JP7528461B2 - Inkjet recording method, water-based ink composition, and inkjet recording apparatus - Google Patents

Description

The present invention relates to an inkjet recording method, a water-based ink composition, and an inkjet recording device.

The inkjet recording method is capable of recording high-definition images using relatively simple equipment, and has been developed in various fields. For example, in label printing, inkjet recording methods that can record images not only on ink-absorbent recording media such as high-quality paper (hereinafter also referred to as "absorbent recording media"), but also on low-absorbent or non-absorbent recording media such as film (hereinafter also referred to as "low-absorbent recording media") are being considered.

Specifically, a recording method is disclosed that uses ink containing 1,2-hexanediol and propylene glycol (1,2-propanediol) as solvents to produce recorded material with a stable optical density (OD value) regardless of the properties of the recording medium (see, for example, Patent Document 1).

JP 2016-60168 A

However, while it is easy to obtain image quality with high OD values and excellent color development on low non-absorbent recording media by using ink with excellent wetting and spreading properties, it is difficult to obtain an OD value and image quality with excellent color development on absorbent recording media because the ink easily penetrates the media. Furthermore, if the moisturizing properties of the solvent contained in the ink are poor, the ink drying in the nozzles may impair the ejection stability. Thus, it cannot be said that there is yet a sufficient balance between improving image quality on both low non-absorbent recording media and absorbent recording media and ensuring the ejection stability of the ink.

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One aspect of the inkjet recording method according to the present invention comprises:
An inkjet recording method for performing ink jet recording on a recording medium using a water-based ink composition,
an ink depositing step of ejecting the water-based ink composition from an inkjet head and depositing the water-based ink composition on the recording medium;
The water-based ink composition contains an organic solvent A which is a 1,2-alkanediol having a surface tension of 30 mN/m or less at 25° C., and an organic solvent B which is an alkanediol having a normal boiling point of 250° C. or less and a carbon number of 3 or more at both ends,
The inkjet head includes a circulation mechanism for circulating the water-based ink composition.

One embodiment of the aqueous ink jet composition according to the present invention is
It is intended to be used in the ink jet recording method.

One aspect of the inkjet recording apparatus according to the present invention is to
an ink depositing means for ejecting the water-based ink composition from an inkjet head and depositing the ink composition on a recording medium;
The water-based ink composition contains an organic solvent A which is a 1,2-alkanediol having a surface tension of 30 mN/m or less at 25° C., and an organic solvent B which is an alkanediol having a normal boiling point of 250° C. or less and a carbon number of 3 or more at both ends,
The inkjet head includes a circulation mechanism for circulating the water-based ink composition.

FIG. 1 is a schematic diagram of an example of an inkjet recording apparatus according to an embodiment of the present invention. FIG. 2 is a schematic perspective view of the periphery of a carriage of an example of an inkjet recording apparatus according to the present embodiment. FIG. 1 is a block diagram of an example of an inkjet recording apparatus according to an embodiment of the present invention. FIG. 2 is a schematic cross-sectional view of an inkjet head of the inkjet recording device. FIG. 4 is a schematic cross-sectional view of the ink-jet head in the vicinity of a circulating fluid chamber. FIG. 1 is a schematic cross-sectional view showing a part of a line-type recording apparatus.

Several embodiments of the present invention are described below. The embodiments described below are merely examples of the present invention. The present invention is not limited to the following embodiments, and includes various modified forms that are implemented within the scope of the present invention. Note that not all of the configurations described below are necessarily essential configurations of the present invention.

1. Inkjet Recording Method An inkjet recording method according to one embodiment of the present invention is an inkjet recording method performed on a recording medium using an aqueous ink composition, and includes an ink deposition step of ejecting the aqueous ink composition from an inkjet head and depositing it on the recording medium, the aqueous ink composition containing an organic solvent A which is a 1,2-alkanediol having a surface tension of 30 mN/m or less at 25° C. and an organic solvent B which is an alkanediol having a normal boiling point of 250° C. or less and having 3 or more carbon atoms at both ends, and the inkjet head includes a circulation mechanism for circulating the aqueous ink composition. Note that in the inkjet recording method according to this embodiment, one or more aqueous ink compositions are ejected from the inkjet head and deposited on the recording medium, and when there are two or more ink compositions, it is sufficient that at least one of them corresponds to the aqueous ink composition described above, and it is not necessary that all of the ink compositions correspond to the aqueous ink composition described above.

Below, we will explain each step of the inkjet recording method according to this embodiment, the recording medium that can be used, the water-based ink composition, and the inkjet recording device in that order.

In the ink application process, the above-mentioned water-based ink composition is ejected from an inkjet head equipped with a circulation mechanism for circulating the water-based ink composition inside, and applied to a recording medium. By providing the inkjet head with a circulation mechanism, the water-based ink composition in the vicinity of the nozzles can be circulated, the water-based ink composition that is beginning to dry can be restored, and the ejection stability at the nozzles can be improved.

In the ink application process, the water-based ink composition may be applied to the recording medium in a heated state. Even under such drying conditions, the inkjet head can have good ejection stability at the nozzles by providing a circulation mechanism. Furthermore, by applying the water-based ink composition to a recording medium that has been heated in advance, the drying speed of the water-based ink composition is further increased, and the transport speed of the recording medium can be increased.

This process may be performed using a serial type recording device or a line type recording device.

The inkjet recording method according to this embodiment may include a plurality of ink deposition steps. The inkjet recording method according to this embodiment may further include a drying step of drying the water-based ink composition deposited on the recording medium, a heating step of the recording medium, a lamination step, and the like.

The inkjet recording method according to this embodiment may have a drying step. The inkjet recording method according to this embodiment may include a drying step of drying the recording medium before or during the ink application step. The drying step can be performed by a means of stopping recording and leaving the recording medium as it is, or by a means of drying the recording medium using a drying mechanism.

Means of drying using a drying mechanism include means for blowing room temperature air or hot air to the recording medium (air blowing type), means for irradiating the recording medium with radiation (infrared rays, etc.) that generates heat (radiation type), members that contact the recording medium and transfer heat to the recording medium (conduction type), and combinations of two or more of these means. Among drying processes, those that involve heating are also called primary heating processes. A drying process using a drying mechanism immediately promotes the drying of the water-based ink composition that has adhered to the recording medium. When a drying process is performed, the drying of the water-based ink composition that has adhered to the recording medium is promoted, and image deterioration due to bleeding of the water-based ink composition can be reduced. Such a drying process is also called a primary drying process.

On the other hand, it is also preferable not to perform a drying process using a drying mechanism. The water-based ink composition used in this embodiment contains organic solvent B with a normal boiling point of 250°C or less, and therefore has a fast drying speed. Therefore, even if a drying process using a drying mechanism is not performed, it is possible to prevent the water-based ink composition attached to the recording medium from bleeding and deteriorating the image. Also, by not performing a drying process using a drying mechanism, ejection stability at the nozzles is superior, and the ink can spread well, resulting in better image quality.

The surface temperature of the recording medium when the aqueous ink composition is applied is preferably 45°C or less, more preferably 43°C or less, even more preferably 40°C or less, more preferably 38°C or less, and particularly preferably 35°C or less. On the other hand, the lower limit is preferably 20°C or more, more preferably 23°C or more, even more preferably 25°C or more, particularly preferably 28°C or more, even more preferably 30.0°C or more, and more preferably 32.0°C or more. It is further preferably 35.0°C or more, and more preferably 37.0°C or more.

Moreover, 20°C or higher and 45°C or lower are more preferable. Also, 27°C or higher and 45°C or lower are more preferable, 28°C or higher and 43°C or lower are more preferable, 30°C or higher and 40°C or lower are even more preferable, and 32°C or higher and 38°C or lower are particularly preferable. This temperature is the surface temperature of the portion of the recording surface of the recording medium that receives the adhesion of the water-based ink composition in the adhesion process, and is the highest temperature in the adhesion process in the recording area. It is the surface temperature of the recording medium at the position facing the inkjet head during recording. If the surface temperature is below the above upper limit, it is more preferable in terms of suppressing image deterioration, reducing clogging, and achieving high gloss. If it is above the above lower limit, it is more preferable in terms of robustness, good ink spread, and excellent image quality.

The surface temperature of the recording medium at the time of attachment can be made relatively high by performing a drying process using a drying mechanism, or relatively low by not performing the drying process.

When a drying step is performed, it can be performed simultaneously with one or more of the ink application steps described above. Even when the drying step is performed simultaneously with the application step, it is preferable that the surface temperature of the recording medium in the application step be within the above range. When the drying step is performed in this manner, this step is sometimes called the first heating step.

1.1.2.2. Heating Step The inkjet recording method according to this embodiment may include a heating step of heating the recording medium after the ink application step. The heating step can be performed, for example, by using an appropriate heating means. The heating step after the ink application step is performed, for example, by an after-heater (corresponding to the heater 5 in the example of the inkjet recording device described later). The heating means is not limited to the heating means provided in the inkjet recording device, and other heating means may be used. This allows the obtained image to be dried and fixed more sufficiently, so that, for example, the recorded matter can be made usable sooner. The heating step is also called a secondary heating step or an after-heating step.

In this case, the temperature of the recording medium is not particularly limited, but can be set, for example, taking into consideration the Tg of the resin particles contained in the recording material. When taking into consideration the Tg of the resin particles, it is advisable to set the temperature at least 5°C higher than the Tg of the resin particles, and preferably at least 10°C higher.

The surface temperature of the recording medium reached by heating in the heating step is preferably 30°C or higher and 120°C or lower, particularly preferably 40°C or higher and 100°C or lower, more preferably 50°C or higher and 95°C or lower, and even more preferably 70°C or higher and 90°C or lower. It is particularly preferably 60°C or higher. If the temperature of the recording medium is within this range, the resin particles contained in the recorded matter can be coated and flattened, and the resulting image can be dried and fixed more sufficiently.

In addition, the inkjet recording method according to this embodiment uses a water-based ink composition, which dries quickly, and therefore requires less energy to dry the image.

1.2. Recording medium The recording medium used in the inkjet recording method according to this embodiment may be an absorbent recording medium or a low non-absorbent recording medium. A low non-absorbent recording medium (low absorbent recording medium and non-absorbent recording medium) refers to a recording medium that has the property of absorbing almost no ink, absorbing only a small amount of ink, or absorbing no ink at all. Quantitatively, the low non-absorbent recording medium used in this embodiment refers to a recording medium having a water absorption amount of 10 mL/ ^m2 or less from the start of contact to 30 msec ^1/2 in the Bristow method. This Bristow method is the most popular method for measuring the amount of liquid absorbed in a short period of time, and is also adopted by the Japan Pulp and Paper Technology Association (JAPAN TAPPI). Details of the test method are described in Standard No. 51 "Paper and Paperboard - Liquid Absorbency Test Method - Bristow Method" of the "JAPAN TAPPI Paper and Pulp Test Method 2000 Edition". Such low non-absorbent recording media include recording media that do not have an ink-receiving layer having ink absorbency on the recording surface, and recording media that have a coating layer having low ink absorbency on the recording surface.

Non-absorbent recording media are not particularly limited, but examples include plastic films that do not have an ink-absorbing layer, substrates such as paper coated with plastic or the like, and substrates with a plastic film attached. Coatings made of plastic or the like are non-ink-absorbent coatings. Examples of plastics include polyvinyl chloride, polyethylene terephthalate, polycarbonate, polystyrene, polyurethane, polyolefin, etc. Examples of polyolefins include polyethylene and polypropylene.

Examples of low-absorbency recording media include, but are not limited to, coated paper with a coating layer on the surface. The coating layer is made of, for example, resin or inorganic fine particles, and is a layer with low ink absorption. Examples of coated paper include, but are not limited to, printing paper such as art paper, coated paper, and matte paper.

The absorbent recording medium refers to the above-mentioned "recording medium having a water absorption amount of more than 10 mL/ ^m2 from the start of contact to 30 msec ^1/2 in the Bristow method." Examples of the absorbent recording medium include paper such as ordinary paper and inkjet paper, and cloth.

According to the inkjet recording method of this embodiment, the aqueous ink composition contains organic solvent A in particular, and therefore the ink has excellent wetting and spreading properties on low-absorbency recording media, making it possible to obtain image quality with a high OD value and excellent color development. Furthermore, according to the inkjet recording method of this embodiment, the aqueous ink composition contains organic solvent B in particular, and therefore the ink is prevented from penetrating into absorbent recording media, so that the colorant remains on the surface, making it possible to obtain image quality with a high OD value and excellent color development.

The recording medium may be in the form of a bag or a sheet. The recording medium may be subjected to a surface treatment such as a corona treatment or a primer treatment in advance, and such a surface treatment may improve the releasability of the ink from the recording medium.

The inkjet recording method according to the present embodiment may be a recording method using an inkjet recording device that uses a water-based ink composition to record on a low non-absorbent recording medium and on an absorbent recording medium. It may also be a recording method using an inkjet recording device to record on either a low non-absorbent recording medium or an absorbent recording medium. For example, the inkjet recording device has recording conditions set so that it can record on both a low non-absorbent recording medium and an absorbent recording medium using the water-based ink composition of the present embodiment. From these recording condition settings, recording on a low non-absorbent recording medium or recording on an absorbent recording medium is selected, and recording is performed using the selected recording condition settings. The recording conditions are not limited to, but may be, for example, the amount of ink attached, the recording resolution, or the temperature in the drying process.

1.3. Water-Based Ink Composition The water-based ink composition that can be used in the inkjet recording method according to this embodiment contains organic solvent A, which is a 1,2-alkanediol having a surface tension of 30 mN/m or less at 25° C., and organic solvent B, which is an alkanediol having a normal boiling point of 250° C. or less and a carbon number of 3 or more at both ends. By containing organic solvent A and organic solvent B, the water-based ink composition can be used for recording on low-absorbency recording media and for recording on absorbent recording media. In addition, the water-based ink composition is ejected from an inkjet head equipped with a circulation mechanism for circulating the ink inside, and used for recording. Each component contained in the water-based ink composition will be described below.

1.3.1. Organic solvent A
The water-based ink composition contains organic solvent A, which is a 1,2-alkanediol having a surface tension of 30 mN/m or less at 25° C. Organic solvent A has the effect of increasing the wetting and spreading property of the ink on low non-absorbent recording media, while at the same time promoting the penetration of the ink into absorbent recording media. This results in excellent wetting and spreading property of the ink on low non-absorbent recording media, making it possible to obtain image quality with a high OD value and excellent color development on low non-absorbent recording media.

The surface tension of organic solvent A at 25°C is 30 mN/m or less, preferably 29 mN/m or less, more preferably 28 mN/m or less, and particularly preferably 27 mN/m or less. The surface tension of organic solvent A at 25°C is preferably 10 mN/m or more, more preferably 15 mN/m or more, and particularly preferably 20 mN/m or more. 1,2-alkanediols with a surface tension at 25°C within the above range are useful as penetrating solvents and can improve the wetting and spreading of ink on low non-absorbent recording media. The method for measuring the surface tension can be, for example, a method of measuring the surface tension at a liquid temperature of 25°C using a commonly used surface tensiometer (for example, a surface tensiometer CBVP-Z manufactured by Kyowa Interface Science Co., Ltd.) by the Wilhelmy method.

As such organic solvent A, 1,2-alkanediols having 5 or more carbon atoms are preferred, and 1,2-alkanediols having 5 to 7 carbon atoms are more preferred. Specific examples of organic solvent A include 1,2-pentanediol, 1,2-hexanediol, and 1,2-heptanediol, with either 1,2-pentanediol or 1,2-hexanediol being preferred, and 1,2-hexanediol being particularly preferred.

The upper limit of the content of organic solvent A is preferably 10% by mass or less, more preferably 8% by mass or less, and particularly preferably 7% by mass or less, based on the total mass of the water-based ink composition. The lower limit of the content of organic solvent A is preferably 0.5% by mass or more, more preferably 1% by mass or more, even more preferably 2% by mass or more, and particularly preferably 3% by mass or more, based on the total mass of the water-based ink composition. When the content of organic solvent A is within the above range, the wetting spreadability on low non-absorbent recording media can be sufficiently increased, so that image quality with a high OD value and excellent color development is easily obtained on low non-absorbent recording media. In addition, organic solvent A works to reduce the dynamic surface tension of the ink, which may cause ink mist, but if the content of organic solvent A is within the above range, such adverse effects can be prevented.

1.3.2. Organic solvent B
The water-based ink composition contains organic solvent B, which is an alkanediol having a normal boiling point of 250° C. or less and a carbon number of 3 or more at both ends. Organic solvent B has the function of suppressing the penetration of the ink into the absorbent recording medium, which is promoted by organic solvent A. This suppresses the penetration of the ink into the absorbent recording medium, so that the colorant remains on the surface, and image quality with a high OD value and excellent color development can be obtained, particularly on the absorbent recording medium.

The reason why organic solvent B has this effect is speculative, but it is thought that the structure with hydroxyl groups at both ends contributes, and that these organic solvents B tend to have a slightly high viscosity. However, the reasons are not limited to these.

The normal boiling point of organic solvent B is 250°C or less, preferably 245°C or less, and particularly preferably 240°C or less. If the normal boiling point of organic solvent B is within the above range, organic solvent B can be quickly volatilized when the ink is applied to a low non-absorbent recording medium to form an image, making it suitable for inkjet recording methods on low non-absorbent recording media. In addition, drying properties and image quality are more excellent, making it preferable.

On the other hand, the normal boiling point of organic solvent B is preferably 160°C or higher, more preferably 180°C or higher, even more preferably 200°C or higher, particularly preferably 210°C or higher, even more preferably 220°C or higher, and particularly preferably 230°C or higher. When the normal boiling point is in the above range or higher, ejection reliability is more excellent and it is preferable. In addition, it is presumed that organic solvent B, which has the function of suppressing the penetration of the ink into the absorbent recording medium promoted by organic solvent A, tends to have a normal boiling point in the above range. In this specification, "normal boiling point" refers to the boiling point under a pressure of 1 atm.

As such organic solvent B, alkanediols having 3 or more carbon atoms at both ends can be mentioned, and alkanediols having 3 to 7 carbon atoms at both ends are preferred. Specific examples of organic solvent B include 1,3-propanediol (214°C), 1,4-butanediol (228°C), 1,5-pentanediol (239°C), 1,6-hexanediol (250°C), etc., with 1,3-propanediol, 1,5-pentanediol, and 1,6-hexanediol being preferred, and 1,5-pentanediol being particularly preferred. The numbers in parentheses indicate the standard boiling points.

The upper limit of the content of organic solvent B is preferably 30.0% by mass or less, more preferably 25.0% by mass or less, and particularly preferably 20.0% by mass or less, based on the total mass of the water-based ink composition. It is further preferably 17.0% by mass or less, and more preferably 15.0% by mass or less. On the other hand, the lower limit of the content of organic solvent B is preferably 4.0% by mass or more, more preferably 6.0% by mass or more, and particularly preferably 7.0% by mass or more, based on the total mass of the water-based ink composition. It is further preferably 10.0% by mass or more, and more preferably 14.0% by mass or more. When the content of organic solvent B is within the above range, the penetration of the ink into the absorbent recording medium promoted by organic solvent A can be sufficiently suppressed, so that image quality with a high OD value and excellent color development can be easily obtained on a low non-absorbent recording medium.

The upper limit of the total content of organic solvent A and organic solvent B is preferably 30.0% by mass or less, more preferably 25.0% by mass or less, and particularly preferably 20.0% by mass or less, based on the total mass of the water-based ink composition. The lower limit of the total content of organic solvent A and organic solvent B is somewhat preferably 3.0% by mass or more, preferably 5.0% by mass or more, more preferably 7.0% by mass or more, and particularly preferably 10.0% by mass or more, based on the total mass of the water-based ink composition. Furthermore, 13.0% by mass or more is preferable. Both organic solvent A and organic solvent B are hydrophilic organic solvents and therefore highly soluble in water, but as long as the total content of organic solvent A and organic solvent B is within the above range, deterioration of image quality can be reduced even when the ink is applied to a low-absorbency recording medium.

In the water-based ink composition, the upper limit of the mass ratio ( _MB / _MA ) of the content ( _MB ) of the organic solvent B to the content (MA) of the organic solvent _A is somewhat preferably 20.0 or less, preferably 16.0 or less, more preferably 10.0 or less, and particularly preferably 6.0 or less. Furthermore, 5.0 or less is preferable. On the other hand, the lower limit of the mass ratio ( _MB / _MA ) is preferably 0.2 or more, more preferably 0.5 or more, and particularly preferably 1 or more. Furthermore, 2.0 or more is preferable, 3.0 or more is more preferable, and 4.0 or more is more preferable. If the mass ratio ( _MB / _MA ) is within the above range, the balance of the contents of the organic solvent A and the organic solvent B is good, so that it is easy to improve the image quality on both low non-absorbent recording media and absorbent recording media, and it is easy to ensure the ejection stability of the ink.

1.3.3. Water The water-based ink composition contains water. In this specification, "water-based" refers to the inclusion of water as one of the main solvent components. Water is included as a main solvent component, and is a component that evaporates and disperses when dried. The water is preferably pure water or ultrapure water such as ion-exchanged water, ultrafiltered water, reverse osmosis water, distilled water, etc., from which ionic impurities have been removed as much as possible. In addition, it is preferable to use water sterilized by ultraviolet irradiation or addition of hydrogen peroxide, etc., since it is possible to suppress the generation of mold and bacteria when storing the water-based ink composition for a long period of time. The content of water is not particularly limited, but is preferably 40.0% by mass or more, more preferably 50.0% by mass or more, more preferably 70.0% by mass or more, even more preferably 75.0% by mass or more, even more preferably 80.0% by mass or more and 98.0% by mass or less, and particularly preferably 85.0% by mass or more and 95.0% by mass or less, based on the total mass of the water-based ink composition.

The weighted average of the standard boiling points of water and each organic solvent contained in the water-based ink composition and the content of each in the water-based ink composition (hereinafter also referred to as the "solvent composition boiling point") is preferably 130°C or less, more preferably 90 to 120°C, and particularly preferably 95 to 115°C. The organic solvents are organic solvents A and B, and other organic solvents if contained. If the solvent composition boiling point is within the above range, the solvent contained in the ink can be quickly volatilized, especially when the ink is applied to a low-absorption recording medium, so that a viscous image is unlikely to be formed, and image quality with a high OD value and excellent color development is likely to be obtained.

The solvent composition boiling point is calculated by multiplying the standard boiling point of each organic solvent and water component by the content (mass %) of that component relative to the ink (ink 100 mass %), calculating the sum for each component, and then dividing the sum by 100. This value takes into account not only the ratio of the content of each component to the total of each organic solvent and water, but also the total ratio of each organic solvent and water to the total ink.

1.3.4. Other Components 1.3.4.1. Colorant The water-based ink composition may contain a colorant. As the colorant, either a pigment or a dye may be used, and examples of the colorant that may be used include inorganic pigments including carbon black and titanium white, organic pigments, oil-soluble dyes, acid dyes, direct dyes, reactive dyes, basic dyes, disperse dyes, and sublimation dyes. The water-based ink composition preferably contains a pigment, and the pigment may be dispersed by a dispersing resin.

Examples of inorganic pigments that can be used include carbon blacks (C.I. Pigment Black 7) such as furnace black, lamp black, acetylene black, and channel black, iron oxide, titanium oxide, zinc oxide, and silica.

Examples of organic pigments include quinacridone pigments, quinacridonequinone pigments, dioxazine pigments, phthalocyanine pigments, anthrapyrimidine pigments, anthanthrone pigments, indanthrone pigments, flavanthrone pigments, perylene pigments, diketopyrrolopyrrole pigments, perinone pigments, quinophthalone pigments, anthraquinone pigments, thioindigo pigments, benzimidazolone pigments, isoindolinone pigments, azomethine pigments, and azo pigments.

Specific examples of organic pigments that can be used in the water-based ink composition include the following:

Cyan pigments include C.I. Pigment Blue 1, 2, 3, 15:3, 15:4, 15:34, 16, 22, 60, etc.; C.I. Bat Blue 4, 60, etc., and preferably one or a mixture of two or more selected from the group consisting of C.I. Pigment Blue 15:3, 15:4, and 60.

Examples of magenta pigments include C.I. Pigment Red 5, 7, 12, 48 (Ca), 48 (Mn), 57 (Ca), 57:1, 112, 122, 123, 168, 184, 202; C.I. Pigment Violet 19, and the like. Preferred examples include one or a mixture of two or more selected from the group consisting of C.I. Pigment Red 122, 202, and 209, and C.I. Pigment Violet 19.

Examples of yellow pigments include C.I. Pigment Yellow 1, 2, 3, 12, 13, 14C, 16, 17, 73, 74, 75, 83, 93, 95, 97, 98, 119, 110, 114, 128, 129, 138, 150, 151, 154, 155, 180, and 185, and preferably one or a mixture of two or more selected from the group consisting of C.I. Pigment Yellow 74, 109, 110, 128, and 138.

Pigments of other colors can also be used, for example orange pigments, green pigments, etc.

The pigments exemplified above are examples of suitable pigments, and the present invention is not limited thereto. These pigments may be used alone or in a mixture of two or more kinds, or may be used in combination with a dye.

The pigment may be dispersed using a dispersant selected from water-soluble resins, water-dispersible resins, surfactants, etc., or may be dispersed as a self-dispersing pigment by oxidizing or sulfonating the pigment surface with ozone, hypochlorous acid, fuming sulfuric acid, etc.

When the pigment is dispersed in the aqueous ink composition using a dispersing resin, the ratio of the pigment to the dispersing resin is preferably 10:1 to 1:10, and more preferably 4:1 to 1:3. In addition, the volume average particle size of the pigment when dispersed is preferably such that the maximum particle size measured by dynamic light scattering is less than 500 nm and the average particle size is 300 nm or less, and more preferably the average particle size is 200 nm or less.

The content of the coloring material can be adjusted appropriately depending on the application, but is preferably 0.1% by mass or more and 17.0% by mass or less, more preferably 0.2% by mass or more and 15.0% by mass or less, even more preferably 1.0% by mass or more and 10.0% by mass or less, and particularly preferably 2.0% by mass or more and 5.0% by mass or less, based on the total mass of the water-based ink composition.

When a pigment is used as the colorant, the volume average particle size of the pigment particles is preferably 10 to 200 nm or less, more preferably 30 to 200 nm, even more preferably 50 to 150 nm, and particularly preferably 70 to 120 nm.

Resin particles The water-based ink composition preferably contains resin particles, which may improve the water resistance and abrasion resistance of recorded matter.

Examples of such resin particles include urethane-based resins, acrylic-based resins, fluorene-based resins, polyolefin-based resins, rosin-modified resins, terpene-based resins, polyester-based resins, polyamide-based resins, epoxy-based resins, vinyl chloride-based resins, and ethylene vinyl acetate-based resins. These resin particles are often handled in the form of an emulsion, but may also be in the form of a powder. Furthermore, the resin particles may be used alone or in combination of two or more types.

Urethane resin is a general term for resins that have urethane bonds. In addition to urethane bonds, urethane-acrylic resins that contain an acrylic skeleton in the main chain, polyether-type urethane resins that contain ether bonds in the main chain, polyester-type urethane resins that contain ester bonds in the main chain, and polycarbonate-type urethane resins that contain carbonate bonds in the main chain may also be used as urethane resins. As the urethane resin, commercially available products may be used, for example, Superflex 210, 460, 460s, 840, E-4000 (trade names, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), Resamine D-1060, D-2020, D-4080, D-4200, D-6300, D-6455 (trade names, manufactured by Dainichi Seiyaku Chemicals Co., Ltd.), Takelac WS-6020, WS-6021, W-512-A-6 (trade names, manufactured by Mitsui Chemicals Polyurethanes Co., Ltd.), Sancure 2710 (trade name, manufactured by LUBRIZOL), and Parmarin UA-150 (trade name, manufactured by Sanyo Chemical Industries, Ltd.) may be selected and used.

Acrylic resin is a general term for polymers obtained by polymerizing at least an acrylic monomer such as (meth)acrylic acid or a (meth)acrylic acid ester as one component. Examples include resins obtained from acrylic monomers and copolymers of acrylic monomers with other monomers. Examples include acrylic-vinyl resins, which are copolymers of acrylic monomers and vinyl monomers. Further examples include copolymers with vinyl monomers such as styrene. Acrylamide, acrylonitrile, etc. can also be used as acrylic monomers. Urethane-acrylic resins are considered to be included in the above urethane resins.

For resin emulsions using acrylic resin as a raw material, commercially available products may be used, such as FK-854, Mowinyl 952B, 718A (product names, manufactured by Japan Coating Resins Co., Ltd.), Nipol LX852, LX874 (product names, manufactured by Nippon Zeon Co., Ltd.), Polysol AT860 (manufactured by Showa Denko KK), Boncoat AN-1190S, YG-651, AC-501, AN-1170, 4001 (product names, manufactured by DIC Corporation, acrylic resin emulsions), etc.

In this specification, the acrylic resin may be a styrene-acrylic resin as described above. In addition, in this specification, the term "(meth)acrylic" means at least one of acrylic and methacrylic.

Styrene-acrylic resins are copolymers obtained from styrene monomers and acrylic monomers, and examples include styrene-acrylic acid copolymers, styrene-methacrylic acid copolymers, styrene-methacrylic acid-acrylic acid ester copolymers, styrene-α-methylstyrene-acrylic acid copolymers, and styrene-α-methylstyrene-acrylic acid-acrylic acid ester copolymers. Styrene acrylic resins may be commercially available products, such as Joncryl 62J, 7100, 390, 711, 511, 7001, 632, 741, 450, 840, 74J, HRC-1645J, 734, 852, 7600, 775, 537J, 1535, PDX-7630A, 352J, 352D, PDX-7145, 538J, 7640, 7641, 631, 790, 780, 7610 (product names, manufactured by BASF Corporation), and Mowinyl 966A and 975N (product names, manufactured by Japan Coating Resins Co., Ltd.).

The vinyl chloride resin may be a vinyl chloride-vinyl acetate copolymer.

Polyolefin resins have an olefin such as ethylene, propylene, or butylene in the structural skeleton, and known resins can be appropriately selected and used. As the olefin resin, commercially available products can be used, and for example, Arrowbase CB-1200, CD-1200 (product names, manufactured by Unitika Ltd.), etc. can be selected and used.

The resin particles may also be supplied in the form of an emulsion. Examples of commercially available resin emulsions include Microgel E-1002 and E-5002 (product names of Nippon Paint Co., Ltd., styrene-acrylic resin emulsions), Boncoat AN-1190S, YG-651, AC-501, AN-1170, 4001, and 5454 (product names of DIC Corporation, styrene-acrylic resin emulsions), Polysol AM-710, AM-920, AM-2300, AP-4735, AT-860, and PSASE-4210E (acrylic resin emulsions), and Polysol AP-7020 (styrene-acrylic resin emulsion), Polysol SH-502 (vinyl acetate resin emulsion), Polysol AD-13, AD-2, AD-10, AD-96, AD-17, AD-70 (ethylene-vinyl acetate resin emulsion), Polysol PSASE-6010 (ethylene-vinyl acetate resin emulsion) (product name, manufactured by Showa Denko K.K.), Polysol SAE1014 (product name, styrene-acrylic resin emulsion, manufactured by Zeon Co., Ltd.), Saivinol SK-200 (product name, acrylic resin emulsion, manufactured by Saiden Chemical Co., Ltd.), AE-120A (product name, manufactured by JSR Corporation, acrylic resin emulsion), AE373D (E-tech (manufactured by Nissin Chemical Industry Co., Ltd., product name, carboxy-modified styrene-acrylic resin emulsion), Seikadyne 1900W (manufactured by Dainichiseika Chemical Industry Co., Ltd., product name, ethylene-vinyl acetate resin emulsion), Vinyblan 2682 (acrylic resin emulsion), Vinyblan 2886 (vinyl acetate-acrylic resin emulsion), Vinyblan 5202 (acrylic acetate resin emulsion) (manufactured by Nissin Chemical Industry Co., Ltd., product name), Vinyblan 700, 2586 (manufactured by Nissin Chemical Industry Co., Ltd.), Elitel KA-5071S, KT-8803, KT-9204, KT-8701, KT-8904, KT-0507 (manufactured by Unitika Ltd., product name, polyester resin emulsion) ), Hitec SN-2002 (manufactured by Toho Chemical Industry Co., Ltd., polyester resin emulsion), Takelac W-6020, W-635, W-6061, W-605, W-635, W-6021 (manufactured by Mitsui Chemicals Polyurethanes, Inc., urethane resin emulsion), Superflex 870, 800, 150, 420, 460, 470, 610, 620, 700 (manufactured by Daiichi Kogyo Seiyaku Co., Ltd., urethane resin emulsion), Parmarin UA-150 (manufactured by Sanyo Chemical Industries, Ltd., urethane resin emulsion), Suncure 2710 (manufactured by Lubrizol Japan, urethane resin emulsion), NeoRez R-9660, R-9637, R-940 (manufactured by Kusumoto Chemicals Co., Ltd., urethane resin emulsion), Adekabontiter HUX-380, 290K (made by ADEKA Corporation, urethane resin emulsion), Mowinyl 966A, Mowinyl 7320 (made by Japan Coating Resins), Joncryl 7100, 390, 711, 511, 7001, 632, 741, 450, 840, 74J, HRC-1645J, 734, 852, 7600, 775, 537J, 1535, PDX It may be selected from among -7630A, 352J, 352D, PDX-7145, 538J, 7640, 7641, 631, 790, 780, 7610 (all manufactured by BASF), NK Binder R-5HN (manufactured by Shin-Nakamura Chemical Co., Ltd.), Hydran WLS-210 (non-crosslinked polyurethane: manufactured by DIC Corporation), Joncryl 7610 (manufactured by BASF), etc.

The upper limit of the resin particle content is preferably 17.0% by mass or less, more preferably 15.0% by mass or less, and particularly preferably 10.0% by mass or less, as solid content, relative to the total mass of the water-based ink composition. It is further preferably 7.0% by mass or less. The lower limit of the resin particle content is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, and particularly preferably 1.0% by mass or more, as solid content, relative to the total mass of the water-based ink composition. It is further preferably 3.0% by mass or more, and more preferably 5.0% by mass or more. When the resin particle content is within the above range, the ink ejection stability may be better. In addition, the water resistance and abrasion resistance of the recorded matter are more excellent, which is preferable.

The total content of the colorant and the resin particles is preferably 3.0% by mass or more, as solids, relative to the total mass of the water-based ink composition. On the other hand, it is preferably 20.0% by mass or less. More preferably, it is 3.0% by mass or more and 20.0% by mass or less, and particularly preferably 4.0% by mass or more and 15.0% by mass or less. If the total content of the colorant and the resin particles is within the above range, the solids concentration is appropriate, and the ink has the characteristic that the viscosity of the ink increases rapidly when the solvent component in the ink evaporates. This suppresses the penetration of the ink into the absorbent recording medium, so the colorant remains on the surface, and image quality with a high OD value and excellent color development, especially on absorbent recording media, is obtained.

Among these resin particles, acrylic resin, urethane resin, or polyester resin is preferred, as they are easily formed into a film on the recording medium and have superior water resistance and abrasion resistance.

The glass transition temperature of the resin of the resin particles is preferably 70°C or lower, since it is easy to form a film on the recording medium and has better abrasion resistance. On the other hand, it is preferably -50°C or higher, since it has hardness and therefore has better abrasion resistance and better blocking show-through resistance. Furthermore, it is preferably -20°C or higher, more preferably -10°C or higher, even more preferably 0°C or higher, particularly preferably 10°C or higher, and even more particularly preferably 20°C or higher. On the other hand, it is preferably 50°C or lower, more preferably 45°C or lower, even more preferably 40°C or lower, and particularly preferably 30°C or lower.

Furthermore, the temperature is preferably -20°C or higher and 60°C or lower, more preferably -30°C or higher and 50°C or lower, even more preferably 20°C or higher and 50°C or lower, even more preferably 25°C or higher and 45°C or lower, and even more preferably 30°C or higher and 40°C or lower. The glass transition temperature (Tg) of the resin constituting the resin particles can be confirmed by a standard method using differential scanning calorimetry (DSC) or the like.

The water-based ink composition may contain an organic solvent other than the organic solvent A and the organic solvent B. Examples of such organic solvents include esters, alkylene glycol ethers, cyclic esters, nitrogen-containing solvents, and polyhydric alcohols.

Esters include glycol monoacetates such as ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, ethylene glycol monobutyl ether acetate, diethylene glycol monomethyl ether acetate, diethylene glycol monoethyl ether acetate, diethylene glycol monobutyl ether acetate, propylene glycol monomethyl ether acetate, dipropylene glycol monomethyl ether acetate, and methoxybutyl acetate; Examples of glycol diesters include ethylene glycol diacetate, propylene glycol diacetate, dipropylene glycol diacetate, ethylene glycol acetate propionate, ethylene glycol acetate butyrate, diethylene glycol acetate butyrate, diethylene glycol acetate propionate, diethylene glycol acetate butyrate, propylene glycol acetate propionate, propylene glycol acetate butyrate, dipropylene glycol acetate butyrate, and dipropylene glycol acetate propionate.

As the alkylene glycol ethers, monoethers or diethers of alkylene glycols are preferred, and alkyl ethers are more preferred. Specific examples include ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monoisopropyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol monobutyl ether, tetraethylene glycol monomethyl ether, tetraethylene glycol monoethyl ether, tetraethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, propylene glycol monobutyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol monopropyl ether, dipropylene glycol monobutyl ether, tripropylene glycol monobutyl ether, and propylene glycol monomethyl ether. and alkylene glycol dialkyl ethers such as ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol dibutyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, diethylene glycol methyl ethyl ether, diethylene glycol methyl butyl ether, triethylene glycol dimethyl ether, triethylene glycol diethyl ether, triethylene glycol dibutyl ether, triethylene glycol methyl butyl ether, tetraethylene glycol dimethyl ether, tetraethylene glycol diethyl ether, tetraethylene glycol dibutyl ether, propylene glycol dimethyl ether, propylene glycol diethyl ether, dipropylene glycol dimethyl ether, dipropylene glycol diethyl ether, and tripropylene glycol dimethyl ether.

Examples of cyclic esters include cyclic esters (lactones) such as β-propiolactone, γ-butyrolactone, δ-valerolactone, ε-caprolactone, β-butyrolactone, β-valerolactone, γ-valerolactone, β-hexanolactone, γ-hexanolactone, δ-hexanolactone, β-heptanolactone, γ-heptanolactone, δ-heptanolactone, ε-heptanolactone, γ-octanolactone, δ-octanolactone, ε-octanolactone, δ-nonalactone, ε-nonalactone, and ε-decanolactone, and compounds in which the hydrogen of the methylene group adjacent to the carbonyl group is replaced by an alkyl group having 1 to 4 carbon atoms.

Nitrogen-containing solvents include cyclic amides and non-cyclic amides. Non-cyclic amides include alkoxyalkylamides. Cyclic amides include pyrrolidones. Pyrrolidones include 2-pyrrolidone and pyrrolidones having a substituent.

Polyhydric alcohols are organic solvents having two or more hydroxyl groups in the molecule. For example, the number of carbon atoms in the polyhydric alcohols is 1 to 10, more preferably 2 to 6. The number of hydroxyl groups in the polyhydric alcohols is preferably 1 to 4. In addition, the polyhydric alcohols may have, for example, an alkyl group or an alkylene group having 1 to 7 carbon atoms in the structure. The number of carbon atoms in the group is preferably 2 to 6, more preferably 2 to 3. Among polyhydric alcohols, those in which an alkane having 4 or less carbon atoms has two or more hydroxyl groups, and those in which the hydroxyl groups of a diol of an alkane having 4 or less carbon atoms are condensed between molecules are called polyols. For those condensed between molecules, the condensation number is preferably 2 to 4. Polyols (those other than organic solvent B) have better moisturizing properties. On the other hand, such polyols do not have the same effect as organic solvent B in suppressing the penetration of ink into absorbent recording media, and in this respect are inferior to organic solvent B.

Examples of polyhydric alcohols include 1,2-alkanediols (e.g., alkanediols such as ethylene glycol, propylene glycol, 1,2-butanediol, and 1,2-octanediol), and polyhydric alcohols other than 1,2-alkanediols (e.g., diethylene glycol, propylene glycol, dipropylene glycol, 1,3-butanediol, 2-ethyl-2-methyl-1,3-propanediol, 2-methyl-2-propyl-1,3-propanediol, 2-methyl-1,3-propanediol, 2,2-dimethyl-1,3-propanediol, 3-methyl-1,3-butanediol, 2-ethyl-1,3-hexanediol, 3-methyl-1,5-pentanediol, 2-methylpentane-2,4-diol, trimethylolpropane, and glycerin).

These organic solvents may be used alone or in combination of two or more. By including such an organic solvent, the wettability of the water-based ink composition to the recording medium may be improved, and the moisture retention of the water-based ink composition may be improved, resulting in good ejection stability.

The content of other organic solvents is preferably 10.0% by mass or less, more preferably 8.0% by mass or less, and particularly preferably 5.0% by mass or less, based on the total mass of the water-based ink composition. The content of other organic solvents is 0% by mass or more, and more preferably 1.0% by mass or more.

The water-based ink composition preferably does not contain more than 4% by mass of polyol organic solvents with a normal boiling point of more than 280°C in the ink, more preferably does not contain more than 1% by mass, and even more preferably does not contain more than 0.5% by mass. "Does not contain more than" means that it is acceptable to contain them as long as it does not exceed the amount, and it is not necessary to contain them.

Furthermore, it is preferable that the content of the organic solvent having a normal boiling point of more than 280°C in the water-based ink composition is within the above range. The organic solvents here are the above-mentioned organic solvents A and B, and other organic solvents. The pH adjusters described below are not included in the organic solvents. Organic solvents having a normal boiling point of more than 280°C, particularly polyols, function well as humectants, but tend to slow down the drying of the ink after it is applied to the recording medium, and it is preferable to keep the content within the above range, as this provides better drying properties and image quality.

The organic solvent contained in the water-based ink composition preferably has a normal boiling point of 160 to 280°C.

The aqueous ink composition may contain a surfactant. The surfactant has a function of reducing the surface tension of the aqueous ink composition and improving the wettability with a recording medium or a base. Among the surfactants, acetylene glycol surfactants, silicon surfactants, and fluorine surfactants can be preferably used.

Acetylene glycol surfactants are not particularly limited, but examples thereof include Surfynol 104, 104E, 104H, 104A, 104BC, 104DPM, 104PA, 104PG-50, 104S, 420, 440, 465, 485, SE, SE-F, 504, 61, DF37, CT111, CT121, CT131, CT136, TG, GA, DF110D (all trade names, manufactured by Air Products & Chemicals), Olfine B, Y, P, A, STG, SPC, E1004, E1010, PD-001, PD-002W, PD-003, PD-004, EXP. 4001, EXP. 4036, EXP. 4051, AF-103, AF-104, AK-02, SK-14, AE-3 (all trade names, manufactured by Nissin Chemical Industry Co., Ltd.), Acetylenol E00, E00P, E40, E100 (all trade names, manufactured by Kawaken Fine Chemical Co., Ltd.).

The silicon-based surfactant is not particularly limited, but a polysiloxane-based compound is preferred. The polysiloxane-based compound is not particularly limited, but an example thereof is polyether-modified organosiloxane. Commercially available polyether-modified organosiloxanes include, for example, BYK-306, BYK-307, BYK-333, BYK-341, BYK-345, BYK-346, and BYK-348 (all trade names, manufactured by BYK Japan), KF-351A, KF-352A, KF-353, KF-354L, KF-355A, KF-615A, KF-945, KF-640, KF-642, KF-643, KF-6020, X-22-4515, KF-6011, KF-6012, KF-6015, and KF-6017 (all trade names, manufactured by Shin-Etsu Chemical Co., Ltd.).

As the fluorine-based surfactant, it is preferable to use a fluorine-modified polymer, and specific examples include BYK-3440 (manufactured by BYK Japan), Surflon S-241, S-242, S-243 (all trade names, manufactured by AGC Seimi Chemical Co., Ltd.), and Futergent 215M (manufactured by Neos Co., Ltd.).

When the aqueous ink composition contains a surfactant, multiple types of surfactants may be contained. When the aqueous ink composition contains a surfactant, the content is preferably 0.1% by mass or more and 2.0% by mass or less, more preferably 0.2% by mass or more and 1.5% by mass or less, and particularly preferably 0.3% by mass or more and 1.0% by mass or less, based on the total mass of the aqueous ink composition.

1.3.4.5. pH Adjuster The water-based ink composition may contain a pH adjuster. By containing a pH adjuster, for example, it is possible to suppress or promote the elution of impurities from the member forming the ink flow path, and to adjust the cleaning properties of the water-based ink composition. Examples of pH adjusters include ureas, amines, morpholines, piperazines, and amino alcohols such as triethanolamine.

1.3.4.6 Other Components The water-based ink composition may contain additives such as wax, a chelating agent, an anti-rust agent, an anti-fungal agent, an antioxidant, and an anti-reducing agent, as necessary.

Examples of waxes include polyolefin waxes such as polyethylene wax, paraffin wax, etc.

Examples of chelating agents include ethylenediaminetetraacetate (EDTA), ethylenediamine nitrilotriacetate, hexametaphosphate, pyrophosphate, and metaphosphate.

1.3.5. Method for producing water-based ink composition The method for producing the water-based ink composition is not particularly limited, but the water-based ink composition can be produced, for example, by mixing the ink components described above in any order and removing impurities by filtration, etc., as necessary. As a method for mixing the components, a method in which the materials are added sequentially to a container equipped with a stirring device such as a mechanical stirrer or a magnetic stirrer, and then stirred and mixed is preferably used.

From the viewpoint of a balance between image quality and reliability as an ink for inkjet recording, the water-based ink composition preferably has a surface tension of 20 mN/m to 40 mN/m, and more preferably 20 mN/m to 35 mN/m at 25° C. The surface tension can be measured, for example, by using an automatic surface tensiometer CBVP-Z (product name, manufactured by Kyowa Interface Science Co., Ltd.) to confirm the surface tension when a platinum plate is wetted with the ink in an environment of 20° C.

The viscosity of the water-based ink composition at 25°C is preferably 4.5 mPa·s or more. On the other hand, it is preferably 10.0 mPa·s or less. It is more preferably 5.0 mPa·s or more and 10.0 mPa·s or less. If the viscosity of the water-based ink composition at 25°C is within the above range, the ink is more likely to be inhibited from penetrating into the absorbent recording medium, so that the coloring material remains on the surface, and image quality with a high OD value and excellent color development can be obtained, particularly on absorbent recording media. The viscosity can be measured, for example, using a viscoelasticity tester MCR-300 (product name, manufactured by Pysica) in an environment of 25°C.

1.3.7. Characteristics of the Water-Based Ink Composition According to the inkjet recording method of this embodiment, by using a water-based ink composition containing organic solvent A and organic solvent B, it is possible to obtain image quality with a high OD value and excellent color development, regardless of whether the recording medium is a low-absorbency recording medium or an absorbency recording medium. The mechanism is presumed to be as follows. That is, organic solvent A has the effect of increasing the wet spreadability on the low non-absorbency recording medium, but on the other hand, promoting penetration into the absorbency recording medium. As a result, the wet spreadability of the ink on the low non-absorbency recording medium is excellent, so that image quality with a high OD value and excellent color development can be obtained on the low non-absorbency recording medium. On the other hand, organic solvent B has the effect of suppressing the penetration of the ink into the absorbency recording medium, which is promoted by organic solvent A. As a result, the penetration of the ink into the absorbency recording medium is suppressed, so that the coloring material remains on the surface, and image quality with a high OD value and excellent color development can be obtained even on the absorbency recording medium.

However, neither organic solvent A nor organic solvent B contained in the water-based ink composition necessarily has excellent moisturizing performance. Therefore, in an inkjet recording method using the water-based ink composition, the ink may dry out in the nozzle, causing the ejection stability to be impaired. Therefore, the inkjet recording method according to this embodiment is performed using an inkjet recording device having an inkjet head equipped with a circulation mechanism for circulating the ink inside, as described below, thereby improving image quality on both low non-absorbent recording media and absorbent recording media, and ensuring the ejection stability of the ink. Next, the inkjet recording device used in the inkjet recording method according to this embodiment will be described.

2. Inkjet Recording Apparatus An inkjet recording apparatus according to one embodiment of the present invention comprises an ink deposition means for ejecting an aqueous ink composition from an inkjet head and depositing it on a recording medium, the aqueous ink composition containing organic solvent A which is a 1,2-alkanediol having a surface tension of 30 mN/m or less at 25° C. and organic solvent B which is an alkanediol having a normal boiling point of 250° C. or less and having 3 or more carbon atoms at both ends, the inkjet head comprising a circulation mechanism for circulating the aqueous ink composition. The ink deposition means and the aqueous ink composition are the same as those described above, and therefore a description thereof will be omitted.

The inkjet recording device according to this embodiment is characterized in that the inkjet head is equipped with a circulation mechanism for circulating the water-based ink composition. The water-based ink composition contains organic solvent A and organic solvent B, and therefore cannot be said to have excellent moisturizing performance, and if the ink dries in the nozzle or near the nozzle, the ejection stability may be impaired. Therefore, by using an inkjet head equipped with a circulation mechanism for circulating the water-based ink composition, the ink near the nozzle can be circulated to restore the ink that is beginning to dry, thereby improving the ejection stability of the ink. Below, an overview of the inkjet recording device according to this embodiment will be described.

2.1. Overview of Inkjet Recording Apparatus An example of an inkjet recording apparatus suitable for the above-mentioned water-based ink composition will be described with reference to the drawings. In each drawing used in the following description, the scale and relative dimensions of each component have been appropriately changed so that each component is of a recognizable size.

Figure 1 is a schematic cross-sectional view showing an inkjet recording device 1. Figure 2 is a perspective view showing an example of the configuration around the carriage of the inkjet recording device 1 of Figure 1. As shown in Figures 1 and 2, the inkjet recording device 1 includes an inkjet head 2, an IR heater 3, a platen heater 4, a heating heater 5, a cooling fan 6, a pre-heater 7, a ventilation fan 8, a carriage 9, a platen 11, a cartridge 12, a carriage movement mechanism 13, a transport means 14, and a control unit CONT. The operation of the entire inkjet recording device 1 is controlled by the control unit CONT shown in Figure 2.

The inkjet head 2 is configured to perform recording on the recording medium M by ejecting and depositing an aqueous ink composition from the nozzles of the inkjet head 2. In this example, the inkjet head 2 is a serial type recording head, and scans multiple times in the main scanning direction relative to the recording medium M to deposit the aqueous ink composition on the recording medium M. The inkjet head 2 is mounted on a carriage 9 shown in FIG. 2. The inkjet head 2 is scanned multiple times in the main scanning direction relative to the recording medium M by the operation of a carriage movement mechanism 13 that moves the carriage 9 in the medium width direction of the recording medium M. The medium width direction is the main scanning direction of the inkjet head 2. Scanning in the main scanning direction is also called main scanning.

Here, the main scanning direction is the direction in which the carriage 9 carrying the inkjet head 2 moves. In FIG. 1, it is the direction intersecting with the sub-scanning direction, which is the transport direction of the recording medium M, indicated by the arrow SS. In FIG. 2, the width direction of the recording medium M, that is, the direction indicated by S1-S2, is the main scanning direction MS, and the direction indicated by T1→T2 is the sub-scanning direction SS. Note that scanning is performed in the main scanning direction, that is, in either the direction indicated by the arrow S1 or the arrow S2, in one scan. Then, recording is performed on the recording medium M by repeating the main scan of the inkjet head 2 and the sub-scan, which is the transport of the recording medium M, multiple times. In other words, the ink deposition process is performed by multiple main scans in which the inkjet head 2 moves in the main scanning direction, and multiple sub-scans in which the recording medium M moves in the sub-scanning direction that intersects the main scanning direction.

The cartridge 12 that supplies the water-based ink composition to the inkjet head 2 includes a plurality of independent cartridges. The cartridge 12 is removably mounted on the carriage 9 on which the inkjet head 2 is mounted. Each of the plurality of cartridges is filled with a different type of water-based ink composition or other composition, and the water-based ink composition or other composition is supplied from the cartridge 12 to each nozzle. Note that, although an example in which the cartridge 12 is mounted on the carriage 9 is shown, this is not limiting, and the cartridge 12 may be provided at a location other than the carriage 9 and may supply the ink to each nozzle via a supply pipe (not shown).

Conventionally known methods can be used for ejecting ink from the inkjet head 2. Here, a method is used that ejects droplets using the vibration of a piezoelectric element, that is, an ejection method that forms ink droplets by mechanically deforming an electrostrictive element.

The inkjet recording device 1 can be equipped with a drying mechanism that performs a drying process to dry the recording medium M when the aqueous ink composition is discharged from the inkjet head 2 and adhered to the recording medium. Drying can be performed by heating or blowing air. The drying mechanism can be a conduction type, a blowing type, a radiation type, or the like. The conduction type conducts heat to the recording medium from a member that contacts the recording medium. For example, a platen heater can be used. The blowing type sends room temperature air or hot air to the recording medium to dry the ink. For example, a blowing fan can be used. The radiation type radiates heat-generating radiation to the recording medium to heat the recording medium. For example, IR radiation can be used. These drying mechanisms can be used alone or in combination.

For example, the drying mechanism includes an IR heater 3 and a platen heater 4. When drying the recording medium M in the drying process, the IR heater 3, ventilation fan 8, etc. can be used.

When the IR heater 3 is used, the recording medium M can be radiatively heated by radiating infrared rays from the inkjet head 2 side. This makes it easier for the inkjet head 2 to heat at the same time, but compared to heating from the back side of the recording medium M using a platen heater 4 or the like, the temperature can be increased without being affected by the thickness of the recording medium M. In addition, various fans (e.g., ventilation fan 8) may be provided to blow warm air or air at the same temperature as the environment onto the recording medium M to dry the water-based ink composition on the recording medium M.

The platen heater 4 can heat the recording medium M through the platen 11 at a position opposite the inkjet head 2 so that the aqueous ink composition discharged by the inkjet head 2 can be dried quickly from the time it is applied to the recording medium M. The platen heater 4 can heat the recording medium M by conduction and is used as necessary in the inkjet recording method. When used, it is preferable to control the surface temperature of the recording medium M to be 45.0°C or lower. In a line-type inkjet recording device described later, the platen heater 4 corresponds to an under-heater. If a drying process using a drying mechanism is not performed, it is not necessary to provide a drying mechanism.

In addition, the surface temperature of the recording medium M in the ink attachment process is preferably in the range described above. Here again, for example, it is preferably 45.0°C or less, more preferably 40.0°C or less, even more preferably 38.0°C or less, and particularly preferably 35.0°C or less. In addition, the lower limit of the surface temperature of the recording medium M is preferably 25.0°C or more, more preferably 28.0°C or more, even more preferably 30.0°C or more, and particularly preferably 32.0°C. When the surface temperature of the recording medium M in the ink attachment process is in these ranges, the drying and composition fluctuation of the water-based ink composition in the inkjet head 2 can be suppressed, and the adhesion of the water-based ink composition and resin to the inner wall of the inkjet head 2 can be suppressed. In addition, the water-based ink composition can be fixed on the recording medium M early, offset can be suppressed, and image quality can be improved.

After the ink application process, a post-heating process may be performed in which the recording medium is heated to dry and fix the ink. Post-heating is also called secondary heating.

The heater 5 used in the post-heating process dries and solidifies the water-based ink composition attached to the recording medium M, that is, it is a heater for secondary heating or secondary drying. The heater 5 can be used in the post-heating process. When the heater 5 heats the recording medium M on which an image has been recorded, the moisture and other components contained in the water-based ink composition evaporate and dissipate more quickly, and an ink film is formed by the resin and other components that may be contained in the water-based ink composition. In this way, the ink film is firmly fixed or adhered on the recording medium M, resulting in excellent film-forming properties, and an excellent, high-quality image can be obtained in a short time.

In the secondary heating, the surface temperature of the recording medium M is preferably in the range described above. To state again here, the upper limit is preferably 120.0°C or less, more preferably 100.0°C or less, and even more preferably 90.0°C or less. The lower limit of the surface temperature of the recording medium M is preferably 60.0°C or more, more preferably 70.0°C or more, and even more preferably 80.0°C or more. By having the surface temperature of the recording medium M in the above range, a high-quality image can be obtained in a short time. In addition, in a line-type inkjet recording device described later, the heater 5 corresponds to an after-heater and is composed of a carbon heater or the like.

The inkjet recording device 1 may have a cooling fan 6. After the water-based ink composition recorded on the recording medium M is dried, the ink on the recording medium M is cooled by the cooling fan 6, so that an ink coating film with good adhesion can be formed on the recording medium M.

The inkjet recording device 1 may also include a preheater 7 that preheats the recording medium M before the water-based ink composition is applied to the recording medium M. The inkjet recording device 1 may also include a ventilation fan 8 so that the water-based ink composition applied to the recording medium M can be dried more efficiently. The preheater 7 may also be provided in a line-type inkjet recording device, which will be described later.

Below the carriage 9 are a platen 11 that supports the recording medium M, a carriage movement mechanism 13 that moves the carriage 9 relative to the recording medium M, and a transport means 14, which is a roller that transports the recording medium M in the sub-scanning direction. The operations of the carriage movement mechanism 13 and the transport means 14 are controlled by the control unit CONT.

Figure 3 is a functional block diagram of the inkjet recording device 1. The control unit CONT is a control unit for controlling the inkjet recording device 1. The interface unit 101 (I/F) is for transmitting and receiving data between the computer 130 (COMP) and the inkjet recording device 1. The CPU 102 is an arithmetic processing device for controlling the entire inkjet recording device 1. The memory 103 (MEM) is for securing an area for storing programs for the CPU 102, a working area, etc. The CPU 102 controls each unit through a unit control circuit 104 (UCTRL). The detector group 121 (DS) monitors the situation inside the inkjet recording device 1, and the control unit CONT controls each unit based on the detection results.

The transport unit 111 (CONVU) controls the sub-scanning (transport) of inkjet recording, specifically, the transport direction and transport speed of the recording medium M. Specifically, it controls the transport direction and transport speed of the recording medium M by controlling the rotation direction and rotation speed of a transport roller driven by a motor.

The carriage unit 112 (CARU) controls the main scan (pass) of inkjet recording, and more specifically, moves the inkjet head 2 back and forth in the main scan direction. The carriage unit 112 includes a carriage 9 that carries the inkjet head 2, and a carriage movement mechanism 13 for moving the carriage 9 back and forth.

The head unit 113 (HU) controls the amount of water-based ink composition ejected from the nozzles of the inkjet head 2. For example, if the nozzles of the inkjet head 2 are driven by piezoelectric elements, it controls the operation of the piezoelectric elements in each nozzle. The head unit 113 controls the timing of deposition of each water-based ink composition, dot size, etc. Also, the amount of water-based ink composition deposited per scan is controlled by a combination of controls of the carriage unit 112 and the head unit 113.

The drying unit 114 (DU) controls the temperature of various heaters such as the IR heater 3, pre-heater 7, platen heater 4, and heating heater 5.

The inkjet recording device 1 alternately repeats an operation of moving the carriage 9 carrying the inkjet head 2 in the main scanning direction and a transport operation (sub-scanning). At this time, when performing each pass, the control unit CONT controls the carriage unit 112 to move the inkjet head 2 in the main scanning direction, and controls the head unit 113 to eject droplets of the water-based ink composition from predetermined nozzle holes of the inkjet head 2 and deposit the droplets of the water-based ink composition on the recording medium M. The control unit CONT also controls the transport unit 111 to transport the recording medium M in the transport direction at a predetermined transport amount (feed amount) during the transport operation.

In the inkjet recording device 1, the recording area to which multiple droplets have been attached is gradually transported by repeating main scanning (passes) and sub-scanning (transport operation). The droplets attached to the recording medium M are then dried by a heater 5 to complete the image. The completed recording may then be wound into a roll by a winding mechanism or transported by a flatbed mechanism.

Inkjet head equipped with a circulation mechanism The inkjet recording apparatus according to this embodiment ejects the water-based ink composition using an inkjet head equipped with a circulation mechanism for circulating at least the water-based ink composition. That is, at least the water-based ink composition is circulated by the circulation mechanism. The circulation mechanism has a path for passing the water-based ink composition through a pressure chamber and causing it to flow back into the pressure chamber.

In this embodiment, the inkjet head 2 is equipped with a circulation mechanism for circulating the water-based ink composition. When the water-based ink composition dries, even if the concentration of the solids in the water-based ink composition increases, the circulation mechanism for the water-based ink composition allows the water-based ink composition with the increased concentration to be returned to the upstream side and mixed with new water-based ink composition, ensuring good ejection stability.

Figure 4 is a schematic diagram of a cross section of the inkjet head 2 perpendicular to the transport direction of the recording medium M (sub-scanning direction SS, see Figure 2) which is the Y direction. In Figure 4, a plane parallel to the surface of the recording medium M is the X-Y plane, and the direction perpendicular to the X-Y plane is hereinafter referred to as the Z direction. The direction in which the water-based ink composition is ejected by the inkjet head 2 corresponds to the Z direction.

The multiple nozzles N of the inkjet head 2 are arranged in the Y direction to form a nozzle row. In the following explanation, the plane that passes through the central axis of the inkjet head 2 parallel to the Y direction and is parallel to the Z direction, i.e., the Y-Z plane O, is referred to as the "central plane."

As shown in FIG. 4, the inkjet head 2 has a structure in which elements related to each nozzle N in the first row L1 and elements related to each nozzle N in the second row L2 are arranged symmetrically across the central plane O. That is, the structure of the recording head 2 is essentially the same for a portion P1 on the positive side in the X direction (hereinafter also referred to as the "first portion") and a portion P2 on the negative side in the X direction (hereinafter also referred to as the "second portion") across the central plane O. The multiple nozzles N in the first row L1 are formed in the first portion P1, and the multiple nozzles N in the second row L2 are formed in the second portion P2. The central plane O corresponds to the boundary surface between the first portion P1 and the second portion P2.

Here, each nozzle N in the second row L2 and each nozzle N in the first row L1 in FIG. 4 constitute a nozzle row (not shown) filled with the above-mentioned water-based ink composition. Here, the region of the inkjet head from which the water-based ink composition is ejected (the nozzle row (not shown) filled with the above-mentioned water-based ink composition) is not described, but may be configured in the same way.

As shown in FIG. 4, the inkjet head 2 includes a flow path forming section 30. The flow path forming section 30 is a structure that forms a flow path for supplying a water-based ink composition to a plurality of nozzles N. In this embodiment, the flow path forming section 30 is configured by laminating a first flow path substrate 32 and a second flow path substrate 34. Each of the first flow path substrate 32 and the second flow path substrate 34 is a plate-like member that is elongated in the Y direction. The second flow path substrate 34 is attached to the surface Fa of the first flow path substrate 32 on the negative side in the Z direction, for example, by using an adhesive.

As shown in FIG. 4, on the surface Fa of the first flow path substrate 32, in addition to the second flow path substrate 34, the vibration section 42, the piezoelectric element 44, the protective member 46, and the housing section 48 are installed. On the other hand, on the positive side of the first flow path substrate 32 in the Z direction, that is, on the surface Fb opposite to the surface Fa, a nozzle plate 52 and a vibration absorber 54 are installed. Each element of the inkjet head 2 is roughly a plate-like member elongated in the Y direction, similar to the first flow path substrate 32 and the second flow path substrate 34, and is bonded to each other, for example, using an adhesive. It is also possible to grasp the direction in which the first flow path substrate 32 and the second flow path substrate 34 are stacked, the direction in which the first flow path substrate 32 and the nozzle plate 52 are stacked, or the direction perpendicular to the surface of each plate-like element as the Z direction.

The nozzle plate 52 is a plate-like member in which a plurality of nozzles N are formed, and is installed on the surface Fb of the first flow path substrate 32, for example, using an adhesive. Each of the plurality of nozzles N is a circular through-hole that allows the water-based ink composition to pass through. The nozzle plate 52 is formed with a plurality of nozzles N constituting the first row L1 and a plurality of nozzles N constituting the second row L2. Specifically, the nozzles N of the first row L1 are formed along the Y direction in the region on the positive side of the X direction of the nozzle plate 52 as viewed from the center plane O, and the nozzles N of the second row L2 are formed along the Y direction in the region on the negative side of the X direction. The nozzle plate 52 is a single plate-like member that is continuous over the portion in which the plurality of nozzles N of the first row L1 are formed and the portion in which the plurality of nozzles N of the second row L2 are formed. The nozzle plate 52 is manufactured by processing a single crystal silicon substrate using semiconductor manufacturing technology, for example, processing technology such as dry etching or wet etching. However, any known material or manufacturing method may be used to manufacture the nozzle plate 52.

4, the first flow path substrate 32 has a space Ra, a plurality of supply paths 61, and a plurality of communication paths 63 for each of the first portion P1 and the second portion P2. The space Ra is an opening formed in a long shape along the Y direction when viewed in a plan view, i.e., when viewed from the Z direction, and the supply path 61 and the communication path 63 are through holes formed for each nozzle N. The communication paths 63 are arranged in the Y direction when viewed in a plan view, and the supply paths 61 are arranged in the Y direction between the arrangement of the communication paths 63 and the space Ra. The supply paths 61 are commonly connected to the space Ra. In addition, any one communication path 63 overlaps with the nozzle N corresponding to the communication path 63 in a plan view. Specifically, any one communication path 63 of the first portion P1 is connected to one nozzle N corresponding to the communication path 63 in the first row L1. Similarly, any one of the communication passages 63 in the second portion P2 communicates with one nozzle N in the second row L2 that corresponds to that communication passage 63.

As shown in FIG. 4, the second flow path substrate 34 is a plate-like member in which a plurality of pressure chambers C are formed for each of the first portion P1 and the second portion P2. The plurality of pressure chambers C are arranged in the Y direction. Each pressure chamber C is formed for each nozzle N and is an elongated space along the X direction in a plan view. The first flow path substrate 32 and the second flow path substrate 34 are manufactured by processing a single crystal substrate of silicon using, for example, semiconductor manufacturing technology, similar to the nozzle plate 52 described above. However, any known material or manufacturing method may be used to manufacture the first flow path substrate 32 and the second flow path substrate 34. As shown in the above example, the flow path forming portion 30 and the nozzle plate 52 include a substrate formed of silicon. Therefore, by using semiconductor manufacturing technology, for example, as in the above example, there is an advantage that fine flow paths can be formed with high precision in the flow path forming portion 30 and the nozzle plate 52.

As shown in FIG. 4, a vibration section 42 is provided on the surface of the second flow path substrate 34 opposite the first flow path substrate 32. The vibration section 42 is a plate-like member that can vibrate elastically. Note that it is also possible to integrally form the second flow path substrate 34 and the vibration section 42 by selectively removing a portion in the plate thickness direction from an area of a plate-like member of a predetermined thickness that corresponds to the pressure chamber C.

As shown in FIG. 4, the surface Fa of the first flow path substrate 32 and the vibration section 42 face each other with a gap between them inside each pressure chamber C. The pressure chamber C is a space located between the surface Fa of the first flow path substrate 32 and the vibration section 42, and generates a pressure change in the water-based ink composition filled in the space. Each pressure chamber C is a space with the X direction as its longitudinal direction, for example, and is formed individually for each nozzle N. A plurality of pressure chambers C are arranged in the Y direction for each of the first row L1 and the second row L2.

As shown in FIG. 4, the end of any one pressure chamber C on the central plane O side overlaps the communication passage 63 in a plan view, and the end on the opposite side to the central plane O overlaps the supply passage 61 in a plan view. Therefore, in each of the first portion P1 and the second portion P2, the pressure chamber C communicates with the nozzle N via the communication passage 63, and communicates with the space Ra via the supply passage 61. It is also possible to add a predetermined flow passage resistance by forming a throttle flow passage in the pressure chamber C, where the flow passage width is narrowed.

As shown in FIG. 4, a plurality of piezoelectric elements 44 corresponding to different nozzles N are installed on the surface of the vibration part 42 opposite to the pressure chamber C for each of the first part P1 and the second part P2. The piezoelectric elements 44 are elements that deform when a drive signal is supplied. The plurality of piezoelectric elements 44 are arranged in the Y direction so as to correspond to each pressure chamber C. Any one piezoelectric element 44 is, for example, a laminate in which a piezoelectric layer is interposed between two electrodes facing each other. It is also possible to define the part that deforms when a drive signal is supplied, that is, the active part that vibrates the vibration part 42, as the piezoelectric element 44. In this embodiment, when the vibration part 42 vibrates in conjunction with the deformation of the piezoelectric element 44, the pressure in the pressure chamber C changes, and the water-based ink composition filled in the pressure chamber C passes through the communication passage 63 and the nozzle N to be ejected.

The protective member 46 in FIG. 4 is a plate-like member for protecting the multiple piezoelectric elements 44, and is placed on the surface of the vibration section 42 or the surface of the second flow path substrate 34. The material and manufacturing method of the protective member 46 are arbitrary, but similar to the first flow path substrate 32 and the second flow path substrate 34, the protective member 46 can be formed, for example, by processing a single crystal silicon substrate using semiconductor manufacturing technology. The multiple piezoelectric elements 44 aligned in the Y direction in the figure are housed in a recess formed on the surface of the protective member 46 facing the vibration section 42.

An end of the wiring board 28 is joined to the surface of the vibration section 42 opposite the flow path forming section 30, or to the surface of the flow path forming section 30. The wiring board 28 is a flexible mounting component on which multiple wires (not shown) are formed to electrically connect the control unit and the inkjet head 2. The end of the wiring board 28 that passes through an opening formed in the protective member 46 and an opening formed in the housing section 48 and extends to the outside is connected to the control unit. For example, a flexible wiring board 28 such as an FPC (flexible printed circuit) or FFC (flexible flat cable) is preferably used.

The housing portion 48 is a case for storing the water-based ink composition to be supplied to the multiple pressure chambers C and further to the multiple nozzles N. The surface of the housing portion 48 on the positive side in the Z direction is bonded to the surface Fa of the first flow path substrate 32, for example, with an adhesive. Any known technology or manufacturing method may be used to manufacture the housing portion 48. For example, the housing portion 48 can be formed by injection molding of a resin material.

As shown in FIG. 4, a space Rb is formed in each of the first portion P1 and the second portion P2 in the housing portion 48. The section Rb of the housing portion 48 and the space Ra of the first flow path substrate 32 are mutually connected. The space formed by the space Ra and the space Rb functions as a liquid storage chamber R that stores the water-based ink composition supplied to the multiple pressure chambers C. The liquid storage chamber R is a common liquid chamber shared by the multiple nozzles N. A liquid storage chamber R is formed in each of the first portion P1 and the second portion P2. The liquid storage chamber R of the first portion P1 is located on the positive side of the X direction as viewed from the central plane O, and the liquid storage chamber R of the second portion P2 is located on the negative side of the X direction as viewed from the central plane O. An inlet 482 is formed on the surface of the housing portion 48 opposite to the first flow path substrate 32 to introduce the water-based ink composition supplied from the cartridge 12 into the liquid storage chamber R.

As shown in FIG. 4, a vibration absorber 54 is provided on the surface Fb of the first flow path substrate 32 for each of the first portion P1 and the second portion P2. The vibration absorber 54 is a flexible film, i.e., a compliance substrate, that absorbs pressure fluctuations of the water-based ink composition in the liquid storage chamber R. For example, the vibration absorber 54 is provided on the surface Fb of the first flow path substrate 32 so as to block the space Ra of the first flow path substrate 32 and the multiple supply paths 61, and forms the wall surface, specifically the bottom surface, of the liquid storage chamber R.

As shown in FIG. 4, a space (hereinafter referred to as a "circulation fluid chamber") 65 is formed on the surface Fb of the first flow path substrate 32 facing the nozzle plate 52. The circulation fluid chamber 65 is an elongated bottomed hole extending in the Y direction in a plan view. The opening of the circulation fluid chamber 65 is blocked by the nozzle plate 52 joined to the surface Fb of the first flow path substrate 32. The circulation fluid chamber 65 is continuous across multiple nozzles N along the first row L1 and the second row L2, for example. Specifically, the circulation fluid chamber 65 is formed between the arrangement of multiple nozzles N in the first row L1 and the arrangement of multiple nozzles N in the second row L2. Therefore, the circulation fluid chamber 65 is located between the communication passage 63 of the first part P1 and the communication passage 63 of the second part P2. Thus, the flow path forming section 30 is a structure in which the pressure chamber C and the communication passage 63 in the first portion P1, the pressure chamber C and the communication passage 63 in the second portion P2, and the circulating fluid chamber 65 located between the communication passage 63 in the first portion P1 and the communication passage 63 in the second portion P2 are formed. As shown in FIG. 4, the flow path forming section 30 includes a wall-shaped portion (hereinafter referred to as a "partition portion") 69 that separates the circulating fluid chamber 65 from each communication passage 63.

As described above, the multiple pressure chambers C and multiple piezoelectric elements 44 are arranged in the Y direction in each of the first part P1 and the second part P2. Therefore, it is also possible to say that the circulating liquid chamber 65 extends in the Y direction so as to be continuous across the multiple pressure chambers C or multiple piezoelectric elements 44 in each of the first part P1 and the second part P2. It is also possible, as shown in FIG. 4, for the circulating liquid chamber 65 and the liquid storage chamber R to extend in the Y direction with a gap between them, and for the pressure chamber C, the communication passage 63, and the nozzle N to be located within that gap.

Figure 5 is an enlarged cross-sectional view of the inkjet head 2 near the circulating liquid chamber 65. As shown in Figure 5, one nozzle N includes a first section n1 and a second section n2. The first section n1 and the second section n2 are cylindrical spaces that are formed coaxially and communicate with each other. The second section n2 is located on the flow path forming section 30 side as viewed from the first section n1. In this embodiment, the central axis Qa of each nozzle N is located on the opposite side to the circulating liquid chamber 65 as viewed from the central axis Qb of the communication passage 63. The inner diameter d2 of the second section n2 is larger than the inner diameter d1 of the first section n1. According to the above-mentioned configuration in which each nozzle N is formed in a stepped shape, there is an advantage that the flow path resistance of each nozzle N can be easily set to a desired characteristic. In this embodiment, the central axis Qa of each nozzle N is located on the opposite side to the circulating liquid chamber 65 as viewed from the central axis Qb of the communication passage 63.

As shown in FIG. 5, a plurality of discharge paths 72 are formed for each of the first portion P1 and the second portion P2 on the surface of the nozzle plate 52 facing the flow path forming portion 30. The plurality of discharge paths 72 of the first portion P1 correspond one-to-one to the plurality of nozzles N of the first row L1 or the plurality of communication paths 63 corresponding to the first row L1. The plurality of discharge paths 72 of the second portion P2 correspond one-to-one to the plurality of nozzles N of the second row L2 or the plurality of communication paths 63 corresponding to the second row L2.

In an inkjet head, a flow path that supplies ink and a flow path that discharges ink are collectively referred to as a circulation path. The flow path that discharges ink is a flow path through which ink deviates from the path through which ink passes before being supplied to the inkjet head and ejected from the nozzle, and exits the path. The flow path that supplies ink is a flow path through which ink that has exited the path by the flow path that discharges ink re-enters the path. The flow path that supplies ink may constitute a part of the path. In other words, it is sufficient if it supplies ink that has exited the path back to the path.

For example, in the example of FIG. 4, the combination of at least the supply path 61 and the discharge path 72 is considered to be the circulation path. This is a flow path that allows liquid supplied from the supply path 61 to be ejected from the nozzle N to be ejected from the liquid path from the supply path 61 to the nozzle N without being ejected from the nozzle N, and then to be supplied again to the liquid path from the supply path 61 to the nozzle N.

Each discharge channel 72 is a groove portion extending in the X direction, i.e., a long bottomed hole, and functions as a flow path for distributing the water-based ink composition. The discharge channel 72 is formed at a position spaced apart from the nozzle N, specifically, on the circulating liquid chamber 65 side as viewed from the nozzle N corresponding to the discharge channel 72. For example, the multiple nozzles N, particularly the second section n2 and the multiple discharge channels 72 are formed collectively in a common process by semiconductor manufacturing technology, such as processing technology such as dry etching or wet etching.

5, each discharge path 72 is formed in a straight line with a flow path width Wa equivalent to the inner diameter d2 of the second section n2 of the nozzle N. The width of the discharge path 72 in the Y direction is smaller than the width of the pressure chamber C in the Y direction. Therefore, it is possible to increase the flow path resistance of the discharge path 72 compared to a configuration in which the flow path width of the discharge path 72 is larger than the flow path width of the pressure chamber C. It is also acceptable to configure the flow path width to be larger than the flow path width of the pressure chamber C. On the other hand, the depth Da of the discharge path 72 with respect to the surface of the nozzle plate 52 is constant over the entire length. In this example, each discharge path 72 is formed to a depth equivalent to the second section n2 of the nozzle N. The discharge path 72 and the second section n2 may be configured to be formed to different depths, but this has the advantage of making it easier to form the discharge path 72 and the second section n2. The "depth" of the flow path means the depth of the flow path in the Z direction, for example, the height difference between the formation surface of the flow path and the bottom surface of the flow path.

Any one of the discharge paths 72 in the first portion P1 is located on the circulation liquid chamber 65 side as viewed from the nozzle N corresponding to the discharge path 72 in the first row L1. Any one of the discharge paths 72 in the second portion P2 is located on the circulation liquid chamber 65 side as viewed from the nozzle N corresponding to the discharge path 72 in the second row L2. The opposite side of each discharge path 72 from the center plane O overlaps with one of the communication paths 63 corresponding to the discharge path 72 in a plan view. That is, the discharge path 72 communicates with the communication path 63. On the other hand, the end of each discharge path 72 on the center plane O side overlaps with the circulation liquid chamber 65 in a plan view. That is, the discharge path 72 communicates with the circulation liquid chamber 65. In this way, each of the multiple communication paths 63 communicates with the circulation liquid chamber 65 via the discharge path 72. Therefore, as shown by the dashed arrow in FIG. 5, the water-based ink composition in each communication path 63 is supplied to the circulation liquid chamber 65 via the discharge path 72. That is, in this embodiment, the multiple communication passages 63 corresponding to the first row L1 and the multiple communication passages 63 corresponding to the second row L2 are in common communication with one circulating fluid chamber 65.

5 shows the flow path length La of the portion of any one discharge path 72 that overlaps with the circulating fluid chamber 65, the flow path length of the portion of the discharge path 72 that overlaps with the communication passage 63, i.e., the dimension Lb in the X direction, and the flow path length of the portion of the discharge path 72 that overlaps with the partition wall portion 69 of the flow path forming portion 30, i.e., the dimension Lc in the X direction. The flow path length Lc corresponds to the thickness of the partition wall portion 69. The partition wall portion 69 functions as a throttle portion of the discharge path 72. Therefore, the longer the flow path length Lc corresponding to the thickness of the partition wall portion 69, the greater the flow path resistance of the discharge path 72. The relative lengths of the flow path length La and the flow path length Lc are arbitrary, but in this example, the relationship that the flow path length La is longer than the flow path length Lb and the flow path length La is longer than the flow path length Lc is established. Furthermore, in this example, the relationship that the flow path length Lb is longer than the flow path length Lc is established. The above configuration has the advantage that the water-based ink composition can more easily flow from the communication passage 63 through the discharge passage 72 into the circulating liquid chamber 65, compared to a configuration in which the flow path length La and the flow path length Lb are shorter than the flow path length Lc.

In this way, in the inkjet head 2, the pressure chamber C is indirectly connected to the circulating liquid chamber 65 via the communication passage 63 and the discharge passage 72. That is, the pressure chamber C and the circulating liquid chamber 65 are not directly connected. In the above configuration, when the pressure in the pressure chamber C fluctuates due to the operation of the piezoelectric element 44, a part of the water-based ink composition flowing in the communication passage 63 is ejected to the outside from the nozzle N, and the remaining part flows from the communication passage 63 to the discharge passage 72 and into the circulating liquid chamber 65. The inertance between the communication passage 63, the nozzle N, and the discharge passage 72 is selected so that the amount of the water-based ink composition ejected through the nozzle N among the water-based ink compositions flowing through the communication passage 63 by one drive of the piezoelectric element 44 exceeds the amount of the water-based ink composition flowing through the communication passage 63 and flowing into the circulating liquid chamber 65 through the discharge passage 72. Assuming that all the piezoelectric elements 44 are driven simultaneously, it is also possible to say that the total amount of circulation flowing into the circulating fluid chamber 65 from the multiple communication passages 63, for example the flow rate per unit time in the circulating fluid chamber 65, is greater than the total amount of spray from the multiple nozzles N.

Specifically, the flow path resistances of the communication path 63, the nozzle, and the discharge path 72 are determined so that the ratio of the circulated amount of the water-based ink composition flowing through the communication path 63 is 70% or more, that is, the ratio of the spray amount of the water-based ink composition is 30% or less. With the above configuration, it is possible to effectively circulate the water-based ink composition near the nozzle to the circulation liquid chamber 65 while ensuring the spray amount of the water-based ink composition. In general, there is a tendency that the greater the flow path resistance of the discharge path 72, the smaller the flow path resistance of the discharge path 72, the greater the circulation amount and the greater the spray amount.

For example, the inkjet recording device 1 is configured to include a circulation mechanism. The circulation mechanism is a mechanism for resupplying, i.e. circulating, the aqueous ink composition in the circulating liquid chamber 65 to the liquid storage chamber R. The circulation mechanism is a mechanism that includes at least the discharge path 72. For example, the ink is discharged from the discharge path 72 through the circulating liquid chamber 65 to the outside of the inkjet head, and the mechanism may include a suction mechanism (e.g., a pump) that sucks the aqueous ink composition to the outside, a filter mechanism that collects air bubbles and foreign matter mixed in the aqueous ink composition, a heating mechanism that dries and heats the aqueous ink composition to reduce thickening, and the like, as necessary, and the ink is supplied again to the inkjet head through these mechanisms. The entire path through which the ink circulates is the circulation mechanism. The circulated ink may be merged with new ink outside and supplied to the inkjet head again.

The water-based ink composition, from which air bubbles and foreign matter have been removed and from which thickening has been reduced by the circulation mechanism, is supplied from the circulation mechanism to the liquid storage chamber R via the inlet 482. This causes the water-based ink composition to circulate, for example, through the liquid storage chamber R → supply path 61 → pressure chamber C → communication path 63 → discharge path 72 → circulating liquid chamber 65 → outside → liquid storage chamber R. In other words, the circulation mechanism has a path that allows the water-based ink composition to pass through the pressure chamber C and flow back into the pressure chamber C. The circulation path described above can also be said to be part of the circulation mechanism.

In this way, when the discharge passage 72 that connects the communication passage 63 and the circulation liquid chamber 65 is formed in the nozzle plate 52, the water-based ink composition near the nozzle N can be efficiently circulated to the circulation liquid chamber 65. In addition, since the communication passage 63 corresponding to the first row L1 and the communication passage 63 corresponding to the second row L2 are commonly connected to the circulation liquid chamber 65 between them, there is an advantage that the configuration of the liquid ejection head is simplified and thus miniaturization is realized compared to a configuration in which the circulation liquid chamber connected to each discharge passage 72 corresponding to the first row L1 and the circulation liquid chamber connected to each discharge passage 72 corresponding to the second row L2 are separately provided.

In addition, the discharge path 72 and the nozzle N may be configured to be continuous with each other, instead of being separated from each other. Also, in addition to the circulation fluid chamber 65, a circulation fluid chamber corresponding to each of the first part P1 and the second part P2 may be formed.

The flow rate of the aqueous ink composition circulating through the circulation mechanism (also referred to as the circulation amount or circulation flow rate) may be set to be slightly more preferably 0.1 to 5.0 times, more preferably 0.2 to 4.0 times, more preferably 0.3 to 3.0 times, even more preferably 0.5 to 2.0 times, and particularly preferably 0.7 to 1.5 times, of the maximum ejection amount of the aqueous ink composition ejected from the inkjet head to the recording medium in the recording method. In this way, the ejection amount and the circulation amount of the aqueous ink composition are well balanced, and the aqueous ink composition can be sufficiently attached to the recording medium, and thickening of the aqueous ink composition can be efficiently suppressed.

The maximum ejection amount of the water-based ink composition is the maximum amount of droplets of the water-based ink composition ejected per ejection performed during recording, and is the amount of the water-based ink composition ejected from the inkjet head when the water-based ink composition is ejected from all nozzles used for recording with the inkjet head at the maximum ejection frequency of the water-based ink composition ejected during recording.

The circulation amount is the total flow rate of the water-based ink composition circulating through each discharge path provided in the inkjet head and connected to each nozzle of the inkjet head. Both the circulation amount and the maximum discharge amount are expressed as the mass of ink per unit time.

The unit of circulation volume is mass/time, for example, mass (g)/time (sec). The flow rate is the total discharge volume from the discharge path, as above.

Both the circulation amount and the maximum ejection amount are values per inkjet head. The circulation amount is preferably 1.0 (g/min) or more per inkjet head. It is also preferably 12.0 (g/min) or less. It is more preferably 2.0 (g/min) or more and 10.0 (g/min) or less, and even more preferably 3.0 (g/min) or more and 7.0 (g/min) or less. Here, the inkjet head refers to a unit consisting of all the nozzles that eject the water-based ink composition introduced from one inlet. The number of nozzles per unit inkjet head is not limited, but may be, for example, 50 to 1000, 100 to 700, 150 to 500, or 200 to 400.

The inkjet head 2 also includes a pressure chamber C that applies pressure to the water-based ink composition to eject it from the nozzle. As in the example of FIG. 4, it is preferable that the circulation path circulates the water-based ink composition that has passed through the pressure chamber C. In other words, it is preferable that the water-based ink composition that has passed through the pressure chamber C is circulated and supplied again to the pressure chamber. In this case, the discharge path can be provided in the pressure chamber or at a position downstream of the pressure chamber. In this case, ejection stability is particularly excellent and is preferable.

Alternatively, the circulation path may be provided with a discharge path at a position upstream of the pressure chamber in the inkjet head, and the water-based ink composition may be discharged and circulated through the discharge path. The water-based ink composition may then be circulated and supplied to the same position again. In this case, the ink is circulated before passing through the pressure chamber. In this case, too, if foreign matter or thickening of the water-based ink composition reaches the upstream side of the pressure chamber, this can be eliminated, resulting in excellent ejection stability. An example of the upstream position is the liquid storage chamber R.

The circulation flow path may circulate the water-based ink composition that has passed through the discharge path within the inkjet head and supply it again to the water-based ink composition path, or may be configured to discharge the water-based ink composition that has passed through the discharge path outside the inkjet head 2 and supply the discharged water-based ink composition again to the recording head, thereby circulating the water-based ink composition. Of these, the former is preferred in terms of ease of manufacturing the circulation path, etc.

By using an inkjet head having a circulation path as described above, it is possible to suppress a decrease in the ejection reliability of the water-based ink composition even if the solids concentration increases due to drying of the water-based ink composition.

A serial type recording device equipped with a serial type inkjet head and performing a serial type recording method has been described above. On the other hand, the inkjet head 2 may be a line type head. Even in a line type head, by circulating the water-based ink composition, it is possible to obtain the effect of suppressing the decrease in ejection reliability caused by the water-based ink composition drying and thickening. The inkjet head of the line type recording device is a head in which nozzles are arranged over a length equal to or greater than the recording width of the recording medium M, and the water-based ink composition can be applied to the recording medium M in a single pass.

Figure 6 is a schematic cross-sectional view showing a part of a line-type recording device equipped with a line-type head (line-type recording head) and performing a line-type inkjet recording method. Part 200 of the recording device includes first ink deposition means 220 including an inkjet head 221 for a water-based ink composition, second ink deposition means 230 including an inkjet head 231 for a water-based ink composition, recording medium transport means 210 including a transport roller 211 for transporting the recording medium M, and post-heating means 240 for performing a post-heating process on the recording medium. Inkjet heads 231 and 221 are line-type recording heads with nozzle rows extending in the width direction of the recording medium M, which is the front-to-back direction of the figure.

In a line-type recording device, the recording medium M is transported in the transport direction, which is the direction of the arrow in Figure 6, and while moving the relative positions of the recording heads 231, 221 and the recording medium M, the water-based ink composition is ejected from the inkjet head and deposited on the recording medium M. This is called scanning. Scanning is also called main scanning or pass. The line-type recording method is a one-pass recording method in which the recording heads 231, 221 are used to deposit the water-based ink composition on the transported recording medium M in one pass to perform recording.

The line-type recording device can be configured similarly to the serial-type inkjet recording device 1 described above, except that it is equipped with a line-type recording head and performs a line-type recording method. The line-type recording device may be equipped with a drying means for performing a drying process. For example, drying means such as the ventilation fan 8 and IR heater 3 above the inkjet head 2 in FIG. 1 may be provided above the inkjet heads 231 and 221 in FIG. 6, and drying means such as an under-heater corresponding to the platen heater 4 below the inkjet head 2 in FIG. 1 may be provided below the inkjet heads 231 and 221 in FIG. 6.

3. Examples The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. In the following, "%" is based on mass unless otherwise specified.

3.1. Preparation of Water-Based Ink Compositions Inks 1 to 23 with different material compositions were prepared using the material compositions shown in Tables 1 to 3. Each ink was prepared by placing the materials shown in Tables 1 to 3 in a container, stirring and mixing for 2 hours using a magnetic stirrer, and then filtering through a membrane filter with a pore size of 5 μm to remove impurities such as dust and coarse particles. Note that the numerical values for each component in Tables 1 to 3 all indicate mass %, and water was added so that the total mass of the composition was 100 mass %.

The pigment (carbon black) used in the preparation of the water-based ink composition was mixed in advance with a pigment dispersant (not shown in the table) which is a water-soluble styrene-acrylic resin in a mass ratio of 2:1 (pigment:pigment dispersant) in water and thoroughly stirred to prepare a pigment dispersion which was used in the preparation of the ink. The pigment dispersion column in Tables 1 to 3 lists the content (mass %) of the pigment dispersion with a pigment solids concentration of 15 mass %. The resin dispersion column in Tables 1 to 3 lists the content (mass %) of an acrylic resin emulsion (manufactured by BASF Japan, product name "Joncryl 537J") with a solids concentration of 30 mass %.

The components used in Tables 1 to 3 are as follows:
<Pigment Dispersion>
Carbon black: pigment (carbon black) dispersion prepared above, solid content concentration 15% by mass
<Resin Dispersion>
Acrylic resin emulsion: BASF Japan, product name "Joncryl 537J", solid content concentration 30% by mass
<Surfactant>
Silicone surfactant: BYK Corporation, product name "BYK-348"
Fluorosurfactant: DIC Corporation, product name "Megafac F-444"
<Organic solvent A>
1,2-Pentanediol: normal boiling point = 210°C, surface tension (25°C) = 27.7 mN/m
1,2-Hexanediol: normal boiling point = 223°C, surface tension (25°C) = 26.4 mN/m
<Organic Solvent B>
・1,5-pentanediol: normal boiling point = 239 ° C.
・1,6-Hexanediol: Normal boiling point = 250 ° C.
・1,3-propanediol: normal boiling point = 214 ° C.
<Other organic solvents>
1,2-butanediol: normal boiling point = 194 ° C, surface tension (25 ° C) = 31.6 mN / m
Diethylene glycol monoethyl ether: normal boiling point = 196°C
Glycerin: Normal boiling point = 290°C
・1,2-propanediol: normal boiling point = 188 ° C.

The viscosity of each ink was measured at 25°C using a viscoelasticity tester MCR-300 (product name, manufactured by Pysica).

3.2. Evaluation method 3.2.1. Recording test A modified version of Seiko Epson SC-S80650 (hereinafter also referred to as the "modified machine") was used as the inkjet recording device. Two types of heads were prepared: a circulation head with a circulation mechanism and a normal head without a circulation mechanism, and either of the heads was attached to the inkjet recording device. The head was filled with the ink prepared above. During recording on the recording medium, the platen heater was adjusted to set the surface temperature of the recording medium to 40°C. The nozzle density per nozzle row was 600 npi, and the number of nozzles was 600. The recording resolution was 1200 x 1200 dpi. After the ink was attached, it was dried for 1 minute at 70°C using an after-heater. The amount of ink attached was 7 mg/ ^inch2 . This amount of ink attached was considered to be a printing rate of 100%. In this recording test, recording was performed on either a low non-absorbent recording medium or an absorbent recording medium. For the low non-absorbent recording medium, Topcoat+ (manufactured by Oji Paper Co., Ltd.) was used, and for the absorbent recording medium, Fine Paper 55PW (manufactured by Lintec Corporation) was used.

3.2.2. Ejection reliability evaluation <Intermittent ejection property>
The ink was allowed to circulate and left in an environment of 25°C with the nozzles open. After leaving the ink, a nozzle check pattern was recorded to check for the presence or absence of non-ejecting nozzles and evaluation was performed. The evaluation criteria are as follows. The evaluation results are also shown in Tables 4 to 6. The amount of circulation of the head was set to 1.0 times the amount of ejection (maximum amount of ejection) when printing on all recordable areas of the printing medium at a print rate of 100%.
(Evaluation criteria)
S: No non-ejecting nozzles even after leaving for 6 hours.
A: No non-ejecting nozzles even after leaving for 4 hours.
B: No non-ejecting nozzles even after leaving for 2 hours.
C: When recording was performed after leaving for 1 hour, non-ejecting nozzles were observed.

<Continuous ejection stability>
Printing was performed while circulating the ink. Ink was ejected at a drive frequency of 30 to 40 kHz. Printing was performed continuously for 30 minutes. After printing, a nozzle inspection was performed. The evaluation criteria were as follows. The evaluation results are also shown in Tables 4 to 6. Ejection disturbance was determined to exist when the impact position on the recording medium was shifted from the original position by more than half the distance between adjacent nozzles.
(Evaluation criteria)
S: No irregular ejection or non-ejection was observed.
A: Disturbances in ejection or non-ejection occurred in 5 or fewer nozzles.
B: Disturbances in ejection or non-ejection occurred in 10 or fewer nozzles.
C: Disturbances in ejection or non-ejection occurred in 11 or more nozzles.

3.2.3. Image quality evaluation <Whiteout>
A solid print was made on the recording medium with a printing rate of 100%, and the degree of whiteout in the print was visually confirmed. The evaluation criteria are as follows. The evaluation results are also shown in Tables 4 to 6. Whiteout means that the background of the recording medium is not filled in with ink in the image, and the background of the recording medium is visible. This is an evaluation of the filling of the recording medium with ink.
(Evaluation criteria)
S: The ink spreads sufficiently, there are no visible white spots, and there is no unevenness in density, resulting in a uniform image. There are no visible white spots even when the printing rate is 90%.
A: The ink spreads well, there are no visible white spots, and there is no unevenness in density, resulting in a good image. There are no visible white spots even when the printing rate is 95%. However, there are visible white spots at a printing rate of 90%.
B: The ink spreads adequately and there are no visible white spots. However, white spots were observed with the naked eye at a printing rate of 95%.
C: The ink does not spread sufficiently, and slight white spots are visually observed.

<Beading>
A solid square print with a printing rate of 100% was made on a recording medium, and the degree of beading of the print was visually confirmed. The evaluation criteria are as follows. The evaluation results are shown in Tables 4 to 6.
(Evaluation criteria)
S: No color unevenness, very clear image.
A: There is some color unevenness, but the image is clear enough.
B: Slight color unevenness was observed, and the image clarity was somewhat inferior. The outline of the solid area was straight. C: Significant color unevenness was observed, and the image lacked clarity. The outline of the solid area was not straight, and the outline was distorted.

<Color Density>
A solid print was made on the recording medium with a printing rate of 100%, and the OD value of the print was measured using a spectrometer (manufactured by X-rite, product name "i1Pro2"). The evaluation criteria are as follows. The evaluation results are also shown in Tables 4 to 6. Color density is an evaluation of the color development of the ink in an image when the ink is recorded on the recording medium.
(Evaluation criteria)
S: OD value is 1.4 or more.
A: OD value is 1.2 or more and less than 1.4.
B: OD value is 1.0 or more and less than 1.2.
C: OD value is 0.8 or more and less than 1.0.
D: OD value is less than 0.8.

<Drying property>
A solid print with a printing rate of 100% was made on the recording medium, and dried in an air oven at 70°C for various times. After that, the coating surface of the print was lightly rubbed with a fingertip, and it was visually confirmed whether the ink was attached to the fingertip. The evaluation criteria were as follows. The evaluation results are shown in Tables 4 to 6.
(Evaluation criteria)
S: After drying for 1 minute, no ink was observed on the fingertip.
A: After drying for 2 minutes, no ink was found to adhere to the fingertip, but after drying for 1 minute, ink was found to adhere to the fingertip.
B: After drying for 3 minutes, no ink was found to adhere to the fingertip, but after drying for 2 minutes, ink was found to adhere to the fingertip.
C: After drying for 3 minutes, some ink was found to adhere to the fingertip.

3.3. Evaluation Results Tables 4 to 6 show the recording test conditions and evaluation results for each of the examples and comparative examples.

All of the inkjet recording methods of Examples 1 to 14 according to the present invention had excellent evaluations of whiteout when recording on low non-absorbent recording media, excellent evaluations of color density when recording on absorbent recording media, and excellent ejection reliability. In contrast, all of the comparative examples not according to the present invention had poor evaluations of whiteout when recording on low non-absorbent recording media, evaluations of color density when recording on absorbent recording media, and ejection reliability. Details are given below.

From Example 11, it was found that inks with higher viscosity had better beading evaluation and drying properties.

From Examples 12 and 13, it was found that a higher ink mass ratio (organic solvent B/organic solvent A) resulted in better ejection reliability and color density on absorbent recording media, while a lower ink mass ratio resulted in better evaluations of whiteout and beading on less absorbent recording media.

From Example 14, the ink with a lower total content (organic solvent B + organic solvent A) had better drying properties on low-absorbency recording media.

From Example 10, it was found that inks with a lower content of organic solvents with normal boiling points of over 280°C had better beading evaluation and drying properties on low-absorbency recording media.

From Examples 2 and 4, the higher the content of organic solvent B, the better the color density on the absorbent recording medium.

From Examples 3 and 6, the higher the content of organic solvent A, the better the evaluation of whiteout on low non-absorbent recording media.

From Examples 1 and 8, when organic solvent A contained 1,2-hexanediol, the evaluation of whiteout on low non-absorbent recording media was superior.

From Examples 1, 5, and 9, when organic solvent B contained 1,5-pentanediol, the color density and ejection reliability on absorbent recording media were superior.

In Comparative Examples 1 to 4, which used inks that did not contain organic solvent B, the ink easily penetrated into the absorbent recording medium and was unable to retain the color material on the surface of the absorbent recording medium, resulting in poor color density and low-density image quality (low OD value).

Comparative Examples 5 to 8, which used inks that did not contain organic solvent A, had poor evaluations of whiteout on low-absorbent recording media, and also had poor beading. In addition, because inks that did not contain organic solvent A were used, the ink had low penetration into the absorbent recording media, and the image quality when recorded on absorbent recording media was relatively high in color density.

Comparative Example 9, which used an ink that did not contain either organic solvent A or organic solvent B, showed poor ink filling and beading when printed on a low-absorbency recording medium. Furthermore, because the ink did not contain organic solvent A, the ink had low penetration into the absorbent recording medium even though it did not contain organic solvent B, and the image quality when printed on an absorbent recording medium was relatively high in color density.

In Comparative Example 10, which used ink 17 that does not contain organic solvent B and a head without an ink circulation mechanism, the ink easily penetrates into the absorbent recording medium and the coloring material cannot be retained on the surface of the absorbent recording medium, resulting in image quality with low color density (low OD value). On the other hand, ink 17 contains glycerin, so it has low drying properties. Therefore, even when a head without an ink circulation mechanism is used, the ink is less likely to dry around the nozzles, and the ejection reliability was relatively good. Although not shown in the table, when ejection reliability evaluation was performed in the same manner as in Comparative Example 10 using inks 15, 18, 19, and 21 to 23, the ejection reliability was similar to that of Comparative Example 10. However, when ejection reliability evaluation was performed in the same manner as in Comparative Example 10 using inks 16 and 20, the ejection reliability was inferior.

Comparative Example 11, which used ink 1 containing organic solvent A and organic solvent B and a head without an ink circulation mechanism, produced no blank spots when printed on low-absorbent recording media, and produced high-color image quality when printed on absorbent recording media. On the other hand, because a head without an ink circulation mechanism was used, the ink was prone to drying around the nozzles, resulting in a loss of ejection reliability. Although not shown in the table, ejection reliability evaluation was performed in the same manner as Comparative Example 11 using inks 2, 4 to 9, and 11 to 14, and the ejection reliability was similar to that of Comparative Example 11. However, when ejection reliability evaluation was performed in the same manner as Comparative Example 11 using inks 3 and 10, the ejection reliability was good.

Although not shown in the table, in Example 6, the platen heater was adjusted during recording on the recording medium, and recording was performed in the same manner except that the surface temperature of the recording medium was set to 35°C. Compared to Example 6, the ejection reliability was improved and beading on the low non-absorbent recording medium was slightly reduced. From this, the lower the recording medium surface temperature, the better the ejection reliability, and the higher the recording medium surface temperature, the better the image quality.

The following can be derived from the above-described embodiment:

One aspect of the inkjet recording method is
An inkjet recording method for performing ink jet recording on a recording medium using a water-based ink composition,
an ink depositing step of ejecting the water-based ink composition from an inkjet head and depositing the water-based ink composition on the recording medium;
The water-based ink composition contains an organic solvent A which is a 1,2-alkanediol having a surface tension of 30 mN/m or less at 25° C., and an organic solvent B which is an alkanediol having a normal boiling point of 250° C. or less and a carbon number of 3 or more at both ends,
The inkjet head includes a circulation mechanism for circulating the water-based ink composition.

This inkjet recording method can improve image quality on both low-absorbency and absorbency recording media while ensuring ink ejection stability.

In one embodiment of the inkjet recording method,
The total content of the organic solvent A and the organic solvent B may be 25 mass % or less with respect to the total mass of the water-based ink composition.

Both organic solvent A and organic solvent B are hydrophilic organic solvents and therefore highly soluble in water, but if the total content of organic solvent A and organic solvent B is within the above range, degradation of image quality can be reduced even when the ink is applied to a low-absorbency recording medium.

In any one of the inkjet recording methods,
In the water-based ink composition, the mass ratio (M _B /M _A ) of the content of the organic solvent B (M _B ) to the content of the organic solvent A (M _A ) may be 1-6.

When the mass ratio ( _M / _M ) is within the above range, the contents of organic solvent A and organic solvent B are well balanced, which makes it easier to improve image quality on both low non-absorbent recording media and absorbent recording media, and also makes it easier to ensure ink ejection stability.

In any one of the inkjet recording methods,
The water-based ink composition may have a viscosity of 4.5 mPa·s or more at 25° C.

If the viscosity of the water-based ink composition at 25°C is within the above range, the ink is more likely to be inhibited from penetrating into absorbent recording media, so that the colorant remains on the surface, and image quality with high OD values and excellent color development can be obtained, particularly on absorbent recording media.

In any one of the inkjet recording methods,
the water-based ink composition further contains a colorant and a resin,
The total content of the coloring material and the resin may be 3 mass % or more with respect to the total mass of the water-based ink composition.

If the total content of colorant and resin particles is within the above range, the solids concentration is appropriate, and the ink has the characteristic of rapidly increasing viscosity when the solvent component in the ink evaporates. This suppresses the ink from penetrating into the absorbent recording medium, so the colorant remains on the surface, resulting in image quality with a high OD value and excellent color development, especially on absorbent recording media.

In any one of the inkjet recording methods,
The content of the organic solvent A may be 1 to 10% by mass with respect to the total mass of the water-based ink composition.

When the content of organic solvent A is within the above range, the wetting and spreading properties on low non-absorbent recording media can be sufficiently increased, making it easier to obtain image quality with high OD values and excellent color development on low non-absorbent recording media. In addition, organic solvent A acts to lower the dynamic surface tension of the ink, which can cause ink mist, but when the content of organic solvent A is within the above range, such adverse effects can be prevented.

In any one of the inkjet recording methods,
The content of the organic solvent B may be 4 to 30% by mass with respect to the total mass of the water-based ink composition.

When the content of organic solvent B is within the above range, the penetration of the ink into the absorbent recording medium, which is promoted by organic solvent A, can be sufficiently suppressed, making it easier to obtain image quality with a high OD value and excellent color development on low-absorbent recording media.

In any one of the inkjet recording methods,
The weighted average of the normal boiling points of water and the organic solvents contained in the water-based ink composition and their contents in the water-based ink composition may be 130° C. or less.

When this value is within the above range, the solvent contained in the ink can be volatilized quickly, particularly when the ink is applied to a low-absorption recording medium, making it difficult for a viscous image to be formed, and making it easier to obtain image quality with a high OD value and excellent color development.

In any one of the inkjet recording methods,
The organic solvent A may be either 1,2-hexanediol or 1,2-pentanediol.

In any one of the inkjet recording methods,
The organic solvent B may be any one of 1,3-propanediol, 1,5-pentanediol, and 1,6-hexanediol.

Any of the aspects of the inkjet recording method may further include
The inkjet recording is performed using an inkjet recording apparatus including the inkjet head,
the inkjet recording apparatus performs recording on a low non-absorbent recording medium and recording on an absorbent recording medium by using the water-based ink composition,
This can be done on either low non-absorbent recording media or absorbent recording media.

One embodiment of the water-based ink composition is
The ink jet recording method is intended to be used in any one of the above-mentioned ink jet recording methods.

The water-based ink composition according to one embodiment of the present invention comprises
It may be used for recording on a low non-absorbent recording medium and for recording on an absorbent recording medium.

This water-based ink composition contains organic solvent A, which allows the ink to spread well on low-absorbency recording media, resulting in high OD values and image quality with excellent color development. In addition, the inclusion of organic solvent B suppresses the ink from penetrating absorbent recording media, allowing the colorant to remain on the surface, resulting in image quality with high OD values and excellent color development.

One aspect of the inkjet recording apparatus is
an ink depositing means for ejecting the water-based ink composition from an inkjet head and depositing the ink composition on a recording medium;
The water-based ink composition contains an organic solvent A which is a 1,2-alkanediol having a surface tension of 30 mN/m or less at 25° C., and an organic solvent B which is an alkanediol having a normal boiling point of 250° C. or less and a carbon number of 3 or more at both ends,
The inkjet head includes a circulation mechanism for circulating the water-based ink composition.

This inkjet recording device can improve image quality on both low-absorbency and absorbency recording media while ensuring ink ejection stability.

The present invention is not limited to the above-described embodiments, and various modifications are possible. For example, the present invention includes configurations that are substantially the same as those described in the embodiments (for example, configurations with the same functions, methods, and results, or configurations with the same purpose and effect). The present invention also includes configurations in which non-essential parts of the configurations described in the embodiments are replaced. The present invention also includes configurations that achieve the same effects as the configurations described in the embodiments, or that can achieve the same purpose. The present invention also includes configurations in which publicly known technology is added to the configurations described in the embodiments.

1...inkjet recording device, 2...inkjet head, 3...IR heater, 4...platen heater, 5...heating heater, 6...cooling fan, 7...preheater, 8...ventilation fan, 9...carriage, 11...platen, 12...cartridge, 13...carriage movement mechanism, 14...transport means, 28...wiring board, 30...flow path forming section, 32...first flow path board, 34...second flow path board, 42...vibration section, 44...piezoelectric element, 46...protective member, 48...housing section, 482...inlet, 52...nozzle plate, 54...vibration absorber, 61...supply path, 63...connecting path, 65...circulating fluid chamber, 69...partition wall section, n1...first section, n2...second section, 72...discharge path, 101...interface unit, 102...CPU, 103...memory, 104...unit control circuit, 111...transport unit, 112...carriage unit, 113...head unit, 114...drying unit, 121...detector group, 130...computer, 200...line type recording device part, 210...recording medium transport means, 211...transport roller, 220...first ink attachment means, 221...inkjet head, 230...second ink attachment means, 231...inkjet head, 240...post-heating means, CONT...control unit, MS...main scanning direction, SS...sub-scanning direction, M...recording medium, N...nozzle

Claims (14)

This is carried out using an inkjet recording device equipped with an inkjet head,
An inkjet recording method for performing ink jet recording on a recording medium using a water-based ink composition,
the inkjet recording apparatus performs recording on a low non-absorbent recording medium and recording on an absorbent recording medium by using the water-based ink composition,
an ink depositing step of ejecting the water-based ink composition from the inkjet head and depositing the water-based ink composition on the recording medium;
The recording medium is either a low non-absorbent recording medium or an absorbent recording medium,
The water-based ink composition contains an organic solvent A which is a 1,2-alkanediol having a surface tension of 30 mN/m or less at 25° C., and an organic solvent B which is an alkanediol having a normal boiling point of 250° C. or less and a carbon number of 3 or more at both ends,
the total content of the organic solvent A and the organic solvent B is 17% by mass or less with respect to the total mass of the water-based ink composition;
the inkjet head is provided with a circulation mechanism for circulating the water-based ink composition;
Inkjet recording method. The inkjet recording method according to claim 1, wherein the total content of the organic solvent A and the organic solvent B is 3.0 to 17% by mass relative to the total mass of the water-based ink composition. 3. The inkjet recording method according to claim 1, wherein in the water-based ink composition, a mass ratio (M _B /M _A ) of the content (M _A ) of the organic solvent B to the content (M _A ) of the organic solvent A is 1 to 6. The inkjet recording method according to any one of claims 1 to 3, wherein the viscosity of the water-based ink composition at 25°C is 4.5 mPa·s or more. the water-based ink composition further contains a colorant and a resin,
The inkjet recording method according to claim 1 , wherein a total content of the coloring material and the resin is 3% by mass or more with respect to a total mass of the water-based ink composition. The inkjet recording method according to any one of claims 1 to 5, wherein the content of the organic solvent A is 1 to 10% by mass relative to the total mass of the water-based ink composition. The inkjet recording method according to any one of claims 1 to 6, wherein the content of the organic solvent B is 4 to 15.0% by mass relative to the total mass of the water-based ink composition. The inkjet recording method according to any one of claims 1 to 7, wherein the weighted average of the normal boiling points of water and each organic solvent contained in the water-based ink composition and the content of each in the water-based ink composition is 130°C or less. The inkjet recording method according to any one of claims 1 to 8, wherein the organic solvent A is either 1,2-hexanediol or 1,2-pentanediol. The inkjet recording method according to any one of claims 1 to 9, wherein the organic solvent B is any one of 1,3-propanediol, 1,5-pentanediol, and 1,6-hexanediol. The inkjet recording method according to any one of claims 1 to 10, wherein the absorbent recording medium is paper, either plain paper or inkjet paper, or cloth. The inkjet recording method according to any one of claims 1 to 11, wherein the inkjet recording device has a drying mechanism that dries the water-based ink composition that has been applied to the recording medium before or during the ink application process. The inkjet recording method according to any one of claims 1 to 12, wherein the content of organic solvents other than the organic solvent A and the organic solvent B in the water-based ink composition is 5.0 mass % or less with respect to the total mass of the water-based ink composition. An inkjet recording apparatus for performing recording according to the inkjet recording method of any one of claims 1 to 13,
an ink-adhering unit that ejects the water-based ink composition from an ink-jet head and adheres the water-based ink composition to a recording medium; and
the inkjet head includes a circulation mechanism for circulating the water-based ink composition,
An inkjet recording apparatus which performs recording on a low non-absorbent recording medium and recording on an absorbent recording medium using the water-based ink composition.

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