JP4273104B2 - Aqueous ink, ink jet recording method, ink cartridge, recording unit, ink jet recording method, and image forming method - Google Patents

Description

  The present invention relates to a water-based ink, and more specifically, a recording method and a recording apparatus using an ink-jet recording method, a water-based ink suitable for an ink-jet recording method (image forming method or recording method), and an ink-jet recording method using the same. The present invention relates to an ink cartridge, a recording unit, an ink jet recording apparatus, and an image forming method.

  Conventionally, as a writing instrument (fountain pen, sign pen, water-based ballpoint pen, etc.) or an ink-jet ink, an ink containing a pigment which is a colorant capable of giving a printed matter having high printing density and excellent fastness. Proposed.

  In particular, in recent years, with the aim of performing good recording on plain paper such as copy paper, report paper, notebook, notepaper, bond paper, and continuous slip paper generally used in offices, etc., the ink composition and Detailed research and development has been done from various aspects such as physical properties.

  As a pigment ink having the properties described above, for example, there is a proposal of an aqueous pigment ink containing carbon black and a dispersant (see, for example, Patent Documents 1 and 2).

  In addition, when carbon black is used as a pigment and an ink containing a dispersant is further used as an ink for an ink jet recording apparatus, the ink ejection becomes unstable and a sufficient print density cannot be obtained. As an ink that can solve such a problem, there is a proposal of an aqueous pigment ink containing so-called self-dispersing carbon black that can disperse a pigment without using a dispersant. (For example, refer to Patent Document 3).

Aqueous pigment ink as described above is used as a black ink in combination with another color ink (for example, at least one selected from magenta ink, cyan ink, yellow ink, red ink, green ink and blue ink). When printing a color image, the following problems occur. That is, there is a phenomenon (hereinafter referred to as “bleed”) in which the color is blurred at the boundary between the black image and the color image formed on the recording medium, or the quality of the image is deteriorated due to non-uniform mixing of the ink. appear. As a means for suppressing this bleed, that is, improving the bleed resistance, a proposal for improving the permeability of the ink into the recording medium by adding a surfactant to the ink (see, for example, Patent Document 4), There is a proposal to improve the drying speed of ink applied to a recording medium by using a volatile solvent as a main solvent of the ink (see, for example, Patent Document 5). Furthermore, there is a proposal to improve not only bleed resistance but also character quality and print density by using a black ink containing self-dispersing carbon black and a specific salt (for example, Patent Documents). 6 and 7).
JP-A 61-283875 JP-A 64-6074 JP-A-8-3498 JP 55-65269 A JP-A-55-66976 JP 2000-198955 A JP 2002-80763 A

  As described above, by using a water-based ink containing self-dispersing carbon black and a salt, image characteristics such as bleed resistance, character quality, and print density have reached a level with no problem.

  In order to provide an image of even better quality, the present inventors have studied in detail the phenomenon occurring in the recording medium. As a result, it was found that the type and structure of the surface functional group of the self-dispersing pigment are greatly involved in improving the image characteristics as described above. The self-dispersing pigment contained in the ink applied to the recording medium becomes unstable in dispersion state and causes aggregation due to evaporation and diffusion of water, a change in the ink component ratio, and the like. At this time, by comparing the specific type and structure of the surface functional group of the self-dispersing pigment, it is compared with the image characteristics obtained using a conventional water-based ink containing a self-dispersing pigment and a salt. Thus, it was found that image characteristics such as bleed resistance, character quality, and print density can be greatly improved.

  As a result of investigations by the present inventors, as described above, the type and structure of the surface functional group of the self-dispersing pigment are specified, and the type of salt used together with the self-dispersing pigment is appropriately selected. By selecting the ink, it was found that the ink was excellent in characteristics such as water resistance and dispersion stability during water evaporation.

  Accordingly, an object of the present invention is to form an image having superior bleeding resistance, character quality, and printing density as compared with an image formed using a conventional self-dispersing pigment and a salt-containing ink. It is an object of the present invention to provide an aqueous ink that can be used.

  Another object of the present invention is to provide a water-based ink capable of forming an image having good water resistance in addition to the above effects.

  Another object of the present invention is to provide a water-based ink having good ink characteristics such as dispersion stability at the time of water evaporation in addition to the above effects.

  Another object of the present invention is to provide an ink jet recording method, an ink cartridge, a recording unit, and an ink jet recording apparatus using the water-based ink having the above structure.

  Another object of the present invention is to effectively suppress color mixing (bleeding) at the boundary between black ink and color ink areas when color image recording is performed in which different color areas are adjacent to plain paper. Another object of the present invention is to provide an image forming method that can be used.

The above object is achieved by the present invention described below. That is, the water-based ink of the present invention is characterized by containing a self-dispersing pigment having a -R- (COOM ₁ ) _n group bonded to the surface of pigment particles and a salt. (In the formula, R is an alkylene group or an aromatic ring, M ₁ is a hydrogen atom, an alkali metal, ammonium or organic ammonium, and n is an integer of 2 or more.)
An ink jet recording method according to another embodiment of the present invention is characterized in that in the ink jet recording method including a step of ejecting ink by an ink jet method, the ink is a water-based ink having the above-described configuration.

  An ink cartridge according to another embodiment of the present invention is an ink cartridge provided with an ink storage portion for storing ink, wherein the ink is a water-based ink having the above-described configuration.

  According to another embodiment of the present invention, there is provided a recording unit comprising an ink storage portion for storing ink and a recording head for discharging ink, wherein the ink is a water-based ink having the above configuration. It is characterized by that.

  An ink jet recording apparatus according to another embodiment of the present invention is an ink jet recording apparatus having an ink containing portion for containing ink and a recording head for discharging ink, wherein the ink is an aqueous ink having the above-described configuration. It is characterized by being.

  An image forming method according to another embodiment of the present invention is an image forming method in which black ink and at least one color ink are used for recording on plain paper by an inkjet recording method. After forming an image by scanning with black ink when forming an image in which an image formed by using the water-based ink and the black ink and an image formed by the color ink are adjacent to each other The method is characterized in that scanning is performed to apply color ink to the area where the image is formed.

The aqueous ink according to another embodiment of the present invention, -R- the surface of the pigment particles (CO O ^-) self-dispersing _{pigment n} group is bonded, and contains a M ₁ ⁺ (formula Wherein R is an alkylene group or an aromatic ring, M ₁ is a hydrogen atom, an alkali metal, ammonium or organic ammonium, and n is an integer of 2 or more), NO ₃ ⁻ , CH ₃ COO ⁻ , At least one selected from the group consisting of C ₆ H ₅ COO ⁻ , C ₂ H ₄ (COO ⁻ ) ₂ , C ₆ H ₄ (COO ⁻ ) ₂ and SO ₄ ²⁻ , and M ₂ ⁺ (wherein M ₂ is an alkali metal, ammonium, or organic ammonium)).

  According to the present invention, it is possible to form an image having superior bleed resistance, character quality, and print density as compared with an image formed using a conventional self-dispersing pigment and a salt-containing ink. An aqueous ink that can be provided can be provided. Further, according to another embodiment of the present invention, in addition to the above effects, an aqueous ink capable of forming an image having good water resistance can be provided. Further, according to another embodiment of the present invention, in addition to the above effects, it is possible to provide an aqueous ink having good ink characteristics such as dispersion stability during evaporation of moisture. Further, according to another embodiment of the present invention, an ink jet recording method, an ink cartridge, a recording unit, and an ink jet recording apparatus using the water-based ink having the above-described configuration can be provided. According to another embodiment of the present invention, when color image recording in which different color areas are adjacent to each other on plain paper is performed, color mixing (bleeding) at the boundary portion of each color image is effectively suppressed. It is possible to provide an image forming method.

  Hereinafter, the present invention will be described in more detail with reference to the best mode for carrying out the invention.

The water-based ink according to the present invention is a self-dispersing pigment in which —R— (COOM ₁ ) _n group is bonded to the surface of pigment particles (wherein R is an alkylene group or an aromatic ring, and M ₁ is a hydrogen atom) , Alkali metal, ammonium or organic ammonium, and n is an integer of 2 or more) as a coloring material, and further contains a salt.

By using a self-dispersing pigment in which -R- (COOM ₁ ) _n group is bonded to the surface of the pigment particle as a coloring material, it is more resistant to bleeding than a conventional water-based ink containing a self-dispersing pigment. The reason why the properties, print quality, print density and the like are further improved is presumed that the interaction between the self-dispersing pigment and the water-soluble organic solvent in the ink is greatly involved. That is, as a coloring material, -R- to the surface of the pigment particles (COOM ₁₎ When using the self-dispersion _{pigment n} group is bonded, in particular, the the surface of the pigment particles -R- (COOM _{1) n} group It is considered that the following phenomenon occurs when is bonded at a higher density.

In the ink, since the —R— (COOM ₁ ) _n group bonded to the surface of the pigment particle is present, steric hindrance is more likely to occur. Therefore, the pigment having the —R— (COOM ₁ ) _n group bonded thereto The water-soluble organic solvent present in the vicinity of the particles is less likely to solvate as compared with the conventional self-dispersing pigment and the water-soluble organic solvent present in the vicinity thereof. As a result, it is considered that when the ink is applied to the recording medium, separation (solid-liquid separation) between the water-soluble organic solvent in the ink and the solid content including the pigment is caused very quickly. Also, when the water-soluble organic solvent contained in the ink is difficult to solvate with respect to the pigment, the effect of dispersion stability of the pigment due to the solvation in the ink is reduced, and therefore the aggregation of the pigments occurring in the recording medium is more It is thought that it will occur remarkably.

Furthermore, the present inventors have described a counter ion of a self-dispersing pigment in which the -R- (COOM ₁ ) _n group is bonded to the surface of the pigment particle, and a salt contained in the ink in combination with the self-dispersing pigment. Various studies were conducted. As a result, in the specific combination of the self-dispersing pigment and the salt, not only the excellent effects of improving the bleed resistance, character quality, and print density described above, but also water resistance and water evaporation It has been found that ink characteristics such as dispersion stability in can also be improved. The specific reason why the above-mentioned effects can be obtained by combining a specific self-dispersing pigment with a specific salt is not clear, but the molecular structure and dissociation equilibrium constant for the functional group and salt bonded to the pigment surface. This is presumably due to solubility.

  The solvation in the present invention means the affinity between the pigment and the water-soluble organic solvent, and depends on the extent to which the pigment has an affinity for the water-soluble organic solvent. Examples of the site having affinity for the water-soluble organic solvent include a site where an ionic group is not bonded on the surface of the pigment particle. For example, when ionic groups are bonded to the surface of the pigment particle at a high density, the area where the portion having affinity for the water-soluble organic solvent is exposed on the surface of the pigment particle is small. In addition, when the ionic group covers the pigment particle surface at a higher density, the synergistic effect of the steric hindrance due to the ionic group and the reduction of the portion of the pigment having affinity for the water-soluble organic solvent. The water-soluble organic solvent is presumed to be less solvated with respect to the pigment.

[Water-based ink]
Hereinafter, the self-dispersing pigment, salt, aqueous medium, and other components constituting the aqueous ink of the present invention will be described.

<Self-dispersing pigment>
The color material used in the aqueous ink according to the present invention is a self-dispersing pigment in which —R— (COOM ₁ ) _n group is bonded to the surface of pigment particles (wherein R is an alkylene group or an aromatic ring). And M ₁ is a hydrogen atom, an alkali metal, ammonium or organic ammonium, and n is an integer of 2 or more.) The form of the —R— (COOM ₁ ) _n group in the ink may be any form of a partly dissociated state or a completely dissociated state.

In particular, a pigment obtained by a diazo coupling method and having the above-described compound having a structure of -R- (COOM ₁ ) _n group in part as a surface can be suitably used. Of course, the present invention is not limited to this. These self-dispersing pigments can be used alone or in combination of two or more.

  Examples of the alkylene group in the present invention include a methylene group, an ethylene group, a propylene group, and the like. In addition, examples of the aromatic ring in the present invention include a benzene ring and a naphthalene ring. Of course, the present invention is not limited to this.

Further, as a more preferred embodiment, in the -R- bonded to the surface of the pigment particle, - (COOM ₁₎ is a carbon atom adjacent to the carbon atom to which they are attached, - (COOM ₁₎ bonded to the In the case where n is 2, the case where R is C ₆ H ₃ or the like, the effect of the present invention is more remarkably exhibited. Note that in -R- bonded to the surface of the pigment particle, - (COOM ₁₎ is a carbon atom adjacent to the carbon atom to which they are attached, - the fact that by combining (COOM _1), As shown in the following structural formula (1), two or more adjacent carbon atoms in R each have a — (COOM ₁ ) group. In the present invention, it is preferable to use a self-dispersing pigment in which a group represented by the following structural formula (1) is bonded to the surface of the pigment particle. Of course, the present invention is not limited to this.

  Structural formula (1)

In the water-based ink according to the present invention, when the -R- (COOM ₁ ) _n groups are bonded to the pigment particle surface at a higher density, for example, the ionic group density on the pigment particle surface is 2. The amount of 00 μmol / m ² or more is particularly preferable because solid-liquid separation due to the degree of solvation described above is further promoted and the effects of the present invention can be obtained more remarkably. In the present invention, the ionic group density on the pigment particle surface is greatly affected by the specific surface area of the pigment, the structure of the functional group bonded to the pigment particle surface, etc. Absent.

Furthermore, in the water-based ink according to the present invention, when M ₁ is ammonium, it is particularly preferable because better water resistance can be obtained. This is because, when the ink is applied to the recording medium, the ammonium is decomposed, the ammonia is evaporated, and the ionic group bonded to the surface of the carbon black becomes H type (acid type), and the hydrophilicity is lowered. This is probably due to this. Here, the self-dispersing carbon black in which M ₁ is ammonium can be obtained by the following method. For example, self-dispersing carbon black in which M ₁ is an alkali metal is used to replace M ₁ with ammonium by performing an ion exchange method, or after adding acid to make H type, ammonium hydroxide is added. And a method in which M ₁ is converted to ammonium.

<Pigment particles>
The pigment particles that can be used in the aqueous ink according to the present invention are not particularly limited, and any of those listed below can be used. When the aqueous ink of the present invention is used as a black ink, it is preferable to use carbon black as pigment particles.

  Specific examples of carbon black include furnace black, lamp black, acetylene black, channel black, and the like. Specifically, for example, Raven 7000, Ray Van 5750, Ray Van 5250, Ray Van 5000 ULTRA, Ray Van 3500, Ray Van 2000, Ray Van 1500, Ray Van 1250, Ray Van 1200, Ray Van 1190 ULTRA-II, Ray Van 1170, Ray Van 1255 (or more, Colombia), Black Pearls L, Regal 400R, Regal 330R, Legal 660R, Mogul L, Monarch 700, Monak 800, Monak 880, Monak 900, Monak 1000, Monak 1100 Monak 1300, Monak 1400, Monak 2000, Vulcan XC-72R (above, Ki Bot), Color Black FW1, Color Black FW2, Color Black FW2V, Color Black FW18, Color Black FW200, Color Black S150, Color Black S160, Color Black S170, Printex 35, Printex U , Printex V, Printex 140U, Printex 140V, Special Black 6, Special Black 5, Special Black 4A, Special Black 4 (above, manufactured by Degussa), No. 25, no. 33, no. 40, no. 47, no. 52, no. 900, no. Commercial products such as 2300, MCF-88, MA600, MA7, MA8, MA100 (manufactured by Mitsubishi Chemical) can be used. Carbon black newly prepared for the present invention can also be used. However, the present invention is not limited to these, and any conventionally known carbon black can be used. Further, the material is not limited to carbon black, and magnetic fine particles such as magnetite and ferrite, titanium black, and the like may be used as a black pigment.

  Examples of the pigment particles used in addition to the black ink include various organic pigment particles. Specifically, the organic pigment particles are, for example, insoluble azo pigments such as toluidine red, toluidine maroon, Hansa yellow, benzidine yellow, and pyrazolone red, soluble azo pigments such as lithol red, heliobordeaux, pigment scarlet, and permanent red 2B. Derivatives from vat dyes such as alizarin, indanthrone, thioindigo maroon, phthalocyanine pigments such as phthalocyanine blue and phthalocyanine green, quinacridone pigments such as quinacridone red and quinacridone magenta, and perylene pigments such as perylene red and perylene scarlet Isoindolinone pigments such as isoindolinone yellow and isoindolinone orange, benzimidazolone yellow, benzimidazolone orange and benzimidazolone red Imidazolone pigments, pyranthrone pigments such as pyranthrone red, pyranthrone orange, indigo pigments, condensed azo pigments, thioindigo pigments, diketopyrrolopyrrole pigments, flavanthrone yellow, acylamide yellow, quinophthalone yellow, nickel azo Yellow, copper azomethine yellow, perinone orange, anthrone orange, dianslaquinonyl red, dioxazine violet and the like. Of course, it is not limited to these, Other organic pigments may be used.

The organic pigments that can be used in the present invention are indicated by the color index (COLOUR INDEX) number, and the following can be mentioned.
C. I. Pigment Yellow: 12, 13, 14, 17, 20, 24, 74, 83, 86, 93, 97, 109, 110, 117, 120, 125, 128, 137, 138, 147, 148, 150, 151, 153 154, 166, 168, 180, 185 etc. C.I. I. Pigment Orange: 16, 36, 43, 51, 55, 59, 61, 71 etc. C.I. I. Pigment Red: 9, 48, 49, 52, 53, 57, 97, 122, 123, 149, 168, 175, 176, 177, 180, 192, 215, 216, 217, 220, 223, 224, 226, 227 228, 238, 240, 254, 255, 272 etc. C.I. I. Pigment violet: 19, 23, 29, 30, 37, 40, 50, etc. C.I. I. Pigment Blue: 15, 15: 1, 15: 3, 15: 4, 15: 6, 22, 60, 64 etc. C.I. I. Pigment Green: 7, 36 etc. C.I. I. Pigment Brown: 23, 25, 26, etc. The pigment content (% by mass) in the aqueous ink according to the present invention is preferably 0.1% by mass to 15% by mass with respect to the total mass of the ink, in particular. It is preferable that it is 1 mass%-10 mass%.

<Salt>
It is essential that the aqueous ink according to the present invention contains a salt. The form of the salt in the ink may be any form in which a part thereof is dissociated or completely dissociated.

Specific examples of the salt that can be used in the aqueous ink according to the present invention include (M ₂ ) NO ₃ , CH ₃ COO (M ₂ ), C ₆ H ₅ COO (M ₂ ), C ₂ H ₄ (COO). (M ₂ )) ₂ , C ₆ H ₄ (COO (M ₂ )) ₂ , (M ₂ ) ₂ SO ₄ (wherein M ₂ is an alkali metal, ammonium or organic ammonium). Of course, it is not limited to these as long as the requirements of the present invention are satisfied.

  The salt content in the water-based ink according to the present invention only needs to be within a range in which the effects of the present invention can be sufficiently obtained. Specifically, the salt content (% by mass) is preferably 0.05% by mass to 10.0% by mass with respect to the total mass of the ink. When the content is less than 0.05% by mass, the effect of the present invention may not be obtained. When the content is more than 10.0% by mass, the storage stability of the ink may not be obtained.

In the water-based ink according to the present invention, when M ₂ is ammonium, more excellent water resistance is obtained, which is more preferable. Among these, NH ₄ NO ₃ , C ₂ H ₄ (COONH ₄ ) ₂ , C ₆ H ₄ (COONH ₄ ) ₂ , (NH ₄ ) ₂ SO _{4 and the} like exhibit water resistance in a relatively short time. preferable.

In the water-based ink according to the present invention, the salt is C ₂ H ₄ (COO (M ₂ )) ₂ , C ₆ H ₄ (COO (M ₂ )) ₂ , (M ₂ ) ₂ SO _4. The dispersion stability of the pigment when the water contained in the ink evaporates is particularly excellent, which is more preferable.

Further, in the self-dispersing pigment in which the -R- (COOM ₁ ) _n group is bonded to the surface of the pigment particle, for example, when n is 2, divalent as a salt used in combination with the self-dispersing pigment. In other words, when the valence of the functional group on the surface of the pigment particle and the valence of the salt are the same, the effects of the present invention can be obtained more significantly, which is particularly preferable. Specifically, a self-dispersing pigment having —R— (COOM ₁ ) ₂ groups bonded to the pigment particle surface, C ₂ H ₄ (COO (M ₂ )) ₂ , C ₆ H ₄ (COO (M ₂ )) ₂ , (M ₂ ) ₂ SO _{4 and} the like. Of course, the present invention is not limited to this.

<Aqueous medium>
The aqueous medium used in the aqueous ink according to the present invention is water alone or a mixed solvent of water and a water-soluble organic solvent. The water-soluble organic solvent is particularly preferably one having an effect of preventing ink drying. Moreover, it is preferable to use deionized water instead of general water containing various ions.

  Specific examples of the water-soluble organic solvent include alkyl having 1 to 4 carbon atoms such as methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, sec-butyl alcohol, tert-butyl alcohol, and the like. Alcohols; Amides such as dimethylformamide and dimethylacetamide; Ketones or ketoalcohols such as acetone and diacetone alcohol; Ethers such as tetrahydrofuran and dioxane; Polyalkylene glycols such as polyethylene glycol and polypropylene glycol; Ethylene glycol and propylene Such as glycol, butylene glycol, triethylene glycol, 1,2,6-hexanetriol, thiodiglycol, hexylene glycol, diethylene glycol, etc. Alkylene glycols having 2 to 6 carbon atoms in the len group; lower alkyl ether acetates such as polyethylene glycol monomethyl ether acetate; glycerin; ethylene glycol monomethyl (or ethyl) ether, diethylene glycol methyl (or ethyl) ether, triethylene glycol Lower alkyl ethers of polyhydric alcohols such as monomethyl (or ethyl) ether; N-methyl-2-pyrrolidone, 2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone and the like. You may use said water-soluble organic solvent individually or as a mixture.

  The content of the water-soluble organic solvent in the aqueous ink according to the present invention is not particularly limited, but is preferably 3% by mass or more and 50% by mass or less with respect to the total mass of the ink. The water content in the water-based ink is preferably 50% by mass or more and 95% by mass or less with respect to the total mass of the ink.

<Other ingredients>
The water-based ink according to the present invention may use a moisturizing compound such as urea, urea derivative, trimethylolpropane, trimethylolethane or the like as an ink component in addition to the components described above for maintaining the moisturizing property. In general, the content of moisturizing compounds such as urea, urea derivatives, and trimethylolpropane is preferably 0.1% by mass to 20.0% by mass with respect to the total mass of the ink, and preferably 3.0% by mass to It is more preferable to set it as 10.0 mass%.

  Further, the water-based ink according to the present invention includes a surfactant, a pH adjuster, an antifoaming agent, a rust preventive, and a preservative as necessary in addition to the above components in order to obtain an ink having a desired physical property value. Various additives such as an antifungal agent, an antioxidant, an anti-reduction agent, an evaporation accelerator, a chelating agent, and the like may be added, and a commercially available water-soluble dye or the like may be added.

  When it is necessary to adjust the surface tension of the ink, it is effective to appropriately add a surfactant such as acetylene alcohol represented by the following structural formula (2), a penetrating solvent, or the like to the ink.

  Structural formula (2)

  In addition, it is possible to improve scratch resistance and marker resistance by adding a polymer or the like to the ink as necessary. In particular, a nonionic polymer having no ionic group has little influence on the reliability of the ink and can be suitably used.

[Color ink]
An image forming method according to the present invention is an image forming method in which recording is performed on plain paper using black ink and at least one color ink, and the aqueous ink having the above-described configuration is used for black ink. In addition, when forming an image in which an image formed by the black ink and an image formed by the color ink are adjacent to each other, the image is formed by performing scanning to which the black ink is applied, and then the image Scanning for applying color ink to the region where the ink is formed is performed. Here, the color ink used when the water-based ink of the present invention is used only for the black ink will be described. In the image forming method according to the present invention, any conventionally known color ink for ink jet recording can be used.

  Examples of the color material of the color ink include water-soluble dyes, and it is particularly preferable to use a water-soluble dye having an anionic group as a solubilizing group. The color ink used in the present invention can be appropriately selected from, for example, cyan, magenta, yellow, red, green, blue and orange.

  The water-soluble dye having an anionic group used in the present invention is not particularly limited as long as it is a water-soluble acidic dye, a direct dye, or a reactive dye described in the color index (COLOUR INDEX). Even dyes not described in the color index can be used. In particular, those having an anionic group such as a sulfonic acid group are preferably used. These dyes are used in the ink in an amount of 1 to 10% by mass, preferably 1 to 5% by mass.

Specific dyes include the following.
C. I. Direct yellow: 8, 11, 12, 27, 28, 33, 39, 44, 50, 58, 85, 86, 87, 88, 98, 100, 110, etc. I. Direct Red: 2, 4, 9, 11, 20, 23, 24, 31, 39, 46, 62, 75, 79, 80, 83, 89, 95, 197, 201, 218, 220, 224, 225, 226 227, 228, 230 etc. C.I. I. Direct Blue: 1, 15, 22, 25, 41, 76, 77, 80, 86, 90, 98, 106, 108, 120, 158, 163, 168, 199, 226, etc. C.I. I. Acid Yellow: 1, 3, 7, 11, 17, 23, 25, 29, 36, 38, 40, 42, 44, 76, 98, 99 etc. C.I. I. Acid Red: 6, 8, 9, 13, 14, 18, 26, 27, 32, 35, 42, 51, 52, 80, 83, 87, 89, 92, 94, 106, 114, 115, 133, 134 145, 158, 198, 249, 265, 289 etc. C.I. I. Acid Blue: 1, 7, 9, 15, 22, 23, 25, 29, 40, 43, 59, 62, 74, 78, 80, 90, 100, 102, 104, 117, 127, 138, 158, 161 Etc. Color materials for color inks include the following 1 to 3 in addition to the above water-soluble dyes. These coloring materials are preferable because many of them exhibit excellent water resistance when applied to a recording medium.
1. 1. A dye having a carboxyl group as a solubilizing group 2. Oil-soluble dyes The pigment oil-soluble dye is not particularly limited as long as it is described in the color index. Even if it is a new dye not described in the color index, there is no particular limitation. Specific examples include the following. These dyes are preferably used in the ink in an amount of 1% by mass to 10% by mass, and more preferably 1% by mass to 5% by mass.
C. I. Solvent Yellow: 1, 49, 62, 74, 79, 82, 83, 89, 90, 120, 121, 151, 153, 154 etc. C.I. I. Solvent Red: 25, 31, 86, 92, 97, 118, 132, 160, 186, 187, 219, etc. C.I. I. Solvent Blue: 33, 38, 42, 45, 53, 65, 67, 70, 104, 114, 115, 135, etc. When a pigment is used as the color material of the color ink, the pigment content is based on the total mass of the ink. It is preferable to set it as 1 mass%-20 mass%, and also 2 mass%-12 mass%. Examples of the pigment that can be used in the present invention include the following. Of course, the present invention is not limited to these. Of course, pigments newly produced for the present invention can also be used.
C. I. Pigment Yellow: 1, 2, 3, 13, 16, 74, 83, 128, etc. C.I. I. Pigment Red: 5, 7, 12, 48 (Ca), 48 (Mn), 57 (Ca), 112, 122, etc. C.I. I. Pigment Blue: 1, 2, 3, l5: 3, l6, 22 etc. C.I. I. Vat Blue: 4, 6, etc. In addition, when a pigment is used as the color material of the color ink, the dispersant for dispersing the pigment in the ink is not particularly limited as long as it is a water-soluble resin, but the weight average molecular weight Is preferably in the range of 1,000 to 30,000, and more preferably in the range of 3,000 to 15,000. Specific examples of such dispersants include styrene, styrene derivatives, vinyl naphthalene, vinyl naphthalene derivatives, aliphatic alcohol esters of α, β-ethylenically unsaturated carboxylic acids, acrylic acid, acrylic acid derivatives, maleic acid, and the like. , At least two monomers selected from maleic acid derivatives, itaconic acid, itaconic acid derivatives, fumaric acid, fumaric acid derivatives, vinyl acetate, vinylpyrrolidone, acrylamide, and derivatives thereof (of which at least one is hydrophilic) Monomer), a random copolymer, a graft copolymer, or a salt thereof. Natural resins such as rosin, shellac and starch can also be preferably used. These resins are soluble in an aqueous solution in which a base is dissolved, and are alkali-soluble resins. The content of the water-soluble resin used as the pigment dispersant is preferably in the range of 0.1 to 5% by mass with respect to the total mass of the ink.

  The aqueous medium used for the color ink is water or a mixed solvent of water and a water-soluble organic solvent. It is preferable to use ion-exchanged water (deionized water) instead of general water containing various ions.

  Specific examples of the water-soluble organic solvent include, for example, alkyl alcohols having 1 to 4 carbon atoms such as methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, sec-butyl alcohol, and tert-butyl alcohol. Amides such as dimethylformamide and dimethylacetamide; ketones or ketoalcohols such as acetone and diacetone alcohol; ethers such as tetrahydrofuran and dioxane; polyalkylene glycols such as polyethylene glycol and polypropylene glycol; ethylene glycol, propylene glycol; Alkyles such as butylene glycol, triethylene glycol, 1,2,6-hexanetriol, thiodiglycol, hexylene glycol, diethylene glycol Alkylene glycols containing 2 to 6 carbon atoms; glycerin; lower polyhydric alcohols such as ethylene glycol monomethyl (or ethyl) ether, diethylene glycol methyl (or ethyl) ether, triethylene glycol monomethyl (or ethyl) ether Alkyl ethers; N-methyl-2-pyrrolidone, 2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone and the like. Among these water-soluble organic solvents, polyhydric alcohols such as diethylene glycol and lower alkyl ethers of polyhydric alcohols such as triethylene glycol monomethyl (or ethyl) ether are particularly preferable.

  The content of the water-soluble organic solvent in the color ink is preferably 3% by mass to 50% by mass, and more preferably 3% by mass to 40% by mass with respect to the total mass of the ink. The water content in the color ink is preferably in the range of 10% by mass to 90% by mass, and more preferably 30% by mass to 80% by mass with respect to the total mass of the ink.

  In addition to the above-mentioned components, the color ink used in the present invention is appropriately added with a surfactant, an antifoaming agent, a preservative, etc. in order to obtain an ink having a desired physical property value as necessary. Can be added.

<Ink physical properties>
It is preferable that the black and color inks used in the present invention, which are composed of the components described above, have characteristics that allow them to be ejected favorably from an inkjet recording head. From the viewpoint of ejection from an ink jet recording head, the ink characteristics are, for example, a viscosity of 1 mPa · s to 15 mPa · s, a surface tension of 25 mN / m or more, and a viscosity of 1 mPa · s to 5 mPa · s. The surface tension is preferably 25 mN / m to 50 mN / m. Further, when black ink and color ink are used in combination, it is more preferable that the surface tension of the color ink is lower than the surface tension of the black ink. Specifically, the surface tension of the black ink is preferably 35 mN / m to 50 mN / m, and the surface tension of the color ink is preferably 25 mN / m to 35 mN / m.

A Ka value obtained by the Bristow method is a measure representing the penetrability of ink into a recording medium. That is, when the ink permeability is expressed by the ink amount V per 1 m ² , the ink penetration amount V (ml / m ² = μm) after a predetermined time t has elapsed since the ink droplet was ejected. ) Is represented by the Bristow formula (formula (1)) shown below.

  Most of the ink immediately after being applied to the recording medium is absorbed by the uneven portion (rough portion of the recording medium surface) on the surface of the recording medium and hardly penetrates into the inside (depth direction) of the recording medium. . The time during this period is the contact time (tw), and the amount of ink absorbed in the uneven portion of the recording medium at the contact time is Vr. After the ink is applied to the recording medium, when the contact time is exceeded, the time exceeding the contact time, that is, the amount of ink proportional to the power of 1/2 of (t-tw) is increased inside the recording medium ( It penetrates in the depth direction) and the amount of penetration increases. Ka is a proportional coefficient of this increase, and takes a value corresponding to the penetration rate. The Ka value can be determined using a Bristow method liquid dynamic permeability tester (for example, trade name: Dynamic permeability tester S; manufactured by Toyo Seiki Seisakusho).

Further, according to the study by the present inventors, the Ka value in the ink is less than 1.5 (ml / m ² / msec ^1/2 ) from the viewpoint of further improving the quality of the formed recorded image. It is preferable to adjust so that the Ka value is 0.2 (ml / m ² / msec ^1/2 ) or more and less than 1.5 (ml / m ² / msec ^1/2 ). It is preferable. That is, if the ink is configured to have a Ka value of less than 1.5 (ml / m ² / msec ^1/2 ), solid-liquid separation occurs at an early stage in the process of ink penetrating into the recording medium. High-quality images can be formed.

  The Ka value according to the Bristow method in the present invention is a PB used for plain paper (for example, a copying machine using an electrophotographic method, a page printer (laser beam printer) manufactured by Canon, or a printer using an ink jet recording method). It is a value measured by using paper or PPC paper which is paper for a copying machine using an electrophotographic method as a recording medium. The measurement environment is assumed to be a normal office environment, for example, a temperature of 20 ° C. to 25 ° C. and a humidity of 40% to 60%.

  In order to give the ink the physical properties as described above, the water-based ink according to the present invention includes, for example, glycerin, trimethylolpropane, thiodiglycol, ethylene glycol, diethylene glycol, isopropyl alcohol, and acetylene alcohol as a water-soluble organic solvent. It is particularly preferable to contain.

[Image forming method]
The image forming method according to the present invention will be described below with specific examples. The image forming method according to the present invention is an image forming method in which black ink and at least one color ink are used to perform recording on plain paper by an ink jet recording method. The black ink is a water-based ink having the configuration described above. When the image formed by using the black ink and the image formed by the color ink having the configuration described above are adjacent to each other, scanning for applying the black ink is performed. After the image is formed, scanning for applying color ink to the region where the image is formed is performed. The image forming method according to the present invention will be described in detail below.

  FIG. 8 is an example of a recording head used when carrying out the image forming method according to the present invention. As shown in FIG. 8, the recording head includes an ejection port array (Bk) for ejecting black ink, and three colors of cyan (C), magenta (M), and yellow (Y) as color inks. And an ejection port array for ejecting each of the inks.

  In the image forming method of the present invention, when forming a full-color image, the black ink discharge port array for discharging the black ink and the color ink discharge port array for discharging the color ink are arranged in the sub-scanning direction. It is preferable to use a recording head arranged so as to be shifted. Specifically, for example, when forming an image using the recording head shown in FIG. 8, when forming an image of only black, the entire ejection port array for black ink is used, When forming a full-color image in which an image and a color image are mixed, the black ink is a part of the black ink ejection port array, and the C, M, and Y color inks are the color ink ejection port array. It is preferable to form an image using the part b. Hereinafter, the case of forming an image in which a black image and a color image are mixed will be described in more detail.

  FIG. 8 shows an example of a recording head that can be used in the present invention. The recording head includes an ejection port array (Bk) for ejecting black ink, an ejection port array for ejecting three color inks of cyan (C), magenta (M), and yellow (Y). It has. First, a black image is formed on a recording medium by one-pass printing by scanning the print head in the horizontal direction (main scanning direction) in the drawing using the portion a of the black ink ejection port array. Next, the recording medium is transported by a distance a in the vertical direction (sub-scanning direction) in the drawing, and in the forward scanning process of the next print head, the portion b of the color ink ejection port array is used. A color image is formed on the recording medium by one-pass printing in the image area formed in the portion a of the black ink ejection port array. At this time, the portion a of the black ink ejection port array forms an image in the next area. By repeating this, an image in which a black image and a color image are mixed is formed.

  FIG. 9 shows another example of a recording head that can be used in the present invention. In FIG. 9, as in FIG. 8, the black ink includes the a portion of the black ink discharge port array, and the C, M, and Y color inks include the b portion corresponding to the entire region of the color ink discharge port array. In the same manner as described above, an image in which a black image and a color image are mixed is formed.

  FIG. 10 shows another example of a recording head that can be used in the present invention. Also in FIG. 10, as in the case of FIG. 8, the black ink includes the a portion of the black ink discharge port array, and the C, M, and Y color inks include the b portion corresponding to the entire region of the color ink discharge port array. Used to form an image in which a black image and a color image are mixed. Here, in the recording head shown in FIG. 10, a distance of one paper feed amount a ′ is placed between the a portion of the black ink ejection port array and the b portion of the color ink ejection port array. It has been. For this reason, in the recording head having such a configuration, there is an extra time difference for one scanning in a reciprocating period between the formation of a black image and the formation of a color image. Therefore, the recording head shown in FIG. 10 has a more advantageous configuration for suppressing bleeding between the black image and the color image than the configuration of the recording head shown in FIG.

  FIG. 11 shows another example of a recording head that can be used in the present invention. When using a recording head in which the black ink ejection port array and the color ink ejection port array are arranged in a row in the sub-scanning direction as in the recording head shown in FIG. A color image is formed after the black image is formed.

  FIG. 12 shows another example of a recording head that can be used in the present invention. In the recording head shown in FIG. 12, the color ink ejection port arrays are arranged with cyan ink (C1, C2), magenta ink (magenta ink) so that the color ink ejection order is the same in the forward direction and the backward direction of main scanning. Two rows of M1, M2) and yellow ink (Y1, Y2) are provided symmetrically in the main scanning direction. As a result, bidirectional printing is possible in forming an image in which a black image and a color image are mixed. In this case, first, a black image is formed using the portion a of the black ink ejection port array, and then the recording medium is transported by the distance a in the sub-scanning direction, and the main scanning in the next print head is performed. In the backward direction process, a color image is printed on the recording medium by one-pass printing in the image area formed by the a portion of the black ink discharge port array using the b portion of the color ink discharge port array. Form. At this time, the portion a of the black ink ejection port array forms an image in the next area. By repeating this, an image in which a black image and a color image are mixed is formed.

  Also in the recording head corresponding to bidirectional printing as shown in FIG. 12, similarly to the recording head described in FIG. 10, the portion a of the black ink ejection port array and the portion b of the color ink ejection port array The distance between the paper feed amount a ′ is one (see FIG. 13), and it is once in a reciprocation between the black image formation and the color image formation. It is possible to provide a more advantageous configuration for suppressing bleeding between the black image and the color image by providing a time difference corresponding to the scanning time.

  The image forming method according to the present invention has been described above. Of course, the form of the recording head that can be used in the image forming method according to the present invention is not limited to FIGS. Further, since the number of passes varies depending on the recording apparatus to be used, it is not limited to one-pass printing.

  In the case of forming an image in which a black portion and a color portion are mixed on plain paper, if the aqueous ink according to the present invention is used as the black ink, as described above, the black ink is formed on the paper surface. It is considered that the aggregation or dispersion destruction of the coloring material that progresses proceeds relatively quickly as compared with other inks. In the image forming method according to the present invention, the aqueous ink according to the present invention is used as the black ink, and the image formation with the color ink is performed after the image formation with the black ink, and more preferably, the scanning for applying the black ink is performed. Later, by performing scanning that applies color ink after at least one scanning interval, even if black ink and color ink come into contact with each other, mixed color bleeding between the black ink and color ink on the paper surface occurs. Therefore, it is possible to form an image having excellent bleeding resistance. In other words, it is possible to perform multi-pass printing that requires printing time to complete printing by scanning multiple times, or to recover with black ink and color ink, only by performing image formation with black ink and color ink with a time difference. The above-described excellent effects can be obtained without requiring a method for increasing the size of the equipment such as separate systems.

[Inkjet recording method, ink cartridge, recording unit, inkjet recording apparatus]
Next, an example of an ink jet recording apparatus suitable for the present invention will be described below. First, FIG. 1 and FIG. 2 show an example of the configuration of a recording head that is a main part of an ink jet recording apparatus using thermal energy. FIG. 1 is a cross-sectional view of the recording head 13 along the ink flow path, and FIG. 2 is a cross-sectional view taken along the line AB of FIG. The recording head 13 is obtained by bonding a heating element substrate 15 to a glass, ceramic, silicon, or plastic plate having a flow path (nozzle) 14 through which ink passes.

  The heating element substrate 15 includes a protective layer 16 made of silicon oxide, silicon nitride, silicon carbide, etc., electrodes 17-1 and 17-2 made of aluminum, gold, aluminum-copper alloy, etc., HfB2, TaN, TaAl From a heating resistor layer 18 formed from a high melting point material such as, a heat storage layer 19 formed from thermal silicon oxide, aluminum oxide or the like, and a substrate 20 formed from a material with good heat dissipation such as silicon, aluminum or aluminum nitride. Composed.

  When a pulsed electrical signal is applied to the electrodes 17-1 and 17-2 of the recording head 13, the region indicated by n of the heating element substrate 15 rapidly generates heat, and the ink 21 in contact with the surface is in contact with the ink 21. Bubbles are generated, the meniscus 23 protrudes by the pressure, 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 recording 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 illustrated 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, reference numeral 63 denotes an ink absorber provided adjacent to the blade 61 and, like the blade 61, is held in a form protruding in the moving path of the recording head 65. 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 which has discharge energy generating means and performs recording by discharging ink onto a recording medium facing the discharge port surface where the discharge port is arranged. Reference numeral 66 denotes a movement of the recording head 65 by mounting the recording head 65. It is a carriage for performing. 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 section 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 ejection port surface of the recording head 65, and discharged to a paper discharge unit 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. 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 the above-described wiping position. 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 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. An ink absorber 44 receives waste ink. The ink container preferably has a liquid contact surface made of polyolefin, particularly polyethylene.

  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 as described above, and is preferably used also in an apparatus in which they are integrated as shown in FIG. . 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. The material of the ink absorber is preferably polyurethane. Alternatively, a structure may be used in which the ink container is an ink bag with a spring or the like inside without using an ink absorber. 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, a preferred example of an ink jet recording apparatus using mechanical energy will be described. An ink jet recording apparatus using mechanical energy includes a nozzle forming substrate having a plurality of nozzles, a pressure generating element made of a piezoelectric material and a conductive material arranged opposite to the nozzles, and ink filling the periphery of the pressure generating element. And an on-demand ink jet recording head in which a pressure generating element is displaced by an applied voltage and a small droplet of ink is ejected from a 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, a vibration plate 82 that directly applies pressure to ink, and the vibration plate 82. And a substrate 84 for supporting and fixing the orifice plate 81, the diaphragm 82 and the like.

  In FIG. 7, the ink flow path 80 is formed of a photosensitive resin or the like, and the orifice plate 81 is formed with a discharge port 85 by performing drilling or the like by electroforming or press working on a metal such as stainless steel or nickel. The plate 82 is formed of a metal film such as stainless steel, nickel, or titanium and a highly elastic resin film, and 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 a distortion stress, and the energy deforms the vibration plate bonded to the piezoelectric element 83, so that the ink in the ink flow path 80 is obtained. Is pressed vertically and ink droplets (not shown) are ejected from the ejection ports 85 of the orifice plate 81 to perform recording. 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.

  Next, the present invention will be described more specifically with reference to examples, comparative examples and reference examples. The present invention is not limited by the following examples as long as the gist thereof is not exceeded. In the text, “parts” and “%” are based on mass unless otherwise specified.

[Preparation of pigment dispersion]
(Preparation of pigment dispersion A)
To a solution obtained by dissolving 5 g of concentrated hydrochloric acid in 5.5 g of water, 1.5 g of 4-amino-1,2-benzenedicarboxylic acid was added while being cooled to 5 ° C. Next, the container containing the solution was placed in an ice bath and the solution was stirred to keep the solution constantly at 10 ° C. or lower, and 1.8 g of sodium nitrite was dissolved in 9 g of water at 5 ° C. The solution was added. After the solution was further stirred for 15 minutes, 6 g of carbon black having a specific surface area of 220 m ² / g and a DBP oil absorption of 105 mL / 100 g was added with stirring. Thereafter, the mixture was further stirred for 15 minutes. The obtained slurry was filtered with a filter paper (trade name: Standard filter paper No. 2; manufactured by Advantech), and then the particles were sufficiently washed with water and dried in an oven at 110 ° C. to prepare self-dispersing carbon black A. Further, water was added to the self-dispersing carbon black A obtained above to disperse the pigment so that the pigment concentration became 10% by mass to prepare a dispersion. By the above method, a pigment dispersion A was obtained in which self-dispersing carbon black A in which —C ₆ H ₃ — (COONa) ₂ groups were introduced on the surface of the carbon black particles was dispersed in water.

The ionic group density of the self-dispersing carbon black A prepared above was measured and found to be 3.1 μmol / m ² . The measuring method of the ionic group density used in this case is to measure the sodium ion concentration in the pigment dispersion A prepared above using an ion meter (manufactured by Toa DKK), and from that value, the self-dispersing carbon black A It converted to the ionic group density.

(Preparation of pigment dispersion B)
Self-dispersion type carbon black B was prepared by replacing sodium ion with ammonium ion by the ion exchange method for the pigment dispersion A obtained above. Further, water was added to the self-dispersing carbon black B obtained above to disperse the pigment so that the pigment concentration became 10% by mass to prepare a dispersion. By the above method, Pigment Dispersion Liquid B was obtained in a state where self-dispersing carbon black B in which —C ₆ H ₃ — (COONH ₄ ) ₂ groups were introduced on the surface of carbon black particles was dispersed in water.

The self-dispersing carbon black B prepared above had an ionic group density of 3.1 μmol / m ² .

(Preparation of pigment dispersion C)
To a solution prepared by dissolving 5 g of concentrated hydrochloric acid in 5.5 g of water, 1.55 g of p-aminobenzoic acid was added while being cooled to 5 ° C. Next, the container containing the solution was placed in an ice bath and the solution was stirred to keep the solution constantly at 10 ° C. or lower, and 1.8 g of sodium nitrite was dissolved in 9 g of water at 5 ° C. The solution was added. After the solution was further stirred for 15 minutes, 6 g of carbon black having a specific surface area of 220 m ² / g and a DBP oil absorption of 105 mL / 100 g was added with stirring. Thereafter, the mixture was further stirred for 15 minutes. The obtained slurry was filtered with a filter paper (trade name: Standard filter paper No. 2; manufactured by Advantech), and then the particles were sufficiently washed with water and dried in an oven at 110 ° C. to prepare self-dispersing carbon black C. Further, water was added to the self-dispersing carbon black C obtained above to disperse the pigment so that the pigment concentration became 10% by mass to prepare a dispersion. By the above method, Pigment Dispersion Liquid C was obtained in a state where self-dispersing carbon black C in which —C ₆ H ₄ —COONa groups were introduced on the surface of carbon black particles was dispersed in water.

When the ionic group density of the self-dispersing carbon black C prepared above was measured by the same method as that for the self-dispersing carbon black A, it was 2.6 μmol / m ² .

(Preparation of pigment dispersion D)
For the pigment dispersion C obtained above, sodium ions were replaced with ammonium ions by an ion exchange method to prepare self-dispersing carbon black D. Furthermore, water was added to the self-dispersing carbon black D obtained above to disperse the pigment so that the pigment concentration became 10% by mass to prepare a dispersion. By the above method, a pigment dispersion D was obtained in which self-dispersing carbon black D in which —C ₆ H ₄ —COONH ₄ groups were introduced on the surface of the carbon black particles was dispersed in water.

The self-dispersing carbon black D prepared above had an ionic group density of 2.6 μmol / m ² .

[Preparation of ink]
The ingredients listed in Table 1 below were mixed, dissolved or dispersed with sufficient stirring, and then filtered under pressure with a microfilter (made by Fuji Film) having a pore size of 3.0 μm. Examples 1 to 8 and Reference Examples 1-3 inks were prepared.

[Evaluation]
The following evaluation was performed using the ink obtained above.

For the production of printed matter, a modified version of an inkjet recording apparatus BJS700 (manufactured by Canon) having an on-demand type multi-recording head that ejects ink by applying thermal energy to the ink in accordance with a recording signal is used. It was. The printer driver selected the default mode. The default mode setting conditions are as follows.
-Paper type: Plain paper-Print quality: Standard-Color adjustment: Automatic

(Print density)
Using each of the inks of Examples 1 to 8 and Reference Examples 1 to 3, the discharge amount per dot of ink was set within 30 ng ± 10%, and a solid portion of 2 cm × 2 cm was formed on the following five types of recording media. A printed matter on which characters including the character were printed was prepared. The print density of the solid part after storing the printed matter for 1 day was measured. For the measurement of the print density, a reflection densitometer (trade name: Macbeth RD-918; manufactured by Macbeth) was used.
・ PPC paper office planner (Canon)
・ PPC paper GF-500 (Canon)
・ PPC paper 4024 (Xerox)
・ PPC paper prober bond (manufactured by Fox River)
・ Canon PPC paper (made by Neuzidra)
The evaluation criteria for the print density are as follows. The evaluation results are shown in Table 2.
A: The average print density of the five types of recording media is 1.45 or more.
B: The average print density of the five types of recording media is 1.40 or more and less than 1.45.
C: The average print density of the five types of recording media is less than 1.40.

(Character quality)
Using each of the inks of Examples 1 to 8 and Reference Examples 1 to 3, printed materials on which characters of several font sizes were printed were produced, and the bleeding of the characters was visually confirmed. Note that an office planner (manufactured by Canon) was used for the production of printed matter. The evaluation criteria for character quality are as follows. The evaluation results are shown in Table 2.
A: The bleeding of characters is hardly noticeable.
B: Although there is some blurring of characters, it is a level at which there is no problem in actual use.
C: Character bleeding is conspicuous.

(Bleed resistance)
Color inks (three colors of cyan, magenta, and yellow) were prepared for evaluation of bleed resistance. The components shown below were mixed and sufficiently stirred, and then pressure filtration was performed with a micro filter (manufactured by Fuji Film) having a pore size of 0.2 μm to prepare each color ink. In the following color ink composition, acetylenol E-100 (manufactured by Kawaken Fine Chemicals) is an acetylene alcohol surfactant represented by the above structural formula (2).

(Cyan ink)
DBL (direct blue) 199 3.5 parts glycerin 7.5 parts diethylene glycol 7.5 parts acetylenol E-100 1.0 part pure water 80.5 parts (magenta ink)
AR (acid red) 289 2.5 parts glycerin 7.5 parts diethylene glycol 7.5 parts acetylenol E-100 1.0 part pure water 81.5 parts (yellow ink)
DY (direct yellow) 86 2.5 parts glycerin 7.5 parts diethylene glycol 7.5 parts acetylenol E-100 1.0 part pure water 81.5 parts

Using each of the black inks of Examples 1 to 8 and Reference Examples 1 to 3, and the color ink obtained above, an inkjet recording apparatus modified to have a recording head having the configuration shown in FIG. A printed matter was produced in which solid portions of black and color (yellow, magenta, cyan) were printed adjacent to each other. The degree of bleeding at the boundary between black and color of the obtained printed matter was visually observed. Note that an office planner (manufactured by Canon) was used for the production of printed matter. The evaluation criteria for bleed resistance are as follows. The evaluation results are shown in Table 2.
AA: The bleed cannot be visually recognized.
A: Bleed is hardly noticeable.
B: Bleed, but at a level where there is no problem in actual use.
C: Bleed so that the color boundary line is not clear.

  From Table 2, it can be seen that the print density and bleed resistance are clearly improved when the inks of Examples 1 to 8 are used, as compared with the case of using the inks of Reference Examples 1 to 3. Further, it can be seen that the bleed resistance is better in each of the examples when the recording head having the configuration shown in FIG. 13 is used than when the recording head having the configuration shown in FIG. 12 is used. Moreover, it turns out that a character quality is a level comparable to Examples 1-8 and Reference Examples 1-3.

(water resistant)
Using each ink of Examples 1 to 8, a printed matter on which characters including a solid portion were printed was produced. After a predetermined time had elapsed since printing, the soiled state when the printed part was exposed to running water was visually evaluated. The following five types of recording media were used for the production of printed matter.
・ PPC paper office planner (Canon)
・ PPC paper GF-500 (Canon)
・ PPC paper 4024 (Xerox)
・ PPC paper prober bond (manufactured by Fox River)
・ Canon PPC paper (made by Neuzidra)
The evaluation criteria for water resistance are as follows. The evaluation results are shown in Table 3.
AA: In all of the five types of recording media, the background stains are not noticeable within 1 hour after printing.
A: Background stains are not noticeable within one day after printing on all five recording media.
B: There is paper on which background stains are conspicuous even after one day or more after printing.

(Dispersion stability: Dispersion stability of pigment when water evaporates)
Each ink of Examples 1 to 8 was put in an open container, and water and the like were evaporated at a temperature of 60 ° C., and each ink was concentrated to a certain amount, for example, 60% of the initial mass. This is because the ink according to the present invention is excellent in dispersion stability by evaluating the dispersion stability under more severe conditions. The pigment dispersion stability during water evaporation was evaluated from the viscosity of the concentrated ink and the degree of pigment aggregate formation. The evaluation criteria for the dispersion stability of the pigment at the time of water evaporation are as follows. The evaluation results are shown in Table 3.
AA: There is little change in the viscosity of the ink and the formation of pigment agglomerates before and after standing.
A: There is a change in the viscosity of the ink or the formation of pigment aggregates before and after standing, but this is a level that does not cause any problems in actual use.
B: The change in the viscosity of the ink before and after being left is large, or pigment aggregates are formed.

  From Table 3, it can be seen that when the inks of Examples 2 to 8 are used, the water resistance is at a level causing no problem in actual use. In particular, when the inks of Examples 5 to 8 were used, good water resistance was developed in a relatively short time after printing. It can also be seen that the dispersion stability of the pigment during evaporation of water is at a level that does not cause a problem in actual use when the inks of Examples 6 to 8 are used. In particular, when the inks of Examples 7 and 8 were used, the pigment dispersion stability during evaporation of moisture was particularly excellent.

It is a longitudinal cross-sectional view of an inkjet recording device head. It is a vertical and horizontal view of an inkjet recording device head. FIG. 2 is an external perspective view of a head in which the head shown in FIG. It is a perspective view which shows an example of an inkjet recording device. It is a longitudinal cross-sectional view of an ink cartridge. It is a perspective view which shows an example of a recording unit. FIG. 3 is a diagram illustrating an example of a configuration of a recording head. It is an example of the recording head used for this invention. It is an example of the recording head used for this invention. It is an example of the recording head used for this invention. It is an example of the recording head used for this invention. It is an example of the recording head used for this invention. It is an example of the recording head used for this invention.

Explanation of symbols

13 Recording Head 14 Ink Nozzle 15 Heating Element Substrate 16 Protective Layer 17-1, 17-2 Electrode 18 Heating Resistor Layer 19 Heat Storage Layer 20 Substrate 21 Ink 22 Discharge Orifice (Micropore)
23 Meniscus 24 Ink Drop 25 Recording Medium 26 Multi Nozzle 27 Glass Plate 28 Heating Head 40 Ink Bag 42 Plug 44 Ink Absorber 45 Ink Cartridge 51 Paper Feeder 52 Paper Feed Roller 53 Paper Discharge Roller 61 Blade 62 Cap 63 Ink Absorber 64 Ejection recovery unit 65 Recording head 66 Carriage 67 Guide shaft 68 Motor 69 Belt 70 Recording unit 71 Head unit 72 Atmospheric communication port 80 Ink flow path 81 Orifice plate 82 Vibration plate 83 Piezoelectric element 84 Substrate 85 Ejection port

Claims (20)

A water-based ink comprising a self-dispersing pigment having a -R- (COOM ₁ ) _n group bonded to the surface of a pigment particle, and a salt.
(In the formula, R is an alkylene group or an aromatic ring, M ₁ is a hydrogen atom, an alkali metal, ammonium or organic ammonium, and n is an integer of 2 or more.) 2. The water-based ink according to claim ₁ , wherein a carbon atom adjacent to the carbon atom to which — (COOM ₁ ) is bonded in —R— is bonded to — (COOM ₁ ).   The water-based ink according to claim 1, wherein the n is 2. The water-based ink according to claim 1, wherein the R is C ₆ H ₃ . The water-based ink according to claim 1, wherein M ₁ is ammonium. The salt is (M ₂ ) NO ₃ , CH ₃ COO (M ₂ ), C ₆ H ₅ COO (M ₂ ), C ₂ H ₄ (COO (M ₂ )) ₂ , C ₆ H ₄ (COO (M The aqueous ink according to claim 1, which is at least one selected from the group consisting of ₂ )) ₂ and (M ₂ ) ₂ SO ₄ . (Wherein M ₂ is an alkali metal, ammonium or organic ammonium) The salt is selected from the group consisting of (M ₂ ) NO ₃ , C ₂ H ₄ (COO (M ₂ )) ₂ , C ₆ H ₄ (COO (M ₂ )) ₂ and (NH ₄ ) ₂ SO _4. The water-based ink according to any one of claims 1 to 5 , which is at least one kind. (Wherein M ₂ is an alkali metal, ammonium or organic ammonium) The salt is at least one selected from the group consisting of C ₂ H ₄ (COO (M ₂ )) ₂ , C ₆ H ₄ (COO (M ₂ )) ₂ and (M ₂ ) ₂ SO _4. The water-based ink according to any one of 1 to 5 . (Wherein M ₂ is an alkali metal, ammonium or organic ammonium) The water-based ink according to any one of claims 6 to 8 , wherein the M ₂ is ammonium.   The water-based ink according to claim 1, wherein the water-based ink is for inkjet.   The inkjet recording method which has the process of discharging an ink with the inkjet method, The said ink is the water-based ink in any one of Claims 1-10, The inkjet recording method characterized by the above-mentioned.   11. An ink cartridge comprising an ink containing portion for containing ink, wherein the ink is the water-based ink according to claim 1.   11. A recording unit comprising an ink storage portion for storing ink and a recording head for discharging ink, wherein the ink is the water-based ink according to claim 1. Recording unit.   An ink jet recording apparatus comprising an ink containing portion for containing ink and a recording head for discharging ink, wherein the ink is the water-based ink according to any one of claims 1 to 10. Inkjet recording apparatus.   In an image forming method for recording on plain paper by an inkjet recording method using black ink and at least one color ink, the aqueous ink according to any one of claims 1 to 10 is used as the black ink, and When forming an image in which an image formed by the black ink and an image formed by the color ink are adjacent to each other, the image is formed after the scan is applied to apply the black ink to form the image. A method of forming an image, comprising performing scanning for applying color ink to the region.   The image forming method according to claim 15, wherein after performing scanning for applying black ink, scanning for applying color ink is performed after a time difference corresponding to at least one scanning is provided.   The ink application is performed using a recording head in which an ejection port array for ejecting black ink and an ejection port array for ejecting color ink are arranged shifted in the sub-scanning direction. Image forming method. A self-dispersing pigment having —R— (COO ⁻ ) _n group bonded to the surface of the pigment particle, and M ₁ ⁺ (wherein R is an alkylene group or an aromatic ring, and M ₁ is hydrogen) An atom, an alkali metal, ammonium, or organic ammonium, and n is an integer of 2 or more.) Further, NO ₃ ⁻ , CH ₃ COO ⁻ , C ₆ H ₅ COO ⁻ , C ₂ H ₄ (COO ⁻ ) ₂ , At least one selected from the group consisting of C ₆ H ₄ (COO ⁻ ) ₂ and SO ₄ ²⁻ , and M ₂ ⁺ (wherein M ₂ is an alkali metal, ammonium or organic ammonium). A water-based ink characterized by containing. -C on the surface of pigment particles ₆ H ₃ -(COOM ₁ ) ₂ A self-dispersing pigment having a group bonded thereto, and a salt, ₆ H ₃ -In-(COOM ₁ ) The carbon atom adjacent to the carbon atom to which the group is attached is-(COOM ₁ ) And the salt is (M ₂ ) NO ₃ , CH ₃ COO (M ₂ ), C ₆ H ₅ COO (M ₂ ), C ₂ H ₄ (COO (M ₂ )) ₂ , C ₆ H ₄ (COO (M ₂ )) ₂ And (M ₂ ) ₂ SO ₄ A water-based ink comprising at least one selected from the group consisting of: (Where M ₁ Is a hydrogen atom, alkali metal, ammonium or organic ammonium, M ₂ Is an alkali metal, ammonium or organic ammonium. ) -C on the surface of pigment particles ₆ H ₃ -(COONH ₄ ) ₂ A self-dispersing pigment having a group bonded thereto, and a salt, ₆ H ₃ -In-(COONH ₄ ) The carbon atom adjacent to the carbon atom to which the group is attached is-(COONH ₄ ) And the salt is C ₆ H ₄ (COO (NH ₄ )) ₂ And (NH ₄ ) ₂ SO ₄ An aqueous ink, characterized in that it is at least one selected from the group consisting of:

Images