JP2001287353A - Ink jet recording method and ink jet recording ink - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ink jet recording method and an ink jet recording ink satisfying three points, (1) an image is reproduced clearly on a plain paper with excellent print quality, (2) shortening of drying time is realized on a plain paper while ensuring high speed print aptitude, and (3) high reliability is realized at the time of preservation and use. SOLUTION: In the ink jet recording method, an ink jet recording ink containing at least a self dispersible pigment, water, a water soluble organic solvent, a water soluble polymer and a surfactant, and satisfying following conditions (a)-(e) is printed on a recording medium at a drop quantity of 5-25 pl. (a) Number-average mean grain size of dispersion particles in the pigment is in the range of 10-60 nm, (b) surface tension is in the range of 30-50 mN/m, (c) viscosity is in the range of 1.5-5.0 mPa.s, (d) conductivity is in the range of 0.001-0.4 S/m, and (e) pH is in the range of 6-11.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ink jet recording method for recording an image by discharging ink, and an ink jet recording ink used in the ink jet recording method.

[0002]

2. Description of the Related Art Liquid or molten solid ink is discharged from nozzles, slits, porous films, etc.
A so-called ink jet recording type printer that performs recording on a cloth, a film, or the like has various advantages such as small size, low cost, and quietness. In particular, it can print three or four colors at a time and easily print a full-color image. Can now be widely spread.

[0003] However, in general, an ink containing a liquid as a main component has a reduced resolution / edge sharpness on a recording medium such as plain paper, and the printing quality is degraded. To improve print quality, low-permeability ink is generally used to suppress bleeding on paper, but the drying time of the ink is extremely slow, and high-speed printability is not exhibited.

[0004] On the other hand, in order to shorten the drying time, an ink having high permeability is generally used. For example, JP-A-5-125309
In Japanese Patent Application Publication No. JP-A-2002-209, a method for lowering the ink surface tension is disclosed. Further, Japanese Patent Application Laid-Open No. Hei 5-19491 discloses a method of adding alcohol to ink.
Japanese Patent Application Laid-Open No. 6-256696 discloses a method of adding a surfactant to ink. These methods are effective for improving the permeability and shortening the drying time,
Regarding the print quality, satisfactory satisfaction cannot be obtained. As described above, compatibility between a short drying time having high-speed printing suitability and high printing quality comparable to that of a laser printer has not yet reached a satisfactory level.

[0005]

Accordingly, the present invention provides
An object of the present invention is to provide an inkjet recording method and an inkjet recording ink that can satisfy the following three points in inkjet printing. To reproduce images clearly on plain paper and obtain excellent print quality. Achieving drying time on plain paper with high-speed printing suitability. High reliability during storage and use.

[0006]

Means for Solving the Problems As a result of intensive studies, the present inventors have found that the above objects can be achieved by the following present invention. That is, the inkjet recording method of the present invention comprises at least a self-dispersible pigment, water, a water-soluble organic solvent, a water-soluble polymer and a surfactant, and satisfies the following conditions (a) to (e). The recording ink is printed on a recording medium such that the drop amount is 5 to 25 pl. (A) The number average particle diameter of the dispersed particles of the pigment is 10 to 6
0 nm range (b) Surface tension is in the range of 30 to 50 mN / m (c) Viscosity is in the range of 1.5 to 5.0 mPa · s (d) Conductivity is 0.001 to 0.4 S / m (E) pH is in the range of 6 to 11

The ink jet recording ink of the present invention is an ink jet recording ink used in the above ink jet recording method of the present invention, wherein at least a self-dispersible pigment, water, a water-soluble organic solvent, a water-soluble polymer and a surfactant It is characterized by containing an agent and satisfying the above conditions (a) to (e).

[0008] By the ink jet recording method and the ink jet recording ink of the present invention, excellent print quality,
Short drying times and high reliability could all be satisfied. The print quality deteriorates when the penetration of the recording medium (for example, paper) in the horizontal direction increases, and improves when the penetration decreases. Further, the drying time on the surface of the recording medium is not actually the time for drying the liquid in the ink, but the effect of the time for penetrating the recording medium. Therefore, in order to shorten the so-called drying time, it is necessary to increase the permeability.

From the viewpoint of print quality, it is necessary to suppress the permeability in the horizontal direction on the surface of the recording medium. On the other hand, from the viewpoint of the drying time, it is necessary to increase the permeability in the vertical direction of the recording medium. In the case of a penetrant such as a surfactant which has been conventionally used for an ink, the penetration is high in both the horizontal and vertical directions, so that it was not possible to shorten the drying time while obtaining high print quality. According to the present invention, it is possible to suppress permeation in the horizontal direction of the recording medium, and it is possible to achieve both high printing quality and a short drying time.

The specific structure of the present invention is as follows. As the colorant, a pigment having good edge sharpness is used to obtain high image quality. A penetrant is added to shorten the drying time. Generally, the penetrant has a surface active action and a hydrophobic action. In a pigment dispersed by an ordinary dispersant, the penetration agent is replaced with an adsorbent / dispersant on the pigment surface, and it is difficult to secure dispersion stability. For this reason, in the present invention, in particular, a self-dispersed pigment in which a hydrophilic functional group is chemically bonded directly to the pigment surface is employed.

On the other hand, when a general carbitol or a low-molecular surfactant is used alone as a penetrant added to shorten the drying time, the penetrant penetrates the recording medium in both the horizontal and vertical directions and reduces the penetration in the horizontal direction. It cannot be suppressed and may cause deterioration of print quality. Therefore, in the present invention, by adding a water-soluble polymer together with a surfactant, the above conflicting functions can be achieved. With such a configuration, the mechanism capable of achieving both of the above contradictory functions is not clear, but is interpreted as the following operation.

A low surface tension ink containing a pigment having high image sharpness and the water-soluble polymer suppresses the penetration in the horizontal direction of the recording medium, thereby achieving both high printing quality and short drying time. It is supposed to be. That is, at the same time as the ink lands on the surface of the recording medium, the water-soluble polymer contained in the ink is richly present at the gas-liquid interface of the landed ink due to its surface activity. Further, it is considered that the water-soluble polymer causes a rapid thickening at the gas-liquid interface due to the penetration of water. It is presumed that this thickening suppresses the ink movement in the horizontal direction (gas-liquid interface) and shortens the drying time while maintaining high image quality.

These effects are obtained when the ink drop amount is 5 to 5.
Experiments have shown that it works only in the range of 25 pl. That is, when the ink is a small drop of 5 to 25 pl, the image quality is dramatically improved by the thickening action of the water-soluble polymer when the ink lands on the recording medium. However, if the ink drop amount exceeds 25 pl, the image quality deteriorates. This can be interpreted as being that if the amount of ink drop becomes too large, the weight of the ink drop will break the barrier caused by the increase in the viscosity of the water-soluble polymer.

In general, when the added amount of the water-soluble polymer is increased, the dispersion stability of the ink, the clogging resistance (pigment solubility at the time of evaporation of water at the nozzle tip), or the recovery from standing (long-term storage stability) ) Gets worse. This is considered to be because the water-soluble polymer surrounds the pigment, and the water-soluble polymers are mutually bonded. It has been clarified that by adding a low molecular surfactant (preferably in a trace amount) to this state, the image quality is not deteriorated and the reliability is dramatically improved. That is, it is considered that the addition of the low-molecular surfactant causes the low-molecular surfactant to enter between the water-soluble polymers surrounding the pigment, and the hydrophilic group of the pigment itself functions sufficiently to maintain reliability. From the above effects, according to the present invention, high printing quality, reduced drying time,
And high reliability can be achieved.

In the present invention, the ink jet recording ink in the above ink jet recording method of the present invention (including the ink jet recording ink of the present invention; hereinafter, may be abbreviated as "ink of the present invention" or simply "ink"). The weight average molecular weight of the water-soluble polymer is 10
It is preferable to set it in the range of 00 to 20000,
Is preferably in the range of 5 to 16. It is desirable that the water-soluble polymer has a surface-active action capable of keeping the ink surface tension in the range of 35 to 50 mN / m by adding it alone to the ink. The water-soluble polymer is desirably nonionic or anionic containing a -COO ^- M ⁺ group (M is an alkali metal, ammonium, or organic onium compound).

In the present invention, the molecular weight of the surfactant is desirably in the range of 150 to 1,000, the HLB is desirably in the range of 5 to 14, and the surfactant is a nonionic surfactant. Is desirable. The content ratio of the water-soluble polymer to the surfactant in the ink is preferably in the range of 20: 1 to 2: 1, and the content is 0.01 to the total amount of the ink. It is preferably in the range of 〜4% by weight.

The self-dispersible pigment in the ink is desirably carbon black. It is desirable that the ink further contains a low molecular alcohol or urea.

In the ink jet recording method of the present invention, it is desirable that one or more liquid compositions be attached to a recording medium prior to or simultaneously with printing with the ink jet recording ink. At this time, the liquid composition desirably contains a surfactant, and the surface tension of the liquid composition is as follows:
Desirably, it is 20 to 40 mN / m. It is desirable that the liquid composition contains a coloring agent, and the coloring agent is preferably a dye.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail. <Inkjet recording ink> The ink of the present invention will be described separately for its constituent components, physical properties, and its preparation.

[Components of Ink] The ink of the present invention comprises:
At least a self-dispersible pigment, water, a water-soluble organic solvent,
It preferably contains a water-soluble polymer and a surfactant, and further contains at least one of a low molecular weight alcohol and urea. Also, if necessary, pH adjusters, hydrotropes, chelating agents, inclusion compounds, oxidants, antioxidants, reducing agents, enzymes, bactericides, defoamers, abrasives, etc.
Other additives can be added.

(Self-dispersible Pigment) In the ink of the present invention, a pigment that can be dispersed in a solvent by itself without containing a so-called polymer dispersant is used. Generally, self-dispersible pigments have a hydrophilic functional group on the surface. In the present invention, whether or not the pigment is “self-dispersible” is confirmed by the following self-dispersibility test.

Self-dispersibility test A pigment to be measured is added to water and dispersed using an ultrasonic homogenizer, a nanomizer, a microfluidizer, a ball mill, or the like without a dispersant, so that the initial pigment concentration becomes about 5%. A dispersion is prepared by diluting with water to obtain a dispersion.
After the initial pigment concentration and 100 g of the dispersion are placed in a glass bottle having a diameter of 40 mm and allowed to stand for one day, the pigment concentration of the upper layer is measured. When the ratio of the pigment concentration after standing for one day to the initial pigment concentration (hereinafter referred to as “self-dispersibility index”) is 98% or more, it was evaluated as “self-dispersibility”.

At this time, the method for measuring the pigment concentration is not particularly limited, and may be any of a method of measuring the solid content by drying the sample, a method of diluting the sample to an appropriate concentration and obtaining from the transmittance, and the like. As long as there is a method for accurately determining the pigment concentration, that method may be used.

The hydrophilic functional group contained in the self-dispersing pigment may be any of nonionic, anionic and cationic hydrophilic functional groups.
A hydroxyl group, a sulfonic acid group, and a phosphoric acid group alone or in combination of two or more are preferable, and among them, a carboxyl group alone or a combination of two or more containing a carboxyl group is more preferable. When it has a carboxyl group, a sulfonic acid group, or a phosphoric acid group, it can be used as it is in the form of a free acid. However, a case where a part or all of the salt forms a salt is advantageous in terms of dispersibility and is preferred. Various basic substances can be used as the substance that forms the salt, but alkali metals, ammonia, and organic onium compounds are preferably used alone or in combination of two or more.

The number of hydrophilic functional groups on the surface of the pigment depends on the type of the hydrophilic functional group and, if a salt is formed, the type of the substance forming the salt, and cannot be determined unconditionally. When the acidic functional group is -COONa,
0.8-4 mmol / g is preferred.

As the pigment for introducing a hydrophilic functional group, both inorganic and organic pigments can be used. As the black pigment, carbon black pigments such as furnace black, lamp black, acetylene black, and channel black are preferable. For example, Raven 7000, Rave
n5750, Raven5250, Raven5000
ULTRAII, Raven3500, Raven250
0ULTRA, Raven2000, Raven150
0, Raven 1250, Raven 1200, Rav
en1190ULTRAII, Raven1170, Ra
ven 1255, Raven 1080 ULTRA, Ra
ven1060ULTRA, Raven790ULTR
A, Raven780ULTRA, Raven760U
LTRA (all manufactured by Columbia), Regal400
R, Regal330R, Regal660R, Mog
ul L, Black Pearls L, Black
Pearls 1300, Monarch 700,
Monarch 800, Monarch 880, M
onarch 900, Monarch 1000, M
onarch 1100, Monarch 1300,
Monarch 1400 (all manufactured by Cabot), C
color Black FW1, ColorBlack
FW2, Color Black FW2V, Color
or Black 18, Color Black F
W200, Color BlackS150, Colo
r Black S160, Color Black
S170, Printex35, PrintexU, P
printxV, Printex140U, Print
ex140V, Special Black 6, Sp
electrical Black 5, Special Bla
No. ck 4A, Special Black 4 (all manufactured by Degussa), 25, no. 33, no. 40, N
o. 47, no. 52, no. 900, No. 230
0, MCF-88, MA600, MA7, MA8, MA
100 (all manufactured by Mitsubishi Chemical Corporation) can be used, but the present invention is not limited to these. Further, magnetic fine particles such as magnetite and ferrite, titanium black and the like may be used as a black pigment.

Examples of the cyan pigment include C.I. I. Pigme
nt Blue-1, C.I. I. Pigment Blu
e-2, C.I. I. Pigmet Blue-3, C.I.
I. Pigmet Blue-15, C.I. I. Pigm
ent Blue-15: 1, C.I. I. Pigment
Blue-15: 3, C.I. I. Pigment Bl
ue-15: 34, C.I. I. Pigment Blue
-16, C.I. I. Pigment Blue-22,
C. I. Pigment Blue-60, but not limited to these.

Examples of the magenta pigment include C.I. I. Pigm
ent Red 5, C.I. I. Pigment Red
7, C.I. I. Pigment Red 12, C.I.
I. Pigment Red 48, C.I. I. Pigm
ent Red 48: 1, C.I. I. Pigment
Red 57, C.I. I. Pigment Red 11
2, C.I. I. Pigment Red 122, C.I.
I. Pigment Red 123, C.I. I. Pig
Ment Red 146, C.I. I. Pigment
Red 168, C.I. I. Pigment Red 1
84, C.I. I. Pigment Red 202, etc., but is not limited thereto.

As the yellow pigment, C.I. I. Pigm
ent Yellow-1, C.I. I. Pigment
Yellow-2, C.I. I. Pigment Yellow
ow-3, C.I. I. Pigment Yellow-1
2, C.I. I. Pigment Yellow-13, C.I.
I. Pigment Yellow-14, C.I. I. P
pigment Yellow-16, C.I. I. Pigm
ent Yellow-17, C.I. I. Pigment
Yellow-73, C.I. I. Pigment Ye
low-74, C.I. I. Pigment Yellow
w-75, C.I. I. Pigment Yellow-8
3, C.I. I. Pigment Yellow-93,
C. I. Pigment Yellow-95, C.I.
I. Pigment Yellow-97, C.I. I. P
pigment yellow-98, C.I. I. Pigm
ent Yellow-114, C.I. I. Pigmen
tYellow-128, C.I. I. Pigment Y
yellow-129, C.I. I. Pigment Yel
low-151, C.I. I. Pigment Yellow
w-154 and the like, but are not limited thereto.

For the present invention, a newly synthesized pigment may be used, or two or more kinds of pigments may be mixed and used. In addition to black, cyan, magenta, and yellow primary color pigments, specific color pigments such as red, green, blue, brown, and white, gold,
A metallic luster pigment such as silver, a colorless extender, a plastic pigment, or the like may be used. A particularly preferred pigment is carbon black.

As a method for introducing a hydrophilic functional group to the surface of these pigments, any of known methods and newly invented methods can be used. For example, oxidation treatment with an oxidizing agent (for example, nitric acid, permanganate, dichromate, hypochlorite, ammonium persulfate, hydrogen peroxide, ozone, etc.), treatment with a coupling agent such as a silane compound, polymer grafting In addition to known methods such as a chemical treatment and a plasma treatment, newly developed methods can be used, and these methods may be combined.

It is desirable that the obtained pigment into which the hydrophilic functional group is introduced is purified by removing residual impurities such as oxidizing agent and other inorganic and organic impurities. In particular, the content of calcium, iron, and silicon in the ink is desirably 10 ppm or less, preferably 5 ppm or less. In the present invention, the content of these inorganic impurities was measured by high frequency inductively coupled plasma emission spectrometry. These impurities can be removed, for example, by washing with water, a reverse osmosis membrane, an ultrafiltration membrane, a method such as an ion exchange method, or an adsorption method using activated carbon, zeolite or the like, alone or in combination.

These self-dispersible pigments having a hydrophilic functional group introduced therein are, in addition to those newly prepared for the present invention,
Commercially available self-dispersible hydrophilic treated pigments can also be used. Commercially available self-dispersible hydrophilic treatment pigments include, for example, MICROJET BLACK CW-1 (manufactured by Orient Chemical Industries, Ltd.) and CAB-O-JET200.
(Manufactured by Cabot), CAB-O-JET300 (manufactured by Cabot) and the like. All of these commercially available self-dispersible hydrophilic pigments have a self-dispersibility index of 100.
%. It is preferable that the number of coarse particles in the pigment dispersion is reduced in advance by a method such as dispersion treatment, centrifugation, or filtration.

The self-dispersible pigment is generally 0.5 to 20% by weight, preferably 2 to 10% by weight based on the total weight of the ink.
Used in the range of wt%. If the content of the pigment is too large, clogging is likely to occur at the nozzle tip, and the abrasion resistance of the image is also deteriorated. On the other hand, if the content is 0.5 wt% or less, it is difficult to obtain an effective optical density.

The number average particle diameter of the pigment dispersed particles in the ink must be in the range of 10 to 60 nm, preferably 15 to 50 nm, more preferably 20 to 50 nm. Number average particle size is 1
If it is less than 0 nm, the viscosity of the ink tends to increase, and clogging tends to occur. On the other hand, if it exceeds 60 nm, the reliability of the ink tends to decrease.

The particle size distribution mv / mn expressed by the ratio of the volume average particle diameter mv to the number average particle diameter mn of the pigment dispersed particles in the ink is preferably 3 or less, more preferably 2 or less. .2 or less. When the particle size distribution is widened, the penetration rate becomes slow, and the scratch resistance tends to decrease. In particular, when carbon black subjected to a hydrophilic treatment is used as the self-dispersible pigment, it is preferable that the carbon black be 2.2 or less from the viewpoint of abrasion resistance of an image. In addition,
The particle size distribution mv / mn is 1 in monodispersion, and ideally it is desired to approach this. However, it is actually difficult to make the particle size distribution mv / mn = 1 into a monodispersed state. .1 or more.

In the present invention, the particle size of the dispersed particles of the pigment in the ink can be measured using a Microtrac UPA particle size analyzer 9340 (manufactured by Leeds & Northrup) in which the pigment to be measured is dispersed (hereinafter, referred to as an ink). "Ink to be measured") was measured without dilution. As parameters to be input at the time of measurement, the viscosity of the ink to be measured was input as the viscosity, and the density of the pigment was input as the density of the dispersed particles. The density of the latter is, for example, 1.8 g /
cm ² .

Preferably, among the dispersed particles of the pigment contained per liter of ink, a particle diameter of 0.5
The number of μm or more is 7.5 × 10 ¹⁰ or less. 0.
The number of dispersed particles of 5 μm or more is
TM770 OpticalParticle Siz
er (ParticleSizing Systems)
Is preferably used as the measuring device. This device detects particles passing through a measuring unit by an optical method. For the measurement, 2 μl of the ink to be measured is put into a measurement cell, and the measurement is performed in accordance with a predetermined measurement method of the above-described measuring device, and a value converted to a value in 1 liter is used.

(Water) The water used in the ink of the present invention is not particularly limited. In order to prevent impurities from being mixed, ion-exchanged water, ultrapure water, distilled water, and ultrafiltered water are used. Is preferred.

(Water-soluble organic solvent) The water-soluble organic solvent used in the ink of the present invention includes polyhydric alcohols and their derivatives such as alkyl ethers, which can prevent solidification of the ink and adjust the viscosity. Can be used. For example, glycerin, diethylene glycol, (2 (2-butoxyethoxy) ethanol), diethylene glycol phenyl ether, propylene glycol, propylene glycol monomethyl ether, butylene glycol, triethylene glycol, thiodiglycol, hexylene glycol, ethylene glycol methyl ether, diethylene glycol methyl Ether, pentanediol,
Hexanetriol, trimethylolpropane and the like. These may be used alone or in combination of two or more.

Other components include alcohols such as hexyl alcohol and benzyl alcohol, amides such as dimethylformamide and dimethylacetamide, ketones such as acetone and diacetone alcohol, keto alcohols, triethanolamine, diethanolamine, and the like.
High-boiling nitrogen-containing solvents such as pyrrolidone, N-methyl-2-pyrrolidone, and 1,3-dimethyl-2-imidazolidinone;
Sulfur-containing solvents such as dimethyl sulfoxide, diethyl sulfoxide, sulfolane and thiodiethanol, sugars such as glucose, maltose, amylose (dextrin), cellulose and sodium alginate and derivatives thereof, and gum arabic can be used. It is not limited.

Among these water-soluble organic solvents, solvents selected from ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, glycerin, thiodiethanol, propylene glycol, and dipropylene glycol have the highest compatibility with water-soluble polymers and are the most preferable.

These water-soluble organic solvents can be used alone or in combination of two or more. The content of the water-soluble organic solvent is preferably 1 to 50% by weight based on the total weight of the ink. If it is less than 1% by weight, a moisturizing effect may not be obtained. On the other hand, if it exceeds 50% by weight, poor ejection may be induced due to an increase in ink viscosity.

(Water-soluble polymer) The water-soluble polymer used in the ink of the present invention may be any of natural, semi-synthetic and synthetic water-soluble polymers. Further, it may be in the form of an aqueous polymer colloid (polymer emulsion). Examples of the natural water-soluble polymer include starch starch, potato starch, tapioca starch, wheat starch, corn starch and other starchy substances, konjac and other mannan, and seaweeds such as sea urchin, galactan, sodium alginate, trollooi, tragacanth gum And gums such as gum arabic, dextran and levan, and proteins such as glue, gelatin, casein and collagen.

Examples of the semisynthetic water-soluble polymer include celluloses such as viscose, methylcellulose, ethylcellulose, hydroxycellulose, carboxymethylcellulose, hydroxypropylcellulose, and hydroxypropylmethylcellulose; soluble starch, carboxymethyl starch, and dialdehyde starch. , Starch such as hydroxymethyl starch, starch acetate, dextrin, cyclodextrin and the like.

As the copolymer in the synthetic water-soluble polymer, a homopolymer of a hydrophilic monomer component comprising a hydrophobic portion and a hydrophilic portion having an SO ₃ H group or a salt thereof, a hydrophobic monomer component, A copolymer of a hydrophilic monomer component having an SO ₃ H group or a salt thereof A homopolymer of a hydrophobic monomer component or a copolymer of two or more hydrophobic monomer components is subjected to a hydrophilization treatment by sulfonation. Or a salt thereof, a homopolymer of a hydrophilic monomer component comprising a hydrophobic part and a hydrophilic part having an H ₃ PO ₄ group, or a salt thereof, a hydrophobic monomer component, and an H ₃ PO ₄ group A homopolymer of a hydrophilic monomer component comprising a copolymer of a hydrophilic monomer component having the following formula or a salt thereof, a hydrophobic portion and a hydrophilic portion having a COOH group or a salt thereof, a hydrophobic monomer component, and C A hydrophilic monomer component having an OH group, and copolymers or salts thereof of. Further, other components can be copolymerized as needed. Further, these can be used in combination.

The copolymer may have any structure such as random, graft, block and the like. These salts are preferably used alone or in combination of two or more of alkali metals, ammonia and organic onium compounds, but are not limited thereto.

The hydrophilic monomer component having an SO ₃ H group includes styrene sulfonic acid, styrene sulfonic acid derivative, benzene sulfonic acid, benzene sulfonic acid derivative, naphthalene sulfonic acid, naphthalene sulfonic acid derivative, toluene sulfonic acid, and toluene sulfonic acid. Derivatives, vinylsulfonic acid, and vinylsulfonic acid derivatives.

Examples of the hydrophilic monomer component having an H ₃ PO ₄ group include a higher alkyl phosphate ester salt and a phosphate ester salt of a higher alcohol ethylene oxide adduct. Examples of the hydrophilic monomer component having a COOH group include α, β-ethylenically unsaturated carboxylic acid and its aliphatic alcohol ester, acrylic acid, acrylic acid derivative, methacrylic acid, methacrylic acid derivative, maleic acid, maleic acid derivative, itacone Acids, itaconic acid derivatives, fumaric acid, fumaric acid derivatives and the like. Hydrophobic monomer components include styrene, styrene derivatives, vinyl toluene, vinyl toluene derivatives, vinyl naphthalene, vinyl naphthalene derivatives, butadiene, butadiene derivatives, isoprene, isoprene derivatives, ethylene, ethylene derivatives, propylene, propylene derivatives, alkyl acrylates Esters, alkyl esters of methacrylic acid, and the like.

Other components which can be copolymerized include acrylamide, acrylamide derivatives, dimethylaminoethyl methacrylate, ethoxyethyl methacrylate, butoxyethyl methacrylate, ethoxytriethylene methacrylate, vinyl pyrrolidone, vinyl pyridine, alkyl ethers and methoxy polyethylene glycol methacrylate, Examples include components containing polyoxyethylene such as polyethylene glycol methacrylate, and components containing hydroxyl groups such as hydroxymethyl methacrylate, hydroxyethyl methacrylate, and vinyl alcohol. In addition to the above, a water-soluble polymer can be obtained by addition-polymerizing a hydrophilic monomer component using a condensation polymer (a polyester-based condensation polymer) of an unsaturated carboxylic acid, an alcohol or a glycol as a hydrophobic component. .

The monomer ratio between the hydrophobic unit and the hydrophilic unit of these water-soluble polymers is preferably from 30:70 to 60:40. When the hydrophobic unit is reduced below 30:70, the hydrophilicity becomes strong and the optical density may not be kept high.
On the other hand, if the hydrophobic unit is higher than 60:40, it may be difficult to dissolve in water.

Further, the synthetic water-soluble polymer may be a synthetic product obtained by adding ethylene oxide to glycerin, diglycerin or the like. In addition, examples of the single composition synthetic polymer include polyvinyl alcohol, polyethylene glycol, polyvinyl pyrrolidone, polyacrylamide, and polypropylene glycol.

As the synthetic water-soluble polymer, a so-called polymer surfactant may be diverted. Examples of the polymer surfactant include polyoxyethylene nonyl phenyl ether, polyoxyethylene octyl phenyl ether, polyoxyethylene dodecyl phenyl ether, polyoxyethylene alkyl ether, polyoxyethylene fatty acid ester, sorbitan fatty acid ester, polyoxyethylene Silicone surfactants such as ethylene / polyoxypropylene block copolymers, polyoxyethylene sorbitan fatty acid esters, and polysiloxane polyoxyethylene adducts, and fluorine surfactants such as oxyethylene perfluoroalkyl ether are included. However, the present invention is not limited to these.

As the polymer colloid, for example,
Acrylic resin emulsion, vinyl acetate resin emulsion, urethane resin emulsion, acryl-styrene resin emulsion, butadiene resin emulsion, styrene resin emulsion, polyester resin emulsion, silicone resin emulsion, fluororesin emulsion, acrylic silicone Based resin emulsions and the like. These water-soluble polymers may be used alone or as a mixture of two or more.

The weight-average molecular weight of the water-soluble polymer in the present invention is preferably in the range of 1,000 to 20,000, more preferably 2,000 to 15,000.
Range. If the weight average molecular weight is less than 1,000, high printing quality may not be obtained. On the other hand, if the weight average molecular weight exceeds 20,000, clogging and poor injection may occur due to thickening of the nozzle surface, which is not preferable. Methods for measuring the weight average molecular weight include light scattering, small-angle X-ray scattering, sedimentation equilibrium, diffusion, ultracentrifugation, various types of chromatography, and, for example, GPC.
A value in terms of polyethylene glycol measured by the method can be used.

In the present invention, the content of the water-soluble polymer is
It is preferably in the range of 0.01 to 4% by weight, more preferably 0.03 to 3% by weight, based on the total amount of the ink. If it is less than 0.01% by weight, the effect of adding the water-soluble polymer cannot be obtained. On the other hand, if the content exceeds 4% by weight, reliability such as dispersion stability and clogging will be deteriorated.

In the present invention, the content ratio of the water-soluble polymer and the surfactant is preferably in the range of 20: 1 to 2: 1, and more preferably in the range of 20: 1 to 5: 1. Is more preferable. When the ratio of the water-soluble polymer is higher than 20: 1, the reliability of the ink may be deteriorated. On the other hand, when the ratio of the surfactant is higher than 2: 1, image quality may be deteriorated. further,
In the present invention, the ratio between the self-dispersible pigment and the water-soluble polymer is preferably in the range of 1: 1 to 10: 0.1, and more preferably in the range of 2: 1 to 10: 0.3. It is more preferable to be within. When the ratio of the water-soluble polymer is increased, the reliability of the ink may be deteriorated.

The HLB of the water-soluble polymer is 5 to
It is preferably in the range of 16, more preferably 5 to
14 range. If the HLB is lower than 5, it may not be possible to dissolve in water. On the other hand, if the HLB exceeds 16, the hydrophilicity becomes too high and the optical density may not be kept high.

Note that various methods have been proposed for measuring and calculating the HLB, and the values obtained by the methods have some differences. Therefore, in the present invention, a value calculated based on the method proposed by Davies in 1957 was used (Introduction to New Surfactants, written by Takehiko Fujimoto, published by Sanyo Chemical Industry Co., Ltd., page 133, page 2 Chapter 6). In particular,
The HLB calculation method for a polymer polymer is divided into a hydrophilic part and a hydrophobic part, and the HLB of each part is calculated by the following (Equation 1). Next, the value obtained by weighting and averaging each HLB value using the following (Equation 2) is used as the H value of the polymer polymer.
Defined as LB.

[0060]

(Equation 1)

In the above formula, HLBx indicates the HLB of each hydrophilic portion or each hydrophobic portion only, and Wx indicates the weight of each hydrophilic portion or each hydrophobic portion. The number of hydrophilic groups is a positive value, and the number of hydrophobic groups is a negative value.

Of these water-soluble polymers, particularly preferred are nonionic water-soluble polymers and -COO ^- M ⁺
It is an anionic water-soluble polymer having a group. Examples of the nonionic water-soluble polymer include a nonionic polymer surfactant, polyethylene glycol, and polypropylene glycol. Examples of the anionic water-soluble polymer having a —COO ⁻ M ⁺ group include an acrylic acid-based copolymer and a methacrylic acid-based copolymer.

As the water-soluble polymer, those having a surface active action and capable of controlling the ink surface tension within the range of 35 to 50 mN / m when added alone to the ink are preferred. Examples of the water-soluble polymer having such a function include nonionic and anionic water-soluble polymers, and examples of the nonionic water-soluble polymer include polyoxyethylene / polyoxypropylene block copolymer and polypropylene glycol. Is mentioned. Examples of the anionic water-soluble polymer include styrene / acrylic acid copolymer, styrene / methacrylic acid copolymer, n-butyl methacrylate / acrylic acid copolymer, n-butyl methacrylate / methacrylic acid copolymer, 2- Ethylhexyl methacrylate / acrylic acid copolymer, 2-ethylhexyl methacrylate / methacrylic acid copolymer and the like can be mentioned.

(Surfactant) The ink of the present invention contains various known surfactants to shorten the drying time during printing. Examples of the surfactant include known various surfactants, and any of nonionic, anionic, cationic and amphoteric surfactants may be used. In order to suppress the interaction of the same, the same type of ionic or nonionic is preferable, and a nonionic surfactant is particularly preferable. The surfactant is used in combination with the water-soluble polymer.

Examples of the nonionic surfactant include polyoxyethylene nonyl phenyl ether, polyoxyethylene octyl phenyl ether, polyoxyethylene dodecyl phenyl ether, polyoxyethylene alkyl ether, polyoxyethylene fatty acid ester, sorbitan fatty acid ester, and polyoxyethylene fatty acid ester. Oxyethylene / polyoxypropylene block copolymer, polyoxyethylene sorbitan fatty acid ester, fatty acid alkylolamide, acetylene glycol derivative (Sufinol) and the like can be mentioned.

Examples of the anionic surfactant include alkyl benzene sulfonate, alkyl naphthalene sulfonate, formalin condensate of alkyl naphthalene sulfonate, higher fatty acid salt, higher fatty acid ester sulfate, higher fatty acid ester sulfonate. , Sulfates and sulfonates of higher alcohol ethers, alkylcarboxylates of higher alkylsulfonamides, sulfosuccinates and esters thereof, alkyl phosphites, alkylphosphates, alkylphosphonates and esters thereof And higher alcohol phosphate ester salts.

Examples of the cationic surfactant include primary, secondary, and tertiary amine salts, and quaternary ammonium salts. Examples of the amphoteric surfactant include betaine, sulfobetaine, sulfate betaine, and the like.

Other silicone surfactants such as polysiloxane polyoxyethylene adducts, fluorine surfactants such as perfluoroalkyl carboxylic acid, perfluoroalkyl sulfonic acid, oxyethylene perfluoroalkyl ether, natural or biosurfactants And lecithin, spiculisporic acid, rhamnolipid, saponin, cholate and the like.

These surfactants may be used alone or in combination of two or more. It is desirable that the molecular weight of these surfactants is in the range of 150 to 1,000. Surfactants having a molecular weight of less than 150 are substantially absent. On the other hand, when the molecular weight is 1,000 to 20,000, it can be used as a water-soluble polymer. In the present invention, the content of the surfactant is 0.1 to the total amount of the ink.
It is preferably in the range of 01 to 1.5% by weight, more preferably in the range of 0.01 to 1% by weight. 0.01
If the amount is less than 10% by weight, the effect of adding the surfactant cannot be obtained.
On the other hand, if the content exceeds 1.5% by weight, the penetrating effect on the recording medium becomes too high, which may cause deterioration in image quality.

In the present invention, the HLB of the surfactant is preferably in the range of 5 to 14, more preferably 5 to 12. If the HLB is lower than 5, it may not be possible to sufficiently dissolve in water. On the other hand, if the HLB exceeds 14, the hydrophilicity becomes too high, and the optical density may not be kept high. It is desirable that the HLB of the surfactant is close to the HLB of the water-soluble polymer. HL of both
The difference of B is preferably within ± 5, more preferably within 2.5.

(Low-Molecular Alcohol and Urea) The ink of the present invention preferably contains a low-molecular alcohol and / or urea in order to improve reliability such as dispersion stability and prevention of clogging. The low molecular alcohol and urea may be used alone or in combination. It can be used for any purpose.

As the low molecular weight alcohol, methanol,
Ethanol, 1-propanol, 2-propanol, 2
-Methyl-2-propanol, 1-butanol, 2-butanol, isobutanol, 1-pentanol, 2-pentanol, 3-pentanol, allyl alcohol, propargyl alcohol, benzyl alcohol, cyclohexanol and the like having 10 or less carbon atoms Alcohols.

The content of the low-molecular alcohol is preferably in the range of 0.1 to 10% by weight, and more preferably in the range of 0.5 to 5% by weight, based on the total amount of the ink. 0.1
If the amount is less than 10% by weight, the effect of improving the reliability of the ink by adding a low molecular alcohol cannot be obtained. On the other hand, if it exceeds 10% by weight, bleeding deterioration on the paper may progress and the print quality may be reduced.

The urea content is preferably in the range of 1 to 10% by weight, more preferably 2 to 7% by weight, based on the total amount of the ink. If it is less than 1% by weight,
The effect of improving the reliability of the ink by adding urea cannot be obtained.
On the other hand, if it exceeds 10% by weight, it may precipitate on the paper, causing irregularities to appear on the image, which may lower the print quality.

(Various Additives) Other additives can be added to the ink of the present invention as needed. As the other additives, pH adjusters, hydrotropes, chelating agents, clathrates, oxidants, antioxidants,
Examples thereof include a reducing agent, an enzyme, a bactericide, an antifoaming agent, and an abrasive.

As pH adjusters for adjusting pH as necessary, sodium hydroxide, potassium hydroxide, lithium hydroxide, sodium sulfate, acetate, lactate, benzoate, triethanolamine, ammonia, Alkali such as 2-amino-2-methyl-1-propanol (AMP), ammonium phosphate, sodium phosphate and lithium phosphate, acetic acid, hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, propionic acid, and P-toluenesulfonic acid And organic acids and inorganic acids. In addition, other general pH buffers, good buffers and the like can also be mentioned. However, the pH adjuster is not limited to these. The pH of the ink of the present invention will be described later.

Examples of the hydrotrope include carboxylate such as sodium butyrate and sodium salicylate, aromatic sulfonate such as sodium toluenesulfonate, lower alcohol such as ethyl alcohol, urea, acetamide and the like. As chelating agents, ethylenediaminetetraacetic acid (EDTA), iminodiacetic acid (ID
A), ethylenediamine-di (o-hydroxyphenylacetic acid) (EDDHA), nitrilotriacetic acid (NTA), dihydroxyethylglycine (DHEG), trans-
1,2-cyclohexanediaminetetraacetic acid (CyDT
A), diethylenetriamine-N, N, N ', N ",
N "-pentaacetic acid (DTPA), glycol ether diamine-N, N, N ', N'-tetraacetic acid (GEDTA) and the like.

Examples of the inclusion compound include thiourea, desoxycholic acid, bis- (N, N'-tetramethylenebenzidine), cyclophan and the like. In addition, conventionally known oxidizing agents, antioxidants, reducing agents, enzymes, germicides, defoamers, abrasives, and the like can be used without any problems.

[Physical Properties of Ink] The ink of the present invention satisfies the following conditions (b) to (e) as physical properties. (B) The surface tension is in the range of 30 to 50 mN / m. (C) The viscosity is in the range of 1.5 to 5.0 mPa · s. (D) The conductivity is in the range of 0.001 to 0.4 S / m. e) pH is in the range of 6 to 11 Hereinafter, each physical property will be described.

(B) Surface Tension The surface tension of the ink of the present invention is 30 to 50 mN /
m. If the surface tension is lower than this range, when printing on so-called plain paper as a recording medium,
Bleeding easily occurs, and a high-resolution image cannot be obtained.
On the other hand, if the surface tension is higher than this range, the permeation into the recording medium becomes slow, and the drying time of the image becomes long, which is a problem. The surface tension of the ink of the present invention is 30 to 45 m.
N / m is preferable, and when carbon black is used as the self-dispersible pigment, adjustment to the desired range can be performed without causing bleeding and obtaining a high-resolution image. Especially desirable.

The surface tension of the ink can be adjusted by appropriately controlling the type and amount of the water-soluble polymer and / or surfactant described above. In addition, in this invention, the value measured using the Wilhelmy type surface tensiometer in the environment of 23 degreeC and 55% RH was used for the surface tension.

(C) Viscosity The ink of the present invention has a viscosity of 1.5 to 5.0 mPa.
・ S is essential, and is preferably in the range of 1.5 to 3.5 mPa · s, more preferably 1.
It is adjusted in the range of 7 to 3.5 mPa · s. The viscosity is 1.
If it is less than 5 mPa · s, the storage stability of the ink will decrease. On the other hand, when the viscosity is larger than 5.0 mPa · s, the ink ejection force is reduced, and problems such as difficulty in recovery when the ejection nozzle is clogged occur. In particular,
When carbon black subjected to hydrophilic treatment is used as the self-dispersible pigment, it is preferable that the above range is more preferable from the viewpoint of ink ejection properties.

The viscosity of the ink can be adjusted by the type and amount of the water-soluble organic solvent, the type, molecular weight, and the amount of the water-soluble polymer. In the present invention, the viscosity is
The value measured using Rheomat 115 (manufactured by Contraves) as a measuring device was used. The measurement was carried out by placing the ink to be measured in a measuring container and mounting the ink on the measuring device by a predetermined method in the measuring device. Measurement temperature is 23
° C and a shear rate of 1400 s ^-1 .

(D) Conductivity The ink of the present invention has a conductivity of 0.001 to 0.4.
It is essential to adjust to the range of S / m, and preferably to the range of 0.005 to 0.3 S / m. If the conductivity is less than 0.001 S / m, it becomes difficult to recover the ejection when printing is stopped and left for a long time.
/ M, the storage stability of the ink tends to deteriorate. In particular, when carbon black subjected to hydrophilization treatment is used as the self-dispersible pigment, it is desirable to set the range of 0.005 to 0.3 S / m from the viewpoint of ejection recovery after long-term storage.

The conductivity of the ink can be adjusted by the amount of water, the type and amount of the water-soluble organic solvent, the type and amount of the electrolyte substance, and other compositions. In the present invention, the conductivity is measured at 23 ° C. in a conductivity meter AOL-.
The value measured using 40-3302 (manufactured by DKK) as a measuring device was used.

(E) pH It is essential that the pH of the ink of the present invention is adjusted within the range of 6.0 to 11.0, and preferably 7.5 to 11.0.
It is adjusted to the range of 9.0. If the pH is less than 6.0, the ink tends to be clogged, and if it exceeds 11.0, the head components are easily corroded or dissolved. In particular, when carbon black subjected to hydrophilization treatment is used as a self-dispersible pigment, 6.0 to 6.0 is preferable in terms of nozzle clogging.
It is desirable to set it in the range of 9.5.

The pH of the ink can be adjusted by adding various acids, various salts, pH adjusters, or buffers. In addition, in this invention, the value measured using the glass pH electrode in the environment of 23 degreeC was used for pH.

[Preparation of Ink] The ink of the present invention can be prepared by mixing the above-mentioned components and dissolving and / or dispersing them. Particularly, in order to adjust the self-dispersible pigment to the number average particle diameter of the predetermined dispersed particles in the present invention, the pigment is dispersed in an aqueous medium (a liquid composition mainly composed of water, a water-soluble organic solvent, a water-soluble organic solvent, (A polymer, a surfactant, etc. may be contained.).

In the step of dispersing the pigment in an aqueous medium,
Various stirring and dispersing devices can be used, but if a dispersing machine using so-called dispersing media such as glass, ceramic, metal balls or beads is used, the dispersing media and the dispersing container may be worn in the pigment crushing and dispersing steps. In many cases, a large amount of inorganic impurities are mixed into the pigment dispersion or the ink. Therefore, it is desirable to use a dispersion apparatus that does not use a dispersion medium. In particular, the dispersion is preferably performed by at least one or more devices selected from the group consisting of an ultrasonic homogenizer and a high-pressure homogenizer. When dispersing with an ultrasonic homogenizer, it is preferable to perform degassing and degassing by vacuum evacuation, heating, and a commercially available degassing / degassing device before dispersing. When a dispersion apparatus using a dispersion medium is used, mixed inorganic impurities are removed as necessary.

<Inkjet Recording Method> The inkjet recording method of the present invention is characterized in that the above-described ink of the present invention is printed on a recording medium so that the drop amount is 5 to 25 pl. Of course, in the present invention, “printing” is a concept including not only recording characters but also recording all images such as characters, pictures, symbols, patterns, and photographs on a recording medium.

The ink-jet recording method includes a so-called charge control method in which ink is ejected by using electrostatic attraction, a so-called pressure pulse method in which ink is ejected by using the oscillating pressure of a piezo element, and a bubble method by heating ink. A so-called thermal ink jet method in which ink droplets are formed by utilizing pressure generated by forming and growing a liquid crystal. Among these, the thermal ink jet method is particularly preferable because a full-color image can be provided at a small size and at low cost.

In the present invention, the drop amount of the ink discharged at the time of printing must be 5 to 25 pl, more preferably 5 to 20 pl. If the drop amount of the ink is less than 5 pl, it is difficult to use the pigment because the dispersed particles of the pigment are likely to be clogged in the flow path. On the other hand, if the ink drop amount exceeds 25 pl, the image quality will rapidly deteriorate. In the present invention, the ink of the present invention is used, and the drop amount of the ink is 5 to 25 p.
For the first time, high image quality, shortening of the drying time and reliability can be ensured by setting the value to 1.

According to the ink jet recording method of the present invention, the ink of the present invention can be recorded alone.
It is preferable that one or more liquid compositions are attached to the image-receiving part and / or the adjacent part thereof. The adhesion of the liquid composition is performed prior to or simultaneously with printing with the ink. By attaching the liquid composition to a recording medium, the drying time is reduced, the optical density is increased,
It exerts effects such as prevention of color mixing due to contact with multicolor ink and improvement of image fixing strength.

The liquid composition is mainly composed of water and a water-soluble organic solvent, and may optionally contain a colorant, a surfactant, a fixing promoter, and other additives. As the water, the water-soluble organic solvent, and the surfactant in the liquid composition, known substances can be used, and those described for the ink of the present invention can be used without any problem. When a colorant is contained, the colorant may be any of a dye, a pigment and a mixture thereof, but a dye is preferable. Known dyes and pigments can be used.

As the fixing promoter in the liquid composition, various water-soluble polymers and polymer emulsions can be used. As the water-soluble polymer or polymer emulsion, for example, an acrylic polymer, polyester, polyvinyl alcohol, polyvinyl pyrrolidone, polyurethane and the like are preferable. A combination in which the pigment in the ink of the present invention has an anionic hydrophilic functional group and the fixing accelerator is a water-soluble polymer having a cationic group is particularly preferable.

Examples of the water-soluble polymer having a cationic group include monomers having a cationic functional group, for example, N,
Copolymer or homopolymer containing at least N-dimethylaminoethyl methacrylate, N, N-dimethylaminoethyl acrylate, N, N-dimethylaminomethacrylamide, N, N-dimethylaminoacrylamide, vinylpyridine, vinylpyrrolidone, etc. And polyethyleneimine, polyamines, polyamides and the like.

When the hydrophilic functional group of the pigment in the ink of the present invention comprises at least an anionic group, it is preferable that the pigment contains an inorganic polyvalent cation as a fixing agent accelerator. Examples of the inorganic polyvalent cation include Ca ²⁺ ,
Mg ²⁺ , Al ³⁺ , Fe ²⁺ , Fe ³⁺ , Zn ²⁺ , Ni ²⁺ , C
o ²⁺ , Cu ^{2+ and the} like.

The liquid composition preferably contains a surfactant from the viewpoint of image drying properties. The surface tension of the liquid composition is preferably in the range of 20 to 40 mN / m.

In the above-described ink jet recording method of the present invention, an apparatus having a function of heating a recording paper at 50 ° C. to 200 ° C. before or before and after printing with ink to promote print fixing is provided. Can also be used. Also, plain paper, glossy paper, special paper, cloth, film, O
In addition to the method of printing directly on a recording medium such as an HP, printing may be performed on an intermediate such as a drum or a belt, an ink image may be arranged on the surface of the intermediate, and then transferred to a recording medium for printing.

[0100]

EXAMPLES [Preparation of Pigment Dispersion] (Dispersion 1) CAB-O-JET300 (manufactured by CABOT / solid content 15.2%, self-dispersibility index 100%) was evaluated as 8%.
After centrifugation at 000 rpm for 30 minutes, the mixture was diluted with pure water to obtain a pigment dispersion having a solid content of 10%, to obtain a dispersion 1.

(Dispersion 2) Styrene / methacrylic acid copolymer Na salt (monomer ratio 50/50, weight average molecular weight =
A water-soluble polymer of 7000, calculated HLB = 14.1) was used as a dispersant for pigment dispersion.

45 parts by weight of the above water-soluble polymer (solid content: 10
% Aqueous solution) and 210 parts by weight of ion-exchanged water, and while stirring, 45 parts by weight of carbon black BPL (manufactured by CABOT, self-dispersibility index: 0%) was added and stirred for 30 minutes. Then, use a microfluidizer with 10,000
psi / 30 path dispersed. After dispersion, 1N-NaO
The pH was adjusted to 9 using an aqueous H solution. Furthermore, after performing centrifugation at 8000 rpm for 15 minutes using a centrifuge, the mixture was passed through a 2 μm membrane filter. The resulting dispersion was diluted with pure water to obtain a pigment dispersion having a solid content of 10%, which was designated as Dispersion 2.

[Preparation of Inkjet Recording Ink] To 30 parts by weight of pure water, each component of the ink excluding the pigment dispersion was added according to Tables 1 and 2 below, and stirred for 30 minutes. A pigment dispersion was added to the obtained liquid, and pure water was further added so that the total amount was 100 parts by weight. Thereafter, the particles were treated with an ultrasonic homogenizer (300 W, 400 μA) for 15 minutes to adjust the particle size. Further, the mixture was passed through a 2 μm membrane filter to prepare an ink jet recording ink.

[0104]

[Table 1]

[0105]

[Table 2]

[Measurement of Physical Properties of Ink] The following physical properties were measured for each of the obtained inks of Examples and Comparative Examples.
The results are shown in Table 3 below. 1) Viscosity The viscosity of the ink was determined by using Rheomat 115 (Contrave).
s). Specifically, the ink to be measured was placed in a measurement container, and mounted on the apparatus by a predetermined method in the apparatus, and the measurement was performed. The measurement temperature is 23 ° C and the shear rate is 140
It was measured at ^{0 s -1} .

2) Surface tension The surface tension of the ink was measured using a Wilhelmy type surface tensiometer. Measurement environment: temperature 23 ° C, humidity 55% R
H.

3) Conductivity The conductivity of the ink was measured using a conductivity meter AOL-40-3302.
(Manufactured by DKK). The measurement temperature was measured at 23 ° C.

4) pH The pH of the ink was measured using a glass pH electrode. The measurement temperature was measured at 23 ° C.

5) Dispersion Particle Diameter of Pigment The average diameter (dispersion particle diameter) of the pigment dispersion particles is determined by using a Microtrac UPA particle size analyzer 9340 (Leeds & N).
orthrup) without dilution. As input parameters, the viscosity was ink viscosity, and the density of dispersed particles was 1.8 g / cm ² .

[Printing Test] Using each of the inks obtained in the above Examples and Comparative Examples, a printing test was conducted with a prototype inkjet printer in an environment of 23 ° C. and 55% RH. Two kinds of heads having different drop amounts are used, specifically, 800 dpi (drop amount is about 15p).
1) and 400 dpi (drop amount: about 50 pl) were used. FX-L paper (manufactured by Fuji Xerox Co., Ltd.) was used as typical paper. The printed image is of two types: a solid patch (3 cm square) and one dot line. The obtained images were evaluated as described below.

1) Measurement of Optical Density One day after printing, the solid patch was
4 (manufactured by X-Rite).

2) Print quality evaluation test One dot line portion was subjected to a sensory evaluation according to the following criteria. 1: No bleeding 2: Slight bleeding is recognized but acceptable range 3: Bleeding 4: Beard-like bleeding in many parts

3) Drying Time The drying time of the ink was measured from the time immediately after printing to the time when the ink liquid disappeared (visual judgment) in the solid patch portion.

[Reliability of Ink] The following tests were conducted on the reliability of each of the inks obtained in Examples and Comparative Examples. The results are shown in Table 3 below. 1) Stability test 50 g of each ink was sealed in a glass tube with a lid, and 70 ° C.
An acceleration test was performed for a total of four cycles, in which the cycle was left for 4 hours in an atmosphere and for 4 hours in an atmosphere of -20 ° C. Take 5 g of the sample before and after the test, perform vacuum filtration using a 1 μm mesh filter and a glass holder having an effective filtration diameter of 2.5 cm ² , and measure the time required to filter the entire sample. Evaluation was based on criteria.

A: Increase in filter passage time after acceleration test is less than 20% O: Increase in filter passage time after acceleration test is 20%
Not less than 50% Δ: increase in filter passage time after accelerated test is 50%
Not less than 100% ×: increase in filter passage time after acceleration test is 100
%that's all

2) Recovery Test After confirming that the printing was normally performed using the above-described printing device equipped with an 800 dpi head, the device was left uncapped at 23 ° C. and 55% RH for one month. The recovery operation by vacuum was repeated until normal printing was performed, and the number of times was recorded, and evaluated according to the following criteria. ：: Normal printing from the beginning, or recovery once: ○: Recovery two to three times △: Recovery after four to five times ×: No recovery after five times

[0118]

[Table 3]

[0119]

As described above, according to the ink jet recording method and the ink jet recording ink of the present invention, an image can be clearly reproduced on plain paper, and excellent print quality can be obtained. In addition, the shortening of the drying time having the suitability for high-speed printing can be realized on plain paper. Further, high reliability during storage and use can be realized.

Therefore, according to the present invention, report paper,
A short drying time and a clear image can be formed on plain paper such as copy paper, bond paper, and high-quality paper, and also on recycled paper for which it has been difficult to form a clear image. The present invention is a thermal ink jet system, piezo system, ultrasonic, about the ink jet recording using an electric field, etc.
It can be suitably applied.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2C056 EA13 FC01 2H086 BA52 BA53 BA59 BA60 BA61 4J039 AB01 AB02 AB04 AB07 AD03 AD04 AD06 AD08 AD09 AD12 AD22 AE07 AE11 BA04 BC05 BC07 BC08 BC09 BC10 BC14 BC15 BC19 BC37 BC54 BC56 BE01 BE02 BE12 BE22 CA06 EA10 EA42 EA44 EA46 EA47 GA24

Claims (2)

[Claims] 1. An ink jet recording ink containing at least a self-dispersible pigment, water, a water-soluble organic solvent, a water-soluble polymer and a surfactant and satisfying the following conditions (a) to (e): An ink jet recording method, wherein printing is performed on a recording medium such that a drop amount is 5 to 25 pl. (A) The number average particle diameter of the dispersed particles of the pigment is 10 to 6
0 nm range (b) Surface tension is in the range of 30 to 50 mN / m (c) Viscosity is in the range of 1.5 to 5.0 mPa · s (d) Conductivity is 0.001 to 0.4 S / m (E) pH is in the range of 6 to 11 2. An ink jet recording ink used in the ink jet recording method according to claim 1, comprising at least a self-dispersible pigment, water, a water-soluble organic solvent, a water-soluble polymer and a surfactant, and , The following (a)-
An ink jet recording ink satisfying the condition (e). (A) The number average particle diameter of the dispersed particles of the pigment is 10 to 6
0 nm range (b) Surface tension is in the range of 30 to 50 mN / m (c) Viscosity is in the range of 1.5 to 5.0 mPa · s (d) Conductivity is 0.001 to 0.4 S / m (E) pH is in the range of 6 to 11