Water-based white ink composition for table-top flexible packaging

Abstract

Provided is a water-based white ink composition for surface-printed flexible packaging, which is excellent in heat resistance, blocking resistance, alcohol resistance, scratch resistance, solid printing uniformity, and bleeding resistance. A water-based white ink composition for surface-printed flexible packaging, comprising a white pigment, an acrylic resin emulsion emulsified by a polymer, N-oleoyl sarcosine, a hydrazine-based compound having at least two or more hydrazine residues in the molecule, and a wax, the content of the acrylic resin emulsion being 3 to 40 mass% in terms of solid content, and the glass transition temperature of the acrylic resin emulsion being -40 to 30°C.

Description

Technical Field

[0001] This invention relates to a water-based white ink composition for surface printing on flexible packaging. More specifically, this invention relates to a water-based white ink composition for surface printing on flexible packaging that exhibits excellent heat resistance, anti-blocking properties, alcohol resistance, scratch resistance, uniform printing coverage, and bleed-proofing. Background Technology

[0002] Previously, flexible packaging materials have been used for food, snacks, household goods, pet food, etc., based on considerations such as design, economy, content protection, and transportability. Various plastic films have been used in these flexible packaging materials. Furthermore, gravure or flexographic printing has been applied to many flexible packaging materials. Surface printing has been performed on the surface of the substrate film of the flexible packaging material. White ink is printed on the film surface to allow for vivid designs. Therefore, a white ink composition for surface printing of flexible packaging materials has been developed (e.g., Patent Document 1). The ink composition described in Patent Document 1 contains anionic surfactants to improve heat resistance.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 2020-59822 Summary of the Invention

[0006] The ink composition described in Patent Document 1 has potential for improvement in heat resistance. Furthermore, the ink composition described in Patent Document 1 also has potential for improvement in anti-blocking properties, alcohol resistance, and overall printing uniformity.

[0007] The present invention was made in view of such existing problems, and its object is to provide a water-based white ink composition for surface printing flexible packaging with excellent heat resistance, anti-blocking, alcohol resistance, scratch resistance, uniform printing on the entire surface and impermeability.

[0008] In order to solve the above-mentioned problems, the inventors conducted in-depth research and found that by combining N-oleoylsarcosine, which has been used as a rust inhibitor in the past, the heat resistance of the ink composition was significantly improved. Furthermore, the inventors discovered that by combining a specific amount of a polymerically emulsified acrylic resin emulsion exhibiting a specific glass transition temperature, a hydrazine compound with a specific structure, and a wax, the above-mentioned problems could be solved simultaneously, thus completing the present invention.

[0009] To address the aforementioned issues, one aspect of the present invention provides an aqueous white ink composition for flexible packaging printing, comprising: a white pigment, an acrylic resin emulsion emulsified by a polymer, N-oleoylsarcosine, a hydrazine compound having at least two hydrazine residues within its molecule, and a wax; wherein the acrylic resin emulsion comprises 3-40% by mass (based on solids content), and the acrylic resin emulsion has a glass transition temperature of -40 to 30°C. Detailed Implementation

[0010] <Water-based white ink composition for surface printing on flexible packaging>

[0011] An embodiment of the present invention provides a water-based white ink composition (hereinafter also referred to as ink composition) for surface printing on flexible packaging, comprising a white pigment, an acrylic resin emulsion emulsified by a polymer, N-oleoylsarcosine, a hydrazine compound having at least two hydrazine residues in its molecule, and a wax. The content of the acrylic resin emulsion is 3 to 40% by mass, calculated based on solids. The glass transition temperature of the acrylic resin emulsion is -40 to 30°C. These will be described separately below.

[0012] (White pigment)

[0013] There is no particular limitation on white pigments. For example, white pigments can be various inorganic white pigments, organic white pigments, etc. Inorganic white pigments include titanium dioxide, zinc oxide, cerium oxide, silicon dioxide, aluminum oxide, magnesium oxide, zirconium dioxide, yttrium-stabilized zirconium oxide, indium oxide, antimony oxide, tin oxide, barium titanate, barium sulfate, calcium carbonate, micronized silicate, calcium silicate, talc, and clay, etc. Organic white pigments include organic compound salts shown in Japanese Patent Application Publication No. 11-129613, alkylene dimelamine derivatives shown in Japanese Patent Application Publication No. 11-140365, and Japanese Patent Application Publication No. 2001-234093, etc. Among these, from the perspective of excellent concealment, various types of titanium dioxide such as rutile and anatase are preferred as white pigments, and titanium dioxide whose surface has been coated with aluminum oxide, silicon dioxide, organic matter, etc., is more preferred.

[0014] 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, more preferably 150 nm or more. Furthermore, the average particle size of the white pigment is preferably 500 nm or less, more preferably 400 nm or less. With the average particle size of the white pigment within the above range, the ink composition exhibits excellent concealment. It should be noted that in this embodiment, the average particle size is the volume average particle size measured by laser diffraction particle size analysis using a Nanotrac (UPA-EX150, manufactured by Nikkiso Co., Ltd.).

[0015] The content of white pigment is not particularly limited. As an example, the content of white pigment in the ink composition is preferably 5% by mass or more, more preferably 10% by mass or more. Furthermore, the content of white pigment in the ink composition is preferably 20% by mass or less, more preferably 15% by mass or less. With the white pigment content within the above range, the ink composition exhibits excellent concealment. Additionally, after the ink composition is coated onto flexible packaging material, designs and other patterns are easily visible when printed on it.

[0016] (An acrylic resin emulsion emulsified with polymers)

[0017] The acrylic resin emulsion of this embodiment is an acrylic resin emulsion emulsified by a polymeric compound. Furthermore, the glass transition temperature of the acrylic resin emulsion is -40 to 30°C. The polymeric acrylic resin emulsion can employ a core-shell structure consisting of a polymer shell acting as a polymeric emulsifier and a core, wherein the core is composed of a resin with stronger hydrophobicity than the shell. It should be noted that the polymeric acrylic resin emulsion of this embodiment is, for example, different from acrylic resin emulsions emulsified by surfactants or other emulsifiers acting as low-molecular-weight compounds.

[0018] There is no particular limitation on the acrylic resin emulsion ...

[0019] The glass transition temperature (Tg) of the polymer-emulsified acrylic resin emulsion only needs to be -40°C or higher, preferably -20°C or higher. Furthermore, the glass transition temperature (Tg) of the polymer-emulsified acrylic resin emulsion only needs to be 30°C or lower, preferably 20°C or lower. When the Tg is less than -40°C, the ink composition suffers from reduced anti-blocking properties of the coating film. On the other hand, when the Tg exceeds 30°C, the ink composition suffers from decreased adhesion to the film and reduced coating film durability. It should be noted that when the resin is an acrylic copolymer resin, the glass transition temperature of the resin in this embodiment is the theoretical glass transition temperature calculated using the following Wood formula.

[0020] Wood formula: 1 / Tg=W1 / Tg1+W2 / Tg2+W3 / Tg3+·····+Wx / Tgx

[0021] [In the formula, Tg1~Tgx represent the glass transition temperatures of the homopolymers of monomers 1, 2, 3...x constituting the resin, W1~Wx represent the polymerization fractions of monomers 1, 2, 3...x, and Tg represents the theoretical glass transition temperature. The glass transition temperature in Wood's formula is an absolute temperature.]

[0022] The acid value of the acrylic resin emulsion emulsified by the polymer is preferably 10 mg KOH / g or more, more preferably 40 mg KOH / g or more. Furthermore, the acid value is preferably 100 mg KOH / g or less, more preferably 80 mg KOH / g or less. With an acid value within the above range, the ink composition has the advantage of not becoming excessively soluble relative to water, and improved scratch resistance and alcohol resistance of the coating film. It should be noted that, in this embodiment, the acid value of the acrylic resin emulsion is a theoretical acid value obtained by arithmetically calculating the number of mg 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.

[0023] The content of the polymer-emulsified acrylic resin emulsion in the ink composition, calculated as solids, only needs to be 3% by mass or more, preferably 10% by mass or more. Furthermore, the content of the polymer-emulsified acrylic resin emulsion in the ink composition, calculated as solids, only needs to be 40% by mass or less, preferably 25% by mass or less. When the content of the polymer-emulsified acrylic resin emulsion is less than 3% by mass, the ink composition exhibits poor alcohol resistance. On the other hand, when the content of the polymer-emulsified acrylic resin emulsion exceeds 40% by mass, the ink composition suffers from reduced storage stability.

[0024] (N-Oleoylsarcosine)

[0025] N-Oleylsarcosine is formulated to impart heat resistance to the ink composition. Thus, the ink composition of this embodiment has the following characteristics: N-Oleylsarcosine, which has been used as a rust inhibitor in the past, can further impart heat resistance without reducing various properties when used in water-based white ink compositions for surface printing on flexible packaging.

[0026] The content of N-oleoylsarcosine is not particularly limited. As an example, the content of N-oleoylsarcosine in the ink composition is preferably 0.05% by mass or more, more preferably 0.1% by mass or more. Furthermore, the content of N-oleoylsarcosine in the ink composition is preferably 6% by mass or less, more preferably 2% by mass or less. With the content of N-oleoylsarcosine within the above range, the ink composition exhibits excellent heat resistance. In addition, the ink composition demonstrates excellent storage stability.

[0027] (Hydrazine compounds having at least two hydrazine residues within the molecule)

[0028] Hydrazine compounds having at least two hydrazine residues within the molecule are formulated to impart alcohol resistance to ink compositions.

[0029] The hydrazine compound has two or more hydrazine residues, and is preferably a water-soluble polyhydrazine or acylhydrazine compound. In addition, the hydrazine compound is preferably a hydrazine and an alkylene dihydrazine represented by the following general formula (1), or a diacylhydrazine compound of a saturated aliphatic diacid or an unsaturated diacid.

[0030] H2N-NH-X-NH-NH2 (1)

[0031] (In the formula, X represents an alkylene group having 1 to 8 carbon atoms, or a residue of a saturated or unsaturated dicarboxylic acid having 1 to 10 carbon atoms).

[0032] Alkyl dihydrazides include methylene dihydrazide, ethyl dihydrazide, propyl dihydrazide, and butyl dihydrazide. Diacyl hydrazides of saturated aliphatic dicarboxylic acids include oxalate dihydrazide, malonate dihydrazide, succinate dihydrazide, glutarate dihydrazide, adipic acid dihydrazide, and sebacic acid dihydrazide. Diacyl hydrazides of unsaturated dicarboxylic acids include phthalate dihydrazide, fumarate dihydrazide, and itaconic acid dihydrazide.

[0033] The content of hydrazine compounds having at least two hydrazine residues within the molecule is not particularly limited. As an example, the content of hydrazine compounds having at least two hydrazine residues within the molecule in the ink composition is preferably 0.05% by mass or more, more preferably 0.1% by mass or more. Furthermore, the content of hydrazine compounds having at least two hydrazine residues within the molecule in the ink composition is preferably 6% by mass or less, more preferably 3% by mass or less. By having the content of hydrazine compounds having at least two hydrazine residues within the molecule within the above range, the ink composition exhibits excellent alcohol resistance. In addition, the ink composition demonstrates excellent storage stability.

[0034] (wax)

[0035] Waxes are formulated to improve scratch resistance. There are no specific limitations on the type of wax. For example, waxes include beeswax, lanolin wax, whale wax, candelilla wax, carnauba wax, rice wax, wood wax, jojoba oil, and other plant and animal waxes; lignite wax, ceresin wax, pure ceresin wax, paraffin wax, microcrystalline wax, petrolatum, and other mineral and petroleum-based waxes; Fischer-Tropsch wax, polyethylene wax, oxidized polyethylene wax, oxidized polypropylene wax, and other synthetic hydrocarbon waxes; polytetrafluoroethylene wax and other fluoropolymer waxes; mixtures of polytetrafluoroethylene wax and polyethylene wax; modified waxes such as lignite wax derivatives, paraffin wax derivatives, and microcrystalline wax derivatives; hydrogenated castor oil, hydrogenated castor oil derivatives, and other hydrogenated waxes; and polytetrafluoroethylene wax, etc. Among these, polyethylene wax, mixtures of polytetrafluoroethylene wax and polyethylene wax, fluoropolymer waxes, and Fischer-Tropsch wax are preferred.

[0036] 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, more preferably 0.1 μm or more. Furthermore, the average particle size of the wax is preferably 6 μm or less, more preferably 5 μm or less. The ink composition of this embodiment improves anti-blocking properties by incorporating wax with a relatively large particle size. It should be noted that in this embodiment, the average particle size of the wax can be measured using a Nanotrac (UPA-EX150, manufactured by Nikkiso Co., Ltd.).

[0037] The wax content is not particularly limited. As an example, the wax content in the ink composition, calculated as solids, is preferably 0.05% by mass or more, more preferably 0.1% by mass or more. Furthermore, the wax content in the ink composition, calculated as solids, is preferably 12% by mass or less, more preferably 4% by mass or less. With the wax content within the above range, the ink composition exhibits excellent anti-blocking properties.

[0038] (Chlorinated polyolefins)

[0039] The ink composition of this embodiment may also contain chlorinated polyolefins. Chlorinated polyolefins are preferably used in the form of chlorinated polyolefin emulsions. Chlorinated polyolefin emulsions are obtained by chlorinating and emulsifying a polyolefin resin.

[0040] Chlorinated polyolefins are not particularly limited. Examples of chlorinated polyolefins include chlorinated polypropylene resin and chlorinated polyethylene resin. Furthermore, chlorinated polyolefins can also be modified. Modifiers are not particularly limited. Examples of modified chlorinated polyolefins include substances obtained by graft polymerization of polymeric acrylic compounds (acrylic acid, methacrylic acid, or their alkyl esters, etc.) or unsaturated polycarboxylic acids (maleic acid, maleic anhydride, itaconic acid, itaconic anhydride, etc.) with chlorinated polyolefins, or substances obtained by chlorinating polyolefins obtained by graft polymerization of the aforementioned unsaturated polycarboxylic acids.

[0041] The chlorine content in the chlorinated polyolefin is not particularly limited. As an example, the chlorine content is preferably 1% by mass or more relative to the total resin content, more preferably 10% by mass or more. Furthermore, the chlorine content is preferably 40% by mass or less relative to the total resin content, more preferably 30% by mass or less. With the chlorine content within the above range, the chlorinated polyolefin is easily soluble in solvents, and the adhesion between the substrate and the ink composition is excellent.

[0042] When chlorinated polyolefins are included, the content of the chlorinated polyolefins is not particularly limited. As an example, the content of chlorinated polyolefins in the ink composition, calculated as solids, is preferably 0.5% by mass or more, more preferably 1% by mass or more. Furthermore, the content of chlorinated polyolefins in the ink composition, calculated as solids, is preferably 5% by mass or less, more preferably 2% by mass or less. With the chlorinated polyolefin content within the above range, the ink composition exhibits excellent adhesion to polyolefin films such as OPP.

[0043] (Water-soluble organic solvent)

[0044] The ink composition of this embodiment preferably further comprises a water-soluble organic solvent. By comprising a water-soluble organic solvent, the overall printing uniformity of the ink composition is further improved.

[0045] There are no particular limitations on the water-soluble organic solvent. However, to give an example, the preferred water-soluble organic solvent is an alcohol or polyol solvent, more preferably 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, triethylene glycol monoethyl ether, triethylene glycol monobutyl ether, triethylene glycol monomethyl ether, triethylene glycol monoethyl ... Diethylene 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, 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, ethylene glycol dibutyl ether, glycerin, etc.

[0046] When a water-soluble organic solvent is included, the content of the water-soluble organic solvent is not particularly limited. As an example, the content of the water-soluble organic solvent in the ink composition is preferably 0.1% by mass or more, 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, more preferably 10% by mass or less. With the content of the water-soluble organic solvent within the above range, the overall printing uniformity of the ink composition is further improved.

[0047] (Any ingredients)

[0048] The ink composition of this embodiment may also be appropriately combined with various additives such as tackifiers, crosslinking agents, lubricants, antiblocking agents, antistatic agents, surfactants, chelating agents, and hard resins.

[0049] (Method for manufacturing ink composition)

[0050] The method for manufacturing the ink composition of this embodiment is not particularly limited. As an example, the ink composition can be prepared by mixing white pigment, acrylic resin emulsion emulsified by polymer, N-oleoylsarcosine, hydrazine compound having at least two hydrazine residues in the molecule, wax, and various other arbitrary components, and then mixing them using various mixing machines, such as bead mills, ball mills, sand mills, grinding mills, roller mills, pearl mills, etc.

[0051] The resulting ink composition preferably has a viscosity of 10 to 1000 mPa·s. Furthermore, when used in gravure printing, the ink composition is preferably diluted with water or an organic solvent to a flow rate of approximately 12 to 23 seconds / 25°C for Zein Cup 3 and approximately 14 to 16 seconds / 25°C for high-speed printing, so that the viscosity is appropriate according to the printing conditions and ambient temperature.

[0052] The resulting ink composition can be printed onto various flexible packaging materials, such as plastic films, using a water-based white ink composition for surface printing, for example, by gravure printing. Examples of plastic films suitable for integrated printing with packaging materials include stretched and unstretched polyolefins such as polyethylene and polypropylene, polyester, nylon, celluloid, and vinylon. The resulting printed material can be used to make bags for use as packaging containers for food and other products.

[0053] According to this embodiment, the ink composition exhibits excellent heat resistance, anti-blocking properties, alcohol resistance, scratch resistance, uniformity of printing across the entire surface, and resistance to bleed-through.

[0054] The above description describes one embodiment of the present invention. The present invention is not particularly limited to the above embodiment. It should be noted that the above embodiment mainly describes an invention having the following configuration.

[0055] (1) A water-based white ink composition for surface printing flexible packaging, comprising a white pigment, an acrylic resin emulsion emulsified by a polymer, N-oleoylsarcosine, 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% by mass in terms of solid content, and the glass transition temperature of the acrylic resin emulsion is -40 to 30°C.

[0056] Based on this composition, the water-based white ink composition for surface printing on flexible packaging exhibits excellent heat resistance, anti-blocking properties, alcohol resistance, scratch resistance, uniformity of printing across the entire surface, and resistance to bleed-through.

[0057] (2) The water-based white ink composition for printing flexible packaging according to (1), wherein the average particle size of the wax is 0.1 to 6 μm.

[0058] Based on this composition, the anti-blocking properties of the water-based white ink composition for surface printing flexible packaging are further improved.

[0059] (3) The water-based white ink composition for surface printing flexible packaging according to (1) or (2), wherein it further comprises a water-soluble organic solvent.

[0060] Based on this composition, the uniformity of the water-based white ink composition for surface printing on flexible packaging is further improved.

[0061] Example

[0062] The present invention will now be described in more detail with reference to the embodiments. The present invention is not limited to these embodiments in any way. It should be noted that, unless otherwise specified, "%" refers to "percentage by mass" and "parts" refers to "parts by mass".

[0063] The raw materials and preparation methods used are shown below.

[0064] <Water-based resin varnish>

[0065] 20 parts by mass of an acrylic acid / n-butyl acrylate / benzyl methacrylate / styrene copolymer with a glass transition temperature of 40℃, a weight-average molecular weight of 30000, and an acid value of 185 mgKOH / g were 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 solid content of 20%.

[0066] <Preparation of Water-Based White Ink Base>

[0067] Add 10.0 parts by weight of water to 30.0 parts by weight of the above-mentioned waterborne resin varnish and mix to prepare a pigment dispersion resin varnish. Further add 60 parts by weight of titanium dioxide (R-960, manufactured by DuPont) to the varnish, stir and mix, and then knead using a wet circulating mill to prepare a waterborne white ink base.

[0068] <Resin Emulsion>

[0069] (An acrylic resin emulsion emulsified with polymers)

[0070] PE-1126 (41.5% solids, high molecular weight emulsified acrylic resin emulsion, manufactured by Starlight PMC Co., Ltd., Tg: -12℃)

[0071] JE-1113 (42.5% solids, high molecular weight emulsion acrylic resin emulsion, manufactured by Starlight PMC Co., Ltd., Tg: -24℃)

[0072] HE-1335 (45.5% solids, high molecular weight emulsion acrylic-styrene resin emulsion, manufactured by Starlight PMC Co., Ltd., Tg: 15℃)

[0073] QE-1042 (40.5% solids, high molecular weight emulsion acrylic-styrene resin emulsion, manufactured by Starlight PMC Co., Ltd., Tg: 53℃)

[0074] (Acrylic resin emulsion emulsified by emulsifier)

[0075] Mowinyl 7320 (40.0% solids, emulsified acrylic resin emulsion, manufactured by Japan CoatingResin Co., Ltd., Tg: -20℃)

[0076] Mowinyl 730L (46.0% solids, emulsified acrylic resin emulsion, manufactured by Japan CoatingResin Co., Ltd., Tg: -13℃)

[0077] Neo-Cryl A-1125 (19.5% solids, emulsified acrylic resin emulsion with emulsifier, manufactured by DSM Neoresins, Tg: 13℃)

[0078] Neo-Cryl A-1093 (45.5% solids, emulsified acrylic-styrene resin emulsion, manufactured by DSM Neoresins, Tg: 17℃)

[0079] <Wax Emulsion>

[0080] AQUACER531 (45% solids, polyethylene resin emulsion, average particle size 160nm, manufactured by BYK)

[0081] Chemipearl W-400 (40% solids, polyethylene resin emulsion, average particle size 4.0 μm, manufactured by Mitsui Chemicals Co., Ltd.)

[0082] <Examples 1-17, Comparative Examples 1-10>

[0083] (Preparation of ink composition)

[0084] According to the mass ratios (mass%) shown in Tables 1 and 2 below, the materials were mixed using a paint mixer to prepare ink compositions. The storage stability of the obtained ink compositions was evaluated. Furthermore, the obtained ink compositions were subjected to gravure printing under the following conditions to obtain printed materials. The uniformity of printing across the entire surface, fine lines (bleed resistance), roll adhesion (anti-blocking), scratch resistance, alcohol resistance, and heat resistance of the obtained printed materials were evaluated according to the following evaluation methods. The results are shown in Tables 1 and 2.

[0085] <Conditions for the Production of Printed Materials>

[0086] Using a gravure printing press, an ink composition is printed onto the treated surface of a substrate under the following printing conditions and then dried to obtain a printed product.

[0087] (Printing conditions)

[0088] Substrate: Biaxially stretched polypropylene film, P-2111, manufactured by Toyobo Co., Ltd., with a thickness of 20 μm, treated with corona discharge.

[0089] Printing equipment: Gravure printing machine

[0090] Printing plate: 175-line engraving full-page plate

[0091] Printing speed: 15m / minute

[0092] Drying conditions: 80℃

[0093] <Preservation Stability>

[0094] The ink compositions of the above-described examples and comparative examples were taken separately into glass bottles, and their viscosity at 25°C was measured using a viscometer (RE100L type, manufactured by Toki Sangyo Co., Ltd.). The bottles were then sealed tightly and stored at 60°C for one month. The viscosity after storage (25°C) was measured using the viscometer. The stability over time was evaluated using the viscosity change rate (100 × (viscosity after 1 month at 60°C - viscosity before storage) / viscosity before storage).

[0095] (Evaluation Criteria)

[0096] ○: Viscosity change rate is less than 5%.

[0097] △: The viscosity change rate is greater than 5% but less than 10%.

[0098] ×: The viscosity change rate is greater than 10% but less than 30%.

[0099] <Uniformity of printing across the entire surface>

[0100] The uniformity of printing on the entire surface of the printed material is observed visually and evaluated according to the following evaluation criteria.

[0101] (Evaluation Criteria)

[0102] ○: The printed material is free of unevenness and streaks.

[0103] △: Slight unevenness and streaks are visible in the printed material.

[0104] ×: Visually, the printed material is uneven and has streaks.

[0105] <Fine Line>

[0106] Using the water-based white ink composition of the examples and comparative examples, fine lines of about 0.5 mm were printed on the flexible packaging. The thickening caused by seepage was observed by visual inspection and evaluated using the following criteria.

[0107] (Evaluation Criteria)

[0108] ○: No bleeding, allowing printing to proceed at the original thickness.

[0109] △: Some areas show signs of thickening, but no thickening exceeding 2 times was observed.

[0110] ×: Overall, the thickness increased by more than 2 times.

[0111] <Wrap-up Adhesion>

[0112] The following method is used to evaluate the roll adhesion to determine whether the printed material can be pulled out of the roller immediately without resistance or peeling noise after printing using a gravure printing press.

[0113] (Evaluation Criteria)

[0114] ○: There was no resistance when peeling the film, and the ink did not peel off from the printed surface.

[0115] △: There is resistance when peeling the film, but the ink does not peel off from the printed surface.

[0116] ×: There is resistance when peeling the film, and the ink is peeled off from the printed surface.

[0117] <Abrasion Resistance>

[0118] The obtained printed material was cut into 2.5cm×25cm pieces to make test pieces. Using a vibratory abrasion tester (manufactured by Daiei Scientific Instruments Co., Ltd.), bleached cloth was brought into contact with the printed surface and subjected to a load of 500g for 100 cycles. The abrasion resistance was evaluated according to the following evaluation criteria based on the degree of ink fading.

[0119] (Evaluation Criteria)

[0120] ○: The white ink coating has not peeled off at all.

[0121] △: The white ink coating has slightly peeled off.

[0122] ×: Most of the white ink coating has peeled off.

[0123] <Alcohol Resistance>

[0124] The obtained printed material was cut into 2.5cm×25cm pieces to make test pieces. Using a vibratory friction tester (manufactured by Daiei Scientific Instruments Co., Ltd.), bleached cloth with 5 drops of 70% ethanol aqueous solution injected through an injection needle was brought into contact with the printed surface and subjected to a load of 200g for 10 cycles. The alcohol resistance was evaluated according to the following evaluation criteria based on the degree of ink detachment.

[0125] (Evaluation Criteria)

[0126] ○: The white ink coating has not peeled off at all.

[0127] △: The white ink coating has slightly peeled off.

[0128] ×: Most of the white ink coating has peeled off.

[0129] <Heat resistance>

[0130] Using a heat-sealing tester equipped with a hot plate tilted at 160–200°C, the printed surface and aluminum foil were subjected to a heat seal test at 2.0 kg / cm². 2 Press the pressure for 1 second. Evaluate the heat resistance according to the following evaluation criteria based on the lowest temperature at which the ink on the printed surface transfers to the aluminum foil.

[0131] (Evaluation Criteria)

[0132] ○: The minimum temperature at which the ink on the printed surface is transferred to the aluminum foil is above 200°C.

[0133] △: The minimum temperature at which the ink on the printed surface is transferred to the aluminum foil is above 160℃ and below 200℃.

[0134] ×: The minimum temperature at which the ink on the printed surface transfers to the aluminum foil is less than 160°C.

[0135] [Table 1]

[0136]

[0137] [Table 2]

[0138]

Claims

1. An aqueous white ink composition for overprint soft packaging, comprising a white pigment, an acrylic resin emulsion emulsified by a polymer, N-oleoyl sarcosine, a hydrazine-based compound having at least two or more hydrazine residues in a molecule, and a wax, the acrylic resin emulsion is contained in an amount of 3 to 40% by mass in terms of solid content, the acrylic resin emulsion has a glass transition temperature of -40 to 30°C, and the hydrazine-based compound having at least two or more hydrazine residues in a molecule includes a dihydrazide compound of a saturated aliphatic dibasic acid.

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

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

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