JP2018141126A - Oily inkjet ink - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide oily inkjet ink capable of obtaining a printed image excellent in image density, and reducing striking-through, mist generation and roller transfer dirt.SOLUTION: In oily inkjet ink including a pigment, a pigment dispersant and a non-aqueous solvent, the non-aqueous solvent contains silicone oil having a surface tension of 19.0 mN/m or higher, and below 24.0 mN/m, and a polar solvent having a surface tension of 27.0 mN/m or higher, and the surface tension of the ink is 23.0 mN/m or higher, and below 27.0 mN/m.SELECTED DRAWING: None

Description

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

  The ink jet recording method is a method in which ink jet ink having high fluidity is ejected as droplets from fine nozzles, and an image is recorded on a recording medium placed facing the nozzles, and high speed printing can be performed with low noise. Therefore, it has been spreading rapidly in recent years. As an ink used in such an ink jet recording method, an aqueous ink containing water as a main solvent, an ultraviolet curable ink (UV ink) containing a polymerizable monomer as a main component and a high content, and a wax as a main component are high. A so-called non-aqueous ink containing a non-aqueous solvent as a main solvent together with hot-melt ink (solid ink) contained in a content is known. Non-aqueous inks can be classified into solvent ink (solvent ink) whose main solvent is a volatile organic solvent, and oil ink (oil ink) whose main solvent is a low-volatile or nonvolatile organic solvent. The solvent ink is dried on the recording medium mainly by evaporation of the organic solvent, whereas the oil-based ink is dried mainly by penetrating into the recording medium.

As oil-based inks, those containing silicone oil have been proposed.
In Patent Document 1, ink stability, nozzle clogging, and clear file deformation are improved by a non-aqueous pigment ink for inkjet that contains a silicone solvent and a pigment, and further contains a specific modified silicone oil as a dispersant. Propose that.
In Patent Document 2, an ink for ink-jet recording containing 2 to 95 wt (%) of a silicone solvent having a boiling point of 100 ° C. to 250 ° C. and a colorant insoluble in the solvent, good print quality regardless of paper quality. In addition, it is proposed that a sufficient printing durability can be obtained within a few seconds after printing, and a clear image without color mixture can be obtained in a color image.

  In Patent Document 3, ink for an ink jet printer using an insulating solvent having a siloxane bond in the molecular skeleton enables clear printing at a high concentration, has scratch resistance, and enables stable ejection. Has proposed.

JP 2004-217703 A JP-A-4-248879 Japanese Patent Laid-Open No. 4-161467

In general, it is desirable that the printed matter has a high image density.
Further, it is desirable to suppress the occurrence of show-through, which is a phenomenon in which a printed image can be seen through from the back side of the printed matter.
In ink jet printing, a part of the ink ejected from the ink jet head may form mist, and the ink mist adheres to the inside of the recording medium or the ink jet printer, and the recording medium or ink jet. The inside of the printer may get dirty.
In ink jet printing, ink on a recording medium adheres to a roller surface of an ink jet printer, such as a driving roller or a driven roller, and the ink adheres to a recording medium that is subsequently conveyed from the roller surface, resulting in transfer contamination. (Roller transfer contamination) may occur.

  An object of the present invention is to provide an oil-based inkjet ink that can obtain a printed image having an excellent image density, and that can reduce back-through, mist generation, and roller transfer stains.

  According to an embodiment of the present invention, the non-aqueous solvent includes a pigment and a non-aqueous solvent, the silicone oil having a surface tension of 19.0 mN / m or more and less than 24.0 mN / m and a surface tension of 27.0 mN / m or more. Provided is an oil-based inkjet ink containing a polar solvent and having an ink surface tension of 23.0 mN / m or more and less than 27.0 mN / m.

  According to the embodiment of the present invention, it is possible to provide an oil-based inkjet ink that can obtain a printed image having an excellent image density, and that can reduce back-through, occurrence of mist, and roller transfer stains.

Hereinafter, although embodiment of this invention is described, the following embodiment does not limit this invention.
Hereinafter, the oil-based inkjet ink may be simply referred to as “ink”.

An oil-based inkjet ink according to an embodiment includes a pigment and a non-aqueous solvent, and the non-aqueous solvent includes a silicone oil having a surface tension of 19.0 mN / m or more and less than 24.0 mN / m and a surface tension of 27.0 mN / m or more. This is an oil-based ink-jet ink having a surface tension of 23.0 mN / m or more and less than 27.0 mN / m.
According to this oil-based inkjet ink, it is possible to obtain a printed image having an excellent image density, and it is possible to reduce back-through, mist generation, and roller transfer contamination.

  The reason for this is not limited by a specific theory, but is a flying process in which the ejected ink flies, a wetting and spreading process in which ink droplets spread on the recording medium, and a penetrating process in which the ink penetrates into the recording medium. It is presumed that this works as follows.

The occurrence of mist in the process of flying the ejected ink tends to be affected by the surface tension of the ink. If the surface tension of the ink is low, mist is likely to occur. Further, when static electricity is generated, mist is likely to be generated. When the ink contains a polar solvent, the generation of static electricity tends to be suppressed. For this reason, it is thought that generation | occurrence | production of mist can be reduced because the surface tension of an ink is 23.0 mN / m or more and an ink contains a polar solvent.
When the ink lands on the recording medium, dots are formed through a wetting and spreading process in which ink droplets spread on the recording medium and a permeation process infiltrating the recording medium.
In the wetting and spreading process, the surface tension of the ink tends to affect, and when the surface tension of the ink is low, the dot diameter tends to widen. It is considered that when the surface tension of the ink is less than 27.0 mN / m, it is easy to obtain a large dot diameter, which makes it easy to fill a white background and easily obtain a high image density.
In the infiltration process, the surface tension of the solvent tends to affect the infiltration. A low surface tension silicone oil having a surface tension of less than 24.0 mN / m tends to permeate rapidly, and it is considered that roller transfer contamination can be reduced by using this silicone oil.
On the other hand, when the solvent penetrates to the back of the recording medium such as paper, the recording medium is easily seen through and the back-through is likely to occur. When the surface tension of the silicone oil is 19.0 mN / m or more, excessive penetration of the silicone oil can be suppressed. In addition, a polar solvent having a surface tension of 27.0 mN / m or more has a high surface tension, so that the penetration is slow, and the polar solvent tends to be familiar with the pigment dispersant as compared with the silicone oil. Therefore, by using a polar solvent having a surface tension of 27.0 mN / m or more, the pigment and the dispersant tend to remain on the recording medium together with the polar solvent. As described above, it is considered that the use of the silicone oil having a surface tension of 19.0 mN / m or more and the polar solvent having a surface tension of 27.0 mN / m or more can reduce the see-through.
Further, as described above, since the surface tension of the ink is as low as less than 27.0 mN / m, the ink droplets that have landed on the recording medium have a large wetting and spreading during the wetting and spreading process, and the white background is filled when a solid image is formed. Cheap. Furthermore, as described above, the polar solvent having a high surface tension tends to leave the pigment on the recording medium such as paper during the permeation process. As a result, even when printing a solid image, it is considered that a solid image with a high image density can be printed in a state where there is little show-through.

  Here, the surface tension of the ink and each solvent can be determined according to a bubble pressure method (maximum bubble pressure method). For example, the surface tension can be measured by using “SITA Testtechnik GmbH science line 60” manufactured by SITA Process Solutions.

The ink preferably contains a pigment as a coloring material.
As the pigment, organic pigments such as azo pigments, phthalocyanine pigments, polycyclic pigments and dyed lake pigments; 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 phthalocyanine pigments include metal phthalocyanine pigments and metal-free phthalocyanine pigments. 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 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 dispersion form of the pigment may be a so-called capsule pigment in which the pigment is coated with a non-oil-soluble resin or a dispersion in which colored resin particles are dispersed with a pigment dispersant. However, the pigment dispersant is directly adsorbed on the pigment surface. A dispersed dispersion is preferred.

The average particle diameter 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 viewpoint of ejection stability and storage stability.
The pigment is usually 0.01 to 20% by mass with respect to the total amount of the ink, and is preferably 1 to 15% by mass, and more preferably 5 to 10% by mass, from the viewpoint of printing 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. An ester, a copolymer of vinyl pyrrolidone and a long-chain alkene, a modified polyurethane, a modified polyacrylate, a polyether ester type anionic activator, a polyoxyethylene alkyl phosphate ester, a polyester polyamine and the like are preferably used.

Examples of commercially available pigment dispersants include, for example, “Antalon V216 (vinyl pyrrolidone / hexadecene copolymer), V220 (vinyl pyrrolidone / eicosene copolymer)” (both products) manufactured by ISP Japan Co., Ltd. Name);
“Solsperse 13940 (polyesteramine type), 16000, 17000, 18000 (fatty acid amine type), 11200, 24000, 28000” manufactured by Nippon Lubrizol Co., Ltd. (all trade names);
“Fuka 400, 401, 402, 403, 450, 451, 453 (modified polyacrylate), 46, 47, 48, 49, 4010, 4055 (modified polyurethane)” manufactured by BASF Japan Ltd. (all trade names);
“Disparon KS-860, KS-873N4 (polyester amine salt)” manufactured by Enomoto Kasei Co., Ltd. (both are trade names);
“Discall 202, 206, OA-202, OA-600 (multi-chain polymer nonionic)” manufactured by Daiichi Kogyo Seiyaku Co., Ltd. (all trade names);
"DISPERBYK2155, 9077" (all trade names) manufactured by Big Chemie Japan, Inc .;
Examples include “Hypermer KD2, KD3, KD11, KD12” (all trade names) manufactured by Croda Japan.

The pigment dispersant need only be an amount that can sufficiently disperse the pigment in the ink, and can be appropriately set. For example, the pigment dispersant can be blended with the pigment 1 at a mass ratio of 0.1 to 5, preferably 0.1 to 1. For example, the pigment dispersant can be blended in an amount of 0.01 to 10% by mass, preferably 0.01 to 5% by mass, based on the total amount of ink.
In the ink, the resin component containing the pigment dispersant can be blended in an amount of 10% by mass or less, more preferably 7% by mass or less, and still more preferably 5% by mass or less based on the total amount of the ink. As a result, an increase in ink viscosity can be prevented, and the ejection performance can be further improved.

The ink preferably contains a silicone oil having a surface tension of 19.0 mN / m or more and less than 24.0 mN / m.
The surface tension of the silicone oil is preferably 19.0 mN / m or more, and more preferably 20.0 mN / m or more. As a result, excessive penetration of silicone oil into the recording medium is easily suppressed, and back-through is easily reduced.
The surface tension of the silicone oil is preferably less than 24.0 mN / m, and more preferably 23.0 mN / m or less. As a result, the silicone oil can be rapidly permeated to reduce roller transfer contamination.

The silicone oil is not particularly limited as long as the surface tension is 19.0 mN / m or more and less than 24.0 mN / m, and a silicon atom and a carbon atom are contained in one molecule, and a liquid compound is used at 23 ° C. it can.
As the silicone oil, a compound having a silyl group, a compound having a silyloxy group, a compound having a siloxane bond, and the like can be used, and a polysiloxane compound can be particularly preferably used.

As the silicone oil, for example, chain silicone oil, cyclic silicone oil, modified silicone oil and the like can be used.
The chain silicone oil is preferably a chain polysiloxane having a silicon number of 7 to 30, more preferably 7 to 20, and even more preferably 7 to 10. Examples of the chain silicone oil include linear dimethyl silicone oil such as hexadecamethylheptasiloxane, and branched dimethyl silicone oil such as methyltris (trimethylsiloxy) silane and tetrakis (trimethylsiloxy) silane.
The cyclic silicone oil is preferably a cyclic polysiloxane having 5 to 9 silicon atoms, and cyclic such as decamethylcyclopentasiloxane, dodecamethylcyclohexasiloxane, hexadecamethylcyclooctasiloxane, octadecamethylcyclononasiloxane and the like. 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. In the modified silicone oil, it is preferable that all silicon atoms are bonded only to either carbon atoms or oxygen atoms of siloxane bonds. The modified silicone oil is preferably a non-reactive silicone oil. In the modified silicone oil, the constituent atoms are preferably composed of only silicon atoms, carbon atoms, oxygen atoms, and hydrogen atoms.
Examples of the modified silicone oil include a group in which at least one methyl group contained in a linear or cyclic dimethyl silicone oil is composed of an alkyl group, a carboxylic ester bond-containing group, an aromatic ring-containing group, and an ether bond-containing group. The compound substituted by 1 or more types selected from can be used.
In addition, 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 dimethylsilicone oil bonded through 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 substituted by one or more selected from the group consisting of
Examples of the modified silicone oil include alkyl-modified silicone oil, aryl-modified silicone oil such as phenyl-modified silicone oil and aralkyl-modified silicone oil, carboxylic acid ester-modified silicone oil, alkylene-modified silicone oil, and polyether-modified silicone oil. .
The modified silicone oil preferably has a silicon number of 2 to 20, more preferably 2 to 10, still more preferably 2 to 6, and still more preferably 3 to 6.

  Examples of the phenyl-modified silicone oil include trimethylsiloxyphenyl dimethicone, phenyl trimethicone, diphenylsiloxyphenyl trimethicone, 1,1,1,5,5,5-hexamethyl-3-phenyl-3- (trimethylsilyloxy) trisiloxane. Methylphenyl silicone and the like can be used.

  An example of the modified silicone oil has an organic group having 2 to 6 silicon atoms per molecule, a carbon atom directly bonded to a silicon atom, and a total of 4 or more carbon atoms and oxygen atoms. Silicone oil having a total of 4 to 20 carbon atoms and oxygen atoms contained in an organic group having 4 or more carbon atoms and oxygen atoms in the molecule is included. Hereinafter, this silicone oil is also referred to as modified silicone oil S.

Modified silicone oil S can have 1 or more types selected from the group which consists of following (A)-(D) as an organic group whose total of carbon number and oxygen number is 4 or more.
(A) An alkyl group having 4 or more carbon atoms.
(B) A carboxylic acid ester bond-containing group having a total of 4 or more carbon atoms and oxygen atoms.
(C) an aromatic ring-containing group having 6 or more carbon atoms.
(D) an alkylene group having 4 or more carbon atoms.

The modified silicone oil S preferably has 4 to 12 carbon atoms and oxygen atoms contained in an organic group having a total of 4 or more carbon atoms and oxygen atoms in one molecule.
The modified silicone oil S preferably has a total number of carbon atoms and oxygen numbers of 8 to 20 contained in an organic group in which the total number of carbon atoms and oxygen number in one molecule is 4 or more.
When two or more organic groups having a total number of carbon atoms and oxygen of 4 or more are contained in one molecule of the modified silicone oil S, the organic group having a total number of carbon atoms and oxygen of 4 or more in one molecule The total number of carbon atoms and oxygen number is the sum of the carbon number and oxygen number of the organic group in which the total number of carbon atoms and oxygen is 2 or more.

  An example of the modified silicone oil S includes a silicone oil that is a compound represented by the following general formula (X).

In general formula (X),
R ¹ is an oxygen atom or a divalent organic group in which a carbon bond is directly bonded to a silicon atom, and R ² is independently a monovalent organic group in which a carbon bond is directly bonded to a silicon atom. , M and n are each independently an integer of 0 to 4, p is each independently an integer of 0 to 2, the number of silicon in one molecule is 2 to 6, and R ¹ And at least one of R ² is an organic group having a total carbon number and oxygen number of 4 or more, and the number of oxygen contained in the organic group having a total carbon number and oxygen number of 4 or more in one molecule And the sum total of carbon number is 4-20.

In General Formula (X), R ¹ is an oxygen atom or a divalent organic group having a total of 4 or more carbon atoms and oxygen numbers, and R ² is independently a methyl group or a carbon number. And a monovalent organic group having a total of 4 or more oxygen atoms.

Preferably, in General Formula (X), R ¹ is an oxygen atom or an alkylene group having 4 or more carbon atoms, and R ² is independently a methyl group, an alkyl group having 4 or more carbon atoms, or a carbon number. And a carboxylic ester bond-containing group having a total number of oxygen of 4 or more, or an aromatic ring-containing group having 6 or more carbon atoms, and at least one of R ¹ and R ² is an alkylene group having 4 or more carbon atoms, Selected from the group consisting of an alkyl group having 4 or more carbon atoms, a carboxylic acid ester bond-containing group having a total of 4 or more carbon atoms and an oxygen number, and an aromatic ring-containing group having 6 or more carbon atoms. 4 or more alkylene groups, 4 or more alkyl groups, carboxylic acid ester bond-containing groups having a total of 4 or more carbon atoms and oxygen numbers, and aromatic ring-containing groups having 6 or more carbon atoms The total number is 4 ~ 20.

  Other examples of the modified silicone oil S include silicone oil which is a compound represented by the following general formula (X-1).

In General Formula (X-1), each R ² is independently a monovalent organic group in which a carbon atom is directly bonded to a silicon atom, n is an integer of 0 to 4, and p is each Independently, 0 or 1, the number of silicon in one molecule is 2 to 6, and at least one of R ² is an organic group having a total of 4 or more carbon atoms and oxygen number, The total number of oxygen atoms and carbon atoms contained in the organic group having 4 or more carbon atoms and oxygen atoms in the molecule is 4 to 20.

In General Formula (X-1), each R ² is preferably independently a methyl group or a monovalent organic group having a total of 4 or more carbon atoms and oxygen atoms.
In General Formula (X-1), at least one of R ² is an alkyl group having 4 or more carbon atoms, a carboxylic acid ester bond-containing group having a total of 6 or more carbon atoms, and a carbon number. Is preferably one or more selected from the group consisting of aromatic ring-containing groups having 6 or more.

In the modified silicone oil S, the alkyl group having 4 or more carbon atoms may have a straight chain or a branched chain, and may be a chain or alicyclic.
The alkyl group has preferably 4 or more carbon atoms, more preferably 6 or more, more preferably 8 or more, and still more preferably 10 or more.
The number of carbon atoms of the alkyl group may be, for example, 20 or less, preferably 18 or less, more preferably 16 or less, and still more preferably 12 or less.

Examples of the alkyl group having 4 or more carbon atoms include n-butyl group, isobutyl group, tert-butyl group, pentyl group, hexyl group, heptyl group, octyl group, isooctyl group, nonyl group, decyl group, dodecyl group, tetradecyl, A hexadecyl group, octadecyl, etc. can be mentioned.
An octyl group, a decyl group, a dodecyl group, and a hexadecyl group are preferable, and a decyl group and a dodecyl group are more preferable.

  For the modified silicone oil S having an alkyl group, for example, a compound represented by the following general formula (1) can be used.

  In General Formula (1), R is an alkyl group having a linear or branched chain having 4 to 20 carbon atoms, m and n are each independently an integer of 0 to 2, and m + n ≦ 2. .

In the general formula (1), R is an alkyl group having a linear or branched chain having 4 to 20 carbon atoms. The number of carbon atoms of the alkyl group represented by R is preferably 4 or more, more preferably 6 or more, still more preferably 8 or more, and still more preferably 10 or more.
The number of carbon atoms of the alkyl group represented by R is preferably 20 or less, more preferably 18 or less, still more preferably 16 or less, and still more preferably 12 or less.

  The compound represented by the general formula (1) is preferably the following compound in which m and n are each 0. In the following compounds, R is the same as in general formula (1).

In the modified silicone oil S, the carboxylic acid ester bond-containing group is represented by —R ^Bb —O— (CO) —R ^Ba in which the carboxylic acid ester bond is bonded to the silicon atom of the main chain siloxane bond via an alkylene group. Or a group represented by —R ^Bb — (CO) —O—R ^Ba can be preferably used.
Here, R ^Ba may have a straight or branched chain having 1 or more carbon atoms, and is preferably a chain or alicyclic alkyl group. R ^Bb may have a linear or branched chain having 1 or more carbon atoms, and is preferably a chain or alicyclic alkylene group. More preferably, the alkylene group connecting the silicon atom of the siloxane bond in the main chain and the carboxylic acid ester bond has 2 or more carbon atoms.
The total number of carbon atoms and oxygen number of the carboxylic acid ester bond-containing group is one carbon atom and two oxygen atoms of the ester bond (—O— (CO) —), and the carbon number of the alkyl group (R ^Ba ). And the carbon number of the alkylene group (R ^Bb ).

In the carboxylate bond-containing group, the alkyl group (R ^Ba ) is, for example, a methyl group, an ethyl group, a propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a tert-butyl group, a pentyl group, a hexyl group, or a heptyl group. Group, octyl group, isooctyl group, nonyl group, decyl group, dodecyl group, hexadecyl group, heptadecyl group and the like.
A pentyl group, a heptyl group, a nonyl group, and a tridecyl group are preferable, and a heptyl group and a nonyl group are more preferable.

In the carboxylic acid ester bond-containing group, the alkylene group (R ^Bb ) is preferably a linear alkylene group having 1 to 8 carbon atoms, such as a methylene group, an ethylene group, a propylene group, a trimethylene group, n-butylene, Examples thereof include an isobutylene group, a pentylene group, a hexylene group, a heptylene group, an octylene group, and an isooctylene group.
Preferably, it is an ethylene group.

In the modified silicone oil S having a carboxylate bond-containing group, in the general formula (X-1), R ² is independently a methyl group or a carbon atom directly bonded to a silicon atom, And a carboxylic ester bond-containing group having a total number of oxygen of 4 or more, n is an integer of 0 to 4, p is independently 0 or 1, and the number of silicon in one molecule 2 to 6 and at least one of R ² is the carboxylic acid ester bond-containing group, and the total number of oxygen atoms and carbon atoms contained in the carboxylic acid ester bond-containing group in one molecule is 4 to 4 A compound of 20 can be preferably used.

In the modified silicone oil S, the aromatic ring-containing group is a group represented by -R ^{Ca in} which the aromatic ring is directly bonded to the silicon atom of the main chain siloxane bond, or an alkylene group is added to the silicon atom of the main chain siloxane bond. A group represented by —R ^Cb —R ^{Ca to} which an aromatic ring is bonded can be preferably used.
Here, R ^Ca is preferably an aromatic ring having 6 or more carbon atoms. R ^Cb may have a straight chain or branched chain having 1 or more carbon atoms, and is preferably a chain or alicyclic alkylene group.
When the aromatic ring-containing group is a group represented by -R ^{Ca in} which the aromatic ring is directly bonded to the silicon atom of the main chain siloxane bond, a branched chain such as a trimethylsilyloxy group from the main chain siloxane bond is used as a side chain. It is preferably branched. The aromatic ring-containing group is more preferably a group represented by —R ^Cb —R ^Ca in which the aromatic ring is bonded to the silicon atom of the main chain siloxane bond via an alkylene group.
The carbon number of the aromatic ring-containing group is the sum of the carbon number of the aromatic ring (R ^Ca ) and the carbon number of an arbitrary alkylene group (R ^Cb ).

In the aromatic ring-containing group, the aromatic ring moiety (R ^Ca ) is, for example, a phenyl group, a tolyl group, a xylyl group, a trimethylphenyl group, a biphenyl group, a naphthyl group, an anthracenyl group, or the like, or at least one hydrogen atom thereof. The functional group substituted by the alkyl group can be mentioned.

In the aromatic ring-containing group, the arbitrary alkylene group (R ^Cb ) is preferably an alkylene group which may have a straight or branched chain having 1 to 8 carbon atoms, such as a methylene group, an ethylene group, or propylene. Group, trimethylene group, n-butylene group, isobutylene group, pentylene group, hexylene group, heptylene group, octylene group, isooctylene group and the like.
A propylene group, a methylethylene group, and an ethylene group are preferable.

In the modified silicone oil S having an aromatic ring-containing group, in the general formula (X-1), each R ² is independently a methyl group or a silicon atom directly bonded to a carbon atom, and has 6 carbon atoms. An aromatic ring bond-containing group, wherein n is an integer of 0 to 4, p is independently 0 or 1, and the number of silicon atoms in one molecule is 2 to 6, R ^At least one of 2 is the aromatic ring bond-containing group, and a compound having a total of 6 to 20 carbon atoms contained in the aromatic ring bond-containing group in one molecule can be preferably used.

  One embodiment of the modified silicone oil S is a compound having 2 to 6 silicon atoms and an alkylene group having 4 or more carbon atoms, preferably carbons at both ends of the alkylene group having 4 or more carbon atoms. A compound in which a silyl group or at least one siloxane bond is bonded to each atom.

The alkylene group having 4 or more carbon atoms includes, for example, n-butylene group, isobutylene group, pentylene group, hexylene group, heptylene group, octylene group, isooctylene group, nonylene group, decylene group, dodecylene group, hexadecylene group, eicosylene group and the like. Can be mentioned.
An octylene group, a decylene group, and a dodecylene group are preferable, and an octylene group and a decylene group are more preferable.

In the modified silicone S having an alkylene group, in the above general formula (X), R ¹ is an alkylene group having 4 or more carbon atoms, R ² is a methyl group, and m and n are independent of each other. In particular, it is an integer of 0 to 4, and p is independently an integer of 0 to 2, and a compound having 2 to 6 silicon atoms in one molecule can be preferably used.

Although the above-mentioned modified silicone oil S is not limited to this, it can be manufactured by the following method.
For example, the modified silicone oil S can be obtained by reacting a siloxane raw material with a reactive compound having a reactive group together with an organic group having a total number of carbon atoms and oxygen number of 4 or more in an organic solvent. . The siloxane raw material and the reactive compound are preferably reacted in a molar ratio of the reactive group of the siloxane raw material and the reactive group of the reactive compound in a molar ratio of 1: 1 to 1: 1.5. In the reaction, a catalyst such as a platinum catalyst such as a zerovalent platinum olefin complex, a zerovalent platinum vinylsiloxane complex, a divalent platinum olefin complex halide, or chloroplatinic acid can be preferably used.

  Examples of the siloxane raw material include 1,1,1,3,3-pentamethyldisiloxane, 1,1,1,3,5,5,5-heptamethyltrisiloxane, 1,1,1,3,3 , 5,7,7,7-nonamethyltetrasiloxane, 1,1,1,3,3,5,7,7,9,9,9-undecamethylpentasiloxane, pentamethyldisiloxane, 1,1 , 3,3,5,5,5-heptamethyltrisiloxane, 1,1,3,3-tetramethyldisiloxane, 1,1,3,3,5,5-hexamethyltrisiloxane, 1,1,3 3,3,5,5,7,7-octamethyltetrasiloxane, 1,1,3,3,5,5,7,7,9,9-decamethylpentasiloxane, 1,1,1,3 5,5,5-heptamethyltrisiloxane, 1,1,1,5,5,5-hexa Til-3- (trimethylsilyloxy) trisiloxane, 1,1,1,5,5,5-hexamethyltrisiloxane, 1,1,1,3,5,7,7,7-octamethyltetrasiloxane, 1 , 1,3,5,5-pentamethyl-3- (dimethylsilyloxy) trisiloxane, 1,1,3,3,5,5,7,7,9,9,11,11-dodecamethylhexasiloxane, 1,1,1,5,5,5-hexamethyl-3- (trimethylsilyloxy) trisiloxane or the like can be used.

The reactive compound preferably has a carbon double bond as a reactive group.
In order to introduce an alkyl group into the modified silicone oil S, 1-butene, 2-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 2-octene, 1-nonene are used as reactive compounds. Alkenes having 4 or more carbon atoms such as 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-eicosene, and the like can be used.
In addition to alkenes, alicyclic hydrocarbon groups having an ethylenically unsaturated double bond such as vinylcyclohexane can be used.

  In order to introduce an ester bond-containing group into the modified silicone oil S, as a reactive compound, vinyl acetate, vinyl propionate, vinyl butyrate, vinyl isobutanoate, vinyl pentanoate, vinyl pivalate, vinyl hexanoate, vinyl heptanoate Carbon number and oxygen number of vinyl 2-ethylhexanoate, vinyl octoate, vinyl isooctanoate, vinyl nonanoate, vinyl decanoate, vinyl laurate, vinyl myristate, vinyl palmitate, vinyl eicoate, allyl hexanoate, etc. A fatty acid vinyl or a fatty acid allyl compound having a total of 6 or more can be used.

  In order to introduce an aromatic ring-containing group into the modified silicone oil S, as reactive compounds, styrene, 4-methylstyrene, 2-methylstyrene, 4-tert-butylstyrene, allylbenzene, 1-allylnaphthalene, 4- Phenyl-1-butene, 2,4-diphenyl-4-methyl-1-pentene, 1-vinylnaphthalene, α-methylstyrene, 2-methyl-1-phenylpropene, 1,1-diphenylethylene, triphenylethylene, An aryl compound having a vinyl bond and an aromatic ring having 6 or more carbon atoms such as 2,4,6-trimethylstyrene, cis-β-methylstyrene, trans-β-methylstyrene, and 3-phenyl-1-propene is used. be able to.

  In order to introduce an alkylene group into the modified silicone oil S, 1,3-butadiene, 1,3-pentadiene, 1,4-pentadiene, 1,5-hexadiene, 1,6-heptadiene, 1 , 7-octadiene, 1,8-nonadiene, 1,9-decadiene, 1,11-dodecadiene, 1,10-undecadiene, 1,13-tetradecadiene, hexadecadiene, eicosadiene and the like having 4 or more carbon atoms A certain diene compound etc. can be used.

  Examples of the silicone oil include “KF-96L-5CS” and “KF-56A” manufactured by Shin-Etsu Chemical Co., Ltd .; “DC246 Fluid”, “DC345 Fluid”, “FZ-3196” and “SS-” manufactured by Toray Dow Corning Co., Ltd. 3408 ";" 1,1,1,5,5,5-hexamethyl-3-phenyl-3- (trimethylsilyloxy) trisiloxane "," decamethylcyclopentasiloxane "," dodecamethylcyclohexasiloxane "manufactured by Tokyo Chemical Industry Co., Ltd. Commercial products such as “sasiloxane” may be used.

One kind of silicone oil having a surface tension of 19.0 mN / m or more and less than 24.0 mN / m may be used alone, or a plurality of kinds may be used in combination.
The amount of the silicone oil having a surface tension in the ink of 19.0 mN / m or more and less than 24.0 mN / m is the total amount of the non-aqueous solvent in the ink from the viewpoint of further improving the effect of reducing the back-through and the roller transfer stain. On the other hand, 5 mass% or more is preferable, 10 mass% or more is more preferable, 15 mass% or more is further more preferable, and 20 mass% or more is further more preferable.
The amount of silicone oil having a surface tension in the ink of 19.0 mN / m or more and less than 24.0 mN / m is, for example, 90% by mass or less, 80% by mass or less, 70% by mass with respect to the total amount of the non-aqueous solvent in the ink. Or 60 mass% or less.

The amount of silicone oil whose surface tension in the ink with respect to the total amount of ink is 19.0 mN / m or more and less than 24.0 mN / m varies depending on the total amount of non-aqueous solvent used. From the viewpoint of further improving the effect, 5% by mass or more is preferable, 10% by mass or more is more preferable, 15% by mass or more is further preferable, and 20% by mass or more is more preferable.
The amount of the silicone oil whose surface tension in the ink with respect to the total amount of the ink is 19.0 mN / m or more and less than 24.0 mN / m is, for example, 80% by mass or less, 70% by mass or less, 60% by mass or less, or 55% by mass or less. It may be.

The ink preferably contains a polar solvent having a surface tension of 27.0 mN / m or more. Thereby, it is easy to improve the image density and reduce the occurrence of mist.
The surface tension of the polar solvent is preferably 27.0 mN / m or more, and more preferably 30.0 mN / m or more.
The surface tension of the polar solvent having a surface tension of 27.0 mN / m or more is preferably 40.0 mN / m or less, and more preferably 35.0 mN / m or less.

The polar solvent having a surface tension of 27.0 mN / m or more is preferably a liquid compound at 23 ° C.
Examples of polar solvents having a surface tension of 27.0 mN / m or more include, for example, ester solvents (fatty acid ester solvents such as fatty acid mono-, di- or triester solvents, fatty acid ester solvents) having a surface tension of 27.0 mN / m or more. Monobasic acid, dibasic acid or tribasic acid ester solvents other than solvents), higher alcohol solvents, higher fatty acid solvents, glycol ether solvents (glycol monoalkyl ether, glycol dialkyl ether, etc.) and the like can be used.
Among alcohol solvents, for example, higher alcohol solvents are generally not so high in polarity as compared to lower alcohol solvents such as ethanol, and thus have excellent stability.

Examples of ester solvents having a surface tension of 27.0 mN / m or more include isotridecyl isononanoate, methyl laurate, isopropyl laurate, hexyl laurate, isopropyl myristate, isopropyl palmitate, hexyl palmitate, isooctyl palmitate, Isostearyl palmitate, methyl oleate, ethyl oleate, isopropyl oleate, butyl oleate, hexyl oleate, methyl linoleate, ethyl linoleate, isobutyl linoleate, butyl stearate, hexyl stearate, isooctyl stearate, isostearic acid The number of carbon atoms in one molecule such as isopropyl acid, 2-octyldecyl pivalate, soybean oil methyl, soybean oil isobutyl, tall oil methyl, tall oil isobutyl is preferably 13 or more, more preferably 15 to 30 fatty acid ester solvents;
Carbon number in one molecule such as decanol, tetradecanol, hexanol, 2-ethylhexanol, isostearyl alcohol, isomyristyl alcohol, isopalmityl alcohol, isostearyl alcohol, oleyl alcohol, isoeicosyl alcohol, decyltetradecanol Is a higher alcohol solvent having 6 or more, preferably 10 to 20 carbon atoms in one molecule, such as a higher alcohol solvent of 12 to 20;
A higher fatty acid solvent having 12 or more, preferably 14 to 20 carbon atoms in one molecule, such as lauric acid, isomyristic acid, palmitic acid, isopalmitic acid, α-linolenic acid, linoleic acid, oleic acid, and isostearic acid;
Examples thereof include glycol ether solvents such as tetraethylene glycol dimethyl ether and triethylene glycol monobutyl ether.

  The boiling point of the polar solvent having a surface tension of 27.0 mN / m or more is preferably 150 ° C. or more, more preferably 200 ° C. or more, and further preferably 250 ° C. or more. The non-aqueous solvent having a boiling point of 250 ° C. or higher includes non-aqueous solvents that do not exhibit a boiling point.

A polar solvent having a surface tension of 27.0 mN / m or more may be used alone or in combination of two or more.
The amount of the polar solvent having a surface tension of 27.0 mN / m or more in the ink is 5% by mass with respect to the total amount of the non-aqueous solvent in the ink from the viewpoint of further improving the effect of improving the image density and the effect of reducing the generation of mist. The above is preferable, 10% by mass or more is more preferable, 15% by mass or more is further preferable, and 20% by mass or more is more preferable.
The amount of the polar solvent having a surface tension of 27.0 mN / m or more in the ink is, for example, 80% by mass or less, 70% by mass or less, 60% by mass or less, or 55% by mass with respect to the total amount of the non-aqueous solvent in the ink. It may be the following.

The amount of the polar solvent having a surface tension in the ink of 27.0 mN / m or more relative to the total amount of the ink varies depending on the amount of the non-aqueous solvent used as a whole, but further improves the effect of improving image density and the effect of reducing mist generation. From a viewpoint, 5 mass% or more is preferable, 10 mass% or more is more preferable, 15 mass% or more is further more preferable, and 20 mass% or more is further more preferable.
The amount of the polar solvent having a surface tension in the ink of 27.0 mN / m or more with respect to the total amount of the ink may be, for example, 70% by mass or less, 60% by mass or less, 55% by mass or less, or 50% by mass or less.

The ink may contain other non-aqueous solvents.
As the other non-aqueous solvent, any of a non-polar organic solvent and a polar organic solvent having a surface tension of less than 27.0 mN / m can be used. In the present embodiment, it is preferable to use a water-insoluble organic solvent that does not uniformly mix with the same volume of water at 1 atm 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 paraffinic, isoparaffinic, and naphthenic nonaqueous solvents. Commercially available products include 0 solvent L, 0 solvent M, 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 No. 4, AF solvent No. 5, AF Solvent No. 6, AF Solvent No. 7, Naphthezol 160, Naphthezol 200, Naphthezol 220 (all manufactured by JXTG Energy Co., Ltd.); Isopar G, Isopar H ISOPAR L, ISOPAR M, EXSOL D40, EXSOL D60, EXSOL D80, EXSOL D95, EXSOL D110, EXSOL 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- Preferred examples include 350P (both manufactured by MORESCO Corporation).
Preferred examples of the aromatic hydrocarbon solvent include grade alkene L, grade alkene 200P (all manufactured by JXTG Energy Co., Ltd.), Solvesso 100, Solvesso 150, Solvesso 200, Solvesso 200ND (all manufactured by ExxonMobil). it can.
The distillation initial boiling point of the petroleum hydrocarbon solvent is preferably 100 ° C. or higher, more preferably 150 ° C. or higher, and even more preferably 200 ° C. or higher. The distillation initial boiling point can be measured in accordance with JIS K0066 “Method for Distillation Test of Chemical Products”.

Examples of the polar organic solvent having a surface tension of less than 27.0 mN / m include fatty acid ester solvents such as isononyl isononanoate, isodecyl isononanoate, and ethyl 2-methylpentanoate.
The boiling point of the polar organic solvent is preferably 150 ° C. or higher, more preferably 200 ° C. or higher, and further preferably 250 ° C. or higher. The non-aqueous solvent having a boiling point of 250 ° C. or higher includes non-aqueous solvents that do not exhibit a boiling point.

  These non-aqueous solvents may be used alone or in combination of two or more as long as a single phase is formed.

  In addition to the above components, the oil-based ink may contain various additives as long as the effects of the present invention are not impaired. As additives, nozzle clogging inhibitors, antioxidants, conductivity modifiers, viscosity modifiers, surface tension modifiers, oxygen absorbers, and the like can be appropriately added. These types are not particularly limited, and those used in the field can be used.

The ink can be prepared by mixing each component including a coloring material and a non-aqueous solvent.
Preferably, the ink can be prepared by mixing or stirring the components together or divided. Specifically, it can be prepared by adding all components to a dispersing machine such as a bead mill in a lump or divided and dispersing them, and if desired, passing through a filtering machine such as a membrane filter.

The surface tension of the ink is preferably 23.0 mN / m or more, and more preferably 24.0 mN / m or more. Thereby, it is easy to reduce generation | occurrence | production of mist.
The surface tension of the ink is preferably less than 27.0 mN / m, and more preferably less than 26.0 mN / m. This makes it easy to increase the dot diameter and increase the image density.
The surface tension of the ink is preferably 23.0 mN / m or more and less than 27.0 mN / m, and more preferably 24.0 mN / m or more and less than 26.0 mN / m.

  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, but in general, it is preferably 5 to 30 mPa · s at 23 ° C., preferably 5 to 15 mPa · s. It is more preferable that it is about 10 mPa · s.

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

  In the present embodiment, the recording medium is not particularly limited, and printing paper such as plain paper, coated paper, special paper, cloth, inorganic sheet, film, OHP sheet, etc., and these are used as a base material and an adhesive layer on the back An adhesive sheet or the like provided with can be used. Among these, printing paper such as plain paper and coated paper can be preferably used from the viewpoint of ink permeability.

  Here, the 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 of μm form voids of several tens to several hundreds of μm.

  As the coated paper, matte paper, glossy paper, semi-glossy paper or other inkjet coated paper, or so-called coated printing paper can be preferably used. Here, the coated printing paper is a printing paper conventionally used in letterpress printing, offset printing, gravure printing, etc., and has an inorganic pigment such as clay or calcium carbonate on the surface of high-quality paper or medium-quality paper. A printing paper provided with a coating layer by a paint containing a binder such as starch. Coated printing paper can be applied to fine coated paper, high-quality lightweight coated paper, medium-weight lightweight coated paper, high-quality coated paper, medium-coated paper, art paper, cast coated paper, etc., depending on the coating amount and coating method 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 modified silicone 2-4"
Table 1 shows the formulations of modified silicones 2-4. Modified silicone 2 was synthesized as follows.
A four-necked flask was charged with 50 parts by mass of hexane, 10 parts by mass of 1,1,1,3,5,5,5-heptamethyltrisiloxane, and 9.7 parts by mass of 1-tetradecene. To this, 0.02 part by mass of platinum catalyst (“1,3-divinyl-1,1,3,3-tetramethyldisiloxane platinum complex” manufactured by Sigma-Aldrich) was added dropwise and stirred at room temperature for 2 to 3 hours. did. Thereafter, the reaction solvent (hexane) and unreacted raw materials were distilled off under reduced pressure to obtain the desired product.
Modified silicones 3 and 4 were synthesized in the same manner as above except that a siloxane compound and a reactive compound were blended in the formulation shown in Table 1.
In the synthesis of the modified silicones 2 to 4, they were blended so that the molar ratio of the siloxane compound and the reactive compound was 1: 1.1.
1,1,1,3,5,5,5-heptamethyltrisiloxane, 1,1,1,3,3-pentamethyldisiloxane and reactive compounds in Table 1 are obtained from Tokyo Chemical Industry Co., Ltd. be able to.

<Preparation of ink>
Ink formulations are shown in Tables 2-5.
According to the blending amount shown in each table, the pigment, the pigment dispersant, and various solvents shown in each table are mixed, and the bead mill “Dynomill KDL-A” (manufactured by Shinmaru Enterprises Co., Ltd.) is used for a residence time of 15 minutes. Sufficiently dispersed the pigment. Subsequently, coarse particles were removed with a membrane filter to obtain an ink.

  The surface tension of each ink and each solvent shown in Tables 2 to 5 was determined under the measurement conditions of 23 ° C. and 0.05 Hz using “SITA Messtechnik GmbH science line t60” manufactured by SITA Process Solutions.

The materials used are as follows.
(Pigment)
“Carbon Black 1”: “MA77” manufactured by Mitsubishi Chemical Corporation
“Carbon Black 2”: “NEROX500” manufactured by Evonik Japan

(Pigment dispersant)
“Solsperse 18000”: manufactured by Nippon Lubrizol Co., Ltd. (active ingredient 100% by mass)
“Solsperse 13940”: manufactured by Nippon Lubrizol Co., Ltd. (active ingredient 40% by mass)

(Silicone oil)
“Chain Silicone 1”: “KF96L-2CS” manufactured by Shin-Etsu Chemical Co., Ltd., dimethyl silicone oil “Chain Silicone 2”: “KF96L-5CS” manufactured by Shin-Etsu Chemical Co., Ltd., dimethyl silicone oil “Modified Silicone 1”: “FZ-3196” manufactured by Toray Dow Corning Co., Ltd., alkyl-modified silicone oil (3-octylheptamethyltrisiloxane)
“Modified silicone 2”: synthesized above, alkyl-modified silicone oil (3-tetradecylheptamethyltrisiloxane)
“Modified silicone 3”: synthesized above, alkyl-modified silicone oil (1-dodecylpentamethyldisiloxane)
“Modified silicone 4”: synthesized above, alkyl-modified silicone oil (3-eicosyl heptamethyltrisiloxane)

(Polar organic solvent: Ester solvent)
“Ethyl 2-methylpentanoate”: manufactured by Toyo Gosei Co., Ltd.
"Ethyl oleate": manufactured by Tokyo Chemical Industry Co., Ltd.
“Isotridecyl isononanoate”: “KAK139” manufactured by Higher Alcohol Industry Co., Ltd.
“Neopentyl glycol diethylhexanoate”: “KAK NDO” manufactured by Higher Alcohol Industry Co., Ltd.

(Polar organic solvent: alcohol solvent)
"Ethanol": manufactured by Tokyo Chemical Industry Co., Ltd. "Decanol": manufactured by Tokyo Chemical Industry Co., Ltd. "Tetradecanol": manufactured by Tokyo Chemical Industry Co., Ltd.

(Polar organic solvent: glycol ether solvent)
"Tetraethylene glycol dimethyl ether": manufactured by Tokyo Chemical Industry Co., Ltd.
"Triethylene glycol monobutyl ether": manufactured by Tokyo Chemical Industry Co., Ltd.

(Petroleum hydrocarbon solvent: paraffin solvent)
"Hexane": manufactured by Tokyo Chemical Industry Co., Ltd.
(Petroleum hydrocarbon solvent: isoparaffin solvent)
“Isopar M”: manufactured by ExxonMobil Corporation (petroleum hydrocarbon solvent: naphthenic solvent)
"Exor D130": manufactured by ExxonMobil

<Evaluation>
Each of the inks described above is loaded into a line-type inkjet printer “Olfis FW5230” (manufactured by Riso Kagaku Co., Ltd.), and 100 sheets of solid images are printed on plain paper “ideal paper thin mouth” (manufactured by Nippon Paper Industries Co., Ltd.) A printed material was obtained. Printing was performed at a resolution of 300 × 300 dpi under an ejection condition where the ink amount per dot was 42 pl.
Note that the “Orifice FW 5230” is a system that uses a line-type inkjet head and conveys paper in the sub-scanning direction orthogonal to the main scanning direction (the direction in which the nozzles are arranged) to perform printing.
The obtained 100th printed material and the ink jet printer after printing 100 sheets were evaluated by the following methods. These evaluation results are shown in Tables 2-5.

(Roller transfer dirt)
The roller transfer stain at the boundary between the solid image portion and the non-printing portion of the 100th printed material obtained above was visually observed and evaluated according to the following evaluation criteria.
A: Almost no dirt can be confirmed.
B: Level at which dirt is confirmed but no problem in actual use.
C: A level at which contamination is remarkable and there is a problem in actual use.

(Image density (surface density))
The image density (surface density) of the solid image portion of the 100th printed material obtained above after standing for 1 day was measured, and the measured value was evaluated according to the following evaluation criteria. For the measurement of image density, an optical densitometer (RD920, manufactured by Macbeth Co.) was used.
A: OD value 1.10 or more
B: OD value of 1.05 or more and less than 1.10
C: OD value less than 1.05

(Back-through (back-side density))
The OD value on the back side of the solid image portion after the 100th printed material obtained above was left for 1 day was measured, and the measured value was evaluated according to the following evaluation criteria.
A: Back side OD value less than 0.15 B: Back side OD value 0.15 or more and less than 0.20 C: Back side OD value 0.20 or more

(Mist generation)
The mist contamination in the machine after printing 100 solid images was evaluated according to the following evaluation criteria.
A: Almost no dirt can be confirmed.
B: Level at which dirt is confirmed but no problem in actual use.
C: A level at which contamination is remarkable and there is a problem in actual use.

  As shown in each table, with the inks of the respective examples, it was possible to suppress the occurrence of roller transfer stains, back-through and mist, and an image having a high image density was obtained.

  On the other hand, in the comparative example 1 in which the surface tension of the silicone oil is low, it is not possible to suppress the breakthrough. Further, in Comparative Example 2 in which the surface tension of the silicone oil is high, roller transfer contamination cannot be suppressed. In Comparative Examples 3 and 4 where the surface tension of the polar solvent is low, the image density is low. Further, in Comparative Example 5 in which a petroleum hydrocarbon solvent having a surface tension of 28.0 mN / m is used instead of a polar solvent, generation of mist cannot be suppressed. Further, in Comparative Example 6 in which a polar solvent having a relatively low surface tension of 22.3 mN / m is used instead of silicone oil, the image density is low, and the show-through cannot be suppressed. Further, even in Comparative Example 7 in which a petroleum hydrocarbon solvent having a relatively low surface tension of 20.3 mN / m is used instead of silicone oil, the image density is low and the back-through cannot be suppressed. Further, in Comparative Example 8 where the surface tension of the ink is low, the generation of mist cannot be suppressed. In Comparative Example 9 where the surface tension of the ink is high, the image density is low.

Claims (4)

Including pigments, pigment dispersants and non-aqueous solvents,
The non-aqueous solvent includes a silicone oil having a surface tension of 19.0 mN / m or more and less than 24.0 mN / m and a polar solvent having a surface tension of 27.0 mN / m or more,
The surface tension of the ink is 23.0 mN / m or more and less than 27.0 mN / m,
Oil-based inkjet ink.   The oil-based inkjet ink according to claim 1, wherein the surface tension of the ink is 24.0 mN / m or more and less than 26.0 mN / m.   The oil-based inkjet ink of Claim 1 or 2 whose surface tension of the said silicone oil is 20.0 mN / m or more and 23.0 mN / m or less.   The oil-based inkjet ink of any one of Claims 1-3 whose surface tension of the said polar solvent is 30.0 mN / m or more.