HK1138867B

HK1138867B - Inkjet ink and printing method using same

Info

Publication number: HK1138867B
Application number: HK10105015.8A
Authority: HK
Inventors: 矶部浩三
Original assignee: 通用株式会社
Priority date: 2004-07-01
Filing date: 2007-12-03
Publication date: 2013-05-16

Description

Inkjet ink and printing method using the same

This application is a divisional application, the application number of its parent application: 200580021980.2, filing date: 2005.6.30, title of the invention: an inkjet ink and a printing method using the same.

Technical Field

The present invention relates to an inkjet ink particularly suitable for printing on a hydrophobic medium such as an offset coated medium, and a method for printing on a hydrophobic medium using the same.

Background

Conventionally, in an inkjet printing method using an aqueous inkjet ink, printing is generally performed on a medium having water absorption properties, such as plain paper such as high-quality paper or special paper designed to have a typical high ink absorption property. However, the surface of a substrate of an offset coating medium suitable for offset printing is coated with a hydrophobic smooth porous coating film, and therefore, the coating is not suitable for printing using conventional aqueous inkjet ink.

Even when printing is performed with an aqueous inkjet ink, since the coating film does not absorb the aqueous inkjet ink, the inkjet ink repels or smears on the surface of the coating film, and sharp printing with sharp edges cannot be performed. Further, since the drying property of printing is poor and the fixing property is insufficient even when the printing is dried, there is a problem that bleeding is easily caused by rubbing. Therefore, in order to perform good printing on offset coated media by an inkjet printing method using an aqueous inkjet ink, development of a new technique is also required.

In order to perform satisfactory printing on an offset coating medium by the inkjet printing method, it is first considered to improve the affinity of the inkjet ink for the hydrophobic coating film, and for this reason, studies have been made on the kind of surfactant, and it has been proposed to add a glycol ether or a wetting agent having compatibility with water and affinity for the hydrophobic coating film. In addition, in order to improve the affinity and the fixing property of the ink-jet ink to the coating film after printing, it has been proposed to add a water-soluble or water-dispersible binder resin (carrier) (for example, see patent documents 1 and 2 below).

In addition, in consideration of using a solvent compatible with water and permeable to a hydrophobic coating film in combination with water, it has been proposed to use an aprotic polar solvent as the solvent (patent document 3).

Patent document 1: japanese patent laid-open No. 2003-206426 (claims, columns 0009 to 0010)

Patent document 2: japanese patent application laid-open No. 2004-510028 (claims, column 0012)

Patent document 3: japanese patent laid-open publication No. 2003-268279 (claims, column 0009)

As described in patent documents 1 and 2, among them, only surfactants, glycol ethers, wetting agents, binder resins, and the like, which are known components in aqueous inkjet inks, have been studied, and the effects are limited, and it is difficult to perform printing on the surface of an offset coating medium better than ever.

On the other hand, since the aprotic polar solvent described in patent document 3 has good permeability to a coating film generally used for an offset printing coating medium, it is expected that separation or blurring of an inkjet ink on the surface of the coating film can be prevented to enable sharp printing with sharp edges, and the drying property of the inkjet ink after printing can be improved by allowing the aprotic polar solvent to be absorbed into the coating film. However, the configuration of the ink jet ink described in patent document 3 is still insufficient in effect even if the ink jet ink contains an aprotic polar solvent, and the like.

Disclosure of Invention

The purpose of the present invention is to provide an aqueous inkjet ink which enables better printing on a hydrophobic medium such as an offset coated medium than ever, and a method for printing on a hydrophobic medium using the same.

The present invention provides an inkjet ink for printing on a hydrophobic medium, characterized by containing a pigment, water, a surfactant, and an aprotic polar solvent having a molecular weight of 40 to 130, and the content ratio of the aprotic polar solvent is 40 to 75% by weight.

The boiling point of the aprotic polar solvent is preferably 150 to 250 ℃. The aprotic polar solvent is preferably at least one selected from the group consisting of 1, 3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, formamide, N-methylformamide, N-dimethylformamide, N-diethylpropionamide, and γ -butyrolactone.

The surfactant preferably has a dynamic contact angle of 20 ° or less at 23 ℃. The surfactant is preferably a silicone surfactant, and the mixing ratio (weight ratio) of the aprotic polar solvent P to the silicone surfactant S is preferably 45/1 to 70/1.

The inkjet ink of the present invention contains a pigment, water, a surfactant, and an aprotic polar solvent having a molecular weight of 40 to 130, and is characterized in that the aprotic polar solvent is contained in an amount of 40 to 75 wt% as the surfactant, and the inkjet ink contains a compound represented by formula (1):

[ solution 1]

[ in the formula, R¹Represents a polyalkylene oxide chain containing at least one of an oxyethylene group and an oxypropylene group, and x represents a number of 1 or more.]The silicone surfactant S₁And formula (2):

[ solution 2]

[ in the formula, R²Represents a polyalkylene oxide chain containing at least one of an oxyethylene group and an oxypropylene group, and y represents a number of 1 or more.]The silicone surfactant S₂And the mixing ratio (weight ratio) of the two organosilicon surfactants is S₁/S₂6/4-4/6. An aprotic polar solvent P and two silicone surfactants S₁+S₂The mixing ratio (weight ratio) of (A) to (B) is preferably P/(S)₁+S₂)＝45/1～70/1。

The invention provides an inkjet ink for printing on a hydrophobic medium, which is characterized by comprising a pigment, water, a surfactant and an aprotic polar solvent with a molecular weight of 40-130, wherein the content ratio of the aprotic polar solvent is 40-75 wt%, and the surfactant is represented by formula (3):

[ solution 3]

C_mF_2m+1COONH₄ (3)

[ in the formula, m represents a number of 1 or more. And the mixing ratio (weight ratio) of the aprotic polar solvent P to the fluorine-based surfactant F is preferably 100/1 to 45/1. Further, the surface of the pigment is preferably modified with a carboxyl group.

The printing method of the present invention includes a step of printing on a hydrophobic medium using the inkjet ink of the present invention and a step of heating the printed hydrophobic medium.

In the inkjet ink described in patent document 3, the aprotic polar solvent is contained in an amount of 5 to 40 wt% based on the total amount of the inkjet ink, but according to the study of the present inventors, in the case of the content of such a degree, the permeability to the hydrophobic surface such as a coating layer of an offset coating medium is increased by containing the aprotic polar solvent, and the effect of improving the printing dryness and the like cannot be sufficiently obtained.

Although it is necessary to contain a larger amount of the aprotic polar solvent in order to improve the permeability into a coating layer or the like, if the aprotic polar solvent having a large molecular weight is contained in an amount of 40 wt% or more based on the total amount of the inkjet ink, the viscosity of the inkjet ink increases, and the ejection stability of the head of the inkjet printer when the ink is ejected from the fine nozzles may deteriorate.

On the other hand, in the present invention, since the aprotic polar solvent described in patent document 3 is selected for use as a type having a molecular weight of 130 or less and the content ratio thereof is limited to 40% by weight or more, the ink-jet ink is improved in permeability to a hydrophobic surface and the drying property of printing and the like are improved more than ever, while suppressing the increase in viscosity of the ink-jet ink and ensuring good ejection stability. Therefore, the inkjet ink of the present invention can perform printing on a hydrophobic medium such as an offset coated medium more favorably than ever before.

In the present invention, the reason why the molecular weight of the aprotic polar solvent is limited to 40 or more is that: when a low molecular weight aprotic polar solvent having a molecular weight of less than 40 is used, the inkjet ink is easily dried, and clogging of the fine nozzles is easily caused. The reason why the content of the aprotic polar solvent is limited to 75% by weight or less is that: when the content ratio exceeds 75% by weight, the viscosity of the inkjet ink increases and the ejection stability when ejected from a fine nozzle decreases even if the molecular weight of the aprotic polar solvent is limited to 130 or less.

In the present invention, the boiling point of the aprotic polar solvent is preferably set to 150 to 250 ℃. If the boiling point of the aprotic polar solvent is less than 150 ℃, the inkjet ink is easily dried and easily clogged at the nozzle or the like, whereas if it exceeds 250 ℃, the inkjet ink is difficult to dry and drying property after printing may be deteriorated. On the other hand, when the boiling point of the aprotic polar solvent is set to 150 to 250 ℃, these problems are avoided, and the hydrophobic medium can be printed more favorably.

Suitable aprotic polar solvents satisfying these conditions include at least one selected from the group consisting of 1, 3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, formamide, N-methylformamide, N-dimethylformamide, N-diethylpropionamide, and γ -butyrolactone. If these aprotic polar solvents are used, not only the various effects listed above can be obtained, but also the dispersion stability of the pigment in the inkjet ink can be improved, although the details thereof are not clear.

The surfactant preferably has a dynamic contact angle of 20 ° or less at 23 ℃. When a surfactant having a dynamic contact angle of more than 20 ° at 23 ℃ is used, the inkjet ink is heated without sufficiently wetting the hydrophobic surface, and thus sharp printing with sharp edges may not be possible.

On the other hand, when a surfactant having a dynamic contact angle of less than 20 ° at 23 ℃ is used, the inkjet ink quickly wets the hydrophobic surface before heating, and thus sharp printing with sharp edges can be performed.

As a surfactant having a dynamic contact angle of 20 ° or less at 23 ℃, the surface tension of the inkjet ink is reduced, and the inkjet ink has an excellent effect of improving the wetting effect on a hydrophobic surface, and does not have a risk of affecting the environment as compared with a pfos (perfluorooctane sulfonate) -based surfactant having the same excellent effect.

The mixing ratio (weight ratio) of the aprotic polar solvent P to the silicone surfactant S having a dynamic contact angle of 20 DEG or less at 23 ℃ is preferably 45/1 to 70/1. When the amount of the silicone surfactant is less than the above range, the silicone surfactant is also excellent in compatibility with the aprotic polar solvent, and therefore the function of the silicone surfactant as a surfactant is impaired, and the effect of improving the wetting effect of the ink-jet ink on a hydrophobic surface may be insufficient.

When the amount of the silicone surfactant is more than this range, the wettability of the ink-jet ink with respect to the hydrophobic surface is too excellent, and the ink-jet ink may bleed before heating, and conversely, sharp printing with sharp edges may not be performed. In addition, a part of the excessive silicone surfactant is dissociated and hydrolyzed to generate a siloxane monomer insoluble in water, and the siloxane monomer is separated from the inkjet ink, which may reduce uniformity of the inkjet ink and decrease ejection stability when ejected from the fine nozzle.

On the other hand, when the mixing ratio (weight ratio) of the aprotic polar solvent P and the silicone surfactant S is set to P/S of 45/1 to 70/1, these problems can be prevented from occurring, and the printing can be performed on the hydrophobic medium more favorably.

As the surfactant, it is preferable to use the silicone surfactant S represented by the above formula (1) together with₁And a silicone surfactant S represented by the formula (2)₂. When these two surfactants are used simultaneously, stable and good printing can be performed on the hydrophobic media in various surface states in a wide range from the above-mentioned smooth (gloss) offset coated media having a gloss at 60 ° of 70 ° or more, measured using micro-TRI-gloss manufactured by BYK-Gardner corporation, for example, to matte (mat) offset coated media having a gloss at 60 ° of 20 ° or less. Further, as described above, compared with PFOS-based surfactants, there is also an advantage that there is no risk of environmental impact.

That is, the silicone surfactant S of the formula (1)₁The ink composition has extremely high wettability to a hydrophobic medium such as an offset coated medium, is not easily wetted with an aqueous inkjet ink, and can print well even on a smooth offset coated medium, but since the wettability is too high, the matte offset coated medium is affected by fine irregularities on the surface thereof, and may cause print bleeding.

On the other hand, by using the silicone surfactant S of the formula (1) in combination₁And a silicone surfactant S of formula (2) having less wettability than the same₂The occurrence of bleeding on the surface of the matte offset-printing coated medium can be prevented, and good printing can be performed even on the matte offset-printing coated medium.

In the above-mentioned combination system, the blending ratio (weight ratio) of the two silicone surfactants is preferably S₁/S₂6/4-4/6. When the organosilicon surfactant S of the formula (1)₁Less than this range, byThe silicone surfactant S₁The effect of improving the wettability of the ink-jet ink is insufficient, and particularly, when printing is performed on a smooth offset-coated medium, detachment may easily occur.

On the contrary, when the silicone surfactant S of the formula (2)₂Less than the above range, the surfactant S is added to the silicone surfactant₂The effect of suppressing the wettability of the ink-jet ink is insufficient, and particularly when printing is performed on an offset lithographic coated medium, bleeding may easily occur.

On the other hand, when the blending ratio (weight ratio) of the two silicone surfactants is S₁/S₂When 6/4 to 4/6 are used in combination, the synergistic effect of the two silicone surfactants is obtained, and thus stable and satisfactory printing can be performed on hydrophobic media having various surface states in a wide range from smoothness to matting property as described above.

Aprotic polar solvent P and two silicone surfactants S₁、S₂The mixing ratio (weight ratio) of (A) to (B) is preferably P/(S)₁+S₂) The reason for 45/1 to 70/1 is the same as that for the silicone surfactant having a dynamic contact angle of 20 ° or less at 23 ℃.

As the surfactant, a fluorine-based surfactant represented by formula (3) is also suitably used. When the fluorine-based surfactant of the formula (3) is used, stable and satisfactory printing can be performed on the above-mentioned hydrophobic media in various surface states in a wide range from the smooth offset coated media having a gloss at 60 ° of 70 ° or more to the matte offset coated media having a gloss at 60 ° of 20 ° or less. Further, the fluorine-based surfactant represented by the formula (3) has an advantage that it does not have a risk of affecting the environment, as compared with the PFOS-based surfactant, like the silicone-based surfactant.

The mixing ratio (weight ratio) of the aprotic polar solvent P to the fluorine-based surfactant F is preferably 45/1 to 100/1 in terms of P/F. When the fluorine-based surfactant is less than this range, the effect of improving the wettability of the inkjet ink by the fluorine-based surfactant is insufficient, and particularly, when printing is performed on a smooth offset printing coated medium, detachment may easily occur.

When the amount of the fluorine-based surfactant is more than this range, not only a preferable effect cannot be obtained, but also foaming is likely to occur, and the ejection stability when ejected from a fine nozzle may be deteriorated. On the other hand, when the mixing ratio (weight ratio) of the aprotic polar solvent P and the fluorine-based surfactant F is preferably 45/1 to 100/1, such a problem can be prevented from occurring, and more stable and favorable printing can be performed on the hydrophobic medium.

It is preferable that the surface of the pigment contained in the inkjet ink is modified with a carboxyl group. Thus, the pigment can be imparted with appropriate hydrophilicity, thereby improving its dispersion stability in the inkjet ink.

When printing is performed on a hydrophobic medium such as an offset coated medium using the inkjet ink of the present invention, it is preferable to heat and dry immediately after printing. Thus, the aprotic polar solvent is allowed to penetrate into the hydrophobic surface such as a coating layer of an offset coated medium, and the effect of improving the drying property of the inkjet ink is enhanced, so that the hydrophobic medium can be printed at the same printing speed as that of the surface of a water-absorbing object to be printed by using a normal aqueous inkjet ink.

Detailed Description

The present invention will be explained below.

Ink-jet ink

< aprotic polar solvent >

As the aprotic polar solvent, a species having a molecular weight of 40 to 130 can be selected from various aprotic polar solvents which cannot generate and accept hydrogen ions. The content ratio is limited to 40 to 75 wt% based on the total amount of the inkjet ink. The reasons for this are as described above. As described above, it is preferable to use a polar aprotic solvent having a boiling point of 150 to 250 ℃. In addition, the molecular weight of the aprotic polar solvent is preferably in the above range, particularly 45 to 115, from the viewpoint of suppressing the increase in viscosity of the inkjet ink and further improving the ejection stability of the inkjet ink. In addition, from the viewpoint of suppressing the increase in viscosity of the inkjet ink and further improving the ejection stability, the content ratio of the aprotic polar solvent is preferably in the above range, particularly 45 to 70% by weight.

Examples of suitable aprotic polar solvents satisfying these conditions include 1, 3-dimethyl-2-imidazolidinone [ molecular weight: 114.2, boiling point: 225.5 ℃ C., N-methyl-2-pyrrolidone [ molecular weight: 99.1, boiling point: 202 ℃ C., 2-pyrrolidone [ molecular weight: 85.1, boiling point: 245 ℃, formamide [ molecular weight: 45.0, boiling point: 210 ℃, N-methylformamide [ molecular weight: 59.1, boiling point: 197 ℃ and N, N-dimethylformamide [ molecular weight: 73.1, boiling point: 153 ℃ and N, N-diethyl propionamide [ molecular weight: 129.2, boiling point: 195 deg.c ] and gamma-butyrolactone [ molecular weight: 86.1, boiling point: 204 ℃. ] or more.

< surfactant I >

Among various surfactants known in the art, a surfactant having a dynamic contact angle at 23 ℃ of 20 ° or less is preferable. Further, as the surfactant having a dynamic contact angle of 20 ° or less at 23 ℃, a silicone surfactant is preferable. When the surfactant having a dynamic contact angle of 20 ° or less at 23 ℃ is a silicone surfactant, the mixing ratio (weight ratio) of the aprotic polar solvent P and the silicone surfactant S is preferably 45/1 to 70/1 as described above. The reasons for this are as described above.

Although the lower limit of the dynamic contact angle is not particularly limited, when the dynamic contact angle of the surfactant is too small, the wettability of the ink-jet ink with respect to the hydrophobic surface is too good, and the ink-jet ink may bleed before heating, and conversely, sharp printing with sharp edges may not be obtained. Therefore, the dynamic contact angle at 23 ℃ is preferably 15 ° or more.

The dynamic contact angle is specified as follows: for example, a 0.1% aqueous solution of the surfactant to be measured was dropped on the surface of a stainless SUS304 substrate in an environment of 23 ℃ using an automatic contact angle meter CA-V manufactured by Kyowa interface science, Ltd, and the angle formed between the droplet and the substrate surface was measured 300ms after the droplet was brought into contact with the substrate surface.

Suitable surfactants satisfying these conditions include オルフイン (registered trademark) PD-501 manufactured by Nissan chemical industry, Ltd.

< surfactant II >

In other inkjet inks of the present invention, as the surfactant, the formula (1):

[ solution 4]

[ solution 5]

[ in the formula, R²To representA polyalkylene oxide chain containing at least one of an oxyethylene group and an oxypropylene group, and y represents a number of 1 or more.]The silicone surfactant S₂。

In the system using both of these silicone surfactants, the mixing ratio (weight ratio) of the two silicone surfactants must be S₁/S₂6/4-4/6. An aprotic polar solvent P and the two silicone surfactants S₁、S₂The mixing ratio (weight ratio) of (A) to (B) is preferably P/(S)₁+S₂) 45/1-70/1. The reasons for this are as described above.

Suitable examples of the silicone surfactant represented by formula (1) include SILWET L-77 manufactured by Toho レ, ダウコ - ニングシリコ - ン (strain), KF-643 manufactured by Xinyue シリコ - ン (strain), and the like. Suitable examples of the silicone surfactant represented by formula (2) include SILWET L-720 manufactured by Toho レ, ダウコ - ニングシリコ - ン (strain).

The inkjet ink using the two silicone surfactants is preferably adjusted to have a pH of 7.3 to 7.7. When the pH is outside this range, the silicone surfactant represented by formula (1) may change with time, and the wettability of the inkjet ink, particularly with respect to a smooth offset-coated medium, may deteriorate. In addition, if the pH is less than 7.3, in order to improve the water resistance of printing, when the binder resin is combined with an aqueous alkali solution which is substantially insoluble in water and soluble in an aqueous alkali solution in which an alkali substance is dissolved, the binder resin may not be well dissolved in the ink-jet ink. In order to adjust the pH of the inkjet ink within the above range, an arbitrary alkaline substance may be added.

< surfactant III >

In another inkjet ink of the present invention, as the surfactant, a surfactant of formula (3):

[ solution 6]

C_mF_2m+1COONH₄ (3)

[ in the formula, m represents a number of 1 or more. A fluorine-based surfactant. The reasons for this are also as described above.

As a suitable example of the fluorine-based surfactant represented by the formula (3), サ - フロン (registered trademark) S-111N manufactured by セイミケミカル (strain) can be mentioned. The サ - フロン S-111N is a solution obtained by dissolving a mixture of components represented by the formula (3) wherein m is 8 and m is 10, 12 in a mixed solvent of isopropyl alcohol and water, and the concentration of the above compound as an active ingredient is 30% by weight.

< pigments >

As the pigment, any inorganic pigment and/or organic pigment generally used in inkjet ink for inkjet can be used. Among these, examples of the inorganic pigment include one or more of metal compounds such as titanium oxide and iron oxide, carbon black produced by a known method such as a contact method, a furnace method, and a thermal method, and the like.

Examples of the organic pigment include one or more of azo pigments (including azo lakes, insoluble azo pigments, condensed azo pigments, chelate azo pigments, and the like), polycyclic pigments (for example, phthalocyanine pigments, perylene pigments, perinone pigments, anthraquinone pigments, quinacridone pigments, dioxazine pigments, thioindigo pigments, isoindolinone pigments, quinophthalone pigments, and the like), dye chelates (for example, basic dye chelates, acidic dye chelates, and the like), nitro pigments, nitroso pigments, aniline black, and the like.

Specific examples of the pigments include yellow pigments such as c.i. pigment yellow 74, 109, 110 and 138, magenta pigments such as c.i. pigment red 122, 202 and 209, cyan pigments such as c.i. pigment blue 15:3 and 60, black pigments such as c.i. pigment black 7, orange pigments such as c.i. pigment orange 36 and 43, and green pigments such as c.i. pigment green 7 and 36.

The pigment may be used in one kind or two or more kinds depending on the color tone of the inkjet ink. The content of the pigment is preferably 0.1 to 30 wt% based on the total amount of the inkjet ink.

In order to impart hydrophilicity to a pigment and improve dispersion stability in an inkjet ink, it is preferable to modify the surface thereof and introduce a hydrophilic group in advance. Examples of the hydrophilic group introduced on the pigment surface by modification include a carboxyl group and a sulfonic acid group, and a carboxyl group is particularly preferable. Since the sulfonic acid group-modified pigment is too hydrophilic, the dispersion stability of the inkjet ink of the present invention containing a large amount of aprotic polar solvent may be deteriorated, whereas the pigment provided with suitable hydrophilicity by the carboxyl group modification has excellent dispersion stability particularly in the inkjet ink of the present invention. The pigment is preferably used for the production of the inkjet ink of the present invention in a state of being dispersed in water using a dispersant to form a pigment dispersion liquid.

The inkjet ink of the present invention may contain, in addition to the above-described various components, an ethylene oxide adduct of an organic acid described below and other components.

< ethylene oxide adducts of organic acids >

If the ink jet ink contains an ethylene oxide adduct of an organic acid salt, the ejection stability of the ink jet ink can be improved particularly for the ink jet ink of the thermal jet (registered trademark) system.

Although the reason is not clear, it is considered that the reason is that, in the inkjet ink of the thermal jet method, when the inkjet ink is heated at a high temperature (about 400 ℃ C.) instantaneously, the ethylene oxide adduct of the organic acid salt adheres to the pigment surface to act, and the dispersion stability of the pigment is prevented from being deteriorated, so that the dispersion is stabilized.

Examples of the ethylene oxide adduct of the organic acid salt include compounds obtained by adding ethylene oxide to alkali metal salts such as sodium salts and potassium salts of various mono-to tricarboxylic acids such as citric acid, gluconic acid, tartaric acid, lactic acid, D-malic acid, and L-malic acid, and ammonium salts thereof.

In particular, from the viewpoint of improving the ejection stability of the inkjet ink, formula (4):

[ solution 7]

[ in the formula, M¹、M²And M³The same or different alkali metal salts such as sodium and potassium, ammonium groups or hydrogen. But M is¹、M²And M³Not hydrogen at the same time. n is a number of 1 to 28.]At least one of ethylene oxide adducts of alkali metal salts of citric acid such as sodium citrate and potassium citrate, and ethylene oxide adducts of ammonium citrate.

The compound having n exceeding 28 in the formula may increase the viscosity of the inkjet ink, or may precipitate from the inkjet ink due to a decrease in water solubility, resulting in a deterioration in ejection stability. The content ratio of the compound is preferably 0.1 to 5.0 wt%, more preferably 0.3 to 3.0 wt%, based on the total amount of the inkjet ink. If the content ratio is less than this range, the effect of improving the ejection stability of the inkjet ink by containing the compound may be insufficient. Further, if the amount exceeds this range, clogging of the nozzle or the like may occur.

< polyoxyethylene phenyl ether, polyoxyethylene alkylphenyl ether >

If the inkjet ink contains formula (5):

[ solution 8]

[ wherein p is a number of 3 to 28. Polyoxyethylene phenyl ether represented by the formula (6):

[ solution 9]

[ in the formula, R³Is an alkyl group having 8 to 10 carbon atoms, and r is a number of 3 to 28.]At least one of the polyoxyethylene alkylphenyl ethers described above can function to enhance the function of the ethylene oxide adduct of the organic acid salt, thereby further improving the ejection stability of the inkjet ink.

Among them, the reason why p is preferably 3 to 28 in the formula (5) is that: the effect of p as a compound outside this range to enhance the function of the ethylene oxide adduct of the organic acid salt may be insufficient. In particular, a compound having p exceeding 28 may increase the viscosity of the inkjet ink, or may precipitate from the inkjet ink due to a decrease in water solubility, resulting in a decrease in ejection stability.

Specific examples of the polyoxyethylene phenyl ether of formula (5) include those having p of 6, formula (5-1):

[ solution 10]

The compound shown in the specification.

In addition, in the polyoxyethylene alkylphenyl ether represented by the above formula (6), R is preferably 3 to 28, and R is preferably³The reason why the carbon number of the alkyl group is 8 to 10 is that: r is a compound outside of this range, or R³The effect of the compound having an alkyl group with a carbon number outside the range to enhance the function of the ethylene oxide adduct of the organic acid salt may be insufficient. In addition, in particular, compounds in which R exceeds 28, and R³The compound having an alkyl group with more than 10 carbon atoms may increase the viscosity of the inkjet ink or may precipitate from the inkjet ink due to a decrease in water solubilityThe ejection stability can be deteriorated.

Specific examples of the polyoxyethylene alkylphenyl ether of the formula (6) include those wherein R is 25 and R is³A formula (6-1) wherein the carbon number of the alkyl group is 8:

[ solution 11]

The compound shown in the specification. Also, in the compound of formula (6), R is present³Three compounds in which an alkyl group is bonded to an ortho-position, a meta-position, and a para-position with respect to a polyoxyethylene group on a phenyl group may be used in the present invention. In addition, a mixture of two or more of these compounds may also be used.

The polyoxyethylene phenyl ether of formula (5) and/or the polyoxyethylene alkylphenyl ether of formula (6) is contained in an amount of preferably 0.1 to 7.0 wt%, more preferably 0.5 to 6.0 wt%, based on the total amount of the inkjet ink. If the content ratio is less than this range, the effect of enhancing the ejection stability of the inkjet ink by containing these compounds may be insufficient. In addition, if the range is exceeded, clogging of the head may occur.

In addition, the content ratio is a content ratio of the compound alone when any one of the compounds of formulae (5) and (6) is used alone, and a total content ratio of the compounds used in combination when two or more compounds are used simultaneously. Considering that the respective enhancing mechanisms of the compounds of the formulae (5) and (6) are different, it is preferable to use both of them simultaneously. In particular, a system using both the compound of the formula (5-1) and the compound of the formula (6-1) is preferable from the viewpoint of enhancing the effect.

< acetylene glycols and glycol ethers >

When the acetylene glycol and/or the glycol ether are contained in the inkjet ink, these compounds have an effect of improving the enhancing action of the polyoxyethylene phenyl ether of the formula (5) and/or the polyoxyethylene alkylphenyl ether of the formula (6), and therefore, the ejection stability of the inkjet ink can be further improved.

The acetylene glycols include one or more of サ - フイノ - ル (registered trademark) 104 manufactured by エア - プロダクツ, サ - フイノ - ル 420, 440, 465 and 485 manufactured by the same company, ダイノ - ル 604 manufactured by the same company, オルフイン E4001, 4036 and 4051 manufactured by Nissan chemical industry Co., Ltd.

The content of the acetylene glycol is preferably 0.01 to 5.0 wt%, more preferably 0.05 to 3.0 wt%, based on the total amount of the inkjet ink. If the content ratio does not fall within this range, the perfecting effect achieved by the inclusion of the above-mentioned compound may be insufficient. If the amount exceeds this range, the water resistance of the printing may be lowered.

Further, when the above-mentioned two silicone surfactants are used in combination, or the fluorine surfactant of the formula (3) is used in combination with the surfactant of the formula (7):

[ solution 12]

[ in the formula, s and t each represent a number of 0 to 40. However, when s and t are not 0 at the same time and s + t represents a number of 1 to 40 ], the combination of acetylene glycols can achieve not only the above-mentioned advantageous effects but also the effect of improving the wettability of the ink-jet ink, particularly with respect to a smooth offset-coated medium.

The acetylene glycols represented by the formula (7) include サ - フイノ - ル 420[ consisting of a mixture of a plurality of components having different s and t values in the formula (7), and having an average value of s + t of 1.3], 440[ consisting of a mixture of a plurality of components having different s and t values in the formula (7), and having an average value of 3.5], 465[ consisting of a mixture of a plurality of components having different s and t values in the formula (7), and having an average value of 10], 485[ consisting of a mixture of a plurality of components having different s and t values in the formula (7), and having an average value of 30] manufactured by エア - プロダクツ among the above-exemplified compounds.

On the other hand, examples of the glycol ethers include one or more of ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, ethylene glycol monoisobutyl ether, diethylene glycol monoisobutyl ether, ethylene glycol monohexyl ether, diethylene glycol monohexyl ether, ethylene glycol mono 2-ethylhexyl ether, diethylene glycol mono 2-ethylhexyl ether, and the like.

The content of the glycol ethers is preferably 0.5 to 10.0 wt%, more preferably 2.0 to 7.0 wt%, based on the total amount of the inkjet ink. If the content ratio does not fall within this range, the above-mentioned perfecting effect by containing the above-mentioned compound may be insufficient. When the amount exceeds this range, the inkjet ink may not be easily dried because the compound is a nonvolatile liquid. In addition, the storage stability of the inkjet ink may also be reduced.

< adhesive resin I >

When the binder resin is contained in the ink jet ink, the binder resin functions as a binder for the hydrophobic surface such as a coating layer of an offset coating medium and the pigment, and therefore, the water resistance, the scratch resistance, the sharpness of printing, and the like of the printing can be improved. In particular, if a binder resin which is substantially insoluble in water and soluble in an aqueous alkali solution formed by dissolving an alkaline substance is used as the binder resin, the water resistance of printing can be further improved.

The alkali-soluble binder resin is preferably a resin which has a carboxyl group in its molecule and is not itself soluble in water, but when added to an aqueous alkali solution in which an alkali substance such as ammonia, organic amine, or caustic alkali is dissolved, the carboxyl group portion of the resin can react with the alkali substance to form a water-soluble salt, thereby dissolving the resin.

Suitable examples thereof include acrylic resins such as polyacrylic acid, acrylic acid-acrylonitrile copolymer, potassium acrylate-acrylonitrile copolymer, vinyl acetate-acrylic ester copolymer, acrylic acid-alkyl acrylate copolymer and the like; styrene-acrylic resins such as styrene-acrylic acid copolymers, styrene-methacrylic acid-alkyl acrylate copolymers, styrene- α -methylstyrene-acrylic acid copolymers, and styrene- α -methylstyrene-acrylic acid-alkyl acrylate copolymers; the molecular weight and acid value of the maleic acid resin, fumaric acid resin, styrene-maleic acid copolymer resin, styrene-maleic anhydride copolymer resin, and the like are adjusted to those having the above-mentioned characteristics, and particularly, one or two or more kinds of the high acid value resins are used.

Among them, alkali-soluble acrylic resins are preferable, and specific examples thereof include ネオクリル (registered trademark) B-817 (weight-average molecular weight Mw: 23,000) manufactured by アビシア (strain), ネオクリル B-890 (weight-average molecular weight Mw: 12,500), ジヨンクリル (registered trademark) 67 (weight-average molecular weight Mw: 12,500) manufactured by ジヨンソンポリマ (strain), and the like.

In view of improving the water resistance and scratch resistance of printing, the weight average molecular weight Mw of the alkali-soluble binder resin is preferably 10,000 or more. However, if the molecular weight is too high, precipitation or precipitation of the resin is likely to occur, and the ejection of the inkjet ink may become unstable. In addition, the inkjet ink may be liable to precipitate or precipitate when stored. Therefore, the weight average molecular weight Mw of the binder resin is preferably within the above range, particularly 50,000 or less, and more preferably about 20,000 to 40,000 in consideration of these characteristics.

The content ratio of the binder resin is preferably 0.1 to 3.0 wt%, more preferably 0.5 to 2.0 wt%, based on the total amount of the inkjet ink. If the content ratio is less than this range, the effect of fixing the pigment on a nonaqueous surface or the like to improve the water resistance, scratch resistance, and sharpness of printing may be insufficient. If the amount of the binder resin is more than this range, the viscosity of the inkjet ink in the printer head locally increases due to vaporization of water, which may cause instability in ink ejection and precipitation of an excessive amount of the binder resin, resulting in clogging of the head.

< Binder resin II >

In an ink jet printer of the type that normally closes the nozzles by capping when the head is returned to its original position when the printer is not in use, but an operation of returning the head may be manually set, and if the head is forgotten to be returned and the nozzles are left in an uncapped state for a while, the viscosity of the ink jet ink in the nozzles increases, and a printing failure such as fading (かすれ) is likely to occur at the initial stage of restarting printing.

Therefore, in the ink jet ink used in the ink jet printer of the type in which the head return operation is manually performed, in order to reliably prevent printing defects such as fading, it is preferable to use a binder resin having a weight average molecular weight Mw of 1,000 to 3,000, particularly 1,000 to 2,000. The inkjet ink containing such a binder resin having a small weight average molecular weight Mw does not undergo a sharp increase in viscosity even when left uncapped for a while, and therefore, does not cause print defects such as discoloration at the initial stage of restarting printing.

Further, even when printing is performed on a general paper using a binder resin having a weight average molecular weight Mw of 1,000 to 3,000 in an aqueous inkjet ink, the effect of improving the water resistance and the scratch resistance of the printing is not achieved. However, the inkjet ink of the present invention, which contains a large amount of the aprotic polar solvent of 40 to 75 wt% and is printed by penetrating the coating layer of the offset coating medium into the coating layer while dissolving the coating layer to a certain extent by the aprotic polar solvent, can sufficiently improve the water resistance and the scratch resistance of the printing to such an extent that no practical problem occurs even when a binder resin having a weight average molecular weight Mw of 1,000 to 3,000 is used.

Other characteristics of the binder resin are preferably the same as those of the above binder resin having a large molecular weight. That is, the binder resin is preferably insoluble in water and soluble in an aqueous alkali solution formed by dissolving an alkaline substance, because the water resistance of printing is improved. Examples of the binder resin having a weight average molecular weight Mw of 1,000 to 3,000 satisfying these conditions include ジヨンクリル 682 (weight average molecular weight Mw: 1,700) manufactured by ジヨンンンポリマ - (ltd.).

The content ratio of the binder resin is preferably 0.1 to 3.0 wt%, more preferably 0.5 to 2.0 wt%, based on the total amount of the inkjet ink. If the content ratio is less than this range, the water resistance and scratch resistance of the printing may not be practically problematic, or the printing may not be performed clearly. Further, beyond this range, the printing may be discolored or cause clogging of the head.

< basic substance >

The alkaline substance is used to make the inkjet ink alkaline, dissolve the binder resin as described above, while preventing corrosion of the head, and ensure dispersion stability of the pigment. As the alkaline substance, ammonia, organic amines, caustic alkali, and the like as described above are preferable.

Examples of the organic amine include one or more of monoethanolamine, diethanolamine, triethanolamine, ethylmonoethanolamine, ethyldiethanolamine, monoisopropanolamine, diisopropanolamine, triisopropanolamine, mono-1-propanolamine, 2-amino-2-methyl-1-propanol, and derivatives thereof.

The amount of the alkaline substance to be added may be suitably adjusted depending on the acid value indicating the free fatty acid content of the binder resin, the pH of the inkjet ink in a state where no alkaline substance is added, and the like, but is usually preferably 0.05 to 2 parts by weight, more preferably 0.075 to 1.5 parts by weight, based on 1 part by weight of the binder resin. If the amount of addition is less than this range, the binder resin may not be sufficiently dissolved, and thus a uniform inkjet ink may not be obtained. If the pH exceeds this range, the ink may have an excessively high pH, which may cause a safety problem or may corrode a head of an ink jet printer.

< other additives >

In addition to the above-mentioned various components, various additives known in the art for use in ink can be added to the ink jet ink composition of the present invention. Examples of the additive include a pigment dispersant, a fungicide, and a bactericide.

The ink composition thus produced can be used in a so-called continuous ink jet printer which performs printing by forming ink droplets while circulating ink, in addition to the so-called on-demand ink jet printer such as the above-mentioned thermal ink jet printer and piezoelectric ink jet printer.

Printing method

The printing method of the present invention is characterized by comprising: a step of printing on a hydrophobic medium by an inkjet printing method using the inkjet ink of the present invention; and heating the printed hydrophobic medium.

In the printing step, printing may be performed under normal conditions using a so-called on-demand ink jet printer such as the above-described thermal ink jet type and piezoelectric type, and a continuous ink jet printer. In the heating step, for example, a heater or the like connected to the printed matter outlet of the inkjet printer may be provided and heated at a predetermined temperature for a predetermined time. The heating temperature and the heating time are not particularly limited, but setting the heating time to 10 seconds or less, preferably about 1 to 5 seconds is effective for preventing the printing time from being lengthened.

Examples

The present invention will be described below based on examples and comparative examples.

EXAMPLE 1

< production of inkjet ink >

The carbon black dispersion [ CABOJET300 manufactured by CABOT キヤボツト (CABOT) K.K., carboxyl-modified, aqueous dispersion, 15% by weight of the solid content%]As the pigment, 1, 3-dimethyl-2-imidazolidinone [ molecular weight: 114.2, boiling point: 225.5 deg.C]As aprotic polar solvent. As the surfactant, a silicone surfactant [ オルフイン PD-501 manufactured by Nissan chemical industry, Ltd., dynamic contact angle at 23 ℃ C.: 16.1 degree.]As the ethylene oxide adduct of an organic acid, those wherein p is 6 and M is represented by the above formula (4) are used¹～M³Ethylene oxide adducts of sodium citrate, both sodium.

As the binder resin, an alkali-soluble acrylic resin [ ネオクリル B-817 (weight average molecular weight Mw: 23,000) manufactured by アビシア (ltd.) ] was used, and as the basic substance to be dissolved in the inkjet ink, 2-amino-2-methyl-1-propanol was used. As the polyoxyethylene phenyl ether, the compound represented by the above formula (5-1) is used, and as the polyoxyethylene alkylphenyl ether, the compound represented by the above formula (6-1) is used. オルフイン E4001 manufactured by Nissan chemical industry Co., Ltd was used as the acetylene glycol, and プロキセル (registered trademark) XL-2 manufactured by ゼネカ was used as the bactericide.

The above-mentioned components were mixed with ion-exchanged water at the following ratio, stirred and mixed, and then filtered through a 5 μm membrane filter to prepare an ink-jet ink. The mixing ratio (weight ratio) P/S of the aprotic polar solvent P and the silicone surfactant S was 61/1.

(ingredient) (parts by weight)

Carbon Black Dispersion 15

1, 3-dimethyl-2-imidazolidinone 48.5

Silicone surfactant 0.8

Adhesive resin 1

2-amino-2-methyl-1-propanol 0.2

Ethylene oxide adduct of sodium citrate 0.5

C₆H₅O(CH₂CH₂O)₆H 0.5

C₈H₁₇C₆H₄O(CH₂CH₂O)₂₅H 0.5

Ethanol 2

Acetylene glycols 1

0.2 Fungicide

Ion exchange water 29.8

EXAMPLES 2 to 8

As the aprotic polar solvent, the following was used in place of 1, 3-dimethyl-2-imidazolidinone: equivalent amounts of N-methyl-2-pyrrolidone [ molecular weight: 99.1, boiling point: 202 ℃ (example 2), 2-pyrrolidone [ molecular weight: 85.1, boiling point: 245 ℃ (example 3), formamide [ molecular weight: 45.0, boiling point: 210 ℃ (example 4), N-methylformamide [ molecular weight: 59.1, boiling point: 197 ℃ (example 5), N-dimethylformamide [ molecular weight: 73.1, boiling point: 153 ℃ C. ] (example 6), N-diethylpropionamide [ molecular weight: 129.2, boiling point: 195 ℃ (c) (example 7) and gamma-butyrolactone [ molecular weight: 86.1, boiling point: 204 c (example 8), the same operation as in example 1 was carried out to prepare an ink-jet ink.

EXAMPLE 9

An inkjet ink was prepared in the same manner as in example 1 except that the amount of 1, 3-dimethyl-2-imidazolidinone as the aprotic polar solvent was 40 parts by weight, the amount of the silicone surfactant was 0.7 parts by weight, the ratio P/S of the two was 57/1, and the amount of the ion-exchanged water was 38.4 parts by weight.

EXAMPLE 10

An ink jet ink was prepared in the same manner as in example 1 except that the amount of the aprotic polar solvent, i.e., 1, 3-dimethyl-2-imidazolidinone, the amount of the silicone surfactant, the ratio P/S of the two, and the amount of the ion-exchanged water were 70 parts by weight, 1.1 parts by weight, 64/1, and 8 parts by weight, respectively.

EXAMPLE 11

An ink jet ink was prepared in the same manner as in example 1 except that the amount of the aprotic polar solvent, i.e., 1, 3-dimethyl-2-imidazolidinone, the amount of the silicone surfactant, the ratio P/S of the two, and the amount of the ion-exchanged water were 75 parts by weight, 1.2 parts by weight, 63/1, and 2.9 parts by weight, respectively.

EXAMPLE 12

An inkjet ink was prepared in the same manner as in example 1, except that オルフイン PD-501 was replaced with the same amount of a silicone surfactant having a dynamic contact angle of 19.8 ° at 23 ℃.

EXAMPLE 13

An inkjet ink was prepared in the same manner as in example 1, except that オルフイン PD-501 was replaced with the same amount of a silicone surfactant having a dynamic contact angle of 24.3 ° at 23 ℃.

EXAMPLE 14

An ink jet ink was prepared in the same manner as in example 1 except that the amount of 1, 3-dimethyl-2-imidazolidinone as the aprotic polar solvent was set to 48 parts by weight, the amount of the silicone surfactant was set to 1.2 parts by weight, the ratio P/S of the two was 40/1, and the amount of the ion-exchanged water was set to 29.9 parts by weight.

EXAMPLE 15

An ink jet ink was prepared in the same manner as in example 1 except that the amount of the aprotic polar solvent, i.e., 1, 3-dimethyl-2-imidazolidinone, the amount of the silicone surfactant, the ratio P/S of the two, and the amount of the ion-exchanged water were 49.5 parts by weight, 1.1 parts by weight, 45/1, and 18.5 parts by weight, respectively.

EXAMPLE 16

An ink jet ink was prepared in the same manner as in example 1 except that the amount of 1, 3-dimethyl-2-imidazolidinone as a polar solvent was set to 48.5 parts by weight, the amount of the silicone surfactant was set to 0.7 parts by weight, the ratio P/S of the two was 69/1, and the amount of the ion-exchanged water was set to 29.9 parts by weight.

EXAMPLE 17

An ink jet ink was prepared in the same manner as in example 1 except that the amount of the aprotic polar solvent, i.e., 1, 3-dimethyl-2-imidazolidinone, the amount of the silicone surfactant, the ratio P/S of the two, and the amount of the ion-exchanged water were 52.5 parts by weight, 0.7 part by weight, 75/1, and 25.9 parts by weight, respectively.

EXAMPLE 18

An inkjet ink was prepared in the same manner as in example 1 except that an equal amount of carbon black dispersion [ CABOJET200, sulfonic acid group-modified, aqueous dispersion, solid matter 15 wt%, manufactured by キヤボツト ], was used instead of CABOJET 300.

Comparative example 1

An ink jet ink was prepared in the same manner as in example 1 except that the amount of 1, 3-dimethyl-2-imidazolidinone as the aprotic polar solvent was set to 35 parts by weight, the amount of the silicone surfactant was set to 0.6 parts by weight, the ratio P/S of the two was 61/1, and the amount of the ion-exchanged water was set to 33.5 parts by weight.

Comparative example 2

An ink jet ink was prepared in the same manner as in example 1 except that the amount of 1, 3-dimethyl-2-imidazolidinone as the aprotic polar solvent was 77.9 parts by weight, the amount of the silicone surfactant was 1.2 parts by weight, the ratio P/S of the two was 66/1, and no ion-exchanged water was added.

Comparative example 3

Except that N, N-dibutylformamide [ molecular weight: 157.3, boiling point: 240 c ] as an aprotic polar solvent, the same operation as in example 1 was carried out to prepare an ink jet ink.

The following tests were carried out on the inkjet inks prepared in the examples and comparative examples, and the characteristics thereof were evaluated.

Test for spray stability

The ink Jet inks of examples and comparative examples were charged into a black empty ink cartridge used in a thermal Jet type ink Jet printer [ Desk Jet 970Cxi manufactured by ヒユ - レツトパツカ - ド (Ltd.) ] [ manufactured by ヒユ - レツトパツカ - ド (Ltd.; product No. 51645A ]), and a line having a line width of 0.5 lb was printed on a commercially available glossy paper. Then, the printing was observed, and the ejection stability of the inkjet ink was evaluated according to the following criteria.

Very good: it is possible to perform printing in which the printing starts without fading and the lines are not broken in the middle. The ejection stability was evaluated to be excellent.

O: printing may be performed such that the color fades slightly at the start of printing, but the subsequent lines are not broken in the middle. The ejection stability was evaluated to a practical level.

X: the line is broken halfway. The ejection stability was evaluated as poor.

Dryness test

The inkjet inks of examples and comparative examples were used in the same thermal Jet inkjet printer [ Desk Jet 970Cxi manufactured by ヒユ - レツトパツカ - ド (ltd) ] as described above, and printing was performed on an offset coated medium (the packaging material of the ink cartridge described above), followed by heating at 500W power for 2 seconds with an oven, and thereafter the printing was applied with a load of 20g and rubbed with a cotton swab. Then, the printing was observed, and the drying property of the inkjet ink was evaluated according to the following criteria. Further, the gloss at 60 ℃ of the above-mentioned offset-coated medium was measured using Micro-TRI-gloss manufactured by BYK-Gardner, and found to be 46.5 ℃.

Very good: no slight bleeding occurred. The drying property was evaluated to be excellent.

O: slight bleeding occurred, but the drying property was evaluated to reach a practical level.

X: the bleeding was large, and the dryness was evaluated to be poor.

Test for distinctness of image on printing I

The inkjet inks of examples and comparative examples were used in the same thermal Jet inkjet printer [ Desk Jet 970Cxi manufactured by ヒユ - レツトパツカ - ド (ltd) ] as described above, and 10-pound alphabets were printed on an offset-printed coating medium (the packaging material of the ink cartridge described above), followed by heating with an oven at 500W power for 2 seconds. Then, the printing was observed, and the printing sharpness of the inkjet ink was evaluated according to the following criteria.

Very good: the edges are clear. The evaluation was that the printing vividness was excellent.

O: there were some portions with slightly poor sharpness, and it was evaluated that the sharpness of printing reached a practical level.

X: printing was unclear and poor in printing clarity was evaluated.

The results are shown in tables 1 to 3.

TABLE 1

TABLE 2

TABLE 3

As can be seen from the results of examples 1 to 8 and comparative example 3 in the table, it is necessary to use a polar aprotic solvent having a molecular weight of 40 to 130, and from the results of examples 1 and 9 to 11 and comparative examples 1 and 2, it is necessary to control the content of the polar aprotic solvent to 40 to 75 wt%. It is also understood from the results of examples 1, 12 and 13 that a dynamic contact angle of a surfactant at 23 ℃ of 20 ° or less is preferable, and from the results of examples 1 and 14 to 17, a blending ratio (weight ratio) P/S of the aprotic polar solvent P and the silicone surfactant S is preferably 45/1 to 70/1, and from the results of examples 1 and 18, it is preferable that the pigment surface is modified with a carboxyl group.

EXAMPLE 19

< production of inkjet ink >

As a pigment, a carbon black dispersion [ CABOJET300, carboxyl-modified, aqueous dispersion, solid content 15 wt%, manufactured by キヤボツト ], a pigment prepared by using 1, 3-dimethyl-2-imidazolidinone [ molecular weight: 114.2, boiling point: 225.5 ℃ C. ] as aprotic polar solvent. As the surfactant, SILWET L-77 manufactured by Toho レ, ダウコ - ニングシリコ - ン (strain) as the silicone surfactant represented by the above formula (1) and SILWET L-720 manufactured by Toho レ, ダウコ - ニングシリコ - ン (strain) as the silicone surfactant represented by the above formula (2) were used.

As the ethylene oxide adduct of an organic acid, an organic acid in which p is 6 and M is represented by the formula (4) above is used¹～M³Ethylene oxide adducts of sodium citrate, both sodium. As the binder resin, an alkali-soluble acrylic resin [ ネオクリル B-817 (weight-average molecular weight Mw: 23,000) manufactured by アビシア (Ltd.) was used]As an alkaline substance to be dissolved in the ink jet ink, 2-amino-2-methyl-1-propanol is used. As the polyoxyethylene phenyl ether, the compound represented by the above formula (5-1) is used, and as the polyoxyethylene alkylphenyl ether, the compound represented by the above formula (6-1) is used. Further, as the acetylene glycol, サ - フイノ - ル 420[ consisting of a mixture of a plurality of components having different numbers of s and t in the formula (7), and having an average value of s + t of 1.3, manufactured by エア - プロダクツ and manufactured by]プロキセル XL-2 manufactured by ゼネカ was used as a bactericide.

The above-mentioned components were mixed with ion-exchanged water at the following ratio, stirred and mixed, and then filtered through a 5 μm membrane filter to prepare an ink-jet ink. Two kinds of organosilicon surfactants S₁、S₂The mixing ratio (weight ratio) of (B) is S₁/S₂5/5. Further, an aprotic polar solvent P and a silicone surfactant S₁+S₂The mixing ratio (weight ratio) of (A) to (B) of (B) P/(S)₁+S₂)＝48.5/1。

(ingredient) (parts by weight)

Carbon Black Dispersion 15

1, 3-dimethyl-2-imidazolidinone 48.5

SILWET L-77 0.5

SILWET L-720 0.5

Adhesive resin 1

2-amino-2-methyl-1-propanol 0.1

Ethylene oxide adduct of sodium citrate 0.5

C₆H₅O(CH₂CH₂O)₆H 0.5

C₈H₁₇C₆H₄O(CH₂CH₂O)₂₅H 0.5

Ethanol 2

Acetylene glycols 1

0.2 Fungicide

Ion exchange water 29.7

EXAMPLES 20 to 23

SILWET L-77 manufactured by Toho レ, ダウコ - ニングシリコ - ン (strain) as a silicone surfactant represented by the above formula (1) and a silicone surfactant S as the above formula (2)₂SILWETL-720 manufactured by Tokyo レ & ダウコ - ニングシリコ - ン (strain) in S₁/S₂4/6 (example 20), S₁/S₂6/4 (example 21), S₁/S₂3/7 (example 22), S₁/S₂7/3 (example 23) and two silicone surfactants S₁、S₂In a total amount of 1 part by weight, and an aprotic polar solvent P and two silicone surfactants S₁、S₂The mixing ratio (weight ratio) of (A) to (B) of (B) P/(S)₁+S₂) An inkjet ink was prepared by following the same procedure as in example 19, except that the ratio was 48.5/1.

The inkjet inks produced in the above examples were subjected to the above ejection stability test I, the drying property test, and the following tests to evaluate the properties thereof.

Determination of pH value

The pH of the inkjet ink of the examples was measured using HM-40V manufactured by east Asia electric wave industries, Ltd.

Test for distinctness of image on printing II

The ink-Jet inks of examples were used in the same thermal Jet type ink-Jet printer [ Desk Jet 970Cxi manufactured by ヒユ - レツトパツカ - ド (Co., Ltd.) as described above ], and 10 pounds of alphabets were printed on a smooth offset coating medium having a gloss of 85.8 ℃ at 60 ℃ measured by micro-TRI-gloss manufactured by BYK-Gardner and a matte offset coating medium having a gloss of 17.2 ℃ at 60 ℃ measured in the same manner, respectively, and then heated in an oven at a power of 500W for 2 seconds. Then, the printing was observed, and the printing sharpness of the inkjet ink was evaluated according to the following criteria.

X: printing was unclear and poor in printing clarity was evaluated.

The above results are shown in table 4.

TABLE 4

From the results of examples 19 to 23 in the table, it was found that if the silicone surfactant represented by the formula (1) and the silicone surfactant represented by the formula (2) are used together as the surfactant, stable and good printing can be performed on the offset coating medium having various surface states in a wide range from smoothness to matte properties. Further, when the examples are compared, it can be judged that the two types of silicone surfactants are presentAgent S₁、S₂Mixing ratio of S₁/S₂The preferred ranges are 6/4-4/6.

EXAMPLE 24

As a pigment, a carbon black dispersion [ CABOJET300, carboxyl-modified, aqueous dispersion, solid content 15 wt%, manufactured by キヤボツト ], a pigment prepared by using 1, 3-dimethyl-2-imidazolidinone [ molecular weight: 114.2, boiling point: 225.5 ℃ C. ] as aprotic polar solvent. As the surfactant, サ - フロン S-111N manufactured by セイミケミカル (strain) which is a fluorine-based surfactant represented by the above formula (3) was used.

The above-mentioned components were mixed with ion-exchanged water at the following ratio, stirred and mixed, and then filtered through a 5 μm membrane filter to prepare an ink-jet ink. The mixing ratio (weight ratio) P/F of the aprotic polar solvent P and the fluorine-based surfactant (the active ingredient in サ - フロン S-111N) F was 67.4/1.

(ingredient) (parts by weight)

Carbon Black Dispersion 15

1, 3-dimethyl-2-imidazolidinone 48.5

S-111N 2.4

Adhesive resin 1

2-amino-2-methyl-1-propanol 0.1

Ethylene oxide adduct of sodium citrate 0.5

C₆H₅O(CH₂CH₂O)₆H 0.5

C₈H₁₇C₆H₄O(CH₂CH₂O)₂₅H 0.5

Ethanol 2

Acetylene glycols 1

0.2 Fungicide

Ion exchange Water 28.3

EXAMPLE 25

An inkjet ink was prepared in the same manner as in example 24 except that サ - フロン S-111N as the fluorine-based surfactant was changed to 1.7 parts by weight, the blending ratio (weight ratio) P/F of the aprotic polar solvent P to the fluorine-based surfactant F was changed to 95.1/1, and the amount of ion-exchanged water was changed to 29.0 parts by weight.

EXAMPLE 26

An inkjet ink was prepared in the same manner as in example 24 except that the amount of the fluorine-based surfactant サ - フロン S-111N was 1.5 parts by weight, the blending ratio (weight ratio) P/F of the aprotic polar solvent P to the fluorine-based surfactant F was 107.8/1, and the amount of the ion-exchanged water was 29.2 parts by weight.

EXAMPLE 27

An inkjet ink was prepared in the same manner as in example 24 except that the amount of the fluorine-based surfactant サ - フロン S-111N was 3.5 parts by weight, the blending ratio (weight ratio) P/F of the aprotic polar solvent P to the fluorine-based surfactant F was 46.2/1, and the amount of the ion-exchanged water was 27.2 parts by weight.

EXAMPLE 28

An inkjet ink was prepared in the same manner as in example 24 except that the amount of the fluorine-based surfactant サ - フロン S-111N was 3.8 parts by weight, the blending ratio (weight ratio) P/F of the aprotic polar solvent P to the fluorine-based surfactant F was 42.5/1, and the amount of the ion-exchanged water was 26.9 parts by weight.

The inkjet inks produced in the above examples were subjected to the above ejection stability test I, drying property test, and print sharpness test II, and their characteristics were evaluated. The results are shown in Table 5.

TABLE 5

As can be seen from the results of examples 24 to 28 in the table, when the fluorine-based surfactant represented by the formula (3) was used as the surfactant, stable and good printing was possible on the offset coated media having various surface states in a wide range from smoothness to matte property. Further, when the examples are compared, it can be judged that the mixing ratio (weight ratio) P/F of the aprotic polar solvent P and the fluorine-based surfactant F is 45/1 to 100/1, which is preferable.

EXAMPLE 29

An ink jet ink was prepared in the same manner as in example 24 except that ジヨンクリル 682 (weight average molecular weight Mw: 1,700) of ジヨンソンポリマ - (strain) in the same amount was used as a binder resin.

EXAMPLE 30

An ink jet ink was prepared in the same manner as in example 24 except that ジョンクリル 586 (weight average molecular weight Mw: 4,600) of ジヨンソンポリマ - (strain) in the same amount was used as a binder resin.

The inkjet inks produced in the above examples were subjected to the above ejection stability test I, drying property test, print sharpness test II, and the following tests, and their characteristics were evaluated.

Test for spray stability II

The ink Jet inks of examples and comparative examples were charged into a black empty ink cartridge [ manufactured by ヒユ - レツトパツカ - ド (strain, product number 51645A) ] used in an ink Jet printer of thermal Jet system [ task Jet 6127 (manufactured by ヒユ - レツトパツカ - ド (strain) ]. Then, the sheet was left for 5 minutes in a state where the head was not returned and the nozzles were not capped, and then a 1cm × 1cm full print was printed on a commercially available glossy paper. The printing was observed, and the ejection stability of the inkjet ink was evaluated according to the following criteria.

Very good: no fading occurred in the overall printing. The ejection stability after the printing was resumed was evaluated to be excellent.

O: only a little discoloration occurs in the initial part of the overall printing, but then the overall printing can be performed without discoloration. The ejection stability after the printing was resumed was evaluated to a practical level.

X: fading occurs during the entire printing process. The ejection stability after printing was resumed was evaluated as poor.

The above results are shown in table 6.

TABLE 6

As can be seen from the results of examples 29 and 30 in the table, it was found that it is preferable to use a binder resin having a weight average molecular weight Mw of 1,000 to 3,000 for reliably preventing print failures such as fading in the inkjet ink used in the type of inkjet printer in which the head return operation is manually performed

Claims

1. An inkjet ink comprising a pigment, water, a surfactant and an aprotic polar solvent having a molecular weight of 40 to 130, wherein the aprotic polar solvent is contained in an amount of 40 to 75% by weight, and the surfactant is represented by formula (1):

[ solution 1]

Organic of the expressionSilicon surfactant S₁And formula (2):

[ solution 2]

The silicone surfactant S₂The weight ratio of the two organosilicon surfactants is S₁/S₂＝6/4～4/6；

In the formula (1), R¹Represents a polyalkylene oxide chain containing at least one of an oxyethylene group and an oxypropylene group, x represents a number of 1 or more, and R in the formula (2)²Represents a polyalkylene oxide chain containing at least one of an oxyethylene group and an oxypropylene group, y represents a number of 1 or more,

wherein the aprotic polar solvent P and two silicone-based surfactants S₁+S₂In a weight ratio of P/(S)₁+S₂)＝45/1～70/1。

2. A printing method comprising a step of printing on a hydrophobic medium using the inkjet ink according to claim 1 and a step of heating the printed hydrophobic medium.