JP5355065B2 - Ink set and ink jet recording method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ink which can improve the abrasion resistance of images when subjected to inkjet recording on glossy paper although the ink has a low carbon black concentration, and to provide an ink set comprising a thick and light shade inks containing carbon black, which improves the abrasion resistance of images and can reduce unevenness in the gloss of images. <P>SOLUTION: In the ink for inkjet recording containing at least an aqueous medium, carbon black, and a dispersed resin, the concentration of the carbon black is 2 mass% or less, and the DBP oil absorption of the carbon black is 120 ml/100 g or more. The ink set is obtained by combining the above light shade ink with a thick ink of a specific structure having a higher concentration of carbon black than that of the light shade ink. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

The present invention is, at least, an aqueous medium, an ink set having a carbon black, and Louis ink compositions contain a dispersing resin, and to an ink jet recording method. Specifically, in case where the ink jet recording or the like glossy paper, is excellent in resistance to abrasion resistance, ink set capable of forming the images with improved gloss unevenness, and an ink jet recording method.

  The ink jet recording method is a method for ejecting ink as small droplets from a fine nozzle and recording characters and figures on the surface of a recording medium. As an ink jet recording method, there is a method in which an electric signal is converted into a mechanical signal using an electrostrictive element and ink stored in a nozzle head portion is intermittently ejected to record characters and symbols on the surface of the recording medium.

  Also, as an ink jet recording method, ink stored in the nozzle head part is intermittently ejected by volume expansion caused by bubbles generated by rapidly heating a part very close to the ejection part, and characters and characters are recorded on the surface of the recording medium. A method of recording symbols has also been put into practical use. Further, as an ink supply mode in ink jet recording, a method of using an ink set formed by combining a plurality of different color inks is known.

  According to such an ink set, it is possible to easily obtain a high-quality color image by appropriately selecting the type of each ink ejected from the ink jet recording apparatus according to a signal based on the image information. There is an advantage. In general, inks constituting such an ink set are prepared by dissolving various water-soluble dyes in an aqueous medium. Recently, pigments are dispersed in an aqueous medium by a dispersant. Ink is also provided. This is because an ink using a pigment (hereinafter also referred to as a pigment ink) has a feature that the weather resistance (water resistance, light resistance, etc.) in an image is superior to an ink using a water-soluble dye.

  However, when ink jet recording is performed on so-called glossy paper using an ink set having a conventionally known pigment ink, there are the following problems. That is, there is a difference between the glossiness in an image area having a large number of ink dots per unit area (Duty) and the glossiness in an image area having a small duty, and uneven glossiness of the image due to this difference is visually recognized. There was a problem. On the other hand, Patent Document 1 proposes a method for improving this problem.

  Specifically, an ink set is disclosed in which the ratio of the mass of the resin to the mass of the pigment in the ink composition is higher in the light ink composition than in the dark ink composition. However, when the amount of resin in the ink composition is increased, the proportion of the pigment in the colored layer formed on the recording medium decreases when the ink composition is applied, resulting in the formation of printed matter. In this case, there is a problem that printing stains due to rubbing after printing become obvious. That is, there is still room for improvement in the scratch resistance of the image formed by the light ink composition. In particular, an ink composition containing carbon black as a pigment, which can be said to be essential for image formation, and a set of dark and light ink compositions having different carbon black contents are very useful if this problem is improved. . Hereinafter, the ink composition may be referred to as ink.

Japanese Patent No. 3741273

Use is therefore an object of the present invention, along with improving the scratch resistance of images, an ink set composed of dark and light inks containing carbon black capable of reducing the gloss unevenness of the image, and the upper listening Nkusetto Another object of the present invention is to provide an ink jet recording method.

As a result of intensive studies on the problems of the prior art, the present inventors have found that in an ink set having a dark ink and a light ink, the mass ratio of the pigment and the dispersion resin contained in each ink, and the pigment contained in each ink. It has been found that by optimizing the DBP (dibutyl phthalate) oil absorption, the scratch resistance and gloss unevenness of the image can be improved. That is, the present invention is as follows.

This onset Ming, at least, contain aqueous medium, carbon black, and dispersion resin, light and ink density of the carbon black is not more than 2 wt%, and containing at least an aqueous medium, carbon black, and dispersion resin And an ink set for ink jet recording having at least a dark ink having a carbon black concentration exceeding 2% by mass, wherein the DBP oil absorption of carbon black in the light ink is 120 ml / 100 g or more, and the dark ink The DBP oil absorption of carbon black in the ink is 80 ml / 100 g or less, and the ratio (P1 / B1) between the concentration P1 (mass%) of carbon black and the concentration B1 (mass%) of the dispersed resin in the light ink Is the concentration P2 (mass%) of carbon black in the dark ink and the dispersion resin. An ink set of equal to or less than the concentration B2 ratio (mass%) (P2 / B2).

Yet another embodiment of the present invention, prior SL using the ink set of the present invention, ejecting droplets of the ink composition, and characterized by performing printing depositing the droplets onto a recording medium This is an ink jet recording method.

According to the present invention, together with improving the scratch resistance of images, an ink set composed of dark and light inks containing carbon black that uneven brightness can be reduced in the image, and an ink jet recording method is provided.

Next, the present invention will be described in more detail with reference to preferred embodiments.
<Ink, ink set>
The ink composition of the present invention is an ink composition for inkjet recording containing at least an aqueous medium, carbon black, and a dispersion resin. And the density | concentration of this carbon black is 2 mass% or less, and DBP oil absorption of this carbon black is 120 ml / 100g or more, It is characterized by the above-mentioned.

  The ink set of the present invention is for inkjet recording and has the following configuration. That is, a light ink composition containing an aqueous medium, carbon black, and a dispersion resin, the concentration of the carbon black being 2% by mass or less, an aqueous medium, carbon black, and a dispersion resin are contained, and It has a dark ink composition having a concentration of more than 2% by mass. Further, the DBP oil absorption amount of carbon black in the light ink composition is 120 ml / 100 g or more, and the DBP oil absorption amount of carbon black in the dark ink composition is 80 ml / 100 g or less. Further, the ratio (P1 / B1) of the carbon black concentration P1 and the dispersion resin concentration B1 in the light ink composition is equal to the carbon black concentration P2 and the dispersion resin concentration B2 in the dark ink composition. And a ratio (P2 / B2) or less. Hereinafter, the ink of the present invention and the ink components constituting the ink set will be described in detail.

(Pigment)
Conventionally known carbon black can be used as the pigment contained in the ink of the present invention and the ink constituting the ink set. For example, carbon black produced by a known method such as a furnace method or a channel method can be used. The ink of the present invention is a light ink containing such carbon black at a concentration of 2% by mass or less. The ink set of the present invention is a combination of the light ink and a dark ink having a carbon black concentration exceeding 2% by mass. The lower limit value of the carbon black concentration in the light ink is not particularly limited but is preferably 0.01% by mass or more, and the upper limit value of the carbon black concentration in the dark ink is not particularly limited. It is preferable that it is 15 mass% or less.

  The carbon black used in the present invention has a DBP oil absorption of 120 ml / 100 g or more when applied to a light ink having a carbon black concentration of 2 mass% or less. The reason is as follows.

  First, the DBP oil absorption is measured based on JIS K6217 or DIN 53 601 and means the degree of connection between primary particles of carbon black. The increase in DBP oil absorption is between primary particles. It means that connection is big. In general, the pigment used in the black ink for printing on glossy media such as glossy paper has a DBP oil absorption amount so as to reduce the thickness of the formed colored layer in order to increase the glossiness of the image. Small carbon black is used.

  Specifically, carbon black having a DBP oil absorption of 80 ml / 100 g or less is often used. However, according to the study by the present inventors, it is not always necessary to reduce the DBP oil absorption amount of the pigment for the light ink containing carbon black at a concentration of 2% by mass or less. The reason for this is that, in the case of light ink, a resin containing the amount of resin in the ink in the dark ink in order to give the same glossiness as that of the image formed by applying the dark ink having a high carbon black concentration. It is because the thickness of a colored layer is made comparable by making it contain more than the quantity.

  In view of the scratch resistance, the present inventors have intensively studied to find an optimum DBP oil absorption amount of carbon black for a light ink having a carbon black concentration of 2% by mass or less. The present invention has been achieved. Specifically, it has been found that by setting the DBP oil absorption amount of carbon black used for the light ink to 120 ml / 100 g or more, the scratch resistance of the formed image is remarkably improved and the printing stain can be improved. The present inventors have obtained the reason why such an effect is obtained by increasing the DBP oil absorption amount of carbon black so that the carbon black existing in the colored layer formed by ink being ejected onto the recording medium can be obtained. It is estimated that the increase in effective volume is related. That is, it is presumed that this is because the colored layer has become stronger than when carbon black having a small DBP oil absorption amount is used. The light ink constituting the ink set of the present invention is an ink having a carbon black concentration of 2% by mass or less in the above-described present invention. Therefore, hereinafter, it is simply referred to as the light ink constituting the present invention.

  In the dark ink constituting the ink set of the present invention, carbon black having a DBP oil absorption of 80 ml / 100 g or less is used for the reason described above.

(Dispersed resin)
The dark and light ink constituting the present invention is desirably a resin-dispersed pigment ink obtained by dispersing a pigment in an aqueous medium with a dispersion resin. Any dispersion resin can be used, but a block copolymer, a random copolymer, and at least two monomers (of which at least one is a hydrophilic monomer) as listed below: It is preferable to use a graft copolymer and a salt thereof. In particular, block copolymers are preferred. Examples of the monomer include the following. Styrene and its derivatives, vinyl naphthalene and its derivatives, aliphatic alcohol esters of α, β-ethylenically unsaturated carboxylic acids, acrylic acid and its derivatives, maleic acid and its derivatives, itaconic acid and its derivatives, fumaric acid and its Derivative.

  The weight average molecular weight (Mw) of the dispersion resin is not particularly limited, but is preferably in the range of 1,000 to 30,000. The acid value of the dispersion resin is not particularly limited, but is preferably in the range of 80 mgKOH / g to 430 mgKOH / g.

  The concentration (B1, B2) of the dispersion resin in the dark and light ink constituting the present invention is set within a range of 0.1% by mass or more and 10% by mass or less based on the total mass of the ink. From the viewpoints of performance and dischargeability.

  The ink of the present invention is preferably designed so that the ratio (P1 / B1) between the carbon black concentration P1 (mass%) and the dispersion resin concentration B1 (mass%) is 1.0 or less. . Accordingly, when this light ink is used together with the dark ink, it is possible to reduce uneven glossiness of the image while maintaining the robustness of the image.

  As a result of intensive studies, the present inventors have determined that in the dark and light inks constituting the ink set of the present invention, in order to match the glossiness of the image formed by each of the light and dark inks while ensuring the robustness of the image. It has been found that it is effective to make the relationship of the amount of the dispersed resin as follows. That is, the ratio of the concentration P1 (mass%) of carbon black in the light ink to the concentration B1 (mass%) of the dispersion resin is defined as the concentration P2 (mass%) of the carbon black in the dark ink and the density B2 of the dispersion resin ( It was found that it was necessary to make the ratio equal to or less than the ratio to (mass%). That is, in order to obtain the above-described effect, it has been found that the value of P1 / B1 needs to be equal to or less than the value of P2 / B2. More preferably, it is configured as follows. The ratio (P1 / B1) between the carbon black concentration P1 and the dispersion resin concentration B1 in the light ink is set to 1.0 or less, and the ratio between the carbon black concentration P2 and the dispersion resin concentration B2 in the dark ink (P2). / B2) is preferably 1.0 or more. Furthermore, it was found that P2 / B2 is more preferably 1.0 or more and 2.0 or less. The present inventors presume that the above-described configuration may reduce the surface roughness of the printed image formed on the recording medium. In the present invention, the lower limit of the ratio (P1 / B1) between the carbon black concentration P1 and the dispersion resin concentration B1 in the light ink is not particularly limited.

(Aqueous medium)
The dark and light ink constituting the present invention contains water or an aqueous medium that is a mixed solvent of water and a water-soluble organic solvent. The water is preferably deionized water. The content of water in the ink is preferably 50% by mass or more and 95% by mass or less based on the total mass of the ink. The content of the water-soluble organic solvent in the ink is preferably 3% by mass or more and 50% by mass or less based on the total mass of the ink. The following are mentioned as an example of the water-soluble organic solvent used preferably. Alcohols (eg, methanol, ethanol, propanol, isopropanol, butanol, isobutanol, secondary butanol, tertiary butanol, pentanol, hexanol, cyclohexanol, benzyl alcohol, etc.). Polyhydric alcohols (for example, ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, propylene glycol. Dipropylene glycol, polypropylene glycol, butylene glycol, hexanediol, pentanediol, glycerin, hexanetriol, thiodiglycol, etc.). Polyhydric alcohol ethers (for example, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether. Diethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monobutyl ether, ethylene glycol monomethyl Ether acetate, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol monobutyl ether, ethylene glycol monophenyl ether, propylene glycol monophenyl ether). Amines (eg, ethanolamine, diethanolamine, triethanolamine, N-methyldiethanolamine, N-ethyldiethanolamine, morpholine, N-ethylmorpholine. Ethylenediamine, diethylenediamine, triethylenetetramine, tetraethylenepentamine, polyethyleneimine, pentamethyl Diethylenetriamine, tetramethylpropylenediamine, etc.). Amides (for example, formamide, N, N-dimethylformamide, N, N-dimethylacetamide and the like). Heterocycles (eg 2-pyrrolidone, N-methyl-2-pyrrolidone, cyclohexyl pyrrolidone, 2-oxazolidone, 1,3-dimethyl-2-imidazolidinone). Sulfoxides (for example, dimethyl sulfoxide). Sulfones (for example, sulfolane). Urea, acetonitrile, acetone, etc.

(Surfactant)
The dark and light ink constituting the present invention may contain a surfactant as necessary. In the present invention, examples of the surfactant preferably used for each ink include the following. Anionic surfactants such as dialkylsulfosuccinates, alkylnaphthalenesulfonates and fatty acid salts. Nonionic surfactants such as polyoxyethylene alkyl ethers, polyoxyethylene alkyl allyl ethers, acetylene glycols and polyoxyethylene / polyoxypropylene block copolymers. Cationic surfactants such as alkylamine salts and quaternary ammonium salts. In particular, an anionic surfactant and a nonionic surfactant can be preferably used. Furthermore, acetylene glycols are preferable.

(PH buffer)
The dark and light ink constituting the present invention may contain a pH buffer as necessary. The pH buffering agent is not particularly limited as long as it is a buffering agent capable of adjusting the ink to pH 8 to pH 10. Specific examples include the following. Potassium hydrogen phthalate, potassium dihydrogen phosphate, disodium hydrogen phosphate, sodium tetraborate, potassium hydrogen tartrate, sodium hydrogen carbonate, sodium carbonate, tris (hydroxymethyl) aminomethane, and / or tris (hydroxymethyl) amino Methane hydrochloride. The content of the pH buffering agent in the ink is preferably such an amount that the ink becomes approximately pH 8 to pH 10 from the viewpoint of the durability of the head member and the stability of the inkjet pigment ink.

(Other additives)
In addition to the above, the dark and light ink constituting the present invention may contain antiseptics, antifungal agents, antifoaming agents, moisturizing agents, viscosity modifiers, and the like as necessary. When a humectant is included, saccharides are preferable, and examples of saccharides include monosaccharides, disaccharides, oligosaccharides (including trisaccharides and tetrasaccharides), and polysaccharides. Preferably, glucose, mannose, fructose, ribose, xylose, arabinose, galactose, aldonic acid, glycidyl, sorbit, maltose, cellobiose, lactose, sucrose, trehalose, maltotriose and the like can be mentioned.

<Inkjet recording method>
The ink jet recording method of the present invention uses the ink of the present invention described above or the dark and light ink constituting the ink set of the present invention, ejects droplets of these inks, and deposits the droplets on a recording medium. It is characterized in that printing is performed by adhering.

<Inkjet recording apparatus>
Next, an example of an ink jet recording apparatus suitable for recording using the ink or ink set of the present invention will be described below. First, FIG. 1 and FIG. 2 show an example of a head configuration which is a main part of an ink jet recording apparatus using thermal energy. 1 is a cross-sectional view of the head 13 along the ink flow path 14, and FIG. 2 is a cross-sectional view taken along the line AB of FIG. The head 13 is obtained by adhering a heating element substrate 15 and a glass, ceramic, silicon, or plastic plate having an ink flow path (nozzle) 14 through which ink passes. The heating element substrate 15 has the following configuration. That is, the protective layer 16 formed of silicon oxide, silicon nitride, silicon carbide, or the like. Electrodes 17-1 and 17-2 formed of aluminum, gold, aluminum-copper alloy, or the like. A heating resistor layer 18 formed of a high melting point material such as HfB ₂ , TaN, TaAl or the like. A heat storage layer 19 formed of thermally oxidized silicon, aluminum oxide or the like. The substrate 20 is made of a material with good heat dissipation such as silicon, aluminum, and aluminum nitride.

  When pulsed electric signals are applied to the electrodes 17-1 and 17-2 of the head 13, the region indicated by n of the heating element substrate 15 rapidly generates heat, and the ink 21 in contact with this surface Bubbles are generated. Then, the meniscus 23 protrudes by the pressure, and the ink 21 is ejected through the nozzle 14 of the head, becomes an ink droplet 24 from the ejection orifice 22, and flies toward the recording medium 25. FIG. 3 shows an external view of an example of a multi-head in which a large number of heads shown in FIG. 1 are arranged. This multi-head is made by adhering a glass plate 27 having multi-nozzles 26 and a heating head 28 similar to that described in FIG.

  FIG. 4 shows an example of an ink jet recording apparatus incorporating this head. In FIG. 4, reference numeral 61 denotes a blade as a wiping member, one end of which is held and fixed by a blade holding member, and forms a cantilever. The blade 61 is disposed at a position adjacent to the recording area by the recording head 65, and in the case of this example, is held in a form protruding in the moving path of the recording head 65.

  Reference numeral 62 denotes a cap on the projection port surface of the recording head 65, which is disposed at a home position adjacent to the blade 61, moves in a direction perpendicular to the moving direction of the recording head 65, contacts the ink ejection port surface, and performs capping. The structure to perform is provided. Further, 63 is an ink absorber provided adjacent to the blade 61, and is held in a form protruding in the moving path of the recording head 65, similar to the blade 61. The blade 61, the cap 62, and the ink absorber 63 constitute an ejection recovery unit 64, and the blade 61 and the ink absorber 63 remove moisture, dust, and the like from the ejection port surface.

  Reference numeral 65 denotes a recording head that has discharge energy generating means and performs recording by discharging ink onto a recording medium facing the discharge port surface on which the discharge ports are arranged. Reference numeral 66 denotes a recording head mounted with the recording head 65. It is a carriage for moving. The carriage 66 is slidably engaged with the guide shaft 67, and a part of the carriage 66 is connected to a belt 69 (not shown) driven by a motor 68. As a result, the carriage 66 can move along the guide shaft 67, and the recording area and its adjacent area can be moved by the recording head 65.

  51 is a paper feeding unit for inserting a recording medium, and 52 is a paper feed roller driven by a motor (not shown). With these configurations, the recording medium is fed to a position facing the discharge port surface of the recording head 65, and is discharged to a paper discharge portion provided with a paper discharge roller 53 as recording progresses. In the above configuration, when the recording head 65 finishes recording and returns to the home position, the cap 62 of the ejection recovery unit 64 is retracted from the moving path of the recording head 65, but the blade 61 protrudes into the moving path. Yes. As a result, the ejection port of the recording head 65 is wiped.

  When the cap 62 is in contact with the ejection surface of the recording head 65 to perform capping, the cap 62 moves so as to protrude into the moving path of the recording head. When the recording head 65 moves from the home position to the recording start position, the cap 62 and the blade 61 are at the same position as that at the time of wiping described above. As a result, the ejection port surface of the recording head 65 is wiped even during this movement. The above-mentioned movement of the recording head to the home position is not only at the end of recording or at the time of ejection recovery, but also to the home position adjacent to the recording area at a predetermined interval while the recording head moves the recording area for recording. Then, the wiping is performed with this movement.

  FIG. 5 is a diagram illustrating an example of an ink cartridge 45 that contains ink supplied to the recording head via an ink supply member, for example, a tube. Here, reference numeral 40 denotes an ink container, for example, an ink bag, in which supply ink is stored, and a rubber plug 42 is provided at the tip thereof. By inserting a needle (not shown) into the stopper 42, the ink in the ink bag 40 can be supplied to the head. Reference numeral 44 denotes an ink absorber that receives waste ink. As the ink storage portion, a liquid contact surface with ink is preferably formed of polyolefin, particularly polyethylene.

  As described above, the ink jet recording apparatus used in the present invention is not limited to the one in which the head and the ink cartridge are separated, and is suitable for those in which they are integrated as shown in FIG. Used for. In FIG. 6, reference numeral 70 denotes a recording unit, in which an ink storage portion that stores ink, for example, an ink absorber is stored, and the ink in the ink absorber from the head portion 71 having a plurality of orifices. It is configured to be ejected as ink droplets. It is preferable for the present invention to use polyurethane as the material of the ink absorber. Alternatively, a structure in which the ink container is an ink bag with a spring or the like inside without using an ink absorber may be used. Reference numeral 72 denotes an atmosphere communication port for communicating the inside of the cartridge with the atmosphere. The recording unit 70 is used in place of the recording head 65 shown in FIG. 4 and is detachable from the carriage 66.

  Next, as a preferred example of an ink jet recording apparatus using mechanical energy, one having an on-demand type ink jet recording head having the following configuration can be cited. Specifically, the ink jet recording apparatus includes a nozzle forming substrate having a plurality of nozzles, and a pressure generating element made of a piezoelectric material and a conductive material disposed to face the nozzles. Then, ink filling the periphery of the pressure generating element is provided, the pressure generating element is displaced by the applied voltage, and a small droplet of ink is ejected from the nozzle. An example of the configuration of a recording head which is a main part of the recording apparatus is shown in FIG.

  The head includes an ink flow path 80 communicating with an ink chamber (not shown), an orifice plate 81 for ejecting ink droplets of a desired volume, and a vibration plate 82 that directly applies pressure to the ink. In addition, it has a piezoelectric element 83 joined to the vibration plate 82 and displaced by an electric signal, and a substrate 84 for indicating and fixing the orifice plate 81, the vibration plate 82 and the like.

  In FIG. 7, the ink flow path 80 is formed of a photosensitive resin or the like. A discharge port 85 is formed in the orifice plate 81 by drilling a metal such as stainless steel or nickel by electroforming or pressing. The diaphragm 82 is formed of a metal film such as stainless steel, nickel, or titanium and a highly elastic resin film. The piezoelectric element 83 is formed of a dielectric material such as barium titanate or PZT. The recording head configured as described above applies a pulsed voltage to the piezoelectric element 83 to generate strain stress. The energy deforms the vibration plate bonded to the piezoelectric element 83, pressurizes the ink in the ink flow path 80 vertically, and discharges ink droplets (not shown) from the discharge port 85 of the orifice plate 81 for recording. Works to do. Such a recording head is used by being incorporated in an ink jet recording apparatus similar to that shown in FIG. The detailed operation of the ink jet recording apparatus can be performed in the same manner as described above.

  EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated further more concretely, the embodiment of this invention is not limited to these. In the following examples, “parts” and “%” are based on mass unless otherwise specified. The “remainder” refers to a remainder obtained by subtracting each component from 100 parts as a whole.

<Preparation of pigment dispersion>
(Pigment dispersion 1)
300 mL Kolben equipped with a mechanical stirrer was placed in the tank of the ultrasonic generator, and 8 g of dispersion resin A, 6 g of carbon black, and 100 mL of tetrahydrofuran were added thereto, and mixed well until the pigment surface was sufficiently wetted with the solvent. Next, the phase was reversed by dropping and injecting an alkaline aqueous solution containing KOH (potassium hydroxide) that has a neutralization rate of 100% for the dispersion resin A, which is a block polymer. Thereafter, premixing was performed for 30 minutes, and dispersion was performed using Nanomizer YSNM-2000AR (manufactured by Yoshida Kikai Kogyo Co., Ltd.) until the average particle size of the pigment became 100 nm or less. Tetrahydrofuran was removed from the obtained dispersion using a rotary evaporator, and the concentration was adjusted to obtain a pigment having a pigment concentration (P) of 6%, a dispersion resin concentration (B) of 8%, and P / B = 0.75. Dispersion 1 was obtained. The dispersion resin A used above is a styrene acrylic acid block copolymer, having an Mw (weight average molecular weight) of 8,000 and an acid value of 120 mgKOH / g. The carbon black used above is “Color Black FW18” (manufactured by Degussa) and has a DBP oil absorption of 160 ml / 100 g.

(Pigment dispersion 2)
A pigment dispersion 2 was obtained in the same manner as the pigment dispersion 1 except that “PRINTEX L6” (manufactured by Degussa, DBP oil absorption: 123 ml / 100 g) was used instead of “Color Black FW18”.

(Pigment dispersion 3)
A pigment dispersion 3 was obtained in the same manner as the pigment dispersion 1 except that “Color Black FW200” (manufactured by Degussa, DBP oil absorption: 150 ml / 100 g) was used instead of “Color Black FW18”.

(Pigment dispersion 4)
Pigment Dispersion 1 except that “PRINTEX L6” (manufactured by Degussa, DBP oil absorption: 123 ml / 100 g) is used instead of “Color Black FW18” and the amount of the dispersion resin A used is 6 g. Pigment dispersion 4 was obtained in the same manner.

(Pigment dispersion 5)
Pigment Dispersion 1 except that “PRINTEX L6” (manufactured by Degussa, DBP oil absorption: 123 ml / 100 g) is used instead of “Color Black FW18”, and the amount of dispersion resin A used is 4 g. Pigment dispersion 5 was obtained in the same manner.

(Pigment dispersion 6)
Instead of dispersion resin A, dispersion resin B (styrene acrylic acid random copolymer (Mw = 8,000, acid value; 120 mgKOH / g)) is used in the same manner as pigment dispersion 1 except that pigment dispersion is used. 6 was obtained.

(Pigment dispersion 7)
Pigment dispersion 1 except that “PRINTEX L6” (manufactured by Degussa, DBP oil absorption: 123 ml / 100 g) is used instead of “Color Black FW18”, and dispersion resin B6 g is used instead of dispersion resin A8 g. Pigment dispersion 7 was obtained in the same manner.

(Pigment dispersion 8)
Pigment dispersion 8 was obtained in the same manner as pigment dispersion 1, except that “# 2600” (manufactured by Mitsubishi Chemical Corporation, DBP oil absorption: 77 ml / 100 g) was used instead of “Color Black FW18”.

(Pigment dispersion 9)
Pigment dispersion 9 was obtained in the same manner as pigment dispersion 1, except that “# 2300” (manufactured by Mitsubishi Chemical Corporation, DBP oil absorption: 64 ml / 100 g) was used instead of “Color Black FW18”.

(Pigment dispersion 10)
Pigment dispersion 1 except that “# 2300” (manufactured by Mitsubishi Chemical Co., Ltd., DBP oil absorption: 64 ml / 100 g) is used instead of “Color Black FW18”, and the amount of dispersion resin A used is 6 g. Pigment dispersion 10 was obtained in the same manner as above.

(Pigment dispersion 11)
Pigment dispersion 1 except that “# 2600” (manufactured by Mitsubishi Chemical Corporation, DBP oil absorption amount: 77 ml / 100 g) is used instead of “Color Black FW18”, and dispersion resin B is used instead of dispersion resin A Pigment dispersion 11 was obtained in the same manner as above.

<Preparation of ink>
(Pigment ink 1)
Next, using the pigment dispersion 1 obtained above, a pigment ink 1 was prepared with the following composition. Specifically, each of the following blending components was mixed and then passed through a glass filter (Millipore Corporation; AP20) to obtain pigment ink 1. “Acetylenol EH” is a nonionic surfactant manufactured by Kawaken Fine Chemical Co., Ltd.
・ Pigment dispersion 1 33.3 parts ・ Diethylene glycol 5 parts ・ Glycerol 7 parts ・ Trimethylolpropane 5 parts ・ Acetylenol EH 0.5 part ・ Ion-exchanged water balance

(Pigment ink 2)
A pigment ink 2 was obtained in the same manner as the pigment ink 1 except that the pigment dispersion 2 was used instead of the pigment dispersion 1 as the pigment dispersion.

(Pigment ink 3)
Pigment ink 3 was obtained in the same manner as pigment ink 1 except that 25 parts of pigment dispersion 2 was used instead of 33.3 parts of pigment dispersion 1 as the pigment dispersion.

(Pigment ink 4)
Pigment ink 4 was obtained in the same manner as pigment ink 1 except that 8.3 parts of pigment dispersion 1 was used instead of 33.3 parts of pigment dispersion 1 as the pigment dispersion.

(Pigment ink 5)
As a pigment dispersion, pigment ink 5 was obtained in the same manner as pigment ink 1 except that 16.7 parts of pigment dispersion 3 was used instead of 33.3 parts of pigment dispersion 1.

(Pigment ink 6)
Pigment ink 6 was obtained in the same manner as Pigment ink 1 except that 16.7 parts of pigment dispersion 2 were used instead of 33.3 parts of pigment dispersion 1 as the pigment dispersion.

(Pigment ink 7)
As a pigment dispersion, pigment ink 7 was obtained in the same manner as pigment ink 1 except that 16.7 parts of pigment dispersion 4 were used instead of 33.3 parts of pigment dispersion 1.

(Pigment ink 8)
As a pigment dispersion, pigment ink 8 was obtained in the same manner as pigment ink 1, except that 16.7 parts of pigment dispersion 5 was used instead of 33.3 parts of pigment dispersion 1.

(Pigment ink 9)
Pigment ink 9 was obtained in the same manner as Pigment ink 1 except that 16.7 parts of pigment dispersion 6 were used instead of 33.3 parts of pigment dispersion 1 as the pigment dispersion.

(Pigment ink 10)
Pigment ink 10 was obtained in the same manner as Pigment ink 1 except that 16.7 parts of pigment dispersion 7 was used instead of 33.3 parts of pigment dispersion 1 as the pigment dispersion.

(Pigment ink 11)
A pigment ink 11 was obtained in the same manner as the pigment ink 1 except that the pigment dispersion 8 was used instead of the pigment dispersion 1 as the pigment dispersion.

(Pigment ink 12)
A pigment ink 12 was obtained in the same manner as the pigment ink 1 except that the pigment dispersion 9 was used instead of the pigment dispersion 1 as the pigment dispersion.

(Pigment ink 13)
Pigment ink 13 was obtained in the same manner as pigment ink 1 except that 25 parts of pigment dispersion 8 was used instead of 33.3 parts of pigment dispersion 1 as the pigment dispersion.

(Pigment ink 14)
A pigment ink 14 was obtained in the same manner as the pigment ink 1 except that 16.7 parts of the pigment dispersion 8 was used instead of 33.3 parts of the pigment dispersion 1 as the pigment dispersion.

(Pigment ink 15)
Pigment ink 15 was obtained in the same manner as Pigment ink 1 except that 16.7 parts of pigment dispersion 9 was used instead of 33.3 parts of pigment dispersion 1 as the pigment dispersion.

(Pigment ink 16)
As a pigment dispersion, pigment ink 16 was obtained in the same manner as pigment ink 1 except that 16.7 parts of pigment dispersion 10 were used instead of 33.3 parts of pigment dispersion 1.

(Pigment ink 17)
Pigment ink 17 was obtained in the same manner as Pigment ink 1 except that 16.7 parts of pigment dispersion 11 were used instead of 33.3 parts of pigment dispersion 1 as the pigment dispersion.

The inks obtained above were referred to as Reference Examples 1 to 10 and Comparative Examples 1 to 7, and their configurations are shown in Table 1. “P / B” in Table 1 is the ratio of the pigment concentration P (mass%) to the dispersed resin concentration B (mass%) in the ink.

<Evaluation>
(Evaluation method)
Each ink obtained above is mounted on an ink jet recording apparatus (trade name: BJ F900, manufactured by Canon Inc.), and an image is formed on PR101 (trade name, manufactured by Canon Inc.), which is glossy paper. The image was evaluated for scratch resistance by the following evaluation method. With the above apparatus, an image was formed so as to be 50% Duty under the conditions of resolution 1200 dpi × 1200 dpi, discharge amount 4.8 pl / dot, and 8-pass bidirectional printing. Next, the obtained image was scratched with a nail, the scratched portion (scratched portion) was visually observed, and scratch resistance was evaluated according to the following evaluation criteria. The evaluation results are shown in Table 1.
(Evaluation criteria)
(Double-circle): A scraping part hardly changes.
○: Slightly changes to the extent that the scratched part is not a concern.
X: It changes to such an extent that the scratched part is worrisome (the scratched part looks darker than the non-scratched part).

<Preparation of pigment dispersion>
(Pigment dispersion 12)
Pigment Dispersion 1 except that “# 2600” (manufactured by Mitsubishi Chemical Co., Ltd., DBP oil absorption: 77 ml / 100 g) is used instead of “Color Black FW18”, and the amount of dispersion resin A used is 6 g. Pigment dispersion 12 was obtained in the same manner as above.

(Pigment dispersion 13)
Similar to Pigment Dispersion 1 except that “Color Black FW200” (manufactured by Degussa, DBP oil absorption: 150 ml / 100 g) is used instead of “Color Black FW18” and the amount of dispersion resin A used is 6 g. The pigment dispersion 13 was obtained by the method.

(Pigment dispersion 14)
Pigment Dispersion 1 except that “# 2300” (manufactured by Mitsubishi Chemical Co., Ltd., DBP oil absorption: 64 ml / 100 g) is used instead of “Color Black FW18”, and the amount of dispersion resin A used is 3 g. Pigment dispersion 14 was obtained in the same manner as above.

(Pigment dispersion 15)
Pigment dispersion 1 except that “# 2300” (manufactured by Mitsubishi Chemical Co., Ltd., DBP oil absorption: 64 ml / 100 g) is used instead of “Color Black FW18”, and the amount of dispersion resin A used is 4 g. Pigment dispersion 15 was obtained in the same manner as above.

(Pigment dispersion 16)
A pigment dispersion except that “# 2600” (manufactured by Mitsubishi Chemical Co., Ltd., DBP oil absorption: 77 ml / 100 g) is used instead of “Color Black FW18”, and dispersion resin B6 g is used instead of dispersion resin A8 g. A pigment dispersion 16 was obtained in the same manner as in Example 1.

(Pigment dispersion 17)
Pigment dispersion 1 except that “PRINTEX L6” (manufactured by Degussa, DBP oil absorption: 123 ml / 100 g) is used instead of “Color Black FW18”, and dispersion resin B is used instead of dispersion resin A Pigment dispersion 17 was obtained in the same manner as above.

(Pigment dispersion 18)
A method similar to that of Pigment Dispersion 1 except that “Color Black FW200” (manufactured by Degussa, DBP oil absorption: 150 ml / 100 g) is used instead of “Color Black FW18” and the amount of dispersion resin A used is 4 g. A pigment dispersion 18 was obtained.

(Pigment dispersion 19)
Pigment Dispersion 1 except that “# 2300” (manufactured by Mitsubishi Chemical Co., Ltd., DBP oil absorption: 64 ml / 100 g) is used instead of “Color Black FW18” and the amount of dispersion resin A used is 12 g. A pigment dispersion 19 was obtained in the same manner as above.

(Pigment dispersion 20)
Pigment Dispersion 1 except that “# 2600” (manufactured by Mitsubishi Chemical Co., Ltd., DBP oil absorption: 77 ml / 100 g) is used instead of “Color Black FW18” and the amount of the dispersion resin A used is 12 g. Pigment dispersion 20 was obtained in the same manner as above.

(Pigment dispersion 21)
Pigment dispersion, except that “# 2300” (manufactured by Mitsubishi Chemical Corporation, DBP oil absorption: 64 ml / 100 g) is used instead of “Color Black FW18” and the amount of dispersion resin A used is 2.4 g. A pigment dispersion 21 was obtained in the same manner as for the body 1.

(Pigment dispersion 22)
Pigment dispersion 1 except that “PRINTEX L6” (manufactured by Degussa, DBP oil absorption: 123 ml / 100 g) is used instead of “Color Black FW18”, and dispersion resin B is used instead of dispersion resin A A pigment dispersion 22 was obtained in the same manner as above.

<Preparation of ink>
(Pigment ink 18)
As a pigment dispersion, pigment ink 18 was obtained in the same manner as pigment ink 1 except that 50.0 parts of pigment dispersion 12 were used instead of 33.3 parts of pigment dispersion 1.

(Pigment ink 19)
As a pigment dispersion, pigment ink 19 was obtained in the same manner as pigment ink 1 except that 25.0 parts of pigment dispersion 13 were used instead of 33.3 parts of pigment dispersion 1.

(Pigment ink 20)
A pigment ink 20 was obtained in the same manner as the pigment ink 1 except that 41.7 parts of the pigment dispersion 14 was used instead of 33.3 parts of the pigment dispersion 1 as the pigment dispersion.

(Pigment ink 21)
Pigment ink 21 was obtained in the same manner as Pigment ink 1 except that 16.7 parts of pigment dispersion 13 was used instead of 33.3 parts of pigment dispersion 1 as the pigment dispersion.

(Pigment ink 22)
A pigment ink 22 was obtained in the same manner as the pigment ink 1 except that 41.7 parts of the pigment dispersion 15 was used instead of 33.3 parts of the pigment dispersion 1 as the pigment dispersion.

(Pigment ink 23)
As a pigment dispersion, pigment ink 23 was obtained in the same manner as pigment ink 1 except that 41.7 parts of pigment dispersion 16 was used instead of 33.3 parts of pigment dispersion 1.

(Pigment ink 24)
A pigment ink 24 was obtained in the same manner as the pigment ink 1 except that 16.7 parts of the pigment dispersion 17 was used instead of 33.3 parts of the pigment dispersion 1 as the pigment dispersion.

(Pigment ink 25)
Pigment ink 25 was obtained in the same manner as Pigment ink 1 except that 25.0 parts of pigment dispersion 18 were used instead of 33.3 parts of pigment dispersion 1 as the pigment dispersion.

(Pigment ink 26)
As a pigment dispersion, pigment ink 26 was obtained in the same manner as pigment ink 1 except that 41.7 parts of pigment dispersion 19 was used instead of 33.3 parts of pigment dispersion 1.

(Pigment ink 27)
A pigment ink 27 was obtained in the same manner as the pigment ink 1 except that 50.0 parts of the pigment dispersion 20 was used instead of 33.3 parts of the pigment dispersion 1 as the pigment dispersion.

(Pigment ink 28)
A pigment ink 28 was obtained in the same manner as the pigment ink 1 except that 50.0 parts of the pigment dispersion 13 was used instead of 33.3 parts of the pigment dispersion 1 as the pigment dispersion.

(Pigment ink 29)
Pigment ink 29 was obtained in the same manner as Pigment ink 1 except that 50.0 parts of pigment dispersion 5 were used instead of 33.3 parts of pigment dispersion 1 as the pigment dispersion.

(Pigment ink 30)
As a pigment dispersion, pigment ink 30 was obtained in the same manner as pigment ink 1 except that 41.7 parts of pigment dispersion 21 was used instead of 33.3 parts of pigment dispersion 1.

(Pigment ink 31)
A pigment ink 31 was obtained in the same manner as the pigment ink 1 except that 41.7 parts of the pigment dispersion 22 was used instead of 33.3 parts of the pigment dispersion 1 as the pigment dispersion.

(Pigment ink 32)
Pigment ink 32 was obtained in the same manner as Pigment ink 1 except that 16.7 parts of pigment dispersion 7 were used instead of 33.3 parts of pigment dispersion 1 as the pigment dispersion.

  The inks 18 to 32 obtained above and the inks 4 and 6 obtained previously were combined as shown in Table 2, and Examples 11 to 16 and Comparative Examples 8 to 8 made of dark ink and light ink were combined. 13 ink sets were obtained. The outline of the constitution of each ink is shown in Table 2. “P / B” in Table 1 is the ratio of the pigment concentration P (mass%) to the dispersed resin concentration B (mass%) in the ink.

<Evaluation>
(Evaluation method: scratch resistance)
The ink constituting each ink set obtained above was mounted on an ink jet recording apparatus (trade name: BJ F900, manufactured by Canon Inc.). Next, images were formed on PR101 (trade name, manufactured by Canon Inc.), which is glossy paper, and each of the obtained images was evaluated for scratch resistance and gloss unevenness by the following evaluation methods. The image was formed by using dark and light inks constituting each ink set, with a resolution of 1200 dpi × 1200 dpi, an ejection amount of 4.8 pl / dot, and an 8-pass bidirectional recording condition of 25% duty and 50% duty in total. Next, the obtained image was scratched with a nail, the scratched portion (scratched portion) was visually observed, and scratch resistance was evaluated according to the following evaluation criteria. The evaluation results are shown in Table 2.
(Evaluation criteria)
(Double-circle): A scraping part hardly changes.
○: Slightly changes to the extent that the scratched part is not a concern.
X: It changes to such an extent that the scratched part is worrisome (the scratched part looks darker than the non-scratched part).

(Evaluation method: uneven gloss)
An image for observation was formed using the same ink jet recording apparatus as used in the scratch resistance evaluation, using an ink set composed of the combination of dark and light inks shown in Table 2 below. In other words, 4 cm square glossy paper (PR paper, manufactured by Canon Inc.) was printed such that the left half was dark ink and 50% Duty, and the right half was light ink and 50% Duty. The obtained print sample was visually observed, and gloss unevenness was evaluated according to the following evaluation criteria. The evaluation results are shown in Table 2 below.
(Evaluation criteria)
(Double-circle): There is no big difference in the glossiness of the printing sample by dark ink and light ink.
◯: There is a slight difference in glossiness of the print sample with dark ink and light ink.
X: There is a clear difference in glossiness of the print sample by the dark ink and the light ink.

As described above, according to the present invention, using different shades inks mosquitoes over carbon black concentration, together with scratch resistance of images is improved, the ink set image formation can with a reduced gloss unevenness of the image, and An ink jet recording method can be provided.

It is a longitudinal cross-sectional view which shows an example of the head of an inkjet recording device. It is a cross-sectional view showing an example of the head of the ink jet recording apparatus. FIG. 2 is an external perspective view of a head in which the head shown in FIG. It is a schematic perspective view which shows an example of an inkjet recording device. It is a longitudinal cross-sectional view which shows an example of an ink cartridge. It is a perspective view which shows an example of a recording unit. It is a schematic sectional drawing which shows another structural example of an inkjet recording head.

Claims (4)

A light ink composition containing at least an aqueous medium, carbon black, and a dispersion resin, the concentration of the carbon black being 2% by mass or less, and containing at least an aqueous medium, carbon black, and a dispersion resin; In an ink set for inkjet recording, having at least a dark ink composition having a black density of more than 2% by mass,
The DBP oil absorption of carbon black in the light ink composition is 120 ml / 100 g or more, and the DBP oil absorption of carbon black in the dark ink composition is 80 ml / 100 g or less,
Furthermore, the ratio (P1 / B1) of the concentration P1 (mass%) of carbon black and the concentration B1 (mass%) of the dispersed resin in the light ink composition is the ratio of carbon black in the dark ink composition. An ink set having a ratio (P2 / B2) or less of a density P2 (mass%) and a dispersion resin density B2 (mass%). Wherein the dark ink composition, according to claim 1 ratio between the concentration of carbon black P2 concentration (mass%) and the dispersion resin B2 (wt%) (P2 / B2) is 1.0 to 2.0 The ink set described in 1. The ink set according to claim 1 or 2 , wherein the dispersion resin contained in at least the light ink composition and the dark ink composition is a block copolymer. Using the ink set according to any one of 請 Motomeko 1 to 3, ejecting droplets of the ink composition, and performs printing by depositing the droplets onto a recording medium inkjet Recording method.

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