Layer formation method, substrate regeneration method, and printed matter production method

Abstract

To provide a layer formation method which does not cause an odor problem resulting from containing a photopolymerization initiator, suppresses deterioration of a printed matter, allows easy reuse of a substrate, and can reduce risks to people and the environment.SOLUTION: A layer formation method includes: an application step of applying or ejecting, onto a sheet 6, an aqueous composition containing water and a polymerizable compound that is soluble in water and that undergoes a polymerization reaction due to irradiation with an electron beam; and a drying step of drying the aqueous composition applied or ejected onto the sheet 6, wherein the aqueous composition is free of a photopolymerization initiator excitable by ultraviolet light, and wherein a peelable coating layer 7 is formed on the sheet 6 using the above aqueous composition.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present disclosure relates to a layer forming method for forming a peelable coating layer on a substrate, a substrate recycling method, and a printed matter manufacturing method. [Background technology]

[0002] In recent years, growing environmental awareness has led to increased attention being paid to recycling. In the printing industry, there is a growing need to remove ink from printed packaging and recycle the substrate used in packaging after use. For example, plastic packaging and plastic bottles, among other plastic products, are a problem of environmental pollution in the ocean. Because plastics are difficult to decompose in nature, some plastics are separated, collected, and recycled. However, if printed plastic products are mixed in during the recycling process, they can discolor the recycled products, rendering them unusable. Such printed plastic products are often discarded rather than reused. When discarded plastic products end up in the ocean, they decompose in seawater and become microplastics. When marine organisms, such as fish, ingest microplastics, they accumulate in their bodies. This raises concerns about the potential impact on human health if humans consume such marine organisms as food. This issue is not limited to plastics; it is thought to apply to other printed substrates as well.

[0003] Methods for removing printed matter from substrates have been studied in order to recycle substrates on which printing or the like has been performed. For example, the recording medium forming method described in Patent Document 1 includes the steps of forming a removable film on the surface of a hydrophobic transparent recording medium, the removable film consisting of an adhesive layer containing an ultraviolet-curable component and a substrate layer, and forming an image on the surface of the substrate layer of the removable film. In this recording medium forming method, when reusing the transparent recording medium, an operator irradiates the removable film with ultraviolet light to cause a polymerization reaction of the ultraviolet-curable component, thereby shrinking the removable film. As a result, the adhesive strength of the removable film to the transparent recording medium decreases, and the removable film is removed from the transparent recording medium. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2000-98648 Summary of the Invention [Problem to be solved by the invention]

[0005] In the recording medium forming method, the adhesive layer of the removable film is composed of a hydrophobic oil-based composition. There is a risk that this oil-based composition may be exposed to workers or may have a negative impact on the environment. Furthermore, because the adhesive layer is hydrophobic, while the adhesion between the hydrophobic transparent recording medium and the adhesive layer is high, there is a risk that the adhesive layer may be difficult to remove from the transparent recording medium even when irradiated with ultraviolet light during the recycling process.

[0006] Furthermore, a photopolymerization initiator is present in the adhesive layer, and there is a possibility that the photopolymerization initiator may corrode into the transparent recording medium. Therefore, even if the adhesive layer can be removed from the transparent recording medium, this corrosion may cause a change in the properties of the recording medium, making it impossible to reuse the transparent recording medium. Furthermore, if a photopolymerization initiator is present in the adhesive layer, the adhesive layer may shrink in natural light, which may unintentionally deteriorate the recording medium containing the adhesive layer. In addition, there is a concern that the photopolymerization initiator may cause an odor in the printed material.

[0007] An object of the present invention is to provide a layer forming method, a substrate recycling method, and a printed matter manufacturing method that, by containing a photopolymerization initiator, are free from the problem of odor generation, suppress deterioration of printed matter, facilitate the reuse of substrates, and reduce risks to people and the environment. [Means for solving the problem]

[0008] (1) The present invention relates to a layer forming method, which includes a coating step of coating or discharging onto a substrate an aqueous composition containing water and a polymerizable compound that is soluble in water and undergoes a polymerization reaction upon irradiation with an electron beam, and a drying step of drying the aqueous composition coated or discharged onto the substrate. The aqueous composition does not contain a photopolymerization initiator that is excited by ultraviolet light. A peelable coating film layer made of the aqueous composition is formed on the substrate.

[0009] Even if the aqueous composition does not contain a photopolymerization initiator that is excited by ultraviolet light, workers can shrink the coating layer by irradiating it with an electron beam to polymerize the polymerizable compound. As a result, the adhesion of the coating layer to the substrate decreases, allowing workers to peel the coating layer from the substrate and reuse the substrate. Since the peelable coating layer is a coating layer of an aqueous composition, risks to people and the environment can be reduced. Moreover, even when a coating layer is formed on a hydrophobic substrate such as plastic, the adhesion between the coating layer and the substrate can be appropriately controlled, reducing excessive adhesion. Therefore, in the recycling process after printing on a substrate using this layer formation method, the coating layer can be easily peeled from the substrate by irradiating the coating layer with an electron beam. This facilitates reuse of the substrate. Furthermore, changes in the properties of the substrate caused by the inclusion of a photopolymerization initiator are suppressed, thereby improving the reusability of the substrate after peeling the coating layer from the substrate. Therefore, printing on a wide variety of substrates, including plastics, is possible, improving recyclability after printing. Since the aqueous composition does not contain a photopolymerization initiator excited by ultraviolet light, the odor of the printed material after drying, which occurs when a photopolymerization initiator is included, is suppressed. Furthermore, since the aqueous composition does not contain a photopolymerization initiator excited by ultraviolet light, the coating layer does not shrink due to natural light after drying, so deterioration of the printed material is suppressed compared to when a photopolymerization initiator is included in the aqueous composition. When the polymerizable compound polymerizes by irradiation with an electron beam, no heat is generated, so damage to the substrate is suppressed. Since electron beams have higher transparency than ultraviolet light, they easily polymerize the polymerizable compound even when the coating layer is thick.

[0010] (2) In the coating step, the aqueous composition may be ejected onto the substrate using an inkjet head.

[0011] The coating layer can be easily formed on the substrate.

[0012] (3) The coating layer may be a printed layer.

[0013] Since the printed layer is formed by forming a coating layer on the substrate, it is possible to reduce the amount of excess coating layer. In addition, since the coating layer can be formed locally, it is possible to reduce traces of the aqueous composition remaining.

[0014] (4) The aqueous composition may be an aqueous ink containing a coloring material, and the coating step may be a printing step of coating or ejecting the aqueous ink onto the substrate.

[0015] Because the aqueous composition is an aqueous ink containing a colorant, the coating step serves to perform printing using the aqueous ink. Therefore, an image is formed by forming a coating layer on the substrate, making printing easier than when an image formation step is performed after a step of forming a coating layer on the surface of the substrate. Furthermore, during recycling, the aqueous composition is peeled from the substrate by electron beam irradiation, thereby removing the aqueous ink from the substrate. Therefore, a highly environmentally friendly layer formation method can be provided that shortens printing time while enabling substrate recycling.

[0016] (5) The layer forming method may further include a printing step of discharging or applying a printing ink onto the coating layer applied or discharged onto the substrate. The drying step may be performed after the printing step or between the application step and the printing step.

[0017] In the printing process, the aqueous composition serves as a base for printing with printing ink. During recycling, the aqueous composition also serves to remove the printing ink layer from the substrate by being peeled off from the substrate together with the printing ink layer by electron beam irradiation. This provides an environmentally friendly layer formation method that enables the substrate to be recycled.

[0018] (6) The aqueous composition may contain a binder resin that forms the coating layer. The drying step may be a step of drying the aqueous composition applied or discharged onto the substrate in the application step at a temperature in the range of 50°C to 220°C.

[0019] In the drying step, the film-forming properties of the binder resin in the aqueous composition are improved, and the adhesion of the aqueous composition to the substrate can be improved.

[0020] (7) The aqueous composition may contain a binder resin that forms the coating layer. The drying step may be a step of drying the aqueous composition applied or discharged onto the substrate in the application step at a temperature in the range of 50°C to 150°C.

[0021] In the drying step, the film-forming properties of the binder resin in the aqueous composition are improved, and the adhesion of the aqueous composition to the substrate can be improved.

[0022] (8) The aqueous composition contains a binder resin that forms the coating layer, and may be in the form of an emulsion in which the binder resin is dispersed in the water.

[0023] When the aqueous composition is dried in the drying step, the binder resin is more likely to be uniformly fixed to the substrate.

[0024] (9) The substrate may be an impermeable substrate.

[0025] When the coating step is carried out, the binder resin of the aqueous composition is prevented from penetrating into the substrate, and therefore, in the recycling process of a printed matter formed by the above-mentioned layer formation method, the coating layer can be easily removed by irradiating the printed matter with an electron beam.

[0026] (10) The substrate may be a transparent substrate.

[0027] When the coating step is carried out, the binder resin of the aqueous composition is prevented from penetrating into the transparent substrate, and therefore, in the recycling process of a printed matter formed by the above-mentioned layer formation method, the coating layer can be easily removed by irradiating the printed matter with an electron beam.

[0028] (11) The present invention relates to a substrate recycling method, which includes an irradiation step of irradiating the coating layer formed by the layer forming method with an electron beam at a dose in the range of 1 to 150 kGy.

[0029] The polymerizable compound present in the coating layer on the substrate undergoes a polymerization reaction, causing the coating layer to shrink, thereby reducing the adhesion of the coating layer to the substrate. This allows the coating layer to be easily peeled off from the substrate, making it possible to easily recycle the substrate. Furthermore, compared to conventional methods of recycling substrates using physical or chemical methods, damage to the substrate during the recycling process can be suppressed, increasing the number of times the substrate can be reused.

[0030] (12) The present invention relates to a substrate recycling method, which includes an irradiation step of irradiating the coating layer formed by the layer forming method with an electron beam at a dose in the range of 30 to 100 kGy.

[0031] The polymerizable compound present in the coating layer on the substrate undergoes a polymerization reaction, causing the coating layer to shrink, thereby reducing the adhesion of the coating layer to the substrate. This allows the coating layer to be easily peeled off from the substrate, making it possible to easily recycle the substrate. Compared to conventional methods of recycling substrates using physical or chemical methods, this method can reduce damage to the substrate during the recycling process, thereby increasing the number of times the substrate can be reused.

[0032] (13) The irradiation step may be a step of irradiating the surface of the substrate on which the coating layer is formed with the electron beam.

[0033] Since the electron beam is likely to hit the polymerizable compound present in the coating layer, the polymerization reaction of the polymerizable compound is likely to proceed, which makes the coating layer more likely to shrink, thereby improving the releasability of the coating layer from the substrate.

[0034] (14) The irradiation step may be a step of irradiating the surface of the substrate on which the coating layer is formed with the electron beam.

[0035] Since the electron beam is likely to hit the polymerizable compound present in the coating layer, the polymerization reaction of the polymerizable compound is likely to proceed, which makes the coating layer more likely to shrink, thereby improving the releasability of the coating layer from the substrate.

[0036] (15) In the irradiation step, the electron beam may be irradiated onto the back surface of the substrate opposite to the surface on which the coating layer is formed.

[0037] The coating layer can be shrunk by polymerizing the polymerizable compound present in the coating layer while suppressing deterioration of the surface of the substrate on which the coating layer is formed.

[0038] (16) In the irradiation step, the electron beam may be irradiated onto the back surface of the substrate opposite to the surface on which the coating film layer is formed.

[0039] The coating layer can be shrunk by polymerizing the polymerizable compound present in the coating layer while suppressing deterioration of the surface of the substrate on which the coating layer is formed.

[0040] (17) The present invention relates to a method for producing a printed matter, which includes a coating step of coating or discharging onto a substrate an aqueous composition containing water and a polymerizable compound that is soluble in water and undergoes a polymerization reaction upon irradiation with an electron beam, and a drying step of drying the aqueous composition coated or discharged onto the substrate. The aqueous composition does not contain a photopolymerization initiator that is excited by ultraviolet light. A peelable printed layer made of the aqueous composition is formed on the substrate.

[0041] Even if the aqueous composition does not contain a photopolymerization initiator that is excited by ultraviolet light, workers can shrink the coating layer by irradiating the coating layer with an electron beam to polymerize the polymerizable compound. As a result, the adhesion of the printed layer to the substrate decreases, allowing workers to peel the printed layer from the substrate and reuse the substrate. Because the peelable printed layer is formed from an aqueous composition, risks to people and the environment can be reduced. Moreover, even when a printed layer is formed on a hydrophobic substrate such as plastic, the adhesion between the printed layer and the substrate can be appropriately controlled, reducing excessive adhesion. Therefore, during the recycling process after forming a printed layer on a substrate using this printed matter production method, the printed layer can be easily peeled from the substrate by irradiating the printed layer with an electron beam. This facilitates reuse of the substrate. Furthermore, since changes in the properties of the substrate caused by the inclusion of a photopolymerization initiator can be suppressed, the reusability of the substrate after peeling the printed layer from the substrate can be improved. Therefore, printing on a wide variety of substrates, including plastics, can be performed, improving recyclability after printing. Since the aqueous composition does not contain a photopolymerization initiator excited by ultraviolet light, the odor of the printed material after drying, which is caused by the inclusion of a photopolymerization initiator, is suppressed. Furthermore, since the aqueous composition does not contain a photopolymerization initiator excited by ultraviolet light, the printed layer does not shrink after drying due to natural light, and deterioration of the printed material is suppressed compared to when a photopolymerization initiator is included in the aqueous composition. Since no heat is generated when the polymerizable compound polymerizes upon irradiation with electron beams, damage to the substrate is suppressed. Because electron beams are more transparent than ultraviolet light, they easily polymerize the polymerizable compound even when the printed layer is thick. The phrase "forming a peelable printed layer on a substrate using an aqueous composition containing a polymerizable compound and water" includes both a form in which the aqueous composition contains a colorant and a printed layer of the aqueous composition is formed on the substrate, and a form in which a coating layer of an aqueous composition not containing a colorant is formed on the substrate, a colorant layer of an ink containing a colorant is formed on the coating layer, and a printed layer consisting of the coating layer and the colorant layer is formed on the substrate.

[0042] (18) The aqueous composition may contain a binder resin and may be in the form of an emulsion in which the binder resin is dispersed in the water.

[0043] When the aqueous composition is dried in the drying step, the binder resin is more likely to be uniformly fixed to the substrate.

[0044] (19) The substrate may be an impermeable transparent substrate.

[0045] During the printing process, the aqueous composition can be prevented from penetrating into the transparent substrate, and during the subsequent recycling process, the aqueous composition can be easily removed by irradiating the printed matter produced by this printed matter production method with an electron beam. [Effects of the Invention]

[0046] The layer forming method, substrate recycling method, and printed matter manufacturing method according to the present invention contain a photopolymerization initiator, which eliminates the problem of odor generation, suppresses deterioration of printed matter, makes it easy to reuse the substrate, and reduces risks to people and the environment. [Brief explanation of the drawings]

[0047] [Figure 1] FIG. 1 is a simplified structural diagram of an image recording apparatus 10 in which a layer forming method according to one embodiment of the present invention is used. [Figure 2] FIG. 2 is a schematic diagram of a coating layer 7 formed on the upper surface 6a of a sheet 6 by a layer forming method according to one embodiment of the present invention. [Figure 3] Figure 3 is a diagram illustrating how the adhesion between the coating layer 7 and the sheet 6 is reduced when an electron beam is irradiated onto the printed matter 9 using a substrate recycling method according to one embodiment of the present invention. [Figure 4] FIG. 4 is a schematic diagram of a coating layer 12 and a color material layer 11 formed by a layer forming method according to a modified example of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0048] A preferred embodiment of the present invention will be described below. It should be noted that this embodiment is merely one example of the present invention, and it goes without saying that the example can be modified without departing from the spirit and scope of the present invention.

[0049] [Internal configuration of image recording device 10] 1, an image recording device 10 used in the layer forming method and printed matter producing method according to the present invention includes a supply roll 23, multiple transport shafts 26, a web cleaner 27, a tension control 28, a recording unit 29, a heater 35, a tension control 36, and a rewinder 24 in a housing (not shown). The image recording device 10 records an image on a sheet 6.

[0050] The sheet 6 is an example of a substrate. The sheet 6 is a sheet cut to a predetermined size. The sheet 6 is a transparent, impermeable substrate. The impermeable substrate is a substrate having a surface with low water permeability. Specifically, the impermeable substrate is a substrate having a low water permeability within 30 msec from the start of contact in the Bristow method. 1 / 2 Water absorption up to 10mL / m 2 The term "impermeable" refers to a substrate that is less than or equal to 0.5%. Furthermore, "impermeable or low-permeable" may refer to a water absorption rate of less than 0.2% over 24 hours measured in accordance with ASTM D570. More specifically, "impermeable" refers to a water absorption rate of less than 0.2%, and "low-permeable" refers to a water absorption rate of 0.2% or more but less than 0.5%. The "%" unit of water absorption is based on mass. Examples of materials for transparent impermeable substrates include plastics (e.g., polypropylene, polyethylene, polyethylene terephthalate, polyvinyl chloride resin, polycarbonate, etc.). The transparent impermeable substrate is preferably in the form of a film or a plate. The impermeable substrate does not have to be transparent.

[0051] The sheet 6 may be a permeable substrate. In this case, the sheet 6 may be one that is pulled out from a roll wound into a cylindrical shape, or may be a fanfold type. Examples of permeable substrates include plain paper and coated paper. "Coated paper" refers to plain paper made of pulp, such as high-quality printing paper or medium-quality printing paper, to which a coating agent has been applied in order to improve smoothness, whiteness, gloss, etc., and specific examples include high-quality coated paper and medium-quality coated paper.

[0052] The supply roll 23 is located at the bottom of the housing. The sheet 6 is wound around the supply roll 23. The supply roll 23 is rotated by a motor (not shown). The rotating supply roll 23 feeds the sheet 6 to a plurality of conveying shafts 26.

[0053] The plurality of conveying shafts 26 are rotated by a motor (not shown). The rotating plurality of conveying shafts 26 convey the sheet 6 sent out from the supply roll 23.

[0054] The web cleaner 27 is located upstream of the recording unit 29 in the conveying direction of the sheet 6. The web cleaner 27 includes a rubber roller 27A and an adhesive roller 27B. The web cleaner 27 captures dust adhering to the sheet 6 with the rubber roller 27A and transfers it to the adhesive roller 27B, thereby cleaning the sheet 6.

[0055] The tension control 28 is located upstream of the recording unit 29 in the conveying direction of the sheet 6. The tension control 28 adjusts the tension applied to the sheet 6.

[0056] The recording unit 29 has a print head 34 (an example of an inkjet head) and a print head 33. The print head 34 is located downstream of the tension control 28 in the conveyance direction of the sheet 6. The print head 34 may be a so-called serial head or a so-called line head. The print head 34 has an internal flow path through which the aqueous composition described below flows. The flow path is connected to a tank by a tube. In other words, the aqueous composition stored in the tank is supplied to the print head 34 through the tube. The print head 33 is located downstream of the print head 34 in the conveyance direction of the sheet 6. The print head 33 has inkjet heads for four colors: cyan, magenta, yellow, and black.

[0057] The heater 35 is located downstream of the print head 33 in the conveyance direction of the sheet 6. The heater 35 is a so-called halogen heater. The heater 35 has a halogen lamp, which is a heating element that radiates infrared rays, a reflector, and a housing. Heat from the halogen lamp and reflector is radiated to the outside or blocked through openings in the housing.

[0058] The heater 35 heats at least one of the sheet 6 passing near the heater 35 and the aqueous composition attached to the sheet 6. In this embodiment, the heater 35 heats both the sheet 6 and the aqueous composition. By heating the aqueous composition, the binder resin (described below) in the aqueous composition softens, forming the coating layer 7 shown in FIG. 2 on the sheet 6. Then, the sheet 6 and coating layer 7 passing near the heater 35 cool, solidifying the coating layer 7. This fixes the coating layer 7 to the sheet 6. The heater 35 is not limited to a halogen heater, as long as it can heat the sheet 6 or the aqueous composition. For example, the heater 35 may be a carbon heater, a dryer, an oven, a belt conveyor oven, or the like.

[0059] The tension control 36 is located downstream of the heater 35 in the conveying direction of the sheet 6. The tension control 36 adjusts the tension applied to the sheet 6.

[0060] The rewinder 24 is located at the most downstream side of the conveying path and winds up the sheet 6 conveyed by a plurality of conveying shafts 26.

[0061] [Composition of aqueous composition] The aqueous composition will be described in detail below. The aqueous composition contains a polymerizable compound, a binder resin, a colorant, an organic solvent, a surfactant, and water. The aqueous composition does not contain a photopolymerization initiator that is excited by ultraviolet light. Some photopolymerization initiators produce odors and migration, and this is to avoid these odor and migration problems. Furthermore, this is to prevent the polymerizable compound contained in the coating layer 7 from undergoing a polymerization reaction due to natural light, which could cause the coating layer 7 to peel off from the sheet 6. The aqueous composition is an aqueous ink in which a polymerizable compound, a binder resin, a colorant, and an organic solvent are dissolved in water.

[0062] The polymerizable compound is a water-soluble compound that undergoes a polymerization reaction upon irradiation with an electron beam. The polymerizable compound is in a state of being dissolved in water. The state in which the polymerizable compound is dissolved in water refers to a state in which 1 wt % or more of the polymerizable compound is dissolved in 100 g of water. Examples of the polymerizable compound include N,N'-1,2-ethanediylbis{N-[2-(acryloylamino)ethyl]acrylamide}, N,N'-(((2-acrylamido-2((3-(buta-1,3-diene-2-ylamino)propoxy-1,3-diyl)bis(oxy))bis(propane-3,1-diyl))diacrylamide, N,N-bis(2-acrylamidoethyl)acrylamide, N,N'-{oxybis(2,1-ethanediyloxy-3,1-propanediyl)}bis Acrylamide, 4-[(3-methacrylamidopropyl)dimethylammonio]butane-1-sulfonic acid, 2-(methacryloyloxy)ethyl 2-(trimethylammonio)ethyl phosphate, polyethylene glycol dimethacrylate, N-isopropylacrylamide, hydroxypropyl methacrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, N-vinylacetamide, N-methoxymethylmethacrylamide, bisphenol A ethylenediamine oxide adduct diacrylate, polyethylene glycol monomethyl ether methacrylate, 2-hydroxy-3-phenoxypropyl acrylate, etc. Among these, N,N'-1,2-ethanediylbis{N-[2-(acryloylamino)ethyl]acrylamide}, N,N'-(((2-acrylamido-2((3-(buta-1,3-dien-2-ylamino)propoxy-1,3-diyl)bis(oxy))bis(propanol), etc., which have two or more acrylamide functional groups, are preferred. Preferred are N,N-bis(2-propanediyloxy-3,1-propanediyl)diacrylamide, N,N'-{oxybis(2,1-ethanediyloxy-3,1-propanediyl)}bisacrylamide, N,N'-bis(2-propanediyloxy-3,1-propanediyl)diacryl ...

[0063] The binder resin is used to fix the coating layer 7 made of the aqueous composition to the sheet 6. For example, commercially available products can be used as the binder resin. The binder resin may contain, for example, styrene, vinyl chloride, or the like as a monomer. The binder resin may be dissolved in the aqueous composition or may be in the form of an emulsion in which the binder resin is dispersed as resin particles. These binder resins can be used alone or in combination of two or more. Examples of binder resins include acrylic acid-based resins, maleic acid-based ester resins, vinyl acetate-based resins, carbonate-based resins, polycarbonate-based resins, styrene-based resins, ethylene-based resins, polyethylene-based resins, propylene-based resins, polypropylene-based resins, urethane-based resins, polyurethane-based resins, polyester-based resins, and copolymer resins thereof.

[0064] The binder resin may be, for example, a resin having a glass transition temperature (Tg) in the range of -30°C to 200°C. More preferably, the glass transition temperature (Tg) is -30°C to 180°C, and even more preferably, -30°C to 150°C.

[0065] The emulsion may be, for example, a commercially available product. Examples of commercially available products include "Superflex (registered trademark) 870" (Tg: 71°C) and "Superflex (registered trademark) 150" (Tg: 40°C) manufactured by Daiichi Kogyo Seiyaku Co., Ltd., "Mowinyl (registered trademark) 6760" (Tg: -28°C) and "Mowinyl (registered trademark) DM774" (Tg: 33°C) manufactured by Japan Coating Resins Co., Ltd., "Polysol (registered trademark) AP-3270N" (Tg: 27°C) manufactured by Showa Denko K.K., and "Hi-Loss-X (registered trademark) KE-1062" (Tg: 112°C) and "Hi-Loss-X (registered trademark) QE-1042" (Tg: 69°C) manufactured by Seiko PMC Corporation.

[0066] The average particle diameter of the binder resin is, for example, in the range of 30 nm to 200 nm. The average particle diameter can be measured as an arithmetic mean diameter using, for example, a dynamic light scattering particle size distribution analyzer "LB-550" manufactured by Horiba, Ltd.

[0067] The content (R) of the binder resin in the total amount of ink is, for example, preferably in the range of 0.1 wt% to 30 wt%, more preferably in the range of 0.5 wt% to 20 wt%, and particularly preferably in the range of 1.0 wt% to 15.0 wt%. One type of binder resin may be used alone, or two or more types may be used in combination.

[0068] The colorant is a pigment that can be dispersed in water using, for example, a pigment dispersing resin (resin dispersant). Examples of colorants include carbon black, inorganic pigments, and organic pigments. Examples of carbon black include furnace black, lamp black, acetylene black, and channel black. Examples of inorganic pigments include titanium oxide, iron oxide-based inorganic pigments, and carbon black-based inorganic pigments. Examples of organic pigments include azo pigments such as azo lake, insoluble azo pigment, condensed azo pigment, and chelate azo pigment; polycyclic pigments such as phthalocyanine pigments, perylene and perinone pigments, anthraquinone pigments, quinacridone pigments, dioxazine pigments, thioindigo pigments, isoindolinone pigments, and quinophthalone pigments; dye lake pigments such as basic dye lake pigments and acid dye lake pigments; nitro pigments; nitroso pigments; and aniline black daylight fluorescent pigments.

[0069] The solid content of the colorant in the total amount of ink is not particularly limited and can be appropriately determined depending on, for example, the desired optical density or saturation. The solid content of the colorant is, for example, preferably in the range of 0.1 wt% to 20.0 wt%, more preferably in the range of 1.0 wt% to 15.0 wt%. The solid content of the colorant is the weight of the pigment only and does not include the weight of the binder resin. One type of colorant may be used alone, or two or more types may be used in combination.

[0070] The organic solvent is a solvent that is uniformly mixed with water when mixed at a 1:1 ratio. There are no particular limitations on the organic solvent, and any organic solvent can be used. Examples of the organic solvent include propylene glycol, ethylene glycol, 1,2-butanediol, propylene glycol propyl ether, dipropylene glycol propyl ether, diethylene glycol monobutyl ether, and 1,6-hexanediol, with propylene glycol or 1,2-butanediol being preferred. Examples of other organic solvents include alkyl alcohols having 1 to 4 carbon atoms, such as methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, sec-butyl alcohol, and tert-butyl alcohol; alkylene glycols having an alkylene group containing 2 to 6 carbon atoms, such as ethylene glycol, propylene glycol, butylene glycol, triethylene glycol, 1,2,6-hexanetriol, thiodiglycol, hexylene glycol, and diethylene glycol; glycerin, ethylene glycol monomethyl (or ethyl, propyl, or butyl) ether, diethylene glycol monomethyl (or ethyl, propyl, or butyl) ether, lower alkyl ethers of alkylene glycols such as ethylene glycol monomethyl (or ethyl, propyl, butyl, hexyl) ether, triethylene glycol monomethyl (or ethyl, propyl, butyl, hexyl) ether, tetraethylene glycol monomethyl (or ethyl, propyl, butyl, hexyl) ether, propylene glycol monomethyl (or ethyl, propyl, butyl) ether, dipropylene glycol monomethyl (or ethyl, propyl, butyl) ether, tripropylene glycol monomethyl (or ethyl, propyl, butyl) ether, and tetrapropylene glycol monomethyl (or ethyl) ether; N-methyl-2-pyrrolidone, 2-pyrrolidone, and 1,3-dimethyl-2-imidazolidinone.

[0071] The content of the organic solvent in the total amount of ink is, for example, preferably in the range of 1 wt % to 70 wt %, and more preferably in the range of 3 wt % to 50 wt %.

[0072] The water is preferably ion-exchanged water or pure water. The water content of the total ink is, for example, preferably in the range of 15 wt% to 95 wt%, more preferably in the range of 25 wt% to 85 wt%. The water content may be, for example, the remainder of the other components.

[0073] The aqueous composition may further contain conventionally known additives as needed. Examples of additives include surfactants, pH adjusters, viscosity adjusters, surface tension adjusters, preservatives, antifungals, leveling agents, antifoaming agents, light stabilizers, antioxidants, nozzle drying inhibitors, polymer components such as emulsions, and dyes. The surfactant may further contain a nonionic surfactant. Commercially available nonionic surfactants may be used. Examples of commercially available nonionic surfactants include "Olfine (registered trademark) E1010," "Olfine (registered trademark) E1006," and "Olfine (registered trademark) E1004" manufactured by Nissin Chemical Industry Co., Ltd. The content of the nonionic surfactant in the total amount of ink is, for example, 5 wt% or less, 3 wt% or less, or 0.1 wt% to 2 wt%. Examples of viscosity adjusters include polyvinyl alcohol, cellulose, and water-soluble resins.

[0074] The aqueous composition can be prepared, for example, by uniformly mixing a polymerizable compound, a binder resin, a colorant, an organic solvent, water, and, if necessary, other additives, using a conventionally known method, and then removing insoluble matter using a filter or the like.

[0075] Next, a layer forming method and a printed matter producing method using the image recording device 10 will be described. In the layer forming method and the printed matter producing method, a coating step and a drying step are carried out in this order. In the following, reference will be made to FIGS. 1 and 2.

[0076] In the coating step, the aqueous composition is ejected onto the sheet 6. Specifically, in the coating step, a printing step is carried out in which the aqueous composition is ejected as droplets from the print head 34 toward the upper surface 6a of the sheet 6, the tension of which has been adjusted by the tension control 28. Note that in the coating step, the aqueous composition may be applied to the sheet 6.

[0077] After the application process, a drying process is performed. In the drying process, the aqueous composition dispensed onto the sheet 6 is dried. Specifically, in the drying process, both the sheet 6 and the aqueous composition passing below the opening 43 of the heater 35 are dried by radiant heat from the heater 35. The drying temperature is in the range of 40°C to 230°C. More preferably, the drying temperature is in the range of 50°C to 220°C. Particularly preferably, the drying temperature is in the range of 50°C to 150°C. When the drying process is performed, the binder resin of the aqueous composition softens and forms a film, thereby forming a coating layer 7 (an example of a printed layer) on the upper surface 6a of the sheet 6. The coating layer 7 is composed of a transparent clear layer made of the binder resin and a colorant. Thereafter, the sheet 6 and the coating layer 7 cool, solidifying the coating layer 7. As a result, the coating layer 7 is fixed to the upper surface 6a of the sheet 6, as shown in FIG. 2. The coating layer 7 contains a polymerizable compound. The drying process may be omitted.

[0078] In this disclosure, "printing" refers to the reproduction of letters, pictures, photographs, etc. by selectively applying or discharging ink. "Printing" includes not only so-called inkjet printing, but also screen printing, etc. "Printed layer" refers to a layer formed by selectively applying or discharging ink.

[0079] Next, a substrate recycling method for peeling off the coating layer 7 from the printed matter 9 (see FIG. 3) produced by the above-described layer forming method and printed matter production method will be described. The substrate recycling method is carried out when recycling the sheet 6 after the printed matter 9 has been produced by the above-described layer forming method and printed matter production method. In the substrate recycling method, an irradiation step is carried out.

[0080] In the irradiation process, as shown in FIG. 3 , an electron beam is irradiated onto the upper surface 6a (an example of a surface) of the sheet 6 on which the coating layer 7 is formed. An electron beam is a stream of numerous electrons that, when impinging on a substance, emit secondary electrons or X-rays, and exhibit diffraction, fluorescence, ionization, photographic effects, and the like. When the electron beam irradiation device 115 irradiates the upper surface 6a of the sheet 6 on which the coating layer 7 is formed with an electron beam, the polymerizable compound contained in the coating layer 7 undergoes a polymerization reaction. As a result, the coating layer 7 shrinks, reducing the adhesion between the coating layer 7 and the sheet 6, and the coating layer 7 can easily peel off from the sheet 6.

[0081] The electron beam irradiated to shrink the coating layer 7 has a dose of, for example, 1 kGy to 150 kGy. Preferably, the electron beam has a dose of 10 kGy to 150 kGy. More preferably, the electron beam has a dose of 30 kGy to 100 kGy. Even more preferably, the electron beam has a dose of 50 kGy to 100 kGy. The dose refers to the absorbed dose (kGy), which represents the amount of energy absorbed by a substance per unit mass by irradiation with radiation. For example, an absorbed dose of 1 J of energy absorbed per 1 kg is 1 Gy.

[0082] The electron beam irradiation device for irradiating the electron beam is not particularly limited as long as it can irradiate an electron beam at a specific dose. Known electron beam irradiation devices can be used. For example, a curtain-type electron irradiation device (LB1023, manufactured by i-Electron Beam Co., Ltd.) or a line-irradiation-type low-energy electron beam irradiation device (EB-ENGINE, manufactured by Hamamatsu Photonics K.K.) can be suitably used.

[0083] The oxygen concentration in the electron beam irradiation apparatus is preferably 500 ppm or less, more preferably 300 ppm or less, and even more preferably 100 ppm or less. By performing electron beam irradiation under such conditions, it is possible to suppress the generation of ozone and also to prevent the radicals generated by electron beam irradiation from being deactivated by oxygen in the atmosphere. Such conditions can be achieved, for example, by creating an inert gas (nitrogen, argon, etc.) atmosphere inside the electron beam irradiation apparatus.

[0084] [Effects of the embodiment] In the layer formation method and the printed matter production method, the coating layer 7 formed on the upper surface 6a of the sheet 6 contains a polymerizable compound that initiates a polymerization reaction upon irradiation with an electron beam. Therefore, even if the coating layer 7 does not contain a photopolymerization initiator that is excited by ultraviolet light, workers can irradiate the coating layer 7 with an electron beam to shrink the coating layer 7. As a result, the adhesion of the coating layer 7 to the sheet 6 decreases, allowing workers to peel the coating layer 7 from the sheet 6 and reuse the sheet 6. Because the peelable coating layer 7 is an aqueous composition, risks to humans and the environment are reduced. Moreover, even if the coating layer 7 is formed on a hydrophobic sheet 6 such as plastic, the adhesion between the coating layer 7 and the sheet 6 can be appropriately controlled, reducing excessive adhesion. Therefore, during the recycling process after printing on the sheet 6 using the layer formation method and the printed matter production method, the coating layer 7 can be easily peeled off from the sheet 6 by irradiating the coating layer 7 with an electron beam. This facilitates reuse of the sheet 6. Furthermore, because the inclusion of a photopolymerization initiator can suppress changes in the properties of the sheet 6, the reusability of the sheet 6 after the coating layer 7 is peeled off from the sheet 6 can be improved. This allows printing on a wide variety of substrates, including plastics, improving post-printing recyclability. The absence of a UV-excited photopolymerization initiator in the coating layer 7 suppresses odors in the printed matter 9 after drying. The absence of a UV-excited photopolymerization initiator in the dried coating layer 7 also prevents the dried coating layer 7 from shrinking under natural light, suppressing deterioration of the printed matter 9. Since no heat is generated when the polymerizable compound polymerizes upon irradiation with electron beams, damage to the sheet 6 is suppressed. Because electron beams have higher transmittance than UV rays, they easily polymerize the polymerizable compound even when the coating layer 7 is thick.

[0085] In the above-described layer forming method and printed matter producing method, the aqueous composition is ejected onto the sheet 6 by the print head 34, so that the coating layer 7 can be easily formed on the sheet 6.

[0086] In the above-described layer forming method and the above-described method for producing a printed matter, the printed layer is formed by forming the coating layer 7 on the sheet 6, so that it is possible to reduce the amount of excess coating layer. In addition, because the coating layer can be formed locally, it is possible to reduce traces of the aqueous composition remaining.

[0087] In the layer forming method and the printed matter producing method, the aqueous composition is dried after the coating step of ejecting the aqueous composition onto the sheet 6, so that the aqueous composition is easily fixed to the sheet 6. Therefore, the aqueous composition has high adhesion to the sheet 6.

[0088] In the above-described layer formation method and printed matter production method, the aqueous composition is an aqueous ink containing a colorant, and therefore the coating step serves to perform printing using the aqueous ink. Therefore, an image is formed by forming a coating layer 7 on the sheet 6, making printing easier than when a printing step for forming an image is performed after a process including a coating step and a drying step. Furthermore, during recycling, the aqueous composition is peeled from the sheet 6 by electron beam irradiation, thereby removing the aqueous ink from the sheet 6. This provides an environmentally friendly layer formation method that shortens printing time while enabling the sheet 6 to be recycled.

[0089] In the above layer formation method and the above printed matter manufacturing method, when the aqueous composition ejected onto the sheet 6 in the coating process is dried at a temperature in the range of 50°C to 220°C in the drying process, the binder resin in the aqueous composition has high film-forming properties, and therefore the aqueous composition has high adhesion to the sheet 6.

[0090] In the above-described layer forming method and printed matter manufacturing method, when the aqueous composition ejected onto the sheet 6 in the coating step is dried in the drying step at a temperature in the range of 50°C to 150°C, the binder resin in the aqueous composition has high film-forming properties, and therefore the aqueous composition has high adhesion to the sheet 6. Furthermore, because the temperature at which the sheet 6 is dried in the drying step is 150°C or lower, damage to the sheet 6 is suppressed.

[0091] In the above layer formation method and the above printed matter production method, the aqueous composition is in an emulsion state in which the binder resin is dispersed in water, so when the aqueous composition is dried in the drying process, the binder resin is easily fixed uniformly to the sheet 6.

[0092] In the layer formation method and the printed matter production method, the sheet 6 is an impermeable substrate, and therefore, when the coating step is carried out, the binder resin of the aqueous composition is inhibited from permeating into the sheet 6. Therefore, in the recycling process after the printed matter 9 is produced by the layer formation method and the printed matter production method, the coating layer 7 can be easily removed by irradiating the printed matter 9 with an electron beam.

[0093] In the layer formation method and the printed matter production method, the sheet 6 is a transparent substrate, and therefore, when the coating step is carried out, the binder resin of the aqueous composition is prevented from penetrating into the sheet 6. Therefore, in the recycling process after the printed matter 9 is produced by the layer formation method and the printed matter production method, the coating layer 7 can be easily removed by irradiating the printed matter 9 with an electron beam.

[0094] In the above-mentioned layer forming method and the above-mentioned method for producing a printed matter, N,N'-1,2-ethanediylbis{N-[2-(acryloylamino)ethyl]acrylamide}, N,N'-(((2-acrylamido-2((3-(buta-1,3-dien-2-ylamino)propoxy-1,3-diyl)bis(oxy))bis(propane-3,1-diyl))diacrylamide, N,N-bis(2-acrylamidoethyl)acrylamide, N,N'-{oxybis(2,1-ethanediyloxy-3,1-propanediyl)}bisacrylamide When an amide is used as the polymerizable compound, the coating layer 7 exhibits high peelability from the sheet 6 when irradiated with an electron beam. This is because these four polymerizable compounds have an acrylamide functional group and two or more functional groups. In other words, the greater the number of functional groups in the polymerizable compound, the greater the number of sites for polymerization reaction, and the greater the shrinkage of the coating layer 7 due to the polymerization reaction of the polymerizable compound in the coating layer 7. The greater the shrinkage of the coating layer 7, the greater the peelability of the coating layer 7 from the sheet 6.

[0095] In the above-described substrate recycling method, when the printed matter 9 formed by the above-described layer formation method is irradiated with an electron beam at a dose of 1 kGy to 150 kGy in the irradiation step, the polymerizable compound present in the coating layer 7 on the upper surface 6a of the sheet 6 undergoes a polymerization reaction, causing the coating layer 7 to shrink. As a result, the adhesion of the coating layer 7 to the sheet 6 decreases, and the coating layer 7 is easily peeled off from the sheet 6. This makes it possible to easily recycle the sheet 6. Compared to conventional methods of recycling the sheet 6 using physical or chemical methods, damage to the sheet 6 during the recycling process is suppressed, and the number of times the sheet 6 can be recycled can be increased.

[0096] In the above-described substrate recycling method, when the printed matter 9 formed by the above-described layer formation method is irradiated with an electron beam at a dose of 30 kGy or more and 100 kGy or less in the irradiation step, the polymerizable compound present in the coating layer 7 on the upper surface 6a of the sheet 6 undergoes a polymerization reaction, causing the coating layer 7 to shrink. As a result, the adhesion of the coating layer 7 to the sheet 6 decreases, and the coating layer 7 is easily peeled off from the sheet 6. This makes it possible to easily recycle the sheet 6. Compared to conventional methods of recycling the sheet 6 using physical or chemical methods, damage to the sheet 6 during the recycling process is suppressed, and the number of times the sheet 6 can be recycled can be increased.

[0097] In the above-described substrate recycling method, in the irradiation step, an electron beam is irradiated onto the upper surface 6a of the sheet 6 on which the coating layer 7 is formed. Therefore, the electron beam is likely to hit the polymerizable compound present in the coating layer 7, and the polymerization reaction of the polymerizable compound is likely to proceed. Therefore, the coating layer 7 is likely to shrink, and the coating layer 7 is easily peeled from the sheet 6.

[0098] [Variations] In the above-described layer forming method, a printing step is carried out in which the aqueous composition is ejected as droplets from the print head 34 onto the upper surface 6a of the sheet 6 in the coating step, but a printing step may also be carried out in which a printing ink is ejected onto the coating layer 7. In this case, the printing ink is ejected from the print head 33 onto the coating layer 7, and the aqueous ink serves as a base for printing with the printing ink. There are no particular restrictions on the printing ink, as long as it can form an image on the coating layer 7.

[0099] In this case, the drying step may be performed after the first printing step or after the second printing step. Alternatively, the drying step may be performed both after the first printing step and after the second printing step. For example, if the printing ink does not require a drying step, the drying step may be performed after the application or ejection of the aqueous composition, and then the printing step may be performed. On the other hand, if the printing ink requires a drying step, the drying step may be performed after the application or ejection of the aqueous composition and then the printing step, or the drying step may be performed after the application or ejection of the aqueous composition, and then the printing step may be performed, and then the drying step may be performed again.

[0100] Although the aqueous composition described above contains a colorant, the colorant may be omitted. In this case, a drying process may be performed after a colorant-free aqueous composition is applied to the sheet 6 in the coating process. A transparent coating layer 12 made of a binder resin is formed on the sheet 6. After the drying process, a printing process may be performed in which printing ink is ejected onto the coating layer 12. In this case, the colorant-free aqueous composition is ejected from a print head 34. The printing ink is ejected from a print head 33. The aqueous composition serves as a base for printing with the printing ink. The drying process may be performed after the coating process and the printing process. When the printing process is performed, a colorant layer 11 made of the colorant contained in the printing ink is formed on the upper surface 12a of the colorant-free transparent coating layer 12. Note that the sheet 6 is omitted from FIG. 4 for simplicity. In this case, the coating layer 12 and the colorant layer 11 form a printing layer. During recycling, the coating layer 12 is peeled off from the sheet 6 together with the color material layer 11 by electron beam irradiation, thereby removing the color material layer 11 from the sheet 6. This makes it possible to provide an environmentally friendly layer formation method that enables the sheet 6 to be recycled.

[0101] In the above-described substrate recycling method, in the irradiation step, the upper surface 6a of the sheet 6 on which the coating layer 7 is formed is irradiated with an electron beam, but the lower surface 6b (an example of a back surface) opposite to the upper surface 6a of the sheet 6 may also be irradiated with an electron beam. In this way, deterioration of the upper surface 6a of the sheet 6 on which the coating layer 7 is formed can be suppressed, while the coating layer 7 can be shrunk by the polymerization reaction of the polymerizable compound present in the coating layer 7.

[0102] In the above-described substrate recycling method, the upper surface 6a or the lower surface 6b of the sheet 6 on which the coating layer 7 is formed is irradiated with an electron beam in the irradiation step. However, it is sufficient if ionizing radiation including an electron beam is irradiated onto the upper surface 6a or the lower surface 6b on which the coating layer 7 is formed of the sheet 6. Examples of ionizing radiation include electron beams, α-rays, β-rays, neutron beams, proton beams, X-rays, and γ-rays, with electron beams being preferred. This is because electron beams are more directional than X-rays and γ-rays, which are electromagnetic waves among ionizing radiation, and have a higher absorbed dose rate (throughput). The absorbed dose rate (kGy / s) refers to the absorbed dose per unit time. [Example]

[0103] Examples of the present invention will be described below.

[0104] Example 1 The aqueous composition used contained 5.0 wt% N,N'1,2-ethanediylbis{N-[2-(acryloylamino)ethyl]acrylamide} as a polymerizable compound, 5.0 wt% Movinyl 6760 as a binder resin, 10.0 wt% propylene glycol as an organic solvent, and the remainder was ion-exchanged water as a solvent. The drying temperature in the drying step was 90°C. In the irradiation step, an electron beam was irradiated at a dose of 60 kGy onto the upper surface of the sheet on which the coating layer was formed.

[0105] Example 2 This example differs from Example 1 in that 5.0 wt % of Mowinyl 6960 (manufactured by Japan Coating Resin Co., Ltd.) is used as the binder resin. The other conditions are the same as those of Example 1.

[0106] Example 3 This example differs from Example 1 in that 5.0 wt % of Mowinyl 6901 (manufactured by Japan Coating Resin Co., Ltd.) was used as the binder resin. The other conditions were the same as those of Example 1.

[0107] Example 4 This example differs from Example 1 in that 5.0 wt % of Superflex 460 (manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.) is used as the binder resin. The other conditions are the same as those of Example 1.

[0108] Example 5 This example differs from Example 1 in that 5.0 wt % of Mowinyl 6800 (manufactured by Japan Coating Resin Co., Ltd.) is used as the binder resin. The other conditions are the same as those of Example 1.

[0109] Example 6 Example 6 differs from Example 1 in that black ink (LC3139 manufactured by Brother Industries, Ltd.) was further used. Other conditions were the same as those of Example 1. In Example 6, the aqueous composition was applied to a sheet (substrate) in the application step, and then a drying step was carried out. After the drying step, a printing step was carried out in which black ink was applied as a printing ink onto the coating layer.

[0110] Example 7 This example differs from Example 6 in that Mowinyl 6960 is used as the binder resin. The other conditions are the same as those of Example 6.

[0111] Example 8 This example differs from Example 1 in that 5.0 wt % of N,N'-(((2-acrylamide-2((3-(buta-1,3-diene-2-ylamino)propoxy-1,3-diyl)bis(oxy))bis(propane-3,1-diyl))diacrylamide was used as the polymerizable compound. The other conditions were the same as those of Example 1.

[0112] Example 9 This example differs from Example 8 in that 5.0 wt % of N,N-bis(2-acrylamidoethyl)acrylamide was used as the polymerizable compound. The other conditions were the same as those of Example 8.

[0113] Example 10 This example differs from Example 8 in that 5.0 wt % of N,N'-{oxybis(2,1-ethanediyloxy-3,1-propanediyl)}bisacrylamide was used as the polymerizable compound. The other conditions were the same as those of Example 8.

[0114] Example 11 This example differs from Example 1 in that the aqueous composition contains 1.0 wt% of N,N'1,2-ethanediylbis{N-[2-(acryloylamino)ethyl]acrylamide} as a polymerizable compound. The other conditions are the same as those of Example 1.

[0115] Example 12 This example differs from Example 11 in that the aqueous composition contains 2.5 wt% of N,N'1,2-ethanediylbis{N-[2-(acryloylamino)ethyl]acrylamide} as a polymerizable compound. The other conditions are the same as those of Example 11.

[0116] Example 13 This example differs from Example 11 in that the aqueous composition contains 10.0 wt% of N,N'1,2-ethanediylbis{N-[2-(acryloylamino)ethyl]acrylamide} as a polymerizable compound. The other conditions are the same as those of Example 11.

[0117] Example 14 This example differs from Example 11 in that the aqueous composition contains 40.0 wt% of N,N'1,2-ethanediylbis{N-[2-(acryloylamino)ethyl]acrylamide} as a polymerizable compound. The other conditions are the same as those of Example 11.

[0118] Example 15 This example differs from Example 1 in that the aqueous composition contains 1.0 wt% of N,N'1,2-ethanediylbis{N-[2-(acryloylamino)ethyl]acrylamide} as a polymerizable compound, and further contains 5.0 wt% of carbon black dispersion as a colorant and 0.5 wt% of Olfine E1010 as a surfactant. Other conditions were the same as those of Example 1. The carbon black pigment dispersion was prepared as follows: First, 40 g of Mitsubishi Chemical Corporation's carbon black "#2650" was mixed with 200 g of ion-exchanged water and pulverized in a bead mill. A carboxyl group agent was added to the mixture, and the mixture was heated and stirred for oxidation. Next, the resulting liquid was washed several times with a solvent, poured into water, washed again, and then filtered to obtain a carbon black pigment dispersion.

[0119] Example 16 This example differs from Example 1 in that the aqueous composition further contains 5.0 wt % of a carbon black dispersion as a coloring material. The other conditions are the same as those of Example 1.

[0120] Example 17 This example differs from Example 1 in that the aqueous composition further contains 5.0 wt% of carbon black dispersion as a coloring material and 0.5 wt% of Olfine E1010 as a surfactant. The other conditions are the same as those of Example 1.

[0121] Example 18 This example differs from Example 1 in that the dose of the electron beam irradiated in the irradiation step is 10 kGy. The other conditions are the same as those in Example 1.

[0122] Example 19 This example differs from Example 1 in that the dose of the electron beam irradiated in the irradiation step is 30 kGy. The other conditions are the same as those in Example 1.

[0123] Example 20 This example differs from Example 1 in that the electron beam is irradiated onto the lower surface of the sheet in the irradiation step. The other conditions are the same as those in Example 1.

[0124] (Comparative Example 1) This example differs from Example 1 in that the aqueous composition further contains 1.0 wt % of lithium phenyl-2,4,6-trimethylbenzoylphosphinate as a photopolymerization initiator excited by ultraviolet light, and in that no irradiation step was performed. Other conditions were the same as those of Example 1.

[0125] (Comparative Example 2) This example differs from Example 1 in that in the irradiation step, ultraviolet light with a peak wavelength of 395 nm was irradiated onto the top surface of the coating layer for 10 seconds. The other conditions were the same as those of Example 1. A UV-LED light [UV-LED series for printing E075Z HC (manufactured by Ushio Inc.), 395 nm] was used as the ultraviolet irradiation device for irradiating ultraviolet light.

[0126] (Comparative Example 3) This example differs from Example 1 in that the aqueous composition does not contain a polymerizable compound. The other conditions are the same as those of Example 1.

[0127] [Layer formation method] In the following, the coating layer formed on the sheet using the aqueous composition was tested for adhesion, durability, peelability, and odor.

[0128] [Fixation test] In Examples 1 to 5, 8 to 20 and Comparative Examples 1 to 3, 50 mg / cm 2 was applied to the upper surface of the sheet in the application step. 2 The aqueous composition was dropped with a dropper so that the aqueous composition was applied to the upper surface of the sheet at a drying temperature of 90°C for 3 hours in a drying process, thereby forming a coating layer of the aqueous composition on the upper surface of the sheet. Thereafter, an adhesive tape was attached to the upper surface of the coating layer of the sheet, and a fixation test was performed in which the adhesive tape was peeled off from the coating layer. In Examples 6 and 7, after the coating process and drying process, a 50 mg / cm 2The black ink was dropped onto the top surface of the coating layer using a dropper as the printing ink, forming a colorant layer on top of the coating layer. An adhesive tape was then attached to the top surface of the printing layer consisting of the coating layer and the colorant layer, and a fixation test was conducted in which the adhesive tape was peeled off from the printing layer. PET film was used as the sheet. Cellophane tape [Cellotape (registered trademark) CT-12 (Nichiban)] was used as the adhesive tape. The fixation of the coating layer to the sheet was evaluated using the following evaluation criteria. A: No peeling B: Peeled off

[0129] [Durability test] The sheet was left for two weeks near a window exposed to direct sunlight, and then the durability of the coating layer on the top surface of the sheet was tested under the following conditions. Conditions: After leaving the sheet near a window exposed to direct sunlight for two weeks, the sheet and coating layer (printed layer in Examples 6 and 7) were folded in half and then returned to their original state. Adhesive tape was then attached to the top surfaces of the sheet and coating layer (printed layer in Examples 6 and 7), and the adhesive tape was peeled off from the coating layer (printed layer in Examples 6 and 7). Note that folding the sheet and coating layer (printed layer in Examples 6 and 7) in half creates cracks in the coating layer, improving peelability. Cellophane tape [Cellotape (registered trademark) CT-12 (Nichiban)] was used as the adhesive tape. The durability of the coating layer was evaluated using the following criteria. A: No peeling B: Peeled off

[0130] [Peeling test] The electron beam exit window of the electron beam irradiation device was installed at a position 10 mm above the stage. In the irradiation process, the stage carrying the sheet was moved at a speed of 100 mm / sec, while the electron beam was directed downward from the electron beam exit window, thereby irradiating the upper surface of the coating layer (the printing layer in Examples 6 and 7) with the electron beam. The electron beam irradiation device used was an electron beam irradiation device manufactured by Hamamatsu Photonics KK. The oxygen concentration inside the electron beam irradiation device was set to 100 ppm or less. The acceleration voltage was set to 100 kV. Thereafter, a peel test was performed under the following two conditions. Condition 1: An adhesive tape was attached to the upper surfaces of the sheet and coating layer (printed layer in Examples 6 and 7) after electron beam irradiation, and the adhesive tape was peeled off from the coating layer (printed layer in Examples 6 and 7). Condition 2: After electron beam irradiation, the sheet and coating layer (printed layer in Examples 6 and 7) were folded in half and then returned to their original state. Adhesive tape was then attached to the top surfaces of the sheet and coating layer (printed layer in Examples 6 and 7), and the adhesive tape was peeled off from the coating layer (printed layer in Examples 6 and 7). Note that folding the sheet and coating layer (printed layer in Examples 6 and 7) in half under Condition 2 causes cracks in the coating layer, improving peelability. Cellophane tape [Cellotape (registered trademark) CT-12 (Nichiban)] was used as the adhesive tape. The peelability of the coating layer from the sheet was evaluated using the following criteria. A: Peeled off under both conditions 1 and 2 B: No peeling under condition 1, peeling under condition 2 C: No peeling occurred under either condition 1 or condition 2

[0131] [Odor test] In Examples 1 to 5, 8 to 20 and Comparative Examples 1 and 2, the odor of the coating layer formed on the upper surface of the sheet after the coating and drying processes was evaluated according to the following evaluation criteria. In Examples 6 and 7, the odor of the coating layer on which a colorant layer was formed after the coating, drying, and printing processes was evaluated according to the following evaluation criteria. A: The worker's sense of smell barely detects any odor. B: The worker's sense of smell clearly detected the odor.

[0132] [Table 1] TIFF2025137186000003.tif82150 TIFF2025137186000004.tif98150

[0133] [Fixation test evaluation] As shown in Table 1, none of Examples 1 to 20 and Comparative Examples 1 to 3 peeled off, and were therefore rated A. This is thought to be because the drying temperature in the drying step was 90°C, which is higher than the glass transition temperature of the binder resin, and the binder resin in the aqueous composition became sufficiently soft, allowing film formation of the binder resin to proceed sufficiently, resulting in increased adhesion between the upper surface of the sheet and the binder resin. The drying temperature in the drying step was set to 90°C to prevent the sheet from deteriorating due to heat.

[0134] [Durability test evaluation] As shown in Table 1, in Examples 1 to 20 and Comparative Examples 2 and 3, the coating layer did not peel off, and therefore was rated A. This is thought to be because the aqueous composition did not contain a photopolymerization initiator excited by ultraviolet light, so the polymerizable compound in the coating layer did not undergo a polymerization reaction under natural light. In contrast, in Comparative Example 1, the coating layer peeled off, and therefore was rated B. This is thought to be because the aqueous composition contained 1.0 wt% of a photopolymerization initiator excited by ultraviolet light, which caused the polymerization reaction of the polymerizable compound in the coating layer to proceed, resulting in the coating layer shrinking, and therefore reducing the adhesion of the coating layer to the sheet.

[0135] [Peeling test evaluation] As shown in Table 1, in all of Examples 1 to 20, peeling occurred under Condition 1 or Condition 2, and therefore the evaluation was B or higher. This is thought to be because, in the irradiation step, the upper surface of the sheet on which the coating layer was formed was irradiated with an electron beam, which caused the polymerization reaction of the polymerizable compound in the coating layer to proceed and the coating layer to shrink, thereby sufficiently reducing the adhesion of the coating layer to the sheet.

[0136] In contrast, in Comparative Examples 1 to 3, no peeling occurred under either Condition 1 or Condition 2, and therefore the sheet was rated C. In Comparative Example 1, the upper surface of the sheet on which the coating layer was formed was not irradiated with an electron beam in the irradiation step, so the polymerization reaction of the polymerizable compound in the coating layer did not proceed at all, and the adhesion of the coating layer to the sheet was not reduced. In Comparative Example 2, the upper surface of the coating layer was irradiated with ultraviolet light rather than an electron beam in the irradiation step, so the polymerization reaction of the polymerizable compound in the coating layer did not proceed at all, and the adhesion of the coating layer to the sheet was not reduced. In Comparative Example 3, the aqueous composition did not contain a polymerizable compound, so the adhesion of the coating layer to the sheet was not reduced even when the upper surface of the sheet on which the coating layer was formed was irradiated with an electron beam.

[0137] Furthermore, in Examples 11 and 15, peeling occurred under condition 2 and was therefore rated B, whereas in the other Examples, peeling occurred under condition 1 and was therefore rated A. This is thought to be because the polymerizable compound contained in the aqueous composition in Examples 11 and 15 was 1.0 wt%, whereas the polymerizable compound contained in the aqueous composition in the other Examples was 5.0 wt%, and the wt% of the polymerizable compound contained in the aqueous composition in Examples 11 and 15 was lower than in the other Examples.

[0138] [Odor test evaluation] As shown in Table 1, in Examples 1 to 20, the workers could hardly detect any odor with their sense of smell, and so they were rated A. This is thought to be because the aqueous compositions in Examples 1 to 20 did not contain a photopolymerization initiator that is excited by ultraviolet light. In contrast, in Comparative Example 1, the workers could clearly detect an odor with their sense of smell, and so they were rated B. This is thought to be because the aqueous composition in Comparative Example 1 contained 1.0 wt % of a photopolymerization initiator that is excited by ultraviolet light.

[0139] From the above, it can be seen that even if the aqueous composition containing the polymerizable compound does not contain a photopolymerization initiator that is excited by ultraviolet light, when the aqueous composition is dried in the drying step and the coating layer on the upper surface of the sheet is irradiated with an electron beam in the irradiation step, the fixability will be rated A and the peelability will be rated A. It can also be seen that if the aqueous composition containing the polymerizable compound does not contain a photopolymerization initiator that is excited by ultraviolet light, the durability will be rated A and the odor will be rated A. [Explanation of symbols]

[0140] 6. Sheet (an example of a substrate) 6a...Top surface 6b...Bottom surface 7. Coating layer (an example of a coating layer and a printed layer) 34 Print head (an example of an inkjet head)

Claims

1. a coating step of coating or discharging onto a substrate an aqueous composition containing water and a polymerizable compound that is soluble in water and undergoes a polymerization reaction when irradiated with an electron beam; a drying step of drying the aqueous composition applied or ejected onto the substrate, The aqueous composition does not contain a photopolymerization initiator that is excited by ultraviolet light, A layer forming method for forming a peelable coating layer on the substrate using the aqueous composition.

2. The layer forming method according to claim 1, wherein the aqueous composition is ejected onto the substrate by an inkjet head in the coating step.

3. 2. The layer forming method according to claim 1, wherein the coating layer is a printed layer.

4. the aqueous composition is an aqueous ink containing a colorant, The layer forming method according to claim 1 , wherein the coating step is a printing step of coating or ejecting the water-based ink onto the substrate.

5. The method further includes a printing step of discharging or applying a printing ink onto the coating layer that has been applied or discharged onto the substrate, The layer forming method according to claim 1 , wherein the drying step is carried out after the printing step or between the coating step and the printing step.

6. the aqueous composition contains a binder resin that forms the coating layer, 6. The layer forming method according to claim 1, wherein the drying step is a step of drying the aqueous composition applied or ejected onto the substrate in the application step at a temperature in the range of 50°C to 220°C.

7. the aqueous composition contains a binder resin that forms the coating layer, 6. The layer forming method according to claim 1, wherein the drying step is a step of drying the aqueous composition applied or ejected onto the substrate in the application step at a temperature in the range of 50°C to 150°C.

8. 6. The layer forming method according to claim 1, wherein the aqueous composition contains a binder resin that forms the coating layer, and the binder resin is in an emulsion state dispersed in the water.

9. 9. The method for forming a layer according to claim 8, wherein the substrate is an impermeable substrate.

10. The layer forming method according to claim 9 , wherein the substrate is a transparent substrate.

11. A substrate recycling method comprising an irradiation step of irradiating a coating layer formed by the layer forming method according to any one of claims 1 to 5 with an electron beam at a dose in the range of 1 to 150 kGy.

12. A substrate recycling method comprising an irradiation step of irradiating a coating layer formed by the layer forming method according to any one of claims 1 to 5 with an electron beam at a dose in the range of 30 to 100 kGy.

13. The substrate recycling method according to claim 11, wherein the irradiation step is a step of irradiating the electron beam onto the surface of the substrate on which the coating layer is formed.

14. The substrate recycling method according to claim 12, wherein the irradiation step is a step of irradiating the electron beam onto the surface of the substrate on which the coating layer is formed.

15. The method for recycling a substrate according to claim 11, wherein in the irradiation step, the electron beam is irradiated onto a rear surface of the substrate opposite to the front surface on which the coating layer is formed.

16. The method for recycling a substrate according to claim 12, wherein in the irradiation step, the electron beam is irradiated onto a rear surface of the substrate opposite to the front surface on which the coating layer is formed.

17. a coating step of coating or discharging onto a substrate an aqueous composition containing water and a polymerizable compound that is soluble in water and undergoes a polymerization reaction when irradiated with an electron beam; a drying step of drying the aqueous composition applied or ejected onto the substrate, The aqueous composition does not contain a photopolymerization initiator that is excited by ultraviolet light, A method for producing a printed matter, which comprises forming a peelable printed layer on a substrate using the aqueous composition.

18. 18. The method for producing a printed matter according to claim 17, wherein the aqueous composition contains a binder resin, and the binder resin is in an emulsion state dispersed in the water.

19. 19. The method for producing a printed matter according to claim 17 or 18, wherein the substrate is an impermeable transparent substrate.

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