JP5783665B2 - Ink set for inkjet recording and inkjet recording method - Google Patents

Description

  The present invention relates to an ink set for ink jet recording and an ink jet recording method.

  2. Description of the Related Art Conventionally, as one of recording methods for characters, images, and the like, an ink jet recording method for performing recording by attaching ink ejected from nozzles of a recording head to a recording medium is performed. In this ink jet recording method, various methods are adopted to improve printing quality. One of the techniques is to use an ink having permeability to a recording medium suitable for ink jet recording.

  For example, for the purpose of improving the density and sharpness of characters, line drawings and the like, a technique is known that uses ink that has a low permeation speed to recording paper, which is a recording medium, and has a large amount attached to the surface of the recording medium. In addition, a technique using an ink having a high penetration speed into a recording medium in order to increase the fixing speed is also known. In general, an ink having a low permeation rate is often referred to as “overlay ink” because it remains in a large amount on the surface of the recording medium. On the other hand, ink having a high permeation speed is referred to as “super-penetrating ink”.

  When superpermeable ink having a high permeation speed is used, the ink 51 dropped on the recording medium 52 penetrates into the recording medium 52 immediately after adhering to the recording medium 52 as shown in FIG. Therefore, the amount of ink remaining on the surface of the recording medium 52 is small. Further, the permeability to the recording medium 52 is high, and depending on the permeability and the material of the recording medium 52, it penetrates deeply to the vicinity of the back surface of the recording medium 52.

  If the ink that has landed on the recording medium permeates quickly, there is little mixing with other ink on the recording medium, and there is an advantage that bleeding at the boundary between different colors hardly occurs. However, since the ink penetrates deeply into the recording medium and diffuses over a wide range, the pigment or dye component of the dye is dispersed. At the same time, light incident on the recording medium is reflected at a deep position from the surface of the recording medium, so that the density of the recorded image tends to be low. In addition, the size of the recording dot is excessively diffused around the ink 51, or a whisker-like blurring (feathering) occurs on the outer periphery of the dot, so that an image with an unclear outline tends to be formed.

  On the other hand, when the overlay ink with low permeability is used, as shown in FIG. 5B, components such as the solvent of the ink 53 are evaporated while remaining on the surface of the recording medium 52 in a convex shape. Easy to do. Therefore, the amount of ink 53 dropped on the recording medium 52 penetrates in the thickness direction of the recording medium 52 is small.

  Thus, if the amount of ink remaining on the surface of the recording medium is large, the image density tends to be high. In addition, when viewed with a single dot, the amount of ink diffusing into the recording medium is very small compared to the superpermeable ink, so that there is an advantage that a sharp image can be recorded. However, since the penetration speed into the recording medium is slow and the time required until the ink remaining on the surface of the recording medium is fixed becomes longer, if other ink adheres to a nearby position, the ink is not transferred between the two inks. It will flow out. For this reason, bleeding occurs at the boundary with the different color, and as a result, the image quality is likely to deteriorate.

  Conventionally, it has been common to use a low penetrability ink to form a black image and to use a highly penetrable ink to form other color images. Black ink is often used for recording characters and line drawings that are required to be easy to see because images of fine lines and dots formed can be clearly seen. For this reason, an overlay ink that has a high recording density and a clear outline can be used as the black ink. On the other hand, for the recording of a color image in which dots of different colors are often recorded adjacent to each other, a super-penetrating ink that does not easily cause bleeding at the boundary of different colors and can clearly record the boundary is used. It was.

  However, depending on the characteristics of the recorded image, the following problems may occur even when recording is performed using inks having different penetrability between black and other colors. That is, as shown in FIG. 5 (c), when the black dots 54 formed with low penetrability ink and the color dots 55 formed with high penetrability ink are adjacent to each other, the ink flows out between the adjacent dots. As a result, the recording quality may be deteriorated. In the black dots 54, the ink that remains convex on the surface of the recording medium 52 flows out from the boundary portion 56 toward the color dot 55, and the density decreases at the boundary portion 56 on the black dot 54 side. As a result, the density of the outline of the black dots 54 decreases, resulting in a whitish and unclear image (referred to as white haze). Also in the color dots 55, black ink is mixed in the boundary portion 56, and the outline becomes unclear (referred to as bleed). As described above, when ink dots having different penetrability are adjacent to each other, white fog or bleed occurs at the boundary portion 56, and the recording quality is easily deteriorated due to these. Such a phenomenon is particularly likely to occur when images are recorded at high speed.

  Until now, various methods have been proposed as means for preventing bleeding. Patent Document 1 discloses a method using an ink having an equivalent surface tension (30 dyn / cm (mN / m) or more and 60 dyn / cm (mN / m) or less at 20 ° C.) as each color ink forming a color image. Has been. However, according to the study by the present inventors, it has been difficult to obtain a sufficient optical density in an image formed using the ink described in Patent Document 1, particularly a black ink. Further, since the occurrence of bleeding cannot be sufficiently prevented, there is a problem that sufficient image quality cannot be obtained. In addition, there are various types of plain paper used in ink jet recording, depending on the region and location, but even if these various papers are used, the density of the black image and the sharpness of the edges are particularly significant. It is required to be satisfactory at a higher level.

  Patent Document 2 discloses a technique for improving the image quality of black ink and preventing bleeding with a color image portion by using a self-dispersing pigment ink containing salt. However, with the recent increase in speed and image quality in inkjet recording, it is desired to develop a technique for suppressing bleeding at a higher level even when the difference in printing time between black ink and color ink is very short.

  As another method, there is a technique in which a black ink is allowed to stand for a long time to fix the ink to a recording medium to such an extent that bleed does not occur even if the ink has low permeability. However, this method needs to provide a long time difference between the black ink discharge and the color ink discharge, and the throughput (printing time) is lowered. Therefore, this method is not suitable for high-speed recording.

Furthermore, in order to forcibly evaporate the ink, fixing means using a heater is also provided. However, if the fixing means is provided, the apparatus becomes large and the energy is uneconomical.
JP-A-60-197778 JP 2000-198955 A

Therefore, the object of the present invention is to produce a sharp and clear image with little occurrence of white haze and bleeding at the boundary between the color ink and the black ink even when the time difference between the inks is small. and to provide a less good inkjet recording ink set and a recording method of scanning time difference Bandomura in. Another object of the present invention is to provide an ink jet recording method capable of forming the above-described excellent image using such an ink set for ink jet recording.

The above object is achieved by the present invention described below. That is, the present invention relates to an ink set for ink jet recording used in an ink jet recording method in which a recording head scans the same area of a recording medium a plurality of times to record a recorded image, and the ink set includes black ink and a plurality of different ink sets. A color ink of a color, wherein the black ink contains a pigment , a water-soluble organic solvent, water and a surfactant, and each of the plurality of different color inks contains a dye , The surface tension γ ₁ is 37.5 dyn / cm (mN / m) or more and 41.5 dyn / cm (mN / m) or less, and the surface tension γ _{1 of the} black ink and the plurality of different color inks among the most tension gamma ₂ of the difference between the high lightness color color inks (γ ₁ -γ ₂₎ may, 0dyn / cm (mN / m ) greater than, 3.3dyn / cm (mN / m The difference in surface tension between the color ink having the highest surface tension and the color ink having the lowest surface tension among the surface tensions of the color inks of different colors is 3.0 dyn / cm (mN / m). less der is, an ink jet recording ink set in which the recording medium is characterized in plain paper der Rukoto.

  According to the ink set for ink jet recording and the recording method of the present invention, even when the time difference between application of ink is short, the occurrence of white smear at the boundary between the color ink and the black ink is small, and the optical density of black is high and clear. Images can be obtained. In addition, there is little occurrence of bleeding at the boundary between the color ink and the black ink, and a sharp and clear image can be obtained.

  Next, the present invention will be described in more detail with reference to preferred embodiments.

  The ink set of the present invention is an ink set used in a method of recording a recorded image by scanning a recording head in the same area of a recording medium a plurality of times, that is, an ink jet recording method using a so-called multipass recording method.

  The present invention relates to a color blur or color that occurs between an ink set having a black color and a plurality of color inks, particularly an ink of a color with the lowest brightness and an ink of a color with the highest brightness, used in the recording method. It suppresses the occurrence of bleeding, feathering, and the like. Further, the present invention relates to an ink set and a recording method in which band unevenness due to a difference in time for ink ejection is reduced.

  The ink set of the present invention contains black ink and a plurality of different color inks. Examples of the plurality of different color inks include color inks such as yellow, cyan, and magenta.

  In the ink set of the present invention, the combination in which color bleeding or color bleeding at the boundary between different colors is most conspicuous is the ink with the highest brightness and the ink with the lowest brightness among the inks included in each ink set. Is a combination. Color blur and color bleed generated at the boundary between them are most noticeable. By using the ink set of the present invention, the most noticeable color blur and color bleed can be effectively suppressed.

  In general, in the full color ink set of yellow, cyan, magenta, and black, the ink having the lowest lightness is the black ink. In the three color ink sets of yellow, cyan, and magenta, the ink with the highest brightness is the yellow ink, and the ink with the lowest brightness is the cyan ink.

  The surface tension of the black ink constituting the ink set according to the present invention is 37.5 dyn / cm (mN / m) or more and 41.5 dyn / cm (mN / m) or less in order to obtain high image quality. is necessary. Moreover, it is preferable that it is 39.0 dyn / cm (mN / m) or more. Moreover, it is preferable that it is 40 dyn / cm (mN / m) or less.

  The viscosity of the black ink is preferably 1.0 cp (mPa · s) or more, and more preferably 1.5 cp (mPa · s) or more. Moreover, it is preferable that it is 10.0 cp (mPa * s) or less, and it is preferable that it is 5.0 cp (mPa * s) or less. By satisfying this condition, the black ink can be more stably ejected from the inkjet nozzle at a high frequency.

  The surface tension of the color ink constituting the ink set according to the present invention is preferably 40 dyn / cm (mN / m) or less. By satisfying this condition, it is possible to suppress the occurrence of bleed in the boundary area between different color images adjacent to each other. In consideration of the ink ejection characteristics, the surface tension of the color ink is preferably 28 dyn / cm (mN / m) or more.

  As in the case of the black ink described above, increasing the surface tension of the ink is certainly advantageous for the character quality, but it improves the image uniformity of the primary color and the secondary color. Therefore, it is effective to reduce the surface tension of the color ink. On the other hand, since the present inventors can say that yellow ink has the highest lightness among color inks, even if the surface tension of the ink is increased to the same level as that of black ink, the images of primary and secondary colors are uniform. Focusing on the fact that the property does not deteriorate, the present invention has been made. For cyan and magenta color inks, which are lighter than yellow inks, the surface tension is preferably as low as 38 dyn / cm (mN / m) or less from the viewpoint of image uniformity.

  The viscosity of the color ink is preferably 1 cp (mPa · s) or more, and more preferably 1.5 cp (mPa · s) or more. Further, it is preferably 10 cp (mPa · s) or less, more preferably 5 cp (mPa · s) or less. By satisfying these conditions, the color ink can be more stably ejected from the inkjet nozzle at a high frequency.

  In particular, the inventors have found the following and accomplished the present invention. First, in the case where the difference between the surface tension of the black ink and the surface tension of the color ink having the highest brightness among the plurality of different color inks is 3.3 dyn / cm (mN / m) or less. , Generation of white haze and bleed can be satisfactorily suppressed. Furthermore, the difference in surface tension between the color ink having the highest surface tension and the color ink having the lowest surface tension among the surface tensions of the color inks of different colors is less than 3.0 dyn / cm (mN / m). Thus, the occurrence of bleeding can be satisfactorily suppressed. Further, the surface tension of the black ink having the lowest brightness is set higher than that of the color ink having the highest brightness, and the difference in surface tension between these inks is less than 3.0 dyn / cm (mN / m). When adjusted to, higher effects can be obtained.

  By configuring as described above, the density of the black ink is higher and clearer, and further, a white haze and color blur generated between the black ink and the color ink, a large suppression effect of color bleed, and between colors A great suppression effect of bleeding is obtained.

  In the ink jet recording method using the ink set of the present invention, one ink droplet when discharging black ink is configured to be 30 ng or less, and one ink droplet when discharging color ink is further 15 ng. It is preferred to record below. When adjacent pixels are printed at high speed with high surface tension ink, two ink droplets may merge and overflow from a predetermined pixel portion, which may impair the sharpness of the image. However, it is possible to obtain a high-density and high-quality image without impairing the drying property of the ink by recording the droplet amount of each ink to be ejected within the above-described range. On the other hand, if the drop amount of each ink is too large, the drying time of the applied ink tends to be long and the image quality is likely to deteriorate. It is preferable to form.

  Further, by feeding the paper in the sub operation direction after image formation, it is possible to suppress time difference band unevenness due to a driving time difference due to reciprocating scanning during multi-pass printing.

<Black ink>
(Coloring material in black ink)
First, the black ink constituting the present invention will be described. As a coloring material in the black ink, a pigment is used instead of a dye. The reason is as follows. In the image formation with dye ink, an image is formed by dyeing the dye into the recording medium to dye the recording medium itself, and the dye hardly stays on the surface of the recording medium. On the other hand, in the image formation with the pigment ink, pigment particles far larger than the dye are held on the surface of the recording medium, and an image is formed by coloring the pigment particles themselves on the surface. Pigment ink is considered to be dispersed instability in the process of evaporation of the solvent after the impact on the surface of a relatively permeable recording medium such as plain paper, and solid-liquid separation is promoted to form aggregates of pigment particles. . Since the black ink has a high surface tension and low permeability as described above, the concentration of the pigment fixed on the recording medium is high when the black ink alone is applied onto the recording medium. Therefore, the optical density is higher than that of the dye black ink. In addition, when black ink and color ink are applied on a recording medium, after landing, solid-liquid separation is promoted and pigment particles form aggregates, so that the color ink is less likely to enter the black ink. . Further, according to the study by the present inventors, when the surface tensions of the color ink and the black ink are the same, the ink does not easily move on the recording medium, so that the color ink is less likely to enter the black ink. I understood that.

  For example, carbon black is preferably used as the pigment in the black ink. The dispersion mode of carbon black in the ink is more preferably a self-dispersion type. Examples of the self-dispersing carbon black include carbon in which at least one hydrophilic group (anionic group or cationic group) is bonded to the surface of the carbon black as an ionic group directly or via another atomic group. Black. By using this, good dispersibility can be obtained without adding a dispersant to disperse carbon black. Furthermore, the self-dispersing carbon black can easily control the aggregation of ink after landing on the recording medium, and can easily suppress bleeding. Therefore, in the ink set of the present invention, when self-dispersing carbon black is used as the pigment contained in the black ink, the occurrence of bleeding can be further suppressed.

In the case of carbon black in which an anionic group is bonded to the surface directly or through another atomic group, examples of the hydrophilic group bonded to the surface include, for example, —COO (M2), —SO ₃ (M2 _{), - PO 3 H (M2} ), - such as PO 3 _{(M2) 2} and the like. In the above formula, “M2” represents a hydrogen atom, an alkali metal, ammonium or organic ammonium. Among these, self-dispersing carbon black in which —COO (M2) and —SO ₃ (M2) are bonded to the surface of carbon black and anionicly charged is excellent in dispersibility in ink. It can be particularly suitably used for the black ink constituting the present invention.

  By the way, in the hydrophilic group, among those represented as (M2), specific examples of the alkali metal include Li, Na, K, Rb and Cs. Specific examples of organic ammonium include the following. For example, monomethylammonium, dimethylammonium, trimethylammonium, ethylammonium, diethylammonium, triethylammonium, monomethanolammonium, dimethanolammonium, trimethanolammonium and the like.

  The ink containing self-dispersing carbon black in which (M2) is ammonium or organic ammonium can further improve the water resistance of the recorded image, and can be particularly preferably used in this respect. This is considered to be due to the fact that when the ink is applied onto the recording medium, ammonium is decomposed and ammonia is evaporated. Here, there are the following methods for producing a self-dispersing carbon black in which (M2) is ammonium. For example, self-dispersing carbon black in which (M2) is an alkali metal is substituted by ammonium using an ion exchange method. Other examples include a method of adding acid to form H and then adding ammonium hydroxide to make (M2) ammonium. An example of a method for producing an anionically charged self-dispersing carbon black is a method of oxidizing carbon black with sodium hypochlorite. By this method, a -COONa group is chemically bonded to the carbon black surface. Can be made.

  In the case of cationically charged carbon black, for example, a hydrophilic group bonded directly or through another atomic group is bonded to at least one selected from quaternary ammonium groups shown below.

In the above formula, R represents a linear or branched alkyl group having 1 to 12 carbon atoms, a phenyl group which may have a substituent, or a naphthyl group which may have a substituent. Incidentally, the cationic group of the as counter ion, for example, NO ₃ ^- and _CH 3 COO ^- is present. There are the following methods for producing a self-dispersing carbon black having a hydrophilic group bonded thereto and charged cationically. For example, a method for binding an N-ethylpyridyl group having the structure shown below will be described as an example. A method for treating carbon black with 3-amino-N-ethylpyridinium bromide may be mentioned.

  Thus, carbon black charged anionic or cationic by introducing a hydrophilic group onto the surface of carbon black has excellent water dispersibility due to repulsion of ions. Therefore, even when it is contained in the water-based ink, a stable dispersion state is maintained without adding a dispersant or the like. By the way, the various hydrophilic groups as described above may be directly bonded to the surface of the carbon black, or other atomic groups may be interposed between the carbon black surface and the hydrophilic group so as to form the hydrophilic group. The functional group may be indirectly bonded to the carbon black surface.

Here, specific examples of the other atomic groups include, for example, a linear or branched alkylene group having 1 to 12 carbon atoms, a substituted or unsubstituted phenylene group, and a substituted or unsubstituted naphthylene group. . Here, examples of the substituent of the phenylene group and the naphthylene group include a linear or branched alkyl group having 1 to 6 carbon atoms. Specific examples of the combination of another atomic group and the hydrophilic group, for _{example, -C 2 H 4 COOM, -Ph} -SO 3 M, -Ph- (COOM) m etc. (although, Ph is a benzene ring M represents 1 or 2). Further, M in the formula represents a hydrogen atom, an alkali metal, ammonium, or organic ammonium, as in the above (M2).

  By the way, in the present invention, two or more of the above self-dispersing carbon blacks may be appropriately selected and used as a color material for black ink. Further, the addition amount of the self-dispersing carbon black in the black ink is preferably 0.1% by mass or more, more preferably 1% by mass or more of the total mass of the black ink. Moreover, it is preferable to set it as 15 mass% or less, Furthermore, it is preferable to set it as 10 mass% or less. By satisfying these conditions, the self-dispersing carbon black can maintain a sufficiently dispersed state in the ink. Furthermore, for the purpose of adjusting the color tone of the ink, a dye may be added as a coloring material in addition to the self-dispersing carbon black.

(Salt of black ink)
In the present invention, in order to increase the cohesiveness of the pigment, the black ink preferably contains at least one salt selected from the following. _{That, (M1) 2 SO 4,} CH 3 COO (M1), Ph- (COO (M1)) n, (M1) NO 3, (M1) Cl, (M1) Br, (M1) I, (M1) It is preferable to contain at least one selected from ₂ SO ₃ and (M1) ₂ CO ₃ . In the above formula, M1 represents an alkali metal, ammonium or organic ammonium, Ph represents a benzene ring, and n represents 1 or 2. The salt content is preferably 0.05% by mass or more based on the total mass of the ink. Moreover, it is preferable that it is 10.0 mass% or less. When the content is less than 0.05% by mass, an image having a high optical density may not be obtained. Further, if it exceeds 10.0% by mass, the storage stability of the ink may not be obtained.

  And as a specific example of an alkali metal, Li, Na, K, Rb, Cs etc. are mentioned, for example. Specific examples of organic ammonium include the following. For example, monomethylammonium, dimethylammonium, trimethylammonium, monoethylammonium, diethylammonium, triethylammonium and the like. Moreover, monomethanol ammonium, dimethanol ammonium, trimethanol ammonium, monoethanol ammonium, diethanol ammonium, triethanol ammonium, etc. are mentioned.

(Solvent in black ink)
The black ink constituting the present invention is produced using, for example, water or a mixed medium of water and a water-soluble organic solvent as a solvent or dispersion medium such as the above-described coloring material. Specific examples of the water-soluble organic solvent include those listed below. 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 having an average molecular weight of about 200 to 2,000. Alkylene glycols in which an alkylene group contains 2 to 6 carbon atoms, such as ethylene glycol, propylene glycol, butylene glycol, triethylene glycol, 1,2,6-hexanetriol, thiodiglycol, hexylene glycol, and diethylene glycol; Alkyl ether acetates such as polyethylene glycol monomethyl ether acetate. Glycerin. Alkyl ethers of polyhydric alcohols such as ethylene glycol monomethyl (or ethyl) ether, diethylene glycol methyl (or ethyl) ether, triethylene glycol monomethyl (or ethyl) ether. N-methyl-2-pyrrolidone, 2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone and the like.

  The content of the water-soluble organic solvent in the black ink is not particularly limited, but is preferably in the range of 3% by mass to 50% by mass with respect to the total mass of the black ink. The water content in the black ink is preferably in the range of 50% by mass to 95% by mass with respect to the total mass of the black ink. The black ink constituting the present invention is applied to a recording medium by an ink jet recording method (for example, a bubble jet (registered trademark) method). Therefore, it is preferable to adjust the viscosity and surface tension of the ink so as to satisfy the requirements defined in the present invention and at the same time have excellent ink jet discharge characteristics. The surface tension of the black ink can be adjusted by, for example, a method of adding a surfactant. The surfactant used in this case is not particularly limited, but the following are more preferable. Nonionic surfactants such as an ethylene oxide adduct of alcohol, an ethylene oxide adduct of alkylphenol, an ethylene oxide-propylene oxide copolymer, and an ethylene oxide adduct of acetylene glycol can be used.

(Other components in black ink)
The black ink may contain a moisturizing solid content such as urea, a urea derivative, trimethylolpropane, and trimethylolethane in addition to the above components. The content (% by mass) of the moisturizing solid content in the black ink is 0.1% by mass or more and 20.0% by mass or less, and further 3.0% by mass or more and 10.0% by mass based on the total mass of the black ink. % Or less is preferable.

<Color ink>
(Coloring material in color ink)
Next, the color ink constituting the present invention will be described. As the color material in the color ink, known dyes and pigments can be used. As the dye, for example, an acid dye or a direct dye can be used. For example, the anionic dye may be an existing one or a newly synthesized one. As long as they have an appropriate color tone and density, most of them can be used. Moreover, it is also possible to mix and use any of these. Below, the specific example of an anionic dye is given for every color.

(dye)
(Coloring material for yellow)
C. I. Direct yellow: 8, 11, 12, 27, 28, 33, 39, 44, 50, 58, 85, 86, 87, 88, 89, 98, 100, 110, 132. C. I. Acid Yellow: 1, 3, 7, 11, 17, 23, 25, 29, 36, 38, 40, 42, 44, 76, 98, 99. C. I. Reactive yellow: 2, 3, 17, 25, 37, 42. C. I. Food yellow: 3 etc.

(Coloring material for red)
C. 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, 229, 230. C. I. Acid Red: 6, 8, 9, 13, 14, 18, 26, 27, 32, 35, 42, 51, 52, 80, 83, 87, 89, 92, 106, 114, 115, 133, 134, 145 158, 198, 249, 265, 289. C. I. Reactive red: 7, 12, 13, 15, 17, 20, 23, 24, 31, 42, 45, 46, 59. C. I. Food Red: 87, 92, 94, etc.

(Coloring material for blue)
C. I. Direct blue: 1, 15, 22, 25, 41, 76, 77, 80, 86, 90, 98, 106, 108, 120, 158, 163, 168, 199, 226. C. 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 . C. I. Reactive blue: 4, 5, 7, 13, 14, 15, 18, 19, 21, 26, 27, 29, 32, 38, 40, 44, 100, etc.

(Coloring material for black)
C. I. Direct black: 17, 19, 22, 31, 32, 51, 62, 71, 74, 112, 113, 154, 168, 195. C. I. Acid Black: 2, 48, 51, 52, 110, 115, 156. C. I. Food black: 1, 2, etc.

  Since the color ink used in the present invention is used for inkjet recording, the content of the color material in the color ink is such that the ink has excellent inkjet ejection characteristics and has a desired color tone and density. It may be determined as appropriate. As a standard, for example, 3% by mass or more of the total mass of the color ink is preferable. Further, the color material concentration in the color ink is preferably 10% by mass or less of the total mass of the color ink including the color material in consideration of the occurrence of uneven image density due to the ink application sequence.

(Organic pigment)
The following are mentioned as an organic pigment. Insoluble azo pigments such as Toluidine Red, Toluidine Maroon, Hansa Yellow, Benzidine Yellow, and Pyrazolone Red. Soluble azo pigments such as Ritolol Red, Helio Bordeaux, Pigment Scarlet, and Permanent Red 2B. Derivatives from vat dyes such as alizarin, indanthrone and indigo maroon. Phthalocyanine pigments such as phthalocyanine blue and phthalocyanine green. Quinacridone pigments such as quinacridone red and quinacridone magenta. Perylene pigments such as perylene red and perylene scarlet. Isoindolinone pigments such as isoindolinone yellow and isoindolinone orange. Imidazolone pigments such as benzimidazolone yellow, benzimidazolone orange, and benzimidazolone red. Pilanthrone pigments such as pyranthrone red and pyranthrone orange. Thioindigo pigment. Condensed azo pigment. Diketopyrrolopyrrole pigment. Flavanthrone yellow, acylamide yellow, quinophthalone yellow, nickel azo yellow, copper azomethine yellow, perinone orange, anthrone orange, dianthraquinonyl red, dioxazine violet, etc. Other pigments can be exemplified.

  Moreover, when an organic pigment is shown by a color index (CI) number, the following can be used. 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. C. I. Pigment Orange 16, 36, 43, 51, 55, 59, 61, 71. C. 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. C. I. Pigment violet 19, 23, 29, 30, 37, 40, 50. C. I. Pigment Blue 15, 15: 1, 15: 3, 15: 4, 15: 6, 22, 60, 64. C. I. Pigment Green 7, 36. C. I. Pigment Brown 23, 25, 26 and the like can be exemplified.

  Among these pigments, those listed below are preferable. C. I. Pigment yellow 74, 93, 97, 110, 120, 128, 138, 147, 148, 150, 151, 154, 180, 185, and the like. C. I. Pigment red 122, C.I. I. Pigment violet 19, C.I. I. Pigment Blue 15, 15: 1, 15: 3, 15: 4 and the like are preferable.

(Solvent or dispersion medium in color ink)
The color ink constituting the present invention is produced using, for example, water or a mixed medium of water and a water-soluble organic solvent as a solvent or dispersion medium such as the coloring material mentioned above. Examples of the water-soluble organic solvent used at this time are the same as those described for the black ink. The content of the water-soluble organic solvent in the color ink is not particularly limited, but is preferably 3% by mass or more, and preferably 50% by mass or less, based on the total mass of the color ink. The water content in the color ink is preferably 50% by mass or more, and preferably 95% by mass or less, based on the total mass of the color ink. Each color ink constituting the present invention is applied to a recording medium by an ink jet recording method. Therefore, it is preferable to adjust the viscosity and surface tension of the ink so as to satisfy the requirements defined in the present invention and at the same time have excellent ink jet discharge characteristics. The surface tension of the color ink can be adjusted by, for example, a method of adding a surfactant. The surfactant used in this case is not particularly limited, but the following are more preferable. Nonionic surfactants such as an ethylene oxide adduct of alcohol, an ethylene oxide adduct of alkylphenol, an ethylene oxide-propylene oxide copolymer, and an ethylene oxide adduct of acetylene glycol can be used.

(Other components of color ink)
In addition to the above components, the color ink may contain a moisturizing solid content such as urea, a urea derivative, trimethylolpropane, and trimethylolethane in the same manner as described for the black ink. The content (mass%) of the moisturizing solid content in the color ink is preferably 0.1 mass% or more, more preferably 3.0 mass% or more, based on the total mass of the color ink. Moreover, it is preferable to set it as 20.0 mass% or less, Furthermore, it is preferable to set it as 10.0 mass% or less.

<Inkjet recording method>
The ink jet recording method of the present invention is an ink jet recording method for recording a recorded image by causing the recording head for ejecting the ink of the ink set of the present invention to scan the same region of the recording medium a plurality of times.

  Further, it is preferable that the black ink and the color ink with the highest brightness are respectively ejected and applied so that the black ink and the color ink with the highest brightness are brought into contact with each other on the recording medium. In the inkjet recording method of the present invention, it is preferable that the black ink and the color ink having the highest brightness are brought into contact with each other on the recording medium as follows. Of the black ink and the color ink having the highest brightness, the ink ejected first is configured to remain in a liquid state on the recording medium. By adopting such a configuration, it is possible to reduce white haze and bleed at the boundary between the black ink and the color ink, and to obtain an image with a higher black optical density.

(Recording head configuration and printing method)
First, a configuration of a recording head and a printing method that can be suitably used in the inkjet recording method of the present invention will be described with reference to the schematic diagrams shown in FIGS. FIG. 2A is a diagram of the recording head mounted on the printer as viewed from the recording medium side, and is a schematic diagram illustrating the arrangement of the recording chips. As shown in the figure, the recording head is formed by connecting a color ink chip 1100 and a black ink chip 1200 to a base material 1000. The color ink chip 1100 is formed by arranging a cyan ink discharge port array 22, a magenta ink discharge port array 23, and a yellow ink discharge port array 24 for discharging the color ink. The black ink chip 1200 is an array of ejection port arrays 21 for ejecting the black ink. The chip 1200 is a chip that is longer in the recording medium conveyance direction (sub-scanning direction) than the color ink chip 1100, that is, a chip in which the ejection port array range is long.

  As shown in FIG. 2A, the black ink chip 1200 is a chip that is longer in the recording medium conveyance direction (sub-scanning direction) than the color ink chip 1100, that is, a chip in which the ejection port arrangement range is long. This is because importance is attached to the recording speed when a document or the like is recorded using the black ink chip 1200. That is, since the discharge port array arranged in the sub-scanning direction of the black ink chip 1200 is long, the width in the sub-scanning direction that can be recorded in one scan of the chip is longer than the recording by the color ink chip 1100. It has become. The ejection port array 21 for ejecting black ink and the ejection port array for each ink of the color ink chip 1100 are provided by being shifted by a predetermined amount in the sub-scanning direction.

  By using such a type of recording head having many overlapping portions of the black ink ejection port array and the color ink ejection port array, it is possible to perform recording more efficiently. That is, when recording is performed using the overlapping portion of the black ink ejection port array and the color ink ejection port array, the same (single) recording scan is performed on the same recording area on the recording medium. Black ink and color ink can be recorded. With this configuration, it becomes possible to perform printing efficiently using many nozzles. In this method, black ink and color ink are recorded in the same recording area on the recording medium in the same (one-time) recording scan. Therefore, the time difference from when the black ink is ejected from the black ink chip 1200 for recording to when the color ink is ejected from the color ink chip 1100 for recording is very short.

  Further, the order of applying the black ink and the color ink to the recording medium is changed depending on the recording scanning direction. In this way, a printing method for recording black ink and color ink on the same recording area on the recording medium by the same (one-time) recording scanning using the recording head as shown in FIG. This is called “0 scan delay printing”. Note that the same recording area is an area for one band through which the recording head passes in the same (one time) recording operation. When the recording head shown in FIG. 2A is used, printing is efficiently performed by scanning the recording head in a direction perpendicular to the direction in which the recording medium is conveyed. There are two methods for this “0 scan delay printing”. One is a method in which the amount of ink applied in one scan is reduced (thinning out), and the other is a method of performing recording while moving the recording medium in the sub-scanning direction for each scan. The other is a method of moving the recording medium by forming an image in the sub-scanning direction after forming an image for one band of the recording head by multipass.

  Further, FIG. 2B shows a black ink chip in which a black ink chip and a color ink chip are separately connected to a base material 1300 and a color ink chip is connected to the base material 1400, respectively. FIG. 4 is a diagram of a color ink independent type recording head viewed from the recording medium side. As shown in the drawing, the black ink and the color ink are independent type recording heads, and the black ink ejection port array and the color ink ejection port array in the recording medium conveyance direction as in the head shown in FIG. This type of recording head has many overlapping parts.

  The inkjet recording method of the present invention is an inkjet recording method based on a so-called multi-pass recording method in which a recording head that discharges ink of an ink set is scanned a plurality of times in the same area of a recording medium to record a recorded image.

  Hereinafter, although it demonstrates more concretely using an Example and a comparative example, this invention is not limited by the following Example, unless the summary is exceeded. In the following description, “parts” and “%” are based on mass unless otherwise specified. The term “remaining” means that the total content of the compounds contained in each ink is adjusted to 100 parts with water. Acetylenol EH (trade name: manufactured by Kawaken Fine Chemical Co., Ltd.) in the composition is an acetylene glycol ethylene oxide adduct.

  The black ink was prepared by mixing the following components, sufficiently stirring and dissolving, and then pressure-filtering with a micro filter (manufactured by Fuji Film) having a pore size of 3.0 μm.

(Black pigment ink: Bk1)
・ Black self-dispersion pigment dispersion (trade name: CABOJET300;
50 parts ・ Ammonium sulfate 1 part ・ Trimethylolpropane 5 parts ・ Glycerin 5 parts ・ 2-Pyrrolidone 5 parts ・ Acetylenol EH 0.2 part ・ Water balance The following components are mixed in the color ink. Then, after sufficiently stirring and dissolving, it was prepared by pressure filtration with a micro filter (manufactured by Fuji Film Co., Ltd.) having a pore size of 0.2 μm.

(Yellow ink 1: Y1)
-Acetylenol EH 0.2 part-Trimethylolpropane 5 parts-Glycerin 5 parts-2-Pyrrolidone 5 parts-C.I. I. Direct Yellow 86 5 parts, remaining water
(Magenta ink 1: M1)
-Acetylenol EH 0.4 part-Trimethylolpropane 5 parts-Glycerin 5 parts-2-Pyrrolidone 5 parts-C.I. I. Acid Red 289 5 parts, remaining water (Cyan ink 1: C1)
-Acetylenol EH 0.2 part-Trimethylolpropane 5 parts-Glycerin 5 parts-2-Pyrrolidone 5 parts-C.I. I. Acid Blue 9 5 parts, water balance

<Example>
<Ink set 1>
The surface tension γ of the black ink and color ink prepared above was measured using a Kyowa CBVP surface tension meter A-1 type (manufactured by Kyowa Kagaku Co., Ltd.). Specifically, 5 ml to 6 ml of the ink to be measured was put in a petri dish and measured in an environment with a set temperature of 25 ± 0.2 ° C. The results for the four types of ink constituting the ink set 1 were as follows.
Black ink 1 (Bk1): 41.5 dyn / cm (mN / m)
Yellow ink 1 (Y1): 40.0 dyn / cm (mN / m)
Cyan ink 1 (C1): 38.0 dyn / cm (mN / m)
Magenta ink 1 (MI): 38.0 dyn / cm (mN / m)

<Ink set 2>
An ink set 2 was obtained by combining the following inks. These black ink 2 (Bk2), yellow ink 2 (Y2), cyan ink 2 (C2) and magenta ink 2 (M2) were prepared as follows. That is, the amount of acetylenol EH in the composition of the black ink 1 (Bk1), yellow ink 1 (Y1), cyan ink 1 (C1) and magenta ink 2 (M2) used in the ink set 1 is changed. The surface tension was adjusted to the following numerical value.
Black ink 2 (Bk2): 40.0 dyn / cm (mN / m)
Yellow ink 2 (Y2): 37.0 dyn / cm (mN / m)
Cyan ink 2 (C2): 35.0 dyn / cm (mN / m)
Magenta ink 2 (M2): 36.0 dyn / cm (mN / m)

<Ink set 3>
An ink set 3 was obtained by combining the following inks.
Black ink 3 (Bk3): 37.5 dyn / cm (mN / m)
Yellow ink 3 (Y3): Same as yellow ink 2 (Y2) of ink set 2 Cyan ink 3 (C3): Same as cyan ink 2 (C2) of ink set 2 Magenta ink 3 (M3): Magenta of ink set 2 Same as ink 2 (M2). Note that the black ink 3 was prepared by changing the amount of acetylenol EH contained in the black ink 1 and adjusting the surface tension to the above value.

<Comparative example>
<Ink set 4>
An ink set 4 was obtained by combining the following inks.
Black ink 4 (Bk4): 37.0 dyn / cm (mN / m)
Yellow ink 4 (Y4): Same as yellow ink 2 (Y2) of ink set 2 Cyan ink 4 (C4): Same as cyan ink 1 (C1) of ink set 1 Magenta ink 4 (M4): Magenta of ink set 2 Same as ink 2 (M2) The black ink 4 was prepared by changing the amount of acetylenol EH contained in the black ink 1 so as to achieve the above surface tension. The yellow ink 4 was prepared by changing the amount of acetylenol EH contained in the yellow ink 1 to adjust to the above surface tension.

<Ink set 5>
An ink set 5 was obtained by combining the following inks.
Black ink 5 (Bk5): Same as black ink 1 (Bk1) of ink set 1 Yellow ink 5 (Y5): 38.0 dyn / cm (mN / m)
Cyan ink 5 (C5): Same as cyan ink 1 (C1) of ink set 1 Magenta ink 5 (M5): Same as magenta ink 1 (M1) of ink set 1 Note that yellow ink 5 is included in yellow ink 1 It was prepared by changing the amount of acetylenol EH to be adjusted to the above surface tension.

<Ink set 6>
An ink set 6 was obtained by combining the following inks.
Black ink 6 (Bk6): Same as black ink 2 (Bk2) of ink set 2 Yellow ink 6 (Y6): Same as yellow ink 5 (Y5) of ink set 5 Cyan ink 6 (C6): Cyan of ink set 2 Same as ink 2 (C2) Magenta ink 6 (M6): Same as magenta ink 1 (M1) of ink set 1 Each ink constituting the ink sets 1 to 6 prepared above is summarized in Table 1 below. In addition, the color ink of the Kak ink set, the color ink having the highest brightness was the yellow ink.

<Evaluation of ink set>
Using the ink sets 1-6 produced above,
1. Black ink print density,
2. Black ink and color ink bleed, white haze, and
3. Bleeding between color inks,
This point was evaluated by the following method and criteria.

  Printing was performed by forming an image for one band of a two-pass print recording head for 0-scan delay printing in two reciprocations and then moving the recording medium by the amount of image formation in the sub-scanning direction.

  Note that 0-scan delay printing is a printing method in which black ink and color ink are applied to the same area on a recording medium by one recording scan of the recording head. For the evaluation, an ink jet recording apparatus (trade name: Pixus ip5200R; manufactured by Canon Inc.) can be applied to a 1/600 inch square area by black ink 30 ng and color ink equivalent to 12 ng of ink 0 scan delay two-pass printing. The one modified as described above was used.

1. Evaluation items for black ink and evaluation criteria for printing density Using the ink jet recording apparatus, solid printing was performed on plain paper for PPC and dried at 25 ° C. for 1 hour, and this printed matter was then printed with Macbeth RD918 manufactured by Macbeth. The print density was measured, and the print density was evaluated based on the following criteria.
A: The average density of five sheets of plain paper a, b, c, d and e is 1.4 or more.
B: The average density of five papers of plain papers a, b, c, d and e is 1.3 or more and less than 1.4.
C: The average of the printing density of plain papers a, b, c, d and e is less than 1.3.
Note that the following plain paper was used.
a: manufactured by Canon Inc., PPC paper office planner b: manufactured by Canon Inc., PPC paper GF-500
c: Xerox Co., Ltd., PPC paper 4024
d: manufactured by Fox River, PPC paper prober bond e: manufactured by Neuzidra, PPC paper office for Canon 80

2. Evaluation items between black ink and color ink (bleed and white haze)
As the print pattern, a pattern in which the color and black image areas are adjacent to each other as shown in FIG. 4 was printed, and the evaluation of the bleed in the boundary portion and the white haze in the black area was performed visually. As a recording medium, Canon GF-500 plain paper for PPC manufactured by Canon Inc. was used.
-Evaluation criteria for bleed A: No blurring at the boundary.
B: Bleeding is conspicuous at the boundary.
・ Evaluation criteria for white haze A: No white haze.
B: White haze is slightly noticeable.

3. The evaluation items printing pattern in the color inks, in FIG. 4, replacing the image of the black ink to an image of cyan ink, (surface tension of the highest color inks in Examples 1 to 3) and yellow ink (Embodiment An image having an adjacent image area with cyan ink (which is the color ink having the lowest surface tension in Examples 1 to 3) was printed, and the intercolor bleeding at the boundary portion was visually evaluated. In Comparative Examples 1 to 3, evaluation was performed using yellow ink and cyan ink for comparison. As a recording medium, Canon GF-500 plain paper for PPC manufactured by Canon Inc. was used.
-Evaluation criteria for bleed A: No blurring at the boundary.
B: Slight blurring is noticeable at the boundary.

  Regarding the above evaluation items, ink sets 1 to 3 were evaluated without feeding 0-scan 2-pass printing paper, and Examples 1-3 were evaluated, and ink sets 4 to 6 were evaluated with 0-scan delay 2-pass printing. These were made into Comparative Examples 1-3.

  The evaluation results of the above examples and comparative examples are shown in Table 2 below.

  From the results of Examples 1-3 and Comparative Examples 1-3, when the surface tension of the black ink is as high as 37.5 dyn / cm (mN / m) to 41.5 dyn / cm (mN / m), the black ink It can be seen that the print density is particularly good. Further, the difference between the surface tension of the black ink and the surface tension of the color ink having the highest brightness among the color inks is set to 3.3 dyn / cm (mN / m) or less, so It turns out that generation | occurrence | production of the bleeding in can be suppressed. Further, by setting the difference in surface tension between the color ink having the highest surface tension and the color ink having the lowest surface tension among the surface tensions of the color ink to be less than 3.0 dyn / cm (mN / m), the color ink It turns out that generation | occurrence | production of the bleeding between can be suppressed.

  The recording heads used in the evaluation tests of Examples 1 to 3 have a chip arrangement as shown in FIG. 2A. However, the BK chip and the color chip as shown in FIG. The same effect can be obtained with this type of recording head.

  Here, the ink permeation process in the case where the black ink is applied to the paper surface prior to the color ink in the zero scan delay two-pass printing using the ink set 1 according to the first embodiment is illustrated in FIGS. ). In Example 1, the surface tension of yellow ink 1 (Y1) having the highest brightness is higher than that of other color inks, and the surface tension difference from black ink 1 (Bk1) is 1.5 dyn / cm (mN / m). ) Is within.

  First, the black ink (Bk1) 101 having low permeability covers the recording medium 52 as shown in FIG. Reference numeral 103 denotes pigment particles contained in the black ink 101 (Bk1). In this state, the black ink (Bk1) 101 penetrates at a low speed because of low permeability to the recording medium 52 (penetration direction 104). Thereafter, yellow ink (Y1) 102 having low permeability is applied (FIG. 1B). Since there is almost no difference in surface tension between the black ink (Bk1) 101 and the yellow ink (Y1) 102, the ink slowly moves into the recording medium 52 with little ink movement at the interface between the black ink 101 and the yellow ink 102. It can be estimated (FIG. 1 (c)).

  FIG. 1D is a view of the boundary 56 between the black ink (Bk1) 101 and the yellow ink (Y1) 102 as viewed from above. Since the black ink (Bk1) 101 and the yellow ink (Y1) 102 have substantially the same physical property values, the infiltration was completed in a state where the ink remaining in a liquid state on the surface of the recording medium was not mixed at the boundary portion 56. As a result of intensive studies by the present inventor, it is particularly important that the black ink (Bk1) or color ink applied to the recording medium 52 permeates in the permeation direction 104, the ink droplet amount, and the surface tension. I understood.

  Conversely, the ink permeation process when the color ink is applied to the paper surface prior to the black ink will be described with reference to FIGS. In this case, as shown in FIG. 1E, the yellow ink 102 having a high lightness is first applied to the recording medium 52, and then the black ink 101 having a low lightness as shown in FIG. 1F. Is applied to the recording medium 52. Since the black ink 101 and the yellow ink 102 have almost no difference in surface tension between them, it can be estimated that the ink moves slowly into the recording medium 52 in a state where the ink movement at the interface is small (FIG. 1G). (FIG. 1 (h)). FIG. 1 (i) is a view of the boundary portion 56 where the black ink and the yellow ink are in contact, as viewed from above. Since the black ink 101 and the yellow ink 102 have substantially the same physical property values, the permeation is completed in a state where inks remaining in a liquid state on the surface of the recording medium 52 are not mixed at the boundary portion 56.

Next, the ink permeation process in Comparative Example 2 when black ink is applied to the paper surface prior to the color ink by 0-scan delay 2-pass printing using the ink set 5 is shown in FIG. ). In Comparative Example 2 , the surface tension of the yellow ink (Y5) having the highest brightness is equal to the surface tension of the other color inks, and the difference from the surface tension of the black ink (Bk5) is 3.5 dyn / cm (mN / m). ) And big. In this case, when the black ink 101 is applied to the recording medium 52, the black ink 101 with low permeability covers the recording medium 52 as shown in FIG. Reference numeral 103 denotes pigment particles contained in the black ink 101.

  In this state, since the black ink 101 has low permeability to the recording medium 52, the black ink 101 penetrates at a low speed (penetration direction 104). Thereafter, yellow ink 102 having high permeability is applied (FIG. 3B). At this time, since the surface tension difference between the black ink 101 and the yellow ink 102 is large, ink movement (301 in FIG. 3B) at the interface between the black ink 101 and the yellow ink 102 occurs violently and penetrates into the recording medium 52. It can be estimated that it will continue (FIG. 3 (c)).

  FIG. 3D is a view of the boundary portion 56 between the black ink 101 and the yellow ink 102 as viewed from above. Since the black ink 101 and the yellow ink 102 have a large difference in physical properties, the ink remaining in a liquid state on the surface of the recording medium 52 is mixed with each other at the boundary portion 56 and the bleeding is conspicuous. Similarly, when the color ink was applied to the paper surface prior to the black ink, the blurring of the boundary portion 56 was also conspicuous. The ink permeation process in this case will be described with reference to FIGS.

  First, as shown in FIG. 3E, the yellow ink 102 with high brightness is applied to the recording medium 52 first, and then the black ink 101 with low brightness is recorded as shown in FIG. 3F. Applied to the medium 52. Thereafter, since the surface tension difference between the black ink 101 and the yellow ink 102 is large, ink movement (301 in the figure) at the interface between the black ink 101 and the yellow ink 102 occurs vigorously (FIG. 3G). Then, it can be estimated that the black ink 101 and the yellow ink 102 penetrate into the recording medium 52 while causing the ink movement (FIG. 3 (h)). FIG. 3I is a view of the boundary portion 56 between the black ink and the yellow ink as viewed from above. Since the black ink 101 and the yellow ink 102 have a large difference in physical properties, the ink remaining in a liquid state on the surface of the recording medium 52 is mixed with each other at the boundary portion 56 and the bleeding is conspicuous.

  According to the present invention, even when the application time difference between the inks is small, there is little white haze or bleeding at the boundary between the color ink and the black ink, the black density is high, and a sharp and clear image can be obtained. A recording ink set and a recording method can be provided.

(A)-(c) and (e)-(h) are schematic diagrams showing in time series how black ink and yellow ink penetrate into a recording medium in the embodiment. Further, (d) and (i) are diagrams in which the boundary portion between the black ink and the yellow ink in the embodiment is viewed from the upper surface of the recording medium. (A), (b) is the schematic diagram which showed the example of arrangement | positioning relationship of a color chip and a black chip in the inkjet recording head used by this invention. (A)-(c), (e)-(h) is the schematic diagram which showed the mode of penetration | invasion to the recording medium of the black ink and yellow ink in a comparative example in time series. Further, (d) and (i) are diagrams in which the boundary between the black ink and the yellow ink in the comparative example is viewed from the upper surface of the recording medium. Print pattern used for bleed and white haze evaluation experiments. It is explanatory drawing which shows the ink droplet formation state in the conventional inkjet recording method.

Explanation of symbols

21 Black ink ejection port array 22 Cyan ink ejection port array 23 Magenta ink ejection port array 24 Yellow ink ejection port array 51 Ink 52 Recording medium 53 Ink 54 Black dot 55 Color dot 56 Ink boundary 101 Black ink 102 Yellow ink 103 Pigment Particle 104 Penetration direction 301 Ink movement direction 1000 Base material 1100 Chip for color ink 1200 Chip for black ink 1300 Base material 1400 Base material

Claims (14)

An ink set for inkjet recording used in an inkjet recording method for recording a recorded image by causing a recording head to scan the same area of a recording medium a plurality of times,
The ink set has a black ink and a plurality of different color inks, and the black ink contains a pigment , a water-soluble organic solvent, water and a surfactant,
Each of the plurality of different color inks contains a dye,
The surface tension γ _{1 of the} black ink is 37.5 dyn / cm (mN / m) or more and 41.5 dyn / cm (mN / m) or less,
The difference (γ ₁ −γ ₂ ) between the surface tension γ _{1 of the} black ink and the surface tension γ ₂ of the color ink having the highest brightness among the color inks of different colors is 0 dyn / cm (mN / m ) Greater than or equal to 3.3 dyn / cm (mN / m),
Of the surface tension of the different colors the color inks of the plurality of the difference in surface tension of the lowest color ink having the highest color ink and the surface tension surface tension is Ri 3.0dyn / cm (mN / m) less than Der ,
An ink set for ink-jet recording said recording medium, characterized in plain paper der Rukoto.   2. The ink set for ink jet recording according to claim 1, wherein the color ink having the highest brightness is a yellow ink. The ink set for inkjet recording according to claim 1 or 2 , wherein the pigment contained in the black ink is self-dispersing carbon black. The difference (γ ₁ −γ ₂ ) between the surface tension γ _{1 of the} black ink and the surface tension γ ₂ of the color ink having the highest brightness among the plurality of different color inks is 0 dyn / cm (mN / m 4) The ink set for ink jet recording according to any one of claims 1 to 3 , wherein the ink set is less than 3.0 dyn / cm (mN / m). The black ink is (M1) ₂ SO ₄ , CH ₃ COO (M1), Ph— (COO (M1)) n, (M1) NO ₃ , (M1) Cl, (M1) Br, (M1) I, ( At least one salt selected from M1) ₂ SO ₃ and (M1) ₂ CO ₃ (M1 represents an alkali metal, ammonium or organic ammonium, Ph represents a benzene ring, and n represents 1 or 2) The ink set for inkjet recording according to any one of claims 1 to 4 . The ink set for inkjet recording according to claim 5 , wherein the salt content is 0.05% by mass or more and 10.0% by mass or less based on the total mass of the ink. The ink set for inkjet recording according to any one of claims 1 to 6 , wherein a surface tension of the black ink is 39.0 dyn / cm (mN / m) or more and 41.5 dyn / cm (mN / m) or less. . An inkjet recording method for recording a recorded image by causing a recording head for discharging ink of an ink set to scan the same area of a recording medium a plurality of times,
The ink set has a black ink and a plurality of different color inks, and the black ink contains a pigment , a water-soluble organic solvent, water and a surfactant,
Each of the plurality of different color inks contains a dye,
The surface tension γ _{1 of the} black ink is 37.5 dyn / cm (mN / m) or more and 41.5 dyn / cm (mN / m) or less,
The difference (γ ₁ −γ ₂ ) between the surface tension γ _{1 of the} black ink and the surface tension γ ₂ of the color ink having the highest brightness among the color inks of different colors is 0 dyn / cm (mN / m ) Greater than or equal to 3.3 dyn / cm (mN / m),
Of the surface tension of the different colors the color inks of the plurality of the difference in surface tension of the lowest color ink having the highest color ink and the surface tension surface tension is Ri 3.0dyn / cm (mN / m) less than Der ,
The ink jet recording method in which the recording medium is characterized in plain paper der Rukoto. As contacting with black ink on the recording medium and most high lightness color color ink, according to claim 8 which imparts the black ink and the most high lightness color of the color ink on a recording medium by ejecting each Inkjet recording method. Wherein when making on the recording medium into contact with the color ink having the highest lightness and black ink color, previously discharged towards ink the recording of the black ink and the most high lightness color color inks The ink jet recording method according to claim 8 , wherein the ink jet recording method remains in a liquid state on the medium. The inkjet recording method according to any one of claims 8 to 10 , wherein the color ink having the highest brightness is a yellow ink. Wherein the pigment black ink is contained in the ink-jet recording method according to any one of claims 8 to 11 which is a self-dispersion carbon black. The black ink is (M1) ₂ SO ₄ , CH ₃ COO (M1), Ph— (COO (M1)) n, (M1) NO ₃ , (M1) Cl, (M1) Br, (M1) I, ( At least one salt selected from M1) ₂ SO ₃ and (M1) ₂ CO ₃ (M1 represents an alkali metal, ammonium or organic ammonium, Ph represents a benzene ring, and n represents 1 or 2) The ink jet recording method according to any one of claims 8 to 12 . The black surface tension of the ink is 39.0dyn / cm (mN / m) or more, 41.5dyn / cm inkjet recording method according to any one of claims 8 to 13 is (mN / m) or less.

Images