JP2022111657A - Oil-based inkjet ink - Google Patents

Abstract

To provide an oil-based inkjet ink that solves the problem in which: a printed material including the inkjet ink causes a degradation or deformation of a resin product.SOLUTION: An oil-based inkjet ink contains a colorant and a nonaqueous solvent. The nonaqueous solvent contains a compound represented by general formula (1) at a rate of more than 40 mass% to the total amount of the nonaqueous solvent. R1-(O-R2)m-R3-(R4-O)n-R5 (1) (where, R1 and R5 independently represent a C1-4 alkyl group, R2 and R4 independently represent a C1-6 alkylene group, R3 is represented by -O-C(=O)-R3a-(C=O)-O-, -C(=O)-O-R3a-O-(C=O)-, or -O-(C=O)-O-, R3a is a single bond or a diester group as a C1-4 divalent hydrocarbon group, m and n independently represent an integer of 1-3).SELECTED DRAWING: None

Description

The present invention relates to oil-based inkjet inks.

The inkjet recording method ejects droplets of highly fluid inkjet ink from fine nozzles to record an image on a recording medium placed facing the nozzles, enabling high-speed printing with low noise. Therefore, it has spread rapidly in recent years. The inks used in such an inkjet recording method include water-based inks containing water as the main solvent, ultraviolet curable inks (UV inks) containing a high content of polymerizable monomers as the main component, and high inks containing wax as the main component. A so-called non-aqueous ink containing a non-aqueous solvent as a main solvent is known together with a hot-melt ink (solid ink) that contains a content. Non-aqueous ink can be classified into solvent ink (solvent-based ink) whose main solvent is a volatile organic solvent, and oil-based ink (oil-based ink) whose main solvent is a low-volatile or non-volatile organic solvent. Solvent ink dries on the recording medium mainly by evaporation of the organic solvent, whereas oil-based ink dries mainly by permeation into the recording medium.

When a printed material formed with an image using an oil-based inkjet ink is sandwiched between clear files made of polypropylene (PP) or the like for storage, there is a problem that the clear files warp and deform. One reason 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 component. Thus, when the printed surface comes into contact with the resin product, the resin product may change in quality, and a film-shaped resin product may be deformed. It has been found that the influence of such printed matters on resin products is greatly affected by the solvent among the ink components.

As a technique using a combination of various solvents, Patent Document 1 discloses that in an oil-based inkjet ink, a hydrocarbon-based solvent (A) having low polarity and a highly polar solvent having at least an ester group and an ether group in one molecule By using the solvent (B) in combination with the solvent (C) that dissolves in the solvent (A) and the solvent (B), the ink permeates into the recording medium and dries well, thereby suppressing roller transfer contamination of printed matter. is proposed.

On the other hand, in the inkjet recording method, ink droplets ejected from a nozzle fly in a trailing manner, and a time difference and a speed difference occur between the leading portion and the trailing portion of the flying droplets. For this reason, unnecessary minute droplets (satellites) may be generated accompanying the preceding main droplets. When an ink droplet is ejected from a nozzle and adheres to a recording medium, if a satellite lands on the recording medium out of alignment with the main droplet of ink, it causes contamination of the printing surface.

As a technique to prevent this satellite phenomenon, Patent Document 2 discloses that a specific water-insoluble resin and a water-soluble resin are used together with a pigment and a non-aqueous solvent to reduce the viscosity of the ink and suppress the generation of satellites. It is proposed to
Further, in Patent Document 3, along with a coloring material and a non-aqueous solvent, a specific non-aqueous resin and a water-soluble resin are used to reduce the viscosity of the ink and suppress the generation of satellites, and the ink to the nozzle plate is suppressed. It has been proposed to suppress the wettability of the ink and improve the ejection stability.

JP 2012-12432 A JP 2014-15491 A JP 2015-89933 A

In Patent Document 1, specific examples of the solvent (B) include bisethoxydiglycol cyclohexanedicarboxylate, bisethoxydiglycol succinate, and diethoxyethyl succinate. It is blended at 34.8% by mass. Japanese Patent Application Laid-Open No. 2002-200001 discloses that ink that does not contain a solvent (B) has a lower penetration drying property into a recording medium, and causes roller transfer contamination depending on the type of recording medium. However, Patent Document 1 does not consider the influence of printed matter on resin products such as clear files.

The disclosures of Patent Documents 2 and 3 only specify the resin component for reducing the viscosity of the ink, and do not attempt to reduce the viscosity of the ink or prevent satellites from the viewpoint of non-aqueous solvents. Although the inks disclosed in Patent Documents 2 and 3 have low viscosity, they have a low surface tension due to non-aqueous solvents, and may cause staining of the printing surface due to satellites. In addition, the inks disclosed in Patent Documents 2 and 3 may cause deterioration or deformation of resin products such as deformation of clear files.

One object of the present invention is to suppress deterioration or deformation of resin products due to printed matter.

One aspect of the present invention includes a coloring material and a non-aqueous solvent, and the non-aqueous solvent contains more than 40% by mass of the compound represented by the following general formula (1) with respect to the total amount of the non-aqueous solvent. Oil-based inkjet ink.
R ¹ —(OR ² ) _m —R ³ —(R ⁴ —O) _n —R ⁵ (1)
(In general formula (1), R ¹ and R ⁵ are each independently an alkyl group having 1 to 4 carbon atoms, R ² and R ⁴ are each independently an alkylene group having 1 to 6 carbon atoms, R ³ is -O-C(=O)-R ^3a -(C=O)-O-, -C(=O)-O-R ^3a -O-(C=O)-, or -O-( C=O)—O—, R ^3a is a single bond or a diester group that is a divalent hydrocarbon group having 1 to 4 carbon atoms, and m and n are each independently an integer of 1 to 3; be.)

ADVANTAGE OF THE INVENTION According to one Embodiment of this invention, generation|occurrence|production of deterioration or deformation|transformation of the resin product by printed matter can be suppressed.

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

The oil-based inkjet ink (hereinafter sometimes simply referred to as oil-based ink or ink) according to one embodiment contains a coloring material and a non-aqueous solvent, and the non-aqueous solvent is represented by the following general formula (1): It is characterized by containing more than 40% by mass of the compound with respect to the total amount of the non-aqueous solvent.
R ¹ —(OR ² ) _m —R ³ —(R ⁴ —O) _n —R ⁵ (1)
(In general formula (1), R ¹ and R ⁵ are each independently an alkyl group having 1 to 4 carbon atoms, R ² and R ⁴ are each independently an alkylene group having 1 to 6 carbon atoms, R ³ is -O-C(=O)-R ^3a -(C=O)-O-, -C(=O)-O-R ^3a -O-(C=O)-, or -O-( C=O)—O—, R ^3a is a single bond or a diester group that is a divalent hydrocarbon group having 1 to 4 carbon atoms, and m and n are each independently an integer of 1 to 3; be.)
According to this oil-based inkjet ink, it is possible to suppress deterioration or deformation of resin products caused by printed matters. For example, deformation of the film can be prevented in a state where a thin resin film such as a clear file is in contact with the printed matter. Moreover, according to this oil-based inkjet, it is possible to prevent the printing surface of the printed matter from being smeared.
Hereinafter, the compound represented by the general formula (1) is also referred to as a diester compound (1).

Since the diester compound (1) exhibits relatively high polarity, the polarity of the ink can be increased by blending it in the ink. Such an ink can suppress permeation into the resin product surface. For example, when a print is stored in a clear file made of polypropylene (PP), the ink on the surface of the print comes into contact with the inner surface of the clear file, and if the inner surface of the clear file swells due to the influence of the ink components, the clear file will be damaged. There is a phenomenon of bending outward. For such a phenomenon, the ink containing the diester compound (1) can suppress the penetration of the ink into the inner surface of the clear file and prevent the deformation of the clear file. Deformation can be similarly prevented for thin-film resin products such as clear files. In addition, it is possible to prevent deterioration of the surface of strong resin products, and to improve, for example, weather resistance and durability.
The diester compound (1) is a solvent that exhibits a high surface tension, and by adding it to the ink, the surface tension of the ink can be increased. Therefore, it is possible to suppress the generation of satellites in printing and prevent contamination of the printing surface.
In the ink jet recording method, an ink droplet ejected from a nozzle flies in a trailing manner, and a time difference and a speed difference occur between the leading portion and the trailing portion of the flying droplet. For this reason, unnecessary minute droplets (satellites) may be generated accompanying the preceding main droplets. When an ink droplet is ejected from a nozzle and adheres to a recording medium, if a satellite lands on the recording medium out of alignment with the main droplet of ink, it causes contamination of the printing surface. In addition, the satellites become mist and float in the space between the nozzle surface of the inkjet head and the transport path. It may adhere and stain the device.
When the diester compound (1) is contained in the ink, the surface tension of the liquid ejected from the nozzle is increased, and the formation of satellites can be prevented.

When the diester compound (1) is contained in an amount of more than 40% by mass with respect to the total amount of the non-aqueous solvent, the effect of suppressing the penetration of the ink into the resin product can be obtained. When a diester compound is blended to promote the penetration and drying of the ink into the recording medium, the effect can be obtained even if the amount of the diester compound blended is small. However, the effect of suppressing the penetration of ink into resin products cannot be sufficiently obtained with a small amount of the diester compound (1), and the effect can be exhibited only when the amount of the diester compound (1) is increased.

In one embodiment, the ink can contain a diester compound (1) represented by the following general formula (1).
R ¹ —(OR ² ) _m —R ³ —(R ⁴ —O) _n —R ⁵ (1)
(In general formula (1), R ¹ and R ⁵ are each independently an alkyl group having 1 to 4 carbon atoms, R ² and R ⁴ are each independently an alkylene group having 1 to 6 carbon atoms, R ³ is -O-C(=O)-R ^3a -(C=O)-O-, -C(=O)-O-R ^3a -O-(C=O)-, or -O-( C=O)—O—, R ^3a is a single bond or a diester group that is a divalent hydrocarbon group having 1 to 4 carbon atoms, and m and n are each independently an integer of 1 to 3; be.)

Since the diester compound (1) has two ester bonds in one molecule, it can exhibit high surface tension and high polarity. In addition, the diester compound (1) has two ester bonds in one molecule, so that it can be provided as a low-viscosity solvent, and can contribute to reducing the viscosity of the ink.

The diester compound (1) can exhibit high polarity by having one or more ether bonds each sandwiching the diester structure.
The diester compound (1) preferably has an alkyl group as a linear terminal group having one or more ether bonds across the diester structure. That is, R ¹ and R ⁵ are preferably alkyl groups. This can provide a highly polar solvent.

The diester compound may be a compound represented by the following general formula (1-1), (1-2), or (1-3).
R ¹ -(OR ² ) _m -O-C(=O)-R ^3a -(C=O)-O-(R ⁴ -O) _n -R ⁵ (1-1)
R ¹ —(OR ² ) _m —C(═O)—OR ^3a —O—(C═O)—(R ⁴ —O) _n —R ⁵ (1-2)
R ¹ —(OR ² ) _m —O—(C=O) —O—(R ⁴ —O) _n —R ⁵ (1-3)

The diester compound represented by general formula (1-1) has a structure derived from esterification of dicarboxylic acid, and the diester compound represented by general formula (1-2) has a structure derived from esterification of diol. and the diester compound represented by the general formula (1-3) has a structure derived from a diester carbonate.

In general formula (1), R ¹ and R ⁵ are preferably each independently an alkyl group having 1 to 4 carbon atoms.
The alkyl groups represented by R ¹ and R ⁵ may each independently be linear or branched, but linear alkyl groups are preferred.
The number of carbon atoms in R ¹ and R ⁵ is each independently preferably 4 or less, more preferably 3 or less, and still more preferably 1 or 2.
R ¹ and R ⁵ may each independently be methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl, or tert-butyl. Among these, it preferably has 3 or less carbon atoms, more preferably a methyl group, an ethyl group or an n-butyl group, and still more preferably a methyl group or an ethyl group.
In the general formula (1), when the terminal group is a methoxy group or an ethoxy group, the polarity of the diester compound (1) tends to be high. In particular, the polarity of the diester compound (1) having a methoxy terminal group tends to be high. As a result, penetration of the solvent into the surface of the resin product can be suppressed, and deformation of the clear file can be further prevented.

In general formula (1), R ² and R ⁴ are preferably each independently an alkylene group having 1 to 6 carbon atoms.
The alkylene groups represented by R ² and R ⁴ may each independently be linear or branched, but linear alkylene groups are preferred. When R ² and R ⁴ are straight-chain alkylene groups, the polarity becomes higher and the penetration of the ink into the resin product can be further suppressed.
The number of carbon atoms in R ² and R ⁴ is each independently preferably 6 or less, more preferably 4 or less, still more preferably 1 to 3, and still more preferably 2 or 3.
R ² and R ⁴ each independently include a methylene group, ethylene group, propylene group, trimethylene group, n-butylene, isobutylene group, pentylene group, hexylene group, heptylene group, octylene group, isooctylene group, and the like. can. Among these, a methylene group, ethylene group, propylene group, trimethylene group, n-butylene or isobutylene group is preferred, methylene group, ethylene group, propylene group or trimethylene group is more preferred, and still more preferred. is a methylene group, an ethylene group, or a propylene group.

In general formula (1), R ³ is -O-C(=O)-R ^3a -(C=O)-O-, -C(=O)-O-R ^3a -O-(C=O) - or -O-(C=O)-O-, wherein R ^3a is preferably a single bond or a diester group which is a divalent hydrocarbon group having 1 to 4 carbon atoms.

R ^3a is preferably a single bond or a divalent hydrocarbon group having 1 to 4 carbon atoms.
The divalent hydrocarbon group represented by R ^3a may be either a saturated hydrocarbon group or an unsaturated hydrocarbon group, preferably a saturated hydrocarbon group.
The divalent hydrocarbon group represented by R ^3a may be linear or branched, but is preferably a linear hydrocarbon group.
Among them, the divalent hydrocarbon group represented by R ^3a is preferably an alkylene group, more preferably a linear alkylene group.
The number of carbon atoms in R ^3a is preferably 4 or less, more preferably 3 or less, and even more preferably 1 or 2.
R ^3a is a single bond; an alkylene group having 1 to 4 carbon atoms such as a methylene group, ethylene group, propylene group, trimethylene group, n-butylene and isobutylene group; or a divalent unsaturated hydrocarbon having 2 to 4 carbon atoms. can be a base. Among these, a single bond or an alkylene group having 1 to 4 carbon atoms is preferred, a single bond, a methylene group, an ethylene group or a propylene group is more preferred, and a methylene group or an ethylene group is even more preferred.

In general formula (1), m and n are each independently preferably an integer of 1 to 3, more preferably 1 or 2, and still more preferably 2.
This makes it possible to prevent an increase in viscosity while maintaining the high polarity of the diester compound (1).

In the general formula (1), when m is 2 or 3, the groups represented by (OR ² ) _m are two or three (OR ² ) groups, and all R ² are the same However, some or all of them may be different. Similarly, in general formula (1), when n is 2 or 3, the group represented by (R ⁴ —O) _n is between two or three (R ⁴ —O) and R ⁴ may be all the same or partly or wholly different.

In general formula (1), R ¹ and R ⁵ , R ² and R ⁴ , m and n may be the same or different, but are preferably the same. In general formula (1), the group represented by R ¹ —(OR ² ) _m — and the group represented by —(R ⁴ —O) _n —R ⁵ may be the same Although they may be different, they are preferably the same.

In the diester compound (1), the total carbon number of the group represented by R ¹ —(OR ² ) _m — is, for example, preferably 2 to 20, more preferably 3 to 10, even more preferably 4 to 8. .
In the diester compound (1), the total carbon number of the groups represented by —(R ⁴ —O) _n —R ⁵ is, for example, preferably 2 to 20, more preferably 3 to 10, even more preferably 4 to 8. .

The diester compound (1) preferably has 7 or more carbon atoms per molecule, more preferably 8 or more carbon atoms, and still more preferably 10 or more carbon atoms. This makes it possible to provide a solvent with a high boiling point, suppress the contact of the solvent with the surface of the resin product, and further prevent the penetration of the solvent into the surface of the resin product. In addition, the volatilization of the solvent from the inkjet nozzle can be prevented, and the ejection property can be further improved.
The diester compound (1) preferably has 50 or less carbon atoms in one molecule, more preferably 30 or less carbon atoms, still more preferably 20 or less carbon atoms, even if it has 16 or less carbon atoms. good. With the number of carbon atoms in this range, the diester compound (1) itself has a low viscosity, and the viscosity of the ink as a whole can be lowered to further improve the ejection performance.
The diester compound (1) preferably has, for example, 7 to 20 carbon atoms, more preferably 8 to 16 carbon atoms, and still more preferably 10 to 16 carbon atoms in one molecule.
The diester compound (1) having a dicarboxylic acid or diol structure preferably has, for example, 8 to 16 carbon atoms, more preferably 10 to 14 carbon atoms per molecule.
The diester compound (1) having a carbonic acid diester structure preferably has, for example, 7 to 10 carbon atoms, more preferably 7 to 9 carbon atoms in one molecule.

The diester compound (1) includes an ester of a dicarboxylic acid having two carboxyl groups and a monohydric alcohol having one or more ether bonds, a monocarboxylic acid having one or more ether bonds and two hydroxyl groups. and a compound obtained by adding a monohydric alcohol having one or more ether bonds to a diester carbonate.
Each of the dicarboxylic acid and the diol preferably has a saturated hydrocarbon group, and more preferably has a linear or branched alkyl group.

Examples of dicarboxylic acids include oxalic acid, malonic acid, methylmalonic acid, ethylmalonic acid, succinic acid, methylsuccinic acid, glutaric acid, 2-methylglutaric acid, 3-methylglutaric acid, adipic acid, fumaric acid, and maleic acid. , glutaconic acid, itaconic acid, citraconic acid, mesaconic acid, dicarboxylic acids such as muconic acid, and anhydrides thereof.

Examples of diols include ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol and 2,3-butanediol. etc.

Carbonic acid diesters include, for example, dimethyl carbonate, diethyl carbonate, ethylmethyl carbonate, dibutyl carbonate, diphenyl carbonate, dibenzyl carbonate and the like.
From the viewpoint of reactivity, the diester carbonate preferably has a linear or branched alkyl group. Among them, dimethyl carbonate is preferred.

As the monohydric alcohol having one or more ether bonds, for example, glycol monoalkyl ether can be used.
Glycol monoalkyl ethers having an added mole number of 1 include, for example, 2-methoxyethanol, 2-ethoxyethanol; ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monoisopropyl ether, ethylene glycol monobutyl ether, ethylene glycol mono-tert-butyl ether, ethylene glycol monoisobutyl ether; 1-methoxy-2-propanol, 1-ethoxy-2-propanol, 1-propoxy-2-propanol, 1-butoxy-2-propanol, 1-(tert-butoxy)-2-propanol, 1-isobutoxy-2-propanol, 1-methoxy-2-methyl-2-propanol; 1-methoxy-2-butanol, 2-methoxy-1-butanol, 3- methoxy-1-butanol, 3-methoxy-3-methylbutanol, 4-methoxy-1-butanol; 4-methoxy-2-methylpentanol and the like.

Examples of the glycol monoalkyl ether having an added mole number of 2 include diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether; dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether and the like.

Examples of the glycol monoalkyl ether having an added mole number of 3 include triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol monoisopropyl ether, triethylene glycol monobutyl ether, tripropylene glycol monomethyl ether, and the like. be done.

Monocarboxylic acids having one or more ether bonds include, for example, 3-methoxypropionic acid, 3-ethoxypropionic acid, 4-methoxybutanoic acid, methoxyacetic acid, 2-(2-methoxyethoxy)acetic acid, (2- Alkoxycarboxylic acids such as (2-methoxyethoxy)ethoxy)acetic acid and the like can be mentioned.

Specific examples of the diester compound (1) include bis(2-methoxyethyl) succinate, bis(2-ethoxyethyl) succinate, bis(2-propoxyethyl) succinate, and bis(2-butoxyethyl) succinate. , bis(2-methoxy-1-methylethyl) succinate, bis(2-ethoxy-1-methylethyl) succinate, bis(3-methoxy-3-methylbutyl) succinate, bis(3-ethoxy- 3-methylbutyl), bis(2-(2-methoxyethoxy)ethyl) succinate, bis(2-(2-ethoxyethoxy)ethyl succinate and other succinic acid diesters; bis(2-methoxyethyl) malonate, malon bis(2-ethoxyethyl)malonate, bis(2-propoxyethyl)malonate, bis(2-butoxyethyl)malonate, bis(2-methoxy-1-methylethyl)malonate, bis(2-ethoxymalonate) -1-methylethyl), bis(3-methoxy-3-methylbutyl)malonate, bis(3-ethoxy-3-methylbutyl)malonate, bis(2-(2-methoxyethoxy)ethyl)malonate, malonic acid Malonic acid diesters such as bis(2-(2-methoxyethoxy)ethyl), bis(2-(2-ethoxyethoxy)ethyl) malonate; bis(2-methoxyethyl) oxalate, bis(2-ethoxy) oxalate ethyl), bis(2-propoxyethyl) oxalate, bis(2-butoxyethyl) oxalate, bis(2-methoxy-1-methylethyl) oxalate, bis(2-ethoxy-1-methylethyl) oxalate , bis(3-methoxy-3-methylbutyl) oxalate, bis(3-ethoxy-3-methylbutyl) oxalate, bis(2-(2-methoxyethoxy)ethyl) oxalate, bis(2-(2 -methoxyethoxy)ethyl), oxalic acid diesters such as bis(2-(2-ethoxyethoxy)ethyl) oxalate, and the like.

Also included are ethylene glycol esters such as ethylene glycol dimethoxyacetate and ethylene glycol di-3-methoxypropionate.
In addition, bis(2-methoxyethyl) carbonate, bis(2-ethoxyethyl) carbonate, bis(2-propoxyethyl) carbonate, bis(2-butoxyethyl) carbonate, bis(2-methoxy-1-methylethyl) carbonate , bis(2-ethoxy-1-methylethyl) carbonate, bis(3-methoxy-3-methylbutyl) carbonate, bis(3-ethoxy-3-methylbutyl) carbonate, bis(2-(2-methoxyethoxy)ethyl carbonate ), bis(2-(2-methoxyethoxy)ethyl)carbonate, and bis(2-(2-ethoxyethoxy)ethyl)carbonate.
You may use the above-described diester compound (1) individually or in combination of 2 or more types. For example, an ester of a dibasic acid, an ester of a diol, and a diester carbonate may be used singly or in combination of two or more, or in combination with each other.

The method for synthesizing the diester compound (1) is not particularly limited, and the diester compound (1) can be obtained by subjecting an acid component and an alcohol component to an esterification reaction according to a conventional method. In another method, the diester compound (1) can be obtained by adding an alcohol component to a carbonic acid diester having a short-chain alkyl group. An example of the method for synthesizing the diester compound (1) is described below. Note that the diester compound (1) is not limited to those synthesized by the following synthesis method.

An ester of a dicarboxylic acid and a monohydric alcohol can be obtained by reacting a dicarboxylic acid or an acid anhydride thereof with a monohydric alcohol having one or more ether bonds. As the dicarboxylic acid and monohydric alcohol, those mentioned above can be used.
An esterified product of a monocarboxylic acid and a diol can be obtained by reacting a monocarboxylic acid having one or more ether bonds with a diol. As the monocarboxylic acid and the diol, those mentioned above can be used.
In the esterification reaction, the reaction temperature can be adjusted within the range of 80 to 230°C depending on the types of acid component and alcohol component. The reaction time can be adjusted in the range of 1 to 48 hours depending on the types of acid component and alcohol component and the amount of raw materials used. It is preferable to remove water generated during the esterification reaction. The reaction can be carried out by introducing two components into a synthetic solvent such as cyclohexane.
Since the dicarboxylic acid and the monohydric alcohol react at a molar ratio of 1:2, it is preferable to introduce the raw materials into the synthesis system at such a molar ratio. Since the monocarboxylic acid and the diol react at a molar ratio of 2:1, it is preferable to introduce the raw materials into the synthesis system at such a molar ratio.
In the reaction, a suitable amount of a catalyst such as concentrated sulfuric acid, p-toluenesulfonic acid monohydrate, methanesulfonic acid and the like may be used.

An esterified product of a carbonic acid diester and a monohydric alcohol can be obtained by reacting a carbonic acid diester with a monohydric alcohol having one or more ether bonds. As the carbonate diester and the monohydric alcohol, those described above can be used.
The reaction temperature can be adjusted in the range of 80 to 230°C depending on the types of acid component and alcohol component. The reaction time can be adjusted in the range of 1 to 48 hours depending on the types of acid component and alcohol component and the amount of raw materials used. It is preferable to remove by-products such as methanol produced during the reaction.
Since the carbonic acid diester and the monohydric alcohol react at a molar ratio of 1:2, it is preferable to introduce the raw materials into the synthesis system at this molar ratio. When dimethyl carbonate is used as the carbonate diester, dimethyl carbonate is azeotropically removed together with the reaction product, methanol.
During the reaction, a suitable amount of a catalyst such as potassium carbonate may be used.

The diester compound (1) is preferably liquid at 23°C.
The boiling point of the diester compound (1) is preferably 150° C. or higher, more preferably 200° C. or higher, and even more preferably 260° C. or higher.

The diester compound (1) preferably exceeds 40% by mass, more preferably 60% by mass or more, and even more preferably 80% by mass or more, relative to the total amount of the non-aqueous solvent. As a result, the property that the diester compound (1) is difficult to permeate into the surface of the resin product is exhibited, and deformation of the clear file can be further prevented. In addition, the entire ink exhibits high surface tension, suppressing the generation of satellites from the ink droplets ejected from the nozzles, thereby further preventing contamination of the printing surface.
The diester compound (1) is preferably 100% by mass or less than 100% by mass, and may be 90% by mass or less, or may be 80% by mass or less, relative to the total amount of the non-aqueous solvent. By using the diester compound (1) as a single component of the non-aqueous solvent, deterioration or deformation of the resin product can be further prevented, and contamination of the printing surface can be further prevented. It should be noted that it can be used in appropriate combination with other non-aqueous solvents depending on the application of the ink.
For example, the diester compound (1) is preferably more than 40% by mass and 100% by mass or less, more preferably 60% by mass or more, still more preferably 80% by mass or more, with respect to the total amount of the non-aqueous solvent, 80% by mass or more and 90% by mass It may be below.

The diester compound (1) is preferably 30% by mass or more than 30% by mass, more preferably 50% by mass or more, and even more preferably 60% by mass or more, relative to the total amount of the ink.
The diester compound (1) is preferably 95% by mass or less than 95% by mass, may be 90% by mass or less, or may be 85% by mass or less, relative to the total amount of the ink.

The oil-based inkjet ink may contain other non-aqueous solvents in addition to the fatty acid ester solvent (A) and the fatty acid ester solvent (B).
As other non-aqueous solvents, both non-polar organic solvents and polar organic solvents can be used. In one embodiment, the non-aqueous solvent is preferably a non-water-soluble organic solvent that does not uniformly mix with the same volume of water at 1 atmospheric pressure and 20°C.
Other non-aqueous solvents include, for example, nonpolar organic solvents such as petroleum hydrocarbon solvents such as aliphatic hydrocarbon solvents, alicyclic hydrocarbon solvents, and aromatic hydrocarbon solvents; higher alcohol solvents, higher fatty acid solvents; A polar organic solvent such as a solvent and the like are included. Further, the oil-based ink may contain other fatty acid ester solvents other than the diester compound (1).

Examples of aliphatic hydrocarbon solvents and alicyclic hydrocarbon solvents include non-aqueous solvents such as paraffinic solvents, isoparaffinic solvents, and naphthenic solvents. 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, Isosol 300, Isosol 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, Naphthesol 160, Naphthesol 200, Naphthesol 220 (both manufactured by JXTG Nippon Oil & Energy Corporation); Isopar G, Isopar H, Isopar L, Isopar M, Exol D40, Exol D60, Exol D80, Exol D95, Exol D110, Exol D130 (all ExxonMobil) ) etc. can be mentioned preferably.
Preferred aromatic hydrocarbon solvents include Grade Alkene L, Grade Alkene 200P (all manufactured by JXTG Nippon Oil & Energy Corporation), Solvesso 100, Solvesso 150, Solvesso 200, and Solvesso 200ND (all manufactured by ExxonMobil). can.
The initial boiling point of the petroleum-based hydrocarbon solvent is preferably 100°C or higher, more preferably 150°C or higher, still more preferably 200°C or higher, and even more preferably 260°C or higher. The distillation initial boiling point can be measured according to JIS K0066 "Distillation test method for chemical products".

Preferred examples of polar organic solvents include higher alcohol solvents, higher fatty acid solvents, and other fatty acid ester solvents.
Higher alcohol-based solvents include, for example, isomyristyl alcohol, isopalmityl alcohol, isostearyl alcohol, oleyl alcohol, isoeicosyl alcohol, decyltetradecanol, 1-octadecanol, and the like, which have 6 carbon atoms per molecule. Above, preferably 12 to 20 higher alcohol solvents and the like.
Higher fatty acid-based solvents include, for example, lauric acid, isomyristic acid, palmitic acid, isopalmitic acid, α-linolenic acid, linoleic acid, oleic acid, isostearic acid, etc., each having 12 or more carbon atoms per molecule, preferably 14 to 20 higher fatty acid solvents and the like.
Other fatty acid ester solvents include, for example, isononyl isononanoate, isodecyl isononanoate, 2-ethylhexyl isononanoate, methyl laurate, isopropyl laurate, hexyl laurate, isopropyl palmitate, methyl oleate, ethyl oleate, olein 13 carbon atoms per molecule such as isopropyl acid, butyl oleate, methyl linoleate, ethyl linoleate, isobutyl linoleate, butyl stearate, isopropyl isostearate, 2-octyldecyl neopentanoate, 2-octyldodecyl neopentanoate, etc. Above, preferably 16 to 30 fatty acid ester solvents and the like are mentioned.
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 further preferably 260° C. or higher. Preferably, 360° C. or higher is more preferable.

When the other non-aqueous solvent described above is used in combination with the diester compound (1), it is preferable to use a polar solvent as the other non-aqueous solvent, and it is preferable to use another fatty acid ester solvent. By combining solvents with similar polarities, the compatibility of the solvents is improved, and the storage stability of the ink can be better maintained.
When a polar solvent containing other fatty acid ester solvent is blended, the polar solvent may be less than 60% by mass, may be 40% by mass or less, and preferably 20% by mass or less with respect to the total amount of non-aqueous solvent. .
Although not particularly limited, when a non-polar solvent containing a petroleum hydrocarbon solvent is blended, the non-polar solvent may be 30% by mass or less with respect to the total amount of the non-aqueous solvent, and 20% by mass or less. 10% by mass or less is preferable, and 5% by mass or less is more preferable. A decrease in the storage stability of the ink can be further prevented by reducing the ratio of the solvents with different polarities.

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

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

A pigment dispersant can be used together with the pigment to stably disperse the pigment in the ink.
Examples of pigment dispersants include hydroxyl-containing carboxylic acid esters, salts of long-chain polyaminoamides and high-molecular-weight acid esters, salts of high-molecular-weight polycarboxylic acids, salts of long-chain polyaminoamides and polar acid esters, and high-molecular-weight unsaturated acids. Esters, copolymers of vinylpyrrolidone and long-chain alkenes, modified polyurethanes, modified polyacrylates, polyether ester type anionic surfactants, polyoxyethylene alkyl phosphate esters, polyester polyamines and the like are preferably used.

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

The amount of the pigment dispersant is sufficient as long as it can sufficiently disperse the pigment in the ink, and the amount can be set as appropriate. For example, the weight ratio of the pigment dispersant to 1 part of the pigment can be 0.1 to 5, preferably 0.3 to 1. Also, the pigment dispersant can be blended in an amount of 0.01 to 10% by mass, preferably 0.1 to 8% by mass, more preferably 1 to 8% by mass, based on the total amount of the ink.

Any dyes commonly used in the art can be used as the dye. Oil-based inks preferably use oil-soluble dyes because the dyes have an affinity for the non-aqueous solvent of the ink, thereby improving the storage stability.
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, and phthalocyanine dyes. Dyes, metal phthalocyanine dyes and the like can be mentioned. You may use these individually or in combination of multiple types.
The amount of the dye is usually 0.01 to 20% by mass, preferably 1 to 15% by mass, more preferably 5 to 10% by mass, based on the total amount of the ink, from the viewpoint of printing density and ink viscosity. .

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 inhibitors, antioxidants, conductivity modifiers, viscosity modifiers, surface tension modifiers, oxygen absorbers, and the like can be added as appropriate. In addition to the pigment, a dye may be further added from the viewpoint of color development. These types are not particularly limited, and those used in the relevant field can be used.

The method for producing the oil-based ink is not particularly limited, but one method is to mix and stir each component all at once or separately to produce the ink. Specifically, it can be produced by putting all the components together or separately into a dispersing machine such as a bead mill, dispersing them, and passing them through a filtering machine such as a membrane filter if desired.

The viscosity of the oil-based inkjet ink varies depending on the nozzle diameter of the ejection head of the inkjet recording system, the ejection environment, and the like. and more preferably 8 to 13 mPa·s. In the present disclosure, ink viscosity is a numerical value measured at 23° C. using a rotational viscometer. As a viscosity measuring device, for example, "Rheometer MCR302" manufactured by Anton Paar Japan Co., Ltd. can be used.

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

In one embodiment, the base material is not particularly limited, and printing paper such as plain paper, coated paper, and special paper, cloth, inorganic sheet, film, OHP sheet, etc. may be used as the base material, and an adhesive layer may be formed on the back surface thereof. can be used. Among these, permeable substrates are preferable from the viewpoint of ink permeability, and printing paper such as plain paper and coated paper can be preferably used.

Here, plain paper is ordinary paper on which an ink-receiving layer, a film layer, or the like is not formed. Examples of plain paper include high-quality paper, medium-quality paper, PPC paper, rough paper, recycled paper, and the like. Plain paper has paper fibers with a thickness of several μm to several tens of μm forming voids of several tens to several hundreds of μm, so that the ink easily permeates the paper.

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

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

"Synthesis of diesters"
Table 1 shows the raw material acid component and the raw material alcohol component of the diester as the diester compound and the molecular structure. Table 2 shows details when the diester is represented by formula (1-1) or formula (1-3). Diesters were synthesized according to the following procedure.
(Synthesis of diesters 1-7)
A dicarboxylic acid and an alcohol as raw materials, cyclohexane as a solvent, and p-toluenesulfonic acid monohydrate as a catalyst were placed in a four-necked flask and mixed and stirred to obtain a uniform solution. A Dean-Stark device was attached to the four-necked flask so that if the charged raw materials reacted and water was generated, it could be removed. A four-necked flask containing a homogeneous solution was heated to initiate synthesis. The heating temperature was set to 110° C. at which the solvent was refluxed. The heating reaction time was set to 1 to 48 hours. After the reaction, in order to remove unreacted raw materials and impurities, the obtained solution was distilled under reduced pressure or column-purified to obtain a diester.
Dicarboxylic acid and alcohol were mixed in a molar ratio of 1:2.

(Synthesis of diesters 8-10)
Dimethyl carbonate and alcohol as raw materials were placed in a four-necked flask and mixed with stirring to obtain a uniform solution. A four-necked flask was equipped with a Dean-Stark apparatus so that if the charged raw materials reacted to generate methanol, it could be removed. An appropriate amount of potassium carbonate was added as a catalyst to the four-necked flask containing the uniform solution, and the entire system was heated. The heating temperature was set at 110°C. The heating reaction time was set to 24 hours. During the reaction, methanol and the raw material dimethyl carbonate were azeotropically removed, so the reaction was carried out by adding dimethyl carbonate as appropriate. After the reaction, the resulting solution was distilled under reduced pressure to remove unreacted raw materials and impurities to obtain a carbonate ester.

"Creating Ink"
Ink formulations are shown in Tables 3 and 4. Pigment, pigment dispersant, and solvent are mixed according to the blending amounts shown in the table, and the pigment is sufficiently removed by a bead mill "Dyno Mill KDL-A" (manufactured by Shinmaru Enterprises Co., Ltd.) under conditions of a residence time of 15 minutes. Dispersed. Subsequently, coarse particles were removed with a membrane filter to obtain an ink. "-" in the table indicates no addition.

The components used are as follows.
(pigment)
Carbon black: "MOGUL L" (trade name) manufactured by Cabot Specialty Chemicals, Inc.;
Copper phthalocyanine: "Heliogen Blue D7115F" (trade name) manufactured by BASF.
(dispersant)
Solsperse 33000: "Solsperse 33000" (trade name) manufactured by Nippon Lubrizol Co., Ltd., active ingredient 100% by mass.

(solvent)
Diesters 1-10 were obtained by the synthetic methods described above. Diester 11 is dibutyl succinate and is available from Tokyo Chemical Industry Co., Ltd.
Aliphatic monoester solvent: 2-ethylhexyl isononanoate, manufactured by KOKYU ALCOHOL KOGYO CO., LTD.
Petroleum-based hydrocarbon solvent: "Isopar M" (trade name) manufactured by ExxonMobil.

"evaluation"
The above inks were evaluated by the following methods. These evaluation results are also shown in each table.
(Prevention of printing surface contamination)
The obtained ink is loaded into a line-type inkjet printer "Orphis GD9630" (manufactured by Riso Kagaku Corporation), and the main droplets are arranged in one line on plain paper "Riso Paper Multi" (manufactured by Riso Kagaku Corporation). I printed it out. The contamination of the stamp surface due to satellites on the obtained image was visually observed and evaluated according to the following criteria.
S: Almost no contamination on the printing surface is observed, and the image quality is good.
A: Stain on the printed surface is observed, but the image quality is at a level that can withstand actual use.
B: Smearing on the printed surface is conspicuous, and the image quality is at a level that cannot withstand actual use.

(Prevention of rippling of clear files)
For the evaluation of waviness of the clear file, one printed matter was sandwiched between PP (polypropylene) clear files, left at room temperature, left for one week, and then the amount of deformation of the clear file was measured and evaluated according to the following criteria. The thickness of one sheet of clear file was 0.2 mm. Deformation of the clear file is observed by laying the clear file with the printed material on a flat surface so that the upper one of the clear files is bent outward. The amount of deformation of the clear file is the distance from the plane to the maximum height when the upper clear file is warped outward.
The printed material is a line-type inkjet printer "Orphis GD9630" (manufactured by Riso Kagaku Corporation) loaded with ink, and printed on plain paper "Riso Paper Multi" (manufactured by Riso Kagaku Corporation) with a length of about 51 mm in the main scanning direction (nozzle 600 This was produced by printing a solid image of 260 mm in the sub-scanning direction on one side.
SS: The clear file does not transform.
S: The amount of deformation of the clear file is less than 1 cm.
A: The amount of deformation of the clear file is 1 cm or more and less than 3 cm.
B: The amount of deformation of the clear file is 3 cm or more and less than 10 cm.
C: The amount of deformation of the clear file is 10 cm or more.

As shown in the table, the ink of each example was able to prevent deformation of the clear file. In addition, the ink of each example was able to prevent contamination of the printing surface. In addition, although not shown in the table, the ink of each example had a viscosity suitable for inkjet printing, had good ejection performance, and had good image quality of the printed matter including print density.

Through Examples 1 to 5, it was found that the more the diester compound (1) was added, the more the clear file was prevented from deforming. It can be seen that contamination of the printing surface is further prevented.
Through Examples 1 and 6, it can be seen that deformation of the clear file tends to be prevented when the terminal group of the diester compound (1) is a methoxy group rather than a butoxy group.
Through Examples 1, 7 and 8, it can be seen that deformation of the clear file tends to be prevented when the alkylene groups of the R ² and R ⁴ moieties of the diester compound (1) are linear rather than branched.
In Examples 9 to 11, the structure of the dicarboxylic acid moiety is different, but in each case the terminal group of the diester compound (1) is a methoxy group, and the alkylene groups of the R ² and R ⁴ moieties are linear, so that the good results were obtained.

Examples 12 to 14 are examples using the diester compound (1) having a diester carbonate structure.
Throughout Examples ^12-14 , ^more Good results were obtained. Since the terminal group of the diester compound (1) is a methoxy group, the diester compound (1) exhibits higher polarity, which is thought to help prevent deformation of the clear file.

Comparative Example 1 is an example using a fatty acid monoester-based solvent, and deformation of the clear file occurred.
Comparative Example 2 is an example using a petroleum-based hydrocarbon solvent, and deformation of the clear file occurred.
Comparative Example 3 is an example in which diester 11, which is a succinic acid diester but does not have an ether bond, was used, and deformation of the clear file occurred. Since this diester 11 exhibits low polarity, it is considered that deformation of the clear file occurred.
In Comparative Example 4, the compounding amount of Diester 1 was 30.0% by mass, which was the same as in Example 1, and therefore the effect of preventing deformation of the clear file was not sufficiently obtained.

Claims (3)

An oil-based inkjet ink comprising a coloring material and a non-aqueous solvent, wherein the non-aqueous solvent contains more than 40% by mass of a compound represented by the following general formula (1) relative to the total amount of the non-aqueous solvent.
R ¹ —(OR ² ) _m —R ³ —(R ⁴ —O) _n —R ⁵ (1)
(In general formula (1), R ¹ and R ⁵ are each independently an alkyl group having 1 to 4 carbon atoms, R ² and R ⁴ are each independently an alkylene group having 1 to 6 carbon atoms, R ³ is -O-C(=O)-R ^3a -(C=O)-O-, -C(=O)-O-R ^3a -O-(C=O)-, or -O-( C=O)—O—, R ^3a is a single bond or a diester group that is a divalent hydrocarbon group having 1 to 4 carbon atoms, and m and n are each independently an integer of 1 to 3; be.) The oil-based inkjet ink according to claim 1, wherein ^R1 and R5 in the general formula ( ¹ ) are methyl groups. 3. The oil-based inkjet ink according to claim 1, wherein m and n are 2 in the general formula (1).