JP7285666B2 - Oil-based inkjet ink and base for oil-based inkjet ink - Google Patents

Description

TECHNICAL FIELD The present invention relates to an oil-based inkjet ink and a base for an oil-based inkjet ink.

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 are deformed. One of the reasons for this is that when the clear file comes into contact with the printed surface, one side of the clear file deteriorates and swells due to the ink component.
In Patent Document 1 (Japanese Unexamined Patent Publication No. 2007-154149), a non-aqueous ink composition for inkjet that has high ejection stability without significantly deforming a transparent file contains a pigment, a dispersant, and a non-aqueous solvent. , proposed an ink in which 50% or more of the total weight of the non-aqueous solvent is an ester solvent having 24 to 36 carbon atoms.

In Patent Document 2 (Japanese Patent Application Laid-Open No. 2018-172657), in order to prevent deterioration and deformation of resin products such as clear files and to improve ejection properties of ink from inkjet nozzles, one molecule of oil-based inkjet ink is added. It has been proposed to use a fatty acid ester-based solvent having 12 to 23 carbon atoms and a branched alkyl group having a side chain of 4 or more carbon atoms bonded to an ester bond.

JP 2007-154149 A JP 2018-172657 A

High carbon number ester compounds tend to have relatively high viscosity. An ink using a high-viscosity ester compound has a problem in that sufficient ejection performance from an inkjet nozzle cannot be obtained. In Patent Document 1, since an ester-based solvent having a high carbon number is used, the ink is heated to lower its viscosity before being ejected.
Moreover, even if the ester compound has a high carbon number, if the carbon chain that binds to the ester bond is straight, there is a tendency that the effect of preventing deformation of the clear file cannot be sufficiently obtained. The same tendency is also observed when the carbon chain bonded to the ester bond has a side chain with 1 carbon atom.

In Patent Document 2, the branched structure of a fatty acid ester solvent is studied, and when the fatty acid ester solvent has a branched alkyl group having a side chain with 4 or more carbon atoms, the side chain portion becomes a steric hindrance, resulting in a clear file. You are trying to prevent the solvent from entering the surface.
Further, from the viewpoint of preventing deformation of resin products such as clear files and improving ejection performance from ink-jet nozzles, solvents for better blending with ink have been studied.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an oil-based inkjet ink that prevents resin products from being degraded by printed matter and that improves ejection performance from inkjet nozzles.

One embodiment of the present invention is an oil-based inkjet ink containing an ester compound represented by the following general formula (1) as a base for an oil-based inkjet ink.
R ¹ -CO-O-R ² general formula (1)
(In general formula (1), R ¹ is an aliphatic hydrocarbon group having 9 to 17 carbon atoms, R ² has a side chain having 2 or 3 carbon atoms, and It is an aliphatic hydrocarbon group.)
Another embodiment of the present invention is a base for the oil-based inkjet ink described above.

According to one embodiment of the present invention, it is possible to provide an oil-based inkjet ink that prevents resin products from being degraded by printed matter and improves ejection performance from inkjet nozzles.

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

An oil-based inkjet ink (hereinafter sometimes simply referred to as ink) according to one embodiment is characterized by containing an ester compound represented by the following general formula (1) as an oil-based inkjet ink base.
R ¹ -CO-O-R ² general formula (1)
(In general formula (1), R ¹ is an aliphatic hydrocarbon group having 9 to 17 carbon atoms, R ² has a side chain having 2 or 3 carbon atoms, and It is an aliphatic hydrocarbon group.)

By using this oil-based inkjet ink, it is possible to prevent resin products from being degraded by printed matters, and to improve ejection performance from inkjet nozzles.

In particular, according to the ink using the ester compound represented by the general formula (1) as a base material, deformation of the clear file can be prevented when the printed matter is sandwiched between clear files made of polypropylene (PP) or the like. . The clear file is a transparent to translucent resin sheet, or may be a colored opaque resin sheet.
When the inner surface of the clear file comes into contact with the printed matter, the ink component acts on the clear file, the inner surface of the clear file changes in volume, and the clear file may warp. It is considered that this becomes conspicuous when the ink component, particularly the solvent component, enters the micropores on the surface of the clear file and swells the clear file.

In addition, by using the ester compound represented by the general formula (1), the side chain portion becomes a steric hindrance, and this ester compound can be prevented from entering the micropores of the clear file surface. By using this ester compound, it is possible to prevent deformation of the clear file due to the printed material.
In this ester compound, the carbon chain R ² on the alcohol side has a branched structure having a side chain with 2 or 3 carbon atoms, so that the side chain part becomes a three-dimensional structure, and this ester Compounds can be prevented from entering.
In addition, since this ester compound has a side chain with 2 or 3 carbon atoms in the carbon chain ^R2 on the alcohol side, it has a relatively low viscosity and a high boiling point. In this case, it is possible to improve the ejection performance of the ink from the inkjet nozzle. In addition, since this ester compound has a relatively high boiling point, it can prevent volatilization of the ink from the inkjet nozzle and prevent deterioration of ejection performance over a long period of time.

A base for oil-based inkjet inks is a composition containing components that can be commonly used in multiple types of inks. An ink can be provided by adding a coloring material or the like to this base. For example, a multicolor ink can be provided by collectively preparing a base in advance and adding different coloring materials to each of a plurality of subdivided bases.
The base mainly contains a solvent. The base may contain components other than the solvent, but preferably contains a solvent as a main component, and more preferably consists of only the solvent, so that it can be applied to various inks and is suitable for long-term storage.

The oil-based inkjet ink preferably contains an ester compound represented by the following general formula (1) as a base for oil-based inkjet ink.
R ¹ -CO-O-R ² general formula (1)
In general formula (1), R ¹ is preferably an aliphatic hydrocarbon group having 9 to 17 carbon atoms.
R ¹ may be a saturated or unsaturated, linear or branched aliphatic hydrocarbon group, specifically a linear or branched alkyl group or a linear or branched unsaturated hydrocarbon group It is preferably a linear alkyl group or a linear unsaturated hydrocarbon group. When R ¹ is a branched alkyl group or a branched unsaturated hydrocarbon group, the number of carbon atoms in the side chain is preferably 3 or less, more preferably 2 or 3.

The number of carbon atoms in R ¹ is preferably 9 or more, more preferably 10 or more, even more preferably 11 or more. As a result, both ^R2 and ^R1 form a carbon chain of a certain length through an ester bond, so volatilization of the solvent can be suppressed.
The number of carbon atoms in R ¹ is preferably 17 or less, more preferably 15 or less, even more preferably 13 or less. As a result, since the carbon chain R ² on the alcohol side has a certain length, the carbon number of the carbon number R ¹ on the fatty acid side is within this range, thereby preventing the solvent from becoming highly viscous and the ink. , the ejection performance of the ink can be further improved.
For example, R ¹ preferably has 9 to 17 carbon atoms, more preferably 10 to 15 carbon atoms, and may be 11 to 13 carbon atoms.

Examples of alkyl groups represented by R ¹ include nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, isononyl and isoundecyl groups.
The unsaturated hydrocarbon group represented by R ¹ includes, for example, a monovalent unsaturated chain hydrocarbon group (alkenyl group) having one carbon-carbon double bond, two carbon-carbon double bonds, A divalent unsaturated chain hydrocarbon group having a bond, a trivalent unsaturated chain hydrocarbon group having three carbon-carbon double bonds, and the like. For example, it is a functional group derived from oleic acid, linoleic acid, linolenic acid, elaidic acid, myristoleic acid, palmitoleic acid, and the like.

In general formula (1), R ² preferably has a side chain with 2 or 3 carbon atoms and is an aliphatic hydrocarbon group with 9 to 18 carbon atoms.
R ² may be a saturated or unsaturated branched aliphatic hydrocarbon group, specifically a branched alkyl group or a branched unsaturated hydrocarbon group, preferably a branched alkyl group.
R ² preferably has a side chain with 2 or 3 carbon atoms, and specifically preferably has an ethyl group, a propyl group, or an isopropyl group as the side chain. This can prevent deterioration of the resin product.
R ² more preferably has a side chain with 3 carbon atoms, and more preferably the side chain is a propyl group. Thereby, the molecular structure of the ester compound becomes bulky, and deterioration of the resin product can be further prevented.

R ² may have one or more side chains having 2 or 3 carbon atoms. R ² may further have a methyl group having 1 carbon atom as a side chain. In addition, R ² may further have a side chain with 4 or more carbon atoms. On the other hand, R ² has a side chain with 2 or 3 carbon atoms, and the total number of carbon atoms is 9 to 18, so that the molecular structure can be sufficiently bulky and the viscosity can be low. Therefore, in R ² , all side chains preferably have 2 or 3 carbon atoms. Furthermore, R ² preferably has 1 side chain and 2 or 3 carbon atoms in the side chain.

The carbon number of R ² is preferably 9 or more, more preferably 10 or more. As a result, both R ¹ and R ² form a carbon chain of a certain length through an ester bond, so volatilization of the solvent can be suppressed.
The number of carbon atoms in R ² is preferably 18 or less, more preferably 16 or less, even more preferably 14 or less. As a result, it is possible to prevent the viscosity of the solvent from increasing due to the carbon number of ^R2 becoming high, and to further improve the ejection performance of the ink.
For example, R ² preferably has 9 to 18 carbon atoms, more preferably 10 to 16 carbon atoms, and may be 10 to 14 carbon atoms.

Branched alkyl groups represented by R ² include, for example, 2-propylhexyl group, 2-ethylheptyl group, 2-propylheptyl group, 2-ethyloctyl group, 2-propylnonyl group, 2-propylun Decyl group, 2-propyldodecyl group, 2-propyltridecyl group, 1-ethylheptyl group, 1-propylhexyl group, 1-propylheptyl group, 1-ethylnonyl group, 1-propyloctyl group, 1-ethyldecyl group , 1-ethylhexadecyl group, and the like.

In the ester compound represented by the general formula (1), the number of carbon atoms per molecule is preferably 19 or more, more preferably 20 or more. As a result, the number of carbon atoms in each of R ¹ and R ² is sufficiently secured, the molecular structure of the ester compound is increased, the solvent is prevented from entering the resin product surface, and the resin product is prevented from deteriorating. can be done. Moreover, within this range, the volatility of the ester compound is suppressed, and deterioration of the resin product due to volatile components can be further prevented. In addition, it is possible to suppress the volatilization of volatile components from the ink contained in the inkjet nozzles, thereby preventing deterioration in ejection performance over a long period of time.
In the ester compound represented by the general formula (1), the number of carbon atoms per molecule is preferably 36 or less, more preferably 30 or less, and more preferably 28 or less. When the number of carbon atoms is high, the viscosity may be high. Therefore, when the number of carbon atoms in the ester compound is within this range, the viscosity of the ink can be lowered and the ejection performance can be improved. From the viewpoint of ejection performance, the number of carbon atoms in the ester compound is preferably 23 or less, more preferably 22 or less.
For example, in the ester compound represented by general formula (1), the number of carbon atoms per molecule is preferably 19-36, more preferably 20-30, and may be 20-28.

Preferred specific examples of the ester compound represented by the general formula (1) include ester compounds of 2-propyl-1-heptanol and fatty acids such as decanoic acid, dodecanoic acid, tetradecanoic acid and oleic acid. can.
More specifically, 2-propylheptyl decanoate, 2-propylheptyl dodecanoate, 2-propylheptyl tetradecanoate, 2-propylheptyl oleate and the like can be preferably used.

In the oil-based inkjet ink, the base may be a single-component solvent containing one of the ester compounds represented by formula (1) above.
Further, the base may be a mixed solvent containing two or more solvents, and one or more of the two or more solvents is preferably an ester compound represented by general formula (1).
When the base is a mixed solvent containing two or more solvents, all of the solvents may be solvents selected from the ester compounds represented by the above general formula (1), or the above general It may be a combination of the ester compound represented by Formula (1) and another solvent.
Other solvents to be combined with the ester compound represented by formula (1) may be other ester compounds, petroleum hydrocarbon solvents, alcohol solvents, fatty acid solvents, etc., or combinations thereof.

Preferably, the base contains two or more ester compounds, and one or more of the two or more ester compounds is an ester compound represented by general formula (1).
When an ester compound other than the ester compound represented by the general formula (1) is used as the mixed solvent, the other ester compound may be a straight chain having straight carbon chains on both the alcohol side and the fatty acid side. It may be a chain fatty acid ester, or a branched fatty acid ester having a side chain on at least one of the carbon chains on the alcohol side and the fatty acid side.

More preferably, the base has 19 to 36 carbon atoms per molecule and contains two or more ester compounds having a side chain with 2 or 3 carbon atoms, At least one of the ester compounds having a side chain having 19 to 36 carbon atoms and 2 or 3 carbon atoms is an ester compound represented by general formula (1).
When two or more kinds of ester compounds are used, the viscosity of the mixed solvent tends to decrease because the molecular structures are similar because the side chains of the different ester compounds each have 2 or 3 carbon atoms. and can be more useful in improving the jetting performance of the ink.
In the case of using two or more ester compounds, the ester compound represented by the general formula (1) is an ester compound having 3 carbon atoms in the side chain of R ² in the ester compound represented by the general formula (1). It is preferable to include one or more, more preferably two or more.
Furthermore, when using two or more ester compounds, it is preferable that all the ester compounds are ester compounds represented by the general formula (1). It is preferable that the ester compound to be used has 3 carbon atoms in the side chain of R ² .

When two or more ester compounds are used, each of the two or more ester compounds preferably has 19 or more carbon atoms per molecule, more preferably 20 or more carbon atoms. As a result, the volatility of the ester compound can be suppressed to further suppress penetration into the surface of the resin product, and the ejection performance of the ink can be further improved.
When two or more kinds of ester compounds are used, each of the two or more kinds of ester compounds preferably has 36 or less carbon atoms per molecule, more preferably 30 or less carbon atoms, and still more preferably 28 or less carbon atoms. As a result, it is possible to suppress the increase in the viscosity of the ester compound and further improve the ejection performance of the ink.
For example, when two or more kinds of ester compounds are used, each of the two or more kinds of ester compounds preferably has 19 to 36 carbon atoms, more preferably 20 to 30 carbon atoms, and may have 20 to 28 carbon atoms per molecule.

Among other ester compounds, ester compounds having a side chain having 19 to 36 carbon atoms per molecule and 2 or 3 carbon atoms include, for example, 2-ethylhexyl dodecanoate and 2-ethylhexanoic acid. dodecyl, cetyl 2-ethylhexanoate, isocetyl 2-ethylhexanoate and the like.

Furthermore, as other ester compounds, for example, ester compounds having 19 to 36, preferably 20 to 34, more preferably 22 to 30 carbon atoms per molecule can be preferably used. Specifically, dodecane Octyl acid, hexyl palmitate, octyl palmitate, methyl oleate, ethyl oleate, butyl oleate, hexyl oleate, methyl linoleate, ethyl linoleate, butyl stearate, hexyl stearate, methyl soybean oil, methyl tall oil Linear fatty acid esters such as isodecyl isononanoate, isotridecyl isononanoate, isostearyl palmitate, isopropyl isostearate, isopropyl palmitate, isooctyl palmitate, isopropyl oleate, isobutyl linoleate, isooctyl stearate, soybean oil isobutyl, Examples include fatty acid esters having an alkyl group having one carbon atom in the side chain, such as tall oil isobutyl.

The ester compound represented by the general formula (1) may be contained in an amount of 10% by mass or more relative to the total amount of the base, although not particularly limited.
From the viewpoint of preventing deformation of the clear file, in order to eliminate the influence of other solvents, the ester compound represented by the general formula (1) is preferably 40% by mass or more, more preferably 40% by mass or more, based on the total amount of the base. is 50% by mass or more, more preferably 70% by mass or more, and may be, for example, 90% by mass or more, or even 100% by mass.

When the base contains other ester compounds, the amount of the other ester compounds is preferably 10% by mass or more, more preferably 20% by mass or more, relative to the total amount of the base. By containing other ester compounds within this range, the mixed solvent can be made to have a low viscosity. In particular, when using an ester compound having a side chain having 19 to 36 carbon atoms per molecule and 2 or 3 carbon atoms as the other ester compound, the ester compound represented by the general formula (1) can make the mixed solvent more viscous than when used alone.
Moreover, other ester compounds are preferably 60% by mass or less, more preferably 30% by mass or less, relative to the total amount of the base. Within this range, the mixing ratio with the ester compound represented by the general formula (1) is in a more preferable range, and it is possible to improve the deterioration prevention and ejection performance of the resin product in a well-balanced manner.

In the state of the ink in which a coloring material or the like is added to the base, the blending amount of the ester compound represented by the general formula (1) with respect to the total amount of the ink is 10 to 98% by mass, although it varies depending on the amount used of the entire base. may be contained in 20 to 90% by mass.
The ester compound represented by general formula (1) is preferably 20% by mass or more, more preferably 30% by mass or more, and even more preferably 50% by mass or more, relative to the total amount of the ink. This makes it possible to further prevent deterioration of the resin product.

When the base contains another ester compound, the amount of the other ester compound blended with respect to the total amount of the ink in the state of the ink in which a coloring material or the like is added to the base varies depending on the amount of the entire base used. It may be contained in an amount of 5 to 60% by mass, and may be contained in an amount of 10 to 30% by mass.

Although the ester compound represented by the general formula (1) is not limited thereto, it can be synthesized by the following method.
The ester compound represented by general formula (1) can be obtained by reacting an alcohol with a fatty acid. An alcohol having a carbon number of 9 or more and having a side chain of 2 or 3 carbon atoms in the raw material alcohol can be used. Moreover, a secondary alcohol having a hydroxy group at the 3-position and having 9 or more carbon atoms, a secondary alcohol having a hydroxy group at the 4-position and having 9 or more carbon atoms, or the like can be used.
The reaction temperature can be adjusted in the range of 80-230° C. depending on the type of fatty acid and alcohol. The reaction time can be adjusted in the range of 1 to 48 hours depending on the type of fatty acid and alcohol and the amount of raw materials used. It is preferable to remove water generated during the esterification reaction.
Fatty acid and alcohol are preferably reacted at a molar ratio of 1:1.
A suitable amount of catalyst may be used in the reaction. Examples of catalysts include acid catalysts such as concentrated sulfuric acid, p-toluenesulfonic acid and methanesulfonic acid; alkali catalysts such as sodium hydroxide and potassium hydroxide; and Lewis acid catalysts such as aluminum tetraisopropoxide and titanium tetraisopropoxide. etc.

Further, as a method of producing a base that is a mixed solvent containing two or more ester compounds, at least one of alcohol and fatty acid is two or more, a mixture of alcohol and fatty acid is prepared, and this mixture is converted into an ester. Two or more kinds of ester compounds can be obtained by the conversion.
In addition, by synthesizing an ester compound using one kind of alcohol and one kind of fatty acid, and mixing two or more kinds of ester compounds after the synthesis, the base is a mixed solvent containing two or more kinds of ester compounds. can also be produced.

Alcohols having a side chain of 2 or 3 carbon atoms as raw materials include, for example, 2-propyl-1-hexanol, 2-ethyl-1-heptanol, 2-propyl-1-heptanol, and 2-ethyl-1-octanol. , 2-propyl-1-nonanol, 2-propyl-1-undecanol, 2-propyl-1-dodecanol, 2-propyl-1-tridecanol and the like.

Examples of secondary alcohols as raw materials include 3-nonanol, 4-nonanol, 4-decanol, 3-undecanol, 4-undecanol, 3-dodecanol, and 3-octadecanol.

As the raw material fatty acid, it is preferable to use a linear saturated or unsaturated linear fatty acid. Isoundecanoic acid, oleic acid, linoleic acid, linolenic acid, myristoleic acid, palmitoleic acid, elaidic acid and the like can be mentioned.

The oil-based inkjet ink may contain, as a base, other non-aqueous solvents in addition to the ester compounds described above.
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.

Among other non-aqueous solvents, the distillation initial boiling point of non-polar organic solvents such as petroleum hydrocarbon solvents is preferably 100° C. or higher, more preferably 150° C. or higher, and 200° C. or higher. is more preferable. The distillation initial boiling point can be measured according to JIS K0066 "Distillation test method for chemical products".
Among other non-aqueous solvents, the boiling point of polar organic solvents such as higher alcohol solvents and higher fatty acid solvents is preferably 150° C. or higher, more preferably 200° C. or higher, and 250° C. or higher. is more preferred. Non-aqueous solvents having a boiling point of 250° C. or higher also include non-aqueous solvents having no boiling point.

When using the above-mentioned other non-aqueous solvents in combination with the ester compound represented by the general formula (1), use a high boiling point solvent as the other non-aqueous solvent in order to prevent deformation of the clear file. is preferred. As the high boiling point solvent, it is preferable to use a non-polar organic solvent having an initial distillation point of 200° C. or higher, a polar organic solvent having a boiling point of 250° C. or higher, or a combination thereof.

The oil-based inkjet ink according to one embodiment may contain the ester compound represented by the general formula (1) as a base, and may further contain a coloring material.

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.

The average particle size of the pigment is preferably 300 nm or less, more preferably 200 nm or less, still more preferably 150 nm or less, and still more preferably 100 nm or less, from the viewpoint of ejection stability and storage stability. .
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 phosphates, 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-Chemie Japan; "Hypermer KD2, KD3, KD11, KD12" (both trade names) manufactured by Croda Japan Co., Ltd.; .

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 0.1 to 1. Further, the pigment dispersant can be blended in an amount of 0.01 to 10% by mass, preferably 0.01 to 8% by mass, more preferably 0.1 to 6% 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 4 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. These types are not particularly limited, and those used in the relevant field can be used.

The ink can be produced by mixing each component including a coloring material and a base. Preferably, the ink can be produced by mixing and stirring each component all at once or separately. Specifically, it can be prepared by putting all the components into a dispersing machine such as a bead mill all at once or separately, dispersing them, and passing them through a filtering machine such as a membrane filter if desired.

The suitable range of 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.

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 recording medium.
Since the ink according to one embodiment is low in viscosity and suitable for ejection from an inkjet nozzle while preventing deformation of the clear file, it can be appropriately ejected at around room temperature (23° C.).

In one embodiment, the recording medium is not particularly limited, and printing paper such as plain paper, coated paper, special paper, etc., cloth, inorganic sheet, film, OHP sheet, etc., using these as a base material with an adhesive layer on the back can be used. Among these, from the viewpoint of ink permeability, 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. In the plain paper, paper fibers with a thickness of several μm to several tens of μm form 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.

"Preparation of ester compounds"
Ester compounds were prepared as bases 1 to 13 according to the following procedure. Details of the ester compounds of Bases 1 to 13 are shown in Table 1. In the base ester compound (R ¹ —CO—O—R ² ), the number of carbon atoms in R ¹ , the number of carbon atoms in R ² , and the number of carbon atoms in the side chain of R ² are shown in the table. The table also shows the mass ratio of the ester compounds for the base containing two types of ester compounds.
In the following description, components not specifically described can be obtained from Kao Corporation or Tokyo Chemical Industry Co., Ltd.

(Base 1: 2-propylheptyl decanoate)
700 g (4.07 mol) of decanoic acid and 770 g (4.87 mol) of 2-propyl-1-heptanol were placed in a 3 L four-necked flask equipped with a stirrer, Dean Stark trap, nitrogen inlet and flow meter. ), 5 g of p-toluenesulfonic acid, and 800 ml of toluene were charged and refluxed for 13 hours in a nitrogen atmosphere, whereupon 73 ml of water flowed out. After cooling to room temperature, the extract was washed with a saturated aqueous sodium hydrogencarbonate solution, further washed with water, washed with a saturated saline solution, and dried over anhydrous sodium sulfate. After filtration, toluene was distilled off with an evaporator, and after unreacted alcohol was distilled off, fractions at 180 to 210°C were collected by simple distillation under a reduced pressure of 40 Pa or less, and 1200 g of 2-propyl decanoate was obtained as a colorless transparent oil. I got heptyl. Yield was 95%. Purity was 99.6% by gas chromatographic analysis.

(Base 2: 2-propylheptyl dodecanoate)
2-Propylheptyl dodecanoate was obtained in the same manner as Base 1 except that dodecanoic acid was used instead of decanoic acid. The molar ratio of fatty acid and alcohol was set to be the same as in base 1 above.

(Base 3: 2-propylheptyl decanoate and 2-propylheptyl dodecanoate (1:1))
The 2-propylheptyl decanoate of the base 1 and the 2-propylheptyl dodecanoate of the base 2 were mixed at a mass ratio of 1:1 to obtain a base 3.

(Base 4: 2-propylheptyl decanoate and 2-propylheptyl dodecanoate (about 3:1))
191 g (1.115 mol) of decanoic acid, 68 g (0.34 mol) of dodecanoic acid and 2-propyl are placed in a 1 L four-necked flask equipped with a stirrer, Dean Stark trap, nitrogen inlet and flow meter. 275 g (1.74 mol) of -1-heptanol and 0.26 g of titanium tetraisopropoxide were charged, heated to 100° C. and dissolved. After that, the temperature was raised to 200° C. over 2 hours, and the reaction was continued for 2 hours until no more water flowed out. The amount of distilled water was 26 ml. Then, the reaction solution was cooled to 70° C., 10 ml of water was added, and the mixture was stirred for 30 minutes to precipitate a white solid. The temperature was raised to 170° C. again, and excess unreacted alcohol was distilled off under a reduced pressure of 1 kPa while blowing nitrogen and steam into the system. After no more alcohol was distilled off, the mixture was kept for 2 hours, and then cooled to 70°C. After adding 10 g each of adsorbent (Kyoward) and filter aid (Radiolite) and stirring for 30 minutes, the adsorbent and filter aid were removed by filtration through a membrane filter (opening 0.2 μm). A mixed fatty acid ester was obtained as a clear, colorless oil. Purity was 99.9% or more by gas chromatographic analysis.
The resulting mixed fatty acid ester contained 2-propylheptyl decanoate and 2-propylheptyl dodecanoate in a weight ratio of about 3:1 (shown as 3:1 weight ratio in the table).

(Base 5: 2-propylheptyl oleate)
2-Propylheptyl dodecanoate was obtained in the same manner as Base 1 except that oleic acid was used instead of decanoic acid. The molar ratio of fatty acid and alcohol was set to be the same as in base 1 above.
(Base 6: 2-propylheptyl decanoate and 2-ethylhexyl dodecanoate (3:1))
2-Propylheptyl decanoate (Base 1) and 2-ethylhexyl dodecanoate (Base 13) were mixed at a mass ratio of 3:1 to obtain Base 6.
(Base 7: 2-ethylhexyl dodecanoate and 2-propylheptyl oleate (6:4))
2-Ethylhexyl dodecanoate as Base 13 described below and 2-propylheptyl oleate as Base 5 were mixed at a mass ratio of 6:4 to obtain Base 7.
(Base 8: octyl dodecanoate and 2-propylheptyl oleate (6:4))
Octyl dodecanoate and 2-propylheptyl oleate of Base 5 were mixed at a mass ratio of 6:4 to obtain Base 7.
Octyl dodecanoate was obtained in the same manner as in Base 1 except that dodecanoic acid was used instead of decanoic acid and n-octanol was used instead of 2-propyl-1-heptanol. rice field.

(Base 9: isotridecyl isononanoate and 2-propylheptyl behenate (1:1))
80 g (0.25 mol) of behenic acid ("Lunac BA" manufactured by Kao Corporation), 2-propyl- 60 g (0.38 mol) of 1-heptanol, 2 g of p-toluenesulfonic acid and 500 ml of toluene were charged and refluxed for 6 hours under nitrogen atmosphere, and about 5 ml of water flowed out. After cooling to room temperature, it was washed with a saturated aqueous sodium hydrogencarbonate solution. Further, after washing with water and saturated saline, it was dried over anhydrous magnesium sulfate. After filtration, toluene and unreacted alcohol were distilled off to give 2-propylheptyl behenate as a viscous pale yellow clear oil. This was further heated to 50° C., diluted and mixed with the same mass of isotridecyl isononanoate while stirring to obtain a base 9 .
The same isotridecyl isononanoate used in base 10 was used.

(Base 10: isotridecyl isononanoate)
Isotridecyl isononanoate was obtained from KOKYU ALCOHOL KOGYO CO., LTD.
(Base 11: 2-ethylhexyl decanoate)
2-Ethylhexyl decanoate was obtained in the same manner as Base 1 except that 2-ethyl-1-hexanol was used instead of 2-propyl-1-heptanol. The molar ratio of fatty acid and alcohol was set to be the same as in base 1 above.
(Base 12: 2-propylheptyl nonanoate)
2-Propylheptyl nonanoate was obtained in the same manner as Base 1 except that nonanoic acid was used instead of decanoic acid. The molar ratio of fatty acid and alcohol was set to be the same as in base 1 above.
(Base 13: 2-ethylhexyl dodecanoate)
2-Ethylhexyl dodecanoate was prepared in the same manner as Base 1 except that dodecanoic acid was used instead of decanoic acid and 2-ethyl-1-hexanol was used instead of 2-propyl-1-heptanol. Obtained. The molar ratio of fatty acid and alcohol was set to be the same as in base 1 above.

"Creating Ink"
Ink formulations are shown in Tables 2 to 4. Regarding the base ester compound, each table shows the number of carbon atoms in R ¹ , the number of carbon atoms in R ² , and the number of carbon atoms in the side chain of R ² in R ¹ —CO—O—R ² . In addition, each table shows the mass ratio of the ester compounds for the base containing two kinds of ester compounds.
The pigment, pigment dispersant, and base are mixed according to the blending amounts shown in each table, and the pigment is sufficiently mixed with a bead mill "Dyno Mill KDL-A" (manufactured by Shinmaru Enterprises Co., Ltd.) under the conditions of a residence time of 15 minutes. distributed. Subsequently, coarse particles were removed with a membrane filter to obtain an ink.

The components used are as follows.
Carbon black "MA77": "MA77" manufactured by Mitsubishi Chemical Corporation.
Carbon black "NEROX500": "NEROX500" manufactured by Evonik Japan.
Solsperse 18000 (100% active ingredient): "Solsperse 18000" manufactured by Nippon Lubrizol Co., Ltd., 100% by mass of active ingredients.
Solsperse 13940 (40% active ingredient): "Solsperse 13940" manufactured by Nippon Lubrizol Co., Ltd., 40% by mass of active ingredients.

"evaluation"
The inks of the above Examples and Comparative Examples were evaluated by the following methods. These evaluation results are shown in Tables 2 to 4.

(Prevention of clear file deformation)
A line-type inkjet printer "ORPHIS FW5230" (manufactured by Riso Kagaku Corporation) was loaded with each ink described above, and a solid image was printed on plain paper "Riso Paper Multi" (manufactured by Riso Kagaku Corporation).
The "ORPHIS FW5230" is a system that uses a line-type inkjet head and conveys paper in the sub-scanning direction perpendicular to the main scanning direction (the direction in which the nozzles are arranged) for printing.
Ten sheets of the resulting printed material were sandwiched between clear files "FL-183HO 88-149" manufactured by Plus Co., Ltd. and left at room temperature for 3 days. After that, the deformation prevention of the clear file was evaluated according to the following criteria.
A: Slight deformation of the clear file was observed.
B: Deformation of the clear file was observed, but within an acceptable range.
C: Large deformation of the clear file was observed.

(Ejection performance)
Using each of the inks described above, printing was performed in the same manner as for preventing deformation of the clear file, and then the inkjet printer was left for one month with the ink loaded. After leaving for 1 month, printing was carried out in the same manner as for the prevention of deformation of the clear file, the first printed matter was observed, and the ejection performance was evaluated according to the following criteria based on the occurrence of white streaks.
A: One or less white streak.
B: Two to four white streaks.
C: Five or more white streaks.

As shown in the table, the ink of each example was able to prevent deformation of the clear file and had good ejection performance in inkjet printing.
Examples 1, 2 and 5 use bases 1, 2 and 5 containing only one type of ester compound. Bases 1, 2 and 5 each had a side chain of 3 carbon atoms on the carbon chain on the alcohol side, and good results were obtained. From Examples 1, 2 and 5, it can be seen that better results are obtained when the number of carbon atoms in the carbon chain on the fatty acid side is 11 or more. Further, it is found that the higher the number of carbon atoms in the carbon chain on the fatty acid side, the higher the viscosity of the ester compound, which tends to lower the ejection performance.

In Example 3, the base 3 obtained by combining the base 1 of Example 1 and the base 2 of Example 2 was used, and good results were obtained.
In Example 4, two types of fatty acid and alcohol were mixed and synthesized, and base 4, which had the same combination as base 3 in Example 3, was used, and good results were obtained as in Example 3. Got.

In Example 6, an ester compound having a side chain with 3 carbon atoms on the alcohol side of base 1 and an ester compound of base 13 having a side chain with 2 carbon atoms but a small number of carbon atoms in the carbon chain on the alcohol side. were combined with good results.
In Example 7, an ester compound having a side chain with 3 carbon atoms on the alcohol side of base 5 and an ester compound of base 13 having a side chain with 2 carbon atoms but a small number of carbon atoms in the carbon chain on the alcohol side. were combined with good results.
In Example 8, an ester compound having a side chain with 3 carbon atoms on the alcohol side of the base 5 and an ester compound having a straight carbon chain on both the alcohol side and the fatty acid side were combined, and good results were obtained. was taken.
Through each example, it can be seen that when two or more kinds of ester compounds are used, the ejection performance is improved by combining compounds having a side chain with 2 or 3 carbon atoms.
Examples 1 and 9 show that good results can be obtained regardless of the type of pigment and pigment dispersant.

Comparative Example 1 uses base 9 in which an ester compound having 3 carbon atoms in the side chain on the alcohol side and 21 carbon chains on the fatty acid side is combined with a comparative ester compound. No. 9 had a high viscosity and lowered ejection performance.
In Comparative Example 2, a comparative ester compound having a carbon number of 1 in the side chain of the carbon chain on the alcohol side was used, and deformation of the clear file occurred.
Comparative Examples 3 and 5 used a comparative ester compound in which the number of carbon atoms in the side chain in the carbon chain on the alcohol side was 2, but the total number of carbon atoms was small. . Furthermore, the comparative ester compound of Comparative Example 3 had a small number of carbon atoms in the carbon chain on the fatty acid side, and the discharge performance was lowered.
Comparative Example 4 used a comparative ester compound having a small number of carbon atoms in the carbon chain on the fatty acid side, which easily volatilized and caused deformation of the clear file.

Claims (7)

One molecule has 19 to 36 carbon atoms, and two or more kinds of ester compounds having a side chain with 2 or 3 carbon atoms are included as bases for oil-based inkjet inks, and one molecule of the two or more kinds has a carbon number of An oil-based inkjet ink , wherein at least one ester compound having a side chain having 19 to 36 carbon atoms and 2 or 3 carbon atoms is an ester compound represented by the following general formula (1).
R ¹ -CO-O-R ² general formula (1)
(In general formula (1),
R ¹ is an aliphatic hydrocarbon group having 9 to 17 carbon atoms,
R ² is an aliphatic hydrocarbon group having 9 to 18 carbon atoms having a side chain of 2 or 3 carbon atoms. ) An oil-based inkjet ink containing an ester compound represented by the following general formula (1) as a base for an oil-based inkjet ink.
R ¹ -CO-O-R ² general formula (1)
(In general formula (1),
R ¹ is an aliphatic hydrocarbon group having 9 to 17 carbon atoms,
R ² is an aliphatic hydrocarbon group with 9 to 18 carbon atoms having a side chain of 3 carbon atoms. ) One or more of the two or more ester compounds having a side chain having 19 to 36 carbon atoms per molecule and having 2 or 3 carbon atoms is the side chain of R ² in the general formula (1) The oil-based inkjet ink according to claim 1 , wherein is an ester compound having 3 carbon atoms. Two or more of the two or more ester compounds having a side chain having 19 to 36 carbon atoms per molecule and having 2 or 3 carbon atoms are the side chains of R ² in the general formula (1) The oil-based inkjet ink according to claim 1 , wherein is an ester compound having 3 carbon atoms. 5. The oil-based inkjet ink according to any one of claims 1 to 4 , comprising an ester compound in which R ² has 9 to 14 carbon atoms in the general formula (1). The oil-based inkjet ink according to any one of claims 1 to 5 , comprising 40% by mass or more of the ester compound represented by formula (1) with respect to the total amount of the base. A base for an oil-based inkjet ink according to any one of claims 1 to 6 .