Inkjet recording method and packaging method for a packaged body

Abstract

The present invention provides an inkjet recording method and a packaging method for a packaged body, in which when the recording object is heated and shrunk, the color difference of the shrunk image is not obvious. The inkjet recording method includes: an ejection step of ejecting a radiation-curable inkjet composition and attaching it to a recording medium that shrinks by heating; and a curing step of irradiating the radiation-curable inkjet composition attached to the recording medium with radiation to cure the radiation-curable inkjet composition. When the recording object shrinks by heating and is closely attached to the packaged body, it has a first region and a second region with different shrinkage rates in the main surface direction, and the shrinkage rate of the first region in the main surface direction is larger than that of the second region in the main surface direction. The radiation-curable inkjet composition is attached in such a way that the film thickness of the cured film formed in the first region is smaller than the film thickness of the cured film formed in the second region.

Description

Technical Field

[0001] The present invention relates to an inkjet recording method and a method for packaging a packaged body. Background Art

[0002] An inkjet recording method can record high-definition images using a relatively simple device and has achieved rapid development in various aspects. For example, Patent Document 1 describes an inkjet printer that ejects a UV ink that is cured by irradiating ultraviolet rays onto a resin substrate or a shrink film that shrinks upon heating as a recording medium, and records by irradiating ultraviolet rays onto the recording medium. Since the shrink film shrinks upon heating, it can be made to conform to the outer shape of a packaged body such as a container. By recording an image or the like on the shrink film and heating the recorded object to shrink it, it can be widely used for purposes such as packaging of goods.

[0003] Patent Document 1: International Publication No. 2003 / 57488

[0004] However, when the packaged body such as a container has irregularities, the outer dimensions of the packaged body may sometimes be irregular. In such a case, the shrinkage rate of the shrink film may vary depending on the position on the film. On the other hand, when the shrink film shrinks, the image formed on the shrink film also shrinks as the shrink film shrinks. Therefore, in the case where it is desired to exhibit the same color and form an ink coating film of the same film thickness, there is a problem that the color of the image formed in the portion of the shrink film having a large shrinkage rate is darker than the color of the image formed in the portion having a small shrinkage rate. That is, there is a need for an inkjet recording method that takes into account the shrinkage rate of the shrink film and makes the color difference of the shrunk image less noticeable. Summary of the Invention

[0005] The inkjet recording method includes: an ejection step of ejecting a radiation-curable inkjet composition containing a coloring material and a polymerizable compound so as to adhere it to a recording medium that shrinks upon heating; and a curing step of irradiating the radiation-curable inkjet composition adhered to the recording medium with radiation to cure the radiation-curable inkjet composition to obtain a recorded object, the recorded object having a first region and a second region in which the shrinkage rate in the main surface direction caused by the heating is different when the recording medium shrinks upon heating and conforms to the packaged body, the shrinkage rate of the first region in the main surface direction being larger than the shrinkage rate of the second region in the main surface direction, and in the ejection step, the radiation-curable inkjet composition is adhered in such a manner that the film thickness of the cured film formed in the first region is smaller than the film thickness of the cured film formed in the second region.

[0006] The packaging method of the object to be packaged includes: a step of disposing the recording object obtained by the above-described inkjet recording method around the object to be packaged; and a step of heating the recording object to shrink the recording object. Detailed Embodiment

[0007] 1. Radiation-curable inkjet composition

[0008] Before describing the inkjet recording method of the present embodiment, the radiation-curable inkjet composition used in the inkjet recording method will be described.

[0009] The radiation-curable inkjet composition refers to an inkjet composition that is cured by irradiating radiation. In addition, in the following description, the radiation-curable inkjet composition may sometimes be simply referred to as "ink composition". Examples of the radiation include ultraviolet rays, electron rays, infrared rays, visible light, X-rays, etc. Among them, as the radiation, from the aspects that the radiation source is easily obtained and widely used, and the materials suitable for curing based on ultraviolet irradiation are easily obtained and widely used, ultraviolet rays are preferred.

[0010] The ink composition contains a colorant and a polymerizable compound.

[0011] 1.1. Colorant

[0012] The ink composition contains a colorant. The colorant contained in the ink composition is not particularly limited, and a non-white colorant is preferred. The non-white colorant refers to a colorant other than white, including a colored colorant or a black colorant. As the non-white colorant, at least one of a pigment and a dye can be used.

[0013] By using a pigment as the colorant, the light resistance of the ink composition can be improved. As the pigment, any of an inorganic pigment and an organic pigment can be used.

[0014] As the inorganic pigment, carbon blacks such as furnace black, lamp black, acetylene black, channel black (C.I. (Colour Index Generic Name) Pigment Black 7), iron oxide, etc. can be used.

[0015] As the organic pigment, azo pigments such as insoluble azo pigments, condensed azo pigments, azo lakes, chelate azo pigments, phthalocyanine pigments, perylene and violanthrone pigments, anthraquinone pigments, quinacridone pigments, dioxane pigments, thioindigo pigments, isoindolinone pigments, quinophthalone pigments, etc., polycyclic pigments, dye chelates (for example, basic dye type chelates, acid dye type chelates, etc.), dyed lakes (basic dye type lakes, acid dye type lakes), nitro pigments, nitroso pigments, aniline black, daylight fluorescent pigments, etc. can be cited.

[0016] Examples of pigments for yellow ink include C.I. Pigment Yellow 1, 2, 3, 4, 5, 6, 7, 10, 11, 12, 13, 14, 16, 17, 24, 34, 35, 37, 53, 55, 65, 73, 74, 75, 81, 83, 93, 94, 95, 97, 98, 99, 108, 109, 110, 113, 114, 117, 120, 124, 128, 129, 133, 138, 139, 147, 151, 153, 154, 155, 167, 172, 180, etc.

[0017] Examples of pigments for magenta ink include C.I. Pigment Red 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 14, 15, 16, 17, 18, 19, 21, 22, 23, 30, 31, 32, 37, 38, 40, 41, 42, 48(Ca), 48(Mn), 57(Ca), 57:1, 88, 112, 114, 122, 123, 144, 146, 149, 150, 166, 168, 170, 171, 175, 176, 177, 178, 179, 184, 185, 187, 202, 209, 219, 224, 245 or C.I. Pigment Violet 19, 23, 32, 33, 36, 38, 43, 50, etc.

[0018] Examples of pigments for cyan ink include C.I. Pigment Blue 1, 2, 3, 15, 15:1, 15:2, 15:3, 15:34, 15:4, 16, 18, 22, 25, 60, 65, 66, C.I. Vat Blue 4, 60, etc.

[0019] In addition, examples of pigments other than magenta, cyan and yellow include C.I. Pigment Green 7, 10, C.I. Pigment Brown 3, 5, 25, 26, C.I. Pigment Orange 1, 2, 5, 7, 13, 14, 15, 16, 24, 34, 36, 38, 40, 43, 63, etc.

[0020] Examples of pigments for black ink include No. 2300, No. 900, MCF88, No. 33, No. 40, No. 45, No. 52, MA7, MA8, MA100, No. 2200B, etc. of Mitsubishi Chemical Corporation; Raven (registered trademark) 5750, Raven 5250, Raven 5000, Raven 3500, Raven 1255, Raven 700, etc. of Columbian Carbon Company; Regal 400R, Regal 330R, Regal660R; Mogul (registered trademark) L, Monarch (registered trademark) 700, Monarch800, Monarch 880, Monarch 900, Monarch 1000, Monarch 1100, Monarch 1300, Monarch1400, etc. of CABOT Corporation (Color Black FW1, Color Black FW2, Color Black FW2V, ColorBlack FW18, Color Black FW200, Color Black S150, Color Black S160, Color BlackS170, Printex 35, Printex U, Printex V, Printex 140U, Special Black 6, SpecialBlack 5, Special Black4A, Special Black 4, etc. of Degussa Corporation).

[0021] The pigment can be used in the form of a pigment dispersion, and a dispersant can be used as needed. The dispersant is not particularly limited, and examples thereof include dispersants commonly used in the preparation of pigment dispersions such as polymer dispersants. Specific examples thereof include dispersants mainly composed of one or more of polyoxyalkylene polyalkylenepolyamines, vinyl-based polymers and copolymers, acrylic-based polymers and copolymers, polyesters, polyamides, polyimides, polyurethanes, amino-based polymers, silicon-containing polymers, sulfur-containing polymers, fluorine-containing polymers, and epoxy resins. The dispersant can be used alone or in combination of two or more.

[0022] Examples of commercially available polymer dispersants include the AJISPER (registered trademark) series of Ajinomoto Fine-Techno Co., Inc.; the Solsperse series (Solsperse (registered trademark) 36000, etc.) of Lubrizol Corporation; the DISPERBYK series of BYK Additives & Instruments GmbH; the DISPARLON (registered trademark) series of Kusumoto Chemicals, Ltd.

[0023] The content of the dispersant is preferably 0.1% by mass to 2.0% by mass, more preferably 0.1% by mass to 1.0% by mass, and still more preferably 0.1% by mass to 0.5% by mass, relative to the total mass of the ink.

[0024] In the case where a dye is used as the colorant, there is no particular limitation on the dye, and acid dyes, direct dyes, reactive dyes, basic dyes, etc. can be used. Examples of the dye include C.I. Acid Yellow 17, 23, 42, 44, 79, 142, C.I. Acid Red 52, 80, 82, 249, 254, 289, C.I. Acid Blue 9, 45, 249, C.I. Acid Black 1, 2, 24, 94, C.I. Food Black 1, 2, C.I. Direct Yellow 1, 12, 24, 33, 50, 55, 58, 86, 132, 142, 144, 173, C.I. Direct Red 1, 4, 9, 80, 81, 225, 227, C.I. Direct Blue 1, 2, 15, 71, 86, 87, 98, 165, 199, 202, C.I. Direct Black 19, 38, 51, 71, 154, 168, 171, 195, C.I. Reactive Red 14, 32, 55, 79, 249, C.I. Reactive Black 3, 4, 35, etc.

[0025] The above dyes can be used alone or in combination of two or more.

[0026] A white pigment can also be used as the colorant. There is no particular limitation on the white pigment for the ink composition, and examples thereof include white inorganic pigments such as titanium oxide, zinc oxide, zinc sulfide, antimony oxide, magnesium oxide, and zirconium oxide. In addition to white inorganic pigments, white organic pigments such as white hollow resin particles and polymer particles can also be used.

[0027] The content of the colorant in the ink composition is preferably 0.2% by mass to 20.0% by mass, more preferably 0.5% by mass to 15.0% by mass, and still more preferably 1.0% by mass to 10.0% by mass, relative to the total mass of the ink composition.

[0028] 1.2. Polymerizable compound

[0029] The ink composition contains a polymerizable compound. Preferably, the ink composition contains a monofunctional monomer as the polymerizable compound.

[0030] 1.2.1. Monofunctional monomer

[0031] Relative to the total mass of the polymerizable compounds contained in the ink composition, the monofunctional monomer is preferably 35% by mass or more and 90% by mass or less, more preferably 40% by mass or more and 85% by mass or less, and still more preferably 50% by mass or more and 80% by mass or less.

[0032] By making the content of the monofunctional monomer within the above range, a soft cured film can be obtained, and the adhesion of the cured film to the recording medium can be increased. As a result, when the recorded object is heated and shrinks, the cured film is less likely to crack. In addition, when the recorded object is heated and shrinks and the recording surface of the recorded object is adhered to the package, adhesion between the cured film and the package can be suppressed.

[0033] The monofunctional monomer is not particularly limited, and examples thereof include monofunctional monomers having an alicyclic group, monofunctional monomers having an aromatic group, monofunctional monomers having a nitrogen-containing heterocycle, and the like. As the monofunctional monomer, monofunctional monomers other than the above may also be used.

[0034] 1.2.1.1. Monofunctional monomers having an alicyclic group

[0035] The monofunctional monomer having an alicyclic group is not particularly limited, and examples thereof include (meth)acrylates containing an alicyclic group such as dicyclopentenyl (meth)acrylate, dicyclopentenyl oxyethyl (meth)acrylate, dicyclopentyl (meth)acrylate, 3,3,5-trimethylcyclohexyl (meth)acrylate, isobornyl (meth)acrylate, tert-butylcyclohexanol (meth)acrylate, and 2-(meth)acrylic acid-1,4-dioxaspiro[4,5]dec-2-ylmethyl ester.

[0036] Among them, dicyclopentene (meth)acrylate (DCPA) and isobornyl acrylate (IBXA) are preferred.

[0037] 1.2.1.2. Monofunctional monomers having an aromatic group

[0038] The monofunctional monomer having an aromatic group is not particularly limited, and examples thereof include phenoxyethyl (meth)acrylate, benzyl (meth)acrylate, alkoxylated 2-phenoxyethyl (meth)acrylate, ethoxylated nonylphenol (meth)acrylate, alkoxylated nonylphenol (meth)acrylate, p-cumylphenol EO-modified (meth)acrylic acid, and 2-hydroxy-3-phenoxypropyl (meth)acrylate.

[0039] Among them, phenoxyethyl acrylate (PEA) is preferred. By using such a monofunctional monomer containing an aromatic group, the solubility of the photopolymerization initiator is further improved, and the curability of the ink composition is further improved. In addition, when an acylphosphine oxide-based photopolymerization initiator or a thioxanthone-based photopolymerization initiator is used, the solubility of the photopolymerization initiator becomes better.

[0040] 1.2.1.3. Nitrogen-containing monofunctional monomer

[0041] The nitrogen-containing monofunctional monomer is not particularly limited, and examples thereof include nitrogen-containing monofunctional vinyl monomers such as N-vinylcaprolactam, N-vinylformamide, N-vinylcarbazole, N-vinylacetamide, vinylmethyl oxazolidinone, and N-vinylpyrrolidone; nitrogen-containing monofunctional acrylate monomers such as acryloylmorpholine; and nitrogen-containing monofunctional acrylamide monomers such as (meth)acrylamide, N-hydroxymethyl(meth)acrylamide, diacetoneacrylamide, N,N-dimethyl(meth)acrylamide, and benzyl chloride quaternary salt of dimethylaminoethyl acrylate.

[0042] Among them, N-vinylcaprolactam, N-vinylcarbazole, N-vinylpyrrolidone, vinylmethyl oxazolidinone (VMOX), or acryloylmorpholine (ACMO) and other monomers having a nitrogen-containing heterocyclic structure are more preferred, and acryloylmorpholine is further preferably included.

[0043] 1.2.2. Polyfunctional monomer

[0044] The ink composition contains a polymerizable compound, and as the polymerizable compound, a polyfunctional monomer may be included. The polyfunctional monomer is not particularly limited, and examples thereof include vinyl-containing (meth)acrylates and polyfunctional (meth)acrylates.

[0045] 1.2.2.1. Vinyl-containing (meth)acrylate

[0046] The vinyl-containing (meth)acrylate is not particularly limited, and examples thereof include the compound represented by the formula (1).

[0047] H2C=CR 1 -CO-OR 2 -O-CH=CH-R 3 …(1)

[0048] (In the formula, R 1 is a hydrogen atom or a methyl group, R 2 is a divalent organic residue having 2 to 20 carbon atoms, and R 3 is a hydrogen atom or a monovalent organic residue having 1 to 11 carbon atoms)

[0049] In the above formula (1), as the divalent organic residue having 2 to 20 carbon atoms represented by R 2 there may be mentioned a linear, branched or cyclic alkylene group having 2 to 20 carbon atoms which may be substituted, an alkylene group having 2 to 20 carbon atoms which may be substituted and has an oxygen atom based on an ether bond and / or an ester bond in the structure, and a divalent aromatic group having 6 to 11 carbon atoms which may be substituted.

[0050] Among them, preferred are alkylene groups having 2 to 6 carbon atoms such as ethylene, n-propylene, isopropyl and butylene, and alkylene groups having 2 to 9 carbon atoms which have an oxygen atom based on an ether bond in the structure such as oxyethylene, oxy-n-propylene, oxyisopropyl and oxybutylene. Further, from the viewpoint of making the ink have a lower viscosity and further improving the curability of the ink, R 2 is more preferably a compound having a glycol ether chain which is an alkylene group having 2 to 9 carbon atoms such as oxyethylene, oxy-n-propylene, oxyisopropyl and oxybutylene and has an oxygen atom based on an ether bond in the structure.

[0051] In the above formula (1), as the monovalent organic residue having 1 to 11 carbon atoms represented by R 3 there may be mentioned a linear, branched or cyclic alkyl group having 1 to 10 carbon atoms which may be substituted, and an aromatic group having 6 to 11 carbon atoms which may be substituted.

[0052] Among them, it is preferable to use an alkyl group having 1 to 2 carbon atoms such as methyl or ethyl, and an aromatic group having 6 to 8 carbon atoms such as phenyl and benzyl.

[0053] As a specific example of the compound of formula (1), there is no particular limitation, and for example, 2-(2-vinyloxyethoxy)ethyl (meth)acrylate can be mentioned, and preferably 2-(2-vinyloxyethoxy)ethyl acrylate (VEEA).

[0054] In particular, it is preferable that the ink composition contains a vinyl group-containing (meth)acrylate represented by the above formula (1) as a polyfunctional monomer. Thereby, the curability of the ink composition is further improved.

[0055] Relative to the total mass of the polymerizable compounds contained in the ink composition, the content of the vinyl group-containing (meth)acrylate is preferably 1% by mass to 25% by mass, more preferably 2% by mass to 20% by mass, and still more preferably 3% by mass to 15% by mass. By making the content of the vinyl group-containing (meth)acrylate within the above range, an increase in the viscosity of the ink composition can be suppressed, thereby providing an ink composition having excellent ejection stability.

[0056] 1.2.2.2 Polyfunctional (meth)acrylate

[0057] As the polyfunctional (meth)acrylate, there is no particular limitation, and examples thereof include bifunctional (meth)acrylates such as dipropylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, and triethylene glycol di(meth)acrylate; trifunctional or higher polyfunctional (meth)acrylates such as trimethylolpropane tri(meth)acrylate, EO-modified trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, and dipentaerythritol hexa(meth)acrylate, etc.

[0058] Relative to the total mass of the polymerizable compounds contained in the ink composition, the content of the polyfunctional (meth)acrylate is preferably 5% by mass to 35% by mass, more preferably 10% by mass to 30% by mass, and still more preferably 15% by mass to 25% by mass. By the content of the polyfunctional (meth)acrylate being within the above range, the curability and scratch resistance of the ink composition are further improved.

[0059] 1.3. Photoinitiator

[0060] Preferably, the ink composition contains a photoinitiator. As the photoinitiator, there is no particular limitation as long as it generates active seeds by irradiation with radiation, and examples thereof include known photoinitiators such as acylphosphine oxide-based photoinitiators, alkylbenzophenone-based photoinitiators, titanocene-based photoinitiators, and thioxanthone-based photoinitiators. Among them, acylphosphine oxide-based photoinitiators are preferred. By using such a photoinitiator, the curability of the ink composition is further improved, especially the curability of the curing process realized by the light of UV-LED is further improved. The photoinitiator can be used alone or in combination of two or more.

[0061] As the acylphosphine oxide-based photoinitiator, there is no particular limitation, and examples thereof include 2,4,6-trimethylbenzoyl diphenylphosphine oxide, bis-(2,4,6-trimethylbenzoyl)-phenylphosphine oxide, and bis-(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide, etc.

[0062] As commercially available products of such acylphosphine oxide-based photoinitiators, examples include IRGACURE (registered trademark) 819 (bis-(2,4,6-trimethylbenzoyl)-phenylphosphine oxide), IRGACURE 1800 (a mixture of bis-(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide and 1-hydroxy-cyclohexyl-phenylketone with a mass ratio of 25:75), and IRGACURE TPO (2,4,6-trimethylbenzoyl diphenylphosphine oxide) of BASF Corporation, etc.

[0063] The content of the photopolymerization initiator is preferably 3.0% by mass to 15.0% by mass, more preferably 5.0% by mass to 13.5% by mass, and still more preferably 8.0% by mass to 12.0% by mass, relative to the total mass of the ink composition. By the content of the photopolymerization initiator being within the above range, the curability of the ink composition is further improved, and the solubility of the photopolymerization initiator is further improved.

[0064] 1.4. Polymerization inhibitor

[0065] The ink composition may contain a polymerization inhibitor. There is no particular limitation on the polymerization inhibitor, and examples thereof include p-methoxyphenol, hydroquinone monomethyl ether (MEHQ), 4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxide, hydroquinone, cresol, tert-butylcatechol, 3,5-di-tert-butyl-4-hydroxytoluene, 2,2'-methylenebis-(4-methyl-6-tert-butylphenol), 2,2'-methylenebis-(4-ethyl-6-butylphenol), 4,4'-thiobis-(3-methyl-6-tert-butylphenol), hindered amine compounds, and the like. The polymerization inhibitor may be used alone or in combination of two or more.

[0066] The content of the polymerization inhibitor is preferably 0.05% by mass to 1.00% by mass, more preferably 0.05% by mass to 0.50% by mass, relative to the total mass of the ink composition.

[0067] 1.5. Lubricant

[0068] The ink composition may contain a lubricant. The purpose of using the lubricant is to improve the scratch resistance of the cured film. As the lubricant, a silicone-based surfactant is preferred, and polyester-modified silicone or polyether-modified silicone is more preferred.

[0069] As the lubricant, commercially available products can be used, and examples thereof include polyester-modified silicones such as BYK (registered trademark)-347, 348, BYK-UV3500, 3510, 3530 of BYK Additive&Instruments Co., Ltd., and polyether-modified silicones such as BYK-3570. The lubricant may be used alone or in combination of two or more.

[0070] The content of the lubricant is preferably 0.01% by mass to 2.00% by mass, more preferably 0.05% by mass to 1.00% by mass, relative to the total mass of the ink composition.

[0071] 1.6. Other included components

[0072] In order to improve the storage stability of the ink composition, to maintain the ejection stability of the inkjet head well, to improve clogging, or to prevent the deterioration of the ink composition, dissolution aids, viscosity regulators, pH regulators, antioxidants, preservatives, fungicides, corrosion inhibitors, and non-organic solvent humectants, and various additives for the purpose of capturing metal ions that affect dispersion can be appropriately added.

[0073] 2. Ink Preparation Method

[0074] The ink composition can be manufactured by dispersing / mixing the above-mentioned components by an appropriate method. When a pigment is used as the coloring material, it is preferable to first mix a part of the polymeric compound composed of the pigment, dispersant, and solvent using an appropriate disperser to prepare a uniform pigment dispersion liquid. Then, the components contained in the other ink composition are added and sufficiently stirred to prepare an ink solution. After sufficient stirring, filtration is performed to remove coarse particles and foreign matters that cause clogging, whereby the target ink composition can be obtained.

[0075] 3. Inkjet Device

[0076] The inkjet device for the inkjet recording method used in this embodiment will be described. As the inkjet device, a known device such as an inkjet printer can be applied. Specifically, an on-rack or off-rack serial printer and a line printer can be cited.

[0077] The inkjet device has an inkjet head. The inkjet head ejects droplets of the ink composition and attaches them to a recording medium or the like. Therefore, the inkjet head has an actuator as a driving unit. As the actuator, a piezoelectric element that utilizes the deformation of a piezoelectric body, an electromechanical conversion element that utilizes the displacement of a diaphragm based on electrostatic adsorption, an electrothermal conversion element that utilizes bubbles generated by heating, etc. can be cited. In this embodiment, an inkjet device having an inkjet head equipped with a piezoelectric element is applied.

[0078] The inkjet device has a light source device that cures the ink composition attached to the recording medium. The light source device is a radiation irradiation device and includes a light-emitting element such as a UV-LED (ultraviolet light-emitting diode). The radiation emitted from the light source device is not limited to ultraviolet light, and can also be infrared light, electron rays, visible light, X-rays, etc. In addition, in the light source device, a lamp or the like can be used instead of a light-emitting element such as an LED (light-emitting diode) or an LD (semiconductor laser). Furthermore, the light source device is not limited to being provided in the inkjet device, and can also be provided separately from the inkjet device.

[0079] By irradiating droplets of an ink composition adhered to a recording medium with radiation from a light source device, a photopolymerization reaction of a polymerizable compound contained in the ink composition is caused, so that the droplets of the ink composition are cured to form a cured film of the ink composition.

[0080] 4. Recording Medium

[0081] The recording medium used in the present embodiment is a recording medium that shrinks by heating. Specifically, a plastic film subjected to a stretching process can be cited. That is, by subjecting the plastic film to a stretching process, it can be oriented in the stretching direction. When the oriented plastic film is heated, the stress based on the molecular orientation is relaxed, and it has the property of shrinking to the size before stretching.

[0082] Examples of the plastic film having such properties include polyolefin films such as polypropylene films and polyethylene films stretched in a uniaxial or biaxial direction, polyvinyl chloride films, polystyrene films, polyethylene terephthalate films, etc. Among them, polyolefin films and polyethylene terephthalate films are preferred. Polyolefin films and polyethylene terephthalate films can preferably be used as films for packaging objects to be packaged.

[0083] 5. Inkjet Recording Method

[0084] The inkjet recording method includes: an ejection step of ejecting an ink composition containing a coloring agent and a polymerizable compound and attaching it to a recording medium that shrinks by heating; and a curing step of irradiating the ink composition attached to the recording medium with radiation to cure the ink composition to obtain a recorded object. The recorded object has a first region and a second region in the main surface direction where the shrinkage rate caused by heating is different when it shrinks by heating and is brought into close contact with the object to be packaged. The shrinkage rate of the first region in the main surface direction is larger than the shrinkage rate of the second region in the main surface direction. Here, in the ejection step, the ink composition is attached in such a manner that the film thickness of the cured film formed in the first region is smaller than the film thickness of the cured film formed in the second region.

[0085] 5.1. Ejection Step

[0086] In the ejection step, the ink composition is ejected from the inkjet head of the inkjet device and attached to the recording medium. Specifically, a piezoelectric element is driven to eject the ink composition filled in the pressure generation chamber of the inkjet head from the nozzle.

[0087] At this time, the ink composition is attached in such a manner that the film thickness of the cured film formed in the first region in the cured film formed in the subsequent curing step is smaller than the film thickness of the cured film formed in the second region.

[0088] Here, the first region and the second region refer to regions on a recording obtained by irradiating a radiation to an ink composition adhered to a recording medium during a curing process. When the recording is heated and shrunk to be closely adhered to a package, the shrinkage rates of the recording in the main surface direction caused by heating are different, and the shrinkage rate of the first region in the main surface direction is larger than that of the second region in the main surface direction.

[0089] The film thickness of the cured film refers to the film thickness of the cured film in the recording when printing is performed at 100% of the ink dot generation amount. Specifically, the film thickness of the cured film can be measured as follows. That is, a recording is cut using a microtome or the like to prepare a sliced specimen or a cross-sectional specimen, and the film thickness is measured using a microscope. Alternatively, the film thickness is measured in a non-destructive manner using a laser microscope. The above-mentioned any operation is performed on five or more parts of the printing area with 100% of the ink dot generation amount in the recording, and the average value of the obtained values is used as the film thickness of the cured film.

[0090] In addition, as defined above, the film thickness of the cured film is the film thickness of the cured film in the recording when printing is performed at 100% of the ink dot generation amount. However, when the ink dot generation amount is less than 100% or the ink dot generation amount exceeds 100%, a value obtained by multiplying the film thickness of the cured film in the recording when printing is performed at 100% of the ink dot generation amount by the ink dot generation amount is used.

[0091] The reason is as follows. In order to represent an image with continuous gray levels, an inkjet recording method adopts an area gray level method. Therefore, in a region where the ink dot generation amount is less than 100%, when a certain region is observed, there are pixels to which droplets of the ink composition are adhered and pixels to which droplets of the ink composition are not adhered. In addition, in a region where the ink dot generation amount exceeds 100%, multiple droplets are adhered to one pixel.

[0092] Thus, in the inkjet recording method adopting the area gray level method, when the film thickness of the cured film is measured in pixel units, discrete values are obtained, and it is not suitable to use them as the film thickness of the cured film. It is appropriate to calculate the average value of the film thickness for a certain region and use it as the film thickness of the cured film.

[0093] When the film thickness of the cured film in the recording when printing is performed at 100% of the ink dot generation amount is known, the average value of the film thickness of a certain region can be obtained by multiplying the film thickness of the cured film in the recording when printing is performed at 100% of the ink dot generation amount by the ink dot generation amount of the region.

[0094] For example, when the film thickness of the cured film in the recording when printing is performed at 100% of the ink dot generation amount is 10.0 μm, the film thickness of the cured film in the region with an ink dot generation amount of 50% is 5.0 μm. Similarly, the film thickness of the cured film in the region with an ink dot generation rate of 25% is 2.5 μm.

[0095] 5.2. Curing Process

[0096] In the curing process, radiation is irradiated onto the ink composition attached to the recording medium to cure the ink composition. When radiation is irradiated, the polymerization reaction of the polymerizable compound contained in the ink composition starts, whereby the ink composition cures and forms a cured film. At this time, when a photopolymerization initiator is present in the ink composition, active seeds (initiating seeds) such as free radicals, acids, and bases are generated, and the polymerization reaction of the polymerizable compound is promoted by the function of the initiating seeds.

[0097] For the recording material produced by the above-described method for producing a recording material, when the recording material is heated and shrunk, the first region of the recording material shrinks more in the main surface direction than the second region and adheres to the object to be packaged. At this time, the cured film formed on the recording medium also shrinks as the recording medium shrinks, but the film thickness of the cured film formed in the first region is smaller than that of the cured film formed in the second region. Therefore, even when the shrinkage rate of the first region of the recording material in the main surface direction is larger than that of the second region in the main surface direction, it is possible to suppress the color of the image in the first region from being darker than the color of the image in the second region, thereby suppressing color unevenness from occurring on the shrunk image.

[0098] That is, when the recording material is heated and shrunk and the recording material is adhered to the object to be packaged, the following effects can be achieved: suppressing the color of the image in the first region from being darker than the color of the image in the second region, and suppressing color unevenness from occurring on the shrunk image.

[0099] Preferably, the film thickness of the cured film formed in the second region is two times or less that of the cured film formed in the first region. Thereby, after shrinkage, it is possible to reduce the deviation in the film thickness of the cured film between the first region and the second region. In addition, even when the shrinkage rate of the recording material in the main surface direction in the first region is larger than that of the second region in the main surface direction, it is possible to more effectively suppress the color of the image in the first region from being darker than the color of the image in the second region.

[0100] In addition, the maximum film thickness of the cured film is preferably 20 μm or less, and more preferably 10 μm or less. By making the film thickness of the cured film within the above range, when the recording material shrinks, it is possible to appropriately suppress the cured film from peeling off from the recording medium and wrinkles from occurring on the cured film.

[0101] Moreover, since the film thickness of the cured film is small, when the recording material is wound around a roller, it is possible to suppress the thickening of the roller during winding, thereby improving the storage efficiency of the roller.

[0102] Preferably, the colorant contains a non-white colorant. In the method for manufacturing a recording medium of the present invention, by forming the cured film of the first region to be smaller than the film thickness of the cured film of the second region, when the recording medium is heated and shrunk, even if the first region of the recording medium shrinks more in the main surface direction than the second region, color unevenness on the shrunk image can be suppressed. When the ink composition contains a non-white colorant as the colorant, compared with the case where no non-white colorant is contained, for example, the case where only a white colorant is contained as the colorant or the case where no colorant is contained at all, when the color of the image changes due to the shrinkage of the recording medium, the visual stimulus is greater. That is, in the case where a non-white colorant is contained as the colorant, the effect of the present invention of suppressing color unevenness of the image generated when the recording medium is shrunk can be more significantly exhibited.

[0103] 6. Packaging process of the object to be packaged

[0104] The packaging method of the object to be packaged includes: a process of disposing the recording medium obtained by the above inkjet recording method around the object to be packaged; and a process of heating the recording medium to shrink the recording medium.

[0105] Thus, when the recording medium is heated and shrunk, the first region of the recording medium shrinks more in the main surface direction than the second region, and the recording medium can be made to conform to the object to be packaged. At this time, the cured film formed on the recording medium also shrinks as the recording medium shrinks, but the cured film formed in the first region is formed to have a smaller film thickness than the cured film formed in the second region. Therefore, even when the shrinkage rate of the first region of the recording medium in the main surface direction is larger than the shrinkage rate of the second region in the main surface direction, it is possible to suppress the color of the image in the first region from being darker than the color of the image in the second region, and thus it is possible to suppress color unevenness on the shrunk image.

[0106] The method of disposing the recording medium around the object to be packaged is not particularly limited, and any method such as a method of processing the recording medium into a cylindrical shape and winding it around the object to be packaged, a method of temporarily fixing the recording medium to the object to be packaged with an adhesive or the like, a method of covering the object to be packaged with the recording medium, and a method of placing the recording medium on the object to be packaged can be adopted.

[0107] The method of heating the recording medium to shrink the recording medium is not particularly limited. Specifically, any method such as a method of putting the recording medium and the object to be packaged together into a thermostatic bath, a method of applying heated air to the recording medium, and a method of pressing a heated object such as a heater against the recording medium can be adopted. It is also possible to preheat the object to be packaged before heating the recording medium.

[0108] 7. Examples

[0109] Hereinafter, the present invention will be specifically described using examples and comparative examples. The present invention is not restricted by any of the following examples.

[0110] 7.1. Preparation of Ink Composition

[0111] Weigh a part of the colorant, dispersant, and each polymerizable compound and put them into a pot for pigment dispersion. By stirring together with ceramic beads with a diameter of 1 mm, a pigment dispersion liquid in which the colorant is dispersed in the polymerizable compound is obtained.

[0112] Next, according to the components described in Table 1, put the remaining polymerizable compound, photoinitiator, inhibitor, and lubricant into a mixing pot made of stainless steel, mix and stir them to completely dissolve, and then add the above-obtained pigment dispersion liquid and mix and stir at room temperature for 1 hour. Then, filter it using a 5-μm membrane filter to obtain Inks 1 to 5. In addition, the numerical values of each component shown in the table are in mass%.

[0113]

Table 1

[0114]

[0115] The materials described in Table 1 are as follows.

[0116] Colorant (Pigment)

[0117] · Pigment Blue 15:3 (PB15:3)

[0118] Dispersant

[0119] · Solsperse 36000 (Lubrizol Corporation, polymer dispersant)

[0120] Monofunctional Monomer

[0121] · IBXA (Osaka Organic Chemical Industry Co., Ltd., isobornyl acrylate)

[0122] · PEA (trade name “VISCOAT#192”, Osaka Organic Chemical Industry Co., Ltd., phenoxyethyl acrylate)

[0123] · ACMO (KJ Chemical Co., Ltd., acryloylmorpholine)

[0124] Polyfunctional Monomer

[0125] · VEEA (Nippon Catalyst Co., Ltd., 2-(2-vinyloxyethoxy)ethyl acrylate)

[0126] · DPGDA (Sartomer Company, dipropylene glycol diacrylate)

[0127] ·ADPH (Pentaerythritol hexaacrylate, Shin-Nakamura Chemical Co., Ltd., Pentaerythritol hexaacrylate)

[0128] Photoinitiator

[0129] ·819 (Trade name “IRGACURE 819”, BASF Corporation, Bis-(2,4,6-trimethylbenzoyl)-phenylphosphine oxide)

[0130] ·TPO (Trade name “IRGACURE TPO”, BASF Corporation, 2,4,6-Trimethylbenzoyldiphenylphosphine oxide)

[0131] ·DETX (Trade name “Speedcure DETX”, Lambson Limited, 2,4-Diethylthioxanthone-9-one)

[0132] Polymerization inhibitor

[0133] ·MEHQ (Trade name “p-Methoxyphenol”, Kanto Chemical Co., Inc., Hydroquinone monomethyl ether)

[0134] Lubricant

[0135] ·BYK-UV3500 (BYK Additives & Instruments GmbH, Polyether-modified silicone with acryloyl groups)

[0136] In Table 1, “the content of the monofunctional monomer relative to the total mass of the polymerizable compounds” represents the ratio (mass %) of the content of the monofunctional monomer relative to the total content of the polymerizable compounds.

[0137] 7.2. Evaluation method

[0138] 7.2.1. Preparation of the recording material

[0139] Using an inkjet printer “PX-G5000” (product name, manufactured by Seiko Epson Corporation), a sample for evaluating color unevenness was prepared. At normal temperature and pressure, a solid pattern image was printed on a PET film “Bonset” (product name, manufactured by TAKIRON Co., Ltd.) as the recording medium under the conditions of a recording resolution of 600 dpi × 600 dpi and a droplet weight of 20 ng, that is, printed with a dot generation amount of 100%, and a printed sample with a film thickness of 10 μm was obtained. In addition, the solid pattern image is an image formed by recording ink dots on all pixels of the pixels in the smallest recording unit area defined by the recording resolution. After performing the above printing, ultraviolet rays were irradiated from a UV-LED installed in an ultraviolet irradiation device beside the carriage, and a recording material with a cured film of the ink composition having a film thickness of 10 μm formed on the recording medium was obtained.

[0140] In addition to changing the amount of ink dots generated, recordings with different film thicknesses of the cured film formed on the recording medium were produced in the same manner as described above. Specifically, recordings with a cured film having a film thickness of 5 μm were produced by setting the amount of ink dots generated to 50%, and recordings with a cured film having a film thickness of 20 μm were produced by setting the amount of ink dots generated to 200%.

[0141] 7.2.2. Packaging of the object to be packaged

[0142] The recordings obtained as described above were wound with the cured film on the inside and processed into a cylindrical shape. This recording was placed around a container (glass bottle) serving as the object to be packaged that had been preheated in a thermostatic bath, and left to stand in the thermostatic bath at 90°C for 10 seconds, causing the recording to shrink and conform tightly to the container.

[0143] The shrinkage rate can be defined by the following formula (2). In this embodiment, two standards of 40% (first region) and 10% (second region) were set for the shrinkage rate. In addition, the shrinkage rate of the recording was adjusted by changing the length of the cylindrical recording in the circumferential direction with respect to the outer circumference of the container serving as the object to be packaged.

[0144] Shrinkage rate (%) = (Length before shrinkage - Length after shrinkage) / Length before shrinkage... (2)

[0145] 7.2.3. Evaluation of color unevenness

[0146] For the combinations of ink and film thickness of the cured film shown in Table 2, the OD values (Optical Density) after shrinkage were measured separately for the case where the recording was shrunk at a shrinkage rate of 40% (first region) and the case where the recording was shrunk at a shrinkage rate of 10% (second region), and the OD value difference was calculated according to the following formula (3). The OD value difference was evaluated according to the following evaluation criteria, and the results were recorded in Table 2.

[0147]

[0148] (where OD value L : The larger of the OD value after shrinkage in the first region or the OD value after shrinkage in the second region; OD value S : The smaller of the OD value after shrinkage in the first region or the OD value after shrinkage in the second region)

[0149] Evaluation criteria

[0150] A: The OD value difference is 5% or less.

[0151] B: The OD value difference exceeds 5% and is 10% or less.

[0152] C: The OD value difference exceeds 10% and is less than or equal to 20%.

[0153] D: The OD value difference exceeds 20%.

[0154] 7.2.4. Evaluation of wrinkles

[0155] In the packaging of the above-mentioned packaged body, the generation state of wrinkles after shrinkage was visually observed and evaluated according to the following evaluation criteria. The results are shown in Table 2.

[0156] Evaluation criteria

[0157] A: No wrinkles were found in the cured film.

[0158] B: Slight wrinkles were found in the cured film.

[0159] C: Large wrinkles were found in the cured film.

[0160] 7.2.5. Evaluation of adhesion

[0161] In the packaging of the above-mentioned packaged body, for the recording material that shrinks and conforms to the packaged body, it was visually observed whether there was a trace of the cured film transferred and pasted on the container to evaluate the presence or absence of pasting, and the judgment was made according to the following evaluation criteria.

[0162] Evaluation criteria

[0163] A: No cured film was found pasted on the container.

[0164] B: A small amount of cured film was found pasted on the container.

[0165] C: The cured film was found pasted on the container.

[0166]

Table 2

[0167]

[0168] 7.3. Evaluation results

[0169] The evaluation results are shown in Table 2. For Examples 1 to 6 in which a cured film with a smaller film thickness was formed in the first region with a shrinkage rate of 40% than in the second region with a shrinkage rate of 10%, good results were obtained in the evaluation of color unevenness. In contrast, for Comparative Examples 1 to 5 in which cured films with the same film thickness were formed in both the first region and the second region, the results in the evaluation of color unevenness were unsatisfactory.

[0170] In the evaluation of wrinkles, good results could be confirmed in the ink containing 69% to 76% by mass of monofunctional monomers based on the total mass of the polymerizable compound.

[0171] That is, in Examples 3, 5, and 6 and Comparative Examples 3 to 5, Ink 3 to 5 was used, and the film thickness of the cured film was 5 μm and 10 μm with a shrinkage rate of 10%, or the film thickness of the cured film was 5 μm or 10 μm with a shrinkage rate of 40%. In any case, no wrinkles were found to be generated, showing good results. It is speculated that this is because the ink composition contains a large amount of monofunctional monomers relative to the total mass of the polymerizable compound, so that a soft cured film can be formed. When the recording material shrinks, the cured film also shrinks as the recording medium shrinks.

[0172] However, when the cured film with a film thickness of 20 μm in Example 4 was shrunk at a shrinkage rate of 10%, it was found that the cured film generated some wrinkles. It is speculated that this is because the cured film is as thick as 20 μm, so the flexibility of the cured film is lost, and when it shrinks, the cured film peels off from the recording medium and wrinkles are generated.

[0173] In the evaluation of adhesion, a preferable tendency was found in the ink composition in which the content of the monofunctional monomer relative to the total mass of the polymerizable compound was small. That is, it was found that Ink 1 used in Examples 1 and Comparative Example 1, which contains 70% by mass or less of the monofunctional monomer relative to the total mass of the polymerizable compound, showed good results in the adhesion evaluation.

Claims

1. An inkjet recording method, characterized in that, The inkjet recording method has: An ejection step of ejecting a radiation-curable inkjet composition containing a coloring agent and a polymerizable compound, and attaching it to a recording medium that shrinks by heating; and A curing step of irradiating the radiation-curable inkjet composition attached to the recording medium with radiation to cure the radiation-curable inkjet composition to obtain a recorded object, The recorded object has a first region and a second region with different shrinkage rates in the main surface direction caused by the heating when shrinking by the heating and conforming to the object to be packaged, The shrinkage rate of the first region in the main surface direction is larger than the shrinkage rate of the second region in the main surface direction, In the ejection step, the radiation-curable inkjet composition is attached in such a manner that the film thickness of the cured film formed in the first region is smaller than the film thickness of the cured film formed in the second region, The first region and the second region refer to regions on the recorded object obtained by irradiating the radiation-curable inkjet composition attached to the recording medium with radiation in the curing step, The film thickness of the cured film refers to the film thickness of the cured film in the recorded object when printing with 100% ink dot generation amount; when the ink dot generation amount is less than 100% or more than 100%, a value obtained by multiplying the film thickness of the cured film in the recorded object when printing with 100% ink dot generation amount by the ink dot generation amount.

2. The inkjet recording method according to claim 1, wherein: The maximum film thickness of the cured film is 10 μm or less.

3. The inkjet recording method according to claim 1, wherein: The radiation-curable inkjet composition contains a monofunctional monomer as the polymerizable compound, The content of the monofunctional monomer is 40% by mass or more and 85% by mass or less based on the total mass of the polymerizable compound contained in the radiation-curable inkjet composition.

4. The inkjet recording method according to claim 1, wherein: The coloring agent contains a non-white coloring agent.

5. The inkjet recording method according to any one of claims 1 to 4, wherein: The recording medium is any one of a polyethylene terephthalate film and a polyolefin film.

6. A packaging method for an object to be packaged, characterized in that: The packaging method includes: A step of disposing the recorded object obtained by the inkjet recording method according to any one of claims 1 to 4 around the object to be packaged; and A step of heating the recorded object to shrink the recorded object.

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