Water-based white ink composition for surface printing on flexible packaging

Abstract

To provide a water-based white ink composition for surface printed flexible packaging having excellent heat resistance, blocking resistance, alcohol resistance, scratch resistance, solid uniformity, and bleeding resistance.SOLUTION: A water-based white ink composition for surface printed flexible packaging contains a white pigment, a polymer-emulsified acrylic resin emulsion, an N-oleoyl sarcosine, a hydrazine compound that has two or more hydrazine residues in the molecule, and a wax, wherein the content of the acrylic resin emulsion is 3-40 mass% in terms of solid content, and the glass transition temperature of the acrylic resin emulsion is between -40 and 30°C.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a water-based white ink composition for surface printing on flexible packaging. More specifically, the present invention relates to a water-based white ink composition for surface printing on flexible packaging that has excellent heat resistance, blocking resistance, alcohol resistance, abrasion resistance, solid uniformity, and bleeding resistance. [Background technology]

[0002] Conventionally, flexible packaging materials using various plastic films have been used for foods, confectioneries, household goods, pet food, etc., from the viewpoints of design, economy, content protection, transportability, etc. Furthermore, many flexible packaging materials are subjected to gravure printing or flexographic printing. The surface of the base film of a flexible packaging material is subjected to surface printing. To print clear designs, etc., a white ink is printed on the film surface. Therefore, white ink compositions used for surface printing of flexible packaging materials have been developed (for example, Patent Document 1). The ink composition described in Patent Document 1 contains an anionic surfactant to improve heat resistance. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2020-59822 Summary of the Invention [Problem to be solved by the invention]

[0004] The ink composition described in Patent Document 1 has room for improvement in terms of heat resistance, as well as blocking resistance, alcohol resistance, and solid uniformity.

[0005] The present invention has been made in view of the above-mentioned conventional problems, and has an object to provide an aqueous white ink composition for surface printing on flexible packaging, which has excellent heat resistance, blocking resistance, alcohol resistance, abrasion resistance, solid uniformity, and bleeding resistance. [Means for solving the problem]

[0006] The present inventors conducted extensive research to solve the above problems and found that the heat resistance of ink compositions can be significantly improved by incorporating N-oleoyl sarcosine, which has traditionally been used as a rust inhibitor. Furthermore, the present inventors discovered that the above problems can be simultaneously solved by incorporating a specific amount of a polymer-emulsified acrylic resin emulsion exhibiting a specific glass transition temperature, a hydrazine compound with a specific structure, and a wax, leading to the completion of the present invention. The present invention, which solves the above problems, mainly comprises the following features:

[0007] (1) A water-based white ink composition for surface-printing flexible packaging, comprising: a white pigment; an acrylic resin emulsion emulsified with a polymer; N-oleoyl sarcosine; a hydrazine compound having at least two hydrazine residues in the molecule; and a wax, wherein the content of the acrylic resin emulsion is 3 to 40 mass % in terms of solid content, and the glass transition temperature of the acrylic resin emulsion is −40 to 30° C.

[0008] According to this configuration, the water-based white ink composition for surface printing on flexible packaging has excellent heat resistance, blocking resistance, alcohol resistance, abrasion resistance, solid uniformity, and bleeding resistance.

[0009] (2) The water-based white ink composition for surface-printing flexible packaging according to (1), wherein the wax has an average particle size of 0.1 to 6 μm.

[0010] According to this configuration, the water-based white ink composition for surface printing on flexible packaging has even better blocking resistance.

[0011] (3) The water-based white ink composition for surface-printing flexible packaging according to (1) or (2), further comprising a water-soluble organic solvent.

[0012] According to this configuration, the water-based white ink composition for surface printing on flexible packaging has even better solid uniformity. [Effects of the Invention]

[0013] According to the present invention, it is possible to provide a water-based white ink composition for surface printing on flexible packaging, which has excellent heat resistance, blocking resistance, alcohol resistance, abrasion resistance, solid uniformity, and bleeding resistance. DETAILED DESCRIPTION OF THE INVENTION

[0014] <Water-based white ink composition for surface printing on flexible packaging> An aqueous white ink composition for surface-printing flexible packaging (hereinafter also referred to as ink composition) according to one embodiment of the present invention contains a white pigment, an acrylic resin emulsion emulsified with a polymer, N-oleoyl sarcosine, a hydrazine compound having at least two hydrazine residues in the molecule, and a wax. The content of the acrylic resin emulsion is 3 to 40 mass % in terms of solid content. The glass transition temperature of the acrylic resin emulsion is -40 to 30°C. Each of these components will be described below.

[0015] (white pigment) The white pigment is not particularly limited. Examples of the white pigment include various inorganic white pigments and organic white pigments. Inorganic white pigments include titanium oxide, zinc oxide, cerium oxide, silica, alumina, magnesium oxide, zirconium dioxide, yttria-stabilized zirconium, indium oxide, antimony oxide, tin oxide, barium titanate, barium sulfate, calcium carbonate, finely powdered silicic acid, calcium silicate, talc, and clay. Organic white pigments include organic compound salts disclosed in JP-A-11-129613, and alkylene bismelamine derivatives disclosed in JP-A-11-140365 and JP-A-2001-234093. Among these, various types of titanium oxide, such as rutile and anatase types, are preferred because of their excellent hiding power. Titanium oxide whose surface is coated with alumina, silica, an organic substance, or the like is more preferred.

[0016] The average particle size of the white pigment is not particularly limited. For example, the average particle size of the white pigment is preferably 100 nm or more, and more preferably 150 nm or more. The average particle size of the white pigment is preferably 500 nm or less, and more preferably 400 nm or less. When the average particle size of the white pigment is within the above range, the ink composition has excellent hiding power. In this embodiment, the average particle size is the volume average particle size measured by a laser diffraction particle size measurement method using a Nanotrac (UPA-EX150, manufactured by Nikkiso Co., Ltd.).

[0017] The content of the white pigment is not particularly limited. For example, the content of the white pigment in the ink composition is preferably 5% by mass or more, and more preferably 10% by mass or more. Furthermore, the content of the white pigment in the ink composition is preferably 20% by mass or less, and more preferably 15% by mass or less. When the content of the white pigment is within the above range, the ink composition has excellent hiding power. Furthermore, when the ink composition is applied to a flexible packaging material and a design or the like is printed thereon, the design or the like is easily visible.

[0018] (acrylic resin emulsion emulsified with polymer) The acrylic resin emulsion of this embodiment is an acrylic resin emulsion emulsified with a polymer compound. The glass transition temperature of the acrylic resin emulsion is −40 to 30° C. The acrylic resin emulsion emulsified with a polymer may have a core-shell structure consisting of a shell made of a polymer that functions as a polymer emulsifier and a core made of a resin that is more hydrophobic than the shell. The acrylic resin emulsion emulsified with a polymer of this embodiment is distinguished from acrylic resin emulsions emulsified with an emulsifier such as a low-molecular-weight compound surfactant.

[0019] The acrylic resin emulsion emulsified with a polymer is not particularly limited. Examples of acrylic resin emulsions emulsified with a polymer include acrylic resin emulsions, styrene-acrylic resin emulsions, acrylic-vinyl acetate resin emulsions, acrylic-vinyl chloride resin emulsions, acrylic-silicone resin emulsions, and acrylic-colloidal silica resin emulsions. Among these, the acrylic resin emulsion emulsified with a polymer is preferably an acrylic resin emulsion emulsified with a polymer (i.e., an "acrylic resin emulsion" rather than a "mixed acrylic "resin emulsion") because of its excellent transparency and coating film resistance.

[0020] The glass transition temperature (Tg) of the acrylic resin emulsion emulsified with a polymer may be -40°C or higher, and preferably -20°C or higher. The glass transition temperature (Tg) of the acrylic resin emulsion emulsified with a polymer may be 30°C or lower, and preferably 20°C or lower. If the Tg is lower than -40°C, the ink composition may produce a coating film with reduced blocking resistance. On the other hand, if the Tg is higher than 30°C, the ink composition may produce a coating film with reduced adhesion to films, resulting in reduced coating resistance. In this embodiment, when the resin is an acrylic copolymer resin, the glass transition temperature of the resin is the theoretical glass transition temperature calculated using Wood's equation below. Wood's formula: 1 / Tg = W1 / Tg1 + W2 / Tg2 + W3 / Tg3 + + Wx / Tgx [In the formula, Tg1 to Tgx represent the glass transition temperatures of the respective homopolymers of monomers 1, 2, 3, x constituting the resin, W1 to Wx represent the polymerization fractions of the respective monomers 1, 2, 3, x, and Tg represents the theoretical glass transition temperature. However, the glass transition temperature in Wood's formula is expressed in absolute temperature.]

[0021] The acid value of the acrylic resin emulsion emulsified with a polymer is preferably 10 mgKOH / g or more, more preferably 40 mgKOH / g or more. The acid value is preferably 100 mgKOH / g or less, more preferably 80 mgKOH / g or less. Having an acid value within the above range prevents the ink composition from becoming too soluble in water, which has the advantage of improving the abrasion resistance and alcohol resistance of the coating film. In this embodiment, the acid value of the acrylic resin emulsion is a theoretical acid value calculated arithmetically from the number of milligrams of potassium hydroxide theoretically required to neutralize 1 g of the acrylic resin emulsion based on the composition of the monomers used to synthesize the acrylic resin emulsion.

[0022] The content of the acrylic resin emulsion emulsified with a polymer in the ink composition, calculated as solid content, may be 3% by mass or more, and preferably 10% by mass or more. The content of the acrylic resin emulsion emulsified with a polymer in the ink composition, calculated as solid content, may be 40% by mass or less, and preferably 25% by mass or less. If the content of the acrylic resin emulsion emulsified with a polymer is less than 3% by mass, the ink composition will have poor alcohol resistance. On the other hand, if the content of the acrylic resin emulsion emulsified with a polymer exceeds 40% by mass, the ink composition will have a problem of reduced storage stability.

[0023] (N-oleoyl sarcosine) N-oleoyl sarcosine is blended to impart heat resistance to the ink composition. Thus, the ink composition of this embodiment is characterized in that N-oleoyl sarcosine, which has conventionally been used as a rust inhibitor, can impart additional heat resistance without deteriorating various properties when used as a water-based white ink composition for surface-printing flexible packaging.

[0024] The content of N-oleoyl sarcosine is not particularly limited. For example, the content of N-oleoyl sarcosine in the ink composition is preferably 0.05% by mass or more, and more preferably 0.1% by mass or more. Furthermore, the content of N-oleoyl sarcosine in the ink composition is preferably 6% by mass or less, and more preferably 2% by mass or less. When the content of N-oleoyl sarcosine is within the above range, the ink composition has excellent heat resistance. Furthermore, the ink composition has excellent storage stability.

[0025] (hydrazine-based compounds with at least two hydrazine residues in the molecule) The hydrazine-based compound having at least two hydrazine residues in the molecule is blended to impart alcohol resistance to the ink composition.

[0026] The hydrazine compound has two or more hydrazine residues and is preferably a water-soluble polyhydrazine or hydrazide compound. The hydrazine compound is preferably hydrazine or an alkylene dihydrazine represented by the following general formula (1), or a dihydrazide compound of a saturated aliphatic dibasic acid or an unsaturated dibasic acid. H2N-NH-X-NH-NH2(1) (wherein X represents an alkylene group having 1 to 8 carbon atoms or a residue of a saturated or unsaturated dibasic acid having 1 to 10 carbon atoms).

[0027] Alkylene dihydrazines include methylene dihydrazine, ethylene dihydrazine, propylene dihydrazine, butylene dihydrazine, etc. Dihydrazide compounds of saturated aliphatic dibasic acids include oxalic dihydrazide, malonic dihydrazide, succinic dihydrazide, glutaric dihydrazide, adipic dihydrazide, sebacic dihydrazide, etc. Dihydrazide compounds of unsaturated dibasic acids include phthalic dihydrazide, fumaric dihydrazide, itaconic dihydrazide, etc.

[0028] The content of the hydrazine-based compound having at least two hydrazine residues in the molecule is not particularly limited. For example, the content of the hydrazine-based compound having at least two hydrazine residues in the molecule is preferably 0.05% by mass or more, and more preferably 0.1% by mass or more, in the ink composition. Furthermore, the content of the hydrazine-based compound having at least two hydrazine residues in the molecule is preferably 6% by mass or less, and more preferably 3% by mass or less, in the ink composition. By ensuring that the content of the hydrazine-based compound having at least two hydrazine residues in the molecule is within the above range, the ink composition has excellent alcohol resistance. Furthermore, the ink composition has excellent storage stability.

[0029] (wax) Waxes are blended to improve abrasion resistance. The wax is not particularly limited. Examples of waxes include animal and plant waxes such as beeswax, lanolin wax, spermaceti, candelilla wax, carnauba wax, rice wax, Japan wax, and jojoba oil; mineral waxes such as montan wax, ozokerite, ceresin, paraffin wax, microcrystalline wax, and petrolatum; petroleum waxes; synthetic hydrocarbon waxes such as Fischer-Tropsch wax, polyethylene wax, oxidized polyethylene wax, and oxidized polypropylene wax; fluororesin waxes such as polytetrafluoroethylene wax; mixtures of polytetrafluoroethylene wax and polyethylene wax; modified waxes such as montan wax derivatives, paraffin wax derivatives, and microcrystalline wax derivatives; hydrogenated waxes such as hydrogenated castor oil and hydrogenated castor oil derivatives; and polytetrafluoroethylene wax. Among these, preferred waxes are polyethylene wax, mixtures of polytetrafluoroethylene wax and polyethylene wax, fluororesin waxes, and Fischer-Tropsch wax.

[0030] The average particle size of the wax is not particularly limited. For example, the average particle size of the wax is preferably 0.05 μm or more, and more preferably 0.1 μm or more. The average particle size of the wax is preferably 6 μm or less, and more preferably 5 μm or less. By blending wax with a relatively large particle size in this manner, the ink composition of this embodiment can have improved blocking resistance. In this embodiment, the average particle size of the wax can be measured using a Nanotrac (UPA-EX150, manufactured by Nikkiso Co., Ltd.).

[0031] The wax content is not particularly limited. For example, the wax content in the ink composition, calculated as solid content, is preferably 0.05% by mass or more, and more preferably 0.1% by mass or more. Furthermore, the wax content in the ink composition, calculated as solid content, is preferably 12% by mass or less, and more preferably 4% by mass or less. When the wax content is within the above range, the ink composition has excellent blocking resistance.

[0032] (chlorinated polyolefin) The ink composition of this embodiment may contain a chlorinated polyolefin. The chlorinated polyolefin is preferably used in the form of a chlorinated polyolefin emulsion. The chlorinated polyolefin emulsion is obtained by chlorinating a polyolefin resin and emulsifying it.

[0033] The chlorinated polyolefin is not particularly limited. Examples of the chlorinated polyolefin include chlorinated polypropylene resin and chlorinated polyethylene resin. The chlorinated polyolefin may also be a modified product. The modified product is not particularly limited. Examples of the modified chlorinated polyolefin include a chlorinated polyolefin graft-polymerized with a polymerizable acrylic compound (acrylic acid, methacrylic acid, or an alkyl ester thereof, etc.) or an unsaturated polycarboxylic acid (maleic acid, maleic anhydride, itaconic acid, itaconic anhydride, etc.), or a chlorinated polyolefin graft-polymerized with the above-mentioned unsaturated polycarboxylic acid.

[0034] The chlorine content of the chlorinated polyolefin is not particularly limited. For example, the chlorine content is preferably 1% by mass or more, and more preferably 10% by mass or more, based on the total mass of the resin. Furthermore, the chlorine content is preferably 40% by mass or less, and more preferably 30% by mass or less, based on the total mass of the resin. When the chlorine content is within the above range, the chlorinated polyolefin is easily soluble in a solvent and exhibits excellent adhesion between the substrate and the ink composition.

[0035] When a chlorinated polyolefin is contained, the content of the chlorinated polyolefin is not particularly limited. For example, the content of the chlorinated polyolefin in the ink composition, calculated as solid content, is preferably 0.5% by mass or more, and more preferably 1% by mass or more. Furthermore, the content of the chlorinated polyolefin in the ink composition, calculated as solid content, is preferably 5% by mass or less, and more preferably 2% by mass or less. When the content of the chlorinated polyolefin is within the above range, the ink composition has excellent adhesion to polyolefin films such as OPP.

[0036] (Water-soluble organic solvent) The ink composition of this embodiment preferably further contains a water-soluble organic solvent. By including a water-soluble organic solvent, the ink composition has even better solid uniformity.

[0037] The water-soluble organic solvent is not particularly limited. For example, the water-soluble organic solvent is preferably an alcohol or polyhydric alcohol solvent, and examples thereof include methanol, ethanol, propanol, butanol, hexanol, 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, and triethylene glycol monopropyl ether. More preferred are propylene glycol ether, triethylene glycol monobutyl ether, propylene glycol, propylene glycol monoethyl ether, propylene glycol monopropyl ether, propylene glycol monobutyl ether, dipropylene glycol, dipropylene 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, dibutyl glycol, glycerin, and the like.

[0038] When a water-soluble organic solvent is contained, the content of the water-soluble organic solvent is not particularly limited. For example, the content of the water-soluble organic solvent in the ink composition is preferably 0.1% by mass or more, and more preferably 0.5% by mass or more. Furthermore, the content of the water-soluble organic solvent in the ink composition is preferably 20% by mass or less, and more preferably 10% by mass or less. By having the content of the water-soluble organic solvent within the above range, the ink composition has even better solid uniformity.

[0039] (optional ingredient) The ink composition of this embodiment may contain various additives such as a tackifier, a crosslinking agent, a lubricant, an anti-blocking agent, an antistatic agent, a surfactant, a chelating agent, and a hard resin, as appropriate.

[0040] (Method of producing ink composition) The method for producing the ink composition of this embodiment is not particularly limited. As an example, the ink composition can be prepared by stirring and mixing a white pigment, an acrylic resin emulsion emulsified with a polymer, N-oleoyl sarcosine, a hydrazine compound having at least two hydrazine residues in the molecule, wax, and various optional components, and then grinding the mixture using various grinding machines, such as a bead mill, a ball mill, a sand mill, an attritor, a roll mill, or a pearl mill.

[0041] The resulting ink composition preferably has a viscosity of 10 to 1000 mPa·s. When used in gravure printing, the ink composition is preferably diluted with water or an organic solvent to achieve an appropriate viscosity depending on the printing conditions at the ambient temperature during printing, specifically, until the Zahn cup No. 3 outflow time is 12 to 23 seconds / 25°C, or approximately 14 to 16 seconds / 25°C in high-speed printing.

[0042] The obtained ink composition can be printed on an adherend such as a plastic film for various flexible packaging, for example, by gravure printing or the like, as an aqueous white ink composition for surface printing of flexible packaging. Examples of plastic films include oriented and unoriented polyolefins such as polyethylene and polypropylene, polyester, nylon, cellophane, vinylon, etc., which can be printed integrally with the packaging material. The obtained printed matter can be made into bags and used as packaging containers for food, etc.

[0043] As described above, according to this embodiment, the ink composition has excellent heat resistance, blocking resistance, alcohol resistance, abrasion resistance, solid uniformity, and bleeding resistance. [Example]

[0044] The present invention will be described in more detail below with reference to examples. The present invention is not limited to these examples. Unless otherwise specified, "%" means "% by mass" and "parts" means "parts by mass."

[0045] The raw materials and preparation methods used are shown below. <Water-based resin varnish> 20 parts by mass of an acrylic acid / n-butyl acrylate / benzyl methacrylate / styrene copolymer having a glass transition temperature of 40°C, a weight average molecular weight of 30,000, and an acid value of 185 mgKOH / g was dissolved in a mixed solution of 2.5 parts by mass of potassium hydroxide and 77.5 parts by mass of water to obtain an aqueous resin varnish with a solids content of 20%. <Preparation of Water-Based White Ink Base> 30.0 parts by mass of the aqueous resin varnish was mixed with 10.0 parts by mass of water to prepare a resin varnish for pigment dispersion. 60 parts by mass of titanium oxide (R-960, manufactured by DuPont) was further added to this varnish, stirred and mixed, and then milled in a wet circulation mill to prepare an aqueous white ink base. <Resin emulsion> (acrylic resin emulsion emulsified with polymer) PE-1126 (solid content 41.5%, polymeric acrylic resin emulsion, manufactured by Seiko PMC Corporation, Tg: -12°C) JE-1113 (solid content 42.5%, polymeric acrylic resin emulsion, manufactured by Seiko PMC Corporation, Tg: -24°C) HE-1335 (solid content 45.5%, polymeric acrylic-styrene resin emulsion, manufactured by Seiko PMC Corporation, Tg: 15°C) QE-1042 (solid content 40.5%, polymeric acrylic-styrene resin emulsion, manufactured by Seiko PMC Corporation, Tg: 53°C) (acrylic resin emulsion emulsified with an emulsifier) Movinyl 7320 (solid content 40.0%, emulsifier-emulsified acrylic resin emulsion, manufactured by Japan Coating Resin Co., Ltd., Tg: -20°C) Movinyl 730L (solid content 46.0%, emulsifier-emulsified acrylic resin emulsion, manufactured by Japan Coating Resin Co., Ltd., Tg: -13°C) Neo-Cryl A-1125 (solid content 19.5%, emulsifier-emulsified acrylic resin emulsion, manufactured by DSM Neoresins, Tg: 13°C) Neo-Cryl A-1093 (solid content 45.5%, emulsifier-emulsified acrylic-styrene resin emulsion, manufactured by DSM Neoresins, Tg: 17°C) <Wax emulsion> AQUACER 531 (45% solids, polyethylene resin emulsion, average particle size 160 nm, manufactured by BYK) Chemipearl W-400 (40% solids, polyethylene resin emulsion, average particle size 4.0 μm, manufactured by Mitsui Chemicals, Inc.)

[0046] <Examples 1 to 17 and Comparative Examples 1 to 10> (Preparation of Ink Composition) Ink compositions were prepared by kneading the materials in a paint conditioner according to the mass ratios (mass %) shown in Tables 1 and 2 below. The storage stability of the resulting ink compositions was evaluated. Furthermore, gravure printing was performed on the resulting ink compositions under the following conditions to obtain printed matter. The resulting printed matter was evaluated for solid uniformity, fine lines (bleed resistance), winding blocking resistance (blocking resistance), abrasion resistance, alcohol resistance, and heat resistance according to the following evaluation methods. The results are shown in Tables 1 and 2.

[0047] <Conditions for creating printed materials> The ink composition was printed on the treated surface of the substrate using a gravure printing machine under the following printing conditions, followed by drying to obtain a printed matter. (Printing conditions) Substrate: Corona discharge treated biaxially oriented polypropylene film, P-2111, manufactured by Toyobo Co., Ltd., thickness 20 μm Printing equipment: Gravure printing machine Printing plate: Helio 175 line solid plate Printing speed: 15m / min Drying conditions: 80℃

[0048] <Storage stability> The ink compositions of the above examples and comparative examples were each placed in a glass bottle, and their viscosities at 25°C were measured using a viscometer (RE100L model, manufactured by Toki Sangyo Co., Ltd.). The bottles were then sealed and stored at 60°C for one month, and the viscosity (25°C) after storage was measured using the viscometer. The stability over time was evaluated as the rate of viscosity change (100 x (viscosity after one month at 60°C - viscosity before storage) / viscosity before storage). (Evaluation criteria) ○: The viscosity change rate was less than 5%. △: The viscosity change rate was 5% or more and less than 10%. ×: The viscosity change rate was 10% or more and less than 30%. <Solid uniformity> The solid uniformity of the resulting print was visually observed and evaluated according to the following evaluation criteria. (Evaluation criteria) ○: The printed matter was free of unevenness and streaks. △: Slight unevenness and streaks were observed on the printed matter. ×: The print was visually inspected to have unevenness and streaks. <thin line> A thin line of about 0.5 mm was printed using the aqueous white ink compositions for surface printing of flexible packaging of the Examples and Comparative Examples, and the thickening due to bleeding was visually observed and evaluated according to the following criteria. (Evaluation criteria) ○: There was no bleeding and printing was possible with the original thickness. △: Some weight gain was observed, but no weight gain of more than two times was observed. ×: Overall weight gain of more than two times was observed. <Winding blocking property> Immediately after printing on the gravure printing machine, whether the printed matter could be pulled out from the roll without resistance or peeling noise was evaluated for winding blocking property by the following method. (Evaluation criteria) ◯: There was absolutely no resistance when the film was peeled off, and the ink did not peel off from the printed surface. △: There was resistance when peeling off the film, but the ink did not peel off from the printed surface. ×: There was resistance when peeling off the film, and the ink peeled off from the printed surface. <Abrasion resistance> The resulting print was cut into a 2.5 cm x 25 cm test piece, and a Gakushin friction tester (manufactured by Daiei Scientific Instruments Manufacturing Co., Ltd.) was used to place a bleached cloth against the printed surface and rub it back and forth 100 times with a load of 500 g. The degree of ink removal was used to evaluate the abrasion resistance according to the following evaluation criteria. (Evaluation criteria) ◯: The white ink coating film did not peel off at all. △: The white ink coating film peeled off a little. ×: The white ink coating film was almost completely peeled off. <Alcohol resistance> The resulting print was cut into a 2.5cm x 25cm test piece, and using a Gakushin friction tester (manufactured by Daiei Scientific Instruments Manufacturing Co., Ltd.), a bleached cloth soaked in five drops of 70% ethanol water solution with a syringe needle was placed against the printed surface, and the cloth was rubbed back and forth 10 times with a load of 200g.The alcohol resistance was evaluated based on the degree to which the ink came off, according to the following evaluation criteria. (Evaluation criteria) ◯: The white ink coating film did not peel off at all. △: The white ink coating film peeled off a little. ×: The white ink coating film was almost completely peeled off. <Heat resistance> Using a heat seal tester equipped with a hot plate with a thermal gradient of 160 to 200°C, the printed surface and aluminum foil were pressed together with a force of 2.0 kg / cm 2 The pressure was applied for 1 second at a pressure of 1000 kJ / cm. The heat resistance was evaluated according to the following criteria, based on the lowest temperature at which the ink on the printed surface was transferred to the aluminum foil. (Evaluation criteria) ○: The minimum temperature at which the ink on the printed surface was transferred to the aluminum foil was 200°C or higher. △: The minimum temperature at which the ink on the printed surface was transferred to the aluminum foil was 160°C or higher and less than 200°C. ×: The minimum temperature at which the ink on the printed surface was transferred to the aluminum foil was less than 160°C.

[0049]

Table 1

[0050]

Table 2

Claims

1. The composition comprises a white pigment, an acrylic resin emulsion emulsified with a polymer, N-oleoyl sarcosine, a hydrazine compound having at least two hydrazine residues in the molecule, and a wax; The hydrazine-based compound having at least two hydrazine residues in the molecule includes hydrazine and alkylene dihydrazine represented by the following general formula (1), or a dihydrazide compound of a saturated aliphatic dibasic acid, or a dihydrazide compound of an unsaturated dibasic acid, H 2 N-NH-X-NH-NH 2 (1) (wherein X represents an alkylene group having 1 to 8 carbon atoms or a residue of a saturated or unsaturated dibasic acid having 1 to 10 carbon atoms). The content of the acrylic resin emulsion is 3 to 40 mass% in terms of solid content, The water-based white ink composition for surface printing on flexible packaging, wherein the acrylic resin emulsion has a glass transition temperature of -40 to 30°C.

2. 2. The water-based white ink composition for surface printing on flexible packaging according to claim 1, wherein the wax has an average particle size of 0.1 to 6 μm.

3. The water-based white ink composition for surface printing on flexible packaging according to claim 1 or 2, further comprising a water-soluble organic solvent.

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