JP6890517B2 - Oil-based inkjet ink - Google Patents

Description

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

The inkjet recording method injects highly fluid inkjet ink as droplets from a fine nozzle and records an image on a recording medium placed facing the nozzle, enabling high-speed printing with low noise. Therefore, it has spread rapidly in recent years. As inks used in such an inkjet recording method, water-based inks containing water as a main solvent, ultraviolet curable inks (UV inks) containing a high content of polymerizable monomers as main components, and wax as main components are high. A so-called non-aqueous ink containing a non-aqueous solvent as a main solvent is known as well as a hot melt ink (solid ink) contained in a content. Non-aqueous inks can be classified into solvent inks (solvent-based inks) in which the main solvent is a volatile organic solvent and oil-based inks (oil-based inks) in which the main solvent is a low-volatile or non-volatile organic solvent. The solvent ink dries on the recording medium mainly by evaporation of the organic solvent, whereas the oil-based ink dries mainly by penetrating into the recording medium.

As the oil-based ink, those containing silicone oil have been proposed.
In Patent Document 1, a non-aqueous pigment ink for inkjet, which contains a silicone-based solvent and a pigment and further contains a specific modified silicone oil as a dispersant, improves ink stability, nozzle clogging, and clear file deformation. I am proposing that.
In Patent Document 2, an inkjet recording ink containing 2 to 95 wt (%) of a silicone-based solvent having a boiling point of at least 100 ° C. to 250 ° C. and a coloring material insoluble in the solvent provides good print quality regardless of paper quality. It is proposed that sufficient printing durability can be obtained within a few seconds after printing, and a clear image without color mixing can be obtained in a color image.

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

Japanese Unexamined Patent Publication No. 2004-217703 Japanese Unexamined Patent Publication No. 4-248879 Japanese Unexamined Patent Publication 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 strike-through, which is a phenomenon in which the printed image can be seen through from the back surface of the printed matter.
Further, in inkjet printing, a part of the ink ejected from the inkjet head may form a mist, and the mist of such ink adheres to the inside of a recording medium or an inkjet printer to form a recording medium or an inkjet printer. It may stain the inside of the printer.
Further, in inkjet printing, ink on a recording medium adheres to a roller surface of an inkjet printer such as a driving roller or a driven roller, and ink adheres to a recording medium subsequently conveyed from the roller surface to cause transfer stains. (Roller transfer stains) may occur.

An object of the present invention is to provide an oil-based inkjet ink capable of obtaining a printed image having excellent image density and reducing strike-through, mist generation, and roller transfer stain.

According to the embodiment of the present invention, the non-aqueous solvent contains a pigment and a non-aqueous solvent, and the non-aqueous solvent contains 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. 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 is provided.

According to the embodiment of the present invention, it is possible to provide an oil-based inkjet ink capable of obtaining a printed image having excellent image density and reducing strike-through, mist generation, and roller transfer stain.

Hereinafter, embodiments of the present invention will be described, but the following embodiments do not limit the present invention.
Hereinafter, the oil-based inkjet ink may be simply referred to as "ink".

The oil-based inkjet ink according to one embodiment contains a pigment and a non-aqueous solvent, and the non-aqueous solvent is 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 inkjet ink containing the polar solvent of the above and 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, a printed image having excellent image density can be obtained, and strike-through, mist generation, and roller transfer stains can be reduced.

The reasons for this are not limited to a specific theory, but are the flight process in which the ejected ink flies, the wetting and spreading process in which the ink droplets wet and spread on the recording medium, and the penetration process in which the ink permeates the recording medium. So, it is presumed that it works as follows.

The surface tension of the ink tends to affect the generation of mist in the process of flying the ejected ink on the recording medium, and when the surface tension of the ink is low, mist is likely to be generated. Moreover, 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. Therefore, it is considered that the generation of mist can be reduced when the surface tension of the ink is 23.0 mN / m or more and the ink contains a polar solvent.
When the ink lands on the recording medium, dots are formed through a wetting and spreading process in which the ink droplets wet and spread on the recording medium and a penetration process in which the ink droplets permeate the recording medium.
In the process of wetting and spreading, 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 obtain a high image density.
During the permeation process, the surface tension of the solvent tends to affect permeation. Silicone oil with a low surface tension of less than 24.0 mN / m tends to permeate quickly, and it is considered that roller transfer stains can be reduced by using this.
On the other hand, when the solvent penetrates to the back of a recording medium such as paper, the recording medium is easily transparent and strike-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. Further, a polar solvent having a surface tension of 27.0 mN / m or more has a high surface tension and therefore has a slow penetration, and the polar solvent tends to be more compatible with a pigment dispersant than a 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 strike-through can be reduced by using a silicone oil having a surface tension of 19.0 mN / m or more and a polar solvent having a surface tension of 27.0 mN / m or more.
Further, as described above, since the surface tension of the ink is as low as less than 27.0 mN / m, in the process of wetting and spreading, the wetting and spreading of the ink droplets that have landed on the recording medium are large, and the white background is filled when the solid image is formed. Cheap. Further, as described above, the polar solvent having a high surface tension tends to leave the pigment on a 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 having a high image density and a state where there is little strike-through can be printed.

Here, the surface tension of the ink and each solvent can be determined according to the bubble pressure method (maximum bubble pressure method). For example, the surface tension can be measured using "SITA Mechanism GmbH Science line t60" 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 soluble azo lake pigments, insoluble azo pigments and condensed azo pigments. Examples of the phthalocyanine pigment include metal phthalocyanine pigments and non-metal phthalocyanine pigments. Polycyclic pigments include quinacridone pigments, perylene pigments, perinone pigments, isoindolin pigments, isoindolinone pigments, dioxazine pigments, thioindigo pigments, anthracinone pigments, quinophthalone pigments, and metal complex pigments. And diketopyrrolopyrrole (DPP) and the like. 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, but the pigment dispersant is directly adsorbed on the pigment surface. It is preferably a dispersed dispersion.

The average particle size of the pigment is preferably 300 nm or less, more preferably 200 nm or less, still more preferably 150 nm or less, 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 ink, and is preferably 1 to 15% by mass, 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. Esters, copolymers of vinylpyrrolidone and long-chain alkene, modified polyurethanes, modified polyacrylates, polyether ester-type anionic activators, polyoxyethylene alkyl phosphates, polyester polyamines and the like are preferably used.

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

The pigment dispersant may be appropriately set as long as the amount of the pigment can be sufficiently dispersed in the ink. For example, in terms of mass ratio, the pigment dispersant can be blended in an amount of 0.1 to 5 with respect to the pigment 1, preferably 0.1 to 1. Further, 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 the ink.
The resin component containing the pigment dispersant can be blended in the ink in an amount of 10% by mass or less, more preferably 7% by mass or less, still more preferably 5% by mass or less, based on the total amount of the ink. As a result, it is possible to prevent an increase in ink viscosity and further improve the ejection performance.

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, more preferably 20.0 mN / m or more. As a result, excessive permeation of the silicone oil into the recording medium is likely to be suppressed, and strike-through is likely to be reduced.
The surface tension of the silicone oil is preferably less than 24.0 mN / m, more preferably 23.0 mN / m or less. As a result, the silicone oil can be quickly permeated and the roller transfer stains can be reduced.

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 may be contained in one molecule, and a liquid compound at 23 ° C. may be used. 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 7 to 30 silicon atoms, 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 numbers, and is a cyclic such as decamethylcyclopentasiloxane, dodecamethylcyclohexasiloxane, hexadecamethylcyclooctasiloxane, and 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 the 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 carbon atoms or siloxane-bonded oxygen atoms. The modified silicone oil is preferably a non-reactive silicone oil. The modified silicone oil preferably has only silicon atoms, carbon atoms, oxygen atoms, and hydrogen atoms as constituent atoms.
The modified silicone oil is, for example, a group in which at least one methyl group contained in a chain or cyclic dimethyl silicone oil is composed of an alkyl group, a carboxylic acid ester bond-containing group, an aromatic ring-containing group, and an ether bond-containing group. Compounds substituted by one or more selected from are available.
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 bonded via an alkylene group is composed of an alkyl group, a carboxylic acid 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.
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, further preferably 2 to 6, and even more preferably 3 to 6.

Examples of the phenyl-modified silicone oil include trimethylsiloxyphenyldimethicone, phenyltrimethicone, diphenylsiloxyphenyltrimethicone, 1,1,1,5,5,5-hexamethyl-3-phenyl-3- (trimethylsilyloxy) trisiloxane. Or the like, methylphenyl silicone or the like can be used.

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

The modified silicone oil S can have one or more selected from the group consisting of the following (A) to (D) as an organic group having a total of 4 or more carbon atoms and oxygen numbers.
(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 numbers.
(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 a total of 4 to 12 carbons and oxygens contained in an organic group having a total of 4 or more carbons and oxygens in one molecule.
Further, the modified silicone oil S preferably has a total of 8 to 20 carbon atoms and oxygen numbers contained in an organic group having a total carbon number and oxygen number of 4 or more in one molecule.
When one molecule of the modified silicone oil S contains two or more organic groups having a total of 4 or more carbon atoms and oxygen numbers, an organic group having a total of 4 or more carbon atoms and oxygen numbers in one molecule. The total number of carbon atoms and oxygen number of 2 or more is the total number of carbon atoms and oxygen number of organic groups having a total number of 2 or more carbon atoms and oxygen number of 4 or more.

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

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

In the 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 of carbon atoms. And a monovalent organic group having a total oxygen number of 4 or more is preferable.

Preferably, in the 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, and a carbon number of carbons, respectively. And a carboxylic acid ester bond-containing group having a total oxygen number 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, the number of carbon atoms in one molecule. The number of oxygen and carbon contained in an alkylene group having 4 or more, 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. 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 the general formula (X-1), R ² is a monovalent organic group in which a carbon atom is directly bonded to a silicon atom independently, n is an integer of 0 to 4, and p is each. Independently, it is 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 and oxygen, and 1 The total number of carbon atoms and the number of carbon atoms in the molecule is 4 or more. The total number of oxygen numbers and the number of carbon atoms contained in the organic group is 4 to 20.

In the general formula (X-1), R ² is preferably a methyl group or a monovalent organic group having a total of 4 or more carbon atoms and oxygen numbers, respectively.
In the 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 an oxygen number, and a carbon number of carbon atoms. It is preferable that the number is 1 or more selected from the group consisting of aromatic ring-containing groups having a value of 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 an alicyclic.
The number of carbon atoms of this alkyl group is preferably 4 or more, more preferably 6 or more, more preferably 8 or more, and further preferably 10 or more.
The number of carbon atoms of this alkyl group may be, for example, 20 or less, preferably 18 or less, more preferably 16 or less, and further preferably 12 or less.

Alkyl groups having 4 or more carbon atoms include, for example, 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, Hexadecyl groups, octadecyl and the like can be mentioned.
It is preferably an octyl group, a decyl group, a dodecyl group or a hexadecyl group, and more preferably a decyl group or a dodecyl group.

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

In the general formula (1), R is an alkyl group having a straight chain or a branched chain having 4 to 20 carbon atoms, and m and n are independently integers of 0 to 2 and m + n ≦ 2. ..

In the general formula (1), R is an alkyl group having a straight chain or a 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, 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, 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 0, respectively. In the following compounds, R is the same as the 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 siloxane bond in the main chain via the alkylene group. Or ^{a group represented by −R Bb} − (CO) −OR ^Ba can be preferably used.
Here, R ^Ba may have a linear or branched chain having one or more carbon atoms, and is preferably a chain or alicyclic alkyl group. Further, R ^Bb may have a linear or branched chain having 1 or more carbon atoms, and is preferably a chain or alicyclic alkylene group. The alkylene group that connects the silicon atom of the siloxane bond in the main chain and the carboxylic acid ester bond is more preferably having 2 or more carbon atoms.
The total number of carbon atoms and oxygen number of the carboxylic acid ester bond-containing group is the number of carbon atoms of one carbon atom and two oxygen atoms of the ester bond (-O- (CO)-) and the number of carbon atoms of the alkyl group (R ^Ba ). And the number of carbon atoms of the alkylene group ( ^RBb).

In the carboxylic acid ester 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 and a heptyl group. Examples thereof include a group, an octyl group, an isooctyl group, a nonyl group, a decyl group, a dodecyl group, a hexadecyl group, a heptadecyl group and the like.
A pentyl group, a heptyl group, a nonyl group and a tridecylic 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 ( ^RBb ) is preferably a linear alkylene group having 1 to 8 carbon atoms, for example, a methylene group, an ethylene group, a propylene group, a trimethylene group, n-butylene, and the like. Examples thereof include an isobutylene group, a pentylene group, a hexylene group, a heptylene group, an octylene group, an isooctylene group and the like.
It is preferably an ethylene group.

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

In modified silicone oil S, the aromatic ring-containing group is a group the aromatic ring to the silicon atom of the siloxane bond in the main chain is represented by a direct bond to -R ^Ca, or an alkylene group to the silicon atom of the siloxane bond in the main chain ^{A group represented by -RCb-} R ^{Ca to} which an aromatic ring is bonded can be preferably used.
Here, ^RC is preferably an aromatic ring having 6 or more carbon atoms. Further, ^RCb may have a linear or branched chain having 1 or more carbon atoms, and is preferably a chain or alicyclic alkylene group.
Aromatic ring-containing group, if the aromatic ring to the silicon atom of the siloxane bond in the main chain is a group represented by direct binding to -R ^Ca, as branched side chain, such as trimethylsilyloxy group from the siloxane bond in the main chain It is preferable that it is branched. The aromatic ring-containing group is more preferably a group represented by ^-RCb- R ^{Ca in} which an aromatic ring is bonded to a silicon atom of a siloxane bond in the main chain via an alkylene group.
The carbon number of the aromatic ring-containing group is the sum of ^{the carbon number of the aromatic ring (RCa} ) and the carbon number of any alkylene group ( ^RCb).

In the aromatic ring-containing group, the aromatic ring moiety ( ^RCa ) contains, for example, a phenyl group, a tolyl group, a xsilyl group, a trimethylphenyl group, a biphenyl group, a naphthyl group, an anthracenyl group, or at least one hydrogen atom thereof. A functional group substituted with an alkyl group can be mentioned.

In the aromatic ring-containing group, any alkylene group ( ^RCb ) is preferably an alkylene group which may have a linear or branched chain having 1 to 8 carbon atoms, for example, a methylene group, an ethylene group, or a propylene. Examples thereof include a group, a trimethylene group, an n-butylene group, an isobutylene group, a pentylene group, a hexylene group, a heptylene group, an octylene group, an isooctylene group and the like.
Preferably, it is a propylene group, a methylethylene group, or an ethylene group.

In the modified silicone oil S having an aromatic ring-containing group, in the above general formula (X-1), R ² independently has a carbon atom directly bonded to a methyl group or a silicon atom and has 6 carbon atoms. The above aromatic ring bond-containing group, n is an integer of 0 to 4, p is independently 0 or 1, and the number of silicon in one molecule is 2 to 6, and R ^At least one of the two is the aromatic ring bond-containing group, and a compound having a total number of carbon atoms contained in the aromatic ring bond-containing group in one molecule of 6 to 20 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, an n-butylene group, an isobutylene group, a pentylene group, a hexylene group, a heptene group, an octylene group, an isooctylene group, a nonylene group, a decylene group, a dodecylene group, a hexadecylene group, an ecosilene group and the like. Can be mentioned.
It is preferably an octylene group, a decylene group, or a dodecylene group, and more preferably an octylene group or a decylene group.

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. Therefore, a compound which is an integer of 0 to 4, p is an integer of 0 to 2 independently, and the number of silicon in one molecule is 2 to 6 can be preferably used.

The modified silicone oil S described above is not limited to this, and can be produced by the following method.
For example, a 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 of 4 or more carbon atoms and oxygen numbers in an organic solvent. .. The siloxane raw material and the reactive compound are preferably reacted with 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. Further, in the reaction, a catalyst such as a zero-valent platinum olefin complex, a zero-valent platinum vinyl siloxane complex, a divalent platinum olefin complex halide, or a platinum catalyst such as 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, 3,3,5,5,7,7-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-hexamethyl-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 and the like can be used. it can.

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 and 1-nonene are used as reactive compounds. , 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-eicosene and the like having 4 or more carbon atoms can be used.
In addition to the alkene, an alicyclic hydrocarbon group 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 reactive compounds, vinyl acetate, vinyl propionate, vinyl butyrate, vinyl isobutate, vinyl pentanate, vinyl pivalate, vinyl hexanoate, vinyl heptate are used. , 2-ethylhexanoate, vinyl octanoate, vinyl isooctanoate, vinyl nonanoate, vinyl decanoate, vinyl laurate, vinyl myristate, vinyl palmitate, vinyl eicoate, allyl hexanoate, etc. A fatty acid vinyl, a fatty acid allyl compound, or the like 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, the reactive compounds include 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, Use an allyl compound having a vinyl bond such as 2,4,6-trimethylstyrene, cis-β-methylstyrene, trans-β-methylstyrene, 3-phenyl-1-propene and an aromatic ring having 6 or more carbon atoms. 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, 1,6-heptadiene, 1 , 7-Octadiene, 1,8-Nonadiene, 1,9-Decadiene, 1,11-Dodecadiene, 1,10-Undecadiene, 1,13-Tetradecadiene, Hexadecadiene, Eikosaziene, etc. A certain diene compound or the like 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 "," dodecamethylcyclohexane "manufactured by Tokyo Kasei Kogyo Co., Ltd. Commercially available products such as "Sasiloxane" may be used.

As the silicone oil having a surface tension of 19.0 mN / m or more and less than 24.0 mN / m, one type may be used alone, or a plurality of types may be used in combination.
The amount of silicone oil having a surface tension of 19.0 mN / m or more and less than 24.0 mN / m in the ink is the total amount of non-aqueous solvent in the ink from the viewpoint of further improving the effects of reducing strike-through and roller transfer stains. On the other hand, 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 further preferable.
The amount of silicone oil having a surface tension of 19.0 mN / m or more and less than 24.0 mN / m in the ink is, for example, 90% by mass or less, 80% by mass or less, or 70% by mass with respect to the total amount of the non-aqueous solvent in the ink. It may be less than or equal to 60% by mass or less.

The amount of silicone oil whose surface tension in the ink is 19.0 mN / m or more and less than 24.0 mN / m with respect to the total amount of ink varies depending on the total amount of the non-aqueous solvent used, but it reduces strike-through and roller transfer stains. From the viewpoint of further improving the effect of the above, 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 further 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 with respect to the total amount of ink 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 there.

The ink preferably contains a polar solvent having a surface tension of 27.0 mN / m or more. As a result, it is easy to improve the image density and reduce the generation of mist.
The surface tension of the polar solvent is preferably 27.0 mN / m or more, 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, 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.
As a polar solvent having a surface tension of 27.0 mN / m or more, for example, an ester solvent (a fatty acid ester solvent such as a fatty acid mono, di or triester solvent, a fatty acid ester solvent) having a surface tension of 27.0 mN / m or more. Monobasic acid, dibasic acid or tribasic acid ester solvent other than the solvent), higher alcohol solvent, higher fatty acid solvent, glycol ether solvent (glycol monoalkyl ether, glycol dialkyl ether, etc.) and the like can be used.
Among alcohol-based solvents, for example, higher alcohol-based solvents are generally less polar than lower alcohol-based solvents such as ethanol, and therefore have excellent stability.

Examples of the ester solvent 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, and 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, isostearate The number of carbon atoms in one molecule such as isopropyl acid acid, 2-octyldecyl pivalate, methyl soybean oil, isobutyl soybean oil, methyl toll oil, isobutyl toll oil is preferably 13 or more, and more preferably 15 to 30 fatty acid esters. solvent;
Number of carbon atoms in one molecule such as decanol, tetradecanol, hexanol, 2-ethylhexanol, isostearyl alcohol, isomyristyl alcohol, isopalmityl alcohol, isostearyl alcohol, oleyl alcohol, isoeicosyl alcohol, decyltetradecanol, etc. 6 or more, preferably 12 to 20 higher alcohol-based solvents, etc., which have 6 or more carbon atoms in one molecule, preferably 10 to 20 higher alcohol-based solvents;
Higher fatty acid-based solvents such as lauric acid, isomyristic acid, palmitic acid, isoparmitic acid, α-linolenic acid, linoleic acid, oleic acid, and isostearic acid having 12 or more carbon atoms in one molecule, preferably 14 to 20 carbon atoms;
Glycol ether-based solvents such as tetraethylene glycol dimethyl ether and triethylene glycol monobutyl ether can be mentioned.

The boiling point of the polar solvent having a surface tension of 27.0 mN / m or more is preferably 150 ° C. or higher, more preferably 200 ° C. or higher, and even more preferably 250 ° C. or higher. The non-aqueous solvent having a boiling point of 250 ° C. or higher also includes a non-aqueous solvent having a boiling point.

As the polar solvent having a surface tension of 27.0 mN / m or more, one type may be used alone, or a plurality of types may be used in combination.
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 further 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 amount of the polar solvent having a surface tension of 27.0 mN / m or more in the ink with respect to the total amount of the ink varies depending on the total amount of the non-aqueous solvent used, but further improves the effect of improving the image density and the effect of reducing the generation of mist. From the viewpoint, 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 further 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, either a non-polar organic solvent or 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.

As the non-polar organic solvent, for example, petroleum-based hydrocarbon solvents such as aliphatic hydrocarbon solvents, alicyclic hydrocarbon solvents, and aromatic hydrocarbon solvents can be preferably mentioned.
Examples of the aliphatic hydrocarbon solvent and the alicyclic hydrocarbon solvent include non-aqueous solvents such as paraffin-based, isoparaffin-based, and naphthenic-based 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 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, Naftesol 160, Naftesol 200, Naftesol 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 Exxon Mobile); 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-350P (all manufactured by MORESCO Co., Ltd.) and the like are preferably mentioned. be able to.
Preferred examples of the aromatic hydrocarbon solvent include Grade Alken L, Grade Alken 200P (all manufactured by JXTG Energy Co., Ltd.), Solbesso 100, Solbesso 150, Solbesso 200, and Solbesso 200ND (all manufactured by ExxonMobil). it can.
The distillation initial distillation point of the petroleum-based hydrocarbon solvent is preferably 100 ° C. or higher, more preferably 150 ° C. or higher, and even more preferably 200 ° C. or higher. The distillation initial distillation point can be measured according to JIS K0066 "Distillation test method for 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, isodecil isononanoate, and ethyl 2-methylpentaneate.
The boiling point of the polar organic solvent is preferably 150 ° C. or higher, more preferably 200 ° C. or higher, and even more preferably 250 ° C. or higher. The non-aqueous solvent having a boiling point of 250 ° C. or higher also includes a non-aqueous solvent having a 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 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 the additive, a nozzle clogging inhibitor, 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 ink can be produced by mixing each component including a coloring material and a non-aqueous solvent.
Preferably, each component can be collectively or divided, mixed and stirred to prepare an ink. Specifically, all the components can be collectively or divided and dispersed in a disperser such as a bead mill, and if desired, can be prepared by passing through a filter such as a membrane filter.

The surface tension of the ink is preferably 23.0 mN / m or more, more preferably 24.0 mN / m or more. This makes it easy to reduce the generation of mist.
The surface tension of the ink is preferably less than 27.0 mN / m, more preferably less than 26.0 mN / m. As a result, the dot diameter can be increased and the image density can be easily increased.
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 appropriate range of the viscosity of the oil-based inkjet ink varies depending on the nozzle diameter of the ejection head of the inkjet recording system, the ejection environment, etc., but in general, it is preferably 5 to 30 mPa · s at 23 ° C., and 5 to 15 mPa · s. It is more preferable that it is about 10 mPa · s, and 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 the piezo method is preferable. When an inkjet recording device is used, it is preferable to eject the ink according to the present embodiment from the inkjet head based on a digital signal so that the ejected ink droplets adhere to the recording medium.

In the present embodiment, the recording medium is not particularly limited, and a printing paper such as plain paper, coated paper, or special paper, cloth, an inorganic sheet, a film, an OHP sheet, or the like is used as a base material and an adhesive layer is formed on the back surface. An adhesive sheet or the like provided with the above 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 a paper in which an ink receiving layer, a film layer, or the like is not formed on the ordinary paper. Examples of plain paper include high-quality paper, medium-quality paper, PPC paper, stencil paper, recycled paper, and the like. Plain paper is a paper in which ink easily permeates because paper fibers having a thickness of several μm to several tens of μm form voids of several tens to several hundreds of μm.

Further, as the coated paper, an inkjet coated paper such as matte paper, glossy paper, or semi-glossy paper, or so-called coated printing paper can be preferably used. Here, the coating printing paper is a printing paper that has been conventionally used for 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 using a paint containing a binder such as starch. Coated printing paper can be used for finely coated paper, high-quality lightweight coated paper, medium-quality lightweight coated paper, high-quality coated paper, medium-quality coated paper, art paper, cast-coated paper, etc., depending on the amount of paint applied and the 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 Silicones 2-4"
Table 1 shows the formulations of modified silicones 2-4. The modified silicone 2 was synthesized as follows.
Hexane was charged in 50 parts by mass, 1,1,1,3,5,5,5-heptamethyltrisiloxane in 10 parts by mass, and 1-tetradecene in 9.7 parts by mass in a four-necked flask. 0.02 parts by mass of a platinum catalyst (“1,3-divinyl-1,1,3,3-tetramethyldisiloxane platinum complex” manufactured by Sigma-Aldrich) was added dropwise thereto, and the mixture was stirred at room temperature for 2 to 3 hours. did. Then, the reaction solvent (hexane) and the unreacted raw material were distilled off by vacuum distillation to obtain the desired product.
The modified silicones 3 and 4 were synthesized in the same manner as described above, except that the siloxane compound and the reactive compound were blended according to the formulations shown in Table 1.
In the synthesis of the modified silicones 2 to 4, the siloxane compound was blended so that the molar ratio of the reactive compound was 1: 1.1.
The 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.

<Making ink>
The ink formulations are shown in Tables 2-5.
Pigments, pigment dispersants, and various solvents shown in each table are mixed according to the blending amount shown in each table, and the residence time is 15 minutes with the bead mill "Dynomill KDL-A" (manufactured by Simmal Enterprises Co., Ltd.). , The pigment was sufficiently dispersed. Subsequently, coarse particles were removed with a membrane filter to obtain ink.

The surface tensions of each ink and each solvent shown in Tables 2 to 5 were determined using "SITA Mestechnik GmbH science line t60" manufactured by SITA Process Solutions Co., Ltd. under measurement conditions of 23 ° C. and 0.05 Hz.

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

(Pigment dispersant)
"Solsperse 18000": Made by Japan Lubrizol Co., Ltd. (100% by mass of active ingredient)
"Solsperse 13940": Made by Japan 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-methylpentaneate": manufactured by Toyo Gosei Co., Ltd.
"Ethyl oleate": Made by Tokyo Chemical Industry Co., Ltd.
"Isotridecyl isononanoate": "KAK139" manufactured by Higher Alcohol Industry Co., Ltd.
"Neopentyl glycol diethylcaproate": "KAK NDO" manufactured by Higher Alcohol Industry Co., Ltd.

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

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

(Petroleum hydrocarbon solvent: Paraffin solvent)
"Hexane": Made by Tokyo Chemical Industry Co., Ltd.
(Petroleum hydrocarbon solvent: Isoparaffin solvent)
"Isoper M": Made by ExxonMobil (Petroleum-based hydrocarbon solvent: Naphthenic-based solvent)
"Exor D130": Made by ExxonMobil

<Evaluation>
Each of the above inks is loaded into the line-type inkjet printer "Orphis FW5230" (manufactured by Riso Kagaku Corporation), and 100 solid images are printed on plain paper "Ideal Paper Thin Mouth" (manufactured by Nippon Paper Industries Co., Ltd.). I got a printed matter. Printing was performed under the ejection conditions of a resolution of 300 × 300 dpi and an ink amount of 42 pl per dot.
The "Orphis FW5230" is a system that uses a line-type inkjet head to convey paper in a sub-scanning direction orthogonal to a main scanning direction (direction in which nozzles are lined up) for printing.
The obtained 100th printed matter and the inkjet printer after printing 100 sheets were evaluated by the following methods. The evaluation results are shown in Tables 2-5.

(Roller transfer dirt)
The roller transfer stains at the boundary between the solid image portion and the non-printed portion of the 100th printed matter obtained above were visually observed and evaluated according to the following evaluation criteria.
A: Almost no dirt can be confirmed.
B: Dirt is confirmed, but there is no problem in actual use.
C: A level where dirt is noticeable and there is a problem in actual use.

(Image density (table density))
The image density (table density) of the solid image portion of the 100th printed matter obtained above after being left for one day was measured, and the measured values were evaluated according to the following evaluation criteria. An optical densitometer (RD920, manufactured by Macbeth) was used for measuring the image density.
A: OD value 1.10 or more
B: OD value 1.05 or more and less than 1.10
C: OD value less than 1.05

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

(Generation of mist)
The mist stain in the machine body after printing 100 solid images was evaluated according to the following evaluation criteria.
A: Almost no dirt can be confirmed.
B: Dirt is confirmed, but there is no problem in actual use.
C: A level where dirt is noticeable and there is a problem in actual use.

As shown in each table, with the ink of each example, it was possible to suppress the generation of roller transfer stains, strike-through and mist, and an image having a high image density was obtained.

On the other hand, in Comparative Example 1 in which the surface tension of the silicone oil is low, strike-through cannot be suppressed. Further, in Comparative Example 2 in which the surface tension of the silicone oil is high, the roller transfer stain cannot be suppressed. Further, in Comparative Examples 3 and 4 in which the surface tension of the polar solvent is low, the image density is low. Further, in Comparative Example 5 in which a petroleum-based hydrocarbon solvent having a surface tension of 28.0 mN / m was used instead of the polar solvent, the generation of mist could not be suppressed. Further, in Comparative Example 6 in which a polar solvent having a relatively low surface tension of 22.3 mN / m was used instead of silicone oil, the image density was low and strike-through could not be suppressed. Further, even in Comparative Example 7 in which a petroleum-based hydrocarbon solvent having a relatively low surface tension of 20.3 mN / m was used instead of silicone oil, the image density was low and strike-through could not be suppressed. Further, in Comparative Example 8 in which the surface tension of the ink is low, the generation of mist cannot be suppressed. Further, in Comparative Example 9 in which the surface tension of the ink is high, the image density is low.

Claims (4)

Contains pigments, pigment dispersants and non-aqueous solvents
The non-aqueous solvent contains 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 silicone oil is 5% by mass or more based on the total amount of ink.
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 according to claim 1 or 2, wherein the surface tension of the silicone oil is 20.0 mN / m or more and 23.0 mN / m or less. The oil-based inkjet ink according to any one of claims 1 to 3, wherein the surface tension of the polar solvent is 30.0 mN / m or more.