JP2023144607A - Inkjet ink, inkjet recording device and inkjet recording method - Google Patents

Abstract

To provide an inkjet ink capable forming an image having less bleeding and unevenness on a low absorbing recording medium and a non-absorbing recording medium.SOLUTION: There is provided an inkjet ink which contains a pigment and an aqueous medium. The aqueous medium contains a first glycol ether and a second glycol ether. The first glycol ether has a boiling point of 100°C or more and 150°C or less. The second glycol ether has a boiling point of more than 150°C and 300°C or less. The total percentage content of the first glycol ether and the second glycol ether is 5 mass% or more and 24 mass% or less based on the mass of the ink. The mass ratio of the first glycol ether is 0.3 or more and 3 or less based on the mass of the second glycol ether.SELECTED DRAWING: Figure 1

Description

The present invention relates to an inkjet ink, an inkjet recording device, and an inkjet recording method.

For printing labels and packages, low-absorbency recording media that absorb less water and non-absorbent recording media that do not absorb water are sometimes used. Inkjet recording methods that can form images with less unevenness on low-absorption recording media and non-absorption recording media are being studied. For example, in the inkjet recording method described in Patent Document 1, three or more types of water-based inks having different static surface tensions are used, and the water-based inks having the highest static surface tension are ejected onto the recording medium in order. In this inkjet recording method, the recording medium is heated, for example, by an under heater provided on a surface facing the recording head and on the back side of the surface of the recording medium.

Japanese Patent Application Publication No. 2020-175663

However, the inkjet recording method described in Patent Document 1 has room for improvement in terms of forming images with less bleeding and unevenness on low-absorption recording media and non-absorption recording media.

The present invention has been made in view of the above problems, and its purpose is to provide an inkjet ink that can form images with less bleeding and unevenness on low-absorption recording media and non-absorption recording media. be. Another object of the present invention is to provide an inkjet recording apparatus and an inkjet recording method that can form images with less bleeding and unevenness on low-absorption recording media and non-absorption recording media.

The inkjet ink according to the present invention is an ink containing a pigment and an aqueous medium. The aqueous medium includes a first glycol ether and a second glycol ether. The boiling point of the first glycol ether is 100°C or more and 150°C or less. The boiling point of the second glycol ether is higher than 150°C and lower than 300°C. The total content of the first glycol ether and the second glycol ether with respect to the mass of the ink is 5% by mass or more and 24% by mass or less. The mass ratio of the first glycol ether to the mass of the second glycol ether is 0.3 or more and 3 or less.

An inkjet recording apparatus according to the present invention includes a recording head, a first heating section, and a second heating section. The recording head discharges ink onto a recording medium. The first heating section is provided upstream of the recording head in the conveying direction of the recording medium, and heats the recording medium to a first temperature. The second heating section is provided downstream of the recording head in the conveyance direction of the recording medium, and heats the recording medium to a second temperature. The second temperature is higher than the first temperature. The ink contains a pigment and an aqueous medium. The aqueous medium includes a first glycol ether and a second glycol ether. The boiling point of the first glycol ether is 100°C or more and 150°C or less. The boiling point of the second glycol ether is higher than 150°C and lower than 300°C. The total content of the first glycol ether and the second glycol ether with respect to the mass of the ink is 5% by mass or more and 24% by mass or less. The mass ratio of the first glycol ether to the mass of the second glycol ether is 0.3 or more and 3 or less.

The inkjet recording method according to the present invention includes a first heating step of first heating a recording medium to a first temperature, a discharging step of discharging ink from a recording head onto the first heated recording medium, and a discharging step of discharging ink from a recording head onto the first heated recording medium. and a second heating step of heating the ejected recording medium to a second temperature. The second temperature is higher than the first temperature. The ink contains a pigment and an aqueous medium. The aqueous medium includes a first glycol ether and a second glycol ether. The boiling point of the first glycol ether is 100°C or more and 150°C or less. The boiling point of the second glycol ether is higher than 150°C and lower than 300°C. The total content of the first glycol ether and the second glycol ether with respect to the mass of the ink is 5% by mass or more and 24% by mass or less. The mass ratio of the first glycol ether to the mass of the second glycol ether is 0.3 or more and 3 or less.

The inkjet ink according to the present invention can form images with less bleeding and unevenness on low-absorption recording media and non-absorption recording media. Further, the inkjet recording apparatus and inkjet recording method according to the present invention can form images with less bleeding and unevenness on low-absorption recording media and non-absorption recording media.

FIG. 3 is a diagram showing an example of an inkjet recording apparatus according to a second embodiment of the present invention. It is a micrograph showing an example of an image without unevenness. It is a micrograph showing an example of an image in which unevenness has occurred.

First, the terms described in this specification will be explained. Unless otherwise specified, the cumulative 50% value (D ₅₀ ) in the volume-based particle size distribution of particles is determined using a laser diffraction/scattering particle size distribution analyzer (“LA-950” manufactured by Horiba, Ltd.). This is the measured median diameter. The surface tension of the ink is measured by the Wilhelmy method (plate method) at a temperature of 25°C using a surface tension meter ("Automatic Surface Tensiometer DY-300" manufactured by Kyowa Kaimen Kagaku Co., Ltd.), unless otherwise specified. This is the value measured based on Each component described in this specification may be used alone or in combination of two or more. The terms described in this specification have been explained above.

[First embodiment: inkjet ink]
The inkjet ink (hereinafter, sometimes simply referred to as "ink") of the first embodiment of the present invention will be described below. The ink of the first embodiment contains a pigment and an aqueous medium. The aqueous medium includes a first glycol ether and a second glycol ether. The boiling point of the first glycol ether is 100°C or more and 150°C or less. The boiling point of the second glycol ether is higher than 150°C and lower than or equal to 300°C. The total content of the first glycol ether and the second glycol ether with respect to the mass of the ink is 5% by mass or more and 24% by mass or less. The mass ratio of the first glycol ether to the mass of the second glycol ether is 0.3 or more and 3 or less.

Hereinafter, the "first glycol ether" may be referred to as "low boiling point glycol ether." "Second glycol ether" may be described as "high boiling point glycol ether." "The total content of the first glycol ether and the second glycol ether relative to the mass of the ink" may be referred to as "GE content". "The mass ratio of the first glycol ether to the mass of the second glycol ether" may be described as "low GE/high GE ratio."

The ink of the first embodiment can form images with less bleeding and unevenness on low-absorption recording media and non-absorption recording media. The reason is inferred as follows. Hereinafter, an inkjet recording apparatus that performs preheating and main drying and includes a plurality of recording heads will be described as an example. Note that details of the inkjet recording apparatus will be described later in the second embodiment. Further, "a low-absorption recording medium and a non-absorption recording medium" may be referred to as a "predetermined recording medium".

The ink of the first embodiment contains glycol ethers, such as low-boiling glycol ethers and high-boiling glycol ethers. Since glycol ether has relatively high hydrophobicity, ink containing glycol ether has appropriate hydrophobicity. Therefore, the ink ejected from the recording head suitably wets and spreads on a predetermined highly hydrophobic recording medium, making it possible to form an image with less bleeding.

Furthermore, the GE content of the ink of the first embodiment is 5% by mass or more and 24% by mass or less. When the GE content is 5% by mass or more, appropriate hydrophobicity is imparted to the ink. As a result, the ink uniformly wets and spreads on the predetermined recording medium, making it possible to form an image with less unevenness. On the other hand, when the GE content is 24% by mass or less, the ink on the predetermined recording medium is sufficiently dried by preheating and main drying. As a result, an image with less blur can be formed.

Further, the ink of the first embodiment contains a low boiling point glycol ether and a high boiling point glycol ether as the glycol ether. When the ink is ejected onto a preheated predetermined recording medium, at least a portion of the low boiling point glycol ether contained in the ink evaporates. Evaporation of the low boiling glycol ether reduces the amount of aqueous medium in the ink. For example, after the amount of the aqueous medium in the first color ink is reduced, the second color ink is ejected onto the first color ink. Therefore, it is possible to prevent the first color ink and the second color ink from bleeding into each other and causing color mixing. As a result, an image with less blur can be formed.

Here, the glycol ether, for example, makes the pigment and non-coloring component (more specifically, pigment dispersion resin, binder resin, etc.) contained in the ink compatible. Even when ink is ejected onto a preheated predetermined recording medium, the high boiling point glycol ether contained in the ink is difficult to evaporate. Therefore, the amount of glyco-el ether in the ink does not decrease too much, the compatibility between the pigment and the non-coloring component is maintained, and separation is suppressed. As a result, an image with less unevenness can be formed. Note that the high boiling point glycol ether in the ink evaporates during the main drying after preheating.

Furthermore, the low GE/high GE ratio of the ink of the first embodiment is 0.3 or more. When the low GE/high GE ratio is 0.3 or more, the amount of low boiling point glycol ether in the ink is not too small. Therefore, when the ink is ejected onto a preheated predetermined recording medium, the low boiling point glycol ether contained in the ink evaporates, and the aqueous medium in the ink is appropriately reduced. As a result, an image with less blur can be formed.

Furthermore, the low GE/high GE ratio of the ink of the first embodiment is 3 or less. When the low GE/high GE ratio is 3 or less, there is not too much low boiling point glycol ether in the ink. Therefore, when the ink is ejected onto a preheated predetermined recording medium, the amount of glycol ether in the ink does not decrease too much, and separation of the pigment and non-colored components is suppressed. As a result, an image with less unevenness can be formed.

The reason why the ink of the first embodiment can form an image with less bleeding and unevenness on a predetermined recording medium has been explained above. Since it has such advantages, the ink of the first embodiment can be suitably used for printing on a predetermined recording medium. Note that when two or more kinds of inks of the first embodiment are used, the surface tensions of the two or more kinds of inks may have the same value or different values. The ink of the first embodiment will be further explained below.

<Aqueous medium>
The aqueous medium contained in the ink is, for example, a medium containing water. The aqueous medium may function as a solvent or a dispersion medium. Aqueous media include glycol ethers in addition to water. The water-soluble organic solvent may further contain a water-soluble organic solvent other than glycol ether (hereinafter sometimes referred to as "other water-soluble organic solvent"), if necessary.

(Glycol ether)
Examples of glycol ethers include monoalkylene glycol ethers, dialkylene glycol ethers, and trialkylene glycol ethers. Examples of the monoalkylene glycol ether include ethylene glycol monomethyl ether, ethylene glycol monobutyl ether, propylene glycol monomethyl ether, and propylene glycol monopropyl ether. Examples of the dialkylene glycol ether include diethylene glycol diethyl ether, diethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol diethyl ether, dipropylene glycol monomethyl ether, and dipropylene glycol monopropyl ether. Examples of the trialkylene glycol ether include triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, and triethylene glycol monobutyl ether. In the ink of the first embodiment, the aqueous medium contains a low boiling point glycol ether and a high boiling point glycol ether as the glycol ether.

(low boiling point glycol ether)
The boiling point of the low boiling point glycol ether is 100°C or more and 150°C or less. Examples of the low boiling point glycol ether include glycol ethers having a boiling point of 100° C. or higher and 150° C. or lower among those exemplified above as “glycol ethers”.

The low boiling point glycol ether preferably contains monoalkylene glycol, more preferably propylene glycol monomethyl ether or propylene glycol monopropyl ether. The ink may contain only one type of low-boiling point glycol ether, or may contain two or more types of low-boiling point glycol ethers.

(High boiling point glycol ether)
The boiling point of the high boiling point glycol ether is higher than 150°C and lower than 300°C. Examples of high boiling point glycol ethers include glycol ethers having a boiling point of more than 150° C. and 300° C. or less among those exemplified above as “glycol ethers”.

The high boiling point glycol ether preferably includes dialkylene glycol ether or trialkylene glycol ether, and more preferably includes dipropylene glycol monomethyl ether, dipropylene glycol monopropyl ether, or triethylene glycol monobutyl ether. The ink may contain only one type of high-boiling point glycol ether, or may contain two or more types of high-boiling point glycol ethers.

The low-boiling glycol ether and high-boiling glycol ether are preferably propylene glycol monomethyl ether and dipropylene glycol monomethyl ether, respectively. It is also preferred that the low boiling point glycol ether and the high boiling point glycol ether are propylene glycol monopropyl ether and dipropylene glycol monopropyl ether, respectively. It is also preferred that the low-boiling glycol ether and high-boiling glycol ether are propylene glycol monomethyl ether and triethylene glycol monobutyl ether, respectively. It is also preferred that the low boiling point glycol ether and the high boiling point glycol ether are propylene glycol monopropyl ether and dipropylene glycol monomethyl ether, respectively.

As already mentioned, the GE content is 5% by mass or more and 24% by mass or less. In order to form an image with less bleeding and unevenness on a predetermined recording medium, the GE content is preferably 7% by mass or more and 20% by mass or less, and more preferably 10% by mass or more and 12% by mass or less. The GE content is calculated from the formula: GE content = 100 x (mass of low-boiling glycol ether + mass of high-boiling glycol ether)/mass of ink.

As already mentioned, the low GE/high GE ratio is 0.3 or more and 3 or less. In order to form an image with less bleeding and unevenness on a predetermined recording medium, the low GE/high GE ratio is preferably 0.5 or more and 2 or less. The low GE/high GE ratio is calculated from the formula "low GE/high GE ratio=mass of low boiling point glycol ether/mass of high boiling point glycol ether".

The GE content and low GE/high GE ratio are determined by, for example, measuring the ink using a gas chromatograph mass spectrometer (GC-MS) and quantifying each glycol ether contained in the ink based on the calibration curve method. This is what is required.

The boiling point of the high boiling point glycol ether is preferably 35° C. or more higher than the boiling point of the low boiling point glycol ether. That is, the difference (BP2-BP1) between the boiling point (BP2) of the high boiling point glycol ether and the boiling point (BP1) of the low boiling point glycol ether is preferably 35° C. or more. The difference (BP2-BP1) is more preferably 50°C or higher, even more preferably 60°C or higher, and even more preferably 65°C or higher. The difference (BP2-BP1) is preferably 160°C or less.

(Other water-soluble organic solvents)
Examples of other water-soluble organic solvents include glycol compounds, lactam compounds, nitrogen-containing compounds, acetate compounds, thiodiglycol, glycerin, and dimethyl sulfoxide.

Examples of glycol compounds include ethylene glycol, 1,3-propanediol, 1,2-propanediol, 1,2-pentanediol, 1,5-pentanediol, 1,2-octanediol, and 1,8-octanediol. diols, 3-methyl-1,3-butanediol, 3-methyl-1,5-pentanediol, diethylene glycol, triethylene glycol, tetraethylene glycol, and polypropylene glycol.

Examples of lactam compounds include 2-pyrrolidone and N-methyl-2-pyrrolidone.

Examples of nitrogen-containing compounds include 1,3-dimethylimidazolidinone, formamide, and dimethylformamide.

Examples of the acetate compound include diethylene glycol monoethyl ether acetate.

As other water-soluble organic solvents, glycol compounds are preferred, and 1,2-propanediol is more preferred.

The content of other water-soluble organic solvents is preferably 5% by mass or more and 40% by mass or less, and more preferably 10% by mass or more and 30% by mass or less, based on the mass of the ink.

(water)
From the viewpoint of satisfactorily drying the ink that has landed on a predetermined recording medium, the water content is preferably 30% by mass or more and 70% by mass or less based on the mass of the ink.

<Pigment>
Pigments contained in the ink are not particularly limited, but include, for example, black pigments, cyan pigments, magenta pigments, yellow pigments, white pigments, and pigments other than these (hereinafter sometimes referred to as other pigments). It will be done.

Examples of black pigments include carbon black. Examples of carbon black include carbon black produced by a furnace method or a channel method.

Examples of cyan pigments include C.I. I. Pigment Blue (1, 2, 3, 15:3, 15:4, 16, and 22), C.I. I. Bat Blue (4 and 6) are mentioned.

Examples of magenta pigments include C.I. I. Pigment Red (5, 7, 12, 48 (Ca), 48 (Mn), 57 (Ca), 57:1, 112, 122, 123, 146, 168, 184, and 202), and C.I. I. pigment violet 19.

Examples of yellow pigments include C.I. I. pigment yellow (12, 13, 14, 17, 74, 83, 93, 94, 95, 120, 128, 138, 150, 151, 154, 155, 180, and 185).

Examples of white pigments include C.I. I. pigment white (4, 5, 6, 6:1, 7, 18, 19, 20, 21, 23, 24, 25, 26, 27, and 28).

Other pigments include, for example, C.I. I. Pigment Green (7, 10, and 36), C.I. I. Pigment Brown (3, 5, 25, and 26), and C.I. I. pigment orange (2, 5, 7, 13, 14, 15, 16, 24, 34, 36, 38, 40, 43, 62, 63, 64, and 71).

From the viewpoint of optimizing the image density of the formed image and the ejection performance of the ink from the recording head, the pigment content is 0.1% by mass or more and 15% by mass or less based on the mass of the ink. It is preferable that

The pigment is preferably used by being dispersed in a dispersion medium (for example, water). The method for dispersing the pigment is not particularly limited, but includes, for example, a method of dispersing the pigment in a dispersion medium using a dispersant, or a method of dispersing the pigment in a dispersion medium without using a dispersant. The pigment is, for example, a pigment that is dispersed in a dispersion medium using a dispersant (non-self-dispersing pigment). Examples of the dispersant include surfactants and polymer dispersants (hereinafter sometimes referred to as "pigment dispersion resin"). Note that the surfactant will be described later.

For example, the pigment dispersion resin is attached (for example, adsorbed) to the pigment. For example, the pigment constitutes pigment particles together with a pigment dispersion resin. Pigment particles are composed of, for example, a core containing a pigment and a pigment dispersion resin covering the core. Note that a part of the pigment dispersion resin may be free in the aqueous medium without being adsorbed by the pigment. Examples of the pigment dispersion resin include acrylic resin, styrene-acrylic resin, styrene-maleic acid resin, and urethane resin.

As the pigment dispersion resin, commercially available products can be used. Commercially available pigment dispersion resins include, for example, Joncryl (registered trademark) 586 and Joncryl 611 manufactured by BASF Japan Co., Ltd.; DISPERBYK (registered trademark) -190 and DISPERBYK-191 manufactured by BYK Chemie Japan Co., Ltd. and Solsperse 20000 and Solsperse 27000 manufactured by Japan Lubrizol Co., Ltd.

The ratio of the mass of the pigment dispersion resin to the mass of the pigment is preferably 0.01 or more and 0.50 or less. From the viewpoint of dispersibility of pigment particles in the ink, the content of the pigment dispersion resin is preferably 0.1% by mass or more and 3% by mass or less based on the mass of the ink.

<Binder resin>
From the viewpoint of forming an image with excellent scratch resistance, the ink preferably contains a binder resin. The binder resin is, for example, a water-insoluble resin. The binder resin is, for example, in the form of emulsified particles and dispersed in an aqueous medium. That is, the ink contains emulsified particles made of binder resin.

Binder resins are not particularly limited, but include, for example, urethane resins, acrylic resins, styrene-acrylic resins, acrylic-urethane resins, polyester resins, and modified polyolefin resins. As the binder resin, urethane resin is preferable.

The urethane resin is not particularly limited as long as it has a urethane bond in its molecule. Commercially available urethane resin emulsions include, for example, Superflex (registered trademark) 170, Superflex 210, Superflex 820, and Superflex 870 manufactured by Daiichi Kogyo Seiyaku Co., Ltd.; Examples include Takelac (registered trademark) W-6010 and Takelac W-6020.

From the viewpoint of optimizing the ejection properties of the ink from the recording head, the content of the binder resin is preferably 1% by mass or more and 10% by mass or less based on the mass of the ink.

<Surfactant>
The ink may contain a surfactant. Examples of the surfactant include acetylene surfactants, acrylic surfactants, silicone surfactants, and fluorine surfactants. As the surfactant, silicone surfactants are preferred. As used herein, silicone surfactant means a surfactant having a siloxane bond within its molecule. Commercially available silicone surfactants include, for example, Silface (registered trademark) SAG002 and Silface SAG503A manufactured by Nissin Chemical Industry Co., Ltd. The content of the surfactant is preferably 0.05% by mass or more and 2% by mass or less based on the mass of the ink.

<Other ingredients>
The ink may contain other components as necessary. Other components include, for example, pH adjusters, chelating agents, preservatives, and fungicides.

<Ink manufacturing method>
The ink manufacturing method of the first embodiment includes, for example, a pigment dispersion preparation step and a mixing step.

(Preparation process of pigment dispersion)
In the step of preparing a pigment dispersion, a pigment, a pigment dispersion resin, and an aqueous medium are mixed to obtain a pigment dispersion. In the pigment dispersion, D ₅₀ of the pigment particles constituted by the pigment and the pigment dispersion resin is preferably 70 nm or more and 130 nm or less. The pigment dispersion can be prepared by wet-dispersing the components contained in the pigment dispersion using a media-type wet dispersion machine. Media-type wet dispersers include, for example, ball mills and bead mills (more specifically, "Atraitor (registered trademark)" manufactured by Nippon Coke Industry Co., Ltd., "Sand Grinder" manufactured by Imex Co., Ltd., and "Dyno (registered trademark)" manufactured by WAB Co., Ltd.). (registered trademark) Mill" and "Ultra Apex Mill" manufactured by Hiroshima Metal & Machinery Co., Ltd.).

(Mixing process)
In the mixing step, a pigment dispersion containing a pigment, an aqueous medium, and optional components (for example, a binder resin and/or a surfactant) are mixed using a stirrer. After mixing the components of the ink, foreign matter and coarse particles may be removed using a filter (for example, a filter with a pore size of 5 μm or less).

[Second embodiment: inkjet recording device]
Next, an inkjet recording apparatus according to a second embodiment of the present invention will be described. The inkjet recording apparatus of the second embodiment mainly includes a first heating section, a recording head, and a second heating section. The first heating section is provided upstream of the recording head in the conveyance direction of the recording medium, and heats the recording medium to a first temperature. The print head ejects ink onto a print medium. The second heating section is provided on the downstream side of the print head in the transport direction of the print medium, and heats the print medium to a second temperature. The second temperature is higher than the first temperature. The ink ejected from the print head is the ink of the first embodiment.

As described in the first embodiment, the ink of the first embodiment can form an image with less bleeding and unevenness on a predetermined recording medium. For this reason, the inkjet recording apparatus of the second embodiment, which is equipped with the recording head that ejects the ink of the first embodiment, produces images with less bleeding and unevenness on a predetermined recording medium for the same reason as described in the first embodiment. can be formed.

The details of the inkjet recording apparatus of the second embodiment will be described below with reference to FIG. Note that the drawings referred to schematically show each component mainly for ease of understanding, and the size, number, etc. of each component shown in the diagram may differ from the actual one. .

FIG. 1 shows an inkjet recording apparatus 100, which is an example of an inkjet recording apparatus according to a second embodiment. The inkjet recording apparatus 100 shown in FIG. 1 includes a first heating section 2, a first recording head 4a, a second recording head 4b, a third recording head 4c, a fourth recording head 4d, a fifth recording head 4e, and a second heating Mainly includes section 5. The inkjet recording apparatus 100 further includes a feeding section 1 , a first temperature sensor 3 , a second temperature sensor 6 , a third heating section 7 , a winding section 8 , and a control section 9 . Hereinafter, if there is no need to distinguish, the first recording head 4a, second recording head 4b, third recording head 4c, fourth recording head 4d, and fifth recording head 4e will be simply referred to as "recording head 4." May be stated.

The inkjet recording apparatus 100 includes a feeding section 1, a first heating section 2, a first temperature sensor 3, a first recording head 4a, a second recording head 4b, a third recording head 4c, a fourth recording head 4d, and a fifth recording head. The head 4e, the second heating section 5, the second temperature sensor 6, the third heating section 7, and the winding section 8 are provided in the order described in the conveyance direction D1 of the recording medium P. A control section 9 is provided at an arbitrary position of the inkjet recording apparatus 100. Further, a plurality of conveyance rollers 21 to 32 for conveying the recording medium P are provided along the conveyance path of the recording medium P from the sending section 1 to the winding section 8. The recording medium P is conveyed from the sending section 1 to the winding section 8 via the conveying rollers 21 to 32.

The recording medium P is wound into a roll around the feeding section 1. Examples of the recording medium P include a predetermined recording medium. Among the predetermined recording media, examples of low-absorbency recording media that have low water absorption include art paper, coated paper, and cast coated paper. Among the predetermined recording media, examples of non-absorbent recording media that do not absorb water include foil paper, synthetic paper, and plastic substrates. Examples of the plastic base material include a polyester (PET) base material, a polypropylene base material, a polystyrene base material, and a polyvinyl chloride base material. One or both sides of the predetermined recording medium may be surface-treated. Examples of surface treatments include corona discharge treatment, plasma treatment, and primer treatment.

A recording medium P is set in the feeding section 1. The feeding section 1 is rotationally driven by, for example, a drive belt (not shown) to feed the recording medium P to the first heating section 2 .

The first heating unit 2 is provided upstream of the recording head 4 (for example, the first recording head 4a) in the conveyance direction D1 of the recording medium P. The first heating unit 2 heats the recording medium P to a preset first temperature (first heating), for example. Hereinafter, the "first temperature" may be referred to as "preheat temperature." Further, "heating by the first heating unit 2" may be referred to as "preheating". The first heating unit 2 is, for example, a hot air dryer.

The preheat temperature is preferably 40°C or higher and 75°C or lower. If the preheat temperature is 40° C. or higher, at least a portion of the low boiling point glycol ether contained in the ink will easily evaporate when the ink is ejected onto the preheated recording medium P. As a result, as described in the first embodiment, an image with less blur can be formed. When the preheat temperature is 75° C. or lower, when the ink is ejected onto the preheated recording medium P, the high boiling point glycol ether contained in the ink is difficult to evaporate. As a result, as described in the first embodiment, an image with less unevenness can be formed.

The first heating unit 2 is provided on the front side of the recording medium P (the side on which ink is ejected), and heats the recording medium P from the front side. Furthermore, as already described, the first heating section 2 is provided on the upstream side of the recording head 4 in the conveyance direction D1 of the recording medium P. Therefore, the first heating section 2 is not an underheater, but more specifically an underheater provided on the back side of the recording medium P (the side opposite to the side from which ink is ejected) and facing the recording head 4. isn't it. Therefore, the recording head 4 is less likely to be heated by the first heating section 2, and the ink in the ejection holes of the recording head 4 can be prevented from drying and solidifying.

The first temperature sensor 3 detects the preheat temperature of the recording medium P. The first temperature sensor 3 is provided on the front side of the recording medium P, and detects the preheat temperature of the recording medium P from the front side. The first temperature sensor 3 is close to the recording medium P. The first temperature sensor 3 is not arranged facing the first heating section 2. Therefore, the first temperature sensor 3 can detect the preheat temperature of the recording medium P without being affected by the temperature of the first heating section 2 as much as possible.

The recording head 4 discharges ink onto the recording medium P from a plurality of discharge holes (not shown) provided on its discharge surface. For example, the first recording head 4a to the fifth recording head 4e eject first to fifth inks (for example, cyan ink, magenta ink, yellow ink, black ink, and white ink) onto the recording medium P, respectively. . As a result, a color image is formed on the recording medium P. The recording head 4 is, for example, a piezo type or thermal inkjet type line head, although it is not particularly limited.

The second heating unit 5 is provided on the downstream side of the recording head 4 (for example, the fifth recording head 4e) in the conveyance direction D1 of the recording medium P. The second heating unit 5 heats the recording medium P to a preset second temperature (second heating), for example. Hereinafter, the "second temperature" may be referred to as "main drying temperature". Further, "heating by the second heating unit 5" may be referred to as "main drying". The second heating unit 5 is, for example, a hot air dryer.

The main drying temperature is higher than the preheating temperature. When the ink is ejected onto the preheated recording medium P, at least a portion of the low boiling point glycol ether contained in the ink evaporates. Next, when the recording medium P is subjected to main drying, the high boiling point glycol ether contained in the ink evaporates on the recording medium P heated to the main drying temperature which is higher than the preheat temperature.

The main drying temperature is preferably 80°C or higher and 120°C or lower. The main drying temperature is preferably higher than the preheating temperature by 35°C or more and 70°C or less. That is, the difference (T2-T1) between the main drying temperature (T2) and the preheating temperature (T1) is preferably 35°C or more and 70°C or less.

The second temperature sensor 6 detects the main drying temperature of the recording medium P. The second temperature sensor 6 is provided on the front side of the recording medium P, and detects the main drying temperature of the recording medium P from the front side. The second temperature sensor 6 is close to the recording medium P. The second temperature sensor 6 is not arranged facing the second heating section 5. Therefore, the second temperature sensor 6 can detect the main drying temperature of the recording medium P without being influenced by the temperature of the second heating section 5 as much as possible.

The third heating section 7 includes a roller 71 and a heating box 72 that covers the roller 71. The heating box 72 is composed of a housing-like heat insulating wall. The heating box 72 is provided with an inlet 72a and an outlet 72b for the recording medium P. The recording medium P entered through the entrance 72a is conveyed inside the heating box 72 along the circumferential surface of the roller 71, and is discharged through the exit 72b. The third heating unit 7 further heats the recording medium P to a preset third temperature (third heating), for example. Specifically, by heating the inside of the heating box 72 included in the third heating section 7 with hot air, the recording medium P is heated to the third temperature while the recording medium P passes through the inside of the heating box 72. The third temperature is preferably a temperature of 60°C or higher and 70°C or lower.

The winding unit 8 winds up the recording medium P discharged from the heating box 72 included in the third heating unit 7 into a roll. The winding unit 8 is rotationally driven by, for example, a drive belt (not shown) and winds up the recording medium P.

The control unit 9 includes, for example, a CPU (Central Processing Unit), a ROM (Read Only Memory), and a RAM (Random Access Memory). The control unit 9 can control the entire inkjet recording apparatus 100.

For example, the control unit 9 controls the output of the first heating unit 2 so that the temperature of the recording medium P reaches the preheat temperature set based on the current temperature of the recording medium P detected by the first temperature sensor 3. Execute feedback control to control. More specifically, the control unit 9 controls the second duty ratio according to the difference between the temperature of the recording medium P indicated by the first electric signal input from the first temperature sensor 3 and the set preheat temperature. Generate electrical signals. The control unit 9 inputs the generated second electric signal to the first heating unit 2 and controls the output of the first heating unit 2 .

Similarly, the control unit 9 controls the second heating unit 5 so that the temperature of the recording medium P reaches the set main drying temperature based on the current temperature of the recording medium P detected by the second temperature sensor 6. Execute feedback control to control the output of Similarly, the control unit 9 sets the temperature of the recording medium P based on the current temperature of the recording medium P detected by a third temperature sensor (not shown) provided in the third heating unit 7. Feedback control is executed to control the output of the third heating section 7 so that the third temperature is reached.

The inkjet recording apparatus 100, which is an example of the inkjet recording apparatus of the second embodiment, has been described above with reference to FIG. However, the inkjet recording apparatus of the second embodiment is not limited to the above inkjet recording apparatus 100, and can be modified as follows, for example. Although an example has been described in which the first heating section 2 is provided on the front side of the recording medium P, the first heating section 2 may be provided on the back side of the recording medium P and heat the recording medium P from the back side. . Although an example in which the sheet is preheated by the first heating section 2 has been described, the sheet may be preheated by the conveyance roller 22 having a heater inside. In this case, the first heating section 2 may be omitted. Although an example has been described in which the second heating section 5 is provided on the front side of the recording medium P, the second heating section 5 may be provided on the back side of the recording medium P and heat the recording medium P from the back side. . Although an example in which main drying is performed by the second heating unit 5 has been described, main drying may be performed by the conveyance roller 23 equipped with a heater inside. In this case, the second heating section 5 may be omitted. Although the example in which the third heating section 7 includes the heating box 72 has been described, the third heating section 7 may be a hot air dryer or a heater. Although an example including five first to fifth recording heads 4a to 4e has been described, the number of recording heads 4 may be 1 to 4 or 6 or more. Although an example without a wiping blade has been described, a wiping blade for wiping the ejection surface of the recording head 4 may be provided. Although an example has been described in which a conveyance plate and a conveyance belt are not provided, a conveyance plate or a conveyance belt that conveys the recording medium P may be provided. The inkjet recording apparatus of the second embodiment has been described above with reference to FIG.

[Third embodiment: inkjet recording method]
Continuing with reference to FIG. 1, an inkjet recording method according to a third embodiment of the present invention will be described. The inkjet recording method according to the third embodiment of the present invention includes a first heating step, a discharge step, and a second heating step. In the first heating step, the recording medium P is first heated to a first temperature. In the ejection step, ink is ejected from the recording head 4 onto the first heated recording medium P. In the second heating step, the recording medium P on which the ink has been ejected is heated to a second temperature for a second time. The second temperature is higher than the first temperature. The ink ejected from the recording head 4 is the ink of the first embodiment. It is preferable that a discharge step is performed after the first heating step. It is preferable that a second heating step is performed after the discharge step.

As described in the first embodiment, the ink of the first embodiment can form an image with less bleeding and unevenness on a predetermined recording medium. For this reason, the inkjet recording method of the third embodiment, which includes the ejection step of ejecting the ink of the first embodiment, produces an image with less bleeding and unevenness on a predetermined recording medium for the same reason as described in the first embodiment. can be formed.

The inkjet recording method of the third embodiment is implemented using, for example, the inkjet recording apparatus 100 of the second embodiment. The first heating in the first heating step corresponds to the preheating described in the second embodiment. The second heating in the second heating step corresponds to the main drying described in the second embodiment. The inkjet recording method of the third embodiment has been described above with reference to FIG.

Examples are shown below to explain the present invention in more detail, but the present invention is not limited thereto.

<Manufacture of pigment dispersion C>
First, a pigment dispersion C was produced for use in producing ink. 15 parts by mass of cyan pigment (C.I. Pigment Blue 15:3, "Heliogen (registered trademark) Blue D 7088" manufactured by BASF Japan Co., Ltd.), pigment dispersion resin (manufactured by BYK Chemie Japan Co., Ltd., product name: DISPERBYK-190) , nonvolatile content: 40% by mass, dispersion medium: water), and 75 parts by mass of water were mixed and predispersed using a disper to obtain a predispersion. Next, the preliminary dispersion was further dispersed using a 0.6 L bead mill ("Dyno (registered trademark) mill" manufactured by WAB) filled with 1800 g of zirconia beads with a diameter of 0.1 mm, to obtain a cyan pigment dispersion. I got a C. The pigment solid content concentration in Pigment Dispersion C was 15% by mass.

<Manufacture of pigment dispersion BK>
A black pigment dispersion BK was obtained in the same manner as the pigment dispersion C, except that the cyan pigment was changed to a black pigment ("Printex (registered trademark) 85" manufactured by Orion Engineered Carbon). The pigment solid content concentration in pigment dispersion BK was 15% by mass.

<Manufacture of cyan ink>
Next, cyan inks (1-1) to (9-1) were produced. The blending amounts of these cyan inks are shown in Tables 2 to 4, which will be described later.

(Manufacture of cyan ink (1-1))
Ink (1-1) was prepared to have the formulation shown in the cyan ink (1-1) column of Table 2. Using a stirrer, pigment dispersion C, propylene glycol monomethyl ether, dipropylene glycol monomethyl ether, 1,2-propanediol, binder (polyurethane emulsion, "Superflex 820" manufactured by Daiichi Kogyo Seiyaku Co., Ltd., non-volatile content: 30 Mass%, dispersion medium: water), surfactant ("Silface (registered trademark) SAG503A" manufactured by Nissin Chemical Industry Co., Ltd., active ingredient concentration: 100% by mass), and water were mixed to obtain a mixed solution A. Ta. The amounts of each component were as shown in the cyan ink (1-1) column of Table 2. The "residual amount", which is the amount of water added shown in Table 2, means the amount of mixed liquid A that is 100.0 parts by mass. The mixture was filtered using a membrane filter with an opening of 5 μm to obtain cyan ink (1-1).

(Production of cyan ink (2-1) to (9-1))
The same method as cyan ink (1-1) was used except that each component was mixed to have the formulation shown in each of the cyan ink (2-1) to (9-1) columns of Tables 2 to 4. Cyan inks (2-1) to (9-1) were produced.

<Manufacture of black ink>
Next, black inks (1-2) to (9-2) were produced. The blending amounts of these black inks are shown in Tables 2 to 4 below. The same method as cyan ink (1-1) was used except that each component was mixed to have the formulation shown in each of the black ink (1-2) to (9-2) columns of Tables 2 to 4. Black inks (1-2) to (9-2) were produced.

Note that the surface tensions of the inks used in combination in each Example and each Comparative Example (for example, the cyan ink (1-1) and black ink (1-2) used in combination in Example 1) are the same value. Met.

[evaluation]
The following evaluation was performed under a normal temperature and normal humidity environment (temperature 25° C. and humidity 60% RH environment). As an evaluation device, an inkjet recording device (prototype manufactured by Kyocera Document Solutions Co., Ltd.) equipped with a line-type recording head was used. This evaluation machine was equipped with a first heating section that performs preheating and a second heating section that performs main drying. The amount of ink ejected per pixel was set to 3 pL. The conveyance speed of the recording medium was set to 50 m/min. The preheat temperature was set to the temperatures shown in Tables 2 to 4. The main drying temperature was set at 110°C. The cyan ink tank of the evaluation machine was filled with the cyan ink obtained in the above <Production of cyan ink>. The black ink tank of the evaluation machine was filled with the black ink obtained in the above <Manufacture of black ink>. As a recording medium, a PET film ("Polyester Film Lumirror (registered trademark) S10#50" manufactured by Toray Industries, Inc.) was used.

<Evaluation of bleeding>
Image A was printed on one recording medium using an evaluation machine to obtain an evaluation image. Image A consists of a black rectangular solid image area (image area BK) parallel to the length direction of the recording medium, and a cyan rectangular solid image area (image area C) parallel to the width direction of the recording medium. ) were images that were orthogonal to each other. The area where image area BK and image area C were orthogonal (orthogonal image area) had a size of 5 mm in length and 5 mm in width. The orthogonal image area of the evaluation image was observed, and the width of ink of one color bleeding into the image area (image area BK or C) of the other color (extrusion width) was measured. The protrusion width was measured at five locations, and the average value was taken as the evaluation value. It was determined whether an image with less blur could be formed according to the following criteria. The determination results are shown in Tables 2 to 4.

(Standards for bleeding)
A (little bleeding): Evaluation value is less than 150 μm.
B (normal): The evaluation value is 150 μm or more and less than 300 μm.
C (a lot of bleeding): The evaluation value is 300 μm or more.

<Evaluation of unevenness>
Image B was printed on one recording medium using an evaluation machine to obtain an evaluation image. Image B was a cyan one-dot line image. The evaluation image was observed at a magnification of 100 times using a microscope, and the presence or absence of unevenness in the evaluation image was confirmed.

The presence or absence of unevenness will be described below with reference to FIGS. 2 and 3. FIG. 2 is a micrograph showing an example of an image without unevenness. FIG. 3 is a micrograph showing an example of an image in which unevenness has occurred. In the dot image 200 shown in FIG. 2, no dark colored portions or light colored portions are observed, and no unevenness occurs. On the other hand, in the dot image 300 shown in FIG. 3, a dark color portion 301 and a light color portion 302 are confirmed. The dark color portion 301 is caused by, for example, pigment particles. The light colored portion 302 is caused by, for example, non-colored components (more specifically, a pigment dispersion resin separated from pigment particles, a binder resin, etc.).

Based on the results of checking the presence or absence of unevenness in the evaluation image, judgment was made according to the following criteria. The determination results are shown in Tables 2 to 4. Note that the black ink has the same formulation as the cyan ink except for the difference in the type of pigment, so this evaluation was omitted.

(Standard for unevenness)
A (good): No unevenness occurred.
B (Poor): Unevenness occurred.

Table 1 shows the abbreviations in Tables 2 to 4 and boiling points for the glycol ethers used in the production of each ink. The terms listed in Tables 2 to 4 are as follows.
Low GE: Low boiling point glycol ether High GE: High boiling point glycol ether PD: 1,2-propanediol Boiling point difference: Difference between the boiling point (BP2) of high boiling point glycol ether and the boiling point (BP1) of low boiling point glycol ether (BP2) -BP1)
Bleeding: Evaluation of bleeding Unevenness: Evaluation of unevenness

As shown in Table 4, the low GE/high GE ratio of cyan ink (6-1) and black ink (6-2) was less than 0.3. When these inks were used, it was not possible to form an image with little bleeding on a given recording medium.

As shown in Table 4, the low GE/high GE ratio of cyan ink (7-1) and black ink (7-2) was more than 3. When cyan ink (7-1) was used, it was not possible to form an image with little unevenness on a given recording medium.

As shown in Table 4, the GE content of the cyan ink (8-1) and black ink (8-2) was less than 5% by mass. When cyan ink (8-1) was used, it was not possible to form an image with little unevenness on a given recording medium.

As shown in Table 4, the GE content of the cyan ink (9-1) and black ink (9-2) was more than 24% by mass. When these inks were used, it was not possible to form an image with little bleeding on a given recording medium.

On the other hand, as shown in Tables 2 and 3, cyan inks (1-1) to (5-1) and black inks (1-2) to (5-2) had the following configurations. That is, it contained a pigment and an aqueous medium. The aqueous medium contained a low boiling glycol ether and a high boiling glycol ether. The GE content was 5% by mass or more and 24% by mass or less. The low GE/high GE ratio was 0.3 or more and 3 or less. When cyan inks (1-1) to (5-1) and black inks (1-2) to (5-2) were used, an image with little bleeding could be formed on a given recording medium. When cyan inks (1-1) to (5-1) were used, images with less unevenness could be formed on the specified recording medium.

From the above, it is determined that the ink according to the present invention and the inkjet recording apparatus using this ink can form images with less bleeding and unevenness on a predetermined recording medium.

The inkjet recording device and inkjet recording method according to the present invention can be used to form an image on a recording medium.

2: First heating section 4: Recording head 5: Second heating section 100: Inkjet recording device D1: Conveyance direction P: Recording medium

Claims (9)

An ink containing a pigment and an aqueous medium,
The aqueous medium includes a first glycol ether and a second glycol ether,
The boiling point of the first glycol ether is 100°C or more and 150°C or less,
The boiling point of the second glycol ether is higher than 150°C and lower than or equal to 300°C,
The total content of the first glycol ether and the second glycol ether with respect to the mass of the ink is 5% by mass or more and 24% by mass or less,
An inkjet ink, wherein a mass ratio of the first glycol ether to the mass of the second glycol ether is 0.3 or more and 3 or less. The inkjet ink according to claim 1, wherein the boiling point of the second glycol ether is 35°C or more higher than the boiling point of the first glycol ether. The inkjet ink according to claim 1 or 2, wherein the first glycol ether includes propylene glycol monomethyl ether or propylene glycol monopropyl ether. The inkjet ink according to any one of claims 1 to 3, wherein the second glycol ether includes dipropylene glycol monomethyl ether, dipropylene glycol monopropyl ether, or triethylene glycol monobutyl ether. The inkjet ink according to any one of claims 1 to 4, further comprising a urethane resin. a recording head that ejects ink onto a recording medium;
a first heating section that is provided upstream of the recording head in the conveying direction of the recording medium and heats the recording medium to a first temperature;
a second heating section that is provided on the downstream side in the conveyance direction of the recording medium with respect to the recording head and heats the recording medium to a second temperature;
the second temperature is higher than the first temperature,
The ink contains a pigment and an aqueous medium,
The aqueous medium includes a first glycol ether and a second glycol ether,
The boiling point of the first glycol ether is 100°C or more and 150°C or less,
The boiling point of the second glycol ether is higher than 150°C and lower than or equal to 300°C,
The total content of the first glycol ether and the second glycol ether with respect to the mass of the ink is 5% by mass or more and 24% by mass or less,
An inkjet recording apparatus, wherein a mass ratio of the first glycol ether to the mass of the second glycol ether is 0.3 or more and 3 or less. The inkjet recording apparatus according to claim 6, wherein the first temperature is 40°C or more and 75°C or less. The inkjet recording apparatus according to claim 6 , wherein the second temperature is higher than the first temperature by 35° C. or more and 70° C. or less. a first heating step of first heating the recording medium to a first temperature;
a discharging step of discharging ink from a recording head onto the first heated recording medium;
a second heating step of heating the recording medium onto which the ink has been ejected to a second temperature;
the second temperature is higher than the first temperature,
The ink contains a pigment and an aqueous medium,
The aqueous medium includes a first glycol ether and a second glycol ether,
The boiling point of the first glycol ether is 100°C or more and 150°C or less,
The boiling point of the second glycol ether is higher than 150°C and lower than or equal to 300°C,
The total content of the first glycol ether and the second glycol ether with respect to the mass of the ink is 5% by mass or more and 24% by mass or less,
An inkjet recording method, wherein a mass ratio of the first glycol ether to the mass of the second glycol ether is 0.3 or more and 3 or less.

Images