Inkjet Ink Composition and Recording Method

Abstract

To provide an ink jet ink composition that gives a recorded media having curling resistance and improved coloration, and also prevents clogging and a viscosity rise.SOLUTION: An ink jet ink composition includes: a colorant; silica particles; 1-(2-hydroxyethyl)-2-pyrrolidone; and water. The silica particles have, in a TEM image thereof, a Di (diameter of the maximum inscribed circle) / Dc (diameter of the minimum circumscribed circle) of 0.7 or more.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to an inkjet ink composition and a recording method.

Background Art

[0002] The inkjet recording method uses a relatively simple device and can record high-definition images, and has been rapidly developed in various fields. Among them, studies have been made on improving printing density and stacking properties by including inorganic particles other than pigments. For example, Patent Document 1 discloses an ink composition containing a self-dispersing pigment and metal oxide particles having a predetermined particle size for the purpose of improving printing density and the like, and Patent Document 2 discloses an ink composition containing a pigment, colloidal silica, and an amino acid for the purpose of improving stacking properties.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] As shown in Patent Documents 1 and 2, by using colloidal silica or the like, the printing density and stacking properties are improved. However, when the content of colloidal silica is high, there is a problem that the nozzles are likely to be clogged when the ink dries near the inkjet head nozzles. In order to suppress such drying, it is conceivable to include a humectant in the ink composition. However, humectants with high humectant power are often solids or high-viscosity liquids at room temperature, and there is a problem that they rather cause an increase in the viscosity of the ink composition.

Means for Solving the Problems

[0005] The present invention relates to an inkjet ink composition containing a coloring material, silica particles, 1-(2-hydroxyethyl)-2-pyrrolidone, and water, wherein Di (diameter of the maximum inscribed circle) / Dc (diameter of the minimum circumscribed circle) in the TEM image of the silica particles is 0.7 or more.

[0006] The present invention also relates to a recording method including a discharging step of discharging the above inkjet ink composition onto a recording medium.

Brief Description of the Drawings

[0007]

Figure 1

Embodiments for Carrying Out the Invention

[0008] Hereinafter, embodiments of the present invention (hereinafter referred to as "the present embodiment") will be described in detail with reference to the drawings as necessary. However, the present invention is not limited thereto, and various modifications can be made without departing from the gist thereof. In the drawings, the same elements will be denoted by the same reference numerals, and redundant descriptions will be omitted. Also, the positional relationships such as up, down, left, and right are based on the positional relationships shown in the drawings unless otherwise specified. Furthermore, the dimensional ratios in the drawings are not limited to the illustrated ratios.

[0009] 1. Inkjet Ink Composition The inkjet ink composition of the present embodiment (hereinafter also simply referred to as "ink composition") contains a coloring material, silica particles, 1-(2-hydroxyethyl)-2-pyrrolidone, and water, and Di (diameter of the maximum inscribed circle) / Dc (diameter of the minimum circumscribed circle) in the TEM image of the silica particles is 0.7 or more.

[0010] Conventionally, by using colloidal silica or the like, improvement in printing density and stacking property has been studied. On the other hand, such an ink composition has a problem that nozzle clogging is likely to occur during drying.

[0011] In contrast, in the present embodiment, by using 1-(2-hydroxyethyl)-2-pyrrolidone, which has excellent moisture retention and solubility and can suppress clogging of an ink composition containing silica, in combination with silica particles having a shape that is less likely to cause an increase in viscosity, it is possible to provide an ink composition that is excellent in clogging resistance and has a suppressed viscosity while achieving the effects of silica particles such as curl suppression and color development improvement. Each component will be described in detail below.

[0012] 1.1. Colorant Examples of the colorant include pigments or dyes. Among these, it is preferable to use a pigment.

[0013] The pigment is not particularly limited. For example, azo pigments (including, for example, azo lakes, insoluble azo pigments, condensed azo pigments, chelate azo pigments, etc.), polycyclic pigments (such as phthalocyanine pigments, perylene pigments, perinone pigments, anthraquinone pigments, quinacridone pigments, dioxazine pigments, thioindigo pigments, isoindolinone pigments, quinophthalone pigments, etc.), nitro pigments, nitroso pigments, organic pigments such as aniline black; carbon black (such as furnace black, thermal lamp black, acetylene black, channel black, etc.), inorganic pigments such as metal oxides, metal sulfides, metal chlorides; extender pigments such as calcium carbonate and talc can be used.

[0014] The dye is not particularly limited. For example, acidic dyes, basic dyes, direct dyes, reactive dyes, and disperse dyes can be mentioned.

[0015] The content of the colorant is 1.0 to 12.5% by mass, preferably 2.5 to 10% by mass, more preferably 5.0 to 8.0% by mass with respect to the total amount of the ink composition.

[0016] 1.2. Silica Particles By using silica particles, curling can be suppressed and color developability can be improved. Generally, from the perspective of curling suppression, it is considered to reduce the water content in the ink composition. However, when the water content in the ink composition is reduced, there is a problem that the viscosity increases and the ejection stability decreases. Here, by using silica particles, even if the water content in the ink composition is reduced, an increase in viscosity can be suppressed. This is presumably because the repulsion due to the charge resistance of the silica particles and the slipperiness due to the shape are improved. Further, by containing silica particles, a plugging effect is exhibited on the paper and the penetration of moisture into the recording medium is suppressed, so that curling can be suppressed and color developability can also be improved.

[0017] It has been found that the suppression of the increase in viscosity due to the slipperiness of such silica particles and the suppression of curling due to the plugging effect depend on the shape of the silica particles. Therefore, as the silica particles used in the present embodiment, colloidal silica in which silica particles are dispersed using the solvent constituting the ink as a dispersion medium is preferable. Di (diameter of the maximum inscribed circle) / Dc (diameter of the minimum circumscribed circle) in the TEM image of the silica particles is 0.7 or more, preferably 0.8 to 1.0, and more preferably 0.9 to 1.0. When Di (diameter of the maximum inscribed circle) / Dc (diameter of the minimum circumscribed circle) is 0.7 or more, the silica particles do not form clusters, and the shape of the silica particles becomes closer to a true sphere. Thus, even when a large amount of silica particles are used in terms of curling suppression and color developability improvement, the viscosity of the ink composition hardly increases and the ejection stability is further improved.

[0018] Di (diameter of the maximum inscribed circle) / Dc (diameter of the minimum circumscribed circle) is calculated from the average values of the diameter (Di) of the maximum inscribed circle and the diameter (Dc) of the minimum circumscribed circle of 20 silica particles by taking a TEM image of the dispersion liquid of each silica particle using a transmission electron microscope. The maximum inscribed circle and the minimum circumscribed circle are defined as the minimum circumscribed circle for the outer circle and the maximum inscribed circle for the inner circle when the difference in diameter between the outer circle and the inner circle is minimized when the contour of each silica particle is sandwiched between two circles.

[0019] The average particle diameter of the silica particles is preferably 10 to 80 nm, more preferably 15 to 65 nm, and still more preferably 20 to 50 nm. When the average particle diameter of the silica particles is within the above range, clogging and an increase in viscosity tend to be more suppressed.

[0020] The content of the silica particles is preferably 1.0 to 15% by mass, preferably 2.0 to 12.5% by mass, and preferably 4.0 to 10% by mass with respect to the total amount of the ink composition. When the content of the silica particles is 1.0% by mass or more, curling and color developability tend to be more improved. Further, when the content of the silica particles is 15% by mass or less, clogging and an increase in viscosity tend to be more suppressed.

[0021] The content of the silica particles is preferably 50 to 500 parts by mass, more preferably 100 to 400 parts by mass, and still more preferably 150 to 300 parts by mass with respect to 100 parts by mass of 1-(2-hydroxyethyl)-2-pyrrolidone. When the content of the silica particles with respect to 1-(2-hydroxyethyl)-2-pyrrolidone is 50 parts by mass or more, curling and color developability tend to be more improved. Further, when the content of the silica particles is 500 parts by mass or less, clogging and an increase in viscosity tend to be more suppressed.

[0022] 1.3. 1-(2-Hydroxyethyl)-2-pyrrolidone By using 1-(2-hydroxyethyl)-2-pyrrolidone, it has excellent moisture retention and solubility, and can suppress clogging of the ink composition containing silica particles. On the other hand, 1-(2-hydroxyethyl)-2-pyrrolidone has a relatively high viscosity and tends to cause an increase in the viscosity of the ink composition. However, by using it in combination with the silica particles having the above predetermined shape, such an increase in viscosity can be made less likely to occur. Therefore, by using 1-(2-hydroxyethyl)-2-pyrrolidone and silica particles having a predetermined shape in combination, even if the ink composition contains silica particles for the purpose of suppressing curling and improving color developability, clogging is less likely to occur and an increase in viscosity is suppressed, so that an ink composition excellent in ejection stability can be achieved.

[0023] The content of 1-(2-hydroxyethyl)-2-pyrrolidone is preferably 0.5 to 10% by mass, preferably 0.5 to 7.5% by mass, and preferably 1.0 to 5.0% by mass with respect to the total amount of the ink composition. When the content of 1-(2-hydroxyethyl)-2-pyrrolidone is 0.5% by mass or more, moisture retention is exhibited, and clogging is less likely to occur. Further, when the content of 1-(2-hydroxyethyl)-2-pyrrolidone is 10% by mass or less, an increase in the viscosity of the ink composition is more likely to be suppressed.

[0024] 1.4. Water The content of water is 45 to 70% by mass, preferably 50 to 65% by mass, and more preferably 55 to 65% by mass with respect to the total amount of the ink composition. When the content of water is 70% by mass or less, curling of the obtained recording material is likely to be suppressed. Further, when the content of water is 45% by mass or more, clogging and an increase in viscosity are more likely to be suppressed.

[0025] 1.5. Other components The ink composition of the present embodiment may further contain betaines, alkalis, water-soluble organic solvents, surfactants, and other additives, if necessary.

[0026] 1.5.1. Betaines Betaines refer to compounds that have non-adjacent positive and negative charges within the same molecule and have no charge as a whole molecule. The positive charge site is preferably a quaternary ammonium cation. Such betaines are not particularly limited, and examples include trimethylglycine, γ-butyrobetaine, homarine, trigonelline, carnitine, homoserine betaine, valine betaine, lysine betaine, ornithine betaine, alanine betaine, stachydrine, and glutamate betaine. Among these, trimethylglycine, γ-butyrobetaine, and carnitine are preferred, and trimethylglycine is more preferred. By using such betaines, clogging tends to be more suppressed. Note that betaines may be used alone or in combination of two or more.

[0027] The content of betaines is preferably 2.0 to 16% by mass, more preferably 4.0 to 14% by mass, and still more preferably 6.0 to 12% by mass based on the total amount of the ink composition. When the content of betaines is within the above range, the formation of hard aggregates when silica particles aggregate due to drying is suppressed, and the dispersion stability of silica particles is improved, so clogging tends to be more suppressed.

[0028] The content of betaines is preferably more than the content of the solid content of silica particles on a mass basis. Specifically, the content of betaines is preferably 1.05 to 5.0 times, more preferably 1.1 to 4.0 times, and still more preferably 1.1 to 3.0 times the content of the solid content of silica particles on a mass basis. When the content of betaines is within the above range, clogging tends to be more suppressed.

[0029] 1.5.2. Alkali The alkali is not particularly limited, and examples include organic bases such as triethanolamine, diethanolamine, monoethanolamine, and tripropanolamine; and inorganic bases such as lithium hydroxide, sodium hydroxide, and potassium hydroxide.

[0030] Among these, organic bases are preferred. Different from inorganic bases such as sodium hydroxide, since the acid dissociation constant (pKa) at room temperature of the organic base falls within the range of 7 to 10, the extraction of protons occurs reversibly in the ink and can function as a buffer to improve the stability of silica particles.

[0031] The content of the alkali is preferably 0.05 to 1.5% by mass, more preferably 0.10 to 1.0% by mass, and still more preferably 0.20 to 0.75% by mass with respect to the total amount of the ink composition. When the content of the alkali is within the above range, the dispersion stability of the silica particles is further improved, and thus clogging is more likely to be suppressed.

[0032] 1.5.3. Water-soluble organic solvent The inkjet ink of the present embodiment may contain a water-soluble organic solvent other than the above-mentioned 1-(2-hydroxyethyl)-2-pyrrolidone (hereinafter referred to as "other water-soluble organic solvents").

[0033] The other water-soluble organic solvents are not particularly limited. For example, glycerin; nitrogen-containing solvents such as 2-pyrrolidone and N-methylpyrrolidone; glycols such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, propane diol, butane diol, pentane diol, and hexylene glycol; glycol monoalkyl ethers such as ethylene glycol monomethyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, and triethylene glycol monobutyl ether.

[0034] The content of the other water-soluble organic solvents is preferably 3.0 to 25% by mass, more preferably 5.0 to 20% by mass, and still more preferably 7.5 to 15% by mass with respect to the total amount of the ink composition.

[0035] 1.5.4. Surfactant The surfactant is not particularly limited, and examples thereof include acetylene glycol-based surfactants, fluorine-based surfactants, and silicone-based surfactants. Among these, acetylene glycol-based surfactants are preferred.

[0036] The acetylene glycol-based surfactant is not particularly limited, and for example, one or more selected from 2,4,7,9-tetramethyl-5-decyne-4,7-diol and alkylene oxide adducts of 2,4,7,9-tetramethyl-5-decyne-4,7-diol, and 2,4-dimethyl-5-decyne-4-ol and alkylene oxide adducts of 2,4-dimethyl-5-decyne-4-ol are preferred.

[0037] The fluorine-based surfactant is not particularly limited, and examples thereof include perfluoroalkyl sulfonates, perfluoroalkyl carboxylates, perfluoroalkyl phosphates, perfluoroalkyl ethylene oxide adducts, perfluoroalkyl betaines, and perfluoroalkyl amine oxide compounds.

[0038] Examples of the silicone-based surfactant include polysiloxane-based compounds and polyether-modified organosiloxanes.

[0039] The content of the surfactant is preferably 0.3 to 2.0% by mass, more preferably 0.5 to 1.5% by mass, and still more preferably 0.75 to 1.25% by mass with respect to the total amount of the ink composition.

[0040] 1.6. Viscosity The viscosity of the ink composition at 20°C is preferably 7.0 mPa·s or less, more preferably 1.0 to 7.0 mPa·s, and still more preferably 1.0 to 5.0 mPa·s. When the viscosity is within the above range, the ejection stability tends to be further improved.

[0041] 2. Recording Method The recording method of the present embodiment includes a discharging step of discharging the above ink composition onto a recording medium by an inkjet method, and may include a drying step or the like as necessary.

[0042] 2.1. Discharging step In the discharging step, ink is discharged from an inkjet head and adhered to a recording medium. More specifically, pressure generating means provided in the inkjet head is driven to discharge the ink filled in the pressure generating chamber of the inkjet head from the nozzles. Such a discharging method is also called an inkjet method.

[0043] Examples of the inkjet head used in the discharging step include a line head that performs recording by a line method and a serial head that performs recording by a serial method.

[0044] In the line method using a line head, for example, an inkjet head having a width equal to or greater than the recording width of the recording medium is fixed to a recording apparatus. Then, the recording medium is moved along the sub-scanning direction (the conveyance direction of the recording medium), and ink droplets are discharged from the nozzles of the inkjet head in conjunction with this movement, thereby recording an image on the recording medium.

[0045] In the serial method using a serial head, for example, an inkjet head is mounted on a carriage movable in the width direction of the recording medium. Then, the carriage is moved along the main scanning direction (the width direction of the recording medium), and ink droplets are discharged from the nozzles of the head in conjunction with this movement, thereby recording an image on the recording medium.

[0046] 2.2. Recording medium The recording medium used in the present embodiment is not particularly limited, and examples thereof include absorbent or non-absorbent recording media. Among these, since absorbent recording media are likely to cause problems such as curling, the present invention is effective.

[0047] The absorbent recording medium is not particularly limited. For example, it includes ordinary paper such as electrophotographic paper with high ink permeability, inkjet paper (inkjet dedicated paper equipped with an ink absorption layer composed of silica particles or alumina particles, or an ink absorption layer composed of a hydrophilic polymer such as polyvinyl alcohol (PVA) or polyvinyl pyrrolidone (PVP)), and art paper, coated paper, cast paper, etc. used for general offset printing with relatively low ink permeability.

[0048] Among these, it is preferable that the recording medium is ordinary paper. Since problems such as curling are likely to occur in ordinary paper, the present invention is effective.

[0049] Here, the "absorbent recording medium" refers to a recording medium in which the water absorption amount from the start of contact to 30 msec in the Bristow method exceeds 10 mL / m 2 This Bristow method is the most popular method for measuring the liquid absorption amount in a short time and is also adopted by the Japan Paper Pulp Technology Association (JAPAN TAPPI). The details of the test method are described in Standard No. 51, "Paper and Paperboard - Liquid Absorbency Test Method - Bristow Method" of "JAPAN TAPPI Paper Pulp Test Methods 2000 Edition".

[0050] 3. Recording Device The recording device of this embodiment includes an inkjet head having nozzles for discharging inkjet ink onto a recording medium, and conveying means for conveying the recording medium. The inkjet head includes a pressure chamber to which ink is supplied and nozzles for discharging ink. Also, the conveying means is composed of conveying rollers and conveying belts provided in the recording device.

[0051] Hereinafter, the recording device according to this embodiment will be described with reference to FIG. 1. In FIG. 1, the X - Y - Z coordinate system shown indicates that the X direction is the length direction of the recording medium, the Y direction is the width direction of the recording medium in the conveying path within the recording device, and the Z direction is the device height direction.

[0052] As an example, the recording device 10 is a line-type inkjet printer capable of high-speed and high-density printing. The recording device 10 includes a feeding unit 12 for storing a recording medium P such as paper, a conveying unit 14, a belt conveying unit 16, a recording unit 18, an Fd (face-down) discharging unit 20 as a "discharging unit", an Fd (face-down) placing unit 22 as a "placing unit", a reversing path unit 24 as a "reversing conveyance mechanism", an Fu (face-up) discharging unit 26, and an Fu (face-up) placing unit 28.

[0053] The feeding unit 12 is disposed at the lower part of the recording device 10. The feeding unit 12 includes a feeding tray 30 for storing the recording medium P and a feeding roller 32 for sending out the recording medium P stored in the feeding tray 30 to the conveyance path 11.

[0054] The recording medium P stored in the feeding tray 30 is fed by the feeding roller 32 along the conveyance path 11 to the conveying unit 14. The conveying unit 14 includes a conveying drive roller 34 and a conveying driven roller 36. The conveying drive roller 34 is rotationally driven by a drive source (not shown). In the conveying unit 14, the recording medium P is nipped between the conveying drive roller 34 and the conveying driven roller 36 and conveyed to the belt conveying unit 16 located on the downstream side of the conveyance path 11.

[0055] The belt conveying unit 16 includes a first roller 38 located on the upstream side in the conveyance path 11, a second roller 40 located on the downstream side, an endless belt 42 rotatably attached to the first roller 38 and the second roller 40, and a support 44 for supporting the upper section 42a of the endless belt 42 between the first roller 38 and the second roller 40.

[0056] The endless belt 42 is driven by the first roller 38 or the second roller 40 driven by a drive source (not shown) to move in the +X direction to the -X direction in the upper section 42a. For this reason, the recording medium P conveyed from the conveying unit 14 is further conveyed to the downstream side of the conveyance path 11 in the belt conveying unit 16.

[0057] The recording unit 18 includes a line-type inkjet head 48 and a head holder 46 that holds the inkjet head 48. Incidentally, the recording unit 18 may be of a serial type in which an inkjet head is provided on a carriage that reciprocates in the Y-axis direction. The inkjet head 48 is disposed so as to face an upper section 42a of an endless belt 42 supported by a support 44. When the recording medium P is conveyed in the upper section 42a of the endless belt 42, the inkjet head 48 discharges ink toward the recording medium P to perform recording. The recording medium P is conveyed to the downstream side of the conveyance path 11 by the belt conveyance unit 16 while recording is being performed.

[0058] Incidentally, a line-type inkjet head is a head used in a recording apparatus that is provided such that a region of nozzles formed in a direction intersecting the conveyance direction of the recording medium P can cover the entire intersecting direction of the recording medium P, and an image is formed by fixing one of the head or the recording medium P and moving the other. Incidentally, the region of nozzles in the intersecting direction of the line head does not necessarily have to cover the entire intersecting direction of all the recording media P with which the recording apparatus is compatible.

[0059] Also, a first branching unit 50 is provided on the downstream side of the conveyance path 11 of the belt conveyance unit 16. The first branching unit 50 is configured to be switchable between a conveyance path 11 that conveys the recording medium P to the Fd discharge unit 20 or the Fu discharge unit 26 and a reversing path 52 of a reversing path unit 24 that reverses the recording surface of the recording medium P and conveys the recording medium P to the recording unit 18 again. Incidentally, the recording medium P that is switched to the reversing path 52 by the first branching unit 50 and conveyed has its recording surface reversed during the conveyance process in the reversing path 52, and is conveyed again to the recording unit 18 such that the surface opposite to the first recording surface faces the inkjet head 48.

[0060] Further downstream of the first branching unit 50 along the conveyance path 11, a second branching unit 54 is provided. The second branching unit 54 is configured to be able to switch the conveyance direction of the recording medium P so as to convey the recording medium P toward the Fd discharge unit 20 or to convey the recording medium P toward the Fu discharge unit 26.

[0061] In the second branch portion 54, the recording medium P conveyed toward the Fd discharge portion 20 is discharged from the Fd discharge portion 20 and placed on the Fd placement portion 22. At this time, the recording surface of the recording medium P is placed so as to face the Fd placement portion 22. Further, the recording medium P conveyed toward the Fu discharge portion 26 in the second branch portion 54 is discharged from the Fu discharge portion 26 and placed on the Fu placement portion 28. At this time, the recording surface of the recording medium P is placed so as to face the side opposite to the Fu placement portion 28.

[0062] In an inkjet recording apparatus, since liquid ink is attached to a recording medium, problems such as curling occur in the recording medium, particularly in absorbent recording media such as plain paper and inkjet paper. On the other hand, in the present embodiment, by using silica particles, curling can be suppressed and the color developability of the obtained recording can be improved.

[0063] In the above description, an example in the case of using a line type inkjet head has been described. However, the recording apparatus according to the present embodiment may be a printer (serial printer) using a serial type inkjet head. In a serial printer, printing is performed by moving the inkjet head in a direction intersecting the conveyance direction while conveying the recording medium in the conveyance direction.

Example

[0064] Hereinafter, the present invention will be described more specifically using examples and comparative examples. The present invention is not limited by the following examples.

[0065] 1. Preparation of Ink The components were put into a mixture tank so as to have the composition shown in Table 1, mixed and stirred, and further filtered through a 5 μm membrane filter to obtain an inkjet ink composition for each example. Note that the numerical values of the components shown in each example in the table represent mass% unless otherwise specified. Also, in the table, the numerical value of the pigment represents the mass% of the solid content.

[0066]

Table 1

[0067] The abbreviations and product components used in Table 1 are as follows. 〔Pigment〕 Aqua-Black: Self-dispersible carbon black "Aqua-Black 162" (product name, manufactured by Tokai Carbon Co., Ltd.) 〔Silica particles〕 Colloidal silica A (manufactured by Nissan Chemical Industries, ST-CM, particle size 22 nm, solid content 30%, spherical) Colloidal silica B (manufactured by Nissan Chemical Industries, ST-OL, particle size 45 nm, solid content 20%, spherical) Colloidal silica C (manufactured by Nissan Chemical Industries, ST-OUP, primary particle size 12 nm, solid content 15%, chain-like) Colloidal silica D (manufactured by Fuso Chemical, PL-3, particle size 34 nm, solid content 19.5%, non-spherical) 〔Surfactant〕 Orfin E1010 (product name manufactured by Air Products, acetylene glycol-based surfactant) Surfynol 104 (product name manufactured by Nissin Chemical Industry Co., Ltd., acetylene glycol-based surfactant) 〔Water-soluble organic solvent〕 1-(2-Hydroxyethyl)-2-pyrrolidone 2-Pyrrolidone TEGmBE (triethylene glycol monobutyl ether) Glycerin 〔Betaines〕 Trimethylglycine (anhydrous betaine, manufactured by Tokyo Chemical Industry Co., Ltd.) 〔Alkali〕 Triethanolamine (manufactured by Tokyo Chemical Industry Co., Ltd.)

[0068] 1.1. Measurement methods for Di and Dc Using Tecnai G2 F30 (manufactured by FEI), TEM images of the dispersion of each silica particle were taken, and 20 silica particles were selected from the TEM images. When the contour of each selected silica particle was sandwiched between two circles, when the difference in the diameters of the outer circle and the inner circle was minimized, the outer circle was defined as the minimum circumscribed circle and the inner circle was defined as the maximum inscribed circle. Di / Dc was calculated from the average values of the diameters (Di) of the maximum inscribed circles and the diameters (Dc) of the minimum circumscribed circles of the 20 silica particles.

[0069] 2. Evaluation method 2.1. Curl evaluation The ink prepared as described above was filled into an EPSON printer PX-S840, and a Microsoft Word document (font size 11, standard, MSP Gothic) at a rate of 700 characters per page was printed on a recording medium (Xerox P paper of A4 size, copy paper manufactured by Fuji Xerox Co., Ltd., basis weight 64 g / m 2 , paper thickness 88 μm) under an environment of a temperature of 25°C and a humidity of 50%. After printing, it was placed face down on the floor, and the angle formed between the paper and the floor at the installation point and the edge of the paper was measured to evaluate the curl. 〔Evaluation criteria〕 A: Maximum curl angle less than 90° B: Maximum curl angle 90° or more and less than 100° C: Maximum curl angle 100° or more

[0070] 2.2. Color development The ink cartridge of an EPSON printer PX-S840 was filled with ink, and a solid pattern was printed on a recording medium (Xerox P paper of A4 size, copy paper manufactured by Fuji Xerox Co., Ltd., basis weight 64 g / m 2 , paper thickness 88 μm) under an environment of a temperature of 25°C and a humidity of 50% with a printing duty of 100% and an ink adhesion amount of 4.5 mg / inch 2 . Then, the OD value was measured using a colorimeter (manufactured by Xrite, Xrite i1), and the color development was evaluated according to the following evaluation criteria. 〔Evaluation criteria〕 A: OD value 1.3 or more B: OD value 1.2 or more and less than 1.3 C: OD value less than 1.2

[0071] 2.3. Viscosity The viscosity of the ink composition obtained as described above was measured under the conditions of a shear rate of 200 using a rheometer (MCR300 manufactured by Anton Paar) in an environment of a temperature of 20°C and a humidity of 50%. 〔Evaluation Criteria〕 A: Viscosity is 5.0 mPa·s or less B: Viscosity exceeds 5.0 mPa·s and is less than 7.0 mPa·s C: Viscosity exceeds 7.0 mPa·s

[0072] 2.4. Clogging Resistance The ink was filled into the ink cartridge of EPSON printer PX-S840, and a test chart issued by the Japanese Society for Imaging Science and Technology with an image coverage of 5% was continuously printed 5000 sheets on a recording medium (Xerox P paper of A4 size, copy paper manufactured by Fuji Xerox Co., Ltd., basis weight 64 g / m 2 、paper thickness 88 μm) in an environment of a temperature of 40°C and a humidity of 20%. Then, whether there are white streaks due to nozzle deviation or nozzle dropout and the number thereof were confirmed in the solid printed part after printing 5000 sheets, and the clogging resistance was evaluated according to the following evaluation criteria based on the number thereof. 〔Evaluation Criteria〕 A: Less than 3 B: 3 or more and less than 10 C: 10 or more

[0073] 3. Evaluation Results Table 1 shows the composition of the ink used in each example and the evaluation results. From Table 1, it was found that by using silica particles of a predetermined shape and 1-(2-hydroxyethyl)-2-pyrrolidone in combination, curling of the recorded matter can be suppressed, color development property is improved, and clogging and viscosity increase are suppressed.

Explanation of Signs

[0074] 10 Recording device, 11 Conveyor path, 12 Feeding unit, 14 Conveyor unit, 16 Belt conveyor unit, 18 Recording unit, 20 Fd discharge unit, 22 Fd placement unit, 24 Inversion path unit, 26 Fu discharge unit, 28 Fu placement unit, 30 Feeding tray, 32 Feeding roller, 34 Conveyor drive roller, 36 Conveyor driven roller, 38 First roller, 40 Second roller, 42 Endless belt, 42a Upper section of the endless belt, 44 Support, 46 Head holder, 48 Inkjet head, 50 First branch section, 52 Inversion path, 54 Second branch section, 56 Discharge roller pair, 64 Discharge drive roller, 68 Drive shaft, 76 Placement surface, 78 Convex portion, 80 First biasing member, 82 Second biasing member, 84, 86 Support shaft, P Recording medium

Claims

1. An inkjet ink composition (excluding those containing a polymerizable compound), comprising a coloring material, silica particles, 1-(2-hydroxyethyl)-2-pyrrolidone, and water, wherein Di (diameter of the maximum inscribed circle) / Dc (diameter of the minimum circumscribed circle) in the TEM image of the silica particles is 0.7 or more, and the content of the silica particles is 150 to 500 parts by mass with respect to 100 parts by mass of the 1-(2-hydroxyethyl)-2-pyrrolidone. An inkjet ink composition (excluding those containing a polymerizable compound).

2. The inkjet ink composition according to Claim 1, wherein the silica particles are colloidal silica. The inkjet ink composition according to Claim 1.

3. The inkjet ink composition according to Claim 1 or 2, wherein the average particle diameter of the silica particles is 10 to 80 nm. The inkjet ink composition according to Claim 1 or 2.

4. The inkjet ink composition according to any one of Claims 1 to 3, wherein the content of the silica particles is 1.0 to 15% by mass with respect to the total amount of the inkjet ink composition. The inkjet ink composition according to any one of Claims 1 to 3.

5. The inkjet ink composition according to any one of Claims 1 to 4, wherein the content of the water is 50 to 65% by mass with respect to the total amount of the inkjet ink composition. The inkjet ink composition according to any one of Claims 1 to 4.

6. The inkjet ink composition according to any one of Claims 1 to 5, wherein the content of the 1-(2-hydroxyethyl)-2-pyrrolidone is 0.5 to 10% by mass with respect to the total amount of the inkjet ink composition. The inkjet ink composition according to any one of Claims 1 to 5.

7. The inkjet ink composition according to any one of Claims 1 to 6, wherein the viscosity at 20°C is 7.0 mPa·s or less. The inkjet ink composition according to any one of Claims 1 to 6.

8. A recording method, comprising a discharging step of discharging the inkjet ink composition according to any one of Claims 1 to 7 onto a recording medium. A recording method.

9. The recording method according to Claim 8, wherein the recording medium is plain paper. The recording method according to Claim 8.

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