CN110776783B - Oil-based inkjet ink set and printing method - Google Patents

Abstract

The present invention relates to an oil-based inkjet ink set and a printing method. One of the technical problems is to prevent the deterioration of a resin product due to a printed matter, to increase the surface density of the printed matter, and to prevent strike-through. The solution is an oil-based inkjet ink set comprising a 1 st ink and a 2 nd ink, wherein the 1 st ink contains a coloring material and a non-aqueous solvent, the non-aqueous solvent contains a fatty acid ester having a side chain of 4 or more carbon atoms and 20 or more carbon atoms in 1 molecule, the 2 nd ink contains a coloring material and a non-aqueous solvent, and the 20% distillation temperature is 300 ℃ or lower.

Description

Oil-based inkjet ink set and printing method

Technical Field

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

Background

The inkjet recording system is a system in which an inkjet ink having high fluidity is ejected as droplets from fine nozzles and an image is recorded on a recording medium provided to face the nozzles, and high-speed printing can be achieved with low noise, and therefore, the inkjet recording system has been rapidly spread in recent years. As inks used in such an ink jet recording system, an aqueous ink containing water as a main solvent, an ultraviolet-curable ink (UV ink) containing a polymerizable monomer at a high content as a main component, a hot-melt ink (solid ink) containing a wax at a high content as a main component, and a so-called non-aqueous ink containing a non-aqueous solvent as a main solvent are known. The non-aqueous ink can be classified into a solvent ink (solvent-based ink) in which a volatile organic solvent is a main solvent and an oil-based ink (oil-based ink) in which an organic solvent having low volatility or non-volatility is a main solvent. The solvent ink is mainly dried on the recording medium by evaporation of the organic solvent, whereas the oil-based ink is mainly dried by permeation into the recording medium.

In the oil-based ink, when a solvent penetrates into a recording medium such as paper, the solvent may penetrate even into the back surface of the paper to cause strike-through. The occurrence of offset is more problematic when the oil-based ink contains a large amount of a low-volatility solvent and the amount of the solvent penetrating into the back surface of the paper increases. The low-volatility solvent also stays on the surface of the paper and causes oil bleeding.

Patent document 1 (japanese patent application laid-open No. 2004-002666) proposes: a non-aqueous ink composition comprising a non-polar organic solvent having a 50% cut-off point of 280 ℃ or lower in an amount of 10% by weight or more and a polar organic solvent having a 50% cut-off point of 300 ℃ or more in an amount of 20% by weight or more in a solvent reduces the occurrence of strike-through and oil bleed and further reduces the clogging of a nozzle.

On the other hand, when a printed matter on which an image is formed with an oil-based ink is stored while being sandwiched between transparent folders made of polypropylene (PP), there is a problem that the transparent folders are deformed. One of the reasons for this is that when the transparent folder contacts the printed surface, one surface of the transparent folder swells due to the ink component.

Patent document 2 (jp 2007 a-154149) proposes an ink containing a pigment, a dispersant, and a nonaqueous solvent, wherein 50% or more of the total weight of the nonaqueous solvent is an ester-based solvent having 24 to 36 carbon atoms.

Disclosure of Invention

Problems to be solved by the invention

Patent document 1 proposes: print-through and oil bleeding are improved by controlling the amount of a plurality of solvents having different 50% distilling points in one ink. When the amount of the highly volatile solvent is increased to prevent offset, the ink may not sufficiently penetrate into the paper, and the surface concentration may decrease. In addition, highly volatile solvents also cause distortion of the transparent folder.

Patent document 2 proposes: the deformation of the transparent folder is prevented by increasing the amount of the ester solvent having a high carbon number. The ester solvent having a high carbon number has low volatility and causes strike-through by penetrating into the paper after printing.

Further, since the ester solvent having a high carbon number has a high viscosity, there is a problem that the ink using the ester solvent cannot obtain sufficient ejection performance from the ink jet nozzle. In patent document 2, ink is heated to reduce viscosity and ejected. In this case, after printing, the ester-based solvent having a high carbon number and a low volatility stays on the paper and gradually penetrates into the paper, and therefore, strike-through becomes a problem.

The following methods are also available: an image is formed by overlapping 2 or more inks, thereby increasing the surface density of the image. For example, the following methods are used: the black ink and the color ink are printed in an overlapping manner to form a composite black image. Such an ink set also has problems such as deformation of the transparent folder, reduction in surface density, and occurrence of strike-through.

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

Means for solving the problems

An embodiment of the present invention is an oil-based inkjet ink set including a 1 st ink and a 2 nd ink, wherein the 1 st ink contains a coloring material and a non-aqueous solvent, the non-aqueous solvent contains a fatty acid ester having a side chain of 4 or more carbon atoms and having 20 or more carbon atoms in 1 molecule, and the 2 nd ink contains a coloring material and a non-aqueous solvent, and has a 20% distillation temperature of 300 ℃ or lower.

In another embodiment of the present invention, the printing method is a printing method using the oil-based inkjet ink set, wherein one of the 1 st ink and the 2 nd ink is ejected onto a recording medium, and then the other ink is ejected to overlap a printing region of the one ink.

Invention ofEffect

According to one embodiment of the present invention, it is possible to prevent the resin product from being deteriorated due to the printed matter, to increase the surface density of the printed matter, and to prevent the strike-through.

Detailed Description

The present invention will be described below with reference to an embodiment. The following embodiments are illustrative and not intended to limit the present invention.

An oil-based inkjet ink set (hereinafter, may be simply referred to as an ink set) according to an embodiment includes a 1 st ink and a 2 nd ink, the 1 st ink including a pigment and a non-aqueous solvent, the non-aqueous solvent including a fatty acid ester having a side chain of 4 or more carbon atoms and 20 or more carbon atoms in 1 molecule, the 2 nd ink including a pigment and a non-aqueous solvent, and a 20% distillation temperature of 300 ℃ or lower.

Hereinafter, a fatty acid ester having a side chain of 4 or more carbon atoms and 20 or more carbon atoms in 1 molecule will also be referred to as a fatty acid ester E.

According to the oil-based inkjet ink set, it is possible to prevent the deterioration of a resin product due to a printed matter, to increase the surface density of the printed matter, and to prevent strike-through.

In the ink set according to one embodiment, by ejecting one of the 1 st ink and the 2 nd ink to the recording medium and then ejecting the other one in an overlapping manner, the surface density of a printed matter can be increased by overlapping the one ink and the other ink on the recording medium, and offset printing can be prevented.

Further, according to the ink, the transparent folder can be prevented from being deformed when the printed matter is sandwiched between the transparent folders made of polypropylene (PP) or the like. The transparent folder is made of a transparent or translucent resin sheet, and may be made of a colored opaque resin sheet.

When a printed matter is sandwiched between transparent folders, particularly transparent folders made of polypropylene (PP), when an ink component of the printed matter, particularly a nonaqueous solvent component, volatilizes and comes into contact with the transparent folders, the inner side surfaces of the transparent folders are greatly denatured and swell or shrink with respect to the outer side surfaces of the transparent folders, and the transparent folders may be deformed.

This is likely to be a problem when the oil-based ink contains a large amount of volatile solvent, and the volatile solvent gradually comes into contact with the inner surface of the transparent folder.

Further, among the non-aqueous solvents used in the oil-based ink, petroleum-based hydrocarbon solvents are likely to have a structure similar to that of polypropylene of a transparent folder. Similarly to the petroleum hydrocarbon solvent, when the fatty acid ester solvent, the higher fatty acid solvent, the higher alcohol solvent, and the like are similar in structure to the polypropylene, the transparent folder may be deformed in the same manner.

In the ink set of an embodiment, the 1 st ink contains the fatty acid ester E having a side chain of 4 or more carbon atoms and 20 or more carbon atoms in the 1 st molecule, whereby the transparent folder can be prevented from being deformed.

The fatty acid ester E is a solvent having a high carbon number and therefore low volatility, and can suppress volatilization from a printed matter after printing, and can exert an effect of preventing deformation of the transparent folder.

Further, the fatty acid ester E has a side chain having 4 or more carbon atoms, and thus the molecular structure becomes a three-dimensional structure and becomes huge, so that the resin product having a linear structure such as polypropylene is less likely to be deteriorated, and the function of preventing the transparent folder from being deformed can be exerted.

Since the molecular structure of the fatty acid ester E is three-dimensional, the surface tension tends to be lower than that of a linear nonaqueous solvent. When the 1 st ink containing the fatty acid ester E is ejected in a dot shape onto a recording medium, the fatty acid ester E having a low surface tension diffuses on the recording medium, and the dot diameter diffuses, so that the surface density of the printed matter appears to be high.

Further, the fatty acid ester E is a solvent having a low volatility because of its high molecular weight, and can remain on the surface of a printed matter without volatilizing from the surface after printing. When the low-volatility solvent stays at the surface of the printed matter, the surface concentration of the printed matter appears to become high due to the penetration phenomenon.

In order to increase the surface density of a printed matter while preventing deformation of a transparent folder, if the printed matter is produced using only the 1 st ink containing the fatty acid ester E, the solvent component that volatilizes from the surface of the printed matter after printing decreases, the penetration phenomenon becomes excessive, and there is a case where the strike-through of the printed matter becomes a problem.

In order to solve this problem, the use of the 2 nd ink having a 20% distillation temperature of 300 ℃ or lower makes it easy for the non-aqueous solvent to volatilize from the printed matter after printing, and the penetration phenomenon is suppressed to some extent after the ejection of the 1 st ink and the 2 nd ink, thereby preventing the strike-through of the printed matter.

The surface of paper or the like as a recording medium has fine fibrous irregularities, and the nonaqueous solvent penetrates and stays in the irregularities, whereby the diffusion of light is suppressed, and the surface density of the printed matter appears to be high. This phenomenon is referred to as breakthrough. On the other hand, when the penetration phenomenon becomes excessive, the strike-through of the printed matter is observed to be increased.

From the viewpoint of strike-through, the surface density and strike-through of the printed matter are opposite effects, but by ejecting the 1 st ink and the 2 nd ink onto the recording medium, the two effects of the surface density and strike-through of the printed matter can be exhibited in a balanced manner.

(ink set)

The ink set includes the 1 st ink and the 2 nd ink.

The 1 st ink preferably contains a coloring material and a non-aqueous solvent, and the non-aqueous solvent contains a fatty acid ester having a side chain of 4 or more carbon atoms and having 20 or more carbon atoms in 1 molecule.

The ink 2 preferably contains a coloring material and a non-aqueous solvent, and has a 20% distillation temperature of 300 ℃ or lower.

In addition, as a printing method according to an embodiment, there is provided a printing method of performing printing using the above-described oil-based inkjet ink set, in which one of the 1 st ink and the 2 nd ink is ejected onto a recording medium, and then the other ink is ejected to overlap a printing region of the one ink.

The 20% distillation temperature of the ink is: in a thermal analysis (TG) apparatus, a temperature at which the mass reduction rate of the ink population when the temperature of the ink is raised from 23 ℃ to 500 ℃ at 15 ℃/minute is set to be 20% of the mass reduction rate of the ink population when 100%.

The 1 st ink and the 2 nd ink are preferably printed so as to overlap each other on the recording medium. By superimposing the 1 st ink and the 2 nd ink on the recording medium, the solvent of each ink acts on the recording medium, whereby the transparent folder can be further prevented from being deformed, and the surface density and the strike-through can be further improved. It is preferable that the printing is performed so that the other ink overlaps a part or the whole of the printing region of one of the 1 st ink and the 2 nd ink.

The ejection order of the 1 st ink and the 2 nd ink is not particularly limited, and the 2 nd ink may be ejected after the 1 st ink, or may be in the reverse order.

The 1 st ink and the 2 nd ink may be each independently a black ink or a color ink.

At least one of the 1 st ink and the 2 nd ink is preferably a black ink. Further, it is preferable that one of the 1 st ink and the 2 nd ink is a black ink and the other is a color ink. Further, it is preferable that the 1 st ink is a black ink and the 2 nd ink is a color ink.

As the color ink, yellow ink, magenta ink, cyan ink, and the like can be cited. When a black ink and a color ink are used in combination, the color ink is preferably a cyan ink in order that the surface density of black can be further increased.

The 1 st ink and the 2 nd ink are independently discharged at an amount of preferably 2 to 50pl, more preferably 5 to 40 pl. The ejection amount of the 1 st ink is preferably larger than the ejection amount of the 2 nd ink. In particular, when the 1 st ink is a black ink and the 2 nd ink is a color ink, the ejection amount of the 1 st ink is preferably larger than the ejection amount of the 2 nd ink.

For example, in order to print the 1 st ink and the 2 nd ink in a superimposed manner and further increase the surface density of the composite black, the 1 st ink is preferably a black ink and the 2 nd ink is preferably a color ink. In this case, since the ejection amount of the 1 st ink as the black ink is large, the surface density of the printed matter can be further increased while preventing the transparent folder from being deformed by the action of the fatty acid ester E of the 1 st ink. Further, the 2 nd ink as the color ink suppresses the strike-through phenomenon, and thereby it is possible to prevent the printed matter from being strikethrough in a well-balanced manner.

The 1 st ink and the 2 nd ink can be used to produce a printed matter by ejecting one ink on a recording medium and then ejecting the other ink.

The 1 st ink and the 2 nd ink can be preferably used for a line inkjet printer. A line inkjet printer is a system that includes a line inkjet head and performs printing by conveying a recording medium in a sub-scanning direction orthogonal to a main scanning direction, which is a nozzle arrangement direction. By arranging a plurality of line heads in the transport direction of the recording medium, and filling the 1 st ink in one line head and the 2 nd ink in the other line head, it is possible to perform printing by continuously ejecting the 1 st ink and the 2 nd ink onto the recording medium while transporting the recording medium 1 time.

The ink set may contain 1 or 2 or more types of the 1 st ink, and may also contain 1 or 2 or more types of the 2 nd ink. When the 1 st ink contains 2 or more kinds of inks, the inks may be the same color as each other or different colors from each other. The same applies to the 2 nd ink.

Further, the ink set may contain other inks in addition to the 1 st ink and the 2 nd ink. For example, a composite black image may be formed using the 1 st ink and the 2 nd ink, and a color image may be formed using another ink.

(1 st ink)

The 1 st ink preferably contains a coloring material and a non-aqueous solvent, and the non-aqueous solvent contains a fatty acid ester (fatty acid ester E) having a side chain of 4 or more carbon atoms and having 20 or more carbon atoms in 1 molecule.

The 1 st ink may contain a coloring material. As the coloring material, a pigment, a dye, or a combination of these may be used.

As the pigment, organic pigments such as azo pigments, phthalocyanine pigments, polycyclic pigments, dye lake pigments, and the like; and inorganic pigments such as carbon black and metal oxides. As the azo pigment, there can be mentioned: soluble azo lake pigments, insoluble azo pigments, condensed azo pigments, and the like. As the phthalocyanine pigment, there can be mentioned: metal phthalocyanine pigments such as copper phthalocyanine pigments and metal-free phthalocyanine pigments. As polycyclic pigments, mention may be made of: quinacridone pigments, perylene pigments, perinone pigments, isoindoline pigments, isoindolinone pigments, dioxazine pigments, thioindigo pigments, anthraquinone pigments, quinophthalone pigments, metal complex pigments, and pyrrolopyrrole Diketones (DPP). Examples of carbon black include: furnace black, lamp black, acetylene black, channel black, and the like. As the metal oxide, there can be mentioned: titanium oxide, zinc oxide, and the like. These pigments may be used alone or in combination of two or more.

The average particle diameter of the pigment is preferably 300nm or less, more preferably 200nm or less, and still more preferably 150nm or less, from the viewpoint of ejection stability and storage stability.

The pigment is usually 0.01 to 20% by mass relative to the total amount of the ink, and preferably 1 to 15% by mass from the viewpoint of print density and ink viscosity.

In order to stably disperse the pigment in the ink, a pigment dispersant may be used together with the pigment.

As the pigment dispersant, for example: hydroxyl-containing carboxylic acid esters, salts of long-chain polyaminoamides with high-molecular-weight acid esters, salts of high-molecular-weight polycarboxylic acids, salts of long-chain polyaminoamides with polar acid esters, high-molecular-weight unsaturated acid esters, copolymers of vinylpyrrolidone and long-chain olefins, modified polyurethanes, modified polyacrylates, polyether ester type anionic active agents, polyoxyethylene alkyl phosphate esters, polyester polyamines, and the like.

Examples of commercially available products of pigment dispersants include: "antaron V216 (vinylpyrrolidone-hexadecene copolymer), V220 (vinylpyrrolidone-eicosene copolymer)" (both trade names) manufactured by ISP Japan ltd; solsperse 13940 (polyesteramine series), 16000, 17000, 18000 (fatty acid amine series), 11200, 24000, 28000 (all trade names) manufactured by The Lubrizol Corporation; "Efka 400, 401, 402, 403, 450, 451, 453 (modified polyacrylate), 46, 47, 48, 49, 4010, 4055 (modified polyurethane)" (trade name, all) manufactured by BASF Japan ltd.; "Disparlon KS-860 and KS-873N4 (amine salt of polyester)" manufactured by Nanguo Kabushiki Kaisha (trade name); "Discol 202, 206, OA-202, OA-600 (Multi-chain Polymer nonionic system)" manufactured by first Industrial pharmaceutical Co., Ltd. (trade name); DISPERBYK-2155, BYK-9076, 9077 (trade names) manufactured by BYK-Chemie Japan K.K.; "HypermerKD 2, KD3, KD11, KD 12" (trade names) manufactured by Croda Japan K.K, and the like.

The pigment dispersant is sufficient as long as it is an amount that can sufficiently disperse the pigment in the ink, and can be appropriately set. For example, the pigment dispersant may be added to the pigment 1 in a mass ratio of 0.1 to 5, preferably 0.1 to 1. The pigment dispersant may be added in an amount of 0.01 to 15% by mass, preferably 0.1 to 10% by mass, based on the total amount of the ink.

As the dye, a dye generally used in the art may be arbitrarily used. In the oil-based ink, an oil-soluble dye is preferably used as the dye in order to exhibit affinity for a non-aqueous solvent of the ink and to improve storage stability.

As the oil-soluble dye, there can be mentioned: azo dyes, metal complex salt dyes, naphthol dyes, anthraquinone dyes, indigo dyes, carbonium dyes, quinonimine dyes, xanthene dyes, cyanine dyes, quinoline dyes, nitro dyes, nitroso dyes, benzoquinone dyes, naphthoquinone dyes, phthalocyanine dyes, metal phthalocyanine dyes, and the like. These may be used alone as , or a plurality of them may be used in combination.

The dye is usually 0.01 to 20% by mass relative to the total amount of the ink, and preferably 1 to 15% by mass from the viewpoint of print density and ink viscosity.

The nonaqueous solvent may contain a fatty acid ester (fatty acid ester E) having a side chain of 4 or more carbon atoms and 20 or more carbon atoms in 1 molecule.

One example of the fatty acid ester E includes a compound represented by the following general formula (1).

R¹-COO-R²General formula (1)

In the general formula (1), R¹And R²Each independently is alkyl, R¹And R²The alkyl group of at least one of the above groups is a branched alkyl group having a side chain having 4 or more carbon atoms.

May be R¹And R²One of them is straight-chain alkyl, R¹And R²The other of which is a branched alkyl group. In addition, R may be¹And R²Both are branched alkyl groups.

Herein, R is¹And R²Respectively main chain ofA carbon chain having the largest number of carbon atoms from the number of carbon atoms bonded to the ester bond portion "-COO-". Will be derived from the R¹And R²The carbon chain branched from the main chain of (2) is a side chain. At R¹And/or R²When the side chain is present, each side chain may be linear or branched.

In addition, when R is¹And R²Wherein when a plurality of carbon chains each having the largest carbon number are present from the carbon number bonded to the ester bond, the carbon chain having the largest carbon number is the main chain.

In addition, when R is¹And R²Wherein a plurality of carbon chains each having the largest number of carbon atoms from the number of carbon atoms bonded to the ester bond are present, and the number of carbon atoms of the side chains included in the plurality of carbon chains is the same, and the main chain is the one having the smallest number of side chains.

In the fatty acid ester E, the number of carbon atoms in 1 side chain is preferably 4 to 12, more preferably 4 to 10, and still more preferably 4 to 8.

The 1 side chain may be a straight chain alkyl group, or a branched alkyl group further branched to have a side chain. In order to make the carbon chain of the side chain, and thus the fatty acid ester E, larger, the side chain bonded to the main chain of the fatty acid ester E is preferably a straight-chain alkyl group.

The fatty acid ester E may have 1 or 2 or more side chains in 1 molecule.

When the fatty acid ester E contains 2 or more side chains, at least 1 side chain may have 4 or more carbon atoms, and the remaining side chains may contain 3 or less carbon atoms.

When the fatty acid ester E contains 2 or more side chains, the total number of carbon atoms of the side chains in 1 molecule is preferably 5 to 20, and more preferably 6 to 12.

In the fatty acid ester E, examples of the side chain having 4 or more carbon atoms include: n-butyl, isobutyl, t-butyl, pentyl, hexyl, heptyl, octyl, isooctyl, nonyl, decyl, dodecyl and the like.

N-butyl, hexyl, octyl are preferred.

In the general formula (1), R¹When having a side chain of 4 or more carbon atoms, R¹The number of carbon atoms of the main chain of (2) is preferably 6 or more, more preferably 7 or more.

In this case, R¹The number of carbon atoms of the main chain of (2) is preferably 16 or less, more preferably 12 or less.

R¹When having a side chain of 4 or more carbon atoms, R¹The total number of carbon atoms of (A) is preferably 9 to 30, more preferably 10 to 24, and still more preferably 10 to 20.

R²When having a side chain of 4 or more carbon atoms, R²The number of carbon atoms of the main chain of (2), R²The total number of carbon atoms of (2) and the above R¹The same applies.

R¹When the side chain is straight or has 3 or less carbon atoms, R¹The total number of carbon atoms of (A) is preferably 1 to 30, more preferably 6 to 20, and still more preferably 8 to 18.

R²When the side chain is straight or has 3 or less carbon atoms, R²The total number of carbon atoms of (2) and the above R¹The same applies.

R¹And R²The number of carbons of the side chain and the number of carbons of the main chain of (b) are adjusted depending on the length of the main chain, the number of carbons of the side chain, and the number of carbons of the fatty acid ester E as a whole.

The number of carbon atoms in 1 molecule of the fatty acid ester E is preferably 20 or more, and more preferably 21 or more. Thus, the fatty acid ester E has low volatility, and the fatty acid ester E has a side chain of an appropriate length and becomes bulky, and the absorption of the ink component into the transparent folder can be further suppressed. In addition, bulky fatty acid esters have low surface tension and thus can be penetrated to further increase the surface concentration.

The number of carbon atoms in 1 molecule of the fatty acid ester E is preferably 40 or less, more preferably 30 or less, and still more preferably 28 or less. Since the fatty acid ester E may have a high viscosity when it has a high carbon number, the ink can have a low viscosity and the ejection performance can be further improved by setting the carbon number of the fatty acid ester E in this range.

Specific examples of the fatty acid ester E include: 2-octyldodecyl neopentanoate, 2-hexyldecyl hexanoate, 2-hexyldecyl heptanoate, 2-butyloctyl octanoate, 1-hexyloctyl octanoate, 2-hexyldecyl 2-ethylhexanoate, 2-butyloctyl nonanoate, 1-hexyloctyl nonanoate, 1-butylhexyl decanoate, 2-butyloctyl decanoate, 2-hexyldecyl laurate, 2-octyldodecyl decanoate, octyl 2-butyloctanoate, 2-ethylhexyl 2-butyloctanoate, nonyl 2-butyloctanoate, decyl 2-butyloctanoate, 1-butylhexyl 2-butyloctanoate, 2-hexyldecyl myristate, hexyl 2-hexyldecanoate, and the like.

These may be used alone, or two or more kinds may be used in combination.

The fatty acid ester E can be produced by the following method, but is not limited to this method.

The fatty acid ester E can be obtained by reacting a fatty acid with an alcohol. At least one of the fatty acid and the alcohol as the raw material is a raw material having a side chain having 4 or more carbon atoms.

In order to introduce a side chain to the alcohol moiety of the fatty acid ester E, a secondary alcohol having a hydroxyl group at a position of 9 or more carbon atoms and 5 or more carbon atoms may be used.

The reaction temperature can be adjusted within the range of 80-230 ℃ according to the types of fatty acid and alcohol. The reaction time can be adjusted within the range of 1-48 hours according to the types of fatty acid and alcohol and the usage amount of raw materials. It is preferable to remove the water produced during the esterification reaction.

The fatty acid and alcohol are preferably present in a molar ratio of 1: 1, and (c).

In the reaction, a catalyst such as concentrated sulfuric acid, p-toluenesulfonic acid, methanesulfonic acid or the like may be used in an appropriate amount.

Examples of the fatty acid having a side chain of 4 or more carbon atoms as a raw material include: 2-butyloctanoic acid, 2-hexyldecanoic acid, 2-octyldodecanoic acid, and the like.

Examples of the raw material straight-chain fatty acid or fatty acid having a side chain of 3 or less carbon atoms include: acetic acid, butyric acid, valeric acid, pivalic acid, caproic acid, enanthic acid, caprylic acid, 2-ethylhexanoic acid, pelargonic acid, capric acid, undecanoic acid, dodecanoic acid, tetradecanoic acid, and the like.

Examples of the alcohol having a side chain of 4 or more carbon atoms as a raw material include: 2-butyl-1-octanol, 2-hexyl-1-decanol, 2-octyl-1-dodecanol, and the like.

Examples of the secondary alcohol having a hydroxyl group at 5 or more as a raw material include: 5-decanol, 7-tetradecanol, and the like.

Examples of the raw material alcohol include a linear alcohol or an alcohol having a side chain of 3 or less carbon atoms: 1-butanol, 1-pentanol, 1-hexanol, 1-heptanol, 1-octanol, 2-ethylhexanol, 1-nonanol, 1-decanol, 1-undecanol, 1-dodecanol, and the like.

In the ink 1, the amount of the fatty acid ester E is preferably 10 to 100% by mass based on the total amount of the nonaqueous solvent.

The proportion is preferably 10% by mass or more, more preferably 40% by mass or more, and further preferably 50% by mass or more. Further, the proportion is preferably 60% by mass or more, more preferably 80% by mass or more, and still more preferably 90% by mass or more, so as not to inhibit the effect of the present invention by adding another nonaqueous solvent.

In the ink 1, the fatty acid ester E is preferably incorporated in an amount of 5 to 98% by mass, more preferably 10 to 90% by mass, based on the total amount of the ink.

The ink 1 may contain other nonaqueous solvents in addition to the fatty acid ester E.

As the other nonaqueous solvent, either a nonpolar organic solvent or a polar organic solvent can be used. In one embodiment, a non-water-soluble organic solvent that is not uniformly mixed with an equal volume of water at 1 atmosphere and 20 ℃ is preferably used as the non-aqueous solvent.

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 nonaqueous solvents such as paraffin type, isoparaffin type, and naphthene type solvents. Preferred examples of commercially available products include: solvent number 0, 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, CaCus Normal Paraffin NP, CaCus Normal Paraffin SHNP, Isosol 300, Isosol 400, Teclean N-16, Teclean N-20, Teclean N-22, AF solvent number 4, AF solvent number 5, AF solvent number 6, AF solvent number 7, Naphtesol 160, Naphtesol 200, Naphtesol 220 (all XTG Nippon & Engy Corporation); isopar G, Isopar H, Isopar L, Isopar M, Exxsol D40, Exxsol D60, Exxsol D80, Exxsol D95, Exxsol D110, Exxsol D130 (all manufactured by Exxon Mobil Corporation); MORESCO WHIT P-40, MORESCO WHIT P-60, MORESCO WHIT P-70, MORESCO WHIT P-80, MORESCO WHIT P-100, MORESCO WHIT P-120, MORESCO WHIT P-150, MORESCO WHIT P-200, MORESCO WHIT P-260, MORESCO WHIT P-350P (all manufactured by MORESCO, Inc.), and the like.

As the aromatic hydrocarbon solvent, Grade alkenone L, Grade alkenone 200P (all manufactured by JXTG Nippon Oil & Energy Corporation), Solvesso 100, Solvesso 150, Solvesso 200ND (all manufactured by Exxon Mobile Corporation) and the like are preferably listed.

The initial distillation boiling point of the petroleum-based hydrocarbon solvent is preferably 100 ℃ or higher, more preferably 150 ℃ or higher, and still more preferably 200 ℃ or higher. The initial distillation point can be measured according to JIS K0066 "method for testing chemical products by distillation".

The polar organic solvent preferably includes a fatty acid ester-based solvent other than the fatty acid ester E, a higher alcohol-based solvent, a higher fatty acid-based solvent, and the like.

Examples of other fatty acid ester solvents include: a solvent having a linear alkyl group such as dodecyl caproate, methyl laurate, hexyl palmitate, hexyl caproate, methyl oleate, ethyl oleate, butyl oleate, hexyl oleate, methyl linoleate, ethyl linoleate, butyl stearate, hexyl stearate, soybean oil methyl ester, and tall oil methyl ester, the total number of carbon atoms of which is 12 or more, preferably 16 to 30; and a solvent having a side chain of 3 or less carbon atoms in 1 molecule, such as 2-ethylhexyl ethylhexanoate, 2-ethylhexyl stearate, isodecyl isononanoate, isotridecyl isononanoate, isopropyl isostearate, isononyl isononanoate, isopropyl laurate, isopropyl myristate, isopropyl palmitate, isooctyl palmitate, isopropyl oleate, isobutyl linoleate, isooctyl stearate, soybean oil isobutyl ester, tall oil isobutyl ester, and isostearyl palmitate (having 34 carbon atoms).

The higher alcohol solvent is preferably a higher alcohol solvent having 6 or more, preferably 12 to 20 carbon atoms in 1 molecule, and examples thereof include: primary alcohols such as 1-octadecanol, isomyristyl alcohol, isopalmitol, isostearyl alcohol, oleyl alcohol, isoeicosyl alcohol, and decyltetradecyl alcohol; and secondary alcohols such as 2-ethyl-1, 3-hexanediol.

Examples of the higher fatty acid solvent include higher fatty acid solvents having 12 or more, preferably 14 to 20 carbon atoms in 1 molecule, such as lauric acid, isomyristic acid, palmitic acid, isopalmitic acid, α -linolenic acid, linoleic acid, oleic acid, and isostearic acid.

Further, as other non-aqueous solvent, silicone oil can be cited.

Examples of the silicone oil include chain silicone oils, cyclic silicone oils, modified silicone oils, and the like.

The chain silicone oil is preferably a chain polysiloxane having a silicon number of 2 to 30. The number of silicon in the chain silicone oil is more preferably 2 to 20, and still more preferably 3 to 10.

Examples of the chain silicone oil include: linear dimethylsilicone fluids such as tetradecyl hexasiloxane, hexadecyl heptamethyl siloxane, and eicosyldimethyl decasiloxane; and branched dimethylsilicone oils such as methyltris (trimethylsiloxy) silane and tetrakis (trimethylsiloxy) silane.

The cyclic silicone oil is preferably a cyclic polysiloxane having a silicon number of 5 to 9, and cyclic dimethylsilicone oil such as decamethylcyclopentasiloxane, dodecamethylcyclohexasiloxane, hexadecylcyclooctasiloxane, and octadecylcyclononasiloxane can be preferably used.

As the modified silicone oil, silicone oil in which various organic groups are introduced into a part of silicon atoms of chain or cyclic dimethylsilicone oil can be used. As the modified silicone oil, it is preferable that all silicon atoms are bonded to only either carbon atoms or oxygen atoms of siloxane bonds. As the modified silicone oil, a non-reactive silicone oil is preferable. The modified silicone oil preferably contains constituent atoms including only silicon atom, carbon atom, oxygen atom, and hydrogen atom. As the modified silicone oil, for example, a compound in which at least 1 methyl group contained in a chain or cyclic dimethylsilicone oil is substituted with 1 or more selected from the group consisting of an alkyl group, a group containing a carboxylic ester bond, a group containing an aromatic ring, and a group containing an ether bond can be used.

Further, as the modified silicone oil, for example, a compound in which silicon atoms of another chain or cyclic dimethylsilicone oil are further bonded to at least 1 silicon atom contained in the chain or cyclic dimethylsilicone oil through an alkylene group can be used. In this case, at least 1 methyl group contained in the chain or cyclic dimethylsilicone oil bonded via an alkylene group may be substituted by 1 or more selected from the group consisting of an alkyl group, a group containing a carboxylic ester bond, a group containing an aromatic ring, and a group containing an ether bond.

Examples of the modified silicone include: aryl-modified silicone oils such as alkyl-modified silicone oils, phenyl-modified silicone oils, and aralkyl-modified silicone oils; carboxylate modified silicone oil; an alkylene-modified silicone oil; polyether-modified silicone oil, etc.

The modified silicone oil preferably has a silicon number of 2 to 20, more preferably 2 to 10, even more preferably 2 to 6, and even more preferably 3 to 6.

The boiling point of the polar organic solvent such as a fatty acid ester solvent, a higher alcohol solvent, or a higher fatty acid solvent, or the silicone oil is preferably 150 ℃ or higher, more preferably 200 ℃ or higher, and still more preferably 250 ℃ or higher. The non-aqueous solvent having a boiling point of 250 ℃ or higher also includes a non-aqueous solvent not having a boiling point.

These nonaqueous solvents may be used alone, or 2 or more kinds may be used in combination as long as they form a single phase.

When other non-aqueous solvent is added to the 1 st ink, it is preferable to use a non-aqueous solvent having a boiling point or initial boiling point of more than 300 ℃.

(ink 2 nd)

The ink 2 preferably contains a coloring material and a non-aqueous solvent, and has a 20% distillation temperature of 300 ℃ or lower.

Unless otherwise specified, the same components as those of the first ink 1 can be used for various components such as the coloring material and the nonaqueous solvent in the second ink 2, and therefore, the description thereof is omitted.

The non-aqueous solvent of ink No. 2 can be used by appropriately selecting 1 or 2 or more from the non-aqueous solvents described in ink No. 1 above.

For example, the 20% distillation temperature of the 2 nd ink can be set to 300 ℃ or lower by appropriately selecting the kind and amount of the non-aqueous solvent, the combination of 2 or more types, the blending ratio, and the like.

From the viewpoint of making the 20% distillation temperature of the 2 nd ink 300 ℃ or lower, the 2 nd ink preferably contains at least 1 kind of non-aqueous solvent having a boiling point or initial boiling point of 300 ℃ or lower.

Among petroleum hydrocarbon solvents, there are mixed solvents containing a plurality of solvent components. The mixed solvent may be used in a temperature range from the initial boiling point to the dry point, and a solvent having a dry point of 300 ℃ or lower even if it exceeds 300 ℃ and the initial boiling point may be preferably used. Further, it is more preferable to use a solvent having both an initial boiling point and a dry point of 300 ℃ or lower.

Since the polar solvent including the fatty acid ester solvent, the alcohol solvent, and the higher fatty acid solvent, and the silicone oil are single components, the initial boiling point and the boiling point are the same, and a solvent having a boiling point of 300 ℃ or lower can be preferably used. In the case of a mixed solvent in which 2 or more solvents cannot be separated and supplied, the boiling point may be in a range. In this case, the upper limit of the boiling point range is preferably 300 ℃ or less.

The ratio of the amount of the non-aqueous solvent having a boiling point or initial boiling point of 300 ℃ or lower to the total amount of the non-aqueous solvent in the second ink is preferably 20% by mass or more, more preferably 30% by mass or more, and still more preferably 50% by mass or more. The 2 nd ink can volatilize the solvent from the surface of the recording medium by increasing the amount of the highly volatile solvent to be blended, suppress the strike-through phenomenon, and prevent the strike-through of the printed matter.

Further, from the viewpoint of limiting the amount of the low-volatility solvent to be blended, the ratio of the second ink 2 is preferably 80% by mass or more, more preferably 90% by mass or more, and may be 100% by mass.

The non-aqueous solvent having a boiling point or initial boiling point of 300 ℃ or lower is preferably 20 to 98% by mass, more preferably 30 to 95% by mass, and still more preferably 50 to 90% by mass of the total amount of the ink 2.

The fatty acid ester (fatty acid ester E) having a side chain of 4 or more carbon atoms and 20 or more carbon atoms in 1 molecule is a solvent having a high boiling point, and therefore, it is preferable to limit the amount of the fatty acid ester in the second ink 2.

In the second ink 2, the amount of the fatty acid ester E is preferably less than 80% by mass, more preferably 60% by mass or less, even more preferably 50% by mass or less, and even more preferably less than 10% by mass, based on the total amount of the nonaqueous solvent. The 2 nd ink may contain no fatty acid ester E.

In the ink 2, the fatty acid ester E is preferably incorporated in an amount of 0 to 80% by mass, more preferably 0 to 60% by mass, even more preferably 0 to 50% by mass, and even more preferably less than 10% by mass, based on the total amount of the ink.

The solvent of the 2 nd ink is highly volatile compared to the solvent of the 1 st ink, so that when the 1 st ink and the 2 nd ink are overprinted, it is possible to prevent the transparent folder from being deformed and improve the surface density by the 1 st ink, and to further prevent strike-through of the printed matter since the solvent of the 2 nd ink is easily volatilized to suppress the strike-through phenomenon.

In the ink set, it is preferable that the ratio of the amount of the fatty acid ester E contained in the 1 st ink to the total amount of the non-aqueous solvent contained in the 1 st ink is larger than the ratio of the amount of the fatty acid ester E contained in the 2 nd ink to the total amount of the non-aqueous solvent contained in the 2 nd ink.

The fatty acid ester E has an effect of improving the deformation and surface concentration of the transparent folder, and has a problem that the penetration phenomenon becomes excessive due to a high carbon number and a low surface tension, and it is difficult to suppress the strike-through. By limiting the amount of the fatty acid ester E blended in the 2 nd ink, the strike-through phenomenon can be suppressed in a well-balanced manner, and the strike-through of the printed matter can be further prevented.

The 1 st ink and the 2 nd ink may contain various additives as long as the effects of the present invention are not impaired, in addition to the above components. As the additive, a nozzle clogging preventive agent, an antioxidant, a conductivity modifier, a viscosity modifier, a surface tension modifier, an oxygen absorber, and the like can be added as appropriate. The kind of them is not particularly limited, and those used in this field can be used.

The 1 st ink and the 2 nd ink can be prepared by mixing respective components including a coloring material and a non-aqueous solvent. The ink can be preferably prepared by mixing and stirring the components at once or in portions. Specifically, the ink can be prepared by dispersing all the components in a dispersing machine such as a bead mill all at once or in a batch and passing the dispersion through a filter such as a membrane filter as desired.

The 1 st ink and the 2 nd ink can be preferably provided as oil-based inkjet inks.

The viscosity of the oil-based ink-jet ink varies depending on the nozzle diameter of an ejection head of an ink-jet recording system, the ejection environment, and the like, and is preferably 5 to 30mPa · s, more preferably 5 to 15mPa · s, and still more preferably 8 to 13mPa · s at 23 ℃.

The printing method using the oil-based inkjet ink is not particularly limited, and may be any of a piezoelectric method, an electrostatic method, a thermal method, and the like. When an inkjet recording apparatus is used, it is preferable to eject ink according to one embodiment from an inkjet head based on a digital signal and attach the ejected ink droplets to a recording medium.

In one embodiment, the recording medium is not particularly limited, and the following may be used: printing paper such as plain paper, coated paper, special paper and the like; cloth, inorganic sheet, film, OHP sheet, etc.; and pressure-sensitive adhesive sheets comprising these as a base material and an adhesive layer provided on the back surface thereof. Among these, from the viewpoint of ink permeability, printing paper such as plain paper and coated paper can be preferably used.

Here, plain paper is paper on which an ink-receiving layer, a thin film layer, and the like are not formed on ordinary paper. Examples of plain paper include high-quality paper, medium paper, PPC paper, wood pulp paper, and recycled paper. In plain paper, paper fibers having a thickness of several μm to several tens of μm form voids of several tens to several hundreds of μm, and thus, the paper is easily penetrated by ink.

As the coated paper, inkjet coated paper such as matte paper, glossy paper, and semi-glossy paper, so-called coated printing paper, can be preferably used. Here, the coated printing paper is a printing paper in which a coating layer is provided on the surface of a printing paper, a high-quality paper, a medium paper, or the like, which has been used in relief printing, offset printing, gravure printing, or the like, with a coating material containing an inorganic pigment such as clay or calcium carbonate and a binder such as starch. Coated printing paper is classified into micro-coated paper, high quality light coated paper, medium light coated paper, high quality coated paper, medium coated paper, high gloss printing paper, and the like according to the coating amount of the coating material and the coating method.

[ examples ]

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

Synthesis of fatty acid ester "

The synthesis formula of the synthesized fatty acid ester is shown in table 1.

Fatty acid and alcohol were added to a four-necked flask according to the formulation shown in table 1, and mixed and stirred to obtain a uniform solution. A Dean-Stark apparatus was installed in the four-necked flask so that water was removed when the added raw materials reacted to generate water. To the four-necked flask to which the homogeneous solution was added, an appropriate amount of sulfuric acid was further added as a catalyst, and the whole system was heated. The heating temperature is set to 80 to 230 ℃ depending on the types of fatty acid and alcohol. The heating reaction time is set to 1 to 48 hours. After the reaction, the resulting solution was distilled under reduced pressure to remove unreacted raw materials and impurities, thereby obtaining a fatty acid ester.

Fatty acids and alcohols in a molar ratio of 1: 1, and mixing.

The fatty acid and alcohol are available from Tokyo chemical industry Co., Ltd. and SIGMA-ALDRICH.

The following commercially available fatty acid esters were used.

2-hexyldecyl 2-ethylhexanoate: "ICEH" manufactured by higher alcohols industries, Ltd.

2-octyldodecyl neopentanoate: the solar chemical company "Elefac I-205".

Myristic acid 2-hexyldecyl ester: "ICM-R" manufactured by higher alcohols industries, Ltd.

Hexyl caproate: tokyo chemical industry Co.

In table 2, the fatty acid ester includes 1 molecule carbon number, 1 molecule carbon number of the side chain having the largest carbon number (the largest carbon number of the side chain), and R¹-COO-R²R in the structural formula¹Carbon number of (2), side chain number, carbon number of each side chain, R²The number of side chains, and the number of carbon atoms of each side chain.

[ Table 1]

[ Table 1] Synthesis of fatty acid esters

Fatty acid esters	Name of fatty acid	Name of alcohol
			2-Butyloctyl octanoate	Octanoic acid	2-butyl-1-octanol
2-butyl Nonoxinyl octanoate	2-Butyloctanoic acid	1-nonanol
			Decanoic acid 2-butyl octyl ester	Capric acid	2-butyl-1-octanol
2-Butyloctanoic acid 1-butylhexyl ester	2-Butyloctanoic acid	5-decanol
			1-hexyl octyl nonanoate	Pelargonic acid	7-tetradecanol
Lauric acid 2-hexyldecyl ester	Lauric acid (dodecanoic acid)	2-hexyl-1-decanol
			Dodecyl 2-ethylhexanoate	2-ethyl hexanoic acid	1-dodecanol
Dodecyl caproate	Hexanoic acid	1-dodecanol

[ Table 2] details of fatty acid esters

Preparation of ink "

The formulations of the 1 st ink and the 2 nd ink are shown in tables 3 and 4. The fatty acid ester has the number of carbons (C number) in 1 molecule and the number of carbons (maximum C number of side chains) in the side chain having the largest number of carbons in 1 molecule shown in the table.

The pigment, the pigment dispersant and the solvent were mixed in the amounts shown in the tables, and the pigment was sufficiently dispersed with a bead Mill "Dyno Mill KDL-A" (manufactured by SHINMAU ENTERPRISES CORPORATION) for a retention time of 15 minutes. Next, coarse particles were removed by a membrane filter to obtain an ink.

The ratio (% by mass) of the fatty acid ester E to the total amount of the solvent is shown in table 1. With respect to ink 2, the 20% distillation temperature (. degree. C.) is shown in the table.

The 20% distillation temperature of the 2 nd ink was determined from the temperature at which the mass reduction rate of the entire ink when the temperature of the ink was raised from 23 ℃ to 500 ℃ at 15 ℃/min was set to 100% in a thermal analysis (TG) apparatus, and the mass reduction rate of the entire ink was reduced by 20%.

As a thermal analysis device, a THERMO PLUS EVO2 differential type differential thermal balance TG8121 (RIGAKU, K.K.) was used, and as a sample cell, an aluminum liquid sample plate and a sample cover (Item No.8580, manufactured by RIGAKU, K.K.) were used. The measurement samples were prepared as follows: a sample cover was provided with a pinhole (measured as phi 150 to 160 μm) using a fine needle, and about 10mg of a sample was placed in a sample pan, and pressure-bonded and sealed with a sample seal (Item No.8395D1, RIGAKU, Co., Ltd.).

TABLE 3 formulation of ink No. 1

TABLE 4 formulation of ink No. 2

[ Table 5] ink set and evaluation results

Other ingredients are as follows.

(pigment)

Carbon black 1: "SUNBLACK X25" manufactured by Asahi Carbon corporation.

Carbon black 2: the Evonik Japan K.K. "Special Black 350".

Copper phthalocyanine blue: a Blue pigment, FASTOGEN Blue LA5380 available from DIC.

Soluble azo lake pigment: magenta pigment, "SYMULER BRILLIANT CARMINE 6B 401" available from DIC K.K.

Insoluble azo pigment: a YELLOW pigment, and SYMULER FAST YELLOW 4GO, manufactured by DIC.

(pigment dispersant)

Solsperse 18000: 100% by mass of The effective ingredient, manufactured by The Lubrizol Corporation.

BYK-9076: BYK-Chemie Japan K.K., 100% by mass of the active ingredient.

DISPERBYK-2155: BYK-Chemie Japan K.K., 100% by mass of the active ingredient.

(other solvents)

1-octadecanol: alcohol solvent, Tokyo chemical industry Co., Ltd.

2-ethyl-1, 3-hexanediol: alcohol solvent, Tokyo chemical industry Co., Ltd.

Dimethyl silicone: silicone oil, "KF-96L-2 cs" available from shin-Etsu chemical industries, Ltd.

Exxsol D110: petroleum hydrocarbon solvent, manufactured by Exxon Mobil Corporation.

"evaluation"

The above-described 1 st ink and 2 nd ink were prepared as ink sets in accordance with the combinations shown in table 5. The evaluation was performed by the following method using this ink set. The evaluation results are shown in table 5.

(variants of the transparent folder)

In the line inkjet printer "orpis FW 5230" (manufactured by ideal scientific industries, ltd.) 2 kinds of inks were filled in the inkjet cartridge in accordance with the combination of the ink set shown in table 5, and the 1 st ink was discharged to the plain paper "ideal paper sheet outlet" (manufactured by ideal scientific industries, ltd.) and the 2 nd ink was discharged in an overlapping manner, thereby performing single-sided printing of 1 solid image to obtain a printed matter.

The printed matter was sandwiched between PP (polypropylene) transparent folders having a thickness of 0.2mm, and left to stand at room temperature for 1 week. After placement, the transparent folder is placed on a flat surface. When the transparent folder is deformed, the maximum height from the plane is measured as the amount of deformation in a state where the transparent folder is tilted from the plane.

"ORPHIS FW 5230" is a system that performs printing by conveying a sheet in a sub-scanning direction orthogonal to a main scanning direction (nozzle arrangement direction) using a line-type inkjet head.

A: the deformation of the transparent folder is less than 3 cm.

B: the deformation amount of the transparent folder is more than 3cm and less than 5 cm.

C: the deformation amount of the transparent folder is more than 5 cm.

(surface concentration)

A printed matter was obtained in the same manner as the evaluation of the deformation of the transparent folder.

The OD value of the surface of the printed matter was measured using a colorimeter "X-Rite eXact" manufactured by Videojet X-Rite K.K., and the surface concentration of the synthetic black was evaluated according to the following criteria.

A: the surface OD value is 1.12 or more.

B: the surface OD value is 1.07 or more and less than 1.12.

C: the surface OD value is less than 1.07.

(show through)

A printed matter was obtained in the same manner as the evaluation of the deformation of the transparent folder.

The OD value of the back surface of the printed matter and the OD value of the unprinted paper (white paper) were measured using a colorimeter "X-Rite eXact" made by Videojet X-Rite K.K., and the strike-through of the synthetic black color was evaluated from the difference between the OD value of the back surface and the OD value of the white paper according to the following criteria.

A: the difference in OD values is less than 0.05.

B: the difference in OD values is 0.05 or more and less than 0.07.

C: the difference in OD value is 0.07 or more.

As shown in the table, the inks of the respective examples can prevent the transparent folder from being deformed, can increase the surface density of the synthetic black, and can prevent strike-through.

Although detailed, the viscosity of the ink of each example is also suitable.

In examples 1 to 9, various fatty acid esters were used in ink No. 1, and good results were obtained.

As is clear from examples 1 to 9, the carbon number of 1 molecule of the fatty acid ester of the 1 st ink was 21 or more, and the deformation of the transparent folder was further prevented.

From examples 1 to 9, it is clear that the fatty acid ester of the 1 st ink having 23 or less carbon atoms in 1 molecule can further prevent strike-through.

As is clear from example 10, good results were obtained regardless of the types of the pigment and the pigment dispersant of the 1 st ink.

In examples 11 and 12, the same fatty acid ester and other solvents as in example 1 were used in ink No. 1, and good results were obtained. In example 1, the fatty acid ester having a side chain of 4 or more carbon atoms and 20 or more carbon atoms in 1 molecule was contained in a large amount in the 1 st ink, and the surface concentration was high.

In examples 13 and 14, the solvent formulation of the 2 nd ink was changed from that of example 1, and good results were obtained.

In examples 15 and 16, good results were obtained using magenta ink and yellow ink as the 2 nd ink. As compared with example 1, it is preferable to use cyan ink in the 2 nd ink from the viewpoint of the surface density of the synthetic black.

In comparative example 1, the number of carbons in the side chain of the fatty acid ester in the 1 st ink was 2, and the transparent folder was deformed.

In comparative example 2, the number of carbons in 1 molecule of the fatty acid ester in the 1 st ink was 18, the transparent folder was deformed, and the surface concentration was decreased.

In comparative example 3, the 20% distillation temperature of the ink 2 exceeded 300 ℃, and therefore show-through occurred.

In comparative example 4, printing was performed using ink K1 as the 1 st ink and only black ink. Other printing conditions were the same as in example 1. The surface density and the strike-through effect were not sufficiently obtained only by monochrome printing of the black ink K1.

Claims (5)

1. An oil-based inkjet ink set comprising a 1 st oil-based ink and a 2 nd oil-based ink, wherein the 1 st oil-based ink contains a coloring material and a non-aqueous solvent, the non-aqueous solvent contains a fatty acid ester having a side chain of 4 or more carbon atoms and 20 or more carbon atoms in 1 molecule, the 2 nd oil-based ink contains a coloring material and a non-aqueous solvent, and the 20% distillation temperature is 300 ℃ or lower,

the 2 nd oil-based ink contains 20 to 98 mass% of a water-insoluble organic solvent having a boiling point or initial boiling point of 300 ℃ or lower with respect to the total amount of the ink.

2. The oil-based inkjet ink set according to claim 1, wherein the 1 st oil-based ink contains 10% by mass or more of the fatty acid ester having a side chain of 4 or more carbon atoms and having 20 or more carbon atoms in 1 molecule, based on the total amount of the nonaqueous solvent.

3. The oil-based inkjet ink set according to claim 2, wherein the 1 st oil-based ink contains 40% by mass or more of the fatty acid ester having a side chain of 4 or more carbon atoms and having 20 or more carbon atoms in 1 molecule, based on the total amount of the nonaqueous solvent.

4. The oil-based inkjet ink set according to any one of claims 1 to 3, wherein the 1 st oil-based ink is a black ink, and the 2 nd oil-based ink is a color ink.

5. A printing method of performing printing using the oil-based inkjet ink set according to any one of claims 1 to 4, wherein any one of the 1 st oil-based ink and the 2 nd oil-based ink is ejected onto a recording medium, and then the other ink is ejected to overlap a printing region of the one ink.