JP2001098194A - ink - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ink which gives recording images having high image concentration, excellent scratch resistance, excellent water resistance and excellent marker pen ink resistance, and has excellent extrusion stability from a recording head, when used for ink jet recording. SOLUTION: This ink comprises a coloring agent-encapsulating resin encapsulating the coloring agent, and a pigment. Therein, the resin is a copolymer comprising a hydrophilic polymer chain portion and a hydrophobic polymer chain portion in a polymer ratio of 15:85 to 50:50.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is suitable for ink jet recording, has excellent reliability, can provide a high image density even on plain paper, and forms an image having excellent water resistance and line marker resistance. Regarding the ink obtained.

[0002]

2. Description of the Related Art In an ink jet recording method, recording is performed by discharging ink and attaching the ink to a recording medium such as paper. For example, Japanese Patent Publication No. 61-59911, Japanese Patent Publication No. 61-59912 and Japanese Patent Publication No.
No. 59914 or the like, that is, an ink jet recording method of discharging an ink by using an electrothermal converter as a discharge energy supply means and applying thermal energy to the ink to generate bubbles. Thus, it is possible to easily realize a high density multi-orifice of the recording head, and to record a high-resolution and high-quality image at a high speed. Such a scheme is
This is one of the mainstays of the ink jet recording method that is currently in practical use.

[0003] By the way, as a coloring material in the ink used in such an ink jet recording method, for example, a water-soluble dye is used. There is a demand for improved line marker resistance on plain paper (hereinafter simply referred to as marker resistance). In order to solve such a problem, in particular, a number of means for improving the density and water resistance of a recorded image have been proposed so far, one of which is to use a pigment as a coloring material and disperse the ink in water. Technology. For example, a pigment-dispersed ink using carbon black as a coloring material can provide a recorded image having high image density and excellent water resistance. However, in such a recorded image, there is still room for improvement in scratch resistance and marker resistance particularly in an image formed on plain paper.

[0004]

To solve the above-mentioned problems, there is known a technique for improving the fixing property of an image by adding a resin to the ink. For example, Japanese Patent Application Laid-Open No. 3-172
No. 362 discloses a technique for improving the fixability of an ink containing a dye or a pigment as a coloring material on a recording medium by incorporating a cationic emulsion in which resin particles are dispersed as a fixing agent in the ink. Have been. Also, Japanese Patent Application Laid-Open
Japanese Patent Application No. 239610 discloses an aqueous pigment composition for inkjet containing a pigment, a coloring resin and a humectant as essential components, whereby a printed matter having excellent coloration properties and excellent water resistance can be obtained. Is disclosed.

Here, according to the study of the present inventors, the upper limit of the amount of the pigment or resin that can be contained in the ink for ink jet recording is naturally determined in consideration of the ejection stability of the ink. Therefore, in the ink containing the pigment, the amount of the pigment that affects the image density of the recorded image and the amount of the resin that affects the fixability of the recorded image are not appropriately selected depending on the balance between the image density and the image fixability. It was concluded that the pigment-based inks proposed so far have not yet fully exploited the merits of using pigments as coloring materials.

Further, when the ratio of the hydrophilic group of the contained resin is increased for the purpose of improving the dispersion stability and the ejection stability, a large number of hydrophilic groups are present on the resin surface on the paper. Therefore, it is presumed that such recorded images do not exhibit sufficient water resistance and marker resistance. Therefore, an object of the present invention is to provide high image density and excellent scratch resistance,
Gives a recorded image with water resistance and marker resistance, and
An object of the present invention is to provide an ink that is excellent in ejection stability from a recording head when used for ink jet recording.

[0007]

The above objects are achieved by the present invention described below. That is, the first invention of the present invention relates to an ink containing a colorant-encapsulating resin containing a colorant and a pigment, wherein the resin comprises a hydrophilic polymer chain and a hydrophobic polymer chain. An ink, comprising a polymer, wherein the polymerization ratio of the hydrophilic polymer chain portion to the hydrophobic polymer chain portion of the copolymer is in the range of 15:85 to 50:50. A second invention of the present invention relates to an ink containing a pigment having a cationic group or a pigment and a pigment dispersant having a cationic group, and a colorant-encapsulating resin encapsulating a colorant, wherein the resin has a hydrophilic polymerization property. A copolymer comprising a chain portion and a hydrophobic polymer chain portion, wherein the polymerization ratio of the hydrophilic polymer chain portion to the hydrophobic polymer chain portion of the copolymer is 15:85 to 50:50. Characterized by the following: A.

The present inventors have conducted intensive studies to solve the above-mentioned problems of the prior art. As a result, if the ink composition is made as in the above first and second inventions, the resin having an appropriate hydrophilic portion can be obtained. Is contained in the ink while maintaining the reliability at the time of recording, and after recording, the hydrophobic part of the abundant resin occupies most of the surface of the recorded image. The expression of excellent marker resistance that could not be obtained becomes possible. That is, the ink having such a configuration has high image density and excellent water resistance, and
It can provide high-quality inkjet recorded images with good fixability and excellent marker resistance and abrasion resistance, and at the same time, reliability during inkjet recording (ejection durability, ejection stability, clogging resistance, etc. ) Was found to be superior to the present invention.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, the ink according to the first invention of the present invention contains a colorant-encapsulating resin encapsulating a colorant and a pigment. Hereinafter, each constituent material will be described in the following order. (1) Colorant-encapsulated resin (2) Pigment (3) Aqueous medium, other additives, etc.

(1) Colorant-Encapsulated Resin As the colorant-encapsulated resin encapsulating the colorant, for example, a resin in which the colorant is encapsulated in a resin microcapsule,
Alternatively, a resin emulsion in which a dye or a pigment dissolved or dispersed in an oily solvent is dispersed in an aqueous medium may be mentioned. In particular, it is preferable to use a microencapsulated resin containing a colorant. That is, for example, when a hydrophobic colorant such as an oil-based dye or a pigment is used as a colorant, the microencapsulation makes it easy for these colorants to interact with the hydrophobic portion of the resin. It is presumed that the portion tends to be hardly oriented in the aqueous system. As a result, when the inkjet ink containing the colorant-encapsulated resin is ejected from the inkjet printer, adhesion and deposition of the resin on the water-repellent nozzle-formed surface of the inkjet head are suppressed, and the ink can be used for a long period of time. It is expected that this will contribute to a further improvement in the ejection stability over the entire area.

[0011] A resin in which a colorant is microencapsulated is defined as a solution in which the above-mentioned colorant is dissolved or dispersed in an oily solvent, emulsified and dispersed in water, and further micro-encapsulated by a conventionally known appropriate method. A resin dispersion obtained by performing encapsulation.

As the colorant used at this time, for example, a water-insoluble colorant such as a pigment or an oil-soluble dye is preferably used. That is, these water-insoluble colorants are easy to produce a resin in which the colorant is microencapsulated. Specifically, for example, carbon black or the like can be used as the black (Bk) pigment. Here, 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%.
-40 nm, specific surface area by BET method is 50-300 m
² / g, DBP oil absorption 40-150ml / 100g,
Those having characteristics such as a volatile content of 0.5 to 10% and a pH value of 2 to 9 are preferably used.

[0013] Commercial products having such properties include:
For example, no. 2300, no. 900, MCF88,
No. 33, no. 40, no. 45, no. 52, M
A7, MA8, No. 2200B (above, manufactured by Mitsubishi Chemical), RAVEN 1255 (above, manufactured by Columbia), R
EGAL400R, REGAL330R, REGAL6
60R, MOGUL L (all made by Cabot), Co
lor Black FW-1, Color Blac
k FW18, Color Black S170, C
color Black S150, Prtex 3
5, Printex U (all manufactured by Degussa) and the like.

Further, as the oil-soluble dye, the following dyes can be preferably used. C. I. Solvent yellow 1, 2, 3, 13, 19,
22, 29, 36, 37, 38, 39, 40, 43, 4
4, 45, 47, 62, 63, 71, 76, 81, 8
5, 86, etc. C. I. Solvent Red 8, 27, 35, 36, 3
7, 38, 39, 40, 58, 60, 65, 69, 8
1, 86, 89, 91, 92, 97, 99, 100, 1
09, 118, 119, 122 and the like. C. I. Solvent Blue 14, 24, 26, 34, 3
7, 38, 39, 42, 43, 45, 48, 52, 5
3, 55, 59, 67 and the like. C. I. Solvent Black 3, 5, 7, 8, 14, 1
7, 19, 20, 22, 24, 26, 27, 28, 2
9, 43, 45 and the like. Further, among various conventionally known water-soluble dyes, those obtained by exchanging their counter ions (usually sodium, potassium and ammonium ions) with an organic amine or the like can be used.

As the above-mentioned various colorants, those having the same color tone as the pigment are preferably selected in order to adjust or supplement the color tone of the pigment described later. Thereby, the density of the recorded image can be further improved. For example, when carbon black is used as a pigment as described later, it is preferable to use carbon black also as a coloring agent included in the resin. Further, as the coloring agent included in the resin, two or more kinds of coloring materials selected from those described above may be used. In this case, each colorant may be separately included in a resin, or each colorant may be included in a common resin to prepare a colorant-containing resin.

Next, a method for producing a colorant-encapsulating resin in a mode in which the above-described colorant is microencapsulated will be described. First, the colorant as described above is dissolved or dispersed in an oily solvent, and then the oily solvent is emulsified and dispersed in water. Examples of the method for emulsifying and dispersing the oily solvent in which the colorant is dissolved or dispersed in water at this time include a dispersion method using ultrasonic waves, a method using various dispersers, and a stirrer. At this time, if necessary, various emulsifiers and dispersants, and also emulsifying or dispersing aids such as protective colloids can be used.
As these emulsifiers or dispersion aids, PVA, PV
In addition to high molecular substances such as P and gum arabic, anionic surfactants, nonionic surfactants and the like can be used.

As a method for microencapsulation of the above-mentioned emulsion, a method of dissolving a colorant and a resin in a water-insoluble organic solvent (oil-based solvent) and then inverting the aqueous phase to emulsify the organic phase, An interfacial polymerization method in which a polymerization reaction is caused at an interface with an aqueous phase to form microcapsules, a material forming a wall only in an organic phase is dissolved or present to form microcapsules, a so-called In-Situ polymerization method,
A coacervation method, in which the concentrated phase of the polymer is phase-separated by changing the pH, temperature, concentration, etc. of the aqueous solution of the polymer to form microcapsules, may be mentioned. After forming the microcapsules, a step of removing the oily solvent is added. The colorant-encapsulated resin obtained as described above has an average particle diameter of 0.01 to 2.0 μm.
m, more preferably 0.05 to 1
It is preferably in the range of μm.

The resin used in the first invention of the present invention is a copolymer comprising a hydrophilic polymer chain and a hydrophobic polymer chain, wherein the copolymer has a hydrophilic polymer. A polymer having a polymerization ratio between the coalesced chain portion and the hydrophobic polymerized chain portion in the range of 15:85 to 50:50, more preferably in the range of 20:80 to 40:60 is used. That is, when the hydrophilic portion is less than 15 wt%,
If sufficient dispersibility or ejection stability of the resin in the ink is not obtained, but the hydrophobic portion is less than 50 wt%, an image formed by such an ink will have sufficient water resistance and marker resistance. It does not have the property.

As a method for synthesizing a copolymer, a macromonomer method, an ionic polymerization method, a chain transfer method, a method of forming an active site in a polymer by radiation, and a method of polymerizing a different kind of monomer have been conventionally known. In the case of the copolymer used in the present invention, the macromonomer method is preferred because it is necessary to structurally control the degree of polymerization of the hydrophobic and hydrophilic polymer chains and the manner of chaining.

As a method of synthesizing a macromonomer,
Various methods are known. For example, there is a method in which a chain transfer agent and a polymerization initiator are added to a monomer to carry out solution polymerization, and a glycidyl group-containing monomer is subjected to a catalytic reaction.
Further, the macromonomer thus obtained is subjected to radical copolymerization in the presence of an optional hydrophilic monomer, a hydrophobic monomer and an initiator, to thereby form a copolymer suitable as a constituent material of the ink of the present invention. Can be synthesized.

The hydrophilic monomer having an anionic hydrophilic group that can be used in this case generally includes a sulfonic acid monomer and a carboxylic acid monomer. Examples of the sulfonic acid monomer include styrene sulfonic acid and salts thereof, vinyl sulfonic acid and salts thereof, and the like. Examples of the carboxylic acid monomer include α, β-ethylenically unsaturated carboxylic acid, α, β-ethylenically unsaturated carboxylic acid derivative, acrylic acid, acrylic acid derivative, methacrylic acid, methacrylic acid derivative, maleic acid, and maleic acid derivative. , Itaconic acid, itaconic acid derivatives, fumaric acid,
And fumaric acid derivatives.

Examples of the hydrophobic monomer as the hydrophobic component include styrene, styrene derivatives, vinyl toluene, vinyl toluene derivatives, vinyl naphthalene, vinyl naphthalene derivatives, butadiene, butadiene derivatives, isoprene, isoprene derivatives, ethylene, ethylene derivatives, and the like. Examples thereof include propylene, propylene derivatives, alkyl esters of acrylic acid, and alkyl esters of methacrylic acid.

The salts of the copolymers of these hydrophilic monomers and hydrophobic monomers include, for example, alkali metal salts; ammonium salts, organic ammonium salts, phosphonium salts, sulfonium salts, oxonium salts, stibonium salts, stannonium salts. Examples include, but are not limited to, onium salts such as salts and iodonium salts.

Further, a polyoxyethylene group, a hydroxyl group or the like may be introduced into the above copolymer or a salt thereof, or acrylamide, acrylamide derivatives, dimethylaminoethyl methacrylate, ethoxyethyl methacrylate, butoxyethyl methacrylate, ethoxytriethyl Ethylene methacrylate, methoxypolyethylene glycol methacrylate, vinyl pyrrolidone, vinyl pyridine, vinyl alcohol, alkyl ether and the like may be appropriately copolymerized.

(2) Pigment As the pigment, conventionally known pigments, for example, carbon black and organic pigments can be used without any problem. When preparing the Bk ink, it is preferable to use a self-dispersion type carbon black in which at least one kind of hydrophilic group is bonded to the surface of the carbon black directly or by bonding with another atomic group. That is, when the self-dispersion type carbon black is used, a dispersant for dispersing the pigment in the ink is not added, or the amount of the dispersant can be significantly reduced. As the dispersant, a conventionally known water-soluble polymer or the like is usually used. However, such a polymer may precipitate on the ink ejection surface of the inkjet recording head and reduce the ejection stability of the ink. There is. However, by using the above-described self-dispersion type carbon black as the pigment, the content of such a polymer in the ink can be made zero or significantly reduced. As a result, the ejection stability during inkjet recording can be further improved.

Next, a self-dispersion type carbon black suitable for the ink of the present invention will be described in detail. The self-dispersion type carbon black is preferably ionic, and for example, anionically charged one can be suitably used. Examples of the anionic charged carbon black include carbon black having the following hydrophilic groups bonded to the surface of the carbon black.

Of these, -COO (M2) and-
Carbon black having SO ₃ (M2) bonded to the surface of carbon black and anionically charged has good self-dispersibility in the ink, and therefore can be particularly preferably used in the first invention of the present invention. .

By the way, among the hydrophilic groups represented by "M2", specific examples of the alkali metal include, for example, Li, Na, K, Rb and Cs.
Specific examples of the organic ammonium include, for example, methyl ammonium, dimethyl ammonium, trimethyl ammonium, ethyl ammonium, diethyl ammonium, triethyl ammonium, monohydroxymethylamine, dihydroxymethylamine, trihydroxymethylamine, ethanolammonium, diethanolammonium, Triethanol ammonium and the like.

Examples of a method for producing self-dispersible carbon black charged anionic include a method in which carbon black is oxidized with sodium hypochlorite.
ONa groups can be chemically bonded.

(3) Aqueous medium, other additives, etc. The colorant-encapsulated resin and pigment described in (1) and (2) above are held in a dispersed state in an aqueous medium to constitute an ink. It is preferable that the aqueous medium contains at least water. The ratio of water to the total weight of the ink is, for example, 20 to 95 wt%, particularly 40 to 9 wt%.
It is preferably 5 wt%, more preferably 60 to 95 wt%. The aqueous medium may contain a water-soluble organic solvent.

The water-soluble organic solvent preferably used includes, for example, alkyl alcohols having 1 to 4 carbon atoms (eg, methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, sec- Butyl alcohol, tert-butyl alcohol, etc.), ketone or keto alcohols (eg, amides such as dimethylformamide, dimethylacetamide, acetone, diacetone alcohol, etc.), ethers (eg, tetrahydrofuran, dioxane, etc.), polyalkylene glycol (Eg, polyethylene glycol, polypropylene glycol, etc.) and alkylene glycols in which the alkylene group contains 2 to 6 carbon atoms (eg, ethylene glycol, propylene glycol, butylene glycol) , Triethylene glycol, 1,2,6-hexanetriol, thiodiglycol, hexylene glycol, diethylene glycol, etc.) and alkyl ethers such as polyhydric alcohols (for example, ethylene glycol methyl ether, ethylene glycol ethyl ether, Ethylene monomethyl ether, triethylene glycol monoethyl ether, etc.),
Furthermore, N-methyl-2-pyrrolidone, 2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone and the like can be mentioned. The total amount of the water-soluble organic solvent in the ink is 2 to 60% by weight based on the total amount of the ink, and more preferably 5 to 25% by weight.

Further, a preferred water-soluble organic solvent is glycerin, and its added amount is 2 to 3% by weight in the ink.
0 wt%, and more preferably 5 to 15 wt%. Further preferable water-soluble organic solvent is a mixed solvent containing glycerin and a polyhydric alcohol (for example, diethylene glycol or ethylene glycol). The mixing ratio of glycerin and other polyhydric alcohol is glycerin:
It is preferably between 10: 5 and 10:50 for other polyhydric alcohols. Other polyhydric alcohols of glycerin include:
Examples include diethylene glycol, ethylene glycol, polyethylene glycol and propylene glycol. These glycerin or a mixture of glycerin and a polyhydric alcohol can be used by further mixing with another water-soluble organic solvent.

The ink according to this embodiment is suitably used in an ink jet recording method in which an ink is ejected from a recording head by thermal energy or mechanical energy and adheres to a recording medium to record an image. When the ink according to the present embodiment is particularly suitable for ink jet recording, the surface tension of the ink at 25 ° C. is 15 to 60 dyn / cm, and furthermore, 20 to 25 dyn / cm.
~ 50 dyn / cm, viscosity less than 15 cP, especially 1
It is preferably 0 cP or less, more preferably 5 cP or less. The pH range is preferably from 3 to 11, and more preferably from 3.5 to 8.

As specific ink compositions that can achieve such characteristics, for example, various inks used in Examples described later can be mentioned. The ink of the first invention of the present invention contains, in addition to the resin and pigment containing the colorant obtained as described above, various additives such as a surfactant, a pH adjuster, and a fungicide. May be added.

The ink of the second invention of the present invention contains a pigment having a cationic group or a pigment and a pigment dispersant having a cationic group, and a colorant-containing resin containing a colorant. Hereinafter, the constituent materials of the present invention will be described in the following order. (4) Colorant-encapsulated resin, particularly a resin having a cationic hydrophilic group on its surface (5) Pigment having a cationic group, or pigment dispersant having a pigment and a cationic group (6) Aqueous medium, other additives etc

(4) Colorant-encapsulated resin, especially resin having a cationic hydrophilic group on the surface In the second invention of the present invention, as in the first invention,
Although a colorant-encapsulating resin that encloses a colorant is used, it is particularly preferable to use a colorant-encapsulating resin having a cationic hydrophilic group on the surface. As the colorant-encapsulating resin, for example,
A resin in which a colorant is microencapsulated, an aqueous dispersion of a resin having a cationic group, which contains a colorant by emulsifying a dye or pigment dispersed or dissolved in an oily solvent and including the colorant, and in particular, is colored. A resin in which the agent is microencapsulated is preferable. The resin in which the colorant is microencapsulated is obtained by dissolving or dispersing the colorant in an oily solvent, emulsifying and dispersing the same in water, and further performing microencapsulation by a conventionally known appropriate method. It is a resin dispersion. As the coloring agent, those described above in (1) can be used.

Next, a method for preparing a resin in which a colorant is microencapsulated as the colorant-containing resin will be described. First, the colorant is dissolved or dispersed in an oily solvent, and then the oily solvent containing the colorant is emulsified and dispersed in water. Examples of the method of emulsifying and dispersing the oily solvent in which the colorant is dissolved or dispersed in water include a dispersion method using ultrasonic waves, a method using various dispersers, and a stirrer. At this time, if necessary, various emulsifiers and dispersants, and further, emulsifying or dispersing aids such as protective colloids can be used.
As these emulsifiers or dispersion aids, PVA, PV
In addition to high molecular substances such as P and gum arabic, anionic surfactants, nonionic surfactants and the like can be used.

As a method for microencapsulation of the above-mentioned emulsion, a method of dissolving a colorant and a resin in a water-insoluble organic solvent (oil-based solvent) and then inverting the aqueous phase to emulsify the organic phase, An interfacial polymerization method in which a polymerization reaction is caused at an interface with an aqueous phase to form microcapsules, a material forming a wall only in an organic phase is dissolved or present to form microcapsules, a so-called In-Situ polymerization method,
A coacervation method, in which the concentrated phase of the polymer is phase-separated by changing the pH, temperature, concentration, etc. of the aqueous solution of the polymer to form microcapsules, may be mentioned. After forming the microcapsules, a step of removing the oily solvent is added. The average particle diameter of the colorant-containing resin obtained as described above is 0.01 to 2.0 μm.
m, preferably in the range of 0.05 to 1 μm.

In the second invention of the present invention, the resin is a copolymer composed of a hydrophilic polymer chain and a hydrophobic polymer chain, wherein the copolymer is a hydrophilic polymer. The polymerization ratio between the chain portion and the hydrophobic polymerization chain portion is 1
5:85 to 50:50, more preferably 20:50.
A resin in the range of 80 to 40:60 is used. These resins can be obtained by the same method as described in (1).

In the second aspect of the present invention, the colorant-containing resin preferably has a cationic hydrophilic group. In order to obtain a resin having a cationic group, a polymer and a salt thereof may be synthesized using a monomer having a cationic group as described below. Examples of the monomer having a cationic group include N, N-dimethylaminoethyl methacrylate [CH ₂ ＣC (CH ₃ ) —
_{COO-C 2 H 4 N (} CH 3) 2 ], N, = N-dimethylaminoethyl acrylate _{[CH 2 CH-COO-C 2} H 4 N
(CH ₃ ) ₂ ], N, N-dimethylaminopropyl methacrylate [CH ₂ ＣC (CH ₃ ) —COO—C ₃ H ₆ N (C
H _{3) 2],} N, N-dimethylaminopropyl acrylate _{[CH 2 = CH-COO-C} 3 H 6 N (CH 3) 2 ], N,
N-dimethylacrylamide [CH ₂ ＣＨCH-CON (C
H ₃ ) ₂ ], N, N-dimethylmethacrylamide [CH ₂ ＝
_{C (CH 3) -CON (CH} 3) 2 ], N, N-dimethylaminoethyl acrylamide [CH ₂ = CH-CONHC ₂ H
₄ N (CH ₃ ) ₂ ], N, N-dimethylaminoethyl methacrylamide [CH ₂ ＣC (CH ₃ ) -CONHC ₂ H ₄ N (C
H _{3) 2],} N, N-dimethylaminopropyl acrylamide _{[CH 2 = CH-CONH-C} 3 H 6 N (CH 3) 2 ],
N, N-dimethylaminopropyl methacrylamide [C
_{H 2 = C (CH 3)} -CONH-C 3 H 6 N (CH 3) 2 ], and the like.

Compounds for forming salts include:
In the case of a tertiary amine, hydrochloric acid, sulfuric acid, acetic acid and the like are used, and as the compound used for quaternization, methyl chloride, dimethyl sulfate, benzyl chloride, epichlorohydrin and the like are used.

(5) Pigment having cationic group, pigment and pigment dispersant having cationic group As the pigment used in the second invention of the present invention, conventionally known carbon black and organic pigment can be used without any problem. It is particularly preferable to use a self-dispersion type carbon black in which at least one kind of cationic hydrophilic group is bonded to the surface of the carbon black directly or through association with another atomic group. A specific example will be described below.

(I) Pigment Having a Cationic Group (Cationically Charged Carbon Black) As the cationically charged carbon black, at least one of the following cationic groups selected from the following cationic groups may be used on the surface of carbon black. One in which one is bonded. However,
In the following formula, R represents a linear or branched alkyl group having 1 to 12 carbon atoms, a substituted or unsubstituted phenyl group, or a substituted or unsubstituted naphthyl group.

[0044]

As a method for producing a cationically charged self-dispersible carbon black having a hydrophilic group bonded thereto as described above, for example, a method of bonding an N-ethylpyridyl group having the following structure is exemplified. As an example, there is a method of treating carbon black with 3-amino-N-ethylpyridinium bromide. Since the carbon black charged cationically by the introduction of the hydrophilic group on the surface of the carbon black has excellent water dispersibility due to repulsion of ions, even when the carbon black is contained in the aqueous ink, a dispersant or the like is used. A stable dispersion state can be maintained without the addition of.

[0046]

Incidentally, the various cationic hydrophilic groups as described above may be those directly bonded to the surface of carbon black, or other atomic groups may be provided between the carbon black surface and the hydrophilic groups. The hydrophilic group may be indirectly bonded to the carbon black surface by interposing. Here, specific examples of the other atomic groups include, for example, carbon atoms of 1
To 12 linear or branched alkylene groups, substituted or unsubstituted phenylene groups, and substituted or unsubstituted naphthylene groups. Here, examples of the substituent of the phenylene group and the naphthylene group include a linear or branched alkyl group having 1 to 6 carbon atoms. Further, specific examples of the combination of another atomic group and the hydrophilic group, for example, _{-C 2 H 4 -COOM, -Ph-} SO 3 M, -Ph-C
OOM and the like (where Ph represents a phenyl group).

By the way, in the second invention of the present invention, from the above-mentioned self-dispersion type carbon black, 2
Seeds or more may be appropriately selected and used as a coloring material for the ink. The amount of the self-dispersion type carbon black in the ink is 0.1 to
It is preferably in the range of 15% by weight, particularly 1 to 10% by weight. By setting the content within this range, the self-dispersion type carbon black can maintain a sufficient dispersion state in the ink.

(Ii) Pigment and Pigment Dispersant Having Cationic Group In the second invention of the present invention, not only the above-mentioned self-dispersible carbon black containing a cationic group but also a pigment having a cationic group A pigment dispersion in which the above-described conventionally known pigment such as carbon black is dispersed as a dispersant may be used. The cationic pigment dispersant used in this case is illustrated below, but the cationic dispersant that can be used in the present invention is not limited to these.

Examples of the cationic dispersant include those obtained by polymerization of a vinyl monomer, and a cationic polymer dispersant using a cationic monomer as a monomer for constituting at least a part of the obtained polymer. And an amine salt type or quaternary ammonium salt type cationic surfactant.

The cationic monomer used at this time includes, for example, N, N-dimethylaminoethyl methacrylate [CH ₂ ＣC (CH ₃ ) —COO—C ₂ H ₄ N (C
H _{3) 2],} N, N-dimethylaminoethyl acrylate _{[CH 2 = CH-COO-C} 2 H 4 N (CH 3) 2 ], N, N
-Dimethylaminopropyl methacrylate [CH ₂ ＣC
_{(CH 3) -COO-C 3} H 6 N (CH 3) 2 ], N, N-dimethylaminopropyl acrylate [CH ₂ = CH-CO
_{O-C 3 H 6 N (} CH 3) 2 ], N, N-dimethylacrylamide _{[CH 2 = CH-CON (CH} 3) 2 ], N, N-dimethyl methacrylamide [CH ₂ = C (CH ₃₎ −CON (C
H _{3) 2],} N, N-dimethylaminoethyl acrylamide _{[CH 2 = CH-CONHC 2 H} 4 N (CH 3) 2 ], N,
N-dimethylaminoethyl methacrylamide [CH ₂ =
_{C (CH 3) -CONHC 2 H} 4 N (CH 3) 2 ], N, N-dimethylaminopropyl acrylamide [CH ₂ = CH-
_{CONH-C 3 H 6 N (} CH 3) 2 ], N, N-dimethylaminopropyl methacrylamide _{[CH 2 = C (CH 3)} -CO
_{NH-C 3 H 6 N (} CH 3) 2 ], and the like.

In the case of the tertiary amine type, examples of the compound for forming a salt include hydrochloric acid, sulfuric acid, and acetic acid, and the compounds used for quaternization include methyl chloride, dimethyl sulfate, and the like. Benzyl chloride, epichlorohydrin and the like can be mentioned. Among them, methyl chloride, dimethyl sulfate and the like are preferable in preparing the pigment dispersant used in the second invention of the present invention. The tertiary amine salt or ammonium compound as described above behaves as a cation in water, and under neutralized conditions, acidity is a stable dissolution region. The content of these monomers in the polymer is from 20 to
A range of 60% by weight is preferred.

Other monomers used in the constitution of the cationic polymer dispersant include, for example, 2-hydroxyethyl methacrylate, acrylic acid having a hydroxy group such as acrylic acid ester having a long ethylene oxide chain in the side chain. Examples of hydrophobic monomers such as esters and styrene-based monomers and water-soluble monomers soluble in water near pH 7 include acrylamides, vinyl ethers, vinylpyrrolidones, vinylpyridines, and vinyloxazolines.

As the hydrophobic monomer, styrene,
Hydrophobic monomers such as styrene derivatives, vinyl naphthalene, vinyl naphthalene derivatives, alkyl esters of (meth) acrylic acid, and acrylonitrile are used. In the polymer dispersant obtained by copolymerization, a water-soluble monomer is used to make the copolymer stably exist in an aqueous solution.
The hydrophobic monomer is used in an amount of 5 to 35% by weight and is used in an amount of 2 to increase the dispersing effect of the copolymer on the pigment.
It is preferable to use it in the range of 0 to 40% by weight.

When a pigment is dispersed using such a cationic water-soluble polymer as a dispersant, pigments having an isoelectric point of 6 or more are preferred from the viewpoint of physical properties.
Alternatively, a pigment having a neutral or basic pH, such as a pigment having a pH of 7 or more and 10 is preferable in terms of dispersibility. This is understood to be due to the strong ionic interaction between the pigment and the cationic water-soluble polymer. In order to obtain a fine particle aqueous dispersion of a pigment using the above materials, for example, carbon black is subjected to a premixing treatment in a cationic dispersant solution, subsequently milled with a high shear rate dispersion device, and diluted. A centrifugation process is performed to remove coarse particles.
Thereafter, a material for a desired ink formulation is added, and an aging treatment is performed in some cases. Thereafter, an aqueous dispersion of carbon black can be obtained by performing centrifugal separation to finally obtain a pigment dispersion having a desired average particle size. The pH of the aqueous dispersion of carbon black thus produced is preferably in the range of 3 to 7.

(6) Aqueous medium, other additives, etc. The colorant-encapsulating resin having a cationic group containing the colorant of (4) and the cationic pigment or pigment dispersant of (5) have a cationic property. As the aqueous medium which holds the pigment dispersion in a dispersed state and is used as an ink, those described in the constituent material (3) of the first invention can be appropriately used. The ratio of water to the total weight of the ink is, for example, 20 to 95 wt%, particularly preferably 40 to 95 wt%, and more preferably 60 to 95 wt%. Further, as the water-soluble organic solvent that may be added to water, those described in the above (3) can be used. Further, a preferred water-soluble organic solvent is glycerin, and its addition amount is preferably 2 to 30% by weight, more preferably 5 to 15% by weight in the ink.

A more preferred water-soluble organic solvent is a mixed solvent containing glycerin and a polyhydric alcohol such as diethylene glycol or ethylene glycol. The mixing ratio of glycerin and other polyhydric alcohol is glycerin: other polyhydric alcohol. Alcohol is preferably between 10: 5 and 10:50. Other polyhydric alcohols of glycerin include, for example, diethylene glycol, ethylene glycol, polyethylene glycol and propylene glycol. These glycerin or a mixture of glycerin and another polyhydric alcohol can be used by further mixing with another water-soluble organic solvent.

The ink according to the second aspect of the present invention is suitably used in an ink jet recording method for recording an image by discharging ink from a recording head by thermal energy or mechanical energy and attaching the ink to a recording medium. . When the ink according to the present embodiment is particularly suitable for inkjet recording use, as the physical properties at 25 ° C., the surface tension is 15 to 60 dyn / cm, further 20 to 50 dyn / cm, and the viscosity is 15 cP or less, particularly It is preferably at most 10 cP, more preferably at most 5 cP. The pH range is preferably from 3 to 8, and more preferably from 3.5 to 8.

As specific ink compositions that can achieve such characteristics, there can be mentioned, for example, various inks used in Examples described later. Further, in addition to the resin and the pigment containing the colorant obtained as described above, the ink according to the present embodiment may contain various additives such as a surfactant, a pH adjuster, and a fungicide. Good.

[0060]

The present invention will be described more specifically with reference to the following Examples and Comparative Examples, but the present invention is not limited to the following Examples unless it exceeds the gist of the invention. In the following description, parts and percentages are by weight unless otherwise specified. In the following examples, the average particle size is a value measured using a dynamic light scattering method (trade name: ELS-800; manufactured by Otsuka Electronics Co., Ltd.).

<Examples 1 and 2> First, C-1 was prepared as a dispersion of carbon black. (Preparation of carbon black dispersion C-1)
It was prepared as follows. Cationic polymer P-1 containing acrylamide and trimethylaminopropylacrylamide sulfate in a monomer weight ratio of 70:30 (weight average molecular weight = 11,000, pH of aqueous solution = 3.26)
Was used as a dispersant to prepare a carbon black dispersion C-1 with the following composition and method.

Next, these materials were charged in a batch type vertical sand mill (made by Imex), filled with glass beads of 1 mm diameter as a medium, and subjected to a dispersion treatment for 3 hours while cooling with water. The viscosity of the liquid after dispersion was 28 cps, and the pH was 4.05. The dispersion was centrifuged to remove coarse particles to obtain a dispersion C-1 having an average particle size of 0.12 μm. The total solids weight of this dispersion was 10 wt%.

(Synthesis of Copolymers 1 and 2) Copolymer 1 containing styrene and acrylamide at a weight ratio of 85:15 was synthesized by a macromonomer method. A copolymer 2 containing styrene, N, N-dimethylaminoethyl methacrylate and acrylamide at a weight ratio of 50:20:30 was polymerized in the same manner.

(Colorant-Encapsulated Resin Dispersions MC-1 and MC
Preparation of -2) Further, MC-1 and MC-2 were prepared as a dispersion of a resin containing a colorant. (Preparation of MC-1) The following materials were mixed and dissolved. The above mixture was subjected to phase inversion emulsification using acetic acid as a neutralizing agent, and methyl ethyl ketone was removed.
An aqueous dispersion of microcapsules having an average particle diameter of 0.08 μm was obtained at t%.

(Preparation of MC-2) The same procedure was followed except that the resin used in MC-1 was changed to copolymer 2 (molecular weight: 35,000). An aqueous dispersion of 0.13 μm microcapsules was obtained.

(Preparation of Inks of Examples 1 and 2) Each of the dispersions prepared as described above was mixed so that each solid content was as shown in Table 1, and then glycerin 16w
Each solvent was mixed so that the total solid content in the ink of the carbon black and the resin containing the colorant was 8 wt%. C. shown in Table 1. B. / MC indicates the final solid concentration of the completed ink. still,
The amount of carbon black in Example 1 shown in Table 1 represents the total solid content of the carbon black and the dispersant.

Comparative Example 1 (Synthesis of Copolymer 3) Copolymer 3 containing styrene and acrylamide at a weight ratio of 5:95 was synthesized by a macromonomer method.

(Preparation of MC-3 and Preparation of Ink) MC
In the same manner, except that the resin used in -1 was changed to copolymer 3 (molecular weight 35,000), the solid content concentration was finally 20 wt.
%, An aqueous dispersion of microcapsules having an average particle diameter of 0.13 μm was obtained. Using the obtained MC-3, an ink of Comparative Example 1 was prepared in the same manner as in Example.

[0069]

<Evaluation> Example 1 thus completed,
The three types of inks of Comparative Example 1 and Comparative Example 1 were used with Canon Color B
The black ink tank of the BJ cartridge BC-21 mounted on the J printer BJC-420J is filled, and the BJC-420J “plain paper, 360 × 360DP”
In the "I, HQ mode", printing was performed on Canon PB paper, both of which are BJ-electrophotographic paper manufactured by Canon. The image density, water resistance, and line marker resistance were evaluated by the following methods and criteria.

(1) Image Density After a solid image was allowed to stand for 12 hours after printing, it was measured using a reflection density meter Macbeth RD-918 (manufactured by Macbeth). The evaluation results were classified as follows.

(2) Water resistance Using the same solid image as the one for which the image density was evaluated,
Leave for 2 hours. Then, the printed matter was allowed to stand in tap water for 3 seconds, and the reflection density after the water was dried was measured, and the residual ratio of the reflection density before and after the water resistance test was determined and used as a measure of the water resistance. . The evaluation results were classified as follows.

(3) Line Marker Resistance The character portion was marked once with normal writing pressure using a yellow fluorescent pen spot writer yellow manufactured by Pilot Corporation at 15 minutes and 1 hour after printing the character. The evaluation of the line marker resistance was classified as follows.

A: Fifteen minutes after printing the character, no bleeding or stain on the white background was recognized on the printed matter, and the pen tip was not stained. B: Fifteen minutes after printing the character, the printed matter was not stained on the white background. Although not recognized, the pen tip is slightly stained, but one hour after printing the character, no bleeding or stain on the white background is recognized on the printed matter and the pen tip is not stained. C: One hour after printing the character No stain on white background is found on printed matter, but pen tip is slightly stained D: Stain on white background is seen on printed matter

(4) Dischargeability The periphery of the discharge port was observed with a microscope.

The evaluation results are shown in Table 2 below.

From the above examples, as shown in 2, by using the ink used in each example, the image density on plain paper was sufficiently high, the water resistance was excellent, and the line marker resistance was also high. A sufficiently satisfactory recorded image was obtained.
In addition, as shown in Table 2, in the case of the comparative example in which the resin containing the colorant contains a large amount of the hydrophilic polymer chain portion, the result that the image density, the water resistance, and the line marker resistance are all satisfied at a high level. Was not obtained.

[0078]

As described above, according to the present invention,
An ink suitable for inkjet recording, which has a high image density, excellent water resistance, and a high quality recorded image with excellent line marker resistance, and also has a good ink ejection property.

Continued on the front page (72) Inventor Mikishi Ogasawara 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc. (72) Inventor Hiroyuki Takuhara 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc. (72) Inventor Yutaka Kurabayashi F-term (reference) 2C056 EA13 EA21 FA03 FC02 2H086 BA55 BA59 BA62 4J039 BE01 BE02 BE22 CA11 GA24

Claims (4)

[Claims] 1. An ink containing a colorant-encapsulating resin containing a colorant and a pigment, wherein the resin is a copolymer comprising a hydrophilic polymerized chain portion and a hydrophobic polymerized chain portion, The polymerization ratio of the hydrophilic polymer chain portion to the hydrophobic polymer chain portion of the copolymer is 15:85 to 50: 5.
An ink characterized by being in the range of 0. 2. An ink containing a pigment having a cationic group or a pigment and a pigment dispersant having a cationic group, and a colorant-encapsulating resin encapsulating a colorant, wherein the resin has a hydrophilic polymer chain portion. A copolymer comprising a hydrophobic polymer chain portion, wherein the polymerization ratio of the hydrophilic polymer chain portion to the hydrophobic polymer chain portion of the copolymer is 15:
An ink characterized by being in the range of 85 to 50:50. 3. The ink according to claim 2, wherein the colorant-containing resin has a cationic hydrophilic group on the surface. 4. A hydrophilic polymer chain portion of the copolymer,
The polymerization ratio of the hydrophobic polymerization chain portion is from 20:80 to 4
The ink according to any one of claims 1 to 3, wherein the ratio is in the range of 0:60.