JP2005154615A - Aqueous curing type ink for ink jet and recording method using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an aqueous curing type ink for ink jet retaining high fastness of image which pigment has, further realizing highly precise image formation and, capable of realizing rapid crosslinking and setting of ink by photoirradiation and exhibiting long-term storage stability as ink and stable discharge reliability in a thermal ink jet system and to provide a recording method using the ink. <P>SOLUTION: The aqueous curing type ink for ink jet comprises an oligomer or a monomer having a photopolymerizable functional group and a hydrophilic part, a pigment, a photopolymerization initiator and water. In the aqueous ink, the pigment is a disperse pigment utilizing electrostatic repulsive force and the polymerization initiator has one or more ethylene oxide parts A represented by the formula: (CH<SB>2</SB>CHO)<SB>m</SB>(m is 7-12) or two or more ethylene oxide parts B represented by the formula: (CH<SB>2</SB>CHO)<SB>n</SB>(n is 1-5) and total amount of the oligomer and the monomer is 20% to 50% and the viscosity is ≤4.0 cps. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an ink used in an ink jet recording method for recording an image by discharging ink, and a recording method using the ink.

  The ink jet method is a method for recording images, characters, and the like by ejecting micro droplets of ink by various operating principles and attaching them to a recording medium (paper, etc.). It has features such as easy, high flexibility of recording patterns, no need for development and fixing, and is rapidly spreading in various applications. Furthermore, in recent years, full-color multi-color inkjet recording technology has been developed, and it is also possible to form multi-color images that are comparable to multi-color printing by plate-making methods and printing by color photographic methods. When the amount of ink is small, a printed matter can be obtained at a lower cost than ordinary multicolor printing or printing, so that it is widely applied to the field of full-color image recording.

  2. Description of the Related Art Conventionally, ink jet recording apparatuses and recording methods have been improved in accordance with demands for improving recording characteristics such as higher recording speed, higher definition, and full color.

  Among them, various attempts have been made not only to increase the definition of recorded images but also to improve image robustness. Therefore, development of pigment inks using pigments as color materials instead of using dyes as color materials is active.

  However, pigment inks also have unique problems. For example, when these pigment inks are used to record on a medium having a high surface gloss such as an ink-jet glossy paper or an ink-jet glossy film, the glossiness of the glossy media tends to be lost in the print area. . In addition, the rubbing property of the printed part is often inferior to that of the dye ink. In addition, when printing on plain paper, problems such as insufficient color developability and image density and insufficient fixability occur.

  Various technical means have been devised for these conventional problems. For example, JP-B-62-1426, JP-A-55-157668, JP-A-3-160068, and JP-A-4-18427 describe that a water-insoluble resin emulsion is added to a pigment ink. However, these resin emulsion-added inks are not sufficient in terms of clogging at the head and ink dispersion stability, but the above disadvantages have not been solved. Even if such a resin emulsion is added to the ink, the pigment after printing does not permeate and diffuse into the recording medium, and is only present on the surface of the medium. I was still not satisfied.

  JP-A-9-151342, JP-A-2001-234097, and the like are inks coated with a pigment, and JP-A-2001-247800 discloses an aqueous dispersion of polymer particles containing a pigment. A water-based ink containing is described. Further, as described in JP-A-10-316909, a method for adjusting a pigment coated with a resin is described. That is, a reactive surfactant is used to coat and process a pigment as a coloring material, and the pigment surface is coated as a polymer obtained by copolymerization with a monomer. However, here, the photopolymerization functional group reacts at the time of copolymerization at the time of ink ejection and landing, and does not contribute to the subsequent fixability because it does not exist in the ink and in the vicinity of the pigment surface. In addition, in the ink in which the polymer resin is arranged around the pigment, there are others, but generally, it is not sufficient to secure the gloss of the printed part, the scratch, and the color density of the glossy paper.

  In contrast to these methods, a method using an ink containing a photopolymerizable compound that is crosslinked by ultraviolet rays or electron beams is known. Here, most of these curable inks that use energy rays such as ultraviolet rays are non-aqueous inks, and typical examples thereof are organic solvents such as toluene and methyl ethyl ketone. Oil-based inks in which pigments are dispersed are used. Further, there is known an ink composed of a monomer, an oligomer, and a pigment dispersion without using a solvent as described in JP-B-5-64667. However, these inks are not suitable for precise printing because the viscosity of the ink does not become sufficiently low. In addition, oil-based inks need to be used with care from an environmental point of view.

  On the other hand, the viscosity can be lowered by the water-based ultraviolet inkjet ink, and a high-definition image is also possible. However, since water-based ultraviolet inkjet ink uses water as a solvent, it has been pointed out that water is disadvantageous in drying compared with an organic solvent.

  However, the water-based ultraviolet inkjet curing technology is useful because it is an image recording method that uses energy-saving, environmental pollution, and environmental impact-free curing technology, and can obtain a high-definition and highly robust image. It is believed that there is.

  For such water-based ultraviolet inkjet ink, a material having low viscosity and good fluidity that can be used for a high-density nozzle is required. As a result, the amount of the polymerizable compound added in the ink can be increased, the substantial curing time can be shortened, and the cured ink film when the ink is cured after being discharged to a predetermined portion on the non-recording medium. Therefore, it is necessary to select a polymerizable substance or a photocatalyst having good compatibility with the coloring material in order to sufficiently secure the physical properties.

  Examples of the water-soluble ultraviolet curable material include, for example, an acid group and a (meth) acryloyl group or vinyl group in the molecule, and a water-soluble polymerizable compound includes, for example, succinic anhydride And esters of 2-hydroxyethyl (meth) acrylate, esters of orthophthalic anhydride and 2-hydroxyethyl (meth) acrylate, vinyl naphthalenesulfonic acid, and the like are in practical use. However, since the number of polymerizable functional groups is one per molecule, the polymerization rate is slow, and the degree of crosslinking of the cured product is extremely low. Not enough.

  On the other hand, as an industrially produced compound that is soluble in water and has two or more polymerizable functional groups in one molecule, a polymerizable compound imparted with hydrophilicity by a polyethylene oxide chain is known. Yes. Examples of such include (meth) acrylic acid esters of polyhydric alcohols such as diethylene glycol di (meth) acrylate and tetraethylene glycol di (meth) acrylate. However, according to the study of the present inventors, these groups of compounds are not water-soluble when the length of the ethylene oxide chain is short, while water solubility is obtained when the length of the ethylene oxide chain is long, There arises a problem that solid physical properties when polymerized or cured are often insufficient in performance required for paints and inks such as hardness and adhesion.

  JP-A-8-165441 discloses a polyfunctional water-soluble polymerizable compound. The compound disclosed here uses a technique for obtaining water solubility by increasing the number of hydroxyl groups in the molecule in order to impart water solubility. Furthermore, in Japanese Patent Application Laid-Open No. 2000-117960, (meth) acrylic acid ester of a hydrophilic polyepoxide derived from glycerin and the like are put into practical use. However, although these are certainly excellent in the polymerization property by ultraviolet rays and in the physical properties of the cured product, there remains a problem that the viscosity of the aqueous solution is slightly higher than the level required for the inkjet ink.

Japanese Patent Application Laid-Open No. 2002-187918 discloses a photocurable resin composition containing a water-soluble photopolymerization initiator in order to form a higher quality image, wherein the polymerizable substance contains two or more polymers. An aqueous photocurable resin composition which is a substance having a functional functional group and one or two anionic functional groups, and an aqueous ink using the same are disclosed. This greatly improved image definition and polymerization speed, but there is still room for improvement in long-term storage stability as an ink and securing some ejection reliability in the thermal ink jet recording system.
Japanese Examined Patent Publication No. 62-1426 JP 55-157668 A Japanese Patent Laid-Open No. 3-160068 JP-A-4-18427 Japanese Patent Laid-Open No. 9-151342 JP 2001-234097 A JP 2001-247800 A Japanese Patent Laid-Open No. 10-316909 Japanese Patent Publication No. 5-64667 JP-A-8-165441 JP 2000-117960 A JP 2002-187918 A

  Therefore, the present invention solves the above-mentioned problems, maintains high image fastness of the pigment as the color material, and further achieves high-definition image formation with the pigment ink, and promptly cross-links the ink by light irradiation. An object of the present invention is to provide an aqueous curable ink-jet ink capable of realizing fixing and further providing long-term storage stability as an ink and stable ejection reliability in a thermal ink-jet method, and a recording method using the same.

In the aqueous inkjet ink containing an oligomer or monomer having a photopolymerizable functional group and a hydrophilic part, a pigment, a photopolymerization initiator, and water, the pigment is a dispersed pigment using electrostatic repulsion, and the polymerization initiator Has one or more ethylene oxide moieties — (CH ₂ CHO) m— (m = 7 to 12), or two or more ethylene oxide moieties B: — (CH ₂ CHO) n— (n = 1 to 5) An aqueous curable ink-jet ink is provided, wherein the total amount of the oligomer and the monomer is in the range of 20% to 50% and the viscosity is 4.0 cps or less.

  Further, according to the recording method of the present invention, 1) the step of ejecting the ink from the ejection port of the thermal ink jet head and adhering it to a predetermined portion of the recording medium. 2) There is provided a recording method comprising a step of irradiating the predetermined portion ejected in step 1) with light to cure the ink.

  As described above, according to the present invention, high-definition image formation can be realized with pigment ink, and further, rapid cross-linking and fixing of ink by light irradiation can be realized. Further, long-term storage stability as ink and An aqueous curable ink-jet ink capable of obtaining stable ejection reliability in a thermal ink-jet method and a recording method using the same are provided.

  Next, the present invention will be described in detail with reference to preferred embodiments. In order to solve the above-described problems of the prior art, the present inventors have proposed a pigment in an aqueous inkjet ink containing a photopolymerizable functional group, an oligomer or monomer having a hydrophilic part, a pigment, a photopolymerization initiator, and water. As a result of intensive studies on the characteristics and structure of the photopolymerization initiator, as a result of increasing the content of the photopolymerizable compound in the conventional aqueous curable inkjet ink or when using a specific pigment type, The present invention has led to the realization of an aqueous curable inkjet ink that prevents aggregation of pigments, has a low viscosity, can be stably ejected, and has a good crosslinking reaction by light irradiation.

  Generally, when a pigment contained in an ink is dispersed by adsorption of a water-soluble polymer, the dispersibility is maintained due to steric hindrance. In the case of a conventional pigment ink containing a pigment using a conventional water-soluble polymer as a dispersant, it is generally 20% or more when a solvent component other than water is added. In this case, it is considered to combine various solvents, and low-viscosity ink-jet inks have been realized. However, in the photopolymerizable compound used in the aqueous curable ink-jet ink, the viscosity can be lowered when the content is relatively small, but when using a highly functional polyfunctional compound, etc. In some cases, a sudden increase in viscosity may occur. As disclosed in JP-A No. 2002-187918, various water-soluble photopolymerizable compounds and photopolymerization initiators having high reactivity have been proposed. In order to ensure ejection reliability, the present inventors have intensively studied paying attention to the stability of pigment dispersion in an aqueous curable ink-jet ink and have reached the present invention.

That is, when used in a thermal ink jet method, and when using a highly functional polyfunctional compound, in order to obtain high reliability in ejection characteristics, the pigment is a dispersed pigment using electrostatic repulsion. In addition, the photopolymerization initiator has one or more ethylene oxide sites A: — (CH ₂ CHO) m— (m = 7 to 12) or ethylene oxide sites B: — (CH ₂ CHO) By using together what has two or more of n- (n = 1-5), it came to discover that the aggregation by the dispersion | distribution destruction of a pigment was prevented and a viscosity rise could be suppressed. This is presumably because the initiator not only serves to initiate the original polymerization but also acts on the pigment dispersion simultaneously. As a result, not only long-term stability of the ink itself but also securing of ejection stability, which is a problem in thermal ink jet recording, can be realized.

  The discharge stability, which is a problem here, will be described in detail. That is, in the thermal ink jet recording system, there is a problem of reliability that must be ensured during use of the recording apparatus, such as intermittent ejection of ink and ink fixation, as well as long-term stable ejection. Specifically, the intermittent ejection property of ink is, for example, after ejecting ink from a predetermined nozzle of an ink jet recording head, and then again after the ejection of ink from that nozzle has been stopped for a certain long time (for example, about 12 hours). When ink is re-discharged from the nozzle, ink re-discharge is not stably performed and printing may be disturbed. In this way, the operation of ejecting ink from a predetermined nozzle and stopping the ejection from the nozzle for a predetermined time and then ejecting the ink again from the nozzle is called “intermittent ink ejection”. Instability is referred to as “intermittent ejection performance is poor”.

  Ink stickiness means that after ink ejection has been stopped for a long time (for example, several days or more), when ink is re-ejected from that nozzle again, ink that has increased in viscosity or solidified in the nozzle is eliminated. In order to obtain stable re-ejection, the recovery operation is necessary to obtain a stable re-ejection. What is required is called “poor adhesion”.

  Next, various materials used in the present invention will be described in detail.

(Pigment)
Specific examples of the pigment used in the present invention include carbon black as a pigment used in black ink. The carbon black is, for example, a carbon black produced by a furnace method or a channel method, and has a primary particle diameter of 15 to 40 mμ, a specific surface area by a BET method of 50 to 300 m ² / g, and a DBP oil absorption of 40 to 150 ml. / 100 g, a volatile component of 0.5 to 10%, a pH value of 2 to 9 and the like are preferably used. Examples of commercially available products having such characteristics include No. 2300, no. 900, MCF88, No. 33, no. 40, no. 45, no. 52, MA7, MA8, no. 2200B (Mitsubishi Kasei), RAVEN 1255 (Columbia), REGAL400R, REGAL 330R, REGAL 660R, MOGUL L (Cabot) Printex U (manufactured by Degussa) and the like can be used preferably.

  Examples of the yellow pigment include Pigment Yellow 1, Pigment Yellow 2, Pigment Yellow 3, Pigment Yellow 12, Pigment Yellow 13, Pigment Yellow 14, Pigment Yellow 16, Pigment Yellow 17, Pigment Yellow 55, Pigment Yellow 73, and Pigment Yellow 74. Pigment Yellow 75, Pigment Yellow 83, Pigment Yellow 93, Pigment Yellow 95, Pigment Yellow 97, Pigment Yellow 98, Pigment Yellow 109, Pigment Yellow 110, Pigment Yellow 114, Pigment Yellow 128, Pigment Yellow 138, Pigment Yellow 139, Pigment Yellow 150, pigment yellow 151, pigment yellow 154, Pigment Yellow 155 and Pigment Yellow 180, and the like.

  Examples of magenta pigments include, for example, Pigment Red 5, Pigment Red 7, Pigment Red 12, Pigment Red 48 (Ca), Pigment Red 48 (Mn), Pigment Red 57: 1, Pigment Red 57 (Sr), and Pigment Red 57: 2, Pigment Red 122, Pigment Red 123, Pigment Red 168, Pigment Red 184, Pigment Red 202, Pigment Red 238, and the like.

  Examples of cyan pigments include Pigment Blue 1, Pigment Blue 2, Pigment Blue 3, Pigment Blue 16, Pigment Blue 22, Pigment Blue 60, Pigment Blue 15: 2, Pigment Blue 15: 3, Bat Blue 4 and Bat Blue 60. Etc.

  The average particle diameter of the pigment particles is preferably in the range of about 25 nm to 200 nm. Although this range depends on the use of the printed matter, it is sufficiently smaller than the wavelength of visible light, so that it can be said that the printed matter can be said to be sufficiently clear if the scattering is small.

  The content of the pigment in the ink is appropriately selected depending on the marking application and the photographic image forming application, but it is preferably contained in the range of 0.1% to 10% in terms of solid content with respect to the entire ink.

  In the present invention, the surface modification of the carbon black and the organic pigment and the production of a dispersed pigment using electrostatic repulsion are disclosed in US Pat. Nos. 5,554,739 and 5,837,045. It is possible by the way you are. Specifically, it is a pigment having at least one hydrophilic organic group bonded thereto, and the organic group includes at least one aromatic group and at least one ionic group or ionizable group, or ion This is a surface-modified pigment that contains a mixture of ionic groups or ionizable groups. Unlike pigments that are dispersed in water using steric hindrance due to water-soluble polymers, they use electrostatic repulsion. Are distributed.

  Here, a preferable organic group that can be bonded to the pigment is an ionic group as a functional group or an organic group substituted with an ionic group. An ionic group is a group capable of generating an ionic group in the medium used. The ionic group can be an anionic group or a cationic group, and the ionic group can generate an anion or a cation.

Examples of ionic functional groups that generate anions include acidic groups and salts of acidic groups. Thus, organic groups include groups derived from organic acids. Preferably, when comprising an ionic group that forms an anion, this organic group is a) an aromatic group or a C1-C12 alkyl group, and b) at least one acidic group having a pKa of less than 11, or a pKa of less than 11. A salt of at least one acid group having a pKa of less than 11 and a salt of at least one acid group having a pKa of less than 11. The pKa of an acidic group refers to the pKa of an organic group as a whole, and is not limited to an acidic substituent. More preferably, the pKa is less than 10 and most preferably less than 9. Preferably, the aromatic group or alkyl group of the organic group is directly bonded to carbon. The aromatic group can be further substituted, for example with an alkyl group, and need not be substituted. The C1-C12 alkyl group may be branched or unbranched and is preferably ethyl. More preferably, the organic group is a phenyl group or a naphthyl group, and the acidic group is a sulfonic acid group, a sulfinic acid group, a phosphonic acid group, or a carboxylic acid group. _{Examples, -COOH, -SO 3 H, -PO} 3 H 2, -SO 2 NH 2, -SO 2 NHCOR, and their salts for example ^{_{-COONa, -COOK, -COO-NR 4}} +, -SO ₃ Na, —HPO ₃ Na, —SO ₃ —NR ₄ ⁺ , PO ₃ Na _{2 and the} like, where R is an alkyl group or a phenyl group. Particularly preferred ionic substituents are —COOH, —SO ₃ H, and sodium and potassium salts thereof.

  More preferably, the organic group is a substituted or unsubstituted sulfophenyl group or a salt thereof, a substituted or unsubstituted (polysulfo) phenyl group or a salt thereof, a substituted or unsubstituted sulfonaphthyl group or a salt thereof, a substituted or unsubstituted (Polysulfo) naphthyl group or a salt thereof. A preferred substituted sulfophenyl group is a hydroxysulfophenyl group or a salt thereof.

Specific organic groups having ionic functional groups that generate anions are p-sulfophenyl, 4-hydroxy-3-sulfophenyl, and 2-sulfoethyl. An amine is an example of an ionic functional group that generates a cationic group and can be bonded to the same organic group described above for an ionic group that generates an anion. For example, amines can be protonated in acidic media to produce ammonium groups. Preferably, the organic group having an amine substituent has a pKb of less than 5. Quaternary ammonium groups (—NR ₃ ⁺ ) and quaternary phosphonium groups (—PR ₃ ⁺ ) are also examples of cationic groups that bind to the same organic groups described above for ionic groups that generate anions. be able to. Preferably, the organic group includes an aromatic group such as a phenyl group or a naphthyl group, a quaternary ammonium group, or a quaternary phosphonium group. The aromatic group is preferably bonded directly to the carbon. Quaternized cyclic amines and quaternized aromatic amines can also be used as organic groups. That is, from this aspect, nitrogen-substituted pyridinium compounds such as N-methyl-pyridyl can also be used. Examples of organic groups include, but are not limited _{to, 3-C 5 H 4 N} (C 2 H 5) +, C 6 H 4 NC 5 H 5 +, C 5 H 4 COCH 2 N (CH ^{_{3) 3 +, C 5 H}} 4 COCH 2 (NC 5 H 5) +, 3-C 5 H 4 N (CH 3) +, C 5 H 4 CH 2 N (CH 3) 3 + , and the like.

  The water dispersibility of a dispersed pigment having an ionic group or an organic group substituted with an ionic group used in the present invention and utilizing electrostatic repulsion is generally the number of organic groups bonded to the pigment having an ionic group. Or an increase in the number of ionic groups attached to a given organic group. That is, the pigment used in the present invention increases the number of organic acids bonded to the pigment having an ionic group or the number of ionic groups bonded to a predetermined organic group, thereby increasing the water dispersibility. It is possible to adjust the water dispersibility to a level of 5%, and a stable dispersibility can be obtained even in the presence of the photopolymerizable compound used in the aqueous curable inkjet ink of the present invention.

  It should also be noted that when an amine is included as an organic group bonded to the pigment used in the present invention, it can be increased by acidifying the aqueous vehicle.

In the present invention, the pigment content in the ink is preferably 0.3 to 7% by weight from the relationship between the image density and the viscosity of the recorded matter.
(Photopolymerization initiator)
The photopolymerization initiator used in the present invention has one or more ethylene oxide moieties A: — (CH ₂ CHO) m— (m = 7 to 12) effective to affect the dispersibility of the pigment, or ethylene oxide use those having site _{B :-( CH 2 CHO) n- (} n = 1~5) of two or more.

  The number of ethylene oxide moieties added to these photopolymerizable initiators has an optimum value from the relationship between the hydrophilicity of the initiator itself, the increase in viscosity due to the addition, and the effect on the dispersibility of the pigment. That is, m = 7 to 10 is suitable for those having one or more ethylene oxide sites A, and n = 1 to 5 is suitable for each having two or more ethylene oxide sites B. . If it is less than this range, the hydrophilicity of the photopolymerizable initiator itself cannot be obtained, and at the same time, the effect of acting on the dispersibility of the pigment cannot be sufficiently obtained. On the other hand, when it is larger than this range, a tendency to increase the viscosity is observed during the addition, so that it is difficult to add an amount that can provide a sufficient effect.

  In addition, as these photopolymerization initiators, for example, those having a wavelength of up to about 400 nm are listed as having a sensitivity to generate radicals upon receiving ultraviolet rays.

  Specifically, preferable compounds include the following compounds (1) to (4).

（式中、Ｒ_１及びＲ_２は各々独立に、水素原子、または置換基もしくは未置換のアルキル基を表す。）

(In the formula, R ₁ and R ₂ each independently represents a hydrogen atom, or a substituted or unsubstituted alkyl group.)

（式中、Ｒ_３は各々独立に、水素原子、または置換基もしくは未置換のアルキル基を表す。）

(In the formula, each R ₃ independently represents a hydrogen atom or a substituted or unsubstituted alkyl group.)

本発明において上記化合物の中ではチオキサントン誘導体とαヒドロキシフェニルケントン誘導体が特に好ましく用いられる。

In the present invention, among the above compounds, thioxanthone derivatives and α-hydroxyphenylkenton derivatives are particularly preferably used.

  It should be noted that the ionicity of the compound affects the dispersion of the pigment, and does not have any ionic dissociation group, that is, a nonionic compound is selected.

  In the present invention, even if the amount of the oligomer or monomer having a photopolymerizable functional group is increased, the dispersion stability of the pigment can be maintained and the increase in viscosity can be suppressed. However, securing the discharge stability is not limited to the increase in viscosity. In such a combination of a pigment and a photopolymerization initiator, it is presumed to suppress the generation of kogation that reduces ink ejection or to suppress the deposition on the heater board portion of the thermal ink jet print head.

  In the present invention, the above compounds may be used alone or in combination of two or more. The addition amount is preferably 0.5 to 3 parts by mass from the relationship between the pigment dispersion stabilizing action and the viscosity increase, and is adjusted to a viscosity within the range of 4.0 cps that can realize stable ejection in the thermal ink jet recording system. .

In addition, the photoinitiator used for this invention is not limited to the said compound.
(Hydrophilic oligomer / monomer having a photopolymerizable functional group)
In addition, the hydrophilic oligomer or monomer having a polymerizable functional group that can be used in the present invention is polymerized by irradiation with ultraviolet rays in the presence of a photopolymerization initiator to obtain desired cured film characteristics, and The ink jet ink satisfying the characteristics as an inkjet ink is used.

  Specifically, what is used as a conventional ultraviolet curable material for water-based inkjet can be used, and as a monofunctional one, both an acidic group and a (meth) acryloyl group or vinyl group are present in the molecule, and Examples of water-soluble polymerizable compounds include esters of succinic anhydride and 2-hydroxyethyl (meth) acrylate, esters of orthophthalic anhydride and 2-hydroxyethyl (meth) acrylate, vinyl naphthalene sulfone. An acid or the like is used. Further, methoxypolyethylene glycol methacrylate, methoxypolyethylene glycol acrylate, etc. are used. As the water-soluble monomer, acryloyl morphophorin (ACMO), diacetone acrylamide, N-vinyl-2-pyrrolidone, N-vinyl-formamide and the like are used.

  Furthermore, a water-soluble polyfunctional polymerizable compound is selected in order to increase the reactivity with the pigment used in the present invention. For example, a compound having two or more acryloyl groups in one molecule is suitable, and a compound having a solubility in water of 10% by weight or more can be suitably used. Examples thereof include (meth) acrylic acid esters of polyhydric alcohols and (meth) acrylic acid esters of glycidyl ethers derived from polyhydric alcohols. Specific examples of the (meth) acrylic acid ester of a polyhydric alcohol include polyethylene glycols such as polyethylene glycol diacrylate and polyethylene glycol dimethacrylate. Specific examples of the (meth) acrylic acid ester of glycidyl ether include (meth) acrylic acid esters of polyhydric alcohols and the like. Specific examples include the following compounds.

（式中ｎ＋ｍ＋ｌ＝１〜１５）

(Where n + m + 1 = 1-15)

尚、これらの多価アルコール類は、エチレンオキシドの付加によって内部がエチレンオキシド鎖で鎖長が延長されたものであってもよい。また、以上に挙げた水溶性の光重合性官能基を有するオリゴマーやモノマーは上記のものに限定されるものではない。

In addition, these polyhydric alcohols may have an ethylene oxide chain and an extended chain length by addition of ethylene oxide. Further, the oligomers and monomers having the water-soluble photopolymerizable functional groups mentioned above are not limited to the above.

  In the present invention, it is contained in an amount of 20 to 50% by weight with respect to the whole ink composition in order to increase the reactivity of light irradiation.

(Sensitizer)
Further, a sensitizer may be added to accelerate the reaction. Specifically: 1) Amine-based: aliphatic amine, amine containing aromatic group, piperidine 2) Urea: allyl-based, o-tolylthiourea 3) Sulfur compound: sodium diethyldithiophosphate, soluble salt of aromatic sulfinic acid 4 ) Nitrile compound: N, N, di-substituted p-aminobenzonitrile 5) Phosphorus compound: Tri-n-butylphosphine, Netium diethyldithiophosphide 6) Nitrogen compound: Michler's ketone, N nitrisohydroxylamine derivative, oxazolidine compound, tetrahydro 1 3) Condensation product of oxazine compound, formaldehyde or acetaldehyde and diamine 7) Polymerized amine of reaction product of epoxy resin and amine, triethanolamine triacrylate The addition amount of the sensitizer is usually 0.1 to 3% by weight with respect to the whole ink composition.

(Additive)
In the present invention, the ink may contain any additive in addition to the above substances. Examples of such additives include pH modifiers, leveling agents, viscosity modifiers, antioxidants, hindered amine light stabilizers (HALS), preservatives, fungicides and the like. Furthermore Useful additives in the present invention oxide moiety _- include nonionic surfactants having a (CH 2 CHO) n- (n = 10 or more). Specific examples include those obtained by adding ethylene oxide to acetylene glycol and those obtained by adding ethylene oxide to polyoxyethylene alkyl ether. By adding a small amount of these nonionic surfactants, it is possible to improve the dispersion stability by acting on the pigment dispersion together with the photopolymerization initiator, and the storability and dischargeability of the ink become stable. In addition, when using said additive, it is contained 0.1 to 5% by weight normally with respect to the whole ink composition.

(Diluted solvent component)
As a diluent solvent other than pigments, photopolymerization initiators, oligomers or monomers having photopolymerizable functional groups and hydrophilic sites, sensitizers, additives, etc., stable ejection in inkjet recording, particularly in thermal inkjet recording systems. In order to obtain, water is mainly used, but an aqueous polymerization-reactive low-viscosity monomer can be used. The advantage of using such substances, not usually solvents, is that these substances do not remain as plasticizers in post-reaction solids that have been cured with UV light, thus reducing the effect on solid physical properties. . Examples of the reactive diluent solvent component selected for such purposes include acryloyl morphophorin, N-2-vinylpyrrolidone, acrylamide, methylenebisacrylamide, monosaccharide monoacrylate, oligoethylene oxide mono- acrylate as mentioned above. Compounds such as acrylic acid esters and monobasic acid acrylic acid esters are listed.

  In the present invention, it is also possible to add a solvent component conventionally used in water-based inkjet inks. However, as described above, a solvent to be added in order to reduce the influence on the solid physical properties of the cured product. It is necessary to pay careful attention to the type and amount of components, the absorbability of the recording medium, and the like. That is, when 10% or more of the solvent component used in the conventional ink-jet ink is used, it is a recording medium having a certain wetting, penetrating, and absorbing properties, and is covered with a gap type (consisting of inorganic particles and a binder). It is desirable to use a recording medium. That is, glossy paper, coated paper, etc. are desirable.

  Further, these solvent components are preferably those which are evaporated and dried relatively easily, and can be arbitrarily added from the following. For example, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monoisopropyl ether, ethylene glycol monoallyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, propylene glycol Examples thereof include glycol ethers such as monomethyl ether and dipropylene glycol monomethyl ether, and monohydric alcohols.

  In the present invention, an ink is prepared using the above-described substances. Many of the above-described oligomers having a photopolymerizable functional group and a hydrophilic portion have an acidic functional group. It is desirable to have a neutralized and dissociated state. Therefore, it is usually adjusted from neutral to basic by alkali metal, alcohol amine, ammonia, morpholine, piperidine, etc., and then dissolved in water. At this time, the use of a compound having a primary or secondary amino group may be avoided because addition of a polymerizable substance to a double bond (Michael addition) may occur even in an aqueous solution. Good. Since this reaction is inhibited by polar groups, the reaction proceeds very little as long as water is present in a large amount. Therefore, the extent to which the use of compounds having primary and secondary amino groups should be avoided depends on the shelf life guarantee of the composition. The ink may be mixed in any order with the raw materials to be used, but in order to ensure stability during mixing, the ink is not uniform when mixed in order to modify the dispersibility of the pigment depending on the pH range. It is preferable to stir quickly so as not to hold it for a long time. Moreover, after mixing, it is preferable to perform further stirring so as not to impair the uniformity.

(Recording system)
As an apparatus suitable for performing recording using the ink according to the present invention described above, for example, a method of applying thermal energy corresponding to a recording signal to ink in a recording head chamber and generating droplets by the thermal energy. And devices.

  Specifically, as shown in the schematic diagram of the front of the printer in FIG. 1, an ink tank unit 1 that holds the ink of the present invention, and a head unit 2 that is attached with an ink tank and actually performs recording (here, the head is Equipped with a large number of multi-heads), a lamp unit 3 that emits light for curing, a drive unit 4 that drives the head unit and the lamp unit, and a paper discharge unit 5 that transports the recording medium to be recorded When the recording apparatus is used, image recording and crosslinking are effectively performed. In addition to these, a wiping unit, a capping unit, a paper feeding unit, a drive motor unit, etc. (not shown) are provided.

  In FIG. 1, a head unit 2 and a lamp unit 3 are simultaneously scanned left and right to sequentially record and irradiate a recording medium. As shown in FIG. 1, the lamp unit 3 may be arranged on the left or right side of the head unit 2 or may be arranged on either one of them. Details of the lamp will be described later.

  In this case, the tank unit 1 is arranged with four colors of black (Bk), cyan (C), magenta (M), and yellow (Y), but light cyan (LC) is used to record a higher-definition image. Alternatively, six colors of light magenta (LM) may be arranged. Further, since the reactivity of black is inferior to that of other colors, a three-color arrangement that forms a process black combining cyan, magenta, and yellow may be used. In the present invention, it is preferable that the tank can block light.

  In the present invention, in addition to the recording system described above, a lamp is disposed on the front surface of the paper discharge unit, a paper feed / discharge is performed by being wound around a rotating drum, and a drying unit is separately provided. Things can be selected as appropriate.

(Light irradiation lamp)
The ultraviolet irradiation lamp used for curing the ink composition particularly suitable in the present invention will be described below. The ultraviolet irradiation lamp is preferably a so-called low-pressure mercury lamp, high-pressure mercury lamp, mercury lamp coated with a phosphor, or the like whose mercury vapor pressure is 1 to 10 Pa during lighting. The emission spectrum of these mercury lamps in the ultraviolet region is in the range of 184 nm to 450 nm, and is suitable for efficiently reacting a polymerizable substance in black or colored ink. Also, a small power supply can be used for mounting the power supply in the printer, which is also suitable in that sense. For example, metal halide lamps, high-pressure mercury lamps, ultra-high-pressure mercury lamps, xenon flash lamps, deep UV lamps, lamps that excite mercury lamps from the outside using microwaves, UV lasers, etc. are in practical use. Since the wavelength range includes the above range, it is basically applicable if the power source size, input intensity, lamp shape, etc. are allowed. The light source is selected according to the sensitivity of the catalyst used.

The necessary UV integrated intensity is preferably about 500 to 5,000 mJ / cm ² in terms of the polymerization rate, with the total energy amount in the UV part being about 500 to 5,000 mJ / cm ² . If the integrated irradiation amount is insufficient, the adhesion force of the ink adhered to a predetermined portion on the recording medium cannot be sufficiently exhibited. Furthermore, in color recording, there is a deficiency in the fastness of the printed recorded image, which is an object of the present invention, such as insufficient water resistance.

  Next, an Example and a comparative example are given and this invention is demonstrated concretely. The present invention is not limited by the following examples unless it exceeds the gist. In the text, “part” or “%” is based on mass unless otherwise specified.

  The recording ink 1 used in Example 1 and the comparative ink 1 used in Comparative Example 1 were prepared as follows.

  First, the dispersion pigment was adjusted using electrostatic repulsion. 4.0 parts by mass of sulfanilic acid was mixed with 20 parts by mass of phthalocyanine blue (Pigment Blue 15: 3, manufactured by Clariant). This mixture was placed in a beaker in a 70 ° C. water bath.

  Next, a solution consisting of 1.68 parts by weight of sodium nitrite dissolved in 74.32 parts by weight of distilled water was added to the beaker with rapid mixing to form a pigmented slurry. Hydrochloric acid was added to this solution and the slurry was adjusted to pH2. The slurry was rapidly mixed at 70 ° C. for 1 hour using a magnetic stirrer and then dried in a 70 ° C. oven. The resulting material was dried and obtained as a surface-modified colored pigment. Next, 6 parts by weight of this sample was extracted with methanol in a Sockley extractor for 10 hours to remove any reaction by-products and re-dried. The obtained pigment was collected, ion-exchanged water was added, and an aqueous dispersion was prepared at a pigment addition level of 20 parts by mass. Next, using this dispersion, each ink was prepared with the following composition.

  Here, the structures of the photopolymerization initiator and the photopolymerizable oligomer are as follows. Acroyl morphophorin was used as a monomer, and triethanolamine was used as a pH adjuster.

顔料分散体 １２部
光重合性開始剤 １．５部
モノマー希釈剤（ＡＣＭＯ） １０部
光重合性オリゴマー ２０部
ｐＨ調整剤（ＴＥＡ） ０．５部
イオン交換水 残部
得られたインク組成物を０．５μｍのメンブランフィルターにてろ過し、粘度を不図示のＥ型粘度計にて測定したところ３．１ｃｐｓであった。

Pigment dispersion 12 parts Photopolymerizable initiator 1.5 parts Monomer diluent (ACMO) 10 parts Photopolymerizable oligomer 20 parts pH adjuster (TEA) 0.5 parts Ion-exchanged water remainder The resulting ink composition is 0 It was 3.1 cps when it filtered with a 0.5 micrometer membrane filter and the viscosity was measured with the E-type viscosity meter not shown.

(Comparative Example 1)
Ink of Comparative Example 1 was produced in the same manner as in Example 1 except that the pigment dispersion obtained by dispersing the pigment dispersion with a styrene acrylic acid copolymer in Example 1 was used.

  At this time, the pigment dispersion was prepared as follows. That is, it was set as the following mixing | blending and the dispersion process was carried out for 5 hours with the roll mill not shown.

Phthalocyanine blue (Pigment Blue 15: 3, manufactured by Clariant) 30 parts by weight Water-soluble polymer: Styrene-acrylic copolymer (molecular weight 10,000, acid value 200) 10 parts by weight Ion-exchanged water The remainder was obtained in the same manner as in Example 1. The ink composition was filtered through a 0.5 μm membrane filter, and the viscosity was measured with an E-type viscometer (not shown) to be 4.8 cps.

(Comparative Example 2)
Ink of Comparative Example 1 was produced in the same manner as in Example 1 except that a photopolymerization initiator having the structure shown below was used.

実施例1と同様にして得られたインク組成物を0.5μｍのメンブランフィルターにてろ過し、粘度を不図示のＥ型粘度計にて測定したところ５．２ｃｐｓであった。

The ink composition obtained in the same manner as in Example 1 was filtered through a 0.5 μm membrane filter, and the viscosity was measured with an E-type viscometer (not shown) to be 5.2 cps.

(Comparative Example 3)
In Example 1, an ink composition obtained in the same manner as in Example 1 except that the pigment dispersion prepared in Comparative Example 1 and the photopolymerization initiator used in Comparative Example 2 were used. It was 7.3 cps when it filtered with the filter and the viscosity was measured with the E-type viscosity meter not shown.

(Print evaluation)
Printing evaluation was performed with the inks of Example 1 and Comparative Examples 1 to 3 described above. As the ink jet recording apparatus used here, the same recording apparatus as shown in FIG. 1 was used. The recording head used had a recording density of 1200 dpi, and the driving condition was a driving frequency of 10 kHz. When a 1200 dpi head was used, a discharge amount per dot was 5.0 pL. The center emission wavelength of the lamp is 365 nmM, and the intensity at the irradiation position is 300 mW / cm 2. These recording conditions are the same throughout the examples and comparative examples.

  In Example 1 and Comparative Examples 1 to 3, a pattern and a 16-point character with cyan ink obtained by using this recording apparatus were formed. The recording paper used for the evaluation is A4 size glossy paper GP-301 (manufactured by Canon).

(Evaluation 1)
For the print samples of Example 1 and Comparative Examples 1 to 3 prepared under the above-described conditions, the image uniformity, whether the formed film has sufficient strength, is rubbed, water resistant, The line marker property was tested as follows.

(1) Image uniformity The uniformity of the printed image of the solid portion of the sample was visually evaluated according to the following criteria.

A: The printed image is uniform without blurring or streaks.
B: Faint or streaks are seen in the printed image and slightly uneven.
C: Fading and streaks are conspicuous and uneven in the printed image.
(2) Scratch resistance When the sample was left for 24 hours after printing, when the paper was placed on the printed paper and the weight of 40 g / cm ² was placed on the recording surface, the paper was pulled. Whether or not the non-printed portion (white background portion) and the Sylbon paper were stained due to rubbing of the printed portion was visually observed and evaluated according to the following criteria.

A: Dirt due to rubbing is not seen.
B: There is almost no dirt due to rubbing.
C: The dirt part by a blur is conspicuous.
(3) Line marker resistance For the above sample that was left for 1 hour after printing, the yellow fluorescent pen spot lighter yellow manufactured by Pilot Co., Ltd. was used to mark the character part once with normal writing pressure. Observed and evaluated according to the following criteria.

A: Character disturbance due to the marker does not occur.
B: Character disturbance due to the marker occurs slightly.
C: Character disturbance due to the marker is remarkably generated.
(4) Water resistance About the sample which was left for 24 hours after printing, about 1 g of water was dropped with a dropper and the presence or absence of ink bleeding was visually observed, and the result was evaluated according to the following criteria.

A: There is almost no ink bleeding.
B: Slight ink bleeding occurs.
C: Ink bleeding is noticeable.

(Evaluation 2)
Furthermore, in order to evaluate the ejection stability of Example 1 and Comparative Examples 1 to 3 and the stability of the ink itself using the recording apparatus described above, the following tests were conducted.

(5) Intermittent ejection property The above ink-jet recording apparatus is allowed to stand in a constant temperature and humidity chamber at 15 ° C./10% for 1 hour, and then discharged from each nozzle one dot at a time, after 5 seconds, The printing cycle for discharging one dot from each nozzle was repeated 10 times. Each dot printing was evaluated according to the following criteria.

A: There is no printing disturbance in all nozzles in all 10 printing cycles.
B: There is almost no disturbance that causes printing problems for all nozzles in all 10 printing cycles.
C: Printing is disturbed after 10 printing cycles.

(6) Adhesiveness Using each of the inks and the ink jet recording apparatus, after initial printing, no discharge was performed for 240 hours, and then printing was performed again. The sticking property of each ink was evaluated from the number of recovery operations of the recording apparatus required to recover the printing after discharging for 240 hours to the initial printing state.

A: It recovers once.
B: Recovers 3 times.
C: It does not recover even after 4 times.

(7) Storage stability The storage stability of each black ink was evaluated. That is, two 100 ml glass containers (manufactured by Schott) are prepared, and 100 ml of each black ink is put in each glass container, and left in a 60 ° C. environment for one month. The presence or absence was observed. The results were evaluated according to the following criteria.

A: Almost no change in ink viscosity before and after standing.
B: There is a slight change in the viscosity of the ink before and after standing.
C: The change in the viscosity of the ink is large before and after being left.

  The results of Evaluation 1 and Evaluation 2 are shown in Table 1.

  In Example 1, the ink of Example 2 was prepared in the same manner as in Example 1 except that the photopolymerization initiator having the structure shown below was used. The ink was evaluated in the same manner, and the evaluation results are shown in Table 1.

  In Example 1, the ink of Example 3 was prepared in the same manner as in Example 1 except that the photopolymerization initiator having the structure shown below was used. The ink was evaluated in the same manner, and the evaluation results are shown in Table 1.

  Ink was prepared in the same manner except that 0.1 part by mass of a nonionic surfactant (BC-20TX manufactured by Nikko Chemicals Co., Ltd.) obtained by adding ethylene oxide to polyoxyethylene alkyl ether in Example 3 was evaluated in the same manner. However, there was a tendency for further improvement in intermittent discharge stability.

  Ink was prepared in the same manner as in Example 1 with m = 2, 8, 12, and 15 of the ethylene oxide part A:-(CH2CHO) m- of the photopolymerization initiator used in Example 1, viscosity measurement and intermittent printing. When the characteristics were evaluated, the following results were obtained, and it was found that ejection stability was obtained in the ink of the present invention.

FIG. 2 is a schematic view of the front of a suitable printer used in the present invention.

Explanation of symbols

1 An ink tank section for holding the ink of the present invention.
2 Head section with an ink tank that actually performs recording.
3 Lamp unit that performs light irradiation for curing.
4 Drive unit for driving the head unit and the lamp unit.
5 A paper discharge unit for conveying a recording medium to be recorded.

Claims (5)

In an aqueous inkjet ink comprising an oligomer or monomer having a photopolymerizable functional group and a hydrophilic site, a pigment, a photopolymerization initiator, and water, the pigment is a dispersed pigment using electrostatic repulsion, and the polymerization initiator There oxide moiety _{a :-( CH 2 CHO) m- (} m = 7~12) having one or more, or oxide moiety _{B :-( CH 2 CHO) n- (} n = 1~5) two or more A water-based curable ink-jet ink, wherein the total amount of the oligomer and the monomer is in the range of 20% to 50%, and the viscosity is 4.0 cps or less.   2. The aqueous curable inkjet ink according to claim 1, wherein the surface functional group of the pigment is selected from any of a sulfonic acid group or a carboxylic acid group, a sulfinic acid group, and a phosphonic acid group. The polymerization initiator is selected from any of thioxanthone having an ethylene oxide moiety A: — (CH ₂ CHO) m— (m = 7 to 12), an α-hydroxyphenylkenton derivative, an acridone derivative, and a benzophenone derivative. Item 8. The aqueous curable inkjet ink according to Item 1. The aqueous curable inkjet ink according to claim 1, comprising a nonionic surfactant having an ethylene oxide moiety — (CH ₂ CHO) n — (n = 10 or more). 1) a step of discharging the ink from a discharge port of a thermal ink jet head and attaching it to a predetermined portion of the recording medium; and 2) irradiating the predetermined portion discharged in step 1) with light to cure the ink. A recording method comprising a step.

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