JP2012071240A - Ink-jet coating method - Google Patents

Abstract

An inkjet coating method for forming an arbitrary image on a three-dimensional substrate having unevenness with an elevation difference of 5 mm or more is provided.
A distance from an object to be coated to an inkjet head is 80 mm or less, a head orifice size is 45 μm to 200 μm, and a pressure for ejecting ink is 0.005 to 0.5 MPa. And a solenoid valve type ink jet coating method, wherein the ink jet head is covered with an air curtain.
[Selection] Figure 1

Description

  The present invention relates to an ink-jet coating method for forming an image on a substrate, and can be arbitrarily applied to a car body surface such as an automobile, a bus, or a vehicle, a wall surface of a building, a three-dimensional object such as a home appliance, a mobile phone, etc. The present invention relates to an ink jet coating method for forming an image.

  In the conventional inkjet method, since the distance between the inkjet head and the object to be coated is about 5 mm at the longest, it is difficult to form an arbitrary image on a three-dimensional substrate having unevenness with a height difference of 5 mm or more. (For example, Patent Document 1).

JP 2010-168583 A

  An object of the present invention is to provide an inkjet coating method for forming an arbitrary image on a three-dimensional substrate having unevenness with a height difference of 5 mm or more.

  As a result of intensive studies to achieve the above object, the present inventors have found that the above problem can be solved by making the distance from the object to be coated to the inkjet head much larger than usual. The invention has been completed.

  According to the present invention, the distance from the object to be coated to the inkjet head is 80 mm or less, the size of the head orifice is 45 μm to 200 μm, and the pressure for ejecting ink is 0.005 to 0.5 MPa. A solenoid valve type inkjet coating method is provided.

  By the inkjet coating method of the present invention, an arbitrary image is formed on a body surface of a car, bus, vehicle or the like having unevenness with a height difference of 5 mm or more, a wall surface of a building, or a three-dimensional substrate such as a home appliance or a mobile phone. It became possible.

It is the schematic of the inkjet coating method which covers the circumference | surroundings of an inkjet head with an air curtain.

  In media such as paper, the printing surface is flat. In such a case, the distance from the inkjet head to the media is usually several millimeters, and the closer the ink is, the better the ink landing accuracy and the higher the image accuracy. . However, the object to be coated in the present invention is assumed to be a three-dimensional object having irregularities, and it is necessary to ensure a sufficient distance from the inkjet head to the object to be coated. As a result of intensive studies, high-definition printing has become possible by using the method of the present invention as long as it is 80 mm or less. When the distance exceeds 80 mm, the accuracy of the landing positions of the main particles is lowered, and the landing positions of the main particles and the satellite particles start to shift, resulting in a phenomenon that the image is disturbed.

  The orifice of the inkjet head has a correlation with the droplet size. If the size of the head orifice is less than 45 μm, the flight speed is stalled significantly due to the influence of air resistance, and the landing position accuracy is lowered. On the other hand, when the size of the head orifice exceeds 200 μm, the stall due to the air resistance is eliminated, but the droplet diameter after landing on the object to be coated becomes large and the image resolution is lowered.

  Solenoid valve inkjet uses gas pressure to discharge, but the pressure is 0.005 mPa to 0.5 mPa. If the pressure is less than 0.005 mPa, the force for pushing out ink is weak and stable discharge is impossible. . On the other hand, when the pressure exceeds 0.5 mPa, the movement of the solenoid becomes dull and the valve cannot be opened and closed properly, making it impossible to discharge, or even if it can be discharged, the length of the discharged ink is long and the difference in velocity between the main particles and satellite particles is large. It becomes large and the image is easily disturbed.

  The viscosity of the ink before ejection is desirably 2 mPa · S to 100 mPa · S. When the ink viscosity is less than 2 mPa · S, many satellite particles are generated, and when it exceeds 100 mPa · S, ejection may not be possible. In addition, the volatile components of the ink diffuse into the atmosphere and the viscosity of the ink increases during the flight until the ejected ink lands on the object to be coated, so that the sagging and bleeding properties of the ink after landing are suppressed. It is desirable that the viscosity after landing increases to 100% to 200% with respect to the viscosity before discharge. If it is higher than 200%, the ink is dried at the orifice of the inkjet head before discharging, and the possibility of clogging the orifice becomes high.

  Since the distance from the inkjet head to the object to be coated is several to several tens of times the usual, it is easily affected by the wind, and the landing position accuracy can be improved by covering the circumference of the inkjet head with an air curtain. In the case where the ink has a volatile component, drying of the ink landed on the object to be coated is promoted. FIG. 1 shows a schematic diagram of a structure in which the area around the inkjet head is covered with an air curtain. In the structure of FIG. 1, the inkjet head is covered with a double cylinder, and air is uniformly discharged from between the cylinders to form an air curtain. The air wind speed is preferably adjusted to be 1 m / s to 5 m / s.

  An image printed on a solid object, which is the object to be coated, with a straight line connecting both ends of the orifice of the ink-jet head being always horizontal so that the pressure distribution of the ink in the ink-jet head is always kept constant. Reproducibility can be improved.

As a pigment that can be used as a colorant, for example,
Pigment Yellow 12, 13, 14, 17, 20, 24, 31, 55, 74, 83, 86, 93, 109, 110, 117, 120, 125, 128, 129, 137, 138, 139, 147, 148, 150, 151, 153 (Nitron type nickel complex yellow), 154, 155, 166, 168, 180, 181, 185,
Pigment Orange 16, 36, 38, 43, 51, 55, 59, 61, 64, 65, 71,
Pigment Red 9, 48, 49, 52, 53, 57, 97, 122 (Quinacridone Magenta), 123, 149, 168, 177, 180, 192, 202, 206, 215, 216, 217, 220, 223, 224, 226, 227, 228, 238, 240, 244, 254,
Pigment violet 19 (quinacridone violet), 23, 29, 30, 32, 37, 40, 50,
Pigment blue 15 (phthalocyanine blue), 15: 1, 15: 3, 15: 4, 15: 6, 22, 30, 64, 80,
Pigment green 7 (chlorinated phthalocyanine green), 36 (brominated phthalocyanine green),
Pigment brown 23, 25, 26,
Pigment black 7 (carbon black), 26, 27, 28,
Examples thereof include titanium oxide, iron oxide, ultramarine, yellow lead, zinc sulfide, cobalt blue, barium sulfate, and calcium carbonate.

  When a pigment is used as the colorant, the volume average particle size is generally preferably 50 to 500 nm, and more preferably 80 to 300 nm.

Further, as a dye that can be used as a colorant, for example,
Diarylide Yellow,
Acid Yellow 13,
Solvent Yellow 13,
Acid Green 73,
Solvent Red 125,
Acid Green 73,
Solvent Red 25,
Acid Yellow 166,
Acid Blue 260,
Acid Blue 229,
Acid Black 52
Etc.

  Although the compounding quantity of a coloring agent changes with kinds etc. of coloring agent to be used, generally it is used in the quantity which occupies 0.5-40 mass%. When a pigment is used as the colorant, it is necessary to add it to such an extent that the nozzles of the printer head are not clogged.

  In order to ensure adhesion to the substrate, a binder resin can be contained. Examples of the binder resin include alkyd melamine resin, acrylic melamine resin, epoxy resin, phenol resin, novolak resin, rosin modified phenol resin, amino resin such as melamine, benzoguanamine, polyamide resin, UV curable resin, and urethane resin as the type to be crosslinked. Cellulose ester resins such as cellulose diacetate, cellulose triacetate, nitrocellulose, cellulose nitrate, cellulose propionate, cellulose acetate butyrate, methyl cellulose, ethyl cellulose, benzyl cellulose, trityl cellulose, cyanethyl cellulose, carboxy Cellulose ether resins such as methylcellulose, carboxyethylcellulose, aminoethylcellulose, Riesuteru resin, acrylic resin or the like.

  These resins can be used alone or in combination of two or more. The type of binder resin is not particularly limited, but when a coating film is formed on the substrate in order to ensure adhesion to the substrate, it should contain the same type of binder resin as the main resin system. Is preferred. For example, when the main resin system of the coating film formed on the substrate is an acrylic resin, it is better to contain the acrylic resin in the binder resin. The blending amount of the same type of binder resin system as the main resin system of the coating film formed on the substrate is preferably 5 to 100% by mass of the total binder resin in the ink.

  The applied film thickness is preferably 1 to 20 μm, and more preferably 5 to 15 μm. If the film thickness is less than 1 μm, the problem of poor concealment tends to occur, and if it exceeds 20 μm, sagging tends to occur during application, which is not preferable.

As the polyester resin, either saturated polyester or unsaturated polyester resin can be used. The polyester resin is obtained by a condensation reaction between a polybasic acid and a polyhydric alcohol. As the polybasic acid, for example,
Aromatic dicarboxylic acids such as phthalic acid, isophthalic acid, terephthalic acid, 1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 9,10-anthracenedicarboxylic acid, diphenic acid;
aromatic oxycarboxylic acids such as p-oxybenzoic acid and p- (hydroxyethoxy) benzoic acid;
Aliphatic dicarboxylic acids such as succinic acid, adipic acid, azelaic acid, sebacic acid, dodecanedicarboxylic acid;
Aliphatic unsaturated polycarboxylic acids such as fumaric acid, maleic acid, itaconic acid, mesaconic acid, cyclohexene dicarboxylic acid, dimer acid, trimer acid and tetramer acid;
Alicyclic dicarboxylic acids such as hexahydrophthalic acid and tetrahydrophthalic acid;
Examples thereof include polyvalent carboxylic acids such as trimellitic acid, trimesic acid and pyromellitic acid. A small amount of a monobasic acid may be used in combination with a polybasic acid. Examples of monobasic acids include benzoic acid, chlorobenzoic acid, bromobenzoic acid, parahydroxybenzoic acid, t-butylbenzoic acid, naphthalenecarboxylic acid, 3-methylbenzoic acid, 4-methylbenzoic acid, salicylic acid, and thiosalicylic acid. , Phenylacetic acid, naphthalenecarboxylic acid, anthracenecarboxylic acid, t-butylnaphthalenecarboxylic acid, cyclohexylaminocarbonylbenzoic acid, and the like.

Examples of polyhydric alcohols used in the production of polyester resins include:
Ethylene glycol, propylene glycol, 1,3-propanediol, 2,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, neopentyl glycol, diethylene glycol, dipropylene glycol Aliphatic diols such as 2,2,4-trimethyl-1,3-pentanediol, polyethylene glycol, polypropylene glycol, polytetramethylene glycol,
Aliphatic polyhydric alcohols such as triols and tetraols such as trimethylolethane, trimethylolpropane, glycerin and pentaerythritol;
Alicyclic polyhydric alcohols such as 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, spiroglycol, bisphenol A, hydrogenated bisphenol A, tricyclodecanediol, tricyclodecane dimethanol;
Aromatic polyhydric alcohols such as para-xylene glycol, meta-xylene glycol, ortho-xylene glycol and 1,4-phenylene glycol can be exemplified. A small amount of monohydric alcohol may be used in combination with the polyhydric alcohol.

  In the present invention, the number average molecular weight of the polyester resin is preferably in the range of 1000 to 50000, and more preferably in the range of 2000 to 20000. When the number average molecular weight of the polyester resin is less than 1000, the adhesion to the substrate is deteriorated. When the number average molecular weight is more than 50000, the ink stringing phenomenon tends to occur, and the ink discharge performance is not stable. Since it may occur, it is not preferable.

As the acrylic resin, those obtained by copolymerizing a commonly used radical polymerizable monomer can be used. As a radical polymerizable monomer, for example,
Acrylic esters such as methyl acrylate, ethyl acrylate, isopropyl acrylate, n-butyl acrylate, 2-ethylhexyl acrylate;
Methacrylic acid esters such as methyl methacrylate, ethyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, t-butyl methacrylate, cyclohexyl methacrylate, 2-ethylhexyl methacrylate;
Aromatic vinyls such as styrene, vinyltoluene, α-methylstyrene;
Vinyl esters such as vinyl acetate and vinyl propionate;
Heterocyclic vinyl compounds such as vinylpyrrolidone;
Vinyl halides such as vinyl chloride, vinylidene chloride and vinylidene fluoride;
Vinyl ethers such as ethyl vinyl ether and isobutyl vinyl ether;
Examples include α-olefins such as ethylene and propylene.

Moreover, the polymerizable monomer containing functional groups, such as an acid and a base, can also be used. As a functional group-containing monomer, for example,
Carboxyl group-containing monomers such as acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid, mono n-butyl maleate, mono n-butyl fumarate, mono n-butyl itaconic acid, crotonic acid;
(Meth) acrylic acid 2-hydroxyethyl, (meth) acrylic acid 2-hydroxypropyl, (meth) acrylic acid 3-hydroxypropyl, (meth) acrylic acid 4-hydroxybutyl, acrylic acid (2-hydroxymethyl) ethyl, (2-hydroxymethyl) butyl acrylate, (4-hydroxymethylcyclohexyl) methyl (meth) acrylate, glycerol mono (meth) acrylate, 2- (meth) acryloyloxyethyl 2-hydroxypropyl phthalate, 2-hydroxy-3 -Hydroxyl group-containing (meth) acrylic acid esters such as phenoxypropyl (meth) acrylate;
Amide group-containing monomers such as acrylamide, methacrylamide, maleic acid amide, diacetone acrylamide;
Glycidyl group-containing monomers such as glycidyl methacrylate and allyl glycidyl ether;
Cyano group-containing monomers such as acrylonitrile and methacrylonitrile;
Dienes such as butadiene and isoprene;
Hydroxyl-containing allyl compounds such as allyl alcohol and 2-hydroxyethyl allyl ether;
Tertiary amino group-containing monomers such as dimethylaminoethyl methacrylate and diethylaminoethyl methacrylate;
Vinyltrimethoxysilane, vinyltriethoxysilane, vinyltriisopropoxysilane, vinyltris (β-methoxyethoxy) silane, vinylmethyldimethoxysilane, vinylmethyldiethoxysilane, vinyldimethylmethoxysilane, vinyldimethylethoxysilane, 3-methacryloxy Examples thereof include alkoxysilyl group-containing monomers such as propyltrimethoxysilane, 3-methacryloxypropyltriethoxysilane, 3-methacryloxypropylmethyldimethoxysilane, and 3-methacryloxypropylmethyldiethoxysilane. In addition, monomers having two or more unsaturated bonds in one molecule such as diallyl phthalate, divinylbenzene, allyl acrylate, and trimethylolpropane trimethacrylate can be used. These monomers may be used alone or in combination of two or more.

  Various vinyl chloride resins can be used, and examples thereof include copolymer resins of vinyl chloride and other monomers such as vinyl acetate, vinylidene chloride, acrylic, and maleic acid. A preferred vinyl chloride resin is a vinyl chloride / vinyl acetate copolymer resin obtained by copolymerizing vinyl chloride and vinyl acetate, and particularly preferred is a copolymer resin having a molecular weight of 30,000 or less.

  As the resin other than the above, any resin used in a normal ink composition can be used. For example, alkyd melamine resin, acrylic melamine resin, epoxy resin, phenol resin, novolac resin, rosin modified phenol resin, amino resin such as melamine, benzoguanamine, polyamide resin, UV curable resin, urethane resin, cellulose diacetate, cellulose triacetate, nitro Examples include cellulose ester resins such as cellulose, cellulose nitrate, cellulose propionate, and cellulose acetate butyrate, cellulose ether resins such as methyl cellulose, ethyl cellulose, benzyl cellulose, trityl cellulose, cyanethyl cellulose, carboxymethyl cellulose, carboxyethyl cellulose, and aminoethyl cellulose. Can do. These resins can be used alone or in combination with other resins.

  The compounding amount of the resin used in the colored ink composition is preferably 1 to 20% by mass, and more preferably 2 to 10% by mass. If the amount of the resin is less than 1% by mass, the adhesion to the undercoat paint film may be insufficient, and if it is more than 20% by mass, the viscosity of the ink composition becomes high and the ejection property becomes unstable. Inconvenience such as may occur, which is not preferable.

  The colored ink composition used in the present invention desirably uses a pigment dispersant in order to improve the dispersibility of the pigment. As pigment dispersant, polyamide resin, hydroxyl group-containing carboxylic acid ester, salt of long chain polyaminoamide and high molecular weight acid ester, salt of high molecular weight polycarboxylic acid, salt of long chain polyaminoamide and polar acid ester, high molecular weight unsaturated Acid ester, modified polyurethane, modified polyacrylate, polyether ester type anionic activator, naphthalene sulfonic acid formalin condensate salt, aromatic sulfonic acid formalin condensate salt, polyoxyethylene alkyl phosphate ester, polyoxyethylene nonyl phenyl ether Stearylamine acetate and the like can be used. Among these dispersants, it is preferable to use a polyester polyamide resin having two or more amide groups in one molecule and having a number average molecular weight of 700 to 15000. The blending amount of the pigment dispersant varies depending on the type of pigment used and the like, but is usually preferably 0.1 to 15% by mass, more preferably 0.5 to 10% by mass of the ink composition. It is preferable because the pigment dispersibility is further improved.

  The polyester polyamide resin is produced by reacting an acid-terminated polyester resin with a polyamine compound having two or more amino groups in one molecule. Examples of the polyester polyamide resin include Solsperse 32000, Solsperse 32500, Solsperse 32600, Solsperse 33500, Solsperse 34750, Solsperse 35100, Solsperse 37500, etc. manufactured by Lubrizol, BYK9077 manufactured by BYK Chemie.

  In addition, when the number of amide groups of the polyester polyamide resin is less than 2 in one molecule, the pigment dispersibility is lowered, which is not preferable. Further, when the number average molecular weight is less than 700, the pigment dispersibility is lowered, and when the number average molecular weight exceeds 15,000, the dispersibility in the ink is lowered, which is not preferable.

The colored ink composition used in the present invention uses an organic solvent used in ordinary solvent-based inks. As an organic solvent, for example,
Alcohols such as methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, tridecyl alcohol, cyclohexyl alcohol, 2-methylcyclohexyl alcohol;
Glycols such as ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, glycerin;
Ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, ethylene glycol diethyl ether, ethylene glycol dimethyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, diethylene glycol ethyl methyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, Diethylene glycol dibutyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monobutyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, Lopylene glycol dimethyl ether, dipropylene glycol dimethyl ether, propylene glycol diethyl ether, dipropylene glycol diethyl ether, ethylene glycol monomethyl acetate, ethylene glycol monoethyl acetate, ethylene glycol monobutyl acetate, diethylene glycol monomethyl acetate, ethylene glycol monomethyl ether acetate, ethylene glycol mono Ethyl ether acetate, ethylene glycol monobutyl ether acetate, propylene glycol monomethyl ether acetate, propylene glycol monoethyl ether acetate, diethylene glycol monoethyl acetate, diethylene glycol monobutyl acetate, triethylene glycol Glycol ethers such as monomethyl ether;
Esters such as ethyl acetate, isopropylene acetate, n-butyl acetate, methyl lactate, ethyl lactate, butyl lactate;
Ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, isophorone, diacetone alcohol;
Nitrogen-containing compounds such as N-methyl-2-pyrrolidone and N-ethyl-2-pyrrolidone;
Toluene, xylene, acetonitrile, γ-butyrolactone, γ-valerolactone,
Etc. With respect to these organic solvents, various solvents are selected from the viewpoints of compatibility with the characteristics of the head nozzle during printing, safety, and drying properties, and a plurality of solvents can be mixed and used as necessary.

  The inkjet ink composition used in the present invention preferably contains glycol ethers as the organic solvent. Among them, diethylene glycol monomethyl ether, diethylene glycol monobutyl ether, diethylene glycol dimethyl ether, diethylene glycol ethyl methyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, dipropylene glycol monomethyl ether, dipropylene glycol dimethyl ether, propylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, Ethylene glycol monobutyl ether acetate, diethylene glycol monoethyl ether acetate, and diethylene glycol monobutyl ether acetate are particularly preferred because they are excellent in re-dissolvability of ink at the printer head portion.

  The colored ink composition used in the present invention may contain additives such as a surface conditioner, a light stabilizer, an antioxidant, a plasticizer, and a rust inhibitor.

  A conventionally known solenoid valve type printer head can be used as a printer head for applying colored ink by an inkjet method used for forming an image, and examples thereof include P16 series manufactured by Printos.

  As for the image forming method, an image is formed by applying a colored ink, and after the image is formed, it is forced to dry at 60 to 200 ° C., for example, depending on the type of binder resin in the colored ink.

  In the present invention, after the image forming step, it is preferable to further include a step of forming a clear coat on the image in consideration of prevention of color fading and weather resistance. In this case, after the image is formed, it varies depending on the type of the binder resin in the colored ink, but for example, a method of forced drying at 60 to 200 ° C., then applying a clear paint and drying at room temperature to 200 ° C. is adopted. Alternatively, after forming an image, a clear paint may be applied after an interval of 1 to 60 minutes and forcedly dried.

  The topcoat clear paint that can be used in the present invention is a clear paint that has been generally used. However, an acrylic copolymer, a hindered amine group-containing acrylic copolymer, a hydrolyzable silyl group-containing acrylic copolymer, In order to obtain a high degree of weather resistance, it is necessary to use a clear clear coating containing at least one selected from the group consisting of a fluorine copolymer, a hydrolyzable silyl group-containing fluorine-containing copolymer, and an alkoxysilane condensate as a binder. preferable.

  In addition, the top clear paint that can be used in the present invention is a matte agent, extender pigment, colored pigment or colored mica, urethane-based, acrylic-based colored beads, urethane-based, acrylic-based transparent, etc. as long as transparency is not lost. Various pigments such as beads, flaky graphite, flaky iron oxide, plated glass flakes, and aluminum foil color clear coated and cut products can be contained.

  Furthermore, the top coat clear paint that can be used in the present invention can be used by appropriately mixing various additives and modifiers as necessary. Examples of various additives and modifiers include dispersants, suspending agents, surface modifiers, ultraviolet absorbers, light stabilizers, moisture scavengers, conductivity modifiers, and surfactants. These components can be used in the range of 0.1 to 10 parts by mass with respect to 100 parts by mass of the solid content of the binder.

  This overcoat clear coating can be suitably applied using a known coating method such as conventional air spray, airless spray, electrostatic coating, roll coater, flow coater and the like. In addition, this clear top coating can be applied repeatedly even when the coating film of the colored ink is in an undried state or in a dry state.

  Furthermore, in order to improve the clearness of the clear top coat, etc., so-called double clear, in which clear coating is further performed after clear coating, may be performed. Moreover, the drying conditions of this overcoat clear are 3 minutes-24 hours in the temperature range of normal temperature-200 degreeC.

  Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples.

  Colored inks 1 to 3 were prepared by kneading the mixtures containing the blending amounts shown in Table 1 with a pigment disperser.

Magenta pigment: Fastgen Super Magenta RG manufactured by DIC Corporation
Polyester resin: made by Mitsui Chemicals, Almatex P645
Acrylic resin: DIC Corporation, ACRYDIC A-430-60
Melamine resin: Mitsui Chemicals, Uban 125
UV resin: Nippon Synthetic Chemical Co., Ltd., UV-7605B
Initiator: Irgacure 379, manufactured by Ciba Specialty Chemicals
Organic Solvent A: Cyclohexanone Organic Solvent B: Ethylene Glycol Monobutyl Ether Acetate Organic Solvent C: Exbes Mobil Corp., Solvesso 150
Organic solvent D: Butyl acetate Organic solvent E: Isobornyl acrylate Each ink was filtered through a 500 mesh stainless steel filter.

(Examples 1-26 and Comparative Examples 1-3)
An alkyd melamine-based paint (Dainippon Paint Co., Ltd .: Delicon 100) is applied onto a steel sheet provided with an electrodeposition coating, dried at 150 ° C. for 30 minutes, and then an acrylic melamine-based paint (Dainippon Paint Co., Ltd .: Acrose). # 9900) was applied and dried at 150 ° C. for 30 minutes to produce a flat substrate.

  In addition, an acrylic melamine-based paint (Dainippon Paint Co., Ltd .: Acrose # 9900) is applied on a corrugated board conforming to JIS G3316 corrugated board No. 1 and dried at 150 ° C. for 30 minutes to form a corrugated board having irregularities of 18 mm. Produced.

  In Examples 1 to 26 and Comparative Examples 1 to 3, a solenoid valve type inkjet head (manufactured by Printos; P16) was controlled using HPB-PR-M8 manufactured by Global inkjet Systems, and inks 1 to 1 obtained above were used. 3 was discharged. Further, a solenoid valve type ink jet head was attached to a robot arm (manufactured by Rivast Co., Ltd .: RCS5000), and printing was performed on a substrate so that a straight line connecting both ends of the orifice of the ink jet head was always horizontal.

  The results are shown in Tables 2-4.

  The viscosity was measured at 25 ° C. using a rheometer (manufactured by Anton Paar; Physia MCR301).

  The method for measuring the rate of change in viscosity due to the flight of ink is to place the mouth of the 9 ml sample tube at a predetermined distance from the ejection nozzle of the head, and from one nozzle until the ink is stored in about 2 ml in the sample tube. After discharging, the viscosity of the obtained ink was measured and compared with the viscosity before discharging.

  A compressor (manufactured by Anest Iwata; SLP-07ED) was used and a regulator was installed in the piping to adjust the pressure to a predetermined value.

  In order to promote the formation of a coating film on the ink, after the ink has landed on the substrate, UV irradiation with a UV lamp (USHIO Inc .; SP9-250UB) or a halogen lamp (Mitsubishi Electric OSRAM Co .; JD110V60W / SP / K5E) The light amount was adjusted using a slidac (manufactured by Tokyo Riko Co., Ltd .: RSA-2), and the light was irradiated.

  As shown in FIG. 1, the inkjet head was covered with double cylinders, air was uniformly discharged from between the cylinders, and the wind speed was adjusted to 1 m / s to 5 m / s. The wind speed was measured using YK-2005AH (Sato Corporation).

<Impact accuracy>
The ink was ejected, and the evaluation was made based on the difference in landing position between the main particles and the satellite particles.
A: The difference between the central part of the main particle and the central part of the satellite particle is less than 0.5 mm.
A: The difference between the central part of the main particle and the central part of the satellite particle is 0.5 mm to 1.0 mm.
X: The difference between the central part of the main particle and the central part of the satellite particle exceeds 1.0 mm.

<Sag evaluation>
The ink dripping property was visually observed.
A: The solid print surface is uniform and does not sag at all.
○: There is a slight rise at the edge of the solid print surface.
X: There is a streak-like sag from the edge of the solid print surface.

  As is apparent from Tables 2 to 4, an image having good landing accuracy and good sagging property was obtained by the present invention.

  The substrate on which image formation is performed in the present invention is not particularly limited, and examples thereof include passenger cars, trucks, buses, trains and other vehicle bodies, building walls, home appliances, mobile phones, and the like. In addition, it can be used by printing regardless of the vertical plane.

Claims (4)

  Solenoid valve type characterized in that the distance from the coated object to the inkjet head is 80 mm or less, the size of the head orifice is 45 μm to 200 μm, and the pressure for ejecting ink is 0.005 to 0.5 MPa. Inkjet painting method.   2. The inkjet ink according to claim 1, wherein the viscosity before discharge is 2 mPa · S to 100 mPa · S, and the viscosity is 100% to 200% before discharge in flight until the discharged ink lands on the object. The solenoid valve type inkjet coating method described.   The solenoid valve type inkjet coating method according to claim 1 or 2, wherein the periphery of the inkjet head is covered with an air curtain.   The solenoid valve type inkjet coating method according to claim 1, wherein a straight line connecting both ends of the orifice of the inkjet head is always horizontal.

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