Aqueous resin composition, image forming method, printed matter, and aqueous coating liquid

Abstract

Provided is an aqueous resin composition for forming an adhesive layer on a printing medium by coating, which has high initial peel resistance, water resistance, and lamination strength for printed matter after printing of 100 m or more, is less likely to contaminate printing machine components, and can achieve excellent image quality. [Solution] The above problem is solved by an aqueous resin composition containing at least a polyurethane resin having carboxylate groups and a crosslinking agent having at least two carbodiimide groups per molecule, in which the molar ratio of the carbodiimide groups of the crosslinking agent to the carboxylate groups of the polyurethane resin is 5.1 or more and 40 or less.

Description

[Technical Field]

[0001] The present invention relates to an aqueous resin composition to be applied to a printing medium. The present invention also relates to an image forming method, a printed matter, and an aqueous coating liquid using the aqueous resin composition. [Background technology]

[0002] Digital printing, such as electrophotography and inkjet printing, particularly for commercial printing applications, requires proper printing on a variety of printing media, such as plastic films and coated paper. In this case, an adhesive layer (also known as an undercoat layer or primer layer) is often formed on the printing media to ensure adhesion between the toner or ink and the various printing media. In this case, from the perspective of environmental compatibility, an aqueous resin composition is preferably used as the coating liquid for the adhesive layer. As aqueous resin compositions for adhesive layers, water-soluble resins such as polyethyleneimine (Patent Document 1) and dispersions of acrylic resins and polyurethane resins (Patent Document 2) have been proposed.

[0003] However, when conventional aqueous resin compositions are used as adhesive layers, the durability of the printed matter after coating is insufficient in terms of water resistance, heat resistance, solvent resistance, etc. Therefore, studies have been conducted to improve the water resistance and solvent resistance of such aqueous resin compositions by causing a crosslinking action in the adhesive layer after coating (Patent Documents 3 and 4). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Special Publication No. 2018-533032 [Patent Document 2] U.S. Patent No. 7,470,736 [Patent Document 3] International Publication No. 2019 / 131414 [Patent Document 4] Japanese Patent Application Laid-Open No. 2011-137080 Summary of the Invention [Problem to be solved by the invention]

[0005] In order to improve the peel resistance (particularly the peel resistance immediately after printing) between the adhesive layer and the printed layer (ink layer) formed thereon in Patent Documents 3 and 4, it was necessary to include in the adhesive layer an equivalent amount of crosslinking agent that was greater than the acidic groups that contributed to crosslinking of the resin used in the adhesive layer. However, using such an excessive amount of crosslinking agent reduces water resistance, contaminates contacting parts such as the intermediate transfer body and transport rollers, and leads to problems such as a deterioration in image quality, which hinder practical use. These issues are also a concern when printing lengths of 100 m or more.

[0006] The present invention has been made in view of the above-mentioned conventional techniques, and an object of the present invention is to provide an aqueous resin composition that exhibits good initial peel resistance (peel resistance immediately after printing), water resistance, lamination strength, low staining, and image quality even after printing of 100 m or more. [Means for solving the problem]

[0007] As a result of extensive research, the present inventors have found that an aqueous resin composition containing at least a polyurethane resin having a carboxylate group and a crosslinking agent having at least two carbodiimide groups per molecule, wherein the molar ratio of the carbodiimide groups of the crosslinking agent to the carboxylate groups of the polyurethane resin is within a specific range, exhibits good initial peel resistance (peel resistance immediately after printing), water resistance, lamination strength, low staining, and image quality, particularly in printed matter of 100 m or more, and have completed the present invention as described below.

[0008] That is, the gist of the present invention is as follows: <1> ~ <8> It resides in.

[0009] <1> An aqueous resin composition comprising at least a polyurethane resin having a carboxylate group and a crosslinking agent having at least two carbodiimide groups per molecule, wherein the molar ratio of the carbodiimide groups of the crosslinking agent to the carboxylate groups of the polyurethane resin is 5.1 or more and 40 or less. <2> The polyurethane resin is a saturated hydrocarbon-based polyether polyurethane resin and has an ammonium carboxylate group. <1> The aqueous resin composition according to claim 1. <3> Further containing polyalkylene glycol <1> or <2> The aqueous resin composition according to claim 1. <4> The polyalkylene glycol is contained in an amount of 1 part by mass or more and 20 parts by mass or less relative to 100 parts by mass of the polyurethane resin. <3> The aqueous resin composition according to claim 1. <5> The molecular weight of the polyalkylene glycol is 200 or more and 900 or less. <3> or <4> The aqueous resin composition according to claim 1. <6> On print media, <1> ~ <5> 1. An image forming method using a digital printing method, comprising: applying the aqueous resin composition according to any one of 1 to 3 to form an adhesive layer; and then forming an ink layer using an ink containing a resin having a carboxy group. <7> A water-based coating liquid containing at least a polyurethane resin having a carboxylate group and a crosslinking agent having at least two carbodiimide groups per molecule, The aqueous coating liquid has a molar ratio of carbodiimide groups in the crosslinking agent to carboxylate groups in the polyurethane resin of 5.1 or more and 40 or less. <8> A method for producing an aqueous resin composition, comprising separately producing a base agent whose main component is a polyurethane resin having carboxylate groups and a curing agent whose main component is a crosslinking agent having at least two carbodiimide groups per molecule, and mixing the base agent and the curing agent before use. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide an aqueous resin composition that exhibits good initial peel resistance (peel resistance immediately after printing), water resistance, lamination strength, low staining, and image quality even in printed matter of 100 m or more. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a schematic cross-sectional view showing one embodiment of an electrophotographic digital printing machine to which the present invention is applied. DETAILED DESCRIPTION OF THE INVENTION

[0012] The following describes in detail the embodiments of the present invention. However, the description of the components described below is a representative example of an embodiment of the present invention, and can be modified as appropriate within the scope that does not deviate from the spirit of the present invention. Unless otherwise specified, the measurement of various physical properties and the operation steps in the following description are based on conditions of room temperature and normal pressure.

[0013] [Aqueous resin composition] The aqueous resin composition of the present invention can be suitably used as an aqueous coating liquid, and in particular, can be suitably used as an aqueous coating liquid for an adhesive layer (hereinafter, sometimes referred to as an undercoat layer or primer layer) for ensuring adhesion between a printing medium and a toner or ink. In other words, the aqueous resin composition of the present invention can be suitably used as a primer for forming a primer layer.

[0014] The primary requirements for aqueous resin compositions used in adhesive layers for digital printing are peel resistance between the adhesive layer and the print medium, peel resistance between the adhesive layer and the ink layer, and water resistance of the adhesive layer. In addition, when used in packaging materials, etc., the composition is required to have sufficient lamination strength when laminated onto the ink layer, and to minimize contamination of intermediate transfer bodies, transport rollers, and other components that come into direct contact with the adhesive layer during printing. In the aqueous resin composition of the present invention, the crosslinking reaction between the polyurethane resin having a carboxylate group and the crosslinking agent having at least two carbodiimide groups per molecule can improve the peel resistance between the adhesive layer and the print medium and the water resistance of the adhesive layer. Specifically, the crosslinking fixes the adhesive layer in close contact with the print medium and has the effect of suppressing the penetration of water and solvents. At the same time, the peel resistance between the adhesive layer and the ink layer can be improved by the reaction between the crosslinking agent contained in the adhesive layer and the resin contained in the ink layer and / or by improving the chemical affinity between them, which also improves the laminate strength when a laminate is formed on the ink layer. Furthermore, by ensuring that the molar ratio of the carboxylate groups in the polyurethane resin to the carbodiimide groups in the crosslinking agent is within a specific range, contamination of intermediate transfer bodies, transport rollers, and the like that come into direct contact with the adhesive layer during printing can be suppressed.

[0015] Furthermore, it is preferable that the aqueous resin composition used in the adhesive layer for digital printing has good liquid stability during transportation and storage, and also good liquid stability when the liquid is used once and then reused. Regarding the former, it is necessary to suppress changes in liquid properties such as an increase in liquid viscosity or gelation due to the reaction between the polyurethane resin and the crosslinking agent, an increase in the particle size of the resin particles, etc. If such changes in liquid properties occur, uniform coating may not be possible, the coating film thickness may not be constant, or the liquid properties may deviate from those appropriate for coating, making coating impossible. The latter includes not only the case where the residual liquid is reused after one coating, but also the case where the residual liquid is mixed with new liquid and used. In these cases, it is necessary that the liquid properties, coating quality, and performance as an adhesive layer after coating do not deteriorate compared to when the entire amount of liquid is used as new. If these performances deteriorate and the residual liquid can no longer be used, it will have to be discarded, which is disadvantageous in terms of cost. In the aqueous resin composition of the present invention, the polyurethane resin-based liquid and the crosslinker-based liquid are separated and mixed before use, i.e., before printing. This ensures liquid stability during transportation, which can be subject to high thermal loads and temperatures of 40 to 60°C, and also ensures good liquid stability at room temperature during repeated use after mixing. The reason for this is presumed to be as follows: The polyurethane resin is dispersed in a particulate form in the coating liquid and stabilized by counterions and amine compounds. Meanwhile, the carbodiimide-containing crosslinker typically reacts with carboxylate groups at room temperature. However, by adjusting the blending ratio within an appropriate range, forming a micellar structure surrounded by hydrophilic groups, or by isolating the crosslinker from the polyurethane resin through spatial and electrical repulsion with a stabilizer such as an amine compound, crosslinking reactions in the liquid are minimized, and at least interparticle crosslinking of the polyurethane resin in the liquid after mixing is suppressed, which is thought to improve liquid stability at room temperature after mixing.

[0016] The nonvolatile component concentration of the aqueous resin composition is preferably 10% by mass or more, more preferably 20% by mass or more, and even more preferably 25% by mass or more. On the other hand, it is preferably 50% by mass or less, more preferably 40% by mass or less, and even more preferably 35% by mass or less. The nonvolatile component concentration refers to the proportion (% by mass) of the total amount of components that are solid at 25°C and components that are liquid at 25°C and have a boiling point of 150°C or higher relative to the total amount of the aqueous resin composition. The viscosity of the aqueous resin composition is preferably 1 mPa·s or more, more preferably 5 mPa·s or more, and even more preferably 10 mPa·s or more, while it is preferably 200 mPa·s or less, more preferably 100 mPa·s or less, and even more preferably 50 mPa·s or less.

[0017] <Polyurethane resin> The polyurethane resin contained in the aqueous resin composition of the present invention may be a water-soluble polyurethane resin or a dispersible polyurethane resin, but from the viewpoint of performance as an adhesive layer and liquid stability, a dispersible polyurethane resin is preferred. Here, "dispersible" means water-dispersible, i.e., suspendable, and means water-insoluble. That is, in the aqueous resin composition of the present invention, the polyurethane resin is preferably stably dispersed as particles. Furthermore, from the viewpoint of sufficiently obtaining the function as an adhesive layer, the polyurethane resin is preferably a self-dispersing type.

[0018] The polyurethane resin is preferably one obtained by reacting a polyol with a polyisocyanate and extending the chain with a low-molecular-weight compound having two or more active hydrogen atoms, such as a diol, a diamine, or a dicarboxylic acid. In this case, a polyurethane resin using a polyol component having a carboxylate group as part of the polyol component is preferably used. Furthermore, by neutralizing the carboxylate group with a basic component, good dispersibility in water can be maintained. Furthermore, from the viewpoint of initial peel resistance to a variety of printing media and smoothness during application, polyether polyurethane resins are preferred, and among these, saturated hydrocarbon-based polyether polyurethane resins are more preferred.

[0019] (Polyol) Examples of polyhydric alcohols that serve as precursors to polyol components include ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, 1,6-hexanediol, 3-methyl-1,5-pentanediol, 1,9-nonanediol, trimethylolpropane, glycerin, pentaerythritol, cyclohexanedimethanol, bishydroxyethoxybenzene, N-alkyldiethanolamine, and polymers thereof (dimers, octamers, etc.). Among these, propylene glycol, 1,6-hexanediol, 3-methyl-1,5-pentanediol, and cyclohexanedimethanol are preferred, with 1,6-hexanediol and cyclohexanedimethanol being more preferred, from the standpoint of adhesion to polyolefin-based printing media. These polyhydric alcohols can be used alone or in combination of two or more. As the polyol, polyester polyols, polyether polyols, and polycarbonate polyols are preferred from the viewpoint of durability such as water resistance, and among these, polyether polyols and polycarbonate polyols are more preferred, and polyether polyols are even more preferred from the viewpoint of initial peel resistance to various printing media. These polyols can be used alone or in combination of two or more kinds.

[0020] Examples of polyether polyols include saturated hydrocarbon polyether polyols obtained by addition polymerization of saturated hydrocarbon alkylene oxides such as ethylene oxide, propylene oxide, and butylene oxide to the polyhydric alcohols, and aromatic polyether polyols obtained by addition polymerization of aromatic alkylene oxides such as styrene oxide. Among these, saturated hydrocarbon polyether polyols are preferred from the viewpoint of adhesion to polyolefin printing media. Examples of saturated hydrocarbon polyether polyols include polyethylene glycol, polypropylene glycol, poly(1,6-hexanediol), etc. Among these, from the viewpoints of ease of production and flexibility, polyethylene glycol and polypropylene glycol are preferred, and polypropylene glycol is more preferred. Examples of polycarbonate polyols include polytetramethylene carbonate diol, polyhexamethylene carbonate diol, polydecamethylene carbonate diol, poly-3-methyl-1,5-pentane carbonate diol, poly-1,4-cyclohexanedimethylene carbonate diol, etc. Among these, polytetramethylene carbonate diol and polyhexamethylene carbonate diol are preferred from the viewpoint of durability.

[0021] (Polyisocyanate) Examples of polyisocyanates include saturated hydrocarbon diisocyanates such as hexamethylene diisocyanate, isophorone diisocyanate, and 4,4'-methylenebis(cyclohexylisocyanate); aromatic diisocyanates such as metaxylene diisocyanate and tolylene diisocyanate; unsaturated hydrocarbon diisocyanates such as dimer acid diisocyanate; and reaction products of these compounds with polyhydric alcohols. Among these, saturated hydrocarbon diisocyanates are preferred from the viewpoint of adhesion to various printing media. These can be used alone or in combination of two or more.

[0022] The acid value (the amount of potassium hydroxide required for neutralization, unit: mgKOH / g) can be used as an indicator of the amount of carboxylate groups contained in the polyurethane resin. The acid value of the polyurethane resin of the present invention is preferably 2 mgKOH / g or more, more preferably 5 mgKOH / g or more, and even more preferably 10 mgKOH / g or more. On the other hand, it is preferably 50 mgKOH / g or less, more preferably 20 mgKOH / g or less, and even more preferably 15 mgKOH / g or less. If the acid value is above the lower limit, crosslinking after coating and drying is likely to proceed, while if the acid value is below the upper limit, an increase in the particle size of the polyurethane resin particles and an increase in the viscosity of the coating liquid can be suppressed. The carboxylate groups of the polyurethane resin of the present invention, when dispersed in water, may have hydrogen ions as counter ions, or may have quaternary ammonium ions derived from ammonia or amine compounds added during resin production. Therefore, the acid value of the polyurethane resin of the present invention can be quantitatively measured by volatilizing the ammonia or amine compounds from the aqueous dispersion of the polyurethane resin to completely convert the counter ions of the carboxylate groups to hydrogen ions, volatilizing the water to dry the resin, completely dissolving the dried resin in a solvent, and titrating with an aqueous potassium hydroxide (KOH) solution. Examples of the solvent that can be used include ethanol, isopropanol, and acetone.

[0023] As described above, the carboxylate groups of the polyurethane resin of the present invention may have hydrogen ions or quaternary ammonium ions as counter ions when dispersed in water. In other words, the polyurethane resin of the present invention may have carboxy groups or ammonium carboxylate groups when dispersed in water. Among these, from the viewpoint of self-dispersibility, it is preferable that the polyurethane resin have ammonium carboxylate groups. Note that polyurethane resins having ammonium carboxylate groups can be produced, for example, by using ammonia as a neutralizing agent during production. Furthermore, the aqueous resin composition of the present invention is required to have uniform film-forming properties after coating. In particular, from the viewpoint of forming a submicron thin film, the particle diameter of the polyurethane resin particles is preferably 200 nm or less, more preferably 100 nm or less, and even more preferably 50 nm or less.

[0024] The content of the polyurethane resin of the present invention as solid content in the aqueous resin composition is preferably 8% by mass or more, more preferably 15% by mass or more, and on the other hand, is preferably 25% by mass or less, more preferably 22% by mass or less. When the content is equal to or more than the lower limit, the initial peel resistance and water resistance after coating are improved, and when the content is equal to or less than the upper limit, the liquid stability after mixing is good.

[0025] <Crosslinking agent> The crosslinking agent contained in the aqueous resin composition of the present invention is a crosslinking agent containing at least two carbodiimide groups per molecule, from the viewpoints of safety to the human body and low-temperature reactivity. If there are fewer than two carbodiimide groups per molecule, the carboxylate groups in the polyurethane resin cannot be sufficiently crosslinked, making it difficult to achieve the desired performance. From the viewpoint of adhesive layer performance and liquid stability, the crosslinking agent is preferably not completely water-soluble and has a micelle structure surrounded by sterically bulky hydrophilic groups. The bulky structure that causes steric hindrance can reduce the chance of contact with the polyurethane resin.

[0026] A known carbodiimide compound can be used as the crosslinking agent in the aqueous resin composition of the present invention. The carbodiimide compound can be obtained, for example, by synthesizing an isocyanate-terminated polycarbodiimide compound through a condensation reaction involving the decarbonation of an organic diisocyanate compound, and then reacting the isocyanate terminal with a highly hydrophilic organic compound. Examples of the highly hydrophilic organic compound include polyalkylene oxides, dialkylamino alcohols, alkyl esters of hydroxycarboxylic acids, dialkylaminoalkylamines, and alkyl sulfonates, each end-capped with an alkoxy group or a phenoxy group. Among these, polyalkylene oxides end-capped with an alkoxy group or a phenoxy group are preferred from the viewpoint of spatially isolating the carbodiimide group from the polyurethane resin by forming stable micelles in water. In this case, stable micelles with a particle size of about 10 nm covered with hydrophilic groups are formed, which is thought to exhibit good liquid stability.

[0027] The carbodiimide compound is preferably a polycarbodiimide obtained by polymerizing two or more molecules of a diisocyanate compound. Furthermore, an aliphatic or aromatic carbodiimide compound is preferred, and an aliphatic carbodiimide compound is more preferred. The degree of polymerization of the carbodiimide compound is preferably 2 or more. On the other hand, it is preferably 100 or less, more preferably 10 or less. Examples of the polymerized unit of the aliphatic carbodiimide compound include 4,4'-dicyclohexylmethanecarbodiimide, diisophoronemethanecarbodiimide, cyclohexylcarbodiimide, isopropylcarbodiimide, methylcarbodiimide, isobutylcarbodiimide, octylcarbodiimide, t-butylcarbodiimide, etc. Among these, from the viewpoints of low toxicity and liquid stability, it is effective to use a sterically bulky structure, and 4,4'-dicyclohexylmethanecarbodiimide, diisophoronemethanecarbodiimide, and cyclohexylcarbodiimide are preferred, with 4,4'-dicyclohexylmethanecarbodiimide being more preferred. Examples of the polymerized unit of the aromatic carbodiimide compound include phenylcarbodiimide, β-naphthylcarbodiimide, tetramethylxylylenecarbodiimide, etc. Among these, tetramethylxylylenecarbodiimide is preferred from the viewpoints of low toxicity and liquid stability. These carbodiimide compounds may be used alone or in combination of two or more. When two or more carbodiimide compounds are used in combination, it is preferable to mix two or more carbodiimide compounds having different carbodiimide group equivalents to achieve a balance between reactivity and liquid stability. As an index of the amount of carbodiimide groups (N=C=N groups) in one molecule of a carbodiimide compound, the carbodiimide group equivalent is defined as follows. (Carbodiimide group equivalent) = (chemical formula weight of structural units of carbodiimide compound per 1 mole of carbodiimide group) (unit: mol -1 ) The smaller the carbodiimide group equivalent weight, the greater the amount of carbodiimide groups contained in one molecule, and conversely, the larger the carbodiimide group equivalent weight, the fewer the amount of carbodiimide groups contained in one molecule. The preferred carbodiimide group equivalent of the carbodiimide compound is preferably 300 mol -1 More preferably, 350 mol -1 More preferably, 400 mol -1 On the other hand, preferably 600 mol -1 Less than 500 mol, preferably -1 When the carbodiimide group equivalent is equal to or greater than the lower limit, the solution stability is improved, and when the carbodiimide group equivalent is equal to or less than the upper limit, the crosslinkability is improved.

[0028] The content of the crosslinking agent in the aqueous resin composition of the present invention as solids is preferably 6% by mass or more, more preferably 9% by mass or more. On the other hand, it is preferably 18% by mass or less, more preferably 14% by mass or less. When the content is equal to or greater than the lower limit, sufficient crosslinking is achieved, improving initial peel resistance and water resistance. When the content is equal to or less than the upper limit, liquid stability during mixing is improved.

[0029] The aqueous resin composition of the present invention is characterized in that the molar ratio of the carbodiimide groups in the crosslinking agent to the carboxylate groups in the polyurethane resin is 5.1 or more and 40 or less. If the molar ratio is greater than 40, i.e., if the amount of carbodiimide groups is too high relative to the amount of carboxylate groups, the carbodiimide compound may migrate from non-printed areas to contact members such as an intermediate transfer body or a transport roller during printing, which may result in contamination or deterioration of print image quality. If the molar ratio is less than 5.1, i.e., if the amount of carbodiimide groups is too low relative to the amount of carboxylate groups, the initial peel resistance and lamination strength of printed matter after printing 100 m or more may deteriorate. That is, the molar ratio of the carbodiimide groups in the crosslinking agent to the carboxylate groups in the polyurethane resin is 5.1 or more, preferably 8.0 or more, more preferably 9.0 or more, and 40 or less, preferably 20 or less, more preferably 15 or less. The amount of carboxylate groups in the polyurethane resin can be calculated from the acid value described above, and the amount of carbodiimide groups in the crosslinking agent can be calculated from the carbodiimide group equivalent weight described above. The content ratio (mass ratio) of the crosslinking agent to the polyurethane resin is preferably 0.26 or more, more preferably 0.30 or more, from the viewpoints of initial peel resistance and water resistance in printed matter after printing of 100 m or more, while from the viewpoints of contact member contamination and image quality, it is preferably 2.0 or less, more preferably 1.0 or less, and even more preferably 0.60 or less.

[0030] <Polyalkylene glycol> The aqueous resin composition of the present invention may further contain a polyalkylene glycol. In the present invention, the polyalkylene glycol is represented by the general formula H(O[CH2] m ) n OH (m and n are integers of 1 or more). Examples of polyalkylene glycols in the present invention include polymethylene glycol, polyethylene glycol, polypropylene glycol, polybutylene glycol, polypentylene glycol, polyhexylene glycol, polyheptylene glycol, polyoctylene glycol, polynonylene glycol, polydecylene glycol, etc. Among these, from the viewpoint of affinity with water at room temperature, polyethylene glycol, polypropylene glycol, and polybutylene glycol are preferred, polyethylene glycol and polypropylene glycol are more preferred, and polyethylene glycol is even more preferred.

[0031] The polyalkylene glycol may be a mixture of two or more different types of polyalkylene glycols. Furthermore, when the polyalkylene glycol has a branched structure or structural isomers, a mixture of the branched structure or structural isomers may be used.

[0032] The polyalkylene glycol in the present invention can be produced by a conventional method in the field of organic synthetic chemistry, or commercially available products can be used. In particular, for polyethylene glycol, commercially available products with various molecular weights such as polyethylene glycol 200 (meaning an average molecular weight of 200, the same applies below), polyethylene glycol 300, polyethylene glycol 400, polyethylene glycol 600, polyethylene glycol 1000, polyethylene glycol 1540, polyethylene glycol 4000, polyethylene glycol 6000, polyethylene glycol 8000, polyethylene glycol 12000, and polyethylene glycol 20000 (all manufactured by Fujifilm Wako Pure Chemical Industries) can be suitably used.

[0033] In the present invention, the polyalkylene glycol is thought to have the function of preventing the crosslinking agent from being exposed on the surface of the adhesive layer and migrating to the contact member, and also to promote the demulsification of the carbodiimide compound crosslinking agent as the adhesive layer dries, thereby increasing the reaction between the carboxylate groups of the polyurethane resin and the carbodiimide compound crosslinking agent. The average molecular weight of the polyalkylene glycol of the present invention is preferably 200 or more, more preferably 300 or more, and even more preferably 500 or more, from the viewpoint of suppressing migration of the crosslinking agent to the contact member. On the other hand, from the viewpoint of promoting demulsification of the crosslinking agent, it is preferably 2000 or less, more preferably 1500 or less, and even more preferably 900 or less. When the carbodiimide compound of the crosslinking agent is in a micellar state with high affinity for water and the amount of crosslinking agent used is within the preferred range of the present invention, if drying during application is insufficient, the micelles may not be sufficiently demulsified, resulting in insufficient crosslinking with the polyurethane resin and reduced water resistance. In such cases, the polyalkylene glycol is thought to play a role in helping to promote demulsification of the crosslinking agent micelles and improving water resistance.

[0034] <Amine compounds> The aqueous resin composition of the present invention may further contain an amine compound. By containing an amine compound in the aqueous resin composition, the amine compound is present around the polyurethane resin, which is expected to prevent the crosslinking reaction between the polyurethane resin and the crosslinking agent in the liquid, thereby improving the liquid stability. The amine compound preferably has a pKb of 3.5 or more and 5.0 or less. pKb means the base dissociation constant and is generally used as an index of base strength. The smaller the pKb value, the stronger the base.

[0035] Generally, ammonia (pKb: 4.75) is preferably used as a neutralizing agent during the production of polyurethane resin dispersions, but the aqueous resin composition of the present invention preferably contains an amine compound added during the production of the aqueous resin composition. In other words, it is preferable to add an amine compound during the production of the aqueous resin composition of the present invention. The reason for this is believed to be as follows. Because ammonia is highly volatile, even if it is used in the production of a polyurethane resin dispersion, it is likely to disappear from the aqueous resin composition during production. As a result, the polyurethane resin in the produced aqueous resin composition is not neutralized, resulting in reduced self-dispersibility and reduced liquid stability. Therefore, adding an amine compound during the production of an aqueous resin composition allows the polyurethane resin to be stably dispersed in the liquid by stably protecting the carboxylate groups of the polyurethane resin and forming hydrogen bonds with urethane bonding groups, etc. Furthermore, the presence of the amine compound around the dispersed polyurethane resin particles in an electric double layer creates electrical repulsion with the carbodiimide group-containing crosslinker in the liquid, thereby slowing the reaction rate between the polyurethane resin and the crosslinker in the liquid.

[0036] The pKb of the amine compound is preferably 3.5 or more and 5.0 or more. A pKb value less than the lower limit is undesirable from the viewpoint of safety to the human body, whereas a pKb value greater than the upper limit may reduce the effect of stabilizing the liquid. That is, the pKb of the amine compound is preferably 3.5 or more, more preferably 4.0 or more, and preferably 5.0 or less, more preferably 4.7 or less, even more preferably 4.5 or less, and particularly preferably 4.2 or less. Furthermore, from the viewpoint of heat resistance during printing or processing, the boiling point of the amine compound is preferably 130° C. or higher, and more preferably 151° C. or higher. A boiling point of 130° C. or higher reduces the risk of odor leakage during printing, and when used in a printing machine having a mechanism for recovering and reusing solvent, the amine compound can be prevented from contaminating the recovered solvent, thereby preventing odor generation and deterioration in print quality.

[0037] Examples of suitable amine compounds include monoethanolamine (pKb: 4.56, boiling point: 170°C), N,N-diethylethanolamine (pKb: 4.13, boiling point: 163°C), 2-amino-2-methyl-1-propanol (pKb: 4.70, boiling point: 165.5°C), and 2-(dimethylamino)ethanol (pKb: 4.77, boiling point: 133°C). Among these, from the viewpoints of odor and liquid stability, N,N-diethylethanolamine and 2-amino-2-methyl-1-propanol are preferred, and N,N-diethylethanolamine is more preferred. These amine compounds may be used alone or in combination of two or more.

[0038] The content of the amine compound in the aqueous resin composition of the present invention is preferably 0.1% by mass or more, more preferably 0.2% by mass or more, and even more preferably 0.3% by mass or more. On the other hand, it is preferably 5% by mass or less, more preferably 2% by mass or less, and even more preferably 1% by mass or less. When the content is equal to or greater than the lower limit, the liquid stability effect is enhanced, and when the content is equal to or less than the upper limit, it is preferable in terms of safety to the human body. The content ratio (mass ratio) of the amine compound to the polyurethane resin is preferably 0.4 mass % or more, more preferably 0.8 mass % or more, from the viewpoint of liquid stabilization, while it is preferably 6 mass % or less, more preferably 4 mass % or less, from the viewpoint of odor reduction. The content ratio (mass ratio) of the amine compound to the crosslinking agent is preferably 10% by mass or more, more preferably 18% by mass or more, from the viewpoint of liquid stabilization, while it is preferably 60% by mass or less, more preferably 40% by mass or less, from the viewpoint of crosslinkability.

[0039] <Aqueous medium> The "aqueous resin composition" of the present invention means a composition containing a resin and an aqueous medium. Furthermore, the "aqueous coating liquid" of the present invention means a coating liquid containing an aqueous medium. The aqueous medium is water and / or a water-soluble organic solvent. It is preferable that the aqueous medium used in the present invention is only water, i.e., does not contain a water-soluble organic solvent. In the present invention, the water-soluble organic solvent refers to a compound that is soluble in water, and although the solubility in water is not limited, a compound that can dissolve in water at any ratio is preferred. Furthermore, even if a compound is difficult to have the properties of a solvent by itself (for example, a compound that is solid or has high viscosity at room temperature), the compound is included in the water-soluble organic solvent as long as it can be used as a solvent by being uniformly mixed with water. Examples of the water-soluble organic solvent include methanol, ethanol, propanol, ethylene glycol, propylene glycol, ethylene glycol dimethyl ether, propylene glycol dimethyl ether, N-methylpyrrolidone, N,N-dimethylformamide, etc. These water-soluble organic solvents may be used alone or in combination of two or more.

[0040] <Other additives> The aqueous resin composition of the present invention may contain antioxidants, antifungal agents, ultraviolet absorbers, leveling agents, surfactants, dispersing aids, fixing agents, pH adjusters, thickeners, colorants, deodorizers, fragrances, and the like, within the range that does not impair the effects of the present invention.

[0041] [Method of producing aqueous resin composition] In the present invention, it is preferable to separately prepare a base agent containing a polyurethane resin having carboxylate groups as a main component and a curing agent containing a crosslinking agent having at least two carbodiimide groups per molecule, and then mix the base agent and curing agent before use, i.e., before printing, to obtain an aqueous resin composition for coating, from the viewpoint of minimizing reaction between the base agent and curing agent before use. Here, "mixing before use" may mean mixing immediately before use, or there may be a period of storage at room temperature between mixing and use. The term "main component" means that 50% by mass or more of the nonvolatile components contained in each agent are that component.

[0042] If the base agent and hardener are manufactured, packaged, and stored separately, a chemical reaction between them will not occur, even if they are exposed to high temperatures during transportation (e.g., 40°C for one month), which is advantageous in terms of liquid stability compared to transporting them mixed together. If the base agent and hardener are delivered to users such as printers without being mixed, they can be mixed immediately before printing, and it is also easier to store them at room temperature (e.g., below 30°C) after mixing, making temperature control more convenient than during transportation. In other words, it is more advantageous in terms of liquid stability and liquid lifespan to have users such as printers mix them after delivery, rather than packaging and shipping them in a mixed form.

[0043] Known manufacturing methods can be applied to the production of each of the base agent and the curing agent. Also, known mixing and blending methods can be applied to the method of mixing and blending the base agent and the curing agent before printing.

[0044] The method for producing the base material containing the polyurethane resin as a main component is not particularly limited, but it is preferable to produce a polyurethane resin dispersion through a prepolymer production process, an emulsification process, and a chain extension process. In this case, it is preferable to use a neutralizing agent in the emulsification process to neutralize the carboxylate groups in the polyurethane structure and exhibit self-emulsifying properties. As the neutralizing agent, it is preferable to use ammonia or an amine compound, and among them, it is preferable to use ammonia.

[0045] The curing agent containing the crosslinking agent as a main component is produced by adding a crosslinking agent having at least a carbodiimide group to an aqueous medium and stirring the mixture at room temperature. Known mixing methods can be used. For example, methods using general anchor blades or turbine blades for stirring and mixing, or dispersion and mixing methods that apply shear force, such as a homogenizer, a homomixer, an attritor, or high-pressure liquid collision, can be used. However, from the viewpoint of maintaining the dispersibility of the liquid, stirring and mixing methods that do not apply shear force are preferred.

[0046] The polyalkylene glycol and amine compound may be added to either the base agent or the curing agent, or both, but from the viewpoint of liquid production and management, it is preferable to add them to the curing agent side.

[0047] To prepare the aqueous resin composition of the present invention, the base agent and the curing agent must be mixed. Known mixing methods can be used. For example, simple mixing using a shaker or rotor, mixing without an agitator, stirring and mixing using anchor blades or turbine blades, and mixing methods that apply shear force, such as using a homogenizer, homomixer, attritor, sand grinder, or high-pressure liquid collision, can be used. However, from the viewpoint of maintaining the dispersibility of the liquid, simple mixing and stirring and mixing methods that do not apply shear force are preferred. The temperature during the preparation of the base agent and curing agent, and during mixing of the base agent and curing agent, is preferably 10°C or higher and 30°C or lower, more preferably 15°C or higher and 25°C or lower.

[0048] [Coating method] The aqueous resin composition of the present invention is applied to a part or the entire surface of a printing medium before printing, i.e., before ink or toner is applied. For coating, rubber roll coating, die coating, microgravure coating, slit reverse coating, anilox roll coating, or the like is preferably used to form a high-speed, uniform coating film. Drying after coating is preferably carried out to remove as much water as possible, and an appropriate drying temperature is set depending on the appropriate airflow strength and the heat resistance of the printing medium. The drying temperature is preferably 50°C or higher, more preferably 60°C or higher, while it is preferably 80°C or lower, more preferably 70°C or lower. The thickness of the adhesive layer after drying is preferably 0.05 μm or more, more preferably 0.1 μm or more, and even more preferably 0.15 μm or more, and is preferably 2 μm or less, more preferably 1 μm or less, and even more preferably 0.6 μm or less.

[0049] [Print Media] Printing media to be coated or printed on include metal substrates such as aluminum, nickel, stainless steel, steel, magnesium, etc., flexible substrates such as polyethylene, polypropylene, polyethylene terephthalate, polyethylene naphthalate, polyamide, polyurethane, polyvinyl chloride, thermoplastic elastomer, laminates of these with aluminum foil, vapor-deposited aluminum, or vapor-deposited silicon oxide, glass, natural materials, resin-coated paper such as polyethylene-coated paper, etc. Flexible substrates may be stretched, porous, foamed, etc.

[0050] [ink] From the viewpoint of reactivity with the carbodiimide group of the crosslinking agent contained in the aqueous resin composition of the present invention, it is preferable that the ink or toner used for printing contains a resin having a carboxy group. In this case, it is preferable that the resin having a carboxy group is the main component of the ink or toner. Here, "main component" means that the resin accounts for 50% by mass or more of the resin contained in the ink or toner. Examples of the resin having a carboxy group include poly(ethylene / methacrylic acid) resin, poly(ethylene / acrylic acid) resin, polyester resin, poly(styrene / acrylic acid) resin, and polymethyl acrylate resin, and among these, poly(ethylene / methacrylic acid) resin and poly(ethylene / acrylic acid) resin are preferred. From the viewpoint of fixation to various printing media, the softening point of the resin having a carboxy group is preferably 120° C. or less, and more preferably 100° C. or less. A softening point of 120° C. or less can suppress problems such as thermal deformation or melting of the printing medium when fixing the ink to the printing medium. As the carrier liquid for the ink, it is preferable to use an aliphatic hydrocarbon organic solvent with a high boiling point of about 200°C.

[0051] [Printing method (image forming method)] The aqueous resin composition of the present invention is used, for example, in an electrophotographic digital printing machine as shown in Fig. 1, and after an adhesive layer is formed from the aqueous resin composition, printing is performed to produce a printed matter. The digital printing machine is composed of, for example, a print media unwinding unit 10, an adhesive layer coating unit 1, a printing unit 2, a printing machine control unit 100, and a print media winding unit 111. A printing method (image forming method) using the digital printing machine of Fig. 1 will be described below. First, printing medium 11 unwound from printing medium unwinding unit 10 is corona treated in corona treatment unit 12 in adhesive layer coating unit 1, and the surface energy is adjusted to be appropriate for printing. Then, aqueous resin composition 13 is applied from coating bath 14 containing aqueous resin composition to coating rolls 15 to 17, and the aqueous resin composition is applied onto printing medium 11, and dried in drying unit 18 to form an adhesive layer of a predetermined thickness. Next, digital image data from the printer control unit 100 is converted into a light pattern by an exposure device 102, and is irradiated onto a photoconductor 105 that has been uniformly charged in advance by a charging device 101. The electrostatic latent image thus formed is developed onto the photoconductor 105 by a developing device 104 with ink, which is the developer, supplied from a developer tank 103. The developer developed on the photoconductor 105 is primarily transferred to an intermediate transfer body 107 by electrostatic force. After the developer has been transferred to the intermediate transfer body 107, excess developer is removed from the photoconductor 105 by a cleaning device 106, and the process moves on to the next image formation. The developer that has been primarily transferred from the photoreceptor 105 onto the intermediate transfer member 107 is dried and melted by the internal heater 109 and external heater 108 of the intermediate transfer member 107, and then secondarily transferred and fixed onto the printing medium 11, on which an adhesive layer has been formed, by the pressure roller 110, forming the desired image, and the printed matter is taken up by the printing medium take-up unit 111. The solvent (carrier liquid) generated when the ink used in this printing press dries may be recovered within the press and reused. In this case, it is important that the recovered carrier liquid does not contain components of the aqueous resin composition of the present invention, and it is particularly important that amine compounds are not mixed in.

[0052] [Printed material] The aqueous resin composition of the present invention can be applied to a printing medium and dried by heating to form an adhesive layer. A printed matter can be obtained by applying an ink onto the adhesive layer or by transferring the ink onto the adhesive layer and then drying the ink. In the printed matter, the adhesive layer has a crosslinked structure between a polyurethane resin having a carboxylate group and a crosslinking agent having a carbodiimide group, which allows the printed matter to exhibit high water resistance and high laminate strength. [Example]

[0053] The following examples further illustrate the present invention, but the examples are provided to explain the present invention in detail, and the present invention is not limited to the examples shown below and can be modified as desired without departing from the gist of the present invention. In the following examples, polyurethane resin dispersion may be abbreviated as PUD, polyethylene glycol as PEG, biaxially oriented polypropylene as BOPP, oriented polyester as PET, and low-density polyethylene as LDPE. In the following, room temperature is 25°C.

[0054] [Example 1] <Production of Aqueous Resin Composition 1> As the main component, 542.5 g of a saturated hydrocarbon polyether polyurethane resin dispersion (trade name NeoRez R600, manufactured by DSM, solid content 33%, acid value 13 mgKOH / g, ammonia used as a neutralizer during production) was prepared. Next, an aliphatic carbodiimide compound (a mixture of Carbodilite SV-02 and Carbodilite V-02-L2 in a weight ratio of 1:1) was used as a crosslinking agent (Carbodilite SV-02: manufactured by Nisshinbo Chemical Co., Ltd., solid content 40%, carbodiimide group equivalent weight 430 mol -1 ) (Trade name: Carbodilite V-02-L2: manufactured by Nisshinbo Chemical Co., Ltd., solid content 40%, carbodiimide group equivalent weight 385 mol -1 264.3 g of ethylene glycol (trade name Polyethylene Glycol 600, abbreviated as PEG600, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), 9.0 g of polyethylene glycol (trade name Polyethylene Glycol 600, abbreviated as PEG600, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), 3.0 g of N,N-diethylethanolamine (abbreviated as DEEA, pKb: 4.13) as an amine compound, and 181.2 g of dilution water were mixed to obtain 457.5 g of curing agent. The base resin and the curing agent were mixed 30 minutes before printing, which will be described later, to produce 1000 g of aqueous resin composition 1.

[0055] [Example 2] <Production of Aqueous Resin Composition 2> 1000 g of aqueous resin composition 2 was produced in the same manner as aqueous resin composition 1, except that the aliphatic carbodiimide compound was changed to 239.6 g of a mixture of Carbodilite SV-02 (trade name) and Carbodilite V-02-L2 (trade name) in a weight ratio of 3:1, and the blending amounts were changed accordingly as shown in Table 1.

[0056] [Example 3] <Production of Aqueous Resin Composition 3> 1000 g of aqueous resin composition 3 was produced in the same manner as aqueous resin composition 1, except that the aliphatic carbodiimide compound was changed to 165.1 g of a mixture of Carbodilite SV-02 (trade name) and Carbodilite V-02-L2 (trade name) in a weight ratio of 3:1, and the blending amounts were changed accordingly as shown in Table 1.

[0057] [Example 4] <Production of Aqueous Resin Composition 4> 1000 g of aqueous resin composition 4 was produced in the same manner as aqueous resin composition 1, except that the aliphatic carbodiimide compound was changed to 278.4 g of a mixture of Carbodilite SV-02 (trade name) and Carbodilite V-02-L2 (trade name) in a weight ratio of 3:1, polyethylene glycol was not used, and the blending amounts were changed accordingly as shown in Table 1.

[0058] [Example 5] <Production of Aqueous Resin Composition 5> 1000 g of aqueous resin composition 5 was produced in the same manner as aqueous resin composition 1, except that the aliphatic carbodiimide compound was changed to 270.2 g of a mixture of Carbodilite SV-02 (trade name) and Carbodilite V-02-L2 (trade name) in a weight ratio of 3:1, and the blending amounts were changed accordingly as shown in Table 1.

[0059] [Example 6] <Production of Aqueous Resin Composition 6> 1000 g of aqueous resin composition 6 was produced in the same manner as in the production of aqueous resin composition 5, except that the amount of polyethylene glycol (trade name: Polyethylene Glycol 600) used was changed to 16.9 g and the blending amounts were changed accordingly as shown in Table 1.

[0060] [Example 7] <Production of Aqueous Resin Composition 7> 1000 g of aqueous resin composition 7 was produced in the same manner as aqueous resin composition 5, except that the amount of polyethylene glycol (trade name: Polyethylene Glycol 600) used was changed to 24.2 g and the blending amounts were changed accordingly as shown in Table 1.

[0061] [Example 8] <Production of Aqueous Resin Composition 8> 1000 g of aqueous resin composition 8 was produced in the same manner as in the production of aqueous resin composition 5, except that the amount of polyethylene glycol (trade name: Polyethylene Glycol 600) used was changed to 30.0 g and the blending amounts were changed accordingly as shown in Table 1.

[0062] [Example 9] <Production of Aqueous Resin Composition 9> 1000 g of aqueous resin composition 9 was produced in the same manner as aqueous resin composition 6, except that the aliphatic carbodiimide compound was changed to 301.7 g of a mixture of Carbodilite SV-02 (trade name) and Carbodilite V-02-L2 (trade name) in a weight ratio of 3:1, and the blending amounts were changed accordingly as shown in Table 1.

[0063] [Example 10] <Production of aqueous resin composition 10> 1000 g of aqueous resin composition 10 was produced in the same manner as aqueous resin composition 6, except that the aliphatic carbodiimide compound was changed to 354.4 g of a mixture of Carbodilite SV-02 (trade name) and Carbodilite V-02-L2 (trade name) in a weight ratio of 3:1, and the blending amounts were changed accordingly as shown in Table 1.

[0064] [Example 11] <Production of Aqueous Resin Composition 11> 1000 g of aqueous resin composition 11 was produced in the same manner as in the production of aqueous resin composition 8, except that the aliphatic carbodiimide compound was changed to 467.5 g of a mixture of Carbodilite SV-02 (trade name) and Carbodilite V-02-L2 (trade name) in a weight ratio of 3:1, and the blending amounts were changed accordingly as shown in Table 1.

[0065] [Example 12] <Production of Aqueous Resin Composition 12> 1000 g of aqueous resin composition 12 was produced in the same manner as in the production of aqueous resin composition 5, except that the aliphatic carbodiimide compound was changed to 270.2 g of Carbodilite SV-02 (trade name) and the blending amounts were changed accordingly as shown in Table 1.

[0066] [Example 13] <Production of Aqueous Resin Composition 13> 1000 g of aqueous resin composition 13 was produced in the same manner as in the production of aqueous resin composition 5, except that the aliphatic carbodiimide compound was changed to 270.2 g of Carbodilite V-02-L2, and the blending amounts were changed accordingly as shown in Table 1.

[0067] [Example 14] <Production of Aqueous Resin Composition 14> A base agent and a curing agent were prepared in the same manner as in the production of aqueous resin composition 1. The base agent and the curing agent were each stored in a sealed state at 40°C for one month, and then mixed in the same manner as in aqueous resin composition 1 to produce 1000 g of aqueous resin composition 14.

[0068] [Example 15] <Production of Aqueous Resin Composition 15> 1000 g of aqueous resin composition 15 was produced in the same manner as in the production of aqueous resin composition 5, except that the same amount of polyethylene glycol (trade name: polyethylene glycol 1000, abbreviated as PEG1000, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was used instead of polyethylene glycol (trade name: polyethylene glycol 600).

[0069] [Example 16] <Production of Aqueous Resin Composition 16> 1000 g of aqueous resin composition 16 was produced in the same manner as in the production of aqueous resin composition 5, except that the same amount of polyethylene glycol (trade name: polyethylene glycol 1540, abbreviated as PEG1540, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was used instead of polyethylene glycol (trade name: polyethylene glycol 600).

[0070] [Example 17] <Production of Aqueous Resin Composition 17> 1000 g of aqueous resin composition 17 was produced in the same manner as in the production of aqueous resin composition 5, except that the same amount of polyethylene glycol (trade name: polyethylene glycol 200, abbreviated as PEG200, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was used instead of polyethylene glycol (trade name: polyethylene glycol 600).

[0071] [Example 18] <Production of Aqueous Resin Composition 18> A base agent and a curing agent were prepared in the same manner as in the production of aqueous resin composition 4. 1000 g of aqueous resin composition 18 was produced in the same manner as in the production of aqueous resin composition 4, except that after mixing the base agent and the curing agent, the mixture was allowed to stand at room temperature in a sealed state for 2 months.

[0072] [Example 19] <Production of Aqueous Resin Composition 19> In the production of aqueous resin composition 4, no amine compound was used, and the base agent and curing agent were prepared in the amounts shown in Table 1. 1000 g of aqueous resin composition 19 was produced in the same manner as aqueous resin composition 4, except that after mixing the base agent and the curing agent, the mixture was allowed to stand at room temperature in a sealed state for 2 months.

[0073] [Comparative Example 1] <Production of Comparative Aqueous Resin Composition 1> In the production of aqueous resin composition 1, the aliphatic carbodiimide compound was changed to 148.5 g of a mixture of Carbodilite SV-02 (trade name) and Carbodilite V-02-L2 (trade name) in a 1:1 weight ratio, and polyethylene glycol was not used. The blending amounts were accordingly changed as shown in Table 1 to prepare the base resin and curing agent. 1000 g of comparative aqueous resin composition 1 was produced in the same manner as in the production of aqueous resin composition 1, except that after mixing the base resin and curing agent, the mixture was allowed to stand at room temperature in a sealed state for 2 months.

[0074] Comparative Example 2 <Production of Comparative Aqueous Resin Composition 2> 1000 g of comparative aqueous resin composition 2 was produced in the same manner as in the production of aqueous resin composition 1, except that the aliphatic carbodiimide compound was changed to 82.5 g of a mixture of Carbodilite SV-02 (trade name) and Carbodilite V-02-L2 (trade name) in a weight ratio of 3:1, polyethylene glycol was not used, and the blending amounts were changed accordingly as shown in Table 1.

[0075] Comparative Example 3 <Production of Comparative Aqueous Resin Composition 3> The aliphatic carbodiimide compound was Carbodilite V-02 (manufactured by Nisshinbo Chemical Co., Ltd., solid content 40%, carbodiimide group equivalent weight 590 mol -1 1000 g of comparative aqueous resin composition 3 was produced in the same manner as in the production of aqueous resin composition 1, except that the amount of polyethylene glycol was changed to 64.4 g, polyethylene glycol was not used, and the blending amounts were changed accordingly as shown in Table 1.

[0076] Comparative Example 4 <Production of Comparative Aqueous Resin Composition 4> 1000 g of Comparative Aqueous Resin Composition 4 was produced in the same manner as Comparative Aqueous Resin Composition 2, except that the aliphatic carbodiimide compound was changed to 666.7 g of a mixture of Carbodilite SV-02 (trade name) and Carbodilite V-02-L2 (trade name) in a weight ratio of 3:1, polyethylene glycol was not used, and the blending amounts were changed accordingly as shown in Table 1.

[0077] Comparative Example 5 <Preparation of Comparative Aqueous Resin Composition 5> 1000 g of Comparative Aqueous Resin Composition 5 was produced in the same manner as Comparative Aqueous Resin Composition 2, except that the aliphatic carbodiimide compound was changed to 600.0 g of a mixture of Carbodilite SV-02 (trade name) and Carbodilite V-02-L2 (trade name) in a weight ratio of 3:1, polyethylene glycol was not used, and the blending amounts were changed accordingly as shown in Table 1.

[0078] Comparative Example 6 <Production of Comparative Aqueous Resin Composition 6> In the production of aqueous resin composition 1, a polyurethane resin dispersion containing aromatic polyester polyol as one of the raw materials (trade name Hydran AP201, manufactured by DIC Corporation, solids content 23%, acid value 25 mgKOH / g, triethylamine used as a neutralizing agent during production) was used as the polyurethane resin dispersion, polyethylene glycol was not used, the solids concentration after mixing was set to 25%, and the blending amounts were changed accordingly as shown in Table 1. 1000 g of comparative aqueous resin composition 6 was produced in the same manner as aqueous resin composition 1.

[0079] [Table 1]

[0080] The aqueous resin compositions obtained in the above Examples and Comparative Examples and the comparative aqueous resin compositions were evaluated for initial peel resistance, water resistance, lamination strength, low-staining properties, and image quality after printing 100 m or more. The evaluation methods for each were explained below. The evaluation results are shown in Table 2.

[0081] <Evaluation of initial peel resistance> 1000 g of each of the aqueous resin compositions obtained in the above Examples and Comparative Examples and the comparative aqueous resin composition was placed in a coating tray of an in-line primer coater of an electrophotographic liquid developing printer (product name HP Indigo WS6600, manufactured by HP Inc.), and with the liquid circulation stopped, the composition was coated onto the entire surface of a BOPP film (film thickness 20 μm, corona treated, surface free energy: 38 mN / m or more) and a PET film (film thickness 12 μm), dried, and then a test pattern of approximately 100 m was printed on each film. Immediately after printing, i.e., within 3 minutes after printing was completed, masking tape (product name: Scotch (registered trademark) Mending Tape 810, manufactured by 3M) was applied to the obtained evaluation sample, and a tape peeling test was conducted in accordance with ASTM D3330, and the initial peel resistance was evaluated according to the following criteria. The evaluation results are shown in Table 2. A score of + or above is considered a pass level. ++: The remaining rate for both BOPP film and PET film is 80% or more. +: The remaining rate of either the BOPP film or the PET film is 80% or more, and the remaining rate of the other is 60% or more but less than 80%. - : For both BOPP film and PET film, the residual rate is 60% or more but less than 80%. --: Either the BOPP film or the PET film has a residual rate of less than 60%, and the other has a residual rate of 60% or more but less than 80%. ---: The remaining rate is less than 60% for both BOPP film and PET film.

[0082] <Water resistance evaluation> A sample with the same specifications as the evaluation sample used in the initial peel resistance evaluation was immersed in water at room temperature for 2 hours, removed, and the water was wiped off. A tape peel test was then conducted in the same manner as in the initial peel resistance evaluation. The evaluation criteria were the same as those used in the initial peel resistance evaluation. The evaluation results are shown in Table 2.

[0083] <Laminate strength evaluation> Two-component curing solvent-free polyurethane adhesive (product name: LOCTITE LIOFOL LA7732 / LA6159) was mixed in a mass ratio of LA7732:LA6159=2:1, and applied at a coating rate of approximately 3 g / m2 to the printed surface of the PET printed film prepared for the initial peel resistance evaluation described above. 2 After coating so that the thickness was as shown, an 80 μm LDPE film was laminated to it at 50°C, and after storing at 50°C for 3 days, the T-peel strength between the PET and LDPE was measured and recorded as the laminate strength (N / inch). The laminate strength was evaluated according to the following criteria. + or above is a passing level. ++: Laminate strength ≥ 3.5N / inch + :3.5N / inch>Laminate strength≧2N / inch - :2N / inch> Lamination strength

[0084] <Low contamination evaluation> After printing 1000 m on a PET film in the same manner as in the evaluation of initial peel resistance, the aqueous resin composition and ink remaining on the intermediate transfer body were visually confirmed. The degree of contamination was evaluated according to the following criteria: + or above is an acceptable level. ++: Neither the aqueous resin composition nor the ink was observed to adhere. +: Adhesion of the aqueous resin composition was observed, but adhesion of the ink was not observed. -: Adhesion of both the aqueous resin composition and ink was observed.

[0085] <Image quality evaluation> 1000 g of each of the aqueous resin compositions obtained in the above Examples and Comparative Examples and the comparative aqueous resin composition was placed in the coating tray of an in-line primer coater in an electrophotographic liquid developing printer (product name HP Indigo WS6600, manufactured by HP Inc.). With the liquid circulation stopped, the composition was applied to the entire surface of a BOPP film (20 μm thick, corona-treated, surface free energy: 38 mN / m or more) and a PET film (12 μm thick), and then dried. After that, a test pattern of approximately 100 m was printed on each film, and the image quality was evaluated according to the following criteria. The evaluation results are shown in Table 2. + or higher indicates a pass level. ++: The image quality was good, and no adhesive layer and / or ink layer remained on the intermediate transfer member. +: The image quality was good, and although there was a small amount of adhesive layer and / or ink layer remaining on the intermediate transfer member, it was easily removed. -: Image quality was defective, and adhesive layer and / or ink layer remained on the intermediate transfer member, but could be easily removed. --: Image quality was defective, and adhesive and / or ink layers remained on the intermediate transfer member and could not be easily removed.

[0086] [Table 2]

[0087] From the results of Examples 1 to 19 shown in Table 2, it was found that when the aqueous resin composition of the present invention was applied to a printing medium to form an adhesive layer and then printed on top of that for 100 m or more, the initial peel resistance between the printing medium and the adhesive layer, and between the adhesive layer and the ink layer was good, that is, the peel resistance was good immediately after printing, the printed matter also had good water resistance, high lamination strength, low contamination of contact members, and good image quality. Furthermore, from Examples 18 and 19, it can be seen that even when the aqueous resin composition is stored at room temperature for a long period of time after mixing the base resin and the curing agent, the aqueous resin composition after mixing has good initial peel resistance and water resistance in printed matter of 100 m or more, has high lamination strength, is less likely to stain contact members, and has good image quality. On the other hand, in Comparative Examples 1 to 3, in which the molar ratio of carbodiimide groups in the crosslinking agent to carboxylate groups in the polyurethane resin was less than 5.1, the initial peel resistance and laminate strength were insufficient. In Comparative Examples 4 and 5, in which the molar ratio of carbodiimide groups in the crosslinking agent to carboxylate groups in the polyurethane resin was greater than 40, component contamination and image degradation were observed, and in Comparative Example 6, deterioration in initial peel resistance and water resistance was observed. [Industrial Applicability]

[0088] The aqueous resin composition of the present invention is used in the production and processing of coated / printed materials such as signs, advertisements, posters, signage, and menu lists, food and industrial packaging materials such as seal labels, shrink labels, pouches, and bags, and decorative films for electronic products, vehicles, aircraft, building materials, decorations, smartphones, and the like, which require initial peel resistance, water resistance, and high lamination strength. [Explanation of symbols]

[0089] 1. Adhesive layer coating unit 2 Printing Unit 10 Print media unwind unit 100 Printing press control unit 111 Print media take-up unit

Claims

1. An aqueous resin composition comprising at least a polyurethane resin having a carboxylate group and a crosslinking agent having at least two carbodiimide groups per molecule, wherein the molar ratio of the carbodiimide groups of the crosslinking agent to the carboxylate groups of the polyurethane resin is 5.1 or more and 40 or less.

2. 2. The aqueous resin composition according to claim 1, wherein the polyurethane resin is a saturated hydrocarbon-based polyether polyurethane resin and has an ammonium carboxylate group.

3. The aqueous resin composition according to claim 1, further comprising a polyalkylene glycol.

4. The aqueous resin composition according to claim 3 , wherein the polyalkylene glycol is contained in an amount of 1 part by mass or more and 20 parts by mass or less per 100 parts by mass of the polyurethane resin.

5. The aqueous resin composition according to claim 3, wherein the molecular weight of the polyalkylene glycol is 200 or more and 900 or less.

6. A digital printing image forming method, comprising: applying the aqueous resin composition according to any one of claims 1 to 5 onto a printing medium to form an adhesive layer; and then forming an ink layer using an ink containing a resin having a carboxy group.

7. An aqueous coating liquid containing at least a polyurethane resin having a carboxylate group and a crosslinking agent having at least two carbodiimide groups per molecule, The aqueous coating liquid has a molar ratio of carbodiimide groups in the crosslinking agent to carboxylate groups in the polyurethane resin of 5.1 or more and 40 or less.

8. A method for producing an aqueous resin composition, comprising separately producing a base agent whose main component is a polyurethane resin having a carboxylate group and a curing agent whose main component is a crosslinking agent having at least two carbodiimide groups per molecule, and mixing the base agent and the curing agent before use.

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