Aqueous inkjet composition and method for forming printing substrate using said composition

Abstract

The purpose of the present disclosure is to provide an aqueous inkjet composition which has improved dischargeability and from which a printed layer having high smoothness is obtained.　An aqueous inkjet composition according to the present disclosure is characterized by containing at least three surfactants, wherein at least one of the surfactants is a surfactant A having an HLB value of 9 or less and a weight average molecular weight of 4,000 or more.

Description

Aqueous inkjet composition, and method for forming a printing substrate using the composition.

[0001] This disclosure relates to an aqueous inkjet composition and a method for forming a printing substrate using the composition.

[0002] In recent years, inkjet printing, a digital printing method that does not require platemaking, has rapidly become popular in order to handle the printing of a wide variety of products in small batches. The inks used in inkjet printing are classified into solvent-based, water-based, and active energy ray-curing types, and among these, the demand for water-based inks has been increasing in recent years due to considerations and measures to address harmful effects on the environment and people.

[0003] For example, Patent Document 1 contains a colorant, water, an organic solvent, and a surfactant, wherein the organic solvent has an SP value of 9.0 to 12.0 (cal / cm³). 3 ) 1 / 2 An inkjet ink is disclosed that contains glycol ether and is characterized by containing (a) a silicone-based surfactant and (b) a nonionic surfactant as the surfactant. Patent Document 2 also describes the use of a non-white aqueous inkjet ink containing a non-white colorant and a silicone-based surfactant A having a specific molecular weight distribution, and a white aqueous inkjet ink containing a white colorant and a silicone-based surfactant B having a specific molecular weight distribution and an HLB value of 10.5 or less as an ink set for use in an inkjet recording method. Patent Document 3 also discloses an ink for thermal inkjet printing composed of an aqueous solution, an auxiliary solvent, a dye soluble in the auxiliary solvent, a surfactant, a pH adjuster, a viscosity modifier, and a biocide, wherein the surfactant is a nonionic surfactant with an HLB of 16 to 18, a nonionic surfactant with an HLB of 10 to 14, and diethylene glycol monohexyl ether.

[0004] Japanese Patent Publication No. 2020-50705, Japanese Patent Publication No. 2023-27950, Japanese Patent Publication No. Hei 8-41392

[0005] Incidentally, it has been found that with conventional water-based inkjet inks, the ejected ink dries from the edges, causing liquid to flow towards the edges (outside), resulting in the inside of the printed layer being thinner than the outside. Furthermore, it has been found that conventional water-based inkjet inks can cause clogging of the inkjet nozzles, meaning that the ejection performance may not be sufficient.

[0006] Therefore, this disclosure aims to provide an aqueous inkjet composition with improved ejection properties and smoothness of the resulting printed layer, as well as a printing method.

[0007] As a result of diligent research to solve the aforementioned problems, the inventors have discovered that by using three or more surfactants in combination in an aqueous inkjet composition, and by adjusting the HLB value and weight-average molecular weight of at least one of the surfactants to a specific range, the ejection performance and the smoothness of the resulting printed layer can be improved, thus completing the present invention.

[0008] In other words, the present disclosure is as follows: [1] An aqueous inkjet composition containing at least three types of surfactants, wherein at least one of the surfactants is surfactant A having an HLB value of 9 or less and a weight-average molecular weight of 4000 or more. [2] The aqueous inkjet composition according to [1], wherein surfactant A is a silicone-based surfactant. [3] The aqueous inkjet composition according to [1] or [2], wherein the surfactant comprises surfactant B1 other than surfactant A, and surfactant B1 is an acetylene-based surfactant. [4] The aqueous inkjet composition according to any one of [1] to [3], wherein the surfactant comprises surfactant B1 other than surfactant A, and surfactant B1 has an HLB value of 9 or less and a weight-average molecular weight of less than 4000. [5] The aqueous inkjet composition according to [3] or [4], wherein the mass ratio (B1 / A) of surfactant B1 to surfactant A is 0.7 or more. [6] The aqueous inkjet composition according to any one of [1] to [5], wherein the surfactant comprises surfactant B2 other than surfactant A, and surfactant B2 is a silicone-based surfactant. [7] The aqueous inkjet composition according to any one of [1] to [6], wherein the surfactant comprises surfactant B2 other than surfactant A, and surfactant B2 has an HLB value greater than 9 and a weight-average molecular weight of less than 4000. [8] The aqueous inkjet composition according to [6] or [7], wherein the mass ratio (B2 / A) of surfactant B2 to surfactant A is 1 or more. [9] The aqueous inkjet composition according to any one of [1] to [8], used for printing on a substrate made of plastic and / or metal.

[10] The aqueous inkjet composition according to any one of [1] to [9], used for transfer printing.

[11] The aqueous inkjet composition according to any one of [1] to

[10] , used for transfer printing on cloth.

[12] A method for forming a printing substrate, comprising ejecting the aqueous inkjet composition according to any one of [1] to

[11] onto a substrate using an inkjet method to form a printing layer.

[13] The method for forming a printing substrate according to

[12] , wherein the total amount of the aqueous inkjet composition ejected to form the printing layer is greater than the amount that the substrate can absorb.

[0009] The aqueous inkjet composition and printing method disclosed herein make it possible to achieve both good ejection performance and smoothness of the resulting printed layer.

[0010] Figure 1 is a schematic diagram showing the inner and outer regions of a solid pattern used for evaluating smoothness.

[0011] One embodiment of this disclosure will be described below, but the contents of this disclosure are not limited thereto. Unless otherwise specified in this specification, "A to B" representing a numerical range means "A or more, B or less". Also, "(meth)acrylic acid" means acrylic acid or methacrylic acid, and "(meth)acrylate" means acrylate or methacrylate. The same applies to terms such as "(meth)acryloxy" and "(meth)acryloyl". Furthermore, "structural unit derived from ~" corresponds to a structure in which the carbon-carbon double bond of each monomer component is replaced by a carbon-carbon single bond and two bonds attached to each carbon.

[0012] 1. Aqueous Inkjet Composition The aqueous inkjet composition disclosed herein contains at least three types of surfactants, and at least one of the surfactants is surfactant A, which has an HLB value of 9 or less and a weight-average molecular weight of 4000 or more. Because the aqueous inkjet composition contains surfactant A, which has an HLB value of 9 or less and a high molecular weight, the surfactant forms a high-viscosity layer on the surface of the ejected droplet of the composition, allowing the droplet to dry while remaining fixed. This suppresses liquid flow to the edges of the droplet during drying, thereby improving the smoothness of the printed layer. Furthermore, by having three different types of surfactants in the aqueous inkjet composition, the ejection performance during inkjet printing can be improved while maintaining the above-mentioned smoothness effect.

[0013] In this specification, "aqueous inkjet composition" refers to an ink composition used for inkjet printing, which contains water as a solvent.

[0014] 1-1. Surfactants 1-1-1. Surfactant A The HLB value of surfactant A is 9 or less, preferably 3.0 to 8.5, and more preferably 3.5 to 8.0. By adjusting the HLB value of surfactant A to below the above upper limit, the smoothness is improved, possibly because surfactant A moves more easily to the droplet surface. Also, by adjusting the HLB value of surfactant A to above the above lower limit, the solubility of surfactant A in water can be improved. Here, HLB value is an abbreviation for Hydrophile-Lipophile Balance Value, and is a parameter that is generally known as a concept that quantifies the balance between hydrophilic and lipophilic groups of a surfactant. The HLB value can be determined by known methods such as calculation by the Griffin method or the measurement method described below, but it is preferable to adopt the value obtained by the Griffin method, and if calculation by the Griffin method is difficult, it is preferable to adopt the value obtained by the measurement method described below. To explain the specific measurement method, 0.5 g of the target surfactant is dissolved in 5 mL of ethanol, and then the solution is titrated with a 2% by mass phenol aqueous solution while stirring at 25°C. The endpoint is reached when the solution becomes turbid, and the amount of phenol aqueous solution added up to that endpoint (let's call it A (mL)) is used to calculate the HLB value using the following formula (1): HLB value = 0.89 × A + 1.11 Formula (1)

[0015] The weight-average molecular weight (Mw) of surfactant A is 4000 or more, preferably 4500 to 30000, and more preferably 5000 to 20000. By adjusting the Mw of surfactant A to above the lower limit, the viscosity of the layer formed from surfactant A is increased, making it easier to fix droplets, and thus improving smoothness. Conversely, by adjusting the Mw of surfactant A to below the upper limit, the viscosity of the ink can be suitably adjusted. In this specification, the Mw of a surfactant refers to the value measured by the standard polystyrene equivalent method using gel permeation chromatography (GPC) when the surfactant has a repeating structure, and the molecular weight of the compound constituting the surfactant itself when the surfactant does not have a repeating structure. When measuring Mw by GPC, it is sufficient to measure it under the conditions described in the examples below.

[0016] The type of surfactant A is preferably a nonionic surfactant from the viewpoint of water resistance of the printed material. Examples of surfactant A include silicone-based surfactants, acetylene-based surfactants, and fluorine-based surfactants, among which silicone-based surfactants are preferred from the viewpoint of wettability of the ink to the substrate and slipperiness of the printed material surface, and nonionic silicone-based surfactants are more preferred.

[0017] The aqueous inkjet composition of the present disclosure may contain one or more surfactants A. If the aqueous inkjet composition of the present disclosure contains three or more surfactants A, it does not need to contain surfactants other than surfactant A; however, from the viewpoint of further improving ejection performance, it is preferable to include at least one surfactant other than surfactant A.

[0018] The content of surfactant A is preferably 0.01 to 2% by mass, more preferably 0.02 to 1% by mass, even more preferably 0.03 to 0.5% by mass, and particularly preferably 0.03 to 0.3% by mass, based on 100% by mass of the aqueous inkjet composition. By adjusting the content of surfactant A to be above the lower limit, the smoothness of the printed layer is further enhanced, and by adjusting it to be below the upper limit, a better balance between the smoothness and ejection properties of the printed layer is achieved.

[0019] Furthermore, the content of surfactant A is, for example, 0.1 to 100% by mass of the total surfactants contained in the aqueous inkjet composition, preferably 0.5 to 50% by mass, more preferably 1 to 25% by mass, and even more preferably 2 to 15% by mass.

[0020] 1-1-2. Surfactant B The aqueous inkjet composition of the present disclosure preferably contains surfactant B, which is different from surfactant A. That is, surfactant B is a surfactant that satisfies at least one of the following (1) and (2): (1) HLB value greater than 9 (2) Weight-average molecular weight less than 4000

[0021] The type of surfactant B is preferably a nonionic surfactant from the viewpoint of water resistance of printed materials. Examples of surfactant B include silicone-based surfactants, acetylene-based surfactants, and fluorine-based surfactants, among which silicone-based surfactants and / or acetylene-based surfactants are preferred, nonionic silicone-based surfactants and / or nonionic acetylene-based surfactants are more preferred, and it is even more preferable to include both nonionic silicone-based surfactants and nonionic acetylene-based surfactants.

[0022] The weight-average molecular weight (Mw) of surfactant B is preferably less than 4000, more preferably 100 to 3500, and even more preferably 200 to 3000, from the viewpoint of further improving dispensing performance.

[0023] The aqueous inkjet compositions of the present disclosure may contain one or more surfactants B. In particular, it is more preferable to use two or more surfactants B that differ from each other in at least one of the following requirements: HLB value, weight-average molecular weight, and type, and even more preferable to use two or more surfactants B that differ from each other in at least one of the following requirements: HLB value and type.

[0024] The total surfactant content (i.e., the total content of surfactants A and B) is preferably 0.3 to 8% by mass, more preferably 0.8 to 5% by mass, and even more preferably 1.0 to 3% by mass, based on 100% by mass of the aqueous inkjet composition.

[0025] As the surfactant B, it is preferable to include an acetylene-based surfactant or a surfactant having a weight average molecular weight of less than 4000 and an HLB value of 9 or less (hereinafter referred to as surfactant B1). Particularly, it is more preferable to include an acetylene-based surfactant having a weight average molecular weight of less than 4000 and an HLB value of 9 or less as the surfactant B1. By using the surfactant B1 together with the surfactant A, the ejection property can be further enhanced. The aqueous inkjet composition of the present disclosure may have one or more surfactants B1.

[0026] From the viewpoint of the water resistance of the printed matter, the type of the surfactant B1 is preferably a nonionic surfactant. Examples of the type of the surfactant B1 include silicone-based surfactants, acetylene-based surfactants, fluorine-based surfactants, etc. Among them, an acetylene-based surfactant is preferable from the viewpoint of further enhancing the ejection property, and a nonionic acetylene-based surfactant is more preferable.

[0027] The weight average molecular weight (Mw) of the surfactant B1 is preferably less than 4000, more preferably 100 to 3500, still more preferably 200 to 3000, and may be 100 to 2000, 100 to 1000, or 100 to 600. By adjusting the Mw of the surfactant B1 within the above range, the viscosity of the ink can be suitably adjusted.

[0028] The HLB value of the surfactant B1 is preferably 9 or less, more preferably 3.5 to 8.5, still more preferably 4.0 to 8.0. By adjusting the HLB value of the surfactant B1 to be below the above upper limit value, the ejection property can be further enhanced, and by adjusting it to be above the above lower limit value, the solubility of the surfactant B1 in water can be enhanced.

[0029] The content of the surfactant B1 is preferably 0.1 to 3% by mass, more preferably 0.2 to 1.5% by mass, still more preferably 0.3 to 0.8% by mass in 100% by mass of the aqueous inkjet composition. By adjusting the content of the surfactant B1 within the above range, the ejection property can be further enhanced.

[0030] Further, the mass ratio of surfactant B1 to surfactant A (B1 / A) is preferably 0.7 to 30, more preferably 1.5 to 20, and even more preferably 2.0 to 15. By adjusting the mass ratio (B1 / A) within the above range, the balance between the smoothness and the ejection property of the printing layer becomes better.

[0031] Further, as the surfactant B, it is preferable to include a silicone-based surfactant or a surfactant (hereinafter referred to as surfactant B2) having a weight average molecular weight of less than 4000 and an HLB value exceeding 9. Particularly, it is more preferable to include a silicone-based surfactant having a weight average molecular weight of less than 4000 and an HLB value exceeding 9 as the surfactant B2. By using the surfactant B2 together with the surfactant A, the smoothness of the printing layer can be further enhanced. The aqueous inkjet composition of the present disclosure may have one or more kinds of the surfactant B2.

[0032] The type of the surfactant B2 is preferably a nonionic surfactant from the viewpoint of the water resistance of the printed matter. Examples of the type of the surfactant B2 include silicone-based surfactants, acetylene-based surfactants, fluorine-based surfactants, etc. Among them, a silicone-based surfactant is preferable from the viewpoint of the wettability to the substrate, and a nonionic silicone-based surfactant is more preferable.

[0033] The weight average molecular weight (Mw) of the surfactant B2 is preferably less than 4000, more preferably 100 to 3500, even more preferably 500 to 3000, and particularly preferably 800 to 2500. By adjusting the Mw of the surfactant B2 to be below the above upper limit value, the viscosity of the ink can be suitably adjusted, and by adjusting it to be above the above lower limit value, the wettability can be further enhanced.

[0034] The HLB value of the surfactant B2 is preferably more than 9, more preferably 9.1 to 15.0, and even more preferably 9.5 to 14.0. By adjusting the HLB value of the surfactant B2 to be below the above upper limit value, the wettability can be increased, and by adjusting it to be above the above lower limit value, the solubility of the surfactant B2 in water can be enhanced. <0000i00>

[0035] The content of surfactant B2 is preferably 0.1 to 4.0% by mass, more preferably 0.5 to 2.5% by mass, and even more preferably 0.8 to 1.5% by mass, based on 100% by mass of the aqueous inkjet composition. By adjusting the content of surfactant B2 within the above range, the smoothness of the printed layer can be further improved.

[0036] Furthermore, the mass ratio of surfactant B2 to surfactant A (B2 / A) is preferably 1 to 50, more preferably 2 to 35, and even more preferably 3 to 25. By adjusting the mass ratio (B2 / A) to the above range, the smoothness of the printed layer can be further improved.

[0037] The aqueous inkjet composition of this disclosure preferably contains surfactant A and surfactant B1 and / or surfactant B2, and more preferably contains surfactant A, surfactant B1 and surfactant B2.

[0038] The total content of surfactant A, surfactant B1, and surfactant B2 is, for example, 70% by mass or more, preferably 80% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, and may be 100% by mass, based on 100% by mass of the total amount of surfactants contained in the aqueous inkjet composition.

[0039] 1-2. Resin The aqueous inkjet composition of the present disclosure preferably further comprises a resin. As the resin, known resins used in the art can be used.

[0040] The weight-average molecular weight (Mw) of the resin can be adjusted as appropriate depending on its application, but from the viewpoint of suppressing the flow of the water-based inkjet composition during printing and improving the durability of the printed layer, it is preferably 5,000 or more, more preferably 20,000 or more, and even more preferably 50,000 or more. Furthermore, from the viewpoint of film-forming properties and water resistance, the Mw of the resin is preferably 5,000,000 or less. When used as an adhesive ink, from the viewpoint of improving transferability, the upper limit of the Mw of the resin is preferably 700,000 or less, and more preferably 550,000 or less. That is, from the viewpoint of transferability, the Mw of the resin is preferably 5,000 to 500,000, more preferably 20,000 to 550,000, and even more preferably 50,000 to 550,000. The Mw of the resin can be calculated by the standard polystyrene equivalent method using gel permeation chromatography (GPC).

[0041] The glass transition temperature (Tg) of the resin can be adjusted as appropriate depending on its application, but is preferably -50 to 35°C, more preferably -40 to 20°C, and even more preferably -30 to 10°C. By adjusting the resin's Tg to above the lower limit, the strength of the printed layer can be increased. Furthermore, by adjusting the resin's Tg to below the upper limit, cracking of the printed layer can be suppressed even under harsh conditions such as washing and tumble drying. Also, when used as an adhesive ink, the resin can be quickly softened during transfer printing, improving transferability. The resin's Tg can be measured by differential scanning calorimetry (DSC).

[0042] Examples of the aforementioned resins include vinyl resins, (meth)acrylic resins, polyester resins, olefin resins, urethane resins, fluororesins, silicone resins, epoxy resins, phenoxy resins, phenolic resins, and xylene resins. The aqueous inkjet composition of this disclosure may contain one or more resins. Among these, at least one selected from the group consisting of (meth)acrylic resins, polyester resins, and urethane resins is preferred, and (meth)acrylic resins are particularly preferred.

[0043] The (meth)acrylic resin preferably contains structural units derived from alkyl (meth)acrylate, and in particular, structural units derived from alkyl (meth)acrylate (hereinafter sometimes referred to as low-Tg alkyl (meth)acrylate) having a glass transition temperature (Tg) of the homopolymer of -20°C or lower, and / or C methacrylate. 1-5 It is preferable that the resin contains structural units derived from alkyl esters, and more preferably that it contains structural units derived from low-Tg alkyl (meth)acrylates. By appropriately adjusting the content of these monomer-derived structural units, the Tg of the resin can be easily adjusted.

[0044] In this specification, the "glass transition temperature of a homopolymer" may be the value listed in, for example, "Polymer Handbook Third Edition" (by J. Brandrup and E. H. Immergut, 1989, published by John Wiley & Sons, Inc., pp. VI / 209 to VI / 277) (if multiple Tg values ​​are listed, the lowest value may be used). Furthermore, for compounds not listed in "POLYMER HANDBOOK THIRD EDITION," you may use values ​​(calculated values) obtained by computer using commercially available glass transition temperature calculation software (for example, "MATERIALS STUDIO" from Accelrys Software Inc., version: 4.0.0.0, module: Synthia, conditions: calculation with an average polymerization molecular weight of 100,000).

[0045] Examples of the low-Tg alkyl esters include ethyl acrylate, n-propyl acrylate, n-butyl acrylate, isobutyl acrylate, n-pentyl acrylate, n-hexyl acrylate, n-octyl acrylate, 2-octyl acrylate, 2-ethylhexyl acrylate, n-nonyl acrylate, and isononyl acrylate. Among these, at least one selected from n-butyl acrylate, 2-octyl acrylate, and 2-ethylhexyl acrylate is preferred.

[0046] The aforementioned methacrylic acid C 1-5Alkyl esters refer to compounds in which the alkyl group constituting the alkyl methacrylate has 1 to 5 carbon atoms. Among these, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, tert-butyl methacrylate, and other C methacrylates are examples of alkyl methacrylates. 1-4 Chain-like alkyl esters are preferred, and methyl methacrylates are more preferred.

[0047] The (meth)acrylic resin may further contain one or more structural units derived from acid group-containing monomers. Including structural units derived from acid group-containing monomers can improve the stability of emulsion particles composed of the (meth)acrylic resin.

[0048] Examples of acid group-containing monomers include unsaturated monocarboxylic acids such as (meth)acrylic acid, cinnamic acid, and crotonic acid; unsaturated dicarboxylic acids such as maleic acid, fumaric acid, itaconic acid, and citraconic acid; monoesters of unsaturated dicarboxylic acids such as monomethyl maleic acid, monobutyl maleic acid, monomethyl itaconic acid, and monobutyl itaconic acid; anhydrides of unsaturated dicarboxylic acids such as maleic anhydride; and 2-acryloyloxyethyl succinic acid, 2-acryloyloxyethyl phthalic acid, and 2-acryloyloxyethyl hexahydrophthalic acid. Among these, unsaturated monocarboxylic acids are preferred as acid group-containing monomers, and (meth)acrylic acid is more preferred.

[0049] The (meth)acrylic resin may further contain one or more structural units derived from styrene monomers. The styrene monomers include styrene; halogen atoms (e.g., fluorine atoms, chlorine atoms, bromine atoms, iodine atoms); alkyl groups (e.g., methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, tert-butyl group, etc.). 1-4 Alkyl groups, vinyl groups, alkoxysilyl groups (e.g., trimethoxysilyl group, triethoxysilyl group, etc.) 1-4Styrene having one or more substituents such as an alkoxysilyl group); and the like. As the substituent, at least one selected from a halogen atom and an alkyl group is preferable. Specific examples of the styrene monomer include vinyltoluenes such as styrene, α-methylstyrene, p-methylstyrene, tert-butylstyrene, chlorostyrene, chloromethylstyrene, divinylbenzene, p-styryltrimethoxysilane, 2-styrylethyltrimethoxysilane, and the like. Among the styrene monomers, styrene is preferable from the viewpoint of enhancing the water resistance of the printing layer.

[0050] In particular, the (meth)acrylic resin preferably contains a structural unit derived from a low-Tg (meth)acrylic acid alkyl ester and a structural unit derived from a methacrylic acid C 1-5 alkyl ester and / or a styrene monomer (Aspect A). From the viewpoint of enhancing the water resistance of the printing layer, it is more preferable to contain a structural unit derived from a low-Tg (meth)acrylic acid alkyl ester and a structural unit derived from a styrene monomer (Aspect B). Further, since the stability of the (meth)acrylic resin tends to be improved and the durability of the obtained printing layer tends to be further enhanced, it is more preferable to further contain a structural unit derived from an acid group-containing monomer in Aspect A and Aspect B (Aspect C).

[0051] In 100% by mass of the (meth)acrylic resin, the total content of the structural units derived from the low-Tg (meth)acrylic acid alkyl ester, methacrylic acid C 1-5 alkyl ester, styrene monomer, and acid group-containing monomer is preferably 60% by mass or more, more preferably 80% by mass or more, still more preferably 90% by mass or more, and may be 100% by mass. The content of the structural unit derived from the low-Tg (meth)acrylic acid alkyl ester in 100% by mass of the (meth)acrylic resin may be appropriately adjusted according to the target Tg, but is preferably 20 to 90% by mass, more preferably 30 to 70% by mass, and still more preferably 40 to 60% by mass. Methacrylic acid C 1-5The total content of structural units derived from alkyl esters and styrene monomers is preferably 10 to 350 parts by mass, more preferably 40 to 200 parts by mass, and even more preferably 65 to 150 parts by mass, per 100 parts by mass of structural units derived from low-Tg alkyl (meth)acrylate. The total content of structural units derived from styrene monomers is, for example, 0 to 100 parts by mass, preferably 10 to 80 parts by mass, and more preferably 20 to 60 parts by mass, per 100 parts by mass of structural units derived from low-Tg alkyl (meth)acrylate. The content of structural units derived from acid group-containing monomers is low-Tg alkyl (meth)acrylate and C methacrylate. 1-5 For every 100 parts by mass of the total structural units derived from alkyl esters and styrene monomers, the amount is, for example, 0 to 8 parts by mass, preferably 0.1 to 5 parts by mass, and more preferably 0.3 to 2 parts by mass.

[0052] (Meth)acrylic resins may have one or more structural units derived from alkyl (meth)acrylates, acid group-containing monomers, and monomers other than styrene monomers. Other monomers are not particularly limited and include, for example, hydroxyl group-containing monomers (e.g., hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate), etc.), alkoxyalkyl group-containing (meth)acrylates (e.g., methoxyethyl (meth)acrylate, methoxybutyl (meth)acrylate), piperidine group-containing (meth)acrylates (e.g., 4-(meth)acryloyloxy-2,2,6,6-tetramethylpiperidine, 4-(meth)acryloyloxy-1,2,2,6,6-pentamethylpiperidine), etc. Examples include meth)acrylic monomers; addition polymerizable oxazolines such as 2-vinyl-2-oxazoline, 2-vinyl-4-methyl-2-oxazoline, 2-vinyl-5-methyl-2-oxazoline, 2-isopropenyl-2-oxazoline, 2-isopropenyl-4-methyl-2-oxazoline, 2-isopropenyl-5-methyl-2-oxazoline, and 2-isopropenyl-5-ethyl-2-oxazoline; vinyl monomers such as vinyl acetate, vinyl chloride, and vinyl benzoate; acrylonitrile; (meth)acrylamide monomers such as (meth)acrylamide, N-monomethyl(meth)acrylamide, N-monoethyl(meth)acrylamide, and N,N-dimethyl(meth)acrylamide; olefin monomers such as ethylene and propylene; and the like.

[0053] The aforementioned resin may be a commercially available product or may be synthesized as appropriate. For example, when obtaining a (meth)acrylic resin by synthesis, it can be produced by conventionally known polymerization methods (e.g., solution polymerization, bulk polymerization, suspension polymerization, emulsion polymerization, etc.), with emulsion polymerization being preferred. Specifically, a preferred method involves emulsion polymerization of monomer components that form the constituent units of the (meth)acrylic resin (alkyl methacrylate, acid group-containing monomer, styrene monomer, other monomer) in water in the presence of an emulsifier and a polymerization initiator. By employing emulsion polymerization, an emulsion in which the resin is dispersed in water as emulsion particles is obtained, making it easy to prepare an aqueous inkjet composition. The specific means and conditions for polymerization can be appropriately selected and adopted from conventionally known means and techniques.

[0054] Furthermore, the polymerization reaction may be carried out in the presence of a chain transfer agent in order to adjust the weight-average molecular weight of the resulting resin. Examples of chain transfer agents include 2-ethylhexyl thioglycolate, tert-dodecyl mercaptan, n-octyl mercaptan, n-dodecyl mercaptan, mercaptoacetic acid, mercaptopropionic acid, 2-mercaptoethanol, α-methylstyrene, and α-methylstyrene dimer. These chain transfer agents may be used individually or in combination of two or more. The amount of chain transfer agent used should be adjusted as appropriate according to the desired weight-average molecular weight, but it is preferably 0.01 to 10 parts by mass, more preferably 0.1 to 5 parts by mass, and even more preferably 0.2 to 2 parts by mass, per 100 parts by mass of monomer component.

[0055] When a resin is included in the aqueous inkjet composition of this disclosure, it is preferable to add it as an emulsion, that is, in the aqueous inkjet composition, the resin is preferably included as emulsion particles. The shape of the emulsion particles is not particularly limited, but is usually spherical. The emulsion particles may be resin particles having a single-phase structure, or resin particles having a multi-phase structure (preferably a core-shell structure). The average particle diameter of the emulsion particles is, for example, 30 to 500 nm, preferably 80 to 475 nm, more preferably 100 to 450 nm, and even more preferably 150 to 400 nm.

[0056] The emulsion is preferably adjusted to a pH of 7 to 10 at 25°C, and more preferably to 7 to 9. The pH of the emulsion can be adjusted by adding pH adjusting agents such as alkali metal compounds such as sodium hydroxide and potassium hydroxide; alkaline earth metal compounds such as calcium hydroxide and calcium carbonate; ammonia; and water-soluble organic amines such as dimethylaminoethanol, monomethylamine, dimethylamine, trimethylamine, monoethylamine, diethylamine, triethylamine, monopropylamine, dimethylpropylamine, monoethanolamine, diethanolamine, triethanolamine, ethylenediamine, and diethylenetriamine. These pH adjusting agents can be used individually or in combination of two or more.

[0057] The resin content in the solids (non-volatile components) of the aqueous inkjet composition disclosed herein can be appropriately adjusted depending on the application, but is, for example, 20 to 99% by mass, preferably 30 to 98% by mass, and more preferably 40 to 97% by mass. In particular, when used as a color ink such as a white ink, the resin content in the solids (non-volatile components) of the aqueous inkjet composition is preferably 20 to 99% by mass, more preferably 30 to 90% by mass, and even more preferably 40 to 85% by mass. When used as a clear ink such as an adhesive ink, the resin content in the solids (non-volatile components) of the aqueous inkjet composition is preferably 60 to 99% by mass, more preferably 80% to 98% by mass, and even more preferably 90 to 97% by mass.

[0058] 1-3. Solvent The aqueous inkjet composition of the present disclosure preferably further contains a solvent. The solvent acts as a diluent to adjust the viscosity of the aqueous inkjet composition. The solvent content in the aqueous inkjet composition may be set according to the desired viscosity of the aqueous inkjet composition and is not particularly limited, but is, for example, 40 to 95% by mass, preferably 50 to 90% by mass, and more preferably 55 to 85% by mass.

[0059] The solvent contained in the aqueous inkjet composition of the present disclosure is preferably a solvent mainly composed of water, and the water content in the solvent is, for example, 50% by mass or more, preferably 60% by mass or more, more preferably 70% by mass or more, and may be 100% by mass.

[0060] The aforementioned solvent may contain a water-soluble organic solvent along with water. A water-soluble organic solvent is an organic solvent that dissolves in water at a concentration of 0.01% by mass or more at 25°C and 1 atmosphere. By including a water-soluble organic solvent in the water-based inkjet composition, the moisturizing properties and compatibility with resins can be improved. The water-soluble organic solvent may be used alone or in combination of two or more types. The content of the water-soluble organic solvent is preferably 11 to 55 parts by mass, more preferably 17 to 45 parts by mass, and even more preferably 22 to 40 parts by mass, per 100 parts by mass of water contained in the water-based inkjet composition.

[0061] Examples of water-soluble organic solvents include lower alcohols such as methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, and tert-butyl alcohol (preferably C 1-4 Alcohols; Glycols such as propylene glycol, 1,3-propanediol, dipropylene glycol, tripropylene glycol, ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol; Glycerin; Monoalkyl ethers of monoalkylene glycols (preferably mono-C) such as monoethylene glycol monomethyl ether, monoethylene glycol monoethyl ether, monoethylene glycol monopropyl ether, monoethylene glycol monoisopropyl ether, monoethylene glycol monobutyl ether, monoethylene glycol monoisobutyl ether, monopropylene glycol monomethyl ether, monopropylene glycol monoethyl ether, monopropylene glycol monopropyl ether, monopropylene glycol monoisopropyl ether, monopropylene glycol monobutyl ether, monopropylene glycol monoisobutyl ether, and monoalkyl ether. 2-3 Alkylene glycol mono C 1-4 Alkyl ethers); monoalkyl ethers of dialkylene glycols such as diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monopropyl ether, diethylene glycol monoisopropyl ether, diethylene glycol monobutyl ether, diethylene glycol monoisobutyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol monopropyl ether, dipropylene glycol monoisopropyl ether, dipropylene glycol monobutyl ether, dipropylene glycol monoisobutyl ether, etc. (preferably diC 2-3 Alkylene glycol mono C 1-4Alkyl ethers); Monoalkyl ethers of polyalkylene glycols (preferably polyC) such as monomethyl ether of polyethylene glycol, monoethyl ether of polyethylene glycol, monopropyl ether of polyethylene glycol, monoisopropyl ether of polyethylene glycol, monobutyl ether of polyethylene glycol, monoisobutyl ether of polyethylene glycol, monomethyl ether of polypropylene glycol, monoethyl ether of polypropylene glycol, monopropyl ether of polypropylene glycol, monoisopropyl ether of polypropylene glycol, monobutyl ether of polypropylene glycol, monoisobutyl ether of polypropylene glycol, etc. 2-3 Alkylene glycol mono C 1-4 Examples include alkyl ethers; heterocyclic compounds such as 2-pyrrolidone and N-methyl-2-pyrrolidone; ketones such as acetone and methyl ethyl ketone; and so on. The number of moles of alkylene oxide added to the monoalkyl ether of the polyalkylene glycol is preferably 2 to 10, and more preferably 2 to 4.

[0062] In particular, from the viewpoint of further enhancing moisturizing properties, among the water-soluble organic solvents, solvents with a boiling point of 150°C or higher are preferred, solvents with a boiling point of 180°C or higher are more preferred, and solvents with a boiling point of 200°C or higher are even more preferred. Examples of water-soluble organic solvents with a boiling point of 150°C or higher include propylene glycol, diethylene glycol, triethylene glycol, and glycerin. The content of the water-soluble organic solvent that further enhances moisturizing properties is preferably 10 to 50 parts by mass, and more preferably 15 to 40 parts by mass, per 100 parts by mass of water contained in the water-based inkjet composition. Furthermore, from the viewpoint of further enhancing compatibility with the resin, among the water-soluble organic solvents, water-soluble organic solvents having hydrophobic groups (e.g., alkyl groups) and hydroxyl groups are preferred, and monoalkyl ethers of dialkylene glycol and / or monoalkyl ethers of polyalkylene glycol (number of alkylene oxide addition moles = 2 to 10, preferably 2 to 4) are more preferred, and diC 2-3 Alkylene glycol mono C 1-4Alkyl ethers and / or polycarbonates 2-3 Alkylene glycol mono C 1-4 Alkyl ethers (number of alkylene oxide addition moles = 2 to 10, preferably 2 to 4) are more preferred, and at least one selected from the group consisting of diethylene glycol monoisopropyl ether, diethylene glycol monobutyl ether, diethylene glycol monoisobutyl ether, triethylene glycol monobutyl ether, and tripropylene glycol monomethyl ether is even more preferred. The content of the water-soluble organic solvent that further enhances compatibility is preferably 1 to 15 parts by mass, and more preferably 2 to 8 parts by mass, per 100 parts by mass of water contained in the water-based inkjet composition.

[0063] 1-4. Pigments The aqueous inkjet compositions disclosed herein may further contain colorants. By containing colorants, the aqueous inkjet compositions can function as color inks and can be used as color inks for forming images such as desired characters or patterns, or as white inks for forming a white printing layer that serves as a base for images.

[0064] As the colorant, general colorants used in the field of inkjet inks can be used. The colorant may be a dye or a pigment, but from the viewpoint of improving the fastness of the resulting printed layer, a pigment is preferred. Examples of the pigment include organic pigments and inorganic pigments, which may be used individually or in combination of two or more types. In addition, if necessary, they may be used in combination with extender pigments.

[0065] Examples of organic pigments include azo pigments such as benzidine and Hansa Yellow, diazo pigments, azomethine pigments, methine pigments, anthraquinone pigments, phthalocyanine pigments such as phthalocyanine blue, perinone pigments, perylene pigments, diketopyrrolopyrrole pigments, thioindigo pigments, isoindolinone pigments such as iminoisoindoline pigments and iminoisoindolinone, dioxazine pigments, quinacridone pigments such as quinacridone red and quinacridone violet, flavanthron pigments, indanthron pigments, anthrapyrimidine pigments, carbazole pigments, monoallylide yellow, diallylide yellow, benzimimidazolone yellow, toryl orange, naphthol orange, and quinophthalone pigments.

[0066] Other specific examples of organic pigments include product codes such as C.I. Pigment Yellow, C.I. Pigment Red, C.I. Pigment Orange, C.I. Pigment Violet, C.I. Pigment Blue, and C.I. Pigment Green.

[0067] Examples of inorganic pigments include titanium dioxide, antimony trioxide, zinc oxide (such as zinc oxide), lithopone, lead white, red iron oxide, black iron oxide, chromium green oxide, carbon black, lead yellow, molybdenum red, ferric ferrocyanide (Prussian blue), ultramarine, and lead chromate. Further examples of inorganic pigments include extender pigments such as mica, clay, aluminum powder, talc, aluminum silicate, calcium carbonate, magnesium hydroxide, aluminum hydroxide, barium sulfate, and magnesium carbonate. In addition, examples of carbon black include furnace black, thermal lamp black, acetylene black, and channel black.

[0068] Among inorganic pigments, titanium dioxide, antimony trioxide, zinc oxide such as zinc oxide, lithopone, lead white, calcium carbonate, magnesium hydroxide, aluminum hydroxide, barium sulfate, magnesium carbonate, clay, talc, and aluminum silicate are preferred as white pigments. Titanium dioxide is preferred from the viewpoint of having a high refractive index and excellent opacity. Among titanium dioxide, titanium dioxide with a rutile crystal structure is preferred.

[0069] Furthermore, as pigments exhibiting hues other than white, such as chromatic colors and black (hereinafter referred to as coloring pigments), the above-mentioned organic pigments, red iron oxide, black iron oxide, chromium oxide green, carbon black, lead yellow, molybdenum red, ferric ferrocyanide (Prussian blue), ultramarine, lead chromate, etc. are preferred.

[0070] In an aqueous inkjet composition, the pigment is preferably dispersed and stabilized by a dispersant. For this reason, in the production of an aqueous inkjet composition containing a pigment, it is preferable to prepare a pigment dispersion in which the pigment is dispersed in the solvent by mixing the pigment, a dispersant, and a solvent (preferably water or a solvent mainly composed of water) and performing a dispersion treatment using a bead mill or the like, and then mixing this with other components to produce an aqueous inkjet composition.

[0071] Examples of the dispersant mentioned above include poly(meth)acrylic acid, poly(meth)acrylic acid salts, etc.; copolymers of (meth)acrylic acid salt with one or more of the monomer components other than (meth)acrylic acid salt, such as alkyl (meth)acrylic acid esters, (meth)acrylamide, styrene, maleic acid, maleic anhydride, maleic acid esters, vinyl acetate, etc.; polyvinyl alcohol; polyvinylpyrrolidone, etc. The content of the dispersant is preferably 1 to 100 parts by mass, more preferably 2 to 50 parts by mass, and even more preferably 3 to 30 parts by mass, per 100 parts by mass of the colorant.

[0072] When a water-based inkjet composition contains a colorant, the content of the colorant in the solids (non-volatile components) of the water-based inkjet composition is preferably 1 to 80% by mass, and more preferably 10 to 60% by mass. When the colorant is a white pigment, the content of the white pigment in the solids (non-volatile components) of the water-based inkjet composition is preferably 20 to 80% by mass, and more preferably 40 to 60% by mass. In particular, when the water-based inkjet composition is used as a white ink, it is preferable to adjust the content of the white pigment to the above range. When the colorant is a coloring pigment, the content of the coloring pigment in the solids (non-volatile components) of the water-based inkjet composition is preferably 1 to 30% by mass, and more preferably 10 to 20% by mass. Furthermore, when the water-based inkjet composition is used as an adhesive ink, it is preferable that the content of the colorant in the solids (non-volatile components) of the water-based inkjet composition be low, for example, 5% by mass or less, preferably 3% by mass or less, more preferably 1% by mass or less, and may even be 0% by mass.

[0073] 1-5. Crosslinking Agents The aqueous inkjet compositions of the present disclosure may further contain crosslinking agents. By using crosslinking agents, a crosslinked structure can be formed through interaction with resins, etc., or through chemical reactions, and a tough printed layer can be formed, which tends to improve the durability of the resulting printed material.

[0074] Examples of the crosslinking agent include isocyanate compounds, epoxy compounds, melamine compounds, metal chelate compounds, aziridine compounds, mercapto compounds, and oxazoline compounds, with oxazoline compounds being preferred. The crosslinking agent may be used alone or in combination of two or more types.

[0075] The content of the crosslinking agent is not particularly limited, but is, for example, 0 to 10 parts by mass, preferably 0.1 to 10 parts by mass, more preferably 0.5 to 8 parts by mass, and even more preferably 1 to 5 parts by mass, per 100 parts by mass of the resin.

[0076] 1-6. Additives The aqueous inkjet compositions of this disclosure may contain additives other than those described above, to the extent that the objectives of this disclosure are not hindered. For example, one or more additives such as dispersants, leveling agents, pH adjusters, UV absorbers, UV stabilizers, thickeners, wetting agents, plasticizers, stabilizers, defoamers, antioxidants, crosslinking accelerators, preservatives, chain transfer agents, and chelating agents may be included in appropriate amounts.

[0077] When adding the above-mentioned additives, the content is not particularly limited, but is preferably 2% by mass or less, and more preferably 1% by mass or less, based on 100% by mass of the aqueous inkjet composition of the disclosed herein. Furthermore, in order to exert the additive effect, it is preferably 0.01% by mass or more, and more preferably 0.05% by mass or more.

[0078] 1-7. Physical Properties The pH of the aqueous inkjet composition at 25°C is preferably 7 to 10, and more preferably 7 to 9. By adjusting the pH of the aqueous inkjet composition to the above range, the dispersion stability of the composition can be improved.

[0079] The aqueous inkjet composition preferably has a viscosity of 2 to 10 mPa·s at 25°C, and more preferably 3 to 7 mPa·s. By adjusting the viscosity of the aqueous inkjet composition to be above the lower limit, uneven drying can be reduced, and by adjusting it to be below the upper limit, ejection performance can be further improved. The viscosity can be measured using an E-type viscometer at a measurement temperature of 25°C.

[0080] 1-8. Applications The aqueous inkjet compositions of this disclosure can be used for inkjet printing on substrates, and the use of the aforementioned aqueous inkjet compositions for inkjet printing is also included in the scope of this disclosure. In particular, the aqueous inkjet compositions of this disclosure are suitable for printing on substrates that do not easily absorb liquid, such as those made of plastic and / or metal. Printed substrates obtained by printing the aqueous inkjet compositions of this disclosure onto a substrate may be used as products as they are, but are also suitable for use as transfer sheets for transfer printing. That is, it is also preferable to use the aqueous inkjet compositions of this disclosure for transfer printing, and more preferably for transfer printing on fabrics. The aqueous inkjet compositions of this disclosure can be used as both color inks containing colorants and clear inks without colorants. In particular, since the aqueous inkjet compositions of this disclosure can form a smooth printed layer even when the amount of ink used per unit area is large, they are suitable for use in applications where the amount of ink used per unit area is large, for example, as a white ink used to form a base (white printed layer) to enhance the color development of the target image, or as an adhesive ink used in transfer printing to ensure close adhesion between the object to be transferred and the image.

[0081] 2. A method for forming a printing substrate is also included in this disclosure, which involves ejecting the aforementioned aqueous inkjet composition onto a printing substrate using an inkjet method to form a printed layer.

[0082] The substrate can be appropriately selected depending on the application, and examples of substrate materials include metal, wood, plastic, or paper. Examples of metals include aluminum and copper, with aluminum being preferred from a cost standpoint. Examples of plastics include polyolefin resin, polyester resin, polyamide resin, and polycarbonate resin. Examples of paper include plain paper, fine paper, and coated paper.

[0083] In particular, the substrate material is preferably plastic and / or metal. By using such a substrate, it is possible to suppress the complete absorption of the water-based inkjet composition into the substrate, thereby making it easier to achieve a smooth surface. Among these, plastic is preferred from the viewpoint of cost, polyester resin is more preferred from the viewpoint of good heat resistance, aromatic polyester is even more preferred, and polyethylene terephthalate is particularly preferred.

[0084] The shape of the substrate is not particularly limited and can be appropriately selected according to the purpose, but from the viewpoint of handling, it is preferable to be in the form of a film. For example, when a film-like substrate (especially a plastic film) is used as the substrate, the resulting printing substrate is preferable because it can be suitably used as a flexible package or a transfer sheet. When the substrate is in the form of a film, its thickness is not particularly limited, but is for example 10 to 500 μm, and preferably 30 to 200 μm.

[0085] The substrate may, if necessary, have a functional layer on its surface. If the substrate has a functional layer, it is preferable that the functional layer is formed on at least the surface on which the printed layer is formed.

[0086] The functional layer can be a known functional layer used in this field, such as a primer layer to improve adhesion between the printed layer and the substrate, an ink receiving layer to receive ink printed on the substrate, or a release layer to facilitate peeling of the interface between the printed layer and the substrate. One or more of these processing layers can be provided.

[0087] For example, when a printing substrate is used as a flexible packaging material, it is preferable to have the primer layer on at least the surface on which the printing layer is formed. Also, when a printing substrate is used as a transfer sheet, it is preferable to have the ink receiving layer on at least the surface on which the printing layer is formed. Furthermore, in order to improve transferability, it is preferable to have the release layer on at least the surface on which the printing layer is formed. When the substrate has an ink receiving layer and a release layer, it is preferable that the ink receiving layer and the release layer are laminated on the substrate surface, with the ink receiving layer side being the substrate surface.

[0088] Preferably, the substrate is one that does not absorb all of the aqueous inkjet composition ejected onto it; that is, it is preferable that at least a portion of the printed layer formed from the aqueous inkjet composition is laminated on the substrate in the resulting printed substrate.

[0089] When ejecting the aqueous inkjet composition onto the substrate using an inkjet method, an inkjet recording device may be used. When an inkjet recording device is used, the aqueous inkjet composition is ejected from the inkjet head and adhered to a predetermined portion on the substrate, thereby forming a printed layer on the substrate. Note that "ejecting the aqueous inkjet composition onto the substrate using an inkjet method" includes not only the method of directly ejecting the aqueous inkjet composition onto the substrate using an inkjet method, but also the method of ejecting the aqueous inkjet composition onto a laminate in which an image layer and / or other layers such as a base layer are provided on the substrate using an inkjet method.

[0090] The image layer is a layer that forms an image such as characters or patterns. The image layer may be formed by inkjet printing with known color inks used in this art, or by inkjet printing with an aqueous inkjet composition of the disclosure containing a colorant. The background image is a layer provided on the back surface of the image layer in the final product to enhance the color development of the image. The background layer may be formed by inkjet printing with known white inks used in this art, or by inkjet printing with an aqueous inkjet composition of the disclosure containing a white pigment.

[0091] As described above, the aqueous inkjet composition disclosed herein can form a smooth printed layer even when a large amount of ink is used. The total amount of the aqueous inkjet composition ejected to form the printed layer is preferably greater than the amount that the substrate can absorb, and specifically, preferably 1 mg / cm³. 2 More preferably, 3 mg / cm³ 2 More preferably 7 mg / cm³ 2 More preferably 10 mg / cm³ 2 In particular, 12 mg / cm³ is preferred. 2 That concludes the explanation. Furthermore, from the viewpoint of suppressing the flow of the water-based inkjet composition during printing, the total discharge amount is 60 mg / cm³. 2 The following are preferable.

[0092] In forming the printing substrate, a drying treatment may be performed as needed. This drying treatment can be described as a process of evaporating some or all of the components (i.e., the solvent) of the aqueous inkjet composition excluding the solids.

[0093] Examples of drying methods include natural drying, heating, and drying under reduced pressure, but heating drying is preferred. For example, light drying may be performed using a platen heater in an inkjet recording device or a rubber heater, which is installed on the platen and used as an alternative to the platen heater, followed by thorough drying using a heating device with a hot air heater, infrared heater, etc. Hereinafter, the process of drying using a platen heater or a planar heating element as an alternative thereto will be referred to as the first drying process, and other drying processes performed after the first drying process will be referred to as the second drying process. The first drying process may also be referred to as the first heating process, but these terms are synonymous. Similarly, the second drying process may also be referred to as the second heating process, but these terms are synonymous.

[0094] The first drying step may be performed simultaneously with the step of ejecting the aqueous inkjet composition using an inkjet method (hereinafter sometimes referred to as the printing step), after the printing step, or simultaneously with and after the printing step. When the first drying step is performed simultaneously with the printing step, it may be performed continuously from the start to the end of the printing step, or intermittently. The heating temperature in the first heating step is preferably 30 to 80°C, more preferably 35 to 70°C, and even more preferably 40 to 60°C. By adjusting the heating temperature to be above the lower limit, the heating time can be shortened, and by adjusting it to be below the upper limit, nozzle blockage due to heat transfer to the inkjet head can be suppressed.

[0095] The second heating step is preferably performed after the first heating step and after the printing step. The heating temperature in the second heating step is preferably 40 to 180°C, more preferably 80 to 160°C, and even more preferably 95 to 150°C. The heating time and hot air contact time are preferably 0.5 to 30 minutes, and more preferably 1 to 15 minutes.

[0096] The printing substrate formation method of this disclosure includes, for example, (1) an embodiment in which a printing layer (i.e., an image layer) is formed by ejecting color ink onto a substrate using an inkjet method; (2) an embodiment in which a white printing layer (i.e., a base layer) is formed by ejecting white ink onto a substrate using an inkjet method, and a printing layer (i.e., an image layer) is formed by ejecting color ink onto the white printing layer forming surface using an inkjet method; (3) an embodiment in which a color printing layer (i.e., an image layer) is formed by ejecting color ink onto a substrate using an inkjet method, and a white printing layer (i.e., a base layer) is formed by ejecting white ink onto the color printing layer forming surface using an inkjet method; (4) an embodiment in which a color printing layer (i.e., an image layer) is formed by ejecting color ink onto a substrate using an inkjet method, a white printing layer (i.e., a base layer) is formed by ejecting white ink onto the color printing layer forming surface using an inkjet method, and an adhesive layer is formed by ejecting adhesive ink onto the white printing layer forming surface using an inkjet method; (5) A method comprising: ejecting color ink onto a substrate using an inkjet method to form a color printing layer (i.e., an image layer); ejecting white ink onto the surface forming the color printing layer using an inkjet method to form a white printing layer (i.e., a base layer); coating the surface forming the white printing layer with adhesive resin powder and then heating it to melt the adhesive resin powder and form an adhesive layer; and so on, and it is preferable to use the aqueous inkjet composition of the present disclosure as at least one type of ink in each of these methods.

[0097] The printing substrates obtained by the methods described in (1) to (3) above can be used as final products, specifically as flexible packaging. In particular, (2) can form a printing substrate with enhanced color development of images in front printing, and (3) can form a printing substrate with enhanced color development of images in back printing. In (2) and (3), it is preferable to use the aqueous inkjet composition of the present disclosure as at least the white ink.

[0098] Furthermore, the printing substrate obtained by the methods of (4) and (5) above can be used as a transfer sheet. For example, transfer printing can be performed by bringing the adhesive layer-forming surface of the printing substrate into contact with the transfer medium under heating and pressure, and then peeling the substrate from the transfer medium. The transfer medium is not particularly limited and can be metal, wood, plastic, paper, fabric, etc., but the use of fabric is particularly preferred. In (4), it is preferable to use the aqueous inkjet composition of the present disclosure as the white ink and / or adhesive ink, and in (5), it is preferable to use the aqueous inkjet composition of the present disclosure as the white ink.

[0099] By using the aqueous inkjet composition of the present disclosure as the color ink for forming the image layer, the smoothness of the image layer can be improved and uneven color development of the image can be suppressed. Furthermore, by using the aqueous inkjet composition of the present disclosure as the white ink, the smoothness of the base layer can be improved, which can suppress uneven color development of the image and further improve the smoothness of the adhesive layer formed on the base layer. Furthermore, by using the aqueous inkjet composition of the present disclosure as the adhesive ink, the smoothness of the adhesive layer can be improved, which in turn can suppress peeling and cracking of the image in the printed material after transfer printing.

[0100] This application claims the benefit of priority based on Japanese Patent Application No. 2024-227824, filed on 24 December 2024. The entire specification of Japanese Patent Application No. 2024-227824, filed on 24 December 2024, is incorporated herein by reference.

[0101] The contents of this disclosure will be explained in more detail below with reference to examples, but the contents of this disclosure are not limited by the examples below, and it is certainly possible to implement the disclosure with appropriate modifications to the extent that it is in line with the spirit of the preceding and following, and all such modifications are included in the technical scope of this disclosure. In the following, unless otherwise specified, "parts" means "parts by mass" and "%" means "percent mass".

[0102] [Measurement and Calculation Methods for Various Physical Properties] (Measurement of Average Particle Size of Pigments and Emulsion Particles) The average particle size of pigments and emulsion particles was measured at 25°C using a particle size distribution analyzer (Otsuka Electronics Co., Ltd., model number: FPAR-1000) that uses dynamic light scattering, and determined using cumulant analysis. For the measurement of the average particle size of pigments, the pigment dispersion obtained in the following manufacturing example was used as the measurement sample, and for the measurement of the average particle size of emulsion particles, the emulsion obtained in the following manufacturing example was used as the measurement sample.

[0103] (Measurement of weight-average molecular weight of resins and surfactants) The weight-average molecular weight (Mw) of surfactants and resins constituting emulsion particles was measured by GPC (gel permeation chromatography) under the following measurement conditions. Measuring instrument: HLC-8320GPC (Tosoh Corporation) Molecular weight column: TSK-GEL SuperMultiporeHZ (Tosoh Corporation) Eluent: Tetrahydrofuran (THF) Calibration standard: Polystyrene (Tosoh Corporation) Measurement method: The sample to be measured was dissolved in THF to a solid content of approximately 0.2% by mass, filtered, and the molecular weight was measured using the resulting sample. The flow rate of the liquid delivery pump was set to 0.35 mL / min.

[0104] (Calculation of HLB values ​​of surfactants) The HLB values ​​of surfactants were calculated using the values ​​defined by the Griffin method.

[0105] [Manufacturing Example] (Emulsion Manufacturing Example 1) 280 parts of deionized water were charged into a polymerizer equipped with a stirrer, reflux condenser, thermometer, nitrogen inlet tube, and dropping funnel. The internal temperature was then raised to 75°C while stirring under a nitrogen gas flow. Meanwhile, a monomer emulsion consisting of monomer components 300 parts methyl methacrylate, 200 parts n-butyl acrylate, 5 parts acrylic acid, 300 parts 2-ethylhexyl acrylate, 195 parts styrene, 5.0 parts t-dodecyl mercaptan as a polymerization chain transfer agent, 62.5 parts of softanol 300 (manufactured by Nippon Shokubai) and 62.5 parts of latemul WX (manufactured by Kao Corporation), which were pre-prepared as 20% aqueous solutions, and 183.0 parts of deionized water was charged into the dropping funnel. Next, while maintaining the internal temperature of the polymerizer at 75°C, 27.0 parts of the monomer emulsion, 5 parts of a 5% potassium persulfate aqueous solution and 10 parts of a 2% sodium bisulfite aqueous solution, which are polymerization initiators, were added to start the initial polymerization. After 40 minutes, while maintaining the reaction system temperature at 80°C, the remaining monomer emulsion was uniformly added dropwise over 210 minutes. Simultaneously, 95 parts of a 5% potassium persulfate aqueous solution and 90 parts of a 2% sodium bisulfite aqueous solution were uniformly added dropwise over 210 minutes. After the addition was complete, the same temperature was maintained for 60 minutes to complete the polymerization. After cooling the resulting reaction solution to room temperature, 8.0 parts of 2-dimethylethanolamine and 47 parts of deionized water were added to obtain an acrylic resin emulsion (hereinafter referred to as emulsion 1). The solid content of emulsion 1 was 56%, the average particle size of the emulsion particles contained in emulsion 1 was 180 nm, and the weight-average molecular weight of the resin constituting the emulsion particles was 150,000.

[0106] (Pigment Dispersion Production Example 1) Five parts of the dispersant Discoat N-14 (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), six parts of propylene glycol, seventy parts of deionized water, and one hundred parts of titanium dioxide CR-95 (manufactured by Ishihara Sangyo Co., Ltd.) were packed into a 50% volume fraction of zirconia beads with a particle size of 0.5 mm. The mixture was dispersed using a bead mill and filtered through a 1 μm pore size filter (manufactured by Advantec, MCP-1-C10S) to obtain a white pigment dispersion containing 55% pigment (hereinafter referred to as Pigment Dispersion 1). The average particle size of the pigment was 330 nm.

[0107] [Examples and Comparative Examples] (Example 1: Preparation of Ink Composition 1-1) Ink composition 1-1 was prepared by mixing 15 parts of emulsion 1 as emulsion particles, 23 parts of pigment dispersion 1, 1.2 parts of Epocross WS-700 (manufactured by Nippon Shokubai, 25% solids content) (0.3 parts as solids), 2 parts of diethylene glycol monobutyl ether, 15 parts of propylene glycol, 0.5 parts of the surfactant Olfin E1004, 1.0 part of BYK-345, 0.05 parts of BYK-3480, and deionized water to a total of 100 parts, and filtering the mixture through a 1 μm pore size filter (manufactured by Advantec, MCP-1-C10S).

[0108] (Examples 2-3, Comparative Examples 1-3: Preparation of ink compositions 1-2 to 1-6) Ink compositions 1-2 to 1-6 were prepared in the same manner as in Example 1, except that the type and amount of surfactant were changed as shown in Table 2, and the amount of deionized water added was adjusted so that the total amount was 100 parts.

[0109] (Example 4: Preparation of Ink Composition 2-1) Ink composition 2-1 was prepared by mixing 20 parts of emulsion 1 as emulsion particles, 2 parts of diethylene glycol monobutyl ether, 15 parts of propylene glycol, 0.5 parts of the surfactant Olphine E1004, 1.0 part of BYK-345, 0.05 parts of BYK-3480, and deionized water to a total of 100 parts, and filtering the mixture through a 1 μm pore size filter (Advantec, MCP-1-C10S).

[0110] (Examples 5-6, Comparative Examples 4-6: Preparation of ink compositions 2-2 to 2-6) Ink compositions 2-2 to 2-6 were prepared in the same manner as in Example 4, except that the type and amount of surfactant were changed as shown in Table 2, and the amount of deionized water added was adjusted so that the total amount was 100 parts.

[0111] The details of the surfactants used in the examples and comparative examples are as follows.

[0112]

[0113] Inkjet printing was performed using the ink compositions obtained in the above examples and comparative examples, and various characteristics were evaluated. The following equipment was used for inkjet printing. (Inkjet ejector) An inkjet ejector was manufactured by modifying an Image Magic DTTS-602 series DTF printer. This inkjet ejector was a multi-pass system equipped with three Epson Precision Core I3200 heads, and the printing width was 600 mm. The three heads were designated as the first head, second head, and third head in order from the upstream side in the substrate transport direction. One of the ink compositions 1-1 to 1-6 was filled into the second head, and one of the ink compositions 2-1 to 2-6 was filled into the third head. A platen heater was placed directly below the head as the heating device for the first heating process. (Second heating device) An Image Magic DTTS-BF602 binder coating machine was used as the second heating device. No hot melt powder was applied, and only an infrared heating device was used.

[0114] [Manufacturing of Printing Substrate] A substrate (PET film roll DFR-600 manufactured by Image Magic Co., Ltd.) was set in the inkjet ejection device, and inkjet printing was performed with each ink composition. After the printed substrate was subjected to a first heating process for 4 minutes using a platen heater placed in the inkjet ejection device, the heated substrate was transferred to a second heating device, and a second heating process using infrared heating was performed for 10 minutes to produce a printing substrate. The temperatures for the first and second heating processes were set by measuring the surface temperature of the printed substrate in the central part of each device using a K-type thermocouple (AS ONE Corporation, KTO-10100M3), and setting the temperature so that it was 40°C in the first heating process and 100°C in the second heating process.

[0115] [Ejection Performance Evaluation] In the above inkjet printing, a nozzle check pattern was printed and the percentage of non-ejected material was evaluated. The nozzle consists of 8 rows of 400 nozzles each, for a total of 3200 nozzle holes. The percentage of non-ejected material was calculated using the following formula, rounded to the nearest whole number. A lower percentage of non-ejected material indicates better ejection performance. Ejection performance was evaluated according to the following criteria, and a score of 4 or higher was considered a pass. (Percentage of non-ejected material) = (Number of non-ejected locations on the nozzle check pattern) / 3200 × 100 (%) - Criteria - 1: Percentage of non-ejected material is 86% or higher 2: Percentage of non-ejected material is 71-85% 3: Percentage of non-ejected material is 56-70% 4: Percentage of non-ejected material is 41-55% 5: Percentage of non-ejected material is 26-40% 6: Percentage of non-ejected material is 11-25% 7: Percentage of non-ejected material is 10% or lower

[0116] [Smoothness Evaluation] In the above inkjet printing, the total ink ejection volume was 20 mg / cm². 2 Adjust so that it becomes a solid pattern (3 x 3 cm) 2 The solid pattern was printed on the resulting printed substrate (2.5 × 2.5 cm). 2 In the solid pattern 100, the thickness of the printed layer was measured at 10 random locations, and the average value was taken as the inner film thickness. In addition, the thickness of the printed layer in the area other than the inner region of the solid pattern (outer region) was measured at 10 random locations, and the average value was taken as the outer film thickness. Figure 1 is a schematic diagram showing the inner region 1 and outer region 2 of the solid pattern 100. The thickness of the printed layer was measured using a stand-type constant-pressure thickness gauge (manufactured by Teclock Co., Ltd.). The difference between the inner and outer film thicknesses of the printed layer measured above was calculated. The smaller the difference in film thickness between the inside and outside of the printed layer, the better the smoothness. The smoothness of the printed layer was evaluated according to the following criteria, and a score of 4 or higher was considered a pass. - Criteria for Judgment - 1: Difference in film thickness between inside and outside is 26 μm or more 2: Difference in film thickness between inside and outside is 23 to 25 μm 3: Difference in film thickness between inside and outside is 20 to 22 μm 4: Difference in film thickness between inside and outside is 17 to 19 μm 5: Difference in film thickness between inside and outside is 14 to 16 μm 6: Difference in film thickness between inside and outside is 11 to 13 μm 7: Difference in film thickness between inside and outside is 10 μm or less

[0117]

[0118] As shown in Examples 1 to 6, when three or more surfactants containing a specific surfactant A were used, both discharge performance and smoothness were good. On the other hand, as shown in Comparative Examples 1 to 6, when two or fewer surfactants were used or surfactant A was not included, either discharge performance or smoothness was poor, and it was not possible to achieve both. For example, the ink compositions of Examples 1 to 3 can be suitably used as white inks, and the ink compositions of Examples 4 to 6 can be suitably used as adhesive inks.

[0119] 100 Solid pattern 1 Inner area 2 Outer area

Claims

1. An aqueous inkjet composition containing at least three types of surfactants, wherein at least one of the surfactants is surfactant A, which has an HLB value of 9 or less and a weight-average molecular weight of 4000 or more.

2. The aqueous inkjet composition according to claim 1, wherein the surfactant A is a silicone-based surfactant.

3. The aqueous inkjet composition according to claim 1, wherein the surfactant comprises a surfactant B1 other than surfactant A, and the surfactant B1 is an acetylene-based surfactant.

4. The aqueous inkjet composition according to claim 1, wherein the surfactant comprises a surfactant B1 other than surfactant A, and the surfactant B1 has an HLB value of 9 or less and a weight-average molecular weight of less than 4000.

5. The aqueous inkjet composition according to claim 3, wherein the mass ratio of surfactant B1 to surfactant A (B1 / A) is 0.7 or more.

6. The aqueous inkjet composition according to claim 1, wherein the surfactant comprises a surfactant B2 other than surfactant A, and the surfactant B2 is a silicone-based surfactant.

7. The aqueous inkjet composition according to claim 1, wherein the surfactant comprises surfactant B2 other than surfactant A, and surfactant B2 has an HLB value greater than 9 and a weight-average molecular weight of less than 4000.

8. The aqueous inkjet composition according to claim 6, wherein the mass ratio of surfactant B2 to surfactant A (B2 / A) is 1 or more.

9. The aqueous inkjet composition according to claim 1, used for printing on a substrate made of plastic and / or metal.

10. The aqueous inkjet composition according to claim 1, used for transfer printing.

11. The aqueous inkjet composition according to claim 1, used for transfer printing onto fabric.

12. A method for forming a printing substrate, comprising ejecting the aqueous inkjet composition described in claim 1 onto a substrate using an inkjet method to form a printed layer.

13. The method for forming a printing substrate according to claim 12, wherein the total amount of the aqueous inkjet composition ejected to form the printing layer is greater than the amount that the substrate can absorb.

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