JP7633857B2 - Oil-based inkjet ink - Google Patents

Description

The present invention relates to an oil-based inkjet ink.

Inkjet recording is a method of ejecting highly fluid inkjet ink as droplets from a fine nozzle to record an image on a recording medium placed opposite the nozzle. This method has been rapidly spreading in recent years due to its low noise and high speed printing capabilities. Inks used in inkjet recording include aqueous inks containing water as the main solvent, ultraviolet curable inks (UV inks) containing a high content of polymerizable monomers as the main component, and hot melt inks (solid inks) containing a high content of wax as the main component, as well as so-called non-aqueous inks containing a non-aqueous solvent as the main solvent. Non-aqueous inks can be classified into solvent inks (solvent-based inks) whose main solvent is a volatile organic solvent, and oil-based inks (oil-based inks) whose main solvent is a low-volatility or non-volatile organic solvent. Solvent inks dry on the recording medium mainly due to the evaporation of the organic solvent, whereas oil-based inks mainly penetrate the recording medium.

Patent Document 1 (JP 2014-15491 A) proposes a non-aqueous pigment ink that contains a pigment, a non-aqueous solvent, a non-water-soluble resin, and a water-soluble resin, in which the non-water-soluble resin is an acrylic polymer and the water-soluble resin is polyethyleneimine. This ink has the advantages of being able to suppress strike-through while realizing low ink viscosity and excellent storage stability, and being able to achieve high print density. This ink also has the advantage of suppressing the occurrence of satellites.

On the other hand, when a printed matter with an image formed by oil-based inkjet ink is sandwiched and stored in a clear file made of polypropylene (PP) or the like, there is a problem that the clear file will warp and become deformed. One of the reasons for this is thought to be that when the clear file comes into contact with the printed surface, one side of the clear file swells due to the ink components. In this way, when the printed surface comes into contact with a resin product, the resin product may be altered, and in the case of a film-like resin product, deformation may be caused. It has been found that the effect of such printed matter on resin products is largely influenced by the solvent, among the ink components.
Furthermore, if a printed item printed with ink that contains a large amount of highly polar solvent is placed on top of a printed item printed using an electrophotographic method that uses toner, the highly polar solvent may dissolve the toner, causing the printed items to stick together.

Patent Document 2 (JP 2013-166813 A) proposes a non-aqueous inkjet ink that suppresses deformation of clear files, reduces toner solubility, and improves ejection performance, and that contains, as an organic solvent, a pivalic acid ester having 25 or more carbon atoms and an ethylene glycol monoalkyl ether.
Patent Literature 3 (JP 2018-141123 A) proposes an oil-based inkjet ink that prevents deformation of clear files, improves the wettability of the ink to the nozzle plate, and also improves ejection performance, and that contains a specific modified silicone oil as a non-aqueous solvent.

JP 2014-15491 A JP 2013-166813 A JP 2018-141123 A

Although the inks disclosed in Patent Documents 2 and 3 are effective in suppressing deformation of clear files, there is room for improvement in the ejection performance during printing.
Furthermore, if a highly polar solvent is used to prevent deformation of a clear file, when a printed matter on which an oil-based ink image is formed comes into contact with a printed matter on which a toner image is formed, the toner image may be more likely to dissolve due to the oil-based ink image, which may cause toner transfer.

One objective of the present invention is to improve ejection properties, suppress deterioration or deformation of resin products caused by printed matter, and prevent toner transfer to printed matter.

One aspect of the present invention is an oil-based inkjet ink comprising a diester solvent (A) having a dispersion term _δD in the Hansen solubility parameters of 15.7 MPa ^1/2 or less, a monoester solvent (B) having a boiling point of 300° C. or more, and a colorant.

According to one embodiment of the present invention, it is possible to improve ejection properties, suppress deterioration or deformation of resin products caused by printed matter, and prevent toner transfer to printed matter.

The present invention will be described below using one embodiment. The examples in the following embodiment do not limit the present invention.

An oil-based inkjet ink (hereinafter, may be simply referred to as oil-based ink or ink) according to one embodiment is characterized by including a diester solvent (A) having a dispersion term _δD in the Hansen solubility parameters of 15.7 MPa ^1/2 or less, a monoester solvent (B) having a boiling point of 300° C. or more, and a colorant.
This oil-based inkjet ink can improve the ejection properties, suppress the deterioration or deformation of resin products caused by printed matter, and prevent toner transfer to printed matter. For example, deformation of a thin resin film such as a clear file can be prevented when the printed matter comes into contact with the printed matter. In addition, this oil-based inkjet ink can prevent the printed surface of the printed matter from being soiled.
Hereinafter, a diester solvent (A) having a dispersion term _δD in the Hansen solubility parameters of 15.7 MPa ^1/2 or less will also be referred to as a diester solvent (A), and a monoester solvent (B) having a boiling point of 300° C. or more will also be referred to as a monoester solvent (B).

When a printed matter is stored in a polypropylene (PP) clear file folder, if the ink on the surface of the printed matter comes into contact with the inner surface of the clear file and the inner surface of the clear file swells due to the influence of the ink components, the clear file may deform and warp outward. This phenomenon can also occur with thin resin products such as clear files. In addition, the surface of strong resin products may change, for example reducing weather resistance and durability.
On the other hand, in printed matter formed using a toner, the toner often exhibits high polarity, and therefore when a printed matter on which a toner image is formed comes into contact with a high polarity component, the toner image may dissolve and transfer to a mating material. When a high polarity component remains on a printed matter on which an oil-based ink image is formed by oil-based ink, the toner may easily dissolve when the oil-based ink image comes into contact with a toner image, and the toner image may be transferred to the oil-based ink image. This phenomenon is also called toner transfer. Even if the toner image is not transferred, the toner image may be altered by the high polarity component of the oil-based ink image, resulting in a decrease in image quality. Toner transfer is particularly likely to occur in printed matter formed using a styrene-acrylic copolymer type toner.

There is a concept called Hansen solubility parameter for predicting interactions between substances. The cohesive energy density of a substance is divided into three components: δ _D (dispersion term), δ _P (polarity term), and δ _H (hydrogen bond term), and the interaction can be predicted from the parameter distance between substances. Since clear files and toner, which are polymers, also have this parameter, the interaction (solubility) with a solvent can be expressed as a numerical value. δ _D is influenced by the size and weight of the molecule, δ _P is influenced by the charge imbalance within the molecule, and δ _H is influenced by the presence or absence of hydrogen bonds.

When solubility is divided into three components, δ _D , δ _P , and δ _H , and expressed three-dimensionally, a solvent that has parameters outside the range of the three-dimensional space represented by the three components of the polymer is a solvent that has a weak interaction with the polymer. Since the polymer has a relatively large δ _D , it is important to keep the δ _D of the solvent low in order to suppress the interaction between the solvent and the polymer. In addition, it is important to select a solvent that has δ _P and δ _H outside the range of the three-dimensional space of the polymer.
It was found that a diester structure is suitable in terms of δ _P and δ _H as a structure having parameters outside the range of the three-dimensional space of the polymer component of the clear file and the polymer component of the toner. However, since diester structures generally have a large δ _D , many of them fall within the range of the three-dimensional space of the polymer component in terms of δ _D. Therefore, by selecting a solvent with a small δ _D from among solvents having a diester structure, it is possible to suppress the interaction with the polymer component. In other words, among diester solvents, a solvent with a small δ _D is less likely to interact with the clear file and can prevent the deformation of the clear file, and is also less likely to interact with the polymer component of the toner, making it possible to suppress toner dissolution and prevent toner transfer.

However, a diester solvent with a small _δD alone has a relatively low solubility of a toner image, but dissolves the toner to some extent. Therefore, in this embodiment, a diester solvent with a small _δD is combined with a monoester solvent. A monoester solvent is a solvent with small three components, _δD , _δP , and _δH . By combining these two solvents, it is possible to reduce the interaction with the polymer component of the toner, and the problem of the solubility of the toner image caused by the ink component can be improved. Another problem is that the monoester solvent interacts with the clear file. Therefore, a solvent with a high boiling point is selected from the monoester solvents to prevent the monoester solvent from volatilizing from the printed matter, suppress the contact between the clear file and the monoester solvent, and prevent the clear file from being deformed.
Although not bound by the above theory, using the above theory as one factor, by combining a diester solvent (A) having a dispersion term _δD in the Hansen solubility parameters of 15.7 MPa ^1/2 or less with a monoester solvent (B) having a boiling point of 300° C. or more, deformation of a clear file can be prevented and toner transfer can be prevented.

Furthermore, the monoester solvent (B) tends to have a high surface tension due to its ester structure. By using an ink containing the monoester (B) with high surface tension, the surface tension of the ink droplets ejected from the nozzles is increased, making it possible to prevent the generation of satellites as minute droplets from the main ink droplet.
In the inkjet recording method, ink droplets ejected from the nozzle fly with a trailing tail, and there is a time difference and a speed difference between the leading and trailing parts of the flying droplets. This can cause unnecessary small droplets (satellites) to be generated in addition to the leading main droplets. When ink droplets are ejected from the nozzle and adhere to the recording medium, if the satellites land on the recording medium at a position different from the main ink droplets, they can cause the printing surface to be dirty. In addition, the satellites become mist and float in the space between the nozzle face of the inkjet head and the transport path, and can adhere to the recording medium at a position different from the ink droplets, reducing the printing quality, or can adhere to the inside of the device and dirty the device.

The oil-based ink may contain a diester solvent (A) having a dispersion term δ _D in the Hansen solubility parameters of 15.7 MPa ^1/2 or less.

In terms of Hansen solubility parameters, the diester solvent (A) preferably has the following properties:
The dispersion parameter _δD of the diester solvent (A) is preferably 15.7 MPa ^1/2 or less, and more preferably 15.6 MPa ^1/2 or less, so that the diester solvent (A) is less likely to interact with the polymer components of the clear file and the toner, and deformation of the clear file and toner transfer can be prevented.
From the viewpoint of preventing a decrease in surface tension, the dispersion term _δD of the diester solvent (A) is preferably 13 MPa ^1/2 or more, more preferably 14 MPa ^1/2 or more, and even more preferably 14.5 MPa ^1/2 or more. By including a solvent having a high surface tension in the ink, it is possible to prevent satellites from being generated from the ink droplets ejected from the nozzles, and to prevent staining of the printed surface. From the viewpoint of suppressing the generation of satellites, the dispersion term _δD of the diester solvent (A) is preferably 15.0 MPa ^1/2 or more.

The polar term _δP and hydrogen bond term _δH of the diester solvent (A) are components that are affected by the charge imbalance in the molecule and the presence or absence of hydrogen bonds, respectively, and are specified within the following ranges depending on the diester structure. Since these ranges are outside the three-dimensional space of the polymer components of the clear file and toner, the diester solvent (A) acts to help prevent deformation of the clear file and toner transfer.
The polarity parameter δ _P of the diester solvent (A) is preferably from 1.0 to 5.0 MPa ^1/2 , more preferably from 1.0 to 4.0 MPa ^1/2 , and even more preferably from 1.5 to 3.0 MPa ^1/2 .
The hydrogen bond parameter δ _H of the diester solvent (A) is preferably from 1.0 to 10.0 MPa ^1/2 , more preferably from 1.5 to 6.0 MPa ^1/2 , and even more preferably from 2.0 to 4.0 MPa ^1/2 .

A method for calculating the Hansen solubility parameter (HSP value) is described below. In the present disclosure, the three-dimensional Hansen solubility parameter proposed by Hansen in 1967 is used.
The Hansen solubility parameters are the Hansen solubility parameters introduced by Hildebrand, which are divided into three components, the dispersion term δ _D , the polarity term δ _P , and the hydrogen bond term δ _H, and expressed in a three-dimensional space. The dispersion term indicates the effect of dispersion forces, the polarity term indicates the effect of dipole-dipole forces, and the hydrogen bond term indicates the effect of hydrogen bonding forces. More details are described in POLYMER HANDBOOK. FOURTH EDITION. (Editors. J. BRANDRUP, E.H. IMMERGUT, and E.A. GRULKE.) and the like.
Specifically, the calculation was performed using the Hansen Solubility Parameter calculation software "HSPiP: Hansen Solubility Parameters in Practice" ver. 5.3 by Charles M. Hansen et al. The same applies below.

The boiling point of the diester solvent (A) is not particularly limited, but is preferably less than 360° C. A low boiling point solvent has a relatively low viscosity, and thus the ink can be made more ejectable by including a low boiling point solvent in the ink. The diester solvent (A) can prevent deformation of the clear file and toner transfer even when it has a low boiling point and low viscosity by having a dispersion term _δD in the above-mentioned range.
The boiling point of the diester solvent (A) is preferably less than 360° C., and more preferably not more than 300° C. In order to prevent the solvent from volatilizing from the inkjet nozzle, the boiling point of the diester solvent (A) is preferably 150° C. or more, more preferably 200° C. or more, and more preferably 250° C. or more.
In this disclosure, the boiling point of a solvent refers to the boiling point at 1 atmospheric pressure. The boiling point of a solvent can be measured in accordance with (1) the initial boiling point method of JIS K2254 "Petroleum products - Distillation test method". The same applies below.

The surface tension of the diester solvent (A) is preferably 20 mN/m or more at 23°C.
The diester solvent (A) has a dispersion term _δD in the above range, and thus tends to have a relatively high surface tension. The inclusion of a solvent with high surface tension in the ink makes it possible to prevent satellites from being generated from the ink droplets ejected from the nozzles, and thus to prevent staining of the printed surface.
The surface tension of the diester solvent (A) at 23° C. is preferably 20 mN/m or more, more preferably 22 mN/m or more, and even more preferably 26 mN/m or more, so that the generation of satellites can be further prevented.
The surface tension of the diester solvent (A) is not particularly limited, but from the viewpoints of solvent miscibility and pigment affinity, it is preferably 40 mN/m or less, and more preferably 35 mN/m or less at 23°C.
In the present disclosure, the surface tension of a solvent is a value measured by a maximum bubble pressure method under the measurement conditions of 23° C. and 0.05 Hz. For example, a surface tension measuring device (SITA Messtechnik GmbH science line t60 (product name) manufactured by SITA Process Solutions) can be used as the measuring device. The same applies below.

The viscosity of the diester solvent (A) at 23° C. is preferably from 1 to 20 mPa·s, more preferably from 1 to 10 mPa·s, and even more preferably from 2 to 8 mPa·s.
In the present disclosure, the solvent viscosity is a value measured at 23° C. using a rotational viscometer. For example, a “Rheometer MCR302” manufactured by Anton Paar Japan Co., Ltd. can be used as the viscosity measuring device. The same applies below.

The diester solvent (A) is a compound having two ester bonds in one molecule. The diester solvent (A) is preferably in a liquid state at 23°C.
The diester solvent (A) may be an ester of a dicarboxylic acid having two carboxy groups and a monohydric alcohol, an ester of a monocarboxylic acid and a diol having two hydroxyl groups, a carbonic acid diester, etc. Among these, a dicarboxylic acid diester, a diol diester, or a combination thereof is preferred.
In the diester solvent (A), the hydrocarbon groups contained in the units derived from the acid component and the units derived from the alcohol component may each independently be saturated or unsaturated hydrocarbon groups, and may be chain hydrocarbon groups, alicyclic hydrocarbon groups, or aromatic hydrocarbon groups. If the chain hydrocarbon group is a chain hydrocarbon group, it may be linear or branched.
Preferably, in the diester solvent (A), the units derived from the acid component and the units derived from the alcohol component each independently have a saturated chain hydrocarbon group, which may be linear or branched.

In the diester solvent (A), some or all of the hydrogen atoms may be substituted. In view of the Hansen solubility parameter and the stability as a solvent, the substituents are preferably fluorine atoms.
When the diester solvent (A) has a substituent, it is preferable that the substituent is introduced to a carbon atom between two ester bonds rather than to the terminal group of the ester bond, so that the dispersion term _δD can be set in a more preferable range while maintaining the solvent miscibility.

The diester solvent (A) preferably has 6 to 30 carbon atoms in one molecule, more preferably 8 to 22, and even more preferably 8 to 20. Within this range, the boiling point and viscosity of the diester solvent (A) become more appropriate, and the ejection properties can be further improved.

一般式（１）において、Ｒ^１及びＲ^２はそれぞれ独立的にイソプロピル基、ｓｅｃ－ブチル基、又はｔｅｒｔ－ブチル基である。 An example of the diester solvent (A) may include a diester represented by the following general formula (1):

In general formula (1), R ¹ and R ² each independently represent an isopropyl group, a sec-butyl group, or a tert-butyl group.

The diester represented by the general formula (1) is an esterification product of 2,2,4-trimethyl-1,3-pentanediol and a monocarboxylic acid, such as isobutyric acid, 2-methylbutanoic acid, or pivalic acid.
In the diester represented by the general formula (1), R ¹ and R ² may be different from each other, but are preferably the same from each other. By increasing the symmetry of the molecular structure, the polarity of the molecule is decreased, which reduces the solubility of the toner image by the ink components, and makes it possible to more effectively prevent toner transfer.

In the diester represented by the general formula (1), some or all of the hydrogen atoms may be substituted with fluorine atoms. For example, the hydrogen atoms at the site derived from 2,2,4-trimethyl-1,3-pentanediol may be substituted with fluorine atoms, the hydrogen atoms at the site derived from monocarboxylic acid may be substituted with fluorine atoms, or all of the hydrogen atoms contained in one molecule may be substituted with fluorine atoms. This allows the dispersion term _δD of the Hansen solubility parameter to be set lower, and staining of the printed surface caused by satellites can be more effectively prevented.

Other examples of the diester solvent (A) can include fluorine-substituted diesters having 8 to 22 carbon atoms in one molecule, in which 6 or more of the hydrogen atoms are substituted with fluorine atoms.
The fluorine-substituted diester may be an esterification product in which at least one of the acid component and the alcohol component has a fluorine atom.
For example, in an esterification product of a dicarboxylic acid and a monohydric alcohol, or an esterification product of a monocarboxylic acid and a diol, a compound having a fluorine atom in at least one of the acid component and the alcohol component can be used.

Examples of dicarboxylic acids having fluorine atoms include hexadecafluorosebacic acid, hexafluoroglutaric acid, dodecafluorosuberic acid, and octafluoroadipic acid.

Examples of monocarboxylic acids having fluorine atoms include heptafluorobutyric acid, 4,4,4-trifluorobutyric acid, tricosafluorododecanoic acid, 3,3,3-trifluoropropionic acid, tricosafluorododecanoic acid, pentafluoropropionic acid, pentadecafluorooctanoic acid, nonadecafluorodecanoic acid, and nonafluorovaleric acid.

Examples of monohydric alcohols having fluorine atoms include 4,4,4-trifluoro-1-butanol, 2-(perfluorohexyl)ethanol, 2,2,2-trifluoroethanol, 2,2,3,3,3-pentafluoro-1-propanol, 1H,1H-pentadecafluoro-1-octanol, 2,2,3,3,4,4,5,5-octafluoro-1-pentanol, 1H,1H-nonadecafluoro-1-decanol, 1H,1H-nonafluoro-1-pentanol, 1H,1H,2H,2H-nonafluoro-1-hexanol, 1H,1H-heptadecafluoro-1-nonanol, and 2,2,3,3,4,4,4-heptafluoro-1-butanol.

Examples of dihydric alcohols having fluorine atoms include 1H,1H,10H,10H-hexadecafluoro-1,10-decanediol, hexafluoro-2,3-bis(trifluoromethyl)-2,3-butanediol, 1H,1H,10H,10H-hexadecafluoro-1,10-decanediol, and 2,2,3,3,4,4,5,5,6,6,7,7-dodecafluoro-1,8-octanediol.

The unsubstituted monohydric alcohol, dihydric alcohol, monocarboxylic acid, and dicarboxylic acid may be saturated or unsaturated linear or branched chain monohydric alcohol, dihydric alcohol, monocarboxylic acid, and dicarboxylic acid, each of which has carbon atoms in the range of 8 to 22 carbon atoms in one molecule of the diester. Preferably, the monohydric alcohol, dihydric alcohol, monocarboxylic acid, and dicarboxylic acid are saturated linear or branched chain monohydric alcohol, dihydric alcohol, monocarboxylic acid, and dicarboxylic acid.

The synthesis method of the diester solvent (A) is not particularly limited, and the diester solvent (A) can be obtained by an esterification reaction between an acid component and an alcohol component according to a conventional method. An example of a synthesis method of the diester solvent (A) is described below. Note that the diester solvent (A) is not limited to those synthesized by the following synthesis method.

The ester of a dicarboxylic acid with a monohydric alcohol can be obtained by reacting a dicarboxylic acid or an anhydride thereof with a monohydric alcohol. The dicarboxylic acid and the monohydric alcohol can be the same as those described above.
The ester of a monocarboxylic acid and a diol can be obtained by reacting a monocarboxylic acid with a diol. The monocarboxylic acid and the diol can be the same as those described above.
In the esterification reaction, the reaction temperature can be adjusted in the range of 80 to 230°C depending on the types of acid and alcohol components. The reaction time can be adjusted in the range of 1 to 48 hours depending on the types of acid and alcohol components and the amounts of raw materials used. It is preferable to remove water generated during the esterification reaction. The reaction can be carried out by putting the two components into a synthesis solvent such as cyclohexane.
Since dicarboxylic acid and monohydric alcohol react in a molar ratio of 1:2, it is recommended to charge the raw materials to the synthesis system in this molar ratio. Since monocarboxylic acid and diol react in a molar ratio of 2:1, it is recommended to charge the raw materials to the synthesis system in this molar ratio.
In the reaction, a suitable amount of a catalyst such as concentrated sulfuric acid, p-toluenesulfonic acid monohydrate, or methanesulfonic acid may be used.

Specific examples of diesters represented by general formula (1) include 2,2,4-trimethyl-1,3-pentanediol diisobutyrate and its fluorine-substituted derivatives, 2,2,4-trimethyl-1,3-pentanediol di-2-methylbutyrate and its fluorine-substituted derivatives, etc.

Specific examples of fluorine-substituted diesters include dimethyl octafluoroadipate, bis(2,2,3,3,3-pentafluoro-1-propyl) adipate, bis(4,4,4-trifluoro-1-butyl) adipate, and 1,6-hexanediol bis(pentafluoropropionate).
The above diester solvents (A) may be used alone or in combination of two or more kinds.
When the oil-based ink contains two or more diester solvents (A), it is preferable that each of the diester solvents (A) satisfies the above-mentioned ranges of physical property values such as δ _D. It is more preferable that the mixed solvent of two or more diester solvents (A) satisfies the above-mentioned ranges of physical property values such as δ _D.

The diester solvent (A) is preferably 10% by mass or more, more preferably 20% by mass or more, and even more preferably 30% by mass or more, based on the total amount of the non-aqueous solvent. This allows the diester solvent (A) to exhibit the property of being less likely to interact with the polymer component, and can better prevent deformation of clear files and toner transfer. In addition, the ink as a whole exhibits high surface tension, and can better prevent staining of the printed surface caused by satellites.
The diester solvent (A) is preferably 90% by mass or less, more preferably 80% by mass or less, and further preferably 60% by mass or less, based on the total amount of the non-aqueous solvent. By combining the diester solvent (A) with the monoester solvent (B) within a range in which the content of the diester solvent (A) exhibiting high polarity is limited, dissolution of the toner image by the ink components can be suppressed, and toner transfer can be further prevented.
For example, the amount of the diester solvent (A) is preferably from 10 to 90% by mass, more preferably from 20 to 80% by mass, and even more preferably from 30 to 60% by mass, based on the total amount of the non-aqueous solvent.

The diester solvent (A) is preferably present in an amount of 5 to 90% by mass, more preferably 15 to 80% by mass, and even more preferably 25 to 60% by mass, based on the total amount of the ink.

The oil-based ink may contain a monoester solvent (B) having a boiling point of 300° C. or higher.
The boiling point of the monoester solvent (B) is preferably 300° C. or higher, more preferably 330° C. or higher, and even more preferably 360° C. or higher. By using a combination of the diester solvent (A) and the monoester solvent (B), toner transfer can be more effectively prevented. Furthermore, by using the monoester solvent (B) with a high boiling point, the volatilization of the solvent from the printed matter can be suppressed, the penetration of the solvent into the clear file can be suppressed, and the deformation of the clear file can be more effectively prevented.
The boiling point of the monoester solvent (B) is not particularly limited, but since a solvent with a high boiling point has a high viscosity and is one of the causes of reduced ejection properties, the boiling point is preferably 450° C. or lower, and more preferably 400° C. or lower.

In terms of Hansen solubility parameters, the monoester solvent (B) preferably has the following properties:
The dispersion term _δD of the monoester solvent (B) is preferably 17.0 MPa ^1/2 or less, more preferably 16.5 MPa ^1/2 or less, and even more preferably 16.1 MPa ^1/2 or less. When the monoester solvent (B) is used alone, _δD is in a relatively large range, but when the diester solvent (A) is combined with the monoester solvent (B) and the _δD of the monoester solvent (B) is in this range, the ink components are less likely to interact with the polymer components of the toner, and toner transfer can be more effectively prevented. Since the monoester solvent (B) has a high boiling point, it is possible to prevent deformation of the clear file, and by selecting a monoester solvent (B) with a small _δD within this range, deformation of the clear file can be more effectively prevented.
From the viewpoint of preventing a decrease in surface tension, the dispersion term _δD of the monoester solvent (B) is preferably 13 MPa ^1/2 or more, more preferably 14 MPa ^1/2 or more, and even more preferably 15 MPa ^1/2 or more. By including a solvent having a high surface tension in the ink, it is possible to prevent satellites from being generated from the ink droplets ejected from the nozzles, and to further prevent staining of the printed surface.

The polar term δ _P and hydrogen bond term δ _H of the monoester solvent (B) are components that are influenced by the charge imbalance in the molecule and the presence or absence of hydrogen bonds, respectively, and are greatly influenced by the monoester structure. In many cases, the Hansen solubility parameter of the monoester solvent (B) is outside the three-dimensional space of the polymer component of the toner, so the monoester solvent (B) acts to help prevent toner transfer.
The polarity parameter δ _P of the monoester solvent (B) is preferably from 1.0 to 5.0 MPa ^1/2 , more preferably from 1.0 to 4.0 MPa ^1/2 , and even more preferably from 1.5 to 3.0 MPa ^1/2 .
The hydrogen bond parameter δ _H of the monoester solvent (B) is preferably from 1.0 to 5.0 MPa ^1/2 , more preferably from 1.0 to 4.0 MPa ^1/2 , and even more preferably from 1.5 to 3.0 MPa ^1/2 .

The surface tension of the monoester solvent (B) at 23° C. is preferably 20 mN/m or more, more preferably 25 mN/m or more, and even more preferably 28 mN/m or more.
The monoester solvent (B) tends to have a relatively high surface tension. By including a solvent with a high surface tension in the ink, it is possible to prevent satellites from being generated from the ink droplets ejected from the nozzles, and to prevent staining of the printed surface.
The surface tension of the monoester solvent (B) is not particularly limited, but from the viewpoints of solvent miscibility and pigment affinity, it is preferably 40 mN/m or less, and more preferably 35 mN/m or less at 23°C.

The viscosity of the monoester solvent (B) at 23°C is preferably 1 to 30 mPa·s, more preferably 1 to 20 mPa·s, and even more preferably 5 to 15 mPa·s. Since the monoester solvent (B) is a high boiling point solvent, it tends to have a high viscosity, but when the viscosity of the monoester solvent (B) is in this range, it can be combined with the diester solvent (A) to further prevent a decrease in ejection properties.

The monoester solvent (B) is a compound having one ester bond in one molecule. The monoester solvent (B) is preferably liquid at 23°C.
As the monoester solvent (B), a monocarboxylic acid monoester or the like can be used.
In the monoester solvent (B), the hydrocarbon groups contained in the units derived from the acid component and the units derived from the alcohol component may each independently be saturated or unsaturated hydrocarbon groups, and may be chain hydrocarbon groups, alicyclic hydrocarbon groups, or aromatic hydrocarbon groups. If the chain hydrocarbon group is a chain hydrocarbon group, it may be linear or branched.
Preferably, in the monoester solvent (B), the unit derived from the acid component and the unit derived from the alcohol component each independently have a saturated chain-like hydrocarbon group, and may be a straight chain or a branched chain. From the viewpoint of preventing a decrease in the solubility of the toner image, the monoester solvent (B) is preferably a monoester of a saturated fatty acid and a saturated alcohol.

The monoester solvent (B) preferably has 14 to 30 carbon atoms in one molecule, more preferably 18 to 28, and even more preferably 20 to 24. Within this range, the boiling point and viscosity of the monoester solvent (B) become more appropriate, and the ejection properties can be further improved.

Specific examples of monoester solvents (B) include isostearyl neopentanoate, isocetyl isooctanoate, isopropyl palmitate, 2-octyldecyl neopentanoate, 2-octyldodecyl neopentanoate, isotridecyl isononanoate, isononyl isononanoate, isodecyl isononanoate, hexyl laurate, butyl stearate, isopropyl isostearate, 5,7,7-trimethyl 2-(1,3,3-trimethylbutyl)octyl 3,5,5-trimethylhexanoate, 1,1-diethylpropyl 2-(1,3,3-trimethylbutyl)-5,7,7-trimethyloctanoate, 2-hexyldecyl 3,5,5-trimethylhexanoate, 3,7-dimethyloctanol 9,9-dimethyldecanoate, and 3,5,5-trimethylhexyl 9,9-dimethyldecanoate.

The above monoester solvents (B) may be used alone or in combination of two or more kinds.
When the oil-based ink contains two or more monoester solvents (B), it is preferable that each of the monoester solvents (B) satisfies the above-mentioned range of physical property values such as boiling point, etc. More preferably, the mixed solvent of two or more monoester solvents (B) satisfies the above-mentioned range of physical property values such as boiling point, etc.

The monoester solvent (B) is preferably 10% by mass or more, more preferably 20% by mass or more, and even more preferably 30% by mass or more, based on the total amount of the non-aqueous solvent. By combining the diester solvent (A) and the monoester solvent (B), the solubility of the toner image by the ink components can be reduced, and toner transfer can be more effectively prevented.
The content of the monoester solvent (B) is preferably 90% by mass or less, more preferably 80% by mass or less, and further preferably 70% by mass or less, based on the total amount of the non-aqueous solvent, thereby limiting the content of the monoester solvent (B) which exhibits a relatively high viscosity, lowering the viscosity of the ink, and further improving the ejection properties.
For example, the amount of the monoester solvent (B) is preferably from 10 to 90% by mass, more preferably from 20 to 80% by mass, and even more preferably from 30 to 70% by mass, based on the total amount of the non-aqueous solvent.

The diester solvent (B) is preferably present in an amount of 5 to 90% by mass, more preferably 15 to 80% by mass, and even more preferably 25 to 70% by mass, based on the total amount of the ink.

The mass ratio A/B of the diester solvent (A) to the monoester solvent (B) is preferably from 1/9 to 9/1, more preferably from 1/4 to 4/1, and even more preferably from 3/7 to 3/2.
The mass ratio A/B is preferably 3/7 or more, more preferably 2/3 or more. This ensures a sufficient content of the diester solvent (A) and can prevent the clear file from being deformed. In addition, the content of the monoester solvent (B) can be controlled to an appropriate amount to prevent the ink from becoming too viscous, and improve the ejection properties.
The mass ratio A/B is preferably 3/2 or less, and by combining the diester solvent (A) and the monoester solvent (B), the solubility of the toner image by the ink components can be reduced, and toner transfer can be more effectively prevented.

The total amount of the diester solvent (A) and the monoester solvent (B) is preferably 10 to 98% by mass, more preferably 50 to 95% by mass, and even more preferably 70 to 90% by mass, based on the total amount of the ink.

In addition to the diester solvent (A) and the monoester solvent (B), the oil-based inkjet ink may contain other non-aqueous solvents as long as the effects of the present invention are not impaired.
As the other non-aqueous solvent, either a non-polar organic solvent or a polar organic solvent can be used. Note that, in one embodiment, it is preferable to use a water-insoluble organic solvent that is not uniformly mixed with the same volume of water at 20° C. under 1 atmosphere as the non-aqueous solvent.
Examples of other non-aqueous solvents include non-polar organic solvents such as petroleum-based hydrocarbon solvents, such as aliphatic hydrocarbon solvents, alicyclic hydrocarbon solvents, and aromatic hydrocarbon solvents, and polar organic solvents, such as higher alcohol solvents and higher fatty acid solvents. The oil-based ink may also contain other fatty acid ester solvents other than the diester solvent (A) and the monoester solvent (B).

Examples of the aliphatic hydrocarbon solvent and the alicyclic hydrocarbon solvent include non-aqueous solvents such as paraffin, isoparaffin, and naphthene, and examples of commercially available products include No. 0 Solvent L, No. 0 Solvent M, No. 0 Solvent H, Cactus normal paraffin N-10, Cactus normal paraffin N-11, Cactus normal paraffin N-12, Cactus normal paraffin N-13, Cactus normal paraffin N-14, Cactus normal paraffin N-15H, Cactus normal paraffin YHNP, Cactus normal paraffin SHNP, and Isozol. Preferred examples of the present invention include 300, Isozol 400, Teclean N-16, Teclean N-20, Teclean N-22, AF Solvent No. 4, AF Solvent No. 5, AF Solvent No. 6, AF Solvent No. 7, Naphtesol 160, Naphtesol 200, and Naphtesol 220 (all manufactured by JXTG Nippon Oil & Energy Corporation); Isopar G, Isopar H, Isopar L, Isopar M, Exxol D40, Exxol D60, Exxol D80, Exxol D95, Exxol D110, and Exxol D130 (all manufactured by Exxon Mobil Corporation).
Preferred examples of the aromatic hydrocarbon solvent include Grade Alkene L and Grade Alkene 200P (all manufactured by JXTG Nippon Oil & Energy Corporation), Solvesso 100, Solvesso 150, Solvesso 200 and Solvesso 200ND (all manufactured by Exxon Mobil Corporation).
The initial distillation point of the petroleum-based hydrocarbon solvent is preferably 100° C. or higher, more preferably 150° C. or higher, and even more preferably 200° C. or higher. The initial distillation point can be measured in accordance with JIS K0066 "Distillation test method for chemical products."

Preferred examples of the polar organic solvent include higher alcohol solvents, higher fatty acid solvents, and other fatty acid ester solvents.
Examples of higher alcohol solvents include isomyristyl alcohol, isopalmityl alcohol, isostearyl alcohol, oleyl alcohol, isoeicosyl alcohol, tetradecanol, decyltetradecanol, 1-octadecanol, etc. The number of carbon atoms in one molecule of the higher alcohol solvent is preferably 6 or more, and more preferably 12 to 20.
Examples of higher fatty acid solvents include lauric acid, isomyristic acid, palmitic acid, isopalmitic acid, α-linolenic acid, linoleic acid, oleic acid, isostearic acid, etc. The number of carbon atoms in one molecule of the higher fatty acid solvent is preferably 12 or more, and more preferably 14 to 20.
Examples of other fatty acid ester solvents include 2-ethylhexyl isononanoate, methyl laurate, isopropyl laurate, etc. The number of carbon atoms in one molecule of the other fatty acid ester solvent is preferably 13 or more.

The boiling point of polar organic solvents such as fatty acid ester solvents, higher alcohol solvents, and higher fatty acid solvents is preferably 150° C. or higher, more preferably 200° C. or higher, and even more preferably 250° C. or higher.
When other non-aqueous solvents are used, they are preferably solvents that can form a single phase with the diester solvent (A) and the monoester solvent (B). As the other non-aqueous solvent, from the viewpoint of suppressing deformation of the clear file, in order to suppress volatilization of the solvent from the printed surface, it is preferable that the non-polar solvent has a high initial distillation point, and that the polar solvent has a high boiling point.

The ink may include a pigment, a dye, or a combination thereof as a colorant.
Examples of the pigment include organic pigments such as azo pigments, phthalocyanine pigments, polycyclic pigments, and dye lake pigments; and inorganic pigments such as carbon black and metal oxides. Examples of the azo pigments include soluble azo lake pigments, insoluble azo pigments, and condensed azo pigments. Examples of the phthalocyanine pigments include metal phthalocyanine pigments such as copper phthalocyanine pigments, and metal-free phthalocyanine pigments. Examples of the polycyclic pigments include quinacridone pigments, perylene pigments, perinone pigments, isoindoline pigments, isoindolinone pigments, dioxazine pigments, thioindigo pigments, anthraquinone pigments, quinophthalone pigments, metal complex pigments, and diketopyrrolopyrrole (DPP). Examples of the carbon black include furnace carbon black, lamp black, acetylene black, and channel black. Examples of the metal oxides include titanium oxide and zinc oxide. These pigments may be used alone or in combination of two or more.

From the viewpoints of ejection stability and storage stability, the average particle size of the pigment is preferably 300 nm or less, more preferably 200 nm or less, even more preferably 150 nm or less, and even more preferably 100 nm or less, as a volume-based average value in a particle size distribution measured by a dynamic light scattering method.
The amount of the pigment is usually 0.01 to 20% by mass based on the total amount of the ink, and from the viewpoints of print density and ink viscosity, it is preferably 1 to 15% by mass, and more preferably 4 to 10% by mass.

In order to stably disperse the pigment in the ink, a pigment dispersant can be used together with the pigment.
Preferred examples of pigment dispersants include hydroxyl group-containing carboxylates, salts of long-chain polyaminoamides and high molecular weight acid esters, salts of high molecular weight polycarboxylates, salts of long-chain polyaminoamides and polar acid esters, high molecular weight unsaturated acid esters, copolymers of vinylpyrrolidone and long-chain alkenes, modified polyurethanes, modified polyacrylates, polyether ester-type anionic surfactants, polyoxyethylene alkyl phosphates, and polyester polyamines.

Examples of commercially available pigment dispersants include "Antaron V216 (vinylpyrrolidone-hexadecene copolymer) and V220 (vinylpyrrolidone-eicosene copolymer)" (all trade names) manufactured by ISP Japan Co., Ltd.; "Solsperse 13940 (polyester amine type), 16000, 17000, 18000 (fatty acid amine type), 11200, 24000, 28000" (all trade names) manufactured by Lubrizol Japan Co., Ltd.; and "EFKA 400, 401, 402, 403, 450, 451, 453 (modified polyacrylate), 46, 47, 48, 49, 4010, 4055 (modified polyurethane)" (all trade names) manufactured by BASF Japan Co., Ltd. (all trade names); Kusumoto Chemicals Co., Ltd.'s "Disparlon KS-860, KS-873N4 (amine salt of polyester)" (all trade names); Daiichi Kogyo Seiyaku Co., Ltd.'s "Discol 202, 206, OA-202, OA-600 (multi-chain polymer nonionic)" (all trade names); BYK Japan KK's "DISPERBYK2155, 9077" (all trade names); Croda Japan KK's "Hypermer KD2, KD3, KD11, KD12" (all trade names); Lubrizol Japan Co., Ltd.'s "Solsperse 24000SC, 24000GR, 32000, 33000, 3900, etc." (all trade names).

The amount of pigment dispersant used may be set appropriately as long as it is an amount that can adequately disperse the pigment in the ink. For example, the pigment dispersant may be blended in a mass ratio of 0.1 to 5 parts by mass of pigment to 1 part by mass of pigment, and preferably 0.3 to 1 part by mass. The pigment dispersant may be blended in an amount of 0.01 to 10% by mass of the total amount of ink, and preferably 0.1 to 8% by mass, and more preferably 1 to 8% by mass.

As the dye, any dye generally used in the art can be used. In the case of oil-based ink, it is preferable to use an oil-soluble dye, since the dye has affinity for the non-aqueous solvent of the ink and thus has better storage stability.
Examples of oil-soluble dyes include azo dyes, metal complex dyes, naphthol dyes, anthraquinone dyes, indigo dyes, carbonium dyes, quinoneimine dyes, xanthene dyes, cyanine dyes, quinoline dyes, nitro dyes, nitroso dyes, benzoquinone dyes, naphthoquinone dyes, phthalocyanine dyes, metal phthalocyanine dyes, etc. These may be used alone or in combination.
The amount of the dye is usually 0.01 to 20% by mass based on the total amount of the ink, and from the viewpoints of print density and ink viscosity, it is preferably 1 to 15% by mass, and more preferably 5 to 10% by mass.

In addition to the above components, the oil-based ink may contain various additives as long as they do not impair the effects of the present invention. As additives, nozzle clogging prevention agents, antioxidants, conductivity regulators, viscosity regulators, surface tension regulators, oxygen absorbers, etc. can be added as appropriate. There are no particular limitations on the types of these additives, and any additives used in the relevant field can be used.

There are no particular limitations on the method for producing oil-based ink, but one method is to prepare the ink by mixing and stirring each component all at once or in portions. Specifically, the ink can be prepared by dispersing all the components in a dispersing machine such as a bead mill, either all at once or in portions, and passing the mixture through a filter such as a membrane filter, if desired.

The suitable range of viscosity for oil-based inkjet ink varies depending on the nozzle diameter of the ejection head of the inkjet recording system and the ejection environment, but generally, it is preferably 5 to 30 mPa·s at 23°C, more preferably 5 to 15 mPa·s, and even more preferably 8 to 13 mPa·s. In this disclosure, the ink viscosity can be measured using the same method as the solvent viscosity.

The printing method using the inkjet ink is not particularly limited, and may be any method such as a piezoelectric method, an electrostatic method, a thermal method, etc. When an inkjet recording device is used, it is preferable to eject the ink according to one embodiment from an inkjet head based on a digital signal, and to cause the ejected ink droplets to adhere to a substrate.
The ink according to one embodiment has low viscosity and is suitable for ejection from an inkjet nozzle, so that it can be ejected appropriately at around room temperature (23° C.).

In one embodiment, the substrate is not particularly limited, and examples thereof include printing paper such as plain paper, coated paper, and special paper, cloth, inorganic sheets, films, and OHP sheets, as well as adhesive sheets having an adhesive layer on the back surface of the substrate. Among these, permeable substrates are preferred from the viewpoint of ink permeability, and printing paper such as plain paper and coated paper can be preferably used.

Here, plain paper is paper that does not have an ink receiving layer or film layer formed on it. Examples of plain paper include fine paper, medium-quality paper, PPC paper, sawdust, and recycled paper. Plain paper has paper fibers that are several μm to tens of μm thick, forming gaps of tens to hundreds of μm, making it easy for ink to penetrate.

As coated paper, inkjet coated paper such as matte paper, glossy paper, and semi-glossy paper, and so-called coated printing paper can be preferably used. Here, coated printing paper is printing paper that has been used conventionally in letterpress printing, offset printing, gravure printing, etc., and is printing paper in which a coating layer is provided on the surface of fine or medium-quality paper with a paint containing an inorganic pigment such as clay or calcium carbonate and a binder such as starch. Coated printing paper is classified into lightly coated paper, fine lightweight coated paper, medium lightweight coated paper, fine coated paper, medium coated paper, art paper, cast coated paper, etc., depending on the amount of paint applied and the coating method.

The present invention will be described in detail below with reference to examples. The present invention is not limited to the following examples.

"Ink Creation"
The ink solvent formulations are shown in Tables 1 to 3. In each table, "-" indicates not added or not measured.
The ink of Example 1 was prepared by mixing 5% by mass of carbon black ("MA77" (product name) manufactured by Mitsubishi Chemical Corporation), 5% by mass of "Solsperse 18000" (product name, manufactured by Lubrizol Japan, non-volatile content 100% by mass), and 90% by mass of solvent, and dispersing the pigment sufficiently using a bead mill "DYNOMILL KDL-A" (product name, manufactured by Shinmaru Enterprises Co., Ltd.) for a residence time of 15 minutes. Subsequently, coarse particles were removed using a membrane filter to obtain an ink.
The ink of Example 2 was obtained by the same procedure as in Example 1 above, except that 4 mass % of a copper phthalocyanine pigment ("FASTGEN Blue LA5380" (product name) manufactured by DIC Corporation), 3.5 mass % of "Solsperse 13940" (product name, manufactured by Lubrizol Japan, Inc., non-volatile content 40 mass %), and 92.5 mass % of a solvent were mixed.
In Examples 3 to 10 and Comparative Examples 1 to 6, inks were obtained in the same manner as in Example 1 above.
The solvents were added in the proportions shown in each table. In each table, A and B indicate diester solvent (A) and monoester solvent (B), respectively, A' and B' indicate comparative solvents for diester solvent (A) and monoester solvent (B), respectively, and C indicates other solvents.

The diester solvents and monoester solvents shown in each table, as well as other solvents, are available from Tokyo Chemical Industry Co., Ltd. or Takakyu Alcohol Kogyo Co., Ltd.
Each table gives the δ _D , δ _P , δ _H , viscosity, surface tension, and boiling point of the solvent.
The units of δ _D , δ _P and δ _H are MPa ^1/2 . The Hansen solubility parameters of the solvents were calculated using the Hansen solubility parameter calculation software "HSPiP: Hansen Solubility Parameters in Practice" ver. 5.3 by Charles M. Hansen et al.
The viscosity is a value measured at 23° C. using a rotational viscometer, and the unit is mPa·s.
The surface tension is a value measured using a surface tension measuring device by the maximum bubble pressure method (SITA Messtechnik GmbH science line t60 (product name) manufactured by SITA Process Solutions) under measurement conditions of 23° C. and 0.05 Hz, and the unit is mN/m.
The boiling point is the boiling point at 1 atmosphere and is expressed in °C.
The solvent ratio shown in each table indicates the ratio (A/B) of the total amount of diester solvent (A) to the total amount of monoester solvent (B). When comparative solvents were used in the comparative examples, the contents of comparative solvents A' and B' were included in the contents of diester solvent (A) and monoester solvent (B), respectively.

"evaluation"
The inks were evaluated by the following methods, and the results are shown in the tables below.
(Prevents deformation of clear files)
The deformation of the clear file was evaluated by placing one printed sheet in a polypropylene (PP) clear file and leaving it at room temperature for one week, and checking the amount of deformation of the clear file after leaving it for one week, and evaluating it according to the following criteria. The thickness of one sheet of the clear file was 0.2 mm.
The deformation of the clear file is observed by placing the clear file containing the printed matter on a flat surface and bending the top sheet of the clear file outward. The deformation of the clear file is the distance from the flat surface to the maximum height of the top sheet of the clear file when it is bent outward.
The prints were produced by loading the ink into a line-type inkjet printer “Orphis GD9630” (manufactured by Riso Kagaku Corporation) and printing a solid image measuring approximately 51 mm (600 nozzles) in the main scanning direction by 260 mm in the sub-scanning direction on one side of plain paper “Riso Paper Thin” (manufactured by Riso Kagaku Corporation).
S: The deformation of the clear file is less than 1 cm.
A: The deformation of the clear file is 1 cm or more and less than 3 cm.
B: The deformation of the clear file is 3 cm or more.

(Prevention of toner transfer)
A laser printer "Satera LBP9100C" manufactured by Canon Inc. was used to produce a printout of a toner image in which a black solid image was formed on plain paper "Riso Paper Thin" (manufactured by Riso Kagaku Corporation). 10 minutes after the toner image was formed, 10 μL of the ink obtained in the above examples and comparative examples was dropped onto the solid image of the printout, and plain paper "Riso Paper Thin" was placed on top of it. A PET film was placed on top of this, and a weight was also placed on top. In this state, the paper was left in an environment of 23° C. for 3 days, and the degree of adhesion of the toner to the paper after leaving it was examined and evaluated according to the following criteria.
S: Almost no toner adhesion.
A: Toner sticks slightly.
B: There is a lot of toner adhesion.

(Ejectability)
The ejection property was evaluated by printing a solid image on one side of 100 sheets of plain paper "Riso Paper Thin" (manufactured by Riso Kagaku Corporation) using a line-type inkjet printer "Orphis GD9630" (manufactured by Riso Kagaku Corporation) in succession to obtain a print. The printing conditions were the same as those for the evaluation of the deformation of the clear file.
Non-ejection of ink from the inkjet nozzle can be confirmed by the occurrence of non-printed areas on the printed matter as white streaks. The occurrence or number of such white streaks was observed among 100 printed matters. The ejection performance was evaluated based on the total number of white streaks observed among the 100 printed matters. The evaluation criteria are as follows:
S: 0 white streaks.
A: There are 1 or 2 white streaks.
B: There are three or more white streaks.

(Prevention of stains on the printed surface)
The obtained ink was loaded into a line-type inkjet printer "ORPHIS GD9630" (manufactured by Riso Kagaku Corporation) and printed on plain paper "Riso Paper Multi" and matte paper "Riso Paper Matte IJ (W)" (manufactured by Riso Kagaku Corporation) so that the main droplets were aligned in a line. The obtained images were visually observed for stains on the printed surface due to satellites and evaluated according to the following criteria.
S: Almost no staining of the printed surface was observed even when printed on matte paper. No staining of the printed surface was observed even when printed on plain paper.
A: Almost no staining of the printed surface was observed on plain paper. Slight staining of the printed surface was observed on matte paper.
B: Staining of the printed surface is observed on both plain paper and matte paper.

As shown in each table, the ink of each example was able to prevent deformation of clear files, prevent toner transfer, and improve ejection properties. The ink of each example was also able to prevent staining of the printed surface. In addition, although not listed in the tables, the ink of each example produced good image quality in printed matter, including print density.

In Examples 1 to 11, various diester and monoester solvents were combined, and good results were obtained.
Examples 4 to 7 are examples in which the solvent ratio between the diester solvent and the monoester solvent is different. Through these examples, it can be seen that when the content of the diester solvent is high and the solvent ratio A/B is 4/1, some toner transfer occurs. It can also be seen that when the content of the monoester solvent is high and the solvent ratio A/B is 1/4, some deformation of the clear file occurs and the ejection performance is slightly reduced.
In Examples 1 to 3 and 10, a diester solvent represented by the general formula (1) was used, which has a high surface tension and prevents satellites from being generated, and prevents staining of the printed surface. In addition, in Examples 1 to 3 and 10, a monoester solvent with a higher boiling point was used, which prevents deformation of the clear file.
In Example 11, good results were obtained even when a certain amount of other solvent was included.

In Comparative Examples 1 and 2, the diester solvent had a large _δD , and the clear file was deformed and toner transfer occurred.
Comparative Example 3 is an example in which the boiling point of the monoester solvent is low, and deformation of the clear file occurred.
Comparative Example 4 is an example in which only a diester solvent was used, and the toner solubility was high, resulting in toner transfer.
Comparative Example 5 is an example in which only a monoester solvent having a high boiling point was used, and the ink viscosity increased and the ejection properties decreased.
Comparative Example 6 is an example in which only a monoester solvent having a lower boiling point than Comparative Example 5 was used. The ejection properties were improved, but the volatility of the solvent was high, causing deformation of the clear file.

Claims (3)

A diester solvent (A) having a dispersion term _δD in the Hansen solubility parameter of 15.7 MPa ^1/2 or less;
An oil-based inkjet ink comprising: a monoester solvent (B) having a boiling point of 300° C. or higher; and a coloring material. The oil-based inkjet ink according to claim 1, wherein the mass ratio of the diester solvent (A) to the monoester solvent (B) satisfies A/B = 3/7 to 3/2. The oil-based ink-jet ink according to claim 1 , wherein the diester solvent (A) comprises a diester represented by the following general formula (1):

(In general formula (1), R ¹ and R ² are each independently an isopropyl group, a sec-butyl group, or a tert-butyl group.)