JP6967865B2 - Water-based inkjet ink and inkjet recording method - Google Patents

Description

Embodiments of the present invention relate to water-based inkjet inks and inkjet recording methods.

Inkjet printers are widely used, and the demand for high-speed printing is increasing year by year.
The inkjet printing method includes a serial head method in which the inkjet head is reciprocated a plurality of times in a direction intersecting the transport direction of the recording medium for printing, and a fixed arrangement in the direction in which the inkjet head intersects the transport direction of the recording medium. There is a line head method. In order to meet the demand for high-speed printing, the ink jet head does not move back and forth on the recording medium, and the number of times the paper passes under the inkjet head is once, a so-called line head method that can form an image in one pass. Is suitable.

Inkjet inks include UV inks, oil-based inks, and water-based inks. Water-based ink is said to have a low impact on the environment, but since water-based ink contains water as a solvent, the recording medium may absorb the water in the ink and cause paper deformation such as curling and cockling. .. In addition, the deformation of the paper may affect the transportability of the recording medium, such as the printed matter coming into contact with the inkjet head.

Patent Documents 1 and 2 propose means for suppressing deformation of paper by using a low-polarity solvent such as dipropylene glycol monomethyl ether or triethylene glycol monobutyl ether.

Japanese Unexamined Patent Publication No. 2005-220296 Japanese Unexamined Patent Publication No. 2009-52018

One object of the present invention is to provide a water-based inkjet ink capable of producing a printed matter having less strike-through and paper deformation.

Another object of the present invention is to provide an inkjet recording method capable of producing a printed matter having less strike-through and paper deformation.

According to one embodiment of the present invention, the water-based inkjet ink containing water, a coloring material, and tetraethylene glycol has a tetraethylene glycol content (mass) a and water content (mass) b of 0. The water-soluble organic solvent satisfying the relationship of 21 ≦ a / b ≦ 0.42 and having a boiling point of 280 ° C. or less is 1.0% by mass or less with respect to the total amount of the water-based inkjet ink, and the SP value is 11 (cal / cm). ³ ) ^{A water-based inkjet ink having a water-soluble organic solvent of 1/2} or less in an amount of 1.0% by mass or less based on the total amount of the water-based inkjet ink is provided.
According to another embodiment of the present invention, an inkjet recording method comprising a step of printing on a recording medium by an inkjet recording method using the water-based inkjet ink, and an amount of ink applied to the recording medium is 15 g / m ² or less. Is provided.
According to another embodiment of the present invention, the recording medium includes a step of printing by an inkjet recording method with a line head type inkjet printer using the water-based inkjet ink, and the inkjet printer prints one side of the recording medium. An inkjet recording method is provided that comprises a line head for printing and a line head for printing the other side of the recording medium.

According to one embodiment of the present invention, it is possible to provide a water-based inkjet ink capable of producing a printed matter having less strike-through and paper deformation.
According to another embodiment of the present invention, it is possible to provide an inkjet recording method capable of producing a printed matter having less strike-through and paper deformation.

Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to the following embodiments.

The water-based inkjet ink of the first embodiment of the present invention contains water, a coloring material, and tetraethylene glycol, and the content (mass) a of tetraethylene glycol and the content (mass) b of water are 0.21 ≦. The water-soluble organic solvent satisfying the relationship of a / b ≦ 0.42 and having a boiling point of 280 ° C. or less is 1.0% by mass or less with respect to the total amount of the water-based inkjet ink, and the SP value is 11 (cal / cm ³ ) ^{1. A water-based inkjet ink having a water-soluble organic solvent of / 2} or less in an amount of 1.0% by mass or less based on the total amount of the water-based inkjet ink.
According to the above-mentioned water-based inkjet ink, it is possible to produce a printed matter with less strike-through and paper deformation.

The inkjet recording method of the second embodiment of the present invention is an inkjet recording method including a step of printing on a recording medium by an inkjet recording method using the water-based inkjet ink of the first embodiment.
One embodiment of the inkjet recording method of the second embodiment includes a step of printing on a recording medium by an inkjet recording method using the aqueous inkjet ink of the first embodiment, and the amount of ink applied to the recording medium is 15 g. It is an inkjet recording method of / m ^{2 or less.}
Another embodiment of the inkjet recording method of the second embodiment includes a step of printing by an inkjet recording method with a line head type inkjet printer using the water-based inkjet ink of the first embodiment on a recording medium. , An inkjet recording method, wherein the inkjet printer includes a line head for printing one side of a recording medium and a line head for printing the other side of the recording medium.
According to the above-mentioned inkjet recording method, it is possible to produce a printed matter with less strike-through and paper deformation.

The water-based inkjet ink of the first embodiment (hereinafter, may be simply referred to as “ink”) will be described.
The ink of the first embodiment contains water, a coloring material, and tetraethylene glycol.

Tetraethylene glycol is a water-soluble organic solvent having a structure represented by _{HO (CH 2} CH ₂ O) ₃ CH ₂ CH _{2 OH.}
Since tetraethylene glycol has OH groups at both ends, it has an appropriate water retention capacity. Therefore, when an ink containing tetraethylene glycol is used, nozzle clogging tends to be less likely to occur.
On the other hand, the number of OH groups per molecular weight of tetraethylene glycol is smaller than that of glycerin, ethylene glycol, etc., which are often used in general water-based inkjet inks, and the water retention capacity tends to be weaker than these. Therefore, when an ink containing tetraethylene glycol is used, it is considered that the printed matter is less likely to hold water and the paper deformation due to water is more likely to be reduced than those having a large number of OH groups per molecular weight such as glycerin and ethylene glycol. ..

Further, tetraethylene glycol has a high boiling point and is not a VOC (Volatile Organic Compounds), so that it is excellent in environmental suitability and safety.

The content of tetraethylene glycol in the ink is a / when the content (mass) of tetraethylene glycol is a and the content (mass) of water is b in relation to the content of water in the ink. b is preferably 0.21 or more, and more preferably 0.25 or more. When a / b is within this range, the printed surface becomes concave and the positive curl that the end portion is lifted tends to be easily reduced.
The a / b is more preferably 0.42 or less, further preferably 0.40 or less, and further preferably 0.35 or less. When a / b is within this range, the negative curl on which the printed surface becomes a convex surface tends to be reduced easily.
For a / b, for example, it is preferable to satisfy the relationship of 0.21 ≦ a / b ≦ 0.42, and it is more preferable to satisfy the relationship of 0.25 ≦ a / b ≦ 0.35.

The content of tetraethylene glycol in the ink is preferably 12 to 28% by mass with respect to the total amount of the ink.
The content of tetraethylene glycol in the ink is preferably 12% by mass or more, more preferably 14% by mass or more, further preferably 16% by mass or more, and even more preferably 17% by mass, based on the total amount of the ink. When the content of tetraethylene glycol in the ink is within this range, the printed surface becomes concave and the positive curl that the end portion is lifted tends to be easily reduced.
The content of tetraethylene glycol in the ink is preferably 28% by mass or less, more preferably 27% by mass or less, still more preferably 26% by mass or less, based on the total amount of the ink. When the content of tetraethylene glycol in the ink is in this range, the negative curl on which the printed surface becomes a convex surface tends to be easily reduced.

The ink may contain other water-soluble organic solvents in addition to tetraethylene glycol. The other water-soluble organic solvent can be appropriately selected from organic compounds which are liquid at room temperature and can be dissolved in water.
Examples of the water-soluble organic solvent that may be contained in the ink together with tetraethylene glycol include glycerin, triethylene glycol, polyethylene glycol (average molecular weight 600) and the like.

The content of tetraethylene glycol in the ink is preferably 50% by mass or more, more preferably 80% by mass or more, based on the total amount of the water-soluble organic solvent in the ink. The content of tetraethylene glycol in the ink may be 100% by mass of the total amount of the water-soluble organic solvent in the ink.

The content of the water-soluble organic solvent having a boiling point of 280 ° C. or lower in the ink is preferably 1.0% by mass or less, and more preferably 0.5% by mass or less, based on the total amount of the ink, from the viewpoint of reducing the amount of VOC generated. It is more preferable that the ink does not contain any water-soluble organic solvent having a boiling point of 280 ° C. or lower.
Further, when the content of the water-soluble organic solvent having a boiling point of 280 ° C. or lower in the ink is 1.0% by mass or less with respect to the total amount of the ink, the paper is less likely to be deformed. Although this mechanism is not clear, when the content of the water-soluble organic solvent having a boiling point of 280 ° C. or less is 1.0% by mass or less with respect to the total amount of the ink, the highly volatile water-soluble organic solvent evaporates on the printed matter. It is presumed that the decrease in the solvent ratio of the water is reduced and the influence of water is less likely to become apparent.
Examples of the water-soluble organic solvent having a boiling point of 280 ° C. or lower include 2-pyrrolidone, ethylene glycol, diethylene glycol, triethylene glycol monomethyl ether, triethylene glycol monobutyl ether and the like.

The content of the water-soluble organic solvent having an SP value of 11 (cal / cm ³ ) ^1/2 or less in the ink is preferably 1.0% by mass or less with respect to the total amount of the ink from the viewpoint of reducing strike-through. It is more preferably 5% by mass or less, and further preferably, the ink does not contain any water-soluble organic solvent having an SP value of 11 or less. A low-polarity water-soluble organic solvent having an SP value of 11 (cal / cm ³ ) ^1/2 or less tends to reduce the surface tension of the ink and may cause strike-through, but in the ink. When the content of the ink is 1.0% by mass or less with respect to the total amount of the ink, strike-through tends to be less likely to occur.
A water-soluble organic solvent having an SP value of 11 (cal / cm ³ ) ^1/2 or less and a boiling point of 280 ° C. or less tends to be less likely to cause paper deformation, but may cause strike-through. be. However, when the content is 1.0% by mass or less with respect to the total amount of ink, strike-through tends to be less likely to occur.

Here, the SP value is an SP value obtained by the Fedors formula, and specifically, is a value calculated by the following formula proposed by Fedors. In the following equation, Δei is the evaporation energy of the atom or atomic group of the i component, and Δvi is the molar volume of the atom or atomic group of the i component (Hansen Solution Parameters: A User's Handbook, Second Edition, Charles). See M. Hansen, CRC Press, 2007).
δ = [(sumΔei) / (sumΔvi)] ^1/2

Examples of the water-soluble organic solvent having an SP value of 11 (cal / cm ³ ) ^1/2 or less include triethylene glycol monomethyl ether (SP value 10.8 (cal / cm ³ ) ^1/2 ) and triethylene glycol monoethyl. Ether (SP value 10.6 (cal / cm ³ ) ^1/2 ), triethylene glycol monobutyl ether (SP value 10.3 (cal / cm ³ ) ^1/2 ), tetraethylene glycol monobutyl ether (SP value 10. 2 (cal / cm ³ ) ^1/2 )) and the like can be mentioned.

The ink is a SP value of 11 (cal ^/ cm ^{3) 1/2} or less, and, if it contains a boiling point 280 ° C. or less of the solvent, SP value of 11 (cal ^/ cm ^{3) 1/2} or less of water The content of the sex organic solvent has an SP value of 11 (cal / cm ³ ) ^1/2 or less and an SP value of 11 (cal / cm 3) including the water-soluble organic solvent having a boiling point of 280 ° C. or less. cm ³ ) The content of the water-soluble organic solvent is ^{1/2 or less.} Similarly, the content of the water-soluble organic solvent having a boiling point of 280 ° C. or lower includes such a water-soluble organic solvent having an SP value of 11 (cal / cm ³ ) ^1/2 or less and a boiling point of 280 ° C. or lower. The content of the water-soluble organic solvent having a boiling point of 280 ° C. or lower, including the above.

As the water, it is preferable to use pure water such as ion-exchanged water or distilled water, or ultrapure water.

The content of water in the ink is not particularly limited, but is preferably 62 to 75% by mass with respect to the total amount of the ink.
The content of water in the ink is preferably 62% by mass or more, more preferably 64% by mass or more, based on the total amount of the ink. When the water content in the ink is in this range, the negative curl tends to be reduced easily.
The water content in the ink is preferably 75% by mass or less with respect to the total amount of the ink. When the water content in the ink is in this range, the plus curl tends to be reduced easily.

The color material will be described.
As the coloring material, pigments and dyes can be used alone or in combination.

Examples of the pigment include organic pigments such as azo-based, phthalocyanine-based, dye-based, condensed polycyclic, nitro-based, and nitroso-based organic pigments (Brilliant Carmine 6B, Lake Red C, Watching Red, Disazo Yellow, Hansa Yellow, Phthalocyanine Blue, etc. Phthalocyanine green, alkaline blue, aniline black, etc.); Metals such as cobalt, iron, chromium, copper, zinc, lead, titanium, vanadium, manganese, nickel, metal oxides and sulfides, and ocher, ultramarine, dark blue, etc. Carbon blacks such as inorganic pigments, furnace carbon black, lamp black, acetylene black, and channel black can be used.

When the pigment is contained in the ink, a pigment dispersant can be added in order to stably disperse the pigment in the ink. Examples of the pigment dispersant include higher fatty acid salts, alkyl sulfates, alkyl ester sulfates, alkyl sulfonates, sulfosuccinates, naphthalene sulfonates, alkyl phosphates, polyoxyalkylene alkyl ether phosphates, and polys. Activators such as oxyalkylene alkylphenyl ether, polyoxyethylene polyoxypropylene glycol, glycerin ester, sorbitan ester, polyoxyethylene fatty acid amide, amine oxide, or styrene, styrene derivative, vinylnaphthalene derivative, acrylic acid, acrylic acid derivative , Maleic acid, maleic acid derivative, itaconic acid, itaconic acid derivative, fumaric acid, block copolymer consisting of two or more kinds of monomers selected from fumaric acid derivative, random copolymer and salts thereof. Can be done.

A self-dispersing pigment may be used as the pigment. The self-dispersible pigment is preferably one in which a hydrophilic functional group having ionicity is introduced into the pigment surface, and the pigment particles are subjected to electrostatic repulsion by charging the pigment surface anionicly or cationically. Can be stably dispersed in water. As the anionic functional group, a sulfonic acid group, a carboxy group, a carbonyl group, a hydroxy group, a phosphonic acid group, a phosphoric acid group and the like are preferable. As the cationic functional group, a quaternary ammonium group, a quaternary phosphonium group and the like are preferable. Of these, anionic groups such as a carboxy group, a hydroxy group and a phosphoric acid group are preferable.

These hydrophilic functional groups may be bonded directly to the pigment surface or may be bonded via other atomic groups. Examples of other atomic groups include, but are not limited to, an alkylene group, a phenylene group, and a naphthylene group. Examples of the method for treating the pigment surface include diazotization treatment, sulfonate treatment, hypochlorous acid treatment, humic acid treatment, and vacuum plasma treatment.

Commercially available self-dispersible pigments include CAB-O-JET300 and CAB-O-JET400 manufactured by Cabot Corporation, BONJET BLACK CW-1, CW-1S, CW-2 manufactured by Orient Chemical Industries Co., Ltd., and Tokai Carbon Co., Ltd. A company-made Aqua-Black 162 and the like can be exemplified.

Examples of the dye include basic dyes, acidic dyes, direct dyes, soluble bat dyes, acidic medium dyes, medium dyes, reactive dyes, bat dyes, sulfide dyes and the like, and among these, water-soluble dyes are preferable. More specifically, examples of the dye include azo dye, methine dye, azomethin dye, xanthene dye, quinone dye, phthalocyanine dye, triphenylmethane dye, diphenylmethane dye and the like.

These pigments and dyes may be used alone or in combination as appropriate.

The content of the coloring material (coloring material solid content) in the ink may be, for example, 1 to 20% by mass, preferably 3 to 15% by mass, and more preferably 3 to 10% by mass with respect to the total amount of the ink. ..
The content of the coloring material (coloring material solid content) is preferably 1% by mass or more from the viewpoint of visibility, and preferably 20% by mass or less from the viewpoint of the viscosity of the ink in the vicinity of the nozzle.

If necessary, the ink may contain various additives usually used in the art, as long as the object of the present invention is not impaired.

Specifically, as a pigment dispersant, an antifoaming agent, a surface tension lowering agent, etc., an anionic surfactant, a cationic surfactant, an amphoteric surfactant, a nonionic surfactant, or a polymer-based, silicone-based, or fluorine-based agent. The system surfactant can be contained in the ink.
The surfactant is not particularly limited, but for example, acetylene glycol-based surfactants, polyoxyethylene alkyl phenols, polyoxyethylene alkyl ethers, polyoxyethylene fatty acid esters and the like are preferable. Examples of the acetylene glycol-based surfactant include Surfinol 465, Surfinol 104 (manufactured by Air Products and Chemicals), Orfin STG, and Orfin E1010 (manufactured by Nisshin Kagaku Kogyo Co., Ltd.).

An electrolyte can be added to the ink to adjust the viscosity of the ink. Examples of the electrolyte include sodium sulfate, potassium hydrogen phosphate, sodium citrate, potassium tartrate, sodium borate, and the like, and two or more thereof may be used in combination.

Known pH regulators can also be added to adjust the pH of the ink. Sulfuric acid, nitric acid, acetic acid, sodium hydroxide, potassium hydroxide, ammonium hydroxide, triethanolamine and the like can be used as a pH adjuster or as an ink thickening aid.

By blending an antioxidant, it is possible to prevent the oxidation of ink components and improve the storage stability of the ink. As the antioxidant, for example, L-ascorbic acid, sodium L-ascorbic acid, sodium isoascorbate, potassium sulfite, sodium sulfite, sodium thiosulfate, sodium dithionate, sodium pyrosulfite and the like can be used.

By blending an antiseptic, it is possible to prevent the ink from spoiling and improve the storage stability. Examples of preservatives include 5-chloro-2-methyl-4-isothiazolin-3-one, 2-methyl-4-isothiazolin-3-one, 2-n-octyl-4-isothiazolin-3-one, 1 , 2-Benzoisothiazolin-3-one and other isothiazolone preservatives; hexahydro-1,3,5-tris (2-hydroxyethyl) -s-triazine and other triazine preservatives; 2-pyridinethiol sodium-1- Ppyridine / quinoline preservatives such as oxide, 8-oxyquinoline; dithiocarbamate preservatives such as sodium dimethyldithiocarbamate; 2,2-dibromo-3-nitrilopropionamide, 2-bromo-2-nitro-1,3 -Organic bromine preservatives such as propanediol, 2,2-dibromo-2-nitroethanol, 1,2-dibromo-2,4-dicyanobutane; methyl p-hydroxybenzoate, ethyl p-hydroxybenzoate, sorbin Potassium acid, sodium dehydroacetate, salicylic acid and the like can be used.

The ink according to the present embodiment can be adjusted by collectively or dividing each component, mixing them, and appropriately dispersing them with a disperser.

The viscosity of the ink is generally preferably 1 to 30 mPa · s at 23 ° C. The viscosity of the ink at 23 ° C. is more preferably 3.0 to 10.0 mPa · s, and even more preferably 3.0 to 5.0 mPa · s. When it is 3.0 mPa · s or more, fine print bleeding is less likely to occur, and when it is 10.0 mPa · s or less, it is easy to further reduce the power consumption.

The viscosity of the ink viscosity at 23 ° C. can be measured using a rheometer AR2 manufactured by TA Instruments.

The ink of the first embodiment may be used for, for example, plain paper, coated paper, finely coated paper, glossy paper, and the like.

The inkjet recording method of the second embodiment will be described.
The inkjet recording method of the second embodiment includes a step of printing on a recording medium by an inkjet recording method using the water-based inkjet ink of the first embodiment described above.

Examples of the recording medium include paper such as plain paper, coated paper, finely coated paper, and glossy paper. Plain paper refers to paper that does not have a coating layer containing pigments.
As the plain paper, it is preferable to use plain paper having a basis weight of 60 g / m ^{2 or more.} Further, the basis weight of this plain paper is more preferably ^{60 to 70 g / m 2.}
When plain paper having a basis weight of 60 g / m ² or more is used, it is easy to reduce the deformation of the paper after drying. Examples of commercially available plain paper having a basis weight of 60 g / m ² or more include "Ideal Paper Thin Mouth" and "Ideal Paper Multi" manufactured by Riso Kagaku Corporation.
For the basis weight, a value measured according to JIS P8124 is adopted.

The inkjet recording method may be any of the thermal inkjet method, the piezo inkjet method, the electrostatic suction method, and the like. For example, the ink according to the present embodiment is ejected from the inkjet head based on a digital signal. A method may be used in which the ejected ink droplets are attached to the recording medium.

As the inkjet printer, a line head type inkjet printer is preferable.
Further, those provided with a line head for printing one side of the recording medium and a line head for printing the other side of the recording medium are also preferable. By using a line head system that can form an image in one pass and having at least a line head that prints one side and a line head that prints the other side, high-speed double-sided printing becomes possible.
It is also possible that the line heads are in one row, and after printing on one side of the recording medium, the inverted recording medium passes under the line head again to print the other side of the recording medium. It is possible.

High-speed printing is susceptible to paper deformation. If the paper deformation is large, for example, in an inkjet printer equipped with a first line head for printing one side of a recording medium and a second line head for printing the other side, printing is performed with the first line head. The recording medium may come into contact with the second head, and the recording medium may be soiled or the nozzle may be damaged. However, according to the above-mentioned method for producing a printed matter including a step of printing by an inkjet recording method using the water-based inkjet ink of the first embodiment as a recording medium, paper deformation is reduced and paper transportability is good. Therefore, high-speed printing can also be preferably performed. Further, a line head type inkjet printer such as an inkjet printer provided with a line head for printing one side of a recording medium and a line head for printing the other side of the recording medium can be preferably used.

The print resolution is preferably 600 dpi or more in both the transport direction of the recording medium and the direction intersecting the transport direction.
When the print resolution in both directions is 600 dpi or more, it is easy to recognize fine characters when an image is formed in one pass.

The amount of ink applied to the recording medium ^{is preferably 15 g / m 2} or less, more preferably 10 g / m ^{2 or less.} Generally, as the amount of ink applied increases, the paper deformation tends to increase. When the amount of ink applied is 15 g / m ² or less, it is easy to further reduce paper deformation and also to reduce strike-through. The amount of ink applied to the recording medium may be, for example, 2 g / m ² or more. Here, the amount of ink applied to the recording medium is the total amount of these inks when two or more types of ink are overlapped.

The embodiments of the present invention include, but the present invention is not limited to the following embodiments.
<1> A water-based inkjet ink containing water, a coloring material, and tetraethylene glycol.
The relationship between the content (mass) a of the tetraethylene glycol and the content (mass) b of the water satisfies the relationship of 0.21 ≦ a / b ≦ 0.42.
The water-soluble organic solvent having a boiling point of 280 ° C. or lower is 1.0% by mass or less based on the total amount of the water-based inkjet ink.
The amount of the water-soluble organic solvent having an SP value of 11 (cal / cm ³ ) ^1/2 or less is 1.0% by mass or less based on the total amount of the water-based inkjet ink.
Water-based inkjet ink.
<2> The water-based inkjet ink according to <1>, wherein the content of the tetraethylene glycol is 12 to 28% by mass with respect to the total amount of the water-based inkjet ink.
<3> In <1> or <2>, where the content (mass) a of the tetraethylene glycol and the content (mass) b of the water satisfy the relationship of 0.25 ≦ b / a ≦ 0.35. The water-based inkjet ink described.
<4> The recording medium includes a step of printing by an inkjet recording method using the water-based inkjet ink according to any one of <1> to <3>, and the amount of ink applied to the recording medium is 15 g / m. ^An inkjet recording method of 2 or less.
<5> The inkjet printer includes a step of printing by an inkjet recording method with a line head type inkjet printer using the water-based inkjet ink according to any one of <1> to <3> as a recording medium. However, an inkjet recording method comprising a line head for printing one side of a recording medium and a line head for printing the other side of the recording medium.
<6> Using a line head type inkjet printer, the inkjet printer includes a line head for printing one side of a recording medium and a line head for printing the other side of the recording medium, in <4>. The inkjet recording method described.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited thereto.

<Ink preparation>
Tables 1 and 2 show the ink formulations of Examples and Comparative Examples. The raw materials shown in Tables 1 and 2 are mixed in the ratios shown in the table, stirred at a rotation speed of 60 rpm for 1 minute using a three-one motor, and after stirring, filtered through a membrane filter having a pore size of 0.8 μm. Inks for each example and comparative example were obtained.
The black dyes and black pigments shown in Tables 1 and 2 are aqueous solutions or aqueous dispersions containing water. In Tables 1 and 2, the amounts of "black pigment" and "black dye" both indicate the amount as a pigment or dye solid content. Further, in Tables 1 and 2, the amount of "water" is the water content of the entire ink including the water of the black dye or the black pigment.

The materials used are shown below.
1. 1. Organic solvent, glycerin: manufactured by Wako Pure Chemical Industries, Ltd., boiling point 290 ° C, SP value 16.4 (cal / cm ³ ) ^1/2 )
-Ethylene glycol: manufactured by Wako Pure Chemical Industries, Ltd., boiling point 198 ° C, SP value 17.8 (cal / cm ³ ) ^1/2 )
2-Pyrrolidone: manufactured by Wako Pure Chemical Industries, Ltd., boiling point 251 ° C, SP value 12.3 (cal / cm ³ ) ^1/2 )
-Triethylene glycol monomethyl ether: manufactured by Tokyo Chemical Industry Co., Ltd., boiling point 249 ° C, SP value 10.8 (cal / cm ³ ) ^1/2 )
-Triethylene glycol monobutyl ether: manufactured by Tokyo Chemical Industry Co., Ltd., boiling point 272 ° C., SP value 10.3 (cal / cm ³ ) ^1/2 )
-Tetraethylene glycol: manufactured by Kanto Chemical Co., Inc., boiling point 314 ° C, SP value 12.6 (cal / cm ³ ) ^1/2 )

2. 2. Water / ion exchange water 3. Surfactant Orfin E1010: Acetylene glycol-based surfactant, manufactured by Nisshin Kagaku Kogyo Co., Ltd. 4. Color material / Food Black 2: Made by Daiwa Kasei Co., Ltd., black dye, dye solid content 100% by mass
-Acid Black 2: Orient Chemical Industries Co., Ltd., black dye, dye solid content 14% by mass
-Reactive Black8: Black dye manufactured by Sensient, dye solid content 14% by mass
BONJET CW-2: Self-dispersed carbon black dispersion (black pigment) manufactured by Orient Chemical Industries Co., Ltd., pigment solid content 15% by mass
CAB-O-JET300: Self-dispersed carbon black dispersion (black pigment) manufactured by Cabot Corporation, pigment solid content 14.9% by mass

<Measurement of VOC>
The water-soluble organic solvent used in the production of each ink was analyzed by gas chromatograph using "TD-20" manufactured by Shimadzu Corporation, and a peak was detected between n-hexane and n-hexadecane, which are indicators of VOC. I checked if it would be done. In the table, those in which a peak was detected between n-hexane and n-hexadecane were described as VOC, and those in which no peak was detected were described as non-VOC.

<Evaluation>
1. 1. Ink Viscosity The viscosity of each ink at 23 ° C. was measured using a rheometer AR-G2 (cone angle 2 °, diameter 40 mm) manufactured by TA Instruments.

2. 2. Paper deformation Using plain paper cut to 50 mm x 100 mm, each ink produced using the wire bar P0.08H4S (manufactured by OSG Products System Co., Ltd.) has the amount of ink applied as shown in the table. So, I painted this plain paper. After coating, it was left in an environment of 23 ° C. and 50% for 24 hours with the printed surface facing up. The amount of deformation after 10 seconds and 24 hours of coating was determined. The amount of deformation is a measurement of the maximum height of the portion of the paper that has been deformed and lifted from the horizontal plane when the paper is placed on a horizontal plane with the ink coated surface facing up. In both the minus curl that deforms to a convex shape so that the ink coated surface becomes a convex surface and the plus curl that deforms to a concave shape so that the ink coated surface becomes a concave surface, based on the absolute value of the paper deformation amount, Paper deformation was evaluated according to the following evaluation criteria. The results are shown in the table.
A: The absolute value of the amount of paper deformation is less than 15 mm.
B: The absolute value of the amount of paper deformation is 15 mm or more and less than 20 mm.
C: The absolute value of the amount of paper deformation is 20 mm or more. The plain papers listed in the table are as follows.
・ Plain paper 1: "Ideal paper thin mouth" manufactured by Riso Kagaku Corporation, basis weight 62 g / m ²
-Plain paper 2: "Ideal paper multi" manufactured by Riso Kagaku Corporation, basis weight 70 g / m ²

3. 3. After the image density paper deformation measurement, the OD value of the coated surface was measured using a spectrocolorimeter i1i0 manufactured by X-Rite, and the obtained OD value was evaluated according to the following evaluation criteria. The results are shown in the table.
A: 1.10 or more
B: 0.90 or more and less than 1.10
C: Less than 0.90

4. After measuring the strike-through image density, the OD value of the back surface of the coated surface was measured using a densitometer manufactured by X-Rite, and the OD value of the obtained back surface was evaluated according to the following evaluation criteria. The results are shown in the table.
A: Less than 0.20
B: 0.20 or more and less than 0.25
C: 0.25 or more

In Examples 1 to 13, the strike-through was small and the amount of paper deformation was small without impairing the image density. In Examples 1 to 11 in which the ratio a / b of the content (mass) a of tetraethylene glycol and the content (mass) b of water is in the range of 0.25 to 0.35, the result of paper deformation is particularly high. It was good.

<Evaluation by inkjet printing>
Next, for each of the ink of Example 4 and the ink of Comparative Example 1, printed matter was prepared as follows and evaluated.
Ink of Example 4 and ink of Comparative Example 1 were introduced into a line-type inkjet printer, respectively, and the resolution was 600 dpi x 600 dpi for ^{"Ideal Paper Thin Mouth" manufactured by Riso Kagaku Corporation, with a basis weight of 62 g / m 2.} Ink single color solid printing was performed with an ink application amount of 7 g / m ^2.
Ten printed matter obtained by using each ink was left in a 23 ° C. and 50% RH environment for 24 hours, and the state after leaving was observed.
In the printed matter using the ink of Example 4 after being left for 24 hours, the printed surface was concave and the edges were raised, but the amount of deformation was small, so that the printed surface could be seen. On the other hand, in the printed matter using the ink of Comparative Example 1, the printed matter could not be seen because the plus curl was greatly deformed into a cylindrical shape. Similar results were obtained for the remaining 9 printed matter using the ink of Example 4 and the remaining 9 printed matter using the ink of Comparative Example 1.
With respect to the printed matter using the ink of Example 4, after the paper deformation measurement, the image density (OD value of the printed surface) was measured and evaluated in the same manner as above. Further, this printed matter was evaluated by measuring the strike-through (back OD) in the same manner as described above after measuring the image density. The image density (front OD value) was B in the above evaluation criteria, and the strike-through (back OD value) was A in the above evaluation criteria.

Claims (5)

A water-based inkjet ink containing water, colorants, and tetraethylene glycol.
The coloring material contains a pigment and
The relationship between the content (mass) a of the tetraethylene glycol and the content (mass) b of the water satisfies the relationship of 0.28 ≦ a / b ≦ 0.35.
The water-soluble organic solvent having a boiling point of 280 ° C. or lower is 1.0% by mass or less based on the total amount of the water-based inkjet ink.
The amount of the water-soluble organic solvent having an SP value of 11 (cal / cm ³ ) ^1/2 or less is 1.0% by mass or less based on the total amount of the water-based inkjet ink.
Water-based inkjet ink. The water-based inkjet ink according to claim 1, wherein the content of the tetraethylene glycol is 12 to 28% by mass with respect to the total amount of the water-based inkjet ink. An inkjet recording method comprising a step of printing on a recording medium by an inkjet recording method using the water-based inkjet ink according to claim 1 or 2 ^{, wherein the amount of ink applied to the recording medium is 15 g / m 2} or less. A line in which a line head type inkjet printer prints by an inkjet recording method using the water-based inkjet ink according to claim 1 or 2 as a recording medium, and the inkjet printer prints one side of the recording medium. An inkjet recording method comprising a head and a line head for printing the other side of the recording medium. Using an inkjet printer of line head type, the ink jet printer, a line head for printing on one side of the recording medium, and a line head for printing the other side of the recording medium, ink jet according to claim 3 Recording method.