Water-based flexographic ink

Abstract

The present invention aims to provide a water-based flexographic ink that achieves excellent plate cleaning properties, concentration stability, and stability over time, and further possesses excellent water-resistance and friction resistance, which are required for water-based flexographic inks. [Solution] An aqueous flexographic ink comprising an emulsion-type styrene-acrylic resin (A) having a core layer and a shell layer, wherein the span value of the emulsion-type styrene-acrylic resin (A) represented by the following formula (1) is 3 or less. Equation (1): Span value = (D90 - D10) / D50 D10, D50, and D90 are the following values ​​obtained by laser diffraction-scattering particle size distribution measurement of emulsion-type styrene-acrylic resin (A). D10: Cumulative 10% diameter of volume-based particle size distribution D50: Cumulative 50% diameter of volume-based particle size distribution D90: Cumulative 90% diameter of volume-based particle size distribution

Description

[Technical Field]

[0001] This invention relates to water-based flexographic ink and printed materials thereof. [Background technology]

[0002] In recent years, in water-based flexographic printing for packaging applications, there has been an increase in the use of high-fine-line anilox rolls and low ink application rates. Low ink application rates make it easier for density changes to occur during long runs, and the ink film dries more easily on the plate. As a result, dirt on printing press equipment such as flexographic plates and anilox rolls becomes difficult to remove, making plate cleaning a challenge. In particular, with water-based flexographic ink compositions containing water-based acrylic resins, the deterioration of plate cleaning performance of flexographic plates is significant due to the solubility of the resin. Furthermore, water-based flexographic ink compositions generally require long-term stability and water abrasion resistance, making it a challenge to achieve both plate cleaning performance and density stability. Conventionally, the problem of density stability was caused by changes in the properties of the ink during printing. This phenomenon occurs because the particle size of the emulsion-type particles contained in the ink is non-uniform. However, precisely controlling the particle size distribution is technically difficult, and in addition, it was necessary to achieve this while also addressing issues such as long-term stability, plate washability, and water abrasion resistance.

[0003] Patent Document 1 discloses an aqueous flexographic ink using an emulsion-type styrene-acrylic resin as a binder resin. However, there is no disclosure whatsoever regarding the particle size and particle size distribution of the emulsion-type styrene-acrylic resin, nor is there any disclosure regarding the particle size or whether the emulsion-type styrene-acrylic resin has a core-shell structure, raising concerns about its stability over time. Patent Document 2 discloses an aqueous printing ink composition containing a core-shell structure emulsion-type resin with an average particle size of 30 to 200 nm, having an intermediate layer containing components obtained from biomass-derived raw materials between the core layer and the shell layer. However, there is no disclosure regarding the particle size distribution of the core-shell structure emulsion-type resin, and since the plate cleaning test evaluates the ink coating by wiping off the ink film swollen with water, there are concerns that the solubility in water is insufficient, and therefore concerns regarding plate cleaning performance. Patent documents 3 and 4 disclose aqueous flexographic inks using a composite emulsion resin of styrene acrylic and polysaccharides. However, there is no disclosure whatsoever regarding the particle size of the composite emulsion resin, raising concerns about insufficient stability over time and solubility in water, and therefore concerns about plate cleaning performance. In addition, water-based flexographic inks are generally prone to ink component separation and tend to have poor concentration stability and stability over time. Patent documents 1 to 4 do not provide any evaluation regarding concentration stability and stability over time, raising concerns about these aspects. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2019-108529 [Patent Document 2] Japanese Patent Publication No. 2021-107495 [Patent Document 3] Japanese Patent Publication No. 2021-167377 [Patent Document 4] Japanese Patent Publication No. 2022-096161 [Overview of the project] [Problems that the invention aims to solve]

[0005] The present invention aims to provide a water-based flexographic ink that achieves excellent plate cleaning properties, concentration stability, and stability over time, and further possesses excellent water-resistance and friction resistance, which are required for water-based flexographic inks. [Means for solving the problem]

[0006] As a result of diligent research into the aforementioned problems, the inventors have found that the above problems can be solved by using the packaging material described below, and have thus come to the present invention.

[0007] In other words, the present invention is an aqueous flexographic ink comprising an emulsion-type styrene-acrylic resin (A) having a core layer and a shell layer. This invention relates to an aqueous flexographic ink in which the span value of the emulsion-type styrene-acrylic resin (A), represented by the following formula (1), is 3 or less. Equation (1): Span value = (D90 - D10) / D50 D10: Cumulative 10% diameter of volume-based particle size distribution obtained by laser diffraction-scattering particle size distribution measurement of emulsion-type styrene-acrylic resin (A) D50: Cumulative 50% diameter of volume-based particle size distribution obtained by laser diffraction-scattering particle size distribution measurement of emulsion-type styrene-acrylic resin (A) D90: Cumulative 90% diameter of volume-based particle size distribution obtained by laser diffraction-scattering particle size distribution measurement of emulsion-type styrene-acrylic resin (A)

[0008] In other words, the present invention relates to an aqueous flexographic ink in which an emulsion-type styrene-acrylic resin (A) contains a rosin resin and / or polysaccharide in the core layer and / or shell layer.

[0009] In other words, the present invention relates to an aqueous flexographic ink in which the proportion of particles with a particle size of 350 nm or more, as determined by laser diffraction-scattering particle size distribution measurement, in an emulsion-type styrene-acrylic resin (A) is 20% by mass or less per 100% by mass of the emulsion-type styrene-acrylic resin (A).

[0010] In other words, the present invention relates to an aqueous flexographic ink in which the full width at half maximum of the volume-based particle size distribution obtained by laser diffraction-scattering particle size distribution measurement of an emulsion-type styrene-acrylic resin (A) is 200 nm or less.

[0011] That is, the present invention further relates to the aqueous flexographic ink containing an extender pigment.

[0012] That is, the present invention relates to the aqueous flexographic ink in which the solid content mass ratio of the extender pigment and the emulsion type styrene acrylic resin (A) is 15:85 to 65:35.

[0013] That is, the present invention relates to the aqueous flexographic ink in which the ratio of D50 of the extender pigment obtained by laser diffraction / scattering type particle size distribution measurement to D50 of the emulsion type styrene acrylic resin (A) is 95:5 to 60:40.

[0014] That is, the present invention further relates to the aqueous flexographic ink containing a urea compound represented by the following general formula (1). General formula (1) [Chemical formula] [In general formula (1), R 1 represents an oxygen atom or a sulfur atom. R 2 and R 3 each independently represent a hydrogen atom, an alkyl group having 1 to 4 carbon atoms which may have a substituent, or an aryl group having 6 to 9 carbon atoms which may have a substituent. However, R 2 and R 3 may form a ring via an alkylene group having 1 to 3 carbon atoms.]

[0015] That is, the present invention relates to the aqueous flexographic ink in which the mass ratio of the core layer and the shell layer of the emulsion type styrene acrylic resin (A) is 90:10 to 40:60.

[0016] That is, the present invention further relates to the aqueous flexographic ink containing an alcohol having a valence of 3 or more.

[0017] That is, the present invention relates to the aqueous flexographic ink for use on a paper substrate.

[0018] In other words, the present invention relates to a printed material having a printed layer formed on a substrate using the aqueous flexographic ink.

[0019] In other words, the present invention further relates to the aqueous flexographic ink comprising a rosin resin emulsion and / or a water-soluble rosin resin.

[0020] In other words, the present invention further relates to the aqueous flexographic ink comprising biomass-derived components (excluding rosin resin and polysaccharide resin). [Effects of the Invention]

[0021] The present invention makes it possible to provide an aqueous flexographic ink that is excellent in plate cleaning properties, concentration stability, aging stability, and water abrasion resistance. [Brief explanation of the drawing]

[0022] [Figure 1] Volume-based particle size distribution curve [Figure 2] Volume-based particle size distribution curve [Modes for carrying out the invention]

[0023] The aqueous flexographic ink of the present invention will be described in detail below.

[0024] [Water-based flexographic ink] The present invention relates to an aqueous flexographic ink comprising an emulsion-type styrene-acrylic resin (A) having a core layer and a shell layer. The emulsion-type styrene-acrylic resin (A) is characterized in that the span value represented by the following formula (1) is 3 or less. Equation (1): Span value = (D90 - D10) / D50 D10: Cumulative 10% diameter of volume-based particle size distribution obtained by laser diffraction-scattering particle size distribution measurement of emulsion-type styrene-acrylic resin (A) D50: Cumulative 50% diameter of volume-based particle size distribution obtained by laser diffraction-scattering particle size distribution measurement of emulsion-type styrene-acrylic resin (A) D90: Cumulative 90% diameter of volume-based particle size distribution obtained by laser diffraction-scattering particle size distribution measurement of emulsion-type styrene-acrylic resin (A) The span value is an indicator of the uniformity of the emulsion particle size of emulsion-type styrene-acrylic resin (A). A smaller value indicates higher uniformity of the emulsion particle size of emulsion-type styrene-acrylic resin (A). The aqueous flexographic ink of the present invention contains an emulsion-type styrene-acrylic resin (A) having a core layer and a shell layer. When the span value of the emulsion-type styrene-acrylic resin (A) is 3 or less, the uniformity of the particle size of the emulsion-type styrene-acrylic resin (A) is high, resulting in good ink properties, which are particularly effective in flexographic printing. Specifically, the ink exhibits good dispersion stability and transferability to the substrate, and also achieves a balance between solubility and film-forming properties, resulting in excellent plate cleaning properties, concentration stability, aging stability, and water abrasion resistance.

[0025] (Emulsion-type styrene-acrylic resin having a core layer and a shell layer (A)) In the present invention, the emulsion-type styrene-acrylic resin (A) having a core layer and a shell layer is insoluble or sparingly soluble in water, but is dispersed and stabilized by a surfactant or the like.

[0026] The span value of the emulsion-type styrene-acrylic resin (A) is preferably 3 or less, more preferably 1 to 2.5, and even more preferably 1 to 1.5. When the span value of the emulsion-type styrene-acrylic resin (A) is within the above range, the uniformity of the emulsion particle size is high, resulting in uniform solubility, dispersibility, and transferability to the substrate for each emulsion particle of the emulsion-type styrene-acrylic resin (A), improving plate cleaning performance, stability over time, and concentration stability. The cumulative 50% (D50) of the volume-based particle size distribution obtained by laser diffraction-scattering particle size distribution measurement of emulsion-type styrene-acrylic resin (A) is preferably 20 to 1500 nm, more preferably 30 to 700 nm, and even more preferably 50 to 300 nm. When the cumulative 50% (D50) of the volume-based particle size distribution obtained by laser diffraction-scattering particle size distribution measurement of emulsion-type styrene-acrylic resin (A) is within the above range, plate washability, concentration stability, and aging stability are improved. The cumulative 10% (D10) of the volume-based particle size distribution is preferably 5 to 1000 nm, more preferably 10 to 500 nm, and even more preferably 15 to 200 nm. The cumulative 90% (D90) of the volume-based particle size distribution is preferably 100 to 3000 nm, more preferably 130 to 1000 nm, and even more preferably 150 to 400 nm. The proportion of particles with a particle size of 350 nm or more in the emulsion-type styrene-acrylic resin (A) is preferably 20% by mass or less, preferably 10% by mass or less, and more preferably 0 to 5% by mass, based on 100% by mass of the emulsion-type styrene-acrylic resin (A). When the proportion of particles with a particle size of 350 nm or more in the emulsion-type styrene-acrylic resin (A) is within the above range, the solubility, dispersibility, and transferability to the substrate of each emulsion particle of the emulsion-type styrene-acrylic resin (A) are good, which tends to improve plate cleaning performance, concentration stability, and long-term stability. The full width at half maximum (FWHM) of the volume-based particle size distribution of the emulsion-type styrene-acrylic resin (A) is preferably 200 nm or less, more preferably 10 to 180 nm, even more preferably 30 to 150 nm, and particularly preferably 50 to 120 nm. When the FWHM of the volume-based particle size distribution of the emulsion-type styrene-acrylic resin (A) is within the above range, the solubility, dispersibility, and transferability to the substrate of each emulsion particle of the emulsion-type styrene-acrylic resin (A) become uniform, thereby improving plate cleaning performance, long-term stability, and concentration stability.

[0027] (Measurement of particle size distribution of emulsion-type styrene-acrylic resin (A)) The particle size distribution of emulsion-type styrene-acrylic resin (A) can be measured using a laser diffraction / scattering particle size distribution analyzer (Microtrac MT-3000EX(II), manufactured by Microtrac-Bell) with water as the dispersion medium. The span values ​​and other properties of the present invention can be obtained from the obtained volume frequency particle size distribution curve by the following method.

[0028] (Method for calculating the span value of emulsion-type styrene-acrylic resin (A)) The span value of emulsion-type styrene-acrylic resin (A) can be calculated using Equation 1. Equation (1): Span value = (D90 - D10) / D50 D10: Cumulative 10% diameter of volume-based particle size distribution obtained by laser diffraction-scattering particle size distribution measurement of emulsion-type styrene-acrylic resin (A) D50: Cumulative 50% diameter of volume-based particle size distribution obtained by laser diffraction-scattering particle size distribution measurement of emulsion-type styrene-acrylic resin (A) D90: Cumulative 90% diameter of volume-based particle size distribution obtained by laser diffraction-scattering particle size distribution measurement of emulsion-type styrene-acrylic resin (A)

[0029] (Method for calculating the full width at half maximum of emulsion-type styrene-acrylic resin (A)) The full width at half maximum (FWHM) of the emulsion-type styrene-acrylic resin (A) can be calculated using Equation 2 by reading the particle diameters X1 and X2 (where X2 > X1) at which the main peak of the obtained volume-based particle size distribution curve is half the maximum value of the frequency (Y), as shown in Figure 1. If multiple peaks exist in the obtained volume-based particle size distribution curve, the peak with the highest particle frequency is considered the main peak. Formula (2): Half width (nm)=X2-X1

[0030] (Method for calculating the relative abundance of particles with a particle size of 350 nm or larger in emulsion-type styrene-acrylic resin (A)) The relative abundance of particles with a particle diameter of 350 nm or more in the emulsion-type styrene-acrylic resin (A) can be obtained as the ratio of the area between the volume-based particle size distribution curve for particles with a particle diameter of 350 nm or more and the particle diameter axis, with the area between the volume-based particle size distribution curve for the entire particle size range and the particle diameter axis being set to 100 in the obtained volume-based particle size distribution. Specifically, the relative abundance of particles with a particle diameter of 350 nm or more in the emulsion-type styrene-acrylic resin (A) can be calculated using Equation 3, as shown in Figure 2, from the area S1 in the range of particle diameters between 0 nm and less than 350 nm and the area S2 in the range of particle diameters of 350 nm or more in the obtained volume-based particle size distribution curve. Equation (3): Abundance ratio (mass%) of particles with a particle diameter of 350 nm or more =S2 / (S1+S2)×100

[0031] There are no particular limitations on the method for controlling the proportion of particles with a span value, full width at half maximum, and particle diameter of 350 nm or more in the emulsion-type styrene-acrylic resin (A). For example, the particle size distribution can be measured using laser diffraction / scattering particle size distribution measurement on commercially available products, and the appropriate product can be used. Another method is to adjust the particle size after synthesis by centrifugation, for example. In the present invention, the emulsion-type styrene-acrylic resin (A) obtained by laser diffraction-scattering particle size distribution measurement of the emulsion-type styrene-acrylic resin (A) satisfies one of the following conditions: a span value of 3 or less and a full width at half maximum of 200 nm or less, or a span value of 3 or less and a particle diameter of 350 nm or more, with an abundance ratio of 20% by mass or less. For example, commercially available emulsion-type styrene-acrylic resins such as the Joncryl series from BASF and the Hyros series from Seikoh PMC can be used after performing laser diffraction-scattering particle size distribution measurement on them. Examples of commercially available products that satisfy the above span value, full width at half maximum, and abundance ratio of particles with a particle diameter of 350 nm or more include BASF's Joncryl PDX-7109 and Joncryl PDX-7193.

[0032] The weight-average molecular weight of the emulsion-type styrene-acrylic resin (A) is preferably 1500 to 1500000, more preferably 3000 to 1200000, and even more preferably 5000 to 1000000. When the weight-average molecular weight of the emulsion-type styrene-acrylic resin (A) is within the above range, the plate cleaning properties and water-resistant friction properties are improved. The glass transition temperature (Tg) of the emulsion-type styrene-acrylic resin (A) is preferably -40°C to 120°C, more preferably -10°C to 100°C, even more preferably 0 to 90°C, and particularly preferably 0 to 50°C. When the glass transition temperature (Tg) of the emulsion-type styrene-acrylic resin (A) is within the above range, the plate cleaning properties and water friction resistance are improved.

[0033] <Measurement of glass transition temperature (Tg)> The glass transition temperature of the present invention can be measured by simultaneous thermogravimetric and differential thermal analysis (TG-DTA) using a Shimadzu DTG-60A or similar instrument. Specifically, under conditions of a nitrogen atmosphere, a measurement temperature range of -100 to 200°C, and a heating rate of 1°C / min, the temperature at the inflection point in the baseline shift was defined as the glass transition temperature (Tg).

[0034] The emulsion-type styrene-acrylic resin (A) preferably has acid groups. The acid value of the emulsion-type styrene-acrylic resin (A) is preferably 10 to 200 mg KOH / g, and more preferably 50 to 150 mg KOH / g. When the acid value of the emulsion-type styrene-acrylic resin (A) is within the above range, the plate cleaning properties and water friction resistance are improved.

[0035] If the emulsion-type styrene-acrylic resin (A) has acidic groups, it is preferable that the acidic groups are neutralized with a basic compound. Suitable basic compounds include, for example, amine compounds and alkali metals. Examples of the amine compounds mentioned above include ammonia; alkylamines such as diethylamine, triethylamine, and ethylenediamine; and alkanolamines such as monoethanolamine, ethylethanolamine, diethylethanolamine, diethanolamine, and triethanolamine. Examples of the alkali metals mentioned above include sodium hydroxide and potassium hydroxide. These may be used individually or in combination of two or more.

[0036] Emulsion-type styrene-acrylic resin (A) contains polymers of styrene monomer and acrylic monomer. Examples of styrene monomers that constitute the emulsion-type styrene-acrylic resin (A) include styrene, α-methylstyrene, and β-methylstyrene. These may be used individually or in combination of two or more. In particular, it is preferable that the styrene monomer contains α-methylstyrene. Furthermore, suitable acrylic monomers for the emulsion-type styrene-acrylic resin (A) include acrylic acid esters and methacrylic acid esters. For example, suitable acrylic acid esters include methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, hexyl acrylate, 2-ethylhexyl acrylate, cyclohexyl acrylate, benzyl acrylate, dimethylaminoethyl acrylate, hydroxyethyl acrylate, hydroxypropyl acrylate, and glycidyl acrylate. Suitable methacrylic acid esters include methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, hexyl methacrylate, 2-ethylhexyl methacrylate, cyclohexyl methacrylate, benzyl methacrylate, dimethylaminoethyl methacrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, and glycidyl methacrylate. These may be used individually or in combination of two or more. Furthermore, carboxylic acid-containing monomers such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid, and itaconic acid, or their anhydrides and half-esters, can also be used. These may be used individually or in combination of two or more. Among the above, it is preferable that the acrylic monomer includes methyl acrylate, ethyl acrylate, hexyl acrylate, 2-ethylhexyl acrylate, cyclohexyl acrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, hexyl methacrylate, 2-ethylhexyl methacrylate, cyclohexyl methacrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, acrylic acid, methacrylic acid, maleic acid, and itaconic acid.

[0037] The emulsion-type styrene-acrylic resin (A) preferably contains a rosin resin and / or a polysaccharide, and more preferably contains a polysaccharide. The inclusion of the rosin resin and / or the polysaccharide in the emulsion-type styrene-acrylic resin (A) improves dispersibility and resolubility, which tends to improve concentration stability, plate cleaning properties, and long-term stability. The rosin resin and / or the polysaccharide are preferably contained in the core layer and / or shell layer of the emulsion-type styrene-acrylic resin (A), and more preferably in the shell layer of the emulsion-type styrene-acrylic resin (A). The emulsion-type styrene-acrylic resin (A) may form a chemical bond with the rosin resin and / or polysaccharide contained in the emulsion-type styrene-acrylic resin (A).

[0038] (Emulsion-type styrene-acrylic resin containing polysaccharides (A)) The polysaccharides contained in the emulsion-type styrene-acrylic resin (A) are not particularly limited, but examples include maltodextrin, carrageenan, xanthan gum, gum arabic, pectin, guar gum, pullulan, glycogen, cellulose, starch, and starch derivatives. Preferably, it is at least one selected from the group consisting of starch, cellulose, and maltodextrin, and more preferably starch.

[0039] (Emulsion-type styrene-acrylic resin containing rosin resin (A)) The rosin resin contained in the emulsion-type styrene-acrylic resin (A) is not particularly limited, but examples include rosin esters such as maleated rosin and fumarated rosin, and rosin derivatives such as acrylic rosin and hydrogenated rosin. The acid value of the rosin resin contained in the shell layer of the emulsion-type styrene-acrylic resin (A) is preferably 0 to 350 mg KOH / g. The softening point of the rosin resin is preferably 80 to 200°C.

[0040] The total mass content of rosin resin and polysaccharides in the emulsion-type styrene-acrylic resin (A) is preferably 10 to 60% by mass, and more preferably 15 to 50% by mass, based on the solid content ratio of 100% by mass of the emulsion-type resin (A). When the total mass of rosin resin and polysaccharides in the emulsion-type styrene-acrylic resin (A) is within the above range, the long-term stability and water friction resistance are improved. The total mass content of rosin resin and polysaccharides contained in the shell layer of emulsion-type styrene-acrylic resin (A) is preferably 40 to 90% by mass, and more preferably 60 to 80% by mass, based on the solid content mass ratio of 100% by mass of emulsion-type resin (A). When the total mass of rosin resin and polysaccharides contained in the shell layer of emulsion-type styrene-acrylic resin (A) is within the above range, the long-term stability and water friction resistance are improved. The mass ratio of the core layer to the shell layer of the emulsion-type styrene-acrylic resin (A) is preferably 90:10 to 40:60, more preferably 80:20 to 45:55, and even more preferably 70:30 to 50:50. When the mass ratio of the core layer to the shell layer of the emulsion-type styrene-acrylic resin (A) is within the above range, the plate washability, concentration stability, aging stability, and water friction resistance are improved.

[0041] The solid content of the emulsion-type styrene-acrylic resin (A) is preferably 1 to 30% by mass, more preferably 2 to 20% by mass, and even more preferably 3 to 10% by mass, based on 100% by mass of the aqueous flexographic ink. When the solid content of the emulsion-type styrene-acrylic resin (A) is within the above range, the plate cleaning properties and water abrasion resistance are improved.

[0042] (Other emulsion-type resins) The aqueous flexographic ink of the present invention may also contain known emulsion-type resins as other emulsion-type resins, such as rosin resin emulsion (excluding emulsion-type styrene-acrylic resin (A) containing rosin resin) and urethane resin emulsion.

[0043] (Rosin resin emulsion (excluding emulsion-type styrene-acrylic resin (A) containing rosin resin)) Examples of rosin resin emulsions include rosin esters such as maleated rosin and fumarated rosin, and rosin derivatives such as hydrogenated rosin. However, emulsion-type styrene-acrylic resin (A) containing the above-mentioned rosin resin is excluded. The acid value of the rosin resin emulsion is preferably 0 to 350 mg KOH / g. The softening point of the rosin resin emulsion is preferably 50 to 200°C, and more preferably 80 to 150°C. When the softening point of the rosin resin emulsion is within the above range, water friction resistance, concentration stability, and aging stability tend to improve. The solid content of the rosin resin emulsion is preferably 1 to 30% by mass, more preferably 2 to 20% by mass, and even more preferably 3 to 10% by mass, based on 100% by mass of the aqueous flexographic ink. When the solid content of the rosin resin emulsion is within the above range, water friction resistance, concentration stability, and stability over time tend to improve. The solid content ratio of the emulsion-type styrene-acrylic resin (A) to the rosin resin emulsion is preferably 80:20 to 20:80, and more preferably 65:35 to 35:65. When the solid content ratio of the emulsion-type styrene-acrylic resin (A) to the rosin resin emulsion is within the above range, water friction resistance, concentration stability, and aging stability tend to improve.

[0044] The span value of the rosin resin emulsion is preferably 3 or less, more preferably 1 to 2.5, and even more preferably 1 to 1.5. When the span value of the rosin resin emulsion is within the above range, water friction resistance, concentration stability, and aging stability tend to improve. The cumulative 50% (D50) of the volume-based particle size distribution obtained by laser diffraction / scattering particle size distribution measurement of the rosin resin emulsion is preferably 20 to 1500 nm, and when the cumulative 50% (D50) of the volume-based particle size distribution obtained by laser diffraction / scattering particle size distribution measurement of the rosin resin emulsion is within the above range, water friction resistance, concentration stability, and aging stability tend to improve. The cumulative 10% (D10) of the volume-based particle size distribution of the rosin resin emulsion is preferably 5 to 1000 nm, more preferably 10 to 500 nm, and even more preferably 100 to 400 nm. The cumulative 90% (D90) of the volume-based particle size distribution of the rosin resin emulsion is preferably 100 to 2000 nm, and more preferably 500 to 1500 nm. The proportion of particles with a particle size of 350 nm or more in the rosin resin emulsion is preferably 90% by mass or less out of 100% by mass of the rosin resin emulsion. The full width at half maximum of the volume-based particle size distribution of the emulsion-type styrene acrylic resin (A) is preferably 700 nm or less, and more preferably 300 to 650 nm.

[0045] As a commercially available rosin resin emulsion, products such as the Hariester series manufactured by Harima Chemicals Co., Ltd. can be used.

[0046] (Water-soluble resin) The aqueous flexographic ink of the present invention can further improve the dispersibility of the ink, as well as the solubility and film-forming properties of the coating film, by including a water-soluble resin other than the emulsion-type styrene-acrylic resin (A), thereby achieving even better plate cleaning properties, long-term stability, and water-resistant friction. The water-soluble resin in this application is soluble or dispersible in water, and specifically includes water-soluble acrylic resins, water-soluble rosin resins, and water-soluble polysaccharides.

[0047] (Water-soluble acrylic resin) The water-soluble acrylic resin in the present invention refers to an acrylic resin obtained by solution polymerizing monomers containing acrylic monomers in an organic solvent, then desolventing the resulting solid resin and dissolving it in water or the like under alkaline conditions. The acrylic monomer constituting the water-soluble acrylic resin can be in the form of the (emulsion-type styrene-acrylic resin (A)) described above. Furthermore, the water-soluble acrylic resin may further contain styrene monomers, and the styrene monomers can be in the form of the (emulsion-type styrene-acrylic resin (A)) described above. Moreover, the water-soluble acrylic resin may contain polysaccharides or rosin resins, and the polysaccharides can be in the form of the (polysaccharides contained in the (emulsion-type styrene-acrylic resin (A)) described above, and the rosin resins can be in the form of the (rosin resin contained in the (emulsion-type styrene-acrylic resin (A)) described above. The water-soluble acrylic resin is preferably a styrene-acrylic copolymer resin, more preferably a styrene-acrylic copolymer resin containing polysaccharides and / or a styrene-acrylic copolymer resin containing rosin resin, and even more preferably a styrene-acrylic copolymer resin containing polysaccharides. When the above resin is used as a water-soluble acrylic resin, the plate cleaning properties, concentration stability, aging stability, and water friction resistance can be improved.

[0048] If the above-mentioned water-soluble acrylic resin contains polysaccharides and / or rosin resin, the polysaccharides and / or rosin resin contained in the water-soluble acrylic resin may form a chemical bond with the water-soluble acrylic resin, and it is preferable that a chemical bond is formed.

[0049] The weight-average molecular weight of the water-soluble acrylic resin is preferably 1,000 to 100,000, more preferably 1,500 to 50,000, and even more preferably 2,000 to 30,000. When the weight-average molecular weight of the water-soluble acrylic resin is within the above range, the plate cleaning properties, resolubility, stability over time, and water friction resistance are improved. The water-soluble acrylic resin preferably has acid groups, and if it has acid groups, the acid value is preferably 150 to 350 mgKOH / g, and more preferably 200 to 300 mgKOH / g. When the acid value of the water-soluble acrylic resin is within the above range, the plate cleaning properties and stability over time are improved.

[0050] (Water-soluble rosin resin (excluding acrylic resins containing rosin resin)) Water-soluble rosin resins exclude acrylic resins containing rosin resin. Specifically, examples include rosin esters such as maleated rosin and fumarated rosin, and rosin derivatives such as hydrogenated rosin. Rosin-based resins having an acid value of 100 to 350 mg KOH / g can be used after neutralizing part or all of the acid value with a basic compound and dissolving it in water. Examples of basic compounds include ammonia, organic amines, and alkali metal hydroxides. Specifically, examples of organic amines include alkylamines such as diethylamine, triethylamine, and ethylenediamine, and alkanolamines such as monoethanolamine, ethylethanolamine, diethylethanolamine, diethanolamine, and triethanolamine. Examples of alkali metal hydroxides include sodium hydroxide and potassium hydroxide. Among these, it is desirable to use both volatile and non-volatile basic compounds in combination from the viewpoint of coating film properties and resolubility. The softening point of the water-soluble rosin is preferably 80 to 200°C. The weight-average molecular weight of the water-soluble rosin resin is preferably 10,000 to 200,000.

[0051] Examples of the aforementioned water-soluble rosin resins include Harima Chemicals' Harimac T-80, Arakawa Chemical's Sizepine GF, and Marquid 32-30WS.

[0052] (Water-soluble polysaccharides (excluding acrylic resins containing polysaccharides)) The water-soluble polysaccharide excludes acrylic resins containing polysaccharides. As the water-soluble polysaccharide, the form of the polysaccharide contained in the emulsion-type styrene-acrylic resin (A) described above (Emulsion-type styrene-acrylic resin (A) containing polysaccharides) can be used. The weight-average molecular weight of the water-soluble polysaccharide is preferably 10,000 to 5,000,000.

[0053] The solid content of the water-soluble resin is preferably 10 to 35% by mass, more preferably 15 to 30% by mass, and even more preferably 17 to 25% by mass, based on the total mass of the ink. The solid content mass ratio of the emulsion-type styrene-acrylic resin (A) to the water-soluble resin is preferably 80:20 to 30:70, and more preferably 60:40 to 40:60. When the solid content mass ratio of the emulsion-type styrene-acrylic resin (A) to the water-soluble resin is within the above range, the plate cleanability, concentration stability, and stability over time are improved.

[0054] (solvent) The aqueous flexographic ink of the present invention preferably contains a solvent. The solvent is preferably water, but depending on the printing conditions (speed, plate depth, design, drying temperature), in addition to water, polar organic solvents such as alcohol-based organic solvents and glycol-based organic solvents can be used. The solvent is preferably present in an amount of 20 to 80% by mass, and more preferably 40 to 70% by mass, of the total mass of the aqueous flexographic ink. Furthermore, the content of the polar organic solvent is preferably 40% by mass or less of the total mass of the aqueous flexographic ink.

[0055] Examples of alcohol-based organic solvents include methanol, ethanol, propanol, isopropanol, isobutanol, n-butanol, tert-libutanol, hexanol, octanol, and decanol. Examples of glycol-based organic solvents include ethylene glycol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monobutyl ether, ethylene glycol monooctyl ether, diethylene glycol, diethylene glycol monoethyl ether, diethylene glycol monopropyl ether, diethylene glycol monobutyl ether, triethylene glycol, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol monopropyl ether, triethylene glycol monobutyl ether, propylene glycol, propylene glycol monoethyl ether, propylene glycol monopropyl ether, propylene glycol monobutyl ether, dipropylene glycol, dipropyl glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol monopropyl ether, dipropylene glycol monobutyl ether, tripropylene glycol, tripropylene glycol monomethyl ether, tripropylene glycol monoethyl ether, tripropylene glycol monopropyl ether, tripropylene glycol monobutyl ether, and dibutyl glycol. These may be used individually or in combination of two or more.

[0056] (Pigments (excluding extender pigments)) Pigments used in the aqueous flexographic ink of the present invention can be those conventionally used in aqueous flexographic printing ink compositions. Specifically, examples of inorganic pigments include colored pigments such as titanium dioxide, red iron oxide, antimony red, cadmium yellow, cobalt blue, Prussian blue, ultramarine, carbon black, and graphite. Examples of organic pigments include oil-soluble azo pigments, insoluble azo pigments, azo lake pigments, condensed azo pigments, copper phthalocyanine pigments, and condensed polycyclic pigments. These may be used individually or in combination of two or more. The content of the above pigments is preferably 1 to 60% by mass of the total mass of the aqueous flexographic ink.

[0057] (Extender pigments) The aqueous flexographic ink of the present invention preferably contains an extender pigment. The inclusion of an extender pigment allows the emulsion-type resin (A) to adsorb onto the surface of the extender pigment, further improving resolubility, dispersion stability, and transferability to the substrate, thus tending to improve plate cleaning properties, aging stability, and concentration stability. However, the above effects are based on scientific considerations, and the present invention is not limited to inks exhibiting these effects. The extender pigment content is preferably 0.1 to 10% by mass, and more preferably 1 to 5% by mass, relative to the total mass of the aqueous flexographic ink. When the extender pigment content is within the above range, plate cleanability, resolubility, and stability over time are improved. Known extender pigments can be used as the extender pigment, but it is preferable to include at least one selected from the group consisting of barium sulfate, calcium carbonate, magnesium carbonate, kaolin clay, and silica, more preferably at least one selected from the group consisting of barium sulfate and silica, and even more preferably barium sulfate. When the above extender pigment is included, plate cleanability, resolubility, and stability over time are improved. The extender pigment such as barium sulfate has a D50 of preferably 10 to 5000 nm, more preferably 30 to 2000 nm, and more preferably 100 to 700 nm. When the D50 of the extender pigment is within the above range, plate cleanability, resolubility, and stability over time are improved. Here, D50 of the extender pigment refers to the cumulative 50% diameter of the volume-based particle size distribution obtained by laser diffraction-scattering particle size distribution measurement.

[0058] The solid content mass ratio of the extender pigment to the emulsion-type styrene-acrylic resin (A) is preferably 15:85 to 65:35, and more preferably 25:75 to 45:55. When the solid content mass ratio of the emulsion-type styrene-acrylic resin (A) to the extender pigment is within the above range, the plate cleaning properties, concentration stability, and stability over time are improved. The ratio of D50 of the extender pigment obtained by laser diffraction / scattering particle size distribution measurement to the D50 of the emulsion-type styrene-acrylic resin (A) obtained by laser diffraction / scattering particle size distribution measurement is preferably 95:5 to 60:40, and more preferably 85:15 to 65:35. When the ratio of D50 of the extender pigment obtained by laser diffraction / scattering particle size distribution measurement to the D50 of the emulsion-type styrene-acrylic resin (A) is within the above range, concentration stability, plate cleanability, and aging stability tend to improve.

[0059] (Urea-based compounds) The aqueous flexographic ink of the present invention preferably further contains a urea-based compound represented by the following general formula (2). By including the urea-based compound, the urea-based compound and the emulsion-type styrene acrylic resin (A) form a hydrogen bond network, increasing the water retention capacity. As a result, the plate cleaning property and the stability over time tend to improve. In addition, it is difficult to dry on the plate, and the transferability to the substrate can be maintained well, so the concentration stability also tends to improve. However, the above effects are based on scientific considerations, and the present invention is not limited to those having only the above effects. General formula (2)

Chemical formula

[0060] Examples of the above substituents include a hydroxy group, an amino group, a carboxyl group, a halogen atom, a cyano group, a thio group, a silyl group, and a nitro group. Among them, a hydroxy group is preferable. Examples of the alkyl group having 1 to 4 carbon atoms include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a sec-butyl group, and a tert-butyl group. Among them, a methyl group and an ethyl group are preferable. Examples of the aryl group having 6 to 9 carbon atoms include a phenyl group, a tolyl group, and a xylyl group, and a phenyl group is preferable. Examples of the alkylene group having 1 to 3 carbon atoms include a methylene group, an ethylene group, and a propylene group, and an ethylene group is preferable.

[0061] Examples of urea compounds represented by the above general formula (2) include urea, 2-hydroxyethylurea, thiourea, 1,3-dimethylurea, ethylene urea derivatives synthesized by reacting ammonium carbamate with a titanium catalyst, and thiourea derivatives such as N-phenylthiourea. Among these, urea, 2-hydroxyethylurea, and 1,3-dimethylurea are preferred, and urea and 1,3-dimethylurea are more preferred. These may be used individually or in combination of two or more.

[0062] The content of the urea-based compound is preferably in the range of 1 to 10% by mass of the total ink mass, and more preferably in the range of 3 to 8% by mass. When the content of the urea-based compound is within the above range, the plate cleaning properties, resolubility, and stability over time are improved. Furthermore, the urea-based compound is preferably soluble in water at 25°C at 20% by mass or more, and more preferably at 30% by mass or more. When the solubility of the urea-based compound in water at 25°C is within the above range, the plate cleaning properties and stability over time are improved. The mass ratio of the urea-based compound to the emulsion-type styrene-acrylic resin (A) is preferably 10:90 to 75:25, more preferably 15:85 to 70:30, and even more preferably 20:80 to 60:40. When the mass ratio of the urea-based compound to the emulsion-type styrene-acrylic resin (A) is within the above range, the plate cleaning properties and long-term stability are improved.

[0063] (Additives) Various additives may be used in the aqueous flexographic ink of the present invention as needed. For example, dispersants, waxes, tackifiers, leveling agents, defoamers, film-forming aids, etc. Specifically, various additives such as hydrocarbon waxes like polyethylene wax to improve water friction resistance, tackifiers to improve water friction resistance, leveling agents to improve leveling properties, defoamers to provide defoaming properties, basic compounds such as sodium hydroxide and potassium hydroxide to provide resolubility, and film-forming aids may be added.

[0064] (Dispersant) The aqueous flexographic ink of the present invention preferably contains a dispersant from the viewpoint of improving plate cleaning properties, resolubility, and stability over time. As the dispersant, it is preferable to use a surfactant such as a polyether compound, an acetylene glycol compound, or a nonionic compound.

[0065] For example, among polyether compounds, copolymerized polyethers are preferred, and are not limited to them, but compounds in which polypropylene glycol (propylene oxide) and polyethylene glycol (ethylene oxide) are copolymerized are preferred. The weight-average molecular weight of the polypropylene glycol-polyethylene glycol copolymer resin is preferably 500 to 30000, more preferably 1000 to 5000, and when it is within this range, the plate cleaning properties, resolubility, and stability over time are improved. In addition, the amount of ethylene oxide added is preferably 10 to 95% by mass of the total molecule, and more preferably 30 to 90% by mass. When the amount of ethylene oxide added is within this range, the plate cleaning properties, resolubility, and stability over time are improved. Acetylene glycol compounds are also preferred, and acetylene glycol compounds having ethylene oxide and / or propylene oxide are preferred. As an example of an acetylene glycol compound, the Surfinol series (manufactured by Air Products Co., Ltd.) is commercially available.

[0066] The dispersant content is preferably in the range of 0.1 to 10% by mass, and more preferably in the range of 1 to 8% by mass, relative to the total mass of the ink. When the dispersant content is within the above range, plate cleaning performance, concentration stability, and stability over time are improved.

[0067] (Hydrogen-based wax) Examples of hydrocarbon waxes include polyethylene wax and Fischer-Tropsch wax. The hardness (penetration) of the hydrocarbon wax at 25°C as specified in JIS K2207 is 12 or less, preferably between 0.5 and 8, more preferably between 1 and 5, even more preferably between 2 and 4, and particularly preferably between 2.5 and 3.5. When the hardness (penetration) of the hydrocarbon wax at 25°C as specified in JIS K2207 is within the above range, the plate cleaning properties and water friction resistance are improved. The density of hydrocarbon waxes at 23°C, as specified in JIS K7112 (Method B), is 900-990 kg / m³. 3 Preferably, it is 925-990 kg / m³ 3 It is more preferable that the density of the hydrocarbon wax at 23°C as specified in JIS K7112 (Method B) is within the above range, which improves the plate cleaning properties and water friction resistance. The softening point of the hydrocarbon wax is preferably 50 to 200°C, and more preferably 90 to 130°C. When the softening point of the hydrocarbon wax is within the above range, the plate cleaning properties, resolubility, and water friction resistance are improved. The melting point of hydrocarbon waxes in DSC measurement is preferably 90 to 150°C, and more preferably 100 to 125°C. When the melting point of hydrocarbon waxes in DSC measurement is within the above range, plate cleaning performance, redissolvability, and water friction resistance are improved. Note that the melting point of hydrocarbon waxes represents the melting point of the peak top (minimum value) of the endothermic peak in the DSC heating curve. The D50 of hydrocarbon waxes is preferably 0.5 to 12 μm, more preferably 1 to 10 μm, and even more preferably 1.5 to 4 μm. When the D50 of hydrocarbon waxes is within the above range, plate cleaning performance and water friction resistance are improved. Note that D50 for hydrocarbon waxes represents the value of the cumulative 50% diameter of the volume-based particle size distribution in laser diffraction-scattering particle size distribution measurement.

[0068] In the aqueous flexographic ink of the present invention, the hydrocarbon wax content is preferably 0.1 to 10% by mass, and more preferably 0.5 to 5% by mass, based on 100% by mass of the ink. When the hydrocarbon wax content is within the above range, plate cleaning properties and water friction resistance are improved.

[0069] (Polyethylene wax) Polyethylene wax is not limited to, but examples include high-density polymerized polyethylene, low-density polymerized polyethylene, oxidized polyethylene, acid-modified polyethylene, and special monomer-modified polyethylene. Polyethylene wax has a density of 925-990 kg / m³ at 23°C as specified in JIS K7112 (Method B). 3 It is preferable that the polyethylene wax has a melt viscosity at 140°C measured in accordance with JIS K6862, which is preferably 50 to 8000 mPa·s. The polyethylene wax may also have an acid value. If it has an acid value, it is preferably 0.5 to 70 mg KOH / g. Furthermore, the polyethylene wax has a melting point of 90 to 150°C as measured by DSC, and more preferably 100 to 125°C.

[0070] (Alcohols with a hydride of 100% or higher) The aqueous flexographic ink of the present invention preferably further contains a trivalent or higher alcohol from the viewpoint of plate cleaning properties and concentration stability. Trivalent or higher alcohols have high moisturizing properties, which suppress ink drying on the plate, and further tend to improve concentration stability by suppressing penetration into paper. In addition, they tend to improve plate cleaning properties due to their high affinity with water. The trivalent or higher alcohol can be any compound having three or more hydroxyl groups in one molecular structure, excluding the <water-soluble polysaccharides> mentioned above. Examples of trivalent or higher alcohols include sugar alcohols such as glycerin, pentaerythritol, arabitol, tagatose, galactitol, and xylitol, as well as trimethylolpropane and trimethylolethane. Among these, the inclusion of sugar alcohols is preferable from the viewpoint of good affinity with water and high moisturizing properties, and the inclusion of glycerin is more preferable.

[0071] The content of trivalent or higher alcohols in the aqueous flexographic ink is preferably 0.1 to 10% by mass, and more preferably 0.5 to 5% by mass, based on 100% by mass of the aqueous flexographic ink. When the content of trivalent or higher alcohols in the aqueous flexographic ink is within the above range, the plate cleaning properties and concentration stability tend to improve. The solid content ratio of trivalent or higher alcohol to emulsion-type styrene-acrylic resin (A) is preferably 5:95 to 54:46, and more preferably 10:90 to 37:63. When the solid content ratio of trivalent or higher alcohol to emulsion-type styrene-acrylic resin (A) is within the above range, the plate cleaning properties and concentration stability tend to improve.

[0072] Fischer-Tropsch wax is a wax produced using carbon monoxide and hydrogen as raw materials by the Fischer-Tropsch process, and consists of a nearly saturated, unbranched, linear molecular structure. Due to this linear structure, it has a high melting point, low viscosity, and hardness. Fischer-Tropsch wax exhibits extremely high thermal stability, showing almost no degradation even when exposed to heat for long periods. Preferably, Fischer-Tropsch wax has a number-average molecular weight of 400 to 2000. Furthermore, Fischer-Tropsch wax has a density of 925 to 990 kg / m³ at 23°C, as specified in JIS K7112 (Method B). 3 It is preferable that the Fischer-Tropsch wax has an acid value. If it does have an acid value, it is preferably 0.5 to 50 mg KOH / g. Furthermore, it is preferable that the melting point of the Fischer-Tropsch wax in DSC measurement is 90 to 130°C, and more preferably 100 to 120°C.

[0073] (Biomass-derived ingredients) The aqueous flexographic ink of the present invention preferably further contains biomass-derived components. Biomass-derived components are monomers or polymers obtained from renewable resources such as plants, which constitute part or all of the ink. However, rosin resins and polysaccharide resins are excluded. Examples of biomass-derived components include cellulose fiber, lignin, vegetable oils such as soybean oil and rapeseed oil, chitin, chitosan, gelatin, polylactic acid, polyhydroxyalkanoate, biopolyethylene, biopolyethylene terephthalate, and polybutylene succinic acid, with cellulose fiber being particularly preferred. The above components can be used individually or in combination of two or more. The content of biomass-derived components is preferably 0.1 to 10% by mass, and more preferably 0.5 to 5% by mass, based on 100% by mass of the aqueous flexographic ink solids.

[0074] (Cellulose fiber) Cellulose fiber is a plant-derived fiber, a natural material mainly obtained from plant resources such as wood and cotton. It is made by processing cellulose, which constitutes the cell walls of plants, and the molecular chains of the resin aggregate to form a fibrous primary structure that is dispersed in water. The primary structure of cellulose fiber may exist individually or aggregate to form a secondary structure. The fiber diameter of the primary structure of cellulose fiber is preferably 0.001 to 50 μm, more preferably 0.1 to 30 μm, and even more preferably 1 to 20 μm. The appearance of the primary and secondary structures of cellulose fiber is not particularly limited, but may be fibrous, rod-shaped, particulate, etc., with particulate being preferred. When the primary and secondary structures of cellulose fibers are rod-shaped or particulate, the D50 measured by laser diffraction / scattering is preferably 1 to 20 μm, and more preferably 5 to 15 μm. When the D50 of cellulose fibers is within the above range, water friction resistance tends to improve. The bulk density of cellulose fibers is preferably 100 to 300 g / L, and more preferably 150 to 220 g / L. When the bulk density of cellulose fibers is within the above range, water friction resistance tends to improve. The ignition residue of cellulose fibers (850°C, 4h) is preferably 0.01 to 3% by mass, and more preferably 0.1 to 0.5% by mass. The pH value of cellulose fibers (10% suspension) is preferably 3 to 9, and more preferably 5 to 7.5. The cellulose fiber content is preferably 0.1 to 10% by mass, and more preferably 0.5 to 5% by mass, per 100% by mass of the aqueous flexographic ink solids. When the cellulose fiber content is within the above range, water and abrasion resistance tends to improve.

[0075] For cellulose fiber, commercially available products such as the ARBOCEL series manufactured by Rettenmeyer Japan can be used.

[0076] (Method of manufacturing water-based flexographic ink) The method for producing the aqueous flexographic ink of the present invention will now be described. The method for producing the aqueous flexographic ink of the present invention involves, for example, stirring and mixing a solvent, pigment (excluding extender pigment), extender pigment, dispersant, emulsion-type styrene acrylic resin (A), and water-soluble resin, etc. Then, dispersing the pigment using various mixing machines, such as a bead mill, pearl mill, sand mill, ball mill, attritor, roll mill, etc. Further, predetermined materials and additives such as emulsion resin (A) and water-soluble resin are added and stirred to obtain the ink. It is preferable to use a bead mill for pigment dispersion. The viscosity of the aqueous flexographic ink of the present invention is preferably 10 to 20 seconds in Zahn Cup No. 3 at 25°C.

[0077] [Method for manufacturing printed materials having a printed layer formed with water-based flexographic ink] Examples of methods for manufacturing printed materials having a printed layer formed with water-based flexographic ink include printing on the surface of paper or resin, particularly on paper containers such as paper cups and paper plates, or on paper containers whose surfaces are coated with a resin layer, thin paper for food packaging, or materials thereof, using the above-mentioned water-based flexographic ink and a flexographic printing press.

[0078] (Flexographic printing method) Examples of flexographic printing methods include the two-roll method, the doctor method, and the doctor chamber method. In both the doctor method and the doctor chamber method, an aqueous flexographic ink composition is supplied to an anilox roll on which cells are formed on the surface, and after a process in which excess aqueous flexographic ink on the surface of the anilox roll is scraped off by a doctor blade, the ink is finally printed on the substrate through a resin plate. When the aqueous flexographic ink of the present invention is printed using a flexographic printing method, a printed material with excellent aesthetic appeal can be obtained even on substrates with rough surfaces such as paper substrates.

[0079] (Flexographic printing method; anilox roll) The anilox used in the flexographic printing method for manufacturing flexographic printed materials of the present invention can be a ceramic anilox roll with cell engraving, a chrome-plated anilox roll, or the like. The cell shape can be a honeycomb pattern, a diamond pattern, a helical pattern, or any of these patterns. The role of the anilox is to receive the ink supplied from the doctor chamber (or fountain roll) uniformly and in a fixed quantity, and then transfer it to the printing plate. The screen ruling of the anilox roll is preferably 50 to 2000 lines / inch, and more preferably 100 to 1200 lines / inch.

[0080] (Flexographic printing method; flexographic plate) The printing plates used in the flexographic printing method for the flexographic printing method of the present invention include photosensitive resin plates that utilize ultraviolet curing by a UV light source or elastomer material plates that use a direct laser engraving method. Any type of sleeve or cushioning tape can be used to attach the plate. The screen ruling of the flexographic plate is preferably 80 to 200 lines / inch, and more preferably 125 to 175 lines / inch.

[0081] (Flexographic printing method; printing press) Flexographic printing presses include CI-type multi-color flexographic printing presses and unit-type multi-color flexographic printing presses. Ink supply methods include chamber type and two-roll type, and suitable printing presses such as hand presses can be used. The printing speed is preferably 50 to 500 m / min, and more preferably 100 to 300 m / min.

[0082] (base material) Examples of substrates (printed materials) include plastic films such as polyethylene, polypropylene, polyethylene terephthalate, and nylon; cellophane; paper; aluminum foil; or films, sheets, etc. made from composite materials thereof; and food packaging such as wrapping paper and paper bags; paper products such as paper containers having a resin layer such as polyolefin laminated to the surface; paper products such as paper containers having a resin coating layer such as polyolefin on the surface; and paper products such as uncoated paper containers without a resin layer on the surface. In the present invention, paper substrates are particularly preferred. Preferably, the paper substrate is selected from uncoated paper, one-sided glossy kraft paper with one side of the substrate treated, bleached kraft paper, unbleached kraft paper, liner paper, etc. [Examples]

[0083] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. In these examples, unless otherwise specified, "%" means "mass percent" and "parts" means "parts by mass". The numbers for the quantities of each material in the table are also in "parts by mass". The units for hydroxyl value and acid value are mgKOH / g.

[0084] (Example 1) [Preparation of water-based flexographic ink S1] First, the following mixture of raw materials was kneaded and dispersed in a bead mill. ·Wednesday: 28 parts ·PigmentBlack7: 18 copies Barium sulfate (manufactured by Sakai Chemical Industry Co., Ltd., Variace B-35, D50 300nm, solids content 100%): 4 parts ·Urea: 4 parts • PEG-PPG (a copolymer resin of polyethylene glycol (PEG) and polypropylene glycol (PPG), PEG / PPG = 40 / 60, weight-average molecular weight 2800, solids content 100%): 2.5 parts • Acetylene glycol (100% solids): 0.5 parts • Styrene acrylic resin SAC11 solution: 17 parts Next, the following raw materials were added and stirred to obtain aqueous flexographic ink S1. • Styrene acrylic resin SAC1 dispersion: 15 parts • Styrene acrylic resin SAC10 solution: 5 parts • Polyethylene wax dispersion (D50 4μm, softening point 110℃, solids content 40%): 3 parts Nonionic surfactant (60% solids): 2 parts Triethanolamine: 1 part

[0085] (Examples 2-19, Comparative Examples 1-2 [Preparation of water-based flexographic inks S2-S21]) Aqueous flexographic inks S2-21 were obtained using the same method as in Example 1, except that the raw materials and formulations listed in Tables 2-1 and 2-2 were changed. The properties of the resins used are shown in Table 1.

[0086] (Examples 20-22 [Preparation of water-based flexographic inks S22-S24]) Aqueous flexographic inks S22-24 were obtained by the same method as in Example 1, except that the raw materials and formulations listed in Table 3 were changed.

[0087] (Examples 23 and 24 [Preparation of aqueous flexographic inks S25 and S26]) Aqueous flexographic inks S25 and S26 were obtained in the same manner as in Example 1, except that the raw materials and formulations listed in Table 4 were changed.

[0088] [Table 1]

[0089] Other raw materials listed in Tables 2-1, 2-2, and 3 are as follows: Calcium carbonate: D50 40nm, oil absorption capacity 40ml / 100g ·Silica: D50 150nm, oil absorption 200ml / 100g Magnesium carbonate: D50 3000nm, oil absorption capacity 110ml / 100g ·Kaolin clay: D50 200nm, oil absorption 50ml / 100g

[0090] The other ingredients listed in Table 4 are as follows: Rosin resin emulsion: Span value 1.0, width at half maximum 510 nm, tail abundance 85%, acid value 120 mg KOH / g, solids content 50%, Cellulose fiber: Ignition residue (850°C, 4h) 0.15%, pH value (10% suspension) 6.2, D50 9μm, bulk density 185g / l

[0091] (evaluation) The following evaluations were performed using the obtained aqueous flexographic ink and printed materials having a printed layer formed with the obtained aqueous flexographic ink. The evaluation results are shown in Tables 2-1, 2-2, 3, and 4.

[0092] (Printing plate cleaning ability) Water-based flexographic ink was applied to a flexographic resin plate using a bar coater (Miyabar #4). The flexographic resin plate was then left to stand at 25°C, and washed with water at 15-minute intervals, changing the location each time. The appearance after washing at each interval was evaluated. <Evaluation Criteria> 6. After washing with water 60 minutes after the coating has dried, the area free of ink residue accounts for 98% or more of the total surface area of ​​the flexographic resin plate. 5. After washing with water 60 minutes after the coating has dried, the area free of ink residue is 95% or more but less than 98% of the total surface area of ​​the flexographic resin plate. 4. After washing with water 45 minutes after the coating dried, the area free of ink was 95% or more of the total surface area of ​​the flexographic resin plate. However, after washing with water 60 minutes after the coating dried, the area free of ink was less than 95% of the total surface area of ​​the flexographic resin plate. 3. After washing with water 30 minutes after the coating dried, the area free of ink was 95% or more of the total surface area of ​​the flexographic resin plate. However, after washing with water 45 minutes after the coating dried, the area free of ink was less than 95% of the total surface area of ​​the flexographic resin plate. 2. After washing with water 15 minutes after the coating dried, the area free of ink was 95% or more of the total surface area of ​​the flexographic resin plate. However, after washing with water 30 minutes after the coating dried, the area free of ink was less than 95% of the total surface area of ​​the flexographic resin plate. 1: After washing with water 15 minutes after the coating has dried, the area free of ink residue is less than 95% of the total surface area of ​​the flexographic resin plate. The above ratings indicate levels of industrial applicability: 3, 4, 5, and 6.

[0093] (concentration stability) The resulting water-based flexographic ink was printed using a flexographic printing press on unbleached kraft paper: kraft paper made from unbleached kraft pulp (Nippon Paper Industries Co., Ltd. Double-sided kraft K, basis weight 50g / m²). 2The print was 2000m long to form an ink coating, and the print density was evaluated using a colorimeter. A PANTONE X-Rite eXact spectrophotometer was used for the measurements. The measurement conditions were: illuminant / observer field of view: D50 / 2°, density status: ISO status E, density white standard: absolute value. <Evaluation Criteria> 5. The density difference between the printing point and the 2000m point is less than 0.02. 4. The density difference between the printing point and the 2000m point is 0.02 or greater and less than 0.04. 3. The density difference between the printing point and the 2000m point is 0.04 or greater and less than 0.06. 2: The density difference between the printing point and the 2000m point is 0.06 or greater and less than 0.08. 1: The density difference between the printing point and the 2000m point is 0.08 or greater. The above ratings indicate levels of industrial applicability: 3, 4, and 5.

[0094] (Stability over time) First, the viscosity of the water-based flexographic ink immediately after manufacturing was measured using a Zahn cup No. 3 at 25°C to obtain the ink viscosity before storage. Next, the water-based flexographic inks were stored under the following storage conditions, and the viscosity of each ink was measured using a Zahn cup No. 3 at 25°C to obtain the ink viscosity after storage under each condition. Then, for each ink, the absolute value of the difference between the ink viscosity after storage under condition 1 or condition 2 and the ink viscosity before storage was determined, and the larger of the two absolute values ​​of the difference was taken as the viscosity change of that ink, and the time-dependent stability was evaluated based on the following criteria. <Storage conditions> Condition 1: Store in a refrigerator at -5°C for one week. Condition 2: Store in a 40°C oven for one week. <Evaluation Criteria> 5: Those with viscosity change in less than 3 seconds. 4: Viscosity change of 3 seconds or more but less than 5 seconds. 3: Those with a viscosity change of 5 seconds or more but less than 7 seconds. 2: Those with a viscosity change of 7 seconds or more but less than 10 seconds. 1: Those with viscosity changes exceeding 10 seconds. The above ratings indicate levels of industrial applicability: 3, 4, and 5.

[0095] (Water friction resistance) Water-based flexographic inks S1-26 were printed at a speed of 50 m / min using a hand-puller (cell volume 10cc) on unbleached kraft paper (kraft paper made from unbleached kraft pulp, Nippon Paper Industries Co., Ltd. double-sided kraft K, basis weight 50 g / m²). 2 The material was then spread and left to stand at 25°C for 24 hours to form a coating. Next, a 2.5 cm x 17 cm printed surface was subjected to a friction fastness test using a JSPS-type friction fastness tester. A Kanakin cloth with 5 drops of water was used as the test paper, and the water friction resistance was evaluated from the ratio of the exposed area of ​​the base paper after a load of 200 g x 3 back-and-forth passes. Evaluation Criteria 5. The exposed area ratio of the base paper is less than 1%. 4. The exposed area ratio of the base paper is 1% or more but less than 5%. 3: The exposed area ratio of the base paper is 5% or more but less than 10%. 2: The exposed area ratio of the base paper is 10% or more but less than 20%. 1: The exposed surface area ratio of the base paper is 20% or more. The above ratings indicate levels of industrial applicability: 3, 4, and 5.

[0096] [Table 2-1]

[0097] [Table 2-2]

[0098] [Table 3]

[0099] [Table 4]

[0100] Comparative Example 1 had poor water resistance, concentration stability, and long-term stability because the span value of the emulsion-type styrene-acrylic resin (A) was greater than 3. Comparative Example 2 had poor concentration stability and plate cleaning properties because the emulsion-type styrene-acrylic resin did not have a core layer and a shell layer. On the other hand, in the example, the emulsion-type styrene-acrylic resin (A) having a core layer and a shell layer had a span value of 3 or less, resulting in good water friction resistance, concentration stability, plate cleaning properties, and aging stability. [Explanation of symbols]

[0101] Y...Maximum peak intensity, X1...Particle diameter at half the maximum frequency (Y), X2...Particle diameter at half the maximum frequency (Y), S1...Area of ​​particle size distribution in the range of particle diameters from 0 nm to less than 350 nm, S2...Area of ​​particle size distribution in the range of particle diameters of 350 nm or more

Claims

1. This is an aqueous flexographic ink containing an emulsion-type styrene-acrylic resin (A) having a core layer and a shell layer. The span value of the emulsion-type styrene-acrylic resin (A) represented by the following formula (1) is 3 or less, A water-based flexographic ink in which the D50 of the emulsion-type styrene-acrylic resin (A) below is 20 to 1500 nm. Equation (1): Span value = (D90 - D10) / D50 D10: Cumulative 10% diameter of volume-based particle size distribution obtained by laser diffraction / scattering particle size distribution measurement of emulsion-type styrene-acrylic resin (A) D50: Cumulative 50% diameter of the volume-based particle size distribution obtained by laser diffraction / scattering particle size distribution measurement of emulsion-type styrene-acrylic resin (A) D90: Cumulative 90% diameter of the volume-based particle size distribution obtained by laser diffraction / scattering particle size distribution measurement of emulsion-type styrene-acrylic resin (A)

2. The aqueous flexographic ink according to claim 1, wherein the emulsion-type styrene-acrylic resin (A) comprises a rosin resin and / or polysaccharide in the core layer and / or shell layer.

3. The aqueous flexographic ink according to claim 1 or 2, wherein the proportion of particles with a particle size of 350 nm or more, as determined by laser diffraction-scattering particle size distribution measurement, in the emulsion-type styrene-acrylic resin (A) is 20% by mass or less per 100% by mass of the emulsion-type styrene-acrylic resin (A).

4. The aqueous flexographic ink according to claim 1 or 2, wherein the full width at half maximum of the volume-based particle size distribution obtained by laser diffraction / scattering particle size distribution measurement of emulsion-type styrene acrylic resin (A) is 200 nm or less.

5. Furthermore, the aqueous flexographic ink according to claim 1 or 2, further comprising an extender pigment.

6. The aqueous flexographic ink according to claim 5, wherein the solid content mass ratio of the extender pigment to the emulsion-type styrene acrylic resin (A) is 15:85 to 65:

35.

7. The aqueous flexographic ink according to claim 5, wherein the ratio of D50 of the extender pigment to D50 of the emulsion-type styrene acrylic resin (A), obtained by laser diffraction / scattering particle size distribution measurement, is 95:5 to 60:

40.

8. Furthermore, the aqueous flexographic ink according to claim 1 or 2 further comprises a urea-based compound represented by the following general formula (1). General formula (1) 【Chemistry 1】 [In general formula (1), R １ This represents an oxygen atom or a sulfur atom. R ２ and R ３ Each of these independently represents a hydrogen atom, an alkyl group having 1 to 4 carbon atoms which may have substituents, or an aryl group having 6 to 9 carbon atoms which may have substituents. However, R ２ and R ３ The ring may be formed via an alkylene group having 1 to 3 carbon atoms.

9. The aqueous flexographic ink according to claim 1 or 2, wherein the mass ratio of the core layer to the shell layer of the emulsion-type styrene-acrylic resin (A) is 90:10 to 40:

60.

10. Furthermore, the aqueous flexographic ink according to claim 1 or 2, further comprising a trivalent or higher alcohol.

11. A water-based flexographic ink according to claim 1 or 2, for use with a paper substrate.

12. A printed article having a printed layer formed on a substrate using the aqueous flexographic ink described in claim 1 or 2.

13. Furthermore, the aqueous flexographic ink according to claim 1 or 2 further comprises a rosin resin emulsion and / or a water-soluble rosin resin.

14. Furthermore, the aqueous flexographic ink according to claim 1 or 2, further comprising biomass-derived components (excluding rosin resin and polysaccharide resin).

Images