Water-based ink composition for flexographic printing and method for producing the same

Abstract

The present invention relates to an aqueous ink composition for flexographic printing and a method for manufacturing the same. The aqueous ink composition for printing according to the present invention utilizes the pH-changing principle of phenolphthalein to periodically add ammonia and adjust the pH during dispersion, thereby improving dispersibility using a minimal amount of dispersion resin without affecting the drying of the ink, and can be utilized for various printing applications such as paper and film through a base dispersed in high concentration and low particle size.

Description

Technology Field

[0001] The present invention relates to an aqueous ink composition for flexographic printing and a method for manufacturing the same. Background Technology

[0002] Flexographic printing is a label printing process widely used for the production of self-adhesive labels. Flexography is a rotational embossing (raised) printing process in which ink is applied to a printing plate and then applied to the surface of a label or flexible packaging material. The printing plate is typically made of softer, more elastic rubber or flexible photopolymer, which is the reason for the name "flexographic printing," and it utilizes a flexible printing plate that encloses a printing cylinder. The ink-laid plate has a raised image and rotates at high speed to transfer ink from a roll to the printed material through small holes.

[0003] The advantages of the flexographic printing process include high-quality image reproduction, the ability to use various ink types including water-based, solvent-based, and UV-curable inks, automated performance that provides a fast and efficient printing process, high speed, and cost efficiency.

[0004] Recently, as interest in eco-friendly inks and packaging materials that reduce CO2 emissions and minimize ink consumption has increased, water-based inks that use water as a solvent are attracting attention. However, water-based inks have a problem in that they lack pigment wettability compared to conventionally used organic solvents, making it difficult to disperse them into small particles.

[0005] While researching water-based inks for flexographic printing to solve the above problem, the applicant confirmed that an ink composition manufactured through a pigment dispersion process of a base composition containing ammonia water and phenolphthalein has the effect of improving dispersibility by using a minimum amount of dispersion resin without affecting the drying of the ink, and thus completed the present invention. The problem to be solved

[0006] The present invention was conceived to solve the aforementioned problems and aims to provide a water-based ink composition for flexographic printing and a method for manufacturing the same. means of solving the problem

[0007] To achieve the above technical objectives, the present invention provides an aqueous ink composition for printing, characterized by being prepared through a pigment dispersion process of a base composition comprising a styrene acrylic polymer; a pigment; ammonia water (NH3); water; and phenolphthalein.

[0008] In addition, the present invention provides a method for preparing a water-based ink composition for printing, comprising: (a) a step of preparing a base composition by dissolving a styrene acrylic polymer, a pigment, ammonia water, and phenolphthalein in water; (b) a pigment dispersion step of dispersing the base composition by introducing it into a bead mill; (c) a step of visually checking the color change of the composition during bead milling and replenishing the ammonia water to maintain a pH of 9 or higher; and (d) a letdown step of mixing the dispersed composition with a binder and an antifoaming agent. Effects of the invention

[0009] The aqueous ink composition for printing according to the present invention utilizes the pH change principle of phenolphthalein to periodically add ammonia and adjust the pH during dispersion, thereby improving dispersibility using a minimal amount of dispersion resin without affecting the drying of the ink, and can be used for various printing applications such as paper and film through a base dispersed in high concentration and low particle size.

[0010] The effects of the present invention are not limited to those mentioned above, and may also include other effects that are clearly understood by a person skilled in the art from the description throughout the specification but are not explicitly mentioned. Brief explanation of the drawing

[0011] Figure 1 is a figure showing the types of bead mills that can be used for water-based ink. FIG. 2 is a schematic diagram showing a method for manufacturing water-based ink for printing according to the present invention. Specific details for implementing the invention

[0012] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the attached drawings. The advantages and features of the present invention and the methods for achieving them will become clear by referring to the embodiments described below in detail together with the attached drawings. However, the present invention is not limited to the embodiments disclosed below but can be implemented in various different forms. These embodiments are provided merely to ensure that the disclosure of the present invention is complete and to fully inform those skilled in the art of the scope of the invention, and the present invention is defined only by the scope of the claims. Throughout the specification, the same reference numerals refer to the same components.

[0013] Unless otherwise defined, all terms used herein (including technical and scientific terms) may be used in a meaning commonly understood by those skilled in the art to which the present invention pertains. Furthermore, terms defined in commonly used dictionaries are not to be interpreted ideally or excessively unless explicitly and specifically defined otherwise. The terms used herein are for describing embodiments and are not intended to limit the present invention. In this specification, the singular form includes the plural form unless specifically stated otherwise in the text.

[0014] As used in the specification, "comprises" and / or "comprising" do not exclude the presence or addition of one or more other components, steps, actions, and / or elements to the mentioned components, steps, actions, and / or elements.

[0016] First, the present invention provides an aqueous ink composition for printing, characterized by being prepared through a pigment dispersion process of a base composition comprising a styrene acrylic polymer; a pigment; ammonia water (NH3); water; and phenolphthalein.

[0017] The present invention will be described in more detail below.

[0018] The present invention is a Resin Minimum Pigment Concentrate System (RMPC) that applies a polymer dispersant to add pigment at a high concentration, wherein a styrene acrylic polymer is used as the polymer dispersant.

[0019] The above styrene acrylic polymer is preferably a modified styrene acrylic polymer, wherein it is a (α-methyl)styrene-acrylic acid polymer, a (α-methyl)styrene-acrylic acid-acrylic acid ester polymer, a (α-methyl)styrene-methacrylic acid polymer, a (α-methyl)styrene-methacrylic acid-acrylic acid ester polymer, a (α-methyl)styrene-(anhydrous)maleic acid copolymer, an acrylic acid ester-(anhydrous)maleic acid polymer, a (α-methyl)styrene-acrylic acid ester-(anhydrous)maleic acid polymer, an acrylic acid ester-allylsulfonic acid ester polymer, an acrylic acid ester-styrenesulfonic acid polymer, a (α-methyl)styrene-methacrylic sulfonic acid polymer, a polyester-acrylic acid polymer, a polyester-acrylic acid-acrylic acid ester polymer, or a polyester-methacrylic acid polymer. It may be a polyester-methacrylic acid-acrylic acid polymer ester.

[0020] The above pigment is a pigment capable of changing the hue or providing opacity, and preferably, it may be one or more selected from the group consisting of CI Pigment Red 146, carbon black, CI Pigment Blue 15:3, CI Pigment Yellow 13, and CI Pigment Yellow 14.

[0021] The above base composition is suitable for improving the wettability of the aqueous ink composition at pH 9. For the above pH, alkaline substances such as ammonia, triethylamine, dimethylaminoethanol, diethanolamine, triethanolamine, aminomethyl propanol, organic amines such as polyethylene glycol, polypropylene glycol monoamine, coconut amine, octylamine, dodecylamine, stearylamine, oleylamine, lithium hydroxide, sodium hydroxide, and potassium hydroxide may be used, but since they may affect the drying of the ink during film printing, the present invention uses highly volatile ammonia that does not contain organic substances.

[0022] Ammonia has the effect of improving dispersibility without affecting the drying of the ink, and preferably, an ammonia solution with a concentration of 25 to 30%, more preferably an ammonia solution with a concentration of 28%, can be used.

[0023] When the above base composition is formulated, the pH of the particle surface varies depending on the type of pigment, and due to the heat generated during the dispersion process, ammonia continues to volatilize, making it difficult to maintain the pH of the composition, and it is difficult to expect a sustained effect when the pH is maintained at 9 or higher.

[0024] However, by adding phenolphthalein to the dispersion base, the color change can be visually confirmed, and the pH can be maintained by continuously replenishing the ammonia water.

[0025] The above phenolphthalein has the chemical formula C 20 H 14 As a phenolic solution of O4, it is colorless in acidic solutions and turns red in basic solutions with a pH of 9 or higher, so it is widely used in acid-base titrations. After pigment dispersion in the base composition, the pH of the ink composition becomes 8.5 or lower, so the red color of phenolphthalein disappears from the ink.

[0026] The above base composition may preferably comprise, based on the total weight of the base composition, 20 to 30 weight% of styrene acrylic polymer, 30 to 40 weight% of pigment, 3 to 10 weight% of ammonia water; and 25 to 45 weight% of water.

[0027] The ink composition may further include one or more extender pigments selected from the group consisting of barium sulfate, calcium carbonate, magnesium carbonate, white carbon, talc, aluminum hydroxide, magnesium hydroxide, alumina white, silica powder, diatomaceous earth, synthetic silica, calcium silicate, attapulgite, sericite, mica, hydrotalcite, bentonite, zeolite, kaolin clay, and pyrophyllite, and preferably may include barium sulfate.

[0028] The above-mentioned extender pigment is a colorless pigment that can reinforce the film and opacity, and is mixed with other pigments to increase the amount or dilute the concentration.

[0029] The ink composition according to the present invention may preferably be for flexographic printing.

[0030] Flexo printing is a relief printing method that uses flexible typography printing technology, and is also called flexography or mesh printing.

[0031] In addition, the ink composition of the present invention may provide an aqueous ink composition for film printing that further comprises a polyurethane prepolymer, an acrylic emulsion, and an antifoaming agent together with the base composition.

[0032] The above polyurethane prepolymer and acrylic emulsion may affect the adhesiveness, durability, and chemical stability as binders of the ink composition.

[0033] The above defoaming agent can improve the mechanical strength of the coating layer by removing bubbles that may occur in the coating layer. The above defoaming agent may include silicone-based defoaming agents, mineral oil-based defoaming agents, non-silicone-based defoaming agents, alcohol-based defoaming agents, etc., and preferably, BASF’s Foamstar product, which is a non-silicone-based defoaming agent, may be used.

[0034] The above film printing ink composition may preferably comprise, based on the total weight, 40 to 50 weight% of a base composition; 30 to 35 weight% of a polyurethane prepolymer; 15 to 25 weight% of an acrylic emulsion; and 0.2 to 0.7 weight% of an antifoaming agent.

[0035] In addition, the present invention may provide an aqueous ink composition for paper printing comprising, together with the base composition, an acrylate methacrylate copolymer, an antifoaming agent, and water.

[0036] The above acrylate methacrylate copolymer may affect the adhesiveness, durability, and chemical stability as a binder of the ink composition, and preferably, BASF’s Joncryl may be used.

[0037] The above defoaming agent can improve the mechanical strength of the coating layer by removing bubbles that may occur in the coating layer. The above defoaming agent may include silicone-based defoaming agents, mineral oil-based defoaming agents, non-silicone-based defoaming agents, alcohol-based defoaming agents, etc., and preferably, BASF’s Foamstar product, which is a non-silicone-based defoaming agent, may be used.

[0038] The above paper printing ink composition may preferably comprise, based on the total weight, 40 to 50 weight% of a base composition; 40 to 45 weight% of an acrylate methacrylate copolymer; 0.2 to 0.7 weight% of an antifoaming agent; and 5 to 15 weight% of water.

[0040] In addition, the present invention provides a method for preparing a water-based ink composition for printing, comprising: (a) a step of preparing a base composition by dissolving a styrene acrylic polymer, a pigment, ammonia water, and phenolphthalein in water; (b) a pigment dispersion step of dispersing the base composition by introducing it into a bead mill; (c) a step of visually checking the color change of the composition during bead milling and replenishing the ammonia water to maintain a pH of 9 or higher; and (d) a letdown step of mixing the dispersed composition with a binder and an antifoaming agent.

[0041] The above step (a) is a step of preparing a base composition, which is prepared by dissolving a styrene acrylic polymer, a pigment, ammonia water, and phenolphthalein in water, and preferably may comprise, based on the total weight of the base composition, 20 to 30 weight% of styrene acrylic polymer, 30 to 40 weight% of pigment, 3 to 10 weight% of ammonia water; and 25 to 45 weight% of water.

[0042] The above styrene acrylic polymer is preferably a modified styrene acrylic polymer, wherein it is a (α-methyl)styrene-acrylic acid polymer, a (α-methyl)styrene-acrylic acid-acrylic acid ester polymer, a (α-methyl)styrene-methacrylic acid polymer, a (α-methyl)styrene-methacrylic acid-acrylic acid ester polymer, a (α-methyl)styrene-(anhydrous)maleic acid copolymer, an acrylic acid ester-(anhydrous)maleic acid polymer, a (α-methyl)styrene-acrylic acid ester-(anhydrous)maleic acid polymer, an acrylic acid ester-allylsulfonic acid ester polymer, an acrylic acid ester-styrenesulfonic acid polymer, a (α-methyl)styrene-methacrylic sulfonic acid polymer, a polyester-acrylic acid polymer, a polyester-acrylic acid-acrylic acid ester polymer, or a polyester-methacrylic acid polymer. It may be a polyester-methacrylic acid-acrylic acid polymer ester.

[0043] The above pigment is a pigment capable of changing the hue or providing opacity, and preferably, it may be one or more selected from the group consisting of CI Pigment Red 146, carbon black, CI Pigment Blue 15:3, CI Pigment Yellow 13, and CI Pigment Yellow 14.

[0044] The above base composition is suitable for improving the wettability of the aqueous ink composition at pH 9. For the above pH, alkaline substances such as ammonia, triethylamine, dimethylaminoethanol, diethanolamine, triethanolamine, aminomethyl propanol, organic amines such as polyethylene glycol, polypropylene glycol monoamine, coconut amine, octylamine, dodecylamine, stearylamine, oleylamine, lithium hydroxide, sodium hydroxide, and potassium hydroxide may be used, but since they may affect the drying of the ink during film printing, the present invention uses highly volatile ammonia that does not contain organic substances.

[0045] Ammonia has the effect of improving dispersibility without affecting the drying of the ink, and preferably, an ammonia solution with a concentration of 25 to 30%, more preferably an ammonia solution with a concentration of 28%, can be used.

[0046] The above phenolphthalein has the chemical formula C 20 H 14 As a phenolic solution of O4, it is colorless in acidic solutions and turns red in basic solutions with a pH of 9 or higher, so it is widely used in acid-base titrations. After pigment dispersion in the base composition, the pH of the ink composition becomes 8.5 or lower, so the red color of phenolphthalein disappears from the ink.

[0047] Step (b) above is a pigment dispersion step in which the base composition is fed into a bead mill and dispersed, wherein the bead mill may preferably be a disc type, pin type, or turbo type, but is not limited thereto.

[0048] The above bead milling process can preferably be performed for 1 to 10 hours at 500 to 6000 RPM conditions, and more preferably for 4 hours at 4000 RPM conditions.

[0049] If bead milling is performed for less than 1 hour, sediment may remain, and if it exceeds 10 hours, aggregation may occur. Additionally, if the rotor speed of the bead mill is less than 500 rpm, the particle size increases, which leads to a decrease in dispersion power and an increase in resistivity. Conversely, if the rotor speed of the bead mill exceeds 6000 rpm and is too fast, it cannot provide sufficient energy for crushing, which actually results in a decrease in dispersion power.

[0050] Although it is difficult to maintain the pH of the composition because the ammonia continues to volatilize due to the heat generated in the dispersion process of step (b) above, the pH can be maintained at a constant level of 9 or higher by continuously replenishing the ammonia water while visually checking the color change of the added phenolphthalein as in step (c) above.

[0051] The pigment that has undergone the above dispersion process can preferably exhibit an average size of 1 μm.

[0052] The above step (d) is a letdown step of mixing the dispersed composition with a binder and an antifoamer, preferably by mixing with a polyurethane prepolymer, an acrylic emulsion, and an antifoamer to prepare an aqueous ink composition for film printing.

[0053] The above polyurethane prepolymer and acrylic emulsion may affect the adhesiveness, durability, and chemical stability as binders of the ink composition.

[0054] The above defoaming agent can improve the mechanical strength of the coating layer by removing bubbles that may occur in the coating layer. The above defoaming agent may include silicone-based defoaming agents, mineral oil-based defoaming agents, non-silicone-based defoaming agents, alcohol-based defoaming agents, etc., and preferably, BASF’s Foamstar product, which is a non-silicone-based defoaming agent, may be used.

[0055] The method for preparing the above film printing ink composition may preferably comprise, based on the total weight, 40 to 50 weight% of a base composition; 30 to 35 weight% of a polyurethane prepolymer; 15 to 25 weight% of an acrylic emulsion; and 0.2 to 0.7 weight% of an antifoaming agent.

[0056] In addition, the above step (d) can preferably be performed by mixing an acrylate methacrylate copolymer, an antifoaming agent, and water to prepare an aqueous ink composition for paper printing.

[0057] The above acrylate methacrylate copolymer may affect the adhesiveness, durability, and chemical stability as a binder of the ink composition, and preferably, BASF’s Joncryl may be used.

[0058] The above defoaming agent can improve the mechanical strength of the coating layer by removing bubbles that may occur in the coating layer. The above defoaming agent may include silicone-based defoaming agents, mineral oil-based defoaming agents, non-silicone-based defoaming agents, alcohol-based defoaming agents, etc., and preferably, BASF’s Foamstar product, which is a non-silicone-based defoaming agent, may be used.

[0059] The above method for preparing a paper printing ink composition may preferably comprise, based on the total weight, 40 to 50 weight% of a base composition; 40 to 45 weight% of an acrylate methacrylate copolymer; 0.2 to 0.7 weight% of an antifoaming agent; and 5 to 15 weight% of water.

[0060] The ink composition prepared according to the manufacturing method of the present invention may preferably be for flexographic printing.

[0061] The aqueous ink composition for printing according to the present invention utilizes the pH change principle of phenolphthalein to periodically add ammonia and adjust the pH during dispersion, thereby improving dispersibility using a minimal amount of dispersion resin without affecting the drying of the ink, and can be used for various printing applications such as paper and film through a base dispersed in high concentration and low particle size.

[0063] Embodiments of the present invention will be described below with reference to the attached drawings. However, those skilled in the art will understand that the present invention may be implemented in other specific forms without changing its technical concept or essential features. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive.

[0065] Example 1. Preparation of water-based ink for flexographic printing

[0066] The manufacturing process of an aqueous ink for flexographic printing according to the present invention is schematically illustrated in FIG. 2. The specific manufacturing process according to FIG. 2 is as follows.

[0068] 1-1. Manufacture of Water-based Ink for Film Printing

[0069] A base composition was prepared by dissolving 20 to 30 wt% of modified styrene acrylic polymer, 30 to 40 wt% of pigment, and 3 to 10 wt% of 28% ammonia water in water, and adding phenolphthalein. Then, the prepared base composition was fed into a bead mill, and a bead milling process was performed for 4 hours at 4000 RPM. During the process, ammonia water was continuously replenished so that the color of the composition remained red. Subsequently, the obtained composition was set to 40 to 50 wt%, and an aqueous ink for film printing was prepared by mixing 30 to 35 wt% of Lamberti’s PU835 (polyurethane prepolymer), 15 to 25 wt% of Lamberti’s AC 200 (acrylic emulsion), and 0.2 to 0.7 wt% of BASF’s FOAMSTAR ST 2410.

[0071] 1-2. Manufacture of Water-based Ink for Paper Printing

[0072] A base composition was prepared by dissolving 20 to 30 wt% of modified styrene acrylic polymer, 30 to 40 wt% of pigment, and 3 to 10 wt% of 28% ammonia water in water, and adding phenolphthalein. Then, the prepared base composition was fed into a bead mill, and a bead milling process was performed for 4 hours at 4000 RPM. During the process, ammonia water was continuously replenished so that the color of the composition remained red. Subsequently, the obtained composition was set to 40 to 50 wt%, and an aqueous ink for paper printing was prepared by mixing 40 to 45 wt% of BASF’s Joncryl (acrylate methacrylate copolymer), 0.2 to 0.7 wt% of BASF’s FOAMSTAR ST 2410, and 5 to 15 wt% of water.

Claims

Claim 1 A water-based ink composition for printing, comprising a styrene acrylic polymer; a pigment; water ammonia (NH3); water; and phenolphthalein, wherein the base composition is dispersed while maintaining a pH of 9 or higher by continuously replenishing water ammonia while visually checking whether the red color expressed by phenolphthalein at a pH of 9 or higher is maintained during a pigment dispersion process by bead milling, wherein the pigment undergoing the dispersion process exhibits an average size of 1 μm, and the pH of the final ink composition after the dispersion process is adjusted to 8.5 or lower so that the red color of phenolphthalein disappears. Claim 2 A water-based ink composition for printing according to claim 1, characterized in that the base composition comprises, based on the total weight, 20 to 30 weight% of a styrene acrylic polymer; 30 to 40 weight% of a pigment; 3 to 10 weight% of ammonia water; and 25 to 45 weight% of water. Claim 3 A water-based ink composition for printing, characterized in that, in claim 1, the ink composition is for flexographic printing. Claim 4 delete Claim 5 delete Claim 6 A water-based ink composition for printing according to claim 1, characterized by further comprising a polyurethane prepolymer, an acrylic emulsion, and an antifoaming agent together with the base composition. Claim 7 An aqueous ink composition for printing according to claim 6, characterized in that the ink composition comprises, based on the total weight, 40 to 50 weight% of a base composition; 30 to 35 weight% of a polyurethane prepolymer; 15 to 25 weight% of an acrylic emulsion; and 0.2 to 0.7 weight% of an antifoaming agent. Claim 8 A water-based ink composition for printing, characterized in that, in addition to the base composition of claim 1, it further comprises an acrylate methacrylate copolymer, an antifoaming agent, and water. Claim 9 An aqueous ink composition for printing according to claim 8, characterized in that the ink composition comprises, based on the total weight, 40 to 50 weight% of a base composition; 40 to 45 weight% of an acrylate methacrylate copolymer; 0.2 to 0.7 weight% of an antifoaming agent; and 5 to 15 weight% of water. Claim 10 (a) a step of preparing a base composition having a pH of 9 or higher by dissolving a styrene acrylic polymer, a pigment having an average particle size of 1 μm or less, ammonia water, and phenolphthalein in water; (b) a pigment dispersion step in which the base composition is introduced into a bead mill and dispersed, wherein ammonia volatilizes due to heat generated during bead milling and reduces the pH of the base composition, and ammonia water is continuously replenished to maintain a pH of 9 or higher while visually checking whether the red color of phenolphthalein is maintained; (c) a step in which, after the pigment dispersion is completed, the pH of the base composition becomes 8.5 or lower and the red color of phenolphthalein disappears; and (d) a letdown step in which the dispersed composition is mixed with a binder and an antifoaming agent; comprising a method for preparing an aqueous ink composition for printing. Claim 11 A method for preparing an aqueous ink composition for printing, wherein, in claim 10, the base composition of step (a) comprises, based on the total weight, 20 to 30 weight% of a styrene acrylic polymer; 30 to 40 weight% of a pigment; 3 to 10 weight% of ammonia water; and 25 to 45 weight% of water. Claim 12 delete Claim 13 A method for manufacturing an aqueous ink composition for printing, characterized in that, in claim 10, the bead milling of step (b) is performed for 1 to 10 hours under conditions of 500 to 6000 rpm. Claim 14 A method for manufacturing a water-based ink composition for printing, characterized in that, in claim 10, the bead mill in step (b) above is of the disc type, pin type, or turbo type. Claim 15 delete

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