JP2020019872A - Oily inkjet ink set and printing method - Google Patents

Abstract

To prevent degradation of a resin product due to a printed matter, and increase surface concentration of the printed matter and prevent occurrence of bleed-through.SOLUTION: An oily inkjet ink set has first ink containing a colorant and a nonaqueous solvent, where the nonaqueous solvent has a fatty acid ester having a side chain with 4 or more carbon atoms, and having 20 or more carbon atoms in one molecule, and second oily ink containing a colorant and a nonaqueous solvent and having a 20% distillation temperature of 300°C or less.SELECTED DRAWING: None

Description

  The present invention relates to an oil-based inkjet ink set and a printing method.

  The ink jet recording method is a method in which a highly fluid ink jet ink is ejected as droplets from a fine nozzle, and an image is recorded on a recording medium placed opposite to the nozzle, and high-speed printing with low noise is possible. Therefore, it has been spreading rapidly in recent years. Examples of the ink used in such an ink jet recording method include an aqueous ink containing water as a main solvent, an ultraviolet curable ink (UV ink) containing a polymerizable monomer as a main component at a high content, and a wax containing a wax as a main component. A so-called non-aqueous ink containing a non-aqueous solvent as a main solvent together with a hot melt ink (solid ink) contained in a content is known. Non-aqueous inks can be classified into solvent inks (solvent-based inks) whose main solvent is a volatile organic solvent and oil-based inks (oil-based inks) whose main solvent is a low-volatile or non-volatile organic solvent. The solvent ink dries mainly on the recording medium due to the evaporation of the organic solvent, whereas the oil ink dries mainly due to the penetration into the recording medium.

  In the case of oil-based ink, when the solvent permeates a recording medium such as paper, the solvent may penetrate to the back surface of the paper, and strikethrough may occur. The occurrence of strike-through becomes more problematic when the oil-based ink contains a large amount of low-volatile solvent, because the amount of solvent that penetrates to the back surface of the paper increases. Solvents with low volatility remain on the surface of the paper and cause oil bleeding.

  Patent Literature 1 (Japanese Patent Application Laid-Open No. 2004-002666) discloses that a solvent containing a nonpolar organic solvent having a 50% distillation point of 280 ° C or lower in an amount of 10% by weight or more and a 50% distillation point of 300 ° C or higher. It has been proposed that a non-aqueous ink composition containing 20% by weight or more of an organic solvent in a solvent can reduce strikethrough, oil bleeding, and nozzle clogging.

On the other hand, if the printed matter formed with the oil-based ink is sandwiched between clear files made of polypropylene (PP) or the like and stored, there is a problem that the clear files are deformed. One reason for this is that when the clear file contacts the printing surface, one side of the clear file swells due to the ink component.
Patent Document 2 (Japanese Patent Application Laid-Open No. 2007-154149) discloses a pigment, a dispersant, and a non-aqueous solvent as an inkjet non-aqueous ink composition having high ejection stability without swelling or significantly deforming a transparent file. And an ink in which 50% or more of the total weight of the nonaqueous solvent is an ester solvent having 24 to 36 carbon atoms.

JP-A-2004-002666 JP 2007-154149 A

  Patent Literature 1 proposes to control strike-through and oil bleeding by controlling the amount of a plurality of solvents having different 50% distillation points in one ink. If the amount of the highly volatile solvent is increased in order to prevent strike-through, the ink may not sufficiently penetrate the paper, and the surface density may decrease. In addition, highly volatile solvents also cause clear file deformation.

Patent Document 2 proposes preventing the deformation of the clear file by increasing the amount of the ester solvent having a high carbon number. Ester solvents having a high carbon number have relatively low volatility, penetrate into the paper after printing, and cause strikethrough.
Further, since the ester solvent having a high carbon number has a relatively high viscosity, there is a problem that the ink using the ester solvent cannot sufficiently discharge the ink from the inkjet nozzle. In Patent Literature 2, the ink is heated to reduce the viscosity to discharge the ink. Even in this case, after printing, the ester solvent having a high carbon number and low volatility stays on the paper and further penetrates into the paper.

  There is a method of increasing the surface density of an image by forming an image by using two or more kinds of inks in an overlapping manner. For example, there is a method in which a black ink and a color ink are superimposed and printed to form a composite black image. Even in such an ink set, the above-described deformation of the clear file, a decrease in the surface density, and the occurrence of strikethrough occur.

  An object of the present invention is to prevent deterioration of a resin product due to a printed matter, increase the surface density of the printed matter, and prevent strikethrough.

As one embodiment of the present invention, a coloring material and a non-aqueous solvent are included, and the non-aqueous solvent includes a fatty acid ester having a side chain having 4 or more carbon atoms and having 20 or more carbon atoms in one molecule. An oil-based inkjet ink set including a first ink, a second oil-based ink including a coloring material and a non-aqueous solvent, and having a 20% distillation temperature of 300 ° C. or lower.
According to another embodiment of the present invention, there is provided a method of printing using the oil-based inkjet ink set, wherein one of the first ink and the second ink is discharged onto a recording medium, This is a printing method in which the other ink is discharged while being superimposed on a print area of the one ink.

  ADVANTAGE OF THE INVENTION According to one Embodiment of this invention, while preventing the deterioration of the resin product by a printed matter, the surface density of a printed matter can be raised and strikethrough can be prevented.

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

The oil-based inkjet ink according to one embodiment (hereinafter, may be simply referred to as an ink) includes a pigment and a non-aqueous solvent, and the non-aqueous solvent has a side chain having 4 or more carbon atoms and is contained in one molecule. A first ink containing a fatty acid ester having 20 or more carbon atoms, and a second oil-based ink containing a pigment and a non-aqueous solvent and having a 20% distillation temperature of 300 ° C. or less. I do.
Hereinafter, a fatty acid ester having a side chain having 4 or more carbon atoms and having 20 or more carbon atoms in one molecule is also referred to as a fatty acid ester E.

According to this, the deterioration of the resin product due to the printed matter can be prevented, the surface density of the printed matter can be increased, and strike-through can be prevented.
In the ink set according to one embodiment, one of the first ink and the second ink is ejected onto the recording medium, and then the other ink is ejected onto the recording medium, whereby one ink and the other ink are ejected on the recording medium. When superimposed, the surface density of the printed matter can be increased, and strikethrough can be prevented.
Further, according to this ink, when the printed matter is sandwiched between clear files made of polypropylene (PP) or the like, deformation of the clear files can be prevented. The clear file is a transparent to translucent resin sheet, or may be a colored opaque resin sheet.

When sandwiching a printed material using a clear file, particularly a polypropylene (PP) clear file, the ink component of the printed material, particularly the non-aqueous solvent component, evaporates, and when the clear file comes into contact with the clear file, the inner surface of the clear file becomes large. The clear file may be deformed and swell or shrink on the outer surface of the clear file to deform the clear file.
This is likely to be a problem when the oil-based ink contains a large amount of volatile solvent because the volatile solvent comes into contact with the inner surface of the clear file.
Further, if the structure of the petroleum hydrocarbon solvent among the non-aqueous solvents used in the oil-based ink is similar to that of the polypropylene of the clear file, it easily occurs. As with petroleum hydrocarbon solvents, fatty acid ester solvents, higher fatty acid solvents, higher alcohol solvents, and the like may also cause deformation of the clear file if the structure is similar to polypropylene.

In the ink set according to the embodiment, the first ink includes a fatty acid ester E having a side chain having 4 or more carbon atoms and having 20 or more carbon atoms in one molecule, thereby preventing deformation of the clear file. can do.
Since the fatty acid ester E has a relatively high carbon number, it is a solvent having low volatility, can suppress volatilization from printed matter after printing, and can act to prevent deformation of the clear file. it can.
Further, since the fatty acid ester E has a side chain having 4 or more carbon atoms, the molecular structure becomes three-dimensional and bulky, so that a resin product having a linear structure such as polypropylene is prevented from being degraded. It can act to prevent deformation.

Since the fatty acid ester E has a three-dimensional molecular structure, its surface tension tends to be lower than that of a linear non-aqueous solvent. When the first ink containing the fatty acid ester E is ejected in the form of dots on a recording medium, the fatty acid ester E having a low surface tension spreads on the recording medium, so that the dot diameter increases, and the printed matter is printed. It is observed that the table density increases.
In addition, since the fatty acid ester E has a relatively high molecular weight, it is a solvent having low volatility, and does not volatilize from the surface of the printed matter after printing, but remains on the surface. If the low-volatile solvent stays on the surface of the print, it is observed that the surface density of the print becomes higher due to the phenomenon of see-through.

In order to prevent the deformation of the clear file and increase the surface density of the printed matter, when the printed matter is produced using only the first ink containing the fatty acid ester E, the solvent component volatilized from the surface of the printed matter after the printing is reduced. In some cases, the phenomenon of see-through becomes excessive, and strikethrough of printed matter may become a problem.
On the other hand, by using the second ink having a 20% distillation temperature of 300 ° C. or lower, the non-aqueous solvent is easily volatilized from the printed matter after printing, and the first ink and the second ink are ejected after the ejection. In addition, it is possible to suppress the phenomenon of see-through to some extent, and to prevent strike-through of printed matter.

The surface of paper or the like as a recording medium has fine fibrous irregularities, and the non-aqueous solvent penetrates and stays in these irregularities, suppressing light diffusion and observing a high surface density of printed matter. Become like This phenomenon is transparent. On the other hand, when the see-through phenomenon becomes excessive, it is observed that strikethrough of the printed matter is deteriorated.
From the viewpoint of see-through, the surface density and strikethrough of the printed matter have opposite effects, but by separately discharging the first ink and the second ink onto the recording medium, the surface density and strikethrough of the printed matter are obtained. Both effects can be exhibited in a well-balanced manner.

(Ink set)
The ink set includes a first ink and a second ink.
The first ink contains a colorant and a non-aqueous solvent, and the non-aqueous solvent preferably contains a fatty acid ester having a side chain having 4 or more carbon atoms and having 20 or more carbon atoms in one molecule.
The second ink preferably contains a coloring material and a non-aqueous solvent, and preferably has a 20% distillation temperature of 300 ° C. or lower.
Further, as a printing method according to one embodiment, there is provided a method of printing using the above-described oil-based inkjet ink set, wherein one of the first ink and the second ink is ejected to a recording medium, and then the other is ejected. A printing method can be provided in which the above-mentioned ink is ejected while being superimposed on the printing area of one of the inks.

  The 20% distilling temperature of the ink is calculated by using a thermal analysis (TG) apparatus, where the mass reduction rate of the entire ink when the temperature of the ink is increased from 23 ° C. to 500 ° C. at 15 ° C./min is 100%. Is the temperature when the mass of the entire ink is reduced by 20%.

It is preferable that the first ink and the second ink are printed so as to overlap each other on the recording medium. Since the first ink and the second ink overlap on the recording medium, the solvents of the respective inks act on the recording medium to further prevent the deformation of the clear file, and further reduce the surface density and strikethrough. Can be improved. It is preferable that the printing is performed so that the other ink overlaps a part or the entirety of one of the printing areas of the first ink and the second ink.
The ejection order of the first ink and the second ink is not particularly limited, and the second ink may be ejected after the first ink, or vice versa.

The first ink and the second ink may be each independently a black ink or a color ink.
Preferably, at least one of the first ink and the second ink is a black ink. Further, it is preferable that one of the first ink and the second ink is a black ink, and the other is a color ink. Further, it is preferable that the first ink is a black ink and the second ink is a color ink.
Examples of the color ink include a yellow ink, a magenta ink, and a cyan ink. When a black ink and a color ink are used in combination, the surface density of black can be further increased, and therefore, the color ink is preferably a cyan ink.

  The ejection amounts of the first ink and the second ink are each independently preferably 2 to 50 pl, more preferably 5 to 40 pl. The ejection amount of the first ink is preferably larger than the ejection amount of the second ink. In particular, when the first ink is a black ink and the second ink is a color ink, the ejection amount of the first ink is preferably larger than the ejection amount of the second ink.

  For example, in order to print the first ink and the second ink in a superimposed manner to further increase the surface density of the composite black, the first ink is a black ink and the second ink is a color ink. Is preferred. In this case, since the ejection amount of the first ink, which is the black ink, is increased, the action of the fatty acid ester E of the first ink can prevent the clear file from being deformed and further increase the surface density of the printed matter. . Then, with the second ink, which is a color ink, the phenomenon of see-through can be suppressed, and the occurrence of strikethrough of printed matter can be prevented in a well-balanced manner.

Using a printing apparatus, one of the first ink and the second ink is ejected onto a recording medium and then the other is ejected, whereby a printed matter can be produced.
The first ink and the second ink can be preferably used for a line type ink jet printer. A line-type inkjet printer is a system that includes a line-type inkjet head and performs printing by transporting a recording medium in a sub-scanning direction orthogonal to a main scanning direction in which nozzles are arranged. By arranging a plurality of line-type inkjet heads in the transport direction of the recording medium, loading one line-type inkjet head with the first ink and loading the other line-type inkjet head with the second ink. While the recording medium is conveyed once, the first ink and the second ink can be continuously discharged onto the recording medium to perform printing.

The ink set may include one or more first inks, and may include one or more second inks. When two or more inks are included in the first ink, they may be the same color or different colors. The same applies to the second ink.
Further, the ink set may include other inks in addition to the first ink and the second ink. For example, a composite black image can be formed using the first ink and the second ink, and a color image can be formed using other inks.

(First ink)
The first ink contains a coloring material and a non-aqueous solvent, and the non-aqueous solvent contains a fatty acid ester (fatty acid ester E) having a side chain having 4 or more carbon atoms and having 20 or more carbon atoms in one molecule. It is preferred to include.

The first ink can include a coloring material. As the coloring material, a pigment, a dye, or a combination thereof can be used.
As pigments, organic pigments such as azo pigments, phthalocyanine pigments, polycyclic pigments, dyed lake pigments and the like; and inorganic pigments such as carbon black and metal oxides can be used. Examples of the azo pigment include a soluble azo lake pigment, an insoluble azo pigment, and a condensed azo pigment. Examples of the phthalocyanine pigment include a metal phthalocyanine pigment such as a copper phthalocyanine pigment, and a metal-free phthalocyanine pigment. Polycyclic pigments include quinacridone pigments, perylene pigments, perinone pigments, isoindoline pigments, isoindolinone pigments, dioxazine pigments, thioindigo pigments, anthraquinone pigments, quinophthalone pigments, metal complex pigments And diketopyrrolopyrrole (DPP). Examples of the carbon black include furnace carbon black, lamp black, acetylene black, and channel black. Examples of the metal oxide 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, and still more preferably 150 nm or less, from the viewpoints of ejection stability and storage stability.
The pigment is usually 0.01 to 20% by mass based on the total amount of the ink, and preferably 1 to 15% by mass from the viewpoints of print density and ink viscosity.

In order to stably disperse the pigment in the ink, a pigment dispersant can be used together with the pigment.
Examples of the pigment dispersant include a hydroxyl group-containing carboxylic acid ester, a salt of a long-chain polyaminoamide and a high-molecular-weight acid ester, a salt of a high-molecular-weight polycarboxylic acid, a salt of a long-chain polyaminoamide and a polar acid ester, and a high-molecular-weight unsaturated acid. Esters, copolymers of vinylpyrrolidone and long-chain alkenes, modified polyurethanes, modified polyacrylates, polyetherester-type anionic activators, polyoxyethylene alkyl phosphates, polyesterpolyamines and the like are preferably used.

  Examples of commercially available pigment dispersants include, for example, "ANTALON V216 (vinylpyrrolidone-hexadecene copolymer), V220 (vinylpyrrolidone-eicosene copolymer)" (produced by IPS Japan). "Solsperse 13940 (polyesteramine-based), 16000, 17000, 18000 (fatty acid amine-based), 11200, 24000, 28000" manufactured by Japan Lubrizol Co., Ltd. (all trade names); "Efka 400" manufactured by BASF Japan Ltd. , 401, 402, 403, 450, 451, 453 (modified polyacrylate), 46, 47, 48, 49, 4010, 4055 (modified polyurethane) "(all of which are trade names);" DISPARON KS- "manufactured by Kusumoto Kasei Co., Ltd. 860, KS-873N4 (Polyes) Amine salts) ”(all trade names);“ Discol 202, 206, OA-202, OA-600 (multi-chain polymer nonionic) ”(all trade names) manufactured by Daiichi Kogyo Seiyaku Co., Ltd. ); "DISPERBYK-2155, BYK-9076, 9077" (all trade names) manufactured by BYK Japan KK; .

  The pigment dispersing agent is sufficient as long as the pigment can be sufficiently dispersed in the ink, and can be appropriately set. For example, the pigment dispersant can be blended in a mass ratio of 0.1 to 5 with respect to the pigment 1, and preferably 0.1 to 1. Further, the pigment dispersant can be blended at 0.01 to 15% by mass, and preferably 0.1 to 10% by mass, based on the total amount of the ink.

As the dye, those generally used in the technical field can be arbitrarily used. In oil-based inks, it is preferable to use oil-soluble dyes, because the dyes exhibit an affinity for the non-aqueous solvent of the ink, thereby improving the storage stability.
As the oil-soluble dyes, azo dyes, metal complex dyes, naphthol dyes, anthraquinone dyes, indigo dyes, carbonium dyes, quinone imine dyes, xanthene dyes, cyanine dyes, quinoline dyes, nitro dyes, nitroso dyes, benzoquinone dyes, naphthoquinone dyes, phthalocyanines Dyes and metal phthalocyanine dyes. These may be used alone or in combination of two or more.
The amount of the dye is usually 0.01 to 20% by mass based on the total amount of the ink, and preferably 1 to 15% by mass from the viewpoints of print density and ink viscosity.

  The non-aqueous solvent may include a fatty acid ester (fatty acid ester E) having a side chain having 4 or more carbon atoms and having 20 or more carbon atoms in one molecule.

One example of the fatty acid ester E includes a compound represented by the following general formula (1).
R ¹ —COO—R ² General formula (1)
In the general formula (1), R ¹ and R ² are each independently an alkyl group, and at least one of R ¹ and R ² is a branched alkyl group having a side chain having 4 or more carbon atoms. .
One of R ¹ and R ² may be a linear alkyl group, and the other of R ¹ and R ² may be a branched alkyl group. Further, both R ¹ and R ² may be a branched alkyl group.

Here, the main chain of R ¹ and R ² is a carbon chain having the largest number of carbon atoms counted from the carbon atoms bonded to the ester bond “—COO—”. The carbon chain branched from the main chain of R ¹ and R ² is defined as a side chain. When R ¹ and / or R ² has a side chain, each side chain may be linear or branched.
Further, in R ¹ and R ² , when there are a plurality of carbon chains having the largest number of carbon atoms counted from the carbon atoms bonded to the ester bond, the one having the largest number of carbon atoms in the side chain is defined as the main chain. .
Further, in R ¹ and R ² , there are a plurality of carbon chains having the largest number of carbon atoms counted from the carbon atoms bonded to the ester bond portions, and the carbon numbers of the side chains included in the plurality of carbon chains are the same. In this case, the main chain having the least number of side chains is used.

In the fatty acid ester E, the number of carbon atoms in one side chain is preferably 4 to 12, more preferably 4 to 10, and even more preferably 4 to 8.
One side chain may be a straight chain alkyl group or a branched alkyl group that is further branched and has a side chain. Since the fatty acid ester E becomes bulkier due to the long side chain carbon chain, the side chain bonded to the main chain of the fatty acid ester E is preferably a linear alkyl group.

The fatty acid ester E may have one or two or more side chains in one molecule.
When two or more side chains are contained in the fatty acid ester E, as long as at least one side chain has 4 or more carbon atoms, the remaining side chains may contain side chains having 3 or less carbon atoms. .
When the fatty acid ester E contains two or more side chains, the total number of carbon atoms in the side chains in one molecule is preferably 5 to 20, and more preferably 6 to 12.

In the fatty acid ester E, examples of the side chain having 4 or more carbon atoms include n-butyl, isobutyl, tert-butyl, pentyl, hexyl, heptyl, octyl, isooctyl, nonyl, and decyl groups. , Dodecyl group and the like.
Preferably, they are an n-butyl group, a hexyl group, and an octyl group.

In the general formula (1), when R ¹ has a side chain having 4 or more carbon atoms, the main chain of R ¹ preferably has 6 or more carbon atoms, and more preferably 7 or more carbon atoms.
In this case, the carbon number of the main chain of R ¹ is preferably 16 or less, more preferably 12 or less.
When R ¹ has a side chain having 4 or more carbon atoms, the total number of carbon atoms of R ¹ is preferably 9 to 30, more preferably 10 to 24, and still more preferably 10 to 20.
When R ² has a number 4 or more side chain carbon, carbon atoms in the main chain of R ^2, the total number of carbon atoms in R ² are the same as in the above R ^1.

When R ¹ is linear or has a side chain having 3 or less carbon atoms, the total carbon number of R ¹ is preferably 1 to 30, more preferably 6 to 20, and further preferably 8 to 18. preferable.
When R ² is linear or has a side chain having 3 or less carbon atoms, the total number of carbon atoms of R ^{2 is} the same as that of R ¹ described above.
The carbon number of the side chain and the carbon number of the main chain of R ¹ and R ² are adjusted according to the length of the main chain, the carbon number of the side chain, and the carbon number of the whole fatty acid ester E.

The number of carbon atoms in one molecule of the fatty acid ester E is preferably 20 or more, and more preferably 21 or more. As a result, the fatty acid ester E becomes relatively low in volatility, and furthermore, the fatty acid ester E becomes bulky by providing a side chain of an appropriate length, whereby the absorption of the ink component into the clear file can be further suppressed. . In addition, since the bulky fatty acid ester has a low surface tension, the surface concentration can be further increased by see-through.
The number of carbon atoms in one molecule of the fatty acid ester E is preferably 40 or less, more preferably 30 or less, and even more preferably 28 or less. Since the fatty acid ester E may have a high viscosity when the carbon number is high, the fatty acid ester E having the carbon number within this range can lower the viscosity of the ink and further improve the ejection performance.

Specific examples of the fatty acid ester E include, for example, 2-octyldodecyl neopentanoate, 2-hexyldecyl hexanoate, 2-hexyldecyl heptanoate, 2-butyloctyl octanoate, 1-hexyloctyl octanoate, 2-octyl octanoate, Hexyldecyl, 2-hexyldecyl 2-ethylhexanoate, 2-butyloctyl nonanoate, 1-hexyloctyl nonanoate, 1-butylhexyl decanoate, 2-butyloctyl decanoate, 2-hexyldecyl laurate, decanoic acid 2-octyldodecyl, octyl 2-butyloctanoate, 2-ethylhexyl 2-butyloctanoate, nonyl 2-butyloctanoate, decyl 2-butyloctanoate, 1-butylhexyl 2-butyloctanoate, 2-hexyl myristate Decyl, hexyl 2-hexyldecanoate Mention may be made of the Le and the like.
These may be used alone or in combination of two or more.

The fatty acid ester E can be produced by, but not limited to, the following method.
The fatty acid ester E can be obtained by reacting a fatty acid with an alcohol. A raw material having at least one of a fatty acid and an alcohol having a side chain having 4 or more carbon atoms is used. In order to introduce a side chain into the alcohol portion of the fatty acid ester E, a secondary alcohol having 9 or more carbon atoms and having a hydroxyl group at the 5th or more position can be used.
The reaction temperature can be adjusted in the range of 80 to 230 ° C depending on the type of the fatty acid and the alcohol. The reaction time can be adjusted in the range of 1 to 48 hours depending on the types of fatty acids and alcohols and the amounts of raw materials used. It is preferable to remove water generated during the esterification reaction.
Preferably, the fatty acid and the alcohol are reacted at a molar ratio of 1: 1.
In the reaction, an appropriate amount of a catalyst such as concentrated sulfuric acid, p-toluenesulfonic acid, methanesulfonic acid or the like may be used.

Examples of the raw material fatty acid having a side chain having 4 or more carbon atoms include 2-butyloctanoic acid, 2-hexyldecanoic acid, and 2-octyldodecanoic acid.
Examples of the straight-chain fatty acid or fatty acid having a side chain having 3 or less carbon atoms as a raw material include acetic acid, butanoic acid, pentanoic acid, neopentanoic acid, hexanoic acid, heptanoic acid, octanoic acid, 2-ethylhexanoic acid, and nonanoic acid , Decanoic acid, undecanoic acid, dodecanoic acid, tetradecanoic acid and the like.

Examples of the starting material alcohol having a side chain having 4 or more carbon atoms include 2-butyl-1-octanol, 2-hexyl-1-decanol, 2-octyl-1-dodecanol, and the like.
Examples of the secondary alcohol having a hydroxyl group at the 5-position or higher as a raw material include 5-decanol and 7-tetradecanol.

  Examples of the straight-chain alcohol or alcohol having a side chain having 3 or less carbon atoms as a raw material include 1-butanol, 1-pentanol, 1-hexanol, 1-heptanol, 1-octanol, 2-ethylhexanol, and 1-butanol. Nonanol, 1-decanol, 1-undecanol, 1-dodecanol and the like can be mentioned.

In the first ink, the ratio of the amount of the fatty acid ester E to the total amount of the non-aqueous solvent is preferably from 10 to 100% by mass.
This ratio is preferably at least 10% by mass, more preferably at least 40% by mass, even more preferably at least 50% by mass. Furthermore, this ratio is preferably 60% by mass or more, more preferably 80% by mass or more, and still more preferably 90% by mass or more so that the effects of the present invention are not impaired by the addition of other non-aqueous solvents.
In the first ink, the fatty acid ester E is preferably blended in an amount of 5 to 98% by mass, more preferably 10 to 90% by mass, based on the total amount of the ink.

The first ink may contain other non-aqueous solvents in addition to the fatty acid ester E described above.
As other non-aqueous solvents, both non-polar organic solvents and polar organic solvents can be used. In one embodiment, it is preferable to use a water-insoluble organic solvent that does not mix uniformly with the same volume of water at 1 atmosphere and 20 ° C. as the non-aqueous solvent.

Preferred examples of the nonpolar organic solvent include petroleum hydrocarbon solvents such as aliphatic hydrocarbon solvents, alicyclic hydrocarbon solvents, and aromatic hydrocarbon solvents.
Examples of the aliphatic hydrocarbon solvent and the alicyclic hydrocarbon solvent include non-aqueous solvents such as paraffinic, isoparaffinic, and naphthenic solvents. Commercially available products include No. 0 Solvent L, No. 0 Solvent M, No. 0 Solvent H, Cactus Normal Paraffin N-10, Cactus Normal Paraffin N-11, Cactus Normal Paraffin N-12, Cactus Normal Paraffin N-13, Cactus Normal Paraffin 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 4, AF Solvent No. 5, AF Solvent 6, AF Solvent 7, Naphthesol 160, Naphthesol 200, Naphthesol 220 (all manufactured by JXTG Energy Co., Ltd.); Isopar G, Isopar H Isopar L, Isopar M, Exol D40, Exol D60, Exol D80, Exol D95, Exol D110, Exol D130 (all manufactured by ExxonMobil); Moresco White P-40, Moresco White P-60, Moresco White P -70, Moresco White P-80, Moresco White P-100, Moresco White P-120, Moresco White P-150, Moresco White P-200, Moresco White P-260, Moresco White P- Preferable examples include 350P (all manufactured by MORESCO Co., Ltd.).
Preferred examples of the aromatic hydrocarbon solvent include Grade Alken L, Grade Alken 200P (all manufactured by JXTG Energy Co., Ltd.), Solvesso 100, Solvesso 150, Solvesso 200, Solvesso 200ND (all manufactured by ExxonMobil), and the like. it can.
The initial distillation point of the petroleum hydrocarbon solvent is preferably 100 ° C. or higher, more preferably 150 ° C. or higher, even more preferably 200 ° C. or higher. The initial distillation point can be measured according to JIS K0066 "Testing method for distillation of chemical products".

Preferred examples of the polar organic solvent include other fatty acid ester solvents other than the fatty acid ester E, higher alcohol solvents, higher fatty acid solvents, and the like.
As other fatty acid ester solvents, for example, the total number of carbon atoms is 12 or more, preferably 16 to 30, dodecyl hexanoate, methyl laurate, hexyl laurate, hexyl palmitate, hexyl hexanoate, oleic acid Solvent having a linear alkyl group such as methyl, ethyl oleate, butyl oleate, hexyl oleate, methyl linoleate, ethyl linoleate, butyl stearate, hexyl stearate, methyl soybean oil, methyl tall oil; 2-ethyl Dodecyl hexanoate, 2-ethylhexyl stearate, isodecyl isononanoate, isotridecyl isononanoate, isopropyl isostearate, isononyl isononanoate, isopropyl laurate, isopropyl myristate, isopropyl palmitate, palmitate Solvents such as isooctyl, isopropyl oleate, isobutyl linoleate, isooctyl stearate, isobutyl soybean oil, isobutyl tall oil, and isostearyl palmitate (34 carbon atoms) having 3 or less carbon atoms in one molecule. No.

As the higher alcohol solvent, a higher alcohol solvent having 6 or more carbon atoms in one molecule, preferably 12 to 20 carbon atoms can be preferably used. For example, 1-octadecanol, isomyristyl alcohol, isopalmityl alcohol And primary alcohols such as isostearyl alcohol, oleyl alcohol, isoeicosyl alcohol and decyltetradecanol; and secondary alcohols such as 2-ethyl-1,3-hexanediol.
As the higher fatty acid-based solvent, for example, lauric acid, isomyristic acid, palmitic acid, isopalmitic acid, α-linolenic acid, linoleic acid, oleic acid, isostearic acid, etc., has 12 or more carbon atoms in one molecule, preferably And 14-20 higher fatty acid solvents.

Further, other non-aqueous solvents include silicone oil.
As the silicone oil, for example, a chain silicone oil, a cyclic silicone oil, a modified silicone oil, or the like can be used.
The chain silicone oil is preferably a chain polysiloxane having 2 to 30 silicon atoms. The silicon number of the chain silicone oil is more preferably 2 to 20, and still more preferably 3 to 10.
Examples of the chain silicone oil include linear dimethyl silicone oils such as tetradecamethylhexasiloxane, hexadecamethylheptasiloxane, and docosamethyldecasiloxane, and branched dimethyls such as methyltris (trimethylsiloxy) silane and tetrakis (trimethylsiloxy) silane. And silicone oil.
The cyclic silicone oil is preferably a cyclic polysiloxane having 5 to 9 silicon atoms, and is preferably a cyclic polysiloxane such as decamethylcyclopentasiloxane, dodecamethylcyclohexasiloxane, hexadecamethylcyclooctasiloxane, or octadecamethylcyclononasiloxane. Dimethyl silicone oil can be preferably used.

As the modified silicone oil, a silicone oil in which various organic groups are introduced into some silicon atoms of a chain or cyclic dimethyl silicone oil can be used. As the modified silicone oil, it is preferable that all silicon atoms are bonded only to either a carbon atom or a siloxane-bonded oxygen atom. The modified silicone oil is preferably a non-reactive silicone oil. It is preferable that the constituent atoms of the modified silicone oil include only silicon, carbon, oxygen and hydrogen atoms. As the modified silicone oil, for example, at least one methyl group contained in a chain or cyclic dimethyl silicone oil is selected from the group consisting of an alkyl group, a carboxylate bond-containing group, an aromatic ring-containing group, and an ether bond-containing group. Compounds substituted by one or more selected ones can be used.
Further, as the modified silicone oil, for example, a silicon atom of another chain or cyclic dimethyl silicone oil is bonded to at least one silicon atom contained in the chain or cyclic dimethyl silicone oil via an alkylene group. Compounds can be used. In this case, at least one methyl group contained in the chain or cyclic dimethyl silicone oil linked via an alkylene group is an alkyl group, a carboxylate ester bond-containing group, an aromatic ring-containing group, and an ether bond-containing group. It may be replaced by one or more selected from the group consisting of:
Examples of the modified silicone include an alkyl-modified silicone oil, an aryl-modified silicone oil such as a phenyl-modified silicone oil and an aralkyl-modified silicone oil, a carboxylic acid ester-modified silicone oil, an alkylene-modified silicone oil, and a polyether-modified silicone oil.
The modified silicone oil preferably has 2 to 20 silicon atoms, more preferably 2 to 10, more preferably 2 to 6, and still more preferably 3 to 6.

  Fatty acid ester solvents, higher alcohol solvents, polar organic solvents such as higher fatty acid solvents, and the boiling point of silicone oil are preferably 150 ° C. or higher, more preferably 200 ° C. or higher, and more preferably 250 ° C. or higher. Is more preferable. The non-aqueous solvent having a boiling point of 250 ° C. or higher includes a non-aqueous solvent having no boiling point.

These non-aqueous solvents may be used alone or in combination of two or more as long as they form a single phase.
In the case where another non-aqueous solvent is blended in the first ink, a non-aqueous solvent having a boiling point or an initial boiling point exceeding 300 ° C. can be preferably used from the other non-aqueous solvents described above.

(Second ink)
The second ink preferably contains a coloring material and a non-aqueous solvent, and preferably has a 20% distillation temperature of 300 ° C. or lower.
Unless otherwise specified, the components of the second ink, such as the coloring material and the non-aqueous solvent, can be the same components as those of the first ink, and the description thereof is omitted.

In the second ink, the non-aqueous solvent can be appropriately selected from one or more of the non-aqueous solvents described in the first ink.
For example, when the type and amount of the non-aqueous solvent in the second ink are two or more, the combination and the mixing ratio are appropriately selected so that the 20% distillation temperature of the second ink can be reduced to 300 ° C. or less. can do.

From the viewpoint of reducing the 20% distillation temperature of the second ink to 300 ° C. or lower, the second ink preferably contains at least one non-aqueous solvent having a boiling point or initial boiling point of 300 ° C. or lower.
Petroleum hydrocarbon solvents include mixed solvents containing multiple types of solvent components. In the case of this mixed solvent, there is a temperature range from the initial boiling point to the dry point, but a solvent having an initial boiling point of 300 ° C. or less even when the dry point exceeds 300 ° C. can be preferably used. Further, it is more preferable to use a solvent having both an initial boiling point and a dry point of 300 ° C. or less.

  Fatty acid ester-based solvents, alcohol-based solvents, polar solvents including higher fatty acid-based solvents, and silicone oils are solvents having a single boiling point and a boiling point of 300 ° C. or lower because they are single components. It can be preferably used. In the case of a mixed solvent provided without isolating two or more kinds of solvents, the boiling point may vary. In this case, the upper limit of the boiling point width is preferably 300 ° C. or less.

In the second ink, the ratio of the amount of the non-aqueous solvent having a boiling point or initial boiling point of 300 ° C. or lower to the total amount of the non-aqueous solvent is preferably 20% by mass or more, more preferably 30% by mass or more, and 50% by mass. % Or more is more preferable. In the second ink, by increasing the blending amount of the highly volatile solvent, the solvent is volatilized from the recording medium surface, and the phenomenon of see-through can be suppressed, and strike-through of the printed matter can be prevented. .
Further, from the viewpoint of limiting the blending amount of the low-volatile solvent in the second ink, the ratio is preferably equal to or greater than 80% by mass, more preferably equal to or greater than 90% by mass, and may be equal to or greater than 100% by mass.
In the second ink, the non-aqueous solvent having a boiling point or initial boiling point of 300 ° C. or lower is preferably 20 to 98% by mass, more preferably 30 to 95% by mass, and more preferably 50 to 90% by mass based on the total amount of the ink. More preferred.

Since the fatty acid ester having a side chain of 4 or more carbon atoms and having 20 or more carbon atoms in one molecule (fatty acid ester E) is a relatively high boiling point solvent, the amount of the fatty acid ester in the second ink is Preferably, it is restricted.
In the second ink, the ratio of the amount of the fatty acid ester E to the total amount of the non-aqueous solvent is preferably less than 80% by mass, more preferably 60% by mass or less, further preferably 50% by mass or less, and more preferably less than 10% by mass. More preferred. The fatty acid ester E may not be contained in the second ink.

  In the second ink, the fatty acid ester E is preferably blended in an amount of 0 to 80% by mass, more preferably 0 to 60% by mass, still more preferably 0 to 50% by mass, and less than 10% by mass based on the total amount of the ink. Is more preferred.

  Because the solvent of the second ink is more volatile than the solvent of the first ink, when the first ink and the second ink are overprinted and printed, the first ink deforms the clear file. In addition to improving the surface density and preventing the solvent of the second ink from evaporating easily, the phenomenon of see-through can be suppressed, and strike-through of the printed matter can be further prevented.

In the ink set, the ratio of the amount of the fatty acid ester E contained in the first ink to the total amount of the non-aqueous solvent contained in the first ink is determined based on the total amount of the non-aqueous solvent contained in the second ink. It is preferable that the ratio is larger than the ratio of the amount of the fatty acid ester E contained in the second ink.
The fatty acid ester E acts to improve the deformation of the clear file and the surface concentration, but has a problem that the see-through phenomenon becomes excessive due to the high carbon number and low surface tension, making it difficult to suppress strike-through. By limiting the blending amount of the fatty acid ester E in the second ink, the see-through phenomenon can be suppressed in a well-balanced manner, and strikethrough of the printed matter can be further prevented.

  The first ink and the second ink may contain various additives in addition to the components described above, as long as the effects of the present invention are not impaired. As an additive, an anti-clogging agent for a nozzle, an antioxidant, a conductivity adjuster, a viscosity adjuster, a surface tension adjuster, an oxygen absorber and the like can be appropriately added. These types are not particularly limited, and those used in the art can be used.

  The first ink and the second ink can be manufactured by mixing respective components including a coloring material and a non-aqueous solvent, respectively. Preferably, the respective components are collectively or separately mixed and stirred to prepare an ink. Specifically, it can be prepared by putting all the components into a disperser such as a bead mill or the like in a lump or dividedly and dispersing them, and, if desired, by passing through a filter such as a membrane filter.

Each of the first ink and the second ink can be preferably provided as an oil-based inkjet ink.
The suitable range of the viscosity of the oil-based inkjet ink varies depending on the nozzle diameter and the ejection environment of the ejection head of the inkjet recording system, but is generally preferably 5 to 30 mPa · s at 23 ° C., and 5 to 15 mPa · s. Is more preferable, and 8 to 13 mPa · s is more preferable.

  The printing method using the oil-based inkjet ink is not particularly limited, and may be any method such as a piezo method, an electrostatic method, and a thermal method. When an ink jet recording apparatus is used, it is preferable that the ink according to one embodiment is ejected from an ink jet head based on a digital signal, and the ejected ink droplets adhere to a recording medium.

  In one embodiment, the recording medium is not particularly limited, printing paper such as plain paper, coated paper, special paper, cloth, inorganic sheet, film, OHP sheet, etc. And the like. Among them, printing paper such as plain paper and coated paper can be preferably used from the viewpoint of ink permeability.

  Here, plain paper is paper in which an ink receiving layer, a film layer, and the like are not formed on normal paper. Examples of plain paper include high quality paper, medium quality paper, PPC paper, reprinted paper, recycled paper, and the like. Plain paper is a paper in which ink easily penetrates because paper fibers having a thickness of several μm to several tens μm form voids of several tens to several hundreds of μm.

  As the coated paper, coated paper for inkjet such as matte paper, glossy paper, semi-glossy paper, and so-called coated printing paper can be preferably used. Here, the coated printing paper is printing paper conventionally used in letterpress printing, offset printing, gravure printing, and the like, and an inorganic pigment such as clay or calcium carbonate is attached to the surface of high-quality paper or medium-quality paper. And printing paper provided with a coating layer using a paint containing a binder such as starch. Depending on the amount of coating and the method of coating, coated printing paper can be used for finely coated paper, high quality lightweight coated paper, medium lightweight coated paper, fine coated paper, medium coated paper, art paper, cast coated paper, etc. being classified.

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

"Synthesis of fatty acid esters"
Table 1 shows the synthesis formula of the synthesized fatty acid ester.
According to the recipe shown in Table 1, the fatty acid and the alcohol were put in a four-necked flask and mixed and stirred to obtain a uniform solution. The four-necked flask was equipped with a Dean-Stark apparatus, so that when the charged raw materials reacted and water was generated, it could be removed. An appropriate amount of sulfuric acid was further added as a catalyst to the four-necked flask containing the homogeneous solution, and the whole system was heated. The heating temperature was set at 80C to 230C depending on the type of fatty acid and alcohol. 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 to obtain a fatty acid ester.
Fatty acids and alcohols were mixed at a molar ratio of 1: 1.
Fatty acids and alcohols can be obtained from Tokyo Chemical Industry Co., Ltd. and SIGMA-ALDRICH.

The following fatty acid esters were used as commercial products.
2-Hexyldecyl 2-ethylhexanoate: "ICEH" manufactured by Higher Alcohol Industry Co., Ltd.
2-octyldodecyl neopentanoate: "Elefac I-205" from Nikko Chemicals Co., Ltd.
2-hexyldecyl myristate: “ICM-R” manufactured by Higher Alcohol Industry Co., Ltd.
Hexyl hexanoate: Tokyo Chemical Industry Co., Ltd.

In Table 2, regarding the fatty acid ester, the number of carbon atoms in one molecule, the number of carbon atoms in the side chain having the largest number of carbon atoms among the side chains in the molecule (the maximum number of carbon atoms in the side chain), R ¹ -COO-R ² In the structural formula represented by, the number of carbon atoms of R ¹ , the number of side chains, the number of carbon atoms of each side chain, the number of carbon atoms of R ² , the number of side chains, and the number of carbon atoms of each side chain are shown.

"Preparation of ink"
Tables 3 and 4 show the formulations of the first ink and the second ink. For the fatty acid ester, the number of carbon atoms in one molecule (C number) is shown in the table, and the number of carbon atoms in the side chain having the largest number of carbon atoms among the side chains in one molecule (maximum C number of side chains) is shown in the table.
The pigment, the pigment dispersant, and the solvent are mixed according to the compounding amounts shown in each table, and the pigment is sufficiently dispersed using a bead mill “Dynomill KDL-A” (manufactured by Shinmaru Enterprises Co., Ltd.) under a residence time of 15 minutes. Dispersed. Subsequently, coarse particles were removed with a membrane filter to obtain an ink.

For the first ink, the ratio (% by mass) of the fatty acid ester E to the total amount of the solvent is shown in the table. The 20% distillation temperature (° C.) for the second ink is shown in the table.
The 20% distilling temperature of the second ink is 100% by a thermal analysis (TG) apparatus when the temperature of the ink is raised from 23 ° C. to 500 ° C. at a rate of 15 ° C./min. In this case, the temperature was determined from the temperature at which the mass of the entire ink was reduced by 20%.
A THERMO PLUS EVO2 differential type differential thermal balance TG8121 (Rigaku Corporation) was used as a thermal analyzer, and an aluminum liquid sample pan and a sample lid (Rigaku Corporation Item No. 8580) were used as cells. For the measurement sample, a pinhole (φ150 to 160 μm in actual measurement value) was opened using a fine needle for the sample lid, about 10 mg of the sample was put in a sample pan, and a sample sealer (Item No. 8395D1 manufactured by Rigaku Corporation) was used. It was manufactured by pressing and sealing.

Other components are as follows.
(Pigment)
Carbon black 1: "SUNBLACK X25" manufactured by Asahi Carbon Co., Ltd.
Carbon Black 2: "Special Black 350" manufactured by Evonik Japan.
Copper phthalocyanine blue: a blue pigment, "FASTOGEN Blue LA5380" manufactured by DIC Corporation.
Soluble azo lake pigment: Magenta pigment, "SYMULER BRILLIANT CARMINE 6B401" manufactured by DIC Corporation.
Insoluble azo pigment: Yellow pigment, "SYMULER FAST YELLOW 4GO" manufactured by DIC Corporation.
(Pigment dispersant)
Solsperse 18000: manufactured by Japan Lubrizol Co., Ltd., 100% by mass of active ingredient.
BYK-9076: manufactured by BYK Japan KK, 100% by mass of active ingredient.
DISPERBYK-2155: manufactured by BYK Japan KK, 100% by mass of active ingredient.

(Other solvents)
1-octadecanol: alcoholic solvent, manufactured by Tokyo Chemical Industry Co., Ltd.
2-ethyl-1,3-hexanediol: alcohol-based solvent, manufactured by Tokyo Chemical Industry Co., Ltd.
Dimethyl silicone: silicone oil, "KF-96L-2cs" manufactured by Shin-Etsu Chemical Co., Ltd.
Exol D110: Petroleum hydrocarbon solvent, manufactured by ExxonMobil.

"Evaluation"
The first ink and the second ink were prepared as an ink set in combinations shown in Table 5. Using this ink set, evaluation was performed by the following method. Table 5 shows the results of these evaluations.

(Transformation of clear file)
Two types of inks are loaded into a line type inkjet printer "Orphis FW5230" (manufactured by Riso Kagaku Kogyo Co., Ltd.) in combination with the ink sets shown in Table 5, and plain paper "Ideal paper thin mouth" (Riso Kagaku Kogyo Co., Ltd.) (Manufactured by Co., Ltd.) and the second ink were superposed on the first ink and ejected to print one solid image on one side to obtain a printed material.
The printed matter was sandwiched between clear files made of PP (polypropylene) having a thickness of 0.2 mm, and left at room temperature for one week. After standing, the clear file was placed on a flat surface. Check that the clear file is deformed with the clear file placed on the plane, and if it is deformed, measure the maximum height from the plane as the amount of deformation with the clear file raised from the plane .
The “Orifice FW5230” is a system that uses a line-type inkjet head to convey paper in a sub-scanning direction orthogonal to the main scanning direction (the direction in which the nozzles are arranged) to perform printing.
A: The deformation amount of the clear file is less than 3 cm.
B: The deformation amount of the clear file is 3 cm or more and less than 5 cm.
C: The deformation amount of the clear file is 5 cm or more.

(Table concentration)
A printed matter was obtained in the same manner as in the evaluation of the deformation of the clear file.
The OD value of the surface of the printed matter was measured using a colorimeter “X-rite eXact” manufactured by VideoJet X-Rite Co., Ltd., and the surface density of the composite black was evaluated according to the following criteria.
A: Surface OD value is 1.12 or more.
B: Surface OD value is 1.07 or more and less than 1.12.
C: Surface OD value is less than 1.07.

(Through)
A printed matter was obtained in the same manner as in the evaluation of the deformation of the clear file.
The OD value of the back side of the printed matter and the OD value of the unprinted paper (paper white) were measured using a colorimeter “X-write eXact” manufactured by VideoJet X-Rite Co., Ltd. From the difference in OD value of white, strike-through of composite black was evaluated according to the following criteria.
A: Difference in OD value is less than 0.05.
B: Difference in OD value is 0.05 or more and less than 0.07.
C: Difference in OD value is 0.07 or more.

  As shown in the table, with the inks of the examples, the deformation of the clear file could be prevented, the surface density of the composite black could be increased, and strike-through could be prevented. Although not described in detail, the viscosity of the ink of each example was also appropriate.

In Examples 1 to 9, various fatty acid esters were used in the first ink, and good results were obtained.
It can be seen from Examples 1 to 9 that when the number of carbon atoms in one molecule of the fatty acid ester of the first ink is 21 or more, the deformation of the clear file is further prevented.
Examples 1 to 9 show that strike-through is further prevented when the number of carbon atoms in one molecule of the fatty acid ester of the first ink is 23 or less.
Example 10 shows that good results can be obtained regardless of the types of the pigment and the pigment dispersant of the first ink.

In Examples 11 and 12, in the first ink, other solvents were used together with the fatty acid ester common to Example 1, and good results were obtained in both cases. In Example 1, in the first ink, the amount of the fatty acid ester having a side chain having 4 or more carbon atoms and having 20 or more carbon atoms in one molecule was large, and the table concentration was higher.
In Examples 13 and 14, the solvent formulation of the second ink was changed from that of Example 1, and good results were obtained in both cases.
In Examples 15 and 16, magenta ink and yellow ink were used as the second ink, and good results were obtained. As compared with Example 1, it is understood that it is preferable to use the cyan ink as the second ink from the viewpoint of the surface density of the composite black.

In Comparative Example 1, in the first ink, the number of carbon atoms in the side chain of the fatty acid ester was 2, and the clear file was deformed.
In Comparative Example 2, in the first ink, the number of carbon atoms in one molecule of the fatty acid ester was 18, the deformation of the clear file occurred, and the surface density further decreased.
In Comparative Example 3, strike-through occurred because the 20% distillation temperature of the second ink was higher than 300 ° C.

  In Comparative Example 4, printing was performed using only the black ink using the ink K1 from the first ink. Other printing conditions were the same as in Example 1. In the case of printing only the single color of the black ink K1, the effects of the surface density and the strike-through were not sufficiently obtained.

Claims (5)

  A color material, and a non-aqueous solvent, wherein the non-aqueous solvent has a side chain of 4 or more carbon atoms, a first ink containing a fatty acid ester having 20 or more carbon atoms in one molecule, and a color material; And a second oil-based ink comprising a nonaqueous solvent and a 20% distillation temperature of 300 ° C. or lower.   2. The first ink according to claim 1, wherein the fatty acid ester having a side chain having 4 or more carbon atoms and having 20 or more carbon atoms in one molecule is 10% by mass or more based on the total amount of the non-aqueous solvent. Oil-based inkjet ink set.   3. The first ink according to claim 2, wherein the fatty acid ester having a side chain having 4 or more carbon atoms and having 20 or more carbon atoms in one molecule is 40% by mass or more based on the total amount of the non-aqueous solvent. Oil-based inkjet ink set.   The oil-based inkjet ink set according to any one of claims 1 to 3, wherein the first ink is a black ink, and the second ink is a color ink.   A method for printing using the oil-based inkjet ink set according to claim 1, wherein one of the first ink and the second ink is ejected to a recording medium. And then ejecting the other ink over the print area of the one ink.