JP2020200402A - Ink, image forming method and image forming device - Google Patents

Abstract

To provide an ink that has a high image density even in commercial printing that prints at high speed of 0.8 m/sec or more on a recording medium.SOLUTION: Provided is an ink containing carbon black, water, a compound represented by the following general formula (1), and 2-ethyl-1,3-hexanediol, and in which, characterized, the content of the compound represented by the following general formula (1) is 0.5 mass% or more and 1.0 mass% or less for the total mass of the ink, and the content of 2-ethyl-1,3-hexanediol is 1.5 mass% or more and 2.5 mass% or less for the total mass of the ink. H2m+1Cm-(O-CH2-CH2)n-OH -- general formula (1). (In the general formula (1), m represents an integer of 12 to 15, and n represents an integer of 3 to 15).SELECTED DRAWING: Figure 1

Description

The present invention relates to inks, image forming methods and image forming devices.

The inkjet recording method is a method of recording characters and images by flying a small amount of ink droplets from a fine nozzle and attaching them to a recording medium such as paper, which is easy to use with low noise, a simple process, and colorization. Because of this, it is widely used as a home printer. In recent years, the inkjet recording method has been expanding as commercial printing because of its advantages such as high-speed printing. In commercial printing, in order to perform high-speed printing of 0.8 m / sec or more, a method of transporting a recording medium at high speed (hereinafter referred to as a line printer) is often adopted instead of fixing an inkjet head having a nozzle. In line printers, in order to print at a higher speed, a drying mechanism such as a hot air device or a hort plate that quickly dries the ink adhering to the recording medium is often used. When the ink has a drying mechanism, the drying by the drying mechanism starts immediately after the ink lands on the recording medium, so that the ink does not spread sufficiently on the recording medium and may not reach the target dot diameter. In order to increase the dot diameter, it is effective to reduce the contact angle between the ink and the recording medium, and a surfactant is added to increase the dot diameter. For example, Patent Document 1 discloses an inkjet recording ink containing a plurality of surfactants in plain paper in order to adjust the tot diameter and obtain excellent color development.

However, the ink containing a plurality of surfactants as described above has the following problems. That is, when a non-penetrating recording medium such as coated paper is used, the dots spread in the case of a single dot, but when they land so as to be continuously connected like a line, the line is drawn along the printing direction. As shown in the drawing, when the ink suitable landing after the ink droplet that landed first, the density difference from the ink droplet that landed later occurs due to the evaporation of water from the ink droplet that landed first, so the ink droplet that landed later Is sucked into the ink droplets that landed first, the filling rate occupied by the ink droplets becomes small, and white streaks may occur. As a result, the image density may decrease.

Therefore, an object of the present invention is to provide an ink having a high image density even in commercial printing in which high-speed printing of 0.8 m / sec or more is performed on a recording medium.

The above problem is solved by the following configuration 1).
An ink containing carbon black, water, a compound represented by the following general formula (1), and 2-ethyl-1,3-hexanediol, which is represented by the following general formula (1). The content of the compound is 0.5% by mass or more and 1.0% by mass or less with respect to the total mass of the ink, and the content of 2-ethyl-1,3-hexanediol is the total mass of the ink. On the other hand, an ink characterized by being 1.5% by mass or more and 2.5% by mass or less.
_{H 2m + 1 C m - (} O-CH 2 -CH 2) n -OH Formula (1)
(In the above general formula (1), m represents an integer of 12 to 15 and n represents an integer of 3 to 15.)

According to the present invention, it is possible to provide an ink having a high image density even in commercial printing in which high-speed printing of 0.8 m / sec or more is performed on a recording medium.

It is the schematic of an example of a recording device.

Hereinafter, an embodiment of the present invention will be described.

<< Ink >>
The ink of the present invention contains carbon black, water, a compound represented by the following general formula (1), and 2-ethyl-1,3-hexanediol, and is represented by the following general formula (1). The content of the compound to be added is 0.5% by mass or more and 1.0% by mass or less with respect to the total mass of the ink, and the content of 2-ethyl-1,3-hexanediol is the total content of the ink. It is characterized in that it is 1.5% by mass or more and 2.5% by mass or less with respect to the mass.
_{H 2m + 1 C m - (} O-CH 2 -CH 2) n -OH Formula (1)
(In the above general formula (1), m represents an integer of 12 to 15 and n represents an integer of 3 to 15.)

<Compound represented by the general formula (1)>
By containing the compound represented by the general formula (1), the ink of the present invention causes the ink dots to spread more on the recording medium after the ink is ejected as droplets and landed on the recording medium. Therefore, during the drying step after landing, the water content in the ink dots evaporates quickly, so that beading in the ink dots can be suppressed.

The compound represented by the general formula (1) is preferably a compound represented by the following structural formula (1) from the viewpoint of improving the effect of the present invention.

The compound represented by the general formula (1) is preferably n = 5 to 7 in the structural formula (1) from the viewpoint of improving the effect of the present invention.

A commercially available product may be used as the compound represented by the general formula (1). Examples of this commercially available product include TRITON (TM) HW-1000, TMN-3, TMN-6, TMN-100X, TMN-10 (all manufactured by Dow Chemical Co., Ltd.), and among these, TRITON. (TM) HW-1000 and TMN-6 (all manufactured by Dow Chemical Co., Ltd.) are particularly preferable.

TRITON (TM) HW-1000 is a compound having n = 6 in the structural formula (1), and TMN-6 is a compound having n = 7 in the structural formula (1).

The compound represented by the general formula (1) is preferably contained in an amount of 0.5% by mass or more and 1.0% by mass or less with respect to the total mass of the ink. When the compound represented by the general formula (1) is less than 0.5% by mass with respect to the total amount of ink, the dots do not spread after the ink lands on the recording medium, the dot diameter becomes small, and the target image It is difficult to obtain the concentration. On the other hand, when the compound represented by the general formula (1) is contained in an amount of more than 1.0% by mass with respect to the total amount of ink, the surface tension becomes low, and after ejection from a means for ejecting ink such as an inkjet head, the nozzle Since it takes a long time for the ink overflowing from the nozzle to return to the inside of the nozzle, there is a risk that ejection bending will occur frequently.

<Penetrating agent>
The ink of the present invention contains 2-ethyl-1,3-hexanediol as a penetrant. After the ink has landed on the recording medium, the penetrant promotes penetration into the recording medium, the ink on the recording medium becomes thickened, and the fluidity quickly disappears.

The penetrant in the ink is preferably contained in an amount of 1.5% by mass or more and 2.5% by mass or less, more preferably 1.5% by mass or more and 2.0% by mass or less, based on the total mass of the ink. .. If the penetrant is less than 1.5% by mass with respect to the total mass of the ink, the dots landing on the recording medium have a relatively low viscosity and fluidity until the dots land on the recording medium, so that the ink landing later is pulled. There is a risk that white streaks will occur. On the other hand, if the penetrant is contained in an amount of more than 2.5% by mass with respect to the total amount of the ink, satellites are likely to be generated, and the resolution of the printed matter may be lowered.

<Carbon black>
Examples of carbon black include furnace black, lamp black, acetylene black, and channel black.

In order to disperse carbon black in ink, a method of introducing a hydrophilic functional group into the carbon black to obtain a self-dispersing carbon black, a method of coating the surface of the carbon black with a resin and dispersing it, and a dispersant are used. And the method of dispersing.
As a method of introducing a hydrophilic functional group into carbon black to self-disperse the carbon black, for example, when a functional group such as a sulfone group or a carboxyl group is added to the carbon black, it is dispersed in water.
As a method of coating the surface of carbon black with a resin and dispersing it, a method in which carbon black is encapsulated in microcapsules and can be dispersed in water can be used. This can be rephrased as resin-coated carbon black. In this case, it is not necessary that all the carbon black blended in the ink is coated with the resin, and the uncoated carbon black or the partially coated carbon black is contained in the ink as long as the effect of the present invention is not impaired. May be dispersed in.
Examples of the method of dispersing using a dispersant include a method of dispersing using a known low-molecular-weight dispersant and high-molecular-weight dispersant represented by a surfactant. As the dispersant, for example, an anionic surfactant, a cationic surfactant, an amphoteric surfactant, a nonionic surfactant, or the like can be used depending on the carbon black.
RT-100 (nonionic surfactant) manufactured by Takemoto Resin Co., Ltd. and a naphthalene sulfonate Na formalin condensate can also be used as a dispersant in a good drop.
The dispersant may be used alone or in combination of two or more.

The content of carbon black in the ink of the present invention is not particularly limited and can be appropriately selected according to the intended purpose, but it enhances good image density, improves fixability in gray scale, and is good. From the viewpoint of obtaining excellent ejection stability, 0.34% by mass or more and 5.1% by mass or less is preferable, and 0.34% by mass or more and 4.3% by mass or less is more preferable with respect to the total mass of the ink.

<Carbon black dispersion>
It is possible to obtain ink by mixing a material such as water or an organic solvent with carbon black. It is also possible to produce an ink by mixing a material such as water or an organic solvent with a carbon black dispersion obtained by mixing carbon black and other water or a dispersant.

<Organic solvent>
The organic solvent used in the present invention is not particularly limited, and a water-soluble organic solvent can be used. Examples thereof include ethers such as polyhydric alcohols, polyhydric alcohol alkyl ethers and polyhydric alcohol aryl ethers, nitrogen-containing heterocyclic compounds, amides, amines and sulfurized compounds.
Specific examples of the water-soluble organic solvent include, for example, ethylene glycol, diethylene glycol, 1,2-propanediol, 1,4-butanediol, 2,3-butanediol, 3-methyl-1,3-butanediol, 1 , 2-Pentanediol, 1,3-Pentanediol, 1,4-Pentanediol, 2,4-Pentanediol, 1,5-Pentanediol, 1,5-Hexanediol, Glycerin, 1,2,6-hexane Polyhydric alcohols such as triol, ethyl-1,2,4-butanetriol, 1,2,3-butanetriol, 2,2,4-trimethyl-1,3-pentanediol, petriol, ethylene glycol monoethyl Polyhydric alcohol alkyl ethers such as ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, tetraethylene glycol monomethyl ether, propylene glycol monoethyl ether, ethylene glycol monophenyl ether, ethylene glycol monobenzyl Polyhydric alcohol aryl ethers such as ethers, 2-pyrrolidone, N-methyl-2-pyrrolidone, N-hydroxyethyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone, ε-caprolactam, γ-butyrolactone Nitrogen-containing heterocyclic compounds such as, formamide, N-methylformamide, N, N-dimethylformamide, 3-methoxy-N, N-dimethylpropionamide, 3-butoxy-N, N-dimethylpropionamide and other amides, Examples thereof include amines such as monoethanolamine, diethanolamine and triethylamine, sulfur-containing compounds such as dimethylsulfoxide, sulfolane and thiodiethanol, propylene carbonate and ethylene carbonate. It is preferable to use an organic solvent having a boiling point of 250 ° C. or lower because it not only functions as a wetting agent but also has good drying properties.

Polyol compounds having 8 or more carbon atoms and glycol ether compounds are also preferably used. Specific examples of the polyol compound having 8 or more carbon atoms include 2,2,4-trimethyl-1,3-pentanediol.
Specific examples of the glycol ether compound include polyvalent alcohol alkyls such as ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, tetraethylene glycol monomethyl ether, and propylene glycol monoethyl ether. Ethers: Polyhydric alcohol aryl ethers such as ethylene glycol monophenyl ether and ethylene glycol monobenzyl ether can be mentioned.

The polyol compound having 8 or more carbon atoms and the glycol ether compound can improve the permeability of the ink when paper is used as the recording medium.

The content of the organic solvent in the ink is not particularly limited and can be appropriately selected depending on the intended purpose, but from the viewpoint of ink drying property and ejection reliability, it is preferably 10% by mass or more and 60% by mass or less. , 20% by mass or more and 60% by mass or less is more preferable.

<Water>
The content of water in the ink is not particularly limited and can be appropriately selected depending on the intended purpose, but from the viewpoint of ink drying property and ejection reliability, 10% by mass 90% by mass or less is preferable, and 20% by mass is preferable. % Or more and 60% by mass or less are more preferable.

<Additives>
If necessary, an antifoaming agent, an antiseptic antifungal agent, a rust preventive agent, a pH adjuster and the like may be added to the ink.

<Defoamer>
The defoaming agent is not particularly limited, and examples thereof include a silicone-based defoaming agent, a polyether-based defoaming agent, and a fatty acid ester-based defoaming agent. These may be used alone or in combination of two or more. Among these, a silicone-based defoaming agent is preferable because it has an excellent defoaming effect.

<Preservatives and fungicides>
The antiseptic and antifungal agent is not particularly limited, and examples thereof include 1,2-benzisothiazolin-3-one.

<Rust inhibitor>
The rust preventive is not particularly limited, and examples thereof include acidic sulfites and sodium thiosulfate.

<pH adjuster>
The pH adjusting agent is not particularly limited as long as the pH can be adjusted to 7 or more, and examples thereof include amines such as diethanolamine and triethanolamine.

The physical properties of the ink are not particularly limited and can be appropriately selected depending on the intended purpose. For example, the viscosity, surface tension, pH and the like are preferably in the following ranges.
The viscosity of the ink at 25 ° C. is preferably 5 mPa · s or more and 30 mPa · s or less, preferably 5 mPa · s or more and 20 mPa · s or less, from the viewpoint of improving the print density and character quality and obtaining good ejection properties. More preferred. Here, for the viscosity, for example, a rotary viscometer (RE-80L manufactured by Toki Sangyo Co., Ltd.) can be used. As the measurement conditions, it is possible to measure at 25 ° C. with a standard cone rotor (1 ° 34'x R24), a sample liquid volume of 1.2 mL, a rotation speed of 50 rpm, and 3 minutes.
The surface tension of the ink is preferably 35 mN / m or less, more preferably 32 mN / m or less at 25 ° C. from the viewpoint that the ink is preferably leveled on the recording medium and the drying time of the ink is shortened.
The pH of the ink is preferably 7 to 12, more preferably 8 to 11, from the viewpoint of preventing corrosion of the metal member in contact with the liquid.

The particle size of the solid content in the ink is not particularly limited, and can be appropriately selected according to the purpose. From the viewpoint of improving image quality such as ejection stability and image density, the maximum frequency of the particle size of the solid content in the ink is preferably 20 nm or more and 1,000 nm or less, and more preferably 20 nm or more and 150 nm or less in terms of the maximum number. The solid content includes resin particles and carbon black. The particle size can be measured using a particle size analyzer (Nanotrack Wave-UT151, manufactured by Microtrac Bell Co., Ltd.).

<Resin>
The type of resin contained in the ink is not particularly limited and can be appropriately selected according to the purpose. For example, urethane resin, polyester resin, acrylic resin, vinyl acetate meter resin, styrene resin, butadiene. Examples thereof include based resins, styrene-butadiene resins, vinyl chloride resins, acrylic styrene resins, and acrylic silicone resins.
Resin particles made of these resins may be used. It is possible to obtain ink by mixing resin particles with a material such as a coloring material or an organic solvent in the state of a resin emulsion in which water is dispersed as a dispersion medium. As the resin particles, those that have been properly synthesized may be used, or commercially available products may be used. Further, these may be used alone or in combination of two or more kinds of resin particles.

The volume average particle diameter of the resin particles is not particularly limited and can be appropriately selected depending on the intended purpose, but is preferably 10 nm or more and 1,000 nm or less from the viewpoint of obtaining good fixability and high image hardness. It is more preferably 10 nm or more and 200 nm or less, and particularly preferably 10 nm or more and 100 nm or less.
The volume average particle size can be measured using, for example, a particle size analyzer (Nanotrack Wave-UT151, manufactured by Microtrac Bell Co., Ltd.).

The content of the resin is not particularly limited and can be appropriately selected according to the purpose, but from the viewpoint of fixability and storage stability of the ink, 1% by mass or more and 30% by mass with respect to the total amount of the ink. The following is preferable, and 5% by mass or more and 20% by mass or less is more preferable.

<Recording medium>
The recording medium can be used without particular limitation, and examples thereof include plain paper, glossy paper, and special paper.

<Recorded material>
The ink recording material of the present invention has an image formed by using the ink of the present invention on a recording medium.
It can be recorded by an inkjet recording device and an inkjet recording method to obtain a recorded material.

<Ink container>
The ink container of the present invention comprises an ink containing portion containing the ink of the present invention, and further comprises other members appropriately selected as necessary.
The ink container is not particularly limited, and its shape, structure, size, material, etc. can be appropriately selected according to the purpose. For example, an ink container formed of an aluminum laminate film, a resin film, or the like. Such as, for example, a main tank having an ink accommodating portion, a main cartridge, and the like are preferably mentioned.

<< Image formation method >>
The image forming method of the present invention includes an ink ejection step of ejecting the ink of the present invention onto a recording medium. In a preferred embodiment, the image forming method of the present invention ejects ink in order to suppress the occurrence of beading and / or the drying step of drying the ink of the present invention ejected onto the recording medium after the ink ejection step. Before the step, there is a pretreatment step of applying the pretreatment liquid to the recording medium.

<Pretreatment liquid>
The pretreatment liquid contains a coagulant, an organic solvent, and water, and may contain a surfactant, an antifoaming agent, a pH adjuster, an antiseptic / antifungal agent, an anticorrosive agent, and the like, if necessary.
As the organic solvent, surfactant, defoaming agent, pH adjuster, antiseptic / antifungal agent, and rust preventive, the same materials as those used for ink can be used, and other materials used for known treatment liquids can be used. ..
The type of flocculant is not particularly limited, and examples thereof include water-soluble cationic polymers, acids, and polyvalent metal salts.

<Ink ejection process>
Examples of the method of ejecting ink to a recording medium include an inkjet method, a blade coating method, a gravure coating method, a bar coating method, a roll coating method, a dip coating method, a curtain coating method, a slide coating method, a die coating method, and a spray coating method. However, the inkjet method is preferable.

<Drying process>
In the drying step of drying the ink of the present invention ejected onto the recording medium after the ink ejection step, a warm air device that directly blows high-temperature air to the surface on which the ink of the recording medium is ejected and the ink of the recording medium are used. An example is a heating device that applies heat to the opposite surface. It is preferable that air of 100 ° C. or higher and 140 ° C. or lower is applied at 20 m / sec from the warm air device, and heat of 100 ° C. or higher and 120 ° C. or lower is preferably applied from the heating device. It is more preferable to have both a hot air device and a heating device at the same time.

<Recording device, recording method>
The ink of the present invention can be suitably used for various recording devices by an inkjet recording method, for example, a printer, a facsimile device, a copying device, a printer / fax / copier multifunction device, a three-dimensional modeling device, and the like.
In the present invention, the recording device and the recording method are devices capable of ejecting ink, various processing liquids, and the like to a recording medium, and a method of recording using the device. The recording medium means a medium to which ink and various treatment liquids can adhere even temporarily.
This recording device can include not only a head portion that ejects ink, but also means related to feeding, transporting, and discharging paper of a recording medium, and other devices called pretreatment devices and posttreatment devices. ..
The recording device and recording method may include a heating means used in the heating step and a drying means used in the drying step. The heating means and the drying means include, for example, means for heating and drying the print surface and the back surface of the recording medium. The heating means and the drying means are not particularly limited, but for example, a hot air heater and an infrared heater can be used. Heating and drying can be performed before printing, during printing, after printing, and the like.
Further, the recording device and the recording method are not limited to those in which significant images such as characters and figures are visualized by ink. For example, those that form patterns such as geometric patterns and those that form a three-dimensional image are also included.
Further, the recording device includes both a serial type device that moves the discharge head and a line type device that does not move the discharge head, unless otherwise specified.
Further, as this recording device, not only a desktop type but also a wide recording device capable of printing on an A0 size recording medium, or, for example, continuous paper wound in a roll shape can be used as a recording medium. A continuous line printer is also included.

An example of the recording device will be described with reference to FIG. FIG. 1 is a schematic view of the device. The recording device includes an inkjet head 2 that ejects ink 3 to a recording medium 1, a warm air device 4 and a heating roller 7 for drying the ink 3 on the recording medium 1, and a pretreatment liquid in a pretreatment liquid container 14. It is composed of a coating device 9 including coating rollers 10, 11 and 12 for coating 13 on the recording medium 1, and transport rollers 5, 6, 8, 15, 16 and 17 for transporting the recording medium 1. There is. Here, since the coating device 9 is removable as needed, it is not necessary to mount the coating device 9.

In addition, image formation, recording, printing, printing, etc. in the terms of the present invention are all synonymous.

Hereinafter, the present invention will be further described with reference to Examples and Comparative Examples, but the present invention is not limited to these examples.

<Preparation of carbon black dispersion>
62.0 g (525 mmol) of 1,6-hexanediol (manufactured by Tokyo Chemical Industry Co., Ltd.) was dissolved in 700 mL of methylene chloride, and 20.7 g (262 mmol) of pyridine was added. A solution prepared by dissolving 50.0 g (262 mmol) of 2-naphthalenecarbonyl chloride (manufactured by Tokyo Chemical Industry Co., Ltd.) in 100 mL of methylene chloride was added dropwise to this solution with stirring over 2 hours, and then at room temperature for 6 hours. Stirred. After washing the obtained reaction solution with water, the organic phase was isolated, dried over magnesium sulfate, and the solvent was distilled off. The residue was purified by silica gel column chromatography using a mixed solvent of methylene chloride / methanol (volume ratio 98/2) as an eluent to obtain 52.5 g of 2-naphthoic acid-2-hydroxyethyl ester. Next, 42.1 g (155 mmol) of 2-naphthoic acid-2-hydroxyethyl ester was dissolved in dry methyl ethyl ketone and heated to 60 ° C. A solution prepared by dissolving 24.0 g (155 mmol) of 2-methacryloyloxyethyl isocyanate (Carens MOI, manufactured by Showa Denko KK) in 20 mL of dry methyl ethyl ketone was added dropwise to the solution with stirring over 1 hour. The mixture was stirred at 70 ° C. for 12 hours. After cooling to room temperature, the solvent was distilled off. The residue is purified by silica gel column chromatography using a mixed solvent of methylene chloride / methanol (volume ratio 99/1) as an eluent, and has a structure represented by the following structural formula (2) of 57.0 g. Monomer M-1 was obtained.

Then, 1.20 g (16.7 mmol) of acrylic acid (manufactured by Sigma-Aldrich Japan LLC) and 7.12 g (16.7 mmol) of monomer M-1 were dissolved in 40 ml of dry methyl ethyl ketone to prepare a monomer solution. After heating 10% of the monomer solution to 75 ° C. under an argon stream, 0.273 g (1.67 mmol) of 2,2'-azoiso (butyronitrile) (manufactured by Tokyo Chemical Industry Co., Ltd.) is dissolved in the remaining monomer solution. The solution was added dropwise over 1.5 hours and stirred at 75 ° C. for 6 hours. The mixture was cooled to room temperature, and the obtained reaction solution was dropped onto hexane. The precipitated copolymer was filtered off and dried under reduced pressure to obtain 8.13 g of the copolymer (weight average molecular weight (Mw): 9200, number average molecular weight (Mn): 3100).

Next, 2.00 g of the obtained copolymer was dissolved in an aqueous solution of tetraethylammonium hydroxide so that the concentration of the copolymer was 2.38% and the pH was 8.0, and the copolymer was prepared. An aqueous solution was prepared.
16.0 parts of carbon black (NIPEX150, manufactured by Degussa) was added to 84.0 parts of the prepared aqueous solution of the copolymer, and the mixture was stirred for 12 hours. The obtained mixture was circulated and dispersed at a peripheral speed of 10 m / s for 1 hour using a disk-type bead mill (manufactured by Simmal Enterprises, KDL type, media: using zirconia balls having a diameter of 0.1 mm), and then the pore diameter was 1. The mixture was filtered through a 2 μm membrane filter, and an adjusted amount of ion-exchanged water was added to obtain 95.0 parts of a pigment dispersion (pigment solid content concentration: 16%).

<Examples 1 to 6, Comparative Examples 1 to 6>
The materials of the formulations shown in Table 1 were mixed and stirred, and then filtered through a 1.5 μm polypropylene filter to prepare the inks of Examples 1 to 6 and Comparative Examples 1 to 6. The types of carbon black used for each ink, the compound represented by the general formula (1), the penetrant, the organic solvent, the resin, and the like, and the blending ratios thereof are shown in Examples and Comparative Examples of Table 1. That's right. The numerical value of the addition amount shown in Table 1 is "mass%".

In Table 1, the product names of the ingredients and the names of the manufacturing companies are as follows.
・ Superflex 420 (Daiichi Kogyo Seiyaku Co., Ltd.)
・ ACRYCOTE AF-7800 (APEC Co., Ltd.)

[Dot diameter]
The ink dot diameters landed on the recording medium in the inks 1 to 12 produced in Examples 1 to 6 and Comparative Examples 1 to 6 were evaluated. The above-produced ink is filled in an inkjet head (device name: MH5220, manufactured by Ricoh Co., Ltd.), and the ink is adjusted so that the ejection speed is 7 m / sec, the drive frequency is 2 kHz, and the appropriate volume is 2.5 pL. Printing was performed on a recording medium of Lumi Art Gloss 130 g / m ² (coated paper, manufactured by Stora Enso) attached to a drum rotating at 3 rpm with a diameter of 10 cm 1 mm below the inkjet head. The dot diameter of the ink landed on the recording medium was measured using a digital microscope (device name: VHX-1000, manufactured by KEYENCE CORPORATION) and evaluated based on the following evaluation criteria. The results are shown in Table 2. A case where the evaluation was B or higher was evaluated as practically preferable.
(Evaluation criteria)
A: 40 μm or more B: 35 μm or more and less than 40 μm C: 30 μm or more and less than 35 μm D: less than 30 μm

[Discharge bend]
Ink ejection bending was evaluated using the inks prepared in Examples 1 to 6 and Comparative Examples 1 to 6. The ink produced above is filled in an inkjet head (device name: MH5220, manufactured by Ricoh Co., Ltd.), and the ink is adjusted to have an ejection speed of 7 m / sec, a drive frequency of 2 kHz, and 2.5 pL per drop, and continuously ejected for 30 minutes. After stopping for 5 minutes, the bending angle was observed from the flying ink droplets when the ink was re-discharged. In addition, the flight behavior of ink droplets was observed using an observation device (device name: EV1000, manufactured by Ricoh Co., Ltd.) and evaluated based on the following evaluation criteria. The results are shown in Table 3. A case where the evaluation was B or higher was evaluated as practically preferable.
(Evaluation criteria)
A: 5 mrad or less B: 5 mrad excess 10 mrad or less C: 10 mrad excess

[Image filling rate]
Using the inks produced in Examples 1 to 6 and Comparative Examples 1 to 6, a 6 cm square solid image was printed on a Lumi Art Magnification 130 g / m ² using a printer (model name: VC60,000, manufactured by Ricoh Co., Ltd.). In the printed image, the image filling rate was determined using an image magnified at 200 magnification of a digital microscope (device name: VHX-1000, manufactured by KEYENCE CORPORATION). The filling rate was obtained by binarizing the original image using ImageJ, an image processing program. The results are shown in Table 4. A case where the evaluation is B or more is evaluated as practically preferable.
(Evaluation criteria)
A: 98% or more B: 95% or more and less than 98% C: 90% or more and less than 95% D: less than 90%

<Image density>
Using the inks prepared in Examples 1 to 6 and Comparative Examples 1 to 6, a printer (model name: VC60,000, manufactured by Ricoh Co., Ltd.) was used on Lumi Art Gross 130 g / m ² , and the printing speed was 0.83 m / sec. The image density was measured with a reflection type color spectroscopic measurement densitometer (manufactured by X-Rite Co., Ltd.) in a 100-duty-printed 6 cm square solid image, and evaluated based on the following evaluation criteria. The results are shown in Table 5. A case where the evaluation was B or higher was evaluated as practically preferable.
(Evaluation criteria)
A: 1.90 or more B: 1.80 or more and less than 1.90 C: less than 1.80

From the results in each table, it was found that the ink of each example has high image density and high resolution even in commercial printing in which high-speed printing of 0.8 m / sec or more is performed on a recording medium.

1 Recording medium 2 Ink head 3 Ink 4 Hot air device 5, 6, 8, 15, 16, 17 Conveying roller 7 Heating roller 9 Coating device 10, 11, 12 Coating roller 13 Pretreatment liquid 14 Pretreatment container

JP-A-2010-163533

Claims (7)

An ink containing carbon black, water, a compound represented by the following general formula (1), and 2-ethyl-1,3-hexanediol, which is represented by the following general formula (1). The content of the compound is 0.5% by mass or more and 1.0% by mass or less with respect to the total mass of the ink, and the content of 2-ethyl-1,3-hexanediol is the total mass of the ink. On the other hand, an ink characterized by being 1.5% by mass or more and 2.5% by mass or less.
_{H 2m + 1 C m - (} O-CH 2 -CH 2) n -OH Formula (1)
(In the above general formula (1), m represents an integer of 12 to 15 and n represents an integer of 3 to 15.) The ink according to claim 1, wherein the compound represented by the general formula (1) is a compound represented by the following structural formula (1).
The ink according to claim 1 or 2, wherein n is 5 to 7. An image forming method comprising an ink ejection step of ejecting any of the inks of claims 1 to 3 onto a recording medium. The image forming method according to claim 4, further comprising a drying step of drying the ink ejected onto the recording medium after the ink ejection step. The image forming method according to claim 4 or 5, further comprising a pretreatment step of applying a pretreatment liquid to the recording medium before the ink ejection step. The ink according to any one of claims 1 to 3 and
An image forming apparatus having means for ejecting the ink.