Method for producing decorated metal can

Abstract

To provide a method for manufacturing a decorative metal container (metal can body) which suppresses the discharge of carbon dioxide, reduces consumption and waste resources, exhibits excellent productivity, and can impart various decorative properties.SOLUTION: A method for producing a decorative metal can, comprising a step of bonding an outer surface protective layer of a laminate having the outer surface protective layer on a release film, or a printed layer of a laminate having the outer surface protective layer and the printed layer on a release film, to a can barrel portion of a metal can body via an active energy ray-curable adhesive layer, and a step of irradiating the adhesive layer with active energy rays to cure the adhesive layer and peeling off the release film.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing decorated metal cans, particularly beverage cans and aerosol cans, which involves surface decoration and forming an outer protective layer on a metal can body, suppressing carbon dioxide emissions, consuming less and disposing of less resources, demonstrating excellent productivity, and enabling the imparting of a variety of aesthetic qualities. [Background technology]

[0002] Currently, metal cans (metal containers) known on the market as beverage cans and food cans include seamless metal cans with one-piece bottoms made of steel or aluminum, three-piece cans with a bottom lid and top cover (including easy-open can lids) fastened at both ends, and resealable cans such as bottle-shaped cans with a cap fastened around a threaded opening that has a resealable function.

[0003] Various types of cans are decorated with graphics, trademarks, and other designs for rust prevention and design reasons. One method for applying such decorations to metal cans is to attach a printed film via an adhesive layer to the outer surface of a two-piece can body, which has no seams on the sides and is formed integrally with the body and bottom. This technique has been proposed in many cases and is already being used commercially, as disclosed in Patent Documents 1 and 2.

[0004] Furthermore, Patent Document 3 discloses the concept of attaching a printed film (film label) with an adhesive layer to a three-piece can body made by rolling a metal plate and joining both ends of the outer periphery to form a seam on the side.

[0005] Patent Document 4 discloses a method in which a varnish is applied to the outside of a film, the can body side of the film is printed, an adhesive is applied to the printed surface and dried, and the edge is overlapped and laminated to the outer periphery of the can body using a laminating device. Patent Document 4 also explains that a PET film can be decorated in advance by various printing methods such as flexographic printing, lithographic printing, screen printing, gravure printing, electrophotographic printing, and inkjet printing, and then attached to the outer surface of the can body via an adhesive layer.

[0006] Furthermore, recent changes in consumer trends and needs, such as the diversification of products and the need for rapid and timely product shipments, have led to a demand for the production and shipment of a wide variety of types and in small lots. In order to meet such production and shipment requirements, Patent Document 5 describes a metal can in which the can body is wrapped or covered with a pre-printed heat-shrinkable film or a cylindrical heat-shrinkable tube and then heat-shrunk.

[0007] Furthermore, Patent Document 6 describes a method in which sublimation ink is used to print characters or figures on a medium such as paper or plastic film by inkjet printing or laser printing, and the printed medium is then wrapped around a metal can so that the printed surface comes into contact with the surface of the can. The metal can and medium are heated in an oven to adhere and fix the ink to the metal can, and then the medium is removed to obtain a printed metal can.

[0008] As mentioned above, as product varieties and small lot production become more common, there is a growing need for shorter delivery times and cost considerations, increasing the need for rapid and timely product shipments. To meet these demands, for example, a manufacturing method in which pre-printed films are separately manufactured and then used to cover metal cans in response to customer orders is advantageous in terms of shortening product delivery times. However, preparing and holding large quantities of a wide variety of printed films in stock until customer orders are received is not economically satisfactory.

[0009] Furthermore, when a film printed by a plate contact printing method such as gravure printing is attached to a can body, a master plate for printing must be produced, which incurs plate-making costs.In addition, the plate and ink must be replaced for each lot, which requires setting changes and reduces printing efficiency.

[0010] On the other hand, by using non-contact printing methods such as electrophotographic printing and inkjet printing as exemplified in Patent Documents 4 and 5, it becomes unnecessary to prepare a master plate, plate-making costs can be reduced, and setting changes for each lot can be minimized. This reduces product costs, improves printing efficiency, and enables the production of a wide variety of products in small lots.

[0011] However, such non-contact printing methods, such as inkjet printing, have problems such as ink bleeding on the film, which can lead to unstable print quality. Furthermore, there is also the problem that the heat applied during sterilization processes such as retort sterilization, which is carried out after the contents are filled and sealed in the can, can reduce the ink's adhesion. In these respects, there is still room for improvement.

[0012] Patent Document 7 addresses the above-mentioned technical problems and proposes a manufacturing method in which a printed film on which ultraviolet-curable ink is inkjet-printed is attached to the can body.

[0013] The invention of Patent Document 7 includes a printing step in which an adhesive is applied and thermally dried to form a printed film, and a film attachment step in which the printed film is attached, with the adhesive layer facing toward the can body part of a cylindrical can body that has been heated to a temperature range above the glass transition point and below the melting point of the film. [Prior art documents] [Patent documents]

[0014] [Patent Document 1] Japanese Patent Application Publication No. 3-230940 [Patent Document 2] Japanese Patent Application Publication No. 10-683 [Patent Document 3] Japanese Patent Application Publication No. 52-24789 [Patent Document 4] Japanese Patent Application Laid-Open No. 2003-54567 [Patent Document 5] Japanese Patent Application Publication No. 9-226738 [Patent Document 6] Japanese Patent Application Laid-Open No. 2001-315495 [Patent Document 7] Japanese Patent Application Laid-Open No. 2006-248573 Summary of the Invention [Problem to be solved by the invention]

[0015] However, this method of manufacturing can bodies with printed film attachment not only requires multiple hot air drying and heat curing processes before the adhesive's final performance is achieved, but also requires a resin layer with a thickness of 10 μm or more, even excluding the printed layer, because the outer protective layer of the can body consists of an outer clear paint layer, a plastic film, and an anchor coat layer. Therefore, there is still room for improvement in terms of reducing thermal energy consumption, organic resource use, and ultimately carbon dioxide emissions.

[0016] The present invention has been made in consideration of the above circumstances, and aims to provide a method for manufacturing decorated metal containers (metal can bodies) that involves a process for surface decoration and forming an outer protective layer on a metal can body, suppresses carbon dioxide emissions, consumes and disposes of fewer resources, exhibits excellent productivity, and can impart a variety of aesthetic qualities. [Means for solving the problem]

[0017] As a result of extensive research into the above-mentioned problems, the inventors have found that the above-mentioned problems can be solved by using the following embodiments, and have thus achieved the present invention.

[0018] [1] A method for manufacturing a decorated metal can, comprising the steps of: bonding an outer surface protective layer of a laminate having an outer surface protective layer on a release film, or the printing layer of a laminate having an outer surface protective layer and a printing layer on a release film, to the can body of a metal can body via an active energy ray-curable adhesive layer; and irradiating the adhesive layer with active energy rays to cure it and peeling off the release film.

[0019] [2] A method for manufacturing a decorated metal can according to [2], comprising the step of applying an active energy ray-curable adhesive to the can body of a metal can body.

[0020] [3] A method for producing a decorated metal can according to [1] or [2], which comprises a step of forming a printed layer using an active energy ray-curable ink.

[0021] [4] The method for producing a decorated metal can according to any one of [1] to [3], wherein the outer surface protective layer is curable with active energy rays.

[0022] [5] The method for producing a decorated metal can according to any one of [1] to [4], wherein the adhesive layer is electron beam curable.

[0023] [6] The method for producing a decorated metal can according to any one of [1] to [5], wherein the outer surface protective layer is electron beam curable. [Effects of the Invention]

[0024] According to the present invention, a method for manufacturing a decorated metal can can be provided that suppresses carbon dioxide emissions, consumes and disposes fewer resources, exhibits excellent productivity, and can impart a variety of aesthetic qualities during the processes of surface decoration and outer surface protective layer formation of the decorated metal can. [Brief explanation of the drawings]

[0025] [Figure 1] 1 is a side view showing an example of a metal can body to which the present invention is applied. [Figure 2] FIG. 2 is a schematic diagram showing a laminate having an outer surface protective layer on a release film. [Figure 3]1 is a schematic diagram showing a laminate having an outer surface protective layer and a printed layer on a release film. [Figure 4] 1 is a schematic diagram showing a cross section of a decorated metal can manufactured by the method of the present invention. [Figure 5] 1A to 1C are schematic diagrams showing the manufacturing process of a decorated metal can according to the manufacturing method of the present invention. [Figure 6] 1 is a schematic diagram showing an apparatus for manufacturing a decorated metal can according to a manufacturing method of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0026] The method for manufacturing a decorated metal can of the present invention includes a step of bonding an outer surface protective layer of a laminate having an outer surface protective layer on a release film, or a printing layer of a laminate having an outer surface protective layer and a printing layer on a release film, to the can body of a metal can body via an active energy ray-curable adhesive layer, and a step of irradiating active energy rays to cure the adhesive layer and peeling off the release film.

[0027] This process allows metal cans to be decorated without relying on thermal curing using a dielectric heating device or gas oven heating. The use of an active energy ray irradiation device with excellent energy conversion efficiency allows for low cost and reduced environmental impact. Furthermore, because the release film serves as the support for the outer protective layer, the tension applied during the manufacturing process can be supported by the support, making it possible to produce a thinner outer protective layer. Furthermore, by irradiating the can body with active energy rays through the release film, the active energy ray-curable adhesive reacts without being inhibited by oxygen in the air, enabling an efficient and economical production process. Furthermore, peeling off the release film reproduces the shape of the interface between the release film and the outer protective layer. Therefore, if a hologram pattern or fine irregularities are formed on the surface of the release film facing the outer protective layer, such patterns can be reproduced on the can body surface. This allows for the creation of a variety of aesthetic features that were difficult and costly to achieve using conventional manufacturing processes.

[0028] The method for producing a decorated metal can of the present invention preferably includes a step of applying an active energy ray-curable adhesive to the can body of the metal can body.

[0029] This process prevents the solvent or diluent contained in the adhesive from penetrating into the outer protective layer or printed layer that has been formed in advance on the release film. In other words, by applying the adhesive to the can body of a metal can body, it is possible to minimize the adverse effects of the adhesive on the outer protective layer or printed layer, thereby maintaining excellent protective performance and a high-quality printed layer.

[0030] The method for producing a decorated metal can of the present invention preferably includes a step of forming a print layer using an active energy ray-curable ink.

[0031] This process eliminates the need for solvent drying, which is required when printing with inks that use aqueous or organic solvents, and also prevents the solvent from penetrating into the outer protective layer that has been pre-formed on the release film. Furthermore, the active energy ray-curable ink can improve the reaction rate and exhibit excellent durability in the process of curing the active energy ray-curable adhesive. Furthermore, when forming a printing layer on the outer protective layer, it can be dried or cured without using thermal curing with a dielectric heating device or gas oven heating. The use of active energy rays, which have excellent energy conversion efficiency, can provide low cost, low environmental impact, and excellent adhesion and productivity.

[0032] In the method for producing a decorated metal can of the present invention, the outer surface protective layer is preferably active energy ray curable.

[0033] According to this configuration, the final strength of the outer protective layer can be achieved by the active energy ray curing reaction. Therefore, when an inner coating process follows the metal can decorating process, there is no need to cause a crosslinking reaction of the outer protective layer during the heat curing process of the inner coating. Furthermore, when a metal plate with a plastic film layer is used on the inner surface of the metal container instead of the inner coating, the heating process after the decorating process in the metal can manufacturing process can be eliminated, thereby achieving a significant reduction in energy costs and carbon dioxide emissions.

[0034] In the method for producing a decorated metal can of the present invention, the adhesive layer is preferably electron beam curable.

[0035] With this configuration, the adhesive layer can be cured by electron beams, and the adhesive sandwiched between the printed layer formed as needed on the outer surface protective layer and the can body can absorb the electron beams without being exposed to oxygen in the air, thereby achieving a highly efficient reaction without the need for an inert gas. Furthermore, even when the printed layer contains colorants or additives that have ultraviolet absorbing properties, it is possible to supply sufficient active energy rays to the adhesive, thereby imparting stable adhesive performance.

[0036] In the method for producing a decorated metal can of the present invention, the outer surface protective layer is preferably electron beam curable.

[0037] The outer protective layer of a decorated metal can manufactured in this manner can be made thinner, which reduces carbon dioxide emissions during the can recycling process.

[0038] The present invention will now be described in more detail. The metal can body 1 shown in FIG. 1 is the target metal can body of the present invention. The metal sheet used for the can body 1 can be aluminum, aluminum alloy, surface-treated steel such as tin-free steel, tinplate, chrome-plated steel, aluminum-plated steel, nickel-plated steel, or any other alloy-plated steel sheet. It is also possible to use a metal sheet in which at least the surface that will become the can's inner surface is coated with an oriented thermoplastic resin. This metal can body can be a three-piece can consisting of a can body 1a, a top, and a bottom lid, or a seamless can in which the can bottom and can body 1a are integrally formed, i.e., a two-piece can, such as a drawn can, redrawn can, stretch can, drawn and ironed can, or impact can. Typically, the open end of the can body 1a is subjected to necking and flange processing to form a necked-in portion and a flange, and finally, the top is seamed.

[0039] The release film that serves as the support for the outer protective layer transferred to the metal can body is preferably a resin release film. Specifically, a resin film made of a polymer resin selected from polyester resins such as polyethylene terephthalate resin and polybutylene terephthalate resin, copolymer polyester resins such as copolymers of polyethylene terephthalate and isophthalic acid, polypropylene resin, polycarbonate resin, polystyrene resin, polyolefin resin, vinyl chloride resin, and polyvinylidene chloride copolymer, or a composite of these resins, can be used. Among these, polyethylene terephthalate resin film is preferred from the viewpoint of resource recycling, as it can be stretched to some extent in the circumferential direction of the can body 1 at a linear pressure of 147 to 588 N / cm (15 to 60 kgf / cm) during the transfer process. The thickness of the resin film can be determined as appropriate; for example, a resin film with a thickness of approximately 10 to 30 μm can be used.

[0040] The surface of the release film 2 shown in FIG. 2 that contacts one of the outer surface protective layers 3 (transfer layer 5) can be physically shaped in advance. The physically shaped surface includes a smooth surface, and refers to an uneven surface created by a hologram, microlens, matte finish, embossed finish, etc. The manufacturing method of the present invention makes it possible to transfer the physical shape to the metal can body. Note that, in the present invention, decoration also includes the application of a design to the outer surface protective layer using a release film.

[0041] The outer surface protective layer (transfer layer) formed on this release film is not particularly limited as long as it is a resin used in existing can outer surface coatings. Specific examples include a resin base such as polyester resin, epoxy resin, epoxy-modified polyester resin, or acrylic resin, to which a curing agent such as an amino resin has been added. It may also contain a well-known lubricant. For example, the polyester resin may contain organic or inorganic fine particles as a lubricant, as needed, to improve the film's winding and transportability during film formation. Examples of such fine particles include calcium carbonate, calcium oxide, aluminum oxide, kaolin, silicon oxide, zinc oxide, crosslinked acrylic resin particles, crosslinked polystyrene resin particles, urea resin particles, melamine resin particles, and crosslinked silicone resin particles. In addition to the fine particles, colorants, antistatic agents, antioxidants, lubricants, catalysts, and other resins such as polyethylene, polypropylene, ethylene-propylene polymers, and olefin-based ionomers may also be optionally added as long as they do not impair transparency. The outer surface protective layer is preferably reactive. The term "reactivity" refers to thermosetting properties, curability with active energy rays such as ultraviolet rays and electron beams, hybrid curability of thermosetting properties and active energy beam curability, and in particular, electron beam curability is more preferable in terms of reducing carbon dioxide emissions and productivity.

[0042] When the outer protective layer is made electron beam curable, the resin used for the outer protective layer is not particularly limited as long as it is a resin used in existing active energy ray-curable outer coatings for cans. For example, resins having reactive functional groups crosslinkable by active energy rays are preferred. Specific examples include resins obtained by modifying polyester resins, epoxy resins, epoxy-modified polyester resins, and acrylic resins with active energy ray-reactive groups such as acryloyl groups and vinyl groups. Furthermore, resins having a main chain structure that favors electron beam crosslinking are also preferred. Specific examples include resins incorporating polyethylene chains, polypropylene chains, polyvinyl chloride chains, etc. into the resin structure. The modification rate of the active energy ray-reactive groups (acrylic equivalent in the case of acryloyl groups) and the main chain structure that favors electron beam crosslinking can be appropriately determined depending on the usage conditions, such as irradiation conditions and the ambient atmosphere. As a result, when the outer surface protective layer is transferred to the can body after the curing process of the curable adhesive, the crosslink density of the outer surface protective layer itself is improved, which not only improves the peelability of the outer surface protective layer from the release film, which is the outer surface protective layer alone, but also improves the film strength of the outer surface protective layer. Furthermore, when the inner surface protective film is pre-laminated on the inner surface side of the can body, this makes it possible to eliminate the heating step in a gas oven in the process after transferring the outer surface protective layer to the can body.

[0043] The outer surface protective layer can be formed in a semi-cured state, for example, by applying the composition for forming the outer surface protective layer onto a release film by roll coating or the like and then heating it.

[0044] FIG. 3 is a schematic diagram of a laminate in which an outer surface protective layer and a printed layer 4 are formed on a release film.

[0045] 3, a transfer layer 5 including the outer protective layer 3 and the printed layer 4 is formed by printing as needed, and a decorated metal can having the printed layer 4 applied by transfer can be obtained. There are no particular restrictions on the method for forming the printed layer 4, but digital printing methods such as inkjet printing, laser printing, and electrophotography (toner) printing are preferred from the standpoint of economic efficiency depending on the number of cans to be manufactured. For example, inks used in inkjet printing include aqueous inks in which a dye is dissolved in an aqueous solvent, oil-based inks, and active energy ray-curable inks. To form a printed layer on an outer protective layer made of resin, active energy ray-curable inks can be preferably used.

[0046] In addition, active energy ray-curable inks are also preferred from the viewpoints of low viscosity, low volatility, and low scattering properties. To reduce the viscosity of the ink and improve its fluidity, an active energy ray-curable monomer can be used as a reactive diluent, or an organic solvent that dissolves the active energy ray-curable component can be added. The active energy ray-curable ink used in the present invention partially cures immediately after ink landing during printing, and the outer surface protective layer and the printed layer are bonded to the can body with an active energy ray-curable adhesive. Therefore, it is preferable to use a reactive diluent and to be solvent-free. Furthermore, being solvent-free can avoid problems such as deterioration of solvent resistance and volatile organic compounds (VOCs) from residual solvents. Examples of active energy rays include electron beams and ultraviolet rays, with ultraviolet rays being preferably selected.

[0047] The viscosity of UV-curable ink is typically preferably 50 mPa·s or less at 25°C, and even more preferably 30 mPa·s or less. UV-curable ink is formulated to achieve an ideal ratio of pigment to resin binder. Resin binders include epoxy acrylate resin, polyester acrylate resin, polyurethane acrylate resin, polyether acrylate resin, and polybutadiene acrylate resin, and any resin that undergoes a polymerization reaction under UV light is suitable. The above UV-curable resins can be used alone or as a mixture of two or more types.

[0048] Specific examples of UV-curable monomers (reactive diluents) include monofunctional monomers such as 2-hydroxyethyl acrylate, tetrahydrofurfuryl acrylate, dicyclopentenyl acrylate, and dicyclopentenyloxyethyl acrylate; bifunctional monomers such as 1,3-butanediol diacrylate, 1,4-butanediol diacrylate, 1,6-hexanediol diacrylate, diethylene glycol diacrylate, neopentyl glycol diacrylate, and tripropylene glycol diacrylate; and trifunctional or higher monomers such as trimethylolpropane triacrylate, pentaerythritol tri-tetraacrylate, ditrimethylolpropane tetraacrylate, and dipentaerythritol hexaacrylate.

[0049] It is preferable to blend a photopolymerization initiator into the ink composition. Specific examples of photopolymerization initiators include acetophenone, benzophenone, Michler's ketone, benzil, benzoin, benzoyl isobutyl ether, benzine methyl ketal, tetramethylthiuram sulfide, azobisisobutyronitrile, benzoyl peroxide, di-tert-butyl peroxide, 1-hydroxycyclohexyl phenyl ketone, 2-hydroxy-2-methyl-1-phenyl-propan-1-one, 1-(4-isopropylphenyl)-2-hydroxy-2-methylpropan-1-one, 2-chlorothioxanthone, and methylbenzoyl formate. These photopolymerization initiators may be used alone or in combination.

[0050] Furthermore, color printing can be performed using four inks: cyan (C), yellow (Y), magenta (M), and black (K). Alternatively, six-color printing can be performed by adding a pale magenta (LM) and pale cyan (LC) to CMYK. Six-color printing can also be performed by adding orange and green inks to CMYK. Alternatively, colors that can be used in existing inkjet printing, such as white (W), can be used. The pigment dispersion is preferably performed to achieve an average particle size of 0.08 to 0.5 μm, with a maximum particle size of 0.3 to 10 μm, preferably 0.3 to 3 μm. The selection of pigment, dispersant, dispersion medium, dispersion conditions, and filtration conditions are appropriately set to achieve this. Such particle size control prevents clogging of the head nozzles and maintains the ink's storage stability, ink transparency, and curing sensitivity.

[0051] In addition to the additives described above, various additives may be used in the ultraviolet-curable ink according to the present invention, such as surfactants, polyester resins, polyurethane resins, vinyl resins, acrylic resins, rubber resins, waxes, and the like, for adjusting the film properties.

[0052] The ejection conditions for UV-curable ink may be those that are already commercially available and are common. Typically, the head and ink are heated to 35 to 100°C, preferably 40 to 80°C, to improve the fluidity of the ink before ejection, which is preferred from the viewpoint of ejection stability. UV-curable inks have a large viscosity fluctuation range due to temperature fluctuations, and viscosity fluctuations directly affect droplet size and droplet ejection speed, resulting in image quality degradation. Therefore, it is necessary to raise the temperature of the UV-curable ink while maintaining it as constant as possible. The ink temperature control range is within the set temperature ±5°C, preferably ±2°C, and even more preferably ±1°C.

[0053] Furthermore, by dividing the ultraviolet irradiation into two stages, i.e., first depositing the ultraviolet-curable ink, irradiating it with ultraviolet light to temporarily cure it, and then, when transferring the printed layer to the can body using an active energy ray-curable adhesive, irradiating it with active energy rays to fully cure it, it is possible to suppress the shrinkage of the outer surface protective layer that occurs when the ink cures.

[0054] The curing time of the UV-curable ink varies depending on factors such as the thickness of the release film, the UV source, the photopolymerization initiator, the reactive diluent, the distance between the UV source and the coating surface to be cured, and the desired curing state, but is appropriately determined within the range of 0.001 to 2.0 seconds. Adjusting the curing time of the UV-curable ink can improve the ink's conformability and print appearance during post-processing, such as necking and thread forming, after the transfer layer consisting of the outer surface protective layer and the printing layer is transferred to the can body. In other words, the applied ink is partially pre-cured to achieve a tack-free state. Specifically, it is preferable to cure the ink surface approximately 80% to eliminate surface stickiness. At this time, the interior of the ink cures at a slower rate than the surface, reaching a degree of cure of, for example, approximately 30%. This also improves manufacturing efficiency.

[0055] The outer protective layer preferably has ink receptivity, and from the viewpoint of ink receptivity, it is preferable for the outer protective layer to be a semi-cured active energy ray-curable resin. Ink receptivity refers to the ability to improve adhesion with UV-curable ink deposited by inkjet printing, to prevent the deposited ink dots from becoming large, and to prevent ink bleeding. To achieve ink receptivity, the outer protective layer preferably contains a mixture of a thermosetting resin and a UV-curable resin, or a porous material. Examples of thermosetting resins include polyester resin, acrylic resin, and epoxy resin. Suitable porous materials include silica, which allows the ink to penetrate small depressions and holes in the silica surface, preventing ink bleeding. The particle size of the silica is preferably 0.3 to 5 μm, preferably approximately 0.8 to 3 μm, and the amount of silica added is preferably approximately 0.1 to 2%. Adding silica in an amount of 2% or less is preferable in terms of print appearance, as the transparency of the outer protective layer is not reduced. Furthermore, when the amount of silica added is 0.1% or more, the effect of preventing ink bleeding is easily obtained. In the present invention, an anchor layer can be formed on the outer surface protective layer to impart ink receptivity.

[0056] The present invention includes a step of bonding an outer surface protective layer or a printed layer of a laminate as shown in FIGS. 2 and 3 to a can barrel portion of a metal can body via an active energy ray-curable adhesive layer (uncured adhesive layer), and a step of irradiating the adhesive layer with active energy rays to cure the adhesive layer and peeling off the release film.

[0057] Specific examples of active energy ray-curable adhesives include those containing, relative to the total mass % of the active energy ray-curable adhesive, 15 to 20 mass % of a resin component such as a polyester resin, epoxy resin, or polyurethane resin; 5 to 10 mass % of a (meth)acrylate oligomer component such as a polyester (meth)acrylate, epoxy (meth)acrylate, or urethane (meth)acrylate; 10 to 15 mass % of a tackifier component such as a terpene resin, rosin resin, or petroleum resin; and 50 to 60 mass % of a (meth)acrylate monomer component having a viscosity of 0.1 to 1000 mPa·s (25°C).

[0058] The active energy ray-curable adhesive may further contain known additives as appropriate. Examples include polymerization inhibitors, antioxidants, photopolymerization initiators, light stabilizers, ultraviolet absorbers, sensitizers, fluorescent brighteners, curing agents, coupling agents, plasticizers, leveling agents, surface conditioners, antifoaming agents, substrate wetting agents, adhesion promoters, antistatic agents, coloring pigments, extender pigments, and pigment dispersants. An adhesive prepared by diluting with an organic solvent or water can be used, but the active energy ray-curable adhesive used in the present invention is preferably solvent-free because it is completely cured when the outer surface protective layer and the printing layer are transferred to the can body.

[0059] The photopolymerization initiator may be the same as that exemplified in the ink composition. In the case of an electron beam curable adhesive, it is preferable that the adhesive does not substantially contain a photopolymerization initiator. That is, the content of the photopolymerization initiator in the total mass of the active energy beam curable adhesive is preferably 0.5 mass% or less, and may be 0 mass%.

[0060] The application method is preferably a roll coating method, and more preferably, the active energy ray-curable adhesive is applied to the can body by roll coating, and then the transfer layer side of the laminate is laminated. If the active energy ray-curable adhesive is applied to the outer surface protective layer by roll coating instead of the can body, the active energy ray-curable adhesive may penetrate the provisionally cured ink and the outer surface protective layer, potentially impairing the design and outer surface protective function of the transferred reactive outer surface protective layer. Therefore, it is preferable to apply the active energy ray-curable adhesive to the can body. Furthermore, if the outer surface protective layer and the printing layer have a high degree of curing, and the protective performance and high-quality printing layer can be maintained, the active energy ray-curable adhesive may be applied directly to the transfer layer. Immediately after lamination, the adhesive is cured by irradiation with active energy rays, and the release film is peeled off, allowing the transfer layer to be transferred to the can body. The application amount of the active energy ray-curable adhesive is 10 to 50 mg / dm 2 is preferred.

[0061] Furthermore, it is also possible to blend a thermosetting adhesive with an adhesive curable with active energy rays such as ultraviolet rays or electron beams. In this case, epoxy resins, amino resins, etc. are preferred. The blending ratio with the thermosetting adhesive can be appropriately set depending on the ultraviolet-curable ink, the irradiation conditions of the electron beam or ultraviolet rays in the curing device that cures the adhesive, and the environmental atmosphere. In this case, the adhesive can be completely cured in the inner surface coating process after the decoration process.

[0062] 4 shows a schematic cross section of a decorated metal can after the above steps have been completed, with a printed layer 4 inkjet-printed with ultraviolet-curable ink on the underside of the outer protective layer 2. A cured adhesive layer 6a is formed on the underside of the printed layer 4, and the outer protective layer 3 and the can body 1 are bonded together via the adhesive layer 6a.

[0063] 5 is a schematic diagram showing an example of a manufacturing process for a decorated metal can according to the present invention. The film, which is delivered with an outer protective layer already formed on a release film, is unwound from a winding roll, and a notch (half die) appropriate to the dimensions of the can body is made in the outer protective layer to a degree that does not impair the strength of the release film, forming a peelable area for the outer protective layer. Then, ultraviolet-curable inks, such as yellow (Y), magenta (M), cyan (C), and black (B), are applied from an inkjet printer head to the peelable area for the outer protective layer of the film.

[0064] The outer protective layer also serves as an ink-receiving layer to prevent the ink from bleeding. After the ink is used to form a printed layer of letters, pictures, or other designs using the inkjet method, ultraviolet light is irradiated from an ultraviolet irradiation device to temporarily cure the ink composition, removing the ink surface's adhesiveness and forming a printed layer. The curing light source can be a standard ultraviolet curing light source (wavelength 300-450 nm) or an LED-UV light source (wavelength 385 nm), depending on the absorption wavelength of the photopolymerization initiator used.

[0065] Meanwhile, during the process of forming and transporting cylindrical can bodies (two-piece cans), an electron beam curable adhesive is applied to the can body using a roll coater, filling the gap between the transported can body and the outer protective layer and printed layer, which have been formed in advance using a half die at intervals corresponding to one circumference of the can body. At the same time, the outer protective layer and printed layer are transferred to the can body by electron beams irradiated from the outer surface of the release film, and the release film is peeled off from the outer protective layer and taken up.

[0066] When the outer surface protective layer and the printed layer are transferred to the can body, the ultraviolet curable ink, which was in a partially cured state, is completely cured by the electron beam, thereby obtaining a decorated metal can.

[0067] Thereafter, if the can body is a seamless can such as a two-piece can or a bottle-shaped can, the rib portion of the can bottom of the can body may be painted with a thermosetting paint (not shown), and then heated in an oven to form a lubricant-containing protective coating layer on the rib portion.

[0068] The inner surface of the can body is then painted with a predetermined paint and dried by heating (inner surface painting process). If the active energy ray-curable adhesive used to transfer the outer surface protective layer and the printed layer to the can body contains a thermosetting resin, the thermosetting resin is also dried by heating, thereby improving the adhesion between the outer surface protective layer and the printed layer and the can body. After that, subsequent processes (not shown), such as necking, are sequentially performed.

[0069] Figure 6 is a schematic diagram of an example of a manufacturing apparatus for decorated metal cans according to the present invention. Prior to the process shown in Figure 6, there are installed a group of devices related to can body molding (not shown), a rotary die cutter (not shown) that sandwiches the outer protective layer and release film and cuts them into lengths corresponding to one circumference of the can body, and a printing press. This rotary die cutter is equipped with a cutter that cuts the outer protective layer into lengths corresponding to one circumference of the can body with each rotation but is adjusted so as not to cut the release film carrying the outer protective layer, and is configured to rotate in synchronization with the running of the film. Furthermore, subsequent processes, such as inner surface coating, baking, beading, trimming, and palletizing (not shown), follow the process shown in Figure 6.

[0070] A roll coater 14, which applies an active energy ray-curable adhesive to the can bodies, is located at a predetermined position close to the revolving circle of multiple mandrels 11 that revolve around can bodies fitted around them. A can body supply station 12 is provided upstream of the revolving circle in the direction of the mandrels' rotation, and a can body supply conveyor 13 is arranged facing this can body supply station. This can body supply conveyor conveys can bodies 1, which are formed by drawing or drawing and ironing processes using metal plate such as aluminum, in a line, and at its forefront, the can bodies are handed over to the mandrels at the can body supply station for fitting.

[0071] The transfer station 16 is located at the point of the mandrel's rotation circle closest to the adhesive coating roll coater. The outer protective layer on the release film, cut by the rotary die cutter, comes into contact with the can body with the printed surface facing upward, i.e., with the printed surface facing the can body at the bonding station. Immediately after this, the film is irradiated with active energy rays, and a length of film equivalent to one can is transferred and wrapped around the can body.

[0072] Contiguous to the transfer station, downstream in the mandrel rotation direction, are a release film take-up station 18 and a can body discharge station 19, where the peeled release film is wound up and collected and discharged for recycling, and the can bodies are sent out to a can body discharge conveyor 20. This can body discharge conveyor is a conveyor that transports the can bodies, to which the outer surface protective layer and printed layer have been transferred, to subsequent processes such as necking-in, flanging, or can lid seaming.

[0073] Although the above specific examples have been described with reference to two-piece cans as the can body, the present invention is not limited thereto and can also be applied to three-piece cans such as welded cans and bottle-shaped cans. Furthermore, in the case of film-laminated cans formed from resin-coated laminated sheets that do not require interior painting, the interior painting step can be omitted and the present invention can be similarly applied to other steps. Furthermore, in the case of laminated cans formed from resin-coated film-laminated sheets, or in the case of two-piece cans formed from metal sheets coated with a thermosetting coating such as polyester resin, or bottle-shaped cans, painting of the rib portion of the can bottom can also be omitted. [Example]

[0074] Next, an example of the present invention will be described. An outer protective layer-forming composition (a resin composition blending a thermosetting polyester resin and an electron beam-curable acrylic resin in a mass ratio of 1:4) was applied to the surface of a 25 μm-thick polyethylene terephthalate (PET) release film, and heated at 170°C for 6 minutes to form an outer protective layer with a thickness of 5 μm. At this point, the outer protective layer was in a semi-cured state, having been partially cured by heat.

[0075] Four UV-curable inks (yellow, magenta, cyan, and black) were applied to the outer protective layer side of the PET release film using the inkjet method to form a printed layer, and then UV light was irradiated onto the printed layer to temporarily cure it to an incomplete state with a cure rate of 30-80%. The UV-curable ink is primarily composed of UV-curable resin, and its composition is a mixture of 95 parts binder by weight and 5 parts pigment by weight.

[0076] The ultraviolet curable ink was applied to a thickness of 1.0 μm, and the curing time by ultraviolet irradiation for provisional curing was set to 0.5 seconds.

[0077] A steel DI can was formed into a cylindrical shape from a steel metal plate and the surface was coated with an electron beam curable adhesive, which was a mixture of 14 parts polyester resin, 14 parts petroleum resin, 10 parts urethane (meth)acrylate, and 60 parts ethylenically unsaturated monomer, by roll coating to a concentration of 30 mg / dm 2 The adhesive layer was formed by applying the adhesive to a thickness of 1000 μm.

[0078] Then, in the transfer station, the printed layer on the PET release film and the adhesive layer on the can body were bonded together, and an electron beam was irradiated from the PET release film side toward the can body to cure the adhesive layer, fully cure the printed layer, and peel off the release film. At this point, the outer surface protective layer was partially cured by heat and in a semi-cured state by electron beam curing.

[0079] Next, in the coating and heating station, the ribs on the bottom of the can were coated with a thermosetting paint containing lubricant, which was then dried and cured. After that, the can was rotated while the inside was coated and heated and dried. Here, the outer protective layer, which contained a thermosetting polyester resin, was completely cured.

[0080] When the resulting decorated metal can was visually inspected, no peeling of the outer protective layer was observed as the can body was rotated, and the effects of color image bleeding and dot gain were within a range that could be ignored in practical use. No abnormalities were observed in the patterns or letters, and a beautiful, high-quality printed image with high gloss was obtained.

[0081] Furthermore, when necking and flange processing were performed, no wrinkles or peeling of the transfer layer occurred.Furthermore, to sterilize the contents of the can body, a sterilization process such as retort sterilization, which is performed after the contents are filled and sealed in the can body, was performed, but there were no problems with the adhesion of the transfer layer. [Explanation of symbols]

[0082] 1.Can body 1a.Can body 2.Release film 3. Outer protective layer 4. Printing layer 5. Transfer layer 6. Active energy ray curable adhesive layer 6a. Cured adhesive layer 7. Adhered transfer layer 11. Mandrel 12. Can body supply station 13. Can body supply conveyor 14. Adhesive coating roll coater 15. Transfer roll 16. Transfer station 17. Electron beam irradiation device 18. Release film winding station 19. Can body removal station 20. Can body carrying conveyor

Claims

1. a step of bonding an outer surface protective layer of a laminate having an outer surface protective layer on a release film, or a printed layer of a laminate having an outer surface protective layer and a printed layer on a release film, to a can body portion of a metal can body via an active energy ray-curable adhesive layer; a step of curing the adhesive layer by irradiating it with active energy rays and peeling off the release film; A method for manufacturing a decorated metal can comprising the steps of:

2. 2. The method for manufacturing a decorated metal can according to claim 1, further comprising the step of applying an active energy ray-curable adhesive to the can body of the metal can body.

3. 3. The method for manufacturing a decorated metal can according to claim 1, further comprising a step of forming a print layer using an active energy ray-curable ink.

4. 3. The method for producing a decorated metal can according to claim 1, wherein the outer protective layer is curable by active energy rays.

5. 3. The method for manufacturing a decorated metal can according to claim 1, wherein the adhesive layer is electron beam curable.

6. 3. The method for manufacturing a decorated metal can according to claim 1, wherein the outer protective layer is electron beam curable.

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