side using a Canon RA-532H surface analyzer under conditions of an incident angle of 20 degrees and a receiving angle of 20 degrees, as well as under conditions of an incident angle of 60 degrees and a receiving angle of 60 degrees.
A: 400 or more B: 300 or more, less than 400 C: Less than 300 The evaluations for practical use are A and B.

<VOC emissions>
The evaluation inks were assessed in three stages based on the solid content of the diluted ink after dilution with a solvent (MEK) to achieve the viscosity required for gravure printing or spray painting (a higher solid content in the diluted ink is preferable as it reduces the amount of VOCs discharged during drying). The viscosity was 200 mPa·s for gravure printing and 30 mPa·s for spray painting.
A: 8% or more B: 5% or more, less than 8% C: Less than 5% The practically preferable evaluations are A and B.

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 (7)

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. 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. 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. 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°. A method for manufacturing a millimeter-wave transmitted printed material according to claim 1 or 2, wherein the gravure plate format is compressed, normal, elongated, coarse, or fine. A method for producing a millimeter-wave-transmitting printed material according to claim 1 or 2, wherein the plastic substrate is an acrylic substrate. 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.